"GER 4192 - Combustion Modification An Economic Alternative for"
g GER-4192 GE Power Systems Combustion Modification – An Economic Alternative for Boiler NOx Control Blair A. Folsom Thomas J. Tyson GE Power Systems Schenectady, NY Combustion Modification – An Economic Alternative for Boiler NOx Control Contents Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Regulatory Drivers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Reburn and Advanced Reburn. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Comparative Economics of SIP Call Compliance with Combustion Modification and SCR . 8 No NOx Trading Scenario – Control to 0.15 lb/10 6 Btu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 NOx Trading Scenario. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Dense Pack Steam Turbine Uprate. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Integrated System (AGR-DP) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Conclusion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 List of Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 List of Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 GE Power Systems GER-4192 (04/01) s s i Combustion Modification – An Economic Alternative for Boiler NOx Control GE Power Systems GER-4192 (04/01) s s ii Combustion Modification – An Economic Alternative for Boiler NOx Control Abstract Introduction Several provisions of the Clean Air Act This paper presents an overview of compliance Amendments of 1990 will require “deep” NOx alternatives for U.S. coal-fired utility boilers fac- control on a large number of large utility and ing requirements for deep NOx control under industrial boilers in the eastern United States. Title I (Attainment of National Ambient Air EPA’s final ruling on Section 126 petitions filed Quality Standards for ozone) of the Clean Air by several northeastern states (December 1999) Act Amendments of 1990. The focus is on the and the more recent revival of the “NOx SIP performance and economic tradeoffs between Call” both include provisions for trading of Combustion Modification, using Reburn and NOx credits and state-wide NOx budgets that Advanced Reburn, and Selective Catalytic are based on emissions of 0.15 lb/106 Btu of Reduction (SCR). The regulations and implica- heat input. tions for NOx reduction requirements are dis- Selective Catalytic Reduction (SCR) and cussed first. Then, the Reburn and Advanced Combustion Modification using Reburn or Reburn technologies are presented including Advanced Reburn are the only commercially design factors and performance experience on viable alternatives capable of reducing NOx to coal-fired utility applications. The economic this level. Although the optimum cost effective tradeoffs between Combustion Modification approach for any given unit will depend on site and SCR alternatives are then addressed for specific factors, the general trend is expected to both emissions trading and non-trading scenar- be towards SCR as the technology of choice for ios. Finally, the integration of Advanced Gas the larger, higher baseline NOx units and for Reburn with GE’s Dense Pack steam turbine Combustion Modification (with Reburn or technology is discussed including an overview Advanced Reburn) for smaller units or units of the technology and the economic benefits with lower baseline NOx emissions. for deep NOx control applications. Reburn is a commercially proven control tech- nology that can reduce NOx by as much as 60% Regulatory Drivers by the staging of fuel and air within the furnace. The NOx emissions from many U.S. coal-fired The level of NOx reduction can be increased to utility boilers must be reduced due to several over 70% by integrating a “trim” Selective Non- recent and ongoing regulatory actions under Catalytic Reduction system with the basic the Clean Air Act of 1990 designed to achieve Reburn system (the integrated system is attainment of the ambient air quality standards referred to as Advanced Reburn). Although for ozone. In September 1998, the EPA issued both Reburn and Advanced Reburn systems can a ruling regarding NOx emissions from a 22 utilize a wide range of fuels, natural gas gener- State region in the eastern U.S. that were con- ally produces the deepest NOx control. tributing to ozone levels exceeding the national By integrating Advanced Reburn using natural ambient air quality during a five month summer gas as the reburn fuel (Advanced Gas Reburn) period (the ozone season). The EPA established with Dense Pack steam turbine technology, reduced NOx budgets for each state in the deep NOx control can be achieved along with region and required them to submit state additional power generating capacity and heat Implementation Plans (the “NOx SIP Call”) rate improvement. The economics of this inte- wherein NOx emissions would be reduced to grated approach are particularly attractive. meet those NOx budgets. The NOx budgets GE Power Systems GER-4192 (04/01) s s 1 Combustion Modification – An Economic Alternative for Boiler NOx Control were prepared assuming that NOx emissions acid rain mitigation. The Title IV NOx reduc- from utility power plants as a group would aver- tion requirements were established by EPA age 0.15 lb/106 Btu (SIP Call NOx Level) in based on the capabilities of “Low NOx Burner 2007. Technology” and are not as stringent as Title I. In May 1999, the U.S. Court of Appeals Table 1 lists the Title IV target NOx levels for reviewed the SIP Call and indefinitely suspend- boilers by firing configuration. ed EPA’s implementation schedule. More recently (March 2000), the court removed this Firing suspension of the NOx SIP Call and confirmed Configuration Title IV NOx (lb/106 Btu) its provisions but reduced the 22-state region to 19 states. Tangential 0.40 In the midst of this NOx SIP Call activity, EPA Wall 0.46 also implemented other provisions (Section Cell 0.68 126) of the Clean Air Act that require compara- Cyclone 0.86 ble ozone season emission reductions from about 400 industrial and utility plants within the Table 1. Title IV target NOx levels same region. There are also several other areas in the U.S. with local ambient ozone problems, Title IV allows intra-utility trading and requires such as Atlanta and Texas, that are implement- compliance in 2000 on an annual average basis. ing additional NOx control regulations. Since the compliance dates for the Title I NOx These ozone season regulations typically regulations discussed above are in the 2003- include the potential for emissions trading 2005 time frame, plant owners must provide among affected units. With emission trading, it additional control beyond the Title IV target is not necessary to control each unit to meet the levels over a 3-5 year period to meet the ozone specific NOx emission limit. Plant owners have season NOx regulations. the flexibility to over-control some units where Figure 1 shows the NOx reduction required to site specific factors reduce the NOx control cost achieve 0.15 and 0.20 lb/106 Btu as a function and to use the extra NOx reduction (below the of the initial NOx level, presumably the level NOx emission limit) to offset higher NOx on required for compliance with Title IV. The other units where deep NOx control may be nominal maximum NOx reduction capabilities particularly expensive. of Reburn, Advanced Reburn and Selective While the final requirements and implementa- Catalytic Reduction (SCR) are overlaid. tion schedules may well be resolved in the The NOx control capability of SCR can be courts, it is clear that a large number of coal- adjusted by varying the volume of the catalyst fired utility boilers will need deep NOx emis- and/or rate of ammonia injection. NOx reduc- sion control to near the SIP Call NOx level in tions as high as 90% are achievable. This is suf- the next few years to meet these ozone season ficient to reduce baseline NOx from as high as NOx regulations. 1.50 lb/106 Btu to the SIP Call NOx Level and Annual NOx emission control is required thus covers the full range of Title IV baseline under Title IV of the Clean Air Act of 1990 for levels. GE Power Systems GER-4192 (04/01) s s 2 Combustion Modification – An Economic Alternative for Boiler NOx Control Also, cell burner units, where site specific fac- tors allow low NOx burners to control NOx x below the Title IV target level to 0.55, may also use Combustion Modification. Reburn and Advanced Reburn Reburn and Advanced Reburn are combustion modification NOx control technologies. Reburn integrates fuel and air staging tech- niques and has been applied commercially to a broad range of coal-fired utility boilers. Table 2 shows GE EER’s experience to date. Any hydrocarbon fuel can be used to provide NOx at Title 4 Compliance (lb/106 Btu) the staged fuel for Reburn. Most Reburn instal- Figure 1. NOx reduction required to achieve SIP call lations to date have utilized natural gas as the NOx limit from Title IV target NOx levels Reburn fuel (Gas Reburn) since it provides the As will be discussed in Figure 1, Combustion greatest NOx reduction and lowest retrofit cost. Modification via Reburn and Advanced Reburn With Gas Reburn, NOx emissions are typically can typically achieve NOx reductions of 60% reduced by about 60% [References 1-3]. and greater than 70%, respectively. This is suf- Advanced Gas Reburn (AGR) is the integration ficient to meet the SIP Call NOx Level from of Gas Reburn with injection of a nitrogen con- baselines as high as 0.55 lb/106 Btu. Thus, tan- taining NOx reduction agent (N-Agent) such as gential and wall-fired units operating at the urea or ammonia. This can be accomplished in Title IV target levels of 0.40 and 0.46 lb/106 a number of configurations which may be Btu, respectively, can use Combustion selected based on site specific conditions Modification to meet the SIP Call NOx limit. [References 4-7]. Kodak Park 15 Table 2. GE EER reburn experience on utility boiler GE Power Systems GER-4192 (04/01) s s 3 Combustion Modification – An Economic Alternative for Boiler NOx Control Figure 2. Schematic diagram of reburn and advanced reburn Figure 2 is a schematic representation of Gas injected to complete the combustion of fuel Reburn and AGR. The combustion process is fragments exiting the reburn zone. The overfire divided into three zones. In the Burner Zone air injection system is designed for variable the main fuel is burned with combustion air. injection to optimize mixing of the overfire air Although no changes to the main burners are with the furnace gases as the reburn fuel injec- required, it is generally cost-effective to replace tion rate is varied. the existing burners with low NOx burners or Advanced Gas Reburn adds a trim NOx reduc- modify them to achieve comparable low NOx tion via injection of a N-Agent. The N-Agent can performance for additional NOx reduction. be injected in a number of configurations The main burners are turned down to accom- including: downstream of the overfire air, with modate the subsequent injection of the Reburn the overfire air, and into the reburn zone. Site fuel (natural gas for Gas Reburn) and are oper- specific factors determine the optimum injec- ated at the lowest excess air commensurate with tion configuration. Injection downstream of the satisfactory lower furnace performance consid- overfire is equivalent to the Selective Non- ering flame stability, flame shape, combustion Catalytic Reduction (SNCR) process. This is a efficiency and ash deposition. The reburn fuel commercial process offered by several vendors is injected downstream of the flames. The using ammonia and urea as the N-Agents. reburn fuel injection system is designed to pro- duce locally fuel rich zones operating at approx- Reburn and Advanced Reburn can be applied imately 90% theoretical air (TA) which is opti- to boilers with all firing configurations. As an mum for NOx reduction. The NOx reduction example, Figure 3 shows the application increases with the reburn fuel injection rate. Advanced Gas Reburn to a front wall fired utili- For low injection rates, the reburn fuel is strati- ty boiler. The main burners can be convention- fied to produce locally fuel rich zones. As the al or low NOx burners and the flames from reburn fuel injection rate is increased, these these burners are in the Burner Zone. The locally fuel rich zones eventually merge to cover reburn fuel injectors are positioned on the fur- the entire furnace cross-section. Overfire air is nace walls above the top row of main burners. GE Power Systems GER-4192 (04/01) s s 4 Combustion Modification – An Economic Alternative for Boiler NOx Control flow rate so that optimum mixing can be main- tained as the reburn gas injection rate (and hence overfire air injection rate) and load vary. Nitrogen Agent The burnout zone is the region between the overfire air ports and the convective pass. Overfire Air Figure 3 shows N-Agent injectors above the over- fire air ports to complete the Advanced Gas Reburn Fuel Reburn process. GE EER has developed a design methodology for applying Reburn and Advanced Reburn. It Main Fuel uses physical flow and Computational Fluid Dynamic (CFD) modeling along with heat Combustion transfer and chemical kinetic codes in the con- Air text of GE EER’s extensive database on pilot and full-scale Reburn applications to optimize Figure 3. Advanced reburn on a wall-fired boiler the design for site specific factors. The specific reburn fuel injection elevation is Figure 4 shows the NOx reduction achieved with selected to be close to the burners where tem- several commercial Reburn systems on coal perature is high, but displaced enough so that fired utility boilers. These applications repre- the combustion in the flames is essentially com- sent a broad range of unit and fuel characteris- plete. GE EER utilizes second generation gas tics: wall, tangential and cyclone firing; coal injectors for Gas Reburn systems to convert the and gas as the main and Reburn fuels; baseline pressure in the natural gas supply line to high NOx ranging from 0.13 to 2.0 lb/106 Btu; and injection velocity. The injector arrangement is unit capacities from 40 to 330 MW. (A 600 MW optimized based on site specific factors to pro- Gas Reburn system is being installed in Spring duce optimum mixing over the full operating 2000.) The NOx reductions for all units in the range of the boiler and with variable natural gas figure exceed 60% with some substantially high- injection rates. This generally involves multiple er. injectors grouped in several tubewall penetra- For maximum NOx reduction and minimum tions. The Reburn Zone extends from the gas NH3 slip from the SNCR component, the N- injectors to the overfire air ports which are Agent must be injected so that it is available for higher in the furnace. reaction with the furnace gases within a tem- The elevation of the overfire air ports is select- perature window close to 1800°F. This typically ed by balancing the need for residence time in requires multiple N-Agent injection elevations the Reburn Zone with completion of combus- in the upper furnace and/or convective pass to tion prior to the convective pass. This generally accommodate varying load and ash deposition results in positioning the overfire air ports near patterns over the sootblowing cycle. However, if the nose of the furnace. GE EER uses a dual the NOx reduction requirement is reduced, a concentric overfire air port design with variable much simpler SNCR system can be employed. swirl. This allows the overfire air injection veloc- In conjunction with Elkraft Power Company of ity to be varied independent of the injection Denmark, GE EER has applied this simplified GE Power Systems GER-4192 (04/01) s s 5 Combustion Modification – An Economic Alternative for Boiler NOx Control Figure 4. NOx control results from GE EER reburn applications on utility boilers SNCR concept to a 285 MW utility boiler NOx reduction level corresponds to nitrogen [Reference 8]. Figure 5 shows the NOx reduc- stoichiometric ratio (NSR) of 0.5 to 0.7 and tion and ammonia (NH3) slip for injection of results in NH3 slip well under 2 ppm. NH3 slip urea through a single elevation for two loads. of 2 ppm or less avoids air heater plugging with At 46% load, the urea is injected at near opti- high sulfur coals. mum temperature so that NOx reduction is With AGR, the NOx reduction is produced by maximized with low NH3 slip. At full load, the two components: Gas Reburn and SNCR. This same injection location achieves less NOx provides the opportunity to adjust the relative reduction and NH3 slip is higher. The 30% contribution of the two components to opti- mize performance. Figure 6 illustrates these tradeoffs for NOx reduction to the SIP Call NOx level for wall and tangentially fired units operating with low NOx burners at the Title IV target levels of 0.46 and 0.40 lb/106 Btu, respec- tively. For example, for the wall fired unit NOx must be reduced by 67% reduction to meet 0.15 lb/106 Btu. This can be achieved with the Gas Reburn component at 53% reduction and the SNCR component at 30% reduction, respec- tively, both conservative levels for the respective technologies. The modest NOx reduction from the Gas Reburn component allows the reburn fuel injection rate to be lowered which reduces Figure 5. NOx reduction and NH3 slip for SNCR on 285 operating cost. The modest level of NOx reduc- MW utility boiler tion from SNCR can be achieved with a much GE Power Systems GER-4192 (04/01) s s 6 Combustion Modification – An Economic Alternative for Boiler NOx Control Figure 6. Advanced Reburn tradeoffs for SIP Call compliance: Reburn and SNCR components simpler system than the conventional highly zone and multiple stages of N-Agent injection tuned SNCR system and with reduced risk of [References 6-7]. These alternate configurations NH3 slip (and air heater plugging). provide retrofit flexibility and by optimizing the Figure 7 shows the cumulative NOx reduction coupling the N-Agent injection with the Reburn achievable by layering combustion modification system, NOx reduction is synergistically NOx control technologies on a typical wall-fired enhanced. boiler. Low NOx burners provide the initial 50% reduction from 0.92 lb/106 Btu down to the Title IV target level of 0.46 lb/106 Btu. Gas Reburn reduces NOx by an additional 53 to 60% depending on the reburn fuel flow of 13 to 16%, respectively. Adding SNCR (AGR) reduces NOx further to less than 0.15 lb/106 Btu. The 0.12 lb/106 Btu point corresponds to 16% reburn fuel and 33% NOx reduction from SNCR. The 0.15 lb/106 Btu point corresponds to 13% reburn fuel with 30% NOx reduction from SNCR. Figure 8 shows these same points as circles on a plot of NOx vs. gas injection rate to better illustrate the tradeoffs. The preceding discussion focused on AGR with the N-Agent injection downstream of the reburn overfire air. A number of other config- urations are under development including Figure 7. Cumulative NOx for layered combustion injection with the overfire air, into the reburn modification technologies GE Power Systems GER-4192 (04/01) s s 7 Combustion Modification – An Economic Alternative for Boiler NOx Control by reducing catalyst volume. Table 3 lists the parameters for each NOx control technology; Title IV Wall-Fired the key parameters are highlighted below. The Low NOx Burner Baseline ratio of reburn NOx reduction to reburn fuel flow is the Reburn Efficiency Factor (REF). Based on EER's full scale experience, the REF was approximated as 5.0 and 3.0 for less than and greater than 30% NOx reduction, respec- tively. Maximum Reburn and Advanced Reburn NOx reductions were capped at 60 and 73% respectively corresponding to a maximum of 33% NOx reduction from the SNCR compo- nent. For SCR, the catalyst cost and life was based on the work of Cichanowicz [Refer- Figure 8. Effect of gas firing rate on reburn and ence 9]. advanced reburn NOx The analysis utilized a modified Electric Power Comparative Economics of SIP Call Research Institute (EPRI) Technology Assessment Guide methodology which has been Compliance with Combustion widely used to compare the economics of emis- Modification and SCR sion control alternatives. This involves deter- A comparative economic analysis of Reburn mining the total annual cost of NOx control in and Advanced Reburn (using coal, oil and nat- $/ton. The retrofit capital cost is estimated and ural gas as Reburn fuels) and overfire air (OFA) then distributed over the life of the equipment with SCR has been conducted. OFA was includ- as a series of constant annual costs. The first ed with SCR since it results in a slightly lower year operating cost is also estimated and con- net NOx control cost compared to SCR alone verted to a series of annual costs accounting for Table 3. NOx control technologies in economic analysis GE Power Systems GER-4192 (04/01) s s 8 Combustion Modification – An Economic Alternative for Boiler NOx Control inflation, etc. These two annual cost compo- level to 0.15 lb/106 Btu. Figure 9 shows Reburn nents are then added and divided by the annu- and Advanced Reburn using coal, oil and gas as al NOx reduction to calculate the total cost of the reburn fuels with variable reburn fuel to NOx control in $/ton. Table 4 shows the eco- coal cost differential. Figure 10 shows the Figure nomic factors and other parameters used in the 9 Reburn and Advanced results as an outline analysis. and adds OFA-SCR with variable SCR cost. Two scenarios were evaluated: No trading and In Figure 9, the maximum NOx reduction for full inter-utility trading. Reburn has been set at 60%, a conservative level Table 4. Economic analysis parameters Figure 9. NOx control cost for Reburn and Advanced Reburn to 0.15 lb/106 Btu – No NOx Trading Scenario – effect of initial NOx Control to 0.15 Lb/106 Btu based on full-scale utility boiler experience. For This “no trading” scenario involves comparison Advanced Reburn, the maximum NOx reduc- of the NOx control costs to meet 0.15 lb/106 tion has been set at 73% which corresponds to Btu for each technology. The following vari- 33% reduction from the Reburn level. Based on ables were evaluated. (See Table 5.) these reductions, to achieve 0.15 lb/106 Btu, the maximum initial NOx is 0.38 and 0.55 Parameter Range Units lb/106 Btu, respectively. For all Reburn and Baseline NOx 0.25 – 1.6 Lb/106 Btu Advanced Reburn configurations, the cost of NOx control decreases as the initial NOx Boiler Capacity 50 - 1,300 MW increases. Reburn Fuel Cost 0.00 - 1.50 $/106 Btu over coal The reburn fuels include coal and oil with dif- SCR Installed Cost 40 - 80 $/kw for 300 MW ferential costs over coal of $0.00 and $0.50/106 Btu, respectively, and natural gas with differen- Table 5. NOx control costs per variable tial costs over coal of $1.00 and $1.50/106 Btu. For both Reburn and Advanced Reburn, the Figures 9 and 10 show the results for a 300 MW differential cost of the reburn fuel over the unit with NOx reduced from a variable initial main coal fuel is the key variable influencing GE Power Systems GER-4192 (04/01) s s 9 Combustion Modification – An Economic Alternative for Boiler NOx Control the total cost of NOx reduction. For the initial stantial. For example at an initial NOx of 0.40 NOx range where Reburn can be applied, lb/106 Btu, the highest cost for Advanced Reburn is lower in cost than Advanced Reburn Reburn is 68% of the cost for the Nominal SCR except at the highest reburn fuel cost differen- case. tial (natural gas at $1.50 /106 Btu). For higher As with Reburn and Advanced Reburn, the initial NOx, the NOx control cost of Advanced NOx control cost for SCR decreases as the ini- Reburn continues to decrease down into the tial NOx increases. Thus, for high initial NOx, same $/ton range as Reburn. such as from a cell or cyclone unit, the NOx In Figure 10, the full range of the Reburn and control cost for SCR drops into the $/ton range Advanced Reburn results from Figure 9 are for Reburn and Advanced Reburn at lower ini- shown as an enclosed region. It should be noted tial NOx. that this includes all reburn fuels with reburn All of the preceding results were for a 300 MW fuel to coal cost differentials ranging from 0.00 unit. Similar analyses were conducted for a to $1.50/106 Btu. OFA-SCR results are shown range of unit capacities from 50 to 1300 MW. for SCR capital costs ranging from $40 to Since the capital cost of the OFA-SCR systems is $80/KW. The center of the range ($60/KW) substantially greater than the Reburn and corresponds to a straightforward application Advanced Reburn systems, the capacity effect is (Nominal). The low end of the range greater for OFA-SCR. At high capacity, the costs ($40/KW) corresponds to an advanced low cost for OFA-SCR approach those for Reburn and future SCR application. The high end of the Advanced Reburn. range ($80/KW) represents an increase from In summary, for control to 0.15 lb/106 Btu, the Nominal but is by no means the maximum. selection of the lowest cost technology depends Several utilities have recently been quoted SCR on the initial NOx. For initial NOx less than systems at well over $100/KW. The NOx control about 0.55 lb/106 Btu, Reburn and Advanced costs for all of the SCR cases are higher than the Reburn have lower cost than OFA-SCR. For ini- highest Reburn and Advanced Reburn results at tial NOx greater than 0.55 lb/106 Btu, Reburn the same initial NOx. The differences are sub- and Advanced Reburn cannot meet the require- ment and OFA-SCR must be used with $/ton cost approaching or lower than those of Reburn and Advanced Reburn, especially for the large high baseline NOx units. NOx Trading Scenario The preceding analysis showed that two key boiler variables, initial NOx and boiler capacity have significant effects on the NOx control cost with the cost decreasing as both initial NOx and boiler capacity increase. This suggests the potential for reducing total NOx control cost by over-controlling on the large, high initial Figure 10. NOx control cost for all technologies to NOxunits (where $/ton costs are low) and 0.15 lb/106 Btu – effect of initial NOx under controlling on the other units. It is GE Power Systems GER-4192 (04/01) s s 10 Combustion Modification – An Economic Alternative for Boiler NOx Control expected that the final ozone related NOx reg- Unit Capacity (MW) 300 ulations will allow emission trading similar to Firing Configuration Tang. the Title IV SO2 allowance trading system where Title 4 NOx lb/106 Btu 0.40 SO2 prices are established by market forces on a Ozone Season Cap. Fac. (%) 65 $/ton basis. Of course, there is potential for SO2 Allow. Price (%/ton) 200 more complex trading structures which may Life (Years) 15 Interest Rate (%) 8 limit trading to specific geographical areas or Dollars Con. make a ton of NOx in one region equivalent to Adv. a different amount in another region. Technology Reburn Reburn SCR The cost of NOx allowances available on the Capital Cost ($/kW) 10 22 50 open market has a significant impact on the NOx Reduction (%) 50 72 80 selection of the lowest cost NOx control Reburn Fuel - Coal ($/106 Btu) 1.00 1.00 approach. An analysis has been conducted to Catalyst Life (Years) 4 evaluate the economic tradeoffs of such trad- ing. Table 6 lists the parameters used in the Table 6. Trading analysis parameters analysis. The objective is to determine the low- level. The excess NOx reduction is est cost NOx control strategy for a 300 MW tan- sold as NOx allowances on the open gentially fired boiler operating at the Title IV market. NOx limit of 0.40 lb/106 Btu to reach 0.15 lb/106 Btu via emission control and/or pur- The results are shown in Figure 11 where the chased allowances. Four alternatives are consid- total annual cost of NOx control is plotted as a ered: function of the NOx allowance trading price for each control approach. Lines which slope s Do Nothing. In this case the required upward as NOx emission allowance trading NOx allowances are purchased on the price increases correspond to under-control open market. and vice versa. s Gas Reburn. Gas Reburn can be applied to reduce NOx by 60% to 0.16 lb/106 Btu, just slightly above the 0.15 lb/106 Btu level. This requires Annual NOx Control Cost ($10 6/Year) purchasing a small amount of NOx emission allowances on the open market. s Advanced Reburn. Advanced Reburn can be applied to reduce NOx by 73% to 0.11 lb/106 Btu, which is below the 0.15 lb/106 Btu level. The excess NOx reduction is sold as NOx allowances on the open market. s SCR. An SCR system is installed to reduce NOx by 80% to 0.08 lb/106 Figure 11. NOx control cost for trading, 300 MW Btu, well below the 0.15 lb/106 Btu wall-fired boiler, initial NOx 0.40 lb/106 Btu GE Power Systems GER-4192 (04/01) s s 11 Combustion Modification – An Economic Alternative for Boiler NOx Control For low NOx allowance trading price (less than parameters, the NOx allowances should trade about $1,900/ton), the lowest cost approach is in the range of $2,000 to $3,000/ton. Thus, in to Do Nothing and simply purchase all required the case presented above (300 MW tangentially NOx allowances. At high NOx emission fired unit), Reburn and Advanced Reburn will allowance trading price (greater than about be the technology of choice. The results also 4,000 $/ton), the lowest cost approach is to showed that the NOx control market will be massively over-control with SCR and sell the shared between Reburn, Advanced Reburn and extra NOx allowances at the high price. For SCR with the distribution depending on site intermediate NOx emission allowance trading specific factors. Generally, SCR is favored for prices ($1,900 to $4,000/ton) Reburn and large high baseline NOx units and Reburn and Advanced Reburn are the lowest cost approach- Advanced Reburn are favored for units with ini- es. Thus the market price for NOx allowances is tial NOx typical of the dry bottom wall and tan- a key factor affecting both the selection of the gentially fired units with penetration increasing lowest cost approach and the total cost of NOx as unit capacity decreases. control. An analysis has been conducted to estimate the Dense Pack Steam Turbine Uprate NOx allowance market price in a free trade sce- Dense Pack is a retrofit steam turbine modifica- nario. In such a scenario, each utility will con- tion technology developed by GE Power duct its own analysis of applicable NOx control Systems to increase the efficiency and power technologies, estimate risks and project a NOx generating capacity of utility steam turbines. allowance price. To simulate this, GE EER has Dense Pack is custom designed for each turbine conducted a systematic analysis of all coal fired to achieve the most efficient steam path in the utility boilers in the SIP Call region. These units existing turbine section outer shell. This high were grouped into categories based on their ini- efficiency steam path produces a lower heat rate tial NOx and capacity and an analysis similar to and increased output for the same steam flow. that outlined above was conducted for each The maintenance requirements of the steam combination of initial NOx and capacity. The turbine are also reduced due to decreased lowest cost NOx control approach was identi- bucket and nozzle solidity and reduced rotor fied as a function of the NOx allowance trading diameters which reduce solid particle erosion price. Then, the NOx credit allowance price was with internal repair/inspection intervals iterated while monitoring the total NOx extended to ten or more years. allowances bought and sold. At low NOx Dense Pack is the latest evolution of GE steam allowance trading price, the purchases exceed- turbine designs that began in 1903. Figure 12 ed the sales and the NOx allowance trading shows the improvement in high pressure steam price was iterated upwards. This process was path efficiency achieved over the last 40 years. continued until the amount of purchases and High pressure section efficiency is now in the sales balanced. This analysis was then repeated 94–95% range. This improvement was the result for a range of parameters such as cost of reburn of a systematic analysis of steam turbine per- fuel, future cost reductions in SCR, etc. formance to identify the sources of inefficiency The results showed that for a broad range of followed by development of improvement for the critical components. GE Power Systems GER-4192 (04/01) s s 12 Combustion Modification – An Economic Alternative for Boiler NOx Control Shaft Packing Figure 12. GE high pressure steam turbine Figure 14. Distribution of high pressure section efficiency improvement history steam turbine losses components to provide the most efficient steam path that will fit within an existing outer turbine shell. In short, the Dense Pack replaces the existing turbine stages with a larger number of stages in the same space. A Dense Pack section replacement includes the following eight basic components and features: 1. New, high efficiency, high pressure or high pressure / intermediate pressure turbine rotor with increased number of stages Figure 13. Irreversibilities in typical 700 MW 2. Optimized steam path diameter steam turbine 3. New, high efficiency diaphragms Figure 13 shows the loss (irreversibility) compo- 4. New high efficiency first stage nozzle nents for a typical steam turbine (GE G3 box plate or nozzle diaphragm Turbine with 700 MW capacity). Except for the loss due to the condenser, the high pressure tur- 5. Lower bucket and nozzle solidity bine section contributes the greatest irre- (decreased number of buckets and versibility and was the focus of the improve- nozzles per stage) ments. Figure 14 shows the efficiency losses with- 6. New inner shell(s) in the high pressure section. Nozzle and bucket 7. New shaft packing, packing heads and aerodynamic profile losses, secondary flow loss- steam inlet ring assemblies es, and leakage losses account for roughly 80% 8. Improved shaft and bucket sealing to 90% of the total stage losses. Hence, to capability ensure high-efficiency turbine designs, it is nec- essary to use highly efficient nozzle and bucket The basis of Dense Pack design is the funda- profiles and to minimize leakage flows without mental thermodynamic principal that more tur- sacrificing turbine reliability. bine stages at smaller wheel diameters creates a more efficient steam path. Recent steam tur- Dense Pack replaces steam turbine internal bine technology advances now allow an GE Power Systems GER-4192 (04/01) s s 13 Combustion Modification – An Economic Alternative for Boiler NOx Control sure for increased power generating capacity. Depending on the capabilities of the boiler, generator and other components, it may be pos- sible to boost heat input by as much as 17%. Table 7 summarizes the baseline and Dense Pack performance where the Dense Pack is designed for a more modest 12% flow increase. When the turbine is operated at the normal MCR steam flow, turbine efficiency is increased by 1.4% resulting in a commensurate 1.4% increase in power generating capacity. When steam flow is increased to 12% above MCR, steam turbine efficiency decreases slightly to a 1.2% improvement over baseline resulting in a 13.3% power generation increase. To avoid throttling losses, in this example the boiler is Figure 15. Comparison of high pressure steam tur- operated in sliding pressure service. bines: baseline and Dense Pack GE introduced Dense Pack in 1998. To date 13 increased number of stages in the same span. units have been sold totaling over 6,000 MW. Figure 15 compares a conventional turbine with The first units will enter commercial service in a Dense Pack. 2000. Each Dense Pack is custom designed for the specific turbine and steam flow conditions. In Integrated System (AGR-DP) general it is possible to recover all efficiency loss By integrating AGR with Dense Pack (AGR-DP) due to aging and to increase the efficiency designed for flow increase, NOx can be reduced above the original as new steam turbine condi- to SIP Call levels, power generating capacity can tion. Since the high pressure section(s) is/are be increased, and heat rate can be decreased. replaced, there is potential to design Dense This section discusses the performance of this Pack to match the normal MCR steam condi- integrated technology focusing on application tions or alternate conditions. This includes the to a 300 MW wall-fired boiler operating with case of interest here for integration with AGR NOx at the Title IV level of 0.46 lb/106 Btu where the Dense Pack is configured for where the Dense Pack is designed for a steam increased flow at the design point steam pres- flow increase of 12%. Steam Flow Steam Turbine Power Steam Turbine Enthalpy Efficiency Generation Configuration (% of MCR) (% of Baseline) (% of Baseline) Baseline (as new) 100.0 100.0 100.0 Dense Pack 100.0 101.4 101.4 Dense Pack 112.0 101.2 113.3 Table 7. Baseline and Dense Pack performance summary GE Power Systems GER-4192 (04/01) s s 14 Combustion Modification – An Economic Alternative for Boiler NOx Control The four equipment and operating scenarios One possible strategy for optimum use of AGR- (Cases) listed in Table 8 will be discussed: DP is as follows. During the summer ozone sea- Figure 16 shows the fuel flows and power gener- son when deep NOx control is required and ation and Figure 17 shows the emissions for the power sells for a premium, AGR-DP is operated four conditions. Case A is the baseline MCR in case D with the AGR system in service and operating condition where the turbine is oper- maximum steam flow to the turbine. NOx is ating in the “as new” condition with no aging reduced to the SIP Call NOx level, SO2 and par- loses. Case B is AGR applied at MCR. Cases C ticulate emissions are reduced slightly (since and D are AGR-DP; Case C is operation at MCR less coal is fired) and power generation is and Case D is operation with the 12% flow increased 13.3% over MCR. For the rest of the increase. With AGR-DP, NOx, SO2 and particu- year, when the low NOx burners alone can meet late emissions are less than baseline levels even the NOx requirements and power prices are with an increase in power generation by 13.3%. lower, the system is operated in Case C with the Note that the total fuel flow for AGR-DP reflects AGR system out of service and MCR steam flow to the turbine. Due to the efficiency increase, Turbine NOx Control Steam Flow Case Configuration Technology (% of MCR) A Baseline (as new) Low NOx Burners 100% B Baseline (as new) Low NOx Burners + AGR 100% C Dense Pack Low NOx Burners + AGR 100% D Dense Pack Low NOx Burners + AGR 112% Table 8. Four equipment and operating cases the increase in steam flow plus a slight heat rate power output is up by 1.4% firing 100% coal penalty for AGR, primarily due to the increased and emissions are at baseline. latent heat loss of natural gas compared to coal. An economic analysis has been conducted to illustrate the costs and benefits of this integrat- ed technology comparing three approaches to reducing NOx to the SIP Call NOx level: s The base turbine (as new) with SCR s The base turbine (as new) with AGR s AGR-DP The AGR-DP configuration operates at peak flow in the summer and nominal flow for the rest of the year as discussed above. The SCR and AGR cases without Dense Pack operate only at Figure 16. Firing rates and power generation for MCR. various technologies The economic factors used in the analysis are GE Power Systems GER-4192 (04/01) s s 15 Combustion Modification – An Economic Alternative for Boiler NOx Control Figure 17. Emissions for various technologies summarized in Table 9. The technology per- from the incremental power sales are formance factors and capital costs are typical credited against the cost of NOx values which will vary with site specific factors. control at market value The capital costs are expressed in terms of the s Cost of incremental power generation $/KW of the original MCR capacity of the unit. where the value of the NOx reduction Note that the capital cost for the Dense Pack of is credited against the cost of power $30/KW of MCR capacity corresponds to generation at market value $225/KW for the increased power generation s Payback analysis where the costs are capacity (13.3%). credited by both the incremental The results will be considered from three view- power sales and value of NOx points: reduction s Cost of NOx control where the profits Figure 18 shows the NOx control cost where the Table 9. AGR-DP analysis parameters GE Power Systems GER-4192 (04/01) s s 16 Combustion Modification – An Economic Alternative for Boiler NOx Control Figure 18. NOx control cost for various technolo- Figure 20. Incremental power generation cost for gies AGR-DP incremental power is credited at $25/MWH. the value of NOx reduction increases. It is Compared to SCR, AGR reduces cost by 22% expected that the trading price of NOx and AGR-DP reduces cost by 34%. The effect of allowances will be in the range of $2000- the sale price of the incremental power is shown 2500/ton when the market matures. This corre- in Figure 19. Note that as the incremental power sponds to incremental power generation costs sale price increases, the effective cost of NOx of $14-20/MWH. This means that sale of the reduction decreases. At $44/MWH, the cost of incremental power at a price greater than this NOx control drops to zero. This means that the amount will be profit to the utility. sales of the incremental power at $44/MWH Finally, Figure 21 shows the payback for investing entirely pay for the capital cost (annual capital in the integrated AGR Dense Pack technology charges) of the AGR-DP system and the operat- ing cost of AGR Figure 20 shows the cost of incremental power generation as a function of the value of the NOx reduction. The cost of power decreases as Simple Payback (Years) Figure 21. Payback for AGR-DP based on variable values for NOx and power generation. The payback can be less than two years depending on the prices. Figure 19. Effect of incremental power sale price on AGR-DP NOx control cost GE Power Systems GER-4192 (04/01) s s 17 Combustion Modification – An Economic Alternative for Boiler NOx Control Conclusion significant increase in power generation capaci- ty. During the summer the AGR system is in Title IV will result in most units meeting the service controlling NOx to the SIP Call level EPA target NOx levels using low NOx burner (0.15 lb/106 Btu) and power generation is technology. For the additional NOx reduction increased by over 13%. Other pollutants (SO2 required for SIP Call compliance, the primary and particulates) are slightly reduced. For the alternatives are Combustion Modification (with rest of the year, the AGR system is out of service Reburn and Advanced Reburn) and Selective and the boiler heat input is entirely from coal at Catalytic Reduction (SCR). If the final regula- the normal full load heat input. Power is tions or utility preference require that the 0.15 increased by 1.4% with no change in emissions lb/106 Btu level be achieved, SCR will be the from baseline. Thus, this approach ensures that only technology for initial NOx greater than there is no increase in annual emissions of any about 0.55 lb/106 Btu. However for lower initial pollutant. NOx, including the 80% of the units which have The overall economics of AGR-DP are quite dry bottom wall and tangentially fired boilers, favorable to the utility: NOx is reduced at a cost Reburn or Advanced Reburn will substantially that is low compared to projected NOx undercut the cost of SCR on the smaller units. allowances, the incremental power generation Under a NOx trading scenario, the NOx cost is low compared to summer power sales allowance trading price will be the key factor prices and payback can be under two years. affecting both the selection of the lowest cost NOx control technology and the total cost of It should be recognized that the NOx control NOx control. A free trading scenario should levels, steam turbine performance and costs dis- result in NOx allowances trading in the range of cussed in this paper are examples of the typical $2,000-3,000/ton. values expected in commercial US utility appli- cations. Site specific factors may alter these fac- The integrated AGR-DP system is a cost effective tors. A site specific study must be conducted to approach for deep NOx control to meet ozone- confirm the design, performance factors and related regulations with the added benefit of a economics. GE Power Systems GER-4192 (04/01) s s 18 Combustion Modification – An Economic Alternative for Boiler NOx Control References 1. C. Latham, et. al., “NOx Control Using Combustion Modification Technologies,” presented at Electric Power 2000, Cincinnati, Ohio, April 2000. 2. B. A. Folsom, et. al., “Updated Experience Using Reburn Technology for Utility Boiler NOx Emissions Reduction,” presented at the EPRI-EPA-DOE Combined Utility Air Pollutant Control Symposium, Atlanta, GA, August, 1999. 3. B. A. Folsom, et. al., “Field Experience -- Reburn NOx Control,” presented at the EPRI-DOE-EPA Combined Utility Air Pollutant Control Symposium (The Mega Symposium), Washington DC, EPRI Report No. TR-108683-V1, 1997. 4. B. A. Folsom, et. al., “Advanced Gas Reburning Demonstration and Commercial Gas Reburning System Upgrade,” Pittsburgh Coal Conference, 1996. 5. B. A. Folsom, et. al., “Advanced Reburning with New Process Enhancements,” presented at the EPRI/EPA 1995 Joint Symposium on Stationary Combustion NOx Control, Kansas City, Missouri, 1995. 6. V. Zamansky, et. al., “Combined Reburning/N-Agent Injection Systems for Over 90% NOx Control,” presented at the EPRI-DOE-EPA Combined Utility Air Pollutant Control Symposium (The Mega Symposium), Washington DC, EPRI Report No. TR-108683-V1, 1997. 7. V. Zamansky, et. al., “Enhanced NOx Control Via Gas Reburning With Injection of Additives in the Reburning Zone,” presented at the International Gas Research Conference, San Diego, California, 1998. 8. M. Berg, et. al., “NOx Reduction by Urea Injection in a Coal Fired Utility Boiler,” NOx Symposium, 1993. 9. J. Cichanowicz, “SCR for Coal-Fired Boilers: A Survey of Recent Utility Cost Estimates,” present- ed at the EPRI-DOE-EPA Combined Utility Air Pollutant Control Symposium (The Mega Symposium), Washington DC, EPRI Report No. TR-108683-V1, 1997. GE Power Systems GER-4192 (04/01) s s 19 Combustion Modification – An Economic Alternative for Boiler NOx Control List of Figures Figure 1. NOx reduction required to achieve SIP call NOx limit from Title IV target NOx levels Figure 2. Schematic diagram of reburn and advanced reburn Figure 3. Advanced reburn on a wall-fired boiler Figure 4. NOx control results from GE EER reburn applications on utility boilers Figure 5. NOx reduction and NH3 slip for SNCR on 285 MW utility boiler Figure 6. Advanced Reburn tradeoffs for SIP Call compliance: Reburn and SNCR components Figure 7. Cumulative NOx for layered combustion modification technologies Figure 8. Effect of gas firing rate on reburn and advanced reburn NOx Figure 9. NOx control cost for Reburn and Advanced Reburn to 0.15 lb/106 Btu – effect of initial NOx Figure 10. NOx control cost for all technologies to 0.15 lb/106 Btu – effect of initial NOx Figure 11. NOx control cost for trading, 300 MW wall-fired boiler, initial NOx 0.40 lb/106 Btu Figure 12. GE high pressure steam turbine efficiency improvement history Figure 13. Irreversibilities in typical 700 MW steam turbine Figure 14. Distribution of high pressure section steam turbine losses Figure 15. Comparison of high pressure steam turbines: baseline and Dense Pack Figure 16. Firing rates and power generation for various technologies Figure 17. Emissions for various technologies Figure 18. NOx control cost for various technologies Figure 19. Effect of incremental power sale price on AGR-DP NOx control cost Figure 20. Incremental power generation cost for AGR-DP Figure 21. Payback for AGR-DP List of Tables Table 1. Title IV target NOx levels Table 2. GE EER reburn experience on utility boiler Table 3. NOx control technologies in economic analysis Table 4. Economic analysis parameters Table 5. NOx control costs per variable Table 6. Trading analysis parameters Table 7. Baseline and Dense Pack performance summary Table 8. Four equipment and operating cases Table 9. AGR-DP analysis parameters GE Power Systems GER-4192 (04/01) s s 20