JPS6346293A - Controlling method for outlet temperature of cracking furnace - Google Patents

Abstract

PURPOSE:To automatically correct outlet temperature, by obtaining the present theoretical value of fuel feed rate from the relationship between the raw material feed rate and the fuel feed rate in assuming that there is no coking and estimating the coking amount from the difference between the theoretical value and the observed value of the present fuel. CONSTITUTION:In a cracking furnace for thermally cracking raw material naphtha and delivering the resultant cracked gas to a purification system, the theoretical value of the fuel feed rate at the present feed rate of the raw material is obtained on the basis of the relationship between the raw material feed rate and the fuel feed rate in assuming that there is no coking. The coking amount is estimated from the difference between the theoretical value and the observed value to correct the set value of the above-mentioned outlet temperature by a correction factor based on the estimated value. Thereby the fluctuation of thermal conductivity is automatically corrected to carry out control of the outlet temperature of the thermal cracking furnace.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to an improvement in the control method of the outlet temperature, which is most important for the operation of a cracking furnace in an ethylene plant.

<Prior Art> The ratio of multiple products extracted from the cracking furnace, which is the first step in an ethylene plant, varies depending on the temperature of the cracking furnace. Therefore, in order to operate to maximize the yield of the target components, it is extremely important to control the temperature at the outlet of the cracking furnace.

FIG. 2 is a conventional configuration diagram of an ill device for controlling the exit temperature of a cracking furnace. 1 is a cracking furnace, 201 is a first cracking pipe line arranged at the upper part of the cracking furnace, 202 is a second cracking pipe line arranged at the lower part, 203 is a first cracking pipe line arranged at the lower part. This is a connecting pipe for the second cracking pipe and receives steam input outside the cracking furnace.

3 is a supply pipe for the raw material Nafuna N from the previous process, and is connected to the input part of the first decomposition pipe 201. 4 is a supply pipe for steam S, and the above is mixed with the raw material in the connecting pipe 203.

5 is a fuel F supply pipe, which is connected to a burner 6 for heating the second decomposition pipe.

Reference numeral 7 denotes an output pipe, which transports the cracked gas that has passed through the second cracking pipe to the next cooling step. The present invention relates to controlling the outlet temperature in this output line.

8 is the outlet temperature 1 true sensor, PV+ is its measured value, 9 is the fuel F supply amount control valve, 10 is the outlet temperature controller, m
constant'm PV + tom 11[gfJ constant[ISV
The +I difference is controlled by the nozzle and the operating output M V + is given to the supply amount control valve 9, and the supply amount of the fuel F is υIIIXI so that the outlet temperature follows the set value.

11 is a sensor for the supply amount of raw material N, and PV2 is its measured value,
12 is a feed rate control valve for raw material N, and 13 is a raw material feed rate regulator, which controls and calculates the deviation between the measured value PV2 and the supply setting W1S V2, and supplies the manipulated output M V 2 to the supply ffi control valve 12. Then, the feed ffi control valve is operated so that the feedstock follows the set value.

14 is a raw material density sensor, and its measured value P V
3 is led to the indicator 15 and also to the raw material supply ffl controller 13, where density correction of the supply ffi measured value P V 2 is executed.

16 is a steam S supply amount sensor, P V a is its measured value, 17 is a steam S supply amount control valve, and 18 is a steam supply amount controller, which measures the measured value PV4 and the set supply amount S V a. Control the difference and supply the manipulated output M V aff
i Ill tlo valve 17 and operate the dissection piece so that the steam supply follows the setting.

19 is a ratio setting device, which sets the steam supply amount by multiplying the raw material supply amount measurement value P V 2 by a constant ratio R.
S V 4 is calculated and set in the steam supply amount controller 18. 20 is a setting device for setting the raw material supply amount setting fflSV2.

A, B in each conduit 3.4.5.7.

Symbols shown as C and D have the same structure f, 11 till
△
Only series are shown.

In such a configuration, the decomposition temperature is often set at a little over 800° C., and since the amount of each component produced changes depending on the outlet temperature, the set temperature is determined by the requirements on the downstream side.

Furthermore, steam supply ffi Q s and raw material supply ff1QN
The ratio Q s / Q N is the ratio! If constant value control is performed by the control system, the outlet 2HIfiT has a property that can be uniquely determined by the raw material supply amount QN.

FIG. 3 is a characteristic diagram showing the functional relationship between the raw material supply amount QN and the outlet temperature T. However, in reality, there is a difference with the theoretical formula, and carbon adhesion occurs on the inner wall of the cracking pipe after 11 hours of operation.
Since the heat transfer coefficient α changes as the amount of coking increases, as shown in FIG. 4, the heat transfer coefficient α increases α1°α2. αco...The functional relationship is X according to αn! l X2 +X3... It is necessary to perform a change operation like XTL.

An example of such a functional relationship changing operation will be explained with reference to FIG. 211.212...217L is the heat transfer coefficient α1.
α2...Characteristics corresponding to αn
. . . A polygonal leap number calculation means for extracting Xu, which commonly inputs the raw material supply ffi setting value QN and transmits outlet temperature setting signals T+, T2, . . . T1 according to each functional relationship.

22+, 222...22m are holding means for the outputs T+, T2...Tn of the polygonal function calculation means, and n outputs of this holding means are selected by the switching means 23,
Set till temperature controller 10 via output boat 24
Supplied as S V + .

25 is a correction coefficient setting device, which allows correction (
By setting the numbers α, α2...α1, the operation output M for manipulating the selection target of the holding means of the switching means 23
Send Vs.

Operators can monitor operating hours, raw material supply, and ingredients.

The outlet temperature and the like are monitored, and if it is determined to be appropriate, the correction coefficient a setting device 25 is operated at the time of Ic.

<Problems to be Solved by the Invention> In operations where correction coefficients are switched depending on the operator's experience and factors, the quality of the product may vary due to misunderstandings, or abnormal heating may cause an operational failure. There was a possibility that

An object of the present invention is to provide a control method that avoids variations in quality and operational failure due to abnormal heating by automating the setting of correction coefficients.

Means for Solving the Problems〉 The feature of the method of the present invention is that the raw material supply l, assuming that there is no coking, in the cracking furnace that thermally decomposes the raw naphna and sends the cracked gas to the next stage refining system. Find the theoretical value of the fuel supply amount at the current raw material supply amount l, - based on the relationship between and fuel supply, estimate the coking darkness from the difference between this theoretical value and the actual value, and calculate the correction coefficient based on this estimated value. The purpose is to automatically correct variations in heat transfer coefficient by correcting the set value of the outlet temperature.

According to the present invention, the theoretical value of the fuel supply amount at the current raw material supply amount is determined from the relationship between the raw material supply amount and the fuel supply amount assuming that there is no coking, and this theoretical value and the current The amount of coking is estimated from the difference between the measured value of the fuel and the set value of the outlet temperature is automatically corrected based on this estimated value.

<Example> Based on Figure 1, the actual M! An example will be explained.

Components that are the same as those described in FIG. 2 are given the same reference numerals, and their description will be omitted.

Assuming that there is no kneeing, it is easy to use the characteristics shown in Figure 3 to calculate the outlet temperature based on the amount of raw material supplied, but in reality coking occurs, so the Like n1ll fold 111rI111
! l Requires a means of performance.

In the prior art, the corrected outlet temperature set value was obtained by switching the outputs of these function calculation means manually by an operator, but the present invention provides a method for automatically performing this switching.

26 is a program setting device, which inputs the correction coefficient α from the input port 27 and outputs the corrected Onmaro set value T from the output port 28. The function of this program setting device is a polygonal function calculation means, which is a polygonal polygonal function calculation means.
212...21vt output T+.

T2...The break point is constantly updated by TTL.

Therefore, when the correction coefficient α is input, the corrected stage setting waterfall a
can be obtained immediately and continuously.

Next, a method for estimating the correction coefficient α will be explained.

The relationship between the raw material supply amount and the fuel supply amount when it is assumed that there is no coking is shown in FIG. 6.

Therefore, using this relationship, the current raw material supply ff1Q
Once N is determined, the required fuel supply without coking 1
1Qp can be found. In general, the correction that increases the set value of the outlet temperature in proportion to the amount of coking produced increases the amount of fuel supplied. In other words, the increase in fuel is proportional to the amount of coking produced, so there is no coking. Coking can be estimated by taking the difference between the theoretical fuel supply amount and the actual fuel flow rate.

Therefore, the relationship shown in FIG. 5, that is, the theoretical value QF of the fuel supply amount with respect to the raw material supply ff1QN is determined using the polygonal line function m calculation means 29. On the other hand, the current fuel supply amount is determined as a measurement WJ P V 5 by a flow fence sensor 30 inserted into the fuel supply pipe 5, and this measured value is led to a detensioner 32 via an indicator 31. It is reduced to the above theoretical value Q%.

The output X of the subtraction device 32 is expressed as x-Q%-PV5, and this is expressed as
, a calculation of α-ax+b is executed, and a correction coefficient α related to the amount of coking is calculated and input to the input port 27 of the program setting device 26. The program setting device 26 is a leap a*
The output point 11°T2 of the calculating means has the function of depleting the TTI in a straight line, so it is possible to obtain a continuous temperature a stage setting 1iflT in response to a continuous input of the correction coefficient α.

<Effects of the Invention> As explained above, according to the present invention, it is no longer necessary to correct the heat transfer coefficient, which was conventionally changed based on the operator's experience and intuition, and it is possible to change the theoretical fuel supply amount and the current fuel supply ffi. It becomes possible to automatically correct the set value of the outlet temperature based on the correction coefficient α estimated from the difference, and it is possible to improve the quality of the product and prevent the risk of operation stoppage due to abnormal heating.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of an outlet temperature control device to which the method of the present invention is applied, FIG. 2 is a block diagram showing an example of a conventional technique, and FIGS. 3 and 4 are diagrams explaining its operation. FIG. 5 is a characteristic diagram that does not show the relationship between the theoretical value of the fuel supply amount and the raw material supply amount. 1... Decomposition furnace 201... First cracking pipe line 20
2... 2nd minute wE pipe line 3... Raw material supply pipe line
4.・, Steam supply pipe 5...Fuel supply pipe 6
...Burner 7...Output pipe 8...Outlet 4 Sensor 9...Fuel supply amount υJllll valve 10...
Fuel supply ffi controller 11... Raw material supply amount sensor 12... Raw material supply amount control valve 13... Raw material supply ff1UA saving meter 14... Raw material fi degree sensor 15
... Density indicator 16 ... Steam supply sensor 1
7... Steam supply amount 1ilI1111 18...
Steam supply amount controller 19...Ratio setting device 21t
~21u...Folded am number performance means 26...Program setting device 29...Folded line interleave number performance means 3
0...Flow m sensor 31...Instruction: 132...
・Bullet reduction device 33...Function rod Figure 3 Figure 4

Claims (1)

[Claims] In a cracking furnace that thermally decomposes raw material Nafuna and sends the cracked gas to the next stage refining system, the fuel supply at the current raw material supply amount is based on the relationship between the raw material supply amount and fuel supply amount assuming that there is no coking. The amount of coking is estimated from the difference between the theoretical value and the measured value, and the set value of the outlet temperature is corrected using a correction coefficient based on this estimated value to automatically compensate for fluctuations in the heat transfer coefficient. A method for controlling outlet temperature of a pyrolysis furnace, characterized by correcting the temperature.