Determining the diameter of the pipeline. Hydraulic calculation of steam pipelines of low and high pressure steam heating systems

The steam line diameter is defined as:

Where: D - the maximum amount of steam consumed by the site, kg / h,

D= 1182.5 kg/h (according to the schedule of machines and devices for the cottage cheese production site) /68/;

- specific volume of saturated steam, m 3 / kg,
\u003d 0.84 m 3 / kg;

- the speed of steam in the pipeline, m/s, is assumed to be 40 m/s;

d=
=0.100 m=100 mm

A steam pipeline with a diameter of 100 mm is connected to the workshop, therefore, its diameter is sufficient.

Steam pipelines steel, seamless, wall thickness 2.5 mm

4.2.3. Calculation of the pipeline for the return of condensate

The pipeline diameter is determined by the formula:

d=
, m,

where Mk is the amount of condensate, kg/h;

Y - specific volume of condensate, m 3 /kg, Y = 0.00106 m 3 /kg;

W – condensate movement speed, m/s, W=1m/s.

Mk=0.6* D, kg/h

Mk=0.6*1182.5=710 kg/h

d=
=0.017m=17mm

We select the standard diameter of the pipeline dst = 20mm.

4.2.3 Calculation of insulation of heat networks

In order to reduce the loss of thermal energy, pipelines are insulated. Let's calculate the insulation of the supply steam pipeline with a diameter of 110 mm.

Insulation thickness for temperature environment 20ºС for a given heat loss is determined by the formula:

, mm,

where d is the diameter of an uninsulated pipeline, mm, d=100mm;

t - temperature of an uninsulated pipeline, ºС, t=180ºС;

λiz - coefficient of thermal conductivity of insulation, W/m*K;

q- heat losses from one linear meter of the pipeline, W / m.

q \u003d 0.151 kW / m \u003d 151 W / m²;

λout=0.0696 W/m²*K.

Slag wool is used as an insulating material.

=90 mm

The thickness of the insulation should not exceed 258 mm with a pipe diameter of 100 mm. Obtained δfrom<258 мм.

The diameter of the insulated pipeline will be d=200 mm.

4.2.5 Checking the savings in thermal resources

Thermal energy is determined by the formula:

t=180-20=160ºС

Figure 4.1 Piping Diagram

The pipeline area is determined by the formula:

R= 0.050 m, H= 1 m.

F=2*3.14*0.050*1=0.314m²

The heat transfer coefficient of an uninsulated pipeline is determined by the formula:

,

where a 1 \u003d 1000 W / m² K, a 2 \u003d 8 W / m² K, λ \u003d 50 W / mK, δst \u003d 0.002 m.

=7,93.

Q \u003d 7.93 * 0.314 * 160 \u003d 398 W.

The thermal conductivity coefficient of an insulated pipeline is determined by the formula:

,

where λout=0.0696 W/mK.

=2,06

The area of ​​the insulated pipeline is determined by the formula F=2*3.14*0.1*1=0.628m²

Q=2.06*0.628*160=206W.

The calculations performed showed that when using insulation on a 90 mm thick steam pipeline, 232 W of thermal energy is saved per 1 m of the pipeline, that is, thermal energy is spent rationally.

4.3 Power supply

At the plant, the main consumers of electricity are:

Electric lamps (lighting load);

Power supply at the enterprise from the city network through a transformer substation.

The power supply system is a three-phase current with an industrial frequency of 50 Hz. Internal network voltage 380/220 V.

Energy Consumption:

At peak load hour - 750 kW / h;

The main consumers of energy:

Technological equipment;

Power plants;

Enterprise lighting system.

The 380/220V distribution network from switch cabinets to machine starters is made with a cable of the LVVR brand in steel pipes, to the LVP motor wires. The neutral wire of the mains is used as grounding.

General (working and emergency) and local (repair and emergency) lighting is provided. Local lighting is powered by low power step-down transformers at a voltage of 24V. Normal emergency lighting is powered by a 220V electrical network. In case of complete loss of voltage on the busbars of the substation, emergency lighting is powered by autonomous sources (“dry batteries”) built into the luminaires or from the AGP.

Working (general) lighting is provided at a voltage of 220V.

Luminaires are provided in a design corresponding to the nature of production and environmental conditions of the premises in which they are installed. In industrial premises, they are provided with fluorescent lamps installed on complete lines from special hanging boxes located at a height of about 0.4 m from the floor.

For evacuation lighting, emergency lighting shields are installed, connected to another (independent) lighting source.

Industrial lighting is provided by fluorescent lamps and incandescent lamps.

Characteristics of incandescent lamps used to illuminate industrial premises:

1) 235- 240V 100W Base E27

2) 235- 240V 200W Base E27

3) 36V 60W Base E27

4) LSP 3902A 2*36 R65IEK

Name of fixtures used to illuminate refrigerating chambers:

Cold Force 2*46WT26HF FO

For street lighting are used:

1) RADBAY 1* 250 WHST E40

2) RADBAY SEALABLE 1* 250WT HIT/ HIE MT/ME E40

Maintenance of electric power and lighting devices is carried out by a special service of the enterprise.

4.3.1 Calculation of the load from technological equipment

The type of electric motor is selected from the catalog of technological equipment.

P nop, efficiency - passport data of the electric motor, selected from electrical reference books /69/.

Р pr - connecting power

R pr \u003d R nom /

The type of magnetic starter is selected specifically for each electric motor. The calculation of the load from the equipment is summarized in table 4.4

4.3.2 Calculation of lighting load /69/

hardware shop

Determine the height of the suspension fixtures:

H p \u003d H 1 -h St -h p

Where: H 1 - the height of the premises, 4.8 m;

h sv - the height of the working surface above the floor, 0.8 m;

h p - the estimated height of the suspension fixtures, 1.2m.

H p \u003d 4.8-0.8-1.2 \u003d 2.8 m

We choose a uniform system for distributing lamps at the corners of the rectangle.

Distance between lamps:

L= (1.2÷1.4) H p

L=1.3 2.8=3.64m

N sv \u003d S / L 2 (pcs)

n sv \u003d 1008 / 3.64m 2 \u003d 74 pcs

We accept 74 lamps.

N l \u003d n sv N sv

N l \u003d 73 2 \u003d 146 pcs

i=A*B/H*(A+B)

where: A - length, m;

B is the width of the room, m.

i=24*40/4.8*(24+40) = 3.125

From the ceiling-70%;

From walls -50%;

From the working surface-30%.

Q=E min *S*k*Z/N l *η

k - safety factor, 1.5;

N l - the number of lamps, 146 pcs.

Q=200*1.5*1008*1.1/146*0.5= 4340 lm

Choose a lamp type LD-80.

Curd shop

Approximate number of lighting lamps:

N sv \u003d S / L 2 (pcs)

where: S is the area of ​​the illuminated surface, m 2;

L - distance between lamps, m.

n sv \u003d 864 / 3.64m 2 \u003d 65.2 pcs

We accept 66 fixtures.

Determine the approximate number of lamps:

N l \u003d n sv N sv

N sv - the number of lamps in the lamp

N l \u003d 66 2 \u003d 132 pcs

Let's determine the coefficient of use of the luminous flux according to the table of coefficients:

i=A*B/H*(A+B)

where: A - length, m;

B is the width of the room, m.

i=24*36/4.8*(24+36) = 3

We accept light reflection coefficients:

From the ceiling-70%;

From walls -50%;

From the working surface-30%.

According to the index of the room and the reflection coefficient, we select the coefficient of use of the luminous flux η = 0.5

Determine the luminous flux of one lamp:

Q=E min *S*k*Z/N l *η

where: E min - minimum illumination, 200 lx;

Z - linear illumination coefficient 1.1;

k - safety factor, 1.5;

η is the utilization factor of the luminous flux, 0.5;

N l - the number of lamps, 238 pcs.

Q \u003d 200 * 1.5 * 864 * 1.1 / 132 * 0.5 \u003d 4356 lm

Choose a lamp type LD-80.

Whey processing workshop

n sv \u003d 288 / 3.64 2 \u003d 21.73 pcs

We accept 22 fixtures.

Number of lamps:

i=24*12/4.8*(24+12)=1.7

Luminous flux of one lamp:

Q=200*1.5*288*1.1/56*0.5=3740 lx

Choose a lamp type LD-80.

Reception department

Approximate number of fixtures:

n sv \u003d 144 / 3.64m 2 \u003d 10.8 pcs

We accept 12 lamps

Number of lamps:

Luminous flux utilization factor:

i=12*12/4.8*(12+12)=1.3

Luminous flux of one lamp:

Q=150*1.5*144*1.1/22*0.5=3740 lx

Choose a lamp type LD-80.

Installed power of one lighting load P = N 1 * R l (W)

Calculation of the lighting load by the method of specific power.

E min \u003d 150 lux W * 100 \u003d 8.2 W / m 2

Recalculation for illumination of 150 lux is carried out according to the formula

W \u003d W * 100 * E min / 100, W / m 2

W \u003d 8.2 * 150/100 \u003d 12.2 W / m 2

Determination of the total power required for lighting (P), W.

Hardware shop Р= 12.2*1008= 11712 W

Curd shop Р= 12.2*864= 10540 W

Reception department Р=12.2*144= 1757 W

Whey processing shop Р= 12.2* 288= 3514 W

We determine the number of capacities N l \u003d P / P 1

P 1 - power of one lamp

N l (hardware shop) = 11712/80= 146

N l (curd shop) \u003d 10540 / 80 \u003d 132

N l (admission department) = 1756/80= 22

N l (whey processing workshops) = 3514/80 = 44

146+132+22+44= 344; 344*80= 27520 W.

Table 4.5 - Calculation of the power load

Table 4.6 - Calculation of the lighting load

4.3.3 Verification calculation of power transformers

Active power: R tr \u003d R poppy / η networks

where: R poppy \u003d 144.85 kW (according to the schedule "Power consumption by hours of the day")

network η =0.9

P tr \u003d 144.85 / 0.9 \u003d 160.94 kW

Apparent power, S, kVA

S=P tr /cosθ

S=160.94/0.8=201.18 kVA

For the transformer substation TM-1000/10, the total power is 1000 kVA, the total power at the load existing at the enterprise is 750 kVA, but taking into account the technical re-equipment of the curd section and the organization of whey processing, the required power should be: 750 + 201.18 = 951 .18 kVA< 1000кВ·А.

Electricity consumption per 1 ton of manufactured products:

R =

where M - mass of all produced products, t;

M =28.675 t

R \u003d 462.46 / 28.675 \u003d 16.13 kWh / t

Thus, from the graph of electricity consumption by hours of the day, it can be seen that the greatest power is required in the time interval from 8 00 to 11 00 and from 16 up to 21 hours. During this period of time, the acceptance and processing of incoming raw milk, the production of products, and the bottling of drinks take place. Small jumps are observed between 8 up to 11 when most of the milk processing processes to obtain products take place.

4.3.4 Calculation of sections and selection of cables.

The cable cross section is found by voltage loss

S=2 PL*100/γ*ζ*U 2 , where:

L is the cable length, m.

γ is the specific conductivity of copper, OM * m.

ζ - allowable voltage losses,%

U- network voltage, V.

S \u003d 2 * 107300 * 100 * 100 / 57.1 * 10 3 * 5 * 380 2 \u003d 0.52 mm 2.

Conclusion: the cross-section of the VVR brand cable used by the enterprise is 1.5 mm 2 - therefore, the existing cable will provide the sites with electricity.

Table 4.7 - Hourly consumption of electricity for the production of products

Energy consumption chart.

Pipelines for the transport of various liquids are an integral part of units and installations in which work processes related to various fields of application are carried out. When choosing pipes and piping configuration, the cost of both the pipes themselves and the pipeline fittings is of great importance. The final cost of pumping the medium through the pipeline is largely determined by the size of the pipes (diameter and length). The calculation of these values ​​is carried out using specially developed formulas specific to certain types of operation.

A pipe is a hollow cylinder made of metal, wood or other material used to transport liquid, gaseous and granular media. The transported medium can be water, natural gas, steam, oil products, etc. Pipes are used everywhere, from various industries to domestic applications.

A variety of materials can be used to make pipes, such as steel, cast iron, copper, cement, plastics such as ABS, polyvinyl chloride, chlorinated polyvinyl chloride, polybutene, polyethylene, etc.

The main dimensional indicators of a pipe are its diameter (outer, inner, etc.) and wall thickness, which are measured in millimeters or inches. Also used is such a value as the nominal diameter or nominal bore - the nominal value of the internal diameter of the pipe, also measured in millimeters (indicated by Du) or inches (indicated by DN). The nominal diameters are standardized and are the main criterion for the selection of pipes and fittings.

Correspondence of nominal bore values ​​in mm and inches:

A pipe with a circular cross section is preferred over other geometric sections for a number of reasons:

• The circle has a minimum ratio of perimeter to area, and when applied to a pipe, this means that with equal throughput, the material consumption of round pipes will be minimal compared to pipes of a different shape. This also implies the minimum possible costs for insulation and protective coating;
• A circular cross section is most advantageous for the movement of a liquid or gaseous medium from a hydrodynamic point of view. Also, due to the minimum possible internal area of ​​the pipe per unit of its length, friction between the conveyed medium and the pipe is minimized.
• The round shape is the most resistant to internal and external pressures;
• The process of manufacturing round pipes is quite simple and easy to implement.

Pipes can vary greatly in diameter and configuration depending on the purpose and application. Thus, main pipelines for moving water or oil products can reach almost half a meter in diameter with a fairly simple configuration, and heating coils, which are also pipes, have a complex shape with many turns with a small diameter.

It is impossible to imagine any industry without a network of pipelines. The calculation of any such network includes the selection of pipe material, drawing up a specification, which lists data on the thickness, pipe size, route, etc. Raw materials, intermediate products and / or finished products pass through the production stages, moving between different apparatuses and installations, which are connected using pipelines and fittings. Proper calculation, selection and installation of the piping system is necessary for the reliable implementation of the entire process, ensuring the safe transfer of media, as well as for sealing the system and preventing leakage of the pumped substance into the atmosphere.

There is no single formula and rule that can be used to select pipeline for every possible application and working environment. In each individual area of ​​application of pipelines, there are a number of factors that need to be taken into account and can have a significant impact on the requirements for the pipeline. So, for example, when dealing with sludge, a large pipeline will not only increase the cost of the installation, but also create operational difficulties.

Typically, pipes are selected after optimizing material and operating costs. The larger the diameter of the pipeline, i.e. the higher the initial investment, the lower the pressure drop will be and, accordingly, the lower the operating costs. Conversely, the small size of the pipeline will reduce the primary costs for the pipes themselves and pipe fittings, but an increase in speed will entail an increase in losses, which will lead to the need to spend additional energy on pumping the medium. Speed ​​limits fixed for different applications are based on optimum design conditions. The size of pipelines is calculated using these standards, taking into account the areas of application.

Pipeline design

When designing pipelines, the following main design parameters are taken as a basis:

• required performance;
• entry point and exit point of the pipeline;
• medium composition, including viscosity and specific gravity;
• topographic conditions of the pipeline route;
• maximum allowable working pressure;
• hydraulic calculation;
• pipeline diameter, wall thickness, tensile yield strength of the wall material;
• number of pumping stations, distance between them and power consumption.

Pipeline reliability

Reliability in piping design is ensured by adherence to proper design standards. Also, personnel training is a key factor in ensuring the long service life of the pipeline and its tightness and reliability. Continuous or periodic monitoring of pipeline operation can be carried out by monitoring, accounting, control, regulation and automation systems, personal control devices in production, and safety devices.

Additional pipeline coating

A corrosion resistant coating is applied to the outside of most pipes to prevent the damaging effects of corrosion from the outside environment. In the case of pumping corrosive media, a protective coating can also be applied to the inner surface of the pipes. Before commissioning, all new pipes intended for the transport of hazardous liquids are tested for defects and leaks.

Basic provisions for calculating the flow in the pipeline

The nature of the flow of the medium in the pipeline and when flowing around obstacles can differ greatly from liquid to liquid. One of the important indicators is the viscosity of the medium, characterized by such a parameter as the viscosity coefficient. The Irish engineer-physicist Osborne Reynolds conducted a series of experiments in 1880, according to the results of which he managed to derive a dimensionless quantity characterizing the nature of the flow of a viscous fluid, called the Reynolds criterion and denoted by Re.

Re = (v L ρ)/μ

where:
ρ is the density of the liquid;
v is the flow rate;
L is the characteristic length of the flow element;
μ - dynamic coefficient of viscosity.

That is, the Reynolds criterion characterizes the ratio of the forces of inertia to the forces of viscous friction in the fluid flow. A change in the value of this criterion reflects a change in the ratio of these types of forces, which, in turn, affects the nature of the fluid flow. In this regard, it is customary to distinguish three flow regimes depending on the value of the Reynolds criterion. At Re<2300 наблюдается так называемый ламинарный поток, при котором жидкость движется тонкими слоями, почти не смешивающимися друг с другом, при этом наблюдается постепенное увеличение скорости потока по направлению от стенок трубы к ее центру. Дальнейшее увеличение числа Рейнольдса приводит к дестабилизации такой структуры потока, и значениям 23004000, a stable regime is observed, characterized by a random change in the speed and direction of the flow at each individual point, which in total gives an equalization of the flow rates throughout the volume. Such a regime is called turbulent. The Reynolds number depends on the head supplied by the pump, the viscosity of the medium at operating temperature, and the size and shape of the pipe through which the flow passes.

Velocity profile in the stream
laminar flow	transitional regime	turbulent regime
The nature of the flow
laminar flow	transitional regime	turbulent regime

The Reynolds criterion is a similarity criterion for the flow of a viscous fluid. That is, with its help, it is possible to simulate a real process in a reduced size, convenient for studying. This is extremely important, since it is often extremely difficult, and sometimes even impossible, to study the nature of fluid flows in real devices due to their large size.

Pipeline calculation. Calculation of pipeline diameter

If the pipeline is not thermally insulated, that is, heat exchange between the transported and the environment is possible, then the nature of the flow in it can change even at a constant speed (flow rate). This is possible if the pumped medium has a sufficiently high temperature at the inlet and flows in a turbulent regime. Along the length of the pipe, the temperature of the transported medium will drop due to heat losses to the environment, which may lead to a change in the flow regime to laminar or transitional. The temperature at which the mode change occurs is called the critical temperature. The value of the viscosity of a liquid directly depends on the temperature, therefore, for such cases, such a parameter as the critical viscosity is used, which corresponds to the point of change in the flow regime at the critical value of the Reynolds criterion:

v cr = (v D)/Re cr = (4 Q)/(π D Re cr)

where:
ν kr - critical kinematic viscosity;
Re cr - critical value of the Reynolds criterion;
D - pipe diameter;
v is the flow rate;
Q - expense.

Another important factor is the friction that occurs between the pipe walls and the moving stream. In this case, the coefficient of friction largely depends on the roughness of the pipe walls. The relationship between the coefficient of friction, the Reynolds criterion and the roughness is established by the Moody diagram, which allows you to determine one of the parameters, knowing the other two.

The Colebrook-White formula is also used to calculate the coefficient of friction for turbulent flow. Based on this formula, it is possible to plot graphs by which the coefficient of friction is established.

(√λ ) -1 = -2 log(2.51/(Re √λ ) + k/(3.71 d))

where:
k - pipe roughness coefficient;
λ is the coefficient of friction.

There are also other formulas for the approximate calculation of friction losses during the pressure flow of liquid in pipes. One of the most frequently used equations in this case is the Darcy-Weisbach equation. It is based on empirical data and is mainly used in system modeling. Friction loss is a function of the fluid velocity and the resistance of the pipe to fluid movement, expressed in terms of the pipe wall roughness value.

∆H = λ L/d v²/(2 g)

where:
ΔH - head loss;
λ - coefficient of friction;
L is the length of the pipe section;
d - pipe diameter;
v is the flow rate;
g is the free fall acceleration.

Pressure loss due to friction for water is calculated using the Hazen-Williams formula.

∆H = 11.23 L 1/C 1.85 Q 1.85 /D 4.87

where:
ΔH - head loss;
L is the length of the pipe section;
C is the Haizen-Williams roughness coefficient;
Q - consumption;
D - pipe diameter.

Pressure

The working pressure of the pipeline is the highest excess pressure that provides the specified mode of operation of the pipeline. The decision on the size of the pipeline and the number of pumping stations is usually made based on the working pressure of the pipes, pumping capacity and costs. The maximum and minimum pressure of the pipeline, as well as the properties of the working medium, determine the distance between the pumping stations and the required power.

Nominal pressure PN - nominal value corresponding to the maximum pressure of the working medium at 20 ° C, at which continuous operation of the pipeline with given dimensions is possible.

As the temperature increases, the load capacity of the pipe decreases, as does the allowable overpressure as a result. The pe,zul value indicates the maximum pressure (g) in the piping system as the operating temperature increases.

Permissible overpressure schedule:

Calculation of the pressure drop in the pipeline

The calculation of the pressure drop in the pipeline is carried out according to the formula:

∆p = λ L/d ρ/2 v²

where:
Δp - pressure drop in the pipe section;
L is the length of the pipe section;
λ - coefficient of friction;
d - pipe diameter;
ρ is the density of the pumped medium;
v is the flow rate.

Transportable media

Most often, pipes are used to transport water, but they can also be used to move sludge, slurries, steam, etc. In the oil industry, pipelines are used to pump a wide range of hydrocarbons and their mixtures, which differ greatly in chemical and physical properties. Crude oil can be transported over longer distances from onshore fields or offshore oil rigs to terminals, waypoints and refineries.

Pipelines also transmit:

• refined petroleum products such as gasoline, aviation fuel, kerosene, diesel fuel, fuel oil, etc.;
• petrochemical raw materials: benzene, styrene, propylene, etc.;
• aromatic hydrocarbons: xylene, toluene, cumene, etc.;
• liquefied petroleum fuels such as liquefied natural gas, liquefied petroleum gas, propane (gases at standard temperature and pressure but liquefied by pressure);
• carbon dioxide, liquid ammonia (transported as liquids under pressure);
• bitumen and viscous fuels are too viscous to be transported through pipelines, so distillate fractions of oil are used to dilute these raw materials and result in a mixture that can be transported through a pipeline;
• hydrogen (for short distances).

The quality of the transported medium

The physical properties and parameters of the transported media largely determine the design and operating parameters of the pipeline. Specific gravity, compressibility, temperature, viscosity, pour point and vapor pressure are the main media parameters to consider.

The specific gravity of a liquid is its weight per unit volume. Many gases are transported through pipelines under increased pressure, and when a certain pressure is reached, some gases may even undergo liquefaction. Therefore, the degree of compression of the medium is a critical parameter for the design of pipelines and the determination of throughput capacity.

Temperature has an indirect and direct effect on pipeline performance. This is expressed in the fact that the liquid increases in volume after an increase in temperature, provided that the pressure remains constant. Lowering the temperature can also have an impact on both performance and overall system efficiency. Usually, when the temperature of a liquid is lowered, it is accompanied by an increase in its viscosity, which creates additional frictional resistance along the inner wall of the pipe, requiring more energy to pump the same amount of liquid. Very viscous media are sensitive to temperature fluctuations. Viscosity is the resistance of a medium to flow and is measured in centistokes cSt. Viscosity determines not only the choice of pump, but also the distance between pumping stations.

As soon as the temperature of the medium drops below the pour point, the operation of the pipeline becomes impossible, and some options are taken to resume its operation:

• heating the medium or insulating pipes to maintain the operating temperature of the medium above its pour point;
• change in the chemical composition of the medium before it enters the pipeline;
• dilution of the conveyed medium with water.

Types of main pipes

Main pipes are made welded or seamless. Seamless steel pipes are made without longitudinal welds by steel sections with heat treatment to achieve the desired size and properties. Welded pipe is manufactured using several manufacturing processes. These two types differ from each other in the number of longitudinal seams in the pipe and the type of welding equipment used. Steel welded pipe is the most commonly used type in petrochemical applications.

Each pipe section is welded together to form a pipeline. Also, in main pipelines, depending on the application, pipes made of fiberglass, various plastics, asbestos cement, etc. are used.

To connect straight sections of pipes, as well as to transition between pipeline sections of different diameters, specially made connecting elements (elbows, bends, gates) are used.

elbow 90°	elbow 90°	transition branch	branching
elbow 180°	elbow 30°	adapter	tip

For the installation of individual parts of pipelines and fittings, special connections are used.

welded	flanged	threaded	coupling

Thermal expansion of the pipeline

When the pipeline is under pressure, its entire inner surface is subjected to a uniformly distributed load, which causes longitudinal internal forces in the pipe and additional loads on the end supports. Temperature fluctuations also affect the pipeline, causing changes in the dimensions of the pipes. Forces in a fixed pipeline during temperature fluctuations can exceed the permissible value and lead to excessive stress, which is dangerous for the strength of the pipeline, both in the pipe material and in flanged connections. Fluctuations in the temperature of the pumped medium also create a temperature stress in the pipeline, which can be transferred to valves, pumping stations, etc. This can lead to depressurization of pipeline joints, failure of valves or other elements.

Calculation of pipeline dimensions with temperature changes

The calculation of the change in the linear dimensions of the pipeline with a change in temperature is carried out according to the formula:

∆L = a L ∆t

a - coefficient of thermal elongation, mm/(m°C) (see table below);
L - pipeline length (distance between fixed supports), m;
Δt - difference between max. and min. temperature of the pumped medium, °С.

Table of linear expansion of pipes from various materials

The numbers given are averages for the listed materials and for the calculation of pipelines from other materials, the data from this table should not be taken as a basis. When calculating the pipeline, it is recommended to use the coefficient of linear elongation indicated by the pipe manufacturer in the accompanying technical specification or data sheet.

Thermal elongation of pipelines is eliminated both by using special compensatory sections of the pipeline, and by using compensators, which may consist of elastic or moving parts.

Compensation sections consist of elastic straight parts of the pipeline, located perpendicular to each other and fastened with bends. With thermal elongation, the increase in one part is compensated by the deformation of the bending of the other part on the plane or the deformation of bending and torsion in space. If the pipeline itself compensates for thermal expansion, then this is called self-compensation.

Compensation also occurs due to elastic bends. Part of the elongation is compensated by the elasticity of the bends, the other part is eliminated due to the elastic properties of the material of the section behind the bend. Compensators are installed where it is not possible to use compensating sections or when the self-compensation of the pipeline is insufficient.

According to the design and principle of operation, compensators are of four types: U-shaped, lens, wavy, stuffing box. In practice, flat expansion joints with an L-, Z- or U-shape are often used. In the case of spatial compensators, they are usually 2 flat mutually perpendicular sections and have one common shoulder. Elastic expansion joints are made from pipes or elastic disks, or bellows.

Determination of the optimal size of the pipeline diameter

The optimal diameter of the pipeline can be found on the basis of technical and economic calculations. The dimensions of the pipeline, including the dimensions and functionality of the various components, as well as the conditions under which the pipeline must operate, determine the transport capacity of the system. Larger pipes are suitable for higher mass flow, provided the other components in the system are properly selected and sized for these conditions. Usually, the longer the length of the main pipe between pumping stations, the greater the pressure drop in the pipeline is required. In addition, a change in the physical characteristics of the pumped medium (viscosity, etc.) can also have a great influence on the pressure in the line.

Optimum Size - The smallest suitable pipe size for a particular application that is cost effective over the lifetime of the system.

Formula for calculating pipe performance:

Q = (π d²)/4 v

Q is the flow rate of the pumped liquid;
d - pipeline diameter;
v is the flow rate.

In practice, to calculate the optimal diameter of the pipeline, the values ​​​​of the optimal speeds of the pumped medium are used, taken from reference materials compiled on the basis of experimental data:

From here we get the formula for calculating the optimal pipe diameter:

d o = √((4 Q) / (π v o ))

Q - given flow rate of the pumped liquid;
d - the optimal diameter of the pipeline;
v is the optimal flow rate.

At high flow rates, pipes of a smaller diameter are usually used, which means lower costs for the purchase of pipeline, its maintenance and installation work (denoted by K 1). With an increase in speed, there is an increase in pressure losses due to friction and in local resistances, which leads to an increase in the cost of pumping liquid (we denote K 2).

For pipelines of large diameters, the costs K 1 will be higher, and the costs during operation K 2 will be lower. If we add the values ​​of K 1 and K 2 , we get the total minimum cost K and the optimal diameter of the pipeline. Costs K 1 and K 2 in this case are given in the same time period.

Calculation (formula) of capital costs for the pipeline

K 1 = (m C M K M)/n

m is the mass of the pipeline, t;
C M - cost of 1 ton, rub/t;
K M - coefficient that increases the cost of installation work, for example 1.8;
n - service life, years.

The indicated operating costs associated with energy consumption:

K 2 \u003d 24 N n days C E rub / year

N - power, kW;
n DN - number of working days per year;
C E - costs per kWh of energy, rub/kW*h.

Formulas for determining the size of the pipeline

An example of general formulas for determining the size of pipes without taking into account possible additional factors such as erosion, suspended solids, etc.:

Optimal flow rate for various piping systems

The optimal pipe size is selected from the condition of minimum costs for pumping the medium through the pipeline and the cost of pipes. However, speed limits must also be taken into account. Sometimes, the size of the pipeline line must meet the requirements of the process. Just as often, the size of the pipeline is related to the pressure drop. In preliminary design calculations, where pressure losses are not taken into account, the size of the process pipeline is determined by the allowable speed.

If there are changes in the direction of flow in the pipeline, then this leads to a significant increase in local pressures on the surface perpendicular to the direction of flow. This kind of increase is a function of fluid velocity, density, and initial pressure. Because velocity is inversely proportional to diameter, high velocity fluids require special attention when sizing and configuring pipelines. The optimum pipe size, for example for sulfuric acid, limits the velocity of the medium to a value that prevents wall erosion in the pipe bends, thus preventing damage to the pipe structure.

Fluid flow by gravity

Calculating the size of the pipeline in the case of a flow moving by gravity is quite complicated. The nature of the movement with this form of flow in the pipe can be single-phase (full pipe) and two-phase (partial filling). A two-phase flow is formed when both liquid and gas are present in the pipe.

Depending on the ratio of liquid and gas, as well as their velocities, the two-phase flow regime can vary from bubbly to dispersed.

bubble flow (horizontal)	projectile flow (horizontal)	wave flow	dispersed flow

The driving force for the liquid when moving by gravity is provided by the difference in the heights of the start and end points, and the prerequisite is the location of the start point above the end point. In other words, the height difference determines the difference in the potential energy of the liquid in these positions. This parameter is also taken into account when selecting a pipeline. In addition, the magnitude of the driving force is affected by the pressures at the start and end points. An increase in the pressure drop entails an increase in the fluid flow rate, which, in turn, allows you to select a pipeline of a smaller diameter, and vice versa.

In the event that the end point is connected to a pressurized system, such as a distillation column, the equivalent pressure must be subtracted from the height difference present to estimate the actual effective differential pressure generated. Also, if the starting point of the pipeline will be under vacuum, then its effect on the total differential pressure must also be taken into account when choosing a pipeline. The final selection of pipes is made using differential pressure, taking into account all of the above factors, and not based only on the difference in heights of the start and end points.

hot liquid flow

In process plants, various problems are usually encountered when working with hot or boiling media. The main reason is the evaporation of part of the hot liquid flow, that is, the phase transformation of the liquid into vapor inside the pipeline or equipment. A typical example is the cavitation phenomenon of a centrifugal pump, accompanied by point boiling of a liquid, followed by the formation of vapor bubbles (steam cavitation) or the release of dissolved gases into bubbles (gas cavitation).

Larger piping is preferred due to the reduced flow rate compared to smaller diameter piping at constant flow, resulting in a higher NPSH at the pump suction line. Points of sudden change in flow direction or reduction in pipeline size can also cause cavitation due to pressure loss. The resulting gas-vapor mixture creates an obstacle to the passage of the flow and can cause damage to the pipeline, which makes the phenomenon of cavitation extremely undesirable during the operation of the pipeline.

Bypass pipeline for equipment/instruments

Equipment and devices, especially those that can create significant pressure drops, that is, heat exchangers, control valves, etc., are equipped with bypass pipelines (to be able not to interrupt the process even during maintenance work). Such pipelines usually have 2 shut-off valves installed in line with the installation and a flow control valve in parallel to this installation.

During normal operation, the fluid flow passing through the main components of the apparatus experiences an additional pressure drop. In accordance with this, the discharge pressure for it, created by the connected equipment, such as a centrifugal pump, is calculated. The pump is selected based on the total pressure drop across the installation. During movement through the bypass pipeline, this additional pressure drop is absent, while the operating pump pumps the flow of the same force, according to its operating characteristics. To avoid differences in flow characteristics between the apparatus and the bypass line, it is recommended to use a smaller bypass line with a control valve to create a pressure equivalent to the main installation.

Sampling line

Usually a small amount of fluid is sampled for analysis to determine its composition. Sampling can be carried out at any stage of the process to determine the composition of a raw material, an intermediate product, a finished product, or simply a transported substance such as waste water, heat transfer fluid, etc. The size of the section of pipeline on which sampling takes place usually depends on the type of fluid being analyzed and the location of the sampling point.

For example, for gases under elevated pressure, small pipelines with valves are sufficient to take the required number of samples. Increasing the diameter of the sampling line will reduce the proportion of media sampled for analysis, but such sampling becomes more difficult to control. At the same time, a small sampling line is not well suited for the analysis of various suspensions in which solid particles can clog the flow path. Thus, the size of the sampling line for the analysis of suspensions is highly dependent on the size of the solid particles and the characteristics of the medium. Similar conclusions apply to viscous liquids.

Sampling line sizing typically considers:

• characteristics of the liquid intended for selection;
• loss of the working environment during selection;
• safety requirements during selection;
• ease of operation;
• selection point location.

coolant circulation

High velocities are preferred for lines with circulating coolant. This is mainly due to the fact that the cooling liquid in the cooling tower is exposed to sunlight, which creates the conditions for the formation of an algae-containing layer. Part of this algae-containing volume enters the circulating coolant. At low flow rates, algae begin to grow in the pipeline and after a while create difficulties for the circulation of the coolant or its passage to the heat exchanger. In this case, a high circulation rate is recommended to avoid the formation of algae blockages in the pipeline. Typically, the use of a high circulation coolant is found in the chemical industry, which requires large pipelines and lengths to provide power to various heat exchangers.

Tank overflow

Tanks are equipped with overflow pipes for the following reasons:

• avoidance of fluid loss (excess fluid enters another reservoir, rather than pouring out of the original reservoir);
• preventing leakage of unwanted liquids outside the tank;
• maintaining the liquid level in the tanks.

In all the above cases, the overflow pipes are designed for the maximum allowable flow of liquid entering the tank, regardless of the flow rate of the liquid leaving. Other piping principles are similar to gravity piping, i.e. according to the available vertical height between the start and end points of the overflow piping.

The highest point of the overflow pipe, which is also its starting point, is at the connection to the tank (tank overflow pipe) usually near the very top, and the lowest end point can be near the drain chute near the ground. However, the overflow line can also end at a higher elevation. In this case, the available differential head will be lower.

Sludge flow

In the case of mining, ore is usually mined in hard to reach areas. In such places, as a rule, there is no rail or road connection. For such situations, hydraulic transportation of media with solid particles is considered as the most acceptable, including in the case of the location of mining plants at a sufficient distance. Slurry pipelines are used in various industrial areas to convey crushed solids along with liquids. Such pipelines have proven to be the most cost-effective compared to other methods of transporting solid media in large volumes. In addition, their advantages include sufficient safety due to the lack of several types of transportation and environmental friendliness.

Suspensions and mixtures of suspended solids in liquids are stored in a state of periodic mixing to maintain uniformity. Otherwise, a separation process occurs, in which suspended particles, depending on their physical properties, float to the surface of the liquid or settle to the bottom. Agitation is provided by equipment such as a stirred tank, while in pipelines, this is achieved by maintaining turbulent flow conditions.

Reducing the flow rate when transporting particles suspended in a liquid is not desirable, since the process of phase separation may begin in the flow. This can lead to blockage of the pipeline and a change in the concentration of the transported solids in the stream. Intense mixing in the flow volume is promoted by the turbulent flow regime.

On the other hand, an excessive reduction in the size of the pipeline also often leads to blockage. Therefore, the choice of pipeline size is an important and responsible step that requires preliminary analysis and calculations. Each case must be considered individually as different slurries behave differently at different fluid velocities.

Pipeline repair

During the operation of the pipeline, various kinds of leaks may occur in it, requiring immediate elimination in order to maintain the system's performance. Repair of the main pipeline can be carried out in several ways. This can be as much as replacing an entire pipe segment or a small section that is leaking, or patching an existing pipe. But before choosing any method of repair, it is necessary to conduct a thorough study of the cause of the leak. In some cases, it may be necessary not only to repair, but to change the route of the pipe to prevent its re-damage.

The first stage of repair work is to determine the location of the pipe section requiring intervention. Further, depending on the type of pipeline, a list of the necessary equipment and measures necessary to eliminate the leak is determined, and the necessary documents and permits are collected if the pipe section to be repaired is located on the territory of another owner. Since most pipes are located underground, it may be necessary to extract part of the pipe. Next, the coating of the pipeline is checked for general condition, after which part of the coating is removed for repair work directly with the pipe. After repair, various verification activities can be carried out: ultrasonic testing, color flaw detection, magnetic particle flaw detection, etc.

While some repairs require the pipeline to be shut down completely, often only a temporary shutdown is sufficient to isolate the repaired area or prepare a bypass. However, in most cases, repair work is carried out with a complete shutdown of the pipeline. Isolation of a section of the pipeline can be carried out using plugs or shut-off valves. Next, install the necessary equipment and carry out direct repairs. Repair work is carried out on the damaged area, freed from the medium and without pressure. At the end of the repair, the plugs are opened and the integrity of the pipeline is restored.

Steam pipelines are mounted on objects:
1. enterprises using steam for technological steam supply (steam-condensate systems at reinforced concrete products plants, steam-condensate systems at fish processing plants, steam-condensate systems at dairy plants, steam-condensate systems at meat processing plants, steam-condensate systems at pharmaceutical plants, steam/condensate systems in cosmetics factories, steam/condensate systems in laundry factories)
2. in systems of steam heating of factories and industrial enterprises. It was used in the past but is still used by many enterprises. As a rule, factory boiler houses were built according to standard drawings using DKVR boilers for technological steam supply and heating. At present, even at those enterprises and factories where the need for technological steam has become absent, heating is still carried out by steam. In some cases, it is inefficient without condensate return.
3. in thermal power plants to supply steam to steam turbines to generate electricity.

Steam pipelines serve to transfer steam from the boiler house (steam boilers and steam generators) to steam consumers.

The main elements of the steam pipeline are:
1.steel pipes
2. connecting elements (bends, bends, flanges, expansion joints)
3. shut-off and shut-off and control valves (gate valves, gates, valves)
4. fittings for removing condensate from steam pipelines - steam traps, separators,
5. Devices for reducing steam pressure to the required value - pressure regulators
6. Mechanical mud filters with replaceable filter elements for steam cleaning in front of pressure reducing valves.
7. fastening elements - sliding supports and fixed supports, suspensions and fastenings,
8. thermal insulation of steam pipelines - temperature-resistant basalt mineral wool Rockwool or Parok is used, asbestos fluff cord is also used.
9. control and measuring devices (KIP) - pressure gauges and thermometers.

Requirements for the design, construction, materials, manufacture, installation, repair and operation of steam pipelines are regulated by regulatory documents.
- Pipelines transporting water vapor with a working pressure of more than 0.07 MPa (0.7 kgf / cm2) are subject to the Rules for the Design and Safe Operation of Steam and Hot Water Pipelines (PB 10-573-03).
- Calculation for the strength of such steam pipelines is carried out in accordance with the "Standards for calculating the strength of stationary boilers and pipelines of steam and hot water" (RD 10-249-98).

Steam pipelines are routed taking into account the technical feasibility of laying along the shortest laying path to minimize heat and energy losses due to the length of the laying and the aerodynamic resistance of the steam path.
The steam pipeline elements are connected by welding joints. Installation of flanges during the installation of steam pipelines is allowed only for connecting steam pipelines with fittings.

Supports and suspensions of steam pipelines can be movable and fixed. Lyre-shaped or U-shaped expansion joints are installed between adjacent fixed supports in a straight section, which reduce the consequences of deformation of the steam pipeline under the influence of heating (1 m of the steam pipeline lengthens by an average of 1.2 mm when heated by 100 °).
Steam pipelines are mounted with a slope and condensate traps are installed at the lowest points to drain the condensate that forms in the pipes. The horizontal sections of the steam pipeline must have a slope of at least 0.004. At the entrance of the steam pipelines to the workshops, at the exit of the steam pipelines from the boiler rooms, in front of the steam-consuming equipment, steam separators are installed complete with condensate traps.
All elements of steam pipelines must be thermally insulated. Thermal insulation protects personnel from burns. Thermal insulation prevents excessive condensation.
Steam pipelines are a hazardous production facility and must be registered with specialized registration and supervisory authorities (in Russia - the territorial department of Rostekhnadzor). A permit for the operation of newly installed steam pipelines is issued after their registration and technical examination.

The wall thickness of the steam pipeline, according to the strength condition, must be at least where
P - design steam pressure,
D - outer diameter of the steam pipeline,
φ - design coefficient of strength, taking into account welds and weakening of the section,
σ - allowable stress in the metal of the steam pipeline at the design temperature of the steam.

The diameter of the steam pipeline is usually determined based on the maximum hourly steam flow rates and the allowable pressure and temperature losses by the velocity method or the pressure drop method. Speed ​​method.
Given the steam flow rate in the pipeline, its inner diameter is determined from the mass flow equation, for example, by the expression:
D= 1000 √ , mm
Where G is the mass flow rate of steam, t/h;
W-velocity of steam, m/s;
ρ- vapor density, kg/m3.

The choice of steam velocity in steam lines is important.
According to SNiP 2-35-76, steam speeds are recommended no more than:
- for saturated steam 30 m/s (with pipe diameter up to 200 mm) and 60 m/s (with pipe diameter over 200 mm),
- for superheated steam 40 m/s (with pipe diameter up to 200 mm) and 70 m/s (with pipe diameter over 200 mm).

Factories for the production of steam equipment recommend that when choosing the diameter of the steam pipeline, the steam velocity should be within 15-40 m / s. Mixed steam/water heat exchanger suppliers recommend a maximum steam velocity of 50 m/s.
There is also a pressure drop method based on the calculation of pressure losses caused by the hydraulic resistance of the steam pipeline. To optimize the choice of the steam pipeline diameter, it is also advisable to evaluate the steam temperature drop in the steam pipeline, taking into account the thermal insulation used. In this case, it becomes possible to choose the optimal diameter in relation to the pressure drop of the steam to the decrease in its temperature per unit length of the steam pipeline (there is an opinion that it is optimal if dP / dT = 0.8 ... 1.2).
The right choice of a steam boiler and the steam pressure that it provides, the choice of configuration and diameters of steam pipelines, steam equipment by class and by manufacturers, these are the components of a good operation of the steam-condensate system in the future.

The calculation formula is as follows:

where:
D - pipeline diameter, mm

Q - flow rate, m3/h

v - allowable flow velocity in m/s

The specific volume of saturated steam at a pressure of 10 bar is 0.194 m3/kg, which means that the volumetric flow rate of 1000 kg/h of saturated steam at 10 bar will be 1000x0.194=194 m3/h. The specific volume of superheated steam at 10 bar and a temperature of 300°C is 0.2579 m3/kg, and the volume flow with the same amount of steam will already be 258 m3/h. Thus, it can be argued that the same pipeline is not suitable for transporting both saturated and superheated steam.

Here are some examples of pipeline calculations for different media:

1. Wednesday - water. Let's make a calculation at a volume flow rate of 120 m3/h and a flow velocity v=2 m/s.
D= =146 mm.
That is, a pipeline with a nominal diameter of DN 150 is required.

2. Medium - saturated steam. Let's make a calculation for the following parameters: volume flow - 2000 kg / h, pressure - 10 bar at a flow rate of 15 m / s. In accordance with the specific volume of saturated steam at a pressure of 10 bar is 0.194 m3/h.
D= = 96 mm.
That is, a pipeline with a nominal diameter of DN 100 is required.

3. Medium - superheated steam. Let's make a calculation for the following parameters: volume flow - 2000 kg/h, pressure - 10 bar at a flow rate of 15 m/s. The specific volume of superheated steam at a given pressure and temperature, for example, 250°C, is 0.2326 m3/h.
D= =105 mm.
That is, a pipeline with a nominal diameter of DN 125 is required.

4. Medium - condensate. In this case, the calculation of the diameter of the pipeline (condensate pipeline) has a feature that must be taken into account in the calculations, namely: it is necessary to take into account the share of steam from unloading. Condensate, passing through the steam trap, and getting into the condensate pipeline, is unloaded (that is, condensed) in it.
The share of steam from unloading is determined by the following formula:
Share of steam from unloading = , where

h1 - enthalpy of condensate in front of the steam trap;
h2 - enthalpy of condensate in the condensate network at the corresponding pressure;
r is the heat of vaporization at the corresponding pressure in the condensate network.
According to a simplified formula, the share of steam from unloading is determined as the temperature difference before and after the steam trap x 0.2.

The formula for calculating the diameter of the condensate line will look like this:

D= , where
DR - share of condensate discharge
Q - amount of condensate, kg/h
v” - specific volume, m3/kg
Let's calculate the condensate pipeline for the following initial values: steam consumption - 2000 kg/h with pressure - 12 bar (enthalpy h'=798 kJ/kg), unloaded to a pressure of 6 bar (enthalpy h'=670 kJ/kg, specific volume v” =0.316 m3/kg and heat of condensation r=2085 kJ/kg), flow velocity 10 m/s.

Share of steam from unloading = = 6,14 %
The amount of unloaded steam will be: 2000 x 0.0614=123 kg/h or
123x0.316= 39 m3/h

D= = 37 mm.
That is, a pipeline with a nominal diameter of DN 40 is required.

PERMISSIBLE FLOW RATE

The flow rate is an equally important indicator in the calculation of pipelines. When determining the flow rate, the following factors must be taken into account:

Pressure loss. At high flow rates, smaller pipe diameters can be selected, but there is a significant pressure loss.

pipeline cost. A low flow rate will result in larger piping diameters being selected.

Noise. A high flow rate is accompanied by an increased noise effect.

Wear. High flow rates (especially in the case of condensate) lead to pipe erosion.

As a rule, the main cause of problems with the removal of condensate is precisely the underestimated diameter of the pipelines and the wrong selection of condensate traps.

After the steam trap, particles of condensate, moving through the pipeline at the speed of steam from unloading, reach the turn, hit the wall of the turn, and accumulate at the turn. After that, they are pushed along the pipelines at high speed, leading to their erosion. Experience shows that 75% of leaks in condensate lines occur in pipe bends.

In order to reduce the likely occurrence of erosion and its negative impact, it is necessary to take a flow velocity of about 10 m/s for systems with float steam traps for calculation, and 6 -8 m/s for systems with other types of steam traps. When calculating condensate pipelines in which there is no steam from unloading, it is very important to make calculations, as for water pipelines with a flow rate of 1.5 - 2 m / s, and in the rest, take into account the share of steam from unloading.

The table below shows the flow rates for some media:

It can be seen from formula (6.2) that pressure losses in pipelines are directly proportional to the density of the coolant. The range of temperature fluctuations in water heating networks. Under these conditions, the density of water is .

The density of saturated steam at is 2.45 i.e. about 400 times smaller.

Therefore, the allowable steam velocity in pipelines is assumed to be much higher than in water heating networks (about 10-20 times).

A distinctive feature of the hydraulic calculation of the steam pipeline is the need to take into account when determining hydraulic losses change in vapor density.

When calculating steam pipelines, the steam density is determined depending on the pressure according to the tables. Since the steam pressure, in turn, depends on hydraulic losses, the calculation of steam pipelines is carried out by the method of successive approximations. First, the pressure losses in the section are set, the vapor density is determined from the average pressure, and then the actual pressure losses are calculated. If the error is unacceptable, recalculate.

When calculating steam networks, the steam flow rates, its initial pressure and the required pressure in front of installations using steam are given.

The specific disposable pressure loss in the line and in separate calculated sections, , is determined by the disposable pressure drop:

, (6.13)

where is the length of the main settlement highway, m; the value for branched steam networks is 0.5.

The diameters of the steam pipelines are selected according to the nomogram (Fig. 6.3) with equivalent pipe roughness mm and vapor density kg / m 3. Valid values R D and steam velocities are calculated from the average actual steam density:

where and values R and , found from Fig. 6.3. At the same time, it is checked that the actual steam velocity does not exceed the maximum allowable values: for saturated steam m/s; for superheated m/s(values ​​in the numerator are accepted for steam pipelines with a diameter of up to 200 mm, in the denominator - more than 200 mm, for taps these values ​​can be increased by 30%).

Since the value at the beginning of the calculation is unknown, it is given with subsequent refinement using the formula:

, (6.16)

where , the specific gravity of the steam at the beginning and end of the section.

test questions

1. What are the tasks of hydraulic calculation of heat network pipelines?

2. What is the relative equivalent roughness of the pipeline wall?

3. Give the main design dependencies for the hydraulic calculation of pipelines of a water heating network. What is the specific linear pressure loss in the pipeline and what is its dimension?

4. Give the initial data for the hydraulic calculation of an extensive water heating network. What is the sequence of individual settlement operations?

5. How is the hydraulic calculation of the steam heating network performed?