Technology
- How does the plant generate electricity from straw?
- How can we be sure that the process will work?
- Can the plant burn waste?
- Why is the efficiency of the plant so low?
- How can burning straw reduce carbon dioxide emissions?
- How does the plant supply 90,000 homes?
How does the plant generate electricity from straw?
The plant burns straw in a boiler to produce high pressure, high temperature steam. This steam is fed to a steam turbine generator in which the steam's energy is converted first to the mechanical energy of the steam turbine rotor and then into electricity. The spent steam is condensed back into water in a bank of radiators and fans called the air cooled condenser; the water is then fed back into the boiler to begin the cycle again.
How can we be sure that the process will work?
The underlying process is grate combustion, which is an established technology for power stations, albeit highly evolved over its long history. Specifically, Sleaford REP will use the same technology that already applied at the Elean Straw Fired Power Station and many other straw-fired plants around the world. The process is proven to be very reliable.
Operation of the plant will be monitored by the Environment Agency under the Pollution Prevention and Control regulations.
Can the plant burn waste?
No. The technology is designed around the combustion of clean biomass such as straw and wood chip; any other material would bring the project into a wholly different regulatory regime and would, in effect, require a different plant. This are no circumstances under which this plant could, or would, burn waste.
Why is the efficiency of the plant so low?
Electrical efficiencies in combustion-based generating plant are limited by thermodynamic laws to what appear, on the face of it, to be modest efficiencies. Theoretical thermodynamics dictate that there will always be a considerable amount of waste heat. In this context, the electrical efficiency of this plant, at over 30%, is actually very high for a plant of this size (larger plants can achieve higher efficiencies but they use fossil fuels; biomass is cleaner but would need to travel huge distances to meet the equivalent capacity of a large fossil fuel plant).
Efficiency would be dramatically increased if large, reliable, long term users for heat can be found within a reasonable distance of the plant. Eco2 is actively pursuing possible heat use opportunities.
How can burning straw reduce carbon dioxide emissions?
The burning of biomass as a fuel does release carbon dioxide into the atmosphere, however, this is the same carbon dioxide that the wheat takes from the atmosphere as it grows. The process is therefore said to be 'carbon neutral'. The reduction in carbon dioxide is due to the fact that if the electricity wasn't being produced from a renewable resource then a fossil fuel power station would need to be used instead.
How does the plant supply 90,000 homes?
The plant does not supply any homes directly. The electricity exported is fed into the local distribution system and, once there, it will be used as demand for electricity requires.
The 90,000 homes statistic is derived from the standard assumption used within the utilities industry that the average home in the UK uses 3,300 kWh of electricity per year. The plant is designed to generate 40 MW (i.e. 40,000 kW) on a continuous basis. This, after allowances for maintenance, equates to 300,000,000 kWh per year. This is equivalent to 90,000 homes at 3,300 kWh per year per household.
The industry standard figure of 3,300 kWh is the subject of some debate and it has recently become clear that the actual UK average household consumption is higher, at around 4,600 kWh per household. Eco2 now accepts that this higher is more accurate. Accordingly, all future statistics will quote a lower equivalent number of households - 65,000 - based on 4,600 kWh per year per household.
