Dennis A. Horazak and Justin Zachary Siemens Westinghouse Power Corporation

Transcription

1 Gasification Technology Conference, San Francisco, California, October 4-7, ASME PTC 47 GASIFICATION COMBINED CYCLE PLANT PERFORMANCE: PROGRESS AND CHALLENGES Dennis A. Horazak and Justin Zachary Siemens Westinghouse Corporation ABSTRACT Performance Test Code (PTC) 47 is currently being written to define procedures for testing the performance of gasification combined cycle plants. This code is unique in that it pertains to a technology that is now being demonstrated but has not yet been commercialized. It is also different from previously written test codes in three other areas: it can be used to test the overall plant and its major subsystems simultaneously; its procedures can accommodate a variety of fuels, including coal, oil, biomass, and other alternative fuels; and it can be used to test product gases and other co-products along with electric power. This paper describes the development of PTC 47 and the technical challenges related to measuring the performance of gasification combined cycle plants. Discussion includes the application of performance simulation in the testing process, and the potential affect of this code on the development of gasification combined cycles. OBJECTIVES OF PTC 47 The first performance test code was Code of Rules for Boiler Tests, written in 1884 to provide accurate and reliable methods for testing boiler performance, replacing the confusion of often exaggerated claims promoted by boiler vendors (Scharp, 1993). Performance Test Code 47, Gasification Combined Cycle Plant Performance, is being written to define the significant performance factors in a gasification combined cycle plant and suggest how these factors might be calculated from measurements. The objective of PTC 47 is to provide procedures for the determination of power plant thermal performance, electrical output, and product gas stream output for the IGCC power plant and its subsystems at a specified cycle configuration, operating disposition, and/or fixed power level, and at a specific set of base reference conditions. Integrated Gasification Combined Cycle (IGCC) is a relatively new technology that uses coal and alternate fuels to generate power and possibly produce heat and chemical feedstocks. Currently there are at least 20 coal gasification technologies that are compatible with power generation using a gas turbine (Bannister and others, 1997). PTC 47 is unique in that it provides a test code for a technology that is now being demonstrated, but has not yet been commercialized. IGCC Measurements for Acceptance Testing The basic functions of an IGCC plant are to convert solid or liquid fuel into a gaseous feedstock, clean and cool the fuel gas, and generate electric power. The gasification process may be either air-blown or oxygen-blown, leading to three fundamental arrangements of IGCC plants: air-blown plants; oxygen-blown plants with oxygen supplied over the fence from a separate facility; and, oxygen-blown plants in which oxygen is supplied by an ASU that is considered part of the plant. Besides generating electricity, IGCC plants may also produce synthesis gas, export steam, heated oxygendepleted air, byproduct liquid oxygen or nitrogen (from ASUs), and sulfur byproducts, as shown in Table 1. Any or all of these products may be the subject of acceptance tests, and PTC 47 is being written to accommodate all of their measurements.

2 EQUIPMENT PRODUCTS Table 1 Equipment and Products Associated with Various IGCC Plant Configurations Arrangement Air-blown O 2 -blown, OTF 1 O 2 -blown w/asu 2 Air Separation Unit Gasifier Block X X X Fuel Gas Cleaning X X X Block X X X Electric X X X Synthesis Gas Optional Optional Optional Export Optional Optional Optional Heated, O 2 -depleted Air Optional Optional Optional Liquid Oxygen Liquid Nitrogen X Optional Optional Sulfur Byproducts Optional Optional Optional 1 Off-site oxygen supplied over the fence. ASU not included within scope of test. 2 ASU included within scope of test. The testing of an IGCC plant requires the accurate measurement of key input flows and useful output flows that cross the test boundary of an IGCC plant. A test boundary is similar to a control volume in that only streams crossing it need to be measured, but it is unlike a control volume because it does not require the calculation of a complete heat balance. Figures 1 and 2 show the test boundaries for air-blown and oxygen-blown IGCC plants, respectively, including test boundaries for the major plant sections: the air separation unit (ASU, for oxygen blown gasifiers), the gasification process (including gas cleanup), and the power block. PTC 47 tests will determine the quantity and quality of fuel gas by its temperature, pressure, composition, heating value, and its content of contaminants. Contaminants are compounds that are either potentially deleterious to the gas turbine and power block in general, or are precursors to stack emissions.

3 Secondary Fuel Synthesis Gas Vent Gas HRSG Exhaust Raw Fuel Sorbent Byproducts Ash Spent Sorbent Sulfur PTC 47.3 Fuel Gas Cleaning Raw Gas PTC 47.2 Gasification Block Fuel Gas Process Process Water Condensate Gasifier PTC 47.4 Block Net Export Cooling Water/Air PTC 47.3 PTC 47.2 Test Boundaries Air PTC 47.4 PTC 47 Test Boundaries Required for test calculation Ambient Air Not required for test calculation Makeup Water - Condensate Cooling Water/Air Figure 1 - Air-Blown IGCC Plant Block Flow Diagram Secondary Fuel Synthesis Gas Vent Gas HRSG Exhaust Raw Fuel Sorbent Byproducts Ash Spent Sorbent Sulfur PTC 47.3 Fuel Gas Cleaning Raw Gas PTC 47.2 Gasification Block Fuel Gas Process Process Water Condensate Gasifier PTC 47.4 Block Net Export Cooling Water/Air PTC 47.3 PTC 47.2 PTC 47.1 Test Boundaries Ambient Air O 2 N 2 PTC 47.1 Air Separation Unit Nitrogen Air Cooling Water Process Water PTC 47.4 PTC 47 Test Boundaries Required for test calculation Not required for test calculation Byproducts Liquid Gases O 2, N 2 Vent N 2 Makeup Water - Condensate Cooling Water/Air Figure 2 - Oxygen-Blown IGCC Plant Block Flow Diagram

4 Efficiency Depends on Configuration Efficiency and heat rate useful output divided by thermal input and its reciprocal are simple to calculate for IGCC plants that produce electric power as their only product. For these power-only IGCC plants, the code provides procedures for determining net power, heat input, and heat rate, all corrected to reference conditions. If the IGCC plant performance test also includes exported synthesis gas, process steam, or some other combination of byproducts, the code provides procedures for determining net power, heat input, product gas flow and properties, product gas contaminant content, and net steam export energy. However, there is no commonly accepted definition of efficiency for these multiple-product plants. The problem is that each co-product requires a different amount of energy to produce, so the efficiency changes with product mix. In a cogeneration plant, for example, each unit of electrical output requires about three times as much energy to produce as a unit of thermal output, so cogeneration plants that mainly produce power seem to have lower efficiencies (and higher heat rates) than plants that mainly produce process steam. Any calculation of efficiency would require some adjustment for the relative energy needs of each product, and agreement on this issue (even in the relatively simple case of two-product cogeneration) has not been forthcoming during the last decade. In order to avoid the controversies associated with multiple products, the proposed approach for PTC 47 is to measure all significant streams entering and leaving the plant, from which a variety of ratios can be calculated, if desired. Historical Reasons for IGCC Code The initial IGCC demonstration plants were subsidized projects that generated electric power from coal. The technology has matured to become commercially viable, and most IGCC projects are now chosen based on economic criteria (Chambers, 1997). Two emerging trends in gasification are the shift from power generation to industrial cogeneration and trigeneration, and the use of heavy petroleum byproducts instead of coal Table 2 shows the worldwide variety of IGCC applications. In response to this variety, PTC 47 is being written to include performance tests for alternative fuels and multiple byproducts as well as coal-fueled power applications.

5 International Table 2 New Gasification Based Capacity (in operation, or active development since 1990) Ref Plant Name, Country Feedstock Product Capacity* Startup 1 Buggenum, Netherlands Coal Electricity Schwarze Pumpe, Germany Coal, Wastes Methanol, Electricity SUV/EGT, Czech Republic Coal Cogeneration Ilva, Italy Blast Furnace Gas Electricity Pernis, Netherlands Oil, Visbroken Tar H 2, Electricity Puertollano, Spain Coal, Petcoke Electricity Sokolovska Uheina, Czech Republic Lignite Electricity IBIL/Sanghi, India Lignite Electricity API Energia Oil, Visbroken Tar Electricity ISAB Energy, Italy Oil, Asphalt Electricity, H 2, [2] Sarlux, Italy Oil, Visbroken Tar Electricity, H 2 [2] EPZ, Netherlands Wood Wastes Electricity Exxon Singapore Petroleum Hydrogen, CO Celanese Singapore Residual Oil Hydrogen, CO Fife, Scotland Coal, Sludge Electricity General Sekiyu K.K., Japan Vacuum Residue Electricity Bioelettrica Biomass Electricity AGIP Petroli, Italy Oil Electricity, H 2, NPRC, Japan Vacuum Residue Electricity Subtotal Int l 4,808 USA Ref Plant Name (State) Feedstock Product Capacity Startup 1 Wabash River IGCC (IN) Coal Electricity (repower) 1 Polk IGCC (FL) Coal Electricity (repower) 2 Texaco El Dorado (KS) Petcoke Electricity, Cogeneration Pinon Pine IGCC (NV) Coal Electricity Star Delaware City (DE) Petcoke Electricity Farmland Industries (KS) Petcoke Ammonia Exxon Baytown (TX) Petcoke H 2, Electricity Subtotal USA 1,242 World Total 6,050 *Capacity in megawatts electricity equivalent based on syngas output. References 1 Gasification Technologies Council, August 25, Chambers, 1998.

6 STATUS OF PTC 47 In order for the Code to be a useful document, it must prescribe procedures that are technically correct and fair to all interests normally present at an acceptance test. To accomplish these goals, the 23-member PTC 47 Code Committee includes a balanced representation of equipment users, equipment designers and manufacturers, and members with general technical interest, such as academic experts and architect engineers. The Committee is organized into five subgroups to produce five individual code documents: the air separation unit, raw gasification block, fuel gas cleaning, and power block (PTC 47.1, PTC 47.2, PTC 47.3, and PTC 47.4, respectively), and an overall IGCC code (PTC 47). Each code document is organized into the same standard sections: Object and Scope, Definitions and Description of Terms, Guiding Principles, Instruments a Methods of Measurement, Calculations and Results, Report of Results, and non-mandatory appendixes. The Objects and Scopes have been drafted and approved, and the remaining sections are being developed. The ongoing work of the PTC 47 Committee has been reported in a series of technical papers (Bannister and others, 1997; Horazak and others, 1998a, 1998b). Draft test codes are currently being developed for the IGCC plant and its subsystems by the five subgroups. When completed, the draft codes will be reviewed by the entire Committee, then sent to the Board and to a large number of industry representatives for review. The Committee addresses comments received, and a revised code is then sent to the Board for final review, approval, and publication. Experience with other codes has shown that the resolution of different perspectives from within the Committee and from the larger industry review is an iterative, non-linear process, so the process of writing and publishing the Code is expected to take several years. Air Separation Unit: PTC 47.1 The air separation unit (ASU) test code will define methods for testing the performance of all units that separate air into oxygen, nitrogen, or argon. The primary stream measurements needed for performance calculations are ambient or compressed air inputs, electric power inputs, product outputs, and heat sink conditions. The fundamental equations, test boundaries, measurement requirements, and testing procedures have been developed to date. Measurement uncertainties and sample calculations will be developed later (Smith, 1998). Gasifier Island: PTC 47.2 Performance testing of the gasification island is the subject of PTC In the current draft, the thermal efficiency of the gasifier island is defined as heat output divided by heat input, where the input streams are coal and high-pressure feedwater, and the output streams are product gas and high-pressure steam. Working with these current definitions, representative efficiency and uncertainty calculations have been performed for an entrained-flow, oxygen-blown gasification island. (Mirolli and Doering, 1998). Ultimately, gasification testing will require resolution of two key issues: an accurate method for determining gasifier fuel input energy, and methods for correcting to reference conditions. Gas Cleaning: PTC 47.3 Performance measurement of fuel gas cleaning equipment is a new subject for an ASME test codes, so PTC 47.3 will be the first of its kind. The scope of this code will be limited to gaseous and condensable contaminants and particulate matter in the fuel gas stream. Contaminants included under the code must be associated with a cleanup process step, and must be precursors to either turbine contaminant species or turbine exhaust emission species. This code does not include stack emission measurements or the determination of the thermal performance of the fuel gas cleanup system (Newby, 1998). The range of fuel gas contaminants of interest have been identified, and information about measuring procedures and their limitations has been gathered. As much as possible, PTC 47.3 will organize and supplement existing methods, most of which are based on EPA sampling techniques. Technical challenges include sampling at high temperatures in corrosive environments, developing effective, reliable sampling methods for fuel gas metal species (which do not currently exist), and establishing the accuracy of established industrial test methods. Island: PTC 47.4 A gas turbine combined cycle is the power island in an IGCC plant. Many of the performance characteristics of the IGCC power island are similar to those addressed in an existing ASME code for Overall Plant Performance,

7 PTC 46. However, IGCC plants have potential variations in gas turbine fuel quality (particularly in syngas from waste or biomass gasifiers), increased complexity of interfacing with the rest of the IGCC plant, and increased number of streams and coproducts, all of which somewhat transcend the scope of PTC 46. As a result, PTC 47.4 is being developed as an IGCC power island code (Horazak and others, 1998b). TECHNICAL ACCURACY ISSUES Status of Uncertainty Analysis Test uncertainties reflect the experimental error associated with measurement of input and output parameters, and probable errors in the calculated results. Errors that contribute to test uncertainty are generated by instrumentation and measurement system inaccuracies, by process and ambient unsteadiness, and by inaccuracies in correction algorithms. The measurement systems, instrumentation, and methods needed to for performance testing are being specified, along with their characteristic uncertainties. In many instances, the required measurements and instrumentation are similar to those in prior codes -- specifically, fired steam generators (PTC 4, Gerhart and others, 1992), Overall Plant Performance (PTC 46, 1996), and Gas Turbines (PTC 22, 1997). In some instances, however, novel measurement systems, instrumentation and sampling, will be required to provide the necessary test data particularly for hot fuel gases, hot spent solids, and fuel gas contaminants. The PTC 47 Committee is making sample calculations based on plant design flow sheets and plant models. These performance parameter computations will include correction factors and uncertainty calculations, which will provide preliminary estimates of the accuracy expected from the test methods, test measurement systems, and instrumentation proposed in the code (Archer and others, 1998), Efficiency Calculation Methods The thermal input to the IGCC plant is the product of the heat of combustion of the fuel supplied to the plant multiplied by its flow rate. Natural gas and processed oil fuels have relatively consistent compositions, but coal and alternate or waste fuels may be heterogeneous and their physical and chemical characteristics may vary significantly with time. Therefore, both their heating value and flow may be difficult to measure. PTC 46, Overall Plant Performance, recommends the energy balance method (Gerhart and others, 1992) over the input/output method for determining the thermal input to power plants burning coal. This method is preferred by PTC 4 for fired steam generators because of its higher accuracy and compatibility with correction factors. However, the input/output method includes measurements of syngas properties, which are needed as inputs to the power block and secondary outputs from the IGCC plant, so the choice of calculation method is still unresolved. In principle, the energy balance method can also be used to determine the thermal input with the gasifier serving as a calorimeter. However, the energy balance calculations require measurements of the heating value and flow of the output fuel gas, a high-pressure, high-temperature, high-flow stream that is difficult to characterize, measure or sample. Also, the energy content of the ash, spent sorbent, and other solids removed from the gasifier or suspended in the fuel gas stream may be difficult to characterize, The test boundaries of the gasifier calorimeter can be expanded to include the heat recovery, gas cleaning, and ash and sorbent processing equipment, but the question remains concerning the ease and accuracy of the energy balance method for determining thermal input to an IGCC plant compared to the difficulty, if not impossibility, of the direct measurement of fuel input heating value and flow (Archer and others, 1998), Correction Procedures Factors Method plant performance is the result of equipment operating within a given set of ambient conditions, heat sink conditions and interaction with the power grid. Guaranteed or expected performance is defined at some other reference conditions. Ideal tests would be run at conditions as close as possible to the design or reference assumptions. Unfortunately in real life this is not always possible. The classical method of data conversion from one set of conditions to the other is the use of correction factors. They can be additive or multiplicative referring

8 to their mathematical application in the correction equations. Correction curves are created by varying only one variable at the time and registering the effect on all the other parameters that cross (in or out) the control volume boundaries. The process is done using a computer simulation code, assuming that all the other independent variables remain constant during this process. The final result of the effect due to all the small variations is achieved by adding or multiplying of all the correction factors. This methodology is described and used in PTC 46 and can be applied in a similar fashion to PTC 47 overall IGCC plant performance. Since PTC 47 goals go one step further to include boundaries between the systems, the number of correction factors will drastically increased, depending on the number of streams crossing the boundaries and the specific nature of the system (gasifier, ASU, power island). Computerized Simultaneous Corrections There is a difference between the "corrected" power output or the heat rate obtained using assembled correction factors, (the PTC46 method) and the values obtained using the simulation code. The simulation code ensures that the mass and energy are balanced at all times. The more complex is the model and the further away are the guaranteed conditions from the test conditions, the more chances are that the correction factors method will not produce realistic results. The complexity and multi-dimentional relationships between the various subsystems make the correction factors method also very difficult to handle. In PTC22 -test code for Gas Turbines or PTC46 test code for Combined Cycles, the influence of one parameter, let say, ambient temperature, could be easily understood and applied in one curve. This is not the case for many of the influence factors in PTC47. Since the computer power now available allows access to enormous calculation capability, PTC47 will consider the use of fully computerized methods for conversion of the test performance data into performance at reference conditions, with all the thermodynamic processes properly simulated and mass and energy balances maintained. It should be recalled that correction factors are created using a simulation program, where other parameters are maintained constant. Fuel Quality Issues Another area requiring resolution in PTC 47 is the use of inconsistent solid fuels fuels with heating values that vary more than 2 percent during the course of a test. The procedures in PTC 46 are limited to consistent solid fuels and result in tests with heat rate and net power uncertainties of 3% and 1%, respectively. Various fuels such as biomass, heavy oils, or solid wastes with inconsistent properties may fuel the gasifiers within the scope of PTC 47. The procedures in PTC 47 are intended to accommodate this wide range of fuels while testing the performance of the IGCC and its subsystems with minimal uncertainty. CHALLENGES AND IMPLICATIONS OF THE CODE The total power output that IGCC power plants will produce in the next few years is approaching 6,000 MW, as shown in Table 2. Developing appropriate procedures for performance testing is more important than ever. It is imperative to achieve the highest possible accuracy and confidence in the test results corrected to guarantee conditions. Great challenges are facing the code. Test uncertainty, plant configuration, calculation conversion and simultaneous subsystems testing are some of the issues that will need resolution. We invite any interested party to provide input and to make a meaningful contribution to the unique performance test code. CONCLUSIONS The PTC 47 Committee is developing procedures for the performance testing of IGCC power plants to determine fuel gas quantify and quality, heat rate and power output at specified operating conditions for three different gasifiers. The development of the PTC47 will greatly contribute to the commercialization of the IGCC technology, by creating reliable and consistent methods of performance evaluation, not only in the conventional terms of power and heat rate but in the capability to quantify other byproducts: sygas, steam, oxygen, nitrogen, etc. The uncertainty analysis will offer a tool to assess the test accuracy and guidance for existing technical limitations when commercial issues of test tolerance are negotiated.

9 Tackling the difficult problems of subsystems performance in an interactive operational mode, could also lead to many technological improvements. Novel and innovative evaluation and measurement methods are required. The REFERENCES: IGGC: Emphasis Shifts Away from Coal and Electric Utilities,, January/February Archer, D. H., R. L. Bannister, and D. A. Horazak, ASME PTC 47, Gasification Combined Cycle Performance - Uncertainty, presented at the 1998 International Joint Generation Conference & Exposition, Baltimore, Maryland, August 24-26, ASME Performance Test Code 16, 1958, "Gas Producers and Continuous Gas Generators," ASME, New York, NY. ASME Performance Test Code 46, 1996, "Overall Plant Performance," ASME, New York, NY. Bannister, R. L., Archer, D. H., Doering, E. L., McNeilly, J. D., Newby, R. A., and Smith, A. R., 1997, ASME PTC47 - Development of a New Code for Integrated Gasification Combined Cycle Performance Testing, PWR - Vol. 32, Proceedings International Joint Generation Conference, Vol. 2, pp Chambers, A., IGCC Offers Diversity for Competitive Generation, Engineering, November Gerhart, P. M., Phillips, J. T. and Davidson, P.G., 1992, "Measurement Uncertainty and the New Performance Test Code for Generators (PTC 4)," ASME Paper 92-JPGC-PTC6. Horazak, D. A., D. H. Archer, and R. L. Bannister, The Development of an ASME Performance Test Code for IGCC Plants, presented at the Pittsburgh Coal Conference, Pittsburgh, Pennsylvania, September 14-18, 1998a. Horazak, D. A., D. H. Archer, R. L. Bannister, and J. J. Zachary, Distinctive Characteristics of ASME Performance Test Code 47, and Comparison with Performance Test Code 46, presented at the 1998 International Joint Generation Conference & Exposition, Baltimore, Maryland, August 24-26, 1998b. Mirolli, M. D., and E. L. Doering, ASME PTC 47 - IGCC Performance Testing: Gasification Island Thermal Performance Testing, presented at the 1998 International Joint Generation Conference & Exposition, Baltimore, Maryland, August 24-26, Newby, R. A., PTC 47 - Fuel Gas Contaminant Sampling for Gasification-Based Plants, presented at the 1998 International Joint Generation Conference & Exposition, Baltimore, Maryland, August 24-26, Scharp, C. B., 1993, Almost Everything You Wanted to Know about ASME Performance Test Codes but Were Afraid to Ask Smith, A. R., PTC 47 - IGCC Performance Testing: Air Separation Issues, presented at the 1998 International Joint Generation Conference & Exposition, Baltimore, Maryland, August 24-26, 1998.