JP6862986B2 - How to operate the gas preheater - Google Patents

Description

The present invention relates to an operation method of a gas preheating device that preheats a fuel gas including a blast furnace gas by an exhaust gas.

A mixed gas of blast furnace gas and linz-Donaw gas (hereinafter referred to as fuel gas) is used as fuel for some boilers used in steelworks.
Since the exhaust gas emitted by the boiler is hot, it is important to recover this heat from the viewpoint of energy saving and environmental problems.
It is efficient to use the exhaust heat from this boiler for preheating the fuel gas of the same boiler.

The gas preheater of the boiler will be described.
The gas preheating device includes a gas flow path 10 and a heat exchanger 20.
The gas flow path 10 is a pipe or duct through which the fuel gas G including the blast furnace gas flows, in which the fuel gas G is preheated.
The heat exchanger 20 is formed by connecting a heat transfer tube 21 having fins 22 to a tube side 24 via a tube base 23. Then, the circulating heat medium W is allowed to flow inside, and the heat of the exhaust gas is preheated to the fuel gas via the circulating heat medium W.
More specifically, there are a plurality of heat exchangers 20, and one or more heat exchangers 20 are arranged close to each other as a group in the gas flow path 10. This group was designated as the nth group (n = 1, 2, 3, ...) In ascending order from the upstream with respect to the fuel gas.
Further, each part of the heat exchanger 20 is made of carbon steel.

Here, the blast furnace gas contains a corrosive component such as ammonium chloride, and the heat exchanger 20 that exchanges heat with the fuel gas containing the blast furnace gas is exposed to a highly corrosive environment.
When the heat transfer tube 21 is corroded and the corrosion progresses, the circulating heat medium W in the heat transfer tube 21 leaks.

If even one heat transfer tube 21 of each group leaks, the function of the entire group deteriorates and the heat exchange efficiency drops significantly. Therefore, the leaking pipe must be repaired.
The method of repairing the leaked portion is to cut off the leaked pipe and weld a closing plug to the pipe base 23 on the side of the pipe side 24, so that the number of operating heat transfer tubes 21 is reduced and the overall efficiency of the heat exchanger 20 is reduced. Means that is reduced.

Therefore, there is disclosed a boiler in which the material of the heat transfer tube in a corrosive environment (here, alkaline corrosion) has a Cr content of 9% or more (see, for example, Patent Document 1).
According to the invention described in Patent Document 1, the alkali corrosion rate decreases as the Cr content in the material increases, and when the Cr content is 9% or more, substantially no corrosion occurs.
Therefore, it is possible to prevent alkaline corrosion of a superheater that obtains superheated steam in a waste incineration power generation facility or the like, and the cost is low.

Further, a stainless steel having improved corrosion resistance by being subjected to shot peening processing is disclosed (see, for example, Patent Document 2).
According to the invention described in Patent Document 2, by performing shot peening processing, compressive stress is applied to the surface of stainless steel to relax tensile stress, thereby improving corrosion resistance and thus suppressing stress corrosion cracking.

JP-A-11-2014402 Japanese Unexamined Patent Publication No. 2001-198828

However, all of them are insufficient as measures against corrosion in an environment exposed to blast furnace gas.
In such a situation where corrosion countermeasures are inadequate, the heat exchanger 20 of the first group 101 corrodes in a short period of time, and when its function is lost, the corrosion range expands to the downstream group at an accelerating rate. ..

Even if the spread of such corrosion can be detected early and the new heat exchanger 20 is replaced, the boiler will be stopped unexpectedly, which is time consuming and costly.
On the other hand, if the boiler cannot be stopped or if the discovery of the spread of corrosion is delayed, the heat exchangers 20 will stop functioning steadily from the upstream side, and finally the entire plurality of heat exchangers 20 will not function. It ends up.

Therefore, an object of the present invention is to provide a method of operating a gas preheating device capable of extending the life of a plurality of heat exchangers as a whole.

In order to achieve the above object, the method of operating the gas preheater according to claim 1 of the present invention is a gas flow path (10) in which a fuel gas (G) including a blast furnace gas which is a fuel for a boiler flows inside. A plurality of heat transfer tubes (31) through which the circulating heat medium (W) flows, fins (32) provided on the outer surfaces of the plurality of heat transfer tubes (31), and the plurality of heat transfer tubes (31). A plurality of heat exchangers (30) having a tube side (34) connected to both ends via a tube base (33), and one or more of the above in the gas flow path (10). The heat exchangers (30) are arranged close to each other as one group, and the group is designated as the nth group (n = 1, 2, 3, ...) In ascending order from the upstream with respect to the fuel gas (G), and at least the first group. It is an operation method of a plurality of gas preheaters arranged in three groups (103) or more, and the heat transfer tubes (31) of the first group (101) and the second group (102) are made of a corrosion-resistant stainless steel material. Before both the heat exchangers (30) of the first group (101) and the second group (102) lose their heat exchange function due to corrosion at the same time, the first group (101) and the second group (102) The heat exchanger (30) of one group of the heat exchangers (30) of the above is updated.

The loss of this heat exchange function is not limited to the one that completely loses the heat exchange function, and the first group (101) and the first group (101) and the heat exchangers (30) after the third group (103) are rapidly corroded. It means that the heat exchanger (30) of the second group (102) has lost the heat exchange function.

Further, the method of operating the gas preheating device according to claim 2 is characterized in that the heat transfer tube of the heat exchanger of the third group (103) or later is made of carbon steel. The third group (103) and subsequent groups refer to other groups excluding the first group (101) and the second group (102).

Further, in the method of operating the gas preheating device according to claim 3, the distance between the fins (32) of the heat exchangers (30) of the first group (101) is set to the distance between the fins (32) of the heat exchangers (30) of the other group. The fins (32) are wider than the distance between the fins (32).

Further, in the operation method of the gas preheating device according to claim 4, the fin (32) is not provided in the heat exchanger (30) of the first group (101), and the heat transfer tube (31) is a bare tube. It is characterized by being.

Here, the symbols in parentheses indicate the corresponding elements or corresponding items described in the drawings and the embodiment for carrying out the invention described later.

According to the operating method of the gas preheating device according to claims 1 and 2 of the present invention, since the heat transfer tubes of the first group and the second group are made of corrosion-resistant stainless steel, they are made of carbon steel which is usually used. Corrosion can be suppressed compared to heat transfer tubes. As a result, even if the heat exchangers of the first group are corroded and the downstream side becomes a highly corroded environment, the heat exchangers of the second group are slowly corroded, so that the heat exchangers of the third and subsequent groups can be suppressed from being corroded.
Then, before both the first group and the second group heat exchangers lose their heat exchange function due to corrosion at the same time, the heat exchangers of one of the first group and the second group heat exchangers are updated. , It is possible to extend the life of multiple heat exchangers as a whole.
In addition, since the heat exchangers in the first group and the heat exchangers in the second group are slowly corroded, the heat exchange rate of the heat exchangers in one group is lowered or renewed, unlike the case where the corrosion progresses in a short period of time. From the corrosion status that can be confirmed at the time, it is possible to infer the corrosion status of the heat exchangers of the other group. Therefore, the heat exchangers of the other group can be updated at the optimum timing based on the guess.

Further, according to the operation method of the gas preheater according to claim 3, in addition to the action and effect of the invention according to claim 1 or 2, the distance between the fins of the heat exchanger of the first group is set to the heat of the other group. Since the distance between the fins of the exchanger is wider, corrosive substances in the fuel gas are less likely to clog the fins, and corrosion can be suppressed.

Further, according to the operation method of the gas preheating device according to claim 4, in addition to the action and effect of the invention according to claim 1 or 2, the heat exchanger of the first group is not provided with fins and the heat transfer tube is a bare tube. Therefore, the corrosive substance in the fuel gas is less likely to adhere to the heat transfer tube, and the corrosion can be further suppressed.
As a result of taking the above measures, the life of the entire heat exchanger has been significantly extended from two years to five years or more.

When the heat exchanger of one group of the first group and the second group corrodes and the circulating heat medium leaks from the heat transfer tube as in the operation method of the gas preheater of the present invention, the heat of the other group is generated. The point of updating one group of heat exchangers before the circulating heat medium of the exchanger leaks is not described at all in Patent Document 1 described above.

It is the schematic which shows the gas flow path and the heat exchanger in the gas preheater which concerns on embodiment of this invention. It is the schematic which shows the heat exchanger shown in FIG. It is the schematic which shows the gas flow path and the heat exchanger in the gas preheater which concerns on the prior art. It is the schematic which shows the heat exchanger shown in FIG. 1 and FIG.

A method of operating the gas preheating device according to the embodiment of the present invention will be described with reference to FIGS. 1, 2, and 4.
The same parts as those shown in the conventional example are designated by the same reference numerals.
This gas preheating device includes a gas flow path 10 and a plurality of heat exchangers 30, and preheats the fuel gas G of a boiler used in a steel mill.
The fuel gas G is a mixed gas of a blast furnace gas (BFG) and a linz-Donaw gas (LDG) produced at a steel mill, and the blast furnace gas contains a corrosive component such as ammonium chloride.

The gas flow path 10 is a pipe or duct through which the fuel gas G flows, and preheats (heats) the fuel gas G inside the pipe or duct.
The inner diameter of the gas flow path 10 is larger than the length of one heat exchanger 30, and a plurality of heat exchangers 30 are arranged inside. In order to transfer heat from the outside of the gas flow path 10 to the heat exchanger 30 inside the gas flow path 10, the gas flow path 10 is appropriately communicated with the outside via a pipe, and the circulating heat medium W is the heat exchanger 30. It is designed to flow to.

The heat exchanger 30 includes a heat transfer tube 31, fins 32, a tube base 33, and a tube side 34.
The gas preheater according to the present embodiment also separately includes a heat exchanger 30 that acquires heat from the high temperature exhaust gas of the boiler, but here, a gas that applies heat to the fuel gas G that is lower in temperature than the exhaust gas. The heat exchanger 30 arranged in the flow path 10 will be mainly described.

The heat exchangers 30 are arranged in the gas flow path 10 in close proximity to each other with one or more heat exchangers 30 as one group, and such groups are arranged in the nth group in ascending order from the upstream with respect to the fuel gas G. A plurality of them were arranged as (n = 1, 2, 3, ...).
In this embodiment, the first group 101 to the sixth group are provided.
This close arrangement means that the fuel gas G is arranged close to each other in the flow direction (upstream / downstream direction).

That is, the first group 101 is a group of heat exchangers 30 located on the most upstream side with respect to the flow of the fuel gas G, and the second group 102 is a heat exchange arranged on the downstream side of the first group 101. The group of vessels 30, and the third group 103 is a group of heat exchangers 30 arranged on the downstream side of the second group 102.
The third group 103 or less, the fourth group 104, the fifth group 105, and the sixth group are the same in order.
Then, each group was composed of 44 rows and 3 stages. That is, each group includes 132 heat transfer tubes 31.

The heat transfer tube 31 is a pipe through which the circulating heat medium W flows. The circulating heat medium W is heated by the exhaust gas of the boiler before reaching the gas flow path 10.
A tube side 34 is connected to both ends of the heat transfer tube 31 via a tube base 33, and a plurality of heat transfer tubes 31 are gathered at the tube side 34, thereby forming one heat exchanger 30.

The fins 32 are spirally provided on the outer surface of each of the heat transfer tubes 31 of the second to sixth groups in order to increase the substantial surface area of the heat transfer tubes 31.
The pitch of the fins 32 was 4 to 5 mm.
On the other hand, the heat transfer tube 31 of the first group 101 is not provided with the fin 32, and the heat transfer tube 31 of the first group 101 is a bare tube.

Then, the heat transfer tubes 31 of the first group 101 and the second group 102, the tube base 33, and the fins 32 of the second group 102 were made of a corrosion-resistant stainless steel material. This corrosion-resistant stainless steel material is a trade name manufactured by the applicant: NSS SCR, and its representative component is 18.5Cr-12Ni-3Si-2Cu-0.8Mo.
Further, the pipe section 34 was composed of SUS316L.
Further, the tube base 33 of the first group 101 was subjected to shot peening treatment so that ^{the residual stress was 10 kg / mm 2 or less.}
Further, the welded portion of the tube base 33 of the first group 101 is coated with a heat resistant anticorrosive coating at 300 ° C.

On the other hand, the heat transfer tubes 31, fins 32, tube bases 33, and tube sections 34 of the third to sixth groups are made of carbon steel as before.
That is, the heat exchanger 30 of the first group 101 had the highest corrosion resistance, and then the heat exchanger 30 of the second group 102 had the highest corrosion resistance.

Next, the corrosive environment in the gas flow path 10 will be described.
The ambient environment (atmosphere) of Group 1 101 has a pH of 5.0, a relative humidity of 100 to 45%, ^{and a maximum cl −} of 1500 ppm.
Since the fuel gas G that has passed through the location of the first group 101 receives heat and raises the temperature, the relative humidity decreases. As a result, the ambient environment of the second group 102 or less becomes a low corrosion environment as compared with the ambient environment of the first group 101. That is, the ambient environment of the first group 101, which is the most upstream side, is the harshest condition for corrosion, but the heat exchanger of the second group, which is not placed in the highly corroded environment, is also intentionally improved in corrosion resistance. ..

The relative humidity of the gas is less than 45% when the first group 101 is functioning, but when the function of the first group 101 deteriorates, the temperature of the fuel gas G does not rise when it passes through the first group 101 ( Since the temperature rise is insufficient), the relative humidity around the second group 102, which is downstream of the temperature rise, rises to 45% or more. In particular, it has been found that corrosion progresses rapidly when the relative humidity is 60% or more.
That is, if the heat exchange function of the first group 101 deteriorates, the second group 102 and the downstream side thereof become a highly corrosive environment.

Next, the effect of the gas preheating device configured as described above and its operation method (repair / renewal method) will be described.
First, the gas preheater is operated normally.
Since the heat exchanger 30 of the first group 101 is made of a corrosion-resistant stainless steel material and shot peening is applied to the tube base 33, the corrosion resistance is improved. Further, since the heat exchanger 30 of the first group 101 is not provided with fins 32 and is a bare tube, corrosive substances in the fuel gas G are less likely to adhere to the heat transfer tube 31, and corrosion can be further suppressed.

In this way, the corrosion resistance of the heat exchanger 30 of the first group 101 is particularly improved, but as described above, the area around the first group 101 is the most severe corrosion environment, so someday the heat exchanger of the first group 101 Stress corrosion cracking or the like occurs in 30, and the circulating heat medium W in the heat transfer tube 31 leaks.

At the timing of stopping the boiler, the leaked heat transfer tube 31 of the first group 101 is cut off and a closing plug is welded.
As the heat transfer tubes 31 that have been stopped by the repair expand to a plurality of heat transfer tubes 31 and the heat exchange efficiency of the entire first group 101 decreases, the area around the second group 102 becomes a highly corrosive environment.
Then, the heat transfer tube 31 of the second group 102 also has an increased number of stoppers due to corrosion and repair.

Here, before both the heat exchangers 30 of the first group 101 and the second group 102 lose their heat exchange functions due to corrosion at the same time, one of the heat exchangers 30 of the first group 101 and the second group 102 Update the heat exchanger 30. That is, instead of stopping the plug, the heat exchanger 30 is replaced with a new one.
In this respect, since the corrosion resistance of the heat exchangers 30 of the first group 101 and the second group 102 is improved, even if the heat exchangers 30 of the first group 101 are corroded and the downstream side becomes a highly corroded environment, the second group The corrosion of the heat exchangers 30 of the group 102 is gradual, and the corrosion of the heat exchangers of the third and subsequent groups can also be suppressed. Therefore, the acceleration of corrosion in the heat exchanger 30 in the group downstream of the third group 103 is suppressed.
In this way, the life of the plurality of heat exchangers 30 as a whole can be extended.

Further, since the heat exchanger 30 of the first group 101 and the heat exchanger 30 of the second group 102 are slowly corroded, the heat exchange of the heat exchanger 30 of one group is different from the case where the corrosion progresses in a short period of time. It is possible to infer the corrosion status of the heat exchanger 30 of the other group from the corrosion status that can be confirmed at the time of decrease in rate or renewal. Therefore, the heat exchangers of the other group can be updated at the optimum timing based on the guess.

In the present embodiment, shot peening is performed on the tube base 33 of the first group 101, but the present invention is not limited to this, and shot peening is also performed on the tube base 33 of the second group 102. May be good.
Similarly, the welded portion of the tube base 33 of the second group 102 may also be coated with a heat resistant anticorrosive coating at 300 ° C.

Further, the heat exchanger 30 of the first group 101 is not provided with fins 32 and is a bare tube, but the present invention is not limited to this, and the distance between the fins 32 of the heat exchanger 30 of the first group 101 is set to another. Even if the distance between the fins 32 of the heat exchangers 30 of the group is made wider, the corrosive substances in the fuel gas G are less likely to be clogged in the fins 32, and corrosion can be suppressed.
Of course, the intervals of the fins 32 may be equal in the first to sixth groups.

In addition, although the arrangement is made up to the sixth group, the present invention is not limited to this, and may be more or less than this.
Furthermore, the number of heat transfer tubes 31 in one group is not limited to that of the present embodiment.

10 Gas flow path 20 Heat exchanger 21 Heat transfer tube 22 Fin 23 Tube base 24 Tube side 30 Heat exchanger 31 Heat transfer tube 32 Fin 33 Tube base 34 Tube side 101 1st group 102 2nd group 103 3rd group 104 4th group 105 Group 5 G Fuel gas W Circulating heat medium

Claims (4)

A gas flow path through which fuel gas including blast furnace gas, which is the fuel for the boiler, flows inside,
A plurality of heat transfer tubes through which a circulating heat medium flows, fins provided on the outer surfaces of the plurality of heat transfer tubes, and pipes connected to both ends of the plurality of heat transfer tubes via a tube stand. With a heat exchanger,
In the gas flow path, one or more heat exchangers are arranged close to each other as one group, and the nth group (n = 1, 2, 3,) is arranged in ascending order from the upstream with respect to the fuel gas. ...), and it is a method of operating a plurality of gas preheaters arranged at least in the third group or more.
The heat transfer tubes of the first group and the second group are made of a corrosion-resistant stainless steel material.
Before both the heat exchangers of the first group and the second group lose their heat exchange function due to corrosion at the same time, the heat exchangers of one of the heat exchangers of the first group and the second group are updated. A method of operating a gas preheater, which is characterized by doing so. The method for operating a gas preheater according to claim 1, wherein the heat transfer tube of the heat exchanger of the third group or later is made of carbon steel. The method for operating a gas preheater according to claim 1 or 2, wherein the distance between the fins of the heat exchangers of the first group is wider than the distance between the fins of the heat exchangers of the other group. .. The method for operating a gas preheating device according to claim 1 or 2, wherein the heat exchanger of the first group is not provided with the fins and the heat transfer tube is a bare tube.

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