1. Gas internal combustion engine combustion for power generation
Fuel and air are mixed, compressed, ignited, and burned in an appropriate proportion in the cylinder of a gas internal combustion engine. The flame quickly spreads throughout the entire combustion chamber, while releasing a large amount of heat energy. The combustion gas expands rapidly, the pressure and temperature rise rapidly, pushing the piston to move back and forth, driving the crankshaft to do work through the connecting rod, driving the generator to generate electricity, and the kinetic energy is converted into electric energy. The efficiency of using Primary energy such as gas and fuel oil as fuel for power generation is usually about 30~40%, and nearly half of the heat is usually lost directly, which not only causes a large waste of energy, but also aggravates environmental pollution. If the high-temperature exhaust gas from a gas internal combustion engine is recycled and reduced to 20 ℃, it can increase energy utilization efficiency by approximately 40-50%.
2. High temperature flue gas waste heat utilization
The exhaust gas temperature of gas internal combustion engines is generally around 450~550 ℃. The exhaust gas is collected through the flue and transported to the waste heat boiler (with a rated steam pressure of 2.5MPa). The heat is recovered and utilized through the waste heat boiler. The three-way valve of the exhaust gas is adjusted according to the user's steam demand to control the amount of exhaust gas entering the waste heat boiler, producing saturated steam that can be used to fill mobile heating vehicles. When the waste heat boiler is not running, By adjusting the flue gas three-way valve, the flue gas is discharged from the chimney. The matching of gas internal combustion engines and waste heat boilers can be based on the specific situation of the project, which can be a single gas internal combustion engine corresponding to one waste heat boiler (one-to-one), or multiple gas internal combustion engines corresponding to one waste heat boiler (many-to-one). The above-mentioned waste heat boiler equipment adopts a double drum vertical arrangement, and the boiler body is mainly composed of pressure components such as upper and lower steam drums, convection tube bundles, etc. Its characteristics are that the upper and lower steam drums in the boiler body are of the same length, and the lower and upper steam drums are connected by convection tube bundles, with a large heating area and a certain overload capacity. It belongs to a fully water-cooled structure, operates naturally, and operates safely and steadily
3. Low temperature flue gas waste heat recovery
After the utilization of the waste heat boiler, the low-temperature flue gas temperature is still around 100-190 ℃. An energy-saving device is installed at the exhaust port of the waste heat boiler, and the treated boiler make-up water is transported through pipelines to the energy-saving device. This part of the low-temperature flue gas heat is used to heat the boiler make-up water, further recovering the exhaust heat of the waste heat boiler, reducing the exhaust temperature, and finally being discharged from the chimney. Compared with conventional boilers, recovering this heat can increase the efficiency by more than 5%. However, the exhaust gas temperature should not be too low. On the one hand, it is necessary to increase the heat exchange area and increase equipment investment. On the other hand, if the exhaust gas temperature is too low, it will generate sulfuric acid, corrode the heat exchange pipeline in the energy-saving device, that is, the acid dew point corrosion, and affect the safe and stable operation of the system. Generally, the designed exhaust gas temperature should be above 10 ℃ above the acid dew point temperature of the exhaust gas ; If there is no sulfur in the fuel of the gas internal combustion engine, it is necessary to ensure that the heating surface of the energy-saving device does not produce condensation, that is, the exhaust temperature after the low-temperature flue gas heat is recovered by the energy-saving device should be more than 10 ℃ higher than the dew point temperature of the water . Therefore, considering the effectiveness of flue gas waste heat recovery and equipment investment, energy-saving devices can choose materials with higher cost-effectiveness, such as ND steel.
It should be noted that the exhaust gas of the gas internal combustion engine passes through the flue gas pipeline, flue gas three-way valve, waste heat boiler, energy-saving device, and chimney in sequence. The pressure loss needs to be carefully calculated, so that the final exhaust pressure must be limited to the maximum allowable exhaust back pressure value of the gas internal combustion engine to ensure the stable operation of the gas internal combustion engine.
In addition, when designing the system, appropriate pipeline insulation materials and thickness should be selected according to standards, and the length of the flue gas pipeline between the gas internal combustion engine and the waste heat boiler should be minimized as much as possible. This not only reduces the heat loss during the transmission process of the exhaust gas from the gas internal combustion engine, but also reduces the pressure loss.
4. Makeup water for waste heat boiler
The make-up water of the waste heat boiler treated by the water treatment equipment needs to be thermally deoxidized by the deaerator, and then sent to the energy-saving device for heating, providing uninterrupted water source for the operation of the waste heat boiler. In addition, to prevent cavitation during the boiler water replenishment process, a pressurized pump is installed between the boiler water replenishment pump group and the deaerator. The water treatment device can use conventional fully automatic water softeners to produce boiler soft water, or other water treatment devices such as reverse osmosis equipment, ion exchange, EDI electric desalination system devices, etc. can be used based on the quality of boiler makeup water.
The waste heat boiler sewage is discharged into the sewage expansion tank for pressure reduction treatment, which not only improves the safety performance of system operation, but also generates secondary steam in the sewage expansion tank, which is then preheated into the make-up water tank to improve energy utilization efficiency.
2.5 Steam transportation process
The saturated steam produced by the waste heat boiler is sent to the sub cylinder through a steam pipeline, and then from the outlet of the sub cylinder to the main pipe of the filling system. The mobile heating vehicle is filled with steam through the branch pipes of the filling system, and finally transported to the user to release the steam required by the user. The schematic diagram of the steam filling system is shown in Figure 2. In addition, a portion of steam is extracted from other outlets of the sub cylinder for thermal deoxygenation of the waste heat boiler's makeup water.