1. Performance parameters
Thermoelectric output characteristics of gas turbine and internal combustion unit will affect the performance of distribution system. Small gas turbine unit is suitable for large-scale distribution system, and internal combustion unit is suitable for small-scale distribution system. Under similar power generation, the efficiency of internal combustion unit is higher than that of small gas turbine unit, but the exhaust gas temperature of the former is lower. In addition, compared with internal combustion units, the performance of gas turbine units is greatly affected by altitude and ambient temperature, but under the premise of determining the site of the plant, the impact of load changes on the performance of the two generators is more prominent.
Variable operating characteristics
In the distributed system, the generator set often runs under partial load, and its off-design characteristics have great influence on the comprehensive performance of the distributed system. Taking gas turbine and internal combustion unit with generating power of 3 MW as an example, the thermal efficiency and power generation efficiency change with load rate. It can be seen that, with the reduction of load rate, the generation efficiency of the two generators shows a downward trend, but the generation efficiency of the internal combustion unit is about 10% (absolute value) higher than that of the gas turbine unit. The thermal efficiency of gas turbine unit is obviously higher than that of internal combustion unit. The thermal efficiency of the former decreases with the decrease of load rate, while that of the latter increases with the decrease of load rate. From the above analysis, it can be seen that although the two generators have roughly the same total thermoelectric efficiency (the sum of thermal efficiency and power generation efficiency) under rated conditions, the off-design characteristics of internal combustion units are better.
Waste heat characteristics
A. gas turbine unit
The flue gas temperature of the micro gas turbine set is low, which is concentrated around 300 C. It is mainly used for refrigeration, heating and domestic hot water preparation. In a few cases, it is used to produce low pressure steam. The flue gas temperature of small gas turbine is higher, 68.5% of the units whose flue gas temperature is above 500 C and 93.8% of the units whose flue gas temperature is above 450 C. It is mainly used to produce high pressure steam. Besides directly utilizing and utilizing steam absorption chiller to refrigerate, it can also drive steam turbine generator to generate electricity and form gas. The steam turbine is a steam combined cycle system.
B. internal combustion unit
The waste heat of internal combustion engine is divided into two parts: one part is the waste heat of cylinder liner cooling water, which is to ensure the normal working temperature of the gas internal combustion engine, and the heat carried by the cooling system is relatively low; the other part is the waste heat of flue gas, which is carried by the flue gas after the work of fuel combustion. The heat and flue gas temperature are basically between micro and small gas turbine units. Because the cylinder liner cooling water temperature is low, mainly used for heating, preparation of domestic hot water, flue gas can be used to drive absorption chillers and production steam outward.
4. Gas inlet pressure
In general, the order of gas intake pressure from low to high is: internal combustion unit, micro gas turbine unit, small gas turbine unit. The intake pressure of small gas turbines is relatively high, usually high pressure or sub-high pressure, so it is necessary to add gas compressor. The process of gas compression needs to consume a lot of energy, which affects the actual output power of small gas turbines. Some projects even need to consume 15%-20% output power of small gas turbines. The intake pressure of internal combustion units and micro gas turbine units is low, usually low or medium pressure.
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