Recovery of waste farm after methanation by evaporation on inclined plate

Abstract

This work addresses the recovery of a liquid effluent by thermal evaporation. It is a digestate of pig manure, rich in N, P, and K (Granier et al. 1995; Latimier et al. 1996; Levasseur, TECHNI 21(4):16–19, 1998). The effluent was subjected to anaerobic digestion and phase separation by centrifugation. Several recovery scenarios for the liquid phase of a waste with 2.3% DM (dry matter) are analyzed. Because of the high consumption of fossil energy in the world, we analyzed in this work the evaporation of this effluent using solar energy, in order to concentrate N, P, and K elements. The device consists of a stainless steel plate with a tilt angle of 30° and isn’t covered with glass. The liquid circulates as a film on the steel plate and is exposed to a 6000, W solar simulator. This work is divided into two primary parts. The first part is a thermophysical characterization of the effluent comparing to water. In the second part, evaporation tests with liquid effluent were performed. So, experimental tests will be valid by determining the equations of heat and mass balances on the plate and on the film (Bouchekima et al. 2001; Chen et al. 1986; Brau, Support de cours de convection pour 3 GCU, Insa de Lyon, département de Génie Civil et Urbanisme, 2006). Before starting tests, the plate is exposed to solar radiation until stabilization of its temperature. A validation of the temperature of the plate, depending on solar flux and temperature of air, in laminar regime, was performed (Huetz-Aubert and Sacadura 1981). We find that when the solar flux increases, the temperature of the plate increases. However, if solar flux is constant, the temperature of the plate decreases when the air temperature increases. The liquid circulates as a film flowing from the top of the plate. Local heat flux measurements, temperatures, and evaporated flow for input flow rate from 1 to 5, g/s are determined and compared with experimental results.