Wood-chip boiler replaces oil in Suffolk school

Published:  16 June, 2008

With a output of 450 kW, modulating down to 30%, this wood-chip boiler supplied by Broag replaces three elderly oil boilers at Stradbroke Business & Enterprise College in Suffolk.

Biomass in the form of wood chips for heating provides a very effective approach for reducing carbon emissions when it can be used to replace existing plant such as oil-fired boilers, as a school project in Suffolk demonstrates.

Renewable energy is a vital component to reducing the UK’s carbon emissions. Of a range of possible options, biofuels can be relied on to provide energy whenever required, unlike the Sun and wind. And of the range of biofuels available, wood chips are the most effective at reducing carbon emissions, as the replacement of oil-fired boilers at a school in Suffolk demonstrates.

Stradbroke Business & Enterprise College, is a mixed secondary school near the town of Eye in Eastern England with around 370 pupils.

The boiler room was stripped of its three elderly oil boilers and a single 450 kW wood-chip boiler from Broag installed in their place. At the same time, the opportunity was taken to create three separate heating zones in the school and upgrade the controls.

Specified by Suffolk County Council and installed by Elyo Services Ipswich branch the UTSK 450 kW boiler was supplied by Broag-Remeha and made by Austrian company Gilles as a replacement for oil-fired boiler plant.

The boiler is connected to a low-loss header as if it were a conventional pressure jet boiler. It has fully controlled modulating combustion, so there is no need for a buffer vessel or thermal store.

The build quality and ability to work without a buffer vessel are the two main attributes that put this make of boiler above all others on the market, according to specifier Peter Brown of Suffolk County Council, who has experience of the four other biomass boilers on the UK market.

Other advantages of the boiler include its capacity to burn chips or pellets, an automatic feed system, automatic ignition, automatic ash removal, automatic daily cleaning of heat exchanger and modulation down to 30% of full output as well as 91 to 93% efficiency.

The original round concrete flue stack was retained, and the old oil tank room converted into a chip store to hold around 38 m3 — in excess of a full lorry load. Fuel is blown into the store by Suffolk CC supplier and partner Eastern Woodfuels based at Bentwaters Park near Ipswich.

Nine solar panels are connected to the second coil of two HWS calorifiers. Out of the heating season these panels are supported by a Broag Quinta 65 kW boiler in case the Sun does not shine.

Solar thermal contributes to the domestic-hot-water requirements of Stradbroke Business & Enterprise College in Suffolk, supported by a 65 kW boiler outside of the heating season if there is not enough energy from the Sun. Note the concrete flue stack which was retained to serve the new biomass boiler.

Should the panels produce more energy than is required — a problem associated with schools in summer holidays — excess heat is blown into the fuel store through a fan-coil unit — an idea devised by Peter Brown, technical co-ordinator with Suffolk County Council, and implemented by Elyo Services.

The installation strengthens the school’s green credentials, as Dave Hardwicke, of Broag, explains.

‘In the case of Stradbroke, the boiler installation will stop the school burning 45 000 litres a year of gas oil and reduce the carbon emissions of the site by approximately 120 tonnes annually.

‘The idea with a woodchip boiler is that as wood grows it absorbs carbon. We then convert that wood into fuel, and the carbon is released back into the atmosphere when the wood is burnt. The carbon released is then re-absorbed as new wood grows, and this carbon cycle closes the circle. So, during the lifetime of the boiler installation, we contribute less to global warming because most of the carbon produced can be fixed in the carbon cycle described — rather than the one-way release of carbon into the atmosphere from fossil fuels laid down millions of years ago. Indeed, if we keep adding new wood by planting trees, that can only make things better.’

For Dave Hardwicke, the best thing about biomass production is the big return on the energy needed to get the fuel in the first instance: ‘If you put 1 kW worth of effort into creating wood-chips you get 20 kW of heat back — you get 20 times as much back as you put in — whereas for burning wheat and similar crops you get about a 10-fold return and for bio-diesel there is a 4-fold return because it takes a lot of energy to extract the fuel from the ground in the first place, refine it, deliver it and so on.

‘Biomass is by far the most efficient way of getting heating equipment to run on low- to zero-carbon fuel, and also works regardless of the weather, i.e. whether or not the Sun is shining or the wind blowing. These other technologies have their place, and all will be needed to help meet carbon-reduction commitments the UK, but if heat is required on demand then biomass, particularly the fully controllable boilers supplied by Broag, is the solution.’

Broag can supply a range of biomass boilers from 50 kW to 2000 kW.

The old oil tank room can store some 38 m3 of wood chips.
For more information on this story, click here: Jun, 08 79

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