Operation and Maintenance Manual for Pressurized Turbine Expander

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Operating and Maintenance Manual for Boost Turbine Expanders I. Overview II. Unit Introduction 1. Structure of the Turbine Expander 2. Booster 3. Oil Supply System 4. Flow Regulation of the Expander 5. Rapid Safe Shutdown 6. Boost Gas Filter 7. Cooler for Gas at the Booster’s Outlet 8. Booster Return Valve III. Operating Instructions 1. Preparatory Work and Inspection Items Before Startup 2. Starting the Expander 3. Inspections During Operation 4. Shutting Down the Expander IV. Disassembly and Assembly Instructions V. Maintenance Instructions VI. Major Faults and Their Solutions VII. Sealer Running-in This standard applies to turbine expander units with booster braking, whose working wheel diameter ranges from Ø100 millimeters to Ø450 millimeters, and which use oil bearings. I. Overview: This unit utilizes gas to undergo adiabatic expansion through an expander, thereby generating the cooling capacity required by the air separation plant. The mechanical work produced is then absorbed by a compressor, which uses it to increase the pressure of the compressed gas. The gas used by the unit should be clean gas free of mechanical impurities (metal dust, molecular sieve, perlite powder, etc.) and having undergone purification. II. Unit Introduction The unit consists of the following main components: (The specific items delivered shall be subject to the contract and the product packing list.) ) 1. Turbine expander with insulated box and chassis ； 2. Fuel supply device ； 3. Booster pump ； 4. Intake gas filter for booster pump ； 5. Gas cooler at the outlet of the booster pump ； The main components of the unit, except for the booster pump, gas filter, and gas cooler, are mounted on a common chassis to form a single unit, which is fixed to a concrete foundation using anchor bolts. It is necessary to prevent vibrations and shocks from the surrounding environment from reaching the turbine unit. When rotating the inlet and outlet pipes, it must be ensured that the forces and moments exerted on the flanges of the turbine’s inlet and outlet pipes by external factors do not exceed the allowable values (see Figure 1). The insulation material and lubricant required for the words and sentences shall be provided by the user. I. Structure of the turbine expander (hereinafter referred to as the expander) Refer to the overall diagram of the expander. Gas enters the volute through the inlet pipe, passes through the nozzle vane channels to reach the working wheel where mechanical work is performed, and then is discharged through the diffuser chamber. The flow control system of the expander operates by using an actuator mounted on top of the cold box to rotate the nozzle vanes, thereby changing the cross-sectional area of the passage. 1. Expander volute: The volute is directly fixed to the frame and supports the main expander unit as well as the booster. The volute houses the expander impeller and nozzle ring. On the exhaust side, there is a pressure ring that presses against the nozzle vanes via an elastic clamping mechanism, ensuring no gaps at the end faces of the nozzle vanes. 2. Expander shaft: Installed in two bearings; one end of it is equipped with the expander impeller, and the other end with the booster wheel, forming a rigid rotor. 3. Impeller: The expander impeller is a radial-axis flow reaction impeller, and its profile is designed and calculated based on three-dimensional flow principles. The boosters are triple-element impellers, and both are constructed from forged aluminum. 4. Bearings: Radial and thrust bearings, which are designed based on the theory of hydrodynamic oil film lubrication; as long as they are installed correctly and provided with clean and sufficient lubricating oil, they can ensure the proper operation of the rotor without causing wear. The oil drained from the bearings returns to the oil tank through the return pipe. The bearing temperature is measured using a platinum resistance thermometer. 5. Shaft seal: On the exhaust side of the expander, a seal is installed at the working wheel end to prevent gas from passing between the nozzle and the working wheel and leaking directly into the diffuser chamber. Additionally, on the back side of the working wheel, a graphite-lined internal shaft seal is provided to prevent low-temperature, pressurized gas from leaking outward, ensuring a very small gap. The leakage rate through the shaft seal is a function of the pressure upstream and downstream of the shaft seal, the gap size, and the length of the shaft seal, whereas the pressure upstream of the shaft seal depends on the gap pressure. Therefore, in order to control gas leakage, a sealing gas (dry air or nitrogen) must be supplied to the shaft seal, and its pressure must be controlled based on the gap pressure. Therefore, a differential pressure control valve is installed; during adjustment, the pressure of the sealing gas should be higher than the gap pressure (the specific values are shown in the expander flow diagram). To prevent backflow in the shaft seal. In addition, a seal is installed on the impeller of the booster; meanwhile, a graphite-lined external shaft seal is provided on the back side of the booster impeller, and sealing gas is supplied. The leakage gases from both the internal and external shaft seals are led outside through pipes in order to reduce the load on the bearing housing. II. Booster Pump The booster pump consists of an inlet convergent duct, an impeller, a diffuser, and a volute; the impeller and the impeller of the expander are mounted on the same shaft to form the rotor. The power required is provided by the expander. The gas is drawn in axially, accelerated within the impeller of the booster, and its pressure increases; as a result, as the gas flows through the diffuser-shaped flow channel, its kinetic energy is converted into potential energy. Subsequently, the gas converges toward the booster volute ； After being cooled by the air cooler, it enters the heat exchanger in the cold box for heat exchange. The booster pump volute is connected to the bearing housing, with the inlet and outlet pipes of the booster pump attached to it; the volute houses the impeller, end caps, and sealers of the booster pump. The end cover and the volute form a diffuser-shaped flow channel to collect the gas, converting the gas’s kinetic energy into pressure energy thereby increasing the gas pressure. III. Oil Supply System: The lubricating oil is pumped from the tank through the oil pump into the oil supply pipes, passes through the oil cooler and the switchable oil filter, is then distributed to various lubrication points, and returns to the tank via the oil return pipes. In addition, an oil reservoir is provided; when the oil pump starts, it fills itself with oil to ensure the necessary lubrication in case of an interlocked shutdown due to a drop in oil pressure. The oil pressure can be adjusted using a relief valve. To maintain the cleanliness of the machinery and the workshop, it is required to route the oil vapor from the oil-gas separator to an outdoor vent. Lubricating oil shall be L-TSA32 turbine oil in accordance with GB11120-89. To ensure the quality of the machine oil, it should be changed for the first time after 200 hours of operation; thereafter, it should be replaced at least once a year, provided that the oil filter is cleaned. The oil change interval can only be extended if the properties of the oil have been checked and confirmed to be good. IV. Expansion turbine flow regulation The expansion turbine flow regulation is achieved by using an actuator to change the nozzle angle. For the relationship between nozzle width and valve stem travel, refer to the diagram in the \"Technical Parameters Summary Table\": Relationship between nozzle width and valve stem travel. V. Rapid and safe shutdown: An emergency shut-off valve is installed at the inlet of the expander; its purpose is to cut off the gas supply within a very short time (1.0 second) when the expander is in a dangerous condition, thereby enabling rapid shutdown and providing safety protection. The instrument air used for the operation of the emergency shut-off valve is supplied through a three-way solenoid valve. In the event of an accident, the power to the solenoid valve is cut off, and the air trapped beneath the pneumatic diaphragm of the emergency shut-off valve is released to the atmosphere through a rapid exhaust valve; as a result, the valve closes quickly due to the force of the spring. At the same time, the return valve of the pressure increase unit opens fully automatically to prevent surging in the pressurizer. VI. Pressurized Gas Filter: To further remove residual mechanical impurities present in the incoming gas, a gas filter is installed on the inlet pipeline of the compressor. VII. Gas cooler at the compressor outlet: To cool the high-temperature gas exiting the compressor to meet the requirements of the process, a cooler is installed, which uses cooling water for cooling. Adjusting the water inflow amount can achieve the purpose of regulating the temperature of the gas at the outlet. VIII. Booster Recirculation Valve: This valve serves three purposes: 1. Pressure regulation: As required by the air separation process, it is generally necessary to maintain a constant pressure at the outlet of the booster. By opening or closing this valve, the pressure can be reduced or increased; when controlled automatically by the instrumentation and control system, this valve helps to maintain a constant pressure. 2. Surge prevention: At certain inlet pressures, rotational speeds, and valve openings, when the outlet pressure of the booster rises to a specific level, surge can occur. At this point, the pressure fluctuates significantly, and vibrations accompanied by a loud \"surging\" sound are generated, which can damage the machine. To prevent this from happening, the valve opens fully when the pressure reaches a certain value. The given anti-surge pressure value is specified under conditions where both the inlet pressure and speed are at their rated values; when these conditions differ, the anti-surge pressure value must be adjusted (if anti-surge protection is achieved through simultaneous control of pressure and flow, the valve will adjust itself or open fully when the pressure and flow reach certain values, and the requirements for this are specified in the Technical Parameters Summary Table). 3. During the running-in of the sealer, due to the low speed, it is difficult for the bearings to form an oil film; in order to reduce the load on the thrust bearings, the booster should draw air from the atmosphere, so that the pressurized air can bypass through this valve and reach the expander. III. Operating Instructions I. Preparatory work and inspection items before starting the machine: 1. Check whether there are any foreign objects inside the turbine unit ； 2. Fill the fuel tank with fuel until the normal level is reached ； 3. Inspect it in accordance with the requirements of the fuel supply device ； 4. Is the oil filter clean? ； 5. Are the filters installed in the inlet pipes of the expander and booster correctly? ； 6. Are all instrument control and electrical control circuits and devices properly connected? ； 7. Are all valves in the correct “open” and “closed” positions? ； 8. Is the seal gas connection correct? ； 9. Check the proper operation of the nozzle control valve ； 10. Check that the emergency shut-off valve operates correctly (it should close within 1 second from the open position). II. Expander startup: 1. Pre-startup checks: (1) The oil level indicator in the fuel tank is normal ； (2) The heating gas valve is closed ； (3) Nozzle vanes closed ； (4) Emergency shut-off valve closed ； (5) Close the inlet and outlet valves of the expander ； (6) Close the inlet and outlet valves of the booster pump ； (7) Fuel tank temperature: If it is below 15°C, the fuel heater should be turned on to heat it ； (8) Bearing temperature: As long as the temperature of any bearing is below 15°C, lubricating oil must be supplied to heat the bearing (Note: sealed gas must be supplied first); if this does not work, heating gas must be used to heat the expander (see III, IV, 2, (2)). (9) The oil filter is clean, and the fuel supply system is functioning properly ； (10) The booster return valve is fully open (as a condition for starting the expander) ； The instrumentation and control systems are functioning normally. 2. Start the expander ； (1) Connect the seal gas and process gas supplies ； (2) Connect the instrument’s electrical power supply ； (3) Start the oil pump ； (4) Supply cooling water to the oil cooler (if the oil temperature is low, water supply can be postponed), and at the same time supply cooling water to the gas cooler behind the booster ； (5) Open the expansion turbine outlet valve ； (6) Open the expansion turbine inlet valve ； (7) Open the booster pump outlet valve ； (8) Open the booster pump inlet valve ； (9) Open the nozzle control valve to 30% of the design operating condition ； (10) The emergency shut-off valve is opened, the turbine starts to operate, and quickly reaches a lower speed. Immediately increase the nozzle control valve to bring the rotational speed to 40% of the design value (except during the running-in period of the sealers, when low-speed operation is permitted according to the General Operating Instructions for Pressurized Turbine Expansion Units, normal operation should avoid running at low speeds as much as possible). (11) Gradually open the nozzle control valve, while gradually closing the booster pump return valve, until the rated operating conditions are reached ； (12) During startup, as the inlet temperature of the expander decreases, its speed also drops; therefore, it is necessary to adjust this by frequently closing the booster return valve ； (13) Check the bearing temperature at all times during startup. Is the clearance pressure normal and is the overall operation of the machine in order? ； (14) During startup, briefly open the purging valves of the machine and instrument pipelines, then close them tightly. III. Inspections during operation: The inspection items during the unit’s operation are as follows: 1. Every two hours: (1) Inlet and outlet temperatures of the expander, inlet and outlet temperatures of the booster ； (2) Inlet and outlet pressures of the expander and clearance pressure, inlet and outlet pressures of the booster ； (3) Bearing temperature ； (4) Bearing oil inlet pressure, oil temperature ； (5) Sealing gas pressure. 2. Daily: Fuel level in the tank ； (1) The tightness of all pipes. 2. Emergency shut-off valve: It should be inspected regularly, each time before starting up and after shutting down. The testing method is as follows: with the valve in the open position, use the emergency stop button to cut off the power supply to the solenoid valve, thereby deactivating it. If the emergency shut-off valve closes immediately and the booster pump’s return valve opens automatically, then its function is satisfactory. 3. At least once every 2 months: (1) Check the lubricating properties of the oil (appearance, viscosity, composition, flow point, flash point, etc.) ； (2) Check the cleanliness of the oil filter. (3) Check the oil level in the pressure oil tank (when this level rises to the upper limit, gas should be added promptly to bring the level back to the required value; this measure is crucial for providing protection in cases of shutdown due to interlock of the oil pump motor or power failure). 4. Annually: The expander should be thoroughly inspected, and all worn parts should be replaced. 5. Monitoring of clearance pressure: Special attention should be paid to the clearance pressure; the pressure difference between the clearance pressure and the outlet pressure is directly related to the load on the thrust bearings. A controller is provided to monitor this pressure difference. This pressure difference must not exceed its specified maximum value. If the measured clearance pressure is higher than the normal value, the possible reasons are: (1) The actual operating parameters deviate from the design values. (2) Incorrect installation. (3) The liquid enters the space between the nozzle and the impeller. (4) There is an ice blockage in the impeller flow channel of the expander. To prevent machine failures caused by excessive clearance pressure, it is necessary to identify the cause when such pressure becomes too high and take action promptly. IV. Stoppage of the expander: 1. Stop operation: (1) Fully open the booster reflux valve. (2) Close the emergency shut-off valve. (3) Nozzle vanes. (4) Pressure booster inlet valve. (5) Pressure booster outlet valve. (6) Close the expansion turbine inlet valve. Close the expander outlet valve. 1. Post-stopping procedures: (1) For temporary stops, maintain the supply of sealing gas and lubricating oil, keep the electrical and control systems operational, and be ready to restart. (2) For long-term parking, it is necessary to warm and thaw the expander; the procedure is as follows: 1) Maintain the supply of seal gas and lubricating oil, and keep the electrical control system in operational mode. 2) Open the emergency shut-off valve. 3) Open the nozzle blades. 4) Open all blowdown valves on the expander. 5) Check whether the inlet and outlet valves of the expander are tightly closed. 6) Open the heating gas valve to heat the expander. Reverse the flow direction of the heated gas passing through the expander, with the temperature not exceeding 60 oC. Heating is completed when the temperature at the hot gas outlet is roughly the same as that at the inlet. The dew point of the heating gas should be below –40 oC. It should be noted that throughout the heating process, the heating gas must be controlled so as not to cause the turbine rotor to rotate. 7) Close all purge valves. 8) Stop heating and close the heating gas valve. 9) Close the emergency shut-off valve. 10) Nozzle vane. 11) Stop the lubricant supply. 12) Cut off the seal gas supply after 15 minutes. It should be noted that the inlet and outlet valves of the expander must be tightly closed, so as to prevent the bearings from becoming over-cooled upon restart during long periods of shutdown due to the infiltration of cold gas, especially when the distillation tower is still in operation. It is also important to ensure that the emergency shut-off valve and the nozzle vanes are opened first before heating gas is introduced, in order to avoid damaging the machinery. IV. Assembly and Disassembly Instructions The assembly and disassembly of the expander must be carried out under very clean conditions; all components, especially bearings, seals, impellers, compression mechanisms, and nozzle rings, must be handled with great care. The cold box, volute, emergency shut-off valve, and nozzle adjustment mechanism of the expander are generally not removed, as the internal components can be taken out directly from the hot side of the expander. The steps for removing the internal components of the expander are as follows: first, remove the inlet and outlet connections of the booster; then remove the oil pipes, seal gas pipes, and instrumentation connections. Remove the end cover of the booster, and use special tools to take off the booster wheel (see Figure 2), followed by removing the booster volute. Then the entire expansion engine assembly can be removed from the expansion engine volute using special tools and placed on a cleaning table for further disassembly. Further disassembly of the expander rotor begins with the nozzle clamping mechanism in the diffuser chamber; after removing the impeller screws, the expander impeller can be removed from the shaft using special tools (see Figure 2). Next, remove the nozzle ring (it can be pushed out using a set screw). Then remove the intermediate flange, shaft seal, oil baffle ring, and speed sensing connector. Then remove it from the booster side. First, remove the outer seal and oil baffle. Use a set screw to push out the outer bearing (the other end of the spindle must be supported), then pull the spindle along with the outer bearing out, and finally remove the inner bearing. Then, the components on the main shaft are further disassembled; a special tool should be used when removing the thrust ring (see Figure 3 – this step can be omitted for rotors without a thrust ring structure). The assembly procedure for the expander is the reverse of the disassembly procedure mentioned above; the main assembly clearances are shown in the turbine assembly clearance diagram included in the \"Technical Parameters Summary Table\". The following points should be noted when disassembling and assembling: 1. When disassembling, corresponding markings should be made on each main component, and assembly should be carried out according to these markings. 2. The thrust bearing clearance is non-adjustable; no adjustments are permitted. The thrust clearance of the bearing should be checked every time it is installed. 3. When replacing rotor parts or when there are doubts about the rotor’s dynamic balance (unbalance can also be detected during operation by an increase in operating noise), it is necessary to correct the dynamic balance in accordance with the requirements specified in the rotor’s drawings. 4. It is necessary to adjust the gasket between the nozzle ring and the shaft seal in accordance with the requirements specified in the turbine assembly clearance diagram, so as to align the nozzle blades with those at the inlet of the impeller. 5. The gaskets between the compressor volute and the bearing housing must be checked in accordance with the requirements specified in the turbine assembly clearance diagram, so as to ensure that the blades at the compressor wheel outlet are aligned with the diffuser section at the volute inlet. 6. When installing or removing the shaft, one principle must be followed: a speed sensing connector should not be installed. If this is not done and the measuring surface beneath the speed sensing connector moves, an out-of-range peak will appear on the tachometer. 7. The sliding surfaces between the two end faces of the nozzle vanes and the disk should be coated with a low-temperature lubricant to prevent scuffing during transmission or installation/removal. V. Maintenance Instructions 1. Nozzle ring: As long as the gas supplied is clean, even if the shine of the nozzle blades fades, it will not affect efficiency. However, if the gas contains larger, even small amounts of solid particles, or carbon dioxide, and liquid droplets are formed, it will cause erosion of the nozzle blades; in severe cases, pits may form, which significantly reduces efficiency. In such situations, the nozzle blades need to be replaced. Abrasion is most likely to occur during the startup of the device; therefore, special care must be taken when operating it. 2. Expander impeller: For the same reasons as the nozzle ring, it may also cause erosion on the inlet side of the impeller blades. If the abrasion is severe or pits appear, the working wheel should be replaced. It should be noted that the measuring instruments used on site are not accurate enough for measuring the efficiency of the expander. Therefore, they cannot be used as a basis for changes in efficiency or to determine whether to replace the nozzle ring and impeller. 3. Impeller sealing of expanders and boosters: The sealers are prone to slight wear, which leads to a decrease in efficiency; if significant wear occurs, they must be replaced. Their installation clearance is shown in the turbine installation clearance diagram. 4. Shaft sealing: The seal sleeve of the stone mill also experiences slight wear during operation. However, if the wear is severe, the shaft seal should be replaced, as excessive wear can lower the bearing temperature and increase air leakage losses. This situation usually doesn’t occur until after one year. The specified radial clearance for sealing is 0.05 mm; it should be replaced when it increases to 0.1 mm. 5. Bearings: The bearing profile is designed based on hydraulic theory and ensured through machining. Therefore, no modifications are allowed to its inner bore and thrust surface. If bearing damage is found to be caused by temporary overload or poor lubrication, the bearings should be replaced even more urgently. 6. Booster pump impeller: If the gas supplied is not clean, it can cause abrasion of the impeller blades of the booster pump, leading to a loss of dynamic balance. This situation is similar to the loss of dynamic balance in the expander pump impeller. If the wear is severe or pits appear, the booster wheel should be replaced. It should be noted that whenever the impeller of either the expander or the booster needs to be replaced, the entire rotor must be replaced rather than just the impeller. If only the impeller is replaced, it must be done by a specialized manufacturer of Hangyang expanders; otherwise, Hangyang will not assume any responsibility for the consequences. 7. The oil cooler should generally be cleaned once a year; if the cooling water is not clean, the cleaning frequency needs to be increased. 8. If an obvious increase in filter resistance is detected in the oil filter, it should be cleaned or the filter element replaced. VI. Major Faults and Their Solutions The following lists common major faults along with their causes, so that appropriate actions can be taken to address them. 1. Bearing temperature too high: (1) Insufficient oil supply. (2) Dirty oil circuit (clogged oil filter). The rotating component is unbalanced. 1. The temperature of the inner bearing is too low; the consequences of this are that such a low temperature can result in excessively small bearing clearances, which affects normal operation, and in severe cases it can even cause the lubricating oil to solidify. The reasons are: (1) The shaft seal gap is too large. (2) The shaft seal air pressure is too low. (3) When parked, cold air flow can leak in, so the oil pump must be started to warm the bearings. 2. Liquid in the expander: When there is a large amount of liquid at the exit of the expander (well above the designed level), it can easily damage the nozzle ring and impeller. Additionally, since the impeller acts as a pump in this situation, the gap pressure increases, which raises the load on the thrust bearings and may lead to damage to these bearings and other components. 3. Solid particles entering the expander: This can also damage the nozzle ring and impeller, so it is necessary to check whether the pre-filter before the machine is functioning properly. VII. Running-in of the sealer For shaft seals that have been reinstalled, running-in is necessary; the procedure is as follows: Remove the inlet and outlet pipes of the booster, seal the removed pipe ends with plugs, and allow gas to flow into the expander via the bypass valve. Maintain the supply of seals and lubricating oil, open the expander outlet valve, open the emergency shut-off valve and the nozzle vanes, and rely entirely on the inlet valve to control the speed. Gradually open the valve, and increase the speed in stages at 20%, 35%, 60%, and 85% of the operating speed; run at each speed level for 10 minutes, then stop for 10 minutes to allow the seal of the stone mill, which heats up during operation, to cool down. Finally, restart the expander to increase its speed to the operating speed and run it for another 10 minutes; thus, the running-in process is completed.