JPH0323832B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an air liquefaction separation device equipped with a gas bearing expansion turbine.

Air liquefaction separation equipment is usually equipped with an expansion turbine to generate cold.There are two types of expansion turbines: oil-lubricated type and gas-lubricated type.The gas-lubricated type is superior in terms of cost and maintenance, so This method tends to be widely adopted. As the lubricating gas, separated nitrogen gas or the like, which does not contain impurities and whose supply pressure is stable, is mainly used. This is because impurities can clog the lubricating gas ejection holes or cause the bearing to gall if the supply pressure fluctuates. However, even if the supply of lubricating gas is satisfactory, galling may also occur if the pressure and discharge pressure of the gas supplied to the expansion turbine fluctuate. In particular, regarding the discharge pressure, in the case of an air separation device in which the discharge gas of the expansion turbine is introduced into the lower column, the pressure in the lower column fluctuates depending on the height of the liquid level on the evaporation side and the condensation side of the main condenser. In conjunction with this, the discharge pressure of the expansion turbine changes. Therefore, it has been found that the balance of the gas-lubricated expansion turbine is lost, especially when starting or restarting, and the galling phenomenon repeatedly occurs in the bearing. This can be explained with reference to FIG. 1, which shows an example of an air liquefaction separation device using a conventional gas-lubricated expansion turbine. Pressurized feed air introduced from a pipe 1 is introduced into a heat exchanger 2, where it exchanges heat with return gas. It is cooled to near the liquefaction point, expanded and liquefied by the expansion valve 3, and introduced into the lower column 4 of the main rectification column. Rectification is performed in the lower column 4, and liquid air accumulates at the bottom of the column 4. This liquid air is passed through the pipe 5.
and is sent to the upper tower 6. On the other hand, the nitrogen gas separated in the upper part of the lower column passes through the pipe 7, enters the condensing pipe 8, exchanges heat with the liquid oxygen distilled at the lower part of the upper column 6, liquefies it, flows down the pipe 9, and enters the upper part of the lower column 4. It returns and flows down the tower as a reflux liquid from the tower 4. The pipe 9 branches into a pipe 10 in the middle, and the liquid nitrogen flowing in the pipe 10 is introduced into the top of the upper column 6 and becomes a reflux liquid flowing down in the column 6. Final rectification is carried out in the upper column 6, and liquid oxygen accumulates in the lower part of the column 6. Nitrogen on the condensation side of the condenser 8 is liquefied and nitrogen itself is vaporized and led out through the pipe 11, and then transferred to the heat exchanger 2. The cold water is recovered and brought to almost room temperature and sent to the user through the pipe 12. On the other hand, nitrogen gas is led out from the upper part of the upper column 6 through a pipe 13, and similarly the cold gas is recovered by the heat exchanger 2, and the nitrogen gas is supplied to a user through a pipe 14 after being brought to approximately room temperature.

Next, a part of the pressurized raw air cooled by the heat exchanger 2 enters the expansion turbine 16 from the branch pipe 15 in the heat exchanger 2, expands, lowers the pressure, and lowers the temperature to form the pipe 1.
Enter the lower part of lower tower 4 from 7. The power obtained by the expansion turbine 16 is recovered by driving a generator 19 via a shaft 18 and converting it into electricity. This axis 1
8 uses a bearing with gas lubrication as described above, and product nitrogen or the like is supplied to the pipe 20 as the bearing gas.
Supplied at a more constant and stable pressure.

In an air separation device configured in this way, for example, if the amount of liquid on the evaporation side of the condenser is large, the effective heat transfer area is large, so the rising gas (nitrogen gas) in the lower column is likely to be liquefied, and the pressure in the lower column will therefore decrease. On the other hand, when the liquid amount on the evaporation side is small, the effective heat transfer area is small, so nitrogen gas is more difficult to liquefy than in the lower column, and the pressure in the lower column becomes higher. Since the expansion turbine discharge pressure is regulated by the lower tower pressure, the expansion turbine discharge pressure changes depending on the amount of liquid on the evaporator side, which causes the expansion turbine bearing to become unbalanced and cause a galling phenomenon. Therefore, this galling phenomenon occurs even during steady operation when the liquid level in the condenser fluctuates, but if the operating conditions are stable, there is generally little risk of this happening.
This tends to occur when operating conditions change at startup or restart. Particularly during restart, if the liquid acid level is high and the liquid acid purity is low, the discharge pressure of the expansion turbine will be low. That is, the amount of heat exchanged in the condenser Q [Kcal/h] Condenser heat transfer area A [m ² ] Average temperature difference △Tm [℃] Overall heat transfer coefficient U [Kcal/m ² h℃] Q = UA There is a relationship of △Tm, but as mentioned above, when the liquid acid level is high, A becomes large, and when the liquid acid purity is low, △Tm becomes large, Q becomes large, the amount of nitrogen condensed becomes large, and the turbine discharge Pressure decreases.

In this type of air separation equipment that uses a gas lubrication method for the expansion turbine and introduces the discharge gas into the lower column, it is necessary to keep the discharge pressure constant in order to maintain the dynamic balance of the expansion turbine. As mentioned above, the turbine discharge pressure is affected by the heat transfer area of the condenser, and the effective heat transfer area also changes depending on the height of the liquid level on the condensing side of the condenser, so the liquid height of this liquid nitrogen is controlled. This allows the expansion turbine discharge pressure to be kept constant. That is, as shown in FIG. 2, if a valve V is provided in the pipe 9 that leads out liquid nitrogen from the condenser 8 and this valve is throttled, the liquid level L of the liquid nitrogen becomes higher, the heat transfer area A becomes smaller, and the condenser The opposite is true if the capacity is reduced and valve V is opened.

For this reason, the present invention provides an air separation system equipped with a gas-lubricated expansion turbine, in which the expansion turbine is discharged not only during steady operation, but also at startup, restart, and regardless of the amount of liquid in the condenser. This allows the expansion turbine to operate stably by keeping the pressure constant. That is, in an air liquefaction separation device using a gas-lubricated expansion turbine, the condenser reflux liquid nitrogen return valve is used as an automatic pressure control valve, and the lower tower pressure or the expansion turbine discharge pressure is detected and the automatic pressure control is thereby performed. This is an air liquefaction separation device configured to keep the turbine outlet pressure constant by opening and closing a valve. Hereinafter, the present invention will be explained in detail with reference to the drawings. FIG. 3 is a diagram showing an embodiment of the air liquefaction separation apparatus according to the present invention, and parts common to the conventional apparatus shown in FIG. 1 are indicated by the same symbols and explanations thereof will be omitted. Reference numeral 23 designates an automatic pressure control valve provided in the pipe 9 in order to change the condensation side of the condenser 8 and control the amount of liquid nitrogen led out through the pipe 9 for the above-mentioned reason. A regulator 26 is connected via a line or pipe 25, which is further connected via a pipe 27 to the lower column 4. As a result, the controller 26 detects the discharge pressure of the expansion turbine 16 or the pressure of the lower column 4, converts this into a signal, and transmits it to the control valve 24 of the automatic pressure regulating valve 23 via the line or pipe 25. Controls the opening and closing of the valve 23. Therefore, for example, as mentioned above, if there is a large amount of liquid acid on the evaporation side of the condenser 8 during restart, and the purity of the liquid acid is lower than in steady operation, the discharge pressure of the expansion turbine will be lower, but the adjustment that detects this will lower the liquid acid purity. Total 26
The automatic pressure control valve 23 operates in the closing direction in response to the signal, and as a result, the liquid level of liquid nitrogen on the condensing side of the condenser 8 rises, the effective heat transfer area decreases, the amount of nitrogen gas liquefied decreases, and the lower column 6, that is, the discharge pressure of the expansion turbine 16 increases. In this way, the automatic pressure control valve 23
By providing this, even if the liquid level and liquid composition of the evaporated liquid in the condenser 8 change, the heat transfer area is automatically adjusted to keep the condensing side pressure constant, so the discharge pressure of the expansion turbine 16 remains constant. Therefore, the turbine 1
It is possible to operate stably without losing the dynamic balance of 6.

The lower column pressure automatic control mechanism according to the present invention has a feed air amount of 1950Nm ³ /h and a product oxygen amount of 50Nm ³ /h.
h, Product gas nitrogen amount 243Nm ³ /h, Product gas nitrogen amount 243Nm 3 /h, Product gas nitrogen amount
49Nm ³ /h, product argon amount 7Nm ³ /h air separation operation, the valve 23 is a pneumatic automatic control valve with a diameter of 50φ, and the controller 26 is a PIC (pneumatic indicating controller) as shown in Fig. 3. When the expansion turbine 16 was installed in accordance with the system and restarted and steady operation was performed, no galling phenomenon occurred in the expansion turbine 16.

As described above, the present invention provides an air separation apparatus using a gas-lubricated expansion turbine, in which a control valve is provided in the condenser reflux liquid nitrogen return path, and the opening and closing of the control valve is automatically controlled. The equipment is operated while keeping the outlet pressure constant. This allows stable operation by keeping the dynamic balance of the expansion turbine constant, and eliminates the galling phenomenon that tends to occur especially during startup and restart. . Therefore, it has become possible to operate the expansion turbine with high efficiency, and it has also become possible to shorten the restart time.

[Brief explanation of the drawing]

Fig. 1 is a system diagram showing an example of an air liquefaction separation device using a conventional gas-lubricated expansion turbine, Fig. 2 is a sectional view of a condenser, and Fig. 3 is an embodiment of an air liquefaction separation device according to the present invention. FIG. 4 is a lower column, 6 is an upper column, 8 is a condenser, 9 is a liquid nitrogen outlet pipe, 16 is an expansion turbine, 23 is an automatic pressure control valve, and 26 is a controller.

Claims (1)

[Claims] 1. In air separation equipment using a gas bearing expansion turbine, an automatic pressure control valve is installed in the liquid nitrogen outlet pipe connecting the lower part of the main rectification column condenser and the upper part of the lower column, and the lower column pressure or the expansion turbine outlet pressure is adjusted. 1. An air separation device using a gas bearing type expansion turbine, characterized in that the detection signal is detected and inputted to an opening control end of the automatic pressure regulating valve via a controller.