Thermal Properties of Biogas from Tea leaves Substrate

Abstract

Currently, about 75% of the energy consumed in the world comes from fossils fuels and Kenya is no exception. Fossils fuels are delectable besides creating other environmental issues like global warming through the emission of green gases. Wood as a source of thermal heat energy is used in tea industries in energizing boilers for tea leaves drying. There is need to explore safer energy technologies. This research was exploring the thermal potential of biogas from tea leaves as a clean source of energy, its ability in powering tea industries boiler plant and its potential to reduce greenhouse gas emissions from the tea industries. Kisii county in Kenya is an agriculturally rich area in terms of tea as well as banana production. It has been observed that a considerable amount of tea leaves rejected at the factory and tea buying centers is just wasted away. The production of biogas was investigated in the laboratory using the simple single-state digester. The digester was fed with crashed tea leaves of about 500 grams and operated at room temperature of about (21-26 °C) for 20 days. The amount of biogas generated in terms of volume by a given mass of the tea leaves was also determined and Boswell equation was used to determine the thermal value of biogas produced. Data from the digester was collected daily and recorded in the laboratory spread sheet. The gas was analyzed by a gas Chromatograph machine model 8610C connected to a display computer. Tea substrates were categorized into four samples, sample S1 was fresh tea leaves from farms, sample S2 was tea leaves from composite pits of tea factory, for sample S3 and S4 was same as S1 and S2 respectively with an addition of 10ml of 1 molar sodium hydroxide  to create a slightly alkaline environment. 500g of each of the samples of tea substrate were mixed after crushing them using a blander and were mixed with water to a volume of 5000 ml. It was observed that samples with sodium hydroxide (S3 and S4) produced more biogas (3800-4000ml) than those without (S1 and S2) (1800-2000ml) which was attributed to the basic environment which make the anaerobic digestion faster. The gas production was optimum after about 7-12 days. The thermal value of biogas was about 22MJ m-3 and the thermal value of methane was about 36MJ m-3, which has an electrical value of 6.1 kWh. From the results the thermal value of biogas from tea leaves can easily operate the boilers if the biogas is produced in large scale, besides reducing cases of deforestation and greenhouse gas emission to the environment.