A method for diagnosing and analyzing the quality pipe loss of a steam heating pipe network

Abstract

The present invention discloses a method for diagnosing and analyzing the mass pipe loss of a steam heating pipe network. The method is as follows: First, analyze the steam transmission and distribution process in the pipe network and establish a physical model; then, based on the mass conservation and energy conservation, establish the steam transmission process equation; next, simplify and solve the steam transmission process equation to obtain the calculation formula for the mass pipe loss of the steam heating pipe network; finally, analyze the composition of the losses during the steam transmission process in the pipe network according to the calculation results. According to the analysis results, the composition of the losses during the steam transmission process in the pipe network can be diagnosed, analyzed and evaluated, thereby providing a basis for implementing targeted loss reduction measures. At the same time, a method for monitoring the pipe network leakage is provided, which is beneficial for the heat network operators to discover and handle in time when an accidental pipe network LOCA occurs in extreme cases, thereby improving the safe operation level of the pipe network.

Description

Technical Field

[0001] The present invention relates to the technical field of energy-saving and optimized operation control of steam pipe networks, and particularly relates to a method for diagnosing and analyzing the quality pipe loss of a steam heating pipe network. Background Art

[0002] Heating is an important foundation and guarantee for people's livelihood projects and industrial production. The heating industry in China, especially industrial steam heating, currently shows complexity. On the one hand, the industry is developing towards centralization, regionalization, and intelligentization, which effectively promotes the improvement of China's energy utilization level; on the other hand, the scale of heating pipe networks is expanding day by day, the pipe network structure is becoming increasingly complex, and the management and control levels of thermal power plants and heating companies for pipe networks are uneven, and the losses in the steam transmission and distribution process vary greatly. At present, the industry has not proposed a specific calculation method for the composition of the quality pipe loss of steam heating pipe networks, so it is difficult to evaluate the operation status of pipe networks and it is also difficult to give corresponding measures to reduce pipe loss. Summary of the Invention

[0003] The purpose of the present invention is to provide a method for diagnosing and analyzing the quality pipe loss of a steam heating pipe network, which can solve one or more of the above technical problems.

[0004] In order to achieve the above purpose, the technical solution proposed by the present invention is as follows:

[0005] A method for diagnosing and analyzing the quality pipe loss of a steam heating pipe network. First, analyze the steam transmission and distribution process in the pipe network and establish a physical model; then, based on the mass conservation and energy conservation, establish an equation for the steam transmission process; then, simplify and solve the equation for the steam transmission process to obtain a calculation formula for the loss in the pipe network transmission and distribution process; finally, analyze the composition of the loss of steam in the pipe network transmission process according to the calculation results.

[0006] The analysis of the steam transmission and distribution process in the pipe network and the establishment of a physical model are specifically as follows:

[0007] Based on the consideration of simplified analysis, the heat network is abstracted into a long cylindrical container, with the heat source as the starting end, users concentratedly arranged at the end, and drainage and leakage distributed in the middle of the long cylindrical container.

[0008] The steam transmission and distribution process in the pipe network is as follows:

[0009] (1) Select a period of time during continuous heating. Superheated steam with a cumulative mass and energy of M o (t), Q o (kJ) enters the steam pipe network at the heat source outlet. The enthalpy value of the superheated steam is H o (kJ / kg), and the enthalpy value of the saturated steam corresponding to the outlet pressure is H bq (kJ / kg);

[0010] (2) Under the action of temperature difference, although heat insulation has been carried out, the all-steam pipe network still continuously dissipates heat to the outside world. The heat loss caused within the selected time period is called the heat dissipation loss of the pipe network, denoted as Q 散 (kJ);

[0011] (3) At the local low points and ends of the steam pipe network, a small amount of steam in the pipe network will condense into water and be discharged by automatic steam traps. At this time, energy loss and mass loss will be formed. Suppose there are n steam trap points in the pipe network, and the mass and heat of the water discharged at each point are M Si (t), Q Si (kJ), and the enthalpy value of the steam in the pipe network is considered to be fixed at H s (kJ / kg);

[0012] (4) In the steam pipe network, due to reasons such as the possible entrainment of a small amount of steam when the steam trap discharges water and the difficulty of completely closing the bypass pipeline of the steam trap, there may be multiple leakage points or micro-leakage points in the steam pipe network. Suppose there are n steam leakage points in the pipe network, and the mass and energy of the steam lost at each point are M qi (t), Q qi (kJ);

[0013] (5) The mass and energy of the steam reaching each point at the heat user's place within the selected time period are M i (t), Q i (kJ), the enthalpy value of the steam at the user's place is H i (kJ / kg), and the corresponding saturated steam enthalpy value is H bqi (kJ / kg);

[0014] (6) When reaching the heat user's place within the selected time period, the steam may reach the saturated state and thus carry some moisture. Since the volume ratio of liquid water in the steam is very small, the commonly used vortex street type and orifice plate type steam flowmeters at present cannot measure it, and it is also considered to form energy loss and mass loss. The mass and heat of the liquid water reaching the user are also included in M Si (t), Q Si (kJ).

[0015] Based on the mass conservation and energy conservation, establish the steam transportation process equation.

[0016] Furthermore, in actual engineering, there are relevant meters at the outlet of the general heat source and the inlet of all heat users, which can monitor temperature, pressure and flow. Therefore, there is a condition to adopt the inverse balance method to study the pipe network loss situation in the steam transmission and distribution process.

[0017] During the steam transmission and distribution process, the difference ΔM between the cumulative mass value at the heat source outlet and the total cumulative mass value of steam used by users within a certain period is the mass loss of the pipe network, which is called mass pipe loss or pipe loss. Generally speaking, the mass pipe loss consists of two parts: the mass loss of condensate drainage and the mass loss of steam leakage.

[0018] The steam at the outlet of the unit is supersaturated steam, which will continuously dissipate heat to the outside during the transmission in the pipe network. When dissipating heat, it will first consume the superheat part of the steam heat; after the superheat part of the heat is consumed, the steam will enter the saturated state. At this time, during continuous transmission and heat dissipation, while consuming the latent heat of vaporization of the steam, the steam will condense into saturated water.

[0019] After the saturated water is formed, losses will inevitably occur due to external drainage and internal leakage. This is because when the saturated water accumulates to a certain extent, the steam flow rate is low or at the low point of the pipe network, it will be discharged externally through the automatic condensate drainer; the saturated water that is not discharged reaches the user. Since the volume ratio of saturated water is much smaller than that of steam, the steam flowmeter cannot measure it, which is equivalent to forming internal leakage.

[0020] Based on the above analysis and derivation through the energy balance equation, the calculation formula for the mass loss of condensate drainage can be obtained as follows:

[0021]

[0022] Furthermore, the calculation of the heat loss of the pipeline is a relatively classic heat transfer problem. The steam flows in the pipe at a relatively high temperature, passes through the pipe wall metal and multiple insulation structures, and transfers heat to the environment under the combined action of convection and radiation. The calculation method is shown in Equation 2.

[0023] Q 散 =∑(πD 2i L i q i ) (2)

[0024] In the formula, D 2i is the insulated outer diameter of each section of the pipeline, with the unit of m; L i is the length of each section of the pipeline with different pipe diameters and insulation, with the unit of m; q i is the heat loss per unit area of each section of the pipeline with different pipe diameters and insulation, with the unit of W / m 2 ,q i The calculation formula is shown in Equation 3:

[0025]

[0026] In the formula, T is the steam temperature inside the pipe, with the unit of K; T a$T_{0}$ is the external environmental temperature, with the unit of K; $D_{2}$ is the outer diameter of the pipeline insulation, with the unit of m; $\lambda$ is the equivalent thermal conductivity of the insulation material, with the unit of W / (m·K); $D_{1}$ is the outer diameter of the metal pipeline, with the unit of m; $\alpha$ is the heat transfer coefficient between the outer surface of the insulation layer and the surrounding air, with the unit of W / (m²·K), which consists of two parts: the radiation heat transfer coefficient and the convective heat transfer coefficient. $\alpha$ is affected by many factors such as the environmental temperature, the emissivity of the outer surface material of the insulation structure, the outer surface temperature of the insulation structure, and the environmental wind speed, and the calculation is relatively complex, as shown in Equations 4 to 8.

[0027] $\alpha=\alpha_{r}+\alpha_{c}$ (4) r +α c (4)

[0028] In the formula:

[0029]

[0030] When there is no wind:

[0031] When there is wind and $WD\leq0.8m$ 2 / s:

[0032] When there is wind and $WD\gt0.8m$ 2 / s:

[0033] In the formula, $\varepsilon$ is the emissivity of the surface material, $T_{1}$ s is the temperature inside the pipe, with the unit of K; $T_{0}$ a is the environmental temperature, with the unit of K; $W$ is the environmental wind speed, with the unit of m / s.

[0034] Furthermore, the mass loss of steam leakage can be obtained according to the mass conservation, as shown in Equations 9 and 10:

[0035] $M_{in}-\sum M_{out}=\sum M_{loss}+\sum M_{leakage}$ (9) o -∑M i =∑M si +∑M qi (9)

[0036] $\sum M_{loss}=\Delta M-\sum M_{leakage}$ (10) qi =ΔM-ΣM si (10)

[0037] According to the calculation results, evaluate and analyze the composition of the losses during the steam transportation process in the pipeline network.

[0038] (1) The ratio of the mass loss of steam leakage to the cumulative value of the mass at the heat source outlet within a certain period is called the steam leakage rate of the pipeline network, $\eta$ q =ΣM qi / M o× 100%; When the steam leakage rate of the pipe network is greater than 1.0%, the steam leakage situation of the pipe network cannot be ignored, and it is necessary to strengthen the inspection of the pipe network, and regularly check and renovate the meter deviation, steam entrainment in the drainage of the steam trap, leakage of the drain bypass valve, and other accidental leakage situations of the pipe network.

[0039] (2) According to the national standard GB / T 4272 "General Requirements for Equipment and Pipeline Thermal Insulation Technology", when 150 °C < T ≤ 200 °C, q i should be less than or equal to 84 W / m 2 ; when 200 °C < T ≤ 250 °C, q i should be less than or equal to 147 W / m 2 ; when 250 °C < T ≤ 300 °C, q i should be less than or equal to 167 W / m 2 ; when the heat loss per unit area of the pipe network exceeds the above limits, it is necessary to check the insulation status of the pipe network, renovate the aging, subsiding, and damaged areas, and transform the ordinary pipe supports into insulated pipe supports to reduce the heat loss of the pipe network.

[0040] The beneficial effects of the present invention are as follows:

[0041] The present invention can obtain the specific composition of the pipeline loss by establishing a physical model and setting up a system of equations for the pipeline transportation process, which helps the design institute to consider the heat source parameters and the design of the insulation material and thickness of the pipeline network, and can calculate the pipeline drainage and pipeline loss indicators at the design stage; it is also beneficial for the design institute and the power plant to diagnose and analyze the operation and pipeline loss of the pipeline network, understand the key points and influencing factors of the mass loss of the drainage during the steam transportation process, so as to take targeted measures to reduce the loss; it can also compare the heat loss per unit area of the pipeline network with the standard to evaluate the insulation status of the pipeline network, so as to provide a basis for implementing targeted loss reduction measures; furthermore, the present invention also provides a method for monitoring pipeline network leakage, which is beneficial for the heat network operation personnel to discover and handle in time when an accidental pipeline network LOCA occurs in extreme situations, thereby improving the safe operation level of the pipeline network.

[0042] Other features and advantages of the present invention will be described in the following specification, and, in part, will be obvious from the specification, or will be understood by implementing the present invention.

[0043] To make the above objects, features, and advantages of the present invention more obvious and understandable, the following specific preferred embodiments are given, and in conjunction with the accompanying drawings, the detailed description is as follows. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] The attached drawings forming a part of this application are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention.

[0045] In the accompanying drawings:

[0046] Figure 1 is a flow chart of a method for calculating the pipeline loss of a steam heating pipeline network in the present invention;

[0047] Figure 2 is a simplified model diagram of the steam transmission and distribution process in the present invention. Detailed implementation manners

[0048] The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments, in which the illustrative embodiments and descriptions are only used to explain the present invention, but not to limit the present invention inappropriately.

[0049] It should be noted that, without conflict, the embodiments in the present application and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and embodiments.

[0050] It should be noted that the terms used herein are only for describing specific implementation manners and are not intended to limit the exemplary implementation manners according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or their combinations.

[0051] For the sake of description, spatial relative terms such as "above...", "over...", "on the upper surface of...", "above" and the like can be used herein to describe the spatial position relationship of a device or feature shown in the figure with other devices or features. It should be understood that the spatial relative terms are intended to include different orientations in use or operation in addition to the orientation described in the figure of the device. For example, if the device in the figure is inverted, the device described as "above other devices or structures" or "over other devices or structures" will be positioned as "below other devices or structures" or "under other devices or structures" afterwards. Thus, the exemplary term "above..." can include both the orientations of "above..." and "below...". The device can also be positioned in other different ways (rotated 90 degrees or in other orientations), and the corresponding explanations are made for the spatial relative descriptions used herein.

[0052] As Figure 1 shown, the present invention analyzes the steam transmission and distribution process in the pipeline network and establishes a simplified model. Based on the mass conservation and energy conservation, the steam transmission process equation is established; the equation is simplified and solved to obtain the calculation formula for the mass pipeline loss of the steam heating pipeline network; according to the equation and the solution results, the composition of the loss of steam in the pipeline network transmission process is analyzed, so as to provide a basis for implementing targeted loss reduction measures.

[0053] As Figure 2 shown, for the sake of simplified analysis, the heat network is abstracted into a long cylindrical container, with the heat source as the starting end, users concentratedly arranged at the end, and drain and leakage distributed in the middle of the long cylindrical container, as Figure 2 shown.

[0054] The steam transmission and distribution process is as follows:

[0055] (1) Select a period of time during continuous heating. Superheated steam with a cumulative mass and energy of M o (t) and Q o (kJ) at the heat source outlet enters the steam pipe network. The enthalpy value of the superheated steam is H o (kJ / kg), and the enthalpy value of the saturated steam corresponding to the outlet pressure is H bq (kJ / kg);

[0056] (2) Under the action of temperature difference, although insulated, the entire steam pipe network still continuously dissipates heat to the outside world. The heat loss caused during this period is called the heat dissipation loss of the pipe network, denoted as Q 散 (kJ);

[0057] (3) At the local low points and the end of the steam pipe network, a small amount of steam in the pipe network will condense into water and be discharged by the automatic drain valve. At this time, energy loss and mass loss will be formed. Suppose there are n drain points in the pipe network, and the mass and heat of the water discharged at each point are M Si (t) and Q Si (kJ) respectively. The enthalpy value of the drain in the pipe network is considered to be fixed at H s (kJ / kg);

[0058] (4) In the steam pipe network, due to reasons such as the possible entrainment of a small amount of steam when the drain valve drains and the difficulty of completely closing the bypass pipeline of the drain valve, there may be multiple leakage points or micro-leakage points in the steam pipe network. Suppose there are n steam leakage points in the pipe network, and the mass and energy of the steam lost at each point are M qi (t) and Q qi (kJ);

[0059] (5) The mass and energy of the steam finally reaching each point at the heat user during this period are M i (t) and Q i (kJ) respectively. The enthalpy value of the steam at the user is H i (kJ / kg), and the corresponding enthalpy value of the saturated steam is H bqi (kJ / kg);

[0060] (6) During the time period, when the steam finally reaches the heat users, it may reach the saturated state and thus carry some moisture. Since the volume ratio of liquid water in the steam is very small, the commonly used vortex street type and orifice plate type steam flowmeters cannot measure it, and it is also considered to have caused energy loss and mass loss. The mass and heat of the liquid water reaching the users are also included in M Si (t), Q Si (kJ). According to the energy balance equation, the calculation formula for the mass loss of the steam trap can be obtained as follows:

[0061]

[0062] Among them, Q 散 is the heat loss of the pipe network in kJ, H o is the enthalpy value of superheated steam in kJ / kg, H bq is the enthalpy value of saturated steam, M o is the mass of superheated steam supplied in t, H i is the enthalpy value of the steam at the users in kJ / kg, H bqi is the enthalpy value of saturated steam at the users, H s is the enthalpy value of the steam trap in the pipe network.

[0063] The mass loss of the steam leakage can be obtained according to the law of conservation of mass:

[0064] ΣM qi =ΔM - ΣM si .

[0065] Based on the above calculation results, the operation of the pipe network and the situation of pipe losses are diagnosed and analyzed. The specific method is as follows:

[0066] The ratio of the mass loss of the steam leakage to the cumulative value of the mass at the heat source outlet within a period of time is called the steam leakage rate of the pipe network, η q =ΣM qi / M o ×100%; when the steam leakage rate of the pipe network is greater than 1.0%, the steam leakage situation of the pipe network cannot be ignored, and it is necessary to strengthen the inspection of the pipe network, and regularly check and transform the meter deviation, the steam carried by the drain of the steam trap, the leakage of the drain bypass valve, and other accidental leakage situations of the pipe network;

[0067] The heat loss per unit area; according to the national standard GB / T 4272 "General Requirements for Equipment and Pipeline Insulation Technology", when 150°C < T ≤ 200°C, q i should be less than or equal to 84 W / m 2 ; when 200°C < T ≤ 250°C, q i should be less than or equal to 147 W / m 2 ; when 250°C < T ≤ 300°C, q i should be less than or equal to 167 W / m 2; When the heat dissipation loss per unit area of the pipe network exceeds the above limit, it is necessary to check the insulation status of the pipe network, transform the aging, subsiding, and damaged areas, and transform the ordinary pipe supports into adiabatic pipe supports to reduce the heat dissipation loss of the pipe network.

[0068] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for diagnosing and analyzing the quality pipe loss of a steam heating pipe network, characterized in that, First, analyze the steam transmission and distribution process in the pipe network and establish a physical model; then, based on the mass conservation and energy conservation, establish the steam transmission process equation; next, simplify and solve the steam transmission process equation to obtain the calculation formula for the mass pipe loss of the steam heating pipe network; finally, analyze the composition of the steam loss during the pipe network transmission process according to the calculation results The calculation formula for the mass pipe loss of the steam heating pipe network is as follows: During the steam transmission and distribution process, the difference ΔM between the cumulative mass value at the heat source outlet and the total cumulative mass value of the steam used by users within a certain period is the mass pipe loss of the steam heating pipe network. The mass pipe loss consists of two parts: the mass loss of condensate and the mass loss of steam leakage; According to the energy balance equation, the calculation formula for the mass loss of condensate is as follows: Among them, Q 散 is the heat loss of the pipe network, with the unit of kJ; H o is the enthalpy value of superheated steam, with the unit of kJ / kg; H bq is the enthalpy value of saturated steam, with the unit of kJ / kg; M o is the mass of superheated steam supplied, with the unit of t; H i is the enthalpy value of steam at the user end, with the unit of kJ / kg; H bqi is the enthalpy value of saturated steam at the user end, with the unit of kJ / kg; H s is the enthalpy value of condensate in the pipe network, with the unit of kJ / kg; Q 散 = ∑(πD 2i L i q i ) Among them, D 2i is the insulated outer diameter of each section of pipeline, with the unit of m; L i is the length of each section of pipeline with different pipe diameters and insulation, with the unit of m; q i is the heat dissipation loss per unit area of each section of pipeline with different pipe diameters and insulation, with the unit of W / m 2 ; where T is the steam temperature inside the pipe, in K; T a is the external ambient temperature, in K; D2 is the insulated outer diameter of the pipe, in m; λ is the equivalent thermal conductivity of the insulation material, in W / (m·K); D1 is the outer diameter of the metal pipe, in m; α is the heat transfer coefficient between the outer surface of the insulation layer and the surrounding air, in W / (m 2 ·K), which consists of two parts: the radiative heat transfer coefficient and the convective heat transfer coefficient; According to the mass conservation, the calculation formula for the mass loss of steam leakage is as follows: ΣM qi = ΔM - ΣM si .

2. The diagnostic and analysis method for the quality pipe loss of a steam heating pipe network according to claim 1, wherein Diagnose and analyze the operation of the pipe network and the pipe loss situation based on the calculation results of the mass pipe loss. The specific method is as follows: (1) The ratio of the mass loss of steam leakage to the cumulative mass value at the heat source outlet within a certain period is called the steam leakage rate of the pipe network, η q = ΣM qi / M o × 100%; When the steam leakage rate of the pipeline network is greater than 1.0%, the steam leakage situation of the pipeline network cannot be ignored. It is necessary to strengthen the inspection of the pipeline network and conduct regular inspections and renovations on meter deviation, steam entrainment in the drainage of steam traps, leakage of steam trap bypass valves, and other accidental leakage situations in the pipeline network; (2) According to the national standard GB / T 4272 General Requirements for Equipment and Pipeline Thermal Insulation Technology, when 150 °C < T ≤ 200 °C, q i shall be less than or equal to 84 W / m 2 ; When 200 °C < T ≤ 250 °C, q i should be less than or equal to 147 W / m 2 ; When 250°C < T ≤ 300°C, q i should be less than or equal to 167 W / m 2 ; When the heat dissipation loss per unit area of the pipe network exceeds the above limit, it is necessary to check the insulation status of the pipe network, transform the aging, subsiding, and damaged areas, and transform the ordinary pipe supports into adiabatic pipe supports to reduce the heat dissipation loss of the pipe network.

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