Lurgi rectisol process

These tests demonstrated that the Lurgi Rectisol process provides an extremely pure synthesis gas which can be charged directly to the metha-nation plant without problems of sulfur poisoning of the nickel catalyst. However, in order to cope with a sudden sulfur breakthrough from Rectisol as a result of maloperation, a commercial methanation plant should be operated with a ZnO emergency catchpot on line. 

The raw gas is purified in the Lurgi Rectisol process (cold methanol scrubbing) where various by-products (eg tar naphthas) and impurities (eg CO2 and H2S) are removed. 

The elemental sulfur is removed by conventional technology. The gases are purified by the Lurgi Rectisol process which uses a low temperature methanol wash to remove H2S, COS and CO2. The acid gas stream is then passed to a Stretford unit which is preferred to the Claus unit because of the high percentage of carbon dioxide in the stream. Sulfur in the stack gas would be removed by conventional flue gas desulfurization techniques and the sulfur would then remain as sulphite sludge and not be recovered as elemental sulfur. 

The German Lurgi Company and Linde A. G. developed the Rectisol process to use methanol to sweeten natural gas. Due to the high vapor pressure of methanol this process is usually operated at temperatures of -30 to -100°F. It has been applied to the purification of gas 1 plants and in coal gasification plants, but is not used commonlv natural gas streams. 

The Rectisol process [667], [707], [711]-[715] seems to be the prime choice in partial oxidation plants. The process, invented by Lurgi and developed further by Linde, operates with chilled methanol, a cheap and readily available solvent, in which carbon dioxide, hydrogen sulfide and carbonyl sulfide (COS) are readily soluble at low operating temperatures of below - 30 °C. The Henry absorption coefficient for H2S is about six times higher than for C02-... 

The Rectisol process, developed by Lurgi, is the most widely used physical solvent gas treating process in the world. More than 100 Rectisol units are in operation or under construction worldwide. Its most prevalent application is for deep sulfur removal from syngas that subsequently undergoes catalytic conversion to such products as ammonia, hydrogen, and Fischer-Tropsch liquids. 

Operation at very low temperatures with very sharp separations results in relatively complex flow schemes. This, combined with the need for low level refrigeration, leads to high plant costs. As a result, most applications of the Rectisol process represent relatively difficult gas treating conditions where other gas treating processes are not suitable for one reason or another. Typical applications are the purification of gas streams in the heavy oil partial oxidation processes of Shell and Texaco and the Lurgi coal gasification process, as used at the Sasol plants in South Africa. 

The Rectisol process was initially developed in Germany by Luigi GmbH. It was developed further Jointly with Linde AG (Kriebel, 1989) and is now offered by both firms. The major use of the process is in coal- and heavy oil-based facilities to produce ammonia, methanol, hydrogen, SNG, Fischer-Tropsch liquids, and 0x0 alcohols. In 1996 it was reported that more than 100 units were in operation or under construction (Lurgi Ol-Gas-Chemie GmbH and Linde AG, 1996). 

The Amisoi process is similar to the Sulfinol process in that it u.ses a combination of a physical and chemical solvent for acid gas removal. It was developed by Lurgi GmbH and employs methanol as the physical solvent, as does the Rectisol process, which was co-dcvel-oped by Lurgi (Bratzler and Doerges, 1974). The first plants practicing ihe Amisoi process used alkanolamines (MEA and DEA) as the chemical solvents however, the more recent plants, where selective H2S removal was an objective, have used alphatic alkylamines (Kriebel, 1985, 1989). 

This system is licensed by Lurgi GmbH, and more than 65 units are in operation. The methanol is cooled to — 50°C, at which temperature the vapor pressure is less than 1 mm Hg. The Rectisol process, described in U.S. Patent 2,863,527, is used chiefly for the following applications ... 

Cold methanol has proven to be an effective solvent for acid gas removal. Cold methanol is nonselective in terms of hydrogen sulfide and carbon dioxide. The carbon dioxide is released from solution easily by reduction in pressure. Steam heating is required to release the hydrogen sulfide. A cold methanol process is Hcensed by Lurgi as Rectisol and by the Institute Francaise du Petrole (IFP) as IFPEXOL. 

Consequently, two semicommercial pilot plants have been operated for 1.5 years. One plant, designed and erected by Lurgi and South African Coal, Oil, and Gas Corp. (SASOL), Sasolburg, South Africa, was operated as a sidestream plant to a commercial Fischer-Tropsch synthesis plant. Synthesis gas is produced in a commercial coal pressure gasification plant which includes Rectisol gas purification and shift conversion so the overall process scheme for producing SNG from coal could be demonstrated successfully. The other plant, a joint effort of Lurgi and El Paso Natural Gas Corp., was operated at the same time at Petrochemie Schwechat, near Vienna, Austria. Since the starting material was synthesis gas produced from naphtha, different reaction conditions from those of the SASOL plant have also been operated successfully. 

SASOL [Suid-Afrikaans Sintetiese Olie] Not a process but a large coal gasification complex in South Africa, operated by the South African Oil and Gas Corporation. It first operated in 1955 but took several years to be fully commissioned. A Lurgi fixed-bed gasification unit is used for the primary process. Downstream processes include the following ones, described under their respective names Aige, Fischer-Tropsch, Rectisol, Sulfohn, Synthol. 

In another case, when the acid gas is very rich in CO2 (i.e. 90 percent or higher) and contains olefins, the author knows no suitable process other than Stretford or Unisulf. An example is Rectisol offgas downstream of a Lurgi gasifier the Stretford process has been used, although with some problems. 

Rectisol A process for removing sulfur compounds from gas mixtures resulting from the partial oxidation of hydrocarbons, based on physical absorption in methanol at low temperatures. Originally developed in 1951 by Lurgi Gesellschaft fur Warmetechnik for the SASOL coal gasification plant... 

Rectisol is licensed by the two companies that developed it, Lurgi and Linde. It uses cold methanol as a solvent and can remove total sulfur down to below 100 ppb. It will also remove other impurities present in synthesis gas such as cyanides and carbonyls. Although not cheap, the gas purity achievable with this process makes it a prime candidate for applications processing syngas to chemicals such as ammonia or methanol. 

Lurgi 01-Gas-Chemie GmbH, and Linde AG, 1996, Rectisol, Hydro. Process, Gas Processes 96, p. 134. 

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