HG/T 20570.11-1995 Selection of thermal insulation and heat preservation types
Some standard content:
Selection of heat insulation and thermal insulation types
HG/T20570.1195
Compiled by: China Wuhuan Chemical Engineering Corporation Approved by: Ministry of Chemical Industry
Implementation date: September 1996
Compiled by:
China Wuhuan Chemical Engineering Corporation
Auditors:
Luo Yining, Wu Qiying
China Wuhuan Chemical Engineering Corporation
Wu Bingyong
Chemical Industry Ministry Process System Design Technology Center Feng Shuyuan Gong Renwei 1.0.1 Types of heat insulation and thermal insulation
1 Types and professional division of labor
The heat insulation (also called thermal insulation) of equipment and pipelines generally refers to heat insulation, cold insulation, personal protection (anti-scalding), anti-freezing, etc. Thermal insulation generally refers to heating protection insulation, such as heating pipes, jacketed pipes, etc. 1.0.2 Professional division of labor for thermal insulation and heat preservation design 1.0.2.1 Chemical process specialty
Chemical process specialty proposes requirements for thermal insulation (cold insulation) and heat preservation (including insulation type and heat source medium) in the process data sheets of equipment and pipelines.
1.0.2.2 Pipeline material specialty
Pipeline material specialty proposes in the design regulations for thermal insulation and heat preservation (or thermal insulation and heat preservation instructions): (1) The thickness of the thermal insulation (cold insulation) layer for thermal insulation, cold insulation, and personal protection (anti-scalding) of equipment and pipelines at different temperatures and diameters. Except for those with special thermal insulation requirements in the process. (2) Relevant data on heating and heat preservation of equipment and pipelines, such as the number of heating pipes, the diameter of heating pipes, the number and specifications of electric heating tapes, etc.
(3) A summary list of materials required for thermal insulation (cold insulation) and heat preservation. 1.0.2.3 Process System Specialty
(1) The data sheet of the common material system equipment in the proposed device should contain the requirements for the equipment's thermal insulation (cold) and thermal insulation (including thermal insulation type and thermal insulation heat source medium). (2) In the fifth unit of the pipeline number on the PI diagram, the thermal insulation (cold) and thermal insulation type shall be marked according to the specified text code.
(3) In the thermal insulation type and thermal insulation thickness columns in the pipeline naming table, fill in the thermal insulation (cold), thermal insulation type and thickness.
(4) Submit a summary table of equipment thermal insulation conditions, and attach a thermal insulation symbol diagram of the equipment when necessary. For the content and format of the summary table and symbol diagram, refer to Sections 1.19 and 1.18 of the industry standard "Regulations on the Content of Documents Submitted by Process System Specialty" (HG20558.2-93). 381
2.0.1 Selection scope
2 Selection of insulation type
All equipment, pipelines, pipe fittings, valves, etc. (hereinafter referred to as pipelines) with any of the following conditions must take insulation measures.
2.0.1.1 Equipment and pipelines with surface temperature greater than 50℃ and external surface temperature less than or equal to 50℃ according to production process requirements (except equipment and pipelines that do not require or cannot be insulated in the process). 2.0.1.2 Equipment and pipelines with medium freezing point higher than ambient temperature. 2.0.1.3 Equipment and pipelines with surface temperature exceeding 60℃ that do not require insulation and require frequent maintenance but cannot take other measures to prevent scalding should be equipped with anti-scalding insulation layers within the following ranges: (1) The height from the ground or working platform is less than 2.1m (2) The distance from the operating platform is less than 0.75m; 2.0.1.4 It is necessary to prevent or reduce the cold loss of cold medium and cold-carrying medium during production and transportation. 2.0.1.5 It is necessary to prevent or reduce the temperature rise of cold medium and cold-carrying medium during production and transportation. 2.0.1.6 It is necessary to prevent condensation on the outer wall surface of low-temperature equipment and pipelines. 2.0.1.7 Condensate is generated due to the influence of external temperature, thereby corroding equipment and pipelines. 2.0.1.8 When the noise emitted by equipment and pipelines is greater than the allowable noise level specified in the project, it is necessary to wrap the equipment and pipelines with sound insulation materials (usually thermal insulation materials) to reduce the noise. 2.0.2 Selection of thermal insulation layer thickness
The thickness of the thermal insulation layer of equipment and pipelines should be selected based on the thermal insulation requirements of the equipment in the process data table published by the chemical process and process system majors, the medium temperature and other characteristics, combined with the "Thermal Insulation Design Regulations" published by the pipeline material major. Except for those with special thermal insulation requirements for the process. 382
3 Selection of heat tracing and insulation
When heat insulation cannot meet the thermal insulation requirements of process materials, heat tracing and insulation are generally used. Heat tracing and heat preservation usually include steam tracing, hot water tracing, heat transfer oil tracing and electric belt tracing. 3.0.1 Steam tracing heat preservation
3.0.1.1 Scope of application of steam tracing heat preservation When the freezing point and viscosity of the medium in the equipment and pipeline are large, the temperature that the process medium needs to maintain is high, or the explosion-proof level of the area where the equipment and pipeline are located is high, and the corrosiveness and heat sensitivity of the medium are strong, the heat preservation form of steam tracing should be selected.
3.0.1.2 Selection of heat source medium
Steam tracing usually uses saturated steam as the heat source medium. The steam pressure is usually determined by the steam temperature, and the steam temperature is determined according to the insulation requirements of the process medium. In general, the steam should be higher than the temperature of the insulated medium. The selected steam temperature should take into account the characteristics of the process material, such as freezing point, freezing point, etc. The steam pressure used is generally equal to or lower than 1300kPa, commonly 350~1000kPa, and the minimum is 200kPa. When the pressure is too low, the pressure of steam will be reduced due to the resistance of the pipeline, which will produce condensate. Therefore, the length of the steam tracing pipe is relatively short. Steam tracing pipes with a pressure lower than 200 kPa are generally not used in engineering. The steam heat source should not be interrupted during operation and when starting or stopping. 3.0.1.3 Design requirements for heating and insulation of steam tracing pipes (1) Design requirements for heating and insulation of equipment tracing pipes When the medium in the equipment is acid or other severely corrosive materials, the equipment should be heated externally if it needs to be heated and insulated. For other materials, external heating or internal heating can be used. The process system major calculates the heating length and spacing of the tracing pipes of the equipment according to the requirements for heating and insulation proposed in the equipment process data sheet published by the chemical process major. (2) Design requirements for heating and insulation of pipeline tracing pipes Material pipelines generally use external heating. The process system major shall specify the number of steam tracing pipes of the pipe in the "Pipeline Nomenclature Table Description" based on the conditions of the chemical process major and the number of heating pipes required for the heating and insulation pipeline proposed by the pipeline material major and other requirements. 3.0.1.4 Calculation of heat insulation for steam tracing pipes
(1) Calculation of heat insulation for steam tracing pipes for equipmenta. Selection of the diameter of the equipment tracing pipes
The specifications of the equipment tracing pipes usually adopt pipes with a diameter of DN15 to DN25. If necessary, a larger diameter can also be used.
Calculation of heat loss of the equipment tracing pipes after insulationb.
(α) Heat transfer coefficient from the surface of the thermal insulation layer to the surrounding air (αo)αgα+ak
Heat transfer coefficient from the surface of the thermal insulation layer to the surrounding air, W/m2·℃); radiation heat transfer coefficient of the thermal insulation layer, W/(m·℃) Convective heat transfer coefficient, W/(m.℃). Radiation heat transfer coefficient (αt)
[+273)(+273)
-external surface temperature of thermal insulation layer, ℃;(3.0.1-1)
(3.0.1-2)
ta-ambient temperature, ℃ (for outdoor year-round operation, the average annual average temperature of all previous years is taken; for seasonal operation, the average daily average temperature of all previous years is taken, or selected according to engineering standards; for indoor operation, 25℃ is taken or selected according to engineering standards); C-radiation coefficient, W/(m2·℃*).
Thin iron or painted surface C=5.23, aluminum plate surface C=0.33Convection heat transfer coefficient (αk)
①In the case of no wind indoors
V397+ter
The average temperature of the thermal insulation layer, ℃;
（a+t)
Di——Outer diameter of the thermal insulation layer, m. If the shape of the equipment is not circular, then D, where
P-outer circumference of the cross section, m
Yuan—pi (Yuan=3.14).
The remaining symbols are the same as those in formula (3.0.1-1) and formula (3.0.1-2). ② In the case of wind outdoors, if WD, < 0.8m/s, then α = 4.04×Wo a18, if WD, > 0.8m/s, then α = 4.24×, W = wind speed, m/s. The average wind speed in winter is used for heat insulation, and the average wind speed in summer is used for cold insulation, or selected according to engineering standards. The remaining symbols are the same as those in formula (3.0.1-1) to formula (3.0.1-3). ③ In engineering calculations, the following simple calculation method can also be used to determine the heat transfer coefficient from the surface of the insulation layer to the surrounding air. When indoors, αg = 9.76 + 0.07 (t, -t) - generally take tt = 15 ~ 20 ℃
Outdoors, % = % + 6.97VW
For thermal insulation or heating protection insulation structure, generally α = 11.62W/(m2.℃) (b) Heat transfer coefficient of heat loss (K)
K - heat transfer coefficient of heat loss, W/(m2·℃); a
(3.0.1-6)|| tt||(3.0.1-7)
(3.0.1-8）
The heat transfer coefficient of the air between the outer wall of the equipment and the inner space of the thermal insulation layer, W/(m2:℃), in general engineering calculations, αi=11.62~13.95W/(m2.℃); 02—thickness of the thermal insulation layer, m;
in2—thermal conductivity of the thermal insulation layer, W/(m·℃). The remaining symbols are the same as those in formula (3.0.1-1) to formula (3.0.1-7). (c) Heat transfer temperature difference of heat loss (△t)
The heat transfer of the medium inside the thermal insulation equipment to the outer wall is generally negligible, so the temperature of the outer wall of the equipment (t) and the working temperature inside the equipment (t) can be regarded as the same.
At=tw-ta-t
At-heat transfer temperature difference of heat loss, ℃;
external wall temperature of insulation equipment, ℃
(3.0.1—9)
-working temperature inside insulation equipment, ℃. The remaining symbols are the same as those in formula (3.0.1-1) and formula (3.0.1-8). (d) Heat loss load (Q)
QK·F·At
Q-heat loss load, W;
F-surface area of equipment, m.
The remaining symbols are the same as those in formula (3.0.1-1) to formula (3.0.1-9). Calculate the length of the heating pipe (L)
(a) Heat transfer coefficient between the heating pipe and the thermal insulation equipment (K,) Ki=
1+8+1+1
K,-Heat transfer coefficient between the heating pipe and the thermal insulation equipment, W/(m2℃)(3.0.1-10)
(3.0.1-11)
αz--Steam condensation heat transfer coefficient in the heating pipe, generally taken as 11622.50W/(m2.℃); 8The wall thickness of the heating pipe, m;
In-Thermal conductivity of the heating pipe, W/(m·℃)a3
-Heat transfer coefficient from the steam heating pipe to the air in the thermal insulation layer, W/(m?.℃); Heat transfer coefficient from the air in the thermal insulation layer to the heated equipment, W/(m?·℃). The empirical data of α3 and α4 are shown in Table 3.0.1-1~2. Heat transfer coefficient (α) from steam tracing pipe to air in thermal insulation layer Table 3.0.1-1 Steam temperature (t)
Nominal diameter of tracing pipe
Heat transfer coefficient (αa) from air in thermal insulation layer to heated equipment ℃
Steam temperature (t)
Heat transfer coefficient (αa)
（6）Heat transfer temperature difference (△ti) between tracing pipe and thermal insulation equipment 151
Table 3.0.1-2
From the above, it can be seen that the outer wall temperature (t) of the equipment and the working temperature (t) inside the equipment can be regarded as the same. Atit,-twt-t
t—The working temperature of steam in the tracing pipe, ℃. The remaining symbols are the same as those in formula (3.0.1-1) to formula (3.0.1-11). (c) Heating pipe area (F)
The symbols are the same as those in (3.0.1-1) to (3.0.1-12). (d) Heating pipe length (L)
2-r-d
-Heating pipe length, m;
Outer radius of heating pipe, m;
d-Outer diameter of heating pipe, m.
The remaining symbols are the same as those in (3.0.1-1) to (3.0.1-13). Precautions for using this calculation method
(a) The above method is applicable when there is an air layer between the heating pipe and the wall of the insulated equipment. The outer diameter of the insulated equipment (cylindrical)>1m. (6)
Calculation example of equipment heating pipe
Calculate the length of the heating pipe of a certain equipment
List the known conditions
The diameter of the insulation equipment is 400mm, and the height is about 3000mm; the material temperature in the equipment is 160℃;
According to the engineering standard ambient temperature-10℃;
The diameter of the insulation pipe is d=25mm, and the thickness is ?=3mm(3.0.1-12)
(3.0.1—13)
(3.0.1—-14)
The thickness of the insulation layer is 100mm;
The average wind speed in winter is 7m/s;
(g) The saturated steam temperature is 175℃, and the pressure is 900kPa. b.
Calculation of heat lossbZxz.net
(a) Heat loss heat transfer coefficient (K)
The heat transfer coefficient (α) from the surface of the thermal insulation layer to the surrounding air is obtained by formula (3.0.1-7): aomαo+6.97w-11.62+6.977=30.06W/(m2C),d. Take 11.62. The heat transfer coefficient (αl) of the air between the outer wall of the equipment and the inner space of the thermal insulation layer is taken as αj=11.62W/(m2.C)
The thermal conductivity of the thermal insulation layer (λ2)
λ2=0.0604W/(m.℃)
Heat loss heat transfer coefficient (K)
From formula (3.0.1-8):
α. α
30.06T11.62
=0.56W/(m2.℃)
（b）Surface area of equipment (F) F=3.14×1.4×3=13.19m2（c）Heat loss heat transfer temperature difference (△t) is obtained from formula (3.0.1-9):
At=tw-t160-(10)=170
（d）Heat loss (Q)||t t||From formula (3.0.1-10):
QK.F·At-0.56X13.19X170-1255.69WCalculation of the length of the heat tracing pipe
(a) Heat transfer area (F)
①Heat transfer coefficient between the heat tracing pipe and the insulation equipment (K) Steam condensation heat transfer coefficient (αa)
Take αz-11622.50W/(m2.℃)
Steel pipe guide Heat transfer coefficient in = 46.52W/(m·℃) Heat transfer coefficient from the heat tracing pipe to the air in the thermal insulation layer (αs) See Table 3.0.1-1αg-22.08W/(m2.℃)388
Heat transfer coefficient from the air in the thermal insulation layer to the heated equipment (αa) See Table 3.0.1-2α=14.53W/(m2.℃), wall thickness of the tracing pipe 8=3mm Heat transfer coefficient between the tracing pipe and the thermal insulation equipment (K,) From formula (3.0.1-11), we get:
=8.75W/(m2.℃)
②The heat transfer temperature difference (At) between the heating pipe and the insulation equipment is obtained from formula (3.0.1-12):
At-t-tw-175-160-15℃
Heat transfer area (F)）
From formula (3.0.1-13), we get:
F1=K,Ar=8. 75X15
(b) Length of tracing pipe (L)
From formula (3.0.1-14):
#d-3.14X0.025
(3) Pipeline steam tracing pipe heating and insulation
Selection of pipeline tracing pipe diameter
Generally, pipes with a diameter of DN15 to DN25 are used for process and public engineering pipelines. If necessary, tracing pipes with a diameter greater than DN25 can be selected
b. Determination of the number of pipeline tracing pipes
The number of pipeline tracing pipes is related to the conditions of the process medium in the heated pipe and the diameter of the process pipeline. It should be based on the requirements of this project design item. The pipeline material professional shall prepare the "Insulation Design Regulations", specify the insulation grade and related data, and determine the number of pipeline tracing pipes. Other design requirements
Pipelines conveying corrosive or heat-sensitive media must not be in direct contact with companion pipes. A layer of isolation board (such as asbestos paper or asbestos board) must be added between the pipeline and the companion pipe. 3.0.2 Steam jacketed pipe heating and insulation
If the medium requires a higher insulation temperature and requires uniform heating at each point, that is, strict temperature control, and steam companion pipe heating cannot meet the insulation requirements of the process medium, then jacket heating should be used. When the freezing point of the conveying process material 389
is equal to or higher than 150℃ and uniform insulation is required, steam jacketed pipe insulation is generally used. The size of the steam jacketed pipe is selected according to the requirements of the "Insulation Design Regulations" for the project published by the pipeline material major. 3.0.3 Electric heating and insulation
3.0.3.1 Overview of electric heating
Electric heating is to use electric heat to supplement the heat lost by the heated object during the process, so as to maintain the medium temperature within a certain range.
3.0.3.2 Characteristics and application scope of electric heating
When the temperature of the process medium to be insulated is not high (generally the medium temperature needs to be maintained at 30-120℃), the fire and explosion protection requirements are not high, or the equipment, pumps and pipelines far away from the steam source, electric heating can be used for insulation. Electric heating has high efficiency, generally up to 80%-90%, and the heating temperature can be adjusted. It has the advantages of simple construction, reliable operation and no need for frequent maintenance. However, since it is not easy to find the electric heating belt after it burns out, and the power consumption is large, it is generally not recommended for use. Electric heating belts are only used for pipes and dead sections far away from the steam source or without steam and must be heated.
3.0.3.3 Types of electric heating
Electric heating can be divided into the following six forms according to its structure. (1) Constant power electric heating belt
This type of electric heating belt can maintain the medium temperature of the pipeline or heating body more accurately, and is suitable for underground laying or places with corrosive gases.
(2) Three-phase constant power electric heating belt
It is suitable for heating and heat tracing and heat preservation of long-distance and large-diameter pipelines. (3) Self-limiting electric heating belt
The characteristic of this type of electric heating belt is that it can automatically control the temperature so that the heating basically tends to thermal equilibrium. It is suitable for antifreeze and heat preservation of pipelines, valves, and pump bodies with medium temperatures below 35°C, as well as maintaining the process temperature of instrument pipelines. (4) Flexible electric heating plate
Flexible electric heating plate has high thermal efficiency, light weight, easy installation, strong adaptability, good heat and cold resistance, can maintain the temperature of the container at 120°C, and can still remain flexible at a low temperature of -30°C. It can be used indoors, outdoors and in explosive gas places in Zone I and Zone II of the factory. It is suitable for heating and heat preservation of oil tanks, tanks and containers. (5) High temperature electric heating belt
High temperature electric heating belt is used for heating and heat preservation of tanks, pipes and tanks of industrial equipment and laboratories in places with relative humidity less than 80% and no explosion hazard. It can also be used for heating other containers. The maximum heat-resistant temperature is close to 450℃, and it is recommended to use less than 350℃.
(6) Marine electric heating belt
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