FEATURE: BIOENERGY IN INDUSTRY Bioenergy International No 79, 3-2015 17 Sánchez, agricultural engineer, adding that this opens up the possibility of supplying other heat consumers in the future. Agro-waste feedstock only The feedstock varies over the course of the year and is fed into the digester in liquid and semisolid form; potato peels, leek and other vegetable leaves, grass and maize silage along with a fraction of sludge from vegetable processing industries. Animal by-products are not permitted. – The plant only uses vegetable agro-food waste as feedstock, no manure. This involves a complex biological process, which is always talked about but rarely implemented, and this facility proves it is feasible, said Enrique Sánchez highlighting another distinguishing feature of the plant. The feedstock is delivered to a reception area where a shredder supplied by local manufacturer Tabarés is located. The shredder has been modified to incorporate a feed hopper and discharge auger to transfer the shredded material to a slurry tank. The plant currently processes around 15 tonnes per day. The slurry tank has a capacity of 30 tonnes and is equipped with an agitator and pump to keep the prepared feedstock homogenised. From here the homogenised mixture is pumped to the 700 m3 main digester. Being a mesophyll process the digester temperature is kept at 37°C and the residence time is 25-30 days. – The bacteria population should suit the substrate employed. It is essential to maintain the balance and volume to quickly digest the material and achieve maximum production, emphasised Enrique Sánchez. The estimated self-consumption of heat to keep the digester at the correct temperature is between 10 and 25 percent of the final production though as Enrique Sánchez points out it will take another 18 months or so to get full data from two years of operations. From the digester there are two outgoing pipes, one for the digested residue, digestate, and one for the biogas. The latter enters a 550 m3 double diaphragm gas storage tank. Air is blown in the space between the inner and outer membrane. This regulates the variation in gas input and gas output, keeping the gas pressure inside the storage tank at a constant level of 300 mm water column, approximately 0.029 bar, and the external membrane rigid. A gas flare and vacuum valve ensure safe and stable operations. The liquid digestate is pumped to the bottom of the gas storage tank to capture any remaining biogas before it is pumped to an 800 m3 storage pool representing about three months of operational storage capacity. – The digestate can be applied to crops directly as is, by using a conventional liquid slurry spreader. The digestate can also be dewatered and even pelletised for use as a solid fertiliser, said Juan María Sánchez adding that the average market value for the liquid digestate is EUR 130 – 140 per tonne. Test, improve and market The project is still under development including a remote operation control system that allows access to system operation by smart phone. Development of the project biology is being done with assistance of the Spanish consultant BIOVEC. There is no shortage of ideas. – This plant is a prototype and the idea now is to use this facility as a pilot plant where improvement to the whole process can be made. We want to inspire new customers with heat needs, for instance installing a greenhouse where the heat and carbon dioxide is consumed, ended Juan María Sánchez. Text & photo: Ana Sancho BIE BI79/4824/AS First EnviTec plant in Japan connected to the grid German biogas technology supplier EnviTec Biogas GmbH has commissioned its first biogas plant with grid connection in Japan. Located in Osaka prefecture the 250 kW plant is a pilot project between EnviTec and its Japanese partner Renagen Inc., a biogas company and subsidiary of REMATEC Group, a waste recycling company based in Japan and South-East Asia. – With this plant we, together with EnviTec Biogas, can for the first time demonstrate the enormous efficiency of the waste-to-energy technology used here to the Japanese market, said Daisuke Mishima, CEO of Renagen. The plan within the partnership is to establish up to ten biogas plants per annum taking advantage of fixed feed-in tariffs currently at the equivalent of EUR 0.3 per kW. – The initial steps for two additional plants have already been introduced, said Roel Slotman, Chief Commercial Officer, EnviTec Biogas in a statement. BI79/4838/AS
Bioenergy no 3 May 2015
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