Biogas Reactors - Operation
The biogas reactor is a fabricated vertical steel tank being insulated on the outside. It has heating coils and a stirring mechanism usually of a paddle design built into the tank.
The pretreated slurry is pumped into the top of the tank, spraying downwards to build up at the bottom of the tank.
Here it is stirred continuously whilst being heated to the temperature required by the particular process.
As we have seen earlier, the most common process is Mesophilic, the optimum temperature to suit the micro-organisms being 95-98°F, so we will examine this process.
The process begins with the circulation of the organic slurry from the holding tank through the pasteurization tanks, of which there are three. These heat the slurry to 160°F; holding the temperature for at least one hour, ensuring that any pathogens are eradicated.
It is then pumped into the biogas reactor where the organic slurry is degraded by the inherent micro-organisms. Using a combination of the application of the right degree of heat in the absence of oxygen, these micro-organisms multiply as the anaerobic process advances, which can be continuous or batch. We shall examine a batch process, where from entering the biogas reactor as slurry and exiting as biogas, takes an average of 28 days of processing.
In the anaerobic conditions and the temperature of the reactor, the micro-organisms degrade the components of the slurry, processing them in the manner shown in the following flow diagram:
As shown in the flow diagram, there are four definitive stages for the organic slurry to undergo inside the anaerobic reactor before the biogas is finally produced, taking almost a month per batch.
Once the process is complete (through practice the operators of the plant will know when this stage is reached) the reactor is opened and the residual sludge removed for further processing to dry or wet agricultural fertilizer. This is a great saving in energy and CO2 emissions, as synthetic fertilizers are a large source of this major component of greenhouse gases.
biogas - production of biogas.
esrustrath - processing biogas
proactivenergy - latest technology.
- energyfromwaste - A Bright Hub article on energy from waste.