CA1043693A - Process for treating flue gas from furnace - Google Patents
Process for treating flue gas from furnaceInfo
- Publication number
- CA1043693A CA1043693A CA208,349A CA208349A CA1043693A CA 1043693 A CA1043693 A CA 1043693A CA 208349 A CA208349 A CA 208349A CA 1043693 A CA1043693 A CA 1043693A
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- flue gas
- water vapor
- cooling
- cooling water
- vapor content
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Abstract
PROCESS FOR TREATING FLUE
GAS FROM FURNACE
ABSTRACT OF THE DISCLOSURE
When a flue gas from furnace, especially an incinerator is discharged to atmosphere after wet scrubbing, the flue gas having a high water vapor content, for example 30% by volume of water vapor or more, resulting from the scrubbing, is contacted with a large amount of cooling water, thereby cooling the flue gas down to a lower temperature, nearly the atmospheric air temperature, thereby bringing the water vapor content in the flue gas to the corresponding saturation con-dition and then the flue gas is discharged to the atmosphere. Then, the dehumidified flue gas is heated, if the heating is necessary according to the cooling temperature or climatic conditions. Cooling water running through a dehumidification is preferably cooled through contact with the atmospheric air and recycled.
Generation of white smoke from the flue gas can be prevented thereby, and also dusts can be caught from the flue gas. Furthermore, heating can be omitted before discharging the flue gas to the atmosphere, or fuel consumption can be largely reduced, even if the heating is carried out.
GAS FROM FURNACE
ABSTRACT OF THE DISCLOSURE
When a flue gas from furnace, especially an incinerator is discharged to atmosphere after wet scrubbing, the flue gas having a high water vapor content, for example 30% by volume of water vapor or more, resulting from the scrubbing, is contacted with a large amount of cooling water, thereby cooling the flue gas down to a lower temperature, nearly the atmospheric air temperature, thereby bringing the water vapor content in the flue gas to the corresponding saturation con-dition and then the flue gas is discharged to the atmosphere. Then, the dehumidified flue gas is heated, if the heating is necessary according to the cooling temperature or climatic conditions. Cooling water running through a dehumidification is preferably cooled through contact with the atmospheric air and recycled.
Generation of white smoke from the flue gas can be prevented thereby, and also dusts can be caught from the flue gas. Furthermore, heating can be omitted before discharging the flue gas to the atmosphere, or fuel consumption can be largely reduced, even if the heating is carried out.
Description
This invention relates to an improved process for treating a flue gas from a furnace, particularly an incinerator, and more particularly to a process for making the flue gas harmless before discharging the flue gas to the atmosphere.
A flue gas from a furnace, for example, incinerator, is precooled in a waste heat boiler or other cooling means, then scrubbed with water or an aqueous alkaline solution, thereby eliminating harmful materials contained in the flue gas, and discharged ~ -to the atmosphere according to the conventional art~
The flue gas discharged to the atmosphere after said wet scrubbing is usually at a considerably higher temperature than the atmospheric air temperature ~herein-after also referred to as "ambient temperature") and saturated with water vapor, though such depends upon a temperature of flue gas or climatic conditions, and the water vapor contained in the flue gas is condensed upon its contact with the atmospheric air. Especially when a flue gas having a higher water vapor content is discharged at a higher temperature, the flue gas is discharged to the atmosphere as much more white smoke.
Furthermore, the remaining dusts contained in the flue gas are humidified by water vapor and water droplets formed by the condensation, and scattered as wet dusts at that time.
From the standpoint of abating these harmful effluents to a minimum, it has been so far keenly desired to prevent generation of white smoke due to flue gas.
When the flue gas to be treated is in relatively -;.
11)43t~
small amount, and also has a low watervapor content, the white smoke of flue gas can be prevented by heat-ing the flue gas with a fuel such as kerosene or town gas, thereby heating the flue gas into an unsaturated state. The flue gas thus treated is then discharged -to the atmosphere. However, when the flue gas to be treated is in a large volume, and also has a high water vapor content, an equipment necessary for`the heating will be very large, and much fuel expense will be required. Furthermore, there will appear a genera-~ ~ .
tion of harmful gas due to combustion of the fuel for the heating, and therefore it is desirable to dis-charge the flue gas to the atmosphere, if possible, without any heating.
An object of the present invention is to prevent any generation of white smoke due to flue gas.
Another object of the present invention is to eliminate any hazard due to wet dusts accompanying the generation of the white smoke.
Other object of the present invention is to ~
. , .
provide a process for saving a fuel required for heat-ing.
Further object of the present invention is to provide a process for commercially advantageously making harmless a flue gas from a furnace.
The present inventors have found that it is very difficult to reduce white smoke and dusts con-tained in the white smoke when a large volume of a flue gas from a large incinerator is treated according -to the conventional process for preventing generation ~
: .
, : -.
. .
~ - 2 -10~3~;g3 1 of white smoke by direct:Ly heating the flue gas having a high water vapor content just after wet scrubbing.
As a result of studies and researches, the present inventors have further found that most of water vapor in the flue gas is condensed by directly contacting the flue gas coming from the wet scrubbing with cooling water, thereby cooling the flue gas to a lower tempera-ture near the ambient temperature~ thereby bringing the water vapor content in the flue gas to the correspond-ing saturation condition such as to make the watervapor content of the flue gas25~ by volume or less, and so long as the water vapor content of unit volume of the flue gas is reduced, any successive heating will not be required~ or even if required, the heating can be carried out with a very small amount of fuel, and that as a result prevention of white smoke and reduction in the amount of dusts discharged together with the flue gas can be attained at the same time thereby.
According to the present invention, a process for treating a flue gas from a furnace comprises pre-cooling a hot flue gas from a furnace, wet-scrubbing the flue gas, contacting the flue gas having a high water vapor content with cooling water, thereby cooling the flue gas to a lower temperature thereby bringing the water vapor content in the flue gas to the corres-ponding saturation condition, and discharging the flue gas to the atmosphere, if necessary, after heating.
Now~ the present invention will be described, by way of the accompanying drawings.
.. .. . . , . . . . -- . . .
:' .' : : ! ' .~ . :: -1 ~ 3U~ 3 l Figure l is a diagram showing a principle of the present invention.
Figure 2 is a flow diagram showing one embodiment of the present invention~ based on said 5 principle of the present invention shown in Figure 1. ~
In Figure l, a correlation is shown between ~-temperature and water vapor content until a combustion flue gas from a furnace is discharged to the atmosphere, where the abscissa shows a water vapor content, and the ordinate shows a temperature. Line y in the diagram is a water vapor saturation curve of flue gas, and line w is a boundary curve indicating a possible generation of visible white smoke when a flue gas ;
is discharged to the atmosphere at an ambient tempera-ture of 20C and a relative humidity of 70%. The line w is drawn as a tangent to the saturation curve y at a point g corresponding to the temperature and rela-tive humidity conditions of the atmosphere. A combus-tion flue gas from the furnace approximately at a point a (temperature 800C~ water vapor content lO~
by volume) is directly contacted with water in a cooling unit~ in which water is sprayed, and cooled. The water vapor content of the flue gas is increased thereby, and~the flue gas arrives approximately at a point (temperature 300C, water vapor content 34%
by volume) at the outlet of the cooling unit. Further~
the flue gas is cooled down to approximately a boiling point of washing water, then washed with a scrubbing -solution~ depending upon the kinds of components con-tained in the fIue gas, usually water or an aqueous -- It -- -.~
:
,.;.,.,, .~. : . .: . ; . . . .
10~69~
1 alkaline solution in a wet scrubbing and arrives approximately at a point c on the water saturation curve ~ (temperature 77.5C, water vapor content 42 by volume). When the flue gas in such a state is discharged to the atmosphere as such~ white smoke is generated, and such a flue gas is heated to elevate its temperature approximately to a point e (tempera-ture 360C, water vapor content 42% by volume) on the line w, and then discharged to the atmosphere accord-ing to the conventional process. That is~ a fuelcorresponding to a segment of line c ~ e is required, but in the present invention said flue gas is directly contacted with cooling water, thereby cooling the flue gas approximately to a point d (temperature 45C, water vapor content 10% by volume) on the water vapor saturation curve ~, which is preferably as near the ambient temperature as possible. Therefore, in the present invention~ only a heating corresponding to a segment of line d f drawn to a point f (temperature 60~ water vapor content 10% by volume) on the boundary curve w is requlred for preventing the white smoke when the flue gas is discharged after the cooling. As is apparent from Figure 1, especially from comparison of the length of the segement c -~ e when the flue gas is heated as such to the length of the segment d ~ f when the flue gas is cooled down to the point d and then heated, as well as reduction in water vapor volume, that is, reduction in height c -~ d in the present invention it is seen that the present invention has a remarkable effect upon saving of a fuel.
.: , .. - ' .. ' . '' :~09~;~693 1 Furthermore, in most cases~ the heating corresponding to the segment d -~ f is not substantial]y required by cooling the flue gas down as nearly to the ambient temperature as possible, or depending upon climatic conditions. Furthermore, an amount of catching the entrained dusts is considerabl~ increased by said direct cooling with cooling water and resulting condensation of water vapor contained in the flue gas.
The present invention is based on the fore- -going principle~ and one embodiment of the present invention will be described by way of Figure 2. - ~ -A hot flue gas discharged from a furnace 1 is cooled in a water spray tower 2, further cooled to a temperature almost equal to a boiling point of a quenching solution in a quenching chamber 4 provided ~ ,.
at an upstream side to a wet scrubbing tower 3, and sent to the wet scrubbing tower 3, wherein harmful gas components and dust are removed from the flue gas.
The scrubbing solution used is water or an aqueous :` .
alkaIine solution~ which is identical with those usually used in scrubbing towers.
Effluent flue gas leaving the scrubbing tower is sent to a heating unit 5 according to the conven- ;
tional process, but in~the present invention the effluent gas is sent to a dehumidifying tower 6 from ~the scrubbing tower 3~ and the flue gas is dehumidified through contact with cooling water in thè dehumidifying tower 6. The dehumidified flue gas is discharged directly to the atmosphere fram a stack (not shown in the drawing), or if necessary treated in the heating - G -:
j, ~
iO43~93 1 unit 5~ and then discharged to the atmosphere from a stack (not shown in the drawing).
In the dehumidifying tower 6 of the present invention, the flue gas is cooled to a lower temperature as near the ambient temperature as possible, preferably a temperature having a temperature difference of not more than 25C from the ambient temperature, thereby bringing the water vapor content in the flue gas to the correspond-ing saturation condition. In that case, it will be sometimes necessary to heat the flue gas before dls-charging it to the atmosphere, depending upon climatic conditions, for example, a low ambient temperature and high humidity. However, when the flue gas is cooled down to a temperature having a temperature difference 1~ of not more than 10C from the ambient temperature~
the heating is not substantially required. In the dehumidifying tower, a ratio of cooling water to flue gas can be freely selected in a range of 0.31 or more /m3 It is advantageous to use cooling water used in the dehumidifying tower of the present invention by cooling the cooling water leaving the dehumidifying tower by a cooler 7 utilizing air, such as an air cooler or cooling tower~ and returning the cooled cooling water to the dehumidifying tower as a recycle.
Sometimes~ other cooling means~ for example, cooling means using sea water or other cooling media can be used. When the cooling water is cooled by an indirect heat exchanger such as an air cooler, there is no loss of water due to spontaneous evaporation, and thus the 1043~93 1 volume of cooling water is gradually increased by the condensation of water vapor contained in the flue gas.
Thus, the increment must be withdrawn and used as cooling water for the water spray tower 2 or the quenching chamber 4, or make-up water for the wet scrubbing tower 3, whereby a water balance can be advan-tageously maintained.
The heretofore well known wet scrubbing tower can be used in the present invention, but since the flue gas to be treated is a flue gas resulting from burning of domestic wastes, waste plastics, fuel oil, and other industry wastes, the flue gas is liable to contain much harmful gas components as well as much dusts~ and therefore a gas-liquid contact part of the wet scrubbing tower is preferably of such a type that has a good gas-liquid contact efficiency and a less occurrence of clogging, for example, preferably a tray consisting of entirely tiltable tray elements as ; disclosed in Japanese Patent Pub7ication No. 44429/72 20 ~or Japanese Patent Publication No. 3749/73. In the gas-liquid contactor, a high gas-liquid contact effici-ency can be obtained only with a few trays and there is no fear of cloggings due to the deposition of dusts or formed salts.
At the upstream side of the wet scrubbing tower~ a quenching unit such as venturi scrubber and wetted wall tower is usually installed, and the flue gas is brought into contact with the quènching solution, and cooled therein. By the quenching unit, the scrubbing efficiency is also increased at the same time.
,.. .. ... . . . . . . .
.: .. .. . .. ., . ., ~ . .. , ... , ,,, .. I ,~
1043$,93 1 As the successive dehumidifying apparatus, a dehumidifying tower, wetted-wall tower, packed tower~
water spray tower, etc. containing hurdles within the tower can be used. A compact unit containing the humidifying apparatus and said scrubbing tower in one common shell can be advantageously utilized in the flue gas treatment of the present invention.
The heating which is practised, if necessary, in the present invention, is carried out by burning kerosene or town gas or heat exchanging the flue gas with steam, hot process gas or other heat source.
According to the present invention~ the flue gas from a furnace is purified by the precooling ;~
and wet scrubbing, and further subjected to condensa-lS tion in the dehumidifying tower~ and then discharged to the atmosphere. Therefore, the water vapor content of the final flue gas is so small that there is a very little possibility of generation of white smoke.
Therefore, a fuel required for heating, which is practised if necessary~ can be greatly saved, as compared with the conventional process. The cooling water used in the dehumidifying tower is cooled through contact with atmospheric air, and the expense for the cooling is so small that it is easy to install a furnace at an inconvenient, distant site. The con-densation of water vapor in the dehumidifying tower is effective upon considerable increase in the amount of the caught dusts.
The present process is most suitable to a flue gas from a furnace, especially incinerator, but ... . ... . . .. . . .
1(J43~93 is also applicable to treatment of a flue gas having a high water vapor content of 30% by volume or more and containing dusts, such as a flue gas from a fuel oil-fired boiler, etc.
Now, the present invention will be explained in detail, referring to examples.
Example 1 A flue gas at abou~ 800C evolved from an incinerator for burning domestic wastes was cooled down to about 300C in a water spray tower by 0.5 m3/hr of water, led to a quenching unit provided at an up-stream side of a wet scrubber, and further cooled down to 90C by quenching solution. Then, the flue gas was led to the wet scrubber and scrubbed with 10 m3/hr of an aqueous 8 wt.% caustic soda solution.
About 8,650 Nm3/hr (wherein "N" designates "normal state", i.e. an atmospheric pressure of 760mm H~
[1 atm (absolute)] and a temperature of 0C) of the flue gas (water vapor content 48% by volume) at 81C leaving the wet scrubber was led to a cooling water spray tower, through gas (water vapor content 7.5% by volume) was reduced to 4,860 Nm3/hr.
The flue gas was then discharged to the -atmosphere at an ambient temperature of 25C and rela-tive humidity of 70%, but no visible white smoke was observed. On the other hand, the water leaving the cooling water spray tower was at 42C, and thus was sent to a cooling tower, cooled and reused.
. . . ~, . .. -~. , ,- . ............... . , -- .: - . . ~ : ~ - - . . .
1 Example 2 ~043uj93 The flue gas leaving the wet scrubber under the same conditions and at the same flow rate as in Example 1 was cooled down to 63C in a cooling water spray tower through which 97 m3/hr of water at 28C
was circulated~ whereby the flow rate of flue gas (water vapor content 22% by volume) was reduced to about 5,770 Nm3/hr. When the effluent flue gas was discharged to the atmosphere from a stack without burning in an after-burnin~ unit, a slight visible white smoke was observed. ~hus, the flue gas was heated to 130C in the after-burning unit, it was discharged to the atmosphere from the stack. No white smoke was observed. Kerosene required for the 1~ heating amounted to only 20 ~/hr.
For comparison~ when the flue gas leaving said wet scrubber was heated directly without cooling, a heating temperature necessary for putting out the visible white smoke was as high as 400C, and the kerosene required for the heating amounted to 127 l/hr.
Example 3 A flue gas discharged at about 800C from an incinerator was cooled down to about 280C in a water spray tower by 5 m3/hr of water, further cooled to 90C in a quenching unit provided at an upstream side of a wet scrubber in counter current contact with 10 m3/hr of water, and scrubbed in the wet scrubber with 36 m3/hr of an aqueous 10 wt.% caustic soda solu-tion. When about 80~000 Nm3/hr (water vapor content ..... . .... . . .. . . . . ~ , ., . ~ ., 1 47% by volume~ dust content 0.073 g/Nm3) of flue gas discharged at 80C from the wet scrubber was dis-charged to the atmosphere at an ambient temperature -of 20C and a relative humidity of 60%~ a white smoke as high as about 20 m was observed. Thus, the flue gas was cooled down to 28C in a cooling water spray tower through which 1,180 m3/hr of water was circulated at 24C, whereby the flow rate of the flue gas (water vapor content 3.7% by volume, dust content 0.027 g/Nm3) was reduced to about 43,300 Nm3/hr. When the resulting flue gas was discharged as such from a stack, no visible white smoke was observed at all.
The cooling water leaving the cooling water spray tower was cooled by an air cooler to 24C from 40C in this Example.
Since the amount of the cooling water cir-culating the cooling water spray tower was increased by condensation of water vapor in the flue gas, the increment of water was supplied to the preceding precooling and quenching units, and the remaining water was utilized in wetting incineration askes or other uses.
~ , . ~ ,, , ~ ... . .
A flue gas from a furnace, for example, incinerator, is precooled in a waste heat boiler or other cooling means, then scrubbed with water or an aqueous alkaline solution, thereby eliminating harmful materials contained in the flue gas, and discharged ~ -to the atmosphere according to the conventional art~
The flue gas discharged to the atmosphere after said wet scrubbing is usually at a considerably higher temperature than the atmospheric air temperature ~herein-after also referred to as "ambient temperature") and saturated with water vapor, though such depends upon a temperature of flue gas or climatic conditions, and the water vapor contained in the flue gas is condensed upon its contact with the atmospheric air. Especially when a flue gas having a higher water vapor content is discharged at a higher temperature, the flue gas is discharged to the atmosphere as much more white smoke.
Furthermore, the remaining dusts contained in the flue gas are humidified by water vapor and water droplets formed by the condensation, and scattered as wet dusts at that time.
From the standpoint of abating these harmful effluents to a minimum, it has been so far keenly desired to prevent generation of white smoke due to flue gas.
When the flue gas to be treated is in relatively -;.
11)43t~
small amount, and also has a low watervapor content, the white smoke of flue gas can be prevented by heat-ing the flue gas with a fuel such as kerosene or town gas, thereby heating the flue gas into an unsaturated state. The flue gas thus treated is then discharged -to the atmosphere. However, when the flue gas to be treated is in a large volume, and also has a high water vapor content, an equipment necessary for`the heating will be very large, and much fuel expense will be required. Furthermore, there will appear a genera-~ ~ .
tion of harmful gas due to combustion of the fuel for the heating, and therefore it is desirable to dis-charge the flue gas to the atmosphere, if possible, without any heating.
An object of the present invention is to prevent any generation of white smoke due to flue gas.
Another object of the present invention is to eliminate any hazard due to wet dusts accompanying the generation of the white smoke.
Other object of the present invention is to ~
. , .
provide a process for saving a fuel required for heat-ing.
Further object of the present invention is to provide a process for commercially advantageously making harmless a flue gas from a furnace.
The present inventors have found that it is very difficult to reduce white smoke and dusts con-tained in the white smoke when a large volume of a flue gas from a large incinerator is treated according -to the conventional process for preventing generation ~
: .
, : -.
. .
~ - 2 -10~3~;g3 1 of white smoke by direct:Ly heating the flue gas having a high water vapor content just after wet scrubbing.
As a result of studies and researches, the present inventors have further found that most of water vapor in the flue gas is condensed by directly contacting the flue gas coming from the wet scrubbing with cooling water, thereby cooling the flue gas to a lower tempera-ture near the ambient temperature~ thereby bringing the water vapor content in the flue gas to the correspond-ing saturation condition such as to make the watervapor content of the flue gas25~ by volume or less, and so long as the water vapor content of unit volume of the flue gas is reduced, any successive heating will not be required~ or even if required, the heating can be carried out with a very small amount of fuel, and that as a result prevention of white smoke and reduction in the amount of dusts discharged together with the flue gas can be attained at the same time thereby.
According to the present invention, a process for treating a flue gas from a furnace comprises pre-cooling a hot flue gas from a furnace, wet-scrubbing the flue gas, contacting the flue gas having a high water vapor content with cooling water, thereby cooling the flue gas to a lower temperature thereby bringing the water vapor content in the flue gas to the corres-ponding saturation condition, and discharging the flue gas to the atmosphere, if necessary, after heating.
Now~ the present invention will be described, by way of the accompanying drawings.
.. .. . . , . . . . -- . . .
:' .' : : ! ' .~ . :: -1 ~ 3U~ 3 l Figure l is a diagram showing a principle of the present invention.
Figure 2 is a flow diagram showing one embodiment of the present invention~ based on said 5 principle of the present invention shown in Figure 1. ~
In Figure l, a correlation is shown between ~-temperature and water vapor content until a combustion flue gas from a furnace is discharged to the atmosphere, where the abscissa shows a water vapor content, and the ordinate shows a temperature. Line y in the diagram is a water vapor saturation curve of flue gas, and line w is a boundary curve indicating a possible generation of visible white smoke when a flue gas ;
is discharged to the atmosphere at an ambient tempera-ture of 20C and a relative humidity of 70%. The line w is drawn as a tangent to the saturation curve y at a point g corresponding to the temperature and rela-tive humidity conditions of the atmosphere. A combus-tion flue gas from the furnace approximately at a point a (temperature 800C~ water vapor content lO~
by volume) is directly contacted with water in a cooling unit~ in which water is sprayed, and cooled. The water vapor content of the flue gas is increased thereby, and~the flue gas arrives approximately at a point (temperature 300C, water vapor content 34%
by volume) at the outlet of the cooling unit. Further~
the flue gas is cooled down to approximately a boiling point of washing water, then washed with a scrubbing -solution~ depending upon the kinds of components con-tained in the fIue gas, usually water or an aqueous -- It -- -.~
:
,.;.,.,, .~. : . .: . ; . . . .
10~69~
1 alkaline solution in a wet scrubbing and arrives approximately at a point c on the water saturation curve ~ (temperature 77.5C, water vapor content 42 by volume). When the flue gas in such a state is discharged to the atmosphere as such~ white smoke is generated, and such a flue gas is heated to elevate its temperature approximately to a point e (tempera-ture 360C, water vapor content 42% by volume) on the line w, and then discharged to the atmosphere accord-ing to the conventional process. That is~ a fuelcorresponding to a segment of line c ~ e is required, but in the present invention said flue gas is directly contacted with cooling water, thereby cooling the flue gas approximately to a point d (temperature 45C, water vapor content 10% by volume) on the water vapor saturation curve ~, which is preferably as near the ambient temperature as possible. Therefore, in the present invention~ only a heating corresponding to a segment of line d f drawn to a point f (temperature 60~ water vapor content 10% by volume) on the boundary curve w is requlred for preventing the white smoke when the flue gas is discharged after the cooling. As is apparent from Figure 1, especially from comparison of the length of the segement c -~ e when the flue gas is heated as such to the length of the segment d ~ f when the flue gas is cooled down to the point d and then heated, as well as reduction in water vapor volume, that is, reduction in height c -~ d in the present invention it is seen that the present invention has a remarkable effect upon saving of a fuel.
.: , .. - ' .. ' . '' :~09~;~693 1 Furthermore, in most cases~ the heating corresponding to the segment d -~ f is not substantial]y required by cooling the flue gas down as nearly to the ambient temperature as possible, or depending upon climatic conditions. Furthermore, an amount of catching the entrained dusts is considerabl~ increased by said direct cooling with cooling water and resulting condensation of water vapor contained in the flue gas.
The present invention is based on the fore- -going principle~ and one embodiment of the present invention will be described by way of Figure 2. - ~ -A hot flue gas discharged from a furnace 1 is cooled in a water spray tower 2, further cooled to a temperature almost equal to a boiling point of a quenching solution in a quenching chamber 4 provided ~ ,.
at an upstream side to a wet scrubbing tower 3, and sent to the wet scrubbing tower 3, wherein harmful gas components and dust are removed from the flue gas.
The scrubbing solution used is water or an aqueous :` .
alkaIine solution~ which is identical with those usually used in scrubbing towers.
Effluent flue gas leaving the scrubbing tower is sent to a heating unit 5 according to the conven- ;
tional process, but in~the present invention the effluent gas is sent to a dehumidifying tower 6 from ~the scrubbing tower 3~ and the flue gas is dehumidified through contact with cooling water in thè dehumidifying tower 6. The dehumidified flue gas is discharged directly to the atmosphere fram a stack (not shown in the drawing), or if necessary treated in the heating - G -:
j, ~
iO43~93 1 unit 5~ and then discharged to the atmosphere from a stack (not shown in the drawing).
In the dehumidifying tower 6 of the present invention, the flue gas is cooled to a lower temperature as near the ambient temperature as possible, preferably a temperature having a temperature difference of not more than 25C from the ambient temperature, thereby bringing the water vapor content in the flue gas to the correspond-ing saturation condition. In that case, it will be sometimes necessary to heat the flue gas before dls-charging it to the atmosphere, depending upon climatic conditions, for example, a low ambient temperature and high humidity. However, when the flue gas is cooled down to a temperature having a temperature difference 1~ of not more than 10C from the ambient temperature~
the heating is not substantially required. In the dehumidifying tower, a ratio of cooling water to flue gas can be freely selected in a range of 0.31 or more /m3 It is advantageous to use cooling water used in the dehumidifying tower of the present invention by cooling the cooling water leaving the dehumidifying tower by a cooler 7 utilizing air, such as an air cooler or cooling tower~ and returning the cooled cooling water to the dehumidifying tower as a recycle.
Sometimes~ other cooling means~ for example, cooling means using sea water or other cooling media can be used. When the cooling water is cooled by an indirect heat exchanger such as an air cooler, there is no loss of water due to spontaneous evaporation, and thus the 1043~93 1 volume of cooling water is gradually increased by the condensation of water vapor contained in the flue gas.
Thus, the increment must be withdrawn and used as cooling water for the water spray tower 2 or the quenching chamber 4, or make-up water for the wet scrubbing tower 3, whereby a water balance can be advan-tageously maintained.
The heretofore well known wet scrubbing tower can be used in the present invention, but since the flue gas to be treated is a flue gas resulting from burning of domestic wastes, waste plastics, fuel oil, and other industry wastes, the flue gas is liable to contain much harmful gas components as well as much dusts~ and therefore a gas-liquid contact part of the wet scrubbing tower is preferably of such a type that has a good gas-liquid contact efficiency and a less occurrence of clogging, for example, preferably a tray consisting of entirely tiltable tray elements as ; disclosed in Japanese Patent Pub7ication No. 44429/72 20 ~or Japanese Patent Publication No. 3749/73. In the gas-liquid contactor, a high gas-liquid contact effici-ency can be obtained only with a few trays and there is no fear of cloggings due to the deposition of dusts or formed salts.
At the upstream side of the wet scrubbing tower~ a quenching unit such as venturi scrubber and wetted wall tower is usually installed, and the flue gas is brought into contact with the quènching solution, and cooled therein. By the quenching unit, the scrubbing efficiency is also increased at the same time.
,.. .. ... . . . . . . .
.: .. .. . .. ., . ., ~ . .. , ... , ,,, .. I ,~
1043$,93 1 As the successive dehumidifying apparatus, a dehumidifying tower, wetted-wall tower, packed tower~
water spray tower, etc. containing hurdles within the tower can be used. A compact unit containing the humidifying apparatus and said scrubbing tower in one common shell can be advantageously utilized in the flue gas treatment of the present invention.
The heating which is practised, if necessary, in the present invention, is carried out by burning kerosene or town gas or heat exchanging the flue gas with steam, hot process gas or other heat source.
According to the present invention~ the flue gas from a furnace is purified by the precooling ;~
and wet scrubbing, and further subjected to condensa-lS tion in the dehumidifying tower~ and then discharged to the atmosphere. Therefore, the water vapor content of the final flue gas is so small that there is a very little possibility of generation of white smoke.
Therefore, a fuel required for heating, which is practised if necessary~ can be greatly saved, as compared with the conventional process. The cooling water used in the dehumidifying tower is cooled through contact with atmospheric air, and the expense for the cooling is so small that it is easy to install a furnace at an inconvenient, distant site. The con-densation of water vapor in the dehumidifying tower is effective upon considerable increase in the amount of the caught dusts.
The present process is most suitable to a flue gas from a furnace, especially incinerator, but ... . ... . . .. . . .
1(J43~93 is also applicable to treatment of a flue gas having a high water vapor content of 30% by volume or more and containing dusts, such as a flue gas from a fuel oil-fired boiler, etc.
Now, the present invention will be explained in detail, referring to examples.
Example 1 A flue gas at abou~ 800C evolved from an incinerator for burning domestic wastes was cooled down to about 300C in a water spray tower by 0.5 m3/hr of water, led to a quenching unit provided at an up-stream side of a wet scrubber, and further cooled down to 90C by quenching solution. Then, the flue gas was led to the wet scrubber and scrubbed with 10 m3/hr of an aqueous 8 wt.% caustic soda solution.
About 8,650 Nm3/hr (wherein "N" designates "normal state", i.e. an atmospheric pressure of 760mm H~
[1 atm (absolute)] and a temperature of 0C) of the flue gas (water vapor content 48% by volume) at 81C leaving the wet scrubber was led to a cooling water spray tower, through gas (water vapor content 7.5% by volume) was reduced to 4,860 Nm3/hr.
The flue gas was then discharged to the -atmosphere at an ambient temperature of 25C and rela-tive humidity of 70%, but no visible white smoke was observed. On the other hand, the water leaving the cooling water spray tower was at 42C, and thus was sent to a cooling tower, cooled and reused.
. . . ~, . .. -~. , ,- . ............... . , -- .: - . . ~ : ~ - - . . .
1 Example 2 ~043uj93 The flue gas leaving the wet scrubber under the same conditions and at the same flow rate as in Example 1 was cooled down to 63C in a cooling water spray tower through which 97 m3/hr of water at 28C
was circulated~ whereby the flow rate of flue gas (water vapor content 22% by volume) was reduced to about 5,770 Nm3/hr. When the effluent flue gas was discharged to the atmosphere from a stack without burning in an after-burnin~ unit, a slight visible white smoke was observed. ~hus, the flue gas was heated to 130C in the after-burning unit, it was discharged to the atmosphere from the stack. No white smoke was observed. Kerosene required for the 1~ heating amounted to only 20 ~/hr.
For comparison~ when the flue gas leaving said wet scrubber was heated directly without cooling, a heating temperature necessary for putting out the visible white smoke was as high as 400C, and the kerosene required for the heating amounted to 127 l/hr.
Example 3 A flue gas discharged at about 800C from an incinerator was cooled down to about 280C in a water spray tower by 5 m3/hr of water, further cooled to 90C in a quenching unit provided at an upstream side of a wet scrubber in counter current contact with 10 m3/hr of water, and scrubbed in the wet scrubber with 36 m3/hr of an aqueous 10 wt.% caustic soda solu-tion. When about 80~000 Nm3/hr (water vapor content ..... . .... . . .. . . . . ~ , ., . ~ ., 1 47% by volume~ dust content 0.073 g/Nm3) of flue gas discharged at 80C from the wet scrubber was dis-charged to the atmosphere at an ambient temperature -of 20C and a relative humidity of 60%~ a white smoke as high as about 20 m was observed. Thus, the flue gas was cooled down to 28C in a cooling water spray tower through which 1,180 m3/hr of water was circulated at 24C, whereby the flow rate of the flue gas (water vapor content 3.7% by volume, dust content 0.027 g/Nm3) was reduced to about 43,300 Nm3/hr. When the resulting flue gas was discharged as such from a stack, no visible white smoke was observed at all.
The cooling water leaving the cooling water spray tower was cooled by an air cooler to 24C from 40C in this Example.
Since the amount of the cooling water cir-culating the cooling water spray tower was increased by condensation of water vapor in the flue gas, the increment of water was supplied to the preceding precooling and quenching units, and the remaining water was utilized in wetting incineration askes or other uses.
~ , . ~ ,, , ~ ... . .
Claims (10)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A process for treating a flue gas from a furnace, which comprises precooling a hot flue gas from a furnace, wet scrub-bing the flue gas, contacting the resulting flue gas having a high water vapor content with cooling water, thereby cooling the flue gas down to a lower temperature while dehumidifying the flue gas, thereby bringing the water vapor content in the flue gas to the corresponding saturation condition, and discharging the flue gas to atmosphere.
2. A process according to Claim 1, wherein the gas to be treated is a flue gas from an incinerator.
3. A process according to Claim 1, wherein the flue gas having a high water vapor content after the wet scrubbing is cooled to a temperature differing by not more than 25°C from the atmospheric air temperature in the contact of the cooling water.
4. A process according to Claim 1, wherein the cooling water after the contact with the flue gas having a high water vapor content resulting from the wet scrubbing is brought in contact with atmospheric air, thereby being cooled, and recyclically reused.
5. A process according to Claim 1, wherein the cooling water for the dehumidification is cooled in an air cooler, and the cooling water condensed in the de-humidifier is sent to the precooling and reused.
6. A process for treating a flue gas from a furnace, which comprises precooling a hot flue gas from a furnace, wet scrubbing the flue gas, contacting the resulting flue gas having a high water vapor content with cooling water, thereby cooling the flue gas down to a lower temperature while dehumidifying the flue gas, thereby bringing the water vapor content in the flue gas to the corresponding saturation condition, heating the flue gas and discharging the flue gas to atmosphere.
7. A process according to Claim 6, wherein the gas to be treated is a flue gas from an incinerator.
8. A process according to Claim 6, wherein the flue gas having a high water vapor content after the wet scrubbing is cooled to a temperature differing by not more than 25°C from the atmospheric air temperature in the contact of the cooling water.
9. A process according to Claim 6, wherein the cooling water after the contact with the flue gas having a high water vapor content resulting from the wet scrubbing is brought in contact with atmospheric air, thereby being cooled, and recyclically reused.
10. A process according to Claim 6, wherein the cooling water for the dehumidification is cooled in an air cooler, and the cooling water condensed in the de-humidifier is sent to the precooling and reused.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA208,349A CA1043693A (en) | 1974-09-03 | 1974-09-03 | Process for treating flue gas from furnace |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA208,349A CA1043693A (en) | 1974-09-03 | 1974-09-03 | Process for treating flue gas from furnace |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1043693A true CA1043693A (en) | 1978-12-05 |
Family
ID=4101039
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA208,349A Expired CA1043693A (en) | 1974-09-03 | 1974-09-03 | Process for treating flue gas from furnace |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1043693A (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN104226088A (en) * | 2014-09-12 | 2014-12-24 | 中国华能集团清洁能源技术研究院有限公司 | Ultralow-temperature ultra-clean flue gas exhausting system and method for thermal power plant |
| CN105582764A (en) * | 2016-02-29 | 2016-05-18 | 西安西热锅炉环保工程有限公司 | Treatment system and method for flue gas generated by wet desulphurization device in thermal power plant |
| CN111001288A (en) * | 2019-12-18 | 2020-04-14 | 航天环境工程有限公司 | Efficient direct contact type condensation system for eliminating white smoke plume by wet desulphurization of flue gas and application |
-
1974
- 1974-09-03 CA CA208,349A patent/CA1043693A/en not_active Expired
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN104226088A (en) * | 2014-09-12 | 2014-12-24 | 中国华能集团清洁能源技术研究院有限公司 | Ultralow-temperature ultra-clean flue gas exhausting system and method for thermal power plant |
| CN105582764A (en) * | 2016-02-29 | 2016-05-18 | 西安西热锅炉环保工程有限公司 | Treatment system and method for flue gas generated by wet desulphurization device in thermal power plant |
| CN111001288A (en) * | 2019-12-18 | 2020-04-14 | 航天环境工程有限公司 | Efficient direct contact type condensation system for eliminating white smoke plume by wet desulphurization of flue gas and application |
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