CN117146178A - Buried LNG storage tank heat tracing system and method - Google Patents
Buried LNG storage tank heat tracing system and method Download PDFInfo
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- CN117146178A CN117146178A CN202311298301.2A CN202311298301A CN117146178A CN 117146178 A CN117146178 A CN 117146178A CN 202311298301 A CN202311298301 A CN 202311298301A CN 117146178 A CN117146178 A CN 117146178A
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- 238000000034 method Methods 0.000 title claims abstract description 22
- 239000012530 fluid Substances 0.000 claims abstract description 61
- 239000004567 concrete Substances 0.000 claims abstract description 10
- 230000000149 penetrating effect Effects 0.000 claims abstract description 4
- 238000010438 heat treatment Methods 0.000 claims description 39
- 238000004364 calculation method Methods 0.000 claims description 37
- 230000004907 flux Effects 0.000 claims description 26
- 238000013461 design Methods 0.000 claims description 25
- 239000012774 insulation material Substances 0.000 claims description 18
- 238000012546 transfer Methods 0.000 claims description 16
- 230000008569 process Effects 0.000 claims description 10
- 230000008020 evaporation Effects 0.000 claims description 8
- 238000001704 evaporation Methods 0.000 claims description 8
- 238000010586 diagram Methods 0.000 claims description 7
- 230000008878 coupling Effects 0.000 claims description 6
- 238000010168 coupling process Methods 0.000 claims description 6
- 238000005859 coupling reaction Methods 0.000 claims description 6
- 238000009413 insulation Methods 0.000 claims description 5
- 239000011810 insulating material Substances 0.000 claims description 4
- 239000000463 material Substances 0.000 claims description 3
- 239000003949 liquefied natural gas Substances 0.000 description 62
- 239000002609 medium Substances 0.000 description 17
- 239000002689 soil Substances 0.000 description 13
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 6
- 230000002500 effect on skin Effects 0.000 description 4
- 230000000694 effects Effects 0.000 description 4
- 230000007613 environmental effect Effects 0.000 description 4
- 238000005485 electric heating Methods 0.000 description 3
- 238000007710 freezing Methods 0.000 description 3
- 230000008014 freezing Effects 0.000 description 3
- 239000002918 waste heat Substances 0.000 description 3
- 238000003889 chemical engineering Methods 0.000 description 2
- 238000010276 construction Methods 0.000 description 2
- 239000000498 cooling water Substances 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- 238000003466 welding Methods 0.000 description 2
- 229910000831 Steel Inorganic materials 0.000 description 1
- 230000002159 abnormal effect Effects 0.000 description 1
- 230000001133 acceleration Effects 0.000 description 1
- 229910045601 alloy Inorganic materials 0.000 description 1
- 239000000956 alloy Substances 0.000 description 1
- 238000004458 analytical method Methods 0.000 description 1
- 230000002457 bidirectional effect Effects 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 230000005484 gravity Effects 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 238000012423 maintenance Methods 0.000 description 1
- 239000012913 medium supplement Substances 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 229920001983 poloxamer Polymers 0.000 description 1
- 239000011513 prestressed concrete Substances 0.000 description 1
- 230000009467 reduction Effects 0.000 description 1
- 239000010935 stainless steel Substances 0.000 description 1
- 229910001220 stainless steel Inorganic materials 0.000 description 1
- 239000010959 steel Substances 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
Classifications
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
- F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
- F17C3/00—Vessels not under pressure
- F17C3/005—Underground or underwater containers or vessels
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
- F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
- F17C13/00—Details of vessels or of the filling or discharging of vessels
- F17C13/02—Special adaptations of indicating, measuring, or monitoring equipment
- F17C13/026—Special adaptations of indicating, measuring, or monitoring equipment having the temperature as the parameter
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
- F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
- F17C3/00—Vessels not under pressure
- F17C3/02—Vessels not under pressure with provision for thermal insulation
- F17C3/04—Vessels not under pressure with provision for thermal insulation by insulating layers
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
- F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
- F17C2227/00—Transfer of fluids, i.e. method or means for transferring the fluid; Heat exchange with the fluid
- F17C2227/03—Heat exchange with the fluid
- F17C2227/0302—Heat exchange with the fluid by heating
- F17C2227/0304—Heat exchange with the fluid by heating using an electric heater
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- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- General Engineering & Computer Science (AREA)
- Physics & Mathematics (AREA)
- Thermal Sciences (AREA)
- Filling Or Discharging Of Gas Storage Vessels (AREA)
Abstract
The invention relates to a buried LNG storage tank heat tracing system and a buried LNG storage tank heat tracing method, wherein the buried LNG storage tank heat tracing system comprises a tank bottom fluid heat tracing system, and the buried LNG storage tank heat tracing system comprises a temperature acquisition module, a pressure acquisition module, a flow acquisition module, a heat tracing module and a working medium pump module, wherein the temperature acquisition module and the heat tracing module are arranged in a bearing platform of an LNG storage tank, the pressure acquisition module and the flow acquisition module are both arranged at a total inlet and a total outlet of fluid entering the heat tracing module, and the working medium pump is arranged at the total inlet of the heat tracing module to provide pressure for fluid heat exchange; the tank wall electric tracing system comprises a temperature acquisition module and an electric tracing module, wherein the temperature acquisition module and the electric tracing module are arranged in the concrete outer tank wall of the LNG storage tank in a penetrating way in a heat tracing belt mode; and the control system is electrically connected with the tank bottom fluid heat tracing system and the tank wall electric heat tracing system respectively.
Description
Technical Field
The invention relates to a buried LNG storage tank heat tracing system and method, and belongs to the technical field of liquefied natural gas storage tanks.
Background
Under the background of lack of land and increasingly severe ecological environment, the design of the LNG storage tank rapidly develops to large-scale and invisible. Because the overhead storage tank field has a severe site selection requirement, in order to meet the construction requirement of the LNG storage tank in the region with poor geological conditions, the tank types of the ground-sitting type storage tank, the semi-underground type storage tank, the underground type storage tank and the like are adopted to make up for the defect of the construction of the overhead storage tank.
Because the tank body is in direct contact with the soil, no air flows, and the influence of the low temperature of the liquid in the storage tank on the foundation cannot be compensated. Therefore, in order to prevent the tank bottom soil from freezing, a heating system is required to be arranged at the tank bottom so as to ensure the consistency and the continuity of the temperature of the protection area, and the economy of the LNG storage tank is reduced due to the fact that the LNG cooled in the tank cannot be boiled.
The three heating modes mainly applied in the current chemical industry field are fluid heat tracing, skin effect electric heating and resistance type electric heat tracing respectively. The fluid heat tracing mode has the advantages of more equipment, complex structure and difficult temperature control, but has certain economic advantages for chemical engineering projects (such as waste heat sources in factories or a large amount of cooling water needed by process circulation in the vicinity of the power plants, so that a large amount of low-cost steam sources can be provided) with low-cost heat sources or heat mediums easily obtained; the local heat tracing effect of skin effect electric tracing mode is general, and exists because the corruption risk that leaks voltage and bring, still needs to satisfy the welding requirement simultaneously, lays in the cushion cap structure difficultly to be big, is not applicable to in the higher LNG storage tank heat tracing system of temperature control precision, position requirement.
Disclosure of Invention
According to the buried LNG storage tank heat tracing system and method, heat tracing can be provided for the buried LNG storage tank, cold leakage of the storage tank can be monitored and compensated in real time, and the economic efficiency of the storage tank is reduced due to the fact that LNG in the storage tank is evaporated due to excessive compensation while the temperature consistency and the continuity of a compensated area are guaranteed.
In order to achieve the above purpose, the present invention adopts the following technical scheme:
a buried LNG storage tank heat trace system, comprising:
the tank bottom fluid heat tracing system comprises a temperature acquisition module, a pressure acquisition module, a flow acquisition module, a heat tracing module and a working medium pump module, wherein the temperature acquisition module and the heat tracing module are arranged in a bearing platform of an LNG storage tank, the pressure acquisition module and the flow acquisition module are both arranged at a total inlet and a total outlet of fluid entering the heat tracing module, and the working medium pump is arranged at the total inlet of the heat tracing module to provide pressure for fluid heat exchange;
the tank wall electric tracing system comprises a temperature acquisition module and an electric tracing module, wherein the temperature acquisition module and the electric tracing module are arranged in the concrete outer tank wall of the LNG storage tank in a penetrating way in a heat tracing belt mode;
and the control system is electrically connected with the tank bottom fluid heat tracing system and the tank wall electric heat tracing system respectively.
Preferably, the heat tracing module comprises a plurality of heating pipes laid in the bearing platform and heating media positioned in the heating pipes.
In the buried LNG storage tank heat tracing system, preferably, a plurality of heating pipes are arranged in the bearing platform at intervals in parallel.
In the buried LNG storage tank heat tracing system, preferably, a plurality of heating pipes are arranged in the bearing platform in a grid mode in a warp-weft staggered mode.
The second aspect of the invention provides a heat tracing calculation method of a buried LNG storage tank heat tracing system, which comprises the following steps:
acquiring information required by heat tracing calculation of the LNG storage tank;
according to the classification of the structural form of the LNG storage tank and the division of the heat tracing areas, the BOG evaporation capacity of the LNG storage tank is calculated, and the heat exchange capacity requirement of the required heat tracing areas is determined, namely: heat flux at the bottom and walls of the tank;
after the heat flux of the tank wall is obtained, the fluid heat tracing medium, the pipeline and the pipe diameter are calculated respectively, and after an optimal coupling scheme is obtained, the tank bottom fluid heat tracing design is carried out;
after the heat flux of the tank wall is obtained, the electric tracing band selection, the power density and the arrangement method are respectively determined, and after the optimal coupling scheme is obtained, the tank wall electric tracing design is carried out.
The heat tracing calculation method preferably comprises the following steps: the information required by heat tracing calculation of the LNG storage tank comprises basic parameters of the LNG storage tank, storage tank design data and basic data, wherein the basic parameters comprise: ambient temperature, humidity, altitude, supply voltage level; the storage tank design data includes: LNG storage tank design specification, storage tank BOG evaporation rate calculation report, storage tank overall structure diagram and storage tank electrical system description; the basic data comprises: the cold insulation materials of the storage tank are made of materials, thickness and heat conductivity coefficients.
The heat tracing calculation method preferably comprises the following steps: heat flux at the bottom = rate of heat leak at the bottom center region + rate of heat leak at the bottom a region + rate of heat leak at the bottom B region.
The heat tracing calculation method preferably comprises the following steps: the heat flux calculation formula of the tank bottom is as follows:
in which Q Bottom Representing tank bottom heat flux; q (Q) b Indicating the rate of heat leak in the central region of the tank bottom; q (Q) bA Indicating the area A of the tank bottomIs a heat leak rate of (2); q (Q) bB The heat leakage rate of the tank bottom B area is represented; a is that b The heat exchange area of the central area of the tank bottom is represented; a is that bA The heat exchange area of the tank bottom A area is represented; a is that bB The heat exchange area of the tank bottom B area is represented; t (T) a Representing the tank bottom temperature; t (T) LNG Represents the temperature of LNG; λ represents the thermal conductivity of the cold-insulating material of the cold-insulating layer; t represents the thickness of the cold insulation material of the cold insulation layer; i is the heat insulation material of each layer at the center of the tank bottom; j is the heat insulation material of each layer in the area A of the tank bottom; k is the heat insulation material of each layer in the area B of the tank bottom.
In the heat tracing calculation method, preferably, the heating fluid flow rate is calculated as follows:
Q bottom ＝Q+Q Damage to
Wherein Q represents the heat flux of the process, and the heat exchange efficiency is calculated as 75% because of the heat balance state, A h The effective heat exchange area of the heat exchange tube is shown; t (T) a Representing the average temperature of the tank wall bottom; t is t 1 Indicating the fluid inlet temperature; t is t 2 Indicating the fluid outlet temperature; c represents the specific heat of the fluid; k (K) a Representing the total heat transfer coefficient of the hot fluid to the storage tank; q (Q) Damage to Representing the heat flux lost during heat tracing; m represents the fluid mass flow rate.
Due to the adoption of the technical scheme, the invention has the following advantages:
1. the buried LNG storage tank heat tracing system and the buried LNG storage tank heat tracing method can carry out system calculation and arrangement on the buried storage tank heat tracing, specifically analyze heat flux requirements, carry out heat tracing calculation, and can be coupled through various input conditions according to calculation results, so that an optimal heat tracing scheme is obtained, and the purposes of safe and stable operation of the LNG storage tank are guaranteed.
2. The heat tracing calculation method and system provided by the invention provide theoretical reference for heat tracing of the semi-underground LNG storage tank, are also suitable for heat tracing of the overground LNG storage tank, and fill up the blank of heat tracing of the semi-underground LNG storage tank.
3. According to the invention, the fluid heat tracing is coupled with the electric heat tracing, so that the diversity of a heat tracing method is improved, the surrounding waste heat sources can be effectively utilized, the heat tracing economy of the storage tank is improved, and the operation and maintenance cost is greatly reduced.
Drawings
Fig. 1 is a schematic diagram of tank bottom fluid heating in a buried LNG tank heat tracing system according to an embodiment of the present invention;
fig. 2 is a schematic diagram of a fluid heat exchange model in a buried LNG tank heat tracing system according to the embodiment of the present invention;
fig. 3 is a schematic diagram of the overall structure of a buried LNG storage tank including a heat tracing system according to the embodiment of the present invention;
the figures are marked as follows:
1-LNG storage tanks; 2-heating pipes; 3-heating the medium; 4-concrete; 5-soil; 6-inner tank wall plate; 7-a prestressed concrete outer wall; 8-a bearing platform; 9-concrete cushion rings; 10-radial heating pipes; 11-a circumferential heating pipe; 12-an inner annular heat tracing belt of an outer wall of the tank wall.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the present invention more apparent, the technical solutions in the present invention will be clearly and completely described below, and it is apparent that the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by one of ordinary skill in the art without undue burden from the present disclosure, are intended to be within the scope of the present disclosure.
Unless defined otherwise, technical or scientific terms used herein should be given the ordinary meaning as understood by one of ordinary skill in the art to which this invention belongs. The terms "first," "second," "third," "fourth," and the like as used herein do not denote any order, quantity, or importance, but rather are used to distinguish one element from another. The word "comprising" or "comprises", and the like, means that elements or items preceding the word are included in the element or item listed after the word and equivalents thereof, but does not exclude other elements or items. The terms "connected" or "connected," and the like, are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect.
For ease of description, spatially relative terms, such as "inner," "outer," "lower," "upper," and the like, may be used herein to describe one element or feature's relationship to another element or feature as illustrated in the figures. Such spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures.
The three heating modes mainly applied in the current chemical industry field are fluid heat tracing, skin effect electric heating and resistance type electric heat tracing respectively. The fluid heat tracing mode has the advantages of more equipment, complex structure and difficult temperature control, but has certain economic advantages for chemical engineering projects (such as waste heat sources in factories or a large amount of cooling water needed by process circulation in the vicinity of the power plants, so that a large amount of low-cost steam sources can be provided) with low-cost heat sources or heat mediums easily obtained; the local heat tracing effect of skin effect electric tracing mode is general, and exists because the corruption risk that leaks voltage and bring, still needs to satisfy the welding requirement simultaneously, lays in the cushion cap structure difficultly to be big, is not applicable to in the higher LNG storage tank heat tracing system of temperature control precision, position requirement.
Based on the problems, the invention provides a buried LNG storage tank heat tracing system and a buried LNG storage tank heat tracing method, which can provide heat tracing for the buried LNG storage tank, can monitor and compensate the cold leakage of the storage tank in real time, and avoid the economic reduction of the storage tank caused by LNG evaporation in the tank due to excessive compensation while ensuring the consistency and the continuity of the temperature of a compensated area.
As shown in fig. 1 and 2, the buried LNG tank heat tracing system according to the present invention includes:
the tank bottom fluid heat tracing system comprises a temperature acquisition module, a pressure acquisition module, a flow acquisition module, a heat tracing module and a working medium pump module, wherein the temperature acquisition module and the heat tracing module are arranged in a bearing platform of the LNG storage tank 1, the pressure acquisition module and the flow acquisition module are both arranged at a total inlet and a total outlet of fluid entering the heat tracing module, and the working medium pump is arranged at the total inlet of the heat tracing module to provide pressure for fluid heat exchange; the tank wall electric tracing system comprises a temperature acquisition module and an electric tracing module, wherein the temperature acquisition module and the electric tracing module are arranged in the concrete outer tank wall of the LNG storage tank 1 in a penetrating manner in a heat tracing belt mode; and the control system is electrically connected with the tank bottom fluid heat tracing system and the tank wall electric heat tracing system respectively.
Further, the heat tracing module comprises a plurality of heating pipes 2 paved in the bearing platform and heating mediums 3 positioned in the heating pipes 2.
In some specific preferred examples, several heating pipes 2 are arranged in parallel at intervals in the bearing platform, more preferably, several heating pipes 2 are arranged in a grid-like manner in a warp and weft staggered manner in the bearing platform.
The second aspect of the invention also provides a heat tracing calculation method of the buried LNG storage tank heat tracing system, which comprises the following steps: acquiring information required by heat tracing calculation of the LNG storage tank 1; according to classification of the structural form of the LNG storage tank 1 and division of heat tracing areas, the BOG evaporation capacity of the LNG storage tank 1 is calculated, and the heat exchange capacity requirement of the required heat tracing areas is determined, namely: heat flux at the bottom and walls of the tank; after the heat flux of the tank wall is obtained, the fluid heat tracing medium, the pipeline and the pipe diameter are calculated respectively, and after an optimal coupling scheme is obtained, the tank bottom fluid heat tracing design is carried out; after the heat flux of the tank wall is obtained, the electric tracing band selection, the power density and the arrangement method are respectively determined, and after the optimal coupling scheme is obtained, the tank wall electric tracing design is carried out.
Specifically, the information required for heat tracing calculation of the LNG tank 1 includes basic parameters of the LNG tank 1, tank design data, basic data, the basic parameters including: ambient temperature, humidity, altitude, supply voltage level; the storage tank design data includes: LNG storage tank design specification, storage tank BOG evaporation rate calculation report, storage tank overall structure diagram and storage tank electrical system description; the basic data comprises: the cold insulation materials of the storage tank are made of materials, thickness and heat conductivity coefficients.
Further, in the design of the tank bottom fluid heat tracing system, heat tracing calculation is divided into five areas: fluid type, working medium pump, piping, (including piping, tubing, valves, brackets) and fluid heater.
In order to prevent the influence of soil freezing in winter on the storage tank structure foundation caused by low-temperature LNG leakage, the design temperature of the tank bottom of the LNG storage tank 1 is not lower than 5 ℃, and cold fluid LNG in the design conducts heat and convects through the concrete on the inner tank of the storage tank and the outer wall of the cold insulation layer storage tank; the thermal fluid (water) medium conducts and convects heat to the inside of the tank through the bearing platform concrete layer, the outer tank cold insulation layer and the inner tank, and conducts and convects heat to the soil layer through the bearing platform concrete layer; in addition, the heat transfer process also has the effect of dissipating heat to the surrounding environment, resulting in some heat loss. Considering the convenience of design calculation, the above heat exchange model is simplified as follows (as shown in fig. 2):
1) Considering that the fluid heat exchange pipeline is made of stainless steel and has smaller wall thickness, the heat resistance of the steel is smaller than that of the cold insulation material, and the influence of the heat exchange pipeline is ignored in calculation.
2) Under different environmental temperatures, the heat dissipating capacity Q5 is greatly changed, and the fluid heat tracing requirement of the project under the working condition of winter is considered, so that the environmental temperature is selected to be the extreme environmental temperature-13.2 ℃ for safety, and the extreme environmental temperature is taken as the heat dissipating calculation basis.
3) Project initial soil temperature assuming a uniform constant temperature, winter soil temperature T3 is measured at 5 ℃.
4) Considering the workability of the tank bottom distribution pipe, the effective contact area of the heat exchange model is calculated by 70% of the bottom area.
5) Because the heat transfer of the fluid medium is bidirectional, the LNG cold leakage also has stepped transfer, and the equivalent heat transfer process is a three-layer heat conduction structure in which LNG cold leakage to a heat exchange medium and the heat exchange medium transfers heat to soil.
6) The project is designed to prevent frozen soil, assuming q2=q4, the soil temperature remains unchanged during heat transfer, and the heat of the heat exchange medium supplements the external leaked cold of LNG.
7) In order to avoid abnormal evaporation of LNG in the tank and prevent frozen soil, the tank bottom interface temperature T2 is controlled at 5 ℃.
8) And under the stable heat tracing working condition, the heat is in an equilibrium state, and the temperature of the contact surface of the heating medium and the tank bottom is uniform and stable.
The thermal conductivity of the insulating material takes the highest value under ambient conditions.
The technical scheme of the invention is described in detail below with reference to specific examples.
In the embodiment, circulating hot water is used as a heating and heat preserving medium for analysis, other medium scheme principles can be synchronously referred, and the heat transfer characteristic is based on a specific medium. In addition to the electric heating technology, the LNG project semi-underground storage tank heating system decomposes the heat exchange model according to a storage tank overall structure diagram (figure 3), and cold insulation materials and corresponding heat exchange area parameters adopted in calculation are shown in the following table.
TABLE 1 Cold insulation Material Performance parameter Table
Table 2 heat exchange area parameter table for each zone
| Region(s) | Area (m) 2 ) |
| Tank bottom center area A b | 5674.50 |
| Tank bottom area A (ring beam) A bA | 270.18 |
| Can bottom zone B (annular space) A bB | 137.44 |
The heat flux calculation formula of the tank bottom is as follows:
wherein Q is Bottom Representing the heat flux of the tank bottom, W; q (Q) b The heat leakage rate of the central area of the tank bottom is represented by W; q (Q) bA The heat leakage rate of the area A of the tank bottom is represented by W; q (Q) bB The heat leakage rate of the tank bottom B area is represented by W; a is that b Represents the heat exchange area of the central area of the tank bottom, m 2 ；A bA Represents the heat exchange area of the tank bottom A area, m 2 ；A bB Represents the heat exchange area of the tank bottom B area, m 2 ；T a The temperature of the tank bottom is expressed, and the temperature is controlled to be 5 ℃; t (T) LNG Represents the temperature of LNG, -165 ℃; λ represents the coefficient of thermal conductivity of the cold-insulating material of the cold-insulating layer, W/(m·k); t represents the thickness of the cold insulation material of the cold insulation layer, and m; i is the heat insulation material of each layer at the center of the tank bottom; j is the heat insulation material of each layer in the area A of the tank bottom; k is the heat insulation material of each layer in the area B of the tank bottom.
The heat flux at the bottom of the tank is calculated as shown in Table 3:
TABLE 3 tank bottom heat flux
The heating fluid flow is calculated as follows:
taking 40 ℃ hot water as an example, the required heating fluid flow is calculated. The hot fluid is involved in the heat exchange process as above.
Q Bottom ＝Q+Q Damage to
Wherein Q represents the heat flux of the process, and the heat exchange efficiency is calculated as 75% because of the heat balance state. A is that h Represents the effective heat exchange area of the heat exchange tube, m 2 The method comprises the steps of carrying out a first treatment on the surface of the Ta represents the average temperature of the tank wall bottom and is 5 ℃; t1 represents the fluid inlet temperature, in 40 ℃; t2 represents the fluid outlet temperatureTaking a temperature difference of 10 ℃ and taking t2 to be 30 ℃; c represents the specific heat of the fluid; q (Q) Damage to Representing the heat flux lost during heat tracing; m represents the fluid mass flow rate; ka represents the total heat transfer coefficient of the hot fluid to the tank, W/(m) 2 K), ka can be calculated by:
wherein R represents the heat resistance of pipeline fouling, comprehensively considering the influence of scale and the like on heat transfer, and the boiler water is 0.00026 (m 2 k)/W; h represents the surface heat transfer coefficient from the outermost layer of the heating tube to the outside of the storage tank.
According to the formula of Dittus-Boelter associated with forced turbulent heat exchange in a tube:
Nu f ＝0.023×Re f 0.8 ×Pr f 0.3
wherein Nu is the number of Nuschel quasi-numerals,h is the surface heat transfer coefficient from the outermost layer of the heating pipe to the outside of the storage tank; d is the pipe diameter; pr is pluronic number, < >>Mu is a roughness coefficient; c p Specific heat for constant pressure; re is the Reynolds number of the alloy,ρ is the fluid density; v is the kinematic viscosity.
By adopting hot water fluid, the design needs to set initial fluid pressure characteristics and heating pipe diameter initial values, heat exchange area requirements are calculated, whether the heating pipe quantity arrangement requirements can be met under the bottom area of the storage tank is determined, pipeline pressure drop and preset initial pressure ratio pairs are estimated according to the heating pipe conditions, and trial calculation is carried out continuously so as to select proper heating pipe diameters and quantity under the corresponding fluid temperature, and project heating requirements are met.
If the heat conduction oil is adopted for heating, the following heat exchange series formula is adopted for calculation, and other iterative design calculation processes are the same as the water medium.
H is the surface heat transfer coefficient from the outermost layer of the heating pipe to the outside of the storage tank; epsilon is the convection coefficient; gr is the Gray dawn number; d, d 0 Is the inner diameter of the pipeline; g is gravity acceleration; beta is the volume expansion coefficient; Δt is the temperature difference;
in the design of the tank wall electric tracing system, the capacity and the safety coefficient of the electric tracing heat exchange quantity are calculated as follows:
in order to prevent the influence of the freezing of soil in winter on the storage tank structure foundation caused by the leakage of low-temperature LNG, the design temperature of the tank wall of the LNG storage tank is not lower than 5 ℃, and in the design, an electric tracing band transfers heat to a soil layer through a concrete layer on the outer wall of the storage tank; in addition, the heat transfer process also has the effect of dissipating heat to the surrounding environment, resulting in some heat loss.
(1) Heat tracing cable power density:
under the condition of 5 ℃ and 220V, the voltage loss of the powered end of the electric equipment is considered according to the voltage drop of 5% of a power supply line (according to the specification of GB50052-2011, the voltage loss of the powered end of the electric equipment is not more than 5%).
(2) The total length of the heat tracing cable;
(3) Heat trace system capacity Qh:
the calculation formula of the heat tracing system capacity Qh is as follows: qh=ph×lh, where Ph is the electrical heat tracing band power density; lh is the length of the electric tracing band;
(4) Safety factor Sf:
the safety coefficient calculation formula is as follows: sf=qh/Q;
(5) Duty cycle Dc:
the duty ratio defines the working time of the heat tracing system in one period, and the duty ratio of the system is calculated by using a central horizontal arrangement cable with a small safety coefficient:
dc=100/Sf, where Sf is a safety factor;
finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present invention, and are not limiting; although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit and scope of the technical solutions of the embodiments of the present invention.
Claims (9)
1. A buried LNG storage tank heat tracing system, comprising:
the tank bottom fluid heat tracing system comprises a temperature acquisition module, a pressure acquisition module, a flow acquisition module, a heat tracing module and a working medium pump module, wherein the temperature acquisition module and the heat tracing module are arranged in a bearing platform of an LNG storage tank (1), the pressure acquisition module and the flow acquisition module are both arranged at a total inlet and a total outlet of fluid entering the heat tracing module, and the working medium pump is arranged at the total inlet of the heat tracing module to provide pressure for fluid heat exchange;
the tank wall electric tracing system comprises a temperature acquisition module and an electric tracing module, wherein the temperature acquisition module and the electric tracing module are arranged in the concrete outer tank wall of the LNG storage tank (1) in a penetrating manner in a heat tracing belt mode;
and the control system is electrically connected with the tank bottom fluid heat tracing system and the tank wall electric heat tracing system respectively.
2. Buried LNG tank heat tracing system according to claim 1, characterized in that the heat tracing module comprises a number of heating pipes (2) laid in the deck and a heating medium (3) located in the heating pipes (2).
3. Buried LNG tank heat tracing system according to claim 2, characterized in that several heating pipes (2) are arranged in parallel at intervals in the platform.
4. Buried LNG tank heat tracing system according to claim 2, characterized in that several heating pipes (2) are arranged in grid-like manner in the platform.
5. A heat tracing calculation method of a buried LNG tank heat tracing system according to any one of claims 1 to 4, comprising the steps of:
acquiring information required by heat tracing calculation of the LNG storage tank (1);
according to classification of the structural form of the LNG storage tank (1) and division of heat tracing areas, BOG evaporation capacity of the LNG storage tank (1) is calculated, and heat exchange capacity requirements of the required heat tracing areas are determined, namely: heat flux at the bottom and walls of the tank;
after the heat flux of the tank wall is obtained, the fluid heat tracing medium, the pipeline and the pipe diameter are calculated respectively, and after an optimal coupling scheme is obtained, the tank bottom fluid heat tracing design is carried out;
after the heat flux of the tank wall is obtained, the electric tracing band selection, the power density and the arrangement method are respectively determined, and after the optimal coupling scheme is obtained, the tank wall electric tracing design is carried out.
6. The heat tracing calculation method according to claim 5, wherein: the information required by heat tracing calculation of the LNG storage tank (1) comprises basic parameters, storage tank design data and basic data of the LNG storage tank (1), wherein the basic parameters comprise: ambient temperature, humidity, altitude, supply voltage level; the storage tank design data includes: LNG storage tank design specification, storage tank BOG evaporation rate calculation report, storage tank overall structure diagram and storage tank electrical system description; the basic data comprises: the cold insulation materials of the storage tank are made of materials, thickness and heat conductivity coefficients.
7. The heat tracing calculation method according to claim 5, wherein: heat flux at the bottom = rate of heat leak at the bottom center region + rate of heat leak at the bottom a region + rate of heat leak at the bottom B region.
8. The heat tracing calculation method according to claim 7, wherein: the heat flux calculation formula of the tank bottom is as follows:
in which Q Bottom Representing tank bottom heat flux; q (Q) b Indicating the rate of heat leak in the central region of the tank bottom; q (Q) bA The heat leak rate of the tank bottom A area is shown; q (Q) bB The heat leakage rate of the tank bottom B area is represented; a is that b The heat exchange area of the central area of the tank bottom is represented; a is that bA The heat exchange area of the tank bottom A area is represented; a is that bB The heat exchange area of the tank bottom B area is represented; t (T) a Representing the tank bottom temperature; t (T) LNG Represents the temperature of LNG; λ represents the thermal conductivity of the cold-insulating material of the cold-insulating layer; t represents the thickness of the cold insulation material of the cold insulation layer; i is the heat insulation material of each layer at the center of the tank bottom; j is the heat insulation material of each layer in the area A of the tank bottom; k is the heat insulation material of each layer in the area B of the tank bottom.
9. The heat trace calculation method according to claim 5, wherein the heating fluid flow rate is calculated as follows:
Q bottom ＝Q+Q Damage to
Wherein Q represents the heat flux of the process, and the heat exchange efficiency is calculated as 75% because of the heat balance state, A h The effective heat exchange area of the heat exchange tube is shown; t (T) a Representing the average temperature of the tank wall bottom; t is t 1 Indicating the fluid inlet temperature; t is t 2 Indicating the fluid outlet temperature; c represents the specific heat of the fluid; k (K) a Indicating hot fluid to tankIs a heat transfer coefficient of the heat exchanger; q (Q) Damage to Representing the heat flux lost during heat tracing; m represents the fluid mass flow rate.
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| CN202311298301.2A CN117146178A (en) | 2023-10-09 | 2023-10-09 | Buried LNG storage tank heat tracing system and method |
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| CN202311298301.2A CN117146178A (en) | 2023-10-09 | 2023-10-09 | Buried LNG storage tank heat tracing system and method |
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