Synthetic diesel and gasoline have been important sources of transportation fuel since World War II, when Axis forces needed a way to power their fleets after the Allies cut off much of their access to petroleum. Traditionally, synthetic fuels are made from coal which is converted into synthesis gas—a mixture of hydrogen and carbon monoxide that can be produced in a device called a gasifier. Gasifiers are widely used today to produce syngas from not just coal, but biomass, petroleum coke, and heavy petroleum oils and residues. “Syngas is an important chemical building block which can be converted into all sorts of synthetic products, such as synthetic fuels, chemicals, and even electricity,” says Jaffer Ghouse, PhD student and lead author in their recently published study. “It is an important part of many next generation energy systems which can produce many of the same energy products we use today, but with less dependence on crude oil supply and potentially with much lower CO2 emissions.” For example, gasifiers are an important part of the new Integrated Gasification Combined Cycle process, or IGCC, which has been constructed in Edwardsport, Indiana, and will have the capability to capture up to 90% of the CO2 emissions with a much lower energy penalty than if a CO2 capture systems were retrofitted to a traditional coal power plant.
Gasifiers often operate at very high temperatures of over 1350°C, and so the syngas it generates must be cooled before it can be used, otherwise it would melt the steel piping. Currently, the most efficient cooling system available for gasifiers uses radiant cooling, in which the heat from the extremely hot syngas radiates into pipes containing high pressure cooling water, which then boil to make high pressure steam. Although steam can be useful, Ghouse and Prof. Thomas A. Adams II have designed a new device that provides the cooling in a creative and more efficient way. “In our design, we use a mixture of natural gas and steam as the coolant instead of water,” says Ghouse. “The cooling pipes are filled with a reforming catalyst which causes the natural gas and steam to react into hydrogen rich syngas.” The result is a system where syngas with different molar hydrogen and carbon monoxide compositions can be made from a combination of coal and natural gas, which not only is more efficient, but has lower carbon intensity since natural gas has a lower carbon content than coal. In other words, using this device can lead to increased efficiency and lower CO2 emissions than before, regardless of whether the syngas is used to make electricity, fuels, or chemicals.
Over the past two years, the team developed a mathematical model which was then used in computer simulations to help design the device and predict its dynamic behaviour. The model factors in many details such as heat and mass flows throughout the different parts of the radiant cooler, and can be used to identify “hot spots” in the catalyst or in the steel walls of the tubes and shell. In addition, recent MACC graduate Dominik Seepersad (now at Union Gas) developed control systems which can be added to the new radiant cooling device in order to control it and run it safely under a variety of operating scenarios. Now, the team is working on a variant that will run on petroleum coke (a waste product of heavy oil refining) instead of coal, which will be attractive for waste coke cleanup applications in Alberta.
The results of their research will be published in a three part series appearing in the journals Fuel Processing Technology as well as Chemical Engineering Research & Design, and advanced copies can be read by journal subscribers at the links below. The publisher version first article, which will appear in the October issue of Fuel Processing Technology, is currently free to the general public until September 4, 2015.
- Ghouse, J., Seepersad, D., Adams, T. A. II Modelling, simulation, and design of an integrated radiant syngas cooler and steam methane reformer for use with coal gasification, Fuel Process Technol,, 138 378-389 (2015) [ Publisher Version| Open Access Version (free) ]
- Seepersad, D., Ghouse, J., Adams, T. A. II Dynamic Simulation and Control of an Integrated Gasifier/Reformer System. Part II: Discrete and Model Predictive Control, Chem Eng Res Des, (2015) [ Publisher Version ]
- Seepersad, D., Ghouse, J., Adams, T. A. II Dynamic Simulation and Control of an Integrated Gasifier/Reformer System. Part I: Agile Case Design and Control, Chem Eng Res Des, (2015) [ Publisher Version ]
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