JPH11337009A - Flash type deaerator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a simple and lower cost flash type deaerator which can improve the efficiency of a plant by eliminating the need for a high temperature steam from a waste heat recovery steam generator. SOLUTION: This flash type deaerator is provided with a deaerator 5, a first pipe to guide a part of condensate discharged from a condenser 2 to the deaerator 5, a second pipe 7 to guide a rest part as main stream of the condensate discharged from the condenser 2 to the deaerator 5 via a preheater 8 and a pressure reducing valve 9 provided in the course of the second pipe 7.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flash deaerator for degassing condensate generated in a power plant by reducing pressure. More specifically, the present invention recovers heat of flue gas exhausted from a gas turbine for power generation in a power plant as high-temperature steam, guides the steam to a high-pressure / medium-pressure steam turbine, and further to a low-pressure steam turbine, In a system for generating further electric power, the present invention relates to a technique for degassing dissolved oxygen in condensed water generated on the downstream side of a low-pressure steam turbine by flashing under reduced pressure to prevent corrosion of equipment.

[0002]

2. Description of the Related Art Conventionally, as a deaerator in a power plant, a two-body spray tray type deaerator or a one-body sparger type deaerator has been used. However, these degassing devices require hot steam for degassing. Therefore, the exhaust heat recovery steam generator (HRSG; heat)
The high-temperature steam generated by the recovery steam generator) is led to the deaerator by piping. The exhaust heat recovery steam generator is a steam generating means installed in a flue of high-temperature combustion exhaust gas discharged from the gas turbine. In the case of using the steam from the exhaust heat recovery steam generator in this way, the installation of piping becomes complicated, the entire device related to degassing becomes large, and the entire plant is reduced by the amount of steam required for degassing. Efficiency decreases.

On the other hand, in a gas-fired combined plant employing a direct contact condenser cooled by seawater or the like, the dissolved oxygen in the condensate reaches an allowable level in HRSG, and the deaerator can be omitted. However, in a plant employing an air-cooled condenser, the amount of dissolved oxygen in the condensate is large, and the deaerator cannot be omitted. Therefore, particularly in a plant employing an air-cooled condenser, there is a demand for a compact and low-cost deaerator.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to improve the efficiency of a plant that is compact, low cost, and does not require hot steam from a heat recovery steam generator (HRSG). It is an object of the present invention to provide a flash type deaerator capable of performing the above-mentioned operations.

[0005]

According to the present invention, there is provided a deaerator comprising: a deaerator; a first pipe for guiding a portion of the condensate discharged from the condenser to the deaerator; A second pipe for guiding the remainder, which is the main stream of condensate discharged from the condenser, to the deaerator via the inside of the preheater, and a pressure reducing valve provided in the middle of the second pipe. It is characterized by comprising.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a deaerator according to the present invention will be described with reference to FIG.
It will be described based on. In FIG. 1, steam discharged from a steam turbine 1 has a low temperature (for example,
(44 ° C). The condensate is circulated in the pipe by the condensate pump 3, and at a branch point, a small part of the condensate (for example, 0.55 ton / hour) passes through the first pipe 4.
It goes directly to the deaerator 5 and is supplied to the deaerator in a thermal sleeve 6 of the deaerator.

At the branch point, most of the condensate (for example, 489 tons / hour) is once sent to the preheater 8 through the second pipe 7 and becomes high temperature (for example, 138 ° C.). , Heading to the deaerator 5 and the pressure reducing valve 9 in front of the deaerator 5
(For example, 9.9 × 10 ³ hPa is reduced to 3.5).
The pressure is reduced to × 10 ³ hPa) and supplied to the deaerator 5 from the supply port 10. Note that the area from the pressure reducing valve 9 to the supply port 10 is referred to as a degassing zone.

The mechanism of deaeration in the deaerator of the present invention will be described as follows. The low-temperature condensate supplied from the first pipe 4 condenses the steam in the deaerator 5, and the same amount of gas as the condensed amount is supplied to the high-temperature condensate supplied through the second pipe 7. Supplied by evaporation. Degassing of high-temperature condensate is called turbulent mixing in the floss flow and bubble flow (flash phenomenon) generated in the degassing zone due to depressurization, and degassing due to turbulent mixing when flowing into the deaerator. Happens in shape. As described above, the condensed water can be effectively degassed by the small amount of low-temperature condensed water supplied by the first pipe 4 and the pressure reducing valve 9 provided in the middle of the second pipe 7.

[0009] The temperature of the condensate supplied through the first pipe 4 is usually about 40 to 50 ° C, and the temperature of the condensate supplied through the second pipe 7 is usually about 120 to 150 ° C. It is. The amount of bubbles generated in the degassing zone of the second tube 7 is controlled by the amount of cold condensate supplied by the first tube 4. The amount of condensate supplied by the first pipe 4 is 0.01-1% of the total condensate, preferably 0.0
5 to 0.5%. When the amount is less than 0.01%,
Degassing may be insufficient. When the amount exceeds 1%, a spray flow (mist flow) is generated in the degassing zone, and the degassing effect is reduced.

The gas in the deaerator is exhausted from the hole of the thermal sleeve 6 and exhausted out of the system via the valve 11. Part of the condensate stored in the deaerator 5 is a low pressure boiler supply pump (LP BFP).
feeding pump) 12 to save low pressure
O) 13 and further low pressure evaporator (LP EVA)
14. Low pressure super heater (LP SH)
eater) (not shown). The remainder of the condensate in the deaerator is supplied to the high / medium pressure boiler supply pump (HP / IPBF).
P) 15 leads to economizers (not shown).

FIG. 2 shows a structure near the thermal sleeve 6 of the deaerator 5 in FIG. In FIG. 2, a first pipe 4 from a condenser is inserted into a thermal sleeve 6, and condensate is supplied from a jet port 16. Gas generated by degassing is discharged from the hole 17 of the thermal sleeve located above the jet port 16 via the valve 11.

FIG. 3 shows a structure around a pressure reducing valve (ball-shaped valve) 9 provided in the middle of the second pipe 7 from the condenser 2. The condensate becomes a high-speed floss flow after passing through the pressure reducing valve 9, the flow adheres to the pipe wall downstream thereof, and then flows into the deaerator as a bubble flow. The gas phase volume fraction in the floss flow and bubble flow regions is less than 65%. As the pressure reducing valve, a valve such as a gate valve or a needle valve or an orifice can be used in addition to the ball valve. Further, a plurality of these valves or orifices may be provided in series.

The length (L) of the pipe downstream of the pressure reducing valve 9, that is, the length of the deaeration zone from the pressure reducing valve 9 to the supply port 10 in FIG. 1, is determined by the inner diameter (D) of the second pipe. 5 times or more, preferably 7 to 20 times, particularly preferably 8 to 12 times. If the length (L) is less than 5 times the inner diameter (D), degassing may be insufficient. For example, if the inner diameter of the second tube is 20 cm, the preferred length of the degassing zone is around 200 cm.

The inner diameter of the second tube is determined by the following equation.
This is because the flow rate needs to be increased in order for the deaeration zone to be a bubble / floss flow. D = (WVe / 2.356 (g) ^1/2 ) ^0.4 (W: flow rate (kg / s), Ve: liquid specific volume (m ³ / k)
g), g: gravitational acceleration (= 9.8 m ² / s), D: pipe inner diameter (m)) For example, W = 500 tons / hour, Ve = 0.00108
In the case of m ³ / kg, D = 20 cm. However, in general, the inner diameter of the second pipe is equal to the calculated value of 0.
What is necessary is just to design so that it may be in the range of 5 to 2 times. According to the deaerator of the present invention, the amount of dissolved oxygen in the condensate is reduced to 20 pp.
b to 7 ppb or less, theoretically 2 ppb.

[0015]

The flash deaerator of the present invention is simple and inexpensive, and does not require high-temperature steam from the exhaust heat recovery steam generator, thereby improving the efficiency of the plant.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating a deaerator according to the present invention.

FIG. 2 is a vertical cross-sectional view of the vicinity of a thermal sleeve of the deaerator.

FIG. 3 is a longitudinal sectional view illustrating a state of a pressure reducing valve and a water flow on a downstream side thereof.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Steam turbine 2 Condenser 3 Condensate pump 4 First pipe 5 Deaerator 6 Thermal sleeve 7 Second pipe 8 Preheater 9 Pressure reducing valve 10 Supply port 11 Valve 12 Low pressure boiler supply pump (LP BFP) 13 Low pressure Economizer (LP ECO) 14 Low pressure evaporator (LP EVA) 15 High pressure / medium pressure boiler supply pump (HP / IP BF)
P) 16 spouts 17 holes

Claims (1)

[Claims] 1. A deaerator, a first pipe for guiding a part of the condensate discharged from the condenser to the deaerator, and a main flow of the condensate discharged from the condenser. A flash type degassing system comprising a second pipe for guiding a certain part to the deaerator through the preheater, and a pressure reducing valve provided in the middle of the second pipe. Qi device.