JP2001241753A - Steam heater for low-temperature fluid and heating method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heater capable of heating low-temperature fluid directly by steam and controlling the temperature of the low-temperature fluid accurately. SOLUTION: In the steam heater for heating a low-temperature fluid passing through a heat transfer tube by steam, a steam supplying tube 11 is connected to the upper part of a heater cylinder 10, a condensed water discharging tube 12 is connected to the lower part of the same cylinder 10 while a condensed water phase 13 is formed in the lower part of the heater cylinder 10, and a steam phase 14 is formed in the upper part of the same to provide a heat transfer tube 15, though which the low-temperature fluid is passed, through the steam phase 14 and, subsequently, the condensed water phase 13 sequentially.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steam heater for a low-temperature fluid such as liquefied hydrocarbon and liquefied ammonia.

[0002]

2. Description of the Related Art Generally, in a plant, a heater using steam is used to heat various fluids.

[0003] In the case of heating a liquefied hydrocarbon, liquefied ammonia, or other low-temperature fluid from a supercooled state to a temperature close to a saturation temperature with the steam heater, the low-temperature fluid flows into the heat transfer tube, and the heat transfer tube is accommodated. Steam is supplied into the body of the heater to heat the low-temperature fluid in the heat transfer tube, but it is usually very difficult to accurately control the outlet temperature of the heat transfer tube. Since the temperature of the low-temperature fluid is 0 ° C. or lower, there is a possibility of freezing, and there are few cases of direct heating by steam using a heat transfer tube.

When heating the low-temperature fluid from a supercooled state to a temperature close to the saturation temperature, if the outlet temperature control is not performed accurately, the outlet temperature becomes higher than the saturation temperature and the low-temperature fluid is gasified. Therefore, accurate heating of such a low-temperature fluid requires accurate temperature control, and heating with steam is not suitable.

[0005] The reason why the temperature cannot be accurately controlled by direct steam heating is that the condensation heat transfer coefficient of steam is extremely large as compared with other fluids, or the heat capacity of the steam phase of the heater is small. it is conceivable that.

[0006] For this reason, the minute pressure of steam, flow rate,
It is presumed that the temperature control is too sensitive to fluctuations in the degree of superheat, other external conditions, or the like, or the temperature cannot be stably controlled as a result of being unable to follow.

[0007] In order to prevent such a problem from occurring, a hot water bath type heater generally achieves the object by controlling and mixing the fluid that bypasses the heater in order to set the outlet fluid temperature to a set value. are doing.

FIG. 5 shows a heater of a hot water bath type. A heating tank 50 is filled with hot water 51, and the heating tank 50 filled with the hot water is supplied with a low-temperature fluid as a fluid to be heated. Is provided at the bottom of the heating tank 50, and a steam supply pipe 53 is provided at the bottom of the heating tank 50.
4, the control valve 55 connected to the steam supply pipe 53
To control the temperature of the hot water 51 by controlling the amount of steam blown.

[0009]

In this type, hot water 5
Since a large amount of 1 is stored, the heat capacity is large and the temperature cannot be controlled accurately with respect to a change in the flow rate of the fluid to be heated. Therefore, a three-way valve 56 is provided at the inlet side of the heat transfer tube 52 and a thermometer is provided at the other outlet side It is necessary to control the outlet temperature by switching the three-way valve 56 so that the temperature detected by the thermometer 57 becomes the set temperature, and bypassing the low-temperature fluid to the outlet side by the bypass pipe 58. Become. Further, a pressure control valve 59 is provided to maintain a pressure higher than the saturation pressure at the target temperature so that the fluid does not gasify.

[0010] This hot water bath type heater has a large heat capacity for the fluid to be heated, and when the flow rate is changed to a low flow rate, the low-temperature fluid as the fluid to be heated is gasified, so that the temperature accuracy is poor. Become.

In order to improve the temperature control, a method of heating the intermediate heat medium without directly heating the fluid with steam is also used.

In this heater, as shown in FIG. 4, an intermediate heat medium 41 such as LPG is accommodated in a heating drum 40, and a heat transfer tube 42 through which a fluid to be heated passes is disposed on the gas phase side thereof.
A heat transfer tube 43 through which steam on the liquid phase passes is arranged, and a thermometer 44 is provided at the outlet side of the heat transfer tube 42 through which the fluid to be heated passes. A control valve 45 is controlled by a detection value of the thermometer 44 to control the amount of steam. I try to control.

In this heater, if an intermediate heat medium such as LPG is used, since the condensation heat transfer film coefficient is not as large as that of steam, the temperature difference between the LPG vapor and the fluid to be heated across the heat transfer tube 42 is obtained. The balance is very good compared to the case of direct steam. Further, the steam heats the liquid phase of the LPG, which is the intermediate heat medium 41, and accumulates heat in the liquid of the intermediate heat medium 41. Therefore, the steam changes the pressure (temperature) of the LPG vapor phase due to the fluctuation of the fluid to be heated. The heat is absorbed and stable heat transfer can be performed.

Further, since the minute change in steam is leveled by absorbing the large heat capacity of the liquid, the temperature accuracy of the system can be precisely controlled, and the heat which does not solidify even at that temperature depending on the heating temperature of the low temperature fluid. If you select a medium, there is no problem of freezing like steam.

However, since two types of heat transfer tubes 42 and 43 are required, the apparatus becomes large and the intermediate heat medium 4
No. 1, there is a problem that the cost is increased because the heating drum is required to withstand pressure depending on the pressure of the gas phase.

Further, since the heat transfer mechanism has two stages as described above, the required temperature difference increases, and the heat transfer area increases. For this reason, the temperature range of use of the heating fluid is reduced.

It is an object of the present invention to solve the above-mentioned problems and to provide a heater that directly heats a low-temperature fluid by steam and that can accurately control the temperature of the low-temperature fluid.

[0018]

In order to achieve the above object, the present invention is directed to a low-temperature fluid steam heater for heating a low-temperature fluid passing through a heat transfer tube with steam. Connect the steam supply pipe and the condensed water discharge pipe at the lower part, form the condensed water phase at the lower part inside the heater body and form the steam phase at the upper part, and connect the heat transfer pipe through which the low temperature fluid passes to the heater body. This is a low-temperature fluid steam heater provided so as to pass from the steam phase to the condensed phase.

According to a second aspect of the present invention, there is provided a control device, wherein a thermometer is provided on the outlet side of the heat transfer tube, a control valve is connected to the steam supply pipe, and the control valve controls the control valve in accordance with the temperature detected by the thermometer. A low temperature fluid steam heater according to claim 1 provided.

According to a third aspect of the present invention, there is provided the low temperature fluid steam heater according to the first or second aspect, wherein the heater body is provided with a liquid level adjusting means for adjusting the liquid level of the condensed water phase.

According to a fourth aspect of the present invention, the heater body and the heat transfer tube are formed by a horizontal shell-and-tube heat exchanger, and a plurality of heads serving as low-temperature fluid inlet / outlet chambers are formed from the upper part to the lower part. The heat transfer tube is formed by a U-shaped tube connecting these chambers, and is formed in the heating body such that the liquid level of the condensed water phase is located between the upper and lower chambers. A steam heater for a low-temperature fluid according to claim 1.

According to a fifth aspect of the present invention, there is provided a method for heating a low-temperature fluid passing through a heat-transfer tube with steam to near a saturation temperature under the pressure, wherein a steam supply pipe is connected to an upper portion of a heater body. At the same time, a condensed water discharge pipe is connected to the lower part, a condensed water phase is formed at the lower part of the heater body, a steam phase is formed at the upper part, and the heat transfer pipe through which the low-temperature fluid passes through the heater body is condensed from the steam phase. This is a method for heating a low-temperature fluid which is provided so as to pass through a phase and controls the steam supply amount according to the outlet temperature of the low-temperature fluid of the heat transfer tube.

According to a sixth aspect of the present invention, a set pressure in the heater body is set in accordance with a set flow rate of the low-temperature fluid, the flow rate of the low-temperature fluid at the inlet side of the heat transfer tube is detected, and the steam phase in the heater body is detected. Pressure in the steam phase, set the pressure in the steam phase according to the detected flow rate of the low-temperature fluid, feed-forward control the steam amount so as to reach the set pressure, and adjust the steam amount according to the outlet temperature of the heat transfer tube. 6. The method for heating a low-temperature fluid according to claim 5, wherein feedback control is performed.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 shows a schematic configuration of the present invention.

In the figure, a steam supply pipe 11 is connected to an upper portion of a heater body 10 and a condensed water discharge pipe 12 is connected to a bottom portion.
Are connected, a condensed water phase 13 and a steam phase 14 are formed in the heater body 10, and a heat transfer tube 15 is provided so as to pass through the steam phase 14 and the condensed water phase 13.

A low-temperature fluid supply pipe 16 such as liquefied ammonia is connected to an upper inlet side of the heat transfer pipe 15, and a low-temperature fluid discharge pipe 17 is connected to a lower outlet side.

The heater body 10 is provided with level adjusting means 18 for adjusting the level L in the condensed water phase 13. The level adjusting means 18 includes a level meter 19 for detecting the level L in the condensed water phase 13, and an adjusting valve valve 20 connected to the discharge pipe 12 and controlled by the level meter 19.
The level adjusting means 18 is not limited to this example, and other means may be used.

A flow meter 21 and a flow regulating valve 22 are connected to the low temperature fluid supply pipe 16, and a control valve 23 is connected to the steam supply pipe 11. Further, the heater body 10 is provided with a pressure gauge 24 for detecting the pressure in the steam phase 14,
The low temperature fluid discharge pipe 17 is provided with a thermometer 25 for detecting the outlet temperature of the low temperature fluid from the heat transfer pipe 15.

The detected values of the pressure gauge 24 and the thermometer 25 are inputted to the control means 26, and the control device 26
However, the control valve 23 is controlled.

FIGS. 2 and 3 show the heater body 10 and the heat transfer tube 1.
5 shows a specific example, in which the heater body 10 and the heat transfer tube 15 are formed by a horizontal shell-and-tube heat exchanger.

This horizontal shell-and-tube type heat exchanger comprises a heater body 10 serving as a heat exchanger body, a steam supply port 11a formed at an upper portion, and a condensed water discharge port 12a formed at a lower portion. A head 30 is provided on the side of the head 30 to form an inlet / outlet for the low-temperature fluid F.
0 is an entrance chamber 27, an intermediate chamber 28,
The heat transfer tube 15 is formed by being partitioned by the outlet chamber 29, and is formed of a U-shaped tube connecting the inlet chamber 27 and the intermediate chamber 28.
s, and a heat transfer tube 15 d formed of a U-shaped tube connecting the intermediate chamber 28 and the outlet chamber 29. The inlet chamber 27 is provided with a supply port 16 a for the low-temperature fluid F, and the outlet chamber 29 is configured to discharge the low-temperature liquid F. An outlet 17a is provided.

The heat transfer tube 15 is provided inside the heater body 10.
s and the heat transfer tube 15d are formed so that the liquid level of the condensed water phase 13 is located.

In this heater comprising a horizontal shell-and-tube heat exchanger, the head 30 has an inlet chamber 2
7, the intermediate chamber 28 and the outlet chamber 29 have been described. However, the intermediate chamber 28 is not necessarily provided.
7 and the outlet chamber 29, the heat transfer tube 15 may be provided so as to connect the inlet and outlet chambers 27, 29, and conversely, the intermediate chamber 28
Are formed, and the heat transfer tube 15 is connected to these upper and lower chambers 27 and 2.
It is also possible to configure so as to connect 8, 29.

Further, in this case, the liquid level of the condensed water phase 13 may be formed so as to be located substantially in the middle of these chambers 27, 28 and 29.

Next, a method of heating a low-temperature fluid using steam with the heater will be described.

Example of heating liquefied ammonia (boiling point at atmospheric pressure −33.4 ° C.) as a low temperature fluid from a subcooled state (−33 ° C.) under pressure to + 1 ° C. near a saturated gas temperature at that pressure Will be described.

Steam is supplied to the steam phase 14 in the heater body 10 from the steam supply pipe 11, and the low-temperature fluid from the low-temperature fluid supply pipe 16 flows through the heat transfer pipe 15 s of the steam phase 14, and is heated. The steam in 14 is partially condensed by the heating and accumulates in the condensed water phase 13. Thereafter, the cryogenic fluid is transferred to the heat transfer tubes 15 in the condensed water phase 13.
Then, it is heated by the condensed phase warm water through d and discharged from the low temperature fluid discharge pipe 17.

The outlet temperature of the low-temperature liquid F is determined by the temperature detector 2
5, the control device 23 controls the opening of the control valve 23 so that the temperature becomes a set temperature (for example, 1 ° C.), and performs feedback control of the steam amount.

As described above, the low-temperature fluid passes through the heat transfer tube 15,
By heating with the steam of the steam phase 14 first and then with the hot water in which the steam of the condensed phase 13 is condensed, the outlet temperature can be quickly and accurately heated.

Generally, the heat transfer film coefficient at the time of condensation of steam is very large, 20 to 100 times or more as compared with the film transfer coefficient in the low temperature fluid of the heat transfer tube 15. In this region, the temperature difference between the steam and the pipe wall is very small compared to the temperature difference between the pipe wall and the cryogenic fluid.
However, even if the temperature changes slightly, the ratio of the heat transfer to the temperature difference becomes considerably large.

That is, assuming that the temperature of the outside tube is To, the tube wall temperature of the heat transfer tube is Tp, and the temperature of the low-temperature fluid is Ti, the temperature difference between the outside tube and the heat transfer tube is ΔTo (= To−Tp). Assuming that the temperature difference of the fluid is ΔTi (= Tp−Ti), ΔTi is sufficiently larger than ΔTo (ΔTi / ΔTo> 20) in relation to the heat transfer film coefficient. It takes time for a small change to be transmitted to the low-temperature fluid side.

Therefore, even if the low-temperature fluid is simply heated with steam and the outlet temperature of the low-temperature fluid is detected and the steam amount is feedback-controlled, the outlet temperature of the low-temperature fluid is not stabilized because of a response delay, and the accuracy is low. Good temperature control cannot be performed, and the feedback control of the steam amount at the outlet temperature cannot be practically realized unless the minute pressure change of the steam is reduced.

In the present invention, a steam phase 14 and a condensed water phase 13 are formed, and a slight pressure change in the steam phase 14 is dealt with by the condensed water stored in the condensed phase 13.

That is, the temperature of the hot water stored in the condensed phase 13 gradually decreases from the surface to the discharge pipe 12 at the bottom, but the surface of the condensed phase 13 is in contact with the steam phase 14 and the vapor pressure is Since the temperature is at an equilibrium saturated pressure, a slight pressure change in the gas phase pressure is mitigated by the surface hot water. In other words, if the steam amount is reduced and the steam phase 14 is reduced below the set pressure, the condensed phase 13
If the hot water evaporates from the surface of the gas and the pressure increases, the steam in the steam phase 14 condenses, so that the pressure fluctuation of the steam is absorbed. It is generally known that the speed of these phase changes is very fast when the amount is small.

Therefore, the temperature can be detected by the thermometer 25, and the control device 26 controls the control valve 23 in accordance with the temperature, so that accurate feedback control can be performed.

Although the heat transfer tubes 15 of the heat exchanger have been described in the vertical arrangement, the arrangement of the heat transfer tubes 15 may be horizontal. However, in this case, one or more intermediate chambers 28 may be provided, and the liquid level of the condensed phase 13 may be set between the upper heat transfer tube 15s and the lower heat transfer tube 15d.

The above-described control is a description of a stable steady state in which the flow rate of the low-temperature fluid has reached the set flow rate of 100%. In actual operation, steam is supplied into the heater body 10 to condense. Thus, the steady-state operation must be performed by gradually increasing the flow rate of the low-temperature fluid to 100% while forming the condensed phase 13 and the steam phase 14.

In this case, in the above-described feedback control, a delay in the control system is essential. Therefore, in the present invention, an appropriate pressure in the steam phase 14 in the heater body 10 is controlled with respect to the set flow rate. The flow rate of the low-temperature fluid is detected by the flow rate detector 21 at the same time, and the pressure in the heater body 10 is simultaneously detected by the pressure gauge 24 and the control valve 23 is controlled in accordance with the flow rate value. By doing so, the outlet temperature of the low-temperature fluid is controlled in a feed-forward manner.

That is, the flow rates are 100%, 50%, 24%
In order to maintain the outlet temperature of the low-temperature fluid at the set value at the flow rate of 15% or 15%, the necessary steam amount is previously calculated, and the heat amount of the condensed water is calculated from the volume in the heater body 10 with respect to the steam amount. By setting an appropriate pressure in the heater body 10 in consideration of the above, stable and accurate low-temperature fluid outlet temperature control can be performed from the start of operation to a steady operation at a 100% flow rate.

More specifically, the relationship between the steam amount and the set pressure when the flow rate load is set to 100%, 50%, 25%, and 15% is set, for example, as shown in the following table.

Flow rate Steam amount Condensate outlet temperature Heater body pressure setting 100% 0.34 MPa 77.8 ° C. 0.247 MPa 50% 0.25 MPa 43.3 ° C. 0.182 MPa 25% 0.15 MPa 10.3 ° C. 0 .167 MPa 15% 0.1 MPa 2.9 ° C. 0.120 MPa In order to increase the flow rate of the low-temperature fluid from the start, the set pressure in the heater body is increased stepwise as shown in the above table. By controlling the control valve 23 so as to obtain a pressure corresponding thereto and performing feedforward control on the steam amount corresponding to the flow rate, and further performing feedback control on the steam amount based on the detection value of the thermometer 25, over a wide flow rate range. ,
Heat can be done with high accuracy. Conversely, when the flow rate is reduced stepwise, such as at the end of operation, the set pressure value may be reduced, and the steam amount may be gradually reduced.

The level adjusting means 18 can set the level L by controlling the discharge amount of the control valve 23 and can change the volume ratio of the condensed water phase 13 and the steam phase 14 at the level L. By adjusting the level, it is possible to appropriately maintain the matching of the heat exchange amount due to seasonal load fluctuation, steam pressure fluctuation, and the like.

[0054]

In summary, according to the present invention, it is possible to heat a low-temperature fluid with steam with high precision and to reduce the cost.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an embodiment of the present invention.

FIG. 2 is a sectional view showing a specific example of the heater of FIG.

FIG. 3 is a diagram showing a side cross section and a plane of FIG. 2;

FIG. 4 is a schematic sectional view of a conventional heater using an intermediate heat medium.

FIG. 5 is a schematic view showing a conventional steam heater.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Heater body 11 Steam supply pipe 12 Condensed water discharge pipe 13 Condensed water phase 14 Steam phase 15 Heat transfer pipe

Claims (6)

[Claims] 1. A low-temperature fluid steam heater for heating a low-temperature fluid passing through a heat transfer tube by steam, wherein a steam supply pipe is connected to an upper portion of a heater body, and a condensed water discharge pipe is connected to a lower portion of the heater body. The condensed water phase is formed on the upper part of the lower part of the vessel body and the steam phase is formed on the upper part. Steam heater. 2. A thermometer is provided on the outlet side of the heat transfer tube, a control valve is connected to the steam supply pipe, and a control device for controlling the control valve in accordance with the temperature detected by the thermometer is provided. 2. A steam heater for cryogenic fluid according to claim 1. 3. A heater level adjusting means for adjusting a liquid level of a condensed water phase in a heater body.
A cryogenic fluid steam heater as described. 4. A heater body and a heat transfer tube are formed by a horizontal shell-and-tube heat exchanger, and a head serving as an inlet / outlet chamber for a low-temperature fluid is formed by partitioning a plurality of chambers from an upper part to a lower part. The heat transfer tube is formed by a U-shaped tube connecting these chambers, and the heat transfer tube is formed in the heating body such that the liquid level of the condensed water phase is located between the upper and lower chambers.
A cryogenic fluid steam heater according to any of the preceding claims. 5. A method for heating a low-temperature fluid passing through a heat transfer tube with steam to near a saturation temperature under the pressure, wherein a steam supply pipe is connected to an upper portion of a heater body and condensed to a lower portion. A water discharge pipe is connected, a condensed water phase is formed at the lower part of the heater body, a steam phase is formed at the upper part, and a heat transfer pipe through which a low-temperature fluid passes through the heater body is passed from the steam phase to the condensed phase. A method for heating a low-temperature fluid, wherein the steam supply amount is controlled according to an outlet temperature of the low-temperature fluid of the heat transfer tube. 6. A set pressure in the heater body is set according to a set flow rate of the low temperature fluid, and a flow rate of the low temperature fluid at an inlet side of the heat transfer tube is detected, and a pressure in a steam phase in the heater body is detected. Requesting to set a pressure in the steam phase according to the detected flow rate of the low-temperature fluid, feed-forward control the steam amount so as to reach the set pressure, and feedback-control the steam amount according to the outlet temperature of the heat transfer tube. Item 6. The method for heating a low-temperature fluid according to Item 5.