JP2004167486A - Method for reducing emission of waste oxide gas in industrial process - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To economically reduce the emissions of nitrogen oxides (NOx) generated from a waste destruction process without significant loss of overall waste destruction efficiency. <P>SOLUTION: The emissions of waste oxide gas generated in a thermal oxidizer can be reduced by the use of a multizone waste thermal oxidizer comprising at least one primary combustion zone and at least one downstream waste destruction zone, and by performing the primary combustion of fuel prior to the destruction of at least a portion of the waste. <P>COPYRIGHT: (C)2004,JPO

Description

  The present invention relates to a method for reducing unwanted emissions in industrial processes. More particularly, the present invention relates to a method for reducing the production of oxide waste gas during the course of thermal oxidation.

  Thermal oxidizers are often used to dispose of waste streams from industrial processes. In a typical thermal oxidizer, a waste stream and an oxidizer are compounded at an elevated temperature to decompose the waste. If the waste stream is well mixed with the oxidant and the waste is maintained at a high temperature in the thermal oxidizer for a sufficient time, waste decomposition occurs through a combination of oxidation reactions. It may also be necessary to provide a fuel flow to the thermal oxidizer. The fuel streams are simultaneously burned in a thermal oxidizer to maintain a desired waste decomposition temperature. In some cases, a waste heat recovery device such as a heat recovery steam boiler (HRSB) may also be incorporated into the thermal oxidizer, but this is not the primary purpose. For thermal oxidizers, it is necessary to maximize waste decomposition efficiency, and the use of HRSB is entirely optional.

  Oxide waste gas "WOG" is often produced as a by-product of the thermal oxidizer operation because of the high temperatures required to maintain cracking efficiency (typically 600 ° C. or higher). The oxide waste gas is a gas containing a nitrogen-based oxide (NOx), a sulfur-based oxide (SOx), a carbon-based oxide (COx), or a combination thereof. The oxide waste gases are produced by a variety of processes, including chemical, combustion or thermal processes.

  When introduced into the environment, oxide waste gases can produce undesirable effects. For example, nitrogen-based oxides play a major role in ozone formation and are thought to be responsible for the nitric acid component of acid rain. Sulfur-based oxides are associated with acidification of lakes and rivers, increased corrosion of buildings and monuments, reduced visibility and adverse health effects. Carbon-based oxides, most notably carbon monoxide, can pose a serious public health problem and have been associated with global warming. Because of these serious environmental and health hazards, the introduction of oxide waste gases into the environment is tightly regulated by both national and local government agencies. These regulations are expected to be more restrictive in the coming era.

  One purpose of thermal oxidizers is to break down waste compounds and convert them preferentially to harmless carbon dioxide and water. Thus, the occurrence of WOG described above is an undesirable effect that industry dares to minimize. Many different designs and structures have been proposed for thermal oxidizers, but all include at least one hot waste decomposition zone and therefore produce at least some WOG.

  In contrast to thermal oxidizers, industrial boilers convert heat from fuel combustion into steam. Industrial boilers (also referred to as utility boilers, commercial boilers, utility boilers or direct-fired boilers) have at least one combustion zone (commonly referred to as a "furnace" section) and at least one steam boiler section. Including. Steam generated from industrial boilers can be used for heating applications-for example, operating distillation columns in refineries-but more typically, the steam provides power for operating a steam turbine coupled to a generator. Used for Despite this objective difference, industrial boilers also produce WOG as a result of this operation.

  Because there are more industrial boilers in use than thermal oxidizers, most of the WOG emission reduction efforts to date have focused on improving industrial boilers rather than thermal oxidizer operations. Was. In particular, the United States government and many industrial boiler manufacturers have devoted considerable research effort to reducing NOx emissions produced by industrial boilers. The emission reduction method developed as a result of this work is that industrial boilers utilize a limited number of fuels-mainly coal and high-purity natural gas-and these fuels have a relatively constant composition, It takes advantage of the fact that it is used at an essentially constant burning rate.

  It is proposed that some of the known industrial boiler emission reduction methods may also be applicable to industrial process thermal oxidizers. Unfortunately, these methods are only for limited use. All industrial boiler emission reduction methods involve substantial capital, operating or maintenance costs. They make these methods economically unattractive when applied to waste decomposition systems. In addition, blind applications of boiler-related methods to industrial thermal oxidizers can result in reduced waste decomposition efficiency, and often are themselves harmful to the environment as oxide waste gas. It produces certain by-products.

  Traditional oxide waste gas reduction methods for industrial boilers can be grouped into two broad categories: combustion improvement and post-combustion processes. Reduction methods that prevent NOx formation are termed "combustion improvement" and include low NOx burners, overfire air, reburning, flue gas recirculation, and operational improvements. Reduction methods that break down once formed NOx are referred to as "post-combustion processes." Post-combustion processes include selective catalytic reduction, selective non-catalytic reduction, and hybrid processes.

  Low NOx burners (LNBs) are one method of improving combustion and are designed to regulate the mixing of fuel and air to reach some of the staged combustion. Staged combustion involves some combustion in the primary stage and additional combustion in the reburn stage portion of the waste cracker. Consequently, step reduction reduces both flame temperature and oxygen concentration in the course of some combustion phases, which in turn reduces both thermal NOx and fuel NOx production. To achieve staged combustion, it is required that fuel gas be provided to the reburn stage in addition to the fuel gas delivered to the primary stage. The potential benefits of this implementation are offset by excessive fuel gas consumption in the reburn portion of the device.

  Changing certain boiler operating parameters can create conditions in the furnace that will reduce NOx production-these changes are commonly referred to as operational improvements. Examples include burners-out-of-service (BOOS), low excess air (LEA), and biased firing (BF).

  Conventional combustion improvement methods as described above are either very capital intensive or, in the case of operational improvements, detrimental to achieving the required waste decomposition efficiency. As mentioned above, the method of decomposing NOx once formed is called "post-combustion process" and includes selective catalytic reduction (SCR), selective non-catalytic reduction (SNCR) and hybrid processes.

  It should be noted that while conventional post-combustion methods can achieve a certain level of reduction in WOG emissions, they are not without undesirable environmental deficiencies. For example, the use of SNCR results in the release of ammonia and nitrous oxide into the environment. The released ammonia can have deleterious effects downstream of the SNCR system, including air heater contamination, plume formation and other significant fly ash contamination. SCRs may also have undesirable effects, including, for example, the release of ammonia, the accelerated production of undesirable sulfur oxides, and high gas-side pressure drops. Further, the ammonia handling and storage required by SNCR and SCR methods poses serious safety issues. Furthermore, SCR reduction methods use zeolites or noble metal catalysts. Such catalysts are not only expensive to purchase, but also expensive to dispose of when their expiration date has expired. The catalyst is also sensitive to contaminants, such as sulfur-containing compounds, and the system can be easily contaminated (eg, in-situ formation of ammonium sulfate). Also, for oxide decomposition methods, maintenance costs are increased and specialized continuous emission monitoring equipment is often required to monitor system performance.

  Accordingly, there are many deficiencies with current industrial methods for reducing oxide waste gas associated with thermal oxidizers. For simple, low-capacity, high-efficiency processes in which thermal oxidizers can be operated with minimal oxide waste gas emissions in industrial processes, while maintaining optimal cracking efficiency during the waste cracking process There is a need for. Further, there is a need for a thermal oxidizer that can produce reduced amounts of oxide waste gas without requiring the need for fuel gas downstream of the primary combustion zone.

  Therefore, one aspect of the present invention provides a novel method for reducing oxide waste gas emissions in industrial processes. Another aspect of the present invention provides a novel waste decomposition method that results in lower oxide waste gas emissions. These and other novel features will be apparent to those of ordinary skill in the art after reading this specification and the claims.

  Accordingly, one aspect of the present invention provides a novel process for reducing the occurrence of NOx emissions. These processes direct the waste stream to a thermal oxidizer; burn at least a portion of the waste stream in a primary combustion zone of the thermal oxidizer; and dispose of the waste stream in a waste decomposition zone downstream of the thermal oxidizer. And injecting at least a portion of the material stream. The waste stream contains at least about 0.5 mole% of reactive waste components and no more than about 99.5 mole% of inert components. Preferably, the waste stream contains at least about 2.0 mole% of reactive waste components and no more than about 98 mole% of inert components.

  The method of the present invention further includes providing an aqueous waste stream to the primary combustion zone. Also included in the present invention is the step of providing associated waste to a downstream waste decomposition zone, wherein the associated waste is selected from the group consisting of aqueous waste and alternative waste.

  The process of the present invention is characterized in that the product produced by the industrial process is selected from the group consisting of acrylic acid, methacrylic acid, acrolein, methacrolein, hydrogen cyanide, acrylonitrile, methacrylonitrile, phthalic anhydride, maleic anhydride and mixtures thereof. Can be combined with industrial processes.

  In an alternative embodiment of the present invention, the industrial chemical process is a product selected from the group consisting of methacrylic acid, acrolein, methacrolein, hydrogen cyanide, acrylonitrile, methacrylonitrile, phthalic anhydride, maleic anhydride and mixtures thereof. And a method for reducing the emission of waste oxide gases of industrial chemical processes. Alternative aspects of the invention include directing the waste stream to a horizontal thermal oxidizer; burning at least a portion of the waste stream in a primary combustion zone of the thermal oxidizer; and further decomposing the waste downstream of the thermal oxidizer. Injecting at least a portion of the waste stream into the zone. In an alternative embodiment, the waste stream comprises at least about 0.5 mole% reactive waste components and no more than about 99.5 mole% inert components. An alternative aspect of the invention also includes providing an aqueous waste stream to the primary combustion zone. An alternative embodiment of the present invention also includes providing associated waste to a downstream waste decomposition zone, wherein the associated waste is selected from the group consisting of aqueous waste and alternative waste. You.

  The present invention relates to a method for reducing oxide waste gas emissions. Specifically, oxide waste gas emissions produced in the thermal oxidizer are reduced by use of a multi-band waste thermal oxidizer that includes at least one primary combustion zone and at least one downstream waste decomposition zone. obtain. Performing primary combustion of the fuel prior to at least partial decomposition of the waste reduces oxide waste gas emissions from the waste decomposition process economically and without significant loss of overall waste decomposition efficiency It has been found that this can be done. Further, it has been found that the addition of an aqueous waste stream to the primary combustion zone can also serve to reduce oxide waste gas emissions.

  Referring to the drawings herein, a method for reducing oxide waste gas content in an effluent according to one aspect of the present invention is illustrated in FIG. Like numbers represent like flows, steps and elements. The thermal oxidizer 20 of FIG. 1 is shown in a schematic diagram as a multi-stage horizontal thermal oxidizer. In the embodiment of FIG. 1, oxidant stream 10 is combusted with combustion fuel stream 12 in primary combustion zone 22 of thermal oxidizer 20. Oxidant stream 10 contains one or more gases and contains 1 to 100% oxygen. Examples of suitable oxidants include, but are not limited to, air, 100% pure oxygen, oxygen-enriched air, ozone, or an oxygen-containing process vent gas. In some embodiments, rather than providing a mixed oxidant stream, it may be beneficial to utilize two separate oxidant streams, which can be separated into the thermal oxidizer but immediately inside the thermal oxidizer. Is introduced very close enough to promote good mixing. For example, for safety and operability reasons, the atmospheric flow can be injected from the nozzle separately, but in close proximity to the pure oxygenation lance.

  As shown in FIG. 1, a portion of the oxidant stream 10 may also be optionally diverted at the tee 11 to provide a supplemental oxidant stream 13. Injecting make-up oxidant stream 13 into one or more downstream waste decomposition zones can increase waste decomposition efficiency. In the embodiment of FIG. 1, supplemental oxidant 13 is provided to secondary waste decomposition zone 26 via addition point 23.

  Preferably, the combustion fuel 12 is natural gas, but the combustion fuel may include any mixture of one or more components that can release heat when reacted with an oxidant. Examples of suitable combustion fuel components include, but are not limited to, fuel oils, hydrocarbon gases, hydrogen, flammable organics, and coal. FIG. 1 illustrates a combustion fuel stream 12 injected into a primary combustion zone 22 at a single point. However, the combustion fuel stream 12 may be added through multiple points or the primary combustion zone 22 via a burner, wind box, mixer, distributor, injector, nozzle or other device that delivers combustion fuel to the combustion zone 22. Can be introduced.

  Similarly, many options can be used for oxidant addition to the combustion zone 22 and the waste decomposition zone 26. In the primary combustion zone 22, the oxidant stream 10 and the combustion fuel stream 12 are mixed and burned to generate heat. In some embodiments, it may be beneficial to compound the combustion fuel and oxidizer prior to or simultaneously with the addition to the combustion zone, and common equipment such as mixers, low NOx burners (LNB) or atomizers may be used. Can be used for the purpose. The selection of the appropriate fuel and oxidizer addition equipment is within the capabilities of those skilled in the art and depends on a number of variables including the type of fuel and oxidizer used, the structure of the thermal oxidizer and economic factors.

NOx is generated during combustion as a result of the high temperatures present in primary combustion zone 22 and the presence of nitrogen in oxidant stream 10 and / or combustion fuel stream 12. The combustion process typically also produces some amounts of carbon dioxide, carbon monoxide and water.
Heat and combustion products from the primary combustion zone 22 flow into an adjacent primary waste decomposition zone 24 and into a secondary waste decomposition zone 26. Accordingly, primary waste decomposition zone 24 is termed as being “downstream” of primary combustion zone 22 and secondary waste decomposition zone 26 is downstream of primary waste decomposition zone 24.

  The waste stream 14 is introduced into the thermal oxidizer 20 via a first waste decomposition zone waste stream addition point 25. The waste stream 14 generally contains components or streams to be decomposed from an industrial process. The waste stream 14 may include a gas, a liquid, or a mixture of both, and may also include inert components such as water, diatomic nitrogen or carbon dioxide. The actual composition of the waste gas stream 14 will depend on the particular industrial process under consideration, but must include at least a minimum amount of reactive waste components. By "reactive waste component" is meant a waste component that can react with oxygen that is part of the oxide waste gas molecules. Examples of such reactive waste components include, but are not limited to, aliphatic hydrocarbons, ammonia, acrolein, hydrogen, hydrogen cyanide, carbon monoxide, urea, and aromatics. The compounds described above can contain oxygen atoms as part of their structure, such as carbon monoxide, but compounds that do not contain oxygen are generally preferred.

  To effectively reduce WOG emissions, the waste stream injected into the downstream waste cracking zone contains at least 0.5 mol% of reactive waste components or no more than 99.5 mol% of inert components. Is preferred. It is particularly preferred that the waste stream contains at least 2 mol% of reactive waste components or up to 98 mol% of inerts.

  In the embodiment of FIG. 1, the first waste cracking zone waste stream addition point 25 is a single connection on the outer surface of the thermal oxidizer 20, which is a series of radials on the inside of the thermal oxidizer 20. Connected to the distribution nozzle located at The nozzles provide a flow that is distributed around the circumference of the thermal oxidizer 20 for improved mixing and decomposition efficiency. The high temperature and oxygen in the thermal oxidizer decompose waste components.

  As a result of exposure to high temperatures in a thermal oxidizer, some reactive waste components form radicals that can scavenge oxygen from WOG compounds such as NOx, thereby converting them to diatomic nitrogen and other substances. To such an inert compound. Said thermally initiated radicals are referred to herein as "reducing radicals". Although the formation of reducing radicals should theoretically occur in any high temperature environment, their presence is generally short-lived in the primary combustion zone. As a result, no significant reduction in WOG emissions is obtained.

  It has been found that the desired result of reduced WOG emissions can be obtained if at least some of the reactive waste components are introduced after primary combustion has occurred. The post-primary injection described above delays the formation of reactive radicals and improves their efficiency in reducing WOG emissions. Thus, WOG emissions are effectively reduced when reactive waste components are present in the waste decomposition zone downstream of the primary combustion zone.

  Industrial chemistry processes associated with the horizontal aspects of the thermal oxidizer can include processes that produce hydrogen cyanide, acrolein, acrylonitrile, methacrylonitrile, methacryloline, methacrylic acid, phthalic anhydride, maleic anhydride, and mixtures thereof. .

  Some reactive waste components are more effective than others in forming thermally initiated reducing radicals at a given temperature, and therefore due to their greater WOG reduction capacity. To be preferred. Thus, aliphatic hydrocarbons (eg, hexane) are a preferred class of reactive waste components for aromatic ring compounds (eg, benzene) and alkanes (eg, propane, butane) are alkenes (eg, propylene, Butylene) is preferred as a reactive waste component.

  Accordingly, industrial chemical processes that utilize alkanes rather than alkenes as the primary feed are particularly preferred for use with the method of the present invention. Examples of such alkane-based processes include, but are not limited to, the production of acrolein, acrylic acid and acrylonitrile via the catalysis of propane, and the production of methacrylic acid and methacrolein from the reaction of C4-alkanes. .

  In the specific case of the exemplary process described above, an absorber offgas waste stream is typically generated and comprises at least some unreacted alkane feed. When said waste streams are injected into a thermal oxidizer according to the method of the present invention, they are expected to reduce NOx more effectively than comparable waste streams derived from similar alkene-based processes. Can be done.

Also, compounds such as CO, H ₂ and NH ₃ are known to be effective reducing agents and therefore would be desirable reactive waste components when utilized in accordance with the method of the present invention. Be recognized.

  As shown in FIG. 1, a portion of the waste stream 14 can also be optionally diverted at a tee 15 to provide a supplemental waste stream 17. By injecting make-up waste stream 17 into one or more downstream waste decomposition zones, WOG emission reduction efficiency can be improved. In the embodiment of FIG. 1, make-up waste stream 17 is supplied to secondary waste decomposition zone 26 via waste stream addition point 27. The addition point 27 can consist of a burner, wind box, mixer, distributor, injector, nozzle or other such injection hardware.

The reactive waste components of the supplemental waste stream 17 react with the oxide waste gas present in the secondary waste decomposition zone 26 without being removed in the primary waste decomposition zone 24. Ideally, these WOG compounds are converted in the secondary waste destruction zone within 26 release, contamination is not a compound, for example N _2, CO ₂ and H _{2 O,} and the into the atmosphere as exhaust stream 32 innocuous Can be done. In some embodiments, the ancillary waste stream is injected into the thermal oxidizer either through a dedicated injection point or by mixing the ancillary waste stream into the waste stream 14 or alternatively into the make-up waste stream 17. It is envisioned that may be beneficial.

  Ancillary waste streams include waste streams that may originate from other parts of the present industrial process or from completely different processes. The associated waste stream may or may not contain significant amounts of reactive waste components, and may also include solids, liquids, gases or mixtures of two or more thereof. Examples of such incidental wastes include, but are not limited to, recovered fuel waste, organic contaminated wastewater, process vent gas, polymer solids or mineral acid residues. The associated waste stream may also include MMA light boiling ends (including acetone, methanol, and methyl methacrylate) and certain amine process residues (t-alkyl primary amines and C6 + hydrocarbons). it can.

  If significant liquid waste components are present in a given waste stream, e.g., in embodiments where the waste stream contains organically contaminated wastewater, at least some of the liquid waste components will be in the zone upstream of the thermal oxidizer Preferably, the injection and residence time is maximized, thereby improving waste decomposition efficiency. It is particularly preferred that the liquid component is at least partially injected into the primary combustion zone.

  It should be noted that dotted line 29 represents the boundaries between the various zones within thermal oxidizer 20. The lines are dashed, indicating that the actual boundaries between these zones in the thermal oxidizer are not static, but instead change places during the waste decomposition process. Because the thermal oxidizer is a dynamic system, the boundary at which primary combustion ends and waste decomposition begins is not completely stationary, but instead moves back and forth along the limited length of the thermal oxidizer 20 be able to. From a practical point of view, placing the flow injection point at a distance of about 0.15 meters (0.5 feet) or more downstream of the fuel or waste injection point described above generally requires maintaining an independent downstream zone. It is far enough away.

  The exit stream exiting the secondary waste decomposition zone 26 proceeds to an exit stream stack 30 to the atmosphere. Optionally, the exhaust stream 32 communicates with a heat recovery steam boiler (HRSG) 28 or other heat recovery device to recover some of the thermal energy contained in the exhaust stream 32. Recovering the thermal energy of the effluent stream 32 improves the energy efficiency of the overall waste decomposition process, by recovering the thermal energy from the thermal oxidizer effluent stream as steam.

  FIG. 2 illustrates, in schematic form, a preferred embodiment of the present invention in which thermal oxidizer 120 is a two-stage vertical thermal oxidizer. Vertical embodiments are generally preferred due to their reduced size and lower capital cost as compared to thermal oxidizers in the horizontal embodiment. In a vertical aspect, oxidant stream 110 and combustion fuel 112 are delivered to primary combustion zone 122 of thermal oxidizer 120 where the contents of oxidant stream 110 and combustion fuel stream 112 are burned. Hot NOx and other oxide waste gases are produced during combustion in primary combustion zone 122.

  Oxidant stream 110 contains one or more gases and contains 1 to 100% oxygen. Examples of suitable oxidants include, but are not limited to, air, 100% pure oxygen, oxygen-enriched air, ozone, or an oxygen-containing process vent gas. In some embodiments, rather than providing a mixed oxidant stream, it may be beneficial to utilize two separate oxidant streams, which may be separate to the thermal oxidizer but immediately inside the thermal oxidizer. Is introduced very close enough to promote good mixing. For example, for safety and operability reasons, the atmospheric flow can be injected from the nozzle separately, but in close proximity to the pure oxygenation lance.

  Although the combustion fuel 112 is preferably natural gas, the combustion fuel can include any mixture of one or more components that can release heat when reacted with an oxidant. Examples of suitable combustion fuels include, but are not limited to, fuel oils, hydrocarbon gases, hydrogen, flammable organics, and coal. FIG. 2 illustrates the combustion fuel stream 112 injected into the primary combustion zone 122 at a single point. However, the combustion fuel stream 112 may be added through multiple points or may be introduced through a burner, wind box, mixer, distributor, injector, nozzle, or other device that delivers combustion fuel to the primary combustion zone 122.

  Also, many options can be used for oxidant addition to primary combustion zone 122 and waste decomposition zone 124. In the primary combustion zone 122, the oxidant stream 110 and the combustion fuel stream 112 are mixed and burned to generate heat. In some embodiments, it may be beneficial to compound the combustion fuel and oxidizer prior to or simultaneously with the addition to the combustion zone, and common equipment such as mixers, low NOx burners (LNB) or atomizers may be used. Can be used for the purpose. The selection of the appropriate fuel and oxidizer addition equipment is within the abilities of those skilled in the art and depends on many variables including the type of fuel and oxidizer used, the structure of the thermal oxidizer and economic factors.

  Another advantage of the vertical configuration of thermal oxidizer 120 is that it is facilitated with respect to any non-gas components, such as liquid combustion fuels and solid waste. In a horizontal thermal oxidizer, complete combustion of the liquid component relies on the thermal oxidizer in the form of uniform small droplets that can rapidly evaporate and mix within the combustion zone. Typically, the droplets are formed using a device such as a pressure atomizer. Failure to properly operate these injectors can damage the liquid reservoir at the bottom of the horizontal thermal oxidizer, requiring costly repairs and downtime. When a vertical thermal oxidizer configuration is used, sensitivity to spray variables is greatly reduced, and liquid droplets make available the full length of the thermal oxidizer and achieve complete combustion.

  The use of a vertical thermal oxidizer as compared to a horizontal thermal oxidizer provides yet additional benefits. Vertical thermal oxidizers require less square feet to install, which is important for certain facilities. The space available for capital expansion in existing industrial facilities is often limited and may not be available. Thus, there is a distinct advantage to the method of introducing a device that requires less space. To reduce the space required, the vertical thermal oxidizer can be located closer to the operating hardware of the relevant industrial process. The tubing connecting the process to the thermal oxidizer typically has a large bore, often well over 30 inches. Positioning the thermal oxidizer closer to the process not only reduces the capital cost of many straight-foot, expensive, large diameter pipes, but also reduces the pressure drop encountered in the connecting pipe. This, in turn, will cause the industrial process to operate at lower pressure, which in some cases will increase product yield efficiency, thereby increasing total product output.

  The vertical thermal oxidizer embodiment illustrated in FIG. 2 also includes an optional aqueous waste stream 102. In this embodiment, the aqueous waste stream 102 is injected into the combustion zone 122 and includes water and at least one additional compound, such as acetic acid, cyanide, inorganic salts, benzene, toluene, MIBK, and the like. Alternatively, the aqueous waste stream 102 can further include one or more waste streams (associative waste) emanating from other parts of the present industrial process or from a completely different process. Preferably, the aqueous waste stream 102 is a liquid, but can be a gas or a mixture of a gas and a liquid.

  The aqueous waste stream 102 may further include one or more waste streams (associative aqueous waste) emanating from other parts of the industrial process or from a completely different process. Examples of such streams include, but are not limited to, the waste of light-boiling targets from the ethyl acrylate process (including ethyl acrylate, ethyl acetate and water), and the waste ester distillate from the methacrylate ester process ( Methyl methacrylate, methanol and water).

  In some embodiments, it may be beneficial to mix the aqueous waste stream with the oxidizer 110 or fuel 112 prior to injection into the combustion zone 122. It will also be apparent to those skilled in the art that if any aqueous waste stream 102 has a positive net heating value, it is possible to reduce the combustion fuel required in a thermal oxidizer. Would.

  The waste stream 114 and the supplemental oxidant stream 117 are integrated into a waste decomposition zone inlet line 118 and then connected to one or more waste decomposition zone injection points 127. The make-up oxidant stream 117 may have the same composition as the oxidant 110, or may have a higher or lower oxygen content. In some embodiments, the oxidant stream 110 can include air and the supplemental oxidant stream 117 can include an oxygen-containing process vent gas. Through injection point 127, the waste oxidant stream in inlet line 118 is injected into waste decomposition zone 124 of thermal oxidizer 120.

  The injection point 127 can be radially located along the exterior of the thermal oxidizer 120 and near the waste decomposition zone 124, or in some other form that promotes uniform mixing within the waste decomposition zone. Can be done. Each of the injection points 127 provides a premix feed of the waste stream 114 and the supplemental oxidant stream 117. Premixing the waste stream 114 and the make-up oxidant stream 117 improves decomposition efficiency and reduces the number of inlets required.

  Fewer inlets reduce the size required by the waste decomposition zone 124 as well as the overall size and cost of the thermal oxidizer 120. Under certain circumstances, it may be advantageous to inject the supplemental oxidant stream 117 and the waste stream 114 independently into the waste decomposition zone 124 or to omit the use of the supplemental oxidant stream 117 used together when possible. It is assumed that it is possible.

  Waste stream 114 generally contains components or streams to be decomposed from an industrial process. The waste stream 114 may include a gas, a liquid, or a mixture of both, and may also include inert components such as water, diatomic nitrogen or carbon dioxide. The actual components of the waste gas stream 14 will depend on the particular industrial process under consideration, but must include at least a minimum amount of reactive waste components. Examples of such reactive waste components include, but are not limited to, aliphatic hydrocarbons, ammonia, acrolein, hydrogen, hydrogen cyanide, carbon monoxide, urea, and aromatics. The compounds described above can contain oxygen atoms as part of their structure, such as carbon monoxide, but compounds that do not contain oxygen are generally preferred. To effectively reduce WOG emissions, the waste stream injected into the downstream waste cracking zone contains at least 0.5 mol% of reactive waste components or no more than 99.5 mol% of inert components. Is preferred. It is particularly preferred that the waste stream contains at least 2 mol% of reactive waste components or no more than 98 mol% of inert components. The industrial chemical processes associated with the vertical aspect of the thermal oxidizer are hydrogen cyanide, acrolein, acrylic acid, acrylonitrile, methacrylonitrile, methacrylonitrile, methacrylic acid, phthalic anhydride, maleic anhydride and mixtures thereof. Can be included.

  In some embodiments, the ancillary waste stream is injected into the thermal oxidizer 120, either through a dedicated injection point, or by mixing the ancillary waste into the waste stream 114 or alternatively into the supplemental waste stream 117. It is envisioned that doing so may be beneficial. Ancillary waste streams include waste streams that may originate from other parts of the present industrial process or from completely different processes. The associated waste stream may or may not contain significant amounts of reactive waste components, and may also include solids, liquids, gases or mixtures of two or more thereof. Examples of such incidental wastes include, but are not limited to, recovered fuel waste, organic contaminated wastewater, process vent gas, polymer solids or mineral acid residues.

  If significant liquid waste components are present in a given waste stream, e.g., where the waste stream contains organically contaminated wastewater, at least some of the liquid waste components are located in a zone upstream of the thermal oxidizer. Preferably, it is injected. This upstream injection maximizes the residence time, thereby improving the decomposition efficiency. It is particularly preferred that a part of the liquid component is injected into the primary combustion zone.

  As previously described for the horizontal thermal oxidizer 20, at least a portion of the reactive waste components injected into the vertical thermal oxidizer 120 are converted to reducing radicals in the waste decomposition zone 124. The reducing radicals then react with the oxide waste gas present in the waste decomposition zone, reducing WOG emissions from the waste decomposition process. The effluent exiting the waste decomposition zone 124 proceeds to an effluent stack 130 towards the atmosphere. Optionally, the exhaust stream 132 is directed to a heat recovery steam boiler (HRSG) 128 or other heat recovery device to recover some of the thermal energy contained in the exhaust stream 132 before entering the exhaust stream stack 130. be able to. Recovering the thermal energy of the effluent stream 132 improves the energy efficiency of the overall waste decomposition process, by recovering the thermal energy from the thermal oxidizer effluent stream as steam.

  An example is now provided illustrating a specific aspect of the invention having improved and novel features with respect to the process configuration of FIG. This particular embodiment relates to an acrylic acid production process.

  For purposes of illustration, the operation of the thermal oxidizer 20 depicted in FIG. 1 will be described with respect to its application to an industrial chemical process that produces acrylic acid by catalytic oxidation of propylene. However, the method of the present invention can be used for other industrial processes, and the following examples are not intended to limit the scope of the present invention in any way.

Example 1
In an industrial chemical process for producing acrylic acid from a propylene feed, a horizontal three-stage thermal oxidizer of the type illustrated in FIG. 1 was used to dispose of a waste stream. The furnace portion of the thermal oxidizer (from point of addition 21 to the end of the waste decomposition zone 26) was approximately 15.9 meters (52 feet) long. The inner diameter of the primary waste decomposition zone 24 was 1.8 meters (6 feet) and the inner diameter of the secondary waste decomposition zone 26 was 3.2 meters (10.5 feet). Base load NOx emissions for the thermal oxidizer were determined as follows.

Natural gas from a commercial pipeline was used as the combustion fuel stream 12 and was injected into the primary combustion zone at a rate of 24,525 liters / minute (866 scfm). Ambient temperature atmosphere was used as oxidant stream 10. The air stream is injected into the primary combustion zone 22 at a rate of 310,387 l / min (10,960 scfm) and into the secondary waste decomposition zone 26 at a rate of 310,387 l / min (10,960 scfm). Was. The firebox temperature averaged 818 ° C. (1505 ° F.) and the oxygen level (measured wet) of the stack 33 was 13 mol%. No waste stream was fed to the incinerator (stream 14 flow rate was 0) and the baseload NOx emission rate was 1.51 × 10 ⁻⁰⁴ mg NOx / cal (0.084 lb NOx / MM BTU). It has been determined that it has been burned.

Comparative Example 1
In the same industrial chemistry process of producing acrylic acid from a propylene feed and using the same horizontal three-stage thermal oxidizer as in Example 1, operation of the thermal oxidizer was used to achieve reduced NOx emissions. Adjusted according to the method. The specific operation is as follows:

Natural gas from a commercial pipeline was used as the combustion fuel stream 12 and was injected into the primary combustion zone at a rate of 36,306 l / min (1282 scfm). Ambient temperature air is used as the oxidant stream 10 and is injected into the primary combustion zone 22 at a rate of 646,262 liters / minute (22,820 scfm) and is injected at a rate of 431,030 liters / minute (15,220 scfm). It was injected into the next waste decomposition zone 26. The firebox temperature averaged 862 ° C. (1583 ° F.) and the oxygen level (measured wet) of the stack 30 was 3 mol%. At 60 ° C. (140 ° F.), 98 mol% of inerts (eg, nitrogen, water, carbon dioxide, oxygen and argon), 0.9 mol% of aliphatic hydrocarbons (eg, propylene, propane) and 1 mol A gaseous waste stream 14 containing 0.1 mole% of other reactive waste components (eg, carbon monoxide, acetic acid, acrolein, etc.) is provided to the incinerator and 2 mole% of the total reactive waste component feedstock is provided. The concentration was obtained. The waste stream 14 is separated into two parts at a tee 15, the first part at a rate of 658,723 liters / minute (23,260 scfm) through a 12-hole circumferential distributor (at point 25). Located approximately 0.76 meters (2.5 feet) downstream of the oxidant injection point 21), the second portion is a 30-hole circle at a rate of 329,362 liters / minute (11,630 scfm). The secondary waste decomposition zone (at point 31, located approximately 0.76 meters (2.5 feet) downstream of the waste stream injection point 21) was injected through a circumferential distributor. The resulting NOx emission rate was determined to be burned at 7.2 × 10 ⁻⁵ mg NOx / cal (0.040 lb NOx / MM BTU), which was compared to the base load case of Example 1. NOx emissions by more than 50%. Thus, the method of the present invention may be shown to provide a significant reduction in WOG emissions from waste decomposition processes.

  The invention described herein is therefore well suited to accomplish the objects and achieve the objects and advantages set forth above, as well as others substantially as set forth herein. While some presently preferred embodiments of the invention have been given for disclosure purposes, many modifications of the detailed procedure can be made to achieve the desired result. For example, the present invention can involve handling any industrial process waste stream, which includes waste decomposition as part of the process. In addition, the present invention relates to the production of industrial chemical process waste streams such as (meth) acrolein, hydrogen cyanide, (meth) acrylonitrile, (meth) acrylic acid, phthalic anhydride, maleic anhydride and other similar products. It will be clear that they are particularly well suited to handle what is done. Additionally, in some embodiments, it is envisioned that it would be beneficial to combine prior art WOG emission reduction techniques, such as low NOx burners and selective catalytic reduction systems, with the methods of the present invention. These and other similar changes will be readily suggested to those skilled in the art, and are intended to be included within the scope of the invention disclosed herein and the scope of the appended claims. Is intended.

FIG. 1 schematically illustrates one embodiment of the present invention as applied to a horizontal multi-stage thermal oxidizer. FIG. 2 schematically illustrates one embodiment of the present invention as applied to a vertical multi-stage thermal oxidizer.

Explanation of reference numerals

REFERENCE SIGNS LIST 10 Oxidant stream 11 Tee 12 Combustion fuel stream 13 Supplementary oxidant stream 14 Waste stream 15 Tee 17 Supplementary waste stream 21 Addition point 22 Primary combustion zone 23 Addition point 24 Primary waste decomposition zone 25 Primary waste decomposition zone disposal Waste stream addition point 26 Secondary waste decomposition zone 28 Heat recovery steam boiler (HRSG)
Reference Signs List 30 discharge stream stack 31 point 32 discharge stream 102 aqueous waste stream 110 oxidant stream 112 combustion fuel 114 waste stream 117 make-up oxidant stream 118 inlet line 120 thermal oxidizer 122 primary combustion zone 124 waste decomposition zone 127 injection point 128 Heat recovery steam boiler (HRSG)
130 discharge flow stack 132 discharge flow

Claims (9)

a) directing the waste stream to a thermal oxidizer;
b) burning at least a portion of the waste stream in a primary combustion zone of the thermal oxidizer; and c) injecting at least a portion of the waste stream into a waste decomposition zone downstream of the thermal oxidizer. A method to reduce the emission of oxide waste gas in the process.   The method of claim 1, wherein the waste stream comprises at least about 0.5 mole percent reactive waste components and no more than about 99.5 mole percent inert components.   The method of claim 1 further comprising providing an aqueous waste stream to the primary combustion zone. 2. The method of claim 1, further comprising providing associated waste to a downstream waste decomposition zone.
Wherein the associated waste is selected from the group consisting of aqueous waste and alternative waste.   The product according to claim 1, wherein the product produced by the industrial process is selected from the group consisting of acrylic acid, methacrylic acid, acrolein, methacrolein, hydrogen cyanide, acrylonitrile, methacrylonitrile, phthalic anhydride, maleic anhydride and mixtures thereof. The described method. A method for reducing the emission of oxide waste gas of an industrial chemical process,
The industrial chemistry process produces a product selected from the group consisting of methacrylic acid, acrolein, methacrolein, hydrogen cyanide, acrylonitrile, methacrylonitrile, phthalic anhydride, maleic anhydride and mixtures thereof;
a) directing the waste stream to a horizontal thermal oxidizer;
b) burning at least a portion of the waste stream in a primary combustion zone of the thermal oxidizer; and c) injecting at least a portion of the waste stream into a waste decomposition zone downstream of the thermal oxidizer.   7. The method of claim 6, wherein the at least one waste stream comprises at least about 0.5 mole% of a reactive waste component and no more than about 99.5 mole% of an inert component.   7. The method of claim 6, further comprising providing an aqueous waste stream to the primary combustion zone. 7. The method of claim 6, further comprising providing ancillary waste to a downstream waste decomposition zone, wherein the ancillary waste is selected from the group consisting of aqueous waste and alternative waste.

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