Case study of varnish removal of expander bearings in a petrochemical enterprise’s PTA unit

The expander is a key part necessary for air separation units, natural gas/petroleum gas liquefaction separation units, and low-temperature crushing equipment to obtain cold capacity. It is the heart that ensures the stable operation of the entire unit. Its stable operation is related to the normal production and energy consumption of the entire cracking unit. As a key component of the expander, the bearing has a high surface operating temperature, and the varnish is easily attached to the surface. If the varnish is not removed in time, it will cause great damage to the bearing and the unit over time! This article will introduce the current mainstream varnish removal process through the case of abnormal bearing temperature of a domestic turbine expander!

1. Expander operating conditions and customer pain points

The customer’s 60t/a PTA unit air compressor unit uses equipment from Germany’s MAN Turbine Company. The unit is a three-in-one unit, in which the air compressor unit is a multi-shaft five-stage turbine unit, the condensing steam turbine is the main driver of the air compressor unit, and the turbine expander is the auxiliary driver of the air compressor. The turbine expander adopts high and low two-stage expansion, each with an inlet and an exhaust port, and the impeller adopts a three-dimensional impeller. The three-in-one unit adopts a forced lubrication method with centralized oil supply from the lubricating oil station.

In 2018, in order to meet the VOC emission requirements, the device added a VOC unit to treat the tail gas of the oxidation reactor, and the treated tail gas was still injected into the expander. Since the bromine salt in the original tail gas has bromide ions after high-temperature oxidation, in order to prevent the bromine ions in the tail gas from condensing and precipitating when expanding and working in the expander, causing pitting corrosion to the expander and subsequent equipment, it is necessary to increase the intake temperature and exhaust temperature of the high-pressure side and low-pressure side of the expander unit.

Before the VOC transformation, the bearing temperature on the non-impeller side of the low-pressure end of the expander has been stable at around 80°C (the alarm temperature of the bearing at this location is 110°C and the high alarm temperature is 120°C). After the VOC transformation was started, the bearing temperature on the non-impeller side of the low-pressure end of the expander rose slowly, reaching a maximum of 120°C. There was no significant change in the vibration parameters during this period. The disassembly inspection found that the gap between the bearing and the shaft, as well as the meshing clearance of the gear teeth were normal. Except for the suspected varnish on the non-impeller side bearing surface of the low-pressure end of the expander, no abnormalities were found in other bearings.

Before the VOC transformation, the temperature of the non-impeller side bearing at the low-pressure end of the expander was stable at around 80°C (the alarm temperature of the bearing was 110°C and the high alarm temperature was 120°C). After the VOC transformation was started on January 6, 2019, the temperature of the non-impeller side bearing at the low-pressure end of the expander rose slowly, and the highest temperature was close to the high alarm temperature of 120°C, but the vibration parameters did not change significantly during this period. After checking and analyzing the temperature fluctuation trend of the turbine bearing, excluding the problems of on-site instrument display, process fluctuations, static electricity transmission of turbine brush wear, equipment speed fluctuations, and accessory quality, the main reasons for the fluctuation of bearing temperature are: the gap between the bearing and the shaft, as well as the meshing clearance of the gear teeth are normal, except for the suspected varnish on the non-impeller side bearing surface of the low-pressure end of the expander.

• non-drive bearing and moving pair of expander

As the lubricant was replaced less than a year ago, the oil quality was tested and qualified before driving. In order to eliminate doubts, the customer company sent the lubricant to a professional company for testing and analysis. The professional company confirmed that the attachment on the bearing surface was an early paint film, but the varnish tendency index in the oil sample sent was very low. The customer conducted an investigation around the equipment body support, inlet and outlet pipeline connection stress, oil system leak detection, and the integrity of the temperature probe. It was found that the vibration value of the displacement probe on the non-impeller side shaft of the low-pressure side always remained between 7-9μm and did not change with the change of temperature. Only when the temperature exceeded 110℃ did the vibration value change dramatically, indicating that the varnish attached to the surface of the shaft and the bearing shell during this period may be scratched.With the formation of the paint film, the thickness of the oil film in a non-free state is occupied by the paint film, and the renewal speed of the oil film is reduced. The gradual increase in temperature increases the friction between the bearing shell surface and the shaft. At the same time, the deposited varnish causes poor heat dissipation and oil temperature rise, resulting in an increase in the bearing shell temperature. Finally, the journal rubs against the paint film, which is manifested in violent fluctuations in shaft vibration.

2. Solution

Removing the accumulation of varnish at the bearing can ensure that the unit bearing runs at a controllable temperature. Through research, the customer chose the Weishengda environmental protection varnish removal oil purifier in July 2019, which solved the dissolved varnish through resin adsorption and solved the precipitated varnish through electrostatic adsorption, thus completely solving the influence of bearing temperature fluctuation and vibration change caused by the paint film.Technical analysis of Weishengda environmental protection varnish removal oil purifier. The Weishengda environmental protection varnish removal oil purifier effectively combines electrostatic adsorption purification technology and ion exchange technology, which can effectively remove and prevent soluble and insoluble sludge generated during the normal operation of large units, so that varnish cannot be generated.

Removal of insoluble sludge/paint film by electrostatic adsorption Electrostatic adsorption technology can remove insoluble pollutants as early as possible during the degradation of oil quality. A large number of cases have proved that the principle of electrostatic adsorption can adsorb hard and soft pollutants in the system through the flow of charged particles during the oil circulation process, keeping the system away from sludge/paint film pollution. Compared with other similar technologies, Weishengda’s environmentally friendly electrostatic adsorption technology can increase the speed of sludge removal by at least 200%.

• on site installation

3. Application effect and economic benefit analysis

Since the use of the Weishengda environmental varnish removal oil purifier, the bearing temperature has been stabilized through a combination of electrostatic adsorption and ion exchange resin. Since its operation, the bearing temperature has always been maintained at around 90°C, and the unit has remained normal. After disassembly, there is basically no varnish on the bearing surface and the journal.

• Actual picture of the bearing disassembly after installing the WSD varnish removal unit

Through the installation and operation of the Weishengda environmental varnish removal oil purifier, the problem of the slow increase in the non-impeller side bearing temperature at the low-pressure end of the turbine expander of the customer’s PTA unit has been effectively solved, avoiding the huge losses caused by the unit shutdown (the unit is shut down for at least 3 days, with a loss of at least 4 million RMB; the bearing replacement takes 1 day and a loss of 1 million RMB), as well as the spare parts loss caused by the slow increase in the bearing temperature to the rotating and sealing components (the loss is between 500,000 and 8 million RMB). The unit was filled with 160 barrels of oil in total. After high-precision filtration to remove the paint film, the oil fully met the qualified indicators, saving 500,000 RMB in oil replacement costs.

Media Contact
Company Name: Kunshan Winsonda Environmental Protection Equipment Co., Ltd.
Email: Send Email
Country: China
Website: https://www.winsonda.com/

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