Exchange Rate Project - City Gas Distribution System Project

I. Content of the draft.

The exchange rate project consists of an explanatory note and a project of the city gas distribution system, where calculations of the city's annual gas consumption, hourly design costs should be performed; characteristics of combustible gas; the distribution system of high (medium) and low pressure gas pipelines was designed and its hydraulic calculation was carried out; the main technical and economic indicators of the adopted gas supply system are given.

The explanatory note describes the justifications of the design solutions, provides calculations with the necessary explanations. At the end of the note is a list of reference literature

II.2.2. Hourly non-uniformity of gas consumption

City gas networks calculate the maximum hourly gas flow rate, which can be determined if there are data on hourly fluctuations in gas consumption. The most hourly unevenness of gas consumption is distinguished by household and communal consumers. Gas consumption for central heating needs during the day remains almost unchanged. Gas consumption for the technological needs of industrial enterprises depends on the nature of technological processes and the shift of work.

The procedure for determining the hourly flow rate of gas is numerically set out in II.2.1. However, to determine the fraction of the hourly flow rate of gas by the i-th category of consumers, a thorough study of the gas consumption modes is required from the daily flow rate. During operation of gas supply systems for each city separately.

II.3. Gas supply system

II.3.1. Determination of the number of GVs.

One of the important issues when developing a fundamental scheme for gas supply to the city is the rational placement of gas distribution stations (GRS) and the determination of their optimal number. With an increase in the number of RRs, the loads and radius of urban highways decrease, which leads to a significant decrease in their sections. Accordingly, metal consumption and investment in high (medium) pressure urban networks are reduced. In addition, a larger number of GPUs provides greater reliability of gas supply systems.

At the same time, it should be borne in mind that with an increase in the number of RRs, the costs of their construction and construction of gas main pipelines increase, and operational costs are increased due to the maintenance personnel on the RRS.

When determining the number of trunk sources, you should focus on the following:

a) for small cities with a population of up to 100200 thousand people, the most rational are systems with one GRS;

b) for cities with a population of up to 200300 thousand people, the most rational are systems with two, three GRS;

c) for cities with a population of up to 300500 thousand people, the most economical are systems with three GRS.

To power city gas pipelines in this course project, two GRS are adopted, located outside the city limits on opposite sides of the city. The gas at the GPC is cleaned, odorized, reduced to the upper stage pressure in the city networks and supplied to the distribution gas pipelines.

II.3.1.2. Determination of the number of pressure stages in gas distribution lines

By the number of pressure stages in the practice of gas supply to cities, the following are used:

• two-stage stages consisting of low and medium or low and high (up to 0.6 MPa) pressure networks;

• three-stage, including low, medium and high (up to 0.6MPa) pressure pipelines;

• multistage, consisting of low, medium and high pressure networks (up to 0.6MPa and up to 1.2MPa).

For small and medium-sized cities with a population of up to 100 and 500 thousand inhabitants, respectively, two-stage gas supply systems are used as the most economical, consisting of low and high (0.6 MPa) gas pipelines or low and medium pressures. Medium pressure is used only if it is impossible to lay high pressure gas pipelines. Such a case may arise with the gas supply of old cities with dense buildings or during the reconstruction of the gas supply system. If the development of the city is heterogeneous and characterized by different densities, three-stage gas supply systems are used with the laying of low and medium pressure gas pipelines in areas where high pressure networks cannot be laid (usually the central part of old cities and low-rise buildings), and high pressure in areas of new development.

Multi-stage systems are used only in large cities with a number of inhabitants above 1mn. a man.

In this course design, a two-stage gas supply system with maximum overpressure in networks P = 0.6 MPa was adopted.

II.3.1.3. Selection of gas networks structural diagram.

Gas distribution systems can be dead end, annular and mixed. For large and medium cities, high and medium pressure networks are designed in ring, for small cities, the ring of high pressure gas pipelines is carried out only if necessary. Low-pressure gas pipelines should be provided with ring lines with the separation of main directions, i.e., such lines through which the main part of the gas transit flow is transported. In this case, the metal consumption of the ring will be minimal. In order to improve the reliability of the low pressure system, the dedicated main lines should be circular. Access to consumers is provided, as a rule, with dead ends.

II.3.3. Pipes and Connectors

Installation of distribution gas pipelines should be provided underground. In justified cases, above-ground laying of gas pipelines on the walls of buildings inside residential buildings and quarters, as well as on certain sections of the route, including at sections of crossings through artificial and natural barriers, at the intersection of underground communications, is allowed.

When designing underground gas pipelines, it is recommended to provide polyethylene pipes, except when these pipes cannot be used according to the gasket conditions, pressure and type of transported gas.

Polyethylene pipes GOST R 5083895 * are used for the construction of gas pipelines.

Steel pipes shall be used for construction of above ground and above ground gas pipelines.

Selection of pipe material, pipeline shutoff valves, connecting parts should be made taking into account gas pressure, diameter and thickness of the gas pipeline wall, design ambient air temperature in the construction area and pipe wall temperature during operation, soil and natural conditions, presence of vibration loads.

The thickness of the pipe walls should be determined by calculation and its nominal value should be taken equal to the value of the nearest larger according to GOST (TU).

It is allowed to use connecting parts from steel seamless and welded pipes and sheet rolled steel, the metal of which meets the requirements for the metal of the pipe and the field of application of the gas pipeline for which the connecting parts are intended.

Steel underground gas pipelines for high pressure networks of category II and underground polyethylene pipelines for low pressure networks were designed in the course design.

In the course design, it is proposed to select steel pipes for the gas pipeline in accordance with GOST 1070491 * "Steel electric welded straight-joint pipes ."

III. Design of internal house gas supply network

III.1. Requirements for internal gas pipelines

Gas is supplied to residential, public and communal buildings through gas pipelines from the intra-quarter distribution network. These gas pipelines consist of subscriber branches supplying gas to the building and internal gas pipelines that transport gas inside the building and distribute it among individual gas devices. In internal gas networks of residential, public and communal buildings, only low-pressure gas (not more than 3 kPa) can be transported.

The gas pipeline is introduced into residential and public buildings through non-residential rooms accessible for pipe inspection. Gas pipelines are introduced into public and communal buildings directly into the premises in which gas devices are installed. The inputs of the wet gas pipelines should be laid with a slope towards the distribution gas pipeline .

At the gas pipeline inlet to the buildings the disconnecting device is installed, which is mounted outside the building. The installation site shall be available for maintenance and quick shutdown of the gas pipeline .

Gas risers are laid in kitchens. It is impossible to lay risers in residential premises, bathrooms and sanitary units. If gas is supplied from one inlet to a residential building to several risers, then a crane or gate valve is installed on each of them. In one-five-story buildings, disconnecting devices are not installed on risers. Transit gas pipelines cannot be laid through residential premises. Cranes are installed in front of each gas device. Burns are provided on gas pipelines after cranes along the gas flow. If there is a gas counter, the valve is also installed in front of it. Gas pipelines inside the building are made of steel and copper pipes. Pipes are welded. Threaded and flange connections are allowed only in places where disconnecting devices, valves and instruments are installed.

Gas pipelines in buildings are laid openly. With appropriate justification, hidden gasket is allowed in furrows of walls, which are covered with shields with holes for ventilation. Gas pipelines for dried gas are laid without slope, and for wet gas with slope not less than 0.002. If there is a gas meter, the slope has a direction from the meter to the riser and gas devices .

Gas pipelines crossing foundations, floors, walls and partitions should be enclosed in steel cases. Within the case, the gas pipeline must not have butt joints, and the space between it and the case must be sealed with a ground pack and filled with bitumen. The end of the case is brought out over the floor for 3 cm.

In residential buildings, gas pipelines are fixed to the walls using hooks. If the pipe diameter is more than 40 mm, attachment is performed using brackets. The distance between the supports is accepted no more than: 2.5 m (at Ø pipes 15 mm), 3.5 m (at Ø 25 mm), 5 m (at Ø 50 mm). The gap between the pipe and the wall is taken to be 1.52 cm. The distance between the open electrical wire and the gas pipeline wall should be at least 10 cm.