Mechanical durability of digestate briquettes mixed with mineral additives
2016
Brunerova, A., Czech Univ. of Life Sciences, Prague (Czech Republic) | Ivanova, T., Czech Univ. of Life Sciences, Prague (Czech Republic) | Brozek, M., Czech Univ. of Life Sciences, Prague (Czech Republic)
Briquettes produced from digestate have its specific properties which directly affect briquettes’ quality and must be determined. Mechanical durability (DU) is considered as a main indicator of physical quality of briquettes and its determination is essential in overall quality evaluation. The study was designed to determine mechanical durability of briquettes from pure digestate, digestate mixed with zeolite and dolomitic limestone both added in ratio 6:1 (digestate: additive). Use of additives is common practice which improves quality of briquettes. All briquettes were produced under the same production conditions by hydraulic briquetting piston press (working pressure of 18 MPa) into the cylindrical shapes (diameter 65 mm, length from 30-80 mm) and subsequently divided according to feedstock into three groups: Group A-briquettes from pure digestate, Group B–briquettes from digestate + zeolite and Group C–briquettes from digestate + dolomitic limestone. All groups were stored for four months (constant air temperature 23 ºC and relative air humidity 45-60 % in average). Standard laboratory analysis of pure digestate properties determined gross calorific value (wet basis) equal to 17.02 MJ•kgE-1, moisture content 9.21 % and ash content 15.71 %. During storage period were samples repeatedly (n = 4) submitted to test for mechanical durability determination by using of special rotating drum. Overall mechanical durability of groups was calculated and afterwards the result values were divided according to briquette weights into four groups for each feedstock and statistically tested. Final results of experimental testing showed that highest average mechanical durability was determined equal to 98.9 % for Group A, 98.2 % for Group B and the worst results 97.3 % were achieved by Group C. Upward trend of mechanical durability was observed during testing process for all groups. The findings of this study suggests that all tested groups fulfilled requirements for commercial briquette production at highest grade (DU is greater or equal to 95 %) according to standard EN 15210- 2:2010, however it was proved that mixing digestate with additives did not improve its properties.
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