Cryogenic low pressure expander bearing temperature analysis

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Cryogenic apparatus using the expander is a velocity-type turboexpander, speed changes in the gas flow to transfer energy, high-pressure gas within the expansion machine close to isentropic expansion to generate enthalpy drop. Meanwhile, the output power, energy consumption, to increase the enthalpy drop, so that the gas outlet temperature is reduced, to achieve the refrigeration purposes. The expansion diameter axial flow impeller belongs reactionary to the heart closed impeller, coaxial brake booster impeller centrifugal semi-open, expander and booster are stand-alone. Expander cryogenic station cooling system equipment, and it is charged with the important role of the cooling and energy recovery. The design flow rate of the high and low pressure expansion machine respectively 18623/17388Nm3/h speed is 39000/47000r/min high, the low-pressure expansion machine imported a temperature of -69.15/21.55 ° C, outlet temperature: -105.32/-39.55 ℃. Analyzed expander bearing temperature lubricants, water cooler, seal gas, accessories, quality, maintenance quality lubricant film thickness which is the main reason for restricting the bearing temperature, bearing temperature impact expansion captain cy cle, the key to efficient operation.ceramic ball bearing

An expansion unit a problem

May 2005 expansion unit for a week and more appear bearing temperature chain downtime phenomenon (data shown in Table 1), resulting in the unit at a low load operation state, the refrigeration negative temperature around -50 ℃, a far cry from the design cooling temperature.

2 expander bearing lubrication mechanism

Expansion machine shaft and the bearing lubrication, cooling by the lubricating oil, the main role of the lubricating oil is an axis, the bearing, the seal to provide lubrication and cooling effect. Dynamic pressure oil film between the journal and bearing a certain thickness is formed, constituting the film contact, the film will hold the shaft, the bearing and the shaft is not in direct contact between the shaft and the bearing for the liquid friction, the friction factor is small. The same time, the friction pair shedding metal shavings, impurities are lubricants away, to reduce abrasive wear to take away the heat generated by friction, and to prevent the shaft and bearing temperature and Burnt -.

Three low-pressure expansion machine structure and lubricant oil flow

The structure of the low-pressure expansion machine mainly by the expander casing, the rotor shaft, the impeller, the bearing, the key back to take the bolts, the insulation plate, the back pressure seal, sealing gasket, and a temperature probe, a vibration probe. Auxiliary system booster, seal gas system, blowing cold system pressure accumulator, balancing valves, etc..

Lubrication of the bearing and shaft of the low-pressure expansion machine uses

No. L-TSA68 turbine oil for lubrication, lubricant viscosity index of the 55.08 ~ 82.28mm2 / s, Flash point (COC) index of ≥ of 185 ° C. The flow of lubricating oil is the fue l tank - coarse filter - pump - lubricants water cooler - double filter - pipeline valves - front filter - expander shaft, bearings and other parts to be lubricated.

The 4 troubleshooting and analysis

4.1 checking instrument system

Bearing temperature data REF of the low-expansion machine bearing back to the oil temperature field data with the main control room computer display, and then back to the control of measurement data with an infrared thermometer, the measured data is substantially the same, the error is about 2 ℃; check the low-expansion machine temperature probe installed, if loose or probe linear probe mounting bad, will affect the data changes, re-check the temperature of the scene, re-confirm the sensitivity of the instrument probe through the examination did not reveal any abnormalities.

4.2 check the fuel tank lubricants laboratory indicators, temperature and pressure

Lubricants laboratory indicators af fecting the bearing temperature is the kinematic viscosity and lightning. The kinematic viscosity is higher than the standard value, the resistance to movement of the oil film between the journal and the bearing the motion generated heat can not be away, easily lead to the high temperature of the low-pressure expansion machine bearings; kinematic viscosity is less than the standard value, the journal and bearing can not form between the oil film thickness, hydrodynamic lubrication, boundary friction between the shaft and the bearing, the heat generated by the friction factor several times between liquid lubrication, shaft and bearing, easy cause low pressure expander bearings temperature; boundary friction in the lubricating oil the Lightning is low, the thinning of the oil film between the journal and the bearing can not form a film or the formation of the shaft and bearing, easy cause low pressure expander bearings temperature. Influence of the lubricating oil temperature of the bearing in the tank, the tank temperature is too high (normal tank temperature of 58 ° C), and the lubricating oil of the heat exchanger of the water cooler area is constant, the temperature of the lubricating oil is also correspondingly becomes high, causing the bearings of the low-pressure expansion machine temperature, the tank pressure on the bearing temperature, the tank pressure is too high, the direct impact on the speed of the lubricating oil back to the tank, this could easily lead to the low-pressure expansion machine bearing temperature. Therefore, to ensure that the low pressure expander bearing temperature must be controlled the good lubricants laboratory indicators, fuel tank temperature and pressure.

4.3 lubricant water cooler effect of heat transfer

The expansion machine lubricating water cooler is the random introduction of the heat exchanger, the heat exchanger area of ??34m2, copper material, the copper material of the heat exchanger is better than other materials, the medium is circulating water tubes, designed to / return water temperature of 30 / 60 ℃, shell medium lubricants, design / out the lubricating oil temperature of 60 ° C / 40 ° C. Incoming water temperature is high, after water cooler heat exchanger, oil temperature does not drop down, bearing temperature rise caused by low pressure expander. The lubricant water cooler effect of heat transfer, prolonged use of water coolers, scaling the wall, deposited silt clogging water cooler effect of heat transfer caused by the high temperature low pressure expander bearing. Assurance measures are to be cleaned regularly lubricating water cooler and another cycle control power water runoff temperature, runoff temperature control in less than 30 ℃.

4.4 Check the pump operating parameters

The pump flow 216L/min, inlet pressure of 0.5MPa, the the export pressure to 4.86MPa. If the pump outlet pressure is low, th e amount of oil pump, lubricating oil circulation slows, lubricating oil is not working properly, unable to meet the lubrication of bearings and seals, could easily lead to high bearing temperature. This may be the oil pump seal is broken, large leakage caused by gas or pump inlet filter clogging caused may also damage caused the pump impeller, the pump outlet pressure checked scene 4.5MPa required to meet expander run .

4.5 Checking pipeline

Exchange of the oil return tube for many years running fouling is not smooth, affect the bearing back oil, or adjust the valve plug the switch is not flexible, causing the oil line is not smooth, affect the bearing temperature. Shutdown, expander lubricating oil piping and control valve check, cleaning, instrument air purge line, did not find any foreign body.

4.6 Check the expander quality accessories

Expander accessories domestic development processing accessories bearing accessories from Si chuan Jianyang cryogenic plant processing, suspected to have quality problems, wrong orientation of bearings back hole or small hole, causing the oil return is not smooth, and introduction accessories contrast, check whether the hole to plug, and instrument air purge and found no abnormalities. Check the thermal pad back hole the blockage phenomenon exists, check the bearings and thermal pad. Not the cause of the reasons of the low pressure expander bearing temperature.industrial bearings

4.7 check with the gap

Bearings and shaft with the gap is too small, too small to cause the thickness of the oil film between the bearing and the shaft, causing bearing and journal to generate edge of friction, resulting in excessive bearing temperature. Check maintenance records, the assembly size of order requirements.

4.8 the pressure of the seal gas is not adjusted properly

In order to prevent the oil from entering into the process gas, or process gas and oil contact one seal gas is injected in the middle of the labyrinth seal, the sealing gas flow is slightly higher than the amount of leakage from the seal, the sealed gas pressure differential 0.15MPa. Further, the seal gas can not contain heavy hydrocarbons, heavy hydrocarbons will cause the lubricating oil viscosity decrease. The inspection found no abnormalities.

4.9 meter software failure

From the field one by one investigation does not find the root cause of high expansion machine bearing temperature, check the computer program system, checked that the instrument software failures caused by expansion machine running bearing temperature is normal, troubleshooting,double roller bearing

5 Conclusion

The expansion unit is the main unit of the cryogenic station cooling system, expansion unit to ensure smooth, efficient operation, lower failure frequency, it must be strict control unit operating parameters, to ensure the unit is running in the best condition, good quality parts and service quality and to reduce the number of stops, to avoid damage to the expander.