4 replies to this topic

[Govind]

Dear All,

I have a question, which I would put it after the following example.

EXAMPLE:
The analysis of coal indicates 70% of C; 20% of H: and 2% S and the balance non-combustible ash ( by weight). All the ash and 6% of the carbon in the fuel leave the furnace as molten slag; the remainder of the carbon leaves the stack as CO and CO2; the hydrogen in the coal is oxidiised to water and Sulphur emerges as SO2. The selectivity of CO2 to Co production is 10:1


(a) Calculate the percent of excess air fed to the reactor.


This a part of the question, which is relevant to the my problem. The available air blower for combustion with us has a specification as: It delivers air at 6032m3/hour at 7.6Kpa pressure. The above is for a Coal Gasifier producing producer gas. The main constituent of the gas is CO, H, CH4.

My calculation suggests that the air required for complete combustion is 2594.3 kmol/hour, whereas, I have only 260kmol/hour air through the air blower at the maximum revloution of the blower motor. This a case of limited reactant. Now the question is how much CO is produced with the limited reactant which is Oxygen.

[kkala]

Can you also give rate of coal feeding the gasifier? This would help mass balance.

[Govind]

Can you also give rate of coal feeding the gasifier? This would help mass balance.

Ok the rate of coal feeding is 2500 Kg of bituminous coal per hour

[Govind]

Can you also give rate of coal feeding the gasifier? This would help mass balance.

OK the feed rate of coal is 2500 Kg per hour of bituminous coal

[kkala]

Attached "gasifierR1.xls" is a try to show a way, for want of something better by somebody having experience on the subject. Following is noted.
1.The air introduced into gasifier seems to be about 5 times less than what stoichiometry requires for complete combustion (260 vs 1255 kgmol/h).
2. Supposing that no H is burnt to H2O, part of H is transformed to CH4, no C is burnt to CO2, resulting flue gas composition is as per G of "gasifierR1.xls" to satisfy the limited combustion air flow of 260 kgmol/h. That is CH4=31, H2=188, CO=106 kgmol/h.
3. Nevertheless supposed assumptions are probably not realistic, since part of H will be burnt to H2O and part of C to CO2, dictated by equilibrium at operating conditions and probably kinetics.
Besides estimate is typically based on given combustion air flow, without feeling of the gasification (lack of experience).
4. There is hope of "experienced" help by others on this matter, not being an issue of stoichiometry. Otherwise you can search the relevant literature, or go to the supplier of this gasifier for advice.

Attached Files

•  gasifierR1.xls   24.5KB   26 downloads

Edited by kkala, 27 July 2011 - 02:24 AM.