GHG/07/42
IEA GREENHOUSE GAS R&D PROGRAMME
32nd EXECUTIVE COMMITTEE MEETING
CO-PRODUCTION OF HYDROGEN AND ELECTRICITY
BY COAL GASIFICATION WITH CO2 CAPTURE
Introduction
Hydrogen may become widely used in future as a low-CO2 energy carrier for vehicles and distributed heat and power generation using fuel cells. In the near term the cheapest way to produce hydrogen with low CO2 emissions is expected to be by use of fossil fuels with CO2 capture and storage. Hydrogen can be produced from fossil fuels in stand-alone plants with CO2 capture but it may be advantageous to co-produce hydrogen and electricity because of synergies within the production plant and to cope with variations in the demands for the two products.
If the use of hydrogen as an energy carrier becomes widespread, coal is expected to become the most important fuel for hydrogen production. This study focuses on estimating the costs of producing hydrogen and electricity by coal gasification with CO2 capture and the advantages of flexible co-production. The study was undertaken by Foster Wheeler Italiana.
Study description
The study includes the following:
· Screening assessment of the performance and costs of hydrogen and electricity co-production plants with CO2 capture, based on three coal gasifiers (Shell, GE Energy and Siemens) and two acid gas removal processes (Selexol and Rectisol), leading to the selection of preferred technologies for later detailed assessments.
· Assessment of the performance and costs of the following coal gasification plants:
1. Production of electricity, without CO2 capture
2. Production of electricity, with CO2 capture
3. Production of hydrogen and sufficient electricity for internal plant consumption, with CO2 capture
4. Co-production of hydrogen and electricity (fixed ratio), with CO2 capture
5. Co-production of hydrogen and electricity (flexible ratio), with CO2 capture
· Assessment of current markets for electricity, natural gas and road vehicle fuels in The Netherlands and USA, including the variability in consumptions throughout the year.
· An outline projection of the potential future market for hydrogen as an energy carrier, assuming it is used to replace natural gas for small scale energy users and petrol and diesel fuel for road vehicles.
· Review of published information on large scale underground storage of hydrogen.
· Modelling of scenarios in which different types of plants are used to meet demands for hydrogen and electricity:
1. Electricity-only and hydrogen-only plants without hydrogen storage
2. Non-flexible co-production plants without hydrogen storage
3. Non-flexible co-production plants with hydrogen storage
4. Flexible co-production plants without hydrogen storage
5. Flexible co-production plants with hydrogen storage
The scenarios are based on the variations in energy demands in the Netherlands and USA. In the scenarios with co-production plants, electricity-only and hydrogen-only plants are also used where necessary.
Study results
Technology selection
The costs of electricity were very similar for the three gasification processes considered in this study. Shell gasification was selected for the more detailed case studies mainly because it had the highest thermal efficiency and the lowest production of CO2, which would result in the lowest cost for CO2 transport and storage. The contractor also had more up to date cost data for the Shell gasifier. Selexol was found to give the best overall economics for acid gas removal.
Performance and costs of hydrogen and electricity production plants
The performances and costs of hydrogen and electricity production plant operating at base load are summarised in table 1.
Table 1 Plant performance and costs
Without CO2 capture / With CO2 captureElectricity / Electricity / Hydrogen / Electricity and hydrogen (fixed ratio) / Electricity and hydrogen (variable, low H2) / Electricity and hydrogen (variable, high H2)
Performance
Coal feed, MW (LHV) / 1800.8 / 1962.5 / 1962.5 / 1962.5 / 1962.5 / 1962.5
Electricity gross output, MW / 891.9 / 875.0 / 208.6 / 518.1 / 565.0 / 443.4
Electricity net output, MW / 762.3 / 655.8 / 0.1 / 317.1 / 363.1 / 236.6
Hydrogen net output, MW / - / - / 1110.7 / 599.0 / 484.0 / 734.1
Hydrogen: electricity ratio / 1.89 / 1.33 / 3.10
Efficiency to electricity, % / 42.3 / 33.4 / - / 16.2 / 18.5 / 12.1
Efficiency to hydrogen, % / - / - / 56.6 / 30.5 / 24.7 / 37.4
Costs
Capital cost, M€ / 1266 / 1560 / 1196 / 1337 / 1350 / 1350
Capital cost €/kWe / 1661 / 2379 / 4216 / 3718 / 5706
Cost of hydrogen, €/GJ[1] / - / - / 9.45 / 8.8 / 8.8 / 8.8
Cost of electricity, €/kWh / 0.052 / 0.072 / - / 0.071 / 0.073 / 0.078
Cost of CO2 avoided, €/t / 31.3
The costs of the electricity-only plants are higher than in IEA GHG’s previous study on bituminous coal IGCC plants with CO2 capture (report PH4/19) because costs of process plants have recently increased substantially, particularly due to increases in materials costs.
The electricity and hydrogen costs of the fixed-ratio co-production plant are lower than those of the electricity-only and hydrogen-only plants, which demonstrates the synergies of co-production.
The flexible plant can vary the hydrogen: electricity net output ratio between 1.3:1 and 3.1:1, while continuing to operate the coal gasifiers and gas turbine at full load. Including this flexibility slightly increases the capital and operating costs. However, as described later in the scenario analyses, flexibility has the advantage of enabling plants to meet the varying market demands more effectively and at lower costs.
Electricity and hydrogen demands
Scenarios involving varying demands for hydrogen and electricity were assessed to illustrate the benefits of flexible co-production. The scenarios were based on current monthly energy consumptions in the USA and the Netherlands, assuming that hydrogen replaces natural gas currently used for non-industrial consumers and gasoline and diesel fuel used for motor vehicles. It is emphasised that these are only hypothetical scenarios to illustrate the potential benefits of flexible co-production. Prediction of future energy demands is complex and beyond the scope of the study. An Excel tool was developed to enable different hydrogen and electricity demand scenarios to be evaluated if required.
The main differences between the Netherlands and USA scenarios is that there is a greater variation in the electricity demand throughout the year in the USA and a greater variation in the fuel (hydrogen ) demand in the Netherlands. Also, the peak demands for electricity and hydrogen tend to be at broadly the same time of year in the Netherlands but different times of year in the USA.
Co-production scenarios
Five scenarios were assessed, in which the different types of plants shown in table 1 were used to satisfy projected electricity and hydrogen demands of the Netherlands and USA. In the scenarios it is assumed that only coal gasification plants are used to meet the electricity and hydrogen demands. Including other technology options could be advantageous but the analysis would have become much more complex. Other researchers could use the plant performance and cost data provided by this study to carry out more complex scenario analyses if required.
Hydrogen storage was included in some of the scenarios to help to smooth out fluctuations in hydrogen demand. Underground storage of natural gas is widely used and there are some places where hydrogen is commercially stored underground, e.g. in the UK and Texas. Potential issues to be assessed on a site specific basis include costs, potential loss of hydrogen by seepage from the store and contamination of the hydrogen product.
Conclusions of the scenario analysis are:
§ Co-production reduces the overall coal consumption, CO2 emissions, capital cost and cost of electricity compared to using electricity-only and hydrogen-only plants.
§ Including hydrogen storage improves the costs of non-flexible and flexible co-production plants.
§ The lowest costs are for the scenario based on flexible co-production and hydrogen storage. The main advantage is a higher average plant utilisation compared to scenarios with non-flexible plants and scenarios with no hydrogen storage.
Electricity grids in future are expected to include greater amounts of variable renewable energy sources (wind, solar, marine energy etc.). Flexible hydrogen and electricity co-production plants with hydrogen storage may be a relatively low cost way of accommodating large proportions of renewable energy in electricity grids but assessment of this was beyond the scope of this study.
Conclusion
The least cost way of meeting hydrogen and electricity demands using coal gasification plants with CO2 capture is to use flexible co-production plants, in combination with underground buffer storage of hydrogen.
Recommendation for further work by IEA GHG
Further work should be carried out to compare costs of abating CO2 emissions from small stationary sources by CO2 capture and storage or use of low-CO2 energy carriers produced by large plants with CCS. A proposal for such a study was included in the set of proposals recently put forward to Members (proposal reference number 32-11) but it did not receive sufficient votes.
4
[1] For the co-production plants an arbitrary assumption has to be made about the split between the revenues associated with hydrogen and electricity. The hydrogen value of €8.8/GJ (LHV) assumed for the co-production plants gives similar electricity costs for the fixed-ratio co-production plant and the electricity-only plant.