Performance of an IGCC Plant with Carbon Capture and Coal-CO2

Article pubs.acs.org/IECR

Performance of an IGCC Plant with Carbon Capture and CoalCO2‑Slurry Feed: Impact of Coal Rank, Slurry Loading, and Syngas Cooling Technology Cristina Botero,*,† Randall P. Field,† Robert D. Brasington,† Howard J. Herzog,† and Ahmed F. Ghoniem† †

Massachusetts Institute of Technology, Cambridge, Massachusetts, United States ABSTRACT: The high heat capacity and latent enthalpy of vaporization of water lead to a low gasification efficiency in gasifiers fed with coal-water slurry. Liquid carbon dioxide, CO2(l), has been suggested as an alternative slurrying medium to improve the efficiency of low-rank coal gasification in integrated gasification combined cycle power plants with carbon capture. Steady-state process simulation is used in this work to confirm published findings and present a comprehensive assessment of the impact of the coal rank, gasifier cooling technology, and CO2 slurry loading uncertainty on the performance advantage of CO2 slurry-fed plants. A power generation efficiency improvement of up to 25% (5%-points) is predicted, which is shown to increase with decreasing coal rank and to be highest for full-quench gasifier cooling technology; the latter is a significant source of capital cost savings and is especially attractive when combined with CO2 slurry feed. Using CO2(l) instead of water slurry reduces the performance penalty of low-rank coal gasification by half, thus substantially improving the feedstock flexibility of the plant. With a single exception, the performance benefit of coal-CO2 slurry was found to be outside the uncertainty range of the slurry loading, which is still one of the key unknowns of this alternative feed system.

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This is especially problematic for a fluid with a high heat capacity and latent enthalpy of vaporization, such as water, since it leads to increased oxygen consumption and reduced gasifier efficiency. These result, in turn, in a low net power generation efficiency in the IGCC plant. Furthermore, singlestage, slurry-fed entrained-flow gasifiers are considered uneconomical for the gasification of low-rank coals because of their high moisture content, which does not contribute to the transport properties of the slurry but adds to the thermal burden of water.6 Dry-fed gasifiers have a higher efficiency, and hence better feedstock flexibility, than single-stage, slurry-fed gasifiers. Typical cold gas efficiencies are in the range 69−77% for the case of single-stage slurry feed and 78−83% for dry feed, on a higher heating value (HHV) basis.7 A resulting net IGCC efficiency benefit of an estimated 3%-points has been predicted for dry-fed systems in plants operating on bituminous coal without CO2 capture.8 On the other hand, dry feeding systems based on lock hoppers are very costly. The coal preparation and feed system for such gasifiers has been estimated to cost about three times that of the corresponding equipment for a slurry-fed design of equal electrical output.8 In addition, dry feeding systems are operationally more complex and become increasingly inefficient at pressures beyond 30−40 bar, since the amount of transport gas becomes very high.6 The possibility of using CO2 as a liquid carrier for slurry-fed gasifiers has been suggested in the past as a means of achieving the gasification efficiency of dry feeding systems at the low cost,

INTRODUCTION Integrated Gasification Combined Cycle (IGCC) plants are attractive alternatives to Pulverized Coal (PC) plants for CO2lean power generation from carbonaceous fuels such as coal. The integration of a gasifier with a combined gas turbine/steam turbine arrangement has the potential of a much smaller environmental footprint, including an order of magnitude lower pollutant emissions and lower carbon dioxide capture costs.1 Despite its environmental advantages, broad commercialscale deployment of IGCC plants has been hampered by the lack of stringent greenhouse gas emissions regulations worldwide as well as the high capital cost and lower availability record of this technology.1−4 While several commercial gasification technologies exist and many more are under development, pressurized entrained-flow gasifiers are most often selected for IGCC plants.5 This type of reactor allows for the production of large flows of tar-free gas in a relatively compact vessel; high temperatures above 1400 °C, high pressures above 30 bar, and nearly complete carbon conversion are typical characteristics of this design. Entrained-flow gasifiers can be broadly classified as dry-fed or slurry-fed. Commercial dry feeding systems use lock-hoppers to transport coal in its dense phase into a pressurized environment with the help of an inert gas, typically nitrogen. Slurry feeding systems, on the other hand, use a liquid to produce a suspension, or slurry, which can be pumped to the required pressure, and water is typically used as a slurrying medium. Slurry feed not only is the simplest and cheapest method of feeding a solid material like coal into a pressurized vessel but also has the advantage that very high pressures can be achieved.6 However, only a fraction of the slurry water is required for the gasification reaction. The majority of the water constitutes a thermal load, since it must be vaporized and heated to the high temperatures inside the gasifier. © XXXX American Chemical Society

Received: July 8, 2012 Revised: August 22, 2012 Accepted: August 23, 2012

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dx.doi.org/10.1021/ie3018093 | Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

Industrial & Engineering Chemistry Research

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reliability, and feedstock flexibility of slurry feeding.4,6,9 The thermophysical properties of liquid CO2 appear to have advantages over those of water for this kind of reactor. Until very recently, however, investigation of the coal-CO2 slurry concept was limited to only two public studies, both conducted as early as 1986 for the Electric Power Research Institute (EPRI). The first focused on the rheology of suspensions of lignite in liquid CO2,10 while the latter looked at the thermoeconomics of a lignite-CO2 slurry feed system with slurry skimming, rather than direct slurry injection, in an IGCC plant separating CO2 for the sole purpose of preparing the slurry;11 the economics of the process were found to be unfavorable relative to those of dense-phase feeding systems. While other earlier studies on coal-CO2 slurry exist,12−15 all of them focused on its potential application for pipeline transportation of coal, concluding that the economics would be favorable if there was a market for CO2 at the end of the pipeline. Carbon dioxide has also attracted interest beyond the feed system of the gasifier. The injection of gaseous CO2 has been studied in the past as a means of enhancing the reactivity and the gasification chemistry of biomass and coal.16,17 With global warming now widely accepted as a reality within the scientific community, Carbon Capture and Storage (CCS) has been identified as a key technology for significantly reducing CO2 emissions while allowing fossil fuels such as coal to meet a significant fraction of the world’s energy needs.18 Interest in coal-CO2 slurry for gasification-based plants has since been revived, since its economics are favored by the availability of CO2(l) in plants with CCS. While using liquid CO2 instead of water in the feeding system is expected to improve the gasifier thermodynamics, it is the overall effect on the net plant efficiency that determines the real performance benefit of this concept. The energy required for recapturing and recompressing the CO2(l) recirculated for slurry preparation must be quantified, calling for system-level analyses. Dooher et al. used an Aspen Plus flowsheet model to simulate an IGCC plant gasifying sub-bituminous coal-CO2 slurry; a net plant efficiency increase of 9% (2.8%-points) is reported, relative to a plant with coal-water slurry feed, as well as 7%-points higher cold gas efficiency and a 13% lower oxygen-to-coal requirement.19 Solids loadings of 48% and 55% were assumed in their analyses of water slurry and CO2 slurry, respectively, based on a combination of rheological testing and modeling using the Dooher Institute Slurry Model (DISM), a physics-based tool developed by the same research group.20,21 The Aspen Plus flowsheet model used for this assessment was provided by EPRI. The reactor is a generic single-stage entrained flow gasifier operating at 1,260 °C, 50 bar, and over 90% conversion; combined radiant-quench gas cooling and integration of the gas turbine and air separation unit were assumed in this work. The significant performance improvement reported by Dooher et al. for a plant with CO2 slurry feed reveals its potential and the need to develop a more fundamental understanding of the differences between water and liquid carbon dioxide as slurrying media and how these may affect individual process units for coals of different rank. Furthermore, clearly stated and realistic modeling assumptions are key for allowing the assessment and development of this technology. The present study is a rigorous evaluation of the technical characteristics and trade-offs associated with coal-CO2 slurry

feed. Detailed insight into the properties of liquid CO2 as a potential slurrying medium is provided, followed by a study of the thermodynamics of the process at the system level using flowsheet modeling and simulation. An IGCC plant with CCS is used as an application; the net IGCC efficiency is identified as the figure of merit for quantifying overall performance and comparing it with that of a state-of-the-art coal-water slurry-fed system. The Aspen Plus flowsheet model used for the analysis is described in detail and has been made available online by the authors.22 While this work confirms the conclusions by Dooher et al. for sub-bituminous coal gasification in a radiant-quench cooled reactor with a realistic CO2 slurry loading, it focuses for the first time on the impact of the coal rank and syngas cooling technology on CO2 slurry-fed plant performance and compares each case with the respective state-of-the-art system using a common modeling framework. Furthermore, the uncertainty in the maximum achievable CO2 slurry loading and its effect on plant performance are quantified here; this is one of the main unknowns of coal-CO2 slurry feed and had been assigned a fixed value in previously published analyses. The economics of the process are currently being studied and will be presented separately.

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THERMODYNAMICS OF COAL SLURRY GASIFICATION The main gasification reactions occurring at high temperatures are the steam-gasification and CO2-gasification (Boudouard) reactions. These yield a mixture of H2 and CO known as synthesis gas, or syngas, and are given by C(s) + H 2O ⇌ CO + H 2 C(s) + CO2 ⇌ 2CO

+131 MJ/kmol

+ 172 MJ/kmol

(1) (2)

6

respectively; the heats of reaction are given above. Oxygen is required in the gasifier for oxidation reactions such as6 C(s) +

1 O2 → CO 2

CO +

1 O2 → CO2 2

−283 MJ/kmol

H2 +

1 O2 → H 2O 2

−242 MJ/kmol

−111 MJ/kmol

(3)

(4)

(5)

These exothermic reactions enable the reactor to operate near autothermal conditions by providing the energy necessary a) to heat up the reactants, b) for the endothermic gasification reactions, and c) to make up for any heat losses to the environment. Apart from the char gasification and oxidation reactions, the water-gas shift (WGS) reaction also plays an important role inside the gasifier6 CO + H 2O ⇌ CO2 + H 2

−41 MJ/kmol

(6)

The gasifier efficiency is typically defined as the fraction of the feedstock’s chemical energy that is retained in the cooled gaseous product. This performance measure is termed the Cold Gas Efficiency (CGE). Combustion reactions not only increase the gasifier oxygen demand but are also a major source of CGE loss: feedstock is burnt for the purpose of providing heat, and B



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most importantly, a larger need for the supply of oxygen. Because oxygen production with current cryogenic technology consumes electricity, recovery of the thermal energy contained in the gasifier products cannot make up for this investment. The previous discussion is true for all types of coal, but the situation is especially critical for low-rank coals, such as lignite, due to their high moisture content. This explains why the more expensive dry-fed gasifiers, which require coal drying, are preferred for low-rank coals. Liquid Carbon Dioxide as Slurrying Medium. The properties of CO2(l) are compared to those of H2O in Table 1

the resulting combustion products are of negligible heating value. It is important to distinguish between the gasifier efficiency and the overall IGCC plant efficiency. For a given syngas output, high gasifier efficiencies lead to a reduction in both the solid fuel consumption and the power consumption of the Air Separation Unit (ASU) delivering O2 to the gasifier. Both of these directly benefit the net efficiency of the IGCC plant, so achieving high cold gas efficiencies is key for maximizing the overall IGCC plant performance. Gasifier efficiency is, however, not a direct measure of plant performance. The latter is affected by multiple process variables including carbon conversion in the gasifier, steam extraction for the water-gas shift reactor, process integration scheme, etc. In addition to improving the plant performance, lower O2 consumption can significantly reduce the capital costs of the plant. The production and supply of oxygen is not only very energy consuming but also capital intensive. The ASU alone accounts for about 15% of the total capital cost of an IGCC plant based on a single-stage, slurry-fed gasifier.8 Water as Slurrying Medium. The total flow as well as the properties of the feedstock liquid carrier are key determinants of gasifier performance. Slurry loading is used to quantify the percentage of coal in the mixture of coal and water or CO2(l). It is defined as the weight percent (%-wt.) of moisture-free coal and is also referred to as the slurry’s dry solids content. Bituminous coal-water slurry typically has a dry solids loading of about 65%, i.e. about 35%-wt. of the feed stream is water. This amount is in excess of what is required for the steam gasification reactions. A detailed calculation of the stoichiometric water requirement inside a coal gasifier is outside the scope of the present work. A good indication, however, is the amount of steam used in dry-fed entrained flow gasifiers such as Shell’s. According to published estimates, a slurry water content of less than 9%-wt. would be sufficient for the steam gasification reaction of bituminous coal.8 Feeding excess water into the gasifier aggravates the thermal burden it intrinsically represents. This burden can be observed in Figure 1, which shows that an estimated 5,600 kJ are required to heat up and vaporize each kilogram of H2O inside the reactor. Slurrying the feed with water hence comes at the expense of a higher feedstock consumption for a given syngas output, and,

Table 1. Properties of Pure H2O and CO223−27 at Representative Slurry and Gasifier Conditions8 H2O critical temperature critical pressure Slurry (25 °C, 72 bar) liquid viscosity liquid density Gasifiera (55 bar) surface tension heat capacity of liquid vaporization enthalpy heat capacity of vapor

CO2

374 °C 221 bar

31 °C 74 bar

0.89 cP 1,000 kg/m3

0.06 cP 752 kg/m3

47 · 103 N/m 4.6 kJ/(kg K) 1,605 kJ/kg 3.6 kJ/(kg K)

1.4 · 103 N/m 4.2 kJ/(kg K) 146 kJ/kg 2.4 kJ/(kg K)

a

Properties at average liquid and vapor phase temperatures of 150 and 840 °C for H2O and 18 and 710 °C for CO2, respectively. Isentropic expansion of CO2 through slurry injector assumed.

at representative conditions. The attractiveness of CO2(l) as a liquid carrier in coal slurries for gasification-based plants with CCS arises as a combination of its availability and the merits of its thermophysical properties. Liquid Viscosity. Because CO2(l) has an order of magnitude lower viscosity than H2O, CO2 slurry is expected to have a lower viscosity than water slurry for the same coal loading and otherwise identical conditions. Experimental investigations have reported achievable dry solids loadings of up to 78%-wt. for surface-dried lignite in liquid CO2.10 More recent studies have, nevertheless, cast doubts on these findings, concluding that loadings of about 70% seem more realistic.20 The low viscosity of coal-CO2 slurry is also expected to benefit the slurry atomization process directly through the Reynolds’ number and indirectly through the critical Weber number for droplet breakup.20 Enthalpy of Vaporization and Heat Capacity. The enthalpy of vaporization of CO2(l) is at least 1 order of magnitude lower than that of H2O, which results in a significant reduction of the energy required to vaporize the slurry inside the gasifier. Additionally, the amount of sensible heat that must be provided to the subcooled liquid is negligible, since the CO2 is either very close to or beyond the saturated liquid line when exposed to gasifier pressure. This is illustrated in Figure 2, where the extreme cases of isentropic and isothermal expansion of the slurry through the injector nozzle are illustrated; in reality, a polytropic change of state is expected. Flash vaporization of the slurry occurs when it enters the gasifier since the pressure inside the reactor is below the saturation value for CO2 at that temperature. A maximum of 1,900 kJ are necessary to heat up every kg of pure CO2 to the gasifier temperature; this is about a third of the energy requirement of pure H2O under identical conditions.

Figure 1. Pressure-enthalpy diagram of pure H2O. State points for the transition from subcooled liquid to superheated vapor at representative gasifier conditions8 are shown. C



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self-sustaining agglomerate shell.28 It is precisely due to this agglomeration that extremely fine grinding of coal is not considered to be beneficial for coal-water slurries, unless the atomizer is capable of producing droplets of about the same size as the coal particles.29 The effective particle size distribution of coal agglomerates after atomization of the slurry is believed to be determined by the size distribution of the droplets rather than by the initial coal particle size.30 The low surface tension of CO2 hence holds the potential of offering better atomization and agglomeration characteristics for coal slurry. This could lead to a reduction in the cost and complexity of the slurry injector. Liquid Density. The density of the slurry liquid carrier is especially important for sizing of the feed preparation and transportation equipment. CO2(l) is about 25% less dense than H2O at slurry feed pressure, which implies that slurry vessels must be sized an estimated 33% larger in order to accommodate the same mass of slurry. This raises the specific capital cost of the feedstock preparation equipment. Achieving water-like density would require cooling the CO2(l) stream below the freezing point of water, which is likely to be prohibitively expensive.

Figure 2. Pressure-enthalpy diagram of pure CO2. State points for the transition from subcooled liquid to superheated vapor at typical gasifier conditions8 are shown. Both isentropic (−) and isothermal (---) expansion of the slurry during injection to the gasifier are illustrated.

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This can be attributed not only to the low vaporization enthalpy of CO2 but also to the low heat capacity of its vapor phase. Surface Tension. Surface tension forces at the liquid interface play an important role in both the slurry atomization process and the agglomeration behavior of coal particles at the injector outlet. The surface tension of CO2(l) is over an order of magnitude lower than that of water. It is thus expected that atomizing CO2 slurry will yield a smaller mean droplet diameter than for water slurry. Surface tension affects the Weber number directly, which determines the droplet size distribution. In addition, capillary forces between particles are an inverse function of the surface tension. These forces become important when the slurry liquid carrier begins evaporating inside the gasifier and are thought to play a key role in the formation of a

PROCESS DESCRIPTION AND METHODOLOGY The coal-CO2 slurry feed concept applied to an IGCC plant is illustrated in Figure 3. It corresponds to the arrangement proposed by Dooher et al.,19 in which the slurry transport medium is directly injected into the gasifier with the solid feedstock and O2. The hot syngas produced in the gasifier is cooled down and cleaned of particulates and other minor species. Its CO content is subsequently converted to CO2 through reaction with H2O in a WGS reactor. Next, CO2 and H2S are separated from the gas in an Acid Gas Removal (AGR) unit. The decarbonized syngas is diluted with N2 from the ASU before being combusted in a gas turbine (GT), which produces most of the power in the IGCC plant. The gas turbine exhaust is used to produce steam in a Heat Recovery Steam Generator

Figure 3. Schematic of IGCC plant with CCS and a) coal-water slurry or b) coal-CO2 slurry feed. Slurry is directly injected to the gasifier. Process integration is not shown. D



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simulations were carried out for an upper, a nominal, and a lower loading, as indicated above. Low-rank coals were studied in addition to bituminous coal because they are expected to benefit the most from a CO2 slurry feed. Furthermore, low-rank coal is very appealing due to its low cost, availability, and, in the case of Powder River Basin (PRB) coal, low sulfur content. Finally, full-quench cooling was considered in addition to combined radiant-quench (rad-quench) syngas cooling. The radiant cooler has been reported to represent as much as 10% of the total IGCC capital cost.31 Full-quench cooling is hence attractive as a cost-effective method for simultaneously cooling and adding the moisture required by the downstream WGS reactor in plants with CCS. One of the eighteen CO2 slurry cases considered has been studied in the past under similar conditions, namely subbituminous coal with radiant-quench cooling and a nominal slurry loading;19 our results will be compared with those from that work. None of the other CO2 slurry cases presented have been assessed in previous publications, including lignite-CO2 slurry, whose past study is limited to a system with slurry skimming rather than direct slurry injection.11 Coal Moisture. Water slurry feeding of high-moisture coal would result in an extremely high oxygen consumption in a single-stage gasifier. In the case of CO2 slurry feed, however, the thermal burden of slurry water has been eliminated so more moisture can be tolerated. The possibility of feeding as-received (ar) low-rank coal to the gasifier is considered to be one of the merits of this feeding system. Preparation of low-rank coal slurry without coal drying has been carried out successfully in the past for gasification in a two-stage gasifier.7,8 In this study, as-received coal moisture has been assumed for all cases. Retaining the coal moisture not only simplifies the feedstock preparation system but may also prove beneficial in the case of CO2 slurry, where coal moisture is the only source of H2O entering the gasifier. The moisture helps increase the content of H2 in the syngas and possibly also carbon conversion; the intrinsic char gasification rate in pure CO2 has been observed to be slower than in pure H2O.32,33 The kinetics of coal-CO2 slurry gasification at pressurized, entrained-flow gasifier conditions are a topic of current research.34 Maximum Solids Loading. The maximum viscosity allowable for slurry transportation and pumping is typically around 1000 cP with current technology.35,36 To comply with this, the slurry must contain a minimum fraction of slurrying medium, XSM,

(HRSG) and subsequently released to the atmosphere. Steam is delivered to process units which require it, such as the WGS reactor, and to a Steam Turbine (ST), which produces additional electric power in the plant. The CO2 captured in the AGR unit is brought to a high pressure of typically above 100 bar through a combination of intercooled compression and pumping to supercritical pressures. If the plant has a CO2 slurry feed system, a fraction of the dense-phase CO2 is recirculated back to the slurry preparation unit. For plants operating with water slurry, the entire CO2 stream is sent for storage. The CO2 used for the slurry will have liquid-like density and will be close to its critical point; the exact conditions of the recirculated stream will determine whether it is in its liquid or supercritical phase. The term liquid carbon dioxide, or CO2(l), is used here to denote dense-phase carbon dioxide at a pressure close to or above the critical pressure and a temperature below the critical point. Coal-CO2 Slurry Preparation Equipment. The CO2 slurry preparation and feeding system performance, reliability, and capital costs are key determinants of the attractiveness of this feeding method. While the focus of the present work is on the thermodynamics and plant performance only, research is currently also being conducted on the design and economics of the slurry preparation and feeding system. A semicontinuous method for the preparation of coal-CO2 slurry was successfully tested by Arthur D. Little in the 1980s at both lab and pilot scales.10 In this method, coal is initially charged to a pressure vessel at atmospheric conditions, and gaseous CO2 is then injected until the vessel reaches saturation pressure. This is followed by the injection of liquid CO2, which brings the mixture to final pressure. A mixer is activated once the desired liquid level is reached and the homogeneous slurry mixture is fed to the slurry pump. The semicontinuous process described above resembles a lock hopper similar to that used in dry-fed gasifiers. This undermines the simplicity of the slurry feeding system, which is one of the main motivations for using CO2 slurry feed in the first place. Alternative approaches are currently being studied. The results are outside the scope of this publication and will be presented separately. Cases Studied. A total of 24 different cases were studied in this work by accounting for different coal types, slurrying media, solids loading in the CO2 slurry, and syngas cooling method. These are listed in Table 2. Table 2. Cases Studied slurrying medium H2O(l)

CO2(l)

slurry loading nominal

nominal upper limit lower limit

syngas cooling

coal rank

radiant-quench quench-only

bituminous sub-bituminous lignite

radiant-quench quench-only

bituminous sub-bituminous lignite

XSM =

ṁ SM ṁcoal + ṁ SM

(7)

which provides the lubricating effect required for slurry fluidity. Here, ṁ coal and ṁ SM are the mass flows of as-received coal and slurrying medium (e.g., water or liquid CO2), respectively. The slurrying medium does not include coal moisture. The slurrying medium content requirement limits the maximum loading of dry solids in the slurry since inherent moisture does not contribute to the fluidity of the suspension; this is especially problematic for high-moisture coal. The maximum slurry solids loading must be determined experimentally and it is feedstock as well as slurrying mediumspecific. Solids loading is defined as

The study of coal-water slurry in parallel with coal-CO2 slurry allows for a fair comparison between both cases; the relative performance between the two feeding systems is considered to be the figure of merit. Because the maximum achievable solids loading for CO2 slurry is still uncertain, E



Xsol =

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ṁcoal (1 − X m) ṁcoal + ṁ SM

described in detail and made available online by the authors.22 The model was modified to accommodate CO2(l) recirculation for the feed system. The key assumptions and process variables of the IGCC plants simulated in this study are summarized in Table 4 and are briefly described in what follows. For further details, the reader is referred to the original contribution.

(8)

where Xm is the mass fraction of moisture in the coal, on a wet basis. Measurements by Atesok et al.36 confirm that the dry solids loading in coal-water slurry varies strongly with coal rank. However, for a given average particle size, the minimum XSM remains more or less constant for all coals. For 50 μm particles, for example, Atesok’s measurements show that the slurrying medium content is within the narrow range 34−37% for coals ranging from bituminous to lignite and moisture contents from 4% to 16%. As a first order approximation, thus, the minimum XSM can be considered independent of the rank-specific surface properties of the coal. Based on the observations above, a constant value of XSM = 29% was used for coal-water slurry in this study for all coals; this value corresponds to the 63% solids loading reported by NETL for bituminous coal-water slurry in their IGCC plant assessment.8 The solids loading of coal-water slurry calculated from XSM = 29% and the feedstock moisture is presented in Table 3 for all feedstocks studied. The estimated values agree

Table 4. Key Assumptions for IGCC Plant Modeling parameter Feedstock coal type

coal flow coal composition feeding system solids loading Gasifier type stages temperature pressure oxidant oxidant supply carbon conversion heat losses syngas cooling

Table 3. Dry Solids Loading (wt.-%) in Water Slurry and CO2 Slurry for All Coals Studieda bituminous (Xm = 11%)

sub-bituminous (Xm = 28%)

lignite (Xm = 32%)

XSM water-slurry

29%

63%

51%

48%

CO2-slurry lower limit upper limit

20% 29% 12%

71% 63% 78%

58% 51% 63%

54% 48% 59%

a

WGS Reactor H2O:CO AGR Unit solvent H2S removal CO2 capture Power Island steam turbine condenser pressure syngas diluent gas turbine fuel gas HHV ASU integration CO2 compression intercooler temperature compressor pressure pump pressure

As-received coal moisture has been assumed.

well with those observed in the Polk IGCC Power Station for bituminous coal slurry as well as those reported by ConocoPhillips for bituminous, PRB, and lignite coals.8,37−39 For liquid CO2 slurry, the minimum slurrying medium content was assumed to be a nominal 20% for all coals. This corresponds to a solids content of 71% for lignite dried to 11% moisture, which was the feedstock used by Peirson et al. in their experimental measurements of coal-CO2 slurries;10 it is considered realistic based on recent assessments.20,40 The corresponding dry solids loading of the different as-received coals studied in liquid CO2 can also be found in Table 3. The upper limit for the CO2 slurry loading assumes that the 78% maximum solids reported by Peirson et al. are achievable. The conservative case assumes that CO2(l) slurry can carry only as much solids as H2O slurry. Tools. Steady-state process simulation using Aspen Plus41 was applied to assess the overall plant performance and quantify the advantages and disadvantages of the coal-CO2 slurry feed system, relative to state-of-the-art water-slurry feed, for the case of an IGCC plant. The characteristics of the plant correspond to a large extent to Case 2 in NETL’s thorough assessment of commercial gasification technologies for IGCC.8 It is an IGCC plant with CO2 capture and a single-stage, slurry-fed gasifier resembling GE Energy technology. The Aspen Plus flowsheet model used to simulate the IGCC plant described above was developed by Field et al.; it has been

value bituminous sub-bituminous lignite 5,450 tonne/day as-received (see Table 5) coal slurry at 72 bar see Table 3 entrained-flow 1 1,370 °C 56 bar 95%-vol. O2 at 68 bar ASU: 1,370 kJel/kg 98% 1% of HHV radiant-quench (ΔTeq. = −200 K) full-quench (ΔTeq. = −10 K) 2:1 Selexol 99.6% 90% (overall) 12.4 MPa/538/538 51 mmHg N2/H2O advanced F-class 4.8 MJ/Nm3 none 30 °C 80 bar 153 bar

Feedstock and Oxidant Feed. Pulverized coal with its asreceived moisture content is mixed with the slurrying medium to prepare slurry with the specified solids loading. The slurry feedstock is pumped and fed into the gasifier, together with O2 from the ASU. The flow of O2 is controlled in order to achieve a gasifier temperature of 1,370 °C Gasification and Syngas Cooling. The syngas produced in the gasifier is made up primarily of CO, H2, CO2, and H2O, plus minor concentrations of other species such as HCl, NH3, H2S, and COS. The gas is cooled either by a combination of radiant and quench cooling or through quench cooling alone. In the former case, the gas is first brought to a temperature of about 600 °C in the radiant cooler, which raises intermediate pressure steam for the bottoming cycle with the recovered heat. In both cases, the quench cooler uses liquid water to cool down the gas F



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Acid Gas Removal. CO2 and H2S are separated from the synthesis gas in the AGR unit. The physical solvent Selexol is used for this purpose. Note that in order to achieve an overall CO2 capture level of 90%, more than 90% of this gas must be separated locally in the Selexol unit; unconverted CO is oxidized to CO2 in the gas turbine and released to the atmosphere, thus reducing the overall capture level. The two-stage Selexol process used for acid gas removal was modeled rigorously in Aspen Plus. The H2S-loaded solvent from the first absorption stage is regenerated thermally in a stripper; the CO2-loaded solvent from the second stage is regenerated through pressure drop in multiple subsequent flash drums at high pressure (HP), intermediate pressure (IP), and low pressure (LP). High pressure CO2 is compressed and recycled to the CO2 absorber in order to minimize the amount of H2 losses in the AGR unit. CO2 from the IP and LP drums is delivered to the CO2 compressor and brought to the conditions required for transportation to the storage site. The Selexol unit consumes thermal and electrical energy. Steam is required for solvent regeneration in the stripper, whereas electricity is required to drive the solvent recirculation pumps and chiller. The later is used in order to increase the CO2 and H2S solubility in the absorbers. Sulfur Recovery (Claus Unit). H2S is separated from the syngas in the AGR process and delivered to the Claus unit, where it is converted to elemental sulfur, which can be sold as a byproduct. The reactions taking place in the Claus process can be represented by the overall expression

Table 5. Coal Composition (Dry Basis) rank

bituminous8

seam

Illinois # 6 (Herrin)

moisture (ar) ash volatile matter sulfur fixed carbon LHV, kJ/kg

11.12 10.91 36.55 2.82 49.72 29,544

moisture (ar) carbon hydrogen nitrogen chlorine sulfur ash oxygen

11.12 71.72 5.06 1.41 0.33 2.82 10.91 7.75

sub-bituminous47

Wyodak-Anderson (PRB) proximate analyses (weight %) 28.09 8.77 44.73 0.63 45.87 26,176 ultimate analyses (weight %) 28.09 68.43 4.88 1.02 0.03 0.63 8.77 16.24

lignite Beulah-Zap

32.24 9.72 44.94 0.80 44.54 24,625 32.24 65.85 4.36 1.04 0.04 0.80 9.72 18.19

through evaporative cooling, bringing it to saturation conditions; no steam is generated in the process. Most of the homogeneous gasification reactions inside an entrained-flow gasifier can be assumed to reach equilibrium at the gasifier temperature.42 The WGS reaction is an exception, though, since it is favored at low temperatures and proceeds until the gas is quenched. The departure from equilibrium of the WGS reaction was modeled by using a temperature approach to equilibrium in Aspen Plus. This is a simple method which allows for the use of equilibrium constants to estimate product composition in cases where equilibrium is not achieved. The equilibrium constant is calculated at a temperature which deviates from the actual temperature by a given value ΔTeq.. In the gasifier, the exact value of this approach depends on the cooling rate and was chosen for each of the syngas cooling configurations through comparison of the syngas composition with experimental data for a gasifier of similar characteristics.43 Gas Scrubbing. A water wash is used to remove chlorides and particulates from the gas in a real IGCC plant. The model represents only the removal of the chlorides, since all particulates are assumed to leave with the slag. The temperature of the gas drops by a few Kelvin in the process. Water-Gas Shift Reactor. A 2-stage catalytic reactor is used to convert most of the CO content of the syngas into CO2 and more H2 according to the water-gas shift reaction 6. The H2O:CO molar ratio is adjusted to 2:1 prior to the first reactor; steam extraction from the power plant’s bottoming cycle is used for this purpose, where necessary, resulting in a reduction of the steam turbine power output. The humidity content of the gas before the shift determines whether steam extraction must be carried out or not. WGS reactors are required when high CO2 capture rates are desired. For chemical and fuel synthesis processes, the need for this unit depends on the syngas composition requirements. The product of the WGS reactor consists primarily of H2, CO2, and H2O. It then passes through a series of heat exchangers and is cooled down until a temperature of about 40 °C is reached, as required by the acid gas removal unit. Steam for the steam turbine is generated in the process.

H 2S +

1 O2 ⇌ H 2O + S 2

(9)

which is exothermic and thus makes this process area a net exporter of steam. Power Island. The power island consists of syngas expander, one or more gas turbines, and a Rankine cycle. Syngas Expander. Decarbonized syngas from the AGR unit is reheated and expanded to about 30 bar before being delivered to one or more gas turbines, which were modeled as a single gas turbine for simplicity. The gasifier studied produces gas at a pressure higher than that required by the gas turbine combustor and the use of an expander thus allows for additional power production in the plant. Gas Turbine. The expanded syngas is diluted with N2 from the ASU, to the extent required to achieve the heating value indicated in Table 4, before it is fed to the gas turbine combustor. Dilution is necessary in diffusion-flame gas turbines, such as those burning H2, in order to avoid excessively high peak temperatures and keep NOx emissions at acceptable levels. Steam extracted from the bottoming cycle of the power plant is used as diluent if the ASU cannot provide enough N2. Since this reduces the power generated in the steam turbine, N2 dilution is preferred, wherever possible. Bottoming Cycle. The energy contained in the gas turbine exhaust, together with that available from other streams, is used for additional power generation in a bottoming Rankine cycle. A Heat Recovery Steam Generator produces steam for the steam turbine generator. Steam is also provided to process units that require it, such as the WGS reactor. Air Separation Unit. The ASU uses air to produce the oxygen required inside the gasifier. Nitrogen is delivered as G



Article

less oxygen per unit feedstock HHV than a water slurry-fed one. This reduces not only the auxiliary power consumption of the air separation unit but also most importantly its size and thus capital cost. The 15% lower specific oxygen consumption observed for sub-bitumonus coal is in close agreement with the 13% reduction reported by Dooher et al. for a similar feedstock.19 Notice that oxygen consumption does not decrease proportionally to the large reduction in the heat capacity and enthalpy of vaporization of CO2, relative to H2O, see Table 1. This can be attributed to the fact that the CO2 gasification reaction 2, which plays an increasingly important role when CO2 slurry feed is used, is about 30% more endothermic than the H2O gasification reaction 1. This difference is significant since the gasification reactions dominate the energy requirement of the gasifier. While chemical equilibrium was assumed in this work, the actual contribution of the more endothermic CO 2 gasification reaction to the overall carbon conversion is determined by the heterogeneous reaction kinetics; this is a topic of current research.34 Cold Gas Efficiency. The gasifier cold gas efficiency is presented in Figure 5 for all coals. This performance measure is

syngas diluent but also for the Selexol unit. Modeling of the ASU focuses on the compression power requirement; rigorous modeling of the cryogenic process was not carried out. CO2 Compression. A multiple-stage intercooled compression process brings CO2 separated in the Selexol unit to 80 bar, which is the pressure required for the formation of a dense phase at the intercooler temperature of 30 °C. The CO2(l) has a liquid-like density and is at a subcritical temperature, but its pressure is supercritical. It is subsequently pumped to the final pressure required for transportation to the storage site. A fraction of the CO2(l) flow is recirculated if the plant operates with coal-CO2 slurry feed. Heat Integration. Heat integration is a trade-off between capital costs and plant efficiency. In the IGCC model used, the heat integration degree is fairly typical. Hot water and steam for the power island are produced from the heat available in the syngas at different temperature levels. Heat from the radiant syngas cooler and from the coolers prior to the shift reactors are typical examples of such. Heat from lower temperature sources, such as the CO2 compressor intercoolers, is not recovered but rejected to the cooling water.

■

RESULTS Results obtained from the system simulations are presented and discussed in what follows. A unit feedstock energy basis has been used to normalize the results, where relevant. Results for radiant-quench and full-quench cooling are presented side-toside only if they are different. Oxygen Consumption. Figure 4 presents the specific oxygen consumption for all coals studied. Oxygen consumption

Figure 5. Cold gas efficiency of gasifier for coal-water slurry (□) and coal-CO2 slurry (■) feed. The HHV of the feedstock and syngas have been used for the calculation.

directly linked to the oxygen consumption and similar trends are thus observed; oxygen is required for the combustion reactions which constitute the main source of cold gas efficiency loss. The cold gas efficiency of 82% observed for a gasifier operating with bituminous coal and CO2 slurry feed is within the range of 78−83% typical for dry-fed systems gasifying a similar coal6 and is far superior to the 75% resulting for conventional water-slurry feed. Overall, operation with CO2 slurry leads to a significant increase in the cold gas efficiency, which ranges from an estimated 7%-points for bituminous coal to more than 11%-points for sub-bituminous coal and ligniteslurry. The 11%-point increase observed for sub-bituminous coal is superior to the 7%-points reported by Dooher et al. for a similar feedstock. This deviation is likely to be the result of different assumptions regarding gasifier operation, such as conversion, temperature, or water-gas shift equilibrium, which are not reported in Dooher’s original work.19 Gasifier cold gas efficiency decreases steadily with the coal rank. Note, however, that gasification of lignite-CO2 slurry results in a cold gas efficiency of 72%, which is almost as high as the 75% of bituminous coal-water slurry gasification. In other

Figure 4. Specific oxygen consumption for a gasifier with coal-water slurry (□) and coal-CO2 slurry (■) feed. The coal HHV has been used to normalize the results.

is lowest for bituminous coal-CO2 slurry, which is the case with the highest solids loading, see Table 3. The high loading is as a result of the low moisture in bituminous coal and of the use of CO2(l) as slurrying medium. The results agrees well with the expectations: the higher the solids loading of the slurry entering the gasifier, the lower its water content and hence the lower the flow of oxygen required for providing heat to vaporize moisture through reactions 3−5. Accordingly, lignite coal-water slurry, which has the lowest solids loading, has the highest demand for oxygen of all cases studied. The effect of substituting water for liquid CO2 is very significant: on average, a CO2 slurry-fed gasifier consumes 15% H



Article

Figure 6. Molar ratio of hydrogen to carbon monoxide in raw syngas leaving the gasifier cooler for coal-water slurry (□) and coal-CO2 slurry (■) feed.

Figure 7. Specific shift steam requirement for plants with coal-water slurry (□) and coal-CO2(l) slurry (■) feed. The coal HHV has been used to normalize the results. Missing data points indicate that enough H2O is contained in the gas and shift steam extraction is not required.

words, if water is substituted by CO2(l) as slurrying medium, lignite coal can be gasified nearly as efficiently as bituminous coal in water slurry. A higher cold gas efficiency signifies that more of the coal’s energy content is retained in the synthesis gas. This is especially relevant for low-rank coal gasification, which typically requires large equipment and multiple process trains as a result of its low energy efficiency. The development of gasifiers with favorable economics for the gasification of low-rank coal has been identified as one of the key areas of future research for gasification-based plants.44,45 Gas Composition and Shift Steam Requirements. Figure 6 shows the H2:CO ratio in the raw syngas leaving the gasifier cooler for all cases studied. For a given feedstock and slurrying medium, a gasifier with radiant-quench cooling

produces raw syngas with a higher H2:CO ratio than the corresponding full-quench option. This can be attributed to its slower cooling rate, which was modeled through a larger temperature approach to equilibrium, see Table 4, and allows for the water-gas shift reaction 6 to proceed further before its rate freezes at lower temperatures. The figure shows that the CO2 gasification reaction 2 becomes increasingly important when the concentration of carbon dioxide in the feed increases: raw syngas produced in the CO2 slurry-fed gasifier has a H2:CO ratio which is as low as half that of its water slurry-fed counterpart. In general, the lower the total (slurrying medium plus coal moisture) amount of water in the feed, the lower the H2:CO ratio of the syngas. The high CO content of the syngas produced from CO2 slurry-fed gasifiers leads to a higher shift steam requirement for I



Article

Figure 8. Evolution of material streamflow and composition for the exemplary case of lignite-water slurry (left-hand side bar) and lignite-CO2 slurry (right-hand side bar) feed and rad-quench cooling. The volatile matter (VM) content of the feedstock is indicated at the gasifier inlet.

the water-gas shift reactor. The specific flow of steam extracted from the steam turbine for this purpose is presented in Figure 7; this is important since it translates directly to a reduction in the steam turbine power output. For bituminous coal gasification and radiant-quench cooling, the syngas produced in a plant with CO2 slurry feed requires more than twice the amount of shift steam than that of a plant with water slurry feed. This is the only water slurry-fed case for which steam extraction is necessary; excess water is present in the syngas for all other water slurry cases. Note that while radiant-cooling produces a gas with a higher H2:CO ratio than full-quench cooling, its low moisture results in an overall higher shift steam extraction than for full-quench cooled cases. Full-quench cooling can hence be implemented as a way to reduce the high shift steam requirement in plants with CO2 slurry feed. This cost-effective cooling method introduces moisture while cooling the gas through direct contact with water. As depicted in Figure 7, the shift steam extraction in plants with CO2 slurry is reduced by almost half for bituminous coal and is made completely unnecessary for sub-bituminous coal and lignite if full-quench cooling is used. Figure 8 compares the gas flow and composition history in a plant with water slurry with one based on CO2 slurry for the exemplary case of lignite and rad-quench cooling; the material streams are presented for selected relevant locations throughout the plant. The results show that the composition difference between the syngas produced with either slurrying medium is evened out in the WGS reactor, where most of the CO is converted to CO2 and H2. From this point onward, there is no significant difference between the composition of the gas produced with either water slurry or CO2 slurry. Noteworthy is the fact that for a given as-received coal flow, up to 20% higher flow of gas turbine fuel is produced if CO2 slurry is used instead of H2O slurry. This is a direct result of the higher cold gas efficiency in a CO2 slurry-fed gasifier. Auxiliary Power Consumption. The air separation unit, acid gas removal unit, and CO2 compression chain are the most important sources of auxiliary power consumption which are directly affected by the change of slurrying medium. The

specific power consumption for each of these is presented in Figure 9 for each case.

Figure 9. Specific power consumption of ASU, Selexol unit, and CO2 compression chain for plants with coal-water slurry (□) and coal-CO2 slurry (■) feed. The coal HHV has been used to normalize the results. The total power consumption of the three units per MWel of gross plant output is presented in parentheses.

The results show that the specific power consumption of the Selexol unit and CO2 compression chain is on average 15% higher for plants with CO2 slurry feed; this results directly from the 15% CO2 recirculation required, on average, for slurry preparation. The specific ASU power reduction is, nevertheless, much larger and dominates the total auxiliary power consumption. An average 10% less power is consumed per unit feedstock energy input in the ASU of plants with CO2 slurry feed as a result of the reduced oxygen requirement. Overall, the total specific power consumption of the air separation unit, the acid gas removal unit, and the CO2 compression chain is only modestly lower for a plant with CO2 slurry feed; it consumes an average of 4% less power per unit feedstock HHV in these process units. This corresponds to J



Article

Figure 10. Net efficiency of IGCC plant with CCS and coal-water slurry (□) or coal-CO2 slurry (■) feed. The relative plant efficiency increase resulting from a switch to CO2 slurry feed is presented in parentheses. Error bars indicate the uncertainty associated with the maximum achievable slurry loading.

Effect of Syngas Cooling Method. Figure 10 shows that combined radiant-quench cooling results in an estimated 2− 4%-point higher plant efficiency than full-quench cooling. This is expected since steam produced in the radiant cooler contributes to the power production in the steam turbine, while there is no steam generated in a full-quench cooled gasifier. While radiant cooling always results in a higher plant efficiency than full-quench cooling, this may not be the most economically attractive option for cases where the shift steam requirement of the WGS reactor is high, i.e. for syngas with a low H2:CO ratio like that produced in a gasifier with CO2 slurry feed. For such cases, a significant fraction of the steam produced in the radiant cooler must then be extracted from the turbine and mixed with the syngas to provide enough moisture for the water-gas shift reaction; the decision to invest in a radiant cooler is questionable in the first place. Alternatively, a fullquench cooler can be installed; it supplies most of the moisture required in the WGS reactor through evaporative cooling and is a more cost-effective option. The relative plant efficiency benefit of a plant with CO2 slurry feed can be more than doubled if full-quench cooling is used, as the numbers in parentheses in Figure 10 indicate. This is particularly true for high-rank coal, which produces a relatively dry syngas as a result of its low moisture content. In other words, the relative IGCC efficiency reduction resulting from full-quench cooling is up to 40% lower if the feed system uses liquid carbon dioxide rather than water. The effect of fullquench cooling had not been published before in the context of CO2 slurry-fed gasifiers; the economic advantages of this combination are currently being assessed. Effect of Slurry Loading. The calculated net IGCC efficiency observed in Figure 10 changes by a maximum of 1%-point as a result of the slurry loading uncertainty, which had not been considered in public studies. The plant efficiency increase predicted for systems with CO2 slurry feed is outside the

a total auxiliary-to-gross power reduction of 7% in the case of sub-bituminous coal, as indicated in the figure, which agrees with the reduction reported by Dooher et al. for a similar coal. Note, however, that the absolute auxiliary-to-gross power is lower in the work by Dooher as a result of the integration between gas turbine and air separation unit.19 Net IGCC Efficiency. The net power generation efficiency of the IGCC plant is presented in Figure 10 for all cases. The effect of the slurrying medium, coal rank, and syngas cooling method on the net system performance is shown. In addition, the uncertainty associated with the CO2 slurry loading is indicated in the form of error bars. The results of this work show that the net power generation efficiency of plants with coal-CO2 slurry feed is higher than that for plants with water slurry feed. Gasification of bituminous coal with radiant-quench cooling is the only exception, in which case the net plant efficiency is almost identical for both feeding systems. An up to 25% (5%-points) higher plant efficiency can be achieved for lignite, which benefits the most from the CO2 slurry feeding system. The 10% (2.7%-point) higher IGCC efficiency predicted for sub-bituminous coal and rad-quench cooling agrees well with the 9% (2.8%-point) increase predicted by Dooher et al. for a similar feedstock.19 Effect of Coal Rank. The net system efficiency decreases with coal rank regardless of the slurrying medium used; the high moisture of low-rank coals -and thus low slurry loading- is responsible for this. What is noticeable is the fact that the plant efficiency drop resulting from switching to a lower rank coal is only about half as much if CO2(l) is used for the slurry, instead of H2O. For combined radiant-quench cooling, for example, a switch from bituminous coal feedstock to lignite leads to an net IGCC efficiency reduction of an estimated 26% (8.6%-points) for coal-water slurry, while only 12% (3.9%-points) plant efficiency is lost for coal-CO2 slurry. A rigorous analysis of the significant role of coal rank on the performance of a CO2 slurryfed gasifier had not been published before. K



■

OUTLOOK Ongoing work is focusing on coal-CO2 slurry gasification from a component-level perspective. Specifically, the heterogeneous gasification kinetics are being evaluated34 as well as the characteristics and economics of the slurry preparation and feeding system. Future work will address not only the economics of the overall plant but also the physics behind the atomization and agglomeration properties of coal slurry; the real potential of CO2 slurries in achieving smaller effective particle sizes inside the gasifier is yet to be understood.

uncertainty range associated with the maximum achievable slurry loading for all cases. The only exception is for gasification of bituminous coal and radiant-quench cooling, in which case the net IGCC efficiency difference between both feeding concepts is within the loading uncertainty range.

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Article

CONCLUSIONS

Steady-state process simulation was used to assess the performance of an IGCC plant with CCS and coal-CO2 slurry feed and compare it with that of a state-of-the-art water slurryfed plant. By studying bituminous coal, sub-bituminous coal, and lignite feedstocks, this work addresses the rank-dependence of the performance benefits from CO2 slurry feed and extends previous analyses to high-rank coal. Furthermore, this work quantifies the impact of the coal-CO2 slurry loading uncertainty on the plant efficiency. Finally, full-quench syngas cooling technology is considered in addition to radiant-quench cooling in the context of CO2 slurry feed; it is identified to be an especially attractive capital cost saving measure in plants with this feed system. For a gasifier with radiant-quench cooling, a 10% (3%points) higher net plant efficiency is estimated for subbituminous coal, which agrees well with results from Dooher et al. for a similar feedstock;19 furthermore, this work also reports an up to 19% (5%-points) plant efficiency increase for lignite, while no net performance difference is observed for bituminous coal if the gasifier uses radiant-quench cooling. For gasifiers with the more cost-effective full-quench cooling technology, the IGCC efficiency improvements increase to 3% (1%-points), 19% (4%-points), and 25% (5%-points) for bituminous coal, sub-bituminous coal, and lignite, respectively. This finding is of especial significance given the need to reduce capital costs while increasing feedstock flexibility in Integrated Gasification Combined Cycle plants.46 The rank-dependency analysis quantified the degree to which the feedstock flexibility of an IGCC plant can be improved if CO2(l) is used for the feed system, instead of water. Accordingly, the up to 30% reduction in plant efficiency which results when switching from bituminous to low-rank coal can be reduced by almost half, to an estimated 18%, if CO2(l) is used for the slurry feed system instead of water. The performance advantage of CO2 slurry feed was found to be outside the uncertainty range of the slurry loading for all cases studied, except for bituminous coal gasification with radiant-quench cooling, in which case no performance difference is observed. CO2 slurry loading is still one of the main unknowns of this feed system, and its effect on plant performance had not been accounted for in previous publications. Finally, simulation results show that a plant with CO2 slurry feed will consume an average 15% less oxygen and have smaller equipment upstream of the gas turbine because up to 20% more fuel gas is produced per unit feedstock energy input. This is expected to significantly benefit the economics of the plant and is a result of the gasifier’s superior cold gas efficiency; it is true even for bituminous coal-CO2 slurry, which otherwise showed little to no advantage in terms of overall IGCC efficiency and had not been considered before in public studies of coal-CO2 slurry feed.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS

■

REFERENCES

The authors would like to acknowledge Prof. Janos Beer for his ongoing support. Many thanks also to Jeff Phillips, from EPRI, for sharing past and present experience on the subject to support this work, as well as to BP for the funding and Aspen Technology, Inc. for the simulation software.

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Performance of an IGCC Plant with Carbon Capture and Coal-CO2

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