Optimal Performance of Combined Cycles With Chemical Looping Combustion for CO2 Capture

2007 ◽  
Author(s):  
Rehan Naqvi ◽  
Olav Bolland
Keyword(s):  
Metal Oxide ◽  
Co2 Capture ◽  
Combined Cycle ◽  
Optimal Performance ◽  
Chemical Looping Combustion ◽  
Chemical Looping ◽  
Part Load ◽  
Fuel Reactor ◽  
Combined Cycles ◽  
Base Load

Chemical Looping Combustion (CLC) is an ingenious concept of CO2 capture from fossil fuels combustion. CLC is closely related to oxy-fuel combustion as the chemically bound oxygen reacts in a stoichiometric ratio with the fuel. In CLC, the overall combustion takes place in two steps while air and fuel are kept away from each other in two separate reactors. The necessary oxygen is supplied to the fuel by a certain metal oxide (Me/MeO). In a fuel reactor, the fuel reacts with the metal oxide and reduces it to metal (Me). The reduced metal oxide (Me) circulates to a separate air reactor where it reacts with oxygen in the air and gets oxidised back to metal oxide. The metal oxide keeps circulating between the two reactors in a loop while taking part in the successive chemical reactions. CLC can be applied in conventional circulating fluidised bed reactors. The air reactor product is hot oxygen-depleted air and the fuel reactor exhaust ideally consists of hot CO2/steam mixture. The exhaust can be condensed to separate steam and CO2 is compressed. Hence, energy penalty for CO2 capture is lower as compared to pre- and post-combustion capture methods. When the reactors are pressurised, CLC can be applied in combined cycles. This paper addresses optimal performance of two CLC-combined cycle configurations. In order to obtain optimal efficiency at base-load, thermodynamic analysis has been carried out and design point established. Further, the cycles’ performance at different load conditions has been analysed. The cycles are also compared with two conventional combined cycles including post-combustion CO2 capture in amine solution. The results show that the CLC-combined cycles exhibit higher net plant efficiencies at base-load as well as at part-load with close to 100% CO2 capture as compared to conventional combined cycles with post-combustion CO2 capture. Also, the CLC-combined cycles have better relative net plant efficiencies at part-load compared to conventional combined cycles. This work concludes that the CLC-combined cycles have high potential of efficient power generation with high degree of CO2 capture at base-load as well as part-load. The challenges with respect to cycles control have also been identified and control strategies discussed.

Chemical Looping Combustion-Analysis of Natural Gas Fired Power Cycles With Inherent CO2 Capture

2004 ◽  
Author(s):  
Rehan Naqvi ◽  
Olav Bolland ◽  
O̸yvind Brandvoll ◽  
Kaare Helle
Keyword(s):  
Metal Oxide ◽  
Co2 Capture ◽  
Oxygen Carrier ◽  
Fuel Combustion ◽  
Combined Cycle ◽  
Reactor System ◽  
Chemical Looping Combustion ◽  
Chemical Looping ◽  
Turbine Cooling ◽  
Steam Cycle

In this paper an alternative to so-called ‘oxy-fuel’ combustion has been evaluated. Chemical Looping Combustion (CLC) is an innovative concept of CO2 capture from combustion of fossil fuels in power plants. CLC is closely related to oxy-fuel combustion as the chemically bound oxygen reacts in a stoichiometric ratio with the fuel. In CLC, the overall combustion takes place in two steps. In a reduction reactor fuel is oxidised by the oxygen carrier i.e. the metal oxide MeO which is reduced to metal oxide with a lower oxidation number, Me. Me flows to an oxidation reactor where it is oxidised by oxygen in the air. In this way pure oxygen is supplied to fuel without using an energy intensive traditional air separation unit. This paper presents thermodynamic cycle analysis of a CLC-power plant. A steady-state model has been developed for the solid-gas reactions occurring in the reactor system. The model is applied to analyse the system under two configurations; a combined cycle and a conventional steam cycle. A turbine-cooling model has also been implemented to evaluate the turbine cooling penalty in the combined cycle configuration. Effects of exhaust recirculation for coking prevention and incomplete fuel conversion have also been investigated. Performance of the oxygen carrier has been idealised except for the degrees of reduction and oxidation. Energy needs for CO2 capture have properly been taken into account. The results show that an optimum efficiency of 49.7% can be achieved under given conditions with a CLC-combined cycle at zero emissions level. With turbine cooling, efficiency falls by 1.2% points under the same conditions. The CLC-steam cycle is capable of achieving 40.1% efficiency with zero emissions. The results show that CLC has high potential for power generation with inherent CO2 capture. This work will be useful in designing CLC systems after the reactor system has been analysed experimentally for long-term operations.

Chemical-Looping Combustion for Combined Cycles With CO2 Capture

2006 ◽  
Vol 128 (3) ◽  
pp. 525-534 ◽  
Author(s):  
Stefano Consonni ◽  
Giovanni Lozza ◽  
Giampaolo Pelliccia ◽  
Stefano Rossini ◽  
Francesco Saviano
Keyword(s):  
Metal Oxide ◽  
Gas Turbines ◽  
Exothermic Reaction ◽  
Combined Cycle ◽  
Oxidation Products ◽  
Chemical Looping Combustion ◽  
Excess Oxygen ◽  
Chemical Looping ◽  
Combined Cycles ◽  
Oxidation Reactor

Chemical-Looping Combustion (CLC) is a process where fuel oxidation is carried out through an intermediate agent—a metal oxide—circulated across two fluidized bed reactors: a reduction reactor, where an endothermic reaction reduces the metal oxide and oxidizes the fuel, and an oxidation reactor, where an exothermic reaction oxidizes the metal oxide in air. Overall, the system carries out the same job of a conventional combustor, with the fundamental advantage of segregating the oxidation products (CO2 and H2O) into an output flow free of nitrogen and excess oxygen. The flow exiting the reduction reactor consists of water and CO2, the latter readily available for liquefaction, transport and long-term storage. The hot, vitiated air from the oxidation reactor is the means to produce power through a thermodynamic cycle. This paper reports of a study supported by the ENI group to assess the potential of the integration between CLC and combined gas-steam power cycles. More specifically, we focus on four issues: (i) optimization of plant configuration; (ii) prediction of overall efficiency; (iii) use of commercial gas turbines; (iv) preliminary economic estimates. The CLC system is based on iron oxides which, to maintain their physical characteristics, must operate below 900–1000°C. Given the crucial importance of the temperature of the vitiated air generated by CLC on the performance of the combined cycle, we consider two options: (i) “unfired” systems, where natural gas is fed only to the CLC system, (ii) “fired” systems, where the vitiated air is supplementary fired to reach gas turbine inlet temperatures ranging 1000–1200°C. Results show that unfired configurations with maximum process temperature 850–1050°C and zero emissions reach net LHV plant efficiencies ranging 43%–48%. Fired cycles where temperature is raised from 850 to 1200°C by supplementary firing can achieve 52% net LHV efficiency with CO2 emission about one half of those of a state-of-the-art combined cycles. Fired configurations allow significant capital cost and fuel cost savings compared to unfired configurations; however, a carbon tax high enough to make them attractive (close to 50 €/ton) would undermine these advantages.

Chemical-Looping Combustion for Combined Cycles With CO2 Capture

2004 ◽  
Author(s):  
Stefano Consonni ◽  
Giovanni Lozza ◽  
Giampaolo Pelliccia ◽  
Stefano Rossini ◽  
Francesco Saviano
Keyword(s):  
Metal Oxide ◽  
Gas Turbines ◽  
Exothermic Reaction ◽  
Combined Cycle ◽  
Oxidation Products ◽  
Chemical Looping Combustion ◽  
Excess Oxygen ◽  
Chemical Looping ◽  
Combined Cycles ◽  
Oxidation Reactor

Chemical-Looping Combustion (CLC) is a process where fuel oxidation is carried out through an intermediate agent — a metal oxide — circulated across two fluidized bed reactors: a reduction reactor, where an endothermic reaction reduces the metal oxide and oxidizes the fuel, and an oxidation reactor, where an exothermic reaction oxidizes the metal oxide in air. Overall, the system carries out the same job of a conventional combustor, with the fundamental advantage of segregating the oxidation products (CO2 and H2O) into an output flow free of nitrogen and excess oxygen. The flow exiting the reduction reactor consists of water and CO2, the latter readily available for liquefaction, transport and long-term storage. The hot, vitiated air from the oxidation reactor is the means to produce power through a thermodynamic cycle. This paper reports of a study supported by the ENI group to assess the potential of the integration between CLC and combined gas-steam power cycles. More specifically, we focus on four issues: (i) optimization of plant configuration; (ii) prediction of overall efficiency; (iii) use of commercial gas turbines; (iv) preliminary economic estimates. The CLC system is based on iron oxides which, to maintain their physical characteristics, must operate below 900–1000°C. Given the crucial importance of the temperature of the vitiated air generated by CLC on the performance of the combined cycle, we consider two options: (i) “unfired” systems, where natural gas is fed only to the CLC system, (ii) “fired” systems, where the vitiated air is supplementary fired to reach gas turbine inlet temperatures ranging 1000–1200°C. Results show that unfired configurations with maximum process temperature 850–1050°C and zero emissions reach net LHV plant efficiencies ranging 43–48%. Fired cycles where temperature is raised from 850 to 1200°C by supplementary firing can achieve 52% net LHV efficiency with CO2 emission about one half of those of a state-of-the-art combined cycles. Fired configurations allow significant capital cost and fuel cost savings compared to unfired configurations; however, a carbon tax high enough to make them attractive (close to 50 €/ton) would undermine these advantages.

Inherent CO2 Capture Using Chemical Looping Combustion in a Natural Gas Fired Power Cycle

2004 ◽  
Vol 126 (2) ◽  
pp. 316-321 ◽  
Author(s):  
O̸. Brandvoll ◽  
O. Bolland
Keyword(s):  
Metal Oxide ◽  
Co2 Capture ◽  
Exergy Analysis ◽  
Oxygen Carrier ◽  
Fuel Combustion ◽  
Chemical Looping Combustion ◽  
Chemical Looping ◽  
Conventional Combustion ◽  
Oxidation Reactor ◽  
Cycle Efficiency

In this paper an alternative to the so-called “oxy-fuel” combustion for CO2 capture is evaluated. “Chemical looping combustion” (CLC), is closely related to oxy-fuel combustion as the chemically bound oxygen reacts in a stoichiometric ratio with the fuel. In the CLC process the overall combustion reaction takes place in two reaction steps in two separate reactors. In the reduction reactor, the fuel is oxidized by the oxygen carrier, i.e., the metal oxide MeO. The metal oxide is reduced to a metal oxide with a lower oxidation number, Me, in the reaction with the fuel. In this manner, pure oxygen is supplied to the reaction with the fuel without using a traditional air separation plant, like cryogenic distillation of air. The paper presents a thermodynamic cycle analysis, where CLC is applied in a humid air turbine concept. Main parameters are identified, and these are varied to examine the influence on cycle efficiency. Results on cycle efficiency are presented and compared to other CO2 capture options. Further, an evaluation of the oxygen carrier, metals/oxides, is presented. An exergy analysis is carried out in order to understand where losses occur, and to explain the difference between CLC and conventional combustion. The oxidation reactor air inlet temperature and the oxidation reactor exhaust temperature have a significant impact on the overall efficiency. This can be attributed to the controlling effect of these parameters on the required airflow rate. An optimum efficiency of 55.9% has been found for a given set of input parameters. Crucial issues of oxygen carrier durability, chemical performance, and mechanical properties have been idealized, and further research on the feasibility of CLC is needed. Whether or not the assumption 100% gas conversion holds, is a crucial issue and remains to be determined experimentally. Successful long-term operation of chemical looping systems of this particular type has not yet been demonstrated. The simulation points out a very promising potential of CLC as a power/heat generating method with inherent capture of CO2. Exergy analysis show reduced irreversibilities for CLC compared to conventional combustion. Simulations of this type will prove useful in designing CLC systems in the future when promizing oxygen carriers have been investigated in more detail .

Techno-Economic Analysis of a Carbon Capture Chemical Looping Combustion Power Plant

2018 ◽  
Vol 140 (11) ◽  
Author(s):  
Oghare Victor Ogidiama ◽  
Mohammad Abu Zahra ◽  
Tariq Shamim
Keyword(s):  
Power Plant ◽  
Natural Gas ◽  
Co2 Capture ◽  
Payback Period ◽  
Combined Cycle ◽  
Chemical Looping Combustion ◽  
Chemical Looping ◽  
Natural Gas Combined Cycle ◽  
Energy Penalty ◽  
The Cost

High energy penalty and cost are major obstacles in the widespread use of CO2 capture techniques for reducing CO2 emissions. Chemical looping combustion (CLC) is an innovative means of achieving CO2 capture with less cost and low energy penalty. This paper conducts a detailed techno-economic analysis of a natural gas-fired CLC-based power plant. The power plant capacity is 1000 MWth gross power on a lower heating value basis. The analysis was done using Aspen Plus. The cost analysis was done by considering the plant location to be in the United Arab Emirates. The plant performance was analyzed by using the cost of equipment, cost of electricity, payback period, and the cost of capture. The performance of the CLC system was also compared with a conventional natural gas combined cycle plant of the same capacity integrated with post combustion CO2 capture technology. The analysis shows that the CLC system had a plant efficiency of 55.6%, electricity cost of 5.5 cents/kWh, payback time of 3.77 years, and the CO2 capture cost of $27.5/ton. In comparison, a similar natural gas combined cycle (NGCC) power plant with CO2 capture had an efficiency of 50.6%, cost of electricity of 6.1 cents/kWh, payback period of 4.57 years, and the capture cost of $42.9/ton. This analysis shows the economic advantage of the CLC integrated power plants.

Inherent CO2 Capture Using Chemical Looping Combustion in a Natural Gas Fired Power Cycle

2002 ◽  
Author(s):  
O̸yvind Brandvoll ◽  
Olav Bolland
Keyword(s):  
Metal Oxide ◽  
Co2 Capture ◽  
Exergy Analysis ◽  
Oxygen Carrier ◽  
Fuel Combustion ◽  
Chemical Looping Combustion ◽  
Chemical Looping ◽  
Conventional Combustion ◽  
Oxidation Reactor ◽  
Cycle Efficiency

In this paper an alternative to the so-called “oxy-fuel” combustion for CO2 capture is evaluated. “Chemical looping combustion” (CLC), is closely related to oxy-fuel combustion as the chemically bound oxygen reacts in a stoichiometric ratio with the fuel. In the CLC process the overall combustion reaction takes place in two reaction steps in two separate reactors. In the reduction reactor, the fuel is oxidised by the oxygen carrier, i.e. the metal oxide MeO. The metal oxide is reduced to a metal oxide with a lower oxidation number, Me, in the reaction with the fuel. In this manner, pure oxygen is supplied to the reaction with the fuel without using a traditional air separation plant, like cryogenic distillation of air. The paper presents a thermodynamic cycle analysis, where CLC is applied in a Humid Air Turbine concept. Main parameters are identified, and these are varied to examine the influence on cycle efficiency. Results on cycle efficiency are presented and compared to other CO2 capture options. Further, an evaluation of the oxygen carrier, metals/oxides, is presented. An exergy analysis is carried out in order to understand where losses occur, and to explain the difference between CLC and conventional combustion. The oxidation reactor air inlet temperature and the oxidation reactor exhaust temperature have a significant impact on the overall efficiency. This can be attributed to the controlling effect of these parameters on the required airflow rate. An optimum efficiency of 55.9% has been found for a given set of input parameters. Crucial issues of oxygen carrier durability, chemical performance and mechanical properties have been idealized, and further research on the feasibility of CLC is needed. Whether or not the assumption 100% gas conversion holds, is a crucial issue and remains to be determined experimentally. Successful long-term operation of chemical looping systems of this particular type has not yet been demonstrated. The simulation points out a very promising potential of CLC as a power/heat generating method with inherent capture of CO2. Exergy analysis show reduced irreversibilities for CLC compared to conventional combustion. Simulations of this type will prove useful in designing CLC systems in the future when promising oxygen carriers have been investigated in more detail.

A Novel Solar-Hybrid Gas Turbine Combined Cycle With Inherent CO2 Separation Using Chemical-Looping Combustion by Solar Heat Source

2006 ◽  
Vol 128 (3) ◽  
pp. 275-284 ◽  
Author(s):  
Hui Hong ◽  
Hongguang Jin ◽  
Baiqian Liu
Keyword(s):  
Metal Oxide ◽  
Thermal Energy ◽  
Combined Cycle ◽  
Solar Thermal ◽  
Chemical Looping Combustion ◽  
Co2 Separation ◽  
Inlet Temperature ◽  
Low Grade ◽  
Chemical Looping ◽  
Solar Thermal Energy

In this paper we propose a novel CO2-recovering hybrid solar-fossil combined cycle with the integration of methane-fueled chemical-looping combustion, and investigate the system with the aid of the Energy-Utilization Diagram (EUD). Chemical-looping combustion (CLC) consists of two successive reactions: first, methane fuel is oxidized by metal oxide(NiO)as an oxygen carrier (reduction of metal oxide); and second, the reduced metal (Ni) is successively oxidized by combustion air (the oxidation of metal). The oxidation of methane with NiO requires a relative low-grade thermal energy at 300°C-500°C. Then concentrated solar thermal energy at approximately 450°C-550°C can be utilized to provide the process heat for this reaction. By coupling solar thermal energy with methane-fueled chemical-looping combustion, the energy level of solar thermal energy at around 450°C-550°C can be upgraded to the chemical energy of solid fuel Ni for better utilization of solar energy to generate electricity. The synergistic integration of solar thermal energy and chemical-looping combustion could make the exergy efficiency and the net solar-to-electric efficiency of the solar hybrid system more than 60% and 30%, respectively, at a turbine inlet temperature (TIT) of 1200°C. At the same time, this new system has an extremely important advantage of directly suppressing the environmental impact due to lack of energy penalty for CO2 recovery. Approximately 9–15 percentage points higher efficiency can be achieved compared to the conventional natural gas-fired combined cycle with CO2 separation. The results obtained here are promising and indicate that this novel solar hybrid combined cycle offers the new possibility of CO2 mitigation using both green energy and fossil fuels. These results also provide a new approach for highly efficient use of solar thermal energy to generate electricity.

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