KR20040044378A - Method for Reducing Waste Oxide Gas Emissions in Industrial Processes - Google Patents

Abstract

PURPOSE: A reduction method of exhausted waste NOx(Nitric Oxide) is provided to operate a thermal oxygenator with the minimum waste NOx gas emission and to maintain the optimum resolution efficiency during a waste resolution. CONSTITUTION: A waste stream(14) is fed to a thermal oxygenator. The minimum part of the waste stream is combusted in a primary combustion area(22) of the thermal oxygenator. The minimum part of the waste stream is injected to a downstream waste resolution area(26) of the thermal oxygenator. Thereby, the emission of waste NOx from the thermal oxygenator is reduced. Therefore, the NOx emission in a waste resolution process is reduced without decreasing the entire waste resolution efficiency.

Description

Method for Reducing Waste Oxide Gas Emissions in Industrial Processes

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

Thermal oxidizers are often used for the treatment of waste streams in industrial processes. In a typical thermal oxidizer, a waste stream and an oxidant are combined at high temperatures to decompose the waste. If the waste stream is well mixed with the oxidant and the waste is kept at high temperature in a thermal oxidizer for a sufficient time, the waste will be decomposed by the combination of oxidation reactions. There is also a need to provide a fuel stream to the thermal oxidizer. The fuel stream is burned simultaneously in a thermal oxidizer to maintain the desired waste cracking temperature. In some instances, waste heat recovery devices such as heat recovery steam boilers (HRSB) may also be incorporated into the thermal oxidizer but this is not the primary purpose. In the case of thermal oxidizers, first of all, maximization of waste decomposition efficiency is required, and the use of HRSB is arbitrary.

Due to the high temperatures (typically above 600 ° C.) required to maintain decomposition efficiency, waste oxide gas (“WOG”) is frequently produced as a byproduct of thermal oxidizer operation. The waste oxide gas is a gas containing nitrogen-based oxides (NOx), sulfur-based oxides (SOx), carbon-based oxides (COx), or mixtures thereof. Such waste oxide gases are produced by a variety of processes including chemical, combustion or heat treatment.

When introduced into the environment, waste oxide gases can produce undesirable effects. Nitrogen-based oxides, for example, play a major role in ozone formation, which is believed to be responsible for the nitrate component of acid rain. Sulfur-based oxides are associated with acidification of lakes and streams, which promote corrosion of buildings and artifacts, reducing visibility and adversely affecting health. Carbon-based oxides, in particular carbon monoxide, cause serious health problems for the general public, which is a global concern. Due to this serious adverse environmental and health adverse effects, the introduction of waste oxide gas into the environment is strictly regulated nationally and regionally. Such regulations are expected to be more stringent in the near future.

One purpose of thermal oxidizers is to destroy waste compounds, preferably to convert them into harmless carbon dioxide and water. Accordingly, the generation of WOG is undesirable because it is to be minimized in the industry. Various and different designs and structures of thermal oxidizers have been proposed, but they all contain at least one hot waste cracking zone, thus producing at least some WOG.

In contrast to thermal oxidizers, industrial boilers convert heat to steam with fuel-combustion. Industrial boilers (also called utility boilers, commercial boilers, utility boilers, or direct-heat boilers) comprise at least one combustion zone (generally referred to as a "furnace" section) and at least one steam boiler section. . Steam generated in an industrial boiler can be used for heating applications, such as the operation of a distillation tube in a refinery, or in general, steam provides the driving force for a steam turbine drive coupled to electrical power generation. Despite this difference in purpose, industrial boilers also produce WOG as a result of their operation.

Since more industrial boilers are used than thermal oxidizers, most of the recent WOG emission-reduction operations focus on improving industrial boilers rather than thermal oxidizer operations. In particular, as well as the US government, many industrial boiler manufacturers are studying the reduction of NOx emissions produced by industrial boilers. The resulting emission reduction method utilizes industrial boilers with a limited number of fuels, mainly coal and high purity natural gas, which have a relatively constant composition and are essentially used at a constant combustion rate.

It has been suggested that some known industrial boiler emission reduction methods can also be applied to industrial process thermal oxidizers. Unfortunately this method is of limited use. All industrial boiler emission reduction methods involve substantial capital, operating or maintenance costs. This method is economically undesirable when applied to waste cracking systems. In addition, unplanned application of boiler-related methods to industrial thermal oxidizers reduces waste cracking efficiency and often generates harmful environmental by-products from the waste oxide gas itself.

Common waste oxide gas reduction methods for industrial boilers can be divided into two broad categories: combustion reforming and post-combustion processes. Reduction methods that inhibit the formation of NOx are referred to as "combustibles", which include low NOx combustors, overburn air, reburn, associated gas recirculation and operational reform. The reduction method of decomposing NOx once formed is referred to as "postburning process". The postcombustion process includes a selective catalytic reduction, a selective non-catalytic reduction and a hybrid process.

Low NOx combustors (LNBs) are a single combustion reforming method designed to control the mixing of fuel and air using some amount for staged combustion. Staged combustion includes some combustion in the first stage and additional combustion in the reburn portion of the waste cracking device. As a result, the gradual reduction reduces both flame temperature and oxygen concentration during some phases of combustion, which in turn reduces thermal NOx and fuel NOx production. It is required to be provided in a reburn stage to achieve not only staged combustion fuel gas but also fuel gas delivered to the primary combustion stage. A potential advantage of this practice is the consumption of excess fuel gas in the reburn portion of the device.

Changes in certain boiler operating parameters create furnace conditions that lower the production of NOx-these changes are generally referred to as operational reforming methods. Examples include combustor-out-of-service (BOOS), low excess air (LEA), and deflection ignition (BF).

Conventional combustion reforming methods as described above are very capital intensive or disadvantageous in achieving the required waste decomposition efficiency in the case of operational reforming. As noted above, the process of decomposing NOx once formed is referred to as a "postcombustion process", which includes selective catalytic reduction (SCR), selective non-catalytic reduction (SNCR), and hybrid processes.

Conventional post-combustion methods can be achieved with slightly reduced levels of WOG emissions, but this is not free of undesirable environmental deficiencies. For example, the use of SNCR releases ammonia and nitrite oxides into the environment. The released ammonia can adversely affect downstream of the SNCR system, including contamination of air heaters, smoke plume formations, and prominent blowing materials. SCR also has an undesirable effect, such as ammonia, and increases the production of undesirable sulfur oxides and high gas-side pressure drops. In addition, the handling and storage of ammonia required by the SNCR and SCR methods is a serious one for stability. In addition, the SCR mitigation method uses a zeolite or precious metal catalyst. Such catalysts are not only expensive to purchase but also expensive to dispose of after their useful life. The catalyst is also susceptible to contamination, such as sulfur-containing compounds, and the system can be easily contaminated (eg, in-situ formation of ammonia sulphate). Maintenance costs are also increased by the oxide decomposition method and specialized continuous emission monitoring devices are often required to monitor the performance of the system.

Therefore, there are many problems in the current method of reducing waste oxide gas associated with thermal oxidizer. There is a need for a simple, low cost, high efficiency process in which thermal oxidizers are operated with minimal waste oxide gas emissions within an industrial process and maintain optimum decomposition efficiency during waste decomposition. Furthermore, there is a need for a thermal oxidizer capable of producing a reduced amount of waste oxide gas without the need for fuel gas downstream of the primary combustion zone.

1 is a horizontal multistage thermal oxidizer corresponding to one embodiment of the present invention.

2 is a vertical multistage thermal oxidizer corresponding to an alternative implementation of the invention.

Description of the main reference numerals

Oxidant Stream ... 10 Auxiliary Oxidant Stream ...

Primary combustion zone ... 22 Waste decomposition zone ... 26

Oxidant stream ... 110 Combustion fuel stream .......... 122

Primary combustion zone ......... 122 Waste decomposition zone .......... 124

Thus, one embodiment of the present invention provides a new method of reducing waste gas oxide emissions in industrial processes. Another embodiment of the present invention is to provide a new waste cracking process that produces lower waste gas oxide emissions. This will be more apparent through the following description.

Accordingly, one embodiment of the present invention is to provide a new method of reducing the occurrence of NOx emissions. This process comprises: sending a waste stream to the thermal oxidizer; Combusting at least a portion of the waste stream in a primary combustion zone of a thermal oxidizer; And injecting at least a portion of the waste stream into a waste cracking zone downstream of the thermal oxidizer. The waste stream comprises at least about 0.5 mole percent of reactive waste components and up to about 99.5 mole percent of inert components. The waste stream preferably comprises at least about 2.0 mole percent of reactive waste components and up to about 98 mole percent of inert components.

The method further comprises feeding an aqueous waste stream to the primary combustion zone. The present invention also includes supplying incidental waste to a downstream waste cracking zone, wherein the incidental waste is selected from the group consisting of aqueous waste and alternative waste.

The process of the invention can be combined with industrial processes and the products produced by industrial processes are acrylic acid, methacrylic acid, acrolein, methacrolein, hydrogen cyanide, acrylonitrile, methacrylonitrile, phthalic anhydride, maleic anhydride And mixtures thereof.

An alternative embodiment of the present invention provides a method for reducing waste oxide gas emissions in an industrial chemical process, the industrial chemical process comprising: methacrylic acid, acrolein, methacrolein, hydrogen cyanide, acrylonitrile, methacrylonitrile To a product selected from the group consisting of phthalic anhydride, maleic anhydride, and mixtures thereof. Optional implementations of the invention include directing a waste stream to a horizontal thermal oxidizer; Combusting at least a portion of the waste stream in the primary combustion zone of the thermal oxidizer; And injecting at least a portion of the waste stream into a waste cracking zone downstream of the thermal oxidizer. An alternative embodiment waste stream comprises at least about 0.5 mole percent of reactive waste components and up to about 99.5 mole percent of inert components. Optional implementations of the invention also include feeding an aqueous waste stream to the primary combustion zone. Optional implementations of the invention also include supplying incidental waste to the downstream waste cracking zone, wherein the incidental waste is selected from the group consisting of aqueous waste and alternative waste.

Hereinafter, the present invention will be described in detail.

The present invention relates to a method of reducing waste oxide gas emissions. In particular, the waste oxide gas emissions produced in the thermal oxidizer can be reduced by the use of a multi-zone waste thermal oxidizer comprising at least one primary combustion zone and at least one downstream waste cracking zone. By performing the primary combustion of the fuel prior to at least a fraction of the waste decomposition, it has been found that waste oxide gas emissions in the waste decomposition process can be economically reduced without significant loss of overall waste decomposition efficiency. It has further been found that aqueous waste streams can be added to the primary combustion zone to reduce waste oxide gas emissions.

In the drawings of the present invention, a method of reducing the waste oxide gas content in the discharge according to one embodiment of the present invention is shown in FIG. The numbers in the figures represent streams, steps and elements. Thermal oxidizer 20 of Figure 1 is a representative view of 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. The oxidant stream 10 contains one or more gases, which contain 1-100% oxygen. Examples of suitable oxidants include, but are not limited to, atmosphere, pure 100% oxygen, oxygen-enriched air, ozone or oxygen-containing process vent gas. In some implementations, rather than providing a mixed oxidant stream, it may be advantageous to use two independent oxidant streams introduced separately into the thermal oxidizer, but close enough to facilitate mixing inside the thermal oxidizer. . For example, in terms of stability and operability, the atmospheric stream can be injected through a very adjacent nozzle that is separate from the pure-oxygenated lance.

As in FIG. 1, a portion of oxidant stream 10 may also optionally be converted at ti 11 to provide auxiliary oxidant stream 13. Waste cracking efficiency can be increased by injecting an auxiliary oxidant stream 13 into one or more downstream waste cracking zones. In the embodiment of FIG. 1, the auxiliary oxidant 13 is provided to secondary waste cracking zone 26 via addition point 23.

Combustion fuel 12 is natural gas, but it is preferred that the combustion fuel can comprise 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. 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 in multiple points, but this is a combustor that delivers combustion fuel to the combustion zone 22. It can be introduced into the primary combustion zone 22 via a windbox, mixer, distributor, injector, nozzle or other device.

Similarly, various options may be used to add oxidant to combustion zone 22 and waste cracking 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 implementations, it may be beneficial to combine combustion fuel and oxidant prior to or concurrent with addition to the combustion zone; General apparatus such as mixers, low NOx combustors (LNBs), or atomizers can be used for this purpose. The choice of a suitable fuel and oxidant addition device is within the skill of the art and will depend on various variables including the type of fuel and oxidant used, thermal oxidizer structure, and economic factors.

NOx occurs during combustion as a result of the high temperatures present in the primary combustion zone 22 and the presence of nitrogen in the oxidation stream 10 and / or combustion fuel stream 12. In general, combustion processes produce small amounts of carbon dioxide, carbon monoxide and water.

Heat and combustion products in the primary combustion zone 22 flow to adjacent waste cracking zones 24 and secondary waste cracking zones 26. The primary waste cracking zone 24 is thus referred to as "downstream" of the primary combustion zone 22 and the second waste cracking zone 26 is downstream of the primary waste cracking zone 24.

Waste stream 14 is introduced into thermal cracker 20 via a first waste cracking zone waste stream addition point 25. In general, the waste stream 14 comprises a component or stream of an industrial process which is subject to decomposition. The waste stream 14 may comprise a gas, a liquid or a mixture thereof and may also comprise an inert component such as water, diatomic nitrogen, or carbon dioxide. The actual configuration of the waste gas stream 14 depends on the particular industrial process under consideration, but should contain at least the minimum amount of reactive waste components. By "reactive waste component" is meant a waste component capable of reacting with oxygen, which is part of the waste oxide 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. Such compounds may contain oxygen atoms as part of their structure, such as carbon monoxide, but generally compounds without oxygen are preferred.

The waste stream injected into the downstream waste cracking zone preferably contains at least 0.5 mol% of reactive waste components or up to 99.5 mol% of inert components to effectively reduce WOG emissions. In particular, the waste stream preferably contains at least 2 mol% of reactive waste components or up to 98 mol% of inert material.

In the embodiment of FIG. 1, the first waste cracking zone waste stream addition point 25 is single connected to the outer surface of the thermal oxidizer 20, which is a radially oriented distribution nozzle on the interior of the thermal oxidizer 20. Connected with The nozzle provides a decomposition flow around the thermal oxidizer 20 for improved mixing and distribution efficiency. Waste components are decomposed by high temperature and oxygen in the thermal oxidizer.

As a result of exposure to high temperatures in thermal oxidizers, some reactive waste components form radicals capable of removing oxygen from WOG compounds such as NOx, thus converting them into inert compounds such as diatomic nitrogen and the like. Such thermally initiated radicals are referred to herein as "reducing radicals". The formation of reducing radicals should theoretically produce some high-temperature environment, but their presence is generally short in the primary combustion zone. This sufficient reduction in WOG emissions is not obtained.

It has been found that the desired result of reduced WOG release can be obtained if at least a portion of the reactive waste components are introduced after the first combustion takes place. This first combustion injection then delays the formation of reactive radicals and increases the efficiency of reducing WOG emissions. Thus, WOG emissions are effectively reduced when reactive waste components are present downstream of the waste cracking zone of the primary combustion zone.

Industrial chemical processes associated with the horizontal implementation of thermal oxidizers include the preparation of hydrogen cyanide, acrolein, acrylonitrile, methacrylonitrile, methacrolein, methacrylic acid phthalic anhydride, maleic anhydride and mixtures thereof. Can be.

It has been found that some reactive waste components are more effective in the formation of thermally initiated reducing radicals at a given temperature and are therefore preferred due to the greater WOG reduction capacity. Thus aliphatic hydrocarbons (e.g. hexanes) will be the preferred type of reactive waste components for aromatic ring-compounds (e.g. benzene) and alkanes (e.g. propane, butane) are alkenes as reactive waste components. (For example propylene, butylene).

Thus, industrial chemical processes using alkanes rather than alkenes as primary feeds are particularly preferred for use in the process of the present invention. Such alkanes based processes include, but are not limited to, the production of acrolein, acrylic acid and acrylonitrile catalyzed by propane, as well as the production of methacrylic acid and methacrolein from the reaction of C4-alkanes.

In a special case of this implementation process, an absorber off-gas waste stream is generally generated which will include at least a portion of the unreacted alkane feedstock. When such waste streams are injected into the thermal oxidizer according to the method of the invention, they can be expected to reduce NOx more effectively than similar waste streams derived from similar alkene-based processes.

It is also known that compounds such as CO, H2, and NH3 are effective reducing agents and therefore they will be preferred reactive waste components when used according to the process of the present invention.

As shown in FIG. 1, some waste stream 14 is also optionally converted at tee 15 to provide auxiliary waste stream 17. By injecting auxiliary waste stream 17 into one or more downstream waste cracking zones, the effect of reducing WOG emissions can be increased. In the implementation of FIG. 1, auxiliary waste stream 17 is provided to secondary waste cracking zone 26 via waste stream addition point 27. Addition point 27 may consist of a combustor, windbox, mixer, dispenser, injector, nozzle or other injection hardware.

The reactive waste component of auxiliary waste stream 17 reacts with the waste oxide gas present in the secondary waste cracking zone 26 which is not removed in the primary waste cracking zone 24. Ideally, these WOG compounds are converted into compounds such as N 2, CO 2, and H 2 O in secondary waste cracking zone 26, which are not pollutants and can be released to the atmosphere as a harmless effluent 32. In some implementations, it may be desirable to inject the incidental waste stream into the thermal oxidizer through a dedicated injection point or to inject the incidental waste into waste stream 14 or optionally mixed into secondary waste stream 17.

Incidental waste streams include waste streams that can be emitted from other parts of the target industrial process or from other processes as a whole. Such incidental waste streams may or may not contain significant amounts of reactive waste components and may additionally include solids, liquids, gases or mixtures of two or more thereof. Examples of such ancillary wastes include, but are not limited to, recovered waste fuels, organic-contaminated wastewater, process vent gases, polymer solids or mineral acid residues. The incidental waste stream may also include MMA light ends (including acetone, methanol, and methylmethacrylate) and specific-amine process residues (including t-alkyl primary amines and C 6+ hydrocarbons).

In embodiments where significant liquid waste components are present in a given waste stream, when the waste stream comprises organic-contaminated waste water, at least a portion of the liquid waste components is upstream of the thermal oxidizer to maximize residence time. It is desirable to inject into the area, thereby increasing the waste decomposition efficiency. It is particularly preferred that such liquid components be at least partially injected into the primary combustion zone.

Underlined 29 represents the boundary between the various regions within thermal oxidizer 20. The line is underlined to indicate that the exact boundaries between these areas in the thermal oxidizer are not fixed or instead the position during the waste decomposition process is changed. Because the thermal oxidizer is a power system, the boundary at which primary combustion ends and waste decomposition begins is not completely fixed, but instead can move back and forth along the limited length of the thermal oxidizer 20. In practical terms, the location of the stream injection point at about 0.15 meters (0.5 feet) or more downstream of the preceding fuel or waste injection point is generally sufficiently separated to maintain an independent downstream area.

Effluent from secondary waste cracking zone 26 is passed into effluent stack 30 to the atmosphere. Optionally, effluent 32 may be sent through a heat recovery steam boiler (HRSG) 28 or other heat recovery device to recover some of the heat energy contained in effluent 32. The thermal energy of the effluent 32 is recovered to recover the thermal energy from the thermal oxidizer effluent as steam, thereby increasing the energy efficiency of the overall waste cracking process.

2 is a representative of a preferred embodiment of the present invention wherein the thermal oxidizer 120 is a two-stage vertical thermal oxidizer. Vertical structures are generally preferred for vertical structures for thermal oxidizers due to their reduced size and lower capital cost. In a vertical implementation, the oxidant stream 110 and the combustion fuel 112 are delivered to the primary combustion zone 122 of the thermal oxidizer 120 and the contents of the oxidant stream 110 and the combustion fuel stream 112 are combusted. Thermal NOx and other waste oxide gases are produced during combustion in the primary combustion zone 122.

The oxidant stream 110 contains one or more gases and contains 1-100% oxygen. Examples of suitable oxidants include, but are not limited to, atmosphere, pure 100% oxygen, oxygen-enriched air, ozone or oxygen-containing process vent gas. In some implementations, it may be advantageous to use two independent oxidant streams that are introduced independently to the thermal oxidizer rather than provide a mixed oxidant stream but close enough to promote good mixing inside the thermal oxidizer. For example, for stability and manipulation, the atmospheric stream can be injected through a nozzle independent of or close to the pure-oxygenated lance.

Combustion fuel 112 is preferably natural gas, but combustion fuel may comprise 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. 2 shows a combustion fuel stream 112 injected into the primary combustion zone 122 at a single point. However, combustion fuel stream 112 may be added at multiple points or via combustors, wind boxes, mixers, distributors, injectors, nozzles and other devices that deliver combustion fuel to primary combustion zone 122. May be introduced into the primary combustion zone 122.

Similarly, various options may be used for the addition of oxidants to the primary combustion zone 122 and the 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 implementations, it may be beneficial to combine combustion fuel and oxidant prior to or concurrent with addition to the combustion zone; General apparatus such as mixers, low NOx combustors (LNBs), or nebulizers can be used for this purpose. The choice of a suitable fuel and oxidant addition device will depend on the person skilled in the art and will depend on various variables including the type of fuel and oxidant used, thermal oxidizer structure and economic factors.

Another advantage of the vertical form of the thermal oxidizer 120 is that combustion simplifies any non-gaseous components such as liquid combustion fuels and solid waste. The complete combustion of the liquid component in a horizontal thermal oxidizer is dependent on the thermal oxidizer in the form of uniform small diameter droplets which can be easily evaporated and mixed in the combustion zone. Generally, such droplets are formed using a device such as a pressurized nebulizer. Failure to operate these devices properly can damage the liquid buildup on the bottom of the vertical thermal paper, which requires expensive repair costs and delays. When a vertical thermal oxidizer structure is used, the sensitivity to atomization parameters is greatly reduced and has a useful full length in the thermal oxidizer to achieve complete combustion of the liquid droplets.

Additional advantages are provided by using a vertical thermal oxidizer over horizontal. Vertical thermal oxidizers require less square feet for installation, which is important for certain installations. The space available for capital expansion in existing industrial facilities is often limited and sometimes not available. The smaller space required of the tool device thus has a clear advantage in the process. Due to the lower space requirements, vertical thermal oxidizers can be located in close proximity to hardware operations of suitable industrial processes. Pipes connecting the process to thermal oxidizers generally have large diameters and often exceed 30 inches. By placing the thermal oxidizer in close proximity to the process, it not only eliminates the capital cost due to the linear fit of expensive large diameter pipes, but also reduces the pressure drop in the connecting pipes. This allows industrial processes to be operated at low pressures; In some cases, output efficiency can be increased by increasing the total output.

The vertical thermal oxidizer implementation of FIG. 2 also includes any aqueous waste stream 102. In this embodiment, aqueous waste stream 102 is injected into combustion zone 122 and includes water and at least one additional waste compound such as acetic acid, cyanide, inorganic salts, benzene, toluene, MIBK, and the like. Optionally, aqueous waste stream 102 may additionally include one or more waste streams (incidental wastes) emitted from different parts of the desired industrial process or from entirely different processes. The aqueous waste stream 102 is preferably a liquid, which may be a gas or a mixture of gases and liquids.

The aqueous waste stream 102 may additionally comprise one or more waste streams (incidental aqueous waste) emanating from different parts of the desired industrial process or from entirely different processes. Examples of such streams include, but are not limited to, the light end of the ethyl acrylate process (including ethyl acrylate, ethyl acetate and water) and the waste ester distillate of the methacrylate ester process (methyl methacrylate, methanol and water). It includes).

In some implementations, it may be advantageous to mix the aqueous waste stream with the oxidant 110 or fuel 112 before being injected into the combustion zone 122. This will also be apparent to those skilled in the art and can reduce the combustion fuel required for the thermal oxidizer if any aqueous waste stream 102 has a positive net heating value.

The waste stream 114 and auxiliary oxidant stream 117 are combined at waste cracking zone inlet line 118 and then connected to one or more waste cracking zone injection points 127. Auxiliary oxidant stream 117 may have the same composition as oxidant 110 or may have a higher or lower oxygen content. In some implementations, the oxidant stream 110 can comprise an atmosphere and the auxiliary oxidant stream 117 can comprise an oxygen containing process vent gas. Through injection point 127, the waste oxidant stream of inlet line 118 is injected into waste cracking zone 124 of thermal oxidizer 120.

The injection point 127 may be radially oriented along the outside of the thermal oxidizer 120 adjacent the waste cracking zone 124 or arranged in another structure to promote uniform mixing within the waste cracking zone. Each injection point 127 provides a premixed feed of waste stream 114 and auxiliary oxidant stream 117. Premixing of waste stream 114 and auxiliary oxidant stream 117 increases the decomposition efficiency and also reduces the number of injection ports required.

Less injection ports reduce the overall size and cost of waste cracking zone 124 and thermal oxidizer 120 of the required size. Under some conditions it may be advantageous that the auxiliary oxidant stream 117 and the waste stream 114 are independently injected into the waste cracking zone 124 or possibly not using the auxiliary oxidant stream 117 at all.

Waste stream 114 generally includes components or streams of industrial processes that are subject to decomposition. The waste stream 114 may comprise a gas, a liquid or a mixture thereof and may also include an inert component 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 should include at least the 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. Such compounds may contain oxygen atoms as part of their structure, such as carbon monoxide, and in general, compounds without oxygen are preferred. The waste stream injected into the downstream waste cracking zone preferably contains at least 0.5 mol% of reactive waste components or up to 99.5 mol% of inert components to effectively reduce WOG emissions. It is particularly preferred that the waste stream contains at least 2 mol% reactive waste components or up to 98 mol% inert components. Industrial chemical processes involving the vertical implementation of thermal oxidizers are processes for producing hydrogen cyanide, acrolein, acrylic acid, acrylonitrile, methacrylonitrile, methacrolein, methacrylic acid, phthalic anhydride, maleic anhydride and mixtures thereof. It may include.

In some implementations, it may be advantageous to inject the incident waste stream into the thermal oxidizer 120 through a dedicated injection point or to mix and inject the incident waste into waste stream 114 or optionally supplemental waste stream 117. Incidental waste streams include waste streams emitted from other parts of the desired industrial process or from other processes as a whole. Such incidental waste streams may or may not contain significant amounts of reactive waste components and may further comprise solids, liquids, gases or mixtures of two or more thereof. Examples of such ancillary wastes include, but are not limited to, recovered waste fuels, organic-contaminated wastewater, process vent gases, polymer solids or mineral acid residues.

In implementations where significant liquid waste components are present in a given waste stream, when the waste stream comprises organic contaminated waste water, it is preferred that at least a portion of the liquid waste components be injected upstream of the thermal oxidizer. This upstream injection maximizes residence time and thus increases decomposition efficiency. Particular preference is given to injecting some of these liquid components into the primary combustion zone.

As described above in connection with the horizontal thermal oxidizer 20, the minimum portion of 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 waste oxide gas present in the waste cracking zone to reduce WOG emissions in the waste cracking process. The effluent exiting the waste decomposition zone 124 is passed into the effluent stack 130 towards the atmosphere. Optionally, before being introduced to the effluent stack 130, the effluent 132 may be sent through a heat recovery steam boiler (HRSG) 128 or other heat recovery device to recover some thermal energy contained in the effluent 132. The thermal energy of effluent 132 is recovered to recover thermal energy from the thermal oxidizer effluent as steam to increase the energy efficiency of the overall waste cracking process.

Example

With respect to the process structure of FIG. 1, this embodiment is intended to disclose an explanation of the improved and novel features of a particular implementation of the invention. This particular embodiment relates to acrylic acid manufacturing process.

In the description, the operation of the thermal oxidizer 20 shown in FIG. 1 is applied to an industrial chemical process for producing acrylic acid through catalytic oxidation of propylene. However, the method of the present invention can be used with other industrial processes and the following examples do not limit the scope of the present invention.

Example 1

In the industrial chemical process for producing acrylic acid from propylene feed, the type of horizontal three stage thermal oxidizer of FIG. 1 was used for the disposal of the waste stream. The low section of the thermal oxidizer (from point 21 to the end of the waste cracking zone 26) was about 15.9 meters (52 feet) long. The inner diameter of the primary waste cracking zone 24 was 1.8 meters (6 feet) and the inner diameter of the secondary waste cracking zone 26 was 3.2 meters (10.5 feet). The basic charge NOx emission of the thermal oxidizer was measured as follows:

Natural gas from commercial piperine was used as combustion fuel stream 12 and injected into the primary combustion zone at a rate of 24,525 liters / minute (866 scfm). Atmospheric atmosphere was used as oxidant stream 10. The air stream was injected into the secondary waste cracking zone 26 at a rate of 310,387 liters / minute (10,960 scfm) at the first combustion zone 22 and at 310,387 liters / minute (10,960 scfm). The temperature of the firebox averaged 818 ° C (1505 ° F) and the Stack 33 oxygen level (measured on a wet basis) was 13 mol%. No waste stream was fed to the incinerator (stream 14 flow rate was zero) and the base-load NOx release rate was measured to be 1.51 × 10 ^−0.4 mg NOx / cal (0.084 lb NOx / MM BTU).

Comparative Example 1

In the same industrial chemical process for producing acrylic acid in the propylene feed in Example 1 and using the same horizontal three stage thermal oxidizer, the operation of the thermal oxidizer was adjusted according to the method of the present invention such that NOx emissions were reduced. Specific operations are as follows:

Natural gas from commercial piperine was used as combustion fuel stream 12 and injected into the primary combustion zone at a rate of 36,306 liters / minute (1282 scfm). Room temperature atmosphere was used as the oxidant stream 10 and injected into the secondary waste cracking zone 26 at the rate of 646,262 liters / minute (22,820 scfm) at the first combustion zone 22 and at the rate of 431,030 liters / minute (15,220 scfm). The firebox temperature averaged 862 ° C (1583 ° F) and the stack 30 oxygen level (measured on a wet basis) was 3 mol%. 98 mole% of inerts (e.g. nitrogen, water, carbon dioxide, oxygen and argon), 0.9 mole% of aliphatic hydrocarbons (e.g. propylene, propane) and 1.1 mole% of other reactive waste components (e.g. Gaseous waste stream 14 at 60 ° C. (140 ° F.), including carbon monoxide, acetic acid, acrolein, etc., was provided to the incinerator to obtain a total reactive waste component feed concentration of 2 mol%. Waste stream 14 is classified in two parts at tee 15; The first portion is injected through the 12-hole boundary disperser at a rate of 658,723 liters / minute (23,260 scfm) to the primary waste cracking zone (at point 25, about 0.76 meters (2.5 feet) downstream of the oxidant injection point 21). being); The second portion was injected through the 12-hole boundary disperser at a rate of 329,362 liters / minute (11,630 scfm) to the secondary waste cracking zone (at point 31, about 0.76 meters (2.5 feet) downstream of the waste stream injection point 21). Located). Results The NOx release rate was determined to be 7.2 × 10 ^−0.5 mg NOx / cal (0.040 lb NOx / MM BTU), indicating a 50% reduction in NOx release compared to the base-load case of Example 1. The method of the present invention may thus show a significant reduction in WOG emissions in waste cracking processes.

Thus, the present invention applies well to the performance of the object, as well as inherent advantages. With the disclosure of the preferred implementation of the invention, various changes in order may be carried out to achieve the desired results. For example, the present invention may include the handling of any industrial process waste stream including waste decomposition as part of the process. Furthermore, the present invention is directed to treating industrial process waste streams such as those produced in the production of (meth) acrolein, hydrogen cyanide, (meth) acrylonitrile, (meth) acrylic acid, phthalic anhydride, maleic anhydride, and other similar products. Will be considered to be very suitable. It is also believed that in some embodiments it may be beneficial to combine the methods of the present invention with prior art WOG emission reduction techniques such as low NOx combustors and selective catalytic reduction systems. Similar variations can be made by those skilled in the art and are believed to be included within the scope and claims of the invention disclosed herein.

According to the present invention there is provided a method for reducing the emission of waste oxide gas produced in a thermal oxidizer, whereby NOx emissions in the waste cracking process can be reduced economically without a significant loss of overall waste cracking efficiency.

Claims (9)

a. Directing the waste stream to a thermal oxidizer; b. Combusting at least a portion of the waste stream in the primary combustion zone of the thermal oxidizer; And c. Injecting at least a portion of the waste stream into a waste cracking zone downstream of the thermal oxidizer; Method for reducing the waste oxide gas emissions of the industrial process comprising a. The method of claim 1 wherein the waste stream comprises at least about 0.5 mole percent reactive waste components and at most about 99.5 mole percent inactive components. The method of claim 1, further comprising feeding an aqueous waste stream to the primary combustion zone. The method of claim 1, further comprising supplying incidental waste to the downstream waste decomposition zone, wherein the incidental waste is selected from the group consisting of aqueous waste and alternative waste. 2. The product of claim 1 wherein the product produced by the industrial process is acrylic acid, methacrylic acid, acrolein, methacrolein, hydrogen cyanide, acrylonitrile, methacrylonitrile, phthalic anhydride, maleic anhydride, and mixtures thereof. And from the group consisting of: a. Directing the waste stream to a horizontal thermal oxidizer; b. Combusting at least a portion of the waste stream in the primary combustion zone of the thermal oxidizer; And c. Injecting at least a portion of the waste stream into a waste cracking zone downstream of the thermal oxidizer; Including; The products of manufacture in industrial chemical processes are: industrial chemicals selected from the group consisting of methacrylic acid, acrolein, methacrolein, hydrogen cyanide, acrylonitrile, methacrylonitrile, phthalic anhydride, maleic anhydride and mixtures thereof A method of reducing the waste oxide gas emissions of a process. 7. The method of claim 6, wherein the at least one waste stream comprises at least about 0.5 mole percent reactive waste components and at most about 99.5 mole percent inactive components. 7. The method of claim 6, further comprising feeding an aqueous waste stream to the primary combustion zone. 7. The method of claim 6, further comprising supplying additional waste to the downstream waste cracking zone, wherein the additional waste is selected from the group consisting of aqueous waste and alternative waste.