Greenhouse gas emission mitigation calculation of large scale straw biogas centralized supply project

The large straw biogas project is an important way of new energy utilization of straw resource in China. It has great meaning to facilitate the construction of a resource-saving and environment-friendly society and mitigation of climate change. The methods of literature research, fixed point monitoring and quantitative analysis were adopted. Taking the straw biogas project in Gengguan Village of Cangzhou City in Hebei Province of China as an example, this paper establishes a methodology of greenhouse gas emission reduction for large scale straw biogas project. The greenhouse gas emission reduction measures include project boundary, calculation of baseline emissions, project emissions calculation, leakage calculation, emission reduction and project monitoring. Calculation of baseline emissions refer to the greenhouse gas emission by straw stalk treating, rural resident daily used energy, and fertilizer production in farmland under no large straw biogas project. Project emissions calculation refers to the emissions produced by engineering transportation, power consumption, fossil fuel consumption and extra biogas torch combustion. We calculate the greenhouse gas emission reduction of the straw biogas project in 2014. The results show that the baseline CO2 emissions are 5 776.15 t, the project CO2 emissions are 57.53 t, the leakage of CO2 is 136.59 t and the CO2 emission reduction is 5 582.03 t, which is approximately equal to CO2 emissions by 2 100 t standard coal combustion. As required in NY/T 2142-2012 Specification for Process Design of Straw Biogas Engineering, the design working life of straw biogas engineering is no less than 25 a, the Gengguan Village straw biogas centralized gas supply project can at least achieve CO2 emissions of 139 600 t. For every 1 t straw (dry weight) consumed, a net reduction of 3.56 t CO2 emission can be got, and for every 1 m3 methane used, 11.50 kg CO2 emission can be reduced. Through the construction of greenhouse gas emission reduction measurement method of large scale straw biogas centralized gas supply projects, it is helpful to understand the emission reduction utility of large scale straw biogas centralized gas supply projects scientifically, analyze the main greenhouse gas emission sources during the project operation quantitatively, and further enhance the straw emission reduction capacity of biogas centralized gas supply projects. The order of the contribution of greenhouse gas emission is: Leakage > engineering operating power consumption emission > energy consumption emission of coal combustion in engineering operation > engineering transport activity emission. Leakage accounts for 70.36% of the total emissions, engineering operating power consumption emission accounts for 22.41%, energy consumption of coal combustion in engineering operation accounts for 4.71%, and engineering transport accounts for 2.52%. To reduce the operation and leakage emissions, the straw biogas projects should be located in the more concentrated areas of farmers, choose the material with corrosion resistance, good pressure resistance and strong environmental suitability, and change the flange connection and threaded connection to welding. In the meantime, we should strengthen the daily inspection, maintenance and management, upgrade the straw pretreatment (crushing) process technology, promote and use the solar heating, biomass furnace heating, biogas warming and other clean energy warming technology and greenhouse thermal insulation technology measures, and layout the straw storage sites and biogas fertilizer treatment center reasonably to reduce the energy consumption in the transportation. In view of the shortcomings of this study in the parameter selection, regional application and other aspects, we will strengthen the studies on relevant parameters and different regional case further. © 2017, Editorial Department of the Transactions of the Chinese Society of Agricultural Engineering. All right reserved.