Ecological analysis of a typical farm-scale biogas plant in China

The aim of this work was to present the common anaerobic digestion technologies in a typical farm-scale biogas plant in China. The comprehensive benefits of most biogas plants in China have not been fully assessed in past decades due to the limited information of the anaerobic digestion processes in biogas plants. This paper analyzed four key aspects （i.e., operational perfor- mance, nonrenewable energy （NE） savings, CO2 emission reduction （CER） and economic benefits （EBs）） of a typical farm-scale biogas plant, where beef cattle manure was used as feedstock. Owing to the monitoring system, stable operation was achieved with a hydraulic retention time of 18-22 days and a production of 876,000 m3 of biogas and 37,960t of digestate fertilizer annually. This could substantially substitute for the nonrenewable energy and chemical fertilizer. The total amount of NE savings and CER derived from biogas and digestate fertilizer was 2.10× 10^7 MJ （equivalent to 749.7 tee） and 9.71 × 10^5 kg, respectively. The EBs of the biogas plant was 6.84× 10^5 CNY.yr^-1 with an outputs-to-inputs ratio of 2.37. As a result, the monitoring system was proved to contribute significantly to the sound management and quantitative assessment of the biogas plant. Biogas plants could produce biogas which could be used to substitute fossil fuels and reduce the emissions of greenhouse gases, and digestate fertilizer is also an important bio-product.

Performances of an air thermal energy utilization system developed with fan-coil units in large-scale plastic tunnels covered with external blanket

To improve the problem of low temperature at night in winter due to the lack of thermal storage in large-span plastic tunnels,an air thermal energy utilization system(ATEUS)was developed with fan-coil units to heat a large-scale plastic tunnel covered with an external blanket(LPTEB)on winter nights.The ATEUS was composed of nine fan-coil units mounted on top of the LPTEB,a water reservoir,pipes,and a water circulation pump.With the heat exchange between the air and the water flowing through the coils,the thermal energy from the air can be collected in the daytime,or the thermal energy in the water can be released into the LPTEB at night.On sunny days,the collected thermal energy from the air in the daytime(E_(c))and released thermal energy at night(E_(r))were 0.25-0.44 MJ/m^(2) and 0.24-0.38 MJ/m^(2),respectively.Used ATEUS as a heating system,its coefficient of performance(COP),which is the ratio of the heat consumption of LPTEB to the power consumption of ATEUS,ranged from 1.6-2.1.A dynamic model was also developed to simulate the water temperature(T_(w)).Based on the simulation,E_(c) and E_(r) on sunny days can be increased by 60%-73%and 38%-62%,respectively,by diminishing the heat loss of the water reservoir and increasing the indoor air temperature in the period of collecting thermal energy.Then,the COP can reach 2.6-3.8,and the developed ATEUS can be applied to heating the LPTEB in a way that conserves energy.