Analysis of temperature fluctuation of cracking gas compressor and solution measures
(Fujian Gulei Petrochemical Co., LTD., Fujian Zhangzhou 363000)
Chu Jing sheng
Abstract:
The temperature fluctuation of ethylene three machine occurs during the operation of equipment, and the paint film is one of the reasons for the temperature fluctuation of the bush. The paint film will increase the friction of the unit bearing bush, resulting in poor heat dissipation of the bearing bush, endangering the safety and normal operation of the unit. Explore the abnormal temperature of the unit, grasp the risk points of operation, and put forward specific and preventive solutions. The paint film filter can continuously improve the lubricating oil quality of the unit, extend the service cycle of the lubricating oil, improve the operating environment of the oil system, and ensure the long cycle stable operation of the large unit.
1. Company Profile
A petrochemical complex in Fujian Province operates nine major chemical process units, including a 1,000,000 t/a (1.0 Mt/a) ethylene steam cracking unit. It produces 18 major chemical products—including ethylene glycol (EG), ethylene oxide (EO), styrene monomer (SM), polypropylene (PP), ethylene-vinyl acetate copolymer (EVA) resin, raffinate C4, thermoplastic elastomers (TPE), ethylene, C5, C9, toluene, mixed xylenes, aromatic raffinate oil, butadiene, diethylene glycol (DEG), triethylene glycol (TEG), propylene, and pyrolysis naphthalene fraction—and operates five marine terminal berths with an annual throughput capacity of approximately 7.8 million tons.
2. Equipment Overview
The Cracked Gas Compressor Train (hereafter referred to as K-201) of the 1,000,000 t/a steam cracking unit at this Fujian petrochemical company was designed and manufactured by Shenyang Blower Works Group Co., Ltd. (SBW) to compress cracked gas from 0.035 MPa to 3.8 MPa. The compressor consists of three casings arranged from left to right as the Intermediate-Pressure (IP), Low-Pressure (LP), and High-Pressure (HP) cylinders (see Figure 1 for cylinder arrangement), with unit model 2MCL1204 + DMCL1204 + 2MCL1007, connected via diaphragm couplings. The compressor train is driven by an extraction-condensing steam turbine (K-201ST, model EHNK71/90), designed and manufactured by Hangzhou Steam Turbine Co., Ltd. (HTC), with a rated shaft power of 64 MW.
Figure 1: Compressor Cylinder Arrangement Diagram
The rated rotational speed of the train is 4,567 rpm, with a minimum adjustable speed of 3,954 rpm. The compressor features five-stage compression, with a 1st-stage suction pressure of 0.031 MPaG and a 5th-stage discharge pressure of 3.841 MPa. Specifically, the LP cylinder serves as the 1st stage, the IP cylinder serves as the 2nd and 3rd stages, and the HP cylinder serves as the 4th and 5th stages (see Table 1 for detailed parameters). The steam turbine has a rated speed of 4,567 r/min and a rated power of 64 MW; the compressor discharge pressure is 3.84 MPaG, the discharge temperature is 48.9°C, and the mass flow rate is 428,654 kg/h. The compressor train utilizes a centralized forced-lubrication system supplied by a main lube oil station, filled with Shell Turbo S4 GX 46
turbine oil.
Table 1: Performance Parameters of the LP, IP, and HP Cylinders of the Compressor Train
3. Existing Operational Issues of the Unit
Following the commissioning and feed-in startup of the steam cracking unit on August 17, 2021, bearing temperatures across the entire compressor train were normal, with a maximum recorded temperature of 92.4°C. Starting in mid-October 2021, however, the temperature of the non-drive end (NDE) radial journal bearing (TI22217) on the IP cylinder of Cracked Gas Compressor K-201 began to creep steadily upward—rising from 91°C in September 2021 to a peak of 109.2°C on March 21, 2022 (see Figure 2).
Figure 2: Upward Temperature Trend of the Compressor Journal Bearing
During this period, two sudden temperature step-changes (jumps) occurred: the first on January 28, 2022, jumping from 96.5°C to 98.7°C; and the second on February 6, 2022, jumping from 99.2°C to 100.2°C. Following ethylene unit capacity calibration, the bearing temperature rose and failed to return to its previous baseline level (see Figure 3).
Figure 3: Two Step-Changes in the Compressor Journal Bearing Temperature
Furthermore, the temperature fluctuation amplitude at the NDE radial journal bearing (TI22217) grew progressively wider—increasing from 1°C to 3°C—while the bearing metal temperature exhibited periodic fluctuations accompanied by a continuous upward trend (see Figure 4).
Figure 4: Periodic Fluctuations and Upward Trend of the Compressor Journal Bearing Temperature
4. Root Cause Analysis of High Journal Bearing Temperature
4.1 Deterioration of Lubricating Oil Quality
Diagnostic testing of the in-service turbine oil revealed a Membrane Patch Colorimetry (MPC) varnish potential index of 5.7 (see Table 2). Although the bulk oil MPC value was not excessively high, varnish was already present in the lubrication system.
Table 2: Measured MPC Value Prior to Installing the Varnish Removal Oil Purifier
Varnish formation originates primarily from the natural thermal oxidation of the lubricating oil. Oil oxidation generates oxygenated compounds such as carboxylic acids, esters, and alcohols, which subsequently undergo polycondensation reactions to form high-molecular-weight polymers. These polymers initially remain dissolved in the oil; however, once their concentration exceeds the solvency limit of the lubricating oil, the oil becomes saturated and excess degradation byproducts precipitate out to form varnish.
Secondly, adiabatic "micro-dieseling" (micro-combustion) of the oil significantly accelerates varnish generation. Under normal conditions, lubricating oil dissolves a certain volume of air. Once the solubility limit is exceeded, excess air exists as suspended micro-bubbles in the oil. When the oil is pumped rapidly from a low-pressure zone into a high-pressure bearing load zone, these suspended micro-bubbles undergo violent adiabatic compression, causing localized micro-zone oil temperatures to spike instantaneously—sometimes reaching up to 1,100°C. This triggers localized adiabatic "micro-dieseling," generating sub-micron insoluble degradation products that are highly polar, unstable, and prone to adhering onto metal surfaces to form varnish.
Thirdly, electrostatic spark discharge within the oil is another major contributor to varnish formation. In large-scale rotating machinery operating under high temperature, high pressure, and high rotational speed, internal molecular friction generates static electricity as the oil flows through ultra-tight clearances such as valve spools and fine filter elements. Once accumulated static charges suddenly discharge, localized micro-zone temperatures exceeding 1,000°C are generated, readily producing varnish. Generally speaking, while bulk thermal oxidation is a relatively slow process, varnish generation driven by adiabatic "micro-dieseling" occurs far more rapidly.
4.2 Inherent Mechanical and Assembly Deficiencies of the Unit
Insufficient lube oil flow, excessively tight assembly clearances, uneven bearing pad load distribution, or minor manufacturing defects in the journal bearing itself can also accelerate varnish formation.
When the concentration of polar oxidation byproducts in the lubricating oil reaches saturation under specific temperature and pressure conditions, they precipitate onto internal metal surfaces. Once varnish builds up on the bearing Babbitt pads, it reduces the effective hydrodynamic oil film clearance and increases friction—leading to poor heat dissipation, rising bearing temperatures, and accelerated oil oxidation. This impairs bearing heat transfer and causes temperature fluctuations or steady temperature creep. Simultaneously, the sticky varnish layer traps hard contaminant particles, creating an abrasive "sandpaper effect" that exacerbates mechanical wear.
5. Countermeasures and Solutions
5.1 Online Corrective Measures During Unit Operation
After thoroughly inspecting field instrumentation displays, process fluctuations, steam turbine grounding brush wear, and rotational speed stability—and confirming that none of these external factors were responsible for the bearing temperature rise—the following operational adjustments were implemented:
Adjusting Lube Oil Pressure: Supply oil pressure was increased from 0.1 MPa up to a maximum of 0.22 MPa;
Adjusting Lube Oil Temperature: Oil supply temperature was raised from 42°C to 48°C, and subsequently lowered from 48°C to 38°C; however, neither adjustment yielded any noticeable improvement in the bearing temperature fluctuations;
Commissioning the Jacking Oil System: When the high-pressure jacking oil pump was turned on, shaft vibration increased by 1–2 μm while the bearing temperature dropped instantaneously by approximately 10°C. However, as soon as the jacking oil was shut off, both shaft vibration and bearing temperature immediately returned to their prior levels (see Figure 6).
Figure 6: Changes in Shaft Vibration and Bearing Temperature After Commissioning Jacking Oil
Commissioning an Advanced Varnish Removal Purifier — Kunshan WSD (VIFLUTER) WVD-II Dedicated Varnish & Sludge Removal Oil Purifier:
Based on technical benchmarking and proven market performance, we commissioned the explosion-proof WSD (VIFLUTER) WVD-II Dedicated Varnish & Sludge Removal Oil Purifier at 9:30 AM on March 15, 2022, operating in continuous offline kidney-loop circulation on the main lube oil reservoir. The WVD-II purifier synergistically combines Electrostatic Adsorption + Ion-Exchange Resin Adsorption technologies, effectively removing not only suspended insoluble varnish, but also dissolved varnish precursors. Its primary working principles are as follows:
Working Principle of Electrostatic Adsorption — Removing Precipitated/Suspended Varnish (see Figure 7):Figure 7: Principle of Electrostatic AdsorptionElectrostatic adsorption utilizes a circular high-voltage electrostatic field to polarize contaminant particles in the oil so that they carry positive and negative charges. Driven by electrostatic field forces, positively and negatively charged particles migrate toward the negative and positive collecting electrodes respectively, while neutral particles are swept along by the charged particle stream and captured on the collector media. As the electrostatically charged clean oil circulates back through the lubrication system, it actively flushes, desorbs, and carries away sludge, oxidation byproducts, and colloidal deposits adhering to reservoir walls, piping, and bearing surfaces—cleaning the entire internal lubrication loop.
Working Principle of Resin Adsorption — Removing Soluble Varnish:
DICR™ Ion-Exchange Resin selectively removes soluble polar contaminants from turbine oil and guarantees a rapid reduction in MPC values.Because the majority of varnish precursors remain dissolved in the warm oil during turbine operation and only precipitate out upon reaching saturation, standalone electrostatic units cannot remove these dissolved byproducts without resin adsorption (see Figure 8). Figure 8: Adsorption Principle of Ion-Exchange Resin
Adsorption Principle of Ion-Exchange Resin
Prior to commissioning the purifier, the bearing temperature fluctuation curve of the IP cylinder journal bearing was as follows (see Figure 9):
Figure 9: Bearing Temperature Fluctuation Curve from March 10 to March 16, 2022 (Before Treatment)
Within one week of commissioning the varnish removal oil purifier, the bearing temperature curve was as follows (see Figure 10):
Figure 10: Bearing Temperature Fluctuation Curve from March 17 to March 23, 2022 (1 Week After Commissioning)
Figure 11: Bearing Temperature Fluctuation Curve from March 5 to March 31, 2022 (Half a Month After Commissioning)
Fifteen days after commissioning the varnish removal oil purifier, the compressor train's bearing temperatures, rotational speed, shaft vibrations, and lube oil supply temperatures were recorded as follows (see Figure 12):
As demonstrated by the temperature trend curves, after deploying the varnish removal oil purifier, both the peak bearing temperature and the fluctuation amplitude were brought under effective control. Oil sampling and laboratory testing confirmed a steady drop in MPC values and stable control of bearing temperatures (see Table 3).
Table 3: Post-Purification Lube Oil Test Results
5.2 Offline Mechanical Modifications During Scheduled Turnaround
During a scheduled shutdown and turnaround on September 15, 2022, for journal bearing replacement and modification, disassembly inspection confirmed that varnish deposits were indeed present on the bearing pad surfaces, accompanied by surface pitting/indentations measuring 0.02 mm in depth at the varnished zones (see Figure 5). However, visual inspection of the remaining varnish showed irregular, fragmented patches with loose, peeling edges—proving that continuous operation of the varnish removal oil purifier since March had actively stripped and redissolved existing varnish from the bearing pads.
Figure 5: Photograph of the Disassembled Journal Bearing Pads After Shutdown
Following disassembly, the journal bearing underwent replacement and three targeted mechanical modifications:
Machining Oil Wedges and Chamfers: An R3 chamfer and oil wedge were machined along the leading oil-inlet edge of all 5 radial bearing pads in the direction of shaft rotation (see Figure 13).Figure 13: Machined Oil Wedge on the Bearing Pad
Upgrading the Oil Orifice to a Multi-Hole Distributor: The original single orifice plug was removed and replaced with an oil distributor featuring five 3.5 mm orifice holes (see Figure 14).Figure 14: Oil Distributor with Five 3.5 mm Orifice Holes
Modifying the Oil Baffle Ring: 2 mm was machined off the inner ring of the oil baffle ring to increase oil drainage and circulation flow (see Figure 15).Figure 15: Machining 2 mm Off the Inner Ring of the Oil Baffle Ring
5.3 Subsequent Lubrication Management Optimization
Routine lube oil condition monitoring is vital to ensuring safe equipment operation. Establishing a scientific full-lifecycle in-service oil analysis program enables accurate evaluation of lubrication health, early identification of wear locations and severity, and data-driven predictive maintenance. In response to the issues experienced on the cracked gas compressor, the plant formulated and implemented the "Full-Lifecycle In-Service Lubricating Oil Analysis Plan for Critical Rotating Machinery," providing a scientific foundation for condition-based oil changes, root-cause failure elimination, and proactive equipment maintenance.
6. Conclusion
After commissioning the WSD (VIFLUTER) WVD-II Dedicated Varnish & Sludge Removal Oil Purifier in March 2022, the IP cylinder journal bearing temperature was brought under effective control—buying crucial operating time until the scheduled September turnaround and preventing an unplanned shutdown prior to bearing modification. Following the bearing upgrade, the varnish removal oil purifier remained in continuous service, maintaining bearing temperatures consistently below 90°C and ensuring stable, trouble-free compressor train operation.
7. Economic Benefits
The installation and operation of the varnish removal oil purifier prevented catastrophic financial losses from an unplanned shutdown of the ethylene cracked gas compressor train. A single unplanned shutdown of the ethylene compressor train incurs total direct and indirect losses of approximately 30 million RMB, while a 4-to-5-day shutdown for emergency bearing replacement incurs a loss of 10 million RMB. In addition, the compressor lubrication system holds a total of 314 drums of turbine oil; after high-precision varnish removal filtration, every oil quality parameter met specification, saving 1.2 million RMB in new oil replacement costs.
References
[1] Xiong Yao. Development of Low-Varnish Turbine Oil [J]. Synthetic Lubricants, 2022, 49(1): 1–4.[2] Cheng Yong. Installation Completed for Steam Turbine Train of Million-Ton-Scale Ethylene Complex [J]. China Plant Engineering, 2017(6): 7.[3] Wang Jianxin. Formation Mechanism of Lubricating Oil Varnish and Removal Countermeasures [J]. Petro-Chemical Equipment, 2015, 18(5): 76–78.
Author Biography: Chu Jingsheng, male, born in 1979, Bachelor's degree, Engineer. Graduated from Inner Mongolia University of Technology in 2007 majoring in Process Equipment and Control Engineering; currently responsible for equipment management in Chemical Department No. 1 of the Production Operations Division at Fujian Gulei Petrochemical Co., Ltd. Tel: +86-17359698229; Email: [email protected].
