Conclusions

This study carries out the 30kW turbine engine/generators experiments in a swine farm, and the dissertation analyze the performance of power generation on gas turbine through experimental evaluations. When the turbine engine starts, the air and the biogas are sucked into the engine. The flow meters, measure the air and the biogas flow rates, which are automatically adjusted according to the change in engine speed. It is important that not all of the air for combustion, part of the total air is used for cooling the hot gas exhausted from combustor outlet, which prevent turbine blade from heat damage. The sensors which include the biogas flow meter and manometer for the turbine were established to form our test stand. First of all, the compressor would increase the pressure and temperature of biogas by reducing its volume, the compressor outlet temperature is about 40°C, and the pressure of biogas is about 5.6kgf/ . In the second place, the water vapor of biogas is removed by Freeze dryer, the dryer outlet temperature is about 36°C, and then the biogas will be stored in the biogas tank. Finally the fuel is mixed with air and ignited in the chamber. One of the parameters is the turbine operating loads. We collect the data, such as power output, waste gas concentrations, fuel flow rate under various operating loads from15 to 30kW. There are three parts in this research. In the first part,

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experiments were completed to evaluate the thermal efficiency. Secondly, the cost benefit analysis is carried out for the turbine engine. The revenues are calculated as a result of generating capacity in kWh per year, the revenue calculation is based on the present electricity purchase charge which is 2.7 NT$/kWh, and then the economic benefits were estimated by the data obtained by this research. Finally, a comparison with Wu’s [6] rate to the turbine engine is from 184.9 to 251.8L/min with 67%

CH4 of biogas under varying loads from 15 to 30kW, and the maximum power generation, the corresponding thermal efficiency and the CH4 consumption rate is 25.23kW, 23.12%

and 168.7 L/min, respectively. For piston engine, the maximum power generation, the corresponding thermal efficiency and the CH4 consumption rate is 26.48kW, 26.37% and 155.2L/min, respectively. The threshold efficency of turbine engine is 2.97%

lower. Compared with turbine engine, the fuel efficiency and thermal efficiency for piston engine is higher under the higher load operating range (21 to 30kW). However, the turbine engine can provide higher performance with lower efficiency variation compared to those of piston engine in range of 15~ 21 kW.

Remind that the lower load limit is 15kW for this turbine engine,

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whereas piston engine still can be operated as low as 5.4kW.

2. For turbine engine, the maximum power output is only 25.23kW, under the rated power output of 30kW, mention above, since the rotational speeds behind 25kW can no longer increase propotionally but approach a limit value, 96000rpm approximately, it may conclude that the upper operation limit for this type engine is 25kW. On the other hand, the lower limit is 15kW, below which the engine cannot be drived. The thermal efficiency increases with increasing power generation. The probable reason is that when the turbine at high loads with inlet guide vanes in open position, the gas turbine internal friction losses relatively small [9] compared to that when under the low load operating.

3. The average of combustion efficiency of the engine is about 0.85~0.90. In other words, about 10~15% of energy is lost by the form of heat during combustion process. It shall concentrate on the remaining energy. It indicates that about 60% of energy is lost in the form of heat, 15% of energy is lost by the friction, and only about 25% of energy is useful.

4. The average biogas produced is around 0.078 per head pig per day, and the resultant erergy by using piston engine is 1.7 kWh per biogas. For turbine engine, the resultant energy is 1.55kWh per biogas. The estimated overall economic benefits in Taiwan by using biogas for the swine farms with a scale of 3,000 and 5,000 heads can be reached as following:

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 For the swine farms with a scale of 3,000 heads.

Turbine Engine:

Electricity generation: 132,000 kWh per year Electricity charge saved: 356,000 NT$/ year.

Payback period: 26.8 years.

Cost of electricity per kilowatt: 4.9 NT$

Piston Engine:

Electricity generation: 145,000 kWh per year Electricity charge saved: 392,000 NT$/ year.

Payback period: 21.8 years.

Cost of electricity per kilowatt: 4.2 NT$

Based on a cost benefit analysis, using the piston engine to generate electricity in a scale of 3000 swine farm has an advantage over the turbine engine.

 For the swine farms with a scale of 5,000 heads Turbine Engine:

Electricity generation: 219,000 kWh per year Electricity charge saved: 591,000 NT$/ year.

Payback period: 10.9years.

Cost of electricity per kilowatt: 3.0 NT$

Piston Engine:

Electricity generation: 182,000 kWh per year Electricity charge saved: 492,000 NT$/ year.

Payback period: 14.1 years.

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Cost of electricity per kilowatt: 3.4 NT$

The results show that the economic benefits of turbine engine is higher than that of piston engine in a scale of 5000 swine farm.

 For the swine farms with a scale of 10,000 heads Turbine Engine:

Electricity generation: 420,000 kWh per year Electricity charge saved: 1,135,000 NT$/ year.

Payback period: 7.6 years.

Cost of electricity per kilowatt: 2.3 NT$

Piston Engine:

Electricity generation: 350,000 kWh per year Electricity charge saved: 945,000 NT$/ year.

Payback period: 8.7 years.

Cost of electricity per kilowatt: 2.6 NT$