Basic design centrifugal compressor can achieve power balance

In order to meet the needs of economic development, more and more centrifugal air compressors are imported from various places. The main purpose is to provide compressed air for process instrumentation and nitrogen production systems. The installation requirements of large-scale centrifugal units and domestic units in foreign countries are quite different. This paper takes the installation design of American COOP-ER TAS-70/30 centrifugal air compressor and domestic air drying system as an example, and puts forward that it should be noted. Problems and measures.

The design of the centrifugal air compressor station includes two parts: the TAS-70/30 centrifugal air compressor installation design and the HXK-13200/9 air drying system design. TAS-70/30 compressor installation design The TAS-70/30 compressor is mainly composed of compressor, motor, interstage cooler, inlet filter silencer, outlet vent silencer and stage aftercooler. Structure and working principle The TAS-70/30 unit is a full-gear centrifugal type with a three-stage compression unit and an interstage cooler. The compressor and the drive unit are connected by a coupling and fixed to a steel base. The compressor is driven by a large gear to drive two pinions, one of which is symmetrically mounted on one of the pinions and the third of which is mounted on the other. The air enters the first stage impeller through the inlet filter, the inlet control valve and the guide vane; it is cooled by the 1~2 interstage cooler and then enters the secondary impeller compression; after being cooled by the 2~3 interstage cooler, it enters the third stage impeller. Compression; a portion of the compressed 135 ° C compressed air is vented through the vent control valve and the vent silencer, and most (or all) enters the aftercooler and is cooled to 45 ° C into the air drying system. The unit uses a labyrinth seal and an oil seal, and the product air is 100% oil-free. The lubricating oil system includes an auxiliary oil pump, a main oil pump, a water cooler, an electric heater, and a filter.

Features of the unit TAS-70/30 centrifugal air compressor main features: unit junction mm, h = 1981mm; single unit equipment capacity, low power consumption; advanced control methods - micro-computer display panel control, can be automatically turned on; The exhaust pressure is stable, the exhaust air is oil-free, and the purification degree is high, and it can directly enter the wind system; the main oil pump driven by the main shaft provides compressor lubrication during normal operation, and provides inertia protection when the power is off.

Installation Contents TAS-70/30 centrifugal air compressor installation includes equipment foundation, inlet installation and outlet installation. Equipment basic design Centrifugal compressor can achieve power balance at high speed, and does not produce unbalanced force. However, when designing the foundation, it should consider the mechanical engineering design and standard petrochemical automation. The imbalance of the 2003, 2:15 device itself. force. The only vibration generated by the TAS-70/30 centrifugal air compressor is the slight deviation between the drive and the compressor rotor. This kind of vibration energy is not big, but the frequency is very high. Therefore, the basis should meet the following requirements.

Unit inlet design 1) Filter/muffler: The filter removes solid particles from the air, otherwise it will cause the aerodynamic components to wear out; the silencer eliminates the noise generated by the high-speed airflow. The filter/muffler resistance must be within the allowable range and the local climate impact must be considered. There have been major equipment accidents in the country due to frost on the surface of the filter element, sudden increase in resistance, and the filter element being caught in the machine to destroy the impeller. Therefore, the filter/muffler design selection flow rate is at least twice the rated flow rate of the air compressor, which not only can effectively prevent the threat of bad weather (heavy fog, frost or sandstorm) on the safe operation of the air compressor, but also can be greatly extended. The filter replacement cycle allows the compressor to operate safely for long periods of time.

2) Inlet control valve: For constant speed operation, the compressor maintains a constant outlet pressure during start-up and shutdown unloading, preventing the drive from being overloaded and throttling during compressor interruption (full shutdown) operation. The straight pipe section between the air compressor and the air compressor inlet is 4 times the length of the pipe diameter, ensuring uniform airflow through the valve and the primary inlet.

3) Inlet Temporary Filter: To prevent damage to the compressor by preventing dirt from entering the inlet pipe, install a cone filter as close as possible to the compressor before turning on the compressor for the first time. The cone filter can be removed after 40 to 50 hours of operation to resume normal operation.

Petrochemical Automation 2003 4) Elastic joints: The inlet pipe should be fitted with an elastic joint or expansion joint near the compressor to compensate for the stress caused by thermal expansion or pipe displacement. The spring joint should be mounted on a straight pipe section close to the compressor to prevent stresses that are amplified by torque. If a bellows expansion joint is used, a lining should be installed to prevent the airflow from being unstable to the aerodynamic disturbance of the pipeline. Since the pressure inlet and outlet pipes have relatively less influence on pressure and temperature, a relatively simple elastic joint can be used. Two sections of pipes 6 to 8 mm apart can be connected by a reinforced rubber casing and two pipeline clamps, and the practical application effect is ideal.

5) Pipe support: If elastic joints are not used, measures must be taken to reduce the static load applied to the compressor inlet flange, for example with elastic support. If an elastic joint is used, the pipe support can be fixed. The pipe support can withstand the pressure or impact force exerted by the joint, as well as the displacement caused by the misalignment of the support position and the axis of the elastic joint.

6) Inlet pipe: It should have sufficient strength to withstand the negative pressure and structural stress that may be caused in the pipe. The gas flow rate in the pipeline should be no more than 30m/s, and there must be a straight pipe section equivalent to 4 pipe diameters. The flow rate can be reduced by increasing the pipe diameter. Small radius elbows are strictly prohibited on the inlet pipe. The inlet pipe should be corrosion resistant and have a low point condensate port. The inlet pipe can be made of stainless steel, and the allowable minimum of the wall thickness to outer diameter ratio (δ/D) is 0.015. The elbow and the long pipe are connected by flanges to ensure that each part can be touched by hand. The section is dismantled and inspected strictly, the weld is smoothed, and the inner surface of all the pipes is cleaned with mud, to avoid any fatal damage to the high-speed impeller of the compressor.

Unit outlet design Compressor outlet design includes pipelines, expansion joints, vent control valves, vent silencers, post-stage coolers, check valves, globe valves, etc.

1) Export pipeline: The high temperature, high pressure, large span compressor outlet pipeline needs to consider more factors than the low temperature and low pressure inlet pipeline. Although corrosion of the outlet piping will not cause the same problems for the compressor as the inlet piping, it should also be considered. The reason is that the corrosion of the outlet pipe can also affect the instrument, pneumatic tools or processes that require clean air. Corrosion debris is drawn into the compressor when the compressor surges. When the pipeline is prepared, mechanical derusting is required to expose the inner surface to metallic luster. After installation, there shall be no dust or debris in the pipe. A section of the closed section shall be installed to keep it clean. The high temperature, high pressure gas is dried until it is cooled, and a low point condensate port should be set to eliminate condensate in the shutdown or post-stage cooler.

2) Expansion joint: The expansion pipe should be installed in the outlet pipe. Correct calculation, selection, and installation of expansion joints can prevent pipelines and venting valves from applying loads to the compressor flange. The outlet expansion joint is to be directly connected to the outlet flange. The outlet expansion joint must have sufficient strength to withstand the pressure and temperature of the compressor surge.

3) Venting control valve / silencer: The vent control valve should be as close as possible to the compressor outlet pipe. The venting pipe should be as short as possible, and the pipe diameter should be one level larger than the vent control valve. The vent silencer should be properly fixed and protected from rain. The venting valve should be set at the low point of the venting pipe.

The V-type venting pipe is installed at the outlet of the muffler to prevent uneven force on the pipe frame during emergency venting. The two openings of the V-shaped venting pipe are strictly prohibited from facing the human area.

4) Check valve and stop valve: The check valve must be equipped with a check valve to prevent reverse flow when the machine is stopped; the check valve also has the effect of reducing surge. The installation position of the check valve is related to the selection of the vent control valve. The calculation of the air release capacity of the vent control valve is based on the gas volume before the check valve. A shut-off valve should be installed after the check valve to isolate the compressor from other pressurized parts.

HXK-13200/9 air drying system design HXK-13200/9 air drying system is designed and developed by Sinopec Jinan Branch Design Institute and Kaifeng Air Separation Group Co., Ltd., mainly by preheat exchanger, freeze dryer, gas The water separator, the molecular sieve adsorption tower, the regeneration gas vent silencer, the regenerative gas heater and the DCS are composed.

Technical parameters 1) Raw material air standard state flow 13200m state: saturated.

2) Product air standard state flow rate 12200m / h (product air / h (staining nitrogen as regeneration gas); atmospheric pressure dew point: -60 ° C.

3) Regeneration gas nitrogen (or product air) standard state flow rate 1000m / h (product air as regeneration gas); regeneration temperature: 175 ° C.

4) Switching cycle 24h.

The process air is from the TAS-70/30 air compressor aftercooler. The dry air returned by the preheat exchanger is cooled to 25 ° C, and then enters the freeze dryer and continues to cool to 5 ° C ± 3 ° C. The separator is separated, and the air of free water is removed into the molecular sieve adsorption tower for dehydration and drying, and the dry air having a dew point of -60 ° C passes through the dust filter. In the preheat exchanger, it is heated by the raw material air and then enters the purification duct through the buffer tank. network.

In Fig. 1, two molecular sieve adsorption towers of 9-1 and 9-2 are used alternately, one working; one regeneration, and the regeneration flow path is regeneration gas (the nitrogen is taken by air separation equipment or taken through V-13) The product air) is heated to 175 ° C by an electric heater, and enters the 9-2 (or 9-1) molecular sieve adsorption tower to heat and blow off the molecular sieve adsorbent adsorbed by the water. After heating for 12 hours, the electric heater is stopped. The regeneration gas continues to be blown cold, so that the molecular sieve adsorption tower reaches the normal working temperature for the next cycle. The regeneration gas passing through the molecular sieve adsorption tower during the regeneration process is vented through the muffler.

The main process parameters PI-01 into the molecular sieve adsorption tower front pressure monitoring 0.8; PI-02 molecular sieve adsorption tower 9-1 pressure indication 0.8 (work PI-03 molecular sieve adsorption tower 9-2 pressure indication 0.8 (work PI-04 product air to do regeneration The gas pressure indicates 0.02; the PI-05 product air out system pressure indicates 0.75.

TI-01 dry air out preheater temperature 30 ~ 35; TI-02 wet air into preheat exchanger temperature 45; TI-03 wet air out preheater temperature 25 ~ 30; TI-04 gas water separator Air temperature 5±3; TI-07 regeneration gas output molecular sieve adsorption tower temperature indication 10TIC-08 electric heater outlet temperature indication adjustment 10~3) Standard state flow/(mFIQ-01 product air flow indication 12200 (product air as regeneration gas) 13200 (stained nitrogen as regeneration gas); FIQS-02 regeneration gas flow indication adjustment interlocking 10004) analysis AR-01 product air dew point analysis -60 °C.

Equipment Installation Instructions 1) Before installation, all equipment and valves of the drying system should be inspected macroscopically, and the air-sealed test should be carried out according to the relevant requirements.

2) The safety valve is adjusted to the specified take-off pressure and re-sealed.

3) During the installation process, measures should be taken to prevent mechanical impurities such as dust and welding slag from entering the system.

4) Pipes should be arc welded after manual argon arc welding.

5) The installation position of the orifice flowmeter should be guaranteed to be larger than the straight pipe section with 5 times the diameter of the pipe after the first 10 times.

6) After installation, the program-controlled butterfly valve should be removed, all the pipes should be purged and the program-controlled butterfly valve should be re-installed in place to prevent the welding slag from damaging the hard sealing surface of the valve. The system is then thoroughly purged and the purge gas must be dry and oil free. The blown-out inspection can be carried out by using a wet white filter paper or a white cloth placed on the discharge port. After 5 minutes, no obvious mechanical impurities are acceptable.

7) After the blowout is passed, the airtightness test under the injection pressure is performed on the working flow path (0.8 MPa) and the regeneration flow path (0.03 MPa) of the drying system respectively (when the working flow air tightness test is performed, the regeneration flow is performed) The internal valve of the road should be open and open to the atmosphere).

8) After the airtightness test is passed, the high and low temperature equipment and pipelines shall be insulated, and the thermal insulation construction shall be carried out according to the engineering design requirements.

9) After the system is purged and tested, fill the molecular sieve adsorbent and, if necessary, remove the powder by sieving. Immediately after filling, seal the manhole cover and prevent it from getting wet.

Equipment commissioning program 1) Before starting, the instrument control system switching procedure should be put into operation first, in order to ensure that the valve operating time of the switching system is accurate.

2) When debugging, all the valves of the switching system are in the closed state, the switching program control is in the manual position, and the manual valve force is not opened slowly. Open V-10 (V-11) and adjust the manual valve V-17 (V-18) to open. Degree control pressure relief time meets the requirements of the switching procedure, and slowly inflates the adsorption tower 9-1 again, after reaching 0.8MPa, the V-9 is opened, and the pressure is increased to the adsorption tower 9-2, and the manual valve V-19 opening degree is adjusted to control The voltage equalization time meets the requirements of the switching procedure.

3) The freeze dryer is put into operation, and the necessary working conditions are adjusted and maintained according to the maintenance instructions.

4) The instrument control system switching program is put into operation. After the raw material air enters the system, keep the PI-01 at 0.8MPa, slowly open the V-16 valve and gradually increase the system pressure PI-05 to the rated working condition of 0.7MPa or more. The adsorption work begins. Adjust the V-14 opening degree to /h, the regeneration starts, and the entire drying system enters the normal working condition.

5) At any time, the molecular sieve adsorption tower should be charged and depressurized slowly, and the electric heater must not be powered by the regeneration gas.

6) The running status parameter is recorded once every hour, and the abnormality should be checked and processed in time.

7) It should be inspected once every 4 hours, and the gas-water separator trap should work normally.

Design points of air compressor station 1) The cooling water volume is automatically adjusted, and the energy saving effect is remarkable: the air compressor station in petrochemical automation designed cooling water volume of 200t/h in 2003, and the temperature difference of return water is 8~10°C. The actual water volume is generally larger than the designed water volume, the temperature difference is only 2 to 3 ° C, and the water volume does not change with the load and the season, causing the cooling water consumption to increase exponentially. Therefore, the design of the water supply automatic control valve V-15, the valve opening degree is controlled by the cooling water return water temperature, saving more than 50% of the cooling water.

The TAS-70/30 centrifugal air compressor can be automatically started warmly, and the V-15 is interlocked with the air compressor to meet the requirements of the quick start of the unit, and basically does not consume cooling water during hot standby.

2) The drying system realizes low temperature and high pressure adsorption and high temperature and low pressure desorption. The main factors affecting the operation of the adsorption dryer: a) the trace oil in the air will cause poisoning of the adsorbent; b) the inlet air temperature refers to the product air temperature and the regeneration gas temperature. As can be seen from Table 1, the lower the product air temperature, the adsorbent The lower the moisture absorption load, the higher the regeneration gas temperature, the greater the water absorption and absorption of the adsorbent; c) It can be seen from Table 2 that the compressed water saturated water content is inversely proportional to the pressure.

It can be seen from Table 3 that lowering the temperature of the inlet tower can increase the adsorption amount of the adsorbent temperature/°C content temperature/°C air pressure/MPa, but it is extremely unfavorable for the “regeneration” treatment, and the “low temperature desorption” leads to the dehydration of the adsorbent. Incomplete deterioration accelerates, and the amount of regeneration gas is increased. According to economic analysis, appropriately increasing the temperature of the regeneration gas can greatly reduce the regeneration gas consumption and prolong the life of the adsorbent.

The key equipment of HK-13200/9 air drying system is the pre-inlet temperature outlet pressure dew point Note: Table 3 working conditions --- pressure 0.7MPa, adsorption dryer cycle 10min.

Heat Exchanger. The preheat exchanger adopts an Aluminum Plate fin type heat exchanger, which has high heat exchange efficiency and low resistance. First, it greatly reduces the electromechanical consumption of freeze drying.

Secondly, after it is located in the molecular sieve adsorption tower, the inlet air temperature of the molecular sieve adsorption tower is 5 °C ± 3 °C, and the less moisture adsorbed by the molecular sieve adsorption tower, the less the regeneration gas is absorbed by the desiccant. . Third, the electric heating method is used to increase the regeneration gas temperature to 175 ° C, so that the regeneration energy consumption is reduced to the most economical level. The pressure and flow rate of the regeneration gas are accurately adjusted by the automatic control valve. 3) The air separation unit is used as the regeneration gas to save the purified air. The air compressor station is designed as a combined unit with the air separation unit of 1500m/h (standard state, the same below). The 1500m/h air separation unit is filled with /h dirty nitrogen (dew point -70 °C), the air separation unit itself/h is used as regeneration gas, and the remaining about 1500m of nitrogen is emptied. The quality of this part of the contaminated nitrogen is better than that of the purified/h dirty nitrogen used as the regeneration wind for the molecular sieve adsorbent of the air compressor station. In order to ensure the stability of the air separation unit, the control valve V-12 is set. When the molecular sieve adsorption tower is deactivated, the V-12 is opened and the nitrogen gas is directly vented. When the air separation unit starts, the average air purification air is 600m4). The air compressor station adopts DCS control: the air drying equipment (no heat adsorption, thermal adsorption, micro thermal adsorption, freeze adsorption, etc.) produced in China is limited by product price and manufacturer technology. The following problems exist: a) the capacity of a single tower is small (maximum 6000 m/h or so); b) the programming is too simple, generally only 4 program-controlled valves are used, and the adsorption process is instantaneously pressurized and relieved, and the adsorbent is easily broken and easy to run. Material, greatly reducing the service life of the valve and adsorbent; c) PLC control board limits the centralized control of the drying unit, the user is inconvenient to maintain and adjust; d) the energy consumption is high, generally the recycled gas consumption is more than 15%, The dew point is unstable and the orifice plate cannot accurately control the regeneration gas consumption.

In the design of the air compressor station, the adsorption tower adopts a new airflow distribution design, which solves the problem of uneven adsorption and regeneration at large flow rates, so that the single unit capacity can reach more than 36000 m/h. Program control program design, using 11 program-controlled TOMOE pneumatic butterfly valve (V-1 ~ valve), 1 control valve (V-13 or V-14), 3 manual valves (V-17, V-18, V-19 For one commissioning, DN40) and one E+H dew point meter, the regeneration gas flow can be accurately controlled, the charging and pressure relief are slow and stable, and the adsorbent and valve can realize long-term operation. All control valve signals are introduced into the control room for centralized DCS control. The operation engineer can adjust the switching cycle with DCS according to the load and seasonal changes. The product air pressure dew point can be automatically adjusted between -55 and -70 °C. The minimum energy consumption (at normal pressure dew point -70 °C) is equivalent to 7% of regeneration gas consumption.

5) Adopt interlock control to prevent the occurrence of wind supply accidents: In the previous air drying equipment, there were faults such as valve breakage and card position, which could not be detected in time, causing fluctuations in the supply air pressure of the instrument and affecting safe production. Now, DCS can monitor the position of the program-controlled valve switch. If the unexpected switch of the valve is not in place, the program can automatically stop execution. The other valves remain in place to ensure normal air supply, and an alarm signal is issued to prevent the supply air accident. Regenerative gas flow and electric heater interlock, control flow and temperature within the design range, to ensure the quality of regeneration, to prevent electric heaters from burning and other accidents.

Conclusion Since the centrifugal air compressor station was put into operation in October 1999, the TAS-70/30 unit and the HXK-13200/9 air drying system have been running smoothly, the control and adjustment are flexible and convenient, the product air quality is stable, and the energy saving effect is remarkable. The design requirements were met, proving that the installation and design were successful.

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