Here's a link to a paper with some numbers on gas production per liter of sludge:

http://ajes.in/PDFs/09-1/13.%20Biogas%20production%20from%20sludge.pdf

You need to start with the amount of sludge, figure the gas production from it, then size your engine to the gas output.

I would recommend against an internal combustion engine. They tend to be very fussy about fuel quality. The silanes in biogas can really gum up the works.

An external combustion engine (steam boiler) matched to a turbine & generator should give you much better reliability and lower maintenance than an IC motor-generator unit. Emissions can also be lower due to controlled combustion in the firebox.

Hi there,

I agree with your approach. That is the way to go about the sizing issue.

However, my experience would be the other way around expecting that you would be better off with an ICE as the efficiency is higher and the total installation much smaller and cheaper with much less machinery and things that can go wrong.

It might be a matter of preference, size availability and initial costs involved. Of course, you need a good quality ICE derived from a Diesel engine, not a converted gasoline engine. Don't buy a GM Motor for that duty.

Contacting www.agro-biogenics.com could be of help if you are located in India.

There are several manufacturers that produce combined heat and power (CHP) cogeneration systems that are specifically designed to run on biogas. Look into IPower, CAT, or Jenbacher.

At 100 mld I would expect that you will be producing quite a bit of gas and be looking for an engine in the hundreds of kW range if not MWs, in which case CAT or Jenbacher will likely be your best bet. The waste heat can be added to the digester to aid in the digestion process or cut down on the cost of process heating.

The siloxane issue is worth noting and good fuel (gas) treatment is a must for any type of engine, and can pose a considerable cost at start-up as well as during operation.

Estimate your gas production and then contact a manufacturers representative to get the right unit(s) for the project.