KR101969302B1 - Waste heat recovery system and method for protecting low temperature corrosion of a recuperator - Google Patents

Abstract

The present invention relates to a heat exchanger which is installed in a flue gas duct and recovers waste heat from a high temperature flue gas; A first supply conduit for supplying combustion air to the heat exchanger; A second supply conduit for supplying the combustion air heated in the heat exchanger to the combustion device; And a third supply pipe branched from the first supply pipe and supplying combustion air to the combustion device. According to the present invention, it is possible to prevent the occurrence of low-temperature corrosion due to condensation of corrosive components in exhaust gas generated by combustion of a fuel containing an existing corrosive component, thereby preventing deterioration of performance of the heat exchanger due to pitting and corrosion of the heat exchanger, It is possible to prevent frequent facility change.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a waste heat recovery apparatus and a waste heat recovery heat exchanger,

The present invention relates to a waste heat recovery apparatus and a method for preventing low temperature corrosion of a waste heat recovery heat exchanger.

When the material is heated in the furnace, the exhaust gas generated through the burner for burning the fuel is heated to the outside of the furnace after heating the material in the furnace. The amount of heat of the exhaust gas discharged is the largest Respectively.

The heat loss of the flue gas is the second largest after the amount of heat generated by the heating material. In this respect, if the exhaust gas heat is reduced or a part of the exhaust gas heat is recovered, the overall thermal efficiency can be improved.

In this respect, the equipment used for combustion of industrial boilers or fuels or incineration of wastes is to recover the waste heat contained in the exhaust gas discharged to the atmosphere and to reuse it for the supply of hot water or heating or other purposes, Various types of waste heat recovering devices are installed and used so that efficient consumption can be achieved.

A typical example of the waste heat recovering apparatus is a heat exchanger installed in a path through which exhaust gas is discharged, and a combustion air or cold water is introduced into the heat exchanger to heat the waste heat recovering apparatus.

Since the heat exchanger typically uses a metal heat exchanger, the temperature of the exhaust gas is controlled to a certain temperature or lower to prevent breakage due to the high temperature exhaust gas. The temperature of the exhaust gas is usually regulated to about 800 to 820 ° C., Dilution air is injected.

However, if the amount of the dilution air or the amount of the combustion air is excessively supplied to lower the temperature of the heat exchanger in the high temperature part, the exhaust gas temperature of the low temperature part heat exchanger becomes excessively low.

In this case, when corrosive components are contained in the flue gas, these components become liquid in the gaseous state and can cause corrosion of the heat exchanger. Therefore, it is specified in the design of the heat exchanger in general and reflected in the design. .

For example, a combustible material such as an incinerator contains a large amount of flammable sulfur (S). When this sulfur component is burnt, sulfurous acid gas (SO ₂ ) is generated and this sulfurous acid gas combines with excess oxygen during combustion, Sulfuric acid (SO ₃ ) is produced.

In addition, the hydrogen (H ₂ ) component in the burned material is burned to generate water vapor (H ₂ O), which is bound to anhydrous sulfuric acid and transformed into a sulfuric acid (H ₂ SO ₄ ) .

The sulfuric acid component easily condenses on the wall surface of the heat exchanger tube at the downstream portion of the waste heat recovery apparatus where the flue gas becomes low temperature. In particular, when the tube is made of iron, the sulfuric acid component causes severe corrosion.

Therefore, in the waste heat recovery apparatus for treating the exhaust gas containing sulfuric acid component, a method for minimizing the low temperature erosion phenomenon of the heat exchanger tube occurring in the downstream portion of the waste heat recovery apparatus described above should be secured.

However, in view of the possibility that the entire system can be stopped due to leakage in the heat exchanger tube during operation despite the economical efficiency due to the waste heat recovery of the exhaust gas because the measures are not easily secured, There is a situation in which the installation of a waste heat recovery device is abandoned.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and it is an object of the present invention to provide a waste heat recovery apparatus capable of preventing low-temperature corrosion of a heat exchanger included in a waste heat recovery apparatus and heating combustion air to a high temperature.

Another object of the present invention is to provide a method of operating a waste heat recovery apparatus capable of preventing a low temperature erosion phenomenon of a heat exchanger in a waste heat recovery apparatus.

According to an embodiment of the present invention, there is provided a heat exchanger comprising: a heat exchanger installed in an exhaust gas duct to recover waste heat from a hot exhaust gas; A first supply conduit for supplying combustion air to the heat exchanger; A second supply conduit for supplying the combustion air heated in the heat exchanger to the combustion device; And a third supply pipe branched from the first supply pipe and supplying combustion air to the combustion device.

And a bypass conduit branching at the second supply conduit and recirculating the heated combustion air to the first supply conduit.

And a control valve which is located on the first supply pipe and controls opening and closing of the first supply pipe and the third supply pipe.

And a control unit for controlling the opening and closing of the control valve based on the temperature of the exhaust gas.

And a control valve which is located on the second supply pipe and controls opening and closing of the bypass pipe.

And a control unit for controlling the opening and closing of the control valve based on the temperature of the exhaust gas.

And a temperature sensing sensor for measuring the temperature of the exhaust gas.

The heat exchanger may be at least two or more.

The heat exchanger may include a low temperature heat exchanger connected to the first supply duct and a high temperature heat exchanger connected to the second supply duct.

According to another embodiment of the present invention, there is provided a heat exchanger comprising: a heat exchanger installed in an exhaust gas duct to recover waste heat from a hot exhaust gas; A first supply conduit for supplying combustion air to the heat exchanger; A second supply conduit for supplying the combustion air heated in the heat exchanger to the combustion device; A third supply pipe branched from the first supply pipe to supply combustion air to the combustion device; And a bypass pipe for recirculating the heated combustion air from the second supply pipe to the first supply pipe, wherein when the temperature of the exhaust gas is lower than the set temperature, the third supply A waste heat recovery device for supplying combustion air to a combustion device through a conduit and supplying combustion air to a first supply conduit when the temperature of the exhaust gas is equal to or higher than a set temperature, A heat exchanger low temperature corrosion method is provided.

A part of the combustion air supplied to the combustion device through the second supply conduit can be recirculated to the first supply conduit through the bypass conduit.

The temperature of the combustion air supplied through the third supply line may be 10 to 30.

And the temperature of the combustion air supplied through the second supply line may be 550 to 750. [

The temperature of the mixed air in which the combustion air supplied through the first supply conduit and the combustion air recirculated through the bypass conduit are mixed may be 150 to 300 ° C.

According to the present invention, it is possible to prevent the occurrence of low-temperature corrosion due to condensation of corrosive components in exhaust gas generated by combustion of a fuel containing an existing corrosive component, thereby preventing deterioration of performance of the heat exchanger due to pitting and corrosion of the heat exchanger, It is possible to prevent frequent facility change.

In addition, by improving the preheating temperature of the combustion air finally obtained by the rise of the combustion air introduced into the heat exchanger, it is possible to improve the longevity and thermal efficiency of the equipment.

Fig. 1 schematically shows the concept of the waste heat recovery apparatus of the present invention.

Hereinafter, preferred embodiments of the present invention will be described with reference to various embodiments. However, the embodiments of the present invention can be modified into various other forms, and the scope of the present invention is not limited to the embodiments described below.

1 is a schematic view schematically showing the concept of a waste heat recovery apparatus of the present invention. Hereinafter, the waste heat recovery apparatus of the present invention will be described in detail with reference to FIG. However, the present invention is not limited thereto, and the present invention is only defined by the scope of the following claims.

According to an aspect of the present invention, there is provided a heat exchanger comprising: a heat exchanger installed in an exhaust gas duct to recover waste heat from a high temperature exhaust gas; A first supply conduit for supplying combustion air to the heat exchanger; A second supply conduit for supplying the combustion air heated in the heat exchanger to the combustion device; And a third supply pipe branched from the first supply pipe to supply combustion air to the combustion device.

A heat exchanger is a device that allows heat to be exchanged between two fluids, which in a broad sense includes heaters, coolers, and condensers, but usually means heat recovery.

The heat exchanger may be composed of at least two heat exchangers, preferably a low temperature heat exchanger connected to the first supply duct and a high temperature heat exchanger connected to the second supply duct.

The material of the heat exchanger is preferably made of a corrosion-resistant material and may be made of a conventional material. For example, it may be made of stainless steel, high temperature resistant steel (chromium added steel) or the like.

Generally, the heat exchanger installed in the flue gas duct determines the heat exchange area and the shape of the heat pipe in order to recover the maximum amount of waste heat based on the amount of combustion air required for the heating furnace. The heat transfer pipe for the heat exchange and the exhaust gas temperature after heat exchange are determined.

In order to prevent breakage of the heat exchanger made of metallic material by the high-temperature flue gas, the flue gas temperature is controlled to a certain temperature or less. Normally, it is regulated to about 800 to 820 DEG C, and if the exhaust gas temperature is higher than this, dilution air is supplied.

Table 1 shows the calculated values for the amount of exhaust gas generated during the actual heating operation and the temperature and the amount of diluted air injected to protect the heat exchanger.

Referring to Table 1, it can be seen that the amount of exhaust gas shown in the table is 80,000 M ³ / Hr, 910 ° C., and the dilution air amount 9,000 M ³ / Hr is required to satisfy 830 ° C. front heat exchanger temperature.

In addition, when the combustion air amount required for continuous combustion is 77,000 M ³ / Hr, the outlet temperature of the high-temperature heat exchanger is 649.2 ° C and the outlet temperature of the low-temperature heat exchanger is 371 ° C.

At this time, since the outlet temperature of the high temperature heat exchanger is 649.2 DEG C higher than that of the combustion air 630 DEG C, it is required to further lower the outlet flue gas temperature of the high temperature heat exchanger in order to protect the heat exchanger.

Accordingly, in order to prevent overheating of the high temperature heat exchanger, when the combustion air volume is 97,000 M ³ / Hr and the outlet temperature of the high temperature heat exchanger is lowered from 649.2 ° C. to 602.3 ° C., the outlet temperature of the low temperature heat exchanger is changed from 371 ° C. to 251.9 ° C. .

However, if the amount of the dilution air or the amount of the combustion air is excessively supplied to lower the temperature of the heat exchanger at the high temperature part as described above, the temperature of the exhaust gas of the low temperature part heat exchanger becomes excessively low.

If corrosive components are contained in the flue-gas, these components become liquid in the gaseous state and can cause corrosion of the heat exchanger. Therefore, it is prescribed in designing the heat exchanger in general and reflected in design, .

Table 2 shows the specifications considering the reference specifications and the maximum operating conditions of the heat exchanger applied to the heating furnace.

As shown in Table 2, in order to heat the combustion air from 20 ° C to 630 ° C, the exhaust gas temperature was lowered from 830 ° C to 384 ° C, and the condensation temperature of the conventionally known corrosive components SO ₂ , SO ₃ was 150 ° C It can be seen that it is designed to manage the heat exchanger tube temperature.

Table 3 shows the actual operating conditions of the heat exchanger applied to the heating furnace.

Referring to Table 3, the flue gas temperature at the outlet of the heat exchanger is 328 ° C and 265.8 ° C, which shows a situation outside the design condition.

Of course, the temperature is well above 150 ° C, which is known as the condensation temperature of the corrosive component, but the measured temperature at the outlet of the heat exchanger is only one point of the flue gas flow, which is about 4 M * 2.2 M It is hard to imagine that the temperatures at all the points across are the same.

Also, in the case of winter, when cold atmospheric air is introduced, the flue gas on the outgoing side of the heat exchanger, which is in contact with the heat exchange tube that passes cold air in the beginning, is rapidly cooled down and the possibility of the corrosive component is increased .

 Particularly, when the heating device is first started and stopped, the amount of fuel injected is small, and since a large amount of heat from the generated combustion gas is raised at the time of starting the heating device, the heat flux increases to increase the temperature of the exhaust gas The possibility of condensation of the corrosive component is further increased.

When starting and stopping the combustion device in this manner, the combustion device must operate at a considerably low operating rate, not 100% of the operating capacity, since the temperature rise and fall rate must be adhered to for the safety of the thermal equipment concerned. At this time, when the combustion air is preheated through the heat exchanger, the temperature of the heat exchanger is excessively lowered, and the possibility of the corrosive component to be condensed becomes large.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide a combustion apparatus which includes a third supply pipe branched from a first supply pipe and supplying combustion air to a combustion apparatus.

That is, when the combustion apparatus is started and stopped, the air having the sucked temperature is directly blown through the third supply duct connected to the combustion apparatus without preheating the combustion air to be supplied to the combustion facility, .

The temperature of the combustion air supplied to the combustion apparatus through the third supply conduit is not particularly limited to the temperature of the intake air from the outside, but may be, for example, 10 to 30, and preferably 15 to 25 .

On the other hand, in a normal operation state, a part of the combustion air preheated through the heat exchanger can be bypassed and mixed with the combustion air directly supplied from the outside. Accordingly, when the outside air having a low temperature is directly introduced, the temperature of the air passage tube for combustion of the heat exchanger is prevented from being lowered to the temperature at which the corrosive component is condensed, thereby managing the possibility of low temperature corrosion.

To this end, the present invention includes a bypass conduit that branches off from the second supply conduit and recirculates the heated combustion air to the first supply conduit.

In addition, the present invention may include a control valve for controlling opening and closing of the first supply pipe and the third supply pipe, and a control valve for controlling opening and closing of the bypass pipe.

The operation of the control valve may be performed manually by an operator, but the present invention is not limited thereto. The control valve may further include a controller for electronically controlling and actuating the valve using a motorized valve.

To this end, a suitable number of pressure gauges, a thermometer, an orifice part, a flow meter, a flow rate sensor and a temperature sensor are suitably arranged on the first supply pipe and the first supply pipe.

In particular, it is possible to control opening and closing of the control valve according to whether the sensed temperature falls within a predetermined range based on the electric signal received from the temperature sensor, and the control valve can be partially opened.

When the temperature of the flue gas and the temperature of the heat exchanger rise above the set temperature, the combustion air is supplied directly to the heat exchanger through the first supply conduit instead of directly through the third supply conduit, and the combustion air is preheated And supplied to the combustion apparatus.

The temperature of the combustion air heated by the heat exchanger and supplied to the combustion apparatus through the second supply duct may be from 550 to 750, and preferably from 600 to 700. [

The combustion air supplied to the combustion apparatus through the second supply line can be recirculated through a bypass line disposed on the second supply line. The amount of exhaust gas generated at this time, the temperature of the exhaust gas, The amount of combustion air recirculated on the basis of the required amount of combustion air can be increased in consideration of the temperature.

The recirculated combustion air is mixed with the combustion air supplied through the first supply conduit.

As described above, the low-temperature combustion air newly supplied through the first supply conduit is mixed with the high-temperature combustion air recirculated through the bypass conduit and introduced into the heat exchanger, whereby the temperature of the low- The liquefaction temperature of the corrosion component contained in the heat exchanger can be maintained.

The temperature of the mixed air mixed with the combustion air supplied through the first supply duct and the combustion air recirculated through the bypass duct is higher than the liquefying temperature of the corrosive component contained in the exhaust gas and is, for example, 150 to 300 ° C And preferably 180 to 250 ° C.

For example, if the required combustion air volume is 100,000M ³ / Hr and the temperature of the outside air is 20 ° C, the air volume of about 22 to 23% is recirculated if the target combustion air initial target temperature is 150 ° C . In this case, when the amount of air to be preheated in the heat exchanger is increased to 123,000 M ³ / Hr by increasing the amount of air sequentially injected for a predetermined time,

That is, the amount of air 100,000M ³ / Hr and an air pre-heating recycled 23,000 M ³ / Hr, which is pre-heated to 650 ℃ input from the outside is preheated in the heat exchanger, ³ / Hr of which 100,000M is supplied to the combustion device. At this time, 23,000M ³ / Hr can be recycled through the bypass pipe, and the initial temperature of the combustion air injected to the low temperature side of the heat exchanger can be secured at 150 ° C.

Although a specific example has been described above, such an operation method and setting of the initial target air temperature for combustion differ depending on the type of fuel used, the temperature of the exhaust gas generated, and the amount of exhaust gas, and the setting for the recirculated air amount It should be done.

 However, since the above-mentioned matters are the control measures to be operated according to the situation in the field, there is no difference in the application of the technology proposed in the present invention, and in particular, it is possible to worry about the thermal efficiency loss due to application of cold outside air at the time of initial startup and shutdown , Which is a time corresponding to a very small part of the operation of the heating apparatus. Since the exhaust gas heat recoverable through the exhaust gas heat at this time is also insignificant, the effect on the thermal efficiency side of the apparatus will not be large.

For example described way, is set as the combustion air temperature for which input from the outside 20 ℃, 650 ℃ the for the preheated combustion air temperature, the required air quantity 100,000 M ³ / for Hr total heat exchanger 20,628,090 Kcal / Hr I Calories are required.

If at this time the necessary amount of air 100,000 M ³ / Hr addition to inject additional air at 10%, 20%, 30%, further applying the method of recycling the additional amount of air introduced into the 20 ℃ is introduced initially, 100,000 M ³ / Hr air Were measured and shown in Table 4 below.

Referring to Table 4, it can be seen that as the air amount is further increased by 10%, 20%, and 30% at an initial temperature of 20 ° C, the initially introduced temperatures change to 87 ° C, 133 ° C, 172 ° C and 206 ° C, respectively. In addition, the amount of heat required to secure a combustion air temperature of 650 ° C is 20,380,000 to 20,670,000 Kcal / Hr, and it can be seen that there is almost no change in the heat transfer amount of the heat exchanger due to the preheating air recirculation.

As shown in the following Table 5, even when the amount of the preheated air is increased by 27% in the same heat exchanger, the performance against the thermal efficiency can be improved by the increase of the flow rate in the heat exchanger due to the added air amount. 95%, respectively.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary, It will be obvious to those of ordinary skill in the art.

Claims (14)

A heat exchanger installed in the flue gas duct and recovering waste heat from a high temperature flue gas;
A first supply conduit for supplying combustion air to the heat exchanger;
A second supply conduit for supplying the combustion air heated in the heat exchanger to the combustion device;
A bypass conduit branching from the second supply conduit and recirculating the heated combustion air to the first supply conduit; And
And a third supply pipe branched from the first supply pipe and supplying combustion air to the combustion device,
And the combustion air is supplied to the combustion device through the third supply pipe when the combustion device starts and stops.
delete The method according to claim 1,
And a control valve which is located on the first supply conduit and controls opening and closing of the first supply conduit and the third supply conduit.
The method of claim 3,
Further comprising a control unit for controlling the opening and closing of the control valve based on the temperature of the exhaust gas.
The method according to claim 1,
And a control valve located on the second supply line for controlling the opening and closing of the bypass pipe.
6. The method of claim 5,
Further comprising a control unit for controlling the opening and closing of the control valve based on the temperature of the exhaust gas.
The method according to claim 1,
And a temperature sensor for measuring the temperature of the exhaust gas.
The method according to claim 1,
Wherein the heat exchanger has at least two heat exchangers.
The method according to claim 1,
Wherein the heat exchanger comprises a low temperature heat exchanger connected to the first supply duct and a high temperature heat exchanger connected to the second supply duct.
A heat exchanger installed in the flue gas duct and recovering waste heat from a high temperature flue gas; A first supply conduit for supplying combustion air to the heat exchanger; A second supply conduit for supplying the combustion air heated in the heat exchanger to the combustion device; A third supply pipe branched from the first supply pipe to supply combustion air to the combustion device; And a detour conduit for recirculating the heated combustion air branched from the second supply conduit to the first supply conduit, the method comprising the steps of:
The combustion air is supplied to the combustion device through the third supply conduit when the combustion device is started and stopped,
And supplying combustion air to the first supply conduit and supplying the combustion air to the second supply conduit to the combustion device during operation of the combustion device.
11. The method of claim 10,
Wherein a part of the combustion air supplied to the combustion device through the second supply conduit is recirculated to the first supply conduit through the bypass conduit.
11. The method of claim 10,
Wherein the temperature of the combustion air supplied through the third supply conduit is 10 to 30 占 폚.
11. The method of claim 10,
Wherein the temperature of the combustion air supplied through the second supply line is 550 to 750 ° C.
12. The method of claim 11,
Wherein the temperature of the mixed air mixed with the combustion air supplied through the first supply pipe and the combustion air recirculated through the bypass pipe is 150 to 300 ° C.

Images