Decarbonisation of fossil fuels: Hydrogen as an energy carrier

At present the cheapest source of hydrogen is from fossil fuels, but the carbon content of the fossil fuel is released to atmosphere as CO2. In a future where climate change considerations may lead to implementation of means to reduce emissions of CO2, the use of fossil fuels to produce hydrogen has been seen previously to be of little relevance However, this paper describes hydrogen production processes, suitable for a greenhouse gas driven future, in which fossil fuels are decarbonised by capturing and disposing of CO2. The CO2 is produced by shift conversion following reforming or partial oxidation of the fuel. It is captured by solvent absorption and stored deep under ground in a saline aquifer. The product is hydrogen which can be used as an energy carrier. Conversion technologies such as advanced combustion systems and fuel cells are needed to establish a high value for decarbonised hydrogen. If such conversion technologies are available, fossil fuel decarbonisation combined with CO2 storage becomes a relatively low cost approach to reducing emissions of CO2 to the atmosphere. Decarbonisation of fossil fuel derived hydrogen adds about 25-30% to the cost of hydrogen production; for example, using natural gas at 3$/GJ, the without capture cost of hydrogen is increased from 5.6$/GJ to 7.0$/GJ by capture and storage of the associated CO2. The costs of avoiding carbon emissions are about 20 US$/tCO(2) avoided. For comparison purposes, the cost of hydrogen produced by electrolysis of water is included, and results are also contrasted with equivalent costs for the production of electricity from fossil fuels. It is proposed that, for several decades, hydrogen derived from fossil fuels will be cheaper than hydrogen from renewable sources, even taking into account the costs of separating and sequestering the associated carbon. Decarbonised fossil fuels should therefore be seen as the most likely initial route to the establishment of hydrogen as an energy carrier. Decarbonisation makes hydrogen relatively more competitive with electricity as an energy carrier and provides the possibility of deep CO2 emission reductions by replacing dispersed uses of fossil fuels e.g. in transport.