CH4, CO,H2O and CO2 will be the major products in any gasification process (if you have contaminants you might also produce SOx or NOx) the product will be at or near equilibrium (CH4 + H2O ,=> CO + 3H2 and CO + H2O H2 + CO2).  Increasing temperature or decreasing pressure will reduce the amount of CH4 in the product. selectively removing  CO or H2O will increase reaction of CH4 to product but that is difficult to do  

Sir We can not reduce pressure in gasifier as it must be 30 kg/cm2. How much temp is needed to reduce CH4 below 1% in syn gas. Removal of CH4 from CO and H2 is very costly process. Syn gas is to be fed for FT chamber to produce ethylene and propylene. 

Can we separate CH4 and CO/H2 by PSA. If yes then what are operating conditions.

I'm sorry I took so long to respond it depends on how much steam you are using at 3.4 steam to carbon ration the temperature required to achieve 1 mole % CH4 in the dry syngas will be about 1000 C.  I have attached  a spreadsheet that does the equilibrium calculation - note it converges by solving a circular reference so you will need to allow circular references as  shown in the attached word document snip,

PSA or membrane can be used to remove H2 (to adjust H2/CO ratio to the F-T reactor)  You can adjust the amount of steam  used to achieve the desired H2/CO ratio.

The POX_ATR or POX_liquid feed spreasheets are probably closest to the conditions you are trying to model

Saturated steam of 32 kg/cm2 will be used with steam to rice husk ratio of 2.5. Just need H2/CO ratio of 2.5 -3.0. FBC temp is designed to keep around 850 degrees max as it will introduce sintering and ash aggolomoration due to K2O in ash. Problem around this temp CH4 will 4-5%. Can we use molecular seive or PSA to separate CH4 from CO/H2 mixture ??.  The size of CH4 molecule is much bigger than CO/H2. The limit CH4 is also desired so that it does not poision Co/Mn based FT catalyst.

Separating H2 from CO+CH4 is relatively easy with a PSA or a membrane. Separating CO from CH4 is more difficult.  What is your overall objective? Why do you need to remove the CH4 before the F-T reactor?  You are going to produce more CH4 at the F-T reactor that will need to be removed.  The typical way of separating CH4 and ethylene commercially is cryogenic distillation.  I have attached a link with a PFD for a typical Ethylene plant with cryogenic distillation to separate C2= from CH4

http://www.industry.usa.siemens.com/automation/us/en/process-instrumentation-and-analytics/process-analytics/pa-brochures/Documents/PIAAP-00002-0713-Ethylene.pdf

Thanks. Removal of CH4 from CO & H2 is required for conversion efficiency. In atmospheric gasification of biomass CH4 generated is small enough to get ignored and Ft outputs are have less CH4 produced but at elevated pressures CH4 generation is accelerated. Cryogenic distillation is too costly process for CH4 removal syn gas. Can we crack mixture of CO, H2 & CH4 to economically produce syn gas from it ??. The aim is to maximize ethylene and propylene production with least compression cost. 

Upendra,

               You should not expect to produce less than equilibrium CH4 concentration in your syngas and you should expect that your F-T reaction will produce quite a bit of CH4.   

Are you gasifying with air or O2?  Air separation is expensive but if you have a lot of N2 in your syngas you are likely to have NH3 and amines in your product as well and the separation becomes more difficult.

What products are you actually trying to produce?  If you are making commercial grade ethylene and propylene you will probably need a cryogenic distillation.  If you are making an E/P mix for somebody else to fractionate you my be able to avoid cryogenic fractionation.

Separating Ethylene/propylene from methane is not easy. For large scale operation cryogenic separation is the proven commercial solution.  One alternative is to use a sponge oil to remove the ethylene and Propylene from the lighter components.    A light naphtha compounds like Hexane or Heptane will preferentially absorb  propylene and to a lesser extent ethylene. The dissolved propylene/ethylene (and butylene) can be recovered by stripping the light olefin from the naphtha absorbent and recycling,   This will work much better on propylene than ethylene,  but if you circulate enough of the right adsorbent it should work.   This is a common way for refiners to maximize propylene recovery at Fluidized Bed Catalytic Cracking Units (aka FCCU or cat cracking units) 

Sir, we are gasifying with saturated steam at 32 kg/cm2. Rest heat for  initial endothermic reactions is provided by carbonation of CaO. All CO2 generated by gasification is absorbed by CaO at elevated pressures of more than 20 kg/cm2. Same operating conditions encourage CH4 production. In demathanixer column operating at 200 kelvin and 62 kg/cm2 pressure we can very well separate mixture of CO, H2 and CH4 from demethanizer column. Real issue is how to separate CH4 out of CO & H2. As we can not operate FBC more than 850 degrees, one way is reheat product gases at 1000 degrees in presence of Ni catalyst and kill CH4. But on cooling Will CH4 not be regenerated ??.  By generating CO2 free syn gas at elevated pressures like 31 kg/cm2 we have removed first 3 stages of compression and need only 2 stages of compression to acheive 62 bar and less cooling to reach 200k. Cryogenic seperation of CH4 from CO requires cooling at bp of CO which is 150 kelvin which will become a costly affair.

Yes reheating to 1000 C to finish the reforming is a good option.  In  fact 1000 C is the typical operating temperature for most commercial Autothermal Reformers.  You will need to cool the reactor effluent rapidly to avoid carbon deposition (CO + CO => C + CO2) you should not form any CH4 if you cool rapidly in a waste heat boiler producing steam (40 Barg steam is typcal).  You are still likely to form considrable amounts od additional CH4 at the F-T reactor that you will have to deal with..

Also you should only need 1 stage of  recip compression to go from 31 to 62 Barg.  Syngas should be cooled to 100 F (38 C) before compressing

Size of CH4 molecule is 414pm whereas CO & H2 are around 100-140pm. Why they can not be separated by PSA or membrane seperation like O2 and N2 are separated ??. Economical decision has to be there whether to burn to generate steam or separate methane for regasification with C4+ to generate additional syn gas.

Can we separate propylene/butylene  from propane/ butane, isobutane by naptha absorption process ??.