JPS631481B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thermosiphon type vaporizer, and more particularly to a method of operating a thermosiphon type vaporizer.

An example of a flow sheet for a conventional thermosyphon type vaporizer is shown in FIG. This vaporizer is composed of a vaporizer and control equipment, each of which is a combination of an evaporating drum 1 and a reboiler (heat exchanger) 2. The evaporation drum 1 has an inlet pipe 3 for the liquid to be vaporized at the upper side of the drum, an outlet pipe 4 for the vaporized vapor at the top of the tower,
An inlet pipe 5 of the reboiler 2 connected to the bottom of the reboiler 2 is attached to the bottom of the evaporation drum 1, and an outlet pipe 6 of the reboiler connected to the top of the reboiler 2 is attached to the side of the evaporation drum 1. . In addition, the inlet pipe 3 has an inlet flow rate control valve 7, and the outlet pipe 4
is provided with an outlet flow rate control valve 8.

The reboiler 2 is a multi-tubular heat exchanger, in which liquid and steam to be vaporized pass through the inside of the tube, and a heat medium (steam, hot water, etc.) passes through the outside of the tube. 9 and 10 are an inlet pipe and an outlet pipe for the heat medium, respectively. 11
12 is a liquid level gauge for detecting the liquid level in the evaporating drum 1;
is a liquid level control device for adjusting the liquid level height of the evaporation drum 1, and controls the opening degree of the inlet flow rate control valve 7. Reference numeral 13 designates a pump for sending the liquid to be vaporized, reference numeral 14 designates a heat medium tank, and reference numeral 15 designates a heat medium pump that sends the heat medium in the heat medium tank 14 to the reboiler 2. Furthermore, 16 is a pressure gauge for detecting the pressure inside the evaporating drum 1, and 17 is a pressure control device for adjusting the pressure inside the evaporating drum 1 to a predetermined value, which controls the opening degree of the heat medium flow control valve 18. .

In such a conventional process, the liquid to be vaporized is sent to the evaporation drum 1 by the liquid sending pump 13, enters the reboiler 2 through the inlet pipe 5, is heated by a heat medium, and a part of the liquid is converted into steam. The steam once returns to the evaporation drum 1 through the outlet pipe 6, and is led out of the system via the outlet pipe 4. In addition, after the liquid that was not evaporated in the reboiler 2 returns to the evaporation drum 1,
It is recirculated to the reboiler 2 again together with the liquid that came in later and is evaporated. At this time, the liquid level controller 12 controls the opening of the inlet flow rate control valve 7 so that the liquid level in the drum 1 is detected by the liquid level gauge 11 and the liquid level is kept constant at the set value. Adjust and control the inlet liquid flow rate. Further, the pressure control device 17 adjusts the opening degree of the heat medium flow control valve 18 to control the heat medium flow rate so as to maintain the pressure inside the drum 1 at a predetermined value. Thereby, the amount of liquid evaporated in the reboiler 2 is controlled, and the pressure within the evaporation drum 1 can be maintained at a predetermined value.

Conventionally, the vaporization process described above has mostly been operated at the rated value of the vaporization capacity, and even when the amount of evaporation is reduced, it is about 70 to 80% of the rated value. In this case, for stable operation of the apparatus, it is necessary to operate the apparatus so that the circulating flow rate from the evaporating drum 1 to the reboiler 2 is a certain value or higher. Here, as shown in Figure 2, the circulating flow rate is 70~80% of the heat load from 100% to the heat load from the heat medium in reboiler 2.
There is almost no decrease even when the value is lowered to . Therefore, operation when the evaporation amount is reduced to 70 to 80% of the rated value is as follows.
As described above, the liquid level in the evaporating drum 1 can be stabilized by keeping it constant.

However, recently, demands for energy conservation have increased, and the amount of steam required at the outlet of the vaporizer has been increased from the rated value of 20.
It is now necessary to drive at a reduced capacity of 30%. However, in the conventional method described above, when the heat load drops to 20 to 30%, as shown by the solid line in Figure 2, the circulating flow rate decreases extremely, and in areas where the heat load is low, the circulating flow rate becomes 0. A problem arises in that the operation becomes unstable.

As described above, the problem with the conventional process is that when the heat load is small, that is, when the amount of liquid evaporated is small, the circulation flow rate decreases rapidly, and when the heat load is further reduced, circulation stops.

The purpose of the present invention is to improve the drawbacks of the conventional process, and to control the inlet liquid flow rate so as to increase the liquid level in the evaporating drum by a predetermined amount in accordance with the reduction in the heat load on the liquid evaporated in the reboiler. However, when the heat load becomes small, the circulation flow rate from the evaporation drum to the reboiler is increased to ensure stable operation.

The present invention detects, for example, the flow rate of heat medium to a reboiler, and adjusts the opening degree of an inlet flow rate control valve so as to increase the liquid level in the evaporation drum in accordance with the decrease in this flow rate, thereby increasing the inlet liquid flow rate. It is something to control.

In a preferred embodiment of the present invention, the outlet vapor flow rate of the evaporator drum is sensed and the opening of the inlet flow control valve is adjusted to increase the liquid level in the evaporator drum in accordance with the decrease in the flow rate. to control the inlet liquid flow rate.

The present invention will be explained below with reference to embodiments shown in the drawings. FIG. 3 shows a flow sheet of an embodiment of the thermosiphon type vaporizer according to the present invention. In the figure, the same reference numerals as in FIG. 1 indicate the same parts. The heat medium inlet pipe 9 is provided with a heat medium flow meter 21 outside the heat medium flow control valve 18 . Liquid level control device 1
2 controls the opening degree of the inlet flow rate control valve 7 by performing calculations inside the device based on the value measured by the heat medium flow meter 21.

In such a process of the present invention, the liquid to be vaporized is sent to the evaporation drum 1 by the liquid sending pump 13, enters the reboiler 2 through the inlet pipe 5, and is heated with a heating medium, and a part of the liquid is converted into steam. become.
The steam once returns to the evaporation drum 1 through the outlet pipe 6, and is led out of the system via the outlet pipe 4. Further, the liquid that has not been evaporated in the reboiler 2 returns to the evaporation drum 1, and then is recirculated to the reboiler 2 again together with the liquid that has entered later and is evaporated. At this time, it is important to control the height of the liquid level in the evaporating drum 1, and this is carried out by the liquid level control device 12 as follows.
That is, when the operation is performed with the outlet vapor amount at or close to the maximum vaporization capacity, the liquid level gauge 11 measures the level of the liquid inside the evaporating drum 1 so that the liquid level inside the evaporating drum 1 is kept constant at a predetermined value. The liquid level is detected, and the opening degree of the inlet flow rate control valve 7 is adjusted by the liquid level control device 12 to control the inlet liquid flow rate. and,
When operating with the outlet steam volume reduced to approximately 50% or less of the maximum vaporization capacity, the flow meter 21 detects the heat medium flow rate that increases or decreases following the outlet steam volume, and the decrease in the heat medium flow rate is detected by the flow meter 21. The inlet flow rate is controlled by the liquid level control device 12 so that the liquid level height increases by a predetermined amount in accordance with.

In the present invention configured in this manner, experimental results regarding the relationship between the heat load applied from the heating medium to the liquid vaporized in the reboiler 2 and the circulation flow rate circulating between the reboiler 2 and the evaporation drum 1 are shown in FIG. Shown below. This result shows the relationship between the heat load and the circulating flow rate by using Freon as the liquid to be vaporized and changing the liquid level height in the evaporating drum 1. The solid line shows the liquid level height according to the conventional method, and the dashed line shows the liquid level height that is approximately 30% higher than the conventional method due to the difference in liquid level from the liquid level in reboiler 2.
The results are shown when the value is increased. From Figure 2, it can be seen that as the heat load decreases, the circulation flow rate decreases, and by the time the heat load reaches 0, the circulation flow rate becomes 0. Furthermore, if the liquid level height is increased, the circulation flow rate increases. However, it can be seen that the circulation stop point where the circulation flow rate becomes 0 can be lowered to a place where the heat load is smaller than when the liquid level is low. From this, when the heat load is small, that is, when the heat medium flow rate is small, the circulating flow rate decreases and in order to prevent evaporation in reboiler 2 from becoming unstable, it is sufficient to increase the liquid level height. I understand. On the other hand, if the circulating flow rate exceeds a predetermined amount, problems such as unstable flow may occur due to an increase in pressure loss within the outlet piping. That is,
As shown in Figure 2, the liquid level height has been reduced by approximately
If the flow rate is increased by 30%, it becomes possible to increase the circulation flow rate compared to the conventional method (solid line), but due to the increase in the circulation flow rate, the flow resistance in the outlet pipe 6 from the reboiler 2 to the evaporation drum 1 increases. . However, since the inside of the lever outlet pipe 6 is a gas-liquid multiphase flow, if the flow resistance increases, the flow becomes unstable. Therefore, operation above the maximum circulation flow rate (circulation flow rate at 100% heat load) in the conventional method is not preferable. Therefore, it is desirable to be able to operate while maintaining a constant circulation flow rate as much as possible even when the heat load changes.

In response to this requirement, the present invention raises the liquid level to increase the circulating flow rate when the heat load is small, and lowers the liquid level to return to a predetermined position when the heat load is large, as shown by the dotted line in Figure 2. The system operates by maintaining a constant circulation flow rate as much as possible even when the heat load changes. This is shown in a block diagram of the control system as shown in FIG. That is, the heat medium flow rate 24 is detected by the heat medium flow meter 21, and the optimum liquid level height setting value 26 is determined by the calculation unit 25 in the liquid level control device 12 based on the relationship shown by the dotted line in FIG. Calculate. This optimum liquid level height set value 26 is compared with the actual liquid level height 28 to determine the required amount of increase or decrease in the liquid level, and from this the opening degree 27 of the inlet liquid flow rate valve is determined. As a result, the inlet flow rate control valve 7 moves to the commanded opening degree, the inlet liquid flow rate is changed, and the liquid level height 28 is changed. The liquid level control device 12 has the elements of the block surrounded by the dotted line in FIG.

According to the operating method of the present invention, following the reduction in heat load on the liquid evaporated in the reboiler 2,
The liquid level in the evaporating drum 1 can be increased by a predetermined amount, and the circulation flow rate can be increased when the heat load becomes small, thereby allowing stable operation.

Next, another embodiment of the present invention will be described with reference to FIG. In FIG. 5, a flow meter 29 for detecting the outlet flow rate of vaporized steam is installed in place of the heat medium flow meter 21 shown in FIG. 3, and is connected to the liquid level control device 12 in the same manner as in FIG. It is something. In this example, the heat load on the reboiler 2 is calculated based on the measured value of the outlet steam flow rate, the necessary circulation flow rate under this heat load is determined from the dotted line in FIG. This determines the set value of the liquid level inside the chamber and controls the inlet liquid flow rate.

According to this embodiment, in addition to the effects of the embodiment of FIG. 3, there are the following effects. In other words, a change in the heat medium flow rate is caused by a change in the outlet steam flow rate as a pressure fluctuation in the evaporation drum 1, and only when this is detected is the set value of the heat medium flow rate changed. When controlling the liquid level by detecting the outlet steam flow rate, there is less time delay and the followability is better than by controlling the liquid level by detecting the flow rate of the outlet steam.

As described above, according to the present invention, the evaporation operation can be performed at the optimum liquid level height according to the heat load on the reboiler, and stable operation can be performed even when the outlet steam flow rate fluctuates. be.

[Brief explanation of the drawing]

Fig. 1 is a flow sheet of a conventional thermosyphon type vaporizer, Fig. 2 is a characteristic diagram of circulation flow rate with respect to heat load, Fig. 3 is a flow sheet of a thermosyphon type vaporizer of the present invention, and Fig. 4 is a flow sheet of the present invention. A block diagram showing the control method of the invention, and FIG. 5 is a flow sheet of another embodiment of the invention. DESCRIPTION OF SYMBOLS 1... Evaporation drum, 2... Reboiler, 7... Inlet flow rate control valve, 11... Liquid level gauge, 12... Liquid level control device, 21... Heat medium flow meter, 29... Outlet steam flow rate Total.

Claims (1)

[Claims] 1. An evaporating drum and a reboiler are installed in parallel, a lower inlet nozzle of the reboiler is connected to a lower outlet nozzle of the evaporating drum, and an upper outlet nozzle of the reboiler is connected to a side surface of the evaporating nozzle. , in a thermosiphon type vaporizer in which an inlet for a liquid to be vaporized and an outlet nozzle for vaporized vapor are provided on the side and top of the evaporating drum, respectively, as the amount of vaporized vapor in the evaporating drum decreases, the amount of vapor in the evaporating drum increases. A method of operating a thermosiphon type vaporizer, characterized in that the liquid level of the vaporizer is raised. 2. The method of operating a thermosiphon type vaporizer according to claim 1, wherein the liquid level in the evaporating drum is raised in accordance with the decrease in the flow rate of outlet steam from the evaporating drum. 3. The method of operating a thermosyphon type vaporizer according to claim 1, wherein the liquid level in the evaporating drum is raised in accordance with a decrease in the flow rate of heat medium to the reboiler.