Investigation of heat management for CLC of syngas in packed bed reactors

Abstract

h i g h l i g h t sThe feasibility of packed bed CLC with syngas as the fuel is assessed. New operation strategies are discussed to use ilmenite as oxygen carrier.High efficiency process can be obtained also with less active oxygen carriers.

Chemical looping combustion process in fixed-bed reactors using ilmenite as oxygen carrier: Conceptual design and operation strategy

“…Since the oxidation of ilmenite with air is moderately exothermic, the fact that much of the bed is initially at a very high temperature (1187 ºC) may cause the temperature to rise above the maximum allowable value during the oxidation stage, which would have a negative effect on the properties of the oxygen carrier [32]. We therefore propose for this study the addition of a steam reforming stage (B), which would allow the solids bed to cool down to a suitable temperature before the next oxidation stage (C) begins.…”

“…3), which will accelerate the advance of the heat exchange fronts (e 1 and e 2 ) along the bed (bringing u r /u e closer to 1). Moreover, the presence of a large amount of steam and CO 2 in the feed will prevent carbon deposition and the over-reduction of Fe 2 TiO 5 to pure Fe will be kept to a minimum during stage (A) [32].The recirculation of gas can be designed in a manner such that both the reaction front (r) and the heat exchange front (e 2 ) reach the reactor exit at the same time. This will allow the reduction stage (A) to be initiated with only a portion of the bed at 1200 ºC (T s1 in Fig.…”

“…When oxygen carriers with a high carrying capacity and a high oxidation enthalpy, such as Ni or Cu, are used, very low metal loadings (lower than 20 wt.%) are required to limit the increase in temperature during the operation, which means that larger high-pressure reactors are required for a given flow of fuel gas fed into the system. This option has been studied assuming methane [26-28, 30, 31] and syngas [32][33][34] to be the fuel gas. Another alternative is to control the increase in temperature during the oxidation stage by recycling a large amount of the cooled N 2 product gas in order to dilute the O 2 fed into the air reactor [35,36].…”

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

“…Considering the most studied oxygen carriers, only nickel oxide and ilmenite could be applied to achieve such DT, but both have some important drawbacks. Nickel is an expensive and toxic material [13], while ilmenite has a low reactivity at low temperatures [14]. The low reactivity of ilmenite can be circumvented by carrying out the reduction just after the oxidation when the bed is at high temperature and then performing the heat removal on the reduced bed by means of a N 2 stream [14].…”

“…Nickel is an expensive and toxic material [13], while ilmenite has a low reactivity at low temperatures [14]. The low reactivity of ilmenite can be circumvented by carrying out the reduction just after the oxidation when the bed is at high temperature and then performing the heat removal on the reduced bed by means of a N 2 stream [14]. Spallina et al showed that a high efficiency can be obtained in this case by means of a semi-closed N 2 -based gas turbine cycle for power generation [2].…”