JPH01273901A - Boiler - Google Patents

Abstract

PURPOSE:To enable execution of operation through natural circulation or weak forced circulation, by a method wherein a water tube branched at the bending rise part of a hair pin type water tube or in the middle of a water tube into at least two tubes which are joined together at a header once, and the number of water tubes at the outlet of the header is increased over that at the outlet of the header. CONSTITUTION:After a heat transfer water tube running from an inlet header 8 is returned in a manner to be arranged only in one row, it is branched into two tubes to form water tubes 1a and 1b. In this constitution, a circulation ratio is 3:3, but a velocity at the inlet of the heat transfer water tube 1 is at least 0.4m.s, and forms a horizontally-mounted hair pin type water tube boiler which is free from dry-out.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an improved heat exchanger tube structure for a level hairpin type water tube boiler used in a waste heat boiler or an economide.

[Conventional technology]

The water tubes of a conventional level hairpin type water tube type waste heat boiler have a configuration as shown in FIG. 3 or 4, for example.

In this type of conventional boiler, a forced circulation pump (1) is installed in the downcomer pipe (9), and its capacity, head, required power, etc. are determined based on design conditions such as the amount of heat received by the boiler, and the configuration of the boiler. It is designed to minimize this by changing the

(7) is the exhaust gas inlet, (14) is the exhaust gas outlet, (8) is the inlet header, i+o) is the outlet header, (11) is the steam/water separation drum, f12) is the steam side connecting pipe, (l is the steam outlet It is.

Figure 4 shows double the number of rows of heat transfer water tubes in Figure 3, that is, the heat transfer water tubes (I
a), (lb).

However, in the case of Figure 4, the total number of (1a) and (Ib) is changed according to the change in the heat transfer area, and does not necessarily have to be an integral multiple of the number of heat transfer water tubes in Figure 8. It can be changed according to the flow velocity.

Needless to say, it is necessary to devise an arrangement of the heat transfer water tubes for this purpose.

[Problem to be solved by the invention]

Conventional waste heat boiler circulation pumps are required to be highly reliable in order to expect them to operate without failure at all times while the boiler is in operation.Moreover, they require constant power, so if possible, this circulation pump should be used. There is a need for a waste heat boiler that does not require the installation of a pump (15).

That is, if the circulation pump (15) breaks down and its performance deteriorates, there is a problem in that the boiler has no choice but to be shut down.

The reason why it is necessary to stop the boiler operation when the circulation pump 05) stops is because in Figures 3 and 4, when the circulation pump (Illi) breaks down or stops, the heat transfer water pipe fl This is because la)t(lb) is exposed to the risk of burnout.

If this circulation pump stops, the boiler will not be exposed to danger and it can be operated safely, then this circulation pump θ
It turns out that there is no need for Xun.

Alternatively, even if the circulation pump C15) is installed, since the circulation pump is always in operation as described above, it is desirable to minimize its capacity, lift, required power, etc.

This is accomplished by increasing the number of parallel water tubes to reduce flow rates and pressure losses.

In response to the above-mentioned needs, the present invention provides natural circulation or weak forced circulation in a conventional forced circulation boiler, without installing a forced circulation pump or only by installing a forced circulation pump with a significantly smaller capacity than before. The purpose is to provide a boiler that can be operated by circulation.

[Means to solve the problem]

The present invention provides a horizontal hairpin water tube boiler in which at least 2
Regarding a boiler constituted by hairpin-type water pipes branched into main parts, the hairpin-type water pipes are once assembled in a header, and the number of hairpin-type water pipes at the header outlet is greater than the number of water pipes at the header inlet. The present invention relates to hairpin type water tube boilers.

Is it better for the at least two-branched hairpin water pipe of the present invention to branch at the -stage from the inlet header (8), or at the second stage, or at the middle gate of the hairpin water pipe? The decision as to whether it is a good one is determined by estimating the flow pattern of the two-phase flow from the heat load on the boiler heat transfer surface, the arrangement of water pipes, the circulation ratio of the entire boiler, the inlet flow velocity, and even the steam dryness (quality) at each point of the water pipes. It is necessary to.

Furthermore, in order to change the heat load on the local heat transfer surface, the shape of the enlarged heat transfer surface must be changed, for example, if ring fins are provided in the water pipe, the pitch should be one or two per 1 nch. It is also necessary to take appropriate consideration.

Furthermore, in order to prevent water pipes from burning out, a certain level of two-phase flow velocity is required up to a certain level of steam dryness (quality), so the flow velocity is increased up to a certain number of rows of water pipes, and then If it becomes possible to reduce the flow velocity by increasing the number of pipes, the water pipes will be branched at that point.

There are the following forms of branching as described above.

Examples of these are shown in Figure 2 (a) = (b), (c
)It was shown to. FIG. 2(a) shows an example in which the hairpin water pipe branches at the rising part, and it is considered that it is not good to branch at the horizontal part. The reason for this is that there is a risk that the two-phase flow may not be uniformly distributed, and special measures must be taken to prevent this from occurring in the internal device.

Similarly, FIG. 2(b) shows an embodiment of the present invention in which a dedicated branch header (one header is provided).In this case, the ratio of the number of inlet pipes to the number of outlet pipes does not necessarily have to be an integral multiple. No. 2nd
When a header is provided as shown in Figures (b) and (c), it is not necessarily necessary to provide it on the riser pipe. Second
Figure (C) shows an embodiment in which the heat transfer water pipe is provided midway along the horizontal portion.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 shows a schematic sectional view of an embodiment of a hairpin type water tube boiler according to the present invention.

In general, in a horizontal hairpin water tube boiler, when heating gas enters from below, the first row of water tubes facing downward are exposed to the highest gas temperature and therefore the highest heat transfer surface heat load. It will be.

On the other hand, the water side of this part (inside the heat transfer water pipe) has just descended from the drum (11) through the downcomer pipe (9), so its temperature remains at the saturation temperature for the pressure in the drum (11). Alternatively, the temperature is subcooled from the saturation temperature by the amount of the downward position water head. Furthermore, the heat is actually subcooled by the amount of heat radiated, so even if it enters the heat transfer water pipe 10 from the header (8), it will not immediately evaporate and generate bubbles.

In such an environment, if the design of the heat transfer water pipe is incorrect, the steam bubbles generated a little further and the water will separate vertically, creating a laminar flow. The membrane disappears. If the heat transfer coefficient deteriorates significantly due to fold dryout, or if the heat load is high, the main flow is in a subcooled state at a temperature lower than the saturation temperature, but the wall surface transitions from nucleate boiling to film boiling. In the design of a horizontally installed hairpin water tube boiler, the factors that lead to burnout and dryout as mentioned above are caused by ), the pipe diameter of the heat transfer water tube, the placement relationship such as whether the heat transfer water tube (1) is horizontal, inclined, or vertical, the evaporation of water generated by heating the heat transfer water tube,
In other words, the water circulation ratio and water inlet flow velocity (circulation flow velocity) determined by the natural circulation force and forced circulation force generated by the generation of bubbles, and the heat transfer surface heat load such as the ignition of the heat transfer water pipe at the gas inlet. This is related to the distribution of water and, therefore, the distribution of steam dryness (quality) as water transforms into steam bubbles along the pipe.

According to the results of academic research, when the inner diameter of the water pipe is 30 fl, the heat load on the heat transfer surface is +oo, ooo kcal/m!
The critical inlet flow velocity that prevents the heat transfer water pipe from drying out at about 100 m is required to be at least about 0,000 BmlB〇And, as an example, considering a boiler heated with waste heat gas,
In order to enter the inlet conditions at a constant gas amount and gas temperature, and to ensure a constant amount of evaporation, a certain required heat transfer area is calculated.

In this case, the above water circulation calculation shows that in the horizontal hairpin water tube boiler shown in Figure 3, the water circulation force is insufficient and the water cannot be circulated.In other words, a water surface appears in the middle of this tube group, and the evaporation amount is actually less than υ. Not only would the heat transfer water tubes above the water surface be at risk of overheating and burnout, but they would also dry out, resulting in less evaporation and the boiler becoming unusable.

When similar calculations are performed for FIG. 4, the circulation ratio is 4.0, and water circulates, but the inlet flow velocity does not reach 0.27 m/B, and a sufficiently safe horizontal hairpin boiler is not constructed.

Therefore, in FIG. 1 according to the present invention, the above-mentioned drawbacks are eliminated and the water circulation conditions of the water tube group are kept within a safe range by changing the configuration of the boiler heat transfer water tubes. The water pipe +1) is folded back as only the - row, and then branched into two water pipes (Ia) and t(
lb) and the following, which results in a circulation ratio of 3.8, but the flow velocity at the inlet of the heat transfer water pipe fl) is 0.4 m
/B or above, it becomes a horizontal hairpin type water tube boiler that does not cause dryout.

Figures 2(a), (b), and (c) show examples of various branching forms of the heat transfer water tubes of the horizontal hairpin water tube boiler of the present invention; ) is a hairpin type heat transfer water pipe that branches at the rising part, (b) is a type with a dedicated branch header, and (c) is a type where a dedicated header is provided, but it does not necessarily flow into the riser pipe. This shows an example in which the heat transfer water tube is provided in the middle of the hairpin type heat transfer water tube without the need for a heat transfer tube.

〔Effect of the invention〕

The effects of the present invention are summarized as follows.

According to the present invention, firstly, for example, a conventional horizontal hairpin water tube waste heat boiler can be replaced with a natural circulation type without a forced circulation pump or with only a forced circulation pump of extremely small capacity instead of a forced circulation type. Second, by making a slight modification to the horizontal hairpin waste heat boiler 2 where a conventional forced circulation pump is installed, the forced circulation pump can be eliminated. This has the remarkable effect of eliminating the need to stop the boiler 2 even if the circulation pump breaks down or its performance deteriorates.

[Brief explanation of the drawing]

Fig. 1 is a schematic sectional view of one embodiment of the horizontal hairpin type water tube waste heat boiler of the present invention, Fig. 2 [a], (b), [c]
The following are examples showing various branching forms of the horizontal hairpin type water tube of the present invention, in which (a) is an example in which the hairpin type water tube branches at the rising part, and (b) is an example in which the hairpin type water tube is branched at the rising part. An example in which a branch header is provided at the rising part of a hot water pipe,
(c) shows an embodiment in which a branch header is provided in the middle of the horizontal part of a hairpin type water tube (01, la, It), a hairpin type heat transfer water tube 2, a folded branch point 3 of a hairpin type heat transfer water tube, Hairpin type heat transfer water tube fin 5, outer casing 7. Exhaust gas inlet 8, inlet header 9. Downpipe 10, ivy 11 to outlet, steam/water separation drum 13, steam outlet 14. Exhaust gas outlet 15, Forced circulation pump procedure amendment (method) August 12-11, 1932, Case indication 1988 Patent Application No. 105078 2, Name of the invention Point 3, Person making the amendment Related Patent Applicant 4, Agent 550 July 6, 1986 (Shipping mortar 6B, 7.26) 7
, In the 4th to 3rd lines from the bottom of page 11 of the statement of contents of the amendment, next to ``One embodiment'', ``Figures 3 and 4 show the water tube section of a conventional horizontal hairpin type water tube waste heat boiler. Insert "Configuration"

Claims (1)

[Scope of Claim] A horizontally placed hairpin water tube boiler comprising a hairpin water tube that branches into at least two at the rising part of the bend or in the middle of the water tube. 2. Hairpin type water pipes are once assembled in the header,
A boiler comprising hairpin type water tubes according to claim 1, wherein the number of hairpin type water tubes at the header outlet is greater than the number of hairpin type water tubes at the header inlet.