Dear Mirjam,

Biogas typically refers to a mixture of gases produced in result of breakdown of organic matter by the process of anaerobic fermentation. Composition  Methane (CH4) 40-75% Water (H2O) 0-10%  Carbon dioxide (CO2) 25-55% Hydrogen sulfide(H2S) 1-3%  Ammonia (NH3) 0-1% Nitrogen (N2) 0-5%  Oxygen (O2) 0-1% Hydrogen (H2) 0-1%.

Energy calculation of biogas plant  Formula to calculate total gas production For cattle max gas production /kg = 0.05 m3 Total gas =Total dung in kg x 0.05  Calculation for 4 animals each producing 8 kg dung if we are successful to collect that all  Total will be 8x4=32  Total gas=0.05x32 =1.6 m3 if > 1m3 =19 Mega joules So 1.6x19=30MJ To convert it to KWh >> 30/3.6 =8.3 KWh

Conversion to electrical energy  Note: when we convert it to electrical energy 65% of energy lost as Heat & other mechanical losses as utilized by electrical generator. So 8.3*35/100 = 2.91 kWh is available as electrical energy from 32 kg of Cow dung  Consumption  We can run 60watts of 2 bulbs + 1 fan of 80 watts >>For 12 hours easily…on 2.91 kWh (el) energy

Calculation for cooking  Medium Stove uses 9 MJ of energy /hr Manure of 3 animals is fuel for stove to run for 2.5 hrs 8x3=24kg dung =1.2 m3 1.2x19MJ= 22.8 MJ / 9= 2.5 hours.

For more information, please use the following link:

http://www.slideshare.net/alisaqlain111/biogas-plant-designs-and-engery-calculations-ali-saqlain

Hoping this will be helpful,

Rafik

Thank you for your answer. I understand how electric output is calculated. However, I want to know the power capacity and not electric output (so kW instead of kWh). The power capacity depends on the size of the digester I guess, but I can imagine other factors also play a role (e.g. type of feedstock). So how is this calculated?

Dear Mirjam,

I refer you to the following link which I think will be helpful.

http://www.renewableenergyworld.com/articles/print/rewna/volume-1/issue-1/solar-energy/how-to-compare-power-generation-choices.html

Rafik

Dear Mirjam,

Power capacity actually depends on the biogas or methane production. It does not depend on the size of the digester or the feedstock. You can have a big digester and a great feedstock but a poor design and bad operation (bad temperature and agitation systems, too low HRT, etc.).

For instance, some dairy farms have reported yields from 1.2 to 7.1 cows per kW installed capacity (most of them between 4 and 5), so 4 or 5 is a good number to start, but it really depends on the quality of the digester and the conditions under it is operated.

At the end of the day it is necessary to estimate the methane production during a certain period of time, and the efficiency of the generator that will be used.

Let's asume that we produce 1000 m3 of biogas per day with a 60% of CH4. It gives us 600 m3 of methane, which means about 6000 kW-h of energy every day. If the efficiency of the generator is 40%, we can get 2400 kW-h of electrical energy each day. Now, we divide this value by 24 h per day and we get a power capacity of 100 kW. Usually a bigger generator is chosen in case more biogas is produced.

I hope it helps.

Best regards.

Jorge

Dear Mirjam,

Regarding power output of biogas installation, our consideration would merely related to methane (CH4) production, that could be obtained from methane content of the biogas.

This amount of methane then can be converted into energy of around 55.5 MJ/kg.

To obtain the amount of methane production in kilogram, a gas mol calculation could be made, but a simple calculation may use 0.717 g/L at 0 degree C and 1 atm. The methane production in litre need to be adjusted with STP condition, though.

Base on the below power production calculation from biogas, could someone please help me to calculate total installed capacity?

With 1,831,404.4MJ. of energy produced, the expected amount of power to be produced is calculated as follows:

Converting 1,831,404.4MJ. to KJ = 1,831,404.400KJ

Converting KJ to KWh, 1 KJ = 0.00028 KWh

Converting 1,831,404.400 KJ to KWh =1,831,404.400 KJ × 0.00028KWh = 512,793.232KWh.

Using a combined cycle plant with an assumed efficiency of 54%,[1]

= 0.54 × 512,793.23KWh

= 2,769,083.442KWh

= 276,90MWh

In view of the above calculation, the amount of power expected to be produced from the organic component of municipal solid waste in Ghana is 276,90MWh every day which is equivalent to 98,036.444635MWh in a year (assuming a plant availability of 97%). This is equivalent to ….MW in installed capacity.

Power capacity of biogas plants in terms of kW or MW can be determined using following steps,

1. Take 1 cubic meter biogas plant

2. Biogas production throughout year at the rate of 60%. It means total biogas produced in a year will be 0.6 x 365 = 219 cubic meter

3. 1 cubic meter biogas at 60% methane content has 22 MJ energy.

4. At 35% electric energy conversion, it will yield (22/ 3.6)*0.35=2.14 kWh.

5. Based on average production of 0.6 cubic meter biogas , it can be 1.284 kWh / cubic meter biogas per day.

Other way, the heat produced by 1cubic meter biogas equal to (22/3.6 =) 6.1 kWh electricity. Therefore, as per assumption for whole year, one cubic meter biogas plant at 60% efficiency can be said to 3.66 kWh capacity.