WO2003085320A1 - Catalytic combustion unit - Google Patents

Abstract

A catalytic combustion unit that prolongs the life of catalyst of catalytic combustion furnace and enables reducing operating cost. The catalytic combustion unit is operated with the inlet temperature (T1) and outlet temperature (T2) of combustion furnace (11) held at lower limit values while the concentration (A1) of gas component under control of emitted gas does not reach a control level, thereby minimizing the drop of catalyst activity. The catalytic combustion unit is operated with the inlet temperature (T1) and outlet temperature (T2) of combustion furnace (11) increased so that the concentration (A1) of gas component under control becomes a control level after the temperature (A1) of gas under control of emitted gas has reached a control level, thereby minimizing the drop of catalyst activity. When the inlet temperature (T1) or outlet temperature (T2) has reached an upper limit value, alarming is effected and the catalyst is replaced.

Description

 Description Catalytic combustion equipment Technical field

 The present invention relates to a catalytic combustion device, and more particularly to a catalytic combustion device capable of extending the life of a catalyst in a catalytic combustion furnace. Background art

 A catalytic combustion device is a device that burns a combustion target gas such as waste gas by using a catalyst. Many catalysts used in catalytic combustion devices use, for example, expensive platinum or palladium. FIG. 2 is a system diagram of a conventional catalytic combustion device that combusts waste gas generated from an acrylic acid production device that generates acrylic acid using platinum as a catalyst.

 The catalytic combustion unit consists of a catalytic combustion furnace 11 filled with a fixed-bed catalyst, a waste heat recovery piler 1 2 that recovers heat in the exhaust gas from the catalyst combustion furnace 11, and a waste heat recovery piler 1 2 It basically consists of a preheater 13 that preheats the combustion target gas introduced into the catalytic combustion furnace 11 by the residual heat of the passed exhaust gas. In the example of Fig. 2, the gas generated from the acrylic acid production device (oxidation reactor) 14 is introduced into the catalytic combustion device as waste gas after acrylic acid is recovered in the x-inch tower 15. It is released into the atmosphere after being burned by a catalytic combustion device. In the catalytic combustion device, the exhaust gas after combustion in the catalytic combustion furnace 11 is used to recover the reaction heat in the waste heat recovery poirer 12, and is further introduced into the catalytic combustion furnace 11 by the preheater 13. The heat is exchanged with the combustion target gas to be sufficiently cooled and released into the atmosphere. The released gas released into the atmosphere is required to have a flammable gas concentration equal to or lower than a predetermined value, and for this purpose, waste gas generated from the acrylic acid production equipment illustrated in Fig. 2 is burned. In such cases, the concentration of acrolein as a gas component to be managed is controlled so as to be lower than a predetermined value.

 In a catalytic combustion device, the combustion rate generally decreases gradually due to the activity of the catalyst, which gradually deteriorates due to the combustion reaction. Therefore, the capacity of the catalytic combustion furnace is designed with some allowance, and the inlet gas temperature (inlet temperature) and the outlet gas temperature (outlet temperature) are controlled to be constant regardless of the amount of feed waste gas. This controls the combustion in the combustion furnace.

The temperature of the inlet of the catalytic combustion furnace 11, that is, the temperature of the target gas to be introduced from the inlet of the catalytic combustion furnace 11 is controlled by the temperature controller C 1 so as to be constant, and mainly the waste heat recovery boiler 1 It is controlled by adjusting the opening degree of the exhaust gas bypass valve V1 that bypasses 2. In this case, if the opening degree of the exhaust gas bypass valve VI is increased, the temperature of the exhaust gas introduced into the preheater 13, that is, the temperature of the preheater 13 is increased, and the combustion target to be preheated is increased. Since the temperature of the gas increases, the inlet temperature of the catalytic combustion furnace 11 increases. In this control, PID control is performed using the inlet temperature as a control variable and the opening degree of the exhaust gas bypass valve VI as an operation variable.

 In addition, the outlet temperature of the catalytic combustion furnace 11, that is, the temperature of the exhaust gas discharged from the outlet of the catalytic combustion furnace 11 is controlled so as to be constant to the temperature controller C 2. By controlling the opening of the exhaust gas recycle valve V2. In this case, if the opening degree of the exhaust gas recycle valve V2 is increased, the amount of combustion target gas introduced into the catalytic combustion furnace 11 increases, but the amount of heat generated in the catalytic combustion furnace 11 hardly changes. The outlet temperature of the combustion furnace 11 decreases. In this control, the outlet temperature is used as a control variable, and the opening of the recycle valve V 2 is used as an operation variable

PID control is performed.

 In addition, in the above PID control, the catalyst in the catalytic combustion furnace 11 deteriorates and combustion becomes inactive, and the concentration of the target gas component at the outlet of the catalytic combustion furnace 11 rises. When the concentration of the target gas component exceeds a predetermined value, the combustion furnace 11 is operated by PID control in which the set values of the inlet temperature and the outlet temperature are increased, so that the concentration of the management target gas component becomes lower than the predetermined value. Control is performed.

 By the way, the fluctuation of the concentration of the target gas component at the outlet of the catalytic combustion device is caused by the following factors.

 ① Fluctuation in the concentration of the raw material propylene supplied to the acrylic acid production unit (oxidation reactor) causes the conversion rate in the oxidation reactor to fluctuate and is supplied to the catalytic combustion unit via the quench tower. The composition in the combustion target gas fluctuates.

 ② The reaction temperature of the catalytic combustion furnace fluctuates due to disturbances such as fluctuations in the outside air temperature, and the reaction amount of the catalytic combustion furnace, that is, the combustion amount fluctuates accordingly.

 ③ By continuing the combustion operation for a long period, the catalytic activity in the combustion furnace decreases due to the effects of thermal deterioration and catalyst poison, and as a result, the amount of combustion decreases.

 In the above PID control, the concentration of the gas component to be managed in the gas emitted from the catalytic combustion device is monitored, or the rise in the concentration of the gas component to be managed exceeds the control value by a set upper limit alarm. It is possible to recognize and change the set values of inlet temperature and outlet temperature based on the result. .

However, among the above-mentioned fluctuation factors, (i) and (ii) fluctuate in a relatively short period of several minutes to several hours. Therefore, the operator monitors the concentration of the target gas component and monitors the inlet temperature and outlet. Changing the temperature set value requires more frequent operations, which imposes a heavy burden on the operator. If the response is delayed, the concentration of the target gas component in the released gas will exceed the upper limit (control value). There is. For this reason, a method of recognizing an increase in the concentration of the managed gas component is usually adopted by the set upper limit alarm. In this case, in order to prevent the concentration of the managed gas component from exceeding the upper limit depending on the fluctuations caused by ① and ②, Set the temperature and outlet temperature settings sufficiently high. If the concentration of the gas component to be managed exceeds the upper limit due to the fluctuation of factor ③ above, the next set values of the inlet and outlet temperatures will be adopted again.

 Here, in order to reduce the operating cost of the catalytic combustion device, it is essential to prevent the expensive platinum catalyst used in the catalytic combustion furnace from deteriorating and keeping its life long. However, in the operation of the conventional catalytic combustion device, the operation from such a viewpoint was not sufficient, and therefore, the reduction of the operating cost of the catalytic combustion device was insufficient.

 In view of the above, an object of the present invention is to provide a catalytic combustion device capable of reducing operating costs. Disclosure of the invention

 The present inventors have conducted various studies in order to solve the above problems, and as a result, while maintaining the concentration of the target gas component in the gas released from the catalytic combustion device at or below the upper limit, the catalyst of the combustion furnace In order to maintain the activity for the longest period, if the concentration of the gas component to be controlled in the exhaust gas exceeds the upper limit, increase the inlet temperature and Z or outlet temperature of the catalytic combustion furnace, and conversely When the concentration of the gas component does not exceed the upper limit, it is conceived that the process is performed by lowering the inlet temperature and / or the outlet temperature until the concentration of the gas component to be managed reaches the upper limit, and the present invention is reached. did.

 Based on the above, a catalytic combustion device of the present invention comprises: a combustion furnace for combusting a combustion target gas in the presence of a catalyst; a reaction heat recovery device for recovering reaction heat from exhaust gas at the combustion furnace outlet; Downstream of the heat recovery device, an exhaust gas recycle valve for recycling a part of the exhaust gas to the inlet of the combustion furnace, an exhaust gas discharge section for discharging the remainder of the outlet gas to the atmosphere as a release gas, and management of the release gas. And a measuring unit for measuring the concentration of the target gas component.

 In the measuring unit,

 When the concentration of the management target gas component is less than a predetermined value, the opening degree of the exhaust gas recycle valve is adjusted so that each of the inlet gas temperature and the outlet gas temperature is equal to or less than a predetermined value, and When the concentration is equal to or higher than the predetermined value, the opening degree of the exhaust gas recycle valve is adjusted so that the concentration of the gas component to be managed is maintained at the predetermined value.

In the catalytic combustion device of the present invention, when the concentration of the control target gas component in the released gas is equal to or lower than the predetermined value, the control device controls the exhaust gas so that each of the inlet temperature and the outlet temperature of the catalytic combustion furnace is equal to or lower than a predetermined value. By adjusting the opening degree of the recycle valve, the decrease in the activity of the catalyst is kept low, and when the concentration of the gas component to be managed exceeds a predetermined value, the exhaust gas recycle valve is set so that the concentration becomes the predetermined value. Since the opening of the gas is adjusted, the concentration of the gas component to be managed can be maintained at a desired value. In the catalytic combustion device of the present invention, as described above, the activity of the catalyst is reduced. And the operating cost of the catalytic combustion device is reduced, but the operator is not overloaded.

 The catalytic combustion device according to a preferred aspect of the present invention further includes an exhaust gas bypass valve that bypasses the reaction heat recovery device, so that when the concentration of the control target gas component is less than a predetermined value, the inlet gas temperature and the outlet gas The opening degree of the exhaust gas bypass valve and / or the exhaust gas recycle valve is adjusted so that each of the temperatures is equal to or less than a certain value, and when the concentration of the control target gas component is equal to or higher than the predetermined value, the control target The opening degree of the exhaust gas bypass valve and / or the exhaust gas recycle valve is adjusted so as to keep the concentration of the gas component at the predetermined value.

 In a catalytic combustion device according to a further preferred embodiment of the present invention, the opening degree of the exhaust gas bypass valve and / or the exhaust gas recycling valve is adjusted to adjust the inlet gas temperature and the outlet gas temperature of the combustion furnace, and the concentration of the management target gas component. By providing a control unit for controlling, when the concentration of the management target gas component is less than a predetermined value, the control unit controls the exhaust gas bypass so that each of the inlet gas temperature and the outlet gas temperature is equal to or less than a predetermined value. The opening degree of the valve and / or the exhaust gas recycle valve is adjusted. On the other hand, when the concentration of the managed gas component is equal to or higher than the predetermined value, the exhaust gas is maintained so as to maintain the concentration of the managed gas component at the predetermined value. The opening degree of the gas bypass valve and / or the exhaust gas recycle valve is adjusted.

 Further, in the catalytic combustion device according to a preferred embodiment of the present invention, when the activity of the catalyst in the catalytic combustion furnace is sufficiently high and the concentration of the gas component to be managed in the released gas can be maintained below a predetermined value, the control unit Performs control such as multivariable model predictive control, and operates the exhaust gas bypass valve (poirer-bypass valve) and the opening of the Z or exhaust gas recycle valve to keep the inlet and outlet temperatures low. Operate near those lower limits determined by the equipment. As a result, the combustion temperature in the catalytic combustion furnace is maintained at a low value within a range that does not interfere with operation, and the activity of the catalyst is maintained for a long time.

 If the activity of the catalyst decreases due to long-term operation, etc., and the concentration of the controlled gas component in the released gas exceeds a predetermined value, the exhaust gas bypass valve and the Z Or, adjust the opening of the exhaust gas recycle valve. In this case, the inlet temperature and the outlet temperature each exceed the lower limit. Here, the activity of the catalyst is further reduced, and even if the catalyst is operated at the upper limit of the inlet temperature and the upper limit of the outlet temperature determined by the catalytic combustion furnace, the concentration of the target gas component in the released gas can be maintained at a predetermined value or less. If it is gone, the control will generate an alarm. When an alarm occurs, the operator determines whether to operate with a reduced amount of gas to be burned or to operate with a different catalyst.

In the conventional method of operating a catalytic combustion device, in order to keep the set temperature of the inlet and outlet of the catalytic combustion furnace high enough, the catalyst activity deteriorates quickly due to the above factor ③, and the combustion The amount had dropped. Therefore, if it becomes necessary to raise the temperature further, This resulted in a vicious cycle, and as a result, the catalyst deteriorated significantly in a short period of time, and had to be replaced with a new one, resulting in a large economic loss. BRIEF DESCRIPTION OF THE FIGURES

 FIG. 1 is a system diagram showing a configuration of a catalytic combustion device according to an embodiment of the present invention.

 Figure 2: System diagram showing the configuration of a conventional catalytic combustion device.

 FIG. 3 is a system diagram showing a configuration of a catalytic combustion device according to another embodiment of the present invention.

 Explanation of reference numerals

 1 1: Catalytic combustion furnace

 1 2: Waste heat recovery boiler

 1 3: Preheater

 14: Oxidation reactor

 1 5: Quench Tower

 16: Exhaust gas circulation blower

 C1, C2: Temperature controller

 C 3: Control computing unit

 T 1: Inlet temperature

 T 2: Outlet temperature

 A 1: Concentration of managed gas component

 V 1: Exhaust gas bypass valve (boiler bypass valve)

 V 2: Exhaust gas recycle valve Embodiment of the invention

 Hereinafter, the present invention will be described in more detail based on embodiments of the present invention with reference to the drawings. FIG. 1 shows a catalytic combustion device according to an embodiment of the present invention. In this figure, the same reference numerals are given to the same components as those in the conventional catalytic combustion device for easy understanding. This catalytic combustion device is used to combust the waste gas from the acrylic acid production facility to remove the flammable components in the waste gas. Acrolein is selected as the gas component to be managed.

In Figure 1, the catalytic combustion unit consists of a catalytic combustion furnace 11 filled with a fixed-bed catalyst, a waste heat recovery poirer (heat exchanger for steam generation) 1 2 that recovers heat in the exhaust gas from the catalytic combustion furnace 11 1 2 It basically consists of a preheater (heat exchanger for preheating) 13 that preheats the target gas to be introduced into the catalytic combustion furnace 11 by the residual heat of the exhaust gas that has passed through the waste heat recovery poirer 12 . The reaction product gas that has flowed out of the oxidation reactor 14 constituting the acrylic acid production apparatus is supplied to the quench tower 15 where the acrylic acid is recovered by bringing it into countercurrent contact with water. The waste gas from which acrylic acid has been removed from the reaction product gas includes propylene, propane, Includes flammable gas composed of carbon monoxide, nitrogen, oxygen, water, etc. Oxygen is added to this waste gas as needed for combustion and supplied to a preheater 13. Here, air is generally used as a source of oxygen for combustion. The waste gas is preheated by the preheater 13 and then mixed with the exhaust gas from the catalytic combustion furnace 11 to be supplied to the catalytic combustion furnace 11 as a combustion target gas.

 The inlet gas supplied from the inlet of the combustion furnace 11 comes into contact with the fixed-bed catalyst and burns, and is discharged from the combustion furnace 11 as an outlet gas (exhaust gas). The exhaust gas is branched into two pipes at the outlet of the combustion furnace, and the exhaust gas passing through one of the pipes is supplied to a waste heat recovery piler 112, where steam is generated by heat exchange and the exhaust gas itself is cooled. Is done. Exhaust gas passing through the other pipeline bypasses the waste heat recovery boiler 12 and passes through an exhaust gas bypass valve (control valve) VI at high temperature. Exhaust gas passing through both pipelines joins again at the outlet of the waste heat recovery piler 112.

 The combined exhaust gas is branched again into two pipes, and the exhaust gas passing through one of the pipes is supplied to a preheater 13 and used for heating a combustion target gas supplied to a catalytic combustion furnace 11. Exhaust gas passing through the other conduit is sucked by the circulation blower 16, merges with the combustion target gas via the exhaust gas recycle valve V 2, and is supplied again to the inlet of the catalytic combustion furnace 11. The control calculator C 3 controls the opening of the exhaust gas bypass valve V 1 and the exhaust gas recycle valve V 2, thereby releasing the catalyst combustion furnace 11 at the inlet temperature T 1, outlet temperature T 2, and releasing it to the atmosphere. Controls the concentration A1 of acrolein, a gas component to be managed in the gas. Although the concentration of acrolein may be measured directly, it is also possible to measure the concentration of other gas components, for example, propane, and use this as a measure of the concentration of acrolein. For example, when the concentration of acrolein in exhaust gas is low and detection is difficult, it is preferable to select a substance having a higher combustion temperature than acrolein (for example, propane) as the gas to be managed.

 The exhaust gas bypass valve VI is a control valve that adjusts the balance between the amount of exhaust gas supplied to the waste heat recovery boiler 12 and the amount of exhaust gas bypassing the waste heat recovery boiler 12. By increasing the opening of the control valve V1, the temperature of the preheater 13 can be increased, and as a result, the inlet temperature T1 of the catalytic combustion furnace increases, and the effect of the catalytic combustion furnace 11 increases. The outlet temperature T2 also increases. In this case, a rise in the internal temperature of the catalytic combustion furnace 11 promotes the combustion reaction, and the concentration of acrolein in the outlet gas of the waste heat recovery boiler 12 decreases. A valve (not shown) that bypasses the preheater 13 may be provided to adjust the opening.

The exhaust gas recycle valve V 2 is a control valve for adjusting the amount of exhaust gas to be recycled to the inlet of the catalytic combustion furnace 11. By increasing the opening of the control valve V2, the amount of gas passing through the catalytic combustion furnace 11 can be increased, but the amount of heat generated inside the catalytic combustion furnace 11 hardly changes. The catalytic combustion furnace 1 1 outlet temperature T 2 drops, the catalytic combustion furnace The concentration of acrolein A1 in the outlet gas of the gas increases. In addition, the inlet temperature T 1 of the catalytic combustion furnace 11 is temporarily increased by increasing the opening of the recycle control valve V 2 in order to recycle high-temperature combustion exhaust gas before being supplied to the preheater 13. A rise in the inlet temperature T 1 can be seen. However, finally, the temperature T2 of the preheater 13 decreases due to the decrease in the outlet temperature T2 of the catalytic combustion furnace 11 due to the above reasons, and finally, the temperature T1 of the inlet of the combustion furnace 11 decreases. become.

 As described above, regardless of whether the exhaust gas bypass valve V1 or the exhaust gas recycle valve V2 is operated, all of the catalyst combustion furnace inlet temperature T1, outlet temperature T2, and outlet loacrolein concentration A1 are affected. Will have an effect. As described above, since the processes have a strong correlation between the process data, a multivariable control system such as a multivariable model predictive control is used as the control arithmetic unit C3 in order to stably control them. . The following describes how to determine the set value for the control calculator C3.

 Here, the restrictions on each process data in the present combustion device are determined from the process side as follows.

Released gas acrolein concentration A 1

 Upper limit: Operation management upper limit (for example, 2 ppm)

 Lower limit: no lower limit

Combustion furnace inlet temperature T 1

 Upper limit: Temperature at which catalyst degradation proceeds rapidly (for example, 50 O X)

 Lower limit: Minimum temperature required for catalytic combustion reaction (for example, at 210)

The upper and lower limits differ depending on the type of catalyst.

Combustion furnace outlet temperature T 2

 Upper limit: Temperature at which catalyst degradation proceeds rapidly (for example, 50 O)

 Lower limit: minimum temperature required for preheating (for example, 460 V)

The upper and lower limits differ depending on the type of the catalyst and the type of the preheater 13.

Next, the opening operation of the control valves VI and V2 by the control calculator C3 will be described. First, the inlet temperature T1 and outlet temperature T2 measured by the thermometer, and the acrolein concentration A1 measured directly or indirectly by the acrolein analyzer or other component analyzers are calculated by the control arithmetic unit. Entered in C3. The control calculator C 3 performs an adjusting operation to control the opening of the exhaust gas bypass valve V 1 and / or the exhaust gas recycle valve V 2 so that the concentration A 1 of acrolein or the like matches the upper limit value. I do. By this operation, the inlet temperature T1 and the outlet temperature T2 of the catalytic combustion furnace 11 also change, but on the other hand, the upper limit and the lower limit of the inlet temperature T1 and the outlet temperature T2 are also restricted. Therefore, it is controlled so that it does not fall outside the range. Therefore, the opening degree of the exhaust gas bypass valve V 1 and / or the exhaust gas recycle valve V 2 is adjusted so that the inlet temperature T 1, the outlet temperature T 2, and the concentration A 1 of the lower acrolein, etc., satisfy all the upper and lower limits. Is carried out. Here, as described above, since there is a strong correlation between process data, a control law such as multivariable model predictive control is used.

 In the above-mentioned catalytic combustion furnace, when the elapsed time since the start of operation is short and normal operation is performed, the activity of the catalyst is sufficiently high and the reaction amount is sufficiently high, and therefore the concentration of acrolein in the released gas is limited to the upper limit. Value is not reached. In this state, the control calculator C3 performs an operation to increase the concentration of acrolein in the released gas. This is a downward operation for the inlet and outlet temperatures, but both the inlet and outlet temperatures must not fall below the respective lower limit values. That is, as a result, the inlet temperature and the outlet temperature are both controlled so as to be equal to the lower limit, and the acrolein concentration does not reach the upper limit. Eventually, as the operation continues, the activity of the catalyst decreases, and the amount of combustion reaction decreases as the activity decreases. As a result, the concentration of acrolein in the released gas increases and exceeds the upper limit (control value). At this time, the control calculator C3 performs an operation of lowering the acrolein concentration so that the acrolein concentration matches the upper limit value. This operation is an upward operation for the inlet temperature and the outlet temperature. As a result, the inlet temperature and / or the outlet temperature are in the range between the upper limit value and the lower limit value. The ink concentration is controlled to be close to the upper limit.

 A dynamic characteristic model such as a step response model, an impulse response model, and an ARX model is used for the model predictive control for controlling the acrolein concentration to the upper limit. As an example, a method using a step response model will be described.

 The response when a unit step input is entered into the process is a step response model that is arranged in a time series, and when a discrete time expression is used for computer control, the time when the unit step input is entered When the responses in are arranged in the oldest order as an, the result is as follows.

a ₀ , ai, ₂ , '', a, 丄) where s is the time from when a unit step input is input to the process until it is determined that the process has reached a steady state, that is, the settling time. And it is constant at later times, ie,

a _s = a _{s † i} , ι = 1, 2, ···). Assuming that the process is close to linear, when a step-like input A u (t) is added to the process at time t, the response y (t + j) of the process at time t + j is expressed as follows: Is done.

y (t + j) = a】 XA u (t) (2) Therefore, assuming that the operations performed up to now are stepwise inputs of different sizes at regular intervals, the response of the process at time t + j is the response of the past stepwise inputs. It can be considered that the effects are added, and can be expressed as the following formula. y (t + j) = ^ a _k ^ Au (t + j ~ k) (3)

 4 = 1

Here, Au (t + j_k) is the amount of change from the input one cycle before at time t + j-k,

Au (tfj-k) = u (t + j-k) -u (t + j-k-l) (4)

It is. Using equation (3), from the present time, the operation input for the future (L-1) for the control cycle, that is,

 △ u (t), Au (t + 1), Διι (ί + 1), Au (t + L-1)

, The response of the process from the next control cycle to the L control cycles in the future, i.e., y (t + l), y (t + 2), y (t + 3),

Can be predicted. In other words, 1, 2, ···, L may be input to j in equation (3).

 Here, the predicted response and the target value are represented by vectors as follows.

Yp = [y (t + l), y (t + 2),-, y (t + L)] ^T

Yr = [r, r, r,--·, r] ^τ

Note that the subscript 中 で in the equation indicates the transposition of the vector.

 The purpose of the control is to determine the operation input such that the predicted response matches the target value as much as possible. Therefore, the operation input may be determined so that the error area between Υρ and Yr is minimized. Therefore, Au (t), Au (t + 1), and u (t + L-l) that minimize the following evaluation function J may be obtained.

J = (Y r -Yp) ² (5)

Διι (ϋ, Au (t + 1), Au (t + 1), ~ Au (t + Ll) that minimizes J can be obtained by solving the following equation (6) by the least square method.

 dJ / dA = 0 (6) where

△ U = [Διΐ), Au (t + 1), Au (Wl), Au (t + L—l)] ^T

Of the Au (t), Au (t + 1)> Au (t + 1)-Διι + -1) obtained in this way, only the first Διι (t) is input to the process as an operation input. In the next control cycle, It is better to determine Δ ιΐ (t) by repeating the calculation of. The selection of L may be about 1 to 2.5 times the settling time s.

 By the above control, automatic control is realized in which the inlet and outlet temperatures of the catalytic combustion furnace are reduced as much as possible in order to keep the concentration of the released gas acrolein below the upper limit value and to maintain the activity of the catalyst for the longest time. By continuing the operation, the inlet temperature and Z or outlet temperature must be higher than the upper limit in order to make the lower loacrolein concentration close to the upper limit. It is necessary to take measures such as reducing the production volume or replacing the catalyst.

 FIG. 3 shows a catalytic combustion device according to another embodiment of the present invention. This catalytic combustion device is also used to combust the waste gas from the acrylic acid production facility to remove combustible components in the waste gas, and has selected acrolein as the gas component to be managed. . In Fig. 3, catalytic combustion furnace 11, waste heat recovery boiler 12, preheater 13, oxidation reactor 14, quench tower 15, exhaust gas circulation blower 16, inlet temperature T l, outlet temperature Τ 2 The managed gas component concentration Al, the exhaust gas bypass valve VI, and the exhaust gas recycle valve V2 are the same as those shown in FIG. The temperature controller C1 in FIG. 3 is the same as the temperature controller C1 shown in FIG. 2, and the inlet temperature Τ1 is adjusted to a desired set value by adjusting the opening of the exhaust gas bypass valve V1. Control to match. The temperature controller C2 in FIG. 3 is the same as the temperature controller C2 shown in FIG. 2, and the outlet temperature Τ2 is adjusted to a desired set value by adjusting the opening of the exhaust gas recycle valve V2. Control to match.

 By changing the set value of the temperature controller C 1 and / or the set value of the temperature controller C 2, the control calculator C 4 changes the inlet temperature T l, the outlet temperature Τ 2 of the catalytic combustion furnace 11, and controls the temperature. The target gas component concentration A1 is controlled.

 Here, the restrictions on each process data in the present combustion device are determined as follows, as in the description of FIG.

Released gas acrolein concentration A 1

 Upper limit: Operation management upper limit (for example, 2 ppm)

 Lower limit: no lower limit

Combustion furnace inlet temperature T 1

 Upper limit: Temperature at which catalyst degradation rapidly proceeds (for example, 500 ° C)

 Lower limit: Minimum temperature required for catalytic combustion reaction (for example, 210 ° C)

 The upper and lower limits differ depending on the type of catalyst.

Combustion furnace outlet temperature T 2

 Upper limit: Temperature at which catalyst degradation rapidly proceeds (for example, 500 ° C)

 Lower limit: minimum temperature required for preheating (eg 460 ° C)

 The upper and lower limits differ depending on the type of the catalyst and the type of the preheater 13.

Next, an operation of changing the set values of the temperature controllers C1 and C2 by the control arithmetic unit C4 will be described. First, the acrolein concentration A1 measured directly or indirectly by the acrolein analyzer or another component analyzer is input to the control calculator C4. The control calculator C 4 performs an adjustment operation to change the set values of the inlet temperature controller C 1 and / or the outlet temperature controller C 2 so that the input concentration of acrolein A 1 matches the upper limit value. carry out. That is, when the concentration of acrolein A1 is likely to exceed the upper limit, the set value of the inlet temperature controller C 1 and / or the outlet temperature controller C 2 is increased to promote combustion in the catalytic combustion furnace 11. If the acrolein concentration A1 does not reach its upper limit, the inlet temperature controller C1 and / or the outlet temperature controller C By lowering the set value of 2, the combustion in the catalytic combustion device 11 is suppressed, and an adjustment operation is performed to increase the acrolein concentration A1. Here, as for the method of changing the set values of the inlet temperature controller C1 and the outlet temperature controller C2, both may be changed in the same manner, or one of them may be changed preferentially. However, since the inlet temperature T 1 and the outlet temperature T 2 also have an upper limit and a lower limit, respectively, the control arithmetic unit C 4 sets the inlet temperature controller C 1 and the outlet temperature controller C 2 within the upper and lower limits. Change the setting of. When the control calculator C4 determines the set values of the inlet temperature controller C1 and the outlet temperature controller C2, the control rules such as the model prediction control described above may be used.

 Also, depending on the circumstances, before the inlet temperature T 1 and / or the outlet temperature T 2 reach their set values, their operating ends, the exhaust gas bypass valve V 1 and the exhaust gas recycle valve V 2, are fully closed or In such a case, the control arithmetic unit C4 operates only in a direction to release the exhaust gas spy valve V1 or the exhaust gas recycle valve V2 from fully closed or fully opened. Now, the method will be described in detail.

 When the inlet temperature T1 is higher than the set value, the inlet temperature controller C1 performs an operation of closing the exhaust gas bypass V1 so as to match the inlet temperature T1 to the set value, but the inlet temperature T1 If the exhaust gas bypass valve V 1 is fully closed before reaches the set value, the inlet temperature controller C 1 cannot further reduce the inlet temperature T 1, so the control calculator C 4 If the operation to lower the set value of the inlet temperature controller C1 is performed, stop the operation. When it is necessary to increase the set value of the inlet temperature controller C1, the exhaust gas bypass valve is fully closed, so the operation is performed.

 When the inlet temperature T1 is lower than the set value, the inlet temperature controller C1 performs an operation of opening the exhaust gas bypass valve V1 in order to match the inlet temperature T1 to the set value. If the exhaust gas bypass valve V 1 is fully opened before 1 reaches its set value, the inlet temperature controller C 1 cannot perform any further operation to increase the inlet temperature T 1, so the control calculator C 4 If the operation to increase the set value of the temperature controller C1 is performed, stop the operation. When it is necessary to lower the set value of the inlet temperature controller C1, the exhaust gas bypass valve is fully opened, so the operation is performed.

When the outlet temperature T2 is higher than the set value, the outlet temperature controller C2 performs an operation of opening the exhaust gas recycle valve V2 in order to match the outlet temperature T2 to the set value. If the exhaust gas recycle valve V2 is fully opened before T2 reaches its set value, the outlet temperature controller C2 cannot further reduce the outlet temperature Τ2, and therefore the control calculator C4 If the operation of lowering the set value of the outlet temperature controller C2 is performed, the operation is stopped. When it is necessary to increase the set value of the outlet temperature controller C2, perform the operation because the exhaust gas recycle valve is fully opened.

 If the outlet temperature Τ 2 is lower than the set value, the outlet temperature controller C 2 performs an operation of closing the exhaust gas recycle valve V 2 in an attempt to match the outlet temperature Τ 2 to the set value. If exhaust gas recycle valve V 2 is fully closed before 2 reaches its set value, outlet temperature controller C 2 cannot perform any further operation to increase outlet temperature 、 2, and therefore control arithmetic unit C 4 If the operation to increase the set value of the outlet temperature controller C2 is performed, the operation is stopped. When it is necessary to lower the set value of the outlet temperature controller C2, perform the operation because the exhaust gas recycle valve is fully closed.

 The control calculator C 4 changes the set values of the inlet temperature controller C 1 and the outlet temperature controller C 2 to the upper limit of the inlet temperature T 1 and the outlet temperature T 2 so that the acrolein concentration A 1 matches the upper limit. If it is necessary to raise the pressure, or if the exhaust gas bypass valve V1 reaches full open and the exhaust gas recycle valve V2 reaches full close at the same time, an alarm is generated. When the operator detects this alarm, it is necessary to take measures such as reducing the production volume or replacing the catalyst.

 As described above, the present invention has been described based on the preferred embodiment. However, the catalytic combustion device of the present invention is not limited to only the configuration of the above-described embodiment, but may be variously changed from the configuration of the above-described embodiment. Modifications and changes of the above are also included in the scope of the present invention. Industrial applicability

 As described above, according to the present invention, the catalytic combustion device can control the catalyst without lowering the activity and reduce the operating cost, while enabling the control without imposing a large burden on the operator. Is obtained.

Claims

The scope of the claims 1. A combustion furnace that combusts the gas to be burned in the presence of a catalyst, a reaction heat recovery device that recovers reaction heat from exhaust gas at the outlet of the combustion furnace, and a part of the exhaust gas downstream of the reaction heat recovery device. An exhaust gas recycle valve for recycling at the inlet of the combustion furnace, an exhaust gas emission unit that emits the remainder of the outlet gas into the atmosphere as emission gas, and a measurement unit that measures the concentration of the managed gas component in the emission gas. In a catalytic combustion device comprising:  In the measuring section,  When the concentration of the management target gas component is less than a predetermined value, the opening degree of the exhaust gas recycle valve is adjusted so that each of the inlet gas temperature and the outlet gas temperature is equal to or less than a predetermined value, and When the concentration is equal to or higher than the predetermined value, the opening degree of the exhaust gas recycle valve is adjusted so that the concentration of the gas component to be managed is maintained at the predetermined value.  2. An exhaust gas bypass valve for bypassing the reaction heat recovery device is provided, and when the concentration of the target gas component is lower than a predetermined value, the inlet gas temperature and the outlet gas temperature are each equal to or lower than a predetermined value. Adjust the opening of the exhaust gas bypass valve and the Z or exhaust gas recycle valve,  When the concentration of the control target gas component is equal to or higher than the predetermined value, the opening degree of the exhaust gas bypass valve and the Z or the exhaust gas recycle valve is adjusted so as to maintain the concentration of the control target gas component at the predetermined value. The catalytic combustion device according to claim 1, wherein  3. A control unit that controls the opening degree of the exhaust gas bypass valve and the Z or the exhaust gas recycle valve to control the inlet gas temperature and the outlet gas temperature of the combustion furnace and the concentration of the management target gas component, The control unit includes:  When the concentration of the control target gas component is less than a predetermined value, the opening degree of the exhaust gas bypass valve and / or the exhaust gas recycle valve is adjusted so that each of the inlet gas temperature and the outlet gas temperature is equal to or less than a certain value,  When the concentration of the control target gas component is equal to or higher than the predetermined value, the opening degree of the exhaust gas bypass valve and the Z or the exhaust gas recycle valve is adjusted so as to maintain the concentration of the control target gas component at the predetermined value. The device according to claim 2, characterized in that:  4. When the concentration of the gas component to be managed is lower than a predetermined value, the inlet gas temperature and the outlet gas temperature are controlled so as to be lower limit values respectively set in the combustion furnace. An apparatus according to any one of the above.  5. An alarm is generated when either the inlet gas temperature or the outlet gas temperature exceeds an upper limit value defined for each of the catalytic combustion furnaces. Equipment.