JP2018053737A - System for recovering steam from exhaust gas, thermal power generation system, and water steam recovery method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a system for recovering steam from exhaust gas, a thermal power generation system and a water steam recovery method, which can retain a temperature difference between an exhaust gas temperature and an outdoor temperature sufficiently.SOLUTION: According to an embodiment, a system for recovering steam from exhaust gas comprises: a steam separation film for separating steam from flue gas; evacuation means for evacuating the exhaust gas having penetrated said steam separation film; compression means for compressing the exhaust gas having been evacuated by said compression means; and air-cooling means for cooling the exhaust gas having been compressed by said compression means, with ambient air.SELECTED DRAWING: Figure 1

Description

  Embodiments described herein relate generally to an exhaust gas steam recovery system, a thermal power generation system, and a steam recovery method.

In the future, it is expected that thermal power plants will be installed in regions (especially inland areas) where supply cannot catch up with the increase in power demand in emerging countries where industrialization and population growth are remarkable. However, in coal-fired power generation and natural gas combined cycle power generation (hereinafter sometimes abbreviated as “combined cycle power generation”), after turning the turbine with steam obtained by vaporizing water with combustion heat from fuel combustion, For example, a coal-fired power plant requires a cooling medium (such as seawater). Also, the boiler water that moves the steam turbine concentrates and precipitates rust preventives and silica and degrades the equipment, so part of the boiler water is extracted as blow water, and pure water is supplied as make-up water. There is a need to. Usually, clean water or industrial water is supplied from outside the power plant to produce pure water. Furthermore, a coal-fired power plant requires a large amount of water to spray desulfurized water and to prevent scattering of pulverized coal at the coal storage.

For areas where a large amount of cooling water cannot be secured, for example, the cooling water is circulated between the condenser and the cooling tower as a cooling means for coal-fired power plants, and the cooling water is forcibly brought into air contact with the cooling tower. In general, 1.5 to 2% of the gas is vaporized and cooled with the heat of vaporization. However, it is necessary to blow a part of the cooling water to prevent vaporization and precipitation due to salt concentration in the cooling water and machine deterioration due to corrosion.
It is necessary to replenish water (such as industrial water). For example, by using an air-cooled condenser, the amount of makeup water from outside the power plant can be greatly reduced, but it is necessary to supply clean water or industrial water from outside the plant in order to secure boiler makeup water. .

On the other hand, there is a technology for condensing steam in the exhaust gas of a boiler to collect moisture to secure necessary water in the plant. Some of them collect water vapor by separating the water vapor in the exhaust gas with a water vapor separation membrane and then cooling and condensing the steam concentrated exhaust gas. In the water vapor separation membrane, separation is performed using the difference in the passing speed between water vapor and other gas components.

JP 2000-337106 A JP 2006-23053 A JP 2014-129731 A

Since the steam-concentrated exhaust gas that has permeated the steam separation membrane contains non-condensable gas such as CO2, water recovery by cooling under low pressure is not easy. Further, in an environment where it is difficult to secure water, it is difficult to cool by dissipating water such as a cooling tower into the atmosphere, so air cooling by outside air must be used to secure a cold heat source. However, the air cooling by the outside air has a problem that the efficiency of heat transfer is bad and the inside ratio increases or the apparatus becomes large. Furthermore, air cooling by outside air cannot be cooled below the outside air temperature, and the temperature difference from the exhaust gas temperature cannot be secured sufficiently during the summer day. Must be provided.

The problem to be solved by the present invention is to provide a steam recovery system in exhaust gas, a thermal power generation system, and a steam recovery method capable of ensuring a sufficient temperature difference between the exhaust gas temperature and the outside air temperature.

The steam recovery system in the exhaust gas according to the embodiment includes a water vapor separation membrane that separates water vapor from combustion exhaust gas, a decompression unit that decompresses the exhaust gas that has permeated the water vapor separation membrane, and a compression unit that compresses the exhaust gas decompressed by the decompression unit. And air cooling means for cooling the exhaust gas compressed by the compression means with outside air.

Schematic which shows the structure of the thermal power generation system which concerns on this embodiment.

  Hereinafter, embodiments will be described with reference to the drawings.

FIG. 1 is a schematic diagram showing a configuration of a thermal power generation system according to the present embodiment. As an example of a thermal power generation system, a gas turbine combined cycle power plant that is a LNG-only fired thermal power plant is shown. In the combined cycle, the combustor 1 and the gas turbine 2 are generally used.
, Generator 3, exhaust heat recovery boiler 4, stack (chimney) 5, steam turbine 7, condenser 9, water vapor separation membrane 11, vacuum pump 12, compression cooling device 13, water recovery device 14 and water receiving tank 15
It has.

LNG as fuel is mixed with air compressed to a high pressure by an air compressor, led to the combustor 1 and ignited. The energy of the combustion gas exceeding 1000 ° C. is consumed as rotational energy in the gas turbine 2, and is generated by the generator 3 connected to the gas turbine 2.
Generate electricity. The exhaust gas emitted from the gas turbine 2 becomes about 500 to 600 ° C. and flows to the exhaust heat recovery boiler 4 through the denitration device. The exhaust heat recovery boiler 4 is a heat exchange type steam generator that generates steam by the thermal energy of the exhaust gas at 500 ° C. Steam generation is performed more efficiently by being multistaged in the exhaust heat recovery boiler. Steam generated in the exhaust heat recovery boiler 4 is introduced into the steam turbine 7 to rotate the steam turbine 7. The steam turbine 7 is directly connected to the gas turbine 2 coaxially. The gas turbine 2 and the steam turbine 7 are
The generator 3 is simultaneously rotated to generate electricity efficiently.

Since the exhaust gas from the exhaust heat recovery boiler 4 contains water vapor, the water vapor separation membrane 11
To collect water vapor in the exhaust gas. The exhaust gas from which the water vapor in the exhaust gas has been recovered by the water vapor separation membrane 11 is released to the atmosphere through the stack (chimney) 5.

The water vapor separation membrane 11 transmits water vapor (and other exhaust gas components) using the pressure difference between the primary side and the secondary side as a driving force. A vacuum pump 12 is introduced on the secondary side of the water vapor separation membrane 11 to promote water vapor separation by reduced pressure. The pressure is reduced to about several Pa to several tens kPa, preferably about several kPa. Thereby, the water vapor separation membrane 11 can separate the water vapor concentrated exhaust gas mainly containing water vapor in the exhaust gas. The water vapor separation membrane 11 is an exhaust gas component other than water vapor (for example,
NOx, SOx, CO2, etc.) also permeate, so that even when the pressure on the secondary side of the membrane is reduced to near vacuum, non-condensable gas (exhaust gas components other than water vapor) flows into the secondary side of the membrane through the water vapor separation membrane 11.

The steam-concentrated exhaust gas is guided to the secondary side of the vacuum pump 12 and compressed by the compression cooling device 13.
To be cooled. A compressor may be provided for compression, but a configuration in which compression is performed by the vacuum pump 12 is simplified and preferable. Water is condensed by cooling the steam-concentrated exhaust gas.
The cooling device uses an air-cooled cooler in an environment where water is insufficient.

A tube can be used as a container for compression. By using, for example, a low fin tube,
The heat transfer performance during cooling can be kept good. Further, the inside of the pipe is compressed by providing a pressure control valve at the outlet and, if necessary, a pump for discharging non-condensable gas. The required post-compression pressure is calculated from the relationship between the outside air temperature and the compressed gas temperature, the heat transfer performance of the heat exchanger and the gas composition, etc., and is about + 10 ° C or higher than the outside air temperature. It is desirable to set the pressure so as to compress. Depending on various equipment conditions and operating conditions, it is compressed to about 1.5 to 100 times the pressure on the membrane secondary side (absolute pressure) necessary for water vapor separation, to a temperature range that can be cooled with outside air It is possible to compress and further condense the water vapor contained in the gas.

The steam-concentrated exhaust gas is vented to a number of pipes. Further, a large number of tubes are bundled, and the outside air is circulated outside the tubes with a single fan, and then cooled. The exhaust gas temperature is generally higher than that of the outside air, but a temperature difference can be obtained by adding a temperature increase due to compression, and the efficiency of cooling is higher than when compression is not performed. While being cooled, a part of the water vapor condenses and becomes mist.

Here, when the compression cooling device 13 compresses the exhaust gas to a pressure higher than the exhaust gas pressure at the chimney 5 inlet, the steam-concentrated exhaust gas is guided to the water recovery device 14 and discharged into the water recovery device 14 using a nozzle or the like. As a result, the pressure is rapidly released. As the pressure is released, the volume increases and the state becomes close to adiabatic expansion, so that the temperature of the steam-concentrated exhaust gas drops. As the temperature drops, water vapor condenses and water droplets are generated. Here, since the mist separator is provided in the water recovery apparatus 14, the generated water droplets adhere to the mist separator and are recovered. The exhaust gas from which the mist has been recovered is mixed with the exhaust gas from the main pipe, sent to the stack (chimney) 5 and exhausted. When the water vapor concentration is relatively low, an operation for increasing the pressure is required.

When the compression cooling device 13 compresses the exhaust gas to a pressure lower than the exhaust gas pressure at the inlet of the chimney 5, the steam-concentrated exhaust gas is guided to the water recovery device 14 and is generated by the mist separator provided in the water recovery device 14. Mist adheres and is collected. The exhaust gas from which the mist has been recovered is mixed with the exhaust gas from the main pipe by a pump for discharging non-condensable gas, sent to the stack (chimney) 5 and exhausted. When the water vapor concentration is relatively high and condensation occurs even at a low pressure, it is efficient to operate at such a pressure setting.

The water droplets adhering to the mist separator grow gradually and eventually flow down and drop due to gravity.
At this time, when the mist separator is made of a hydrophilic material and has a contact angle of 20 ° or less, water droplets adhering to the mist separator can be quickly flowed down. Specifically, PET (polyethylene terephthalate), PEN (polyethylene naphthalate), PP (polypropylene)
, PE (polyethylene) film or fiber coated with a hydrophilic or super-hydrophilic paint is used.

Water accumulates in a water receiving tank 15 disposed below the water recovery device 14 and is discharged using a pump or the like. Since the discharged water is acidic with non-condensable gas components dissolved, it should be neutralized with an alkali salt or desalted with a reverse osmosis membrane or ion exchange resin, etc. Can do.

In the case of a coal-fired power generation system, the water vapor separation membrane 11 is installed at the subsequent stage of the desulfurization apparatus.

As described in detail above, according to at least one embodiment, a sufficient temperature difference between the exhaust gas temperature and the outside air temperature can be secured.

Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

1 ... Combustor, 2 ... Gas turbine, 3 ... Generator, 4 ... Waste heat recovery boiler, 5 ... Stack (
Chimney), 7 ... Steam turbine, 9 ... Condenser, 11 ... Steam separation membrane, 12 ... Vacuum pump, 13
... compression cooling device, 14 ... water recovery device, 15 ... water receiving tank

Claims (8)

A water vapor separation membrane for separating water vapor from combustion exhaust gas;
Decompression means for decompressing the exhaust gas permeated through the water vapor separation membrane;
Compression means for compressing the exhaust gas decompressed by the decompression means;
An exhaust gas water vapor recovery system comprising: air cooling means for cooling the exhaust gas compressed by the compression means with outside air. The exhaust gas steam recovery system according to claim 1, further comprising mist collecting means for collecting mist in the exhaust gas cooled by the air cooling means. The exhaust gas steam recovery system according to claim 2, further comprising a pressure release means provided in a preceding stage of the mist collecting means for releasing the pressure of the exhaust gas cooled by the air cooling means. The steam recovery system for exhaust gas according to claim 2 or 3, further comprising a water receiving tank for storing mist adhering to the mist collecting means. In exhaust gas applied to a thermal power generation system having a boiler that generates steam using heat generated by burning fuel and a steam turbine that converts the energy of the steam generated in the boiler into the driving force of a generator A steam recovery system,
5. The thermal power generation system according to claim 1, wherein the thermal power generation system is a combined cycle power generation system, the boiler is an exhaust heat recovery boiler, and the water vapor separation device is provided downstream of the exhaust heat recovery boiler. System for collecting water vapor in exhaust gas. In exhaust gas applied to a thermal power generation system having a boiler that generates steam using heat generated by burning fuel and a steam turbine that converts the energy of the steam generated in the boiler into the driving force of a generator A steam recovery system,
The thermal power generation system further includes a desulfurization device that removes sulfides contained in the exhaust gas discharged from the boiler,
The exhaust gas steam recovery system according to any one of claims 1 to 4, wherein the steam separator is provided downstream of the desulfurizer. A thermal power generation system having the steam recovery system in exhaust gas according to any one of claims 1 to 6. Water vapor is separated from the combustion exhaust gas discharged from the boiler by a water vapor separation membrane;
Depressurizing the exhaust gas that has permeated the water vapor separation membrane,
Compress the exhaust gas with reduced pressure,
A method for recovering water vapor in exhaust gas by cooling the compressed exhaust gas with outside air.

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