1 dry gas sealing principle

Dry gas seals are a new type of contactless seal that seals gaseous or liquid media in rotating machinery. The dry gas seal has the characteristics of less leakage, less wear, long service life, low energy consumption, simple and reliable operation, low maintenance, and the sealed gas is not polluted by oil. It is widely used in chemical machinery, especially in toxic. , flammable gas centrifugal compressor, expander. The dry gas seal is similar to the ordinary balance seal. It consists of a static ring and a moving ring. The static ring is loaded by a spring and is sealed by an O-ring. The end face material is made of hard alloy. The dry gas seal ring has a gas groove on the end face. The gas groove is only a few microns deep, and there must be a clean gas between the end faces to ensure a stable gas film between the two end faces, so that a certain sealing gap is maintained between the sealing end faces, the gap is too large, and the sealing effect is deteriorated. If the gap is too small, the sealing surface will contact, and no lubricating oil contact between the end faces will quickly cause the sealing deformation, thereby causing the sealing to fail. The gas medium is decompressed by the action of throttling and blocking when sealing the gap to achieve gas sealing. A few micrometers of clearance keeps the gas leakage rate to a minimum and thus acts as a seal.

The Syngas Centrifugal Compressor of Yanzhou Lunan Fertilizer Plant uses John Crane's dry gas seal, designed and installed between the cylinder block and the compressor bearing. It is connected in three stages: primary seal, secondary seal and isolation. gas. The primary sealing gas uses process gas and nitrogen, and the secondary and isolation gases are nitrogen. The flow and sealing schematic are shown.

The dry gas seal design pressure is the intake pressure of the unit. The pressure of the first-stage sealed intake chamber is slightly higher than the intake pressure. Most of the sealed airflow is sealed into the cylinder through the process gas medium side, and only a small part of the sealed airflow passes between the sealing surfaces, which becomes a leaking gas; the secondary seal leaks large. Part of the gas becomes metered and then vented to the flare line.

2 dry gas sealing process operation and maintenance

2. 1 process operation

(1) Preparation before use, the dry gas sealing system piping is cleaned without any impurities.

(2) Applying the filtration system, the isolation gas secondary sealed gas filter and the primary filter are used in one group, the inlet and outlet valves are opened, and the other group is reserved.

(3) Confirm the valve before and after opening the isolation gas, the front and rear shut-off valves for the secondary seal adjustment, the front and rear shut-off valves of the first-stage seal regulating valve, and the two-shaft air supply valve and the instrument heel valve.

(4) Adjusting the pressure of each sealing gas, the isolation gas is 0. 03MPa, the secondary seal is 0. 15M Pa, the first sealing gas, the differential pressure control is 0. 04MPa.

(5) Inject the sealing gas, open the isolation gas, the secondary seal N 2 supply valve, first establish the isolation gas seal, after the pressure of each point of the isolation gas is normal, the lubricating oil pump can be started, and the first-stage sealed N 2 gas supply valve is opened. The pressure of the two-stage sealing gas is 0. 15MPa.

(6) The process gas introduction pressure is higher than the N 2 pressure, the first seal gas is changed to the process gas seal, and the N 2 is separated from the process gas by the check valve.

(7) The isolation gas has always been N 2, and the oil system cycle cannot be established until the isolation gas is not used. Only the isolation gas is used for 10m in.

2. 2 maintenance

(1) Centrifugal compressor should keep N in the dry gas seal operation, clean the process gas, stabilize the pressure control, and control the temperature at 20 50! .

(2) Dry gas seals should be inspected regularly, cleaned and replaced during operation to ensure gas quality.

(3) During dry gas sealing operation, the primary, secondary and isolated gas seals must ensure that the sealing gas flow and pressure are normal.

(4) The dry gas seal exhaust pressure and flow rate are higher than the set pressure and the flow rate is immediately processed.

(5) After the centrifugal compressor is stopped, the primary sealing gas must be switched from the process gas to the N2 seal.

(6) During the shutdown of the centrifuge, if the system pressure rises, the compressor opens the venting of the low pressure cylinder and the high pressure cylinder to ensure the flow of the dry gas sealing gas.

(7) Prevent the oil seal from leaking oil and contaminating the machine seal.

(8) Regularly clean the sealed chamber and prevent residual impurities.

(9) Dry gas seal operation, record once every hour, and report immediately after the operation is not normal.

(10) The service life of dry gas seal and sealing components is generally 60 months. After the expiration, the rubber ring, spring and static and dynamic ring should be replaced. Personally, in view of the long-term operation of the compressor and the characteristics of the single-machine non-prepared vehicle, it is necessary to replace or inspect it at a suitable opportunity for two years of continuous operation.

(1) Within the range of 2. 0MPa / m in.

When the N2 suddenly stops supplying when the centrifugal compressor is running, it should be noted that: (1) The operator must immediately stop the centrifugal compressor according to the operating procedures.

(2) The on-site personnel immediately hit the centrifugal oil system oil pump to the manual position and stop the oil pump.

(3) Close the centrifugal oil system self-regulating valve, front and rear shut-off valves, and confirm that the oil bypass valve is closed.

(4) Open the centrifuge oil system control oil bypass valve.

(5) The on-site personnel open the compressor vent valve and unload the system pressure to zero.

3 problems encountered during use and processing

In the original design, the first-stage sealing gas of the low-pressure cylinder of the syngas compressor is a process gas of the first-stage outlet, and the gas is 3. 0M Pa, 30! 0MPa,150! After the first-stage compression of the refined water vapor becomes 7. 0MPa, 150! Unsaturated gas, not deeply purified. In the operation in June 2007, the sudden flow of the torch line exceeded the index, which caused the pressure difference of the torch line to increase, resulting in an interlocking jump. The dismantling revealed that more than 60% of the water was accumulated in the filter. After analysis, the primary sealing gas used was 7. 0M Pa, 150! Unsaturated gas, because the sealing gas line has no heat preservation and heating measures, the heat loss of the high temperature gas in the pipeline and the throttle gas regulating valve throttle to 3.2 M Pa, the temperature is greatly reduced, becoming a supersaturated gas, Part of the water vapor is condensed into a liquid, which is accumulated in the filter for a long time to form a liquid, which causes the dry gas seal moving ring to be damaged, and the dry gas seal is invalid, resulting in a large leakage of the first-stage seal. For the first-stage sealing gas process transformation, the original process gas interface point was changed to the deep purified molecular sieve device outlet. And the process gas first-stage sealed gas pipeline is added with the hot steam to completely turn the process gas into absolute dry gas.

4 after the transformation effect

After the transformation, after nearly one year of operation and the dismantling of the filter during the operation, the transformation effect was achieved, the filter element did not have a trace of water, and the dry gas seal assembly also worked well.

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