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Title: Transient studies of an Integrated Gasification Combined Cycle (IGCC) plant with CO2 capture

Abstract

Next-generation coal-fired power plants need to consider the option for CO2 capture as stringent governmental mandates are expected to be issued in near future. Integrated gasification combined cycle (IGCC) plants are more efficient than the conventional coal combustion processes when the option for CO2 capture is considered. However, no IGCC plant with CO2 capture currently exists in the world. Therefore, it is important to consider the operability and controllability issues of such a plant before it is commercially built. To facilitate this objective, a detailed plant-wide dynamic simulation of an IGCC plant with 90% CO2 capture has been developed in Aspen Plus Dynamics{reg_sign}. The plant considers a General Electric Energy (GEE)-type downflow radiant-only gasifier followed by a quench section. A two-stage water gas shift (WGS) reaction is considered for conversion of CO to CO2. A two-stage acid gas removal (AGR) process based on a physical solvent is simulated for selective capture of H2S and CO2. Compression of the captured CO2 for sequestration, an oxy-Claus process for removal of H2S and NH3, black water treatment, and the sour water treatment are also modeled. The tail gas from the Claus unit is recycled to the SELEXOL unit. The clean syngas from themore » AGR process is sent to a gas turbine followed by a heat recovery steam generator. This turbine is modeled as per published data in the literature. Diluent N2 is used from the elevated-pressure ASU for reducing the NOx formation. The heat recovery steam generator (HRSG) is modeled by considering generation of high-pressure, intermediate-pressure, and low-pressure steam. All of the vessels, reactors, heat exchangers, and the columns have been sized. The basic IGCC process control structure has been synthesized by standard guidelines and existing practices. The steady state results are validated with data from a commercial gasifier. In the future grid-connected system, the plant should satisfy the environmental targets and quality of the feed to other sections, wherever applicable, without violating the operating constraints, and without sacrificing the efficiency. However, it was found that the emission of acid gases may far exceed the environmental targets and the overshoot of some of the key variables may be unacceptable under transient operation while following the load. A number of operational strategies and control configurations is explored for achieving these stringent requirements. The transient response of the plant is also studied by perturbing a number of key inputs.« less

Authors:
; ;
Publication Date:
Research Org.:
National Energy Technology Lab. (NETL), Pittsburgh, PA, and Morgantown, WV (United States). In-house Research; National Energy Technology Lab. (NETL), Pittsburgh, PA, and Morgantown, WV (United States)
Sponsoring Org.:
USDOE Assistant Secretary for Fossil Energy (FE)
OSTI Identifier:
1015295
Report Number(s):
NETL-TPR-3035
TRN: US201111%%532
Resource Type:
Conference
Resource Relation:
Conference: AIChE 2010 Annual Meeting, Salt Lake city, UT, November 7-12, 2010
Country of Publication:
United States
Language:
English
Subject:
97 MATHEMATICS AND COMPUTING; COAL; COMBINED CYCLES; COMBUSTION; COMPRESSION; GAS TURBINES; GASES; GASIFICATION; HEAT EXCHANGERS; HEAT RECOVERY; POWER PLANTS; PROCESS CONTROL; REMOVAL; SOLVENTS; STEAM; STEAM GENERATORS; TARGETS; TRANSIENTS; TURBINES; WATER GAS; WATER TREATMENT

Citation Formats

Bhattacharyya, D., Turton, R., and Zitney, S. Transient studies of an Integrated Gasification Combined Cycle (IGCC) plant with CO2 capture. United States: N. p., 2010. Web.
Bhattacharyya, D., Turton, R., & Zitney, S. Transient studies of an Integrated Gasification Combined Cycle (IGCC) plant with CO2 capture. United States.
Bhattacharyya, D., Turton, R., and Zitney, S. Fri . "Transient studies of an Integrated Gasification Combined Cycle (IGCC) plant with CO2 capture". United States. doi:.
@article{osti_1015295,
title = {Transient studies of an Integrated Gasification Combined Cycle (IGCC) plant with CO2 capture},
author = {Bhattacharyya, D. and Turton, R. and Zitney, S.},
abstractNote = {Next-generation coal-fired power plants need to consider the option for CO2 capture as stringent governmental mandates are expected to be issued in near future. Integrated gasification combined cycle (IGCC) plants are more efficient than the conventional coal combustion processes when the option for CO2 capture is considered. However, no IGCC plant with CO2 capture currently exists in the world. Therefore, it is important to consider the operability and controllability issues of such a plant before it is commercially built. To facilitate this objective, a detailed plant-wide dynamic simulation of an IGCC plant with 90% CO2 capture has been developed in Aspen Plus Dynamics{reg_sign}. The plant considers a General Electric Energy (GEE)-type downflow radiant-only gasifier followed by a quench section. A two-stage water gas shift (WGS) reaction is considered for conversion of CO to CO2. A two-stage acid gas removal (AGR) process based on a physical solvent is simulated for selective capture of H2S and CO2. Compression of the captured CO2 for sequestration, an oxy-Claus process for removal of H2S and NH3, black water treatment, and the sour water treatment are also modeled. The tail gas from the Claus unit is recycled to the SELEXOL unit. The clean syngas from the AGR process is sent to a gas turbine followed by a heat recovery steam generator. This turbine is modeled as per published data in the literature. Diluent N2 is used from the elevated-pressure ASU for reducing the NOx formation. The heat recovery steam generator (HRSG) is modeled by considering generation of high-pressure, intermediate-pressure, and low-pressure steam. All of the vessels, reactors, heat exchangers, and the columns have been sized. The basic IGCC process control structure has been synthesized by standard guidelines and existing practices. The steady state results are validated with data from a commercial gasifier. In the future grid-connected system, the plant should satisfy the environmental targets and quality of the feed to other sections, wherever applicable, without violating the operating constraints, and without sacrificing the efficiency. However, it was found that the emission of acid gases may far exceed the environmental targets and the overshoot of some of the key variables may be unacceptable under transient operation while following the load. A number of operational strategies and control configurations is explored for achieving these stringent requirements. The transient response of the plant is also studied by perturbing a number of key inputs.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Fri Jan 01 00:00:00 EST 2010},
month = {Fri Jan 01 00:00:00 EST 2010}
}

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  • An accurate estimation of process state variables not only can increase the effectiveness and reliability of process measurement technology, but can also enhance plant efficiency, improve control system performance, and increase plant availability. Future integrated gasification combined cycle (IGCC) power plants with CO2 capture will have to satisfy stricter operational and environmental constraints. To operate the IGCC plant without violating stringent environmental emission standards requires accurate estimation of the relevant process state variables, outputs, and disturbances. Unfortunately, a number of these process variables cannot be measured at all, while some of them can be measured, but with low precision, lowmore » reliability, or low signal-to-noise ratio. As a result, accurate estimation of the process variables is of great importance to avoid the inherent difficulties associated with the inaccuracy of the data. Motivated by this, the current paper focuses on the state estimation of an acid gas removal (AGR) process as part of an IGCC plant with CO2 capture. This process has extensive heat and mass integration and therefore is very suitable for testing the efficiency of the designed estimators in the presence of complex interactions between process variables. The traditional Kalman filter (KF) (Kalman, 1960) algorithm has been used as a state estimator which resembles that of a predictor-corrector algorithm for solving numerical problems. In traditional KF implementation, good guesses for the process noise covariance matrix (Q) and the measurement noise covariance matrix (R) are required to obtain satisfactory filter performance. However, in the real world, these matrices are unknown and it is difficult to generate good guesses for them. In this paper, use of an adaptive KF will be presented that adapts Q and R at every time step of the algorithm. Results show that very accurate estimations of the desired process states, outputs or disturbances can be achieved by using the adaptive KF.« less
  • The modified Claus process is one of the most common technologies for sulfur recovery from acid gas streams. Important design criteria for the Claus unit, when part of an Integrated Gasification Combined Cycle (IGCC) power plant, are the ability to destroy ammonia completely and recover sulfur thoroughly from a relatively low purity acid gas stream without sacrificing flame stability. Due to these criteria, modifications are often required to the conventional process, resulting in a modified Claus process. For the studies discussed here, these modifications include the use of a 95% pure oxygen stream as the oxidant, a split flow configuration,more » and the preheating of the feeds with the intermediate pressure steam generated in the waste heat boiler (WHB). In the future, for IGCC plants with CO2 capture, the Claus unit must satisfy emission standards without sacrificing the plant efficiency in the face of typical disturbances of an IGCC plant such as rapid change in the feed flowrates due to load-following and wide changes in the feed composition because of changes in the coal feed to the gasifier. The Claus unit should be adequately designed and efficiently operated to satisfy these objectives. Even though the Claus process has been commercialized for decades, most papers concerned with the modeling of the Claus process treat the key reactions as equilibrium reactions. Such models are validated by manipulating the temperature approach to equilibrium for a set of steady-state operating data, but are of limited use for dynamic studies. One of the objectives of this study is to develop a model that can be used for dynamic studies. In a Claus process, especially in the furnace and the WHB, many reactions may take place. In this work, a set of linearly independent reactions has been identified and kinetic models of the furnace flame and anoxic zones, WHB, and catalytic reactors have been developed. To facilitate the modeling of the Claus furnace, a four-stage method was devised so as to determine which set of linearly independent reactions would best describe the product distributions from available plant data. Various approaches are taken to derive the kinetic rate expressions which are either missing in the open literature or found to be inconsistent. A set of plant data is used for optimal estimation of the kinetic parameters. The final model agrees well with the published plant data. Using the developed kinetics models of the Claus reaction furnace, WHB, and catalytic stages, two optimization studies are carried out. The first study shows that there exists an optimal steam pressure generated in the WHB that balances hydrogen yield, oxygen demand, and power generation. In the second study, it is shown that an optimal H2S/SO2 ratio exists that balances single-pass conversion, hydrogen yield, oxygen demand, and power generation. In addition, an operability study has been carried out to examine the operating envelope in which both H2S/SO2 ratio and adiabatic flame temperature can be controlled in the face of disturbances typical for the operation of an IGCC power plant with CO2 capture. Impact of CO2 capture on the Claus process has also been discussed.« less