Abstract: Ethylene plant high-speed centrifugal pump , part of the serial mechanical seal, especially in the operation of naphtha pump failure appeared, high pressure medium through the machine seal, oil seal into the gear box to the top of the oil and trigger the device malfunction. The paper analyzes the operating characteristics of high-speed centrifugal pumps and the causes of equipment damage, and puts forward technical measures for prevention and improvement.
1 Sundyne high-speed centrifugal pump operation Sundyne high-speed centrifugal pump can be used in the media pure, less traffic, high pressure liquid delivery environment. There are 14 Sundyne high-speed centrifugal pumps in the Ethylene Plant of the New Shanzi Petrochemical Company (Dushanzi). From the operating conditions, such pumps in harsh process conditions, operating conditions more stable. However, due to the special nature of high-speed pumps, some faults have also appeared during operation. If the treatment is judged timely, equipment accidents due to "high speed" can be avoided. The following is a pros and cons of the operation of such equipment were analyzed and summarized in order to further improve the operational reliability of such equipment to ensure that the production plant "safe and long" operation.
There are two types of high-speed pumps operating on ethylene plants: one is a high-speed pump with a tandem double-ended mechanical seal and the other is a normal double-ended, mechanically sealed high-speed pump. These two types of high-speed pumps, the speed are in 7500-11O00r / min, the flow in the 6-50m3 / h, discharge pressure at 20-33kg / cm2.
The basic components of high-speed pump high and low speed shaft, double-sided mechanical seal, variable speed mechanism, comes with lubricating oil pump, impeller and pump body. During operation, the liquid enters the impeller from the center of the impeller and increases the pressure by the action of the blades. The pump casing diffuses the influence of the corrosion of the pump casing. The main problems of the high-speed pump are: tandem mechanical seal leakage and lubricating oil System pressure is low, high temperature.
Ethylene delivery pumps (40 to 103), propylene delivery pumps (40 to 104) and naphtha delivery pumps (40 to 101) have been used in the Dushanzi ethylene plant. Sealing leaks have occurred during operation , Machine seal damage, high temperature lubricating oil failure, caused a great threat to safety.
1) tandem mechanical seal leak.
Due to the high speed pump "high speed" operating characteristics, the transport of the media has flammable and explosive properties. Therefore, propylene, ethylene high-speed pump, take a protective double tandem mechanical seal better protection, which can make a large number of leaks after the failure of the machine flammable materials leak through the second sealed leak Sent to the buffer tank, the pressure difference by the role of the outside, the leaking material from the sealed liquid buffer tank sent to the torch system to prevent greater accidents. In the inspection, we must carefully check the pressure of methanol tank, temperature, determine the working condition of the mechanical seal is good, so that timely shutdown. Tandem seal buffer system diagram shown in Figure 1.
Figure 1 tandem seal buffer system is not intended
1. Pump inlet; 2. Pump exports; 3. Pump casing sewage; 4. Gearbox heating steam inlet; 5. Transmission heat steam outlet;
6. Sealing buffer liquid from the pump a sealed cans; 7. Seal buffer liquid from the sealed tank of a pump 8. Observation hole;
9,10. Seal leakage to send torch fuel; 11. Sealing liquid injection hole; PSH pressure alarm
2) Lube oil system pressure is low, high temperature.
High-speed pump lubricant system, more complex than other pumps, including transmission, fuel tank, oil pump, cooler and filter. The lubrication process is to use a lubricating oil pump first oil from the tank, and then through the internal circulation and heat exchanger installed in the external oil pipeline, and then through the filter back to the gearbox lubrication rotary bearing to the tank.
In normal operation, the transmission should not be too high, otherwise it will produce a large number of oil bubbles and cause poor cooling effect.
40-P-103,40 a P-104,40 a P-101 high-speed pump, in the preliminary design taking into account the vinyl pump transport medium temperature of 35 ℃, the pump temperature, the oil temperature will not be too high, so there is no Design oil cooler. However, during the summer operation, the temperature of the ethylene delivery pump reached 92 ° C and the hydraulic pressure dropped to 1.2 kg / cm 2. In order to ensure normal working pressure and temperature, a single external pipe cooler was added to the 40-P-103 and was put into operation at high temperatures in the summer.
Oil system set steam booster, in the winter when the temperature is low, the pump can effectively ensure the required oil temperature. However, during operation, there was an internal heater leak, steam condensate into the tank accident. Due to timely processing, did not cause a big equipment accident occurred. However, the direct contact of the steam heating tube with the lubricating oil does not guarantee the absoluteness of the steam sealing and is still a potential danger to high-speed pumps.
3) tandem mechanical seal leakage, the lubricating oil will be thrown, causing pump stop.
In 2000 1O, July 2001, delivery of naphtha high-speed centrifugal pump 40 a P 101, there seal leaks, the oil is lifted, pump, shaft, machine seal are damaged. It can be seen from this accident that, for running high-speed pumps, rigid inspection of key indicators and regular repair and replacement of wearing parts should be strengthened. The main reason for the failure of the equipment was the sudden failure of the mechanical seal up to 4a, the pressure of 33kg / cm2 of naphtha ejected from the pump housing, through the oil seal, the oil in the gearbox was quickly respirated Valves and liquid level gauge in the discharge, resulting in lack of pump machine, the bearings and other important parts damaged.
To prevent similar accidents, technicians checked and replaced all the high-speed pump vent gauges prepared cap, the inspection hole between the second-stage seal and the oil seal was checked, once the seal leakage or failure, leakage Media from the observation hole discharge, you can check and repair.
3 high-speed pump operation should pay attention to the problem
1) During normal operation, the lubricating oil pressure should always be maintained at 1.2 ~ 4.2kg / cm2, so that the pump has enough oil everywhere.
2) Maintain the oil temperature at 60 ~ 85 ℃. Too low oil temperature, the oil thickens, is not conducive to the normal operation of the pump, too high oil temperature, so that oil thinning, the pressure is affected, can not form a uniform film.
3) tank heater, prevent steam leakage, moisture into the oil. At present, there is no proper solution to this problem. Only from the aspect of maintaining management personnel, doing well external work and discovering the leakage in time.
4) After stopping or restarting or overhauling, the lubricant should be filled up from the top of the filter to prevent other accidents caused by the oil breakage of the system when the momentary start-up is started.
5) Tank through-type cooler, in the summer when the temperature is high, the oil temperature can not be completely lowered, but also need to install cooling fins on the straight tube cooler to increase the heat transfer area, in order to have a better cooling effect.
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