Design and operation of a coal-fired 50 kWth chemical looping combustor

Abstract

CLC technology with solid fuels is being developed mainly by means of two modes: in situ Gasification CLC (iG-CLC) and Chemical Lopping with Oxygen Uncoupling (CLOU). In the iG-CLC concept, coal gasification is an intermediate step taking place inside the fuel reactor, where gasification products (CO+H2) and volatile matter are oxidized by reaction with oxygen carrier particles. The CLOU concept was developed on the strategy of using oxygen carrier materials which can release gaseous oxygen in the fuel reactor environment, and thereby allowing the solid fuel to be quickly burnt with gas phase oxygen. A 50 kWth pilot plant for solid fuels have been designed and constructed to be operated in both iG-CLC and CLOU modes. The design of the concept was based on two interconnected circulating fluidized beds reactors. The coal is fed at the bottom of the fuel reactor to maximize the contact between the volatile matter and the oxygen carrier particles, minimizing the unburnt compounds at the outlet. In iG-CLC mode, residence time of solids in the fuel reactor is low compared to the time to allow complete coal gasification. A carbon stripper has been included between fuel and air reactors to increase the residence time of char particles in the fuel reactor, thus allowing high CO2 capture rates. In this unit, the char particles are separated from the oxygen carrier particles using their different fluidization properties and they are recirculated to the fuel reactor. This unit could be also required for low reactive coals in CLOU mode. Solids circulation flow rate is controlled by using a double loop seal after fuel reactor cyclone. In this device, the solid flow exiting from the fuel reactor splits into two different streams. One goes to the carbon stripper and the other is recirculated to the fuel reactor.