RU2163826C2 - Method of control of complex fractionating plant in oil refining - Google Patents

Abstract

FIELD: control of fractionating processes in oil refining. SUBSTANCE: fractionating plant includes reservoir for starting mixture, heat exchanger, fractionating tower, boiler, condenser, phlegma reservoir, starting material flow regulator, phlegma reservoir level regulator by distillate; pumping units are used for measurement and control of total flow rate in stripping reservoir, phlegma reservoir and fractionating tower, flow rate of distillate from phlegma reservoir, flow rate of finished product in stripping reservoirs and flow rate of stillage residue; to this end, working characteristics of pumping units pertaining to power and pressure head developed by each pump depending on flow rate and flow rate coefficients are determined through subtraction of result of division of power by pressure developed at closed gate valve at pump outlet in the beginning of the working characteristic from result of division of power acting on pump shaft on pressure developed by this pump. According to coefficient thus found, working curve is plotted and its mathematical description is found. Then, magnitude of flow rate is preset for fractionating tower as a whole and actual flow rate is measured and if these magnitude are not equal, signal is furnished to valve under control till these magnitudes become equal. Level in phlegma reservoir and rate of flow of distillate from this reservoir are measured and regulated till preset magnitudes have been obtained; flow rate of raw material fed from tower to each stripping reservoir is measured through differentiating the magnitude of dynamic level in stripping reservoir; level of liquid in each stripping reservoir is regulated through pumping finished product from it by means of pumping unit and measuring its flow rate; rate of crossflow from fractionating tower to stripping reservoir is determined. Rate of crossflow is maintained at constant level through control by means of valve found in crossflow line between stripping reservoir and fractionating tower; control is effected in succession and is continued till magnitude of crossflow becomes equal to preset value; level of stillage residue in fractionating tower is regulated and its flow rate is measured; simultaneously, material balance is maintained in fractionating tower and rate of flow of distillate in phlegm reservoir, rate of flow of finished product in stripping reservoir and flow rate of stillage residue are summed up and magnitude thus obtained is compared with amount of starting material fed to tower; these magnitudes shall be equal. EFFECT: enhanced reliability, accuracy and economical efficiency in maintaining material balance in stripping and phlegma reservoirs and in fractionating tower as a whole. 4 dwg

Description

 The invention relates to the regulation of mass transfer processes in oil refineries and can be used in complex distillation plants in oil refineries.

 It is known "Device for measuring the flow rate of a substance" (RU 1789861 C1, 01/23/1993). In this invention, pumping units are used directly as flowmeters without installing additional technical means in the liquid stream.

 Closest to the claimed decision on the technical essence is a method of controlling a distillation unit in the chemical industry (Kazakov A.V., Kulikov M.V., Melushev M.V., M., "Mechanical Engineering", 1970, pp. 331-336) . The disadvantage of this method is that it lacks the ability to measure the flow from the distillation column into strippers, as well as to measure and control the flow rate of the initial mixture and distillate, flow meters are used with their elements installed directly in the flow of the measured liquid.

 The technical result achieved by the implementation of this invention is to improve the accuracy and reliability of the entire distillation unit.

по вычисленным коэффициентам M строят расходную характеристику M-Q, находят ее математическое описание, по которому расход Q равен:

где A и C - постоянные для данной насосной установки коэффициенты, при измерении действующего расхода эксплуатационный коэффициент M равен:

где N_c, η_эд, η_эк - соответственно активная мощность, потребляемая электродвигателем привода из сети, коэффициент полезного действия электродвигателя, эксплуатационный коэффициент полезного действия насосной установки; p_в, p_п - соответственно давления на выходе из насоса и на его входе; B - постоянный для данной насосной установки коэффициент, задают значение расхода для ректификационной колонны в целом Q_р.з. и измеряют действующее значение Q_р, и если оно не равно заданному, то подают сигнал на регулируемый клапан для изменения расхода в такую сторону и до тех пор, пока действующий расход не будет равен заданному:
Q_р=Q_р.з,
измеряют и регулируют уровень во флегмовой емкости и расход дистиллята из нее до тех пор и в такую сторону, пока расход дистиллята Q_д не будет равен заданному Q_д.з.The specified technical result is achieved by the fact that in each of the stripping tank, reflux tank and distillation column as a whole to measure and control the total flow rate entering the column, the distillate flow rate from the reflux tank, the finished product flow rate in stripping tanks and the bottoms flow rate, as flowmeters use pumping units, for which, when the distillation unit, stripping and reflux tanks are put into operation, the performance characteristics of the pumps in terms of power and at the pressure depending on the flow rate determined for each pump unit consumption ratios M by subtracting from the power dividing the product N, acting on the pump shaft in emerging they pressure p, the result of the power split N _o on the pressure developed by them p _o at the closed valve at the outlet of pump at the beginning of the operating characteristic

using the calculated coefficients M, the flow characteristic MQ is built, its mathematical description is found, according to which the flow Q is:

where A and C are the coefficients constant for a given pump installation, when measuring the actual flow rate, the operational coefficient M is equal to:

where N _c , η _ed , η _ec are respectively the active power consumed by the electric motor of the drive from the network, the efficiency of the electric motor, the operational efficiency of the pumping unit; p _in , p _p - respectively, the pressure at the outlet of the pump and at its inlet; B is a constant constant for a given pump unit; the flow rate for the distillation column as a whole is set to Q _r.s. and measure the effective value of Q _p , and if it is not equal to the set value, then a signal is supplied to the adjustable valve to change the flow rate in such a direction and until the effective flow rate is equal to the set value:
Q _p = Q _p .
measure and adjust the level in the reflux tank and the flow of distillate from it until then and in such a direction until the flow of distillate Q _d is equal to the specified Q _d.z.

где Q_с - расход сырья, поступающего из колонны в каждую стрипинговую емкость, ∂H, t - соответственно, приращение уровня за заданный промежуток времени регулирует уровень жидкость в каждой из стрипинговой емкости путем откачки готового продукта с помощью насосной установки и измерения его расхода Q_г.п и определяют расход перетока Q_п из ректификационной колонны в стрипинговую емкость по формуле:
Q_п = Q_с - Q_г.п,
поддерживают этот расход перетока Q_п постоянным путем регулирования его значения клапаном, находящимся на линии перетока между стрипинговой емкостью и колонной, причем регулирование производят последовательно и продолжают до тех пор, пока величина перетока Q_п не станет равной заданному значению Q_п.з, регулируют уровень кубового остатка в ректификационной колонне и измеряют его расход Q_к.о, одновременно в ректификационной колонне поддерживают материальный баланс, при котором суммируют расход дистиллята по флегмовой емкости, расходы готового продукта по стрипинговым емкостям Q_г.п1, Q_г.п2, Q_г.п3, расход кубового остатка Q_к.о, и полученное значение сравнивают с количеством поступающего исходного сырья в колонну Q_р, которые должны быть равны
Q_р=Q_д+Q_г.п1+Q_г.п2+Q_г.п3+Q_к.о
Доказательство существенных отличительных признаков предлагаемого способа управления ректификационной установкой для химических производств проводилось только по сравнению с указанными выше.Q _d = Q _dz measure the consumption of raw materials coming from the column into each stripping capacity Q _s by differentiating the value of the dynamic level in the stripping capacity according to the formula

where Q _s is the flow rate of raw materials coming from the column to each stripping tank, ∂H, t are, respectively, the level increment for a given period of time regulates the liquid level in each stripping tank by pumping the finished product using a pumping unit and measuring its flow rate Q _{g .p} and determine the flow rate of Q _p from the distillation column into a stripping capacity according to the formula:
Q _n = Q _s - Q _gn ,
maintain this flow rate of the flow Q _p constant by adjusting its value with a valve located on the flow line between the stripping capacity and the column, and the regulation is carried out sequentially and continues until the flow value Q _p becomes equal to the specified value of Q _pz , the level is controlled bottoms in the distillation column and measure its flow rate Q _KO , at the same time in the distillation column maintain a material balance, at which the distillate consumption is summed by reflux capacity, costs the finished product for stripping containers Q _gp1 , Q _gp2 , Q _gp3 , the consumption of _bottoms Q _k.o. , and the obtained value is compared with the amount of incoming feedstock to the column Q _p , which should be equal
Q _p = Q _d + Q _gp1 + Q _gp2 + Q _gp3 + Q _q.o.
The proof of the essential distinguishing features of the proposed method for controlling the distillation unit for chemical production was carried out only in comparison with the above.

 In FIG. 1 is a structural diagram of a complex distillation unit with reflux and stripping containers.

 In FIG. 2 shows the typical and proposed new discharge characteristics of the pumping unit.

 In FIG. 3 is a diagram explaining the operation of a distillation unit with reflux capacity.

 In FIG. 4 is a diagram and algorithms for controlling the operation of stripping capacities.

По найденным расходным коэффициентам строят расходную характеристику M-Q, находят ее математическое описание и расход вычисляют по формуле:

где A, C - постоянные для данной насосной установки,
N = N_c η_эдη_эк кВт, (3)
p = p_в - p_п МПа, (4)
где p_в, p_п - соответственно давление на выходе из насоса и давление на его приеме; N_с - активная мощность, потребляемая электродвигателем привода насоса из сети, кВт; η_эд - электродвигателя, взятые из его рабочей характеристики, η_эк - эксплуатационный коэффициент полезного действия насосной установки, который определяют перед пуском насосной установки в эксплуатацию и равен:

где N_о, N_о.з, p_о p_з.з - соответственно мощности и давления, взятые из рабочей характеристики насоса и полученные при периодическом испытании при закрытой задвижке на выходе из насоса. На фиг. 3 дана схема, поясняющая работу ректификационной установки с флегмовой емкостью. На этой схеме показана ректификационная колонна 3, в которую из емкости исходной смеси 1 насосом 10 с электродвигателем 11 смесь через регулятор 12 подается в колонну. Для измерения и регулирования расхода исходной смеси, поступающей в ректификационную колонну с помощью насосной установки, имеется датчик давления на приеме насоса 13, датчик давления на выходе из насоса 14, преобразователь мощности 15, сигналы с которых поступают на контроллер 16, который осуществляет измерение и стабилизацию подачи исходной смеси в ректификационную колонну по формулам (1, 2). Для разделения исходного продукта на дистиллят и кубовый остаток имеются флегмовая емкость 6. Исходный продукт через конденсатор 5 поступает в емкость 6, а из нее дистиллят откачивается насосом 17 с электродвигателем 18 в сборник, а кубовый остаток через регулируемым клапан 19 возвращается в ректификационную колонну 3. Уровень кубового остатка в колонне поддерживается регулятором уровня 20 и откачивается и измеряется насосом 21 с электродвигателем Д3 и преобразователем мощности 22 с манометрами на приеме насоса 23 и выходе из насоса 24, сигналы с которых подаются в контроллер 25, а с него с ЭВМ 26. Для поддержания материального баланса флегмовой емкости имеется регулятор уровня 27, для измерения расхода флегмы и регулирования производительности используется сама насосная установка, для чего имеется преобразователь мощности 28, датчик давления на приеме насоса 29, датчик давления на выходе из насоса 30, блок управления клапаном 31 на выходе флегмовой емкости, контроллер 32, который осуществляет управление флегмовой емкостью 6.In FIG. 1 is a structural diagram of such an installation for rectification of multicomponent mixtures. It consists of the capacity of the initial mixture 1, the heat exchanger 2, in which the initial mixture is heated to boiling point, a distillation column 3 with a boiler 4, a condenser 5, a reflux tank 6, stripping tanks 7, 8, 9. The task of controlling the rectification process is to obtain products separation - distillate Q _d , finished products Q _gp1 , Q _gp2 , Q _gp3 and _bottoms Q _{q.o. of} certain purity at a given plant capacity Q _p with a minimum consumption of heating steam. A feature of the proposed control method is that for measuring the flow rate of the supplied product into the distillation column, distillate separation products, finished products, bottoms, non-existent measurement methods are used, in which the measuring equipment must be in the flow of the measured liquid, and with the help of directly working pumping devices installations providing the supply of these liquids, as well as the fact that for measuring the flow in stripping capacities the method of Eren flow by measuring product level rate of change in stripingovyh containers by its time derivation. To use the pumping unit as a flow meter during its commissioning, its energy characteristics are removed - the dependence of the flow on the power NQ and the generated pressure HQ (Fig. 2). In this case, the temperature of the liquid is not taken into account, since the flow characteristic does not depend on the density of the pumped liquid. This is clearly seen from the analysis of the recorded characteristics at a density of 1000 kg / m ³ and a density of 710 kg / m ³ . The expenditure coefficients M are calculated over the entire performance range by subtracting from the result of dividing the power N by the developed pressure p the result of dividing the power N _o by the developed pressure p _o with a closed valve at the pump outlet at the beginning of the characteristic:

Using the consumption coefficients found, the MQ flow characteristic is built, its mathematical description is found, and the flow rate is calculated by the formula:

where A, C are constants for a given pump installation,
N = N _c η _ed η _ec kW, (3)
p = p _in - p _p MPa, (4)
where p _in , p _p - respectively, the pressure at the outlet of the pump and the pressure at its intake; N _with - active power consumed by the pump electric motor from the network, kW; η _ed - electric motor, taken from its operating characteristics, η _ek - operational efficiency of the pumping unit, which is determined before putting the pumping unit into operation and is equal to:

where N _o , N _oz , p _o p _zz are, respectively, power and pressure taken from the operating characteristics of the pump and obtained during periodic testing with a closed valve at the outlet of the pump. In FIG. 3 is a diagram explaining the operation of a distillation unit with reflux capacity. This diagram shows a distillation column 3 into which the mixture through the regulator 12 is fed into the column from the reservoir of the initial mixture 1 by a pump 10 with an electric motor 11. To measure and control the flow rate of the initial mixture entering the distillation column using a pump unit, there is a pressure sensor at the pump inlet 13, a pressure sensor at the outlet of the pump 14, a power converter 15, the signals from which are sent to the controller 16, which measures and stabilizes feeding the initial mixture into a distillation column according to the formulas (1, 2). To separate the initial product into distillate and bottoms, there is a reflux vessel 6. The initial product is passed through a condenser 5 to a vessel 6, and the distillate is pumped out of it by pump 17 with an electric motor 18 to the collector, and still bottoms through an adjustable valve 19 are returned to distillation column 3. The level of bottoms in the column is maintained by a level controller 20 and is pumped out and measured by a pump 21 with an electric motor D3 and a power converter 22 with pressure gauges at the intake of the pump 23 and the exit of the pump 24, signals with which are fed into the controller 25, and from it with a computer 26. To maintain the material balance of the reflux capacity, there is a level regulator 27, the pump unit itself is used to measure the reflux rate and regulate the performance, for which there is a power converter 28, a pressure sensor at the pump inlet 29, a pressure sensor at the outlet of the pump 30, a valve control unit 31 at the outlet of the reflux tank, a controller 32 that controls the reflux tank 6.

The management of stripping capacities is carried out as follows (Fig. 4): the material balance of the stripping capacitance 7, as well as similar capacities 8, 9, is implemented according to the same scheme. The liquid from the distillation column 3 through the valve 33 enters the tank 7. The finished separation product Q _{GP1 is} pumped out by a pump 34 with an electric motor DS1 to the collection tank. The liquid level in the stripping tank is regulated by a level regulator 35, and the flow rate of the product entering the tank is measured using a dynamic level gauge 36. A pump unit with a pump 34 and a drive motor DS acts as a flowmeter of the finished product. A power transducer 37 is used to measure active power, a pressure sensor 38 is used to measure the pressure at the pump outlet, and a pressure sensor 39 is used to measure the pressure at the pump intake. To maintain a constant material balance of the stripping capacity, certain conditions must be met. So, if the total flow rate of the mixture entering the stripping capacity is denoted by Q _s , flow rate of the finished product through Q _gp , flow rate through Q _p , then with a known value of Q _s and Q _{gp the} flow rate will be equal to
Q _n = Q _s - Q _gn ,
which is maintained at a given value.

 To implement this material balance, the following method is proposed.

где

- соответственно приращение уровня за заданный промежуток времени.The total flow rate of the product entering the stripping tank from the column is measured by differentiating the changing liquid level in the tank using a dynamic level gauge according to the formula:

Where

- respectively, the increment of the level for a given period of time.

The final value of the H level in the stripping capacity is regulated by a level regulator 3.5, which keeps the level constant at a given value. To measure the finished product flow rate is measured by p the pressure created by the pump 34, which is the difference between the pressure at the outlet of p _pump measured by the sensor 38, and the pressure at the pump intake p _p measured by the sensor 39 in block 40 from the formula p = p _in - p _p , MPa.

Затем определяют расход продукта, поступающего в стрипинговую емкость, по формуле:
Q_c= ∂H/∂t, м³/ч.
После этого с помощью полученного значения расхода готового продукта Q_г.п и продукта, поступающего в стрипинговую емкость Q_с, находится значение расхода перетока из ректификационной колонны в стрипинговую емкость Q_с в блоке 43 контроллера 44 по формуле:
Q_п = Q_с - Q_г.п
Затем задаются значением перетока Q_п.з, и если Q_п ≠ Q_п.з ,то выдается управляющий сигнал в блок 45 контроллера 44 на изменение расхода перетока в стрипинговую емкость помощью регулирующего клапана 33 до тех пор и в такую сторону, пока эти расходы не будут равны:
Q_п = Q_п.з.Using the power converter 37, the active power consumed by the pump drive electric motor from the network N _s is measured, and taking into account the efficiency of the electric motor η _ed and the operating coefficient η _{ek of the} pump installation, the power acting on the pump shaft in block 41 is determined by the formula:
N = N _c η _d η _ec , kW.
The obtained values go to block 42, then to block 43 of the controller 44, which calculates the expenditure coefficient M, the consumption of the finished product Q _gp according to the formulas:

Then determine the flow rate of the product entering the stripping capacity, according to the formula:
Q _c = ∂H / ∂t, m ³ / h.
After that, using the obtained value of the flow rate of the finished product Q _gp and the product entering the strip capacity Q _s , the flow rate from the distillation column to the strip capacity Q _{s is found} in block 43 of the controller 44 according to the formula:
Q _n = Q _s - Q _gn
Then, the overflow value Q _{p.z. is set} , and if Q _p ≠ Q _p.z. , a control signal is issued to the block 45 of the controller 44 to change the flow rate to the stripping capacity using the control valve 33 as long as these costs will not be equal:
Q _p = Q _pz

 At a subsequent discrete time instant, the measurement and control process is repeated again. Thus, the task of maintaining material balance in the stripping capacity is realized. All other stripping capacities work in the same way.

 Considering that it is not possible to measure product flow from a distillation column into a stripping tank due to the lack of pressure drop by existing technical means and methods, the information obtained on its quantity is extremely important and it is practically impossible to obtain the desired quality of the output product without it.

As a result of rectification, separation products are obtained - distillate Q _d , finished products Q _gp1l , Q _gp2 Q _gp3 and _{still bottoms} Q _{q.o. of a} certain purity. The flow rate of the feed mixture entering the column is stabilized by a flow controller. The temperature of the feed mixture and the pressure of the heating steam are controlled using appropriate systems that are not considered in this application. For the stable operation of the column, it is necessary to maintain its material balance, which maintains the equality of nutrition and the amount of expenses of the distillate, bottoms and finished products. With a stable supply, this is achieved by stabilizing the flow rate of one of the products and controlling the flow rate of the second so that their amount remains constant. In a distillation column, this is realized with the help of a flow rate regulator on the feed line and a regulator of the level of bottom product in the column. The existing flow controllers in their reliability do not meet modern requirements, therefore, it is proposed to use a pump unit directly as a flow controller. For this, at a pump installation 10 with an engine 11, the power N _s consumed by the electric drive motor from the network, the pressure at the pump inlet p _p by the pressure sensor 13, the pressure at the outlet of the pump p by the pressure sensor 14 are measured using the PM 15 power converter, and the flow rate is calculated by the formulas : pressure developed by the pump
p = p _in - p _p , MPa,
power on pump shaft
N _a = N _c η _ed η _ec , kW,
where η _ed , η _ec are, respectively, the efficiency of the electric motor, which is taken from the operating characteristics and the operational efficiency of the pumping unit, obtained by removing its operating characteristics before putting the pump into operation, at the time of operation of the pump with a closed valve.

вычисляют расход

Полученные значения расхода сравнивают с заданным значением Q_р.з и при их неравенстве подается команда на прикрытие или приоткрытие клапана 12 на подающим трубопроводе.Determine the expenditure coefficient M

calculate flow

The obtained flow rates are compared with a predetermined value of Q _r.s. and if they are not _{equal, a command is issued} to cover or slightly open valve 12 on the supply pipe.

Further, the consumption of the finished product for all stripping containers, reflux capacity and bottoms is compared with the total flow rate supplied to the distillation column Q _p according to the formula:
Q _p = Q _q.o + Q _d + Q _gn1 + Q _gn2 + Q _gn3 .

Claims (1)

A method for controlling a distillation unit in an oil refinery containing a feed mixture tank, a heat exchanger, a distillation column, a boiler, a condenser, a reflux tank, a feed material flow rate regulator, a distillate reflux tank level controller, characterized in that in each of the stripping tank, reflux tank and distillation tank columns for measuring and regulating the total flow entering the column, the flow of distillate from the reflux tank, the flow rate of the finished product in stripping tanks and the bottom residue flow rate, pump units are used as flow meters, for which, when the distillation unit, stripping and reflux tanks are put into operation, the pump performance is determined by the power and developed head depending on the flow rate, the flow coefficients M are determined for each pump unit by subtracting from the result power split N, acting on the pump shaft on developing them pressure p, the result of dividing the power N _o on developing them at pressure p _o closed valve at the outlet of the district Sosa at the beginning of the performance

the calculated coefficients M build the flow characteristic M - Q, find its mathematical description, according to which the flow rate is

where A and C are constants constant for a given pump installation,
when measuring the actual flow, the operating coefficient M is

where N _c , η _ed , η _ec are respectively the active power consumed by the electric drive motor from the network, kW, the efficiency of the electric motor, the operational efficiency of the pumping unit;
P _in , P _p - respectively, the pressure at the outlet of the pump and at its inlet, MPa;
In - constant for a given pump installation coefficient,
set the flow rate for the distillation column as a whole Q _RZ and measure the actual value of the flow rate Q _p and, if it is not equal to the set, then give a signal to the adjustable valve to change the flow in this direction and until the actual flow is equal to the set
Q _p = Q _p.z. ,
measure and adjust the level in the reflux tank and the flow of distillate from it until then and in such a direction until the flow of distillate Q _d is equal to the specified Q _dz
Q _d = Q _dz ,
measure the flow of raw materials coming from the column into each stripping capacity Q _s by differentiating the value of the dynamic level in the stripping capacity according to the formula

where Q _c is the consumption of raw materials coming from the column into each stripping capacity;
∂H, ∂t - respectively, the level increment for a given period of time,
regulate the liquid level in each stripping capacity by pumping the finished product using a pumping unit and measuring its flow rate Q _g. and determine the flow rate Q _p from the distillation column into a stripping capacity according to the formula
Q _p = Q _c - Q _g.p. ,
maintain this flow rate of flow Q _p constant by adjusting its value with a valve located on the flow line between the stripping tank and the column, and the regulation is carried out sequentially and continues until the flow value Q _p becomes equal to the set value of Q _pz , the level of bottoms remain fractionator and was measured its flow rate Q _to, simultaneously in a distillation column support material balance in which a distillate flow is summed at the reflux vessel costs g tovogo product according stripingovym containers _g.p1 Q, Q _g.p2, Q _g.p3 flow rate Q _to the distillation residue and the resulting value is compared with the number of incoming feedstock to the column Q _p which must be equal
Q _p = Q _d + Q _{gn 1} + Q _{gn 2} + Q _{gn 3} + Q _ko .

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