Design and Improvement of Dewatering System Implemented for Biogas Slurry

Abstract

The report titled "Design and Improvement of Dewatering System Implemented for Biogas Slurry" aims to validate the screw of existing dewatering machine initially created by Sherpa et al. in 2017 and modified by Sujan Jojiju in 2023. The goal is to validate the design, test the modified machine with effective screw press and evaluate its performance with respect to nutrient contents present in input and output materials along with comparison of its efficiency with conventional sun-drying process used in drying the slurry sample. In Nepal, there is a significant demand for organic fertilizers and dewatering the biogas residue could serve as an eco-friendly alternative to chemical fertilizers. The design for validation of screw component and testing of machine are related to research, recommendations from literatures and advice from supervisors. SolidWorks is used for the design process and ANSYS for the simulation works while its testing is conducted at workshop of GRIT Engineering Pvt. Ltd. The biogas slurry used for testing as well as sun-drying is collected from the biogas plant’s prototype of 1m3 capacity present in the premises of Pulchowk Campus, Lalitpur. The machine's performance is evaluated at various operating speeds (36, 25, 20, 15, 10 and 8 rpm) using a Variable Frequency Drive (VFD). The results reveal that the most efficient operating speed being 8 rpm. The liquid yield, extraction efficiency, and extraction losses are determined to be 52.51%, 79.11% and 22.80%, respectively. The slurry sample is sun-dried for 24, 48 and 72 hours whose nutrients concentrations (TS, N, P, K) are tested in Soil Water and Air Testing Laboratories Pvt. Ltd. The results show that optimum duration of sun-drying is 48 hours as its reduction of Total Solid contents is least. The slurry sample before testing in dewatering machine is also pretreated for 24 and 48 hours to check the efficiency of existing machine and compare the results with that of sun-drying process. From Financial analysis, the machine's installation cost is NRs. 392,000, along with the payback period, IRR and NPV are calculated as 1year 10months 23days, 44% and NRs. 353575.86 respectively