There is an urgent need to develop an innovative technology for combined power generation and carbon dioxide sequestration from hydrocarbon fuels to address the increasing CO2 emissions coming from the transportation sector.
The development of sustainable solutions for our future energy needs has gained priority as evidence for anthropologically-induced climate change continues to mount. While most of the CO2 capture efforts are focussed on large-scale point sources of emissions, roughly one-third of global CO2 emissions come from the transportation sector. Thus, there is an urgent need to address this critical challenge by developing an innovative technology for combined power generation and carbon dioxide sequestration from hydrocarbon fuels, which is energy efficient, technologically simple and robust, and suitable for deployment in the transportation sector.
Hydrogen provides an ultimate fuel for any vehicle power plant, be it a hydrogen-fed internal combustion engine or a fuel cell, because of its high energy density (per molecule) and environmentally benign reaction products (water). However, the transportation sector needs a high volume density (liquid) energy carrier similar to gasoline that can be efficiently stored, transported and conveniently loaded onboard the vehicle. Thus, the liquid fuels, synthetic or naturally occurring, need to be processed onboard to produce hydrogen for use in the power plant, while simultaneously capturing CO2, rather than emitting it to the atmosphere, with subsequent storage and sequestration in a centralised location. In such a system, the existing liquid fuel distribution infrastructure would still be used, which makes it an economically plausible solution for the near-term as well as potentially an enabling scheme for the long-term sustainable energy future.
The immediate challenge then lies in invention and development of novel technologies for efficient hydrogen production with synergistic CO2 capture from synthetic (or natural) hydrocarbon fuels for portable / distributed power plants. In the near to mid future, CO2 could be captured onboard, collected through the current refueling stations and delivered to a centralised / sequestration site.
There are various approaches and technologies that can be successfully adopted for CO2 capture onboard the vehicle depending on size/power, driving range and utility of a specific vehicle. Arguably, the easiest from the technical perspective and economically most feasible is fuel de-carbonisation in a catalytic reformer with steam, resulting in high purity hydrogen to be used in the IC engine or a fuel cell (in the future) and highly enriched stream of CO2. This CO2-rich stream can be liquefied into a dense form suitable for onboard storage at the moderately high pressures and near room temperature by using, for example, multi-stage vapour compression refrigeration (VCR) with minimal energetic penalty. The VCR technology is mature, reliable and cheap, and is already in use on most vehicles (e.g. as part of the air conditioning unit).
In general, any high density carbohydrate fuel, including conventional petrol, diesel and biofuels, is amenable to de-carbonisation and onboard CO2 capture. However, synthetic fuels with low carbon content (e.g. methanol) are more advantageous from the CO2-capture perspective, and are also easier to catalytically reform at lower temperatures and with minimal poisoning of the catalyst.
Adding CO2 capture technology would definitely require additional equipment put under the hood of the vehicle, whose operation will have to be integrated with other engine functions. This will incrementally add to the price of the engine. This additional capture equipment is not expected to be bulky as compared to the engine itself and should scale well with the engine power. This suggests that significant changes to the automotive design may not be needed to accommodate the CO2 capture onboard of the vehicle. For example, because of the similarity of densities of the liquid carbohydrates and of the compressed, liquefied CO2, very little, if at all, additional storage room will need to be added to the vehicle as the fuel tank, which will be emptied upon fuel consumption, may be used for storing the captured CO2. Interestingly, although seemingly counter-intuitive, adding the CO2 capture may not become a burden on the engine, but can actually help improve its performance (energy conversion efficiency) and mileage. This is because the onboard-integrated CO2 captures enable regenerative processing of the fuel with minimisation or complete elimination of any residual fuel losses due to incomplete chemical reactions. This result is illustrated as an example in our recent paper "Conceptual study of distributed CO2 capture and the sustainable carbon economy" published by the Journal of Energy Conversion and Management.
I am not aware of any car makers who are actively pursuing incorporation of CO2 capture onboard the vehicle. Toyota Motors expressed interest in such development, but I am not sure what the current status is and how serious these efforts are.
Implementation of CO2 capture technology will probably push the engine manufacturers towards development of the hydrogen-fuelled power generation, be it the hydrogen-charged IC engine in the near term (e.g. BMW vehicles) or fuel cells further down the road, as fuel de-carbonisation will produce a stream of high purity "green" hydrogen fuel. In addition, the engine manufacturers will have to develop an in-house expertise or partner with chemical processing equipment companies to design the catalytic reactors for onboard fuel reformation and CO2 separation. Finally, incorporation of suitable refrigeration/liquefaction technologies for CO2 storage in a high volumetric density, liquid state will be required. For the aftermarket, there will be a challenge of retrofitting the existing vehicles by adding an equipment for fuel de-carbonisation and CO2 capture and storage. This may present some significant technical challenges and impose cost burden on customers.
The fuel reformer for de-carbonisation will be a stand-alone, add-on unit to the engine, and various designs developed over the years can be adopted. Among the most exciting recent innovations is a so-called CHAMP (CO2/H2 Active Membrane Piston) reactor, which offers a highly scalable (for different power loads) solution for transportation applications by exploiting unique advantages of the piston-in-cylinder design of a typical IC engine. The CHAMP reactor, invented at the Georgia Institute of Technology (Atlanta, USA) and whose embodiments are described in the US Patent Application #11/708,772, is not only a very efficient catalytic reaction device, but also well suited for transportation application by offering very fast transient control of the reaction processes, matching any changes in the engine power requirements. This motivates accelerated design, development, and commercialisation of CHAMP technology.
A remarkable change in the market conditions in the last 1-2 years with a dramatic rise of interest in "green" technology, including significant venture funding for development of such technologies may become a strong force which will motivate the automakers to seriously consider the CHAMP and other de-carbonisation technologies for implementation on the next generation vehicles. In addition, it is expected that very stringent government regulations on carbon emission may be invoked in different parts of the world in the next 3-5 years, for example in California, which would in effect force all automakers to embrace onboard CO2 capture / management technologies if they would like to sell their products.
Interview conducted by Omer Ahmed Siddiqui, Assistant Editor, Auto Focus Asia.
