Converting LPG stoves to use biomethane

Abstract

This article presents a study on using portable biomethane for domestic cooking in Thailand in domestic stoves. Thailand presently uses approximately 20,000 tonnes of LPG every day. It is estimated that Thailand has the potential to produce the equivalent of 3,000 tonnes of LPG equivalent energy from compressed biomethane gas (CBG) per day. This assumes full conversion of all agricultural, industrial and municipal wastes into CBG. Since CBG is a form of renewable energy, the use of it for domestic cooking purposes will help to reduce Thailand's dependence on imported energy and have a positive impact on the environment. The difficulty arises when a cylinder of biomethane, which is processed biogas comprising of at least 85% methane, is used instead of LPG, which is comprised of propane and butane, in a cooking stove. The Wobbe index for LPG is approximately double that of biomethane indicating that they are not interchangeable gases. The density of LPG is also 2-3 times that of biomethane which results in incompatible calorific or heating values and flow rates, assuming constant pressure, in domestic stoves. Without modification to the stove or the supply conditions the biomethane will not properly combust. Two domestic stoves types were selected and modified to allow biomethane to be used. An experiment was setup to measure the fuel flow rates, pressure and combustion efficiency in these modified stoves. The results of these experiments point to an optimal design modifications for converting an LPG to a biomethane stove.