JPH08327006A - Supercritical variable pressure once-through boiler - Google Patents

Abstract

PURPOSE: To eliminate the life consumption of a furnace pressure resistant part due to repetitive thermal stress upon load change by obviating the temperature unbalance between the tube groups of a furnace peripheral wall steam tube outlet. CONSTITUTION: A furnace peripheral wall is divided into an upper part 10 and a lower part 11. The peripheral wall of a downstream side 10 of the one combustion gas flow of the divided furnace is used as a steam cooling wall 13, and the peripheral wall of the other upstream side 11 is used as a water cooling wall 3 so that gas-liquid two phase flow always exists at the time of a subcritical operation. Thus, even if the heat absorbing amount at the wall 3 is irregular, the heat transfer tube outlet temperature always becomes a constant saturation temperature.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a furnace system configuration of a supercritical pressure transformer once-through boiler for power utilities and other industries.

[0002]

2. Description of the Related Art FIG. 6 is a system diagram showing an example of the configuration of a conventional supercritical pressure transformer once-through boiler. In the figure, the boiler water exiting the economizer (not shown) arranged in the rear flue (20) passes through the furnace inlet connecting pipe (1) and then moves toward the furnace peripheral wall evaporation pipe inlet pipe located at the lower part of the furnace (22). (4) Enters and goes up to the uppermost part of the furnace while being heated in the furnace peripheral wall evaporation pipe (2) which constitutes the furnace peripheral wall arranged almost vertically. Then, it enters the steam / water separator (7) from the furnace peripheral wall evaporating pipe outlet header (5) through the furnace outlet connecting pipe (6), where it is separated into steam and drain. The steam separated by the steam separator (7) passes through the superheater inlet communication pipe (21) and is passed through the superheater (1
It flows to 7). On the other hand, the drain separated by the steam separator (7) passes through the drain discharge pipe (9) and the circulation pump (1
It is returned to the inlet of the economizer by 9). In this case, as a matter of course, the drain level adjusting valve (1) should be set so that the drain level in the steam separator (7) does not fall below a certain level.
8).

Design considerations for the furnace peripheral wall evaporation pipe (2) of the conventional boiler having such a system are as follows.
Since it is a once-through type, the enthalpy level of the fluid at the outlet of the furnace is set higher than the saturation temperature in the subcritical pressure region as shown in the static characteristic data of the furnace shown in Fig. 5, but due to the reason described in the next section, its overheating It is designed to be as small as possible.

[0004]

In the conventional boiler as described in the preceding paragraph, there is a problem that a temperature imbalance occurs between the tube groups at the outlet of the evaporating tubes of the peripheral wall of the furnace. This is because when there is a deviation in the amount of heat absorption in the wall surface due to the combustion condition in the furnace, this appears as an imbalance in the outlet fluid temperature of each evaporation tube. If an imbalance occurs in the metal temperature of the peripheral wall of the furnace, there is a risk of damage to the pressure-resistant part of the furnace due to the associated thermal stress. Therefore, early establishment of a countermeasure to prevent this temperature imbalance is urgently required.

As a design consideration for this, it is first considered that an orifice or the like is provided at the inlet of each evaporation pipe and the amount of water supplied is adjusted according to the heat absorption deviation to suppress the imbalance of the outlet fluid temperature. However, it is actually difficult to eliminate the temperature imbalance by this method because the deviation of the heat absorption amount and the water supply distribution characteristic change depending on the boiler load.

Therefore, as a fundamental method for eliminating this temperature imbalance, it is conceivable to design the furnace such that the fluid enthalpy level at the outlet of the furnace peripheral wall evaporator tube is in a wet state. Then, even if there is some difference in the amount of heat absorption between a and b of the static characteristic data of the furnace shown in FIG. 5, that is, the imbalance of the fluid enthalpy occurs, the temperature of the fluid is saturated at the saturation temperature. Since it becomes constant, it does not appear as a temperature difference.

However, since the size of the furnace is determined as the space required for complete combustion of the fuel, it is not possible to make the furnace smaller than that and reduce the heat transfer area of the peripheral wall of the furnace. Therefore, there is also an example in which the fluid enthalpy level at the outlet of the furnace peripheral wall evaporation pipe is designed to be wet by adding it to the boiler water system at the outlet of the furnace peripheral wall and further providing a heat transfer surface that functions as an evaporator on the downstream side. there were. FIG. 7 is a diagram showing the furnace characteristics of such a conventional case. However, in this case, even if the static characteristic is wet, as shown in the figure, the dynamic characteristic shows a characteristic that there is a hysteresis between "load increase" and "load decrease" due to the heat storage capacity of the metal. . Especially in the case of "load reduction", a large degree of superheat may occur as shown in the figure. Further, FIG. 8 is different from the case of FIG. 7 in the case of the boiler in which the heat transfer surface composed of the evaporator is not provided in the rear flue, and statically the enthalpy level of the fluid at the furnace peripheral wall evaporation pipe outlet is Although it is higher (dry) than the case of FIG. 7, the characteristic that the dynamic increase in superheat degree is slightly small due to the small metal weight of the evaporator is shown.

When a temperature imbalance occurs due to an increase in the degree of superheat as described above, a large thermal stress is generated in the wall surface of the furnace. Therefore, the thermal resistance of the furnace consumes its life due to the repeated thermal stress caused by the load change. As a result, damage may hinder the operation of the boiler.

[0009]

In order to solve the above-mentioned conventional problems, the present inventor proposes the following supercritical pressure transformer once-through boiler. [1] A furnace having a peripheral wall composed of a heat transfer tube and a burner for injecting fuel and combustion air into the lower part of the furnace for combustion are provided, and combustion gas generated in the furnace is absorbed by the peripheral wall of the furnace. In the supercritical pressure transformer once-through boiler that flows up from the upper part of the furnace to the rear flue while dividing, the furnace peripheral wall is divided into upper and lower parts, and the upper peripheral wall is a steam cooling wall,
A supercritical pressure transformer once-through boiler, wherein the lower peripheral wall is a water-cooled wall in which gas-liquid two-phase flow always exists during subcritical pressure operation. [2] In addition to the requirement of [1] above, the peripheral wall evaporation pipe outlet header provided at the heat transfer pipe outlet of the lower peripheral wall is connected to the inlet of the steam separator, and the steam of the steam separator is provided. A desuperheater whose outlet is connected to a steam-cooling wall inlet header provided at the heat transfer pipe inlet of the upper peripheral wall, and a drain outlet of the steam separator is provided upstream and / or in the middle of the superheater. A supercritical pressure transformer once-through boiler, which is connected to the spray water inlet of. [3] A furnace having a peripheral wall composed of a heat transfer tube and a burner for injecting fuel and combustion air into the upper part of the furnace for combustion are provided, and combustion gas generated in the furnace is absorbed by the peripheral wall of the furnace. In the supercritical pressure transformer once-through boiler flowing down to the rear flue while descending while the furnace peripheral wall is divided into upper and lower, with the lower peripheral wall as a steam cooling wall,
A supercritical pressure transformer once-through boiler, wherein the upper peripheral wall is a water-cooled wall in which gas-liquid two-phase flow always exists during subcritical pressure operation. [4] In addition to the requirement of [3] above, the peripheral wall evaporation pipe outlet header provided at the heat transfer pipe outlet of the upper peripheral wall is connected to the inlet of the steam separator, and the steam outlet of the steam separator is provided. Is connected to a steam-cooling wall inlet pipe provided at the heat transfer pipe inlet of the lower peripheral wall, and a drain outlet of the steam separator is provided at an upstream and / or middle stage of the superheater. A supercritical pressure transformer once-through boiler, which is connected to the spray water inlet of. [5] In addition to the requirement of [2] or [4], the steam outlet of the steam separator is placed horizontally in the rear flue rather than directly in the steaming wall inlet pipe header. The supercritical pressure transformer once-through boiler, which is connected to the steaming wall inlet pipe header through the low temperature superheater and the desuperheater in sequence.

[0010]

In the first and third means for solving the problems, the peripheral wall of the furnace is divided into upper and lower parts, one of the divided peripheral walls of the furnace is used as a steam cooling wall, and the other peripheral wall of the furnace is always operated during subcritical pressure operation. Since it is a water-cooled wall where gas-liquid two-phase flow exists,
Even if the heat absorption amount of each water cooling wall tube is not uniform, the outlet temperature is constant (saturation temperature). Therefore, the unbalance of the furnace wall metal temperature that has been conventionally generated does not occur at all, and the life of the furnace pressure-resistant portion is not consumed due to the repeated thermal stress caused by the load change.

Further, in the second and fourth solving means, the evaporating pipe outlet head of the water cooling wall is connected to the inlet of the steam separator, and the steam outlet of the steam separator is the heat transfer pipe of the steaming wall. The drain outlet of the steam separator is connected to the steam cooling wall inlet header provided at the inlet, and is connected to the spray water inlet of the desuperheater provided upstream and / or in the middle of the superheater. Therefore, the mixed fluid of steam and water generated on the water cooling wall is separated into steam and water by the steam separator, and the separated steam is introduced into the steam cooling wall almost uniformly. The separated water is used as spray water for the desuperheater without waste.

Further, in the fifth solution means, the steam outlet of the steam separator is not directly connected to the inlet of the steam cooling wall inlet, but is a horizontal low temperature superheater arranged in the rear flue and Since it is connected to the steam cooling wall inlet pipe header through the desuperheater in sequence, heat is effectively recovered from the combustion gas, and the plant efficiency is improved.

[0013]

FIG. 1 is a system diagram showing the structure of a supercritical pressure transformer once-through boiler according to a first embodiment of the present invention. This boiler has a furnace structure that stands almost vertically, and is equipped with combustion equipment consisting of a burner for injecting fuel and combustion air for combustion in the lower part, an air jet, etc., and the combustion gas generated in the lower part of the furnace (11) is the peripheral wall of the furnace. The boiler is arranged so as to rise while being absorbed by the heat and flow from the furnace upper part (10) to the rear flue (20). In the present embodiment, the peripheral wall of the furnace upper part (10) is a steam cooling wall (13) composed of a steam cooling pipe, and the peripheral wall of the furnace lower part (11) is a water cooling wall (3) composed of an evaporation pipe.

As for the flow of water and steam, from the outlet of a economizer (not shown) installed in the rear flue (20),
The feed water that has entered the water cooling wall inlet header (4) at the lower part of the furnace via the furnace inlet connecting pipe (1) enters the water cooling wall (2) and rises while absorbing heat from the combustion gas in the furnace, 2) At the upper end, it is collected in the water cooling wall outlet pipe header (5), and reaches the steam separator (7) through the furnace outlet communication pipe (6). The steam separated by the steam separator (7) flows from the steam cooling wall inlet connecting pipe (8) to the steam cooling wall inlet pipe (14) at the upper part of the furnace to the steam cooling wall (13), where it is superheated. After that, it is collected in the steam cooling wall outlet pipe header (15), and the superheater inlet connecting pipe (2
By 1), it goes through the desuperheater (12) to the superheater (17). About half of the drain generated in the steam separator (7) is used as spray water for the desuperheater (12) provided in the superheater inlet communication pipe (21) immediately before the first superheater (17). , The drainage pipe (9), and about half of the remaining amount is used as spray water for the desuperheater (second stage) provided at the inlet of the next superheater (secondary).
At the time of startup, this drain is returned to the economizer inlet water supply pipe by the circulation pump (19). In order to maintain the drain level of the steam separator (7), the drain level adjusting valve (1
8) is a drain discharge pipe (9) before the branch point of the spray water
It is provided in.

Next, the furnace characteristics of this embodiment will be compared and examined with those of the conventional boiler. In particular, the results of a case study at a 30% load as a partial load in which a temperature unbalance is likely to occur in a transformer once-through boiler will be described. Table 1 shows the static characteristic values of each case at this 30% load.

[0016]

[Table 1]

In the conventional boiler, the enthalpy level at the furnace peripheral wall outlet is set to 670 kcal / kg, and the design is made with a superheat of about 10 ° C. In this embodiment, steam and water are enthalpy at point c in FIG. At the level, it is considered to guide it to the steam-water separator through the evaporating tube outlet of the furnace wall.

The examination case is a case where the height of the peripheral wall evaporation pipe outlet of the conventional boiler is H in FIG. 4 and the height 0.7H is used as the peripheral wall evaporation pipe outlet. In this case, the peripheral wall evaporation pipe outlet fluid is The enthalpy is 570 kcal / kg. At this time, in the steam separator, of the evaporation amount of 365 t / h, 99 t /
Drain of h occurs. On the other hand, the steam separated by the steam separator is guided to the upper wall of the furnace, and then goes to the superheater. At this point, it is the saturated vapor temperature at the steam outlet
Overheated from 310 ℃ to 470 ℃. In this study case, a two-stage spray was used in which half of the drainage generated in the steam separator was charged at the superheater inlet and the remaining half was charged at the primary superheater outlet. The temperature before and after spraying is the first step
470 ℃ to 35 ℃ ℃ 2nd stage 470 ℃ to 380 ℃
Further, it was found that it was further heated by the superheater and was superheated at the outlet of the final superheater until the rated temperature of 5700C was reached.

When a trial calculation is made for a case where the water cooling wall at the lower part of the furnace is smaller than that of the above-mentioned study case, for example, the height is set to about 0.5H, in that case, the amount of drain generated in the steam separator is about half of the evaporation amount. In fact, the amount of steam passing through the furnace upper steaming wall is smaller than that in the case studied above, so that the furnace upper steaming wall or the outlet of the primary superheater is overheated to 540 ° C. This is the same level of temperature as the final superheater, which causes technical problems such as problems in tube material selection and a high ratio of drain amount to be injected as a spray. It is considered appropriate to set the level at the above-mentioned study case (that is, 0.7) rather than lowering the furnace peripheral wall evaporation pipe outlet to a certain fluid enthalpy level.

FIG. 2 is a system diagram showing the structure of a supercritical pressure transformer once-through boiler according to a second embodiment of the present invention. This embodiment also has a furnace structure that stands almost vertically as in the first embodiment.
Combustion equipment consisting of burners, air jets, etc. is installed in the upper part of the furnace, and combustion gas generated in the upper part of the furnace descends while being absorbed by the peripheral wall of the furnace, and from the lower part of the furnace to the rear flue (20).
It is designed to flow to. The peripheral wall having a relatively low heat load constituting the lower part (11) of the furnace peripheral wall divided into upper and lower parts is used as a steam cooling wall (13), and the upper part of the furnace (10)
Is a water cooling wall (3) that can always maintain the fluid enthalpy level at the outlet in a sufficiently low wet state. water supply,
The steam flow system is basically the first shown in FIG.
Same as the embodiment, except that there is a difference in the positional relationship between the water cooling wall and the steam cooling wall above and below the furnace.

Since the present embodiment and the first embodiment are the same in terms of heat transfer except for the difference in arrangement or gas flow as described above, their operations are also exactly the same. Therefore, in order to always maintain the enthalpy level of the fluid at the outlet of the furnace wall at a wet level, the fluid temperature level at the outlet of the furnace is set appropriately considering the dynamic characteristics when the load decreases, and the heat transfer area of the water cooling wall of the furnace wall is determined. The remaining peripheral wall of the furnace, which has a relatively low heat load, is composed of a steam cooling wall, and a steam-water separator is installed at the outlet of the furnace peripheral wall evaporation pipe, and the generated drainage is used as a primary or secondary spray to the middle stage of the superheater. If put in, even if there is some difference in heat absorption amount in the water cooling wall pipe,
The outlet temperature becomes a constant saturation temperature. As a result, the furnace wall metal temperature unbalance that has occurred in the past does not occur at all, so the life of the furnace pressure resistant part due to repeated thermal stress due to load changes is eliminated, and further damage to the boiler due to fatigue is prevented. To be done.

FIG. 3 is a boiler system diagram showing a third embodiment of the present invention. Also in this embodiment, the steam-water mixture of the water-cooling wall (3) in the lower part (11) of the furnace is separated from the steam-water outlet through the water-cooling wall outlet pipe (5) and the furnace outlet connecting pipe (6) as in the first embodiment. Enter the vessel (7). After that, in this embodiment, the separated steam does not enter the steam cooling wall (13) directly, but passes through the low-temperature superheater inlet communication pipe (24) and is installed in the rear flue (20) in the horizontal low-temperature superheater (23). ), And after being superheated there, it enters the steam cooling wall inlet pipe header (14) through the steam cooling wall inlet connecting pipe (8) and the temperature reducer (26). The steam superheated by the steam cooling wall (13) enters the superheater (17) through the superheater inlet communication pipe (21) from its outlet pipe, and the desuperheater (12) is in the middle thereof.
Is provided. The separation drain of the steam separator (7) is distributed and injected as spray water into the temperature reducers (12) and (26).

In this embodiment, when the epitarpi level (wetness) of the water-cooled wall outlet fluid in the lower part of the furnace (11) changes due to changes in the operation / combustion state, the steam-cooled wall (1
It is possible to prevent the metal temperature of the steam cooling wall (13) from excessively rising due to a change in the flow rate of steam passing through 3). That is, the low temperature superheater (23) placed in the low temperature part of the gas
Protects the steaming wall (13) placed in the high temperature part of the gas. In this case, since the low temperature superheater (23) is installed in the rear flue (20) where the gas temperature is low,
It is possible to design so that trouble does not occur even if the amount of steam changes a little.

Further, as a fourth embodiment of the present invention, the second
The steam separated by the steam-water separator (7) of the example is not directly introduced into the steam cooling wall (13) at the lower part of the furnace, but is passed through the low temperature superheater and desuperheater in the rear flue and then steamed. A boiler adapted to be installed in the cold wall (13) is also possible. In this case as well, it is possible to obtain the same effect as that of the third embodiment.

If the above-mentioned first to fourth embodiments are adopted and the fluid enthalpy level of the furnace outlet fluid is set to be wet, the metal temperature imbalance at the water cooling wall outlet can be eliminated. You can Here, as in the case of "load reduction", a large degree of superheat occurs due to the dynamic characteristics and hysteresis characteristics due to the heat capacity of the furnace, and as the degree of superheat increases, the temperature becomes unbalanced and large thermal stress occurs in the furnace wall surface. There is a risk of As described above, there is a possibility that the life of the pressure-resistant portion of the furnace will be consumed due to the repeated thermal stress due to the load change, but this problem can be solved by the following processing.

As described above, if the furnace enthalpy fluid enthalpy level is set to the level of the study case, the temperature of the outlet of the steaming wall (13) in the upper part of the furnace or the lower part of the furnace or the outlet of the primary superheater rises to the extent that it is necessary to upgrade the material Since the ratio of steam and spray water is not so large and is within the technically possible range, the water cooling wall heat transfer area corresponding to this is determined, and the remaining peripheral wall of the furnace with a low heat load is steamed. The cold water wall (13) is arranged and arranged, and the system of water supply and steam is constructed as in the above-mentioned embodiments. Then, even if there is a slight difference in heat absorption at the outlet of the water cooling wall (3), the temperature becomes constant at the saturation temperature, so that the above-mentioned conventional problem, that is, the imbalance of the furnace peripheral wall metal temperature, etc. does not occur at all. .

[0027]

As described above, according to the present invention, in order to always maintain the enthalpy level of the fluid at the outlet of the furnace peripheral wall in a wet state, the temperature level of the fluid at the outlet of the furnace considering the dynamic characteristics (during load drop) is also set. After setting, determine the heat transfer area of the water cooling wall of the furnace peripheral wall, and the remaining furnace peripheral wall with a relatively low heat load is composed of the steam cooling wall, and a steam-water separator is provided at the furnace peripheral wall evaporation pipe outlet to generate it. Since the drain is fed to the middle stage of the superheater as a primary or secondary spray, the outlet temperature becomes constant at the saturation temperature even if there is a slight difference in the amount of heat absorption in the water wall of the furnace. Therefore, the unbalanced temperature of the furnace wall metal, which has been generated in the past, does not occur dynamically (when the load drops), so the life of the furnace pressure-resistant part is not consumed due to the repeated thermal stress that accompanies the load change. Boiler damage due to fatigue is prevented. In addition, there is no influence on the steam condition at the final superheater outlet by adding the generated drain separated by the steam separator to the middle stage of the superheater as spray water.

As for the arrangement of the furnace, the effect of the invention is exactly the same regardless of whether the combustion equipment is provided in the lower part or in the upper part of the furnace.

[Brief description of drawings]

FIG. 1 is a system diagram showing a configuration of a supercritical pressure variable pressure once-through boiler according to a first embodiment of the present invention.

FIG. 2 is a system diagram showing a configuration of a supercritical pressure variable pressure once-through boiler according to a second embodiment of the present invention.

FIG. 3 is a system diagram showing a configuration of a supercritical pressure variable pressure once-through boiler according to a third embodiment of the present invention.

FIG. 4 is an explanatory diagram of a model boiler which is a target of a case study according to the present invention.

FIG. 5 is furnace static characteristic data of the model boiler of FIG. 4.

FIG. 6 is a system diagram showing an example of the configuration of a conventional supercritical pressure variable pressure once-through boiler.

FIG. 7 is a diagram showing an example of furnace characteristics of a conventional supercritical pressure variable pressure once-through boiler.

FIG. 8 is a diagram showing another example of furnace characteristics of a conventional supercritical pressure variable pressure once-through boiler.

[Explanation of symbols]

(1) Furnace inlet connection pipe (2) Furnace peripheral wall evaporation pipe (3) Water cooling wall (4) Furnace peripheral wall evaporation pipe inlet alignment (water cooling wall inlet alignment) (5) Furnace peripheral wall evaporation pipe outlet alignment (water cooling wall outlet) (6) Furnace outlet connecting pipe (7) Steam separator (8) Steaming wall inlet connecting pipe (9) Drain discharge pipe (10) Upper furnace (11) Lower furnace (12) Desuperheater (13) ) Steaming wall (14) Steaming wall inlet pipe header (15) Steaming wall outlet pipe header (17) Superheater (18) Drain level control valve (19) Circulation pump (20) Rear flue (21) Superheater Inlet connecting pipe (22) Furnace (23) Low temperature superheater (24) Low temperature superheater Inlet connecting pipe (26) Desuperheater

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takayuki Sudo 1-1 1-1 Atsunouramachi, Nagasaki City Mitsubishi Heavy Industries Ltd. Nagasaki Shipyard Co., Ltd.

Claims (5)

[Claims] 1. A furnace having a peripheral wall formed of a heat transfer tube,
A burner for injecting fuel and combustion air into the lower part of the furnace for combustion is provided, and the combustion gas generated in the furnace rises while being absorbed by the peripheral wall of the furnace and rises from the upper part of the furnace to the rear flue. In a critical pressure once-through boiler, the peripheral wall of the furnace is divided into upper and lower parts, and the upper peripheral wall is a steam cooling wall, and the lower peripheral wall is a water cooling wall in which gas-liquid two-phase flow is always present during subcritical pressure operation. A supercritical pressure variable pressure once-through boiler. 2. A peripheral wall evaporation pipe outlet head provided at the heat transfer pipe outlet of the lower peripheral wall is connected to an inlet of the steam separator, and a steam outlet of the steam separator is transferred to the upper peripheral wall. The drain outlet of the steam separator was connected to the steam cooling wall inlet header provided at the heat pipe inlet and the spray water inlet of the desuperheater provided upstream and / or in the middle of the superheater. The supercritical pressure transformer once-through boiler according to claim 1, characterized in that. 3. A furnace having a peripheral wall composed of a heat transfer tube,
A burner for injecting and burning fuel and combustion air is provided in the upper part of the furnace, and the combustion gas generated in the furnace descends while being absorbed by the peripheral wall of the furnace and flows down from the lower part of the furnace to the rear flue. In a critical pressure transformer once-through boiler, the peripheral wall of the furnace is divided into upper and lower parts, and the lower peripheral wall is a steam cooling wall, and the upper peripheral wall is a water cooling wall in which gas-liquid two-phase flow is always present during subcritical pressure operation. A supercritical pressure variable pressure once-through boiler. 4. A peripheral wall evaporation pipe outlet header provided at the heat transfer pipe outlet of the upper peripheral wall is connected to an inlet of the steam separator, and a steam outlet of the steam separator is transferred to the lower peripheral wall. The drain outlet of the steam separator was connected to the steam cooling wall inlet header provided at the heat pipe inlet and the spray water inlet of the desuperheater provided upstream and / or in the middle of the superheater. The supercritical pressure transformer once-through boiler according to claim 3, wherein 5. The steam outlet of the steam separator is not directly connected to the steam-cooling wall inlet pipe but through the horizontal low-temperature superheater and the desuperheater arranged in the rear flue in order. The supercritical pressure transformer once-through boiler according to claim 2 or 4, wherein the steam-cooling wall inlet pipe header is connected.