Technology and Apparatus on Natural Gas Desulfurization
Development of a Highly Efficient Technique for Natural Gas Desulfurization and Creation on Its Basis of an Economic Compact Desulfurization Apparatus for Fuel Cell-Based Power Plants
Tech Area / Field
- CHE-IND/Industrial Chemistry and Chemical Process Engineering/Chemistry
3 Approved without Funding
VNIIEF, Russia, N. Novgorod reg., Sarov
- Boreskov Institute of Catalysis, Russia, Novosibirsk reg., Akademgorodok
- Netherlands Energy Research Foundation, The Netherlands, Petten
The dominating majority of power plants (PP) based on fuel cells (FC) use natural gas as a fuel, which is reformed catalytically and converted into the gas mixture enriched with hydrogen to be used in a fuel cell stack (FCS) for the electrochemical reaction of oxidation. However, the reformer and the FCS activity is deteriorated rapidly and they stop operating at catalyst poisoning by the poisons contained in natural gas. Therefore, while using natural gas in fuel cells, the need in its preliminary cleaning from sulfur-containing admixtures, in particular, from hydrogen sulphide and mercaptan, arises.
Fuel cell-based power plants use, as a rule, the methods of desulfurization on synthetic zeolites and catalytic absorption of preliminary hydrogenated organic sulphides. In many cases natural gas desulfurization should be preferably conducted under low temperature conditions. Thus, the most widespread domestic method of gas cleaning from sulfur in FC PP is the method of physical adsorption using synthetic zeolites. Such technique is characterized by a low sulfur capacity and a limited selectivity of sulfur-containing elements at presence of other components that leads to increase of weight-dimension characteristics and rise of the apparatus cost. The technique of catalytic absorption is rather complicated in usage, especially when it is necessary to create local gas cleaning systems, since it requires the apparatus heating up to approximately 4000С that extends the start-up time and makes the apparatus operation under varying duties more complicated. In addition, in the above techniques the desulfurization efficiency changes depending on the concentration of sulfur-containing compounds in gas.
The alternative to the said methods is the process of direct dissociation of hydrogen sulphide into hydrogen and elemental sulfur:
H2S <=> H2 + S
This method is attractive owing to the possibility of hydrogen generation, as well as due to utilization of sulfur admixtures in the form of elemental sulfur. The main goal of the current Project is the development of highly efficient chemisorbents-catalysts and a technique of natural gas cleaning before its usage in the FC PP by the method of low-temperature dissociation of hydrogen sulphide into hydrogen and elemental sulfur, as well ad the creation on basis thereof of a highly efficient and economic apparatus for natural gas desulfurization. The efficiency of the chemisorbent-catalyst functioning should not depend on the concentration of hydrogen sulphide in natural gas. The sulfur capacity of the proposed chemisorbent-catalyst should be at least 5% weight. In addition, catalysts for low-temperature removal of mercaptans from natural gas will be developed.
Based on the results of fundamental research fulfilled at the Institute of Catalysis, we are proposing a novel approach towards effecting the reaction of hydrogen sulphide direct dissociation that would provide a highly efficient cleaning of natural gas. In the method proposed we deal with specific chemisorption based on the process running under adsorption-catalytic mode, when the reaction is pided into two stages:
· Hydrogen sulphide adsorption with hydrogen extraction:
H2S + [ ] => H2 + [ S ]· Further periodic regeneration of the chemisorbent-catalyst:
[ S ] => [ ] + SRunning the process under this mode allows to separate the stages of hydrogen sulphide dissociation into hydrogen and elemental sulfur and attain the equilibrium shift towards sulfur and hydrogen formation already at rather low temperatures. The laboratory experiments have shown that it is possible to attain practically 100% conversion of hydrogen sulphide under cyclic operation within the temperature range from room temperature up to (200 ч 400) єС. An instant start-up of the apparatus is possible and its operation stability under transient conditions is provided. The proposed sulfur capacity of the catalyst (at least 5%) will be several times higher than that of synthetic zeolites (about 1%), and unlike the latter it does not depend practically on the concentration of sulfur-containing compounds and the presence of other admixtures in natural gas.
The proposed technique is original and has no analogs in the world. It would allow to provide highly efficient desulfurization of natural gas till 1 ч 0,1 ppm and can be realized as a compact local unit. this reducing its cost by several times as compared with conventional cleaning apparatuses.
All the mentioned advantages of the proposed desulfurization apparatus make it attractive for the application in mobile plants with small power operating under varying power modes. In addition, the proposed method can be applied in every branch, wherein gas desulfurization is required – from chemical industry to autonomous test benches – i.e. every industrial branch that needs a simple by design and efficient apparatus.
To attain the Project goal that is the development of an advanced technique for natural gas desulfurization and an apparatus on the basis thereof, the following works will be fulfilled within the Project frameworks:
1. Search for most efficient chemisorbents-catalysts and optimum operating conditions will be conducted.
2. Samples of desulfurization chemisorbents-catalysts will be developed.
3. Studies on optimization of the chemisorbent-catalyst composition, its preferable shape and the process conditions will be carried out.
4. An original highly active catalyst with improved properties will be applied.
5. A production technology for catalyst manufacturing will be developed and recommendations on the process technological parameters will be issued.
6. A prototype apparatus for gas desulfurization for bench testing will be developed and manufactured.
7. An original design of the desulfurization apparatus, with its design and manufacturing technique to be elaborated, will be applied.
8. A schematic process flow diagram for the desulfurization process will be developed.
This will be of scientific and practical value, since the issue of the FC PP cost reduction is rather urgent for the purpose of commercialization thereof, thus increasing the efficiency of fossil fuel utilization and reducing the man-caused impact on the environment.
The Project will be fulfilled by a team of highly qualified specialists, the majority of which being involved in programs on development of defense products. The team comprises scientists, specialists in chemistry, physics, material studies, catalysis, automation of experimental studies, mathematical modeling, The qualification of participating scientists is confirmed by their expertise in developing desulfurization catalysts (USSR Patents №№ 4131466, 4131457,4131455; RF Patents №№ 4905383, 9400546/26, 94035589/04; US Patents № 4978519, two catalysts are applied successfully in industry) and compact catalytic apparatuses. A group of researchers among the Project participants took part in international Projects (two NATO grants SfP971984 and SfP974217). The participants of the proposed Project worked under the ISTC Projects # 1678 and # 2281р.
The labor effort of the scientists engaged in weapons development and production makes up 3064 men/days (52 % from the total scope of works).
Technical issues will be constantly discussed with Project Collaborators with the purpose of obtaining a commercially viable result right upon the Project completion. Joint experiments and calculations can be conducted.
The proposed Project meets the ISTC goals and objectives and allows to support applied research in the area of FC technology development, which are promising devices for converting the chemical energy of hydrocarbon fuel into electric and heat energy and meet current environmental requirements.
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