Claus Plant Operation

In practice, up to 70% of the reaction can take place in the furnace before the gas is passed directly to the reactors. During the 1950s Claus plants operated at 90-95% conversion and tail gas containing the residual sulfur compounds was passed into the refinery fnel gas systerrr.  

Acid gas from refinery streams contains 70-90% hydrogen srrlfide, whereas acid gas recovered from natural gas is often more diluted. The hydrogen sulfide content of feed gas to the furnace has a significant effect on both plant and catalyst operation. 

With hydrogen sulfide concentrations greater than 60% the flame temperature is stable and all the acid gas and air pass directly to the furnace. With concentrations less than 60% it may be necessary to preheat the gas mixture or even to split the stream so that 37% of the hydrogen sulfide bums in the fimiace and the remainder goes directly to the first catalytic reactor. 

During combustion, some 60-70% of the hydrogen sulfide is converted directly to sulfur. Flame temperature depends on the hydrogen sulfide content of the feed gas and can reach almost 1300°C with more than 90% hydrogen sulfide. 

Carbon disulfide forms by reaction of sitlfur with hydrocarbons  

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Hydrogen sulfide accumulated from desulfurization processes and any onsite sulfur dioxide are converted to elemental sulfur using two or three stages of Claus reactors [61] (Chap. 9). However, Claus plant operation is seldom a profitable operation for a refinery since the recovered sulfur amounts to only a few tonnes per day. However, the improved ambient air quality achieved in the vicinity of the refinery makes this measure worthwhile. 

Naturally, the use of enriched air resulted in an increase in reaction furnace temperature. Both the calculated increased capacity and the theoretical temperature rise in the reaction furnace have previously been published. The observed changes in capacity and temperature for the 50-T/D Claus plants are summarized in Table 5-2. Further information on oxygen enrichment in Claus plant operations can be found in other publications. - - ... 

Another Claus plant operating problem is condensation of sulfur on the catalyst resulting in rapid deactivation. This can be avoided by maintaining the temperature in the catalytic converters above the sulfur dew point of the gas mixture. Should sulfur condense on the catalyst, raising the gas temperature 50°F is usually sufficient to vaporize the condensed sulfur and reestablish catalyst activity (Norman, 1976). 

Typical Claus plant operating conditions are shown in Table 2.9. Temperature in the first reactor is a compromise between the need to remove any carbon oxy-... 

In 1991, there were approximately 418 sulfur production plants associated with oil and gas production in operation throughout the world. Approximately 86% of these plants were based on the Claus process, and there were 118 Claus units operating in natural gas processing faciHties (11). 

In most similar activities in petroleum refineries, the vapors from stripping "sour water" are processed in a Claus plant. With care in design and operation of the stripper, the vapors typically consist of equal volumes of H2S, NH3 and H2O. Such a mixture can support high-temperature reducing flame in which NH3 is destroyed. 

Shell also offers for license a -selective version of the Shell ADIP Process. The ADIP process, which has a flow scheme very similar to Sulfinol, can be used to treat the Sulfinol acid gas to raise the H2S concentration by selectively rejecting the CO2. Some integration of the SCOT process with the ADIP process is often possible thus, reducing overall equipment and operating costs. Costs for the Claus plant are substantially reduced when "selective" ADIP is applied. Two selective ADIP plants are scheduled to come on stream in the first half of 1979. 

Claus plant (including tail gas treatment) are of the order of 32/tonne exclusive of steam credit. Subtracting these costs from the totals in Table I, the overall net revenue from the Claus system would be 21.75/tonne of sulphur produced whereas that from the decomposition process would be 50.50 /tonne - a 230% difference. Even in the unlikely event that the total capital and operating costs for the decomposition process exceed those of the Claus system by 100%, the two processes are still approximately competitive. 

A thorough engineering and economic evaluation of the molten carbonate process was completed by Singmaster and Breyer in 1970, under contract to EPA (8). For the same plant situation, their cost estimates (based on 1970 dollars) were 16.81/kW for the capital investment (not including the Claus plant) and 0.95 mills/kW hr for operating costs without by-product credit. 

The emissions from Claus plants can be expected to present an increasingly serious potential problem in the future as petroleum refineries operate on increasingly sour crudes from the Middle East and elsewhere and as plants are built to desulfurize substitute natural gas (SNG) and liquid fuels from coal. 

The conversion of hydrogen sulfide to elemental sulfur in the Claus process is limited by a combination of equilibrium and kinetic factors. Over the past decade, the pressures of air pollution control requirements have resulted in major improvements in the design and operation of Claus plants, with consequent increases in conversion and reduction of sulfur oxides emissions (74-79). Nevertheless, emissions still commonly exceed the permissible limits coming into force both in the United States and abroad. Sulfur dioxide reduction plants present similar problems. Apart from the initial furnace or reactor, they are essentially Claus plants. 

The Beavon sulfur removal process for the cleanup of Claus plant tail gas is a two-step process in which the sulfur contaminants are first catalytically hydrolyzed and/or hydrogenated to hydrogen sulfide and the hydrogen sulfide is then converted to elemental sulfur and recovered in a Stretford process unit. Commercial plants reduce the concentration of sulfur compounds as hydrogen sulfide in the tail gas from 1-3 vol % to less than 100 ppm. The treated gas contains less than 1 ppm hydrogen sulfide. The chemistry, design criteria, operating experience, and economics of the process are discussed. 

The Beavon sulfur removal process is now a reliable, established method for cleaning up Claus plant tail gas well beyond any proposed regulations. As with any new process, work is currently directed toward reducing capital and operating costs. The capital investment has already been reduced by about 20% over the original design. A further cost reduction now seems possible, thereby increasing the application possibilities of this process. 

Economics. Table II gives specifications for feed from a two-stage 100 LT/D Claus plant with 95% conversion. Table III shows the overall Claus -f- IFP-1500 conversions possible for plants treating tail gas from that Claus unit, with IFP-1500 plants of varying design conversion 90%, 80%, 70%, and 60%. Table IV gives investment and operating costs for these IFP units. 

The Electrochemical Membrane Separator (EMS) technology being developed is compared to a wet removal process with subsequent Claus Plant processing to elemental sulfur and SCOT Tail Gas treatment of flue gases. This wet process utilities aqueous Methyldiethanolamine (MDEA) as an absorbent in a scrubbing operation to bring the HjS level from 1.7% to 4 ppm. The flow rate to these processes is 50MM SCFD and the process pressure is 715 psi. The... 

Paskall, H.G., and J.A. Sames, Optimizing Claus Sulphur Plant Operations, Sulphur 82 Proceedings of the International Conference, London (November 1982). 

A clause for operability of the plant in the range of 80 to 130 % of the capacity in an efficient and safe manner shall be written in the agreement. This is to safeguard when the demand for products is less (to run at 80 % capacity), or at overload of rated capacity (to run up to 130 %) if higher demand for product is to be met urgently. 

Sulfreen tail gas of a Claus plant SO2 from activated carbon + alkaline silicate 20-50 Fixed bed Inert gas at 450°C Industrial operation... 

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