harpers chp

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carbon savings

When compared to alternative methods of heat and electrical production, the carbon savings possible from the use of biomass-fuelled CHP can be substantial. 

The table below shows a comparison between the estimated carbon dioxide emissions from a 3.90 Burkhardt gasifier and ECO 165 CHP system, a natural gas CHP system generating the same amounts of electricty and heat and using mains electricty and oil to generate the heat. Whilst the comparison between the technologies is not strictly realistic, for example, the ratio of electricity to heat from a gas CHP is usually around 1:1 rather than the Burkhardt's 1:1.6, it does give a clear indication of the magnitude of the potential savings that can be made.

Examining the table, it can be seen that compared to mains electricity and generating the heat from an oil boiler, natural gas CHP offers a 41% carbon saving whilst wood pellet CHP offers a 95% saving.

kWh/yr fuel kWh/yr kg CO2/kWh te CO2/yr te CO2/yr saving % saving
Mains electricity electricity 1177500 1177500 0.590 694.7
Oil heat 1950000 2294118 0.314 720.4
Natural gas CHP electricity 1177500 1385294 0.227 314.5
heat 1950000 2294118 0.227 520.8
835.2 579.9 41.0
Wood pellet CHP electricity 1177500 1486417 0.015 22.3
heat 1950000 2461583 0.015 36.9
59.2 1355.9 95.8

For the table calculations, operating hours are assumed to be 7,500 on an annual basis. The electrical production is 1,117 MWh (once the parasitic load of 8 kW is accounted for) and the heat production is 1,950 MWh. The oil boiler and natural gas CHP efficiency is taken to be 85%. 

Figures for the carbon dioxide emissions of different fuels are from the UK Biomass Energy centre. For the wood pellets, the figure for 10% moisture content pellets  from dry wood waste was used as this most closely matches the pellets we use at our site. This figure includes the hammer mill and pelleting process.

However, it must be noted that the potential carbon savings from wood pellets are greatly affected by the type of pellet used. The pellets we use are made from 100% dry wood waste sourced from local sawmills. The carbon savings from wood pellets made from green wood which need drying are several times less. Long distance transport will also have an impact. This could be considerable especially if imported pellets are used.

Harpers CHP, Unit 2, North Road Industrial Estate, INSCH, Aberdeenshire, AB52 6XP

Email: | Phone: (01464) 821822