CN112678904A - Scale cleaning device and method for multistage flash evaporation seawater desalination system - Google Patents

Abstract

The invention relates to a device and a method for cleaning scale of a multistage flash evaporation seawater desalination system, which are characterized in that structural parameters, necessary coefficients and a data acquisition period of the multistage flash evaporation seawater desalination system are given through a human-computer interaction module; the parameters are acquired by a data acquisition module and are sent to a central processing module through an A/D and D/A conversion module; and the central processing module calls the simulation calculation module according to the problem model stored in the central processing module and sends the calculated parameters to the parameter decision module. The parameter decision module estimates the scaling degree of the current system and the next cleaning time of the system, the simulation calculation module and the parameter decision module send the calculation data to the central processing module, and the central processing module arranges the data and sends the data to the display module. And real-time data acquisition is carried out, and the model is used for calculating to obtain the system scaling coefficient so as to judge the scaling condition of the system and guide a factory to carry out corresponding scaling treatment in time and keep the excellent performance of the system.

Description

Scale cleaning device and method for multistage flash evaporation seawater desalination system

Technical Field

The invention belongs to the technical field of chemical production process control, and particularly relates to a device and a method for cleaning scale in a multistage flash evaporation seawater desalination system.

Background

The multistage flash evaporation is the most mature technology in the seawater desalination industry, has the highest operation safety and large elasticity, and is suitable for large-scale and ultra-large-scale desalination devices. Will continue to play an important role in the future field of seawater desalination.

The MSF seawater desalination device has two classical structures, namely a straight-Through Multistage Flash (OT-MSF) seawater desalination device and a Brine circulating Multistage Flash (BR-MSF) seawater desalination device. The OT-MSF device is of simpler construction, while BR-MSF is more commonly used because of its better overall effect. The BR-MSF device consists of a brine heater, a heat recovery section, a heat discharge section and a mixing and separating module. The classical structure flow of the multi-stage flash seawater desalination system is shown in figure 1. The raw seawater firstly enters a heat discharge section, and is preheated and simultaneously condenses steam generated in a flash evaporation chamber. The feed seawater is divided into two parts after being preheated by the heat discharge section, one part returns to the sea, the other part is mixed with the circulating brine and then is pumped into the tail end of the heat recovery section, when the feed seawater flows through a series of heat exchangers from right to left, the feed seawater is gradually heated, and steam flashed out from the flash evaporation chamber is condensed. Finally, the seawater exits the heat exchanger in the first stage flash chamber of the heat recovery section, flows into a brine heater to be further heated, and flows into the first stage flash chamber in the form of hot brine. Because the pressure in the flash chamber is controlled to be lower than the saturated vapor pressure corresponding to the temperature of the hot brine, the hot brine is changed into superheated water after entering the flash chamber and is gasified partially rapidly, and the generated vapor meets the condensing pipe and is condensed and then drops into the fresh water tray. Repeating the steps until the last stage, discharging the strong brine and extracting the fresh water.

Circulating brine in the multistage flash evaporation process is heated by a preheater, and because the salinity, the hardness, the total solid solution and other impurities in the seawater are high, the solubility of certain components can reach supersaturation, so that the seawater is easy to scale on a heat exchange surface of a multistage flash evaporation seawater desalination device, and the method becomes one of the main problems faced by the hot method seawater desalination. The existence of dirt not only increases the fluid resistance, increases the energy consumption and reduces the heat transfer efficiency, but also blocks the pipeline in serious cases to cause the equipment to be paralyzed. However, the performance of the multistage flash evaporation seawater desalination system is influenced by not only dirt parameters but also the flow rate and salinity of the feed seawater, the amount of circulating strong brine, the highest temperature of brine, parameters of a brine heater and the like in the operation process, so that the water production performance is variable. In the operation process of the system, the scaling characteristic of the system cannot be directly measured, and the cleaning and maintenance of the system are generally operated based on experience and lack of scientific basis.

The invention can calculate the scale factor of the current system through the model according to the input and output operation data of the real-time operation of the system, thereby obtaining the scale degree of the system and providing the corresponding system maintenance and scale treatment method.

Disclosure of Invention

The invention aims to provide a cleaning operation guide by estimating the scaling coefficient of the scaling characteristic on line.

The descaling basis of the traditional multistage flash evaporation seawater desalination device is that the water yield and the water generation ratio are far lower than the standard value or the system performance has serious problems, the device may have irreversible damage to the service life cycle of the device, and the device is also tested when being put into production again. The invention discloses estimation and maintenance decision of scaling characteristic parameters of a thermal seawater desalination system, and relates to soft measurement of scaling parameters and guidance of system cleaning operation by calculating heat transfer coefficient and water production performance under the condition of combining physics and modeling. And real-time data acquisition is carried out, and the model is used for calculating to obtain the system scaling coefficient so as to judge the scaling condition of the system and guide a factory to carry out corresponding scaling treatment in time and keep the excellent performance of the system.

A scale cleaning device of a multistage flash evaporation seawater desalination system comprises a sensor module, a data acquisition module, a man-machine interaction module, a simulation calculation module, an A/D and D/A conversion module, a central processing module, a parameter decision module and a display module; the sensor module comprises five flow sensors, four temperature sensors and two seawater salinity sensors; the data acquisition module is used for acquiring the temperature and the salt content of the feed seawater, the fresh water flow, the circulating brine and the heat discharge seawater flow obtained by the sensor module, and the heating steam flow and the temperature; the human-computer interaction module is used for setting the structural parameters of flash chambers at all levels of the multi-level flash seawater desalination system, the parameters of a brine heater and the data acquisition period; the A/D and D/A conversion module is used for converting the received analog quantity into a corresponding digital quantity or converting the received digital quantity into a corresponding analog quantity; the central processing module is used for storing a scaling coefficient processing problem model of the multi-stage flash seawater desalination system and required physical parameters, receiving and storing data acquired by the data acquisition module through the A/D and D/A conversion module, receiving and storing data obtained by processing of the analog computation module and the parameter decision module, and then transmitting the data to the display module; the simulation calculation module calls a system program to calculate according to the currently acquired data to obtain the scaling coefficient f of the current brine heater_BHFouling factor f of flash chamber_j(j is 1,2, …, n is the number of the system flash chamber stages), the water making ratio GOR and the daily operation cost TOC, and the parameters are transmitted to a display module; the parameter decision module analyzes the data stored in the simulation calculation module before, estimates the system scaling degree and the next system cleaning time, and transmits the parameters to the display module; and the display module displays the calculation results of the simulation calculation module and the parameter decision module.

A method for cleaning scale in a multistage flash seawater desalination system comprises the following steps: firstly, an engineer sets the structural parameters of the multistage flash seawater desalination system through a human-computer interaction module, and sets an operation period. Thereafter the device collects the required data in a given cycle, andthe analog signals are sent to a central processing module through an A/D and D/A conversion module, and the central processing module calls an analog calculation module. The simulation calculation module obtains the scaling coefficient f of the brine heater of the current system by calculating the model problem in the central processing module_BHAnd fouling factor f of flash chamber_jGOR (water production ratio), and TOC (total organic carbon) of daily operation cost. And the parameter decision module performs comparison and analysis according to the parameters obtained by the simulation calculation module to obtain the scaling degree of the current system and the next system cleaning time and sends the relevant theory to the system display module. The device repeats the data acquisition, the analog calculation and the comparative analysis process in the next operation period, and continuously estimates the system scaling degree in real time.

The method specifically comprises the following steps:

step A1: an operator or an engineer gives structural parameters, physical property coefficients and a data acquisition period Tc of the multistage flash seawater desalination system through a man-machine interaction module;

step A2: collecting the flow W of the cooling brine entering the hot discharge section at the current time point by using a data collection module_FFlow rate W of circulating seawater_ReHeating steam flow rate W_steamFlow rate W of flash brine_BFlash evaporation fresh water flow W_DTemperature T of feed seawater_seaTemperature T of heating steam_steamTemperature T of flash brine_BFlash fresh water temperature T_DFeed brine concentration C_FConcentration of flash brine C_B. Recording the current time, making a variable T1 equal to the current time, and then sending the parameters to a central processing module through an A/D and D/A conversion module;

step A3: the central processing module calls the simulation calculation module according to the internally stored stable state simulation and daily operation cost model of the multi-stage flash seawater desalination device, so as to calculate the scaling coefficient f of the brine heater at the current T1 moment_BHFouling factor f of flash chamber_jThe water making ratio GOR and the daily operation cost TOC, and then the parameters are sent to the parameter decision module.

Step A4: the parameter decision module makes the parameter set L obtained in the period₁(f_BH,f_jGOR, TOC) andparameter set L obtained in previous periods_i(f_BH,f_jGOR, TOC) ((i ═ 1,2, …, m); m is the current period number), the scaling degree of the current system and the next cleaning time of the system are estimated, and the simulation calculation module and the parameter decision module send the calculation data to the central processing module.

Step A5: the central processing module arranges the data and sends the data to the display module, and the display module displays the current time T1 and the scaling coefficient f of the brine heater_BHFouling factor f of flash chamber_jThe water making ratio GOR, the daily running cost TOC, the system scaling degree and the system cleaning time Tim.

Step A6: recording the current time as T2, and if T2-T1< Tc, continuing to wait; otherwise, go to step A2, and resume data acquisition.

The model of the multistage flash evaporation seawater desalination device in the central processing module for stable state simulation and daily operation cost consists of the formulas (1) to (38);

the steady-state model of the multi-stage flash evaporation seawater desalination device consists of a flash chamber equation, a brine heater equation, a mixing and separating equation and a physical property parameter equation. For the j-th-stage flash chamber, the flash chamber module model consists of the following formulas (1) to (8):

W_Bj-1+W_Dj-1＝W_Bj+W_Dj (1)；

W_Bj-1C_Bj-1＝W_BjC_Bj (2)；

W_Bj-1h_Bj-1＝W_Bjh_Bj+V_Bjh_Vj (3)；

W_Bj-1-W_Bj＝V_Bj (4)；

wherein, W_BjRepresents the mass flow of flashed brine, W, of the j stage_Bj-1Represents the mass flow of the flashed brine, W, of the j-1 th stage_DjThe mass flow of fresh water W representing the j-th output_Dj-1Represents the flash brine mass flow for stage j-1. C_BjDenotes the flash brine concentration of the j stage, C_Bj-1Indicating the flash brine concentration for stage j-1. h is_BjRepresents the specific enthalpy, h, of the j-th stage flash brine_Bj-1Represents the specific enthalpy, h, of the j-1 th stage flash brine_VjSpecific enthalpy, V, of the j-th stage flash steam_BjAnd the evaporation capacity of the brine in the j-stage flash chamber is shown. W_FIndicating the mass flow, CP, of the chilled brine entering the hot discharge section_RjDenotes the heat capacity, CP, of the cooled brine leaving the j-th stage flash chamber_DjDenotes the specific heat capacity, CP, of fresh water leaving the j-th stage flash chamber_Dj-1Denotes the specific heat capacity, CP, of fresh water leaving the j-1 stage flash chamber_BjDenotes the specific heat capacity, CP, of the flashed brine leaving the j-th stage flash chamber_Bj-1Denotes the specific heat capacity, T, of the flashed brine leaving the j-1 stage flash chamber_FjIndicating the temperature, T, of the cooled brine leaving the j-th stage flash chamber_Fj+1Indicating the temperature, T, of the chilled brine entering the j-th stage flash chamber_BjIndicating the temperature, T, of brine leaving the j-th stage flash chamber_Bj-1Indicating the temperature, T, of the brine leaving the j-1 stage flash chamber_DjRepresenting the temperature, T, of the fresh water leaving the j-th flash chamber_Dj-1The temperature of the fresh water leaving the flash chamber of the j-1 th stage is shown, and T represents the flash reference temperature in an ideal state. A. the_jThe heat transfer area of the j-th stage flash chamber is shown,

denotes the heat transfer coefficient of the j-th stage flash chamber, wherein W denotes the feed flow rate of the j-th stage flash chamber, and W is W for the heat discharge section_FDenotes the feed seawater flow rate, and W ═ W for the heat recovery section_RThe feed flow rate to the heat recovery section is indicated,

the outer diameter of each stage of the steaming chamber is expressed,

representing the internal diameter of the condenser tube of each stage of flash chamber, DⁱThe inner diameter is expressed, and the specific formula is expanded in the physical property equation part.

T_Bj＝T_Dj+ΔBPE_j+ΔNETD_j+ΔTL_j (7)；

T_Vj＝T_Dj+ΔTL_j (8)；

Wherein, Δ BPE_jDenotes the boiling point rise of the j-th brine, Δ NETD_jDenotes the unbalance margin, Δ TL_jRepresenting the temperature loss through the demister and condenser. T is_VjIndicating the flash vapor temperature of the flash chamber of stage j.

The brine heater module model consists of equations (9) - (12):

W_B0＝W_R (9)；

C_B0＝C_R (10)；

W_RCP_RH(T_B0-T_F1)＝W_steamλ_s (11)；

wherein,

wherein, W_B0Represents the mass flow of flashed brine, W, exiting the brine heater_RRepresenting the mass flow of chilled brine into the heat recovery section. C_B0Represents the concentration of flashed brine, C, entering the brine heater_RIndicating the concentration of chilled brine entering the heat recovery section. CP (CP)_RHIndicating the cooling brine heat capacity, T, into the brine heater_B0Represents the temperature of the flashed brine, W, exiting the brine heater_steamExpressed as heating steam mass flow, lambda_sRepresenting the latent heat of vapour, T_steamExpressed as brine heater steam temperature. A. the_HTo representThe heat transfer area of the brine heater,

denotes the heat transfer coefficient of the brine heater, wherein W denotes the feed flow W of the brine heater_R，

The outside diameter of the brine heater is shown,

the inner diameter of the condensation pipe of the brine heater is expressed, and a specific formula is developed in a physical property equation part.

The mixed separation module model is composed of formulas (13) to (20):

W_BD＝W_BN-W_Re (13)；

W_m＝W_F-W_r (14)；

S＝W_r-C_w (15)；

W_R＝W_Re+W_m (16)；

W_R·C_R＝W_Re·C_Re+W_m·C_m (17)；

W_R·h_R＝W_Re·h_Re+W_m·h_m (18)；

W_F＝S+W_S (19)；

wherein W_BDRepresents the mass flow of the waste seawater, W_BNRepresenting the mass flow of brine, W, leaving the last stage flash chamber_ReRepresenting the circulating brine mass flow. W_mRepresents the mass flow of make-up brine, W_rRepresenting the hot effluent seawater mass flow. S represents the return flow rate of the hot discharge section, C_wRepresenting the mass flow of brine exiting the hot discharge section. C_ReIndicating circulating saltWater concentration, C_mIndicating the make-up brine concentration. h is_RRepresents the specific enthalpy of the brine entering the heat recovery section, h_ReDenotes the specific enthalpy of the circulating brine, h_mIndicating the make-up brine specific enthalpy. W_SRepresenting the feed seawater mass flow.

Represents the specific enthalpy of the brine at the inlet of the heat discharge section, h_SRepresenting the specific enthalpy of the returned brine in the heat discharge section,

representing the feed seawater specific enthalpy.

The physical property parameter equation model is composed of equations (21) to (31):

CP_B＝[1-C_B(0.011311-1.146×10^-5T_B)]×CP_D (22)；

h_V＝596.912+0.46694T_S-0.000460256T_S ² (23)；

h_B＝CP_B·T_B (24)；

h_D＝CP_D·T_D (25)；

wherein CC ═ (19.819C)_B)/(1-C_B) CC denotes concentration conversion, C_BIndicating the flash brine concentration.

Wherein, ω is_j＝W_F/w_j，ω_jIndicating the mass per unit length of cooling brine entering the hot discharge section at the j-th stageFlow rate, w_jThe width of the condensation pipe of the j-th stage flash chamber is shown.

TL＝exp(1.885-0.02063T_D)/1.8 (28)；

U＝4.8857/(y+z+4.8857f) (29)；

y＝[0.0013(v×Dⁱ)^0.2]/[(0.2018+0.0031×T)v] (30)；

GOR＝W_DN/W_steam (32)；

Wherein CP_DThe specific heat capacity of the fresh water in the flash chamber is shown. CP (CP)_BIndicating the specific heat capacity of brine in the flash chamber, C_BDenotes the flash brine concentration, T_BIndicating the flash brine temperature. h is_vRepresents the enthalpy of the steam, T_SIs the steam temperature. h is_BIndicating the enthalpy of the brine. h is_DRepresents the enthalpy value, T, of fresh water_DRepresenting the fresh water temperature. BPE indicates the brine boiling point rise, where T indicates the brine temperature in the flash chamber or brine heater. NETD denotes the non-equilibrium temperature difference, H_jDenotes the flash brine level, w_jDenotes the width, Δ T, of the condensing tube of the j-th stage flash chamber_BRepresenting the brine temperature difference between the two stages. TL represents the temperature loss through the demister and condenser tube. U represents the heat transfer coefficient of the brine heater or flash chambers of each stage. y is an intermediate expression relating to the flow rate in the tubes, the brine temperature and the diameter in the condenser tubes, z is an intermediate expression relating to the fresh water temperature in the flash chamber, y and z are simply calculations, and f is the fouling factor of the brine heater or the flash chamber. v represents the flow velocity in the tube, DⁱDenotes the internal diameter of the condenser tube and T denotes the temperature of the brine at the outlet of the heat exchanger. W_DNThe mass flow of the total fresh water in the flash chamber is represented, and GOR represents the water production Ratio (gain Output Ratio) is a key index of the performance of the reaction system.

The daily running cost module model is composed of equations (33) to (38):

C1＝22×W_steam×[(T_steam-40)/85]×0.00415 (33)；

C2＝22×(D_N/ρ_w)×0.109 (34)；

C3＝22×(D_N/ρ_w)×0.082 (35)；

C4＝22×(D_N/ρ_b)×0.024 (36)；

C5＝22×(D_N/ρ_w)×0.1 (37)；

TOC＝C1+C2+C3+C4+C5 (38)；

wherein, C1 represents the heating steam cost, C2 represents the electric energy cost consumed by the device, C3 represents the maintenance and idle cost, C4 represents the pretreatment cost, C5 represents the labor cost, and TOC represents the daily operating cost of the system. D_NRepresenting the total fresh water production, p_wDenotes the pure water density, ρ_bRepresents the density of the brine.

The simulation calculation module solves the steady-state simulation problem formed by the calculation formulas (1) to (38) by using a quasi-Newton method to determine the scaling coefficient f of the brine heater of the current system_BHFouling factor f of flash chamber in heat recovery section and heat discharge section_jThe specific steps of the method are as follows:

step B1: the equations of the above equations (1) to (38) for obtaining the unknown quantity are organized into a nonlinear equation system, which is expressed by the following equation (39):

the representation of the vector is:

G(x)＝0 (40)；

here, x ═ x (x)₁,x₂,…,x_p)^T，G＝(g₁,g₂,…,g_q)^T，g_i(i＝1,2,…,q):Rⁿ→R。

Wherein x is₁,x₂,…,x_pP unknowns representing the system of nonlinear equations, and x represents a matrix of p x 1 dimensions formed by the unknowns of the system of equations. g₁,g₂,…,g_qRepresenting a constituent nonlinear squareThe q equations of the set of equations, G, represent a q × p dimensional matrix of equations of the set of nonlinear equations.

Step B2: let the initial iteration number k equal to 0, set the initial value x₀∈RⁿInitial quasi-Newton matrix B_kThe unit matrix is in dimension p multiplied by p, the calculation precision of the function value is epsilon, and the precision of the minimum step length is delta.

Step B3: calculating search direction vector d under iteration times k_kTo get the value of the next point:

x_k+1＝x_k+d_k (41)；

d_k＝-B_kΔG(x_k) (42)；

step B4: calculate G (x)_k) And G (x)_k+1) If G (x)_k+1) | | < epsilon or | | | x_k+1-x_kIf | | < delta, terminating the iteration to obtain the solution of the nonlinear equation set and the scaling coefficient f of the brine heater_BHFouling factor f of flash chamber_jGOR (water production ratio), TOC (total organic carbon) of daily operation cost; otherwise, go to step B5.

Step B5: by modifying B_kTo obtain B_k+1：

Wherein s is_k＝x_k+1-x_k，y_k＝ΔG(x_k+1)-ΔG(x_k)。x_kDenotes the value, x, evaluated at the k-th iteration_k+1Denotes the value, s, evaluated in the (k + 1) th iteration_kThe difference between the two evaluated values is indicated. Δ G (x)_k+1) Represents G (x)_k+1) Gradient vector of, Δ G (x)_k) Represents G (x)_k) Gradient vector of, y_kThe gradient vector difference for the (k + 1) th iteration and the k iterations is expressed.

Step B6: let k ═ k +1, go to step B3 for calculation.

The parameter decision module is used for obtaining the scaling coefficient f of the brine heater at all time points according to the simulation calculation module_BHFouling factor f of flash chamber_jWater producing ratioGOR and daily running cost TOC adopt the least square method to carry out fitting and analysis, carry out reasonable judgement to system's scale deposit degree, and the concrete step is as follows:

step C1: inheriting all data of the analog calculation module from the beginning of data acquisition and aiming at the scaling coefficient f of the brine heater_BHFouling factor f of flash chamber_jGOR (water production ratio), TOC (total organic carbon) of daily operating cost and scaling coefficient f of brine heater_BHSetting the upper limit H₁Fouling factor f of flash chamber_jSetting the upper limit H₂The water making ratio GOR sets the lower limit X₁Daily operating cost TOC setting upper limit X₂。

Step C2: dividing the data into four parts to be fitted respectively, and firstly, fitting the scaling coefficient f of the brine heater_BHAnd (4) performing curve fitting by using a least square method. Suppose a given collected data point (xx)_i,yy_i)(i＝0,1,…,m)，xx_iRepresenting data acquisition time points T_i，yy_iRepresents the scaling coefficient f of the brine heater collected at each time point_BH(i) In that respect The fitting polynomial is

To ensure that the module computation speed makes the polynomial order nn equal to 3, so that

Wherein I is a₀,a₁,a₂,a₃So that the above problem is to find I ═ I (a)₀,a₁,a₂,a₃) The extreme value problem of (2).

Step C3: obtaining the necessary condition of extremum by multivariate function

Namely, it is

Step C4: the formula (46) is rewritten into a normal equation system form

It can be shown that the coefficient matrix of the normal equation set (47) is a symmetric positive definite matrix, so that there is a unique solution. Is solved from formula (47) to obtain a_kk( kk 0,1, …,3), thereby obtaining a polynomial

Step C5: repeating the steps C2 to C4 to respectively obtain the scaling coefficient f of the brine heater_BHFouling factor f of flash chamber_jThe water production ratio GOR and the daily running cost TOC are fitted curves of the running time of the system, and the fitted curve is P₁(t)、P₂(t)、P₃(t) and P₄(t), wherein t represents time.

Step C6: judging whether the current system needs to be cleaned according to the upper and lower limits set by the parameters and the four obtained fitted curves, and deducing the time point Tim to be cleaned of the system under the 4 indexes according to a fitted equation₁、Tim₂、Tim₃、Tim₄。

Step C7: mixing Tim₁、Tim₂、Tim₃、Tim₄And comparing to obtain the latest time node which is recorded as Tim, wherein the time point is the next time point to be cleaned of the system.

Step C8: fouling factor f for brine heater_BHFouling factor f of flash chamber_jThe scale of the system can be obtained according to the numerical value of the current data acquisition point.

Drawings

FIG. 1 is a block diagram of a multi-stage flash seawater desalination system according to the present invention;

FIG. 2 is a schematic view of the overall structure of the present invention;

FIG. 3 is a flow chart of the operation of the present invention;

FIG. 4 is a flow diagram of a simulation calculation module;

FIG. 5 is a flow chart of a parameter decision module.

Detailed Description

The invention is further analyzed with reference to the following figures and specific examples.

As shown in fig. 2, the scaling treatment device of the multistage flash seawater desalination system comprises a sensor module, a data acquisition module, a man-machine interaction module, a simulation calculation module, an a/D and D/a conversion module, a central processing module, a parameter decision module and a display module; the sensor module comprises five flow sensors, four temperature sensors and two seawater salinity sensors; the data acquisition module is used for acquiring the temperature and the salt content of the feed seawater, the fresh water flow, the circulating brine and the heat discharge seawater flow obtained by the sensor module, and the heating steam flow and the temperature; the human-computer interaction module is used for setting the structural parameters of flash chambers at all levels of the multi-level flash seawater desalination system, the parameters of a brine heater and the data acquisition period; the A/D and D/A conversion module is used for converting the received analog quantity into a corresponding digital quantity or converting the received digital quantity into a corresponding analog quantity; the central processing module is used for storing a scaling coefficient processing problem model of the multi-stage flash seawater desalination system and required physical parameters, receiving and storing data acquired by the data acquisition module through the A/D and D/A conversion module, receiving and storing data obtained by processing of the analog computation module and the parameter decision module, and then transmitting the data to the display module; the simulation calculation module calls a system program to calculate according to the currently acquired data to obtain the scaling coefficient f of the current brine heater_BHFouling factor f of flash chamber_j(j is 1,2, …, n is the number of the system flash chamber stages), the water making ratio GOR and the daily operation cost TOC, and the parameters are transmitted to a display module; the parameter decision module analyzes the data stored in the simulation calculation module before to estimate the system scaling degree and the next system cleaningWashing time and transmitting the parameters to a display module; and the display module displays the calculation results of the simulation calculation module and the parameter decision module.

As shown in fig. 3, for a multi-stage flash seawater desalination system using the present invention, in order to estimate the scaling degree of the system on-line and perform the corresponding treatment, the following steps are required:

a1, a user or an engineer gives structural parameters of the multistage flash evaporation seawater desalination system through a human-computer interaction module, wherein the structural parameters comprise a heat recovery section stage number NR equal to 16 and a heat discharge section stage number NJ equal to 3; the size of the brine heater, the flash chamber and other important coefficients; setting a data acquisition period Tc to be 2 hours;

step A2: collecting the flow W of the cooling brine entering the hot discharge section at the current time point by using a data collection module_FFlow rate W of circulating seawater_ReHeating steam flow rate W_steamFlow rate W of flash brine_BFlash evaporation fresh water flow W_DTemperature T of feed seawater_seaTemperature T of heating steam_steamTemperature T of flash brine_BFlash fresh water temperature T_DFeed brine concentration C_FConcentration of flash brine C_B. Recording the current time, making a variable T1 equal to the current time, and then sending the parameters to a central processing module through an A/D and D/A conversion module;

step A3: the central processing module calls the simulation calculation module according to the internally stored stable state simulation and daily operation cost model of the multi-stage flash seawater desalination device, so as to calculate the scaling coefficient f of the brine heater at the current T1 moment_BHFouling factor f of flash chamber_jThe water making ratio GOR and the daily operation cost TOC, and then the parameters are sent to the parameter decision module.

Step A4: the parameter decision module makes the parameter set L obtained in the period₁(f_BH,f_jGOR, TOC) and the parameter set L obtained in the previous cycles_i(f_BH,f_jGOR, TOC) ((i ═ 1,2, …, m); m is the current period number), the scaling degree of the current system and the next time of cleaning the system are estimated, and a simulation calculation module and a parameter decision module are used for simulationThe block sends its calculation data to the central processing module.

Step A5: the central processing module arranges the data and sends the data to the display module, and the display module displays the current time T1 and the scaling coefficient f of the brine heater_BHFouling factor f of flash chamber_jThe water making ratio GOR, the daily running cost TOC, the system scaling degree and the system cleaning time Tim.

Step A6: recording the current time as T2, and if T2-T1< Tc, continuing to wait; otherwise, go to step A2, and resume data acquisition.

The model of the multistage flash evaporation seawater desalination device in the central processing module for stable state simulation and daily operation cost is composed of the following formulas (1) to (38):

the steady-state model of the multi-stage flash evaporation seawater desalination device consists of a flash chamber equation, a brine heater equation, a mixing and separating equation and a physical property parameter equation. For the j-stage flash chamber, the flash chamber module model consists of the following formulas (1) to (8)

W_Bj-1+W_Dj-1＝W_Bj+W_Dj (1)；

W_Bj-1C_Bj-1＝W_BjC_Bj (2)；

W_Bj-1h_Bj-1＝W_Bjh_Bj+V_Bjh_Vj (3)；

W_Bj-1-W_Bj＝V_Bj (4)；

Wherein, W_BjRepresents the mass flow of flashed brine, W, of the j stage_Bj-1Represents the mass flow of the flashed brine, W, of the j-1 th stage_DjThe mass flow of fresh water W representing the j-th output_Dj-1Represents the flash brine mass flow for stage j-1. C_BjDenotes the flash brine concentration of the j stage, C_Bj-1Indicating the flash brine concentration for stage j-1. h is_BjRepresents the specific enthalpy, h, of the j-th stage flash brine_Bj-1Represents the specific enthalpy, h, of the j-1 th stage flash brine_VjSpecific enthalpy, V, of the j-th stage flash steam_BjAnd the evaporation capacity of the brine in the j-stage flash chamber is shown. W_FIndicating the mass flow, CP, of the chilled brine entering the hot discharge section_RjDenotes the heat capacity, CP, of the cooled brine leaving the j-th stage flash chamber_DjDenotes the specific heat capacity, CP, of fresh water leaving the j-th stage flash chamber_Dj-1Denotes the specific heat capacity, CP, of fresh water leaving the j-1 stage flash chamber_BjDenotes the specific heat capacity, CP, of the flashed brine leaving the j-th stage flash chamber_Bj-1Denotes the specific heat capacity, T, of the flashed brine leaving the j-1 stage flash chamber_FjIndicating the temperature, T, of the cooled brine leaving the j-th stage flash chamber_Fj+1Indicating the temperature, T, of the chilled brine entering the j-th stage flash chamber_BjIndicating the temperature, T, of brine leaving the j-th stage flash chamber_Bj-1Indicating the temperature, T, of the brine leaving the j-1 stage flash chamber_DjRepresenting the temperature, T, of the fresh water leaving the j-th flash chamber_Dj-1The temperature of the fresh water leaving the flash chamber of the j-1 th stage is shown, and T represents the flash reference temperature in an ideal state. A. the_jThe heat transfer area of the j-th stage flash chamber is shown,

denotes the heat transfer coefficient of the j-th stage flash chamber, wherein W denotes the feed flow rate of the j-th stage flash chamber, and W is W for the heat discharge section_FDenotes the feed seawater flow rate, and W ═ W for the heat recovery section_RThe feed flow rate to the heat recovery section is indicated,

the outer diameter of each stage of the steaming chamber is expressed,

representing the internal diameter of the condenser tube of each stage of flash chamber, DⁱThe inner diameter is expressed, and the specific formula is expanded in the physical property equation part.

T_Bj＝T_Dj+ΔBPE_j+ΔNETD_j+ΔTL_j (7)；

T_Vj＝T_Dj+ΔTL_j (8)；

Wherein, Δ BPE_jDenotes the boiling point rise of the j-th brine, Δ NETD_jDenotes the unbalance margin, Δ TL_jRepresenting the temperature loss through the demister and condenser. T is_VjIndicating the flash vapor temperature of the flash chamber of stage j.

The brine heater module model consists of equations (9) - (12):

W_B0＝W_R (9)；

C_B0＝C_R (10)；

W_RCP_RH(T_B0-T_F1)＝W_steamλ_s (11)；

wherein,

wherein W_B0Represents the mass flow of flashed brine, W, exiting the brine heater_RRepresenting the mass flow of chilled brine into the heat recovery section. C_B0Represents the concentration of flashed brine, C, entering the brine heater_RIndicating the concentration of chilled brine entering the heat recovery section. CP (CP)_RHIndicating the cooling brine heat capacity, T, into the brine heater_B0Represents the temperature of the flashed brine, W, exiting the brine heater_steamExpressed as heating steam mass flow, lambda_sRepresenting the latent heat of vapour, T_steamExpressed as brine heater steam temperature. A. the_HThe heat transfer area of the brine heater is shown,

denotes the heat transfer coefficient of the brine heater, wherein W denotes the feed flow W of the brine heater_R，

The outside diameter of the brine heater is shown,

the inner diameter of the condensation pipe of the brine heater is expressed, and a specific formula is developed in a physical property equation part.

The mixed separation module model is composed of formulas (13) to (20):

W_BD＝W_BN-W_Re (13)；

W_m＝W_F-W_r (14)；

S＝W_r-C_w (15)；

W_R＝W_Re+W_m (16)；

W_R·C_R＝W_Re·C_Re+W_m·C_m (17)；

W_R·h_R＝W_Re·h_Re+W_m·h_m (18)；

W_F＝S+W_S (19)；

wherein W_BDRepresents the mass flow of the waste seawater, W_BNRepresenting the mass flow of brine, W, leaving the last stage flash chamber_ReRepresenting the circulating brine mass flow. W_mRepresents the mass flow of make-up brine, W_rRepresenting the hot effluent seawater mass flow. S represents the return flow rate of the hot discharge section, C_wRepresenting the mass flow of brine exiting the hot discharge section. C_ReDenotes circulating brine concentration, C_mIndicating the make-up brine concentration. h is_RRepresents the specific enthalpy of the brine entering the heat recovery section, h_ReDenotes the specific enthalpy of the circulating brine, h_mIndicating the make-up brine specific enthalpy. W_SRepresenting the feed seawater mass flow.

Represents the specific enthalpy of the brine at the inlet of the heat discharge section, h_SRepresenting the specific enthalpy of the returned brine in the heat discharge section,

representing the feed seawater specific enthalpy.

The physical property parameter equation model is composed of equations (21) to (31):

CP_B＝[1-C_B(0.011311-1.146×10^-5T_B)]×CP_D (22)；

h_V＝596.912+0.46694T_S-0.000460256T_S ² (23)；

h_B＝CP_B·T_B (24)；

h_D＝CP_D·T_D (25)；

wherein CC ═ (19.819C)_B)/(1-C_B) CC denotes concentration conversion, C_BIndicating the flash brine concentration.

Wherein, ω is_j＝W_F/w_j，ω_jDenotes the mass flow per unit length of the cooled brine entering the hot discharge section of the j-th stage, w_jThe width of the condensation pipe of the j-th stage flash chamber is shown.

TL＝exp(1.885-0.02063T_D)/1.8 (28)；

U＝4.8857/(y+z+4.8857f) (29)；

y＝[0.0013(v×Dⁱ)^0.2]/[(0.2018+0.0031×T)v] (30)；

GOR＝W_DN/W_steam (32)；

Wherein CP_DThe specific heat capacity of the fresh water in the flash chamber is shown. CP (CP)_BIndicating the specific heat capacity of brine in the flash chamber, C_BDenotes the flash brine concentration, T_BIndicating the flash brine temperature. h is_vRepresents the enthalpy of the steam, T_SIs the steam temperature. h is_BIndicating the enthalpy of the brine. h is_DRepresents the enthalpy value, T, of fresh water_DRepresenting the fresh water temperature. BPE indicates the brine boiling point rise, where T indicates the brine temperature in the flash chamber or brine heater. NETD denotes the non-equilibrium temperature difference, H_jDenotes the flash brine level, w_jDenotes the width, Δ T, of the condensing tube of the j-th stage flash chamber_BRepresenting the brine temperature difference between the two stages. TL represents the temperature loss through the demister and condenser tube. U represents the heat transfer coefficient of the brine heater or flash chambers of each stage. y is an intermediate expression relating to the flow rate in the tubes, the brine temperature and the diameter in the condenser tubes, z is an intermediate expression relating to the fresh water temperature in the flash chamber, y and z are simply calculations, and f is the fouling factor of the brine heater or the flash chamber. v represents the flow velocity in the tube, DⁱDenotes the internal diameter of the condenser tube and T denotes the temperature of the brine at the outlet of the heat exchanger. W_DNThe mass flow of the total fresh water in the flash chamber is represented, and GOR represents the water production Ratio (gain Output Ratio) is a key index of the performance of the reaction system.

The daily running cost module model is composed of equations (33) to (38):

C1＝22×W_steam×[(T_steam-40)/85]×0.00415 (33)；

C2＝22×(D_N/ρ_w)×0.109 (34)；

C3＝22×(D_N/ρ_w)×0.082 (35)；

C4＝22×(D_N/ρ_b)×0.024 (36)；

C5＝22×(D_N/ρ_w)×0.1 (37)；

TOC＝C1+C2+C3+C4+C5 (38)；

wherein, C1 represents the heating steam cost, C2 represents the electric energy cost consumed by the device, C3 represents the maintenance and idle cost, C4 represents the pretreatment cost, C5 represents the labor cost, and TOC represents the daily operating cost of the system. D_NRepresenting the total fresh water production, p_wDenotes the pure water density, ρ_bRepresents the density of the brine.

The simulation calculation module solves the steady-state simulation problem formed by the calculation formulas (1) to (38) by using a quasi-Newton method to determine the scaling coefficient f of the brine heater of the current system_BHFouling factor f of flash chamber in heat recovery section and heat discharge section_jThe specific steps of the method are as follows:

step B1: the equations of the above equations (1) to (38) for obtaining the unknown quantity are organized into a nonlinear equation system, which is expressed by the following equation (39):

the representation of the vector is:

G(x)＝0 (40)；

here, x ═ x (x)₁,x₂,…,x_p)^T，G＝(g₁,g₂,…,g_q)^T，g_i(i＝1,2,…,q):Rⁿ→R。

Wherein x is₁,x₂,…,x_pP unknowns representing the system of nonlinear equations, and x represents a matrix of p x 1 dimensions formed by the unknowns of the system of equations. g₁,g₂,…,g_qQ equations constituting the nonlinear equation system are expressed, and G denotes a matrix of q × p dimensions constituted by the equations of the nonlinear equation system.

Step B2: let the initial iteration number k equal to 0, set the initial value x₀∈RⁿInitial quasi-Newton matrix B_kIs in p × p dimension unitThe calculation precision of the matrix and the function value is epsilon, and the minimum step precision is delta.

Step B3: calculating search direction vector d under iteration times k_kTo get the value of the next point:

x_k+1＝x_k+d_k (41)；

d_k＝-B_kΔG(x_k) (42)；

step B4: calculate G (x)_k) And G (x)_k+1) If G (x)_k+1) | | < epsilon or | | | x_k+1-x_kIf | | < delta, terminating the iteration to obtain the solution of the nonlinear equation set and the scaling coefficient f of the brine heater_BHFouling factor f of flash chamber_jGOR (water production ratio), TOC (total organic carbon) of daily operation cost; otherwise, go to step B5.

Step B5: by modifying B_kTo obtain B_k+1：

Wherein s is_k＝x_k+1-x_k，y_k＝ΔG(x_k+1)-ΔG(x_k)。x_kDenotes the value, x, evaluated at the k-th iteration_k+1Denotes the value, s, evaluated in the (k + 1) th iteration_kThe difference between the two evaluated values is indicated. Δ G (x)_k+1) Represents G (x)_k+1) Gradient vector of, Δ G (x)_k) Represents G (x)_k) Gradient vector of, y_kThe gradient vector difference for the (k + 1) th iteration and the k iterations is expressed.

Step B6: let k ═ k +1, go to step B3 for calculation.

The parameter decision module is used for obtaining the scaling coefficient f of the brine heater at all time points according to the simulation calculation module_BHFouling factor f of flash chamber_jThe water making ratio GOR and the daily running cost TOC are fitted and analyzed by adopting a least square method, and the system scaling degree is reasonably judged, and the specific steps are as follows:

step C1: inheriting the place of the analog computation module from the beginning of data acquisitionHas data and aims at the scaling coefficient f of the brine heater_BHFouling factor f of flash chamber_jGOR (water production ratio), TOC (total organic carbon) of daily operating cost and scaling coefficient f of brine heater_BHSetting the upper limit H₁Fouling factor f of flash chamber_jSetting the upper limit H₂The water making ratio GOR sets the lower limit X₁Daily operating cost TOC setting upper limit X₂。

Step C2: dividing the data into four parts to be fitted respectively, and firstly, fitting the scaling coefficient f of the brine heater_BHAnd (4) performing curve fitting by using a least square method. Suppose a given collected data point (xx)_i,yy_i)(i＝0,1,…,m)，xx_iRepresenting data acquisition time points T_i，yy_iRepresents the scaling coefficient f of the brine heater collected at each time point_BH(i) In that respect The fitting polynomial is

To ensure that the module computation speed makes the polynomial order nn equal to 3, so that

Wherein I is a₀,a₁,a₂,a₃So that the above problem is to find I ═ I (a)₀,a₁,a₂,a₃) The extreme value problem of (2).

Step C3: obtaining the necessary condition of extremum by multivariate function

Namely, it is

Step C4: the formula (46) is rewritten into a normal equation system form

It can be shown that the coefficient matrix of the normal equation set (47) is a symmetric positive definite matrix, so that there is a unique solution. Is solved from formula (47) to obtain a_kk( kk 0,1, …,3), thereby obtaining a polynomial

Step C5: repeating the steps C2 to C4 to respectively obtain the scaling coefficient f of the brine heater_BHFouling factor f of flash chamber_jThe water production ratio GOR and the daily running cost TOC are fitted curves of the running time of the system, and the fitted curve is P₁(t)、P₂(t)、P₃(t) and P₄(t), wherein t represents time.

Step C6: judging whether the current system needs to be cleaned according to the upper and lower limits set by the parameters and the four obtained fitted curves, and deducing the time point Tim to be cleaned of the system under the 4 indexes according to a fitted equation₁、Tim₂、Tim₃、Tim₄。

Step C7: mixing Tim₁、Tim₂、Tim₃、Tim₄And comparing to obtain the latest time node which is recorded as Tim, wherein the time point is the next time point to be cleaned of the system.

Step C8: fouling factor f for brine heater_BHFouling factor f of flash chamber_jThe scale of the system can be obtained according to the numerical value of the current data acquisition point.

The foregoing is a further description of the present invention given in connection with the specific examples provided below, and the practice of the present invention is not to be considered limited to these descriptions. Those skilled in the art to which the invention relates will readily appreciate that certain modifications and substitutions can be made without departing from the spirit and scope of the invention.

Claims (4)

1. A scale cleaning device of a multistage flash evaporation seawater desalination system is characterized in that; the system comprises a sensor module, a data acquisition module, a man-machine interaction module, a simulation calculation module, an A/D and D/A conversion module, a central processing module, a parameter decision module and a display module; the sensor module comprises five flow sensors, four temperature sensors and two seawater salinity sensors; the data acquisition module is used for acquiring the temperature and the salt content of the feed seawater, the fresh water flow, the circulating brine and the heat discharge seawater flow obtained by the sensor module, and the heating steam flow and the temperature; the human-computer interaction module is used for setting the structural parameters of flash chambers at all levels of the multi-level flash seawater desalination system, the parameters of a brine heater and the data acquisition period; the A/D and D/A conversion module is used for converting the received analog quantity into a corresponding digital quantity or converting the received digital quantity into a corresponding analog quantity; the central processing module is used for storing a scaling coefficient processing problem model of the multi-stage flash seawater desalination system and required physical parameters, receiving and storing data acquired by the data acquisition module through the A/D and D/A conversion module, receiving and storing data obtained by processing of the analog computation module and the parameter decision module, and then transmitting the data to the display module; the simulation calculation module calls a system program to calculate according to the currently acquired data to obtain the scaling coefficient f of the current brine heater_BHFouling factor f of flash chamber_jThe water making ratio GOR and the daily running cost TOC are obtained, and the parameters are transmitted to a display module; the parameter decision module analyzes the data stored in the simulation calculation module before, estimates the system scaling degree and the next system cleaning time, and transmits the parameters to the display module; and the display module displays the calculation results of the simulation calculation module and the parameter decision module.

2. A method for cleaning scale in a multistage flash seawater desalination system is characterized by comprising the following steps:

the method comprises the following steps: firstly, an engineer sets the structural parameters of the multistage flash seawater desalination system through a human-computer interaction module and sets the parameters for transportationA line period; the device collects the needed data in a given period and sends the data to the central processing module through the A/D and D/A conversion module, and the central processing module calls the simulation calculation module; the simulation calculation module obtains the scaling coefficient f of the brine heater of the current system by calculating the model problem in the central processing module_BHAnd fouling factor f of flash chamber_jGOR (water production ratio), TOC (total organic carbon) of daily operation cost; the parameter decision module performs comparative analysis according to the parameters obtained by the analog calculation module to obtain the scaling degree of the current system and the next system cleaning time and sends the relevant theory to the system display module; in the next operation period, repeating the data acquisition, simulation calculation and comparative analysis processes, and continuously estimating the system scaling degree in real time;

the method specifically comprises the following steps:

step A1: an operator or an engineer gives structural parameters, physical property coefficients and a data acquisition period Tc of the multistage flash seawater desalination system through a man-machine interaction module;

step A2: collecting the flow W of the cooling brine entering the hot discharge section at the current time point by using a data collection module_FFlow rate W of circulating seawater_ReHeating steam flow rate W_steamFlow rate W of flash brine_BFlash evaporation fresh water flow W_DTemperature T of feed seawater_seaTemperature T of heating steam_steamTemperature T of flash brine_BFlash fresh water temperature T_DFeed brine concentration C_FConcentration of flash brine C_B(ii) a Recording the current time, making a variable T1 equal to the current time, and then sending the parameters to a central processing module through an A/D and D/A conversion module;

step A3: the central processing module calls the simulation calculation module according to the internally stored stable state simulation and daily operation cost model of the multi-stage flash seawater desalination device, so as to calculate the scaling coefficient f of the brine heater at the current T1 moment_BHFouling factor f of flash chamber_jThe water making ratio GOR and the daily running cost TOC, and then sending the parameters to a parameter decision module;

step A4: the parameter decision module obtains parameters in the periodNumber set L₁(f_BH,f_jGOR, TOC) and the parameter set L obtained in the previous cycles_i(f_BH,f_jGOR, TOC), i is 1,2, …, m is the current period number, comparative analysis is carried out, the scaling degree of the current system and the next time of cleaning the system are estimated, and the simulation calculation module and the parameter decision module send the calculation data to the central processing module;

step A5: the central processing module arranges the data and sends the data to the display module, and the display module displays the current time T1 and the scaling coefficient f of the brine heater_BHFouling factor f of flash chamber_jThe water making ratio GOR, the daily running cost TOC, the system scaling degree and the system time to be cleaned Tim;

step A6: recording the current time as T2, and if T2-T1< Tc, continuing to wait; otherwise, go to step A2, and resume data acquisition.

3. The method for cleaning the scale in the multi-stage flash evaporation seawater desalination system as claimed in claim 2, wherein: the model of the multistage flash evaporation seawater desalination device in the central processing module for stable state simulation and daily operation cost consists of the formulas (1) to (38);

the steady-state model of the multi-stage flash evaporation seawater desalination device consists of a flash chamber equation, a brine heater equation, a mixing and separating equation and a physical property parameter equation; for the j-th-stage flash chamber, the flash chamber module model consists of the following formulas (1) to (8):

W_Bj-1+W_Dj-1＝W_Bj+W_Dj (1)；

W_Bj-1C_Bj-1＝W_BjC_Bj (2)；

W_Bj-1h_Bj-1＝W_Bjh_Bj+V_Bjh_Vj (3)；

W_Bj-1-W_Bj＝V_Bj (4)；

wherein, W_BjRepresents the mass flow of flashed brine, W, of the j stage_Bj-1Represents the mass flow of the flashed brine, W, of the j-1 th stage_DjThe mass flow of fresh water W representing the j-th output_Dj-1Represents the mass flow of the flash brine of the j-1 stage; c_BjDenotes the flash brine concentration of the j stage, C_Bj-1Represents the flash brine concentration of the j-1 stage; h is_BjRepresents the specific enthalpy, h, of the j-th stage flash brine_Bj-1Represents the specific enthalpy, h, of the j-1 th stage flash brine_VjSpecific enthalpy, V, of the j-th stage flash steam_BjExpressing the evaporation amount of the brine in the j-stage flash chamber; w_FIndicating the mass flow, CP, of the chilled brine entering the hot discharge section_RjDenotes the heat capacity, CP, of the cooled brine leaving the j-th stage flash chamber_DjDenotes the specific heat capacity, CP, of fresh water leaving the j-th stage flash chamber_Dj-1Denotes the specific heat capacity, CP, of fresh water leaving the j-1 stage flash chamber_BjDenotes the specific heat capacity, CP, of the flashed brine leaving the j-th stage flash chamber_Bj-1Denotes the specific heat capacity, T, of the flashed brine leaving the j-1 stage flash chamber_FjIndicating the temperature, T, of the cooled brine leaving the j-th stage flash chamber_Fj+1Indicating the temperature, T, of the chilled brine entering the j-th stage flash chamber_BjIndicating the temperature, T, of brine leaving the j-th stage flash chamber_Bj-1Indicating the temperature, T, of the brine leaving the j-1 stage flash chamber_DjRepresenting the temperature, T, of the fresh water leaving the j-th flash chamber_Dj-1The temperature of the fresh water leaving the j-1 stage flash chamber is shown, and T represents the reference temperature of the flash chamber in an ideal state; a. the_jThe heat transfer area of the j-th stage flash chamber is shown,

denotes the heat transfer coefficient of the j-th stage flash chamber, wherein W denotes the feed flow rate of the j-th stage flash chamber, and W is W for the heat discharge section_FDenotes the feed seawater flow rate, whereas for the heat recovery sectionW＝W_RThe feed flow rate to the heat recovery section is indicated,

the outer diameter of each stage of the steaming chamber is expressed,

representing the internal diameter of the condenser tube of each stage of flash chamber, DⁱThe inner diameter is expressed, and a specific formula is expanded in a physical property equation part;

T_Bj＝T_Dj+ΔBPE_j+ΔNETD_j+ΔTL_j (7)；

T_Vj＝T_Dj+ΔTL_j (8)；

wherein, Δ BPE_jDenotes the boiling point rise of the j-th brine, Δ NETD_jDenotes the unbalance margin, Δ TL_jRepresents the temperature loss through the demister and condenser; t is_VjIndicating the flash steam temperature of the j-stage flash chamber;

the brine heater module model consists of equations (9) - (12):

W_B0＝W_R (9)；

C_B0＝C_R (10)；

W_RCP_RH(T_B0-T_F1)＝W_steamλ_s (11)；

wherein,

wherein, W_B0Represents the mass flow of flashed brine, W, exiting the brine heater_RRepresents the mass flow of chilled brine entering the heat recovery section; c_B0Represents the concentration of flashed brine, C, entering the brine heater_RIndicating cooling into the heat recovery sectionBrine concentration; CP (CP)_RHIndicating the cooling brine heat capacity, T, into the brine heater_B0Represents the temperature of the flashed brine, W, exiting the brine heater_steamExpressed as heating steam mass flow, lambda_sRepresenting the latent heat of vapour, T_steamExpressed as brine heater steam temperature; a. the_HThe heat transfer area of the brine heater is shown,

denotes the heat transfer coefficient of the brine heater, wherein W denotes the feed flow W of the brine heater_R，

The outside diameter of the brine heater is shown,

the diameter of the inside of the condensation pipe of the brine heater is expressed, and a specific formula is developed in a physical property equation part;

the mixed separation module model is composed of formulas (13) to (20):

W_BD＝W_BN-W_Re (13)；

W_m＝W_F-W_r (14)；

S＝W_r-C_w (15)；

W_R＝W_Re+W_m (16)；

W_R·C_R＝W_Re·C_Re+W_m·C_m (17)；

W_R·h_R＝W_Re·h_Re+W_m·h_m (18)；

W_F＝S+W_S (19)；

wherein W_BDRepresents the mass flow of the waste seawater, W_BNRepresenting the mass flow of brine, W, leaving the last stage flash chamber_ReRepresents the circulating brine mass flow; w_mRepresents the mass flow of make-up brine, W_rRepresenting the hot discharge seawater mass flow; s represents the return flow rate of the hot discharge section, C_wRepresenting the mass flow of brine exiting the hot discharge section; c_ReDenotes circulating brine concentration, C_mIndicates make-up brine concentration; h is_RRepresents the specific enthalpy of the brine entering the heat recovery section, h_ReDenotes the specific enthalpy of the circulating brine, h_mRepresents the specific enthalpy of make-up brine; w_SRepresenting the feed seawater mass flow;

represents the specific enthalpy of the brine at the inlet of the heat discharge section, h_SRepresenting the specific enthalpy of the returned brine in the heat discharge section,

represents the specific enthalpy of the feed seawater;

the physical property parameter equation model is composed of equations (21) to (31):

CP_B＝[1-C_B(0.011311-1.146×10^-5T_B)]×CP_D (22)；

h_V＝596.912+0.46694T_S-0.000460256T_S ² (23)；

h_B＝CP_B·T_B (24)；

h_D＝CP_D·T_D (25)；

wherein CC ═ (19.819C)_B)/(1-C_B)，CC denotes concentration conversion, C_BRepresents the flash brine concentration;

wherein, ω is_j＝W_F/w_j，ω_jDenotes the mass flow per unit length of the cooled brine entering the hot discharge section of the j-th stage, w_jThe width of a condensation pipe of a j-stage flash chamber is shown;

TL＝exp(1.885-0.02063T_D)/1.8 (28)；

U＝4.8857/(y+z+4.8857f) (29)；

y＝[0.0013(v×Dⁱ)^0.2]/[(0.2018+0.0031×T)v] (30)；

GOR＝W_DN/W_steam (32)；

wherein CP_DThe specific heat capacity of the fresh water in the flash chamber is represented; CP (CP)_BIndicating the specific heat capacity of brine in the flash chamber, C_BDenotes the flash brine concentration, T_BRepresents the flash brine temperature; h is_vRepresents the enthalpy of the steam, T_SIs the steam temperature; h is_BRepresents the enthalpy of the brine; h is_DRepresents the enthalpy value, T, of fresh water_DRepresents the fresh water temperature; BPE represents the brine boiling point rise, where T represents the brine temperature in the flash chamber or brine heater; NETD denotes the non-equilibrium temperature difference, H_jDenotes the flash brine level, w_jDenotes the width, Δ T, of the condensing tube of the j-th stage flash chamber_BRepresenting the temperature difference of the brine between two stages; TL represents the temperature loss through the demister and condenser tube; u represents the heat transfer coefficient of the brine heater or each stage of flash chamber; y is an intermediate expression relating to flow velocity in the tube, brine temperature and diameter in the condenser tube, z is an intermediate expression relating to fresh water temperature in the flash chamber, y and z are simply calculations, and f is the fouling factor of the brine heater or the flash chamber(ii) a v represents the flow velocity in the tube, DⁱRepresents the internal diameter of the condenser tube, T represents the temperature of the brine at the outlet of the heat exchanger; w_DNThe mass flow of the total fresh water in the flash chamber is represented, and the GOR represents the water generation ratio which is a key index of the performance of the reaction system;

the daily running cost module model is composed of equations (33) to (38):

C1＝22×W_steam×[(T_steam-40)/85]×0.00415 (33)；

C2＝22×(D_N/ρ_w)×0.109 (34)；

C3＝22×(D_N/ρ_w)×0.082 (35)；

C4＝22×(D_N/ρ_b)×0.024 (36)；

C5＝22×(D_N/ρ_w)×0.1 (37)；

TOC＝C1+C2+C3+C4+C5 (38)；

wherein, C1 represents the heating steam cost, C2 represents the electric energy cost consumed by the device, C3 represents the maintenance and idle cost, C4 represents the pretreatment cost, C5 represents the labor cost, and TOC represents the daily operating cost of the system; d_NRepresenting the total fresh water production, p_wDenotes the pure water density, ρ_bRepresents the density of the concentrated brine;

the simulation calculation module solves the steady-state simulation problem formed by the calculation formulas (1) to (38) by using a quasi-Newton method to determine the scaling coefficient f of the brine heater of the current system_BHFouling factor f of flash chamber in heat recovery section and heat discharge section_jThe specific steps of the method are as follows:

step B1: the equations of the above equations (1) to (38) for obtaining the unknown quantity are organized into a nonlinear equation system, which is expressed by the following equation (39):

the representation of the vector is:

G(x)＝0 (40)；

here, x ═ x (x)₁,x₂,…,x_p)^T，G＝(g₁,g₂,…,g_q)^T，g_i(i＝1,2,…,q):Rⁿ→R；

Wherein x is₁,x₂,…,x_pP unknowns representing a nonlinear system of equations, x representing a matrix of dimension p x 1 formed by the unknowns of the system of equations; g₁,g₂,…,g_qRepresenting q equations constituting the nonlinear system of equations, G representing a q × p dimensional matrix constituted by the equations of the nonlinear system of equations;

step B2: let the initial iteration number k equal to 0, set the initial value x₀∈RⁿInitial quasi-Newton matrix B_kThe method is characterized in that the method is a unit matrix of dimension p multiplied by p, the calculation precision of a function value is epsilon, and the precision of the minimum step length is delta;

step B3: calculating search direction vector d under iteration times k_kTo get the value of the next point:

x_k+1＝x_k+d_k (41)；

d_k＝-B_kΔG(x_k) (42)；

step B4: calculate G (x)_k) And G (x)_k+1) If G (x)_k+1) | | < epsilon or | | | x_k+1-x_kIf | | < delta, terminating the iteration to obtain the solution of the nonlinear equation set and the scaling coefficient f of the brine heater_BHFouling factor f of flash chamber_jGOR (water production ratio), TOC (total organic carbon) of daily operation cost; otherwise, go to step B5;

step B5: by modifying B_kTo obtain B_k+1：

Wherein s is_k＝x_k+1-x_k，y_k＝ΔG(x_k+1)-ΔG(x_k)；x_kDenotes the value, x, evaluated at the k-th iteration_k+1Denotes the value, s, evaluated in the (k + 1) th iteration_kRepresenting the difference between the two evaluated values; Δ G (x)_k+1) Watch (A)Show G (x)_k+1) Gradient vector of, Δ G (x)_k) Represents G (x)_k) Gradient vector of, y_kExpressing the gradient vector difference of the (k + 1) th iteration and the (k) th iteration;

step B6: let k ═ k +1, go to step B3 for calculation.

4. The method for cleaning the scale in the multi-stage flash evaporation seawater desalination system as claimed in claim 2, wherein: the parameter decision module is used for obtaining the scaling coefficient f of the brine heater at all time points according to the simulation calculation module_BHFouling factor f of flash chamber_jThe water making ratio GOR and the daily running cost TOC are fitted and analyzed by adopting a least square method, and the system scaling degree is reasonably judged, and the specific steps are as follows:

step C1: inheriting all data of the analog calculation module from the beginning of data acquisition and aiming at the scaling coefficient f of the brine heater_BHFouling factor f of flash chamber_jGOR (water production ratio), TOC (total organic carbon) of daily operating cost and scaling coefficient f of brine heater_BHSetting the upper limit H₁Fouling factor f of flash chamber_jSetting the upper limit H₂The water making ratio GOR sets the lower limit X₁Daily operating cost TOC setting upper limit X₂；

Step C2: dividing the data into four parts to be fitted respectively, and firstly, fitting the scaling coefficient f of the brine heater_BHPerforming curve fitting by adopting a least square method; suppose a given collected data point (xx)_i，yy_i)，i＝0，1，…，m，xx_iRepresenting data acquisition time points T_i，yy_iRepresents the scaling coefficient f of the brine heater collected at each time point_BH(i) (ii) a The fitting polynomial is

To ensure that the module computation speed makes the polynomial order nn equal to 3, so that:

wherein I is a₀,a₁,a₂,a₃So that the above problem is to find I ═ I (a)₀,a₁,a₂,a₃) The problem of extreme values of (a);

step C3: the necessary condition of extreme value is solved by a multivariate function, and the following results are obtained:

namely, it is

Step C4: rewrite equation (46) to normal equation set form:

the coefficient matrix of the normal equation set (47) can be proved to be a symmetrical positive definite matrix, so that a unique solution exists; is solved from formula (47) to obtain a_kk(kk ═ 0,1, …,3), giving a polynomial:

step C5: repeating the steps C2 to C4 to respectively obtain the scaling coefficient f of the brine heater_BHFouling factor f of flash chamber_jThe water production ratio GOR and the daily running cost TOC are fitted curves of the running time of the system, and the fitted curve is P₁(t)、P₂(t)、P₃(t) and P₄(t), wherein t represents time;

step C6: judging whether the current system needs to be cleaned according to the upper and lower limits set by the parameters and the four obtained fitting curves, and deducing the system waiting time under the 4 indexes according to a fitting equationCleaning time Tim₁、Tim₂、Tim₃、Tim₄；

Step C7: mixing Tim₁、Tim₂、Tim₃、Tim₄Comparing to obtain the latest time node which is marked as Tim and is the time point to be cleaned next time;

step C8: fouling factor f for brine heater_BHFouling factor f of flash chamber_jThe scale of the system can be obtained according to the numerical value of the current data acquisition point.

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