United States Environmental Protection Agency Research and Development Air and Energy Engineering Research Laboratory Research Triangle Park, NC 27711 EPA/600/SR-94/184 November 1994 sorEPA Project Summary Demonstration of Sorbent Injection Technology on a Tangentially Coal-Fired Utility Boiler (Yorktown LIMB Demonstration) J. P. Clark, R. W. Koucky, M. R. Gogineni, A. F. Kwasnik Limestone Injection Multistage Burner (LIMB) technology has been successfully demonstrated on a tan- gentially fired coal-burning utility boiler, Virginia Power's 180 MWe Yorktown Unit No. 2. This document summarizes the activities conducted, and results achieved, under this EPA-sponsored demonstration program. LIMB com- bines furnace injection of a calcium- based sorbent for moderate reductions of sulfur dioxide (SO2) with a low-nitrogen-oxide (NOX) firing system for NOX emissions reduction. The pro- cess is attractive for retrofit of existing coal-burning utility boilers, since the capital equipment requirements and overall sulfur reduction costs per ton of sulfur oxide removed are less than for most other options, such as wet flue gas desulfurization. Testing was conducted on an east- ern bituminous coal with a typical sul- fur content of 2.3%. Five sorbents were tested: commercial hydrated lime, with and without calcium lignosulfonate treatment, each from two suppliers, and finely pulverized limestone. Short-term parametric testing showed full-load SO2 removals of up to 56 and 63% at calcium-to-sulfur (Ca/S) ratios of 2:1 and 2.5:1, respectively. Intermediate load performance was higher, with SO2 removals of up to 60 and 67% at Ca/S ratios of 2:1 and 2.5:1, respectively. Results varied with specific LIMB oper- ating conditions, boiler load, and sor- bent used. Results of both extensive parametric testing and continuous long- term operation of the LIMB system are presented. Results of performance test- ing of the Low-NOx Concentric Firing System (LNCFS) Level II firing system are also presented. Typically, under comparable boiler operating conditions, a 42% reduction in NOX at full load and a 33% reduction in NOX at intermediate load, relative to baseline levels, were achieved with the LNCFS Level II Sys- tem. The effects of LIMB operation on boiler, electrostatic precipitator (ESP), and ash handling system performance are also discussed. The most signifi- cant impact on boiler performance was the collection rate of LIMB solids plus fly ash on boiler convective surfaces during continuous operation, resulting in poorer boiler heat transfer perfor- mance and higher temperatures leav- ing the boiler. Continuous operation of the sootblowing system minimized this effect. The results of two ESP perfor- mance tests that were conducted dur- ing continuous LIMB operation are discussed and compared to results from similar testing conducted without LIMB operation. Ash conditioning and disposal during LIMB operation at Yorktown were significantly affected by the unreacted lime in the ash. These problems, as well as suggested pre- cautions to avoid them, are discussed. Recommendations for LIMB com- mercialization and an evaluation of the economics of the technology in comparison to a conventional flue gas desulfurization system are dis- cussed. Printed on Recycled Paper ------- 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 tltlo (sea Project Report ordering Infor- mation at back). Introduction Increasing concern for the environmen- tal effects of acid rain has led to active efforts to control emissions of sulfur diox- ide and oxides of nitrogen, SO2 and NOX, from the fossil-fuel-burning electric utility industry. The choice of control techniques for limiting SO2 and NOX emissions from utility boilers will most likely include a mix of technologies to achieve the desired re- ductions at minimum cost. The primary method for controlling SO2 from new coal- burning boilers is flue gas scrubbing. Of- ten, however, this technique may not be a viable option for existing power plants. Space may not be available for installing scrubbers and disposing of waste from the scrubbers. In addition, the installation of scrubbers may not be a viable eco- nomic choice for older units with less than 10-20 years of remaining useful life. The need for a method of providing a moder- ate degree of emission control at lower cost and with minimal retrofit to an exist- ing boiler and minimal space has led to the development of the LIMB process. In this process for simultaneous SO2 and NOX control, a calcium-containing mate- rial, such as limestone (CaCO3) or hy- drated lime [Ca(OH)A, is injected into the furnace at appropriate temperatures. The material, called the sorbent, breaks down to form lime (CaO). The CaO reacts with SO2 in trie gas to form calcium sulfate (CaSO4). CaSO4 is collected in the boiler's partfeulate removal device, along with the coal ash, and transferred to a landfill site. Concurrent with SO2 control by injection of the calcium-containing material, NOX is controlled by installation of low-NOx burn- ers that provide staged introduction of air to control flame temperature and gas chemistry in the flame region. The LIMB process had its origin in the observation that significant sulfur is re- tained during the burning of coals that are high in alkali-containing ash and low in sulfur. This observation led to several in- vestigations (in Europe, Japan, and the U.S. during the 1960s) of the feasibility of injecting calcium-based sorbents directly Into the furnace of a coal-fired boiler as the primary SO2 control technique. Early field demonstrations of furnace injection, using limestone, produced disappointing levels of SO2 reduction. During the late 1970s, interest in direct sorbent injection for SO2 control waned as emphasis shifted to scrubber development. However, dur- ing the early 1980s, development of im- proved firing systems with lowered combustion zone temperatures, provided the impetus for the development of LIMB as a low-cost retrofittable system for the simultaneous reduction of SO2 and NOX. The EPA established a major research and development program, both at their laboratories and with contractors, to es- tablish LIMB as a viable, low-cost, alter- native to conventional flue gas desulfurization (FGD) systems for attain- ing moderate reductions in SO2 on ex- isting coal-burning boilers. Through early research efforts, LIMB eventually evolved into the more generic "furnace sorbent injection" as sorbents that were more reactive than limestone, such as Ca(OH)2, and injection locations that were more consistent with the optimum SO2 capture "window" of 2300 to 1650°F (1260 to 890°C), such as into the upper furnace, were identified. Because tangential firing introduces special considerations for the design of sorbent injection systems due to the unique aerodynamics in the sorbent mixing region of tangentially fired boilers, the EPA established parallel development programs for LIMB application to both wall- fired and tangentially fired boilers. The Yorktown demonstration project was the culmination of a multiphase program, which included both pilot- and prototype-scale testing, to develop LIMB for tangentially fired boiler applications. The EPA selected Combustion Engineering (C-E) as prime contractor for the demonstration project in 1987. Virginia Power's Yorktown Unit No. 2, a 180-MWe coal-fired boiler located at the Yorktown Power Station in Yorktown, Virginia, was selected as the host unit. C-E, Virginia Power, Stone & Webster, and the U.S. Department of Energy all helped fund the project. The demonstration project objectives were established as at least 50% reduc- tion in SO2 at a Ca/S of 2.5:1 and a reduction in NOX emissions to 0.4 lb/106 Btu (0.17 kg/GJ) or below. These emis- sions would be reduced with no significant adverse impact on boiler pperability and reliability. An eastern bituminous coal with a sulfur content of 2.0 to 2.5% was selected as the demonstration coal. The overall program was conducted in two phases: site-specific studies to sup- • port the system design, and the field dem- onstration itself. The site-specific studies included a boiler characterization test to identify the location of the ideal sulfation zone through extensive mapping of the boiler temperatures profile, identification of promising injection schemes via cold- flow testing on a plastic model of the Yorktown boiler, and pilot-scale combus- tion testing to verify performance of both the most promising injection schemes and the proposed low-NOx firing system. Those injection schemes that performed best during pilot-scale testing were incorporated into the LIMB system design. Computa- tional fluid dynamics computer modeling of the ESP inlet ducts, where the flue gas humidification system would be located, showed that there was insufficient resi- dence time in the ducts to achieve a close approach to the adiabatic saturation tem- perature for enhanced SO2 capture. Humidification for ESP performance main- tenance during LIMB operation had been demonstrated to be effective at two other EPA-sponsored LIMB projects: the Edgewater wall-fired demonstration project and the tangentially fired prototype test program at Richmond Power & Light. En- hanced SO2 capture with a close approach to saturation had already been demon- strated at Edgewater. To avoid incurring additional costs to extensively modify the Yorktown ducts for enhanced SO2 cap- ture, the Yorktown humidification system was designed only to maintain ESP per- formance. While the final system design was es- sentially complete by June 1990, construc- tion did not begin until May 1991 due, in large part, to a 1-year delay in the Unit No. 2 outage, which was rescheduled to allow installation of a new steam turbine/ generator set. A 1-month baseline test to establish the performance of Unit No. 2 with its original firing system was conducted in March 1991, prior to installation of the LIMB sys- tem. An extensive ESP performance test was also conducted. The medium-sulfur eastern bituminous demonstration coal was used for this test. The boiler was returned to service in December 1991, with the LNCFS Level II low-NOx firing system in place and instal- lation of the sorbent injection equipment nearly complete. Performance testing of the LNCFS system was conducted in March 1992. LIMB system start-up/shake- down testing started in May 1992 and continued through August 1992. Perfor- mance testing of the LIMB system, includ- ing three long-term demonstration tests of over 22 days of continuous operation each, extended from September 1992 to Octo- ber 1993. The results of the LIMB and low-NOx testing, plus the effects of LIMB ------- on Unit No. 2 operation, are presented below. NOX Emission Reduction A LNCFS Level II system was installed to meet the project objective of 0.4 lb/106 Btu (0.17 kg/GJ) NOX emissions. The LNCFS Level II system features sepa- rated overfire air (SOFA) for staged com- bustion, flame attachment tips for early fuel ignition, and offset air nozzles to fur- ther minimize NOX formation. During early testing of the LNCFS Level II system, it was determined that the new Unit No. 2 steam turbine had introduced substantial changes in the boiler waterwall and reheater heat absorption requirements. The boiler controls responded by raising burner tilts, which, in turn, adversely af- fected the effectiveness of the LNCFS fir- ing system in reducing NOX. To make the LNCFS performance data fully comparable to baseline data with the original firing system, all NOX emissions were adjusted to the 0° burner tilt used during baseline testing and to a common fuel nitrogen content. The LNCFS system without overfire air performed at essentially the same level as the original baseline sys- tem at full boiler load, suggesting that the concentric firing system, in combination with the flame attachment tips, did not contribute to overall NOX reduction. A 15% reduction in NOX was measured at inter- mediate boiler load. Adding SOFA pro- duced a 42% reduction in NOX at full load and a 33% reduction at intermediate load. Carbon-in-ash levels for the baseline sys- tem and the LNCFS system with SOFA nozzles closed were comparable at ap- proximately 7%, under similar test condi- tions. The effect of fully opening all three SOFA nozzles was to increase carbon-in- ash by about 85%. Comparable effects have been noted on other LNCFS Level ll-equipped units burning similar coals. LIMB System for Yorktown The Yorktown sorbent injection system was designed to provide a great deal of operational flexibility to permit operation of the system over a wide range of boiler and sorbent injection conditions. Three el- evations for injection into the boiler were provided. The elevations were selected based on the results of site-specific stud- ies, including field and pilot-scale testing. The middle and lower elevations each pro- vided for tangential injection of the sor- bent through 16 injectors located at the eight corners of the divided furnace. The lower elevation was designated as the primary injection location for reduced boiler load operation. The middle elevation, lo- cated approximately at the "nose" of the furnace, was designated as the primary injection elevation for full boiler load op- eration. The third elevation, with 16 injec- tors across the front wall of the boiler, above the tangential injector elevations, was an alternate full-load injection loca- tion. Parallel sorbent feed systems supplied sorbent to both sides of the divided fur- nace. Feed rates of from 4 to 15 tons/hr (3.6 to 13.6 tonnes/hr) (total) allowed sub- stantial flexibility in evaluating LIMB sys- tem performance over a range of boiler loads and Ca/S molar ratios. In addition, either sorbent feed-system was capable of feeding both sides of the furnace, if the other feed system was not available. Each feed system consisted of a day bin (65 tons—58.9 tonnes—of hydrate), plus feed- ers and transport blowers. A large fan provided additional air to achieve sorbent injection velocities into the furnace of up to 450 ft/sec (137 m/sec). Sorbent for LIMB testing at Yorktown was delivered by rail to an unloading site approximately 9 miles (14.5 km) from the Yorktown Station. At this site, the sorbent was off-loaded to pneumatic trucks, typi- cally holding 20 tons (18 tonnes) of hy- drated lime, for delivery to the Station where the sorbent was pumped into a long-term storage bin designed to hold 390 tons (354 tonnes) (roughly 2 days supply) of hydrate. The truck unloading system worked well throughout the opti- mization and demonstration test periods. As many as 13 trucks were unloaded in 1 day during demonstration testing. SO2 Removal Performance: Optimizing Testing A parametric test program was con- ducted to evaluate the effectiveness of the LIMB System over a wide range of configuration and operating variables. The primary objective of the program was to identify the LIMB configuration and oper- ating variables that provided the greatest reduction in SO2, consistent with good boiler performance, and identify the opti- mum sorbent system operation for long- term demonstration testing. A total of 147 tests were conducted from September 1992 through September 1993. Full-load tests were conducted at all three injection elevations. One alter- nate injection yaw configuration was tested. Intermediate load tests were con- ducted at two injection elevations. The effect of Ca/S on SO2 capture was evalu- ated. The effect of sorbent mixing on SO2 capture was evaluated by varying injec- tion air plus sorbent discharge velocity from 150 to 450 ft/sec (45.7 to 137.2 m/ sec) (approximately 2.5 to 7.5% of total airflow to the boiler) and injector tilt from -35 to +35° relative to horizontal (0° tilt) injection. Commercial hydrated lime from two suppliers was tested. Tests were also conducted using calcium-lignosul- fonate-treated hydrate from the same two suppliers. In addition, limited testing was conducted using finely pulverized limestone as the sorbent. SO2 capture did not improve significantly when testing with calcium-lignosulfonate- treated hydrate. Data for pulverized lime- stone (95% through 325 mesh) were limited and showed considerable variabil- ity. The limestone tests, which included low- (down to 90 MWe), intermediate- (128 MWe), and full-load (169 MWe) operation, showed a clear advantage for the in- creased residence time available at low load. In general, the SO2 removal perfor- mance for pulverized limestone was about 60% of the performance for hydrated lime. Optimized full-load SO2 removal effi- ciency on hydrated lime was 56% at Ca/S = 2:1 and 63% at Ca/S = 2.5:1. At inter- mediate load, SO2 removal was 60% at Ca/S = 2:1 and 67% at Ca/S = 2.5:1. The increase in SO2 capture at intermediate boiler load is attributed to an increase in residence time in the 2300 to 1650°F (1260 to 890°C) sulfation "window" at intermedi- ate load. SO2 capture improved with in- creasing injector discharge velocity up to 300 ft/sec (91 m/sec). Tests conducted at 450 ft/sec (137 m/sec) showed no addi- tional improvement in SOZ capture. No significant effect of injector tilt on SO2 cap- ture was measured during this optimiza- tion testing. Boiler operation, however, as measured by the ability to. maintain super- heat and reheat outlet temperatures, was improved during injection through the middle elevation when the injectors were tilted downward. Full load boiler operation was further improved by injecting through the lowest elevation with the injectors tilted upward. The overall performance of the sorbent injection system was good throughout the optimization test period. The primary op- erational problem during this period was the unreliability of the solids pumps in both the long term and day bin areas. In the long-term bin area, the solids pump was able to supply only 11 tons/hr (10 tonnes/hr) of sorbent to the day bins ver- sus the design rate of 20 tons/hr (18.1 tonnes/hr). By removing the solids pump and discharging from the existing rotary feeder directly into a "pick-up tee," the required capacity was achieved and main- tained through the remainder of the test ------- program. The solids pumps in the day bin area also proved troublesome. While the pumps were able to achieve the required maximum capacity of 7.5 tons (6.8 tonnes)/ hr/pump, ft was necessary to operate the pumps at the unusually high screw speed of 1500 rpm to attain this feed rate. The pumps were not able to operate continu- ously at this speed. Since this was unac- ceptable for long-term continuous demonstration testing, the solids pumps were removed and replaced with rotary airlock feeders which, in turn, discharged into "pick-up tees." This arrangement op- erated well during both optimization and continuous demonstrating testing, although the rotary feeders repeatedly experienced an unanticipated problem: hard deposits on the feeder drum surfaces. This required occasional cleaning but did not interrupt the demonstration tests. At the discharge of the injectors, hard deposits formed inside the nozzle tips which restricted, but did not completely close, the nozzles. This necessitated peri- odic removal and cleaning of the injectors to permit design air/sorbent flow rates. The mechanism for formation of these de- posits is not yet understood. SO2 Removal Performance: Demonstration Testing A primary objective of the Tangentially Fired LIMB Demonstration Project was to evaluate the long-term effectiveness of the integrated LIMB system in achieving the SO2 and NOX emissions reduction objec- tives and establish the long-term effects on boiler, ESP, and ash handling system operation. Three long-term demonstration tests were conducted. Test duration and gaseous-emission data collection objec- tives for these tests were established in accordance with Performance Testing re- quirements contained in Vol. 44, No. 113 of the Federal Register. These require- ments may be satisfied in as few as 22 days (out of 30) if at least 18 hours of acceptable continuous emissions monitor- ing (GEM) data are produced each day. Because of the high quality of GEM data, H was possible to complete each of the demonstration tests after only 22 to 24 days, having satisfied test duration require- ments. During the demonstration tests, the boiler was operated in its normal duty cycle. Sootblowing and ash handling sys- tem operation were adjusted as required by LIMB operation. ESP operation and humidification of the gas and solids enter- ing the ESP were adjusted to conform to opacity requirements, except during ESP performance tests when additional require- ments were specified. The sorbent injection configurations and operating conditions were selected for the demonstration tests to maintain good boiler performance and operability as well as achieve good SO2 capture performance. Thus, when injection was through the middle elevation, the injectors were tilted downward to improve boiler temperature control. The first demonstration was con- ducted with lignosulfonate-treated hydrate as the sorbent. Untreated commercial hy- drate was used for the second and third demonstration tests. The SO2 removal ef- ficiencies at the Ca/S molar ratios of com- mercial interest (Ca/S = 2:1 and 2.5:1) were essentially the same for all three tests, averaging 44% at Ca/S = 2:1 and 50% at Ca/S = 2.5:1. These levels are lower than those measured during optimi- zation testing. Two factors that adversely impacted the SO2 removal performance were sootblowing requirements and data interval selection. During continuous in- jection of sorbent, the Unit No. 2 sootblowing system was operated almost continuously to maintain critical tempera- tures within limits. Continuous cleaning may reduce secondary SO2 capture by deposited sorbent material, thereby reduc- ing overall. SO2 capture. Sootblowers were not operated during individual optimiza- tion tests. The second factor-data interval selection-was also affected by sootblower operation. While it was possible to deter- mine maximum SO2 capture (minimum CEM SO2) for individual optimization test points without sootblower operation, it was not possible to obtain continuous demon- stration test periods of sufficient duration without including at least one sootblowing cycle. This resulted in the requirements to use average, rather than minimum, CEM SO2 levels to define SO2 capture. There- fore, the impact of the continuous sootblowing requirement tends to be con- siderable. Much of the first demonstration test was conducted at minimum sorbent feed in response to concerns over indications of deposit buildup on the floors and turning vanes of the ESP inlet ducts. The ducts were cleaned during a subsequent non- LIMB-related outage. The second and third demonstration tests were conducted at design sorbent feed rates with minimal deposit problems, reflecting the effective- ness of improved humidification lances that were installed for these tests. ESP and Humidifier Performance The Yorktown Unit No. 2 ESP has a specific collection area (SCA) of 720 ft2/1000 acfm (14 m2/1000 m3/sec) of treated gas. This exceptionally large ESP provided an opportunity to evaluate the impact of LIMB on ESP performance over a wide range of conditions. Prior to the start of optimization testing, a test was conducted with design sorbent feed rates but without humidification. The ESP per- formance deteriorated rapidly after only a few hours of operation. This was consis- tent with results obtained at Edgewater. With the humidification system in opera- tion, it was possible to maintain ESP per- formance at or near its pre-LIMB levels. Throughout the optimization and first dem- onstration test periods, water distribution was poor, resulting in repeated problems with deposits in the ESP ducts, on the ESP inlet turning vanes, and on the humidification lances themselves. Destruc- tive examination of two lances revealed weld cracks that allowed the air and water to mix within the lances, producing severe maldistributions of water. Lances fabricated with revised procedures significantly im- proved water distribution with a dramatic reduction in duct and turning vane depos- its. Opacity was always maintained within compliance limits throughout the three con- tinuous demonstration tests. ESP performance tests were conducted during the baseline test and the first two demonstration tests. Total particulates en- tering and leaving the ESP, particle size distributions, and particle resistivities were measured under various ESP operating conditions. Fields were taken out of ser- vice to simulate smaller ESPs, with the objective of identifying the smallest ESP that could operate with LIMB without modification. Performance test results showed that essentially no performance losses were seen during ESP operation With SCAs of 720 to 480 ft2/1000 acfm (14 to 9 mz/100 m3/sec) of treated gas, under the same LIMB and humidifier operating conditions. Further SCA reductions re- sulted in increases in opacity. Collection efficiencies were comparable during the three performance tests. The average col- lection efficiency with LIMB was 99.21%, versus 99.42% without LIMB. Flyash re- sistivity varied over a narrow range. Baseline resistivity without LIMB was 3.7 x 1010 ohm-cm. Resistivity during the first performance test with LIMB was 1.4 x 10" ohm-cm. During the second performance test with LIMB, resistivity was slightly lower at 1.4 x 1010 ohm-cm, suggesting improved humidification effectiveness with the modi- fied lances. An unexpected ESP performance effect was noted during LIMB testing with pul- verized limestone. The humidifier was turned off during the final 2 days of test- ing. Opacity did not increase above non-LIMB levels. No ESP performance ------- measurements, including flyash resistiv- ity, were made during limestone testing. Ash Handling Effects The Yorktown Ash Handling Facility fea- tures a single ash silo that receives flyash from all three units. When Units No. 1 and 2 were both in operation, LIMB ash from Unit No. 2 was mixed with, and diluted by, ash from Unit No. 1. Under these conditions, the mixed ash was easier to handle and produced less steaming than in previous LIMB field demonstrations. It was, nevertheless, more difficult to entirely remove the ash from ash truck beds than when no LIMB ash was present. When Unit No. 1 was not in operation, the LIMB ash was somewhat more difficult to process through the rotary conditioner, which received the ash frorri the silo, added water while mixing, and discharged the mixture into trucks. Steaming was greater for LIMB-only ash than for the mixed Unit No.1/Unit No. 2 ash. Long-term continuous testing of the LIMB system placed increased strain on the Yorktown ash handling system. The concentration of LIMB ash in the ash silo increased over that experienced during optimization testing. This resulted in a greater degree of steaming of the condi- tioned LIMB ash in the ash trucks and at the disposal site. The LIMB ash exhibited a much greater tendency to set up in the truck beds than did non-LIMB ash or a mixture of Unit No. 1 ash with no LIMB and Unit No. 2 ash with LIMB. Frequent problems of material setting up in the truck beds were experienced. Decreasing the water to the rotary conditioner (mixer) ap- peared to reduce problems of setting up and steaming. The quantity of material produced dur- ing continuous testing taxed the Yorktown ash handling personnel and equipment. A substantial increase in the amount of time Unit No. 2 was operated at full load, fol- lowing the substantial heat rate improve- ment as a result of the steam turbine replacement, contributed to this problem. All of the LIMB ash was placed in one area of a single ash cell at the Yorktown ash disposal site. No significant problems were experienced due to the cementitious properties of the LIMB ash. It was pos- sible to spread the LIMB ash by bulldozer with only occasional steaming problems. Boiler Performance and Operability During LIMB operation, lime, ash, and LIMB products accumulated on boiler heat transfer surfaces at a greater rate than during normal non-LIMB operation. This reduced the heat absorption effectiveness, shifted the gas temperature profile in the boiler downstream, and reduced overall boiler efficiency. Reheat outlet tempera- ture, for example, typically dropped about 30 F° (16.7 C°) during continuous full-load sorbent injection at Ca/S = 2:1. Frequent sootblowing recovered essentially all of the temperature loss, suggesting friable, easily removable deposits. The increase in the temperature of the gas entering the ESP inlet ducts (and the humidifier) as a result of the shift in heat absorption pat- tern during sorbent injection was typically 75 to 80°F (23.9 to 26.7°C). This shift in absorption and the concurrent increase in gas heat loss resulting from the increase in gas flow and deposits on heat transfer surfaces typically resulted in a reduction of 1.5 points in boiler efficiency during continuous sorbent injection relative to the efficiency level during continuous testing without sorbent injection. The net boiler efficiency reduction was about 1 point after adjusting for carbon-in-ash and cal- cination/sulfation effects. Optimized sootblower coverage and operation would likely reduce this penalty. During injection of finely pulverized lime- stone, boiler effects were significantly dif- ferent than those observed during injection of hydrated lime. Superheater and reheater outlet temperatures did not drop as much as during hydrate injection, suggesting a decreased tendency of deposits to build up on the heat transfer surface. As a consequence, sootblowing requirements were significantly reduced. No LIMB-related boiler outages were experienced during any part of the LIMB test program at Yorktown, including the three demonstration tests. Boiler operabil- ity was, however, adversely affected by the demonstration coal and operation of the LIMB system, in addition to the effects of the new Unit No. 2 steam turbine. In- creased slagging at the burner corners was noted throughout the LIMB test pro- gram. However, slag formation on the waterwalls was, generally, not severe and did not require operating the wall sootblowers. Ash/sorbent deposits built up around many of the sorbent injection ports. These deposits would break away and fall into the boiler ash hopper and were ulti- mately removed from the boiler via the wet bottom ash removal system. Occa- sional problems were experienced in the bottom ash removal system due to the high lime content of this material. Economics and Commercialization Capital and operating costs associated with a 180-MWe "base case" LIMB sys- tem were generated, based on actual Yorktown costs, and used as a basis for a sensitivity study on the effects of unit size and various process parameters on LIMB economics. The Yorktown system, plus a new dedicated ash silo, had a total capital requirement of $81/kW, with 2.5% S coal at a Ca/S of 2.5:1. Levelized cost for the base case was $781/ton ($861/tonne) SO2 removed. These costs are lower than those reported for previous LIMB demonstrations, indicating a maturing of this SO2 control technology. Capital investment increased 46%, to $118/kW, for a 100-MWe unit but de- creased 23%, to $62/kW, for a 300-MWe unit, clearly showing the economy of scale for a retrofit LIMB system. LIMB has been demonstrated as a vi- able low-cost option for achieving moder- ate levels of SO2 reduction with capital and operating costs that are substantially below those of conventional flue gas desulfurization systems. The 1990 Clean Air Act Amendments (CAAAs) focus on high SO2 removal efficiency technologies. They also make SO2 allowances (credits) available at a fraction of the cost of FGD systems. Consequently, the domestic mar- ket for LIMB, with its moderate SO2 re- moval, is currently best suited to older, small to intermediate units, which might otherwise be retired, and also to combina- tions of LIMB with back-end SO2 removal processes. An example would be LIMB combined with the ADVACATE process to achieve high overall -SO2 removals. Thus, in the contemporary domestic utility mar- ket, LIMB alone is postured as a "niche" technology for units requiring moderate levels of SO2 control. However, if com- bined with a complementary back-end sys- tem, LIMB can offer the potential for competitive (i.e., 90 +%) SO2 removals at favorable capital and operating costs. Summary and Conclusions The viability of LIMB as a low-cost op- tion for achieving moderate levels of SO2 reduction on tangentially coal-fired utility boilers was established under the EPA-sponsored LIMB Demonstration Pro- gram at Virginia Power's 180-MWe Yorktown Unit No. 2. Extensive paramet- ric testing to evaluate various sorbent in- jection configurations and process variables was conducted over a range of boiler loads. Full-load SO2 removals of up to 56 and 63% at Ca/S molar ratios of 2:1 and 2.5:1, respectively, were achieved, substantially above the project objective of 50% SO2 removal at a Ca/S molar ratio of 2.5:1. Higher SO2 removals were achieved at intermediate boiler load. Test- ing was conducted on calcitic hydrated lime, with and without calcium lignosul- ------- fonata treatment, each from two suppli- ers. SO2 removal did not increase signifi- cantly during testing with the treated hydrates. Three continuous long-term tests of the LIMB system, each of from 22 to 24 days in duration, were conducted over the normal boiler operating range. Lower SO2 removal levels were seen during this con- tinuous testing, due, largely, to the need to continuously operate the sootblowers to remove accumulated LIMB solids from boiler heat transfer surfaces. Commercial LIMB installations would require increased sootblower coverage to maintain boiler surface cleanliness. No boiler outages at- tributable to LIMB were experienced dur- ing the entire LIMB test program. ESP performance was maintained dur- ing LIMB operation by humidification of the gas stream at the inlet to the ESP. No deep humidification for enhanced SO2 re- moval was attempted. Early problems with deposition of LIMB solids on duct sur- faces were resolved by improvements in humidifier lance fabrication procedures. Opacity was maintained within compliance requirements throughout the test program. LIMB ash was collected in, and pro- cessed from, a common ash silo that received material from both coal-burning units. Problems were experienced with material setting up in ash truck beds. Steaming of material in the ash trucks varied with the concentration of LIMB ash, decreasing as dilution from non-LIMB Unit No. 1 ash increased. A dedicated ash silo would be a necessary component of a commercial LIMB installation. The LNCFS Level II firing system achieved a 42% reduction in NOX at full boiler load and 33% reduction in NOX at intermediate boiler load, relative to baseline levels with the original tangential firing sys- tem, under comparable boiler operating conditions. These levels were below the program NOX objective of 0.4 lb/106 Btu (172 mg/J). Capital and levelized costs associated with the 180 MWe Yorktown LIMB system were determined to be $81/kW and $7817 ton ($859/tonne) SO2 removed, respec- tively, based on actual equipment and op- erating costs for the Yorktown system, plus the cost of a new ash silo. Sensitivity studies showed the cost effectiveness of LIMB on tangentially fired units from 100 to 300 MWe operating on coals with 2 to 3% sulfur. The commercial applicability of a stand- alone LIMB system is currently consid- ered to be that of a "niche" technology for certain older units as a result of the 1990 CAAAs. In combination with a comple- mentary "back-end" SO2 removal process, however, LIMB offers the potential of achieving compliance levels of SO2 re- moval at costs that are significantly below those of conventional FGD systems. ------- |