Abstract
This study, as an extension of our previous experimental tests, presented a mechanism analysis of air reactor (AR) coupling in a high-flux coal-direct chemical looping combustion (CDCLC) system and provided a theoretical methodology to the system optimal design with favorable operation stability and low gas leakages. Firstly, it exhibited the dipleg flow diagrams of the CDCLC system and concluded the feasible gas–solid flow states for solid circulation and gas leakage control. On this basis, the semi-theoretical formulas of gas leakages were proposed to predict the optimal regions of the pressure gradients of the AR. Meanwhile, an empirical formula of critical sealing was also developed to identify the advent of circulation collapse so as to ensure the operation stability of the whole system. Furthermore, the theoretical methodology was applied in the condition design of the cold system. The favorable gas–solid flow behaviors together with the good control of gas leakages demonstrated the feasibility of the theoretical methodology. Finally, the theoretical methodology was adopted to carry out a capability assessment of the high-flux CDCLC system under a hot state in terms of the restraint of gas leakages and the stability of solid circulation.
Highlights
Coal-direct chemical looping combustion (CDCLC) has been demonstrated as an attractive combustion technology of coal with the inherent feature for CO2 capture [1,2]
In our previous experimental tests, we have found that the coupling of the counter-flow moving bed (CFMB) air reactor (AR) into the downcomer of the high-flux circulating fluidized bed (HFCFB) fuel reactor (FR) makes the hydrodynamic mechanism of the whole system much more complicated, and leads to crucial effects on the operation independence of the two reactors (i.e., FR and AR) in terms of solid circulation stability and gas leakages [20]
In typical circulating fluidized bed (CFB) reactors, the downcomer dipleg plays a critical role in solid circulation and gas seal
Summary
Coal-direct chemical looping combustion (CDCLC) has been demonstrated as an attractive combustion technology of coal with the inherent feature for CO2 capture [1,2]. By means of the OC particles that deliver oxygen from the AR to FR, the direct mixing of the fuel and air can be avoided, and further highly purified CO2 , without the dilution of N2 , can be acquired at the outlet of the FR via the condensation of steam [3,4,5,6,7,8,9,10,11,12]. The main advantages of this design are that the HFCFB FR can provide high solids concentration over the whole reactor height for favorable gas–solid contact efficiency and reaction performance, and that the CFMB AR possesses steady solids flow and low-pressure drop. An inertial separator, connecting the two reactors, was specially designed
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