Integrated Gasification Combined Cycle Power Research Articles

Techno-economic study of enhanced absorber–regenerator configurations for improving an industrial Sulfinol-M-based acid gas removal processes

Abstract In this study, the rigorous simulation and design of an industrial Sulfinol-M-based acid gas removal (AGR) process was developed. All simulations were performed using Aspen HYSYS with extended NRTL activity coefficient model for the liquid phase and the Peng–Robinson state equation for the vapor fugacity coefficients. The simulation results from VMGSim and Aspen HYSYS were compared with design data from an integrated gasification combined cycle power plant. Several enhanced absorber–regenerator configurations were presented to improve AGR process efficiency. Sustainability analysis was conducted to assess these process alternatives in terms of energy requirements, costs, and environmental impacts. The results showed that the proposed self-heat recuperation configuration could reduce the energy requirements, total annual costs, carbon footprint by 74.7%, 40.1%, and 48.9%, respectively, compared with the conventional configuration.

Performance, economic and exergy analyses of carbon capture processes for a 300 MW class integrated gasification combined cycle power plant

The techno-economic analysis of the CCPs was performed for a 300 MW class integrated coal gasification combined cycle (IGCC) power plant. In the study, the a-MDEA and Selexol processes were selected for the analysis as the representative of the chemical and physical solvent-based carbon capture process (CCPs). A rigorous evaluation of dual-stage CCPs, including power generation, economic evaluations, and exergy destruction, was performed. The net power of a-MDEA and Selexol processes was 267.3 MW and 291.4 MW, respectively, which corresponded to the thermal efficiencies of the dual-stage a-MDEA process of 32.3% and Selexol process of 35.2%. According to the economic analysis, the CAPEX of the Selexol process was approximately 1.39 times more expensive than that of the a-MDEA process. However, the OPEX of the Selexol process for removing a ton of CO2 was approximately one third of that of the a-MDEA process. The exergy flow and destruction were also discussed to evaluate the associated impact on the major components of CCPs. Based on the exergy analysis, the suggestion to improve thermal efficiency was made and result was also briefly discussed. These results can aid in decision-making and in process development for commercial-scale CCPs with respect to thermodynamic and economic analyses.

Dry syngas purification process for coal gas produced in oxy-fuel type integrated gasification combined cycle power generation with carbon dioxide capturing feature

Electricity production from coal fuel with minimizing efficiency penalty for the carbon dioxide abatement will bring us sustainable and compatible energy utilization. One of the promising options is oxy-fuel type Integrated Gasification Combined Cycle (oxy-fuel IGCC) power generation that is estimated to achieve thermal efficiency of 44% at lower heating value (LHV) base and provide compressed carbon dioxide (CO2) with concentration of 93 vol%. The proper operation of the plant is established by introducing dry syngas cleaning processes to control halide and sulfur compounds satisfying tolerate contaminants level of gas turbine. To realize the dry process, the bench scale test facility was planned to demonstrate the first-ever halide and sulfur removal with fixed bed reactor using actual syngas from O2–CO2 blown gasifier for the oxy-fuel IGCC power generation. Design parameter for the test facility was required for the candidate sorbents for halide removal and sulfur removal. Breakthrough test was performed on two kinds of halide sorbents at accelerated condition and on honeycomb desulfurization sorbent at varied space velocity condition. The results for the both sorbents for halide and sulfur exhibited sufficient removal within the satisfactory short depth of sorbent bed, as well as superior bed conversion of the impurity removal reaction. These performance evaluation of the candidate sorbents of halide and sulfur removal provided rational and affordable design parameters for the bench scale test facility to demonstrate the dry syngas cleaning process for oxy-fuel IGCC system as the scaled up step of process development.

Thermal efficiency of advanced integrated coal gasification combined cycle power generation systems with low-temperature gasifier, gas cleaning and CO2 capturing units

Advanced integrated coal gasification combined cycle (A-IGCC) systems have been proposed to obtain higher thermal efficiency than that of IGCC systems by recuperating exhaust heat from a gas turbine to provide the heat source for a gasifier. The performances of the A-IGCC systems with a low-temperature dual-bed fluidized bed gasifier, gas cleaning, CO2 capturing, and the most advanced (1650°C-class) gas turbine units were evaluated using Aspen Plus®. Net thermal efficiency of the A-IGCC model with hot gas desulfurizing unit using ZnO and TiO2 was 53.6% and that with cold gas desulfurizing unit using Selexol® process was 52.0% without CO2 capturing when the cold gas efficiency (CGE) in the gasifier was 80.1%. The net thermal efficiency can be increased to 54.7–57.2% by improving CGE from 80.1 to 85.0%, suggesting the improvement of cold gas efficiency in the gasifier is critical. CO2 emission factors of the A-IGCC system are 505–520kg-CO2/MWh (CGE=80.1%) and 468–490kg-CO2/MWh (CGE=85.0%), and can be decreased to 39.7–112kg-CO2/MWh with 80–95% of CO2 capturing. Compliance to the CO2 emission factor target (<499kg-CO2/MWh) for coal-fired power generation systems can be achieved without CO2 capturing by developing gasifiers whose CGE is 85.0% and integration with 1650°C-glass gas turbine.

Conversion of Petroleum Coke in a High-Pressure Entrained-Flow Gasifier: Comparison of Computational Fluid Dynamics Model and Experiment

High-pressure entrained-flow gasifier technology is used to convert solid carbonaceous feedstocks into synthesis gas, which can be used in an integrated gasification combined cycle power plant or as a feedstock for chemical or synthetic fuel production. Computational fluid dynamics (CFD) models, once validated, can be used to help design full-scale reactors. Model validation entails the comparison of model predictions to lab-scale or pilot-scale measurements. However, experimental measurements of high-pressure pilot-scale gasifiers usually consist only of wall temperatures and outlet gas temperature and composition, which are of limited use for model validation when the gasifier is operating well, providing information only about operating temperature, heat loss, and equilibrium gas composition. These do not provide a strong validation of the CFD model, whose main purpose is to make predictions of the flame size and shape and its ability to convert solid fuel to gas efficiently in a small volume. This paper presents a model validation based on data generated using CanmetENERGY’s 1 MWth high-pressure entrained-flow gasifier. To provide a stronger validation, the approach taken here is to compare the model predictions to the pilot-scale measurements over a range of operating conditions comprising higher (approximately 90%) carbon conversion and lower (approximately 80% or lower) carbon conversion. In effect, the comparison includes operating conditions for which gasification reactions are extended or delayed toward the outlet in order to capture key effects. It is found that the present CFD model is able to track the performance of the gasifier over the range of operating conditions and provides insight into the causes for limited carbon conversion.

More Energy-Efficient CO2 Capture from IGCC GE Flue Gases

Carbon dioxide (CO2) emissions are one of the main reasons for the increase in greenhouse gasses in the earth’s atmosphere and carbon capture and sequestration (CCS) is known as an effective method to reduce CO2 emissions on a larger scale, such as for fossil energy utilization systems. In this paper, the feasibility of capturing CO2 using cryogenic liquefaction and improving the capture rate by expansion will be discussed. The main aim was to design an energy-saving scheme for an IGCC (integrated gasification combined cycle) power plant with CO2 cryogenic liquefaction capture. The experimental results provided by the authors, using the feed gas specification of a 740 MW IGCC General Electric (GE) combustion power plant, demonstrated that using an orifice for further expanding the vent gas after cryogenic capture from 57 bar to 24 bar gave an experimentally observed capture rate up to 65%. The energy-saving scheme can improve the overall CO2 capture rate, and hence save energy. The capture process has also been simulated using Aspen HYSYS simulation software to evaluate its energy penalty. The results show that a 92% overall capture rate can be achieved by using an orifice.

Carbon behavior in the cyclic operation of dry desulfurization process for oxy-fuel integrated gasification combined cycle power generation

The dry sulfur-removal process is essential to provide suitable syngas treatment for the oxy-fuel integrated gasification combined cycle power generation plant. It is required that the dry sulfur-removal process to be durable to the carbon deposition due to syngas containing high concentration of carbon monoxide in addition to achieve sufficient performance for sulfur removal. Zinc ferrite sorbent is the most promising candidate for the dry sulfur-removal process. The sorbent was improved to enhance durability to the carbon deposition by modifying preparation. The improved sorbent was prepared from sulfates as the raw materials of zinc ferrite, while the former sorbent was using nitrates as the raw materials. The improved sorbent as well as the former sorbent were evaluated on the performance and carbon deposition tendency in oxy-fuel syngas condition in a fixed bed reactor at elevated pressure and temperature. The results expressed that the improved sorbent has higher desulfurization performance and durability to carbon deposition in the condition expected for cyclic operation of the sulfur-removal process in comparison with the former sorbent. The improved sorbent possessed the superior desulfurization performance as well as the capability for inhibit carbon deposition in the oxy-fuel syngas conditions. The results confirmed the enhanced feasibility of the dry sulfur-removal process by utilizing the improved sorbent.

Dynamic model-based sensor network design algorithm for system efficiency maximization

A dynamic model-based sensor network design (DMSND) algorithm has been developed for maximizing system efficiency for an estimator-based control system. The algorithm synthesizes the optimal sensor network in the face of disturbances or set point changes. Computational expense of the large-scale combinatorial optimization problem is significantly reduced by parallel computing and by using combination of three novel strategies: multi-rate sampling frequency, model order reduction, and use of an incumbent solution that enables early termination of evaluation of infeasible sensor sets. The developed algorithm is applied to an acid gas removal unit as part of an integrated gasification combined cycle power plant with carbon capture. Even though there are more than thousand process states and more than hundred candidate sensor locations, the optimal sensor network design problem for maximizing process efficiency could be solved within couple of hours for a given budget.

Experimental model validation and thermodynamic assessment on high percentage (up to 70%) biomass co-gasification at the 253 MWe integrated gasification combined cycle power plant in Buggenum, The Netherlands

High percentage (up to 70% energy based) biomass co-gasification tests have been carried out at the 253MWe coal based Willem-Alexander Centrale (WAC), Buggenum in The Netherlands utilizing steam exploded wood pellets to assess feasibility of scaling up and to address stringent EU emission requirements in the coming decades. This principal article for demonstrating high percentage biomass co-gasification in large scale IGCC power plants, presents the obtained experimental results with a detailed and validated steady state thermodynamic model developed as an aid to assess future plant operations. The validated model is also used to predict plant performance involving 70% co-gasification with two fuel blends of torrefied wood pellets since the desired power output of 230MWe could not be achieved with steam exploded wood pellets. The model predicts plant performance and process parameters with reasonable accuracy and gives a net power output of 173MW and a net plant efficiency of about 37.2% with steam exploded wood pellets. A net output of 240MWe and net plant efficiency of 41.7% is predicted for 70% co-gasification with high lower heating value (LHV) torrefied wood pellets. Exergy analysis indicates largest thermodynamic losses in the gasifier and during combustion, providing additional scope for efficiency enhancement. The demonstration of such a high percentage biomass co-gasification test at a large scale power plant is of vital importance for further development of low emission/carbon neutral power plants. The presented test data also serves as a reliable and prime data source for modeling studies. The validated models could serve as a strong platform to plan real plant operation with various biofuels and carry out studies involving novel technology integration, retrofitting and plant optimization.

Process simulation and thermodynamic evaluation of integrated gasification combine cycle power plant using low-grade coal

The electricity generation from coal using conventional coal fired power plant is very expensive when flue gas emissions are considered in the system. The integrated gasification combine cycle (IGCC) is an alternative option which is efficient, environmentally benign, and economically competitive to the conventional coal fired power plants. In this paper, IGCC is modelled and simulated based on low grade coals of Thar coalfields located in Sindh, Pakistan. The simulation model of IGCC consists of coal and slurry preparation (sizing), gasification, syngas cooling, ash removal, acid gas removal and combustion of gaseous fuel in the combine cycle power plant. The thermodynamic model of the process is developed using Aspen Plus process simulation software. The objective of this study is to predict an energy and environmental performance of IGCC based on Thar coalfields. The results indicated that block-5 and block-6 are more efficient in terms of power produced in IGCC.

Prediction of gas–solid bed hydrodynamics using an improved drag correlation for nonspherical particles

Gas–solid beds are ubiquitous in industrial and energy production applications. Examples include fluidized beds, which are used in many systems such as in integrated gasification combined cycle power plants or in chemical looping systems. These examples and others involve complicated interactions between each phase of reactants in the system. The motivation of this work stems from the need for a better understanding of bed hydrodynamics in existing energy systems; results from this work can be used directly in software such as Fluent to more accurately predict flow behaviors of gas and solid phases. The experimental data are collected from two setups including an optically accessible drag measurement facility that was used to obtain the drag coefficient at various particle Reynolds numbers and a lab-scale gas–solid packed bed which was used to validate the computational correlation through pressure drop measurements across the packed bed. Results showed that the new correlation predicted drag coefficients as accurate as 10% and deviated by up to 15% for particles with sphericities less than 0.9. This is a significant improvement compared to existing correlations, which can deviate as much as 50% for the same range of tested values. Similar findings are observed when the drag correlation is implemented into Fluent. It was found that the model predicted pressure drop in a particle bed with nonspherical particles with an error as low as 5% and as high as 28% near the fluidization velocity.

Analyzing the possibility of constructing the air heating system for an integrated solid fuel gasification combined-cycle power plant

Combined-cycle power plants operating on solid fuel have presently been implemented only in demonstration projects. One of possible ways for improving such plants consists in making a shift to hybrid process circuits of integrated gasification combined-cycle plants with external firing of solid fuel. A high-temperature air heater serving to heat compressed air is a key element of the hybrid process circuit. The article describes application of a high-temperature recuperative metal air heater in the process circuit of an integrated gasification combined-cycle power plant (IGCC). The available experience with high-temperature air heating is considered, and possible air heater layout arrangements are analyzed along with domestically produced heat-resistant grades of steel suitable for manufacturing such air heater. An alternative (with respect to the traditional one) design is proposed, according to which solid fuel is fired in a noncooled furnace extension, followed by mixing the combustion products with recirculation gases, after which the mixture is fed to a convective air heater. The use of this design makes it possible to achieve considerably smaller capital outlays and operating costs. The data obtained from thermal and aerodynamic calculations of the high-temperature air heater with a thermal capacity of 258 MW for heating air to a temperature of up to 800°C for being used in the hybrid process circuit of a combined-cycle power plant are presented.

Selecting the process arrangement for preparing the gas turbine working fluid for an integrated gasification combined-cycle power plant

Introduction of a combined-cycle technology based on fuel gasification integrated in the process cycle (commonly known as integrated gasification combined cycle technology) is among avenues of development activities aimed at achieving more efficient operation of coal-fired power units at thermal power plants. The introduction of this technology is presently facing the following difficulties: IGCC installations are characterized by high capital intensity, low energy efficiency, and insufficient reliability and availability indicators. It was revealed from an analysis of literature sources that these drawbacks are typical for the gas turbine working fluid preparation system, the main component of which is a gasification plant. Different methods for improving the gasification plant chemical efficiency were compared, including blast air high-temperature heating, use of industrial oxygen, and a combination of these two methods implying limited use of oxygen and moderate heating of blast air. Calculated investigations aimed at estimating the influence of methods for achieving more efficient air gasification are carried out taking as an example the gasifier produced by the Mitsubishi Heavy Industries (MHI) with a thermal capacity of 500 MW. The investigation procedure was verified against the known experimental data. Modes have been determined in which the use of high-temperature heating of blast air for gasification and cycle air upstream of the gas turbine combustion chamber makes it possible to increase the working fluid preparation system efficiency to a level exceeding the efficiency of the oxygen process performed according to the Shell technology. For the gasification plant’s configuration and the GTU working fluid preparation system be selected on a well-grounded basis, this work should be supplemented with technical-economic calculations.

Correlation between the critical viscosity and ash fusion temperatures of coal gasifier ashes

Coal gasification yields synthesis gas, an important intermediate in chemical manufacturing. It is also vital to the production of liquid fuels through the Fischer-Tropsch process and electricity in Integrated Gasification Combined Cycle power generation. Minerals naturally present in coal become molten in entrained-flow slagging gasifiers. Molten coal ash slag penetrates and dissolves refractory bricks, leading to costly plant shutdowns. The extent of coal ash slag penetration and refractory brick dissolution depends on the slag viscosity, the gasification temperature, and the composition of slag and bricks. We measured the viscosity of several synthetic coal ash slags with a high-temperature rotary viscometer and their ash fusion temperatures through optical image analysis. All measurements were made in a carbon monoxide-carbon dioxide reducing atmosphere that approximates coal gasification conditions. Empirical correlation models based on ash fusion temperatures were used to calculate critical viscosity temperatures based on the coal ash compositions. These values were then compared with those obtained from thermodynamic phase-transition models. An understanding of slag viscosity as a function of ash composition is important to reducing refractory wear in slagging coal gasifiers, which would help to reduce the cost and environmental impact of coal for chemical and electricity production.

Reduced order modeling of a short-residence time gasifier

State-of-the-art gasifiers require rapid mixing of fuel, steam and oxygen to achieve high carbon conversion within a short residence time. This allows reduction of the gasifier’s volume and the associated capital costs. CanmetENERGY of Natural Resources Canada has a pilot-scale gasifier that can convert solid fuels to syngas in less than 1s. This study describes the development of a reduced order model (ROM) for CanmetENERGY’s entrained flow short-residence time gasifier. The model consists of a reactor network that represents the gasifier using a set of chemical reactors that are aimed to capture distinct flow zones of the system. The layout of chemical reactors proposed in this work is based on computational fluid dynamics (CFD) simulations of the gasifier that accounted for the detailed gas and particle flows. The ROM implements sub-models for the simulation of drying, devolatilization, chemical reactions, viscous fluid–solid interactions, pollutant formation and heat transfer through the wall of the reactor. The predictions obtained by the ROM are in reasonable agreement with the CFD simulation data for axial temperature, heat flux, conversion and composition. Having established the flow pattern for a given gasifier and range of operating conditions, the proposed ROM is computationally efficient since it only requires 2.5min to converge whereas CFD simulations require 7–10days. This attractive feature enables integration of the gasifier ROM to process simulators for further development of integrated gasification combined cycle power plants.

Simulation of an integrated gasification combined cycle with chemical-looping combustion and carbon dioxide sequestration

Chemical-looping combustion is an interesting technique that makes it possible to integrate power generation from fuels combustion and sequestration of carbon dioxide without energy penalty. In addition, the combustion chemical reaction occurs with a lower irreversibility compared to a conventional combustion, leading to attain a somewhat higher overall thermal efficiency in gas turbine systems. This paper provides results about the energetic performance of an integrated gasification combined cycle power plant based on chemical-looping combustion of synthesis gas. A real understanding of the behavior of this concept of power plant implies a complete thermodynamic analysis, involving several interrelated aspects as the integration of energy flows between the gasifier and the combined cycle, the restrictions in relation with heat balances and chemical equilibrium in reactors and the performance of the gas turbines and the downstream steam cycle. An accurate thermodynamic modeling is required for the optimization of several design parameters. Simulations to evaluate the energetic efficiency of this chemical-looping-combustion based power plant under diverse working conditions have been carried out, and a comparison with a conventional integrated gasification power plant with precombustion capture of carbon dioxide has been made. Two different synthesis gas compositions have been tried to check its influence on the results. The energy saved in carbon capture and storage is found to be significant and even notable, inducing an improvement of the overall power plant thermal efficiency of around 7% in some cases.

Process simulation of a dual-stage Selexol process for 95% carbon capture efficiency at an integrated gasification combined cycle power plant

It was aimed to simulate a conventional dual-stage Selexol process for removing CO2 and H2S simultaneously from a synthesis gas (syngas) originated from a typical Integrated Gasification Combined Cycle (IGCC) power plant driven by a dry-coal fed gasifier using Honeywell UniSim R400. The solubilities of syngas components on Selexol were predicted by temperature-dependant Henry’s law constants being newly evaluated in this study based on the experimental data in Xu et al. (1992). The operating conditions of the dual-stage Selexol unit were determined so as to meet simultaneously various performance targets, such as 99+% H2 recovery, 90% CO2 recovery, 99+% H2S recovery, and less than 20ppm H2S in CO2 product. By and large the resulting energy consumptions of the Selexol process were in good agreement with those reported in DOE NETL (2010) that this study was based on. It was shown that the integrated dual-stage Selexol unit could achieve 95% carbon capture rate as well as 90% by simply changing the operating conditions. By contrast a CO2 removal Selexol process having not an input of lean solvent generated by thermal regeneration could not achieve 95% carbon capture rate due to a pinch point formed at the top of the CO2 absorber.

Characterization of a Nitrogen Diluted Hydrogen Diffusion Flame for Model Validation

Dilute hydrogen diffusion flames have been considered as a gas turbine combustion strategy that provides relatively low levels of NOx emissions for application in integrated gasification combined cycle power generation. These flames also represent a challenging environment for computational modeling efforts due to the complexity of molecular transport effects, turbulence-chemistry interaction, and near extinction flame conditions. In order to provide data for validation of computational modeling efforts, measurements of major species concentration and flame temperature were made in such a flame using spontaneous Raman scattering. Experimental results demonstrate the importance of differential species diffusion, which occurs due to the disparity between diffusion characteristics of hydrogen and nitrogen. Additionally, the flame temperatures observed were quite low relative to the equilibrium flame temperature, due to flame strain. This confirms the fact that suppression of the thermal mechanism of NOx formation plays a significant role in reducing NOx emissions from this type of flame.

Comparative life cycle analyses of bulk-scale coal-fueled solid oxide fuel cell power plants

Detailed cradle-to-grave life cycle analyses are performed for bulk-scale solid oxide fuel cell power plants fueled by gasified coal. These results are compared to cradle-to-grave life cycle analyses of the supercritical pulverized coal and integrated gasification combined cycle power generation plants, which are also performed as a part of this study. Life cycle inventories for each plant including the inputs (resources and fuels) and outputs (emissions and waste) of the gate-to-gate plants and their associated up- and down-stream sub-processes are computed. The impact of carbon capture and sequestration on each plant is quantified and assessed using the ReCiPe 2008 life cycle inventory method for three socioeconomic perspectives. The results of each coal plant are compared to one another and to plants generating power from natural gas at the end-point level. Results indicate that not only do coal-fed SOFCs generate power with a significantly lower life cycle impact than the current state-of-the-art coal plants, but when carbon capture is enabled they can do so with a lower impact than the most modern plants utilizing natural gas, as well.

CO2 capture in advanced power plants fed by coal and equipped with OTM

Greenhouse gas emissions from human activities contribute greatly towards climate change. In the power generation sector, where fossil fuels are extensively used, these emissions could be reduced by capturing and storing the CO2 emitted. Between the different fossil fuels, coal is very interesting from an economic point of view (coal reservoirs are abundant and distributed homogenously on the earth) even if it produces a lot of carbon dioxide emissions.In this paper we have studied energy and economic performance of an integrated gasification combined cycle power plant (IGCC power plant equipped with an oxygen-blown gasifier) with CO2 capture based on the pre-combustion process and an advanced supercritical steam cycle (SSC) power plant with CO2 capture based on oxy-fuel combustion process. In these power plants great oxygen flow rates are necessary and so we have chosen an innovative technology for oxygen production based on oxygen transport membranes. The goal of this paper is the discussion of the main characteristics and performance of these membranes and the analysis of their integration in advanced coal-fired power plants. For each power plant, a full plant heat and mass balance is calculated in order to compare energy and environmental performance (net efficiency and CO2 specific emissions) and to evaluate the economic impacts of such CO2 emission abatement technologies.