JP2021060000A - Exhaust gas heat recovery method, exhaust gas heat recovery device, and exhaust gas heat recovery system - Google Patents

Abstract

To enable further recovery of heat energy from an exhaust gas which is exhausted from a boiler and from which heat energy is recovered by an economizer and enable desulfurization and denitration that do not need additive agents.SOLUTION: An exhaust gas heat recovery device 3 includes: a shell 31 serving as an exhaust gas passage formed by a tube body made of a corrosion resistant material; a tube 39 disposed within the shell 31 and serving as a cooling medium passage formed by a tube body made of a corrosion resistant material; and an outlet 38 of sulfuric acid generated by reaction between steam, which is contained in an exhaust gas flowing in the shell 31 and cooled by a cooling medium in heat exchange between the cooling medium flowing in the tube 39 and the exhaust gas flowing in the shell 31 to be condensed, and an SOx component.SELECTED DRAWING: Figure 2

Description

The present invention relates to an exhaust gas heat recovery method for recovering heat energy from an exhaust gas such as a boiler, an exhaust gas heat recovery device, and an exhaust gas heat recovery system.

Conventionally, the recovery of heat energy from exhaust gas from boilers is carried out by economizers, etc., but since boilers containing sulfur components are used as fuel, the exhaust gas is generated by combustion. SOx is contained, and if it is exhausted as it is, it may cause air pollution and acid rain.

Therefore, SOx is removed from the exhaust gas, but when the heat is recovered from the exhaust gas, if the temperature of the exhaust gas is lowered too much by heat recovery, the water in the gas is aggregated and the aggregated water reacts with SOx. The sulfuric acid produced by the above corrodes the equipment. Therefore, when recovering heat from the exhaust gas, the recovery temperature must be set high (about 150 ° C. or higher), and there is a limit to the recovery of heat energy. Further, since an additive (slaked lime or the like) is required for the treatment of SOx in the exhaust gas, there is a problem that the cost and the maintenance cost of the device are high and the maintenance cost of the device is high (for example, Patent Document 1). ).

In other words, in boilers (especially coal-cooked / heavy oil-cooked boilers, general waste incineration boilers), NOx (nitrogen oxide) components and SOx (sulfur oxide) components contained in exhaust gas are contained in the low temperature range of about 150 ° C or lower. Reacts with the condensed water and is extracted as corrosive nitrates and sulfuric acid, which causes low-temperature corrosion that corrodes the flue equipment after the economizer, shortening the life of the equipment and thus sufficient heat recovery. In addition, there is a separate cost for treating SOx in the exhaust gas.

Japanese Unexamined Patent Publication No. 2004-309079

The present invention has been made in view of such a situation, and an object of the present invention is to further recover heat energy from exhaust gas discharged from a boiler and recover heat energy by an economizer, and desulfurization that does not require additives. It is to enable desulfurization.

In the exhaust gas heat recovery method according to the present invention, the exhaust gas containing the NOx component and / or the SOx component discharged from the boiler and recovered by the economizer is discharged into an exhaust gas flow path made of a tube made of a corrosion-resistant material. The cooling medium is supplied to the cooling medium flow path made of a tube made of a corrosion-resistant material arranged inside the exhaust gas flow path, and heat is exchanged between the exhaust gas and the cooling medium. The first step and the second step of recovering nitric acid and / or sulfuric acid generated by the reaction between the water vapor in the exhaust gas condensed in the first step and the NOx component and / or the SOx component from the exhaust gas flow path. It is an exhaust gas heat recovery method having.
Further, the exhaust gas heat recovery device according to the present invention recovers heat energy from the exhaust gas containing the NOx component and / or the SOx component discharged from the boiler and the heat energy is recovered by the economizer, and also recovers the NOx component and / or the SOx component. An exhaust gas heat recovery device that removes heat from an exhaust gas, and is a cooling medium composed of an exhaust gas flow path made of a corrosion-resistant material tube and a corrosion-resistant material tube arranged inside the exhaust gas flow path. Water vapor in the exhaust gas in the exhaust gas flow path cooled by the cooling medium by heat exchange between the flow path, the cooling medium flowing in the cooling medium flow path, and the exhaust gas flowing in the exhaust gas flow path, and the exhaust gas in the exhaust gas. An exhaust gas heat recovery device having an outlet for nitric acid and / or sulfuric acid produced by a reaction with a NOx component and / or a SOx component.
Further, the exhaust gas heat recovery system according to the present invention includes an economizer for exchanging heat of exhaust gas containing NOx components and / or SOx components discharged from the boiler, and an exhaust gas heat recovery device according to the present invention. It is a system.

According to the present invention, it is possible to further recover the heat energy from the exhaust gas discharged from the boiler and recover the heat energy by the economizer, and to desulfurize / denitrate the waste without additives.

It is a figure which shows the exhaust gas heat recovery system which concerns on embodiment of this invention. It is a front view which shows the schematic structure of the exhaust gas heat recovery device which concerns on embodiment of this invention. It is a figure which shows the structure of the tube in the exhaust gas heat recovery apparatus which concerns on embodiment of this invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
<Structure of exhaust gas heat recovery system>
FIG. 1 is a diagram showing an exhaust gas heat recovery system according to an embodiment of the present invention. This exhaust gas heat recovery system has a function of recovering heat energy from the exhaust gas containing the SOx component discharged from the boiler 1 and desulfurization (removing the SOx component) without the need for additives as in the conventional case. The economizer 2, the exhaust gas heat recovery device 3, the water supply tank 4, and the deaerator 5 are provided.

In the boiler 1, the exhaust gas containing the SOx component at a predetermined temperature (here, 450 ° C.) is generated by burning the waste containing the sulfur component. The temperature of the exhaust gas changes depending on the combustion state of the boiler 1 and the like, and the above temperature is, for example, the temperature in steady operation. The temperature value is an example.

The economizer 2 converts the exhaust gas discharged from the boiler 1 into a lower temperature (150 ° C. here) exhaust gas by exchanging heat with hot water having a predetermined temperature (155 ° C. here) from the deaerator 5 described later. To do.

In the conventional exhaust gas heat recovery system, the exhaust gas at 150 ° C. is supplied to the desulfurization apparatus, desulfurized using an additive, and the exhaust gas at 150 ° C. after desulfurization is released into the atmosphere. On the other hand, in the exhaust gas heat recovery system according to the embodiment of the present invention, cold water and heat as a cooling medium at a predetermined temperature (here, 20 ° C.) in the exhaust gas heat recovery device 3 are applied to the exhaust gas at 150 ° C. By exchanging it, it is converted into a lower temperature (here, less than 100 ° C.) exhaust gas, and after escaping without using an additive, it is released into the atmosphere from the chimney 6. The mechanism of desulfurization by the exhaust gas heat recovery device 3 will be described later.

The exhaust gas heat recovery device 3 is provided with a tube 39 in a cylindrical shell 31 as described in detail later with reference to FIGS. 2 and 3, and includes cold water flowing in the tube 39 and exhaust gas flowing in the shell 31. The basic configuration is a so-called shell-and-tube heat exchanger that exchanges heat between the two.

In the water supply tank 4, hot water having risen to a predetermined temperature (here, 35 ° C.) is supplied from the exhaust gas heat recovery device 3 by heat exchange (heat energy recovery) with the exhaust gas in the exhaust gas heat recovery device 3. The temperature of the hot water supplied to the water supply tank 4 rises to a higher temperature (65 ° C. in this case) by supplying steam drain from a steam generation source (not shown).

The water whose temperature has risen in the water supply tank 4 is supplied to the deaerator 5. In the deaerator 5, by injecting steam from the steam generation source, gas components such as oxygen dissolved in the water supplied from the water supply tank 4 are separated and removed, and the water temperature is raised.

The water whose gas component is removed by the deaerator 5 and whose temperature has risen is supplied to the economizer 2 and exchanges heat with the exhaust gas from the boiler 1, so that the temperature rises from 155 ° C. to 215 ° C. Is supplied to.

<Outline configuration of exhaust gas heat recovery device>
FIG. 2 is a front view showing a schematic configuration of an exhaust gas heat recovery device according to an embodiment of the present invention. The exhaust gas heat recovery device 3 has a so-called shell-and-tube heat exchanger as a basic configuration, and has concentric tubes 39 as a chilled water flow path in a cylindrical shell (tube body) 31 as an exhaust gas flow path. Heat exchange is performed between the cold water flowing in the tube 39 (for example, 20 ° C.) and the exhaust gas flowing in the shell 31 (for example, 150 ° C.).

More specifically, the exhaust gas heat recovery device 3 includes a shell 31, a pipe plate 32 provided at both ends of the shell 31, a water (cold water) inlet 33 provided at one end (right end in the figure) of the shell 31, and a shell 31. The water (warm water) outlet 34 provided at the other end (left end in the figure) is provided.

Further, a plurality of (three here) exhaust gas inlets 36 are provided on the outer peripheral surface on one side (upper side here) of the shell 31, and one on the outer peripheral surface on the other side (lower side here) of the shell 31. The exhaust gas outlets 37 are provided. Both ends of the tube 39 are connected to the water (cold water) inlet 33 and the water (hot water) outlet 34, and the tubes 39 are concentrically arranged in the shell space 35 inside the shell 31. Here, the exhaust gas inlet 36 near the left end of the shell 31, that is, near the outlet 34 of water (hot water) is used, but by changing the exhaust gas inlet 36 to be used, the flow path length in the shell 31 of the exhaust gas is used. Can be changed to change the degree of heat exchange. The tube 39 is made of a material (for example, fluororesin) having corrosion resistance, heat resistance of 150 ° C. or higher, and flexibility.

Further, a sulfuric acid outlet 38 is provided on the lower outer peripheral surface near the left end of the shell 31. Here, a mechanism in which the SOx component becomes sulfuric acid in the exhaust gas heat recovery device 3 will be described. Water (cold water) is supplied into the tube 39 from the water (cold water) inlet 33 toward the water (hot water) outlet 34, and in the opposite direction to the cold water in the shell 31 from the exhaust gas inlet 36 toward the exhaust gas outlet 37. When the flowing exhaust gas is supplied, the surface of the tube 39 drops below the dew point, and the water vapor in the exhaust gas condenses, and the condensed water _{reacts with the SOx (SO 3} , SO ₂ ) components, resulting in sulfuric acid (sulfur dioxide). (Including) is generated. This sulfuric acid is finally taken out from the sulfuric acid outlet 38 through the inner wall of the shell 31 and the outer surface of the tube 39. Here, for convenience, the exhaust gas supplied into the shell 31 is described so as to flow along the outer peripheral surface of the tube 39, but as will be described later with reference to FIG. 3, the exhaust gas supplied into the shell 31 is described. A part flows in the tube 39 in a zigzag manner.

<Tube configuration>
FIG. 3 shows the configuration of the tube 39 in the exhaust gas heat recovery device according to the embodiment of the present invention. Here, FIG. 3A is a front view of the entire tube, FIG. 3B is a first holding plate (end plate), FIG. 3C is a second holding plate (baffle plate), and FIG. 3D is a third holding plate (baffle plate). It is a front view which shows.

The tube 39 includes a first connecting portion 39a provided at one end in the longitudinal direction (left end in the figure), a second connecting portion 39b provided at the other end in the longitudinal direction, and a core rod 39c provided at the outer peripheral portion. A plurality of chilled water pipes 39d forming a chilled water flow path extending in the longitudinal direction, first holding plates (partition plates) 39e arranged at both ends in the longitudinal direction, and first holding plates 39e at both ends alternately at predetermined intervals. A plurality of pairs of a second holding plate 39f and a third holding plate 39g arranged are provided.

The first connecting portion 39a and the second connecting portion 39b are connected to a water (cold water) inlet 33 and a water (hot water) outlet 34, respectively. Each holding plate is held by passing the core rod 39c through the insertion holes 39e1, 39f1, 39g1 of the first holding plate 39e, the second holding plate 39f, and the third holding plate 39g, respectively.

The chilled water pipe 39d is a thin pipe made of fluororesin, both ends of which are bundled by a first connecting portion 39a and a second connecting portion 39b, and a portion between both ends is a chilled water pipe provided on each holding plate. It is passed through the insertion hole. However, since the notch 39f2 is formed in the outer peripheral portion of the second holding plate 39f and the notch 39g2 is formed in the central portion of the third holding plate 39g, the first of the cold water pipes 39d The chilled water pipe passing through the outer peripheral portion of the holding plate 39e passes through the notch 39f2 of the second holding plate 39f, and the chilled water pipe passing through the central portion of the first holding plate 39e passes through the notch 39g2 of the third holding plate 39g. Therefore, there is a gap through which the exhaust gas flows between the large number of cold water pipes 39d in the notches 39f2 and 39g2.

In the shell 31 having the above configuration, the exhaust gas is supplied into the shell 31 from the exhaust gas inlet 36 and flows through the shell 31. At this time, the exhaust gas flows in a zigzag manner in the longitudinal direction of the shell 31 through the outer peripheral portion of the second holding plate 39f and the central portion of the third holding plate 39g. Therefore, as compared with the case where the exhaust gas flows linearly in the shell 31, the distance through which the exhaust gas flows becomes longer, so that the contact area with the condensed moisture can be widened, and the reaction with the SOx component can be promoted. .. Further, here, the number of the second holding plates 39f is 15 and the number of the third holding plates 39g is 14, but these holding plates are removable, and by increasing or decreasing the respective numbers, the exhaust gas is exhausted. You can increase or decrease the flow distance of. In addition, the tube path and exhaust gas flow can be changed by changing the shape of the second holding plate 39f and the third holding plate 39g (for example, changing the position of the notch, changing the insertion position of the exhaust pipe, etc.), changing the position, changing the interval, and adjusting the number of sheets. The route can be changed.

Next, examples of the present invention will be described.
The configuration of the embodiment is as follows.
System configuration: Same as FIG. 1 Material of shell 31: Stainless steel SUS304
Outer diameter of shell 31: 250 mm
Length of shell 31: 4197 mm
Configuration of tube 39: Same as FIG. 3 Operating conditions: Set to the temperature shown in FIG.

The measured values of the heat exchange capacity and the desulfurization capacity of the exhaust gas heat recovery device 3 in the above examples are shown in Table 1 below.

Here, the heat exchange capacity includes the measured value of the water temperature at the water inlet 33 of the shell 31, the measured value of the water temperature at the water outlet 34, the measured value of the exhaust gas temperature at the exhaust gas inlet 36 of the shell 31, and the exhaust gas at the exhaust gas outlet 37. It is calculated based on a predetermined formula from the measured value of temperature, the flow rate of water per fixed time, and the flow rate of exhaust gas. Also, the desulfurization capacity of SO ₂ component is a measure of the concentration of SO ₂ component in the vicinity of the exhaust gas outlet 37 in the shell 31. The desulfurization capacity of the drain is a measured value of the pH of sulfuric acid taken out from the outlet 38 of sulfuric acid.

From this table, it can be seen that the heat exchange capacity exceeds the target value. Further, _{it can be seen that the desulfurization capacity of the SO 2} component does not reach the target value, but a better value can be obtained than before the introduction of the apparatus.

As described in detail above, according to the exhaust gas heat recovery device 3 according to the embodiment of the present invention, the following effects (1) to (8) can be obtained.
(1) By constructing the flow path of the exhaust gas with a material having corrosion resistance and heat resistance of about 150 ° C. or higher, it is possible to impart resistance to sulfuric acid extracted in a temperature range of about 150 ° C. or lower. It is possible to recover thermal energy in a temperature range of about 150 ° C. or lower.
(2) By using a flexible material such as fluororesin for a material that has corrosion resistance and heat resistance of about 150 ° C or higher, the versatility of the shape design of the device is enhanced when it is additionally installed in existing equipment. ..
(3) By passing a cooling medium for positively dew condensation of water contained in the exhaust gas into the apparatus, the amount of dew condensation of water can be increased and the reaction with the SOx component can be promoted.
(4) By providing a partition plate (baffle plate) in the tube 39, which is the flow path of the exhaust gas, the length of the flow path of the exhaust gas can be increased and the contact area with the condensed moisture can be widened. Reaction can be promoted.
(5) By providing a plurality of exhaust gas inlets and selecting the exhaust gas inlet to be used, the flow path length of the exhaust gas can be changed and the contact area with the condensed moisture can be adjusted, so that the reaction with the SOx component can be adjusted. can do.
(6) Since water as a cooling medium used for promoting dew condensation is discharged in a state where the heat energy in the exhaust gas is passed on, this heat energy can be reused.
(7) By adding a function of recovering sulfuric acid extracted in a temperature range of 150 ° C. or lower in the apparatus, the equipment in the subsequent stage can be kept at the conventional specifications.
(8) Since desulfurization is performed by the reaction between the water contained in the exhaust gas and the SOx component, no additive is required.

As described above, as the embodiment of the present invention, the exhaust gas heat recovery system for treating the exhaust gas containing the SOx component has been described as an example, but the present invention can also be applied to the system for treating the exhaust gas containing the NOx component.

1 ... Boiler, 2 ... Economizer, 3 ... Exhaust gas heat recovery device, 31 ... Shell, 33 ... Water (cold water) inlet, 34 ... Water (hot water) outlet, 35 ... Shell space, 36 ... Exhaust gas inlet, 37 ... Exhaust gas Outlet, 38 ... Sulfuric acid outlet, 39 ... Tube, 39d ... Cold water pipe, 39e ... First holding plate, 39f ... Second holding plate, 39g ... Third holding plate.

Claims (7)

The exhaust gas containing the NOx component and / or the SOx component discharged from the boiler and recovered from the heat energy by the economizer is supplied into the exhaust gas flow path made of a tube made of a corrosion-resistant material, and the exhaust gas flow path of the exhaust gas flow path. The first step of supplying a cooling medium to a cooling medium flow path made of a tube body made of a corrosion-resistant material arranged inside and exchanging heat between the exhaust gas and the cooling medium.
An exhaust gas heat recovery method comprising a second step of recovering nitric acid and / or sulfuric acid generated by the reaction of water vapor in the exhaust gas condensed in the first step with the NOx component and / or the SOx component from the exhaust gas flow path. .. An exhaust gas heat recovery device that recovers heat energy from exhaust gas containing NOx components and / or SOx components that have been discharged from a boiler and whose heat energy has been recovered by an economizer, and also removes NOx components and / or SOx components.
An exhaust gas flow path made of a tube made of a corrosion-resistant material,
A cooling medium flow path made of a corrosion-resistant material tube arranged inside the exhaust gas flow path, and a cooling medium flow path.
Water vapor in the exhaust gas in the exhaust gas flow path that has been cooled by the cooling medium and condensed by heat exchange between the cooling medium flowing in the cooling medium flow path and the exhaust gas flowing in the exhaust gas flow path, the NOx component in the exhaust gas, and / Or the outlet of nitric acid and / or sulfuric acid produced by the reaction with the SOx component,
Exhaust gas heat recovery device with. In the exhaust gas heat recovery device according to claim 2.
The exhaust gas flow path is composed of a cylindrical shell, and a tube as a cooling medium flow path is arranged in the shell, and exhaust gas heat exchanges heat between the cold water flowing in the tube and the exhaust gas flowing in the shell. Recovery device. In the exhaust gas heat recovery device according to claim 3,
An exhaust gas heat recovery device in which exhaust gas inlets are provided at a plurality of positions in the longitudinal direction on the outer peripheral surface of the shell, and the length of the exhaust gas flow path can be changed by changing the exhaust gas inlets to which the tubes are connected. In the exhaust gas heat recovery device according to claim 3,
The tube is provided with a plurality of pairs of a first holding plate arranged at both ends and a detachable second holding plate and a third holding plate alternately arranged at predetermined intervals between the first holding plates. Ori
An exhaust gas heat recovery device capable of changing the exhaust gas flow path by changing the number or shape of the second holding plate and the third holding plate or the position of the tube in the longitudinal direction. In the exhaust gas heat recovery device according to claim 2.
An exhaust gas heat recovery device whose material is fluororesin. An exhaust gas heat recovery system including an economizer that exchanges heat of exhaust gas containing NOx components and / or SOx components discharged from a boiler, and an exhaust gas heat recovery device according to any one of claims 2 to 6.

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