FI63301C - FOERFARANDE OCH ANORDNING FOER REGLERING AV EN UGN - Google Patents

Description

I- - - 'r. ·, ANNOUNCEMENT,,, n „38P * [8] ^ UTLAGONINOSSKRirT 63301 C Patent Issued 10 05 1903 (45) Patent Eeddelnt (51) Kv.ik? / I« e.a3 G 05 D 23/19 FINLAND —FINLAND (21) PmnttlhakMfiut — ΡκμμμΜμΜι 772U18 (22) H »k« mlipllvl - AiwBknlnfadaf 11.08.77 '* (23) AlkuiriUvft — Glkighaodac 11.08.77 (41) Tullut lulklMI

Fatwtti- J »National Board of Registration (44) NihUvUulputon I * kmiLjulkAteun pvm. - λ1 01 3¾

Patent- och registrarstyralsen '' AmMcu utiagdodiutLskrMkMpublkwid jx.ux.ojj (32) (33) (31) Pry4 «* r« cuoHwm-Β ^ μ prior ** 13.08.76

Holland-Holland (NL) 7009007 (71) Shell Internationale Research Maatschappij B.V., Carel van Bylandtlaan 30, The Hague, Holland-Holland (NL) (72) Johan Floris Bos, Amsterdam, Adriaan van der Heijden, Amsterdam,

The present invention relates to a method and an apparatus for controlling the heating of at least two parallel heaters. The present invention relates to a method and an apparatus for controlling the heating of at least two parallel heaters. and / or an oven with a flow tube coil of the substance to be evaporated.

In principle, industrial furnaces consist of piping around one or more flames. The substance to be heated and / or evaporated flows through the piping. This substance is often a liquid, for example an oil or oil derivative. In addition to heating and evaporating, the furnace is also used for the chemical conversion of the substance passing through it. An example of this is the production of ethylene by cracking naphtha. Heat is transferred by radiation and conduction.

Generally, there are two or more parallel coils in the piping. The incoming substance splits into the pipes and reunites at the ends of the pipes. Different flows can be adjusted for each pipe with valves. In this case, it is important to select a distribution of the substance such that local overheating of the pipe and / or the substance flowing through it is prevented. The heat load should also be evenly distributed in the coils. This promotes the economy of the oven and prolongs its service life. Industrial furnaces are usually used for a very long time in continuous use. In such furnaces, the mere maintenance of a preselected distribution of the material flow into the coils is not sufficient, because they exhibit phenomena that require adjustments of this distribution. These factors include e.g. changes in the distribution of fuel and air entering the burners, changes in the position of the flames, partial blockage of the pipes and weather conditions.

The present invention makes it possible to meet the above requirements.

The invention relates to a method for controlling an oven with at least two parallel tube coils, over which coils the substance to be heated and / or vaporized is distributed, which method comprises the steps of measuring the temperature at the lower end of each coil and deriving an average T = - Σ » - n 1 l of the number of parallel coils, each difference T - T ^ is derived, which is used to produce a signal by which the flow of the substance flowing through the coil in question is set to reduce said difference T - T ^. The method is characterized by the following steps: taking the highest temperature Ti from the temperatures T1 and deriving the difference T 1 - Tg, in - T is reduced.

xmax s This control system constantly strives to eliminate temperature differences at the ends of the coils. For this purpose, the average of the temperatures T 1 is used, not the temperature of the combined flow from the furnace. This latter temperature is a weighted average and may deviate from the arithmetic mean T. The deviation may also occur when the substance evaporates after the point where Tj is measured and before the point where TQ is measured. Therefore, the control system according to the present invention always makes it possible to equalize the temperatures T 1 regardless of the magnitude differences of the material flows passing through the coils.

The control of the heat generation of the oven is based on the highest temperature of the coil. As a result, this maximum temperature never exceeds the allowable temperature. In addition, the furnace can actually be operated at maximum load, since all temperatures T 1 are constantly approached the maximum allowable temperature.

Due to the control according to the invention described above, the total flow of material through the furnace 3 63301 does not remain constant. In some cases, however, it is important to keep this flow constant in order to adjust it. By another feature of the present invention, this requirement can be met when each signal generated by deriving and using a difference T-T 1 is used to adjust a setpoint for controlling the flow of matter through that coil relative to the difference T-T. Now the total flow of matter remains constant because The sum of the deviations from the (arithmetic-1 n) mean Z3 (T - T.) is 1 1 always zero and the sum of the changes proportional to the deviations is therefore also zero.

There are also situations where it is necessary to be prepared for the amount of substance entering the furnace to vary. This may be due to the variable supply of the substance, for example from another device, or the varying demand for the final product of the furnace. The invention takes this situation into account by calculating the ratio Ar = C _i for each helix, where C is

Fs is constant and F is the set value for the total flow of material through the furnace,

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and adjusting this ratio with AR 1. the flow of matter through the coil. In this way, each coil receives its share of the incoming material flow Fi, while the advantages of the control system according to the invention

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are preserved. The ratio R. = __i. A common situation in which to come

The magnitude of the material flow Fs varies, is that the liquid flow comes from a state where a constant liquid surface level must be maintained, e.g. on the basis of a distillation column. The setpoint Fg can then be obtained from this liquid surface level. When the liquid level changes, F is adjusted so that

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that the surface level returns to the desired value.

An interesting improvement in the method according to the invention is obtained when the heat production of the furnace is non-linearized by the difference TQ - Tg, namely by increasing the relative control factor and the integrated operating time of the heat production control in question. as the difference increases. This increase is carried out by a factor of no more than 6. This adjustment method reduces the deviations of the value T ^ upwards, max.

The device according to the invention for controlling a furnace with at least two parallel tube coils, the flow of heated and / or evaporating substance of the coils being divided, comprises a meter for the temperature of the substance at the end of each coil, a meter for the flow of substance through each coil; through the calculator to calculate the values “1 n - T = - Σ T ± and = T - T \ for each coil, for which purpose the calculator is connected to meters for the temperature of the substance at the end of each coil, for each coil of the controller whose measured value input is connected to a corresponding meter for the temperature of the substance at the end of each coil and whose setpoint input is connected to the output of a calculator for the corresponding value of Δτ ^: η and whose output is connected to a corresponding control device for the flow of substance through each coil, for the combined meter outlet temperature, for the fuel flow background of the appliance to the furnace burner.

This device according to the invention is characterized by a calculating device for deriving the difference - Tg for which purpose the calculating device is connected to meters for the temperature of the substance at the output of each coil and a controller whose measured value input is connected to the meter for connected flow temperature and whose setpoint input is connected - T for conduction and whose output is connected to an oh-max s shut-off device for fuel flow to the furnace burner.

The device according to the invention is furthermore characterized by a calculating device for deriving a coefficient, for which purpose the calculating device is connected to the output of the conductive glass centrifuge of the difference Tj_ _ T.

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for the temperature of the outlet flow connected to the meter and the meter, the output of which is connected to the input of said controller, the measured value input of which controller is connected to the meter for the temperature of the outlet flow connected to the meter, to set a proportional control factor and the controller operating time.

The control according to the invention can be implemented with conventional control devices and counters (counters if desired electronic). The entire control system can also be implemented on the principle of direct digital control. This option is suitable for large production plants that already use a digital computer or several microcomputers, for example in the control of other plant equipment and in data processing and printing. The invention will now be described with reference to the accompanying figures and examples.

Figures 1, 2 and 3 schematically show a furnace with four parallel coils controlled by variations of the system according to the invention. Figures 4-8 show the results of experiments performed with the control systems according to the invention.

In Figure 1, reference numeral 1 denotes a flame which heats the coils 2, 3, 4 and 5. The fuel of the flame 1 comes from point 6 and the flow is controlled by valve 7. The substance to be heated and / or evaporated enters the system at point 8 and is distributed by valves 9, 10, 11 and 12 to coils 2, 3 4 and 5. The substance leaves the system in combination at point 50.

Each coil has a thermometer (13, 14, 15 and 16) and a flow meter (17, 18, 19 and 20). Flow meters measure the amount of material passing through the coils per unit time. The flow meter 21 measures the fuel flow 6 and the thermometer 22 measures the temperature of the substance 50 leaving the furnace. The temperature controller 23 generates a setpoint for the fuel flow controller 24. Flow regulators 25,26,27 and 28 control valves 9, 10, 11 and 12.

The numbers mentioned so far also mean the same in Fig. 2. In the system of Fig. 1, the signals of the temperature meters 13, 14.15 and 16 go to the counter 29 and the selector 30. The counter 29 calculates the average T of the measured temperatures, i.e. T = - sr- T. setpoint 31, 32, 33 and 34.

4 1

The value T is compared in the controller 31 with the temperature measured by the meter 16 of the coil 5. The output signal of the controller 31 is the setpoint of the controller 28.

The purpose of this adjustment is to make the temperature measured by the meter 16 average. Regulators 32, 33 and 34 have corresponding arrangements.

Selector 30 'selects the highest value of the measured temperatures of coils 2, 3, 4 and 5, T.. The value T. is compared at the control max max 35 with the value Ts, and the output signal of the controller is the set value of the controller 23. A comparison with the measured temperature of the stream 50 gives the setpoint of the flow controller 24 of the fuel flow 6. The temperature of stream 50 follows the setpoint of flow controller 24 of fuel stream 6. The temperature of the stream 50 leaving the furnace is thus determined by the maximum value Si of the coil, which cannot exceed the set value T.

In the system of Fig. 2, the function of the counter 36 is to control the currents flowing through the coils 2, 3, 4 and 5 so that the total current Θ (or 50) remains constant, while the above-mentioned regulators 25, 26, 27 and 26 remain the same; they thus equalize each temperature T \ with the mean T. To this end, the signals from the thermometers 13, 14, 15 and 16 are fed to the counter 36, and the average T is calculated. T - T ^ is then determined for each helix. For each flow controller 25, 26, 27 and 28, a set value based on the difference T - T ^ is then calculated and increased in proportion to the difference T - T ^. The desired value F of the total substance flow 6 is taken into account here (arrow 37).

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Counter 38 performs the same functions as selector 30 and controller 35 in Figure 1. The setpoint T is indicated here by arrow 39. Thus, counter 36 controls

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the total flow through the coils and the balance between the coils, and the counter 38 controls the ratio between the desired temperature and the maximum allowable temperature.

In Figure 3, the incoming flow is removed from the bottom of the column 41 by a pump 40.

The liquid level of the column 41 must remain within a certain range.

For this purpose, the system has a liquid level indicator 42 and a regulator 43. The output signal of the surface regulator 43 goes to the counters 44,45,46j 47. Each counter calculates the difference T-T calculated by the output signal of the surface regulator 43 and the counter 48 for each coil. The amount of liquid discharged from the column 43 by the surface adjuster is thus divided into different coils. In addition, 48 calculates the setting 23 of the controller based on the setpoint T (arrow 49).

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in the same way as the counter 38 in Figure 2.

Fig. 3 also shows a counter 51 with which the relative control factor and the integral operating time of the controller 23 can be adjusted according to the difference T. - T calculated by the counter 48.

1 s max

The above-mentioned control systems can be implemented with conventional controllers and counters (e.g. ratio and average counters, etc.). However, a digital computer can be used for all calculations. The functions of the controllers can also be performed by a digital computer.

7 63301

Example I

Oil with a pulp rate of about 3000 t / day was fed through a four-screw furnace. The maximum allowable temperature was 390 ° C. Figure 4 shows the temperature changes at the ends of each coil 1, 2, 3 and 4 during an arbitrary 120 minute period when the adjustment took place only by hand. The temperature dispersion was about 11 ° C. The changes in the temperature TQ of the combined output stream are shown in Figure 4B on the same temperature and time axes as in Figure 4A. The setpoint T is also shown. Due to the temperature dispersion, the value Tg had to be set to approx. 380 ° C in order to avoid the risk that the temperature of one of the coils would exceed the value T

max

Figures 4C and 4D show the results obtained when using the control system according to the invention for a constant oil supply. The temperature curves for coils 1, 2, 3, and 4 now coincide, and the TQ curve is the same as curves 1, 2, 3, and 4. The setpoint Tg can now be selected much closer to Tmgx, by a distance compared to manual control. In this case, this distance was 6.3 ° C.

Example II

the effect of changing the total amount of oil flow is shown in the furnace of Example I with the control system of the invention. Figure 5A shows the changes in temperature and flow of the coils (4 pcs.) With manual adjustment. The combined output flow temperature TQ is also given. TQ is smaller than any of the temperatures T ^ due to evaporation between the measuring points and TQ. The line Tg indicates the setpoint of the temperature Tq.

Arrow b in Figure 5B indicates the moment when the total oil supply was reduced by 292 t / day, and arrow c indicates the moment when the feed was increased by 292 t / day. Figures 6A and 6B show the effects of these step changes when using the adjustment according to the invention. The initial disturbance of the temperatures T ^ and TQ is clearly compensated quickly. The relative variances of the values are very small.

Example III

The effects of the nonlinearity of the fuel supply regulator as a function of the difference T - T were presented in a similar furnace as in the previous examples (regulator 23 in Figure 3).

There were four cases: I means the normal setting of the controller, II the product of the relative control factor and the integral operating time (DiSta = factor 2, III factor 4 and IV factor 6).

Fig. 7 shows the changes in temperatures T 1 - which coincide each time throughout the coils - in cases I to IV, when the difference Tq - Tg of 8 63301 was more than 1 C. Fig. 8 shows the VP setting of the fuel pipe valve 7. (Figure 3).

Changes in temperatures decrease as the coefficient increases. The valve settings for cases III and IV are shown. Case III is more advantageous than Case IV in terms of minimizing fluctuations in fuel supply.

Claims (8)

9,63301 A method for controlling an oven with at least two parallel tube coils over which the material to be heated and / or evaporated is distributed, the method comprising the steps of measuring the temperature of the material at the lower end of each coil and deriving an average T = ^ έ each difference T - Ti, which is used to produce a signal to set the flow of the substance flowing through the coil in question to reduce said difference T, characterized by the steps of: taking the highest temperature from the temperatures and deriving the difference T. - T (where T is the the set value associated with the combined flow temperature TQ) which is used to generate a signal for controlling the heat generation in the furnace so as to reduce said difference - Tg. max A method according to claim 1, characterized in that each signal generated by deriving and using a difference T - is used to adjust a setpoint for controlling the flow of matter through said coil with respect to the difference T - T 1. A method according to claim 1, characterized by the step of deriving a ratio Φ «* Φ AR for each helix. = C i, where C is a constant and F „is the setpoint for the total flow of the substance-1 ~ 5— s Fs to the furnace, the ratio of which is used to control the flow of the substance through that coil. A method according to claim 3, characterized in that the flow Fg of the liquid substance is derived from the level of the liquid flow fed from the tank. Method according to one of Claims 1 to 4, characterized in that the difference TQ to Tg is applied to the non-linear aris force of the heat supply control furnace, namely by increasing the proportional control factor and the integrated operating time of the heat supply control when said difference becomes larger. Method according to claim 5, characterized in that said growth factor is at most 6. 63301 7. Apparatus for controlling an oven with at least two parallel tubular coils over which the flow of material to be heated and / or evaporated is divided, comprising a meter for the temperature of the substance at the end of each coil, a meter for the flow of substance through each coil; the calculator- - I n _ - I can calculate the values T = - J3 T. and ZlT., = T - T. for each coil, for which purpose the calculator is connected to meters for the temperature of the substance at the end of each coil, the controller for each helix whose controller measured value input is connected to a corresponding meter for the temperature of the substance at the end of each helix and whose setpoint input is connected to a calculator output for a corresponding value of ^ T ^ and whose u input is connected to a corresponding control device for the combined output flow temperature of the meter laa, a control device for the fuel flow to the furnace burner, characterized by a calculating device for deriving the difference T, -T, for which purpose the counting-1max device is connected to meters for the temperature of the substance at the outlet of each coil, and a controller with is connected to the output of the calculating device to derive the difference T. -T and the output of which is 1max connected to the control device for the flow of fuel to the burner of the furnace. Apparatus according to claim 7, characterized by a calculating device for deriving a coefficient, for which purpose the calculating device is connected to the output of the difference T. -T conducting lasmaxmax for the output and meter connected to the meter and has an output connected to the input of said controller. for the combined outlet flow temperature, to set the proportional control factor and the integrated operating time of the controller. 63301 11