JPS6333601B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to once-through boilers, in particular to water-cooled wall tube systems.

BACKGROUND OF THE INVENTION Generally, in a boiler, the water-cooled walls of the furnace are subjected to a high heat load, but the distribution of the heat load to the water-cooled wall tubes is not uniform and changes depending on the operating conditions of the boiler. It is important to provide a highly reliable furnace water-cooled wall pipe system under these conditions, and in this design, it is a requirement to stably secure a flow rate commensurate with the heat load and heat absorption. Orifice devices are installed at the distribution piping and water cooling wall pipe inlet.

Therefore, a conventional once-through boiler equipped with such an orifice device will be described.

FIG. 1 shows an example of a conventional water-cooled wall pipe system, in which the water supply is supplied via a economizer outlet downcomer pipe 1 to a water diversion device 2, i.e., a water bulb or a distribution pipe stopper, and from this water diversion device. Distribution pipe 4-1, 4-2, 4
-3, each water cooling wall inlet header 5-1, 5-2,
It flows into 5-3. The water-cooled pipes 7-1 and 7-2 coming out of the headers 5-1 and 5-2 are a system consisting of water-cooled wall pipes with high flow stability that are classified according to heat load and heat absorption conditions. The system is the water diversion device 2
The flow rate is distributed by orifices 3 provided at the entrances of the distribution pipes 4-1 and 4-2. The system of the water-cooled wall 7-3 coming out from the header 5-3 is a system composed of water-cooled wall pipes with low flow stability. An orifice 6 provided at the inlet of the water-cooled wall tube 7-3 in the stopper 5-3 distributes the flow rate in each water-cooled tube. The fluid flowing through each water-cooled wall pipe passes from the outlet header 8-1, 8-2, 8-3 to the outlet connecting pipe 9-1, 9-2, 9-3 to the delivery pipe 10.
through to a convection heat transfer surface or water separator.

However, in the operation of a once-through boiler, the flow rate passing through the water-cooled wall tube decreases in proportion to the boiler load, and the flow rate at startup and low load decreases to about 1/4 of the maximum flow rate. In such an operating region where a small amount of fluid passes through the water-cooled wall tube, there may be a water-cooled wall tube with low flow stability depending on internal fluid conditions and external heating conditions. In order to prevent such a decrease in the stability of the fluid flow inside the water-cooled wall tube, improve the flow characteristics of the fluid inside the tube, and increase the flow rate, it is necessary to increase the orifice effect in all aspects.

Problems to be Solved by the Invention However, if the pressure loss of the water-cooled wall tube 7-3 is large or if the diameter of the water-cooled wall tube 7-3 is small, the effect of the water-cooled wall tube inlet orifice cannot be increased. Furthermore, if the orifice 6 is made smaller in diameter, the problem of clogging is likely to occur due to foreign matter adhering to the water supply. In addition, in order to secure the necessary flow rate for systems with unstable flow, it is necessary to restrict the distribution pipe orifices 3 of stable systems 7-1 and 7-2. This will cause unnecessary pressure loss to the furnace water control pipe system except at extremely low loads where the effect is required, and it will be necessary to increase the discharge pressure of the water supply pump (not shown) and the design pressure upstream of orifices 3 and 6. This results in an increase in operating power and equipment costs.

Means for Solving the Problems In order to solve these conventional problems, the present invention provides a once-through boiler in which a water-cooled wall pipe system is divided into a system with high flow stability and a system with low flow stability at low loads. , an orifice disposed at the entrance of each distribution pipe of the water-cooled wall pipe system with high flow stability, a water distribution device that supplies water through this orifice, and a first inlet communication pipe on the upstream side of this water distribution device. a variable orifice disposed, an orifice disposed upstream of the variable orifice at the water control wall inlet header of the water-cooled wall pipe system with low flow stability, and a second inlet for supplying water through the orifice; It is equipped with a connecting pipe.

Effect: According to this method, the variable orifice provided in the first inlet connecting pipe of the water-cooled wall pipe system with high flow stability is narrowed, so that it is necessary for the water-cooled wall pipe system with low flow stability at extremely low loads. Since a suitable flow rate can be secured, it is possible to improve flow stability.

Embodiment An embodiment of the once-through boiler according to the present invention will be described below with reference to FIG.

Figure 2 shows a water-cooled wall pipe system, where the water supply passes through the economizer outlet downcomer pipe 1, and at the branch point A, the first and second
The flow is divided into inlet communication pipes 11-1 and 11-2. A system with high flow stability divided by heat load and heat absorption conditions runs from the first inlet connecting pipe 11-1 through a variable orifice 12 placed in the middle of this connecting pipe, and then reaches the water diversion device 2. Similar to the system, the flow rate is distributed by the orifice 3 installed there,
Distribution piping 4-1, 4-2, water cooling wall pipe system 7-1, 7
-2, it communicates with the water-cooled wall outlet header 8-1, 8-2, and the outlet connecting pipe 9-1, 9-2.

On the other hand, the system with low flow stability runs from the inlet connecting pipe 11-2 to the water-cooled wall inlet header 5-3,
After receiving the flow rate distribution in each water-cooled pipe by the orifice 6 provided there, the water-cooled wall pipe system 7-
3. Water cooling pipe outlet header 8-3 and outlet connecting pipe 9
-It is familiar with 3. And exit connecting pipe 9-1,
The fluid passing through 9-2 and 9-3 flows through a convection heat transfer surface or a steam/water separator via a delivery pipe 10.

In this case, the water-cooled wall pipe system 7-
Regarding the level of flow stability of each of 1 to 7-3,
It differs depending on the resistance combustion of the water-cooled wall tube, which is determined by the length of the tube, the number of curved parts, the tube diameter, the difference in water head, etc., and the heated state, which is determined by the amount of heat absorption, the heat absorption pattern, etc.

In addition, these conditions are not uniform for the water-cooled wall tubes 7-1 to 7-3, and due to the arrangement of the furnace wall, for example, it goes without saying that water-cooled wall tubes that constitute the furnace surface directly exposed to the flame from the burner On the other hand, the water-cooled wall tubes that make up the area around the burner (not shown) absorb less heat, and their shape has many curved parts, so the resistance is large and the steam (water) in the water-cooled tubes absorbs less heat. is difficult to flow. In particular, the flow in the water-cooled wall tube at low loads is greatly influenced by natural circulation forces, and in systems with such a small amount of heat absorption, the flow stability becomes low.

Now, understanding the flow stability characteristics of the fluid in the water-cooled wall pipes as described above, the first inlet connecting pipe 11-
A variable orifice 12 is installed in 1 to divide the water cooling wall based on the amount of heat absorption, and the inlet distribution piping 4-1, 4
In order to distribute the flow rate to -2, an orifice 3 with a small pressure loss and preferably the smallest size is provided.

And water-cooled wall pipe system 7-3 with low flow stability.
Then, orifice 6 is installed at the water cooling wall pipe inlet for flow distribution.
is provided in the water-cooled wall inlet header 5-3, and a second inlet communication pipe 11-2 branched from the downcomer pipe 1 is connected to the header 5-3.

With the above configuration, when the once-through boiler is operated at extremely low loads, the variable orifice 12 is throttled to limit the amount of water supplied to the water-cooled wall pipe systems 7-1 and 7-2 on the downstream side, which have high flow stability. However, in order to improve stability by increasing the amount of water supplied to systems with low flow stability on the upstream side, the variable orifice should be fully throttled except at times of extremely low load to reduce pressure loss in the water cooling wall system. becomes.

That is, as shown in Fig. 3, in the general flow characteristics of the fluid in the tubes of heated tubes that are heated from the inside of the furnace, such as water-cooled wall tubes that constitute a boiler furnace including a once-through boiler, firstly, the water-cooled wall Inlet header 5-3
To explain the characteristics when the orifice 6 is not installed in the middle of the flow, in the state of the water-cooled wall pipe system 7-3 with low flow stability shown by the S line, as the flow rate increases, the amount of pressure loss is monotonous. (0 to point A superheated steam range).

Furthermore, as the flow rate increases, the steam flowing inside the pipe becomes a gas phase and a liquid phase (two-phase region between points A and B),
The amount of pressure loss decreases once.

As the flow rate continues to increase, water becomes liquid in the pipe (liquid phase region at points B to C), and the pressure loss increases monotonically again, a well-known characteristic known as the so-called "saddle-shaped characteristic." appears. Therefore, in the water-cooled wall pipe system 7-3 having such characteristics, three different types of pipe conditions can exist, and the flow state of steam (water) in the pipes is unstable, and the flow rate is There is a risk of overheating or burnout in the water-cooled wall tube 7-3 with a small amount of water. (Especially the state of 0 to A point).

Therefore, we improved this saddle shape characteristic by
An orifice 6 is installed in the middle of the water cooling wall inlet header 5-3.
In other words, it is the introduction of a resistor to the fluid within the pipe.

By installing this orifice 6, the flow (low stability) characteristics of the water-cooled wall pipe systems 7-1 and 7-2, which have high flow stability as shown by the S' line in the figure, can be improved.
As in the situation shown in FIG. That is, this means that the flow is stabilized, and a constant flow rate can be ensured for a certain pressure loss.

The flow characteristics can be further improved by installing the orifice 6 in the water cooling wall inlet header 5-3 as described above, but such measures alone are insufficient. Then, the pressure loss of the orifice 6 itself is added to the pressure loss of the water-cooled wall pipe 7-3, and as a result, the amount of pressure loss increases, so if the pressure loss (water head difference) is constant, the flow rate tends to decrease. .

In this case, in order to secure the required flow rate, it is necessary to use another water-cooled wall pipe system 7 that is connected in parallel and has a high flow stability.
It is sufficient to reduce the amount of water supplied to -1 and 7-2 and replenish the reduced amount of water to the water-cooled wall pipe system 7-3, which has low flow stability.

For this purpose, an orifice 3 is provided from the inlet connecting pipe 11-1 to each inlet distribution pipe 4-1, 4-2 in order to increase the pressure loss in the former system 7-1 and 7-2. In this case as well, a fixed orifice is usually used, so the pressure loss in the water-cooled wall pipe system 7-3 is still large in the entire operating load range, causing an increase in the power of the water supply pump as described above. It is also necessary to increase the design pressure on the side.

According to the present invention, the variable orifice 1
By using 2, these problems can be solved. That is, this variable orifice 12 is arranged in the middle of the inlet connecting pipe 11-1 to the water-cooled wall pipe systems 7-1 and 7-2, which have high stability, and stabilize the water-cooled wall pipe system 7-3, which has low stability. At extremely low loads when the performance is particularly low, the orifice effect is applied, that is, the variable orifice 12 is throttled to adjust the water supply flow path and allow a predetermined amount of flow to flow into the latter system 7-3.

By performing such an operation, the flow characteristics of the water-cooled wall pipe system 7-3, which has low flow stability, are improved by providing a restriction with the fixed orifice 6 at the system inlet, and the flow rate to the system is further improved with the variable orifice 12. To ensure stable flow rate by increasing
Flow stability at low loads can be easily improved, and an increase in pressure loss at high loads can also be prevented.

Effects of the invention As a result, by providing a restriction with a fixed orifice at the inlet of the water-cooled wall pipe, the flow characteristics of the water-cooled wall can be improved by
As shown by the S' line in the figure, increasing the flow rate reduces the effect of heat absorption on the flow and stabilizes the flow in the pipe. At the same time, by installing a variable orifice in a system with high flow stability and restricting it, the flow is stabilized. Since the flow rate of a stable system can be increased, the flow stability is increased, and together with the increased flow rate, overheating and damage to the pipes can be avoided and reliability is increased.

In addition, the pressure loss of the fixed throttle is minimized, and the variable orifice is throttled only at extremely low loads, so there is no increase in pressure loss in each water cooling wall pipe system under normal operating conditions, so the design pressure upstream of the orifice and the water pump discharge pressure Since it is not necessary to increase the amount of water and can be minimized, equipment costs can be reduced, and the power consumption of the water pump can also be minimized, making it possible to save on operating costs.

[Brief explanation of the drawing]

FIG. 1 is a water-cooled wall tube system diagram showing a conventional once-through boiler, and FIG. 2 is a water-cooled wall tube system diagram showing an example of a once-through boiler according to the present invention. FIG. 3 is a characteristic curve diagram showing the relationship between flow rate and pressure loss, which shows the improvement in stability of the water-cooled wall tube. 2... Water diversion device, 3, 6... Orifice, 4-
1, 4-2...Each distribution pipe, 5-1 to 5-3...Water-cooled wall inlet header, 7-1 to 7-3...Water-cooled wall pipe system, 11-1, 11-2...Each First and second inlet communication pipes, 12...variable orifice.

Claims (1)

[Claims] 1. In a once-through boiler in which a water-cooled wall pipe system is divided into a system with high flow stability and a system with low flow stability at low loads, an orifice disposed at each distribution pipe inlet of the water-cooled wall pipe system with high flow stability; A water diversion device that supplies water through this orifice, a variable orifice disposed in the first inlet communication pipe on the upstream side of this water diversion device, and the water cooling wall with low flow stability disposed on the upstream side of this variable orifice. A once-through boiler characterized by comprising an orifice disposed at the water-cooled wall inlet header of a pipe system, and a second inlet connecting pipe for supplying water through the orifice.