This project involves the use of various renewable wood based fuels including forest wood and agricultural residues, urban wastes and energy crops, all of which are readily available in the local area. We project managed the £90M development, from design and construction supervision to commission and take over. Construction included the power station in Steven’s Croft, a fuel processing facility and 26km underground electrical cable connecting the station to Chapel Cross substation. Scottish Power completed the installation which incorporates a long directional drill beneath the M74 motorway.
Carbon neutral fuel
The plant is fuelled entirely by biomass material. Over 480,000 tonnes of fuel is needed to power the station every year. Arriving from the local area the fuel comprises:
60% sawmill co-products and small roundwood
20% short rotation coppice (willow)
20% recycled fibre from wood product manufacture
Burning biomass is a clean way of generating electricity and is often called ‘carbon neutral’. The carbon released into the atmosphere when the material is burnt is equivalent to the amount absorbed by the plant during its growth cycle.
Power and fuel supply
The fuel processing facility was designed to store and blend all various fuel sources to provide an homogeneous fuel. It includes up to 14 days of round wood storage, a facility for reception of pre-chipped fuel, up to 6000m3 of covered chipped fuel storage, a round wood chipping facility, fuel reclamation and forwarding equipment with systems for final preparation of the fuel before delivery to the power plant.
The boiler conditions were designed to allow the best efficiency at 537°C, 137 Bar and with a capacity to raise 126MWth of energy. The high steam conditions dictated the need for specialist corrosion resistant materials in the high temperature components and to control fuel quality.
The station is regulated by the Scottish Environmental Protection Agency. The main applicable legislation is the Waste Incineration Directive and the Large Combustion Plant Directive, which defines acceptable emission levels. These regulations demand state of the art equipment, which comply with Best Available Technique guidance. The power station’s emissions are therefore reduced to the minimum level achievable.
The site's surface water drainage system has been designed around the sustainable urban drainage system (SUDS) guidance, to retain water on site and disperse through natural infiltration in the first instance. Rainfall is captured in swales and is retained until the water disperses. On overflow, the surface water is sent to a secondary cleaning facility which comprises a wetlands area. Water travels through this wetlands system and is cleaned before naturally flowing into a watercourse. Aqueous emissions are restricted to blowdown water from the boiler and water treatment effluent. Discharge is to the local watercourse at extremely low flow rates to ensure there is no adverse impact to local water quality.