Objective
The standard plant to manufacture dried forage involves a rotating drum drier charged with high moisture content grass and a furnace to heat the air flow up to 1,000 deg. C. This is delivered to the rotating drum, and passing across the grass charge, reduces the moisture content to 10%, and a mill or press to pelletise the dried product.
The project aims to modify this standard plant in such a way as to recover some of the drying heat, and to achieve a fuel saving of 25%.
26 tests were performed during 2 campaigns (1980-1981) with a view to determining the efficiency of the evaporator as well as protein and dry matter losses in the juice whilst being condensed in the evaporator>
The 1980 programme showed that the efficiency of the evaporator reached 73% of the projected results. After adjustments and minor modifications the efficiency increased to a mean average of 79%.
It would appear from the tests that the evaporator is less efficient with fresh juice input with a higher dry matter content. This phenomenon could reduce the efficiency of the evaporator by 5-8% if this system were installed in drier areas. On the other hand, the efficiency of the evaporator is higher when processing crops of high moisture. In fact, the temperature in the dryer as well as the latent heat value of the steam increase owing to the temperature/moisture combination.
Dry matter and proteins suffered a 1 to 2% loss of value in the evaporator. Further losses were registered after the juice left the dryer. They range from 2 to 3% in the case of dry matter and from to 3 to 5% in the case of nutrients. In fact, dry matter in the juice is in the form of very fine particles which are easily burnt.
FUEL SAVING
The fuel consumption (in gas therms) was the following: 1977-79 average
before modification 121 gas therms/t dried
1980-82 average achieved
after modification 98 gas therms/t dried
fuel saved 23 gas therms/t dried
Due to its conversion the plant saves approximately 19% of energy. 10% of the exhaust gas (and not 30% as expected) can be recycled into the furnace. This discrepancy is due to pressure imbalance in the rotary drum dryer caused by the evaporator.
Due to changes required because of increased capacity of tonne evaporative capacity to 8 tonnes capacity, the Evaporator is now redundant.
However it is envisaged that it will be adopted as part of a Scrubbing System to reduce levels of gas to atmosphere under forthcoming pollution controls.
A nourishing, dense juice is extracted from the moist grass by use of a screw press, collected in a reservoir and then forwarded by pump to the evaporator. This is heated by the combustion taking place in the furnace.
The concentrated juice is returned to the grass charge before it enters the rotating grass drum drier. The mill and/or press for pelletisation is located downstream of the drier as in the standard plant.
Programme(s)
Topic(s)
Call for proposal
Data not availableFunding Scheme
DEM - Demonstration contractsCoordinator
EX37 9LH UMBERLEIGH
United Kingdom