JPH03118801A - Evaporator - Google Patents

Abstract

PURPOSE:To improve response to a change in load on the system side of an evaporator being as an indirect heat exchanger for exchanging heat between a heat supplying fluid and a liq. to be evaporated by making the radiating surface substantially perpendicular. CONSTITUTION:In the evaporator 200 being the indirect heat exchanger where the heat is exchanged between the heat supplying fluid and the liq. to be evaporated, a heat source, the radiating surface 210 for radiating the heat, a heat receiving space brought into contact with the radiating surface 210 in which a liq. is evaporated and a spray 10 for injecting the liq. onto the radiating surface 210 are provided. The radiating surface 210 is made substantially perpendicular. Consequently, since the evaporator is excellent in a cold starting characteristic, the evaporator can be used for an on-site fuel cell, etc. The response to the change in the load on the system side is improved.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an evaporator used in chemical plants, etc., and more particularly, to an evaporator with a relatively similar structure suitable for, for example, an on-site fuel cell reformer. This invention relates to a simple and highly responsive evaporation device for raw materials, etc.

[Conventional technology]

An evaporation device used in chemical plants and industrial equipment, which has a structure in which the liquid to be evaporated is made into fine droplets by spraying, etc., and then sprayed onto the evaporation surface, where it is rapidly evaporated on the heated evaporation surface. There is a device that has this, and it is often used when the required amount of evaporation is relatively small. In this case, the material that constitutes the heat transfer evaporation surface is a backing (filling material) for packed columns that is often used in chemical plants to increase the so-called wetted area and improve contact efficiency. It will be done. Normally, it is constantly supplied with heat, for example from water vapor, and is in a state of stored heat.

As mentioned above, this type of evaporator evaporates instantaneously, so it is possible to quickly supply the required amount of evaporation in a steady state, and is characterized by high responsiveness. be. Furthermore, due to the relatively simple structure,
Widely used as an evaporator.

[Problem to be solved by the invention]

These prior art techniques still have technical issues that require improvement.

Since the above evaporator has a large number of evaporation surfaces,
In other words, in order to form a large number of wetted surfaces and to make it easier to form a thin film on the wetted surfaces, the packing used in packed towers is used, but the heat supply to this is basically through point contact. This is done by heat conduction. In other words, heat is transferred from the pipe wall of the heat transfer coil to the wall of the filling that is in contact with the coil by thermal conduction, and then heat is supplied by thermal conduction between the walls of the adjacent fillings. In both cases, point contact is the main method. For this reason, heat is slow to spread throughout the filling, and in the case of a cold start, it takes a considerable amount of time to reach a predetermined temperature, making it unsuitable when it is desired to shorten the start-up time. For example, in on-site fuel cells, DSS (Daily 5tart and S
In such a case, it is strongly desired to shorten the system start-up time from cold startup as much as possible and quickly supply the required amount of evaporation. In such applications, it is not appropriate to use such conventional evaporation devices.

If the filling is located far from the area where the heat transfer coil is placed, heat transfer will be poor and the temperature will drop significantly.
In order to keep the filling in a uniform temperature state, it is necessary to pay sufficient consideration to the arrangement of the coils, etc. Even with this consideration, in most cases, the specific equipment is not always perfect.
It cannot be said that the surface temperature of the metal filling is sufficiently controlled to be suitable for evaporation. For this reason, it is necessary to provide a margin for operation, which causes problems such as, for example, the need to raise the heating steam temperature higher than necessary. The filling increases the wetted area and occupies a certain amount of spatial volume because it is necessary to allow gas to pass through.

Therefore, there is a limit to miniaturization of the device.

Saturated steam is normally used as the heat supply source, and the steam is supplied into a coil provided inside the container. A metal tube with good heat conductivity is usually used to construct the coil. In this case, heat transfer is performed by heat conduction to the heat transfer coil tube wall, the filling material in contact with the tube wall, and then heat conduction through point contact between the filling materials, and finally the heat necessary for evaporation is transferred. . When the liquid supplied in the form of a fine mist comes into contact with this, a thin liquid film is instantly formed, which receives heat and instantly evaporates.

In other words, something similar to pouring water on a hot stone is being done.

As an evaporation device commonly used in chemical plants, it is a shell-and-tube heat exchanger with a structure in which liquid is held around the outside (shell side) of the heat exchanger tubes, or in some cases inside the tubes (tube side). There is an evaporator. In this case, it is necessary to heat the entire liquid held to the boiling point, which is problematic when responsiveness is required. Furthermore, the heat transfer efficiency of the heat transfer surface is determined by the outer or inner surface area of the tube, and in order to increase the surface area, protrusions are provided on the tube surface on the heat receiving side and/or the heat radiating side. Furthermore, since film boiling occurs on the tube surface, protrusions may be provided on the tube surface on the heat radiation side in order to further improve evaporation efficiency. Such a shell-and-tube heat exchanger is suitable for large-scale equipment, but not for small-sized equipment.

Furthermore, there are also devices that form a thin film using a special method to efficiently exchange heat and evaporate efficiently. In this case, the current methods of forming a thin film include using centrifugal force to force the formation mechanically, or using specially shaped tubes to form the thin film. It is.

Furthermore, to ensure uniform supply of liquid to the evaporation surface,
Usually, various devices are used, and as a result, the structure is usually complicated and large. Therefore, it is limited to special uses.

[Means to solve the problem]

The present invention provides a method for solving the above-mentioned problems, and is an evaporator that is highly responsive to load fluctuations and is an improvement over the conventional evaporator as described above.

That is, the present invention provides an evaporation device having a heat supply source, a heat radiation surface that radiates the heat, a heat receiving space in which a liquid to be evaporated is evaporated and in contact with the heat radiation surface, and a spray that sprays the liquid to be evaporated onto the heat radiation surface. The evaporator is characterized in that the heat radiation surface is substantially vertical.

That is, effective evaporation occurs by spraying the liquid to be evaporated onto the heat dissipating surface. The sprayed liquid applied to the heat dissipating surface evaporates immediately or evaporates very quickly while forming a falling liquid film.

As a highly effective method for forming an evaporative heat transfer surface or additionally a film-forming wetted surface, this method having a substantially vertical heat dissipation surface, rather than a separate filling as in the example of FIG. According to the invention, a device is proposed for spraying a liquid to be evaporated onto a heat dissipating surface in a small space with a small thickness in the direction perpendicular to the surface. The sprayed liquid evaporates as it spreads over the heat radiation surface, and the remaining liquid flows down the heat radiation surface and evaporates.

Since the heat required for evaporation is given directly to the liquid from the heat radiation surface, evaporation is performed efficiently.

The space in which evaporation occurs is preferably a space sandwiched between at least one heat radiation surface and another surface or two heat radiation surfaces.

In order to increase the amount of evaporation by depositing the area of the heat dissipation surface in a well-organized manner within the space occupied by the evaporator of the present invention, the space where evaporation is performed can be made by stacking pieces of the same shape, or by forming a single sheet of the same space into a roll. A suitable configuration is such that the same space is in contact with the heat supply source through the heat radiation surface. The former is a plate type heat exchanger, for example, the plate fin type shown in FIG.
and 230 are excluded. Although the heat transfer or evaporation efficiency is inferior due to the lack of fins, it has the advantage that it can be easily constructed by providing dimples on the plates or stacking the plates with spacers interposed therebetween.

When using the plate fin type, for this purpose, a plate fin is used, in which a fin made by bending a thin stainless steel plate into a wave shape is joined to a partition wall, that is, a plate, by brazing. preferable. These fins simultaneously provide a heat transfer surface (radiation surface) or a wetted surface necessary for forming a thin film.

The heat supply source is a heating fluid at a required high temperature, and the fluid is circulated in contact with the back side of the heat radiation surface, that is, the heat receiving surface. This forms an indirect heat exchanger that supplies heat from the heating fluid to the liquid to be evaporated.

It is preferable that the heating fluid flow path also have fins parallel to the flow path, which are brazed or the like on the heat-receiving surface, for better heat transfer.

The flow path direction of the vapor of the evaporated liquid (evaporated gas) and the heating fluid may be parallel (co-current), counter-current, or alternating current (cross-flow), but generally it depends on the settings of the inlets and outlets for both fluids. etc., it is preferable to use an alternating current with a suitable crossing angle, especially a cross current. Note that the evaporated gas does not necessarily have an entrance to the heat receiving space.

A plate fin is typically a thin corrugated plate that is sandwiched between thin plates (plates) that are in contact with the peaks and valleys of the plate to form a flow path for both the heated fluid and the liquid to be evaporated. A passage through which the heated gas flows, and another passage having a similar structure and in contact with this through the thin plate is used as a heat supply passage (heating fluid flow passage), and these combinations are arranged in sequence. Typically, as described above, a cross heat exchange type heat exchanger is formed, and at least one layer of each of the two types of channels is arranged in this heat exchanger.

When a corrugated sheet is sandwiched between thin sheets in contact with its peaks/valleys, welding or brazing is suitable for metallurgically joining them integrally. Integral metallurgical bonding is adopted because heat transfer is superior to bonding by mere contact.

Making the plates that make up the fins thinner improves heat transfer, equipment weight,
Although welding or the like may be used for this joining since it is preferable in terms of cost, etc., the most efficient method is vacuum brazing using a brazing filler metal.

In order to ensure a uniform supply of liquid to the evaporation surface, typically an appropriate number of sprays are placed near the top of the heat radiation surface or above, or a large number of sprays are placed facing one heat radiation surface. It is also possible to arrange the evaporated gas in multiple stages in series or in a staggered arrangement in the direction of flow of the evaporated gas (see FIGS. 6 to 9, which will be described later), so that it can be sprayed over the entire heat transfer surface of the heat exchanger.

In the latter case, consideration must be given to not providing fins in the heat receiving side space, changing the arrangement of the fins, or making the fins smaller in height (thickness) than the flow path.

This allows the sprayed liquid to be uniformly distributed and supplied in the form of a mist, making it easier to evaporate on the evaporation surface.

The present invention will be described in detail below using drawings showing specific examples. Unless otherwise specified, the same symbols mean the same thing.

FIG. 2 is a longitudinal cross-sectional view of a conventional packed evaporator 100. A heat transfer tube 30 is arranged in a coil shape inside the container,
A packing material (backing) 20 for a packed column is packed around it. For heat supply by conduction, a metal backing is usually used. This backing should preferably have a large contact area per unit volume.

A spray 10 is arranged at the top of the container, which is designed to allow uniform liquid distribution. The liquid is supplied to the backing in the form of a mist and gradually descends downward while forming a thin film.

Since the backing receives heat by conduction from the coiled heat transfer tube, the thin film of liquid formed on the backing surface evaporates instantaneously. The liquid that has not evaporated above the backing layer falls downward and can be further evaporated. However, if the balance between evaporation and heat supply becomes unbalanced due to, for example, improper arrangement of the coiled heat transfer tubes, there will be areas where the liquid flows directly down.

The evaporated gas is guided to the outside through a plurality of openings provided at the bottom of the backing layer and via the nozzle stub 50 of the container. A heating source (usually water vapor) is supplied to the coil via a nozzle 60 and, after imparting heat to the backing, is led out of the system via a nozzle 70.

FIG. 1 is a longitudinal cross-sectional view of an example of an evaporator 200 according to the present invention. In this example, a cross-flow heat exchanger 210 made of multilayer plate fins is used to constitute the evaporation surface (heat radiation surface) and the heat supply section, and the spray 1
At least one 0 is arranged. Water vapor is often used as a heat source to supply heat.
The water vapor used in the evaporator is usually required to be at a high temperature. For this reason, aluminum plate-fin heat exchangers, which are widely used in the refrigeration industry, are not sufficient for this high-temperature use.

Recently, a technique for brazing thin stainless steel sheets has been established, and a plate-fin type heat exchanger suitable for use at such high temperatures has been developed.

Such a heat exchanger is also desirable in the present invention.

Since many of the cross sections and longitudinal sections of the plate-fin type heat exchanger are rectangular, it is desirable that the spray form be suitable for this. In the unlikely event that uniform spraying is not possible, the temperature of the metal part will rise, but the maximum temperature will be the saturated temperature of the steam, and the saturated temperature can be predicted by setting the steam pressure. , there are no design concerns.

As in the conventional evaporator, the liquid that is not evaporated in the upper part falls downward in the passage while forming a thin film, and is successively heated and evaporated.

In orthogonal heat exchangers, the fins on the heat receiving side are metallurgically joined to the fins on the heating source side through a plate by brazing, allowing for efficient heat exchange. . Therefore, the responsiveness can be significantly improved even during a cold start, and the time required to obtain the required amount of evaporation can be significantly shortened.

FIG. 3 is a diagram illustrating an orthogonal plate-fin heat exchanger. 220 is a passage for the liquid to be evaporated, and 230 is a passage on the heat source side.

FIG. 4 is a diagram showing a case where the orthogonal heat exchangers are arranged in multiple stages in series with the evaporative gas side shared in common (the figure shows a case of two stages). If the required amount of evaporation is expected to be significantly large, or if the required amount of heat needs to be replenished due to a drop in temperature on the heat source side, etc., you can place multiple evaporators in series as a backup. , such cases can also be dealt with.

If one heat exchanger is sufficient in terms of capacity, it is not necessarily necessary to use the lower heat exchanger.

Figure 5 shows, for example, a solenoid valve 3 on the upstream side of the sprayer.
00 is provided, and the PWM (Pulse Width Modulation) method is adopted, which makes it possible to respond to load fluctuations by appropriately turning on and off. This is an additional function suitable for adjusting the required amount of evaporation according to fluctuations in the load on the system side.

To adjust the required amount of evaporation, the amount of liquid supplied by a pump is usually adjusted using a control valve or the like. In this case, there is a limit to the minimum discharge amount of the pump, so-called mini-flow, and if the discharge amount is lower than this, mechanical problems usually occur and mechanical efficiency also decreases.

It is possible to reduce the flow rate on the heat source side, but on the heat receiving side there is a portion that does not evaporate, that is, a portion that remains as a liquid.
Since it comes out of the container along with the glass, a separator is required.

The same applies to sprays; if a small injection amount is required, the flow rate can be varied to some extent by reducing the source pressure of the spray using a pressure control valve or the like. however,
If the source pressure is extremely lowered in order to reduce the injection flow rate to a very small amount, injection at an appropriate injection speed and angle will not be possible, and the liquid will drop due to poor dispersion.

Depending on the operating circumstances of the system, while the maximum required flow rate can be ensured, if a very small flow rate is also required, that is, if the turndown ratio is large, some measures are required. One of the methods corresponding to this is the PWM method.

The opening/closing time of an on/off valve (usually a solenoid valve) 300 provided upstream of the sprayer 10 can be appropriately adjusted by the PWM control unit 310 to meet extremely small evaporation demands. That is, when a very small amount of evaporative gas is required, the valve opening time is shortened so that the required amount of evaporative gas is, for example, 100% of the maximum possible amount.
If this amount is required, it can be left open all the time. A well-known example of such a control method is the electronic fuel injection system for automobiles.

FIG. 6a is a diagram showing a case where a plurality of sprays are arranged across the flow direction of the evaporative gas (the figure is an example diagram when they are arranged in series in two stages). Figure 6b is a perspective view of Figure 6a. The sprays 10 are arranged in a grid pattern, but may be arranged in a staggered manner if necessary. The heating fluid side passage 230 is composed of plate fins. 220 is an evaporative gas passage, and on the opposite side of the heating fluid side passage of the thin plate (plate) composing 230, there is a fin 250 with a small height that does not reach the other plates that sandwich the evaporative gas passage. They are joined by brazing or the like, and are provided for the purpose of increasing the heat dissipation (heating and evaporation) surface, and contribute to effectively evaporating the liquid sprayed by the spray 10.

In the example shown in the figure, three sprays are arranged in a straight line in one stage, but the number can be increased or decreased as desired. This makes it possible to deal with the magnitude of the required evaporation amount.

The sprayed liquid is evaporated on the small height fins 250 or is further thinned and then evaporated. In order to ensure sufficient evaporation, the fins 250 are preferably provided at a certain length below the lowest spray.

The evaporated gas is led out of the system through the lower outlet. In the figure, the ascending heating fluid and the descending evaporative gas flow countercurrently, but they may also flow orthogonally as described above.

In this case, it is often preferable to increase the spray arrangement density or liquid spray amount upstream of the heated fluid.

Appropriate holes or notches may be distributed in the portion of the fin 250 facing the spray 10 to utilize the back side of the fin 250.

By standardizing such combinations as one unit and arranging them in series or in parallel, it is possible to deal with the required amount of evaporation. Figure 7 shows the apparatus shown in Figure 6 stacked in two stages in series, with the heated fluid side and evaporative gas side perpendicular to each other, and the spray
This is a side view of the case where it is stepped.

FIG. 8 is a side view of a case where a plurality of sprays are alternately arranged in multiple stages across the evaporation gas flow direction with evaporation spaces in between. Unlike FIG. 6, one side of the heating fluid passage 230 does not function as a heat dissipation surface, so it is preferable to provide a heat insulating material 260 in contact therewith to prevent heat dissipation. Of course, it is preferable that the spray side also has a heat insulating structure. In this case as well, as described above, by standardizing each unit and arranging them in multiple stages, it is possible to deal with the magnitude of the required evaporation amount.

Figure 9 shows the configuration units in Figure 6 arranged in a mirror image manner, with one side of the evaporation space where the spray is placed in common, and when multi-stage or parallel arrangement is not possible. This is effective in cases where miniaturization is required, such as in applications. The heating fluid and the vaporized gas are orthogonal.

In the above, the evaporated gas generated in the heat receiving space is mainly sent out from the exit of the space due to the volume increase due to the change from liquid to gas, but it is always possible to use inert gas or other types of raw material gas as a carrier gas. Alternatively, this may be combined with flushing when necessary.

〔Effect of the invention〕

According to the present invention detailed above, the following effects can be obtained.

1) Since it has excellent cold start characteristics, it can be used for applications such as on-site fuel cells.

2) It is possible to provide an evaporator with good responsiveness to changes in the load on the system side.

3) If a plate or plate-fin heat exchanger type is used, a large evaporation surface can be obtained per unit volume, and a thin film can be easily formed.

4) Heat evaporation is performed efficiently.

5) Enables miniaturization of the device.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of an evaporator according to the present invention. FIG. 2 is a longitudinal sectional view of a conventional evaporator. FIG. 3 is an explanatory diagram of a plate-fin type heat exchanger. FIGS. 4 to 9 are illustrations of embodiments of the evaporator according to the present invention. 10 Spray 20 Metal backing 30 Heat exchanger tube coil 40 Liquid nozzle 50 Gas outlet nozzle 60 Heat medium nozzle 70 Heat medium outlet nozzle 100 Conventional evaporator 200 Evaporator 210 Plate fin heat exchanger 220 Evaporative liquid /Gas side passage 230 Heat source side passage 300 Solenoid valve

Claims (1)

[Scope of Claims] 1. A heat supply source, a heat radiation surface that radiates the heat, a heat receiving space in which a liquid to be evaporated is evaporated and in contact with the heat radiation surface, and a spray that sprays the liquid to be evaporated onto the heat radiation surface. An evaporation device, the evaporation device having a heat dissipation surface that is substantially vertical. 2. The apparatus according to claim 1, wherein the evaporator is an indirect heat exchanger that transfers heat between a heat supply fluid that is a heat supply source and a liquid to be evaporated. 3. The apparatus according to claim 2, wherein the indirect heat exchanger is an AC heat exchanger in which plates or plate fins are laminated. 4. The apparatus according to claim 3, wherein the AC heat exchanger is of the orthogonal type. 5. The apparatus according to claim 1, wherein the injection is performed from near the upper end of the heat radiation surface or above. 6. The apparatus according to claim 1, wherein the heat receiving spaces and spray sets are provided in multiple stages equal to the number of heat receiving spaces by connecting the heat receiving spaces in series. 7. The apparatus according to any one of claims 1 to 6, wherein the supply of the liquid to be evaporated to the spray is controlled by a valve that opens and closes using a pulse width modulation method. 8. The device according to any one of claims 1 to 7, wherein the material of the heat dissipation surface is stainless steel.