Methane losses from floating gasholder type biogas plants in relation to global warming

摘要

Methane losses from uncovered portion of cattle dung slurry in biogas plant of various capacities (3, 6, 9, and 85 m~3) are measured using closed chamber method. Measurements are conducted from January to December 2002 during a year. Mean methane flux from different exposed areas of a biogas plant of 3 m~3 capacity are: (ⅰ) Inlet/outlet pipes; 70 g/m~2/d, (ⅱ) Around gasholder; 87 g/m~2/d, and (ⅲ) Slurry tank; 41 g/m~2/d, and increased by 15-20 per cent with the increase in plant capacity to 85 m~3. Seasonal variation of slurry temperature strongly affects the methane emission. Emission rates during the summer are found to be high (125, 179, 230 and 230 g/m~2/d, respectively, from the holder side of 3, 6, 9, and 85 m~3) at slurry temperatures near optimum mesophilic range (32℃ during June) and drop down considerably (68 to 79 per cent) during winter at slurry temperatures in the lower psychrophilic range (13℃ in December). The correlation coefficient between the CH_4 flux and the slurry temperature is found to be positive (between 0.90 and 0.96) and significant.