Automation of primary oil refining processes
This and the following chapters describe the automation schemes for some basic technological processes without taking into account the systems of emergency protection of processes, the protection of certain types of equipment and the equipment of technological processes in accordance with the requirements of the current technical regulations, norms and rules. The description contains the main typical control loops, which for licensing processes can be supplemented with loops required by the Licensors.
Automation of oil dehydration and desalination processes at CDU-AT and CDU-AVT units
The oil coming from the fields, depending on the group, contains chloride salts (in the amount of 100-900 mg/dm3), including up to 10 mg/dm3 of chlorides in the fraction boiling up to 204 °C, formation waters (up to 1% wt.) and mechanical impurities (up to 0.05% wt.). These parameters are regulated by GOST R 51858-2002 “Oil. General technical conditions”.
In this case, oil and water form hard-to-separate emulsions (mainly a water-in-oil emulsion). For further oil refining, it is required to reduce the salt content to 0.1 wt%. and less, and water – up to 3 … 5 mg / l.
The requirements for limiting the content of salts and water in oil are due to the need to increase the overhaul run of atmospheric and atmospheric vacuum units, reduce corrosion of equipment and apparatus, and improve the quality of boiler fuels, coke and bitumen. In addition, in oil fraction processing plants, an increased content of water and salts leads to an increased consumption of fuel and catalysts.
Most of the water in oil is in the form of emulsions. Resinous substances, asphaltenes, water-soluble organic acids and highly dispersed particles of solid paraffins are adsorbed on the surface of water droplets. To destroy the surface adsorption film, as well as to improve coagulation conditions, demulsifiers are added to the oil. To speed up this process, it is usually carried out at elevated temperatures (100-120 °C). The most stable finely dispersed oil emulsions break down under the action of an electric field. Thus, the process of electrodehydration is facilitated by both demulsifiers and elevated temperature. To reduce the evaporation of oil, the process of electrical desalination is carried out at elevated pressure.
The process of deep dehydration and desalination is carried out on electric desalination plants (ELOU), which are part of ELOU-AT (atmospheric tubular unit) or ELOU-AVT (atmospheric vacuum tubular oil distillation unit).
In practice, two-stage electric desalination schemes are often used using alternating electric current with a voltage of 22-44 kV. At the same time, 75-80% of the mass is removed in the first stage in the electric dehydrators. water and 95-98 wt%. salts, and at the II stage 60-65 wt% is removed. the remaining emulsion water and 89-93 wt%. the remaining salts.
The process of oil desalination is associated with washing it with fresh water, while to reduce water consumption, return (recirculation) water, condensate, purified process water and drainage water are used as fresh water. Oil dehydration processes are carried out in stage I and II electric dehydrators. To break the emulsion (demulsify), a demulsifier (20…25 g/t) is introduced into the crude oil, and alkali is introduced after the heat exchangers to reduce the acidity of the water to values close to neutral.
The electric dehydrator is a horizontal apparatus for oil dehydration and desalting in a high voltage electric field (20…44 kV). The distance between two horizontal electrodes located in the middle part along the entire length of the device is 200…400 mm. The dehydrated oil is discharged through the upper
collector, and the water released from the oil is from the bottom of the apparatus. Oil in the electric dehydrator moves up, passing through the water layer at a speed of 5…7 m/h, and then through the zone of a weak electric field located between the water level and the lower electrode. Then the oil enters the zone of a strong electric field between the two electrodes, in which the process of intensive dehydration takes place, and then through the upper collector it is discharged to the second stage electric dehydrator. The device of the horizontal electric dehydrator is shown in fig. 8.1. Before the electric dehydrator of the second stage, oil is mixed with water heated to 60…70 °C and from the outlet of the electric dehydrator, after additional heating, it enters the distillation column of the atmospheric unit AT or AVT.
The scheme of automation of a two-stage ELOU installation, made in the ISA 55.1-84 (92) standard, is shown in fig. 8.2. In some circuits in the process automation diagrams (see later chapters), the designations of the converters are omitted.
Automation of the process of dehydration and desalting of oil at CDU-AT and CDU-AVT units, as well as automation of other technological processes described in this manual, involves the definition of process performance indicators (PE), goals and process control criteria (CU and CU, respectively). Limitations of state variables (temperature, pressure, level, etc.) are determined by the requirements for fire and explosion safety of processes, as well as requirements for quality indicators of the target product. The limitations also include the content of impurities in the raw material and the target product.
Process efficiency is understood as technological and economic efficiency. Technological efficiency implies the relationship between the resources expended and the products received and is estimated by the criteria of min costs per unit of output and max of the products obtained with a minimum of resources spent on its production.
The economic efficiency of the process means the cost dependence between production costs and income from product sales. The criterion of economic efficiency is obtaining the maximum (max) profit per unit of production costs. The cost of production, taking into account the cost per unit of production, can serve as an integral criterion of economic efficiency.
For most processes, the efficiency indicator can be presented as the composition of the target product (for example, distillate or distillation residue during distillation) or the content of the output component (for example, the yield of acetylene in the pyrolysis process or the concentration of the extracted component in the absorption process), obtained by minimizing the cost per unit of production .
The purpose of process control in this case is to maintain a given composition or output component at a certain value – for example, maintaining a given composition of the target product during rectification or maintaining the acetylene yield at a given value during pyrolysis. For many processes, the goal of control is to stabilize the main adjustable parameters – temperature, pressure, level, flow, concentration, solution pH, etc. Process optimization criteria have minimax values and are determined by technological or economic requirements. Technological control criteria (CS) include min CKO (root mean square deviation) or dispersion of controlled parameters, maximum response speed of transients, etc. Economic optimization criteria imply min cost, min reduced costs per unit of production, min impurity content, max profit from sales products, etc.
The main technological parameters to be controlled, regulated and optimized are temperature, pressure, wash water flow rate and its distribution between a different number of electric desalination stages, demulsifier flow rate, water level and other parameters.
Crude oil is mixed with circulating brine and fresh water and, with the addition of a demulsifier, is supplied by pump H-1 in two parallel flows through a system of heat exchangers T-1 + T-6, in which it is heated to a temperature of 100 … 120 ° C due to the heat of the unit’s oil products AT. Further, crude oil enters the injector mixer, where it is mixed with an alkali solution and a salt solution from the second stage of desalination. Further, the mixture is fed into the collector of the lower part of the horizontal electric dehydrators of the first stage ED-1-nED-Z, operating in parallel.
The number of electric dehydrators is determined by the total salt content of the processed oil, the capacity of the plant and the selected standard size of the electric dehydrators.
To determine the quality of crude oil at the input to the installation, the quality of oil is monitored for the content of water and salts in it and the density is determined (circuits 1-3).
The distribution into two streams is provided by two flow control loops with level correction in the K-1 topping column (circuits 4 and 5) of the AT unit. The oil temperature is also controlled after the heat exchangers at the inlet and outlet of the electric dehydrators ED-1-ED-3 (circuits 6 and 7).
To heat crude oil in heat exchangers T-1…T-4, circulation irrigation (CR) from the AT unit is used, which returns to the AT column through the heat exchangers. Temperature control at the outlet of the heat exchangers is carried out by changing the flow rate with valves on the bypass lines (circuits 8 and 9).
Partially desalinated and dehydrated oil from stage I electric dehydrators enters a common collector and then to stage II electric dehydrators ED-4-ED-6, operating in parallel.
To suppress hydrochloric corrosion, a 1-hour-2% alkali solution is supplied to the collectors in front of the ED-1…ED-3 and ED-4…ED-6 electric dehydrators. The flow rate of the alkali solution supplied to the inputs of the electric dehydrators is stabilized (circuits 10 and 11).
Fresh water is supplied to the intake of the N-1 oil supply pumps and to the mixing valves in front of the ED-4-ED-6 electric dehydrators, the flow rate of which is stabilized (circuits 12 and 13).
Oil enters the electric dehydrators from below through mother liquors, which create a uniform flow of oil from bottom to top in an electric field of alternating current and high voltage over the entire cross section of the apparatus. Dehydrated and desalinated oil is removed from the electric dehydrators ED-4…ED-6 and sent to the AT unit.
Salt solution from the bottom of the electric dehydrators is automatically discharged: from ED-1-ED-3 – into the settling tank E-1, and from ED-4-ED-6 – into the settling tank E-2. The phase separation level in the electric dehydrators ED-1-ED-3 and ED-4-ED-6 is maintained by changing the flow rate of the salt solution discharged from the electric dehydrators (circuits 14 and 15).
Salt solution from the settling tank E-1 is cooled in the air cooler Xv-1 and sent to the plant’s treatment facilities. The level in the tank E-1 is maintained by changing the flow rate of the brine entering the treatment plant (loop 16). Part of the brine from the settling tank E-1 is returned to the crude oil. The brine flow rate is kept constant (circuit 17). The flow rate of the brine discharged from the E-1 sump to the treatment plant is controlled (loop 24).
The temperature of the brine at the outlet of the refrigerator Xv-1 is controlled by changing the speed of the electric motor of the fans of the air coolers using a frequency converter (circuit 18).
Salt solution from the settling tank E-2 is supplied by pumps H-2 for oil washing at the inlet to each electric dehydrator of the I and II stages. The flow rate of the brine supplied to each electric dehydrator is stabilized (circuits 19 and 20). Together with the brine, the oil emulsion may be partially entrained in the settling tanks. As it accumulates, the settled oil is removed from the settling tanks through the X-1 cooler to the intake of the N-1 feedstock pumps.
To determine the efficiency of the desalination unit at the outlet of the ELOU unit (circuits 21 and 23), the desalted and dehydrated oil is monitored for water and salt content, taking into account the temperature of the oil discharged from the electric dehydrator (circuit 22).
Recently, in the construction of new and reconstruction of existing industries, innovative technologies have also been used that make it possible to process large volumes of raw materials in apparatuses with high specific productivity and to combine two stages of desalination in one apparatus. This technology was developed by Natco Group (USA) and is called EDD ® technology (“Dual Polarity Technology” ®).
Dual Polarity® refers to Natco Group ‘s exclusive electrostatic system that uses both an AC and a DC field to extract water more efficiently than a traditional AC electrical system.
The use of EDD ® electrodynamic desalters makes it possible to increase the specific productivity of electric dehydrators up to 3 m 3 /h per 1 m3 of electric dehydrator and achieve the required quality of desalted oil (no more than 2 mg of salts/l in one apparatus).
The combination of two stages of electric desalination in one apparatus also makes it possible to exclude wash water recirculation pumps from the scheme.
The scheme of automation of the electric desalination unit using dual polarity technology, made in a simplified way in accordance with GOST 21.404-85 and GOST 21.408-93, is shown in fig. 8.3. Automation tools for this technological scheme are similar to the automation tools according to fig. 8.2.
Crude oil is pumped by H-1 pumps through heat exchangers T-1 and T-2, being heated by the heat of condensation of the upper streams of the K-1 topping column and the K-2 fractionating column. Thread Distribution
is carried out by flow control with level correction in the topping column K-1 of the AT unit (circuits 1 and 2).
Crude oil after the T-1 and T-2 heat exchangers is heated in the T-3 heat exchanger by the upper circulation irrigation of the K-1 column. The oil heating temperature is maintained by changing the flow rate of the circulation reflux of the K-1 column through the corresponding heat exchanger T-3 using a valve installed on the cooling flow bypass (loop 8).
An oil-soluble demulsifier is supplied to the intake pipeline of the raw pumps N-1.
At the inlet to the unit, the quality of crude oil is monitored for the content of water and salts in it, as well as density control (circuits 5, 6 and 7).
After the T-3 heat exchanger, the oil heated to 115-125 °C is divided into two parallel flows and enters the ED-1 and ED-2 electric dehydrators. Distribution by streams is carried out by regulating the pressure in each stream using differential pressure regulators (circuits 9 and 10).
Before the electric dehydrators, wash water is introduced into each oil flow (circuits 11 and 12), and the other part of the wash water is fed directly into the electric dehydrators through specially designed distributors located above the electrodes in the upper part of the electric dehydrators (circuits 13 and 14).
Oil enters the electric dehydrators from below through mother liquors, which create a uniform flow of oil downwards> upwards in a low-gradient alternating current field, where most of the water coalesces. The fine water droplet emulsion rises into a high-gradient DC current field, which promotes coalescence and separation of the smallest water droplets.
Salt solution with oil content up to 500 mg/l is removed from the lower part of electric dehydrators ED-1 and ED-2, cooled in air coolers Khv-1 and removed from the unit.
Maintenance of the salt solution level in the ED-1 and ED-2 electric dehydrators is carried out by changing the flow rate of the output salt solution (circuits 15 and 16).
The temperature of the salt flow at the outlet of the air cooler is controlled by changing the speed of the fan motor using a frequency converter (circuit 17).
To determine the efficiency of the desalting and dehydration process, the quality of desalted and dehydrated oil at the outlet of the electric dehydrators is monitored by the content of water and salts in it and by determining the density (circuits 18, 19 and 20).
Thus, an indicator of the efficiency of the process is the degree of dehydration and desalting of crude oil. The purpose of the ELOU unit control is to maintain the set value of water and salt content in oil. The control criterion is the min standard deviation (RMS) of these parameters from the given> values.
The purpose of the control of the ELOU unit is to maintain the specified value of the content of water and salt in the oil, and the control criterion or objective function is to minimize these parameters.
As an example, consider the automation equipment for a two-stage ELOU unit (Fig. 8.2) using instruments and regulators from Emerson Siemens and others used in oil refineries.
The following automation tools are used in the automation scheme:
• at the field level — flow transducers 3051 SFC and standard chamber diaphragms DKS 10-20С from Emerson ; 30515 Pressure Transmitters with Diaphragm Seal 1199 Emerson ; interface level meters KSR from KSR KUEBLER or ID 201 from AGAR Comp.; thermo couples THKU 205 Ехіа NPP of the company “Elemer”; Emerson ‘s MicroMotion 7835 flow-through density analyzer; salt content analyzer type 44561 of the PAC group of companies; in-line analyzer of water content type VTN -1; easy-e pneumatic control valves complete with Emerson DVC6000 series electro -eumatic/positioner ; station of distributed I/O and control Simatu ET 200 M or Simatic ET 2005 from Siemens;
• at the controller level – modular programmable logic controller Simatic 57-300 or Simatic 57-400 ;
• at the supervisory level — industrial 19-inch rackmount PCs Simatic Rack PC ( Ethernet, Profibus DP, PROFINET interfaces) with ZCD-monitor of the SCD and SCAD series A – Simatic WinCC V7.0 system.
In the example of automation of a two-stage ELOU block, converters with an output signal of 4 … 20 mA and actuators (control valves with a positioner) with an input signal of 4 … 20 mA are selected Signals from primary converters and signals to actuators are processed by a distributed I / O station Simatic ET 200M connected via PROFINET to a modular PLC Simatic 57-300 .
Station ET-200M includes up to 8-12 signal, functional and communication modules PLB 57-300. The IM 153-4 PN10 interface module is designed to connect the ET-200M station to the PROFI NET network and has a built-in two-channel Industrial Ethernet PB switch and two /(/45 sockets for expanding the topology network.
The distributed I/O network PROFINET Yu, developed on the basis of Profibus and Ethernet networks, is an industrial version of the Ethernet 100 Base TX network. The physical channel is a shielded twisted pair cable of the 5th category.
For input-output of signals from 23 circuits of the automation circuit of a two-stage ELOU block , two SM 331 analog input signal modules (8 AI, 16 bit, 4 … 20 mA), two SM 332 analog output signal modules ( 8 AO, 12 bit, 4…20 mA), one signal module for input of signals from thermal converters SM 331 (8 AI TC), interface module IM 153-4 PN10. In addition, the ET-200M station is equipped with a power supply unit, which is installed on the first seat on the left. An interface module is installed to the right of the power supply, followed by signal modules. The order of placement of signal modules of the controller 57-300 can be arbitrary.
Flow measurement is performed by measuring the differential pressure across the orifice (diaphragm) using the 3051 SFC flow transmitter.
The output signal of the transducer in the range of 4…20 mA is fed to the input of the SM 331 module of the Simatic ET 200 M distributed I/O station, connected via the PROFINET local area network to the Simatic 57-300 modular PLC. When the flow rate deviates from the setpoint, the output signal of the PID controllers from the Simatic 57-300 PLC is fed through the eight-channel analog output module SM 332 to the input of the DFC6000 positioner (4 … 20 mA / HART) controlling the Emerson easy-e control valve (loop 4 , 5, 10-13, 17:19-20).
To maintain the level in electric dehydrators, level control loops are provided. The water level in the dehydrator is measured hydrostatically using Emerson’s Type 30515 Gauge Pressure Transmitter and Type 1199 Diaphragm Seal. The output signal of the converter in the range of 4 … 20 mA is fed to the input of the SM 331 module of the Simatic ET 200 M distributed I/O station. easy-e control valve with DVC6000 positioner (circuits 14 and 15). Maintaining the level in the tank E-1 is carried out by changing the salt solution entering the treatment plant (loop 16).
Oil temperature control after heat exchangers T-1…T-6 at the inlet and outlet of electric dehydrators ED-1…ED-3 is carried out using thermocouples of the TKKU-205 Exia type with an output signal of 4…20 mA by NPP Elemer (circuits 6 and 7). These thermal converters are used in circuits 8 and 9 for maintaining the temperature of the coolant from the I and II CH of the AT unit. Easy -e pneumatic control valves with DVC6000 positioner are also used as actuators. To maintain the temperature of the salt solution entering the treatment plant after the air cooler Xv-1, a frequency converter is used in circuit 18, which changes the speed of rotation of the fan motor.
The quality of crude oil is assessed by its salt and water content, as well as by measuring the density of the oil. Emerson ‘s MicroMotion 7835 in-line density meters or Thermo Scientific ‘s ED900 in-line density meters (loop 3) can be used to monitor oil density. To control the water content in oil, a commercial oil in-line moisture meter VTN-1 or a water-in-oil analyzer of the OW 302 type from AGAR Corp. can be used. Ltd. with an output signal of 4…20 mA (circuits 1 and 21). The control of salt content in the oil sample (circuits 2 and 22) can be determined by salt meters SAN-L, AUM 101, Herzog 5С960 from Walter Herzog GmbH or salt meter 44561 of the PAC group of companies, the characteristics of which are given in Chapter 3.
The distribution of crude oil by flow through the heat exchangers T-1 and T-2 is carried out by flow control with correction by level in the stabilization column of the AT K-1 unit. The oil heating temperature in the T-1-T-3 heat exchangers is controlled by a control circuit, the valve of which is installed on the cooling flow on the bypass of the heat exchangers
The distribution of oil heated to 120 °C along the flows after the T-3 heat exchanger in front of the ED-1 and ED-2 electric dehydrators is carried out by a pressure drop regulator along the flows. Emerson 3051 transmitters complete with a diaphragm seal are used as differential pressure transmitters. Emerson ‘s pneumatic control valves are used as actuators, complete with an electro-pneumatic positioner of the DVC6000 series (4-20 mA/HART).
Regulation of the supply of wash water from the E-5 tank is carried out using flow control circuits.
Saline solution is removed from the electric dehydrator with level control in the electric dehydrators ED-1 and ED-2. The temperature of the salt flow at the outlet of the air cooler is controlled by changing the speed of the fan motor.
A large number of control loops in process automation schemes are cascade control schemes, in which the auxiliary parameter that has the greatest impact on the main output parameter (temperature, level, concentration, etc.) is the flow rate of a liquid or gas, controlled by a pneumatic control valve. The choice of cascade control schemes is due to the fact that in the main circuit when using
pneumatic control valves, there is a delay due to the remoteness of the valves from the place of selection of the main parameter (when using pneumatic lines) and the low speed of valve movement. An auxiliary parameter located in the immediate vicinity of the control valve and which is a disturbance due to a change in pressure or moisture content of a liquid or gas is the flow rate. Thus, the cascade system contains two coupled controllers, one of which (corrective) regulates the main output parameter (for example, temperature, level, etc.) and issues a corrective action to the other controller (stabilizing), which maintains the value of the liquid or gas flow at a given value when disturbances occur (for example, when pressure changes and other uncontrolled parameters).
Other devices and systems can be used as devices, controllers, and distributed I/O systems, a review of which is given in . It also provides information on most foreign and domestic PLCs and distributed control systems.
8.2. Automation of oil refining processes at AT and AVT units
The quality and yields of components of various types of fuel, as well as the quality of raw materials for secondary processes of refining oil fractions and raw materials for petrochemical industries depend on the operation of primary oil distillation units.
The separation of oil into fractions that boil away in different temperature ranges is carried out using the processes of heating, rectification, condensation and cooling. Fractions boiling up to a temperature of 400-420 °C are isolated at atmospheric or slightly elevated pressure, and the residues are isolated under vacuum. AT and AVT installations can be organized according to the scheme of single or double evaporation.
The variety of processed types of oil, the wide range and quality of the products obtained determine the variety of technological schemes. Plants with a preliminary topping column and a main distillation atmospheric column are widely used, which are operable in a wide range of changes in the content of gasoline fractions and dissolved gases in oil.
Superheated steam is used to remove light components from distillate fractions while passing through topping or stripping columns. In some installations, boilers are used for this.
Intermediate circulating irrigation (CH) is widely used in distillation sections of AT and AVT installations. In vacuum columns, a barometric condenser and two- or three-stage ejectors are used to create a vacuum. Two-stage ejector systems provide a vacuum of 6.7 … 13.3 kPa, and three-stage systems – within 6.7 kPa and below.
A high degree of automation has been achieved at the primary oil refining units. Factory plants use automatic in-line analyzers to determine the water and salt content of crude oil, the flash point of aviation kerosene, diesel fuel, oil distillates, the boiling point corresponding to the 90 or 95% light oil sampling point, the viscosity of oil fractions, etc. The steam supply to the bottom of the stripping column is automatically corrected for the flash point of the diesel fuel. Chromatographs are used for automatic continuous determination and registration of the composition of gas flows.
An indicator of the efficiency of the process is the fractional composition of the target products – stable gasoline, kerosene and diesel fractions. The purpose of control is to maintain a given composition of the target products while stabilizing the process parameters: flow rate, temperature, level, pressure. The control criterion is min CKO of process parameters with the maximum selection of target products.
The scheme of automation of the oil distillation process at the AT unit is shown in fig. 8.4.
Desalinated and dehydrated oil from the upper part of the electric dehydrators ED-1 and ED-2 passes in three parallel flows through heat exchangers, being heated by the heat of the atmospheric distillation unit effluents, the heat of the main effluent flows of the vacuum unit and the heat of circulation irrigation of both sections:
• the first flow successively passes through heat exchangers T-4…T-7, where it is heated respectively by the heat of the upper circulating reflux (ERR) of the K-1 topping column, heavy vacuum gas oil, diesel fraction and light vacuum gas oil;
• the second flow successively passes through heat exchangers T-8…T-10, where it is heated, respectively, by the heat of the first circulating reflux (CH I) of the K-2 column, light vacuum gas oil and the second circulating reflux (CH II) of the K-2 column;
• the third flow successively passes through heat exchangers T-11…T-14, where it is heated respectively by the heat of the 1st CH of the K-2 column, diesel fraction, tar and the 2nd CH of the K-2 column.
The consumption of desalted oil in the flows of heat exchangers is controlled by changing the flow of desalted oil (circuits 1, 2 and 3) with valves installed on the oil supply pipelines to the heat exchangers
with pressure correction (loop 4) in the demineralized oil pipeline after the electric dehydrators. The temperature control of the flows at the outlet of the heat exchangers is carried out using the appropriate circuits 5…15.
Then the three oil streams are combined and fed into the T-15 heat exchanger, where they are heated by the heat of heavy vacuum gas oil. The temperature of desalted oil at the outlet of the T-15 heat exchanger is controlled by changing the flow rate through the heat exchanger (circuits 16 and 17).
To protect against corrosion before the heat exchangers for heating desalted oil, a 1-2% aqueous solution of alkali is supplied to each stream. For a good distribution of the alkali solution in the streams, it is recommended to use static mixers.
After the heat exchangers, heated oil with a temperature of 245-255 °C enters the lower part of the K-1 topping column.
From the top of the K-1 topping column, gasoline vapors with dissolved gas and water vapor are taken, which are condensed and cooled in the T-1 crude oil heating heat exchanger, and then enter the E-1 tank. From tank E-1, the gasoline fraction is sent to the tank of total gasoline E-3, and the separated sour water is discharged to the intake of pumps H-13 for pumping out of the unit.
The temperature of the top product after the T-1 heat exchanger is controlled by changing the flow through the heat exchanger with a valve installed on the heat exchanger bypass along the top product of the K-1 topping column (see circuit 3 in Fig. 8.3). The consumption of the gasoline fraction from the tank E-1 is controlled by changing the flow rate of the liquid phase into the tank of the total gasoline E-3 with a correction according to the level in the tank E-1 (circuits 18 and 19). The acid water level in the sedimentation area is maintained by changing the acid water flow rate (loop 20). A constant pH control of acidic water is provided (circuit 21). The pressure in the spray tank E-1 is controlled by discharging the gas phase from the spray tank E-1 into the fuel network to the furnace burners (circuit 22).
Excess heat in the K-1 column is removed by the upper circulating irrigation, which is taken from the K-1 column by the H-3 pumps. The upper circulating irrigation gives off its heat to heat the desalted oil in the T-4 heat exchanger, to heat the crude oil in the T-3 heat exchanger, cools down in the Xv-2 air cooler and returns to the K-1 column on the upper plate.
The temperature on the upper plate is controlled by a cascade circuit with a correction to the flow controller of the upper CH of the topping column K-1 using a valve installed on the VCO line from T-3 of the AT unit (circuits 23 and 24).
The temperature at the outlet of the Khv-2 refrigerator is controlled by changing the speed of the electric motor of the air cooler fans using a frequency converter (circuit 25).
The topped oil from the bottom of the K-1 topping column is taken by the N-2 pumps, heated in the T-16 and T-17 heat exchangers by the heat of heavy vacuum gas oil and tar, and fed into the P-1 topped oil heating furnace.
The level in the K-1 topping column is controlled by a cascade circuit with correction to the oil supply flow rate regulator of the ELOU block using valves installed on the crude oil supply lines to the T-1 and T-2 heat exchangers (see circuits 1 and 2 in Fig. 8.3 and contour 26 in Fig. 8.4).
Heated in the furnace to 370-375 °C, the stripped oil is fed to the K-2 column for rectification. The temperature at the outlet of the P-1 furnace is controlled by a cascade circuit with correction to the fuel gas pressure regulator supplied to the main burners of the P-1 furnace, the valve of which is installed on the fuel gas supply pipeline to the main burners of the P-1 furnace (circuits 27 and 28).
To strip light hydrocarbons, superheated water vapor is supplied to the lower part of the K-2 atmospheric column. The regulation of the flow rate of water vapor is carried out with a correction for the flow rate of fuel oil from column K-2 (circuits 29 and 30).
Gasoline vapors with dissolved gas and water vapor are taken from the top of the column K-2, which are condensed and cooled in the crude oil heating heat exchanger T-2 (see Fig. 8.3), and then enter the spray tank E-2. From the irrigation tank E-2, the gasoline fraction is fed to the intake of pumps H-4, with which it is fed to the column K-2 for irrigation, and the balance excess goes to the tank of the total gasoline E-3. The separated sour water is pumped out from the unit by pumps H-13.
The temperature of the top product after the T-2 heat exchanger is controlled by changing the flow through the heat exchanger with a valve installed on the heat exchanger bypass along the top product of the K-2 topping column (circuit 4 in Fig. 8.3).
The level in the E-2 tank is controlled by a cascade system with a correction to the gasoline fraction flow controller from E-2 using a valve installed on the line for supplying the liquid phase to the total gasoline tank E-3 (circuits 31 and 32).
The temperature on the upper plate of the K-2 column is controlled by a cascade system with correction to the reflux flow rate controller of the fractionating column K-2 using a valve installed on the K-2 reflux line from the H-4 pump (circuits 36 and 37).
The acid water level in the sedimentation area is maintained by changing the acid water flow rate (loop 33). A constant pH control of acidic water is provided (loop 34). The pressure in the irrigation tank E-2 is regulated by the discharge of hydrocarbon gas to the flare (loop 35).
Two side streams are removed from the K-2 column – kerosene fraction 140-220 °C and diesel fraction 180-360 °C. The kerosene fraction with a temperature of 140-220 °C is discharged into the K-3/1 stripping column, from where it is taken by the H-6 pumps and then, after heating the wash water, it is sent to the Khv-6 air cooler, cooled down in the T-20 water cooler and removed from installation. Temperature control at the outlet of the Khv-6 refrigerator is carried out by changing the speed of the electric motor of the fans of the air cooler using a frequency converter (circuit 36). The level of the kerosene fraction in the stripping column K-3/1 is maintained by changing the flow rate of the kerosene fraction from the fractionating column K-2 (loop 48). After the X-20 water cooler, regulation of the flow rate of the kerosene fraction from the plant (loop 39) is provided.