IGCC Process Research Articles

Modeling of pre-combustion carbon capture with CO2-selective polymer membranes

CO2-selective polymer membranes were recently applied to pilot-scale and bench-scale pre-combustion capture and the obtained CO2 capture ratios were reported to be less than 90%, which limits their application in industrial processes such as IGCC plants. This work is aimed to explore the possibility of achieving a CO2 capture ratio >95% and CO2 purity >95% in a gas-separation unit equipped with currently-available CO2-selective polymer membranes. A mathematical model for single-stage membrane gas separation was developed, and the effect of membrane characteristics (permeance and selectivity), as well as the operating parameters such as feed and permeate pressure, and feed flow rate on the performance of CO2 capture was investigated. The simulation results reveal the optimal conditions that are necessary for a high-performance CO2 capture process using the real industrial syngas and highlight the potential of facilitated transport membranes for CO2 removal in both the oxygen-blown and air-blown IGCC processes.

Optimization of Integrated Gasification Combined-Cycle Power Plant for Polygeneration of Power and Chemicals

Efficient and flexible operation is essential for competitiveness in the energy market. However, the CO2 emissions of conventional power plants have become an increasingly significant environmental dilemma. In this study, the optimization of a steam power process of an IGCC was carried out, which improved the overall performance of the plant. CCPP with a subcritical HRSG was modelled using EBSILON Professional. The numerical results of the model were validated by measurements for three different load cases (100, 80, and 60%). The results are in agreement with the measured data, with deviations of less than 5% for each case. Based on the model validation, the model was modified for the use of syngas as feed and the integration of heat into an IGCC process. The integration was optimized with respect to the performance of the CCPP by varying the extraction points, adjusting the steam parameters of the extractions and modifying the steam cycle. For the 100% load case, a steam turbine power achieved increase of +34.2%. Finally, the optimized model was subjected to a sensitivity analysis to investigate the effects of varying the extraction mass flows on the output.

Development of CO2 Molecular Gate Membrane Modules for IGCC Process with CO2 Capture

The molecular gate membranes (=poly(amidoamine) (PAMAM) dendrimer/polymer hybrid membranes) and the membrane elements were developed for CO2 separation from IGCC process. The membranes and the membrane elements were prepared using the modified poly(vinyl alcohol) (PVA)-based materials. The membranes with large membrane area were prepared by continuous membrane-forming method, and the membrane elements were fabricated using the prepared membranes. Membranes were successfully prepared by the continuous membrane-forming method (20 m-roll). The membrane elements showed reasonable separation performance, though CO2/He selectivity was a little lower than that of the membrane itself. The separation performance and robustness of the membranes were examined. It was shown by comparing CO2/He and CO2/N2 separation performance that CO2 separation performance was not affected by N2. It was suggested by H2S exposure test (500ppm H2S) that the membrane is resistant to H2S under this test condition. Regarding the long-term stability of the membranes, the membrane showed stable separation performance for at least 600h at 2.4MPa (supposed pressure in IGCC process).

Process simulation and integration of IGCC systems for H2/syngas/electricity generation with control on CO2 emissions

IGCC is a pre-combustion technology that can be effectively used to produce both hydrogen and electricity while reducing the greenhouse gas (GHG) emissions. Two process models are developed in Aspen Plus® software and are compared techno-economically. The conventional design of IGCC process is taken as case 1, whereas, case 2 represents the conceptual design of sequential integration of reforming model with the gasification unit to enhance the syngas yield. The case 2 utilizes the steam generated in the gasification process to sustain the methane reforming process which consequently enhances both the H2 production capacity and cold gas efficiency. It has been analyzed from results that case 2 can enhance the process performance by 4.77% and economics in terms of cost of electricity by 5.9% compared to the conventional process. However, the utilization of natural gas in the case 2 is considered as a standalone fuel so the process performance of NGCC power plants has been also incorporated to ensure the realistic analysis. The results also showed that case 2 design offers 3.9% higher process performance than the cumulative (IGCC + NGCC) processes, respectively. Moreover, the CO2 specific emissions and LCOE for the case 2 is also lower than the case.

Membrane-based reactive separations for process intensification during power generation

We present here a study of the water gas shift membrane reactor (WGS-MR) in the context of its potential application in the IGCC process for power generation from coal. In our research, we use in the WGS-MR a sour-shift WGS catalyst and carbon molecular sieve (CMS) membranes, and show that the reactor displays higher conversions than a conventional packed-bed reactor (PBR) under the IGCC-relevant conditions, i.e., for temperatures up to 300°C and pressures up to 25bar. Our experimental results manifest the ability of the WGS-MR to operate under the desired conditions and to improve the efficiency of the WGS reaction. They demonstrate, in addition, the potential of the MR to carry out the in-situ separation of hydrogen using the CMS membranes. We conclude from our study, that the CMS-membrane-based WGS-MR is a good candidate technology for incorporation into IGCC power plants for environmentally-benign power generation.

Development of CO2 Molecular Gate Membranes for IGCC Process with CO2 Capture

Carbon dioxide (CO2) capture and storage (CCS) is widely accepted as an important option for mitigating climate change. It is very important to reduce the cost of CO2 capture to implement CCS. CO2 capture by membrane is a promising technique because it is energy efficient and simple to operate. One promising means of reducing CO2 emission is the development of integrated coal gasification combined cycle with CO2 capture & storage (IGCC-CCS). We are currently developing CO2 molecular gate membrane, with the goal of producing a new, high-performance separation membrane modules for IGCC-CCS. In the concept of the molecular gate membrane, the pathway for gas molecules is occupied solely by CO2, which acts as a gate to block the passage of other gases. Consequently, the amount of H2 permeating to the permeate side of the membrane is greatly limited and high concentrations of CO2 can be obtained. As the molecular gate membrane, poly(amidoamine) (PAMAM) dendrimer/polymer hybrid membranes and membrane modules were developed in the METI project, “CO2 Separation Membrane Module Research and Development Project” (2011FY-2014FY). The cost target was 1,500 JPY/ton-CO2. We succeeded in improving the separation performance of such membranes through the modification of poly(vinyl alcohol) (PVA)-based materials, and the target CO2 separation performance was obtained under high-pressure conditions of 2.4MPa using laboratory-scale membranes. It was shown that PAMAM dendrimer/polymer hybrid membrane module is suitable for IGCC process with CO2 capture.

Enhancement of slurryability and heating value of coal water slurry (CWS) by torrefaction treatment of low rank coal (LRC)

To improve cold gas efficiency of entrained-flow gasification, coal water slurry (CWS) as a fuel must have high heating value at low viscosity. Especially, considering unstable supply of bituminous coal, the preparation of CWS with high coal content from low-rank coal remains a challenging topic. In this study, we report a remarkable improvement in coal content of CWS at low viscosity (1000cP) through torrefaction of low-rank coal. Compared to dried coal (moisture-free coal), the torrefaction of low-rank coal leads to an improvement in hydrophobic nature of coal surface and a decrease in coal porosity. The moisture readsorption ratio of the torrefied low-rank coal significantly decreases due to its high hydrophobic nature and low porosity. As a result, Kideco coal showed a 6% and 58.7% increase in the coal content and heating value of CWS after torrefaction at 300°C in comparison to those of CWS made with dried coal. Ultimately, the torrefied coal-based CWS with enhanced coal content and heating value at low viscosity is expected to contribute to an increase in the efficiency of a gasifier and IGCC process.

Integration of IGCC and methane reforming process for power generation with CO2 capture

IGCC is a power generation technology which represents a higher thermal efficiency with large scale implementation of CO2 capture. In this study, two IGCC process models have been evaluated in terms of both the process performance and economics with CO2 capture. Case 1 is based on the conventional IGCC process, whereas, case 2 presents an idea of integrating methane reforming process with an IGCC technology. The high enthalpy steam generated during coal slurry gasification process is used to assist the reforming process for H2 generation. The integration of IGCC with methane reforming process not only supplies the heat required for the endothermic reforming process but also increases the heating value of the resulting syngas. This concept also provides an opportunity for process intensification since shared water gas shift reactors and CO2 capture units will suffice the process needs. In this study, two design cases have been evaluated in terms of their performance, economics and levelized cost of electricity. The integrated process produces high value syngas by making use of heat available from the gasification process. The results show that by integrating the methane reforming process with the coal based IGCC plant improves the overall performance compared to the standalone process design.

Extended Exergy Accounting analysis of IGCC process – Determination of environmental remediation cost of refinery and coke processing waste

This study focuses on determination of environmental remediation cost of energy production from refinery and coke processing solid waste by means of Extended Exergy Accounting methodology. Environmental remediation cost is a novel concept which is proposed by the method of Extended Exergy Accounting and it represents the cumulative resource equivalent of the pollutants to convert them into ideal, zero-impact disposal. In this study, refinery and coke processing waste is subjected to integrated gasification combined cycle which is a gasification and combustion technology. Considered waste composition is based on Turkish industrial waste generation data. This is the first study in the literature that environmental remediation cost of refinery and coke processing residues is obtained in line with the original calculation route by Extended Exergy Accounting methodology, i.e., artificial ways such as determination of environmental remediation cost by converting monetary cost of treatment system into its exergetic equivalent are avoided. Integrated gasification combined cycle is a commercially mature, technically well-known and state-of-the-art industrial treatment system, thus, the obtained environmental remediation cost result has the corresponding importance. Environmental remediation cost of refinery and coke waste combination is determined as 0.138 TJ/Ton and it is seen that resource consumption in required treatment processes for emitted CO2 and waste transportation are the largest constituents of environmental remediation cost.

Dual phase high-temperature membranes for CO2 separation - performance assessment in post- and pre-combustion processes.

Dual phase membranes are highly CO2-selective membranes with an operating temperature above 400 °C. The focus of this work is to quantify the potential of dual phase membranes in pre- and post-combustion CO2 capture processes. The process evaluations show that the dual phase membranes integrated with an NGCC power plant for CO2 capture are not competitive with the MEA process for post-combustion capture. However, dual phase membrane concepts outperform the reference Selexol technology for pre-combustion CO2 capture in an IGCC process. The two processes evaluated in this work, post-combustion NGCC and pre-combustion IGCC, represent extremes in CO2 partial pressure fed to the separation unit. Based on the evaluations it is expected that dual phase membranes could be competitive for post-combustion capture from a pulverized coal fired power plant (PCC) and pre-combustion capture from an Integrated Reforming Cycle (IRCC).

IGCC process intensification for simultaneous power generation and CO2 capture

In this study IGCC process which is a commercial example of pre-combustion technique has been developed in order to analyze the overall plant output with CO2 capture while discussing the process economics. Three different schemes with consistent and transparent methodology have been proposed in order to ensure fair evaluation of analysis. First two cases use water gas shift (WGS) reactions scheme with sour shift catalysis process. The resulted syngas rich of CO2 is treated by CO2 capture unit producing a syngas almost free of CO2 which can be either combusted by air or O2. The first case uses air as an oxidant for burning H2 and the combustor temperature is controlled by air as well. In the second case, O2 is used as an oxidizing agent for H2 combustion and combustion temperature is controlled by recycling the captured CO2. In the third case, WGS reactor and CO2 capture units are removed. The syngas composed of CO and H2 is sent directly for combustion with high purity O2 making it similar to an oxy-fuel combustion process and CO2 is recovered while condensing steam from the flue gas. All the results are compared in terms of both power plant efficiencies and economics.

Detailed exergetic evaluation of heavy-duty gas turbine systems running on natural gas and syngas

Gas turbine systems are widely used for the production of electricity in a simple or combined-cycle mode today. Based on their ability to allow a fast load change, gas turbine systems will become even more important in the future since the volatile production of renewable energies will increase. In this study, a state-of-the-art gas turbine running on natural gas, having an overall net efficiency of approximately 40%, is modeled using Aspen Plus® and characteristic parameters are identified. Based on these parameters, a gas turbine running on syngas was simulated. The emphasis here is on a very detailed evaluation of the inefficiencies. The models consider cooling and sealing flows. The syngas considered in this study is typically used in IGCC processes with carbon capture resulting in a high concentration of hydrogen.For both systems, twelve types of inefficiencies were identified and rated. A comparison of the inefficiencies within each system and between both systems represented by their exergy destruction ratios is presented.In case of the gas turbine running on natural gas, the most important results show that the stoichiometric combustion, followed by the addition of excess air represent the largest inefficiencies. When just applying an isentropic efficiency, the exergy destructions associated with expansion and mixing at different temperatures and pressures of a gas turbine stage cannot be further sub-divided. Hence, this grouping of inefficiencies results to the third position. The effect of mixing at different compositions and the compression follows.In the second case considered here (use of syngas instead of natural gas), the effects of mixing and adding excess air become more significant due to a higher specific heat capacity of the combustion gas. In both cases, the exergy destruction associated with mixing at different compositions can be neglected except the one at the inlet of the pre-mixed combustor, which strongly depends on the particular conditions of the fuel gas. Inefficiencies such as convective cooling of the vanes and blades, heat loss, losses associated with the shaft and generator were found to represent a very small part of the overall exergy destruction. The resulting exergy destructions and losses are shown in an exergy flow diagram.

A numerical model for understanding the behaviour of coals in an entrained-flow gasifier

This paper presents the development of a practical and flexible steady-state gasification model in which existing mechanistic models are incorporated with new knowledge of gasification reaction fundamentals. In particular, intrinsic char gasification kinetics and rates of char gasification are reconciled using a ‘composite effectiveness factor’ by taking into account morphological types of char particles and their impact on char conversion rate. Flows inside an entrained flow gasifier are simplified using ideal chemical reactors consisting of two plug flow and two well stirred reactors. Whilst clearly a simplification of a complex entrained flow gasifier, this approach accounts for the three dimensional aspects of recirculation and mixing and allows rapid convergence as required for incorporation into a practical IGCC process model.Experimental data from gasification of the same coals in a 5MWth entrained flow gasifier were used to validate the performance of the model. Model calculations of the impact of oxygen-carbon stoichiometry on char conversion, cold gas efficiency (CGE) and product gas composition, using laboratory-scale measurements as inputs, are consistent with measurements at pilot-scale. The model results show that maximum CGEs for the higher reactivity coals with relatively high volatile matter are achieved within a narrow range of O:C ratios between 1.05–1.13, whilst the least reactive coal with high fixed carbon achieves its maximum CGE value at a higher O:C ratios of 1.36. Importantly, the model is able to reflect the significant differences in gasification behaviour of the four coals, which is consistent with lab-scale and larger-scale investigations. This work demonstrates the relevance of bench-scale gasification data in the assessment and interpretation of coal gasification behaviour under complex high pressure and high temperature conditions using appropriate mechanisms and sub-models.

Experimental studies of CO2 capture by a hybrid catalyst/adsorbent system applicable to IGCC processes

This paper presents experimental results about CO2 capture in a hybrid adsorbent/catalyst system at both laboratory and bench scale. The proposed novel system consists of a homogeneous mixture of a K-doped hydrotalcite and a high temperature Fe–Cr WGS catalyst in a single reactor, which was selected in previous works. Tests were performed using simulated syngas compositions (CO, CO2, H2, N2, H2O) and simplified binary mixtures (N2/CO and N2/CO2) at temperatures in the range of 300 °C–500 °C and pressures up to 15 bar. The effect of contact time, process temperature and feed gas composition in the CO2 capture capacity of the sorbent was investigated and main results are presented. Moreover, the sorbent showed catalytic activity towards the WGS reaction which was highly dependent on process temperature. Details on the influence of temperature in the catalytic activity of the sorbent are also described in this paper. The influence of temperature and volume ratio adsorbent/catalyst (Vads/Vcat) in the performance of the hybrid system proposed is discussed in terms of CO conversion and CO2 capture capacity of the sorbent.

IGCC 합성가스 급속 냉각시스템의 운전 압력에 따른 열유동 및 입자 거동 특성 연구

In a coal gasifier for IGCC, hot syngas leaving the gasifier at about 1550oC is rapidly quenched by cold syngas recycled from the gas cleaning process. This study investigated the flow and heat transfer characteristics in the gas quench system of a commercial IGCC process plant under different operating pressures. As the operating pressure increased from 30 bar to 50 bar, the reduced gas velocity shortened the hot syngas core. The hot fly slag particles were retained within the core more effectively, and the heat transfer became more intensive around the hot gas core under higher pressures. Despite the high particle concentrations, the wall erosion by particle impaction was estimated not significant. However, large particles became more stagnant in the transfer duct due to the reduced gas velocity and drag force under higher pressures.

Simulation Research on Performance of IGCC System with Brown Coal/Liquid CO<sub>2</sub> Slurry Feed

A simulation research on IGCC process adopting the technique of coal/liquid CO2 (CO2(l)) slurry was proposed. A model of a brown coal slurry fed IGCC system with CO2 capture unit was developed in ASPEN Plus. This model was used to investigate the thermal performance of the IGCC process under different operating conditions. Three kinds of Chinese brown coal were employed in this work. The simulation results show excellent performance of IGCC system when brown coal/CO2(l) slurry feed in gasification system. Enhanced carbon conversion rate and net plant efficiency can be observed with less coal consumption meanwhile. H2O/CO ratio decreases because of more CO and less H2O in the syngas with brown coal /CO2(l) slurry feeding. The net CO2 output from IGCC system also decreases as the advantage of CO2 capture and reuse in coal/CO2(l) slurry.

Simulation of the integration of a bitumen upgrading facility and an IGCC process with carbon capture

Hydrocracking and hydrotreating are bitumen upgrading technologies designed to enhance fuel quality by decreasing its density, viscosity, boiling point and heteroatom content via hydrogen addition. The aim of this study is to evaluate the feasibility of integrating slurry hydrocracking, trickle-bed hydrotreating and residue gasification using the Aspen HYSYS® simulation software. Close-coupling the bitumen upgrading facilities with gasification allows one to achieve a hydrogen and power self-sufficient upgrading facility with CO2 capture. Hydrocracker residue is first withdrawn from a 100,000 BPD Athabasca bitumen upgrading facility, characterized via ultimate analysis and then fed to a gasification unit where it produces hydrogen that is partially recycled to the hydrocracker and hydrotreaters and partially burned for power production in a high hydrogen combined cycle unit. The integrated design is simulated for a base case of 90% carbon capture utilizing a monoethanolamine (MEA) solvent, and compared to 65% and no carbon capture scenarios. The calculated net plant efficiency on a HHV basis is between 29% and 41%. The gasification of 320tonne/h of carbonaceous fuel is required in order to obtain a process that is self-sufficient in hydrogen, power and heating requirements. For this system, co-feeding of petroleum coke is necessary in order to produce 983MW of power and meet the steam demand of the purification units that keep the heteroatom content in the flue gas below environmental regulatory limits while capturing 7.88 milliontonne of CO2 per year. The carbon emission rate is controlled in the simulation by varying the water–gas shift steam consumption and the lean amine circulation rate.

Lab-scale tests of different materials for the selection of suitable sorbents for CO2 capture with H2 production in IGCC processes

In this work two different types of materials, potassium carbonate promoted hydrotalcites and natural dolomites, have been investigated at laboratory scale to select the most promising sorbent to be used in a water gas shift membrane reactor (WGSMR). Sorbents were prepared by calcination in the temperature range of 500–800°C. Two experimental campaigns were carried out, the first one in a thermobalance under dynamic conditions (cooling down in a CO2/N2 stream) and the second one in a fixed bed reactor under isothermal conditions at 300°C. The influence of the preparation method, system pressure and water content in the feed gas on the performance of the sorbents has been investigated and the results obtained are described in this paper.As expected, K-doped hydrotalcite-based sorbents provided higher CO2 capture capacities than natural dolomites, which were found to require a deeper study to optimise their performance. For hydrotalcites, steam partial pressures, Mg/Al ratio and calcination temperature were found to play a crucial role in their CO2 capture capacities. Material Mg61-K2CO3 calcined at 600°C provided an initial CO2 capture capacity of 9mol/kg at PCO2=0.34bar and PH2O=4.55bar so this material was pre-selected to be used in the WGSMR system. Under those operating conditions formation of MgCO3 is suspected to occur so detailed studies are being carried out to confirm this hypothesis. The efficiency of thermal regeneration and depressurisation as regeneration method was explored at 1bar and 5bar in four sorption–desorption cycles and the combination of both approaches was found to provide the best results. Cycling behaviour and optimisation of the regeneration conditions are being carried out before going to the membrane reactor.

IGCC 합성가스 냉각기 GRC의 열유동 및 입자거동 특성에 대한 전산해석 연구

In the Shell coal gasification process, the syngas produced in a gasifier passes through a syngas cooler for steam production and temperature control for gas cleaning. Fly slag present in the syngas may cause major operational problems such as erosion, slagging, and corrosion, especially in the upper part of the syngas cooler (gas reversal chamber, GRC). This study investigates the flow, heat transfer and particle behaviors in the GRC for a 300 MWe IGCC process using computational fluid dynamics. Three operational loads of 100%, 75% and 50% were considered. The gas and particle flows directly impinged on the wall opposite to the syngas inlet, which may lead to erosion of the membrane wall. The heat transfer to the wall was mainly by convection which was larger on the side wall at the inlet level due to the expansion of the cross-section. In the evaporator below the GRC, the particles were concentrated more on the outer channels, which needs to be considered for alleviation of fouling and blockage.

Development of poly(amidoamine) dendrimer/poly(vinyl alcohol) hybrid membranes for CO2 separation

A novel hybrid membrane of poly(amidoamine) (PAMAM) dendrimer/cross-linked poly(vinyl alcohol) (PVA) was developed for the selective separation of CO2 from a mixture of CO2 and H2. PAMAM dendrimers were incorporated into a cross-linked PVA matrix to improve CO2 separation performance at elevated pressures. An organic metal compound di-isopropoxy-bis(triethanol aminato) titanium (Ti cross-linker) was selected as the PVA cross-linker. The characterization of PAMAM/cross-linked PVA hybrid membranes was conducted using Fourier transform infrared spectrometry/attenuated total reflectance (FTIR/ATR), wide-angle X-ray diffraction (WAXD), and small-angle X-ray scattering (SAXS) spectra. Cross-linking of PVA with Ti cross-linker was confirmed by FTIR/ATR spectra. WAXD spectra showed that the relative crystallinity of PAMAM/PVA hybrid membrane decreased greatly when compared with PVA film. SAXS results indicated that PAMAM and PVA are compatible in the PAMAM/PVA hybrid membrane. To improve the CO2 separation performance, the addition of amino acids such as glycine, proline, and 2,3-diaminopropionic acid was investigated. Separation performance was improved by addition of amino acids, such as proline. The resulting PAMAM/cross-linked PVA membrane with 5 wt.% proline addition demonstrated an high CO2/H2 selectivity of 38 with CO2 permeance of 1.9 × 10-12 (m3(STP)/(m2 s Pa)) at CO2 partial pressure of 560 kPa at 60 °C. The PAMAM dendrimer/cross-linked PVA membrane shows great potential for CO2 separation from H2 at elevated pressures that are typically found in IGCC processes.