JPH0473501A - Exhaust heat recovery boiler of natural circulation type - Google Patents

Abstract

PURPOSE:To prevent the water level in the drum from falling right after starting a gas turbine and stabilize the automatic water level control in an exhaust heat recovery boiler of natural circulation type used for a gas turbine, etc., by providing the bottom face of the inlet to a cyclone separator at a position below the water level at starting. CONSTITUTION:The bottom face of the inlet to a cyclone separator 7 is installed lower than the water level 11 at starting. Accordingly, at the time of starting a gas turbine the water level is set at the starting water level 11, but right below the starting water level there is the low water level alarming water level 12, and, furthermore, since the low water level trip water level (not shown) is set, the starting water level can be said to be the limit of the low water level. With this arrangement by installing the bottom face of the inlet to the cyclone separator 7 lower than the starting water level the boiler water from a water ascending pipe 3 passes a curved liquid route 6 that is formed by a shroud 5 and immediately can flow into a steam drum 4 from the bottom face of the inlet to the cyclone separator 7. Namely, it is possible to prevent the drum water level from falling at the time of starting the gas turbine.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a natural circulation type waste heat recovery boiler that utilizes the heat of exhaust gas discharged from various heat generating means such as a gas turbine. Regarding.

(Conventional Technology) In the wake of the energy crisis, there has been a growing movement to save energy in various industrial fields. There is a sudden movement toward energy conservation in the field of power generation, but when you consider the magnitude of consumption, this movement is rather natural. Combined cycle power generation, a method that combines a gas cycle and a steam cycle, has been attracting attention in recent years.It is expected to meet the demands of the times and generate electricity with higher efficiency than traditional power generation methods. It is being Among these types of combined cycle power plants, one that has been particularly developed in recent years is the so-called exhaust heat recovery type.

This system is structured so that the exhaust gas (approximately 500°C to 600°C) is directly led from the gas turbine to the exhaust heat recovery boiler, steam is generated using the heat of the exhaust gas, and the resulting steam is led to the steam turbine and extracted as power. It is said that a relatively large capacity unit configuration is possible.

The exhaust heat recovery boilers used in such combined cycle power plants are classified into forced circulation type and natural circulation type, depending on the method of supplying water to the evaporation tube.

In the natural circulation layer waste heat recovery boiler according to the present invention, the water supplied to the evaporator tube operates as a circulation force by the difference between the average density of the gas-liquid two-phase flow in the evaporator tube and the density of water in the downcomer tube, so the steam drum The difference between the static water head and the inlet of the evaporator tube has a large influence. For this reason, the evaporator tubes are arranged vertically and the exhaust gas flows horizontally. Since the natural circulation bed waste heat recovery boiler is installed horizontally, the installation area is larger than that of the forced circulation type. However, the gas turbine exhaust gas flows smoothly from the inlet to the outlet of the waste heat recovery boiler, which is advantageous in reducing pressure loss. Additionally, since it is possible to have a self-supporting structure, an earthquake-resistant bridge is unnecessary and installation work is easy. moreover,
Since there is no m-ring pump, the plant has features such as improving plant efficiency by reducing internal power consumption.

FIG. 2 shows the structure around the evaporator of the natural circulation bed waste heat recovery boiler, and the flow of steam and boiler water will be explained.

The boiler water filling the inside of the evaporation tube 1 exchanges heat with the high temperature gas 13, and a part of it evaporates, resulting in a gas-liquid two-phase state. Further, the downcomer pipe 2 may be heated by the high-temperature gas 13 or may not be heated, but in either case, no bubbles are generated in the boiler water filling the downcomer pipe 2, or even if bubbles are formed, very few bubbles are generated. It's a small amount. Therefore, a density difference occurs between the fluids in the evaporator tube 1 and the downcomer tube 2, and this becomes a circulating force that causes the boiler water to rise in the evaporator tube 1, and then to the riser tube 3 and the steam drum 4.
, the downcomer pipe 2, and then flows into the evaporation pipe 1 again.

FIG. 3 shows a structural diagram around a steam drum for a conventional natural circulation type waste heat recovery boiler, and the flow inside the steam drum 4 will be described in detail. The steam drum 4 includes a shroud 5 that forms a shroud to guide the gas-liquid two-phase flow from the plurality of risers 3 to the cyclone separator 7, and separates the gas-liquid two-phase flow into steam and boiler water by centrifugal force. cyclone separator 7. The gas-liquid two-phase flow flowing into the steam drum 4 from the riser pipe 3 passes through a curved flow path 6 formed by the steam drum inner surface and the shroud 5, and passes through the cyclone separator 7.
Inside, centrifugal force separates steam and boiler water. Fine water droplets are removed from the steam by a chevron separator 8, and the steam is sent to a superheater (not shown) through a steam pipe 9. On the other hand, the boiler water separated in the cyclone separator 7 flows into the canned water section in the steam drum 4 and is then sent to the downcomer pipe 2.

When the gas turbine is started, the water level in the steam drum 4 is set lower than the water level 10 during normal operation. This water level is called the starting water level, and in conventional steam drums, the bottom surface of the inlet of the cyclone separator turf is set at a position higher than the starting water level 11. In addition, there is a low water level warning water level 12 immediately below the starting water level 11, and a low water level trip water level (not shown).
is set.

(Problem to be Solved by the Invention) In FIG. 2, when high-temperature gas 13 exchanges heat with boiler water flowing in evaporator tube 1 constituting the evaporator, the density of the boiler water in evaporator tube 1 increases with that of downcomer tube 2. The density is smaller than that of boiler water. Therefore, the boiler water in the evaporator tube 1 rises, and the boiler water in the downcomer tube 2 falls. In the conventional steam drum shown in FIG. 3, the bottom surface of the inlet portion of the cyclone separator was set at a position higher than the starting water level 11. Figure 4 shows the cause of water level drop during startup. The figure shows the water level on the evaporator pipe side and the water level on the steam drum/downcomer pipe side. For example, assuming that the equivalent pipe internal cross-sectional areas on the evaporator/rising pipe side and the steam drum/downcomer side are constant, at startup, the water in the left evaporating pipe/rising pipe side is heated and expands, causing the water level to rise. Even if this happens (the average density is decreasing), the mass inside the tube is conserved, so there is no movement of water. In other words, the water level on the steam drum/downcomer side, which is not heated, does not change1.

However, as shown in Figure 5, if the equivalent internal cross-sectional area of the heated evaporator tube/rising tube side is large at the top of the tube, the water level increases less than the volumetric expansion caused by heating, so water flows from the left and right sides. According to the balance of the tube, it moves from the unheated side to the heated side. i.e. unheated steam drum
The water level on the downcomer side will decrease. This drop in water level appears as a drop in the water level in the steam drum.

The water level in the steam drum is adjusted by the boiler expanded by heating on the evaporator tube side, passes through the riser pipe, enters the shroud, and then flows through the cyclone separator into the wood of the drum.

At this time, the steam drum water level is at its lowest. After the boiler water starts flowing into the can water.

The drum water level begins to rise, and thereafter the water level rises rapidly due to swelling. As described above, there is a problem in that the drum water level drops immediately after the gas turbine is started, and a low water level alarm or even a low water level trip occurs due to the drop in the drum water level.

An object of the present invention is to provide a natural circulation type waste heat recovery boiler that prevents a drop in drum water level immediately after starting a gas turbine and enables stable automatic water level control.

[Structure of the invention]

(Means for Solving the Problems) In order to achieve the above-mentioned object, the present invention provides an evaporator panel panel that connects evaporator tubes arranged perpendicularly to the flow of exhaust gas in a horizontal direction with an upper header and a lower header. An evaporator consisting of a plurality of evaporators, a shroud that forms a curved flow path at the inner bottom of a cylindrical steam drum whose top is closed with a shroud, and a plurality of riser pipes that connect the steam drum with the upper header. A natural circulation waste heat recovery boiler having a steam drum equipped with a cyclone separator that separates a two-phase flow into water and steam, characterized in that the bottom surface of the inlet part of the cyclone separator is provided at a position lower than the starting water level. This project proposes a natural circulation type waste heat recovery boiler.

(Function) With the above configuration, boiler water from the riser passes through the curved flow path formed by the shroud and can directly flow into the drum from the bottom surface of the inlet portion of the cyclone separator. Therefore, there is no drop in the drum water level immediately after the gas turbine is started, and a state such as a low water level alarm or low water level trip due to a drop in the drum water level does not occur, making stable automatic water level control possible.

(Example) An embodiment of the present invention will be described with reference to FIG.

In FIG. 1, a steam drum 4 includes a shroud 5 that forms a shroud plate to guide gas-liquid two-phase flows from a plurality of risers 3 to a cyclone separator 7, and a shroud 5 that converts the gas-liquid two-phase flows into steam using centrifugal force. It is equipped with a cyclone separator 7 that separates boiler water.

When starting the gas turbine, the water level is set to the starting water level 11, but there is a low water level warning water level 12 just below the starting water level, and a low water level trip water level (not shown) is also set, so the starting water level can be said to be the limit of low water level. In the conventional steam drum, the bottom surface of the inlet part of the cyclone separator was set at a position higher than the starting water level 11.

Therefore, the boiler water that has risen through the riser pipe 3 accumulates in the curved channel 6 formed by the shroud 5.
Unless the water level in this channel rose to the bottom of the inlet of the cyclone separator, it could not flow into the water section of the steam drum. This caused a drop in the water level, but by setting the bottom of the cyclone separator 7 at a position lower than the starting water level, the boiler water from the riser pipe 3 was channeled through the curved channel formed by the shroud 5. can directly flow into the steam drum 4 from the bottom of the inlet part of the cyclone separator trough. That is, it is possible to prevent the drum water level from dropping when the gas turbine is started.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, the bottom surface of the inlet of the cyclone separator is provided at a position lower than the starting water level, so the boiler water from the riser passes through the curved flow path formed by the shroud. can directly flow into the steam drum from the bottom of the inlet part of the cyclone separator.

Therefore, it is possible to prevent the drum water level from dropping when the gas turbine is started, and stable automatic water level control is possible without generating a low water level alarm or low water level trip due to a drop in the drum water level.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an embodiment of a natural circulation type waste heat recovery boiler according to the present invention, Fig. 2 is a block diagram of a conventional natural circulation type waste heat recovery boiler, and Fig. 3 is a block diagram of a conventional natural circulation type waste heat recovery boiler. A configuration diagram showing a steam drum for a heat recovery boiler, and FIGS. 4 and 5 are explanatory diagrams showing how the drum water level changes when the gas turbine is started. l...Evaporation pipe 2...Downfall pipe 3...Rising pipe 4...Steam drum 5...Shroud
6... Curved channel 6... Cyclone separator 7... Chevron separator 9... Steam pipe 10.
・Water level during normal operation 11 ・Start-up water level 12 ・Low water level warning water level 13 ・High temperature gas agent Patent attorney rules
Kensuke Chika illustration

Claims (1)

[Claims] The evaporator consists of a plurality of evaporator panels that connect evaporator tubes arranged perpendicularly to the horizontal flow of exhaust gas with an upper header and a lower header, and a shroud plate at the inner bottom of the cylindrical steam drum. a steam drum comprising a shroud forming a curved flow path so as to close the upper part thereof, and a cyclone separator for separating a two-phase flow flowing in from a plurality of riser pipes connecting the upper header and the steam drum into water and steam; A natural circulation type waste heat recovery boiler having a natural circulation type waste heat recovery boiler, characterized in that the bottom surface of the inlet part of the cyclone separator is provided at a position lower than a starting water level.