Revision 2 June, 1988 AIR POLLUTION SOURCE FIELD INSPECTION NOTEBOOK Prepared by: Richards Engineering Durham, North Carolina Prepared for: U.S. Environmental Protection Agency Air Pollution Training Institute Purchase Order 6D3843NASA June 16, 1988 ------- DISCLAIMER This manual was prepared by Richards Engineering for the Air Pollution Training Institute of the U.S Environmental Protection Agency in partial fulfillment of Purchase Order 6D3843NASA. The contents of this report are reproduced herein as received from the contractor. The opinions, findings, and conclusions expressed are those of the author and not necessarily those of the U.S. Environ- mental Protection Agency. Any mention of product names does not constitute endorsement by the U.S. Environmental Protection Agency. The safety precautions set forth in this manual and presented at any training or orientation session, seminar, or other presentation using this manual are general in nature. The precise safety precau- tions required for any given situation depend upon and must be tail- ored to the specific circumstances. Richards Engineering expressly disclaims any liability for any personal injuries, death, property damage, or economic loss arising from any actions taken in reliance upon this manual or any training or orientation session, seminar, or other presentations based upon this manual. iii ------- TABLE OF CONTENTS Page Safety Guidelines see cover 1. Inspection of Fabric Filters 1 1.1 Components and operating principles 1 1.2 General safety considerations 14 1.3 Inspection summaries 15 1.4 Inspection procedures 18 2. Inspection of Mechanical Collectors 33 2.1 Components and operating principles 33 2.2 General safety considerations 36 2.3 Inspection summaries 37 2.4 Inspection procedures 39 3. Inspection of Electrostatic Precipitators 49 3.1 Components and operating principles 49 3.2 General safety considerations 56 3.3 Inspection summaries 57 3.4 Inspection procedures 59 4. Inspection of Wet Scrubbers 69 4.1 Components and operating principles 69 4.2 General safety considerations 79 4.3 Inspection summaries • 80 4.4 Inspection procedures ' 83 5. Inspection of Dry Scrubbers 97 5.1 Components and..operating principles 97 5.2 General safety considerations 106 5.3 Inspection summaries 108 5.4 Inspection procedures 112 6. Inspection of Carbon Bed Adsorbers ~3f (?••? 6.1 Components and operating principles 125 6.2 General safety considerations 130 6.3 Inspection summaries 131 6.4 Inspection procedures 133 ------- Table of Contents (Continued) Inspection of Thermal and Catalytic Incinerators 139 7.1 Components and operating principles 139 7.2 General safety considerations 146 7.3 Inspection summaries 147 7.4 Inspection procedures 149 Use of Portable Instruments 155 6.1 VOC detectors 155 6.2 Temperature monitors 170 6.3 Static pressure gauges 174 8.4 Pitot tubes I77 VI ------- 1. INSPECTION OF FABRIC FILTERS The three most common categories of fabric filter systems are addressed in this inspection notebook. The inspection procedures discussed in this section have been tailored to the specific design characteristics and operating problems of these fabric filters. 0 Pulse jet 0 Reverse air c Shaker Inspectors and their supervisors should modify these procedures as necessary for types of fabric filters not specifically discussed in this notebook. 1.1 Components and Operating Principles 1.1.1 Components of Pulse Jet Fabric Filters Pulse jet fabric filters utilize compressed air for routine bag cleaning. This type of fabric filter is used in a wide variety of applications including asphalt batch plants, material transfer operations, and industrial boilers. They are sometimes referred to as "Reverse Jet" fabric filters. The presence of a row of diaphragm valves along the top of the baghouse similar to those shown in Figure 1-1 indicates that the baghouse is a pulse jet unit. These valves control the compressed air flow into each row of bags which is used to routinely clean the dust from the bags. On a few units, the diaphragm valves can not be seen since they are in an enclosed compartment on the top of the unit. In these cases, the pulse jet baghouse can be recognized by the dis- tinctive, regularly occurring sound of the operating diaphragm valves. The shells of pulse jet units are usually small. This is because it is possible to put a relatively high gas flow rate through the types of fabric generally used in pulse jet units. Also, pulse jet units are usually more economical than other types of fabric filters for very small particulate sources. ------- INSPECTION OF FABRIC FILTERS Components and Operating Principles Figure 1-1. Row of diaphragm valves along the top of a pulse jet fabric filter There are two major types of pulse jet baghouses: (1) top access, and (2) side access. Figure 1-2 illustrates the top access design which includes a number of large hatches across the top of the bag- house for bag replacement and maintenance. Another major type has one large hatch on the side for access to the bags. The side access units often have a single small hatch on the top of the shell for routine inspection of the baghbuse. Like most small units, the pulse jet collector depicted in Figure 1-2 is not divided into compartments. These are not needed on small units that operate intermittently since bags are cleaned row- by-row as the unit continues to operate. A few of the large units are divided into separate compartments so that it is possible to perform maintenance work on part of the unit while the other part continues to operate. ------- INSPECTION OF FABRIC FILTERS Components and Operating Principles TOP ACCESS MATCHES . GAS OUTLET FAN IAPHRAGM VALVES AIR MANIFOLD GAS INLET HOPPERS Figure 1-2. Top access pulse jet fabric filter ------- INSPECTION OF FABRIC FILTERS Components and Operating Principles Another distinguishing characteristics of pulse jet units is the use of a support cage for the bags. The cage fits inside the cylin- drical bags and prevents the bags from collasping during filtering. Bags and cages are usually sold separately. The fan shown in Figure 1-2 is after the baghouse. This means that the particulate laden gas stream is "pulled" through the bag- house and that the static pressures throughout the unit are less than atmospheric pressure. Outside air will leak into the baghouse if the hatches are not secure, if the shell is corroded, or if the hopper is not properly sealed. Air infiltration can result in a number of significant baghouse maintenance problems. Pulse jet units operate equally well when the fan is ahead of the baghouse and the gas stream is "pushed" through. In these units, the static pressures are greater than atmospheric pressure and there are potential safety problems with leakage of pollutant laden gas out into the areas surrounding the baghouse. 1.1.2 Pulse Jet Fabric Filter Operating Principles A cross sectional drawing of a pulse jet fabric filter is shown in Figure 1-3 on the next page. Refer to this drawing while reading the following section concerning the basic operating characteristics of pulse jet baghouses. The baghouse is divided into a "clean" side and a "dirty" side by the tube sheet which is mounted near the top of the unit. The dust laden gas stream enters below this tube sheet and the filtered gas collects in a plenum above the tube sheet. There are holes in the tube sheet for each of the bags. The bags are normally arranged in rows. The bags and cages hang from the tube sheet. The dust laden inlet gas stream flows around the outside of each bag and the dust gradually accumulates on the outside surfaces of the bags during filtering. The cleaned gas passes up the inside of the bag and out into the "clean" gas plenum. ------- INSPECTION OF FABRIC FILTERS Components and Operating Principles •LOW TU PILOT VALVE ENCLOSURE DIAPHRAGM VALVE '.PULSE TIMER DIFFERENTIAL PRESSURE. SWITCH IRTY CAS INLET OTARY VALVE Figure 1-3. Cross sectional sketch of pulse jet fabric filter ------- INSPECTION OF FABRIC FILTERS Components and Operating Principles A pulse jet fabric filter uses bags which are supported on cages. The cages hang from the tube sheet near the top of the bag- house. Dust accumulates on the outer surfaces of the bags as the gas stream passes through the bags and into the center of the bags. The filtered gas is collected in a plenum at the top of the baghouse. The dust must occassionaly be removed from the bags in order to avoid exessively high gas flow resistances. The bags are cleaned by introducing a high pressure pulse of compressed air at the top of the bag. The sudden pulse of compressed air generates a pressure wave which travels down inside of the bag. The pressure wave also induces some filtered gas to flow downward into the bag. Due to the combined action of the pressure wave and the reverse gas flow, the bags are briefly deflected outward. This cracks the dust cake on the outside of the bags and causes the dust to fall into the hopper. Cleaning is normally done on a row-by-row basis while the baghouse is operating. The compressed air at pressures from 60 to 90 psig is generated by an air compressor and stored temporarily in the compressed air manifold. When the pilot valve (a standard solenoid valve) is opened by the controller, the diaphragm valve suddenly opens to let compressed air into the delivery tube which serves a row of bags. There are holes in the delivery tube above each bag for injection of the compressed air into the top of each bag. The cleaning system controller can either operate on the basis of a differential pressure sensor as shown in Figure 1-3, or it can simply operate as a timer. In either case, bags are usually cleaned on a relatively frequent basis with each row being cleaned from once every five minutes to once every hour. Cleaning is usually done by starting with the first row of bags and proceeding through the remaining rows in the order that they are mounted." Bags used in pulse jet collectors are generally less than 6 inches in diameter and range in length from 6 to 14 feet. Felted fabric is the most common type of material. One of the basic design parameters of a pulse jet fabric filter is the gas-to-cloth ratio (sometimes called the air-to-cloth ratio) which is simply the number of cubic feet of gas at actual conditions ------- INSPECTION OF FABRIC FILTERS —^ T Components and Operating Principles /"/ passing through the average square/root of cloth per unit of time. The normal units are ft3/min/ft "which can be reduced to ft/min. Most new commercial pulse jet units are designed for an average gas- to-cloth ratio between 3 and 8 depending on the characteristics of the fabric selected, the particle size of the dust to be collected, and the installation and operation costs. Some older pulse jet units were designed for gas-to-cloth ratios up to 15 ft/min. Pulse jet units do not necessarily operate at the design average gas-to-cloth ratio. When production rates are low, the prevailing average gas-to-cloth ratio could be substantially below the design value. Conversely, the average gas-to-cloth ratio could be well above the design value if some of the bags are inadequately cleaned or if sticky or wet material blocks part of the fabric surface. Very high gas-to-cloth ratio conditions can lead to high gas flow resistance which in turn can result in both seepage of dust through the bags and fugitive emissions from the process equipment. The difference between the gas stream pressures before and after the baghouse is called the static pressure drop. The actual static pressure drop depends on the actual average gas-to-cloth ratio, the physical characteristics of the dust, the type of fabric used in the bags, and the adequacy of cleaning. A pulse jet baghouse with new bags that have not yet been exposed to dust would normally have a static pressure drop of 0.5 to 1.5 inches of water. During normal operation, the pulse jet baghouses generally have a static pressure drop between 3 and 8 inches of water. The difference between the static pressure drop across a clean, new unit and one in normal service is due to the gas flow resistance through the dust layer on each of the bags. The dust layer (sometimes called the dust cake) is important since it .is responsible for much of the particle filter- ing. Very low static pressure drops can often indicate inadequate dust layers for proper filtering. Very high static pressure drops often mean that a substantial fraction of the available cloth area has been inadequately cleaned or has been blocked by wet and/or sticky material. High particulate emissions also occur when the static pressure drop is very high. The optimum overall efficiency of a pulse jet baghouse system is generally in the moderate static pressure drop range. ------- INSPECTION OF FABRIC FILTERS Components and Operating Principles 1.1.3 Components of Reverse Air and Shaker Fabric Filters In reverse air and shaker fabric filter systems, the bags are suspended from the top and are attached to a tube sheet which is immediately above the hoppers. As shown in Figure 1-4, the inlet gas enters from the hoppers and passes upward into each of the bags. The dust cake builds up on the inside surface of the bags and filtered gas passes into the chamber surrounding the bags. These baghouses are usually divided into 2 or more compartments. Cleaning of the bags is done by isolating the compartment from the inlet gas stream. In the case of reverse air bags, filterd gas is moved backward through the compartment to break up the dust cake and discharge it to the hoppers below. The cleaning gas from the compart- ment being cleaned is recycled to the inlet gas duct. In the case of shaker baghouses, the compartment is entirely isolated and the top hanger assembly is oscillated to physically dislodge the dust on the bags. In both types of fabric filters, a set of dampers (poppet valves in Figure 1-4) and activators are used. Due to the relatively large size of many commercial bags, a significant gas flow exists at the entrance to the bags. The average gas velocity at this point can be between 300 and 500 feet per minute, depending of the actual gas-to-cloth ratio and the bag size. It is important that the particulate laden air enter the bag in as straight a direction as possible in order to minimize fabric abrasion. The inlet gas stream can also cause fabric damage if the bags are slightly slack and some .of the fabric is folded over the bag inlet. Because of these and other possible problems, the large majority of the bag failures occur near the bottom of the bags. Bags used in reverse air and shaker baghouses generally range in length from 10 to 30 feet. Reverse air bags utilize a set of anti-collaspe rings sewn around the bags at a number of locations on the bag to prevent complete closure of the bag during reverse air cleaning. Woven fabrics are generally used for these types of baghouses. ------- INSPECTION OF FABRIC FILTERS Components and Operating Principles •RFVERSE AIR DUCTS CLEAN GAS AEVERSE AIR -FAN POPPET VALVES AND ACTUATORS WALKWAY 'BAGS TUBE SHEET Figure 1-4. Cross section of a reverse air fabric filter ------- INSPECTION OF FABRIC FILTERS Components and Operating Principles The bags are attached to the tube sheet either by using a snap ring sewn into the bag or by using a thimble and clamp. Figures 1-5 and 1-6 illustrate both of these approaches. Firm bag attachments are important in order to minimize the flow of unfiltered gas through any gaps. Large quantities of dust are often handled by reverse air and shaker baghouses. The types of solids discharge valves and solids handling systems are generally selected based on the overall quantity of material to be transported and on the characteristics of these solids. The most common types of solids discharge systems include (1) rotary valves and screw conveyors, (2) pneumatic systems, and (3) pressurized systems. An isometric drawing of a reverse air baghouse is shown in Figure 1-7. This unit has the main fan downstream of the baghouse. This means that the particulate laden gas stream is "pulled" through the baghouse and that the static pressures throughout the unit are less than atmospheric pressure (termed "negative pressure"). With this type of arrangement, outside air can leak into the baghouse if the hatches are not secure, if the shell is corroded, or if the hopper is not properly sealed. Air infiltration can result in a number of significant baghouse maintenance problems. Reverse air and shaker units operate equally well when the fan is ahead of the baghouse and the gas stream is "pushed" through. In these units, the static pressures are greater than atmospheric pressure (termed "positive pressure") and there can be potential safety problems with leakage of pollutant laden gas out into the areas surrounding the baghouse. In most positive pressure units, the filtered gas from each compartment is released to the atmosphere through a large roof monitor or through a set of short stacks. 10 ------- INSPECTION OF FABRIC FILTERS Components and Operating Principles BAG SNAP RING SEWN INTO BAG TUBE SHEET Figure 1-5. Snap ring attachment for reverse air and shaker bags • BAG .WORM DRIVE CLAMP TUBE SHEET Figure 1-6. Thimble and clamp arrangement for reverse air and shaker bags 11 ------- INSPECTION OF FABRIC FILTERS Components and Operating Principles _ COMPARTMENTS FAN BAGS *T GAS INLET Figure 1-7. Isometric view of reverse air fabric filter 12 ------- INSPECTION OF FABRIC FILTERS Components and Operating Principles 1.1.4 Reverse Air and Shaker Baghouse Operating Principles One of the basic design parameters of reverse air and shaker fabric filters is the gas-to-cloth ratio (sometimes called the air- to-cloth ratio) which is simply the number of cubic feet of gas at actual conditions passing through the average square foot of cloth per unit of time. The normal units are ft3/min/ft which can be reduced to ft/min. Most new commercial reverse air and shaker units are designed for an average gas-to-cloth ratio between 1 and 3 ft/min depending on the characteristics of the fabric selected, the particle size of the dust to be collected, and the necessary installation and operation costs. Reverse air and shaker units do not necessarily operate at the design average gas-to-cloth ratio. When production rates are low, the prevailing average gas-to-cloth ratio could be substantially below the design value. Conversely, the prevailing average gas-to- cloth ratio could be well above the design value if some of the bags are inadequately cleaned or if sticky or wet material blocks part of the fabric surface. Very high gas-to-cloth ratio conditions can lead to high gas flow resistance which in turn can result in both the seepage of dust through the bags and fugitive emissions from the process equipment served by the baghouse. The difference between the gas stream pressures before and after the baghouse is called the static pressure drop. The actual static pressure drop depends on the actual average gas-to-cloth ratio, the physical characteristics of the dust, the type of fabric used in the bags, and the adequacy of cleaning. A reverse air or shaker baghouse with new bags which have not yet been exposed to dust would normally have a static pressure drop of 0.5 to 1.5 inches of water. During normal operation, the baghouses generally have a static pressure drop between 3 and 6 inches of water. The difference between the static pressure drop across a clean, new unit and one in normal service is due to the gas flow resistance through the dust layer on each of the bags. The dust layer (sometimes called the dust cake) is important since it is responsible for most of the particle filtering. Very low static pressure drops can often indicate inadequate dust layers for proper filtering. Very high static pressure drops often mean that a substantial fraction of the available cloth area has been inadequately cleaned or has been blocked by wet and/or sticky material. High 13 ------- INSPECTION OF FABRIC FILTERS Components and Operating Principles particulate emissions also occur when the static pressure drops are very high. The optium overall efficiency of a reverse air or shaker baghouse system is generally in the moderate static pressure drop range. i.2 general Safety Considerations Pulse jet fabric filters often serve relatively hot industrial processes such as asphalt plant driers, clinker coolers, and lime kilns. Uninsulated units can be hot, especially on the baghouse roof. Reverse air and shaker fabric filters often serve combustion sources such as cement kilns, lime kilns, coal-fired boilers, and glass furnaces. Fugitive emissions from positive pressure fabric filter systems can accumulate in poorly ventilated areas around the baghouse such as the walkways between the rows of compartments. The inhalation hazards can include chemical asphyxiants, physical asphyxiants, toxic gases/vapors, and toxic particulate. Inspectors should not enter a fabric filter under any circum- stances. All of the necessary inspection steps can be accomplished without internal inspections. However, in some cases, it is helpful to open one or more of the baghouse top and/or side access hatches in order to observe internal conditions. In these situations, inspectors should request that plant personnel open the hatches. The hopper hatches should not be opened during the inspection since hot, free flowing dust can be released. 14 ------- INSPECTION OF FABRIC FILTERS Inspection Summaries 1.3 Inspection Summaries 1.3.1 Level 1 Inspections Stack ° Visible emissions for 6 to 30 minutes for each stack or discharge vent 0 Presence of condensing plume Baghouse Not applicable Process ° Presence or absence of fugitive emissions 1.3.2 Level 2 Inspections Basic Inspection Points Stack ° Visible emissions for 6 to 30 minutes for each stack or discharge vent 0 Presence of condensing plume 0 Double-pass transmissometer conditions 0 Double-pass transmissometer data Pulse Jet Fabric Filters 0 Static pressure.drop 0 Clean side conditions 0 General physical condition Reverse Air and Shaker Fabric Filters 0 Static pressure drop 0 Compartment static pressure drops during 'cleaning 0 Clean side conditions 0 General physical condition Process e Process operating rate 0 Process operating conditions e Presence or absence of fugitive emissions 15 ------- INSPECTION OF PULSE JET FABRIC FILTERS Inspection Summaries 1.3.2 Level 2 Inspections (Continued) Follow-up Pulse Jet Fabric Filters Compressed air cleaning system operation Bag failure rate and location records Present baghouse inlet gas temperature Baghouse inlet gas temperature records Bag "rip" tests and fabric laboratory analyses 0 Cage characteristics Reverse Air and Shaker Fabric Filters Reverse air fan operation Shaker assembly operation Cleaning system equipment controller Bag failure rate and location records ° Present baghouse inlet gas temperature Baghouse inlet gas temperature records Bag "rip" tests and fabric laboratory analyses Process ° Fugitive emissions 1.3.3 Level 3 Inspections Stack c Visible emissions for 6 to 30 minutes for each stack or discharge vent* 0 Presence or absence of condensing plume* Double-pass transmissometer condition* 0 Double-pass transmissometer data* Pulse Jet Fabric Filters 0 Static pressure drop "-.Inlet and outlet gas temperature 0 Inlet and outlet gas oxygen content 0 Compressed air system operation* 0 General physical condition* 0 Bag failure rate and location records* Baghouse inlet gas temperature records* Bag "rip" tests and fabric laboratory analyses* 8 Cage characteristics* * See Basic Level 2 Inspection Procedures 16 ------- INSPECTION OF FABRIC FILTERS Inspection Summaries 1.3.3 Level 3 Inspections (Continued) Reverse Air and Shaker Fabric Filters 0 Static pressure drop 0 Compartment static pressure drops during cleaning Inlet and outlet gas temperature Inlet and outlet gas oxygen content General physical condition* Bag failure rate and location records* Baghouse inlet gas temperature records* Bag "rip" tests and fabric laboratory analyses* Process Process operating rate* Process operating conditions* Presence or absence of fugitive emissions* 1.3.4 Level 4 Inspections Stack Baghouse Process 0 All elements of a Level 3 inspection 0 All elements of a Level 3 inspection 0 Flowchart of compressed air supply (Pulse jet fabric filters only) 0 Start-up/shut down procedures 0 Locations for measurement ports e Potential inspection safety problems 0 All elements of a Level 3 inspection 0 Basic flowchart of process 0 'Potential inspection safety problems * See Level 2 basic and follow-up inspection procedures. 17 ------- INSPECTION OF FABRIC FILTERS Basic Level 2 Inspection Procedures 1.4 Inspection Procedures Techniques for the inspection of fabric filter systems can be classified as Level 1, 2, 3, or A. The Level 1 inspection consists of a visible emissions observation from outside the plant. This is not discussed in this manual. The Level 2 inspection primarily involves a walkthrough evaluation of the baghouse system and process equipment. All data are provided by on-site gauges. The Level 3 inspection includes all inspection points of the Level 2 inspection and includes independent measurements of baghouse operating conditions when the on-site gauges are not adequate. The Level A inspection is performed by agency supervisors or senior inspectors to acquire baseline data. The scope of the Level A inspection is identical to the Level 3 inspection. I.A.I Level 2 Inspections Evaluate the baghouse visible emissions. If weather conditions permit, determine baghouse effluent average opacity in accordance with U.S. EPA Method 9 procedures (or other required procedure). The observation should be con- ducted during routine process operation and should last 6 to 30 minutes. Fabric filters generally operate with an average opacity less than 5%. Higher opacities indicate baghouse emis- sion problems. Some large, multi-compartment pulse jet baghouses have separate stacks for each compartment. Long term visible emission observations on each of these stacks should be made only when the baghouse is suffering major emission problems. If weather conditions are poor, an attempt should still be made to determine whether there are any visible emissions. Do not attempt to determine "average opacity" during adverse weather conditions. The presence of a noticeable plume generally indicates baghouse operating problems. 18 ------- INSPECTION OF PULSE JET FABRIC FILTERS Basic Level 2 Inspection Procedures Evaluate puffing conditions (PULSE JET UNITS ONLY). Evaluate the frequency and severity of puffs. These are often caused by small holes in one or more rows of bags. Evaluate condensing plume conditions. Condensing plume conditions in fabric filter systems are usually caused by organic vapors generated in the process equip- ment. The vaporous material condenses once the gas enters the cold ambient air. Condensing plumes usually have a bluish-white color. In some cases, the plume forms 5 to 10 feet after leaving the stack. If the baghouse operating temperature drops substan- tially, this material can condense inside the baghouse and cause fabric blinding problems. Corrective actions must focus on the process equipment that is the source of the vaporous material. Evaluate double-pass transmissometer physical conditions. Most fabric filter systems _do not have a transmissometer for the continuous monitoring of visible emissions. If a unit is present, and if it is in an accessible location, check the light source and retroreflector modules to confirm that these are in good working order. Check that the main fan is working and that there is a least one dust filter for the fan. On many commercial models, it is also possible to check the instrument alignment without adjusting the instrument. Note; On some models, moving the dial t£ the alignment check position will cause an alarm in the control room. This is to be moved only by plant personnel and only when it will not disrupt plant operations. Some fabric filters have one or more single pass trans- missometers on outlet ducts. While these can provide some useful information to the system operators, these instruments do not provide data relevant to the inspection. Evaluate double-pass transmissometer data. Evaluate the average opacity data for selected days since the last inspection, if the transmissometer appears to be working properly. Determine the frequency of emission problems and evaluate how rapidly the baghouse operators are able to recognize and eliminate the conditions. 19 ------- INSPECTION OF FABRIC FILTERS Basic Level 2 Inspection Procedures Evaluate the baghouse static pressure drop. The baghouse static pressure drop should be recorded if the gauge appears to be working properly. The gauge "face" should be clear of obvious water and deposits. The gauge should fluc- tuate slightly each time one of the diaphragm valves activates. These valves can be heard easily close to the pulse jet baghouse. If there is any question about the gauge, ask plant personnel to disconnect each line one at a time to see if the gauge responds. If it does not move when a line is disconnected, the line may be plugged. Fabric filters operate with a wide range of static pressure drops (2 to 12 inches W.C.). It is preferable to compare the present readings with the baseline values for this specific source. Increased static pressure drops generally indicate high gas flow rates, and/or fabric blinding, and/or system cleaning problems. Lower static pressure drops are generally due to re- duced gas flow rates, excessive cleaning intensities/frequencies, or reduced inlet particulate loadings. Evaluate baghouse general physical conditions. While walking around the baghouse and its inlet and outlet ductwork, check for obvious corrosion around the potential "cold" spots such as the corners of the hoppers, near the solids dis- charge valve, and the access hatches. On negative pressure bag- houses, check for any audible air infiltration through the cor- roded areas, warped access hatches, eroded solids discharge val- ves, or other sites. On positive pressure baghouses, check for fugitive emissions of dust from any corroded areas of the system. Evaluate the clean side conditions (when possible). If there is-eny question about the performance of the bag- house, request that plant personnel open one or more hatches on the clean side (not available on some commercial models). Note the presence of any fresh dust deposits more than 1/8" deep since this indicates particulate emission problems. In the case of pulse jet fabric filters, also observe the conditions of the bags, cages, and compressed air delivery tubes. The compressed air delivery tubes should be oriented directly 20 ------- INSPECTION OF FABRIC FILTERS Basic Level 2 Inspection Procedures Evaluate the clean side conditions (continued). into the bags so that the sides of the bags are not subjected to the blast of cleaning air. The cages and bags should be securely sealed to the tube sheet in units where the bag comes up through the tube sheet. There should be no oily or crusty deposits at the top of the bags due to oil in the compressed air line. In reverse air and shaker units, also observe the bag tension and status of the bag attachments at the tube sheet. In reverse air baghouses, the bags should have noticeable tension in the vertical direction (some inward deflection of the bags is normal when a compartment is isolated). In shaker units, the bags should not be under any tension and should not be slack. The majority of bag problems generally occur within the bottom 1 to 2 feet of the bags in both types of baghouses. Regulatory agency inspectors should observe conditions from the access hatches and should not enter the compartments under any circumstances. In some cases, operators will be unable to open the access hatches during the inspection. In one compartment units, the entire baghouse must be shut down and locked out before a hatch can be opened. Shutting down the unit may cause significant in- plant inhalation hazards and safety problems. Similar problems can occur on multi-compartment baghouses having only the minimum capacity necessary to handle process gas flow requirements. In a few cases, safety problems near the baghouse preclude clean side checks. Evaluate the process operating rate. Record one or more process operating rate parameters that document that the source conditions are representative of normal operation. 21 ------- INSPECTION OF FABRIC FILTERS Basic Level 2 Inspection Procedures Evaluate process operating conditions. Record any process operating parameters that have an impact on the characteristics and/or quantities of pollutants generated. Some of the important variables are listed below. 8 Gas stream temperatures 0 Gas stream static pressures 0 Gas stream oxygen levels 0 Raw material characteristics Evaluate process fugitive emissions. Perform complete visible emission observations on any major process fugitive emissions. If the conditions preclude a complete observation, note the presence and timing of any fugitive releases. 1.4.2 Follow-up Inspection Points for Level 2 Inspections Evaluate compressed air cleaning system (PULSE JET BAGHOUSES). The purpose of checking the compressed air cleaning system is to determine if this contributes to a significant shift in the baghouse static pressure drop and/or if this contributes to an excess emission problem. The.inspection procedures for the compressed air cleaning system can include one or more of the following. 0 Record the compressed air pressure if the gauge appears to be working properly. It should fluctuate slightly each time a diaphragm valve is activated. Do not remove this valve since the compressed air lines and manifold have high pressure air inside. 0 Listen for operating diaphragm valves. If none are heard over a 10 to 30 minute time period, the cleaning system controller may not be operating. 0 Check the compressed air shutoff valve to confirm that the line is open. 22 ------- INSPECTION OF FABRIC FILTERS Follow-up Level 2 Inspection Procedures Evaluate compressed air cleaning system (PULSE JET FABRIC FILTERS). 0 Count the number of diaphragm valves that do not activate during a cleaning sequence. This can be done by simply listening for diaphragm valve operation. Alternatively, the puff of compressed air released from the trigger lines can sometimes be felt at the solenoid valve (pilot valve) outlet. 0 Check for the presence of a compressed air drier. This removes water which can freeze at the inlet of the diaphragm valves. Also check for compressed air oil filter. 0 Check for a drain on the compressed air supply pipe or on the air manifold. This is helpful for routinely draining the condensed water and oil in the manifold. Confirm operation of reverse air fan (REVERSE AIR BAGHOUSES) Confirm that the reverse air fan is operating by noting that the fan shaft is rotating. This fan is usually located near the top of the baghouse. Confirm operation of shaker assemblies (SHAKER BAGHOUSES) Confirm that each of the shaker assemblies is working by observing the movement of the shaker linkages on the outside of each compartment. Confirm operation of_ cleaning equipment controllers. (REVERSE AIR. SHAKER. AND SOME MULTI-COMPARTMENT PULSE JET FABRIC FILTERS) Observe the baghouse control panel during cleaning of one or more compartments to confirm that the controller is operating properly. Each compartment should be isolated for cleaning before the static pressure drop increases to very high levels that preclude adequate gas flow. Also, cleaning should not be so frequent that the bags do not build-up an adequate dust cake to ensure high efficiency filtration. 23 ------- INSPECTION OF FABRIC FILTERS Follow-up Level 2 Inspection Procedures Confirm operation of cleaning equipment controllers. (REVERSE AIR. SHAKER. AND SOME MULTI-COMPARTMENT PULSE JET FABRIC FILTERS) It is generally good practice to allow a short "null" per- iod of between 5 and 30 seconds between the time a compartment is isolated and the time that reverse air flow or shaking begins. This reduces the flexing wear on the fabric. It is also good practice to have a "null" period of 15 to 60 seconds following cleaning to allow fine dust to settle out of the bags prior to returning to filtering mode. Determine present baghouse inlet gas temperature. The primary purpose of determining the present gas inlet temperature is to evaluate possible excess emission problems and/or high bag failure rate conditions that can be caused by very high or very low gas inlet temperatures. Locate any on-site thermocouples mounted on the inlet to the baghouse. If this instrument appears to be in a representative position, record the temperature value displayed in the control room. The average inlet gas temperature should be 25 to 50 °F below the maximum rated temperature limit of the fabric. Fifteen to thirty minute spikes of less than 25 °F above the maximum rated limit can usually be tolerated without fabric damage. The average inlet gas temperature should be 25 to 50°F above the acid gas dewpoint temperature. For most commercial combustion processes, the acid dewpoint is usually between 225 to 300 °F. The inlet gas temperature should also be above the water vapor dewpoint. Evaluate the baghouse gas temperature records. The purpose of reviewing continuous temperature recorder data is to determine if temperature excursions contribute to excess emission problems and/or high bag failure rates. Review selected strip charts to determine if the gas inlet temperatures have been above the maximum rated fabric temperature or below the acid vapor or water vapor dewpoints. ------- INSPECTION OF FABRIC FILTERS Follow-up Level 2 Inspection Procedures Perform fabric "rip" test and review fabric laboratory analyses. The purpose of evaluating fabric condition is to determine if any corrective actions planned by the owner/operators have a reasonable probability of reducing frequent excess emissions. To perform a "rip" test, ask the plant personnel for a bag that has been recently removed from the baghouse. Attempt to rip the bag near the site of the bag hole or tear. If the bag can not be ripped easily, then the probable cause of the failure is abrasion and/or flex damage. These bags can usually be patched and reinstalled. If the bag can be ripped easily, then the fabric has been weakened by chemical attack or high tempera- ture damage. Weakened bags should not be patched and reinstalled. It may be necessary to install new bags throughout the entire chamber if the bag failure rates are high. Evaluate bag failure records. The purpose of reviewing bag failure records is to deter- mine the present bag failure rate and to determine if the rate of failure is increasing. Plot the number of bag failures per month for the last 6 to 24 months. If there has been a sudden increase, the owner/operators should consider replacing all of the bags in the compartment(s) affected. . If there is a distinct spatial pattern to the failures,.the owner/operators should consider repair and/or modification of the internal conditions causing the failures. Evaluate the bag cages (PULSE JET FABRIC FILTERS). The bag cages are evaluated whenever there are frequent abrasion/flex failures at the bottoms of the bags or along the ribs of the cage*. Ask the plant personnel to provide a spare cage for examination. There should be adequate support for the bag and there should not be any sharp edges along the bottom cups of the cage. Also check the cages for bows that would cause rubbing between two bags at the bottom of the baghouse. Process equipment fugitive emissions. A careful check for process fugitive emissions is necessary whenever the baghouse static pressure drop is substantially higher than the baseline value or when air infiltration is 25 ------- INSPECTION OF FABRIC FILTERS Follow-up Level 2 Inspection Procedures Process equipment fugitive emissions (continued). severe. In both cases, poor capture of the dust at the process equipment is possible. Walk around the process sources to the extent safely possible to evaluate pollutant capture. 1.4.3 Level 3 Inspection Points Procedures for measurement of reverse fabric filter system operating conditions are described below. Other observations to be completed as part of the Level 3 inspection are identical to those included in the basic and follow-up Level 2 inspection. See the Level 2 inspection procedures section for a discussion of these steps. Measure the baghouse static pressure drop. The static pressure drop provides an indication of gas flow rate changes (changes in actual gas-to-cloth ratio), fabric blinding, and cleaning system problems. The steps in measuring the static pressure drop are described below. 0 Locate safe and convenient measurement ports on the inlet and outlet ductwork or on the baghouse shell. In some cases it may be possible to temporarily disconnect the on-site gauge in order to use the portable gauge. 0 Clean any deposits out of the measurement ports. 0 If the inlet and outlet ports are close together, connect both sides of the static pressure gauge to the ports and observe the static pressure for 1 to 5 minutes. 0 If the ports are not close together, measure the static pressure in one port for 10 to 30 seconds and then proceed to the other port for 10 to 30 seconds. As long as the static pressure drop is stable the two values can be sub- tracted to determine the static pressure drop. 0 Under no circumstances should on-site plant instruments be disconnected without the explicit approval of responsible plant personnel. Also, instruments connected to pressure transducers should not be disconnected. 26 ------- INSPECTION OF FABRIC FILTERS Level 3 Inspection Procedures Evaluate inlet and outlet gas temperatures. These measurements are conducted whenever it is necessary to determine if air infiltration is causing fabric chemical attack due to reduced gas outlet temperatures. It is also helpful to measure the inlet gas temperature to evaluate the potential for high gas temperature damage to the bags. The steps in measuring the gas temperature are outlined below. 0 Locate safe and convenient measurement ports on the inlet and outlet ductwork of the collector. Often small ports less than 1/4" diameter are adequate. Measurements using ports on the baghouse shell are often inadequate since moderately cool gas is trapped against the shell. 0 Attach a grounding/bonding cable to the probe if vapor, gas, and/or particulate levels are potentially explosive (a relatively common situation). 0 Seal the temperature probe in the port to avoid any air infiltration that would result in a low reading. 0 Measure the gas temperature at a position near the middle of the duct if possible. Conduct the measurement for several minutes to ensure a representative reading. 0 Measure the gas temperature at another port and compare the values. On combustion sources, a gas temperature drop of more than 20 to 40 °F indicates severe air infiltration. 0 Compare the inlet gas temperature with the maximum rated temperature limit of the fabric present. If the average gas temperature is within 25 to 50 °F of the maximum, short bag life and frequent bag failures are possible. Also, if there are short term excursions more than 25 to 50 °F above the maximum temperature limits, irreversible fabric damage may occur. 27 ------- INSPECTION OF FABRIC FILTERS Level 3 Inspection Procedures Evaluate the inlet and outlet gas oxygen levels. These measurements are performed to further evaluate the extent of air infiltration. However, these tests are limited to combustion sources since they are the only sources with oxygen concentrations in the effluent gas that are less than ambient levels. An increase of more than 1% oxygen going from the inlet to the outlet indicates severe air infiltration (e.g. inlet oxygen at 6.5% and outlet oxygen at 7.5%). The steps involved in measuring the flue gas oxygen levels are itemized below. 0 Locate safe and convenient measurement ports. Generally, the ports used for the temperature measure- ments are adequate for the oxygen measurements. 0 Attach a grounding/bonding cable to the probe if there are potentially explosive vapors, gases, and/or particulate (a relatively common situation). 8 Seal the probe to prevent any ambient air infiltration around the probe. 0 Measure the oxygen concentration at a position near the center of the duct to avoid false readings due to localized air infiltration. The measurement should be repeated twice in the case of gas absorption instruments. For continuous monitoring instruments, the measurement should be conducted for 1 to 5 minutes to ensure a representative value. 0 If possible, measure the carbon dioxide concentration at the same locations. The sum of the oxygen and carbon dioxide concentrations should be in the normal stoichi- ometric range for the fuel being burned. If the sum is not in this range, a measurement error has occurred. 0 As soon as possible, complete the measurements at the other port. Compare the oxygen readings obtained. If the outlet values are substantially higher, severe air infiltration is occurring. 28 ------- INSPECTION OF FABRIC FILTERS Level 4 Inspection Procedures 1.4.4 Level 4 Inspection Procedures The Level 4 inspection includes many inspection steps performed during Level 2 and 3 inspections. These are described in earlier sections. The unique inspection steps of Level 4 inspections are described below. Prepare £ flowchart .of the compressed air system (PULSE JET FABRIC FILTERS). ' The purpose of the flowchart is to indicate the presence of compressed air system components that could influence the vulnerability of the pulse jet baghouse to bag cleaning problems. The flowchart should consist of a simple block diagram showing the following components. 0 Source of compressed air (plant air or compressor) e Air drier (if present) 0 Oil filter (if present) 0 Main shutoff valve(s) 0 Compressed air manifolds on baghouse 0 Drains for manifolds and compressed air lines 0 Heaters for compressed air lines and manifolds 0 Controllers for pilot valves (timers or pneumatic sensors) Evaluate locations for measurement ports. Many existing fabric filters do not have convenient and safe ports that can be used for static pressure, gas tempera- ture, and gas oxygen measurements. One purpose of the Level 4 inspection is to select (with the assistance of plant personnel) locations for ports to be installed at a later date to facili- tate Level 3 inspections. Information regarding possible sample port locations is provided in the U.S. EPA Publication titled, " Preferred Measurement Ports for Air Pollution Control Systems", EPA 340/1-86-034. 29 ------- INSPECTION OF FABRIC FILTERS Level A Inspection Procedures Evaluate start-up and shutdown procedures. The start-up and shutdown procedures used at the plant should be discussed to confirm the following. The plant has taken reasonable precautions to minimize the number of start-up/shutdown cycles. The baghouse system bypass times have been minimized. The baghouse system bypass times have not limited to the extent that irreversible damage which will lead to excess emission problems in the near future. Evaluate potential safety problems. Agency management personnel and/or senior inspectors should identify any potential safety problems involved in standard Level 2 or Level 3 inspections at this site. To the extent pos- sible, the system owner/operators should eliminate these hazards. For those hazards that can not be eliminated, agency personnel should prepare notes on how future inspections should be limited and should prepare a list of the necessary personal safety equipment. A partial list of common health and safety hazards includes the following. 0 Inhalation hazards due to.low stack discharge points 0 Weak catwalk and ladder supports 0 Hot baghouse roof surfaces 0 Compressed air gauges in close proximity to rotating equipment-or hot surfaces 0 Fugitive emissions from baghouse system 0 Inhalation hazards from adjacent stacks and vents 0 Access to system components only available by means of weak roofs or catwalks 30 ------- INSPECTION OF FABRIC FILTERS Level 4 Inspection Procedures Prepare a. system flowchart. A relatively simple flowchart is very helpful in conducting a complete and effective Level 2 or Level 3 inspection. This should be prepared by agency management personnel or senior inspectors during a Level A inspection. It consists of a simple block diagram that includes the following elements. 0 Source(s) of emissions controlled by a single baghouse 0 Location(s) of any fans used for gas movement through the system (used to evaluate inhalation problems due to positive static pressures) 0 Locations of any main stacks and bypass stacks 0 Location of baghouse 0 Locations of major instruments (transmissometers, static pressure gauges, thermocouples) Evaluate potential safety problems in the process area. The agency management personnel and/or senior inspectors should evaluate potential safety,problems in the areas that may be visited by agency inspectors during Level 2 and/or Level 3 inspections. They should prepare a list of the activities which should not be performed and locations to which an inspector should not go as part of these inspections. The purpose of this review is to minimize inspector risk and to minimize liability concerns of plant personnel. 31 ------- 32 ------- 2. INSPECTION OF MECHANICAL COLLECTORS 2.1 Components and Operating Principles 2.1.1 Components of Mechanical Collectors The simple cyclone consists of an inlet, a cylindrical section, a conical section, a gas outlet tube, and a dust outlet tube. On some units, there is a solids discharge valve such as a rotary valve or a flapper valve. A typical tangential inlet, axial outlet cyclone is shown in Figure 2-1. PLAN VIEW GAS INLET GAS IN"1 ^^m CY1 I • • •• ^^•i •^M .INORICAL SECTION SECTIONAL VIEW OUTLET TUBE OUST DISCHARGE TUBE Figure 2-1. Typical cyclone collector 33 ------- INSPECTION OF MECHANICAL COLLECTORS Components and Operating Principles Medium efficiency single cyclones are usually less than 6 feet in diameter and operate at static pressure drops of 1 to 6 inches of water. Overall collection efficiency is a function of the inlet particle size distribution and the gas flow rate. A multiple cyclone consists of numerous small diameter cyclones operating in a parallel fashion. The high efficiency advantage of small diameter tubes is obtained without sacrificing the ability to treat large effluent volumes. The individual cyclones, with diameters ranging from 3 to 12 inches, operate at pressure drops from 2 to 6 inches of water. The inlet to the collection tubes is axial, and a common inlet and outlet manifold is used to direct the gas flow to a number of parallel tubes. The number of tubes per collector may range from 9 to 200 and is limited only by the space available and the ability to provide equal distribution of the gas stream to each tube. Properly designed units can be constructed and operated with a collection efficiency of 90 percent for particles in the 5 to 10 micron range. 2.1.2 Mechanical Collector Operating Principles In a cyclone or a cyclone tube, a vortex is created within the cylindrical section by either injecting the gas stream tangentially or by passing the gas stream through a set of spinner vanes. Due to particle inertia, the particles migrate across the vortex gas stream lines and concentrate near the cyclone wall. Near the bottom of the cyclone cylinder, the gas stream makes a 180 degree turn and the particulate matter is discharged either downward or tangentially into hoppers below. The treated gas passes out of the opposite end of the cyclone. Particle separation is a function of the gas flow throughout the cyclone. At high gas flow rates and small cylinder diameters, the inertial force is high and particle collection efficiency is optimized. However, there is an upper limit to gas flow rate beyond which the increased gas turbulence leads to slightly reduced particle collection efficiency. ------- INSPECTION OF MECHANICAL COLLECTORS Components and Operating Principles The importance of particle size is illustrated in the collection efficiency curves shown in Figure 2-2. For any given particle size, the collection efficiency is also a strong function of the gas flow rate. Multiple cyclones are less efficient at low flow rates. LARGE DIAMETER TUBES MEDIUM DIAMETER TUBES SMALL DIAMETER TUBES 1C 20 30 40 50 60 70 80 AERODYNAMIC PARTICLE DIAMETER, umA 90 100 Figure 2-2. Particulate collection as a function of particle size It is important that the inlet duct to the multiple collector be properly oriented so there is no induced gas maldistribution among the cyclone tubes. There must also be allowances for the expansion of the ductwork and collector as the equipment heats up to normal operating temperatures. 35 ------- INSPECTION OF MECHANICAL COLLECTORS General Safety Considerations 2.2 General Safety Considerations Mechanical collectors often serve combustion sources such as cement kilns, lime kilns, coal-fired boilers, and glass furnaces. Fugitive emissions from positive pressure systems can accumulate in poorly ventilated areas around the collector such as the walkways between the rows of compartments. The inhalation hazards can include chemical asphyxiants, physical asphyxiants, toxic gases/vapors, and toxic particulate. Furthermore, the collectors generally operate at high gas temperatures. Burns can occur while attempting to walk around constricted areas adjacent to the mechanical collector. Poor ventilation can also create potential heat stress problems. Inspectors should not enter a mechanical collector under any circumstances. All of the necessary inspection steps can be accom- plished without internal inspections. Unlike the inspection proce- dures for other types of air pollution control systems, even access hatch observations are not performed for mechanical collectors. This is because the collector access hatches are rarely in a conven- ient location to observe internal problems and because of additional safety hazards in opening the hatches of these units. 36 ------- INSPECTION OF MECHANICAL COLLECTORS Inspection Summaries 2.3 Inspection Summaries 2.3.1 Level 1 Inspections Stack ° Visible emissions for 6 to 30 minutes for each stack or discharge vent 0 Presence of condensing plume Collector ° Not applicable Process ° Presence or absence of fugitive emissions 2.3.2 Level 2 Inspections Basic Inspection Points Stack ° Visible emissions for 6 to 30 minutes for each stack or discharge vent 0 Presence of condensing plume 9 Double-pass transmissometer conditions 0 Double-pass transmissometer data Collector * Static pressure drop 0 General physical condition 0 Solids discharge valve operation Process * Process operating rate 0 Process operating conditions 0 Presence or absence of fugitive emissions Follow-up Collector e Air infiltration indicators 37 ------- INSPECTION OF REVERSE AIR AND SHAKER FABRIC FILTERS Inspection Summaries 2.3.3 Level 3 Inspections Stack Collector Process 0 Visible emissions for 6 to 30 minutes for each stack or discharge vent* Presence or absence of condensing plume* Double-pass transmissometer condition* Double-pass transmissometer data* Static pressure drop Inlet and outlet gas temperature Inlet and outlet gas oxygen content General physical condition* 0 Process operating rate* e Process operating conditions* 0 Presence or absence of fugitive emissions* 2.3.4 Level 4 Inspections Stack ° All elements of a Level 3 inspection Collector Process All elements of a Level 3 inspection Locations for measurement ports Potential inspection safety problems All elements of a Level 3 inspection Basic flowchart of process Potential inspection safety problems * See Level 2 basic and follow-up inspection procedures, 38 ------- INSPECTION OF MECHANICAL COLLECTORS Basic Level 2 Inspection Procedures 2.4 Inspection Procedures Techniques for the inspection of mechanical collectors can be classified as Level 1, 2, 3, or 4. The Level 1 inspection consists of a visible emissions observation from outside the plant. This is not discussed in this manual. The Level 2 inspection primarily involves a walkthrough evaluation of the collector system and process equipment. All data are provided by on-site gauges. The Level 3 inspection includes all inspec- tion points of the Level 2 inspection and includes independent meassurements of collector operating conditions when the on-site gauges are not adequate. The Level 4 inspection is performed by agency supervisors or senior inspectors to acquire baseline data. The scope of the Level 4 inspection is identical to the Level 3 inspection. 2.4.1 Level 2 Inspections Evaluate the collector visible emissions. If weather conditions permit, determine baghouse effluent average opacity in accordance with U.S. EPA Method 9 procedures (or other required procedure). The observation should be made during routine process operation and should last 6 to 30 minutes for each stack and bypass vent. The majority of mechanical col- lectors operate with an average opacity less than 20%. If weather conditions are poor, an attempt should still be made to determine if there are any visible emissions. Do not attempt to determine "average opacity" during adverse weather conditions. The presence of a very noticeable, dark plume generally indicates collector operating problems. *-«• Evaluate condensing plume conditions. Condensing plume conditions in mechanical collector systems are usually caused by partially combusted material generated in the process equipment. The vaporous material condenses once the gas enters the cold ambient air. Condensing plumes usually have a bluish-white color. In some cases, the plume forms 5 to 10 feet after leaving the stack. 39 ------- INSPECTION OF MECHANICAL COLLECTORS Basic Level 2 Inspection Procedures Evaluate double-pass transmissometer physical conditions. Most mechanical collector systems do not have a trans- missometer for the continuous monitoring of visible emissions. If a unit is present, and if it is in an accessible location, check the light source and retroreflector modules to confirm that they are in good working order. Check that the main fan is working and that there is a least one dust filter for the fan. On many commercial models, it is also possible to check the instrument alignment without adjusting the instrument. Note; On some models, moving the dial to the alignment check position will cause an alarm in the control room. This is to be moved only by_ plant personnel and only when It will not disrupt plant operations. Many mechanical collectors serving coal-fired boilers have one or more single pass transmissometers on outlet ducts. While they can provide some useful information to the system operators, these instruments do not provide relevant data. Evaluate double-pass transmissometer data. Evaluate the average opacity data for selected days since the last inspection if the transmissometer appears to be working properly. Determine the frequency of emission problems and evaluate how rapidly the baghouse operators are able to recognize and eliminate the condition. 40 ------- INSPECTION OF MECHANICAL COLLECTORS Basic Level 2 Inspection Procedures Evaluate the mechanical collector static pressure drop. The collector static pressure drop should be recorded if the gauge appears to be working properly. The following items should be checked to confirm the adequacy of the on-site gauge. 0 The gauge "face" should be clear of water and deposits. 0 The gauge value should respond to process operating rate changes. 0 The lines leading to the inlet and outlet of the collector should be intact. If there is any question concerning the gauge, ask plant personnel to disconnect each line one at a time to check if the gauge responds. If it does not move when a line is disconnected, the line may be plugged or the gauge is inoperable. Note; the lines should only be disconnected by_ plant personnel and only when this will not affect plant operations. If the on-site gauge appears to be working properly, record the indicated value. The time that the data was obtained should also be noted if the process operating rates change frequently. The observed static pressure should be corrected for the present operating rate by using the equation* listed below. The corrected value should then be compared with baseline value(s). Csp - Osp (X2/B2) Where: Csp « corrected static pressure drop, inches W.C. Osp'« observed static pressure drop, inches W.C. X • present process operating rate B « baseline process operating rate If the corrected static pressure drop is significantly different from the baseline value(s), then the gas flow resist- ance has changed and particulate emissions have probably increased. *Note: This equation ignores gas density changes 41 ------- INSPECTION OF MECHANICAL COLLECTORS Basic Level 2 Inspection Procedures Evaluate the mechanical collector static pressure drop (cont.) Increased static pressure drops generally indicate solids build-up in the collector, most commonly on the inlet spinner vanes of small diameter multi-cyclone tubes. This causes poor vortex formation and reduced collection efficiency in the affected tubes. Low static pressure drops are generally due to erosion of the outlet extension tubes, corrosion of the clean side tube sheet, or failure of the tube gaskets. These prob- lems allow some of the particulate laden flue gas to "short circuit" the collector. Evaluate mechanical collector general physical conditions. While walking around the mechanical collector and its inlet and outlet ductwork, check for obvious corrosion around the potential "cold" spots such as in the corners of the hoppers, near the solids discharge valve, and on the access hatches. On negative pressure units, check for any audible air infiltration through the corroded areas, warped access hatches, eroded solids discharge valves, or other sites. On positive pressure units, check for fugitive emissions of dust from any corroded areas of the system. Evaluate solids discharge valves and solids discharge rates. For multi-cyclone collectors using rotary discharge valves or flapper valves, check for continuous movement of the valve and for continuous discharge of solids into the screw conveyor or into the disposal container (if safely possible). For multi- cyclone collectors using pneumatic or pressurized hopper dis- charge systems, check for the sound of discharge valve operation at a frequency ranging from once per hour to once per 8 hours. Note; Only plant personnel should open observation hatches on_ screw conveyors gr dust storage/disposal containers and protec- tive goggles and respirators may be needed in some cases. Evaluate the process operating rate. Record one or more process operating rate parameters that document that the source conditions are representative of normal operation. ------- INSPECTION OF MECHANICAL COLLECTORS Basic Level 2 Inspection Procedures Evaluate process operating conditions. Record any process operating parameters which have an impact on the characteristics and/or quantities of pollutants generated. Some of the important variables are listed below. 0 Gas stream temperatures 0 Gas stream static pressures 0 Gas stream oxygen levels 0 Raw material characteristics Evaluate process fugitive emissions. Perform complete visible emission observations on any major process fugitive emissions. If the conditions preclude a complete observation, note the presence and timing of any fugitive releases. 2.4.2 Follow-up Inspection Points for Level 2 Inspections Evaluate air infiltration indicators. Locate any permanently mounted temperature gauges on the inlet and outlet ducts of the mechanical collector. The pres- ence of a thermocouple is indicated by the presence of a thermo- couple "head" connection in the ductwork. If the instrument(s) appears to be in representative locations, check the indicated temperatures at the control room. Compare the inlet and outlet values. In most mechanical collectors serving combustion pro- cesses, the gas temperature drop across the collector is 20 to 40 °F depending primarily on the gas flow rate and the adequacy of insulation. Gas temperature drops that are higher than base- line values suggest significant air infiltration and reduced particulate matter collection efficiency. Also compare the inlet gas temperatures to the baseline levels. If there is a significant difference, check the process operating rate and the process operating conditions. On units having oxygen monitors, check for the increase in flue gas oxygen concentration across the collector. In most cases, it should be less than 1% 02 increase (e.g. 7% inlet, 82 outlet). A3 ------- INSPECTION OF MECHANICAL COLLECTORS Level 3 Inspection Procedures 2.4.3 Level 3 Inspection Points Procedures for measurement of mechanical collector system operating conditions are described below. Other observations to be completed as part of the Level 3 inspection are identical to those included in the basic and follow-up Level 2 inspection. See the Level 2 inspection procedures section for a discussion of these steps. Measure the collector static pressure drop. The static pressure drop provides an indication of gas flow resistance passing through the mechanical collector. The steps in measuring the static pressure drop are described below. 0 Locate safe and convenient measurement ports. In some cases it may be possible to temporarily disconnect the on-site gauge in order to use the portable static pressure gauge. It also may be possible to find small ports in the ductwork ahead of and after the collector. 0 Clean any deposits out of the measurement ports. 0 If the inlet and outlet ports are close together, connect both sides of the static pressure gauge to the ports and observe the static pressure for 1 to 5 minutes. 0 If the ports are not close together, measure the static pressure in one port for 10 to 30 seconds and then proceed to the other port for 10 to 30 seconds. As long as the static pressure drop is reasonably stable (the typical condition), the two values can be subtracted to determine the static pressure drop. 0 Under no circumstances should on-site plant instruments be disconnected without the explicit approval of respon- sible plant personnel. Instruments connected to differ- ential pressure transducers should not be disconnected. The static pressure data should be adjusted to the baseline process operating rate in order to evaluate shifts in gas resistance since the baseline period. The equation presented in section 2.5.1 can be used for this calculation. 44 ------- INSPECTION OF MECHANICAL COLLECTORS Level 3 Inspection Procedures Evaluate inlet and outlet gas temperatures. These measurements are conducted whenever it is necessary to determine if air infiltration is causing reduced particulate matter collection efficiency and/or collector corrosion. The steps in measuring the gas temperature are outlined below. 0 Locate safe and convenient measurement ports on the inlet and outlet ductwork of the collector. Often small ports less than 1/4" diameter are adequate. Measurements using ports on the baghouse shell are often inadequate since moderately cool gas is trapped against the inside wall of the shell. 0 Attach a grounding/bonding cable to the probe if vapor, gas, and/or particulate levels are potentially explosive. 0 Seal the temperature probe in the port to avoid any air infiltration that would result in a low reading. 0 Measure the gas temperature at a position near the middle of the duct if possible. Conduct the measurement for several minutes to ensure a representative reading. 0 Measure the gas temperature at another port and compare the values. On combustion sources, a gas temperature drop of more than 20 to 40 °F indicates severe air infiltration. 45 ------- INSPECTION OF MECHANICAL COLLECTORS Level 3 Inspection Procedures Evaluate the inlet and outlet gas oxygen levels. These measurements are performed to further evaluate the extent of air infiltration. However, these tests are limited to combustion sources since they are the only sources with oxygen concentrations in the effluent gas that are less than ambient levels. An increase of more than 1% oxygen going from the inlet to the outlet indicates severe air infiltration (e.g. inlet oxygen at 6.5% and outlet oxygen at 7.5%). The steps involved in measuring the flue gas oxygen levels are itemized below. 0 Locate safe and convenient measurement ports. Generally, the ports used for the temperature measure- ments are adequate for the oxygen measurements. e Attach a grounding/bonding cable to the probe if there are potentially explosive vapors, gases, and/or particulate. 0 Seal the probe to prevent any ambient air infiltration around the probe. 0 Measure the oxygen concentration at a position near the center of the duct to avoid false readings due to localized air infiltration. The measurement should be repeated twice in the case of gas absorption instruments. For continuous instruments, the measurement should be conducted for 1 to 5 minutes to ensure a representative value. 0 If possible, measure the carbon dioxide concentration at the same locations. The sum of the oxygen and carbon dioxide concentrations should be in the normal stoich- iometric range for the fuel being burned. If the sum is not in this range, a measurement error has occurred. 0 As soon as possible, complete the measurements at another port. Compare the oxygen readings obtained. If the out- let values are substantially higher, severe air infiltra- tion is occurring. 46 ------- INSPECTION OF MECHANICAL COLLECTORS Level A Inspection Procedures 2.A.4 Level A Inspection Procedures The Level A inspection includes many inspection steps per- formed during Level 2 and 3 inspections. These are described in earlier sections. The unique inspection steps of Level A inspections are described below. Evaluate locations for measurement ports. Many existing mechanical collectors do not have safe and convenient ports that can be used for static pressure, gas temperature, and gas oxygen measurements. One purpose of the level A inspection is to select (with the assistance of plant personnel) locations for ports to be installed at a later date to facilitate Level 3 inspections. Information on possible sample port locations is provided in the U.S. EPA Publication titled, " Preferred Measurement Ports for Air Pollution Control Systems", EPA 3AO/1-86-03A. Evaluate potential safety problems. Agency management personnel and/or senior inspectors should identify any potential safety problems involved in standard Level 2 or Level 3 inspections at this site. To the extent possible, the system owner/operators should eliminate these hazards. For those hazards that can not be eliminated, agency personnel should prepare notes on how future inspections should be limited and should prepare a list of the necessary personnel safety equipment. A partial list of common health and safety hazards includes the following. 0 Inhalation hazards due to fugitive leaks into walkways near the collector 0 Inhalation hazards due to exposed friable asbestos insulation on the mechanical collector and hoppers 0 Burn hazards on incompletely insulated surfaces 0 Weak catwalk and ladder supports 0 Heat stress in vicinity of hot collectors A7 ------- INSPECTION OF MECHANICAL COLLECTORS Level 4 Inspection Procedures Evaluate potential safety problems i.n the process area. The agency management personnel and/or senior inspectors should evaluate potential safety problems in the areas which may be visited by agency inspectors during Level 2 and/or Level 3 inspections. They should prepare a list of the activities that should not be performed and locations to which an inspector should not go as part of these inspections. The purpose of this review is to minimize inspector risk and to minimize the liability concerns of plant personnel. Prepare _a system flowchart. A relatively simple flowchart is very helpful in conducting a complete and effective Level 2 or Level 3 inspection. This should be prepared by agency management personnel or senior inspectors during a Level A inspection. It should consist of a simple block diagram that includes the following elements. 0 Source(s) of emissions controlled by a single mechanical collector 0 Location(s) of any fans used for gas movement through the system (used to evaluate inhalation problems due to positive static pressures) 4 Locations of any main stacks and bypass stacks 0 Location of mechanical collector 0 Locations of major instruments (static pressure guages, transmissometers, thermocouples) ------- 3. INSPECTION OF ELECTROSTATIC PRECIPITATORS 3.1 Components and Operating Principles 3.1.1 Components of Electrostatic Precipitators An electrostatic precipitator consists of a large number of discharge electrodes and collection plates arranged in parallel rows along the direction of gas flow. The collection plates are normally grounded along with the hoppers and shell of the precipitator. The discharge electrodes are energized to negative voltages ranging between 15,000 volts and 50,000 volts. The gas velocity through the numerous parallel passages of the precipitator ranges from 3 to 8 feet per second. This represents an order of magnitude decrease in the velocity that exists in the duct- work leading to the precipitator. The deceleration is accomplished in an inlet nozzle at the front of the precipitator. There are normally one or more perforated plates to achieve as uniform gas distribution as possible. The high voltage for the discharge electrodes is provided by a transformer-rectifier set (hereafter termed T-R set). It converts alternating current from a 480 volt supply to direct current at very high voltages. Each T-R set energizes an independent portion of the electrostatic precipitator called a field. The T-R sets are always mounted on the roof of the precipitator since it is difficult to run the high voltage lines for long distances. There are normally 2 to 5 fields in series along the direction of gas flow. However, in some units handling difficult to collect dust and subject to very stringent emission requirements, there can be as many as 14 fields in series. Each field in series removes from 50 to 852 of the incoming particulate matter. Most large precipitators are also divided into parallel chambers. Solid partitions between the chambers prevents gas from passing from one chamber to the other while passing through the precipitator. Each of the chambers is evaluated separately during the inspection. ------- INSPECTION OF ELECTROSTATIC PRECIPITATORS Components and Operating Principles Each of the T-R sets is connected to a control cabinet. This controls the 480 volt alternating current power supply to the T-R set. It contains all of the electrical meters used to evaluate the operating conditions inside each of the precipitator fields. A major part of the inspection involves the interpretation of this electrical data. One of the first steps in the evaluation of the electrical data is to determine how the T-R sets are laid out on the precipitator so that the various control cabinets can be matched up with the T-R sets they control. This is important since the field- by-field trends in a chamber are used to evaluate potential operating problems. The types of meters present on the control cabinet are listed below along with the usual range of the gauge. * Primary voltage, 0 to 500 volts A.C. 0 Primary current, 0 to 200 amps. A.C. e Secondary current, 0 to 2 amps D.C. 0 Secondary voltage, 0 to 50 kilovolts, D.C. 0 Spark Rate, 0 to 200 sparks/minute The primary voltage and current data concerns the ABO volt alternating current power supply to the T-R set. The secondary voltage is the voltage leaving the T-R set and on the discharge electrodes within the precipitator. The secondary current is the direct current flow from the T-R set that passes through the field. The spark rate is the number of short tern arcs that jump between the discharge electrodes and collection plates in the field. 3.2 Operating Principles Electrical conditions can be evaluated using either the primary meters or the secondary meters. Whenever they are available, the secondary meters are generally used since these provide information on the electrical conditions within the precipitator fields. However, many older precipitators were not equipped with secondary voltage meters. For these units, the primary meters can be used. 50 ------- INSPECTION OF ELECTROSTATIC PRECIPITATORS Components and Operating Principles Under normal operating conditions, the values of the primary and secondary meters in each field can not be set intentionally by the operators. Instead, the electrical operating conditions are deter- mined by the characteristics of the particles passing through the precipitator field and by the ability of the power supply to respond to sparks within the field. Some of the most important properties of the dust include the total quantity of dust, the particle size distri- bution of the oust, and the particle resistivity distribution. The dust resistivity is a measure of the ability of the electrons on the surface of the dust particles to pass to the grounded collection plate. If the electrons can flow easily, the dust resistivity is low. As illustrated in Figure 3-1, the electrons can flow around the outside surfaces of particles that comprise the dust layer on the collection plate or they can pass directly through the dust particles. When the particle temperature is above 500 °F, the constitutents within the dust particles generally provide a conductive path. There- fore, the resistivity tends to decrease as the particle temperatures increase above 500 °F. This type of charge dissipation is termed "bulk conductivity". Below 350 °F, compounds such as sulfuric acid and water condense on the particle surfaces to facilitate electron flow around the outer surfaces. Generally the resistivity drops rapidly as the particle temperature drops below 350 °F. Due to the strong temperature dependence of these two separate parts of charge dissipation, the particle resistivity exhibits a peak when the temper- ature is in the range of 350 to 500 °F as illustrated in Figure 3-2. For precipitators designed to operate in the less than 350 °F temperature range, slight changes in the flue gas temperature can have a dramatic impact on the resistivity. Changes of 20 to 25 °F can result in more than a factor of 10 difference in the observed resistivity. This is significant since many commercial precipitators operate on gas streams in which inlet temperature on one side is more than 30 °F different than the inlet temperature on the other side. In these cases, significant differences in the resistivity can exist. 51 ------- INSPECTION OF ELECTROSTATIC PRECIPITATORS Components and Operating Principles Smile Particle lulk CinJuctmty Surface Conductivity firtienlate layer Ctlltction. Plate Figure 3-1. Alternative paths for electron flow through dust layers on collection plates 10 ,12 f ID11 10 = 10 ' ,„• 20C 300 400 WO 600 GAS Figure 3-2. Typical resistivity versus temperature relationship 52 ------- INSPECTION OF ELECTROSTATIC PRECIPITATORS Components and Operating Principles The high resistivity zones in the precipitator generally have low currents, low voltages, and high spark rates. Due to the poor electrical operating conditions, overall particle collection can be quite low. In the low resistivity zones, the currents can be very high while the spark rates are negligible. In these areas, the dust layer on the collection plates is not strongly bonded and even light rapping can result in the reentrainment of the material that had been collected. It is desirable to maintain a precipitator in the moderate resistivity range. The electrical operating conditions of an electrostatic precipitator can be summarized using graphs, and power input totals. Figure 3-3 illustrates graphs of the secondary voltage, secondary currents, and spark rate for a one chamber, four field precipitator. Baseline data for each parameter is provided in the graphs to help identify shifts in these electrical conditions. When all of the fields in a given chamber shift in unison (sometimes there is a several hour time lag for the outlet fields), there has normally been a change in the dust characteristics due to process operating changes or fuel changes. When only one of the fields shifts, there is normal- ly an internal mechanical problem. The advantage of the graphs is that they allow for rapid intrepretation of the large quantity of data obtained while observing the T-R set control cabinets. Another way to summarize the electrical data is to calculate the overall power input for a precipitator chamber. This can be done using either the primary meters using Equation 3-1 or the secondary meters using Equation 3-2. Primary Meters: (Volts, A.C.) x (Amps. A.C.) x 0.75 • (Watts) Equation 3-1 Secondary Meters: (Kilovolts, D.C.) x (Milliamps, D.C.) « (Watts) Equation 3-2 The power input in watts for each field in the chamber is then added to calculate the total power input. If the actual gas flow rate is known, the power input is often presented as total watts per thousand actual cubic feet per minute of gas flow. 53 ------- INSPECTION OF ELECTROSTATIC PRECIPITATORS Components and Operating Principles It should be noted, however, that the power input is usually calculated only for precipitators that consistently operate in either the moderate or high resistivity range. In these ranges, an increase in the power input generally corresponds with a decrease in the particulate emission rate. In the low resistivity range, there is no typical relationship between power input and particulate emission rates. The alignment between the parallel sets of collection plates and discharge electrodes is very important. For units with high resistivity zones, the spacing tolerances must be maintained within plus or minus a quarter inch throughout the unit. Even for units with moderate-to-low resistivity, the alignment must be within plus or minus a half inch throughout the unit. Considering that there are a large number of collection plates and discharge electrodes, maintaining proper alignment is not simple. Large quantities of dust are often handled by electrostatic precipitators. The types of solids discharge valves and solids handling systems are generally selected based on the overall quantity of material to be transported and on the characteristics of these solids. The most common types of solids discharge systems include (1) rotary valves and screw conveyors, (2) pneumatic systems, and (3) pressurized systems. The fan can be either located before or after the electrostatic precipitator. When it is after the precipitator, the gas stream is pulled" through and the static pressure is less than atmospheric pressure (termed "negative pressure")* As with other types of control devices, negative pressure electrostatic precipitators are vulnerable to air infiltration. This can lead to a number of significant operating problems. When the fan is before the precipitator, the gas stream is "pushed" through. This creates static pressures inside the precipi- tator which are greater than atmospheric pressure (termed "positive pressure"). Special care is warranted whenever inspecting these units, since fugitive emissions from the unit can result in very high levels of toxic pollutants in the vicinity of the precipitator. ------- INSPECTION OF ELECTROSTATIC PRECIPITATORS Components and Operating Principles INSPECTION Or ELECTROSTATIC HttCWUTORS 28 20 10 man uu MSUIKE •1500 £1000 500 •• 30 *M 20 1O UTA 'FIELDS • Figure 3-3. Trends in the voltages, currents and spark rates in a precipitator chamber 55 ------- INSPECTION OF ELECTROSTATIC PRECIPITATORS General Safety Considerations 3.2 General Safety Considerations Electrostatic precipitators often serve combustion sources such as cement kilns, lime kilns, coal-fired boilers, and glass furnaces. Fugitive emissions from systems can accumulate in poorly ventilated areas around the precipitator such as the roof and hopper weather enclosures, annular stack monitoring locations, and areas adjacent to cracked breeching expansion joints. The inhalation hazards can include chemical asphyxiants, physical asphyxiants, toxic gases/ vapors, and toxic particulate. Portable instruments should not be used on electrostatic precipitator systems. Very high static voltages can accumulate on probes downstream of precipitators due to the impaction of charged particles. Touching improperly grounded and bonded probes can result in involuntary muscle action that can results in a fall. Furthermore, in some units, the probes could inadvertently approach the electrified zone of the precipitator that operates at 25 to 45 kV. Inspectors should not enter an electrostatic precipitator under any circumstances. All of the necessary inspection steps can be accomplished without internal inspections. Furthermore, the side access hatches and penthouse/roof access hatches should not be opened under any circumstances. The internal components can be at high voltages even though the unit is out-of-service. Also, the hopper hatches should not be opened during the inspection since hot, free flowing dust can be released and since the inrushing air can cause hopper fires in some cases.. 56 ------- INSPECTION OF ELECTROSTATIC PRECIPITATORS Inspection Summaries 3.3 Inspection Summaries 3.3.1 Level 1 Inspections Stack ° Visible emissions for 6 to 30 minutes for each stack or discharge vent 0 Presence of condensing plume Electrostatic Precipitator 0 Not applicable Process ° Presence or absence of fugitive emissions 3.3.2 Level 2 Inspections Basic Inspection Points Stack e Visible emissions for 6 to 30 minutes for each stack or discharge vent 0 Duration and timing of puffing 0 Presence of condensing plume Transmissometer 0 Double-pass transmissometer conditions 0 Average opacity.for at least the last 24 hours Electrostatic Precipitator * Transformer-rectifier set electrical data 0 General physical condition Process "Process operating rate 0 'Process operating conditions Follow-up Electrostatic Precipitator 0 Opacity strip charts/records and transformer- rectifier set records (baseline files) 0 Rapper frequency and intensity 0 Wire failure rate and location records 57 ------- INSPECTION OF ELECTROSTATIC PRECIPITATORS Inspection Summaries 3.3.3 Level 3 Inspections (Identical to Level 2 Inspections) 3.3.4 Level 4 Inspections Stack ° All elements of a Level 3 inspection Transmissometer 0 Location 0 Quality assurance procedures Electrostatic Precipitator 0 All elements of a Level 2/Level 3 inspection 0 Flowchart of compressed air supply 0 Start-up/shut down procedures 0 Potential inspection safety problems Process ° All elements of a Level 3 inspection 0 Basic flowchart of process 0 Potential inspection safety problems 58 ------- INSPECTION OF ELECTROSTATIC PRECIPITATORS Basic Level 2 Inspection Procedures 3. A Inspection Procedures Techniques for the inspection of electrostatic precipi- tators can be classified as Level 1, 2, 3, or A. The Level 1 inspection consists of a visible emission observation from outside the plant. This is not discussed in this manual. The Level 2 inspection primarily involves a walkthrough evaluation of the electrostatic precipitator system and process equipment. All data are provided by on-site gauges. The Level 3 inspection is identical to the Level 2 inspection since it is impractical to use portable instruments to evaluate large electrostatic precipitator systems. Furthermore, there are a number of unique and significant hazards involved in the use of the portable instruments on precipitator systems. The Level 4 inspection is performed by agency supervisors or senior inspectors to acquire baseline data. The scope of the Level A inspection is identical to the Level 2/Level 3 inspection. 3.A.I Level 2 Inspections Evaluate the electrostatic precipitator visible emissions. If weather conditions permit, determine the baghouse effluent average opacity in accordance with U.S. EPA Method 9 procedures (or other required procedure). The observation should be conducted during routine process operation and should last 6 to 30 minutes for each stack and bypass. The majority of units operate with effuent opacities less than 10% on a continuous basis. Higher opacities indicate emission problems. The timing and duration of all significant spikes should be noted after the visible emission observation. This information will be useful in determining some of the possible causes of the spiking condition. Significant puffs on either a regular frequency or on a random basis are not normal. However, in some cases, light puffing can occur even when the operating conditions are optimal. If weather conditions are poor, an attempt should still be made to determine if there are any visible emissions. The pres- ence of a significant plume indicates emission problems. Do not attempt determine the "average opacity" at such times. 59 ------- INSPECTION OF ELECTROSTATIC PRECIPITATORS Basic Level 2 Inspection Procedures Evaluate condensing plume conditions. Condensing plume conditions in electrostatic precipitator systems are usually caused by sulfuric acid vapors, ammonium chloride vapors, and/or ammonium sulfate vapors generated in the process equipment. They can also be caused by improper operation of a flue gas conditioning system (present on some systems). The vaporous material condenses once the gas enters, the cold ambient air. Condensing plumes usually have a bluish- white color. In some cases, the plume forms 5 to 10 feet after leaving the stack. Evaluate double-pass transmissometer physical conditions. Most precipitators have a transmissometer for the continu- ous monitoring of visible emissions. If a unit is present, and if it is in an accessible location, check the light source and retroreflector modules to confirm that these are in good work- ing order. Check that the main fan is working and that there is a least one dust filter for the fan. On many commercial models it is also possible to check the instrument alignment without adjusting the instrument. Note; On some models, moving the dial to the alignment check position will cause an alarm in the control room. This is to be moved only by plant personnel and only when It will not disrupt plant operations. Evaluate double-pass transmissometer data. If the transmissometer appears to be working properly, evaluate the average opacity data for at least the previous 24 hours prior to the inspection. If possible, the average opacity data for selected days since the last inspection should also be reviewed. This evaluation is helpful in confirming that the units being inspected are operating in a representative fashion. If the unit is working better during the inspection than during other periods, it may be advisable to conduct an unscheduled inspection in the future. As part of the review of average opacity, scan the data to determine the frequency of emission problems and to evaluate how rapidly the operators are able to recognize and eliminate the condition. 60 ------- INSPECTION OF ELECTROSTATIC PRECIPITATORS Basic Level 2 Inspection Procedures Evaluate the transformer-rectifier set electrical data. The first step in evaluating the transformer-rectifier (T-R) set electrical data is to obtain or prepare a sketch that indicates the arrangement of the T-R sets on the precipitator. This drawing should indicate the number of chambers in the pre- cipitator and the number of T-R sets in series in each chamber. The T-R set numbers should be included on the sketch. For each chamber, the T-R set electrical data is recorded starting with the inlet field and proceeding to the outlet field. In some cases, the control cabinets are scrambled. The follow- ing data should be recorded. Primary Primary Secondary Secondary Spark Rate Voltage Current Voltage Current (Volts) (Amps) (Kilovolts) (Millamps) (Number/Min.) Inlet Field Second Field nth Field The voltages and currents should be recorded when the gauge reaches the highest stable value for approximately one second or more. If there is any question about the adequacy of the spark rate meter, the spark rate should be determined by counting the number of flucuations of the primary voltage and/or secondary voltage meters. 61 ------- INSPECTION OF ELECTROSTATIC PRECIPITATORS Basic Level 2 Inspection Procedures Evaluate the transformer-rectifier set electrical data. Compare the secondary and/or primary voltages against base- line levels for this unit and against typical values. Generally, the primary voltages are above 250 volts and they are usually in the range of 250 to 380 volts (A.C.). The secondary voltages are normally in the range of 20 to 45 kilovolts (D.C). A drop in the primary voltage of 30 volts (A.C.) or a drop in the sec- ondary voltage of 5 kilovolts (D.C.) in a given field indicates significantly reduced particulate control capability for that field. To check the particle resistivity conditions, plot the voltages, currents, and spark rates for each of the chambers (Figure 3-3). Compare these drawings with similar drawings prepared from baseline data. There has probably been a signi- ficant shift in the particle resistivity if all or most of the fields in a chamber have shifted in the the same direction at approximately the same tine (outlet fields often lag several hours). The symptoms of resistivity shifts are summarized below. 0 Higher resistivity Reduced primary or secondary voltages Reduced primary or secondary currents Increased spark rates . 0 Lower resistivity Reduced primary or secondary voltages Increased primary or secondary currents Decreased spary rates In some units, the resistivity conditions in one chamber are quite different from the resistivity conditions in other adjacent chambers. In these types of units, the changes in the secondary voltages and currents are much greater in some of the chambers. This condition is often caused by slight differences in the flue gas temperatures entering the various chambers and/or by maldistribution of resistivity conditioning materials injected into the system. 62 ------- INSPECTION OF ELECTROSTATIC PRECIPITATORS Basic Level 2 Inspection Procedures Evaluate precipitator general physical conditions. While walking around the precipitator and its inlet and out- let ductwork, check for obvious corrosion around the potential "cold" spots such as the corners of the hoppers, near the solids discharge valve, and the access hatches. On negative pressure units, check for audible air infiltration through the corroded areas, warped access hatches, eroded solids discharge valves, or other sites. On positive pressure units, check for fugitive emissions of dust from any corroded areas of the system. Evaluate the process operating rate. Record one or more process operating rate parameters that document that the source conditions are representative of normal operation. Evaluate process operating conditions. Record any process operating parameters that have an impact on the characteristics and/or quantities of pollutants generated. Some of the important variables are listed below. 0 Gas stream temperatures and static pressures 0 Gas stream oxygen levels 0 Raw material characteristics Evaluate process fugitive emissions. Perform complete visible emission observations on any major process fugitive emissions. If the conditions preclude a com- plete observation, note the presence and timing of any fugitive releases. 3.4.2 Follow-up Inspection Points for Level 2 Inspections Evaluate rapper systems. The collection plate, discharge electrode, and gas distri- bution screen rapping systems are evaluated when low power inputs are observed in one or more fields or when there is puffing. Note any rappers that do not appear to be working or that do not sound proper when activating. A sketch is often a useful way to summarize this information 63 ------- INSPECTION OF ELECTROSTATIC PRECIPITATORS Follow-up Level 2 Inspection Procedures Request that plant personnel open the rapper control cabinets (if they are qualified). Compare the present rapper system intensities with the baseline values. If the intensities are now higher, the unit may have high resistivity dusts, binding or broken rapper shaft connections, or poor start-up procedures. It should be noted that it is rarely possible to minimize high resistivity dust problems simply by increasing rapper intensities and that some rapper shaft and/or collection plate alignment problems can occur at high intensities. 0 If the intensities are now much lower, the unit may have low resistivity dusts, or the rappers may have been temporarily turned down to minimize obvious puffing. Determine the activition frequency of the various groups of rappers. This can often be done by watching selected groups of rappers for a period of 10 to 60 minutes. It can also be determined by checking the timers in the control cabinets. However, the indicated rapper frequencies on the timers are not always reliable. Compare the activation frequencies with the observed frequency of puffing. c If the activation frequency is high, the unit may be having problems with high resistivity dust. It is rarely possible to minimize this condition simply by increasing rapper frequency. 0 If the activation frequency is low, the unit may have lower resistivity dust than during the baseline period. As long as the electrical conditions and the opacity are acceptable, low frequency is desirable. 0 Puffing is often related to the activation frequency of the outlet field collection plate rappers. 0 Note any occasions when more than one rapper is activated simultaneously or when two or more rappers are activated within a period of several seconds. ------- INSPECTION OF ELECTROSTATIC PRECIPITATORS Follow-up Level 2 Inspection Procedures Evaluate the opacity strip charts/records and the transformer-rectifier set records (baseline files). This is a time consuming portion of the inspection. It should be done only when the plant is experiencing frequent and significant excess emission problems and there is some question concerning the proposed corrective actions. Obtain the opacity records and quickly scan the data for the previous 1 to 12 months to determine time periods that had especially high and especially low average opacities. Time periods with and without severe spiking are also of interest. Select the precipitator operating logs and the process opera- ting logs that correspond with the times of the opacity strip charts/records selected. Compare the precipitator operating data and process operating data against baseline information to identify the general category of problem(s) causing the excess emission incidents. Evaluate the source's proposed corrective actions to minimize this problem(s) in the future. Evaluate wire failure and location records. Request the discharge wire failure records from the opera- tors if it appears that wire failures have caused temporary outages of one or more fields since the last inspection. If specific wire failure records are not maintained, attempt to determine how many wires have failed since the last inspection. Most electrostatic precipitors operate with wire failure rates that are much less than 1 per month. Higher failure rates may indicate plate-wire misalignment, clearance problems, improper rapping operation, inadequate wire tension, and/or corrosion. Wire failure is often a symptom of other more substantial problems. Evaluate the owner/operators' plan for minimizing excess emission incidents caused by wire failure. It is generally necessary to fix the underlying cause of the failure rather than simply reinstalling the wire. 3.4.3 Level 3 Inspection Procedures These are identical to Level 2 inspection procedures since portable inspection instruments are not used for precipitators. 65 ------- INSPECTION OF ELECTROSTATIC PRECIPITATORS Level 4 Inspection Procedures 3.4.4 Level 4 Inspection Procedures The Level 4 inspection includes many inspection steps per- formed during Level 2/Level 3 inspections. These are described in earlier sections. The unique inspection steps of Level 4 inspections are described below. Evaluate start-up and shutdown procedures. The start-up and shutdown procedures used at the plant should be discussed to confirm the following. The plant has taken reasonable precautions to minimize the number of start-up/shutdown cycles. The precipitator is energized in a reasonable time after start-up of the process equipment. Inspectors should remember that energizing too early in the start-up process can lead to precipitator explosions or to deposits on the collection plates that reduce the performance capability of the unit. Evaluate potential safety problems. Agency management personnel and/or senior inspectors should identify potential safety problems involved in standard Level 21 Level 3 inspections at this site. To the extent possible, the system owner/operators should eliminate these hazards. For those hazards which can not be eliminated, agency personnel should prepare notes on how future Inspections should be limited and should prepare a list of the necessary personnel safety equipment. A partial list of common health and safety hazards include the following. 0 Inhalation hazards due to fugitive leaks from inlet breech- ings, inlet expansion section, access hatches, hoppers, outlet contraction section, expansion joints, and fans 0 Corroded percipitator roofs ladder supports 0 Ungrounded rappers 0 High voltage in control cabinets 66 ------- INSPECTION OF ELECTROSTATIC PRECIPITATORS Level 4 Inspection Procedures Prepare a_ system flowchart. A relatively simple flowchart is very helpful in conducting a complete and effective level 2/level 3 inspection. This should be prepared by agency management personnel or senior inspectors during a level A inspection. This should consist of a simple block diagram that includes the following elements. 0 Source(s) of emissions controlled by a single precipitator 0 Location(s) of any fans used for gas movement through the system (used to evaluate inhalation problems due to positive static pressures) 0 Locations of any main stacks and bypass stacks 0 Layout and identification numbers of transformer- rectifier sets used in all chambers 0 Locations of major instruments (transmissometers, thermocouples) Evaluate potential safety problems in the process area. The agency management personnel and/or senior inspectors should evaluate potential safety problems in the areas that may be visited by agency inspectors during Level 2/Level 3 inspections. They should prepare a list of the activities that should not be performed and locations that an inspector should not go as part of these inspections. The purpose of this review is to minimize inspector risk and to minimize the liability concerns of plant personnel. 67 ------- A. INSPECTION OF WET SCRUBBERS The most common types of wet scrubber systems are addressed in this inspection notebook. The inspection procedures discussed in this section have been tailored to the specific design characteristics and operating problems of these scrubbers. Spray tower Packed beds Tray tower Mechanically aided Orifice Rod deck Venturi Inspectors and their supervisors should modify these procedures as necessary for types of scrubbers not specifically discussed in this notebook. 4.1 Scrubber system components and operating principles A scrubber is not an isolated piece of equipment. It is a sys- tem composed of a large number of individual components. A partial list of the major components of commercial systems is provided below. Scrubber vessel Gas cooler and humidifier Liquor treatment equipment Gas stream demister . Liquor recirculation tanks, pumps, and piping Alkaline addition equipment Fans, dampers, and bypass stacks One of the first steps in the inspection of any wet scrubber system is to prepare a flowchart that includes any of the components listed directly above. This will be invaluable in evaluating the on-site instrumentation and in identifying system operating problems. 69 ------- INSPECTION OF WET SCRUBBER SYSTEMS Components and Operating Principles 4.1.1 Characteristics of spray tower scrubbers A simplified sketch of a spray tower scrubber is illustrated in Figure 4-1. The gas stream enters near the bottom of the scrubber and goes upward at velocities between 2 and 10 feet per second. The liquor enters at the top of the unit through one or more spray headers. Nozzles are oriented on the headers so that all of the gas stream is exposed to the sprayed liquor. Careful scrubber design is necessary to achieve proper liquor distribution since this is a function of the type of nozzle used, the spray angle of the nozzles, the nozzle placements, and the liquor pressure. It is also important to design the headers so that solids deposits do not accumulate. A spray tower scrubber has only a limited particulate removal capability. It is selected for applications where there is very little particulate matter smaller than 5 microns. These scrubbers can be effective gas absorbers in addition to particulate collectors. Most of these systems are relatively simple and have only limited instrumentation. However, alkaline addition equipment and liquor treatment systems are often necessary when the units are used for gas absorption. Such units can be quite complicated. (tor.. *n Source: APTI Figure 4-1. Spray towei scrubbers Source: APTI 70 ------- INSPECTION OF WET SCRUBBER SYSTEMS Components and Operating Principles 4.1.2 Characteristics of Packed Tower Scrubbers This type of scrubber is used primarily for gas absorption. The large liquor surface area created as the liquor gradually passes over the packing material favors gas diffusion and absorption. Packed bed scrubbers are not effective for collection of small particulate matter since the gas velocity through the bed(s) is relatively slow. Packed beds can be either vertical (as shown in Figure 4-2) or horizontal. Regardless of the orientation of the bed, the liquor is sprayed from the top and flows downward across the bed. Proper liquor distribution is important for efficient removal of gases. This is one of the few types of scrubbers in which the static pressure drop is not very important. One of the major problems with these scrubbers is the accumula- tion of solids at the entry to the bed and within the bed. The dissolved and suspended solids levels in the liquor must be monitored carefully. Source: A?" I Figure 4-2. Packed bed scrubber 71 ------- INSPECTION OF WET SCRUBBER SYSTEMS Components and Operating Principles 4.1.3 Characteristics of Tray Tower Scrubbers A tray tower scrubber (Figure 4-3a) can be used for both particulate and gaseous removal. It consists of a series of trays with holes. The gas stream enters from the bottom and passes upward through the holes. Liquor enters from the top and passes across each tray as it goes downward. Downcomers are used for moving the liquor from one tray to another. Two of the major tray designs are shown in Figure 4-3b. The sieve plate has relatively large holes compared with the impingement tray. The latter has high velocities through the holes and a target directly above the holes. One of the main advantages of this style of scrubber vessel is that there are several opportunities to collect pollutants. Slight gas-liquor maldistribution on one tray can be tolerated since the material can be caught on subsequent trays. The liquor suspended and dissolved solids concentrations are important since it is easy for the holes to plug. Source: Figure 4-3a. Tray tower scrubber Figure A-3b. Common tray designs 72 ------- INSPECTION OF WET SCRUBBER SYSTEMS Components and Operating Principles A.1.4 Characteristics of Mechanically Aided Scrubbers One common type of mechanically aided scrubber is illustrated in Figure 4-4. The gas stream enters axially and is spun outward due to the rapid rotation of the scrubber fan blade. Liquor is sprayed in the inlet duct. Impaction of particles occurs on the initially slow moving droplets. Unlike all other types of scrubbers, this particular design does not have a "pressure drop". The mechanical energy provided by the shaft achieves the scrubbing action and moves the gas stream through the ductwork. There is a static pressure rise across this type of unit. These scrubbers are used only for relatively small systems having gas flows less than 10,000 ACFM. The scrubber systems are relatively simple. However, it is important to have high quality liquor so that erosion and build-up on the fan blades is minimized. Obviously, no fans are necessary with this type of system. Source: APTI Figure 4-4. Mechanically aided scrubber 73 ------- INSPECTION OF WET SCRUBBER SYSTEMS Components and Operating Principles A.1.5 Characteristics of Orifice Scrubbers The orifice scrubber is one of a large number of units which are classified as a gas atomized scrubber. This means that the droplets which serve as impaction targets are formed in high velocity gas streams. A sketch of an orifice scrubber is shown in Figure 4-5. In this unit, the gas enters the vertical tube and makes a 180° turn just above the surface of the liquor. The action of the gas stream atom- izes the liquor that was entrained by the passing gas stream. Baffles included in the scrubber vessel knock down any drops which remain suspended in the gas. Orifice scrubbers are often very small and very simple scrubbers. In some units, there is no recirculation pump and piping system. The inspection of these small orifice scrubbers is often complicated by the almost complete lack of instrumentation. Soi rce: APTT Figure 4-6. Orifice scrubber ------- INSPECTION OF WET SCRUBBER SYSTEMS Components and Operating Principles A.1.7 Characteristics of Venturi Scrubbers A conventional venturi scrubber is shown in Figure 4-7a. The gas stream enters the converging section and is accelerated approx- imately a factor of ten. The liquor is injected just above the throat. Droplets form due to the shearing action of the high gas velocities. Impaction of particles occurs on the droplets which are initially moving slower than the gas stream. The high liquor surface area also allows for gas absorption. The gas stream is decelerated in the diverging section. After the venturi section, the gas stream turns 90° and passes into the demister chamber. The venturi scrubbers are usually part of a large and relatively complex scrubber system. There are a large number of variations to the standard venturi configuration. Figure 4-7b illustrates one common throat design which incorporates internal dampers to vary the gas velocity. These can be opened or closed to maintain a constant static pressure drop when gas flow varies, or the dampers can be used to adjust the static pressure drop when the inlet particle size distribution varies. GAS INLET LIQUOR INLET THROAT DAMPERS GAS OUTLET- Figure 4-7a. Venturi scrubber Figure 4-7b. Throat dampers 75 ------- INSPECTION OF WET SCRUBBER SYSTEMS Components and Operating Principles 4.1.8 Characteristics of Rod Deck Scrubber This type of unit is similar to a venturi scrubber. However, a horizontal deck of rods is used to accelerate the gas stream rather than a conventional venturi. The restricted area between the rods provides for liquor atomization and particle impaction. The numbers of rods and the diameters of the rods can be varied as necessary to achieve the desired gas velocities and static pressure drops. The inspection procedures for this style of scrubber is very similar to that for classical venturi units. The only difference is that there is concern with rod erosion and corrosion in this design. Unlike conventional venturi scrubbers, these units can have several decks in series. The multiple deck arrangement is used primarily for gas absorption rather than particulate control. Source: APTI Figure 4-8. Rod deck scrubbers 76 ------- INSPECTION OF WET SCRUBBER SYSTEMS Components and Operating Principles A.1.9 Operating Principles Impaction is the primary means for collection of particles in wet scrubbers. The effectiveness of impaction is related to the square of the particle diameter and the difference in velocities of the liquor droplets and the particles. The importance of particle size is emphasized in Figure 4-8. For particles greater than 1 to 2 microns, impaction is so effective that penetration (emissions) is quite low. However, penetration of smaller particles, such as the particles in the 0.1 to 0.5 micron range is very high. Unfortunately, some commercial processes can generate substantial quantities of particulate in this submicron range. Most aerosols in this size range are formed from vaporous material that condenses as the gas stream leaves the process equip- ment or as the gas stream enters the relatively cold scrubber. For a constant particle size distribution, the overall particu- late collection efficiency generally increases as the static pressure drop increases. The static pressure drop is a measure of the total amount of energy used in the scrubber to accelerate the gas stream, to atomize the liquor droplets, and to overcome friction. At high static pressure drops, the difference in droplet velocities and particle velocities is high and a large number of small diameter droplets are formed. Both of these conditions favor particle impaction into water droplets. Another important variable is the liquor surface tension. If this is too high, some small particles that impact on the water droplet will "bounce" off and not be captured. High surface tension also has an adverse impact on droplet formation. Unfortunately, the scrubber liquors having surface tensions that provide optimum parti- cle impaction may have poor solids settling properties. Surfactants can be added to reduce surface tension. Conversely, flocculants and anti-foaming agents generally increase the surface tension. 77 ------- INSPECTION OF WET SCRUBBERS Components and Operating Principles 4 S • 7 • Particte Diameter. »m 10 Figure 4-9. Relationship between particle penetration (emissions) and particle size 78 ------- INSPECTION OF WET SCRUBBER SYSTEMS General Safety Considerations A. 2 General Safety Considerations Some wet scrubbers systems operate at much higher positive static pressures that other types of air pollution control systems. Furthermore, there is a significant potential for corrosion and erosion of the scrubber vessel and ductwork. For these reasons, fugitive leaks are a common problem. The inhalation hazards can include chemical asphyxiants, physical asphyxiants, toxic gases, and toxic particulate. Inspectors should avoid all areas with obvious leaks and any areas with poor ventilation. During Level 3 and Level A inspections, only small diameter ports should be used. Extreme care is often necessary when walking around the scrubber and when climbing access ladders. Slip hazards can be created by water droplets reentrained in the exhaust gas, by liquor draining from the pumps, and by liquor seeping from pipes and tanks. These slip hazards are not always obvious. Furthermore, freezing can occur in cold weather. A few systems are subjected to fan imbalance conditions due to the build-up of sludge on the fan blades, the corrosion of the fan blades, the erosion of the fan blades, and a variety of other factors, The inspection should be terminated immediately whenever an inspector observes a severely vibrating fan. A responsible plant representa- tive should be notified once the inspector reaches a safe location. Severely vibrating fans can disintigrate. All liquor samples necessary .for Level 3 or Level A inspections should be taken by the plant personnel, not the inspector. Further- more, the inspectors should only ask responsible and experienced plant personnel to take the samples. Eye injuries and chemical burns (in some cases) ire possible if the samples are taken incor- ectly. Inspectors should not under any circumstances enter a wet scrubber vessel or any tank or confined area used in the system. All of the necessary inspection steps can be accomplished without internal inspections. Access hatches or viewing ports should not be opened during the inspection due to the risk of eye injuries. 79 ------- INSPECTION OF WET SCRUBBERS Inspection Summaries 4.3 Inspection Summaries A.3.1 Level 1 Inspections (All types of scrubbers) Stack ° Visible emissions for 6 to 30 minutes for each stack or discharge vent 0 Mist reentrainment Wet Scrubber e Not applicable Process ° Presence or absence of fugitive emissions A.3.2 Level 2 Inspections Basic Inspection Points Stack ° Visible emissions for 6 to 30 minutes for each stack or discharge vent c Minimum and maximum stort term opacities due to process cycles 0 Droplet reentrainment Scrubber Vessels Spray Tower Scrubbers 0 Inlet liquor pressure 0 General physical condition Packed Bed, Tray Tower, and Mechanically Aided Scrubbers 0 Static pressure change 0 Liquor turbidity and settling rate 0 General physical condition Venturi, Rod Deck and Orifice Scrubbers Static pressure change General physical condition Process Process operating rate Process operating conditions Presence or absence of fugitive emissions 80 ------- INSPECTION OF WET SCRUBBER SYSTEMS Inspection Summaries A.3.2 Level 2 Inspections (Continued) Follow-up Scruber Vessels Spray Tower Scrubbers 0 Scrubber gas flow rate 0 Liquor turbidity and settling rate 0 Liquor distribution from nozzles 0 Demister condition Packed Bed, Tray Tower, and Mechanically Aided Scrubbers 0 Liquor pH 0 Liquor recirculation flow rate 0 Scrubber gas flow rate 0 Tray, bed, and demister condition 0 Mechanically aided scrubber rotational speed Venturi, Rod Deck, and Orifice Scrubbers 0 Liquor pH 0 Liquor turbidity and settling rate 0 Liquor recirculation rate 0 Scrubber gas flow rate 6 Venturi scrubber adjustable throat mechanism condition . 0 Demister condition A.3.3 Level 3 Inspections Stack ° Visible emissions for 6 to 30 minutes for each stack or discharge vent* 0 Maximum and minimum short term opacities during process cycles* 0 Droplet reentrainment* Scrubber Vessels Spray Tower Scrubbers 0 Gas flow rate from scrubber 0 Liquor pH 0 Outlet gas temperature 81 ------- INSPECTION OF WET SCRUBBER SYSTEMS Inspection Summaries 4.3.3 Level 3 Inspections (continued) Packed Bed, Tray Tower, and Mechanically Aided Scrubbers 0 Static pressure change 0 Gas flow rate from scrubber 0 Outlet liquor pH 0 Outlet gas temperature Venturi, Rod Deck, and Orifice Scrubbers Static pressure change Gas flow rate from scrubber Outlet liquor pH Outlet gas temperature Process Process operating rate* Process operating conditions* Presence or absence of fugitive emissions* A.3.4 Level A Inspections Stack e All elements of a Level 3 inspection Wet Scrubber 0 All elements of.a Level 3 inspection 0 Locations for measurement ports e Potential inspection safety problems Process e All elements of a Level 3 inspection * Basic flowchart of process ",Potential inspection safety problems * See Level 2 basic and follow-up inspection procedures. 82 ------- INSPECTION OF WET SCRUBBER SYSTEMS Basic Level 2 Inspection Procedures 4.4 Inspection Procedures Techniques for the inspection of wet scrubber systems can be classified as Level 1, 2, 3, or 4. The Level 1 inspection consists of a visible emission observation from outside the plant. This is not discussed in this manual. The Level 2 inspection primarily involves a walkthrough evaluation of the wet scrubber system and process equipment. All data are provided by on-site gauges. The Level 3 inspection includes all inspec- tion points of the Level 2 inspection and includes independent measurements of wet scrubber operating conditions when the on- site gauges are not adequate. The Level 4 inspection is per- formed by agency supervisors or senior inspectors to acquire baseline data. The scope of the Level 4 inspection is identical to the Level 3 inspection. 4.4.1 Level 2 Inspections Evaluate the wet scrubber visible emissions. If weather conditions permit, determine the baghouse effluent average opacity in accordance with U.S. EPA Method 9 procedures (or other required procedures). The observation should be conducted during routine process operation and should last 6 to 30 minutes for each stack and bypass vent. The observation should be made after the water droplets contained in the plume vaporize (where the steam plume "breaks")' The presence of a particulate plume greater than 10% generally indicates a scrubber operating problem, and/or the generation of high concentrations of submicron particles in the process, and/or the presence of high concentrations of vaporous material in the effluent gas stream. In addition to evaluating the average opacity, inspectors should scan the visible emissions observation to identify the maximum and minimum short term opacities. This is especially useful information if there are variations in the process operating conditions. For processes such as grey iron cupolas and drum mix asphalt plants, the difference in the minimum and maximum opacities provides an indication of changing particle size distributions. B3 ------- INSPECTION OF WET SCRUBBER SYSTEMS Basic Level 2 Inspection Procedures Evaluate the vet scrubber visible emissions, (continued) If weather conditions are poor, an attempt should still be made to determine if there are any visible emissions. Do not attempt to determine "average opacity" during adverse weather conditions. The presence of a noticeable plume generally indicates wet scrubber operating problems. Evaluate droplet reentrainment. Droplet reentrainment indicates a significant demister problem that can create a local nuisance and that can affect stack sampling results. The presence of droplet reentrainment is indicated by the conditions listed below. 0 Obvious rainout of droplets in the immediate vicinity of the stack 0 Moisture and stains on adjacent equipment 0 Mud lip around the stack discharge Evaluate the wet scrubber static pressure change. The wet scrubber static pressure drop* should be recorded if the gauge appears to be working properly. The following items should be checked to confirm the adequacy of the on-site gauge. 0 The gauge "face" should be clear of obvious water and deposits. 0 The lines leading to the inlet and outlet of the baghouse s'hould be intact. If there is any question concerning the gauge, ask plant personnel to disconnect each line one at a time to see if the gauge responds. If it does not move when a line is disconnected, the line may be plugged or the gauge is inoperable. Note: The lines should only be disconnected _by_ plant personnel and only when this will not affect plant operations. * For mechanically aided scrubbers it is a static pressure rise. 84 ------- INSPECTION OF WET SCRUBBER SYSTEMS Basic Level 2 Inspection Procedures Evaluate the wet scrubber static pressure change fcont.). Wet scrubber systems operate with a wide range of static pressure drops as indicated in the list below. Data is not provided for spray tower scrubbers since static pressure drop is not a useful inspection parameter for this type unit. Packed bed 2 to 6 inches W.C. Tray tower 2 to 12 inches W.C. Mechanically Aided 2 to 12 inches W.C. Orifice A to 25 inches W.C. Rod deck 10 to 120 inches W.C. Venturi 10 to 120 inches W.C. It should also be noted that there is a wide range of required static pressure drops for identical wet scrubbers operating on similar industrial processes due to the differ- ences in particle size distributions. For these reasons, it is preferable to compare the present readings with the baseline values for this specific source. Increased static pressure drops* generally indicate the following possible condition(s). Packed bed scrubbers ° High gas flow rates 0 Partial bed pluggage Tray tower scrubbers * High gas flow rate Partial pluggage of trays Mechanically aided ° High rotational speed scrubbers Orifice scrubbers Venturi and Rod deck scrubbers High gas flow rate High liquor levels High gas flow rate High liquor flow rates Reduced rod spacings or constricted venturi throats * Static pressure rise for mechanically aided scrubbers 85 ------- INSPECTION OF WET SCRUBBER SYSTEMS Basic Level 2 Inspection Procedures Evaluate the wet scrubber static pressure change (cont.). Decreased static pressure drops* generally indicate the following possible condition(s). Packed bed scrubbers Tray tower scrubbers Mechanically aided scrubbers Orifice scrubbers 0 Low gas flow rates 0 Bed collaspe 0 High gas flow rate 0 Collaspe of tray(s) e Low liquor flow 0 Low rotational speed Venturi and Rod deck scrubbers Low gas flow rate Low liquor levels Low gas flow rate Low liquor flow rates Eroded rods or venturi dampers Increased rod spacings or increased venturi throat openings Evaluate the liquor inlet pressure. The pressure of the header that supplies the scrubber spray nozzle can provide an indirect indication of the liquor flow rate and the nozzle condition. When the present value is lower than the baseline value(s), the liquor flow rate has increased and there is a possibility of nozzle orifice erosion. Conversely, if the present value is higher than the baseline value(s) the liquor flow rate has decreased and nozzle and/or header pluggage Is possible. Unfortunately, these pressure gauges are very vulnerable to error due to solids deposits and due to corrosion. It is difficult to confirm that they are working properly. For these reasons, other indicators of low liquor flow such as the pump discharge pressure and the outlet gas temperature should be checked whenever low header or pipe pressures are observed. * Static pressure rise for mechanically aided scrubbers 86 ------- INSPECTION OF WET SCRUBBER SYSTEMS Basic Level 2 Inspection Procedures Evaluate the vet scrubber system general physical conditions. While walking around the wet scrubber system and its inlet and outlet ductwork, check for obvious corrosion and erosion. If any material damage is evident, check for fugitive emissions (positive pressure systems) or air infiltration (negative pres- sure systems). Avoid inhalation hazards and walking hazards while checking the scrubber system general physical condition. Prepare a sketch showing the locations of the corrosion and/or erosion damage. In addition to corrosion and erosion, inspectors should also check for any of the conditions listed below. c Severely vibrating fans (Leave area immediately!) 0 Cracked or worn ductwork expansion joints 0 Obviously sagging piping 0 Pipes that can not be drained and/or flushed Evaluate the liquor turbidity and solids settling rate. Ask a responsible and experienced plant representative to obtain a sample of the liquor entering the scrubber vessel. This can usually be obtained at a sample tap downstream from the main recirculation pump. The agency inspector should provide a clear sample bottle. Observe the turbidity of the liquor for a few seconds immediately after the sample is taken. The turbidity should be qualitatively evaluated as clear, very light, light, moderate, heavy, or very heavy. After allowing the sample to settle for five minutes, repeat the evaluation of the liquor turbidity and describe the thickness of the settled solids. Evaluate the process operating rate. Record one or more process operating rate parameters that document that the source conditions are representative of normal operation. 87 ------- INSPECTION OF WET SCRUBBER SYSTEMS Basic Level 2 Inspection Procedures Evaluate process operating conditions. Record any process operating parameters that have an impact on the characteristics and/or quantities of pollutants generated. Some of the important variables are listed below. 0 Gas stream temperatures 0 Gas stream static pressures 0 Gas stream oxygen levels 0 Raw material characteristics Evaluate process fugitive emissions. Perform complete visible emission observations on any major process fugitive emissions. If the conditions preclude a com- plete observation, note the presence and timing of any fugitive releases. 4.4.2 Follow-up Inspection Points for Level 2 Inspections Check liquor pH. Locate the on-site pH meter(s). Permanently mounted units are generally in the recirculation tank or in the liquor outlet lines from the scrubber vessel. Confirm that the instrument is working properly by reviewing the routine calibration records. In some cases, it is possible to watch plant personnel calibrate these instruments during the inspection. If the pH meter(s) appears to be working properly, review the pH data for at least the previous month. In units with instruments on the outlet and the inlet, the outlet values are often 0.5 to 2.0 pH units lower due to the absorption of carbon dioxide, sulfur dioxide, or other acid gases. Generally, all of the pH measurements should be within the range from 5.5 to 10.0. Furthermore, any significant shifts in the pH values from baseline conditions can indicate scrubber system operating problems. Corrosion can be severe in most systems when the pH levels are less than 5.5. Also, high chloride concentrations accelerate corrosion at low pH levels. Precipitation of calcium and magnesium compounds at pH levels above 10 can lead to severe scaling and gas-liquor maldistribution. 88 ------- INSPECTION OF WET SCRUBBER SYSTEMS Follow-up Level 2 Inspection Procedures Evaluate the scrubber liquor recirculation rate. One frequent cause of scrubber emission problems is inade- quate liquor recirculation rate. Unfortunately, many commercial types of liquor flow monitors are subject to frequent maintenance problems and many small systems do not have any liquor flow meters at all. For these reasons, a combination of factors are considered to determine if the scrubber liquor recirculation rate is much less than the baseline level(s). These factors include the following: 0 Liquor flow meter (if available, and if it appears to be working properly) 0 Pump discharge pressure (Higher values indicate lower flow.) 0 Pump motor current (Lower values indicate lower flow.) 0 Nozzle header pressure (Higher values indicate lower flow.) 0 Scrubber exit gas temperature (Higher values indicate lower flow.) 0 Quantity of liquor draining back into recirculation tank or pond (Lower flow rates indicate lower recirculation rates.) Evaluate gas flow rate. Changes in gas flow rate occur routinely in most processes due to variations in process operating rates and conditions. Information concerning gas flow rate changes is necessary when evaluating changes in the scrubber static pressure drop. Check the scrubber system fan motor current. Correct fan motor current to standard conditions using the equation below. Corrected current - Actual Current x (Gas Temp.+ 460)/520 An increase in the fan motor current indicates an increase in the gas flow rate. 89 ------- INSPECTION OF WET SCRUBBER SYSTEMS Follow-up Level 2 Inspection Procedures Evaluate demister conditions. The demister physical condition should be evaluated if substantial liquor reentrainment has occurred recently. It should be noted, however, that there oust be safe and convenient access hatches and that there must not be any process gas in the scrubber at the time of the inspection. Note any deposits on the bottom or the top of the demister. This can lead to localized high gas velocity areas which lead to liquor reentrainment. The appearance of any spray nozzles used for the routine cleaning of the demister should also be noted. Evaluate liquor distribution from spray nozzles (SPRAY TOWER SCRUBBERS ONLY). This inspection step can be performed when the scrubber system is out-of-service. Locate a hatch on the scrubber vessel shell that is above the elevation of the spray nozzles and that has a good view of the spray pattern from the nozzles. Observe the spray pattern from each of the nozzles when there is no process gas being handled by the scrubber and when no moving ambient air is in the scrubber vessel. The spray pattern should appear to be uniform and should completely cover the area of gas flow. Nonuniform spray patterns indicate that the nozzle is partially plugged. If none of the nozzles on a single header are operating, the entrance to the header may be plugged. If a safe and convenient hatch can not be located, do not attempt to perform this inspection step. Also, only the plant personnel should open and close the access hatches. Evaluate mechanically aided scrubber rotational speed. Request that a responsible and experienced plant repre- sentative measure the rotational speed of the scrubber (if this can be done safely). Compare the present speed with the baseline value(s). A higher speed indicates higher gas flow rates and higher static pressure rises across the scrubber. 90 ------- INSPECTION OF WET SCRUBBER SYSTEMS Follow-up Level 2 Inspection Procedures Evaluate physical condition of scrubber packed beds, trays. and venturi throat dampers. This inspection step can be performed only when the scrub- ber system is out-of-service. Locate a hatch on the scrubber vessel shell that is either above or below the internal compon- ent of interest. Look for the problems listed below. Packed bed scrubbers Tray tower scrubber Orifice scrubbers Rod deck scrubbers Venturi scrubbers 0 Corroded or collapsed bed supports 0 Plugged or eroded distribution nozzles e Bowed or sagging trays e Corroded or broken downcomers Plugged tray holes 0 Solids deposits in liquor containers 0 Solids deposits at gas inlet to orifice section * Plugged spray nozzles at gas inlet to orifice section 0 Eroded gas stream baffle at gas inlet to orifice section 0 Solids deposits in demister section 0 Eroded or corroded rods 0 Plugged or eroded liquor nozzles 0 Eroded throat dampers 0 Restricted throat damper movement due to solids deposits Process equipment fugitive emissions. A careful check for process fugitive emissions is necessary whenever the scrubber system static pressure drop is substan- tially higher than the baseline value or when air infiltration is severe. In both cases, poor capture of the dust at the process equipment is possible. Walk around the process sources to the extent safely possible to determine if pollutant capture is adequate. 91 ------- INSPECTION OF WET SCRUBBER SYSTEMS Level 3 Inspection Procedures 4.4.3 Level 3 Inspection Points Procedures for measuring wet scrubber system operating conditions are described below. Other observations to be completed as part of the Level 3 inspection are identical to those included in the basic and follow-up Level 2 inspection. See the Level 2 inspection procedures section for a discussion of these steps. Measure the wet scrubber static pressure drop. The static pressure drop is directly related to the effectiveness of particle impaction for particle capture. Generally, the particulate removal efficiency increases as the static pressure drop increases. The steps in measuring the static pressure drop are described below. 0 Locate safe and convenient measurement ports. In some cases it may be possible to temporarily disconnect the on-site gauge in order to use the portable static pres- sure gauge. It also may be possible to find small ports in the ductwork ahead of and after the scrubber vessel. 0 Clean any deposits out of the measurement ports. 0 If the inlet and outlet ports are close together, connect both sides of the static pressure gauge to the ports and observe the static pressure for a period of 1 to 5 minutes. 0 If the ports are not close together, measure the static pressure in one port for 10 to 30 seconds and then proceed to the other port for 10 to 30 seconds. As long as the static pressure drop is reasonably stable (the typical condition), the two values can be subtracted to determine the static pressure drop. e Under no circumstances should on-site plant instruments be disconnected without the explicit approval of responsible plant personnel. Also, instruments connected to differential pressure transducers should not be disconnected. 92 ------- INSPECTION OF WET SCRUBBER SYSTEMS Level 3 Inspection Procedures Evaluate the outlet gas temperatures. This measurement is conducted whenever it is necessary to determine if poor liquor-gas distribution and/or inadequate liquor flow rate is seriously reducing particulate collection efficiency. The steps in measureing the gas temperature are outlined below. o Locate safe and convenient measurement ports on the outlet portion of the scrubber vessel shell or on the outlet ductwork of the system. Often small ports less than 1/4" diameter are adequate. 0 Attach a grounding/bonding cable to the probe if vapor, gas, and/or particulate levels are potentially explosive 0 Seal the temperature probe in the port to avoid any air infiltration which would result in a low reading. 0 Measure the gas temperature at a position near the middle of the duct if possible. Conduct the measurement for several minutes to ensure a representative reading. Some flucuation in the readings is possible if the probe is occassionally hit by a liquor droplet. 0 Compare the outlet gas temperature with the baseline value(s). If the present value is more than 10 °F higher, then either gas-liquor maldistribution or inadequate liquor is possible. Measure the scrubber outlet liquor pH. Prior to obtaining a liquor sample warm-up, the portable pH meter and chec~k it using at least two different fresh buffer solutions that bracket the normal liquor pH range. Then request that a responsible and experienced plant representative obtain a sample of the scrubber outlet liquor. Measure the liquor pH as soon as possible after obtaining the sample so that the value does not change due to dissolution of alkaline material or due to on-going reactions. Compare this to the baseline value(s). 93 ------- INSPECTION OF WET SCRUBBER SYSTEMS Level 3 Inspection Procedures Evaluate the scrubber outlet gas flow rate. The gas flow rate is measured using an S-type pitot and U.S. EPA Reference Methods 1 and 2. The necessary charts are provided in section 7 of this notebook. It is especially important to check for cyclonic flow before making the pitot traverse. This is a common condition in wet scrubbers since many types of demisters impart cyclonic action in order to reduce the quantity of reentrained liquor droplets in the outlet gas stream. ------- INSPECTION OF WET SCRUBBER SYSTEMS Level 4 Inspection Procedures 4.4.4 Level 4 Inspection Procedures The Level 4 inspection includes many inspection steps per- formed during Level 2 and 3 inspections. These are described in earlier sections. The unique inspection steps of Level 4 inspec- tions are described below. Evaluate locations for measurement ports. Many existing wet scrubber systems do not have safe and convenient ports that can be used for static pressure, gas temperature, and gas oxygen measurements. One purpose of the Level 4 inspection is to select (with the assistance of plant personnel) locations for ports to be installed at a later date to facilitate Level 3 inspections. Information regarding possible sample port locations is provided in the U.S. EPA Publication titled, " Preferred Measurement Ports for Air Pollution Control Systems", EPA 340/1-86-034. Evaluate potential safety problems. Agency management personnel and/or senior inspectors should identify potential safety problems involved in standard Level 2 or Level 3 inspections at this site. To the extent possible, the system owner/operators should eliminate these hazards. For those hazards that can not be eliminated, agency personnel should prepare notes on how future inspections should be limited and should prepare a list of the necessary personnel safety equipment. A partial list of common health and safety hazards include the following. 0 Inhalation hazards due to fugitive leaks from high static pressure scrubber vessels and ducts •V- 0 Eye hazards during sampling of scrubber liquor 0 Slippery walkways and ladders e Fan disintegration 95 ------- INSPECTION OF WET SCRUBBER SYSTEMS Level 4 Inspection Procedures Prepare &_ system flowchart. A relatively simple flowchart is very helpful in conduct- ing a complete and effective Level 2 or Level 3 inspection. This should be prepared by agency management personnel or senior inspectors during a Level A inspection. It should consist of a simple block diagram which includes the following elements: 0 Sources(s) of emissions controlled by a single wet scrubber system 0 Location(s) of any fans used for gas movement through the system (used to evaluate inhalation problems due to positive static pressures) 0 Locations of any main stacks and bypass stacks 0 Location of wet scrubber 0 Locations of major instruments (pH meters, static pressure gauges, thermocouples, liquor flow meters) Evaluate potential safety problems in the process area. The agency management personnel and/or senior inspectors should evaluate potential safety.problems in the areas that may be visited by agency inspectors during Level 2 and/or Level 3 inspections. They should prepare a list of the activities that should not be performed and locations to which an inspector should not go as part of these inspections. The purpose of this review is to minimize inspector risk and to minimize the liabil- ity concerns of plant personnel. 96 ------- 5. INSPECTION OF DRY SCRUBBERS Dry scrubbers utilize absorption and adsorption for the removal of sulfur dioxide, hydrogen chloride, hydrogen fluoride, and other acid gases. Some adsorption of vapor state organic compounds and metallic compounds also occurs in some dry scrubber applications. This relatively new control technology is presently in use on pulverized coal-fired boilers and municipal waste incinerators. Potential future applications could include municipal waste inciner- ators and hospital waste incinerators. 5.1 Components and Operating Principles There is considerable diversity in the variety of processes which are collectively termed "dry scrubbing." This is partially because the technology is relatively new and is still evolving. The diversity also exists because of the differing control requirements of the types of sources being treated. For purposes of this field inspection notebook, the various dry scrubbing techniques have been grouped into three major categories: (1) spray dryer absorbers, (2) dry injection adsorption systems, and (3) combination spray dryer and dry injection systems. Specific types of dry scrubbing processes within each group are listed below. Alternative terms for these categories used in some publications are shown in parentheses. Spray Dryer Absorption (Semi-wet) 0 Rotary atomizer spray dryer systems 0 Air atomizing nozzle spray dryer systems Dry Injection Adsorption (Dry) 0 Dry injection without recycle 0 Dry injection with recycle (sometimes termed "circulating fluid bed adsorption") Combination Spray Dryer and Dry Injection (Semi-wet/dry) 97 ------- INSPECTION OF DRY SCRUBBERS Components and Operating Principles Simplified block diagrams of the three major types of dry scrubbing systems are presented is Figures 5-1, 5-2 and 5-3. The main differences between the various systems are the physical form of the alkaline reagent and the design of the vessel used for con- tacting the acid gas laden stream with the reagent. The alkaline feed requirements are much higher for the dry injection adsoption than the other two categories. Conversely, the spray dryer absorp- tion and combination systems are much more complicated. The pollutant removal efficiencies for all three categories of dry scrubbing systems appear to be very high. In most cases, outlet gas stream continuous monitors emissions provide a direct indication of the system performance. Agency inspections of all three types of dry scrubbing systems are similar with respect to the importance of reviewing the adequacy of these continuous monitors and of reviewing data for selected time periods since the last inspection. Subsequent inspection steps vary substantially for the three types of dry scrubbers due to the difference in the components and operating principles of the systems. It should be noted that the particulate control devices shown on the right hand side of the flowcharts are generally fabric filters or electrostatic precipitators. It is also possible that one and two stage wet scrubbing systems will be used in certain cases. However, the later discussions will primarily focus on fabric filters and precipitators since these dominate present and planned applications. 5.1.1 Spray Dryer Absorbers In this type of dry scrubbing system, the alkaline reagent is prepared as a slurry^containing 5 to 20% by weight solids. This slurry is atomized in a large absorber vessel having a residence time of 6 to 15 seconds. There are two main ways of atomization: (1) rotary atomizers, and (2) air atomizing nozzles. There is generally only one rotary atomizer per scrubber vessel. However, a few facilities have as many as three rotary atomizers. There can be a number of air atomizing nozzles in each scrubbing vessel. 98 ------- INSPECTION OF DRY SCRUBBERS Components and Operating Principles Cump Note: A - Motor current gauge FI - Flowrate gauge TI - Temperature gauge - Density gauge Figure 3-1. Components of a Spray Dryer Absorber System 99 ------- INSPECTION OF DRY SCRUBBERS Components and Operating Principles The shape of the scrubber vessel oust be different to take into account the differences in the slurry spray pattern and the time required for droplet evaporation. The length-to-diaraeter ratio for rotary atomizers is much smaller than that for absorber vessels using air atomizing nozzles. It is important that all of the slurry droplets evaporate to dryness prior to approaching the absorber vessel side walls and prior to exiting the absorber with the gas stream. Accumulations of material on the side walls or at the bottom of the absorber would necessitate an outage of the system since these deposits would further impede drying. Proper drying of the slurry is achieved by the generation of small slurry droplets, by proper flue gas contact, and by use of moderately hot flue gases. Drying that is too rapid can reduce pollutant collection efficiency since the primary removal mechanism is absorption into the droplets. There must be sufficient contact time for the absorption. For this reason, spray dryer absorbers on coal-fired boilers are operated with exit gas temperatures only 20 to 30°F above the saturation temperature. The approach-to-saturation for municipal waste incinerators is 90 to 180 °F. The absorber exit gas temperatures are monitored to ensure proper "approach-to- saturation" and therefore these values are an important inspection point. It is simply the difference between the wet bulb and dry bulb temperature monitors at the outlet of the absorber vessel. In rotary atomizers, a thin film of slurry is fed to the top of the atomizer disk as it rotates at speeds of 10,000 to 17,000 rpm. The disk speeds remain at a constant level regardless of system load. These atomizers generate very small slurry droplets having diameters in the range of 100 microns. The spray pattern is inherently broad due to the geometry of the disk. High pressure air is used to provide the physical energy required for droplet formation in nozzle type atomizers. The typical air pressures are 70 to 90 psig. Slurry droplets in the range of 70 to 200 microns are generated. This type of atomizer can generally operate over wider variations of the gas flow rate than can be used in a rotary atomizer. However, the nozzle atomizer does not have 100 ------- INSPECTION OF DRY SCRUBBERS Components and Operating Principles the slurry feed turndown capability of the rotary atomizer. For these reasons, different approaches must be taken when operating at varying system loads. The alkaline material generally used in a spray dryer absorber is pebble lime. This material must be slaked in order to prepare a reactive slurry for absorption of acid gases. Slaking is the addi- tion of water to convert calcium oxide to calcium hydroxide. While this may appear simple, proper slaking conditions are important to ensure that the resulting calcium hydroxide slurry has the proper particle size distribution and that no coating of the particles has occurred due to the precipitation of contaminants in the slaking water. Some of the important operating parameters of the lime slaker are the quality of the slaking water, the feed rate of lime, and the slurry exit temperature. However, it is difficult to relate present operating conditions or shifts from baseline operating conditions to possible changes in the absorption characteristics of the dry scrubber system. A variety of subtle changes in the slaker can affect the reactivity of the liquor produced. One of the problems which has been reported for spray dryer absorber type systems is the pluggage of the slurry feed line to the atomizer. Scaling of the line can be severe due to the very high pH of this liquor. The flow rate of the liquor to the atomizer is usually monitored by a magnetic flow meter. However, this instrument is also vulnerable to scaling since the flow sensing elements are on the inside surface of the pipe. To minimize the pluggage problems, the lines must be well sloped and include the capability for flushing of the lines immediately after outages. During the inspection, it is essentially impossible to identify emerging slurry line problems. Recycle of the solids collected in the absorber vessel is important in most systems. It increases the solids content of the slurry fed to the atomizer and thereby improves the drying of the droplets. Recycle also maximizes reagent utilization. The rate of solids recycle is monitored on a continuous basis using conventional slurry flowrate monitors. 101 ------- INSPECTION OF DRY SCRUBBERS Components and Operating Principles 5.1.2 Dry Injection Adsorption System This type of dry scrubber uses finely divided calcium hydroxide for the adsorption of acid gases. The reagent feed has particle sizes which are 90% by weight through 325 mesh screens. This is approximately the consistency of talcum powder. This size is important to ensure that there is adequate calcium hydroxide surface area for high efficiency pollutant removal. Proper particle sizes are maintained by transporting the lime to the dry scrubber system by means of a positive pressure pneumatic conveyor. This provides the initial fluidization necessary to break up any clumps of reagent which have formed during storage. The air flow rate in the pneumatic conveyor is kept at a constant level regardless of system load in order to ensure proper particle sizes. Fluidization (mixing unagglomerated particles with the gas stream) is completed when the calcium hydroxide is injected counter- currently into the gas stream. A venturi section is used for the contactor due to the turbulent action available for mixing the gas stream and reagent. The gas stream containing the entrained calcium hydroxide particles and fly ash is then treated in a fabric filter. Adsorption of acid gases and organic compounds (if present) occurs primarily while the gas stream passes through the dust cake composed of calcium hydroxide and fly ash. Pollutant removal efficiency is dependent on the reagent particle size range, on the adequacy of dust cake formation,.and on the quantity of reagent injected. The calcium hydroxide feed rate for dry injection systems is 3 to A times the stoichlpmetric quantities needed. This is much higher than the spray dryer absorber type systems and it makes this approach unattractive for very large systems. In one version of the dry injection system, solids are recycled from the particulate control device back into the flue gas contactor (sometimes termed "reactor"). The primary purpose of the recycle stream is to increase reagent utilization and thereby reduce overall calcium hydroxide costs. 102 ------- INSPECTION OF DRY SCRUBBERS Components and Operating Principles Note: A - Motor current gauge PI - Pressure gauge TI - Temperature gauge Figure 5-2. Components of a Dry Injection Adsorption System 103 ------- INSPECTION OF DRY SCRUBBERS Components and Operating Principles 5.1.3 Combination Spray Dryer and Dry Injection System A flowchart for this system is provided in Figure 5-3. The acid gas laden flue gas is first treated in an upflow type spray dryer absorber. A series of calcium hydroxide sprays near the bottom of the absorber vessel are used for droplet generation. After the upflow chamber, the partially treated flue gas then passes through a venturi contactor section where it is exposed to a calcium silicate and lime suspension. The purpose of the second reagent material is to improve the'dust cake characteristics in the downstream baghouse and to optimize acid gas removal in this dust cake. The calcium silicate reportedly improves dust cake porosity and serves as an adsorbant for the acid gases. Solids collected in the baghouse may be recycled to the venturi contactor. This improves reagent utilization and facilitates additional pollutant removal. 5.1.4 General Comments Corrosion can present major problems for all types of dry scrubbers used on applications with high hydrogen chloride concen- trations such as municipal waste incinerators and hazardous waste incinerators. The calcium chloride reaction product formed in the dry scrubbers and any uncorrected hydrogen chloride are both very corrosive and cause damage in any areas of the absorber vessel or particulate control device where cooling and water vapor conden- sation can occur. Two common reasons for cold localized gas temper- atures include air infiltration and improper insulation around support beams. Due to the potential problems related to corrosion, the inspections should include checks for air infiltration and a visible evaluation of"common corrosion sites. 104 ------- INSPECTION OF DRY SCRUBBERS Components and Operating Principles Pirnip Note: A - Motor current gauge PI - Pressure gauge TI (dry) - Dry bulb temperature gauge TI (wet) - Wet bulb temperature gauge Figure 5-3. Components of a Combination Spray Dryer and Dry Injection Adsorption System 105 ------- INSPECTION OF DRY SCRUBBERS General Safety Considerations 5.2 General Safety Considerations 5.2.1 Inhalation Hazards Around Positive Pressure System Components Poorly ventilated areas in the vicinity of positive pressure dry scrubber absorbers, particulate control systems, and/or ductwork should be avoided. There are a variety of inhalation hazards associated with municipal waste incinerators and coal-fired boilers, including but not limited to the following: 0 hydrogen chloride 0 hydrogen fluoride 0 sulfuric acid mist 0 sulfur dioxide 0 dioxins/furans 0 carbon monoxide 0 heavy metal enriched flyash. Concentrations of these pollutants can conceivably exceed the maximum allowable use levels of air-purifying respirators. Further- more, there is no single type of air-purifying respirator which is appropriate for the wide range of pollutants which are emitted from municipal waste incinerators and coal-fired boilers. Inspectors must be able to recognize and avoid areas of potentially significant exposure to fugitive emissions from the combustion and dry scrubbing systems. A simple flowchart which indicates the locations of all fans is a useful starting point in identifying portions of the system which operate at positive pressure. 5.2.2 Chemical Burns, and Eye Hazards Around the Pebble Lime and/or Calcium Hydroxide Preparation Area The strong alkalis used in dry scrubbing have the potential to cause severe eye damage. While the probability of eye contact and skin contact is relatively small for agency inspectors, it is never- theless important to keep in mind the general first aid procedures. These are briefly summarized below. 106 ------- INSPECTION OF DRY SCRUBBERS General Safety Considerations 0 After eye contact, flushing should be started immediately. 0 Eyes should be flushed for 15 to 30 minutes. 0 After skin contact, all affected clothing should be removed and showering should be done for a minimum of 15 minutes. 0 Medical attention should be obtained in all situations. During the routine inspection, agency personnel should note the locations of all eye wash stations and showers. These are generally located in the immediate vicinities of chemical handling areas. After the first aid procedures are completed, it is especially important to get qualified medical attention regardless of the presumed seriousness of the exposure. All inspectors should have full first aid and safety training before conducting field inspec- tions. 5.2.3 Internal Inspections Prohibited Inspectors should not enter dry scrubber absorber vessels or air pollution control devices under any circumstances. All of the necessary inspection steps can be accomplished without internal inspections. Proper isolation, lockout, and testing of confined areas requires substantial time and safety equipment, neither of which is available to the agency inspector. Furthermore, serious accidents can and have happened to agency inspectors while inside equipment with plant personnel. • 107 ------- INSPECTION OF DRY SCRUBBERS Inspection Summaries 5.3 Inspection Summaries 5.3.1 Level 1 Inspections Stack ° Visible emissions for 6 to 30 minutes for each stack or discharge vent Presence of condensing plume 0 Process ° Presence or absence of fugitive emissions 5.3.2 Level 2 Inspections Basic Inspection Points Stack ° Visible emissions for 6 to 30 minutes for each stack or discharge vent 0 Presence of condensing plume Continuous Monitors for Opacity, Sulfur Dioxide, Hydrogen Chloride, and Nitrogen Oxides 0 Double pass transmissometer physical condition 0 Double pass transmissometer .opacity data for at least the last 3 hours 0 Sulfur dioxide, hydrogen chloride, and nitrogen oxides emissions for at least the last 8 hours Dry Scrubber - General 0 System flowchart 0 General physical condition Dry Scrubber..- Spray Dryer Absorbers and Combination Systems 0 Absorber vessel approach-to-saturation for at least the last 8 hours 9 Make-up reagent feed rates and absorber vessel recycle rates for at least the last 8 hours 0 Nozzle air and slurry pressures (if nozzles present) 0 System flowchart Process e Presence or absence of fugitive emissions 108 ------- INSPECTION OF DRY SCRUBBERS Inspection Summaries 5.3.2 Level 2 Inspection, Basic Inspection Points (Continued) Dry Scrubber - Dry Injection System and Combination Systems 0 Calcium hydroxide feed rate for at least the last 3 hours 0 Calcium silicate/calcium hydroxide feed rates for at least the last 8 hours (if calcium silicate used) 0 Solids recycle rates (if recycle used) Dry Scrubber - Fabric Filter See Sections 1 and 2 Dry Scrubber - Electrostatic Precipitator See Section 3 Process 0 Process operating rate 0 Process operating conditions Follow-up Level 2 Inspection Continuous Monitors for Opacity, Sulfur Dioxide, Hydrogen Chloride, and Nitrogen Oxides - ° Continuous monitoring data for previous 6 to 12 months. Dry Scrubber - Spray Dryer Absorber and Combination Systems G Absorber vessel approach-to-saturation values during past previous 6 to 12 months 0 Reagent feed rates during previous 6 to 12 •; months 0 Absorber vessel inlet gas temperatures during past 6 to 12 months 0 Slaker slurry outlet temperatures during past 6 to 12 months (if slaker present) 0 Slurry density monitor data and slurry flow monitor maintenance information during previous 6 to 12 months 0 Absorber gas flow rates (if monitored) 109 ------- INSPECTION OF DRY SCRUBBERS Inspection Summaries 5.3.2 Level 2 Inspections, Follow-up Inspection Points (Continued) Dry Scrubber - Dry Injection System and Combination Systems 8 Reagent feed rates during previous 6 to 12 months. 0 Calcium silicate/ calcium hydroxide feed rates during previous 6 to 12 months 0 Solids recycle rates during previous 6 to 12 months (if recycle used) Dry Scrubber - Fabric Filters See Sections 1 and 2 Dry Scrubber - Electrostatic Precipitator See Section 3 5.3.3 Level 3 Inspections Dry Scrubber 0 Level 2 follow-up inspection elements 0 Spray dryer absorber wet bulb and dry bulb temperatures 0 Absorber or contactor inlet gas temperature Dry Scrubber - Fabric Filters See Sections 1 or 2 Dry Scrubber - Electrostatic Precipitator See Section 3 5.3.A Level A Inspections Stack 0 All elements of a Level 3 inspection Continuous Emission Monitors for Opacity, Sulfur Dioxide, Hydrogen Chloride, and Nitrogen Oxides 0 All elements of a Level 3 inspection 110 ------- INSPECTION OF DRY SCRUBBERS Level A Inspection Procedures 5.3.4 Level A Inspections (Continued) Dry Scrubber 0 Level 3 inspection elements 0 Flowchart of system 0 Locations of possible measurement ports 0 Start-up/shut down procedures 0 Potential inspection safety problems Process ° All elements of a Level 3 inspection 0 Potential inspection safety problems 111 ------- INSPECTION OF DRY SCRUBBERS Basic Level 2 Inspection Procedures 5. A Inspection Procedures Techniques for the inspection of dry scrubbers can be classified as Level 1, 2, 3, or A. The Level 1 inspection consists of a visible emissions observation from outside the plant. This is not discussed in this manual. The Level 2 inspection primarily involves a walkthrough evaluation of the dry scrubber system and the associated process equipment. All data are provided by on-site gauges. The Level 3 inspection is similar to the Level 2 inspection with the exception that several key dry scrubbing operating parameters are measured using portable instruments supplied by the inspectors. These instruments are used when the on-site gauges are either not present or not reliable. The Level A inspection is performed by agency supervisors or senior inspectors to acquire baseline data. The scope of the Level 4 inspection is identical to the Level 2/Level 3 inspection. 5.A.I Level 2 Inspections Dry scrubber system visible emissions If weather conditions permit, determine the stack effluent average opacity in accordance with U.S. EPA Method 9 procedures (or other required procedures). The observation should be con- ducted during routine process operation and should last 6 to 30 minutes for each stack and bypass vents. The majority of units operate with effluent opacities less than 10% on a continuous basis. Higher opacities indicate emission problems. The timing and duration of all significant spikes should be noted after the visible emissions observation. This will be useful in determining some of the possible causes of the spiking condition. Significant puffs on either a regular frequency or on a random basis are not normal. However, in some cases, light puffing can occur even during optimal operating conditions. If weather conditions are poor, an attempt should still be made to determine if there are any visible emissions. The pres- ence of a significant plume indicates emission problems. Do not attempt to determine the "average opacity" when conformance with U.S. EPA Method 9 is not possible. 112 ------- INSPECTION OF DRY SCRUBBERS Basic Level 2 Inspection Procedures Condensing plume conditions Condensing plume conditions in dry scrubber systems are highly unusual since most vapor state species which could cause such plumes are partially removed. The presence of a condensing plume would indicate a major malfunction of the dry scrubber system. The four principal characteristics of a condensing plume are a bluish-white color, opacities which are higher during cold or humid weather, low opacity at the stack, and increasing opacities in the first few seconds of plume travel. System flowchart A simple flowchart of the entire dry scrubber system and the associated process equipment should be prepared if one is not already available in the agency files. This should consist of a block diagram which includes the absorber or gas contactor, the reagent preparation equipment, the particulate control device, the combustion source, and all instruments relevant to the inspection. Double-pass transmissometer physical conditions Most dry scrubbers have a transmissometer for the continu- ous monitoring of visible emissions. If a unit is present, and if it is in an accessible location, check the light source and retroreflector modules to confirm that these are in good working- order. Check that the main fan is working and that there is at least one dust filter for the fan. On many commercial models, it is also possible to check the instrument alignment without adjusting the instrument. Note; On some models, moving the dial t.o the alignment check position will cause an alarm iji the control room. This is £o be moved only Jjy_ plant personnel and only when it will not disrupt plant operations. Sulfur dioxide, nitrogen oxides, and hydrogen chloride monitor physical conditions If the monitors are in an accessible location, confirm that the instruments are in good mechanical operating condition and that any sample lines are intact. Check calibration and zero check records for all instruments. 113 ------- INSPECTION OF DRY SCRUBBERS Basic Level 2 Inspection Procedures Double-pass transmissometer data If the transmissometer appears to be working properly, evaluate the average opacity data for at least the previous 8 hours prior to the inspection. If possible, the average opacity data for selected days since the last inspection should also be reviewed. This evaluation is helpful in confirming that the units being inspected are operating in a representative fashion. If the unit is working better during the inspection than during other periods, it may be advisable to conduct an unscheduled inspection in the future. As part of the review of average opacity, scan the data to determine the frequency of emission problems and to evaluate how rapidly the operators are able to recognize and eliminate the condition. Sulfur dioxide, nitrogen oxides, and hydrogen chloride emission data If the gas monitors appear to be working properly, evaluate the average emission concentrations for at least the previous 8 hours prior to the inspection. If possible, the average emissions for selected days since the last inspection should also be reviewed. This evaluation is helpful in confirming that the units being inspected are operating in a representative fashion. High emission rates of either sulfur dioxide or hydrogen chloride indicate significant problems with the dry scrubber system. The general classes, of problems include but are not limited to poor alkaline reagent reactivity, inadequate approach-to-saturation (wet-dry systems), low reagent stoichio- metric ratios, low inlet gas temperatures, and make-up reagent supply problems.'" Follow-up Level 2 inspection procedures or Level 3 inspection procedures will be necessary if high emission rates of either sulfur dioxide or hydrogen chloride are observed. High nitrogen oxides concentrations indicates a problem with the combustion equipment operation, an increase in the waste nitrogen content, or a problem with the nitrogen oxides control equipment. 114 ------- INSPECTION OF DRY SCRUBBERS Basic Level 2 Inspection Procedures Spray Dryer Absorber "Approach-to-Saturation" One of the roost important operating parameters affecting the efficiency of a wet-dry type dry scrubber is the approach- to-saturation. This is simply the difference between the wet bulb and dry bulb temperature monitors at the exit of the spray dryer vessel. The normal approach-to-saturation for coal-fired boiler systems varies between 15 and 50 °F with most systems attempting to maintain a 20 to 25 °F value. Very high differ- ences indicate lower acid gas removal efficiencies since the baseline period. Municipal waste incinerator systems operate with an "approach-to-saturation" range of 90 to 180°F. The approach-to-saturation is monitored continuously by a set of dry bulb and wet bulb monitors. An increase in this value is sensed by the automatic control system which quickly reduces the slurry feed rate to the atomizer. Due to the vulnerability of these temperature monitors to scaling and blinding, inspectors should not be surprised to find that some plants must occasionally bypass the automatic process control system and operate manually for limited time periods. This generally means slightly worse approach-to-saturation values so that operators have a margin for error in the event of sudden process changes such as load changes. Gradually plants should be able to increase the reliability of the temperature monitors by relocation of the sensors and by improved operation of the dryer. Spray dryer absorber reagent feed rates The calcium hydroxide (or other alkali) feed rates are important since they partially determine the stoichiometric ratio between the moles of reagent and the moles of acid gas. Low stoichiometric ratios result in reduced efficiencies. The reagent feed rate is generally determined using a magnetic flow meter on the slurry supply line to the atomizer feed tank. It is also necessary to know the slurry density. This is monitored by a nuclear-type density monitor. Typical slurry densities are in the range of 5 to 20% by weight. It should be noted that both the magnetic flow meter and the nuclear density meter are vulnerable to scaling due to the nature of the slurry. 115 ------- INSPECTION OF DRY SCRUBBERS Basic Level 2 Inspection Procedures Spray dryer absorber reagent feed rates (continued) Another way to determine the reagent feed rate is to record the feed rates of new pebble lime and recycled solids indicated by the weigh belt feeders. The weigh belt for the pebble lime is between the lime storage silo and the slaker. The weigh belt feeder for the recycled solids is close to the spray dryer absorber vessel. Both the slurry feed rates and the solids rates should be compared with baseline values at a similar combustion system load to determine if the stoichiometric ratio has dropped significantly. Spray dryer absorber nozzle air and slurry pressures For units equipped with nozzles rather than rotary atomizers, the air pressures and slurry pressures should be recorded and compared with baseline levels. Some variation in the slurry pressures are necessary in order to maintain proper approach-to-saturation values during combustion system load variations. Dry in lection system feed rates The feed rate of calcium hydroxide to the pressurized pneumatic system is generally monitored by either a weigh belt feeder or a volumetric screw-type feeder. Both of these feeders are located close to the calcium hydroxide storage silos, and the feed rates are generally indicated on the main system control panel. These values should be recorded for at least the past 8 hours and compared against baseline values for similar combustion load periods. Decreased reagent feed rates indicate possible reductions in the stoichiometric ratio and thereby a reduction in acid gas collection effectiveness. The blower motor currents and the pneumatic line static pressures should also be recorded and checked against baseline data sets. Higher motor currents and higher conveying line static pres- sures indicate increases in the air flow rates. 116 ------- INSPECTION7 OF DRY SCRUBBERS Basic Level 2 Inspection Procedures Calcium silicate feed rates The Spray absorber/dry injection system utilizes a calcium silicate/calcium hydroxide dry injection system downstream from the calcium hydroxide spray dryer absorber. The feed rate of calcium silicate/calcium hydroxide is monitored by weigh belt feeders or volumetric screw conveyors. Feed rates for the past 8 hours should be recorded and compared with baseline values. Control device solids recycle rates The Spray absorber/dry injection system utilizes a recycle stream from the fabric filter in order to improve overall reagent utilization. The solids recycle rate during the inspection should be recorded and compared to baseline values. Dry scrubber system general physical conditions While walking around the dry scrubber and its inlet and out- let ductwork, check for obvious corrosion around the potential "cold" spots such as the bottom of the absorber vessel and the particulate control device hoppers and around the access hatches. Check for audible air infiltration through the corroded areas, warped access hatches, and eroded solids discharge valves. Process operating rate Record one or more combustion system operating rate para- meters that document that the source conditions are representa- tive of normal operation. For coal-fired boilers, these parameters include the electrical generation rate, the steam generation rate and the coal ultimate analyses. For municipal waste incinerators, the main, process operating parameters include the steam generation rate and the waste charging rate (where monitored). 117 ------- INSPECTION OF DRY SCRUBBERS Basic Level 2 Inspection Procedures Process operating conditions Record any process operating parameters that have an impact on the characteristics and/or quantities of pollutants generated. Some of the important variables for coal-fired boilers are listed below. 0 Air preheater exit gas temperatures and static pressures 0 Economizer exit gas oxygen concentrations For municipal waste incinerators the important process operating parameters may include the following items. 0 Overfire air pressures 0 Undergrate air pressures 0 Uniformity of waste and ash on grates 0 Furnace (or secondary chamber) exit gas oxygen and carbon monoxide concentrations 0 Quantity and type of fuel being fired with refuse derived fuels 0 Extent of supplemental burner operation 5.4.2 Follow-up Inspection Points for Level 2 Inspections Continuous monitoring data for the previous £ £o ^2_ months Obtain the continuous monitoring records and quickly scan the data for the previous 6 to 12 months to determine time periods that had especially high and especially low emission rates. Select the dry scrubber operating logs and the process operating logs that correspond with the times of the monitoring instruments charts/records selected. Compare the dry scrubber operating data and process operating data against baseline information to identify the general category of problem(s) causing the excess emission incidents. Evaluate the source's proposed corrective actions to minimize this problem(s) in the future. 118 ------- INSPECTION OF DRY SCRUBBERS Follow-up Level 2 Inspection Procedures Spray dryer absorber approach-to-saturation values during the previous £ to 12 months The approach-to-saturation value is an important parameter which relates directly to the pollutant removal effectiveness. If there is significant question concerning the ability of the dry scrubber system to maintain proper operation on a long term basis, the approach-to-saturation values indicated on the dry scrubber system daily operating log sheets should be checked. Values much higher than baseline values or permit stipulations indicate chronic problems such as the following. 0 Absorber vessel temperature instruments 0 Absorber vessel atomizer 0 Absorber gas- dispersion equipment 0 Low absorber vessel inlet gas temperatures during low load periods 8 Nozzle erosion or blockage 0 Slurry supply line scaling Spray dryer absorber reagent feed rate data during the previous J5 to jj months The feed rates of make-up pebble lime and recycle solids are generally indicated on the daily operating logs of the dry scrubber system. Values for the last 6 to 12 months should be compared with the corresponding combustion load data to deter- mine if significant changes in the overall reagent stoichio- metric ratios have occurred. Data concerning the system load must be obtained from the combustion system daily operating log sheets. If available, dry scrubber system inlet sulfur dioxide concentrations should also be used in this qualitative evaluation of reagent/acid gas stoichiometric ratios. Slaker slurry outlet temperatures during the previous 6 to 12 months The slaker slurry outlet temperature provides a rough indication of the adequacy of the conversion from lime (calcium oxide) to calcium hydroxide. The temperatures should be compared to baseline values. Improper slaking can result in poor reagent reactivity and reduced acid gas collection efficiency. 119 ------- INSPECTION OF DRY SCRUBBERS Follow-up Level 2 Inspection Procedures Spray dryer absorber slurry flow rate and density monitor maintenance records The calcium hydroxide slurry monitors generally consist of a magnetic flow meter and a nuclear density meter. Both of these are sensitive to scaling especially when slurry densities are high. The plant should have maintenance records for the monitors either in the form of completed work orders, a computer- ized maintenance record, an instrument maintenance log, or notes on the daily dry scrubbing operations log. The records, should be reviewed for the previous 6 months to 2 years whenever there is concern that there are periods of low slurry supply to the atomizer. Spray dryer absorber inlet gas temperatures values during the previous £ £o _12 months Dry scrubbing systems have a limited turndown capability due to the need for complete drying of the atomized slurry. Low gas inlet temperatures during periods of low combustion system load can cause poor drying of the droplets. The process control system is generally designed to block atomizer operation once inlet temperature drops below a preset value. The inlet gas temperature data should be reviewed to confirm that the controller is working properly, since operation under these conditions could lead to absorber vessel deposits and nonideal operation once loads increase. The inlet temperature data may be available on the dry scrubber system daily operating logs, the archived continuous strip charts, or on the computerized data acquistion file. Dry injection system feed rates during the previous _6 _to _12 months The long term performance of the calcium hydroxide supply system should be "checked if the emissions data indicates occasional emission excursions. (See earlier inspection step.) The feed rate data for the previous 6 to 12 months provided by the weigh belt feeder or the volumetric screw feeder should be compared against the combustion system loads and against the inlet acid gas concentration monitors (when available). The automatic control system should be able to vary calcium hydroxide (or other alkali) addition rates with load variations and inlet gas acid gas concentrations. 120 ------- INSPECTION OF DRY SCRUBBERS Follow-up Level 2 Inspection Procedures Calcium silicate/calcium hydroxide feed rates during the previous J3 t£ _12_ months The variability and reliability of the calcium silicate/ calcium hydroxide dry injection system in the spray absorber/dry injection systems should be evaluated by reviewing the daily system operating logs. Some loss in acid gas collection efficiency could occur if feed rates were low. Dry injection system control device solids recycle rates. The recycle rates used in the spray absorber/dry injection systems have some impact on the overall acid gas collection efficiency. Low recycle rates indicate slightly reduced acid gas collection efficiency. 5.4.3 Level 3 Inspection Procedures The Level 3 inspection includes many inspection steps per- formed during Level 2 basic and Level 2 follow-up inspection procedures. These are described in earlier sections. The unique inspection steps of Level 3 inspections are described below. Spray dryer absorber vessel dry bulb and wet bulb outlet gas temperatures. These measurements are taken if there is a significant question concerning the adequacy of the on-site gauges and if there are safe and convenient measurement ports between the absorber vessel and the particulate control device. The measurements should be made at several locations in the duct to ensure that the values observed are representative of actual conditions. The'values should be averaged and compared with the value indicated by the on-site instruments (if operational) and with baseline data sets. It should be noted that it is rarely necessary to make this measurement since the on-site gauges are a critical part of the overall process control system for the dry scrubber system. Failure to maintain these instruments drastically increases the potential for absorber vessel wall deposits and increased emissions. These temper- ature monitors are normally very well maintained. 121 ------- INSPECTION OF DRY SCRUBBERS Level 3 Inspection Procedures Spray dryer absorber vessel or dry injection system inlet gas temperature This measurement is taken when the on-site gauge is not available, is malfunctioning, or is in a potentially nonrepre- sentative location. For spray dryers, the measurement should be taken in the main duct leading to the atomizer or in one or more of the ducts that lead to the gas dispersion system within the vessel. For dry injection systems, the measurement should be taken upstream of the gas stream/reagent mixing point (such as the venturi contactor). The measurements should be taken at several locations in the duct and averaged. Locations near air infiltration sites should be avoided. Procedures for the temp- erature measurements are included in the Appendix. 5.A.4 Level 4 Inspection Procedures The Level 4 inspection includes many inspection steps per- formed during Level 2/Level 3 inspections. These are described in earlier sections. The unique inspection steps of Level 4 inspections are described below. Start-up and shutdown procedures The start-up and shutdown procedures used at the plant should be discussed to confirm the following. 0 The plant has taken reasonable precautions to minimize the number of start-up/shutdown cycles. 0 The dry scrubber is operated in a reasonable time after start-up of the process equipment. Inspectors should remember that starting the atomizer (in spray dryer type systems) when the inlet gas temperatures are low can lead to absorber vessel deposits. Possible locations for measurement ports If the system does not have the necessary measurement ports to facilitate a Level 3 inspection, candidate sites should be identified. These should be in safe and convenient locations which do not disturb plant instruments or operations. 122 ------- INSPECTION OF DRY SCRUBBERS Level 4 Inspection Procedures Potential dry scrubber system safety problems Agency management personnel and/or senior inspectors should identify potential safety problems involved in standard Level 2/ Level 3 inspections at this site. To the extent possible, the system owner/operators should eliminate these hazards. For those hazards which can not be eliminated, agency personnel should prepare notes on how future inspections should be limited and should prepare a list of the necessary personnel safety equipment. A partial list of common health and safety hazards include the following. 0 Inhalation hazards due to fugitive leaks from inlet breech- ings, absorber vessels, particulate control systems, and alkaline reagent storage/preparation/supply equipment 0 Corroded ductwork and particulate control devices 0 Eye hazards due to alkali solids and slurries 0 High voltage in control cabinets Dry scrubber and process system flowchart A relatively simple flowchart is very helpful in conducting a complete and effective Level 2/Level 3 inspection. This should be prepared by agency management personnel or senior inspectors during a Level A inspection. It should consist of a simple block diagram that includes the following elements. 0 Source(s) of emissions controlled the system 0 Location(s) of any fans and blowers used for gas movement and solids conveying 0 Locations of any main stacks and bypass stacks 0 Alkali preparation equipment, adsorber vessel or contactor, particulate control device, and recycle streams 0 Locations of major process instruments and gas • stream continuous monitors 123 ------- INSPECTION OF DRY SCRUBBERS Level 4 Inspection Procedures Potential safety problems in the process area The agency management personnel and/or senior inspectors should evaluate potential safety problems in the areas that may be visited by agency inspectors during Level 2/Level 3 inspections. They should prepare a list of the activities that should not be performed and locations that an inspector should not go to as part of these inspections. The purpose of this review is to minimize inspector risk and to minimize the liability concerns of plant personnel. 124 ------- 6. INSPECTION OF CARBON BED ADSORBERS This section concerns regenerable and nonregenerable carbon bed adsorbers used for the removal of solvent vapors. This type of control system is often used when the gas stream contains one or more valuable organic compounds that can be economically recovered for reuse. It is also ideal for very small systems for which other VOC control techniques are impractical. 6.1 Components and Operating Principles Organic vapors are removed by adsorption as the gas stream passes through a bed of specially "activated" carbon. This material has a very large surface area for adsorption due to the presence of a large number of pores throughout the carbon. The organic vapors diffuse into these pores and are retained on the carbon surfaces due to both chemical and physical forces. There is a fixed quantity of organic vapor that can be adsorbed on the carbon. This limit is a function of (1) the amount of carbon in the bed, (2) the carbon characteristics, (3) the gas stream temper- ature, (4) the organic vapor concentration, and, (5) the chemical characteristics of the organic compound(s) present. The capacity of the bed decreases as the temperature of the organic vapor/air stream increases. A change of only 15 to 20°F can have a significant impact on the organic vapor capacity of a carbon bed system. A change in the chemical characteristics can also affect performance. Generally, high molecular weight organic compounds are retained more effectively than low molecular weight compounds. With all organic vapor compounds, the maximum capacity increases as the vapor concentration increases. Commercial carbon bed systems are designed to operate well below the maximum organic vapor capacity. Equipment designers use a value called the Working Capacity which takes into account losses of carbon adsorption area due to a variety of common operating conditions. The working capacity is generally 25 to 50% of the maximum capacity. 125 ------- INSPECTION OF CARBON BED ADSORBERS Components and Operating Principles GUAM MUWtN MUTlCUATI HI Ik* •UTU9 •00 r •M- •PO- -e»o- WATIM MCANTin > NATIM •TfAM Figure 6-1. Flowchart of a two-bed carbon adsorber system 126 ------- INSPECTION OF CARBON BED ADSORBERS Components and Operating Principles Once the working capacity of organic vapor has been adsorbed, the organic compounds must either be removed, or the carbon must be discarded. Very small systems, such as those used in dry cleaning, usually discard the carbon since the cost of the desorption equip- ment is high. In the case of large systems, the quantities of solvent recovered are large enough to justify the the cost of desorption. The term "regeneration" is often used for the process of desorbing organic vapors from carbon beds. In regenerable systems, the carbon bed is isolated from the gas stream and heated with steam to remove the organic compounds from the carbon. The high gas temperature overcomes the physical and chemical forces binding the organic vapor to the carbon. Once the organic vapors have been removed from the carbon bed, the bed is cooled so that it will be ready when it is placed back into service. The organic vapors released during desorption are condensed along with the steam used in the desorption step. The organic compounds are usually insoluble in the water and float on the surface. The organic compounds can therefore be removed by means of a decanter. A simple flowchart for a two-bed carbon adsorption system is shown in Figure 6-1. The solvent laden air is drawn from the process equipment by a fan. On the discharge side of this fan, the static pressure in the ductwork is positive. Therefore, there is a possibility that some fugitive leaks can occur. The contaminated gas stream is directed to the on-line bed by means of isolation dampers. The cleaned gas stream is then exhausted directly from the carbon bed to the atmosphere. There is usually a VOC detector on the outlet of each- bed. The VOC detector is a very important instrument since it indicates if high VOC concentrations exist in the gas stream that is leaving the carbon bed and entering the ambient air. Initially, the adsorption of organic vapor on the activated carbon is both rapid and efficient. However, as the capacity of the carbon is approached, the efficiency of removal decreases and 127 ------- INSPECTION OF CARBON BED ADSORBERS Components and Operating Principles the effluent VOC concentration begins to rise. The concentration suddenly increases from the normal levels of 100 to 500 ppm (v/v) to levels that ultimately approach the inlet VOC concentration. The beginning point of the concentration rise is called the breakthrough point. Carbon bed systems should be operated so that any one bed of the total system never reaches the breakthrough point, the organic vapor detectors used on many large carbon bed adsorber systems are intended to prevent breakthrough conditions by increasing the fre- quency of bed desorption whenever high concentrations exist. The organic vapor concentration versus time curve shown in Figure 6-2 is a typical "breakthrough" curve. It illustrates the potential organic vapor emissions if a carbon bed is not taken off- line for desorption before it reaches it working capacity. One of the primary functions of the inspector is to confirm that all beds in a system are being desorbed before they reach the breakthrough threshold indicated by the arrow in Figure 6-2. The working capacity of a carbon bed can decrease over time due to the adsorption of compounds which can not be removed by normal desorption procedures. These compounds are held very tightly to the activated carbon and are riot released under the normally mild desorp- tion temperatures. Activity of the carbon bed can also be reduced by the deposition of fine particles which block access to the pores. Due to these problems, carbon beds can suffer breakthrough much sooner than anticipated by the operator. The static pressure drop through the carbon bed is a valuable performance indicator. The pressure drop is proportional to the gas flow rate through a bed that remains in good physical condition. Changes in gas flow rate can be confirmed by comparing the measured static pressures in the inlet ducts with the base-line values. If the gas flow rate has not changed dramatically, the change in ob- served carbon bed pressure drop is probably due to deterioration of the carbon pellets. The physical breakdown of the carbon pellets is usually accompanied by a reduction in VOC removal effectiveness. 128 ------- INSPECTION OF CARBON BED ADSORBERS Components and Operating Principles Nett: This curvt 1s in txMplt. Actual tlM will vtry for application. MO coo I e «00 »0 100 M 1 2 3 OB-St 30 Ttai 40 45 Figure 6-2. Typical breakthrough curve 129 ------- INSPECTION OF CARBON BED ADSORBERS General Safety Considerations 6.2 General Safety Considerations No internal inspections should be conducted. Regulatory agency inspectors should not attempt to enter off-line carbon bed systems for any reason. There are a number of significant hazards, including but not limited to the following. 0 Low oxygen levels due to adsorption of oxygen on the surfaces of wet carbon 0 Hydrogen sulfide gas, hydrochloric acid vapor and other toxic compounds formed on the carbon Only intrinsically safe portable instruments should be used. All portable VOC detectors, temperature monitors, flashlights, and other electrically powered equipment should be rated as intrinsically safe. Respirators should be available for use. Portions of the carbon bed system usually operate under positive static pressure. Leaks from ductwork or the adsorber shell can lead to localized high VOC levels. Inspectors should be fitted and trained in the use of the necessary respirators and should be medically certified as capable of wearing the units. 130 ------- INSPECTION OF CARBON BED ADSORBERS Inspection Summaries 6.3 Inspection Summaries 6.3.1 Level 1 Inspections - No Inspection Steps 6.3.2 Level 2 Inspections Basic Level 2 Inspection Steps Stack/Exhaust 0 Exhaust VOC concentration for 10 - 15 minutes near the end of the adsorption cycle* Carbon Bed Adsorber e Obvious corrosion on the adsorber shell 0 Adsorption/desorption cycle times 9 Steam pressure and temperature during desorption Process Equipment 0 Obvious fugitive emissions* Follow-up Level 2 Inspection Steps Carbon Bed Adsorber 0 Inlet gas temperature 0 Inlet and outlet static pressures 0 Outlet detector calibration and maintenance 0 Quantity of .solvent in recovered solvent tank Process Equipment 0 Maximum production rate during the last 6 months 0 Average production rate during the last 12 months 0 Types of solvents used 0 Quantities of solvents purchased 0 Quantities of solvents sold/discarded 131 ------- INSPECTION OF CARBON BED ADSORBERS Inspection Summaries 6.3.3 Level 3 Inspections Stack/Exhaust c Exhaust VOC concentration for 10 - 15 minutes near the end of the adsorption cycle* 0 Outlet gas temperature* Carbon Bed Adsorber 0 Inlet gas temperature * 0 Obvious corrosion on the adsorber shell* 0 Adsorption/desorption cycle times* 0 Inlet and outlet static pressures* 0 Outlet detector calibration and maintenance* 0 Quantity of solvent in recovered solvent tank* 0 Measure the outlet VOC concentration 0 Measure the inlet gas temperature 0 Measure the static pressure drop Process Equipment 0 Obvious fugitive emissions* 0 Maximum production rate for last 6 months* 0 Average production rate for last 12 months* 0 Types of solvents used* 0 Quantities of solvents purchased* 0 Quantities of solvents sold/discarded* 0 Hood static pressure 6.3.4 Level 4 Inspection Procedures Exhaust Stack 0 All elements. of a Level 3 inspection Carbon Adsorber 8 -All elements of a Level 3 inspection e Locations for measurement ports Potential inspection safety problems 0 Process Equipment 0 All elements of a Level 3 inspection 0 Basic flowchart of process 0 Potential inspection safety problems * Refer to Level 2 Inspection Procedures 132 ------- INSPECTION OF CARBON BED ADSORBERS Basic Level 2 Inspection Procedures 6.4 Inspection Procedures Techniques for the inspection of carbon bed adsorbers can be classified as Level 2 or Level 3. The Level 2 inspections primarily involve a walkthrough evaluation of the carbon bed adsorber system and process equipment using on-site gauges. The Level 3 inspection incorporates all of the inspection points of the Level 2 inspection and includes independent measurements of the adsorber operating conditions. 6.A.I Basic Level 2 Inspections Evaluate the VOC outlet detector. The VOC detectors often used at the outlet of the carbon bed systems are relatively sophisticated instruments which require frequent maintenance. Confirm that they are working properly by reviewing the calibration records since the previous inspection. Maintenance work orders should also be briefly reviewed to determine if the instruments have been operational most of the time. Check carbon bed shell for obvious corrosion. Some organic compounds collected in carbon bed systems can react during steam regeneration. This leads to severe corrosion of the screens retaining the carbon beds and of the unit shell. Observe the adsorption/desorption cycles. Determine the time interval between bed regenerations and compare this with previously-observed values. An increase in this time interval could mean that breakthrough is occurring if the quantities of organic vapor entering the carbon bed have remained unchanged. Systems in which the cycle frequency is controlled by a timer rather than an outlet organic vapor detec- tor are especially prone to emission problems due to longer than desirable cycle times. Check the regeneration steam line pressure. Any decrease in the steam line pressure from previously recorded levels could indicate less than necessary steam flow for regeneration of the carbon beds. 133 ------- INSPECTION OF CARBON BED ADSORBERS Follow-up Level 2 Inspection Procedures 6.4.2 Follow-up Level 2 Inspection Procedures Evaluate carbon bed system static pressure drop. If there are on-site gauges, evaluate any changes in the static pressure drop. A decrease could mean deterioration of the carbon bed to the point that channeling of the gas stream is affecting gas-solid contact. Higher than normal static pressure could mean partial pluggage of the carbon bed due to fines formation or due to material entering with the gas stream. However, gas flow changes could also be responsible for changes in the static pressure drop. Prepare solvent material balances. For some processes, the effectiveness of the carbon bed system can be evaluated by preparing a solvent material balance around the facility for a period of several weeks to a month. The information needed for the calculations includes solvent quantities purchased, changes in solvent storage tank levels, and solvent quantities transferred from the system. Evaluate ventilation system. To the extent safely possible, gas flow rates from process equipment to the carbon bed system should be evaluated. Record hood static pressures (if monitored) and look for any holes or gaps in the ductwork. 6.A.3 Level 3 Inspections Measure the VOC outlet concentrations. The effluent concentration from each bed should be measured if^ there is safe and convenient access to the effluent ductwork. The measurements .should be made with an organic vapor analyzer that is calibrated for 50 to 2000 ppm. The instrument (and its portable recorder, if any) should be certified as intrinsically safe for Class I, Group C and D locations. This means simply that the instrument is incapable of initiating an explosion when used properly. A small port is adequate to draw a 0.5 to 3.0 liter per minute sample into the instrument. An observed VOC concentration greater than 500 ppm (v/v) is a sign that the bed is not performing properly. 134 ------- INSPECTION OF CARBON BED ADSORBERS Level 3 Inspection Procedures Measure the VOC outlet concentration (continued). It is important to determine the approximate desorption cycle of multi-bed systems. Outlet VOC measurements conducted earlier in the adsorption cycle of a bed may appear adequate even when the bed activity is severely reduced. Breakthrough usually does not occur until late in the operating cycle unless the condition of the carbon is extremely poor. Therefore, an effort should be made to measure the outlet VOC concentration of each bed at a time when it is approaching the end of the adsorption mode. The adsorption/desorption cycle is normally controlled by a timer and this can be used to determine the approximate status of each bed. In some commercial multi-bed units there is only poor acces- sibility to the effluent ducts from each unit. In this case, the VOC concentration in the combined duct should be measured at the exhaust point. Obviously, this measurement should be attempted only when there is safe and convenient access to the exhaust. It is especially important to avoid areas where high VOC concentrations could accumulate. Measure the inlet gas temperature. Adsorption is inversely related to the gas temperature entering the carbon bed adsorbers. An increase in the gas temperature from the baseline period could result in a decreased capacity for organic vapors. The gas temperature should be measured in the inlet ductwork, immediately ahead of the carbon bed. Measure the static pressure drop. A change in the static pressure drop since the baseline period is usually due to either a change in the gas flow rate through the carbon bed or due to the physical deterioration of the bed itself. 135 ------- INSPECTION OF CARBON BED ADSORBERS Level 3 Inspection Procedures Measure the static pressure drop (continued). Measurement taps on the adsorber shell should be used, if available. Alternatively, the static pressure drop can be measured using ports in the inlet ductwork to the adsorber system and the outlet duct from the adsorber. Obviously, the static pressure drop should be determined while the adsorber is on-line. Check/measure the hood static pressure. At the hood, the gas stream is accelerated to the velocity of 1200 to 2000 feet per minute. The static pressure in the hood is a useful indicator of the total gas flow rate. A drop in the hood static pressure from previously recorded levels means that the gas flow has decreased. The relationship between gas flow rate and hood static pressure is indicated below. The equation simply illustrates that the gas flow rate is proportional to the square root of the hood static pressure. If the hood static pressure decreases by a factor of 2, the gas flow rate has decreased by approxi- mately a factor of 1.41. G « Where: G » Gas flow rate, ACFM C • Proportionality constant, ACFM/(Inches W.C.) Sph « Hood static pressure 136 ------- INSPECTION OF CARBON BED ADSORBERS Level 4 Inspection Procedures 6.4.4 Level 4 Inspection Procedures The Level 4 inspection includes many inspection steps performed during Level 2 and Level 3 inspections. These are described in earlier sections. The unique inspection steps of Level 4 inspections are described below. Evaluate locations for measurement ports. Many existing carbon bed adsorbers do not have safe and convenient ports that can be used for volatile organic compound concentration, static pressure, and gas temperature measurements. One purpose of the Level 4 inspection is to select (with the assistance of plant personnel) locations for ports to be installed at a later date to facilitate Level 3 inspections. Evaluate potential safety problems. Agency management personnel and/or senior inspectors should identify any potential safety problems involved in standard Level 2 or Level 3 inspections at this site. To the extent possible, the system owner/operators should eliminate these hazards. For those hazards that can not be eliminated, agency personnel should prepare notes on how future inspections should be limited and should prepare a list of the necessary personnel safety equipment. A partial list of common health and safety hazards includes the following. 0 Inhalation hazards due to low stack discharge points 0 Fugitive emissions from process equipment system 0 Inhalation hazards from adjacent stacks and vents 0 Access to system components only available by means of weak roofs or catwalks 137 ------- INSPECTION OF CARBON BED ADSORBERS Level 4 Inspection Procedures Prepare £ system flowchart. A relatively simple flowchart is very helpful in conducting a complete and effective Level 2 or Level 3 inspection. This should be prepared by agency management personnel or senior inspectors during a Level 4 inspection. It should consist of a simple block diagram that includes the following elements. Source(s) of emissions controlled by a single carbon bed adsorber 0 Location(s) of any fans used for gas movement through the system (used to evaluate inhalation problems due to positive static pressures) 0 Locations of any main stacks and bypass stacks 0 Location of any prefilters for particulate removal 0 Location of carbon bed adsorbers 0 Locations of major instruments (VOC concentration, static pressure gauges, thermocouples) Evaluate potential safety problems ±n the process area. The agency management personnel and/or senior inspectors should evaluate potential safety problems in the areas that may be visited by agency inspectors during Level 2 and/or Level 3 inspections. They should prepare a list of the activities that should not be performed and locations to which an inspector should not go as part of these inspections. The purpose of this review is to minimize inspector risk and to minimize the liability concerns of plant personnel. 138 ------- 7. INSPECTION OF THERMAL AND CATALYTIC INCINERATORS This section concerns incinerators that are generally used on curing ovens, driers, and other common process sources. They are used whenever it is uneconomical to recover the organic vapors, and whenever compliance can not be achieved by use of low solvent coatings or inks. In some cases, these control devices have been installed to allow compliance with regulatory requirements until low-solvent coatings and inks can be developed without sacrificing product quality. 7.1 Components and Operating Principles The basic purpose of any incinerator is to raise the temperature of the VOC containing gas stream to a sufficient temperature to allow complete oxidation of the organic compounds. Thermal incinerators utilize a burner flame mounted in the main chamber of the incinerator to generate the necessary quantity of hot combustion gas. This gas then heats the relatively cool VOC containing gas stream to a level several hundred degrees Fahrenheit above the autoignition temperature for the specific organic compound. The autoignition temperature is generally in the range of 800 to 1400 degrees Fahrenheit. In the case of catalytic incinerators, a preheater burner (or burners) is used to raise the gas stream temperature to the level necessary to complete oxidation on the surface of the catalyst bed. Catalytic incinerators generally operate several hundred degrees below thermal incinerators for the same organic compounds since the catalyst pro- motes oxidation reactions. It should be noted that in both thermal and catalytic incinerators, the VOC compounds are not oxidized within the burner flame itself. The burner (or burners) simply provides the turbulent mixing and the hot gas -that is necessary to accomplish VOC oxidation. Thermal and catalytic incinerator inlet gas stream VOC concentrations are usually limited to between 500 ppm and 7,500 ppm for safety reasons. It is generally necessary to maintain VOC concentrations lower than 25% of the Lower Explosive Limit (L.E.L) so that the incinerator flame does not flashback to the process equipment. The 25% L.E.L. value is a widely accepted.upper concen- tration limit which allows for some nonuniformity and variablity in the gas stream VOC levels. The concentrations corresponding to 25% of the L.E.L. are provided in Table 7-1 for a number of common 139 ------- THERMAL AND CATALYTIC INCINERATORS Components and Operating Principles organic chemicals. When mixtures of organic compounds are present in the inlet gas stream, the total concentration is generally limited to 25% of the lowest L.E.L. for the various compounds. Incinerators having VOC concentrations up to 50" of the L.E.L. have recently been installed on systems having continuous inlet VOC concentration monitors. Incinerators on these sources may have higher inlet VOC concentrations than those indicated in Table 7-1. Table 7-1. VOC Concentrations Corresponding to 25% of Lover Explosive Limits Contaminant Concentration, ppm Butane A,750 Ethane 7,500 Ethylene 7,750 Propylene 6,000 Styrene 2,750 Benzene 3,500 Xylene 2.500 Toluene 3,500 Methyl alcohol 18,250 Isopropyl alcohol 5,000 Acetone 7,500 Methyl ethyl ketone A,500 Methyl acetate 7,750 Cellosolve acetate 4,250 Acrolein 7,000 Cyc.lohexanone 2,750 Acetaldehyde 10,000 Furfural 5,250 Source: L.E.L. Data from EPA Publication 600/2-84-118a 140 ------- THERMAL AND CATALYTIC INCINERATORS Components and Operating Principles 7.1.1 Thermal Incinerators The major components of a thermal incinerator include a burner, a refractory lined combustion chamber, and a stack. The burner includes a combustion air supply controller, a fuel rate controller, a flashback arrestor, and a burner assembly. A thermocouple on the discharge of the incinerator is often used to operate the controller which maintains proper air/fuel ratio. In some systems, heat recovery equipment is used on the incinerator discharge to reduce the operating costs. Burners in thermal incinerators generally operate whenever the incinerator is on line since the concentration of the VOC containing waste stream is too low to support combustion. The burners supply the additional heat necessary to achieve oxidation temperatures. Gas streams having a low VOC concentration obviously require slightly less fuel than those with concentrations approaching 25* of the L.E.L. Most operation and maintenance problems associated with thermal incinerators concern the burner since this is the component subjected to the extreme gas velocities and gas temperatures. These problems include poor fuel atomization (oil-fired units), deposits within the burner that cause poor air-fuel mixing, inadequate air supply, and quenching of the flame on refractory surfaces. Routine maintenance on at least a quarterly basis is necessary to clean and readjust the burners for proper operation. Symptoms of poor burner performance include black smoke generation, lower than normal outlet tempera- tures, and higher than normal VOC outlet concentrations. Thermal incinerators are also subject to problems caused by rapidly varying VOC concentrations and gas flow rates. These change the fuel requirements necessary to maintain a stable outlet tempera- ture. A sudden decrease in the VOC concentrations coupled with an increase in the gas flow rate can lead to short term periods with lower than desirable operating temperatures. A sharp increase in the VOC concentration with a decreased gas flow rate can lead to short term excursions above the maximum temperature limits of the combus- tion chamber. 141 ------- THERMAL AND CATALYTIC INCINERATORS Components and Operating Principles 7.1.2 Catalytic Incinerators The basic components of a catalytic incinerator include a preheat burner, a nixing chamber, a catalyst bed, a heat recovery system, and a stack. The preheat burner is used whenever supplemental fuel is needed to achieve the necessary operating temperature. In many cases, the VX contaminants have sufficient heat value to achieve the rela- tively low combustion temperatures without preheat burners. Therefore, inspectors should not conclude that the unit is not operating correctly simply because the preheat burner is not operating at the time of the inspection. It is quite possible that the preheat burner is used only during start-up or during periods of low VOC concentration. The temperatures required for high efficiency oxidation depend on the type of catalyst, the incinerator design, and the type of organic compound. Some typical operating temperatures for common compounds are provided in Table 7-2. Table 7-2. Typical Operating Temperatures for 90% Conversion in Catalytic Incinerator Compound Operating Temperature, Acetylene 200 Propyne 240 Propylene 260 Ethylene 290 n-Heptane . 300 Benzene 300 Toluene 300 Xylene 300 Etha'n'ol 315 Methyl ethyl ketone 370 Methyl isobutyl ketone 370 Propane 410 Ethyl acetone 415 Ethane 430 Cyclopropane 455 Methane 490 142 ------- THERMAL AND CATALYTIC INCINERATORS Components and Operating Principles Catalytic incinerators are vulnerable to a number of operating problems due to the participation of the catalyst in the oxidation reactions. These problems include the following. o Catalyst thermal aging Catalyst burnout due to high temperature fluctuations Catalyst scouring from catalyst bed Soot masking of catalyst due to upset combustion conditions in preheat (oil-fired) burners Particulate masking of catalyst Poisoning of the catalyst by non-VOC contaminants entrained in the gas stream Thermal aging is the inevitable result of gradual recrystalliz- ation of the noble metal catalyst materials due to exposure to the hot combustion products. The catalyst simply becomes less effective in promoting oxidation of VOC compounds. Because of this problem, all noble metal catalysts must eventually be replaced with fresh catalysts. Thermal burnout is the sudden volatilization of the catalytic compounds from the support matrix that comprises the catalyst bed. The temperature excursions that cause catalyst losses are often due to an undesirable increase in the VX concentration in the waste gas stream. The catalyst bed must be replaced once signifi- cant burnout has occurred. Masking inhibits catalyst activity by preventing contact between the vapor phase organic compounds and the surface of the catalyst material. This can be caused by deposition of particulate material in the catalyst bed or by soot formation in the preheat burner. Removal of water soluble materials from the catalyst surface can be accomplished simply by washing with a detergent solution. Non-water soluble materials can sometimes be removed by solvent washing and/or physical scrubbing of the catalyst materials. There is no permanent damage to the catalyst unless the cleaning process results in physical attrition of the catalyst from the surface of the substrate. 143 ------- THERMAL AND CATALYTIC INCINERATORS Components and Operating Principles Poisoning of catalyst involves irreversible chemical reactions between gas stream contaminants and the catalyst materials. There can be significant reductions in VOC oxidation efficiency since the affected catalyst is no longer effective in the oxidation reactions. Therefore, the catalyst bed must be replaced after a significant fraction of the catalyst has been affected. A partial list of common catalyst poisons and masking materials is presented in Table 7-3. It should be noted that the severity of the impact depends on the specific type of catalyst, the gas stream temperatures, and the concentration of the catalyst inhibitor. One indication of catalyst inhibition is a lower than "normal" gas temperature increase across the catalyst bed. Since the oxidation reactions occurring on the catalyst bed are exothermic, there should be a significant temperature increase if the catalyst material is in good condition. Unfortunately, variations in the inlet VOC concentration can also affect the gas temperature rise across the bed. Low VOC concentrations result in a relatively small temperature increase. Therefore, the inspector must attempt to determine if a small temperature increase is due to catalyst inhibition or to a short term decrease in the VOC concentration. ------- THERMAL AND CATALYTIC INCINERATORS Components and Operating Principles Table 7-3. Catalyst Inhibitors Type of Inhibitor Fast Acting Poisons Phosphorus, Bismuth, Lead, Arsenic, Antimony, Mercury Slow Acting Poisons Iron, Tin, Silicon Reversible Inhibitors Sulfur, Halogens, Zinc Surface Maskers Organic solids Effect Irreversible reduction of catalyst activity at a rate dependent on concentration and temperature Irreversible reduction of catalyst activity. Higher concentrations than those of fast activity catalyst inhibitors can be tolerated Reversible surface coating of catalyst active area at a rate dependent on concentration and temperature Reversible surface coating of catalyst active area. Removed by increasing catalyst temperature Surface Eroders and Maskers Surface coating of catalyst active area. Also, erosion of catalyst surface at a rate dependent on particle size, grain loading, and gas stream velocity 145 ------- THERMAL AND CATALYTIC INCINERATORS General Safety Considerations 7.2 General Safety Considerations Areas of potential VOC exposure should be avoided. Thermal and catalytic incinerators are often located on building roofs near numerous uncontrolled process vents. High concentrations of organic compounds and other pollutants can exist in localized areas downwind of these vents. There can also be leaks of the contaminated gas stream from the inlet ductwork and the inciner- ator shell. Inspectors must remain upwind of these vents and leak sites. If this is not possible, the inspection should be terminated. Inspectors should have the appropriate respirator available for use in case there is unexpected exposure to organic compounds, chlorine, or hydrogen chloride. (Chlorine and hydrogen chloride result from oxidation of chlorinated hydrocarbons). Inspectors should be fitted and trained in the use of the specific respirator and be medically certified as capable of wearing the unit. Only intrinsically safe portable instruments should be used. All portable VOC detectors, temperature monitors, flashlights, and other electrically powered equipment should be rated as intrinsically safe for the specific type of hazardous locations that exist in the inspection area. Walking on roofs must be done carefully. Inspectors should avoid roofs that may be structurally weak. Furthermore, they should walk behind plant personnel in order to avoid obscured skylights and weak spots in the roof. No internal inspections should be conducted. Regulatory agency inspectors should not-attempt to enter off-line incinerator systems for any reason. There could be low oxygen levels and high contamin- ant concentrations even though the unit is off-line. Inspectors must avoid hot surfaces. The inlet ductwork, outlet ductwork, and incinerator shell are generally at elevated tempera- tures. Inspectors should avoid leaning on or touching these surfaces. 146 ------- THERMAL AND CATALYTIC INCINERATORS Inspection Summaries 7.3 Inspection Summaries 7.3.1 Level 1 Inspections - Not Applicable 7.3.2 Level 2 Inspections Basic Inspection Points Stack ° Visible emissions Bypass Stack 0 Vapor refraction lines Incinerator Heat recovery outlet gas temperature Incinerator outlet temperature Temperature rise across catalyst bed Audible air infiltration Obvious corrosion Process Equipment 0 Process operating rate Follow-up Incinerator 0 Fan motor current 0 Hood static pressure 7.3.3 Level 3 Inspections Stack °- All elements of a Level 2 Inspection Incinerator 0 All elements of a Level 2 Inspection 0 Inlet gas temperature 0 Inlet VOC concentration 0 Outlet VOC concentration Process * All elements of a Level 2 Inspection 0 Coatings compositions 147 ------- INSPECTION OF THERMAL AND CATALYTIC INCINERATORS Inspection Summaries 7.3.4 Level 4 Inspections Stack 0 All elements of a Level 3 inspection Incinerator 0 All elements of a Level 3 inspection 0 Locations for measurement ports 0 Potential inspection safety problems Process Equipment 0 All elements of a Level 3 inspection 0 Basic flowchart of process 0 Potential inspection safety problems 148 ------- THERMAL AND CATALYTIC INCINERATORS Inspection Procedures 7.4. Inspection Procedures The inspection procedures for incinerators can be classi- fied as Level 2 and Level 3 inspections. The Level 2 inspec- tion is a detailed walkthrough inspection utilizing the on-site incinerator and process instrumentation. The Level 3 inspec- tion includes all of the Level 2 steps and also includes the limited use of portable instruments to verify incinerator per- formance. The instruments generally used are the portable VOC detectors and portable thermocouple thermometers. Instrument measurement procedures and safety considerations are discussed in another section of this notebook. 7.4.1 Basic Level 2 Inspections Observe the Incinerator Exhaust. There should be no visible soot or particulate emissions from the exhaust. Visible emissions are generally due to improper burner operation or condensation of unburned organic compounds. Observe the incinerator bypass stack. Incinerators generally must have bypass stacks so that the process equipment can be safely vented in the event of inciner- ator malfunction. However, during routine operation, there should be no significant leakage of VOC contaminated gas through the bypass stack dampers. The leakage of high VOC concentration gas can often be identified by the wavy light refraction lines at the stack mouth. Record the incinerator operating temperature. For thermal,incinerators, the combustion chamber exhaust gas temperature should be recorded. This is generally monitored by a thermocouple that is used to adjust the main burner firing rate. A reduction in the operating temperature could result in a reduced VOC oxidation efficiency. For catalytic incinerators, the inlet and outlet gas tem- peratures to the catalyst bed should be recorded. The inlet gas temperature is the temperature after the preheat burner and immediately ahead of the catalyst bed. The bed 149 ------- INSPECTION OF THERMAL AND CATALYTIC INCINERATORS Basic Level 2 Inspection Procedures Record the incinerator operating temperature.(Continued) outlet temperature is the temperature before the gas stream enters any of the heat recovery equipment. Smaller than normal temperature increases across the catalyst bed are due to either catalyst inhibition or to a reduced VOC concentration in the inlet gas stream. Listen for air infiltration into the incinerator system. Air infiltration into incinerators under negative pressure (fan downstream of the incinerator) can lead to localized cooling of the gas stream. Incomplete VOC oxidation can occur in these areas. Severe air infiltration into the inlet duct could prevent proper incinerator operating temperatures since this reduces the sensible heat and the heating value of the inlet gas stream. Infiltration also reduces the VOC capture effectiveness at the process source. Check the incinerator shell, outlet ductwork, and stack for obvious corrosion. Hydrochloric acid vapor can be formed in incinerators due to the oxidation of chlorinated hydrocarbons. This can lead to corrosion of the incinerator shell and downstream gas handling equipment. Review the process operating records. Confirm that the incinerator was operated whenever high- solvent materials were being used. 7.4.2 Follow-up Level 2 Inspection Steps Evaluate the fan motor current. A decrease -in the fan motor current as compared to the baseline levels indicates a decrease in the total gas flow from the process equipment. A flow rate decrease could be due to a decrease in the process operating rate or a change in the process operating conditions. Fugitive emissions should be evaluated to the extent possible when there has been a significant decrease in the fan motor currents without process operating changes. 150 ------- INSPECTION OF THERMAL AND CATALYTIC INCINERATORS Follow-up Level 2 Inspection Procedures Measure the hood static pressure. The hood static pressure provides a general indication of the gas flow rate from the process equipment. This data is useful to confirm that there are no significant fugitive VOC emissions. 7.4.3 Level 3 Inspections Measure the VOC outlet concentration. The effluent gas concentration should be measured if there is safe and convenient access to the effluent gas duct. The port should be located downstream of the heat recovery equipment so that the gas temperature is as low as possible. A glass-lined probe is usually advisable to minimize losses of organic vapor to the surfaces of the probe. If the gas temperature is greater than 300 °F, it will probably be necessary to include a condenser and knock-out trap in the sample line in order to protect the VOC detectors. The VOC detector (and its portable recorder, if any) should be certified as intrinsically safe for the type of hazardous location prevailing in the vicinity of the incinerator. No electrically powered equipment should be used that could ignite fugitive VOC vapors. The observed concentration should be less than 5 to 10% of the inlet concentration if the incinerator is operating properly. Measure the inlet VOC concentration. The inlet gas stream VOC concentration can usually be measured using the same VOC instrument used for the outlet port. A dilution probe will often be necessary for photoionization instruments and flame ionization instruments limited to 1000 to 2000 ppm. The condenser and knock-out trap are rarely necessary since the gas stream temperatures are normally less than 250 °F. As in the case with the outlet measurements, the measurement of the inlet concentration should be done only when all safety requirements are satisfied. 151 ------- INSPECTION OF THERMAL AND CATALYTIC INCINERATORS Level 3 Inspection Procedures Measure the incinerator outlet temperature. The measurement of the incinerator outlet temperature is attempted whenever the on-site gauge does not appear to be providing accurate data. However, measurement of the outlet temperature using portable gauges is subject to a number of significant possible errors. These include the following. 0 Higher than actual values due to exposure of the probe to radiant energy from the burner. 0 Lower than actual values due to shielding of the probe behind refractory baffles in the combustion chamber. 0 Non-representative values due to spatial variations of gas temperature immediately downstream of the incinerator. For these reasons, the independent measurement of the incinerator outlet temperature is rarely done by regulatory agency inspectors. Also, battery powered thermocouple ther- mometers are not intrinsically safe and can therefore not be used in certain areas. Measure the hood static pressure. The hood static pressure provides a general indication of the gas flow rate from the process equipment. This data is useful to confirm that there are no significant fugitive VOC emissions. 152 ------- INSPECTION OF THERMAL AND CATALYTIC INCINERATORS Level 4 Inspection Procedures 7.4.A Level 4 Inspection Procedures The Level 4 inspection includes many inspection steps per- formed during Level 2 and 3 inspections. These are described in earlier sections. The unique inspection steps of Level 4 inspections are described below. Evaluate locations for measurement ports. Many existing fabric filters do not have convenient and safe ports that can be used for static pressure, gas temperature, and gas oxygen measurements. One purpose of Level 4 inspections is to select (with the assistance of plant personnel) locations for ports to be installed at a later date to facilitate Level 3 inspections. Evaluate potential safety problems. Agency management personnel and/or senior inspectors should identify any potential safety problems involved in standard Level 2 or Level 3 inspections at this site. To the extent possible, the system owner/operators should eliminate these hazards. For those hazards that can not be eliminated, agency personnel should prepare notes on how future inspections should be limited and should prepare a list of the necessary personal safety equipment. A partial list of common health and safety hazards includes the following. 6 Hot exhaust duct surfaces 0 Inhalation hazards due to low stack discharge points 6 Weak catwalk and ladder supports 0 Fugitive emissions from process equipment 0 Inhalation hazards from adjacent stacks and vents 0 Weak roofs or catwalks 153 ------- INSPECTION OF THERMAL AND CATALYTIC INCINERATORS Level 4 Inspection Procedures Prepare a_ system flowchart. A relatively simple flowchart is very helpful in conducting a complete and effective Level 2 or Level 3 inspection. This should be prepared by agency management personnel or senior inspectors during a Level 4 inspection. This should consist of a simple block diagram that includes the following elements. c Source(s) of emissions controlled by a single incinerator 0 Location(s) of any fans used for gas movement through the system (used to evaluate inhalation problems due to positive static pressures) 0 Locations of any main stacks and bypass stacks 0 Location of incinerator 0 Locations of major instruments (static pressure gauges, thermocouples) Evaluate potential safety problems in the process area. The agency management personnel and/or senior inspectors should evaluate potential safety problems in the areas which may be visited by agency inspectors during Level 2 and/or Level 3 inspections. They should prepare a list of the activities that should not be performed and locations to which an inspec- tor should not go as part of.these inspections. The purpose of this review is to minimize inspector risk and to minimize the liability concerns of plant personnel. 154 ------- 8. USE OF PORTABLE INSTRUMENTS 8.1. VOC Detectors 6.1.1 Types of Instruments There are five basic types of instruments in common use for the measurement of organic vapor concentration. Since each of these uses a different measurement principle, there are substantial differences in the abilities of the instruments to monitor various types of organic compounds. Each of these types of instruments can meet the performance specifications of EPA Reference Method 21. For this reason, the instruments must be chosen for each specific application. 8.1.1.1. Flame lonization Detectors - A gas sample containing the organic vapor is fed into a hydrogen flame. Partial combustion of the organic compounds produces ions which are measured with an electrometer. Common applications - Responds to most organic compounds, including methane, aliphatic hydro- carbons, and aromatic hydrocarbons. Operating limits - Reduced response for oxygenated and chlorinated organic compounds. Does not respond significantly to carbon monoxide, carbon dioxide and water vapor. The portable instruments are different from flame ionization detectors often used on laboratory gas chromatographs. In the portable instruments, the oxygen necessary for hydrogen combustion is supplied by the sample gas stream. Due to the need for oxygen, the instrument flame can be extin- guished if the organic vapor concentration entering the instrument is above the upper explosive limit. 155 ------- USE OF PORTABLE INSTRUMENTS - VOC DETECTORS Types and Operating Principles 8.1.1.2. Photoionization Detectors - High energy ultraviolet light emitted by the instrument lamp is used to ionize a portion of the organic vapor contained in the gas stream. The measured current flow is proportional to the organic vapor concentration. The instrument is generally used for compounds having ionization potentials less than the ratings of the ultraviolet lamps. The lamp intensities range from 10 electron volts (abbreviated e.v.) to more than 11 electron volts. Common applications - Most chlorinated and oxygenated hydro- carbons, aromatic compounds, and high molecular weight aliphatic compounds. Operating limits - Insensitive for methane, ethane, propane, butane, carbon monoxide, carbon dioxide, and water vapor. The electron volt rating applies specifically to the wavelength of the most intense emission line of the lamp's output spectrum. Some compounds with ionization potentials above the lamp rating can still be detected due to the presence of small quantities of more intense light. 6.1.1.3. Catalytic Combustion Detectors - The principle used to de- tect organic vapors is the electrical resistance change in a filament coated with catalyst used to ignite the organic vapors. The filament is part of a Wheatstone bridge circuit so that the resistance change in the coated filament causes a current flow that is proportional to organic vapor concentration. Common application - Most hydrocarbons that can be oxidized. Operating limits - Some chlorinated compounds and lead com- pounds can poison the catalyst. Response to chlorinated and oxygenated compounds is poor. 156 ------- USE OF PORTABLE INSTRUMENTS - VOC DETECTORS Types and Operating Principles 8.1.1.4. Dispersive Infrared Detectors - Absorbance of infrared light occurs in a variable path gas sample cell. Monochromatic light is generated by a spectrometer so that monitoring can be done at a wave- length where the compound of interest absorbs strongly. Common applications - Most hydrocarbons Operating limits - Water vapor absorption will interfere with measurements of many compounds. The response of dispersive infrared units is highly dependent on the specific chemical. 8.1.1.5 Nondispersive Infrared Detectors - Detection of organic vapor is performed by absorption of infrared light. The sample gas contain- ing the organic vapor is passed through one cell and a reference gas is sealed in a second cell. The ultraviolet light is split between the two cells and the differential pressure resulting from the unequal heating is detected. The pressure is proportional to the organic vapor concentration. Common applications - Most hydrocarbons Operating limits - Water vapor and carbon dioxide can absorb infrared energy. 157 ------- USE OF PORTABLE INSTRUMENTS - -VOC DETECTORS Types and Operating Principles 8.1.2 Initial Instrument Checks Prior to leaving for the inspection site and/or conducting calibrations, the instrument should be carefully checked. If the instrument does not pass these routine checks, it should be repaired before it is taken to the inspection site. Leak Checks To leak check the probes on units with flow meters, the,probe outlet should be plugged for one to two seconds while the sample pump is running. If the sample flow rate drops to zero, there are no significant leaks in the entire sampling line. If there is any detec- table sample flow rate, further leak checks will be necessary to prevent dilution of the VOC sample gas during screening tests. The leak checks involve a step-by-step disassembly of the probe/sample line starting at the probe inlet and working backwards toward the instrument. At each step, the probe/sample line is briefly plugged to deter- mine if there is still inleakage at an upstream location. After the problem has been corrected, the probe/sample line is reassembled and rechecked. Units without flow monitors are calibrated in a similar manner. The sound of the pump during temporary blockage of the probe provides an indication that the flow has been stopped and that air infiltration is insignificant. Check Probe Condition The physical condition of the instrument probe should be visual- ly checked before use. These checks include: 0 Presence of any organic deposits on the inside surfaces 0 Presence of a clean particulate filter in the probe and the presence of a glass wool "prefilter". 0 Condition of orifice used to control dilution air flow into probe (dilution probes only). 0 Condition of sealing "0" rings or other seals. 158 ------- USE OF PORTABLE INSTRUMENTS - VOC DETECTORS Initial Instrument Checks Check Probe Condition (Continued) If organic deposits are found on the inside surfaces, they can usually be removed using either acetone or methanol (check instrument manufacturer's recommendations). The cleaned probes must be purged of solvent vapors before reassembly. Check Battery Pack Status The battery pack condition is normally checked simply by switch- ing the instrument to the "Battery Check" position and observing the dial setting. If the battery pack is weak, a new battery pack should be installed. Battery life is especially limited in cold weather. Check Detector The detectors used in each type of instrument are vulnerable to operating problems. The following steps are useful to confirm that the detectors are functioning: 0 Photoionization - Clean the windows and then turn the unit on. It should be possible to obtain a zero reading. 0 Flame lonization - Attempt to ignite the burner. If this can not be done, then there are problems with the batteries, the ignitor, or the hydrogen supply. 0 Catalytic Combustor - Attempt to zero instrument. If this can not be done, the detector has failed. 159 ------- PORTABLE INSTRUMENTS - VOC DETECTORS Calibration Procedures 8.1.3 Calibration Procedures and Requirements Calibration requirements for VOC instruments are specified in EPA Method 21 and in the specific NSPS and NESHAPS regulations applicable to sources of fugitive VOC emissions. A brief summary of the calibration requirements is provided below. 0 The instruments should be calibrated daily. 0 The gas concentration used for calibration should be close to the leak definition concentration. 0 The calibrant gas should be either methane or hexane. 0 A calibration precision test should be conducted every month. 0 If gas blending is used to prepare gas standards, it should provide a known concentration with an accuracy of plus or minus 2%. Calibration Type The NSPS and NESHAPS regulations do not specify the type of calibration to be performed on a daily basis. The inspector should determine whether single point or multi-point calibrations are necessary. All calibrations should be performed with the type of probe and prefilters that will be used in the screening tests. This is impor- tant since these affect response time and the sample flow rate. Calibrant Gases Calibrations can'be performed using either commercially prepared gas mixtures or blended gas mixtures. Disposable cylinders are most convenient when the calibrations are done at the inspection site. The types of calibrant gases normally recommended by the instrument manufacturers are listed in Table 8-1. 160 ------- USE OF PORTABLE INSTRUMENTS - VOC DETECTORS Calibration Procedures Table 8-1. Calibrant Gases and Concentrations Type of Instrument Calibrant Gas and Concentration Flame lonization 10,000 ppm Methane in Air 500 ppm Hexane in Air Photoionization 250 ppm 1,3 Butadiene in Air 250 ppm Benzene in Air Catalytic Combustion 500 ppm Hexane in Air 20,000 ppm Methane in Air Infrared Varies depending on application Consult the instrument operating manual and the manufacturer's representative to obtain more information concerning the types of Calibrant gases and the expected instrument response. Calibration Location The NSPS and NESHAPS regulations do not specify where the cali- brations should be performed. The author recommends that an initial calibration be done at the agency lab before leaving for the inspec- tion site. Calibrations can be performed under more controlled sample flow rate and sample temperature conditions when done in the agency lab. Both factors can influence instrument response. Furthermore, this calibration clearly demonstrates that the unit is operating satisfactorily and can., be taken to the inspection site. 161 ------- USE OF PORTABLE INSTRUMENTS - VOC DETECTORS Calibration Procedures Calibration Apparatus One possible means to calibrate VOC detectors is illustrated in Figure 8-1. A calibrant gas mixture from a disposable cylinder is used to fill a 20 liter Tedlar bag having several Roberts valves. The sample is drawn from the bag into the instrument at a controlled flow rate. The steps involved in calibration using disposable cylinders and Tedlar bags are listed below. This list is based on the assumption that the battery packs, probes, and detectors have been already checked (see Section 8.2). 0 Warm up instrument and assemble calibration apparatus. 0 Flush sample bags with hydrocarbon free air. 0 Confirm that sample flow is within normal range. 0 Reset instrument span and zero. 0 Reflush Tedlar bag and inject different calibrant gas concentration (for multi-point calibration). 0 Record results in lab notebook. Another technique for calibration of VOC instruments is shown in Figure 8-2. This is a relatively simple approach which can be used on instruments which are only slightly flow sensitive, such as the photoionization instruments. The flow meter should be set at a flow rate large enough to ensure that there is an excess of calibra- tion gas for the instrument. Calibration Records The records should be kept in an organized file so that it is possible to demonstrate that the unit was calibrated properly if the agency data are ever challenged.- 162 ------- USE OF PORTABLE INSTRUMENTS - VOC DETECTORS Calibration Procedures Cal. Gas Bag Sample Instrument Figure 8-1. Calibration Apparatus Using Tedlar Bag- Excess Rotameter Instrument Cal. Gas Figure 5-2. Calibration Apparatus Having Flow 'Directly to Instrument 163 ------- USE OF PORTABLE INSTRUMENTS - VOC DETECTORS Field Check Procedures 8.1.A Field Check Procedures There are several routine instrument performance checks which should be conducted during the field work. These demonstrate that the instrument is continuing to perform in a proper manner. Instrument Zero The instrument zero should be rechecked whenever it has been exposed to very high organic vapor concentrations or whenever organic liquids may have been inadvertently sucked into the probe. Even if these situations have not occurred, the zero should be checked several times per day. The instrument zero can be checked by sampling background air upwind of any possible VOC sources. Alternatively, sone hydrocarbon free air can be supplied using a charcoal filter. If the instrument zero has drifted significantly, the probe particulate filter and the prefilter (if used) should be replaced. Also, the probe should be cleaned using acetone or a similar solvent to remove the condensed organics. The instrument should be recalibrated (single point) after changing the filters and cleaning the probe. Instrument Response Confirm that the instrument is responding by sampling a source of VOC emissions. This could be leaking sources at the plant, the calibration gas in the Tedlar bag, or a small portable source of organic vapor. Routine response checks are especially important for flame ionization and catalytic combustion units. The FIDs can flame out above 70,000 ppm of organic vapor due to insufficient oxygen. The catalytic units can suffer catalyst volatilization if exposed to high concentrations of organic vapor over an extended time period. The catalytic units are also subject to catalyst poisoning and catalyst coating in certain sources. Automobile exhaust should NOT be used as a source of organic vapor when checking instrument response. There are large quantities of condensible vapor and particulate that can harm the instrument's detectors and accumulate in the probes. 164 ------- USE OF PORTABLE INSTRUMENTS - VOC DETECTORS Field Check Procedures Battery Condition In the case of some flame ionization detectors, weak batteries will not have enough power to operate the ignitor, even though a proper reading was obtained during the battery check. This can be a problem after the FID has been operated for several hours and after a number of flameouts have occurred. For this reason, the battery condition should be checked several times during the screening tests. Probe/Sampling Line Leakage The probe and sampling line integrity should be checked several times per day by simply plugging the probe inlet. The continual movement of these probes and lines can loosen the connections and allow significant air infiltration. This reduces the ability to identify fugitive VOC sources. 165 ------- USE OF PORTABLE INSTRUMENTS - VOC DETECTORS Special Tests 8.1.5 Special Tests The NSPS and NESHAPS regulations (primarily Method 21) require several instrument tests on an infrequent basis. These include determination of the response time and calibration precision. Response Time The response time of the instrument must be measured prior to using the unit on inspections. It must also be performed whenever there are changes in the probe, sample flow lines, or pump that could conceivably influence the response time. The test is conducted in accordance with paragraph 4.A.3 of Method 21. Hydrocarbon free sample gas is introduced into the instru- ment until a stable zero reading has been obtained. Then a supply of calibration gas of known concentration is quickly substituted for the hydrocarbon free gas. The time required for the instrument to indi- cate 90% of the calibration gas concentration is recorded as the response time. The test sequence is performed three times, and the response time values are averaged. A possible form for recording the response time tests is provided in Figure 8-3. The response time for instruments required in Method 21 tests is 30 seconds. A reduction in the response time of an instrument is generally due to severely reduced sample gas flow rates. Calibration Precision This test must be performed for instruments being used in Method 21 type inspections. The tests must be done before the instruments are used on inspections and at three month intervals during routine use. The test is performed by alternating sampling hydrocarbon free sample gas and a calibration gas. The observed organic vapor concen- trations when sampling the calibration gas are algebraically averaged, divided by the calibration gas concentation, and multiplied by 100. The calibration precision must be equal to or less than 102. A sample form for calibration precision tests is presented in Figure 8-4. 166 ------- USE OF PORTABLE INSTRUMENTS - VOC DETECTORS Special Tests Instrument ID Calibration Gas Concentration 90S Response Time: 1. _____ Seconds 2. _____ Seconds 3. _____ Seconds Mean Response Time Seconds Figure 8-3. Sample Form for Response Time Tests 167 ------- USE OF PORTABLE INSTRUMENTS - VOC DETECTORS Special Tests C*Ubratlo« Precision ID Calibration CM Niitwri Out ligh IM CBlibratloa CM ZBftruwnt Motor Dtfftrtnct.(l) No. CbKMtratioa. ffm 1. 2. 3. 4. 3. 6. U» fash «M£ Olfr. Mm Mffmw* (2) Ctl Error • OlikratloB CM Ceacntrttloa « 100 (1) (2) Akselar* TK!M Figure 8—4. Sample Form for Calibration Precision Tests 168 ------- USE OF PORTABLE INSTRUMENTS - VOC DETECTORS Spare Parts 8.1.6 Spare Parts A minimum number of spare parts are generally advisable to ensure that the VOC detectors can be repaired and maintained during field inspections. A list of recommended spare parts which should be taken to the inspection site is provided in the lists below. The instrument manufacturer should also be consulted regarding the need for spare parts. All Instruments 0 Battery pack 0 Particulate filters e Flexible tubing (l"-2") 0 Glass wool Flame lonization Detectors 0 Flame arrestor 0 Probe Photoionization Detectors 0 Window cleaning kit 0 Lamp 0 Rotameter Catalytic Detectors 0 Detector cell Infrared Detectors 0 Rotameter 169 ------- USE OF PORTABLE INSTRUMENTS - TEMPERATURE MONITORS Types and Operating Principles 8.2 Temperature Monitors Thermocouples and dial-type thermometers are used in inspections of VOC sources. The dial-type units are used primarily for low temp- erature applications such as carbon bed adsorbers. The thermocouples are used to check incinerator outlet gas temperatures. 3.2.1 Types and Operating Principles Thermocouples The electromotive force generated by two dissimilar metals is a function of the temperature. The thermocouple voltage is compared with a reference voltage (equivalent to 32 °F) and amplified by the thermometer. There are a variety of thermocouple types, each designated by letters adopted originally by the Instrument Society of America (ISA) and adopted as American National Standard C96.1-1964. A brief summary of the thermocouple properties and composition is provided below. Type K - This is the most common type of thermocouple used for VOC inspections due to the broad temperature range of -400 °F to + 2300 °F. The thermoelectric elements must be protected by a sheath since both wires are readily attacked by sulfurous compounds and most reducing agents. This sheath must be selected carefully to ensure that it also can take the maximum temperature that the unit will be exposed to. The positive wire is nickel with 10% chromium (trade name - chromel) and the negative wire is nickel with 5 % aluminum and silicon (trade name - alumel). Type E - These generate the highest voltage of any thermo- couple but are limited to a maximum temperature of 1600 °F. The positive wire is nickel with 10% chromium (chromel) and the negative wire is a copper-nickel alloy (constantan). 170 ------- USE OF PORTABLE INSTRUMENTS - TEMPERATURE MONITORS Types and Operating Principles Type J - These have a positive wire composed of iron and a negative wire composed of a copper-nickel alloy (constantan). They can be used up to 1000 °F in most atmospheres and up to 1400 °F if properly protected by a sheath. They are subject to chemical attack in sulfurous atmospheres. Type T - These can be used under oxidizing and reducing conditions. However, they have a very low temperature limit of 700 °F. They are composed of copper positive wire and a copper-nickel alloy (constantan) negative wire. Type R and S - These can be used in oxidizing or inert conditions to 2500 °F when protected by nonmetallic protection tubes. The Type R thermocouples are composed of a positive wire of platinum with 13 % rhodium and a negative wire of platinum. The Type S thermocouples have a positive wire of platinum with 10% rhodium. Both types can be subject to calibration shifts to lower temperature indications due to rhodium diffusion or rhodium volatilization. Type B - The positive wire is composed of platinum with 30% rhodium and the negative wire is platinum with 6% rhodium. These are less sensitive to the calibra- tion drift problems of Type R and S thermocouples. They can be used to a maximum temperature of 3100 °F when protected by nonmetallic protective tubes. 171 ------- USE OF PORTABLE INSTRUMENTS - TEMPERATURE MONITORS Types and Operating Principles Thermocouple Sheaths The maximum temperature that a thermocouple can withstand is dependent on the wire compositions and on the type of sheath wrapped around the thermocouple junction. The temperature limits of common sheath materials are indicated in Table 8-2. Table 8-2. Maximum Operating Temperatures for Common Sheath Materials Sheath Material Temperature Limit, °F Aluminum 700 304 Stainless 1650 316 Stainless 1650 Inconel 2100 Hastelloy 2300 Nickel 2300 Thermocouple Thermometer Limits A hand-held potentiometer is used to convert the thermocouple voltage to a temperature reading. This is a battery powered unit which is generally not rated as intrinsically safe. For this reason, thermocouples can not be taken into hazardous locations. Dial Type Thermometers Temperature is sensed by the the movement of a bimetallic coil composed of materials having different coefficients of thermal expansion. The coil movement is transmitted mechanically to a dial on the front of the thermometer. One of the principle advantages of this type of unit is that no are batteries required and it can be used safely in most areas. The main disadvantage is the relatively short probes of 6 to 12" which make it very difficult to reach locations at representative gas temperatures. Due to the short "reach", the dial-type instruments often indicate lower than actual temperatures. The dial-type units are best when there is very little tempera- ture variation in the measurement location and when there is little or no insulation surrounding the measurement ports. They are gener- ally used for low temperature applications. 172 ------- PORTABLE INSTRUMENTS - TEMPERATURE MONITORS Calibration and Routine Checks 8.2.2 Calibration and Routine Checks Ice and Boiling Water Temperature Measurements Both the thermocouple based thermometers and the dial-type thermometers should be checked prior to leaving for the inspection site. The temperatures of boiling water and a finely crushed ice water mixture should be checked. The indicated temperature of the boiling water should be 212 °F or less depending on elevation. The temperature of the ice water mixture should be between 32 °F and 34 °F depending on how well the ice has been ground and how long the mixture has had to reach thermal equilibrium. Record the thermometer temperatures for boiling water and ice water in a notebook or file which is kept at the agency lab. This simple two point check verifies that the unit is operating satisfactorily. Annual Calibration The thermocouple should be calibrated on an annual basis. This is often done by comparison of the voltage developed by the thermo- couple with the voltage developed by a NBS traceable thermocouple. A set of potentiometers is used to measure the voltages of the two thermocouples placed together in a furnace. Annual calibration of the dial type thermometers is generally not required. The' boiling point and ice point measurements are sufficient for dial type thermometers used in the temperature range of 32 °F to 212 °F. 173 ------- USE OF PORTABLE INSTRUMENTS - STATIC PRESSURE GAUGES Types and Operating Principles 8.3 Static Pressure Gauges Static pressure gauges are used primarily to evaluate the static pressure across carbon bed adsorbers and to evaluate ventilation systems leading to VOC control devices. 8.3.1 Types of Static Pressure Gauges Slack tube manometers, inclined manometers, and diaphragm gauges are used for measurement of static pressure. The inclined manometer is the most accurate instrument for low static pressures of less than 10 inches W.C. However, it is relatively bulky. Slack tubes can be used up to static pressures of 36 inches W.C. Larger slack tube manometers are cumbersome to use. The diaphragm gauges come in various styles, most of which are accurate to plus or minus 3% or 5% of the instrument scale. These gauges are easy to carry. The diaphragm gauges are composed of two chambers separated by a flexible diaphragm. The diaphragm moves when there are unequal pressures on each of the ports leading to the two chambers. The diaphragm deflection is mechanically transmitted to the dial on the front of the unit. No batteries are required. Also, there is no sample gas flow through the instrument. ------- USE OF PORTABLE INSTRUMENTS - STATIC PRESSURE GAUGES Calibration 8.3.2 Calibration The slack tube manometer and the inclined manometer do not need to be calibrated since these indicate static pressure directly. The diaphragm gauges are calibrated by comparison with an inclined man- ometer or a slack tube manometer depending on the static pressure range of interest. The diaphragm gauges can be calibrated by connecting both the manometer and the diaphragm gauge to a source of pressure. One port of each gauge is left open to the atmosphere. A squeeze bulb with check valves on both sides provides a source of positive and negative pressure in the range of -40 inches W.C. to + 40 inches V.C. A hose clamp is necessary to maintain the pressure while both static pressure gauges are being checked. Separate calibration curves should be prepared for the positive and negative pressures. Each curve should be comprised of a minimum of three points to indicate any non-linearities in the gauge response. A sample form for recording and plotting the calibration data is provided in Figure 8-5. Diaphragm gauge calibration should be performed prior to each inspection day. Total time requirements are less than 5 minutes when the manometers and squeeze bulbs are kept in a convenient location. 175 ------- PORTABLE INSTRUMENTS - STATIC PRESSURE GAUGES Calibration PrMaur* Gauge CaBbntton JNCHOWC, MVCMTOHY NUMKA. CAUVUTON DATE _ CALWATMN ITAWAMCL .TIMI. \ WC ions. Figure 8-5. Possible Form for Diaphragm Gauge Calibration 176 ------- USE OF PORTABLE INSTRUMENTS - PITOT TUBES Gas Flow Measurement Procedures 8.4 Pitot Tubes Both S-Type and standard pitot tubes can be used in VX inspec- tions to measure the gas flow rates. The standard pitot tube is most convenient since there is no need to calibrate the unit. However, it should not be used when there is some particulate in the gas stream that could plug the static pressure holes around the circumference of the outer tube. The S-type unit should be used when particulate is present. 8.4.1 Gas Flow Measurement Procedures Selection Measurement Site The measurement port used for the pitot traverse should conform to the minimum distances upstream and downstream of flow disturbances specified in Table 8-3. Preferred measurement site locations are also listed in this table. For rectangular ducts, the equivalent "diameter" of the duct is calculated as follows. Equivalent "Diameter" « 2 x L x W/(L + W) of Rectangular Duct Table 8-3. Measurement Site Characteristics Minimum Distances to Flow Disturbances 0 At least 2 diameters downstream 0 At least 0.5 diamters upstream Preferred Distances to Flow Disturbances 0 At Least 8 diameters downstream 0 At least 2 diameters upstream 177 ------- USE OF PORTABLE INSTRUMENTS - PITOT TUBES Measurement Procedures The minimum number of. traverse points should _be_ determined Figure 8-6. • POU fTACM Oft DUCTS ! j "^kmvmtMCt ;• wt It Figure 8-6. Minimum Number of Traverse Points Necessary Locations of. Traverse Points For circular stacks, the traverse points should be located on two perpendicular diameters of the stack at locations such as shown in Figure 8-7. The traverse point locations are specified in Table 8-4. For stacks with diameters less than 24 inches, do not locate a traverse point within 0.5 inches of the stack wall. For stacks larger than 24 inches, do not locate a traverse point within 1.0 inches of the stack wall. Move the last point away from the wall at least one nozzle diameter. If the adjusted point overlaps with the adjacent traverse point, treat the observed velocity pressure as two points when making the calculations. 178 ------- USE OF PORTABLE INSTRUMENTS - PITOT TUBES Gas Flow Measurement Procedures • I Figure 5-7. Traverse Point Locations TMU t. mean or swa ow*cm nm mm MKL TO runuc POWT rat CIIQIUW mcu IU •.I N.4 M.I •J mj M MJ B.I •.I M.I H.l ,1 ,1 t.1 U.I W.I M H.4 M.I •.I U IM HJ •.4 IM M.I •J •.I ii .1 ,4 W.l I.I M kl l.t M.I U.I H.I lt.4 ••• m.i 9.1 IM JI.I •.I m.% •.* Table 8-4. Locations for Traverse Point for Circular Stacks 179 ------- USE OF PORTABLE INSTRUMENTS - PITOT TUBES Gas Flow Measurement Procedures Locations of_ Traverse Points (Continued) For rectangular stacks determine the grid configuration from Figure 8-8. Notice that the minimum number of traverse points for a rectangular stack is 9. TJ::-- —-,--._ i_ • 1 • 1 1 • 1 * 1 * 1 * — 1 • ! • Figure 8-8. Rectangular Stack Grid Configuration Divide the stack into the grid configuration as determined from Table 8-5. Locate a traverse point at the centroid of each grid. An example is shown in Figure 7-8. Table 8-5. Example Traverse Point Locations - Rectangular Stacks Number of Traverse Points 9 12 16 20 25 30 36 42 Grid Configuration 3x3 4x3 4x4 5x4 5x5 6x5 6x6 7x6 7x7 180 ------- USE OF PORTABLE INSTRUMENTS - PITOT TUBES Gas Flow Measurement Procedures Verification of Absence of Cyclonic Flow The presence or absence of cyclonic flow at the traverse location must be verified if there are any tangential inlets or other duct configurations which tend to introduce gas swirling. Cyclonic flow is evaluated using the following procedure. e Level and zero the manometer. 0 Connect a Type S pitot tube to the manometer. 0 Place the pitot tube at each traverse point so that the face openings of the pitot tube are perpendicular to the stack cross-sectional plane. At this position, the pitot tube is at 0° reference. 0 If the differential pressure is null (zero) at each point, an acceptable flow condition exists. 0 If the differential pressure is not zero at 0° reference, rotate the pitot tube until a zero reading is obtained. 0 Note the angle of the null reading. 0 Calculate the average of the absolute values of the angles. Include those angles of 0°. 0 If the average is greater than 20°, the flow conditions of the sample location are unacceptable. Measure the stack gas velocity and gas flow rate. If the measurement location does not have cyclonic flow, the gas velocity and flow rate are measured using the procedure outlined below. A standard pitot is generally used if the particulate loadings are low. 0 Conduct a pretest leak check of the apparatus. 0 Level and zero the manometer. e Measure the velocity head at each of the traverse points and record the data..on the form presented in Figure 6-9. e Measure the gas temperature at each traverse point. 0 Conduct a post test leak check. 0 Calculate the average stack gas velocity and volumetric flow rate using the simplified equations presented on the next page. 181 ------- USE OF PORTABLE INSTRUMENTS - PITOT TUBES Gas Flow Measurement Procedures Measure the gas velocity and flow rate (continued) . The equation for the gas velocity is based on air at standard pressure. This is generally a valid approximation for VOC sources. Vs « 2.9 Cp (p ) avg. ^(Ts) avg. where: Vs « Average stack gas velocity (ft/sec) Cp « Pitot tube coefficient (dimensionless) Usually 0.99 for standard pitot tubes Usually 0.83 to 0.87 for S-Type pitot tubes Ap * Velocity head measured by pitot tube (inches of water) Ts « Absolute stack temperature (°R) equals stack temperature in °F + 460 The gas flow rate in actual cubic feet per minute is calculated by multiplying the average gas velocity by the stack cross sectional area. Qs - 3600 Vs A where: Vs - Average stack gas velocity, (ft/sec) A « Cross sectional area of stack (ft squared) 182 ------- USE OF PORTABLE INSTRUMENTS - PITOT TUBES Gas Flow Measurement Procedures WLMCV ••(UN* /IT V«1w1* TrmrM 0«U (Proa n. V«l. 42. Ni. 1M. ?fl. 417U. An«. U. W77). ~ Figure 8-9. Velocity Traverse Data Form 183 ------- |