The adopted scheme of heating networks largely determines the reliability of heat supply, the maneuverability of the system, the ease of its operation and economic efficiency. The principles of constructing large heat supply systems from several heat sources, medium and small systems are significantly different.
Large and medium-sized systems must have a hierarchical structure. The highest level consists of trunk networks connecting heat sources with large thermal units - district heating points (RTP), which distribute the coolant over lower-level networks and provide them with autonomous hydraulic and temperature conditions. The need for strict division of heating networks into main lines and distribution networks is noted in a number of works. The lowest hierarchical level consists of distribution networks that transport coolant to group or individual heating points.
Distribution networks are connected to the main ones in the RTP through water-water heaters or directly with the installation of mixing circulation pumps. In the case of connection through water-water heaters, the hydraulic modes of the main and distribution networks are completely isolated, which makes the system reliable, flexible and maneuverable. Strict requirements for pressure levels in main heating pipelines put forward by consumers are lifted here. The only requirements that remain are not to exceed the pressure determined by the strength of the heating network elements, not to boil the coolant in the supply pipeline and to ensure the required available pressure in front of the water heaters. Coolant can be supplied to the network of the highest hierarchical level from various sources with different temperatures, but on condition that they exceed the temperature in the distribution networks. The parallel operation of all heat sources on a unified main network allows for the best possible distribution of the load between them in order to save fuel, ensures redundancy of sources and allows reducing their total power. The looped network increases the reliability of heat supply and ensures the supply of heat to consumers in the event of failure of its individual elements. The presence of multiple power supplies in a ring network reduces the required reserve capacity.
In the heat supply system with pumps in the RTP, there is no complete hydraulic isolation of the main networks from the distribution networks. For large systems with long looped main heat pipelines and several power sources, the problem of controlling the hydraulic mode of the network while observing the pressure restrictions imposed by consumers can be solved only by equipping the RTP with modern automation. These systems also make it possible to maintain an independent circulation mode of the coolant in distribution networks and temperature regime different from the temperature regime in the mains.As a result of installing pressure regulators on the supply and return lines, it is possible to ensure a reduced level of pressure in them.
In Fig. Figure 6.1 shows a single-line schematic diagram of a large heat supply system, which has two hierarchical levels of heat networks. The highest level of the system is represented by a ring backbone network with branches to the RTP. From the RTP there are distribution networks to which consumers are connected. These networks constitute the lowest level. Consumers are not connected to the backbone network. The coolant is supplied to the main network from two thermal power plants. The system has a backup heat source - the district boiler house (RB). The scheme can be made with one type of connection of distribution networks to the RTP (Fig. 6.1,6 or c) or combined with two types.
For systems with two hierarchical levels, only the highest level is reserved. Reliability of heat supply is ensured by choosing such a power distribution transformer at which the reliability of the non-redundant (dead-end) network is sufficient. The accepted level of reliability determines the length and maximum diameters of the distribution network from each distribution point. At the highest level, both heat sources and heat pipes are redundant. Redundancy is carried out by connecting the supply and return lines with appropriate jumpers. There are two types of jumpers (see Fig. 6.1). Some of them reserve the network, “ensuring its reliable operation in the event of failures of sections of heating pipelines, valves or other networks. Others reserve heat sources, ensuring the flow of coolant from the area of one source to the area of another in the event of its failure or repair. Heating mains together with jumpers form a single ring network . The diameters of all heat pipes of this network, including the diameters of the jumpers, must be designed to allow the passage of the required amount of coolant in the most unfavorable emergency situations. In normal mode, the coolant moves along all the heat pipes of the system and the concept of a ring “jumper” loses its meaning, especially since with variable hydraulic modes, the convergence points of the flows can move, and the role of a “jumper” will be played by different sections of the network.Since the backup elements of the heating network are always in operation, such reservation is called loaded.
Systems with a loaded reserve have the operational disadvantage that when an accident occurs, it is very difficult to detect the highway on which it occurred, since all the highways are connected into a common network.
While maintaining the principle of hierarchical construction of the heat supply system, you can apply another method of its redundancy, using
unloaded reserve. In this case, the jumpers that provide redundancy for heat sources are disabled in normal mode and do not work. It should be noted here that since the principle of constructing the system diagram is based on hierarchy and the highest and lowest levels are separated by large thermal units, consumers are not connected to the jumpers, regardless of whether they are a loaded or unloaded reserve. Each thermal power plant provides heat supply to its zone. In situations where there is a need to reserve one source for another, backup jumpers are switched on.
When using the principle of unloaded redundancy, ringing of networks to ensure reliability of heat supply in the event of failures of heating network elements can be carried out using single-pipe jumpers, as was proposed at the Moscow Institute of Civil Engineering named after. V.V. Kuibysheva. At the points where the jumpers are connected to the heat pipes, there are nodes that allow you to switch the jumpers to the supply or return lines, depending on which of them the accident occurred (the probability of simultaneous failure of two elements is negligible).
The use of single-pipe jumpers can significantly reduce additional capital investments in redundancy. In normal mode, the network operates as a dead-end network, i.e., each line has a certain circle of consumers and an independent hydraulic mode. In emergency situations, the necessary backup lanes are switched on. caps. With an unloaded backup, as well as with a loaded one, the diameters of all heat pipes, including jumpers, are designed to allow the passage of the required amount of coolant under the most intense hydraulic conditions in emergency situations. The schematic diagram is retained and can be illustrated in Fig. 6.1. The difference from the loaded redundancy scheme is that jumpers 3 are single-pipe. The system is operated with closed valves on all jumpers 3 and 4. This operating mode is more convenient, since with independent hydraulic modes of the lines it is easier to control their condition. In addition, the use of an unloaded reserve - single-pipe jumpers - provides a significant economic effect.
To ensure reliable and high-quality heat supply, hierarchical design of the circuit and redundancy is not yet enough. It is necessary to ensure controllability of the system. It is necessary to distinguish between two types of system control. The first type ensures the efficiency of heat supply during normal operation, the second type allows for limited heat supply to consumers in emergency hydraulic conditions.
The controllability of a system during operation is understood as a property of the system that allows changing hydraulic and temperature conditions in accordance with changing conditions. To be able to control hydraulic and temperature conditions, the system must have heating points equipped with automation and devices. allowing the implementation of autonomous circulation modes in distribution networks. Systems with a hierarchical structure and RTP meet the controllability requirements to the best extent. RTP with pump connections of distribution networks are equipped with pressure regulators that maintain constant pressure in the return line and a constant pressure difference between the supply and return lines after the RTP. Circulation pumps make it possible to maintain the available pressure drop after the RTS constant with reduced water flow in the external network, as well as reduce the temperature in the networks behind the RTS by mixing water from the return line. RTPs are equipped with automation that allows them to be cut off from the main heat pipelines in the event of accidents in distribution networks. The RTP is connected to the mains on both sides of the sectional valve. This provides power to the RTP in the event of an accident at one of the sites. Sectional valves on highways are installed approximately every 1 km. If the RTP is connected on both sides of each valve, then for mains with an initial diameter of 1200 mm, the RTP load will be approximately 46,000 kW (40 Gcal/h). In new planning solutions for cities, the main urban planning element is a microdistrict with a heat load of 11,000-35,000 kW (10-30 Gcal/h). It is advisable to create large RTPs to ensure heat supply to one or several microdistricts. In this case, the heat load of the RTP will be 35,000-70,000 kW (30-60 Gcal/h):
Another way of connecting distribution networks to the main line is through heat exchangers located in the RTP; it does not require equipping the RTP with a large number of automatic devices, since the hydraulic main and distribution networks are separated. This method is especially advisable to use in difficult terrain and in the presence of zones with low geodetic marks. The choice of method should be based on a technical and economic calculation.
The problem of managing emergency hydraulic mode arises when calculating heat pipelines to pass a limited amount of coolant during accidents.
Taking into account the relatively short duration of emergency situations on heating networks and the significant heat storage capacity of buildings, at MISS. V.V. Kuibyshev developed the principle of justifying the reserve capacity of heating networks based on limited (reduced) heat supply to consumers during emergency repairs on the networks. This principle allows you to significantly reduce additional capital investments - in redundancy. For the practical implementation of limited heat supply, the system must be controllable when switching to emergency hydraulic mode. In other words, consumers must select predetermined (limited) quantities of coolant from the network. To do this, it is advisable to install a flow limiter regulator at each input to the thermal unit on the bypass. If an emergency occurs, the coolant supply to consumers is switched to bypass. Blocks of such regulators should be installed at the input to the RTP. If the RTP is equipped with flow regulators that allow remote reconfiguration, then they can serve as regulators - flow limiters.
If the emergency hydraulic mode is not controlled, then the network capacity reserve must be designed for 100% coolant consumption in case of emergency, which will lead to unreasonable overconsumption of metal.
The practical implementation of control of operational and emergency modes is possible only with the presence of telemechanization. Telemechanization should provide control of parameters, signaling of equipment status, control of pumps and valves, and regulation of network water flow.
The optimal schemes of modern large heat supply systems were discussed above. Small heat supply systems with a load approximately corresponding to the RTP loads are designed
unreserved. Networks are made as branched dead-end networks. As the power of the heat source increases, the need arises to reserve the head part of the heating network.
Controlled systems with a hierarchical structure are modern progressive systems. However, the heating networks that were built until recently and the majority of those in operation belong to the so-called impersonal networks. With this solution, all heat consumers (both large and small) are connected in parallel to the network, both to the mains and to the heat distribution pipelines. As a result of this method of connection, the distinction between main and distribution networks is essentially lost. They represent a single network with a single hydraulic mode; they are distinguished only by the diameter. Such a system does not have a hierarchical structure, is uncontrollable, and its redundancy in order to increase the reliability of heat supply requires significant capital investments. From the above we can conclude that newly built heat supply systems should be designed to be controllable with a hierarchical structure. When reconstructing and developing existing systems, it is also necessary to design RTPs and ensure a clear division between main and distribution networks.
Based on their construction, existing heating networks can be divided into two types: radial and ring (Fig. 6.2). Radial networks are dead-end, non-redundant and therefore they do not provide the necessary reliability. Such networks can be used for small systems if the heat source is located in the heat center - the supplied area.
Depending on the number of consumers, their needs for thermal energy, as well as the requirements for the quality and uninterrupted supply of heat for certain categories of subscribers, heating networks are made radial (dead-end) or ring.
The dead-end circuit (picture) is the most common. It is used when providing thermal energy to a city, neighborhood or village from one source - a combined heat and power plant or a boiler house. As the main line moves away from the source, the diameters of heat pipes 1 decrease, the design, composition of structures and equipment on heating networks are simplified in accordance with the reduction in heat load. This scheme is characterized by the fact that in the event of a mainline failure, subscribers connected to the heating network after the accident site are not provided with thermal energy.
To increase the reliability of providing consumers 2 with thermal energy, jumpers 3 are installed between adjacent lines, which allow the supply of thermal energy to be switched in the event of a failure of any line. According to the design standards for heating networks, the installation of jumpers is mandatory if the power of the mains is 350 MW or more. In this case, the diameter of the lines is usually 700 mm or more. The presence of jumpers partially eliminates the main disadvantage of this scheme and creates the possibility of uninterrupted heat supply to consumers. In emergency conditions, a partial reduction in the supply of thermal energy is allowed. For example, according to the Design Standards, jumpers are designed to provide 70% of the total thermal load (maximum hourly consumption for heating and ventilation and average hourly consumption for hot water supply).
In developing areas of the city, redundant jumpers are provided between adjacent highways, regardless of the thermal power, but depending on the priority of development. Jumpers are also provided between highways in dead-end circuits when supplying heat to an area from several heat sources (CHP, district and block boiler houses 4), which increases the reliability of heat supply. In addition, in the summer, when one or two boiler houses are operating in normal mode, several boiler houses operating at minimum load can be turned off. At the same time, along with increasing the efficiency of boiler houses, conditions are created for timely preventive and major repairs of individual sections of the heating network and the boiler houses themselves. On large branches (see figure) sectional chambers 5 are provided. For enterprises that do not allow interruptions in the supply of thermal energy, heat network circuits with two-way power supply, local backup sources or ring circuits are provided.
Ring circuit(Figure) is provided in large cities. The installation of such heating networks requires large capital investments compared to dead-end ones. The advantage of the ring circuit is the presence of several sources, which increases the reliability of heat supply and requires less total reserve power of boiler equipment. As the cost of the ring main increases, capital costs for the construction of thermal energy sources decrease. Ring main 1 is connected to three thermal power plants, consumers 2 are connected to the ring main via a dead-end circuit through central heating points 6. On large branches, sectional chambers 5 are provided. Industrial enterprises 7 are also connected according to a dead-end circuit.
According to the design of thermal insulation, ductless laying of heat pipelines is divided into backfill, prefabricated, prefabricated-cast and monolithic. The main disadvantage of ductless installation is increased subsidence and external corrosion of heat pipes, as well as increased heat loss in the event of a violation of the waterproofing of the heat-insulating layer. To a large extent, the disadvantages of ductless installations of heating networks are eliminated by using thermal and waterproofing based on polymer concrete mixtures.
Heat pipes in the channels are laid on movable or fixed supports. Movable supports serve to transfer the own weight of the heat pipes to the supporting structures. In addition, they ensure the movement of pipes, which occurs as a result of changes in their length when their length changes when the temperature of the coolant changes. Movable supports can be sliding or roller.
Sliding supports are used in cases where the base for the supports can be made strong enough to withstand large horizontal loads. Otherwise, roller bearings are installed that create smaller horizontal loads. Therefore, when laying large-diameter pipelines in tunnels, on frames or masts, roller supports should be installed.
Fixed supports serve to distribute thermal expansion of the heat pipe between compensators and to ensure uniform operation of the latter. In the chambers of underground channels and during above-ground installations, fixed supports are made in the form of metal structures, welded or bolted to pipes. These structures are embedded in foundations, walls and channel ceilings.
To absorb thermal expansion and relieve heat pipes from temperature stresses, radial (flexible and wavy hinge-type) and axial (gland and lens) compensators are installed on the heating network.
Flexible U- and S-shaped expansion joints are made from pipes and bends (bent, steeply curved and welded) for heat pipelines with a diameter of 500 to 1000 mm. Such compensators are installed in non-passable channels, when it is impossible to inspect the installed heat pipelines, as well as in buildings with ductless installation. The permissible bending radius of pipes in the manufacture of expansion joints is 3.5...4.5 times the outer diameter of the pipe.
In order to increase the compensating capacity of bent expansion joints and reduce compensation stresses, they are usually pre-stretched. To do this, the compensator in a cold state is stretched at the base of the loop, so that when hot coolant is supplied and the heat pipe is correspondingly lengthened, the compensator arms are in a position in which the stresses are minimal.
Stuffing box compensators are small in size and have a large compensating ability to provide little resistance to the flowing fluid. They are manufactured single-sided and double-sided for pipes with a diameter of 100 to 1000 mm. Stuffing box expansion joints consist of a housing with a flange on the widened front part. A movable glass with a flange is inserted into the compensator body for installing the compensator on the pipeline. To prevent the stuffing box compensator from leaking coolant between the rings, stuffing box packing is placed in the gap between the body and the glass. The stuffing box is pressed into the flange liner using studs screwed into the compensator body. Compensators are attached to fixed supports.
The chamber for installing valves on heating networks is shown in the figure. When laying heating networks underground, 3 rectangular underground chambers are installed to service shut-off valves. Branches 1 and 2 of the network to consumers are laid in the chambers. Hot water is supplied to the building through a heat pipe laid on the right side of the channel. The supply 7 and return 6 heat pipes are installed on supports 5 and covered with insulation. The walls of the chambers are made of bricks, blocks or panels, the prefabricated ceilings are made of reinforced concrete in the form of ribbed or flat slabs, the bottom of the chamber is made of concrete. Entrance to the cells is through cast iron hatches. To descend into the chamber, brackets are sealed under the hatches in the wall or metal ladders are installed. The height of the chamber must be at least 1800 mm. The width is chosen so that the distance between the walls and pipes is at least 500 m.
Questions for self-control:
1. What are heat networks called?
2. How are heating networks classified?
3. What are the advantages and disadvantages of ring and stub networks?
4. What is called a heat pipe?
5. Name the methods for laying heating networks.
6. Name the purpose and types of insulation of heat pipelines.
7. Name the pipes from which heating networks are installed.
8. State the purpose of compensators.
In the initial stage of development of centralized heat supply, it covered only existing capital and separately constructed buildings in the areas covered by the heat source. Heat was supplied to consumers through heat inputs provided in the premises of house boiler rooms. Subsequently, with the development of centralized heat supply, especially in areas of new construction, the number of subscribers connected to one heat source increased sharply. A significant number of both central heating and heating substations have appeared at one heat source in...
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HEAT SUPPLY DIAGRAMS AND THEIR DESIGN FEATURES
Depending on the purpose, heating networks from source to consumer are divided into sections called:main, distribution(large branches) and branches to buildings. The task of centralized heat supply is to maximize the thermal energy satisfaction of all consumer needs, including heating, ventilation, hot water supply and technological needs. This takes into account the simultaneous operation of devices with the required different parameters of the coolant. In connection with the increase in the range and number of subscribers served, new, more complex tasks arise in providing consumers with coolant of the required quality and specified parameters. Solving these problems leads to constant improvement of the heat supply scheme, thermal inputs into buildings and the designs of heating networks.
In the initial stage of development of centralized heat supply, it covered only existing capital and separately constructed buildings in the areas covered by the heat source. Heat was supplied to consumers through heat inputs provided in the premises of house boiler rooms. These boiler houses were located, as a rule, directly in heated buildings or next to them. Such heat inputs began to be called local (individual) heat points (MTP). Subsequently, with the development of centralized heat supply, especially in areas of new construction, the number of subscribers connected to one heat source increased sharply. Difficulties arose in providing some consumers with a given amount of coolant. Heating networks were becoming uncontrollable. To eliminate the difficulties associated with regulating the operating mode of heating networks, central heating points (CHS), located in separate buildings, were created in these areas for a group of buildings. The placement of central heating stations in separate buildings was caused by the need to eliminate noise in buildings that occurs during the operation of pumping units, especially in mass-construction buildings (block and panel).
The presence of central heating stations in centralized heat supply systems of large facilities has simplified regulation to some extent, but has not completely solved the problem. A significant number of both central heating stations and heat transfer stations appeared at one heat source, which made it difficult to regulate the heat output by the system. In addition, the creation of central heating centers in areas with old buildings was practically impossible. Thus, MTP and TsTP are in operation.
A technical and economic comparison shows that these schemes are approximately equivalent. The disadvantage of the scheme with MTP is a large number of water heaters; in the scheme with central heating, there is excessive consumption of scarce galvanized pipes for hot water supply and their frequent replacement due to the lack of reliable methods of corrosion protection.
It should be noted that with increasing power of the central heating station, the efficiency of this scheme increases. The central heating hub provides an average of only nine buildings. However, increasing the power of central heating stations does not solve the problem of protecting hot water supply pipelines from corrosion.
In connection with the recent development of new subscriber input schemes and the production of silent, foundationless pumps, centralized heat supply of buildings through MTP has become possible. The controllability of extended and branched heating networks is achieved by ensuring a stable hydraulic regime in individual sections. For this purpose, control and distribution points (CDPs) are provided on large branches, which are equipped with the necessary equipment and instrumentation.
Heat network diagrams. In cities, heating networks are carried out according to the following schemes: dead-end (radial), as a rule, in the presence of one heat source, ring, in the presence of several heat sources, and mixed.
Dead-end circuit (Fig.a) is characterized by the fact that as distance from the heat source increases, the thermal load gradually decreases and the diameters of the pipelines decrease accordingly 1, the design, composition of structures and equipment on heating networks are simplified. To increase the reliability of supply to consumers 2 thermal energy between adjacent lines is arranged by jumpers 3, which allow you to switch the supply of thermal energy in the event of a failure of any line. According to the design standards for heating networks, the installation of jumpers is mandatory if the power of the mains is 350 MW or more. The presence of jumpers partially eliminates the main disadvantage of this scheme and creates the possibility of an uninterrupted supply of heat in an amount of at least 70% of the calculated flow rate.
Jumpers are also provided between dead-end circuits when supplying heat to an area from several heat sources: thermal power plants, district and block boiler houses 4. In such cases, along with increasing the reliability of heat supply, it becomes possible in the summer to turn off several boiler houses operating at minimum load using one or two boiler houses operating in normal mode. At the same time, along with increasing the efficiency of boiler houses, conditions are created for timely preventive and major repairs of individual sections of the heating network and the boiler houses themselves. On large branches (Fig.
- 1, a) control and distribution points are provided 5.
Ring circuit (Fig. b) used in large cities and for heat supply to enterprises that do not allow interruptions in the heat supply. It has a significant advantage over a dead-end system; several sources increase the reliability of heat supply, while less total reserve power of boiler equipment is required. The increase in cost associated with the construction of the ring main leads to a decrease in capital costs for the construction of heat sources. Ring highway 1 (Fig.,b) is supplied with heat from four thermal power plants. Consumers 2 receive heat from central heating points 6, connected to the ring highway according to a dead-end scheme. Control and distribution points are provided at large branches 5. Industrial enterprises 7 are also connected according to a dead-end scheme through the distribution distribution center.
Rice. Heat network diagrams
A dead-end radial; b ring
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5.2. Determination of the diagram and configuration of heating networks.
When designing heating networks, choosing a scheme is a complex technical and economic task. The layout of the heating network is determined not only by the location of heat sources in relation to consumers, but also by the type of coolant, the nature of heat loads and their calculated value.
The main criteria by which the quality of the designed heating network is assessed should be its economic efficiency. When choosing the configuration of heating networks, you should strive for the simplest solutions and, if possible, shorter pipeline lengths.
In heating networks, both water and steam can be used as coolants. Steam as a coolant is used mainly for process loads of industrial enterprises. Typically, the length of steam networks per unit of design heat load is small. If, due to the nature of the technological process, short-term (up to 24 hours) interruptions in the steam supply are permissible, then the most economical and at the same time quite reliable solution is to lay a single-pipe steam pipeline with a wire.
It must be borne in mind that duplication of steam networks leads to a significant increase in their cost and consumption of materials, primarily steel pipelines. When laying, instead of one pipeline designed for full load, two parallel ones designed for half load, the surface area of the pipelines increases by 56%. Accordingly, metal consumption and the initial cost of the network increase.
Choosing the design of water heating networks is considered a more difficult task, since their load is usually less concentrated. Water heating networks in modern cities serve a large number of consumers, often measured in thousands and even tens of thousands of connected buildings located in areas often measured in many tens of square kilometers.
Water networks are less durable than steam networks, mainly due to the greater susceptibility to external corrosion of steel pipelines laid in underground channels. In addition, water heating networks are more sensitive to accidents due to the higher density of the coolant. The emergency vulnerability of water heating networks is especially noticeable in large systems with dependent connection of heating installations to the heating network, therefore, when choosing a scheme for water heating networks, special attention must be paid to the issues of reliability and redundancy of heat supply.
Water heating networks must be clearly divided into current and distribution. TO ny networks usually include heat pipelines connecting heat sources with areas of heat consumption, as well as with each other.
The coolant enters from the distribution networks and is supplied through the distribution networks through group heat substations or local heat substations to the heat consuming installations of subscribers. Direct connection of heat consumers to these networks should not be allowed, with the exception of cases of connection of large industrial enterprises,
New heating networks are divided into sections 1–3 km long using valves. When a pipeline opens (ruptures), the location of the failure or accident is localized by sectional valves. Thanks to this, losses of network water are reduced and the duration of repairs is reduced due to a decrease in the time required to drain water from the pipeline before repairs and to fill the pipeline section with network water after repairs.
The distance between the sectional valves is selected so that the time required for repairs is less than the time during which the internal temperature in the heated rooms, when heating is completely turned off at the design outside temperature for heating, drops below 12 - 14 ° C. This is the minimum limit value that is usually accepted in accordance with the heat supply contract.
The distance between sectional valves should generally be smaller for larger pipeline diameters and at lower design outside temperatures for heating. The time required to carry out repairs increases with increasing pipeline diameter and the distance between sectional valves. This is due to the fact that as the diameter increases, the repair time increases significantly.
If the repair time is longer than permissible, it is necessary to provide for system backup of heat supply in the event of failure of a section of the heating network. One of the redundancy methods is to block adjacent highways. Sectional valves are conveniently placed in connection points between distribution networks and heating networks. In these nodal chambers, in addition to sectional valves, there are also head valves of distribution networks, valves on blocking lines between adjacent mains or between mains and backup heat supply sources, for example, district ones (chamber 4 in Fig. 5.1). There is no need to section steam lines, since the mass of steam required to fill long steam lines is small. Sectional valves must be equipped with an electric or hydraulic drive and have a telemechanical connection with the central control center. Distribution networks must be connected to the main line on both sides of sectional valves so that uninterrupted service to subscribers can be ensured in case of accidents on any sectioned section of the main line.
Rice. 5.1. Principal single-line communication diagram of a two-pipe water heating network with two mains
1 - collector; 2 - network; 3 - distribution network; 4 - sectioning chamber; 5 - sectional valve; 6 - ; 7 - blocking connection
Interlocking connections between highways can be made using single pipes. An appropriate scheme for connecting them to the network may provide for the use of blocking connections for both the supply and return pipelines.
In buildings of a special category that do not allow interruptions in heat supply, provision must be made for backup heat supply from gas or electric heaters or from local heaters in the event of an emergency interruption of centralized heat supply.
According to SNiP 2.04.07-86, it is allowed to reduce the heat supply in emergency conditions to 70% of the total design consumption (maximum hourly for ventilation and average hourly for hot water supply). For enterprises in which interruptions in the heat supply are not allowed, duplicate or ring circuits of heating networks should be provided. Estimated emergency heat consumption must be taken in accordance with the operating mode of enterprises.
In Fig. Figure 5.1 shows a basic single-line diagram of a two-pipe water heating network with an electrical power of 500 MW and a thermal power of 2000 MJ/s (1700 Gcal/h).
The radius of the heating network is 15 km. Heat consumption is transmitted to the final area via two two-pipe transit mains 10 km long. The diameter of the outlet lines is 1200 mm. As water is distributed into associated branches, the diameters of the lines decrease. Heat consumption is introduced into the final area through four mains with a diameter of 700 mm, and then distributed over eight mains with a diameter of 500 mm. Interlocking connections between main lines, as well as redundant substations, are installed only on lines with a diameter of 800 mm or more.
This solution is acceptable in the case when, with the accepted distance between sectional valves (2 km in the diagram), the time required to repair a pipeline with a diameter of 700 mm , less time during which the internal temperature of heated buildings, when the heating is turned off at the outside temperature, will drop from 18 to 12 ºС (not lower).
Interlocking connections and sectioning valves are distributed in such a way that in the event of an accident on any section of a main line with a diameter of 800 mm or more, all subscribers connected to the heating network are provided with. subscribers is violated only in case of accidents on lines with a diameter of 700 mm or less.
In this case, subscribers located behind the accident site (along the heat path) are terminated.
When supplying heat to large cities from several, it is advisable to provide for mutual interlocking by connecting their mains with interlocking connections. In this case, a combined ring can be created
Blocking connections between large-diameter mains must have sufficient capacity to ensure the transmission of redundant water flows. In necessary cases, substations are built to increase the capacity of blocking connections.
Regardless of the blocking connections between the mains, it is advisable in cities with a developed hot water supply load to provide jumpers of a relatively small diameter between adjacent heat distribution networks to reserve the hot water supply load.
When the diameters of the mains emanating from the heat source are 700 mm or less, a radial (radial) heating network diagram is usually used with a gradual decrease in diameter as the distance from the station increases and the connected heat load decreases.
Such a network is the cheapest in terms of initial costs, requires the least metal consumption for construction and is easy to operate. However, in the event of an accident on the backbone of the radial network, the subscribers connected to the accident site are terminated. If an accident occurs on the main line near the station, then all consumers connected to the main line are interrupted. This solution is acceptable if the repair time for pipelines with a diameter of at least 700 mm satisfies the above condition.
The question of what diameters of heat pipelines and which heating network scheme (radial or ring) should be used in district heating systems should be decided based on the specific conditions dictated by the heat supply of heat consumers: whether they allow a break in the supply of coolant or not, what are the costs of redundancy and so on. Therefore, in a market economy, the above regulation of diameters and diagrams of heating networks cannot be considered the only correct solution.
Heat supply systems are a set of devices for the production of thermal energy, its transportation, distribution and consumption.
Scheme:
1) Source of thermal energy (CHP, RK, GK, AK, etc.). 2) Heat pipelines for transporting thermal energy from source to consumer. 3) Heating points for connection, metering and control of thermal energy consumption. 4) Consumers of thermal energy (hot water supply + hot water supply + technological needs).
Types of heating points: 1. central (serve several buildings or blocks and individual buildings). 2. local (serve the building in which they are located).
2. Classification of heat supply systems.
1
) By location of the heat energy source: Centralized (the heat energy source serves 2 or more buildings). Decentralized (serves one building or separate premises). 2) By coolant (water and steam). 3) According to the method of preparing water for DHW: Open (water for DHW is taken from heating networks), Closed (water is prepared in water heaters). 4) By the number of pipelines (heat supply systems are 1,2,3,4,5, etc. pipe). Single-pipe ones are only open:
The main type of heat supply is a two-pipe system. (accepted in cases where the heat load can be provided by one type of coolant and approximately the same temperature. 2-pipe systems can be open and closed.
three-pipe:
four-pipe in a residential area:
to ensure constant water temperature
DHW system with low water intake or when
his absence
5) According to the configuration (vehicles are dead-end, circular and circular with control distribution points).
3. Heat network diagrams.
Dead end: advantages (simple circuit, small investment), disadvantages (low reliability, because the consumer receives thermal energy from only one direction, and in the event of an accident is completely disconnected from the heat supply system).
WITH 
hema:
In order to increase reliability, all vehicles are divided into separate sections with control valves to reduce accident response.
Ring: advantages (higher reliability because consumers can receive thermal energy from two directions. Several sources of thermal energy can be connected to the ring network, which increases reliability. The ability to use thermal energy from sources running on different types of fuel). Disadvantages (increased capital investments by 20-30%. More complex regulation of heat loads).
1. Main pipelines of the vehicle.
2. Distribution
3. Intra-quarter
Ring road with control distribution points.
Scheme:
1.2.3. distribution lines
quarterly. 4. sectional valve
5. head valves of the distributor.
networks. 6. Single or 2 pipe
jumper.
The valve(s) is open. in case of accident(s)
closed, open (c, d).
The KRP device increases
costs by 10%.
4.Supports of heating network pipelines.
Supports can be movable or non-movable. Movable (sliding, hanging, roller, roller). The supports are designed to support the weight of the pipeline and ensure its movement during temperature deformations. Sliding ones are used for all types of gaskets.
1. pipeline
2. sliding support
3. support cushion
4. concrete
Roller support:
1. roller
µ TR = 0,4
Cat support:
1
. ice rink
µ TR = 0,2
Roller and roller bearings are not used for underground channelless, channel and non-through channels, laying, because require maintenance.
Hanging supports:
1. traction
2. spring
3. clamp
Fixed supports are designed to support the weight of the pipeline and rigidly fix the pipeline together with its installation (clamps, panel boards, frontal).
Clamp supports: 1. clamp
2. stops
Suitable for all types of laying
Panel support:
1. reinforced concrete shield
load-bearing.
2. four-legged fixed
support
Applicable for all types
gaskets except overhead
on high supports.
5. Compensators for heating networks and rules for their installation.
Compensators are used to perceive changes in the length of the pipeline during its temperature deformations. Compensators are axial and radial.
Axial (stuffing box, lens, bellows).
Stuffing box:
1. building.2. cup. 3. reference
ring. 4. sealing
ring. 5. Omental packing.
Advantages (small dimensions,
small hydraulic
resistance, small
expenses).
Flaws (require a change
technical service is possible
misalignment of the axes of the body and glass,
which leads to jamming).
Apply (on pipelines
d≥100, at pressures P ≤ 2.5
MPa). ∆L= 350mm.
Lens:
1. lens. 2. metal insert for
reducing hydraulic losses.
compensating ability of one lens
5mm. Installing more than 5 lenses is not recommended.
Advantages (allow radial
movement).
Bellows: + Maintenance free
- Great cost
Radial compensation is carried out due to bends of curved sections, pipeline bends (self-compensation), or due to special inserts.
Self-compensation: Special inserts:
omega compensator
P 
- shaped compensator Advantages of U-shaped compensators:
installed and manufactured directly
especially on construction sites and not large caps.
expenses.
Disadvantages: increased hydraulic
resistance.
Rules for installing compensators: 1. U-shaped compensators are installed between fixed supports in the middle. 2. The devices are installed on the right along the coolant flow. 3. Sharp corners are not allowed; if there is a sharp corner, then a fixed support must be installed in the corner. 4. Stuffing box expansion joints are installed at a fixed support. Stuffing box comp. It is prohibited to install on curved areas. 6. The fittings are installed between the support and the stuffing box.