The Yorkshire and the Humber Authorities Verification Service Notified Body was established in 2006 for the conformity assessment of a range of weighing and measuring equipment. Over the past couple of years, requests for initial qualification work have been received from new sources, including a recently opened E.ON biomass power station, built on the site of a demolished coal-fired power station in Sheffield. E.ON regards this site as a template for future biomass installations it plans to build. The power station will provide up to 30MW of energy, enough for 40,000 homes, with a relatively small footprint – both in terms of its size and its environmental impact. Testing beltweighers Verification officers spent several weeks at this new site testing beltweighers. A host of practical issues, and the sheer enormity of the task, required a lot of problem solving. Solutions were found as this relatively new field of expertise continues to develop. Buckle up, here’s how it works... The handling system for the chipped waste-wood biomass on site uses two beltweighers to weigh it before it reaches the furnaces. These are capable of burning 25 tonnes of biomass per hour and run for 24 hours a day. E.ON specified that both beltweighers should be class 0.5, at a maximum rate of 45 tonnes per hour (tph). The chipped waste wood is delivered by lorry and dropped to a below-ground conveyor system, which feeds it into a 4,000-tonnes capacity wood store. Screw feeders move through the bottom of the wood store and deliver a constant flow of wood to the conveyors, which lead to a hopper before being fed into the furnace. Two single-speed beltweighers are installed on the final belt in the chain before the hoppers. Material and non-material tests are required; material tests take place at maximum, minimum and a mid-range feed rate over a number of pairs of tests. All sounds straightforward, but the design of the beltweigher system prompted plenty of discussions in terms of how to get a known quantity across the beltweigher, either pre-weighed or post-weighed. Dust, dust and more dust! The waste wood contains about 15-20 per cent dust. For post-weighing, the wood was diverted to a 50cm chute, which then fell 20-30m into a waiting lorry. The resulting clouds of dust and substantial loss of weight made this option unworkable. The feeding system could not supply the wood at the minimum rate for testing, 9tph. Going this slow, the machine motors would burn out and a stop/start approach was not acceptable. The beltweighers are part of a belt that is 350m long and travels at 0. metres per second (m/s). With one revolution of the belt taking nearly 10 minutes, even the non-material tests took a great deal of time. Inconsistencies in the thickness of the rubber belt over this length also had a bearing on the zero errors. The number of belts in the system meant too much product was lost after pre-weighing. The solutions included using class 1 waste wood chip (much less dust), which E.ON bought in especially for the testing. To obtain the appropriate feed rates, the lorry was emptied onto a temporary variable speed conveyor, which then fed to the normal conveyor system. The wood store was bypassed and the wood travelled over the beltweigher before dropping down the chute into a further pre-tared lorry. To gain a smooth flow of the feed, the belts were manually started and stopped once the required amount of wood had passed over the belt. Tests abandoned Many attempts to test were abandoned for a variety of reasons, including: lorry breakdown; working over driver hours; blockages on the chutes; problems with the gravity-tensioning system; unavailability of class 1 wood; and poor flow rates. Even when they worked, the testing processes were extremely labour intensive with each test at the minimum flow rate taking more than three hours. Future beltweigher installations will be designed with shorter belts and the means to pass a known quantity over the belt into the system from the start, which is good news. This growth area of work for the regional notified body has been triggered by a conversion to biomass fuels, and instrument manufacturers’ recognition of the expertise and flexibility on offer. Government subsidies for biomass requires weighing equipment to be checked annually, resulting in further certification work for local trading standards services. There is commitment from the regional group to continue supporting the development of expertise in this area, to enable response to future requests.