WO1995034357A1

WO1995034357A1 - Method and apparatus for waste water treatment

Info

Publication number: WO1995034357A1
Application number: PCT/US1995/007365
Authority: WO
Inventors: Mark R. Holst; Richard J. Martin; John T. Schofield; Samson Yee
Original assignee: Thermatrix, Inc.
Priority date: 1994-06-10
Filing date: 1995-06-08
Publication date: 1995-12-21
Also published as: AU2822695A

Abstract

Apparatus and methods for treating waste water streams that are contaminated with organic compounds whereby the contaminants are removed from the stream in a stripping tower (34) and are thereafter destroyed by flameless oxidation within a porous inert media destruction matrix are disclosed. The resultant heat of oxidation of the organic compounds in the flameless oxidizer (10) can be utilized in the initial stripping step either to heat the waste water stream (36) prior to its entry into the stripping tower (34) or directly within the stripping tower (34) by utilizing a portion (58) of the exhaust from the flameless oxidizer (10) as the stripping gas. The destruction matrix is composed of inert ceramic materials that enhance process mixing and provide thermal inertia for process stability, with a resultant minimization of NOx oxidation by-products to levels below those achievable by conventional technologies.

Description

METHOD AND APPARATUS FOR WASTE WATER TREATMENT

Field of the Invention

The field of the present invention is methods and apparatuses for separating volatile organic compounds ("VOC's") from water containing such organics and thereafter destroying such organics. In particular, the present invention relates to apparatuses and methods for controlled exothermic reaction of organic vapors separated from waste water streams using thermal air strippers, although it will be appreciated that the invention in its broader application can be applied to any commercial process wherein volatile organic compounds are separated from a waste water stream.

Background of the Invention

Within the United States, approximately 10% of the volume of today's industrial waste water streams contains chlorinated or sulfonated contaminants. This amounts to approximately 2 billion gallons per year of waste water that must be specially treated. These waste streams are generated by manufacturers of synthetic organic chemicals, pharmaceuticals, pesticides, primary metals, and pulp and paper. By 1996, virtually all of this waste water will require VOC controls under the Clean Air Act Amendments of 1990.

There are two sets of regulations that are driving the need for destruction of organic contaminants in industrial aqueous streams. The Clean Air Act Amendments require the Environmental Protection Agency to identify sources of hazardous air pollutants ("HAP's") and to develop a maximum achievable control technology ("MACT") standard for each source category. Industrial waste water treatment facilities is on such source category. ACT is defined as the maximum degree o reductions in emissions of the HAP's that is achievable takin into account the cost of reduction and environmental impacts. In addition, regulations under the Clean Water Ac will continue to tighten restrictions on discharges fro publicly owned treatment works ("POTW's") to surface waters. These facilities are, in turn, moving away from regulatin discharges to POTW' s on concentration-based limits for particular contaminant to mass-based limits. These mass-base limits restrict total quantities of pollutants that ar discharged to the POTW. Similar to trends in air pollutio control regulations, where higher smoke stacks and greate dispersion were early control methods, water pollution control has abandoned the former strategy of dilution as a solution t pollution. Industries are now faced with the challenge of maximizing the destruction of contaminants rather than merel diluting them in order to comply with current and anticipate tightening regulations. A number of processes can be used to deal with these problems of waste water treatment for VOC removal an destruction. One such overall technique is air stripping. Air stripping maximizes the contact between air (or other gaseous stream) and water to volatilize organic constituents. In a typical method, the water is pumped to the top of an enclosed column and allowed to trickle over a substrate that has a large surface area. Air introduced at the bottom of the column flows countercurrently to the water and strips the organic compounds.

While air stripping is effective in removing some of the organic compounds from waste water, it does not destroy the separated organics and is not as effective as hot air stripping for high molecular weight organic compounds, e.g., chlorinated and sulfonated organics. Consequently, in conventional air stripping applications, the stripped organics are typically removed from the air stream by adsorption on activated charcoal or, alternatively, treated in burners, flares, or incinerators, if destruction of the organic compounds is a requirement. The use of destruction technologies in the processing of volatilized contaminants typically involves the thermo- chemical reformation of the organic compounds into such oxidized products. While this is desirable as a final solution, flame-based destruction process can pose serious performance, regulatory, and public acceptance issues. Incineration is difficult to control and can result in the formation of highly undesirable products such as dioxins, furans and oxides of nitrogen. For example, standard combustors are particularly undesirable when dealing with chlorinated hydrocarbons. Flamed combustion also results, in some instances, in incomplete combustion and uncontrollable production of undesirable side products. Because combustors typically operate at flame temperatures on the order of 3500°F, significant amounts of unwanted N0_X are often produced. The high temperatures also raise significant safety issues.

The difficulties and expense of obtaining operating permits for hazardous waste treatment processes utilizing flame based technologies is also well known.

Alternatively, the encumbrances of dealing with contaminated carbon wastes increases the costs of that type of system and affects operational factors negatively.

Thus, it can be seen that there is a need for a practical means of removing organics from waste water streams that avoids the various difficulties and inefficiencies of the prior art. There is a need for a system that has the advantages of an air stripper while reducing or eliminating the problems arising from the need to carbon filter, incinerate, or otherwise dispose of the volatilized contaminants. There is a further need for such a system to result in high destruction and removal efficiency ("DRE") of the organics while handling a broad range of contaminated liquid waste streams in a cost- effective manner.

Summary of the Invention The present invention is directed to methods an apparatuses for treating waste water streams that ar contaminated with organic compounds whereby the contaminant are removed from the waste water stream using air stripping an are thereafter destroyed by oxidation within a porous iner media destruction matrix contained as part of a flameles oxidizer. The resultant heat of oxidation of the organi compounds in the flameless oxidizer can be utilized in th initial step of removing the contaminants from the waste wate stream.

Thus, the system and process of the present inventio offers operational simplicity, near zero emissions, hea recovery and reuse, and reduced costs.

The destruction matrix is composed of inert cerami materials that enhance process mixing and provide therma inertia for process stability. Such a destruction matrix i designed to produce DRE's of greater than 99.99%, with les than 10 ppmV CO and less than 2 ppmV NO_x. The therma oxidizer/destruction matrix is designed to operate in flameless manner at temperatures of 1550-1800°F, below th normal flammability limits of the volatiles to be destroyed.

The appropriate conversion may be obtained at lowe temperatures and residence times than those required in conventional incinerator. There is also inherent safety in th use of a process in which there are no open flames, and i which the mixture of gasses to be introduced into the matrix i relatively cool, outside the flammability limits of th constituents, and, therefore, not explosive under ambien conditions. Problems of flameouts are avoided. Moreover, fro a practical viewpoint, all of these features should result i the ability to obtain required government permitting mor easily.

Accordingly, it is an object of the present inventio to provide methods and apparatuses capable of meeting existin regulations for the destruction of organic contaminant contained within waste water streams, particularly fo chlorinated or sulfonated hydrocarbon compounds. It is another object of the present invention to provide methods and apparatuses for destruction of organic contaminants contained in waste water streams while minimizing

N0_X oxidation by-products to levels below those achievable by conventional technologies.

It is an additional object of the present invention to utilize the heat generated on oxidation of the stripped organic compounds to assist in the stripping of the waste water. Other and further objects and advantages will appear hereinafter.

Brief Description of the Drawings

Fig. 1 is an embodiment of a flameless oxidizer as might be used in the process and apparatus of the present invention.

Fig. 2 is a flow diagram detailing one embodiment of the apparatus of the present invention using a cold air stripper with no recycling of heat from the oxidizer unit.

Fig. 3 is a flow diagram detailing another embodiment of the apparatus of the present invention using a hot air stripper wherein hot off gases from the oxidizer unit are used in the air stripper.

Fig. 4 is a flow diagram detailing a further embodiment of the apparatus of the present invention wherein the hot off gases from the oxidizer unit are used to preheat the waste water stream prior to its entry into the air stripper.

Detailed Description of the Preferred Embodiments

It has now been discovered that a combination of successfully demonstrated air stripping technology with an innovative high performance flameless oxidation process results in an integrated, closed loop waste water processing unit offering operational simplicity, near zero emissions, and reduced costs. The proposed integrated waste water processing system is designed to operate at reduced temperatures, utilizing the hot, inert off-gas (void of products o incomplete combustion ("PIC's")) from the flameless oxidizer t heat either the contaminated feed or to be used as th stripping gas, thus providing less expensive, yet superior an more reliable, performance.

Significant research into the phenomena of oxidatio within porous inert media ("PIM") has recently been undertaken. Because PIM oxidation can occur outside the normal premixe fueled/air flammability limits, the technology can be calle "flameless." In this regard U.S. Patent Nos. 4,688,495

(Galloway) and 4,823,711 ( roneberger et al . ) disclose earl work on matrix oxidation technology. In addition, U.S. Patent

Nos. 5,165,884 (Martin et al . ) and 5,320,518 (Stilger et al . ) discuss in significant detail the technology involved in a flameless oxidizer. Each of these patents is incorporate herein by reference.

As a treatment technology, such a flameless oxidizer process exhibits most of the advantages of conventional or catalytic thermal combustion, while avoiding many of the disadvantages. Like flame-based thermal combustion, organics are oxidized to harmless product gasses (C0₂, H₂0) or easily neutralized acid gasses (HCl, S0₂) . No waste or residues are created, and the process is suitable for a wide range of compounds or mixtures. Unlike thermal incineration, where the mixing and reaction are interdependent with the flame, these are decoupled in the inventive system, allowing greater flexibility and control, and the elimination of PICs. Additionally, no catalysts are necessary.

The basis for the oxidation process is a "destruction matrix" that fosters the conditions necessary for stable, flameless oxidation of organic compounds, outside their respective flammability limits. The three primary attributes of the destruction matrix that permit flameless oxidation are its interstitial geometry (which enhances mixing) , its thermal inertia (which promotes stability) , and its surface characteristics (which augment heat transfer) . The thermal properties of the matrix allow the mixing zone to be near ambient temperature where the fume enters while the reaction zone, further downstream, is at the appropriate oxidation temperature.

These attributes lead to several performance- and safety-related advantages in practical applications. Among these are the ability to establish a stationary reaction zone

(wherein the rate of fume oxidation is much faster than in the post-flame region of an incinerator) ; the ability to accommodate rapid process fluctuations (as with batch chemical reactor discharges) ; the capability for wide process turndown (for cost effective adaptation to changing conditions) ; the suppression of flashback (by virtue of the matrix's high surface area and heat absorption capability) ; and a high level of manageability and control (compared to a flame) . Turning in detail to the drawings, where like numbers designate like components, Fig. 1 illustrates an embodiment of one such flameless oxidizer as might be used in the process and apparatus of this invention. Typically, the flameless oxidizer

(10) will consist of a suitable matrix bed containment shell (12) that is filled with a quantity of heat resistant material creating a matrix bed (14) . The types of matrix materials used should have high heat conductance by radiation, convection, and conduction. The heat transfer properties of the system are dependent on the ratio of radiative to convective heat- transfer.

The matrix bed (14) may be sized for any desired flow stream by altering the matrix flow cross-section, height, material, void fraction, outlet temperature, and supplemental heat addition, if desired. Preferred matrix materials are ceramic balls or saddles, but other bed materials and configurations may be used, including, but not limited to, other random ceramic packings such as pall rings, structured ceramic packing, ceramic or metal foam, metal or ceramic wool and the like. Generally, the void fraction of the matrix bed will be between 0.3 and 0.9. In addition, the material in the matrix bed will typically have a specific surface area ranging from 40 m²/m³ to 1040 m²/m³. In the preferred embodiment of Fig. 1, two types o heat resistant material are used. In the lower portion of th flameless oxidizer (10) , a bed of ceramic balls acts as mixing zone (16) . This mixing zone (16) would typically hav an interstitial volume of about 40%. Above this bed of balls a bed of ceramic saddles is utilized to create a reaction zon (18) . This reaction zone (18) would typically have a interstitial volume of about 70%.

A preheater apparatus (30) is configured at the bas of flameless oxidizer (10) . This preheater (30) initiall passes hot gas through the matrix bed (14) in order to prehea both the ceramic ball mixing zone (16) and the ceramic saddl reaction zone (18) to normal operating temperatures. In on alternative embodiment, heating elements (not shown) , which ar preferably electric, can surround this containment shell (12) to provide the system with preheating and proper temperatur maintenance during operation.

The entire thermal oxidation assembly will preferabl be designed so as to minimize heat loss to the environment, while ensuring that all exposed surfaces remain below thos temperatures acceptable for a Class I, Division 2, Group area. (The National Electrical Code categorizes locations b class, division, and group, depending upon the properties o the flammable vapors, liquids, or gasses that may be presen and the likelihood that a flammable or oxidizable concentratio or quantity is present. The Code requires that the surfac temperature of any exposed surfaces be below the ignitio temperature of the relevant gas or vapor. )

Inlet gasses (20) from an upstream stripper enter th flameless oxidizer (10) through inlet (22) . While shown i Fig. 1 entering through separate inlet (22) , inlet gasses (20) could enter through the same inlet as that used for preheate (30) , thereby eliminating the need for a separate inlet (22) . In addition, depending upon process conditions, and as neede to provide sufficient heat values so as to maintain a self- sufficient operating environment within the flameless oxidizer, additional air and/or natural gas or other fuel may be added t this inlet stream (20) . There will typically, but not necessarily, be a plenum (24) , preferably made of a heat-resistant material such as a perforated plate, at the bottom of the matrix bed (14) to prevent the heat resistant material (16) from entering the piping below the matrix bed. In the normal flow pattern, where the oxidizer input stream (20) enters the flameless oxidizer (10) near the bottom, this plenum (24) will also act to evenly distribute incoming gasses and further mix these gasses prior to entering the matrix bed (14) . Nevertheless, while Fig. 1 indicates that the input stream (20) enters the flameless oxidizer (10) at the bottom and that the gaseous products (26) exit at the top, and this is the preferred embodiment, the present invention can be operated in an alternate configuration wherein the gasses enter at the top and exit at the bottom.

Within the reactor vessel (10) , during normal processing, the fume stream (20) first enters the mixing zone

(16) , which is at ambient temperature. Upon entering the mixing zone (16) , and thereafter the reaction zone (18) , the inlet gasses will be raised to oxidation temperatures of 1400- 3500°F (760-1925°C) , and preferably 1550-1800°F (845-980°C) . The emissions are then maintained at these temperatures for a sufficient residence time to ensure substantially complete destruction. In normal operation, it is contemplated that this residence time will be less than 2.0 seconds, and preferably less than 0.2 seconds.

After undergoing intimate mixing in the matrix interstices of the mixing zone (16) , the reactant mixture enters the reaction zone (18) where oxidation and heat release occur. As the gasses heat up, they expand, and this expansion is preferably accommodated by an increase in matrix void volume in reaction zone (18) , such as through the use of ceramic saddles within the reaction zone versus ceramic balls within the mixing zone. The result of this heating is the creation of a flameless oxidation zone within the matrix bed (14) whereby the volatile organic compounds are ignited and oxidized to stable products, such as water and carbon dioxide. The oxidation zon is observed as a steep increase in bed temperature from ambien temperature on the inlet side of the zone to approximately th adiabatic oxidation temperature of the mixture on the outle side of the zone. This rapid change takes place over distance of usually several inches in a typical oxidizer, wit the actual distance being dependent upon feed concentrations, feed rates, gas velocity distribution, bed material, and be physical properties, type of specific feed materials, etc. Heat losses in the direction of flow also will have an effec on the length of the oxidation zone. The rapidity of th change allows for use of a very compact reactor.

The temperature of the oxidation is dependent upo feed concentrations, feed rates, gas velocity distribution, be physical properties, type of specific feed materials, hea losses, heat input from the heaters, etc.

By decoupling the mixing from the oxidation, one o three critical parameters (turbulence, the others being tim and temperature) is removed from the design equation. Accomplishing the mixing prior to the reaction achieves tw beneficial results. First, thorough mixing of the fume and ai is ensured, negating the possibility of poorly mixed parcels leaving the system unreacted. Second, the uniformity of th reactant stream also helps to establish the uniformity of the reaction zone. Together, these factors allow the processin rate to be turned up or down, without regard to fluid mechanics constraints, over a much wider range.

After thorough destruction in the flameless oxidize (10) , the product gasses (26) then leave the reactor throug port (28) to any needed post-treatment devices (e.g., an aci gas scrubber) or to the atmosphere, as will be further discussed below.

Thus, the basics of the preferred embodiments of the flameless oxidizer of the present invention have bee disclosed. Many variations on, and additions to, these basic embodiments are also possible. The existence of a uniform, stationary, intramatrix reaction zone perpendicular to the flow axis is the fundamental condition of this flameless oxidation process. In the zone, the reactant gasses are efficiently preheated up to the oxidation temperature by the hot matrix surface, whereupon they are oxidized exothermally. They quickly release their heat back to the matrix, to maintain its local temperature. The unique heat transfer properties of the matrix bed (14) are what allows this stable reaction to occur at organic concentrations well below the lower flammability limit of the constituents. The reaction zone covers the entire flow section of the flameless oxidizer (10) , ensuring that all reactants pass through this highly reactive region. The presence of a large pool of active radicals (H, OH, etc.) in this domain allows the oxidation reactions to occur at rates up to two orders of magnitude faster than the simple thermal decomposition reactions that occur in the post-flame region of a conventional incinerator or thermal oxidizer. Since the inventive process takes advantage of the active radical chemistry (e.g., C ϊ_j, + O = _nH_n.j_. + OH) that is characteristic of combustion chain reactions, the reaction time required to destroy the vast majority of organic molecules is less than 0.1 seconds. This runs counter to the conventional incineration process with the majority of organic molecules being destroyed in the "post- flame" region, where the population of active radicals is low, and slower thermal decomposition reactions (e.g., C^ + M = ^c _m ^H _n-_ι + H + M) govern the chemistry.

These exceptionally fast kinetics eliminate the need for additional residence time, because the reactions proceed to completeness in tens of milliseconds. Therefore, in order to assure high destruction efficiencies, the appropriate constraint in such a flameless oxidizer is design capacity flow rate, rather than residence time. Because maximum flow is determined by device geometry and reaction zone properties, this constraint is device dependent, and not generic, as is residence time for flame-based technologies. The flameless technology is extremely effective a destroying chlorinated organic compounds. Chlorinate compounds are difficult to destroy by flames because of thei narrow flammability range. The present methods, however effectively convert the chlorine to HCl that is easily remove in a scrubber following the oxidizer.

Furthermore, the existence of a uniform reaction zon also minimizes the formation of PICs, which are most commonl formed in the post-flame region of an incinerator, where th organic fragments are more likely to combine with each othe than they would if the radical population was higher.

The uniform reaction zone also eliminates the region of very high temperatures and the step temperature gradient that exist in a flamed device. The present invention's abilit to control the maximum reaction temperature to be equivalent t the average reaction temperature, virtually eliminates th formation of thermal NO_x and CO. In a typical system accordin to the present invention, the DRE of the organic vapors ha been shown to be greater than 99.99%. Because the presen invention typically operates at temperatures (1550-1850°F) significantly below those present in standard combustors (abou 3500°F) , there is less production of the undesirable N0_X by products. Typical N0_X concentrations in the outlet stream ar less than 2 ppmv and CO is generally undetectable. Extensive testing of this technology has bee undertaken in determining the DRE attainable in the treatmen of various hydrocarbons and halogenated hydrocarbons. Thes test results are summarized in Table 1.

Table 1

Summary of Test Conditions and Results -- Volatile

As a totally flameless system, the technical challenges and stigma associated with incineration or other flame-based destruction technologies are avoided. The system's flameless nature will ease the permitting process as well as acceptance by the general public.

The flameless oxidation process itself is inherently energy efficient. Such a system also enhances energy efficient operation of the entire system of the present invention by utilizing the heat generated through oxidizing the VOCs to either heat the waste water stream itself or to act as the stripping gas in the stripper. If the fume contains sufficient organics (enthalpy content approximately 30 BTU/scf or more) , the reaction can be self-sustaining, and no supplementary fuel or heat is required. This behavior is contrary to the operation of a flame-based oxidizer, where the main flame is fueled exclusively by a clean, stable fuel source such as natural gas, regardless of the fume enthalpy content. The ability to operate without a separate fuel source represents a substantial energy savings for applications with non-lea fumes.

Indeed, if the recuperative techniques within th flameless oxidizer, such as those set forth in U.S. Patent No 5,320,518 (Stilger et al . ) , which has been incorporated herei by reference, are used, it is possible to establish a self sustaining reaction with a stream having an enthalpy content a low as 10 BTU/scf.

The process is typically controlled by simpl temperature control. Temperature elements (32) as shown i Fig. 1, can be connected to a programmable control system (no shown) to regulate the flow of supplementary fuel or air in th respective cases of lean or rich fume streams.

The flameless oxidizer reactor vessel is normall insulated for personnel safety and heat retention. Dependin on unit size, the matrix can retain heat for 24 hours or more which helps to reduce operating costs. The matrix also acts a a heat sink, to buffer any possible fluctuations in fume flow concentration, and composition. During the delay period afte a spike or step change in flow or concentration begins t affect the matrix temperature, the supervisory control syste is able to take the appropriate corrective action (addin supplementary fuel or air) to maintain temperature.

The heat capacity and geometry of the matrix als provide an important safety benefit -- an inherent flam arresting capability. In the event that a flammable mixtur enters the reactor, the cold (mixing) region (16) of the matri bed (14) would prevent the backward propagation of a flam upstream. The heat capacity of a unit volume of matrix i typically two or three orders of magnitude greater than th maximum exothermicity in an equivalent volume of flammable gas

Furthermore, the matrix interstices provide both th high quench surface area and tortuous pathways for flo interruption that are intrinsic to commercial flame arrestors By using only inert ceramics, the matrix is no subject to poisoning or thermal deactivation, as are catalyti materials. Also, the high initial and replacement cost o noble-metal-coated packings is avoided. Alternatively, while the present invention contemplates the use of heat resistant bed materials without catalysts, a combined inert bed and catalyst may be used to enhance process characteristics such as reaction rate, if so desired. Catalyst could be impregnated onto the heat resistant materials to alter the oxidation properties. Use of a catalyst may allow for the use of lower operating temperatures.

The types of materials in the matrix bed (14) may be varied so that the inner body heat transfer characteristics, the radiative characteristics, the forced convective characteristics, and the inner matrix solids thermally conductive characteristics may be controlled within the bed. This may be done by varying the radiative heat transfer characteristics of the matrix bed (14) by using different sizes of heat resistant materials (16, 18) to change the mean free radiative path or varying the emissivity of these materials, varying the forced convection heat transfer characteristics of the matrix bed (14) by varying its surface area per unit volume, or geometry, varying the thermally conductive heat transfer characteristics of the matrix bed (14) by using heat resistant materials (16, 18) with different thermal conductivities, or changing the point to point surface contact area of the materials in the bed. These properties may be varied either concurrently or discretely to achieve a desired effect.

In addition to changing the properties of the matrix bed (14) itself, an interface, or several interfaces, can be introduced into the bed where one or more of the heat transfer properties of the bed are discretely or concurrently changed on either side of the interface and wherein this variation serves to help stabilize the reaction zone in that location and acts as an "oxidation zone anchor." This may be done, for example, by introducing an interface where void fractions change across the interface within the matrix bed (14) , such as is represented in Fig. 1 by mixing zone (16) and reaction zone

(18) . The interface may change the mean free radiative path across the interface independent of the void fraction. B changing heat resistant materials, the emissivity may chang across the interface within the matrix bed. Changing the are per unit volume of the heat resistant materials across a interface, the forced convective heat transfer characteristic may change as the gas is passed across the interface.

The matrix bed cross-section perpendicular to the flo axis may be configured in a circular, square, rectangular, o other geometry. The area of the cross-section may b intentionally varied (i.e., as a truncated cone or truncate pyramid) to achieve a wide, stable range of reactant volumetri flow rates at each given matrix burning velocity.

Turning now to the integration of this flameles oxidizer technology within an overall system of waste wate stripping and volatiles destruction, different embodiment employing the same fundamental concepts are shown in Figs. 2-4. In each of these three embodiments, waste water is fed to stripping tower (34) in stream (36) . The stripping tower (34) is typically a packed bed comprised of a substrate having large surface area of the kind known in the art.

After the organic contaminants are volatilized withi the stripping tower (34) , a moist air stream containing th VOC's (38) exits the stripping tower (34) and is pumped vi optional booster fan (40) to the flameless oxidizer (10) . A discussed above, supplemental fuel or air (42) can be added t the inlet stream before entering the flameless oxidizer (10) i combined stream (20) . Optionally, a flame arrestor (not shown) can be located just upstream of the flameless oxidizer (10) . Prior to being vented to the atmosphere or being re- used within the system, the gaseous products from the flameles oxidizer (the off-gas) (26) may be fed through additional ga cleaning systems as needed. These may include a quench (44) and a caustic scrubber (46) in the case of chlorinated o sulfonated contaminants. Such a caustic scrubbing towe provides caustic in stream (48) and results in a dilute sal water stream (50) that may be easily disposed of. In certai situations, such additional processing will be unnecessary an the off-gas (26) would be directly used in the manner of exhaust (52) as described below.

The exhaust (52) from the caustic scrubber (46) is typically in a condition to be vented to the atmosphere. This is shown in the configuration of Fig. 2, which represents a cold stripping system. In such a system, an air stream (54) , typically at ambient temperature, is fed to the bottom of stripping tower (34) and moves countercurrently through the stripping tower (34) with respect to the waste water stream (36) . A stripped water stream (56) exits the bottom of the stripping tower (34) and may thereafter be disposed of or recycled to the plant.

An alternative embodiment is shown in Fig. 3. While similar to the design of Fig. 2 in many respects, this embodiment utilizes a portion of the exhaust (52) as the gas stream (58) used to strip the VOC's in the stripping tower

(34) . This embodiment is advantageous in at least certain circumstances in that the residual heat contained within the gas stream (58) will assist in the volatilization of the VOC's and also act to preheat the stream (20) that is fed to the inlet of the flameless oxidizer (10) .

In such a configuration, the entire waste water stream (36) (including both VOC's and water) may be vaporized in the stripping tower (34) when dealing with difficult to separate organics such as alcohols and ketones. In such an embodiment, there would be no water effluent leaving the stripper (34) in stream (56) .

Still another alternative embodiment is shown in Fig. 4. While again similar to the design of Fig. 2, this embodiment utilizes the residual heat contained in the exhaust stream (52) to preheat the waste water stream (36) . In this embodiment, waste water stream (35) is passed through heat exchanger (60) before being fed to the stripping tower in stream (36) . Exhaust stream (52) is passed through the opposite side of heat exchanger (60) wherein heat is transferred to the incoming waste water stream. Cooled exhaust stream (62) is then quenched, scrubbed, and vented to the atmosphere. In such a configuration, air stream (54) can als optionally be heated prior to being fed to stripping towe (34) .

In any of these embodiments, recuperative technique within the flameless oxidizer, such as those set forth in U.S. Patent No. 5,320,518 (Stilger et al . ) , which has bee incorporated herein by reference, can be used.

It is also possible, as would be readily understoo by those of skill in the art, to design a system that allow for the gaseous products (26) to be used partially for heatin of the waste water stream (36) prior to its entry into th stripper (34) and partially as the stripping gas itself (54 o 58) .

Each of these configurations offers at least one majo advantage. The treatment process is not classified as a incinerator, which greatly facilitates permitting. It can b shown that the integrated waste processing system is scalabl to an economical throughput capacity with system performanc and operational reliability exceeding that of an incineratio system at lower unit operating costs.

Further, the utilization of waste heat to assist i volatilizing the organic contaminants provides energ efficiency and can reduce operating costs, depending upon th VOC system involved. It should be noted, however, that th choice of a cold stripping system, such as that shown in Fig. 2, or a hot stripping system, such as those shown in Figs. 3 and 4, will typically depend upon the miscibility of the VOC's to be stripped in water. If the VOC's are not very miscible, they can be stripped more easily, and there may be no need to provide supplemental heat. If there is no necessity fo supplemental heat, then the recycling embodiments of Figs. 3 and 4 would be disfavored, since these embodiments would end up unnecessarily heating additional moisture in the stripper, leading to more water vapor entering the flameless oxidizer an a requirement for additional oxidation energy towards heatin that water vapor to the oxidation temperatures needed withi the flameless oxidizer. In addition, in either of the recycling embodiments of Figs. 3 and 4, it is important that additional air be added prior to entry into the flameless oxidizer (10) and that at least a portion of the off-gas (26) ultimately be vented. In this manner, the oxygen supply needed within the flameless oxidizer will be continuously replenished.

In a typical system, the stripping column is designed to remove 99.9% of the VOC's. The flameless oxidizer then destroys 99.99% of these VOC's. Finally, the scrubbing tower will remove 99% of any HCl gas.

In summary, apparatuses and methods for stripping and thereafter destroying hazardous organics from a waste water stream using a flameless oxidation system have been described. The oxidation temperature and residence times in the present oxidizer are lower than those of a conventional incinerator, thereby providing a high conversion of reactants to products with a minimum of unwanted by-products such as NO_x. Use of such a flameless oxidation process within a stripping system leads to efficiencies of cost and energy. The present invention has been described in terms of several preferred embodiments. However, the invention is not limited to the embodiments depicted and described, but can have many variations within the spirit of the invention. For example, while quenches and caustic scrubbers are shown and described, it would be obvious to those of skill in the art that other standard gas cleaning systems can be utilized within the framework of the present invention.

Accordingly, the scope of the invention should be determined not by the embodiments illustrated, but rather by the appended claims and their legal equivalents. Having thus described the invention, what is desired to be protected by Letters Patent is presented by the following appended claims.

Claims

What is claimed is:

1. A method for removing volatile contaminants fro a waste water stream comprising the steps of:

(a) stripping the volatile contaminants from th waste water stream in a stripping column utilizing countercurrently flowed stripping gas stream that is below th temperature at which such volatile contaminants would oxidiz or combust, whereby such volatile contaminants are volatilize into a process gas stream; (b) heating at least a portion of a matrix bed o heat resistant material within a flameless oxidizer to a secon temperature above the autoignition temperature of th volatilized contaminants; and

(c) feeding the process gas stream through the matri bed, whereby the volatilized contaminants are oxidized int gaseous products in a flameless reaction zone.

2. The method of claim 1 further comprising the ste of using at least a portion of the oxidized gaseous products t heat additional waste water before such additional waste wate is stripped of volatile contaminants.

3. The method of claim 1 wherein at least a portio of the oxidized gaseous products are used as the stripping gas stream in the stripping column.

4. The method of claim 1 including the further ste of establishing the flow of the process gas stream through the matrix bed so that the heat from the reaction zone is used to preheat the volatilized contaminants as they enter the matri bed.

5. The method of claim 1 comprising the furthe steps of monitoring the temperature of the matrix bed an controlling the position of the reaction zone within the matri bed in response thereto.

6. The method of claim 1 comprising the further step of admixing air, oxygen, supplemental fuel, or both with the process gasses prior to feeding the process gasses to the matrix bed.

7. The method of claim 5 wherein the step of controlling the position of the reaction zone within the matrix bed is achieved by supplying controlled volumes of air, fuel, or oxygen to the matrix bed in addition to the volatilized contaminants.

8. The method of claim 1 further comprising the step of treating the oxidized gaseous products in a scrubber.

9. The method of claim 1 f rther comprising the step of recovering heat from the oxidized gaseous products prior to venting such gaseous products to the atmosphere.

10. The method of claim 1 wherein the matrix bed temperature is maintained between about 1400°F (760°C) and about 3500°F (1925°C) in the reaction zone.

11. The method of claim 1 wherein the process gas stream includes one or more hydrocarbons selected from the group consisting of oxygenated hydrocarbons, halogenated compounds, aminated compounds, and sulphur-containing compounds.

12. The method of claim 1 wherein the oxidized gasses have a NO_x content less than about 2 parts per million by volume and a carbon monoxide content less than about 10 parts per million by volume, on a dry basis, adjusted to 3% oxygen.

13. The method of claim 1 wherein the heat resistant material is chosen from the group consisting of ceramic balls, ceramic saddles, ceramic pall rings, or ceramic raschig rings.

14. The method of claim 1 wherein the matrix be comprises at least two layers of heat resistant materia wherein the layers are comprised of differently sized hea resistant material and the process gas stream passes throug the layer of smaller sized materials first.

15. The method of claim 1 wherein the heat resistan material of the matrix bed comprises a catalyst.

16. The method of claim 1 wherein a destruction an removal efficiency of the volatilized contaminants of at leas 99.99% is achieved.

17. In a method for stripping waste water comprisin the steps of passing such waste water countercurrently to a ga stream in a stripper column comprised of packed material t volatilize the volatile contaminants while maintaining th temperature of such volatile contaminants below that at whic such volatile contaminants would oxidize or combust, whereb such volatile contaminants are volatilized into a process ga stream and are thereafter treated to remove or destroy th volatilized contaminants, the improvement comprising: (a) heating at least a portion of a matrix bed o heat resistant material within a flameless oxidizer above th autoignition temperature of the volatilized contaminants; an

(b) feeding the process gas stream through the matri bed, whereby the volatilized contaminants are oxidized int gaseous products in a flameless reaction zone.

18. The method of claim 17 further comprising th step of using at least a portion of the oxidized gaseou products to heat additional waste water prior to its being fe to the stripper.

19. The method of claim 17 wherein the oxidize gaseous products are used as the stripping gas stream in th stripping column.

20. The method of claim 17 wherein the flow of the process gas stream through the matrix bed is established so that the heat from the reaction zone is used to preheat the volatilized contaminants as they enter the matrix bed.

21. The method of claim 17 comprising the further step of admixing air, oxygen, supplemental fuel, or both with the process gasses prior to feeding the process gasses to the matrix bed so as to control the position of the reaction zone within the matrix bed.

22. The method of claim 17 wherein the matrix bed temperature is maintained between about 1400°F (760°C) and about 3500°F (1925°C) in the reaction zone.

23. The method of claim 17 wherein the oxidized gasses have a N0_X content less than about 2 parts per million by volume and a carbon monoxide content less than about 10 parts per million by volume, on a dry basis, adjusted to 3% oxygen.

24. The method of claim 17 wherein the heat resistant material is chosen from the group consisting of ceramic balls, ceramic saddles, ceramic pall rings, or ceramic raschig rings.

25. The method of claim 17 wherein the matrix bed comprises at least two layers of heat resistant material wherein the layers are comprised of differently sized heat resistant material and the process gas stream passes through the layer of smaller sized materials first.

26. The method of claim 17 wherein a destruction and removal efficiency of the volatilized contaminants of at least 99.99% is achieved.

27. A method for removing volatile contaminants from waste water comprising the steps of: (a) stripping the volatile contaminants from th waste water stream in a stripping column utilizing countercurrent stripping gas stream that is below th temperature at which such volatile contaminants would oxidiz or combust, whereby such volatile contaminants are volatilize into a process gas stream;

(b) heating at least a portion of a matrix bed o heat resistant material chosen from the group consisting o ceramic balls, ceramic saddles, ceramic pall rings, or cerami raschig rings and comprising at least two layers wherein th layers are comprised of differently sized heat resistan material and the process gas stream passes through the layer o smaller sized materials first within a flameless oxidizer abov the autoignition temperature of the volatilized contaminants (c) feeding the process gas stream through the matri bed, whereby the volatilized contaminants are oxidized int gaseous products in a flameless reaction zone;

(d) controlling the position of the reaction zon within the matrix bed by supplying controlled volumes of air fuel, or oxygen to the matrix bed in addition to th volatilized contaminants; and

(e) using at least a portion of the oxidized gaseou products to heat additional waste water prior to its being fe to the stripper column.

28. An apparatus for removing volatile contaminant from waste water comprising:

(a) a stripper column having an upper and a lower en comprising:

(i) a porous bed comprised of material wit high surface area;

(ii) a waste water inlet located near the uppe end of the column and connected to the porous bed;

(iii) a gas inlet located near the lower end o the column and connected to the opposite end of th porous bed from the end to which the waste wate inlet is connected; (iv) a gas outlet located near the upper end of the porous bed in flow communication with the gas inlet; and

(v) a liquid outlet located near the lower end of the porous bed in flow communication with the waste water inlet;

(b) a flameless oxidizer having:

(i) an inlet in flow communication with the outlet of the stripper column; (ii) an outlet for reaction gaseous products; and

(iii) a section located between the inlet and the outlet including a matrix bed of heat resistant material;

(c) a heater for heating at least a portion of the section including a matrix bed of heat resistant material to a temperature exceeding the decomposition temperature of the volatilized contaminants; and

(d) means for creating a gas flow through first the stripper column and thereafter the flameless oxidizer.

29. The apparatus of claim 28 wherein the outlet for reaction gaseous products from the flameless oxidizer is in flow communication with the gas inlet of the stripper column.

30. The apparatus of claim 28 further comprising: a heat exchanger having a cool side and a hot side; an outlet from the cool side of the heat exchanger in flow communication with the waste water inlet of the stripper column; an inlet to the hot side of the heat exchanger in flow communication with the outlet for reaction gaseous products from the flameless oxidizer such that reaction gaseous products can transfer heat to waste water prior to such waste water being fed to the stripper column.

31. The apparatus of claim 28 wherein the section of the flameless oxidizer is configured to create a flow pattern from the inlet to the outlet that allows heat from the matri bed to preheat the volatilized contaminants as they enter th matrix bed.

32. The apparatus of claim 28 wherein the section o the flameless oxidizer is constructed so that it can thermall destroy volatilized contaminants without use or creation of flame.

33. The apparatus of claim 28 further comprising on or more temperature sensors for sensing the temperature of th matrix bed.

34. The apparatus of claim 28 further comprisin means for controllably adding air, oxygen, supplemental fuel, or both to the gas flow between the gas outlet of the strippe column and the matrix bed.

35. The apparatus of claim 28 further comprising scrubber in flow communication with the outlet of the flameless oxidizer.

36. The apparatus of claim 28 wherein the heat resistant material is chosen from the group consisting of ceramic balls, ceramic saddles, ceramic pall rings, or ceramic raschig rings.

37. The apparatus of claim 28 wherein the matrix be comprises at least two layers of heat resistant material wherein the layers are comprised of differently sized heat resistant material and wherein the section of the flameless oxidizer is configured to create a flow pattern from the inlet to the outlet that causes any flow to pass through the layer of smaller sized materials first.

38. The apparatus of claim 28 wherein the heat resistant material of the matrix bed comprises a catalyst.

39. The apparatus of claim 28 wherein the matrix be has a void fraction from 0.3 to 0.9.

40. The apparatus of claim 28 wherein the material in the matrix bed has a specific surface area from 40 m²/m³ t 1040 m²/m³.

41. The apparatus of claim 28 further comprisin means for feeding waste water to the waste water inlet of the stripper column.

42. An apparatus for removing volatile contaminants from waste water comprising:

(a) a stripper column having an upper and a lower en comprising:

(i) a porous bed comprised of material wit high surface area; (ii) a waste water inlet located near the upper end of the column and connected to the porous bed;

(iii) a gas inlet located near the lower end of the column and connected to the opposite end of the porous bed from the end to which the waste water inlet is connected;

(iv) a gas outlet located near the upper end of the porous bed in flow communication with the gas inlet; and

(b) a flameless oxidizer having:

(i) an inlet in flow communication with the outlet of the stripper column; (ii) an outlet for reaction gaseous products;

(iii) a section located between the inlet and the outlet including a matrix bed of heat resistant material having a void fraction from 0.3 to 0.9 and a specific surface area from 40 m²/m³ to 1040 m²/m³ and

(iv) one or more temperature sensors for sensin the temperature of the matrix bed; (c) means for controllably adding air, oxygen supplemental fuel, or both to the gas flow between the ga outlet of the stripper column and the matrix bed;

(d) a heat exchanger having a cool side and a ho side; (e) an outlet from the cool side of the hea exchanger in flow communication with the waste water inlet o the stripper column;

(f) an inlet to the hot side of the heat exchange in flow communication with the outlet for reaction gaseou products from the flameless oxidizer such that reaction gaseou products can transfer heat to waste water prior to such wast water being fed to the stripper column;

(g) a heater for heating at least a portion of th section including a matrix bed of heat resistant material to temperature exceeding the decomposition temperature of th volatilized contaminants; and

(h) means for creating a gas flow through first th stripper column and thereafter the flameless oxidizer.