A method for calculating flow of steam heating network considering the influence of pressure and temperature

Abstract

The present invention discloses a method for calculating the flow of a steam heating network considering the influence of pressure and temperature. The method comprises: S101: reading the parameters of the pipeline; S107: until |T i (k+1) ‑T i (k) |≤ε, ε is a predetermined maximum error; S108: After obtaining the temperature distribution of each node, the pressure distribution can be calculated, and the heating power at the steam source can be calculated by the product formula of the steam enthalpy and the steam flow rate; the present invention can obtain the state variable distribution of the heating network through steam flow calculation, and for the heating system under planning, the flow calculation can be used to verify whether the proposed planning scheme can meet the requirements of various operating modes; for the heating system in operation, the flow calculation can be used to predict whether various load changes and changes in network structure will endanger the safety of the system, and what preventive measures should be taken in advance when safety problems may occur.

Description

Technical Field

[0001] The invention relates to the technical field of steam heating pipe networks, and in particular to a method for calculating a flow of a steam heating pipe network taking into account the influence of pressure and temperature. Background Art

[0002] Steam heating has become increasingly common in industrial production and civil heating. The steam network has also become an important energy conversion and transmission link in the multi-energy complementary integrated energy system. Therefore, the flow solution of the steam network pipeline model and the steam load model is also the basis for system capacity planning, system equipment selection and network structure planning.

[0003] The steam network is mainly provided for industrial users with high requirements for heating quality, and the high-temperature and high-pressure steam is complex to control at the load end, so the steam load at the load end adopts a model of temperature and pressure reducing valve. At present, the flow mathematical model of steam is established through the continuity equation and momentum equation. Combined with the steam state equation, the continuity equation, motion equation and energy conservation equation that the steam flow should follow are combined to form a hydraulic and thermal mathematical model of steam flow. The hydraulic and thermal model is used for calculation, and the node state information is solved by correcting the pipeline flow, pipeline average density and constant pressure specific heat. The state parameters of steam change greatly during the transportation process, and are accompanied by phase change.

[0004] The current hydraulic and thermal calculation methods for steam pipe networks have the following problems: first, steam is regarded as an ideal gas, ignoring the phase change during steam transmission. Second, the loss of steam during transmission is not considered, resulting in a certain deviation in the calculation results. Finally, the impact of thermal calculation is not considered during hydraulic calculation. Summary of the invention

[0005] The object of the present invention is to provide a method for calculating the flow of a steam heating network taking into account the influence of pressure and temperature, so as to solve the problems raised in the above-mentioned background technology.

[0006] To achieve the above object, the present invention provides the following technical solution: a method for calculating the flow of a steam heating network considering the influence of pressure and temperature, the method comprising:

[0007] S101: Read the parameters of the pipeline: pipeline diameter D, friction resistance coefficient λ, gas density ρ, gas flow rate ν, read the parameters of the cooling water: temperature T, pressure P, parameters before the cooling and pressure reducing valve: temperature T1, pressure P1, parameters after the cooling and pressure reducing valve: temperature T2, pressure P2;

[0008] S102: Calculate the flow rate m of the cooling water, the flow rate m1 before the cooling and pressure reducing valve, and the flow rate m2 after the cooling and pressure reducing valve according to the flow continuity equation;

[0009] S103: Calculate the enthalpy value H of the desuperheating water, the enthalpy value H1 before the desuperheating and pressure reducing valve, and the enthalpy value H2 after the desuperheating and pressure reducing valve according to the engineering calculation formula of the enthalpy value;

[0010] S104: Set the initial value T of the temperature before the valve i (k) , and calculate the steam enthalpy before the valve according to the engineering calculation formula of enthalpy;

[0011] S105: Calculate the flow rate of the cooling water by using the flow calculation formula of the cooling water valve according to the enthalpy value H1 before the cooling water valve, the enthalpy value H2 after the cooling water valve, and the enthalpy value H of the cooling water, and calculate the inlet flow rate of the cooling water valve by using the mass balance formula and the heat balance formula;

[0012] S106: Based on the flow conservation principle, the flow of each pipeline is calculated forward, and the temperature of each node is calculated from the steam source node through the pipeline heat loss equation to obtain the temperature update value T before the temperature reduction and pressure relief valve. i (k+1) ;

[0013] S107: Repeat steps S104-S106 until |T is satisfied i (k+1) -T i (k) |≤ε, ε is the maximum error given in advance;

[0014] S108: After obtaining the temperature distribution of each node, the pressure distribution is calculated, and the heating power at the steam source is calculated by the product formula of the steam enthalpy and the steam flow rate.

[0015] Wherein, the flow continuity equation is:

[0016]

[0017] Among them, m is the flow rate, ρ is the gas density, ν is the gas flow velocity, and D is the direct drop in the pipeline.

[0018] Wherein, the engineering calculation formula of the enthalpy value is:

[0019] H=-0.00274×T 2 +1.905×T+2520

[0020] Where H is the enthalpy and T is the temperature.

[0021] The flow calculation formula of the temperature and pressure reducing valve is:

[0022]

[0023] Among them, m sis the maximum flow of steam at the valve inlet, H1 is the enthalpy value before the temperature and pressure reducing valve, H2 is the enthalpy value after the temperature and pressure reducing valve, and H is the enthalpy value of the temperature and pressure reducing water.

[0024] Wherein, the mass balance equation and heat balance equation are:

[0025]

[0026] Among them, the pipeline heat loss equation is:

[0027]

[0028] Where △t is the temperature drop of the pipeline, q is the heat loss per unit length, η is the local heat dissipation correction factor, C p is the specific heat at constant pressure, and m is the pipeline flow rate.

[0029] Wherein, the product formula of the steam enthalpy value and the steam flow rate is:

[0030] Q=m·H

[0031] Among them, Q represents steam power, H is steam enthalpy, and the physical meaning of steam enthalpy is the heat contained in unit mass of steam.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] 1. In the process of calculating the flow of the steam network, the heating demand before the valve is calculated by forward-pushing the parameters of the demand after the valve. The steam generated by the steam boiler has a certain pressure. The parameters of each node are backward-pushed according to the calculated flow rate, and the parameters required after the valve are iteratively optimized to verify the operational reliability of the steam network.

[0034] 2. The present invention can obtain the state variable distribution of the heating network through steam flow calculation. For the heating system under planning, the flow calculation can be used to verify whether the proposed planning scheme can meet the requirements of various operating modes; for the heating system in operation, the flow calculation can be used to predict whether various load changes and changes in network structure will endanger the safety of the system, and what preventive measures should be taken in advance when safety problems may occur. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a schematic diagram of the structure of the physical model of the temperature and pressure reducing valve of the present invention;

[0036] Figure 2 It is a schematic diagram of the steam network flow calculation process structure of the present invention. DETAILED DESCRIPTION

[0037] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0038] See also Figure 1-2 This embodiment provides a technical solution: a method for calculating the flow of a steam heating network considering the influence of pressure and temperature, the method comprising:

[0039] S101: Read the parameters of the pipeline: pipeline diameter D, friction resistance coefficient λ, gas density ρ, gas flow rate ν, read the parameters of the cooling water: temperature T, pressure P, parameters before the cooling and pressure reducing valve: temperature T1, pressure P1, parameters after the cooling and pressure reducing valve: temperature T2, pressure P2;

[0040] S102: Calculate the flow rate m of the cooling water, the flow rate m1 before the cooling and pressure reducing valve, and the flow rate m2 after the cooling and pressure reducing valve according to the flow continuity equation (3);

[0041] S103: Calculate the enthalpy value H of the desuperheating water, the enthalpy value H1 before the desuperheating and pressure reducing valve, and the enthalpy value H2 after the desuperheating and pressure reducing valve according to the engineering calculation formula (9) of the enthalpy value;

[0042] S104: Set the initial value T of the temperature before the valve i (k) , and calculate the steam enthalpy before the valve according to the engineering calculation formula (9) of enthalpy value;

[0043] S105: Calculate the flow rate of the cooling water by using the cooling water flow calculation formula (3) according to the enthalpy value H1 before the cooling water valve, the enthalpy value H2 after the cooling water valve, and the enthalpy value H of the cooling water, and calculate the inlet flow rate of the cooling water valve by using the mass balance formula and the heat balance formula (10);

[0044] S106: Based on the flow conservation principle, the flow of each pipeline is calculated forward, and the temperature of each node is calculated from the steam source node through the pipeline heat loss equation (7) to obtain the temperature update value T before the temperature reduction and pressure relief valve. i (k+1) ;

[0045] S107: Repeat steps S104-S106 until |T is satisfied i (k+1) -T i (k) |≤ε, ε is the maximum error given in advance;

[0046] S108: After obtaining the temperature distribution of each node, the pressure distribution is calculated, and the heating power at the steam source is calculated by the product formula (8) of the steam enthalpy and the steam flow rate.

[0047] Among them, according to the principle of heat balance, the thermal calculation model composed of the temperature drop equation of the pipeline, the heat loss per unit length and the total heat transfer coefficient is used to describe the steam characteristics.

[0048]

[0049] In formula (1), ρ is the gas density, v is the gas flow rate, p is the gas pressure, D is the pipe diameter, T is the gas temperature, and λ is the friction resistance coefficient.

[0050] Among them, the first term on the left side of formula (1) is the convection term, which is meaningful only when the steam flow rate is close to the speed of sound; the third term is the gravity term, which can be ignored because the pipeline is generally placed horizontally; the above formula (1) can be simplified as follows:

[0051]

[0052] The mass flow rate can be obtained from the flow continuity equation:

[0053]

[0054] According to the mass flow equation, the flow rate expression can be derived as:

[0055]

[0056] Substituting formula (4) into formula (3) yields:

[0057]

[0058] Considering λ and T as constants on the pipe section L, integrating both ends of the above equation yields:

[0059]

[0060] Among them, while considering the gas flow characteristics, pipeline heat loss is also one of the important factors affecting heat transfer efficiency; generally, the heating pipeline is composed of multiple layers of materials, and each layer of insulation material has a different thermal conductivity. Heat is exchanged with the external environment according to the temperature difference between the inside and outside of the pipeline; the temperature drop of the general pipeline is related to factors such as the flow rate, heat dissipation coefficient, and density of the pipeline. The pipeline heat loss equation is expressed as follows:

[0061]

[0062] In formula (7), △t is the temperature drop of the pipeline, q is the heat loss per unit length, η is the local heat dissipation correction coefficient, and C pis the specific heat at constant pressure, and m is the pipeline flow rate.

[0063] Among them, in the process of steam load calculation, the steam flow rate is generally used to represent the load size. In the integrated energy system, for the convenience of calculation, the load representation quantity is uniformly classified as a power expression; the physical meaning of steam load power is the heat provided by the steam consumed per unit time; it is generally represented by the product of steam enthalpy and steam flow rate:

[0064] Q = m·H (8);

[0065] In formula (8), Q represents steam power, and H represents steam enthalpy. The physical meaning of steam enthalpy is the heat contained in unit mass of steam.

[0066] Among them, generally for saturated steam, the enthalpy value is given by the engineering calculation formula:

[0067] H=-0.00274×T 2 +1.905×T+2520 (9);

[0068] Among them, the pressure at the steam heating end is generally relatively stable, so the temperature and power can be derived from equation (9) to perform comprehensive energy simulation; secondly, the parameters of each node are calculated by the pipeline flow continuity equation (3) and the pipeline heat loss equation (7) to verify whether the steam operation status meets the production requirements.

[0069] Among them, since the controllability of steam is not strong, and there are certain requirements for steam parameters in production needs, the properties of steam transmitted by pipelines generally cannot meet their needs. Therefore, a temperature and pressure reducing valve device is added at the load end to convert the steam before the valve into steam with constant pressure and temperature.

[0070] Among them, the general temperature reduction and pressure reducing valve is composed of a valve body, a throttling sleeve assembly, a temperature reduction water nozzle and various valves; the temperature reduction process and the pressure reduction process of the temperature reduction and pressure reducing valve are two relatively independent processes; the pressure reduction process is achieved through valve throttling, and the flow process of the fluid through the pressure reducing valve is an adiabatic throttling process, which is an irreversible adiabatic expansion and equal enthalpy flow. After throttling, the enthalpy value remains unchanged, and the temperature is reduced; the temperature reduction process is achieved by a temperature reduction water nozzle to reduce the temperature of steam; the physical model of the temperature reduction and pressure reducing valve structure is shown below, where T, P, H, and m are temperature reduction water parameters, T1, P1, H1, and m1 are the pressure, temperature, enthalpy and flow before the valve, respectively, and T2, P2, H2, and m2 are the parameters after the valve.

[0071] according to Figure 1 , from the mass and heat balance equation:

[0072]

[0073] Among them, the cooling water flow rate is calculated by the enthalpy value before and after the valve:

[0074]

[0075] Among them, m s It is the maximum flow rate of steam at the valve inlet.

[0076] Among them, in the process of steam network flow calculation, the heating demand before the valve is calculated based on the parameters of the demand after the valve. The steam generated by the steam boiler has a certain pressure. The parameters of each node are calculated based on the calculated flow rate, and the parameters required after the valve are iteratively optimized to verify the operational reliability of the steam network.

[0077] Among them, the steam network model includes a pipeline model and a load model. Due to the particularity of the steam load model, the impact of the load in the flow calculation needs to be considered when calculating the steam network flow. The steam required for general industrial production is adjusted to a certain temperature and pressure through a pressure reducing valve. In the flow calculation, the pressure after the valve is set to a constant value, and the steam temperature, pressure and enthalpy after the valve are calculated by the steam state equation. The temperature before the valve is selected as the initial value of the flow calculation, and the flow before the valve is calculated by the temperature reduction and pressure reducing valve model. The flow is calculated forward according to the pipeline model, and then the temperature distribution of each node is calculated from the steam source. After the temperature distribution meets the requirements, the pressure of each node and the heating power at the steam source are calculated.

[0078] In summary, in the process of calculating the flow of the steam network, the heating demand before the valve is calculated by forward-pushing the parameters of the demand after the valve, and the steam generated by the steam boiler has a certain pressure. The parameters of each node are backward-pushed according to the calculated flow rate, and the parameters required after the valve are iteratively optimized to verify the operational reliability of the steam network; and the state variable distribution of the heating network can be obtained through the steam flow calculation. For the heating system in planning, the flow calculation can be used to check whether the proposed planning scheme can meet the requirements of various operating modes; for the heating system in operation, the flow calculation can be used to predict whether various load changes and changes in network structure will endanger the safety of the system, and what preventive measures should be taken in advance when safety problems may occur.

[0079] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

[0080] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for calculating the flow of a steam heating network considering the influence of pressure and temperature, characterized in that: The calculation method includes: S101: Read the parameters of the pipeline: pipeline diameter D, friction resistance coefficient λ, gas density ρ, gas flow rate ν, read the parameters of the cooling water: temperature T, pressure P, parameters before the cooling and pressure reducing valve: temperature T1, pressure P1, parameters after the cooling and pressure reducing valve: temperature T2, pressure P2; S102: Calculate the flow rate m of the cooling water, the flow rate m1 before the cooling and pressure reducing valve, and the flow rate m2 after the cooling and pressure reducing valve according to the flow continuity equation; S103: Calculate the enthalpy value H of the desuperheating water, the enthalpy value H1 before the desuperheating and pressure reducing valve, and the enthalpy value H2 after the desuperheating and pressure reducing valve according to the engineering calculation formula of the enthalpy value; S104: Set the initial value T of the temperature before the valve i (k) , and calculate the steam enthalpy before the valve according to the engineering calculation formula of enthalpy; S105: Calculate the flow rate of the cooling water by using the flow calculation formula of the cooling water valve according to the enthalpy value H1 before the cooling water valve, the enthalpy value H2 after the cooling water valve, and the enthalpy value H of the cooling water, and calculate the inlet flow rate of the cooling water valve by using the mass balance formula and the heat balance formula; S106: Based on the flow conservation principle, the flow of each pipeline is calculated forward, and the temperature of each node is calculated from the steam source node through the pipeline heat loss equation to obtain the temperature update value T before the temperature reduction and pressure relief valve. i (k+1) ; S107: Repeat steps S104-S106 until |T is satisfied i (k+1) -T i (k) |≤ε, ε is the maximum error given in advance; S108: After obtaining the temperature distribution of each node, the pressure distribution is calculated, and the heating power at the steam source is calculated by the product formula of the steam enthalpy and the steam flow rate.

2. A method for calculating the flow of a steam heating network considering the influence of pressure and temperature according to claim 1, characterized in that: The flow continuity equation is: Among them, m is the flow rate, ρ is the gas density, ν is the gas flow velocity, and D is the direct drop in the pipeline.

3. The method for calculating the flow of a steam heating network considering the influence of pressure and temperature according to claim 2, characterized in that: The engineering calculation formula for the enthalpy value is: H=-0.00274×T 2 +1.905×T+2520 Where H is the enthalpy and T is the temperature.

4. The method for calculating the flow of a steam heating network considering the influence of pressure and temperature according to claim 3 is characterized in that: The flow calculation formula of the temperature and pressure reducing valve is: Among them, m s is the maximum flow of steam at the valve inlet, H1 is the enthalpy value before the temperature and pressure reducing valve, H2 is the enthalpy value after the temperature and pressure reducing valve, and H is the enthalpy value of the temperature and pressure reducing water.

5. A method for calculating the flow of a steam heating network considering the influence of pressure and temperature according to claim 4, characterized in that: The mass balance and heat balance are:

6. A method for calculating the flow of a steam heating network considering the influence of pressure and temperature according to claim 5, characterized in that: The pipeline heat loss equation is: Where △t is the temperature drop of the pipeline, q is the heat loss per unit length, η is the local heat dissipation correction factor, C p is the specific heat at constant pressure, and m is the pipeline flow rate.

7. A method for calculating the flow of a steam heating network considering the influence of pressure and temperature according to claim 6, characterized in that: The product formula of the steam enthalpy and the steam flow rate is: Q=m·H Among them, Q represents steam power, and H is steam enthalpy. The physical meaning of steam enthalpy is the heat contained in unit mass of steam.

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