Pre-combustion Capture

Pre-combustion capture technology is a method in which a carbon based fuel is refined before it enters the combustion chamber in order to produce a gas rich in carbon dioxide (CO2) and hydrogen (H2), from which the CO2 is separated and the H2 is used as fuel. First, the fuel is converted into a gaseous state under heat and pressure in the presence of steam. In the combustion chamber, the oxygen supply is controlled such that only a portion of the fuel burns completely. This process produces the heat required to decompose the fuel and produce synthesis gas (syngas) which consist of H2, carbon monoxide (CO), and trace amounts of other gases (see equation A). The CO then reacts with water (H2O) in a water-gas-shift reactor to form CO2 (see equation B). This increases the concentration of CO2 to 40% and H2 to 55%. The higher concentration of CO2 at this point favors separation and capture technologies. The H2 rich syngas is then used as fuel to generate electricity in a combustion turbine (The Energy Lab, 2009).

equation A)

CxHy(s) + xH2O(g) → xCO(g) + (x+y/2)H2(g)
< 0 kJ/mol, where x and y are variables

equation B)

CO + H2O → CH4(g) + H2O(g) -206 kJ/mol
CO(g) + H2O(g) → CO2(g) + H2(g) -41 kJ/mol (Nord, 2009)

Exhaust gases of pre-combustion plants are directed to a heat recovery steam generator, which consists of tubes with water flowing through them. The heat from the exhaust gases dissipates into the water, vaporizing it into steam. The steam flows into a turbine to generate more electricity. As it powers the steam turbine, the steam exits into a condenser, which changes it back to water and the whole process is repeated (Metcalf Energy Center, 2009).

CO2 Reduction:

Current pre-combustion capture plants capture 91.6% of the average plant's CO2 emissions (Simbeck, 2009a).



Efficiency Losses:

Costs Estimates: