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for Gas Purification
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The Rectisol Process
Applications
Production of clean synthesis gas from oil or coal gasification.
The principal uful components of a raw synthesis gas produced from heavy oil or coal gasification are H 2and CO. Dependent on the feedstock and type of gas production process this raw gas can contain 3 - 35 % CO 2 as well as CH 4, H 2O, H 2S, COS and traces of HCN, NH 3, N 2, Ar, gum formers,CS 2, mercaptans, thiophenes, organic sulfides, and higher hydrocarbons.In order to turn this raw synthesis gas into a uful product, the impurities must be partially or totally removed.Sulfur compounds, HCN and NH 3should be discharged in a stream as concentrated as possible so as to im-prove the economics of subquent treatment. The CO 2 must be suffic-iently clean to allow it to be discharged directly to atmosphere or even ud as a product.天堂鸟的寓意
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茶经全文T ypical purity requirements for synthesis gas:T otal sulfur less than 0.1 ppm by volume CO 2
2 ppm to
3 %by volume depending on the type of synthesis
Process Principle
The Rectisol process us cold methanol as a physical solvent.The undesired components of the raw gas, such as CO 2, H 2S, COS and the remaining sulfur compounds, HCN,NH 3 as well as nickel and iron car-bonyls are physically absorbed from the raw gas by the solvent. The components are then desorbed by reducing the pressure of the solvent,stripping and, if required, reboiling the solvent. The absorbed higher hydro-carbons are recovered in an additional extraction stage, if necessary.The solubility of the different compo-nents to be removed varies consider-ably. This also applies to H 2S and CO 2and allows lective removal of the components.
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Lurgi´s classic process for purifying gas from partial oxidation of heavy oils and coal to obtain synthesis gas quality
Purity requirements for CO 2 to atmos-phere in accordance with the German Air Pollution Control Regulations ("TA-Luft"), for example:
H 2S content less than 5 mg/m 3n dry gas.
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Rectisol unit for a 1,400 tpd ammonia and 350 tpd methanol plant
The solubility data of the various gas
in methanol are illustrated in Figure 1.Since the solubility data of H 2S and the organic sulfur compounds are appreci-ably higher than that of CO 2, the H 2S concentration in the Claus gas can be incread to acceptable levels even if the H 2S to CO 2 ratio in the raw gas is unfavourable.
The solubility of the trace components HCN, NH 3 and sulfur compounds like mercaptans are much higher than tho of H 2S (not shown in Figure 1).This makes it possible to remove them parately using a very small solvent rate in a prewash stage. The rich methanol from this prewash stage is regenerated by integrating this loop into the H 2S hot regeneration system so that the trace components are routed directly to the Claus gas.
茶壶英文Fig.1 Absorption coefficient α of various gas in methanol (partial pressure: 1 bar)
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Process Description
Fig.2: Production of gas from partial oxidation of heavy oil
The Rectisol process is extremely flexible, a feature which allows it to be tailored to a large number of different individual applications. The block flow diagram in Figure 2 shows the arrange-ment required for the production of methanol starting with the gasification of heavy oil using the Lurgi Multi Purpo Gasification Process (MPG).Of cour Rectisol is ud in combin-ation with all other types of partial oxidation or gasification process.Additional possibilities for other products are indicated by dotted lines.Particular advantages on the overall arrangements are:
婚姻证明在哪里开s High pressure steam generation s
High achieveable Claus gas concentration
s
Overall CO 2 is available as a sulfur-free product
Figure 3 shows a simplified process flow diagram for this application.The raw gas entering the plant is coo-led. The trace components like HCN and NH 3 are removed in the prewash stage with cold methanol.
Thereafter, the sulfur is removed from the gas using CO 2-laden solvent to a residual sulfur content of below 0.1 ppm.
The solvent from the H 2S absorber is regenerated first by flashing at medi-um pressure to recover the uful gas (H 2 and CO) and then by heating to boiling temperature and stripping with methanol vapour.
In cas where there is sufficient H 2S
贪心的反义词in the raw gas, hot regeneration pro-duces a Claus gas with adequate H 2S content for further treatment without
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Fig.3 Selective desulfurization and CO 2 removal to produce methanol synthesis gas
any special measures needing to be taken. Where the H 2S content of the raw gas is lower or the CO 2 content higher an additional stage, stripping and reabsorption, must be provided as shown in the next example (Figure 4).The portion of the clean gas which has been shifted in the CO shift conversion unit has a typical CO 2 content of 33 %.This gas re-enters the Rectisol unit, is cooled, and CO 2 is removed in a two-stage CO 2 absorber. In the lower c-tion, the CO 2 content of the gas is reduced to about 5 % using flash-regenerated methanol. The remaining
CO 2 is removed using hot regenerated,cold methanol in the upper ction so that about 3 % CO 2 is contained in the synthesis gas.
The flashed CO 2 is free of sulfur and can be discharged directly to atmos-phere. Under certain circumstances a water wash system may be necessary to reduce the quantity of methanol in the CO 2 for environmental reasons.The refrigeration balance of the sys-tem is maintained by the refrigeration plant.