Our Technology
Overview
BioGenpower utilises tried and tested ENERGOS technology for its small scale EfW gasification plants. ENERGOS technology was designed to provide non large city communities in Scandinavia with a cost-effective alternative to conventional ‘mass burn’ incineration.
Traditional incineration was designed to offer a cost-effective large-scale solution, however this requires large volumes of waste, together with significant numbers of associated vehicles movements . The buildings are extremely large, dominating the skyline and because they are burning large volumes of waste, the chimney stack is generally very high too.
Because solid waste is a heterogeneous material, the combustion process (mass burn) is compromised, in order to ensure that the mixture of light, heavy, dry, wet, high and low cv waste (which can all be on the incineration grate at the same time) is burned properly. The result is that NOx levels, the main primary polluting emission, is generally high. It is therefore necessary to install expensive flue gas treatment processes to achieve acceptable emissions that comply with the European Union Waste Incineration Directive (EU WID) levels.
ENERGOS technology operates with exceptionally low emission levels, a result of employing a two stage system that first gasifies the waste to produce a synthetic gas. This syn gas is then transferred to a second stage chamber where it is oxidized. Because the fuel has been converted to a gas, it is much easier to mix thoroughly with air in an enhanced and controlled environment where the flame temperature can be finely controlled, dioxins thoroughly destroyed and NOx emissions minimised.
This well controlled process enables a very simple flue gas treatment system to be employed, while at the same time, delivering reliable and stable emissions well below the limits set by the EU WID.
Plant Operations
Our plants are designed to operate continuously on a 24 hour per day basis, normally for 5.5 days per week. Planned preventative maintenance is carried out periodically and the standard operational time is around 8,000 hours per year.
Waste reception and treatment is normally conducted during normal operating hours, however the gasification process and power generation operations are continuous. Skilled Plant Operators work on a rotating shift system. A typical 80,000 tonne plant will employ approximately 12 people directly, though this does not include additional maintenance personnel required from time to time.
Waste Handling
Our plants are designed to receive several different waste streams, including:
- Residual Municipal Solid Waste (RMSW) (where source separated wastes are collected, such as paper, green waste, plastics, glass, cans, etc).
- Municipal Solid Waste.
- Non Hazardous Commercial and Industrial Wastes (CIW).
- Wastes such as paper reject from the recycling process.
- RDF/SRF and general residual from recycling plants (including MBT).
Our plants operate with a two tier bunker system, a reception bunker and a fuel bunker. Waste is taken from the reception bunker, sorted and shredded. Recyclables such as glass and ferrous metals are removed, leaving the fuel bunker with a high CV waste to fuel the gasifier. The recovered metal and glass is collected in separate skips and periodically collected and sent for further recycling.
The Fuel crane operates on a pre-programmed cycle and moves around to mix the fuel within the bunker. When load sensors detect the need, the crane delivers waste automatically to the fuel delivery chute in order to feed the gasification unit, before retuning to its mixing programme. Mixing promotes a more homogeneous mixture and encourages greater process stability.
The waste and fuel bunker hall is totally enclosed with fast opening and closing doors. Vehicles reverse into the hall and the door is closed before the waste is deposited in the bunker. Air from bunker area is drawn into the Gasification Unit and the High-temperature Oxidation Unit creating a slight sub-atmospheric pressure within the reception hall to prevent the escape of odours.
Gasification Unit
The Gasification Unit is operated at sub-stoichiometric conditions to create a syn-gas.
Bottom ash is discharged from the Gasification Unit to an external ash storage area via a water basin. Bottom ash can be used in a variety of industries such as block making and road construction. The Gasification Unit is equipped with a fuel oil/gas auxiliary burner that is used for pre-heating of the Unit prior to start-up of the system and after programmed shut downs.
ENERGOS Technology Process Flow Diagram
High-temperature Oxidation Unit
Syn-gas from the Gasification Unit is passed via a transfer channel to the High-temperature Oxidation Unit where air and re-circulated flue-gas are injected into the High-temperature Oxidation Unit to obtain complete combustion of CO and TOC, the cracking of dioxins and the production of a flue gas with low NOx content.
The High-temperature Oxidation Unit is equipped with a fuel oil/gas auxiliary burner. The auxiliary fuel burner will only be used for the heating of the combustion system to its normal operating temperature, the maintenance of that temperature, or emission control.
Boiler (HRSG) & Steam Turbine system
The boiler system recovers energy from the flue-gas to produce steam that is utilised in a steam cycle for electricity production. Steam from the HRSG is passed to the steam turbine system, which itself consists of a steam turbine with generator and a water-cooled vacuum condenser with condensate pumps. Generated electricity is connected to the Power Company’s distribution network. Condensate from the water-cooled condenser is fed to the feed-water tank of the boiler system by condensate pumps.
Flue-gas cleaning system
The flue-gas cleaning system consists of a bag-house filter which is injected with a mixture of lime and activated carbon. Cleaned flue-gas from the processing line is passed to a flue-gas stack by use of a flue-gas fan.
Emissions to Air and Water
Other than normal sewage associated with the employees facilities there are no process water emissions. Boiler blow down water is used to provide cooling for bottom ash and the remainder is injected into the oxidation chamber.
Emissions to air are significantly lower than the EU WID limits. The flue stack height is determined by modelling the local air quality and ensuring that the dispersion of the emissions from the plant do not allow the local air quality or local receptors (persons living, working or passing around the plant) to be exposed to harm. It is normal to assume the worst case scenario of the maximum limits allowed under the EU WID. This determines the flue stack height. Under normal operations the emissions are lower and therefore the dispersion is better than predicted.
