United States Environmental Protection Agency Air and Energy Engineering Research Laboratory Research Triangle Park NC 27711 Research and Development EPA/600/S7-87/003 Apr. 1987 Project Summary Evaluation of Sulfur Capture Capability of a Prototype Scale Controlled-Flow/Split-Flame Burner J. Vatsky and E. S. Schindler This report describes large pilot demonstration of sulfur capture using copulverization of limestone with a high sulfur eastern bituminous coal and com- bustion of the mixture using Foster Wheeler's commercial Controlled- Flow/Split-Flame (CF/SF) Low NOX burner. Optimization of the sulfur capture was attempted through the use of overfire air and two proprietary flame temperature control methods. Addi- tionally, the effects of excess air changes, load changes, and different calcium/ sulfur mole ratios (Ca/S) were evaluated. The CF/SF burner was chosen because of its internal staging and proven low IMOX capabilities; its use in combination with two flame tem- perature reduction methods could re- duce the flame temperature to minimize dead burning of limestone and thus enhance SO2 capture. Although the use of flame temperature reduction and overfire air improved the SO2 capture, the optimum SO2 capture of 29% at a Ca/S of 2.15 was low. Operation under optimum SO2 capture mode resulted in measured NO, emissions of 0.19 Ib/106 Btu*; CO was less than 25 ppm at an excess oxygen level of 3.0%. The testing was done at a 42 x 106 Btu/hr heat input horizontally fired pilot plant con- figured like a conventional pulverized- coal-fired boiler. ' Readers more familiar with metric units may use the factors listed at the back of this Summary to convert to that system. This Project Summary was developed by EPA's Air and Energy Engineering Research Laboratory, Research Triangle Park, NC, to announce key findings of the research project that Is fully docu- mented In a separate report of the same title (see Project Report ordering in- formation at back). Introduction This report summarizes a joint Environ- mental Protection Agency (EPA)/Foster Wheeler Energy Corporation (FWEC) test program to evaluate the m-situ SO2 reduction capabilities of limestone injec- tion with a low NOX internally staged burner when the limestone and coal are copulvenzed and injected through the coal nozzle. The tests were performed between April 13 and May 16, 1983. The burner used is Foster Wheeler's com- mercial Controlled-Flow/Split-Flame (CF/SF) burner (Figure i). The test pro- gram was based on EPA's concept that, if the limestone is intimately mixed with the coal during the pulverization process and burned under low NO* conditions, high S02 capture levels can be obtained. When this method of limestone injection is combined with the low flame tempera- ture characteristics of the CF/SF burner and FWEC's proprietary flame tempera- ture reduction methods, the total S02 capture may be enhanced. Successful achievement of the Limestone Injection Multistage Burner (LIMB) process may result in S02 reductions at a much lower cost than with conventional wet removal methods. Although this technique may ------- Table 2. Analysis of Test Limestone Figure 1. Controlled-flow/split-flame (CF/SF) burner not replace wet methods of S02 reduction, it would be appropriate for retrofits of existing uncontrolled boilers firing high sulfur coals. The relatively short flame produced by the CF/SF burner is especially favorable for retrofits where the depth of the fur- nace is limited. Flames do not extend into the upper furnace which would increase the furnace exit gas temperature (FEGT). Increasing FEGT can cause fouling and slagging as well as uncontrolled steam temperatures and reduced efficiency. The tests were run at FWEC's Japanese licensee Ishikawajima Harima Heavy Industries Co., Ltd. (IHI) Aioi Works in Japan where IHI has a large coal com- bustion test facility. The fuel used is a high sulfur western Pennsylvania bitu- minous coal from the Middle Kittaning Seam with a sulfur content of about 3.1%. An analysis of the fuel is shown in Table 1. This fuel was chosen because it is typical of the fuels used in older boilers that may be susceptible to acid rain control legislation. The limestone chosen isVicron from California's Lucerne Valley. It is a high calcium limestone and was chosen because it had been used before in other EPA test programs and would allow more relevant comparison of S02 Table 1. Analysis of Test Fuel Fuel Name Origin Middle Kittaning Western PA Proximate Fixed Carbon,' Volatiles, % Ash.% Moisture, % Ultimate Carbon, % Hydrogen, % Oxygen, % Nitrogen, % Sulfur, % HHV. Btu/lb Operating Conditions Fuel Rate kg/hr Heat Input 106 Btu/hr 50.1 34.6 9.5 S.8 68.7 4.6 7.1 1.2 3.1 12,818 1.500 42.3 capture among EPA test programs. An analysis of the limestone is shown in Table 2. Test Facility Description IHI's test facility is designed to evaluate fuels and combustion systems on a Name Origin CaCO3, % MgC03. % SiO2. % AI2O3, % Fe203 Moisture, % Surface, % Inherent, % Vicron Lucerne Valley, CA 98.1 0.9 0.11 0.01 0.01 0.03 0.1 prototype scale (up to 50 x 106 Btu/hr). Functionally useful steam is not gen- erated so that operation and design changes do not affect the steam supply to industrial or power generation equipment. This provides an atmosphere conducive to testing without interruption. The pulverized coal system differs from that which is in current commercial prac- tice on pulverized coal-fired boilers. An indirect storage system is used and allows wide variations in air/coal ratios. The limestone bunker supplies, via a feeder, a Foster Wheeler vertical pulverizer. The coal and limestone are mixed and pul- verized in the mill to a minimum coal fineness of 70% through 200 mesh. The pulverized fuel is carried pneumatically to a cyclone separator where the fuel is separated from the carrier air and fed into a pulverized fuel bin; a baghouse filters the air before exhausting to the atmosphere, and collects the fines which are also fed into the fuel bin. A screw feeder at the botton of the fuel bin feeds the pulverized fuel over a weighing device and into a fuel/primary air mixer. This allows great flexibility in controlling the primary air to fuel ratio. The facility is fired by a single burner which simplifies burner flame studies since flame interactions do not occur. The furnace is refractory lined to simulate utility size furnace heat release rates. Nine view ports along each side of the furnace at the burner level, along with five others at upper elevations, allow the operator to observe the flame and take temperature measurements at different points along the flame's length. Overfire air ports are available for staging tests. The combustion air takes the following path through the system. A forced draf' ------- ifan supplies atmospheric air to the shell side of a tubular air preheater where it is heated up to the range of 536 to 653°F. Hot air is mixed with cold tempering air to obtain the desired primary air temper- ature. The remaining hot air is then supplied to the wmdbox. Combustion products pass out of the furnace, through a convection section and through the tube side of the preheater, after which it is cleaned of paniculate matter in a multiclone and then a baghouse. After the baghouse, an induced draft fan forces the combustion products to the stack. Ttibiu 3 summarizes basic system parameters. Test Methodology The intention of the test program was to evaluate various operating modes for their potential to improve SO2 reduction obtainable by copulverization of coal and limestone. A number of variables were evaluated: Overfire Air Furnace Excess Oxygen Calcium to Sulfur Mole Ratio Two Proprietary Flame Temperature Reduction Methods Load Overfire Air Injected Higher in the Furnace Burner Parameters These variables were thought to have the greatest potential in improving S02 capture. This was especially true of the two flame temperature reduction methods where, in the past, peak flame temper- ature reductions of 70 to 90°F were seen singly and over 200°F was obtained when these methods were combined The in-depth evaluation consisted of a complete full factorial matrix of tests: testing each variable in combination with every other combination of other vari- ables Furnace excess oxygen was an exception in that only a half factorial was planned Simultaneously with the determination of the effect each variable has on S02 reduction, S03, NOX, CO, and total hydro- carbons were measured. The intention was to observe the effect each variable had on other emission species to evaluate the overall emission characteristics of each combination that improved SO2 reduction. Major Results and Conclusions Gaseous Emission Levels • S02 Emissions The addition of limestone to the fuel at a Ca/S of 2 15 resulted in an Table 3. System Specifications Furnace Burner Coal Handling Pulverizer Width Depth: Height. Coal Overfire Air Heat Liberation- Elevator Bunker- Table Feeder- Type: Capacity. Fineness: Tubular Air Preheater Air Flow Rate: Air Temp. Inlet: Air Temp Outlet: Paniculate Collection Type: Equipment Gas Flow Rate • Oust Loading Inlet: Outlet: Limestone Handling Bunker. Feeder: 3100 mm (10.2 ft) 4500 mm (148 ft> 11,000 mm (36 ft) 200 kg/h (4.400 Ib/h) As Necessary Max 111 x. 10ekcal/m3hx (12.5x 103 Btu/ft3h) 1. 5 T/h (11 x 103 Ib/h) 1. 10m3 (350 ft3) 2. 15 T/h (33 x 103 Ib/h) max. IHI-FW Ring & Roller Mill MBF-16 8 T/h (17 xlO3 Ib/h) 70% through 200 mesh 31 T/h(68x103lb/h) 20°C(70°F) 320°C(610°F) Baghouse following a multiclone 20.000 Nrrf/mm (12440 scfm) 36. g/Nm3 (87 gr/scf) 0.1. g/Nm3 (0.242 gr/scf) 225 kg/h (500 Ib/h) Max. 20-320 kg/h (50-700 Ib/h) optimum emission reduction of 28%. This is an improvement over the 22- 23% found without any changes in operation of the burner-furnace. This optimum was found with a combi- nation of 3% excess O2, 20% overfire air, and with FW's proprietary flame temperature reduction method #2 (FTRM#2). Another combination of operating variables (5% excess O2 and FTRM #2) resulted in higher SO2 reduction at the same Ca/S, but it also increased NOX emissions such that the total of acid forming emissions of SO2 and NOX was higher than for the optimum case. Increasing the limestone addition rate during otherwise normal oper- ating conditions (i.e., optimum NOX burner settings, 3% excess 02, no limestone, no overfire air, full load, and no flame temperature reduction methods in use), to a Ca/S of 3.26 resulted in 33.4% reduction. This increase in S02 reduction is es- sentially linear up to Ca/S = 3.26. If the optimum S02 control method is extrapolated to Ca/S = 3.26, the SO2 reduction would increase to 43%. Although it is generally con- ceded that S02 reduction is not linear with Ca/S, a linear relation- ship was found up to a Ca/S of 3.26, the maximum value tested. However, this optimum occurred with overfire air ports open, resulting in slagging. • NOX Emissions In general, adding limestone to the fuel reduced NOX by 10%. Under normal operating conditions, the NOX emission rate measured for the CF/SF burner was 0.32 lb/106 Btu. This represents a 60% reduction from the predicted uncontrolled NOX emission rate of 0.8 lb/106 Btu using this fuel and a pre-NSPS burner at this test facility. Under the conditions of optimum SO2 reduction, the NOX decreased to 019 lb/106 Btu, an additional 41% reduction from 0.32 lb/106 Btu (or a total of a 76% reduction from the uncontrolled level). About 25 to 30% of this addi- tional NOX reduction can be attributed to overfire air (OFA), 10% can be attributed to adding limestone to the fuel, and 1% is attributed to the use of FWEC's proprietary FTRM #2. The negligible NOX reduction due to the FTRM #2 is expected since the peak flame temperature is already sub- stantially below 2900°F. • CO Emissions In general, adding limestone at a Ca/S of 2.15 reduced CO concen- trations at the economizer outlet to below 35 ppm corrected to 0% excess ------- 02, with one exception. Under normal operating conditions, the CO averaged 39 ppm. Under the opti- mum S02 reduction test conditions, the CO concentration dropped to 24 ppm, a 38% reduction. Half of this reduction can be attributed to lime- stone addition; the remainder can be attributed to FIRM #2. • SO3 Emissions In general, adding limestone to the fuel at a Ca/S = 2.15 always reduced S03 concentrations to below 20 ppm corrected to 0% excess O2 regardless of the initial concentra- tion. Under normal operating condi- tions S03 concentrations averaged 28 ppm. Under conditions of opti- mum SO2 reduction the SO3 con- centrations were reduced to 8 ppm, a 71% reduction. About equal per- centages of this reduction can be attributed to OFA and limestone addition. • Total Hydrocarbons (THC) Limestone addition in many cases decreased the THC emissions, but there were many exceptions The only operating variable that had a consistent effect on THC was FTRM #1, and it increased THC. Neither excess oxygen nor overfire air had a consistent effect on THC. Under normal operating conditions the THC concentrations averaged 3 ppm cor- rected to 0% excess O2. Under conditions of optimal S02 reduction the THC was reduced to 1.7 ppm, a 43% reduction The reduction is at- tributed to a synergistic effect of the combination of OFA, FTRM #2, and limestone addition since none of these (alone) consistently reduced THC SO2 Capture in the Baghouse No significant S02 or SO3 reduc- tion was measured across the bag- house with or without limestone addition. SO3 reduction was mea- sured across the air heater. SO3 change across the air heater cannot be explained; additionally, the re- duction is virtually independent of the presence of limestone. S03 con- centrations dropped from an average 8 ppm to about 0.3 ppm when lime- stone was being added; S03 was reduced from 18.3 to 0.6 ppm when limestone was not being added, and was further reduced to 0 4 ppm across the baghouse. The air heater is tubular with an exit temperature Table 4, Ash Fusibility Temperature Ash Fusion Temperatures, °F Test 42 Test 43 Ca/S Oxidizing Atmosphere Deformation Softening Hemisphere Flow 0 2372 2408 2507 2561 2.15 2426 2453 2516 2705 Reducing Atmosphere Deformation Softening Hemisphere Flow 1940 1958 1976 2453 2156 2246 2345 2552 of about 500°F. Consequently, there should be no S03 condensation prior to the baghouse. At these tempera- tures the SO3 level should remain constant unless absorption is occur- ring on some surface. All test results are corrected to 0% excess oxygen. Effect on Equipment • Furnace and Slagging Potential No detrimental side effects were noted. The addition of limestone to the fuel did not increase the slagging potential of the coal. The coal was considered to be of medium to high slagging potential. During normal combustion, both with and without limestone, slagging was not evident; but, when overfire air was used, slagging was evident, both with and without limestone This was fully expected based on an analysis of the ash constituents and oxidizing/ reducing fusion temperatures shown in Table 4. These results show that the ash fusion temperatures are higher when limestone is being added at a Ca/S mole ratio of 2 15. All ash fusion temperatures in- crease as the furnace conditions change from reducing to oxidizing. In this case the ash softening tem- perature increases by 450°F without limestone addition; and by 207°F with limestone. Also all ash fusion temperatures increase with the addition of limestone The increase is largest under reducing atmo- sphere. The reducing ash softening temperature increases 288°F, and the reducing hemisphere tempera- ture increases by 369°F when lime- stone is added to the fuel. • Baghouse The baghouse operated normally during the test program. No increase in pressure drop was seen. The daily start-up/shutdown cycle did not precipitate any bag blinding. • Burner No detrimental side effects were noticed on the burner, flame, or combustion in general. Metric Conversion Readers more familiar with metric units may use the following factors to convert to that system Nonmetnc Times Yields Metric Btu/hr Btu/lb °F Ib/W6 Btu 1 054 232 5/9(°F-32) 430 kJ/hr J/g °C ng/J ------- J. Vatsky and E. S. Schindler are with Foster Wheeler Energy Corporation, Livingston, NJ 07039. Charles C. Masser is the EPA Project Officer (see below). The complete report, entitled "Evaluation of Sulfur Capture Capability of a Prototype Scale Controlled-Flow/Split-Flame Burner," (Order No. PB 87-168 670/AS; Cost: $18.95, subject to change) will be available only from: National Technical Information Service 5285 Port Royal Road Springfield, VA 22161 Telephone: 703-487-4650 The EPA Project Officer can be contacted at: Air and Energy Engineering Research Laboratory U.S. Environmental Protection Agency Research Triangle Park, NC 27711 United States Environmental Protection Agency Center for Environmental Research Information Cincinnati OH 45268 Official Business Penalty for Private Use $300 EPA/600/S7-87/003 0000329 PS ------- |