JPS6061003A - Device for controlling top temperature of distillation tower - Google Patents

Abstract

PURPOSE:To enable control of top temp. of a distillation tower meeting suitably to the change of flow rate of feed by operating signals from a tower temp. controlling part and feed forward controlling part by a multiplication means and an addition means, and controlling reflux rate. CONSTITUTION:Output signals from a temp. sensing means 17, 18 provided to a tray at the top of a distillation tower 3 are inputted to a controlling part 19 for temp. difference between trays and adjusting operation is performed to adjust the temp. difference between trays to a specified value, and the output signal is inputted to a multiplication means 31. The amt. of feed is detected by an orifice 2, feed flow rate detecting means 21, and a root square extraction operation means 22, and a signal through the feed forward controlling part 23 is inputted to the multiplication means and the addition means. The output from the addition means is inputted as a set signal to a reflux flow rate controlling part 24 and compared with a reflux flow rate signal through an orifice 10, reflux flow rate detecting means 25, and the square root extraction operation means. Thus, the reflux flow rate is controlled so as to adjust the temp. difference between trays to a specified value.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a distillation column top temperature control device that controls the top temperature of a distillation column by adjusting the reflux flow rate.

[Technical background of the invention and its problems]

Raw materials used in the chemical industry are generally required to be highly pure and homogeneous. For this reason, a distillation column is used for raw materials containing impurities? Separate and purify using distillation procedure,
We obtain raw material products with high purity and homogeneous composition. In such distillation operations, when the pressure inside the distillation column is constant, the temperature at the top of the column is controlled to a predetermined value by taking advantage of the fact that there is a fixed relationship between the temperature at the top of the column and the composition of the product obtained at the top of the column. By doing so, the composition of the product is controlled. This is because it is usually difficult to directly and continuously measure the composition, and even if it is possible to measure it, it takes a long time to measure it and there is a large time delay in the measured values, making it difficult to use it for control. be.

A conventional top temperature control device for a distillation column is shown in FIG. The raw material is supplied through a raw material supply pipe 1, and is supplied to a distillation column 3 through an orifice 2 for detecting a raw material flow rate signal. The raw material supplied to the distillation column 3Vc is separated into gas and liquid, with the liquid collecting at the bottom of the column and the gas collecting at the top of the column. The product collected at the top of the column is condensed by a condenser (not shown) and temporarily stored in a reflux tank 5. The top product stored in the reflux tank 5 is transferred to the delivery pipe 6. Flow control valve 8. It is taken out through the orifice 9.

In order to maintain the liquid level in the reflux tank 5 at a predetermined value, the liquid level is detected by the reflux tank liquid level detection means 12, and the reflux tank liquid level controller 13 compares and adjusts the liquid level with a set value. 13 is given as a set value to the distillate flow rate adjusting section 14. The distillate flow rate adjusting section 14 includes an orifice 9 and a distillate flow rate detection means 1.
5. The square root calculation means 16 compares and calculates the obtained distillate flow rate signal and the output signal of the reflux tank liquid level adjustment section 13, which is a set value signal, and applies the output signal to the flow rate control valve 8 to adjust the flow rate of the reflux tank 5. Adjust the flow rate of the product at the top of the tower so that the liquid level is at a predetermined value.

On the other hand, a reflux pipe 7 is branched from the middle of the delivery pipe 6.

The liquid is refluxed to the vicinity of the top of the distillation column 3 through an orifice lO1 flow control valve 11. The output signals of the temperature detection means 17 and 18 provided on the trays of the distillation column 30 are input to the inter-tray temperature difference adjusting section 19, and compared with a predetermined value of the inter-tray temperature difference, and the output signals are inputted to each adding means.

Further, the raw material supply amount is detected by the orifice 2, the raw material supply flow rate detection means 21, and the square root calculation means n, and is inputted to the addition means hole as a signal via the feedforward control section 23ik.

The signal added by the adding means hole is set as a setting value for each reflux flow rate adjusting section, and the signal is added to the orifice 10. Reflux flow rate signal detection means 5. A comparison and adjustment operation is performed with the reflux flow rate signal obtained by the square root calculation means, and the output signal is applied to the flow rate adjustment valve 11 to adjust the reflux flow rate so that the temperature difference between trays becomes a predetermined value.

Since the composition of the tower top product has a predetermined relationship with the temperature difference between trays, it is necessary to control the tower top temperature to a constant value in order to keep the composition of the tower top product uniform. This is the same even when the raw material supply amount changes, and it is required to (1) reduce transient changes due to changes in the raw material supply amount, and (2) stably control the raw material supply amount at any value. However, in the conventional one device for controlling the top temperature of a distillation column, it is possible to adjust the raw material supply amount at a specific point, but if the raw material supply amount deviates from this specific point, it will deviate from the optimal control point, so transient There was a problem that control characteristics and control stability deteriorated.

[Purpose of the invention]

The present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide a top temperature control device for a distillation column that can perform optimal control even when the amount of raw material supplied changes.

[Summary of the invention]

To achieve this objective, according to the invention. The top temperature control device for the distillation column includes a top temperature control unit that inputs the top temperature of the distillation column, compares it with a predetermined set value and calculates adjustment, and inputs the amount of raw material supplied to the distillation column. , a feedforward control unit that controls the feedforward P, a multiplication unit that multiplies the output signal of the top temperature control unit by the output signal of the feedforward control unit, and an output signal of the multiplication unit; an addition means for adding the output signal of the feedforward control section; and a reflux flow rate adjustment section that uses the output signal of the addition means as a setting signal to adjust the reflux flow rate of the top product from the reflux tank of the distillation column. The temperature at the top of the distillation column is controlled by adjusting the reflux flow rate of the top product using the reflux flow rate adjusting section.

The top temperature control device for a distillation column according to the present invention also includes a second multiplier for multiplying the output signal of the forward control section by a difference signal between a predetermined set value of the top temperature and the raw material inlet temperature. It is further characterized in that the output signal of the second multiplication means and the output signal of the feedforward control section are added by the addition means.

[Embodiments of the invention]

FIG. 2 shows a top temperature control device for a distillation column according to an embodiment of the present invention. This device differs from the distillation column top temperature control device shown in FIG. 1 in that it includes a 1 multiplication means 31 and an addition means 32. The output signal of the temperature detection means 17 and 18 provided on the tray at the top of the distillation column 3 is inputted to the inter-tray temperature difference adjustment section 19, and the output signal is adjusted and calculated so that the inter-tray temperature difference becomes a predetermined value. The signal is guided to multiplication means 31. On the other hand, the raw material supply amount is changed to orifice 2. The M material supply flow rate detection means 21 is detected by the square root calculation means η, and the signal passed through the feedforward control section B is inputted to the multiplication means 31 and the addition means 32. The output signal of the multiplication means 31 is input to the addition means 32, where it is combined with the output signal of the feedforward control section B, and is inputted as a setting signal for the reflux flow rate adjustment section B. The reflux flow rate adjustment unit U compares and adjusts this setting signal with the reflux flow rate signal obtained via the orifice IO1 reflux flow rate detection means 5° square root calculation means, and applies the output signal to the flow rate control valve 11. As a result, the reflux flow rate is controlled so that the temperature difference between the trays becomes a predetermined value.

Now, six quantities of this control system are determined as shown in the following table.

tr, the process requirement to keep the inter-tray temperature Q4ΔTib constant is: MV QCFI X (ΔTs+ΔTC)=KXfIX
(Δ1S+Δtc) -■[11] Hail. Here K is a proportionality constant. The above formula expresses only the static relationship, but if we express the dynamic relationship as an expression, MY = f I X GF X (Δt8+Δtc) =
fiXGFXΔts+fl XGyXltc・4・(2
It becomes 1. Here, 9 is the transfer function of the feedforward control unit B. When this control system is drawn as a block diagram from equation (2), it becomes as shown in FIG. 3.

The operation of this embodiment will be explained assuming that the set value Δt of the temperature difference between trays is constant. Temperature difference between trays Δt, reflux flow rate fR,
The output ΔtC of the inter-tray temperature difference adjusting section is expressed by the following equations.

Δt: fiXΔt, ×GD+fRxGp・・・・・・
...(3) fR=fi×Δt, xGF+fiXΔ
tSx GF-(41Δt=(Δt−Δt)XG,
・・・・・・・・・・・・・・・(5) CS Here, GD is the transfer function between the raw material supply amount f and the inter-tray temperature difference Δt, and Gp is the transfer function between the reflux flow rate fR and the tray temperature difference Δt. Gcl is a transfer function between the inter-tray temperature difference Δt and the inter-tray temperature difference adjustment section 19. The formula % formula % (5) )) (6) holds true. In order for Δt to remain a predetermined constant value even if the raw material supply amount f changes, the following equation holds true from equation (6).

fiXΔt, Generally, the transfer functions Gp and GD can be combined as a first-order lag having dead times Lp and LD and time constants T, , TD, so GD=”D-e-LDoS , . . . , (g
)1+TD-8. Here, Kp and KD are gain constants. (Force) From equations (8) and (9), the transfer function GF of the forward control unit B is as shown in the following equation.

Here, K = KD/Kp. Transfer functions G, and GD
If the dead time of , and LD are almost equal, then 00
) is approximated by the following equation.

Since the relationship Tp<TD holds between the time constants Tp and TD, (from equation 10, the transfer function GF of the feedforward control unit B becomes a time delay compensation element.

Although the control system according to this embodiment is shown in FIG. 3, the transfer function GD between the raw material supply amount f and the inter-tray temperature difference Δt is provisionally provided for theoretical calculations, and is different from the actual control system. is as shown in FIG.

In this way, according to this embodiment, the gain of the top temperature control system of the distillation column changes in proportion to the amount of raw material supplied, which is the load on the distillation column, so it can always be controlled with the optimal control loop gain. . Therefore, regardless of the amount of raw material supplied, it is possible to improve transient control characteristics;
Control stability can be improved.

Note that the set value Δt8 of the temperature difference between trays may be constant or variable, but when the set value Δt is constant, a configuration as shown in FIG. 2 is possible.

In the previous embodiment, the temperature difference between trays was controlled, but the absolute value of the top temperature of the distillation column may also be controlled.

In addition, in the previous embodiment, the time constant TD of the disturbance transfer function GD
is assumed to be constant and does not change depending on the magnitude of the raw material supply amount fi, but in reality it changes, so for example, the time constant TD
is as shown in the following equation.

TD=TDo(l+K("-")) i However, TDo is a disturbance time constant when fi=fio, and K is a constant. This is to correct the fact that the time for transferring the raw material to the distillation column changes when the raw material supply amount f changes.

Furthermore, although the previous embodiments used the position type calculation method, the present invention can also be applied to the case of the velocity type calculation method.

〔Effect of the invention〕

As described above, according to the present invention, the control gain of the top temperature control system of the distillation column can be optimized with respect to changes in the raw material supply amount, so no matter what the raw material supply amount is,
It has the great effects of (1) improving the transient control characteristics when the raw material supply amount changes, (2) optimizing the control gain for each raw material supply amount, and improving controllability. Therefore, it is possible to eliminate transient energy loss, improve production efficiency, and produce a homogeneous and high-quality top product.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a conventional distillation column top temperature control device, FIG. 2 is a block diagram of a distillation column top temperature control device according to an embodiment of the present invention, and FIGS. 3 and 4 are respectively FIG. 2 is a block diagram showing the main parts of the tower top temperature control device. l... Raw material supply pipe, 2... Orifice, 3... Distillation column, 4... Delivery pipe, 5... Reflux tank, 6... Delivery pipe, 7... Reflux pipe, 8 . . . Flow rate adjustment valve, 9 . . Orifice, IO .・Distillate flow rate adjustment section. 15... Distillate flow rate detection means, 16... Square root calculation means, 17°18... Temperature detection means, 19... Temperature difference adjustment section between trays. ■... Addition means, 2 pieces... Raw material supply flow rate detection section, 2
2...square root calculation means, field...feed forward control section. U... Reflux flow rate adjustment unit, 25... Reflux flow rate detection means, A... Square root calculation means, 31... Multiplying means, 32.
...Addition means. Applicant's agent Seiwa Inomata 1 Hira 2 Figure 53

Claims (1)

[Scope of Claims] 1. A top temperature control unit that inputs the top temperature of the distillation column and compares it with a predetermined set value and performs adjustment calculations. Input the amount of raw material supplied to the distillation column. and a feedforward control section that performs feedforward control. a multiplier for multiplying the output signal of the tower top temperature control section by the output signal of the feedforward control section; and an addition for adding the output signal of the multiplication means and the output signal of the feedforward control section. and a reflux flow rate adjustment section that uses the output signal of the addition means as a setting signal to adjust the reflux flow rate of the top product from the reflux tank of the distillation column, and the reflux flow rate adjustment section controls the reflux of the top product. A top temperature control device for a distillation column, which controls the top temperature of the distillation column by adjusting a flow rate. 2. In the device according to claim 1. The column top temperature is the temperature of a plurality of trays at the top of the distillation column, and the column top temperature adjustment section compares and adjusts the temperature difference between these trays with a predetermined set value. Tower top temperature control device. 3. A top temperature control unit that inputs the top temperature of the distillation column and compares it with a predetermined set value and calculates the adjustment;
a feedforward control section that performs feedforward control; a first multiplier that multiplies the output signal of the tower top temperature control section by the output signal of the feedforward control section; a second multiplier for multiplying a difference signal between a predetermined set value of the tower top temperature and the raw material inlet temperature; and an output signal of the second multiplier and an output signal of the feedforward control section. and addition means. and a reflux flow rate adjustment section that uses the output signal of the addition means as a setting signal to adjust the reflux flow rate of the top product from the reflux tank of the distillation column, and the reflux flow rate adjustment section adjusts the reflux flow rate of the top product. A top temperature control device for a distillation column, which controls the top temperature of the distillation column by controlling the top temperature of the distillation column. 4. In the device according to claim 3. The tower top temperature is the temperature of a plurality of trays at the top of the distillation column, and the tower top temperature adjusting means compares and adjusts the temperature difference between these trays with a predetermined set value. Distillation column top temperature control device.