Selexol plant

Selexol. licensed by the Norton Company, uses the dimethyl ether of polyethylene glycol. A Selexol plant can be designed to provide some selectivity for H2S. For example, the plant can be designed to provide pipeline quality gas (0.25 grains H S/IOOscf) while slipping 85% of the COi. ... 

The synthesis gas from the waste heat recovery is rich in acid gases and is passed to a "Rectisol" or "Selexol" plant for their removal. During this process small amounts of hydrogen, carbon monoxide, methane, nitrogen and argon are dissolved in the solution and lost from the system in the acid gas stream. 

The "Rectisol" or "Selexol" plant of the "selective" type absorbs both H S and C0 , but in the regeneration section of the plant the H S and CO are separated to provide two streams, one or which is CO, virtually free from H S, and the other is of a suitable CO2/H2S ratio to be processed in a conventional sulfur recovery plant. 

At high syngas pressure, physical solvent-based processes become increasingly attractive, for example, the Rectisol and Selexol processes. There are more than 55 Selexol plants worldwide, treating natural and syngas.51 The Selexol process solvent is a mixture of dimethyl ethers of polyethylene glycol, and has the formulation... 

Union Carbide reported that as of 1992, a total of S3 Selexol plants had been installed. These comprise 10 for CO2 removal from various synthesis gases, 12 for CO2 removal from natural gas, 15 for selective H2S removal (with or without CO2 removal), 8 for desulfurization of synthesis gas, and 8 for landfill gas purification (Epps. 1992A). 

If selective removal of sulfur compounds is required, the Selexol plant consists of an absorber, a flash, and a steam-heated stripping column [see Figure 14-1(C)]. The flashed gas is compressed and recycled to the absorber inlet, and the regenerator effluent is processed for the production of elemental sulfur. 

Table 14-10 Operating Data of SELEXOL Plants Processing Natural Gas ...

The unreacted outlet gas from the methanol synthesis reactor contains mainly CO and H2O. By adding steam, the CO is converted to CO2 according to CO H2O H2 + CO2 in the shift reactors. Like in an IGCC power plant case, a 95 percent conversion of CO has been assumed. The CO2 content in the gas then increases from 14 vol% to 44 vol%. CO2 is captured in a Selexol plant. The removal efficiency has been assumed to be 87 percent, which is close to the assumption for the IGCC power plant case. 

Sepasolv MPE [Methyl isopropyl ester] A variation on the Selexol process, using the methyl isopropyl ethers of polyethylene glycol as the solvent. Developed by BASF. Four commercial plants were operating in 1985, removing hydrogen sulfide from natural gas. Wolfer, W., Hydrocarbon Process., 1982,61(11), 193. 

SOLINOX SO,. Linde NO,] A process for removing both NOx and SOx from fluegases. The SOx is removed by scrubbing with tetra-ethylene glycol dimethyl ether, circulated in a packed tower (the Selexol process). The NOx is destroyed by Selective Catalytic Reduction ( SCR). The sorbent is regenerated with steam the SOx is recovered for conversion to sulfuric acid. Developed by Linde in 1985 and used in a lead smelter in Austria and several power stations in Germany. In 1990 it was announced that it would be used at the titanium pigment plant in The Netherlands operated by Sachtleben. 

The applicability of the Selexol process for partial oxidation gases [568] was already mentioned. With high H2S concentrations in the raw synthesis gas a H2S rich fraction can be separated and fed to a Claus plant for production of elemental sulfur. At lower H2S concentrations a liquid-phase oxidation has to be applied. As shown in the example of Figure 73, two H2S-containing C02 streams are treated in separate... 

According to Kellogg 27.9 GJ/t NH3 can be achieved in a natural gas based plant with minimum energy export, but with export of larger quantities of steam this value could probably be brought down to about 27 GJ/t NH3. Figure 107 shows a simplified flowsheet of the process [1069] with Selexol C02 removal unit. 

In the Canadian plant, only the air compressor is driven by a steam turbine, which receives the total steam generated in the plant and has an electric generator on the same shaft. All other consumers, including synthesis gas compressor, are driven by electric motors. Separate machines are used for makeup gas and recycle compression. The makeup gas compressor is located upstream of the methanator to make use of the compression heat to warm up the cold gas coming from the Selexol carbon dioxide scrubber. 

A further inq)rovement for the conc.-COa-methanol path is the COa-recovery upstream the combustion after CO shift in an IGCC-plant with the selexol absorption process. This technology has a better COa balance than the pulverised coal fired plant with MEA-process technology due to the less decrease in IGCC efSciency from 42% (reference efSciency) to 36% only (after COa capture) [4] but it should be mentioned, that this technology is not state-of-the-art today. The efficiency of the air-COa-methanol vector was calculated to be 38.1%. With more advanced technologies (e.g. high temperature processes), the efSciency can be improved to more than 44% [6]. 

Shah, V.A. and Huurdeman, T.L. (1990) Syndiesis gas treating with physical solvent process using Selexol process technology. Ammonia Plant Safety, AIChE, 86. 279. 

Huurdeman, T. L., and Vinod A. Shah. 1989. Synthesis Gas Treating with Physical Solvent Process using Selexol Process Technology, Ammonia Plant Safety AIChE Symposium. 

The Selexol process has found a very wide range of applications. It was originally used to remove CO2 from an ammonia plant in Nebraska, followed soon after by H2S and CO2 removal from natural gas in the U.S. and in Europe. Other applications include desulfurization and CO2 removal from synthesis gas derived from the partial oxidation of heavy petroleum stocks and from coal gasification. Natural gas treating applications include several, where in addition to production of pipeline specification gas, a relatively pure stream of carbon dioxide is produced for reinjection into oil formations, so-called enhanced oil recovery or EOR. A relatively new use for the process dating back to 1979 is the purification of landfill gas drawn from the biological degradation of municipal waste in sanitary landfills. This application is characterized by the occurrence of chlorinated and aromatic hydrocarbons as impurities in the landfill gas. 

---