The role of a cold oil cooler in a power plant

The steam turbine generator set operates normally, but some work is consumed due to bearing friction, which is converted into heat, raising the temperature of the bearing lubricating oil. If the oil temperature becomes too high, the bearing may suffer from softening, deformation, or burn damage. To ensure the normal operation of the bearing, the oil temperature must be maintained within a certain range. Generally, the oil temperature entering the bearing should be between 35-45°C, and the oil outlet temperature rise is typically 10-15°C. Therefore, the oil discharged from the bearing must be cooled before it can be recirculated for lubrication. The cooler is designed to cool the main engine lubricating oil. Higher-temperature lubricating oil and lower-temperature cooling water undergo heat exchange in the cooler, and the oil temperature is controlled by adjusting the flow rate of the cooling water (at the same time, due to the higher temperature of the rotor, especially on the high-pressure cylinder inlet side, the shaft journals also transfer heat outward, so the lubricating oil also serves to cool the shaft journals).

Advantages and Disadvantages of Series and Parallel Arrangements for Coolant Heaters

The advantages of series operation of oil coolers include: excellent cooling effect and uniform oil temperature.

2. The disadvantages of cold oil cooler series operation: high oil pressure drop, unable to isolate in case of oil leakage.

3. Advantages of parallel operation of oil coolers: minimal pressure drop, easy isolation, and the ability to inspect and maintain one set during operation.

4. The disadvantages of parallel operation of oil coolers: poor cooling effect and uneven oil temperature.

Process requirements for replacing stainless steel tubes in a cold oil cooler

1. Preparation of new stainless steel pipes: Cut the qualified stainless steel pipes according to the size of the cooler, ensuring the pipes are...

Exceeding the tube plate by 4 to 5 millimeters, the ends of the stainless steel tube are deburred, the expansion section is ground smooth, and tempering is carried out approximately 50 millimeters from both ends.

2. Remove old stainless steel pipes: Use a specialized semi-circular triangular chisel for removal, ensuring not to damage the pipe plate. Strip the stainless steel pipe clean, then clean the pipe plate holes thoroughly after removing the old pipe. Sand the surface smooth with fine sandpaper and wipe away the dust with a cloth.

3. Fitting New Tubes and Expanding Ends: After the tube plates and stainless steel tubes are prepared, new stainless steel tubes can be fitted. Be cautious not to apply excessive force or twist, align them with the correct hole positions, ensuring that the exposed ends of the new tubes are equal in length. The diameter of the tube plate holes should be slightly larger than the tube diameter, about 0.5mm, neither too large nor too small. Once the stainless steel tubes are fitted, use a tube expander to expand the ends. During expansion, avoid excessive force or speed; the expanded length should be two-thirds of the tube plate thickness, but not exceed the thickness of the tube plate. After expansion, use a punch to flare the ends.

4. When replacing stainless steel pipes, do half at a time; dismantle half, replace it, and then dismantle the other half.

The primary cause of the excessive supercooling of condensate.

1. Air accumulation on the condenser steam side reduces the steam partial pressure, thereby lowering the condensate temperature.

2. The condenser water level is too high during operation, flooding some cooling water pipes and causing excessive condensate subcooling.

3. Poorly arranged or overly dense condenser cooling water pipes create a water film on the exterior of the condensate cooling water pipes. The outer layer of this water film is close to the saturated steam temperature, while the inner layer is in close contact with the exterior of the stainless steel pipes, thus approaching or equal to the cooling water temperature. When the water film thickens and hangs down into droplets, the temperature of these droplets is the average temperature of the water film, which is obviously lower than the saturated temperature, thus causing supercooling.

Fault Analysis of Main Engine Coolant Separator and Technical Retrofit Recommendations

The main function of the cooler is to cool lubricating oil, maintaining the bearing temperature within the normal range during the operation of steam turbines and generators. The main cooler units #1, #2, and #5, #6 are manufactured by Shanghai Steam Turbine Works. During the operation of the coolers, frequent oil leakage or water leakage from the bottom end cover has been observed. During actual maintenance, the author identified the causes of these frequent failures and proposed corresponding technical improvement measures. These have certain reference value for the design and maintenance of coolers.

1. Operating Principle of Cool Oil Unit

Cooling water enters the cooler through the top cover of the closed-loop cooling system, then flows through the narrow tubes inside the cooler. Countless tiny cooling water pipes are fixed in place by baffles inside the cooler. These baffles divide the cooler into several small compartments. The lubricating oil flows in a serpentine pattern outside the cooling water pipes, which increases the effective heat exchange area and improves the cooling efficiency. A cooling water chamber is formed at the bottom of the cooler. The lubricating oil and cooling water are separated and sealed with two O-rings (glands) and a copper bed.

2. Fault Analysis of Cold Oil Coolers

During the operation of the unit, failures of the bottom end caps of the coolers #1, #2, #5, and #6 have occurred multiple times, either leaking oil or water, particularly during startup or shutdown of the unit, with the frequency of occurrence increasing. The isolation between the oil and water in the coolers, as well as the leakage of oil and water, relies entirely on two O-rings. If either of the O-rings is damaged or displaced, causing a change in gap, leakage is inevitable. Since the sealing surface of these O-rings is on the left and right sides rather than the traditional top and bottom, increasing the tension of the flange bolts does not reduce the leakage amount once a leak occurs.

The author, after analysis, has summarized several causes that are prone to cause the gap variation and damage of O-type seals.

1) During the start-up or shutdown of the unit, pressure fluctuations often occur on the oil side and water side of the cooler, causing the O-ring seal to shift and resulting in leakage.

2) During installation, if the cooler is eccentrically mounted internally, it will cause abnormal gaps in the O-ring seal. During operation, any slight pressure fluctuations (on the oil side or water side) can lead to leakage.

3) During each maintenance process, when replacing the O-ring, due to the limited space at the bottom end cover, installation is often difficult, leading to the O-ring being crushed by the copper bed and subsequently causing leakage. After each maintenance, the probability of leakage on the water side is higher than that on the oil side, further proving that the current design is not conducive to maintenance and ensuring maintenance quality.

3. Economic Analysis of Technical Retrofit for Coolant Coolers

1) Each time a cold oil cooler leaks, it typically requires maintenance during the major or minor overhaul of the unit. During the period of operation with the injury, the workload of the team is increased due to the additional cleaning of leaked oil and water.

2) The cold oil cooler end cover is massive with limited maintenance space, hence, it requires five people to work simultaneously every time an O-ring is installed, resulting in significant labor costs with each maintenance session.

3) Replacing O-rings during maintenance often results in a significant amount of consumables, which increases maintenance costs.

Through the above analysis, it can be proven that there is a necessity and feasibility for the technical overhaul of the cooler, as well as the economic benefits that can be achieved after the overhaul. During the overhaul, a phased approach can be taken, utilizing the major and minor repairs of the units, to progressively overhaul the coolers of Units #1, #2, #5, and #6. Upon completion of the overhaul, it is certain to yield corresponding economic benefits, saving on equipment maintenance and inspection costs.

Oil Cooler (Oil Cooler) Order Instructions

1) Turbine generator model

2) Coolant Oil Volume

3) Oil Cooler Cooling Area

4). Number of Orders