Is Biogas in Your Future?

With the price of natural gas and other hydrocarbon fuels on the rise, it is becoming increasingly important for industry to search for methods to reduce fuel requirements (energy conservation, process optimization, waste minimization, etc.) and identify ways to recover energy for beneficial reuse. One area that should be thoroughly investigated is the potential to produce biogas from organic wastes.

Biogas originates from the bacterial decomposition of organic material under anaerobic (without oxygen) conditions. The natural generation of biogas is a vital part of the biogeochemical carbon cycle. Each year, an estimated 700 to 900 million tons of methane are released worldwide into the atmosphere, of which about 90% is derived from biogenic sources.

On a practical level, for a typical food, beverage, or pulp and paper plant, the range of organics wastes generated on a daily basis represents a significant energy source if processed anaerobically. Typical biogas values (at 60% methane) per unit material degraded are as follows:

Substrate Biogas
(ft
3 per lb)
Carbohydrates 10.4
Fats 27.5
Proteins 13.6
Organic acids 11.2

Biogas is often compared to natural gas to determine its relative energy value. Number-wise, the two compare as follows:

Parameter Natural Gas Biogas
Methane 91% 55-75%
Ethane 5% 0%
Propane 1.8% 0%
Butane 0.9% 0%
Carbon dioxide 0.6% 25-45%
Ammonia 0 ppm 10-200 ppm
Hydrogen sulfide < 1 ppm 10-5,000 ppm
Dew point -5° C saturated
Calorific value 1,050 BTU/ft3 640 BTU/ft3

Do some quick calculations to estimate the energy value of particular organic waste streams at your plant. You will be surprised at the amount of potential energy they represent!

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