JPS5826901A - Recovery boiler for waste heat - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention recovers exhaust heat from exhaust gas from a gas turbine, diesel main engine, or the like. Regarding waste heat recovery boiler for

The exhaust heat recovery boiler 2 recovers the exhaust heat in the exhaust gas of a gas turbine to generate steam and supplies low-pressure steam and high-pressure steam to the steam turbine, and recovers the exhaust heat in the exhaust gas from the main diesel engine in ships. Exhaust heat recovery boilers, which obtain steam to drive power generation turbines and steam for onboard miscellaneous purposes, are both used as energy-saving equipment.

FIG. 1 is a system diagram showing a schematic configuration of a conventional exhaust heat recovery boiler that recovers exhaust heat from a gas turbine, and this will be explained first.

In Fig. 1, 1 is a superheater, 2 is a high-pressure evaporator, 2a is a high-pressure steam drum, 3 is a secondary economizer, 4 is a low-pressure evaporator, 4a
is a low pressure steam drum, 5 is a primary economizer, 6 is a deaerator, 7 is a feed water preheater, la, tb, 5at3b, sa, s'b
,? 'a, 7b is for the husband'y: Indicates. Exhaust gas from a gas turbine (not shown) flows from the superheater 1 to the feed water preheater 7 as indicated by an arrow. On the other hand, the feed water is heated by the exhaust gas while flowing from the feed water preheater 7 toward the superheater 1 side, and its operation will be explained below along the flow of the feed water.

Feed water supplied from a condensate pump or the like (not shown) enters a feed water preheater 7 and is heated, and then is degassed and heated in a deaerator 6.

The degassed and heated feed water is passed through the low pressure steam drum 4a to the low pressure evaporator 4 by a low pressure water pump (not shown).
is supplied to The low pressure steam evaporated here is supplied to the low pressure section of a steam turbine (not shown).

On the other hand, the water that has passed through the deaerator 6 is supplied to the high-pressure evaporator 2 through the primary economizer 5 and secondary economizer 3 via the high-pressure steam drum 2a by a high-pressure water pump (not shown). Ru. Here, the steam becomes high-pressure steam, is superheated by the superheater 1, and then supplied to the high-pressure section of a steam turbine (not shown).

Since the heat transfer surface is configured in this way, the exhaust heat of the gas turbine is efficiently recovered. From the characteristic diagram shown, it can be seen that heat recovery is being carried out efficiently without wastage.However, due to its characteristics, gas turbines exhibit the third exhaust gas characteristic as shown in the diagram.In other words,
The exhaust gas flow rate is not proportional to the gas turbine load and remains approximately constant below about 70% load. On the other hand, the exhaust gas temperature is about 7
The temperature is proportional to the gas turbine load up to 0% load, and the temperature is approximately constant above that.

For this reason, an exhaust gas boiler that is configured to have the best heat recovery effect near the gas turbine rated load, as shown by the solid line in Figure 2, has a second heat recovery effect in the low load range due to its characteristics.
The characteristics shown by the broken lines are shown in the figure.

Comparing the solid line and the broken line, the boiler inlet side (superheater 1 side)
However, as the exhaust gas temperature decreases, the amount of heat absorption decreases in proportion to the gas turbine load.

It can be seen that on the boiler outlet side (feed water preheater 7 side), there is almost no change in exhaust gas temperature and the amount of heat absorption does not decrease much.

Therefore, a comparison of the characteristics of the high-pressure evaporator 2 and the economizer 3 is shown in FIG.

The figure shows a comparison of the evaporation amount of the high-pressure evaporator 2 when the gas turbine is 100% loaded and when the gas turbine is 25% loaded.

When the gas turbine load is 25%, the evaporator is 10
It is approximately 50% at 0% load.

(B) is the same (comparison of heat absorption amount in the economizer 3).

Even if the gas turbine load decreases to 25%, the amount of heat absorbed is approximately 8
There are also 0%.

Therefore, if the amount of water supply is reduced according to the amount of evaporation of high-pressure steam, steaming will occur in the energy saver 3.

Conventional energy savers have a piping structure in which the water supply repeatedly rises and falls relative to the flow of exhaust gas, so if steaming occurs inside the energy saver, uneven flow may occur or Corridor problems occur where stagnation occurs in some pipes.

To prevent this steaming, the temperature of the water supply at the outlet of the economizer should be suppressed (recirculation is performed through the economizer).

Since this recirculation requires releasing the absorbed heat, it is returned to the condenser or the like and is not used effectively.

(C) compares the amount of water supplied including recirculation to prevent steaming in the economizer. Even if the gas turbine load drops to 25%, approximately 76% of the water supply is required,
Moreover, about 40% of that amount (the shaded area) is due to economizer recirculation.・As mentioned above, conventional exhaust heat recovery boilers have the disadvantage that the recovered heat is not used effectively, although this is unavoidable due to the characteristics of the engine or gas turbine. .

The present invention was made with the aim of eliminating the above-mentioned conventional drawbacks, and aims to improve thermal efficiency by effectively utilizing the recovered heat without wasting it. be.

An embodiment of the exhaust heat recovery boiler according to the present invention will be described in detail below with reference to the schematic system diagram shown in FIG. Note that in FIG. 5, the same parts as in FIG. 1 are designated by the same reference numerals, so the explanation of those parts will be omitted.

The present invention is characterized in that an evaporative type economizer 11 is provided between the secondary economizer 3 and the high-pressure evaporator 2. That is, the evaporative economizer 11 is formed only by the riser pipe,
A header 12 and a header 13 are arranged in the lower part and the header 13 in the upper part, respectively, and between each header 12, 13 there is provided an evaporative type economizer 11 consisting only of a riser pipe 11a. Therefore, the feed water heated by the secondary economizer 3 is uniformly distributed to the riser pipe 11a of the evaporative economizer 11 in the lower header 12,
It is further heated by heat exchange with the exhaust gas.

A portion of the supplied water heated by the evaporative economizer 11 evaporates.

Then, since the average specific weight of the feed water in the riser pipe 11a decreases, the upward flow of the feed water is accelerated and the flow in the riser pipe is promoted, so that the feed water together with steam becomes a steam-water mixture and flows into the upper pipe. Gather at Yose 13. The steam-water mixture collected in the header 13 is separated into steam and water by the high-pressure steam drum 2a, and the moisture is sent to the high-pressure evaporator 2 and evaporated by heat exchange with the extracted gas, and this steam is evaporated by the high-pressure steam drum 2a. Evaporation type economizer 11
The mixture is mixed with the vapor evaporated at , and sent to the superheater 1.

The steam superheated to a specified temperature in the superheater 1 is then supplied to the high pressure section of the steam turbine.

As described above, according to the present invention, the evaporative economizer 11 whose heat transfer tubes are composed of only riser tubes is provided between the secondary economizer 3 and the high-pressure evaporator 2, and the evaporative economizer 11 Since a part of the feed water is evaporated, the flow of the feed water is promoted by this steam, and unlike the conventional method, non-uniform flow and stagnation do not occur.

Further, as shown in FIG. 4(D), according to the present invention, when the gas turbine load decreases to 25%, the water supply amount is 100%.
It may be 50% at % load, which is equal to the relationship of high-pressure evaporation amount shown in FIG. 4(A).

As shown in FIG. 4(D), according to the present invention, when the turbine load decreases to 25%, about 13% of the water supply to the evaporative economizer (slanted view) By evaporating the exhaust gas, all of the heat recovered from the exhaust gas can be effectively utilized.

It goes without saying that the present invention is not limited to the above-mentioned embodiment, but can be implemented with various modifications without departing from the scope of the invention. Furthermore, although the present invention has been described as a device for recovering exhaust heat from a gas turbine, the present invention is not limited to this, but can also be used for exhaust heat recovery in a combined plant of a gas turbine and a steam turbine.

[Brief explanation of the drawing]

Figure 1 is a system diagram showing the general configuration of a conventional waste heat recovery boiler, and Figure 2 shows the exhaust gas temperature at each heat transfer section along the flow direction of exhaust gas in the waste heat recovery boiler, and the supply water and steam. Figure 3 is a characteristic diagram showing the relationship between temperature and the relationship between exhaust gas temperature and exhaust gas amount with respect to the load condition of the gas turbine.
FIG. 4 shows a 10-meter scale of a gas turbine in order to compare the effects of a conventional exhaust heat recovery boiler and an exhaust heat recovery boiler according to the present invention.
FIG. 5 is a diagram comparing the characteristics of a full high-pressure evaporator and an energy saver at 0% load and 25% load, and is a system diagram showing a schematic configuration of an embodiment of the exhaust heat recovery boiler according to the present invention. . l...Superheater, 2...High pressure evaporator, 3,5...Economy device,
4. Low pressure evaporator, 6. Deaerator, 7. Water supply preheater,
11. Evaporation type economizer. Figure 3 0
1000 Biting turbine φ printing 2 Fig. 4

Claims (1)

[Claims] a deaerator that deaerates water from the feed water; a first economizer to which the feed water deaerated by the deaerator is supplied; and a first economizer that heats the feed water while repeating rising and falling; and the first economizer. an evaporative type economizer that introduces and heats the feed water heated by An exhaust heat recovery boiler comprising a superheater for superheating the steam evaporated in an evaporator and the steam separated from the steam and water, the exhaust gas flowing from the superheater toward the deaerator.