Air Reactor Temperature Research Articles

Comprehensive analysis of energy, exergy, and economic aspects in a multi-generation system: Power, methanol, and heat generation through plastic waste gasification

The growing apprehensions regarding climate change and the rising levels of carbon dioxide emissions due to fossil fuel usage, in conjunction with the upsurge in plastic waste attributable to population expansion, have catalyzed a heightened consideration of alternative energy carriers as substitutes for fossil fuels. Methanol (MeOH) is emerging as a promising contender for mitigating the challenges encountered by hydrogen in the realms of storage and transportation. This study investigates the application of waste polyethylene gasification with steam for the production of syngas and methanol, utilizing the thermal integration of biogas-fueled chemical looping combustion (CLC). A noteworthy feature of this proposed system is its capability to generate methanol, power and heating without the emission of carbon dioxide into the environment. The powerful software Aspen Plus is utilized for an extensive process simulation. The simulation results reveal that the optimal molar ratio of the oxygen carrier to the biogas in the CLC is 2.6 (At air reactor temperature of 1000 °C). The operational performance evaluation reveals that the suggested system achieves energy efficiency of 69.5% and exergy efficiency of 64.2% The most significant energy destructors are related to the components of the air reactor, combustion chamber, and fuel reactor, respectively. Additionally, the production rate of methanol is 466.2 kg/h, and the minimum selling price of methanol is calculated to be 0.7 USD/kg.

Performance evaluation on the chemical looping combustion of the chromium-containing leather waste and the fate of chromium using thermodynamic analysis

Leather waste (LW) consistently contains a high content of chromium (Cr), which significantly limits its utilization due to the toxicity of hexavalent chromium formed through oxidation. To prevent this oxidation, chemical looping combustion (CLC) is employed to dispose of the chromium-rich LW. First, the gaseous and solid pollutants generated during air combustion and CLC are compared when LW is used as fuel. The results indicate that CLC is an effective way to significantly decrease the oxidation of chromium (Cr(VI)/Crtotal) at typical operating temperatures. Subsequently, various operating parameters, namely the equivalence ratio of oxygen carrier to leather waste (αOC/LW), the equivalence ratio of steam to leather waste (αS/LW), and air reactor (AR) temperature, are changed to investigate their effects on the CLC combustion and pollutant behaviors. The findings reveal that no chromium is oxidized in the fuel reactor. The oxidation in AR is associated with the presence of Na in the AR, which can react with chromium to form Na2CrO4. Increasing αOC/LW from 0.8 to 1.2 reduces the oxidation of chromium in the AR from 11.68% to 1.76%, while increasing αS/LW from 0.2 to 1.6 has the opposite effect, improving the oxidation of chromium in the AR from 3.16% to 5.18%.

Polygeneration of Hydrogen and Power Using Chemical Looping Water Splitting with Dual Loops of Oxygen Carrier

The demand for hydrogen as a fuel, particularly in the transportation and power sectors, has recently been increasing due to its environmental benefit of clean combustion. However, the conventional technologies for hydrogen production involve an energy penalty in purification of hydrogen and the carbon dioxide capture, which reduce the process efficiency, whereas the technique of chemical looping hydrogen production (CLH) has an inherent capacity for CO2 capture and produces pure stream of hydrogen. This paper proposes modifications in the conventional three-reactor CLH setup, leading to elimination of the energy-intensive air separation unit and imparting flexibility in terms of polygeneration (hydrogen and power). The design modification for thermally integrating the air reactor, gasifier, and splitter for an oxygen carrier has facilitated two distinct oxygen carrier loops to meet the polygeneration objectives. The performance metrics based on efficiency have been utilized to assess the performance of the proposed process and demonstrate the flexibility in polygeneration. The effect of varying operational parameters such as split fraction, composition of metal oxide, and temperature of air reactor on the performance of the proposed process has also been evaluated.

Thermodynamic assessment of chemical looping combustion and solar thermal methane cracking-based integrated system for green ammonia production

To attain sustainability, effective use of resources became a basic need for new energy systems. The present study considers a novel integrated system for greener ammonia synthesis using hydrogen produced from solar thermal cracking of methane. The system utilizes chemical looping combustion for the production of electricity with the advantage of carbon capture. The first law and second law analysis of the subsystems and overall system provide deep insights into the performance of the proposed system. The effects of various parameters such as reference temperature, air reactor temperature, ammonia reaction temperature and pressure on energy and exergy efficiencies of component and overall system are analyzed. Overall system energy and exergy efficiencies of 28.8% and 25.8%, respectively are obtained, whereas the subsystems are also found to have energy efficiencies ranging between 18.8 and 42.9%. The highest exergy destruction rate of 20.9 MW is observed for solar thermal cracking. The proposed system can help in the mitigation of carbon emissions accounted for the production of ammonia.

Coal combustion via Chemical Looping assisted by Oxygen Uncoupling with a manganese‑iron mixed oxide doped with titanium

Chemical looping combustion allows the carbon dioxide capture by using an oxygen carrier, which transports the oxygen required for combustion from the air to the fuel. But complete combustion of a solid fuel is not achieved when low cost materials were used as oxygen carriers. Manganese‑iron mixed oxide doped with titanium has been identified as a promising oxygen carrier to improve combustion efficiency due to its oxygen uncoupling capability. The objective of this work was to assess the potential of this oxygen carrier when burning coal in a chemical looping unit. The coal combustion efficiency and carbon dioxide capture were evaluated as a function of the operating conditions both in the fuel and air reactor. Carbon dioxide capture was affected by the solids residence time in the fuel reactor. Coal combustion efficiency increased as the oxygen uncoupling capability was enhanced by using suitable operating conditions in the air reactor. Almost full coal combustion (99.4%) was achieved by setting an air reactor temperature of 880 °C, an air excess of 1.8, a fuel reactor temperature of 925 °C, and an oxygen carrier to fuel ratio >3. The oxygen carrier showed magnetic properties, allowing its re-use after being separated from ash.

Life cycle global warming impact of CO2 capture by in-situ gasification chemical looping combustion using ilmenite oxygen carriers

In-situ gasification chemical looping combustion (iG-CLC), which has been tested on pilot plant level, is regarded as an advanced carbon capture and storage (CCS) technology for reducing CO2 emissions. A life cycle global warming impact (GWI) analysis is performed to consider the lifetime emissions of the low-carbon iG-CLC technology. Herein, the capacity is considered to be 610 MWe using natural ilmenite as oxygen carrier and steam as gasification agent. At the condition of operational pressure of 15 atm and air reactor temperature of 1050 °C, the net power efficiency of 37.7% for achieving 93.5% inherent CO2 capture is obtained in simulations with thermodynamically optimum condition. The life cycle GWI is calculated equal to be 160.3 kg CO2-equivalent/MW h. The effects of several essential parameters, including steam to carbon ratio (S/C), oxygen carrier to fuel ratio (ф), different oxygen carriers and lifetime of oxygen carriers, on the lifecycle GWI have been analyzed and discussed to meet the potential possibility for further reducing greenhouse gas (GHG) emissions. To obtain sufficient carbon capture efficiency, the S/C ratio and ф are suggested to be 1.3 and 1.2 in this study, respectively. The life cycle GWI is heavily dependent on lifetime of ferrum (Fe) when it is less than 2000 h, beyond that range, the GWI is decreasing, but very slowly.

Thermochemical assessment of chemical looping assisted by oxygen uncoupling with a MnFe-based oxygen carrier

A previously developed manganese-iron mixed oxide doped with TiO2 shows promising properties for the combustion of solid fuels with intrinsic CO2 capture by Chemical Lopping assisted by Oxygen Uncoupling (CLaOU) owing to its oxygen uncoupling capability, i.e. ability to generate gaseous oxygen at high temperature, and to oxidize gaseous fuels such as H2, CO or CH4 by reacting with lattice oxygen. In this work, a window of suitable operating conditions was determined to facilitate the use of this material in a CLaOU unit. For this purpose, mass and enthalpy balances were performed for the whole CLaOU unit considering theoretical values of thermochemical parameters, such as the equilibrium constant of relevant reactions in CLaOU and the formation enthalpies of reacting solids. An air reactor temperature of 1148 K and a high air excess ratio are suggested in order to promote the transfer of oxygen via the oxygen uncoupling mechanism, which would be preferable for the combustion of solid fuels. Auto-thermal operation of the CLaOU unit is guaranteed for air excess ratio values λ < 3. The fuel reactor temperature is highly influenced by the oxygen carrier-to-fuel ratio (ϕ) and the oxygen carrier regeneration in the air reactor. Assuming a 50–75% regeneration of the oxygen uncoupling capability, and ϕ = 4–6, the fuel reactor temperature would be between 35 and 50 K above the air reactor temperature. The higher temperature in the fuel reactor could promote the fuel conversion, while oxygen carrier regeneration would be guaranteed by the lower air reactor temperature.

Integration of chemical looping combustion and supercritical CO2 cycle for combined heat and power generation with CO2 capture

Chemical looping combustion (CLC) is an emerging technology for energy conversion with inherent CO2 separation. Supercritical CO2 (sCO2) Brayton cycle is a promising way for efficient power production with compactness. In this work, CLC and sCO2 cycle were integrated for combined heat and power (CHP) cogeneration with CO2 capture. Coal was directly used as fuel for CLC, and CLC acted as heat source to drive a sCO2 cycle with reheating and recompression. The heat in sCO2 cooling and CO2 compression processes was recovered for district heating. A comprehensive analysis with first law based efficiency was performed to investigate the performance of the proposed cycle. For a baseline case of the proposed configuration, the net power efficiency was 41.3%, the heating efficiency was 40.4% and the resulting total efficiency was 81.7%, including CO2 compression to 120 bar. The effects of turbine inlet temperature, turbine inlet pressure, fuel reactor temperature, air reactor temperature, oxygen carrier ratio, inert support ratio, and air ratio on the thermal performance, including net power efficiency, heating efficiency, and total efficiency were analyzed as well.

50-kWth methane/air chemical looping combustion tests with commercially prepared CuO-Fe2O3-alumina oxygen carrier with two different techniques

CuO-Fe2O3/alumina oxygen carriers were manufactured using two different techniques (i.e., spray drying and wet granulation). The spray drying method produced porous, spherical particles in the range of 100–200 µm. The wet granulation, or tumbling method, produced particles in the range of 200–600 µm. Both batches of material showed good gas conversion and particle durability during tests in NETL’s 50-kWth chemical looping circulating fluidized bed combustor unit at 700–900 °C. No agglomeration was observed, even though the oxygen carrier had a high CuO concentration (30%). The particle losses with 200–600 µm batch were significantly lower than that with the 100–200 µm batch. The oxygen carrier materials in the 200–600 µm range were circulated for approximately 3.1 days in the target temperature range (700–850 °C) and a total of approximately 40 h of chemical looping combustion testing was conducted during that time. The average fuel reactor temperatures ranged from 760 to 815 °C for the chemical looping combustion test periods, and the average air reactor temperature ranged from 840 to 915 °C. The fuel conversion from natural gas to CO2 ranged from 50 to 80%. Approximately 1.6 h of continuous operation was achieved with no gas preheat and no natural gas augmented heating. During this test period, the average fuel reactor temperature ranged from 780 to 825 °C, the air reactor temperature ranged from 930 to 960 °C, and the natural gas to CO2 conversion ranged from 50 to 65%. Analysis of the oxygen carrier after the test indicated that there were no significant changes in the particle size or the surface morphology.

Thermodynamic and environmental evaluation of biomass and coal co-fuelled gasification chemical looping combustion with CO2 capture for combined cooling, heating and power production

This work presents a detailed investigation of biomass and coal co-fuelled gasification chemical looping combustion for combined cooling, heating and power (BCCLC-CCHP) generation system from both thermodynamic and environmental aspects. Addition of biomass (corn stover) as blending fuel not only provides possibility of utilizing renewable energy, but also greatly reduces greenhouse gas emissions. The application of chemical looping combustion for oxidation of syngas is aimed at inherent separation of CO2 without extra energy penalty. At based design conditions, the energy efficiency and exergy efficiency can reach 60.16% and 22.16% in summer, respectively. Three key parameters, namely oxygen to carbon ratio (O/C), operating temperature of air reactor in the chemical looping combustion and share of corn, are considered to analyze their influences on system performances. O/C ratio is not sensitive to energy output, however an optimum value of O/C=0.42 is found to obtain maximum system efficiency and primary energy saving ratio (PESR). Increasing AR operating temperature benefits power generation but lowers down cooling and heating production. Increasing corn mass share from absence to 50wt.% to replace part of coal results in energy efficiency losses by approximately 6 point percentages but the PESR is increased by up to 5 point percentages. Capture of photosynthetically-derived CO2 (from corn) by CLC offers negatively cradle-to-grave greenhouse gas emissions in the BCCLC-CCHP process when corn mass share is higher than 15%.

Coal gasification integration with solid oxide fuel cell and chemical looping combustion for high-efficiency power generation with inherent CO2 capture

Abstract Since solid oxide fuel cells (SOFC) produce electricity with high energy conversion efficiency, and chemical looping combustion (CLC) is a process for fuel conversion with inherent CO 2 separation, a novel combined cycle integrating coal gasification, solid oxide fuel cell, and chemical looping combustion was configured and analyzed. A thermodynamic analysis based on energy and exergy was performed to investigate the performance of the integrated system and its sensitivity to major operating parameters. The major findings include that (1) the plant net power efficiency reaches 49.8% with ∼100% CO 2 capture for SOFC at 900 °C, 15 bar, fuel utilization factor = 0.85, fuel reactor temperature = 900 °C and air reactor temperature = 950 °C, using NiO as the oxygen carrier in the CLC unit. (2) In this parameter neighborhood the fuel utilization factor, the SOFC temperature and SOFC pressure have small effects on the plant net power efficiency because changes in pressure and temperature that increase the power generation by the SOFC tend to decrease the power generation by the gas turbine and steam cycle, and v.v.; an advantage of this system characteristic is that it maintains a nearly constant power output even when the temperature and pressure vary. (3) The largest exergy loss is in the gasification process, followed by those in the CO 2 compression and the SOFC. (4) Compared with the CLC Fe 2 O 3 and CuO oxygen carriers, NiO results in higher plant net power efficiency. To the authors’ knowledge, this is the first analysis synergistically combining in a hybrid system: (1) coal gasification, (2) SOFC, and (3) CLC, which results in a system of high energy efficiency with full CO 2 capture, and advances the progress towards the world’s critically needed approach to “clean coal”.

Capture of CO2 from coal using chemical-looping combustion: Process simulation

Coal direct chemical-looping combustion (CLC) and coal gasification CLC processes are the two basic approaches for the application of the CLC technology with coal. Two different combined cycles with the overall thermal input of 1,000MW (LHV) were proposed and simulated, respectively, with NiO/NiAl2O4 as an oxygen carrier using the ASPEN software. The oxygen carrier circulation ratio in two CLC processes was calculated, and the influence of the CLC process parameters on the system performance such as air reactor temperature and the turbine inlet supplementary firing temperature was investigated. Results found were that the circulation ratio of the oxygen carrier in the coal gasification CLC process is smaller than that in the coal direct CLC process. In the coal direct CLC combined system, the system efficiency is 49.59% with the CO2 capture efficiency of almost 100%, assuming the air reactor temperature at 1,200 °C and the fuel reactor temperature at 900 °C. As a comparison, the system efficiency of coal gasification CLC combined system is 40.53% with the CO2 capture efficiency of 85.2% when the turbine inlet temperature is at 1,350 °C. Increasing the supplementary firing rate or decreasing the air reactor temperature can increase the system efficiency, but these will reduce the CO2 capture efficiency.

Integration of in-situ CO2-oxy coal gasification with advanced power generating systems performing in a chemical looping approach of clean combustion

Underground coal gasification (UCG) is a clean coal technology to utilize deep coal resources effectively. In-situ CO2-oxy coal gasification may eliminate the operational difficulty of the steam gasification process and utilize CO2 (greenhouse gas) effectively. Furthermore, it is necessary to convert the clean gasified energy from the UCG into clean combustion energy for an end-use. In order to achieve efficient clean power production, the present work investigates the thermodynamic feasibility of integration of CO2 based UCG with power generating systems operating in a chemical looping combustion (CLC) of product gas. The use of CO enriched syngas from O2/CO2 based UCG reduces the difficulty of the heat balance between a fuel reactor and an air reactor in a nickel oxygen-carrier based CLC system. Thermodynamic analyses have been made for various routes of power generation systems such as subcritical, supercritical and ultra-supercritical boiler based steam turbines and gas turbines for the UCG integrated system. It is shown, based on mass and energy balance analysis, that the integration of CO2 based UCG with the CLC system reduces the energy penalty of carbon capture and storage (CCS) significantly. A net thermal efficiency of 29.42% is estimated for the CCS incorporated system, which operates in a subcritical condition based steam turbine power plant. Furthermore, it is found that the efficiency of the proposed steam turbine system increases to 35.40% for an ultra-supercritical operating condition. The effect of operating temperature of the air reactor and the fuel reactor of the CLC system on the net thermal efficiency of combined cycle power plant is investigated. It is found that a net thermal efficiency of 42.53% can be obtained for the CCS incorporated combined cycle power system operating at an air reactor temperature of 1200°C.

Utilization of ventilation air methane as an oxidizing agent in chemical looping combustion

Release of fugitive methane (CH4) emissions from ventilation air in coal mines is a major source of greenhouse gas (GHG) emissions. Approximately 64% of methane emissions in coal mine operations are the result of VAM (i.e. ventilation air methane) which is difficult for use as a source of energy. A novel ancillary utilization of VAM was thereby proposed. In this proposal, the VAM was utilized instead of air as a feedstock to a chemical looping combustion (CLC) process of coal. In this case, Fe2O3/Fe3O4 particles were shuttled between two interconnected reactors for combustion of syngas produced by an imbedded coal gasifier.The effect of VAM flow rate and methane concentration on the performance of CLC was analyzed thermodynamically using Aspen Plus software. Results indicated that the variations of air reactor temperature with VAM flow rate and methane concentration can be minimized as expected. The effect of temperature and inlet methane concentration on the conversion of CH4 was examined experimentally in a fixed bed reactor with the presence of particles of Fe2O3/Al2O3. Not surprisingly, the reaction temperature put a significant influence on the conversion of CH4. The conversion started at the temperature about 300°C and the temperature to achieve full conversion was around 500°C while the temperature in empty reactor between 665°C and 840°C. This is due to the catalytic effect of oxygen carriers (i.e. Fe2O3/Al2O3) on the conversion of methane. Moreover, it was observed that the methane conversion rate decreased with the increase in inlet methane concentration while increasing with Fe2O3 loading content.

Simulation of a New Chemical-Looping Combustion Process without Sulfur Evolution Based on Ca-Based Oxygen Carrier

Abstract Calcium sulfate (CaSO4) is a promising oxygen carrier for chemical-looping combustion system. The release of sulfurous gas in the circulating of Ca-based oxygen carrier is a crucial problem. In this paper, it is found that the released amount of sulfurous gas is greatly affected by the partial pressure of reductive gas. If the partial pressure of the mixed reductive gases, composed of H2 and CO, maintains higher than 40 kPa, the sulfurous gas can be completely eliminated even at the reacting temperature higher than 1,000°C. Therefore, a new chemical-looping combustion system based on CaSO4 and NiO oxygen carrier, without any sulfur evolution, is simulated using Aspen Plus software. In the system, the syngas is generated from the steam gasification of coal and reacts with CaSO4 and NiO consecutively. The sulfur release occurred in the circulating of Ca-based oxygen carriers can be prevented because the concentrations of CO and H2 keep higher than 45% in the presence of Ca-based oxygen carriers. The suitable operating regime, in which auto-thermally operating of the system, zero-sulfur release and easy sequestration of CO2 from the flue gas are realized, is proposed in this paper. The effects of fuel reactor temperature, air reactor temperature and the recycle rate of oxygen carrier on the released heat from the system and the concentration of CO2 and H2O are also studied in the paper.

Design and evaluation of an IGCC power plant using iron-based syngas chemical-looping (SCL) combustion

Chemical-looping combustion (CLC) is a novel and promising combustion technology with inherent separation of the greenhouse gas CO2. This paper focuses on the design and thermodynamic evaluation of an integrated gasification combined-cycle (IGCC) process using syngas chemical looping (SCL) combustion for generating electricity. The syngas is provided by coal gasification; the gas from the gasifier is cleaned using high-temperature gas desulfurization (HGD). In this study, the oxygen carrier iron oxide (Fe2O3) is selected to oxidize the syngas in a multistage moving-bed reactor. The resulting reduced iron particles then consist of FeO and Fe3O4. To create a closed-cycle operation, these particles are partially re-oxidized with steam in a fluidized-bed regenerator to pure Fe3O4 and then fully re-oxidized in a fluidized-bed air combustor to Fe2O3. One advantage of this process is the co-production of hydrogen diluted with water vapor within the steam regenerator. Both the HGD and CLC systems are not under commercial operation so far. This mixture is fed to a gas turbine for the purpose of generating electricity. The gas turbine is expected to exhibit low NOx emissions due to the high ratio of water in the combustion chamber. Cooling the flue gas in the HRSG condenses the water vapor to yield high-purity CO2 for subsequent compression and disposal. To evaluate the net efficiency, two conventional syngas gasifiers are considered, namely the BGL slagging gasifier and the Shell entrained-flow gasifier. The option of using a CO2 turbine after the SCL-fuel reactor is also investigated. A sensitivity analysis is performed on the SCL-air reactor outlet temperature, this being a key design parameter. It was found that the best net efficiency of 43% (based on HHV) can be obtained using a BGL gasifier without a CO2 turbine at an air reactor temperature of 1000°C including CO2 compression for transport and storage. Simulation data are based on software Aspen Plus® and EES (Engineering Equation Solver).

Chemical Looping Pilot Plant Results Using a Nickel-Based Oxygen Carrier

A chemical looping pilot plant was designed, built and operated with a design fuel power of 120 kW (lower heating value, natural gas). The system consists of two Circulating Fluidized Bed (CFB) reactors. Operating results are presented and evaluated for a highly reactive nickel-based oxygen carrier, total system inventory 65 kg. The performance in fuel conversion achieved is in the range of 99.8% (CH4 conversion) and 92% (CO2 yield). In chemical looping reforming operation, it can be reported that thermodynamic equilibrium is reached in the fuel reactor and that all oxygen is absorbed in the air reactor as soon as the global stoichiometric air/fuel ratio is below 1 and the air reactor temperature is 900°C or more. Even though pure natural gas (98.6 vol.% CH4 ) without steam addition was fed to the fuel reactor, no carbon formation has been found as long as the global stoichiometric air/fuel ratio was larger than 0.4. Based on the experimental findings and on the general state of the art, it is concluded that niche applications such as industrial steam generation from natural gas or CO2 -ready coupled production of H2 and N2 can be interesting pathways for immediate scale-up of the technology.

Off-design performance of a chemical looping combustion (CLC) combined cycle: effects of ambient temperature

The present work investigates the influence of ambient temperature on the steady-state off-design thermodynamic performance of a chemical looping combustion (CLC) combined cycle. A sensitivity analysis of the CLC reactor system was conducted, which shows that the parameters that influence the temperatures of the CLC reactors most are the flow rate and temperature of air entering the air reactor. For the ambient temperature variation, three off-design control strategies have been assumed and compared: 1) without any Inlet Guide Vane (IGV) control, 2) IGV control to maintain air reactor temperature and 3) IGV control to maintain constant fuel reactor temperature, aside from fuel flow rate adjusting. Results indicate that, compared with the conventional combined cycle, due to the requirement of pressure balance at outlet of the two CLC reactors, CLC combined cycle shows completely different off-design thermodynamic characteristics regardless of the control strategy adopted. For the first control strategy, temperatures of the two CLC reactors both rise obviously as ambient temperature increases. IGV control adopted by the second and the third strategy has the effect to maintain one of the two reactors’ temperatures at design condition when ambient temperature is above design point. Compare with the second strategy, the third would induce more severe decrease of efficiency and output power of the CLC combined cycle.

Investigation of Gasification Chemical Looping Combustion Combined Cycle Performance

A novel combined cycle based on coal gasification and chemical looping combustion (CLC) offers a possibility of both high net power efficiency and separation of the greenhouse gas CO2. After pressurization, a coal slurry enters a pipe-type gasifier immersed in the CLC air reactor and takes in the heat released from the air reactor. After removal of particulates, the syngas is used as the fuel of the CLC fuel reactor or the supplementary firing. The technique involves the use of a metal oxide as an oxygen carrier, which transfers oxygen from the combustion air to the fuel, and the avoidance of direct contact between fuel and combustion air. The fuel gas is oxidized by an oxygen carrier, an oxygen-containing compound, in the fuel reactor. The oxygen carrier in this study is NiO. The reduced oxygen carrier, Ni, in the fuel reactor is regenerated by the air in the air reactor. In this way, fuel and air are never mixed, and the fuel oxidation products CO2 and water vapor leave the system undiluted by air. All that is needed to get an almost pure CO2 product is to condense the water vapor and to remove the liquid water. When the technique is combined with gas turbine and heat recovery steam generation technology, a new type of combined cycle is formed which gives a possibility of obtaining high net power efficiency and CO2 separation. The performance of the combined cycle is simulated using the ASPEN software tool in this paper. The influence of the water/coal ratio on the gasification and the influence of the CLC process parameters such as the air reactor temperature, the turbine inlet supplementary firing, and the pressure ratio of the compressor on the system performance are discussed. Results show that, assuming an air reactor temperature of 1200 °C, a gasification temperature of 1100 °C, and a turbine inlet temperature after supplementary firing of 1350 °C, the system has the potential to achieve a thermal efficiency of 44.4% (low heating value), and the CO2 emission is 70.1 g/(kW h), 90.1% of the CO2 captured.

Chemical looping combustion of coal in interconnected fluidized beds

Chemical looping combustion is the indirect combustion by use of oxygen carrier. It can be used for CO2 capture in power generating processes. In this paper, chemical looping combustion of coal in interconnected fluidized beds with inherent separation of CO2 is proposed. It consists of a high velocity fluidized bed as an air reactor in which oxygen carrier is oxidized, a cyclone, and a bubbling fluidized bed as a fuel reactor in which oxygen carrier is reduced by direct and indirect reactions with coal. The air reactor is connected to the fuel reactor through the cyclone. To raise the high carbon conversion efficiency and separate oxygen carrier particle from ash, coal slurry instead of coal particle is introduced into the bottom of the bubbling fluidized bed. Coal gasification and the reduction of oxygen carrier with the water gas take place simultaneously in the fuel reactor. The flue gas from the fuel reactor is CO2 and water. Almost pure CO2 could be obtained after the condensation of water. The reduced oxygen carrier is then returned back to the air reactor, where it is oxidized with air. Thermodynamics analysis indicates that NiO/Ni oxygen carrier is the optimal one for chemical looping combustion of coal. Simulation of the processes for chemical looping combustion of coal, including coal gasification and reduction of oxygen carrier, is carried out with Aspen Plus software. The effects of air reactor temperature, fuel reactor temperature, and ratio of water to coal on the composition of fuel gas, recirculation of oxygen carrier particles, etc., are discussed. Some useful results are achieved. The suitable temperature of air reactor should be between 1050–1150°C and the optimal temperature of the fuel reactor be between 900–950°C.