CAS researchers propose decoupling gasification reactions for greater control and optimized outcomes
02 January 2011
|Two decoupling approaches applied in developing DCG technologies. The shaded rounded rectangles represent the major component reactions in gasification. Credit: ACS, Zhang et al. Click to enlarge.|
Researchers at the State Key Laboratory of Multiphase Complex System, Institute of Process Engineering (IPE), Chinese Academy of Sciences (CAS) are proposing a different approach to gasification based on separating, and in turn, reorganizing at least one of the series of gasification reactions—which include fuel pyrolysis, char gasification, reforming/cracking, and combustible matter combustion—to better realize the effects of polygeneration, low emission, high efficiency, good product quality, and wide fuel adaptability.
Gasification is emerging as a core technology for the production of chemicals and cleaner power, and refers to a process for converting solid fuels, including coal, biomass, and wastes, into either fuel gas (containing CH4 and some N2 usually) or syngas (containing mainly H2 and CO) for subsequent conversion into fuels and chemicals.
In a paper published in the ACS journal Energy & Fuels, Zhang et al. note that in current major commercial gasification technologies, the series of mutually interactive reactions are fully coupled in a singe gasification reactor. The proposed decoupling gasification (DCG) facilitates or suppresses the interactive effects between the separated and other reactions. The paper generalizes the decoupling approach into two types: isolating and synergizing.
The decoupled reactions can be arranged into two isolated reactors to separate their products to realize polygeneration and also suppress the intereffects between the products of the decoupled reactions. This kind of decoupling approach is called “isolating” decoupling, and the resulting technology integrates usually two reactors, thus calling it “dual-bed” technology.
Another approach of decoupling is termed as “synergizing” decoupling...In this method, the decoupled reactions are rearranged to facilitate the beneficial interactions or to suppress the undesired interactions between the linked reactions (for example, the effect of the products from one reaction on the other reaction). Via this kind of decoupling, it is expected to lower pollutant formation, enable high product quality and high conversion efficiency, and/or enhance the fuel adaptability of the technology.—Zhang et al.
|Summary of typical DCG technologies and corresponding decoupling effects. Click to enlarge.|
...the idea of decoupling reactions actually provides a powerful approach/tool to manipulate some complicated reaction networks to optimize the reaction behaviors and performances. As for gasification, the DCG technologies in fact have a very promising future because of their outstanding merits for clean and high-efficiency co-production of high-quality gas and liquids (tar). In fact,many of the DCG technologies mentioned in this paper are in the process of industrial demonstration and making progress toward commercialization.—Zhang et al.
Juwei Zhang, Yin Wang, Li Dong, Shiqiu Gao, and Guangwen Xu (2010) Decoupling Gasification: Approach Principle and Technology Justification. Energy Fuels, 24 (12), pp 6223–6232 doi: 10.1021/ef101036c
I think there are some other objectives researchers should aim for
1) not using coal as a carbon source or alternatively capturing 90% of the CO2. Make bio carbon which is already 'in the loop' the preferred source.
2) not using air as an oxidant. The problems with NOx and low calorific value stem from too much nitrogen. Maybe chemical or electrolytic oxygen will solve that.
3) meeting a price point, say $2 per litre of liquid or $8 per US gallon.
Posted by: Aussie | 02 January 2011 at 03:35 PM
If you use solar thermal PV H2 and O2 you end up with a more controlled reaction and more fuel. The O2 is used in the gasification and the H2 is used with the biomass carbon to make more fuel.
I was told years ago by someone on here that gasification was old technology that it would never be practical. Opinions are abundant, everyone has one but few can be supported by logic and reason. Opinions need to be backed by facts or they are just blind beliefs.
Posted by: SJC | 02 January 2011 at 05:16 PM
if you use an external heat-source (solar, nuclear or simply electrical), you don't need any O2. The O2 is only added as a 'heat source'. Only adding heat and H2 should produce 100% conversion of carbon to fuel. Even the oxygen atoms already present in the coal or biomass is converted to water.
Posted by: Alain | 03 January 2011 at 05:12 AM
From reading about gasification, the output is different if you use air rather than oxygen in the gasification process. From what I could tell the output is more predictable with oxygen.
Posted by: SJC | 03 January 2011 at 11:23 AM
"Added benefits of the steam and oxygen mixture when compared with the more simplistic air gasification approach include less dilution by the inert nitrogen component of air and a more beneficial final composition of the gas stream for applications in FT synthesis."
Posted by: SJC | 03 January 2011 at 11:27 AM