Heat network diagrams. Heat network diagrams, heat network configurations

Reserving heat supply to consumers is the most complex issue in the design of heating networks, which is not fully covered in the regulatory and technical documentation. In this regard, the development of “ Methodological recommendations on the reservation of heating networks” (hereinafter referred to as “Recommendations”), taking into account the latest technological advances and specific operating conditions of Moscow in 2006.

General Director of Kanalstroyproekt LLC – Malinitsky V.S.

Deputy Chief Engineer of Kanalstroyproekt LLC – Lipovskikh V.M.

Chief Project Engineer of Kanalstroyproekt LLC – Areshkin A.A.

Over the past fifty years, network redundancy requirements have changed periodically. For example, for the climatic conditions of Moscow, the reservation requirements were as follows:

– according to clause 4.1. SNiP II-36-73, reservation of heating networks was mandatory for heating mains with a load of more than 300 Gcal/h (for central heating systems with a mode of 150/70°C, starting with heating pipelines 2xDu800 mm and more);

– according to clause 3.1, and table 1 of SNiP 2.04.07-86*, redundancy was mandatory for heat pipelines 2xDu500 mm or more;

– according to clause 6.33. and Table 2 SNiP 41-02-2003 redundancy became mandatory for heat pipelines 2xDu300 mm or more.

At the same time, SNiP 41-02-2003 does not take into account the specific conditions for the ductless installation of factory-made heat pipes with thermal insulation made of polyurethane foam (PPU) in a polyethylene sheath, which provide a cable for preventive remote control condition of heat pipes (hereinafter referred to as ductless installation of heat pipes in polyurethane foam insulation).

As a result, existing heating networks, as well as those designed before 2003, do not comply with the redundancy standards of the current SNiP 41-02-2003. Based on this, when reconstructing existing central heating systems, it is necessary to consider the issue of reserving existing heating networks, depending on the period of their installation (or the last date of relocation) and technical condition.

When considering the issue of redundancy of heating networks, it is necessary to take into account that it leads to additional increase capital costs and therefore should be minimized.

In this regard, when developing schemes and designs of heating networks, it is necessary to proceed from the following provisions:

– the probability of one accident in heating networks during the period of time under consideration;

– ensuring redundancy of the heat source by installing two or more units on it;

— features of connection to heating networks.

Terms and classification

The following terms and classifications are used in these standards.

District heating system– a system consisting of one or more heat sources, heat networks and heat consumers (hereinafter referred to as DHS).

Accident– damage to heating networks, leading to a shutdown of heat supply to consumers for a period of more than 15 hours.

First category of consumers– consumers who do not allow interruptions in the supply of the calculated amount of heat and a decrease in the air temperature in the premises below those provided for by GOST 30494. For example, hospitals, maternity hospitals, preschools with children staying around the clock, art galleries, chemical and special industries, mines, etc.

– residential and public buildings up to 12°C;

– industrial buildings up to 8°C.

Primary heating mains– heating networks directly connected to heat sources without secondary heating mains and quarterly primary heating pipelines.

Secondary heating mains– heating networks connected to primary heating mains without quarterly primary heating pipelines.

Quarterly heat pipelines– distributing primary heating networks within blocks.

Subscriber inputs- heat pipelines from heating mains or quarterly heat pipelines to central heating stations, VTsTP and ITP.

1. General provisions for reservation of heat sources and heating networks

1.1. The issue of reserving heating networks is directly related to the weather conditions of the area and the deadline for completion repair work. In this regard, when developing these “Recommendations”, specific operating conditions were taken into account (depending on operating conditions, preventive measures and efficiency emergency service), established in OJSC Moscow Heating Network Company (MTK) and OJSC Moscow Energy Company (MOEK).

1.2. According to the requirements of SNiP 41-02-2003 “Heat networks”, in the absence of a local backup heat source at category 1 facilities, backup heat networks from a heat source (or from another heat source) to of this object Necessarily.

1.3. According to the requirements of SNiP 41-02-2003 “Heat networks”, it is allowed not to make reservations for heating networks in following cases:

– for sections of overhead laying less than 5 km long;

– if consumers have a local backup heat source;

– for heating networks with a diameter of 250 mm or less.

For other cases, it is necessary to consider the issue of network redundancy taking into account the specific situation.

1.4. Redundancy of heat sources is ensured by the following condition for the selection of boilers - when the most powerful boiler comes out, the performance of the remaining boilers should provide coverage, depending on the design temperature of the outside air, from 78 to 91% of the design load for heating and ventilation for consumers of categories 2 and 3 and 100% of the design load of consumers 1st category.

1.5. There is no reservation of transit heat pipelines from thermal power plants to peak boiler houses if their performance, depending on the design temperature of the outside air, provides coverage from 78 to 91% of the design load for heating and ventilation for consumers of categories 2 and 3 and 100% of the design load of consumers of category 1.

1.6. The main criteria for reserving heating networks are recommended to be:

– the period for draining and filling heating pipelines with network water and the period for eliminating the accident, which must be reduced due to the efficiency of carrying out restoration work to the minimum permissible period, i.e. up to a period of 12 hours or less, which corresponds to the period of liquidation of an accident on a section of a 2xD250 mm heating network with a length of 1000 m (the section between two sectional valves).

– probability of an accident occurring based on service life and technical condition heat pipes, as well as the type of laying of heat pipes and monitoring their condition.

Based on these above criteria, it is recommended to determine the length of unreserved sections of heat pipelines 2xDu300-600 mm.

1.6.1. Calculations and practice of restoration work at MTK and MOEK have shown that for heat pipelines laid in non-passable channels with thermal insulation made of mineral wool products (or channelless laying with thermal insulation made of reinforced foam concrete and polyurethane foam insulation) 2xDu300-600 mm, it is necessary to reduce the length of non-reserved sections to the level given in table 1.1.

Table 1.1

1.6.2. In the case of installing additional drainage devices that provide accelerated emptying of pipelines or increasing the diameter of drainage devices, it is allowed to increase the length of non-reserved sections to the level given in Table 1.2.

Table 1.2

A diagram of heating networks with dead-end sections, ensuring short-term repair work (less than 12 hours) is shown in Fig. 1.1.

Rice. 1.1. Diagram of heating networks with dead-end wiring (no-pass channel, mineral wool), which do not require redundancy

1.6.3. In connection with preventive monitoring of the condition of heat pipes for ductless installation of heat pipes in polyurethane foam insulation, the length of unreserved sections is compared with Table 1.1. can be increased to the level given in table 1.3. In this case, accelerated emptying of pipelines must be ensured by installing additional drain devices or increasing the diameter of drain devices.

Table 1.3

A diagram of heating networks with dead-end sections, ensuring short-term repair work (less than 12 hours) is shown in Fig. 1.2.

Rice. 1.2. Diagram of heating networks with dead-end wiring (ductless laying, PPU), which do not require redundancy

1.7. When providing an area with heat from two or more sources, it is recommended to back up heating networks from each source, i.e. install an emergency jumper between the heating networks of each heat source.

1.8. In what follows, the text considers the issue of reserving heating networks of only closed central heating systems (CHS) when the consumer does not have a local emergency heat source.

2. Technical solutions for redundancy of heating networks

– by two-way connection of secondary heating mains to two primary heating mains (one or two heat sources) without installing sectional valves;

– by unilaterally connecting one end of dead-end secondary heating mains to two parallel primary heating mains (one or two heat sources) without installing sectional valves;

– by looping the primary heating mains (one or two heat sources) with the installation of sectional valves;

– by laying an additional (third) heat pipeline;

– by supplying additional two-pipe heat pipelines to the consumer from the primary heating main or a second heat source (mainly consumers of category 1);

– by combining the above technical solutions.

2.2. A diagram of heating networks in which two-way connection of heating networks is made to two primary heating mains (one or two heat sources) without installing sectional valves is shown in Fig. 2.1. Distinctive feature This technical solution is that consumers are connected exclusively to secondary heating mains.

Rice. 2.1. Scheme of reserved heating networks with two-way connection to two primary heating mains

2.3. The diagram of heating networks in which unilateral connection of dead-end heating networks is made to two primary heating mains (one or two heat sources) without installing sectional valves is shown in Fig. 2.2.

Rice. 2.2. Scheme of reserved heating networks with one-way connection to two primary heating mains

2.4. A diagram of heating networks in which redundancy is provided by looping the primary heating mains (one or two heat sources) is shown in Fig. 2.3. A distinctive feature of this scheme is network loopback , is the connection of dead-end heating networks at one point between two sectional valves of the primary heating main or connection at two points within the girth of one sectional valve of the primary heating main (inset with “pants”).

Rice. 2.3. Scheme of reserved heating networks with one-way connection to looped primary heating mains

2.5. The diagram of heating networks in which redundancy is made by laying an additional (third) dual-purpose heat pipeline is shown in Fig. 2.4. In this case, all heat pipelines must be connected directly to a reserved heating main (or to a heat source); it is advisable to use a double-pipe scheme for separately located areas and category 1 consumers. At the same time, to ensure constant circulation during normal operation, it is recommended to use an additional heat pipe as a return heat pipe.

Rice. 2.4. Scheme of laying three-pipe heating networks with one-way connection to reserved heating mains

2.6. The layout of two additional heat pipelines (supply and return) for redundancy of category 1 facilities is shown in Fig. 2.4. In this case, the main and backup heat pipelines must be connected to two reserved heating mains.

2.7. The configuration of heating networks with non-redundant above-ground sections is shown in Fig. 2.5.

Rice. 2.5. Configuration of heating networks with non-redundant sections of overhead installation

H. Reservation of heating networks during the construction of a new heat source

3.1. When developing a heating network diagram for the construction of a new heat source, it is recommended to develop various options heating network diagrams with consideration of the issue of redundancy.

3.2. For heat sources with a capacity of less than 50 Gcal/h, it is recommended to develop a variant of the circuit only with dead-end wiring without redundant heating networks.

3.3 For heat sources with a capacity from 50 to 200 Gcal/h inclusive, it is recommended to develop both an option with dead-end wiring without redundant heating networks, and options with redundant heating networks and subsequent approval of one of them (or a combined option).

3.4. For heat sources with a capacity of more than 200 Gcal/h, it is recommended to develop several variants of schemes with redundancy of heating networks and subsequent approval of one of them.

3.5. It is allowed to install sections that provide redundancy of heating networks to be carried out on last stage construction after the formation of the thermal district.

4. Redundancy of heating networks during reconstruction of central heating systems

4.1. When reconstructing a central heating system with an increase in the load of the heat source due to the connection of new (reconstructed) consumers, it is allowed for the retained and reconstructed consumers to use existing scheme heating networks. At the same time, it is recommended to develop a scheme for new consumers taking into account the provisions given in Section 3.

4.2. When reconstructing a central heating system with an increase in the load of the heat source only at the expense of reconstructed consumers (without connecting new ones), it is allowed for the retained and reconstructed consumers to use the existing heating network diagram.

4.3. When reconstructing a central heating system in order to increase reliability without increasing the load of the heat source and connecting new consumers, it is recommended to develop a new heating network diagram taking into account the provisions given in Section 3.

5. Schematic diagrams of nodes (cameras) in areas with backup connections

5.1. For two-pipe heating networks, it is permissible to perform the schematic diagrams of the units in a single-pipe design. For three-pipe heating networks, it is recommended to carry out the schematic diagrams of the units in their natural form, i.e. in two and three-pipe versions.

5.2. To ensure proper circulation of the coolant after switching the network water flows in the backup communication areas, it is necessary to perform a transposition of the heat pipes, that is, “overlapping” the network water flows. In this case, the “overlapping” of flows can be carried out by appropriately inserting heat pipes in the chamber or by “overlapping” heat pipes in a section of the heating network.

5.2.2. In order to reduce corrosion processes in backup communication areas, it is necessary to ensure the circulation of network water using an air or drain line.

5.3. To increase reliability on extended sections of backup communications, it is recommended to install shut-off valves on both sides of the section. The maximum length of sections where it is allowed to install a shut-off valve on only one side is given in Table 5.1. The installation of shut-off valves on both sides of shorter sections requires approval from the operating organization.

Table 5.1

5.4. Schematic diagrams of nodes in areas with backup communications are shown in Fig. 5.1

Rice. 5.1. Schematic diagram of nodes (cameras) in the backup communication area

6. Checking the hydraulic and thermal conditions in emergency situations

6.1. For extended heating networks, if necessary, it is recommended to check the hydraulic and thermal conditions in emergency situations, taking into account the provisions set out in paragraph 6.33 and Table 2 of SNiP 41-02-2003 (Appendix 1).

6.2. Verification hydraulic calculations of heating networks in emergency situations are recommended to be carried out according to a special computer program with the construction of a piezometric graph, based on the condition of maintaining pressures at the outlet and inlet of the heat source, characteristic of normal operating conditions.

6.3. It is allowed to carry out calibration hydraulic calculations of heating networks in emergency situations using a computer program for hydraulic calculation dead-end heating networks with a reduction in the flow of network water to the required level in accordance with clause 6.33. and table 2 SNiP 41-02-2003.

6.4. For clauses 6.2 and 6.3 it is possible to use following programs:

– Hydraulic system– hydraulic and thermal-hydraulic calculations, as well as selection of diameters of pipeline systems for various purposes with detailed consideration of local resistances with the ability to automatically construct piezometric graphs. This program supplied by NTP Truboprovod LLC.

– ZuluThermo – hydraulic calculations heating networks with the ability to perform constructive, verification and adjustment thermal-hydraulic calculations of the heating network and the function of constructing piezometric graphs. This program is supplied by Polytherm LLC.

Annex 1

Extract from SNiP 41-02-2003 “Heating networks” clause 6.33:

When laying heating networks underground in non-passing channels and channelless installation, the amount of heat supply (%) to ensure the internal air temperature in heated rooms is not lower than 12 ° C during the repair and restoration period after a failure should be taken according to Table 2.

table 2

I hope that everyone has understood the heat supply schemes, both with and without redundancy. Now, is it clear how the network is looped and what is a dead-end heating network? Write comments and options for your heating network diagrams.

V.Z. Dmitriev, D.V. Zhukov Omsk branch of OJSC "Territorial Generating Company No. 11"

ANNOTATION

Education complex systems heating supply has raised serious problems related to issues of reliability, redundancy, quality, ecology, and efficiency, which do not meet modern requirements. Insufficient attention is paid to the technical equipment, principles of construction and issues of redundancy of heating networks. The increase in the complexity and scale of district heating systems (DHS) is not accompanied by a change in their structure and configuration, which do not meet the requirements for reliability and efficiency of heat supply. Heat networks introduce significant complexity when researching and calculating the optimal configuration of a heat supply system. Consideration of the network component with nonlinear hydraulic and economic characteristics of the elements makes the task of optimal synthesis of the central heating system of the Omsk metropolis a complex nonlinear problem of a network nature.

1. INTRODUCTION

The centralized heat supply system of the Omsk branch includes five heat sources, three of which operate in CHP mode and two in boiler mode, the length of the main heating networks is more than 260 km with an average diameter of 600 mm, 13 pumping stations (PNS) and more than 12.5 thousand thermal points.

The Omsk enterprise “Heat Networks” is about 70 years old. Historically, heating networks were laid from heat sources in a radial pattern. As necessary and current expediency, networks from different thermal power plants were connected by jumpers. Currently, four of the five heat sources included in the energy company are connected by jumpers.

2. FORMATION OF HEAT SUPPLY SYSTEM CONFIGURATION

Today, the heating networks of the city of Omsk are “looped”, but the configuration of the networks does not allow solving problems that are of fundamental importance for complex heat supply systems, these are the questions:

Reliability;

Reservations;

Economical;

Quality management systems (QMS);

Environmental Management Systems (EMS);

Ensuring the connection of promising heat loads of a growing city and others.

All these requirements could be solved by a comprehensive program for the development of a heat supply system with a city development perspective for 20-25 years. But there is no such program. Its implementation requires

significant time, effort and financial resources. The Omsk administration understands the need to develop comprehensive program for the city, but practical solution remains in perspective for now. Our company is developing a concept for the development of energy capacities, which sounds like “Energy survey of structural divisions, development of directions further development and possible measures to increase installed and available capacity.” But everyone understands that the solution to this problem is hampered by the imperfect configuration of heating networks. Meanwhile, today this is the most pressing problem. It is necessary to switch to a ring system of the central heating system on the basis of scientific analysis, to develop the structural formation of the central heating system configuration with multivariate calculations of heat flows from all heat sources.

One example. With intensive development of the left bank part of the city of Omsk, an acute shortage of heating capacity arose, which negatively affected the development of the development zone. Without a developed and approved comprehensive heat supply scheme, the city administration chose the construction of small gas boiler houses with a capacity of 20-40 MW. Thus, several boiler houses have been built in the residential areas of the city, the introduction of which in residential areas of the city is environmentally, economically and technically incorrect. Many articles have been written about the “boiler room” of Russia. The authors of many of them are Omsk power engineers.

The lack of a promising integrated heat supply scheme served as the basis for a compromise solution: an agreement was reached between the city administration and resource supply organizations on the distribution of heat supply zones on a promising site between the energy company and other small owners. Under this agreement, the Omsk branch of OJSC TGC-11 developed a draft investment program for the decomposition of central heating systems based on serious scientific studies, taking into account the requirements of reliability, redundancy, QMS, EMS and efficiency. The investment project includes the following sections:

1) phased construction of a new extended heating main in the area of ​​​​prospective construction of the Left Bank part of the city as it is developed;

2) meeting the requirements of reliability, redundancy during the operation of a new heating main from various heat sources, taking into account the QMS and EMS;

3) reconstruction of the heating plant of one of the thermal power plants located on the right bank, where, as a result of reducing industrial steam consumption, the possibility of realizing additional thermal power of 300 Gcal/h was identified, which allows increasing electricity production at the thermal power plant in the heating cycle and reducing the cost of production of electrical and thermal energy , increase financial profit;

4) redistribution of heat loads between heat sources of the Omsk branch within the existing configuration of heating networks based on the condition of greatest efficiency;

5) creation of a reserve of available thermal capacity to connect additional heat loads in the actively developing central part of the city, which makes it possible to eliminate the issue of shortage of thermal capacity in the next two to three years.

The implementation of this project solved the current problems within the city's central heating system only partially.

Next example. The thermal power plant, located a considerable distance from the city, has a large reserve of thermal power, but due to the lack of a transit heating main, it is not possible to use this power. The implementation of the “locked” thermal capacities of a remote thermal power plant will allow increasing the production of electrical energy in the heating cycle, which will significantly increase efficiency and improve economic performance, ensuring financial profit. "Transfer" of heat to long distance across the Irtysh River has strategic importance, as it will make it possible to postpone the construction of a new thermal power plant on the left bank by 10-12 years, transfer the left bank district boiler house to peak operating mode, and significantly improve the environmental and social situation in the city.

At our heating network enterprise, we annually identify and eliminate existing bottlenecks by solving issues of decomposition of the heating network diagram, using scientific methods of analysis and synthesis, conducting in-depth research and multivariate calculations to improve the city's central heating system.

Research and analysis of multivariate calculations have shown the possibility of eliminating one of the bottlenecks in the configuration of heating networks. From many possible options The most preferable option from the point of view of solving the entire complex of problems was identified as the option of reconstructing most of the existing heating main from the largest thermal power plant running through the city center. This required increasing the capacity of the main pipelines and reconstructing the pumping station. The total cost of this project is about 200 million rubles, with existing tariffs for thermal energy, its payback period will be about three years.

But as it turned out, even for this fragment of changing the configuration of the central heating system there were not enough funds, and we are forced to carry it out in stages. This year, only half has been mastered. More than 3 km of main heating networks were replaced, and, despite

financial constraints, reliability, quality and redundancy issues in this area were successfully resolved using new materials and technologies. But we will not be able to receive financial profit until the implementation of this project is completed in full and the reconstruction of the pumping station, which is planned only for next year.

It must be recognized that optimizing the configuration of the central heating system of a large industrial city on the basis of scientific analysis and transforming it from a predominantly radial one into a real full-scale functional ring requires enormous intellectual and capital costs. The financial benefit significantly exceeds the investment when short term payback. However, the financial crisis is holding back the pace of construction in the city and is reflected in a reduction in investment in the development of central heating systems.

CONCLUSION

Despite the crisis situation, or rather to quickly overcome it, it is necessary to constantly engage in scientific analysis and synthesis, which will allow for the structural formation of the configuration of the central heating system of a large city with a solution for all or the majority existing problems. This follows from the decisive role of the electric power industry in industry. For solutions this issue common efforts of government authorities, resource supply organizations and investors are needed. Until the solution to this issue becomes a necessity for all interested parties, the above problems will be solved locally, without high economic and social results.

BIBLIOGRAPHY

1. Reliability of heat supply systems: Handbook. Volume 4 / ed. E.V. Sennova. Novosibirsk: Nauka, 2000. 350 p.

2. Kuznik I.V. Centralized heating supply. M.: MPEI Publishing House, 2008. 155 p.

3. Nikolaev Yu.E., V dovenko I.A. Comparative analysis options for reconstruction of urban heat supply systems // Industrial Energy. 2009. No. 11. P. 6-10.

4. Bogdanov A.B. Boiler installation in Russia is a disaster on a national scale // Heat supply news. 2007. No. 4, No. 5. P. 28-33, 50-54.

5. Yakovlev B.V. Increasing the efficiency of district heating and heat supply systems // Heating News, 2008. 447 p.

6. Dmitriev V.Z. Networks catch heat // Energy saving and energy in the Omsk region. 2006. No. 2. P. 48-49.

7. Dmitriev V.Z. About heating mains in residential and public areas // Russian Heat Supply. M.: Heat supply news, 2007.

8. Lebedev V.M. A systematic approach to solving problems of energy saving as a development strategy // Energy saving and energy in the Omsk region. 2005. No. 1. P. 26-32.

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 and economic efficiency. When choosing the configuration of heating networks, you should strive for the most simple 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 by nature technological process short-term (up to 24 hours) interruptions in the steam supply are acceptable, 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.

More challenging task The choice of the scheme of water heating networks is considered, since their load is usually less concentrated. Water heating networks in modern cities serve big number consumers, often measured in thousands and even tens of thousands of attached 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 sectional valves is selected so that the time required for repairs is less than the time during which internal temperature in heated rooms with complete shutdown heating when the calculated 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. 5.1 shows the fundamental single line diagram two-pipe water heating network from electrical power 500 MW and thermal power 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. If necessary, to increase bandwidth substations are being built to block 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 to heat consumers: whether they allow an interruption 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.

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.

Schemes 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:

reliability; they must maintain the ability to continuously supply coolant to the consumer at required quantity throughout the year, with the exception of a short break for preventive maintenance in the summer;

controllability – i.e. provide the necessary operating mode, the ability collaboration sources of heat supply and mutual backup of highways.

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 return lines 50С and below;

reservation, 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 backbone networks supplied to distribution networks and through distribution networks through group heating points or local heating points to 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 marked;

after placing the GTP, possible routes of highways and jumpers between them are outlined;

plan the location of distribution networks.

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

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Purpose and classification of heating networks.

The purpose of heating networks is to connect heat sources with places of consumption. External heat networks (with centralized heat supply) are networks that connect the heat source with points that distribute heat, in contrast to heat pipes laid inside buildings and called internal heat pipes.

External heating networks are laid, as a rule, in the ground (in pass-through, semi-through and non-pass-through channels, channelless), openly (on brackets along the walls of buildings, on concrete, reinforced concrete and metal supports, on individual bridge structures when crossing railway tracks and water obstacles) and a siphon. Heating networks passing through basements or technical undergrounds, i.e. inside buildings, are also called external networks, since they connect, as mentioned above, a heat source with heating points in which elevator and heating units, heaters and other devices that distribute warm.

Heat pipes from these nodes to places of heat consumption (heating panels and radiators, air heaters, air conditioners, technological installations, etc.) belong to the heat pipes of internal wiring (central heating and hot water supply systems, wiring inside boiler houses, combined heat and power plants).

Buildings and structures are supplied with heat from local boiler houses, serving one or more usually adjacent buildings, or centrally from large (group) district or block boiler houses, serving all buildings in a district or quarter of the city, and from combined heat and power plants, which combine to produce heat and electrical energy(cogeneration). Centralized heat supply from district or quarterly boiler houses and especially from thermal power plants, compared to heat supply from local boiler houses, is the most promising, economical and is currently increasingly used.

External heating networks are divided into main ones - from the heat source to a microdistrict (quarter) or to an industrial enterprise, into distribution networks - from main heating networks to branches (inputs) to individual buildings, and into branches (inputs) - from distribution or main heating networks to nodes connections of heat consumer systems.

The transported coolant is used for heating, hot water supply and ventilation, as well as for production and technological needs. Depending on the type of coolant, networks are divided into steam and water. When the coolant is steam, condensate returns to the heat source from the places of its consumption. Networks in which a constant amount of coolant circulates (without disassembling it from consumers) are called closed; networks with direct water supply are open.

Based on the nature of consumers, heating networks are divided into industrial, utility and mixed. Currently, two-pipe and multi-pipe heat supply systems are adopted. According to the configuration, heating networks can be radial or ring. Ring networks provide better hydraulic conditions and allow individual network lines to be disconnected for repairs without interrupting the heat supply to consumers.