Choosing a method for laying heating networks. Heating network structures Underground installation of heating networks

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 for the joint laying of 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 undergrounds (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 absorbed by the pipe and the heat-insulating 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. Price channelless installation 25-30% less than in channels, however, the operating conditions of heat pipelines are more difficult.

The depth of laying heat pipes from the upper level of channels or insulating structure (for ductless installation) to the ground surface is 0.5-0.7 m. At a high level groundwater it is artificially reduced by installing associated drainage from gravel, sand and drainage pipes under a channel or insulating structure.

Channels are currently made, as a rule, from standardized prefabricated reinforced concrete parts. To protect against ground and surface water, the outer surface of the channels is 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.

Pass-through channels provide the best conditions for work, operation and repair of heat pipelines, but 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 engineering communications. 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 channel 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, and a 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 - supply 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 recent years, due to the increase in the reliability of ductless installation of heat pipelines (through the introduction of welding, more advanced thermal insulation structures, etc.), they are beginning to use it 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. On the route, only butt welding of individual elements and insulation of butt joints is carried out. 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 materials. thermal insulation materials.

Unloaded structures include those in which the thermal insulation coating has sufficient mechanical strength and relieves the pipelines from external loads (the weight of the soil, the weight of transport passing on the surface, etc.). These include cast (precast) and monolithic shells.

In unloaded structures, external mechanical loads are transmitted 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 a 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. Superstructures trestles 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 with a small number of pipes (two to 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 consumption 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. Electric welded pipes are produced up to nominal diameter 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 corrosion resistance, and polymer and glass pipes have lower roughness compared to steel pipes. Asbestos-cement and glass pipes are connected using special designs, and polymer pipes are welded, which greatly simplifies installation and increases the reliability and tightness of 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.

The main types of shut-off valves for heating networks are gate valves and gate 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 the environment.

Conditional pressure determines the maximum permissible pressure that pipes and fittings of a certain type can withstand for a long time at a normal ambient temperature of + 20°C. As the medium temperature 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 following types of overhead gaskets are currently in use:

On free-standing masts and supports (Fig. 4.1);

Rice. 4.1. Laying pipelines on free-standing masts

Fig. 4.2 - on overpasses with a continuous span in the form of trusses or beams (Fig. 4.2);

Rice. 4.2. Overpass with a span for laying pipelines

Fig. 4.3 - on rods attached to the tops of the masts (cable-stayed structure, Fig. 4.3);

Rice. 4.3. Laying pipes with suspension on rods (cable-stayed design)

On brackets.

Gaskets of the first type are the most rational for pipelines with a diameter of 500 mm or more. Pipelines of larger diameter can be used as load-bearing structures for laying or suspending several small-diameter pipelines that require more frequent installation of supports.

It is advisable to use overpass gaskets with a continuous flooring for passage only when there is a large number of pipes (at least 5 - 6 pieces), as well as when regular supervision of them is necessary. In terms of construction cost, a walk-through overpass is the most expensive and requires the greatest metal consumption, since trusses or beam decking are usually made of rolled steel.

The third type of installation with a suspended (cable-stayed) span structure is more economical, as it allows you to significantly increase the distances between masts and thereby reduce the consumption of building materials. The simplest structural forms of suspended gaskets are obtained with pipelines of equal or similar diameters.

When laying large and small diameter pipelines together, a slightly modified cable-stayed structure is used with purlins made of channels suspended on rods. Purlins allow installation of pipeline supports between masts. However, the possibility of laying pipelines on overpasses and suspended on rods in urban environments is limited and is applicable only in industrial areas. The greatest use has been made for laying water pipelines on free-standing masts and supports or on brackets. Masts and supports are usually made of reinforced concrete. Metal masts are used in exceptional cases for small volumes of work and reconstruction of existing heating networks.

Masts according to their purpose are divided into the following types:

§ for movable supports of pipelines (so-called intermediate);

§ for fixed pipeline supports (anchors), as well as those installed at the beginning and end of a section of the route;

§ tracks installed at turns;

§ used to support pipeline expansion joints.

Depending on the number, diameter and purpose of the pipelines being laid, the masts are made in three different structural forms: single-post, two-post and four-post spatial design.

When designing air spacers, one should strive to increase the distances between masts as much as possible.

However, for unhindered water flow when pipelines are turned off, the maximum deflection should not exceed

f = 0,25∙i∙l,

Where f- pipeline deflection in the middle of the span, mm; i- slope of the pipeline axis; l- distance between supports, mm.

Precast concrete mast structures are usually assembled from the following elements: posts (columns), crossbars and foundations. The dimensions of the prefabricated parts are determined by the number and diameter of the pipelines being laid.

When laying from one to three pipelines, depending on the diameter, single-post free-standing masts with consoles are used; they are also suitable for cable-stayed suspension of pipes on rods; then a top device is provided for attaching the rods.

Masts of a solid rectangular section are permissible if the maximum cross-sectional dimensions do not exceed 600 x 400 mm. For large sizes, to facilitate the structure, it is recommended to provide cutouts along the neutral axis or use prefabricated centrifuged reinforced concrete pipes as racks.

For multi-pipe installations, intermediate support masts are most often designed as a two-post structure, single-tier or two-tier.

Prefabricated two-post masts consist of the following elements: two posts with one or two consoles, one or two crossbars and two glass-type foundations.

The masts on which the pipelines are fixedly fixed are subject to load from horizontally directed forces transmitted by the pipelines, which are laid at a height of 5 - 6 m from the ground surface. To increase stability, such masts are designed in the form of a four-post spatial structure, which consists of four posts and four or eight crossbars (with a two-tier arrangement of pipelines). The masts are installed on four separate glass-type foundations.

When laying large-diameter pipelines above ground, the load-bearing capacity of the pipes is used, and therefore no span structure is required between the masts. Suspension of large-diameter pipelines on rods should not be used, since such a design will practically not work.

Fig.4.4As an example, the laying of pipelines on reinforced concrete masts is shown (Fig. 4.4).

Two pipelines (direct and return) with a diameter of 1200 mm are laid on roller supports on reinforced concrete masts installed every 20 m. The height of the masts from the ground surface is 5.5 - 6 m. Prefabricated reinforced concrete masts consist of two foundations connected to each other by a monolithic joint, two columns of rectangular section 400 x 600 mm and a crossbar.

Rice. 4.4. Laying pipelines on reinforced concrete masts:

1 - column; 2 - crossbar; 3 - communication; 4 - foundation; 5 - connecting joint; 6 - concrete preparation.

The columns are connected to each other by metal diagonal ties made of angle steel. The connection of the ties with the columns is made with gussets welded to the embedded parts, which are embedded in the columns. The crossbar, which serves as a support for pipelines, is made in the form of a rectangular beam with a cross-section of 600 x 370 mm and is attached to the columns by welding embedded steel sheets.

The mast is designed for the weight of the pipe span, horizontal axial and lateral forces arising from the friction of pipelines on the roller supports, as well as for wind load.

Rice. 4.5. Fixed support:

1 - column; 2 - transverse crossbar; 3 - longitudinal crossbar; 4 - cross connection; 5 - longitudinal connection; 6 - foundation

The fixed support (Fig. 4.5), designed for a horizontal force from two pipes of 300 kN, is made of prefabricated reinforced concrete parts: four columns, two longitudinal crossbars, one transverse support crossbar and four foundations connected in pairs.

In the longitudinal and transverse directions, the columns are connected by metal diagonal braces made of angle steel. The pipelines are secured to the supports with clamps covering the pipes and gussets at the bottom of the pipes, which rest against a metal frame made of channels. This frame is attached to reinforced concrete crossbars by welding to the embedded parts.

Laying pipelines on low supports has found wide application in the construction of heating networks in unplanned areas of new urban areas. It is more expedient to cross rough or swampy terrain, as well as small rivers, in this way using the bearing capacity of pipes.

However, when designing heating networks with the laying of pipelines on low supports, it is necessary to take into account the period of planned development of the territory occupied by the route for urban development. If in 10 - 15 years it will be necessary to enclose pipelines in underground channels or reconstruct the heating network, then the use of air laying is inappropriate. To justify the use of the method of laying pipelines on low supports, technical and economic calculations must be performed.

When laying large-diameter pipelines above ground (800-1400 mm), it is advisable to lay them on separate masts and supports using special prefabricated reinforced concrete structures of factory production that meet the specific hydrogeological conditions of the heating main route.

Design experience shows the cost-effectiveness of using pile foundations for the foundations of both anchor and intermediate masts and low supports.

Aboveground heating mains of large diameter (1200-1400 mm) of considerable length (5 - 10 km) are built according to individual designs using high and low supports on a pile foundation.

We have experience in constructing heating mains with pipe diameters D= 1000 mm from the thermal power plant using rack piles in the wetlands of the route, where rocky soils lie at a depth of 4-6 m.

Calculation of supports on a pile foundation for the combined action of vertical and horizontal loads is carried out in accordance with SNiP II-17-77 “Pile foundations”.

When designing low and high supports for laying pipelines, the designs of standardized prefabricated reinforced concrete free-standing supports designed for process pipelines can be used [3].

The design of low supports of the type of “swinging” foundations, consisting of a reinforced concrete vertical shield installed on a flat foundation slab, was developed by AtomTEP. These supports can be used in various soil conditions (with the exception of heavily watered and subsiding soils).

One of the most common types of aerial laying of pipelines is the installation of the latter on brackets fixed in the walls of buildings. The use of this method can be recommended when laying heating networks on the territory of industrial enterprises.

When designing pipelines located on the outer or inner surface of walls, you should choose such a placement of pipes so that they do not cover window openings, did not interfere with the placement of other pipelines, equipment, etc. The most important thing is to ensure that the brackets are securely fastened to the walls of existing buildings. Designing the installation of pipelines along the walls of existing buildings should include an examination of the walls in situ and a study of the designs for which they were built. In case of significant loads transmitted by pipelines to the brackets, it is necessary to calculate the overall stability of the building structures.

The pipelines are laid on brackets with welded sliding support bodies. The use of roller movable supports for external laying pipelines are not recommended due to the difficulty of periodically lubricating and cleaning them during operation (without which they will work as sliding ones).

In case of insufficient reliability of the walls of the building, constructive measures must be taken to disperse the forces transmitted by the brackets by reducing spans, installing struts, vertical racks etc. Brackets installed in places where fixed pipeline supports are installed must be designed to withstand the forces acting on them. Usually they require additional fastening by installing struts in horizontal and vertical planes. In Fig. 4.6 shows a typical design of brackets for laying one or two pipelines with a diameter of 50 to 300 mm.

Rice. 4.6. Laying pipelines on brackets.

One of the main features of heat pipes is the relative heat the product transported through them - water or steam, in most cases exceeding 100 ° C, which largely determines the nature of the design of heating networks, since it requires the installation of thermal insulation and ensuring freedom of movement of pipes when they are heated or cooled.

The presence of thermal insulation and the requirement for free movement of pipes significantly complicates the design of heat pipelines - the latter are laid in channels, tunnels or protective shells.

Periodic heating of the walls of heat pipelines to a temperature of 130-150°C makes anti-corrosion coatings, usually used to protect unheated steel pipelines laid in the ground, unsuitable. To protect heat pipelines from external corrosion, it is necessary to use such building and insulating structures that prevent penetration into the pipelines ground moisture.

The designs of heat pipelines currently used are significantly diverse. According to the method of installation, heating networks are divided into underground and above-ground (air).

Underground installation pipelines of heating networks is carried out:

a) in non-passing and semi-passing channels;

b) in tunnels or sewers together with other communications;

c) in shells various shapes and in the form of backfill gaskets.

When laying underground, chambers, niches for compensators, fixed supports, etc. are built along the route.

Aboveground installation of heating network pipelines is carried out:

a) on overpasses with a continuous span;

b) on separate masts (supports);

c) on suspended spans (cable-stayed).

A special group of structures includes special structures: underwater, overground and underground passages and a number of others.

The main disadvantages of underground heat pipeline structures used in the construction are: fragility, large heat losses, labor-intensive manufacturing, significant consumption of building materials and high construction costs.

The most widely used structures are prefabricated structures of impassable channels with concrete walls. The use of non-passage channels is justified in the case of laying heating networks in wet soils, provided that associated drainage is installed . You should focus on the use of non-passable channels made from standardized prefabricated reinforced concrete parts. The specified reinforced concrete channels can be used for heating networks with a diameter of up to 600 mm. It is possible to use non-passing channels assembled from vibrating rolling plates.

Non-passing channels with suspended thermal insulation forming around the pipes air gap, are indispensable in sections of the route with self-compensation for thermal elongation of heat pipes. Characteristic feature Channel laying of heating networks, in contrast to ductless, is to ensure the movement of heat pipes in the longitudinal and transverse directions.

When laying heat pipes under passages with heavy traffic and improved road surface Semi-through channels made of prefabricated reinforced concrete parts are used. When laying a large number of heat pipes of significant diameters, through-pass tunnels are used.

For heating mains of large diameters, there are also standard channel designs that have proven themselves both in construction and operation. For example, heating mains with a diameter of 700-1200 mm are being built in Moscow. However, channel designs must be improved to achieve more rational decisions. For laying heat pipes, prefabricated reinforced concrete channels of single-cell and double-cell sections are used. Basically, these channels are designed as a semi-through type to allow inspection by maintenance personnel, as well as to ensure maximum reliability of heating mains in operation.

In Moscow and some other cities, ductless laying of heat pipelines with a two-layer cylindrical shell consisting of a reinforced concrete pipe and a heat-insulating layer (mineral wool) has been used.

Reinforced concrete pipes have sufficient mechanical strength, high resistance to shock and vibration loads, and good moisture resistance. Therefore, they reliably protect the heat pipeline from moisture and loads transmitted by the soil. This achieves more favorable conditions for the operation of heat pipelines: stresses in the pipe walls are reduced and the durability of thermal insulation is ensured.

The outer reinforced concrete shell remains motionless when the heat pipe moves in the axial direction due to temperature deformations, which distinguishes this design from a structure with a reinforced foam concrete shell moving on the ground along with the heat pipe.

A similar design is made using asbestos-cement pipes and reinforced concrete half-cylinders as the outer shell.

The use of ductless structures can be recommended when laying in dry soils with the outer surface of the heat pipes protected by two layers of insulation. Channelless installation of heat pipelines with backfill thermal insulation with peat, diatomaceous earth, etc. turned out to be unsuccessful. Experimental work is currently underway to create backfill material.

The chamber designs used in the construction of heating networks are very diverse. Prefabricated chambers made of reinforced concrete parts are designed for heat pipelines of small and medium diameters. Cameras large sizes made of concrete blocks and monolithic reinforced concrete. The structures of fixed supports in the channels are made of monolithic and prefabricated reinforced concrete. In Moscow, Novosibirsk and other cities, so-called common collectors have become widespread, in which heat pipes are laid together with electrical and telephone cables, water supply and other underground networks.

Passage channels and common collectors are equipped with electric lighting, telephone communications, ventilation, and various devices automatic control and drainage facilities.

In ventilated passage tunnels, a favorable temperature and humidity regime of the air environment is ensured, which contributes to the good preservation of heat pipes.

During the construction of general sewers in Moscow using the open-pit method, the design of large ribbed reinforced concrete blocks, proposed by engineers N. M. Davidyants and A. A. Lyamin, worked well.

The method of jointly laying underground networks in common sewers has a number of advantages, of which the most significant are : increasing the durability of the material part of networks and ensuring the best operating conditions. When operating heating networks in collectors, as well as when it is necessary to build new underground networks, it is not necessary to open up urban areas for repairs. Network placement for various purposes in collectors makes it possible to organize their comprehensive and planned design, construction and operation and makes it possible to streamline the entire system of placing underground networks more compactly both in plan and in the cross section of city passages. Underground urban sewers are modern engineering structures.

a - separate;

b - joint;

TK - telephone sewer;

E - electrical cables;

T - heat pipes 2d = 400 mm;

G - gas pipeline d=300 mm

B - water supply d = 300 mm;

C - drain d= 600 mm;

K - sewerage d = 200 mm;

T KAB - telephone cables

Internal view of the common collector

Number of pipelines and cables placed in manifolds of various sections

The design of underground, overground and underwater passages of heat pipelines through natural and artificial obstacles is included in the general complex of designing heating networks and is only in rare cases carried out by specialized organizations.

Underwater crossings of rivers are carried out in the form of passage tunnels and siphons; air crossings across rivers to railway tracks - in the form of bridge crossings. It is also possible to lay heat pipelines along existing bridges and overpasses.

When the route crosses the heating networks of iron and highways, as well as city passages, underground passages are most often constructed, carried out in a closed way to ensure uninterrupted operation expensive

Underground passages are made mainly in the form of tunnels, constructed using metal shields of circular cross-section. These tunnels require significant deepening, and therefore often fall into the groundwater zone, which complicates the work and requires the organization of drainage from the tunnel during operation.

Another type of underground passage is the laying of steel cases, inside of which heat pipes are placed. The cases are laid by pressing or puncturing steel pipes with hydraulic jacks. The implementation of this type of transition is advisable where it is possible to pass above the groundwater level without disturbing existing underground communications.

Underpasses made of steel casings are widely used in the construction of heating networks.

The correct choice of one or another type of transition is the main task in the design, since the cost of these structures is very high and significantly increases the total cost of heating networks.

At industrial enterprises, overhead laying of heat pipelines along trestles, often made of rolled metal, has become widespread.

The design of overpasses using precast reinforced concrete is now significantly easier due to the release of the standard project “Unified prefabricated reinforced concrete free-standing supports for process pipelines” (IS-01-06 series).

In urban heating networks, overhead laying of heat pipelines was carried out mainly along metal masts of a lattice structure. Reinforced concrete masts began to be manufactured only at the present time. For example, reinforced concrete masts made from prefabricated parts for heating mains with a diameter of 1200 mm have found application in Moscow. The structural parts of these masts are manufactured at the factory and assembled on the track.

Channel gasket satisfies most requirements, but its cost, depending on the diameter, is 10-50% higher than channelless. Channels protect pipelines from the effects of ground, atmospheric and flood waters. The pipelines in them are laid on movable and fixed supports, while ensuring organized thermal elongation.

The technological dimensions of the channel are taken based on the minimum clear distance between the pipes and structural elements, which, depending on the diameter of the pipes 25-1400 mm, is respectively taken equal to: to the wall 70-120 mm; to overlap 50-100 mm; to the insulation surface of the adjacent pipeline 100-250 mm. Channel depth

accepted based on the minimum volume earthworks and uniform distribution of concentrated loads from vehicles on the floor. In most cases, the thickness of the soil layer above the ceiling is 0.8-1.2 m, but not less than 0.5 m.

In case of centralized heat supply, non-through, semi-through or through channels are used for laying heating networks. If the laying depth exceeds 3 m, then semi-through or through channels are constructed to make it possible to replace pipes.

Impassable channels used for laying pipelines with a diameter of up to 700 mm, regardless of the number of pipes. The design of the channel depends on the soil moisture. In dry soils, block channels with concrete or brick walls, or reinforced concrete single- and multi-cell ones are more often installed. In soft soils, first perform concrete base, on which a reinforced concrete slab is installed. When the groundwater level is high, a drainage pipeline is laid at the base of the canal to drain it. If possible, the heating network in non-passable channels is placed along the lawns.

Currently, channels are mainly constructed from prefabricated reinforced concrete tray elements (regardless of the diameter of the pipelines being laid) of types KL, KLS, or wall panels of types KS, etc. The channels are covered with flat reinforced concrete slabs. The bases of all types of channels are made of concrete slabs, lean concrete or sand preparation.

If it is necessary to replace failed pipes, or when repairing a heating network in non-passable channels, it is necessary to tear up the soil and dismantle the channel. In some cases, this is accompanied by opening of the bridge or asphalt surface.

Semi-bore channels. In difficult conditions when pipelines of the heating network cross existing underground communications, under the roadway, and at a high level of groundwater, semi-passable channels are installed instead of impassable ones. They are also used when laying a small number of pipes in places where, due to operating conditions, opening of the roadway is excluded, as well as when laying large diameter pipelines (800-1400 mm). The height of the semi-bore channel is taken to be at least 1400 mm. The channels are made from prefabricated reinforced concrete elements - a bottom slab, a wall block and a floor slab.

Passage channels. Otherwise they are called collectors; they are constructed in the presence of a large number of pipelines. They are located under the pavements of large highways, on the territory of large industrial enterprises, in areas adjacent to the buildings of thermal power plants. Together with the heat pipelines, other underground communications are also placed in these channels: electrical and telephone cables, water supply, low-pressure gas pipelines, etc. For inspection and repair in the collectors, free access for service personnel to pipelines and equipment is provided.

Collectors are made of reinforced concrete ribbed slabs, frame structure links, large blocks and volumetric elements. They are equipped with lighting and natural supply and exhaust ventilation with triple air exchange, ensuring an air temperature of no more than 30°C, and a device for removing water. Entrances to the collectors are provided every 100-300 m. To install compensating and shut-off devices on the heating network, special niches and additional manholes must be made.

Channelless installation. To protect pipelines from mechanical influences with this installation method, reinforced thermal insulation - a shell - is installed. The advantages of ductless installation of heat pipelines are the relatively low cost of construction and installation work, a small amount of excavation work and a reduction in construction time. Its disadvantages include the increased susceptibility of steel pipes to external soil, chemical and electrochemical corrosion.

With this type of gasket, movable supports are not used; pipes with thermal insulation are laid directly on a sand cushion poured onto the pre-leveled bottom of the trench. Fixed supports for ductless pipe laying, as well as for channel pipes, are reinforced concrete shield walls installed perpendicular to the heat pipes. For small diameter heat pipes, these supports are usually used outside the chambers or in chambers with a large diameter under large axial forces. To compensate for thermal elongation of pipes, bent or stuffing box expansion joints are used, located in special niches or chambers. At the turns of the route, in order to avoid pinching the pipes in the ground and to ensure their possible movement, impassable channels are constructed.

For channelless installation, backfill, prefabricated and monolithic types of insulation are used. Monolithic shells made of autoclaved reinforced foam concrete have become widespread.

Overhead installation. This type of gasket is the most convenient to operate and repair and is characterized by minimal heat losses and ease of detection of accident sites. Load-bearing structures for pipes there are separate supports or masts that ensure the pipes are located at the required distance from the ground. For low supports, the clear distance (between the insulation surface and the ground) for a group of pipes up to 1.5 m wide is taken to be 0.35 m and at least 0.5 m for larger widths. Supports are usually made of reinforced concrete blocks, masts and overpasses are made of steel and reinforced concrete. The distance between supports or masts when laying pipes with a diameter of 25-800 mm above ground is taken to be 2-20 m. Sometimes one or two intermediate suspended supports are installed using guy wires in order to reduce the number of masts and reduce capital investments in the heating network.

To service fittings and other equipment installed on the pipelines of the heating network, special platforms with fences and ladders are arranged: stationary at a height of 2.5 m or more and mobile at a lower height. In places where main valves, drainage, drainage and air devices are installed, insulated boxes are provided, as well as devices for lifting people and fittings.

5.2. Drainage of heating networks

When laying heat pipes underground, in order to avoid water penetration into the thermal insulation, an artificial lowering of the groundwater level is provided. For this purpose, together with the heat pipes, drainage pipelines are laid 200 mm below the base of the channel. The drainage device consists of a drainage pipe and a filter material of sand and gravel. Depending on the working conditions, various drainage pipes are used: for non-pressure drainage - socketed ceramic, concrete and asbestos-cement, for pressure drainage - steel and cast iron with a diameter of at least 150 mm.

At turns and when there are differences in pipe laying, inspection wells are installed like sewer wells. In straight sections, such wells are provided at least 50 m apart. If drainage of drainage water into reservoirs, ravines or sewers by gravity is not possible, pumping stations are built, which are placed near the wells at a depth depending on the elevation of the drainage pipes. Pumping stations are usually built from reinforced concrete rings with a diameter of 3 m. The station has two compartments - a machine room and a reservoir for receiving drainage water.

5.3. Structures on heating networks

Heating chambers are intended for servicing equipment installed on heating networks with underground installation. The dimensions of the chamber are determined by the diameter of the heating network pipelines and the dimensions of the equipment. Shut-off valves, stuffing box and drainage devices, etc. are installed in the chambers. The width of the passages is at least 600 mm, and the height is at least 2 m.

Heating chambers are complex and expensive underground structures, therefore they are provided only in places where shut-off valves and stuffing box compensators are installed. The minimum distance from the ground surface to the top of the chamber ceiling is taken to be 300 mm.

Currently, heating chambers made of precast reinforced concrete are widely used. In some places, the chambers are made of brick or monolithic reinforced concrete.

On heat pipelines with a diameter of 500 mm and above, electrically driven valves with a high spindle are used, so an above-ground pavilion about 3 m high is built above the recessed part of the chamber.

Supports. To ensure organized joint movement of the pipe and insulation during thermal expansion, movable and fixed supports are used.

Fixed supports, intended for securing pipelines of heating networks at characteristic points, they are used for all installation methods. Characteristic points on the route of the heating network are considered to be the places of branches, the installation sites of valves, stuffing box compensators, mud traps and the installation sites of fixed supports. The most widespread are panel supports, which are used both for ductless installation and for laying heating network pipelines in non-passable channels.

The distances between fixed supports are usually determined by calculating the strength of pipes at a fixed support and depending on the magnitude of the compensating capacity of the adopted compensators.

Movable supports installed for ducted and ductless installation of heating network pipelines. There are the following types of different designs of movable supports: sliding, roller and suspended. Sliding supports are used for all laying methods, except channelless. Rollers are used for overhead laying along the walls of buildings, as well as in collectors and on brackets. Suspended supports are installed when laying above ground. In places where there is possible vertical movement of the pipeline, spring supports are used.

The distance between the movable supports is taken based on the deflection of the pipelines, which depends on the diameter and wall thickness of the pipes: the smaller the diameter of the pipe, the smaller the distance between the supports. When laying pipelines with a diameter of 25-900 mm in channels, the distance between movable supports is taken to be 1.7-15 m. When laying above ground, where a slightly larger deflection of pipes is allowed, the distance between supports for the same pipe diameters is increased to 2-20 m.

Compensators used to relieve temperature stresses that arise in pipelines during elongation. They can be flexible U-shaped or omega-shaped, hinged or stuffing box (axial). In addition, pipeline turns at an angle of 90-120° available on the route are used, which work as compensators (self-compensation). Installation of expansion joints involves additional capital and operating costs. Minimum costs are obtained in the presence of self-compensation areas and the use of flexible compensators. When developing heat network projects, a minimum number of axial expansion joints is used, making maximum use of the natural compensation of heat pipes. The choice of compensator type is determined by the specific conditions for laying pipelines of heating networks, their diameter and coolant parameters.

Anti-corrosion coating of pipelines. To protect heat pipes from external corrosion caused by electrochemical and chemical processes under the influence of the environment, anti-corrosion coatings are used. High quality have coatings made in the factory. The type of anti-corrosion coating depends on the temperature of the coolant: bitumen primer, several layers of insulation over insulating mastic, wrapping paper or putty and epoxy enamel.

Thermal insulation. For thermal insulation of pipelines of heating networks, various materials are used: mineral wool, foam concrete, reinforced foam concrete, aerated concrete, perlite, asbestos cement, sovelite, expanded clay concrete, etc. For channel installation, suspended insulation made of mineral wool is widely used, for channelless installation - from autoclaved reinforced foam concrete, asphalt -toizol, bitumen perlite and foam glass, and sometimes backfill insulation.

Thermal insulation usually consists of three layers: thermal insulation, cover and finishing. The covering layer is designed to protect the insulation from mechanical damage and moisture, i.e. to preserve thermal properties. To construct the covering layer, materials are used that have the necessary strength and moisture permeability: roofing felt, glassine, fiberglass, foil insulation, sheet steel and duralumin.

Reinforced waterproofing and asbestos-cement plaster over a wire mesh frame are used as a covering layer for ductless installation of heat pipes in moderately moist sandy soils; for channel installation - asbestos-cement plaster over a wire mesh frame; for above-ground installation - asbestos-cement half-cylinders, sheet steel casing, galvanized or painted aluminum paint.

Suspended insulation is a cylindrical shell on the surface of a pipe made of mineral wool, molded products (slabs, shells and segments) and autoclaved foam concrete.

The thickness of the thermal insulation layer is taken according to calculation. The maximum coolant temperature is taken as the calculated coolant temperature if it does not change during the operating period of the network (for example, in steam and condensate networks and hot water supply pipes), and the average for the year if the coolant temperature changes (for example, in water networks). The ambient temperature in the collectors is taken to be +40°C, the soil on the pipe axis is the average for the year, the outside air temperature for above-ground installation is the average for the year. In accordance with the design standards for heating networks, the maximum thickness of thermal insulation is taken based on the installation method:

For overhead installation and in collectors with pipe diameter 25-1400
mm insulation thickness 70-200 mm;

In channels for steam networks - 70-200 mm;

For water networks - 60-120 mm.

fittings, flange connections and other shaped parts of heating networks, as well as pipelines, are covered with a layer of insulation with a thickness equal to 80% of the thickness of the pipe insulation.

When laying heat pipes without ducts in soils with increased corrosive activity, there is a danger of pipe corrosion from stray currents. To protect against electrocorrosion, measures are taken to prevent the penetration of stray currents to metal pipes, or arrange so-called electrical drainage or cathodic protection (cathodic protection stations).

Factory information technologies"LIT" in Pereslavl-Zalessky produces flexible thermal insulation products from foamed polyethylene with a closed pore structure "Energoflex". They are environmentally friendly, as they are manufactured without the use of chlorofluorocarbons (freon). During operation and processing, the material does not release toxic substances into the environment and does not have harmful effects on the human body upon direct contact. Working with it does not require special tools or increased safety measures.

"Energoflex" is intended for thermal insulation of engineering communications with a coolant temperature from minus 40 to plus 100 ° C.

Energoflex products are produced in the following forms:

Tubes in 73 sizes with internal diameter from 6 to 160 mm and
wall thickness from 6 to 20 mm;

Rolls are 1 m wide and 10, 13 and 20 mm thick.

The thermal conductivity coefficient of the material at 0°C is 0.032 W/(m-°C).

Mineral wool thermal insulation products are produced by the enterprises of Termosteps JSC (Tver, Omsk, Perm, Samara, Salavat, Yaroslavl), AKSI (Chelyabinsk), Tizol JSC, Nazarovsky ZTI, Komat plant (Rostov -on-Don), CJSC "Mineral Wool" (Zheleznodorozhny, Moscow region), etc.

Imported materials from ROCKWOLL, Ragos, Izomat and others are also used.

Performance properties fibrous thermal insulation materials depend on the composition of the raw materials used by various manufacturers and technological equipment and vary over a fairly wide range.

Technical thermal insulation made of mineral wool is divided into two types: high-temperature and low-temperature. The company JSC "Mineral Wool" produces thermal insulation "ROCKWOLL" in the form of fiberglass mineral wool boards and mats. More than 27% of all fibrous thermal insulation materials produced in Russia are URSA thermal insulation produced by JSC Flyderer-Chudovo. These products are made from staple glass fiber and are characterized by high thermal and acoustic characteristics. Depending on the brand of the product, the thermal conductivity coefficient

such insulation ranges from 0.035 to 0.041 W/(m-°C), at a temperature of 10°C. The products are characterized by high environmental performance; they can be used if the coolant temperature is in the range from minus 60 to plus 180°C.

CJSC "Isolation Plant" (St. Petersburg) produces insulated pipes for heating networks. Reinforced foam concrete is used as insulation here, the advantages of which include:

High maximum application temperature (up to 300°C);

High compressive strength (not less than 0.5 MPa);

Can be used for channelless installation on any depth
without laying heat pipelines and in all soil conditions;

The presence of a passivating protective layer on the insulated surface
film that occurs when foam concrete comes into contact with the metal of the pipe;

The insulation is non-flammable, which allows it to be used in all
types of installation (overground, underground, channel or non-channel).

The thermal conductivity coefficient of such insulation is 0.05-0.06 W/(m-°C).

One of the most promising methods today is the use of pre-insulated ductless pipelines with polyurethane foam (PPU) insulation in a polyethylene sheath. The use of “pipe-in-pipe” type pipelines is the most progressive way of energy saving in the construction of heating networks. In the USA and Western Europe, especially in the northern regions, these designs have been used since the mid-60s. In Russia - only since the 90s.

The main advantages of such designs:

Increasing the durability of structures up to 25-30 years or more, i.e.
2-3 times;

Reduction of heat losses by up to 2-3% compared to existing ones
20^40% (or more) depending on the region;

Reducing operating costs by 9-10 times;

Reducing the cost of repairing heating mains by at least 3 times;

Reducing capital costs during the construction of new heating mains in
1.2-1.3 times and a significant (2-3 times) reduction in construction time;

Significant increase in the reliability of heating mains constructed according to
new technology;

Possibility of using an operational remote control system
control of insulation moisture, which allows timely response
to damage the integrity of a steel pipe or polyethylene guide
insulation coating and prevent leaks and accidents in advance.

On the initiative of the Moscow Government, Gosstroy of Russia, RAO UES of Russia, CJSC MosFlowline, TVEL Corporation (St. Petersburg) and a number of other organizations, the Association of Manufacturers and Consumers of Pipelines with Industrial Polymer Insulation was created in 1999.

CHAPTER 6. CRITERIA FOR SELECTION OF THE OPTIMAL OPTION

Section Contents

Based on the method of installation, heating networks are divided into underground and above-ground (air). Underground installation of heating network pipelines is carried out: in channels of non-through and semi-through cross sections, in tunnels (through channels) with a height of 2 m or more, in common collectors for the joint installation of pipelines and cables for various purposes, in intra-block collectors and technical undergrounds and corridors, without ducts.

Overhead laying of pipelines is carried out on free-standing masts or low supports, on overpasses with a continuous span, on masts with pipes suspended on rods (cable-stayed structure) and on brackets.

A special group of structures includes special structures: bridge crossings, underwater crossings, tunnel crossings and transitions in cases. These structures are usually designed and built according to individual projects with the involvement of specialized organizations.

The choice of method and design for laying pipelines is determined by many factors, the main of which are: the diameter of the pipelines, the requirements for the operational reliability of heat pipelines, the cost-effectiveness of structures and the method of construction.

When locating a heating network route in areas of existing or future urban development, for architectural reasons, underground pipeline installation is usually adopted. In the construction of underground heating networks, the most widely used is the laying of pipelines in non-through and semi-through channels.

The channel design has a number of positive properties that meet the specific operating conditions of hot pipelines. Channels are a building structure that protects pipelines and thermal insulation from direct contact with the soil, which has both mechanical and electrochemical effects on them. The design of the channel completely unloads the pipelines from the action of the soil mass and temporary transport loads, therefore, when calculating their strength, only the stresses arising from the internal pressure of the coolant, its own weight and temperature elongations of the pipeline, which can be determined with a sufficient degree of accuracy, are taken into account.

Laying in channels ensures free temperature movement of pipelines both in the longitudinal (axial) and transverse directions, which allows the use of their self-compensating ability in corner sections of the heating network route.

The use of natural flexibility of pipelines for self-compensation during channel installation makes it possible to reduce the number or completely eliminate the installation of axial (stuffing box) expansion joints, which require the construction and maintenance of chambers, as well as bent expansion joints, the use of which is undesirable in urban environments and leads to an increase in pipe costs by 8- 15%.

The design of the channel laying is universal, as it can be used under various hydrogeological soil conditions.

With sufficient tightness of the building structure of the channel and properly working drainage devices conditions are created that prevent surface and ground water from penetrating into the channel, which ensures that the thermal insulation does not get wet and protects the outer surface of steel pipes from corrosion. The route of heating networks laid in channels (as opposed to channelless) can be selected without significant difficulties along the road and non-road areas of the city together with other communications, bypassing or with a slight approach to existing structures, and also taking into account various planning requirements (prospective changes in the terrain, purpose of the territory, etc.).

One of the positive properties of channel laying is the possibility of using lightweight materials (mineral wool, fiberglass, etc.) with a low thermal conductivity coefficient as suspended thermal insulation for pipelines, which allows reducing heat losses in networks.

In terms of performance, the installation of heating networks in non-through and semi-through channels has significant differences. Impassable channels that are inaccessible for inspection without opening the road surface, excavating the soil and dismantling it building structure, do not allow detecting any damage to thermal insulation and pipelines, as well as preventively eliminating them, which leads to the need for production repair work at the time of emergency damage.

Despite the disadvantages, installation in non-passage channels is a common type of underground installation of heating networks.

In semi-through channels accessible for the passage of operating personnel (with the heat pipes disconnected), inspection and detection of damage to thermal insulation, pipes and building structures, as well as their current repairs can, in most cases, be carried out without digging up and disassembling the channel, which significantly increases the reliability and service life heating networks. However, the internal dimensions of semi-through channels exceed the dimensions of non-through channels, which naturally increases their construction cost and material consumption. Therefore, semi-through channels are used mainly when laying pipelines of large diameters or in certain sections of heating networks when the route passes through an area that does not allow digging, as well as when the channels are laid at a great depth, when the backfill above the ceiling exceeds 2.5 m.

As operating experience shows, large-diameter pipelines laid in non-passable channels inaccessible for inspection and maintenance are most susceptible to emergency damage due to external corrosion. These damages lead to a long-term cessation of heat supply to entire residential areas and industrial enterprises, emergency restoration work, disruption of traffic, disruption of amenities, which is associated with high material costs and danger for operating personnel and the population. The damage caused by damage to large diameter pipelines cannot be compared with damage to medium and small diameter pipelines.

Considering that the increase in the cost of construction of single-cell semi-through channels compared to non-through channels with a heating network diameter of 800 - 1200 mm is insignificant, their use should be recommended in all cases and throughout the entire length of heating mains of the indicated diameters. Recommending the laying of large-diameter pipelines in semi-through channels, one cannot fail to note their advantages over non-through channels in terms of the degree of maintainability, namely the ability to replace worn out pipelines in them over a considerable distance without digging up and dismantling the building structure using closed method production of installation work.

The essence of the closed method for replacing worn-out pipelines is to remove them from the channel by horizontal movement simultaneously with the installation of new insulated pipelines using a jacking installation.

The need for the construction of tunnels (passage channels) arises, as a rule, at the head sections of main heating networks extending from large thermal power plants, when it is necessary to lay a large number of hot water and steam pipelines. In such heating tunnels, laying high and low current cables is not recommended due to the practical impossibility of creating the required constant temperature regime in it.

Heating tunnels are constructed mainly on transit sections of large-diameter pipelines laid from thermal power plants located on the periphery of the city, when above-ground installation of pipelines cannot be allowed for architectural and planning reasons.

Tunnels should be located in the most favorable hydrogeological conditions to avoid the installation of deep associated drainage and drainage pumping stations.

General collectors, as a rule, should be provided in the following cases: if it is necessary to simultaneously place two-pipe heating networks with a diameter of 500 to 900 mm, a water supply system with a diameter of up to 500 mm, communication cables 10 pcs. and more, electrical cables voltage up to 10 kV in quantity of 10 pcs. and more; during the reconstruction of city highways with developed underground infrastructure; when there is insufficient free space in the cross-section of streets to place networks in trenches; at intersections with main streets.

In exceptional cases, in agreement with the customer and operating organizations, it is allowed to lay pipelines with a diameter of 1000 mm and water pipelines up to 900 mm, air ducts, cold pipelines, recycling water supply pipelines and other utility networks in the collector. The laying of gas pipelines of all types in public city sewers is prohibited [1].

Common sewers should be laid along city streets and roads in a straight line, parallel to the axis of the roadway or red line. It is advisable to place collectors on technical strips and under green belts. The longitudinal profile of the collector must ensure gravity drainage of emergency and groundwater. The slope of the collector tray should be at least 0.005. The depth of the collector must be determined taking into account the depth of intersecting communications and other structures, the load-bearing capacity of structures and temperature regime inside the collector.

When deciding whether to lay pipelines in a tunnel or sewer, consideration should be given to the possibility of ensuring the drainage of drainage and emergency water from the sewer into existing storm drains and natural bodies of water. The placement of the collector in plan and profile in relation to buildings, structures and parallel communications should ensure the possibility of carrying out construction work without compromising the strength, stability and working condition of these structures and communications.

Tunnels and sewers located along city streets and roads are usually constructed in an open way using standard prefabricated reinforced concrete structures, the reliability of which must be checked taking into account the specific local conditions of the route (characteristics of hydrogeological conditions, traffic loads, etc.).

Depending on the number and type of utility networks laid together with pipelines, the common collector can be one- or two-section. The choice of the design and internal dimensions of the collector should also be made depending on the presence of laid communications.

The design of general sewers must be carried out in accordance with the scheme for their construction for the future, drawn up taking into account the main provisions of the master plan for the development of the city for the estimated period. When constructing new areas with green streets and free-plan residential development, heating networks, together with other underground networks, are placed outside the roadway - under technical lanes, stripes of green spaces, and in exceptional cases - under sidewalks. It is recommended to place engineering underground networks in undeveloped areas near the right-of-way of streets and roads.

The laying of heating networks on the territory of newly constructed areas can be carried out in collectors constructed in residential areas and microdistricts to accommodate utilities serving this development [2], as well as in technical undergrounds and technical corridors of buildings.

Laying heating distribution networks with a diameter of up to D 300 mm in technical corridors or basements of buildings with a clear height of at least 2 m is allowed provided that their normal operation is possible (ease of maintenance and repair of equipment). Pipelines must be laid on concrete supports or brackets, and compensation for thermal expansions must be carried out using U-shaped bent expansion joints and corner sections of pipes. Technical underground must have two entrances that do not communicate with the entrances to residential premises. Electrical wiring must be carried out in steel pipes, and the design of the lamps must exclude access to the lamps without special devices. It is prohibited to arrange storage or other premises in the areas where the pipeline passes. The laying of heating networks in microdistricts along routes coinciding with other utilities should be combined in common trenches with the placement of pipelines in channels or without channels.

The method of above-ground (aerial) installation of heating networks has limited application in the current and future development of the city due to the architectural and planning requirements for structures of this type.

Overhead laying of pipelines is widely used in industrial zones and individual enterprises, where they are placed on trestles and masts together with production steam pipelines and process pipelines, as well as on brackets mounted on the walls of buildings.

The above-ground method of laying has a significant advantage over the underground method when constructing heating networks in areas with high level standing groundwater, as well as in subsidence soils and in permafrost areas.

It should be taken into account that the design of thermal insulation and the pipelines themselves, when laid by air, are not subject to the destructive action of ground moisture, and therefore their durability is significantly increased and heat losses are reduced. The cost-effectiveness of overhead installation of heating networks is also significant. Even with favorable soil conditions in terms of capital costs and construction materials consumption air gasket pipelines of medium diameters are 20 - 30% more economical than underground installation in channels, and for large diameters - by 30 - 40%.

In connection with the increased design and construction of suburban thermal power plants and nuclear heat supply stations (HPPs) for district heating major cities great importance issues of increasing the operational reliability and durability of transit heating mains of large diameter (1000 - 1400 mm) and length while simultaneously reducing their metal consumption and consumption of material resources are emerging. The existing experience in the design, construction and operation of large-diameter overhead heating mains (1200-1400 mm) with a length of 5-10 km has given positive results, which indicates the need for their further construction. It is especially advisable to lay heating pipelines above ground under unfavorable hydrogeological conditions, as well as on sections of the route located in undeveloped areas, along highways and at the intersection of small water barriers and ravines.

When choosing methods and designs for laying heating networks, special construction conditions in areas should be taken into account: with seismicity of 8 points or more, the distribution of permafrost and subsidence from soaking soils, as well as in the presence of peat and silty soils. Additional requirements for heating networks in special conditions construction are set out in SNiP 2.04.07-86*.