TWI398301B - Nitrogen increase method in air seperation plant - Google Patents

Description

Air separation plant nitrogen production method

This invention relates to a method for nitrogen production in an air separation plant, and more particularly to an improvement in a nitrogen water precooling system in an air separation plant.

The method of separating nitrogen and oxygen from the air is used in a wide range of fields such as iron making, chemical and electronics industries. Although the air separation system has developed to a highly mature state, the separation efficiency is improved and the operating cost is lowered. There are still many areas to be studied and improved, such as improvement in operational stability, and the present invention is a method for improving the actual operation to reduce the operating cost.

Figure 1 is a flow chart of an air separation plant of a conventional air separation plant, which is an air separation device belonging to a molecular sieve adsorption type, hydrogen-free argon-producing process, comprising: an air compressor (1), which is used To provide the pressure required for the process air; an air pre-cooling system for cooling the high-temperature air after the air compressor is pressurized, the air pre-cooling system includes a SC air cooler (2) and EC water cooling Evaporative cooler (3); a molecular sieve adsorber (4) for filtering process air impurities such as hydrocarbons, CO ₂ , N ₂ 0, H ₂ 0, etc.; a main heat exchanger (6) ), which can cool the process air and recover the coldness of the product of the fractionation column, which exchanges oxygen and nitrogen from the fractionation column (5) for heat recovery; and a fractionation tower (5) The structured packing tower or the sieve tray tower separates oxygen, nitrogen and argon by using different boiling points of oxygen, nitrogen and argon under different pressures; a plurality of nitrogen presses (7) and an oxygen press (15), Nitrogen and oxygen products which are compressed out of the fractionation column and reheated by the main heat exchanger (6) for downstream use; (8), which is used to provide the desired degree of supercooling of the entire drive system fractionation.

The entire air separation process is operated by the high temperature air (9) from the air compressor (1) entering the lower part of the SC air cooling tower (2c), and the normal temperature cooling water (11) from the water pump (10a). The middle part of the SC air cooling tower (2b) is in direct contact with the countercurrent, heat exchange is performed, and the air is initially cooled, and then rises to the upper part of the SC air cooling tower (2a), and the low temperature cooling water (12) from the EC water cooling tower (3). After further heat exchange, the SC air cooling tower (2) is discharged, and the process air of the SC air cooling tower (2) is discharged, and after entering the molecular sieve adsorption system (4), heat exchange is performed through the main heat exchanger, and then enters the fractionation tower. Fractionation of oxygen, nitrogen, and argon.

There are two ways of cooling water in the air cooling tower (SC air cooling tower), one way is to enter the EC water cooling tower (12a), and the mixed fractional distillation tower (5) is mixed with nitrogen (nitrogen + waste nitrogen, the waste nitrogen is purer The low crude nitrogen gas is heat exchanged, and after heat exchange with the mixed nitrogen gas, it becomes the low temperature cooling water (12), and the low temperature cooling water (12) is further introduced into the upper portion (2a) of the SC air cooling tower. The other way is the normal temperature cooling water (11) directly sent to the middle of the SC air cooling tower (2b) by the water pump (10a). After the two cooling waters are exchanged with the air, after the lower part of the SC air cooling tower (2d) is collected, That is, the air cooling tower (2) is discharged, and the mixed nitrogen gas is introduced from the lower portion (3a) of the EC water cooling tower, and then discharged from the upper portion (3b) of the EC water cooling tower. In the air cooling system, the supporting equipment includes an air cooling tower (2), a freezer (10c), an EC water cooling tower (3), a water pump (10a, 10b), etc., and the freezer (10c) is generally attached to the EC water cooling tower. System (3).

This air-cooling system process is the most commonly used in recent years. It eliminates the chiller and replaces it with a water-cooled tower, making full use of the hygroscopicity of the by-product of the air separation plant (nitrogen + waste nitrogen) and the freezer (10c). The assistance to get low temperature water, thus greatly reducing energy consumption. The SC air cooling tower (2) and the EC water cooling tower (3) adopt the most advanced packed tower form, which has the advantages of low resistance, high efficiency and strong processing capacity.

The waste nitrogen (14a) and nitrogen (14b) returned from the main heat exchanger, except for a part of the regeneration required for the molecular sieve adsorber (4), enters (3a) from the lower part of the EC water cooling tower. The bottom plate is passed through the tray or packing layer of the EC water cooling tower for heat exchange with the downward sprayed water (12a). Since the waste nitrogen (14a) and nitrogen (14b) correspond to the temperature at that time, some of the water will evaporate into steam into the waste nitrogen (14a) and nitrogen (14b), which can absorb a large amount of latent heat and water when it evaporates. Heat exchange can be made between waste nitrogen (14a) and nitrogen (14b), thus allowing the water to be cooled. The cooled water is pumped by a water pump (10b) to a freezer (10c) and then cooled, and subsequently delivered to the top (2a) of the SC air cooling tower.

In the SC air cooling tower (2), compressed air from the air compressor (1) enters the bottom (2c) of the air cooling tower and passes through the tray and the packing layer from bottom to top. At these gas-liquid contact surfaces, the compressed air exchanges heat with the counter-flowing cooling water (11 & 12), the air temperature is lowered, the saturated moisture content in the air is reduced, and the water vapor is condensed into water and then added to the cooling water. In the EC water cooling tower (3), the mixed nitrogen of waste nitrogen and nitrogen is from bottom to top, the temperature rises, the water content increases; the water goes from top to bottom, the temperature decreases, the water volume decreases, and the bottom of the EC water cooling tower The cooling water of (3c) is sent to the SC air cooling tower (2) by the pressurization of the water pump (10b) and the cooling of the freezer (10c) for cooling.

There are many factors affecting the cooling effect of the EC water cooling tower in the air cooling system, but the key factor is the water-to-gas ratio, that is, the ratio of the amount of spray water to the gas flow. Since the amount of saturated steam in the mixed nitrogen has an upper limit, the degree of water temperature drop in the EC water cooling tower depends on the value of the water-to-gas ratio, and thus the degree of cooling in the EC water cooling tower (3) There is also a limit, and a large flow of mixed nitrogen is required to increase the cooling effect of the EC water cooling tower (3), such as reducing the flow rate of the mixed nitrogen, so that the temperature of the cooling water of the EC water cooling tower (3) rises. This will affect the air cooling effect in the SC air cooling tower (2). For example, the cooling effect in the SC air cooling tower (2) is reduced, and the air will have a higher temperature and a saturated vapor pressure, so that the molecular sieve adsorber will be (4) The adsorption load becomes heavier, which in turn affects the production capacity of the air separation plant.

When there is additional demand for nitrogen production in the gas plant of the present invention, an additional air separation unit and a nitrogen compressor are required to increase the nitrogen production, but the compression limit of the nitrogen compressor is 35000 NM ³ /H, and the nitrogen exceeding the limit will be It is sent to the EC water cooling tower (3) as a refrigerant for cooling water. Generally, the capacity of the air separation unit can be used as a nitrogen product, which accounts for about half of the process air. For example, the process air volume is 160000 NM ³ /H, and the nitrogen production is about 80,000 NM ³ /H, so 45,000 NM ³ /H of nitrogen is sent to the EC water cooling tower (3) without increasing the number of air separation units. In order to maintain the stable operation of the air separation unit, if this part of the nitrogen can be reused, the output of nitrogen can be increased for downstream use and deployment without the need to open additional air separation units, thus saving a lot of energy. Consumption.

The invention provides a method and a device for increasing nitrogen production in an air separation plant, in particular for improving a nitrogen water precooling system in an air separation plant, by reducing the nitrogen flow rate of the nitrogen water precooling system and guiding it to A nitrogen press for subsequent use. In order not to make the gas entering the molecular sieve adsorption system contain high saturated water vapor, the adsorption effect is deteriorated, so the invention increases the freezing capacity of the refrigerator, so that the temperature of the cooling water entering the air cooling tower and the cooling tower can be reduced. The air temperature increases the cooling effect of the air cooling tower, so that the nitrogen production can be increased. This is a simple and scalable invention design. According to the nitrogen stimulation method of the present invention, the number of air separation units can be reduced. And it can save more energy consumption than the increased number or capacity of the refrigeration unit.

Referring to FIG. 2, it discloses a schematic diagram of monitoring parameters of an air separation unit according to an embodiment of the present invention, which includes: an air temperature (T0) of an air compressor (1), and an air temperature of an SC air cooling tower (2) ( T1), the temperature of the chilled water (T2), the water temperature of the EC water cooling tower (3) (T3), the water temperature of the SC air cooling tower (2) (T4), and the air molecular sieve adsorber (4) Temperature (T5), CO ₂ value (A1) of air outlet molecular sieve adsorber (4), H ₂ O value (A2) of air outlet molecular sieve adsorber (4), chilled water flow rate (F1), and fractionation tower (5) The total amount of nitrogen in the upper tower (F2), the flow rate of nitrogen to the EC water cooling tower (3) (F3), the pressure on the column of the fractionation tower (P1), the level of the EC water cooling tower (3) (L1) and compression Air to the control valve (V10) of the EC water cooling tower (3).

The nitrogen gas stimulation method of the air separation system, the first step is to first reduce the low pressure nitrogen gas to the EC cold source and discharge it to test the influence on the operation of the unit equipment, the safety of the system and the stability of the fractionation balance, and confirm the above parameters. Whether there is any abnormality, the second step is to send the nitrogen extracted from the nitrogen to the nitrogen compressor for compression, and turn on the refrigeration unit, slowly reduce the low-pressure nitrogen gas to the EC cold source to reduce 500~1000NM ³ /H each time, observe 20~30 minutes. The air inside the SC air cooling tower temperature change (T1), the chilled water temperature (T2), the EC water cooling tower (3) water temperature (T3), the SC air cooling tower (2) water temperature (T4 ), the CO ₂ value of the air-out molecular sieve adsorber (4) (A1), the H ₂ O value of the air-out molecular sieve adsorber (4) (A2), and the total nitrogen (F2) of the upper tower of the fractionation column (5) The nitrogen flow rate (F3) of the EC water cooling tower (3), in particular, the CO ₂ value (A1) of the air outlet molecular sieve adsorber (4) and the air temperature (T1) of the outlet air cooling tower (2). When (A1) has a high value or a high peak, the adsorption capacity of the molecular sieve adsorber (4) has decreased, and when (T1) is also high, it represents an increase. The freezing capacity of the freezing unit (10c), when reducing the cold source lost by the exchange of EC nitrogen and EC circulating water, to start the two existing freezer to supplement, the refrigeration capacity of a single starting unit can meet the demand. The two start-up chillers can be connected in parallel or in series to increase the refrigeration capacity. The amount of nitrogen that can be compressed by the nitrogen press (7) of the air separation unit depends on the amount of refrigeration produced by the starter chiller (10c) to compensate for the nitrogen. According to the cooling capacity of the water heat exchange, the important reference indicators for the first and second steps are that the air temperature (T1) of the SC air cooling tower (2) needs to be <10 ° C, and the temperature of the chilled water (T2) needs to be < 9 ° C and the air out of the molecular sieve adsorber (4) CO ₂ value (A1) and the air out of the molecular sieve adsorber (4) H ₂ O value (A2), the risk of the second step may occur, if the air separation unit If the instability causes the machine to trip, the nitrogen press (7) will be tripped, and if the air separation unit trips, it will cause the nitrogen pressure of the other air separation unit (7) and the pressure change of the upper part of the fractionation tower (5). Too large will make the fractionation efficiency poor, start the extra freezer (10c), and the freezer enters The water flow is not enough, which may cause the freezer (10c) to trip. However, if the freezer water flow is increased, the SC defogger located in the SC air cooling tower (2) may not be able to filter the water in the process air. , causing the air to bring water into the molecular sieve adsorber (4), causing the molecular sieve adsorber (4) to be poisoned, resulting in failure.

Therefore, in order to avoid the risk of tripping in actual operation, it is possible to first test how much nitrogen flow (F3) to the EC water cooling tower (3) can be taken when starting the two refrigeration units (10c), and the excess nitrogen is discharged first. After the test, excess nitrogen is sent to the nitrogen press (7) for compression, and the inlet guide vane control of the nitrogen press (7) is set to an upper limit value because the inlet guide vane is controlled (Inlet guide) After setting an upper limit value, if there is a nitrogen generator (7), the total amount of nitrogen gas can be stabilized when the machine is tripped. This can reduce the fluctuation of the tower pressure (P1) on the fractionation tower and control the inlet of the refrigeration unit. The water flow rate makes the water flow sufficient to avoid the freezing unit (10c) tripping, and it can be considered to disassemble the unoperated refrigeration unit located in other air separation units to the air separation unit of this demand.

In addition, in order to reduce the temperature of the cooling water of the air cooling tower, another heat exchange system may be utilized, which is located at the outlet air cooling tower (2), and is used to make the air temperature of the air cooling tower below 10 degrees C. . Alternatively, a cooling system can be utilized which is located at the outflowing EC cooling tower (3) to bring the water temperature of the EC cooling tower below 9 degrees C.

According to the adjustment method of the invention, high-purity nitrogen gas (99.99% N2) can be produced from the top of the fractionation column of the air separation plant, and the nitrogen of the denitrification water pre-cooling system can be extracted by the pipeline configuration connected to the nitrogen compressor. .

The monitoring data of the total monitoring parameters are shown in Figure 3 to Figure 10. The air separation unit (A, B) has improved the process and increased the output of a large amount of nitrogen. Each unit has increased by 30,000 NM ³ /H, which is almost twice the original output. The improvement results can be extended to other air separation units. The overall improvement results are as follows:

Table 1 air separation unit to improve efficiency

The improvement results of this case For the oxygen plant, the total nitrogen production capacity of the A and B air separation units is 70,000 NM ³ /H, which is increased by 60,000 NM ³ /H, reaching 130,000 NM ³ /H. The oxygen workshop has more chips to apply, and the units can be matched with the supply and demand of oxygen, nitrogen and argon gases under different environmental conditions, in order to make favorable different combinations.

Taking the air separation plant related to the present invention as an example, in the results of September, October, November and December of 1998, the nitrogen output was increased by using the A air separation unit, and the air separation unit was not operated, and the unit was saved. The power consumption is as follows: (only the air compressor of the air separation unit is used for power consumption, and the oxygen consumption of the oxygen compressor is not included in the calculation)

The air compressor of the B air separation unit has a high load of 14.2 MW and a normal operation of 80% to 90%.

Power saving of B air substation: 14.2MW × 0.8 × 24H / day × 1.95 yuan / KWH = 530,000 yuan / day.

Stop running for 4 months: 530,000 yuan / day × 120 days = 63.6 million yuan.

Annual Benefits: Estimated use of this improvement case (by increasing the amount of nitrogen in the A and B air separation units), operating in this manner (stopping an air separation unit or B air separation unit) is about 4~ a year. June.

Benefits: 530,000 yuan / day / × 150 days = 79.5 million yuan, which can reduce CO ₂ emissions by 26,092 tons.

Therefore, the energy consumption of 14.2MW for starting a single air separation unit is only 166KW compared to multi-starting a refrigeration unit, which can save considerable energy consumption.

While the present invention has been described in its preferred embodiments, it is not intended to limit the scope of the invention, and various modifications and changes can be made without departing from the spirit and scope of the invention. Therefore, the scope of the invention is defined by the scope of the appended claims.

1. . . Air compressor

2. . . SC air cooling tower

2a. . . SC air cooling tower upper part

2b. . . SC air cooling tower middle

2c. . . SC air cooling tower lower part

2d. . . SC air cooling tower bottom

3. . . EC water cooling tower

3a. . . EC water cooling tower lower part

3b. . . Upper part of EC water cooling tower

3c. . . EC water cooling tower bottom

4. . . Molecular sieve adsorber

5. . . Fractionation tower

6. . . Main heat exchanger

7. . . Nitrogen press

8. . . Expansion topping machine

9. . . High temperature air

10a. . . Water pump

10b. . . Water pump

10c. . . Refrigeration unit

11. . . Normal temperature cooling water

12. . . Low temperature cooling water

12a. . . Normal temperature cooling water

14a. . . Waste nitrogen

14b. . . Nitrogen

14c. . . oxygen

15. . . Oxygen press

T0. . . Air temperature of the air compressor

T1. . . Out of the air temperature of the SC air cooling tower

T2. . . Chilled water temperature

T3. . . Out of the water temperature of the EC water cooling tower

T4. . . Water temperature into the SC air cooling tower

T5. . . Air out of the molecular sieve adsorber

A1. . . CO ₂ value of air out molecular sieve adsorber

A2. . . H ₂ O value of air out molecular sieve adsorber

F1. . . Chilled water flow

F2. . . The total amount of nitrogen in the tower on the fractionation tower

F3. . . Nitrogen flow to the EC water cooling tower

P1. . . Tower pressure on the fractionation tower

L1. . . EC water cooling tower level value

V10. . . Compressed air to EC water cooling tower control valve

Figure 1 is a flow chart of an air separation plant of a conventional air separation plant.

2 is a schematic diagram of monitoring parameters of an air separation unit according to an embodiment of the present invention.

FIG. 3 to FIG. 10 are monitoring data diagrams of various monitoring parameters of the present invention.

T0. . . Air temperature of the air compressor

T1. . . Out of the air temperature of the SC air cooling tower

T2. . . Chilled water temperature

T3. . . Out of the water temperature of the EC water cooling tower

T4. . . Water temperature into the SC air cooling tower

T5. . . Air out of the molecular sieve adsorber

A1. . . CO ₂ value of air out molecular sieve adsorber

A2. . . H ₂ O value of air out molecular sieve adsorber

F1. . . Chilled water flow

F2. . . The total amount of nitrogen in the tower on the fractionation tower

F3. . . Nitrogen flow to the EC water cooling tower

P1. . . Tower pressure on the fractionation tower

L1. . . EC water cooling tower level value

V10. . . Compressed air to EC water cooling tower control valve

Claims (4)

An air separation plant nitrogen stimulation production method, comprising the steps of: providing an air compressor to supply the required pressure of the process air; providing an air pre-cooling system to cool the high-temperature air after the air compressor is pressurized; providing a molecular sieve adsorber, The process air impurity is filtered; a main heat exchanger is provided to cool the process air and the product of the fractionation tower is recovered; and a fractionation tower is provided, which uses oxygen, nitrogen and argon at different pressures, and has different boiling points, and oxygen, Nitrogen and argon are separated; an expansion flattening machine is provided to provide the coldness required for the entire fractionation process; a plurality of oxygen compressors are provided, and the oxygen product after the fractionation tower is compressed and reheated by the main heat exchanger is provided; a plurality of nitrogen presses, a nitrogen product that is compressed out of the fractionation column and reheated by the main heat exchanger; a nitrogen gas that is reduced in the fractionation column and enters the nitrogen water cooling tower, and the nitrogen split is introduced into another nitrogen press; The refrigeration capacity of the refrigeration unit of the water cooling tower chilled water pipeline can reduce the temperature of the chilled water entering the air cooling tower, which can improve the adsorption capacity of the molecular sieve adsorber. For example, the nitrogen separation method of the air separation plant of claim 1 of the patent scope includes the provision of multiple start-up of a refrigeration unit, and the two refrigeration units may be connected in series or in parallel. The method for increasing nitrogen production in an air separation plant according to claim 1 of the patent scope, further comprising using another heat exchange system to be disposed at the outlet air cooling tower, and for making the air temperature of the air cooling tower below 10 degrees C. The method for increasing nitrogen production in an air separation plant according to claim 1 of the patent application, further comprising: using another cooling system to be disposed at the outlet water cooling tower of the EC, and for using the cooling water temperature of the air cooling tower below 9 degrees C.