Some standard content:
Calculation of pipeline pressure drop
HG/T20570.7-95
Compiled by: China Chengda Chemical Engineering Co., Ltd. China Huanqiu Chemical Engineering Co., Ltd.
China Tianchen Chemical Engineering Co., Ltd.
Approved by: Ministry of Chemical Industry
Implementation date: September 1, 1996 Compiled by:
Liu Jingfang of China Chengda Chemical Engineering Co., Ltd. (Chapter 1, Chapter 2, Chapter 6) Zhao Min of China Huanqiu Chemical Engineering Co., Ltd. (Chapter 3) Lv Wenpu (Chapter 4) Teng Keli (Chapter 5)||tt| |China Tianchen Chemical Engineering Corporation Tang Yinong (Chapter 7) Reviewer:
China Chengda Chemical Engineering Corporation Zeng Qingxiang (Chapter 1, Chapter 2, Chapter 6) China Huanqiu Chemical Engineering Corporation Wang Qingyu (Chapter 3, Chapter 4) Yang Yi Tan Chong, Third Design Institute of the Ministry of Chemical Industry
System Design Technology Center of the Ministry of Chemical Industry
Sheng Qingping Gong Renwei
1 Single-phase flow (incompressible fluid)
1.1 Brief description
1.1.1 This regulation applies to the calculation of the pressure drop of Newtonian single-phase fluid flowing in the pipeline. When the working pressure of each major equipment has been basically determined by the chemical process specialty, the hydraulic calculation of the system is carried out. According to the requirements of the chemical process, the pressure drop of the pipeline (including pipe sections, valves, control valves, flow meters and pipe fittings, etc.) between the main equipment is calculated to control the total pressure drop of the system within the given working pressure range. On this basis, the pipeline size, equipment connection port size, control valve and flow meter allowable pressure drop, and the discharge pressure of the safety valve and bursting disc are determined. 1.1.2 A Newtonian fluid is a fluid in which the shear stress is proportional to the velocity gradient and the viscosity is its proportional coefficient. All gases are Newtonian fluids. In addition to liquids and muds composed of substances such as polymers, most liquids are also Newtonian fluids.
1.2 Calculation method
1.2.1 Precautions
1.2.1.1 Safety factor
The safety factor is not considered in the calculation method. When calculating, a reasonable value should be selected according to the actual situation. Usually, for steel pipes that need to be used for an average of 5 to 10 years, adding a safety factor of 20% to 30% to the friction coefficient can adapt to changes in its roughness conditions; after 5 to 10 years, the conditions tend to remain stable, but may also deteriorate further. This coefficient does not take into account the increased pressure drop due to the increase in flow, so a safety factor of 10% to 20% must be added. The regulations determine the friction pressure drop of the system by a coefficient of 1.15 times the calculation result of the friction pressure drop, but the static pressure drop and other pressure drops are not multiplied by the coefficient. 1.2.1.2 Calculation accuracy
In engineering calculations, it is advisable to take the two significant figures after the decimal point as the calculation result. For each calculation using equivalent length to calculate the pressure drop, the significant figures taken in the final result shall not exceed the two decimal points. 1.2.2 Pipe diameter
1.2.2.1 General principles for determining pipe diameter
(1) The pipe diameter should be determined according to the design conditions. When necessary, a margin of 15% to 25% of the pressure drop under the design conditions can be allowed, except for the following situations: 151
The size of the discharge pipe of the fuel oil circulation pipeline system should take into account a certain circulation volume: 6. The pipes of pumps, compressors and blowers should be sized according to the maximum process flow (at the flow rate allowed by the equipment design), and not according to the maximum capacity of the machine; the size of the pipes used intermittently (such as the start-up bypass pipe) should be determined according to the possible pressure difference. c.
（2）Within the allowable pressure drop range, the economic pipe diameter should be used. The allowable pressure drop range of fluids in certain pipelines is shown in Table 1.2.2-1.
For certain fluids that are corrosive and abrasive to the pipe wall, the pipe diameter is determined by the flow rate. The flow rate is shown in Table 1.2.2-(3)
1.2.2.2 Pipe diameter calculation
The calculation formula is as follows:
)0.5-18.8(
d-pipe inner diameter, mm,
V-fluid volume flow, m/h;
u-fluid average Flow rate, m/s
W—fluid mass flow, kg/h;
o—fluid density, kg/m.
The pipe diameter can usually be found from Figure 1.2.2-1 or Figure 1.2.2-2. 152
(1.2.2-1)
Inner diameter of pipe (d)
Volume flow (V.)
+50000
20000-
No. 400
-30000
Figure 1.2.2-1
Flow velocity (u)
Flow velocity, flow rate, pipe diameter calculation diagram
Volume flow rate (V.)
E100000
F20000
Economic pipe diameter)
Density (p)
Viscosity）
5000 hands 2000
d(stagnation)
Figure 1.2.2-2 Economic pipe diameter diagram for liquids and gases (P<1000kPa) Serial number
Permissible pressure drop range for fluids in certain pipelines Pipeline types and conditions
Steam P=6.4~10MPa (table)
Main pipe P<3.5MPa (table)||tt ||P≥3.5MPa(table)
Branch pipeP<3.5MPa(table)
P≥3.5MPa(table)
Exhaust pipe
Large compressor>735kW
Small compressor inlet and outlet
Compressor circulation pipeline and compressor outlet pipe safety valve
Inlet pipe (connection point to valve)
Outlet pipe
Outlet main pipe
General low-pressure process gas
General high-pressure process gas
Tower outlet pipe
Water main pipe
Water branch pipe
Inlet pipe
Outlet pipe<34m/h
34~110m/h
>110m/h
Table 1.2.2-1||tt ||Pressure drop range kPa (100m pipe length)
Maximum 3% of set pressure
Maximum 10% of set pressure
Maximum 7.5% of set pressure
Maximum 8
35~138
Flow rate of some fluids that are corrosive and abrasive to the pipe wall Medium conditions
Caustic soda solution (concentration>5%)
Concentrated sulfuric acid (concentration>80%)
Phenol water (containing phenol>1%)
Phenol-containing steam
Pipe diameter ≥900
Pipe diameter <900
Pipeline material
Cement or asphalt lined steel pipe
Cement or asphalt lined steel pipe
Note: When the pipeline is made of nickel-containing stainless steel, the flow rate can sometimes be increased to more than 10 times the flow rate in the table. 1.2.3 Pipelines
1.2.3.1 Simple Pipelines
Any pipeline without branches is called a simple pipeline. (1)
For a simple pipeline with a constant diameter, the flow rate of the fluid through the entire pipeline remains constant. (2) A simple pipeline composed of pipe sections with different diameters is called a series pipeline. a.
The flow rate through each pipe section remains constant. For incompressible fluids, Vr-V-V2-Vf3.....
The pressure drop of the entire pipeline is equal to the sum of the pressure drops of each pipe section, that is, AP-AP+APa+AP.+...
1.2.3.2 Complex Pipelines
Table 1.2.2-2
Maximum Allowable Flow Rate
(1.2.3-1)
(1.2.3-2)
Any pipeline with branches is called a complex pipeline. Complex pipelines can be considered as composed of several simple pipelines. (1) Parallel pipelines branch off from the main pipeline at a certain point and then merge into a main pipeline. α. The pressure drop of each branch is equal, that is,
AP-APi=AP,-AP3=.
When calculating the pressure drop, only one of the pipes needs to be calculated. 6.
The sum of the flow rates of each branch is equal to the flow rate of the main pipeline, that is, Vr=Vn+V+V+
(1.2.3—3)
(1.2.3—4)
Branch pipelines branch off from the main pipeline at a certain point or the branch branch off again without merging into a main pipeline (2)
a. The flow rate of the main pipeline is equal to the sum of the flow rates of each branch; b. The energy required for the branch pipe is calculated based on the branch pipe with the largest energy consumption: C. For more complex branch pipes, they can be divided into several simple pipes at the branch points and calculated separately according to the general simple pipes.
1.2.4 Calculation of pipeline pressure drop
1.2.4.1 Overview
(1) Pipeline pressure drop is the sum of pipeline friction pressure drop, static pressure drop and velocity pressure drop. Pipeline friction pressure drop includes the pressure drop of straight pipes, pipe fittings and valves, as well as the local pressure drop caused by orifice plates, sudden expansion, sudden contraction and pipe ports; static pressure drop is caused by the difference in elevation between the beginning and end of the pipeline; velocity pressure drop refers to the pressure drop caused by the different flow rates of the fluid at the beginning and end of the pipeline. (2) The principle of segmented calculation for complex pipelines is usually to disassemble the branch pipe and the main pipe (or the place where the pipe diameter changes). Pipe fittings (such as reducing tees) should be divided on the main pipe, and the equivalent length should be selected according to the main pipe diameter. The main pipe length is calculated based on the farthest equipment.
(3) For pipelines whose actual pipe diameter is reduced due to scaling, calculation should be based on the actual pipe diameter. Reynolds number is calculated as follows:
=354Ve
dup=354
Reynolds number, dimensionless;
average velocity of fluid, m/s;
inner diameter of pipe, mm;
μ-viscosity of fluid, mPa·s;
mass flow rate of fluid, kg/h,
volume flow rate of fluid, m\/h,
density of fluid, kg/m.
(4) Pipe wall roughnesswwW.bzxz.Net
Pipe wall roughness usually refers to absolute roughness (e) and relative roughness (e/d). (1.2. 4-1)
Absolute roughness refers to the average height of the protruding part of the inner wall of the pipe. When selecting, factors such as corrosion, abrasion, scaling and usage of the pipe wall by the fluid should be considered. For example, for seamless steel pipes, when the fluid is a less corrosive fluid such as petroleum gas, saturated steam, and dry compressed air, the absolute roughness e can be selected as 0.2mm; when conveying water, if it is condensate (with air), e=0.5mm; pure water takes e=0.2mm; untreated water takes e=0.3~0.5mm; 157
For highly corrosive fluids such as acids and alkalis, e-1mm or larger can be selected. For pipes with the same absolute roughness, the smaller the diameter, the greater the impact on the friction coefficient. Therefore, the ratio of e to d s/d is used to represent the pipe wall roughness, which is called relative roughness. When flowing, the pipe wall roughness has a great influence on the friction coefficient of fluid flow.
The relationship between the friction coefficient (a), Reynolds number (Re) and the relative roughness (e/d) of the pipe wall is shown in Figure 1.2.4-1; under the condition of perfect flow, the relationship between the diameter (d) of a clean new pipe and the absolute roughness (e) is shown in Figure 1.2.4-2.
The absolute roughness of some industrial pipelines is shown in Table 1.2.4-1; the relative roughness can be found in Figure 1.2.4-2. Absolute roughness of some industrial pipes
(5) Flow pattern
Pipe types
Seamless brass pipes, copper pipes and lead pipes
New seamless steel pipes or galvanized iron pipes
New cast iron pipes
Seamless steel pipes with slight corrosion
Seamless steel pipes with significant corrosion
Old cast iron pipes
Steel plate pipes
Clean glass pipes
Rubber hoses
Wooden pipes
Clay drain pipes
Smooth joints Cement pipe
Asbestos cement pipe
Table 1.2.4-1
Absolute roughness (e))
0.01~0.05
0.25~0.42
Above 0.5
Above 0.85
0.0015~0.01
0.01~0.03
0.25~1.25
The flow pattern of fluid in the pipeline is divided into laminar flow and flow. There is an unstable critical zone between laminar flow and smooth flow. The smooth flow zone can be divided into transition zone and complete smooth flow zone. Most of the fluid flow patterns in industrial production belong to the transition zone, as shown in Figure 1.2.4-1.
The criterion for determining the flow pattern of fluid in the pipeline is the Reynolds number (Re). 158
500000-号000-号
aot89s
S000o0
200℃
繁等吸
A64/Re
600°0
0.0000054
151001251502
Riveted steel pipe
Concrete main pipe
7501000
15002500
.200250
12502000
Pipe diameter (d)
Figure 1.2.4-2
Roughness of clean new pipe0000054
151001251502
Riveted steel pipe
Concrete main pipe
7501000
15002500
.200250
12502000
Pipe diameter (d)
Figure 1.2.4-2
Roughness of clean new pipe0000054
151001251502
Riveted steel pipe
Concrete main pipe
7501000
15002500
.200250
12502000
Pipe diameter (d)
Figure 1.2.4-2
Roughness of clean new pipe
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