CO2 abatement by the combustion of H2-rich fuels in gas turbines

As a response to the threat of global climate change, a number of technologies have been proposed in which the carbon dioxide produced by combustion of fossil fuels at power stations is captured and stored. A leading option is based on the pre-combustion decarbonisation of fossil fuels to produce hydrogen-rich fuel gases. Such decarbonisation processes integrate the production of a synthesis gas with combined cycle power generation: Synthesis gas (essentially a mixture of hydrogen and carbon monoxide) is produced from a fossil fuel by partial oxidation and/or steam reforming. Carbon monoxide is converted by a water-shift reaction to CO2. The CO2 is then removed from the fuel gas stream using a regenerable solvent and sequestered. The fuel gas, consisting predominantly of hydrogen, is burnt in the gas turbine of a combined cycle. If synthesis gas is produced from natural gas using air as the oxidant, the decarbonised turbine fuel is approximately a 50:50 mixture of hydrogen and nitrogen (volume basis). The paper examines barriers to the availability of suitable turbines for the combustion of the hydrogen-rich fuels produced in decarbonisation processes. Studies carried out on a model of a Modem Reference Engine (MRE) are reported. The MRE model was developed to represent state-of-the-art technology for the gas turbines available from leading manufacturers. Potentially advantageous effects of a hydrogen-rich fuel on turbine performance are reported. The technical modifications needed to bum hydrogen-rich fuels are mainly confined to the combustor, fuel system and control system. Suppression of NOx emissions is a key issue. Hydrogen-rich gas cannot, at present, be burnt in existing pre-mix combustion systems. The implications of suppressing NOx emissions by adding steam to the hydrogen-rich gas are examined. The overall conclusion is that the future availability of gas turbines suitable for use in decarbonisation processes for CO2 abatement is not in jeopardy due to any major technology barriers. Hydrogen is potentially an attractive fuel. Development work is required, but the time-scale and costs involved are not prohibitive. These conclusions are supported by views expressed by manufacturers, users, and other informed parties.