JPH0128312B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the startup operation of an air liquefaction separation device, and particularly to the automatic startup of an air liquefaction separation device.

A regenerator or a switching heat exchanger (hereinafter referred to as a switching heat exchanger) and an expansion engine or an expansion turbine (hereinafter referred to as an expansion machine).
The all-low-pressure air separation equipment has an expansion machine that cools and removes moisture and carbon dioxide from the feed air in a switching heat exchanger while simultaneously precipitating the air and liquefying and rectifying the air at low temperatures. It consists of the process of obtaining

The mechanism for removing moisture and carbon dioxide in a switching heat exchanger is to condense and precipitate moisture and carbon dioxide in air compressed to approximately 5 kg/cm ² G at the saturated vapor pressure at that pressure according to the cooling temperature. Attach to the inner wall of the switching heat exchanger. Next, the heat exchanger is switched and the air flow path is switched to a return gas flow path at approximately atmospheric pressure, and the moisture and carbon dioxide precipitated on the inner wall of the heat exchanger are sublimated and purged by the return gas and entrained in the return gas. Release into the atmosphere. This coagulation precipitation and sublimation purge are
It is executed by the difference in saturated vapor pressure due to the pressure of raw material air and the pressure of return gas, but it is affected by the difference in flow rate and temperature of air and return gas, and the temperature and flow rate of air are as shown in Figure 1. A temperature difference (purge limit temperature difference) at which moisture and carbon dioxide can be sublimated and purged is determined by the difference. That is, lines A and a in Figure 1 are related to moisture, lines B and b are related to carbon dioxide gas, and lines A and B are for the case where the amount of air and the amount of return gas are equal (at the time of starting operation of the air separation device). ) and
a and b represent the case where the return gas amount is the amount obtained by subtracting the product amount from the air amount (during steady operation of the air separation device). Therefore, the temperature distribution of this heat exchanger is
It is necessary that each point be within the range of the critical temperature difference, and for example, it is necessary to have a temperature distribution similar to line C. In order to obtain such a temperature distribution, some of the feed air is returned to the cold end of the heat exchanger,
Either a reheat system is provided to extract air from the intermediate section, or an intermediate extraction system is provided to extract part of the raw air from the intermediate section. (Hereinafter, this reheat system or intermediate extraction system will be abbreviated as the reheat system.) The start-up operation of an air liquefaction separation device that has such a switching heat exchanger and an expansion machine that generates the necessary refrigeration is performed during air liquefaction. Since it is necessary to sequentially cool down the temperature of each part of the separator according to a certain standard and to maintain a constant temperature distribution in each part, careful operation is required and a skilled operator is required.

To explain an example of a conventional startup method, in the first step, after starting the expander using a startup system that directs the air coming out of the cold end of the switching heat exchanger directly to the expander inlet, only the switching heat exchanger The cooling operation begins, and the air that has become low temperature through adiabatic expansion in the expander is returned to the return gas side of the full-volume switching heat exchanger, and the temperature of the air exiting from the cold end of the heat exchanger reaches a temperature at which almost no moisture is present ( Continue cooling the heat exchanger to approximately -60°C. In the second stage, the air from the cold end of the heat exchanger and a portion of the air from the expander outlet are passed through a rectifier, a subcooler, a liquefier, etc. to cool these devices. At this time, while adjusting the flow rate of the reheating system to maintain a temperature difference that allows water to be purged and removed in the heat exchanger, the temperature at which carbon dioxide gas does not condense and precipitate at the outlet of the expander (approximately -
Continue cooling to 130℃). Next, as the third step,
Stop cooling each part and rapidly cool only the switching heat exchanger so that carbon dioxide in the air condenses and precipitates inside the heat exchanger. At this time, the flow rate of the reheat system is adjusted so as to maintain a temperature difference at the cold end of the heat exchanger that makes it possible to purge and remove carbon dioxide gas, and the air passing through the expander is liquefied at the outlet of the expander. In order to prevent damage to the switching heat exchanger, the flow control valve installed in the startup system from the cold end of the switching heat exchanger to the expansion machine inlet is operated to proceed with cooling and to ensure that the switching heat exchanger is fully functioning. Set it in a cooled state (for example, a state in which the temperature of the air exiting from the cold end is about -160°C).

Then, in the fourth stage, in order to cool the rectification column, subcooler, liquefier, etc., as in the second stage, air from the cold end of the switching heat exchanger and a part of the air at the expander outlet are used. is sent to the above equipment. At this time, the amount of air supplied is adjusted so that the air temperature at the cold end of the switching heat exchanger does not exceed a predetermined temperature (approximately -160°C).
The air liquefaction separation device is cooled as a whole until liquid air accumulates at the bottom of the lower tower, and cooling is continued until liquid air finally reaches each stage of the rectification tower. At this time as well, the throughput of the expander is adjusted so that the passing air does not liquefy at the outlet of the expander, and the balance of cooling is adjusted. The complicated start-up cooling operation from the first stage to the fourth stage described above was performed manually by skilled operators using remote control and on-site operation, so it was time-consuming to operate, and the start-up operation was performed only by experienced operators. There were some inconveniences such as not being able to.

This invention was made in view of the above circumstances,
The purpose is to provide an air liquefaction separation device that automatically controls each process of the above-mentioned complicated start-up operation and is capable of automatic start-up operation. A flow rate control valve is installed in each of the start-up line from the end to the expander inlet, and a temperature difference controller is installed to detect the temperature difference between the air at the cold end of the switching heat exchanger and the return gas, and a switching heat exchanger is installed. A temperature controller that detects the air temperature at the outlet of the exchanger reheat system, a temperature controller that detects the air temperature at the expander outlet, and a capacity control valve that adjusts the expander capacity installed at the expander inlet. A polygonal converter incorporates the relationship between the temperature difference between the return gas and the air capable of sublimating and removing moisture and carbon dioxide precipitated in the heat exchanger, and controls the temperature difference controller in cascade, and the air temperature at the outlet of the reheating system is adjusted. A program setting device that gives program commands to the temperature controllers to be detected and a changeover switch mechanism that switches the output signals from these temperature controllers are provided, and the detection signals from each temperature controller can be switched or prioritized by program control. , the capacity of the expander is controlled by a temperature controller that controls the flow rate control valve and detects the air temperature at the outlet of the expander to proceed with cooling, and automatically starts the air liquefaction separation device. It is something.

Hereinafter, the present invention will be explained in detail with reference to the drawings. Figure 3 is a schematic configuration diagram showing an example of the air liquefaction separation device of the present invention, in which air compressed to approximately 5 kg/cm ² G is transferred to an automatic switching valve mechanism that switches between an air flow path and a return gas flow path (not shown). By tube 1 and tube 2
The expanded and cooled return gas is fed into the switching heat exchangers 3, 3', passes through pipes 4, 5, and is discharged to the atmosphere via an automatic switching valve mechanism. The air introduced into the switching heat exchangers 3, 3' is
It is cooled by countercurrent heat exchange with the return gas in 3', condenses and precipitates moisture and carbon dioxide, and reaches the pipe 7 via the return valve 6. During startup cooling of the air liquefaction separation device, the air from pipe 7 is divided into three parts, one part of which is divided into three parts: pipe 8, startup system flow control valve 9, and pipes 10, 11, 12.
and 13, expansion turbines 14 and 15
A part of the air passes through the pipe 16, the reheating system flow control valve 17, and the pipe 18, and is then condensed and precipitated in the switching heat exchangers 3 and 3' so that the carbon dioxide gas is purged and removed. In order to obtain a uniform temperature distribution, the heat exchanger is introduced into the reheat system of the switching heat exchanger 3, 3', and is fed through the pipe 19 to the expansion turbine 14, 15. The remaining air passes through pipe 20 and is used to cool the rectification column, liquefier, and supercooler (all not shown), and passes through pipes 21 and 2.
2. It passes through the return valve 6 and returns to the switching heat exchangers 3, 3' as return gas. On the other hand, expansion turbine 1
The air supplied to tubes 4 and 15 expands adiabatically, lowers its temperature, generates cold air, passes through tubes 23, 24, and 25, and is further divided into tubes 27 and 28 by a three-way valve 26. The air passing through cools the rectification tower, etc., returns to the pipe 21, joins with the air from the pipe 28, and returns to the pipe 2.
2, enters the switching heat exchanger 3, 3', where the condensed and precipitated carbon dioxide and moisture are sublimated and purged, and the temperature is raised while exchanging countercurrent heat with the inflowing air. Passes through pipes 2 and 4, passes through an automatic switching valve mechanism,
released into the atmosphere. In the air liquefaction separation apparatus of the present invention configured as described above, the starting operation will be described below.

FIG. 4 shows the temperature changes in each part when the air liquefaction separation device of the present invention is started from room temperature. In the figure, line A indicates the reheat system outlet temperature of the switching heat exchanger 3. The B line represents the inlet temperature of the expansion turbines 14 and 15, the C line represents the outlet air temperature at the cold end of the switching heat exchanger 3, and the D line represents the return gas inlet temperature at the cold end of the switching heat exchanger 3. The E line is the expansion turbine 14,1
5 represents the outlet temperature. At time θ ₁ , feed air is transferred from tubes 1 (and 2) → switching heat exchangers 3, 3' →
Return valve 6 → Pipe 7 → Pipe 8 → Start-up system flow control valve 9 → Pipe 10 → Pipe 11 → Pipe 12 and pipe 13 → Expansion turbine 14 and 15 → Pipe 23 and 24 → Pipe 25 →
It flows through the route of three-way valve 26 → pipe 28 → pipe 22 → return valve 6 → switching type heat exchanger 3, 3' → pipes 4 and 2,
The two expansion turbines 14 and 15 are activated and cooling of the switching heat exchangers 3 and 3' is started. At this point, only the switching heat exchangers 3 and 3' are being cooled, so
As shown in the time θ ₁ →θ ₂ in Figure 4, the switching heat exchanger 3,
3' is rapidly cooled, moisture in the air quickly precipitates inside the switching heat exchangers 3 and 3', and the intrusion of moisture into the air separation device is minimized. . At time θ ₂ , the outlet temperature (C) of the cold end of the switching heat exchanger 3 reaches a temperature t ₁ (approximately −60
℃), this temperature is detected by the temperature detector 29, and based on this detection signal, the three-way valve 26 is opened to the pipe 27 side to cool the entire system of the air liquefaction separation device. In addition, raw air is also made to flow through the pipe 20. This cools the components, valves, piping, etc. of the air liquefaction separation device, and the air returns through the pipe 21. In this cooling process, the precipitated moisture must be sublimated into the return gas and removed so that the switching heat exchangers 3, 3' are not clogged with the precipitated moisture. Therefore, the switching heat exchanger 3,
It is necessary to suppress the temperature difference between the outlet air and the return gas at the cold end of the switchable heat exchanger 3, 3', and the outlet air pipe 7 and the return gas pipe 22 at the cold end of the switchable heat exchanger 3, 3'. A temperature measuring element is provided at the temperature measuring element, and a temperature difference controller 30 detects the temperature difference detected by the temperature measuring element.
Controls the startup system flow rate control valve 9 and the reheat system flow rate control valve 17. That is, the contact 31 of the changeover switch 31
A is connected to the contact point 31b, and a broken line converter 3 is constructed in which the allowable temperature difference for the cold end air temperature, such as the x-line or y-line shown in FIG. 2, is incorporated in advance.
A temperature difference controller 30 compares the allowable temperature difference signal from 2 and the temperature difference, and the startup system flow rate control valve 9 and the reheat system flow rate control valve 17 are controlled based on the comparison result. For example, if the air temperature is -70℃, x
The allowable temperature difference between the lines is approximately 8°C, and if the temperature difference exceeds 8°C, the reheat system flow control valve 1
7 is controlled in the opening direction, and the starting system flow control valve 9 is controlled in the closing direction.

In this way, cooling is continued while controlling the temperature difference between the outlet air at the cold ends of the switching heat exchangers 3, 3' and the return gas, and the temperature at the outlet of the expansion turbines 14, 15 reaches the carbon dioxide precipitation temperature. When the temperature reaches t ₂ (approximately −130℃),
This is detected by the temperature detectors 33 and 34, and at that point θ ₃ , the three-way valve 26 is closed to the pipe 27 side so that the entire amount flows to the pipe 28, and the flow to the pipe 20 is also stopped, thereby switching heat exchange. Only the heat exchanger 3, 3' is rapidly cooled, and the carbon dioxide in the air is removed by the switching heat exchanger 3,
3' so that it quickly coagulates and precipitates.
During this period θ ₃ -θ ₄ as well, the temperature difference is controlled so that it is always kept within the carbon dioxide purge limit temperature difference. In this way, the switching heat exchanger 3,
When the air temperature at the cold end of tube 3' reaches approximately -160°C, carbon dioxide in the air is almost completely deposited in heat exchangers 3 and ₃ ' and removed; ,
Cooling air is flowed through the pipe 27 to the rectification tower and the like to cool them, but this time too, control is performed based on the temperature difference. During this operation, for example at time θ ₅ , when the outlet temperature of the expansion turbines 14, 15 reaches the temperature at which the air liquefies at the outlet (approximately -188°C), this is detected by the temperature detectors 33, 34, and the changeover switch is activated. 3
The contact 35a of the changeover switch 36 is connected to the contact 36b, the contact 31c of the changeover switch 31 is connected to the contact 31a, and the contact 31d is connected to the contact 31a. The reheat system flow control valve 17 is controlled by outlet temperature controllers 37 and 38 of the expansion turbines 14 and 15, and liquefaction of air at the exits of the expansion turbines 14 and 15 is prevented. This operation increases the flow rate of the reheating system and raises the inlet temperature of the expansion turbines 14 and 15, and works in the direction of reducing the temperature difference between the cold ends of the switching heat exchangers 3 and 3'. The temperature difference control described above may be removed.

As the cooling progresses in this manner, liquid air begins to be generated in the lower cylinder connected to the pipe 27 at time θ ₆ .

Then, at time θ ₇ , when the temperature of the reheat system tube 19 drops to a temperature (approximately -130°C) at which carbon dioxide gas in the air does not precipitate in the middle part of the heat exchangers 3, 3'', this is detected by a temperature detector. 39, the contact 31e of the changeover switch 31 is connected to the contact 31a, and the startup system flow control valve 9 and the reheat system flow control valve 17 are controlled by a reheat system outlet temperature controller 40.This temperature controller 40 is set in cascade by the program setting unit 41, and is a startup system flow control valve so that when the temperature of the pipe 19 is about -130°C, it is maintained at that state, and when this temperature decreases, the flow rate of the reheat system is reduced. 9 is controlled in the opening direction, and the reheat system flow rate control valve 17 is controlled in the closing direction.This operation lowers the inlet temperature of the expansion turbines 14 and 15, and also lowers the outlet temperature.
Among the expansion turbines 14 and 15 operated in the same unit, the capacity of one expansion turbine, for example 14, which is determined in advance to be stopped preferentially, is reduced to reduce the cold generation and prevent a drop in the inlet temperature. do. This includes the contact 35c of the changeover switch 35.
to the contact 35a, and the contact 36c of the changeover switch 36
is connected to the contact point 36a, and the capacity adjustment valves 42, 43 are controlled by the expansion turbine outlet temperature controllers 37, 38. Note that instead of the capacity adjustment valves 42 and 43, the blade openings of the variable nozzles of the expansion turbines 14 and 15 may be changed, or partial admission valves or the like may be used.

As cooling progresses through the above operations and liquefied gas begins to accumulate in the condenser etc. of the air liquefaction separation device, the amount of cold generated by the expansion turbines 14 and 15 becomes small, and one of the expansion turbines 14 is stopped, and then At time θ ₈ , the reheat system outlet temperature controller 40
Using the program setting device 41, change the adjustment set temperature from -130°C to the rated value during steady operation of about -100°C at a constant temperature increase rate of 3°C/h to 10°C/h, and then start. System flow rate control valve 9, reheat system flow rate control valve 17
Follow this and control the reheating system outlet temperature -
Raise the temperature to 100℃ and change from the starting cold state to a steady cold state to complete the startup.

The above explanation is about starting the air liquefaction separation device from a normal temperature state, but the operation is different when starting the air liquefaction separation device when the air liquefaction separation device is in a low temperature state. Fig. 5 shows an example of the temperature drop in each part when starting the air liquefaction separation device in a low temperature state, but when starting from room temperature, the outlet temperature of the expansion turbines 14, 15 ( At the time θ ₃ when the E line) reaches the temperature t ₂ at which carbon dioxide gas is precipitated, the reheating system outlet temperature (A line) of the switching heat exchangers 3 and 3' is still quite high as the temperature t ₃ , but it is at a low temperature. When the expansion turbines 14 and 15 are started at time Θ ₁ , the temperature of each part approaches and is rapidly cooled, causing the carbon dioxide precipitation temperature to drop.
At t ₂ , the outlet temperature of the expansion turbines 14 and 15 (e line)
The reheating system outlet temperature (line a) may reach the temperature during steady operation (approximately -100°C) at time Θ ₂ before the temperature is reached. In this case, the temperature sensor ₃₉
Based on this detection, the reheating system outlet temperature controller 40 is set to approximately -100°C by the program setting device 41, the contact 31a of the changeover switch 31 is connected to the contact 31e, and the startup system flow rate is adjusted. The valve 9 and the reheat system flow rate control valve 17 are connected to the reheat system outlet temperature controller 4.
0 keeps the reheat system outlet temperature constant (approximately -100℃)
While maintaining the temperature balance of the entire system, cooling is continued until the point Θ ₃ when the outlet temperatures of the expansion turbines 14 and 15 reach the temperature t ₂ . Also,
In the case of startup from a low temperature state, the expansion turbine 141
In many cases, the outlet temperature of the expansion turbine 14 reaches the temperature at which the air liquefies (-188°C) at the final point of the startup process. The capacity control valve 42 is controlled by the outlet temperature controller 37 to adjust the capacity of the expansion turbine 14 so that the outlet temperature of the expansion turbine 14 does not reach the air liquefaction temperature -188°C. When the temperature of the entire air liquefaction separation device approaches a steady state due to the above operations, the expansion turbine 1
The outlet temperature of 4 and 15 is stably equal to the air liquefaction temperature (-
188℃), and the entire system becomes stable.
From this point on, the time until liquefied gas is stored in the condenser is set by a timer, and by the _end of this set time, the reheat system outlet temperature controller is 40 adjustment set temperature is set at a constant temperature increase rate (3
℃/h ~ 10℃/h), change from -130℃ to the rated value during steady operation -100℃, and set the reheat system outlet temperature to -100℃.
The air liquefaction separator is brought to a steady state by raising the temperature to
Startup from low temperature state is completed. Note that the a line, b line, c line, d line, and e line in Fig. 5 are the fourth line, respectively.
These correspond to lines A, B, C, D, and E in the figure.

As explained above, the air liquefaction separation device of the present invention includes flow rate control valves in the reheat system path of the switching heat exchanger and the startup system path from the cold end of the switching heat exchanger to the expander inlet. Additionally, a temperature controller is installed to detect the temperature difference between the air at the cold end of the switching heat exchanger and the return gas, a temperature controller to detect the air temperature at the reheat system outlet, and a temperature controller to detect the air temperature at the expander outlet. A temperature controller to detect the temperature, a capacity control valve installed at the inlet of the expander to adjust the capacity of the expander, and air and return gas capable of sublimating and removing moisture and carbon dioxide precipitated in the switching heat exchanger. A linear converter that incorporates the relationship between temperature differences and controls the temperature controller in a cascade manner; a program setting device that provides program commands to the temperature controller that detects the air temperature at the outlet of the reheating system; It has a changeover switch mechanism that switches or prioritizes the detection signals from each temperature controller under program control to control the flow rate control valve and the capacity control valve, and maintains the temperature balance of the main parts of the air liquefaction separation device. As the air liquefaction separator is automatically started up, each step of the complicated start-up operation of the air liquefaction separation device can be automatically controlled, automatic start-up operation is possible, and operation is simplified. This has the advantage that even an inexperienced operator can start up and operate.

[Brief explanation of drawings]

Figure 1 is a graph showing the critical temperature difference for sublimation purge of moisture and carbon dioxide in a switching heat exchanger.
Fig. 2 is a graph showing the temperature difference between the return gas and the air that can sublimate and remove moisture and carbon dioxide set in the polygon converter, and Fig. 3 is a schematic configuration diagram showing an example of the air liquefaction separation device of the present invention. , Fig. 4 is a graph showing the temperature distribution of the main parts of the air liquefaction separation device during start-up operation from a normal temperature state, and Fig. 5 is a graph showing the temperature distribution of the same main parts during start-up operation from a low-temperature state. It is. 3, 3'...Switching heat exchanger, 9...Start-up system flow rate control valve, 14, 15...Expansion turbine, 17...
...Reheat system flow rate control valve, 30...Temperature difference controller, 3
1... Selector switch, 32... Broken line converter, 35
...Selector switch, 36...Selector switch, 3
7, 38... Expansion turbine outlet temperature controller, 40
...Reheat system outlet temperature controller, 41...Program setting device, 42, 43...Capacity control valve.

Claims (1)

[Claims] 1. In an air liquefaction separation device equipped with a regenerator or switching heat exchanger, an expander, a rectification column, etc.
Flow rate control valves are provided in the reheat system or intermediate extraction system of the regenerator or switching heat exchanger, and in the startup system from the cold end of the regenerator or switching heat exchanger to the expander. A temperature difference controller that detects the temperature difference between the air temperature at the cold end of the heat exchanger and the return gas temperature, and a regenerator or the cold end of the switching heat exchanger for cascade control of the temperature difference controller. A polygonal converter that incorporates the temperature difference between the air temperature and the return gas temperature that can sublimate and remove moisture deposited in a regenerator or switching heat exchanger and carbon dioxide gas, and a regenerator or switching heat exchanger. A temperature controller that detects the air temperature at the outlet of the reheat system or intermediate extraction system of the exchanger, a program setting device that gives program commands to the temperature controller at the outlet of the reheat system, and a program setting device that detects the air temperature at the expander outlet. a capacity control valve provided at the inlet of the expander to adjust the capacity of the expander, and a changeover switch mechanism to switch the output signals from these temperature controllers,
When starting up the device, the detection signals from each of the temperature controllers are switched or prioritized by program control to control each of the flow rate control valves, and the temperature controller that detects the air temperature at the outlet of the expander controls the temperature of the expander. An air liquefaction separator characterized in that it is configured to control capacity.