Process Used

Bioenergy, the process of converting biological material into energy, has been established for some time. It provides a renewable, green energy solution that is carbon neutral. If waste is used, as in the innovative BioenNW process, then it also offers an effective waste management solution.

The conversion cycle has four main stages:


01. Pre Processing

Some waste needs to be pre-processed before the pyrolysis stage. This may be as simple as separating out the different types of waste, e.g. municipal waste would need to be sorted before being processed. Some waste, such as sewage, needs more preparation.

Sewage is first processed by anaerobic digestion. An anaerobe is a microorganism that does not require oxygen to metabolise food. Anaerobic digestion occurs when microorganisms feed on the sewage in an oxygen free environment.

These microorganisms convert the sewage into three main products: Water, biogas (a combination of methane and carbon dioxide) and cake or digestate (the remaining residue).

The biogas can be used in a gas engine to produce power, while the cake is used as biomass (feedstock) for the bioenergy reactor.

02. Pyrolysis

This process has been used since ancient times to turn wood into charcoal. Processed waste is fed subjected to elevated temperatures (over 430˚C) and pressure to produce biochar (a type of charcoal), liquids (a combination of oils and water) and vapours (a range of gases depending on the biomass being processed).

03. Gasification

The vapours are taken from the pyrolysis process and the various gasses it contains are separated out. In the case of contaminated waste, some of the separated gasses may be sold to the chemical industry.

The end product of this stage is syngas which is used for power generation.

04. Power Generation

Syngas can be used as fuel for a Combined Heat and Power (CHP) generator.

These generators produce electricity and useful heat in a single process.

They are a very efficient; a traditional coal-fired generator has an average efficiency of 34% while CHP plants work up to an efficiency level of around 80%.