CN111931337A - Type selection construction method for electric tracing band of chemical pipeline - Google Patents
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Abstract
The invention provides a type selection construction method of an electric tracing band of a chemical pipeline, which comprises the following steps: 1) determining the thickness of a heat insulation layer wrapped on the pipeline; 2) calculating the total heat to be supplemented by combining the thickness of the heat preservation layer and the heat loss amount after the pipeline with unit length is corrected; 3) determining the type of the electric tracing band according to the power supply condition, the power grid load and the pipeline condition; 4) determining the length and the laying mode of the electric tracing band; 5) an electric tracing automatic detection system is arranged outside the pipeline, and an alarm and start-stop control scheme of a circuit for laying an electric tracing band is determined through power-on debugging; 6) and (4) wrapping the outer wall of the pipeline with an insulating layer, and laying a construction electric tracing band. The method comprehensively considers the influence of the thickness of the insulating layer of the pipeline on the heat dissipating capacity of the pipeline and the characteristics of various accessory pipe fittings and complex pipeline of the pipeline, accurately calculates the installation length of the electric tracing band of the pipeline, ensures the normal operation of a process pipeline in chemical production, reduces the investment and operation cost of electric tracing products, improves the operation quality of the products and prolongs the service life of the products.
Description
Technical Field
The invention belongs to the technical field of chemical production, and particularly relates to a type selection construction method of an electric tracing band of a chemical pipeline.
Background
In order to ensure the normal operation of process pipelines in chemical production, heat tracing and heat preservation measures are mostly adopted, but heat dissipation loss in the process of storage and transmission of process media is inevitable. Many chemical media with high melting point, high viscosity, easy solidification and easy moisture are likely to have adverse conditions affecting material properties once the process temperature required to be maintained is not reached, and the normal production is seriously affected.
Electric tracing utilizes electric energy to generate heat to compensate heat loss of heat traced pipelines and equipment in the process so as to ensure that the medium temperature meets the requirements in the process flow. Whether the model selection design of the electric tracing product is correct or not relates to whether the whole electric tracing system can normally operate and whether the equipment process requirement can be met, and also relates to the investment cost, the operation quality and the service life of the electric tracing product.
The heat preservation requirement of a process medium and the heat compensation quantity of a system are main factors for determining the model selection of the electric tracing system, and if the calculation and optimization model selection processes of an electric tracing product are lack of research, the smooth implementation of the electrifying temperature rise debugging link is influenced, and unnecessary troubles are brought to the later operation and maintenance support aspect.
In addition, according to the temperature control mode of the electric tracing band, the existing electric tracing band is divided into a constant-power electric tracing band and a self-temperature-control electric tracing band. The self-temperature-control electric tracing band automatically adjusts the output power according to the tracing temperature, the output power is reduced along with the rise of the temperature, and the electric tracing band is started and stopped after the temperature reaches the required heat preservation range. An inspector generally touches the surface of the automatic temperature control electric tracing band by hands to judge whether the tracing temperature is normal or not by experience, but the tracing temperature provided by the automatic temperature control electric tracing band is very low, so that the automatic temperature control electric tracing band is generally applied to the fields of freezing prevention and snow melting of process pipelines and has a narrow application range. The heat tracing temperature of the constant-power electric tracing band is much higher, the constant-power electric tracing band is widely applied in chemical production, but the constant-power electric tracing band needs to be connected with a temperature controller, the temperature controller is used for controlling an electrifying loop of the electric tracing band, and inspectors generally judge whether the temperature of the common electric tracing band is normal or not by checking the temperature in a distribution box of the temperature controller. However, the temperature controller distribution box can only display the whole temperature of the common electric tracing band, and cannot accurately detect the temperature of a specific certain section of non-heating electric tracing band; the method for judging the local temperature difference by touching the temperature self-control electric tracing band by a plurality of hands has large error and large engineering quantity, often cannot find the accurate position of the electric tracing band which is locally damaged and does not generate heat in time, not only influences the heat tracing stability of the whole electric tracing band in the debugging and test operation process, but also can cause the pipeline to be frozen and blocked in normal operation, and is not beneficial to safe production.
Disclosure of Invention
The invention aims to provide a type selection construction method of an electric tracing band of a chemical pipeline, which can accurately calculate the installation length of the electric tracing band of the chemical pipeline by fully considering the characteristics of various auxiliary pipe fittings and complex pipelines of the chemical pipeline, and provides a start-stop control method in the debugging and operation and maintenance processes of the electric tracing band.
The technical scheme of the invention provides a type selection construction method of an electric tracing band of a chemical pipeline, which comprises the following steps:
1) for pipelines wrapped with insulating layers, the heat loss Q of the pipelines with different insulating layer thicknesses in unit length is comparedDecrease in the thickness of the steelDetermining the thickness of the heat insulation layer wrapped on the pipeline by combining the cost of the pipeline;
in the formula, t1Indicating the temperature, t, of the fluid in the pipe2Denotes the ambient temperature outside the thermal insulation layer, d1Representing the diameter of the cylindrical wall, d, calculated as the inner wall of the pipe2Representing the diameter of the cylindrical wall, d, calculated as the outer wall of the pipe3Denotes the cylinder wall diameter, λ, calculated from the outer wall of the insulation layer1Denotes the thermal conductivity, λ, of the material of the tube wall2Representing the thermal conductivity of the thermal insulation material;
2) calculating the heat loss Q of the pipeline with unit length by using the thickness of the heat-insulating layer determined in the step 1)Decrease in the thickness of the steelAnd for this heat loss QDecrease in the thickness of the steelCorrecting to obtain corrected heat loss Q of unit length pipelineRepair theI.e. the total heat Q to be supplemented to the pipeline with unit lengthRepair the；
3) Determining the type of the electric tracing band according to the power supply condition, the power grid load and the pipeline condition;
4) determining the length L of the required electric tracing band and the laying mode thereof according to the heat released by the unit length of the selected type of electric tracing band and the total heat Q required to be supplemented by the unit length pipeline calculated in the step 1);
when the heat released by the electric tracing band in unit length is more than or equal to the total heat Q required to be supplemented by the pipeline in unit length, the length of the electric tracing band is the same as the length of the pipeline, and the electric tracing band is laid on the pipeline in parallel;
when the heat released by the electric tracing band in unit length is less than the total heat Q required to be supplemented by the pipeline in unit length, a plurality of electric tracing bands are laid in parallel or one electric tracing band is wound;
5) arranging an electric tracing automatic detection system outside a pipeline for laying an electric tracing band, and determining an alarm and start-stop control scheme for a laid electric tracing band loop by electrifying and debugging the electric tracing band automatic detection system;
6) after the power-on debugging is finished, wrapping the insulating layer with the thickness determined in the step 1) on the outer wall of the pipeline, and carrying out laying construction on the electric tracing band according to the type, the length and the laying mode of the electric tracing band determined in the steps 3), 4) and 5) and an electric tracing band loop alarming and starting and stopping control scheme.
Further, the heat loss amount of the unit length pipeline corrected in the step 2) is
Wherein k is1Correction of coefficient for environmental conditions, k2Correction factor k for insulating layer material3Correction factor k for the material of the pipe4The deviation coefficient is 1.37-1.4,
the heat loss coefficient of the pipeline accessory; chi shapeiI is the ordinal number of various pipeline accessories and takes the value of 1-n; n represents the sum of the categories of all the pipe attachments.
Furthermore, when the medium in the pipeline needs the electric tracing band for heat preservation, the total heat Q needed to be supplemented for the pipeline in unit length also comprises the heating quantity Q needed for heating the pipeline in unit length and the medium in the pipelineAddingI.e. Q ═ QRepair the+QAdding；
Heating quantity Q required for heating unit length pipeline and internal medium thereofAdding＝(C1×M1+C2×M2)×(tAn-tPhase (C))×kAdding(ii) a Wherein, C1Specific heat of pipe material, C2Specific heat of medium in the pipeline, M1Mass per unit length of pipe, M2Is the mass of the medium in the pipe per unit length, kAddingThe value of the correction coefficient is 1.2 for heating safety; t is tAnThe maximum safe temperature for ensuring that the medium in the pipeline can not generate phase change; t is tPhase (C)The temperature of the medium in the pipeline when the phase change occurs.
Further, when the heat released by the electric tracing band in the step 4) is less than the total heat Q required to be supplemented by the pipeline in unit length, the ratio of the power required by the pipeline in unit length to be compensated to the heat release power of the electric tracing band in unit length is selected as an installation coefficient to be corrected;
if the installation coefficient is more than 1.5, a plurality of electric tracing bands are laid in parallel, and the length L of the electric tracing bands is the length of a pipeline multiplied by the number multiplied by the safety coefficient, wherein the value range of the safety coefficient is 1.05-1.15;
and if the installation coefficient is 1.0-1.5, winding and laying an electric tracing band, wherein the length L of the electric tracing band is the length of the pipeline multiplied by the installation coefficient multiplied by the safety coefficient, and the value range of the safety coefficient is 1.05-1.15.
Further, the length of the electric tracing band in the step 4) further comprises an additional electric tracing band length L for power line connectionAttached with，LAttached withThe value is 1-1.5 m;
when the electric tracing band is wound and laid in the step 4), the winding distance of the electric tracing band is increased
Wherein D is0Is the outer diameter of the pipe, L is the actual length of the pipe, LGeneral assemblyThe total length of the electric tracing band, LGeneral assembly＝L+LAttached with；
And (4) according to the installation coefficient and the diameter of the pipeline, checking the winding distance d 'of the electric tracing band through an electric heating band winding distance table, comparing the values of d' and d, and taking the larger value of the two as the winding distance of the actual engineering.
Further, the automatic electric tracing detection system in the step 5) comprises a plurality of temperature detectors which are arranged on the outer wall of the pipeline at equal intervals, a signal receiving controller, a display and a power supply; the temperature detectors are in wireless connection with the signal receiving controller, the display is electrically connected with the signal receiving controller, and the signal receiving controller and the display are electrically connected with the power supply; the measurement signal of the temperature detector is sent to the signal receiving controller, and is converted to obtain an alarm reminding signal or an interlocking start-stop signal through signal conversion and logic operation of the signal receiving controller, and the alarm reminding signal or the interlocking start-stop signal is sent to the display.
Further, the specific process of power-on debugging in the step 5) is as follows:
comparing the temperature values of the temperature detectors at all positions of the outer wall of the pipeline with the temperature value of the environment temperature detector through a signal receiving controller to obtain an operation difference value;
if the operation difference value is lower than the set value and is not recovered after a period of time, an alarm signal is started, and therefore the part with poor heat tracing effect of the pipeline is specifically positioned; if the temperature continues to drop after any one temperature detector in a certain electric tracing band control loop gives an alarm and reaches a set low interlocking value, the signal receiving controller starts an interlocking signal to forcibly open the electric tracing band loop, and the electric tracing band loop which cannot be opened can determine that a fault exists;
if the operation difference value is higher than the set value and is not recovered after a period of time, an alarm signal is started, and therefore the part with the overhigh local temperature of the pipeline is specifically positioned; if the temperature continues to rise after any temperature detector in a certain electric tracing band control loop gives an alarm and reaches a set high-high interlocking value, the signal receiving controller starts an interlocking signal to forcibly close the electric tracing band control loop.
Further, in the power-on debugging process, the set value of the operation difference value of the signal receiving controller is determined through debugging, and the specific process is as follows: after all electric tracing band loops are started, the length of each reserved section of each control loop is adjusted, so that the temperature of a tracing system is stably increased, the temperature of the whole system is maintained to operate for 10 minutes after the required process tracing temperature is reached, and the difference value between the stably operating temperature and the ambient temperature is used as a set value;
closing the electric tracing band, only keeping one electric tracing loop to continue heating, taking the difference between the temperature corresponding to the system and the ambient temperature after 15 minutes as a set low alarm value, and taking the difference between the temperature corresponding to the system and the ambient temperature after 30 minutes as a set low interlock value;
and closing the electric tracing band, only keeping one electric tracing loop to continue heating, taking the difference between the loop temperature which continues to be heated after 10 minutes and the environment temperature as a set high alarm value, and taking the difference between the loop temperature which continues to be heated after 20 minutes and the environment temperature as a set high interlock value.
Further, when the electric tracing band works normally, the electrified debugging process in the step 5) is adopted to carry out alarming and start-stop control on the laid electric tracing band loop in real time.
Further, when the electric tracing hot-line laying facility in the step 6) works, a head end reserved section and a terminal reserved section are reserved firstly and are fixed on the pipeline through a heat-sensitive adhesive tape, the head end reserved section is connected with a power supply through a head end junction box, the terminal reserved section is connected with a terminal junction box, and the length of the reserved head end reserved section and the reserved terminal reserved section is 1-1.5 m; the electric tracing band is fixed at the flat laying position at intervals of 0.8-1.2 m, and the electric tracing band is fixed at the turning laying position at intervals of 0.4-0.6 m.
Compared with the prior art, the invention has the beneficial effects that:
(1) the type selection construction method of the electric tracing band of the chemical pipeline comprehensively considers the influence of the thickness of the insulating layer of the pipeline on the heat dissipation capacity of the pipeline and the characteristics of various auxiliary pipe fittings and complex pipelines of the chemical pipeline, accurately calculates the installation length of the electric tracing band of the chemical pipeline, ensures the normal operation of a process pipeline in chemical production, reduces the investment cost and the operation cost of an electric tracing product, and improves the operation quality and the service life of the electric tracing product.
(2) According to the type selection construction method of the electric tracing band of the chemical pipeline, provided by the invention, the temperature detector is arranged on the outer wall of the heat tracing pipeline and is tightly attached to the pipe wall at the position of the straight pipeline as much as possible, so that the metal wall temperature of the main part of the pipeline can be detected and sensed, the local heat tracing effect of the medium in the pipe can be directly represented, and the accuracy of detecting the working temperature is improved.
(3) The type selection construction method of the chemical pipeline electric tracing band provided by the invention sets a control scheme for alarming and starting and stopping all electric tracing band loops through the electrifying debugging process, carries out logic programming according to the control scheme, and inputs the control scheme into a program of a signal receiving controller, thereby not only being capable of quickly detecting the position of a fault point of the electric tracing band and quickly checking and solving the problem, but also being capable of avoiding the phenomenon of overheating of a local electric tracing band and ensuring that the whole electric tracing band system is maintained to be in a normal temperature range and stably run, and the method does not need to invest a large amount of energy to carry out corresponding checking work, and can ensure high efficiency and accuracy in both debugging and production processes.
The present invention will be described in further detail below with reference to the accompanying drawings.
Drawings
FIG. 1 is a schematic diagram of an automatic electric tracing detection system in an embodiment of the present invention;
fig. 2 is a logic control schematic diagram of power-on debugging of the electric trace band in the embodiment of the invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The embodiment provides a type selection construction method of an electric tracing band of a chemical pipeline, which comprises the following steps:
(1) for pipelines wrapped with insulating layers, the heat loss Q of the pipelines with different insulating layer thicknesses in unit length is comparedDecrease in the thickness of the steelAnd combined duct construction costDetermining the thickness of a heat insulation layer wrapped on the pipeline;
in the formula, t1Indicating the temperature, t, of the fluid in the pipe2Denotes the ambient temperature outside the thermal insulation layer, d1Representing the diameter of the cylindrical wall, d, calculated as the inner wall of the pipe2Representing the diameter of the cylindrical wall, d, calculated as the outer wall of the pipe3The diameter of the cylinder wall calculated by the outer wall of the heat-insulating layer is expressed as 2 times of the thickness of the heat-insulating layer and the diameter d of the outer wall of the cylinder2Sum, λ1Denotes the thermal conductivity, λ, of the material of the tube wall2Indicating the thermal conductivity of the insulation.
For the heat loss of the pipeline, most of the current specifications suggest to adopt a table look-up method for calculation, that is, according to the pipe diameter of the actual project, the thickness of the heat-insulating layer, the temperature difference value of the fluid temperature to be maintained and the ambient temperature, a pipeline heat-dissipating capacity condition table is inquired to obtain two heat-dissipating capacity values under the relatively close temperature difference value, finally, a theoretical value of the heat loss of each meter of pipeline is obtained by an intermediate interpolation method, and after the theoretical value is multiplied by a proper heat-insulating coefficient, the heat-dissipating capacity of the pipeline in the actual unit. Although the method is simple, convenient and universal, the heat loss value of the pipeline is often not accurate due to the limitation of different working conditions related to a pipeline heat dissipation table and the accuracy degree of the heat dissipation quantity obtained by checking, and in addition, the heat preservation coefficient also belongs to an empirical value, so the finally determined heat dissipation quantity of the pipeline is often greatly different, so that the model selection of the electric tracing band has obvious deviation, and even the fluid temperature required to be maintained cannot be achieved in serious cases.
In the embodiment, the heat loss of the pipeline is directly calculated by adopting the formula, and for the actual electric heat tracing engineering, the influence of the thickness of the heat-insulating material on the heat-insulating effect is very large, the heat-insulating products made of different materials have different heat conductivity coefficients, and the heat-insulating effect is also very different; the influence of the heat insulation material on the heat dissipation capacity can be considered by independently comparing correction systems of different materials, the determination of the thickness of the heat insulation layer occupies a great weight in the calculation of the actual heat dissipation capacity, the optimal thickness is obtained by calculating and comparing different thicknesses in the design process, but the influence of the thickness of the heat insulation layer on the heat loss calculation is usually easy to ignore, the heat insulation thickness is determined only by looking up a table according to specifications, and the heat loss is directly considered according to the single-layer cylinder wall.
From the above-mentioned QDecrease in the thickness of the steelThe calculation formula shows that the larger the thickness of the heat-insulating layer is, the smaller the Q loss is, and further the smaller the power of the electric tracing band in unit length is, the lower the cost of the required electric tracing band is, namely the construction cost Y of the electric tracing band and the thickness of the heat-insulating layer are in inverse function relation,
wherein A, B, C is each according to the above QDecrease in the thickness of the steelInputting a constant obtained by numerical calculation by using the calculation formula; the larger the thickness of the heat-insulating layer is, the higher the construction cost of laying the pipeline is, and the construction cost Y' of the pipeline is D multiplied by VHeat insulation layer＝D×π×d3×L×＝πDL(d2+2), wherein D is the unit price of the heat-insulating layer material per unit volume, so that the pipeline construction cost Y' is in a direct function relationship with the thickness of the heat-insulating layer under the engineering conditions; therefore, two functional relational expressions of the electric tracing band construction cost Y and the pipeline construction cost Y' are simultaneously calculated to obtain a rounded numerical value, namely the optimal thickness of the heat preservation layer of the general contract construction.
(2) Calculating the heat loss Q of the pipeline with unit length by using the thickness of the heat-insulating layer determined in the step (1)Decrease in the thickness of the steelAnd for this heat loss QDecrease in the thickness of the steelCorrecting to obtain corrected heat loss Q of unit length pipelineRepair theI.e. the total heat Q to be supplemented to the pipeline with unit lengthRepair the。
Because the actual factors influencing the heat loss of the pipeline in the electric heat tracing project are more, the heat loss Q loss needs to be corrected to a certain extent on the basis of the heat loss Q loss result calculated by the theory, and the corrected heat loss of the pipeline with unit length is
Wherein k is1Correction of coefficient for environmental conditions, k2Correction factor k for insulating layer material3The correction coefficients for the pipeline material are obtained by table look-up of k1, k2 and k3 according to specific conditions; k4 is a deviation coefficient used for compensating factors such as 10% voltage fluctuation (reduction) and 10% resistance rise, and the value range is 1.37-1.4;
coefficient of heat loss, chi, for pipe accessoriesiFor the number of the pipeline accessories, i represents the ordinal number of various pipeline accessories such as valves, tee joints, elbows, reducing joints, flanges, pipe racks and the like, the value can be from 1 to n, and n represents the sum of the types of all the pipeline accessories; the specific heat loss coefficient value of the pipeline accessory can be obtained by looking up a table, and then multiplied by the number of various pipe fittings, so as to sum up and obtain the comprehensive heat loss correction coefficient of the pipeline accessory.
In addition, for a process pipeline of a special medium, such as a fluid which is easy to solidify and liquefy, the heat preservation of an electric tracing band needs to be considered, if the heat tracing type is considered only, the compensation amount of heat loss is provided, the process requirement cannot be met, the heating of the pipeline and the internal medium needs to be considered to ensure that the physical properties of the medium cannot be influenced due to temperature reduction, in this case, the electric tracing band for heating needs to be considered to be selected, and the total heat Q required to be supplemented for the pipeline with unit length also comprises the heating amount Q required for heating the pipeline with unit length and the internal medium of the pipeline in addition to the normal supplementary heat loss amountAddingI.e. Q ═ QRepair the+QAdding；QAdding＝(C1×M1+C2×M2)×(tAn-tPhase (C))×kAdding(ii) a Wherein, C1Specific heat of pipe material, C2Specific heat of medium in the pipeline, M1Mass per unit length of pipe, M2Is the mass of the medium in the pipe per unit length, kAddingThe value of the correction coefficient is 1.2 for heating safety; t is tAnThe maximum safe temperature for ensuring that the medium in the pipeline can not generate phase change; t is tPhase (C)The temperature of the medium in the pipeline when the phase change occurs.
(3) And determining the type of the electric tracing band according to the power supply condition, the power grid load and the pipeline condition.
Specifically, the electric tracing band is mainly classified into a self-temperature-limiting type and a constant-power type. The self-temperature-limiting type heat-resistant pipeline has a low temperature-resistant range, is suitable for pipelines with low temperature control requirements, is laid in a parallel mode, allows random cutting, can ensure that the electric tracing band achieves the effect, and is suitable for cross overlapping type installation in regions with more valve elbows. The constant-power type heat-resistant range is high, the constant-power type heat-resistant range is suitable for pipelines with strict temperature control, and the pipelines are divided into series type, parallel type or MI type pipelines, the constant-power electric tracing band is generally limited by the node length, if one node length cannot be found during cutting, the part of the electric tracing band does not work, the heat tracing effect of the pipeline is influenced, meanwhile, waste is caused, and cutting and laying are not allowed. Among them, the tandem type and MI type are suitable for long or regular pipeline, and the precise required length needs to be determined according to the actual engineering length, and the design power and the required length must be precisely verified with the actual length of the on-site piping before construction, which often causes design modification and is generally not suitable for use. But the MI type electric tracing band has the highest temperature resistant range and is suitable for the working condition that the pipeline maintains high temperature or the accidental highest operation temperature is larger. The parallel type electric heating belt has wide application range, and is divided into a common type and a reinforced type, the reinforced type electric heating belt is formed by coating a layer of insulating material on the outer layer of the common type electric heating belt, the mechanical strength is high, the corrosion resistance is strong, but the heat conduction performance is slightly lower than that of the common type electric heating belt, and the parallel type electric heating belt is suitable for being buried underground or occasions with corrosive gas.
The principle of determining the electric tracing band model according to the power supply condition and the power grid load is as follows: the three-phase five-wire system power supply condition allows the selection of a constant-power type and a self-temperature-limiting type electric tracing band; the constant power mode cannot be selected under the three-phase four-wire system power supply condition. 660V power supply load is specially used for long-distance (about 1200m or more) pipeline heat tracing, and a series constant-power electric tracing band is suitable to be selected; the power supply load of 380V allows the electric tracing band of constant power type and self-limiting temperature type to be selected; the power supply load of 220V is selected from the temperature-limiting electric tracing band.
The principle of determining the electric tracing band type according to the length of the pipeline and the characteristics of the pipeline is as follows: the pipeline is regular and belongs to a long-distance pipeline (about 1200m or more), and a series constant power type is suitable for selection; the pipeline which is not regular and has strict requirements on temperature control is suitable for selecting a parallel constant power type; the valve elbow is suitable for selecting a self-temperature-limiting type in a pipeline with more regions and low temperature control requirement.
The principle of determining the type selection of the electric tracing band according to the temperature maintained by the pipeline is as follows: the electric tracing band with the highest maintaining temperature higher than the maintaining temperature of the pipeline and the accidental highest operating temperature is required to be selected, especially the pipeline with steam purging is required to be selected, if the steam temperature under the working condition of the sweeping line is very high, the type selection is required according to the highest steam temperature, and the MI type electric tracing band with the highest heat-resisting temperature is suitable to be selected.
(4) And (3) determining the length L of the required electric tracing band and the laying mode thereof according to the heat released by the unit length of the electric tracing band of the selected type and the total heat Q required to be supplemented by the pipeline of the unit length calculated in the step (1).
When the heat quantity released by the electric tracing band in unit length is larger than or equal to the total heat quantity Q required to be supplemented by the pipeline in unit length, the length of the electric tracing band is the same as the length of the pipeline, and the electric tracing band is laid on the pipeline in parallel.
When the heat released by the electric tracing band in unit length is less than the total heat Q required to be supplemented by the pipeline in unit length, a plurality of electric tracing bands are laid in parallel or one electric tracing band is wound.
Specifically, when a heat tracing scheme that the unit heat release quantity of the electric tracing band is smaller than the unit heat release loss quantity of the pipeline is adopted, the ratio of the power required by compensating the pipeline with the unit length to the heat release power of the electric tracing band with the unit length is selected as an installation coefficient to be corrected, and at the moment, the laying scheme of the electric tracing band is as follows:
if the installation coefficient is more than 1.5, a plurality of electric tracing bands are laid in parallel, and the length L of the electric tracing bands is the length of a pipeline multiplied by the number multiplied by the safety coefficient, wherein the value range of the safety coefficient is 1.05-1.15;
and if the installation coefficient is 1.0-1.5, winding and laying an electric tracing band, wherein the length L of the electric tracing band is the length of the pipeline multiplied by the installation coefficient multiplied by the safety coefficient, and the value range of the safety coefficient is 1.05-1.15.
For general contract projects, in order to guarantee project cost and heat tracing effect, a heat tracing scheme that the unit heat release quantity of the electric heat tracing band is smaller than the unit heat release loss quantity of the pipeline is often selected to optimally lay the electric heat tracing band.
Further, the length of the electric trace band should be taken into consideration for the length L of the additional electric trace band for the wiring of the power lineAttached with，LAttached withThe value is 1-1.5 m; therefore, the total length L of the electric tracing band required by the whole systemGeneral assembly＝L+LAttached with。
After the total length of the electric tracing band is obtained, when the electric tracing band is wound and laid, the winding distance of the electric tracing band can be rechecked, and the winding distance of the electric tracing band
Wherein D is0Is the outer diameter of the pipe, L is the actual length of the pipe, LGeneral assemblyThe total length of the electric tracing band, LGeneral assembly＝L+LAttached with(ii) a According to the installation coefficient and the diameter of the pipeline, the winding distance d ' of the electric tracing band is obtained through checking the winding distance table of the electric heating band, the values of d ' and d are compared, the larger value of the d ' and the d is taken as the winding distance of the actual engineering, and therefore the winding method laying mode which is more economical and reasonable can be selected.
(5) An electric tracing automatic detection system is arranged outside a pipeline for laying an electric tracing band, and the electric tracing band automatic detection system is electrified and debugged to determine a scheme for alarming and starting and stopping a laid electric tracing band loop.
Specifically, as shown in fig. 1, the electric tracing automatic detection system comprises a plurality of temperature detectors which are arranged on the outer wall of the pipeline at equal intervals, a signal receiving controller, a display and a power supply; the temperature detectors have the functions of detecting and displaying temperature and position, the temperature detectors are all in wireless connection with the signal receiving controller, the display is electrically connected with the signal receiving controller, and the signal receiving controller and the display are both electrically connected with the power supply; the measurement signal of the temperature detector is sent to the signal receiving controller, and is converted to obtain an alarm reminding signal or an interlocking start-stop signal through signal conversion and logic operation of the signal receiving controller, and the alarm reminding signal or the interlocking start-stop signal is sent to the display, so that a set of control system with functions of automatically alarming, displaying fault positions and interlocking start-stop power supply tracing bands is formed. According to the automatic electric tracing detection system, the temperature detector is arranged on the outer wall of the heat tracing pipeline, the pipe wall is tightly attached to the position of the straight pipeline as much as possible, so that the metal wall temperature of the main part of the pipeline can be detected and sensed, the local heat tracing effect of the medium in the pipe can be directly represented, and the problems that in the prior art, a temperature sensing element is arranged in the pipeline or on an electric tracing belt, or the equipment purchasing and installation cost is high, or the accuracy of detecting the working temperature is low are effectively solved.
The logic control principle of the electric tracing automatic detection system in the power-on debugging process is shown in fig. 2, generally, one electric tracing heat belt control loop corresponds to more than one temperature detector, in a signal receiving controller, the temperature values of the temperature detectors at all positions of the outer wall of a pipeline are compared with the temperature value of an environment temperature detector for operation to obtain an operation difference value, the set value of the operation difference value is determined by debugging, and the environment temperature detector is positioned in a control box, so that the influence of climate change is small, and the relatively constant temperature can be kept.
If the actually detected operation difference value is lower than the set value and is not recovered after a period of time, an alarm signal is started, so that the part with poor heat tracing effect of the pipeline is specifically positioned, an operator is reminded to pay attention, and the problem needs to be checked as soon as possible; if the temperature continues to drop after any one temperature detector in a certain electric tracing band control loop gives an alarm and reaches a set low interlocking value, the signal receiving controller starts an interlocking signal to forcibly open the electric tracing band loop, and the electric tracing band loop which cannot be opened can determine that a fault exists.
If the actual detected operation difference value is higher than the set value and is not recovered after a period of time, an alarm signal is started, so that the part with the overhigh local temperature of the pipeline is specifically positioned, an operator is reminded to pay attention, and the problem needs to be solved as soon as possible; if the temperature of any one temperature detector in a certain electric tracing band control loop continues rising after alarming, and reaches a set high-high interlocking value, the signal receiving controller starts an interlocking signal to forcibly close the electric tracing band loop so as to prevent the local damage of the electric tracing band and the influence of high temperature on the physical properties of a pipeline medium.
In the power-on debugging process, the specific process that the set value of the operation difference value of the signal receiving controller is determined through debugging is as follows: after all the electric tracing band loops are started, the length of each reserved section of the control loop is adjusted, so that the temperature of the heat tracing system is stably increased, the temperature of the whole system is maintained to operate for 10 minutes after the required process tracing temperature is reached, and the difference value between the stably operating temperature and the ambient temperature is used as a set value. And (3) closing the electric tracing band, only keeping one electric tracing loop to continue heating, taking the difference between the temperature corresponding to the system and the ambient temperature after 15 minutes as a set low alarm value, and taking the difference between the temperature corresponding to the system and the ambient temperature after 30 minutes as a set low interlocking value. Similarly, the electric tracing band is closed, only one electric tracing loop is reserved for continuous heating, the difference value between the loop temperature which is continuously heated after 10 minutes and the environment temperature is used as a set high alarm value, and the difference value between the loop temperature which is continuously heated after 20 minutes and the environment temperature is used as a set high interlock value.
Of course, in the working and running process of the electric tracing band, the electrified debugging process can be adopted to carry out alarm and start-stop control on the laid electric tracing band loop in real time. The method has the advantages that a control scheme for alarming and starting and stopping all electric tracing band loops is formulated through the power-on debugging process, logic programming is carried out according to the control scheme, and the control scheme is input into a program of the signal receiving controller, so that the fault point position of the electric tracing band can be quickly detected, problems can be eliminated and solved as soon as possible, the phenomenon of excessive heating of a local electric tracing band can be avoided, the whole electric tracing band loop system is ensured to be maintained in a normal temperature range and stably run, in addition, the method does not need to invest a large amount of energy to carry out corresponding checking work, and high efficiency and accuracy can be ensured in both debugging and production processes.
(6) And (3) after the power-on debugging is finished, wrapping the insulating layer with the thickness determined in the step (1) on the outer wall of the pipeline, and carrying out laying construction on the electric tracing band according to the type, the length and the laying mode of the electric tracing band determined in the steps (3), (4) and (5) and an electric tracing band loop alarm and start-stop control scheme.
Preferably, when the electric tracing band is applied to a facility, a head end reserved section and a terminal reserved section are reserved firstly and are fixed on a pipeline through a heat-sensitive adhesive tape, the head end reserved section is connected with a power supply through a head end junction box, the terminal reserved section is connected with a terminal junction box, the length of the reserved head end reserved section and the length of the reserved terminal reserved section are 1-1.5 m, two joint joints of the electric tracing band are connected through a two-way junction box, and three joint joints are connected through a three-way junction box. The electric tracing band is fixed at the straight laying position at intervals of 0.8-1.2 m, the electric tracing band is fixed at the turning laying position at intervals of 0.4-0.6 m, except for the head end reserved section and the terminal reserved section, the electric tracing band is tightly attached to a chemical pipeline by adopting a special aluminum foil tape, and the special aluminum foil tape not only plays a role in fixing, but also can conduct heat, so that the heat tracing is more uniform.
Furthermore, in the later maintenance work, if the thickness of the heat insulation layer needs to be adjusted, the power-on debugging still needs to be carried out again according to the operation mode. And after the system is stable, a waterproof layer material is wrapped outside the heat insulation layer according to the requirement, the thickness of the waterproof layer material is 200mm, and the waterproof layer material has no heat insulation effect, so that the thickness of the waterproof layer material can not be considered when the electric tracing band type selection calculation is carried out.
The above examples are merely illustrative of the present invention and should not be construed as limiting the scope of the invention, which is intended to be covered by the claims and any design similar or equivalent to the scope of the invention.
Claims (10)
1. A type selection construction method of an electric tracing band of a chemical pipeline is characterized by comprising the following steps:
1) for pipelines wrapped with insulating layers, the heat loss Q of the pipelines with different insulating layer thicknesses in unit length is comparedDecrease in the thickness of the steelDetermining the thickness of the heat insulation layer wrapped on the pipeline by combining the cost of the pipeline;
in the formula, t1Indicating the temperature, t, of the fluid in the pipe2Denotes the ambient temperature outside the thermal insulation layer, d1Representing the diameter of the cylindrical wall, d, calculated as the inner wall of the pipe2Representing the diameter of the cylindrical wall, d, calculated as the outer wall of the pipe3Denotes the cylinder wall diameter, λ, calculated from the outer wall of the insulation layer1Denotes the thermal conductivity, λ, of the material of the tube wall2Representing the thermal conductivity of the thermal insulation material;
2) calculating the heat loss Q of the pipeline with unit length by using the thickness of the heat-insulating layer determined in the step 1)Decrease in the thickness of the steelAnd for this heat loss QDecrease in the thickness of the steelCorrecting to obtain corrected heat loss Q of unit length pipelineRepair theI.e. the total heat Q to be supplemented to the pipeline with unit lengthRepair the；
3) Determining the type of the electric tracing band according to the power supply condition, the power grid load and the pipeline condition;
4) determining the length L of the required electric tracing band and the laying mode thereof according to the heat released by the unit length of the selected type of electric tracing band and the total heat Q required to be supplemented by the unit length pipeline calculated in the step 1);
when the heat released by the electric tracing band in unit length is more than or equal to the total heat Q required to be supplemented by the pipeline in unit length, the length of the electric tracing band is the same as the length of the pipeline, and the electric tracing band is laid on the pipeline in parallel;
when the heat released by the electric tracing band in unit length is less than the total heat Q required to be supplemented by the pipeline in unit length, a plurality of electric tracing bands are laid in parallel or one electric tracing band is wound;
5) arranging an electric tracing automatic detection system outside a pipeline for laying an electric tracing band, and determining an alarm and start-stop control scheme for a laid electric tracing band loop by electrifying and debugging the electric tracing band automatic detection system;
6) after the power-on debugging is finished, wrapping the insulating layer with the thickness determined in the step 1) on the outer wall of the pipeline, and carrying out laying construction on the electric tracing band according to the type, the length and the laying mode of the electric tracing band determined in the steps 3), 4) and 5) and an electric tracing band loop alarming and starting and stopping control scheme.
2. The model selection construction method of the electric tracing band of the chemical pipeline according to claim 1, wherein the heat loss amount of the pipeline per unit length corrected in the step 2) is
Wherein k is1Correction of coefficient for environmental conditions, k2Correction factor k for insulating layer material3Correction factor k for the material of the pipe4The deviation coefficient is 1.37-1.4,
the heat loss coefficient of the pipeline accessory; chi shapeiI is the ordinal number of each pipeline accessory and takes the value of 1-n; n represents the sum of the categories of all the pipe attachments.
3. The model selection construction method of the electric tracing band of the chemical pipeline according to claim 1, wherein when the medium in the pipeline needs to be insulated by the electric tracing band, the total quantity Q of heat to be supplemented to the pipeline per unit length further comprises the quantity Q of heat to be added to the pipeline per unit length and the medium in the pipeline per unit lengthAddingI.e. Q ═ QRepair the+QAdding；
Heating quantity Q required for heating unit length pipeline and internal medium thereofAdding＝(C1×M1+C2×M2)×(tAn-tPhase (C))×kAdding(ii) a Wherein, C1Specific heat of pipe material, C2Specific heat of medium in the pipeline, M1Mass per unit length of pipe, M2Is the mass of the medium in the pipe per unit length, kAddingThe value of the correction coefficient is 1.2 for heating safety; t is tAnThe maximum safe temperature for ensuring that the medium in the pipeline can not generate phase change; t is tPhase (C)The temperature of the medium in the pipeline when the phase change occurs.
4. The model selection construction method of the electric tracing band of the chemical pipeline according to claim 1, wherein when the heat quantity released by the electric tracing band in the unit length in the step 4) is less than the total heat quantity Q required to be supplemented by the pipeline in the unit length, the ratio of the power required for compensating the pipeline in the unit length to the heat release power of the electric tracing band in the unit length is selected as an installation coefficient to be corrected;
if the installation coefficient is more than 1.5, a plurality of electric tracing bands are laid in parallel, and the length L of the electric tracing bands is the length of a pipeline multiplied by the number multiplied by the safety coefficient, wherein the value range of the safety coefficient is 1.05-1.15;
and if the installation coefficient is 1.0-1.5, winding and laying an electric tracing band, wherein the length L of the electric tracing band is the length of the pipeline multiplied by the installation coefficient multiplied by the safety coefficient, and the value range of the safety coefficient is 1.05-1.15.
5. The shape-selecting construction method of the electric tracing band for chemical pipelines according to claim 1, wherein the length of the electric tracing band in the step 4) further comprises an additional electric tracing band length L for power line connectionAttached with，LAttached withThe value is 1-1.5 m;
when the electric tracing band is wound and laid in the step 4), the winding distance of the electric tracing band is increased
Wherein D is0Is the outer diameter of the pipe, L is the actual length of the pipe, LGeneral assemblyThe total length of the electric tracing band, LGeneral assembly＝L+LAttached with；
And (4) according to the installation coefficient and the diameter of the pipeline, checking the winding distance d 'of the electric tracing band through an electric heating band winding distance table, comparing the values of d' and d, and taking the larger value of the two as the winding distance of the actual engineering.
6. The model selection construction method of the electric tracing band of the chemical pipeline according to claim 1, wherein the automatic detection system of the electric tracing band in the step 5) comprises a plurality of temperature detectors, a signal receiving controller, a display and a power supply which are installed on the outer wall of the pipeline at equal intervals; the temperature detectors are in wireless connection with the signal receiving controller, the display is electrically connected with the signal receiving controller, and the signal receiving controller and the display are electrically connected with the power supply; the measurement signal of the temperature detector is sent to the signal receiving controller, and is converted to obtain an alarm reminding signal or an interlocking start-stop signal through signal conversion and logic operation of the signal receiving controller, and the alarm reminding signal or the interlocking start-stop signal is sent to the display.
7. The model selection construction method of the electric tracing band of the chemical pipeline according to claim 6, wherein the specific process of the power-on debugging in the step 5) is as follows:
comparing the temperature values of the temperature detectors at all positions of the outer wall of the pipeline with the temperature value of the environment temperature detector through a signal receiving controller to obtain an operation difference value;
if the operation difference value is lower than the set value and is not recovered after a period of time, an alarm signal is started, and therefore the part with poor heat tracing effect of the pipeline is specifically positioned; if the temperature continues to drop after any one temperature detector in a certain electric tracing band control loop gives an alarm and reaches a set low interlocking value, the signal receiving controller starts an interlocking signal to forcibly open the electric tracing band loop, and the electric tracing band loop which cannot be opened can determine that a fault exists;
if the operation difference value is higher than the set value and is not recovered after a period of time, an alarm signal is started, and therefore the part with the overhigh local temperature of the pipeline is specifically positioned; if the temperature continues to rise after any temperature detector in a certain electric tracing band control loop gives an alarm and reaches a set high-high interlocking value, the signal receiving controller starts an interlocking signal to forcibly close the electric tracing band control loop.
8. The model selection construction method of the electric tracing band of the chemical pipeline, according to claim 7, characterized in that in the power-on debugging process, the setting value of the operation difference value of the signal receiving controller is determined by debugging, and the specific process is as follows: after all electric tracing band loops are started, the length of each reserved section of each control loop is adjusted, so that the temperature of a tracing system is stably increased, the temperature of the whole system is maintained to operate for 10 minutes after the required process tracing temperature is reached, and the difference value between the stably operating temperature and the ambient temperature is used as a set value;
closing the electric tracing band, only keeping one electric tracing loop to continue heating, taking the difference between the temperature corresponding to the system and the ambient temperature after 15 minutes as a set low alarm value, and taking the difference between the temperature corresponding to the system and the ambient temperature after 30 minutes as a set low interlock value;
and closing the electric tracing band, only keeping one electric tracing loop to continue heating, taking the difference between the loop temperature which continues to be heated after 10 minutes and the environment temperature as a set high alarm value, and taking the difference between the loop temperature which continues to be heated after 20 minutes and the environment temperature as a set high interlock value.
9. The model selection construction method of the electric tracing band of the chemical pipeline according to claim 7, wherein when the electric tracing band works, the power-on debugging process in the step 5) is adopted to carry out alarm and start-stop control on the laid electric tracing band loop in real time.
10. The model selection construction method of the electric tracing band of the chemical pipeline according to claim 1, wherein in the step 6), when the electric tracing band is applied to the facility, a head end reserved section and a terminal reserved section are reserved firstly and are fixed on the pipeline through a heat-sensitive adhesive tape, the head end reserved section is connected with a power supply through a head end junction box, the terminal reserved section is connected with a terminal junction box, and the lengths of the reserved head end reserved section and the reserved terminal section are 1-1.5 m; the electric tracing band is fixed at the flat laying position at intervals of 0.8-1.2 m, and the electric tracing band is fixed at the turning laying position at intervals of 0.4-0.6 m.
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Application publication date: 20201113 |