WO2020248167A2 - 一种氧化铝蒸发流程中闪蒸过程的闪蒸速率计算方法 - Google Patents

一种氧化铝蒸发流程中闪蒸过程的闪蒸速率计算方法 Download PDF

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WO2020248167A2
WO2020248167A2 PCT/CN2019/090925 CN2019090925W WO2020248167A2 WO 2020248167 A2 WO2020248167 A2 WO 2020248167A2 CN 2019090925 W CN2019090925 W CN 2019090925W WO 2020248167 A2 WO2020248167 A2 WO 2020248167A2
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flash
pressure
temperature
boiling point
solution
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王良勇
李战辉
柴天佑
贾瑶
唐光振
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Northeastern University China
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    • G16C—COMPUTATIONAL CHEMISTRY; CHEMOINFORMATICS; COMPUTATIONAL MATERIALS SCIENCE
    • G16C20/00—Chemoinformatics, i.e. ICT specially adapted for the handling of physicochemical or structural data of chemical particles, elements, compounds or mixtures
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  • the invention relates to the technical field of industrial automatic control applications, and in particular to a method for calculating the flash evaporation rate of the flash evaporation process in an alumina evaporation process.
  • Evaporation is an important process in the alumina production process. Its task is to evaporate the excess water in the mother liquor and increase the concentration of the circulating mother liquor.
  • the steam consumption of the evaporator occupies a large proportion.
  • domestic alumina plants generally use high efficiency and low energy consumption six-effect tube falling film evaporator and flash evaporator at this stage.
  • the combined evaporation technology and the introduction of raw liquid flash evaporation technology can improve thermal efficiency and reduce steam consumption.
  • the evaporation effect is mainly evaluated by whether the circulating mother liquor concentration is qualified, and the steam consumption is evaluated by indicators such as distilled water volume and steam-water ratio. These evaluation indicators are to evaluate the evaporation effect of the entire evaporation process from a macro perspective, without paying attention to the evaporation effect of a single evaporator, and they are all calculated offline without real-time performance.
  • the technical problem to be solved by the present invention is to provide a method for calculating the flash evaporation rate of the flash evaporation process in the alumina evaporation process in view of the above-mentioned shortcomings of the prior art. Production, improving the evaporation effect of the evaporation process, saving energy and reducing consumption are of great significance.
  • the invention provides a method for calculating the flash evaporation rate of the flash evaporation process in the alumina evaporation process, which includes the following steps:
  • Step 1 Obtain real-time process data of the alumina evaporation system
  • the data includes: the current feed concentration, feed temperature, feed flow rate, discharge temperature, balance pressure in the flash vaporizer, and secondary steam temperature of the current flash vaporizer ;
  • Step 2 Determine whether the feed volume of the flash evaporation system is within the normal working range of 450m 3 /hour to 650m 3 /hour? If yes, go to step 3; if not, go to step 1;
  • Step 3 Obtain the boiling point rise ⁇ ' BPE of the sodium aluminate solution according to the data obtained in step 1;
  • Step 3.1 Calculate the corresponding saturation temperature under the currently obtained pressure
  • b 0 , b 1 , b 2 , b 3 , and b 4 are parameters, and the parameters are obtained from the data in the saturation temperature comparison table corresponding to the saturated steam pressure under the current production conditions through the least square method;
  • Step 3.2 Calculate the boiling point rise of sodium aluminate solution under normal pressure
  • the boiling point rise of sodium aluminate solution is related to the concentration of alkali in the solution and the current solution temperature.
  • the boiling point rise of sodium aluminate solution under normal pressure is related to the relationship of ⁇ BPE :
  • ⁇ BPE c 0 +c 1 Nk+c 2 T in +c 3 NkT in +c 4 Nk 2 +c 5 T in 2 +c 6 NkT in 2 +c 7 Nk 2 T in +c 8 Nk 3 +c 9 T in 3
  • c 0 , c 1 , c 2 , c 3 , c 4 , c 5 , c 6 , c 7 , c 8 , and c 9 are parameters, which are based on the aluminum at the outlet under the current production conditions after concentration of the solution of sodium production and laboratory data obtained on fitting the polynomial regression equation, Nk is the caustic alkali concentration, T in the feed solution temperature;
  • Step 3.3 Correct the boiling point rise ⁇ BPE according to the discourseo formula to obtain the corrected boiling point rise ⁇ ' BPE ;
  • r is the latent heat of vaporization of the secondary steam under the pressure of the current production conditions
  • d 1 , d 2 , and d 3 are parameters, which are obtained by regression fitting the data in the steam temperature and enthalpy table under current production conditions;
  • Step 4 Calculate the flash evaporation rate CFS according to the boiling point rise ⁇ ′ BPE obtained in step 3, and evaluate the flash evaporation intensity in the actual alumina production process in real time according to the obtained CFS, as shown in the following formula:
  • T in is the temperature of the feed solution
  • T out is the temperature of the output solution
  • T sat is the saturation temperature at the pressure corresponding to the solution
  • T sat T p + ⁇ ′ BPE
  • ⁇ is the residence time of the solution in the flash evaporator
  • Q is the feed flow rate
  • ⁇ is the radius of the flasher
  • h is the height of the liquid level in the flasher.
  • the flash evaporation rate calculation method of the flash evaporation process in the alumina evaporation process provided by the present invention uses the online process data provided by the computer system and the conventional detection instrument, and the flash evaporation In the process, the calculation method of the boiling point rise of the sodium aluminate solution is combined with the calculation method of the flash rate, and the index is calculated and analyzed under different feed superheat, feed flow, flasher liquid level, and equilibrium pressure.
  • Figure 1 is a schematic diagram of the flow and device of the raw liquid flash evaporation process loop provided by the embodiment of the present invention, where 1 is a secondary steam thermometer, 2 is a flasher level gauge, 3 is a discharge thermometer, 4 is a flasher pressure gauge, and 5 Is a feed thermometer, 6 is a feed flow meter, 7 is a stock liquid flash evaporator, and 8 is a feed concentration meter;
  • Figure 2 is a flow chart for calculating the flash rate CFS provided by an embodiment of the present invention.
  • FIG. 3 is a graph showing the change of the flash rate CFS provided by the embodiment of the present invention with the degree of superheat when the feed concentration, pressure, liquid level height, and feed flow are basically kept constant;
  • Fig. 5 is a graph showing changes in the flash rate CFS provided by the embodiment of the present invention with pressure when the feed concentration, liquid level height, superheat degree, and feed flow rate remain basically unchanged;
  • Fig. 6 is a graph showing changes in the flash rate CFS provided by the embodiment of the present invention with the feed flow when the feed concentration, liquid level height, superheat and pressure remain basically unchanged;
  • FIG. 7 is a graph showing the change of the flash rate CFS provided by the embodiment of the present invention with the feed concentration when the feed flow rate, liquid level height, superheat degree, and pressure remain basically unchanged.
  • the indicator evaluation method of the flash evaporation system in the alumina evaporation process of the present invention relies on the hardware platform of the flash evaporation system and is realized by a written software program.
  • the program is used to collect the current feed concentration, feed temperature, and feed material of the raw liquid flash evaporator. Flow rate, discharge temperature, balance pressure in the flash evaporator, secondary steam temperature and other data.
  • the core of its hardware platform consists of a liquid flash evaporator and related equipment, and is also equipped with measuring instruments, actuators and a computer system for software calculations.
  • the evaporated raw liquid enters the raw liquid flash evaporator through the feed port for flash evaporation, and then discharges the material through the discharge port into the next effect evaporator to continue evaporation.
  • a large amount of steam will be generated, which enters through the secondary steam outlet at the top of the flash evaporator
  • the next evaporator continues to heat, as shown in Figure 1.
  • the detailed structure is as follows:
  • the flash system with flash evaporator as the core also includes the following measuring instruments:
  • a feed thermometer for online measurement of feed temperature installed on the feed inlet pipe of the stock flash evaporator;
  • a pressure gauge for online measurement of secondary steam pressure installed on the discharge port of the raw liquid flash evaporator
  • the discharge thermometer used for online measurement of the discharge temperature of the raw liquid flash evaporator is installed on the discharge pipe of the raw liquid flash evaporator;
  • a differential pressure level gauge is installed on the flash evaporator to detect the liquid level in the flash evaporator;
  • the flash system is also equipped with a distributed computer control system (DCS), or a programmable logic controller (PLC), or an industrial control computer (IPC), or a discrete industrial regulator; the above measuring instruments and actuators are connected to Control computer, the flash rate calculation method of the alumina evaporation process of the present invention can be run on the monitoring computer of the computer control system, or on an independent optimization setting computer.
  • the software passes through the control computer (distributed computer).
  • the control system (DCS), or programmable logic controller (PLC), or industrial control computer (IPC)) communicates, obtains real-time process data, and gives the calculated value of the flash rate.
  • the method of this embodiment is as follows.
  • the invention provides a method for calculating the flash evaporation rate of the flash evaporation process in the alumina evaporation process, which includes the following steps:
  • Step 1 Obtain real-time process data of the alumina evaporation system
  • Real-time collection of data in the flash evaporation system of the alumina evaporation process which includes: the current feed concentration, feed temperature, feed flow rate, discharge temperature, balance pressure in the flash evaporator, and secondary steam temperature of the current flash evaporator;
  • Step 2 Determine whether the feed volume of the flash evaporation system is within the normal working range of 450m 3 /hour to 650m 3 /hour? If yes, go to step 3; if not, go to step 1;
  • Step 3 Obtain the boiling point rise ⁇ ' BPE of the sodium aluminate solution according to the data obtained in step 1;
  • the increase in the boiling point of the material liquid means that under the same pressure, the boiling point temperature of the material liquid is higher than the boiling point temperature of pure water; during the alumina evaporation production process, the constant change of the material liquid concentration causes the boiling point of the material liquid in the evaporator Different; At the same time, due to a certain pressure in the evaporator, this will also lead to a different boiling point of the material liquid.
  • Step 3.1 Calculate the corresponding saturation temperature under the currently obtained pressure:
  • b 0 , b 1 , b 2 , b 3 , and b 4 are parameters.
  • the parameters are obtained from the saturated vapor pressure on the site of the alumina evaporation process under the current production conditions.
  • the data in the saturation temperature comparison table passes the least squares The method is actually fitted,
  • Step 3.2 Calculate the boiling point rise of sodium aluminate solution under normal pressure
  • the boiling point rise of sodium aluminate solution is related to the concentration of alkali in the solution and the current solution temperature.
  • the boiling point rise of sodium aluminate solution under normal pressure is related to the relationship of ⁇ BPE :
  • ⁇ BPE c 0 +c 1 Nk+c 2 T in +c 3 NkT in +c 4 Nk 2 +c 5 T in 2 +c 6 NkT in 2 +c 7 Nk 2 T in +c 8 Nk 3 +c 9 T in 3
  • c 0 , c 1 , c 2 , c 3 , c 4 , c 5 , c 6 , c 7 , c 8 , and c 9 are parameters, which are based on the aluminum at the outlet under the current production conditions after concentration of the solution of sodium production and laboratory data obtained on fitting the polynomial regression equation, Nk is the caustic alkali concentration, T in the feed solution temperature;
  • the unknown parameters can be obtained by identifying the above formula through actual production and laboratory data:
  • ⁇ BPE 1.5+0.007 ⁇ Nk+3 ⁇ 10 -5 ⁇ T in +2 ⁇ 10 -4 ⁇ Nk ⁇ T in
  • Step 3.3 Correct the boiling point rise ⁇ BPE according to the discourseo formula to obtain the corrected boiling point rise ⁇ ' BPE ;
  • r is the latent heat of vaporization of the secondary steam (saturated steam) under the pressure of the current production conditions, in kJ/kg;
  • d 1 , d 2 , and d 3 are parameters, which are obtained by regression fitting the data in the steam temperature and enthalpy table under current production conditions;
  • Step 4 Calculate the flash evaporation rate CFS according to the boiling point rise ⁇ ′ BPE obtained in step 3, and evaluate the flash evaporation intensity in the actual alumina production process in real time according to the obtained CFS, as shown in the following formula:
  • T in is the temperature of the feed solution
  • T out is the temperature of the output solution
  • T sat is the saturation temperature under the corresponding pressure of the solution
  • T sat T p + ⁇ ′ BPE
  • ⁇ is the residence time of the solution in the flash evaporator
  • Q is the feed flow rate
  • ⁇ is the radius of the flasher
  • h is the height of the liquid level in the flasher.
  • the flash evaporation rate takes into account the residence time of the material liquid in the flash evaporator, so it is a more comprehensive measure of the real intensity of the flash evaporation.
  • This embodiment is a flash evaporation process of raw liquid in a large alumina plant.
  • the model of the stock flash evaporator is ⁇ 4.8m ⁇ 4.5m; first install the following measuring instruments according to the requirements of this method, including: electromagnetic flowmeter to measure the feed flow Q of the stock flash evaporator; thermometer to measure the temperature T of the feed solution of the original flash evaporator in ; Thermometer measures the temperature T out of the original flash evaporator; pressure gauge measures the balance pressure p in the original flash evaporator; Nk concentration meter measures the feed concentration of the original flash evaporator; electric regulating valve controls the feed flow of the original flash evaporator;
  • a distributed computer control system is used to realize the automatic control of the basic control loop.
  • the single loop regulator in the DCS is used to configure the following basic control loop: the original flash feed flow electric regulating valve controls the original flash Feed flow rate,
  • the normal working range of the feed flow rate of the flash evaporation system is: the original flash feed flow rate——450m 3 /hour ⁇ 650m 3 /hour
  • the calculation program of flashing index is compiled with MATLAB application software provided by MathWorks, and runs on a separate optimization computer, which is equipped with OPC Server and is responsible for data communication with DCS and upper computer.
  • the present invention uses actual production data to calculate the flashing rate of the flashing process, where the flashing rate CFS changes with the degree of superheat when the pressure, liquid level height, feed flow rate, and concentration of the original liquid remain basically unchanged.
  • the specific parameters are: -77.2kPa, 0.87m, 572m 3 /h, 177g/l, the result is shown in Figure 3.
  • the flash rate CFS increases with the height of the liquid level when the superheat, pressure, feed flow rate, and concentration of the original liquid remain basically unchanged
  • the specific parameters are: 1.5°C, -72.5kPa, 595m 3 /h, 177g/l, the result is shown in Figure 4; the flashing rate CFS basically maintains the superheat, liquid level height, feed flow rate and concentration of the original liquid
  • the specific parameters are: 1.5°C, 0.77m, 595m 3 /h, 175g/l, the result is shown in Figure 5;
  • the flash rate CFS is in the superheat and pressure, liquid level height, original liquid
  • the specific parameters are: 1.7°C, -74.5kPa, 0.82m, 163g/l, and the result is shown in Figure 6.
  • the flash rate CFS is in the superheat, pressure, liquid
  • the position height and the feed flow rate change with the concentration of the original solution when the position height and the feed flow rate remain basically unchanged.
  • the specific parameters are: 1.7°C, -74.5kPa, 0.82m, 586m 3 /h, and the results are shown in Figure 7.
  • the flash rate CFS of the raw liquid flash evaporator increases with the increase of the feed flow rate and equilibrium pressure, and with the increase of the liquid film height and the feed concentration.
  • the flash rate CFS indicator can reflect the intensity of the flash evaporation effect; in the actual alumina evaporation production process, the calculation method of the flash rate CFS in the alumina evaporation process of the present invention can be used to evaluate the alumina on-line in real time
  • the flash intensity of the flash evaporator in the evaporation process is of great significance for guiding the production of the alumina evaporation process, improving the evaporation effect of the evaporation process, and saving energy and reducing consumption.

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Description

一种氧化铝蒸发流程中闪蒸过程的闪蒸速率计算方法 技术领域
本发明涉及工业自动控制应用技术领域，尤其涉及一种氧化铝蒸发流程中闪蒸过程的闪蒸速率计算方法。
背景技术
蒸发是氧化铝生产工艺中一个重要的工序，其任务是蒸发掉母液中多余的水量，提高循环母液浓度。然而在氧化铝生产过程中蒸发器的蒸汽消耗占有很大比重，为了减少蒸发汽耗，降低生产成本，国内氧化铝厂现阶段普遍采用高效低能耗的六效管式降膜蒸发器与闪蒸器相结合的蒸发技术，另外通过引进原液闪蒸技术，可以提高热效率，降低蒸汽消耗。在实际氧化铝蒸发生产过程中，主要以循环母液浓度是否合格评价蒸发效果，以蒸水量、汽水比等指标来评价蒸汽消耗量。这些评价指标是从宏观上评价整个蒸发流程蒸发效果，没有关注单一蒸发器蒸发效果，并且都是离线计算，没有实时性。由于蒸发过程的闪蒸器的闪蒸效果将直接影响着整个氧化铝蒸发流程的生产效果，但是实际生产过程中并不知道单独的每一个闪蒸器的闪蒸强度，因此通过对氧化铝蒸发过程的单个闪蒸器进行分析研究，利用评价指标在线评价闪蒸器的闪蒸强度，对指导氧化铝生产、提高闪蒸效率具有重要意义。
发明内容
本发明要解决的技术问题是针对上述现有技术的不足，提供一种氧化铝蒸发流程中闪蒸过程的闪蒸速率计算方法，本发明在线评价闪蒸器的闪蒸强度，对指导氧化铝蒸发生产，提高蒸发流程的蒸发效果、节能降耗具有重要意义。
为解决上述技术问题，本发明所采取的技术方案是：
本发明提供一种氧化铝蒸发流程中闪蒸过程的闪蒸速率计算方法，包括如下步骤：
步骤1：获取氧化铝蒸发系统实时过程数据；
实时采集氧化铝蒸发过程闪蒸系统中的过程数据，该数据包括：当前的原液闪蒸器的进料浓度、进料温度、进料流量，出料温度，闪蒸器内平衡压力，二次蒸汽温度；
步骤2：判断闪蒸系统的进料量是否在正常的工作范围450m 3/小时～650m 3/小时？若是，则转到步骤3；若否，则执行步骤1；
步骤3：根据步骤1中得到的数据获得铝酸钠溶液的沸点升△′ BPE；
步骤3.1：计算在当前获得的压力下所对应的饱和温度；
将当前闪蒸器内平衡压力p转为绝压下工程压力P，单位是kg/cm 2，如下式所示：
P＝(p+0.101325)/0.098
二次蒸汽饱和温度T p与其相对应的工程压力P之间的关系式为：
Figure PCTCN2019090925-appb-000001
其中b 0，b 1，b 2，b 3，b 4为参数，所述参数由当前生产工况下饱和蒸汽压力所对应的饱和温度对照表中的数据通过最小二乘方法实际拟合得到；
步骤3.2：计算铝酸钠溶液常压下的沸点升；
铝酸钠溶液的沸点升与溶液中含碱的浓度以及当前溶液温度有关，在氧化铝生产的蒸发工序中，铝酸钠溶液常压下的沸点升△ BPE的关系式为：
△ BPE＝c 0+c 1Nk+c 2T in+c 3NkT in+c 4Nk 2+c 5T in 2+c 6NkT in 2+c 7Nk 2T in+c 8Nk 3+c 9T in 3
其中c 0，c 1，c 2，c 3，c 4，c 5，c 6，c 7，c 8，c 9为参数，所述参数是在当前生产工况下根据出料口处的铝酸钠溶液浓度进行生产与化验得到的数据对上式进行多项式回归拟合后得到，Nk为苛碱浓度,T in为进料溶液温度；
步骤3.3：根据吉辛柯公式对沸点升△ BPE进行修正，得到修正后的沸点升△′ BPE；
由于溶液的压力变化会导致料液沸点变化，根据吉辛柯公式对铝酸钠溶液常压下的沸点升高进行校正，公式为：
△′ BPE＝f△ BPE
其中f为校正系数，其计算公式为：
Figure PCTCN2019090925-appb-000002
其中r为当前生产工况的压强下二次蒸汽的汽化潜热；
通过对蒸汽温度与热焓表进行回归分析，得到蒸汽潜热与温度的关系式为：
r＝d 1-d 2T p-d 3T p 2
其中d 1，d 2，d 3为参数，根据当前生产工况下对蒸汽温度与热焓表中的数据进行回归拟合得到；
通过计算上述步骤计算可得修正后的铝酸钠溶液的沸点升△′ BPE：
Figure PCTCN2019090925-appb-000003
步骤4：根据步骤3得到的沸点升△′ BPE计算闪蒸速率CFS，根据得到的CFS在线实时评价实际氧化铝生产过程中闪蒸的强度，如下式所示：
Figure PCTCN2019090925-appb-000004
其中T in为进料溶液温度，T out为出料溶液温度，T sat为与溶液相对应压力下的饱和温度，T sat＝T p+△′ BPE；τ为溶液在闪蒸器内的停留时间，
Figure PCTCN2019090925-appb-000005
Q为进料流量，α为闪蒸器半径，h为闪蒸器内液位高度。
采用上述技术方案所产生的有益效果在于：本发明提供的一种氧化铝蒸发流程中闪蒸过程的闪蒸速率计算方法，利用计算机系统和常规的检测仪表提供的在线过程数据，通过将闪蒸过程中铝酸钠溶液沸点升的计算方法与闪蒸速率的计算方法相结合，通过在不同的进料过热度，进料流量，闪蒸器液位高度、平衡压力情况下对该指标进行计算分析，结果表明我们可以用闪蒸速率这个指标在线实时评价实际氧化铝生产闪蒸的强度，对指导氧化铝蒸发生产过程，提高蒸发流程的蒸发效果、节能降耗具有重要意义。
附图说明
图1为本发明实施例提供的原液闪蒸过程回路的流程及装置示意图，其中1为二次蒸汽温度计，2为闪蒸器液位计，3为出料温度计，4为闪蒸器压力计，5为进料温度计，6为进料流量计，7为原液闪蒸器，8为进料浓度计；
图2为本发明实施例提供的闪蒸速率CFS计算流程图；
图3为本发明实施例提供的闪蒸速率CFS在进料浓度、压力、液位高度以及进料流量基本保持不变时随着过热度的变化图；
图4为本发明实施例提供的闪蒸速率CFS在进料浓度、过热度、以及进料流量基本保持不变时随着液位高度的变化图；
图5为本发明实施例提供的闪蒸速率CFS在进料浓度、液位高度、过热度以及进料流量基本保持不变时随着压力的变化图；
图6为本发明实施例提供的闪蒸速率CFS在进料浓度、液位高度、过热度以及压力基本保持不变时随着进料流量的变化图；
图7为本发明实施例提供的闪蒸速率CFS在进料流量、液位高度、过热度以及压力基本保持不变时随着进料浓度的变化图。
具体实施方式
下面结合附图和实施例，对本发明的具体实施方式作进一步详细描述。以下实施例用于说明本发明，但不用来限制本发明的范围。
本发明的氧化铝蒸发过程闪蒸系统的指标评价方法依赖于闪蒸系统硬件平台，由编写的软件程序实现，该程序用于采集当前的原液闪蒸器的进料浓度、进料温度、进料流量，出料温度，闪蒸器内平衡压力，二次蒸汽温度等数据。
其硬件平台核心由原液闪蒸器以及相关设备组成，同时配备了测量仪表，执行机构以及进行软件计算的计算机系统。蒸发原液通过进料口进入原液闪蒸器进行闪蒸，然后通过出料口出料进入下一效蒸发器继续进行蒸发，闪蒸过程中会产生大量蒸汽，通过闪蒸器顶部的二次蒸汽出口进入下一蒸发器继续进行加热，如图1所示，详细结构如下：
以闪蒸器为核心的闪蒸系统，还包括以下测量仪表：
用于在线测量进料温度的进料温度计，安装在原液闪蒸器进料入口管道上；
用于在线测量原液闪蒸器进料流量的流量计，安装在原液闪蒸器进料入口管道上；
用于在线测量原液闪蒸器进料浓度的浓度计，安装在原液闪蒸器进料入口管道上；
用于在线测量二次蒸汽压力的压力计，安装在原液闪蒸器出料口上；
用于在线测量原液闪蒸器出料温度的出料温度计，安装在原液闪蒸器的出料管道上；
在原液闪蒸器上装有差压液位计，用来检测闪蒸器内液位；
该闪蒸系统同时配置了分布式计算机控制系统(DCS)、或可编程逻辑控制器(PLC)、或工业控制计算机(IPC)，或分立式工业调节器；上述测量仪表与执行机构连接至控制计算机，本发明的氧化铝蒸发过程的闪蒸速率计算方法既可以运行在计算机控制系统的监控计算机上，也可以运行于独立的优化设定计算机上，该软件通过与控制计算机(分布式计算机控制系统(DCS)、或可编程逻辑控制器(PLC)、或工业控制计算机(IPC))进行通讯，获得实时的过程数据，并给出闪蒸速率的计算值。
如图2所示，本实施例的方法如下所述。
本发明提供一种氧化铝蒸发流程中闪蒸过程的闪蒸速率计算方法，包括如下步骤：
步骤1：获取氧化铝蒸发系统实时过程数据；
实时采集氧化铝蒸发过程闪蒸系统中的数据，该数据包括：当前的原液闪蒸器的进料浓度、进料温度、进料流量，出料温度，闪蒸器内平衡压力，二次蒸汽温度；
步骤2：判断闪蒸系统的进料量是否在正常的工作范围450m 3/小时～650m 3/小时？若是， 则转到步骤3；若否，则执行步骤1；
步骤3：根据步骤1中得到的数据获得铝酸钠溶液的沸点升△′ BPE；
料液沸点升高是指在同等压力的条件下，料液的沸点温度高于纯水的沸点温度；在氧化铝蒸发生产过程中，由于料液浓度的不断变化，致使蒸发器内料液沸点不同；同时由于在蒸发器内存在一定的压力，这也会导致了料液沸点的不同。
由于沸点升对闪蒸过程相关指标的计算有影响，需要大致计算出料液沸点升值，以下为主要的计算步骤：
步骤3.1：计算在当前获得的压力下所对应的饱和温度：
由于实际生产中的二次蒸汽过热，我们可以通过由蒸汽压力得到对应的饱和温度；首先将当前闪蒸器内平衡压力p转为绝压下工程压力P，单位是kg/cm 2，如下式所示：
P＝(p+0.101325)/0.098
二次蒸汽饱和温度T p与其相对应的工程压力P之间的关系式为：
Figure PCTCN2019090925-appb-000006
其中b 0，b 1，b 2，b 3，b 4为参数，所述参数由当前生产工况下氧化铝蒸发过程现场得到的饱和蒸汽压力对应的饱和温度对照表中的数据通过最小二乘方法实际拟合得到，
本实施例中得到：
T p＝68×P 0.3-48011×P -0.0003+48042
步骤3.2：计算铝酸钠溶液常压下的沸点升；
铝酸钠溶液的沸点升与溶液中含碱的浓度以及当前溶液温度有关，在氧化铝生产的蒸发工序中，铝酸钠溶液常压下的沸点升△ BPE的关系式为：
△ BPE＝c 0+c 1Nk+c 2T in+c 3NkT in+c 4Nk 2+c 5T in 2+c 6NkT in 2+c 7Nk 2T in+c 8Nk 3+c 9T in 3
其中c 0，c 1，c 2，c 3，c 4，c 5，c 6，c 7，c 8，c 9为参数，所述参数是在当前生产工况下根据出料口处的铝酸钠溶液浓度进行生产与化验得到的数据对上式进行多项式回归拟合后得到，Nk为苛碱浓度,T in为进料溶液温度；
本实施例为通过实际的生产与化验数据对上式进行辨识可得其中的未知参数：
△ BPE＝1.5+0.007×Nk+3×10 -5×T in+2×10 -4×Nk×T in
+1×10 -4×Nk 2-3.8×10 -8×T in 2+1.7×10 -10×Nk×T in 2
-2.5×10 -7×T in×Nk 2-9×10 -10×Nk 3-8.6×10 -10×T in 3
步骤3.3：根据吉辛柯公式对沸点升△ BPE进行修正，得到修正后的沸点升△′ BPE；
由于溶液的压力变化会导致料液沸点变化，根据吉辛柯公式对铝酸钠溶液常压下的沸点升高进行校正，公式为：
△′ BPE＝f△ BPE
其中f为校正系数，无因次，采用经验计算其计算公式为：
Figure PCTCN2019090925-appb-000007
其中r为当前生产工况的压强下二次蒸汽(饱和水蒸气)的汽化潜热，单位为kJ/kg；
上式中需要二次蒸汽的汽化潜热，然而蒸汽热焓会受到蒸汽压力和温度的影响，对于实际的正常过程，很难得到蒸汽潜热与蒸发器内压力和温度之间的精确数学关系。对饱和水和饱和蒸汽的热力学性质进行分析得知，蒸汽压力的变化对蒸汽的潜热的影响很小，可以忽略其对蒸汽潜热的影响，而蒸汽温度对蒸汽潜热有着较大的影响。所以说可以通过对蒸汽温度与热焓表进行回归分析，得到蒸汽潜热与温度的关系式为：
r＝d 1-d 2T p-d 3T p 2
其中d 1，d 2，d 3为参数，根据当前生产工况下对蒸汽温度与热焓表中的数据进行回归拟合得到；
通过计算上述步骤计算可得修正后理论铝酸钠溶液的沸点升△′ BPE：
Figure PCTCN2019090925-appb-000008
步骤4：根据步骤3得到的沸点升△′ BPE计算闪蒸速率CFS，根据得到的CFS在线实时评价实际氧化铝生产过程中闪蒸的强度，如下式所示：
WangYu等人定义循环闪蒸的闪蒸速率CFS，用来表示闪蒸进行的强度，如下式所示：
Figure PCTCN2019090925-appb-000009
其中T in为进料溶液温度，T out为出料溶液温度，T sat为与溶液相对应压力下的饱和温度， T sat＝T p+△′ BPE；τ为溶液在闪蒸器内的停留时间，
Figure PCTCN2019090925-appb-000010
Q为进料流量，α为闪蒸器半径，h为闪蒸器内液位高度。
通过对实际生产数据进行分析发现，闪蒸速率由于考虑了料液在闪蒸器内的停留时间，所以很够更加全面的衡量闪蒸的真正强度。
本实施例为一个大型氧化铝厂的原液闪蒸过程。其中原液闪蒸器的型号为Φ4.8m×4.5m；首先按照本方法的要求安装如下的测量仪表，包括：电磁流量计测量原液闪蒸器进料流量Q；温度计测量原闪蒸器进料溶液温度T in；温度计测量原闪蒸器出料溶液温度T out；压力计测量原液闪蒸器内平衡压力p；Nk浓度计测量原液闪蒸器进料浓度；电动调节阀控制原液闪蒸器进料流量；
以分布式计算机控制系统(DCS)实现基础控制回路的自动控制，在下位机中，使用DCS中的单回路调节器组态成如下的基础控制回路：原闪进料流量电动调节阀控制原闪进料流量，
在上位机(监控计算机)以Foxview软件实现监控人机界面。该闪蒸系统的进料流量正常工作范围为：原闪进料流量——450m 3/小时～650m 3/小时
闪蒸指标的计算程序用MathWorks提供的MATLAB应用软件编制，并在单独的优化计算机上运行，该计算机上装有OPC Server负责与DCS和上位机进行数据通讯。
本发明利用实际生产数据计算闪蒸过程的闪蒸速率，其中闪蒸速率CFS在压力、液位高度、进料流量、以及原液浓度基本保持不变时随着过热度的变化，具体参数为：-77.2kPa,0.87m,572m 3/h,177g/l,结果如图3所示；闪蒸速率CFS在过热度、压力、进料流量、以及原液浓度基本保持不变时随着液位高度的变化，具体参数为：1.5℃,-72.5kPa,595m 3/h,177g/l,结果如图4所示；闪蒸速率CFS在过热度、液位高度、进料流量以及原液浓度基本保持不变时随着压力的变化，具体参数为：1.5℃,0.77m,595m 3/h,175g/l,结果如图5所示；闪蒸速率CFS在过热度以及压力、液位高度、原液浓度基本保持不变时随着进料流量的变化，具体参数为：1.7℃,-74.5kPa,0.82m,163g/l,结果如图6所示；闪蒸速率CFS在过热度、压力、液位高度、以及进料流量基本保持不变时随着原液浓度的变化，具体参数为：1.7℃,-74.5kPa,0.82m,586m 3/h,结果如图7所示。通过对结果的分析可得：在氧化铝生产过程中，原液闪蒸器的闪蒸速率CFS随着进料流量和平衡压力的增大而增大，随着液膜高度与进料浓度增大而减少，由此闪蒸速率CFS这个指标能够反映闪蒸效果的强度；在实际氧化铝蒸发生产过程中，可以利用本发明中的氧化 铝蒸发流程中闪蒸速率CFS的计算方法在线实时评价氧化铝蒸发过程中闪蒸器的闪蒸强度，对指导氧化铝蒸发流程的生产，提高蒸发流程的蒸发效果、节能降耗具有重要意义。
最后应说明的是：以上实施例仅用以说明本发明的技术方案，而非对其限制；尽管参照前述实施例对本发明进行了详细的说明，本领域的普通技术人员应当理解：其依然可以对前述实施例所记载的技术方案进行修改，或者对其中部分或者全部技术特征进行等同替换；而这些修改或者替换，并不使相应技术方案的本质脱离本发明权利要求所限定的范围。

Claims (1)

  1. 一种氧化铝蒸发流程中闪蒸过程的闪蒸速率计算方法，其特征在于：包括如下步骤：
    步骤1：获取氧化铝蒸发系统实时过程数据；
    实时采集氧化铝蒸发过程闪蒸系统中的过程数据，该数据包括：当前的原液闪蒸器的进料浓度、进料温度、进料流量，出料温度，闪蒸器内平衡压力，二次蒸汽温度；
    步骤2：判断闪蒸系统的进料量是否在正常的工作范围450m 3/小时～650m 3/小时？若是，则转到步骤3；若否，则执行步骤1；
    步骤3：根据步骤1中得到的数据获得铝酸钠溶液的沸点升△′ BPE；
    步骤3.1：计算在当前获得的压力下所对应的饱和温度；
    将当前闪蒸器内平衡压力p转为绝压下工程压力P，单位是kg/cm 2，如下式所示：
    P＝(p+0.101325)/0.098
    二次蒸汽饱和温度T p与其相对应的工程压力P之间的关系式为：
    Figure PCTCN2019090925-appb-100001
    其中b 0，b 1，b 2，b 3，b 4为参数，所述参数由当前生产工况下饱和蒸汽压力所对应的饱和温度对照表中的数据通过最小二乘方法实际拟合得到；
    步骤3.2：计算铝酸钠溶液常压下的沸点升；
    铝酸钠溶液的沸点升与溶液中含碱的浓度以及当前溶液温度有关，在氧化铝生产的蒸发工序中，铝酸钠溶液常压下的沸点升△ BPE的关系式为：
    △ BPE＝c 0+c 1Nk+c 2T in+c 3NkT in+c 4Nk 2+c 5T in 2+c 6NkT in 2+c 7Nk 2T in+c 8Nk 3+c 9T in 3
    其中c 0，c 1，c 2，c 3，c 4，c 5，c 6，c 7，c 8，c 9为参数，所述参数是在当前生产工况下根据出料口处的铝酸钠溶液浓度进行生产与化验得到的数据对上式进行多项式回归拟合后得到，Nk为苛碱浓度,T in为进料溶液温度；
    步骤3.3：根据吉辛柯公式对沸点升△ BPE进行修正，得到修正后的沸点升△′ BPE；
    由于溶液的压力变化会导致料液沸点变化，根据吉辛柯公式对铝酸钠溶液常压下的沸点升高进行校正，公式为：
    △′ BPE＝f△ BPE
    其中f为校正系数，其计算公式为：
    Figure PCTCN2019090925-appb-100002
    其中r为当前生产工况的压强下二次蒸汽的汽化潜热；
    通过对蒸汽温度与热焓表进行回归分析，得到蒸汽潜热与温度的关系式为：
    r＝d 1-d 2T p-d 3T p 2
    其中d 1，d 2，d 3为参数，根据当前生产工况下对蒸汽温度与热焓表中的数据进行回归拟合得到；
    通过计算上述步骤计算可得修正后的铝酸钠溶液的沸点升△′ BPE：
    Figure PCTCN2019090925-appb-100003
    步骤4：根据步骤3得到的沸点升△′ BPE计算闪蒸速率CFS，根据得到的CFS在线实时评价实际氧化铝生产过程中闪蒸的强度，如下式所示：
    Figure PCTCN2019090925-appb-100004
    其中T in为进料溶液温度，T out为出料溶液温度，T sat为与溶液相对应压力下的饱和温度，T sat＝T p+△′ BPE；τ为溶液在闪蒸器内的停留时间，
    Figure PCTCN2019090925-appb-100005
    Q为进料流量，α为闪蒸器半径，h为闪蒸器内液位高度。
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