DESIGN OF 5 TONS PER DAY METHANOL PRODUCTION PLANT FROM SEWAGE WASTE BIOGAS
Abstract: Sustainable Environmental and Resource Management in Zimbabwe-Energy Subtheme
1*M. M. Manyuchi and2K. Kwidini
1-2Department of Chemical and Process Systems Engineering
Harare Institute of Technology, Box BE 277, Belvedere,Harare, Zimbabwe
*Corresponding Author
E-mail address:
[email protected]
Background
A lot of untapped biogas is being generated from municipal sewage waste. This biogas contains methane and other gases such as CO2, H2S and ammonium compounds. Biogas can be used for methanol production. Methanol is an important chemical that can be used for different industrial applications e.g. in blending with diesel and gasoline, manufacture of formaldehydes and biodiesel. Biogas contains greenhouse gases that affect the purity of the gases in the atmosphere degrading the environment. There is therefore need to control the environmental degradation at the same time producing a product from biogas which is of importance such as methanol.
Objectives
This project focused on the design of 5 tons per day methanol producing plant that uses biogas from municipal sewage.
Methodology
4 x 100g municipal solid waste samples were obtained from Kwekwe Sewage Treatment Plant. Biogas was produced at 40-45oC and was collected in gas collectors. The biogas was then first passed through iron salts for removal of H2S and then through water and KOH for removal of ammonium compounds. The methane gas was then passed through superheated steam for conversion of methane to methanol.
Results and Conclusion
The designed process had three main stages which are production of synthesis gas from steam and methane, production of methanol from synthesis gas and the purification of methanol. A yield of 89% was obtained and 90% conversion which gave a product quality of 99.9%. A temperature of 260 0C and a pressure of 45 bars were found to be optimum for methanol synthesis in the reactor. Experimental results obtained were used in mass and energy balances determination and the equipment design. A detailed design was done for the 3m3 plug flow reactor and 2m3 distillation column whereby the volume, residence time of reactants, diameter and height were calculated. The equipment was made up of stainless steel. The HAZOP and process control were analyzed to monitor unsafe deviations that may arise in the plant. An EIA was done for the project and all Zimbabwean environmental regulations were complied on. A site near Kwekwe Northern Sewage Works was chosen as the project location. The project proved to be economically viable for a 80% plant utilization with a payback period of 3.6 years and the return on investment was 27% after investing US$1 417 983. The selling price was $1.38/kg of methanol. It can be concluded that it is possible to optimally produce 5t/day of methanol from biogas.
Keywords: Biogas, Equipment Design, Methanol, Plant design, Plant safety, Sewage waste
