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It is often claimed that the power produced from an Energy from Waste (EfW) plant is renewable. This claim is based on the energy freed from burning biogenic material, ie material that was recently growing such as paper, card and food.
However this claim is often made misleadingly, even claiming, somewhat bizarrely, that burning the water in food waste produces renewable power.
It is also crucially important in making this renewable energy claim that the EfW process is efficient, that as much energy as possible if extracted from renewable, biogenic waste. A claim that a plant is a sustainable source of energy must not waste around 80% of the available energy (as many incinerators do, for example the Gloucestershire plant at Javelin Park) – and sustainability demands that the plant should flexible to advances in recycling and energy extraction technologies. A large, capital intensive incinerator with a 30+ year design life does not meet these requirements.
The best EfW plants will recycle plastics from the input waste prior to energy conversion – this is because the environmental benefit of recycling plastic material is vastly better than burning, particularly if this is done in an inefficient mass burn incinerator. If the resultant material is then refined and dried it can be converted to power much more efficiently.
To illustrate this further figures and claims made for the Gloucestershire Incinerator from UBB are examined in detail in this paper.
This shows that the Gloucestershire Incinerator produces less than a third of the energy that better processes would yield from the same waste input. Of the electrical energy planned only 37.8% is renewable, the balance being from burning of plastics.
It is right that the public demands that for large investments of public money, such as that within the £613m contract for the Gloucestershire Incinerator, large amounts of renewable energy is produced. Yet in practice the Gloucestershire plant yields just 5.5MW of renewable electricity with 80% of the potential energy simply lost.
A well designed EfW process extracts as much useful energy from the material which cannot be recycled.
The Gloucestershire incinerator produces at best 14.5MW (net of parasitic loads) electricity from 190 ktpa of mixed residual waste including plastics. This compares very poorly to better designed processes, such as the Biocentre process illustrated below.
The diagram above shows the energy balance for the Biocentre process using 20 tph of a typical municipal waste mix equivalent to 175,000 tpa.
So as a direct comparison to the Gloucestershire Incinerator the Biocentre process delivers the following typical energy outputs for 190,000 tpa of input, with the fuel going to suitable industrial power plants (steam turbines):
21.7 MW electricity output PLUS 24.9 MW heat output, giving 45.6MW useful power output, over 3X that from the planned Gloucestershire incinerator
Alternatively all of the energy output can be used for heat in which case the process delivers
51.4 MW of fuel suitable for a heat plant
The far greater efficiency from this type of systems compared to mass burn incineration comes from:
· Fuel refined to consistent high specification, low in contaminants. The fuel can be converted in far more efficient and smaller plants, with less parasitic loads.
· The fuel is dried before conversion, using natural bio-drying. In the case of Biocentre this is particularly efficient because the input material is refined prior to drying.
· The fuel can be converted where needed. Either in CHP enabled power plants built on industrial estates with high heat loads, such as at Slough Heat and Power, or in smaller scale heat only, or heat and power plants built on high heat use industrial users. An excellent example in Gloucestershire is Muller which is just a few km from the planned incinerator, but too far to transport heat economically. Taking the fuel to the user is much more efficient.
Fuel can be burnt at the point of use so heat is immediately available to industrial processes. The higher efficiency of this process, combined with the flexibility to use the fuel where needed gives a far better useful renewable power figure than a mass burn incinerator. The carbon footprint is consequently far superior.
Renewable Energy Produced from the Gloucestershire Incinerator
During the application it was misleadingly claimed that 52.6% of the energy in the residual waste stream comes from biomass (biogenic) material and so can be classed as a renewable energy source. This includes a paper and card rich source of commercial and industrial waste, the underlying biogenic material from household sources would be 49.5% - see table below
However this is just the proportion of the calorific value (CV) of biomass in the residual waste, it does not equate to the proportion of power produced from the biomass fraction. In the same way that cardboard has calories but will not make you fat we must also look at the conversion process to calculate the proportion of power which can be classed as renewable. If you have ever tried to set fire to a potato you will know that this is not a useful way to produce heat. Biomass contains far more water than the plastics, and water requires much energy to “burn off”. Energy is required for what is called “activation energy” (the energy required to ignite the material) and to liberate (evaporate) the water in the material. The wetter the material the more energy is lost. Incinerating unprocessed food waste for example which is typically 70% moisture takes more energy to deal with the moisture than is released from the materials CV.
96% of the energy available from biomass in the Gloucestershire waste stream comes from paper and card, itself a recyclable material. It is important that this material is kept dry otherwise further renewable energy may be lost. Water is sometimes added in waste bunkers to prevent spontaneous combustion of the mixed waste.
If you subtract the lost energy in dealing with water from the available energy for the residual waste figures presented by the applicant you can calculated the proportion of power generated by the plant which can be attributed to biogenic (renewable) sources, see table below
This shows that just 37.8% of the power produced by the proposed development can be classed as renewable – that is coming from biogenic / biomass sources.
Given a claimed net electrical output of 14.5MW for the plant this means the county generates just 5.48 MW of renewable energy (48000 MWh per annum) from this enormous investment. The contract cost is around £25M per year so this gives a cost for renewable energy of £520 / MWh, 5 times the cost of other renewable sources such as wind[1].
[1] Onshore wind cost range £80-£110 £/MWh from “Powering the Nation” Parsons Brinkerhoff 2010