JP2000304231A - Heat recovery apparatus from exhaust gas and method of heat recovery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the apparatus and the method of recovering heat from exhaust gas, which can heat cooling water to the temperature higher than the moisture saturation temperature of the exhaust gas without the adhesion of the mist of sulfuric acid and/or soot and dust. SOLUTION: The apparatus of recovering heat from the exhaust gas comprises a casing 1 including an intake 3 introducing exhaust gas 8 and an outlet 4 discharging the cooled exhaust gas, and a cooling water pipe 2 recovering heat from the exhaust gas to the cooling water through a heat exchanging surface arranged inside the casing 1, wherein the cooling water pipe 2 is arranged from the intake side 3 of the outlet side 4 and then back to the intake side 3 of the casing, the mechanism of reversing the direction of the flow of cooling water flowing in the piping is provided, the casing 1 is provided with supply and drain water headers 5 and 6 for connecting to the cooling water piping, the external pipes 12 and 12' are connected to the headers, the pipes are provided with bypass pipes 19 and 20, these pipes are provided with valves 15 to 18 and the direction of the water flowing inside the pipes is reversed by the switching of the valves.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to heat recovery from exhaust gas, and more particularly to a heat recovery apparatus and method for recovering heat from exhaust gas containing water, sulfur oxides and / or dust using cooling water. .

[0002]

2. Description of the Related Art Conventionally, high-temperature gas such as boiler combustion exhaust gas is indirectly exchanged with cooling water through a heat exchange surface to recover heat from the exhaust gas. Exhaust gas is usually combined with water with sulfur oxides and / or
Or dust, which causes various problems. First, when the exhaust gas contains sulfur oxides, particularly, sulfur trioxide in the sulfur oxides absorbs moisture in the exhaust gas to form a sulfuric acid mist, and these are formed on the heat exchange surface on the gas contact side (hereinafter referred to as gas contact gas). The heat exchange surface is corroded by adhering to the surface.
On the other hand, when the exhaust gas contains dust, the dust adheres to the gas contact surface, thereby lowering the heat transfer rate and consequently reducing the amount of heat exchange. To solve these problems,
First, the inventors first adjust the temperature of the cooling water, the flow rate of the cooling water, or at least one of the heat exchange area, so that the surface temperature of the gas contact surface is equal to or lower than the moisture saturation temperature of the exhaust gas. Heat recovery method was proposed. According to this method, the condensed water generated by the condensation of the moisture contained in the high-temperature exhaust gas such as the boiler combustion exhaust gas on the gas contact surface is used to wash out the sulfuric acid mist and / or dust adhering to the gas contact surface. Can solve the problem.

[0003] However, since the surface temperature of the gas contact surface is higher than the temperature of the cooling water in contact with the portion, the exhaust gas and the heat must be reduced to keep the surface temperature of all portions of the gas contact surface below the moisture saturation temperature. The temperature of the cooling water after the replacement needs to be lower than the water saturation temperature of the exhaust gas. Therefore, in order to sufficiently wash out the sulfuric acid mist and / or dust adhering to the gas contact surface, the temperature of the cooling water cannot be higher than the water saturation temperature. Table 1 below shows the water saturation temperature for each water concentration in the exhaust gas. Since the water concentration of the normal boiler combustion exhaust gas is about 5 to 15%,
In order to avoid the problem of sulfuric acid mist and / or dust attached to the gas contact surface, the upper limit of the temperature of the cooling water after heat recovery is about 35 to 55 ° C.

[0004]

[Table 1] Generally, in order to effectively use the recovered heat, it is desired that the temperature of the heat recovery medium be as high as possible. In this manner, if the temperature of the cooling water after the heat recovery is about 33 to 55 ° C. or less. If so, it would be very difficult to use the recovered heat.

[0005]

SUMMARY OF THE INVENTION Accordingly, the present invention is directed to a problem associated with the attachment of sulfuric acid mist and / or dust generated by sulfur oxide from a gas containing moisture and sulfur oxide and / or dust. It is an object of the present invention to provide an apparatus and a method for recovering heat from exhaust gas, which can avoid cooling and can heat the cooling water to a temperature equal to or higher than the water saturation temperature of the exhaust gas.

[0006]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a casing having an intake port for introducing exhaust gas and an exhaust port for discharging exhaust gas after cooling, and a heat pump disposed inside the casing. A heat recovery apparatus for exhaust gas, comprising: a cooling water pipe for recovering heat from the exhaust gas to the cooling water through an exchange surface, wherein the cooling water pipe extends from the intake port side to the exhaust port side of the casing. The heat recovery device is provided so as to return to the intake port side and has a mechanism capable of reversing the direction of cooling water flowing in the pipe. In the heat recovery device, the casing may be provided with a water supply / drain header connected to a cooling water pipe for alternately supplying cooling water and collecting the cooling water, and the cooling water pipe may have an inlet port of the casing. The cooling water pipe may be connected by a U-shaped pipe outside the casing, and the casing may be cooled by the side. A relay header to which a water pipe is connected can be provided, and the cooling water pipe can be a fin tube having a fin on a gas contact side.

In the present invention, the mechanism capable of reversing the direction of the cooling water flowing through the cooling water pipe includes a pipe for supplying and recovering the cooling water connected to the cooling water pipe, and a bypass pipe connecting the two. A switching valve can be arranged in the pipe of the above, and the direction of the water flowing in the cooling water pipe can be reversed by operating the switching valve. Further, in the present invention, a method of recovering heat from exhaust gas, wherein a pipe is provided in an exhaust gas passage through which exhaust gas containing moisture, sulfur oxides and / or dust is passed, and heat is recovered from the exhaust gas through cooling water in the pipe. In the above, the pipe through which the cooling water passes is disposed so as to return from the intake port side of the exhaust gas to the exhaust port side and then return to the intake port side, and the cooling water in the pipe is alternately passed in the reverse direction, Is a heat recovery method in which the temperature of the heat exchange surface on the gas contact side in the portion from the intake port side to the exhaust port side is adjusted to be equal to or lower than the water saturation temperature of the exhaust gas.

In the heat recovery method, the temperature of the gas-exchange side exchange surface is adjusted by at least one of a temperature of a cooling water supplied to the cooling water pipe, a flow rate of the cooling water, and a heat exchange area. it can. Further, in the present invention, in a boiler facility having a boiler, a condenser, a boiler feedwater pump, and a boiler combustion exhaust gas duct, the heat recovery device described above is installed in the boiler combustion exhaust gas duct, and the cooling water of the heat exchanger is used as the cooling water. The boiler equipment supplies all or a part of the condensed water condensed by the condenser and supplies the cooling water after heat recovery to the boiler.

[0009]

According to the heat recovery method of the present invention, the temperature of the gas contact surface of the portion of the cooling water pipe from the intake port side to the exhaust port side (hereinafter referred to as a co-current portion) is determined by the water content of the exhaust gas. Since the water is cooled below the saturation temperature, the condensed water generated by the condensation of the water contained in the exhaust gas flushes out the sulfuric acid mist and / or dust adhering to the gas contact surface of the co-current portion. Can solve the problem that mist and dust adhere. On the other hand, the cooling water that has been heated in the co-current portion at a temperature equal to or lower than the moisture saturation temperature of the high-temperature exhaust gas is further heated in a portion of the cooling water pipe from the exhaust port side to the intake port side (hereinafter, a counter-current portion). Therefore, the cooling water can be finally heated to a temperature equal to or higher than the water saturation temperature of the exhaust gas.

[0010] By the way, the temperature of the gas contact surface of the part where the cooling water flows near the water saturation temperature of the exhaust gas or exceeds the water saturation temperature of the exhaust gas in the counter-current part of the cooling water pipe is lower than the water saturation temperature of the exhaust gas. Therefore, the moisture contained in the exhaust gas does not condense, and therefore, it is not possible to wash away the sulfuric acid mist and / or dust, which are attached to the gas contact surface. In general, the temperature of the cooling water flowing in the countercurrent portion increases as the cooling water approaches the air supply side, and condensed water is not generated. It becomes remarkable. However, in the heat recovery method of the present invention, the direction in which the cooling water flows periodically reverses due to the mechanism of the heat recovery device of the present invention that can reverse the flowing direction of the cooling water. In the next cycle, the cooling water pipe will become a co-current part in the next cycle, and in particular, the part on the air supply side of the It is on the air supply side of the co-current portion where the temperature is the lowest and a large amount of condensed water is generated.

Therefore, since the temperature of the gas contact surface of the cooling water pipe is equal to or higher than the water saturation temperature of the exhaust gas in a certain cycle,
Even if there is a place where the deposits of sulfuric acid mist and / or dust are not washed away, the deposits are washed away by the condensed water generated when the temperature falls below the water saturation temperature in the next cycle. Reversing the flow of cooling water, if it is only necessary to periodically switch the cocurrent portion to the countercurrent portion and the countercurrent portion to the cocurrent portion, if the cooling water pipe is moved from the exhaust port side to the air supply port side After reaching, it is also possible to arrange so as to return to the intake port side, and the gas contact side heat exchange surface (hereinafter, referred to as the counterflow portion in this case) of the cooling water pipe
If the temperature of the gas contact surface is adjusted so as to be equal to or lower than the water saturation temperature of the exhaust gas, an alternative method is also possible in which the condensed water that is periodically generated is used to wash off the deposits that are sulfuric acid mist and / or dust. .

However, in general, since the heat exchange efficiency is higher in the countercurrent flow than in the parallel flow, the heat recovery device having the same heat exchange area is installed in the upstream part of the cooling pipe (in the present invention, the cocurrent part,
If the operation is performed under the condition that the temperature of the gas contact surface of the countercurrent part in the alternative method) is lower than the moisture saturation temperature of the exhaust gas,
The temperature of the finally obtained cooling water is higher in the case of the present invention. Therefore, from the viewpoint of effective use of the heat recovered in the cooling water as the heat recovery medium, the heat recovery apparatus and method of the present invention are more preferable. Hereinafter, the present invention will be described in detail with reference to the drawings. The heat recovery apparatus of the present invention can be variously changed depending on a method of laying a cooling water pipe, and some examples thereof will be described below.

FIG. 1 shows an example of a heat recovery apparatus embodying the present invention, and FIG. 1 (a) is an overall configuration diagram of the present invention.
(B) is AA sectional drawing of (a). In FIG.
1 is a casing, 2 is a cooling water pipe (U-shaped pipe), 3 is an intake port, 4 is an exhaust port, 5 is a plumbing header (intake port side), 6
Is a supply / drain header (exhaust port side), 7 is a condensed water drain port, 8 is an exhaust gas, 9 is an exhaust gas duct, 12 and 12 'are cooling water supply / recovery pipes, 13 is supply cooling water, 14 is recovered cooling water, 15
Numeral 18 denotes a switching valve, and numerals 19 and 20 denote bypass pipes. FIG.
, A cooling water pipe 2 composed of a U-shaped pipe is connected to water supply / drain headers 5 and 6 provided on the side surface of the casing 1, and the cooling water flows from the intake port 3 side of the casing 1 to the exhaust port 4 side, and Return to mouth 3. The supply / drain headers 5 and 6 are separated by a partition plate into an air supply port side 5 and an exhaust port side 6.

The cooling water pipe 2 is connected to supply and recovery pipes 12 and 12 ′ outside the casing, and connected to supply cooling water 13 and recovery cooling water 14 via switching valves 15 and 18, respectively. , Pipes 12 and 12 ′ are connected by bypass pipes 19 and 20 having switching valves 16 and 17. The cooling water is supplied and recovered as shown in Table 2 by opening and closing the switching valves 15 to 18.

[Table 2]

By this valve operation, the flow of the cooling water in the cooling water pipe 2 can be periodically reversed. Also,
The condensed water generated on the surface of the cooling water pipe 2 is discharged from the condensed water discharge port 7. FIGS. 2A and 2B are configuration diagrams showing another example of a heat recovery device embodying the present invention, wherein FIG. 2A is a cross-sectional view along the flow direction of exhaust gas, and FIG.
FIG. 5C is a view taken in the direction of arrows B-B in FIG. 5A, and FIG. 5D is a view taken in the direction of arrows CC in FIG. In FIG. 2, the difference from FIG. 1 is that a U-shaped pipe 2 of a cooling water pipe is provided across the inside of the casing, and is connected by an interruption header 10 on the exhaust port side,
Also, the U-shaped tube 2 is located outside the casing 1
1 in that the connection is made.

As described above, in FIG. 2, the cooling water pipe 2 joined with the U-shaped pipe is connected to the U-shaped pipe 1 outside the heat recovery apparatus.
1 and the other end is connected to the water supply / drainage headers 5 and 6 provided near the intake port 3 or the relay header 10 provided near the exhaust port 4. The supply / drain header is divided by a partition plate into an air supply port side 5 and an exhaust port side 6, and the arrow in FIG. 2 indicates that the cooling water before cooling is supplied to the intake port side 5 and cooled at the exhaust port side 6. The flow of the cooling water in the case where the latter cooling water is collected is shown. The relay header 10 is divided for every two cooling water pipes, and the cooling water flowing from one of the cooling water pipes flows out to a series of cooling water pipes. The flow of the exhaust gas is periodically reversed by the operation of the switching valve similar to that shown in FIG.
The condensed water generated on the surface of the cooling water pipe is discharged from the condensed water discharge port 7.

Next, FIG. 3 shows an example of a process diagram for implementing a boiler facility using the heat recovery apparatus of the present invention. The flue gas discharged from the boiler 31 has a flow rate of 100,000 Nm.
³ / h containing 15% moisture (dry basis), boiler feed water and combustion air 3 with economizer 33 and air heater 34
After being heat-exchanged in step 9 and cooled to 150 ° C., it is introduced into the heat recovery unit 35 of the present invention. After leaving the turbine 32, the steam generated in the boiler 31 is condensed in a condenser 36 and cooled to 30 ° C. 100 tons of condensate
on / n is supplied as cooling water for the heat exchanger 35,
Heated to 75 ° C. by heat recovery from exhaust gas. The exhaust gas is cooled to 50 ° C. by the heat exchanger, and condensed water is generated at 2.5 tons. The cooling water after leaving the heat exchanger 35 is supplied to the boiler 31 after the pressure is increased by the boiler feed pump 37, the temperature is increased by the extraction of heat from the turbine 32 and the heat exchange with the exhaust gas in the economizer 33, and then the boiler 31 is supplied to the boiler 31. . In the heat recovery device 35, the temperature of the boiler feedwater supplied to the boiler is higher than the water saturation temperature of the exhaust gas without the sulfuric acid mist and / or soot and dust attached to the gas contact surface of the heat recovery device growing. Since the temperature can be increased to 75 ° C., the boiler efficiency can be greatly improved.

[0018]

According to the present invention, a sulfuric acid mist and / or dust generated by a sulfur oxide and / or dust from a gas containing moisture and sulfur oxide and / or dust does not adhere to and accumulate on a heat exchange surface. In addition, a heat recovery device from exhaust gas capable of heating the cooling water to a temperature equal to or higher than the water saturation temperature of the exhaust gas can be provided.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an example of a heat recovery apparatus of the present invention, where (a) is an overall view and (b) is a cross-sectional view taken along line AA of (a).

2A and 2B are configuration diagrams showing another example of the heat recovery device of the present invention, in which FIG. 2A is a cross-sectional view in the flow direction of exhaust gas, FIG. () Is a view on arrow BB in (a), and (d) is a view on arrow CC in (a).

FIG. 3 is a process diagram showing an example of a boiler facility using the heat recovery device of the present invention.

[Explanation of symbols]

1: casing, 2: cooling water piping (U-shaped piping), 3: intake port, 4: exhaust port, 5: intake port side supply / drain header, 6: exhaust port side supply / drain header, 7: condensed water drain port, 8: Exhaust gas,
9: exhaust gas duct, 10: relay header, 11: U-shaped pipe outside the casing, 12, 12 ': cooling water supply / recovery pipe, 1
3: supply cooling water, 14: recovered cooling water, 15 to 18: switching valve, 19, 20: bypass piping, 31: boiler, 32:
Turbine, 33: Economizer, 34: Air heater, 3
5: Heat recovery device, 36: Condenser, 37: Boiler feed pump, 38: Drain pump

Claims (10)

[Claims] 1. A casing having an intake port for introducing exhaust gas and an exhaust port for discharging exhaust gas after cooling, and cooling water for recovering heat from the exhaust gas to cooling water via a heat exchange surface provided inside the casing. A heat recovery device from exhaust gas comprising a pipe, wherein the cooling water pipe is disposed so as to return from the intake port side of the casing to the exhaust port side and then return to the intake port side, and A heat recovery device having a mechanism capable of reversing the direction of flowing cooling water. 2. The heat recovery device according to claim 1, wherein the casing is provided with a water supply / drain header connected to a cooling water pipe for alternately supplying cooling water and recovering the cooling water. 3. The heat recovery apparatus according to claim 1, wherein the cooling water pipe is a U-shaped pipe starting from an intake port side of a casing or a pipe connecting the U-shaped pipe. 4. The heat recovery apparatus according to claim 1, wherein the cooling water pipe is connected by a U-shaped pipe outside the casing. 5. The heat recovery device according to claim 1, wherein the casing is provided with a relay header to which a cooling water pipe is connected on a side surface. 6. The cooling water pipe is a fin tube having a fin on a gas contact side.
The heat recovery apparatus according to any one of claims 1 to 5. 7. A mechanism capable of reversing the direction of the cooling water flowing in the cooling water pipe comprises a pipe for supplying and recovering cooling water connected to the cooling water pipe, and a bypass pipe connecting the two. The heat recovery device according to any one of claims 1 to 6, wherein a switching valve is disposed in the pipe. 8. A method for recovering heat from exhaust gas, wherein a pipe is provided in an exhaust gas passage through which exhaust gas containing water, sulfur oxides and / or dust is passed, and heat from the exhaust gas is recovered through cooling water in the pipe. In the above, the pipe through which the cooling water passes is arranged so as to return from the intake port side of the exhaust gas to the exhaust port side and then return to the intake port side, and the cooling water in the pipe is alternately passed in the opposite direction, and from the intake port side. A heat recovery method comprising adjusting a temperature of a heat exchange surface on a gas contact side in a part reaching an exhaust port side to be equal to or lower than a moisture saturation temperature of exhaust gas. 9. The method of adjusting the temperature of the gas contact side heat exchange surface,
The heat recovery method according to claim 8, wherein the heat recovery is performed at least at one of a temperature of a cooling water supplied to the cooling water pipe, a flow rate of the cooling water, and a heat exchange area. 10. A boiler facility having a boiler, a condenser, a boiler feedwater pump, and a boiler combustion exhaust gas duct, wherein the heat recovery device according to any one of claims 1 to 7 is installed in the boiler combustion exhaust gas duct. Boiler equipment, wherein all or part of the condensate condensed in the condenser is supplied as cooling water for the heat exchanger, and the cooling water after heat recovery is supplied to the boiler.