Molecular sieve dryer

Complete removal of water from the pyrolysis gas is achieved with molecular sieve dryers. Typically, there are two dryers one is in normal operation while the other is being regenerated. The dryers are designed for 24 to 48 hours between successive regenerations and high pressure methane heated with steam at 225°C is the preferred regeneration medium. Activated alumina was used in older plants, but it is less selective than molecular sieves (qv). 

Figure 2. Schematic of the apparatus. Key 1, He cylinder 2, O cylinder 3, CO cylinder 4, molecular sieve dryer 5, rotameter 6, fine-control needle valve 7, solenoid valve 8, pressure gauge 9, sand bath 10, preheater 11, reactor 12, IR spectrometer 13, gas bubbler and 14, automatic timer. 

Molecular sieve dryers, 10 613 Molecular-sieve effects, 16 821 Molecular sieve membranes, 15 813t Molecular sieve products commercial, 16 838-839t manufacturing processes for, 16 831 Molecular sieves, 16 811-853. See also Carbon molecular sieves Zeolite entries... 

In the gas-cleaning loop, a catalyst bed system for the removal of hydrocarbons and a molecular sieve dryer for removing moisture is generally preferred to an ethylene glycol scrubber. 

The current ethanol dehydration technology - two-stage distillation followed by a molecular-sieve dryer, as shown in Figure 8.18(a) - uses approximately 16 000-20 000 Btu of energy/gal of ethanol produced. This is about 20% of the energy value of the ethanol produced. There is a considerable interest in membrane technology that would be lower in cost and less energy intensive. 

The use of molecular sieve dryers for removal of the remaining carbon oxides and water in the synthesis gas to levels of < 1 ppm levels has gained prominence in low-energy-consumption ammonia plant designs. Instead of molecular sieves so-called knockout drums (high pressure vessels to remove traces of liquids) can be used as well. 

The sample is weighed and placed in the oven where the water is vaporized. Nitrogen carrier gas flows through the molecular sieve dryer into the oven, where it absorbs the water vapor and transports it to the electrolytic cell. 

In addition to the solvent adsorbed on the AC, there is also moisture given up by the SLA. Owing to its volatility and low molecular weight, this is not strongly adsorbed and is desorbed preferentially. The desorption loop includes a molecular sieve dryer with sieves able to take up water but not solvent (Table 7.8). 

Drying of Synthesis Gas - No water is allowed to enter the synthesis converter because of its adverse effect on the catalyst. The older plants used to remove the residual water by mixing the makeup synthesis gas with the converted gas ahead of the ammonia condensation and separation. However, it required more compression power since converter effluent undergoes recycle compression before product condensation. It also diluted the ammonia concentration of the converted gas and resulted in a lesser amount of ammonia condensed and higher recycle flow rates. Most modern plants use molecular sieve dryers to remove water in the synthesis gas to less than 1 ppmv. The sieves are usually located at the interstage of the synthesis gas compressor [4[. The dried makeup gas can then be combined with the recycle and sent directly to the ammonia converter. 

Other requirements are placed on the carrier gas and the stationary phase. As indicated in the PTGC instrumentation list, the carrier gas must be dry to prevent the accumulation of water (and other volatile impurities) at the cool column inlet (before the start of a run) since this phenomenon will result in ghost peaks during the PTGC run. One conunon solution to this problem is to insert a 5A molecular sieve dryer in the gas line before the instrument. 

Final purification of the synthesis gas uses molecular sieve dryers. This enables the synthesis gas to be added to the synthesis loop at converter inlet instead of upstream of the ammonia separator. 

The gas stream leaving the quench tower mainly consists of ethylene. The gas is compressed in a multistage compressor with intercooUng and then fed to the caustic tower, where CO is absorbed with a sodium hydroxide (NaOH) solution. NaOH in the gas is removed in a water wash section in the tower. The remaining water in the gas stream is removed in a molecular sieve dryer before the gas enters the final purification stage. 

A 5A molecular sieve, not previously soaked in dilute ethylene, was used to dry compressed ethylene gas in a flow system. An exothermic reaction attained red heat and caused explosive failure of the dryer. The smaller-pored 3A sieve is not catalytically active towards ethylene. 

Spray drying is used for obtaining cracking catalysts in the form of microbcads (silica-alumma or silica alumina doped with 5 15% of X or Y molecular sieves exchanged with rare earth) Figure 2a and 2b show two different kinds of particle obtained by different atomizations of a given feed to a spray dryer... 

Desiccant Dryer—A means of removing water from a solvent by adsorption with desiccant, such as a silica gel or molecular sieve. 

While analyzing the phenomena at molecular sieve drier, it understood that during regeneration cycle RSH molecular bed rejects C3-i-hydrocarbon. When newly regenerated dryer bed is brought online the RSH molecular sieve co-adsorbs C3-i- hydrocarbons fi om the feed gas. Resulting in a reduced C3-I- concentration in treated dry feed gas stream till bed becomes saturated. 

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