Depending on the method of heat transfer, there are two main groups of heat exchangers:
1) surface heat exchangers, in which heat transfer between heat-exchanging media occurs through the heat exchange surface separating them - a blank wall;
2) mixing heat exchangers, in which heat is transferred from one medium to another when they are in direct contact.
Regenerative heat exchangers are used much less frequently in the chemical industry, in which heating of liquid media occurs due to their contact with previously heated solids - a nozzle that fills the apparatus, periodically heated by another coolant.
Surface heat exchangers are the most common, and their designs are very diverse. Below are considered typical, mostly normalized, designs of surface heat exchangers and common mixing condensers.
Chemical technology uses heat exchangers made from a wide variety of metals (carbon and alloy steels, copper, titanium, tantalum, etc.), as well as from non-metallic materials, such as graphite, Teflon, etc. The choice of material is dictated mainly by its corrosion resistance and thermal conductivity , and the design of the heat exchanger significantly depends on the properties of the selected material.
The designs of heat exchangers should be simple, easy to install and repair. In some cases, the design of the heat exchanger must ensure the least possible contamination of the heat exchange surface and be easily accessible for inspection and cleaning.
Tubular heat exchangers
Shell and tube heat exchangers. These heat exchangers are among the most commonly used surface heat exchangers. In Fig. VSH-11 A shows a shell-and-tube heat exchanger of rigid construction, which consists of a housing, or casing 1, and tube sheets welded to it 2. A bundle of tubes is fixed in the tube sheets 3. Covers are attached to the tube sheets (on gaskets and bolts) 4.
In a shell-and-tube heat exchanger, one of the heat-exchanging media I moves inside the pipes (in the pipe space), and the other II- in the interpipe space.
The media are usually directed countercurrent to each other. In this case, the heated medium is directed from bottom to top, and the medium that gives off heat is directed in the opposite direction. This direction of movement of each medium coincides with the direction in which this medium tends to move under the influence of changes in its density when heated or cooled.In addition, with the indicated directions of media movement, a more uniform distribution of velocities and identical heat transfer conditions over the cross-sectional area of the apparatus are achieved. Otherwise, for example, when a colder (heated) medium is supplied from above the heat exchanger, the more heated part of the liquid, being lighter, can accumulate in the upper part of the apparatus, forming “stagnant” zones.
Pipes in lattices are usually evenly placed along the perimeters of regular hexagons, i.e., along the vertices of equilateral triangles (Fig. VIII-12, a), less often they are placed in concentric circles (Fig. VIII-12, b).
In some cases, when it is necessary to ensure convenient cleaning of the outer surface of the pipes, they are placed along the perimeter of the rectangles (Fig. VIII-12, c). All these methods pipe placements pursue one goal - to ensure the most compact placement of the required heat exchange surface inside the apparatus. In most cases, the greatest compactness is achieved by placing the tubes along the perimeters of regular hexagons.
Rice. VIII -12. Methods for placing pipes in heat exchangers:
a - along the perimeters of regular hexagons; b - along concentric circles;
V- along the perimeters of rectangles (corridor arrangement)
The heat exchanger shown in Fig. VIII-11, A, is one-way. At relatively low fluid flow rates, the speed of its movement in the pipes of such heat exchangers is low and, consequently, the heat transfer coefficients are low. To increase the latter for a given heat exchange surface, the diameter of the pipes can be reduced, correspondingly increasing their height (length). However, heat exchangers of small diameter and considerable height are inconvenient for installation, require high premises and increased metal consumption for the manufacture of parts not directly involved in heat exchange (device casing). Therefore, it is more rational to increase the heat transfer rate by using multi-pass heat exchangers.
In a multi-pass heat exchanger (Fig. VIII-11, b) housing 1, tube sheets 2, pipes reinforced in them 3 and lids 4 identical to those shown in Fig. VIII-11, A. With the help of transverse partitions 5 installed in the heat exchanger covers, the pipes are divided into sections, or passages, along which the liquid flowing in the pipe space of the heat exchanger sequentially moves. Typically, the division into passages is carried out in such a way that all sections contain approximately the same number of pipes.
Due to the smaller total cross-sectional area of the pipes placed in one section compared to the cross-section of the entire tube bundle, the fluid speed in the pipe space of a multi-pass heat exchanger increases (relative to the speed in a single-pass heat exchanger) by a number of times equal to the number of passes. Thus, in a four-pass heat exchanger (Fig. VIII-11, b), the speed in the pipes, other things being equal, is four times greater than in a single-pass one. To increase the speed and lengthen the path of movement of the medium in the annulus (Fig. VIII-11, b) serve as segmental partitions 6. In horizontal heat exchangers, these partitions are also intermediate supports for the tube bundle.
An increase in heat exchange intensity in multi-pass heat exchangers is accompanied by an increase in hydraulic resistance and a more complex design of the heat exchanger. This dictates the choice of an economically feasible speed, determined by the number of heat exchanger strokes, which usually does not exceed 5-6. Multi-pass heat exchangers operate on the principle of mixed current, which, as is known, leads to a slight decrease in the driving force of heat transfer compared to the purely countercurrent movement of the media involved in heat exchange. In single-pass and especially multi-pass heat exchangers, heat transfer can deteriorate due to the release of air and other non-condensable gases dissolved in the liquid (or steam). For their periodic removal, purge taps are installed in the upper part of the heat exchanger casing.
Single-pass and multi-pass heat exchangers can be vertical or horizontal. Vertical heat exchangers are easier to operate and occupy a smaller production area. Horizontal heat exchangers are usually made multi-pass and operate at high speeds of the media involved in the heat exchange in order to minimize the stratification of liquids due to the difference in their temperatures and densities, as well as to eliminate the formation of stagnant zones.
If the average temperature difference between the pipes and the casing in heat exchangers of a rigid structure, i.e. with fixed tube sheets welded to the body, becomes significant (approximately equal to or greater than 50 ° C), then the pipes and casing elongate unequally. This causes significant stress in the pipes
Rice. VIII-14. Shell and tube heat exchangers with compensating
devices:
A - with lens compensator; b - with a floating head; c - with U-shaped pipes;
1 - compensator; 2 - movable tube sheet; 3 - U-shaped pipes.
gratings, can disrupt the tightness of the connection of pipes with gratings, lead to the destruction of welds, and unacceptable mixing of heat-exchanging media. Therefore, when the temperature difference between the pipes and the casing is greater than 50°C, or when the pipes are of a significant length, shell-and-tube heat exchangers of a non-rigid design are used, allowing some movement of the pipes relative to the casing of the apparatus.
To reduce temperature deformations caused by the large temperature difference between the pipes and the casing, the significant length of the pipes, as well as the difference in the material of the pipes and casing, shell-and-tube heat exchangers with an all-in-one compensator are used (Fig. VIII-14, a), which have a lens compensator 1, subject to elastic deformation. This design is simple, but is applicable for small excess pressures in the annulus, usually not exceeding 6 10 6 N/m 2 (6 at).
If it is necessary to ensure large movements of pipes and casing, a heat exchanger with a floating head is used (Fig. VIII-14, b). Bottom tube sheet 2 is movable, which allows the entire bundle of pipes to move freely regardless of the body of the device. This prevents dangerous temperature deformation of the pipes and disruption of the tightness of their connection with the tube sheets. However, compensation for temperature extensions is achieved in in this case due to the complexity and weight of the heat exchanger design.
In a shell-and-tube heat exchanger with U-shaped pipes (Fig. VIII-14, c), the pipes themselves 3 perform the function of compensating devices. At the same time, the design of the apparatus, which has only one fixed tube sheet, is simplified and simplified. The outer surface of the pipes can be easily cleaned by removing the entire tube from the apparatus body. In addition, in heat exchangers of this design, which are two- or multi-pass, fairly intense heat exchange is achieved. Disadvantages of heat exchangers with U-shaped tubes: difficulty in cleaning the inner surface of the tubes, difficulty in placing a large number of tubes in the tube sheet.
Steel shell-and-tube heat exchangers are standardized according to GOST 9929-67.
IN
In the chemical industry, heat exchangers with double pipes are also used (Fig. VIII-15). On one side of the apparatus there are two tube grids, and a bundle of tubes is fixed in grid 1 2
smaller diameter, open at both ends, and in the lattice 3
- pipes 4
larger diameter with closed left ends, installed concentrically relative to the pipes 2.
Wednesday I moves along the annular spaces between the pipes 2
And 4
and is removed from the inter-tube space of the heat exchanger through pipes 2.
Other environment II moves from top to bottom along the inter-tube space of the heat exchanger housing, washing the pipes 4
outside. In heat exchangers of this design, the pipes can elongate under the influence of temperature, regardless of the heat exchanger body. Elemental heat exchangers. To increase the speed of movement of the medium in the annulus without the use of partitions that make cleaning the apparatus difficult, elemental heat exchangers are used. Each element of such a heat exchanger is a simple shell-and-tube heat exchanger. The heated and cooled media sequentially pass through separate elements consisting of a bundle of pipes in a small-diameter casing. A heat exchanger consisting of such elements (passes) allows significant excess pressure in the inter-tube space; it can be considered as a modification of a multi-pass shell-and-tube heat exchanger.
In elemental heat exchangers, the mutual movement of media approaches an effective scheme of pure counterflow. However, due to the division of the total heat exchange surface into individual elements, the design becomes more cumbersome and the cost of the heat exchanger increases.
Double-tube heat exchangers. Heat exchangers of this design, also called pipe-in-pipe heat exchangers, consist of several tubular elements connected in series, formed by two concentrically arranged pipes (Fig. VIII-16). One coolant moves through the internal pipes 1 , and the other - along the annular gap between the internal 1 and external 2 pipes. Internal pipes (usually 57-108 in diameter mm) are connected by rolls 3, and outer pipes having a diameter of 76-159 mm,- pipes 4.
Rice. VIII-16. Two-pipe heat exchanger: 1 - internal pipes;
2 - external pipes; 3 - kalach; 4 - pipe branch.
Due to the small cross-sections of the pipe and inter-tube space in two-tube heat exchangers, even at low flow rates, fairly high fluid velocities are achieved, usually equal to 1-1.5 m/sec. This makes it possible to obtain higher heat transfer coefficients and achieve higher thermal loads per unit mass of the apparatus than in shell-and-tube heat exchangers. In addition, with increasing coolant velocities, the possibility of contaminant deposition on the heat exchange surface decreases.
At the same time, these heat exchangers are more bulky than shell-and-tube heat exchangers and require a greater consumption of metal per unit of heat exchange surface, which in devices of this type is formed only by internal pipes.
Double-tube heat exchangers can operate efficiently at low coolant flow rates, as well as at high pressures.
If a large heat exchange surface is required, then these devices are made of several parallel sections.
The plate heat exchanger unit, installed and ready for operation, is small in size and high level productivity. Yes, specific working surface such a device can reach 1,500 m 2 /m 3. The design of such devices includes a set of corrugated plates, which are separated from each other by gaskets. The gaskets form sealed channels. The medium that gives off heat flows in the space between the cavities, and inside the cavities there is a medium that absorbs heat or vice versa. The plates are mounted on a rod frame and are located tightly relative to each other.
Each plate is equipped with the following set of spacers:
- a perimeter gasket that limits the channel for the coolant and two openings for its inlet and outlet;
- two small gaskets that isolate the other two corner holes for the passage of the second coolant.
Thus, the design has four separate channels for the entry and exit of two media involved in heat exchange processes. This type of device is capable of distributing flows across all channels in parallel or sequentially. So, if necessary, each flow can pass through all channels or specific groups.
To the advantages of this type devices are usually attributed to the intensity of the heat exchange process, compactness, as well as the possibility full analysis unit for cleaning purposes. The disadvantages include the need for meticulous assembly to maintain tightness (as a result of a large number of channels). In addition, the disadvantages of this design are the tendency to corrosion of the materials from which the gaskets are made and limited thermal resistance.
In cases where contamination of the heating surface by one of the coolants is possible, units are used whose design consists of plates welded in pairs. If contamination of the heated surface is excluded from both coolants, welded non-removable heat exchangers(such as, for example, a device with wavy channels and cross-motion of coolants).
Operating principle of a plate heat exchanger
Plate Heat Exchanger for Diesel Fuel
| Name | Hot side | Cold side |
|---|---|---|
| Consumption (kg/h) | 37350,00 | 20000,00 |
| Inlet temperature (°C) | 45,00 | 24,00 |
| Outlet temperature (°C) | 25,00 | 42,69 |
| Pressure loss (bar) | 0,50 | 0,10 |
| Heat transfer (kW) | 434 | |
| Thermodynamic properties: | Diesel fuel | Water |
| Specific gravity (kg/m³) | 826,00 | 994,24 |
| 2,09 | 4,18 | |
| Thermal conductivity (W/m*K) | 0,14 | 0,62 |
| Average viscosity (mPa*s) | 2,90 | 0,75 |
| Viscosity at the wall (mPa*s) | 3,70 | 0,72 |
| Inlet pipe | B4 | F3 |
| Outlet pipe | F4 | B3 |
| Frame/plate design: | ||
| 2 x 68 + 0 x 0 | ||
| Plates arrangement (passage*channel) | 1 x 67 + 1 x 68 | |
| Number of plates | 272 | |
| 324,00 | ||
| Plate material | 0.5 mm AL-6XN | |
| NITRIL | / 140 | |
| 150,00 | ||
| 16.00 / 22.88 PED 97/23/EC, Kat II, Modul Al | ||
| 16,00 | ||
| Frame type / Finish | IS No 5 / Category C2 | RAL5010 |
| DN 150 Flange St.37PN16 | ||
| DN 150 Flange St.37PN16 | ||
| Liquid volume (l) | 867 | |
| Frame length(mm) | 2110 | |
| Max number of plates | 293 | |
Plate Heat Exchanger for Crude Oil
| Name | Hot side | Cold side |
|---|---|---|
| Consumption (kg/h) | 8120,69 | 420000,00 |
| Inlet temperature (°C) | 125,00 | 55,00 |
| Outlet temperature (°C) | 69,80 | 75,00 |
| Pressure loss (bar) | 53,18 | 1,13 |
| Heat transfer (kW) | 4930 | |
| Thermodynamic properties: | Steam | Raw oil |
| Specific gravity (kg/m³) | 825,00 | |
| Specific heat capacity (kJ/kg*K) | 2,11 | |
| Thermal conductivity (W/m*K) | 0,13 | |
| Average viscosity (mPa*s) | 20,94 | |
| Viscosity at the wall (mPa*s) | 4,57 | |
| Pollution degree (m²*K/kW) | 0,1743 | |
| Inlet pipe | F1 | F3 |
| Outlet pipe | F4 | F2 |
| Frame/plate design: | ||
| Plates arrangement (passage*channel) | 1 x 67 + 0 x 0 | |
| Plates arrangement (passage*channel) | 2 x 68 + 0 x 0 | |
| Number of plates | 136 | |
| Actual heating surface (m²) | 91.12 | |
| Plate material | 0.6 mm AL-6XN | |
| Gasket material / Max. pace. (°C) | VITON | / 160 |
| Max. design temperature(C) | 150,00 | |
| Max. operating pressure/test (bar) | 16.00 / 22.88 PED 97/23/EC, Kat III, Modul B+C | |
| Max. differential pressure (bar) | 16,00 | |
| Frame type / Finish | IS No 5 / Category C2 | RAL5010 |
| Hot side connections | DN 200 Flange St.37PN16 | |
| Joining on cold side | DN 200 Flange St.37PN16 | |
| Liquid volume (l) | 229 | |
| Frame length(mm) | 1077 | |
| Max number of plates | 136 | |
Plate heat exchanger
Plate Heat Exchanger for Propane
| Name | Hot side | Cold side |
|---|---|---|
| Consumption (kg/h) | 30000,00 | 139200,00 |
| Inlet temperature (°C) | 85,00 | 25,00 |
| Outlet temperature (°C) | 30,00 | 45,00 |
| Pressure loss (bar) | 0,10 | 0,07 |
| Heat transfer (kW) | 3211 | |
| Thermodynamic properties: | Propane | Water |
| Specific gravity (kg/m³) | 350,70 | 993,72 |
| Specific heat capacity (kJ/kg*K) | 3,45 | 4,18 |
| Thermal conductivity (W/m*K) | 0,07 | 0,62 |
| Average viscosity (mPa*s) | 0,05 | 0,72 |
| Viscosity at the wall (mPa*s) | 0,07 | 0,51 |
| Pollution degree (m²*K/kW) | ||
| Inlet pipe | F1 | F3 |
| Outlet pipe | F4 | F2 |
| Frame/plate design: | ||
| Plates arrangement (passage*channel) | 1 x 101 + 0 x 0 | |
| Plates arrangement (passage*channel) | 1 x 102 + 0 x 0 | |
| Number of plates | 210 | |
| Actual heating surface (m²) | 131,10 | |
| Plate material | 0.6 mm AL-6XN | |
| Gasket material / Max. pace. (°C) | NITRIL | / 140 |
| Max. design temperature (C) | 150,00 | |
| Max. working pressure/test. (bar) | 20.00 / 28.60 PED 97/23/EC, Kat IV, Modul G | |
| Max. differential pressure (bar) | 20,00 | |
| Frame type / Finish | IS No 5 / Category C2 | RAL5010 |
| Hot side connections | DN 200 Flange AISI 316 PN25 DIN2512 | |
| Cold side connections | DN 200 Flange AISI 316 PN16 | |
| Liquid volume (l) | 280 | |
| Frame length(mm) | 2107 | |
| Max number of plates | 245 | |
Description of plate-fin heat exchangers
The specific working surface of this device can reach 2,000 m2/m3. The advantages of such designs include:
- the possibility of heat exchange between three or more coolants;
- light weight and volume.
Structurally, plate-fin heat exchangers consist of thin plates, between which there are corrugated sheets. These sheets are soldered to each plate. Thus, the coolant is divided into small streams. The device can consist of any number of plates. Coolants can move:
- direct flow;
- cross flow.
Exist following types ribs:
- corrugated (corrugated), forming a wavy line along the flow;
- discontinuous ribs, i.e. offset relative to each other;
- scaly ribs, i.e. having slots that are bent into one or different sides;
- spinous, i.e. made of wire, which can be arranged in a checkerboard or corridor pattern.
Lamellar-ribbed heat exchangers used as regenerative heat exchangers.
Block graphite heat exchangers: description and application
Heat exchangers, made of graphite, are characterized by the following qualities:
- high resistance to corrosion;
- high level of heat conductivity (can reach up to 100 W/(m K)
Thanks to specified qualities, heat exchangers of this type are widely used in the chemical industry. The most widely used are block graphite devices, the main element of which is a graphite block in the shape of a parallelepiped. The block has non-intersecting holes (vertical and horizontal), which are intended for the movement of coolants. The design of a block graphite heat exchanger may include one or more blocks. Through horizontal holes in the block there is a two-way movement of the coolant, which is possible thanks to the side metal plates. The coolant, which moves through the vertical holes, makes one or two moves, which is determined by the design of the covers (top and bottom). In heat exchangers with enlarged side faces, the coolant moving vertically can make two or four passes.
Graphite heat exchanger, impregnated with phenolic polymer, annular block type, with a heat exchange surface of 320 m2
Ring Block Type Graphite Heat Exchanger for H2SO4
| Cooler | |||||
|---|---|---|---|---|---|
| Name | Dimension | Hot side | Cold side | ||
| Entrance | Exit | Entrance | Exit | ||
| Wednesday | H2SO4 (94%) | Water | |||
| Consumption | m³/h | 500 | 552,3 | ||
| Operating temperature | °C | 70 | 50 | 28 | 40 |
| Phys. Properties | |||||
| Density | g/cm³ | 1,7817 | 1,8011 | 1 | |
| Specific heat | kcal/kg °C | 0,376 | 0,367 | 1 | |
| Viscosity | cP | 5 | 11,3 | 0,73 | |
| Thermal conductivity | kcal/hm°C | 0,3014 | 0,295 | 0,53 | |
| Absorbed heat | kcal/h | 6628180 | |||
| Corrected average temperature difference | °C | 25,8 | |||
| Pressure drop (permissible/calculated) | kPa | 100/65 | 100/45 | ||
| Heat transfer coefficient | kcal/hm²°C | 802,8 | |||
| Pollution factor | kcal/hm²°C | 5000 | 2500 | ||
| Design conditions | |||||
| Design pressure | bar | 5 | 5 | ||
| Calculated temperature | °C | 100 | 50 | ||
| Specification/materials | |||||
| Required heat transfer surface area | m² | 320 | |||
| Gaskets, material | teflon (fluoroplastic) | ||||
| Blocks, material | Graphite, impregnated with phenolic-aldehyde polymer | ||||
| Dimensions (diameter×length) | mm | 1400*5590 | |||
| Channel inner diameter, axial / radial | 20mm/14mm | ||||
| Number of passes | 1 | 1 | |||
| Number of blocks | 14 | ||||
Graphite Heat Exchanger for Titanium Dioxide Hydrate Suspension and Sulfuric Acid Solution
Specifications:
| Name | Dimension | Hot side | Cold side | ||
|---|---|---|---|---|---|
| Entrance | Exit | Entrance | Exit | ||
| Wednesday | Suspension of titanium dioxide hydrate and 20% H2SO4 | Water | |||
| Consumption | m³/h | 40 | 95 | ||
| Operating temperature | °C | 90 | 70 | 27 | 37 |
| Operating pressure | bar | 3 | 3 | ||
| Heat transfer surface | m² | 56,9 | |||
| Physical properties | |||||
| Density | kg/m³ | 1400 | 996 | ||
| Specific heat | kJ/kg∙°C | 3,55 | 4,18 | ||
| Thermal conductivity | W/m∙K | 0,38 | 0,682 | ||
| Dynamic viscosity | joint venture | 2 | 0,28 | ||
| Heat resistance to contamination | W/m²∙K | 5000 | 5000 | ||
| Pressure drop(calculated) | bar | 0,3 | 0,35 | ||
| Heat exchange | kW | 1100 | |||
| Average temperature difference | OS | 47,8 | |||
| Heat transfer coefficient | W/m²∙K | 490 | |||
| Design conditions | |||||
| Design pressure | bar | 5 | 5 | ||
| Calculated temperature | °C | 150 | 150 | ||
| Materials | |||||
| Gaskets | PTFE | ||||
| casing | Carbon steel | ||||
| Blocks | Phenolic resin impregnated graphite | ||||
Heat pipes for the chemical industry
A heat pipe is a promising device used in the chemical industry to intensify heat transfer processes. A heat pipe is a completely sealed pipe with any cross-section profile, made of metal. The pipe body is lined with porous capillary material (wick), fiberglass, polymers, porous metals, etc. The amount of coolant supplied must be sufficient to impregnate the wick. The maximum operating temperature ranges from any low to 2000 °C. The following is used as a coolant:
- metals;
- high-boiling organic liquids;
- molten salts;
- water;
- ammonia, etc.
One part of the pipe is located in the heat removal zone, the rest in the vapor condensation zone. In the first zone, coolant vapors are formed, in the second zone they condense. The condensate returns to the first zone due to the action of the capillary forces of the wick. A large number of vaporization centers contributes to a drop in the superheat of the liquid during its boiling. At the same time, the heat transfer coefficient during evaporation increases significantly (from 5 to 10 times). The power indicator of the heat pipe is determined by capillary pressure.
Regenerators
The regenerator has a body, round or rectangular in cross-section. This housing is made from sheet metal or brick, in accordance with the temperature maintained during operation. A heavy filler is placed inside the unit:
- brick;
- fireclay;
- corrugated metal, etc.
Regenerators, as a rule, are paired devices, so cold and hot gas flow through them simultaneously. Hot gas transfers heat to the nozzle, and cold gas receives it. The work cycle consists of two periods:
- warming up the nozzle;
- nozzle cooling.
The brick nozzle can be laid out in a different order:
- corridor order (forms a series of straight parallel channels);
- checkerboard pattern (forms channels of complex shape).
Regenerators can be equipped with metal nozzles. A regenerator equipped with a falling dense layer of granular material is considered a promising device.
Mixing heat exchangers. Mixing capacitors. Bubbler. Coolers
The heat exchange of substances (liquids, gases, granular materials), when they are in direct contact or mixing, is characterized by a maximum degree of intensity. The use of such technology is dictated by the need technological process. For mixing liquids the following is used:
- a container equipped with a stirrer;
- injector (also used for continuous mixing of gases).
Liquids can be heated by condensing steam in them. Steam is introduced through multiple holes in a pipe, which is bent in the shape of a circle or spiral and is located in the lower section of the apparatus. The device that ensures this technological process occurs is called a bubbler.
Cooling of the liquid to a temperature close to 0 °C can be carried out by introducing ice, which is capable of absorbing up to 335 kJ/kg of heat when melting, or liquefied neutral gases characterized by high temperature evaporation. Sometimes refrigeration mixtures are used, which absorb heat after dissolving in water.
The liquid can be heated by contact with a hot gas and cooled, respectively, by contact with a cold one. This process is ensured by scrubbers (vertical devices), where a stream of cooled or heated liquid flows towards the ascending gas flow. The scrubber can be filled with various nozzles to increase the contact surface. The nozzles break the liquid flow into small streams.
The group of mixing heat exchangers also includes mixing condensers, the function of which is to condense vapors through direct contact with water. Mixing capacitors can be of two types:
- direct-flow condensers (steam and liquid move in the same direction);
- counterflow condensers (steam and liquid move in opposite directions).
To increase the contact area between steam and liquid, the liquid flow is divided into small streams.
Finned Tube Air Cooler
Many chemical plants generate a large number of secondary heat that is not recovered in heat exchangers and cannot be reused in processes. This heat released into the environment and therefore there is a need to minimize possible consequences. For these purposes they use Various types coolers.
The finned tube cooler design consists of a series of finned tubes within which the cooled liquid flows. The presence of ribs, i.e. The ribbed design significantly increases the surface of the cooler. The cooler fins are blown by fans.
This type of coolers is used in cases where there is no possibility of drawing water for cooling purposes: for example, at the installation site of chemical plants.
Irrigation coolers
The design of the spray cooler consists of rows of sequentially mounted coils, inside which the cooled liquid moves. The coils are constantly irrigated with water, due to which irrigation occurs.
Cooling towers
The principle of operation of a cooling tower is that heated water is sprayed at the top of the structure and then flows down the packing. In the lower part of the structure, due to natural suction, an air stream flows past the flowing water, which absorbs part of the heat of the water. Plus, some of the water evaporates during the draining process, which also results in heat loss.
The disadvantages of the design include its gigantic dimensions. Thus, the height of a tower cooler can reach 100 m. The undoubted advantage of such a cooler is its operation without auxiliary energy.
Cooling towers equipped with fans work in a similar way. The difference is that the air is pumped through this fan. It should be noted that the design with a fan is much more compact.
Heat exchanger with heat exchange surface 71.40 m²
Technical description:
Item 1: Heat exchanger
| Temperature data | Side A | Side B | ||
|---|---|---|---|---|
| Wednesday | Air | Flue gases | ||
| Operating pressure | 0.028 barg | 0.035 barg | ||
| Wednesday | Gas | Gas | ||
| Inlet flow | 17 548.72 kg/h | 34 396.29 kg/h | ||
| Output flow | 17 548.72 kg/h | 34 396.29 kg/h | ||
| Inlet/outlet temperature | -40 / 100 °C | 250 / 180 °C | ||
| Density | 1.170 kg/m³ | 0.748 kg/m³ | ||
| Specific heat | 1.005 kJ/kg.K | 1.025 kJ/kg.K | ||
| Thermal conductivity | 0.026 W/m.K | 0.040 W/m.K | ||
| Viscosity | 0.019 mPa.s | 0.026 mPa.s | ||
| Latent heat | ||||
Heat exchanger operation
Description of the heat exchanger
Dimensions
| L1: | 2200 mm |
| L2: | 1094 mm |
| L3: | 1550 mm |
| LF: | 1094 mm |
| Weight: | 1547 kg |
| Weight with water: | 3366 kg |
Flanged immersion heat exchanger 660 kW
Specifications:
380 V, 50 Hz, 2x660 kW, 126 working and 13 reserve heating elements, 139 heating elements in total, triangle connection 21 channels of 31.44 kW each. Protection - NEMA type 4.7
Working medium: Regeneration gas (percentage by volume):
N2 - 85%, water vapor-1.7%, CO2-12.3%, O2-0.9%, Sox-100 ppm, H2S-150ppm, NH3-200ppm. There are mechanical impurities - ammonium salts, corrosion products.
List of documents supplied with the equipment:
A passport for a flanged submersible heating section with instructions for installation, start-up, shutdown, transportation, unloading, storage, information on preservation;
Drawing general view sections;
Copper heat exchangers are suitable for chemically clean and non-aggressive environments, such as fresh water. This material has a high heat transfer coefficient. The disadvantage of such heat exchangers is their rather high cost.
The optimal solution for purified aqueous media is brass. Compared with copper heat exchange equipment, it is cheaper and has higher corrosion resistance and strength characteristics. It is also worth noting that some brass alloys are resistant to sea water and high temperatures. The disadvantage of the material is considered to be low electrical and thermal conductivity.
The most common material solution in heat exchangers is steel. Adding various alloying elements to the composition makes it possible to improve its mechanical, physical and chemical properties and expand the range of applications. Depending on the added alloying elements, steel can be used in alkaline, acidic environments with various impurities and at high operating temperatures.
Titanium and its alloys quality material, with high strength and thermal conductivity characteristics. This material is very lightweight and is used in a wide range of operating temperatures. Titanium and materials based on it exhibit good corrosion resistance in most acidic or alkaline environments.
Non-metallic materials are used in cases where heat transfer processes are required in particularly aggressive and corrosive environments. They are characterized high value coefficient of thermal conductivity and resistance to the most chemical active substances, which makes them an indispensable material used in many devices. Non-metallic materials are divided into two types: organic and inorganic. Organic materials include carbon-based materials such as graphite and plastics. Silicates and ceramics are used as inorganic materials.
- the coolant, during the flow of which it is possible to release sediment, is predominantly directed from the side from which it is easier to clean the heat transfer surface;
- the coolant, which has a corrosive effect, is directed through pipes, this is due to the lower requirement for the consumption of corrosion-resistant material;
- to reduce heat loss to the environment, high-temperature coolant is directed through pipes;
- in order to ensure safety when using coolant with high pressure It is customary to pass it through pipes;
- When heat exchange occurs between coolants in different states of aggregation (liquid-steam, gas), it is customary to direct the liquid into the pipes, and the steam into the interpipe space.
Read more about the calculation and selection of heat exchange equipment
Minimum/maximum design metal temperature for parts under pressure: -39 / +30 ºС.
For non-pressure parts, material according to EN 1993-1-10 is used.
Zone classification: non-hazardous.
Corrosivity category: ISO 12944-2: C3.
Type of connection of pipes to the tube sheet: welding.
Electric motors
Version: not explosion-proof
Protection class: IP 55
Frequency converters
Designed for 50% electric motors.
Fans
The blades are made from reinforced material aluminum/plastic with manual pitch adjustment.
Noise level
Does not exceed 85 ± 2 dBA at a distance of 1 m and at a height of 1.5 m from the surface.
External recirculation
Applicable.
Blinds
Top, entrance and recirculation blinds with pneumatic drive.
Water heater coil
Placed on a separate frame. Each heater is located under the tube bundle.
Vibration switches
Each fan is equipped with a vibration switch.
Includes supports, rods, drainage chambers. The complete recycling floor is not included in the scope of delivery.
Mesh protection
Mesh protection for fans and rotating parts.
Spare parts
Spare parts for assembly and startup
- Fasteners for steel structures: 5%
- Fasteners for manifold plate covers: 2%
- Fasteners for vent and drain fittings: 1 set of each type
Spare parts for 2 years of operation (optional)
- Belts: 10% (minimum 1 set of each type)
- Bearings: 10% (minimum 1 piece of each type)
- Gaskets for air vent, drainage: 2 pcs. each type
- Air vent and drain fasteners: 2 sets of each type
- One level sensor for setting the fan blade pitch
- One fin repair kit
Technical documentation in Russian (2 copies + CD)
To approve working documentation:
- General drawing including loads
- Electrical diagram
- Hardware Specification
- Test plan
With equipment:
- Basic documentation on test checks according to standards, codes and other requirements
- User manual
- Comprehensive description of the unit
Test and inspection documentation:
- Test plan for each position
- In-shop inspection
- Hydrostatic test
- Certificates for materials
- Pressure vessel passport
- TUV inspection
Shipping information:
- The tube bundle is fully assembled and tested
- The heating water coil is fully assembled
- Blinds are fully assembled
- Drain chambers in separate parts
- Recirculation blinds with slabs in separate parts
- Fan assemblies
- Steel structures in separate parts
- Electric motors, axial fans, vibration switches and spare parts in wooden boxes
- On-site assembly using fasteners (no welding)
Scope of delivery
The following equipment and project documentation included in the scope of delivery:
- Temperature and mechanical calculations
- Tube bundles with plugs for vent and drainage
- Fan assemblies
- Electric motors
- Frequency converters (50/% of all fans)
- Vibration switches (100% of all fans)
- Drain chambers
- Support structures
- Service platforms for supports and ladders
- External recirculation system
- Temperature sensors on the air side
- Blinds on recirculation/inlet/outlet with pneumatic drive
- Lifting loops
- Grounding
- Surface treatment
- Spare parts for assembly and startup
- Spare parts for 2 years of operation
- Special tool
- Counter flanges, fasteners and gaskets
The following equipment is not included in the scope of delivery:
- Installation services
- Pre-assembly
- Anchor bolts
- Thermal insulation and fire protection
- Cable supports
- Protection against hail and stones
- Platform for accessing electric motors
- Electric heaters
- Control cabinet for frequency converters*
- Materials for electrical installation*
- Connections for pressure and temperature sensors*
- Inlet and outlet manifolds, connecting piping and fittings*
A plate heat exchanger is a device in which one coolant transfers or takes heat from another through a surface called heat exchange. It is formed by a set of thin stamped plates with a surface corrugated in a special way.
Operating principle of a plate heat exchanger.
Plate heat exchanger operating principle - diagram
Collected in a single package, they form channels through which coolants move while exchanging thermal energy with each other. The coolant distribution channels are designed in a special way, in which the incoming and outgoing coolant constantly alternate with each other.
By combining plates inside the heat exchanger, manufacturers achieve optimal option heat transfer for each type of device. The main condition for this The coolant flow in the heat exchanger must be turbulent(indignant). This is the only way to achieve it high efficiency and self-cleaning of the plates. Let us recall that the coolant flow in heat exchangers of the pipe-in-pipe type is laminar, calm, hence the low heat transfer coefficient and big sizes classic shell-and-tube heat exchangers.
Plate heat exchanger layout diagram.
Today, the main manufacturers of plate heat exchangers offer the following layout principle:
A single-pass heat exchanger arrangement is when the coolant is immediately divided into parallel flows, passes through all channels of the plates and, merging into one channel, enters the coolant outlet port.
Multi-pass heat exchanger layout. In this case, more complex circuit, the coolant circulates through the same number of channels, making a turn in the plate. This is achieved by installing dividing plates into which blind partitions fit. It is much more difficult to maintain, clean, disassemble and assemble this one.
The plates of a plate heat exchanger are arranged one after another with a rotation of 180 degrees. Such a heat exchanger creates a package with four collectors for the removal and supply of liquids. The first and last plates, respectively, do not participate in the heat exchange process, the rear plate is blank, without ports.
Rubber gaskets are attached between the plates using a clip connection. It is simple and reliable, and the gaskets are self-centering, which allows for automatic assembly. That is, during installation after cleaning, everything will fall into place without special effort. The gaskets have a cuff-like edging that creates an additional barrier and prevents coolant leakage.
Frame design diagram The heat exchanger is also the simplest: a fixed front and movable rear plate, a tripod, lower and upper guides, coupling bolts.
Plate assembly diagram The heat exchanger is not complicated, the upper and lower guides are fixed on a tripod and a fixed plate. A package of plates and then a movable plate are put on the guides of the future heat exchanger. The movable and fixed plates are tightened together with bolts.
Plate heat exchanger - materials used for manufacturing.
The material used for gaskets is ethylene propylene., abbreviated as "EPDM". It can withstand temperatures from minus 30C to plus 160C and is not destroyed by the action of not only water, but also steam from fats and oils.
It remains only to mention the material used to produce the plates of the plate heat exchanger. Most often this stainless steel AISI 316, after stamping in mandatory The plate is electrochemically polished.
The thickness of the plate depends on the maximum operating pressure. For pressures up to 1 MPa, plates with a thickness of 0.4 mm are used, for pressures up to 1.6 MPa - plates with a thickness of 0.5 mm, for pressures of 2.5 MPa - plates with a thickness of 0.6 mm. Naturally, the cost of the heat exchanger depends on the thickness of the plates, layout and pressure. If it is fundamentally important to you low price heat exchanger, and you know that you do not have aggressive environment can be ordered from AISI 304 steel, it is cheaper.
Shell and tube heat exchanger- This is a device for exchanging heat between two different flows. One medium is heated due to the cooling agent of the other. Two different media can change their state of aggregation, but mixing does not occur during the transfer of energy. Heat exchange occurs through the walls of the device. Pipes are often ribbed to increase the heat transfer surface area.
Types of heat exchangers
There are heat exchangers various types. Their diameter can range from 159 to 3000 mm. Maximum pressure - 160 kg/cm2. The length can vary from several tens to 10,000 mm. Types of units:
- With built-in grilles made in the form of a pipe.
- The design of a shell-and-tube heat exchanger may include a temperature compensator.
- A device equipped with a floating head.
- WITH U shape devices.
- Combined. It has a compensator and a built-in floating head.
In this video you will learn how heat exchangers are classified:
The design of a shell-and-tube heat exchanger, which contains tube sheets, has a rigid coupling of all elements. Such devices are most often used in the oil or chemical industries. This type of device accounts for approximately three-quarters of the total market. In this type, tube sheets are welded from the inside to the walls of the body, and attached to them with a rigid coupling heat exchange pipes. This avoids any shifts of all constituent elements inside the case.
Shell and tube heat exchanger compensates for elongation due to heat by longitudinal compression or with the help of special flexible inserts in expanders. This is a semi-rigid structure.
A device with a floating head is considered much more advanced. The floating head is a special movable grille. It moves throughout the pipe system along with the cover. Such a device is more expensive, but also much more reliable.
There are single-pass and multi-pass heat exchangers For a device with a U-shaped pipe system, two ends are welded to one grid. The rotation angle is 180°, and the radius is from 4 pipe diameters. Thanks to this design, the pipes inside the housing can be freely extended.
There are single-pass and multi-pass heat exchangers. The choice depends on the direction of movement of the coolant inside the apparatus. In a single pass, the filler moves along the shortest path. Most shining example this type of device - This is a GDP water heater, which is used in heating systems. Such a device is best used in places where a high heat transfer rate is not needed (the difference between the temperature environment and the heat carrier is minimal).
Multi-pass devices have special transverse partitions. They provide redirection of coolant flow. Used where high heat transfer rates are required. Tubular devices are also divided into single-flow, cross-flow and counter-flow.
So that the heat exchanger can be operated in extreme conditions, instead of the usual steel pipes use glass or graphite. The housing is sealed using seals.
Principle of operation
The device has a fairly simple principle of operation. A shell and tube heat exchanger separates the media. There is no mixing of products inside the structure. Heat transfer occurs along the walls of the tubular elements, which separate coolants. One carrier is located inside the pipes, and the other is supplied under pressure into the interpipe space. Aggregate states both energy carriers may differ. It can be gas, steam or liquid.
The operating principle of a shell-and-tube heat exchanger is based on the normal processes of energy transfer between liquids and various gases. To increase the coefficient of thermal energy transfer, rather high speeds of movement of products inside the structure are used. For steam or gas, they generate from 8 to 25 m/s. For liquid coolants the minimum speed is 1.5 m per second.
Heat passes through the walls of this unit Design of a shell-and-tube apparatus
The main advantage of a shell-and-tube heat exchanger and main reason its popularity lies in high reliability designs. It includes distribution chambers, which are equipped with tubes. A cylindrical casing, a bundle of pipes and a certain number of gratings are also provided. The entire structure is complemented by covers that are located at the ends. The kit includes supports that allow you to place the device in a horizontal plane. There is also a mount for mounting the device anywhere in space.
To increase heat exchange between the coolant, pipes that are covered with special ribs are used. If the task is to reduce heat transfer, then the body is covered with some kind of heat-insulating layer. This way you can significantly increase the accumulating properties of the product. Special designs are used in which one pipe is located in the second.
Thick sheet steel (from 4 mm) is used to make the casing. To produce gratings, most often the same material is taken, but its thickness is much greater (from 2 cm). The main element is a bundle of pipes made of a material that has high thermal conductivity. This bundle is fixed on one or both sides on tube sheets.
Advantages and disadvantages
These devices have several advantages, which ensures sufficient competitiveness in the market heat exchange systems. Main advantages of the equipment:
- The design provides excellent resistance to hydraulic shocks. Similar systems do not have this characteristic.
- Shell and tube heat exchangers are capable of operating in extreme conditions or with products that are quite heavily contaminated.
- They are very easy to use. Easy to carry out mechanical cleaning equipment, its planned Maintenance. The equipment has high maintainability.
This heat exchanger has both pros and cons Despite all the advantages, this device also has disadvantages. These should be considered before purchasing. Depending on the intended use, other similar systems may be required. Disadvantages of the device:
- The efficiency is lower than that of plate products. This is because shell-and-tube exchangers have less surface area to transfer heat.
- It is large in size. It boosts it final cost, as well as operating costs.
- The heat transfer coefficient is highly dependent on how fast the agent moves.
Despite all their shortcomings, shell-and-tube devices have found their niche in the heat exchanger market. They remain popular and are used in many industries.
Application area
Shell and tube products are used as part of utility networks Housing and communal services. They are also used in heating stations to provide hot water residential buildings. Individual heating points have certain advantages over central heat and water supply: they provide heat to buildings and other objects much more efficiently than a centralized heating network.
Heat exchangers of this type are also used in the oil, chemical and gas industries. They are used in the field of thermal power engineering, where coolants have high temperature transfer rates. And this is not all the industries where such equipment is used. It can be found in reboiler evaporators or in air heat exchange condenser coolers, distillation columns. It has found application in beer production and the food industry.
Operating the device
The tubular heat exchanger has a high service life. In order for it to perform its role efficiently and serve for a long time, it is necessary to carry out scheduled maintenance in a timely manner. Most often, the unit is filled with liquid that has not gone through the filtration stages. This leads to gradual clogging of the tubes, which prevents the coolant fluid from moving freely throughout the system. It is necessary to carry out timely and systematically mechanical cleaning all elements of the shell and tube product. It is also necessary to wash the components under high pressure.
If there is a need to repair a tubular apparatus, the first step is to carry out diagnostic measures. This allows you to discover the main problems. The most vulnerable part is the tubes, which are most often damaged. Diagnostics is carried out using hydraulic tests.
All thermal energy exchange equipment is quite capricious. This includes shell-and-tube devices. When making any interventions in the structure for repairs, it must be taken into account that this may affect the coefficient of thermal conductivity and, accordingly, heat exchange between media. Many businesses and individuals buy several installations at once so that you can quickly connect to another device.
It is important to remember that certain difficulties may arise when regulating equipment based on condensate. Absolutely any changes entail an increase or decrease in heat transfer. It should also be taken into account that the change in area occurs nonlinearly.
Plate heat exchangers used in hot water supply, air conditioning, heating systems of private homes and businesses, in heating points and networks as heaters, refrigerators or condensers. Heat exchangers carry out heat transfer between different media, for example, steam-liquid, steam-gas-liquid, liquid-liquid, gas-gas. Heat is transferred from a hot medium (coolant) to a cold one.
Structurally, the heat exchangers are a recuperative heat exchanger with a system of corrugated stamped plates, closely pressed to each other.
The standard sizes of heat exchangers are described in GOST 15518-87 "Plate heat exchangers. Types, parameters and main dimensions."
Technical parameters for using plate heat exchangers:
- heat exchange area 1-800 m 2
- working pressure - not lower than 0.002 MPa
- temperature of working media - -70°С...+200°С
Operating principle and design of plate heat exchangers
The coolant and the heated medium move towards each other along plates pulled together into a package. The plates in the package have same sizes. The plates are located to each other rotated by 180°C. Slit channels are formed between the machined packages with plates located on the frame. Liquids move through these channels. Thus, there is an alternation of channels through which the coolant moves in one direction and the heated medium in the other. The tightness of the channels is ensured by a rubber contour gasket on each plate. The gasket is installed in four groove holes: through two grooves, liquids are supplied/discharged; the other two holes provide mixing of two liquids of different temperatures. In the event of a possible breakthrough of the grooves, the leaking liquid exits through the drainage grooves.
The tortuous movement of fluids creates turbulence in flows. The intensity of heat exchange increases due to the temperature difference from the counterflow of two different liquids. Hydraulic resistance at the same time quite low. The formation of scale during heat transfer is minimized through the use of corrosion-resistant materials (galvanized steel, titanium, aluminum) processed by cold stamping. Gaskets are traditionally made from rubber-based polymers (natural or synthetic).
Plate heat exchanger drawing
1-fixed plate, 2-upper guide, 3-movable plate, 4-stand, 5, 6-packs of plates, 7-bottom guide, 8-tie bolts
Types of plate heat exchangers
Structurally plate heat exchangers There are two main types:
- gasketed plate heat exchangers
- non-separable plate heat exchangers (brazed, welded)
The most commonly used are gasketed plate heat exchangers, the design of which is described above.
Plate heat exchangers can be manufactured in several designs: single-pass, double-pass, three-pass.
Flow Movement in Single-Pass, Double-Pass and Three-Pass Heat Exchangers
Advantages of plate heat exchangers
- the heat transfer surface is 99-99.8% of the total surface area of the heat exchanger
- high heat transfer coefficient
- reusable
- easy installation, because fastening elements are located on one side of the heat exchanger
- possibility of changing the width and number of channels to reduce hydraulic losses
- the possibility of increasing the heat exchange surface to increase heat transfer by installing additional plates