JP2009019827A - Exhaust heat recovery device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust heat recovery device capable of overcoming a problem of deliquescence corrosion and elongating the service life of incineration equipment at low cost. <P>SOLUTION: In this exhaust heat recovery device, heat-transfer pipes 16, 18, 20 are arranged on an exhaust gas flow passage of an incinerator 40, and heat is recovered by performing heat exchange between fluid inside the heat-transfer pipes 16, 18, 20 and exhaust gas. The heat-transfer pipes 16, 18, 20 are arranged in three divided regions having different temperature ranges in the exhaust gas flow direction, and materials having different degrees of anti-corrosion characteristics are used for the heat-transfer pipes 16, 18, 20 in the respective regions. Thus, such a structure can overcome a problem of deliquescence corrosion and eliminate a temperature reducing tower by declining the exhaust gas outlet temperature of an economizer, achieving cost reduction in the entire incineration system. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a waste heat recovery apparatus in a garbage incineration facility, a power generation facility, a chemical plant, or the like.

  FIG. 6 is a block diagram showing a processing flow of a conventional typical dry incineration system. As shown in this figure, the waste is incinerated in an incinerator 40, and the combustion exhaust gas passes through a boiler 42 and an economizer (exhaust heat recovery device or economizer) 44, and is further removed by a temperature reducing tower 46. The dust collector 48, the desalinator 50, the reheater 52, and the catalytic reaction tower 54 are sent to an exhaust gas treatment device 56, where harmful components are removed and released into the atmosphere. On the other hand, boiler water is supplied from the condensate tank 58 to the boiler 42 via the feed water superheater 60, the deaerator 62, and the economizer 44. In FIG. 6, solid arrows indicate the flow of exhaust gas, and broken arrows indicate the flow of boiler water. The temperature displayed above the arrow is the temperature of the exhaust gas or boiler water at that location.

  As the incinerator 40, a stoker furnace, a fluidized bed furnace, a kiln furnace, or a combination thereof is used. Further, a gasification melting furnace in which a melting furnace is added to an incinerator, a coke bed type direct melting furnace, and the like are also employed. As the exhaust gas treatment device 56, if it is a dry treatment device, a two-stage bag filter combined with a bag filter (BF), an electrostatic precipitator (EP), a cyclone, or a multi-clone (MC) having a multi-stage, or There are combinations of these. In addition, there is a harmful gas removal device that sprays slaked lime, activated carbon, dust-removal aids, etc., in a single installation of these dust collectors. In addition, in the case of a wet processing apparatus, there exists a combination of the said dust collector and the wet harmful gas removal apparatus of a scrubber or a wet electric dust collector (EDV).

  In recent years, dioxins contained in waste gas from incinerators have become a problem. Dioxins are generated due to unstable combustion conditions in the furnace, but it is clear that they are also produced in the cooling process of combustion exhaust gas (temperature range of 200-400 ° C) from trace organic compounds as precursors. ing. In order to suppress this, it is effective to perform rapid cooling, pass through the temperature range of resynthesis in a short time, and collect dust at a low temperature of 200 ° C. or lower. Therefore, for example, a bag filter capable of collecting dust at low temperature and high efficiency is employed. The removal rate of dioxins is improved by lowering the dust collection temperature, and the removal rate reaches 95% or more at 160 ° C. or lower. However, 20-40% of moisture is contained in the waste incineration exhaust gas, and considering the corrosion and ash fixation, about 150-170 ° C. is regarded as the lower limit value of the substantial operating temperature.

  Thus, in a normal plant, it is necessary to lower the bag filter inlet temperature to a predetermined temperature (about 150 to 170 ° C.). However, such rapid cooling and lowering of exhaust gas causes a problem that gaseous acidic substances (SOx, HCl, etc.) contained in the hot exhaust gas are condensed and cause a phenomenon (dew point corrosion) that corrodes the material. It has become. Dew point corrosion becomes a problem when the temperature of the material in contact with the exhaust gas becomes low. Specifically, heat recovery parts such as an economizer and an air preheater, a flue gas treatment device such as a dust collector, smoke Road, chimney inner cylinder, etc. For these facilities, carbon steel, which is excellent in workability and weldability and is inexpensive and is most commonly used industrially, is generally used. However, since carbon steel is poor in corrosion resistance, high temperature strong acid Due to the dew point corrosion that is formed, the corrosion rate is very high, with a thinning of several to several tens of mm per year.

  Especially in a waste combustion environment containing a lot of HCl, the temperature at which the condensed phase is formed is higher than the dew point (about 70 ° C) calculated from the pure gas equilibrium (at least 80 ° C depending on the gas composition). The exhaust gas outlet temperature of the economizer is set higher (about 200 to 180 ° C.) based on the dew point calculated for gas equilibrium.

  In order to avoid such dew-point corrosion, the exhaust gas outlet temperature of the economizer cannot be lowered to a predetermined temperature at the bag filter inlet. Conventionally, as shown in FIG. It is common to provide 46. If it is possible to reduce the exhaust gas temperature to 160 ° C with an economizer, it will be possible to omit the downstream cooling tower, resulting in a significant cost reduction. In order to recover heat by reducing the exhaust gas outlet temperature of the economizer to 160 ° C. or lower, it is necessary to perform heat recovery by setting the temperature of the heat transfer tube below the dew point. Therefore, it is necessary to use a material that can resist dew point corrosion. Non-Patent Document 1 sets the exhaust gas temperature at the economizer outlet to around 160 ° C by using carbon steel above the dew point and highly corrosion-resistant materials below the dew point, based on studies based on exposure tests in actual incinerators. A possible economizer is disclosed.

  By the way, although the above dew point corrosion is a problem at the time of operation of the apparatus, in addition to the dew point corrosion occurring at the time of operation and the corrosion due to the generation of condensed phase, the inventors have found that iron chloride generated and adhered during operation of the apparatus (high temperature) It was discovered that significant corrosion occurs due to liquefaction during shutdown (room temperature). The inventors defined and named the corrosion that occurs during the shutdown as “deliquescent corrosion”. Similar to dew point corrosion, such deliquescent corrosion is caused by contact of exhaust gas with a high concentration of hydrogen chloride and moisture in low temperature conditions, and is not limited to exhaust gas treatment equipment, such as ducts and casings. It is also a problem where the temperature is low. Deliquescent corrosion is a corrosion phenomenon that is not as large as dew point corrosion, which is a high temperature and strong acid environment, but cannot be ignored. Therefore, for example, in order to realize the technique of omitting the above-described temperature reduction tower, it is necessary to take measures against deliquescent corrosion when the operation is stopped in addition to the corrosion during the operation.

Shinichiro Ando and five others, “Improvement of power generation efficiency by introducing low-temperature economizer”, Hitachi Zosen Technical Report Vol.63, No.1, P.17-21 (2002)

  An object of the present invention is to provide an exhaust heat recovery device that can overcome the problems of deliquescent corrosion as described above and can extend the life of an incinerator at low cost. Furthermore, it aims at reducing the cost of the entire incineration system by reducing the temperature at the exhaust gas outlet of the economizer to eliminate the temperature reduction tower.

  In order to achieve the above object, the exhaust heat recovery apparatus according to claim 1, wherein a heat transfer tube is disposed in an exhaust gas flow path of an incinerator and heat exchange is performed between the fluid in the heat transfer tube and the exhaust gas. In the exhaust heat recovery apparatus that performs heat recovery by the above, the heat transfer tubes are divided into at least three regions having different temperature ranges in the flow direction of the exhaust gas, and materials having different degrees of corrosion resistance are disposed on the heat transfer tubes in each region. It is used.

  In the first aspect of the invention, the heat transfer tubes in at least three regions having different temperature ranges are made to have lower corrosion resistance by using materials having different corrosion resistances adapted to the corrosion characteristics formed by the set temperature in each region. An apparatus having sufficient durability while being cost can be configured.

According to a second aspect of the present invention, there is provided the exhaust heat recovery apparatus according to the first aspect of the present invention. A dew point corrosion resistant material is used for the region, a deliquescent corrosion resistant material is used for the medium temperature region, and a general material is used for the high temperature region.
In the invention according to claim 2, the low temperature region and the medium temperature region, which have been conventionally made of the same high corrosion resistance material and have the same cause, are clearly different temperature regions, and each has a dew point corrosion resistant material and a deliquescent corrosion resistant material. By properly using these, it is possible to reduce the amount of expensive dew-point corrosion-resistant material used, and to achieve cost reduction and high durability.

  The occurrence of deliquescent corrosion is caused by the reaction of hydrogen chloride contained in the exhaust gas at the interface between the metal oxide film and the metal underneath when metal is used at the dew point temperature or higher to produce metal chloride. . That is, when a general iron-based material is used, iron chloride is generated, and when the relative humidity exceeds 58% at room temperature when the operation is stopped, it is intensely caused by the strong acid generated by the absorption of iron chloride and the accompanying hydrolysis. Causes a corrosion reaction. Such deliquescent corrosion occurs to some extent even when the material surface temperature during operation is considerably higher than the dew point temperature. Corrosion is not a problem, but when the material surface temperature falls below a predetermined temperature, iron chloride is generated. The amount increases rapidly and the amount of corrosion also increases.

  Furthermore, as the material surface temperature decreases to a temperature at which dew point corrosion becomes a problem, and as the temperature difference between the exhaust gas and the material surface increases, the amount of iron chloride generated increases, and the amount of deliquescent corrosion increases accordingly. To go. Although it is not as fast as dew point corrosion, it is a corrosion phenomenon that cannot be ignored. This deliquescent corrosion has been confused as dew point corrosion because corrosion during operation of the apparatus cannot be observed on the spot. As a result, in an apparatus in which these are mixed, it is regarded as dew point corrosion and excessive measures have been taken. However, in the present invention, these are classified and different materials are used to achieve lower cost. be able to.

The exhaust heat recovery apparatus according to claim 3 is the invention according to claim 2, wherein the surface temperature of the heat transfer tube in the low temperature region is less than 90 ° C, and the surface temperature of the heat transfer tube in the intermediate temperature region is 90 ° C or more and 140 ° C. The surface temperature of the heat transfer tube in the high temperature region is 140 ° C. or higher.
In the invention of claim 3, corrosion classification corresponding to the exhaust gas composition during typical incinerator _{(N 2 -10% O 2 -20} % H 2 O-10% CO 2 -1000ppmHCl-50ppmSO 2) A region is formed, and an efficient effect of improving corrosion resistance can be obtained. In addition, since it is difficult to measure the surface temperature directly with an actual machine in consideration of the environment, the temperature of water supply or exhaust gas is measured with a thermocouple, and the material surface temperature at each thermocouple installation location is estimated from the heat conduction of the material used Can be obtained.

According to a fourth aspect of the present invention, there is provided the exhaust heat recovery apparatus according to the second or third aspect of the invention, wherein the exhaust gas flow path is arranged so that the upstream side is upward and the downstream side is downward. And
In the invention according to claim 4, since the highly corrosive low temperature region is located downward in the exhaust gas flow path, the possibility that the corrosive liquid falls to other regions and has an adverse effect can be eliminated.

According to a fifth aspect of the present invention, there is provided the exhaust heat recovery apparatus according to the fourth aspect, wherein a cleaning water jet nozzle that supplies cleaning water to the low temperature region is disposed between the low temperature region and the intermediate temperature region. It is characterized by.
According to the fifth aspect of the present invention, the cleaning water is supplied to the low temperature region by the cleaning water jet nozzle, and the portion easily contaminated by the condensed water is cleaned without adversely affecting other regions.

  According to the first to fifth aspects of the invention, deliquescent corrosion and dew point corrosion can be suppressed at low cost, the life of the incinerator can be extended, and the exhaust gas outlet temperature of the economizer can be lowered. In this way, the temperature reduction tower can be omitted, and the overall cost of the incineration system can be reduced.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a diagram showing an exhaust heat recovery device (economizer) 10 according to an embodiment of the present invention. In this economizer 10, the temperature of the exhaust gas to be discharged is set to 160 ° C. or less, and as a result, as shown in FIG. Yes. The apparatus is configured to extend in a substantially vertical direction, and an exhaust gas inlet 12 is formed in the upper part and an exhaust gas outlet 14 is formed in the lower part. The exhaust gas inlet 12 is connected to the outlet of the boiler, the exhaust gas outlet 14 is connected to the exhaust gas treatment device 56, and the exhaust gas flows downward from above. In the exhaust heat recovery apparatus 10, for example, heat transfer tube groups extending in the horizontal direction are provided in layers, and heat exchange is performed by efficiently contacting the exhaust gas.

  In the exhaust heat recovery apparatus 10, the heat transfer tube group is divided into three groups. That is, the high-temperature heat transfer tube group 16 on the upstream side of the exhaust gas, the middle-temperature heat transfer tube group 18 in the midstream portion, and the low-temperature heat transfer tube group 20 on the downstream side. The water supply piping 22 to each heat transfer tube group is basically connected in series, and the same water flows from the low temperature heat transfer tube group 20 to the high temperature heat transfer tube group 16 through the intermediate temperature heat transfer tube group 18. While the water flows in a direction opposite to the exhaust gas, the temperature is raised sequentially, and the exhaust gas is cooled sequentially. The water taken out from the high temperature heat transfer tube group 16 is supplied to the boiler and used as boiler water. As will be described later, a washing water jet nozzle 24 for washing the low temperature heat transfer tube group 20 is provided on the upper side of the low temperature heat transfer tube group 20, and a drain for discharging the washed water at the lower end of the apparatus. 26 is provided. A part of the water supplied to the washing water injection nozzle 24 is supplied from the water supply pipe 22 of the heat transfer pipe group.

As shown in FIG. 3, the temperature of these heat transfer tube groups 16, 18, and 20 is controlled as follows. That is, the tube wall surface temperature of the hot heat exchanger tube group 16 is above T _1, the medium-temperature heat-transfer tube group 18 is the surface temperature is lower than T ₁ at T ₂ or more, the low-temperature heat transfer tube group 20 is the surface temperature is lower than T ₂ To be controlled. As will be described later, T ₁ is a temperature T ₁₀ (140 ° C. in this example) at which a deliquescent corrosion is likely to occur on the surface of a general carbon steel, and T ₂ is a dew point at a temperature lower than that. The temperature T ₂₀ at which corrosion is likely to occur (90 ° C. in this example).

Such temperature control is performed by, for example, estimating the surface temperature from temperature sensors T _{s1 to} T _s6 provided in the water supply pipe 22 or a temperature sensor that measures the temperature of exhaust gas (not shown), and controlling the water supply amount and the water supply temperature. be able to. In this case, it is the surface temperature of the heat transfer tube group that is controlled, but it is difficult to measure the surface temperature directly with the actual machine, considering the environment, so measure the temperature of the feed water and exhaust gas with a thermocouple and install each thermocouple. What is necessary is just to presume and obtain | require the material surface temperature in a location from the heat conduction of the material used, and let the temperature be surface temperature. Moreover, if the temperature state according to the combustion state is grasped with an actual machine, it is not always necessary to perform the monitor control.

  The surface temperature of each heat transfer tube group can be controlled by a method in which a bypass line is provided in the piping to control the amount of water supplied to the heat transfer tube group. Specifically, it is possible to provide a bypass line in the exhaust gas duct and the boiler feed water at the rear stage of the heat recovery apparatus. In order to increase the heat transfer tube temperature, the amount of heat absorption decreases by increasing the amount of water supplied to the bypass line and decreasing the amount of water supplied to the heat transfer tube group of the heat recovery device, so the surface temperature of the heat transfer tube can be increased. it can.

The deliquescent corrosion occurrence temperature T ₁₀ and the dew point corrosion occurrence temperature T ₂₀ were determined by a corrosion test in a laboratory simulating the exhaust heat recovery apparatus 10. That is, with a test piece simulating a heat transfer tube cooled to several test temperatures, a test gas having a composition of N ₂ -10% O ₂ -20% H ₂ O -10% CO ₂ -1000 ppm HCl 50 ppm SO ₂ The state of corrosion was investigated by spraying at a gas moving speed of 0.5 cm / sec (wind speed 1.8 m / sec). As a result, as shown in Fig. 4, when the test piece temperature falls below 140 ° C, it was confirmed that the test piece that had not been corroded immediately after the test was severely corroded by raising the humidity to 60% RH. It was. Even if the test piece temperature was 140 ° C. or higher, it was confirmed that a certain amount of cracking occurred, but the corrosion amount was not problematic. In an actual apparatus, it has been confirmed that the amount of corrosion changes drastically around this temperature.

On the other hand, as for the boundary temperature between deliquescent corrosion and dew point corrosion, no dew point corrosion occurred even when the test piece temperature was about 90 ° C, and dew point corrosion occurred when the test temperature dropped to about 80 ° C. In addition to carbon steel, SUS304 and SUS410 were tested in the same manner. As a result, it was confirmed that a deliquescent corrosion reaction occurred even in stainless steel, but the amount of corrosion was considerably small. This is probably because, unlike carbon steel, stainless steel produced iron oxide as well as a dense oxide film with corrosion resistance, and the corrosion reaction caused by hydrochloric acid caused by deliquescence was suppressed. From the above results, the deliquescent corrosion occurrence temperature T ₁₀ and the dew point corrosion occurrence temperature T ₂₀ were determined to be 140 ° C. and 90 ° C., respectively.

  By controlling the temperature as described above, the low temperature region where the low temperature heat transfer tube group 20 is arranged is the dew point corrosion region, the intermediate temperature region where the intermediate temperature heat transfer tube group 18 is arranged is the deliquescent corrosion region, and the high temperature heat transfer tube group 16 is arranged. The high temperature region thus formed becomes a non-corrosion region. In addition, for example, when there is a possibility that the exhaust gas composition may be different due to changes in the quality of the garbage or the incineration process even if the combustion products are different, or even in the case of garbage, this division temperature may also change, It is better to obtain an accurate temperature by conducting a new test.

  Each of these heat transfer tube groups is made of different materials depending on the corrosion characteristics of those regions. That is, the low temperature heat transfer tube group 20 is made of a high corrosion resistance material, the intermediate temperature heat transfer tube group 18 is made of a medium corrosion resistance material, and the high temperature heat transfer tube group 16 is made of a low corrosion resistance material. Moreover, since the device part which touches each area | region is the same corrosive environment as the area | region, it is necessary to employ | adopt the material which has the corrosion resistance of the same grade as the material of the area | region at least. For example, the drain 26 in contact with the low temperature region employs the same high corrosion resistance material as the low temperature heat transfer tube group 20.

  The low-temperature heat transfer tube group 20 is in a temperature region where dew point corrosion is a problem. Therefore, as a highly corrosion resistant material used for this, a material conventionally used for dew point corrosion is used. Dew point corrosion is a well-known phenomenon as shown in Non-Patent Document 1, and many materials that can be countered have been proposed. Accordingly, these materials may be appropriately selected according to the characteristics of the combustion products. For example, a corrosion-resistant material that assumes sulfuric acid seems to be compatible with stainless steel or a nickel-based alloy. On the other hand, when hydrochloric acid is assumed, a further corrosion-resistant material is required. Specifically, when a metal is used, there are nickel chromium alloy (Inconel, Hastelloy), titanium alloy, zirconium, tantalum, molybdenum, tungsten, and the like. Although a heat transfer tube can also be produced by these, it is preferable to use it as a surface film of an iron-based heat transfer tube from the viewpoint of cost and strength. In addition, as an inorganic material that is not affected by acid, an alumina-based or zirconia-based material is preferably used as the surface coating of the heat transfer tube. Resin materials, especially polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene (PCTFE), tetrafluoroethylene perfluoroalkoxy resin (PFA), etc. should be used as the surface coating. Also good.

  As the material of the intermediate temperature heat transfer tube group 18, a material that can withstand deliquescent corrosion is used. As described above, deliquescent corrosion is a phenomenon in which metal chloride is generated by hydrogen chloride contained in exhaust gas, and high-concentration hydrochloric acid is generated by moisture absorption of the metal chloride when operation is stopped. Therefore, when a metal is used as the material of the intermediate temperature heat transfer tube group 18, a corrosion resistant material that is difficult to oxidize and is free from stress corrosion cracking may be used. It is not necessary to use a high-grade material that can withstand dew point corrosion, and ferritic steel is preferable in view of cost, workability, and the like. In addition, it seems that deliquescent corrosion can be suppressed by making the relative humidity of the relevant part 58% or less at the time of operation stop, but considering practicality, it should be implemented as an auxiliary measure when possible. Seem.

  Next, there is no restriction | limiting in particular as a material of the high temperature heat exchanger tube group 16 whose surface temperature is 140 degreeC or more. This is because even when general carbon steel is used, when the material surface temperature is 140 ° C. or higher, the amount of iron chloride produced is extremely reduced, and the amount of deliquescent corrosion does not become a problem.

  Hereinafter, the operation of the exhaust heat recovery apparatus 10 configured as described above will be described. For example, as shown in FIG. 2, the exhaust heat recovery device 10 is used as an economizer that directs the exhaust gas temperature to 160 ° C. or lower and directly sends it to the subsequent dust collector 48. As shown in FIG. 1, the exhaust gas from the boiler 42 that has flowed into the economizer 10 flows from the upper part to the lower part of the apparatus, and sequentially passes through the high temperature heat transfer tube group 16, the intermediate temperature heat transfer tube group 18, and the low temperature heat transfer tube group 20. For example, the amount of water supplied is controlled so that each heat transfer tube group maintains the temperature in the respective temperature range, and each heat transfer tube group and its attached members are related to dew point corrosion during operation and deliquescent corrosion during operation stop. Placed in each corrosive environment.

The relationship of the temperature of each part at this time is shown, for example in FIG. Here, TGi, TGO influx and outflow temperature of the exhaust heat recovery apparatus 10 of the exhaust _gas, the temperature of T s1 _{through T s6} is supplied water measured by the temperature sensor _T s1 _{through T s6,} also, T1i, T1o, T2i, T2o, T3i, and T3o schematically show the tube wall surface temperatures of the high temperature heat transfer tube group 16, the intermediate temperature heat transfer tube group 18, and the low temperature heat transfer tube group 20, respectively. These tube wall surface temperatures are estimated from the feed water and exhaust gas temperatures. T1 and T2 are temperatures at which deliquescent corrosion and dew point corrosion are problems in this exhaust gas environment. In this embodiment, a general exhaust gas composition (N ₂ -10% O ₂ -20% H ₂ O-10 T1 = 140 ° C. and T2 = 90 ° C. assuming% CO ₂ −1000 ppm HCl-50 ppm SO ₂ ). As shown in this figure, the surface temperature of each heat transfer tube group is set to satisfy T1i, T1o ≧ T1> T2i, T2o ≧ T2> T3i, T3o.

By such control, in the high-temperature heat transfer tube group 16, the surface temperature during operation is T1 = 140 ° C. or higher, and dew point corrosion during operation and deliquescent corrosion during stop are not a problem. Therefore, even when general carbon steel is used, durability is high.
Next, in the intermediate temperature heat transfer tube group 18, the surface temperature is less than T1 = 140 ° C., T2 = 90 ° C. or more, iron chloride is generated during operation, and iron chloride attached to the tube wall causes operation. Deliquescent corrosion may occur after stopping. However, sufficient durability can be obtained by using a corrosion-resistant material such as a ferritic steel material that does not easily oxidize and does not cause stress corrosion cracking.

Next, in the low-temperature heat transfer tube group 20, since the surface temperature is less than T2 = 90 ° C., latent heat recovery is performed by dew condensation of exhaust gas, and condensed water containing corrosive components such as sulfuric acid and hydrochloric acid is generated due to dew condensation. Since a highly corrosion resistant material is used, sufficient durability can be obtained. The condensed water generated by the dew condensation falls quickly toward the drain 26 due to gravity and the downward flow of the exhaust gas, and is appropriately discharged from the drain 26.
As described above, in this embodiment, the heat transfer tube group is divided into a plurality of temperature regions that differ to such a degree that corrosion is a problem, and by using materials suitable for each region, the overall cost of the material is low. However, corrosion to the heat transfer tube group could be suppressed, and the durability of the exhaust heat recovery apparatus 10 could be improved.

  Further, in this embodiment, the low temperature heat transfer tube group 20 is installed at the lowermost stage of the exhaust heat recovery device 10, so that corrosive fluid falls to other heat transfer tube groups, and the heat transfer tubes are affected. It prevents the condensed water that has fallen from being re-evaporated and deprived of heat, thereby reducing the amount of heat transferred to the heat transfer tubes. Further, since the exhaust gas is formed as a downward flow, it is possible to prevent an increase in pressure loss and a decrease in heat recovery efficiency due to the turbulence of the exhaust gas flow accompanying the fall of condensed water.

  The cleaning water is periodically sprayed from the cleaning water injection nozzle 24 to clean the surface of the heat transfer tubes of the low temperature heat transfer tube group 20. As a result, the ash / soot in the exhaust gas adhering to the heat transfer tubes of the low-temperature heat transfer tube group 20 via the condensed water can be removed, and a reduction in heat exchange rate and corrosion due to the adhesion of ash / soot can be prevented. The cleaning by the cleaning water jet nozzle 24 is used not only for removing ash but also for spraying steam to increase the moisture concentration of the low-temperature heat transfer tube group 20 and to increase the recovery efficiency of latent heat. . In this case, if this steam is applied to the intermediate temperature heat transfer tube group 18, the dew point temperature rises, which may cause dew point corrosion. In this embodiment, the washing water injection nozzle 24 is installed between the low temperature heat transfer tube group 20 and the intermediate temperature heat transfer tube group 18, and the steam is not applied to the intermediate temperature heat transfer tube group 18 due to the flow of the exhaust gas. .

  In this embodiment, heat recovery is performed by the low temperature heat transfer tube group 20 and the intermediate temperature heat transfer tube group 18, and further, latent heat recovery is performed by the high temperature heat transfer tube group 16, so that the exhaust gas outlet temperature is reduced to 160 ° C. or less only by the latent heat recovery. Compared with the case where it does, the feed water temperature and combustion air temperature to the boiler 42 can be raised, and the heat recovery efficiency of the whole waste treatment apparatus is improved.

Incidentally, deliquescence corroded temperature T ₁₀ and the sulfuric acid dew point corrosion temperature T ₂₀ is different because a different value in the exhaust gas composition, hydrogen chloride concentration and the water content in the exhaust gas changes with extreme changes during operation. If the concentration is increased, dew point corrosion may occur in the midstream heat transfer tube group, and deliquescent corrosion may occur in the upstream heat transfer tube group. Therefore, in such a case, the tube wall surface lower limit temperature T ₁ of the hot heat transfer tube group _16, the medium-temperature heat transfer tube group 18 wall surface lower limit temperature T _2, deliquescence corrosion generation temperature T ₁₀ was determined experimentally and preferably set than on the safe side sulfuric acid dew point corrosion temperature T _20. For example, in the above example, the tube wall surface lower limit temperature (water inflow side temperature) T ₁ of the high temperature heat transfer tube group 16 is set to 150 ° C. instead of 140 ° C., and the tube wall surface lower limit temperature of the medium temperature heat transfer tube group 18 (water Inflow side temperature) T _{2 is set} to 100 ° C instead of 90 ° C.

  Further, in order to prevent deliquescent corrosion and deliquescent corrosion of the water inflow side portion of the high temperature heat transfer tube group 16 and the intermediate temperature heat transfer tube group 18 that are easily affected by the state change, the temperature setting itself is not changed. Without (or in addition to), as shown in FIG. 5, it may be devised to lower the thermal conductivity of these portions. In order to make it difficult for the surface temperature of these portions to be lowered, the coating 32 is formed in the heat transfer tube 30 with a material having a lower thermal conductivity than the material of the heat transfer tube 30 to cover the inner surface. . As this material, for example, a resin such as polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene (PCTFE), or tetrafluoroethylene / perfluoroalkoxy resin (PFA) may be used. Even if the surface temperature of the heat transfer tube inlet does not drop, the water supply and air temperatures will gradually rise, so if you reach a certain point from the inlet, you can avoid the problem of a sudden drop in the surface temperature. Become.

It is a figure which shows the waste heat recovery apparatus of embodiment of this invention. It is a figure which shows the incineration system using the exhaust-heat recovery apparatus of embodiment of this invention. It is a figure which shows the temperature change of each part in an exhaust heat recovery apparatus. It is a figure which shows the change of the corrosion condition by temperature. It is a figure which shows one improvement about a heat exchanger tube. It is a figure which shows the conventional incineration system.

Explanation of symbols

10 Waste heat recovery device (economizer)
16 High Temperature Heat Transfer Tube Group 18 Medium Temperature Heat Transfer Tube Group 20 Low Temperature Heat Transfer Tube Group 24 Wash Water Injection Nozzle 26 Drain 30 Heat Transfer Tube 32 Film 40 Incinerator 42 Boiler 44 Economizer 46 Temperature Reduction Tower 48 Dust Collector T ₁ High Temperature Heat Transfer Tube Group Wall Surface Lower Limit Temperature T ₂ Medium temperature heat transfer tube group wall surface lower limit temperature T ₁₀ Deliquescent corrosion occurrence temperature T ₂₀ Dew point corrosion occurrence temperature

Claims (5)

In an exhaust heat recovery apparatus that arranges a heat transfer tube in an exhaust gas flow path of an incinerator and performs heat recovery by exchanging heat between the fluid in the heat transfer tube and the exhaust gas,
The heat transfer tube is divided into at least three regions having different temperature ranges in the flow direction of the exhaust gas,
An exhaust heat recovery apparatus characterized in that materials having different levels of corrosion resistance are used for the heat transfer tubes in each region.   As the region, a low temperature region downstream of the exhaust gas flow channel, a middle temperature region of the midstream portion and a high temperature region upstream, a dew point corrosion resistant material in the low temperature region, a deliquescent corrosion resistant material in the medium temperature region, The exhaust heat recovery apparatus according to claim 1, wherein a general material is used for the high temperature region.   The surface temperature of the heat transfer tube in the low temperature region is less than 90 ° C, the surface temperature of the heat transfer tube in the medium temperature region is 90 ° C or more and less than 140 ° C, and the surface temperature of the heat transfer tube in the high temperature region is 140 ° C or more. The exhaust heat recovery apparatus according to claim 2.   4. The exhaust heat recovery apparatus according to claim 2, wherein the exhaust gas flow path is disposed so that the upstream side is upward and the downstream side is downward. 5.   The exhaust heat recovery apparatus according to claim 4, wherein a cleaning water injection nozzle that supplies cleaning water to the low temperature region is disposed between the low temperature region and the intermediate temperature region.

Images