A self-feedback online monitoring system and method for wet steam dryness

Abstract

The present invention discloses a self-feedback online monitoring system and method for wet steam dryness, comprising an electric heating dryness measuring probe, an integrated uniformly heated electric heating rod set in the central axis of the outer tube of the thermal insulation measuring probe, the thermal insulation measuring pipeline is divided into a front evaporation section and a rear superheating section, the electric heating rod and the heat exchange surface of the evaporation section are used to heat the wet saturated steam to superheated saturated steam, the electric heating rod and the heat exchange surface of the superheating section are used to further heat the superheated saturated steam, the electric heating rod is connected to a control system via a cable, and the control system is used to adjust the heating power in real time according to the feedback signal. The present invention improves the reliability, real-time performance and economy of the wet saturated steam dryness online monitoring system.

Description

Technical Field

[0001] The present invention belongs to the technical field of thermal instruments in the energy and power industry, and in particular relates to a self-feedback online monitoring system and method for wet steam dryness. Background Art

[0002] Wet saturated steam (generally steam contains both saturated water and saturated steam in dynamic equilibrium) is a working fluid commonly used in the energy and power industry. The wet saturated steam dryness (the content of steam in wet saturated steam) is an important parameter to characterize the physical properties of wet saturated steam. Therefore, a measuring point instrument is required to measure the wet saturated steam dryness simply and accurately. At present, the wet saturated steam dryness measurement methods mainly include thermodynamics, non-thermodynamics and mathematical model methods. Among them, the thermodynamics method specifically includes throttling method, mixing method, heating method, phase separation method, condensation method, etc., and the non-thermodynamic method specifically includes radiation method, microwave method, optical method and chemical method, etc. The non-thermodynamic method has very high requirements on the on-site instrument configuration and measurement conditions. The mathematical model method for indirectly determining the exhaust enthalpy has a complex and cumbersome calculation process. In contrast, the thermodynamic method has the advantages of simple measurement principle, high measurement accuracy and easy use. Among them, the heating method is a method suitable for measuring the humidity of flowing wet steam in actual turbines. The most typical constant pressure heating method steam humidity probe was developed by the Central Electric Research Laboratory (CERL) in the UK. It uses a sleeve-type working section composed of an inner tube and an outer tube. A vacuum is drawn in the sleeve interlayer so that heat dissipation can be ignored during calculation. It needs to measure the flow and temperature parameters of wet saturated steam, which makes the measurement system complex and increases the measurement error. The dual-zone heating method based on this probe divides the heating section into an evaporation section and a superheating section for independent heating. The humidity measuring probe designed based on this principle has a simple structure and uses the superheating section directly as a flow measurement system.

[0003] However, there are still disadvantages: 1) Whether it is the traditional method of winding the outer sleeve with resistance wire or the built-in heating element in the inner tube, it is impossible to ensure the same heating power per unit length of the inner tube. In order to calculate the actual or virtual vaporization length of wet steam over the entire length of the inner tube, the traditional model needs to continuously arrange at least a dozen temperature sensors, which greatly increases the measurement cost and maintenance cost, which is not economical; 2) Because its heating probe has a long length margin, its calculation method takes into account the specific volume change and flow velocity loss of saturated steam and saturated water, which relatively increases the calculation cost; 3) and its heating element (electric heating wire) blocks the steam flow and kinetic energy sampling in the wet saturated steam flow channel, and the problem of backflow of superheated saturated steam exists; 4) and if the temperature of the heating element is preset too high according to the calculation, it will cause the radiation heat dissipation loss to increase to a non-negligible level; 5) in actual industry, the thermal parameters of wet saturated steam working fluid fluctuate greatly, and it is impossible to rely on complex mathematical models to ensure the accuracy and reliability of data in a time-consuming manner.

[0004] Therefore, the heating method monitoring device for wet saturated steam dryness needs to be improved, the real-time calculation model needs to be simplified and a self-feedback control processing method needs to be introduced, two monitoring systems for high and low flow rate steam are needed in energy and power applications, and the online monitoring system needs to improve reliability and practicality. Summary of the invention

[0005] In order to overcome the above technical problems, the present invention provides a self-feedback online monitoring device, system and method for wet steam dryness, which can improve the reliability, real-time and economy of the online monitoring system for wet saturated steam dryness.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] A wet steam electric heating dryness measuring instrument and a self-feedback online monitoring system, comprising an insulated measuring probe outer tube 1, an integrated uniformly heated electric heating rod 4 mounted in the central axis of the measuring probe outer tube 1, the space between the measuring probe outer tube 1 and the electric heating rod 4 being an exhaust steam flow section, which is divided into a front evaporation section 2 and a rear superheating section 3, the heat exchange between the electric heating rod 4 and the evaporation section 2 is used to heat the wet saturated steam to superheated saturated steam, the heat exchange between the electric heating rod 4 and the superheating section 3 is used to further heat the superheated saturated steam, the electric heating rod 4 is connected to a control system 10 via a cable, and the control system 10 is used to adjust the heating power in real time according to a feedback signal.

[0008] The outer tube 1 of the thermal insulation measuring probe is a ceramic thermal insulation tube with an outer surface coated with aluminum silicate thermal insulation material, and the outer surface of the electric heating rod 4 is made of ceramic material.

[0009] A check valve 5 is arranged at the connection between the evaporation section 2 and the superheating section 3 to prevent the backflow of superheated saturated steam. A regulating valve 6 is arranged at the outlet of the probe outer tube 1 to adjust the flow rate of wet saturated steam. A pressure measuring point 7 is arranged at the inlet of the probe outer tube 1, a pressure and temperature measuring point 1 8 is arranged in front of the check valve 5, and a pressure and temperature measuring point 2 9 is arranged in front of the regulating valve 6. At the same time, the electric heating rod 4 itself has an electric power measuring point for feedback regulation.

[0010] The evaporation section 2 and the superheating section 3 have the same tube length.

[0011] A method for adjusting a self-feedback online monitoring system for wet steam dryness comprises the following steps;

[0012] 1) The regulating valve 6 of the electric heating dryness measuring instrument adjusts the flow rate of the input probe according to the pressure of the measured steam (taken from the pressure measuring point 7). The higher the pressure of the steam, the smaller the extraction flow rate should be;

[0013] 2) According to the water vapor temperature enthalpy table, if the pressure and temperature measuring point 8 measures the calculated enthalpy of superheated saturated steam h heatBelow the water vapor saturation line, that is, the program will report an error that the working medium does not meet the conditions of superheated saturated steam according to the input temperature and pressure. At this time, the control system 10 will gradually increase the heating power of the electric heating rod 4 according to self-feedback until the measured enthalpy of superheated saturated steam h is guaranteed. heat The enthalpy value is higher than the saturation state. After several iterations, the new evaporation section heating power W is obtained. heat And superheating section heating power W superheat ,The measurement data in this process are not counted into the real-time database;

[0014] 3) According to the total pressure drop of the probe evaporation section within the general steam turbine operating conditions, taking into account the error of the power regulation system of the electric heating rod 4, the steam temperature difference before and after the superheating section 3 of the superheated saturated steam (taken from the pressure and temperature measuring point 1 8 and the pressure and temperature measuring point 2 9) needs to be greater than 10°C. According to the temperature enthalpy calculation program of water vapor, if t superheat and t heat The difference is less than 10°C. At this time, the control system 10 will gradually increase the heating power of the electric heating rod 4 according to the self-feedback. The superheated saturated steam temperature t after the superheating section of the electric heating rod 4 is measured. superheat The superheated saturated steam temperature after evaporation of saturated steam is t heat It is higher than 10℃ to ensure the accuracy and effectiveness of the heat balance calculation of the superheating section. After several iterations, the new power of the electric heating rod 4 is obtained;

[0015] 4) If the measured enthalpy of superheated saturated steam h heat Higher than the water vapor saturation line 200kj / kg, at the same time t superheat and t heat The difference is greater than 20°C, the control system 10 will gradually reduce the heating power of the electric heating rod 4 according to self-feedback, without violating the requirements of 2) and 3) above, that the wet steam is completely evaporated in the evaporation section 2 and the temperature in the superheating section 3 is increased by at least 10°C, so as to avoid measurement errors caused by radiation heat dissipation due to excessive heating power;

[0016] 5) Since the self-feedback value of the power of the electric heating rod 4 is updated, the data is delayed. The existing conventional temperature and pressure measurement points can calculate the dryness of the wet saturated steam once per second in real time. The monitoring method of the present invention requires updating the self-feedback value of the power of the electric heating rod 4 that can guarantee the calculation result every 10 seconds, that is, the dryness of the wet saturated steam is calculated in real time every 10 seconds. Since the real-time collected data fluctuates, the dryness of the wet saturated steam calculated in real time needs to be smoothed or even smoothed twice to obtain the moving average of the wet saturated steam dryness:

[0017]

[0018] If the value of n meets the requirement of more than 2 minutes, then n≥12; if the value of m meets the requirement of more than 10 minutes, then m≥5.

[0019] Beneficial effects of the present invention:

[0020] 1) The monitoring device proposed by the present invention uses an electric heating rod with a smooth surface and stable guaranteed power to be directly placed on the central axis of the wet saturated steam flow channel, and the outer side of the casing is wrapped with a heat-insulating material to prevent radiation heat dissipation. This integrated heating device with an insulating outer tube has a simple, effective and low-cost structure. The integrated electric heating rod does not need to adjust the electric power of the evaporation section and the superheating section separately, and the uneven electric power per unit length of the local electric heating rod does not affect the calculation and measurement, which greatly increases the robustness and practicality.

[0021] 2) The monitoring method proposed in the present invention obtains a large amount of thermal parameter data of wet saturated steam through high-precision measuring points, and uses it as negative feedback to adjust the power of the electric heating rod in real time, thereby ensuring that the actual vaporization length of the wet saturated steam is sufficient to evaporate the saturated water, and the superheat length is sufficient to heat the superheated steam to a higher parameter. At the same time, the vaporization length and the superheat length will not be too long to cause excessive heating power and temperature, thereby avoiding the introduction of heat dissipation losses and measurement errors.

[0022] 3) The calculation method of the present invention can directly update and calculate the power of the evaporation section and the superheating section in real time, and ignores many unnecessary variables from the mathematical model. For example, there is no need to calculate the heating power of the evaporation section and the heating power of the superheating section separately, and there is no need to calculate the vaporization length and the specific volume of the working fluid. The dryness calculation formula derived from this is simple in principle, compacts the measuring device and improves the reliability of the probe.

[0023] 4) The present invention can accurately adjust the heating power by relying on a high-precision electric power heating rod, thereby ensuring the measurement accuracy of the wet saturated steam dryness when the working fluid thermal parameters fluctuate greatly, and can realize long-term online monitoring of industrial boiler working fluids and turbine exhaust steam. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a structural schematic diagram of the present invention.

[0025] Figure 2 This is a schematic diagram of Example 1 of the present invention.

[0026] Figure 3 This is a schematic diagram of Example 2 of the present invention. DETAILED DESCRIPTION

[0027] The present invention will be further described in detail below in conjunction with the accompanying drawings.

[0028] like Figure 1As shown: a self-feedback online monitoring system for wet steam dryness, including an insulated measuring probe outer tube 1 and an integrated uniformly heated electric heating rod 4 set in the central axis, the measuring probe outer tube 1 is divided into a front evaporation section 2 and a rear superheating section 3, the heat exchange between the electric heating rod 4 and the evaporation section 2 is used to heat the wet saturated steam to superheated saturated steam, the heat exchange between the electric heating rod 4 and the superheating section 3 is used to further heat the superheated saturated steam, the electric heating rod 4 is connected to a control system 10 via a cable, and the control system 10 is used to adjust the heating power in real time according to the feedback signal.

[0029] The outer tube 1 of the heat-insulating measuring probe is made of ceramic with an outer surface coated with aluminum silicate insulation material, and the outer surface of the electric heating rod 4 is made of ceramic material.

[0030] A check valve 5 is arranged at the connection between the evaporation section 2 and the superheating section 3 to prevent the backflow of superheated saturated steam. A regulating valve 6 is arranged at the outlet of the outer tube 1 of the thermally insulated measuring probe to adjust the flow rate of wet saturated steam. A pressure measuring point 7 is arranged at the inlet of the outer tube 1 of the measuring probe, a pressure and temperature measuring point 1 8 is arranged in front of the check valve 5, and a pressure and temperature measuring point 2 9 is arranged in front of the regulating valve 6. At the same time, the electric heating rod 4 is provided with an electric power measuring point for feedback regulation.

[0031] The evaporation section 2 and the superheating section 3 have the same tube length.

[0032] The specific implementation steps of the present invention are:

[0033] Step 1

[0034] Real-time collection of the inlet pressure, outlet pressure and temperature of the wet steam electric heating dryness measuring instrument, the pressure and temperature at the connection between the evaporation section and the superheating section, and the electric power of the electric heating rod.

[0035] Step 2

[0036] Through the water and water vapor temperature enthalpy table, the saturated steam enthalpy of wet saturated steam, the saturated water enthalpy, the superheated saturated steam enthalpy after heating in the evaporation section, and the superheated saturated steam enthalpy after reheating in the superheating section are obtained.

[0037] Step 3

[0038] According to the obtained negative feedback pressure and temperature value, the control system 10 is used to adjust and update the power of the electric heater at any time, and the wet saturated steam dryness x is calculated in real time.

[0039] Step 4

[0040] The real-time calculated wet saturated steam dryness is smoothed to obtain the wet saturated steam dryness after primary and secondary smoothing. and

[0041] The technical principle of the present invention is:

[0042] The wet saturated steam flows through the wet saturated steam electric heating rod 4 and is heated to superheated saturated steam. Its energy balance satisfies the following formula:

[0043] The dryness of wet saturated steam is defined as the mass percentage of water contained:

[0044] h wet =xh steam +(1-x)h water

[0045] Among them, x is the dryness of wet saturated steam, -;

[0046] h wet —— enthalpy of wet saturated steam entering the probe, kJ / kg;

[0047] h steam ——steam enthalpy of wet saturated steam, kJ / kg;

[0048] h water ——Saturated water enthalpy of wet saturated steam, kJ / kg.

[0049] The saturated steam enthalpy and saturated water enthalpy of wet saturated steam are calculated using the water vapor temperature enthalpy table:

[0050] h steam =F(p wet ),

[0051] h water =F (p wet )

[0052] Among them, p wet ——Pressure of wet saturated steam entering the outer tube 1 of the measuring probe, Pa;

[0053] F() is the enthalpy calculation function of the IAPWS-IF97 (The International Association for the Properties of Water and Steam Industrial Formulation 1997) water / steam physical properties open source calculation model.

[0054] For wet saturated steam, only pressure is needed to calculate the enthalpy value, and there is no need to arrange steam temperature measuring points.

[0055] Therefore, the heat balance equation of the evaporation section is:

[0056] W heat η heater =M(h heat -h wet )

[0057] Among them, W heat ——Power of electric heating rod 4 of wet saturated steam in evaporation section 2, kJ / s;

[0058] η heater ——Efficiency of wet saturated steam electric heating rod 4. The efficiency of general electric heaters generally reaches 0.99, which can be simplified as: η heater ≈1.0;

[0059] M——mass flow rate of wet saturated steam, kg / s;

[0060] h heat ——Superheated saturated steam enthalpy after wet saturated steam evaporates 2 times, kJ / kg;

[0061] The enthalpy of superheated saturated steam after evaporation of wet saturated steam is calculated using the water vapor temperature enthalpy table:

[0062] h heat =F(p heat ,t heat )

[0063] Among them, p heat ——Superheated saturated steam pressure after evaporation of wet saturated steam, Pa;

[0064] t heat ——Superheated saturated steam temperature after evaporation of wet saturated steam, °C;

[0065] Then, the superheated saturated steam is heated by the superheating section 3 of the electric heating rod 4 to become superheated saturated steam with higher thermal parameters.

[0066] The energy balance of the superheating section satisfies the following formula:

[0067] W superheat η heater =M(h superheat -h heat )

[0068] Among them, W superheat ——Power of the electric heater for superheated saturated steam in superheating section 3, kJ / s;

[0069] h superheat ——Enthalpy of superheated saturated steam after heating by the superheating section 3 of the electric heating rod, kJ / kg;

[0070] The enthalpy of superheated saturated steam after the superheated saturated steam heater is calculated using the temperature enthalpy table of water vapor:

[0071] h superheat =F(p superheat ,t superheat )

[0072] Among them, p superheat ——Superheated saturated steam pressure after heating in the superheating section of the electric heating rod 4, Pa;

[0073] t superheat ——Temperature of superheated saturated steam after heating by the superheating section of the electric heating rod 4, °C;

[0074] In this way, the dryness of wet saturated steam can be deduced from the above formula:

[0075] x=[h heat -W heat (h superheat -h heat ) / W superheat -h water ] / (h steam -h water )

[0076] Because the evaporation section 2 and the superheating section 3 of the electric heating rod 4 have the same length, W heat =W superheat

[0077] The dryness formula is simplified to:

[0078] x=[2h heat -h superheat -h water ] / (h steam -h water ).

[0079] The specific implementation system scheme of the present invention:

[0080] Solution 1

[0081] The main steam pipeline of the industrial boiler has a fast flow rate and high temperature and pressure parameter values. It is necessary to extract the wet saturated steam in the main steam pipeline 12 in the form of extraction steam and flow it into the electric heating dryness measuring instrument 11 (i.e., attached Figure 1 Device shown), see Figure 2 . Since the main steam pipeline 12 is under pressure, a small amount of wet saturated steam for measurement enters through the inlet A of the connecting pipe 13, passes through the electric heating dryness meter 11, and then returns to the main steam pipeline 12 through the outlet B of the connecting pipe 13. The regulating valve 6 on the electric heating dryness meter 11 needs to adjust the wet saturated steam flow entering the thermal insulation connecting pipe 13 to be as small as possible, and at the same time adjust the output power of the wet saturated steam evaporation section 2 and the superheated saturated steam superheating section 3 to ensure that the wet saturated steam heater 2 will heat the superheated saturated steam.

[0082] Solution 2

[0083] The steam exhaust pipe 14 of the low-pressure cylinder of the steam turbine of the generator set is equipped with a steam extraction device, which inputs a small amount of extraction steam into the electric heating dryness measuring instrument 11 (i.e., the attached Figure 1The device shown in the figure) is then connected to the condenser vacuum pump 16 provided in a general power plant through the connecting pipe 13 to ensure the negative pressure of the condenser 15, forming a measurement system. Figure 3 The regulating valve 6 on the electric heating dryness meter 11 needs to adjust the wet saturated steam flow entering the thermal insulation connecting pipe 13 to be as small as possible, and at the same time, the heating effect of the evaporation section 2 and the superheating section 3 is guaranteed by adjusting the heating power of the integrated electric heating rod. Since the wet saturated steam flow rate is very small, the pressure loss of the wet saturated steam flowing into the electric heating dryness meter 11 can be ignored, and the steam pressure measurement point is not arranged in front of the wet saturated steam heater, and the existing low-pressure cylinder exhaust pressure of the power plant can be directly taken.

Claims

1. A method for adjusting a self-feedback online monitoring system for wet steam dryness. It is characterized in that The steps include: 1) The regulating valve (6) of the electric heating dryness measuring instrument adjusts the flow rate of the input probe according to the pressure of the measured steam. The higher the pressure of the steam, the smaller the extraction flow rate should be; 2) According to the water vapor temperature enthalpy table, if the measured enthalpy of superheated saturated steam h heat Below the water vapor saturation line, the control system (10) will gradually increase the heating power of the electric heating rod (4) according to self-feedback until the measured enthalpy of the superheated saturated steam h is guaranteed. heat The enthalpy value is higher than the saturation state. After several iterations, the new evaporation section heating power W is obtained. heat And superheating section heating power W superheat ,The measurement data in this process are not counted into the real-time database; 3) If t superheat and t heat The difference is less than 10°C. At this time, the control system (10) will gradually increase the heating power of the electric heating rod (4) according to the self-feedback to ensure that the heat balance calculation of the overheating section is accurate and effective. After several iterations, a new power of the electric heating rod (4) is obtained; 4) If the measured enthalpy of superheated saturated steam h heat Higher than the water vapor saturation line 200kJ / kg, at the same time t superheat and t heat If the difference is greater than 20°C, the control system (10) will gradually reduce the heating power of the electric heating rod (4) according to self-feedback without violating the above conditions 2) and 3); 5) The dryness of the wet saturated steam is calculated in real time once every 10 seconds, and the dryness of the wet saturated steam calculated in real time is smoothed or even twice smoothed to obtain a moving average of the dryness of the wet saturated steam; The dryness formula is simplified to: x=[2h heat -h superheat -h water ] / (h steam -h water ); An integrated uniformly heated electric heating rod (4) is mounted in the central axis of the outer tube (1) of the thermally insulated measuring probe; The evaporation section (2) and the superheating section (3) have the same tube length.

2. The method for adjusting the self-feedback online monitoring system of wet steam dryness according to claim 1, It is characterized in that The method is implemented by a self-feedback online monitoring system for wet steam dryness, comprising a heat-insulated measuring probe outer tube (1), a space between the measuring probe outer tube (1) and an electric heating rod (4) being an exhaust steam flow section, which is divided into a front evaporation section (2) and a rear superheating section (3), a heat exchange surface between the electric heating rod (4) and the evaporation section (2) being used to heat wet saturated steam to superheated saturated steam, a heat exchange surface between the electric heating rod (4) and the superheating section (3) being used to further heat superheated saturated steam, the electric heating rod (4) being connected to a control system (10) via a cable, and the control system (10) being used to adjust the heating power in real time according to a feedback signal.

3. The method for adjusting the self-feedback online monitoring system of wet steam dryness according to claim 1, It is characterized in that The outer tube (1) of the heat-insulating measuring probe is a ceramic heat-insulating insulating tube whose outer surface is coated with aluminum silicate heat-insulating material, and the outer surface of the electric heating rod (4) is made of ceramic material.

4. The method for adjusting the self-feedback online monitoring system of wet steam dryness according to claim 1, It is characterized in that A check valve (5) is arranged at the connection between the evaporation section (2) and the superheating section (3) to prevent the superheated saturated steam from flowing back. A regulating valve (6) is arranged at the outlet of the thermal insulation measuring probe outer tube (1) to adjust the flow rate of wet saturated steam. A pressure measuring point (7) is arranged at the inlet of the thermal insulation measuring probe outer tube (1). A pressure and temperature measuring point 1 (8) is arranged in front of the check valve (5). A pressure and temperature measuring point 2 (9) is arranged in front of the regulating valve (6). At the same time, the electric heating rod (4) is provided with an electric power measuring point for feedback regulation.

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