We have lately been reporting on the work at Penn State University, wherein technology is being developed to recycle the Carbon Dioxide by-product of our coal use directly back into valuable fuels and chemicals.In light, especially, of the developments there, one Penn State researcher, Craig Grimes, as we reported, described the geologic sequestration of Carbon Dioxide as "ridiculous".We have also cited the work at Penn State of Dr. Chunsan Song, and the technology he is helping to develop, referred to as "tri-reforming", wherein Carbon Dioxide can be combined with steam and methane to form higher hydrocarbons, i.e., liquid fuels.Following is an excerpt from the enclosed link which more fully explains that concept. We have felt obliged to edit it heavily for presentation herein, and strongly suggest that readers examine it fully through the enclosed link, where the explanatory illustrations, and extensive supporting documentation, are available.Brief comment follows:"Tri-reforming: A new process for reducing CO2 emissionsResearchers at Penn State have developed a new process for the effective conversion and use of carbon dioxide in flue gas from power plants.The threat of global warming has fueled worldwide efforts to develop technology that reduces carbon dioxide emissions. The conversion and utilization of CO2 present an interesting paradigm to scientists and engineers because CO2 is an important source of carbon for fuels and future chemical feedstocks.
In general, CO2 can be separated, recovered, and purified from concentrated CO2 sources by two or more steps based on absorption, adsorption, or membrane separation. Even the recovery of CO2 from concentrated sources requires substantial energy input. The separation and purification steps can produce pure CO2 from power plants’ flue gases, but they also add considerable cost to the conversion or sequestration system. Current CO2 separation processes require significant amounts of energy that reduce a power plant’s net electricity output by as much as 20%. Although new technology developments could make this recovery easier to handle and more economical to operate in power plants, it is highly desirable to develop novel ways to use the CO2 in flue gases without going through the separation step.
The tri-reforming process we are developing at Pennsylvania State University, is a three-step reaction process. It avoids the separation step and has the promise of being cost-efficient for producing industrially useful synthesis gas.
Using flue gas to convert CO2
Flue gases from fossil fuel-based electricity-generating units represent the major concentrated CO2 sources in the United States. If CO2 is separated, as much as 100 MW for a typical 500-MW coal-fired power plant would be necessary for today’s CO2 capture processes based on alkanolamines. It would be highly desirable to use the flue gas mixtures for CO2 conversion without the pre-separation step. On the basis of our research, we believe that there is a unique advantage of using flue gases directly, rather than pre-separated and purified CO2 from flue gases, for the proposed tri-reforming process.
In our proposed tri-reforming process, CO2 from the flue gas does not need to be separated. In fact, water and oxygen along with CO2 in the waste flue gas from fossil fuel–based power plants will be used to tri-reform natural gas and produce synthesis gas (syngas).
Proposed tri-reforming process
Tri-reforming refers to simultaneous reforming of oxidative CO2–steam from natural gas. It is a synergetic combination of endothermic CO2 reforming, steam reforming , and exothermic oxidations of methane.
Coupling CO2 reforming and steam reforming can yield syngas with the desired H2/CO ratios for methanol and Fischer–Tropsch (F–T) synthesis.
Steam reforming is widely used in industry for making H2. When CO-rich syngas for oxo synthesis and syngas with a H2/CO ratio of 2 are needed for F–T synthesis and methanol synthesis, steam reforming alone cannot give the desired H2/CO ratio. Steam reforming gives a H2/CO ratio of 3, which is too high and thus needs to import CO2 for making syngas with H2/CO ratios of 2 or lower.
The CO2 reforming (dry reforming) of methane has attracted considerable attention worldwide. CO2 reforming is 20% more endothermic than steam reforming; however, it is necessary to adjust the H2/CO ratio for making MeOH or F–T syngas. Two industrial processes use this reaction: SPARG and Calcor.
Carbon formation in the CO2 reforming of methane is a major problem, particularly at elevated pressures. When CO2 reforming is coupled to steam reforming, this problem can be mitigated effectively. This carbon formation in CO2 reforming can be reduced by adding oxygen.
The combination of dry reforming with steam reforming can accomplish two important missions: to produce syngas with desired H2/CO ratios and mitigate the carbon formation that is significant for dry reforming. Integrating steam reforming and partial oxidation with CO2 reforming could dramatically reduce or eliminate carbon formation on reforming catalyst, thus increasing catalyst life and process efficiency. Therefore, the proposed tri-reforming can solve two important problems that are encountered in individual processing. Incorporating oxygen in the reaction generates heat in situ that can be used to increase energy efficiency; oxygen also reduces or eliminates the carbon formation on the reforming catalyst. The tri-reforming can be achieved with natural gas and flue gases using the waste heat in the power plant and the heat generated in situ from oxidation with the oxygen that is present in flue gas.
The tri-reforming process ... is the key step in the recently proposed CO2-based tri-generation of fuels, chemicals, and electricity.
In principle, once the syngas with the desired H2/CO ratio is produced from tri-reforming, it can be used to produce liquid fuels by established routes such as F–T synthesis and to manufacture industrial chemicals such as methanol and acetic acid. Syngas also can be used to generate electricity with either integrated gasification combined cycle (IGCC)-type generators or fuel cells.
The tri-reforming concept is consistent, in general, with the goals of Vision 21 EnergyPlex concept, which the U.S. Department of Energy (DOE) is developing. The proposed goals of DOE Vision 21 for power plants include more efficient power generation (>60% with coal, >75% with natural gas), higher overall thermal efficiency (85–90%), near-zero emissions of traditional pollutants, reduction of greenhouse gases (40–50% reduction of CO2 emissions), and co-production of fuels.
The feasibility of tri-reforming
We have not found any previous publications or reports of using flue gases for reforming or CO2 conversion that are related to the proposed concept. Our computational thermodynamic analysis shows there are benefits of incorporating steam and oxygen simultaneously in CO2 reforming of natural gas or methane . Some laboratory studies with pure gases have shown that adding oxygen to CO2 reforming or to steam reforming of methane, can improve energy efficiency or synergetic effects in processing and mitigation of coking. A feasibility analysis by thermodynamic calculation showed that using CO2–water–oxygen–methane to make syngas is feasible. Inui and co-workers have studied energy-efficient hydrogen production by simultaneous catalytic combustion and catalytic CO2–water reforming of methane using a mixture of pure gases including methane, CO2, water, and oxygen. Choudhary and co-workers have reported on their laboratory experimental study on simultaneous steam and CO2 reforming of methane in the presence of oxygen at atmospheric pressure with Ni/CaO . Choudhary’s work shows that it is possible to convert methane into syngas with high conversion and high selectivity for CO and hydrogen. Ross and co-workers have shown that a Pt/ZrO2 catalyst is active for steam and CO2 reforming combined with the partial oxidation of methane.
Therefore, the proposed tri-reforming of natural gas using flue gas from power plants appears to be feasible and safe, although detailed experimental studies, computational analyses, and engineering evaluations are still needed. Recent preliminary experiments in our laboratory showed that syngas with desired H2/CO ratios can be made by tri-reforming methane using simulated flue gas mixtures containing CO2, water, and O2 in a fixed-bed flow reactor. For example, we have studied the proposed tri-reforming in a fixed-bed flow reactor using gas mixtures at atmospheric pressure that simulate the cases with flue gases from coal- and natural gas-fired power plants. As an example, Figure 3 shows the results of tri-reforming methane using simulated flue gas of coal-fired plants at 850 °C for 300 min under atmospheric pressure over a commercially available Haldor–Topsoe R67 catalyst.
Other technical challenges must be overcome before tri-reforming can be successfully upscaled. Flue gases contain inert nitrogen gas in high concentrations, and thus the conversion process design must consider how to dispose of nitrogen. It is possible that oxygen-enriched air or pureoxygen will be used in power plants in the future. If that becomes a reality, then the proposed tri-reforming process will be even more attractive because of much lower inert gas concentrations and higher system efficiency. .
An important feature of the proposed tri-reforming is that it is the first innovative approach to conversion and utilization of CO2 in flue gases from power plants without separating CO2. "
-------Some brief comments and highlights:First: "Coupling CO2 reforming and steam reforming can yield syngas with the desired H2/CO ratios for methanol and Fischer–Tropsch (F–T) synthesis."And, we should all now know what can be obtained from methanol and/or FT synthesis: Gasoline.Second: "In our proposed tri-reforming process, CO2 from the flue gas does not need to be separated."The cost savings from that, in the recycling of CO2 into liquid fuels and chemicals is huge.Finally: "The tri-reforming process ... is the key step in the recently proposed CO2-based tri-generation of fuels, chemicals, and electricity."Our choice is pretty clear: We can either spend a lot of money collecting our CO2 and stuffing it down leaky geologic sequestration rat holes; or, we can collect it and turn it into gasoline.
