RU2342438C1 - Automated method of controlling and managing process for preparing sugar syrup mixture for crystallisation by cooling - Google Patents

Abstract

FIELD: chemistry, sugar production.

SUBSTANCE: proposed automated method of controlling and managing the process of preparing sugar syrup mixture for crystallisation by cooling makes provisions for regulating the volumetric discharge of water entering the mixer and the level of sugar syrup in it. Regulating the level of the sugar syrup in the vertical mould is achieved by acting on the adjustable-frequency electric drive of the sugar syrup pump. Periodically using the lab the density of the ready sugar syrup is controlled at the exit from the mixer. The active electrical power which is used in the electric motor of the sugar syrup pump, the temperature and pressure differential of the sugar syrup mixture, coming from the mixer and water at the entrance of the mixer are all measured. The water-mass density is calculated by its temperature and the density of the sugar syrup mixture by its pressure differential. Afterwards the volume flow rate is worked out by the measured volume flow rate of water, by the estimated value of the density of water and sugar syrup mixture and by the density of ready sugar syrup measured in the laboratory. The dependency ratio of the active electric power from the volume rate of flow of the sugar syrup mixture and the differential in its pressure N=α₁Q³ _УΔP_y+α₂Q_yΔP_y , where N - active electric power; Q_Y - volume rate of flow of sugar syrup mixture entering the mixer; ΔP_Y - pressure differential of the sugar syrup mixture; α₁, α₂ - coefficients. The obtained plot is used for future calculations of volume rate of flow of sugar syrup mixture only with measured values of active electric power and pressure differential of the sugar syrup mixture. The current task of the regulator of the volumetric water discharge is determined on the basis of measured values of this output, estimated values of the density of sugar syrup mixture, water and volume rate of flow of the sugar syrup mixture, the determined value of density of ready sugar syrup mixture and the task of the regulator calculated in the previous control step. The solid content of the original sugar syrup mixture is controlled - by its temperature and density in the ready sugar syrup mixture. This invention makes it possible to reduce the loss of sugar from molasses due to a more qualitative stabilisation of the density of molasses on its exit from the mixer.

EFFECT: reduction in the loss of sugar from molasses due to a more qualitative stabilisation of the density of molasses on its exit from the mixer.

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Description

The invention relates to methods for automatically monitoring and controlling the process of preparing massecuite for crystallization by cooling and can be used in the sugar industry for crystallization of sugar.

There is a method of automatically controlling the process of sugar crystallization in crystallizer mixers by regulating the supply of cooling water to the shirt of the muffle mixer, depending on the measured temperature of the cooled massecuite (Azrilevich M.Ya. et al. Fundamentals of automation of sugar beet production processes. M .: Food industry. - 1968, p. 374).

The disadvantage of this control method is that it does not provide for the regulation of the density of the massecuite supplied to the mold, and cannot be used to control the process of preparing the massecuite for cooling in vertical molds.

The closest in technical essence and the achieved effect to the proposed method is a method for automatically controlling the process of preparing the massecuite for crystallization by cooling in a vertical mold, providing for the regulation of the volumetric flow rate of water into the mixer and the level of the massecuite in it, the regulation of the massecuite level in a vertical mold by influencing the frequency-controlled electric drive of the massecuite pump, including periodic laboratory control of the density of the finished massecuite at the exit of mesitelya. To maintain a given value of the dry matter content after the mixer, periodic analytical control of this indicator is used with correction of the task of the consumption of ammonia water and, if necessary, the coefficient of the massecuite: water ratio (V.N.Kukhar, A.K. Suschenko, Yu.P. Yushkov, E .M. Fedorova, V.M. Posokhov, T.I. Leonov, L.A. Shatalova. Experience in the implementation of vertical crystallizers in sugar plants of RusAgro company. // Sugar. - 2002. - No. 3. - S. 53 ... 55).

A disadvantage of the known control method is that it does not allow the reliable functioning of control loops designed to stabilize the massecuite density at the outlet of the mixer (V.N. Kukhar, A.K. Suschenko and others. Experience of introducing vertical crystallizers in sugar factories of the company “ RusAgro ".// Sugar. - 2002 - No. 3. - P.55, lines 11 ... 33 from above). Also, this method does not automatically control the solids content in the massecuite at the inlet and outlet of the mixer.

The technical task of the invention is to reduce the loss of sucrose with molasses due to better stabilization of the massecuite density at the entrance to the vertical crystallizer and automation of control of the solids content in the initial and finished massecuite.

This result is achieved in that in a method for automatically controlling and preparing the massecuite for crystallization by cooling, which provides for controlling the volumetric flow rate of water into the mixer and the level of the massecuite in it, adjusting the massecuite level in a vertical mold by acting on a frequency-controlled electric drive of the massecuite pump, including periodic laboratory control of the density of the finished massecuite at the outlet of the mixer, new is that additionally measure the active electric m the sensitivity consumed by the electric drive of the massecuite pump, the temperature and pressure drop of the massecuite entering the mixer, the temperature of the water at the inlet of the mixer, calculate the density of water by its temperature and the density of the massecuite by its pressure difference, calculate the volumetric flow rate of the massecuite in the mixer according to the measured volumetric flow rate of water, the calculated values of the density of water and massecuite and the laboratory-measured density of the finished massecuite, determine the coefficients of the dependence of the active electric power on the volume flow of the massecuite differential pressure thereof

where N is the active electric power;

Q _y is the volume flow of massecuite in the mixer;

ΔР _у - massecuite pressure drop;

and ₁ , and ₂ are the coefficients,

and use this dependence for subsequent calculations of the massecuite volumetric flow rate only from the measured values of active electric power and the massecuite pressure drop, determine the current task of the volumetric flow rate regulator based on the measured value of this flow rate, calculated values of the massecuite density, water and the massecuite volumetric flow rate, the specified density value ready massecuite and assignments to this regulator, calculated at the last control step, control the solids content in the original massecuite by its density and temperature, in the finished massecuite by volumetric flow rates and density of the original massecuite and water and by the solids content in the original massecuite.

The technical result of the invention is illustrated by an example of its implementation and figure 1 and 2. Figure 1 shows a control circuit that implements this method. Figure 2 shows the experimentally obtained comparative graphs of the time variation of the density of the finished massecuite at the outlet of the mixer (figa) and the purity of the intercrystal massecuite solution before centrifugation (fig.2b) when controlling the process of preparing the massecuite for crystallization by cooling using a known method (graphs) 1.3) and using the present invention (graphs 2,4).

A method for automatically monitoring and controlling the process of preparing massecuite for crystallization by cooling is implemented as follows.

и задание на плотность готового утфеля

.The massecuite pumping unit 1 supplies the original massecuite through a vertical pipe 2 to the mixer 3. Ammonia water is supplied through the pipe 4 to the mixer 3. From the mixer 3, the finished massecuite enters the vertical crystallizer 5, the level of the massecuite in which is controlled by a circuit including a level sensor 6, a regulator 7 and a frequency converter 8 of the electric drive of the massecuite pump 1. The pressure drop of the original massecuite in the pipeline 2 and the massecuite temperature are measured respectively by sensors 9 and 10. The volumetric flow rate of ammonia water in the mixer 3 is measured by the sensor 11 and regulated using the regulator 12 and the control valve 13. The level in the mixer is regulated using a circuit including a sensor 14, a regulator 15 and a regulating gate 16. The temperature of ammonia water is measured by the sensor 17. The active electric power consumed by the electric drive of the massecuite pump 1 is measured by the sensor 18. Information from the sensors 9, 10, 11, 17, 18 is fed to the inputs of the function block 19, in which the task is calculated for the regulator 12 of the flow of ammonia water in the mixer and the solids content in the initial and finished massecuite is calculated. In block 19 from the process operator also receives information about the laboratory-measured density of the finished massecuite

and the task of the density of the finished massecuite

.

The dependence of massecuite density on the CB content is calculated by a formula that allows one to calculate the density of a sugar solution with estimated accuracy (D.E.Sinat-Radchenko, S.M. Vasilenko, K.O. Shtangeev. Calculated dependences of the thermophysical properties of sugar solutions. // Sugar. - 2004 - No. 1. - P.43):

where ρ _B (t) is the density of water.

The massecuite density is determined by block 19 by the differential pressure of the liquid column measured by the sensor 9:

where ΔР _у - differential pressure measured by the sensor 9, N / m ² ;

g is the acceleration of gravity equal to 9.81 m / s ² ;

N _y - the height of the column of massecuite in the pipeline 2, m. The temperature of the massecuite is measured by a sensor 10, ° C.

Thus, according to formulas 2, 3, 4, the solids content in the massecuite CB _y can be calculated. Calculation of CB _{y is} carried out by block 19 according to the formula:

- текущая плотность утфеля, определенная по формуле 4;Where

- the current density of massecuite, determined by the formula 4;

(CB,t) - рассчитанная по формулам (2) и (3) плотность утфеля при текущей температуре t, измеренной датчиком 10.

(CB, t) is the massecuite density calculated by formulas (2) and (3) at the current temperature t measured by the sensor 10.

, чтобы текущая плотность утфеля, определенная по формуле (4), была равна его плотности, рассчитанной по формулам (2) и (3).The optimization problem (5) is formulated as follows: determine this content value

so that the current massecuite density determined by formula (4) is equal to its density calculated by formulas (2) and (3).

Since in the formula (2) dependence of the content of CB _in the density massecuite substantially nonlinear and can not be solved analytically to calculate the CB _at density and temperature is necessary to use one of the methods of nonlinear programming, such configurations Hooke-Jeeves method (T. solution engineering Shupe tasks on a computer: A practical guide. Translated from English - Moscow: Mir, 1982.- 238 pp. p. 178 ... 182). Due to the fact that when finding SV _, negative values or large 100% can be obtained, it is necessary to impose restrictions on the value of SV _y due to the technological regulations:

Taking into account the constraints (6), the objective function (5) can be written as follows:

будет являться истинным содержанием сухих веществ в утфеле, подаваемом в смеситель. Точность расчета определяется точностью датчиков 9, 10 и точностью зависимости (2). Погрешность алгоритма, реализующего метод Хука-Дживса, обычно составляет не более 10^-5...10^-6.The value found by block 19 according to formula (7)

will be the true solids content in the massecuite served in the mixer. The accuracy of the calculation is determined by the accuracy of the sensors 9, 10 and the accuracy of the dependence (2). The error of the algorithm that implements the Hook-Jeeves method is usually not more than 10 ^-5 ... 10 ^-6 .

Based on the material balance, the density of the finished diluted massecuite at the outlet of the mixer ρ _cm can be determined as follows:

where Q _y , Q _B - volumetric flow rate in the mixer, respectively, the massecuite and water.

, то при установившемся режиме из формулы (8) можно рассчитать объемный расход утфеля Q_y:In the formula (8), the unknown parameters are the massecuite volumetric flow rate Q _y and the diluted massecuite density ρ _cm . If measured by laboratory means the density of massecuite at the outlet of the mixer

, then in the steady state, from the formula (8) it is possible to calculate the volume flow of massecuite Q _y :

On the other hand, the volume flow rate of massecuite is determined based on the active electric power N measured by the sensor 18, consumed by the electric drive of pump 1. To do this, we use the formula (Pavlov KF, Romankov PG, Noskov AA Examples and tasks according to the course of processes and apparatuses of chemical technology. - M.: Chemistry, 1969, 624 p., p. 28, formula 1-32):

where ΔР _C is the hydraulic resistance of the network, N / m ² ;

η - efficiency massecuite pump unit.

The value of ΔP _{C is} calculated as the sum of the following terms ΔP _C = ΔP _ck + ΔP _tr + ΔP _ms + ΔP _under + ΔP _add ,

ΔР _SK - the cost of pressure to create a flow rate, N / m ² ;

ΔР _Tr - pressure loss to overcome the friction resistance, N / m ² ;

ΔР _ms - pressure loss to overcome local resistances, N / m ² ;

ΔР _under - the cost of pressure on the rise of the liquid, N / m ² ;

ΔP _add - losses due to the pressure difference in the suction and discharge spaces of the pump, N / m ² .

Pressure losses on massecuite friction can be determined by the Hagen-Poiseuille formula (Pavlov KF, Romanov PG, Noskov AA Examples and tasks on the course of processes and apparatuses of chemical technology. - M .: Chemistry, 1969, 624 S., p. 30, formula (1-40)):

where L is the length of the massecuite pipeline, m;

d is the inner diameter, m;

ω is the velocity of the laminar flow, m / s;

μ _U - massecuite viscosity, Pa · s.

, а

, тогда получаем:But

, but

then we get:

where Re is the Reynolds criterion.

The pressure loss on the massecuite rise is equal to

The cost of pressure to create a flow rate is expressed by the formula:

Losses ΔР _ms and ΔР _additional make up no more than 5 ... 10% of all pressure losses.

The average value of the Re criterion for pumping massecuite is approximately 1. The error in calculating the friction pressure loss under the assumption that Re≈1 is also no more than 5 ... 10%. Assume that unaccounted loss of pressure, and the calculation error of the frictional pressure losses are part of the total pressure loss? P _{ck ck} +? P +? P _under calculated by formulas (12), (13), (14).

Then the hydraulic resistance of the network will be equal to:

where a is a coefficient less than 1.

Taking into account (15), the active electric power will be equal to:

where is the constant

We substitute (9) into (16) and obtain

Where

From where the value A is easily determined:

where [K] is the adjustment step of model (17), depending on the frequency of laboratory density control.

и автоматически измеренных соответствующих значений расхода воды

, перепада давления столба утфеля

, электрической мощности N^[K], температуры воды

(необходимой для расчета плотности воды по формуле (3)), блок 19 рассчитывает параметр А^[K] по формуле (18).Thus, based on laboratory analysis at the [K] step for adjusting the density of diluted massecuite

and automatically measured corresponding water flow rates

massecuite column pressure drop

, electric power N ^[K] , water temperature

(necessary to calculate the density of water according to the formula (3)), block 19 calculates the parameter A ^[K] according to the formula (18).

Taking into account A ^{[K], the} dependence of the active power on the volume flow of massecuite takes the form:

where [n] is the current measurement and control step.

, блок 19 выполняет методом Хука-Дживса. Для этого вначале составляется функция:The solution of equation (19), in which the volume flow rate of massecuite is unknown

block 19 is executed by the Hook-Jeeves method. For this, the function is first compiled:

целевая функция Ф примет вид: Subject to technological limitations on

objective function f takes the form:

.As a result of solution (21), the current value of massecuite consumption is determined

.

, блок 19 определяет для заданного значения плотности готового утфеля

необходимый расход воды в смесителе

:Calculating the current value of massecuite consumption

, block 19 determines for a given density value of the finished massecuite

required water flow in the mixer

:

The task of the regulator 12 of the water flow is calculated by block 19 according to the formula:

- задание регулятору 12, рассчитанное на прошлом (n-1) шаге управления. На первом шаге оно равно измеренному значению расхода воды.Where

- task to the controller 12, calculated at the last (n-1) control step. In the first step, it is equal to the measured value of the water flow.

- измеренное датчиком 11 на текущем [n] шаге значение расхода воды в смесителе.

- measured by the sensor 11 at the current [n] step, the flow rate of the water in the mixer.

The current task for the water flow controller, calculated by the formula (23), is stored, converted into a control signal and fed from the output of block 19 to the controller’s task chamber 12. The stored task value is used in formula (23) in the next control step as the value of the task of the previous step management.

The determination of parameter A is carried out during the adjustment of the invention. During operation, when only scheduled laboratory analyzes of the density of the diluted massecuite are performed, the value of this coefficient can be adjusted. The formula for the adjustment is as follows:

- рассчитанное по формуле (18) на [К] шаге корректировки значение коэфициента А;Where

- calculated by the formula (18) at the [K] adjustment step, the value of coefficient A;

- сглаженное на [К] шаге значение коэффициента А;

- the value of coefficient A smoothed out at the [K] step;

α is the smoothing coefficient, determined experimentally in the range of 0.5≤α≤1.

The proposed method allows you to reliably stabilize at a given value the density of the finished diluted massecuite at the outlet of the mixer, since formula (19) uniquely relates the volume flow of the massecuite and the active electric power consumed by the electric drive of the massecuite pump, and the density of the massecuite and water are calculated automatically.

The content of CB _cm at the output of the mixer is calculated by block 19 according to the formula:

where G _CB , C _y , G _B are the mass flow rates of dry matter, massecuite and water, respectively, in the mixer, kg / s, equal to:

where CB _y is the concentration of solids calculated by the formula (7).

The method of automatic monitoring and control of the process of preparing massecuite for crystallization by cooling is illustrated by the following examples.

Example 1. Calculation of the task to the water flow controller

The design parameters of the control system that implements the method are equal to: N _y = 14.2 m; L = 22.5 m; d = 0.158 m. Then the construction coefficient B, determined by the formula (16), is equal to:

. Соответствующие этой плотности измеренные значения параметров равны:Laboratory-measured density of finished diluted massecuite

. The measured values of the parameters corresponding to this density are:

ΔР _У = 205000 N / m ² (sensor 9);

Q _B = 0.25 m ³ / h = 6.9444 · 10 ^-5 m ³ / s (sensor 11);

t _B = 72 ° C (sensor 17);

N = 988 W (sensor 18).

The density of water calculated by formula (3) is equal to: ρ _B = 976.93 kg / m ³ (based on information from sensor 7). The massecuite density, determined by the formula (4), is: ρ _у = 1471.62 kg / m ³ (based on information from the sensor 9).

Using the formula (18), we determine the tuning parameter A:

The parameter values measured at the [n] control step were equal to:

=206200 H/м²;

= 206200 N / m ² ;

=0,37 м³/час=1,028·10^-4 м³/сек;

= 0.37 m ³ / h = 1.028 · 10 ^-4 m ³ / s;

=73°С;

= 73 ° C;

N ^[n] = 1090 W.

(формула 4).Then

(formula 4).

=976,33 кг/м³ (формула 3).

= 976.33 kg / m ³ (formula 3).

We compose the cubic equation (19)

+

)·206200·2,463 или1090 = (85191.547

+

) 206200 2.463 or

+

-0,0021462=0.85191,547-

+

-0.0021462 = 0.

=7,5 м³/час=2,083·10^-3 м³/сек;

=4,5 м³/час=1,25·10^-3 м³/сек, получаем

=1,715833 м³/сек=6,177 м³/час.Solving the Composed Cubic Equation under Constraints

= 7.5 m ³ / h = 2.083 · 10 ^-3 m ³ / s;

= 4.5 m ³ / h = 1.25 · 10 ^-3 m ³ / s, we get

= 1.715833 m ³ / s = 6.177 m ³ / hour.

=6,177 м³/час.Thus, the current volume flow rate of massecuite, calculated at the [n] step, is equal to

= 6.177 m ³ / hour.

. По формуле (22) определим задание по расходу воды:Assume that the density task of the finished diluted massecuite is equal to

. By the formula (22) we define the task for water flow:

.

.

, то тогда

=0,394 м² /час.If, for example

, so then

= 0.394 m ² / hour.

Thus, a change in the task for the density of the diluted massecuite by only 10 kg / m ³ leads to a change in the task for water consumption by 0.142 m ³ / h or 25% from the initial task, i.e. channel control sensitivity diluted massecuite density - water consumption is very high. This explains the poor quality of regulation of the density of diluted massecuite in the prototype, which is carried out at a given ratio of massecuite: water.

=0,38 м³/час. Тогда текущее значение задания регулятору 12 (формула 23) равно для

,

=0,38+(0,536-0,37)=0,546 м³/час, а при

,

=0,38+(0,594-0,37)=0,604 м³/час.Suppose the value of the task to the controller 12, calculated by block 19 at the last [n-1] step of the equation, was equal

= 0.38 m ³ / hour. Then the current value of the task to the controller 12 (formula 23) is equal to

,

= 0.38 + (0.536-0.37) = 0.546 m ³ / h, and at

,

= 0.38 + (0.594-0.37) = 0.604 m ³ / hour.

Example 2. The calculation of the concentration of solids

=1480,24 кг/м³, температура утфеля

=69°C. Согласно регламенту

=96,5%,

=90%. Составляем целевую функцию по формуле (7)To calculate the solids content at the inlet to the mixer, use the formula (2). The current value of massecuite density is

= 1480.24 kg / m ³ , massecuite temperature

= 69 ° C. According to regulations

= 96.5%

= 90%. We compose the objective function according to the formula (7)

=94,174%.whose solution is equal

= 94.174%.

Solids consumption is equal to

We find the mass consumption of water and massecuite:

.

.

Then by the formula (25):

.

.

Thus, the concentration of CB at the inlet and outlet of the mixer, respectively, is 94.17% and 90.59%.

Experimental verification of the proposed method for automatically controlling the process of preparing massecuite for crystallization by cooling showed its high efficiency and performance (figure 2). The average purity of the intercrystalline massecuite solution at the outlet of the vertical crystallizer is reduced from 54.24% (when controlled by the known method) to 54.0% (when controlled by the proposed method) (fig.2b.).

The implementation of the functional unit 19 is carried out using computer technology. As primary measuring transducers can be used:

- Intelligent pressure difference sensors Metran-100-DD, measurement error ± 0.1%;

- copper resistance thermoconverters TSM Metran-204 (100M) with a measurement error of ± 0.25 + 0.0035 (t)%;

- Metran-360 flowmeter with an accuracy of ± 0.5%;

- wattmeter Ts-201.

Using the proposed method makes it possible in comparison with the prototype:

- reduce sugar loss with molasses due to better stabilization of massecuite density at the outlet of the mixer;

- automate control of the concentration of dry substances in the massecuite at the inlet and outlet of the mixer.

Claims (1)

A method for automatically monitoring and controlling the process of preparing the massecuite for crystallization by cooling, which includes regulating the volumetric flow rate of water into the mixer and the level of the massecuite in it, adjusting the massecuite level in a vertical mold by acting on a frequency-controlled electric drive of the massecuite pump, including periodic laboratory control of the density of the finished massecuite at the outlet from a mixer, characterized in that it further measures the active electrical power consumed by the electric drive the massecuite pump, the temperature and pressure drop of the massecuite entering the mixer, the water temperature at the inlet to the mixer, calculate the density of water according to its temperature and the density of the massecuite according to its pressure drop, calculate the volumetric flow rate of the massecuite entering the mixer, according to the measured volumetric flow rate, the calculated values of the density of water and massecuite and the laboratory-measured density of the finished massecuite, determine the coefficients of the dependence of the active electric power on the volumetric flow rate of the massecuite and its pressure drop N = α ₁ Q ³ _y ΔP _y + α ₂ Q _y ΔP _y , where N is the active electric power; Q _y - the volume flow of massecuite into the mixer; ΔР _у - massecuite pressure drop; α ₁ , α ₂ - coefficients, and use this dependence for subsequent calculations of the massecuite volumetric flow rate only from the measured values of active electric power and the massecuite pressure drop, determine the current task of the volumetric flow rate regulator based on the measured value of this flow rate, calculated values of the massecuite density, water and the massecuite volumetric flow rate, the specified density value ready massecuite and assignments to this regulator, calculated at the last control step, control the solids content in the original massecuite - according to its density and the temperature in the finished massecuite - according to the volumetric flow rates and density of the original massecuite and water and the solids content in the original massecuite.

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