The function of turbo expander in air filter is just as important as the heart of human body. In the initial stage of air filtration unit, the booster turbine expander will produce enough cooling capacity to cool the low-temperature equipment, so that the air separation can have the state of low-temperature rectification. In the normal operation of the device, it is still necessary to constantly compensate for the loss of cooling capacity caused by the incomplete heat insulation and insufficient heat exchange in the air separation equipment, so as to ensure the normal operation of the air separation. The cooling capacity is generated by pressurizing the working medium of the booster turbine expander through the booster first, then entering the main heat exchanger after cooling, and then entering the expander for adiabatic expansion. At the same time, the mechanical work generated is absorbed by the booster.
Common faults: low inlet pressure of expander
In general, the reason for the low inlet pressure of expander is that there is blockage or too much resistance in the passage in front of expander. With the decrease of inlet pressure, the air flow through the expander is reduced, the enthalpy drop H0 is reduced, and the total cooling capacity is reduced. It is common for CO2 and water vapor to condense into solid at low temperature, which is caused by blockage at the heat exchanger or expansion gas filter. At 1 atm, CO2 condenses into solid (commonly known as dry ice) at - 78.2 ℃, and water vapor condenses into solid ice at 0 ℃. The outlet temperature of the heat exchanger on the fractionation tower, that is, the inlet temperature of the expander is - 85-115 ℃. If the purification effect of the purifier is not ideal, a certain amount of water vapor or CO2 will be brought into the fractionation tower, which will respectively solidify into ice or dry ice at the upper heat exchanger, gradually pile up and block the inlet pipe of the expander, resulting in low inlet pressure.
Because the middle pressure process and the low pressure process air separation tower adopt the positive flow air expansion and the back flow oxygen rich air expansion refrigeration respectively. Therefore, the reasons for the high outlet pressure of the expander are not the same, but there are two things for sure: first, the resistance behind the expander is too large; second, the clearance between the impeller and the inner diffuser wall is too large. The high outlet pressure of the expander will reduce the expansion ratio and the cooling capacity of the expander, which will lead to the imbalance of the cooling capacity of the device.
If the pressure behind the unit caused by the first reason is too high, you can reduce the pressure of the lower tower or heat exchanger for heating and blowing, then the outlet pressure will automatically drop and return to normal. If the outlet pressure caused by the second reason is too high, the expander must be disassembled for inspection, and the clearance must be adjusted to 0.2-0.3mm, otherwise, the insulation efficiency of the expander will be greatly reduced due to the existence of this part of the loss of series flow. Thus, the expander is not refrigerated or the refrigeration effect is poor.
In the start-up stage of air separation plant, the temperature at the outlet of expander is too low, and the expander has liquid fault. Because the outlet temperature of the expander is too low, it is easy to produce liquid drop and break the working wheel, so it is very important to analyze and prevent the occurrence of the expander with liquid fault.
When the operation time of the unit has accumulated to one year, the unit shall be regularly overhauled and maintained to check whether the bearing is worn, whether the seal is damaged, and whether the rotor is damaged. The overhaul and maintenance shall minimize the loss.
Maintenance content: disassembly of expander host: A. disconnect all pipeline joints such as lubricating oil, sealing gas pipeline, instrument gas pipeline, tachometer probe, and seal all pipeline openings to prevent foreign objects from entering the pipe. B. disconnect process and instrument piping. C. remove the oil inlet pipe and oil return pipe of expander. D. remove the turbocharger volute and expander main engine.
Disassembly of expander host: A. remove expander impeller. B. remove the front seal diaphragm and the rear diaphragm. C. remove the bearing and rotor. Inspection of all parts: check the bearing, seal and rotor.
Relevant treatment: the inner surface of the bearing at the expansion end is severely worn up and down, and the bearing is replaced and sealed.