FAQ: The Technology

  • Could the plant explode?

    No. The gasification plant works slightly below atmospheric pressure the whole time, because large fans pull air through the system constantly. There is nothing inside the plant to cause an explosion and there is no pressure to release.

  • How does a gasification facility work?

    Gasification describes the process by which material (RDF in this instance) is converted into a synthetic gas (and ash) by using an external heat source in a low oxygen environment. The process is similar to that used for making town gas from coal, which has been done for decades. The syngas is combusted in a high efficiency boiler and the heat generated is used to raise steam for a turbine, where electricity is generated. In addition, a proportion of the heat generated can be supplied for use in external applications, either as steam or very hot water. Heat is recirculated from the gas combustion process to heat up the incoming RDF to create more syngas so only a small amount of fossil fuel (usually natural gas) is required to kick-start the process. Gasification is classed as an Advanced Conversion Technology (ACT).

  • How efficient is the process?

    Gasification is a very efficient method of converting waste fuel into electricity, which can be made even more efficient by also utilising the heat generated by the facility in the local area. The more heat the facility exports, the higher the overall efficiency achieved. The efficiency of the facility will therefore increase over time, as a heat export network is developed, established and expanded.

  • Is this technology the same as plasma gasification technology?

    No. Plasma gasification uses a very high temperature plasma ‘torch’ to achieve the conversion process, whereas normal gasification technology uses recycled heat from the combustion of the gas in order to create the syngas. This is one reason why the process can be so efficient.

  • Isn’t this just an incinerator?

    No. Incineration is the complete combustion of the waste in an oxygen rich environment, releasing all the energy from the waste at once. Gasification processes, such as proposed here, control combustion through a two stage process. The first (gasification) is to heat the waste in order to generate synthetic gas, which is passed to the second stage. The second stage is the combustion stage where oxygen is introduced and heat generated. Because the combustion occurs between gases, the process can be much better controlled and this means that the plant is clean and efficient in recovering the energy available. Because the energy recovered is used to generate electricity, gasification facilities represent a significant change from incineration plants of the past.

  • What about the ash left over after gasification – is that harmful?

    No. The bottom ash from the gasification process is an inert or inactive material that remains at the end of the cycle and represents around 17% of the intake tonnage. This ash can be recycled in a variety of ways, and will need to comply with the Environment Agency operating permit requirements. Examples of reuse can include as a secondary aggregate replacement material, such as a sub-base for roads. As with the rest of the process, the recycling of ash is strictly regulated and the system is audited on a regular basis.

  • What are the benefits of gasification?

    Gasification is a highly efficient process with very low emissions.  It is a naturally low Nitrogen Oxide (NOx) process - NOx is one of the main road traffic pollutants. Gasification plants may also be more adaptable and flexible in the long term to be converted to an even higher efficiency energy conversion process, where the synthetic gas is burnt in an internal combustion engine.

  • What else is left as a residue from the process?

    There is a small amount of APCR (air pollution control residue), which is sometimes called fly ash. APCR is typically a mixture of ash, carbon and lime (or bicarbonate). It is classed as a hazardous waste because of its high alkaline content from the spent lime, which is used as part of the filtering and cleaning process to remove acid gases.  In the past it was disposed of at a hazardous waste landfill but nowadays it may undergo further processing such as washing or stabilisation before being sent to a non-hazardous landfill. It is a small volume of material from the process.

    However, landfilling of APCR will be discontinued as new regulations come into effect.  Many chemical treatment companies have anticipated this situation, with new facilities being opened which are now capable of achieving ‘end of waste’ status for the washed and cleaned aggregates contained in the APCR.

    There is an amount of ferrous and non-ferrous metal, which can be extracted from the ash or by the mechanical treatment facility (MTF) that will be on site, and sent for reprocessing by a scrap merchant.

  • What is the ‘R1’ efficiency measure that is sometimes talked about?

    The R1 efficiency of a Waste to Energy plant is the efficiency with which it converts the energy within the waste to a usable form (heat or electricity). The greater the efficiency the more energy is produced. Achieving R1 status allows a process to be described as recovery rather than disposal. The proposed facility has been designed to achieve this level of energy efficiency and thus will be classified as a recovery plant.

    The facility will ensure that waste streams delivered to the site have already been subject to recycling and recovery prior to treatment and in this way the facility will provide an essential component part of the recycling process.

    R1 classification is not a requirement to obtain planning consent for a gasification facility. Even so, Rolton Kilbride is confident that the proposals will obtain R1 status during the operational phase, as the facility is designed and intended to be capable of exporting heat to local consumers.

    Further information can be found here.

  • Where else is this technology used?

    Gasification technology has been used for over 100 years, and it was the basis of town gasworks using coal before being replaced by North Sea gas.  The technology has also been used with various types of waste for some decades. Its application to mixed wastes, such as RDF, is more recent, although many commercial scale plants have been constructed in the last 20 years.

    There are numerous working gasification plants successfully using RDF, particularly in Scandinavia and Japan. The technology proposed for this application has a successful track record of dealing with RDF. 

    There are a number of similar gasification plants being built in the UK at present, for example in Milton Keynes, Derby, Hull and Levenseat in Scotland.