Assessment of technological solutions for improving chemical looping combustion of solid fuels with CO2 capture

Abstract

11The chemical looping combustion of solid fuels by in-situ gasification (iG-CLC) has great potential to 12 reduce the economical and energetic cost of CO 2 capture for generating energy from coal. Previous 13 studies have highlighted that a high CO 2 capture rate can be reached, but incomplete combustion is 14 predicted by theoretical models or obtained during experimental work. In this paper, a mathematical 15 model for the fuel reactor and carbon stripper, validated through experimental results, is adapted to 16 evaluate the relevance of several technological improvements in order to increase the combustion 17 efficiency of the iG-CLC process. The technological options evaluated include increasing the gas-solid 18 contact in the fuel reactor, incorporating a secondary fuel reactor, re-circulating exhaust gases to the fuel 19 reactor or the carbon stripper, or feeding coal into the carbon stripper instead in the fuel reactor. Model 20 simulations showed that the use of a secondary fuel reactor has the major impact by reducing the 21 unburnt compounds in the CO 2 stream. The origin of the unburnt compounds is determined from a 22 thorough analysis of the results obtained during the evaluation of these technological options. Thus, a 23 new arrangement of the iG-CLC reactors is proposed, one which would minimise the presence of 24 Submitted, accepted and published by Chemical Engineering Journal 233 (2013) 56-69 2 unburnt compounds. In this concept, exhaust gases from the fuel reactor are sent to the carbon stripper. 1The oxygen demand for this concept is predicted to be  T = 0.9%. 2 3

Sewage sludge combustion in a CLC process using nickel-based oxygen carrier

“…The unconverted compounds, such as CO and H 2 , were also found in previous studies using either coal or biomass [40,43,59]. Therefore, the uncompleted combustion is inevitable in the iG-CLC process especially using solid fuel with a high volatile matter fraction regardless of oxygen carrier used or the operational conditions [60]. Sludge contains low amount of fixed carbon and there are no CO 2 detected in oxidation period, implying that there are no char particles can be reacted in the oxidation period.…”

“…Thus, the incomplete gaseous products in reduction period are the key factor affecting CO 2 capture efficiency. Several technological options have been recently reported in order to improve CO 2 capture efficiency [60]. Re-circulating exhaust gases to the fuel reactor has the major impact by reducing the unburned compounds in the flue gas, as shown in Fig.…”

Fuel reactor modelling in chemical looping with oxygen uncoupling process

“…In order to prevent the char from reaching the air reactor, an intermediate carbon stripper unit can be installed between the air and the fuel reactor [6,36]. The carbon stripper is operated as a bubbling fluidized bed in which the char particles are separated from the oxygen carrier particles through their differences in fluidization properties.…”

“…To enhance the overall carbon capture, a carbon separation unit, namely a carbon stripper, can be implemented between the reactors, as shown in Fig. 1 [6]. In the carbon stripper, the char is separated from the oxygen carrier and sent back to the fuel reactor.…”

Energy analysis of two stage packed-bed chemical looping combustion configurations for integrated gasification combined cycles

“…Solids can be fed directly to the CLC reactors, leading to a relatively simple and high-efficiency power plant configuration. However, problems regarding full conversion of the fuel to CO 2 and H 2 O have been observed in experimental tests [3], which indicate that further process developments are required or a complete novel fuel reactor design [4]. Also, the separation of the uncombusted char from the oxygen carrier transported from the fuel to the air reactor and the recovery of the oxygen carrier from the ash purged from the system have to be performed in dedicated vessels.…”