Dennis Leppin

Desulfurization of fuels with calcium-based sorbents

Abstract Calcium-based sorbents, such as limestone and dolomite, are viable candidates for sulphur-capturing agents in an in-situ coal gasification/desulfurization process. The effect of limestone addition on the hydrodynamics of a fluidized-bed gasifier, desulfurization of the product gas, and stabilization of the solid wastes have been studied. The hydrodynamic characteristics of coal char/limestone mixtures, such as mixing and fines retention, have been studied in a 0.2-m diameter fluidization column. Kinetic data pertaining to the reaction between calcium oxide (which is obtained by calcination of limestone and dolomite) and hydrogen sulfide have been obtained by a gravimetric technique in the temperature range of 650 to 1050°C. Kinetic data relating to the reaction between calcium sulfide (which is obtained by sulfidation of calcium-based sorbents) and oxygen have been obtained in the temperature range of 800 to 1050°C and in the pressure range of 2 to 3.1 MPa. The operating conditions for these reactions have been chosen to be within the application range of a commercial coal gasification process that is accompanied by in situ desulfurization.

An Advanced Coal Gasification Desulfurization Process

The Institute of Gas Technology (IGT) is in the process of developing an advanced coal gasification desulfurization process in which a calcium-based sorbent such as limestone or dolomite is injected into the fluidized-bed gasifier with coal to achieve in-bed desulfurization of coal as it is converted into clean fuel gas. The reactions involving calcium-based sorbents takes place in two steps. In the first step, the desulfurization reaction takes place between hydrogen sulfide and calcium oxide in the reducing zone of the reactor to produce calcium sulfide. The latter subsequently reacts with oxygen in the oxidizing zone of the reactor to produce calcium sulfate which can be safely disposed of along with the coal ash. This process will reduce the capital requirement for coal gasification plants and provide cost effective alternatives to scrubbers for industrial and utility use of high-sulfur coal. This paper addresses the basic research being conducted at IGT to confirm the viability of this process. 9 refs., 3 figs., 1 tab.