scholarly journals Numerical Simulation Comparison of Two Reactor Configurations for Chemical Looping Combustion and Chemical Looping With Oxygen Uncoupling

2016 ◽  
Vol 138 (4) ◽  
Author(s):  
Matthew A. Hamilton ◽  
Kevin J. Whitty ◽  
JoAnn S. Lighty
Keyword(s):  
Carbon Capture ◽  
Fluidized Beds ◽  
Fluid Dynamic ◽  
Oxygen Carrier ◽  
Circulation Rate ◽  
Chemical Looping ◽  
Cfd Simulations ◽  
Choked Flow ◽  
Solids Circulation Rate ◽  
Particle Velocities

Chemical looping with oxygen uncoupling (CLOU) is a carbon capture technology that utilizes a metal oxide as an oxygen carrier to selectively separate oxygen from air and release gaseous O2 into a reactor where fuel, such as coal, is combusted. Previous research has addressed reactor design for CLOU systems, but little direct comparison between different reactor designs has been performed. This study utilizes Barracuda-VR® for comparison of two system configurations, one uses circulating fluidized beds (CFB) for both the air reactor (AR) and fuel reactor (FR) and another uses bubbling fluidized beds for both reactors. Initial validation of experimental and computational fluid dynamic (CFD) simulations was performed to show that basic trends are captured with the CFD code. The CFD simulations were then used to perform comparison of key performance parameters such as solids circulation rate and reactor residence time, pressure profiles in the reactors and loopseals, and particle velocities in different locations of the reactor as functions of total solids inventory and reactor gas flows. Using these simulation results, it was determined that the dual CFB system had larger range for solids circulation rate before choked flow was obtained. Both systems had similar particle velocities for the bottom 80% of particle mass, but the bubbling bed (BB) obtained higher particle velocities as compared to the circulating fluidized-bed FR, due to the transport riser. As a system, the results showed that the dual CFB configuration allowed better control over the range of parameters tested.

A Pb/Zn Based Chemical Looping System for Hydrogen and Power Production With Carbon Capture

2011 ◽  
Author(s):  
Niall R. McGlashan ◽  
Peter R. N. Childs ◽  
Andrew L. Heyes
Keyword(s):  
Power System ◽  
Flue Gas ◽  
Power Output ◽  
Carbon Capture ◽  
Oxygen Carrier ◽  
Fluid Phase ◽  
Chemical Looping Combustion ◽  
Inlet Temperature ◽  
Chemical Looping ◽  
Lower Efficiency

This paper describes an extension of a novel, carbon-burning, fluid phase chemical looping combustion system proposed previously. The system generates both power and H2 with ‘inherent’ carbon capture using chemical looping combustion (CLC) to perform the main energy release from the fuel. A mixed Pb and Zn based oxygen carrier is used, and due to the thermodynamics of the carbothermic reduction of PbO and ZnO respectively, the system generates a flue gas which consists of a mixture of CO2 and CO. By product H2 is generated from this flue gas using the water-gas shift reaction (WGSR). By varying the proportion of Pb to Zn circulating in the chemical loop, the ratio of CO2 to CO can be controlled, which in turn enables the ratio between the amount of H2 produced to the amount of power generated to be adjusted. By this means, the power output from the system can be ‘turned down’ in periods of low electricity demand without requiring plant shutdown. To facilitate the adjustment of the Pb/Zn ratio, use is made of the two metal’s mutual insolubility, as this means they form in to two liquid layers at the base of the reduction reactor. The amount of Pb and Zn rich liquid drawn from the two layers and subsequently circulated around the system is controlled thereby varying the Pb/Zn ratio. To drive the endothermic reduction of ZnO formed in the oxidiser, hot Zn vapour is ‘blown’ into the reducer where it condenses, releasing latent heat. The Zn vapour to produce this ‘blast’ of hot gas is generated in a flash vessel fed with hot liquid metal extracted from the oxidiser. A mass and energy balance has been conducted for a power system, operating on the Pb/Zn cycle. In the analysis, reactions are assumed to reach equilibrium and losses associated with turbomachinery are considered; however, pressure losses in equipment and pipework are assumed to be negligible. The analysis reveals that a power system with a second law efficiency of between 62% and 68% can be constructed with a peak turbine inlet temperature of only ca. 1850 K. The efficiency varies as the ratio between power and H2 production varies, with the lower efficiency occurring at the maximum power output condition.

A single radiotracer particle method for the determination of solids circulation rate in interconnected fluidized beds

1997 ◽  
Vol 92 (1) ◽  
pp. 53-60 ◽  
Author(s):  
R.D. Abellon ◽  
Z.I. Kolar ◽  
W. den Hollander ◽  
J.J.M. de Goeij ◽  
J.C. Schouten ◽  
...  
Keyword(s):  
Fluidized Beds ◽  
Particle Method ◽  
Circulation Rate ◽  
Solids Circulation Rate

scholarly journals Transient Cold Flow Simulation of Fast-Fluidized Bed Air Reactor with Hematite as an Oxygen Carrier for Chemical Looping Combustion

2021 ◽  
Vol 11 (5) ◽  
pp. 2288
Author(s):  
Pulkit Kumar ◽  
Ajit K. Parwani ◽  
Dileep Kumar Gupta ◽  
Vivek Vitankar
Keyword(s):  
Fluidized Bed ◽  
Carbon Capture ◽  
Oxygen Carrier ◽  
Stable Solution ◽  
Flow Simulation ◽  
Chemical Looping Combustion ◽  
Chemical Looping ◽  
Discrete Phase Model ◽  
Particle Injection ◽  
Cold Flow

Chemical looping combustion (CLC) is the most reliable carbon capture technology for curtailing CO2 insertion into the atmosphere. This paper presents the cold flow simulation results necessary to understand the hydrodynamic viability of the fast-fluidized bed air reactor. Hematite is selected as an oxygen carrier due to its easy availability and active nature during the reactions. The dense discrete phase model (DDPM) approach using the commercial software Ansys Fluent is applied in the simulation. An accurate and stable solution is achieved using the second-order upwind numerical scheme. A pressure difference of 150 kPa is obtained between the outlet and inlet of the selected air reactor, which is necessary for the movement of the particle. The stable circulating rate of hematite is achieved after 28 s of particle injection inside the air reactor. The results have been validated from the experimental results taken from the literature.

Fluid dynamic simulation in a chemical looping combustion with two interconnected fluidized beds

2011 ◽  
Vol 92 (3) ◽  
pp. 385-393 ◽  
Author(s):  
Wang Shuai ◽  
Liu Guodong ◽  
Lu Huilin ◽  
Chen Juhui ◽  
He Yurong ◽  
...  
Keyword(s):  
Dynamic Simulation ◽  
Fluidized Beds ◽  
Fluid Dynamic ◽  
Chemical Looping Combustion ◽  
Chemical Looping

scholarly journals Devolatilization of Residual Biomasses for Chemical Looping Gasification in Fluidized Beds Made up of Oxygen-Carriers

Energies ◽  
2021 ◽  
Vol 14 (2) ◽  
pp. 311
Author(s):  
Andrea Di Giuliano ◽  
Stefania Lucantonio ◽  
Katia Gallucci
Keyword(s):  
Fluidized Beds ◽  
Oxygen Carrier ◽  
Reaction Model ◽  
Chemical Looping ◽  
Oxygen Carriers ◽  
First Order ◽  
Fluidizing Agent ◽  
Mitigate Climate Change ◽  
Bubbling Beds ◽  
Better Than

The chemical looping gasification of residual biomasses—operated in fluidized beds composed of oxygen-carriers—may allow the production of biofuels from syngas. This biomass-to-fuel chain can contribute to mitigate climate change, avoiding the accumulation of greenhouse gases in our atmosphere. The ongoing European research project Horizon2020 CLARA (G.A. 817841) investigates wheat-straw-pellets (WSP) and raw-pine-forest-residue (RPR) pellets as feedstocks for chemical looping gasification. This work presents experimental results from devolatilizations of WSP and RPR, in bubbling beds made of three different oxygen-carriers or sand (inert reference), at 700, 800, 900 °C. Devolatilization is a key step of gasification, influencing syngas quality and quantity. Tests were performed at laboratory-scale, by a quartz reactor (fluidizing agent: N2). For each pellet, collected data allowed the quantification of released gases (H2, CO, CO2, CH4, hydrocarbons) and mass balances, to obtain gas yield (ηav), carbon conversion (χavC), H2/CO ratio (λav) and syngas composition. A simplified single-first order-reaction model was adopted to kinetically analyze experimental data. WSP performed as RPR; this is a good indication, considering that RPR is similar to commercial pellets. Temperature is the dominating parameter: at 900 °C, the highest quality and quantity of syngas was obtained (WSP: ηav = 0.035–0.042 molgas gbiomass−1, χavC = 73–83%, λav = 0.8–1.0); RPR: ηav = 0.036–0.041 molgas gbiomass−1, χavC = 67–71%, λav = 0.9–1.0), and oxygen-carries generally performed better than sand. The kinetic analysis suggested that the oxygen-carrier ilmenite ensured the fastest conversion of C and H atoms into gases, at tested conditions.

Carbon Capture and Reduced Irreversibility Combustion Using Chemical Looping

2007 ◽  
Author(s):  
Niall R. McGlashan ◽  
Andrew L. Heyes ◽  
Andrew J. Marquis
Keyword(s):  
Chemical Equilibrium ◽  
Carbon Capture ◽  
Oxidation Reaction ◽  
Solid Phase ◽  
Oxygen Carrier ◽  
Chemical Reactor ◽  
Hydrocarbon Fuel ◽  
Chemical Looping ◽  
Fluidised Bed ◽  
Lost Work

Power generation traditionally depends on combustion to ‘release’ the energy contained in fuels. Combustion is, however, an irreversible process and typically accounts for a quarter to a third of the lost work generation in power producing systems. The source of this irreversibility is the large departure from chemical equilibrium that occurs during the combustion of hydrocarbons. Chemical looping combustion (CLC) is a technology initially proposed as a means to reduce the lost work generation in combustion equipment. However, renewed interest has been shown in the technology since it also facilitates carbon capture. CLC works by replacing conventional “oxy-fuel” combustion with a two-step process. In the first, a suitable oxygen carrier (typically a metal) is oxidised using air. This results in an oxygen depleted air stream and a stream of metal oxide. The latter is then reduced in the second reaction step using a hydrocarbon fuel. The products of this second step are a stream of reduced metal, which is returned to the oxidation reaction, and a stream of CO2 and H2O that can be separated easily. The thermodynamic benefits of CLC stem from the fact that the oxygen carrier is recirculated and can thus be chosen with a reasonable degree of freedom. This enables the chemistry to be optimised to reduce the lost work generation in the two reactors – the reactions can then be operated much closer to chemical equilibrium. It is widely accepted in the literature that a key issue in CLC is identifying the most effective oxygen carrier. However, most previous work appears to consider systems in which a solid phase metallic oxygen carrier is recirculated between two fluidised bed reactors. In the current paper, we explore the possibility of using liquid or gas phase reactions in the two reaction steps since it is hypothesised that these might be compatible with a wider range of fuels including coal. The paper, however, starts by reviewing the existing literature on CLC and the basic thermodynamics of a conceptual CLC power plant. The thermodynamic analysis is extended to include a general method for calculating the lost work generation in a given chemical reactor. Finally, this method is applied to the oxidation reaction of a proposed CLC reaction scheme.

scholarly journals Estimating the solids circulation rate in a 100-kW chemical looping combustor

2017 ◽  
Vol 171 ◽  
pp. 351-359 ◽  
Author(s):  
Carl Linderholm ◽  
Matthias Schmitz ◽  
Anders Lyngfelt
Keyword(s):  
Circulation Rate ◽  
Chemical Looping ◽  
Solids Circulation Rate
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