Solar drying of a solid waste from steel wire industry

• A solar dyer was used to dry industrial solid waste.
• It was used a renewable source of energy.
• Reduction of the product mass reduced transport and disposal costs.
• Water activity was reduced from 68% to 11% in about 8 h.

The solid residue coming from the treatment of effluents generated in pickling steel wire has an inorganic nature. This residue, after the process of moisture removal by a filter press, has high moisture content 70% wet basis. Transport costs and landfill could be significantly reduced with the products drying. The use of solar energy to promote drying of the residue is technically and economically feasible. Environmental benefits are presented, due to its renewable characteristic and exemption for emission of greenhouse gases. This study aimed to evaluate the drying of industrial solid waste, using an active integrated solar dryer. The thermal properties and the thermal efficiency of operation of the device in different operating conditions were studied. Experimental tests were developed to evaluate the operation of the solar dryer, until a moisture content (wet basis) of 30% is reached. The instantaneous thermal efficiency of the dryer varied from 9.7% to 29.5%. In the drying experiments, the drying efficiency ranged from 5.2% to 7.2%. Thermal efficiencies presented suitable values for air heaters. Nevertheless, drying efficiencies were low, but they can be improved if the load is increased.