CN-121971868-A - Energy consumption optimization-oriented MVR evaporation system self-adaptive variable frequency control method

CN121971868ACN 121971868 ACN121971868 ACN 121971868ACN-121971868-A

Abstract

The application relates to the technical field of industrial automatic control, in particular to an adaptive variable frequency control method of an MVR evaporation system oriented to energy consumption optimization. The method comprises the steps of constructing a dynamic heat transfer attenuation index by using pressure drop of a main heat exchanger, feeding temperature and discharging temperature of raw material liquid to be evaporated and concentrated and steam temperature of the raw material liquid after evaporation, acquiring liquid phase temperature and gas phase pressure of a separator and inlet steam pressure of a steam compressor, determining a boiling point characteristic factor based on the liquid phase temperature, the gas phase pressure and the inlet steam pressure, determining a lowest compression ratio by using the dynamic heat transfer attenuation index and the boiling point characteristic factor, and controlling frequency of a variable frequency motor by using a pneumatic characteristic curve of the steam compressor, the lowest compression ratio and a historical heat transfer attenuation index of a previous control period. Through the technical scheme, the MVR evaporation system can be subjected to self-adaptive variable frequency control.

Inventors

WANG HUI
ZHANG ZHIXIONG
PENG WEIJUN
HENG LIN

Assignees

广东中工碧蓝环境科技有限公司

Dates

Publication Date: 20260505
Application Date: 20260331

Claims (10)

1. The utility model provides an MVR vaporization system self-adaptation variable frequency control method towards energy consumption optimization, characterized in that MVR vaporization system includes main heat exchanger, separator, vapor compressor and drive vapor compressor's inverter motor, the method includes: Acquiring pressure drop of a main heat exchanger, feeding temperature and discharging temperature of raw material liquid to be evaporated and concentrated and steam temperature of the raw material liquid after evaporation, and constructing a dynamic heat transfer attenuation index based on the feeding temperature, the discharging temperature, the steam temperature and the pressure drop of the main heat exchanger; Acquiring liquid phase temperature, gas phase pressure and inlet steam pressure of a steam compressor of the separator, and determining a boiling point characteristic factor based on the liquid phase temperature, the gas phase pressure and the inlet steam pressure, wherein the boiling point characteristic factor is used for representing additional thermodynamic work of the MVR evaporation system; Determining the minimum compression ratio required by the vapor compressor to maintain the current evaporation process by utilizing the dynamic heat transfer attenuation index and the boiling point characteristic factor, wherein the minimum compression ratio is used for representing the pneumatic compression ratio corresponding to the minimum mechanical work required to be injected into the raw material liquid to maintain the effective heat exchange temperature difference; And determining a target frequency by utilizing the pneumatic characteristic curve, the lowest compression ratio and the historical heat transfer attenuation index of the previous control period of the steam compressor, and outputting a frequency adjusting instruction for the variable frequency motor so as to control the variable frequency motor to operate according to the target frequency.
2. The energy consumption optimization oriented MVR evaporation system adaptive variable frequency control method of claim 1 wherein constructing a dynamic heat transfer decay index based on feed temperature, discharge temperature, vapor temperature, and main heat exchanger pressure drop comprises: Determining a first temperature difference between the discharging temperature and the feeding temperature of the same sampling point in a sliding window at the current moment and a second temperature difference between the steam temperature and the feeding temperature of the same sampling point, and taking the ratio of the first temperature difference to the second temperature difference as a heat transfer efficiency factor of the sampling point; The method comprises the steps of taking the ratio of the pressure drop of a main heat exchanger to a standard atmospheric pressure reference value as a relative pressure drop, carrying out natural exponential decay mapping according to the product of the relative pressure drop and a pre-calibrated sensitivity coefficient to obtain a pressure drop compensation factor of a sampling point, taking the product of a heat transfer efficiency factor and the pressure drop compensation factor as an instantaneous decay coefficient, and taking the average value of the instantaneous decay coefficients of all the sampling points as a dynamic heat transfer decay index.
3. The energy consumption optimization oriented MVR evaporation system adaptive variable frequency control method of claim 1, wherein determining boiling point characteristic factors based on liquid phase temperature, gas phase pressure, and inlet vapor pressure comprises: Determining the saturated boiling temperature corresponding to pure water under the gas phase pressure of the sampling point in the sliding window at the current moment, determining the temperature deviation value between the liquid phase temperature and the saturated boiling temperature of the separator of the sampling point, taking the ratio of the temperature deviation value to the preset reference temperature as a normalized temperature rise value, and carrying out root mean square processing on the normalized temperature rise value of each sampling point in the sliding window to obtain a boiling point fluctuation characteristic value; and determining the relative pressure change rate between the gas phase pressure at the current moment and the inlet steam pressure, multiplying the relative pressure change rate by a pre-calibrated damping coefficient to obtain a correction term, and determining the boiling point characteristic factor by using the boiling point fluctuation characteristic value and the correction term.
4. The energy consumption optimization oriented MVR evaporation system adaptive variable frequency control method of claim 1 wherein the lowest compression ratio is determined by: Constructing a smooth magnification item by using a boiling point characteristic factor, a dynamic heat transfer attenuation index and a dimensionless mapping gain coefficient through a hyperbolic tangent function, and constructing a differential compensation item by using the change rate of the boiling point characteristic factor along with time; And compensating and adjusting the reference compression ratio calibrated in advance by the vapor compressor aiming at pure water evaporation by utilizing the smooth amplification factor term and the differential compensation term to obtain the adjusted minimum compression ratio.
5. The energy consumption optimization oriented MVR evaporation system adaptive variable frequency control method of claim 1 wherein determining the target frequency using the vapor compressor's aerodynamic characteristics, the lowest compression ratio, and the historical heat transfer decay index of the previous control period comprises: Taking the difference value between the square of the lowest compression ratio and the first preset positive number as a first pneumatic parameter, taking the difference value between the square of the reference compression ratio and the first preset positive number as a second pneumatic parameter, and taking the square root of the ratio of the first pneumatic parameter to the second pneumatic parameter as a rotating speed proportionality coefficient; The method comprises the steps of determining a difference value of a historical heat transfer attenuation index of a previous control period and a dynamic heat transfer attenuation index of a current control period, taking a ratio of the difference value to the historical heat transfer attenuation index as a heat transfer attenuation term, determining a down-conversion coefficient in linear negative correlation with the heat transfer attenuation term, and taking a product of the down-conversion coefficient, a rotating speed proportion coefficient and a rated frequency of a steam compressor as a target frequency.
6. The energy consumption optimization oriented MVR evaporation system adaptive variable frequency control method of claim 1, further comprising: under the condition that the MVR evaporation system is determined to be in an initial cold state starting stage, discarding the received frequency adjusting instruction for the variable frequency motor, and opening an anti-surge bypass valve of the vapor compressor; and calling a pre-configured soft start curve with a fixed slope, and controlling the output frequency of the variable frequency motor to be increased to a safe standby frequency according to a preset time gradient.
7. The energy consumption optimization-oriented adaptive variable frequency control method of an MVR evaporation system according to claim 6, wherein in a process of controlling an output frequency of a variable frequency motor to be increased to a safe standby frequency according to a preset time gradient, the method further comprises: The method comprises the steps of determining a real-time equilibrium state discrimination index, dynamically adjusting the opening of an anti-surge bypass valve by using the equilibrium state discrimination index, wherein the equilibrium state discrimination index is used for representing the thermodynamic stability degree of an MVR evaporation system, and the opening of the anti-surge bypass valve is inversely proportional to the equilibrium state discrimination index.
8. The energy consumption optimization oriented MVR evaporation system adaptive variable frequency control method of claim 7 wherein the equilibrium state discrimination index is determined by: Determining the absolute pressure change rate of the gas phase pressure of the separator, and constructing a pressure fluctuation interference item by using the time smoothing constant, the standard atmospheric pressure reference value and the absolute pressure change rate; Determining a continuous sampling standard deviation of an inlet-outlet temperature difference of a discharging temperature and a feeding temperature of a main heat exchanger, and constructing a temperature fluctuation interference item by using a preset sensitivity weight, a reference temperature parameter and the continuous sampling standard deviation; taking the sum of the pressure fluctuation interference term and the temperature fluctuation interference term as a total interference term, and taking the difference value of the second preset positive number and the total interference term as an equilibrium state discrimination index.
9. The energy consumption optimization oriented MVR evaporation system adaptive variable frequency control method of claim 7, further comprising: And closing the anti-surge bypass valve under the condition that the balance state discrimination indexes of a plurality of continuous control periods are higher than a preset balance threshold value, and controlling the frequency of the variable frequency motor according to the received frequency adjustment instruction of the variable frequency motor.
10. The energy consumption optimization oriented MVR evaporation system adaptive variable frequency control method according to claim 1, wherein the pressure drop of the main heat exchanger, the feed temperature and the discharge temperature of the raw material liquid to be evaporated and concentrated, and the vapor temperature of the raw material liquid after evaporation are obtained by: Pressure drop data of two ends of an inlet and an outlet of the main heat exchanger are continuously collected through a differential pressure transmitter arranged on the main heat exchanger, and the feeding temperature, the discharging temperature and the steam temperature of raw material liquid to be evaporated and concentrated are continuously collected through a temperature sensor arranged on the main heat exchanger.

Description

Energy consumption optimization-oriented MVR evaporation system self-adaptive variable frequency control method Technical Field The application relates to the technical field of industrial automatic control, in particular to an adaptive variable frequency control method of an MVR evaporation system oriented to energy consumption optimization. Background The MVR (MECHANICAL VAPOR RECOMPRESSION ) evaporation system is an evaporation concentration and crystallization system, and a closed-loop thermodynamic cycle system is mainly formed by a main heat exchanger, a gas-liquid separator, a vapor compressor, a variable-frequency driving motor and other core equipment, the MVR evaporation system utilizes a heat exchanger to heat and evaporate low-temperature secondary vapor generated by material, the pressure and saturation temperature are improved after the compression by the vapor compressor, the heat energy level is improved, and then the secondary vapor is re-sent into the heat exchanger to be used as a heating source, so that the cyclic utilization of heat energy is realized, and the dependence on external energy is reduced. The MVR system can achieve and even exceed the energy-saving effect of multi-effect evaporation by driving the compressor through less electric energy, has the advantages of low operation cost, high thermal efficiency, small occupied area and the like, and can be applied to industrial scenes such as high-salt wastewater treatment, chemical concentration and the like. In a conventional mechanical vapor recompression evaporation system, a control strategy usually adopts fixed-frequency operation or simple proportional integral differential adjustment based on single pressure feedback to maintain basic operation of the system, however, when a raw material liquid with complex components and dynamically-changing concentration is processed, the problem of heat transfer efficiency attenuation caused by material boiling point increase and heat exchanger scaling cannot be sensed by a control mode of the fixed-frequency or single pressure feedback. The related technology may cause the steam compressor to frequently deviate from the optimal working interval to operate, which causes the obvious increase of the energy consumption of the system, the insufficient heat exchange temperature difference and other consequences, so that the MVR evaporation system is required to be subjected to self-adaptive variable frequency control. Disclosure of Invention The application provides an energy consumption optimization-oriented MVR evaporation system self-adaptive variable frequency control method, which comprises the steps of obtaining pressure drop of a main heat exchanger, feeding temperature and discharging temperature of raw material liquid to be evaporated and concentrated and steam temperature of the raw material liquid after evaporation, constructing a dynamic heat transfer attenuation index based on the feeding temperature, the discharging temperature, the steam temperature and the pressure drop of the main heat exchanger, obtaining liquid phase temperature, gas phase pressure and inlet steam pressure of a separator, determining boiling point characteristic factors based on the liquid phase temperature, the gas phase pressure and the inlet steam pressure of a steam compressor, wherein the boiling point characteristic factors are used for representing additional work of the MVR evaporation system, determining the lowest compression ratio required by the steam compressor for maintaining the current evaporation process by utilizing the dynamic heat transfer attenuation index and the boiling point characteristic factors, determining a target frequency by utilizing a pneumatic characteristic curve of the steam compressor, the lowest compression ratio and a historical heat transfer attenuation index of a previous control period, and outputting a frequency adjustment instruction for a variable frequency motor so as to control the variable frequency motor to operate according to the target frequency. In this way, by determining the minimum compression ratio required by the vapor compressor to maintain the current evaporation process, the output power of the vapor compressor of the MVR evaporation system can be adaptively controlled. Optionally, constructing a dynamic heat transfer attenuation index based on the feeding temperature, the discharging temperature, the steam temperature and the pressure drop of the main heat exchanger, wherein the dynamic heat transfer attenuation index comprises the steps of determining a first temperature difference between the discharging temperature and the feeding temperature of the same sampling point and a second temperature difference between the steam temperature and the feeding temperature of the same sampling point in a sliding window at the current moment, taking the ratio of the first temperature difference to the second temperature difference as a heat transfer efficie