large-scale biomass combustion

Large scale biomassAs the scale of a biomass combustion system increases beyond the domestic, various other factors change too:

  • The quantum of the pollutants from a single system becomes more significant
  • Regulations are more stringent
  • The combustion process is less variable
  • The range of fuels becomes wider
  • There is a greater likelihood that grant finance is involved, which comes with conditions attached

As a result of these factors, more sophisticated flue-gas treatment approaches are often deployed than in the domestic arena.

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Chemistry Of Large-Scale Biomass Combustion

Biomass is often described as ‘carbon’, and in broad terms this is true, but unfortunately there are quite a lot of other molecules in there as well, which make ‘clean’ combustion more difficult to achieve. Even if we did burn pure carbon, we would still get some pollution due to incomplete combustion, in the form of carbon monoxide and soot particles. In addition, the heat of the combustion process would cause a reaction between the oxygen and nitrogen in the air, resulting in the formation of oxides of nitrogen.

large scale biomass

The non-carbon molecules in the fuel each have their own effect on emissions too. The most important of these are tar compounds, which if not fully combusted can be emitted as volatile organic compounds, some of which may condense to form particulate matter.

Minerals present in the fuel will generally turn into ash, some of which could be released as dust. Biomass made from stem-products such as straw also contains chlorine which will have an impact on the emissions.

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Oxidation of large-scale biomass fumes

Many of the pollutants created when burning biomass are the result of incomplete combustion, for example carbon monoxide, VOCs, tar compounds, etc. Catalytic oxidation can be regarded as a secondary combustion process in which any organic compounds left over from the primary combustion are oxidised into carbon dioxide and water.

Catalytic oxidation is temperature-dependent, and generally requires temperatures in the range 250-450oC to be effective. However, this is significantly lower than is required for non-catalytic oxidation techniques, such as the use of afterburners, and therefore it is often a more economical and environmentally-friendly solution.

When designing a catalytic oxidation system for a large-scale biomass application, the temperature of the flue gases is always the first consideration. The next stage is to think about chaff and dust, to ensure that the design of the catalytic converter prevents it becoming blocked up. Thirdly, we need to consider corrosive substances in the flue gas such as sulphur and chlorine which can shorten the life of the catalyst unless specialist coatings are used.

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Large-Scale Biomass Regulations

Large scale biomass regulationsIn Europe, the biggest development in the regulations covering emissions from industrial-scale burning of biomass is the Medium Combustion Plant Directive (MCPD). This applies to plants with a thermal input in the range 1 to 50 mW and has a range of implementation dates from December 2018 to January 2030 depending on the size of the plants and whether they are new or existing. The main focus of the MCPD is on reducing NOx emissions, however for some fuel types, SO2 and dust are also regulated.

Plants larger than 50 mW are normally regulated under the existing Industrial Emissions Directive.

Plants with a thermal input of less than 1 mW are not covered by the MCPD but are often required to comply with emissions limits in order to be eligible for grant finance.

New equipment used in plants under 1 mW may need to comply with the requirements of the Ecodesign Directive.

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Testing of fumes from large-scale biomass combustion

Large Scale Biomass TestingBoth the Industrial Emissions Directive and the Medium Combustion Plant Directive require periodic monitoring of emissions, and these must be carried out by companies which have the appropriate accreditation (e.g. MCERTS).

However, whilst Whitebeam does not have this accreditation we are able to give our customers an indication of their emissions which is often a good idea in advance of an official test.

Monitoring emissions is also an important stage of the calibration of SCR systems and the sign-off of any new installation. SCR systems may incorporate emissions sensors and a data-logging facility which can be accessed remotely if required.

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Large-scale biomass systems

Large Scale Biomass SystemsWhen dealing with fumes from large-scale biomass combustion the performance criteria are often demanding, and each application may have to be treated as a separate project. There are often multiple elements in an emission-control system, and various other systems which it must interface with.

The annual usage is likely to be intensive and therefore systems are normally designed so that they can be serviced and overhauled at regular intervals.

Diagnostic features are often incorporated to give feedback on the effectiveness of the fume abatement system and to assist with fault finding. Whitebeam is happy to work with OEMs, end users, consultants or flue specialists to deliver effective solutions in this sector.

Relevant Solutions:
SCR Catalytic Converters
SCR Dosing Systems

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Strokovnjaki za zmanjševanje onesnaženosti zraka

Strokovnjaki na področju tehnologije čišćenja vročih plinov za zmanjšanje izpustov pri kuhanju in izgorevanju biomase za izboljšanje kakovosti zraka