Coupling calculation method for pressure drop and temperature drop of high-temperature superheated steam in overhead pipeline

Abstract

The invention discloses a coupling calculation method for pressure drop and temperature drop of high-temperature superheated steam in an overhead pipeline. The coupling calculation method comprises the steps that firstly, the steam pressure, temperature and flow value at the starting end of the pipeline are obtained; steam physical property parameters under the pipeline starting end working condition and the pipeline design working condition are obtained; pressure drop caused by resistance in the pipeline and acceleration effect pressure drop are calculated, and steam pressure at the tail end of the pipeline is obtained through calculation; calculating heat dissipation loss along the pipeline; the enthalpy drop of steam in the pipeline caused by heat dissipation from the starting end to the tail end is calculated; the steam specific enthalpy at the tail end is calculated, the temperature drop of the steam in the pipeline caused by heat dissipation from the starting end to the tail end and the temperature drop of the steam caused by expansion cooling are obtained, and the steam temperature at the tail end of the pipeline is obtained; if the calculation result does not meet the convergence condition, the average pressure and temperature of steam of the whole pipeline are calculated, and the steam physical property parameters under the average working condition of the pipeline are obtained till the result meets the convergence condition. The problem that the pressure drop and the temperature drop cannot be accurately and rapidly calculated when steam is actually transmitted in a pipe network at present is solved.

Description

Technical Field

[0001] The present invention relates to the cross - technical field of thermal energy engineering and fluid mechanics, and particularly to a coupled calculation method for pressure drop and temperature drop of high - temperature superheated steam in an overhead pipeline. Background Art

[0002] Most chemical production process links often require high - quality steam supplied by thermal power plants. In actual situations, the transmission process of steam in the pipe network is very complex due to the mutual coupling of its physical property parameters. At the same time, limited by the current heat supply pipe network information monitoring system, which cannot update data in real - time and there is an obvious hysteresis in the response of the hydraulic and thermal parameters of the steam in the pipe network, how to accurately predict the pressure drop and temperature drop of high - temperature superheated steam in the pipeline has become the core technical requirement for ensuring the safe operation of the system and improving energy utilization efficiency.

[0003] The traditional method of calculating the pressure drop and temperature drop of steam in the pipeline by referring to relevant design manuals is time - consuming and laborious, and there will be a deviation from the actual working conditions; although the CFD fluid simulation technology can improve the calculation accuracy, the large consumption of computing resources and the poor convergence affected by the strong nonlinearity of compressible flow cannot be simply ignored. Therefore, there is an urgent need to develop a new type of pressure - drop and temperature - drop calculation method to achieve accurate calculation of steam parameters in the pipeline.

[0004] The assumptions of the existing theoretical calculation methods for the pressure drop and temperature drop of steam in the pipeline still have limitations: some studies consider the calculation of pressure drop and temperature drop separately, ignoring the coupling relationship between hydraulic calculation and thermal calculation. For example, when calculating the pressure drop, only the influence of resistance loss is considered, but the influence of heat dissipation loss on the pressure drop through density change is ignored; some studies calculate the overall pressure drop and temperature drop by assuming the average value of steam parameters in the pipeline to represent the change trend of real parameters. Considering steam as an incompressible gas simplifies the calculation complexity to a certain extent, but if the result is not corrected, its value will still deviate from the actual working conditions due to ignoring the compressibility of real gases. In the case of long - distance pipeline calculations, the error will accumulate step by step, resulting in a lack of theoretical support for the final result, and the pressure drop and temperature drop are significantly smaller; there are also some related studies that regard the steam in the pipeline as saturated steam or ideal gas. Since the physical property parameters of saturated steam are single - valued functions only related to pressure or temperature, and the ideal gas model simplifies the heat transfer process of steam through a constant gas specific heat capacity, both will significantly reduce the theoretical calculation amount, but the applicable range is relatively limited, and the compatibility of these two calculation methods with the high - temperature superheated steam commonly used in industrial production remains to be discussed.

[0005] In summary, since the pressure drop of superheated steam in a pipeline is related to its density, flow velocity, and kinematic viscosity, and the temperature drop of steam is related to its specific heat capacity at constant pressure, thermal conductivity, and dynamic viscosity, etc., and the calculation of pressure drop is inseparable from the calculation of temperature drop. Therefore, it is necessary to combine the characteristics of existing research and consider the changes in the physical properties of steam in the pipeline and the influence brought by the coupling relationship between pressure drop and temperature drop during the calculation process. Summary of the Invention

[0006] Object of the Invention: Aiming at the technical problem that the pressure drop and temperature drop of steam cannot be accurately and quickly calculated during the actual transmission in the pipeline network in the prior art, the present invention proposes a coupling calculation method for the pressure drop and temperature drop of high-temperature superheated steam in an overhead pipeline, which considers the flow loss, heat dissipation loss, and the change of its physical properties during the transmission of high-temperature superheated steam in the pipeline during the calculation process, and corrects the results by considering the acceleration effect pressure drop and expansion cooling temperature drop generated by the flow of real gas in the pipeline, forming a theoretical calculation method for describing the flow and heat transfer process of steam in the pipeline, and realizing the accurate calculation of temperature drop and pressure drop.

[0007] Technical Solution: To achieve the above object, the coupling calculation method for the pressure drop and temperature drop of high-temperature superheated steam in the overhead pipeline of the present invention includes the following steps:

[0008] Step (1), collect and monitor the steam parameters at special nodes in the pipeline network through the heat network information monitoring system, and obtain the steam pressure P s 、steam temperature T s and steam flow rate G at the beginning of the calculation pipeline through this heat network information monitoring system;

[0009] Step (2), since the physical properties of superheated steam are all binary functions of temperature and pressure, the steam density ρ s 、specific enthalpy H s 、kinematic viscosity γ s 、specific heat capacity at constant pressure and the density ρ, kinematic viscosity γ, dynamic viscosity μ, specific heat capacity at constant pressure c P 、thermal conductivity k of steam under the design conditions of the pipeline are obtained according to the properties of water vapor; convert the steam pressure P s at the beginning of the pipeline into absolute pressure P abs :

[0010] P abs = P s + P a (1)

[0011] P a is the atmospheric pressure of the local area of the steam pipeline, kPa.

[0012] Step (3), if it is the first iteration, use ρs and γ s Perform calculations to determine the flow state of the steam in the pipeline, calculate the pressure drop ΔP1 + ΔP2 caused by the resistance in the pipeline, and calculate the steam pressure P at the end of the pipeline e ; If it does not meet the convergence condition after step (9), that is, it is not the first iteration, then return to this step (3), and substitute the judge the flow state of the steam in the pipeline to calculate ΔP1 + ΔP2, and substitute ρ s and the ρ obtained in the previous step (9) e , solve the pressure drop ΔP3 due to the acceleration effect, and calculate P e ; The process of the first iteration is as follows:

[0013] Step (3.1), according to the inner diameter D of the pipeline in calculate the flow area A of the pipeline s :

[0014]

[0015] D in is the inner diameter of the pipeline, in mm;

[0016] Step (3.2), according to the flow area A of the pipeline obtained in step (3.1) s , the steam density obtained in step (2) (ρ for the first iteration s , and for non-first iterations here is the first iteration) and the steam flow rate G at the beginning of the pipeline obtained in step (1), calculate the steam velocity v in the pipeline:

[0017]

[0018] Step (3.3), according to the steam velocity v obtained in step (3.2), the inner diameter D of the pipeline in and the kinematic viscosity of the steam obtained in step (2) (γ for the first iteration s , and for non-first iterations here is the first iteration), calculate the Reynolds number Re:

[0019]

[0020] Step (3.4), judge the flow state of the steam in the pipeline according to the Reynolds number Re. Since the flow state is in the squared resistance zone (Re > 10 6 ), calculate the pipeline friction resistance coefficient λ:

[0021]

[0022] ε is the absolute roughness of the pipeline;

[0023] Step (3.5), based on the steam density obtained in step (2) (ρ for the first iteration s , and for non-first iterations), the steam flow velocity v obtained in step (3.2), the pipe friction resistance coefficient λ and the pipe inner diameter D obtained in step (3.4) in , calculate the specific frictional resistance R of the pipe m :

[0024]

[0025] Step (3.6), based on the specific frictional resistance R of the pipe obtained in step (3.5) m , calculate the pressure drop ΔP1 caused by the local resistance of the pipe:

[0026] ΔP1 = ∑ξ·R m L·10 -3 (7)

[0027] ΔP1 is the pressure drop caused by the local resistance of the pipe, kPa; ∑ξ is the total local resistance coefficient of each valve and pipe fitting in the pipe;

[0028] Step (3.7), based on the specific frictional resistance R of the pipe obtained in step (3.5) m , calculate the pressure drop ΔP2 caused by the pipe friction resistance:

[0029] ΔP2 = R m L·10 -3 (8)

[0030] ΔP2 is the pressure drop caused by the pipe friction resistance, kPa;

[0031] P e = P s - (ΔP1 + ΔP2)·10 -3 (9)

[0032] Step (4), based on the actual heat transfer temperature difference ΔT, the heat transfer temperature difference ΔT o under the design conditions, the ambient temperature T a of the external environment, and the heat loss q per unit length of the pipe design o , calculate the actual heat loss Q along the pipe:

[0033]

[0034] Q is the actual heat loss along the pipe, kW; q o is the heat loss per unit length of the pipe design, W / m; L is the pipe length, m; ΔT is the actual heat transfer temperature difference of the pipe, °C, and if it is the first iteration, it is the steam temperature T at the beginning of the pipe sThe difference from the external environmental temperature T a ; if it is not the first iteration, it is the average temperature of the steam in the entire pipeline and T a The difference; ΔT o is the designed heat transfer temperature difference of the pipeline, °C;

[0035] Step (5), calculate the enthalpy drop ΔH caused by heat dissipation from the beginning to the end of the steam in the pipeline according to the actual heat dissipation loss Q and the flow rate G of the pipeline:

[0036]

[0037] Step (6), obtain the specific enthalpy H of the steam at the end according to the specific enthalpy H of the steam at the beginning s and the enthalpy drop ΔH caused by heat dissipation; and according to the end pressure P e and the specific enthalpy H e e , obtain the temperature drop ΔT1 caused by heat dissipation of the steam in the pipeline from the beginning to the end through the steam property;

[0038] H e =H s -ΔH (12)

[0039] Step (7), if it is the first iteration, substitute the steam density ρ under the initial condition of the pipeline s , the constant pressure specific heat capacity under the initial condition of the pipeline and ΔP1 + ΔP2, calculate the temperature drop ΔT2 caused by the expansion and cooling of the steam;

[0040] If it is not the first iteration, that is, when the number of iterations is greater than 1, substitute the density of the steam under the average pressure temperature of the pipeline, the density of the steam under the average pressure of the pipeline temperature of the pipeline, the constant pressure specific heat capacity of the steam and ΔP1 + ΔP2 + ΔP3, calculate

[0041] Step (8), calculate the steam temperature T at the end of the pipeline according to the temperature drop ΔT1 caused by heat dissipation of the steam in the pipeline from the beginning to the end and the temperature drop ΔT2 caused by the expansion and cooling of the steam e :

[0042] T e =T s -(ΔT1 + ΔT2) (14)

[0043] Step (9), if the pressure P at the end of the obtained pipelinee When the relative error between the result of the current iteration and that of the previous iteration is less than the set value, the current iteration converges; otherwise, the pressure T at the beginning of the pipeline s , temperature T s and the pressure P at the end of the pipeline e , temperature T e are used to calculate the average pressure of the steam in the entire pipeline Temperature and the density of the steam in the pipeline under the average pressure Temperature condition is obtained according to the properties of water vapor Specific enthalpy Kinematic viscosity Specific heat capacity at constant pressure and the density ρ of the steam under the condition of the pressure P at the end of the pipeline e , temperature T e condition. Then, the above steps (3) to (8) are carried out again until the result meets the convergence condition, and the iteration process ends; e

[0044]

[0045] In step (3), when the number of iterations is greater than 1, according to the steam density ρ at the beginning of the pipeline obtained in step (2) s , the pressure P at the end of the pipeline in the previous iteration obtained in step (9) e , temperature T e condition, and the steam density ρ e under the condition, and the steam flow velocity v in step (3.2), the pressure drop ΔP3 due to the acceleration effect is calculated. If it is the first iteration, this step is ignored:

[0046]

[0047] ΔP3 is the pressure drop due to the acceleration effect, kPa.

[0048] In step 4, the steps for the heat loss q per unit length of the pipeline design are as follows: o

[0049] In step (4.1), based on the thickness of each layer of the pipeline, the thermal conductivity of each layer of material, and the heat transfer coefficients on the inner and outer walls of the pipeline, the total thermal resistance ∑R per unit area of the pipeline is calculated:

[0050]

[0051] ∑R is the total thermal resistance per unit area of the pipeline, (m 2 ·℃) / W; α1 is the convective heat transfer coefficient between the inner wall of the fluid pipeline layer and the steam, W / (m 2 ·℃); k inis the thermal conductivity of the fluid pipeline layer, W / (m·°C); D i is the inner diameter of the i-th layer of the pipeline insulation layer, mm; n is the number of layers of the pipeline insulation layer; k i is the thermal conductivity of the i-th layer of the pipeline insulation layer, W / (m·°C); α2 is the combined heat transfer coefficient between the outer wall of the pipeline insulation layer and the external environment, W / (m 2 ·°C); D out is the outer diameter of the outermost insulation layer of the pipeline, mm.

[0052] In step (4.2), based on the designed heat transfer temperature difference ΔT o of the pipeline, the total thermal resistance per unit area ∑R of the pipeline obtained in step (4.1), and the outer diameter D out of the outermost insulation layer of the pipeline, calculate the heat dissipation loss q per unit length of the designed pipeline o :

[0053]

[0054] Preferably, the steam in the present invention is superheated dry steam. The steam pipeline is laid overhead.

[0055] The iteration is implemented manually or by computer;

[0056] Working principle: Aiming at the energy loss characteristics in the process of superheated steam transportation in the industrial steam pipe network system, the present invention uses the average value of steam parameters to represent the changes in its transportation process. After calculating the flow pressure loss and heat dissipation loss along the way of the pipeline by treating it as an incompressible gas, the differences between the incompressible gas and the compressible gas are corrected by calculating the pressure drop of the pipeline acceleration effect and the temperature drop of expansion cooling, so that the final result can more accurately reflect the change relationship of the true pressure and temperature of the steam in the pipe. A high-precision and fast-converging iterative calculation method is proposed, which is applicable to the design optimization, real-time monitoring and energy efficiency evaluation of the steam pipe network in thermal power generation and district energy supply systems.

[0057] The present invention first obtains the steam pressure, temperature, and flow rate values at the beginning of the pipeline through a heat network information monitoring system; converts the steam pressure at the beginning into absolute pressure, and obtains the corresponding steam physical property parameters under the initial operating conditions and design operating conditions of the pipeline according to the properties of water vapor; then judges the flow state of the steam in the pipeline to calculate the pressure drop caused by the resistance in the pipeline and the pressure drop due to the acceleration effect, and calculates the steam pressure at the end of the pipeline; calculates the actual heat loss along the pipeline; calculates the enthalpy drop caused by heat dissipation of the steam in the pipeline from the beginning to the end; calculates the specific enthalpy of the steam at the end, and obtains the temperature drop caused by heat dissipation of the steam in the pipeline from the beginning to the end and the temperature drop caused by expansion cooling of the steam through relevant formulas related to the properties of water vapor, so as to obtain the steam temperature at the end of the pipeline; if the calculation result does not meet the convergence criterion, calculates the average pressure and temperature of the steam in the entire pipeline, and obtains the steam physical property parameters of the pipeline under the average operating conditions according to the properties of water vapor, and repeats the above steps until the result meets the convergence criterion, ending the entire iterative process, and obtaining the temperature drop and pressure drop of the superheated steam in the overhead pipeline under the corresponding length.

[0058] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0059] (1) In the process of each iterative calculation, the present invention takes into account the change of steam physical property parameters, corrects the result by considering the pressure drop due to the acceleration effect and the temperature drop due to expansion cooling generated by the flow of real gas in the pipeline during the iterative process, and constructs a correction mechanism with mutual feedback between pressure drop and temperature drop. When the calculation result does not meet the convergence criterion, the average pressure temperature of the steam in the entire pipeline is used for re-iteration, and this process is repeated, achieving the effect that the final result gradually approaches the real steam parameters, making the calculated temperature drop and pressure drop values of the pipeline more accurate.

[0060] (2) In the fields of design optimization, real-time monitoring, and theoretical calculation of steam pipe networks in thermal power generation and district energy supply systems, the calculation method proposed by the present invention provides great reference value. Description of the Drawings

[0061] Figure 1 It is a calculation flow chart of the coupling calculation method for the pressure drop and temperature drop of high-temperature superheated steam in the overhead pipeline of the present invention. Specific Embodiments

[0062] The technical characteristics of the method of the present invention are further elaborated below through embodiments, but are not limited to this embodiment.

[0063] Embodiment 1

[0064] The method of the present invention is used to calculate the parameters at the end of an overhead pipeline that conveys superheated steam from a certain power plant to a certain user at a set moment. The length of the pipeline is 1500 m, and the pipe diameter is Φ630×10; the designed working pressure is 1.1 MPa, the designed working temperature is 300 °C, and the designed flow velocity is 30 m / s; the material of the fluid pipeline layer is Q235B, and at the designed average temperature, k in = 46.826 W / (m·°C), and the absolute roughness of the pipe wall ε = 0.2 mm; the insulation layer structure is a four-layer cylindrical surface with a total thickness of 210 mm, and the insulation material is all glass wool. At the designed average temperature, k i = 0.056 W / (m·°C); the ambient temperature is 16 °C. The specific calculation steps are as follows:

[0065] Step (1): Obtain the steam pressure P s = 0.63 MPa, temperature T s = 280.3 °C, and flow rate G = 40.12 t / h, that is, 11.14 kg / s at the beginning of the calculated pipeline through the heat network information monitoring system;

[0066] Step (2): The local atmospheric pressure is taken as P a = 0.101325 MPa, and the obtained steam pressure P s is converted into the absolute pressure P abs = 0.731325 MPa. According to the relevant formulas of water vapor properties, the density ρ s of the steam under the initial conditions of the pipeline is obtained as 2.923 kg / m 3 , the specific enthalpy H s = 3017.26 kJ / kg, the kinematic viscosity γ s = 6.63×10 -6 m 2 / s, and the specific heat capacity at constant pressure Pipeline design conditions: density ρ = 4.681 kg / m 3 , kinematic viscosity γ = 4.31×10 -6 m 2 / s, dynamic viscosity μ = 2.02×10 -5 Pa·s, specific heat capacity at constant pressure c P = 2.174 kJ / (kg·°C), and thermal conductivity k = 0.045 W / (m·°C);

[0067] Step (3): Since it is the first iteration, substitute ρ s , γ s for calculation, judge the flow state of the steam in the pipeline to calculate the pressure drop ΔP1 + ΔP2 caused by the resistance in the pipeline, and calculate the steam pressure P e at the end of the pipeline;;

[0068] Step (3.1): Calculate the flow area A of the pipeline s = 0.2922 m 2 ;

[0069] Step (3.2): Calculate the steam velocity υ in the pipeline = 13.05 m / s;

[0070] Step (3.3): Calculate the Reynolds number Re = 1.201×10 6 ;

[0071] Step (3.4): Since Re > 10 6 , calculate the pipeline friction resistance coefficient λ = 0.0148;

[0072] Step (3.5): Calculate the specific frictional resistance R of the pipeline m = 6.04 Pa / m;

[0073] Step (3.6): Calculate the pressure drop ΔP1 caused by the local resistance of the pipeline = 8.154 kPa;

[0074] Step (3.7): Calculate the pressure drop ΔP2 caused by the pipeline friction resistance = 9.06 kPa;

[0075] Calculate the pressure P at the end of the pipeline e = 0.613 MPa;

[0076] Step (4): The actual heat transfer temperature difference ΔT = 280.3 - 16 = 264.3 °C, the designed heat transfer temperature difference ΔT of the pipeline o = 300 - 16 = 284 °C, calculate the actual heat dissipation loss Q of the pipeline along the way;

[0077] Step (4.1): According to the formula Calculate the total thermal resistance ∑R per unit area of the pipeline;

[0078] According to the formula Calculate the Prandtl number Pr = 0.967;

[0079] Calculate the Reynolds number Re under the designed condition = 4.307×10 6 ;

[0080] Since 10 4 ≤ Re ≤ 5×10 6 , 0.5 ≤ Pr ≤ 2000, use the calculation formula of the Nusselt number Calculate Nu f = 7493.17;

[0081] According to the formula The convective heat transfer coefficient α1 between the inner wall of the fluid pipeline layer and the steam under the design conditions is calculated to be 539 W / (m 2 ·℃);

[0082] According to the formula where the wind speed ω a is taken as 0 m / s, the comprehensive heat transfer coefficient α2 between the outer wall of the pipeline insulation layer and the external environment under the design conditions is calculated to be 11.63 W / (m 2 ·℃);

[0083] The total thermal resistance per unit area of the pipeline ∑R is calculated to be 1.662 (m 2 ·℃) / W;

[0084] Step (4.2): The heat dissipation loss q per unit length of the pipeline is calculated o = 601.25 W / m;

[0085] The actual heat dissipation loss Q along the pipeline is calculated to be 839.315 kW;

[0086] Step (5): The enthalpy drop ΔH caused by heat dissipation is calculated to be 75.34 kJ / kg;

[0087] Step (6): The specific enthalpy H of the steam at the end is calculated e = 2941.92 kJ / kg, and the temperature drop ΔT1 of the steam in the pipeline from the start end to the end caused by heat dissipation is obtained through the relevant formula of water vapor properties = 35.8℃;

[0088] Step (7): The temperature drop ΔT2 caused by steam expansion and cooling is calculated to be 2.8℃;

[0089] Step (8): The steam temperature T at the end of the pipeline is calculated e = 241.7℃;

[0090] Step (9): The calculation result this time does not meet the convergence criterion. The average pressure of the steam in the entire pipeline is calculated Average temperature According to the relevant formula of water vapor properties, the density of the steam under the average pressure Temperature Working condition of the steam Kinematic viscosity Repeat the above steps 3 to 8, and consider step 3.9 in the subsequent iterations until the result meets the convergence criterion, and end the entire iteration process;

[0091] Since the specific calculation process of the iteration is relatively long, only the first calculation process is shown here. The steps of subsequent multiple iterations are the same as the above process. The final calculation result that meets the convergence is: P e= 0.617 MPa, T e = 246.77 °C. The relative error between this result and the actual value is within the allowable range of the relative error in engineering calculations, proving that this iterative calculation model has a high calculation accuracy in this embodiment and meets the application requirements.

[0092] The implementation process of the technical solution described in the present invention has been described in detail above. To facilitate the understanding of the essence and implementation of the present invention, this specification provides an exemplary description of the technical principle, operation steps, and implementation method in combination with specific implementation examples. The explanation of Embodiment 1 aims to reflect the typical application scenarios of the core inventive concept of the present invention. It should be noted that those skilled in the art can make any reasonable adjustments and optimizations based on the basic inventive concept of the present invention on the basis of fully understanding the technical principle of the present invention. Such equivalent replacements or partial adaptive modifications should still fall within the protection scope defined by the claims of the present invention.

Claims

1. A coupled calculation method for pressure drop and temperature drop of high-temperature superheated steam in an overhead pipeline, characterized in that: It includes the following steps: Step (1): Collect and monitor the steam parameters at the nodes in the pipe network to obtain the steam pressure P at the beginning of the pipe s , the steam temperature T s and the steam flow rate G; Step (2), obtaining the steam density ρ at the beginning of the pipeline s , specific enthalpy H s , kinematic viscosity γ s , specific heat capacity at constant pressure and the density ρ, kinematic viscosity γ, dynamic viscosity μ, and specific heat capacity at constant pressure c of the steam under the designed operating conditions of the pipeline P , thermal conductivity k; converting the steam pressure P at the beginning of the pipeline s into the absolute pressure P abs : P abs = P s + P a (1) where P a is the local atmospheric pressure of the steam pipeline, kPa; Step (3), if it is the first iteration, determine the flow state of the steam in the pipeline to calculate the pressure drop ΔP1+ΔP2 caused by the resistance in the pipeline, and calculate the steam pressure P at the end of the pipeline. e ; if it does not meet the convergence condition after step (9), return to the said step (3), and substitute the values obtained in the previous step (9). Determine the flow state of the steam in the pipeline to calculate ΔP1+ΔP2, and substitute ρ. s and the ρ obtained in the previous step (9). e Solve for the pressure drop ΔP3 due to the acceleration effect, and calculate P. e The process of the first iteration is as follows: Step (3.1), according to the inner diameter D of the pipeline in Calculate the flow area A of the pipeline s : D in is the inner diameter of the pipe; Step (3.2), according to the flow area A of the pipeline s , the density ρ of the steam at the beginning of the pipeline s , and the steam flow rate G at the beginning of the pipeline, calculate the steam velocity v in the pipeline: Step (3.3), according to the steam flow velocity v, the inner diameter D of the pipeline in and the kinematic viscosity of the steam is γ s , calculate the Reynolds number Re: Step (3.4), determine the flow state of the steam in the pipeline according to the Reynolds number Re, and calculate the pipeline friction resistance coefficient λ: ε is the absolute roughness of the pipeline; Step (3.5), according to the steam density ρ s , the steam flow velocity v, the pipeline friction resistance coefficient λ and the pipeline inner diameter D in , calculate the specific frictional resistance R of the pipeline m : Step (3.6), according to the specific frictional resistance R of the pipeline m Calculate the pressure drop ΔP1 caused by the local resistance of the pipeline: ΔP1 = ∑ξ·R m L·10 -3 (7) ΔP1 is the pressure drop caused by the local resistance of the pipeline, kPa; ∑ξ is the total local resistance coefficient of the valves and pipe fittings in the pipeline; Step (3.7), according to the specific frictional resistance R of the pipeline m calculate the pressure drop ΔP2 caused by the pipeline frictional resistance: ΔP2 = R m L·10 -3 (8) ΔP2 is the pressure drop caused by the pipeline friction resistance, kPa; P e = P s -(ΔP1 + ΔP2)·10 -3 (9) Step (4), according to the actual heat transfer temperature difference ΔT, the heat transfer temperature difference ΔT o under the design condition, the external environmental temperature T a and the heat dissipation loss q per unit length of the pipeline designed by the pipeline design unit o , calculate the actual heat dissipation loss Q of the pipeline along the way: Q is the actual heat loss along the pipeline, in kW; q o is the heat loss per unit length of the pipeline designed by the design unit, in W / m; L is the length of the pipeline, in m; ΔT is the actual heat transfer temperature difference of the pipeline, in °C. If it is the first iteration, it is the steam temperature T s at the beginning of the pipeline minus the outside ambient temperature T a . Otherwise, it is the average temperature of the steam in the entire pipeline minus T a ; ΔT o is the designed heat transfer temperature difference of the pipeline, in °C; Step (5), calculate the enthalpy drop ΔH caused by heat dissipation of the steam in the pipeline from the start end to the end end according to the actual heat dissipation loss Q and flow rate G of the pipeline: Step (6), based on the specific enthalpy H of the steam at the starting end s and the enthalpy drop ΔH caused by heat dissipation, obtain the specific enthalpy H of the steam at the ending end e , and based on the ending pressure P e and the specific enthalpy H e obtain the temperature drop ΔT1 of the steam in the pipeline from the starting end to the ending end caused by heat dissipation; H e = H s -ΔH (12) Step (7), substitute the steam density ρ s , constant pressure specific heat capacity and ΔP1 + ΔP2, and calculate the temperature drop ΔT2 caused by steam expansion and cooling: Step (8), calculate the steam temperature T at the end of the pipeline according to the temperature drop ΔT1 caused by heat dissipation of the steam in the pipeline from the starting end to the ending end and the temperature drop ΔT2 caused by the expansion and cooling of the steam e : T e = T s - (ΔT1 + ΔT2) (14) Step (9), if the relative error between the pressure P e at the end of the pipeline and the result of the previous iteration is less than the set value, the iteration converges; otherwise, from the pressure P s , temperature T s at the beginning of the pipeline and the pressure P e , temperature T e at the end of the pipeline, calculate the average pressure of the steam in the entire pipeline temperature and obtain the density temperature of the steam under the condition of the average pressure specific enthalpy kinematic viscosity specific heat capacity at constant pressure Then return to steps (3)-(8) until the result meets the convergence condition; 2. The coupled calculation method for pressure drop and temperature drop of high-temperature superheated steam in overhead pipelines according to claim 1, characterized in that: In step (3), when the number of iterations is greater than 1, according to the steam density ρ at the beginning of the pipeline in step (2) s , the end pressure P of the pipeline in the previous iteration in step (9) e , temperature T e Under the working condition, the steam density ρ e , and the steam flow velocity v in step (3.2), calculate the acceleration effect pressure drop ΔP3:

3. The coupled calculation method for pressure drop and temperature drop of high-temperature superheated steam in an overhead pipeline according to claim 1, characterized in that: In step (4), the heat dissipation loss q per unit length of the pipeline design is as follows: o The steps are as follows: (4.1), calculate the total thermal resistance ∑R per unit area of the pipeline according to the thickness of each layer of the pipeline, the thermal conductivity of each layer of material, and the heat transfer coefficients of the inner and outer walls of the pipeline: ∑R is the total thermal resistance per unit area of the pipeline, (m 2 ·℃) / W; α1 is the convective heat transfer coefficient between the inner wall of the fluid pipeline layer and the steam, W / (m 2 ·℃); k in is the thermal conductivity of the fluid pipeline layer, W / (m·℃); D i is the inner diameter of the i-th layer of the pipeline insulation layer, mm; n is the number of layers of the pipeline insulation layer; k i is the thermal conductivity of the i-th layer of the pipeline insulation layer, W / (m·℃); α2 is the combined heat transfer coefficient between the outer wall of the pipeline insulation layer and the external environment, W / (m 2 ·℃); D out is the outer diameter of the outermost insulation layer of the pipeline, mm; (4.2), according to the heat transfer temperature difference ΔT of the pipeline design o , the total thermal resistance ∑R per unit area of the pipeline and the outer diameter D of the outermost thermal insulation layer of the pipeline obtained in step (4.1) out , the heat dissipation loss q per unit length of the pipeline design is obtained o :

4. The coupled calculation method for pressure drop and temperature drop of high-temperature superheated steam in overhead pipelines according to claim 1, characterized in that: In step (7), when the number of iterations is greater than 1, substitute the density of steam under the average pressure temperature of the pipeline into the calculation, and substitute the specific heat capacity at constant pressure of steam under the average pressure temperature of the pipeline into the calculation, and perform the calculation of ΔP1 + ΔP2 + ΔP3 , and the calculation of ΔP1 + ΔP2 + ΔP3 5. The coupled calculation method for pressure drop and temperature drop of high-temperature superheated steam in an overhead pipeline according to claim 1, characterized in that: In step (2), when the number of iterations is greater than 1, the density of the steam at the beginning of the pipeline is 6. The coupled calculation method for pressure drop and temperature drop of high-temperature superheated steam in overhead pipelines according to claim 1, characterized in that: In step (2), when the number of iterations is greater than 1, the kinematic viscosity of the steam is 7. The coupled calculation method for pressure drop and temperature drop of high-temperature superheated steam in overhead pipelines according to claim 1, characterized in that: In step (3.4), the steam flow in the pipeline is in the square resistance region where the Reynolds number Re > 10 6 .

8. The coupled calculation method for pressure drop and temperature drop of high-temperature superheated steam in an overhead pipeline according to claim 1, characterized in that: Collect and monitor the steam parameters of the nodes in the pipe network through the heat network information monitoring system.

9. The coupled calculation method for pressure drop and temperature drop of high-temperature superheated steam in overhead pipelines according to claim 1, characterized in that: The steam in the pipeline is superheated dry steam.

10. The coupled calculation method for pressure drop and temperature drop of high-temperature superheated steam in an overhead pipeline according to claim 1, characterized in that: The steam pipeline adopts an overhead laying form.

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