The Process

Biossence's technology partner is Canadian firm Enerkem (www.enerkem.com). Biossence has the rights to use the Enerkem advanced gasification technology in the UK and Ireland. The technological process is described below.

Inputs

Wastes inputs for conversion to energy include:

  • Pre-processed Municipal Solid Waste - Solid Recovered Fuel (SRF) or Refuse Derived Fuel (RDF), the material remaining after recycling and compositing activities
  • Commercial & Industrial Waste
    • Retail & Office Waste
    • Wood Waste (contaminated and non-contaminated)
  • Construction & Demolition Waste
    • Typically the wood, paper & cardboard fractions
  • Pure biomass
    • Energy crops
    • Forestry by-products

Outputs

Outputs from an advanced gasification process can include:

  • Renewable electricity
  • Renewable heat
  • 2nd generation transportation fuels (e.g. Ethanol)
  • 2nd generation chemicals (e.g. Methanol)

A re-use of the inert waste by product as an aggregate material is also being investigated.

Step 1: Waste Reception

  • Material is delivered to the gate in closed container from pre-treatment facilities (Solid Recovered Fuel or SRF).
  • A small volume of waste is stored on site to provide a buffer to cover non-delivery over weekends or Bank Holidays.
  • Material is fed mechanically into the feed system by a series of conveyors.
  • Feed system matches pressure in gasifier before waste fed into fluidised bed.

Step 2: Gasification

  • The gasifier converts the SRF material into a hydrocarbon rich synthetic gas (syngas) by reacting them with oxygen obtained from adding steam or air.
  • Additional byproducts include inert residues and hydrocarbon vapors which condense out and become liquid oil, waxes and tar.

Step 3: Gas Clean Up

  • Syngas has some corrosive pollutant gases and eroding ash particles in it that we have to take out in a gas cleaning plant because:
    • Environmental emissions will comply with the tightest European standards.
    • Pollutants will damage equipment.
    • Ash will block moving parts of the gas engine machinery.

Step 4: Power Generation

  • The syngas is fed into a series of gas engines which convert the energy in the syngas to both electrical and thermal energy.
  • In this process, the gas reacts with the oxygen in the air to convert the carbon in the syngas to carbon dioxide.
  • The process - combustion - releases large quantities of energy and rapidly increases the temperature of the gases within the engine cylinder. The pressure from the combustion forces the pistons down and this provides the mechanical energy to drive an electrical generator. The engines also produce a significant amount of thermal energy which can be recovered from the engine exhaust.
  • Trace pollutants, especially NOX, must be cleaned from the exhaust gas, which consists mainly of carbon dioxide and nitrogen. A series of abatement measures are used to ensure all emissions will meet the necessary environmental requirements.

Alternative Step 4: 2nd generation bio-fuels

  • The alternative to generating renewable power (electricity and heat) using this process is the production of 2nd generation bio-fuels such as Ethanol and Methanol.
  • This is the business model that Enerkem is pursuing in the North American market where the production of renewable transport fuels and green chemicals is encourages through guaranteed fixed price tariffs.
  • The key difference in the process is Step 4 where the syngas is fed into a chemical process rather than combusted in gas engines.
  • This business model is one Biossence see as an interesting opportunity for future development as the UK Government looks to development a Renewable Transport Obligation (RTO) along similar lines to the existing Renewable Obligation (RO).