CA1171186A - Continuous process for wet oxidation of aqueous waste liquors - Google Patents
Continuous process for wet oxidation of aqueous waste liquorsInfo
- Publication number
- CA1171186A CA1171186A CA000393047A CA393047A CA1171186A CA 1171186 A CA1171186 A CA 1171186A CA 000393047 A CA000393047 A CA 000393047A CA 393047 A CA393047 A CA 393047A CA 1171186 A CA1171186 A CA 1171186A
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- oxygen
- reactor
- gas
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F11/00—Treatment of sludge; Devices therefor
- C02F11/06—Treatment of sludge; Devices therefor by oxidation
- C02F11/08—Wet air oxidation
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- Life Sciences & Earth Sciences (AREA)
- Hydrology & Water Resources (AREA)
- Engineering & Computer Science (AREA)
- Environmental & Geological Engineering (AREA)
- Water Supply & Treatment (AREA)
- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Treatment Of Water By Oxidation Or Reduction (AREA)
- Treatment Of Sludge (AREA)
Abstract
WET OXIDATION PROCESS UTILIZING
DILUTION OF OXYGEN
A B S T R A C T
A continuous process for wet oxidation of aqueous waste liquors using oxygen gas is made safer by injecting an inert gas into the waste liquors at a rate such that oxygen in the gas phase is diluted by the sum of generated water vapor, produced carbon dioxide and injected inert gas to a concentration less than required for spontaneous combustion at every location in the wet oxidation system comprising a reactor, effluent line, pressure control valve and separator, having surfaces not continually exposed to a continuous liquid water phase.
DILUTION OF OXYGEN
A B S T R A C T
A continuous process for wet oxidation of aqueous waste liquors using oxygen gas is made safer by injecting an inert gas into the waste liquors at a rate such that oxygen in the gas phase is diluted by the sum of generated water vapor, produced carbon dioxide and injected inert gas to a concentration less than required for spontaneous combustion at every location in the wet oxidation system comprising a reactor, effluent line, pressure control valve and separator, having surfaces not continually exposed to a continuous liquid water phase.
Description
WET OXIDATION PROCESS UTILIZING
DILUTION OF OXYGEN
This invention relates to safe operation of wet oxidation systems using pure oxygen or oxygen enriched ga~es.
Wet oxidation i8 a well- established process for ~reating aqueous wastewaters, sludges and slurries which contain oxidizable substances; more than one hundred wet oxidation units are in commercial operation. Many pat~nts and other publications disclose wet oxidation processe~
10 using air as the source o~ oxygen for accomplishing the oxidation. U.S. Patents No. 3,042,489 and 3,097,988, and U.S. Patent No. 3,654,070 disclose the applica~ion of pure oxygen or an oxygen enriched gas to wet oxidation processes.
For this discussion, the term "oxygen", when used without 15 a modifying adjective will refer to any gas containing greater than 21 mole percent oxygen, to distinguish it from air.
Increased reaction rates and the opportunity to operate at lower pxessures and temperatures make the use.
20 of oxygen very attractive from a theoretica} starldpointO
In addition, many potential users of the wet oxidation proces~ r such as sewage treatment plants, steel mills t etc.
have existing oxygen generation/storage facilities, making the gas available at low cost.
To date how~ver, no wet oxidation processes have been operated commerci~lly using oxygen. One important reason is that no one has yet shown how oxygen can be safely used in wet oxidation processes under steady state and transient conditions common to such processes.
In wet oxidation systems, aqueous and gaseous ~, ; ~ . .
y ~
DILUTION OF OXYGEN
This invention relates to safe operation of wet oxidation systems using pure oxygen or oxygen enriched ga~es.
Wet oxidation i8 a well- established process for ~reating aqueous wastewaters, sludges and slurries which contain oxidizable substances; more than one hundred wet oxidation units are in commercial operation. Many pat~nts and other publications disclose wet oxidation processe~
10 using air as the source o~ oxygen for accomplishing the oxidation. U.S. Patents No. 3,042,489 and 3,097,988, and U.S. Patent No. 3,654,070 disclose the applica~ion of pure oxygen or an oxygen enriched gas to wet oxidation processes.
For this discussion, the term "oxygen", when used without 15 a modifying adjective will refer to any gas containing greater than 21 mole percent oxygen, to distinguish it from air.
Increased reaction rates and the opportunity to operate at lower pxessures and temperatures make the use.
20 of oxygen very attractive from a theoretica} starldpointO
In addition, many potential users of the wet oxidation proces~ r such as sewage treatment plants, steel mills t etc.
have existing oxygen generation/storage facilities, making the gas available at low cost.
To date how~ver, no wet oxidation processes have been operated commerci~lly using oxygen. One important reason is that no one has yet shown how oxygen can be safely used in wet oxidation processes under steady state and transient conditions common to such processes.
In wet oxidation systems, aqueous and gaseous ~, ; ~ . .
y ~
2--phases coexist at elevated pressures and temperatures~
System pressures are chosen so that there will always be an aqueous phase. Oxidation reactions consume oxygen and ge~erate carbon dioxide. When the aqueous phase has a neutral or low 5 pH, a major portion of the carbon dioxide formed by wet oxidation will remain in the gaseous phase, diluting the oxygen~ When the aqueous phase is caustic, however, much of the carbon dioxide will be absorbed in the aqueous phase.
The quantity of water vapor which is present in 10 the gas phase is a function of temperature, pressure, and quantity of non-condensible gases (NC&~, and can be determined by known thermodynamic ralationships. For a given system operating at a nearly uniform pressure, the degree of gas dilution by water vapor is much greater at the higher lS temperatures.
In prior art processes using air as the source of oxygen, the percentage of oxygen in the gas phase at elevated temperatures and pressures is considerably less than 21 percent, even without any oxyge~ consumption. For example, 20 at 550F. and 1000 psi pressure, water vapor dilutes the oxygen from its original 21 percent to a concentration o~
about 5 percent. As oxygen is consumed its concentration at reactor conditions drops to very low values. Therefore, pure oxygen or oxygen enriched gas can be used advantageously 25 in enhancing the rate and completeness of oxidation, so long as the safety of the process can be ensured.
Gaseous oxygen; when diluted to a concentration of 21 mole percent as in the form of air, is safe to handle, even when compressed to quite high pressures.
However, oxygen at higher concentrations, especiaLly high purity oxygen, is likely to undergo rapid, sponta~eou~
combustion when placed in contact with organic or oth~r oxidizable substances at pressures above atmospheric, even at room temperature. In the wet oxidation process, high 35 concentration~ of oxidizable materials are deliberately oxidized. It is vital to control the process so that transient excursions of temperature, pressure, and thermal ' ~ ' ' ': :
l'7~ 6 ~ 3--efficiency are minimal and ha~ardous operati~g condltions do not occur.
Moreover, many metaLs such as steel, aluminum and titanium, for e~ample, will burn vigorously in the presence 5 of oxygen once an igni~ion has occurred. Titanlum itself has been shown to be capable of undergoiny spontaneous com-bustion under certain conditions in the presence of oxygen and water at elevated pressures, as reported by F.E. Littman and F.M. Church in Flnal ~eport: Reactions of Titanium wîth 10 Water and Aqueous Solutîons, Stanford Research Institute Project No. SD-2116, June 15, 1958.
In the handling of oxygen, tradit1onal sa~ety practice has emphasized selection of materials of construction which will not themselve~ undergo spontaneous combustion at 15 design operating conditions, and strict cleanliness standards to ensure that no contaminants capable of spontaneous com-bustion are present in the system. In wet oxidations, however, ~he cholce of materials of construction is nearly always constrained by th~ corrosive properties of the waste-20 water, sludge, or slurry being oxidlzed. Thus titanium ortitanium alloys may be dic~ated as the material of construction when severe corrosion of iron- or nickel-based alloys ls indicated. Moreover, the wet oxidation system treat~ waste-waters, sludges, or slurries whLch may contain up to ten 25 percent or even higher concentrations of organic substanc~s, and its interior surfaces may always be contaminated with ~ubstances capable of spontaneous combustion upvn contact with oxygen at high pressures.
Therefore, the use of wet oxidatlon employing pure 30 oxygen or an oxygen enriched gas in a system fabrlcated of titanium, where the interior surfaces may aiways be contamin-ated with organic matter appears to be definitely precluded.
On the other hand, the use of oxygen in a wet oxidation installation may be very attractlve. If oxyge~
35 is already available on-site, th~ capital and operating co~t~ -fox a large air compressor are eliminatedO Favorable oxidation kinetics wi11 result in a smaller reactor and~or 7~ 6 lower operating temperature and pressure. Other potent~al advantages of using oxygen may be evident to those famili~r with wet oxidation.
The ob~ect of thls invention, therefore is to make 5 possible the use of pure oxygen or oxygen enrlched gas in a wet oxidation process under conditions o safety comparable to traditional wet oxidatlon processes using air.
According to this invention, a continuous process is provided for wet oxidation of aqueous waste liquors con-lO taining combustible matter, comprising the steps of:
A. continuously introducing aqueous waste liquor andoxygen or oxygen enriched gas into a pressuri~ed reactor operated at eleva~ed temperature; and B. oxidizing therein a major portion of the combustlble 15 matter in said aqueous waste liquor characterized by C. passing offgases from said reactor through a Li~e to a pressure control valve operated to maintain the reactor at a substantially constant pressure; and D. injecting an inert gas into the pressurized aqueou~
20 waste liquor at a rate such that oxygen ln the cJas phase i5 diluted by the sum of generated water vapor, produced carbon dioxide and in~ected inert gas to a concentration less than required for spontaneous combustion at every location in the reactor, effluent line, pressure control valve and separator, 25 having surfaces not continually exposed to a continuous liquid water phase.
Specifically, the process of this invention comprises the steps of:
a. continuously introducing aqueous waste liquor and 30 oxygen or oxygen enriched gas into a pressurlzed reactor operated at el~vated temperature;
b. oxidizing therein a major portion of the combustible matter in said aqueous waste liquor to produce an oxidized liquor and offgases;
c. passin~ oxidized liqu3r and offgases from said reactor through an effluent line to a heat exchanger wh~re oxidized liquor and ofgases are cooled;
.
`
~5--d7 reducing the pressure of cooled oxidized liquor and offgases in a pressure control valve operat~d to maintaln khe reactor at a substantially constant pressur~;
e. separating the offgases from the oxldized liquor 5 in a gas-liquid separator; and f. injecting an inert gas into said pre~surized aqueous waste liquor at a rate such that oxygen in the gas phase is diluted by the sum of generated water vapor, produc~d carbon dioxide, and in~ected inert gas to a concentratlon 10 less than required for spontaneous combustion a~ every location in the reactor, effluent line, pressure control valve, and separator, having surfaces not exposed to a continuous liquid water phase.
In another specific embodiment of the invention, 15 steam or carbon dioxide are safely produced by wet oxidation of combustible matter with pure oxygen or oxygen enriched gas, comprising the steps of:
a. continuously introducing aqueous liquor and oxygen or oxygen enriched gas into a pressurized reactor operated 20 at elevated temperature;
b. oxidizing therein a major portion of the combustlbl~
matter to evaporate substantially all of the water entering the reactor and introducing water to maintain a substantially constant liquid level in the reactor;
c. passing offgase6, including water vapor from the reactor through a line to a pressure control valv~ whereby the reactor pressure is maintained at a substantially constant pressure;
d. passing offgases at reduced pressure to a usiny 30 process; and e. injecting an inert gas into said pressurized liquor at a rate such that oxygen in the gas phase is diluted ~y the sum of generated water vapor, produced carbon dioxide and injected inert gas to a concentration less than requlred for 35 spontaneous ~ombustion at every locat1on in the reactor and lines therefrom including valvesl having surfaces not exposed to a continuous liquid water phase~
Fig. 1 is a flow diagram of a wet oxidation system showing several possible embodiments of this inventlon~
Fig. 2 shows a further embodiment of the invention for generating steam and/or carbon dioxide by wet oxidation.
This invention comprises performing a wet oxidation using pure oxyyen or an oxygen enriched gas under conditions such that at every location in the system where a gas phase containing oxyyen comes into continuous contact with a solid surface which might be contaminated with a deposit of some 10 oxidizable substance or which itself might undergo spontaneous combustion in the presence of oxygen, the oxygen in the gas phase at that location will be diluted to a concentration less than the concentrakion at which a spontaneous ~om~ustion can occur.
Normally, an oxygen concentration of 21 mole percent, the same as in air, is the highest concentration at which spontaneous ccmbustion will not occur. Some materials will ignite only at oxygen concentrations conslderably higher than 21 mole percent. On the other hand, some wastes which contain parti~
20 cularly sensitive substances may ignite at oxygen concentra-tions less than 21 mole percent. ThP ignition concentrat~on can he determined by use of either the Pneumatlc Impact Test or the Mechanical Impact Test, both of which are described in "Safety Considerations Regarding the Use of High PrsssurQ
25 Oxygen" by David L. Pippen, Jack Stradling and Gene W. Frye, NASA, White Sands Testing Facility, Johnson Space Center, September, 1979.
The inert gas which is lnj~cted will typically b~
nitrogen, carbon dioxide, air (because of its nitroyen 30 content) or steam, but other inert gases ma~ be used.
The source of the inert diluent gas is a slgnif1ca~t aspect of this inventionO If air is to be used it ls a simple matter to provide an air compressor for the wet oxidation system. If oxygen is supplied by an air separation 35 plant located close to the wet oxidation system then nitrogen from the air separation plant J taken as either gaseous or liquid nitrogen could be used as the inert diluent gas.
~7~
Carbon dloxide may also he used as the inert yas.
Steam may be a useful "inert" gas par~icular1y for injection into vapor spaces or pipes carry1ng prlmarily vapors. When the steam temperature is greatex than the 5 oxygen containing gas, a portion of the steam will condense, thus wetting the equlpment walls. This condensate is avail~
able to absorb heat generated by spontaneous combustion of organic matter which may be deposited on the equipment walls Most often a combination of two or more of the 10 above listed gases are present and dilute the oxyg~n. For example, in a wet oxidation process which utlllzes pure oxygen to oxidize a waste water containing an organlc pollutant, a small stream of compressed air is added to the system upstream of the reactor. In the reactor and in 15 the reactor effluent, oxygen which has not yet reacted is diluted by a combination of water vapor evaporated from the wastewater, carbon dioxide generatPd by oxidation of the organic pollutants, and nitrogen from the injected airO
Down stream from the heat exchanger where the water vapor 20 is condensed, the oxygen is still diluted by the carbon dioxide and nitrogen. If the was~e concentration drops suddenly, or if the waste flow into the system stops suddenly so that carbon dioxide is no longer generated, there is nevertheless sufficient nitrogen flowing down-25 stream of the heat exchanger so that the oxygen still flow-ing in the line is diluted to a safe concentratiorl.
The locations at which oxygen and any diluent gas are added to the wet oxidation system are important feature~
of this invention. The oxygen is added eithar directly at 30 the reactor bottom or is mixed with the waste aft~r the waste is preheated but before it flows into the reactor. In the latter case, diluent gas is mixed wi~h the waste either upstream, or at the same point at which oxygen is being mixed with the influent liquor which contains combust}ble 35 materials. More specifically, -the diluent gas is added at one or mora of the following locations:
7~ 36 a. direc~ly to the reactor if the oxygen is also ~eing added directly to the reactor bottom;
b. to the preheated waste just upstream from the reactor;
c. to the raw waste before it is preheated ln the heat exchangers; or d. to the oxygen supply line upstream from the point at which oxygen is mixed with wastewater.
The location whexe the diluent gas is to be added 10 to the wet oxidation system is selected so that the diluen~
gas will flow through, dilute out, or purge all locations in the wet oxidation plant where pure oxygen or an oxygen en-riched gas may collect.
At some installations uncontrolled spontaneous 15 combustion is most lLkely to occur in the line carrying co~led reactor offgases. Upon condensation of water vapor, the oxygen con~nt in the offgases markedly increases and may attain a critical level if corrective action is not taken. Furthermore, mechanical shock caused by action of 20 the pressure control valve, or shock caus~d by adiabatic compression downstream of the pressure control valve may `!
result in ignition.
In cases where high oxygen concentra~ion in the absence of a continuous liquid water phase may occur down-25 stream of the reactor but not in the reactor itself, ani~ert gas may be injected downstream of the reactor, typlcally before the mixture of oxidized liquor and offgases is cooled.
The amount of inert diluent gas added to the wet - oxidation process will vary depending on the wastewater bei.ng 30 oxidi7ed and on the conditions under which the system is belng operated. For example, if the wet oxidation process is runnlng at a reasonably steady state and is generati~g enough carbon dioxide to dilute the oxygen contained in the effluent gas stream to less than 21 mole percent, then the flow of the 35 inert diluent gas can be stopped. On the other hand, if the wet oxida~ion process is experiencing some upset, is being shut down, or is about to be start~d up the flow of inert ..t7~ 6 diluent gas should by turned on to prevent any pocket of high purity oxygen from developing in the reactor and down-stream piping and to purge out any oxygen pockets that may have already developed.
The flow rate of the inert diluent gas is sized from a consideration of two criteria. F'irst, the diluent gas flow must be sufficient so that when the oxygen flow is turned down to the minimum allowed by the oxygen flow control system, the inert diluent gas flow rate is sufficient to 10 dilute the oxygen still flowing into the system to 21 mole percent. Thus, if the minimum repeatable oxygen flow is 10 percent of the design oxygen flow rate, then the diluting gas flow is at least 0.376 moles per mole of oxygen fed to ~he plant at the design flow xate~ ~his is about one tenth 15 the flow of air that would be supplied to a wet oxidation process using air as the oxygen source.
Secondly the design flow rate of inert diluent gas must be sufficient so that the oxygen in the effluent from the wet oxidation process will always be diluted ts or 20 below 21 percent even when no diluting gases such as carbon dioxide are produced during the wet oxidation process. Thus if the wet oxidation process is designed for 90 percent oxygen utilization the amount of inert diluent gas needed is 0.376 moles per mole o~ oxygen fed to the normal design ~5 flow rate. If the nitrogen content of air is used at the diluent then the air ~low is 0.376/.79 or .476 moles per mole of oxygen fed.
Normally the flow rate of inerk diluent gas is b tween about 3.76 moles and 0.00376 moles per mole of oxygen 30 fed to the unit at design flow rate, Preferably the flow o~
inert diluent gas is sized for between 0.376 and 0.0376 moles per molQ of oxygen fed to the wet oxidation unit at the normal design flow rate.
Figure 1 illustrates one embodiment of this 35 invention. As shown in the figure, an aqueous wast liquor containing an organic pollutant is pressurized and enters the wet oxidation unit through feed line 1 and then passes l7~ 36 to heat exchanger 2. The waste liquor is preheated by indirect heat exchange with hot o~idized li~usr from reactor 4. The heated liquor then passes through line 3 to reactor 4, where it is mixed and reacted with pure oxygen or oxygen 5 enriched gas entering reactor ~ through line 5. The organlc pollutant in the aqueous waste liquor is oxidized at the elevated (300-650F.) temperatures in the reactor. The reactor pressure is controlled to maintain a liquid phase and is typically 200 to 3200 psig.
Oxidized liquor and offgases pass from the reactor via line 6 to heat exchanger 2, where they are cooled. Much of the water vapor in the offgases is condensed, and the cooled mixture of oxidized liquor and offgases passes through line ~ to pressure control valve 8 which maintains the 15 elevated pressure in the reactor. The mixture passes at reduced pressure through line 7~a to vapor-liquid separator 9 wherein oxidized liquors and offgases are separated.
Control valves ~ and ~ regulate the flow of oxidized li~uor and offgases, respectively, from separator 9.
~ diluent inert gas such as nitrogen, carbon dioxide, air or steam is injected into the waste liquor to result in an oxygen concentration less than necessary for spontaneous combustion to occur wherever a continuous liquid - phase may not exist and oxidizable matter may he present in 25 the system. This gas may be in~ected prior to heat exchange, as through line 16, or following heat exchange, as through line 1~7. Alternatively, the diluent gas may be in~ected into the oxygen or oxygen enriched gas through line ~9 or even directly into the reactor through a separate line, not 30 shown. It is preferred to inject the inert gas either by itself or as a mixture with the waste liquor or oxygen, into the lower portion of the reactor. In any case, at every site in the system where equipment surfaces are not contlnually exp~sed to a continuous liquid water phase, and where oxidiz-35 ~ble matter, whether organic matter or the surface itse1fis present, the concentration of oxygen is maintained at a ; level where spontaneous combustion will not occurO Such sites may exist in reactor 4, effluent lines 6 "7, and 7~a ~rom the reactor (including hea~ exchanger), pre~sure control valve 8 and separator, including its discharge line~. All locations in the system downstream from the location where 5 oxygen and liquor are mixed are potential combustion sites.
Combustion differs from wet oxidation in th~
context of this invention in that wet oxidation occurs in the liquid phase while combustion is a vapor phase oxida~ion Where the pH of the reactor aqueous phase is 10 neutral or acidic, carbon dioxide generated by oxidation largely remains in the vapor phase and dilutes the oxygen.
At any given pressure and temperature, the quantity of water vapor in the gas phase is proportional to the ~uantity of nominally non-condensible gases present. Hence the quantity 15 of injected iner~ gas required in the reactor at steady state operation may be very small, or even none. However, down-stream of heat exchanger 2, in line 7 for i~stance, most of the water vapor has condensed, and additlonal diluent gas may be required to prevent spontaneous combustlon~ In 20 such cases the inert gas may be in~ected into line 6 through line ~8 in order to maintain safe oxygen concentrations i~
heat exchanger 2 and equipment downstream therefrom.
Many methods for controlling the process can ba envisioned. For example, the flow rate of pure oxygen or 25 oxygen enriched gas may be controlled by measurement of oxygen concentration in the gas phase ~offgases~ by analyzer represented in Figure 1 as 21, 22, or 23, whll~ the flow rate of inert gas is maintalned constant. Analyses of the offgas anywhere in the system may be used, provided proper 30 corrections for differences in temperature and pressure~
are made.
Referring again to Figure 1, suppose that the wet oxidation system is designed for 95 percent utilizatlon of the pure oxygen fed to the system, and that the range in 35 flow control through line 5 is a ratio of 20:1.
During normal steady state operation at design conditions the carbon dioxide produced in the oxidation .
~7~8~;
~12-reactions is more than enough to dilute the offy~s oxygen to less than 21 mole percent. Accordingly, the ~low of diluent gas is shut off during st~ady state operation.
However, during the s~art up and shut down, and also during 5 a period of process upset the carbon dioxide produced may not be enough to dilute the oxygen to less than 21 mole percent so according to the criteria described previously an inert diluting gas flow of 0.188 mole per mole o~ oxygen at design flow is required to ensure the saety of the 10 process. If air is used as the inert diluent gas the flow of air must be 0.188/0.79 = 0.238 moie per mole of oxygen since only the nitrogen component of air functions as the inert gas. The oxygen in air would be largely consumed in the wet oxidation.
In another control method, where air is uæed as the diluent, the flow rate of oxygen or oxygen enriched gas is constant, while the air rate is varied in accordance with the measured oxygen concentration in the offgases. In this embodiment, air may supply a significant portion of the 20 oxygen consumed in the process.
The wet oxidation system of Figure 1 i5 now used to treat a highly alkaline waste water containing organic pollutants~ The waste is sufficiently alkaline so that all carbon dioxide produced in the reactor is dissolved in the 25 wastewater as carbonate and is not available for diluting oxygen. Now in the reactor 4 and in line 6 oxygen ~n ~he vapor phase is diluted only by steam and the inert diluent gas. At the effluent end of the heat exchanger 2 and in line 7 the steam has been condensed from the vapor phase so 30 oxygen is diluted only by the inert diluent yas added to the process. Since there is never any produced caxbon dioxide present in the effluent gas phase the flow of inert diluent gas must remain on as long as the wet oxidation system is running.
Again, since the wet oxidation system is designed for 95 percent utilization of oxygen fed to the unit, and since the range of the flow controller controlling the flow .
'7~
of oxygen flow through llne 5 is 20 to 1, the flow of lnert diluent gas should be at least 0.188 moles per mole of oxygen feds The flow rate of the inert gas will range from 5 3.75 to 0.00376 moles per mole of oxygen introduced lnto the reactor, depending upon waste COD and pE~, reactor temperature and pressure, material of equipment constru~tion, and the particular inert gas which is used. In nearly all cases, the inert gas flow is between 0.376 and 0,0376 moles per 10 mole of oxygen introduced, Turning now to Figure 2, we have another em~odiment of this invention, in whlch pure oxygen or oxygen enr~ched gas is u~ed in the wet oxidation of aqueous liquors contain-ing oxidizable matter. In this embodiment, substantially 15 all of the water introduced leaves the reactor as water vapor. In Figure 2, a liquor is pumped through line ~1 lnto reactor 32 where it is mixed with and undergoes reactlon with oxygen or oxygen enriched gas lntroduced through line 4~Q. A liquid level 3~3 is maintained by controlling the flow 20 of water ~hrough line 34 by level controller ~6 r Offgases, including water vapor leave the reactor through line ~7 and pressure control valve 3~8 to a uslng process 3~9, for example, a power generation plant.
When necessary, the small quantity of ash which 25 may accumulate în ~he reactor is discharged as a small stxeam through line 4~6.
The oxygen flow may be controlled by maasurement of oxygen concentration in the offgas by analyzer 4~7. If the rate of oxidizable matter lntroduced lnto the reactor 3Q is precisely known, of course, the oxygen flow rate may be controlled without continuous measurement o~ offgas oxygen~
Noxmally the preferred point of introducing the inert gas is into the aqueous liquor through line 4~1 or into the oxygen through line 4~5. Alternate locations may be 35 through line 42 or 433 directly into the reactor. Introduction into the liquid phase through line ~ ensures diLution at the liquid-vapor interface on the reactor walls.
7~
If the critical ~ite for possible spontaneous combustion lies downstream of reactor 32, for example downstream of valve 38, inert gas may be introducea through line ~4 into vapor line 37~ In this case, the use of steam 5 as the dilutent may be used~
A spent caustic scrubbing liquor was treated by wet oxidation in a pilot plant having the flow configuration of Figure 1. The reactor was operated at a temperature of 10 412F. and a pressure of 335 psig, with a liquLd residence time of 30 minutes. Inert gas (air) was added at the reac~or top through line 20 to Line 6 leaving reactor 4 at a rate sufficient to dilute the residual oxygen to a safe level.
All of the C02 generated by oxidation was absorbed into the 15 liquid phase. Without dilution, the cooled offgas after separation would have been essentiaLly pure oxygen. Air was injected at a rate of 1.01 mole per mole Of original oxygen introduced, resulting in an oxygen concentration of 27 per-cent in the cooled offgases.
A liquor containing waste solvents, with pH of 13.1, was wet oxidized in a pilot plant with the configuration of Figure 1. The reactor conditions were 600F. and 1950 psig pressure, with a liquid residence time of 120 minutes. In 25 ~his case air was added as the inert gas to the liquor throug~
; line ~6 prior to preheating in order to prevent possible polymerization of liquor components in the heat exchang~r.
Pure oxygen was added to the reactor through llne 5~
The ratio of air injected to oxygen was n. 430 moles 30 air/mole oxygen, resulting in an oxygen concentratlon of 19.87 mole percent in the cooled offgases~ The calculated oxygen concentration at the reactor top was 3.0 mole percent, and safe operation was achieved.
' ..
System pressures are chosen so that there will always be an aqueous phase. Oxidation reactions consume oxygen and ge~erate carbon dioxide. When the aqueous phase has a neutral or low 5 pH, a major portion of the carbon dioxide formed by wet oxidation will remain in the gaseous phase, diluting the oxygen~ When the aqueous phase is caustic, however, much of the carbon dioxide will be absorbed in the aqueous phase.
The quantity of water vapor which is present in 10 the gas phase is a function of temperature, pressure, and quantity of non-condensible gases (NC&~, and can be determined by known thermodynamic ralationships. For a given system operating at a nearly uniform pressure, the degree of gas dilution by water vapor is much greater at the higher lS temperatures.
In prior art processes using air as the source of oxygen, the percentage of oxygen in the gas phase at elevated temperatures and pressures is considerably less than 21 percent, even without any oxyge~ consumption. For example, 20 at 550F. and 1000 psi pressure, water vapor dilutes the oxygen from its original 21 percent to a concentration o~
about 5 percent. As oxygen is consumed its concentration at reactor conditions drops to very low values. Therefore, pure oxygen or oxygen enriched gas can be used advantageously 25 in enhancing the rate and completeness of oxidation, so long as the safety of the process can be ensured.
Gaseous oxygen; when diluted to a concentration of 21 mole percent as in the form of air, is safe to handle, even when compressed to quite high pressures.
However, oxygen at higher concentrations, especiaLly high purity oxygen, is likely to undergo rapid, sponta~eou~
combustion when placed in contact with organic or oth~r oxidizable substances at pressures above atmospheric, even at room temperature. In the wet oxidation process, high 35 concentration~ of oxidizable materials are deliberately oxidized. It is vital to control the process so that transient excursions of temperature, pressure, and thermal ' ~ ' ' ': :
l'7~ 6 ~ 3--efficiency are minimal and ha~ardous operati~g condltions do not occur.
Moreover, many metaLs such as steel, aluminum and titanium, for e~ample, will burn vigorously in the presence 5 of oxygen once an igni~ion has occurred. Titanlum itself has been shown to be capable of undergoiny spontaneous com-bustion under certain conditions in the presence of oxygen and water at elevated pressures, as reported by F.E. Littman and F.M. Church in Flnal ~eport: Reactions of Titanium wîth 10 Water and Aqueous Solutîons, Stanford Research Institute Project No. SD-2116, June 15, 1958.
In the handling of oxygen, tradit1onal sa~ety practice has emphasized selection of materials of construction which will not themselve~ undergo spontaneous combustion at 15 design operating conditions, and strict cleanliness standards to ensure that no contaminants capable of spontaneous com-bustion are present in the system. In wet oxidations, however, ~he cholce of materials of construction is nearly always constrained by th~ corrosive properties of the waste-20 water, sludge, or slurry being oxidlzed. Thus titanium ortitanium alloys may be dic~ated as the material of construction when severe corrosion of iron- or nickel-based alloys ls indicated. Moreover, the wet oxidation system treat~ waste-waters, sludges, or slurries whLch may contain up to ten 25 percent or even higher concentrations of organic substanc~s, and its interior surfaces may always be contaminated with ~ubstances capable of spontaneous combustion upvn contact with oxygen at high pressures.
Therefore, the use of wet oxidatlon employing pure 30 oxygen or an oxygen enriched gas in a system fabrlcated of titanium, where the interior surfaces may aiways be contamin-ated with organic matter appears to be definitely precluded.
On the other hand, the use of oxygen in a wet oxidation installation may be very attractlve. If oxyge~
35 is already available on-site, th~ capital and operating co~t~ -fox a large air compressor are eliminatedO Favorable oxidation kinetics wi11 result in a smaller reactor and~or 7~ 6 lower operating temperature and pressure. Other potent~al advantages of using oxygen may be evident to those famili~r with wet oxidation.
The ob~ect of thls invention, therefore is to make 5 possible the use of pure oxygen or oxygen enrlched gas in a wet oxidation process under conditions o safety comparable to traditional wet oxidatlon processes using air.
According to this invention, a continuous process is provided for wet oxidation of aqueous waste liquors con-lO taining combustible matter, comprising the steps of:
A. continuously introducing aqueous waste liquor andoxygen or oxygen enriched gas into a pressuri~ed reactor operated at eleva~ed temperature; and B. oxidizing therein a major portion of the combustlble 15 matter in said aqueous waste liquor characterized by C. passing offgases from said reactor through a Li~e to a pressure control valve operated to maintain the reactor at a substantially constant pressure; and D. injecting an inert gas into the pressurized aqueou~
20 waste liquor at a rate such that oxygen ln the cJas phase i5 diluted by the sum of generated water vapor, produced carbon dioxide and in~ected inert gas to a concentration less than required for spontaneous combustion at every location in the reactor, effluent line, pressure control valve and separator, 25 having surfaces not continually exposed to a continuous liquid water phase.
Specifically, the process of this invention comprises the steps of:
a. continuously introducing aqueous waste liquor and 30 oxygen or oxygen enriched gas into a pressurlzed reactor operated at el~vated temperature;
b. oxidizing therein a major portion of the combustible matter in said aqueous waste liquor to produce an oxidized liquor and offgases;
c. passin~ oxidized liqu3r and offgases from said reactor through an effluent line to a heat exchanger wh~re oxidized liquor and ofgases are cooled;
.
`
~5--d7 reducing the pressure of cooled oxidized liquor and offgases in a pressure control valve operat~d to maintaln khe reactor at a substantially constant pressur~;
e. separating the offgases from the oxldized liquor 5 in a gas-liquid separator; and f. injecting an inert gas into said pre~surized aqueous waste liquor at a rate such that oxygen in the gas phase is diluted by the sum of generated water vapor, produc~d carbon dioxide, and in~ected inert gas to a concentratlon 10 less than required for spontaneous combustion a~ every location in the reactor, effluent line, pressure control valve, and separator, having surfaces not exposed to a continuous liquid water phase.
In another specific embodiment of the invention, 15 steam or carbon dioxide are safely produced by wet oxidation of combustible matter with pure oxygen or oxygen enriched gas, comprising the steps of:
a. continuously introducing aqueous liquor and oxygen or oxygen enriched gas into a pressurized reactor operated 20 at elevated temperature;
b. oxidizing therein a major portion of the combustlbl~
matter to evaporate substantially all of the water entering the reactor and introducing water to maintain a substantially constant liquid level in the reactor;
c. passing offgase6, including water vapor from the reactor through a line to a pressure control valv~ whereby the reactor pressure is maintained at a substantially constant pressure;
d. passing offgases at reduced pressure to a usiny 30 process; and e. injecting an inert gas into said pressurized liquor at a rate such that oxygen in the gas phase is diluted ~y the sum of generated water vapor, produced carbon dioxide and injected inert gas to a concentration less than requlred for 35 spontaneous ~ombustion at every locat1on in the reactor and lines therefrom including valvesl having surfaces not exposed to a continuous liquid water phase~
Fig. 1 is a flow diagram of a wet oxidation system showing several possible embodiments of this inventlon~
Fig. 2 shows a further embodiment of the invention for generating steam and/or carbon dioxide by wet oxidation.
This invention comprises performing a wet oxidation using pure oxyyen or an oxygen enriched gas under conditions such that at every location in the system where a gas phase containing oxyyen comes into continuous contact with a solid surface which might be contaminated with a deposit of some 10 oxidizable substance or which itself might undergo spontaneous combustion in the presence of oxygen, the oxygen in the gas phase at that location will be diluted to a concentration less than the concentrakion at which a spontaneous ~om~ustion can occur.
Normally, an oxygen concentration of 21 mole percent, the same as in air, is the highest concentration at which spontaneous ccmbustion will not occur. Some materials will ignite only at oxygen concentrations conslderably higher than 21 mole percent. On the other hand, some wastes which contain parti~
20 cularly sensitive substances may ignite at oxygen concentra-tions less than 21 mole percent. ThP ignition concentrat~on can he determined by use of either the Pneumatlc Impact Test or the Mechanical Impact Test, both of which are described in "Safety Considerations Regarding the Use of High PrsssurQ
25 Oxygen" by David L. Pippen, Jack Stradling and Gene W. Frye, NASA, White Sands Testing Facility, Johnson Space Center, September, 1979.
The inert gas which is lnj~cted will typically b~
nitrogen, carbon dioxide, air (because of its nitroyen 30 content) or steam, but other inert gases ma~ be used.
The source of the inert diluent gas is a slgnif1ca~t aspect of this inventionO If air is to be used it ls a simple matter to provide an air compressor for the wet oxidation system. If oxygen is supplied by an air separation 35 plant located close to the wet oxidation system then nitrogen from the air separation plant J taken as either gaseous or liquid nitrogen could be used as the inert diluent gas.
~7~
Carbon dloxide may also he used as the inert yas.
Steam may be a useful "inert" gas par~icular1y for injection into vapor spaces or pipes carry1ng prlmarily vapors. When the steam temperature is greatex than the 5 oxygen containing gas, a portion of the steam will condense, thus wetting the equlpment walls. This condensate is avail~
able to absorb heat generated by spontaneous combustion of organic matter which may be deposited on the equipment walls Most often a combination of two or more of the 10 above listed gases are present and dilute the oxyg~n. For example, in a wet oxidation process which utlllzes pure oxygen to oxidize a waste water containing an organlc pollutant, a small stream of compressed air is added to the system upstream of the reactor. In the reactor and in 15 the reactor effluent, oxygen which has not yet reacted is diluted by a combination of water vapor evaporated from the wastewater, carbon dioxide generatPd by oxidation of the organic pollutants, and nitrogen from the injected airO
Down stream from the heat exchanger where the water vapor 20 is condensed, the oxygen is still diluted by the carbon dioxide and nitrogen. If the was~e concentration drops suddenly, or if the waste flow into the system stops suddenly so that carbon dioxide is no longer generated, there is nevertheless sufficient nitrogen flowing down-25 stream of the heat exchanger so that the oxygen still flow-ing in the line is diluted to a safe concentratiorl.
The locations at which oxygen and any diluent gas are added to the wet oxidation system are important feature~
of this invention. The oxygen is added eithar directly at 30 the reactor bottom or is mixed with the waste aft~r the waste is preheated but before it flows into the reactor. In the latter case, diluent gas is mixed wi~h the waste either upstream, or at the same point at which oxygen is being mixed with the influent liquor which contains combust}ble 35 materials. More specifically, -the diluent gas is added at one or mora of the following locations:
7~ 36 a. direc~ly to the reactor if the oxygen is also ~eing added directly to the reactor bottom;
b. to the preheated waste just upstream from the reactor;
c. to the raw waste before it is preheated ln the heat exchangers; or d. to the oxygen supply line upstream from the point at which oxygen is mixed with wastewater.
The location whexe the diluent gas is to be added 10 to the wet oxidation system is selected so that the diluen~
gas will flow through, dilute out, or purge all locations in the wet oxidation plant where pure oxygen or an oxygen en-riched gas may collect.
At some installations uncontrolled spontaneous 15 combustion is most lLkely to occur in the line carrying co~led reactor offgases. Upon condensation of water vapor, the oxygen con~nt in the offgases markedly increases and may attain a critical level if corrective action is not taken. Furthermore, mechanical shock caused by action of 20 the pressure control valve, or shock caus~d by adiabatic compression downstream of the pressure control valve may `!
result in ignition.
In cases where high oxygen concentra~ion in the absence of a continuous liquid water phase may occur down-25 stream of the reactor but not in the reactor itself, ani~ert gas may be injected downstream of the reactor, typlcally before the mixture of oxidized liquor and offgases is cooled.
The amount of inert diluent gas added to the wet - oxidation process will vary depending on the wastewater bei.ng 30 oxidi7ed and on the conditions under which the system is belng operated. For example, if the wet oxidation process is runnlng at a reasonably steady state and is generati~g enough carbon dioxide to dilute the oxygen contained in the effluent gas stream to less than 21 mole percent, then the flow of the 35 inert diluent gas can be stopped. On the other hand, if the wet oxida~ion process is experiencing some upset, is being shut down, or is about to be start~d up the flow of inert ..t7~ 6 diluent gas should by turned on to prevent any pocket of high purity oxygen from developing in the reactor and down-stream piping and to purge out any oxygen pockets that may have already developed.
The flow rate of the inert diluent gas is sized from a consideration of two criteria. F'irst, the diluent gas flow must be sufficient so that when the oxygen flow is turned down to the minimum allowed by the oxygen flow control system, the inert diluent gas flow rate is sufficient to 10 dilute the oxygen still flowing into the system to 21 mole percent. Thus, if the minimum repeatable oxygen flow is 10 percent of the design oxygen flow rate, then the diluting gas flow is at least 0.376 moles per mole of oxygen fed to ~he plant at the design flow xate~ ~his is about one tenth 15 the flow of air that would be supplied to a wet oxidation process using air as the oxygen source.
Secondly the design flow rate of inert diluent gas must be sufficient so that the oxygen in the effluent from the wet oxidation process will always be diluted ts or 20 below 21 percent even when no diluting gases such as carbon dioxide are produced during the wet oxidation process. Thus if the wet oxidation process is designed for 90 percent oxygen utilization the amount of inert diluent gas needed is 0.376 moles per mole o~ oxygen fed to the normal design ~5 flow rate. If the nitrogen content of air is used at the diluent then the air ~low is 0.376/.79 or .476 moles per mole of oxygen fed.
Normally the flow rate of inerk diluent gas is b tween about 3.76 moles and 0.00376 moles per mole of oxygen 30 fed to the unit at design flow rate, Preferably the flow o~
inert diluent gas is sized for between 0.376 and 0.0376 moles per molQ of oxygen fed to the wet oxidation unit at the normal design flow rate.
Figure 1 illustrates one embodiment of this 35 invention. As shown in the figure, an aqueous wast liquor containing an organic pollutant is pressurized and enters the wet oxidation unit through feed line 1 and then passes l7~ 36 to heat exchanger 2. The waste liquor is preheated by indirect heat exchange with hot o~idized li~usr from reactor 4. The heated liquor then passes through line 3 to reactor 4, where it is mixed and reacted with pure oxygen or oxygen 5 enriched gas entering reactor ~ through line 5. The organlc pollutant in the aqueous waste liquor is oxidized at the elevated (300-650F.) temperatures in the reactor. The reactor pressure is controlled to maintain a liquid phase and is typically 200 to 3200 psig.
Oxidized liquor and offgases pass from the reactor via line 6 to heat exchanger 2, where they are cooled. Much of the water vapor in the offgases is condensed, and the cooled mixture of oxidized liquor and offgases passes through line ~ to pressure control valve 8 which maintains the 15 elevated pressure in the reactor. The mixture passes at reduced pressure through line 7~a to vapor-liquid separator 9 wherein oxidized liquors and offgases are separated.
Control valves ~ and ~ regulate the flow of oxidized li~uor and offgases, respectively, from separator 9.
~ diluent inert gas such as nitrogen, carbon dioxide, air or steam is injected into the waste liquor to result in an oxygen concentration less than necessary for spontaneous combustion to occur wherever a continuous liquid - phase may not exist and oxidizable matter may he present in 25 the system. This gas may be in~ected prior to heat exchange, as through line 16, or following heat exchange, as through line 1~7. Alternatively, the diluent gas may be in~ected into the oxygen or oxygen enriched gas through line ~9 or even directly into the reactor through a separate line, not 30 shown. It is preferred to inject the inert gas either by itself or as a mixture with the waste liquor or oxygen, into the lower portion of the reactor. In any case, at every site in the system where equipment surfaces are not contlnually exp~sed to a continuous liquid water phase, and where oxidiz-35 ~ble matter, whether organic matter or the surface itse1fis present, the concentration of oxygen is maintained at a ; level where spontaneous combustion will not occurO Such sites may exist in reactor 4, effluent lines 6 "7, and 7~a ~rom the reactor (including hea~ exchanger), pre~sure control valve 8 and separator, including its discharge line~. All locations in the system downstream from the location where 5 oxygen and liquor are mixed are potential combustion sites.
Combustion differs from wet oxidation in th~
context of this invention in that wet oxidation occurs in the liquid phase while combustion is a vapor phase oxida~ion Where the pH of the reactor aqueous phase is 10 neutral or acidic, carbon dioxide generated by oxidation largely remains in the vapor phase and dilutes the oxygen.
At any given pressure and temperature, the quantity of water vapor in the gas phase is proportional to the ~uantity of nominally non-condensible gases present. Hence the quantity 15 of injected iner~ gas required in the reactor at steady state operation may be very small, or even none. However, down-stream of heat exchanger 2, in line 7 for i~stance, most of the water vapor has condensed, and additlonal diluent gas may be required to prevent spontaneous combustlon~ In 20 such cases the inert gas may be in~ected into line 6 through line ~8 in order to maintain safe oxygen concentrations i~
heat exchanger 2 and equipment downstream therefrom.
Many methods for controlling the process can ba envisioned. For example, the flow rate of pure oxygen or 25 oxygen enriched gas may be controlled by measurement of oxygen concentration in the gas phase ~offgases~ by analyzer represented in Figure 1 as 21, 22, or 23, whll~ the flow rate of inert gas is maintalned constant. Analyses of the offgas anywhere in the system may be used, provided proper 30 corrections for differences in temperature and pressure~
are made.
Referring again to Figure 1, suppose that the wet oxidation system is designed for 95 percent utilizatlon of the pure oxygen fed to the system, and that the range in 35 flow control through line 5 is a ratio of 20:1.
During normal steady state operation at design conditions the carbon dioxide produced in the oxidation .
~7~8~;
~12-reactions is more than enough to dilute the offy~s oxygen to less than 21 mole percent. Accordingly, the ~low of diluent gas is shut off during st~ady state operation.
However, during the s~art up and shut down, and also during 5 a period of process upset the carbon dioxide produced may not be enough to dilute the oxygen to less than 21 mole percent so according to the criteria described previously an inert diluting gas flow of 0.188 mole per mole o~ oxygen at design flow is required to ensure the saety of the 10 process. If air is used as the inert diluent gas the flow of air must be 0.188/0.79 = 0.238 moie per mole of oxygen since only the nitrogen component of air functions as the inert gas. The oxygen in air would be largely consumed in the wet oxidation.
In another control method, where air is uæed as the diluent, the flow rate of oxygen or oxygen enriched gas is constant, while the air rate is varied in accordance with the measured oxygen concentration in the offgases. In this embodiment, air may supply a significant portion of the 20 oxygen consumed in the process.
The wet oxidation system of Figure 1 i5 now used to treat a highly alkaline waste water containing organic pollutants~ The waste is sufficiently alkaline so that all carbon dioxide produced in the reactor is dissolved in the 25 wastewater as carbonate and is not available for diluting oxygen. Now in the reactor 4 and in line 6 oxygen ~n ~he vapor phase is diluted only by steam and the inert diluent gas. At the effluent end of the heat exchanger 2 and in line 7 the steam has been condensed from the vapor phase so 30 oxygen is diluted only by the inert diluent yas added to the process. Since there is never any produced caxbon dioxide present in the effluent gas phase the flow of inert diluent gas must remain on as long as the wet oxidation system is running.
Again, since the wet oxidation system is designed for 95 percent utilization of oxygen fed to the unit, and since the range of the flow controller controlling the flow .
'7~
of oxygen flow through llne 5 is 20 to 1, the flow of lnert diluent gas should be at least 0.188 moles per mole of oxygen feds The flow rate of the inert gas will range from 5 3.75 to 0.00376 moles per mole of oxygen introduced lnto the reactor, depending upon waste COD and pE~, reactor temperature and pressure, material of equipment constru~tion, and the particular inert gas which is used. In nearly all cases, the inert gas flow is between 0.376 and 0,0376 moles per 10 mole of oxygen introduced, Turning now to Figure 2, we have another em~odiment of this invention, in whlch pure oxygen or oxygen enr~ched gas is u~ed in the wet oxidation of aqueous liquors contain-ing oxidizable matter. In this embodiment, substantially 15 all of the water introduced leaves the reactor as water vapor. In Figure 2, a liquor is pumped through line ~1 lnto reactor 32 where it is mixed with and undergoes reactlon with oxygen or oxygen enriched gas lntroduced through line 4~Q. A liquid level 3~3 is maintained by controlling the flow 20 of water ~hrough line 34 by level controller ~6 r Offgases, including water vapor leave the reactor through line ~7 and pressure control valve 3~8 to a uslng process 3~9, for example, a power generation plant.
When necessary, the small quantity of ash which 25 may accumulate în ~he reactor is discharged as a small stxeam through line 4~6.
The oxygen flow may be controlled by maasurement of oxygen concentration in the offgas by analyzer 4~7. If the rate of oxidizable matter lntroduced lnto the reactor 3Q is precisely known, of course, the oxygen flow rate may be controlled without continuous measurement o~ offgas oxygen~
Noxmally the preferred point of introducing the inert gas is into the aqueous liquor through line 4~1 or into the oxygen through line 4~5. Alternate locations may be 35 through line 42 or 433 directly into the reactor. Introduction into the liquid phase through line ~ ensures diLution at the liquid-vapor interface on the reactor walls.
7~
If the critical ~ite for possible spontaneous combustion lies downstream of reactor 32, for example downstream of valve 38, inert gas may be introducea through line ~4 into vapor line 37~ In this case, the use of steam 5 as the dilutent may be used~
A spent caustic scrubbing liquor was treated by wet oxidation in a pilot plant having the flow configuration of Figure 1. The reactor was operated at a temperature of 10 412F. and a pressure of 335 psig, with a liquLd residence time of 30 minutes. Inert gas (air) was added at the reac~or top through line 20 to Line 6 leaving reactor 4 at a rate sufficient to dilute the residual oxygen to a safe level.
All of the C02 generated by oxidation was absorbed into the 15 liquid phase. Without dilution, the cooled offgas after separation would have been essentiaLly pure oxygen. Air was injected at a rate of 1.01 mole per mole Of original oxygen introduced, resulting in an oxygen concentration of 27 per-cent in the cooled offgases.
A liquor containing waste solvents, with pH of 13.1, was wet oxidized in a pilot plant with the configuration of Figure 1. The reactor conditions were 600F. and 1950 psig pressure, with a liquid residence time of 120 minutes. In 25 ~his case air was added as the inert gas to the liquor throug~
; line ~6 prior to preheating in order to prevent possible polymerization of liquor components in the heat exchang~r.
Pure oxygen was added to the reactor through llne 5~
The ratio of air injected to oxygen was n. 430 moles 30 air/mole oxygen, resulting in an oxygen concentratlon of 19.87 mole percent in the cooled offgases~ The calculated oxygen concentration at the reactor top was 3.0 mole percent, and safe operation was achieved.
' ..
Claims (11)
1. A continuous process for wet oxidation of aqueous waste liquors containing combustible matter, comprising the steps of:
A. continuously introducing aqueous waste liquor and oxygen or oxygen enriched gas into a pressurized reactor operated at elevated temperature;
B. oxidizing therein a major portion of the combustible matter in said aqueous waste liquor;
C. passing offgases from said reactor through a line to a pressure control valve operated to maintain the reactor at a substantially constant pressure; and D. injecting an inert gas into the pressurized aqueous waste liquor at a rate such that oxygen in the gas phase is diluted by the sum of generated water vapor, produced carbon dioxide and injected inert gas to a concentration less than required for spontaneous combustion at every location in the reactor, effluent line, pressure control valve and separator, having surfaces not continually exposed to a continuous liquid water phase.
A. continuously introducing aqueous waste liquor and oxygen or oxygen enriched gas into a pressurized reactor operated at elevated temperature;
B. oxidizing therein a major portion of the combustible matter in said aqueous waste liquor;
C. passing offgases from said reactor through a line to a pressure control valve operated to maintain the reactor at a substantially constant pressure; and D. injecting an inert gas into the pressurized aqueous waste liquor at a rate such that oxygen in the gas phase is diluted by the sum of generated water vapor, produced carbon dioxide and injected inert gas to a concentration less than required for spontaneous combustion at every location in the reactor, effluent line, pressure control valve and separator, having surfaces not continually exposed to a continuous liquid water phase.
2. A process according to claim 1, wherein said inert gas is nitrogen, carbon dioxide, steam or air
3. A process according to claim 1 or 2, wherein the inert gas is injected into the lower portion of the reactor.
4. A process according to claim 1 or 2, wherein the inert gas is injected into said oxygen or oxygen enriched gas passing to said reactor.
5. A process according to claim 1 or 2, wherein the inert gas is injected into the aqueous waste liquor and the resulting mixture introduced into said reactor.
6. A process according to claim 1 or 2, wherein inert gas is injected at a constant rate, and the rate of oxygen or oxygen enriched gas to said reactor is controlled by measurement of oxygen concentration in the offgases.
7. A process according to claim 1 or 2, wherein oxygen or oxygen enriched gas is introduced into said reactor at a constant rate, and air is injected as the inert gas at a rate controlled by measurement of oxygen concentration in the offgases, such that a portion of the oxygen in the air is consumed in the reactor.
8. A process according to claim 1 or 2, wherein said inert gas is injected only during non-steady state operation occuring at process start-up, shutdown and transient upsets in temperature, pressure or oxygen requirement.
9. A process according to claim 1 or 2, wherein oxidized liquor and offgases produced in step (b) are passed to a heat exchanger for cooling, the pressure of cooled oxidized liquor and offgases is reduced in said pressure control valve and the offgases are separated from the oxidized liquor in a gas-liquid separator.
10. A process according to claim 1 or 2, wherein substantially all of the water entering the reactor is evaporated and water is introduced to maintain a substantial-ly constant liquid level in the reactor.
11. A process according to claim 1 or 2, wherein the required oxygen concentration in the gas phase to avoid spontaneous combustion is determined by the pneumatic impact test or mechanical impact test.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US06/220,529 US4384959A (en) | 1980-12-29 | 1980-12-29 | Wet oxidation process utilizing dilution of oxygen |
| US220,529 | 1980-12-29 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1171186A true CA1171186A (en) | 1984-07-17 |
Family
ID=22823901
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000393047A Expired CA1171186A (en) | 1980-12-29 | 1981-12-23 | Continuous process for wet oxidation of aqueous waste liquors |
Country Status (10)
| Country | Link |
|---|---|
| US (1) | US4384959A (en) |
| EP (1) | EP0055454B1 (en) |
| JP (1) | JPS57165091A (en) |
| KR (1) | KR830007446A (en) |
| AU (1) | AU547474B2 (en) |
| CA (1) | CA1171186A (en) |
| DE (1) | DE3174024D1 (en) |
| NO (1) | NO814293L (en) |
| WO (1) | WO1982002193A1 (en) |
| ZA (1) | ZA818938B (en) |
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| US4395339A (en) * | 1982-04-01 | 1983-07-26 | Sterling Drug Inc. | Method of operating pure oxygen wet oxidation systems |
| US4728393A (en) * | 1985-11-20 | 1988-03-01 | Domtar Inc. | Methods for obtaining deicers from black liquor |
| US4721575A (en) * | 1986-04-03 | 1988-01-26 | Vertech Treatment Systems, Inc. | Method and apparatus for controlled chemical reactions |
| US4869833A (en) * | 1986-04-03 | 1989-09-26 | Vertech Treatment Systems, Inc. | Method and apparatus for controlled chemical reactions |
| US4744909A (en) * | 1987-02-02 | 1988-05-17 | Vertech Treatment Systems, Inc. | Method of effecting accelerated oxidation reaction |
| US4946555A (en) * | 1989-01-19 | 1990-08-07 | Canadian Liquid Air Ltd./Air Liquide Canada | Apparatus and method for measuring vent gas flow rates and parameters in pulp and paper processing |
| JPH04125514U (en) * | 1991-05-09 | 1992-11-16 | 株式会社神戸製鋼所 | Steel strip side trimming device |
| US5192453A (en) * | 1992-01-06 | 1993-03-09 | The Standard Oil Company | Wet oxidation process for ACN waste streams |
| US5770174A (en) * | 1992-04-16 | 1998-06-23 | Rpc Waste Management Services, Inc. | Method for controlling reaction temperature |
| US5234607A (en) * | 1992-04-22 | 1993-08-10 | Zimpro Passavant Environment Systems Inc. | Wet oxidation system startup process |
| US5354482A (en) * | 1993-05-07 | 1994-10-11 | Merichem Company | Process and apparatus for oxidizing industrial spent caustic and effecting gas-liquid mass transfer and separation |
| US5389264A (en) * | 1993-07-12 | 1995-02-14 | Zimpro Environmental Inc. | Hydraulic energy dissipator for wet oxidation process |
| US6361715B1 (en) * | 1993-09-13 | 2002-03-26 | David Reznik | Method for reducing the redox potential of substances |
| US5340473A (en) * | 1993-12-14 | 1994-08-23 | Zimpro Environmental, Inc. | Gas/liquid mixing apparatus |
| US5491968A (en) * | 1994-03-21 | 1996-02-20 | Shouman; Ahmad R. | Combustion system and method for power generation |
| US5755974A (en) * | 1994-08-01 | 1998-05-26 | Rpc Waste Management Services, Inc. | Method and apparatus for reacting oxidizable matter with a salt |
| US5620606A (en) * | 1994-08-01 | 1997-04-15 | Rpc Waste Management Services, Inc. | Method and apparatus for reacting oxidizable matter with particles |
| US5551472A (en) * | 1994-08-01 | 1996-09-03 | Rpc Waste Management Services, Inc. | Pressure reduction system and method |
| US5545337A (en) * | 1994-11-29 | 1996-08-13 | Modar, Inc. | Ceramic coating system or water oxidation environments |
| GB9425110D0 (en) * | 1994-12-13 | 1995-02-08 | Boc Group Plc | Sewage respiration inhibition |
| US6017460A (en) * | 1996-06-07 | 2000-01-25 | Chematur Engineering Ab | Heating and reaction system and method using recycle reactor |
| SE518803C2 (en) | 1999-09-03 | 2002-11-26 | Chematur Eng Ab | Method and reaction system with high pressure and high temperature suitable for supercritical water oxidation |
| FR2818162B1 (en) * | 2000-12-20 | 2003-03-07 | Air Liquide | IMPROVEMENT IN OXIDATION PROCESSES BY TRANSFER OF OXYGEN WITHIN A LIQUID MEDIUM IN A PRESSURE REACTOR |
| NZ519744A (en) * | 2002-06-24 | 2005-03-24 | Victoria Link Ltd | Wet oxidation of organic waste using metal catalysts |
| ITMI20041240A1 (en) * | 2004-06-21 | 2004-09-21 | 3V Green Eagle S P A | PARTICULAR COATING FOR EQUIPMENT TO REALIZE OXIDATIVE PROCESSES AND EQUIPMENT INCLUDING SUCH COATING |
| SE529006C2 (en) * | 2004-11-15 | 2007-04-03 | Chematur Eng Ab | Process and system for supercritical water oxidation of a stream containing oxidizable material |
| SE528840C2 (en) * | 2004-11-15 | 2007-02-27 | Chematur Eng Ab | Reactor and process for supercritical water oxidation |
| WO2017049394A1 (en) | 2015-09-24 | 2017-03-30 | Iogen Corporation | Wet oxidation of biomass |
| JP7134343B2 (en) * | 2019-04-26 | 2022-09-09 | 三菱電機株式会社 | Elevator renewal method |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3097988A (en) * | 1958-11-12 | 1963-07-16 | Sterling Drug Inc | Process for regenerating black liquor |
| US3042489A (en) * | 1958-11-20 | 1962-07-03 | Sterling Drug Inc | Production of sulfuric acid |
| GB1054239A (en) * | 1964-11-13 | |||
| US3359200A (en) * | 1966-02-24 | 1967-12-19 | Sterling Drug Inc | Partial wet air oxidation of sewage sludge |
| US3808123A (en) * | 1969-06-25 | 1974-04-30 | Buford C | Method and apparatus for the treatment of influent waters such as sewage |
| US3654070A (en) * | 1970-04-02 | 1972-04-04 | Sterling Drug Inc | Oxidation and reuse of effluent from oxygen pulping of raw cellulose |
| GB1354737A (en) * | 1970-08-31 | 1974-06-05 | Ass Pulp & Paper Mills | Wet combustion of waste liquors |
| US3761409A (en) * | 1971-10-06 | 1973-09-25 | Texaco Inc | Continuous process for the air oxidation of sour water |
| US4013560A (en) * | 1975-04-21 | 1977-03-22 | Sterling Drug Inc. | Energy production of wet oxidation systems |
| US4100730A (en) * | 1975-06-04 | 1978-07-18 | Sterling Drug, Inc. | Regulation of a wet air oxidation unit for production of useful energy |
| DE2640603B2 (en) * | 1976-09-09 | 1978-10-19 | Bayer Ag, 5090 Leverkusen | Process for the wet oxidation of organic substances |
| US4191012A (en) * | 1978-07-10 | 1980-03-04 | Stoddard Xerxes T | Wet oxidation engine |
| US4229296A (en) * | 1978-08-03 | 1980-10-21 | Whirlpool Corporation | Wet oxidation system employing phase separating reactor |
| CH649071A5 (en) * | 1978-11-13 | 1985-04-30 | Giuseppe Galassi | WET OXIDATION OF POLLUTANTS BY LIQUID OXYGEN. |
-
1980
- 1980-12-29 US US06/220,529 patent/US4384959A/en not_active Expired - Lifetime
-
1981
- 1981-12-16 NO NO814293A patent/NO814293L/en unknown
- 1981-12-21 EP EP81110667A patent/EP0055454B1/en not_active Expired
- 1981-12-21 DE DE8181110667T patent/DE3174024D1/en not_active Expired
- 1981-12-23 CA CA000393047A patent/CA1171186A/en not_active Expired
- 1981-12-24 AU AU78883/81A patent/AU547474B2/en not_active Ceased
- 1981-12-28 ZA ZA818938A patent/ZA818938B/en unknown
- 1981-12-28 KR KR1019810005184A patent/KR830007446A/en unknown
- 1981-12-29 JP JP56215928A patent/JPS57165091A/en active Granted
- 1981-12-29 WO PCT/US1981/001778 patent/WO1982002193A1/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| AU547474B2 (en) | 1985-10-24 |
| JPS57165091A (en) | 1982-10-09 |
| EP0055454B1 (en) | 1986-03-05 |
| KR830007446A (en) | 1983-10-21 |
| AU7888381A (en) | 1982-07-08 |
| NO814293L (en) | 1982-06-30 |
| DE3174024D1 (en) | 1986-04-10 |
| US4384959A (en) | 1983-05-24 |
| WO1982002193A1 (en) | 1982-07-08 |
| ZA818938B (en) | 1982-11-24 |
| JPH0134115B2 (en) | 1989-07-18 |
| EP0055454A1 (en) | 1982-07-07 |
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