JP3849445B2 - Automatic control system for hydrogenation reactor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an automatic control system for a hydrogenation reaction apparatus used to remove acetylenes and / or dienes, which are impurities of olefin products such as ethylene and propylene, in a petrochemical factory or the like.
[0002]
[Prior art]
In a plant producing olefin products such as ethylene and propylene, acetylenes or dienes in the product must be removed to a certain allowable value or less. For this purpose, an apparatus for removing acetylenes or dienes such as a hydrogenation reactor is required. In the hydrogenation reaction of acetylene and dienes in olefins, a fixed bed catalyst reactor packed with a catalyst in which a precious metal catalyst such as palladium (Pd) is usually supported on an inert material such as alumina is charged with the raw material and hydrogen (H2). The acetylenes or dienes are removed by selectively adding hydrogen to the acetylenes or dienes and converting them to olefins. Hydrogen added depending on the performance of the catalyst is consumed in the addition reaction of acetylenes or dienes with a relatively high selectivity, but other hydrogen is added to olefins and converted to paraffins. Furthermore, if hydrogen is added in excess of the minimum amount necessary for removing acetylenes and dienes to below the allowable value, they are all added to olefins and converted to paraffin.
[0003]
That is, taking the acetylene hydrogenation reaction in ethylene as an example, the following reaction occurs in the reactor.
Reaction A C ₂ H ₂ + H ₂ → C ₂ H ₄
Reaction B C ₂ H ₄ + H ₂ → C ₂ H ₆
[0004]
Here, the reaction A is a main reaction, which is a reaction for removing acetylene as an impurity and converting it to ethylene as a product substance. Reaction B is a side reaction and is a reaction for converting the product substance ethylene to ethane.
[0005]
In the operation of the reaction facility, the reactor inlet temperature is adjusted in order to secure the reaction rate, and hydrogen necessary to make the acetylene concentration at the reactor outlet below the allowable value is added. Since the selectivity of the reaction changes depending on the deterioration of the catalyst and the operating temperature, the amount of hydrogen required for the reaction also changes. Conventionally, even if the required amount of hydrogen changes, the acetylene concentration at the outlet does not exceed the allowable value. An excessive amount of hydrogen is constantly added. Therefore, reaction B, which is a side reaction, proceeds more than necessary, and the amount of ethylene converted to ethane has increased.
[0006]
[Problems to be solved by the invention]
It is desirable from the viewpoint of increasing the product recovery rate and reducing the energy in the downstream distillation column while keeping the impurities acetylene or dienes below the allowable value and minimizing the olefins lost in the side reaction. . Therefore, it is necessary to keep the inlet temperature for maintaining the activity as low as possible and to add the minimum amount of hydrogen while constantly monitoring the activity and selectivity of the reaction equipment.
[0007]
In actual operation, the operator makes such adjustments, but the most important point is that acetylenes and dienes do not leak to the reactor outlet even if the feed flow rate or composition changes. Therefore, the current situation is that a higher inlet temperature is set and hydrogen in excess is added.
[0008]
This adjustment is automated to follow the fluctuations in the flow rate and composition of the feed, and also the fluctuations in the purity of the hydrogen in the hydrogen stream, while always maintaining the impurities acetylene or dienes below the permissible value, and side reactions. It is a problem that the present invention seeks to solve to minimize the olefins lost in the process.
[0009]
[Means for Solving the Problems]
In the operation of the hydrogenation reactor, the present invention relates to the unreacted hydrogen concentration (X) at the reactor outlet as an index representing reaction activity, and the acetylenes or dienes at the reactor outlet as an index representing reaction selectivity. Take the concentration (Y) and adjust the reactor inlet temperature (T) and the hydrogen / (acetylenes + dienes) ratio (R) at the reactor inlet to control this within the upper and lower limits. This is an automatic control system for a hydrogenation reactor.
[0010]
That is, the present invention is an automatic control system for a hydrogenation reactor in which hydrogen is added to a raw material feed containing acetylenes and / or dienes and the acetylenes and / or dienes are converted into olefins. From the molar concentration of acetylenes and dienes in the reactor, the flow rate of the feed and the molar concentration of hydrogen in the hydrogen stream fed to the feed, [number of moles of hydrogen / (acetylenes + dienes) moles at the reactor inlet] The number of hydrogen streams required to maintain the ratio (R) at the set number to a set value, and the reactor inlet temperature (T) and the reactor inlet [hydrogen moles / (acetylene And the molar ratio of unreacted hydrogen at the outlet of the reactor (X), and adjusting T and R to adjust X Those of the automatic control system of the hydrogenation apparatus for automatically controlling between upper and lower limit values determined because.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
In order to remove acetylenes and dienes in the feed by hydrogenation reaction, it is important to maintain high reaction activity and selectivity of the main reaction. For example, if the activity is low, even if a necessary amount of hydrogen is added, the hydrogen does not react and acetylenes remain. In addition, if the selectivity of the main reaction is low, the added hydrogen is consumed much in the side reaction, and the hydrogen used for the main reaction is insufficient.
[0012]
The operating variable for controlling the reaction activity includes the reactor inlet temperature. Specifically, when the reactor inlet temperature is raised, the reaction rate of both the main reaction and the side reaction increases, and the added hydrogen is used for the reaction. On the other hand, if the temperature is raised too much, the selectivity of the main reaction deteriorates and hydrogen becomes insufficient. It is therefore advisable to adjust the temperature as low as necessary to complete the reaction. The reaction activity can be appropriately controlled by a controller that adjusts the reaction temperature so that the unreacted hydrogen concentration at the outlet of the reactor is taken as an index of the reaction activity and this concentration is maintained within a predetermined upper and lower limit value.
[0013]
On the other hand, if the reaction activity is properly maintained, the acetylene concentration can be maintained within an allowable value by adding the necessary amount of hydrogen. The amount of hydrogen required is the sum of the amount of hydrogen required for the main reaction and the amount of hydrogen consumed for side reactions that occur simultaneously at a certain selectivity. If hydrogen is insufficient, acetylenes or dienes will leak to the reactor outlet. If hydrogen is excessive, all of the excess hydrogen is consumed in side reactions, and the loss of olefins increases.
[0014]
Therefore, if the concentration of acetylene or dienes at the outlet of the reactor is monitored and a minute amount within the permissible value is detected, the minimum amount of hydrogen corresponding to the reaction selectivity at that moment is reduced. It will be maintained. Therefore, as an index of reaction selectivity, the concentration of acetylenes or dienes at the outlet of the reactor is taken, and the hydrogen / (acetylenes + dienes at the inlet of the reactor is maintained so as to maintain the concentration within a predetermined upper and lower limit value. ) A minimum amount of hydrogen can be maintained by a controller that adjusts the ratio.
[0015]
As the controller configuration, the reactor inlet temperature (T) and the reactor inlet [number of moles of hydrogen / (number of moles of acetylenes + number of moles of dienes)] (R) are determined in advance. Using a multivariable model predictive control controller that grasps the dynamic correlation between the reaction hydrogen molar concentration (X) and the acetylene or diene molar concentration (Y) at the outlet of the reactor by a plant test and uses this correlation as a model. . Examples of the model representing the dynamic relationship include a step response model, a linear regression model, a PLS model, and a neural network. However, the model is not limited as long as the model appropriately represents the above relationship.
[0016]
The reason for using model predictive control is to incorporate changes such as the reactor feed flow rate and the concentration of acetylenes or dienes at the inlet into the controller as disturbance factors, thereby making the hydrogen concentration at the reactor outlet and acetylene more stable. This is because the concentration of the diene or diene can be maintained.
[0017]
The ratio (R) of [number of moles of hydrogen / number of moles of (acetylenes + dienes)] (R) at the reactor inlet set by the model predictive control controller described above is actually the flow rate of the hydrogen stream added to the feed. Adjusted by.
[0018]
The dynamic correlation model possessed by this controller should have a higher accuracy, but in an actual plant, a situation that could not have been predicted when creating this dynamic correlation model may occur. Therefore, there may be an error in the behavior of the reactor and the actual behavior predicted by this dynamic correlation model. Even in such a case, the molar concentration of acetylenes and dienes at the outlet of the reactor is less than the allowable value. There is a need to. For this purpose, the stoichiometrically required [hydrogen / (acetylenes + dienes)] (R ₀ ) at the reactor inlet is calculated in advance, and a value (R _min ) obtained by multiplying this value by a fixed magnification is calculated. The lower limit of the adjustment range of R adjusted by the controller.
[0019]
Next, a control system according to claim 1 will be described (see FIG. 2. In the case of claim 2, X is replaced with Y). The model predictive controller will set the optimum X setting value (X within the range of the upper and lower limits (X _H , X _L ) so as to keep the constraints of the current process (here, hydrogenation reaction system). _SV ). The deviation between the current value (X) and the set value (X _SV ) is input to the model predictive controller, and the number of moles of [hydrogen moles / (acetylenes + dienes) moles at the reactor inlet to correct this deviation. ] (R) and the set value of the reactor inlet temperature T are output. R is input to the R controller and uses measured values of feed flow rate (F), molar concentration of acetylenes in feed (C _Ai ), and hydrogen concentration (C _Hi ) in hydrogen stream added to feed. Then, the flow rate (F _H ) of the hydrogen stream for the input R is output. As a result, F _H and T are set in the process. F _H and T are always maintained by a general single loop controller so as to have this set value. The process outputs the current value of X in response to F _H and T. In this way, X is maintained between predetermined upper and lower limit values.
[0020]
【The invention's effect】
As described above, according to the present invention, the hydrogenation reaction of acetylenes or dienes that are main reactions can be preferentially performed, and the hydrogenation reaction of olefins that are side reactions can be minimized. . Furthermore, even when there is an error in the dynamic correlation model used by the controller, it is possible to avoid the molar concentration (Y) of acetylene or dienes at the outlet of the reactor from exceeding an allowable value. As a result, the amount of olefins increased in the hydrogenation reactor can be maximized, the recovery rate of the olefin product can be increased, and the energy in the subsequent rectification column can be reduced.
[Brief description of the drawings]
FIG. 1 shows the configuration of a hydrogenation reaction apparatus that is an object of the present invention. As an example, the case of a three-column acetylene hydrogenation reaction apparatus is shown.
FIG. 2 is a conceptual diagram of a control system according to claim 1; (In the case of claim 2, X is replaced with Y.)
[Explanation of symbols]
1: Reactor First tank 2: Reactor Second tank 3: Reactor Third tank 4: First tank inlet heater 5: First tank outlet cooler 6: Second tank outlet cooler F: Raw material feed H1 : Hydrogen H2 in the first tank: Hydrogen H3 in the second tank: Hydrogen in the third tank T1: First tank inlet temperature T2: Second tank inlet temperature T3: Third tank inlet temperature A1: First tank inlet acetylene concentration A2 : First tank outlet (second tank inlet) acetylene concentration A3: second tank outlet (third tank inlet) acetylene concentration A4: third tank outlet acetylene concentration A5: first tank outlet hydrogen concentration A6: second tank outlet hydrogen Concentration A7: Third tank outlet hydrogen concentration

Claims (3)

An automatic control system for a hydrogenation reactor for adding hydrogen to a feed containing acetylenes and / or dienes and converting the acetylenes and / or dienes to olefins, wherein the acetylenes and dienes in the feed The ratio of [number of moles of hydrogen / number of moles of (acetylenes + dienes)] at the inlet of the reactor (R) ) With a controller that controls the flow rate of the hydrogen stream required to maintain the set point, and the reactor inlet temperature (T) and the reactor inlet [number of moles of hydrogen / (acetylenes + dienes)] The number of moles] ratio (R) and the molar concentration (X) of unreacted hydrogen at the outlet of the reactor, and by adjusting T and R, X is a predetermined upper and lower limit. Automatic control systems hydrogenation apparatus for automatically controlled during. An automatic control system for a hydrogenation reactor for adding hydrogen to a feed containing acetylenes and / or dienes and converting the acetylenes and / or dienes to olefins, wherein the acetylenes and dienes in the feed The ratio of [number of moles of hydrogen / number of moles of (acetylenes + dienes)] at the inlet of the reactor (R) ) With a controller that controls the flow rate of the hydrogen stream required to maintain the set point, and the reactor inlet temperature (T) and the reactor inlet [number of moles of hydrogen / (acetylenes + dienes)] The number of moles] ratio (R) and (acetylenes + molar concentration of dienes) (Y) at the outlet of the reactor have a dynamic correlation model, and Y is determined in advance by adjusting T and R. Automatic control systems hydrogenation apparatus for automatically controlled during obtained upper and lower limit values. In the system according to claim 1 or 2, a stoichiometrically required ratio (R ₀ ) of [number of moles of hydrogen / number of moles of (acetylenes + dienes)] at the reactor inlet is calculated. The automatic control system for a hydrogenation reactor according to claim 1 or 2, wherein the constant magnification value R _min is set as a lower limit of the R adjustment range.

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