Water Gas ReactionThere are several steps in coal gasification. Let's focus on step 1: conversion of the solid coal to a burnable gas.
In the gasifier, crushed coal is combined with steam at high pressure and temperature. The quantity of oxygen is limited to prevent complete combustion of the coal. Instead, the carbon reacts with the steam to form a mixture of CO, H2, and other gases.
There is always some combustion, so some CO2 is formed. At these temperatures, the sulfur compounds from the coal react with some of the hydrogen gas to produce H2S and some COS. The nitrogen-containing material is converted to ammonia and HCN. Mercury compounds are also in the gas phase. The remaining minerals mostly fall to the bottom of the gasifier, where they can be removed.
The gas can be scrubbed of acidic compound (hydrogen sulfide and carbon dioxide) by passing it through a basic material, such as CaCO3. Water, mercury, and ammonia are condensable compounds and can be removed by cooling the gas stream. The remaining material is a relatively pure mixture of CO/H2 called syn gas.
Syn gas, previously called town gas, was used as a fuel for gas lights in the 19th and early 20th centuries.
People's Energy Corporation, based in Chicago, began as Peoples Gas Light & Coke Company in 1855 to supply gas for street lighting and home heating and provide coal and coke for both industrial and residential uses.
There was a town gas plant in our town that supplied gas for street lights and homes in Urbana.
Water Gas Shift ReactionThe mixture of CO and hydrogen is a burnable gas but combustion of the CO produces carbon dioxide. Treating the mixture with water vapor over a catalyst converts the CO to CO2 and produces more hydrogen.
There are many transition metal catalysts for the water gas shift reaction, both heterogeneous and homogeneous. In industry, it is typical to use a transition metal or a metal oxide on a solid support for this reaction. We understand the mechanism of the reaction through studies of homogeneous metal complexes. The catalytic cycle for the WGS reaction catalyzed by Fe(CO)5 is shown below. This reactions involves:
Purification of the Gas
Example: Polk Power PlantA power plant in Polk county, Florida has been using the gas from coal as a fuel for electricity. It went online in 1999 and produces 250 megawatts of electricity. More than 94% of the sulfur is removed prior to combustion and the effluent is also lower in nitrogen oxides.