Coal power generation with in-situ CO2 capture-HyPr-RING method: Effect of ash separation on plant efficiency

Abstract

In-situ CO2 capture in coal utilization captures CO2 during coal combustion or gasification such as Oxygen fuel combustion or HyPr-RING. coal gasification processes. Regarding Oxufuel combustion, Callide Oxyfuel Project has been being conducted as the world first project to apply the technology to an existing power plant, Callide A Power Station #4 unit (30MWe) with injection of captured CO2 into the underground. This is a Japan-Australia collaboration project and JCOAL participates in it as a supporting collaborator. JCOAL also proposed a novel coal gasification method-,HyPr-RING (Hydrogen Production by Reaction-Integrated Novel Gasification). HyPr-RING method utilizes a chemical looping with the calcium cycle, in which CaO (or Ca(OH)2) captures CO2 during coal gasification completely to form CaCO3 and release heat for gasification to produce near pure hydrogen in one gasifier. This paper introduces the current developing status of the HyPr-RING method, mainly including the experimental examination of the transition of sorbent particle size distribution, ash and sulfur concentration of materials at several locations of gasification and calcination system for the HyPr-RING process. And the plant cold gas efficiency which should be affected by ash separation was also analyzed. As the results, it was found that coal ash and sulfur concentrated highly in the process of calcination after cyclone. If it is possible, separate and remove ash and sulfur by applying devices like filter or/and cyclone separator, the plant coal gas efficiency may raise 2 points than that in the previous study in which a part of recycled sorbent was rejected without separation. One method for reducing CO2, the green house gas emissions is to capture CO2 before it releases into the atmosphere and then sequestrate it. Active lime (main component, CaO) can be used to capture CO2 in the exhaust gas or in the reactor from fossil fuels utilization effectively. That is calcium oxide (CaO) absorbs CO2 to yield calcium carbonate (CaCO3) (Eq.(1)), then the CaCO3 is thermally decomposed to CaO again and release nearly pure CO2 (Eq. (2)) for sequestration. To obtain a nearly pure CO2 stream from CaCO 3 decomposition, the heat for decomposing CaCO3 can be supplied by combusting fossil fuels, such as coal and natural gas, in a calciner with oxygen fuel combustion. The oxygen diluted by CO2 (CO 2 cycle) or H2O (steam cycle), in order to obtain near pure CO2 stream from CaCO3 decomposition. In our previous studies4-6, it was clarified that calcinations of limestone (main component, CaCO3) in a fluidized bed calciner can be performed in CO2 cycle atmosphere when the bed temperature was raised above 1293 K, whereas with 60% steam cycle in atmosphere, limestone can be decomposed at comparatively lower temperature, such as 1173 K. The decomposition conversions of the limestone were about 95% and 98%, in CO2 cycle and in steam cycle atmospheres, respectively. Reducing the calcinations temperature of limestone was helpful to produce more than 30% active CaO as shown in previous study4-6. In this study, the energy of CaCO3 calcination process by H2O (steam) cycle was analyzed and compared with CaCO 3 calcination process by CO2 cycle. For process calculations, the mass and energy flows were calculated iteratively, based on the input and output balances, until err [(input-output)/input] was < 0.01. Analysis showed that, although H2O (steam) cycle calcination had calcination energy more about 3.6% than CO2 cycle due to water evaporation latent heat loss, however, the calcination energy per active CaO was lowest for H2O (steam) cycle. © 2011 Published by Elsevier Ltd.