THE DEVELOPMENT OF FURNACE - HEAT EXCHANGER SYSTEMS IN WHICH CHOPPED CEREAL STRAW IS THE FUEL
Although most of the world's cereals are harvested with combines there is interest in several countries in a different approach, namely that of whole crop harvesting. In this process of harvesting relatively cheap field machinery is used, then the separation of grain and straw takes place in stationary equipment at the farm buildings. It is a logical development of this process to burn straw to provide heat to dry the grain before it is stored. The requirements for straw for this purpose would be small in most situations, leaving further straw that could be used for heating farm houses and premises throughout the winter. In an earlier Energy from Biomass Programme, aspects of burning straw to dry grain were studied and the first part of the present work involved an examination of the need for control of a large unit designed to carry out this task. In view of the large mass of the equipment and the fact that crop moisture contents usually change slowly, it was decided that automatic control was not required: it is merely necessary to make infrequent adjustment of the proportion of the total amount of chopped straw that needs to be fed into the furnace. Straw which is surplus to the drying requirement should be conveyed onto an uncovered heap, preferably situated on a hard, free draining base. Rainfall has little effect on the moisture content of the bulk of the heap and in any case some wet patches of straw can be tolerated in brick lined furnaces. Heavy snowfalls can cause problems with this cheap form of storage as a disproportionately large amount of snow tends to be picked up when mechanically loading the straw. For this reason it is recommended that a few tonnes of straw is stored under cover for use when there is new snow (a relatively rare occurrence in UK cereal growing areas). The key element in the chopped straw handling system is a purpose-built trailer, used to transfer straw from the storage area to a small furnace and then to meter it into the furnace on demand. An enclosed hopper bottomed trailer was contructed: it was emptied by an auger which ran the full length of the body. Straw bridging was prevented by having four weighted chains which were moved backwards and forwards along the length of a track mounted above the auger. While the overall performance of the large furnace was better than might have been expected, that of the small one fell short of expectations. Part of the problem with the small unit can be attributed to the design of the sloping grate, although the lack of insulation also had an effect. In England and Wales almost half of the 12 million tonnes of cereal straw grown is currently surplus to requirements and at the moment most of this is burned in the fields. The storage and handling aspects of the current work could also be applied to straw from crops which have been harvested by combines.
Bibliographic Reference: EUR 10110 EN (1986) MF, 40 P., BFR 150, BLOW-UP COPY BFR 200, EUROFFICE, LUXEMBOURG, POB 1003
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Record Number: 1989124106300 / Last updated on: 1987-01-01
Available languages: en