The mathematical model established to select biogas utilization for hog farmer, in this study. It was developed through the survey data of pig industry and biogas utilization equipment manufacturers and previous studies about biogas utilization. The reliability of the mathematical model was verified by survey data. It established the applying models and the required equipments for varied scale hog farm
Biogas production factors and biogas utilization model were included in the mathematical model. Biogas production factors included the scale of hog farm, temperature and theoretical hydraulic retention time (HRT). It may be used to determine the theoretical biogas production of hog farm. Biogas utilization models included power generation, heating lamp and direct combustion. The mathematical model can calculate three types of biogas utilization model with equipment specifications and quantity, cost evaluation and carbon reduction.
The mathematical model was verified by the equipment survey data of hog farms. The result show that the number of heating lamp can be calculated by the mathematical model with the maximum biogas production of hog farm. However, the actual number of the heating lamp is related to the field design of farrowing house and nursery house. Thus, the mathematical model can calculate the required number of heat lamps for the hog farms. A 60kw generator was used to verify the mathematical model for a hog farm with the operating time of 12h/day. A 30kw generator was determined by the mathematical model with operating time of 24h/day. The total power generation is the same for both generators. But the cost of generator is significantly reduced and it can supply energy to the cooling equipment in water-pad hog house for long time operation. Thus, the reliability of the mathematical model had been properly verified.
Base on the evaluation results by the mathematical model for power generation, the cost of common generator with washing composite desulfurization is the lowest. The cost of anti-corrosion generator is lower. The cost of common generator with biological desulfurization tower is the highest. Base on the evaluation results by mathematical model, the biogas production of southern Taiwan is the highest among northern, central, and southern Taiwan, due to the highest average temperature. The power generations were evaluated under normal operation of HRT for 1,000, 3,000, 5,000 and 10,000 heads hog farm in southern Taiwan. The cost were 420,000, 595,000, 955,000 and 1,745,000 New Taiwan Dollars (NTD), respectively; payback period were 1.1, 1, 0.8 and 0.7 years, respectively; carbon reduction were 736.6, 2,101.4, 3,537.3 and 7,074.5 tCO2e/year, respectively. The calculation results for the heating lamp were described as followings: the cost were 150,000, 465,000, 765,000 and 1,440,000 NTD; payback period were 3, 3, 3 and 2.8 years; carbon reduction were 395, 1,212.1, 2,121.5 and 4,150.5 tCO2e/year, respectively. The calculation results for direct combustion were described as followings: the cost were 81,000, 203,000, 325,000 and 626,000 NTD; payback period cannot be estimated; carbon reduction were 662, 1,989.4, 3,312.9 and 6,625.7tCO2e/year, respectively.