The problem of too high moisture content of the raw material can significantly increase biomass briquettes’ production costs.
The situation of processing the raw material (in this case, the straw) with exceeded allowable moisture was analyzed. Straw moisture most often occurs as a result of inadequate protection against atmospheric conditions during storage. Particularly affected by this problem is the raw material stored in the form of stacks. The problem of too high raw-material moisture can be solved using the dryers in the production process. Of course, this solution requires investment, and increases expenditures on production. A variant of the production with the use of the dryer were studied. In the calculation of the straw drying cost it was assumed. Estimated cost of drying was 40 PLN per ton. The amortization period of the dryer worth 200.000 PLN is 10 years. Efficiency of the drying process is 400 kg of straw per hour.
In the production, during attempts to produce briquette from material with too high moisture, the following consequences were observed:
− The need to manually reject a large part of raw material by the grinder’s operator.
− The raw material losses at 15% during the initial stage of the biomass grinding.
− Reduction of the grinding process efficiency by about 10 percent.
− Sudden stopping of the briquetting machine resulting in a significant reduction of the efficiency of briquetting process (from the normal level of 350 kg per hour, up to the level 240 kg per hour).
− There was a lower quality of the produced briquettes (briquette flaking, swelling, increased volume of the briquette, in extreme cases - spill).
The range of variability of direct briquette production costs in considered variants is significant and indicates that in the planning of production it is worth to simulate the effects of variable of raw material moisture content on production costs and effectiveness. Furthermore, it should be noted that a key aspect of managing this kind of production is to prevent raw material from absorbing moisture, mainly while storage, but also during harvest, loading or transport.