Calculation method of steam pipeline parameters

Abstract

The invention relates to the technical field of pipeline parameters, and provides a steam pipeline parameter calculation method which comprises the following steps: S1, inputting the length L of a steam pipeline and a steam pressure value Pi, a steam temperature value ti and a steam mass flow qm, i of an inlet of the steam pipeline; s2, determining a steam enthalpy value hi and a steam specific volume Vi of an inlet of the steam pipeline; s3, Vcp = 0.5 (Vi + V0), wherein V0 represents the steam specific volume of the outlet of the steam pipeline; s4, the pressure drop of the steam pipeline is calculated, and the heat dissipation loss of the outer surface of the steam pipeline is calculated; s5, the steam pressure value p0 and the steam enthalpy value h0 of an outlet of the steam pipeline are calculated; s6, the steam temperature value t0 and the steam specific volume V0 of an outlet of the steam pipeline are calculated; s7, if Vo-Vi / Vo is smaller than or equal to 0.2%, calculation is finished, and the steam temperature value t0 of an outlet of the steam pipeline is output; and S8, if Vo-Vi / Vo is greater than 0.2%, returning to the step S3 for recalculation after steam mass loss correction is carried out.

Description

Technical Field

[0001] The invention relates to the technical field of pipeline parameter calculation, and in particular to a method for calculating steam pipeline parameters. Background Art

[0002] During long-distance transportation, the thermal state parameters of steam (such as temperature, pressure and enthalpy) will change significantly. These parameters are coupled with each other and jointly affect the operating conditions of the pipeline. The change of the thermal state of steam not only affects the heat transfer process, but also leads to dynamic changes in hydraulic calculation parameters (such as flow rate, flow rate and pressure drop). Therefore, in the hydraulic calculation of long-distance steam pipelines, considering hydraulic or thermal parameters alone may lead to deviations in results. It is necessary to combine hydraulic calculations with thermal calculations to more accurately predict the changing trends of pressure drop and temperature drop, and provide a scientific basis for pipeline design and operation optimization.

[0003] However, the generation of condensate is an important phenomenon in the operation of steam pipelines. Its generation and distribution directly affect the heat loss and quality loss of steam pipelines, and are closely related to the safety and stability of steam pipelines. For example, the accumulation of condensate in the pipeline may lead to local overheating areas or water hammer, endangering the safe operation of steam pipelines. Therefore, it is an urgent problem to be solved in the optimization design of steam pipelines to study the generation mechanism, influencing factors and distribution characteristics of condensate during steam transportation and improve the operating efficiency and safety of steam pipelines. Summary of the invention

[0004] In view of the defects in the prior art, the object of the present invention is to provide a method for calculating steam pipeline parameters, which can fully take into account the influence of condensed water and improve the operating efficiency and safety of the steam pipeline.

[0005] The present invention provides a method for calculating steam pipeline parameters, which combines a hydraulic calculation model and a thermal calculation model, and comprises the following steps:

[0006] S1, the length L of the steam input pipe, and the steam pressure value P at the inlet of the steam pipe i , steam temperature value t i , steam mass flow rate q m,i ;

[0007] S2. Determine the steam enthalpy value h at the steam pipeline inlet i and steam specific volume V i , tentatively define the steam specific volume V at the steam pipe inlet i The average steam specific volume V of the steam pipeline cp equal;

[0008] S3, let V cp =0.5(Vi +V0), wherein V0 represents the steam specific volume at the outlet of the steam pipeline;

[0009] S4, calculating the pressure drop of the steam pipeline using the hydraulic calculation model, and calculating the heat dissipation loss of the outer surface of the steam pipeline using the thermal calculation model;

[0010] S5, calculating the steam pressure value p0 and the steam enthalpy value h0 at the outlet of the steam pipeline;

[0011] S6, calculating the steam temperature value t0 and the steam specific volume V0 at the outlet of the steam pipeline;

[0012] S7, if |V o -V i | / V o ≤0.2%, the calculation is completed and the steam temperature value t0 at the outlet of the steam pipeline is output;

[0013] S8, if |V o -V i | / V o >0.2%, then after making correction for the steam quality loss, the process returns to step S3 and recalculates.

[0014] Further, the steam quality loss correction includes the following steps:

[0015] S9, first calculating the critical conveying distance L0 of the steam pipeline;

[0016]

[0017] Wherein, t0 is the outer wall temperature of the steam pipe inlet, t a is the ambient temperature, t b is the steam saturation temperature at the steam pipe inlet, c is the steam specific heat capacity, λ is the friction coefficient of the steam pipe, D0 is the outer diameter of the steam pipe, D1 is the inner diameter of the steam pipe insulation layer, α is the heat transfer coefficient of the steam pipe, and q is tentatively set m,i =q m,0 ;

[0018] S10, if L<L0, no condensed water will appear in the steam pipe, and the process returns to step S4;

[0019] S11. If L ≥ L0, condensed water will appear in the steam pipe. Calculate the mass flow rate qmc of the condensed water:

[0020]

[0021] Wherein, φ is the heat dissipation loss of the outer surface of the steam pipe, and γ is the latent heat of vaporization of water;

[0022] Obviously, q m,i =q m,o +q m,c , return to step S9 for iterative calculation.

[0023] Furthermore, in step S11, pressure drop correction and enthalpy value correction need to be performed;

[0024] Pressure drop correction:

[0025] Where q is the average mass flow rate of steam, q = 0.5 × (q m,i +q m,o ), R is the gas constant, m c is the amount of condensed water;

[0026] Enthalpy correction: q m,i ·h i =q m,o ·h o +q m,c ·h c +Φ·L.

[0027] Furthermore, the steam is superheated steam.

[0028] Beneficial effects: The present invention provides a vertical thin-tank docking device based on three-camera measurement and its design method. By monitoring the temperature drop, pressure drop and steam quality loss of the steam pipeline, it can not only fully grasp the dynamic changes of steam in the steam pipeline, but also provide a scientific basis for steam pipeline design, operation optimization and energy-saving management. This calculation method combined with modern monitoring means can effectively improve the operating efficiency and safety of steam pipelines and achieve the goal of efficient and low-carbon heating. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a schematic diagram of the process structure of the present invention. DETAILED DESCRIPTION

[0030] In order to make the technical means, creative features, objectives and effects achieved by the present invention easy to understand, the present invention is further explained below in conjunction with specific implementation methods.

[0031] In the present invention, unless otherwise clearly specified and limited, the terms "connection" and "fixation" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0032] In the description of the present invention, it is necessary to understand that the terms "longitudinal", "lateral", "horizontal", "top", "bottom", "up", "down", "inside" and "outside" etc. indicating orientations or positional relationships are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0033] In addition, the terms "first", "second", etc. are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. In the description of the present invention, the meaning of "plurality" is more than two, unless otherwise clearly and specifically defined.

[0034] like Figure 1 As shown, the present invention provides a method for calculating steam pipeline parameters, combining a hydraulic calculation model and a thermal calculation model.

[0035] In the hydraulic calculation model, the pressure drop calculation formula for steam transport in the steam pipeline is:

[0036]

[0037] Among them, P i is the steam pressure at the steam pipe inlet, in MPa; P o is the steam pressure at the steam pipe outlet, in MPa; ρ is the steam density, in kg / m 3 ; u is the steam flow rate, in m / s; D is the inner diameter of the steam pipe, in m; L is the length of the steam pipe, in m; Ld is the equivalent length of the local resistance of the steam pipe, in m; λ is the friction coefficient of the steam pipe.

[0038] In the thermal calculation model, the calculation formula for the change in enthalpy of steam transported in the steam pipeline is:

[0039] q m,i ·h i =q m,o ·h o +q m,c ·h c +Φ·L;

[0040] Among them, q m,i is the steam mass flow rate at the steam pipe section inlet, in kg / s; q m,o is the steam mass flow rate at the steam pipe outlet, in kg / s; q m,c is the mass flow rate of condensed water in the steam pipeline, in kg / s; h iis the steam enthalpy at the steam pipe inlet, in kJ / kg; h o is the steam enthalpy at the outlet of the steam pipe, in kJ / kg; Φ is the heat loss of the outer surface of the steam pipe, in kW / m.

[0041] The calculation steps of the heat dissipation loss Φ on the outer surface of the steam pipe are:

[0042] a. Average internal and external temperature of the steam pipe insulation layer

[0043] Where T is the steam temperature in the steam pipe, in °C; T a is the ambient temperature in °C.

[0044] b. The thermal conductivity of the steam pipe insulation layer is generally calculated according to the formula provided by the supplier, or can be calculated according to λ=λ0+0.0002·(T m -70) Simplified calculation

[0045] Wherein, λ is the calculated thermal conductivity of the steam pipe insulation layer, in W / (m·K); λ0 is the basic thermal conductivity (70°C) of the steam pipe insulation layer, in W / (m·K).

[0046] C. The heat dissipation loss Φ of the outer surface of the steam pipe can be calculated according to the following formula:

[0047]

[0048] Wherein, D0 is the outer diameter of the steam pipe, in m; D1 is the outer diameter of the steam pipe insulation layer, in m; δ is the thickness of the steam pipe insulation layer, in m; W is the wind speed, in m / s; α is the surface heat transfer coefficient of the steam pipe, in W / (m2·K); K is the margin coefficient, which is 0.8.

[0049] The above contents are all prior art, and the specific principles will not be repeated here.

[0050] The present invention comprises the following steps:

[0051] S1, the length of the steam input pipe L, and the steam pressure value P at the steam pipe inlet i , steam temperature value t i , steam mass flow rate q m,i .

[0052] S2. Determine the steam enthalpy value h at the steam pipe inlet according to the enthalpy entropy table i and steam specific volume V i , tentatively assume the steam specific volume V at the steam pipe inlet i The average steam volume V of the steam pipe cp equal.

[0053] S3, let V cp =0.5(V i +V0), where V0 represents the steam specific volume at the steam pipe outlet.

[0054] S4. Use the hydraulic calculation model to calculate the pressure drop of the steam pipe, and use the thermal calculation model to calculate the heat dissipation loss of the outer surface of the steam pipe.

[0055] S5. Combine steps 1, 2 and 4 to calculate the steam pressure value p0 and steam enthalpy value h at the steam pipe outlet. 0, .

[0056] S6. When the steam pressure value p0 and steam enthalpy value h at the steam pipe outlet 0, After the determination, the IAPWS-IF97 international industrial water and steam thermodynamic property calculation formula can be used to further calculate the outlet steam temperature and steam specific volume V0;

[0057] S7, if V i and V o The difference is less than or equal to 0.2%, that is, |V o -V i | / V o ≤0.2%, the calculation ends and the steam temperature value t0 at the steam pipe outlet is output.

[0058] S8, if V i and V o The difference is greater than 0.2%, that is, |V o -V i | / V o >0.2%, then after making correction for the steam quality loss, the process returns to step S3 and recalculates.

[0059] In one embodiment, steam quality loss correction includes the following steps:

[0060] S9. For long-distance steam pipelines, condensate is usually generated due to factors such as ambient temperature and local insulation failure. The condensate is discharged from the pipeline through the steam trap, which causes steam quality loss. Therefore, the steam quality loss must be corrected.

[0061] First calculate the critical transport distance L0 of the steam pipeline;

[0062]

[0063] Where t0 is the outer wall temperature of the steam pipe inlet, t a is the ambient temperature, t bis the steam saturation temperature at the steam pipe inlet, c is the steam specific heat capacity, λ is the friction coefficient of the steam pipe, D0 is the outer diameter of the steam pipe, D1 is the inner diameter of the steam pipe insulation layer, α is the heat transfer coefficient of the steam pipe, and q is tentatively set m,i =q m,0 ;

[0064] S10. If L<L0, no condensed water will appear in the steam pipe, and the process returns to step S4.

[0065] S11. If L ≥ L0, condensate will appear in the steam pipe. Calculate the mass flow rate qmc of condensate:

[0066]

[0067] Among them, φ is the heat dissipation loss of the outer surface of the steam pipe, and γ is the latent heat of vaporization of water;

[0068] Obviously, q m,i =q m,o +q m,c , return to step S9 for iterative calculation.

[0069] In one embodiment, the presence of condensate will cause the steam mass flow rate q m,i Changes, which in turn affect the steam flow rate, that is, the steam pressure loss and steam enthalpy in the steam pipeline, and then affect the steam pressure drop and temperature drop.

[0070] Therefore, in step S11, pressure drop correction and enthalpy value correction are also required.

[0071] Pressure drop correction:

[0072] Where q is the average mass flow rate of steam, q = 0.5 × (q m,i +q m,o ), R is the gas constant, m c The amount of condensed water.

[0073] Enthalpy correction: q m,i ·h i =q m,o ·h o +q m,c ·h c +Φ·L.

[0074] In one embodiment, the steam is superheated steam.

[0075] By monitoring the temperature drop, pressure drop and steam quality loss of the steam pipeline, the present invention can not only fully grasp the dynamic changes of steam in the steam pipeline, but also provide a scientific basis for the design, operation optimization and energy-saving management of the steam pipeline. This calculation method combined with modern monitoring means can effectively improve the operating efficiency and safety of the steam pipeline and achieve the goal of efficient and low-carbon heating.

[0076] From the perspective of engineering application, the advantages of the present invention in calculating pressure drop and temperature drop enable it to better meet the dual requirements of modern engineering for accuracy and efficiency, and can be compared with real-time measurement point data to discover abnormal operation of steam pipelines.

[0077] The above shows and describes the basic principles and main features of the present invention and the advantages of the present invention. It is obvious to those skilled in the art that the present invention is not limited to the details of the above exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or basic features of the present invention. Therefore, no matter from which point of view, the embodiments should be regarded as exemplary and non-restrictive. The scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims are included in the present invention.

[0078] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A method for calculating steam pipeline parameters, combining a hydraulic calculation model and a thermal calculation model, characterized in that: The following steps are involved: S1, the length L of the steam input pipe, and the steam pressure value P at the inlet of the steam pipe i , steam temperature value t i , steam mass flow rate q m,i ; S2. Determine the steam enthalpy value h at the steam pipeline inlet i and steam specific volume V i , tentatively define the steam specific volume V at the steam pipe inlet i The average steam specific volume V of the steam pipeline cp equal; S3, let V cp =0.5(V i +V0), wherein V0 represents the steam specific volume at the outlet of the steam pipeline; S4, calculating the pressure drop of the steam pipeline using the hydraulic calculation model, and calculating the heat dissipation loss of the outer surface of the steam pipeline using the thermal calculation model; S5, calculating the steam pressure value p0 and the steam enthalpy value h0 at the outlet of the steam pipeline; S6, calculating the steam temperature value t0 and the steam specific volume V0 at the outlet of the steam pipeline; S7, if |V o -V i | / V o ≤0.2%, the calculation is completed and the steam temperature value t0 at the outlet of the steam pipe is output; S8, if |V o -V i | / V o >0.2%, then after making correction for the steam quality loss, the process returns to step S3 and recalculates.

2. A method for calculating steam pipeline parameters according to claim 1, characterized in that: Steam quality loss correction involves the following steps: S9, first calculating the critical conveying distance L0 of the steam pipeline; Wherein, t0 is the outer wall temperature of the steam pipe inlet, t a is the ambient temperature, t b is the steam saturation temperature at the steam pipe inlet, c is the steam specific heat capacity, λ is the friction coefficient of the steam pipe, D0 is the outer diameter of the steam pipe, D1 is the inner diameter of the steam pipe insulation layer, α is the heat transfer coefficient of the steam pipe, and q is tentatively set m,i =q m,0 ; S10, if L<L0, no condensed water will appear in the steam pipe, and the process returns to step S4; S11. If L ≥ L0, condensed water will appear in the steam pipe. Calculate the mass flow rate qmc of the condensed water: Wherein, φ is the heat dissipation loss of the outer surface of the steam pipe, and γ is the latent heat of vaporization of water; Obviously, q m,i =q m,o +q m,c , return to step S9 for iterative calculation.

3. The method for calculating steam pipeline parameters according to claim 1, characterized in that: In step S11, pressure drop correction and enthalpy value correction are also required; Pressure drop correction: Where q is the average mass flow rate of steam, q = 0.5 × (q m,i +q m,o ), R is the gas constant, m c is the amount of condensed water; Enthalpy correction: q m,i ·h i =q m,o ·h o +q m,c ·h c +Φ·L.

4. A method for calculating steam pipeline parameters according to claim 1, characterized in that: The steam is superheated steam.

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