JPH08312903A - Once-through boiler device - Google Patents

Abstract

PURPOSE: To reduce the amount of feed water for a boiler by a method wherein constituting series of water walls are divided into two groups or more with respect to water wall tubes while a switching system for switching the fluid of some group of water wall tube outlet port to conduct whether into a steam separator or the water wall tube inlet port of another group is provided. CONSTITUTION: The water wall 5 of a boiler main body is divided into water walls 52, 53 while a water wall switching valve 59 is interposed i.n a pipeline 43, branched from a pipeline 42 connecting the outlet side of an economizer 4 and the inlet side of the water wall 52. The outlet side of the water wall switching valve 59 is connected to the entrance of a water wall inlet joining part 56 while the outlet side of the joining part 56 is connected to the inlet port of the water wall 53. Further, a pipeline 44, connected to the outlet side of the water wall 52, is divided into two pipes and one of the pipes is provided with a water wall switching valve 57 while the other of the same is provided with another water wall switching valve 58. The outlet side of the water wall switching valve 57 is connected to one of the inlet port of the steam separator inlet port joining part 55 while the outlet side of the water wall switching valve 58 is connected to the other inlet port of the water wall inlet port joining part 56. The outlet side of the joining part 55 is connected to the steam separator 6 to separate moisture from generated steam.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a once-through boiler device, and more particularly to a water wall system configuration that is easy to operate and maintain and economical.

[0002]

2. Description of the Related Art FIG. 2 shows a water wall system of a once-through boiler device according to the prior art. After the water supply is boosted by the boiler water supply pump 1, the boiler water supply flow control valve 2 and the boiler (drain) are sequentially installed.
It is heated through the recirculation / merging unit 3, the economizer 4, and the water wall 5, and then sent to the steam separator 6 for steam separation. Of the separated matter, the drain is stored in the drain tank 8 and then pressurized by the drain recirculation pump 9 and then passed through the drain recirculation flow control valve 10 to recycle the boiler provided at the inlet of the economizer 4. It is returned to the merging unit 3.

Reference numerals 12 and 17 in FIG. 2 respectively show a level control system for the drain tank and a control system for the boiler feed water amount (coal feed water supply amount), and details thereof are shown in FIGS. 3 and 4. ing. First, the control of the drain tank level by the control system 12 is usually performed by operating the drain recirculation flow control valve 10 with the function element 21 in proportion to the drain level detected by the drain tank level detector 11.
When the drain tank level still rises even if the function element 21 fully opens the drain recirculation flow control valve 10, the function element 22 operates the drain tank blow flow control valve 13 to blow the drain, Lower the drain tank level.

On the other hand, the control system 17 controls the amount of water supplied to the economizer, which is usually controlled by the boiler feedwater flow control valve 2 so that the amount of water supplied to the economizer detected by the water wall flow rate detector 15 matches the water supply command 18. It is performed by operating. However, water wall 5
In order to protect the water wall pipe, it is necessary to secure a flow rate (minimum water supply of the water wall) of about 30% of full load of the boiler. It has been converted to a water wall flow rate target value 30 that satisfies the minimum wall water supply requirement. Further, in order to prevent generation of steam (causing water hammer etc.) in the economizer 4, the water wall pressure detected by the water wall pressure detector 20 is passed through the function element 26 to output the temperature of the economizer outlet fluid temperature. A limit value 31 is created, and based on this and the economizer outlet fluid temperature detected by the detector 19, a steaming prevention signal 32 is obtained via a subtraction element 27 and a proportional integration element 28. This signal is a signal height selection element 2 when the fluid temperature at the economizer outlet exceeds the economizer outlet fluid temperature limit value 31.
It has a function of increasing the amount of water supply, thereby lowering the temperature of the fluid in the economizer.

The once-through boiler having such a structure is operated using a recirculation line (recirculation operation) when generating steam below the minimum water supply amount for the water wall, while steam exceeding the minimum water supply amount for the water wall is used. In the case of generating the above, the operation does not use the recirculation line (flow-through operation). And in the middle of them, Benson point (30% of full load in conventional technology)
There is a transition point called the degree.

[0006]

The once-through boiler apparatus according to the prior art shown in FIG. 2 has the following inconveniences.

A) The drain recirculation pump 9 is expensive, maintenance is troublesome, and if the steam is sucked in, the pump will be damaged (so-called cavitation will occur). Therefore, an appropriate water level is secured by the drain tank level control system 12. It is necessary to dispose the drain tank 8 in front, which is uneconomical.

B) Generally, it is desirable that the boiler apparatus can be operated stably even if the load is reduced to about 15% of the full load (below that, combustion becomes unstable if the fuel amount of the burner is reduced). Be done. However, in the once-through boiler device of the prior art, the Benson point is about 30% of the full load, and it is necessary to switch the control method of the steam pressure at that point. That is, the steam pressure basically depends on the evaporation amount, but during the recirculation operation, the water wall flow rate is kept constant under the restriction of the minimum water supply amount, so that the steam pressure control is performed by the fuel amount. However, during the once-through operation, the fluid at the inlet of the steam separator 6 is usually sufficiently dry steam,
The steam pressure control is performed by the amount of water supply (since the amount of fuel changes, only the temperature of steam changes and the amount of evaporation does not change). This is because when the steam pressure decreases, the evaporation amount increases as it is as long as the fluid at the inlet of the steam separator 6 is dry if the supply amount of water is increased.

Further, in the prior art, in addition to such inconvenience of "switching", as in the vicinity of the Benson point,
In a state where the fluid at the inlet of the steam separator 6 is not sufficiently dry steam, an increase in the amount of water supply decreases the fluid enthalpy at the inlet of the steam separator 6, so the amount of water supply should be reduced in response to the decrease in steam pressure. If it increases, the fluid at the inlet of the steam / water separator 6 becomes in a steam / water mixed state, and the amount of evaporation decreases rather, which may lead to a so-called "inverse response of steam pressure control".

C) Since the drain of the steam separator 6 which is generally saturated water is recirculated to the inlet of the economizer 4, the control system 17 requires the steaming prevention circuit described above. Further, when the steaming prevention circuit operates, the start-up time is extended, the drain discharged from the drain blow pipe 14 increases, and the heat loss increases.

Of course, the prior art has a reason as shown in FIG.
The above-mentioned type of once-through boiler device is provided, and its background must be mentioned. That is why the protection of the water wall 5 is the greatest reason. Since the water wall 5 is located in the place where the heat load is highest in the boiler, the heat transfer coefficient between the heat transfer tube and the internal fluid must be kept sufficiently large to prevent the heat transfer tube from burning. However, if the fluid in the heat transfer tube is water or the nucleate boiling state containing a small amount of bubbles, the heat transfer coefficient is large, so there is no problem. In some cases, the heat transfer coefficient may be significantly reduced, which may be dangerous.
Generally, the heat transfer coefficient increases depending on the mass flow rate of the internal fluid (approximately proportional to the 0.8th power), so during boiler operation,
Since the heat transfer tubes are not burned even in the film boiling state, it is of utmost importance to secure the mass flow rate of the internal fluid for each heat transfer tube, and as mentioned above, regardless of the evaporation amount of the boiler, when the boiler is fully loaded. We have secured a flow rate of about 30% (the minimum amount of water supply to the water wall). This is the background of the above inconvenience.

As a method of solving the above problems b) and c) by using a boiler recirculation pump, there is disclosed a "through-flow boiler device" (Japanese Patent Publication No. 4528/1992).
2) has been proposed.

An object of the present invention is to make it possible to reduce the boiler water supply amount to a low value while maintaining the water wall minimum water supply amount without using a boiler recirculation pump.

[0014]

The water wall 5 of the boiler is usually constructed by arranging water wall pipes of the order of several hundreds in parallel, and the water supply to this water wall is controlled based on the water supply command. There is. In the present invention, in order to achieve the above object, the water wall pipes constituting the water wall are divided into a plurality of groups, and the fluid at the water wall pipe outlet of a certain group is allowed to flow into the steam separator. A system for switching whether to flow into the water wall pipe inlet of the group is provided, and at the inlet of the "water wall pipe of the other group", the fluid from the outlet of the "water wall pipe of the certain group" A system for switching the fluid from the outlet of the container 4 is provided. In short, the present invention achieves the object by dividing the water wall pipes into groups, connecting a plurality of water wall pipe groups in series in a small evaporation amount region, and connecting each water wall pipe group in parallel in a large evaporation amount region. To do. Whether the water wall tube groups are connected in series or in parallel is controlled by providing a control unit that operates by using the water supply command as an input.

[0015]

If the water wall tubes are divided into N groups and connected in series, the total water supply of the entire water wall will be 1 / th compared to the conventional parallel connection even if the mass flow rate per heat transfer tube is the same. N. As described above, the protection of the water wall tube of the boiler is performed by ensuring the mass flow rate of the passing fluid for each heat transfer tube. At this time, if it is possible to protect the water wall pipe of the boiler by securing the mass flow rate of the air-water mixture without depending on the content of bubbles in the internal fluid, the water wall pipes can be connected in series in N groups. By connecting, the water supply for water wall protection can be reduced to 1 / N compared to the conventional one. This means that the water supply at Benson Point will be reduced to 1 / N. Therefore, the Benson point can be set lower than the operation load zone of the boiler, and the normal operation is always the once-through operation, so that the drain blow from the steam separator is eliminated.

[0016]

FIG. 1 shows an embodiment of the present invention. This is an example in which the present invention is applied to the boiler of the embodiment of the prior art (FIG. 2) with N = 2, and the Benson point is set to about 15% of the full load. In the boiler main body, the water wall 5 is divided into a water wall A52 and a water wall B53, and a drain recirculation merging section 3, a drain tank 8, a drain recirculation pump 9, a drain recirculation flow control valve 10, a drain tank level detector 11, Drain tank level control system 1
2, drain tank blow flow control valve 13, drain blow piping 14, and boiler feed water amount (coal feed water supply amount) control system 17 for preventing steam economizer steaming, economizer outlet fluid temperature detector 19, water The wall pressure detector 20 is not provided, and the water wall switching valves A57, B58, C59 are provided instead. Instead of the drain blow pipe 14, a drain blow line 63 for directly blowing from the drain tank 6 is provided. The water wall switching valves A57 and B58 constitute water wall pipe outlet switching means, and the water wall switching valves B58 and C59 constitute water wall pipe inlet switching means.

That is, a pipe 43 that branches to a pipe 42 that connects the outlet side of the economizer 4 and the inlet side of the water wall A52 is provided.
3, a water wall switching valve C59 is connected, and one outlet of the water wall B inlet merging portion 56 is connected to the outlet side of the water wall switching valve C59 via a pipe 48 to connect the water wall B inlet merging portion 56 outlet side. Water wall B
The inlet 53 is connected by a pipe 49, the pipe 44 connected to the outlet side of the water wall A is branched into two, and the water wall switching valve A57 is connected to one of the branches and the water wall switching valve B58 is connected to the other,
The outlet of the water wall switching valve A57 is connected to one inlet of the steam / water separator inlet merging portion 55 via the pipe 45, and the water wall switching valve B is connected.
The outlet side of 58 is connected to the other inlet of the water wall B inlet merging portion 56 via a pipe 47, and the outlet side of the water wall B53 and the other inlet of the steam separator inlet merging portion 55 are connected via a pipe 50. The outlet side of the steam / water separator inlet merging portion 55 and the steam / water separator 6 are connected via a pipe 46.

As the control system, a water wall switching control system 54 for controlling the openings of the water wall switching valve A57, the water wall switching valve B58, and the water wall switching valve C59 by using the water supply command 18 as an input, and the water supply command 18 as well. A minimum value limiting element 60 that outputs the water wall flow rate target value 64 as an input, and a signal subtraction element 61 that outputs the deviation between the water wall flow rate target value 64 and the detection value of the flow meter 15,
A proportional and integral element 62, which receives the output of the signal subtraction element 61 as an input and PI-controls the opening of the boiler feedwater flow control valve 2, is provided.

The above structure simplifies the feed water flow rate control, and obtains the water wall flow rate target value 64 from the minimum value limit element 60 which secures a water wall protection flow rate that is about half that of the conventional minimum value limit element 23. The boiler feedwater flow control valve 2 is operated so that the detection value of the water wall flow rate detector 15 matches the target value. The water wall switching valves A, B, C are operated by the water wall switching control system 54 based on the water supply command 18. Specifically, when the load is increased, the valve 5 is operated until the water supply command reaches about 35% of the full load.
8 is opened, valves 57 and 59 are closed, and when the water supply command reaches about 35% of full load, valve 58 is closed and valves 57 and 59 are opened. On the contrary, when the load is decreased, the valve 58 is closed and the valves 57 and 59 are opened until the water supply command becomes about 30% of the full load, and the valve 58 is opened when the water supply command drops to about 30% of the full load. And valve 5
Close 7,59.

When the water wall A and the water wall B are connected in parallel, and the water supply amount corresponding to a load of 30% is the minimum required flow rate, the water supply amount corresponding to a load of 15% is given to each of the water walls A and B. Minimum required flow rate. When the water wall A and the water wall B are connected in series at a load of about 30%, the water supply flow rate corresponding to the load of 30%, which had been separated by 15% into the water wall A and the water wall B until then, was Since the water supply having a load of 30% flows through both the water wall B and the water wall B, the minimum required flow rate is doubled. The feed water flow rate can be reduced to a flow rate corresponding to a load of 15% which is the minimum required flow rate of the water wall A and the water wall B, so that stable operation can be achieved even if the boiler load is reduced to 15%.

A dead band of about 5% is provided here to prevent frequent switching when the water supply command fluctuates.
In this example, the minimum load required for the boiler (about 1 at full load)
(5%) to full load operation is possible, and drainage from the steam separator does not occur except when the boiler is started. The start-up is a limited time during the operation time of the boiler, and the heat loss does not become a problem even if the drain blow is performed only at the start-up.

[0022]

【The invention's effect】

a) The boiler recirculation pump, which is expensive and requires maintenance, is not required, and at the same time, the drain tank 8 and the drain tank level control system 12 are not required, which is economical.

B) In normal operation of the boiler device, it is not necessary to switch the control method of steam pressure. Therefore, the control device is simplified, and the so-called "reverse response of steam pressure control" does not occur.

C) No steaming prevention circuit is required in the economizer 4, since saturated water is not recirculated.

[Brief description of drawings]

FIG. 1 is an example of the present invention.

FIG. 2 is an example of a conventional technique.

FIG. 3 is a diagram showing an example of a control flow of a conventional drain tank level control system.

FIG. 4 is a diagram showing an example of a control flow of a conventional boiler feedwater control system.

[Explanation of symbols]

1 Boiler feed water pump 2 Boiler feed water flow control valve 3 Boiler (drain) recirculation confluence section 4 Coal saver 5 Water wall 6 Steam separator 7 Generated steam 8 Drain tank 9 Drain recirculation pump 10 Drain recirculation flow control valve 11 Drain tank level detector 12 Drain tank level control system 13 Drain tank blow flow control valve 14 Drain blow piping 15 Water wall flow rate detector 17 Boiler water supply (coal supply amount) control system 18 Water supply command 19 Coal outlet liquid Temperature detector 20 Water wall pressure detector 21 Function element 22 Function element 23 Minimum value limiting element 24 Subtraction element 25 Proportional integration element 26 Function element 27 Subtraction element 28 Proportional integration element 29 Signal height selection element 30 Water wall flow rate target value Section 31 Charcoal outlet fluid temperature limit value 32 Steaming prevention signal 40 to 50 Piping 54 Water wall switching control system 55 Steam / water separator Mouth merging part 56 Water wall B inlet merging part 57 Water wall switching valve A 58 Water wall switching valve B 59 Water wall switching valve C 60 Minimum value limiting element 61 Signal subtraction element 62 Proportional integration element 63 Drain blow line 64 Water wall flow rate target value

Claims (3)

[Claims] 1. A once-through boiler apparatus comprising a water wall and a steam separator arranged downstream of the water wall, wherein the system constituting the water wall is divided into two or more groups for water wall pipes. The once-through boiler device is characterized in that a system is provided for switching whether the fluid at the water wall tube outlet of (1) flows into the steam separator or the water wall tube inlet of another group. 2. A water wall disposed downstream of the economizer and a steam separator disposed downstream of the water wall, wherein the amount of water supplied to the boiler is based on a water supply command. In a controlled once-through boiler device, the system constituting the water wall is divided into a plurality of groups for water wall pipes, and the fluid at the outlet of the water wall pipes of a certain group is allowed to flow into the steam separator or the water of another group. Water wall pipe outlet switching means for switching whether to flow into the wall pipe inlet is provided, and the fluid leaving the water wall pipe of the certain group is flowed into the water wall pipes of the other group, or the economizer is used. A once-through boiler device, characterized in that a water wall pipe inlet switching means for switching whether to inflow the fluid that has flowed out is provided. 3. The once-through boiler apparatus according to claim 2, further comprising control means for controlling the operations of the water wall tube outlet switching means and the water wall tube inlet switching means by using a water supply command as an input.