JPH028689A - Waste heat recovery device - Google Patents

Abstract

PURPOSE:To prevent oxidization and corrosion of a pipe within a heat exchanger by a method wherein medium of a low temperature range out of media produced by mixing within a preliminary tank thermal medium of normal temperature with another thermal medium heated in a heat exchanger is supplied to the heat exchanger and medium of high temperature range is recovered. CONSTITUTION:A preliminary tank 11 is composed of an outer tank 13 and an inner tank 14. Water of normal temperature is supplied from a pipe 12 to an outer first tank 13a. Hot water heated by a heat exchanger 3 is supplied to an upper part of the first tank 13a through a pipe 18 and automatically mixed with water of normal temperature. Water of low temperature range collected near a bottom surface of the first tank 13a is heated up to 50 deg.C through its automatic mixing, lifted up by a lifting pipe 15 and a lifting pump 16 and then supplied to the heat exchanger 3. With this arrangement, a temperature at an outer surface of the pipe within the heat exchanger 3 is kept at a temperature higher than its dew point and thus it is possible to prevent any oxidation and corrosion of the pipe. Hot water of high temperature range is discharged and its recovered heat can be utilized.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention is applicable to the recovery of heat from high-temperature gas discharged from steam generation equipment, solution combustion equipment, gas combustion equipment, power generation boilers, diesel engines, etc. The present invention relates to a waste heat recovery device that can be used for.

(Prior art) In general, in chemical substance production factories, etc., in order to incinerate the substances (solid, liquid, gas) used to produce desired products and convert them into harmless substances, for example, liquids such as solutions are incinerated. If high-temperature gas containing components such as sulfur is discharged directly into the atmosphere in solution combustion equipment, it may contribute to pollution, so it is necessary to install a degassing device or to lower the temperature of the high-temperature gas. A waste heat recovery device may be installed to reduce the amount of waste heat to make it harmless and to reuse the waste heat.

Figure 3 shows an example of a conventional waste heat recovery device.
For example, it is applied to the manufacturing process of magnetic recording media such as magnetic tapes.

The solvent gas treatment device 1 is for treating solvent waste liquid or solvent gas during the production of magnetic tapes, and is for removing harmful components such as sulfur from the gas generated by combustion to below the standard amount. The solvent gas treatment device 1 has a temperature of, for example, 800°C.
After burning the solvent waste liquid etc. at a high temperature of about 400°C, removing harmful components and lowering the gas temperature to about 400°C, the gas is transferred to the next processing stage, the steam recovery equipment 2.
supply to.

The steam recovery device 2 removes high-temperature steam from the high-temperature gas and further lowers the temperature to about 250 yen. However, it is dangerous to discharge the gas at about 250°C directly into the atmosphere, and it is desirable from the viewpoint of energy conservation to reuse this waste heat instead of wasting it. For this purpose, a heat exchanger 3 capable of recovering waste heat is provided at -m as a post-treatment process of the steam recovery device 2.

The heat exchanger 3 uses water as a heat medium,
Passing water at room temperature (e.g. 20°C) through high-temperature gas,
The high-temperature gas is cooled to about 180°C, and at the same time, the water is heated to, for example, about 60°C using the temperature of the high-temperature gas. The high-temperature gas cooled by the heat exchanger 3 is discharged into the atmosphere through the chimney 4.

The hot water discharged from the heat exchanger 3 is effectively used for other purposes by recovering as much of the waste heat of the high-temperature gas as possible.

(Problems to be Solved by the Invention) The structure of the heat exchanger 3 is a so-called radiator structure, in which stainless steel or metal pipes with good geothermal conductivity are arranged in a meandering manner in the high-temperature gas, and This is a very common configuration in which the metal pipe is provided with fins, etc., and by supplying the room temperature water into the metal pipe, the temperature of the high-temperature gas is lowered by the water absorbing heat, and the water is heated. It is something.

By the way, in the above configuration, the temperature of the high-temperature gas supplied to the heat exchanger 3 is set at a certain level or higher (this varies depending on various conditions such as the temperature of the water supplied to the metal pipe and the amount of water supplied, but generally 25
If the outside surface of the metal pipe, in other words the surface that comes into contact with the hot gas, is not set at a temperature of around 0°C (its critical temperature is around 0°C), the temperature will drop below what is known by those skilled in the art as the acid dew point (the temperature at which hot gas condenses). The sulfur-containing solution (sulfuric acid) in the hot gas condenses and adheres to the outer surface of the metal pipe.

The phenomenon causes oxidative corrosion of metal pipes,
This significantly shortened the life of the metal pipe.

For this reason, conventionally, replacing the metal pipe required a great deal of cost and effort, which was the biggest drawback of the waste heat recovery device. Moreover, it is not only difficult to significantly lower the temperature of the gas discharged from the chimney 4, but also has the major problem of not being able to improve the heat recovery efficiency.

An object of the present invention is to solve the above-mentioned problems, and to provide a waste heat recovery device that can withstand long-term use and at the same time can recover waste heat more efficiently than before.

(Means for Solving the Problems) The object of the present invention is to supply high-temperature gas to be discharged to a heat exchanger, and supply a low-temperature heat medium to the high-temperature gas in a reflux path provided in the heat exchanger. In a waste heat recovery device that recovers heat from the high-temperature gas by refluxing and using the heat medium, the heat medium at room temperature and the heat medium heated by the reflux in the heat exchanger are stored in a state of natural mixing. a supply means for supplying a medium in a low temperature region of the medium stored in the preliminary tank to a reflux path of the heat exchanger; and a supply means for supplying the medium in a high temperature region in the preliminary tank to the This is achieved by a waste heat recovery apparatus characterized in that the waste heat recovery apparatus includes a recovery means for taking out the heat medium from the tank, and is configured to increase the temperature of the heat medium flowing back through the heat exchanger.

That is, by supplying room temperature gas or liquid into the reserve tank, heating it to a predetermined temperature by heat recovered from the reflux route in the heat exchanger, and supplying it to the input side of the reflux route, The temperature inside the metal pipe serving as the reflux path increases, and the temperature difference between the outside temperature of the metal pipe and the temperature of the high-temperature gas decreases. As a result, even if a higher amount of heat than before is taken from the high-temperature gas pipe and its temperature is lowered, the outside temperature of the metal pipe does not fall below the acid dew point, thereby reducing the condensation and adhesion of sulfuric acid. can prevent oxidative corrosion.

(Embodiment) Next, embodiments of the present invention will be described with reference to the drawings.

Note that FIG. 1 is a schematic configuration diagram of the waste heat recovery apparatus of this embodiment, and parts that operate in the same way as in FIG. 3 are given the same reference numerals to avoid duplication of explanation. Furthermore, FIG. 2 is a schematic diagram using a pipe wall cross section to explain the relationship between the pipe outer surface temperature and the pipe inner surface temperature in the heat exchanger portion.

The waste heat recovery device of this embodiment basically has a structure in which a heat exchanger 3 and a reserve tank 11 are appropriately connected by a pipe system, similar to the conventional one. The water from the water supply pipe 12 is at room temperature (for example, 20
°C) water is supplied to the preliminary tank 11. The reserve tank 11 is composed of an outer tank 13 and an inner tank 14, and water at room temperature is discharged into the first outer tank 13a.

The water supplied to the first tank 13a is transferred from the lower part of the tank 13a (on the opposite side to the water supply pipe 12) to the pumping pipe 15.
, water is pumped up by a water pump 16 and supplied to the heat exchanger 3 via a pipe 17. As a result, the water at room temperature will flow back through the reflux path provided in the heat exchanger 3, and will be heated by absorbing the heat of the high-temperature gas during a predetermined passage time. The hot water heated to about 90°C by this waste heat recovery is transferred to the heat exchanger 3.
is discharged from the output side of the reflux path through the pipe 18,
Water is again supplied into the first tank 13a.

The hot water discharged from the upper part of the first tank 13a into the tank 13a is naturally mixed with the room temperature water that is continuously being supplied from the water supply pipe 12. What is meant by natural mixing here?
Without forcible stirring, high-temperature water gathers near the water surface in the first tank 13a to form a high-temperature region, and low-temperature water gathers near the bottom of the first tank 13a to form a low-temperature region. say what you do In this way, low-temperature water stays in the lower part of the first tank 13a, and relatively high-temperature water stays in the upper part of the first tank 13a. and the first tank 1
When the water level in 3a becomes higher than the height of the inner tank 14 (the upper part is open), the high temperature water, that is, the temperature rises to about 85 ° C due to the above mixing (by adjusting the water supply amount of high temperature water and normal temperature water) The water whose temperature has been slightly lowered (adjustable) flows into the inner tank 14 and is further connected to the drain pipe 19 and the drain pump 2.
0, it is possible to obtain reusable hot water with waste heat recovery.

On the other hand, the temperature of the water staying in the lower part of the first tank 13a is reduced to 5.0 by the mixing (natural mixing without forced stirring).
The temperature can be raised to about 0°C.

Therefore, at the beginning of the operation of the waste heat recovery device of this embodiment, the temperature of the water supplied to the heat exchanger 3 is at room temperature, but after a predetermined period of time has elapsed, that is, waste heat recovery begins. , the water supplied to the heat exchanger 3 is at 50°
Water heated to about C will be pumped. Therefore, it is possible to effectively recover waste heat while maintaining the temperature on the outer surface of the pipe in the heat exchanger 3 at a temperature equal to or higher than the acid dew point and preventing corrosion. For this reason,
The corrosion prevention effect by supplying water heated to about 50°C will be explained below with reference to FIG.

In the heat exchanger 3, a reflux path is constructed of metal pipes as described above, and water W passes through the left side of the pipe wall 30, which is partially enlarged in FIG. 2, and high-temperature gas G flows through the right side.
shall pass. Further, it is assumed that the temperature rises and falls in the vertical direction in the figure along the wall of the pipe wall 30 (higher temperature is higher), and the acid dew point is shown as a point 31.

Therefore, in the figure, the temperature of the high-temperature gas G is located above the point 31, and the temperature of the water W is located below. The temperature of the acid dew point varies depending on various conditions such as the type of high-temperature gas G, gas pressure, and gas temperature, but generally, in the case of a combustion treatment gas for a solvent used in magnetic recording media such as magnetic tape, it is approximately 120°. It is about C.

Therefore, when hot water of about 50'C is supplied from the pipe 17 under conditions where the temperature of the high-temperature gas G supplied from the steam recovery device 2 to the heat exchanger 3 is set to about 250°C, The temperature difference between the inside and outside of the pipe wall 30 results in a temperature gradient X as shown by the solid line, and the actual temperature of the outer surface of the pipe is indicated by the intersection P of the temperature gradient line X and the pipe wall 30. is maintained at a higher temperature than the acid dew point. That is, the internal temperature of the pipe wall 30 has increased by about 30°C compared to the conventional case due to the hot water heated to 50°C, and the temperature gradient line Y
Since the slope is gentle compared to the above, the temperature difference between the inside and outside surfaces of the pipe wall portion 30 is small, and the temperature of the outside surface of the pipe that is in contact with the high-temperature gas G does not drop significantly. It becomes easier to maintain the temperature above the dew point.

As a result, the high-temperature gas G contains sulfur, carbon, oxygen, hydrogen, etc., but since the temperature of the outer surface of the pipe is above the acid dew point, the sulfur content does not condense on the outer surface of the metal pipe. , sulfuric acid water condensation can be completely eliminated, and oxidation corrosion of metal pipes can be prevented.

For comparison, a conventional case in which water at room temperature is supplied to the pipe 17 will be explained using FIG. 2. As the inside temperature and outside temperature of the metal pipe increase, the temperature gradient line Y As the slope increases, the temperature Q of the outer surface of the pipe also decreases significantly, reaching a temperature below the acid dew point. Therefore, as mentioned above, unless waste heat recovery is performed to maintain the temperature of the high-temperature gas G discharged from the heat exchanger 3 at about 180°C or higher, the sulfuric acid water containing sulfur will condense and cause metal Oxidation corrodes the pipes.

Furthermore, according to the configuration of this embodiment, the reserve tank 1
1 and supplying hot water heated to about 50°C to the pipe 17, it is possible not only to prevent the oxidation corrosion, but also to obtain hot water at a higher temperature than before. , gas temperature after hot water recovery,
That is, the temperature of the gas discharged into the atmosphere from the chimney 4 can be lowered to about 150°C, which is lower than before, which is a favorable result from the standpoint of pollution prevention.

The embodiments of the present invention have been described above, but the present invention is the first embodiment.
The configuration is not limited to the one shown in the figure, and various modifications are possible.

For example, waste heat recovery can be performed by supplying another heat medium (liquid or gas) to the heat exchanger instead of water, and
As mentioned at the beginning, gas combustion equipment, power generation boilers,
It can be appropriately used in various devices such as diesel engines.

(Effects of the Invention) As described above, the waste heat recovery device of the present invention has a preliminary tank that stores the heat medium at room temperature and the heat medium heated by reflux in the heat exchanger in a state of natural mixing. and supplying the medium in the low temperature region of the medium stored in the reserve tank to the reflux path of the heat exchanger, and taking out the medium in the high temperature region in the reserve tank from the reserve tank. By doing so, the temperature of the heat medium flowing back through the heat exchanger is increased, so that even if more heat is taken from the high-temperature gas to be disposed of than before and the temperature is lowered, the heat exchanger is The outside temperature of the metal pipe inside the vessel does not drop below the acid dew point, which reduces sulfuric acid condensation and prevents oxidative corrosion, dramatically extending the life of the heat exchanger. Furthermore, according to the present invention, by supplying heated hot water to the metal pipe, hot water at a higher temperature than before can be obtained, and the efficiency of heat recovery can be improved.

[Brief explanation of the drawing]

Figure 1 is a schematic configuration diagram of a waste heat recovery device showing an embodiment of the present invention, and Figure 2 is a pipe wall cross section used to illustrate the relationship between the acid dew point and the temperature on both sides of the metal pipe. The schematic diagram and FIG. 3 are schematic configuration diagrams showing a conventional waste heat recovery device. Reference numeral 1 in the figure: solvent gas treatment device, 3: heat exchanger, 11: reserve tank, 13: outer tank, 14: inner tank, 16: water pump 20. ...Discharge pump 31...Acid dew point. 2... Steam recovery device, 4... Chimney, 12... Water supply pipe, 13a... First tank, 15... Lifting pipe, 17.18... Pipe, 30... Pipe wall Section, Figure Figure

Claims (1)

[Claims] Waste heat in which the high-temperature gas to be discharged is supplied to a heat exchanger, a low-temperature heat medium is refluxed to the high-temperature gas through a reflux path provided in the heat exchanger, and heat is recovered from the high-temperature gas by the heat medium. In the recovery device, a reserve tank is provided to store the heat medium at room temperature and the heat medium heated by reflux in the heat exchanger in a state of natural mixing, and among the medium stored in the reserve tank, A supply means for supplying the medium in the low temperature region to the reflux path of the heat exchanger, and a recovery means for taking out the medium in the high temperature region in the reserve tank from the reserve tank. A waste heat recovery device characterized in that it is configured to increase the temperature of the heat medium that is refluxed.