Design of an Anaerobic Digester for Generation of Biogas Fired in a Burner and Lamp

Abstract

This work presents design of an anaerobic digester for generation of biogas fired in a burner and in a gas mantle lamp. The methodology utilized equations to describe digester that stores slurry and biogas which were discharged according to designed orifices over a period. Models to predict volume of biogas generation over a period of retention, spent slurry discharge height from cylindrical digester to expansion chamber as well as energy delivered to the biogas burner and lamp were developed to promote scale and dimensions of digester systems. The anaerobic digester was determined to have a total plant volume of 10.5 m3. The volume of biogas generated over a period of 42 days retention shows a concave down curve of exponential polynomial equation, with highest rated daily gas production of about 5 m3 occurring between 15-25 days. The spent slurry flows towards expansion chamber as slurry level decreases in the digester and became much pronounced in day 15 of 42 days retention. The burner had specific firing rate of 0.256 m3/s/m2 and heat output per unit port area of 677 W/cm2 while the lamp light output was 1267 lm for an illumination area of 11.3 m2. The cumulative heat load of the burner and lamp reaches about 9.0 kW and 2.0 kW, respectively.Keywords: Anaerobic Digester; Biogas; Burner; Lamp; Models