When designing installations for carrying out typical processes of chemical technology, choosing the principle of calculation and the necessary equipment, chemical processes are of primary importance.
Basic processes and apparatuses of chemical technology
All reference data and general information about chemical production are contained in the design manual edited by Yu. I. Dytnersky “Basic processes and apparatuses of chemical technology”.
The guide says:
- about calculations of heat-exchange and mass-exchange devices;
- on the work of evaporator, distillation and adsorption plants;
- on mechanical calculations of the main components and parts of chemical devices;
- about hydraulic calculations.
The publication contains the principles of operation of membrane separation units and data on crystallization.
Types of chemical processes and technologies
For the production of finished products and intermediate substances by means of chemical processing of the starting material, different techniques and appliances. The basis of most operations is the transfer of a substance.
Based on the future purpose and operation, the following types of processes are distinguished:
- hydromechanical are used for the mechanical separation of heterogeneous mixtures of liquids and gases, their purification from solid particles, for example, sedimentation and sedimentation in a centrifuge;
- thermal, which are based on heat transfer (evaporation, condensation, heating, cooling);
- mass transfer consists in the transfer of matter with the joint transfer of momentum and heat (absorption, adsorption);
- chemical and biochemical occur when varying the chemical content and properties (ionic reactions, glycolysis, fermentation).
Technological processes by duration are divided into:
- periodic;
- continuous;
- combined.
Periodic processes proceed inconsistently, as there is a cyclic laying of the starting materials. The joint loading of raw materials and unloading of products characterizes a continuous process. Combined processes consist of two types of operations or several separate stages together.
In chemical production, emphasis is placed on the use of continuous processes that are fully mechanized and controlled by automation. Continuous processes are more practical than batch operations. In a continuous process, due to the constant flow of operations, financial, resource and labor costs are reduced.
Energy- and resource-saving processes in chemical technology
A set of measures for the careful and effective application elements of production is energy and resource saving, which is achieved through the use of various methods:
- reduction of capital intensity and consumption of finished products;
- productivity growth;
- increasing product quality.
Resource-saving measures make it possible to ensure the production of finished products with a minimum use of fuel and other feedstock, components, fuel, air, water and other sources for technological needs.
Resource saving technologies include:
- closed water supply system;
- use of secondary resources;
- waste recycling.
Resource-saving technologies save the use of materials and reduce the impact of harmful production factors on the environment.
Design and calculation of processes and apparatuses of chemical technology
Calculation of chemical equipment and design are carried out in the following sequence:
- the initial data are analyzed, the direction of the process flow is revealed;
- a material balance sheet is drawn up and quantities material flows. The material balance is the identity of the arrival and consumption of mass flows of elements in one equipment;
- based on the heat balance, determine the heat consumption in the reaction or the flow rate of heat carriers. The heat balance represents the equality of the incoming and outgoing heat flows in the equipment;
- the driving force of the process is determined based on the law of equilibrium;
- the speed coefficient K is calculated, which is inversely proportional to the resistance of the corresponding operation;
- the size of the apparatus is calculated according to the main kinetic regularity. This size most often accounts for the surface of the device. According to the calculated value, using special catalogs or normals, the nearest standard size of the designed equipment is selected.
Companies with chemical process research groups
Companies from research groups chemical processes are large organizations with a large staff of chemical experts. One such organization is Modcon Systems, which develops products, maintains a technical policy to support all types of research activities, and also performs integrated process optimization in the field of oil refining, pipelines, biotechnology and chemistry.
The laboratory complex of the scientific and engineering center of the Mirrico Group of Companies includes research and testing laboratories that develop new types of products and technologies for various purposes.
SRC GC "Mirrico" includes the following industry research laboratories (SRL):
- Research Laboratory "Reagents for drilling and production";
- Research Laboratory of the Mining Division;
- Research Laboratory of Oil and Gas Processing and Petrochemistry "Processes";
- Research Laboratory “Drilling Fluids and Technologies”;
- NIL "Water".
Manufacturers of chemical apparatus
For implementation chemical transformations in the petrochemical sector, chemical reactors and apparatuses are needed. A chemical reactor is a three-walled apparatus that is under pressure or vacuum with different methods heating, has high-speed and low-speed agitators. Based on the value of the heating temperature and the need to control it, the coolant is selected.
The YuVS plant is engaged in the development and manufacture of reactors of various designs, based on the reaction discharge in the equipment, physical condition components, the required mode of heat, pressure, volume, nature of the process flow. In order to accelerate the thermal and mass transfer process, the reactors are equipped with additional elements that are stirred. The quality of the manufactured equipment is strictly controlled due to high technology security. Mechanical strength, resistance to corrosive action of the processed raw materials and the corresponding physical characteristics are the requirements for chemical reactors.
Another company, SibMashPolymer LLC, calculates and manufactures chemical reactors, and also gives guarantees for the high quality of the manufactured devices. The company carries out tests of its products in a laboratory equipped with radiographic control of devices.
The industrial association "Khimstroyproekt" produces energy-saving and heat exchangers, according to the criteria of the Technical Regulations of the Customs Union "On the safety of equipment operating under excessive pressure" (TR CU 032/2013).
REFERENCES 1. Kasatkin AG Basic processes and apparatuses of chemical technology. Ed. 9th, M.: Chemistry. 1973 - 754 p. 2. Planovsky A. N., Nikolaev P. I. Basic processes and apparatuses of chemical and petrochemical technology. Ed. 2nd, M.: Chemistry. 1972 - 493 p. 3. Basic Processes and Apparatuses of Chemical Technology: Design Manual / G. S. Borisov, V. P. Brykov, Yu. I. Dytnersky et al. Ed. Yu. I. Dytnersky. Ed. 2nd, M.: Chemistry. 1991 - 496 p. 4. Aksartov M. M. Basic processes and apparatuses of chemical technology. Lecture course. Ed Kar. GU in 1-2 t.
General principles of analysis and calculation of processes and apparatuses I. General information 1. Subject of the course "Processes and apparatuses" 2. The emergence and development of the science of processes and apparatuses 3. Classification of the main processes 4. General principles of analysis and calculation of processes and apparatuses 5. Various systems units of measurement physical quantities
Classification of the main processes n n n Hydromechanical processes, the speed of which is determined by the laws of hydrodynamics - the science of the movement of liquids and gases. Thermal processes proceeding at a speed determined by the laws of heat transfer - the science of the methods of heat distribution. Mass transfer (diffusion) processes characterized by the transfer of one or more Chemical (reaction) processes that proceed at a rate determined by the laws of chemical kinetics. components of the initial mixture from one phase to another through the interface. Mechanical processes described by the laws of solid mechanics.
According to the method of organization, the processes are divided into: 1. 2. 3. Periodic processes are carried out in apparatuses into which raw materials are loaded at certain intervals; after their processing, the final products are unloaded from these devices. Continuous processes are carried out in flow devices. Combined processes. These include continuous processes, the individual stages of which are carried out periodically, or periodic processes, one or more stages, which proceed continuously.
According to the distribution of residence times, they distinguish: 1. 2. 3. 4. In ideal displacement apparatuses, all particles move in a given direction; without mixing with the particles moving in front and behind and completely displacing the particles in front of the stream. In ideal mixing apparatuses, incoming particles are immediately completely mixed with the particles located there, i.e., they are evenly distributed in the volume of the apparatus. Real continuously operating devices are devices of an intermediate type. Processes can also be classified depending on the change in their parameters (velocities, temperatures, concentrations, etc.) over time. On this basis, the processes are divided into steady (stationary) and non-steady (non-stationary, or transitional).
hydromechanical processes. II. Fundamentals of hydraulics. General issues applied hydraulics in chemical equipment 1. Basic definitions 2. Some physical properties liquids A. Hydrostatics 3. Euler differential equations of equilibrium 4. Basic equation of hydrostatics 5. Some practical applications of the basic equation of hydrostatics
n Newton's law of internal friction Surface tension expressed in the following units: in the SI system [ν] \u003d [j / m 2] \u003d [n m / m] \u003d [n / m] in the CGS system] \u003d erg / cm 2] \u003d [dyn / cm 2] in system MKGSS] \u003d kgf m / m 2] \u003d kgf / m]
For each point of a fluid at rest, the sum of the leveling height and the piezometric head is a constant value. (II, 18) (II, 18 d) n The last equation is an expression of Pascal's law, according to which the pressure created at any point of an incompressible fluid at rest is transferred equally to all points of its volume.
Some practical applications of the basic equation of hydrostatics Equilibrium conditions in communicating vessels: Fig. II-4. Equilibrium conditions in communicating vessels: a - homogeneous liquid; b - dissimilar (immiscible) liquids
In open or closed communicating vessels under the same pressure, filled with a homogeneous liquid, its levels are located at the same height, regardless of the shape and cross section of the vessels
Rice. II-5. To determine the height of the hydraulic seal in a continuously operating liquid separator Fig. II-6. Pneumatic liquid level gauge
HYDROMECHANICAL PROCESSES. B. Hydrodynamics 1. The main characteristics of the movement of liquids 2. The equation of continuity (continuity) of the flow 3. The Euler differential equations of motion 4. The differential equations of motion of the Navier-Stokes 5. The Bernoulli equation 6. Some practical applications of the Bernoulli equation 7. The motion of bodies in liquids 8. Movement of liquids through stationary granular and porous layers 9. Hydrodynamics of fluidized (fluidized) granular layers 10. Elements of hydrodynamics of two-phase flows 11. Structure of flows and distribution of liquid residence time in apparatuses
Hydraulic radius Under the hydraulic radius r (m) is understood the ratio of the area of the flooded section of the pipeline or channel through which the liquid flows, i.e., the living section of the flow, to the wetted perimeter: (II, 26)
The equivalent diameter is equal to the diameter of a hypothetical circular pipeline, for which the ratio of the area S to the wetted perimeter P is the same as for a given non-circular pipeline.
Steady and unsteady flows. The movement of a fluid is steady, or stationary, if the speeds of the flow particles, as well as all other factors affecting its movement (density, temperature, pressure, etc.), do not change in time at each fixed point in space through which the fluid passes. Under these conditions, for each flow section, the flow rates of the liquid are constant in time.
Modes of fluid motion. n n The movement, in which all particles of the liquid move along parallel trajectories, is called jet, or laminar. Disordered motion, in which individual particles of a fluid move along intricate, chaotic trajectories, while the entire mass of fluid as a whole moves in one direction, is called turbulent.
Reynolds Criterion (Re) n The Re Criterion is a measure of the relationship between the forces of viscosity and inertia in a moving stream.
Stokes' law The equation is Stokes' law, which expresses the parabolic distribution of velocities in the pipeline section during laminar motion.
Poiseuille equation n For laminar flow in a pipe average speed liquid is equal to half the velocity along the axis of the pipe.
Turbulent viscosity n Turbulent viscosity, unlike ordinary viscosity, is not a physicochemical constant determined by the nature of the liquid, its temperature and pressure, but depends on the liquid velocity and other parameters that determine the degree of flow turbulence (in particular, the distance from the pipe wall and etc.).
Differential equation of flow continuity for unsteady motion of a compressible fluid. Differential equation for the continuity of an incompressible fluid flow.
Flow constant equation n These expressions represent the flow continuity (density) equation in its integral form for steady motion. This equation is also called the constant flow equation or material flow balance. 1 w 1 S 1 = 2 w 2 S 2 = 3 w 3 S 3 M 1 = M 2 = M 3 n w 1 S 1 = w 2 S 2 = w 3 S 3 = const Q 1 = Q 2 = Q 3
Euler's differential equations of motion n The system of equations (II, 46), taking into account expressions (II, 47), is differential equations movements ideal fluid Euler for steady flow. (II, 46) (II, 47)
Bernoulli's equation n n Bernoulli's equation for an ideal fluid The quantity is called the total hydrodynamic head, or simply the hydrodynamic head.
Therefore, according to the Bernoulli equation, for all cross sections of a steady flow of an ideal fluid, the hydrodynamic head remains unchanged. z - leveling height, also called geometric, or height, pressure (hg), represents the specific potential energy of the position at a given point (a given section); – pressure head (hpress), or piezometric head, characterizes the specific potential energy of pressure at a given point (a given section). The sum z+, called the total hydrostatic, or simply static head (hst), therefore, expresses the total specific potential energy at a given point (a given section).
Bernoulli's equation n n Thus, according to Bernoulli's equation, in the steady motion of an ideal fluid, the sum of velocity and static heads, equal to the hydrodynamic head, does not change when moving from one flow cross section to another. Thus, the Bernoulli equation is a special case of the law of conservation of energy and expresses the energy balance of the flow.
LIQUID HANDLING n 1. 2. 3. 4. 5. Liquid Handling Displacement pumps Displacement pump design Centrifugal pumps Centrifugal pump design Other types of pumps. Siphons
MOVEMENT OF LIQUIDS Depending on the principle of operation of the pump, an increase in the energy and pressure of the liquid can be carried out: 1. in positive displacement pumps, by displacing the liquid from the closed space of the pump by bodies moving reciprocating or rotating; 2. in vane or centrifugal pumps - the centrifugal force that occurs in the liquid during the rotation of the impellers; 3. in vortex pumps - intensive formation and destruction of vortices that occur during the rotation of the impellers; 4. in jet pumps - by a moving jet of air, steam or water; 5. in gas lifts - the formation of foam when air or gas is supplied to the liquid; 6. in installations and siphons - by air, gas or steam pressure on the liquid.
Rice. III-8. valve designs. I - ball valve. 1 - body; 2 - valve; 3 - cover. II - flap valve. 1 - cover; 2 - saddle.
Diaphragm (diaphragm) pumps Fig. III-9. Diaphragm pump: 1 - housing; 2 - valves; 3 - cylinder; 4 - plunger; 5 - diaphragm (membrane).
Centrifugal pumps III-13 Fig. III-13. Scheme of a centrifugal pump: 1 - inlet valve; 2 - suction pipeline; 3 – impeller; 4 - shaft; 5 - body; 6 - valve; 7 - check valve; 8 - discharge pipeline.
Types of stuffing boxes n n I – stuffing box with hydraulic seal: 1 – lantern; 2 - stuffing box. II - stuffing box for acids: 1, 2 - annular cavities; 3, 4 - outlet holes. III - spring gland: 1 - gasket; 2 - spring.
Sealless pump n 1 body, 2 - cover, 3 - impeller, 4 - casing sleeve, 5 - shaped sleeve, 6 - sleeve, 7 - left disk, 8 - stud, 9 - right disk, 10 - tie rod, 11 - spring, 12 - shaft, 13, 14 - rings.
Monteju. Rice. III-8. Monteju: 1 - filling pipe; 2, 3, 4, 5, 8 - cranes; 6 - manometer; 7 - pipes for squeezing
Jet pumps. Steam pump. Rice. III-22. Steam pump. 1 - steam fitting; 2 - steam nozzle; 3 - mixing nozzle; 4 - suction chamber; 5 - suction fitting; 6 - diffuser; 7 - discharge fitting; 8 - condensate fitting; 9, 10 - check valves.
Water jet pump. III-22 Fig. III-22. Water jet pump. 1 - nozzle; 2 - hole; 3 - suction pipeline; 4 1 - nozzle; 2 - hole; 3 - suction fitting pipeline; 4 - fitting III-23
Air lift diagram Fig. III-24. Scheme of the air lift: 1, 2 - pipes; 3 - mixer; 4 - separator III-24
Air lifts (airlifts) and siphons Fig. III-25. Air lift systems 1 - air pipe; 2 - supply pipe for the mixture; 3 - mixer. Rice. III-26. Siphons. 1 - tank; 2 - siphon pipe; 3, 4, 5 - cranes, 6 - viewing channel
Movement and compression of gases (compressor machines) n n n n 1. General information 2. Reciprocating compressors 3. Rotary compressors and blowers 4. Centrifugal machines 5. Axial fans and compressors 6. Screw compressors 7. Vacuum pumps 8. Comparison and applications of compressor machines various types
MOVEMENT AND COMPRESSION OF GASES (COMPRESSOR MACHINES) n n n n General information Machines designed to move and compress gases are called compressor machines. Depending on the degree of compression, the following types of compressor machines are distinguished: fans (3. 0) - to create high pressures; vacuum pumps - for suction of gases at a pressure below atmospheric.
Reciprocating compressors n Single stage horizontal compressor simple action Rice. IV-1. Schemes of single-stage reciprocating compressors: a - single-cylinder single-acting; b - single-cylinder double action; in - two-cylinder single action. 1 = cylinder; 2 - piston; 3 - suction valve; 4 - discharge valve; 5 - connecting rod; 6 - crank; 7 - flywheel; 8 - slider (crosshead)
Multistage compression. Rice. IV-2. Schemes of multistage reciprocating compressors. a, b, c - with compression stages in separate cylinders (a - simultaneous execution; b - two-row execution; c - with a V-shaped arrangement of cylinders); g - with a differential piston: 1 - cylinder; 2 - piston; 3 - suction valve; 4 - discharge valve; 5 - connecting rod; 6 - slider (crosshead); 7 - crank; 8 - flywheel; 9 - intermediate cooler.
Turboblowers. Rice. IV-8. Scheme of a multistage turboblower. 1 - body; 2 - impeller; 3 - guide apparatus; 4 - check valve. Rice. IV-9. Entropy diagram of gas compression in a turbo blower
Separation of inhomogeneous systems V. Separation of inhomogeneous systems 1. Inhomogeneous systems and methods for their separation 2. Separation of liquid systems 2. Material balance of the separation process Filtration baffles 7. Filter arrangement
Continuous settler Fig. IV-3. Settling tank of continuous action with a row mixer 1 – body; 2 - annular chute; 3 - mixer; 4 - blades with strokes; 5 - pipe for supplying the initial suspension; 6 - fitting for the output of clarified liquid; 7 - unloading device for sediment (sludge); 8 - electric motor.
Rice. V-6. Settler of continuous action with conical shelves; 1 - fitting for supplying the suspension to be separated; 2 - conical shelves; 3 - fitting for sludge removal; 4 - channels for draining the clarified liquid; 5 - fitting for the output of clarified liquid
Rice. V-7. Continuous settling tank for separation of suspensions. 1 - fitting for supplying emulsions; 2 - perforated partition; 3 - pipeline for removal of the light phase; 4 - pipeline for removal of the heavy phase; 5 device for breaking the siphon.
B. FILTRATION V-8. Scheme of the filtration process. 1 - filter; 2 - filtering partition; 3 suspension; 5 sediment
Filter arrangement Fig. V-10. Nutsch working under pressure up to 3 atm. 1 - body; 2 - turbine; 3 - removable cover; 4 - filtering bottom; 5 - filtering partition; 6 - supporting partition; 7 - protective mesh; 8 - annular partition; 9 - fitting for supplying the suspension; 10 - fitting for supplying compressed air; 11 - fitting for removing the filtrate; 12 - safety valve
drum filters. Rice. V-13. Scheme of operation of a drum vacuum filter with outer surface filtering. 1 - drum; 2 - connecting tube; 3 - switchgear; 4 - tank for suspension; 5 - rocking mixer; 6, 8 - cavities of the switchgear; 7 - spraying device; 9 - endless tape; 10 - guide roller; 11, 13 - cavities of the switchgear communicating with the source of compressed air; 12 - knife for removing sediment.
B. Centrifugation D. Separation gas systems(gas cleaning) VI. Mixing in liquid media B. Centrifugation 1. Basic provisions 2. Design of centrifuges D. Separation of gas systems (gas purification) 1. General information 2. Gravitational gas purification 3. Gas purification under the action of inertial and centrifugal forces 4. Gas purification by filtration 5. Wet gas scrubbing 6. Electric gas scrubbing VI. Stirring in liquid media 1. General information 2. Mechanical stirring 3. Mechanical stirring devices
The device of centrifuges n Three-column centrifuges. Rice. V-14. Three-column centrifuge. 1 – perforated rotor; 2 - support cone; 3 - log; 4 - the bottom of the frame; 5 fixed casing; 6 - casing cover; 7 - bed; 8 - thrust; 9 - column; 10 - hand brake.
Hanging centrifuges. Rice. V-15. Hanging centrifuge. 1 - pipeline for supplying the suspension; 2 – rotor with solid walls; 3 - shaft; 4 - fixed casing; , 5 liquid removal fitting; 6 - conical cover; 7 - connecting ribs
Horizontal centrifuges with a knife device for sediment removal. Rice. V-16. Horizontal centrifuge with blade for sediment removal. 1 – perforated rotor; 2 - pipe for supplying the suspension; 3 - casing; 4 - fitting for centrate removal; 5 - knife; 6 - hydraulic cylinder for lifting the knife; 7 inclined chute; 8 - channel for sediment removal
Centrifuges with pulsating piston for sludge discharge. Rice. V-17. Centrifuge with pulsating piston for sludge discharge. 1 - pipe for the intake of the suspension; 2 conical funnel; 3 – perforated rotor; 4 - metal slotted sieve; 5 - piston; 6 - fitting for centrate removal; 7 - channel for sediment removal; 8 - stock; 9 - hollow shaft; 10 - a disk moving back and forth
Centrifuges with a screw device for unloading sediment. Rice. V-18. Centrifuge with screw device for unloading sediment. 1 - outer pipe; 2, 4 - hole for the passage of the suspension; 3 - inner pipe; 5 - conical rotor with solid walls; 6 - cylindrical base of the screw; 7 - auger; 8 - casing; 9 - hollow pins; 10 - holes for sediment passage; 11 - sediment chamber; 12 - hole for passage of the centrate; 13 – centrate chamber.
Centrifuges with inertial sludge discharge. Rice. V-19. Centrifuge with inertial unloading of sediment. 1 - funnel for the receipt of the suspension; 2 - rotor; 3 - channel for removal of the liquid phase; 4 - channel for removing the solid phase; 6 - auger.
Liquid separators. Rice. V-20. Disk type liquid separator. 1 - pipe for supplying the emulsion; 2 - plates; 3 - hole for draining a heavier liquid; 4 - holes for draining a lighter liquid; 5 - ribs.
1. 2. 3. 4. 5. SEPARATION OF GAS SYSTEMS (PURIFICATION OF GAS) The following methods of gas purification are distinguished: sedimentation under the action of gravity (gravitational purification); sedimentation under the action of inertial, in particular centrifugal forces; filtration; wet cleaning; deposition under the action of electrostatic forces (electric
Gravitational gas cleaning Dust settling chambers. Rice. V-21. Dust chamber. 1 - camera; 2 - horizontal partitions (shelves); 3 reflective baffle; 4 - doors.
Purification of gases under the action of inertial and centrifugal forces Inertial dust collectors. Rice. V-22. Inertial louvered dust collector. 1 - primary louvered dust collector; 2 - cyclone; 3 - branch pipes for purified gas; 5 - dust outlet pipe.
Cyclone Fig. V-23. Cyclone design NIIOgaz. 1 - body; 2 - conical bottom; 3 - cover: 4 - inlet pipe; 5 - dust collector; 6 - exhaust pipe.
Battery cyclone V-24. V-25. Rice. V-26. Element of a direct-flow battery cyclone. 1 - twisting device; 2 inlet pipe; 3 - annular slotted gap; 4 - exhaust pipe.
Purification of gases by filtration Depending on the type of filter partition, the following filters for gases are distinguished: a) with flexible porous partitions made of natural, synthetic and mineral fibers (fabric materials), non-woven fibrous materials (felt, cardboard, etc.), porous sheet materials rubber, polyurethane foam, etc.), metal fabrics; b) with semi-rigid porous partitions (layers of fibers, shavings, nets); c) with rigid porous partitions made of granular materials (porous ceramics, plastics, sintered or pressed metal powders, etc.); d) with granular layers of coke, gravel, quartz sand, etc.
Filters with flexible porous partitions. Rice. V-27. Bag filter with mechanical shaking and fabric back blowing. I-IV - filter sections; 1, 9 - fans; 2 - inlet gas duct; 3 - camera; 4 - sleeves; 5 - distribution grid; 6, 8 - throttle valves; 7 - exhaust pipe; 10 - shaking mechanism; 11 - frame; 12 - auger; 13 - sluice.
Filters with rigid porous baffles Sintered filter Fig. V-28. Metal-ceramic filter. 1 - body; 2 - metal sleeves; 3 - lattice; 4 - inlet fitting; 5 - outlet fitting; 6 – compressed air collector; 7 - bunker.
Filters with granular layers. Rice. V-29. Continuous filter with a moving layer of granular filter material. 1 - body; 2 - filtering partition; 3 - filtering material; 4 inlet fitting; 5 - outlet fitting; 6 - shutters; 7 - feeders.
V-34
MIXING IN LIQUID MEDIA Mixing methods. Regardless of which medium is mixed with a liquid - gas, liquid or solid bulk substance - there are two main methods of mixing in liquid media: mechanical (using mixers of various designs) and pneumatic (compressed air or inert gas). In addition, mixing in pipelines and mixing with nozzles and pumps are used.
Preface.
The discipline "Processes and Apparatuses of Chemical Technology" (PACT) is one of the fundamental general engineering disciplines. It is the final in the general engineering training of the student and fundamental in the special training.
The production technology of a variety of chemical products and materials includes a number of similar physical and physical and chemical processes, characterized by common patterns. These processes in various industries are carried out in devices similar in principle of operation. Processes and devices common to different industries chemical industry, received the name of the main processes and apparatuses of chemical technology.
The PAH discipline consists of two parts:
· theoretical bases of chemical technology;
· typical processes and devices of chemical technology;
The first part outlines the general theoretical patterns of typical processes; fundamentals of the methodology of the approach to solving theoretical and applied tasks; analysis of the mechanism of the main processes and identification of general patterns of their course; generalized methods of physical and mathematical modeling and calculation of processes and devices are formulated.
The second part consists of three main sections, the content of which reveals the applied engineering issues of the fundamentals of chemical technology:
· hydromechanical processes and devices;
thermal processes and devices;
Mass transfer processes and devices.
In these sections, theoretical substantiations of each typical technological process are given, the main designs of apparatuses and the methodology for their calculation are considered. Lectures, laboratory and practical classes, course design, independent work of students and general engineering production practice provide the acquisition of knowledge, skills and abilities necessary both for further education and for work in production.
Introduction.
1.1 Subjects and objectives of the course.
Technology (techne-art, craftsmanship) is a set of methods of processing, manufacturing, changing the state, properties, form of raw materials, material or semi-finished products in the production process.
The study of technological processes is the subject course. Technology, like science, determines the conditions practical application laws of natural sciences (physics, chemistry, mechanics, etc.) for the most efficient implementation of various technological processes. Technology is directly related to production, and production is constantly in a state of change and development.
The main objective of the course: to identify the general patterns of the processes of transfer and preservation of various substances; development of methods for calculating technological processes and apparatus for their implementation; familiarization with the designs of devices and machines, their characteristics.
As a result of mastering the discipline, students should know:
1. Theoretical foundations of the processes of chemical technology; laws; describing them; the physical essence of the processes, schemes of installations; design of devices and the principle of their work; methodology for calculating processes and apparatuses, including using a computer.
2. Principles of modeling and large-scale transition, the correct choice of equipment for carrying out the corresponding processes and the possibility of their intensification.
3. Modern achievements science and technology in the field of chemical technology.
Skills that students should master:
1. Apply correctly theoretical knowledge when solving specific problems of reasonable choice:
a) the design of apparatus for carrying out certain processes;
b) operating parameters of the devices;
c) schemes for conducting processes.
2. Independently carry out calculations of devices.
3. Independently work on laboratory research facilities, process experimental data, obtain empirical dependencies, analyze calculation methods.
4. Design standard processes and apparatuses, use technical literature and GOSTs, fill out technical documentation in accordance with ESKD.
1.2 Classification of the main processes of chemical technology.
Modern chemical technology studies the processes of production of various acids, alkalis, salts, mineral fertilizers, oil refinery products and hard coal, organic compounds, polymers, etc. However, despite the huge variety of chemical products, their production is associated with a number of similar processes (moving liquids and gases, heating and cooling, drying, chemical interaction, etc.). So, depending on the laws that determine the speed of the processes, they can be combined into the following groups:
1. Hydromechanical processes, the speed of which is determined by the laws of hydromechanics. This includes the transportation of liquids and gases, the production and separation of heterogeneous systems, etc.
2. Thermal processes, the rate of which is determined by the laws of heat transfer (cooling and heating of liquids and gases, condensation of vapors, boiling of liquids, etc.).
3. Mass transfer processes, the rate of which is determined by the laws of mass transfer from one phase to another through the phase interface (absorption, adsorption, extraction, distillation of liquids, drying, etc.)
4. Chemical processes, the speed of which is determined by the laws of chemical kinetics.
5. Mechanical processes that are described by the laws of solid mechanics (grinding, sorting, mixing of solid materials, etc.).
The listed processes form the basis of most chemical industries and therefore are called the main (typical) processes of chemical technology.
PAKhT studies the first three groups, the fourth group studies the OHT discipline, the fifth group - the subject special disciplines profiling departments.
Depending on whether the process parameters (flow rates, temperature, pressure, etc.) change or do not change in time, they are divided into stationary(established) and non-stationary(unsettled). If we denote any parameter by U, then:
Stationary process U(x,y,z)
Non-stationary process U(x,y,z,t)
batch process characterized by the unity of the place of its individual stages. The process is non-stationary.
Continuous process characterized by the unity of the time of the course of all its stages. The process is steady (stationary).
Meet combined processes - separate stages are carried out continuously, separate periodically.
However, the PAKhT course is not built as a presentation of the individual groups listed above. The general theoretical foundations of chemical technology are studied separately, then typical processes and apparatuses of chemical technology are described.
1.3 Continuity hypothesis.
A liquid medium fills one or another volume without any free spaces, in a continuous manner, or is a continuous medium. When describing such media, it is assumed that they consist of particles. Moreover, a particle of a continuous medium does not mean any arbitrarily small part of its volume, but a very small part of it, containing billions of molecules inside. In the general case, the minimum price of division of the macroscopic scale of the spatial Δl or time Δt coordinates should be small enough to neglect the change in macroscopic physical quantities within Δl or Δt, and large enough to neglect fluctuations of microscopic quantities obtained by averaging these quantities over time Δt or particle volume Δl 3 . The choice of the minimum scale division price is determined by the nature of the problem being solved.
The movement of macroscopic volumes of the medium leads to the transfer of mass, momentum and energy.
Classification of the main processes and apparatuses of chemical technology
depending from patterns characterizing the flow, the processes of chemical technology are divided into five main groups.
1. Mechanical processes , whose speed is related to the laws of solid state physics. These include: grinding, classification, dosing and mixing of solid bulk materials.
2. Hydromechanical processes , the flow rate of which is determined by the laws of hydromechanics. These include: compression and movement of gases, movement of liquids, solid materials, sedimentation, filtration, mixing in the liquid phase, fluidization, etc.
3. Thermal processes , the flow rate of which is determined by the laws of heat transfer. These include processes: heating, evaporation, cooling (natural and artificial), condensation and boiling.
4. Mass transfer (diffusion) processes , the intensity of which is determined by the rate of transition of a substance from one phase to another, i.e. the laws of mass transfer. Diffusion processes include: absorption, rectification, extraction, crystallization, adsorption, drying, etc.
5. Chemical processes associated with the transformation of substances and changes in their chemical properties. The rate of these processes is determined by the laws of chemical kinetics.
In accordance with the listed division of processes, chemical apparatuses are classified as follows:
– grinding and classifying machines;
– hydromechanical, thermal, mass transfer devices;
- equipment for the implementation of chemical transformations - reactors.
By organizational and technical structure processes are divided into periodic and continuous.
AT batch process individual stages (operations) are carried out in one place (apparatus, machine), but in different time(fig.1.1). AT continuous process (Fig. 1.2) separate stages are carried out simultaneously, but in different places (devices or machines).
Continuous processes have significant advantages over periodic ones, consisting in the possibility of specializing equipment for each stage, improving the quality of the product, stabilizing the process over time, ease of regulation, automation, etc.
When carrying out processes in any of the listed devices, the values of the parameters of the processed materials change. The parameters characterizing the process are pressure, temperature, concentration, density, flow rate, enthalpy, etc.
Depending on the nature of the movement of flows and changes in the parameters of substances entering the apparatus, all apparatuses can be divided into three groups: ideal (complete )confusion , devices ideal (complete )displacement and devices intermediate type .
It is most convenient to demonstrate the features of the flow of various structures using the example of continuous heat exchangers of various designs. Figure 1.3, a shows a diagram of a heat exchanger operating on the principle of ideal displacement. It is assumed that in this apparatus there is a "piston" flow without mixing. The temperature of one of the coolants varies along the length of the apparatus from the initial temperature to the final temperature as a result of the fact that subsequent volumes of liquid flowing through the apparatus do not mix with the previous ones, completely displacing them. The temperature of the second coolant is assumed to be constant (condensing steam).
In the device perfect mixing subsequent and previous volumes of liquid are ideally mixed, the temperature of the liquid in the apparatus is constant and equal to the final one (Fig. 1.3, b).
In real apparatuses, neither the conditions of ideal mixing nor ideal displacement can be provided. In practice, only a fairly close approximation to these schemes can be achieved, so real devices are intermediate devices (Fig. 1.3, c).
Rice. 1.1. Batch Process Apparatus:
1 - raw materials; 2 - finished product; 3 - steam; 4 - condensate; 5 - cooling water
Rice. 1.2. Apparatus for carrying out a continuous process:
1 - heat exchanger-heater; 2 - apparatus with a stirrer; 3 - heat exchanger-refrigerator; I - raw material; II - finished product; III - steam; IV - condensate;
V - cooling water
Rice. 1.3. Temperature change during liquid heating in apparatuses of various types: a - complete displacement; b - complete mixing; c - intermediate type
The driving force of the considered process of heating the liquid for any element of the apparatus is the difference between the temperatures of the heating steam and the heated liquid.
The difference in the course of processes in each of the types of apparatus becomes especially clear if we consider how the driving force of the process changes in each of the types of apparatus. From the comparison of the graphs it follows that the maximum driving force takes place in the devices of complete displacement, the minimum - in the devices of complete mixing.
It should be noted that the driving force of processes in continuously operating ideal mixing apparatus can be significantly increased by dividing the working volume of the apparatus into a number of sections.
If the volume of an ideal mixing apparatus is divided into n apparatuses and the process is carried out in them, then the driving force will increase (Fig. 1.4).
With an increase in the number of sections in ideal mixing devices, the value of the driving force approaches its value in ideal displacement devices, and when large numbers sections (of the order of 8–12), the driving forces in the devices of both types become approximately the same.
Rice. 1.4. Changing the driving force of the process during sectioning