Gasification is one of the cleanest possible ways to exploit abundant coal reservoirs all over the world to produce electricity and synthesize chemicals. Major challenges in the design of any gasification plant are desulfurization of the gases produced as a result of high sulfur contents in some coal types, removal of tar in the product gas, and costs associated with Air Separation Unit.
For environmental sustenance and energy saving, an indirect gasification scheme for coal is proposed and simulated which uses steam instead of oxygen-steam mixture as the gasification medium. This avoids the need of costly air separation process, while the heat for the endothermic process is supplied by hot flue gases passing through a bayonet heat exchanger installed within the reactor vessel. Simulation is carried out using the Aspen Plus™ software integrated with an MS Excel™ spreadsheet.
The simulation results show a remarkable achievement of cold gas efficiency of 70 %. The utilization of heating value of coal is optimized as the process is fully heat integrated and large amount of surplus superheated high pressure steam is generated providing for the electrical power needs of the installation.
The proposed gasification scheme can be used to convert high sulfur-containing coal to fuels, chemicals and energy in areas like Thar, Pakistan, where there are an estimated 175 billion tons of coal reservoirs with sulfur content as high as 2.9 wt. %.