Put a Lid On It
With the popularity of biomass heating growing, Michael Miles asks: “What about the ancillary equipment playing supporting role in the success of the renewable energy revolution?”
A Biomass bunker in Coed y Brennin
It’s easy to get overexcited about boiler output, cost efficiencies, carbon footprint savings and the sustainability of making the switch to biomass heating. However, consideration should also be given to the less emotive – but still crucial – aspects of the installation: the fuel bunker and its covers.
The boiler will rely on a free-flowing feed of optimum condition biomass material from a well stocked bunker in ord4er to function properly. Wood chip based systems generally present the biggest challenge to bunker cover design. Compared to wood pellets, wood chips are larger and heavier, requiring more storage and space – usually underground – and bigger covers so that material can be tipped straight in from delivery vehicles.
An upstand cover, where the lid wraps over the edge of a raised frame, best meets the need to keep the bunker dry. There are no exposed ingress points for the water and it ensures surface water is shed outboard of the frame. While keeping the bunker waterproof the upstand format also provides natural venting necessary for maintaining correct storage conditions in the bunker.
With biomass bunkers often situated ‘out-f-sight’ at the back of buildings, a risk assessment will be needed to identify an appropriate level of security. While there is no security standard for bunker covers, a manufacturer with a track record in approved security cover design in other sectors will be able to advise on a reli8able specification for biomass bunker protection.
To provide sufficient room for vehicle off-loading, a typical wood chip bunker cover provides a clear opening of around 8.50m2, accessed through twin lids. With what might be a 3m drop below this calls for some form of fall protection, such as a twin-leaf grid, to safeguard against the risk of a fall by an operative or member of the public.
Each presenting some 4m2 of steel to lift, the lids need to be hinged and have a dependable lifting mechanism, such as stainless steel torsion springs and gas-assisted rams. The chosen system should allow single-person operation in line with EC manual handling directives.
The covers will also need a robust safety stay mechanism which should automatically engage to ‘lock’ the lid in open position, but allow easy manual release. The stays should be capable of bracing the open lid against wind forces or accidental impact/ Deflector plates built into the underside of the covers will help guide wood chippings into the chamber below.
The grid covers should also be hinged with torsion spring or other lifting assistance. All cover elements will also need reliable locking provision, such as lever locking plus padlock, preferably in a vandal-resistant housing.
Some access manufacturers will have worked with biomass boiler specialists to standardise the woodchip bunker and cover design, to keep the cost down to clients of ancillary equipment and associated civils work. But special solutions may be required, with timber decking or other special finishes, for example, or flush-fitting covers that allow vehicle over-run.
Flush-fitting covers will require careful attention to the sealing arrangement as well as the lifting mechanism. For HGV load bearing duties, the covers are likely to be fabricated from heavier steel plate with substantial underbracing. A hydraulic lifting system will be needed to cope with the cover weight, with a control box mounted in a location that gives full view of the cover during operation, for safety purposes. Finally, make sure that the chosen bunker cover comes with reliable data on its durability, and that it accounts for local atmospheric corrosivity levels and aggravating factors affecting steel work in the ground.
Michael Miles is Managing Director of Technocover.