JPH0783402A - Exhaust gas boiler - Google Patents

Abstract

PURPOSE:To improve an exhaust gas boiler which contains a vertical gas flow type and horizontally disposed evaporation tube. CONSTITUTION:Vapor drums 8, 9 are installed on an upper support steel frame of a boiler to obtain sufficient natural circulation force in evaporation tubes 3, 5 only by static heads of waters in the drums, and a boiler water circulation pump is eliminated. As a result, a facility cost, a maintenance cost and a power cost of the pump are also obviated. Since the steel frame is used, a steel frame volume is largely reduced as compared with that of prior art.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas boiler in which a vertical gas flow type evaporator and a horizontally arranged evaporator are incorporated and a natural circulation system is applied.

[0002]

2. Description of the Related Art FIG. 4 is a vertical sectional side view showing an example of a conventional gas vertical flow type exhaust gas boiler. In this figure,
(1) is an exhaust gas boiler main body, (2) is a high pressure superheater,
(3) is a high-pressure evaporator, (4) is a high-pressure economizer, (5) is a low-pressure vaporizer, (6) is a low-pressure economizer, (7) is a suspended beam,
(8) is a low pressure steam drum, (9) is a high pressure steam drum,
(10) is a high pressure drum water circulation pump, (11) is a low pressure drum water circulation pump, (12) is a high temperature duct, (13) is a chimney, respectively.

Exhaust gas from a gas turbine (not shown) is guided to the exhaust gas boiler body (1) through a high temperature duct (12). In the exhaust gas boiler, a high pressure superheater (2), a high pressure evaporator (3) with a horizontal heat transfer surface arrangement, a high pressure economizer (4), a low pressure evaporator (5) with a horizontal heat transfer surface arrangement, and a low pressure economizer (6) is arranged, and the gas turbine exhaust gas sequentially exchanges heat with these heat transfer surfaces and is then discharged to the atmosphere through the chimney (13). Each heat transfer surface in the exhaust gas boiler is suspended by the upper support beam (7).

The above-mentioned conventional gas flow type exhaust gas boiler is
The forced circulation system had the evaporators (3) and (5) with the heat transfer surface horizontally arranged. In this case, to ensure circulation,
Equipped with boiler water circulation pumps (10) and (11), consideration was given to performance deterioration and damage to the heat transfer tube due to retention of the steam-water mixture in the horizontal evaporation tube and local overheating.

[0005]

In the conventional gas vertical flow type forced circulation type exhaust gas boiler, it is necessary to constantly operate the boiler water circulation pump in order to secure the circulation amount. Therefore, not only the installation cost of those pumps but also the maintenance work cost thereof were required. Further, by constantly operating the boiler water circulation pump, the auxiliary machine power increased, causing a decrease in plant efficiency.

[0006]

In order to solve the above-mentioned conventional problems, the present invention provides a gas vertical flow type exhaust gas boiler in which a heat transfer surface of an evaporator is horizontally arranged, and a steam drum is supported above a boiler. The proposed exhaust gas boiler is characterized by being installed on a steel frame.

[0007]

In the present invention, since the steam drum is installed on the steel frame supporting the upper part of the boiler, as will be described in detail later, the circulating force in each evaporator is sufficient only by the hydrostatic head of the water in the steam drum. Can be secured. Therefore, the boiler water circulation pump becomes unnecessary, and the cost of pump equipment, the cost of maintenance work, and the cost of drive power are also unnecessary.

Further, since the steam drum is installed by utilizing the supporting steel frame of the boiler, the volume of the steel frame can be greatly reduced as compared with the conventional case.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a vertical sectional side view showing an embodiment of the present invention. In this figure, the same parts as those of the conventional one described with reference to FIG. 4 are designated by the same reference numerals to avoid redundancy, and detailed description thereof is omitted.

In this embodiment, a boiler supporting steel frame is used, a pedestal is provided at a position higher than the height of the supporting beam (7), and steam drums (8) and (9) are installed. Then, due to the static head of the water in the steam drums (8) and (9),
A sufficient circulation amount of horizontal evaporation pipes (3) and (5) is secured, and the boiler water circulation pump (reference numeral (10) in FIG. 4,
(11)) becomes unnecessary. In addition, since the boiler supporting steel frame is used, the volume of the steel frame is greatly reduced compared to the conventional one.

Next, a test conducted for quantitatively grasping the natural circulation amount of the horizontally arranged evaporation pipes and confirming the action and effect of the present invention will be described. Figure 2 shows a horizontal evaporation tube DN
The result of testing the B characteristic (flow rate and tube metal temperature characteristic) is illustrated, and this is also a diagram showing the metal temperature distribution on the inner wall of the evaporation tube at the same time. The horizontal axis of the figure is the quotient of the difference between the saturated water enthalpy due to operating pressure subtracted from the weighted average enthalpy of the actual fluid divided by the latent heat of vaporization due to operating pressure, STEAM QUALITY (mixing ratio of water and steam in the evaporator ) Is shown, it also indicates the position along the length of the evaporation tube. In the figure, the white circles and the solid curve represent the metal temperature at the top of the evaporation tube cross section, the x mark the metal temperature at the bottom of the evaporation tube cross section, and the broken line the fluid temperature in the tube. In addition, P shown as the test condition is the operating pressure on the water side in the horizontal evaporation pipe, G is the weight flow rate of the fluid flowing in the pipe (circulation flow rate (kg / h), the number of tubes and the cross-sectional area per tube (m ² )), q is the heat load on the inner surface of the tube (total heat absorption (kcal / h)
Is divided by the number of tubes and the inner wall surface area (m ² ) per tube).

From the test results as shown in FIG. 2, if a certain circulation ratio (ratio between the circulation amount in the evaporator and the vapor amount generated in the evaporator) is secured, the tube will be overheated or cyclically heated. It was examined whether or not the problem of thermal fatigue could be avoided, and the necessary circulation amount (critical circulation ratio) as shown by the solid line in FIG. 3 was summarized as a parameter of steam pressure. As a result of studying the vertical gas exhaust gas boiler based on this result, basically, a pedestal is installed on the beam above the exhaust gas boiler and a steam drum is installed (in this case, the steam drum and the evaporator inlet pipe It has been clarified that the required circulation amount of the horizontal evaporation pipe can be secured by the height difference H of about 12 m).

[0013]

According to the present invention, it is not necessary to equip the horizontally arranged evaporation pipe with a water circulation pump because only the hydrostatic head of the water in the steam drum can be ensured. As a result, it contributes to the improvement of plant efficiency by reducing the power of auxiliary equipment and the cost reduction by reducing pumps. Further, the volume of the steel frame is significantly reduced as compared with the conventional one, and the cost is also reduced in that respect.

[Brief description of drawings]

FIG. 1 is a vertical sectional side view showing an embodiment of the present invention.

FIG. 2 is a diagram illustrating a result of testing a DNB characteristic of a horizontal evaporation tube.

FIG. 3 is a diagram showing a circulation ratio for establishing a horizontal evaporation pipe by natural circulation.

FIG. 4 is a longitudinal side view showing an example of a conventional gas vertical flow type exhaust gas boiler.

[Explanation of symbols]

 (1) Exhaust gas boiler main body (2) High pressure superheater (3) High pressure evaporator (4) High pressure economizer (5) Low pressure evaporator (6) Low pressure economizer (7) Suspended beam (8) Low pressure steam drum ( 9) High-pressure steam drum (10) High-pressure drum water circulation pump (11) Low-pressure drum water circulation pump (12) High-temperature duct (13) Chimney

Claims (1)

[Claims] 1. An exhaust gas boiler of a gas vertical flow type in which a heat transfer surface of an evaporator is horizontally arranged, wherein a steam drum is installed on a boiler upper supporting steel frame.