Application of the Screw Method of Pressing Water-Containing Composite Raw Materials Based on Sewage Sludge for the Manufacture of a Pilot Batch of Composite Biofuel Pellets

The technological conditions for the production of a pilot batch of biofuel pellets based on sewage sludge from the Dnipro-Kirovograd wastewater treatment plant are substantiated, taking into account their plastic properties. An analysis of the pressing equipment used for pressing water-containing plastic materials was carried out on the example of clays and clay mixtures. A screw press device of a simplified design was selected and tested for the production of a pilot batch of biofuel pellets based on the MOSS of the OKVP ‘DNIPRO- KIROVOGRAD’. The method of calculation of a screw press device of a simplified design and the algorithm of its application are described, and its verification calculation is performed. The main physical and technical properties of biofuel pellets from the manufactured pilot batch were evaluated: density, moisture content, ash content, calorific value. During the experiments, it was not possible to achieve a significant reduction in the moisture content of the pellets compared to the moisture content of the original composite raw material based on sewage sludge. This is partly due to the relatively large size of the holes in the cylinder body, which were intended for the planned drainage of liquid during the pressing of raw materials. However, it turned out that when the pressure was increased to about 5 MPa, raw materials, not liquid, began to flow out through these holes, which made it impossible to increase the pressing pressure to higher values. A decrease in the moisture content of the manufactured pellets in the range of 7 to 10 % was observed with local low-power heating of the screw press cylinder to 45...50 С. Therefore, to reduce the moisture content to a lower value, the manufactured biofuel pellets were dried in an open atmosphere, usually for ≤ 24 h, to a moisture content of ≈18...25 %.