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need regular operation & maintenance, available & responsive biomass engineering expertise and a continuous supply of fuel of the right quality, price and calorific value. An operative will also need to be trained onsite to empty the ash bin, order fuel, submit quarterly meter readings to Ofgem and receive regular

Neil Turner Wood Energy Ltd fuel deliveries.

This may all seem overwhelmingly complicated, but thankfully there are companies out there that have been planning for the RHI for many years and are now ready to deliver your installation, look after it and fuel it for the next 20 years.

Dorset Prison demonstrates the benefits of biomass heating

need for an accumulator

tank is defined during the project scoping period and can sometimes be an essential part of good design. Furthermore, depending on the emission requirements defined by the local authority, systems will need to suitably disperse and control emissions. This means particulate cyclones, ceramic filters and flue height options being considered as part of the design. Finally, all of the equipment described above can be installed within your building or sit externally in a prefabricated plant room such as the ‘Green Heat Module’. If you believe you have the space and the heat demand then this technology is definitely the one for you!

PROCUREMENT We believe the RHI is going to drive procurement decisions in favour of ‘best value’ to the end user rather than ‘lowest cost’ meaning quality, efficient biomass heating systems. The track record and expertise of the designer and installer are critical to success. This contract can then be implemented as part of an energy service contract (heat sold on a p/kWh basis), a lease or a direct purchase. Under all scenarios planning permission will need to be sought and Ofgem will need to accredit the installation for RHI eligibility.

Once your RHI project is installed and running efficiently, output needs to be maintained for 20 years. Biomass boilers


MP Guys Marsh is located near Shaftesbury in Dorset and can accommodate up to 578

prisoners. The majority of the prison campus was heated from a single energy centre using heavy oil boilers dating from 1977. The heat was distributed to the building via underground heat main. An appraisal was undertaken to evaluate the technical and economic viability of constructing a new energy centre comprising of a single wood chip boiler system to act as the lead boiler with natural gas boilers providing standby and peaking capacity. A new pre-insulated heat main was installed to connect into the existing heat main system.

The design settled on a single 1.2MW Binder wood chip boiler with 2 gas boilers each rated at 2400kW of capacity. The Binder boiler has an excellent turndown ratio, being able to operate at 20% of the boiler maximum rated capacity while still offering high efficiency. The load profile of the site indicated that there was sufficient base load demand that an accumulator tank would not be required.

A key challenge for the project was the fuel storage and logistic arrangements for fuel delivery. A below ground fuel store was discounted due to a high water table (in keeping with the site name “Guys Marsh”) which would have presented technical difficulties and high civil costs. The wood fuel solution, therefore, was an above ground walking floor (5m by 8m) and a fast wood chip distribution system. This design enables a tipped delivery of wood chip into a hopper which is then

elevated by a fast vertical auger and distributed evenly onto the walking floor. The wood chip distribution system is capable of moving 120m3

of wood chip per hour, which means a 60m3 wood chip

delivery can be emptied in half an hour. A Binder SRF-s step-grate boiler with gas burner ignition was installed with a robust 330mm diameter auger transport system to move chip from the walking floor to the boiler. This allows wood chip up to 50% moisture content to be burnt efficiently within the boiler and allows a maximum particle size of G100 (on the Austrian O Norm Standard) and P63 on the new European standard for wood chip particle size. This gives flexibility on wood chip procurement into the future allowing lower operating costs.

Another important consideration was to have the most automated system possible, reducing maintenance and cleaning time of the boiler and hence reducing running costs. The Binder GmbH system has fully automatic de-ashing and the boiler heat exchanger tubes have a fully automatic cleaning system; keeping the heat transfer to the water at maximum efficiency and meaning the heat exchanger tubes are only required to be cleaned manually during the annual major service.

The overall system is expected to significantly reduce the prisons heating oil demand (approximately 1,000,000 litres) and use approximately 2,000 tonnes of locally sourced wood chip and result in an estimated annual CO2

saving of over 1,000 tonnes per year. PUBLIC SECTOR SUSTAINABILITY • VOLUME 1 ISSUE 5 27

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