Off-gas incinerator control

Abstract

To provide: a process for minimizing the amount of fuel gas utilized in an absorber off-gas incinerator and better controlling emissions; and a process for reducing the temperature deviation in the absorber off-gas incinerator firebox and for reducing the deviation in the amount of oxygen in the absorber off-gas incinerator stack gas.SOLUTION: A process for operating an off-gas incinerator comprises: introducing a flow of a reactant stream into an ammoxidation reactor; measuring the amount of hydrocarbon in the reactant stream and measuring the feed rate of the reactant stream; conveying a reactor effluent from the ammoxidation reactor to an absorber; supplying an absorber off-gas from the absorber to an absorber off-gas incinerator; and supplying fuel gas and air to the absorber off-gas incinerator.SELECTED DRAWING: None

Description

[Technical field]

[0001] A method for controlling a flue gas incinerator is provided. More specifically, the method includes minimizing the amount of fuel gas utilized in an absorber flue gas incinerator and controlling emissions from the incinerator. [Background technology]

[0002] Acrylonitrile is produced by an ammoxidation process in which air, ammonia and propylene react in the presence of a catalyst in a fluidized bed to form a reactor vaporous effluent. The reactor vaporous effluent then passes through a quench system where it is directly contacted with an aqueous quench liquid, usually water. This quench removes unreacted ammonia and heavy polymers. The quenched gas is then passed to an absorption column. In the absorber, the gas is directly contacted with an absorption liquid, usually water as well. Water, acrylonitrile, acetonitrile, HCN and associated impurities are discharged as an aqueous solution from the bottom of the absorber. Gas is removed from the top of the absorber. The gas removed from the top of the absorber is sent to an absorber off-gas incinerator (AOGI).

[0003] Absorber off-gas incinerators (AOGI) are used in the acrylonitrile process to burn the unabsorbed gas stream containing unreacted hydrocarbons and small amounts of acrylonitrile. The AOGI contains a heat recovery section that produces high pressure steam that is used in other parts of the acrylonitrile process. In the AOGI, air and fuel gas are used to combust the absorber off-gas at high temperatures. The key variables controlled in the AOGI are the incinerator temperature and the flue O2. Tighter control of these two variables is desirable from an emissions control standpoint. This control objective is desirable not only during normal operation, but also during rate changes and when propylene purity changes. Model predictive control (MPC), also known as advanced process control (APC), uses process models to predict future process behavior and then implements optimized control actions to neutralize process deviations from desired targets. Along with controlling the process, MPC varies key process variables to attempt to drive the process to its most "economical" state. Summary of the Invention

[0004] The method provides for minimizing the amount of fuel gas utilized in the absorber flue gas incinerator and for better control of emissions. The method provides for reducing temperature deviations in the absorber flue gas incinerator firebox and for reducing deviations in the amount of oxygen in the absorber flue gas incinerator flue gas. The reduced standard deviations in the absorber flue gas incinerator firebox temperature and the absorber flue gas incinerator flue oxygen result in reduced fuel gas usage and tighter control of environmental variables. These control objectives are achieved during normal operation, during rate changes, and as propylene purity changes. The method also unexpectedly controls AOGI temperature and O2 in the AOGI flue gas by determining the amount of hydrocarbons in the reactor feed stream and the feed rate of the reactor feed stream. The method includes measuring the feed rate of the ammoxidation reactor and the purity of the hydrocarbon feed in the reactor. According to this method, the reactor feed rate and the hydrocarbon purity affect the amount of fuel gas and air flow to the exhaust gas incinerator. In one important aspect, an operator can predict the performance of the exhaust gas incinerator based on the known reactor feed rate and hydrocarbon purity, and then implement controls to minimize deviations in AOGI temperature and oxygen in the exhaust gas incinerator flue gas. A method for operating an exhaust gas incinerator includes the steps of: introducing a reactant stream into an ammoxidation reactor; determining an amount of hydrocarbons in the reactant stream and determining a feed rate for the reactant stream; conveying the reactor effluent from the ammoxidation reactor to an absorber; supplying the absorber exhaust gas from the absorber to an absorber exhaust gas incinerator; and supplying fuel gas and air to the absorber exhaust gas incinerator. The absorber exhaust gas, fuel gas, and air are arranged to produce in the absorber exhaust gas incinerator flue gas no more than about 6 kg NO per ton of AN produced by the plant. x and to the absorber flue gas incinerator in an amount to maintain not more than about 3.5 kg of non-methane hydrocarbons per ton of AN produced by the plant in the flue gas of the absorber flue gas incinerator.

[0005] A method for operating a flue gas incinerator includes the steps of: introducing a reactant stream into an ammoxidation reactor; determining an amount of hydrocarbons in the reactant stream and determining a feed rate of the reactant stream; conveying the reactor effluent from the ammoxidation reactor to an absorber; supplying the absorber tail gas from the absorber to the absorber tail gas incinerator; and supplying fuel gas and air to the absorber tail gas incinerator. In one aspect, the absorber tail gas, fuel gas and air are supplied to the absorber tail gas incinerator in amounts that maintain the temperature in the tail gas incinerator within about 10°F (5.56°C) of the incinerator temperature set point. In another aspect, a method for operating an exhaust gas incinerator includes the steps of: introducing a flow of a reactant stream into an ammoxidation reactor; determining an amount of hydrocarbons in the reactant stream and determining a feed rate of the reactant stream; conveying the reactor effluent from the ammoxidation reactor to an absorber; feeding the absorber exhaust gas from the absorber to an absorber exhaust gas incinerator; and feeding fuel gas and air to the absorber exhaust gas incinerator. In one aspect, a set of manipulated variables includes a fuel gas flow to the absorber exhaust gas incinerator and an air flow to the absorber exhaust gas incinerator, and a set of controlled variables includes an amount of oxygen in the flue of the absorber exhaust gas incinerator and a temperature in the absorber exhaust gas incinerator. The method includes controlling at least one set of controlled variables by adjusting the manipulated variables. In this aspect, the manipulated variables are changed based on the feedforward variables. These and other aspects of the method, features and advantages of some embodiments will become more apparent from the following figures. [Brief description of the drawings]

[0006] [Figure 1] FIG. 1 illustrates the ammoxidation process. [Diagram 2] FIG. 1 shows a more detailed overview of AOGI.

[0007] Corresponding reference characters indicate corresponding components among the several views in the drawings. Those skilled in the art will appreciate that the components in the figures are illustrated for simplicity and clarity and are not necessarily drawn to scale. For example, the dimensions of some components in the figures may be exaggerated relative to other components to aid in a better understanding of the various aspects. Also, common but well-understood components useful or essential in commercially viable aspects are often not depicted to facilitate a non-obtrusive overview of these various aspects. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] The following description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of exemplary embodiments. The scope of the invention should be determined based on the claims. Ammoxidation Process FIG. 1 is a flow diagram of an ammoxidation process. Referring to the diagram, the process includes a reactor 10, a quench vessel 20, an optional effluent compressor 30, and an absorber 40. Ammonia in stream 1 and a hydrocarbon (HC) feed in stream 2 can be fed to the reactor 10 as a combined stream 3. The HC feed stream 2 can include a hydrocarbon selected from the group consisting of propane, propylene, isobutene, isobutylene, and combinations thereof. In one embodiment, the hydrocarbon is primarily propylene. A catalyst (not shown in FIG. 1) can be present in the reactor 10. A gas containing oxygen can be fed to the reactor 10. For example, air can be compressed by an air compressor (not shown in FIG. 1) and fed to the reactor 10. Acrylonitrile is produced in reactor 10 from the reaction of hydrocarbons, ammonia and oxygen in the presence of a catalyst in reactor 10. A stream containing acrylonitrile may exit the top of reactor 10 as reactor effluent stream 4. Reactor effluent stream 4 containing acrylonitrile produced in reactor 10 may be conveyed to quench vessel 20 via line 11.

[0009] In quench vessel 20, reactor effluent stream 4 may be cooled by contact with quench water stream 5 which enters quench vessel 20 via line 12. Quench water stream 5 may contain acid in addition to water. The cooled reactor effluent, including acrylonitrile (including by-products such as acetonitrile, hydrogen cyanide and impurities), may then be conveyed as quench stream 6 via line 13 to effluent compressor 30. The quench stream 6 may be compressed by the effluent compressor 30 and exits the effluent compressor 30 as a compressor effluent stream 7. The method may include the step of operating without a compressor. The compressor effluent stream 7 may be conveyed via line 14 to the bottom of the absorber 40. In the absorber 40, the acrylonitrile may be absorbed in a second or absorber water stream 8, which enters the top of the absorber 40 via line 15. A water stream or rich water stream 18 containing acrylonitrile and other by-products may then be conveyed from the absorber 40 via line 19 to a recovery column (not shown in FIG. 1 ) for further purification of the product. Unabsorbed effluent 9 exits the top of the absorber column 40 through pipe 16. The unabsorbed effluent or absorber effluent 9 may include tail gases that can be combusted in an absorber off-gas incinerator 21 (AOGI) or an absorber off-gas oxidizer (AOGO).

[0010] AOGI Operation A more detailed overview of the AOGI 21 is shown in Figure 2. As shown in Figure 2, absorber exhaust 9, fuel gas 120 and air 125 enter the AOGI 21. AOGI exhaust gas 130 is sent to the AOGI flue 150. Environmental permit requirements can define the operating parameters of the AOGI. For example, environmental requirements can define the maximum allowable NO in the AOGI flue gas. x Operation may require reducing NOx, non-methane hydrocarbons, and / or CO below required levels. Monitoring of the amounts of these compounds in the AOGI flue gas is by methods known in the art. Methods may include a continuous emissions monitoring system (CEMS). Environmental requirements do not directly control the operation of the AOGI, but they help define the operating conditions and set points necessary to achieve the environmental requirements.

[0011] In one aspect, the method comprises operating the AOGI to reduce NO in the AOGI flue gas. x In this embodiment, the method includes controlling the level of about 6 kg or less NO per ton of AN produced in the plant. xIn another embodiment, the plant produces no more than about 5 kg NO per ton of AN produced in the plant. x In another embodiment, about 4 kg / hr or less of NO x (NOx), and in another embodiment, about 3 kg / hr or less NO x In this embodiment, the method includes providing the absorber exhaust, fuel gas, and air to the AOGI in an amount to maintain NO in the AOGI flue gas. x The method includes the step of measuring: In another aspect, the method includes operating the AOGI to control non-methane hydrocarbons (NMHCs) in the AOGI flue gas. In this aspect, the NMHCs primarily include propane, acrylonitrile, acetonitrile, and propylene. In this aspect, the method includes providing absorber effluent, fuel gas, and air to the AOGI in amounts to maintain about 3.5 kg or less of NMHCs per ton of AN produced in the plant, and in another aspect, about 3 kg or less of NMHCs per ton of AN produced in the plant, in another aspect, about 2.5 kg or less of NMHCs, and in another aspect, about 2 kg or less of NMHCs per ton of AN produced in the plant. In this aspect, the method includes measuring NHMCs in the AOGI flue gas.

[0012] In another aspect, the method includes operating the AOGI to control CO in the AOGI flue gas. In this aspect, the method includes providing absorber effluent, fuel gas, and air to the AOGI in an amount to maintain about 3.5 kg CO per ton of AN produced in the plant or less, and in another aspect about 3 kg CO per ton of AN produced in the plant or less, in another aspect about 2.5 kg CO per ton of AN produced in the plant or less, and in another aspect about 2.0 kg CO per ton of AN produced in the plant or less. In this aspect, the method includes measuring CO in the AOGI flue gas. In one aspect, the method includes supplying absorber discharge from the absorber to the AOGI 21, and supplying fuel gas 120 and air 125 to the AOGI 21. The absorber discharge, fuel gas, and air are supplied in amounts to maintain the temperature within the AOGI within about 10° F. (5.56° C.) of the AOGI temperature set point by varying the fuel gas supply rate, and in another aspect, within about 5° F. (2.78° C.) of the AOGI temperature set point. In this aspect, the temperature is measured inside the AOGI 21. The method can include various known configurations for the heat exchanger. In one aspect, the absorber flue gas incinerator temperature set point is determined by measuring the NO 2 in the absorber flue gas incinerator flue gas. x , non-methane hydrocarbons, and / or CO, preferably the minimum temperature required to get below their respective required amounts.

[0013] In one embodiment, the absorber tail gas contains unreacted propylene. The reactor includes control and shutdown systems to ensure that explosive levels of propylene never reach the AOGI. In this embodiment, the reactor temperature control and shutdown systems detect the lack of reaction and prevent excess propylene flow to the AOGI. In another embodiment, the method includes controlling the amount of oxygen in the absorber flue gas incinerator flue gas in part by varying the air supplied to the AOGI 125. In this embodiment, the amount of oxygen in the absorber flue gas incinerator flue gas is about 5% by volume or less, in another embodiment about 3.5% by volume or less, in another embodiment about 3% by volume or less, in another embodiment about 2.5% by volume or less, in another embodiment about 2% by volume or less, and in another embodiment at least about 1% by volume or less. The oxygen is measured in the AOGI flue 150. In another embodiment, the method exhibits an overall process acrylonitrile recovery of about 95 to about 97%. The associated quench and absorber efficiencies are greater than about 99%. In this embodiment, the ratio of fuel gas fed to the absorber tail gas incinerator to acrylonitrile produced is maintained in the range of about 3.3:1 thousand standard cubic feet per ton of acrylonitrile (MSCF / T) to about 3.8:1 (MSCF / T), and in another embodiment, about 3.4:1 (MSCF / T) to about 3.7:1 (MSCF / T). In a related embodiment, the ratio of air fed to the absorber tail gas incinerator to acrylonitrile produced is maintained in the range of about 1.7:1 thousand standard cubic feet per minute per ton of acrylonitrile (MSCFM / T / hr AN) to about 1.9:1 (MSCFM / T / hr AN).

[0014] The fluidized bed reactor is the heart of an acrylonitrile plant. It is desirable to ensure that the reactor's efficiency (including in terms of reagent conversion and catalyst loss) is optimized while amplifying the specific capacity of the reactor. Failure to operate the reactor correctly can significantly affect the efficiency, reliability or production capacity of the entire acrylonitrile plant, causing very widespread production outages. The operation and performance of the fluidized bed are highly sensitive to the specific operating conditions selected, and the industry is very cautious about changes in such conditions. As the operating conditions of the fluidized bed change (e.g., reactor pressure, reactor gas velocity, bed height, ratio of bed pressure drop to grid pressure drop, etc.) and catalyst characteristics (particle size, particle size distribution, fines content, attrition characteristics) change, so can the catalyst performance and associated production capacity and efficiency. The ammoxidation process comprises reacting ammonia, oxygen and a hydrocarbon selected from the group consisting of propane, propylene, isobutane and isobutylene, and combinations thereof, in the presence of a catalyst at a pressure of about 140 kPa or less (absolute) and a velocity of about 0.5 to about 1.2 meters per second to obtain a reactor effluent stream. When using a catalyst having a mean particle diameter of about 10 to 100 microns, with about 0 to 30 mass percent of the particle size distribution greater than about 90 microns and about 30 to 50 mass percent less than 45 microns, the fluidization velocity (based on the volumetric flow rate of the effluent and the cross-sectional area ("CSA") of the reactor, excluding cooling coils and dipleg areas) can be operated up to 1.2 m / s, preferably 0.55 to 0.85. Even up to the indicated velocities, head pressures of about 0.50 to about 0.58 kg / cm can be operated with acceptable catalyst losses. 2 and / or it has been found possible to operate the reactor with a cyclone pressure drop of 15 kPa or less and a fines release height above the top of the fluidized bed of about 5.5 to about 7.5 m. This creates the potential for increased production capacity per unit reactor volume (tangent to tangent) of 0.005 to 0.015 metric tons per cubic meter of reactor volume per hour, in another embodiment about 0.0075 to about 0.0125, and in another embodiment about 0.009 to about 0.01 metric tons per cubic meter of reactor volume per hour.

[0015] In an aspect, the method includes manipulating or reacting hydrocarbons in a reactor, with the volumetric flow rate of the effluent having a velocity of about 0.5 to about 1.05 m / s (based on the volumetric flow rate of the effluent and the cross-sectional area ("CSA") of the reactor excluding cooling coils and dipleg areas, i.e., about 90% of the open CSA). It has been found that it is possible to design and operate a reactor system using this velocity while also achieving good fluidization / catalyst performance, and reasonable catalyst entrainment / catalyst losses from the cyclones, so that velocities can be maintained in approximately this range to the extent that it is possible to increase the capacity of the reactor. In an embodiment, the reactor can be operated at velocities of about 0.75 m / s to about 0.95 m / s (based on 90% of the CSA and the effluent gas), with velocities of about 0.50 to about 0.65 kg / cm 2 and in another embodiment from about 0.52 to about 0.58 kg / cm 2 In one embodiment, the ratio of the cyclone inlet velocity in meters / second to the reactor effluent velocity in meters / second is about 15 or greater, in another embodiment, about 20 or greater, in another embodiment, about 15 to about 30, in another embodiment, about 20 to about 30, in another embodiment, about 22 to about 25, in another embodiment, about 23 to about 26, and in another embodiment, about 27 to about 29.

[0016] In one embodiment, the method includes the step of manipulating or reacting hydrocarbons in a reactor having a fluidized bed height that is from about 25% to about 60%, in another embodiment, from about 25% to about 37%, in another embodiment, from about 42% to about 50%, in another embodiment, from about 45% to about 55%, and in another embodiment, from about 44% to about 47% of the height (tangent to tangent) of the cylindrical reactor. In one embodiment, the method includes the step of manipulating or reacting hydrocarbons in a reactor having a fluidized bed height that is from about 60% to about 110%, in another embodiment from about 60% to about 80%, in another embodiment from about 70% to about 100%, in another embodiment from about 75% to about 90%, in another embodiment from about 80% to about 90%, in another embodiment from about 85% to about 95%, in another embodiment from about 70% to about 85%, and in another embodiment from about 85% to about 90% of the diameter of the reactor.

[0017] In an embodiment, the method includes the step of manipulating or reacting hydrocarbons in a reactor, the reactor having a flow rate of from about 0.50 to about 0.65 kg / cm 2 and in another embodiment, from about 0.52 to about 0.58 kg / cm 2 and in another embodiment, from about 0.54 to about 0.6 kg / cm 2 , and in another embodiment, from about 0.5 to about 0.55 kg / cm 2 The reactor head pressure ranges from about 0.54 to about 0.56 kg / cm. Reactor head pressures in this range provide improved catalyst performance benefits over reactor head pressures higher than this range. In one embodiment, the process comprises from about 0.54 to about 0.56 kg / cm. 2 The method includes operating the reactor in a range of In one embodiment, the method includes manipulating or reacting a hydrocarbon in a reactor, wherein the amount of ammonia in the reactor feed comprises an ammonia to hydrocarbon molar ratio of about 1 to about 2, in another embodiment about 1.25 to about 1.75, in another embodiment about 1.4 to about 1.6, and in another embodiment about 1.25 to about 1.3.

[0018] In another embodiment, the method includes a step of manipulating or reacting hydrocarbons in a reactor, and the amount of air in the reactor feed comprises an air to hydrocarbon ratio in the reactor feed of about 9 to about 12, in another embodiment a ratio of about 9 to about 11, in another embodiment a ratio of about 9 to about 10, in another embodiment a ratio of about 10.5 to about 11, in another embodiment a ratio of about 9.25 to about 9.75, and in another embodiment a ratio of about 9.4 to about 9.6. In a related embodiment, the reactor effluent stream comprises about 0.5 to about 1 wt. % oxygen. The method may further include a step of continuously measuring the amount of oxygen in the reactor effluent and continuously adjusting the molar ratio of air to hydrocarbon accordingly. The oxygen may be measured at any location downstream of the reactor. The process for absorbing a reactor effluent stream containing acrylonitrile includes the steps of quenching the reactor effluent stream with a first water stream to obtain a quench stream containing acrylonitrile; compressing the quench stream to obtain a compressed effluent stream containing acrylonitrile; conveying the compressed effluent stream to an absorber at a pressure of about 300 kPa to about 500 kPa (absolute); and absorbing the acrylonitrile in the second water stream in the absorber to obtain a rich water containing acrylonitrile. In another embodiment, a method for absorbing a reactor effluent stream containing acrylonitrile, the method includes the steps of quenching the reactor effluent stream with a first water stream to obtain a quench stream containing acrylonitrile; compressing the quench stream to obtain a compressed effluent stream containing acrylonitrile; conveying the compressed effluent stream to an absorber; and absorbing acrylonitrile in a second water stream having a temperature of about 4°C to about 45°C in the absorber to obtain a rich water stream containing acrylonitrile.

[0019] Changes in the operation of the reactor, quench and / or absorber can affect the AOGI operating parameters required to achieve the desired emission levels. For example, changes in reactor conversion can affect the absorber tail gas composition, which can affect how much fuel and oxygen need to be fed to the AOGI. In this embodiment, the reactor propylene conversion is from about 95% to less than about 100%. As used herein, "reactor propylene conversion" refers to the percentage of the amount of propylene in the reactor feed that is converted to acrylonitrile and other carbon-containing products. In another embodiment, the operation of the quench column can affect the temperature of the absorber column, which can ultimately affect how much water is in the absorber tail gas. Changes in the water content in the absorber tail gas can then affect the operation of the AOGI. In this embodiment, the quench column effluent having a temperature of about 65° C. to about 85° C. (for one type of quench design), and about 100° C. to about 120° C. (for another type of quench design) is conveyed to the absorber. In a related embodiment, the absorber off-gas has about 5% by weight or less water, and the level of water in the absorber off-gas can vary as the temperature at the top of the absorber changes. In another embodiment, the quench column can exhibit a pH in the condensate from the quench column end cooler of about 3.5 to about 7, in another embodiment about 3.5 to about 6, and in another embodiment about 5 to about 5.5.

[0020] Advanced Process Control Changes in the reactor feed rate (hydrocarbon feed rate) change the amount of propane that enters the absorber and ultimately the AOGI. Propane is found to be inherently inert with the catalyst in the reactor. Propane acts as a fuel and can cause deviations in AOGI temperature and flue O2 if the changes are not countered with fuel gas flow in the feedforward means. The same is seen in the case where the propylene purity changes, and thus different amounts of propane enter the absorber and AOGI. Therefore, knowing the feed rate and propylene purity (as well as their changes) allows for better control of AOGI firebox temperature and flue O2 if the changes are used to predict deviations in AOGI temperature and O2, thereby countering the fuel gas changes.

[0021] Model predictive control (MPC), also known as advanced process control (APC), uses process models to predict future process behavior and then implements optimized control actions to neutralize process deviations from desired targets. Along with controlling the process, MPC varies key process variables to attempt to drive the process to its most "economical" state. Processes include the use of MPC to achieve reduced fuel gas usage and improved AOGI emissions. As used herein, the term "manipulated variable" refers to a variable that is adjusted by an advanced process controller. In this embodiment, the manipulated variables include fuel gas flow rate and air flow rate to the AOGI. The term "controlled variable" refers to a variable that is maintained by an advanced process controller at a predetermined value (set point) or within a predetermined range (set range). In this embodiment, the controlled variables include temperature at the AOGI and O2 in the AOGI flue gas. "Optimizing a variable" refers to maximizing or minimizing a variable, as well as maintaining a variable at a predetermined value. "Feedforward variable" refers to a variable that is used to determine an adjustment value for a manipulated variable. In this embodiment, the feedforward variables include the flow rate of the reactant stream into the ammoxidation reactor and the amount of hydrocarbons in the reactant stream.

[0022] One aspect of model predictive control is that future process behavior is predicted using models of the controlled variables and available measurements. The controller output is calculated to optimize a figure of merit, which is a linear or quadratic function of the predicted error and the calculated future control variations. At each sampling instant, the control calculation is repeated and the prediction is updated based on the latest measurements. In this aspect, a suitable model is one that includes a set of empirical step response models that represent the effect of step responses of manipulated and feedforward variables on the controlled variables. The optimal values ​​of the optimized parameters are obtained from a separate optimization step, and the optimized variables may be included in the performance function. Before model predictive control can be applied, the effect of a step change in the manipulated variables on the variables to be optimized and the controlled variables is first determined, resulting in a set of step response coefficients that form the basis of model predictive control of the process.

[0023] During normal operation, predicted values ​​of the controlled variables are regularly calculated for several future controlled changes. For these future controlled changes, a performance index is calculated. The performance index contains two terms, the first term represents the sum of the future controlled changes of the predicted errors for each controlled change, and the second term represents the sum of the future controlled changes of the changes in the manipulated variables for each controlled change. For each controlled variable, the predicted error is the difference between the predicted value of the controlled variable and the reference value of the controlled variable. The predicted error is multiplied by a weighting factor and the change in the manipulated variable for a controlled change is multiplied by a variation suppression factor. Alternatively, these terms may be a sum of squared terms, in which case the figure of merit is quadratic. Additionally, constraints can be placed on the manipulated variables, changes in the manipulated variables, and the control variables. This results in another set of equations that are solved simultaneously with minimizing the figure of merit. The optimization can be done in two ways; the first is to optimize separately apart from the minimization of the figure of merit, and the second is to optimize within the figure of merit. When the optimization is done individually, the variables being optimized are included as control variables in the error predicted for each control change, and the optimization yields reference values ​​for the control variables. Alternatively, the optimization can be performed within the calculation of the figure of merit, which results in a third term in the figure of merit with appropriate weighting coefficients. In this case, the reference values ​​of the controlled variables are predetermined steady-state values ​​that remain constant.

[0024] The performance index is minimized taking into account the constraints for obtaining the values ​​of the manipulated variables for future control changes. However, only the next control change is executed, so that the calculation of the performance index for the future control changes starts again. The model with step response coefficients and the equations required for model predictive control are part of a computer program that is executed to control the absorber flue gas incinerator process. Computer programs that implement such programs capable of handling predictive control are called advanced process controllers. Commercially available computer programs that can be utilized include, for example, Aspen Technology's DMCplus® and Emerson's PredictPro®. EXAMPLES

[0025] (Example 1) Fuel gas and air consumption at 16T / h of acrylonitrile Effect of AOGI Temperature Change: The following table compares fuel gas and air usage when operating a plant to produce 16 T / hr of acrylonitrile (AN). The baseline operation describes ideal AOGI temperature and flue O2. In practice, the method may include operating the AOGI at about 10°F (5.56°C) higher to provide a buffer for varying feed purity and reactor feed rate. As shown in the table, if the temperature is increased by 10°F (5.56°C) and the flue O2 is held constant, the fuel gas usage and air usage will increase. In this example, compared to baseline operation, fuel gas usage increased by about 6.9% and air usage increased by about 2.1% when operating at +10°. In this embodiment, fuel gas usage may increase by about 6% to about 7.5% and air usage may increase by about 1.5% to about 2.5% compared to operating the AOGI at a temperature about 10°F (5.56°C) above baseline operation. Effect of AOGI temperature change and flue O2 change: As further shown in the table, when flue O2 is increased by 1.4% to 1.6%, fuel gas usage increased by about 15% and air usage increased by about 7.4% compared to baseline operation. In this embodiment, fuel gas usage can be increased by about 12% to about 16% and air usage can be increased by about 6% to about 8% compared to operating the AOGI at about 1.4% flue O2 and baseline temperature. The methods provided herein reduce the need to operate the AOGI at +10°F (5.56°C) above the desired baseline, conserving fuel gas and adding air to the AOGI. Effect of changes in feedstock purity: The following table illustrates the effect of changes in feedstock purity. As shown in the table, if the feedstock purity is reduced by 1% and the fuel gas and air are maintained at baseline levels, the AOGI temperature will increase. If the baseline temperatures are maintained, the fuel gas usage will decrease and the air will remain the same. The methods provided herein allow for pre-adjustment of fuel gas supply to the AOGI based on purity changes in the feedstock. This pre-adjustment of fuel gas supply allows for less fuel gas usage while keeping the AOGI closer to the desired temperature. In this embodiment, fuel gas usage at about 95.4% feedstock purity was about 49.1% less than baseline operation when reduced fuel gas was allowed to maintain AOGI temperature.

[0026] [Table 1]

[0027] (Example 2) Fuel gas and air consumption at 12T / h of acrylonitrile Effect of AOGI Temperature Change: The following table compares fuel gas and air usage when operating a plant to produce 12 T / hr of acrylonitrile (AN). The baseline operation describes ideal AOGI temperature and flue O2. In practice, the method may include operating the AOGI at about 10°F (5.56°C) higher to provide buffers to vary the feed purity and reactor feed rate. As shown in the table, if the temperature is increased by 10°F (5.56°C) and the flue O2 is held constant, the fuel gas usage increases. In this example, the fuel gas usage increased by about 3.7% and the air usage increased by about 0.8% when operating at +10° compared to the baseline operation. In this embodiment, the fuel gas usage may increase by about 3% to about 4% and the air usage may increase by about 0.5% to about 1.0% compared to operating the AOGI at a temperature about 10°F (5.56°C) above the baseline operation.

[0028] Effect of AOGI temperature change and stack O2 change: As further shown in the table, when stack O2 is increased by 2.6% to 2.8% compared to baseline operation, fuel gas usage increased by about 7.7% and air usage increased by about 6.0%. In this embodiment, fuel gas usage may increase by about 5% to about 10% and air usage may increase by about 5% to about 7% compared to AOGI operation at about 2.6% stack O2 and baseline temperature. Effect of change in feedstock purity: The following table illustrates the effect of change in feedstock purity. As shown in the table, if the feedstock purity is decreased by 1% and the fuel gas and air are maintained at the baseline level, the AOGI temperature increases by 5.8% above the baseline temperature. In this embodiment, a decrease in feedstock purity can cause an increase in the AOGI temperature of about 5.5% to about 6.5% above the baseline temperature. If the feedstock purity is increased by 1% and the fuel gas and air are maintained at the baseline level, the AOGI temperature decreases by about 6.2% above the baseline temperature. In this embodiment, an increase in feedstock purity can cause an increase in the AOGI temperature of about 5.5% to about 6.5%.

[0029] [Table 2]

[0030] (Example 3) Effect of raw material purity and feed rate Effect of changes in feedstock purity: The following table illustrates the effect of changes in feedstock purity. As shown in the table, if the feedstock purity increases by 1.1% and the fuel gas and air are maintained at baseline levels, the AOGI temperature decreases by about 4.5%. In this embodiment, an increase of about 1.1% in feedstock purity can cause an approximately 4% to about 5% decrease in the AOGI temperature. If the feed purity is increased by 1.1% and the AOGI temperature is maintained at the baseline level, fuel gas usage will increase by 16.5% and air usage will increase by 0.7%. In this embodiment, if the feed purity is increased by 1.1% and the AOGI temperature is maintained at the baseline level, fuel gas usage may increase by about 16% to about 17% above the baseline level and air usage may increase by about 0.5% to about 1% above the baseline level.

[0031] [Table 3] Effect of reactor feed rate: The following table illustrates the effect of changes in reactor feed rate. As shown in the table, when the feed rate was increased by 5% and fuel gas and AOGI temperatures were maintained at baseline levels, the AOGI temperature decreased by about 2°F (1.11°C) and the flue O2 decreased by about 13.4%. When the feed rate was decreased by 10% and the fuel gas and AOGI temperatures were maintained at baseline levels, the AOGI temperature increased by about 6°F (3.34°C) and the flue O2 increased by about 31%. When the feed rate was decreased by 10% and the AOGI temperature and flue O2 were maintained at baseline levels, the fuel gas usage decreased by about 10% and the air usage decreased to about 10.2%. In this embodiment, a decrease in the feed rate of about 10% can cause a decrease in fuel usage of about 8% to about 12% and a decrease in air usage of about 9.5% to about 10.5%.

[0032] [Table 4] While the invention disclosed herein has been described by specific embodiments, examples and applications thereof, numerous modifications and variations thereto can be made by those skilled in the art without departing from the scope of the invention as set forth in the claims.

Claims

1. 1. A method for operating a flue gas incinerator, comprising: introducing said reactant stream into an ammoxidation reactor; determining an amount of hydrocarbon in the reactant stream and determining a feed rate of the reactant stream; conveying the reactor effluent from the ammoxidation reactor to an absorber; Supplying the absorber exhaust gas from the absorber to an absorber exhaust gas incinerator; and supplying fuel gas and air to an absorber flue gas incinerator; Including, The absorber exhaust gas, fuel gas and air are mixed to produce about 6 kg or less of NO per ton of acrylonitrile produced in the flue gas of the absorber exhaust gas incinerator. x and in an amount to maintain not more than about 3.5 kg of non-methane hydrocarbons per ton of acrylonitrile produced in the flue gas of the absorber flue gas incinerator.

2. 10. The method of claim 1, wherein the temperature in the absorber flue gas incinerator is maintained within about 10°F (5.56°C) of the absorber flue gas incinerator temperature set point.

3. 10. The process of claim 1, wherein the hydrocarbon in the reactant stream is selected from the group consisting of propane, propylene, isobutene, isobutylene, and mixtures thereof.

4. The process of claim 3, wherein the hydrocarbon is propylene.

5. 10. The method of claim 1, providing about 5% by volume or less of oxygen in the flue gas of the exhaust gas incinerator of the absorber.

6. 10. The method of claim 1, wherein the absorber exhaust gas incinerator flue gas maintains no more than about 3.5 kg CO per ton of acrylonitrile produced.

7. The temperature set point of the absorber flue gas incinerator is set to the NO in the flue gas of the absorber flue gas incinerator. x 3. The process of claim 2, wherein the temperature is the minimum temperature necessary to achieve less than the required amount of methane hydrocarbons, non-methane hydrocarbons, and / or CO.

8. introducing said reactant stream into an ammoxidation reactor; determining an amount of hydrocarbon in the reactant stream and determining a feed rate of the reactant stream; conveying the reactor effluent from the ammoxidation reactor to an absorber; Supplying the absorber exhaust gas from the absorber to an absorber exhaust gas incinerator; and supplying fuel gas and air to an absorber flue gas incinerator; Including, A method of operating a flue gas incinerator, wherein absorber flue gas, fuel gas and air are supplied to an absorber flue gas incinerator in amounts that maintain a temperature within the flue gas incinerator within about 10°F (5.56°C) of a temperature set point of the flue gas incinerator.

9. 9. The method of claim 8, wherein the temperature within the flue gas incinerator is maintained within about 5°F (2.78°C) of the flue gas incinerator temperature set point.

10. 9. The process of claim 8, wherein the hydrocarbon in the reactant stream is selected from the group consisting of propane, propylene, isobutene, isobutylene, and mixtures thereof.

11. The method of claim 10, wherein the hydrocarbon is propylene.

12. 9. The method of claim 8, providing less than about 5% by volume oxygen in the flue gas of the exhaust gas incinerator of the absorber.

13. In the flue gas of the exhaust gas incinerator of the absorber, no more than about 6 kg of NO per ton of acrylonitrile produced. x The method of claim 8, wherein

14. 9. The method of claim 8, wherein the absorber exhaust gas incinerator flue gas maintains no more than about 3.5 kg of non-methane hydrocarbons per ton of acrylonitrile produced.

15. 9. The method of claim 8, wherein the absorber exhaust gas incinerator flue gas maintains about 3.5 kg CO per ton of acrylonitrile produced or less.

16. 9. The process of claim 8, wherein the ammoxidation reactor has a propylene conversion of from about 95% to less than about 100%.

17. 9. The process of claim 8, wherein a reactor effluent from an ammoxidation reactor is conveyed to a quench column, and the quench column effluent having a temperature of about 65°C to about 85°C is conveyed to said absorber.

18. 9. The method of claim 8, wherein the absorber off-gas contains about 5% by weight water or less.

19. The temperature set point of the absorber flue gas incinerator is set to the NO in the flue gas of the absorber flue gas incinerator. x 9. The process of claim 8, wherein the temperature is the minimum temperature necessary to achieve less than the required amount of methane, non-methane hydrocarbons, and / or CO.

20. introducing said reactant stream into an ammoxidation reactor; determining an amount of hydrocarbon in the reactant stream and determining a feed rate of the reactant stream; conveying the reactor effluent from the ammoxidation reactor to an absorber; Supplying the absorber exhaust gas from the absorber to an absorber exhaust gas incinerator; and supplying fuel gas and air to an absorber flue gas incinerator; Including, a set of manipulated variables including a fuel gas flow to the absorber flue gas incinerator and an air flow to the absorber flue gas incinerator; a set of controlled variables including an amount of oxygen in the flue gas of the absorber flue gas incinerator and a temperature at the absorber flue gas incinerator; controlling the at least one set of controlled variables includes adjusting manipulated variables; A method for operating a flue gas incinerator, in which a feedforward variable is used to vary a manipulated variable.

21. 21. The method of claim 20, wherein the feedforward variables include the amount of hydrocarbon in the reactant stream and the feed rate of the reactant stream.

22. 21. The method according to claim 20, comprising controlling the amount of oxygen in the flue gas of the absorber exhaust gas incinerator and the temperature in the absorber exhaust gas incinerator based on model predictive control to determine simultaneous control actions of manipulated variables to optimize at least one set of parameters while controlling at least one set of controlled variables.

23. 21. The method of claim 20, wherein the temperature in the absorber flue gas incinerator is within about 10°F (5.56°C) of the flue gas incinerator temperature set point.

24. 24. The method of claim 23, wherein the temperature in the absorber flue gas incinerator is maintained within about 5°F (2.78°C) of the absorber flue gas incinerator temperature set point.

25. 21. The process of claim 20, wherein the hydrocarbon in the reactant stream is selected from the group consisting of propane, propylene, isobutene, isobutylene, and mixtures thereof.

26. 26. The method of claim 25, wherein the hydrocarbon is propylene.

27. 21. The method of claim 20, providing about 5% by volume or less of oxygen in the flue gas of the exhaust gas incinerator of the absorber.

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