Greetings, dear and respected readers of the site “site”. The layout of the heating network is determined by the presence of a heat supply source, their thermal power, as well as the placement of heat supply sources relative to heat consumers. Also, the choice of heating network diagrams depends on the magnitude of the thermal loads of heat consumers, on the nature of heat consumers and on the type of coolant. The heating network design must ensure reliable heat supply and accuracy of its distribution between consumers. The length of the heating network should be minimal, and the configuration should be as simple and economical to operate as possible.
The simplest and most frequently used is the radial (dead-end) heating network diagram.
Schematic diagram radial
1 – heat consumers
2 – heating networks
3 – source of heat supply (boiler house, thermal power plant)
Radial heating networks are characterized by a gradual decrease in pipeline diameters as they move away from the heat supply source and the flow of network water decreases. On the pipelines of heating networks there are placed sectional valves at a distance of 1000 to 1500 m from each other. Sectional valves are also installed on the branches of heat consumers. The purpose of the sectional valve is to localize the location of the heating network failure and disconnect consumers. Radial heating networks are the simplest and require large capital and operating costs.
Main lack of radial heating networks – lack of reservation, i.e. In the event of an accident in one of the sections, for example, section “B-G” in the diagram, the supply of heat to all consumers located after point (section) “D” is stopped.
Increasing the reliability of radial heating networks is possible using the following methods:
- Joint operation of several heat supply sources on a common radial heating network.
- Redundancy of individual elements of the radial heating network (4 instead of 1 supply pipeline, which is designed to pass 100% of the network flow, you can lay 2 pipelines, each of which is designed to pass 50% of the network water flow).
- The use of technical measures that increase the likelihood of failure-free operation of individual elements of the heating network (for example, anti-corrosion protection of pipelines, the use of steel shut-off valves instead of cast iron).
- Installation of duplicate jumpers between heating networks of neighboring areas.
- Use of a gentle mode when operating a radial heating network (for example, operation of heat supply systems at low temperature graphs τ 01<=90 0 C, τ 02 <=60 0 C).
However, increasing the reliability of radial heating networks leads to their significant increase in cost and must be justified by technical and economic calculations.
The continuity of heat supply to consumers is quite well ensured by the ring circuit of the heating network.
In ring heating networks, provision is made for the laying of duplicate main sections ("A-A'-G'-E'-G"), and also for the laying of jumpers (for example, "B-B'; G-G'; D-D'; HER' "). And in the event of an accident in one of the sections, the consumer will receive thermal energy through a backup main line to sections through jumpers.
Ringing increases the reliability of heating networks, but leads to a significant increase in capital and operating costs. The choice of heating network diagram is determined by a feasibility study with mandatory consideration of the reliability of supplying consumers with thermal energy.
Based on the reliability of heat supply, heat consumers are divided into 3 categories:
- Consumers who do not allow interruptions in the supply of the required amount of heat and who do not allow a decrease in the internal air temperature in buildings (hospitals, maternity hospitals, kindergartens with 24-hour stay for children, galleries, mines, etc.).
- Consumers who allow the internal air temperature to decrease for the period of liquidation of the accident. The permissible decrease in internal air temperature for the period of liquidation of the accident is up to 12 0 C for residential, public, administrative buildings, and up to 8 0 C for industrial buildings.
- All other heat consumers (warehouses, garages, storage facilities).
In case of accidents on heating networks or at a heat supply source, the reduction in heat supply to consumers of categories 2 and 3 is shown in the table.
Permissible reduction in heat supply to consumers of categories 2 and 3 during emergency heat supply mode
The estimated time to eliminate the accident and completely restore heat supply is from 15 to 54 hours (depending on the location of the accident and the complexity of the damage).
According to SNiP 41-02-2003 “Heat networks”. All heating networks of settlements and industrial enterprises are divided into:
- main heating networks – designed for transporting coolant from heat supply sources to inputs in residential areas or to inputs to the territory of industrial enterprises.
- heat distribution networks – designed for transporting coolant from main heating networks to heating points in residential areas or industrial enterprises.
- quarterly heating networks or inter-shop heating networks – designed for transporting coolant from heating points to buildings in residential areas or workshops of industrial enterprises.
Schematic diagrams of main, distribution and district heating networks.
1 - heat consumers (buildings)
2 – heat supply sources
3 – sections of the main heating network
4 – heat distribution networks
5 – quarter heating networks
6 – central heating points
Schematic diagram of heating networks with individual heating points
The figures show diagrams of radial main distribution and district heating networks for 2 residential areas in the presence of 2 heat supply sources.
For each residential area, heat supply is provided from any heat supply source (by switching valves on the main and distribution heating networks). Main heating networks and distribution heating networks transport coolant for all types of heat consumption, i.e. in one pipeline there is network water for heating, ventilation, hot water supply and possibly even for the technological needs of heat consumers.
Main heating networks and distribution heating networks are laid, as a rule, with 2 pipes; quarterly and inter-shop networks transport the coolant for each type of heat consumption separately, i.e. networks for heating are laid separately (the so-called heating thermal networks), networks for hot water supply (hot water supply networks) are laid separately, and networks can also be laid at industrial enterprises to cover the technological heat load.
Quarterly and inter-shop heating networks are laid either with 4 pipes or many pipes; in the presence of residential areas or at industrial enterprises, individual heating points, the differences between distribution and quarterly heating networks are practically erased, i.e. In this case, heat distribution networks are laid in the residential areas themselves, or between workshops in industrial enterprises.
The prepared coolant (steam of a certain pressure or water heated to a given temperature) is supplied through heating networks to heat consumers. The heating network consists of heat pipelines, i.e., steel pipes connected by welding, thermal insulation, shut-off and control valves, pumping substations, automatic regulators, thermal expansion compensators, drainage and air vent devices, moving and fixed supports, service chambers and building structures.
Currently, heating networks are mostly made of two pipes, consisting of supply and return heat pipelines for water networks and a steam pipeline with a condensate pipeline for steam networks.
The layout of the heating network is determined by the location of heat sources (CHP or district boiler houses) in relation to the area of heat consumption, the nature of the heat load and the type of coolant. The network design must ensure reliability and cost-effectiveness of operation; The length of the network should be minimal, and the configuration should be as simple as possible.
Steam as a coolant is used mainly for process loads of industrial enterprises. The main load of steam networks is usually concentrated in a relatively small number of nodes, which are the workshops of industrial enterprises. Therefore, the specific length of steam networks per unit of design heat load is, as a rule, small. When, due to the nature of the technological process, short-term (up to 24 hours) interruptions in the steam supply are permissible, the most economical and at the same time quite reliable solution is to lay a single-pipe steam pipeline with a condensate pipeline.
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.
Water heating networks must be clearly divided into main and distribution lines. Main lines usually include heat pipelines that connect heat sources with areas of heat consumption, as well as with each other. The coolant comes from the main lines to the distribution networks and is supplied through the distribution networks through group thermal substations or local thermal substations to the heat-consuming installations of subscribers. Direct connection of heat consumers to main networks should not be allowed, with the exception of cases of connection of large industrial enterprises.
Distinguish radial and annular heating network. The most commonly used are radial networks, which are characterized by a gradual decrease in diameter as they move away from the source of heat supply and the heat load decreases (Fig. 26). Such networks are easy to operate and require the lowest capital costs.
The disadvantage of radial networks is the lack of redundancy. In the event of an accident on one of the highways, for example at the point A highways I, the supply of heat to all consumers located after the point will stop A along the coolant flow. In the event of an accident at the beginning of the main line, the heat supply to all consumers is stopped; connected to this highway. To reserve the supply of heat to consumers, jumpers can be provided between the mains. The jumpers are laid with a larger diameter; they connect the middles or ends of the highways.
When supplying heat to large cities from several thermal power plants, it is advisable to provide for mutual interlocking of thermal power plants by connecting their mains with interlocking connections. In this case, a combined ring heat network with several power sources can be created. The diagram of such a network is shown in Fig. 27. In some cases, the heat networks of thermal power plants and large district or industrial boiler houses can be combined into the same system.
Ringing networks significantly increases the cost of networks, but increases the reliability of heat supply. Ringing of industrial heating networks is sometimes mandatory when supplying heat to consumers who do not allow interruptions in the supply of coolant, usually for technological needs. In this case, ringing can be replaced by duplication, i.e., laying two steam or heat pipelines in parallel. The second steam line or heat line in this case is in the “hot reserve”. With appropriate justification, industrial enterprises provide for reserve capacity of heating networks for subsequent expansion of the enterprise or individual workshops.
The integration of main heating networks of several heat sources, along with heat supply redundancy, makes it possible to reduce the total boiler reserve at a thermal power plant and increase the degree of use of the most economical equipment in the system due to optimal load distribution between heat sources.
Taking into account the dependence of 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 switching 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. 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 based 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. At the same time, 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. At the same time, 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 must be made strong enough to withstand large horizontal loads. Otherwise, roller bearings are installed that create smaller horizontal loads. For this reason, when laying large diameter pipelines in tunnels, on frames or masts, roller bearings 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 temperature elongations and relieve heat pipes from temperature stresses, radial (flexible and wavy hinge-type) and axial (gland and lens) compensators are installed on heating networks.
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 shoulders of the compensator are in a position in which the stresses will be 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 systems 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, 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. It is important to note that to descend into the chamber under the hatches in the wall, brackets are sealed 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.
Commercial risk (risk of reduction in service volumes) is minimized by the correct choice of marketing strategy and promotions, continuous monitoring of customer needs, and the implementation of a flexible assortment policy. It should be noted that during the financial and economic assessment of the project, a cautious assessment of the volume of services was taken.
Profitability risk (failure to achieve the planned level of project profitability) minimized due to a flexible tariff policy, choosing prices for services at the average market level, and cost control.
Political risks to a certain extent can be limited through contacts with city authorities and legal support for the project during its implementation.
HYDRAULIC CALCULATION
TASKS OF HYDRAULIC CALCULATION
Hydraulic calculation tasks:
1) determination of pipeline diameters;
2) determination of pressure drop (pressure);
3) determination of pressures (pressures) at various points in the network;
4) linking all points of the system in static and dynamic modes in order to ensure permissible pressures and required pressures in the network and subscriber systems.
In some cases, the task may also be to determine the throughput of pipelines with a known diameter and a given pressure loss.
The results of hydraulic calculations are used for:
1) determining capital investments, metal (pipes) consumption and the main volume of work on the construction of a heating network;
2) establishing the characteristics of circulation and make-up pumps, the number of pumps and their placement;
3) clarifying the operating conditions of heat sources, the heating network and subscriber systems and selecting schemes for connecting heat-consuming installations to the heating network;
5) development of operating modes for heat supply systems.
The initial data for carrying out a hydraulic calculation must be the design and profile of the heating network, the location of heat sources and consumers and the design loads.
DIAGRAMS AND CONFIGURATIONS OF HEATING NETWORKS
The heating network is the connecting and transport link of the heat supply system.
She must have the following qualities:
1. reliability; they must maintain the ability to continuously supply coolant to the consumer in the required quantity throughout the year, with the exception of a short break for preventive maintenance in the summer;
2. controllability – i.e. ensure the required operating mode, the possibility of joint operation of heat supply sources and mutual redundancy of mains.
The required operating mode is the fast and accurate distribution of coolant to heating points under normal conditions, in critical situations, as well as when heat sources work together to save fuel.
The heating network diagram is determined:
Placement of heat sources (CHP or boiler houses) in relation to the area of heat consumption;
The nature of the heat load of consumers in the area;
Type of coolant.
The basic principles that should be followed when choosing a heating network diagram are the reliability and efficiency of heat supply. When choosing the configuration of heating networks, you should strive to obtain the simplest solutions and the shortest length of heat pipes.
Increasing network reliability is carried out using the following methods:
Increasing the reliability of individual elements included in the system;
Using a “gentle” operating mode of the system as a whole or its most damaged elements by maintaining the water temperature in the supply lines at 100°C and above, and in the return lines at 50°C and below;
Reservations, i.e. the introduction of additional elements into the system that can completely or partially replace failed elements.
According to the degree of reliability, all consumers are divided into two categories:
I – medical institutions with hospitals, industrial enterprises with constant heat consumption for technological needs, groups of urban consumers with a thermal power of 30 MW. A break in the heat supply is allowed only for the switching period, i.e. no more than 2 hours;
II – all other consumers.
Steam as a coolant is used mainly for process loads of industrial enterprises. The main load of steam networks is usually concentrated in a relatively small number of nodes, which are the workshops of industrial enterprises. Therefore, the specific length of steam networks per unit of design heat load is small. When, due to the nature of the technological process, short-term (up to 24 hours) interruptions in the steam supply are permissible, the most economical and at the same time quite reliable solution is to lay a single-pipe steam pipeline with a condensate pipeline.
It must be borne in mind that duplication of networks leads to a significant increase in their cost and consumption of materials, primarily steel pipelines. When laying, instead of one pipeline designed for 100% load, two parallel ones designed for 50% load, the surface area of the pipelines increases by 56%. Accordingly, metal consumption and the initial cost of the network increase.
A more difficult task is the choice of a water heating network scheme, because their load is less concentrated.
Water networks are less durable than steam networks due to:
Greater susceptibility to external corrosion of steel pipelines of underground water networks compared to steam pipelines;
Sensitivity to accidents due to the higher density of the coolant (especially in large systems with dependent connection of heating installations to the heating network).
When choosing a scheme for water heating networks, special attention is paid to issues of reliability and redundancy of heat supply systems.
Water heating networks are divided into main And distribution.
Main lines usually include heat pipelines that connect heat sources with areas of heat consumption, as well as with each other.
The operating mode of main heating networks should ensure the greatest efficiency in the generation and transport of heat due to the joint operation of thermal power plants and boiler houses.
The operating mode of distribution networks should provide the greatest savings in heat when using it by adjusting the parameters and flow of coolant in accordance with the required consumption mode, simplifying the layout of heating points, reducing the design pressure for their equipment and reducing the number of heat supply regulators for heating.
The coolant comes from the main networks to the distribution networks and is supplied through the distribution networks through group heating points or local heating points to the heat consuming installations of subscribers. Direct connection of heat consumers to main networks is allowed only when connecting large industrial enterprises.
Main 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 from the condition that the time required for repairs is less than the time during which the internal temperature in the heated rooms, when the heating is completely turned off at the design outside temperature for heating, does not fall below the minimum limit value, which is usually taken as 12- 14 °C in accordance with the heat supply agreement. The time required to carry out repairs increases with the diameter of the pipeline, as well as the distance between the sectional valves.
Fig.1. Schematic diagram of a two-pipe heating network with two mains: 1 – CHP collector; 2 – backbone network; 3 – distribution network; 4 – sectioning chamber; 5 – sectional valve; 6 – pump; 7 – blocking connection.
The distance between sectional valves should be smaller for larger pipeline diameters and at lower design outside temperatures for heating.
The condition for repairing a large-diameter heat pipeline during the period of permissible decrease in internal temperature in heated buildings is difficult to fulfill, since the repair time increases significantly with increasing diameter.
In this case, it is necessary to provide for system backup of heat supply in the event of failure of a section of the heating network, if the above condition regarding repair time is not met. One of the redundancy methods is to block adjacent highways.
Sectional valves are placed at the junction points of distribution networks to main 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 boiler houses.
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 heat supply to subscribers can be ensured in case of accidents on any sectioned section of the main line.
Interlocking connections between highways can be made using single pipes.
In buildings of a special category that do not allow interruptions in heat supply, the possibility of backup heat supply from gas or electric heaters or from local boiler houses should be provided in case of emergency interruption of centralized heating 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 heating and 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.
The radius of the heating network (Fig. 1) is 15 km. To the final heat consumption area, network water is transmitted through two two-pipe transit mains 10 km long. The diameter of the lines at the exit from the thermal power plant is 1200 mm. As water is distributed into associated branches, the diameters of the main lines decrease. In the final area of heat consumption, network water is introduced through four mains with a diameter of 700 mm, and then distributed through eight mains with a diameter of 500 mm. Interlocking connections between main lines, as well as redundant pumping 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 is less than the time during which the internal temperature of heated buildings when the heating is turned off at an external temperature of 1 will decrease from 18 up to 12 °C (not lower).
Interlocking connections and sectioning valves are distributed in such a way that in the event of an accident on any section of the main line with a diameter of 800 mm or more, heat supply is provided to all subscribers connected to the heating network. Heat supply to subscribers is disrupted only in case of accidents on lines with a diameter of 700 mm or less.
In this case, the heat supply to subscribers located behind the accident site (along the heat flow) is stopped.
When supplying heat to large cities from several thermal power plants, it is advisable to provide for mutual interlocking of thermal power plants by connecting their mains with interlocking connections. In this case, a combined ring heat network with several power sources can be created (Fig. 2). In some cases, the heat networks of thermal power plants and large district or industrial boiler houses can be combined into the same system.
The integration of main heating networks of several heat sources, along with heat supply redundancy, makes it possible to reduce the total boiler reserve at a thermal power plant and increase the degree of use of the most economical equipment in the system due to optimal load distribution between heat sources.
Blocking connections between large-diameter mains must have sufficient capacity to ensure the transmission of redundant water flows. If necessary, pumping 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 (Fig. 3). 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 main line of the radial network, the heat supply to subscribers connected to the site of the accident is stopped. For example, in the event of an accident at point “a” on radial highway 1, the power supply to all consumers located along the route from the thermal power plant after point a is cut off. If an accident occurs on the main line near the station, the heat supply to all consumers connected to the main line is stopped. This solution is acceptable if the repair time for pipelines with a diameter of at least 700 mm satisfies the above condition.
For more reliable heat supply, heating networks should be constructed according to the block principle. The block should be a distribution network with a range of 500-800 m. Each block should provide heat supply to a residential neighborhood of approximately 10 thousand apartments or a thermal power of 30-50 MW. The unit must be directly connected to the source collector, or have a two-way heat supply from heat mains.
On the heat map of the area, the locations of the GTP are tentatively outlined;
After placing the GTP, possible routes of highways and jumpers between them are outlined;
The location of distribution networks is planned.
Distribution networks are designed as dead-end networks; sectional valves are not designed.
Distribution networks are allowed to be laid in the basements of buildings
Thermal energy in the form of hot water or steam is transported from the heat source (CHP or large boiler house) to heat consumers through special pipelines called heating networks.
Heat network- one of the most labor-intensive elements of centralized heating systems. It represents heat pipelines - complex structures consisting of steel pipes connected by welding, thermal insulation, thermal expansion compensators, shut-off and control valves, building structures, movable and fixed supports, chambers, drainage and air release devices.
Based on the number of heat pipes laid in parallel, heat networks can be single-pipe, double-pipe and multi-pipe.
Single pipe networks most economical and simple. In them, network water after heating and ventilation systems must be completely used for hot water supply. Single-pipe heating networks are progressive in terms of significantly accelerating the pace of construction of heating networks. IN three-pipe networks two pipes are used as supply pipes to supply coolant with different thermal potentials, and the third pipe is used as a common return pipe. IN four-pipe networks one pair of heat pipes serves the heating and ventilation systems, and the other - the hot water supply system and technological needs.
Currently the most widespread two-pipe heating networks, consisting of supply and return heat pipelines for water networks and a steam pipeline with a condensate pipeline for steam networks. Due to the high storage capacity of water, which allows for long-distance heat supply, as well as greater efficiency and the possibility of central regulation of heat supply to consumers, water networks are more widely used than steam networks.
Water heating networks According to the method of preparing water for hot water supply, they are divided into closed and open. IN closed networks For hot water supply, tap water is used, heated by network water in water heaters. In this case, the network water is returned to the thermal power plant or to the boiler house. In open networks, water for hot water supply is collected by consumers directly from the heating network and, after use, is not returned to the network.
Heating networks are divided into main, laid in the main directions of populated areas, distribution- inside a block, microdistrict and branches to individual buildings.
Radial networks(Fig. 1a) are constructed with a gradual decrease in the diameters of heat pipes in the direction from the heat source. Such networks are the simplest and most economical in terms of initial costs. Their main disadvantage is the lack of redundancy. In order to avoid interruptions in heat supply (in the event of an accident on the main radial network, the heat supply to consumers connected in the emergency area is stopped), redundancy of heat supply to consumers must be provided through the installation of jumpers between the heating networks of adjacent areas and the joint operation of heat sources (if there are several of them). The range of water networks in many cities reaches a significant value (15–20 km).
Rice. 1. Heat network diagrams: dead-end(A) and ring (b)
1- radial main heat pipeline; 2 - heat consumers; 3 - jumpers; 4 - district (quarter) boiler houses; 5 - sectioning chambers; 6 - ring highway; 7 - central heating points; 8 - industrial enterprises
By installing jumpers, the heating network turns into a radial-ring network, and a partial transition to ring networks occurs. For enterprises where interruptions in heat supply are not allowed, duplication or ring circuits (with two-way heat supply) are provided for heating networks. Although ringing networks significantly increases their cost, in large heat supply systems the reliability of heat supply is significantly increased, the possibility of redundancy is created, and the quality of civil defense is also improved.
Steam networks They are arranged mainly with two pipes. Condensate is returned through a separate pipe - a condensate pipeline. Steam from the thermal power plant travels through a steam pipeline at a speed of 40–60 m/s or more to the point of consumption. In cases where steam is used in heat exchangers, its condensate is collected in condensate tanks, from where it is returned to the thermal power plant by pumps through a condensate pipeline.
Rice. 2. Laying heat pipes on masts
Rice. 3. Passage channel made of prefabricated reinforced concrete blocks
The direction of the route of heating networks in cities and other populated areas should be provided for in areas of the most dense heat load, taking into account existing underground and above-ground structures, data on the composition of soils and the level of groundwater, in the technical strips allocated for engineering networks parallel to the red lines of streets, roads, outside the roadway and green space. You should strive for the shortest route length, and therefore, less work on laying.
Rice. 4. Non-pass channels of the KL (a), KLp (b) and KLS (c) brands
Based on the method of installation, heating networks are divided into underground and above-ground (air). Aboveground laying of pipes (on free-standing masts or trestles, on brackets embedded in the walls of a building) is used in the territories of industrial enterprises, when constructing heating networks outside the city, when crossing ravines, etc. Overground laying of heating networks is recommended mainly at high groundwater standing. The predominant method of laying pipelines for heating networks is underground installation: in passage channels and collectors together with other communications; in semi-passing and non-passing canals; ductless (in protective shells of various shapes and with backfill thermal insulation).
The most advanced, but also more expensive method is the laying of heat pipes in passage channels, which are used when there are several heat pipes of large diameters. When the air temperature in the ducts is more than 50 °C, natural or mechanical ventilation is provided.
Exhaust shafts on the route are placed approximately every 100 m. Supply shafts are located between exhaust shafts and, if possible, combined with emergency hatches. In sections of heating networks with a large number of pipelines and high temperatures of coolants, mechanical ventilation is installed. When the air temperature in the channels is below 40 ° C, they are periodically ventilated by opening hatches and entrances. During repair work, a mechanical mobile ventilation unit can be used. In large cities, so-called urban collectors are built, in which heat pipelines, water supply, electrical and telephone cables are laid.
Semi-bore channels consist of L-shaped wall blocks, reinforced concrete bottoms and floors. They are built under passages with heavy street traffic, under railway tracks, at the intersection of buildings, where it is difficult to open heating pipes for repairs. Their height usually does not exceed 1600 mm, the width of the passage between the pipes is 400–500 mm. In the practice of centralized heating, the most widely used impassable channels.
Rice. 5. Structural elements of heating networks
a - heating network chamber; 1- stuffing box compensators; 2 - pressure gauges; 3 - fixed support; 4 - channel; b - placement of niches along the route of heat pipelines: N - fixed support; P - movable support; c - placement of the compensator in a niche: 1 - supply pipeline; 2 - return pipeline; 3 - wall; G - stuffing box compensator; 1 - pipe; 2 - ground book; 3 - cord packing; 4 - ring sealing; 6 - frame; 6 - counter axle; 7 - safety ring; 8- bolt: 9 - washer; 10 - screw; d - fixed shield support; 1 - reinforced concrete slab-shield; 2 - welded stops; 3-channel; 4 - concrete preparation: 5 - pipelines; 6 - drainage hole; e- roller movable support: 1 - roller; 2 - guides; 3 - metal lining
Rice. 6. Channelless installation of heat pipes in monolithic shells made of reinforced foam concrete
1- reinforced foam concrete shell; 2 - sand bedding; 3 - concrete preparation; 4 - soil
Three types of standard channels have been developed: a KL channel, consisting of trays and reinforced concrete floor slabs; a channel of the KLp brand, consisting of a bottom slab and a tray; and a channel of the KLS brand, consisting of two trays laid one on top of the other and connected with cement mortar using I-beams. Along the route of the underground heat pipeline, special chambers and wells are installed for installing fittings, measuring instruments, gland expansion joints, etc., as well as niches for U-shaped expansion joints. The underground heating pipeline is laid on sliding supports. The distance between the supports is taken depending on the diameter of the pipes, and the supports of the supply and return pipelines are installed staggered.
Heating networks in general, especially main ones, are a serious and responsible structure. Their cost, compared to the costs of constructing a thermal power plant, is a significant part.
Ductless method of laying heat pipes- the cheapest. Its use makes it possible to reduce the construction cost of heating networks by 30–40%, significantly reduce labor costs and the consumption of building materials. Heat pipe blocks are manufactured at the factory. Installation of heat pipes on the route involves only laying the blocks in a trench using a truck crane and welding the joints. The depth of heating networks from the surface of the earth or road surface to the top of the channel or collector slab is taken, m: with a road surface - 0.5, without a road surface - 0.7, to the top of the channelless laying shell - 0.7, to the top of the chamber slab - 0.3.
Currently, over 80% of heating networks are laid in non-passage channels, about 10% are above-ground, 4% are in through channels and tunnels, and about 6% are channelless. The average service life of underground duct heating pipelines is half the standard and does not exceed an average of 10–12 years, and ductless ones with bitumen-based insulation are no more than 6–8 years. The main cause of damage is external corrosion, which occurs due to the absence or poor-quality application of anti-corrosion coatings, unsatisfactory quality or condition of the coating layers, allowing excessive moisture in the insulation, as well as due to flooding of channels due to structural leaks. Both in our country and abroad, a constant search is being carried out, and in recent years especially intensively, in the direction of increasing the durability of heat pipelines, the reliability of their operation and reducing the costs of their construction.