Approximately 12000 Danish farmers produce 24 millions pigs per year, of which 85% are exported. Dealing with the waste is a big part of farm management.
Manure can be gasified under anaerobic conditions and the biogas can be converted into heat and power in combustion plants or engines. Pig farmers in Denmark can choose to utilize pig manure at “farm scale plants” (where pig farmers have their own production units) and “joint biogas plants” (where several farmers share one large production unit).
The main production processes are following:
(1) pig manure is transported from the pig stable to a pre-storage tank
(2) the manure is heated to about 37ºC and transferred to an anaerobic reactor where it is mixed with organic matter from e.g. slaughter houses and fish industry
(3) biogas produced in the reactor from gasification of manure and organic matter from industry is transferred to a gas storage tank
(4) biogas is transferred to a stationary engine or a gas combustion unit which is producing heat and electricity or just heat
(5) degassed manure and organic matter from industry is transferred to a manure storage tank and distributed on agricultural fields as fertilizer
(6) electricity and heat is used locally and/or transferred to the national electric grid respectively the local district heating system.
Average manure transportation distances in step 1 and 4 range between 1.5 km and 7.5 km (Seadi, 2000) at joint scale plants. At farm scale plants, transportation of pig manure is small. About 80% of manure gasified in Denmark is gasified in joint scale units and about 20% is gasified in farm scale units (Biogasbranchen, 2004).
Biogas is to a large extent combusted in stationary engines at both farm and joint scale plants. However, gas furnaces are also used occasionally e.g. in cases of excess gas production and in cases of extraordinary heat demand (personal communication with various actors in business). All electricity produced at both farm scale and joint scale plants is utilized and most of heat produced at joint scale plants is utilized.
More general info on Danish pig farming
If you are interested in the possibility of installing such a system Green Farm Energy, in Denmark are a company at the forefront of this technology.