If it is impossible to provide the specified temperature regime Due to the deepening of heating networks, ventilation of tunnels (channels, casings), replacement of heaving soil at the intersection site or overhead laying of heating networks should be provided.
Aboveground installation of heating networks is carried out: on separate supports (masts); on overpasses with a span in the form of purlins, trusses or suspended (cable-stayed) structures; along the walls of buildings.
Networks intended for centralized heat supply to industrial enterprises, residential buildings, and public buildings are laid in non-through, semi-through and through channels in common collectors together with other communications and without installing channels. It is allowed to lay heating networks above ground in the territories of industrial enterprises and in territories not subject to development.
As for heating networks, in accordance with current regulatory requirements for enterprise sites, above-ground heating networks must be laid on separate low or high supports and on overpasses. The joint installation of above-ground heating networks with process pipelines is allowed, regardless of the parameters of the coolant and the parameters of the environment in the process pipelines.
Electrically driven valves for underground installation are placed in chambers with above-ground pavilions or in underground chambers with natural ventilation, providing air parameters in accordance with the required conditions. At overhead installation In heating networks, valves with electric drives are placed indoors or enclosed in casings that protect the valves and electric drives from precipitation. The valve is installed vertically on horizontal heat pipelines with a flywheel, gearbox or drive upward. In some cases, it is allowed to install valves in the range of 90 between the vertical and horizontal positions of the spindle or in any operating position except the position with the spindle down, since when the valves are open, the disk seats sometimes become clogged with corrosion products, which can lead to disruption of the normal operation of the valve.
Gate valves and shutters with a diameter of 500 mm or more must have an electric drive. When laying heating networks above ground, valves with electric drives must be installed indoors or enclosed in casings that protect the valves and electric drive from precipitation and prevent access to them by unauthorized persons.
Gate valves and shutters with a diameter of 500 mm and more are equipped with an electric drive. When laying heating networks above ground, valves with electric drives are installed indoors or enclosed in casings that protect the valves and electric drive from precipitation and prevent access to them by unauthorized persons.
The water pressure in the supply pipelines during operation of network pumps must be taken based on the conditions of non-boiling water at its maximum temperature at any point in the supply pipeline, in the heat source equipment and in the devices of consumer systems. Both underground and above-ground installation of heating networks is allowed.
Throughout the territory of populated areas, underground installation of heating networks is provided - ductless - in non-passable channels, in citywide or intra-block collectors together with other engineering networks. At enterprise sites, as a rule, overhead installation of heating networks is provided on separate supports and overpasses, although underground installation is allowed.
For trouble-free operation of heating networks, it is necessary that compensating devices be designed for maximum pipeline extensions. Therefore, when calculating extensions, the temperature of the coolant is taken to be maximum, and the temperature of the surrounding environment is taken to be minimum (negative) and equal to: 1) the design temperature of the outside air for designing heating for above-ground installation of heating networks in the open air; 2) the estimated air temperature in the channel for channel laying of networks; 3) soil temperature at the depth of installation of ductless heat pipelines at the design temperature for heating design.
The static pressure in heat supply systems corresponds to that allowed in the heat source equipment in consumer heating systems. When operating feed pumps, the pressure in the heat supply pipelines, in the equipment of the heat source and in the devices and apparatus of consumers is taken from the conditions of compliance with the strength limits of the latter and the non-boiling of water at its maximum temperature at any point in the specified system. Underground and above-ground installation of heating networks is allowed. Heat consumption for heating is determined based on the construction volumes of buildings and structures.
Specific heat losses are determined by the relevant standards and should not exceed them. An increase in heat loss and exceeding the relevant standards occurs due to a violation of the thermal insulation of steam pipelines. Damage to the latter occurs mainly for two reasons: due to poor quality thermal insulation and operational deficiencies. In practice it is more often observed joint action for these reasons, it is therefore necessary to constantly monitor the condition of the thermal insulation of steam pipelines. When laying steam pipelines above ground, this does not cause difficulties and is one of the circumstances as a result of which SNiP P-36-73 recommends above-ground installation of heating networks in the area of industrial enterprises. When laying pipelines underground, control becomes much more complicated. The only exception is installation in through passages; it is practically not used in small enterprises.
Heat pipes are laid underground or above ground. The underground method is the main one in residential areas, since it does not clutter the area and does not deteriorate the architectural appearance of the city. The above-ground method is usually used in the territories of industrial enterprises when laying together energy and process pipelines. In residential areas, the above-ground method is used only in particularly difficult conditions: permafrost soils and soils that subside during thawing, wetlands, a high density of existing underground structures, terrain heavily indented by ravines, the intersection of natural and artificial obstacles.
Underground heat pipelines are currently laid in through and non-through channels (previously used semi-through channels are no longer used) or in a channelless manner. In addition, in residential neighborhoods, distribution networks are sometimes laid in technical underground areas (corridors, tunnels) of buildings, which makes construction and operation cheaper and easier.
When laid in ducts and technical undergrounds of buildings, heat pipes are protected on all sides from mechanical influences and loads and, to some extent, from ground and surface waters. To support the heat pipe's own weight, special movable supports are installed. With ductless installation, heat pipes are in direct contact with the ground and external mechanical loads are perceived by the pipe and the thermal insulation structure. In this case, movable supports are not installed, and the heat pipes are laid directly on the ground or a layer of sand and gravel. The cost of channelless installation is 25-30% less than in channels, but the operating conditions of heat pipelines are more difficult.
The depth of installation of heat pipes from the upper level of channels or insulating structure (for ductless installation) to the ground surface is 0.5--0.7 m. high level groundwater it is artificially reduced by installing associated drainage from gravel, sand and drainage pipes under a duct or insulating structure.
Channels are currently made, as a rule, from standardized prefabricated reinforced concrete parts. For protection against ground and surface water outer surface The channels are covered with bitumen and covered with waterproof roll material. To collect moisture that gets inside the channels, their bottom should be given a transverse slope of at least 0.002 in one direction, where sometimes covered trays (with slabs, gratings) are made, through which the water flows into collection pits, from where it is discharged into drains.
It should be noted that, despite the waterproofing of the channels, the natural moisture contained in the soil penetrates them through their outer walls, evaporates and saturates the air. When humid air cools, moisture accumulates on the ceilings and duct walls, which flows down and can cause the insulation to become moist.
The passage channels provide best conditions for operation, operation and repair of heating pipelines, however, in terms of capital costs they are the most expensive. In this regard, it is advisable to construct them only in the most critical areas, as well as when laying heat pipelines together with other utilities. When various communications are laid together, the passage channels are called collectors. They are now widespread in cities. In Fig. Figure 6.4 shows a cross-section of a typical single-section collector.
Passage channels (collectors) are equipped with natural or forced ventilation, ensuring the air temperature in the duct is not higher than 40°C during repair periods and not higher than 50°C during operation, electric lighting with a voltage of up to 30 V, telephone connection. To collect moisture, pits are installed at low points along the route, connected to drains or equipped with pump-out pumps with automatic or remote control.
Rice. 6.4. Cross section of a typical city sewer
1 and 2 - server and return pipelines; 3 - condensate line; 4 - telephone cables; 5 - power cables; 6 - steam line; 7 - water supply
The overall dimensions of the passage channels (collectors) are selected based on the condition of free access to all elements of the heat pipelines, which allows for a complete overhaul of them without opening or destroying road surfaces. The width of the passage in the channel is taken to be at least 700 mm, and the height is at least 2 m (the height to the beam is allowed to be 1.8 m). Every 200-250 m along the route, hatches are made, equipped with ladders or brackets for descending into the canal. In areas where a large amount of equipment is located, special expansions (chambers) can be installed or pavilions can be built.
Non-pass channels are usually used for heat pipes with a diameter of up to 500-700 mm. They are made in rectangular, vaulted and cylindrical shapes from reinforced concrete slabs and vaults, asbestos-cement and metal pipes etc. In this case, as a rule, an air gap is left between the surface of the heat pipes and the walls of the channel, through which the thermal insulation dries and moisture is removed from the channels. As an example in Fig. Figure 6.5 shows a cross-section of a rectangular non-passable channel made from standardized prefabricated reinforced concrete parts.
Rice. 6.5. Sections of a non-passable channel
1 and 2 - tray blocks, lower and upper, respectively; 3 - connecting element with cement whitening; 4 - base plate; 5 - sand preparation
The overall dimensions of non-pass channels are selected mainly depending on the distance between the heat pipes and between the surfaces of the heat-insulating structure and channels, as well as on the condition of ensuring convenient access to the equipment in the chambers. To reduce the distance between heat pipes, equipment is sometimes installed staggered on them.
Channelless laying is usually used for pipes of small diameters (up to 200-300 mm), since when laying such pipes in non-passable channels, their operating conditions are practically more difficult (due to the inclusion of dirt in the air gap in the channels and the difficulty of removing moisture from them in this case ). IN last years In connection with the increased reliability of ductless installation of heat pipelines (through the introduction of welding, more advanced thermal insulation structures, etc.), it is also beginning to be used for pipes of large diameters (500 mm or more).
Heat pipelines laid in a ductless manner are divided depending on the type of thermal insulation structure: in monolithic shells, cast (precast) and backfill (Fig. 6.6) and depending on the nature of the perception of weight loads: unloaded and unloaded.
Rice. 6.6. Types of ductless heat pipes
a - in a prefabricated and monolithic shell; b-cast and prefabricated cast; c - backfill
Structures in monolithic shells are usually made in factory conditions. Only produced on the track butt welding individual elements and insulation of butt joints. Cast structures can be manufactured both in a factory and on the road by pouring pipes (and butt joints after crimping) with liquid initial thermal insulation materials, followed by their setting (hardening). Backfill insulation is performed on pipelines mounted in trenches and pressed from bulk thermal insulation materials.
Unloaded structures include structures in which the thermal insulation coating has sufficient mechanical strength and relieves the pipelines from external loads (weight of the soil, weight of transport passing on the surface, etc.). These include cast (precast) and monolithic shells.
In unloaded structures, external mechanical loads are transferred through thermal insulation directly to the pipeline. These include backfill heat pipes.
On underground heat pipelines, equipment that requires maintenance (valves, stuffing box expansion joints, drainage devices, vents, vents, etc.) is placed in special chambers, and flexible expansion joints are placed in niches. Chambers and niches, like channels, are constructed from prefabricated reinforced concrete elements. Structurally, the chambers are made underground or with above-ground pavilions. Underground chambers are used for pipelines of small diameters and the use of manually operated valves. Chambers with above-ground pavilions provide better service for large equipment, in particular, valves with electric and hydraulic drives, which are usually installed with pipeline diameters of 500 mm or more. In Fig. Figure 6.8 shows the design of an underground chamber.
The overall dimensions of the chambers are chosen to ensure the convenience and safety of equipment maintenance. To enter underground chambers, hatches are installed in diagonal corners - at least two for an internal area of up to 6 m2 and at least four for larger area. The diameter of the hatch is taken to be at least 0.63 m. Under each hatch, ladders or brackets are installed in increments of no more than 0.4 m for descending into the chambers. The bottom of the chambers is made with a slope > 0.02 to one of the corners (under the hatch), where pits for collecting water with a depth of at least 0.3 m and a plan size of 0.4x0.4 m are installed, covered with a grating on top. Water from the pits is drained by gravity or using pumps into drains or receiving wells.
Rice. 6.8. underground chamber
Aboveground heating pipes laid on free-standing supports (low and high) and masts, on overpasses with a continuous span in the form of trusses or beams and on rods attached to the tops of the masts (cable-stayed structures). In industrial enterprises, simplified gaskets are sometimes used: on consoles (brackets) on building structures and on supports (pillows) on the roofs of buildings.
Supports and masts are usually made of reinforced concrete or metal. Overpass spans and anchor posts (non-moving supports) are usually made of metal. In this case, building structures can be constructed as one-, two-, or multi-tiered.
Laying heat pipes on separate supports and masts is the simplest and is usually used when there is no large number pipes (two - four). Currently, in the USSR, standard designs of free-standing low and high reinforced concrete supports have been developed, made with one rack in the form of a T-shaped support and with two separate racks or frames in the form of U-shaped supports. To reduce the number of racks, large-diameter pipelines can be used as load-bearing structures for laying or hanging small-diameter pipelines from them, which require more frequent installation of supports. When laying heat pipelines on low supports, the distance between their lower generatrix and the ground surface must be at least 0.35 m for a group of pipes up to 1.5 m wide and at least 0.5 m for a group of pipes more than 1.5 m wide.
Laying heat pipes on overpasses is the most expensive and requires the greatest consumption of metal. In this regard, it is advisable to use it when there are a large number of pipes (at least five to six), as well as when regular supervision of them is necessary. In this case, pipelines of large diameters usually rest directly on the racks of the overpasses, and small ones - on supports laid in the span.
Laying heat pipes on suspended (cable-stayed) structures is the most economical, as it allows you to significantly increase the distance between masts and thereby reduce the consumption of building materials. When laying pipelines of different diameters together between masts, runs are made from channels suspended on rods. Such purlins allow the installation of additional supports for small diameter pipelines.
To service equipment (valves, stuffing box expansion joints), platforms with fences and ladders are installed: stationary at a distance from the bottom of the heat-insulating structure to the ground surface of 2.5 m or more, or mobile at a shorter distance, and in hard-to-reach places and on overpasses - walkthrough bridges. When laying heat pipelines on low supports, the ground surface should be covered with concrete at the equipment installation sites, and metal casings should be installed on the equipment.
Pipes and fittings. For the construction of heating networks, steel pipes are used, connected using electric or gas welding. Steel pipes are subject to internal and external corrosion, which reduces the service life and reliability of heating networks. In this regard, for local hot water supply systems, which are subject to increased corrosion, galvanized steel pipes are used. In the near future, it is planned to use enameled pipes.
The steel pipes currently used for heating networks are mainly electric-welded with a longitudinal straight and spiral seam and seamless, hot-deformed and cold-deformed, made from steel grades St. 3, 4, 5, 10, 20 and low alloy. Issued electric welded pipes up to a nominal diameter of 1400 mm, seamless - 400 mm. Water and gas steel pipes can also be used for hot water supply networks.
In recent years, work has been carried out on the use of non-metallic pipes (asbestos-cement; polymer, glass, etc.) for heat supply. Their advantages include high anti-corrosion resistance, and for polymer and glass pipes, lower roughness compared to steel pipes. Asbestos-cement and glass pipes are connected using special structures, and polymer pipes are connected by welding, which greatly simplifies installation and increases the reliability and tightness of the connections. The main disadvantage of these non-metallic pipes is the low permissible temperatures and pressures of the coolant - approximately 100 ° C and 0.6 MPa. In this regard, they can only be used in networks operating with low water parameters, for example, in hot water supply systems, condensate pipelines, etc.
The valves used in heating networks are divided according to their intended purpose into shut-off, control, safety (protective), throttling, condensate drainage and control and measuring valves.
The main general purpose fittings usually include shut-off valves, since they are most widely used directly on the route of heating networks. Other types of fittings are installed, as a rule, in heating points, pumping and throttling substations, etc.
Main types shut-off valves heating networks are valves and valves. Valves are usually used in water networks, valves - in steam networks. They are made of steel and cast iron with flanged and coupling connecting ends, as well as with ends for welding pipes of various nominal diameters.
Shut-off valves in heating networks are installed on all pipelines leaving the heat source, in branch nodes with d y >100 mm, in branch nodes to individual buildings with d y 50 mm and branch length l > 30 m or to a group of buildings with a total load of up to 600 kW (0.5 Gcal/h), as well as on fittings for draining water, releasing air and starting drains. In addition, sectional valves are installed in water networks: for d y >100 mm through l ce kc<1000 м; при d y =350...500 мм через l секц <1500 м при условии спуска воды из секции и ее заполнения водой не более чем за 4 ч, и при d y >600 mm through l c ekts<3000 м при условии спуска воды из секции и ее заполнения водой не более чем за 5 ч.
At the installation sites of sectional valves, jumpers are made between the supply and return pipelines with a diameter equal to 0.3 of the diameter of the main pipelines to create coolant circulation in case of accidents. Two valves and a control valve between them at d y = 25 mm are installed in series on the jumper to check the tightness of the valves.
To facilitate the opening of valves with d y > 350 mm on water networks and with d y > 200 mm and p y >1.6 MPa on steam networks requiring high torque, bypass lines (unloading bypasses) are made with shut-off valve. In this case, the valve is relieved from pressure forces when the valves open and the sealing surfaces are protected from wear. In steam networks, bypass lines are also used to start steam pipelines. Valves with d y > 500 mm, requiring a torque of more than 500 Nm to open or close, must be used with an electric drive. All valves are also equipped with an electric drive for remote control.
Pipes and fittings are selected from the produced assortment depending on the nominal pressure, operating (calculated) parameters of the coolant and environment.
Conditional pressure determines the maximum permissible pressure that pipes and fittings of a certain type can withstand for a long time at normal temperature Wednesday + 20°C. As the temperature of the medium increases, the permissible pressure decreases.
Operating pressures and temperatures of the coolant for the selection of pipes, fittings and equipment of heating networks, as well as for calculating pipelines for strength and when determining loads on building structures should be taken equal, as a rule, to the nominal (maximum) values in the supply pipelines or at the discharge of pumps, taking into account terrain. The values of operating parameters for various cases, as well as restrictions on the selection of pipe materials and fittings depending on the operating parameters of the coolant and the environment, are specified in SNiP II-36-73.
The required pipe wall thickness, mm, is determined depending on the internal (working) pressure of the coolant (other loads are not taken into account), according to the equation
where p slave is the working pressure of the coolant, Pa; D H - outer diameter of the pipe, mm; - permissible stress of the pipe material at the operating temperature of the coolant, Pa; - strength coefficient of the weld; c - increase to the calculated pipe wall thickness, mm.
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Underground installations of heating networks are carried out in through, semi-through and non-through channels, in common collectors with other communications. In recent years - following the example of Leningrad - the most effective channelless installation has begun to be introduced (Table 5), but even in this case, separate sections of heating networks (angles of rotation, compensation niches) are laid in the channels.
When laying a heating network underground in an unplanned area, a local leveling of the ground surface is carried out to drain surface water. The outer surfaces of walls and ceilings of channels, chambers and other structures of heating networks are covered with coating bitumen insulation, and when laying networks under lawns and green spaces - with adhesive waterproofing made from bitumen roll materials. Heating network, laid below the maximum groundwater level, are equipped with associated drainage with a diameter of at least 150 mm.
When laying heating networks underground, installation of compensators in the design position is allowed only after preliminary tests of the pipelines for strength and tightness, backfill underground pipelines, channels, chambers and panel supports.
When laying heating networks underground, underground chambers are installed to service shut-off valves made of reinforced concrete elements or bricks. The main main heating networks pass through the chambers, into which taps are made for branches to consumers (subscriptions) with the installation of shut-off valves. The height of the chamber is mounted such that the safety of maintenance can be ensured.
In large cities, underground installation of heating networks can be used in conjunction with other utility networks: in city and intra-block tunnels with water pipes with a diameter of up to 300 mm, communication cables, power cables voltage up to 10 kV, and in city tunnels also with compressed air pipelines with pressure up to 1 6 MPa and pressure sewerage. In intra-block tunnels, it is allowed to jointly lay water networks with a diameter of no more than 250 mm with gas pipelines natural gas pressure up to 0 005 MPa, diameter up to 150 mm. Heating networks under city passages and areas with improved coverage, as well as at the intersection of major highways, should be laid in tunnels or cases.
Currently, underground installations of heating networks in non-passing channels are widely used.
Throughout the territory of populated areas, underground installation of heating networks is provided - ductless - in non-passable channels, in city-wide or intra-block collectors together with other utility networks. At enterprise sites, as a rule, overhead installation of heating networks is provided on separate supports and overpasses, although underground installation is allowed.
In residential areas, for architectural reasons, underground heating networks are usually used.
This crane can be used not only for underground installations of heating networks, but also for overhead installations, on masts and overpasses, for the construction of above-ground pavilions of pumping stations and office premises on 2-3 floors.
Within a city or town, as a rule, underground installation of heating networks is used - in special collectors together with other communications, in through, semi-through and non-through channels and without channels directly in the ground.
To monitor the condition of building insulation structures, thermal insulation and pipelines in underground heating networks, scheduled preventive excavations must be carried out annually. The number of pits should be determined based on the condition of the underground gaskets and the total length of the heating network.
To lay pipes in a trench, the same mechanisms are used as for underground laying of heating networks: pipe layers, truck cranes, crawler cranes. In the absence of these mechanisms or the impossibility of using them due to cramped working conditions, pipes are lowered into the trench using mounting tripods equipped with hoists or hand winches. Small diameter pipes are usually lowered into trenches by hand using two ropes.
To lay pipes in a trench, the same mechanisms are used as for underground laying of heating networks: pipe layers, truck cranes, crawler cranes. In the absence of these mechanisms or the impossibility of using them due to cramped work conditions, the pipes are lowered into the trench using mounting tripods equipped with hoists or hand winches. Small diameter pipes are usually lowered into trenches by hand using two ropes.
Before generalizing operating experience, bellows expansion joints for underground installation of heating networks in non-passage and ductless channels should be installed, as a rule, in chambers. When laying heating networks underground on overpasses or free-standing supports, the construction of special pavilions for bellows expansion joints is not required. They are installed, as a rule, at fixed supports. Only one compensator should be installed between two fixed supports. Before and after compensators, guide supports must be provided. It is recommended to use a fixed support as one of the guide supports.
