Modeling the optimal condition for drying rumen contents using a solar greenhouse dryer

Abstract

The ruminal content is a biomass waste obtained from the benefit of cattle. This biomass can be used as a fuel for generating part of the thermal energy that is required in the slaughterhouse processes. For this purpose, the ruminal content must be subjected to several pretreatments to facilitate its use as a fuel. The combustion efficiency of the ruminal content is affected by the particle size and the size distribution, as well as the moisture content. The ruminal content has a high moisture content that must be reduced from around 60% to values below 15% (by mass) within a few days so that the conversion efficiency and heating value are not affected. To dry the rumen content, low-cost natural drying systems can be utilized. A numerical approach for the solar greenhouse dryer performance was analyzed for typical local solar irradiation and natural convection conditions, at the greenhouse site of installation. To analyze the rumen content, at variable drying temperatures ranging from 40 °C to 70 °C, a thin layer model was used. Within the temperature range evaluated, the ruminal content effective diffusivity varied from 1.6 × 10−13 to 5.6 × 10−13 m2/s. The dryer was designed as a semi-cylindrical shape with a loading capacity of about 10 000 kg. A set of ordinary differential equations was formulated for modeling and simulating the heat transfer and drying phenomena inside the greenhouse dryer. The method of finite differences was used for solving the system of equations. The estimated drying time of the ruminal content was around 6 days (d) and the final product moisture was 14.10%.