Biomass heating: Making the switch

Biomass heating has great potential to cuts costs and carbon emissions in the industrial sector. In this article, Martin Murrish, technical manager with Hoval, explains how the company approached the process of switching to biomass heating for its factory

While there are a number of renewable energy options available to building operators, it is clear that wood fuel biomass is proving particularly popular in the UK. The concept of burning a fuel is clearly familiar and wellunderstood, retrofitting biomass to an existing heating system is relatively straightforward and there are opportunities for extra revenue through the government's Renewable Heat Incentive (RHI).

In retrofit projects where a fossil fuel boiler is being replaced or supplemented by a biomass boiler, a key advantage is that the biomass boiler will use the same flow and return water temperatures as the previous boiler. Consequently there is no need to change heat emitters, pumps, pressurisation sets and other ancillary items.

Nevertheless, there are some important factors to consider; these can be illustrated through the procedures we followed in installing biomass heating at our factory in Newark-on-Trent. This is the factory where our latest generation STU wood pellet biomass boilers are manufactured and we have two STUs installed at the factory. One 600kW unit replaces the previous gas-fired boiler to deliver hot water (80°C flow/60°C return) to fan coil units mounted in each of the three factory spaces. This boiler is sized to meet all space heating requirements throughout the year and is coupled to a heat meter for the RHI.

In addition, a 195kW STU boiler has been installed for training and demonstration purposes, connected to a small, separate heating system so as not to interfere with metering for the RHI.

The latest STUs use a standardised skid mounted design that includes pumps, fans and fuel delivery augers to reduce footprint, so finding a space for them was straightforward However, we also needed to find space for storage of the fuel as close to the boilers as feasible to keep delivery simple.

The most appropriate solution was to opt for a 35m3 GRP silo just outside the building, connected to the boilers with flexible augers; planning permission was gained for this. The silo holds 20-25 tonnes of wood pellets and uses load cells to track fuel reserves. The system can be set up to send an SMS message to the fuel supplier when reserves reach a predetermined level.

Fuel is delivered in a 'blower' vehicle and blown directly into the silo, so there was no need to make special provision for delivery access.

Flueing is another consideration as biomass boilers have slightly different flue specifications to gas and oil fired boilers. In the event the existing flue for the gas boiler was suitable for the 600kW STU, but we needed to install a new flue for the 195kW model. To optimise performance we have also installed a 6000L thermal store, which helps to spread the residual heat when the boiler switches off. Also, when the water has reached design temperature the boiler will not fire again until the temperature falls to 75°C. So the thermal store acts as a buffer to maintain flow temperatures while reducing the firing of the boiler. It retains much of its heat through the night, which accelerates the warm-up times in the mornings.

For maximum efficiency and control, STU boilers are optimised to run on wood pellets produced to the EN+ A1 standard, thus achieving a close marriage between controls, hardware and fuel to get as close to complete combustion as possible. This avoids problems of inconsistent combustion efficiency caused by the variable moisture content and dimensions of wood chips and some low quality wood pellets.

Given the benefits of using biomass heating, it is certainly worth considering. It also makes sense to work with a supplier that has the technical expertise and practical knowledge to ensure the system delivers maximum performance at every level.