JPH029242B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a waste heat recovery boiler that does not cause so-called water hammer when starting up the boiler and can easily control water supply.

With recent changes in electricity demand, there is a growing trend to adopt gas turbines for peak loads.The heat of the high-temperature gas that provides kinetic energy to the gas turbine is recovered in a waste heat boiler, and further Combined power generation, in which steam generated by a heat boiler drives a steam turbine to generate electricity, is being implemented to save energy.

Figure 1 shows a waste heat recovery boiler (hereinafter simply referred to as "boiler").
The following is an outline of the In the figure, reference numeral 1 denotes a gas turbine, in which high-temperature combustion gas generated by air A and fuel F operates the gas turbine 1 to generate electricity, and then is supplied as waste gas to a boiler 2, to a superheater 3 and an evaporator. 4 and the economizer 5, and then discharged to the outside of the system. On the other hand, the generated steam flows into the superheater 3 from the boiler drum 6, is superheated to a predetermined temperature, and is then supplied to the steam turbine 7 to generate the second power generation, and the used steam is returned to water in the condenser 8. After that, it is supplied to the boiler again as feed water W.

Although the boiler with the above configuration can effectively utilize the generated heat and save energy, it has the following problems.

That is, gas turbines are used for peak loads because they have very good load followability, but as a result, gas turbines are started and stopped many times and often undergo rapid load fluctuations. The waste heat recovery boiler also starts and stops in response to this load change, but when the boiler stops or when the load suddenly decreases, part of the water supplied in the economizer evaporates, causing what is called water hammer when the boiler starts. will occur. The state in which steam is generated within the economizer will be explained with reference to FIG.

Normally, the water supply temperature at the outlet of the economizer is below the saturation temperature (curve A indicates the saturation temperature curve), and for example, the pressure and temperature conditions are operated along curve B. Now pressure the boiler
Suppose that a device that was operating at P ₂ is reduced to pressure P ₁ . In this case, if the pressure drop is gradual, the temperature of the heated water will also decrease T ₂ in response to the pressure drop.
Since the water gradually descends along line B from T1 to _T1 , the water supply never reaches a saturation temperature or higher. On the other hand, if the pressure drop is rapid, the temperature drop of the feed water cannot correspond to the pressure drop, and the pressure drops to P ₁ when the temperature is close to T ₂ .
It will descend to. For this reason, when the feed water temperature is between T ₂ and T' ₁ at pressure P ₁ , the feed water is at or above the saturation temperature, and part of the feed water evaporates and flows through the energy saver, and when the operation is stopped, it stagnates. This change in state occurs more drastically when the boiler operation is abruptly stopped than in the above-mentioned case where the boiler pressure decreases.

In addition to the reasons explained above, a considerable amount of heat remains inside the waste gas duct immediately after the boiler is stopped, and the feed water accumulated in the economizer absorbs this residual heat, causing the temperature to rise and steam to form. promote the occurrence of

If the boiler is restarted with residual steam generated due to these reasons, water hammer may occur due to fluctuations in the water flow in the economizer, resulting in damage to the pipe body due to pipe vibration, or the amount of water supplied to the boiler drum may be reduced. It becomes unstable. Particularly when the feedwater flow is descending, the descending feedwater collides with the rising steam, resulting in severe water hammer.

For this reason, the inventors constructed a single heat transfer panel by connecting the upper and lower ends of the straight pipes with headers, and connected only the upper headers of the plurality of heat transfer panels with a common header to save money. We provided a one-piece charcoal pot. In this type of energy saver, the water supply only ascends through the straight pipes of each panel, so even if steam is generated in the pipes, water hammer hardly occurs, but there are the following problems. That is, since the feed water constantly ascends through each panel while exchanging heat with the endothermic waste gas, a flow section is required that always descends to the next panel, and there is an opportunity for steam to accumulate in the upper headers of the panels.

An object of the present invention is to provide a waste heat recovery boiler that eliminates the above-mentioned problems, prevents water hammer due to steam remaining in the pipes, and allows easy control of water supply during boiler operation. .

In short, this invention connects the upper and lower ends of a plurality of heat transfer tubes placed inside the waste gas duct with headers to form one panel, and connects the plurality of panels with downcomers placed outside the waste gas duct. By doing so, an integrated energy saver is constructed, allowing the feed water inside the energy saver to flow through, increasing thermal efficiency and facilitating water supply control, and by locating the feed water descending section outside the duct, heat reception from waste gas is prevented. This structure is designed to improve the downward movement of water supply and prevent water hammer.

Embodiments of the present invention will be described below with reference to the drawings.

In FIG. 3, an arrow 10 indicates an economizer placed within the gas duct 11. Reference numeral 10a is a carbon saver 10
This figure shows the heat exchanger tube panels that make up the heat exchanger tube panel. This panel consists of a plurality of straight pipes 30 arranged inside the gas duct 11, and an upper header 12 and a lower header 13 that connect both ends of the straight pipes 30 outside the gas duct, and the plurality of panels formed in this way are arranged in parallel. position. Among these panels, the upper header 12 of the panel located on the upstream side of the water supply flow and the lower header 13 of the downstream panel adjacent to this panel are connected to the downcomer pipe 3.
1 to form an integrated energy saver 10 as a whole. Note that the downcomer pipe 31 is disposed outside the gas duct 11 and is configured so as not to absorb heat from the waste gas. Reference numeral 16 is a common header, and the upper header 12 of each panel is a control valve 1.
It is connected to this upper header 16 by a conduit 15 having 4. Next, 20 is a boiler drum, and the water supply outlet of the economizer 10 is connected to an economizer cyclone 21 in the boiler drum 20 through a pipe 19. 27 is a downcomer pipe connected to the boiler drum 20, and a recirculation pipe 26 having a recirculation flow rate control valve 25 is connected to this downcomer pipe 27, and the outlet side of the recirculation pipe 26 is connected to the downcomer pipe 27. It is connected to a water supply pipe line 23 that supplies water to the economizer.
22 is a valve that controls the water supply flow rate, and 24 is a water supply pump.

Reference numeral 28 denotes a control box for storing memory and emitting command signals, which is connected in circuit to the temperature detectors 29 provided in each of the upper headers 12, and also in circuit with the control valves 14, 22, 25 and the control valve 40 provided in the conduit 19. connection and operate these control valves.

In the above device, when the boiler is operating, the valve 14
Water supply W is supplied to the economizer with the valves (generally referred to as valves located at the top of each upper header) fully closed. As a result, the feed water W flowing into the economizer rises through the straight pipe 30, then descends through the descending pipe 31, repeats this upward and downward movement, reaches the outlet of the economizer, and then passes through the pipe line 19 to the boiler drum 20. Inflow. In this case, heat exchange with the waste gas G is performed only in the straight pipe 30 where the feed water rises, and the temperature does not rise in the downcomer pipe 31, so no steam is generated in the downcomer pipe 31.

When the boiler is shut down, steam is generated in the economizer panel due to the drop in pressure inside the drum and the radiant heat from the gas in the duct and the duct wall.
Since there is no water flow inside the economizer, the generated steam remains at the top of each panel, and the temperature in this area is higher than the saturated steam temperature corresponding to the drum internal pressure, so the temperature sensor 29 detects Upon detection, the required valve 14 is opened according to a command from the control box 28, and steam is released to the drum via the common header 16 and valve 40, thereby preventing water hammer at the time of startup. In this case, the valve 25 of the recirculation pipe 26 is also opened at the same time to supply makeup water to the economizer 10.

Further, when a recirculation pump 32 is provided in the pipe line 26, boiler water is supplied from the drum 20 to the outlet pipe line of the water feed pump 24 upon startup, thereby making it possible to hasten the rise in the temperature of the feed water by the energy saver.

By implementing the present invention, steam in the economizer can be removed during stoppage, and water hammer can be prevented when starting up.

[Brief explanation of drawings]

Figure 1 is a system diagram of a conventional waste heat recovery boiler, Figure 2 is a system diagram of a conventional waste heat recovery boiler.
The figure is a diagram showing the relationship between pressure and saturated steam temperature, and FIG. 3 is a system diagram of the boiler according to the present invention. 10... Economizer, 10a... Panel, 11...
Waste gas duct, 12... Upper header, 13... Lower header, 14... Control valve, 16... Common header, 20... Boiler drum, 22... Water supply control valve, 25... Recirculation flow rate control valve, 26 ... Recirculation pipe line, 27 ... Downcomer pipe, 28 ... Control box, 29 ...
...Temperature detector.

Claims (1)

[Claims] 1. In a system in which straight pipes arranged in a waste gas duct are connected by an upper header and a lower header to form a panel, and a plurality of these panels constitute an economizer, these panels are interconnected. placed parallel to
and the upper header of the panel on the upstream side of the water supply flow;
An economizer is constructed by connecting this panel to the lower header of the downstream panel adjacent to it through a downcomer pipe placed outside the waste gas duct, and the upper header of each panel is connected to the common header through a conduit with a control valve. A waste heat recovery boiler for preventing water hammer, characterized in that each of these control valves is circuit-connected to a control box that emits memory and command signals. 2. A patent claim characterized in that a downcomer pipe connected to a boiler drum and a pipe line for supplying water to an economizer are connected by a recirculation pipe line having a control valve, and this control valve is connected in a circuit to a control box. A waste heat recovery boiler that prevents water hammer as described in item 1. 3. A waste heat recovery boiler for preventing water hammer according to claim 1 or 2, characterized in that a temperature sensor is provided in the upper header, and this temperature sensor is circuit-connected to a control box.