Hill brothers nurseries needed to replace an ageing coal fired boiler system. Biomass seemed the obvious answer, with low fuel costs and generous subsidy in the form of RHI. However the customers understanding of the difficulties that can be involved in running solid fuel boilers from decades of firing coal boilers gave some pause for thought. A move to Oil or Gas certainly simplifies the production of energy, and with a much lower capital cost. After considering the long term cost benefits of installing biomass, the decision was made to go ahead, but with a proviso to only install top quality industrial equipment to offer the closest possible match to fossil fuel boilers in terms of dependability, ease of running and lowest possible maintenance time and costs.
dependability, ease of running and lowest possible maintenance time
The Justsen Argusflex boiler was chosen for the project because of its robust industrial design. Traditionally used for town district heating systems, the industrial design principals are evident in the very large grate area and heat exchanger area, heavy duty large diameter auger screws, high chrome water cooled grates and water cooled combustion chamber. These features facilitate trouble free continuous use at high loadings – perfect for installation in the glasshouse environment.
The Justsen Flex boiler is uniquely designed to burn wet or dry fuels. The design of the boiler features a fully water filled combustion chamber module, which means that the side walls and grate of the boiler are cooled by the return water from the heating system. This limits the combustion temperatures, which allow the use of very dry fuels and fuels with high ash content that are prone to the formation of clinker. This set up is most suitable for dry wood fuels up to 35% moisture. To burn wet fuels, ceramic tiles can be installed on the water cooled walls, insulating key areas of the combustion process from the cooling effects, and therefore increasing the maximum fuel moisture the boiler can burn up to 55% moisture. This flexibility allows the use of the wood fuel that is available at the best price in the local area.
robust industrial design
The boiler was installed in autumn 2014 and was sized to handle base load heating duty, with peak load covered by the remaining oil fired boiler. The existing heating system incorporates a large thermal store, which helps to minimise oil consumption by allowing the biomass to run even when there is no or little heating load in the glasshouses. The boiler system is fully incorporated into the existing controls, taking a 0-10v signal from the main control system to determine the power output required. This allows the loading of the buffer tanks to be controlled according to the predicted heat use in the greenhouse and even the current or predicted future weather. It also ensures that the buffer tanks do not become fully charged during warm weather, which would result in the boiler having to shut down. Because of this the boiler can be configured to burn wet fuels up to 55% moisture which is not possible in boilers without continuous heating load.
The fuel feeding system was specified by the client, who chose to use a Flier systems fuel grab crane to pick up fuel from a bulk storage area. An automatically operated grab crane can move over the entire fuel store, measuring the height of fuel remaining. The crane can be programmed to preferentially empty the delivery area to allow tipping space for deliveries. The grab deposits fuel into a small hopper, and from there it is fed by conveyer belt to the stoker screw on the boiler. This method of delivery is highly robust and does not have the same limitations on oversize pieces and fuel dust content associated with conventional auger transport. The system has a simple link with the boiler, with the conveyor belt simply starting on demand from the boiler control panel.
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Hall Farm House, Aldborough
Norwich, Norfolk, NR11 7HU