6 replies to this topic

[Govind]

We are engaged in manufacture of Coal gasifier. The gas contains the following by percentage: CO- 15 to 20 percent; CH4-2 to 6 percent; N2-40 to 50 percent; H2-15 to 20 percent; CO2- 7 to 10 percent. I would like to know how to find the Velocity, Density of the mixed Gas, and the Specific Gas constants of all the contituents. May I inform you that I am a Mechanical Engineer, therefore I have little knowledge of Chemical engineering .I request you to give the details of worksheet in simple calculations. Oophs! I forget to ask as to what should be the size of the pipe to transport it to the length of 20 metres


Thanks

Edited by Govind, 28 May 2011 - 06:53 AM.

[breizh]

Hi .

A few things are missing in your post :
Composition : % Mol or Mass
Working condition : P, T

Breizh

[Govind]

Breizh,

You are right! I have the following information, I hope it'll suffice:

Volume: 8,000 normal cubic metre per hour;
Pressure: 2 Kpa max: temperature at delivery 500 degrees celcius.

You can, I think you can calculate it on 1 Normal metre cube??

Govind.

Edited by Art Montemayor, 06 June 2011 - 08:52 AM.

[kkala]

Attached "gas.xls" can be a first step to your queries. Please note the following.
1. Gas composition should be representative and sum of all components should be exactly 100%.
Assumed percentages in the spreadsheet are arbitrary by me, please revise them in the above sense. Probably additional components should be introduced (e.g. H2O gas, O2, etc).
2. Reported gas pressure of 2 kPa (assumed as 2 kPa above atmospheric pressure, ie 2 kPa g) may be lower than the actual. Please check, this also affects estimated line diameter.
3. Ideal gas behavior has been assumed for the gas mixture, true for low pressures.
4. For reported pressure and temperature, 20" pipe line could be enough, based on Norsok standard P-001, freely available in the WWW, as well as a rough estimate of frictional ΔP. Other standards may give a somehow different diameter. But operating pressure mainly affects pipe diameter.
5. Velocity of gas is about 33 m/s (as reported in gas.xls)for 20" pipe.
Hope above can give some help to you.

Attached Files

•  Gas.xls   16.5KB   47 downloads

Edited by kkala, 05 June 2011 - 01:56 PM.

[Govind]

Dear KKala,

1 The gas pressure of 2Kpa is the gauge pressure at maximum, it never touches the max. However the average pressure is around 1 Kpa. However, I am not getting the reading when I substitute the value in xls. Could you please help? We use a pipe of 820 mm dia (32 inches). How do we get that?

[kkala]

1 The gas pressure of 2Kpa is the gauge pressure at maximum, it never touches the max. However the average pressure is around 1 Kpa. However, I am not getting the reading when I substitute the value in xls. Could you please help? We use a pipe of 820 mm dia (32 inches). How do we get that?

1. For 2 kPa g (0.02 Barg) density calculated in gas.xls is 0.3823 kg/m3. Changing pressure to 1 kPa g (0.01 Barg) will give 0.3786 kg/m3. Since two decimal figures have been defined for density in gas.xls, you will not see a difference unless you define more decimal figures on the density cell.
However this pressure is too small to have any chance on the results. It is also noted that viscosity is practically independent of pressure (up to about 10 Bara).
2. Above reminds a low pressure distribution network (but temperature is too high for it) rather than a gasifier exit; I remember a case when gas pressure downstream of gasifier was much higher. But conditions may be different in your case.
3. A pipe of 32" seems oversized (not prohibited in this case), at least to referred Norsok Standard. Probably the applicable standards in your case call for lower max velocity or pressure drop per 100 m; or there are peaks higher than 8000 Nm3/h; or cases of higher temperature.
4. Correct composition of the gas (the example uses an arbitrary one) could influence density.

Edited by kkala, 08 June 2011 - 01:08 AM.

[Govind]

Given the composition of the coal and its calorific value,is it possible to "predict" to a reasonable extent the composition of the constituent of the gases,( without resorting to analysis of the gases) before the coal is burnt?