Features of open and closed heat supply systems. Heating systems
Topic 6 Heat supply systems
Classification of heat supply systems.
Thermal schemes heat sources.
Water systems.
Steam systems.
Air systems.
The choice of heat carrier and heat supply system.
Classification of heat supply systems (ST)
Heat supply system (ST) is a set of heat sources, devices for heat transport (heat networks) and heat consumers.
The heat supply system (ST) consists of the following functional parts:
Source of heat energy production (boiler house, CHPP);
Transporting devices of thermal energy to the premises (heat networks);
Heat-consuming devices that transmit thermal energy consumer (heating radiators, heaters).
Heat supply systems (ST) are divided into:
1. At the place of heat generation at:
centralized and decentralized.
In decentralized systems the source of heat and heat sinks of consumers are combined in one unit or are close to each other, therefore, special devices for heat transport (heating network) are not required.
In a centralized system The source and consumers of heat supply are significantly removed from each other, so heat is transferred through heating networks.
Systems decentralized heat supplies are divided into individual and local .
ATindividual systems, the heat supply of each room is provided from a separate own source (stove or apartment heating).
ATlocal systems, heating of all premises of the building is provided from a separate common source (house boiler).
centralized heat supply can be divided into:
- for group - heat supply from one source of a group of buildings;
- regional - heat supply from one source of the district of the city;
- urban - heat supply from one source to several districts of the city or even the city as a whole;
- intercity - heat supply from one source of several cities.
2. according to the type of transported coolant :
steam, water, gas, air;
3. According to the number of pipelines for transferring the coolant to:
- one-, two- and multi-pipe;
4. according to the method of connecting hot water supply systems to heating networks:
-closed(water for hot water supply is taken from the water supply and heated in the heat exchanger with network water);
- open(water for hot water supply is taken directly from the heating network).
5. by type of heat consumer for:
- communal - household and technological.
6. according to the schemes for connecting heating installations to:
-dependent(the coolant heated in the heat generator and transported through heating networks enters directly into the heat-consuming devices);
-independent(the coolant circulating through the heating networks in the heat exchanger heats the coolant circulating in the heating system.
Figure 6.1 - Schemes of heat supply systems
When choosing the type of coolant, it is necessary to take into account its sanitary and hygienic, technical, economic and operational indicators.
gasesare formed during the combustion of fuel, they have a high temperature and enthalpy, however, the transportation of gases complicates the heating system and leads to significant heat losses. From a sanitary and hygienic point of view, when using gases, it is difficult to ensure the permissible temperatures of the heating elements. However, being mixed in a certain proportion with cold air, gases in the form of a now gas-air mixture can be used in various technological installations.
Air- easily movable coolant, used in air heating systems, allows you to quite simply regulate the constant temperature in the room. However, due to the low heat capacity (about 4 times less than water), the mass of air heating the room must be significant, which leads to a significant increase in the dimensions of the channels (pipelines, ducts) for its movement, an increase in hydraulic resistance and electricity consumption for transportation. That's why air heating at industrial enterprises, it is carried out either combined with ventilation systems, or by installing special heating installations (air curtains, etc.) in workshops.
Steamduring condensation in heating devices (pipes, registers, panels, etc.) gives off a significant amount of heat due to high specific heat transformations. Therefore, the mass of steam at a given thermal load is reduced compared to other coolants. However, when steam is used, the temperature of the outer surface of the heating devices will be higher than 100 ° C, which leads to the sublimation of the dust that has settled on these surfaces, to the release of harmful substances in the premises and the appearance of unpleasant odors. In addition, steam systems are sources of noise; the diameters of the steam pipelines are quite significant due to the large specific volume of steam.
WaterIt has a high heat capacity and density, which makes it possible to transfer large amounts of heat over long distances with low heat losses and small pipeline diameters. The surface temperature of water heating devices meets sanitary and hygienic requirements. However, the movement of water is associated with high energy costs.
Open and closed heating systems.
Descriptions of open and closed heat supply systems, their fundamental differences on the Internet can be found a huge amount, therefore detailed description we will not give. Let us dwell only on their fundamental differences, without understanding which it will be difficult to understand examples from practice in the future. As a basis, we take what the reader is not yet in the subject. For specialists in housing and communal services, this section can be skipped, rightly believing that this information is not of particular value to him, he already knows everything and understands everything.
So let's start with the main differences. Heat supply systems are fundamentally divided into two main groups. These are open systems and closed systems. The fundamental and main difference is that in open heat supply systems, hot water supply is taken directly from the heat supply system of a residential building (heating system), which creates problems with the quality of hot water supply. The presence of various suspensions, rust and other substances is possible in water. Represents a particular complexity and the possibility of flushing, maintenance of this system. Despite the negative attitude towards the open heating system at the present time, the system became widespread during the construction boom in the second half of the twentieth century due to its simplicity of design and installation in the construction of new houses, relatively low cost. In those years, energy conservation issues were in last place, we somehow did not consider resources, assuming that they were eternal. And the issue of further operation of these systems was not taken into account at all.
In turn, open heat supply systems are divided into dependent and independent. The simplest is an open, dependent heat supply system. The diagram below shows that the coolant goes to the consumer directly from the boiler room and the selection of hot water in a residential building (not shown in the diagram) is taken into DHW system directly from the heating system of a residential building. The simplest and at the same time inefficient heating system.
An open heat supply system (independent) is already a new stage in the development of heat supply systems. The system, due to the use of a heat exchanger in the system, has a separate circuit. That is, boiler water circulates in its own circuit, the consumer's heating system in its own way. When using this system, the organization dealing with the operation of the heating network got the opportunity to chemically treat network water, which undoubtedly affected the durability of the systems and boiler plants. Currently, a mass transfer of systems from a dependent scheme to an independent one is being carried out. However, an independent system did not solve the problem of the quality of hot water supply. DHW remained the most vulnerable system due to the intake of hot water from the heating system.
The final stage in the development of heat supply systems at the present time has rightfully become a closed heat supply system, which solved the problem of providing residents with high-quality hot water supply. There are many schemes for the execution of closed heat supply systems, but the main principle for it is the same. This is the presence of separated circuits, both heating systems and hot water systems. This is clearly seen in the diagram below (to unload the circuit, we did not show the piping of the central heating equipment and the circulation pumps that are present in this diagram).
There are two types of heating- centralized and decentralized. With decentralized heat supply, the source and consumer of heat are close to each other. There is no heating network. Decentralized heat supply is divided into local (heat supply from a local boiler house) and individual (stove, heat supply from boilers in apartments).
Depending on the degree of centralization, district heating systems (DH) can be divided into four groups:
1. group heat supply (TS) of a group of buildings;
2. district - TS of the urban area;
3. city - TS of the city;
4. intercity - vehicles of several cities.
The DH process consists of three operations - heat carrier (HP) preparation, HP transport and HP use.
Preparation of HP is carried out at heat-preparation plants of CHP and boiler houses. HP transport is carried out through heating networks. The use of HP is carried out at heat-using installations of consumers.
The complex of installations designed for the preparation, transport and use of the coolant is called the district heating system.
There are two main categories of heat consumption:
To create comfortable working and living conditions (household load). This includes water consumption for heating, ventilation, hot water supply (DHW), air conditioning;
For the production of products of a given quality (technological load).
According to the temperature level, heat is divided into:
Low potential, with temperature up to 150 0 С;
Medium potential, with temperature from 150 0 С to 400 0 С;
High-potential, with a temperature above 400 0 С.
refers to low-potential processes. The maximum temperature in heat networks does not exceed 150 0 С (in the direct pipeline), the minimum temperature is 70 0 С (in the return pipeline). To cover the technological load, as a rule, water vapor with a pressure of up to 1.4 MPa is used.As heat sources, heat treatment plants of thermal power plants and boiler houses are used. The combined heat and power generation is carried out at the CHPP based on the heating cycle. Separate generation of heat and electricity is carried out in boiler houses and condensing power plants. With combined generation, the total fuel consumption is lower than with separate generation.
The whole complex of equipment for a heat supply source, heating networks and subscriber installations is called a district heating system.
Heat supply systems are classified according to the type of heat source (or method of preparing heat), the type of heat carrier, the method of supplying water to hot water supply, the number of pipelines of the heating network, the method of supplying consumers, the degree of centralization.
By type of heat source There are three types of heat supply:
District heating from CHP, called heating;
Centralized heat supply from district or industrial boiler houses;
Decentralized heat supply from local boiler houses or individual heating units.
Compared with centralized heat supply from boiler houses district heating has a number of advantages, which are expressed in fuel savings due to the combined generation of heat and electricity at CHPPs; in the possibility of widespread use of local low-grade fuel, the combustion of which in boiler houses is difficult; in improving sanitary conditions and cleanliness of the air basin of cities and industrial areas due to the concentration of fuel combustion in a small number of points located, as a rule, at a considerable distance from residential areas, and more rational use nyu modern methods purification of flue gases from harmful impurities.
By type of coolant heating systems are divided into water and steam. Steam systems distributed mainly in industrial enterprises, and water systems are used for heat supply of housing and communal services and some industrial consumers. This is explained by a number of advantages of water as a heat carrier in comparison with steam: the possibility of central high-quality regulation of the heat load, lower energy losses during transportation and a greater range of heat supply, the absence of losses of heating steam condensate, greater combined energy production at CHP, increased storage capacity.
According to the method of supplying water to hot water supply water systems are divided into closed and open.
AT closed systems network water is used only as a heat carrier and is not taken from the system. The local hot water supply installations receive water from the drinking water supply, heated in special hot water heaters due to the heat of the network water.
In open systems network water directly enters the local hot water supply installations. At the same time, additional heat exchangers are not required, which greatly simplifies and reduces the cost of the subscriber input device. However, water losses in an open system increase sharply (from 0.5–1% to 20–40% of the total water consumption in the system) and the composition of water supplied to consumers deteriorates due to the presence of corrosion products and lack of biological treatment.
The advantages of closed heat supply systems are that their use ensures a stable quality of hot water supplied to hot water supply installations, the same as the quality of tap water; hydraulic isolation of water supplied to hot water supply installations from water circulating in the heating network; ease of monitoring the tightness of the system by the amount of make-up.
The main disadvantages of closed systems are the complexity and cost of equipment and operation of subscriber inputs due to the installation of hot water heaters and corrosion of local hot water installations due to the use of non-deaerated water.
The main advantages of open systems heat supply lies in the possibility of maximizing the use of low-grade heat sources for heating a large amount of make-up water. Since in closed systems the make-up does not exceed 1% of the flow of network water, the possibility of utilizing the heat of waste and blowdown water at CHPPs with a closed system is much lower than in open systems. In addition, deaerated water enters local hot water installations in open systems, so they are less susceptible to corrosion and more durable.
The disadvantages of open systems are: the need for a powerful water treatment device at the CHPP to feed the heating network, which increases the cost of station water treatment, especially with increased hardness of the initial raw water; complication and increase in the volume of sanitary control over the system; complication of system tightness control (because the amount of feed does not characterize the density of the system); instability of the hydraulic regime of the network.
By number of pipelines distinguish one-, two- and multi-pipe systems. Moreover, for an open system, the minimum number of pipelines is one, and for a closed system, two. The simplest and most promising for transporting heat over long distances is a single-pipe open heat supply system. However, the scope of such systems is limited due to the fact that its implementation is possible only if the water flow rate necessary to satisfy the heating and ventilation load is equal to the water flow rate for hot water supply to consumers of this district. For most regions of our country, the consumption of water for hot water supply is significantly less (3-4 times) than the consumption of network water for heating and ventilation, therefore, in the heat supply of cities, two-pipe systems are predominantly used. In a two-pipe system heating network consists of two lines: supply and return.
By way of providing heat consumers are distinguished one-
step and multi-stage heat supply systems. In one-
In stepped systems, heat consumers are directly connected to heating networks. Nodes for connecting consumers to the network
are called subscriber inputs or local heating points (MTP). At the subscriber input of each building, hot water heaters, elevators, pumps, instrumentation and control valves are installed to change the parameters of the coolant in local consumer systems.
In multistage systems between the source of heat and consumers are located central heating points or sub-stations (CHP), in which the parameters of the coolant change depending on the consumption of heat by local consumers. The central heating station houses a central heating unit for hot water supply, a central mixing plant for network water, booster pumps for cold tap water, automatic control and instrumentation. The use of multi-stage systems with a central heating substation makes it possible to reduce the initial costs for the construction of a hot water heating plant, pumping units and automatic control devices due to an increase in their unit capacity and a reduction in the number of equipment elements.
The optimal design capacity of the CHP depends on the layout of the area, the mode of operation of consumers and is determined on the basis of technical and economic calculations.
According to the degree of centralization heat supply can be divided into group - heat supply of a group of buildings, district - heat supply of several groups of buildings, urban - heat supply of several districts, intercity - heat supply of several cities.
The device and design of thermal networks.
The main elements of heat networks are a pipeline consisting of steel pipes interconnected by welding; an insulating structure that perceives the weight of the pipeline and the forces that arise during its operation.
Pipes are critical elements of pipelines and must meet the following requirements:
Sufficient strength and tightness at maximum values of pressure and temperature of the coolant,
Low coefficient of thermal deformation,
Providing small thermal stress with alternating thermal mode heating network,
Small roughness of the inner surface,
anti-corrosion resistance,
High thermal resistance of the pipe walls,
Contributing to the preservation of heat and temperature of the coolant,
Invariability of material properties under prolonged exposure to high temperatures and pressures, ease of installation,
Reliability of pipe connections, etc.
Available steel pipes do not fully satisfy all the requirements, however, their mechanical properties, simplicity, reliability and tightness of joints (by welding) ensured their predominant use in heating networks.
Pipes for heating networks are made mainly of steel grades St2sp, St3sp, 10, 20, 10G2S1, 15GS, 16GS.
In thermal networks, seamless hot-rolled and electric-welded ones are used. Seamless hot-rolled pipes are produced with outer diameters of 32 - 426mm. Seamless hot-rolled electric-welded pipes are used in all ways of laying networks. Electrowelded pipes are used in all ways of laying networks. Electrowelded with a spiral seam are recommended for use in channel and overhead network laying.
supports. When constructing heating networks, two types of supports are used: free and fixed. Free supports perceive the weight of the heat pipe and ensure its free movement during temperature deformations. Fixed supports are designed to fix the pipeline at the characteristic points of the network and perceive the forces that arise at the fixation point both in the radial and axial directions under the action of weight, temperature deformations and internal pressure.
Compensators . Compensation for temperature deformations in pipelines is carried out by special devices called compensators. According to the principle of action, they are divided into two groups:
Compensators are radial or flexible, perceiving the elongation of the heat pipe by bending or twisting the curved sections of pipes or by bending special elastic inserts of various shapes;
Axial expansion joints, in which elongation is taken up by telescopic movement of pipes or compression of spring inserts.
The most widely used in practice are flexible expansion joints of various configurations made from the pipeline itself (P - and -S-shaped, lyre-shaped with and without folds, etc.). The simplicity of the device, reliability, no need for maintenance, unloaded fixed supports - the advantage of these compensators.
To disadvantages flexible expansion joints include: increased hydraulic resistance, increased consumption of pipes, transverse movement of deformable sections, which requires an increase in the width of impassable channels and makes it difficult to use backfill insulation, channelless pipelines, as well as large dimensions that make it difficult to use them in cities when the route is saturated with urban underground utilities.
Axial compensators are made of sliding type (omental) and elastic (lens compensators).
Gland compensator It is made from standard pipes and consists of a body, a glass and a seal. When the pipeline is extended, the glass is pushed into the body cavity. The tightness of the sliding connection of the body and the glass is created by stuffing box packing, which is made of a graphite asbestos cord impregnated with oil. Over time, the packing wears out and loses elasticity, so periodic tightening of the stuffing box and replacement of the packing is required. Lens compensators made of sheet steel are free from this disadvantage. Welded type lens compensators are mainly used in low pressure pipelines (up to 0.4-0.5 MPa).
The design of the pipeline elements also depends on the method of its laying, which is selected on the basis of a technical and economic comparison of possible options.
SOURCES OF HEAT
§ 1.1. Classification of heat supply systems
Depending on the location of the heat source in relation to consumers, heat supply systems are divided into two types:
1) centralized;
2) decentralized.
1) The process of district heating consists of three operations: preparation, transport and use of the heat carrier.
The heat carrier is prepared in special heat treatment plants at CHPPs, as well as in city, district, group (quarterly) or industrial boiler houses. The coolant is transported through heating networks, and is used in consumer heat sinks.
In district heating systems, the heat source and heat sinks of consumers are located separately, often at a considerable distance, so heat is transferred from the source to consumers through heating networks.
Depending on the degree of centralization, district heating systems can be divided into the following four groups:
- group - heat supply of a group of buildings;
- district - heat supply of several groups of buildings (district);
- urban - heat supply of several districts;
- intercity - heat supply of several cities.
According to the type of heat carrier, district heating systems are divided into water and steam. Water is used to satisfy the seasonal load and the load of hot water supply (DHW); steam - for industrial process load.
2) In decentralized heat supply systems, the heat source and heat sinks of consumers are combined in one unit or placed so close that heat can be transferred from the source to heat sinks without an intermediate link - a heat network.
Decentralized heat supply systems are divided into individual and local. In individual systems, the heat supply of each room (section of the workshop, room, apartment) is provided from a separate source. These systems include stove and apartment heating. In local systems, heat is supplied to each building from a separate heat source, usually from a local boiler house.
2. Non-traditional and renewable energy sources. Characteristic.
Chapter 1. Characteristics of renewable energy sources and the main aspects of their use in Russia1.1 Renewable energy sources
These are types of energy that are continuously renewable in the Earth's biosphere. These include the energy of the sun, wind, water (including Wastewater), excluding the use of this energy in pumped storage power plants. The energy of tides, waves of water bodies, including reservoirs, rivers, seas, oceans. Geothermal energy using natural underground heat carriers. Low-potential thermal energy of the earth, air, water using special heat carriers. Biomass includes plants specially grown for energy production, including trees, as well as production and consumption wastes, with the exception of wastes obtained in the process of using hydrocarbon raw materials and fuels. As well as biogas; gas emitted by production and consumption wastes in landfills of such wastes; gas from coal mines.
Theoretically, energy is also possible, based on the use of the energy of waves, sea currents, and the thermal gradient of the oceans (HPPs with an installed capacity of more than 25 MW). But so far it hasn't caught on.
The ability of energy sources to be renewed does not mean that a perpetual motion machine has been invented. Renewable energy sources (RES) use the energy of the sun, heat, the earth's interior, and the rotation of the Earth. If the sun goes out, the Earth will cool down, and RES will not function.
1.2 Advantages of renewable energy sources in comparison with traditional ones
Traditional energy is based on the use of fossil fuels, the reserves of which are limited. It depends on the amount of deliveries and the level of prices for it, market conditions.
Renewable energy is based on a variety of natural resources, which makes it possible to conserve non-renewable sources and use them in other sectors of the economy, as well as to preserve environmentally friendly energy for future generations.
Independence of RES from fuel ensures the energy security of the country and the stability of electricity prices
RES are environmentally friendly: there are practically no wastes, emissions of pollutants into the atmosphere or water bodies during their operation. There are no environmental costs associated with the extraction, processing and transportation of fossil fuels.
In most cases, RES power plants are easily automated and can operate without direct human intervention.
Renewable energy technologies implement the latest achievements of many scientific areas and industries: meteorology, aerodynamics, electric power industry, thermal power engineering, generator and turbine construction, microelectronics, power electronics, nanotechnology, materials science, etc. The development of science-intensive technologies allows creating additional jobs by saving and expansion of the scientific, industrial and operational infrastructure of the power industry, as well as the export of science-intensive equipment.
1.3 Most common renewable energy sources
Both in Russia and in the world, this is hydropower. About 20% of the world's electricity generation comes from hydroelectric power plants.
The global wind energy industry is actively developing: the total capacity of wind turbines doubles every four years, amounting to more than 150,000 MW. In many countries, wind energy has a strong position. For example, in Denmark, more than 20% of electricity is generated by wind energy.
The share of solar energy is relatively small (about 0.1% of global electricity production), but has a positive growth trend.
Geothermal energy is of great local importance. In particular, in Iceland, such power plants generate about 25% of electricity.
Tidal energy has not yet received significant development and is represented by several pilot projects.
1.4 The state of renewable energy in Russia
This type of energy is represented in Russia mainly by large hydroelectric power plants, which provide about 19% of the country's electricity production. Other types of RES in Russia are still poorly visible, although in some regions, for example, in Kamchatka and Kuril Islands, they are essential in local power systems. The total capacity of small hydroelectric power plants is about 250 MW, geothermal power plants - about 80 MW. Wind power is positioned by several pilot projects with a total capacity of less than 13 MW.
Ticket number 5
1. Characteristics of steam systems. Advantages and disadvantages.
steam system- a system with steam heating of buildings, where water vapor is used as a heat carrier. A special feature is the combined heat transfer of the working fluid (steam), which not only reduces its temperature, but also condenses on the inner walls heating appliances.
Heat source in the steam heating system can serve as a heating steam boiler. Heating appliances are heating radiators, convectors, finned or smooth pipes. The condensate formed in the heaters returns to the heat source by gravity (in closed systems) or is pumped (in open systems). The vapor pressure in the system can be below atmospheric (vacuum steam systems) or above atmospheric (up to 6 atm.). The steam temperature should not exceed 130 °C. Changing the temperature in the premises is carried out by regulating the flow of steam, and if this is not possible, by periodically stopping the supply of steam. Currently, steam heating can be used both with centralized and autonomous heat supply in industrial premises, in stairwells and lobbies, in heating points and pedestrian crossings. It is advisable to use such systems in enterprises where steam is used in one way or another for production needs.
Steam systems are divided into:
Vacuum-steam (absolute pressure<0,1МПа (менее 1 кгс/см²));
Low pressure (overpressure> 0.07 MPa (more than 0.7 kgf / cm²)):
Open (communicating with the atmosphere);
Closed (not communicating with the atmosphere);
By the method of returning condensate to the system boiler:
Closed (with direct return of condensate to the boiler);
Open circuit (with condensate return to the condenser tank and its subsequent pumping from the tank to the boiler);
According to the scheme of connecting pipes with system devices:
Single-pipe;
Single-pipe.
Advantages:
· small size and lower cost of heating devices;
· Low inertia and fast heating of the system;
· No heat loss in heat exchangers.
Flaws:
High temperature on the surface of heating devices;
Impossibility of smooth regulation of room temperature;
Noise when filling the system with steam;
· Difficulties in installing taps in a running system.
2. Fittings of thermal networks. Classification. Features of use.
According to their functional purpose, valves are divided into shut-off, control, safety, throttling and instrumentation.
Pipe fittings installed on pipelines of ITP, central heating substation, main pipelines, risers and connections to heating devices, piping centrifugal pumps and heaters
The fittings are characterized by three main parameters: nominal diameter Dy, working pressure and temperature of the transported medium.
Shut-off valves are designed to shut off the coolant flow. It includes gate valves, taps, gates, valves, rotary, gates.
Shut-off valves in heating networks are installed:
At all pipeline outlets of heating networks from heat sources;
For sectioning highways;
On branch pipelines;
For draining water and venting air, etc.
In housing and communal services, cast-iron gate valves of the 30ch6bk type for pressure Py = 1 MPa (10 kgf / cm²) and ambient temperatures up to 90 ° C, as well as gate valves of the 30ch6bk type for pressure Py = 1 MPa and ambient temperatures up to 225 ° C . These valves are available in diameters: 50, 80, 100, 125, 200, 250, 300, 350 and 400 mm.
Control valves are used to control the parameters of the coolant: flow, pressure, temperature. Control valves include control valves, pressure regulators, temperature regulators, control valves.
Safety fittings designed to protect heat pipelines and equipment from unacceptable pressure increase by automatically releasing excess heat carrier.
Ticket 6
1. Water heating systems. Advantages and disadvantages of heating systems.
Water heating systems are classified according to various criteria.
According to the location of the basic elements of the system, they are divided into central and local. Local are based on the work of autonomous boiler houses. The central ones use a single thermal center (CHP, boiler house) for heating many buildings.
As a coolant in water systems, not only water can be used, but also antifreeze liquids (antifreezes - mixtures of propylene glycol, ethylene glycol or glycerin with water). According to the temperature of the coolant, all systems can be divided into low-temperature (water is heated up to 70°C, no more), medium-temperature (70-100°C) and high-temperature (more than 100°C). The maximum media temperature is 150°C.
According to the nature of the movement of the coolant, heating systems are divided into gravitational and pumping. Natural (or gravitational) circulation is used quite rarely - primarily in buildings where noise and vibration are unacceptable. Installation of such a system involves the mandatory installation of an expansion tank, which is located in the upper part of the building. Using structures with natural circulation greatly limits the planning possibilities.
Centralized pumping (forced regulation) systems are by far the most popular form of hot water heating. The coolant moves not due to the circulation pressure, but due to the movement created by the pumps. In this case, the pump is not necessarily located in the building itself, it can be located in the district heating point.
According to the method of connection to external networks, the systems are divided into three types:
Independent (closed). The boilers have been replaced with water heat exchangers, the systems use high pressure or a special circulation pump. Such systems allow for some time to maintain circulation in the event of external accidents.
Dependent (open). They use mixing water from the supply and discharge lines. For this, a pump or water jet elevator is used. In the first case, it is also possible to maintain the circulation of the coolant during accidents.
Direct-flow - the simplest systems used for heating several neighboring buildings of one small boiler room. The disadvantage of such solutions is the impossibility of high-quality local control and the direct dependence of the heating mode on the carrier temperature in the supply channel.
According to the method of delivery of the coolant to the heating radiators, the systems are divided into one- and two-pipe systems. A single-pipe scheme is a sequential passage of water throughout the network. The consequence is the loss of heat as you move away from the source and the impossibility of creating a uniform temperature in all rooms and apartments.
Single pipe systems heating is cheaper and more stable hydraulically (at low temperatures). Their disadvantage is the impossibility of individual control of heat transfer. Single-pipe systems have been used in construction since the 1940s, for this reason most buildings in our country are equipped with them. Even today, such systems can be used in those public buildings where separate accounting and regulation of heat supply is not required.
A two-pipe system involves the creation of a single line that supplies heat to each individual room. As a rule, the supply and return risers are installed in the stairwells of houses. To account for heat supply, either apartment meters or an apartment-house system (a common meter for the house and local hot water meters) can be used. AT high-rise buildings with a two-pipe apartment heating scheme, it is possible to regulate the thermal regime in each apartment without causing “damage” to neighbors. It should be noted that due to the fact that low operating pressures are used in two-pipe systems, inexpensive thin-walled radiators can be used for heating.
The choice of the way in which the heat supply of buildings will be carried out depends on the technical characteristics (the ability to connect to a centralized heating system) and on the personal preference of the owner. Each system has its own advantages and disadvantages.
For example, district heating systems are widespread, and due to their wide application, the installation and laying of pipelines are well developed. It is also worth noting the competitiveness of such networks due to the low cost of thermal energy.
But centralized heating networks also have such disadvantages as a high probability of malfunctions and accidents in the system, as well as a rather significant time that it takes to eliminate them. To this we can add the cooling of the coolant, which is delivered to remote consumers.
Autonomous heating networks can operate from various power sources. Therefore, when one of them is turned off, the quality of heat supply remains at the same level. Such systems ensure the supply of heat to the building even in emergency circumstances, when the premises are disconnected from the power grid and the water supply stops. The disadvantage of an autonomous heating network can be considered the need to store fuel reserves, which is not always convenient, especially in the city, as well as dependence on energy sources.
In addition to providing heat to a building, cooling also plays an important role in the functioning of buildings. In commercial premises (warehouses, shops, etc.), refrigeration is a prerequisite for normal operation. In private buildings, air conditioning and refrigeration is relevant in the summer. Therefore, when drawing up design documentation for construction, the design of heat supply and cooling systems must be approached with due attention and professionalism.
2. Protection of hot water systems from corrosion
Water supplied to hot water supply must meet the requirements of GOST. Water should be colorless, odorless and tasteless. Corrosion protection on subscriber inputs is used only for hot water installations. In open heat supply systems for hot water supply, network water that has undergone deaeration and chemical water treatment is used. This water does not need additional treatment at thermal points. In closed heating systems, hot water installations are filled with tap water. The use of this water without degassing and softening is unacceptable, since when heated to 60 ° C, electrochemical corrosion processes are activated, and at the temperature of hot water, the decomposition of temporary hardness salts into carbonates that precipitate and into free carbon dioxide begins. The accumulation of sludge in stagnant sections of pipelines causes pitting corrosion. There are cases when pitting corrosion for 2-3 years completely disabled the hot water supply system.
The method of treatment depends on the content of dissolved oxygen and the carbonate hardness of tap water, therefore, a distinction is made between anti-corrosion and anti-scale water treatment. Soft tap water with a carbonate hardness of 2 mg-eq/l does not produce scale and sludge. When using soft water, there is no need to protect the hot water supply system from sludge. But soft waters are characterized by a high content of dissolved gases and a low concentration of hydrogen ions, so soft water is the most corrosive. Tap water of medium hardness, when heated, forms a thin layer of scale on the inner surface of the pipes, which somewhat increases the thermal resistance of the heaters, but quite satisfactorily protects the metal from corrosion. Water with increased hardness of 4-6 mg-eq/l gives a thick coating of sludge, which completely eliminates corrosion. Hot water installations supplied with such water must be protected against sludge. Water with high hardness (more than 6 mg-eq/l) is not recommended for use due to weak “saponification” according to quality standards. Thus, in closed heat supply systems, hot water installations using soft water need protection against corrosion, and with increased rigidity, from sludge. But since, with hot water supply, low heating of water does not cause decomposition of salts of constant hardness, simpler methods are applicable for its treatment than for make-up water at a thermal power plant or in boiler houses. Protection of hot water supply systems from corrosion is carried out by using anti-corrosion installations at the central heating station or by increasing the anti-corrosion resistance of hot water supply systems.
Ticket number 8
1. Purpose and general characteristics of the deaeration process
The process of removing corrosive gases dissolved in water (oxygen, free carbon dioxide, ammonia, nitrogen, etc.), which, being released in the steam generator and heating network pipelines, cause metal corrosion, which reduces the reliability of their operation. Corrosion products contribute to the violation of circulation, which leads to burnout of the pipes of the boiler unit. The rate of corrosion is proportional to the concentration of gases in water. The most common thermal deaeration of water is based on the use of Henry's law - the law of the solubility of gases in a liquid, according to which the mass amount of gas dissolved in a unit volume of water is directly proportional to the partial pressure under isothermal conditions. The solubility of gases decreases with increasing temperature and is equal to zero for any pressure at the boiling point. During thermal deaeration, the processes of release of free carbon dioxide and decomposition of sodium bicarbonate are interrelated. The process of decomposition of sodium bicarbonate is most intense with an increase in temperature, a longer stay of water in the deaerator, and the removal of free carbon dioxide from the water. For the efficiency of the process, it is necessary to ensure the continuous removal of free carbon dioxide from deaerated water to the steam space and the supply of steam free from dissolved CO2, as well as to intensify the removal of released gases, including carbon dioxide, from the deaerator. 2. Pump selection
The main parameters of the circulation pump are the head (H), measured in meters of water column, and the flow (Q), or performance, measured in m3 / h. The maximum head is the greatest hydraulic resistance of the system that the pump is able to overcome. In this case, its supply is equal to zero. The maximum flow is the largest amount of coolant that the pump can pump in 1 hour with the hydraulic resistance of the system tending to zero. The dependence of pressure on the performance of the system is called the pump characteristic. Single-speed pumps have one characteristic, two- and three-speed pumps have two and three, respectively. Variable speed pumps have many characteristics.
The selection of the pump is carried out, taking into account, first of all, the required volume of coolant, which will be pumped over the hydraulic resistance of the system. The flow rate of the coolant in the system is calculated based on the heat loss of the heating circuit and the required temperature difference between the direct and return lines. Heat losses, in turn, depend on many factors (thermal conductivity of building envelope materials, ambient temperature, orientation of the building relative to cardinal points, etc.) and are determined by calculation. Knowing the heat loss, calculate the required coolant flow rate according to the formula Q = 0.86 Pn / (tpr.t - trev.t), where Q is the coolant flow rate, m3 / h; Pn - the power of the heating circuit necessary to cover the heat losses, kW; tpr.t - temperature of the supply (direct) pipeline; tareb.t - temperature of the return pipeline. For heating systems, the temperature difference (tpr.t - torr.t) is usually 15-20°C, for a floor heating system - 8-10°C.
After determining the required flow rate of the coolant, the hydraulic resistance of the heating circuit is determined. The hydraulic resistance of the elements of the system (boiler, pipelines, shut-off and thermostatic valves) is usually taken from the corresponding tables.
Having calculated the mass flow rate of the coolant and the hydraulic resistance of the system, the parameters of the so-called operating point are obtained. After that, using manufacturers' catalogs, a pump is found whose operating curve lies not lower than the operating point of the system. For three-speed pumps, the selection is carried out, focusing on the second speed curve, so that there is a margin during operation. For getting maximum efficiency device, it is necessary that the operating point is in the middle part of the pump characteristic. It should be noted that in order to avoid the occurrence of hydraulic noise in pipelines, the coolant flow rate should not exceed 2 m/s. When using antifreeze, which has a lower viscosity, as a coolant, a pump is purchased with a power reserve of 20%.
Ticket number 9
1. HEAT CARRIERS AND THEIR PARAMETERS. HEAT OUTPUT CONTROL
4.1. In district heating systems for heating, ventilation and hot water supply of residential, public and industrial buildings, as a rule, water should be taken as a heat carrier. You should also check the possibility of using water as a heat carrier for technological processes.
The use of steam for enterprises as a single coolant for technological processes, heating, ventilation and hot water supply is allowed with a feasibility study.
Paragraph 4.2 shall be deleted.
4.3. The water temperature in hot water supply systems should be taken in accordance with SNiP 2.04.01-85.
Paragraph 4.4 shall be deleted.
4.5. Regulation of heat supply is provided: central - at the source of heat, group - in the control units or in the central heating point, individual in the ITP.
For water heating networks, as a rule, a qualitative regulation of heat supply according to the heating load or according to the combined heating and hot water supply load should be taken according to the schedule of water temperature changes depending on the outside air temperature.
When justified, regulation of heat supply is allowed - quantitative, as well as qualitative
quantitative.
4.6. With central quality regulation in heat supply systems with a predominant (more than 65%)
housing and communal load should be regulated by the combined load of heating and
hot water supply, and when the heat load of the housing and communal sector is less than 65% of the total
heat load and the share of the average load of hot water supply is less than 15% of design load heating - regulation according to the heating load.
In both cases, the central quality control of heat supply is limited by the lowest water temperatures in the supply pipeline, necessary to heat the water entering the hot heat supply systems of consumers:
for closed heat supply systems - not less than 70 °С;
for open heat supply systems - at least 60 °C.
Note. With central quality regulation by combined
load of heating and hot water supply break point of the temperature graph
water in the supply and return pipelines should be taken at a temperature
outside air, corresponding to the break point of the control curve according to
heating load.
4.7. For separate water heating networks from one heat source to enterprises and residential areas
it is allowed to provide different schedules of water temperatures:
for enterprises - by heating load;
for residential areas - according to the combined load of heating and hot water supply.
4.8. When calculating temperature graphs, the following are accepted: the beginning and end of the heating period at a temperature
outside air 8 °C; the average design temperature of the internal air of heated buildings for residential areas is 18 °С, for buildings of enterprises - 16 °С.
4.9. In buildings for public and industrial purposes, for which a reduction is provided
air temperature at night and non-working hours, control of the temperature or flow rate of the heat carrier in heating points should be ensured. 2 Purpose and design of the expansion tank
According to its physicochemical characteristics, water (coolant) is a practically incompressible liquid. It follows from this that when you try to compress water (reduce its volume), it leads to a sharp increase in pressure.
It is also known that in the required temperature range from 200 to 900C, water expands when heated. Taken together, the two properties of water described above lead to the fact that in the heating system, water must be provided with the possibility of changing (increasing) its volume.
There are two ways to ensure this possibility: use an "open" heating system with an open expansion tank at the highest point of the heating system, or use a membrane-type expansion tank in a "closed" system.
In an open heating system, the function of balancing the expansion of water when the “spring” is heated is performed by a column of water up to the expansion tank, which is installed at the top of the heating system. In the heating system closed type the role of the same "spring" in the membrane expansion tank is performed by a compressed air cylinder.
An increase in the volume of water in the system during heating leads to an influx of water from the heating system into the expansion tank and is accompanied by compression of the compressed air cylinder in the expansion tank of the membrane type and an increase in pressure in it. As a result, water has the ability to expand, as is the case with open system heating, but in one case does not come into direct contact with air.
There are a number of reasons why the use of a membrane expansion tank is preferable to an open one:
1. membrane tank can be placed in the boiler room and there is no need to install the pipe to the top point, where, moreover, there is a risk of freezing the tank in winter.
2. In a closed heating system, there is no contact between water and air, which excludes the possibility of oxygen dissolving in water (which provides the boiler and radiators in the heating system with an additional service life).
3. It is possible to provide additional (excessive) pressure even in the upper part of the heating system, as a result of which the risk of air bubbles in radiators located at high points is reduced.
4. In recent years attic space more and more popular: they are often used as living quarters and there is simply nowhere to place an open-type expansion tank.
5. This option is simply significantly cheaper when you consider materials, finishes and work.
Ticket number 11
Heat pipe designs
Rational designs of heat pipelines, firstly, should allow the construction of heat networks by industrial methods and be economical both in terms of consumption building materials, as well as the cost of funds; secondly, they must have considerable durability, ensure minimal heat losses in networks, and not require large material and labor costs for maintenance during operation.
The existing designs of heat pipelines largely meet the above requirements. However, each of these designs of heat pipelines has its own specific features that determine the scope of its application. Therefore, it is important right choice of one or another design in the design of heating networks, depending on local conditions.
The most successful designs should be considered underground laying of heat pipelines:
a) in common collectors from precast concrete blocks together with other underground networks;
b) in prefabricated reinforced concrete channels (impassable and semi-passage);
c) in reinforced concrete shells;
d) in reinforced concrete shells made of centrifuged pipes or half-cylinders with mineral wool thermal insulation;
e) in asbestos-cement shells.
These structures are used in the construction of urban heating networks and are successfully operated.
When choosing designs for laying heat pipes, it is necessary to take into account:
a) hydrogeological conditions of the route;
b) conditions for the location of the route in the urban area;
c) construction conditions;
d) operating conditions.
The hydrogeological conditions of the route are of the most significant importance for the choice of the design of heat pipelines, and therefore they must be carefully studied.
In the presence of sufficiently dense dry soils, there is an opportunity for a large selection of heat pipeline designs. In this case, the final choice depends on the location of the route in the city, as well as on the conditions of construction and operation.
Unfavorable hydrogeological conditions (the presence of a high level of groundwater, soils with weak bearing capacity, etc.) severely limit the choice of heating network designs. At high level groundwater, the most acceptable solution for the underground construction of heat pipelines is the laying of the latter in channels with associated drainage with suspended thermal insulation of pipes. The use of channels with waterproofing is effective only for channels through which the waterproofing can be done with sufficient quality.
Drainage can be additionally organized in the passage channels, which guarantees heat pipelines from flooding groundwater. When designing associated drainage, it is necessary to ensure the reliable discharge of drainage water into urban drains or water bodies.
When designing heat networks in conditions of temporary flooding by groundwater (flood waters), the type of laying heat pipes in semi-through channels without drainage and waterproofing can be adopted. In this case, measures should be taken to protect the thermal insulation and pipes from moisture: coating the pipes with borulin, installing a waterproof asbestos-cement peel over the thermal insulation, etc.
When designing a heat network in wet soils on the territory industrial enterprises the best solution is above-ground laying of heat pipes.
The location of the route in the urban area largely affects the choice of the type of heating pipelines.
When the route is located under the main city passages, the laying of heat pipelines in shells and impassable channels is unacceptable, since during the repair of the heating network it is necessary to open the road pavement over a significant length of the route. Therefore, under the main passages, heat pipelines should be laid in semi-through and through channels, allowing inspection and repair of the heating network without opening.
It is most expedient when designing heat networks to combine them with other underground utilities in a common city collector.
TYPES OF GASING PIPELINES.
Crossing of rivers, railways and highways by heat pipelines. The simplest method of crossing river barriers is to lay heat pipelines along building structure railway or road bridges. However, there are often no bridges across rivers in the area where heat pipelines are laid, and the construction of special bridges for heat pipelines with a long span is expensive. Possible options for solving this problem are the construction of overhead passages or the construction of an underwater siphon.
Heat pipelines that transfer heat energy from a heat source to consumers, IB, depending on local conditions, are laid in various ways. (There are underground and air methods of laying pipelines. In cities, underground laying is usually used. With any method of laying heat pipelines, the main task is to ensure reliable and durable operation of the structure while minimum cost materials and means.
The next type of impassable channels are gaskets, IB of which there is no air gap between the outer surface of the thermal insulation and the channel wall. Such gaskets were made of reinforced concrete half-cylinders, "forming a rigid shell, IB which was enclosed by a pipe wrapped with a layer of mineral wool. This type of heat pipe laying was used for heating networks, but due to design imperfections (iMHOroHiOBHocTb) mineral wool was moistened and the pipes, due to poor anti-corrosion protection due to external corrosion, quickly failed.
2. Characteristics of shell-and-tube heat exchangers. The principle of choice. Shell and tube heat exchangers are among the most common devices. They are used for heat transfer and thermochemical processes between various liquids, vapors and gases - both without change, and with a change in their state of aggregation.
Shell-and-tube heat exchangers appeared at the beginning of the 20th century due to the need of thermal plants for heat exchangers with a large surface, such as condensers and water heaters, operating at relatively high pressure. Shell and tube heat exchangers are used as condensers, heaters and evaporators. At present, their design, as a result of special developments, taking into account operating experience, has become much more advanced. In the same years, the widespread industrial use of shell-and-tube heat exchangers in the oil industry began. Heavy-duty operation required stock heaters and coolers, evaporators and condensers for various fractions of crude oil and associated organic liquids. Heat exchangers often had to work with contaminated liquids at high temperatures and pressures, and therefore they had to be designed so that they could be easily repaired and cleaned.
The casing (body) of a shell-and-tube heat exchanger is a pipe welded from one or more steel sheets. Shells differ mainly in the way they are connected to the tube sheet and covers. The wall thickness of the casing is determined by the pressure of the working medium and the diameter of the casing, but is assumed to be at least 4 mm. To cylindrical edges casing flanges are welded for connection with covers or bottoms. Apparatus supports are attached to the outer surface of the casing.
Ticket number 12
1.PIPELINE SUPPORTS
Pipeline supports are an integral part of pipelines for various purposes: technological pipelines of industrial enterprises, thermal power plants and nuclear power plants, oil and gas pipelines, pipelines of engineering networks of housing and communal services, for completing pipeline systems in shipbuilding. A support is a part of a pipeline intended for its installation or fastening. In addition to the installation and fastening of pipelines, supports are used to relieve various loads on the pipeline (axial, transverse, etc.). As a rule, they are installed as close as possible to the loads: shut-off valves, pipeline parts. Pipeline supports cover the entire range of diameters from 25 to 1400 depending on the diameter of the pipeline. It is also worth noting that the material of the pipeline supports must match the material of the pipe, i.e. if the pipe is from st.20, then the pipeline support must be from st.20. The main material specified in the working drawings - carbon steel - is used for the manufacture of supports used in areas with an estimated outdoor temperature of up to minus 30˚С. In the case of the use of fixed supports in areas with outdoor temperatures down to minus 40 ° C, the material used for manufacturing is low-alloy steel: 17GS-12, 17G1S-12, 14G2-12 according to GOST 19281-89, the dimensions of the supports and their parts remain unchanged . For areas with an estimated outdoor temperature of up to minus 60˚С, steel 09G2S-14 is used in accordance with GOST 19281-89. Supports for pipelines are a necessary part of the heat transfer system. It serves to distribute the load from the pipeline to the ground. Supports for pipelines are divided into:
1. Movable (sliding, roller, ball, spring, frontal guides) and fixed (welded, clamp, thrust).
The sliding (movable) support assumes the weight of the pipeline system, ensuring unhindered vibrations of the pipeline when temperature conditions change.
2. The fixed support is fixed in certain places pipeline, perceiving the loads that occur at these points when temperature conditions change.
The production of pipeline supports is now normalized and unified by machine building standards. Their use is necessary for all design, installation and construction organizations. The OSTs contain all the dimensions of the details of supports for pipelines, the permissible loads on metal supports, including from the friction force of sliding supports. Supports must withstand the loads laid down in state standards and regulatory documentation. After removing the loads from the parts, tears should not appear on them.
2. DESIGN AND OPERATING PRINCIPLE A plate heat exchanger is an apparatus, the heat exchange surface of which is formed from thin stamped plates with a corrugated surface. Working media move in slot channels between adjacent plates. Channels for heating and heated coolants alternate with each other. The corrugated surface of the plates enhances the turbulence of the flow of working media and increases the heat transfer coefficient. Each plate on the front side has a rubber contour gasket that limits the channel for the flow of the working medium and covers two corner holes through which the flow of the working medium passes into the interplate channel and exits it, and the oncoming coolant passes through the other two holes. Gaskets of a collapsible plate heat exchanger are mounted on the plate in such a way that after assembly and compression of the plates, two systems of sealed interplate channels are formed in the apparatus, isolated from each other. Both systems of interplate channels are connected to their manifolds and further to fittings for inlet and outlet of working media located on the pressure plates. The plates are assembled in a package in such a way that each subsequent plate is rotated by 180° relative to the adjacent ones, which creates a grid of intersection of the corrugation tops and supports the plates under the action of different pressures in the media. Plate heat exchangers can be single-pass and multi-pass. In multi-pass devices, two of the four fittings are located on a movable pressure plate, and in the plate package there are special rotary plates with non-punched corner holes to direct the flows along the passages. The plates are assembled in a package on a frame, which consists of two plates (fixed and movable) connected by rods. Plate material - steel 09G2S. Plate material - stainless steel 12X18H10T. Gasket material - thermal rubber of various grades (depending on the properties of the coolant and operating parameters). When choosing a plate heat exchanger at the first stage, it is necessary to correctly formulate the problem of heat transfer, which is solved using a plate heat exchanger. When choosing a heat exchanger, it is advisable to consider all possible cases of load on the heat exchanger (for example: taking into account seasonal fluctuations) and select a heat exchanger according to the most loaded modes. With a high flow rate of heat carriers, it is possible to install several plate heat exchangers in parallel, which improves maintainability thermal unit. The size of the heat exchanger, the number of plates and the layout of the plates can be selected in the following ways:
1. Fill out the questionnaire in the prescribed form and send it to the manufacturer's specialists or dealers.
2. Select a heat exchanger using simplified tables for selecting heat exchangers according to power and purpose (for heating or hot water).
3. Using a computer program for selecting heat exchangers, which can be obtained from the manufacturer's specialists or dealers.
When choosing a heat exchanger, it is necessary to foresee the possibility of increasing the capacity of the apparatus (increasing the number of plates) and inform the manufacturer about this. The pressure loss in the TPR can be either greater or less than the resistance in a shell-and-tube heat exchanger. The resistance of the TPR depends on the number of plates, on the number of strokes, on the consumption of coolants. When filling out the questionnaire, you can specify the required resistance range. The common belief that the TPR resistance is always greater than the resistance of a shell and tube heat exchanger is incorrect - it all depends on the specific conditions.
Ticket number 13
1. Thermal insulation. Classification and scope
Today in the building materials market technical thermal insulation occupies one of the key positions. Not only the level of heat loss, but also energy efficiency, sound protection, as well as the degree of waterproofing and vapor barrier of the object depend on how reliable the thermal insulation of the room will be. There are a large number of thermal insulation materials that differ from each other in purpose, structure and characteristics. In order to understand which material is optimal in a particular case, consider their classification.
Thermal insulation according to the mode of action
preventive thermal insulation - thermal insulation that reduces heat loss as a result of reduced thermal conductivity
reflective thermal insulation - thermal insulation that reduces heat loss by reducing infrared radiation
Thermal insulation according to purpose
1. Technical insulation is used to isolate utilities
"cold" application - the temperature of the medium in the system is less than the ambient air temperature
"hot" application - the temperature of the carrier in the system is higher than the ambient air temperature
2. Building thermal insulation used to insulate building envelopes.
Thermal insulation materials according to the nature of the source material
1. Organic thermal insulation materials
Thermal insulation materials of this group are obtained from materials of organic origin: peat, wood, agricultural waste, etc. Almost all organic heat-insulating materials have low moisture resistance and are prone to biological decomposition, with the exception of gas-filled plastics: foam plastic, extruded polystyrene foam, honeycomb plastic, foam plastic and others.
2. Inorganic thermal insulation materials
Heat-insulating materials of this type are made by processing melts of metallurgical slags or melts rocks. Inorganic heaters include mineral wool, foam glass, expanded perlite, cellular and lightweight concrete, fiberglass, and so on.
3. Mixed thermal insulation materials
A group of heaters based on mixtures of asbestos, asbestos, as well as mineral binders and perlite, vermiculite, intended for installation.
General classification of thermal insulation materials
Thermal insulation according to appearance and form is divided into
rolled and corded - bundles, mats, cords
piece - blocks, bricks, segments, slabs, cylinders
Loose, loose - perlite sand, cotton wool
Thermal insulation materials by type of feedstock
organic
inorganic
mixed
Thermal insulation materials according to the structure are
cellular - foam plastics, foam glass
granular - vermiculite, perlite;
Fibrous - fiberglass, mineral wool
According to their rigidity, thermal insulation materials are classified as soft, semi-rigid, rigid, increased rigidity, and solid.
According to thermal conductivity, thermal insulation materials are divided into:
class A - low thermal conductivity
class B - average thermal conductivity
class B - increased thermal conductivity
Thermal insulation is also classified according to the degree of flammability, here, in turn, the materials are divided into combustible, fireproof, flammable, slow-burning.
The main parameters of thermal insulation materials
1. Thermal conductivity of the insulation
Thermal conductivity - the ability of a material to conduct heat, is the main technical specification all types of thermal insulation. The amount of thermal conductivity of heaters is affected by the dimensions, type, overall density of the material and the location of the voids. The thermal conductivity is directly affected by the humidity and temperature of the material. The thermal resistance of enclosing structures directly depends on thermal conductivity.
2. Vapor permeability of thermal insulation material
Vapor permeability - the ability to diffuse water vapor, is one of the most significant factors that affect the resistance of the building envelope. To avoid the accumulation of excess moisture in the layers of the building envelope, it is necessary that the vapor permeability increases from a warm wall to a cold one.
3. Fire resistance
Thermal insulation materials must withstand high temperatures without breaking the structure, igniting, etc.
4. Breathability
The lower the air permeability characteristic, the higher the thermal insulation properties of the material.
5. Water absorption
Water absorption - the ability of heat-insulating materials to absorb moisture in direct contact with water and retain it in the cells.
6. Compressive strength of thermal insulation material
Compressive strength is the load value (kPa) causing a change in the thickness of the product by 10%.
7. Material density
Density - the ratio of volume to mass of dry material, which is determined at a certain load.
8. Compressibility of the material
Compressibility - change in the thickness of the product under pressure
2. Schematic diagram and principle of operation of a hot water boiler
The operation of a heating boiler room using hot water boilers is carried out as follows. Water from the return line of heating networks with a small pressure enters the suction of the network pump. Water is also supplied there from the make-up pump, which compensates for water leaks in heating networks. Hot water is also supplied to the pump suction, the heat of which is partially used in heat exchangers and for heating, respectively, chemically treated and raw water.
To ensure that the temperature of the water in front of the boiler specified from the corrosion prevention conditions, the required amount of hot water that has left the boiler is supplied to the pipeline after the network pump using a recirculation pump. The line through which hot water is supplied is called recirculation. In all modes of operation of the heating network, except for the maximum winter, part of the water from the return line after the network pump, bypassing the boiler, is fed through the bypass line to the supply line, where it, mixed with hot water from the boiler, provides the specified design temperature in the supply line of heating networks. Water intended for replenishing leaks in heating networks is preliminarily supplied by a raw water pump to the raw water heater, where it is heated to a temperature of 18–20 ºC and then sent to chemical water treatment. Chemically purified water is heated in heat exchangers and deaerated in a deaerator. Water for feeding heating networks from the deaerated water tank is taken by the make-up pump and supplied to the return line. AT boiler houses that use hot water boilers, vacuum deaerators are often installed. But they require careful supervision during operation, so they prefer to install atmospheric deaerators.
Ticket number 14
1. Purpose and general characteristics of calibration and hydraulic calculations of heat networks.
1. Calibration hydraulic calculation of heat networks for non-heating
period is made in order to determine the pressure loss in pipelines from
source of heat supply to each of the consumers of thermal energy at
coolant flow rate in the non-heating period of operation, reduced
compared with the flow rate of the coolant in the heating period. According to the results
verification hydraulic calculation is developed optimal
operational mode of operation of heating networks and is produced
selection of equipment installed at the source of heat supply, for
operation during the non-heating period.
2. The following data are used as initial information for the verification hydraulic calculation of the heat network for the non-heating period:
Calculated values of the coolant flow for each of the systems
heat consumption (hot water supply) connected to the heating network;
Calculation scheme of the heat network with indication of hydraulic characteristics
pipelines (lengths of calculated sections, diameter of pipelines on each
settlement area, characteristics of local resistances).
4.3. The design scheme of the heat network, as a rule, is drawn up for
heating period and containing all the calculated characteristics
pipelines, must be adjusted when used for
verification hydraulic calculation for the non-heating period in part of the list
buildings with hot water supply.
2. The principle of operation of a steam boiler with a description of the scheme.
On fig. 1.1 shows a diagram of a boiler plant with steam boilers. The installation consists of a steam boiler 4, which has two drums - upper and lower. The drums are interconnected by three bundles of pipes forming the heating surface of the boiler. When the boiler is operating, the lower drum is filled with water, the upper drum is filled with water in the lower part, and saturated steam in the upper part. In the lower part of the boiler there is a furnace 2 with a mechanical grate for burning solid fuel. When burning liquid or gaseous fuels, nozzles or burners are installed instead of a grate, through which fuel, together with air, is supplied to the furnace. The boiler is limited by brick walls - brickwork.
Rice. 1.1. Scheme of a steam boiler plant
The working process in the boiler room proceeds as follows. Fuel from the fuel storage is fed by a conveyor to the bunker, from where it enters the grate of the furnace, where it burns. As a result of fuel combustion, flue gases are formed - hot products of combustion. Flue gases from the furnace enter the boiler gas ducts, formed by lining and special partitions installed in pipe bundles. When moving, the gases wash the bundles of pipes of the boiler and superheater 3, pass through the economizer 5 and the air heater 6, where they are also cooled due to the transfer of heat to the water entering the boiler and the air supplied to the furnace. Then, the significantly cooled flue gases are removed by means of a smoke exhauster 5 through the chimney 7 into the atmosphere. Flue gases from the boiler can also be discharged without a smoke exhauster under the action of natural draft created by the chimney. Water from the source of water supply through the supply pipeline is supplied by pump 1 to the water economizer, from where, after heating, it enters the upper drum of the boiler. The filling of the boiler drum with water is controlled by the water-indicating glass installed on the drum. From the upper drum of the boiler, water descends through pipes into the lower drum, from where it rises again through the left bundle of pipes into the upper drum. In this case, the water evaporates, and the resulting steam is collected in the upper part of the upper drum. Then the steam enters the superheater 3, where it is completely dried due to the heat of the flue gases, and its temperature rises. From the superheater, steam enters the main steam pipeline and from there to the consumer, and on after use, it condenses and returns as hot water (condensate) back to the boiler room. Losses of condensate at the consumer are replenished with water from the water supply system or from other sources of water supply. Before entering the boiler, water is subjected to appropriate treatment. The air necessary for fuel combustion is taken, as a rule, from the top of the boiler room and is supplied by fan 9 to the air heater, where it is heated and then sent to the furnace. In boiler rooms of low power, air heaters are usually absent, and cold air is supplied to the furnace either by a fan or due to rarefaction in the furnace created by a chimney. Boiler plants are equipped with water treatment devices (not shown in the diagram), instrumentation and appropriate automation equipment, which ensures their uninterrupted and reliable operation.
In our latitudes, it is impossible to do without heating. Too cool autumn and spring, long winters leave no choice - all rooms have to be heated to create comfortable living conditions. At the same time, along with heat, hot water is also supplied to apartments, organizations and enterprises.
In order to provide heat supply services, in accordance with the law, an appropriate agreement must be concluded between the supplier and the consumer.
Space heating systems are divided into open or closed.
At the same time, heating also happens:
- centralized (when heating is provided by one boiler house for the whole microdistrict);
- local (installed in a separate building or serving a small complex of buildings).
The difference between closed systems and open systems is quite significant. The latter involves the supply of heated water to consumer homes, while taking it directly from the heating network.
Open heating system
In this format, boiling water is sent to the water supply directly from the heating pipes, which allows you to completely avoid full consumption even if its entire volume is taken. In Soviet times, the work of about half of all heating networks was based on this principle. Such popularity was due to the fact that the scheme helped to use energy resources more economically and significantly reduce the cost of heating in the winter and hot water supply.
However, this method, to supply heat and boiling water residential buildings, has many drawbacks. The thing is that very often heated water, due to its dual purpose, does not meet sanitary and hygienic standards. The heat carrier can circulate through metal pipes for quite a long time before it enters the taps. As a result, it often changes its color and acquires bad smell. In addition, employees of the sanitary and epidemiological services have repeatedly identified dangerous microorganisms in it.
The need to filter such water before supplying it to the hot water supply system greatly reduces efficiency and increases the cost of heating. At the same time, until now, there is no real effective way purification of such water. The significant length of the pipelines actually makes this procedure useless.
The circulation of water in such a system occurs due to the consideration of thermodynamic processes in the design. The heated liquid rises and leaves the heater due to the increase in pressure. At the same time, cool water creates a slightly lower pressure at the boiler inlet. This is what allows the coolant to move independently through communications.
Water, like any other liquid, increases in volume when heated. Therefore, in order to prevent excessive load on the heating networks, their design necessarily includes a special open expansion tank located above the level of the boiler and pipes. Excess coolant is squeezed out there. This gives grounds to call such a system open.
Heating in this case occurs up to 65 degrees Celsius, and then water flows directly through the taps to the consumers' houses. This system allows the installation of inexpensive simple mixers.
Due to the fact that it is impossible to predict how much hot water will be used, it is always supplied taking into account the highest demand.
Closed circuit heating systems - what is it
The difference between this scheme of centralized heating of houses and the previous one is that hot water is used exclusively for heating. Hot water supply is provided by a separate circuit or individual heating devices.
The circulation of the coolant occurs in a vicious circle; minor losses that occur are made up for by automatic pumping in case of pressure loss.
