THE HEATING SYSTEM AT WORCESTERSHIRE COUNTY HALL

In May, 2002, Econergy Ltd installed a state-of-the-art, 700-kW, fully automatic, wood-fuelled boiler to provide heat for Worcestershire County Council’s (WCC’s) County Hall and adjacent records office in Worcester, England.

Mr Iain Paul, chief architect, and Mr Jim Moss, chief mechanical engineer at WCC supported by executives and key councillors, were behind the decision to make this project a flagship that would stimulate uptake of the technology across the county, and be the first step in developing a home-grown energy market that would benefit the rural sector. Heating County Hall with fuels from biomass was identified as environmentally friendly, and the most cost-effective route to substantially reduce emissions of fossil CO2.

County Hall was built in the 1970s and, because of the design and construction of the building, it was concluded in the 1990s that renewable heating presented a better option to emissions-reduction than the next available step in energy-efficiency improvements, which would have required substantial works to the entire building. WCC decided to lead by example, thus encouraging the development of a cluster of biomass-heating installations across the region.

The annual demand for wood-fuel is estimated at 530 tonnes at a moisture-content of 40 per cent (wet basis), which is sourced locally from forestry-operations, thereby generating income and supporting employment in the local economy. Forestry-management activities produce thinings, small round-wood and long tops. These and primary-processing co-products, such as slab-wood, are chipped as fuel for the plant; in future, energy-crops may also be used.

The fuel is delivered using a hook-lift, bin system, designed and built by Econergy. Two containerised fuel-storage bins of capacity 35 m3 have been fitted with internal scraper-floors. The fuel is transferred automatically, using augers, to a metering hopper, which in turn feeds the fuel into the stoking auger, and thus on to the grate. The container-system of storage avoids both the tipping of fuel on the site and the need for an underground bunker; all that is required is a concrete pad.

A Compte Compact C70DHV boiler, having a capacity of 700 kW, was installed to provide base-load heating throughout the autumn, winter and spring. The substantial existing capacity (3.5 MW in total) on site provides more than enough fossil-fuelled back-up. The heat-demand of the building is approximately 1,600 MWh/yr. The average heat-load of the building is estimated to rise to around 1,000 kW during the winter months. The heating-regime has been modified to make maximum use of the wood-fired boiler with the aim to provide 75 per cent of the total heat-load from the wood-fired boiler.

On-site staff manage the day-to-day running of the plant; they check its operation, and record the operations of the boiler and the heat-meter. Econergy Ltd manages the purchase and delivery of fuel, which is brought from nearby stores using local haulage contractors. A maximum of two deliveries are required per week.

The ash is automatically extracted into 1,100 litre steel ash-bins that are emptied by a waste-disposal contractor. In the medium-term, it is intended to return the ash to spread on soils on which trees are grown.

Econergy Ltd. provide a call-out service and quarterly / annual maintenance.

Installation, operation, maintenance and fuel-supply are all provided by Econergy Ltd under a ten-year renewable-energy supply-contract. The renewable heat is metered and sold to the WCC at a tariff that is competitive with energy from fossil fuels.

The capital cost of the installation was approximately £150,000 and was paid outright by WCC. The running costs are in commercial confidence as part of the energy-sale agreement. The price of the heat is set at the equivalent annual price of heat from natural gas, and is capped at 150 per cent of the price of gas at the start of contract.

Key facts about the installation at Worcestershire County Hall.

Description of plant

• Compte Compact C70DHV
• Moving-grate, wet wood-fuel boiler rated at 700 kW at 45 per cent fuel moisture-content.
• Toughened grate, hydraulically activated.
• Advanced combustion control: lambda and flame temperature sensing, fully modulating output control.
• Automatic auger fuel-transfer from two 35 m3 hook-lift bins fitted with automatic scraper floor outfeed systems.

Boiler Capacity

• 700 kW

Type of fuel

• Chipped wood from forestry.

Size of fuel storage

• 70 m3 in two containerised fuel storage bins.

Annual consumption of fuel

• Uses approximately 530 tonnes(moisture content c. 40 per cent).

Supplied buildings

• County hall office building 17,091m² and adjacent records office 275m².

Total heat load of the building

• Maximum average monthly load estimated at 1,100 kW. Maximum boost load estimated at up to 2,400 kW.

Annual primary energy demand

• 1,600 MWh/yr heat of which 1,000 to 1,300 MWh per year is from renewable heat.

Year of start-up

• May, 2002

Further details

• Medium-temperature hot-water system at 3.5 bar pressure.
• Wood-boiler operates in pre-heat loop to main system return, with top-up provided by gas boilers as required.

Investment costs

Contact

Mr Jim Birse
Econergy Ltd
69. Hampton Park
Redland
Bristol
BS6 6LQ
UK
Tel: 00 44 (0)117 377 5606
Fax: 00 44 (0)870 121 5812
E-mail: heat@econergy.ltd.uk
Web-site: www.econergy.ltd.uk