Working principle of turbocharger expansion machine
1. Working principle of turbocharger expansion machine
The working medium of the unit is first supercharged by the supercharger, and then cooled into the main heat exchanger, and then into the expansion machine for adiabatic expansion to produce the cold amount required by the air separation device, and at the same time the mechanical work generated is absorbed by the supercharger.
2. Working process and structure of expansion machine
The working medium enters the volute through the inlet pipe, then enters the work rotation through the adjustable nozzle, and then exits through the diffuser chamber and exhaust pipe.
The air volume adjustment of the expansion machine depends on the pneumatic film actuator installed on the top of the cold box to drive the nozzle blade to rotate, so as to change the cross-sectional area of its channel to achieve, the valve stem stroke of the actuator reflects the change in the width of the nozzle channel, the total stroke of the valve stem is about 40 mm, the valve stem moves down to open the nozzle channel, and moves up to close the nozzle channel.
Volute: stainless steel welded structure, fixed on the fuselage, through the fuselage connected to the base, the volute accommodates the nozzle and expansion impeller.
Rotor: two ends are respectively equipped with expansion impeller and supercharger impeller (both are closed), as a rigid rotor, set on the fuselage bearing.
Bearings: Both front and rear bearings are radial thrust combined bearings. Clean and sufficient lubricating oil is supplied by the inlet pipe, so that the rotor can run stable for a long time. The bearing temperature is measured by platinum resistance thermometer.
Shaft seal: A labyrinth sealing sleeve is placed on each shaft near the two impeller, so that the gas leakage is controlled in a minimum range, and the sealing sleeve near the expansion machine is filled with normal temperature sealing gas (dry air or nitrogen) to prevent the low-temperature gas flowing through the expansion machine from leaking out, and run "cold". In order to control the pressure difference between the gas at the nozzle outlet and the sealing gas at the expander end to maintain at about 0.05MPa, a precision pressure reducing valve is set, and the sealing sleeve at the booster end is filled with sealing gas (dry air) with a pressure of ~ 0.5MPa.
3. Centrifugal supercharger
The supercharger is composed of an intake chamber, an impeller, a bladeless diffuser and a volute. The impeller and the expander impeller are placed on the same axis, the speed of both is the same, and the mechanical work emitted by the expander impeller drives it to rotate. After the gas enters the impeller, it is accelerated and pressurized. After cooling, it enters the plate heat exchanger and then enters the expansion machine.
4. Oil supply system
The oil supply system is composed of a single system, which mainly includes a fuel tank, a three-screw oil pump, an oil cooler, a temperature control valve, a bladder accumulator, etc. After the lubricating oil enters the oil pump, it enters the oil cooler and the switching oil filter, then enters the bearing respectively, and finally enters the oil pipe from the fuselage cavity back to the tank, in addition, an accumulator is set up to automatically fill the oil after the oil pump starts, for the oil pressure reduction or the oil pump stops, the unit can continue to supply oil for a period of time (about 1 minute) when the interlock stops, to ensure the safety of the bearing.
The lubricating oil uses N32 turbine oil. In order to ensure the quality of the oil, the oil should be changed once after 300 hours of operation, and the oil should be changed at least once a year after the oil filter is clean. The oil change time can be extended only if the characteristics of the oil are checked and confirmed.
5. Emergency cut off valve
An emergency cut-off valve is arranged at the inlet of the expansion machine. When the unit is in a dangerous state, the valve can be closed in a short time according to the interlock signal issued by each dangerous point, thus cutting off the air source, making it stop quickly and playing a role in safety protection.
In a critical situation, the expansion instrument control system interlocks the power supply of the solenoid valve, so that the emergency break valve is quickly closed at the same time, the booster return valve FCV401 automatically opens.
6. Supercharger aftercooler
In order to cool the high-temperature gas at the outlet of the supercharger to meet the requirements of the air separation process, the cooler is set up, cooled with cooling water, and the inlet water can be adjusted to adjust the outlet gas temperature. The control of the working condition of the cooler is carried out according to its technical parameters and process needs.
6. Booster return valve
The valve is configured for the following three purposes:
a. Pressure regulation: According to the requirements of the air separation process, it is generally hoped that the outlet pressure of the booster is kept constant, and the opening or closing of the valve can reduce or increase the pressure, and the valve can achieve the purpose of constant pressure under the automatic control of the instrument control system.
b. Anti-surge: under a certain inlet flow rate and speed, when the inlet flow rate is small to a certain value, the machine will surge, at this time the pressure will fluctuate greatly, and a strong "gasping" sound and vibration will cause damage to the machine, in order to prevent this situation, the valve will automatically open when the inlet flow rate is small to a certain value. The given anti-surge flow rate is based on the rated value of the inlet pressure, inlet temperature, speed, when these conditions are different, the anti-surge flow value should be corrected.
c. Open the large return valve: can increase the load of the booster to slow down the expansion machine
7. Maintenance instructions
7.1 Nozzle: As long as the supply of gas is clean, even if the luster of the nozzle blade darkens, it will not affect the efficiency, but if the gas contains a large number of solid particles or carbon dioxide generated droplets, it will produce the nozzle blade abrasion, serious pits will appear, so that the efficiency will be significantly reduced, then the nozzle should be replaced. During the start-up of the device, the most likely to produce abrasion. Therefore, special attention should be paid to device operation.
7.2 Expansion impeller: for the same reason as the nozzle blade, it may also cause abrasion on the inlet edge of the blade. If the abrasion is serious or even pits, the working wheel should be replaced.
7.3 Sealing covers of expander and supercharger impellers are prone to slight wear. If the wear is serious, it must be replaced, and the assembly gap is shown in the figure.
7.4 Shaft sealing sleeve: shaft sealing sleeve will also cause slight wear during operation. If the wear is serious, the shaft seal should be replaced, because excessive wear will reduce the bearing temperature and increase the loss of air leakage. The radial clearance of the shaft seal is 0 ~ 0.04mm and should be replaced when it increases to 0.1.
7.5 Bearing: Bearing profile is carefully designed and guaranteed by machining. Therefore, the inner hole and thrust surface are not allowed to be arbitrarily corrected, and if the bearing is found to be damaged due to temporary overload or poor lubrication, the bearing should be replaced.
7.6 Supercharger impeller: If the gas supply is not clean, it will cause the abrasion of the supercharger blade, resulting in damage to the balance, which is similar to the damage of the dynamic balance of the expansion impeller. It should be noted that when the expander impeller, booster impeller or other parts need to be replaced, the entire rotor must be replaced and the impeller or other parts cannot be replaced separately.
7.7 The oil cooler is generally cleaned once a year. If the cooling water is not clean, the number of cleaning should be increased.
7.8 Oil filter, if the filter resistance is found to be significantly increased, it should be cleaned or replaced.
7.9 The supercharger cooler is generally cleaned once a year. If there is leakage during work, the resistance suddenly increases, and the heat transfer effect becomes worse, the cause should be checked immediately and repaired.
