|Process flow diagram for coal-to-liquids production with associated carbon dioxide emissions. Click to enlarge.|
Leading academics from an interdisciplinary MIT panel issued a report last week that examines how the world can continue to use coal in a way that mitigates, instead of worsens, the global warming crisis.
Led by co-chairs John Deutch, Institute Professor, Department of Chemistry, and Ernest J. Moniz, Cecil and Ida Green Professor of Physics and Engineering Systems, the report—The Future of Coal—Options for a Carbon Constrained World—states that carbon capture and sequestration (CCS) is the critical enabling technology to help reduce carbon dioxide emissions significantly while also allowing coal to meet the world’s energy needs.
Coal is a low-cost (per BTU) mainstay of both the developed and developing world, and its use is projected to increase. Because of coal’s high carbon content, increasing use will exacerbate the problem of climate change unless coal plants are deployed with very high efficiency and large-scale CCS is implemented.
As the world’s leading energy user and greenhouse gas emitter, the US must take the lead in showing the world CCS can work. Demonstration of technical, economic and institutional features of CCS at commercial scale coal combustion and conversion plants will give policymakers and the public confidence that a practical carbon mitigation control option exists, will reduce cost of CCS should carbon emission controls be adopted and will maintain the low-cost coal option in an environmentally acceptable manner.—John Deutch
There are many opportunities for enhancing the performance of coal plants in a carbon-constrained world—higher efficiency generation, perhaps through new materials; novel approaches to gasification, CO2 capture and oxygen separation; and advanced system concepts, perhaps guided by a new generation of simulation tools. An aggressive R&D effort in the near term will yield significant dividends down the road and should be undertaken immediately to help meet this urgent scientific challenge.—Ernest Moniz
The study emphasizes the need for a significant charge on carbon emissions is needed in the relatively near term to increase the economic attractiveness of new technologies that avoid carbon emissions and specifically lead to large-scale CCS in the coming decades.
Although the primary focus of the report is on power generation, it also address the use of coal in a Fischer-Tropsch process to produce synthetic fuels and chemicals.
Without carbon capture and sequestration (CCS), we estimate that the Fischer-Tropsch fuels route produces about 150% more CO2 as compared with the use of the petroleum-derived fuel products. For SNG [synthetic natural gas], up to 175% more CO2 is emitted than if regular natural gas is burned. With CCS, the full fuel-cycle CO2 emissions for both liquid fuel and SNG are comparable with traditional production and utilization methods.
Fortunately, CCS does not require major changes to the process, large amounts of additional capital, or significant energy penalties because the CO2 is a relatively pure byproduct of the process at intermediate pressure. CCS requires drying and compressing to supercritical pressure. As a result of this the CO2 avoided cost for CCS in conjunction with fuels and chemicals manufacture from coal is about one third of the CO2 avoided cost for IGCC.
The report did not consider direct liquefaction (Bergius process) due to the cost and the resulting “low-quality liquid products that are expensive to upgrade and do not easily fit current product quality constraints.”
According to the report, the critical technology options for meeting the challenge of CO2 emission reduction are:
Ultra-high efficiency coal combustion plants;
Gasification technologies, including gas treatment
Long-term carbon dioxide sequestration;
Improved methods for CO2 capture and for oxygen production;
Syngas technologies, such as improved hydrogen-rich turbine generators and technologies to convert syngas to chemicals and fuels
Technologies that tolerate variable coal qualities;
Integrated systems with CO2 capture and storage (CCS);
Novel concepts, such as chemical looping, the transport gasifier, the plug flow gasifier, membrane separation of CO2, and others;
Large-scale transport of CO2, captured and pressurized at coal combustion and conversion plants, to injection at storage sites.
According to the authors although the DOE coal RD&D program has had some important successes over the last thirty years, it has also had some significant gaps and needs considerable strengthening and restructuring to meet the current challenges facing coal use. Four primary gaps that need to be addressed are:
T ere has been too little emphasis on improvements in pulverized coal (PC) generating efficiency, such as support for ultra-supercritical boiler and steam cycle technology.
There is a significant lack of modern analytical and simulation tools for understanding the dynamics of complex integrated coal systems, particularly with CCS.
The applied research and technology program has not been robust enough to support the demonstration projects or to explore potential for future innovations.
The DOE has been slow to support advanced technology at process development unit (PDU) scale that explores new options for coal conversion, oxygen separation, and for CO2 capture.
The authors call for large-scale demonstration projects of the technical, economic and environmental performance of an integrated CCS system as soon as possible. They argue that a regulatory regime for large-scale commercial sequestration should be developed with a greater sense of urgency, with the Executive Office of the President leading an interagency process.
Other recommendations in the report include:
The US government should provide assistance only to coal projects with carbon dioxide capture in order to demonstrate technical, economic and environmental performance.
Although today Integrated Gasification Combined Cycle appears to be the economic choice for new coal plants with CCS, this could change with further research development and demonstration. It is not appropriate to pick a single technology winner at this time, especially in light of the variability in coal type, access to sequestration sites and other factors. The government should provide assistance to several first of their kind coal utilization demonstration plants, but only with carbon capture.
Congress should remove any expectation that construction of new coal plants without carbon dioxide capture will be grandfathered and granted emission allowances in the event of future regulation. This is a perverse incentive to build coal plants without carbon dioxide capture today.
Emissions will be stabilized only through global adherence to carbon dioxide emission constraints. China and India are unlikely to adopt carbon constraints unless the United States does so and leads the way in the development of CCS technology.
Key changes must be made to the current Department of Energy research development and demonstration program to successfully promote CCS technologies. The program must provide for demonstration of CCS at scale; a wider range of technologies should be explored; and modeling and simulation of the comparative performance of integrated technology systems should be greatly enhanced.
(A hat-tip to Juniper!)
The Future of Coal (MIT)