Assessment of packaging materials for storage of Biogas in portable containers

Abstract

The production and generation of biogas in Uganda, has not fully solved the greenhouse gas emission challenge, because its use is predominantly onsite. This study aims to provide offsite use of biogas by evaluating materials for its packaging. In the study, four materials were considered, namely: low carbon steel, aluminum, High Density Polyethylene (HDPE) and fiber glass polyester composite. A tensile test was carried out on each of the materials to find out the yield strength and ultimate tensile strength. This was followed by a numerical analysis using the finite element method in which Abaqus 6.13 – 1 was used in order to: simulate the stresses in the gas container and to design the gas container by establishing the minimum thickness, the mass of the empty gas container, the mass of the biogas in the container, and the cost of the containers at the respective internal pressures. Results indicate that, whereas steel ranks highest in many strength parameters, including; tensile strength, yield strength, factor of safety, and the stress carrying capacity, fiber glass polyester composite closely follows in all measures, and has the highest value of specific strength of all the study materials; with over 58% more weight saving as compared to steel. This property explains the strength to weight ratio of a material; which is a key consideration for designing light and strong pressurized gas containers. HDPE ranks least in all aspects of mechanical strength. The established minimum range for thickness in the pressure range of 50 – 250bar is 4.7mm – 11.0mm, and this is true for all study materials except HDPE. Within the established thickness and pressure range of 50 – 250bar, the total mass of the empty portable biogas container is in the range of 3.5 – 50kg, the mass of the biogas in the portable container in the range of 1 – 5kg, and the life cycle cost of the empty container is in the range of UGX 300000 – 870000. Based on the different parameters for suitability of a biogas packaging, including; stress carrying capacity, weight saving, the quantity of biogas carried at a given pressure range, and least life cycle cost at 50 bar, this study recommends fiber glass polyester composite as the most suitable material for packaging biogas.