What can biogas be used for?
Biogas is a carbon neutral energy source, which is often used to generate heat and/or electricity.
Biogas boiler is often used in sewage treatment plant and industrial waste digester as heat is needed to maintain the digester temperature. Modern biogas boiler can achieve heat efficiency over 92%. Boiler can be configured to generate hot water or steam. It can also be designed to use natural gas, LPG or even light diesel, which is often required during starting-up or maintenance period. It is also possible to modify existing boilers to include biogas with existing fuels, like what Fonterra Tirau did.
Combined heat and power (CHP), or cogeneration, refers to the simultaneous generation of both heat and electricity. In almost all
cases this means using small-scale packaged CHP units with internal combustion engines coupled to a generator. The engines run at a constant speed so that the directly coupled generator can provide electrical energy that is compatible with system frequency. The commonly used engines are pilot ignition gas engines and gas spark ignition engines. Depending on the engine size and design, the electricity efficiency is normally 35-43%, while the heat efficiency is around 40-45%.
In Europe, upgrading biogas into biomethane, which is almost the same as natural gas, is an economically feasible option. The extra treatment is to strip CO2 off the biogas. So far this is not a practical option in New Zealand.
Direct discharge of biogas to the atmosphere is prohibited due to the odor and strong greenhouse effect. at certain time or place. At certain circumstances, biogas flare is the only consumer as there is no other suitable user.
The promising use of biogas in the near future is to produce bioplastics (PHA). This technology attracts lots of attention as it is carbon negative (carbon capture), and the production cost can be lower than plastic production from oil.