Exhaust gas incinerator control

Abstract

A method is provided that minimizes the amount of fuel gas used in an absorber off-gas incinerator and better controls emissions. The method provides for a smaller temperature deviation in the absorber off-gas incinerator combustion chamber and a smaller deviation in the amount of oxygen in the absorber off-gas incinerator flue gas.

Description

[0001] This application is a divisional application of the invention patent application filed on May 24, 2016, with application number 201610346931.6 and invention title "Control of Waste Gas Incinerator". Technical Field

[0002] A method is provided for controlling an absorber waste gas incinerator. More specifically, the method includes minimizing the amount of fuel gas used in the absorber waste gas incinerator and controlling emissions from the incinerator. Background Technology

[0003] Acrylonitrile is produced via ammoxidation, in which air, ammonia, and propylene react in a fluidized bed in the presence of a catalyst to form a gaseous reactor effluent. This gaseous reactor effluent is then passed to a quenching system, where it comes into direct contact with an aqueous quenching liquid (typically water). This quenching removes unreacted ammonia and heavy polymers. The quenched gas then enters an absorber. In the absorber, the gas comes into direct contact with an absorbent liquid (also typically water). Water, acrylonitrile, acetonitrile, HCN, and associated impurities remain in the aqueous solution at the bottom of the absorber. The gas is removed from the top of the absorber. The gas removed from the top of the absorber is then sent to an absorber exhaust gas incinerator (AOGI).

[0004] An absorber gas incinerator (AOGI) is used in the acrylonitrile process to burn the unabsorbed gas stream containing unreacted hydrocarbons and a smaller amount of acrylonitrile. The AOGI includes a heat recovery section that generates high-pressure steam for use in other parts of the acrylonitrile process. In the AOGI, air and fuel gas are used to burn the absorber gas at high temperatures. The key variables controlled in the AOGI are incinerator temperature and flue gas O2. From an emissions control perspective, closer control of these two variables is desired. This control objective is desired not only during normal operation but also during rate variations and when propylene purity changes.

[0005] Model predictive control (MPC), also known as advanced process control (APC), uses process models to predict future process behavior and then executes optimal control actions to compensate for process deviations from the desired objectives. Along with controlling the process, MPC also attempts to drive the process to the most "economical" conditions by moving key process variables. Summary of the Invention

[0006] A method is provided to minimize the amount of fuel gas used in an absorber gas incinerator (AOGI) and improve emission control. The method provides smaller temperature deviations in the AOGI combustion chamber and smaller deviations in the amount of oxygen in the AOGI flue gas. Reducing the standard deviations of the AOGI combustion chamber temperature and the AOGI flue gas oxygen provides reduced fuel gas consumption and tighter control over environmental variables. These control objectives are achieved during normal operation, during rate variations, and when propylene purity varies. Unexpectedly, the method provides control over AOGI temperature and O2 in the AOGI flue gas by measuring the amount of hydrocarbons in the reactor feed stream and the reactor feed stream feed rate.

[0007] The method includes measuring the feed rate to the ammonia oxidation reactor and the purity of the hydrocarbons fed to the reactor. According to the method, the reactor feed rate and hydrocarbon purity affect the amount of fuel gas flow and air flow to the waste gas incinerator. In an important aspect, the operator can predict the waste gas incinerator performance based on the known reactor feed rate and hydrocarbon purity, and then implement controls to minimize AOGI temperature and oxygen deviation in the waste gas incinerator flue gas.

[0008] The method of operating the waste gas incinerator includes introducing a reaction stream into the ammonia oxidation reactor; determining the amount of hydrocarbons in the reaction stream and the feed rate of the reaction stream; transferring the reactor effluent from the ammonia oxidation reactor to the absorber; supplying absorber exhaust gas from the absorber to the absorber waste gas incinerator; and supplying fuel gas and air to the absorber waste gas incinerator. The amounts of absorber exhaust gas, fuel gas, and air supplied to the absorber waste gas incinerator are such that, for every tonne of AN produced in the equipment, the NO content in the absorber waste gas incinerator flue gas is maintained. x For approximately 6 kg or less, and for every tonne of AN produced in the equipment, the non-methane hydrocarbons in the absorber exhaust gas incinerator flue gas are approximately 3.5 kg or less.

[0009] A method for operating a waste gas incinerator includes introducing a reaction stream into an ammonia oxidation reactor; determining the amount of hydrocarbons in the reaction stream and the feed rate of the reaction stream; transferring the reactor effluent from the ammonia oxidation reactor to an absorber; supplying absorber exhaust gas from the absorber to the absorber waste gas incinerator; and supplying fuel gas and air to the absorber waste gas incinerator. In one aspect, the absorber exhaust gas, fuel gas, and air are supplied to the absorber waste gas incinerator in amounts that maintain the temperature in the waste gas incinerator within approximately 10°F of the waste gas incinerator's temperature setpoint.

[0010] In another aspect, a method for operating a waste gas incinerator includes introducing a reaction stream into an ammonia oxidation reactor; determining the amount of hydrocarbons in the reaction stream and determining the feed rate of the reaction stream; transferring the reactor effluent from the ammonia oxidation reactor to an absorber; supplying absorber exhaust gas from the absorber to the absorber waste gas incinerator; and supplying fuel gas and air to the absorber waste gas incinerator. In one aspect, the set of manipulated variables includes the fuel gas flow rate to the absorber waste gas incinerator and the air flow rate to the absorber waste gas incinerator, while the set of controlled variables includes the amount of oxygen in the absorber waste gas incinerator flue and the temperature in the absorber waste 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 based on changes in feedforward variables. Attached Figure Description

[0011] The features and advantages of the method described above and in several other aspects are more readily apparent from the following figures.

[0012] Figure 1 Explain the ammonia oxidation process.

[0013] Figure 2 Shows a more detailed view of AOGI.

[0014] Throughout the various accompanying figures, corresponding reference numerals indicate the respective components. Those skilled in the art will understand that the elements in the figures are described for simplicity and clarity and are not necessarily depicted to scale. For example, the dimensions of some elements in the figures may be enlarged relative to other elements to aid in understanding. Furthermore, common but well-known elements that are useful or necessary in industrial practice are generally not depicted to facilitate a less obstructive view of these aspects. Detailed Implementation

[0015] The following description should not be construed as limiting, but is provided only to illustrate the general principles of exemplary embodiments. The scope of the invention should be determined with reference to the claims.

[0016] ammonia oxidation process

[0017] Figure 1 This is a schematic flow diagram of an ammonia oxidation process. Referring to this diagram, the process includes a reactor 10, a quench vessel 20, an optional effluent compressor 30, and an absorber 40. Ammonia from stream 1 and hydrocarbon (HC) feed from stream 2 can be fed into reactor 10 as a combined stream 3. HC feed stream 2 may include hydrocarbons selected from propane, propylene, isobutylene, isobutylene, and combinations thereof. In one aspect, the hydrocarbon is primarily propylene. Catalyst ( Figure 1 (Not shown) may be present in reactor 10. Oxygen-containing gas may be fed into reactor 10. For example, air may be supplied via an air compressor ( Figure 1 (Not shown in the image) is compressed and fed into reactor 10.

[0018] Acrylonitrile is produced in reactor 10 from hydrocarbons, ammonia, and oxygen in the presence of a catalyst. A stream containing acrylonitrile exits from the top of reactor 10 as reactor effluent 4. Reactor effluent 4, containing acrylonitrile produced in reactor 10, can be conveyed via line 11 to quenching vessel 20.

[0019] In the quench vessel 20, the reactor effluent 4 can be cooled by contact with the quenched water stream 5 that enters the quench vessel 20 via line 12. In addition to water, the quenched water stream 5 may include acid. The cooled reactor effluent contains acrylonitrile (including byproducts such as acetonitrile, hydrogen cyanide, and impurities), which can then be delivered as quench stream 6 via line 13 to the effluent compressor 30.

[0020] The quench stream 6 can be compressed by the effluent compressor 30 and exits the effluent compressor 30 as compressor effluent stream 7. The process may include operation without a compressor. The compressor effluent stream 7 can be conveyed through line 14 to the lower part of the absorber 40. In the absorber 40, acrylonitrile can be absorbed in the second or absorber aqueous stream 8, which enters the upper part of the absorber 40 through line 15. The aqueous stream or rich water stream 18, including acrylonitrile and other byproducts, can then be conveyed from the absorber 40 through line 19 to the recovery tower. Figure 1 (Not shown in the image) is used for further product purification. Unabsorbed effluent 9 exits from the top of absorber tower 40 via pipe 16. Unabsorbed effluent or absorber effluent 9 may include exhaust gas, which may be burned in absorber exhaust gas incinerator 21 (AOGI) or absorber exhaust gas oxidizer (AOGO).

[0021] AOGI operation

[0022] A more detailed view of AOGI21 is shown Figure 2 In the middle. For example Figure 2 As shown, absorber effluent 9, fuel gas 120, and air 125 enter AOGI 21. AOGI effluent gas 130 is sent to AOGI flue 150.

[0023] Environmental permission requirements may limit the operating parameters used for AOGI. For example, environmental requirements may require providing less than the required amount of NO in the AOGI flue gas. x The operation involves non-methane hydrocarbons and / or CO. Monitoring of the amount of each of these compounds in the AOGI flue gas is performed using methods known in the art. The process may include a continuous emission monitoring system (CEMS). Environmental requirements do not directly control AOGI operation, but help define operating conditions and the setpoints required to meet environmental requirements.

[0024] In one aspect, the process includes operating the AOGI to control NO in the AOGI flue gas.x Level. In this respect, the process includes providing absorber effluent, fuel gas, and air to the AOGI in amounts such that for every tonne of AN produced in the unit, approximately 6 kg or less of NO is maintained. x On the other hand, about 5 kg or less of NO x On the other hand, approximately 4 kg / hr or less of NO x On the other hand, approximately 3 kg / hr or less of NO x For each ton of AN produced in the equipment, the process includes measuring NO in the AOGI flue gas. x .

[0025] In another aspect, the process includes operating the AOGI to control non-methane hydrocarbons (NMHC) in the AOGI flue gas. In this aspect, NMHC primarily includes propane, acrylonitrile, acetonitrile, and propylene. In this aspect, the process includes supplying absorber effluent, fuel gas, and air to the AOGI in amounts such that for each tonne of AN produced in the unit, approximately 3.5 kg or less of NMHC is maintained, in another aspect, approximately 3 kg or less of NMHC, in another aspect, approximately 2.5 kg or less of NMHC, in another aspect, approximately 2 kg or less of NMHC, for each tonne of AN produced in the unit. In this aspect, the process includes measuring NHMC in the AOGI flue gas.

[0026] In another aspect, the process includes operating the AOGI to control CO in the AOGI flue gas. In this aspect, the process includes supplying absorber effluent, fuel gas, and air to the AOGI in amounts such that for each tonne of AN produced in the unit, approximately 3.5 kg or less CO is maintained, in another aspect, approximately 3 kg or less CO, in another aspect, approximately 2.5 kg or less CO, and in another aspect, approximately 2.0 kg or less CO, for each tonne of AN produced in the unit. In this aspect, the process includes measuring CO in the AOGI flue gas.

[0027] In one aspect, the process includes supplying absorber effluent from the absorber to AOGI 21, and supplying fuel gas 120 and air 125 to AOGI 21. The amounts of absorber effluent, fuel gas, and air supplied to the AOGI are such that the temperature within the AOGI is maintained within approximately 10℉ of the AOGI temperature setpoint by varying the fuel gas supply rate, and in another aspect, within approximately 5℉ of the AOGI temperature setpoint. In this aspect, the temperature inside AOGI 21 is measured. The process may include various known configurations of heat exchangers. In one aspect, the absorber exhaust gas incinerator temperature setpoint is set to obtain a NO content in the absorber exhaust gas incinerator flue gas that is less than a desired amount. xThe minimum temperature required for non-methane hydrocarbons and / or CO, preferably the minimum temperature required to obtain less than the amount required for each of them.

[0028] In one aspect, the absorber exhaust gas includes unreacted propylene. The reactor includes control and shutdown systems to ensure that propylene does not reach explosive levels in the AOGI. In this aspect, the reactor temperature control and shutdown system will detect reaction losses and prevent excessive propylene flow to the AOGI.

[0029] In another aspect, the process includes controlling the amount of oxygen in the absorber flue gas by supplying air 125 to the AOGI. In this aspect, the amount of oxygen in the absorber flue gas is about 5% by volume or less, in another aspect, about 3.5% by volume or less, in another aspect, about 3% by volume or less, in another aspect, about 2.5% by volume or less, in another aspect, about 2% by volume or less, and in another aspect, at least about 1% by volume or less. Oxygen in the AOGI flue 150 is measured.

[0030] On the other hand, the process provides an overall acrylonitrile recovery rate of approximately 95-97%. The associated quenching and absorber efficiencies are greater than approximately 99%. In this respect, the ratio of fuel gas supplied to the absorber waste gas incinerator to the produced acrylonitrile is maintained at approximately 3.3:1 thousand standard cubic feet / tonne acrylonitrile (MSCF / T) to approximately 3.8:1 (MSCF / T), and on the other hand, approximately 3.4:1 (MSCF / T) to approximately 3.7:1 (MSCF / T). Relatedly, the ratio of air supplied to the absorber waste gas incinerator to the produced acrylonitrile is maintained at approximately 1.7:1 thousand standard cubic feet / minute / tonne acrylonitrile (MSCFM / T / hrAN) to approximately 1.9:1 (MSCFM / T / hrAN).

[0031] Fluidized bed reactors are central to acrylonitrile plants. The goal is to optimize reactor efficiency (including reactant conversion and catalyst loss) while increasing the reactor's specific capacity. Improper reactor operation can significantly impact the efficiency, reliability, or production capacity of the entire acrylonitrile plant, and in extreme cases, lead to prolonged production downtime. Fluidized bed operation and performance are highly sensitive to the specific operating conditions selected, and industrial processes exercise extreme caution when altering these conditions. Changes in fluidized bed operating conditions (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, fine powder content, abrasion characteristics) can also alter catalyst performance and associated production capacity and efficiency. The ammonia oxidation process involves reacting ammonia, oxygen, and hydrocarbons selected from propane, propylene, isobutane, and isobutene and combinations thereof in the presence of a catalyst at a pressure (absolute pressure) of approximately 140 kPa or less and a velocity of approximately 0.5–1.2 m / s to provide the reactor effluent stream. When using a catalyst with an average particle size of about 10-100 µm, wherein about 0-30 wt% of the particle size distribution is greater than about 90 µm and about 30-50 wt% of the particle size distribution is less than 45 µm, the fluidization velocity (based on the effluent volumetric flow rate and the reactor cross-sectional area (“CSA”) excluding the area of ​​the cooling coil and the immersion tube) can operate at a maximum of 1.2 m / s, preferably 0.55-0.85. Even at velocities up to those indicated, operation has been found with acceptable catalyst loss, while operating at about 0.50-0.58 kg / cm². 2 The reactor is operated under top pressure and / or the cyclone separator is operated under a pressure drop of 15 kPa or less, with the powder detachment height approximately 5.5–7.5 m above the top of the fluidized bed. This results in the potential for increased production capacity per unit reactor volume (tangential:tangential) of 0.005–0.015 metric tons / hour / m³ reactor volume, on the other hand, approximately 0.0075–0.0125, and on the other hand, approximately 0.009–0.01 metric tons / hour / m³ reactor volume.

[0032] In one aspect, the process involves operating or reacting hydrocarbons in a reactor, wherein the effluent volumetric flow has a velocity of approximately 0.5–approximately 1.05 m / s (based on the effluent volumetric flow rate and the reactor cross-sectional area (“CSA”) excluding the area of ​​the cooling coils and immersion tubes, i.e., ~90% of the open CSA). Reactors have been found to be designed and operated at this velocity while also achieving good fluidization / catalyst performance and reasonable catalyst carryover / catalyst loss from the cyclone separator, allowing the velocity to be maintained near this range to the extent that the reactor capacity can be increased. In one embodiment, the reactor can be operated at a maximum velocity of approximately 0.75–approximately 0.95 m / s (based on 90% CSA and effluent gas) and maintained at approximately 0.50–approximately 0.65 kg / cm³. 2 The top pressure, and on the other hand, approximately 0.52-0.58 kg / cm². 2 In one aspect, the ratio of the cyclone separator inlet velocity (m / s) to the reactor effluent velocity (m / s) is about 15 or greater; in another aspect, about 20 or greater; in another aspect, about 15 to about 30; in another aspect, about 20 to about 30; in another aspect, about 22 to about 25; in another aspect, about 23 to about 26; and in another aspect, about 27 to about 29.

[0033] In one aspect, the process includes operating or reacting hydrocarbons in a reactor having a fluidized bed height of about 25% to about 60% (tangential:tangential) of the reactor cylinder height; in another aspect, about 25% to about 37%; in another aspect, about 42% to about 50%; in another aspect, about 45% to about 55%; and in another aspect, about 44% to about 47%.

[0034] In one aspect, the process includes operating or reacting hydrocarbons in a reactor having a fluidized bed height of about 60% to about 110% of the reactor diameter; in another aspect, about 60% to about 80%; in another aspect, about 70% to about 100%; in another aspect, about 75% to about 90%; in another aspect, about 80% to about 90%; in another aspect, about 85% to about 95%; in another aspect, about 70% to about 85%; and in another aspect, about 85% to about 90%.

[0035] In one aspect, the process includes operating or reacting hydrocarbons in a reactor, wherein the reactor has a density of about 0.50 to about 0.65 kg / cm³. 2 The top pressure, on the other hand, is approximately 0.52-0.58 kg / cm². 2 On the other hand, approximately 0.54-0.6 kg / cm² 2 On the other hand, approximately 0.5-0.55 kg / cm² 2Reactor top pressures within this range provide the benefit of improved catalyst performance at reactor top pressures above this range. In one aspect, the method includes pressures of approximately 0.54–0.56 kg / cm². 2 Lower the operating reactor.

[0036] In one aspect, the process includes operating or reacting hydrocarbons in a reactor, wherein the amount of ammonia in the reactor feed provides an ammonia:hydrocarbon molar ratio of about 1 to about 2, in another aspect, about 1.25 to about 1.75, in another aspect, about 1.4 to about 1.6, and in another aspect, about 1.25 to about 1.3.

[0037] In another aspect, the process includes operating or reacting hydrocarbons in a reactor, wherein the amount of air in the reactor feed provides an air:hydrocarbon ratio of approximately 9 to approximately 12 in the reactor feed, in another aspect, approximately 9 to approximately 11, in another aspect, approximately 9 to approximately 10, in another aspect, approximately 10.5 to approximately 11, in another aspect, approximately 9.25 to approximately 9.75, and in another aspect, approximately 9.4 to approximately 9.6. In a related aspect, the reactor effluent comprises approximately 0.5 to approximately 1% by weight of oxygen. The process may further include continuously measuring the amount of oxygen in the reactor effluent and accordingly continuously adjusting the air:hydrocarbon molar ratio. Oxygen can be measured at any location downstream of the reactor.

[0038] A process for absorbing a reactor effluent comprising acrylonitrile includes quenching the reactor effluent with a first aqueous stream to provide a quenched stream comprising acrylonitrile; compressing the quenched stream to provide a compressor stream comprising acrylonitrile; conveying the compressor stream to an absorber at a pressure of approximately 300 kPa to approximately 500 kPa (absolute pressure); and absorbing acrylonitrile in a second aqueous stream in the absorber to provide a water-rich environment comprising acrylonitrile.

[0039] On the other hand, a process for absorbing a reactor effluent comprising acrylonitrile includes quenching the reactor effluent with a first aqueous stream to provide a quenched stream comprising acrylonitrile; compressing the quenched stream to provide a compressord effluent comprising acrylonitrile; conveying the compressord effluent to an absorber; and in the absorber, absorbing acrylonitrile in a second aqueous stream having a temperature of about 4°C to about 45°C to provide a water-rich environment comprising acrylonitrile.

[0040] Variations in reactor operation, quenching, and / or absorber operation can affect the AOGI operating parameters required to achieve desired emission levels. For example, variations in reactor conversion rates can affect the absorber exhaust gas composition and the amount of fuel and oxygen required to be supplied to the AOGI. In this respect, the reactor propylene conversion rate is approximately 95% to less than approximately 100%. As used herein, “reactor propylene conversion rate” refers to the percentage of propylene in the reactor feed that is converted to acrylonitrile and other carbonaceous products. On the other hand, quench tower operation can affect absorber tower temperature, which can ultimately affect the amount of water in the absorber exhaust gas. Variations in the water content of the absorber exhaust gas can subsequently affect AOGI operation. In this respect, quench tower effluent with temperatures of approximately 65°C to approximately 85°C (for one type of quench design) and approximately 100°C to approximately 120°C (for another type of quench design) is conveyed to the absorber. Relatedly, the absorber exhaust gas has approximately 5% by weight or less water, and the water content in the absorber exhaust gas can vary with variations in the absorber top temperature. On the other hand, the quench tower can provide a pH of about 3.5 to about 7 in the condensate from the quench tower aftercooler, on the other hand, about 3.5 to about 6, and on the other hand, about 5 to about 5.5.

[0041] Advanced process control

[0042] Variations in the reactor feed rate (hydrocarbon feed rate) alter the amount of propane entering the absorber and ultimately the AOGI. Propane has been found to be essentially inert to the catalyst in the reactor. Propane as fuel can cause deviations in AOGI temperature and flue gas O2 if this variation is not compensated for by a feedforward method with fuel gas flow rate. This can also be observed when propylene purity changes, resulting in varying amounts of propane entering the absorber and AOGI. Therefore, it is known that variations in feed rate and propylene purity (and their variations) can provide better control over AOGI combustion chamber temperature and flue gas O2 when used to predict deviations in AOGI temperature and O2 and then compensated for by variations in fuel gas.

[0043] Model predictive control (MPC), also known as advanced process control (APC), uses process models to predict future process behavior and then executes optimal control actions to calculate process deviations based on desired objectives. Along with controlling the process, MPC also attempts to drive the process to the most "economical" conditions by moving key process variables. The processes include using MPC to achieve reduced fuel gas consumption and improved AOGI emissions.

[0044] As used herein, the term "manipulated variable" refers to a variable adjusted by an advanced process controller. In this respect, manipulated variables include the fuel gas flow rate and air flow rate to the AOGI. The term "controlled variable" refers to a variable maintained within a predetermined value (setpoint) or a predetermined range (set range) by an advanced process controller. In this respect, controlled variables include the temperature in the AOGI and the O2 in the AOGI flue gas. "Optimization variable" refers to a variable that maximizes or minimizes its value and maintains it within a predetermined value. "Feedforward variable" refers to a variable used to determine the adjustment of the manipulated variable. In this respect, feedforward variables include the flow rate of the reaction stream entering the ammonia oxidation reactor and the amount of hydrocarbons in the reaction stream.

[0045] One aspect of model predictive control is using the model and available measurements of the controlled variables to predict future process behavior. The controller output is calculated to optimize the performance index, which is a linear or quadratic function of the prediction error and the calculated future control action. At each sampling time, the control calculation and prediction are repeated based on the current measurements. In this regard, a suitable model is one comprising a set of empirical step response models that express the effect of the step responses of the manipulated and feedforward variables on the controlled variables.

[0046] The optimal value of the parameter to be optimized can be obtained by a separate optimization step, or the variable to be optimized can be included in the performance function.

[0047] Before model predictive control can be applied, the effects of a step change in the manipulated variable on the variable to be optimized and on the controlled variable are first determined. This yields a set of step-response coefficients. This set of step-response coefficients forms the basis of model predictive control for the process.

[0048] During normal operation, predicted values ​​of controlled variables are periodically calculated for some future control actions. Performance indices are calculated for these future control actions. The performance index consists of two terms: the first term represents the sum of prediction errors for each control action across all future control actions, and the second term represents the sum of changes in the manipulated variables for each future control action. For each controlled variable, the prediction error is the difference between the predicted value and the reference value of the controlled variable. The prediction error is multiplied by a weighting factor, and the changes in the manipulated variables for each control action are multiplied by an action inhibition factor.

[0049] Alternatively, these terms can be the sum of squared terms, in which case the performance index is quadratic. Furthermore, constraints can be imposed on the manipulator, the changes in the manipulator, and the controlled variable. This yields an independent system of equations, solving which simultaneously minimizes the performance index.

[0050] Optimization can be performed in two ways: one is to optimize separately from minimizing the performance index, and the other is to optimize within the performance index.

[0051] When optimization is performed individually, the variable to be optimized is included as a controlled variable in the prediction error for each control action, and the optimization produces a reference value for the controlled variable.

[0052] Alternatively, optimization can be performed within the performance index calculation, resulting in a third term in the performance index with appropriate weighting factors. In this case, the reference value of the controlled variable is a predetermined steady-state value, which remains constant.

[0053] Considering constraints, the performance exponent is minimized to obtain the values ​​of the manipulation variables used for future control actions. However, only the next control action is executed. Then the calculation of the performance exponent for future control actions begins again.

[0054] The model with step response coefficients and the equations required in model predictive control are part of a computer program that is executed to control the absorber exhaust gas combustion process. A computer program loaded with such a model predictive control-capable program is called an advanced process controller. Commercially available computer programs include, for example, Aspen Technology's DMCplus. ® And Emerson's PredictPro ® . Example

[0055] Example 1: Fuel gas and air consumption at 16T / hr acrylonitrile

[0056] Effects of AOGI Temperature Variation: The table below compares fuel gas and air consumption when operating the equipment to produce 16 T / hr acrylonitrile (AN). Baseline operation describes the optimal AOGI temperature and flue gas O2. In practice, the process may include operating the AOGI at approximately 10°F higher to provide a buffer against variations in feed purity and reactor feed rate. As shown in the table, fuel gas and air consumption increase when the temperature increases by 10°F and flue gas O2 remains constant. In this example, fuel gas consumption increases by approximately 6.9% and air consumption by approximately 2.1% at +10°C operation compared to baseline operation. In this respect, fuel gas consumption can increase by approximately 6%–7.5% and air consumption by approximately 1.5%–2.5% compared to operating the AOGI at a temperature approximately 10°F higher than baseline operation.

[0057] The effects of AOGI temperature and flue gas O2 variations: As further shown in the table, when flue gas O2 increases by 1.4%–1.6%, fuel gas consumption increases by approximately 15% and air consumption by approximately 7.4% compared to baseline operation. In this respect, fuel gas consumption can increase by approximately 12%–16% and air consumption by approximately 6%–8% compared to operating the AOGI at approximately 1.4% flue gas O2 and baseline temperature. The method presented in this paper reduces the need to operate the AOGI at a level 10℉ above the desired baseline and results in savings in fuel gas and air supplied to the AOGI.

[0058] Effects of changes in feedstock purity: The table below illustrates the effects of changes in feedstock purity. As shown in the table, when feedstock purity decreases by 1% while fuel gas and air remain at baseline levels, the AOGI temperature increases. Maintaining the baseline temperature requires a reduction in fuel gas consumption and keeping air consumption constant.

[0059] The method presented herein allows for the pre-conditioning of the fuel gas feed to the AOGI based on variations in feed purity. This pre-conditioning of the fuel gas feed allows the AOGI to be maintained closer to its desired temperature while using less fuel gas. In this respect, at a feed purity of approximately 95.4%, fuel gas consumption is approximately 49.1% lower than baseline operation when it is permissible to reduce fuel gas consumption to maintain the AOGI temperature.

[0060]

[0061] Example 2: Fuel gas and air consumption at 12T / hr acrylonitrile

[0062] Effects of AOGI Temperature Variation: The table below compares fuel gas and air consumption when operating the equipment to produce 12 T / hr acrylonitrile (AN). Baseline operation describes the optimal AOGI temperature and flue gas O2. In practice, the process may include operating the AOGI at approximately 10°F higher to provide a buffer against variations in feed purity and reactor feed rate. As shown in the table, fuel gas consumption increases when the temperature increases by 10°F and flue gas O2 remains constant. In this example, fuel gas consumption increases by approximately 3.7% and air consumption increases by approximately 0.8% at +10°C compared to baseline operation. In this respect, fuel gas consumption can increase by approximately 3%–approximately 4% and air consumption can increase by approximately 0.5%–approximately 1.0% compared to operating the AOGI at a temperature approximately 10°F higher than baseline operation.

[0063] The effects of AOGI temperature and flue gas O2 variations: As further shown in the table, when flue gas O2 increases by 2.6%–2.8%, fuel gas consumption increases by approximately 7.7% and air consumption by approximately 6.0% compared to baseline operation. In this respect, fuel gas consumption can increase by approximately 5%–10% and air consumption by approximately 5%–7% compared to operating the AOGI at approximately 2.6% flue gas O2 and baseline temperature.

[0064] Effects of changes in feedstock purity: The table below illustrates the effects of changes in feedstock purity. As shown in the table, when feedstock purity decreases by 1% while fuel gas and air remain at baseline levels, the AOGI temperature increases by 5.8% compared to the baseline temperature. In this respect, a decrease in feedstock purity can lead to an AOGI temperature increase of approximately 5.5% to approximately 6.5% compared to the baseline temperature. When feedstock purity increases by 1% while fuel gas and air remain at baseline levels, the AOGI temperature decreases by approximately 6.2% compared to the baseline temperature. In this respect, an increase in feedstock purity can lead to an AOGI temperature decrease of approximately 5.5% to approximately 6.5%.

[0065]

[0066] Example 3: Effects of Raw Material Purity and Feed Rate

[0067] Effects of changes in feedstock purity: The table below illustrates the effects of changes in feedstock purity. As shown in the table, when feedstock purity increases by 1.1% and fuel gas and air remain at baseline levels, the AOGI temperature decreases by approximately 4.5%. In this respect, an increase of approximately 1.1% in feedstock purity can lead to a decrease in AOGI temperature of approximately 4% to approximately 5%.

[0068] When the feedstock purity increases by 1.1% and the AOGI temperature remains at the baseline level, the fuel gas consumption increases by 16.5% and the air consumption increases by 0.7%. In this respect, when the feedstock purity increases by 1.1% and the AOGI temperature remains at the baseline level, the fuel gas consumption can increase by about 16% to about 17% compared to the baseline level, while the air consumption can increase by about 0.5% to about 1% compared to the baseline level.

[0069]

[0070] Effect of Reactor Feed Rate: The table below illustrates the effect of changes in reactor feed rate. As shown in the table, when the feed rate increases by 5% while the fuel gas and AOGI temperatures remain at baseline, the AOGI temperature decreases by approximately 2℉ and flue gas O2 decreases by approximately 13.4%. When the feed rate decreases by 10% while the fuel gas and AOGI temperatures remain at baseline, the AOGI temperature increases by approximately 6℉ and flue gas O2 increases by approximately 31%. When the feed rate decreases by 10% while the AOGI temperature and flue gas O2 remain at baseline, the fuel gas consumption decreases by approximately 10% and the air consumption decreases by approximately 10.2%. In this respect, a decrease in feed rate of approximately 10% can result in a reduction in fuel consumption of approximately 8%–approximately 12% and a reduction in air consumption of approximately 9.5%–approximately 10.5%.

[0071]

[0072] Although the invention disclosed herein has been described by way of specific implementations, examples and applications thereof, many modifications and variations may be made thereto by those skilled in the art without departing from the scope of the invention as set forth in the claims.

Claims

1. A method for operating a waste gas incinerator, the method comprising: The reaction stream is introduced into an ammonia oxidation reactor, which contains a catalyst; The amount of hydrocarbons in the reaction stream and the feed rate of the reaction stream were determined. The reactor effluent is transferred from the ammonia oxidation reactor to the absorber; The absorber exhaust gas is supplied from the absorber to the absorber exhaust gas incinerator; and Supply fuel gas and air to the absorber waste gas incinerator; The amounts of fuel gas and air supplied to the absorber incinerator are controlled based on the measured amount of hydrocarbons in the reaction stream and the measured feed rate, ensuring that the amounts of absorber exhaust gas, fuel gas, and air supplied to the absorber incinerator are maintained at less than 6 kg of NO relative to each ton of acrylonitrile produced in the absorber incinerator flue gas. x The non-methane hydrocarbons in the flue gas from the absorber incinerator are less than 3.5 kg per ton of acrylonitrile produced. The hydrocarbons in the reaction stream are propane and propylene, and propane is inert to the catalyst in the reactor. The feedforward variables include the amount of hydrocarbons in the reaction stream and the feed rate of the reaction stream; the control variables include the fuel gas flow rate to the absorber waste gas incinerator and the air flow rate to the absorber waste gas incinerator; and the controlled variables include the amount of oxygen in the flue gas of the absorber waste gas incinerator and the temperature in the absorber waste gas incinerator.

2. The method according to claim 1, wherein the temperature in the absorber waste gas incinerator is maintained within 10℉ of the temperature set point of the absorber waste gas incinerator.

3. The method according to claim 1, wherein the method provides less than 5% by volume oxygen in the flue gas of the absorber incinerator.

4. The method according to claim 1, wherein the method maintains CO in the flue gas of the absorber incinerator at a level of less than 3.5 kg per ton of acrylonitrile produced.

5. The method according to claim 2, wherein the temperature setpoint of the absorber waste gas incinerator is such that less than a desired amount of NO is obtained in the flue gas of the absorber waste gas incinerator. x The minimum temperature required for non-methane hydrocarbons and / or CO.

6. A method for operating an absorber waste gas incinerator, the method comprising: A reactant stream containing hydrocarbons, ammonia, and oxygen-containing gas is introduced into an ammonia oxidation reactor, the ammonia oxidation reactor containing a catalyst, wherein the hydrocarbons are propane and propylene, and the propane is inert to the catalyst in the reactor. The amount of hydrocarbons in the reaction stream was determined; The feed rate of the reaction stream was measured; To produce acrylonitrile by reacting hydrocarbons with ammonia and oxygen; The acrylonitrile-containing effluent discharged from the ammonia oxidation reactor is transferred to the absorber; The absorber exhaust gas is supplied from the absorber to the absorber exhaust gas incinerator; Supply fuel gas and air to the absorber waste gas incinerator; and The amount of hydrocarbons in the reaction stream and the feed rate of the reaction stream are used to effectively maintain the temperature in the absorber waste gas incinerator within 10℉ (5.56℃) of the absorber waste gas incinerator's temperature setpoint and to provide the amount of oxygen in the absorber waste gas incinerator flue gas below 5% by volume, thereby adjusting the fuel gas flow rate and the air flow rate to the absorber waste gas incinerator. The feedforward variables include the amount of hydrocarbons in the reaction stream and the feed rate of the reaction stream; the control variables include the fuel gas flow rate to the absorber waste gas incinerator and the air flow rate to the absorber waste gas incinerator; and the controlled variables include the amount of oxygen in the absorber waste gas incinerator flue gas and the temperature in the absorber waste gas incinerator.

7. The method according to claim 6, wherein the temperature in the waste gas incinerator is maintained within 5℉ of the temperature set point of the waste gas incinerator.

8. The method of claim 6, wherein the method maintains NO levels in the flue gas from the absorber incinerator below 6 kg per ton of acrylonitrile produced. x .

9. The method of claim 6, wherein the method maintains less than 3.5 kg of non-methane hydrocarbons in the absorber exhaust gas incinerator flue gas relative to each ton of acrylonitrile produced.

10. The method of claim 6, wherein the method maintains CO in the flue gas of the absorber incinerator at a level of less than 3.5 kg per ton of acrylonitrile produced.

11. The method of claim 6, wherein the ammonia oxidation reactor has a propylene conversion rate of 95% to less than 100%.

12. The method of claim 6, wherein the reactor effluent from the ammonia oxidation reactor is conveyed to a quench tower and the quench tower effluent having a temperature of 65°C-85°C is conveyed to the absorber.

13. The method of claim 6, wherein the absorber exhaust gas contains less than 5% by weight of water.

14. The method according to claim 6, wherein the temperature setpoint of the absorber waste gas incinerator is such that less than a desired amount of NO is obtained in the flue gas of the absorber waste gas incinerator. x The minimum temperature required for non-methane hydrocarbons and / or CO.

15. A method for operating a waste gas incinerator, the method comprising: The reaction stream is introduced into an ammonia oxidation reactor, which contains a catalyst; The amount of hydrocarbons in the reaction stream and the feed rate of the reaction stream were determined. The reactor effluent is transferred from the ammonia oxidation reactor to the absorber; The absorber exhaust gas is supplied from the absorber to the absorber exhaust gas incinerator; and Supply fuel gas and air to the absorber waste gas incinerator; The feedforward variables include the amount of hydrocarbons in the reaction stream and the feed rate of the reaction stream; the manipulated variables include the fuel gas flow rate to the absorber waste gas incinerator and the air flow rate to the absorber waste gas incinerator; and the controlled variables include the amount of oxygen in the flue gas of the absorber waste gas incinerator and the temperature in the absorber waste gas incinerator. Controlling at least one group of controlled variables includes adjusting manipulator variables. The feedforward variable is used to change the manipulated variable. The hydrocarbons in the reaction stream are propane and propylene, and the propane is inert to the catalyst in the reactor.

16. The method of claim 15, wherein the method comprises controlling the amount of oxygen in the flue gas of the absorber incinerator and the temperature in the absorber incinerator, which is based on model predictive control to determine synchronous control actions for manipulated variables in order to optimize at least one set of parameters while controlling at least one set of controlled variables.

17. The method of claim 15, wherein the method provides a temperature in the absorber waste gas incinerator within 10℉ of the temperature setpoint of the absorber waste gas incinerator.

18. The method of claim 17, wherein the temperature in the absorber waste gas incinerator is maintained within 5℉ of the temperature set point of the absorber waste gas incinerator.

19. The method of claim 15, wherein the method provides less than 5% by volume oxygen in the flue gas from the absorber incinerator.

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