Cooling Oil Separator

The role of the 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 is too high, the bearing may experience softening, deformation, or burn damage. To ensure the normal operation of the bearings, the lubricating oil temperature must be maintained within a certain range. Generally, the oil temperature entering the bearings should be between 35-45°C, and the oil discharge temperature increase is typically 10-15°C. Therefore, the oil discharged from the bearings must be cooled before being recirculated for lubrication. The cooler is designed to cool the main engine lubricating oil. The higher-temperature lubricating oil and the 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 Coolant Recirculators

The advantages of串联 running of oil coolers include: excellent cooling effect and uniform oil temperature.

2. Disadvantages of series operation of cool oilers: significant oil pressure drop, and unable to isolate leaks.

3. Benefits of parallel operation for oil coolers: minimal pressure drop, easy isolation, and the ability to service one set during operation.

4. Drawbacks of parallel operation of oil coolers: poor cooling effect, uneven oil temperature.

Process requirements for replacing cold oil cooler with stainless steel pipe

1. Preparation of new stainless steel pipes: Cut the stainless steel pipes that have passed inspection to fit the dimensions of the cooler, ensuring the pipes are ready for use.

Exceeding the tube plate by 4-5mm, the ends of the stainless steel tube are deburred, the expansion section is polished smooth, and tempering is performed approximately 50mm from both ends.

2. Remove old stainless steel pipes: Use a special 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 Pipes, Expanding Ends: After the tube plate and stainless steel pipes are ready, new stainless steel pipes can be fitted. Be cautious not to apply excessive force or twist; align and insert them into the designated holes. The exposed ends of the new pipes should be equal in length. The diameter of the tube plate holes should be slightly larger than the pipe diameter, approximately 0.5mm, neither too large nor too small. Once the stainless steel pipes are fitted, use a pipe expander to expand the ends. During expansion, the force and speed should not be too high or too low. The expanded length should be two-thirds of the tube plate thickness and should not exceed the thickness of the tube plate. After expansion, use a punch to chamfer the ends.

4. When replacing stainless steel pipes, replace them in halves; dismantle half, replace it, and then dismantle the other half.

The primary reasons for the supercooling of condensate.

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

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

3. Poor arrangement or excessive density of the condenser cooling water pipes results in a water film forming on the exterior of the condensate cooling water pipes. The outer layer of this water film is close to the steam saturation temperature, while the inner layer is in close contact with the exterior of the stainless steel pipes, thus approaching or equaling 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 saturation temperature, thereby causing supercooling.

Fault Analysis of Main Engine Coolant Heat Exchanger and Technical Retrofit Recommendations

The main function of the oil cooler is to cool lubricating oil, maintaining the bearing temperature within the normal range during the operation of steam turbines and generators. The main oil coolers for units #1, #2, and #5, #6 are manufactured by Shanghai Steam Turbine Works. During the operation of the oil cooler, frequent failures such as oil or water leakage from the bottom end cover have occurred. During the actual maintenance process, the author discovered the reasons for the frequent failures and consequently proposed corresponding technical renovation measures, which have certain reference significance for the design and operation and maintenance of oil coolers.

1. Principle of Operation of the Cool Oil Cooler

Cooling water enters the cooler through the top cover and flows through the narrow tubes inside the cooler. Countless tiny cooling water pipes are fixed in place by baffles inside the cooler, creating several small compartments. The lubricant flows in an S-shaped pattern around the cooling water pipes, which increases the effective heat exchange area and enhances the cooling effect. At the bottom of the cooler, a cooling water chamber is formed. The lubricant and cooling water are separated and sealed by two O-rings and a copper bed.

2. Analysis of Cold Oil Cooler Failure Causes

During the operation of the unit, the bottom end covers of the cool oilers for #1, #2, #5, and #6 units have repeatedly experienced leaks or oil leakage. Particularly during startup or shutdown processes, these issues occur more frequently. The isolation between the oil and water in the cool oilers, as well as the leakage, 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 the 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 easily lead to changes in and damage to the clearance of O-rings.

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

2) During installation, if the cooler is eccentrically mounted internally, it will cause an abnormal gap in the O-ring seal. During operation, any slight pressure fluctuations (on the oil 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 cumbersome, 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 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 usually requires maintenance during both major and minor repairs of the unit. During the period of operation with the injury, the workload of cleaning leaked oil and water is increased, thus adding to the team's workload.

2) The oil cooler end cover is large in volume with limited maintenance space, hence, it requires a team of five people to work simultaneously when installing the O-rings. This results in a significant labor cost each time for maintenance.

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

Through the above analysis, it can be proven that there is a necessity and feasibility for the technical renovation of the cooler. After the renovation, it is expected to bring about economic benefits. During the renovation, a step-by-step approach can be adopted, utilizing the regular maintenance of the units to progressively renovate the coolers of Units #1, #2, #5, and #6. Upon completion, it is certain to yield corresponding economic benefits and save on equipment maintenance and repair costs.

Oil Cooler (Oil Cooler) Ordering Instructions

1) Turbine Generator Set Model

2) Coolant Oil Volume

3) Oil cooler cooling surface

4) Number of Orders