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Gas supply to the microdistrict

  • Added: 09.08.2014
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Description

contains note as well as all necessary drawings, NNGASU DWG Format, CDW

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Additional information

Contents

1. Distribution networks of the city district

1.1. Natural Gas Characteristics

1.2. Annual gas consumption

1.3. Gas consumption mode

1.4. Selection of gas supply system

1.5. Hydraulic calculation of gas pipelines

1.6. Low Pressure Network Gas Control Station Equipment

2. Gas supply of residential building

2.1. Construction of internal house gas pipelines

2.2. Gas-using equipment of residential buildings

2.3. Placement of counters

2.4. Exhaust of combustion products

Literature

1 distribution networks of the city area

Modern city distribution systems are a complex complex of structures consisting of the following main elements: low, medium and high pressure gas networks, gas distribution stations (GRS), control and regulatory points, gas control points and installations (GRP and GRU).

The gas supply system shall provide reliable, uninterrupted gas supply to consumers, be safe in operation, simple and convenient to maintain, shall provide for the possibility of disconnecting its individual elements or sections of gas pipelines for repair or emergency work.

The main element of urban gas supply systems is gas networks, which originate from the GRS and serve to supply gas to domestic, municipal and industrial consumers.

Gas pipelines in cities and settlements are classified by pressure, purpose and method of laying, and the gas distribution system is classified by the number of differential pressure stages and the structure of their schemes.

According to safety rules in the gas industry, gas pipelines in the territory of settlements, as well as in industrial, communal and household consumers, can be low (up to 0.005 MPa), medium (up to 0.3 MPa) and high (up to 0.6 or 1.2 MPa) pressure.

By purpose, gas pipelines of settlements are conditionally divided into:

distribution (street) gas pipelines;

branches and inputs to consumers through which gas from gas distribution pipelines is supplied to one or a group of consumers;

intra-facility gas pipelines (courtyard or inter-farm);

internal gas pipelines (internal or internal).

According to the number of pressure stages, gas supply systems are divided into:

1. single-stage;

2. two-stage, consisting of low and medium or low and high pressure networks;

3. three-stage (multi-stage), including low, medium and high pressure gas pipelines.

The choice of the gas supply system is influenced by a number of factors, the main of which are: 1) the nature of the gas source, the properties of the gas, the degree of its purification, the presence of moisture in it; 2) the size of the city, the peculiarities of its layout and development, population density; 3) dimensions of loads of gas consumers; 4) the saturation of street passes with engineering communications; 5) climatic and geological conditions.

When designing a gas supply system, a number of options are being developed, the choice of the best version of the system in each particular case should be made by a technical and economic comparison according to the main indicators: reliability, technological effectiveness, economy.

1.1 Natural Gas Characteristics

Natural gases are widely used to supply gas to cities. They are a mechanical mixture of various hydrocarbons of the methane series, called limit, ballast incombustible gases and impurities (moisture, resin, dust).

The most important characteristic of the fuel is the heat of combustion. This is the amount of heat generated by the complete combustion of a unit volume of gaseous (unit mass of solid or liquid) fuel under normal physical conditions. The highest and lowest heat of fuel combustion are distinguished. If the water vapors contained in the fuel and generated by the combustion of hydrogen of the fuel are present as a liquid, the amount of released heat is characterized by the highest combustion heat Qc, kJ/m3. If water vapors are present as steam, then the heat of combustion is called the lowest Qn, kJ/m3.

Calculation of thermal balances of fuel-using plants and calculation of efficiency are carried out taking into account content of water vapour in combustion products, not water, i.e. based on lower combustion heat.

The thermal balance of the units including the contact heat exchangers under conditions where there is a change in the moisture content of the combustion products should be reduced by the highest heat of combustion of the fuel. Otherwise, the apparent efficiency calculated according to the standard procedure with respect to Qn can exceed 100%.

1.2 annual gas consumption

Annual gas consumption by the city district is the basis for the preparation of a gas supply project. The calculation of annual consumption is carried out in accordance with consumption standards and population size for certain types of loads. All urban gas consumption can be grouped as follows:

a) household consumption (consumption of gas in apartments);

b) consumption in communal and public enterprises;

c) consumption for heating, ventilation and hot water supply of buildings;

d) industrial consumption.

Calculating gas consumption for household, communal and public needs is a difficult task, since the amount of gas consumed by these consumers depends on many factors: gas equipment, improvement and population of apartments; gas equipment of institutions and enterprises; The level of service provided by these institutions; Reach consumers with centralized hot water supply. Most of these factors are not accurately accounted for, so gas consumption is calculated according to average standards. They take into account that the population partially eats in buffets, canteens and restaurants, and also uses the services of public utilities. In apartments, gas is spent on cooking food, hot water and washing laundry.

Gas consumption for heating, ventilation and hot water supply of residential and public buildings is determined by specific heat consumption standards.

Gas consumption for heating, ventilation, hot water supply and technological needs of industrial enterprises are accepted according to the corresponding projects.

1.3 gas consumption mode

All categories of gas consumers are characterized by uneven consumption of gas. Depending on the period during which consumption is taken constant, one distinguishes: 1) seasonal unevenness, or unevenness by months of the year; 2) daily unevenness, or unevenness on the days of a week, month or year; 3) hourly unevenness, or unevenness in hours of day or hours of year. Knowledge of consumption modes in all specified periods makes it possible to identify with the greatest reliability design loads on distribution networks.

The mode of gas consumption by the city depends on the mode of individual categories of consumers and their specific gravity in total consumption. Theoretical accounting of factors affecting the uniformity of consumption is in most cases impossible and therefore the method of determining costs at different periods of time is based on experimental data.

Uneven consumption has a great impact on the economic performance of gas supply systems. The presence of peaks and dips in gas consumption leads to the underutilization of gas fields and the capacity of gas main pipelines, which increases the cost of gas; leads to the need for the construction of underground gas reservoirs and the creation of consumer regulators, which discharge surplus in the summer, which is associated with additional capital investments in gas transportation systems and in the second fuel farms of consumers.

City gas supply systems do not have storage tanks located at consumers, and the capacity of the gas networks themselves is very small. For each pressure stage, it is 3-4% of their maximum-hour throughput, the consequence of this is a tight connection that exists between the supply of gas to the city and its consumption by consumers. Hence, in order for the system to function normally, the hourly supply of gas to the city network must strictly correspond to consumption. If the consumption turns out to be less than the supply, the networks will not accept excess gas; and if it is larger than the supply, then the gas pressure in the networks will begin to drop and the normal gas supply will be disrupted.

The main consequence of tight communication in the city gas distribution system is that the throughput of gas networks and elements of the system must be counted on the peak, maximum hour gas consumption. Since the gas supply system has a high cost and a large metal capacity, the maximum (calculated) gas consumption must be carefully justified.

1.4 Gas Supply System Selection

The presence of numerous gas consumption points, characterized by a wide range of heat loads and consumption mode, makes it necessary to pay great attention to the correct and reasonable choice of the system and configuration of gas networks.

In the development of gas supply systems, the issue of rational connection of concentrated consumers to high or low pressure networks is important. On the one hand, connecting a large number of consumers to high-stage networks leads to their branching and the need to build hydraulic fracturing at each consumer, on the other hand, connecting concentrated consumers to low-pressure gas pipelines requires a significant increase in their diameters in order to maintain the specified pressure parameters in gas pipelines. Typically, small consumers are connected to low-pressure networks, and large consumers are connected to high or medium-pressure networks. But a clear border between large and small consumers cannot be drawn. If you take the same consumer, then for low-pressure and large-diameter gas pipelines it will be small, and for small-diameter gas pipelines - large.

The location of the consumer relative to low, medium or high pressure gas pipelines is also important. When choosing the optimal option for connecting a concentrated consumer to a closely located low-pressure gas pipeline or to a more remote high-pressure gas pipeline, it is recommended to proceed from a cost comparison in both cases.

In some cases, when choosing the best connection option, the following factors should be taken into account: processability, reliability, convenience and cost-effectiveness of operation. Of the total length of urban gas networks, usually 70-80% are low-pressure gas pipelines and 20-30% are medium and high.

The second important issue is the choice of gas network configuration. Networks can be designed in ring, branched and mixed. Usually, project organizations are guided by the principle of reliability and prefer low-pressure ring networks. For the same reasons, in each ring, transit loads tend to be distributed across both semi-rings. But at the same time, the ring has a maximum metal capacity, that is, it is more economical to provide only consumers connected to it with gas through one half-ring, and supply gas through the other half-ring in an amount that provides both consumers connected to it and consumers behind the ring. By allocating sections in the rings for transit costs, you can get the most economical network with the main direction of gas transit flows, as well as by looped transit lines due to the EMG supplying them, you can redistribute the main gas flows, for example, during an accident or repair. At the same time, branches from the main rings carrying small loads and for a limited number of consumers, the network may not ring.

Thus, the rational structure of low pressure urban gas networks should be considered a structure in the form of a combination of looped networks of main guide flows and dead end networks of their branches. At the same time, the main direction connecting the individual GRP should be carried out with one section. The telescopic structure makes it difficult to redistribute flows and turns the zones of action of individual GRP into isolated systems that are hydraulically disconnected from each other, which reduces the reliability of the entire system. Branches from the main directions, on the contrary, are more expedient to build according to the telescopic structure.

This approach to the choice of network configuration concerned low-pressure gas pipelines, the need for their thick wiring throughout the territory is caused by a significant dispersion of household and communal facilities. When choosing the configuration of medium and high pressure distribution networks, preference also remains for ring for the same reasons. But unlike low pressure networks, medium and high pressure networks feed concentrated gas consumers, and their territorial location largely determines the configuration of the networks. Due to this, their looping may in some cases be uneconomical, and the reliability of gas supply during dead end wiring is achieved by increased requirements for the laying and operation of medium and high pressure networks.

The reliability and cost-effectiveness of gas supply systems also depends on the number of GRS supplying a high gas distribution stage. With an increase in the number of GRS, the range of each of them decreases, i.e., metal capacity and investments in a high pressure stage network decrease. At the same time, a large number of GRS increases the reliability of the system by supplying it from several directions. For cities with a population of 100 to 200 thousand people, it is recommended to provide one gas distribution station.

When designing gas supply to cities, the correct choice of the number of low-pressure GRP, their productivity and location is of great importance. Since with an increase in their number, the radii of action and load on the network, and, therefore, the diameters and cost of the network, decrease. But at the same time, the costs of building and operating GRP and medium and high pressure pipelines to them are increasing. Therefore, the selection of the amount of GRP should be made on the basis of a technical and economic calculation, based on the principle of minimum investment and operating costs in this network. In the course project, we use enlarged indicators.

The EMG is located in separate buildings closer to the junction points and to the center of the gasified area with a uniform radius of action so that the points of meeting of the mergers of flows from adjacent EMG are approximately at the same distance.

1.5 hydraulic calculation of gas pipelines

According to [3, item 3.21], the hydraulic modes of operation of low, medium and high pressure distribution gas pipelines should be taken from the conditions of creating, at maximum allowable gas pressure losses, the most economical and reliable system in operation, ensuring stability of operation of FRG and gas control plants (GRU), as well as operation of burners of consumers in permissible gas pressure ranges.

In general, the gas movement in gas pipelines is non-stationary, which leads to a time-varying pressure mode in the gas pipeline and a change in the amount of gas in it, therefore, the calculated internal diameters of gas pipelines must be determined by hydraulic calculation based on the condition of ensuring uninterrupted gas supply to all consumers during the hours of maximum gas consumption.

The calculation shall be based on the design pressure drop ΔRdop, i.e. the allowable gas head at the outlet of the FRG, which can be used to overcome linear and local pipeline resistances in the section from the FRG to any end point of the distribution gas pipeline. So in low-pressure gas pipelines, the estimated total gas pressure losses (from the gas supply source to the most remote device) are accepted no more than 180 daPa, including in 120 daPa distribution gas pipelines, in gas pipelines-inlets and internal gas pipelines - 60 daPa [3, item 3.25]. On the high and medium pressure network, the calculated difference is taken depending on the output and required pressure at the beginning and at the end of the calculated line.

When calculating the gas movement in pipelines, take into account the change in its density. This is because the pressure along the length of the pipeline drops and the density of the gas decreases accordingly. Only low-pressure gas pipelines can be calculated, considering that incompressible liquid moves along them. When calculating high and medium pressure gas pipelines, a compressibility coefficient is introduced, which takes into account deviations in the behavior of natural gases from the laws of ideal gases. The main working formulae are given in [3], which also take into account the change of hydraulic friction coefficient a depending on the gas flow mode, the gas pipeline material, the methods of pipe manufacturing and their connection, the quality of installation and operation of gas pipelines.

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