Common faults and maintenance of mechanical seals in reaction kettles

A reactor is a comprehensive reaction vessel, and the pressure generated during the reaction process requires extremely high sealing of the vessel. The sealing effect of mechanical seals will directly affect the operation of the reactor, and in severe cases, it will cause incalculable losses such as production stoppage, safety accidents, and environmental pollution.

Today, Jinzong Enterprise will take a look at common mechanical seal failures in chemical reaction kettles and how to deal with them.

Regarding the sealing of reaction vessels

The sealing of reaction vessels includes two categories: static sealing and dynamic sealing.

Static sealing:

For a reactor, static sealing is usually used at the leakage points of the head flange and cylinder flange, connecting flange, manhole, handhole, thermometer connecting pipe, sight glass, pressure gauge connecting pipe, etc., because the sealing surface is relatively stationary. Static sealing is relatively easy to solve, and various forms of static sealing gaskets are generally used.

Dynamic sealing:

The leakage point at the gap between the mixing shaft and the kettle body, due to the relative movement between the rotating mixing shaft and the stationary kettle body (upper head), must be prevented from medium leakage by using dynamic sealing devices: mechanical seals and packing seals.

Filler seal: The structure is simple and the packing is easy to assemble and disassemble. However, due to some fatal weaknesses of the packing seal, it has a short service life and is not suitable for high parameter working conditions (high temperature, high pressure, high speed, high vacuum, etc.).

Mechanical seal: Mechanical seal is widely used in reaction vessels, and can be specially designed for the specific working conditions of the reactor. Material selection, lubrication and cooling measures should be considered for the mechanical seal used in the reactor to meet the process requirements.

Compared with soft packing seals, mechanical seals have the following characteristics:

The sealing state is very reliable during long-term operation, with a small leakage rate, and its leakage amount is generally only 1/100 of that of soft packing sealing;

The service life in oil and water media can generally reach 1-2 years or longer, and even in chemical media, it can usually reach more than half a year;

The friction power consumption of mechanical seals is small, and their friction power is only 10% to 50% of that of soft packing seals.

Mechanical seal failure and treatment of reaction kettle

1.Malfunctions and Handling of Mechanical Seal Parts

Cause and phenomenon of malfunction

During the operation of the reactor, the sealing end face often experiences wear, thermal cracking, deformation, damage, etc. The screws, threads, and springs may also loosen, fracture, and corrode after prolonged use. The auxiliary sealing ring may also have cracks, twisting, deformation, and rupture.

Fault handling methods

If the parts of the mechanical seal fail, they need to be replaced or the machining accuracy of the parts needs to be improved. Improving the machining accuracy of the mechanical seal itself and other components of the reaction vessel is very beneficial for the effectiveness of the mechanical seal.

In order to improve the sealing effect, high requirements are placed on the smoothness and flatness of the friction surfaces of the moving and stationary rings. The width of the friction surface between the moving and stationary rings is not large, usually between 2-7 millimeters.

2. Reasons and solutions for mechanical seal vibration and heating faults

Cause and phenomenon of malfunction

During the operation of the reaction vessel, mechanical wear and chemical erosion can cause the mating end face of the dynamic and static rings to be rough. The gap between the dynamic and static rings and the sealing chamber is too small, which can cause collision and vibration due to oscillation.

Sometimes, due to poor temperature resistance of the sealing end face (corrosion resistance and), insufficient cooling, or the inclusion of particle impurities during installation, mechanical seal vibration and heating can also be caused.

Fault handling methods

If the gap between the moving ring, stationary ring, and sealing chamber is too small, it is necessary to increase the inner diameter of the sealing chamber or reduce the outer diameter of the rotation to ensure a gap of at least 0.75mm.

If the friction pair is not properly matched, the material of the moving and stationary rings should be changed to make them resistant to temperature and corrosion. This will reduce the vibration and heating of the mechanical seal.

3. The causes and treatment of mechanical seal leakage

Reasons for leakage during static pressure testing of mechanical seals

Mechanical seals, due to lack of attention during installation, often cause damage, deformation, and damage to the sealing end face, resulting in incomplete cleaning, inclusion of granular impurities, or insufficient precision of the machine and equipment due to loose positioning screws and inadequate compression of the cover, resulting in incomplete sealing of the sealing surface and media leakage. If it is a shaft sleeve leakage, it is due to the shaft sleeve sealing ring not being tightened during assembly, insufficient compression, or damage.

Reasons for periodic or intermittent leakage of mechanical seals

The periodic vibration and large axial displacement of the rotor components in mechanical seals can cause leakage. The sealing surface of a mechanical seal must have a certain specific pressure in order to achieve the sealing effect. This requires the spring of the mechanical seal to have a certain amount of compression, giving a thrust to the sealing end face. The reaction kettle rotates to produce the required specific pressure on the sealing surface.

In order to ensure this specific pressure, mechanical seals require that the shaft cannot have too much displacement, generally within 0.25mm. However, in practical applications, due to unreasonable design, manufacturing errors, assembly errors, and other reasons, the shaft often experiences significant displacement, leading to periodic or intermittent leaks.

Reasons for frequent leakage of mechanical seals

There are many reasons for frequent leakage of mechanical seals:

One is frequent leakage caused by defects in the sealing end face;

The second is the frequent leakage caused by the auxiliary sealing ring;

The third is leakage caused by spring defects;

Other factors include leaks caused by rotor vibration, leaks caused by poor quality or looseness of transmission, locking, and thrust parts, leaks caused by mechanical seal auxiliary mechanisms, and frequent leaks caused by medium problems.

Ways to reduce mechanical seal leakage

Clean and smooth during assembly. The components, tools, lubricating oil, and wiping materials of mechanical seals should be very clean. The sealing end face of the dynamic and static rings should be wiped with a soft gauze.

Trimming chamfers and rounding. The chamfers of the shaft and sealing end cover should be smoothed, and the relevant rounded corners of the shaft and end cover should be sanded and polished.

When assembling the auxiliary sealing ring, the rubber auxiliary sealing ring should not be soaked and washed with gasoline or kerosene to avoid swelling, deformation, and premature aging.

After assembling the dynamic and static rings, press the compensating ring by hand to check if it is in place and flexible; Is the positioning of the elastic opening ring reliable. After the installation of the moving ring, it must be ensured that it moves flexibly axially on the shaft.

4. Excessive vibration of mechanical seals and its treatment methods

Cause and phenomenon of malfunction

If the mechanical seal vibrates excessively, it will ultimately lead to seal failure. However, the reason for the excessive vibration of mechanical seals is not always due to the mechanical seal itself. Other components of the reactor are also the root cause of the vibration, such as unreasonable shaft design, processing reasons, insufficient bearing accuracy, poor parallelism of the coupling, and large radial force.

Fault handling methods

When installing the shaft, sealing chamber, and mechanical seal itself, they should be cleaned thoroughly to prevent impurities from entering the sealing installation area. And reasonably design the balance device for axial force, so that the axial displacement of the rotor of the equipment installed with mechanical seals is ≤ 0.3mm, eliminating axial displacement.