JPH08233208A - Ultracritical variable pressure once-through type axial boiler - Google Patents

Abstract

PURPOSE: To provide an ultracritical variable pressure once-through type axial boiler constructed such that a temperature unbalanced state is not produced among groups of pipes at outlet part of evaporating pipes at a circumferential wall of a furnace as a degree of over-heating at the evaporating pipes at the circumferential wall of the furnace is increased. CONSTITUTION: This boiler comprises an intermediate pipe complex 21 of a circumferential wall of a furnace in which circumferential wall evaporating pipes 2 of a furnace 14 are divided into an upper furnace circumferential wall evaporating pipe 15 and a lower furnace circumferential wall evaporating pip 16, respectively. The evaporating pipe coming out of the intermediate pipe complex 21 of the circumferential wall of the furnace as the upper furnace circumferential wall evaporating pipe 15 is provided with an orifice 20. Although a friction loss is increased at the upper furnace circumferential wall evaporating pipe 15, an entire pressure loss is increased to reduce a flow rate and further to cause a temperature difference to be increased, the orifice 20 is installed there to control the flow rate in correspondence with a thermal absorption distribution at the upper furnace circumferential wall evaporating pipe 15, and then an enthalpy level of the fluid at the outlet of the furnace is made uniform.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a commercial or industrial supercritical pressure transformer once-through boiler.

[0002]

2. Description of the Related Art An example of the structure of a conventional supercritical pressure variable pressure once-through boiler is shown in FIG. In FIG. 9, the feed water exiting the economizer located at the rear flue 12 enters the furnace inlet distribution pipe 18 at the bottom of the furnace 14 via the furnace inlet connecting pipe 1,
Through the furnace distribution pipe 17, it enters the furnace peripheral wall evaporation pipe inlet pipe header 4, and the peripheral wall evaporation pipe 2 constituting the furnace peripheral wall arranged almost vertically rises to reach the uppermost part of the furnace.

In this case, the orifice 20 for controlling the flow rate of the can water passing through each peripheral wall evaporation pipe 2 is provided with the inlet 4 of the furnace peripheral wall evaporation pipe corresponding to the heat load distribution in the wall surface of the peripheral wall of the furnace.
It is installed in the evaporation pipe just above the exit of the.

As described above, the can water of each peripheral wall evaporation pipe 2 whose flow rate has been adjusted has a burner 14 provided with a burner and an air ejection port for injecting and burning fuel and combustion air.
Rises while being heated by the furnace wall constituting the furnace, and flows from the furnace peripheral wall evaporation pipe outlet header 5 into the steam / water separator 7 through the furnace outlet connecting pipe 6, but in the operation in the subcritical pressure region, The steam and drain will be separated. The separated steam in the steam separator 7 flows into the superheater 9 via the superheater inlet communication pipe 13.

On the other hand, the drain separated by the steam separator 7 is returned to the economizer inlet by the circulation pump 11 through the drain discharge pipe 8. As a matter of course, in this case, the drain level adjusting valve 10 controls so that the drain level of the steam separator 7 does not become a certain level or less.

[0006]

In the conventional supercritical pressure variable pressure once-through boiler as described in the preceding paragraph, there is a problem that temperature imbalance occurs between the tube groups at the outlet of the evaporating tube of the furnace peripheral wall. There is a concern that the pressure-resistant part of the furnace will be damaged by thermal stress, and there is an urgent need to establish countermeasures to prevent this temperature imbalance at an early stage.

The unbalance of the metal temperature of the peripheral wall of the furnace is
When the amount of heat absorption in the wall surface varies due to the combustion condition in the furnace, this appears as an imbalance in the outlet fluid temperature of each evaporation tube. As described above, a method has been adopted in which the unbalance of the outlet fluid temperature is suppressed by adjusting the amount of water supply according to the heat absorption deviation by the orifice provided at the inlet of the furnace peripheral wall evaporation pipe.

However, the flow rate control of the feed water by the orifice at the inlet of the furnace of this conventional system is as follows (1),
There are problems such as (2). Due to such problems, the flow rate control of the feed water by the orifice at the furnace inlet of the conventional method may not be sufficient for the purpose of installation. There is.

(1) Since the inlet of the furnace is designed as a subcooled state, the specific volume v is smaller than that of the upper part of the furnace, so that the flow velocity is slow, and therefore the effect is exerted on the pressure loss characteristic of the orifice proportional to the square of the flow velocity. Hard to be done.

(2) Further, when the load is low, the feed water flow rate decreases and the flow velocity decreases, so that the above tendency becomes more and more significant. However, if pressure loss is provided at the orifice so that flow rate control can be performed even at low load, pressure loss at the orifice will be too effective at high load, and an evaporation tube with extremely narrowed flow rate will appear. It will damage.

The occurrence of temperature imbalance due to the increase in the degree of superheat of the peripheral wall evaporation tube causes a large thermal stress in the furnace wall surface. However, the damage to the pressure-resistant part of the furnace will also hinder the operation of the boiler.

The present invention solves such a problem, and the supercritical pressure is constructed so as not to cause a temperature imbalance between the tube groups at the outlet of the furnace peripheral wall evaporation tube as the superheat of the furnace peripheral wall evaporation tube increases. The challenge is to provide a once-through transformer.

[0013]

The present invention has a furnace having a peripheral wall constituted by a water-cooled evaporation pipe, and has a burner and an air jet for injecting and burning fuel and combustion air into the furnace. In order to solve the above-mentioned problems in a supercritical pressure once-through boiler of a type that is equipped with combustion equipment, the combustion gas generated in the furnace flows from the upper part of the furnace to the rear flue side while being absorbed by the peripheral wall of the furnace An orifice is installed in the middle part of the furnace peripheral wall tube where the fluid in the furnace peripheral wall evaporating tube becomes a two-phase flow, and which adjusts the flow rate of the can water corresponding to the heat load distribution in the furnace wall surface.

As described above, in the supercritical pressure variable pressure once-through boiler according to the present invention, in order to improve the function of flow rate control, an orifice is provided in the middle portion of the furnace instead of the conventional orifice at the furnace inlet. Hereinafter, according to the present invention, the effectiveness of providing an orifice in the middle portion of the furnace peripheral wall in the supercritical pressure variable pressure once-through boiler and the verification result thereof will be described. First, the effectiveness of providing an orifice in the middle of the furnace will be described.

(1) In the lower furnace, the temperature is constant (saturation temperature) in the regions a to b shown in the enthalpy / pressure chart of FIG. 5, even if the heat absorption amount Q is different in the wall.
It is not necessary to install an orifice at the furnace inlet in order to make the temperature at the lower furnace outlet uniform.

(2) On the other hand, the upper furnace is always overheated at the outlet of the upper furnace unless a heat transfer surface composed of an evaporator is installed on the downstream side of the upper furnace, and there is a flue evaporator. Even if it does, it can be dynamically overheated, so there is a distribution of the heat absorption amount Q, and if there is a significant difference, it will definitely appear as a temperature difference at the outlet of the upper furnace, so the feed water flow rate G Need to be adjusted.

(3) Further, in the lower furnace area, as shown in FIG.
Since the static pressure loss is dominant as shown in (3), it has a more reliable characteristic with respect to the deviation of the heat absorption amount Q. That is, even in a portion where the heat absorption amount Q is high, the decrease in _static pressure loss (ΔP _static ) is dominant, and the total pressure loss (ΔP _total ) decreases, so that the flow rate in that portion increases. It becomes. This means that it has a self-adjusting ability, and in this respect also, it is not necessary to install an orifice for the purpose of equalizing the temperature of the lower furnace outlet.

(4) On the other hand, in the upper furnace area, as shown in FIG.
On the contrary, the friction loss is dominant as shown in
It has a characteristic of low reliability with respect to the deviation of the heat absorption amount Q. That is, when the heat absorption amount has a distribution, the increase of the friction loss (ΔP _fric ) is dominant in the evaporation pipe having a high heat load,
Since the total pressure loss (ΔP _total ) increases and it becomes difficult to flow, and the flow continues to increase ΔT (temperature difference), it is necessary to control the flow rate G of the upper furnace corresponding to the heat absorption distribution in the actual can. Become.

(5) Considering the points described as the problems at the conventional orifice installation position and the above (1) to (4), in order to adjust the flow rate G, the dryness (St
It can be said that the orifice control in the middle part of the furnace with high eam quality is effective.

Next, the verification result regarding the above will be described. The steam pressure of the once-through type boiler changes depending on the load. Therefore, when the load is low, the steam pressure is low, and the specific heat of steam is smaller than that in the high pressure region, so that the temperature difference becomes large in the overheating region for the heat absorption amount Q having the same enthalpy difference. This is the enthalpy / pressure chart and table 1 in Figure 5.
As shown in.

[0021]

[Table 1]

Therefore, if the flow rate can be controlled accurately with a low load, it can be said that there is little problem with thermal stress even with a slight control under a high load. FIG. 6 is a graph showing the flow distribution characteristics according to the load change, and when the flow distribution of the can water according to the distribution of the furnace heat load at the time of low load (30% ECR) is performed, the high load (75% ECR) is obtained. Then, it is shown how this flow distribution characteristic changes.

In FIG. 6, when the orifice is installed in the lower part of the furnace (dashed line), the load change (30% EC) is larger than when the orifice is installed in the middle part of the furnace (dotted line).
The rate of change in flow distribution is large for R → 75% ECR). Moreover, a tube with a small flow rate will have a smaller flow rate under high load.

From the relationship of Δh = Q / G (Δh: enthalpy difference, Q: heat absorption amount, G = flow rate per tube), if the heat absorption rate Q is constant and the flow rate per tube decreases, Δh May increase the temperature difference.

When the orifice is installed in the lower part of the furnace,
The reason why there is a difference in the flow distribution characteristics due to load changes when installed in the middle of the furnace is based on the following factors (in Tables 2 and 3 when orifices are installed in the lower part of the furnace and in the middle part of the furnace , The ratio of each state quantity with load change is shown).

That is, the pressure loss at the orifice is proportional to the square of the flow velocity in the tube, but in the middle part of the furnace there is almost no change in the flow velocity V in the tube and only in the lower part of the furnace, Since the ratio of the flow velocities V is greatly influenced by the square, and the degree of influence of the orifice changes in accordance with the change of the can water flow rate, the fluctuation of the flow rate distribution with respect to the change of the load (that is, the change of the can water flow rate). Great results.

As described above, setting the orifice in the middle of the furnace is less likely to change the degree of influence of the orifice with respect to the change in the can water flow rate of each load than in the case of installing the orifice in the lower part of the furnace. It is easy to maintain the specified flow rate distribution target value.

[0028]

[Table 2]

[0029]

[Table 3]

From the above description, it is most effective in controlling the flow rate that the orifice provided by the present invention is provided at the exit of the furnace, but normally the furnace wall has a high heat load and the scale from the inner surface of the evaporator tube is large. It is easy to peel off, and the peeled scale on the upstream side of the orifice may block the hole of the orifice, which impairs the reliability of the furnace.

Therefore, in the case of providing an orifice according to the present invention, in the middle part of the furnace, a pipe head is provided which plays a role of a kind of buffer for scale troubles having a large cross section and therefore a small flow velocity, and the flow immediately after that. This furnace is equipped with a perforated plate strainer having a hole smaller than the orifice diameter in order to prevent the scale from closing the orifice hole diameter in front of the orifice by adopting a configuration in which an orifice is arranged in the upper part. By adopting a configuration provided in the central portion of the peripheral wall intermediate pipe, it is possible to eliminate the risk of making the position of the orifice the intermediate portion of the furnace.

[0032]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A supercritical pressure variable pressure once-through boiler according to the present invention will be specifically described below based on an embodiment shown in FIGS. In the following embodiments, the same components as those of the conventional device shown in FIG. 9 are designated by the same reference numerals for the sake of simplicity.

As shown in FIGS. 1 to 4, the boiler according to the present embodiment has a substantially vertical furnace 14 equipped with combustion equipment including a burner for injecting fuel and combustion air for combustion and an air jet and the like. The structure of the furnace 14
The peripheral wall evaporation pipe 2 is divided into an upper furnace peripheral wall evaporation pipe 15 and a lower furnace peripheral wall evaporation pipe 16, and a furnace peripheral wall intermediate header 21 is installed.

This furnace peripheral wall intermediate pipe header 21 is provided on each surface of the furnace 14 one at a time, four in total. The perforated plate strainer 2 is horizontally provided on the entire central surface of the middle wall 21 of the peripheral wall of the furnace.
2 is attached. An orifice 20 having an appropriate hole diameter is attached to each evaporation pipe immediately above the pipe draw (immediate flow) that emerges as the upper furnace peripheral wall evaporation pipe 15 from the pipe draw 21.

As for the water supply and steam system of the boiler having the furnace 14, the furnace inlet distribution pipe 18 is introduced from the outlet of the economizer installed in the rear flue 12 through the furnace inlet connecting pipe 1. The supplied water further enters the furnace peripheral wall evaporation pipe inlet pipe drawer 4 via the furnace distribution pipe 17, and the downstream side thereof forms the peripheral wall of the furnace 14.

While absorbing the heat of the furnace 14, it enters the upper furnace peripheral wall evaporating tube 15 from the lower furnace peripheral wall evaporating tube 16 through the furnace peripheral wall intermediate conduit 21 and exits to the furnace peripheral wall evaporating tube outlet 5 at the top of the furnace 14. The canned water enters the steam separator 7 through the furnace outlet communication pipe 6.

If it is below the critical pressure, it is separated into steam and drain by this steam separator 7, and the steam is connected to the superheater inlet communication pipe 13
Through the drain to the superheater, and the drain is returned to the inlet of the economizer by the circulation pump 11 through the drain discharge pipe 8. In this case, the drain level adjusting valve 10 controls the drain level of the steam separator 7 so as not to fall below a certain level.

The system of the peripheral wall evaporation pipe provided with the furnace peripheral wall intermediate pipe header 21 shown in FIG. 2 has been described with reference to FIG.
A conceptual view of the A cross section is shown in FIG. A horizontal perforated plate strainer 22 as shown in FIGS. 3 and 4 is attached over the entire surface in the center of the cross section of the header 21, and the upper part of the scale in the pipe water from the lower furnace peripheral wall evaporation pipe 16 coming in from below The strainer 22 removes the orifice 20 having a diameter close to the diameter of the orifice 20.

The functions peculiar to the boiler according to this embodiment having the above structure will be described below. In the boiler of the present embodiment, unlike the conventional boiler, the orifice 20 is not installed at the inlet of the furnace 14, the middle section of the furnace has a large cross section and a small flow velocity, and the perforated plate strainer 22 is provided inside the middle wall of the furnace. 21 is installed, and the orifice 20 is provided in the evaporation pipe immediately above, which is the flow immediately thereafter. The function of this structure is summarized, but its features can be summarized in the following three points.

(1) In the lower furnace below the intermediate wall 21 of the peripheral wall of the furnace, the reduction of the _static pressure loss (ΔP _static ) is predominant even if there is a portion with a high heat absorption amount Q even without the orifice 20. As a result, the total pressure loss (ΔP _total ) decreases, and the flow rate of the portion where the heat absorption amount Q is high naturally increases, so-called self-adjustment capability is provided.

(2) On the other hand, the upper furnace absorbs heat.
Evaporation tubes with high quantity Q have friction loss (ΔP _fric) Dominates
The total pressure loss (ΔP_total) Increases and the flow rate is
The temperature difference ΔT is gradually decreasing and increasing.
A fis 20 is provided to make the flow corresponding to the heat absorption distribution of the upper furnace.
Control the amount of enthalpy level of the furnace outlet fluid.
Uniformity becomes possible.

(3) In the middle part of the furnace where scale is apt to occur, the middle part of the furnace peripheral wall 21 serving as a buffer,
Furthermore, by providing the perforated plate strainer 22 inside,
It can be scale-free.

The present invention has been specifically described above based on the illustrated embodiments, but the present invention is not limited to these embodiments, and within the scope of the present invention as set forth in the claims, the specific structure thereof will be described. It goes without saying that various changes may be made.
For example, in the above-described embodiment, the furnace peripheral wall intermediate header 21 with the perforated plate strainer 22 is provided upstream of the orifice 20, but this is not always necessary.

[0044]

As described above, while the conventional method of installing an orifice at the entrance of a furnace may not be sufficient for the purpose of installation, according to the present invention, when partial load is applied. If the orifice is installed in the middle of the furnace peripheral wall tube where the fluid in the furnace peripheral wall evaporation tube becomes a two-phase flow, the lower furnace is self-adjusting by adjusting the flow rate of the can water according to the heat load distribution in the furnace wall surface. According to the capacity, the distribution of the heat absorption amount Q should be adjusted, and it should be installed downstream of the middle wall of the furnace peripheral wall where the flow rate adjustment is really needed, that is, in the upper furnace. hand,
It is possible to make the enthalpy level of the fluid at the furnace outlet uniform.

By providing a furnace peripheral wall intermediate pipe upstream of the orifice, secondary scale troubles caused by installing the orifice in such an intermediate portion can be prevented. Therefore, the degree of superheat of the furnace peripheral wall evaporation pipe can be prevented. This has the effect of preventing the consumption of the life of the pressure-resistant part of the furnace due to the occurrence of temperature imbalance due to the rise in temperature, and eventually the hindrance to the operation of the boiler due to damage.

[Brief description of drawings]

FIG. 1 is a system diagram of a supercritical pressure transformer once-through boiler according to an embodiment of the present invention.

FIG. 2 is a structural explanatory view of a furnace peripheral wall intermediate pipe header in a supercritical pressure variable pressure once-through boiler according to an embodiment of the present invention.

FIG. 3 is an enlarged cross-sectional view taken along the line AA of FIG.

FIG. 4 is a perspective view showing a furnace peripheral wall intermediate pipe breaker.

[Fig. 5] Water / steam enthalpy / pressure chart

FIG. 6 is a flow rate distribution characteristic diagram according to load changes.

FIG. 7 is an explanatory view showing a state of pressure loss in the lower furnace region of the supercritical pressure variable pressure once-through boiler.

FIG. 8 is an explanatory diagram showing a state of pressure loss in the upper furnace region of the supercritical pressure variable pressure once-through boiler.

FIG. 9 is a system diagram of a conventional supercritical pressure transformer once-through boiler.

[Explanation of symbols]

 1 Furnace inlet connecting pipe 2 Circumferential wall evaporating pipe 3 Furnace peripheral wall evaporating pipe outlet 4 Furnace peripheral wall evaporating pipe inlet pipe bringing 5 Furnace peripheral wall evaporating pipe outlet pipe bringing 6 Furnace outlet connecting pipe 7 Steam water separator 8 Drain discharge pipe 9 Superheater 10 Drain Level control valve 11 Circulation pump 12 Rear flue 13 Superheater inlet connecting pipe 14 Furnace 15 Upper furnace peripheral wall evaporating pipe 16 Lower furnace peripheral wall evaporating pipe 17 Furnace distribution piping 18 Furnace inlet distribution piping 20 Orifice 21 Intermediate furnace peripheral pipe drawing 22 Porous Board strainer

Claims (3)

[Claims] 1. A combustion facility having a furnace whose peripheral wall is constituted by a water-cooled evaporation pipe, and having a burner for injecting and burning fuel and combustion air into the furnace, and a combustion facility having an air ejection port,
In the supercritical pressure variable pressure once-through boiler, in which the combustion gas generated in the furnace is absorbed by the peripheral wall of the furnace and flows from the upper part of the furnace toward the rear flue side, the fluid in the evaporative tube of the peripheral wall of the furnace becomes a two-phase flow when partially loaded. A supercritical pressure transformer once-through boiler equipped with an orifice in the middle of the furnace wall that adjusts the flow rate of canned water according to the heat load distribution in the furnace wall. 2. A single or a plurality of furnace peripheral wall intermediate pipe headers are provided in the middle portion of the furnace peripheral wall pipes, and the orifice is installed immediately above (directly after) the outlet. 1. A supercritical pressure transformer once-through boiler according to 1. 3. A perforated plate strainer having a plurality of holes each having a diameter smaller than the hole diameter of the orifice is provided inside the single or a plurality of furnace peripheral wall intermediate pipe headers. Supercritical pressure transformer once-through boiler.