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:
(ft3 per lb)
Biogas is often compared to natural gas to determine its relative energy value. Number-wise, the two compare as follows:
|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!