Carbon dioxide recovery from an integrated coal gasifier, combined cycle plant using membrane separation and a CO₂ gas turbine

Abstract

A scheme is described for electricity production based on coal gasification with recovery of carbon dioxide. In this scheme, coal is gasified into a coal gas, consisting mainly of hydrogen and carbon monoxide. A membrane separates the coal gas into a hydrogen-rich gas and a carbon-rich gas. The hydrogen-rich gas is fed to a conventional gas turbine. The flue gases of this turbine along with a small amount of carbon dioxide are emitted to the atmosphere. The carbon-rich gas is fed to another gas turbine, where it is fired in a mixture of oxygen and carbon dioxide. The exhaust of the latter is almost pure carbon dioxide and can be stored outside the atmosphere.

Two different kinds of membrane can be used: a polymer membrane or a metallic membrane. According to our studies the use of a polymer membrane reduces the specific carbon dioxide emissions from 0.76 to 0.06 kg/kWh. The energy conversion efficiency of the power plant decreases from 43.6% to 37.4%. With metallic membranes, practically pure hydrogen can be recovered, leading to a nearly zero carbon dioxide emission. The energy conversion efficiency decreases from 43.6% to 37.8%.

Application of this carbon dioxide recovery scheme may cause electricity production costs to rise by about one third. It is found that the specific emission reduction costs can be limited to about 14 (metallic) and 17 (polymer) US$ per tonne of carbon dioxide avoided. Omitting the membrane separation unit will increase the recovery costs by 2–5% and 15–20% for polymer and metallic membrane, respectively.

The main technical barrier in this scheme is the development of a new type of gas turbine with carbon dioxide as working fluid, although it might be possible to design a new turbine using existing components. Also further research should be carried out to reduce the influence of coal gas on the permeability of the metallic membranes.