Combustion and gasification of pulverized coal have been investigated experimentally for the conditions under high temperature gradient and CO2-rich atmospheres with 5% and 10% O2. Crushed coal samples were heated rapidly by a CO2 gas laser beam to give a high temperature gradient of order 100 °C!s-1 in order to simulate radiation heat transfer conditions expected in coal gasification furnaces. The rapid heating is able to minimize effects of coal oxidation and combustion compared with previous studies with a TG-DTA that requires much longer time to heat up with oxidation effect. Moreover, coal-water mixture samples with different water/coal mass ratio were used in order to investigate roles of water vapor on the combustion and gasification. The experimental results indicated that coal weight reduction ratio or coal conversion ratio to gases follows the Arrhenius equation with increasing coal temperature; in addition, coal weight reduction ratio of the sample was increased around 5% with adding H2O in CO2-rich atmosphere. Furthermore, generations of CO gas and Hydrocarbons gases (HCs) were mainly dependent on coal temperature and O2 concentration, however, those are also affected by chemical reactions including H2O. Especially, reactions generating CO and HCs gases were stimulated at temperature over 1000 °C in the CO2-rich atmosphere with 5% O2.

1. Introduction

According to the IEA statistics (2007) [1], CO2 emission from fossil energy consumption in China was accounted for about 19% of global CO2 emission, of which coal-fired power plants occupied about 30% of total CO2 emission in China. Conventional coal fired boilers use air for combustion in which N2 gas is 79% in volume ratio, and it dilutes the CO2 gas concentration in the flue gas. CO2 capture cost from flue gases using amine stripping is expected to be relatively high [2]. Consequently, a new zeroemission coal gasification with CO2 and Oxygen combustion technology has been studied for new coal fired power plants [3,4], such as Integrated Gasification Combined Cycle (IGCC), including CO2 Capture and Storage (CCS). In this type of plants, recycled flue gas is used to control flame temperature and make up the volume of the missing N2 gas to ensure there is enough gas to generate energy in a gas turbine and heat in a steam boiler. As a consequence, a flue gas consisting mainly CO2 and water steam are generated, thus CO2 can be easily separated by condensation [5]. In addition, pulverized coal fired power plants could be the best candidates to install CO2 capture system, of which oxy-fuel or CO2/O2 combustion technology is one of promising methods to evade problems of CO2 separation [6].

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