Shell and tube heat exchangers. Heat exchangers and equipment
Mounted and ready for operation, the plate heat exchanger is characterized by small dimensions and a high level of performance. Thus, the specific working surface of 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. 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 gaskets:
- a perimeter gasket that limits the channel for the coolant and two holes for its inlet and outlet;
- two small spacers that isolate the other two corner holes for the passage of the second thermal medium.
Thus, the design has four separate channels for the inlet and outlet of two media involved in heat exchange processes. This type of apparatus is capable of distributing flows across all channels in parallel or in series. So, if necessary, each stream can pass through all channels or certain groups.
To the virtues of this type devices, it is customary to attribute the intensity of the heat exchange process, compactness, as well as the possibility of complete disassembly of the unit for the purpose of cleaning. 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 is 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 with one of the heat carriers is possible, units are used, the design of which consists of pairwise welded plates. If contamination of the heated surface is excluded from both heat carriers, welded non-separable heat exchangers(as, for example, an apparatus with wavy channels and cross-flow of heat carriers).
Principle of operation 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 | ||
| Plate arrangement (pass*channel) | 1 x 67 + 1 x 68 | |
| Number of plates | 272 | |
| 324,00 | ||
| Insert material | 0.5mm AL-6XN | |
| NITRIL | / 140 | |
| 150,00 | ||
| 16.00 / 22.88 PED 97/23/EC, Kat II, Modul Al | ||
| 16,00 | ||
| Frame Type / Coating | 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 (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: | ||
| Plate arrangement (pass*channel) | 1 x 67 + 0 x 0 | |
| Plate arrangement (pass*channel) | 2 x 68 + 0 x 0 | |
| Number of plates | 136 | |
| Actual heating surface (m²) | 91.12 | |
| Insert material | 0.6mm 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 / Coating | IS No 5 / Category C2 | RAL5010 |
| Hot side connections | DN 200 Flange St.37PN16 | |
| Cold side connections | 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 (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: | ||
| Plate arrangement (pass*channel) | 1 x 101 + 0 x 0 | |
| Plate arrangement (pass*channel) | 1 x 102 + 0 x 0 | |
| Number of plates | 210 | |
| Actual heating surface (m²) | 131,10 | |
| Insert material | 0.6mm AL-6XN | |
| Gasket material / Max. pace. (°C) | NITRIL | / 140 |
| Max. design temperature (C) | 150,00 | |
| Max. operating pressure /test. (bar) | 20.00 / 28.60 PED 97/23/EC, Kat IV, Modul G | |
| Max. differential pressure (bar) | 20,00 | |
| Frame Type / Coating | 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 apparatus can reach 2,000 m 2 /m 3. The advantages of such structures include:
- the possibility of heat exchange between three or more heat carriers;
- small 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 apparatus may consist of any number of plates. Heat carriers can move:
- cocurrent;
- cross flow.
The following types of ribs exist:
- corrugated (corrugated), forming a wavy line along the flow;
- broken edges, i.e. offset relative to each other;
- scaly ribs, i.e. having slots that are bent in one or different directions;
- spiny, i.e. made of wire, which can be staggered or in-line.
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)
Due to these qualities, heat exchangers of this type are widely used in the chemical industry. The most widely used block graphite apparatus, the main element of which is a graphite block in the form of a parallelepiped. The block has non-overlapping 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. The two-way movement of the coolant is carried out along the horizontal holes in the block, which is possible due to the side metal plates. The coolant, which moves through the vertical holes, makes one or two strokes, 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 strokes.
Graphite heat exchanger impregnated with phenolic resin, annular block type, with a heat exchange surface of 320 m 2
Graphite ring block heat exchanger for H2SO4
Specifications:
| cooler | |||||
|---|---|---|---|---|---|
| Name | Dimension | hot side | cold side | ||
| Entrance | Output | Entrance | Output | ||
| Wednesday | H2SO4 (94%) | Water | |||
| Consumption | m³/h | 500 | 552,3 | ||
| Working 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 mean temperature difference | °C | 25,8 | |||
| Differential pressure (permissible/design) | 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 | ||
| design temperature | °C | 100 | 50 | ||
| Specification / materials | |||||
| Required heat transfer surface area | m² | 320 | |||
| Gaskets, material | teflon (fluoroplast) | ||||
| Blocks, material | Graphite, impregnated with phenol-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 slurry and sulfuric acid solution
Specifications:
| Name | Dimension | hot side | cold side | ||
|---|---|---|---|---|---|
| Entrance | Output | Entrance | Output | ||
| Wednesday | Suspension of titanium dioxide hydrate and 20% H2SO4 | Water | |||
| Consumption | m³/h | 40 | 95 | ||
| Working 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 | sp | 2 | 0,28 | ||
| Heat resistance to pollution | 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 | ||
| design temperature | °C | 150 | 150 | ||
| materials | |||||
| Gaskets | PTFE | ||||
| casing | Carbon steel | ||||
| Blocks | Graphite impregnated with phenolic resin | ||||
Heat pipelines for the chemical industry
The heat pipeline is a promising device used in the chemical industry to intensify heat transfer processes. The heat conductor is a completely sealed pipe with any 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. Limiting working temperature ranges from any low to 2000 °C. As a coolant use:
- metals;
- high-boiling organic liquids;
- salt melts;
- 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 centers of vaporization contributes to the drop in overheating of the liquid during its boiling. In this case, the heat transfer coefficient during evaporation increases significantly (from 5 to 10 times). The power index of the heat pipe is determined by the capillary pressure.
Regenerators
The regenerator has a body, round or rectangular in cross section. This body is made from sheet metal or brick, according to 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 flows through them simultaneously. The hot gas transfers heat to the nozzle, while the cold gas receives it. The work cycle consists of two periods:
- nozzle heating;
- nozzle cooling.
A brick nozzle can be laid out in a different order:
- corridor order (forms a number of direct parallel channels);
- checkerboard pattern (forms channels of complex shape).
Regenerators can be equipped with metal nozzles. A promising device is a regenerator equipped with a falling dense layer of granular material.
Mixing heat exchangers. Mixing condensers. Bubbler. Coolers
The heat exchange of substances (liquids, gases, granular materials), with their direct contact or mixing, is characterized by the maximum degree of intensity. The use of such technology is dictated by the necessity of the technological process. Used for mixing liquids:
- capacitive apparatus equipped with a stirrer;
- injector (also used for continuous mixing of gases).
Liquids can be heated by condensing steam in them. The steam is introduced through multiple holes in a tube that is curved in the form of a circle or spiral and is located in the lower section of the apparatus. The device that ensures the flow of this technological process is called a bubbler.
Cooling of a 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 or liquefied neutral gases when melting, which are characterized by high temperature evaporation. Sometimes refrigeration mixtures are used that absorb heat after being dissolved in water.
The liquid can be heated by contact with a hot gas and cooled, respectively, by contact with a cold one. Such a process is provided by scrubbers (vertical apparatus), where a stream of cooled or heated liquid flows down towards the ascending gas flow. The scrubber can be filled with various nozzles in order to increase the contact surface. Nozzles break the flow of liquid into small streams.
The group of mixing heat exchangers also includes mixing condensers, the function of which is to condense vapors through their direct contact with water. Mixing condensers can be of two types:
- once-through condensers (vapor and liquid move in the same direction);
- countercurrent condensers (vapor and liquid move in opposite directions).
To increase the area of contact between vapor 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 is removed to environment and therefore there is a need to minimize the possible consequences. For these purposes, apply Various types coolers.
The design of finned tube coolers consists of a series of finned tubes within which the liquid to be cooled flows. The presence of ribs, i.e. ribbing design, significantly increases the surface of the cooler. The cooler fins blow over the fans.
This type of cooler is used in cases where there is no possibility of water intake for cooling purposes: for example, at the installation site of chemical plants.
Irrigation coolers
The design of the spray cooler consists of rows of coils mounted in series, 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 the cooling tower is that heated water is sprayed at the top of the structure, after which it flows down the packing. In the lower part of the structure, due to natural suction, a stream of air flows past the flowing water, which absorbs part of the heat of the water. Plus, some of the water evaporates during the runoff process, which also results in heat loss.
The disadvantages of the design include its gigantic dimensions. Thus, the height of a cooling tower 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. With the difference that the air is blown 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 (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 | ||
| Outlet 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 |
| The 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, delta connection 21 channels of 31.44 kW. Protection - NEMA type 4.7
Working medium: Regeneration gas (volume percent):
N2 - 85%, steam-1.7%, CO2-12.3%, O2-0.9%, Sox-100ppm, H2S-150ppm, NH3-200ppm. There are mechanical impurities - ammonium salts, corrosion products.
List of documents supplied with the equipment:
Passport for a flanged immersion heating section with instructions for installation, start-up, shutdown, transportation, unloading, storage, conservation information;
General view drawing of the section;
Copper heat exchangers are suitable for chemically clean and non-aggressive media such as fresh water. This material has a high heat transfer coefficient. The disadvantage of such heat exchangers is quite high price.
The optimal solution for purified aquatic environments is brass. Compared with copper heat exchange equipment, it is cheaper and has better corrosion resistance and strength. 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. The addition of various alloying elements to the composition makes it possible to improve its mechanical, physicochemical 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 light and can be used in a wide range of operating temperatures. Titanium and materials based on it show good corrosion resistance in most acidic or alkaline environments.
Non-metallic materials are used in cases where heat exchange processes are required in particularly aggressive and corrosive environments. They are characterized high value coefficient of thermal conductivity and resistance to the most chemically 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 precipitation is possible is mainly directed from the side from which it is easier to clean the heat transfer surface;
- the coolant that has a corrosive effect is sent through pipes, this is due to the lower requirement for the consumption of corrosion-resistant material;
- to reduce heat loss to the environment, a heat carrier with a high temperature is sent through pipes;
- in order to ensure safety when using a high-pressure coolant, it is customary to pass it in pipes;
- when heat transfer occurs between heat carriers in different states of aggregation (liquid-steam, gas), it is customary to direct the liquid into the pipes, and the steam into the annulus.
More about the calculation and selection of heat exchange equipment
Minimum / maximum design metal temperature for pressure parts: -39 / +30 ºС.
For non-pressure parts, material according to EN 1993-1-10 is used.
Area classification: non-hazardous.
Corrosivity category: ISO 12944-2: C3.
Type of connection of pipes to the tube sheet: welding.
Electric motors
Execution: not explosion-proof
Protection class: IP 55
Frequency converters
Provided for 50% of electric motors.
Fans
The blades are made of reinforced aluminium/plastic material 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
Applies.
Blinds
Top, entrance and recirculation shutters with pneumatic drive.
Water heater coil
It is 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 of fans, rotating parts.
Spare parts
Spare parts for build and run
- Fasteners for steel structures: 5%
- Fasteners for header 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 of each type)
- Gaskets for air vent, drainage: 2 pcs. each type
- Air vent and drain fittings: 2 sets of each type
Special tool
- One level sensor for setting the pitch of the fan blades
- One fin repair kit
Technical documentation in Russian (2 copies + CD disk)
For approval of working documentation:
- General arrangement drawing including loads
- Wiring diagram
- Hardware Specification
- Test plan
With equipment:
- Basic documentation about test checks according to standards, codes and other requirements
- User manual
- Comprehensive description of the machine
Test and inspection documentation:
- Test plan for each position
- Intra-shop inspection
- hydrostatic test
- Material Certificates
- Passport of the pressure vessel
- TUV Inspection
Shipping information:
- The tube bundle is fully assembled and tested
- Heating water coil fully assembled
- Blinds fully assembled
- Drainage chambers in separate parts
- Recirculation blinds with slabs in separate parts
- Complete fans
- Steel structures in separate parts
- Electric motors, axial fans, vibration switches and spare parts in wooden boxes
- Site assembly with 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 vent and drain plugs
- Complete fans
- Electric motors
- Frequency converters (50/% of all fans)
- Vibration switches (100% of all fans)
- Drainage chambers
- Support structures
- Maintenance platforms for poles and stairs
- External recirculation system
- Temperature sensors on the air side
- Blinds on recirculation / inlet / outlet with pneumatic actuator
- lifting loops
- grounding
- Surface Finishing
- Spare parts for build and run
- Spare parts for 2 years of operation
- Special tool
- Mating 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
- Supports for cables
- Protection against hail and stones
- Platform for access to electric motors
- Electric heaters
- Control cabinet for frequency converters*
- Materials for electrical installation*
- Connections for pressure and temperature sensors*
- Inlet and outlet manifolds, connecting pipes and fittings*
Section content
A shell-and-tube heat exchanger (Fig. 4.9) consists of a casing and a bundle of pipes fixed in tube sheets (boards) to create flow channels. As a rule, less contaminated coolant is supplied to the annular space, and more contaminated coolant is supplied to the pipes. Covers of distributing chambers and casing closing the annulus are equipped with fittings for inlet and outlet of heat carriers.
Fig.4.9. Continuous shell and tube heat exchangers:
a - single-pass with rigidly fixed gratings; b - with concentric; c - with segmental partitions in the annulus; d - with temperature compensators on the body; e - with a floating lower head; e - with U-shaped pipes; g - with stuffing box seal on the upper floating head; 1 - housing or casing; 2 - tube sheets; 3 - pipes; 4 - bottoms and covers of distribution chambers; 5, 6 - flanges; 7 - supports
Shell and tube heat exchangers are used for heating and cooling liquids and gases, as well as for evaporation and condensation of substances in various technological processes. In particular, they are used as regenerative heaters. feed water, in water treatment systems, as oil coolers.
At given flow coolant G, kg/s, and the selected speed of its movement w, m / s, in pipes their number in one pass of the heat exchanger
n= 4G/(w rp d 2).
Heat exchange surface area
F=p d Wed l nz,
where l- working length of pipes; d cp - their calculated diameter, equal to
d cp = 0.5 ( d n + d in);
z- the number of passages of the pipe space. The length of heat exchange pipes is recommended to be 1000, 1500, 2000, 3000, 4000, 6000 and 9000 mm. In shell-and-tube heat exchangers with a surface area up to 300 m 2 - no more than 4000 mm.
Placement of pipes in tube sheets is carried out along the vertices of equilateral triangles, along concentric circles or along the vertices of squares. The most common way is the first option (Fig. 4.10). The number of pipes in the apparatus, depending on their diameter, the diameter of the body and the number of strokes in the pipe space, is indicated in Table. 4.9 [7, 8].
Fig.4.10. Placement of pipes in the tube sheet:
a - along concentric circles; b - along the vertices of equilateral triangles; c - chess; g - corridor
Table 4.9. The number of pipes in shell-and-tube heat exchangers when they are placed along the vertices of equilateral triangles [7, 8]
| apparatus diameter, | Pipe diameter (outer), mm | ||||
| 20 | 25 | 38 | |||
| one-way | two-way | one-way | two-way | one-way | |
| 159 | 19 | 13 | |||
| 273 | 61 | - | 42 | - | - |
| 325 | 91 | 80 | 61 | 52 | - |
| 400 | 181 | 166 | 111 | 100 | - |
| 600 | 393 (423) | 374 (404) | 261 (279) | 244 (262) | 111 (121) |
| 800 | 729 (771) | 702 (744) | 473 (507) | 450 (484) | 197 (211) |
| 1000 | 1177 (1247) | 1142 (1212) | 783 (813) | 754 (784) | 331 (361) |
| 1200 | 1705 (1799) | 1662 (1756) | 1125 (1175) | 1090 (1140) | 473 (511) |
| 1400 | 2369 (2501) | 2318 (2450) | 1549 (1629) | 1508 (1588) | 655 (711) |
Note: In parentheses are the number of pipes for heat exchangers when placed without fenders, when pipes are added on both sides of the large hexagon.
The diameters and pitches of the holes in the tube sheets and heat exchanger baffles, when the pipes are located at the vertices of an equilateral triangle, are determined by the outer diameter of the pipes (Table 4.10).
Table 4.10. Hole diameters in tube sheets and baffles of shell-and-tube heat exchangers [8]
| Outside diameter | Hole diameters d, mm | Step between holes, mm | |
| in the lattice | in the partition | ||
| 16 | 16,3 | 17,0 | 22 |
| 20 | 20,4 | 20,8 | 26 |
| 25 | 25,4 | 26,0 | 32 |
| 38 | 38,7 | 39,0 | 48 |
| 75 | 57,8 | 60,0 | 70 |
When expanding pipes, the step s= (l.3 ¸ 1.6) d n, when welding s= l,25 d n. Minimum thickness: for steel grating d p min = 5 + 0.125 d n, copper d p min \u003d \u003d 10 + 0.2 d n The thickness of the grid is checked by strength calculation, taking into account its weakening by holes and the way the pipes are placed.
Inner diameter of the shell of a single-pass heat exchanger D in = s (b - 1) + 4d n or D c = l,l s\(\sqrt(n)\) ; multi-way - D c = l,l s \(\sqrt(n/\psi)\), where b is the number of pipes on the diagonal of the large hexagon; \(\psi\)- the filling factor of the tube sheet, equal to 0.6 - 0.8.
The calculated value of the internal diameter of the casing is rounded up to the nearest of the following series: 3600, 3800 and 4000 mm. Cylindrical casings of apparatuses can be made of steel pipes with an outer diameter of 159, 219, 273, 325, 377, 426, 480, 530, 720, 820, 920 and 1020 mm.
For heat exchangers without baffles, the free cross-sectional area of the annulus (nd))_(n)^(2)z\right)\text(.)\)
If a f mt > f, where f- the calculated value of the open section of the annular space, then the annular space is divided by partitions into the number of passages i = f mt / f. The number of passes in the annular space is recommended to be taken from the range 1, 2, 3, 4, 6. For a heat exchanger, in which the annulus is divided into i passages by transverse segmental partitions, the reduced section, according to the area of \u200b\u200bwhich the coolant velocity in the annular space is calculated (specified),
\((f)_(\text(pr))=(f)_(\text(mt))(l)_(c)\phi /(L)_(\text(eq)),\)
where l c is the distance between the segment partitions; j - coefficient taking into account the narrowing of the open section of the annulus ())^(2));\]
L eq = l c+ D at 4 b /3 – equivalent path length of the coolant; b- distance from the edge of the segmental partition to the body of the device, b= (0.2 ¸ 0.4) D in.
General purpose shell-and-tube heat exchangers are made of carbon or of stainless steel with a heat exchange surface area from 1 to 2000 m 2 for nominal pressure up to 6.4 MPa. Structurally, they are divided into types shown in Fig. 4.9. The main parameters and dimensions of shell-and-tube heat exchangers are given in Table. 4.11 - 4.16.
Shell-and-tube heat exchangers of the TN type (with fixed grates) and TK (with lens compensators on the casing) are made horizontal and vertical from carbon steel (Fig. 4.11). TH type heat exchangers are used for heating and cooling liquid and gaseous media with temperatures from – 30°С to + 350°С for conditional pressure from 0.6 to 6.4 MPa.
Fig.4.11. Block of two shell-and-tube heat exchangers
If the temperature difference between the heat carriers exceeds 50°C, it is recommended to use collector-type heat exchangers designed for a working pressure of not more than 2.5 MPa.
Heat exchangers of the TN, TK, and TP types made of carbon steel and designed for an explosive or toxic environment, depending on the temperature, must be allowed to operate at reduced pressure according to [8]. At coolant temperatures above 400 ° C, it is necessary to use heat exchangers made of alloyed steel.
The main parameters of welded heat exchangers are given in Table. 4.13 and 4.14.
Pipes for heat exchangers are selected from the operating conditions and the aggressiveness of the environment. For standard heat exchangers, pipes made of carbon steel 10 or 20, corrosion-resistant steel OX18N10T and brass LOMsh 70-1-0.06 are used. Placement of pipes in lattices is carried out along the vertices of equilateral triangles.
Table 4.11. Technical characteristics of water-water heaters, GOST 27590-88 and OST 34-588-68
| Designation | External and internal diameters of the body D n/ D ext, mm | Heater length with rolls | Number of tubes | Surface area heating F, m 2 |
Clear area, m 2 | |
| tubes | annulus f mt | |||||
| 01 OST 34-558-68 02 OST 34-558-68 |
57/50 | 2220 | 4 | 0,37 | 0,00062 | 0,00116 |
| 03 OST 34-558-68 04 OST 34-558-68 |
76/69 | 2300 | 7 | 0,65 | 0,00108 | 0,00233 |
| 05 OST 34-558-68 06 OST 34-558-68 |
89/82 | 2340 | 12 | 1,11 | 0,00185 | 0,00287 |
| 07 OST 34-558-68 08 OST 34-558-68 |
114/106 | 2424 | 19 | 1,76 | 0,00293 | 0,005 |
| 09 OST 34-558-68 10 OST 34-558-68 |
168/158 | 2620 | 37 | 3,4 | 0,0067 | 0,0122 |
| 11 OST 34-558-68 12 OST 34-558-68 |
219/207 | 2832 | 64 | 5,89 | 0,00985 | 0,02079 |
| 13 OST 34-558-68 14 OST 34-558-68 |
273/259 | 3032 | 109 | 10 | 0,01679 | 0,03077 |
| 15 OST 34-558-68 16 OST 34-558-68 |
325/309 | 3232 | 151 | 13,8 | 0,02325 | 0,01464 |
| 17 OST 34-558-68 18 OST 34-558-68 |
377/359 | 3430 | 216 | 19,8 | 0,03325 | 0,05781 |
| 19 OST 34-558-68 20 OST 34-558-68 |
426/408 | 3624 | 283 | 25,8 | 0,04356 | 0,07191 |
| 21 OST 34-558-68 22 OST 34-558-68 |
530/512 | 3552 | 450 | 41 | 0,06927 | 0,11544 |
| 26 OST 34-588-68 27 OST 34-583-68 |
57/50 | 2220 | 4 | 0,36 | 0,00062 | 0,00116 |
| 28 OST 34-588-68 29 OST 34-588-68 |
76/69 | 2300 | 7 | 0,64 | 0,00108 | 0,00233 |
| 30 OST 34-588-68 31 OST 34-588-68 |
89/82 | 2340 | 12 | 1,1 | 0,00185 | 0,00287 |
| 32 OST 34-588-68 33 OST 34-588-68 |
114/106 | 2424 | 19 | 1,74 | 0,00293 | 0,005 |
| 34 OST 34-588-68 35 OST 34-588-68 |
168/158 | 2620 | 37 | 3,39 | 0,0057 | 0,0122 |
| 36 OST 34-588-68 37 OST 34-588-68 |
219/207 | 2832 | 64 | 5,85 | 0,00985 | 0,02079 |
| 38 OST 34-588-68 39 OST 34-588-68 |
273/259 | 3032 | 109 | 9,9 | 0,01679 | 0,03077 |
| 40 OST 34-588-68 41 OST 34-588-68 |
325/309 | 3232 | 151 | 13,7 | 0,02325 | 0,04454 |
| 42 OST 34-588-68 43 OST 34-588-68 |
377/359 | 3430 | 216 | 19,6 | 0,03325 | 0,05781 |
| 44 OST 34-588-68 45 OST 34-588-68 |
426/408 | 3624 | 283 | 25,5 | 0,04356 | 0,071191 |
| 46 OST 34-588-68 47 OST 34-588-68 |
530/512 | 3552 | 450 | 40,6 | 0,06927 | 0,11544 |
Table 4.12. Technical characteristics of horizontal steam-water
heaters, GOST 28679-90, OST 34-351-68, OST 34-352-68,
OST 34-376-68 and OST 34-577-68
| Designation | External and internal diameters of the body D n/ D ext, mm | Length-on-true-side | Number of moves | Number of tubes | The given number of tubes in a vertical row m | Surface area heating F, |
Clear area, m 2 | |
| annular space | single stroke tubes | |||||||
| 01 OST 34-531-68 02 OST 34-531-68 03 OST 34-531-68 04 OST 34-531-68 05 OST 34-531-68 06 OST 34-531-68 07 OST 34-531-68 08 OST 34-531-68 09 OST 34-531-68 |
325/309 | 3000 | 2 | 68 | 8,5 | 9,5 | 0,061 | 0,0052 |
| 11 OST 34-531-68 12 OST 34-531-68 13 OST 34-531-68 14 OST 34-531-68 15 OST 34-531-68 16 OST 34-531-68 17 OST 34-531-68 |
325/309 | 2000 | 2 | 68 | 8,5 | 6,3 | 0,061 | 0,0052 |
| 01 OST 34-532-68 02 OST 34-532-68 03 OST 34-532-68 04 OST 34-532-68 05 OST 34-532-68 06 OST 34-532-68 07 OST 34-532-68 08 OST 34-532-68 09 OST 34-532-68 |
325/309 | 3000 | 4 | 68 | 8,5 | 9,5 | 0,061 | 0,0026 |
| 01 OST 34-576-68 02 OST 34-576-68 03 OST 34-576-68 04 OST 34-576-68 05 OST 34-576-68 06 OST 34-576-68 07 OST 34-576-68 08 OST 34-576-68 09 OST 34-576-68 |
325/309 | 3000 | 2 | 68 | 8,5 | 9,5 | 0,061 | 0,0052 |
| 11 OST 34-576-68 12 OST 34-576-68 13 OST 34-576-68 14 OST 34-576-68 15 OST 34-576-68 16 OST 34-576-68 17 OST 34-576-68 |
325/309 | 2000 | 2 | 68 | 8,5 | 6,3 | 0,061 | 0,0052 |
| 01 OST 34-577-68 02 OST 34-577-68 03 OST 34-577-68 04 OST 34-577-68 05 OST 34-577-68 06 OST 34-577-68 07 OST 34-577-68 08 OST 34-577-68 09 OST 34-577-68 |
325/309 | 3000 | 4 | 68 | 8,5 | 9,5 | 0,061 | 0,0026 |
Tube sheets of heat exchangers with a shell diameter from 600 to 1200 mm, designed for aggressive environments, are made of two layers of steel: VMStZsp together with Kh18N10T or from 16GS together with Kh18N10T.
Heat exchangers of the TN and TK types can be assembled into blocks consisting of several horizontal units. The number of devices in the block and dimensions taken according to the total area of the heat exchange surface [8].
Floating head heat exchangers (Figures 4.3 and 4.12) are used to heat or cool liquid and gaseous media within operating temperatures from – 30 to +450 °С and conditional pressure from 1.6 to 6.4 MPa in the pipe or annular space. The main parameters of vertical and horizontal heat exchangers are given in Table. 4.12, 4.13 and 4.15. The casing, distribution chamber and covers are made of VMStZsp steel or 16GS steel. Depending on the purpose of the apparatus, pipes made of steel 20 or AMg2M alloy are used. For capacitors, pipes made of brass LOMsh 70-1-0.06 or LAMsh 77-2-0.06 are used. For heating or cooling aggressive media, pipes made of X5M steel or OX18N10T corrosion-resistant steel are used. In this case, tube sheets are made of steel 16GS or two layers of steels 16GS and X18X10T.
Fig.4.12. Shell and tube heat exchanger with floating head:
1 - distribution chamber cover; 2 - distribution chamber; 3 - casing; 4 - pipes; 5 - casing cover; 6 - floating head cover; 7 - support
Fig.4.13. Shell and tube heat exchanger with U-tubes:
1 - distribution chamber cover; 2 - casing; 3 - U-shaped pipes; 4 - support
Heat exchangers with U-shaped pipes (Fig. 4.13) are used in heat exchange conditions at operating temperatures of the medium from -30 to +450 ° С. Standard heat exchangers are manufactured with a shell diameter from 325 to 1400 mm and the characteristic parameters indicated in Table. 4.16. The use of heat exchangers with U-shaped pipes is regulated by the nominal pressure, which for neutral and non-explosive media ranges from 1.6 to 6.4 MPa. In heat exchangers with a medium temperature of 100 to 450°C, the working pressure decreases within the limits specified in [8]. The casing and distribution chamber are usually made of VMStZps or 16GS steel. Heat exchange tubes are made of steel 20, and in condensers - from AMg2M alloy.
Strength calculations structural elements heat exchangers made of carbon or alloy steel are made in accordance with the requirements of [9].
Heat exchangers "pipe in pipe" (Fig. 4.14) are used for heating and cooling liquids at pressures up to 2.5 MPa and temperatures up to + 450 ° C. By design, devices are distinguished with a rigid welded structure (type TT), with stuffing boxes at one or both ends of the pipes (type TT-C), with finned tubes (type TT-R). The main parameters and dimensions of the heat exchangers are given in Table. 4.17. They are made from solid-rolled pipes. Pipe material - carbon steel or stainless steel.
Fig.4.14. Heat exchanger type "pipe in pipe":
1 - inner pipe; 2 - outer pipe; 3 - kalach
Serial and parallel connection of individual devices "pipe in pipe" allows you to create heat exchangers with a surface area of 1 to 250 m 2 . The simplicity of the design of devices of this type allows them to be manufactured in repair shops of enterprises.
Table 4.13. Welded shell-and-tube heat exchangers with fixed tube sheets and shell-and-tube heat exchangers with a temperature compensator on the shell [8]
| Diameter Ha D in, mm |
Dove-le- | Dimensions | Quantity | Heat exchange surface area of apparatuses, m 2, with pipe length, mm | Cross-sectional area one pass through the pipes, m 2 10 2 |
Passage area, m 2 .I0 2 | |||||
| 2000 | 3000 | 4000 | 6000 | 9000 | In the cut- | Between partition |
|||||
| 20x2 | 1 | 22 | 34 | 45 | 68 | 3,6 | 2,1 | 2,5 | |||
| 20 x 2 | 2 | 21 | 31 | 41 | 62 | - | 1,7 | ||||
| 400 | 25 x 2 | 1 | 17 | 26 | 35 | 52 | - | 3,8 | 2,2 | 2,1 | |
| 25 x 2 | 2 | 15 | 23 | 31 | 47 | - | 1,7 | ||||
| 1 | 49 | 73 | 98 | 147 | 7,9 | 4,7 | 5,4 | ||||
| 1,0 | 20 x 2 | 2 | 46 42 | 70 | 93 | 140 | - | 3,8 | |||
| 600 | 1,6 | 6 | 43 | 64 | 86 | 129 | - | 1,0 | |||
| 1 | 40 | 61 | 81 | 122 | 9,0 | 4,9 | 5,2 | ||||
| 2,5 | 25 x 2 | 2 | 38 | 57 | 76 | 114 | - | 4,2 | |||
| 4,0 | 4 | 32 | 49 | 65 | 98 | - | 1,8 | ||||
| 6 | 34 | 51 | 68 | 102 | - | 0,9 | |||||
| 1 | 91 | 138 | 184 | 276 | 416 | 14,8 | 7,8 | 7,7 | |||
| 1,0 1,6 | 20 x 2 | 2 | 88 | 132 | 177 | 266 | 400 | 7,1 | |||
| 800 | 1,6 | 4 | 82 | 124 | 165 | 248 | 373 | 3,3 | |||
| 2,5 | 1 | 74 | 112 | 150 | 226 | 339 | 16,7 | 7,7 | 7,9 | ||
| 25 x 2 | 2 | 70 | 106 96 | 142 128 | 212 193 | 320 290 | 7,8 3,1 | ||||
| 4,0 | 6 | 62 | 93 | 125 | 187 | 282 | 2,2 | ||||
| 6,0 | 1 | 220 | 295 | 444 | 667 | 23,8 | 12,5 | 13,5 | |||
| 1,0 | 20 x 2 | 2 4 | - | 214 202 | 286 270 | 430 406 | 648 610 | 11,6 5,1 | |||
| 1,6 | 6 | - | 203 | 272 | 409 | 614 | 3,4 | ||||
| 1000 | 2,5 | 1 | - | 183 | 244 | 366 | 551 | 27,0 | 12,1 | 11,7 | |
| 25 x 2 | 2 | - | 175 | 234 | 353 | 530 | 13,2 | ||||
| 4,0 | 4 | - | 163 | 218 | 329 | 494 | 6,0 | ||||
| 6 | 160 | 214 | 322 | 486 | 3,8 | ||||||
| 1 | 426 | 642 | 964 | 34,5 | 17,3 | 16,5 | |||||
| 0,6 | 20 x 2 | 2 | - | 415 | 626 | 942 | 16,9 | ||||
| 1,0 | 4 | - | - | 396 | 596 | 897 | 7,9 | ||||
| 1200 | 6 | - | - | 397 | 597 | 900 | 5,4 | ||||
| 1 | 348 | 525 | 790 | 39,0 | 16,8 | 15,2 | |||||
| 1,6 2,5 | 25 x 2 | 2 | - | - | 338 | 509 | 766 | 18,9 | |||
| 6 | - | - | 316 | 476 | 716 | 5,7 | |||||
Table 4.14. Shell and tube heat exchangers [ 8 ]
| Main parameters and dimensions | Norms by type | ||||
| TN | TC | TP TU | TS | ||
| 1-2000 | 10-1250 10-1400 | 10-315 | |||
| Nominal pressure in the pipe or annular space p y, MPa | 0,6; 1,0; 1,6; | 0,6; 1,0; | 1,0; 1,6; 2,5; 4,0; 6,4 | 0,6; 1,0 | |
| Casing diameter, mm: external (when made from pipes) internal (in the manufacture of sheet |
159; 273; 325; 426
400; (500); 600; 800; 1000; 1200; 1600; 1800; 2000; 2200 |
325; 426
400; 500; 600; 800; 1000; 1200; 1400 |
400; 500; | ||
| Outer diameter and thickness wall heat exchanger pipes, mm |
(16X1.6); 20X2; 25X2; 25X2.5; 38X2; (38X3); |
20X2; 25X2; 25X2.5 | |||
| Length of heat exchange pipes, mm | 1000; 1500; 2000; 3000;
4000; 6000; 9000 |
3000; 6000; 9000 | |||
| Scheme and placement step heat exchange pipes in tube sheets, mm |
Vertices of equilateral triangles: 21 for pipe diameter 16 |
On the vertices of squares or equilateral triangles: 26 for pipe diameter 20 |
|||
Table 4.15. Floating head shell and tube heat exchangers [ 8 ]
| Casing diameter, mm | Pipe diameter, mm | Number of pipe passes | Heat exchange surface area, m 2, with pipe length, mm, | Square through passage one move through the pipes m 2 × 10 3, at their location |
Checkpoint area sections, m 2 -10 3, at the location of the pipes |
|||||||||
| tops square |
along the vertices of the triangle | along the corners of the square | along the vertices of the triangle | |||||||||||
| 3000 | 6000 | 9000 | 6000 | 9000 | along the corners of the square | along the vertices of the triangle | in the cutout partitions |
between the small towns |
in the cutout partitions |
between partitions | ||||
| D n | 325 | 20 | 2 | 11,7 | 23,4 | - | - | - | 6,0 | - | 1,2 | 2,3 | - | - |
| 426 | 20 | 2 | 23,4 | 47,0 | - | - | - | 13,0 | - | 2,1 | 4,2 | - | -» | |
| 500 | 20 | 2 | 29,4 | 79,0 | - | - | - | 21,0 | - | 2,6 | 6,8 | - | - | |
| D in | 600 | 20 | 2 4 | - | 119,0 111,0 | 179,0 166,0 | 135,0 122,0 | 202,0 183,0 | 32,0 14,0 | 36,0 | 5,3 | 9,6 | 4,7 | 5,8 |
| 25 | 2 | - | 99,0 90,0 | 149,0 135,0 | 109,0 97,0 | 164,0 146,0 | 36,0 16,0 | 40,0 17,0 | 4,9 | 9,6 | 4,6 | 5,5 | ||
| 800 | 20 | 2 | - | 214,0 200,0 | 322,0 300,0 | 249,0 231,0 | 374,0 346,0 | 55,0 27,0 | 64,0 31,0 | 9,2 | 15,6 | 7,7 | 8,6 | |
| 25 | 2 4 | - | 171,0 160,0 | 258,0 240,0 | 196,0 178,0 | 294,0 267,0 | 60,0 30,0 | 69,0 30,0 | 8,4 | 15,6 | 7,5 | 8,8 | ||
| 1000 | 20 | 2 | - | 352,0 336,0 | 528,0 504,0 | 411,0 332,0 | 610,0 576,0 | 92,0 45,0 | 107,0 49,0 | 14,2 | 24,0 | 17,6 | 14,0 | |
| 25 | 2 | - | 291,0 275,0 | 436,0 413,0 | 332,0 308,0 | 502,0 462,0 | 104,0 48,0 | 119,0 56,0 | 12,3 | 24,0 | 11,7 | 12,5 | ||
| 1200 | 20 | 2 | - | 525,0 505,0 | 788,0 756,0 | 611,0 584,0 | 916,0 875,0 | 140,0 68,0 | 162,0 78,0 | 20,5 | 36,0 | 17,0 | 20,0 | |
| 25 | 2 | - | 425,0 405,0 | 636,0 607,0 | 490,0 460,0 | 735,0 693,0 | 155,0 74,0 | 179,0 85,0 | 19,2 | 29,0 | 17,0 | 18,5 | ||
| 1400 | 20 | 2 | - | 726,0 708,0 | 1090,0 1060,0 | 843,0 805,0 | 1260,0 1210,0 | 194,0 91,0 | 222,0 107,0 | 25,0 | 41,0 | 22,0 | 23,0 | |
| 25 | 2 | - | 590,0 567,0 | 885,0 852,0 | 686,0 650,0 | 1030,0 980,0 | 215,0 104,0 | 250,0 116,0 | 24,0 | 40,5 | 22,0 | 21,0 | ||
Table 4.16. Shell and tube heat exchangers with U-shaped
pipes [ 8]
| rowspan="3"| Diameter | Dia- | Heat exchange surface area, m 2, with pipe length, mm, and their arrangement in the grids |
rowspan="3" | The area of the passage section of one pass through the pipes, m 2 io 3, at their location | Checkpoint area sections, m 2 I0 3, pipes at their location |
|||||||||
| along the corners of the square | along the vertices of the triangle | along the corners of the square | along the vertices of the triangle | ||||||||||
| 3000 | 6000 | 9000 | 6000 | 9000 | on vertices of the square |
tops triangle |
in you- partition cut |
inter- do nepe-town-kami |
in you- reze pere-city-ki |
inter- du re-go-rod- kami |
|||
| D n | 325 | 20 | 14 | 28 | - | - | - | 7 | - | 1,0 | 2,5 | - | - |
| 426 | 20 | 28 | 55 | - | - | - | 14 | - | 1,8 | 4,6 | - | - | |
| D ext | 500 | 20 | 44 | 86 | - | - | - | 22 | - | 2,6 | 6,0 | - | - |
| 600 | 20 | - | 126 | 188 | 150 | 224 | 33 | 39 | 5,1 | 10,0 | 4,4 | 6,0 | |
| 800 | 20 | - | 225 | 335 | 263 | 390 | 58 | 68 | 9,3 | 17,0 | 9,0 | 9,0 | |
| 1000 | 20 | - | 383 | 567 | 443 | 656 | 98 | 114 | 13,0 | 25,0 | 12,6 | 13,0 | |
| 1200 | 20 | - | 575 | 850 | 660 | 973 | 148 | 168 | 19,0 | 36,0 | 17,0 | 21,0 | |
| 1400 | 20 | - | 796 665 | 1170 964 | 923 753 | 1361 1108 | 202 227 | 232 262 | 24,0 | 47,0 45,0 | 22,0 | 28,0 22,0 | |
Table 4.17. Heat exchangers of the "pipe in pipe" type [ 8 ]
| Basic parameters (Fig. 4.19) | Apparatus | ||||
| collapsible one- and two-flow small-sized |
non-separable single-thread small-sized |
collapsible in-line |
non-separable in-line |
collapsible lot- in-line |
|
| Outer diameter heat- exchange pipes, mm |
25, 38, 48, 57 | 76, 89, 108, 133, 159 | 38, 48, 57 | ||
| Outer diameter of shell pipes, mm | 57, 76, 89, 108 | 108, 133, 159, 219 | 89, 108 | ||
| Length of casing pipes, m | 1,5; 3,0; 6,0; 4,5 | 4,5; 6,0; | 6,0; 9,0; | 3,0; 6,0; | |
| Heat exchange surface area, m 2 | 0,5–5,0 | 0,1–1,0 | 5,0–18,0 | 1,5–6,0 | 5,0–93,0 |
| Cross section area ny, m 2 .I0 4: inside heat exchangers outside heat exchangers |
2,5–35,0 | 2,5–17,5 | 50–170 | 45–170 | 35–400 |
| Nominal pressure, MPa: inside heat exchangers outside heat exchangers |
6,4; 10,0; | ||||
| 6,4; 10,0; | 1,6; 4,0 | 1,6; 4,0 | 1,6; 4,0 | ||
Shell and tube heat exchangers are among the most common. They are used in industry and transport as heaters, condensers, coolers, for various liquid and gaseous media. Main elements of a shell-and-tube heat exchanger are: casing (housing), tube bundle, cover chambers, branch pipes, shut-off and control valves, control equipment, supports, frame. The casing of the apparatus is welded in the form of a cylinder from one or more, usually steel sheets. The casing wall thickness is determined by the maximum pressure of the working medium in the annular space and the apparatus diameter. The bottoms of the chambers can be spherical welded, elliptical stamped and less often flat. The thickness of the bottoms must not be less than the thickness of the hull. Flanges are welded to the cylindrical edges of the casing for connection with covers or bottoms. Depending on the location of the apparatus relative to the floor of the room (vertical, horizontal), appropriate supports must be welded to the body. Preferred vertical arrangement housing and the entire heat exchanger, since in this case the area occupied by the apparatus is reduced, and its location in the working room is more convenient.
The tube bundle of the heat exchanger can be assembled from smooth steel seamless, brass or copper straight or U- and W-shaped pipes with a diameter from several millimeters to 57 mm and a length from several centimeters to 6-9 m with a body diameter of up to 1.4 m or more . Introduced, especially in refrigeration and transport, samples of shell-and-tube and sectional heat exchangers with low rolling longitudinal, radial and spiral fins. The height of the longitudinal rib does not exceed 12-25 mm, and the height of the protrusion of rolled pipes is 1.5-3.0 mm with 600-800 ribs per 1 m of length. The outer diameter of pipes with low-radial (rolling) fins differs little from the diameter of smooth pipes, although the heat exchange surface increases by 1.5-2.5 times. The shape of such a heat exchange surface ensures high thermal efficiency of the apparatus in working environments with different thermophysical properties.
Depending on the design of the bundle, both smooth and rolled tubes are fixed in one or two-tube gratings by flaring, sorting, welding, soldering or stuffing boxes. Of all the above methods, more complex and expensive stuffing box seals are less commonly used, which allow longitudinal movement of pipes during thermal elongation.
Placement of pipes in tube sheets(Fig. 2.2) can be done in several ways: along the sides and vertices of regular hexagons (chess), along the sides and vertices of squares (corridor), along concentric circles and along the sides and vertices of hexagons with a diagonal shifted by an angle β. Preferably, the pipes are placed evenly over the entire area of the grid along the sides and tops of regular hexagons. Apparatus designed to handle contaminated liquids often adopt a rectangular tube arrangement to facilitate cleaning of the annulus.
Rice. 2.2 - Methods for fixing and placing pipes in tube sheets: a - flaring; b - flaring with flanging; in - flaring in glasses with grooves; d and e - welding; e - with the help of an oil seal; 1 - along the sides and vertices of regular hexagons (triangles); 2 - along concentric circles; 3 - on the sides and tops of the squares; 4 - along the sides and vertices of hexagons with a diagonal shifted by an angle β
AT horizontal shell-and-tube heat exchangers-condensers in order to reduce the thermal resistance on the outer surface of the pipes caused by the condensate film, it is recommended to place the pipes on the sides and vertices of the hexagon with a diagonal shifted by an angle β, while leaving free passages for steam in the annulus.
Some options for the arrangement of tube bundles in the body are shown in (Fig. 2.3). If both gratings of a bundle of straight pipes are clamped between the upper and lower flanges of the body and covers, then such an apparatus will have a rigid structure (Fig. 2.3, a, b). Rigid heat exchangers are used at a relatively small temperature difference between the body and pipes (approximately 25-30 ° C) and under the condition that the body and pipes are made of materials with close values of their elongation coefficients. When designing the apparatus, it is necessary to calculate the stresses arising from the thermal elongation of pipes in the tube sheet, especially at the junctions of the pipes with the sheet. According to these stresses, in each specific case, the suitability or unsuitability of a rigid structure apparatus is determined. Possible options shell-and-tube heat exchangers of non-rigid design are also shown in (Fig. 2.3, c, d, e, f).
Rice. 2.3 - Schemes of shell-and-tube heat exchangers: a - with rigid fastening of tube sheets with segmented partitions; b - with rigid fastening of tube sheets with annular baffles; c - with a lens compensator on the body; g - with U-shaped pipes; d - with double pipes (pipe in pipe); e - with a "floating" chamber of a closed type; 1 - cylindrical body; 2 - pipes; 3 - tube sheet; 4 - upper and lower chambers; 5, 6, 9 - segment, annular and longitudinal partitions in the annulus; 7 - lens compensator; 8 - partition in the chamber; 10 - inner pipe; 11 - outer pipe; 12 - "floating" camera
AT shell-and-tube heat exchanger with a lens compensator on the body(Fig. 2.3, c) thermal elongations are compensated by axial compression or tension of this compensator. Such devices are recommended to be used at an excess pressure in the annular space of not more than 2.5 10 5 Pa and with a deformation of the compensator by no more than 10-15 mm,
AT heat exchangers with U-shaped(Fig. 2.3, d), as well as with W-shaped pipes, both ends of the pipes are fixed in one (more often in the upper) tube sheet. Each of the bundle tubes can be freely extended independently of the extension of other tubes and apparatus elements. At the same time, no stresses arise at the junctions of the pipes with the tube sheet and at the connection of the tube sheet with the body. These heat exchangers are suitable for operation at high heat transfer pressures. However, devices with bent pipes cannot be recognized as the best because of the difficulty of manufacturing pipes with different bending radii, the difficulty of replacing and the inconvenience of cleaning bent pipes.
In addition, under operating conditions, with a uniform distribution of the coolant at the inlet to the pipes, there will be an unequal temperature of this coolant at the exit from them due to different areas of the heat exchange surfaces of these pipes.
AT double tube shell and tube heat exchangers(Fig. 2.3, e) each element consists of two pipes: outer - with a closed lower end and inner - with an open end. Top end inner pipe a smaller diameter is fixed by flaring or welding in the upper tube sheet, and a larger diameter pipe is fixed in the lower tube sheet. Under these installation conditions, each of the elements, consisting of two pipes, can be freely extended without causing thermal stresses. The heated medium moves along the inner pipe, then along the annular channel between the outer and inner pipes. The heat flow from the heating to the heated medium is transferred through the wall of the outer pipe. In addition, the surface of the inner tube also participates in the process of heat transfer, because the temperature of the heated medium in the annular channel is higher than the temperature of the same medium in the inner tube.
AT shell-and-tube heat exchanger with a "floating" chamber of a closed type(Fig. 2.3, e) the tube bundle is assembled from straight tubes connected by two tube sheets. The upper grate is clamped between the upper flange of the body and the flange of the upper chamber. The lower tube sheet is not connected to the body; together with the lower chamber of the inner tube space, it can freely move along the axis of the heat exchanger. These heat exchangers are more advanced than other non-rigid devices. Some increase in the cost of the apparatus due to an increase in the diameter of the body in the area of the "floating" chamber and due to the need to manufacture an additional cover is justified by the simplicity and reliability of operation. Devices can be vertical and horizontal execution.
Other types of heat exchangers with thermal elongation compensation, such as, for example, with a bellows compensator on the upper branch pipe, which removes (supplies) the coolant from the inside of the pipe space, with stuffing box seals in the upper branch pipe or tube sheet, etc. due to the complexity of manufacturing, low reliability in operation and low allowable coolant pressures in the future will be used only in exceptional cases.
The tube and shell spaces of the heat exchangers are separated and form two circuits for the circulation of two heat carriers. But if necessary, not one, but two or even three heated media can be supplied to the intrapipe circuit, separating these flows with partitions placed in the covers of the apparatus.
In practice, when designing such devices, it is possible to substantiate and ensure optimum speed only one coolant passing through the intrapipe circuit, while changing the location of the pipes in the tube sheet and the number of passes through the pipes. Multi-pass devices are created by installing appropriate baffles in the upper and lower chambers of the heat exchanger.
The flow rate in the annular space is determined by the conditions of placement of pipes in the tube sheet. Usually, the free cross section for the passage of the coolant in the annular space is 2-3 times greater than the free cross section of the pipes, therefore, with equal volumetric flow rates of both media, the flow velocity in the annulus is 2-3 times less than in the pipes. If necessary, segmented or annular baffles can be installed in the annulus to reduce the free cross section and stiffen the tube bundle. Naturally, in this case, the flow velocity in the annular space will increase, the longitudinal-transverse washing of the tube bundle will be organized, and the heat transfer conditions will improve.
In water-water or liquid-liquid heat exchangers in general, it is advisable to direct the working medium with a lower flow rate per unit time (or with a higher viscosity) to the intrapipe circuit, although in some cases there may be deviations from this principle, for example, in oil coolers (Fig. 2.3b).
AT vapor-liquid heat exchangers, especially at elevated steam parameters, there is a large difference between the temperatures of the pipe walls and the casing. Therefore, for such cases of liquid heating, devices of a non-rigid design are most often used, with the exception of steam condensers operating under vacuum. Steam usually passes in the annular space from top to bottom, and liquid - inside the pipes. Condensate is removed from the bottom of the housing through a steam trap. A prerequisite for ensuring normal work of a vapor-liquid heat exchanger, is the removal of non-condensable gases from the upper part of the annular space and from the lower volume above the condensate surface. Otherwise, the conditions of heat exchange on the outer surface of the pipes will worsen, and the thermal performance of the apparatus will sharply decrease.
In complex industrial heat and power plants, capacitors are used, which play an auxiliary role in this process. The choice of the type and design of the condenser depends on the pressure at which the phase transition process takes place and on the need to store the condensate. In this regard, surface and mixing capacitors should be considered.
Surface shell and tube condensers of a rigid horizontal type are compact, convenient for placement in combination with other equipment, but at the same time they are more expensive than mixing ones. The arrangement of pipes in the lattice of surface condensers is carried out according to the option shown in fig. 2.2 (4) or fig. 2.2(1). In the course of water in the pipes, the condensers are two- and four-way. The steam condenses in the annular space, in which free passages for steam to the lower rows of pipes are provided. This method of steam condensation ensures the purity of the condensate, which can serve as a nutrient medium for steam generators. These capacitors can be pressurized between 5000 and 3000 Pa.
A large number of various shell-and-tube heat exchangers are mass-produced by specialized factories, so in many cases it is possible to choose a heat exchanger that meets the calculated characteristics from the catalog.
The designs of modern recuperative heat exchangers of the surface type of continuous action are very diverse. Let's consider the most characteristic.
Shell and tube heat exchangers are devices made of tube bundles fastened with tube sheets (boards) and limited by casings and covers with nozzles. The tube and annular spaces in the apparatus are separated, and each of them can be divided by partitions into several passages. Baffles are designed to increase the speed and, consequently, the heat transfer coefficient of heat carriers. Heat exchangers of this type are intended for heat exchange between various liquids, between liquids and steam, between liquids and gases. Typical designs shell-and-tube heat exchangers are used in cases where it is required large surface heat exchange.
When heating a liquid with steam, in most cases, steam is introduced into the annular space, and the heated liquid flows through the tubes. In shell-and-tube heat exchangers, the cross section of the annular space is 2...3 times larger than the cross section inside the tubes. Therefore, at the same flow rates of heat carriers having the same state of aggregation, the coolant velocities in the annular space are lower and the heat transfer coefficients on the surface of the annular space are low, which reduces the heat transfer coefficient in the apparatus. On fig. 4.5 shows various types of shell and tube heat exchangers.
The heat transfer surface of the devices can range from several hundred square centimeters to several thousand. square meters. So, the condenser of a modern steam turbine with a capacity of 300 MW has more than 20 thousand pipes with a total heat exchange surface of about 15 thousand m 2.
The body (casing) of a shell-and-tube heat exchanger is a cylinder welded from one or more steel sheets. The shells differ mainly in the way they are connected to the tube sheet and the covers. The thickness of the shell wall is determined by the maximum pressure of the working medium and the diameter of the apparatus, but not less than 4 mm. Flanges are welded to the cylindrical edges of the casing for connection with covers or bottoms. Branch pipes and apparatus supports are welded on the outer surface of the casing.
The tubes of shell-and-tube devices are made straight or curved (U-shaped) with a diameter of 12 to 57 mm.
The material of the tubes is selected depending on the medium washing its surface. Tubes made of steel, brass and special alloys are used.
Tube sheets are used to fix pipes in them by means of flaring, welding, sealing or stuffing box connections. The tube sheets are bolted between casing and cover flanges or welded to the casing, or bolted only to the free chamber flanges (see Fig. 4.5).
Rice. 4.5. Types of shell and tube heat exchangers:
a - one-way; b - multi-way; in - film; g - with a lens compensator; d - with a floating head of a closed type; e - floating head open type; g - with stuffing box compensator; h - with U-shaped tubes; 1 - casing; 2 - exit chamber; 3 - tube sheet; 4 - pipes; 5 - inlet chamber; 6 - longitudinal partition; 7 - camera; 8 - partitions in the chamber; 9 - lens compensator; 10 - floating head; 11 - stuffing box; 12 - U-shaped pipes; I, II - heat carriers
The covers of shell-and-tube apparatus are in the form of flat plates, cones, spheres, and most often convex or concave ellipses.
Section heat exchangers(Fig. 4.6) are a type of tubular apparatus and consist of several sections connected in series, each of which is a shell-and-tube heat exchanger with a small number of pipes and a shell of small diameter.
In sectional heat exchangers, at the same flow rates of liquids, the rates of movement of heat carriers in the pipes and the annular space are almost equal, which provides increased heat transfer coefficients compared to conventional tubular heat exchangers. The simplest of this type is the tube-in-pipe heat exchanger (a smaller diameter tube is inserted into the outer tube). All elements of the apparatus are connected by welding.
Rice. 4.6. Section heat exchangers:
a - water heater of the heating system; b - type "pipe in pipe"; 1 - lens compensator; 2 - tubes; 3 - tube sheet with a flange connection with a casing; 4 - "kalach"; 5 - connecting pipes
The disadvantages of sectional heat exchangers are: the high cost of a heating surface unit, since dividing it into sections causes an increase in the number of the most expensive elements of the apparatus - tube sheets, flange connections, transition chambers, compensators, etc.; significant hydraulic resistance due to various turns and transitions cause increased consumption electricity to the drive of the coolant pumping pump.
Casings of serial sectional heat exchangers are made from pipes up to 4 m long, with an internal diameter of 50 to 305 mm. The number of pipes in the section is from 4 to 151, the heating surface is from 0.75 to 26 m 2, the pipes are brass with a diameter of 16/14 mm. The ratio of the heating surface to the volume of the heat exchanger reaches 80 m 2 /m 3 , and the specific structural weight is 50...80 kg/m 2 of the heating surface.
Spiral heat exchangers(Fig. 4.7) consist of two spiral channels of rectangular cross section, along which coolants I and II move. The channels are formed by metal sheets that serve as a heat exchange surface. The inner ends of the spirals are connected by a dividing wall. To ensure structural rigidity and fix the distance between the spirals, bosses are welded. From the ends of the spiral, they are closed with lids and tightened with bolts.
Horizontal spiral heat exchangers are used for heat exchange between two fluids. Vertical spiral heat exchangers are used for heat exchange between condensing vapor and liquid. Such heat exchangers are used as condensers and steam heaters for liquids.
Rice. 4.7. Types of spiral heat exchangers:
a - horizontal; b - vertical; 1, 3 - sheets; 2 - dividing wall; 4 - covers; I, II - heat carriers
The advantages of spiral heat exchangers include compactness (larger heat exchange surface per unit volume than that of multi-pass tubular heat exchangers) with the same heat transfer coefficients and lower hydraulic resistance for the passage of heat carriers. The disadvantages are the complexity of manufacturing and repair and the suitability of work under excess pressure of not more than 1.0 MPa.
Plate heat exchangers have flat heat exchange surfaces. Typically, such heat exchangers are used for heat transfer fluids whose heat transfer coefficients are the same.
The disadvantages of the plate heat exchangers manufactured until recently were low tightness and insignificant pressure drops between the heat carriers.
Recently, compact collapsible plate heat exchangers have been manufactured, consisting of stamped metal sheets with external protrusions arranged in a corridor or staggered pattern. Such structures are used for heat exchange between liquids and gases and operate at pressure drops up to 12 MPa. On fig. 4.8 shows several designs of heat exchangers of this type. Due to the small distance between the plates (6...8 mm), these heat exchangers are very compact. The specific heating surface F/V is 200...300 m 2 /m 3 . Therefore, plate heat exchangers in some cases displace tubular and spiral ones.
But such a design has the following disadvantages: the difficulty of cleaning inside the channels, repair, partial replacement of the heat exchange surface, as well as the impossibility of manufacturing plate heat exchangers from cast iron and brittle materials and long-term operation.
Currently, in the heat supply systems of housing and communal services and a number of industrial enterprises, plate heat exchangers (Fig. 4.8) are installed as heaters for hot water supply (DHW) and heating instead of the traditional sectional shell-and-tube heaters previously used for these purposes. This is due to a number of circumstances and advantages:
1. The heat transfer coefficient in plate heat exchangers is 3...4 times higher than in shell-and-tube heat exchangers, due to the special corrugated profile of the flow path of the plate, which ensures a high degree of turbulence of heat carrier flows. Accordingly, the surface of plate heat exchangers is 3...4 times smaller than that of shell-and-tube heat exchangers.
Rice. 4.8. Lamellar water-to-water heat exchanger "Teplotex":
a - general form; b - scheme of movement of heat carriers
2. Plate heat exchangers have low metal consumption, are very compact, and can be installed in a small room.
3. Unlike shell and tube, they are easy to disassemble and clean quickly. This does not require the dismantling of the supply pipelines.
4. In a plate heat exchanger, the plate or gasket can be easily and quickly replaced, and its surface can be enlarged if the heat load increases over time.
Sectional shell-and-tube heat exchangers are difficult to accurately calculate the required thermal performance and allowable pressure loss, since the surface of one section is large and reaches 28 m 2 (at D y \u003d 300 mm).
Plate heat exchangers are assembled from individual plates, the heating surface of which, as a rule, does not exceed one meter. This circumstance, in combination with the optimally selected type of plate, allows you to accurately select the heat transfer surface of the heat exchanger without any extra margin.
According to their technical characteristics, heat exchangers "Teplotex" are collapsible and single-pass; plate material - steel ALSL 316; plate thickness - 0.5 ... 0.6 mm; obscene gaskets - EPDM rubber; maximum operating temperature of the coolant - 150 °C; working pressure - 1 ... 2.5 MPa; water consumption depending on the type of heat exchanger from 2 to 100 kg/s; surface - from 1.5 to 373 m 2.
Finned heat exchangers are used in cases where the heat transfer coefficient for one of the coolants is significantly lower than for the second. The heat exchange surface on the side of the coolant with a low value of α is increased in comparison with the heat exchange surface on the side of the other coolant. In such devices, the heat exchange surface has ribs of various shapes on one side (Fig. 4.9). As can be seen from the figure, finned heat exchangers make the most various designs. At the same time, I make the ribs transverse, longitudinal, in the form of needles, spirals, from twisted wire, etc.
Rice. 4.9. Types of finned heat exchangers:
a - lamellar; b - cast iron pipe with round ribs; c - tube with spiral fins; g - cast-iron pipe with internal fins; d - fin finned tubes; e - cast-iron pipe with double-sided needle finning; g - wire (bispiral) finning of tubes; h - longitudinal finning of pipes; and - multifinned tube
The easiest way to understand how a shell-and-tube type heat exchanger works is by studying its schematic diagram:
Picture 1. The principle of operation of a shell-and-tube heat exchanger. However, this diagram only illustrates what has already been said: two separate, immiscible heat exchange flows passing inside the shell and through the tube bundle. It will be much clearer if the diagram is animated.
Figure 2. Animation of the operation of a shell-and-tube heat exchanger. This illustration demonstrates not only the principle of operation and the design of the heat exchanger, but also how the heat exchanger looks from the outside and inside. It consists of a cylindrical casing with two fittings, in it and two distribution chambers on both sides of the casing.
The pipes are assembled together and held inside the casing by means of two tube sheets - all-metal disks with holes drilled in them; tube sheets separate the distribution chambers from the heat exchanger housing. Pipes on the tube sheet can be fastened by welding, expanding or a combination of these two methods.
Figure 3 Tube sheet with flared bundle tubes. The first coolant immediately enters the casing through the inlet fitting and leaves it through the outlet fitting. The second coolant is first fed into the distribution chamber, from where it is directed to the tube bundle. Once in the second distribution chamber, the flow "turns around" and again passes through the pipes to the first distribution chamber, from where it exits through its own outlet fitting. In this case, the reverse flow is directed through another part of the tube bundle, so as not to interfere with the passage of the "forward" flow.
Technical nuances
1. It should be emphasized that diagrams 1 and 2 show the operation of a two-pass heat exchanger (the heat carrier passes through the tube bundle in two passes - direct and reverse flow). Thus, improved heat transfer is achieved with the same length of pipes and the exchanger body; however, at the same time, its diameter increases due to an increase in the number of pipes in the tube bundle. There are more simple models, in which the coolant passes through the tube bundle in only one direction:
Figure 4 circuit diagram single pass heat exchanger. In addition to one- and two-pass heat exchangers, there are also four-, six- and eight-pass heat exchangers, which are used depending on the specifics of specific tasks.
2. Animated diagram 2 shows the operation of a heat exchanger with baffles installed inside the casing, which direct the heat carrier flow along a zigzag path. Thus, a cross-flow of heat carriers is provided, in which the "external" heat carrier washes the tubes of the bundle perpendicular to their direction, which also increases heat transfer. There are models with a simpler design, in which the coolant passes in the casing parallel to the pipes (see diagrams 1 and 4).
3. Since the heat transfer coefficient depends not only on the trajectory of the flows of working media, but also on the area of their interaction (in this case, on the total area of all pipes of the tube bundle), as well as on the velocities of heat carriers, it is possible to increase heat transfer through the use of pipes with special devices - turbulators .
Figure 5 Pipes for a shell-and-tube heat exchanger with wavy knurling. The use of such pipes with turbulators in comparison with traditional cylindrical pipes allows to increase thermal power the unit by 15 - 25 percent; in addition, due to the occurrence of vortex processes in them, self-cleaning occurs inner surface pipes from mineral deposits.
It should be noted that the heat transfer characteristics largely depend on the pipe material, which must have good thermal conductivity, the ability to withstand high pressure of the working environment and be corrosion resistant. Together, these requirements fresh water, steam and oils the best choice are modern grades of high quality stainless steel; for sea or chlorinated water - brass, copper, cupronickel, etc.
Manufactures standard and retrofit shell and tube heat exchangers according to modern technologies for new installed lines, and also produces units designed to replace heat exchangers that have exhausted their resource. and its manufacture are made according to individual orders, taking into account all the parameters and requirements of a specific technological situation.