Biogas energy recovery plant

The plant is composed of the following sections:

• Collection system
The biogas being produced by biodegradable parts of wastes disposed in the landfill is extracted through a collection system composed of vertical wells and perimeter reception pits.

• Biogas conveying system
Each collection element is connected through a pipe (secondary line) to severalmanifolds (control stations) arranged throughout the perimeter of landfill acting for adjusting the flow rate by means of special valves and monitoring systems. The gas is then conveyed towards the extraction station through underground pipework (primary lines) arranged along the landfill perimeter.

• Extraction and control system
An automatic control system operates for testing all physical parameters of gas flow (flow rate, pressure, temperature) as well as the most important qualitative parameters (% methane and % oxygen).
Physical and chemical parameters are tested automatically by a computer operating for changing regulation in order either to optimise gas quality or stop collection in case of danger. Fromcontrol systems, after being purified, biogas is then conveyed for cooling operation at a temperature near 1°C through a tube bundle-like water-biogas heat exchanger which a chiller is operated with. The core of the extraction and inspection section is an aspiration unit throughwhich the required depression is created for thewhole biogas collection systemand, at the same time, the pressure necessary for biogas to fuel electricity generators and/or torches is supplied.

• Energy Production
The plant for the production of electricity is composed of an electricity-generating set and a voltage transforming system. The incoming gas is conveyed to electricity generators made up of engines fuelled by biogas. Electricity, once transformed from low to medium voltage, is conveyed to the national distribution network. Electricity generators are equipped with an automatic carburation control system guaranteeing, along with the gas purification process, that emissions limits are observed.

• Emergency system
In dumps equipped with systems used for biogas energy recovery, the torch operates as a security system in case of emergency. Should either the biogas rate extracted from dumps be higher than maximum energy requirements of electricity-generating set or the latter be out of order, biogas combustion is carried out in torches in a way that dump safety conditions are maintained constantly.