CA2002342A1 - Method for purification of waste water - Google Patents
Method for purification of waste waterInfo
- Publication number
- CA2002342A1 CA2002342A1 CA 2002342 CA2002342A CA2002342A1 CA 2002342 A1 CA2002342 A1 CA 2002342A1 CA 2002342 CA2002342 CA 2002342 CA 2002342 A CA2002342 A CA 2002342A CA 2002342 A1 CA2002342 A1 CA 2002342A1
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- CA
- Canada
- Prior art keywords
- waste water
- reaction
- wet oxidation
- heat
- gas
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
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Classifications
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
- Y02W10/00—Technologies for wastewater treatment
- Y02W10/10—Biological treatment of water, waste water, or sewage
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- Treatment Of Water By Oxidation Or Reduction (AREA)
Abstract
ABSTRACT
A method for the purification of waste water by effecting wet oxidation of at least one member selected from the group consisting of organic and inorganic substances in said waste water while feeding an oxygen-containing gas, which comprises using a shell-and-tube type reactor having inner tubes, wherein said wet oxidation being carried out at a temperature of not more than 370°C under a pressure high enough for said waste water to remain in the liquid phase, and a gas feed device having gas-feed nozzles, being fitted in the lower parts of said inner tubes, the pressure loss of each of said nozzles being not less than 0.05 Kg/cm2.
A method for the purification of waste water by effecting wet oxidation of at least one member selected from the group consisting of organic and inorganic substances in said waste water while feeding an oxygen-containing gas, which comprises using a shell-and-tube type reactor having inner tubes, wherein said wet oxidation being carried out at a temperature of not more than 370°C under a pressure high enough for said waste water to remain in the liquid phase, and a gas feed device having gas-feed nozzles, being fitted in the lower parts of said inner tubes, the pressure loss of each of said nozzles being not less than 0.05 Kg/cm2.
Description
2~a~2 -METHOD FOR PURIFICATION OF WASTE WATER
BACKGROUND OF THE INVENTION
Field of the Invention:
This invention relates to a method for the purificatio~ of waste water. Particularly, this invention relates to a method for the purification of waste water oontaining chemical oxygen-demanding substances (hereinafter referred to as "~OD component") by wet oxidation. More particularly, this invention relates to a method for effectiYe purification of waste water containing a COD
component, i.e. harmful oxidizable organic or inorganic substances (herein after referred to "impurity"), which method effects the purlfication of the waste water by subjecting the waste water to wet oxidation in the presence of molecular oxygen thereby converting the organic substances into harmless compounds such as carbon dioxide, water, and nitrogen.
Description of the Prior Art:
Among the methods currently available for the treatment of waste water, the biochemical method called the activated slu~ge method and the wet oxidation method called the Zimmermann method have been renowned.
For the wet oxidation method, use of a varying oxidizing catalyst for the purpose of heightening the reaction rate has been proposed. Further, for the wet oxidation method, no matter whether a catalyst is absent from or present in the reaction site, the single cylinder type reaction column is used as the reaction vessel.
The activated sludge method consumes a long time for the decomposition of organic substances and requires the waste water to be diluted to a concentration fit for the growth of algae and bacteria and, therefore, has the disadvantage that the facilities for the treatment of activated sludge occupy a large floor space. Further, in recent years, the handling of the surplus grown sludge has been entailing an immense expenditure particularly in urban ,, .:
,, districts. The Zimmermann method comprises oxidatively decomposing organic substances in an aqueous solution by introducing air into the aqueous solution of the organic substances under a pressure in the range of 20 to 200 atmospheres at a temperature in the range of 200 to 370C.
Since the reaction rate is low and the decomposition consumes a long time, this method necessitates a large reaction vessel made of a highly durable material and attains no real economy because of expensive equipment and expensive operation. Since the liquid phase within the reaction vessel cannot be retained when the reaction temperature is elevated by the heat of reaction, this method has the disadvantage of being incapable of effectively treating waste water whose COD component has a high calorific value. Also for this method, use of a varying oxidi~ing catalyst for the purpose of heightening the reaction rate has been proposed. For the use of such an oxidizing catalyst, none of the conventional methods for waste water treatment is specifically devised to relieve the reaction vessel of the heat of reaction.
There are proposed many methods in order to solve the problems. As the one method, there can be cited a method, which comprises using a shell-and-tube type reactor capable of heat exchanging, thereby removing the generated heat, and maintaining the reaction temperature of constant, thereby enhancing the efficiency of conversion. When u~ing the shell-and-tube type reactor, it is important to feed a waste water and oxygen-containing gas in an equimolar ratio to each of reaction tubes. However, since in the conventional methods, a waste water and oxygen-containing gas are almost fed to one inlet of supply, it does not feed them in an equimolar ratio to each reaction tubes. As a result, there is occurred drift, thereby decreasing the efficiency of treatment.
In the circumstances, in order to feed a waste water and oxygen-containing gas in an equimolar ratio to each :' . `: :
`. ~
reaction tubes in a system for obtaining high efficiency by means of a catalyst, it is necessary to strictly control the pressure loss of each reaction tubes during filling the catalyst. If such a control is not done sufficiently, there is occurred a drift in the reactor, thereby reducing the efficiency.
An object of this invention, there~ore, is to solve the above problems and to provide a method capable of effective purification of waste water containing a COD
component, i.e. harmful organic or inorganic substances, by subjecting the waste water to wet oxidation in the presence of molecular oxygen thereby converting the harmful substances into such harmless compounds as carbon dioxide, water, and nitrogen.
(SUMMAR~ OF THE INVENTION) The above object is accomplished by a method for the purification of waste water by effecting wet oxidation of at least one member selected from the group consisting of organic and inorganic substances in said waste water while feeding an oxygen-containing gas, which comprises using a shell-and-~ube type reactor having inner tubes, wherein said wet oxidation being carried out at a temperature of not more than 370C under a pressure high enough for said waste water to remain in the liquid phase, and a gas feed device having gas-feed nozzles, being fitted in the lower par~s of said inner tubes, the pressure loss of each of said nozzles being not less than 0.05 kg/cm2.
The conventional wet oxidation (Zimmermann) method using the single cylinder type reaction column and not involving use of any catalyst has been incapable of effectively treating waste water containing a COD component in a high concentration because it pays no due consideration to relieving the reaction column of the heat of reaction as pointed out previously as the problem confronting this method. In fact, when the waste water subjected to the treatment is in a highly concentrated form, the amount of .
.
2~23~
the heat generated by the reaction is so large that the temperature of the liquid phase with in the reaction column is elevated conspicuously and the water therein is suffered to pass wholly into the vapor phase and the reaction can no longer be continued. Further, the reaction of this wet oxidation by nature suffers the reaction rate to increase in proportion as the reaction temperature is elevated. When the elevation of the reaction temperature is large, therefore, the reaction itself is accelerated possibly so much as to render the control of the reaction difficult.
We have continued a diligent study to find that the use of a heat-exchanger type reaction vessel as a reactor configured to ensure thorough removal of the heat of reaction is highly effective in the treatment of waste water.
This heat-exchanger type reaction vessel itself shares a common type with reaction vessels frequently used in various vapor phase oxidation reactions. It has not been employed, however, for the wet oxidation method. ~ reaction system which combine the heat-exchanger type reaction vessel and the single cylinder type reaction vessel has never been adopted for the operation of the wet oxidation method. We have found, however, that the use of the heat-exchanger type reaction vessel as a container for the wet oxidation reaction brings about a notable improvement in the capacity for waste water treatment as described hereinafter.
First, since the use of this heat-exchanger type reaction vessel permits thorough removal of the hea~ of reaction from the highly concentrated waste water which the conventional single cylinder type reaction vessel has been unable to treat effectively, the treatment of the waste water can be attained by this reaction vessel without application of unduly high pressure. The upper limited of the COD concentration in the waste water subjected to the treatment, therefore, can be increased from the conventional level of 8% up to 20%. Even when the COD content is low and . ' , , ' i - 2~3 .~
consequently the amount of the heat of reaction is small, the method of this invention obviates the necessity for unduly heightening the reaction pressure in due consideration of the elevation of the liquid temperature.
Further, the amount of the heat to be removed from the reaction vessel can be finely controlled as by adjusting the amount of the heat transfer medium being circulated for cooling within the heat-exchanger part of the reaction system in proportion to the COD concentration in the waste water and the amount of the waste water under treatment.
The heat of reaction recovered from within the reaction vessel may be reclaimed in the form of steam by the use of a steam generating boiler through the medium of a heat medium or effectively recovered and used for preheating the waste water awaiting the treatment. This recovery of the heat of reaction, therefore, proves a generous cut in the expense of equipment and that of operation.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a flow sheet illustrating one embodiment of the reactor of this inventlon, and Fig. 2 is a flow sheet illustrating a method, using the reactor without a gas feed nozzle.
EXPLANATION OF THE PREFERRED EMBODIMBNT
The reaction vessel to be used in this invention is preferably a shell-and-tube heat-exchanger type reactor which comprises a shell and a plurality of inner tubes disposed inside the shell and utilizes the empty space defined by the inner surface of the shell and the outer peripheries of the inner tubes as a passage for the flow of a heat transfer medium. The reaction vessel of this type permits simplification of the configuration of reactor, facilitaters design and maintenance of the reactor and, at the same time 7 allows a decrease in the amount of highly corrosionproof material for use in the reactor parts owing to the passage only through the inner tubes of the waste ~ . ~
, : ` :
` 2~23D~Z
water possibly containing a corrosive substance, and therefore warrants a reduction in the cost of the reactor.
In accordance with the present invention, the shell-and-tube heat-exchanger type reaction vessel is enabled to feed the oxygen-containing gas in an equal volume to the reaction tubes by having gas feed nozzles fitted one each into the lower parts of the reaction tubes. As the result, the waste water is enabled to be fed in an equal volume into the reaction tubes as entrained by the gas issuing from the gas feed nozzles. For the gas to be fed in an equal volume from the gas feed nozzles to the respective reaction tubes, the pressure loss in each of the nozzles is required to be not less than 0.05 kg/cm2, preferably not less than 0.1 kg/cm2. The reason for this particular lower limit, 0.05 kg/cm2, is that if the pressure loss is less than 0.05kg/cm2, the flow volumes of gas fed out of the nozzles are differentiated so much that the flow within the reaction vessel is heavily deflected and, as a result, a supply of the gas in an equal volume to the reaction tubes becomes difficult to attain. The upper limit is usually 2kg/cm27 preferably 1 kg/cm2.
In the present invention, the difference between the pressure losses in the plurality of nozzles used in the gas feed device is required to be within 40%, preferably within 25%. If the difference between the pressure losses in the nozzles exceeds 40%, it become difficult to feed the gas in an equal amount to the reaction tubes and, as the result, ; the waste water is not retained in an equal volume by the gas. Thus, the flow of the gas and that of the waste water both are liable to entail the phenomenon of deflection and the efficiency of treatment is consequently degraded.
The nozzles in the gas feed device of this invention are only required to be so shaped as to impart the specific pressure difference to the flow of the gas. The supply of the gas to the nozzles of the gas feed device may be attained by the use of radially laid pipes 9 annular pipes, or small air reservoir drums.
The shell-and-tube type reactor to be used in this invention is a shell-and-tube heat-exchanger type reactor wherein the waste water is fed through the inner tubes, and a heating medium is fed as a shell side fluid. The heat-exchanger t~pe reaction vessels characterized by the shell-and-tube configuration are broadly divided into the horizontal tube type and the vertical tube type. From the standpoint of the efficiency of vapor-liquid contact, the vertical tube type is believed to be more preferable for this invention. As olassified by the bundling pattern of tubes, the heat-exchanger type reaction vessels characterized by the shell-and-tube configuration fall under the three kinds, the stationary tube plate type, the U-shaped tube type, and the loose head type. The method of this invention manifests its effect invariably with the reaction vessel of any one of these kinds. As regards the direction of the flow of the waste water inside the inner tubes and that of the flow of the heat trans~er medium on the shell side, the two combinations, i.e. the counterflow and the parallel flow, are conceivable. The choice between these two combinations forms no critical problem. ~s the heat transfer medium to be passed on the shell side, any of the conceivable commonly conceivable materials such as water, steam, heat medium quality oil, and molten salt may be used.
The inner tubes of the reaction vessel to be used in the present invention have an inside diameter not less than 10 mm, preferably 10 to 100 mm, most preferably 15 to 80 mm, a length not less than 1 m, preferably 1 to 20 m, most preferably 1 to 10 m. The number of the inner tubes depends on the inside diameter of the inner tubes, the flow volume of the waste water subjected to the treatment, and the like.
Further, we have found that when a catalyst is filled in the inner tubes of heat exchanger type reactor, :' . ~ ~; , :
,, : , :
Z~C~Z3~2 such a rector is suitable for the removal of reaction heat locally generated by the i~provement of reaction velocity, the reactor can be compacted and be improved.
The catalyst which are usable for this purpose include those which are obtained by having such metals as manganese, iron, cobalt, nickel, tungsten, copper, cerium, silver, gold, platinum, palladium, rhodium, ruthenium, and iridium or the compounds thereof insoluble or sparingly soluble in water deposited severally on a carrier of alumina, activated carbon, silica-alumina, zirconia, titania, diatomaceous earth, silica-titania, silica-zirconia, titania-zirconia, for example. The catalyst to be used herein is in the form of pellets, beads, or honeycombs.
The wet oxidation contemplated by this invention is preferable to be carried out at a temperature not more than 370 C, preferably 120 to 370C under a pressure high enough for the waste water under treatment to remain in its liquid state. For the retention of the liquid phase this temperature range must be observed because the critical temperature of water is 370C. Further, for the purpose of curbing the precipitation of inorganic substances in the waste water, it is necessary to set the pressure at a level high enough for the waste water to remain in the liquid state and resist transformation into vapor.
This invention is further characterized by effecting the treatment of waste water which, on being subjected to wet oxidation~ exhibits a calorific value exceeding 20 kcal per liter of waste water. The treatment is sufficiently effective even when the calorific value is less than 20 kcal. Where the waste water has a calorific value of less than 20 kcal, however,- the necessity for employing the method of this invention loses significance because the demerit due to the increase in the cost of the reaction vessel excels the merit of the removal of heat by the use of the heat exchanger type reaction vesselO For the puPpose of improving the effect due to the temperature control of the Z~I~Z3~
reaction vessel and taking and advantage of the merit due to the removal of heat, the waste water subjected to the treatment is preferable to exhibit a calorific value exceeding 5U kcal per liter of waste water. More preferably, this treatment is given to waste water which calorific value exceeds 100 kcal per liter of waste water.
Further, by introducing the remained waste water having low calorific value discharged from the first heat exchange type reactor into the single cylinder type reaction column having no heat exchange capacity, the remained reaction can be adiabatically proceeded.
As the single cylinder type reaction vessel for the second stage, and insulated reaction vessel is used. The reaction vessels of this type are roughly divided into the horizontal tube type and the vertical tube type. From the standpoint of the efficiency of vapor-liqud contact, this invention prefers the reaction vessel to be of the vertical tube type. The reaction tubes are preferable to have an inside diameter in the range of 50 to 2,500 m~, preferably 150 to 1,500 mm, and a length in the range of 1 to 20 m, preferably 1 to 10 m. The inside diameter and the length depend on the residual COD concentration of the waste water at the outlet of the reaction vessel in the first stage, for example.
Similarly to the reaction vessel in the first stage, the reaction vessel in the second stage is allowed to use a catalyst. The amount of this catalyst can be freely selected, depending on the concentration of the waste water, for example. The packing of the catalyst improves the reaction rate and permits compaction of the reaction vessel.
Further, in the second stage o~ the reaction , the heat of reaction posses no problem because the residual calorific value o~ the waste water is small.
Though the ~aste water at the inlet to the second stage has a small calorific value~ the waste water with the progress of the decomposition comes to allow persistance of , :
;23~2 sparingly decomposable substances and accumulation of the product of decomposition and requires much time for decomposition. Preferably, therefore, the reaction vessel in the second stage is provided in the inlet part thereof with a nozzle for introduction of air and consequently enabled to introduce air therein and enhance the efficiency of contact between the waste water and the air and expedite the reaction. Since the reaction vessel of the second stage is not of the heat-exohanger type and in consideration of the generation of heat by the reaction, the calorific value of the waste water at the outlet of the reaction vessel in the first stage is preferable to be less than 20 kcal per liter of waste water.
Now, the present invention will be described more specifically below with reference to working examples. It should be noted, however, that this invention is not limited to these examples.
Example 1 A shell-and-tube heat-exchanger 1 had 10 reaction tubes 11 measuring 50 mm in inside diameter and 5 m in length di~posed in a shell 12 a illustrated in Fig. 1. The reaction tubes 11 were filled with catalyst pellets (0.5 %
by weight of Pd supported on titania zirconia carrier) 5 mm in average particle diameter, each to form a catalyst layer 4 m in length. To this reactor 1, waste water having a COD
(Cr) concentration of 100 g/lit. and a calorific value of 3l10 kcal per liter of waste water was fed through a line 13 in a flow volume of 16 liters/hr per reaction tube. In the meantime, the air was brought in through a line 19 and fed through nozzles 20 at a flow volume of 6,400 N liter/hr per reaction tube. The reaction temperature was 250C and reaction pressure was 75 kg/cm2-G. To the outside of the reaction tubes 11 of the reactor 1, a heat trans~er medium was supplied by a circulation pump 14 to be used for cooling the reactor. The heat transfer medium thus used was discharged through a line 15 and, in a heat-exchanger 4, a .
, 23~2 lowed to exchange heat with the cooling water fed through a line 17. Thus, the recovery of the heat of reaction was attained. The gas feed nozzles 20 used herein had a pressure loss of 0.15 kg/cm2 and a difference of pressure of 18 % between the nozzles. The treated waste waster was discharged through line 18. In this reaction, the conversion of COD was 99.1 %.
Examples 2 ~o 5 Purification o~ waste water was performed by repeating the procedure of Example 1, except that the conditions of the nozzles 20 in the gas feed device were varied. The treated waste water samples were tested for conversion of COD. The results were as shown in Table 1.
Examples 6 to 10 Purification of waste water was performed by repeating the procedure of Example 19 except that the conditions of the nozzles 20 in the gas feed device, concentration of the waste water, the size of the reaction tube and packing catalyst were varied. The treated waste water samples were tested for con~ersion of COD. The results were as shown in Table 1.
Control 1 Fig. 2 is a summarized diagram of a reactor without a gas ~eed nozzle, which is a shell-and-tube type reactor capable of heat exchanging. The number of reaction tube, the inner diameter of reactor tube, the length and the filling of catalyst were the same as Example 1. To the reactor, were introduced a waster water via a line 13~ and an air via a line 19. The conditions, eOg. waster water to be treated, heat exchange in the reactor 1 was the same as Example 1. As a result 7 the conversion of COD was 70 %.
The same numerals disclosed in Fig. 2 as those of Fig. 1 shown the same members in Fig. 1.
Control 2 .
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.
2~Z3~2 The procedure of Example 1 was repeated except that 'A conditions of nozzle of gas feed device varied. The " results, COD conversion, are shown in Table 1.
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., _ _ _ . _ i~ ~ ~ ~_ ~ o U~ ~ ~ ~ ~
~I O ~ _ O O O O O O O O ; ~ _ O O
~ ~ ~ ~ ~n ~ _~_ ~ ~o ~_ ~o o ~ 11~ o u w o w o ~ ~ rl o ~; ~0 ~0 ~0 ~0 ~0 ~ ~ ~ ~ a~
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; _ ~ ~ O _ O O O r ~ 1~ L- I ~ ~ ~
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~ s described above, it is understood that by applying a simple dispersion device for wet oxidation system in which it is difficult to set a complicated dispersion device under high temperatures and high pressures, it can feed both a waste water and a gas, which are most important, in a decreased dri~t state and further improve the efficiency of treatment.
In the oxidation and decomposition step of waste water while feeding an oxygen-containing gas, it is considered that the dissolution of oxygen gas into the waste water (solution) is of a waste-determining step. When using a gas feed nozzle shown in Fig. 1, it can improve the dispersion of gas into the solution, thereby heightening the dissolution velocity of oxygen gas therein, and leads to the improvement of treating efficiency of the waste water.
Since the dispersion of gas into the solution was improved, the amount of gas to be fed can be decreased, the running cost of the equipment can be cut down. Thus, it is economical method. In a system aiming a high treating efficiency using a catalyst, it necessitates the strict control of pressure loss of catalyst bed of reactors, but not in the present invention.
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BACKGROUND OF THE INVENTION
Field of the Invention:
This invention relates to a method for the purificatio~ of waste water. Particularly, this invention relates to a method for the purification of waste water oontaining chemical oxygen-demanding substances (hereinafter referred to as "~OD component") by wet oxidation. More particularly, this invention relates to a method for effectiYe purification of waste water containing a COD
component, i.e. harmful oxidizable organic or inorganic substances (herein after referred to "impurity"), which method effects the purlfication of the waste water by subjecting the waste water to wet oxidation in the presence of molecular oxygen thereby converting the organic substances into harmless compounds such as carbon dioxide, water, and nitrogen.
Description of the Prior Art:
Among the methods currently available for the treatment of waste water, the biochemical method called the activated slu~ge method and the wet oxidation method called the Zimmermann method have been renowned.
For the wet oxidation method, use of a varying oxidizing catalyst for the purpose of heightening the reaction rate has been proposed. Further, for the wet oxidation method, no matter whether a catalyst is absent from or present in the reaction site, the single cylinder type reaction column is used as the reaction vessel.
The activated sludge method consumes a long time for the decomposition of organic substances and requires the waste water to be diluted to a concentration fit for the growth of algae and bacteria and, therefore, has the disadvantage that the facilities for the treatment of activated sludge occupy a large floor space. Further, in recent years, the handling of the surplus grown sludge has been entailing an immense expenditure particularly in urban ,, .:
,, districts. The Zimmermann method comprises oxidatively decomposing organic substances in an aqueous solution by introducing air into the aqueous solution of the organic substances under a pressure in the range of 20 to 200 atmospheres at a temperature in the range of 200 to 370C.
Since the reaction rate is low and the decomposition consumes a long time, this method necessitates a large reaction vessel made of a highly durable material and attains no real economy because of expensive equipment and expensive operation. Since the liquid phase within the reaction vessel cannot be retained when the reaction temperature is elevated by the heat of reaction, this method has the disadvantage of being incapable of effectively treating waste water whose COD component has a high calorific value. Also for this method, use of a varying oxidi~ing catalyst for the purpose of heightening the reaction rate has been proposed. For the use of such an oxidizing catalyst, none of the conventional methods for waste water treatment is specifically devised to relieve the reaction vessel of the heat of reaction.
There are proposed many methods in order to solve the problems. As the one method, there can be cited a method, which comprises using a shell-and-tube type reactor capable of heat exchanging, thereby removing the generated heat, and maintaining the reaction temperature of constant, thereby enhancing the efficiency of conversion. When u~ing the shell-and-tube type reactor, it is important to feed a waste water and oxygen-containing gas in an equimolar ratio to each of reaction tubes. However, since in the conventional methods, a waste water and oxygen-containing gas are almost fed to one inlet of supply, it does not feed them in an equimolar ratio to each reaction tubes. As a result, there is occurred drift, thereby decreasing the efficiency of treatment.
In the circumstances, in order to feed a waste water and oxygen-containing gas in an equimolar ratio to each :' . `: :
`. ~
reaction tubes in a system for obtaining high efficiency by means of a catalyst, it is necessary to strictly control the pressure loss of each reaction tubes during filling the catalyst. If such a control is not done sufficiently, there is occurred a drift in the reactor, thereby reducing the efficiency.
An object of this invention, there~ore, is to solve the above problems and to provide a method capable of effective purification of waste water containing a COD
component, i.e. harmful organic or inorganic substances, by subjecting the waste water to wet oxidation in the presence of molecular oxygen thereby converting the harmful substances into such harmless compounds as carbon dioxide, water, and nitrogen.
(SUMMAR~ OF THE INVENTION) The above object is accomplished by a method for the purification of waste water by effecting wet oxidation of at least one member selected from the group consisting of organic and inorganic substances in said waste water while feeding an oxygen-containing gas, which comprises using a shell-and-~ube type reactor having inner tubes, wherein said wet oxidation being carried out at a temperature of not more than 370C under a pressure high enough for said waste water to remain in the liquid phase, and a gas feed device having gas-feed nozzles, being fitted in the lower par~s of said inner tubes, the pressure loss of each of said nozzles being not less than 0.05 kg/cm2.
The conventional wet oxidation (Zimmermann) method using the single cylinder type reaction column and not involving use of any catalyst has been incapable of effectively treating waste water containing a COD component in a high concentration because it pays no due consideration to relieving the reaction column of the heat of reaction as pointed out previously as the problem confronting this method. In fact, when the waste water subjected to the treatment is in a highly concentrated form, the amount of .
.
2~23~
the heat generated by the reaction is so large that the temperature of the liquid phase with in the reaction column is elevated conspicuously and the water therein is suffered to pass wholly into the vapor phase and the reaction can no longer be continued. Further, the reaction of this wet oxidation by nature suffers the reaction rate to increase in proportion as the reaction temperature is elevated. When the elevation of the reaction temperature is large, therefore, the reaction itself is accelerated possibly so much as to render the control of the reaction difficult.
We have continued a diligent study to find that the use of a heat-exchanger type reaction vessel as a reactor configured to ensure thorough removal of the heat of reaction is highly effective in the treatment of waste water.
This heat-exchanger type reaction vessel itself shares a common type with reaction vessels frequently used in various vapor phase oxidation reactions. It has not been employed, however, for the wet oxidation method. ~ reaction system which combine the heat-exchanger type reaction vessel and the single cylinder type reaction vessel has never been adopted for the operation of the wet oxidation method. We have found, however, that the use of the heat-exchanger type reaction vessel as a container for the wet oxidation reaction brings about a notable improvement in the capacity for waste water treatment as described hereinafter.
First, since the use of this heat-exchanger type reaction vessel permits thorough removal of the hea~ of reaction from the highly concentrated waste water which the conventional single cylinder type reaction vessel has been unable to treat effectively, the treatment of the waste water can be attained by this reaction vessel without application of unduly high pressure. The upper limited of the COD concentration in the waste water subjected to the treatment, therefore, can be increased from the conventional level of 8% up to 20%. Even when the COD content is low and . ' , , ' i - 2~3 .~
consequently the amount of the heat of reaction is small, the method of this invention obviates the necessity for unduly heightening the reaction pressure in due consideration of the elevation of the liquid temperature.
Further, the amount of the heat to be removed from the reaction vessel can be finely controlled as by adjusting the amount of the heat transfer medium being circulated for cooling within the heat-exchanger part of the reaction system in proportion to the COD concentration in the waste water and the amount of the waste water under treatment.
The heat of reaction recovered from within the reaction vessel may be reclaimed in the form of steam by the use of a steam generating boiler through the medium of a heat medium or effectively recovered and used for preheating the waste water awaiting the treatment. This recovery of the heat of reaction, therefore, proves a generous cut in the expense of equipment and that of operation.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a flow sheet illustrating one embodiment of the reactor of this inventlon, and Fig. 2 is a flow sheet illustrating a method, using the reactor without a gas feed nozzle.
EXPLANATION OF THE PREFERRED EMBODIMBNT
The reaction vessel to be used in this invention is preferably a shell-and-tube heat-exchanger type reactor which comprises a shell and a plurality of inner tubes disposed inside the shell and utilizes the empty space defined by the inner surface of the shell and the outer peripheries of the inner tubes as a passage for the flow of a heat transfer medium. The reaction vessel of this type permits simplification of the configuration of reactor, facilitaters design and maintenance of the reactor and, at the same time 7 allows a decrease in the amount of highly corrosionproof material for use in the reactor parts owing to the passage only through the inner tubes of the waste ~ . ~
, : ` :
` 2~23D~Z
water possibly containing a corrosive substance, and therefore warrants a reduction in the cost of the reactor.
In accordance with the present invention, the shell-and-tube heat-exchanger type reaction vessel is enabled to feed the oxygen-containing gas in an equal volume to the reaction tubes by having gas feed nozzles fitted one each into the lower parts of the reaction tubes. As the result, the waste water is enabled to be fed in an equal volume into the reaction tubes as entrained by the gas issuing from the gas feed nozzles. For the gas to be fed in an equal volume from the gas feed nozzles to the respective reaction tubes, the pressure loss in each of the nozzles is required to be not less than 0.05 kg/cm2, preferably not less than 0.1 kg/cm2. The reason for this particular lower limit, 0.05 kg/cm2, is that if the pressure loss is less than 0.05kg/cm2, the flow volumes of gas fed out of the nozzles are differentiated so much that the flow within the reaction vessel is heavily deflected and, as a result, a supply of the gas in an equal volume to the reaction tubes becomes difficult to attain. The upper limit is usually 2kg/cm27 preferably 1 kg/cm2.
In the present invention, the difference between the pressure losses in the plurality of nozzles used in the gas feed device is required to be within 40%, preferably within 25%. If the difference between the pressure losses in the nozzles exceeds 40%, it become difficult to feed the gas in an equal amount to the reaction tubes and, as the result, ; the waste water is not retained in an equal volume by the gas. Thus, the flow of the gas and that of the waste water both are liable to entail the phenomenon of deflection and the efficiency of treatment is consequently degraded.
The nozzles in the gas feed device of this invention are only required to be so shaped as to impart the specific pressure difference to the flow of the gas. The supply of the gas to the nozzles of the gas feed device may be attained by the use of radially laid pipes 9 annular pipes, or small air reservoir drums.
The shell-and-tube type reactor to be used in this invention is a shell-and-tube heat-exchanger type reactor wherein the waste water is fed through the inner tubes, and a heating medium is fed as a shell side fluid. The heat-exchanger t~pe reaction vessels characterized by the shell-and-tube configuration are broadly divided into the horizontal tube type and the vertical tube type. From the standpoint of the efficiency of vapor-liquid contact, the vertical tube type is believed to be more preferable for this invention. As olassified by the bundling pattern of tubes, the heat-exchanger type reaction vessels characterized by the shell-and-tube configuration fall under the three kinds, the stationary tube plate type, the U-shaped tube type, and the loose head type. The method of this invention manifests its effect invariably with the reaction vessel of any one of these kinds. As regards the direction of the flow of the waste water inside the inner tubes and that of the flow of the heat trans~er medium on the shell side, the two combinations, i.e. the counterflow and the parallel flow, are conceivable. The choice between these two combinations forms no critical problem. ~s the heat transfer medium to be passed on the shell side, any of the conceivable commonly conceivable materials such as water, steam, heat medium quality oil, and molten salt may be used.
The inner tubes of the reaction vessel to be used in the present invention have an inside diameter not less than 10 mm, preferably 10 to 100 mm, most preferably 15 to 80 mm, a length not less than 1 m, preferably 1 to 20 m, most preferably 1 to 10 m. The number of the inner tubes depends on the inside diameter of the inner tubes, the flow volume of the waste water subjected to the treatment, and the like.
Further, we have found that when a catalyst is filled in the inner tubes of heat exchanger type reactor, :' . ~ ~; , :
,, : , :
Z~C~Z3~2 such a rector is suitable for the removal of reaction heat locally generated by the i~provement of reaction velocity, the reactor can be compacted and be improved.
The catalyst which are usable for this purpose include those which are obtained by having such metals as manganese, iron, cobalt, nickel, tungsten, copper, cerium, silver, gold, platinum, palladium, rhodium, ruthenium, and iridium or the compounds thereof insoluble or sparingly soluble in water deposited severally on a carrier of alumina, activated carbon, silica-alumina, zirconia, titania, diatomaceous earth, silica-titania, silica-zirconia, titania-zirconia, for example. The catalyst to be used herein is in the form of pellets, beads, or honeycombs.
The wet oxidation contemplated by this invention is preferable to be carried out at a temperature not more than 370 C, preferably 120 to 370C under a pressure high enough for the waste water under treatment to remain in its liquid state. For the retention of the liquid phase this temperature range must be observed because the critical temperature of water is 370C. Further, for the purpose of curbing the precipitation of inorganic substances in the waste water, it is necessary to set the pressure at a level high enough for the waste water to remain in the liquid state and resist transformation into vapor.
This invention is further characterized by effecting the treatment of waste water which, on being subjected to wet oxidation~ exhibits a calorific value exceeding 20 kcal per liter of waste water. The treatment is sufficiently effective even when the calorific value is less than 20 kcal. Where the waste water has a calorific value of less than 20 kcal, however,- the necessity for employing the method of this invention loses significance because the demerit due to the increase in the cost of the reaction vessel excels the merit of the removal of heat by the use of the heat exchanger type reaction vesselO For the puPpose of improving the effect due to the temperature control of the Z~I~Z3~
reaction vessel and taking and advantage of the merit due to the removal of heat, the waste water subjected to the treatment is preferable to exhibit a calorific value exceeding 5U kcal per liter of waste water. More preferably, this treatment is given to waste water which calorific value exceeds 100 kcal per liter of waste water.
Further, by introducing the remained waste water having low calorific value discharged from the first heat exchange type reactor into the single cylinder type reaction column having no heat exchange capacity, the remained reaction can be adiabatically proceeded.
As the single cylinder type reaction vessel for the second stage, and insulated reaction vessel is used. The reaction vessels of this type are roughly divided into the horizontal tube type and the vertical tube type. From the standpoint of the efficiency of vapor-liqud contact, this invention prefers the reaction vessel to be of the vertical tube type. The reaction tubes are preferable to have an inside diameter in the range of 50 to 2,500 m~, preferably 150 to 1,500 mm, and a length in the range of 1 to 20 m, preferably 1 to 10 m. The inside diameter and the length depend on the residual COD concentration of the waste water at the outlet of the reaction vessel in the first stage, for example.
Similarly to the reaction vessel in the first stage, the reaction vessel in the second stage is allowed to use a catalyst. The amount of this catalyst can be freely selected, depending on the concentration of the waste water, for example. The packing of the catalyst improves the reaction rate and permits compaction of the reaction vessel.
Further, in the second stage o~ the reaction , the heat of reaction posses no problem because the residual calorific value o~ the waste water is small.
Though the ~aste water at the inlet to the second stage has a small calorific value~ the waste water with the progress of the decomposition comes to allow persistance of , :
;23~2 sparingly decomposable substances and accumulation of the product of decomposition and requires much time for decomposition. Preferably, therefore, the reaction vessel in the second stage is provided in the inlet part thereof with a nozzle for introduction of air and consequently enabled to introduce air therein and enhance the efficiency of contact between the waste water and the air and expedite the reaction. Since the reaction vessel of the second stage is not of the heat-exohanger type and in consideration of the generation of heat by the reaction, the calorific value of the waste water at the outlet of the reaction vessel in the first stage is preferable to be less than 20 kcal per liter of waste water.
Now, the present invention will be described more specifically below with reference to working examples. It should be noted, however, that this invention is not limited to these examples.
Example 1 A shell-and-tube heat-exchanger 1 had 10 reaction tubes 11 measuring 50 mm in inside diameter and 5 m in length di~posed in a shell 12 a illustrated in Fig. 1. The reaction tubes 11 were filled with catalyst pellets (0.5 %
by weight of Pd supported on titania zirconia carrier) 5 mm in average particle diameter, each to form a catalyst layer 4 m in length. To this reactor 1, waste water having a COD
(Cr) concentration of 100 g/lit. and a calorific value of 3l10 kcal per liter of waste water was fed through a line 13 in a flow volume of 16 liters/hr per reaction tube. In the meantime, the air was brought in through a line 19 and fed through nozzles 20 at a flow volume of 6,400 N liter/hr per reaction tube. The reaction temperature was 250C and reaction pressure was 75 kg/cm2-G. To the outside of the reaction tubes 11 of the reactor 1, a heat trans~er medium was supplied by a circulation pump 14 to be used for cooling the reactor. The heat transfer medium thus used was discharged through a line 15 and, in a heat-exchanger 4, a .
, 23~2 lowed to exchange heat with the cooling water fed through a line 17. Thus, the recovery of the heat of reaction was attained. The gas feed nozzles 20 used herein had a pressure loss of 0.15 kg/cm2 and a difference of pressure of 18 % between the nozzles. The treated waste waster was discharged through line 18. In this reaction, the conversion of COD was 99.1 %.
Examples 2 ~o 5 Purification o~ waste water was performed by repeating the procedure of Example 1, except that the conditions of the nozzles 20 in the gas feed device were varied. The treated waste water samples were tested for conversion of COD. The results were as shown in Table 1.
Examples 6 to 10 Purification of waste water was performed by repeating the procedure of Example 19 except that the conditions of the nozzles 20 in the gas feed device, concentration of the waste water, the size of the reaction tube and packing catalyst were varied. The treated waste water samples were tested for con~ersion of COD. The results were as shown in Table 1.
Control 1 Fig. 2 is a summarized diagram of a reactor without a gas ~eed nozzle, which is a shell-and-tube type reactor capable of heat exchanging. The number of reaction tube, the inner diameter of reactor tube, the length and the filling of catalyst were the same as Example 1. To the reactor, were introduced a waster water via a line 13~ and an air via a line 19. The conditions, eOg. waster water to be treated, heat exchange in the reactor 1 was the same as Example 1. As a result 7 the conversion of COD was 70 %.
The same numerals disclosed in Fig. 2 as those of Fig. 1 shown the same members in Fig. 1.
Control 2 .
~.~
. ' ~' , ~ ~ ; , ~; ' " ;;:
.
2~Z3~2 The procedure of Example 1 was repeated except that 'A conditions of nozzle of gas feed device varied. The " results, COD conversion, are shown in Table 1.
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~ 12-;
i . - ' :
,, , - - - - ~ -_ do ~ c~ o c~ ~ o ~ ~ i~ o ~ ~e u~ ~ c~ O ~ O .~ O c 1, ~e ~ ~
~ j ~ ~ O O _, U~ C~ O ~~ ~O O
., _ _ _ . _ i~ ~ ~ ~_ ~ o U~ ~ ~ ~ ~
~I O ~ _ O O O O O O O O ; ~ _ O O
~ ~ ~ ~ ~n ~ _~_ ~ ~o ~_ ~o o ~ 11~ o u w o w o ~ ~ rl o ~; ~0 ~0 ~0 ~0 ~0 ~ ~ ~ ~ a~
_ _ .. C~
~ O O O O ~ ~O O O ~ O O
~ ,Ei ~ ~ ~ _ ~. _ ~ ~n 1~-- --¦-- `
; _ ~ ~ O _ O O O r ~ 1~ L- I ~ ~ ~
_ _ __ ~ ~o d - ' . , ' -: : ',-.,' : . : : -'' :, .'~''. ' .; ` - :
. ~ , - ' '.'~........ ' ~ .` .
23~
~ s described above, it is understood that by applying a simple dispersion device for wet oxidation system in which it is difficult to set a complicated dispersion device under high temperatures and high pressures, it can feed both a waste water and a gas, which are most important, in a decreased dri~t state and further improve the efficiency of treatment.
In the oxidation and decomposition step of waste water while feeding an oxygen-containing gas, it is considered that the dissolution of oxygen gas into the waste water (solution) is of a waste-determining step. When using a gas feed nozzle shown in Fig. 1, it can improve the dispersion of gas into the solution, thereby heightening the dissolution velocity of oxygen gas therein, and leads to the improvement of treating efficiency of the waste water.
Since the dispersion of gas into the solution was improved, the amount of gas to be fed can be decreased, the running cost of the equipment can be cut down. Thus, it is economical method. In a system aiming a high treating efficiency using a catalyst, it necessitates the strict control of pressure loss of catalyst bed of reactors, but not in the present invention.
;' .
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. : ~
Claims (7)
1. A method for the purification of waste water by effecting wet oxidation of at least one member selected from the group consisting of organic and inorganic substances in said waste water while feeding an oxygen-containing gas, which comprises using a shell and-tube type reactor having inner tubes, wherein said wet oxidation being carried out at a temperature of not more than 370°C under a pressure high enough for said waste water to remain in the liquid phase, and a gas feed device having gas-feed nozzles, being fitted in the lower parts of said inner tubes, the pressure loss of each of said nozzles being not less than 0.05 Kg/cm2.
2. A method according to claim 1, wherein the difference between the pressure losses of the nozzles is within 40 %.
3. A method according to claim l, wherein said wet oxidation is carried out in the presence of a catalyst.
4. A method according to claim 1, wherein said waste water during said wet oxidation exhibits a calorific value of at least 20 kcal per liter of waste water.
5. A method according to claim 1 wherein said wet oxidation is carried out first in a shell-and-tube heat-exchanger type reactor and then in a single cylinder type reactor not vested with a function for exchange of heat.
6. A method according to claim 5, wherein said waste water fed to said shell-and-tube heat-exchanger type reactor exhibits, during the course of said wet oxidation, a calorific value of at least 20 kcal per liter of waste water.
7. A method according to claim 6, wherein said waste water exhibits at the outlet of said shell-and-tube heat-exchanger type reactor, a calorific value of less than 20 kcal per liter of waste water.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP63-279501 | 1988-11-07 | ||
| JP27950188 | 1988-11-07 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2002342A1 true CA2002342A1 (en) | 1990-05-07 |
Family
ID=17611928
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2002342 Abandoned CA2002342A1 (en) | 1988-11-07 | 1989-11-06 | Method for purification of waste water |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2002342A1 (en) |
-
1989
- 1989-11-06 CA CA 2002342 patent/CA2002342A1/en not_active Abandoned
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