JP3300898B2 - Nitrogen production apparatus and its operation method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for producing nitrogen and a method of operating the same, and more particularly, to a method for storing liquefied nitrogen derived from the upper part of a single rectification column in a liquefied nitrogen storage tank. The present invention relates to a nitrogen production apparatus having a configuration for deriving the gas in response to fluctuations in demand, vaporizing it in a condenser, and sending it out, and a method of operating the same.

[0002]

2. Description of the Related Art FIG. 2 shows an example of a conventional nitrogen production apparatus. In this nitrogen production apparatus, the raw material air compressed and purified through a compressor 51, a cooler 52, and an adsorber 53 is cooled in a main heat exchanger 1 and introduced into a lower portion of a single rectification column 2, where the air is cooled. Liquefaction rectification is performed in the rectification column 2 to separate nitrogen gas at the top of the column.

[0003] The nitrogen gas separated at the top of the single rectification column 2 is
The heat is exchanged with the oxygen-enriched liquefied air introduced into the condenser 4 from the bottom of the single rectification column 2 through the tube 5 through the pipe 3 through the pipe 3 and the liquefied nitrogen described below to condense and liquefy. It becomes nitrogen and is introduced as a reflux liquid from the pipe 6 to the top of the single rectification column 2. The liquefied nitrogen introduced into the single rectification column 2 as a reflux liquid is:
After temporarily accumulating in a liquid reservoir (not shown) at the top of the tower, it flows downward toward the bottom of the tower.

[0004] A part of the liquefied nitrogen introduced as the reflux liquid is supplied to a liquefied nitrogen outlet pipe 7 provided above the single rectification column 2.
Is derived from the liquefied nitrogen storage tank 8.
The liquefied nitrogen in the liquefied nitrogen storage tank 8 is withdrawn to a pipe 9 in accordance with the demand amount of the product nitrogen gas, and is heat-exchanged with the nitrogen gas in the condenser 4 to be vaporized to become product nitrogen gas. The gas is sent from the nitrogen gas delivery pipe 10 to the demand destination 11.

[0005] The liquefied nitrogen storage tank 8 is provided with a product liquefied nitrogen derivation pipe 12 for deriving liquefied nitrogen as a product so that the product liquefied nitrogen can be sent out to the lorry 14 via the product liquefied nitrogen storage tank 13. It is configured.

On the other hand, a predetermined amount of the oxygen-enriched air which is led out from the bottom of the single rectification column 2 to the pipe 5 and vaporized in the condenser 4 is mixed with the raw air in the reheat circuit 1 a of the main heat exchanger 1. After the exchange is performed, the temperature is raised to the intermediate temperature, and then introduced into the expansion turbine 15, expanded to generate cold, and is again introduced into the main heat exchanger 1 as raw material air cooling.

In the nitrogen production apparatus having such a configuration, a pressure gauge for detecting the pressure in the product nitrogen gas delivery pipe 10 is used as control means for increasing / decreasing the delivery rate in accordance with the usage amount of nitrogen gas at the destination. 21 and a product delivery valve 2 for adjusting the flow rate of nitrogen gas delivered to the product nitrogen gas delivery pipe 10
The controller 23 opens and closes the product delivery valve 22 according to the pressure detected by the pressure gauge 21 and adjusts the flow rate of the product nitrogen gas according to the demand.

For example, when the amount of nitrogen gas used by a demand destination increases, the pressure in the product nitrogen gas delivery pipe 10 decreases in accordance with the increase, so that the pressure gauge 21 detects this and the controller 23 controls the product. The delivery valve 22 is operated in the opening direction to increase the flow rate in the pipe.

As described above, when the amount of product nitrogen gas delivered increases and the amount of liquefied nitrogen vaporized in the condenser 4 increases, the required amount of nitrogen gas as a heating source for vaporizing the liquefied nitrogen increases. Will also increase. That is, the single rectification column 2
The amount of nitrogen gas which is introduced into the condenser 4 through the pipe 3 from the top and exchanges heat with the liquefied nitrogen which becomes the above-mentioned product nitrogen gas increases. The amount of liquefied nitrogen introduced as a reflux liquid at the top of the column will increase.

[0010] Due to the increase of the liquefied nitrogen, that is, the increase of the amount of the reflux liquid, the amount of cooling in the single rectification column 2 becomes excessive, which appears as a rise in the liquid level of the oxygen-enriched liquefied air accumulated at the bottom of the column.

For this reason, a liquid level gauge 24 is provided at the bottom of the single rectification column 2, and the level of the liquid level detected by the liquid level gauge 24 changes the level of the bypass valve 25 of the expansion turbine 15. It is configured to control the opening degree and adjust the amount of cold generation.

As described above, in the conventional nitrogen production apparatus, an increase or decrease in the amount of cooling caused by a fluctuation in demand for product nitrogen gas is detected by a change in the liquid level at the bottom of the tower, and the amount of cooling generated in the expansion turbine 15 is adjusted. I was

[0013]

However, in the conventional control described above, the amount of the reflux liquid in the single rectification column 2 changes with the change in the amount of product nitrogen gas supplied, and the rectification conditions fluctuate. However, it took a long time for the product nitrogen gas delivery rate to fluctuate and emerge as a change in the liquid level at the bottom of the column, making it difficult to perform appropriate control and causing the entire process to be unstable. .

Further, as described above, when the amount of product nitrogen gas delivered is large, the amount of cooling in the single rectification column 2 becomes excessive, so that the throughput of the expansion turbine 15 is reduced and the apparatus itself is used. Is a light load operation, and when the amount of product nitrogen gas delivered is small, the amount of cooling is insufficient, so that the processing amount of the expansion turbine 15 increases and the apparatus itself becomes a high load operation.

Since the specifications of the apparatus are set based on high-load operation, the capacity of the apparatus is not fully utilized during the light-load operation, resulting in waste of power consumption. Become.

On the other hand, in the liquefied nitrogen storage tank 8, a certain amount of liquefied nitrogen is introduced from the upper part of the single rectification column 2 through the liquefied nitrogen outlet pipe 7 by the flow meter 26 and the flow control valve 27. The amount of liquid stored will fluctuate as the amount of product nitrogen gas delivered increases or decreases. For example, when the usage amount of product nitrogen gas increases and the amount of liquefied nitrogen extracted increases, the storage amount decreases, and when the usage amount of product nitrogen gas decreases, the storage amount increases.

Therefore, when the use amount of the product nitrogen gas is larger than usual, priority is given to the delivery of the nitrogen gas as the main product, so that the amount of liquid sent from the product liquefied nitrogen outlet pipe 12 to the product liquefied nitrogen storage tank 13 is reduced. In some cases, the liquid liquefied nitrogen cannot be shipped because the liquid supply must be stopped or the liquid supply must be stopped. In addition, it was difficult to reliably predict fluctuations in demand for product nitrogen gas, so that lorries for transporting liquefied nitrogen could not be dispatched systematically.

Further, as described above, when the amount of the product nitrogen gas used is large, the operation is a light load operation, and although the apparatus has the ability to produce liquefied nitrogen,
You are not making full use of this ability.

Therefore, according to the present invention, it is possible to carry out a stable operation utilizing the capacity of the apparatus while increasing or decreasing the amount of the product nitrogen gas to be delivered in accordance with the usage amount of the demand destination in the same manner as in the prior art. An object of the present invention is to provide a nitrogen production apparatus capable of stably producing nitrogen and a method of operating the same.

[0020]

In order to achieve the above-mentioned object, a nitrogen production apparatus of the present invention comprises a single rectification column for compressing, purifying and liquefying and separating raw material air, and a single rectification column above the single rectification column. A condenser for liquefying the nitrogen gas by heat exchange between the separated nitrogen gas and the oxygen-enriched liquefied air separated at the bottom of the rectification column,
A liquefied nitrogen outlet pipe for liquefying in the condenser and introducing a part of the liquefied nitrogen introduced into the single rectification column, a liquefied nitrogen storage tank for storing the derived liquefied nitrogen, and liquefied nitrogen from the liquefied nitrogen storage tank A product nitrogen gas delivery pipe which is delivered and introduced into the condenser, and is exchanged with heat after being vaporized by heat exchange with the nitrogen gas,
A valve for detecting the pressure in the product nitrogen gas delivery pipe and adjusting the product nitrogen gas delivery amount, and a product liquefied nitrogen outlet pipe for leading liquefied nitrogen in the liquefied nitrogen storage tank to the product liquefied nitrogen storage tank as product liquefied nitrogen. In the nitrogen production apparatus provided, a flow meter is provided on the product nitrogen gas delivery pipe, and a flow control valve for controlling a flow rate of the liquefied nitrogen discharge pipe according to the flow rate is provided.

The operation method of the present invention is the operation method of the nitrogen production apparatus having the above-mentioned configuration, wherein the flow rate of the product nitrogen gas detected by the flow meter is changed, preferably the flow rate change obtained by the average flow rate every predetermined time. In controlling the flow rate of the liquefied nitrogen outlet pipe with the flow rate control valve, the flow rate control is performed after detecting the change in the flow rate of the product nitrogen gas, detecting the change in the flow rate of the product nitrogen gas, and then performing the liquefaction in the single rectification column. Until the amount of nitrogen changes
The method is characterized in that a predetermined time difference for adjusting the time delay at the time is provided.

[0022]

[Operation] According to the above apparatus configuration, even if the amount of liquefied nitrogen introduced from the condenser to the rectification column increases or decreases due to fluctuations in the demand for product nitrogen gas, the amount of liquefied nitrogen discharged from the liquefied nitrogen discharge pipe can be reduced. By adjusting, the amount of the reflux liquid flowing down the rectification column can be kept substantially constant, and a stable operation state can be maintained. In addition, even when the amount of product nitrogen gas delivered is large and the amount of liquefied nitrogen derived from the liquefied nitrogen storage tank increases, the amount of liquefied nitrogen derived from the upper part of the single rectification column by the liquefied nitrogen discharge pipe also increases. In addition, the product liquefied nitrogen can be supplied stably.

Further, according to the method of the present invention, the amount of nitrogen gas liquefied in the condenser changes after the amount of product nitrogen gas delivered changes, and the amount of liquefied nitrogen introduced into the single rectification column changes. Can be adjusted, so that a change in the amount of liquefied nitrogen actually introduced into the single rectification column and a change in the amount of liquefied nitrogen derived from the liquefied nitrogen outlet pipe can be made to correspond, It is possible to minimize the change in the amount of liquid.

Further, by obtaining the change in the delivery amount of the product nitrogen gas by the average flow rate every predetermined time, useless movement of the control system can be suppressed, and stable control can be performed.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in more detail with reference to an embodiment shown in the drawings. The same elements as those of the conventional example shown in FIG. 2 are denoted by the same reference numerals, and detailed description thereof will be omitted.

The nitrogen production apparatus shown in this embodiment is the same as that shown in FIG.
The product nitrogen gas delivery pipe 1
And a flow control valve for controlling the flow rate of liquefied nitrogen flowing through the liquefied nitrogen outlet pipe 7, that is, the amount of liquefied nitrogen discharged from the upper part of the single rectification column 2. A main controller 32 for setting the opening of the flow rate control valve 31 based on the flow rate detected by the product nitrogen gas flow meter 30; and a liquefied nitrogen for detecting the flow rate of liquefied nitrogen flowing through the liquefied nitrogen outlet pipe 7. A flow meter 33 and a sub-controller 34 for limiting the opening of the flow control valve 31 based on the detected value of the liquefied nitrogen flow meter 33 are provided.

At the end of the product nitrogen gas delivery pipe 10, a product flow control valve 35 controlled by the main controller 32 and a discharge valve are provided to control the flow rate of the product nitrogen gas and to stably operate the apparatus. A valve 36 is provided.

In the above configuration, when the amount of nitrogen gas used by the demander 11 increases, the pressure of the product nitrogen gas delivery pipe 10 first decreases as in the prior art.
Is detected, the controller 23 opens the product delivery valve 22 and increases the amount of liquefied nitrogen derived from the liquefied nitrogen storage tank 8.

When the product delivery valve 22 is opened and the flow rate of the nitrogen gas flowing through the product nitrogen gas delivery pipe 10 increases, the flow rate detected by the flow meter 30 is input to the main controller 32.
The main controller 32 collects the inputs at regular intervals, calculates an average flow rate, compares the average flow rate with the previously calculated average flow rate, and calculates an increase in the flow rate. The main controller 32 is set so as to correct the temperature and pressure for the flow rate data and to process the flow rate data under certain conditions.

Next, the main controller 32 calculates the amount of liquefied nitrogen to be led out of the single rectification column 2 through the liquefied nitrogen outlet pipe 7 in accordance with the flow rate of the product nitrogen gas. The amount is conveyed to the sub-controller 34, and the flow control valve 31 is operated in the opening direction via the sub-controller 34 to increase the amount of liquefied nitrogen derived from the single rectification column 2.

Conversely, when the amount of product nitrogen gas delivered decreases, control is performed in the opposite direction to that described above, and the amount of liquefied nitrogen derived from the single rectification column 2 decreases.

Further, when performing the above control,
The main controller 32 adjusts the time delay from the change in the amount of the product nitrogen gas delivered to the change in the amount of liquefied nitrogen gas in the condenser 4 to the change in the amount of liquefied nitrogen in the single rectification column 2. For this purpose, a control signal is output to the sub-controller 34 with a delay of a preset time, for example, about 2 minutes. This time adjustment is performed by setting a time suitable for the apparatus according to the structure of the condenser 4 and the single rectification column 2, the average throughput, and the like. Can be set to

Further, as described above, by determining the flow rate change by comparing the average flow rate for a certain period of time, for example, one minute, it is possible to prevent a rapid follow-up reaction due to a variation in the amount of nitrogen gas used, thereby achieving stable control. It can be carried out.

In addition, the main controller 32 controls the opening and closing of the product flow control valve 35 and the discharge valve 36 in order to control the flow rate of the product nitrogen gas according to the specifications of the apparatus. That is, when the amount of nitrogen gas used by the demand destination 11 exceeds the maximum amount set in the apparatus, the product flow control valve 35 is opened when the flow rate detected by the flow meter 30 reaches the maximum value. Limit the temperature so that no more nitrogen gas flows.

If the demand for the product nitrogen gas becomes extremely small, the amount of liquefied nitrogen flowing through the condenser 4 will decrease, resulting in insufficient cooling. In this case, the discharge valve 36 is opened. A part of the product nitrogen gas is released, and liquefied nitrogen in the liquefied nitrogen storage tank 8 is introduced into the condenser 4 to replenish the cold.

On the other hand, in the sub-controller 34, the minimum flow rate corresponding to the product liquefied nitrogen production amount is set in order to stably supply the product liquefied nitrogen to the product liquefied nitrogen storage tank 13. Regardless of the delivery amount, a certain amount or more of liquefied nitrogen is always taken out from the single rectification column 2. At the same time, the maximum amount of liquefied nitrogen that can be derived from the single rectification column 2 is also set in the sub-controller 34, and the flow rate of liquefied nitrogen detected by the liquefied nitrogen flow meter 33 determines the range between the minimum flow rate and the maximum flow rate. If it exceeds, the opening degree of the flow control valve 31 is limited, and the result is fed back to the main controller 32 to change the product nitrogen gas delivery amount or release amount.

For example, when the product nitrogen gas increases rapidly and the liquefied amount of nitrogen gas in the condenser 4 increases, and the pressure of the single rectification column 2 and the pressure of the liquefied nitrogen storage tank 8 are reversed, In order to prevent the liquefied nitrogen in the liquefied nitrogen storage tank 8 from flowing back to the single rectification column 2, the minimum flow rate is set, and the timer detects that this set value continues for a certain period of time and detects the flow rate. It also has a function of fully closing the control valve 31.

As described above, by linking the amount of product nitrogen gas delivered and the amount of liquefied nitrogen taken out from the single rectification column, the amount of reflux liquid in the single rectification column can be kept substantially constant. And the vehicle can be driven in a stable state. Also,
Since there is almost no change in the reflux liquid, the liquid level of the oxygen-enriched liquefied air that accumulates at the bottom of the tower is also small, and control of the expansion turbine 15 is easy, so that efficient operation can be performed. Moreover, since the product liquefied nitrogen can be produced stably, the delivery of lorries for transportation can be planned and the production can be significantly increased.

Although the above description has been made with reference to an example of a nitrogen production apparatus of a type in which a rectification tower and a condenser are separately installed, the present invention relates to a type in which a rectification tower and a condenser are integrally formed. The same can be applied to the above device.

[0040]

As described above, according to the present invention,
Even if the output amount of product nitrogen gas changes according to demand, by changing the amount of liquefied nitrogen derived from the single rectification column, the amount of reflux liquid in the single rectification column can be kept substantially constant. ,
Stable operation can be performed, and production of liquefied nitrogen can be increased.

In addition, after the flow rate of the product nitrogen gas is changed and before the liquefied nitrogen discharge amount is changed , the liquefaction in the single rectification column is performed.
By providing a predetermined time difference for adjusting the time delay until the amount of nitrogen changes, it is possible to perform control suitable for the operating state. Further, by comparing the change in the flow rate of the product nitrogen gas with the average flow rate at predetermined time intervals, it is possible to prevent a sudden reaction of the control system and perform stable control.

[Brief description of the drawings]

FIG. 1 is a system diagram of a nitrogen production apparatus showing one embodiment of the present invention.

FIG. 2 is a system diagram showing an example of a conventional nitrogen production apparatus.

[Explanation of symbols]

1: Main heat exchanger 2: Single rectification column 4: Condenser 7
... liquefied nitrogen outlet pipe 8 ... liquefied nitrogen storage tank 10 ... product nitrogen gas delivery pipe 1
3: Product liquefied nitrogen storage tank 21: Pressure gauge 22: Product delivery valve 23: Controller
24: Level gauge 30: Product nitrogen gas flow meter 31: Flow control valve 3
2 ... Main controller 33 ... Liquid nitrogen flow meter 34 ... Sub controller 35 ... Product flow control valve

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) F25J 1/00-5/00

Claims (3)

(57) [Claims] 1. A single rectification column for compressing, purifying and liquefying and separating raw material air, a nitrogen gas separated at the top of the single rectification column and an oxygen-enriched liquefied air separated at the bottom of the rectification column. A condenser for liquefying the nitrogen gas by heat exchange, a liquefied nitrogen outlet pipe for extracting a part of the liquefied nitrogen liquefied by the condenser, a liquefied nitrogen storage tank for storing the liquefied nitrogen derived, Liquefied nitrogen is led out from the nitrogen storage tank, introduced into the condenser, heat-exchanged with the nitrogen gas, vaporized and sent out, and the product nitrogen is detected by detecting the pressure in the product nitrogen gas sending pipe. In a nitrogen production device comprising a valve for adjusting the gas delivery amount and a product liquefied nitrogen outlet pipe for leading liquefied nitrogen in the liquefied nitrogen storage tank as product liquefied nitrogen to the product liquefied nitrogen storage tank, the product nitrogen gas delivery pipe In addition to providing a flow meter, And a flow control valve for controlling a flow rate of the liquefied nitrogen discharge pipe. 2. The method according to claim 1, wherein the flow control valve controls the flow rate of the liquefied nitrogen discharge pipe based on a change in the flow rate of the product nitrogen gas detected by the flow meter. The flow control is performed until the amount of liquefied nitrogen in the single rectification column changes after detecting a change in the flow rate of the product nitrogen gas.
A method for operating a nitrogen production apparatus, characterized in that the method is performed by providing a time difference for adjusting a time delay in the apparatus. 3. The method according to claim 2, wherein the change in the flow rate of the product nitrogen gas is obtained by an average flow rate every predetermined time.