JP2015212583A - Boiler having water-supply preheating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To further reduce energy consumption in a boiler by further increasing the recovery amount of heat by means of water supply in the boiler which performs preheating of supply water by means of drain recovery concurrently with the preheating of supply water by means of an economizer.SOLUTION: In a boiler having a drain recovery device, an economizer 8 and a supply water tank 6, the economizer 8 is installed so as to be divided into a high temperature heat transfer pipe group 4 as the upstream side in an exhaust gas flow and a low temperature heat transfer pipe group 5 as the downstream side, the supply water tank 6 is installed between the low temperature heat transfer pipe group 5 and the high temperature heat transfer pipe group 4, recovered drain is not caused to pass through the low temperature heat transfer pipe group 5, but is directly introduced to the supply water tank 6, thereby, boiler replenishment water subjected to preheating of a first step and recovery drain are mixed in the supply water tank 6 and boiler supply water is supplied to the high temperature heat transfer pipe group 4 from the supply water tank 6 in which the replenishment water performing preheating in the low temperature heat transfer pipe group 5 and the recovered drain are mixed.

Description

The present invention relates to a boiler having a feed water preheating device that preheats feed water to a boiler by recovering heat from exhaust gas discharged from the boiler and drain recovery from steam generated by the boiler. It is.

A steam boiler is widely used as an apparatus for supplying heat. In the boiler, as described in Japanese Patent Application Laid-Open No. 2000-112003, it is also possible to collect drain from load equipment that uses steam from the boiler as a heat source. Widely done. In the invention described in Japanese Patent Application Laid-Open No. 2000-112003, the introduction of steam into a water supply tank, an economizer (heating economizer) that heats the water supply by exhaust gas from the boiler, and the boiler drain are recovered in the water supply tank and reused as water supply. A drain recovery device is provided. The boiler generates high-temperature steam and sends the steam to the load equipment, and when the heat of the steam is used in the load equipment, the steam drops in temperature and returns to liquid. The drain condensed steam has a lot of heat, and when the drain is collected and mixed with the boiler feed water, the feed water temperature rises. If the drain is recovered without being discarded and the feed water temperature is raised by the recovered drain, the amount of energy required in the boiler is reduced, and thus energy is saved. Furthermore, the amount of water used can be reduced by collecting and reusing the drain.

For example, an amount of drain corresponding to 2/3 of the amount of water supply is recovered, the recovered drain temperature is 80 ° C., the remaining 1/3 is new makeup water, and the makeup water temperature is 20 ° C. Suppose. In this case, the amount of water that must be newly supplied as boiler feed water by performing drain recovery is 1/3, and the feed water temperature is 60 ° C. by mixing the drain. Compared to the case where all of the water supply is performed with new water, the temperature can be increased by 40 ° C in the water supply preparation stage, so the boiler does not need to increase the temperature by 40 ° C, and energy consumption is increased accordingly. The amount used can be reduced.

The economizer preheats the water supply with the exhaust gas discharged from the boiler. An economizer that exchanges heat between exhaust gas and boiler feedwater is installed in the exhaust path of the boiler, and water supply to the boiler is performed via the economizer and between the exhaust gas flowing on the outer surface of the economizer The water supply is preheated by heat exchange. For example, it is assumed that the exhaust gas of 240 ° C. is discharged from the boiler and the feed water temperature to the boiler is 20 ° C., and preheating to 75 ° C. can be performed by preheating the feed water with an economizer. In that case, since preheating for 55 ° C. is performed by the economizer, the boiler does not need to increase the temperature by 55 ° C., and the amount of energy used can be reduced accordingly.

Preheating by drain recovery and preheating by an economizer can be used in combination. Also in the invention described in Japanese Patent Application Laid-Open No. 2000-112003, boiler feed water is preheated by drain recovery and preheated by an economizer. If the new feed water temperature was 20 ° C, it would rise to 60 ° C by drain recovery, and if it was preheated to 100 ° C by an economizer, the heat required for heating in a total of 80 ° C would be required in the boiler. Since it becomes unnecessary, the amount of energy used in the boiler can be reduced accordingly.

In the invention of Japanese Patent Laid-Open No. 2000-12103, water supply preheating is also performed by introducing steam into the water supply tank. However, drain recovery and preheating with exhaust gas use waste heat and help reduce energy consumption. However, when preheating using steam, use steam. Since the amount increases, the energy saving effect cannot be obtained. Conversely, when the water supply temperature of the water supply tank is increased, the amount of heat that can be absorbed by the economizer is reduced, so the overall amount of energy used is increased.

In addition, if the economizer is further preheated after the feedwater temperature rises due to drain recovery, the final feedwater temperature will be higher than in the case of only drain recovery or only the economizer, but the temperature rise due to two preheats. It is not the total value. In the above example, the economizer alone could increase the temperature by 55 ° C in the economizer part, but the temperature rise in the economizer part when preheating with the economizer after drain recovery was 40 ° C. It is lower than the preheating of. This is because, when boiler feed water whose temperature has risen to 60 ° C. due to drain recovery is supplied to the economizer, the economizer reduces the temperature difference between the boiler feed water temperature and the exhaust gas, so the amount of heat that can be absorbed by the boiler feed water decreases. By doing. In addition, when the temperature of the water supply flowing through the economizer is low, the exhaust gas can be heat exchanged to a lower temperature, and the exhaust gas can be condensed to recover the latent heat of the exhaust gas. However, if the temperature of the feed water flowing through the economizer is high, the final temperature of the exhaust gas is not so low and the latent heat cannot be recovered, so the amount of heat recovered in the economizer decreases.

Preheating feed water using the heat that was discarded as described above can reduce the amount of energy used in the boiler, but if the boiler feed water temperature rises due to preheating, the boiler feed water The amount of heat that can be absorbed by the economizer decreases. Therefore, it has been desired to preheat the water supply more efficiently.

JP 2000-121033 A

The problem to be solved by the present invention is to further increase the amount of heat recovered by water supply in a boiler that uses both preheating of water supplied by drain recovery and preheating of water supplied by an economizer. It is providing the boiler with the feed water preheating apparatus which can further reduce this.

The invention according to claim 1 is a boiler for generating steam by heating boiler water with a high-temperature gas, and drain recovery for recovering drain condensed by steam supplied to the load equipment from the boiler and reusing it as boiler feed water. A boiler having an economizer for exchanging heat between boiler feed water supplied to a boiler and exhaust gas exhausted from the boiler, and having a water supply preheating device that performs drain recovery and feed water preheating with exhaust gas, The economizer is divided into a high-temperature heat transfer tube group that is upstream in the exhaust gas flow and a low-temperature heat transfer tube group that is downstream in the exhaust gas flow, and boiler makeup water first passes through the low-temperature heat transfer tube group. The first stage of preheating is performed, and the recovered drain is not passed through the low-temperature heat transfer tube group, but is mixed with the boiler replenishment water that has undergone the first stage of heating. The heat transfer tube group, characterized in that it is adapted to supply boiler feedwater of a mixture of a collection drain makeup water was preheated at a low temperature heat transfer tube group.

The invention according to claim 2 is a boiler having the feed water preheating device, wherein a feed water tank for temporarily storing boiler feed water supplied to the boiler is installed between the low temperature heat transfer tube group and the high temperature heat transfer tube group. The first stage preheated boiler makeup water is stored in the water supply tank, and the recovered drain is introduced into the water supply tank so that the first stage preheated boiler makeup water and the collected drain are mixed. The high-temperature heat transfer tube group is supplied with boiler feed water from a feed water tank, and the feed water tank is further connected between the concentrated blow water discharged from the boiler and the boiler feed water stored in the feed water tank. A blow heat exchanger for performing heat exchange is provided. The invention according to claim 3 is the boiler having the feed water preheating device according to claim 2, wherein the blow heat exchanger is installed between the feed water tank and the low-temperature heat transfer tube group. . According to a fourth aspect of the present invention, in the boiler having the feed water preheating device according to the first aspect, the first stage preheating is performed in the low temperature heat transfer tube group between the place where the recovered drain is mixed and the low temperature heat transfer tube group. A blow heat exchanger is provided that performs heat exchange between the supplied water and the concentrated blow water.

Preheating water supply with an economizer means that the heat of the exhaust gas is transferred to the water supply, so the temperature of the exhaust gas becomes lower as it goes downstream. For this reason, in the portion close to the exhaust gas outlet of the economizer, the feed water is preheated with the exhaust gas whose temperature has decreased. At that time, if the boiler feed water is preheated before entering the economizer, heat exchange is performed between the boiler feed water whose temperature has risen and the exhaust gas whose temperature has fallen. As the temperature difference is reduced, the amount of heat that the boiler feed water can take in has been reduced. Further, since the feed water temperature after preheating with the economizer is higher than the drain temperature, the feed water temperature does not rise even if drain is mixed with the preheated water with the economizer.

In the present invention, the economizer is divided into a low temperature heat transfer tube group and a high temperature heat transfer tube group. When boiler feed water that has not been preheated is supplied to the low-temperature heat transfer tube group that is upstream of the boiler feed water flow and downstream of the exhaust gas flow, the temperature of the boiler feed water is low, so the exhaust gas becomes a lower temperature. It is possible to recover the heat up to the exhaust gas, and it is possible to recover the latent heat from the exhaust gas. Furthermore, since the collected drain is mixed into the feed water after preheating by the low temperature heat transfer tube group and before preheating by the high temperature heat transfer tube group, the amount of heat held by the boiler feed water increases, and the feed water temperature is reduced. Can rise. Even in the case of feed water whose temperature has risen due to the mixing of the collected drain, the exhaust gas temperature is higher in the high-temperature heat transfer tube group provided upstream of the exhaust gas flow, so the high-temperature heat transfer tube group also preheats the feed water. be able to. As a result, the total amount of heat absorption increases, so that the amount of energy used in the boiler can be reduced.

By carrying out the present invention, the amount of heat that can be recovered from the drain and the exhaust gas in the boiler feed water increases, so that the amount of energy used in the boiler can be reduced.

Water supply route explanatory diagram of a boiler implementing the present invention Water supply route explanatory drawing of the boiler in the 2nd example of the present invention Boiler water supply route explanatory diagram in the third embodiment of the present invention Boiler water supply route explanatory diagram in the fourth embodiment of the present invention Water supply route explanatory diagram in a conventional boiler for comparison

  Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram for explaining a water supply path of a boiler implementing the present invention. The boiler 1 heats boiler water by performing combustion inside and supplies steam to the load device 2. The boiler 1 is supplied with water adjusted to a water quality suitable for the boiler by removing the hardness component in water with a water softener (not shown) and injecting chemicals as makeup water. In addition, a drain recovery device for recovering the drain generated in the load device 2 and using it as boiler feed water is provided. The load device 2 and the water supply tank 6 are connected by a drain recovery pipe, and a steam trap is provided in the middle of the drain recovery pipe. Of the steam generated in the boiler 1 and supplied to the load device 2, the condensate drained into the liquid by the load device is collected into the feed water tank 6 through the drain collection pipe and reused by mixing with the feed water to the boiler. Like to do.

The boiler heats the boiler water by a combustion device provided therein to generate steam, and the exhaust gas after being used for heating the boiler water is discharged through the exhaust passage 3. Since this exhaust gas is still hot, it is used for preheating boiler feed water. The exhaust passage 3 is provided with an economizer 8 for exchanging heat between the boiler feed water supplied to the boiler and the exhaust gas flowing in the exhaust passage. The economizer 8 is provided with a large number of heat transfer tubes so as to cross the exhaust gas flowing in the exhaust passage, and a long flow path is formed by connecting them. Many heat absorption fins for increasing the heat transfer area are provided on the outer surface of the heat transfer tube. The heat transfer tubes of the economizer 8 are divided into a high temperature heat transfer tube group 4 on the upstream side of the exhaust gas flow and a low temperature heat transfer tube group 5 on the downstream side of the exhaust gas flow.

The water supply to the boiler is connected so that it is first introduced into the low-temperature heat transfer tube group 5 on the upstream side in the feed water flow and then introduced into the high-temperature heat transfer tube group 4. Between the high-temperature heat transfer tube group 4 and the low-temperature heat transfer tube group 5, the water supply pipe goes out of the exhaust passage 3 and is connected to a water supply tank 6 provided outside the exhaust passage 3. The water supply tank 6 temporarily stores the boiler feed water that has been preheated by the first stage in the low temperature heat transfer tube group 5. When supplying water to the high temperature heat transfer tube group 4, the water supply tank 6 and the high temperature heat transfer tube group The water supply is pressurized and supplied by operating a water supply pump provided on the path connecting the four. Further, the steam supplied from the boiler 1 to the load device 2 is condensed in the water supply tank 6 by using heat in the load device 2, and the generated drain is recovered. , The recovered drain is mixed with boiler feed water.

An example of water supply preheating in the present embodiment will be described with numerical values applied. First, it is assumed that the temperature before entering the low-temperature heat transfer tube group 5 of new makeup water that has not been preheated is 20 ° C. and the supply amount of makeup water is 700 L / H. The temperature of the drain collected from the load device 2 is 80 ° C., and the collected amount of drain is 1400 L / H. The temperature of the exhaust gas discharged from the boiler is 240 ° C.

The exhaust gas flowing through the exhaust passage 3 is 240 ° C. in the stage upstream of the economizer 8, but the temperature decreases as heat exchange is performed in the economizer 8, so the temperature becomes lower as the downstream of the exhaust passage 3. . The exhaust gas temperature is 137 ° C. in the portion that has passed through the high-temperature heat transfer tube group 4, and 102 ° C. in the portion that has passed through the low-temperature heat transfer tube group 5. When makeup water is passed through the low-temperature heat transfer tube group 5 in this state, the temperature of the makeup water rises due to the heat of the exhaust gas. The makeup water that has received heat from the exhaust gas in the low-temperature heat transfer tube group 5 rises to 60 ° C. at the outlet of the low-temperature heat transfer tube group 5. In this case, in the low-temperature heat transfer tube group 5, the heat transfer tube that is the most upstream side in the feed water flow and the most downstream side in the exhaust gas flow performs heat exchange with the exhaust gas at 102 ° C. and the makeup water at 20 ° C. In the heat transfer tube which is on the downstream side and is the most upstream side in the exhaust gas flow, heat exchange is performed by exhaust gas at 137 ° C. and makeup water at 60 ° C.

If the temperature of the exhaust gas flowing outside the boiler feed water flowing inside the economizer 8 is higher, the heat of the exhaust gas moves to the boiler feed water and the temperature of the boiler feed water rises, but the temperature of the exhaust gas is the temperature of the boiler feed water If the temperature is not sufficiently higher than that, the amount of heat that can be absorbed by the boiler feed water is reduced. In the low-temperature heat transfer tube group 5 of the present embodiment, the temperature difference between the exhaust gas and the boiler feed water in the most downstream heat transfer tube in the exhaust gas flow is 82 ° C., and the temperature of the exhaust gas and the boiler feed water in the most upstream heat transfer tube in the exhaust gas flow The difference is 77 ° C., and the boiler feed water can absorb heat in the entire low-temperature heat transfer tube group 5.

The exhaust gas temperature on the downstream side of the low-temperature heat transfer tube group 5 is obtained by leveling the temperature variation in the heat transfer tube portion. The temperature of the exhaust gas that has flowed away from the heat transfer tube is higher than the above temperature, but the temperature of the exhaust gas that has flowed along the surface of the heat transfer tube is lower than the above temperature, and condensation of the exhaust gas occurs on the surface of the heat transfer tube. Occur. Therefore, latent heat recovery can also be performed in the low-temperature heat transfer tube group 5.

The makeup water that has passed through the low-temperature heat transfer tube group 5 enters a water supply tank 6 provided outside the exhaust passage 3. In the water supply tank 6, the makeup water preheated by the low-temperature heat transfer tube group 5 and the drain recovered from the load device 2 are mixed. If the recovered drain is 80 ° C. and the recovery amount is 1400 L / H, it is higher than the temperature of the supplementary water preheated in the low-temperature heat transfer tube group 5, and therefore when the drain is mixed, the temperature of the mixed water increases. To do. In this embodiment, the mixed water temperature obtained by mixing the recovered drain and preheated makeup water is 73 ° C.

Next, this mixed water is sent to the high-temperature heat transfer tube group 4 and preheated with exhaust gas again in the high-temperature heat transfer tube group 4. Exhaust gas of 240 ° C. is sent from the upstream side of the exhaust gas flow of the high temperature heat transfer tube group 4. When the boiler feed water in the high temperature heat transfer tube group 4 is heated with this exhaust gas, the temperature of the boiler feed water further increases. . The temperature of the boiler feed water is increased from 73 ° C. to 107 ° C. by performing the second preheating in the high-temperature heat transfer tube group 4. Therefore, in this feed water preheating apparatus as a whole, the boiler feed water temperature can be increased from 20 ° C. to 107 ° C.

When the amount of recovered heat in the economizer 8 in this case is calculated, the amount of recovered heat in the low-temperature heat transfer tube group 5 is 26.0 kW including the latent heat recovery amount 3.6 kW, the high-temperature heat transfer tube group 4 is 65.9 kW, and a total of 91. It became 9kW. In this case, the increase in boiler efficiency in the economizer is 7.2%.

FIG. 5 is an explanatory diagram of a water supply path in a conventional boiler for comparison. The conditions such as the temperature and flow rate of the makeup water and recovered drain used in the comparative example, the temperature of the exhaust gas discharged from the boiler, and the heat transfer area of the economizer 8 are the same as those in the above embodiment. It is said. The difference from the embodiment is that in the embodiment, makeup water is not mixed with the collected drain, preheating with the exhaust gas is performed in the low temperature heat transfer tube group 5, and after the preheating in the low temperature heat transfer tube group 5, In the case of the comparative example, makeup water and recovered drain are mixed in the first stage, and then the high-temperature heat transfer tubes are mixed. This is a part in which preheating is performed by an economizer 8 having the same heat transfer area as both the group 4 and the low-temperature heat transfer tube group 5.

In the comparative example, the water supply tank 6 mixes 20 ° C. makeup water and 80 ° C. recovered drain to form 60 ° C. mixed water, and the mixed water whose temperature has risen is sent to the economizer 8. The exhaust gas flowing in the exhaust passage 3 is 240 ° C. upstream of the economizer 8, but the temperature is lowered by preheating water supply in the economizer 8 portion, and is 106 ° C. downstream of the economizer 8. For this reason, in the heat transfer pipe located on the most upstream side in the water supply flow of the economizer 8, heat exchange is performed between the exhaust gas at 106 ° C. and the makeup water at 60 ° C., and the temperature difference here is 46 ° C. In the example described above, this temperature difference was 82 ° C., but in the comparative example, it decreased to nearly half. If this temperature difference is small, the amount of heat that can be taken in by the boiler feed water will decrease. In other words, in the above embodiment, heat is efficiently absorbed to the most downstream side of the exhaust gas flow, and the overall heat recovery amount is large. In the downstream, heat absorption is reduced, and the overall heat recovery amount is small.

Further, the final exhaust gas temperature in the comparative example is 106 ° C., no condensation of exhaust gas occurs on the surface of the heat transfer tube, and no latent heat recovery is performed. The lower the final exhaust gas temperature, the more the heat of the exhaust gas was absorbed, but in the example, it was 106 ° C compared to 102 ° C, so the example recovered more heat. Will be. Therefore, in the comparative example in which the heat absorption amount is small, the boiler feed water temperature at the outlet of the economizer 8 is 104 ° C., which is lower than 107 ° C. in the above embodiment.

When the amount of heat recovered by the economizer 8 in this case was calculated, the amount of latent heat recovered was 0, and it was 85.8 kW only by sensible heat recovery. In the above example, the total was 91.9 kW, so that in the example, the amount was 6.1 kW higher than the comparative example. In this case, the increase in boiler efficiency in the economizer was 6.7%. Since the increase in the boiler efficiency in the economizer in the above embodiment was 7.2%, the embodiment is 0.5% more.

FIG. 2 is an explanatory view of a water supply path of the boiler in the second embodiment of the present invention. The embodiment of FIG. 2 is a case where feed water preheating by concentration blow is added to the embodiment of FIG. In the boiler, since the boiler water is concentrated by generating steam, a concentration blow for periodically discharging the boiler water is performed for the purpose of preventing the boiler water from being excessively concentrated. In the embodiment of FIG. 2, a blow heat exchanger 7 that performs heat exchange with the concentrated blow water discharged from the boiler 1 is installed in a feed water tank 6 that accumulates water preheated by the low-temperature heat transfer tube group 5. The amount of concentrated blow water discharged from the boiler is smaller than the amount of drain recovered, but since it is boiler water that is discharged, it is hot, and it is passed through the blow heat exchanger 7 to supply water in the water supply tank 6. Can be preheated. Also in this case, the collected drain is mixed and the feed water preheating with the concentrated blow water is performed before the high-temperature heat transfer tube group 4 which is the second stage feed water preheating section, and in the first stage feed water preheating section. A certain low temperature heat transfer tube group 5 is supplied with water having a low temperature. Therefore, also in this case, the low-temperature heat transfer tube group 5 can preheat the water supply from the exhaust gas whose temperature has decreased, and the amount of heat recovered by the economizer 8 can be made larger than that in the comparative example. Furthermore, in the embodiment of FIG. 2, since preheating is performed with concentrated blow water, the amount of preheated water can be increased as compared with the embodiment of FIG.

3 and 4 are also diagrams for explaining the water supply path of the boiler in another embodiment of the present invention. 3 and 4, the blow heat exchanger 7 is installed between the place where the feed water after the first stage preheating and the collected drain are mixed and the low temperature heat transfer tube group 5. In this embodiment, the feed water after the first stage pre-heating in the low-temperature heat transfer tube group 5 is pre-heated by the concentration blow before being mixed with the recovered drain. Further, FIG. 4 shows an embodiment in which the water supply tank 6 is not used. 3 and FIG. 4, in order to perform concentration blow and heat exchange before mixing the feed water after the first stage preheating and the collected drain, the feed water after the first stage preheating is performed. Therefore, preheating can be performed more efficiently, and the preheating amount of the water supply can be increased more than the embodiment of FIG. However, it is better to install a water supply tank 6 in order to stabilize the water supply to the boiler body, and the embodiment of FIG. 3 has a problem that the apparatus is larger than that of FIG. Therefore, the embodiment shown in FIG. 2 is the best when viewed comprehensively. Further, in the present invention, by providing a water supply tank on the downstream side of the low temperature heat transfer tube group, even when the can water flows backward, the water supply tank can be stopped, and the can water does not flow into the low temperature heat transfer tube group. Therefore, it becomes possible to use all-aluminum alloy for the piping and the low temperature heat transfer tube group upstream from the water supply tank, leading to an increase in thermal efficiency (heat absorption rate increase) and downsizing of the low temperature heat transfer tube group.

The present invention is not limited to the embodiments described above, and many modifications can be made by those having ordinary knowledge in the art within the technical idea of the present invention.

1 boiler
2 Load equipment 3 Exhaust passage 4 High temperature heat transfer tube group
5 Low temperature heat transfer tube group 6 Water supply tank 7 Blow heat exchanger 8 Economizer

Claims (4)

A boiler that generates steam by heating boiler water with high-temperature gas, a drain recovery device that collects drain condensed steam supplied to the load equipment from the boiler and reuses it as boiler feed water, boiler feed water supplied to the boiler, In a boiler having a water supply preheating device that has an economizer that exchanges heat between exhaust gases discharged from the boiler, and that performs drain recovery and water supply preheating with exhaust gas, the economizer is located upstream in the exhaust gas flow. It is divided into a high-temperature heat transfer tube group that becomes and a low-temperature heat transfer tube group that is downstream in the exhaust gas flow, and the boiler make-up water first passes through the low-temperature heat transfer tube group to perform the first stage preheating, The recovered drain is not passed through the low-temperature heat transfer tube group, but is mixed with boiler makeup water that has been preheated at the first stage. Boiler having a water preheating device, characterized in that so as to supply the boiler feed water of a mixture of make-up water and recovered drainage was preheated in a group. A boiler having the feed water preheating device according to claim 1, wherein a first stage preheating is performed by installing a feed water tank for temporarily storing boiler feed water supplied to the boiler between the low temperature heat transfer tube group and the high temperature heat transfer tube group. In addition to storing the boiler makeup water that has been used in the feed water tank, the drain that has been collected is introduced into the feed water tank, and the boiler feed water that has been preheated in the first stage in the feed water tank is mixed with the collected drain. Boiler feed water is supplied to the heat transfer tube group from the feed water tank, and the feed water tank is a blower for exchanging heat between the concentrated blow water discharged from the boiler and the boiler feed water stored in the feed water tank. A boiler having a feed water preheating device, characterized in that a heat exchanger is provided. The boiler with the feed water preheating device according to claim 2, wherein the blow heat exchanger is installed between the feed water tank and the low temperature heat transfer tube group. The boiler with the feed water preheating device according to claim 1, wherein the feed water and the concentrated blow water after the first stage preheating is performed in the low temperature heat transfer tube group between the place where the recovered drain is mixed and the low temperature heat transfer tube group. A boiler having a feed water preheating device, characterized in that a blow heat exchanger is provided for exchanging heat with each other.

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