Power Jacks Optimises In-Vessel Composting Plant
The IVC complies with the Animal By-Products Regulations (ABPR) for the processing of food-inclusive material. The Composting Company's IVC vessels are unique in that they have a lifting roof with a patent pending on the system. The reason for this is to allow access for the loading shovels when opened, and when closed it provides a small void space above the material to allow for better control over the process. The roof is positioned by a linear-motion system designed and manufactured by Power Jacks.
Providing the linear motion for each roof are two individually motorised screw-jack systems, synchronised electronically to operate in unison. The jacking system raises and lowers the roof via a simple push-button operation and can lift the roof over its complete two-metre stroke in less than one minute. The screw jacks used in the systems are the classic E-Series single-face screw jack, which offers robustness and reliability. For this application, 100kN-rated capacity models were used to provide adequate load rating and structural rigidity. Originally, when development started in 2007, the application used UE1811 upright rotating screw jacks, however this has changed to ME1810 upright translating screw jacks as the IVC design developed.
This has resulted in an improved roof structure and mechanism that also benefits from the integrated dual-lubrication mechanism inside the E-Series translating screw jack. The screw jacks are aligned along the side wall of each vessel, one at each corner and one in the centre. The screw jacks are situated inside the wall and connected to the roof. Each wall has a motor that drives the screw jacks on that particular wall, with the two motors synchronised for each side of the vessel. When lowered, the screw jacks are protected inside the wall and they operate in a non-hazardous environment as they are outside the vessel, where corrosive atmosphere exists. The composting process starts when material is delivered to site and tipped inside a reception building, where the pre-processing work is carried out.
The material is then shredded and mixed before being removed to the first of two barriers of composting vessels. Moisture is also checked to ensure that it has around 60 per cent moisture, which is important for the composting bacterial activity. The roof on a vessel in Barrier-1 is lifted to its full height by the screw-jack system in less than one minute, to allow access to a loading shovel to load in the shredded, mixed material. When loaded, temperature-monitoring probes are placed into the material and the roof is lowered. The aeration system is activated and this circulates air through the material in the vessel to maintain oxygen levels.
Composting is a natural biological process that requires aerobic conditions and moisture for the composting bacteria to work well. The Composting Company's aeration system monitors the level of oxygen in each individual vessel, as the oxygen demand will vary from vessel to vessel, depending on the mix of material and the stage of the process. When oxygen reaches a minimum parameter, the aeration system automatically draws in fresh air to replenish oxygen and exhausts stale air to a biofilter. A proprietary Scada system monitors both oxygen and temperature and allows for remote alteration of settings if required.
Temperature also has to be monitored to comply with the Animal By-Products Regulations (ABPR) for the processing of food waste, which requires a temperature of 600C to be achieved for at least 48 hours in order to kill off pathogens. In practice, the material stays in the vessel for seven to 11 days as the controlled environment speeds up the composting process. After seven to 11 days, the Barrier-1 vessel is unloaded, from the opposite end to which it was loaded, into Barrier-2, and the process is repeated in compliance with ABPR.
After seven to 11 days in Barrier-2, the material is sanitised and is removed to a maturation pad where it is formed into windrows (long piles of compost) and monitored for temperature and oxygen for four weeks or more, depending on the final application. When it has matured sufficiently for the application, it is screened to a suitable size for the end product and sold to agriculture, landscape gardeners, garden centres or the public. Each building that houses the vessels requires two jacking systems (one per side), each with three screw jacks and one motor. To date, Power Jacks has provided screw-jack systems for 20 IVCs.
There are currently four IVCs at Cumberlow Compost Services and 16 IVCs at The West London Composting Company (WLC), which have been in operation since March 2008. The vessels supplied to the WLC site by The Composting Company make it the largest IVC in Europe, with an annual capacity of 100,000 tonnes. The Composting Company is expanding the number of vessels by four at the Cumberlow site and also have other sites asking for their system. As their supplier, Power Jacks provides on-going support and product development for their business and product development.
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