JP2001248826A - Equipment and method for boiler exhaust gas treatment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technology for solving problems associated with corrosion and material cost of GGH(gas-gas heater) and SGH(steam-gas heater) and lowering of thermal efficiency of a boiler in a system for exhaust gas treatment in a coal fired power plant. SOLUTION: The temperature of exhaust gas entering a GGH reheating side 5 from a desulfurizer 7 is lowered to 40 deg.C or lower. For that purpose, any one of the following three processes is employed; (1) an exhaust gas cooler 19 is disposed upstream of the reheating side 5, (2) an exhaust gas cooling function is provided to a mist separator disposed upstream of the reheating side 5, and (3) an exhaust gas cooler is disposed in the desulfurizer 7. When the exhaust gas temperature in the inlet of the reheating side 5 is lowered to 40 deg.C or lower, the moisture content in the exhaust gas can be lowered 1/2-1/3 as compared with the conventional technology, and if the temperature is lowered further, heat of the exhaust gas and adhesive mist becomes so easy that the quantity of the heat recovered in the GGH heat recovery side 4 suffices for the heating, and the need for installation of the SGH is eliminated. Thus the heating efficiency can be improved (about 1%).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a thermal power plant system, and more particularly to a coal-fired boiler exhaust gas treatment system having excellent energy efficiency.

[0002]

BACKGROUND OF THE INVENTION Coal-fired power plant boiler, nitrogen oxides in the combustion gas (NO, NO ₂ etc., the following N
Ox), dust and sulfur oxides (SO _2, SO
_A boiler exhaust gas treatment device is installed so as not to emit SOx (hereinafter referred to as SOx) into the atmosphere.

FIG. 8 shows a system flow of a current coal-fired thermal power plant. The exhaust gas discharged from the boiler 1 is configured to remove NOx by the denitration device 2, soot and dust by the electric dust collector (EP) 6, and SOx by the desulfurization device 7.
Gas / gas heaters (GGH) 4 and 5 are installed in a normal flue gas treatment system in order to improve dust collection efficiency and desulfurization performance and to heat detoxified exhaust gas to dry and release it to the atmosphere. The harmless exhaust gas is heated by the heat recovered to cool the exhaust gas.

FIG. 9 shows the structure of typical gas / gas heaters (hereinafter, GGH) 4 and 5 of the hot water circulation system. The GGH cooling side 4 exchanges boiler exhaust gas 15 having a temperature of usually 120 to 150 ° C. with hot water flowing in the heat transfer tube 10 and heats the boiler exhaust gas 15 at a temperature of 80 to 120 ° C.
The GGH reheating side 5 is a device that cools the exhaust gas 17 at a temperature of 100 to 130 ° C., and heats the hot water flowing in the heat transfer tube 10 to a temperature of 100 to 130 ° C. This is a device that heats to 80 to 100 ° C. to make a dried exhaust gas 18.

[0005]

The GGHs 4 and 5 are of a non-leak type in that the heat transfer tube 10 is a heat pipe in addition to the hot water circulation system. Harmless exhaust gas 18
Has the merit of maintaining the purity.

On the other hand, the flue gas of a coal-fired boiler contains more chlorides such as hydrogen chloride than a heavy oil-fired boiler, and the chlorine ions (C
l ^-) concentration is tens of thousands ppm from thousands. Most of the mist of the desulfurization absorbent in the gas discharged from the desulfurization device 7 is removed by the mist separator (demister) 8, but a part of the mist is scattered to the GGH reheating side 5. As shown in FIG. 9, high-temperature steam of 150 to 450 ° C. was passed through the heat transfer tube 10 on the inlet side of the normal reheating side GGH 5 in order to quickly and efficiently evaporate and dry the scattered mist. A steam gas heater (hereinafter, SGH) 12 (high-temperature steam inlet 13 and steam outlet 14) is used. This SGH1
The surface of No. 2 is under a condition in which the mist of the weakly acidic desulfurization absorbing liquid containing chlorine ions adheres and evaporates, which is a severe corrosive environment.

[0007] The surface temperature of SGH12 is often higher than 60 ° C, and SUS3 is used as a heat transfer tube material for SGH12.
When 18Cr8Ni-based austenitic stainless steel such as 16L is used, intragranular stress corrosion cracking (hereinafter, referred to as TGSCC) due to a chloride solution occurs, so that a Ni-based alloy called Hastelloy or Inconel or SUS329 is used.
It is necessary to use duplex stainless steel such as J4L. The cost of these materials is several times higher than that of 18Cr8Ni stainless steel, and is economically disadvantageous.

If the amount of scattered mist in the exhaust gas can be reduced to almost zero, the problem of corrosion due to the adhering mist disappears.
The mist collection rate of the mist separator 8 at present is 95% or more, which is more than ten times larger to further improve the mist separator 8 to eliminate the corrosion problem (99.9% or more). Mist separator 8 is necessary and not practical.

In a conventional plant, the mist separator 8 was constantly washed with a large amount of industrial water to reduce the concentration of chlorine ions in the mist scattered into the exhaust gas. Not a good thing.

Further, in the prior art SGH 12, the calorific value of steam generated in the boiler is used to evaporate the mist adhering to the heat transfer tube 10, thereby reducing the thermal efficiency of the boiler. This is also a problem from the viewpoint of the thermal efficiency of the power plant and, eventually, the amount of carbon dioxide emission that contributes to global warming, and the use of boiler steam should be reduced as much as possible.

An object of the present invention is to provide a technique for solving the problems of corrosion of GGH and SGH in a conventional coal-fired thermal power generation exhaust gas treatment system, material cost problems, and a decrease in the thermal efficiency of a boiler.

[0012]

The above objects can be attained by employing the following method. (1) The temperature of the exhaust gas exiting the desulfurization unit and entering the GGH reheating side is reduced to 40 ° C. or less. (2) In order to keep the temperature of the exhaust gas entering the GGH reheating side at 40 ° C. or lower, an exhaust gas cooler (cooler) is installed upstream of the exhaust gas. (3) In order to keep the temperature of the exhaust gas entering the GGH reheating side at 40 ° C. or lower, the mist separator installed upstream of the exhaust gas is provided with an exhaust gas cooling function. (4) An exhaust gas cooler (cooler) is installed in the desulfurization device to keep the temperature of the exhaust gas entering the GGH reheating side at 40 ° C. or less.

[0013]

A feature of the present invention is that the temperature of exhaust gas entering the reheating-side GGH is set to 40 ° C. or less. The temperature in the prior art is 50 to 60 ° C., but this temperature is determined by the amount of water in the boiler exhaust gas and the amount of water supplied to the desulfurization unit. It is in a temperature range of about 50-60 ° C., and the exhaust gas contains water at a saturated concentration at that temperature.

FIG. 10 is a curve of the saturated moisture concentration in the exhaust gas. Exhaust gas at 50-60 ° C. contains 10-16% moisture. On the GGH reheating side and SGH, it is necessary to heat the exhaust gas containing such moisture and evaporate the scattered mist, and the high temperature of 150 to 450 ° C. is applied to the GGH reheating side 5 described in the section of the related art. SGH12 through steam was used.

On the other hand, when the temperature of the exhaust gas entering the GGH reheating side is set to 40 ° C. or less, the saturated water concentration becomes 6% or less, and the water content in the exhaust gas is reduced by half compared to the prior art.
It can be reduced to 1/3. When the amount of water in the exhaust gas decreases and the temperature further decreases, the heating of the exhaust gas and the attached mist becomes easier, and the amount of heat recovered on the GGH heat recovery side can be covered, so that there is no need to install an SGH, The use of boiler steam can be stopped, which can contribute to improvement in thermal efficiency (about 1%).

On the other hand, in the present invention, since the temperature of the exhaust gas on the GGH reheating side and the temperature of the heat transfer tube surface can be reduced, the corrosion reaction rate of the constituent material of the heat transfer tube is reduced. In particular, when the surface temperature of the heat transfer tube is set to 60 ° C. or less, the above-described TGSCC of 18Cr8Ni-based austenitic stainless steel does not occur, so that general-purpose stainless steel such as SUS316L can be used, and material costs can be reduced.

Further, the rate of local corrosion such as general corrosion and pitting corrosion is significantly reduced due to the condition of a decrease in exhaust gas temperature and slight mist evaporation, so that carbon steel or Cr, Mo, Cu or the like of 1% or less may be removed depending on the condition. Low alloy steel (usually referred to as sulfuric acid dew point corrosion resistant steel or weather resistant steel) can be used, and the material cost of the equipment can be further reduced.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a flow of a coal-fired boiler flue gas treatment system according to one embodiment of the present invention. NOx in the exhaust gas discharged from the boiler 1 is removed by a denitration device 2, passes through a boiler combustion air preheater 3, and then is subjected to a gas / gas heater (in order to improve dust collection efficiency and desulfurization performance). GGH) 4. Dust in the cooled exhaust gas is removed by an electric dust collector (EP) 6 and SOx
Is removed by the desulfurizer 7. The exhaust gas after the desulfurization treatment removes the mist of the absorbing solution with the mist eliminator 8,
At the reheating side GGH 5, the gas is heated to a temperature that does not generate white smoke, and is discharged from the chimney 9 to the atmosphere.

The feature of the embodiment shown in FIG.
The exhaust gas cooler 19 is installed in the exhaust gas channel on the downstream side of
The gas temperature on the GH reheating side 5 can be cooled to 40 ° C. or less. The method and apparatus configuration of the exhaust gas cooling in the exhaust gas cooler 19 are not particularly limited, and a multi-tube heat exchanger or the like used in a general gas cooling apparatus may be used, and seawater or industrial water may be used as a cooling medium. Use

FIG. 2 shows a GGH according to an embodiment of the present invention.
4 and 5 show examples. The heat transfer tube 10 arranged on the heat recovery side GGH 4 is connected to the heat transfer tube 10 provided on the GGH reheating side 5 via a pump 11. In the apparatus shown in FIG. 2, the SGH 12 provided on the GGH reheating side 5 of the prior art shown in FIG. 9 is not provided.

The exhaust gas 15 at the inlet of the GGH heat recovery side at 120 to 150 ° C. is cooled at the GGH heat recovery side 4 and
The exhaust gas 16 at the outlet of the GGH heat recovery side at 0 ° C. is obtained. Also 2
Exhaust gas 20 at the GGH reheating side inlet at 5 to 40 ° C is GGH
It is heated on the reheating side 5 and becomes the exhaust gas 21 at the outlet of the GGH reheating side at 40 to 60 ° C.

In the embodiment of FIG. 2, since the temperature of the exhaust gas 20 at the inlet of the GGH reheating side 5 has dropped to 40 ° C. or less, the boiler 1 is used for evaporating the mist adhering to the heat transfer tube 10 and drying and heating the exhaust gas. Eliminates the need to use steam,
All can be heated by the amount of heat recovered on the GGH heat recovery side 4.

Further, the heat transfer tube 1 at the inlet of the GGH reheating side 5
0 surface temperature can be controlled to 60 ° C. or less, and as described above, generation of TGSCC of 18Cr8Ni-based austenitic stainless steel due to an aqueous solution containing chlorine ions (Cl ⁻ ) is eliminated, and drying is performed at a low temperature and early. Because it is possible, carbon steel or low alloy steel can be used.

FIG. 3 shows the flow of a coal-fired boiler flue gas treatment system according to another embodiment of the present invention. FIG.
1 is different from the example shown in FIG. 1 in that the mist separator 22 having the gas cooling function is connected to the desulfurizer 7 and the GGH.
It is installed in the exhaust gas channel between the reheating side 5. This device is intended to simultaneously perform cooling of exhaust gas and separation of mist. This method can reduce the number of devices as compared with the embodiment shown in FIG. 1, and is advantageous in terms of equipment cost and installation area.

FIG. 4 shows a multi-tube separator 23 among the mist separators 22 having the exhaust gas cooling function shown in FIG.
FIG. This is similar in shape to a condenser (condenser) of a power generation boiler, in which cooling water 26 such as seawater is passed through a pipe to cool exhaust gas outside the pipe, and condensed water 27 can be recovered. Therefore, the desulfurization outlet exhaust gas 24
Is cooled to become low-temperature exhaust gas 25.

In the mist separator 22 with the exhaust gas cooling function of the present embodiment, the mist separator function is provided, and in order to obtain a predetermined performance, the cooling pipes serving as the passages for the cooling water 26 are arranged in a staggered arrangement. The exhaust gas passage should collide with the cooling pipe as much as possible.

FIG. 5 is a structural diagram of a corrugated plate type separator 29 of the mist separator 22 having the exhaust gas cooling function shown in FIG. The plate of the corrugated separator 29 is hollowed out so that cooling water can pass therethrough. Since the cooling water flows vertically, the desulfurization outlet exhaust gas 24 is introduced from below, is cooled, and is discharged from above as low-temperature exhaust gas 25.

FIG. 6 also shows an example of the mist separator 22 having the exhaust gas cooling function shown in FIG. It is similar in shape to a Jungstrom-type air preheater (AH). The mist separator 30 is a rotary mist separator, and the mist separator 30 cooled by cooling gas (cooling gas inlet 31, cooling gas outlet 32) or cooling water is rotated, and exhaust gas (desulfurization outlet exhaust gas 24, low-temperature exhaust gas 25 ) To cool down.

In the embodiment shown in FIG. 7, an exhaust gas cooler 33 is installed on the exhaust gas outlet side in the absorption tower of the desulfurization unit 7. The feature of this embodiment is that the condensed water in the exhaust gas collected by the exhaust gas cooler 33 is used as it is as the water for the desulfurization absorption liquid, and in this embodiment, there is an advantage that the recovered water piping and the supply pump are not required. There is.

[0030]

According to the present invention, since it has the above-described configuration, the GGH is used in an exhaust gas treatment system for a coal-fired boiler.
The corrosiveness of the environment on the reheating side is reduced, so that inexpensive materials can be used, and at the same time, the use of steam for mist evaporation boiler is not required, which is advantageous in terms of economy and thermal efficiency.

[Brief description of the drawings]

FIG. 1 is a flow diagram of a coal-fired boiler exhaust gas treatment system and a structural diagram of an exhaust gas cooler according to an embodiment of the present invention.

FIG. 2 is a configuration diagram of GGH in the flow of the boiler exhaust gas treatment system of FIG.

FIG. 3 is a flow diagram of a coal-fired boiler exhaust gas treatment system and a structural diagram of an exhaust gas cooler according to an embodiment of the present invention.

4 is a configuration diagram of a mist eliminator (multi-tube separator) in the flow of the boiler exhaust gas treatment system of FIG.

FIG. 5 is a configuration diagram of a mist eliminator (corrugated plate type separator) in the flow of the boiler exhaust gas treatment system of FIG. 3;

6 is a configuration diagram of a mist eliminator in the flow of the boiler exhaust gas treatment system of FIG.

FIG. 7 is a flow diagram of a coal-fired boiler exhaust gas treatment system and a structural diagram of an exhaust gas cooler according to an embodiment of the present invention.

FIG. 8 is a flow and structure diagram of an exhaust gas treatment system according to the related art.

9 is a configuration diagram of GGH in the flow of the boiler exhaust gas treatment system of FIG.

FIG. 10 is a diagram showing the relationship between the concentration of saturated moisture in exhaust gas and temperature.

[Explanation of symbols]

Reference Signs List 1 boiler 2 denitration device 3 preheater 4 gas / gas heater GGH (heat recovery side) 5 gas / gas heater GGH (reheating side) 6 electric dust collector (EP) 7 desulfurizer 8 mist separator (demister) 9 chimney 10 GGH heat transfer tube 11 Pump 12 Steam gas heater (SGH) 13 High-temperature steam inlet (150-450 ° C) 14 Steam outlet (100-300 ° C) 15 GGH heat recovery side inlet exhaust gas (120-150 ° C)
16 GGH heat recovery side outlet exhaust gas (80 to 120 ° C) 17 GGH reheating side inlet exhaust gas (50 to 60 ° C) 18 GGH reheating side outlet exhaust gas (80 to 100 ° C) 19 Exhaust gas cooler 20 GGH reheating side inlet Exhaust gas (25 to 40 ° C.) 21 GGH reheating side exit exhaust gas (40 to 60 ° C.) 22 Mist separator with exhaust gas cooling function 23 Multi-tubular mist separator with exhaust gas cooling function 24 Desulfurization outlet exhaust gas 25 Low temperature exhaust gas 26 Cooling Water (seawater, etc.) inlet 27 Condensed water 29 Corrugated mist separator with exhaust gas cooling function (double inner surface cooling type) 30 Rotary mist separator with exhaust gas cooling function 31 Cooling gas inlet 32 Cooling gas outlet 33 Desulfurization absorption tower Exhaust gas cooler installed inside

Claims (4)

[Claims] 1. A method for treating a boiler exhaust gas having a reheating gas / gas heater for reheating the exhaust gas after absorbing and removing sulfur oxides in the exhaust gas discharged from the boiler, comprising the steps of: A method for treating boiler exhaust gas, wherein the temperature of the exhaust gas at the inlet of the gas heater is set to 40 ° C. or lower. 2. An exhaust gas treatment system comprising a desulfurization device for absorbing and removing sulfur oxides in the exhaust gas in a flow path of the exhaust gas discharged from the boiler, and a reheating-side gas / gas heater for reheating the desulfurized exhaust gas. An apparatus for treating boiler exhaust gas, wherein a cooling device for cooling the exhaust gas temperature in the exhaust gas channel to 40 ° C. or lower is provided in the exhaust gas channel on the inlet side of the reheating gas / gas heater. 3. The boiler exhaust gas treatment device according to claim 2, wherein a mist separator having an exhaust gas cooling function is provided in an exhaust gas passage on the reheating side gas / gas heater inlet side as a cooling device. 4. The boiler exhaust gas treatment device according to claim 2, wherein an exhaust gas cooler is provided in the desulfurization device as a cooling device.