CN112678904B - Scale cleaning device and method for multistage flash evaporation seawater desalination system - Google Patents
Scale cleaning device and method for multistage flash evaporation seawater desalination system Download PDFInfo
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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
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 preheated in the heat discharge section and then divided into two parts, one part is returned to the sea, the other part is mixed with circulating brine and then 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 in the flash 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 quickly and partially gasified as superheated water after entering the flash chamber, and the generated vapor meets the condensing pipe, 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 breakdown of equipment. 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. During the operation of the system, the scaling characteristics of the system cannot be directly measured, and the cleaning and maintenance of the system are generally operated based on experience, which lacks 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; A/DThe 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 BH Fouling factor f of flash chamber j (j =1,2, …, n, wherein 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 structural parameters of the multistage flash seawater desalination system through a man-machine interaction module, and sets an operation 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 modules, 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 BH And fouling factor f of flash chamber j GOR (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 F Flow rate W of circulating seawater Re Heating steam flow rate W steam Flow rate W of flash-evaporated brine B Flash evaporation fresh water flow W D Temperature T of feed seawater sea Temperature T of heating steam steam Temperature T of flash brine B Flash fresh water temperature T D Feed brine concentration C F Concentration of flash brine C B . Recording the current time, making the variable T1 equal to the current time, and then sending the parameters to the central processing module through the A/D and D/A conversion modules;
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 multistage flash seawater desalination device, so as to calculate the scaling coefficient f of the brine heater at the current T1 moment BH Fouling factor f of flash chamber j The 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 period 1 (f BH ,f j GOR, TOC) and the parameter set L obtained in the previous cycles i (f BH ,f j GOR, 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 BH Fouling factor f of flash chamber j The 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, turning to the step A2 and carrying out data acquisition again.
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-1 C Bj-1 ＝W Bj C Bj (2)；
W Bj-1 h Bj-1 ＝W Bj h Bj +V Bj h Vj (3)；
W Bj-1 -W Bj ＝V Bj (4)；
wherein, W Bj Represents the mass flow of flashed brine, W, of the j stage Bj-1 Represents the mass flow of the flashed brine, W, of the j-1 th stage Dj Represents the fresh water mass flow, W, of the j-th output Dj-1 Represents the flash brine mass flow for stage j-1. C Bj Denotes the flash brine concentration of the j stage, C Bj-1 Indicating the flash brine concentration for stage j-1. h is Bj Represents the specific enthalpy, h, of the j-th stage flash brine Bj-1 Represents the specific enthalpy, h, of the j-1 th stage flash brine Vj Specific enthalpy, V, of the j-th stage flash steam Bj And the evaporation capacity of the brine in the j-stage flash chamber is shown. W F Indicating the mass flow, CP, of the cooling brine entering the hot discharge section Rj Denotes the heat capacity, CP, of the cooled brine leaving the j-th stage flash chamber Dj Indicating departure from grade j flashFresh water specific heat capacity, CP, of the steam chamber Dj-1 Denotes the specific heat capacity, CP, of fresh water leaving the j-1 stage flash chamber Bj Denotes the specific heat capacity, CP, of the flashed brine leaving the j-th stage flash chamber Bj-1 Denotes the specific heat capacity, T, of the flashed brine leaving the j-1 stage flash chamber Fj Indicating the temperature, T, of the cooled brine leaving the j-th stage flash chamber Fj+1 Indicating the temperature, T, of the chilled brine entering the j-th stage flash chamber Bj Indicating the temperature, T, of brine leaving the j-th stage flash chamber Bj-1 Indicating the temperature, T, of the brine leaving the j-1 stage flash chamber Dj Representing the temperature, T, of the fresh water leaving the j-th flash chamber Dj-1 The 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 j The heat transfer area of the j-th stage flash chamber is shown,
denotes the heat transfer coefficient of the j-th stage flash chamber, where W denotes the feed flow to the j-th stage flash chamber, W = W for the heat discharge section F Denotes the feed seawater flow rate, whereas W = W for the heat recovery section R The 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, D i The 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 j Denotes the boiling point rise of the j-th brine, Δ NETD j Denotes the unbalance margin, Δ TL j Representing the temperature loss through the demister and condenser. T is Vj Indicating 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 R CP RH (T B0 -T F1 )＝W steam λ s (11)；
wherein the content of the first and second substances,
wherein, W B0 Represents the mass flow of flashed brine, W, exiting the brine heater R Representing the mass flow of chilled brine into the heat recovery section. C B0 Represents the concentration of flashed brine, C, entering the brine heater R Indicating the concentration of chilled brine entering the heat recovery section. CP (CP) RH Indicating the cooling brine heat capacity, T, into the brine heater B0 Represents the temperature of the flashed brine, W, exiting the brine heater steam Expressed as heating steam mass flow, lambda s Representing the latent heat of vapour, T steam Expressed as brine heater steam temperature. A. The H The 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 condensation pipe of the brine heater is expressed, and the specific formula is developed in the physical property equation part.
The mixed separation module model is composed of equations (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 BD Represents the mass flow of the waste seawater, W BN Representing the mass flow of brine, W, leaving the last stage flash chamber Re Representing the circulating brine mass flow. W m Represents the mass flow of make-up brine, W r Representing the hot effluent seawater mass flow. S represents a return flow rate of a heat discharge section, C w Representing the mass flow of brine exiting the hot discharge section. C Re Denotes circulating brine concentration, C m Indicating the make-up brine concentration. h is R Represents the specific enthalpy of the brine entering the heat recovery section, h Re Denotes the specific enthalpy of the circulating brine, h m Indicating the make-up brine specific enthalpy. W S Representing the feed seawater mass flow.
Represents the specific enthalpy of the brine at the inlet of the heat discharge section, h S Representing 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 -5 T 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 B Indicating the flash brine concentration.
Wherein, ω is j ＝W F /w j ，ω j Denotes the mass flow per unit length of the cooled brine entering the hot discharge section of the j-th stage, w j The 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×D i ) 0.2 ]/[(0.2018+0.0031×T)v] (30)；
GOR＝W DN /W steam (32)；
Wherein CP D The specific heat capacity of the fresh water in the flash chamber is shown. CP (CP) B Indicating the ratio of brine in the flash chamberHeat capacity, C B Denotes the flash brine concentration, T B Indicating the flash brine temperature. h is v Represents the enthalpy of the steam, T S Is the steam temperature. h is B Indicating the enthalpy of the brine. h is D Represents the enthalpy value, T, of fresh water D Representing 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 j Denotes the flash brine level, w j Denotes the width, Δ T, of the condensing tube of the j-th stage flash chamber B Representing 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, D i Denotes the internal diameter of the condenser tube and T denotes the temperature of the brine at the outlet of the heat exchanger. W DN The 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 apparatus, C3 represents the maintenance and idling cost, C4 represents the pretreatment cost, C5 represents the labor cost, and TOC represents the daily operation cost of the system. D N Representing the total fresh water production, p w Denotes the pure water density, ρ b Represents 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 BH Fouling factor f of flash chamber in heat recovery section and heat discharge section j The 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 vector is represented in the form:
G(x)＝0 (40)；
here, x = (x) 1 ,x 2 ,…,x p ) T ，G＝(g 1 ,g 2 ,…,g q ) T ，g i (i＝1,2,…,q):R n →R。
Wherein x is 1 ,x 2 ,…,x p P 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. g 1 ,g 2 ,…,g q Q 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.
And step B2: let initial iteration number k =0, set initial value x 0 ∈R n Initial quasi-Newton matrix B k The 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.
And step B3: calculating search direction vector d under iteration times k k To get the value of the next point:
x k+1 ＝x k +d k (41)；
d k ＝-B k ΔG(x k ) (42)；
and step B4: calculate G (x) k ) And G (x) k+1 ) If G is | | |(x k+1 ) | | < epsilon or | | | x k+1 -x k If | | < delta, terminating the iteration to obtain the solution of the nonlinear equation set and the scaling coefficient f of the brine heater BH Fouling factor f of flash chamber j GOR (water production ratio), TOC (total organic carbon) of daily operation cost; otherwise, go to step B5.
And step B5: by modifying B k To obtain B k+1 ：
Wherein s is k ＝x k+1 -x k ，y k ＝ΔG(x k+1 )-ΔG(x k )。x k Denotes the value, x, evaluated at the k-th iteration k+1 Denotes the value, s, evaluated in the (k + 1) th iteration k The 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 k The gradient vector difference for the (k + 1) th iteration and the k iterations is expressed.
Step B6: and (5) enabling k = k +1, and turning to the 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 BH Fouling factor f of flash chamber j The 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, wherein the concrete 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 BH Fouling factor f of flash chamber j GOR (water production ratio), TOC (total organic carbon) of daily operating cost and scaling coefficient f of brine heater BH Setting the upper limit H 1 Fouling factor f of flash chamber j Setting the upper limit H 2 A lower limit X is set for a water generation ratio GOR 1 Daily operating cost TOC setting upper limit X 2 。
And C2: the data were divided into four parts and fitted separately, first to the brineFouling factor f of heater BH And (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 i Representing data acquisition time points T i ，yy i Represents 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 calculates the speed, the polynomial order nn =3, such that
Wherein I is a 0 ,a 1 ,a 2 ,a 3 So the above problem is to find I = I (a) 0 ,a 1 ,a 2 ,a 3 ) The extreme value problem of (2).
And C3: obtaining the necessary condition of extremum by multivariate function
Namely, it is
And 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 BH Fouling factor f of flash chamber j The 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 P 1 (t)、P 2 (t)、P 3 (t) and P 4 (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 equation 1 、Tim 2 、Tim 3 、Tim 4 。
Step C7: mixing Tim 1 、Tim 2 、Tim 3 、Tim 4 And 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.
And C8: fouling factor f for brine heater BH Fouling factor f of flash chamber j The 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 multi-stage 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 and a parameter decision moduleThe 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 BH Fouling factor f of flash chamber j (j =1,2, …, n, wherein 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, 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.
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 a multistage flash evaporation seawater desalination system through a man-machine interaction module, wherein the structural parameters comprise the number NR =16 of stages of a heat recovery section and the number NJ =3 of stages of a heat discharge section; the size of a brine heater, a flash chamber and other important factors; setting a data acquisition period Tc =2 hours;
step A2: using a data acquisition module to acquire entry at a current point in timeCooling brine flow W of hot exhaust section F Flow rate W of circulating seawater Re Heating steam flow rate W steam Flow rate W of flash brine B Flash evaporation fresh water flow W D Temperature T of feed seawater sea Heating steam temperature T steam Temperature T of flash brine B Flash fresh water temperature T D Feed brine concentration C F Concentration of flash brine C B . Recording the current time, making the variable T1 equal to the current time, and then sending the parameters to the central processing module through the A/D and D/A conversion modules;
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 multistage flash seawater desalination device, so as to calculate the scaling coefficient f of the brine heater at the current T1 moment BH Fouling factor f of flash chamber j The 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 period 1 (f BH ,f j GOR, TOC) and the parameter set L obtained in the previous cycles i (f BH ,f j GOR, 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 BH Fouling factor f of flash chamber j The 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, turning to the step A2 and carrying out data acquisition again.
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-1 C Bj-1 ＝W Bj C Bj (2)；
W Bj-1 h Bj-1 ＝W Bj h Bj +V Bj h Vj (3)；
W Bj-1 -W Bj ＝V Bj (4)；
Wherein, W Bj Represents the mass flow of flashed brine, W, of the j stage Bj-1 Represents the mass flow of the flashed brine, W, of the j-1 th stage Dj Represents the fresh water mass flow, W, of the j-th output Dj-1 Represents the flash brine mass flow for stage j-1. C Bj Denotes the flash brine concentration of the j stage, C Bj-1 Indicating the flash brine concentration for stage j-1. h is Bj Represents the specific enthalpy, h, of the j-th stage flash brine Bj-1 Represents the specific enthalpy, h, of the j-1 th stage flash brine Vj Specific enthalpy, V, of the j-th stage flash steam Bj Indicating the evaporation amount of the brine in the flash chamber of the j stage. W F Indicating the mass flow, CP, of the cooling brine entering the hot discharge section Rj Denotes the heat capacity, CP, of the cooled brine leaving the j-th stage flash chamber Dj Denotes the specific heat capacity, CP, of fresh water leaving the j-th stage flash chamber Dj-1 Denotes the specific heat capacity, CP, of fresh water leaving the j-1 stage flash chamber Bj Denotes the specific heat capacity, CP, of the flashed brine leaving the j-th stage flash chamber Bj-1 Representing flashed brine leaving the j-1 stage flash chamberSpecific heat capacity, T Fj Indicating the temperature, T, of the cooled brine leaving the j-th stage flash chamber Fj+1 Indicating the temperature, T, of the chilled brine entering the j-stage flash chamber Bj Indicating the temperature, T, of brine leaving the j-th stage flash chamber Bj-1 Indicating the temperature, T, of the brine leaving the j-1 stage flash chamber Dj Representing the temperature, T, of the fresh water leaving the j-th flash chamber Dj-1 The 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 j The heat transfer area of the j-th stage flash chamber is shown,
denotes the heat transfer coefficient of the j-th stage flash chamber, where W denotes the feed flow to the j-th stage flash chamber, W = W for the heat discharge section F Denotes the feed seawater flow rate, whereas W = W for the heat recovery section R The 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, D i The 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 j Denotes the boiling point rise of the j-th brine, Δ NETD j Denotes the unbalance margin, Δ TL j Representing the temperature loss through the demister and condenser. T is a unit of Vj Indicating 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 R CP RH (T B0 -T F1 )＝W steam λ s (11)；
wherein the content of the first and second substances,
wherein W B0 Represents the mass flow of flashed brine, W, exiting the brine heater R Representing the mass flow of chilled brine into the heat recovery section. C B0 Represents the concentration of flashed brine, C, entering the brine heater R Indicating the concentration of chilled brine entering the heat recovery section. CP (CP) RH Indicating the cooling brine heat capacity, T, into the brine heater B0 Represents the temperature of the flashed brine, W, exiting the brine heater steam Expressed as heating steam mass flow, lambda s Representing the latent heat of vapour, T steam Expressed as brine heater steam temperature. A. The H The 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 BD Represents the mass flow of the waste seawater, W BN Representing the mass flow of brine, W, leaving the last stage flash chamber Re Representing the circulating brine mass flow. W is a group of m Represents the mass flow of make-up brine, W r Representing the hot effluent seawater mass flow. S represents the return flow rate of the hot discharge section, C w Representing the mass flow of brine exiting the hot discharge section. C Re Denotes circulating brine concentration, C m Indicating the make-up brine concentration. h is R Represents the specific enthalpy of the brine entering the heat recovery section, h Re Denotes the specific enthalpy of the circulating brine, h m Indicating the make-up brine specific enthalpy. W S Representing the feed seawater mass flow.
Represents the specific enthalpy of the brine at the inlet of the heat discharge section, h S Representing 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 -5 T 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 B Indicating the flash brine concentration.
Wherein, ω is j ＝W F /w j ，ω j Denotes the mass flow per unit length of the cooled brine entering the hot discharge section of the j-th stage, w j The 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×D i ) 0.2 ]/[(0.2018+0.0031×T)v] (30)；
GOR＝W DN /W steam (32)；
Wherein CP D The specific heat capacity of the fresh water in the flash chamber is shown. CP (CP) B Indicating the specific heat capacity of brine in the flash chamber, C B Denotes the flash brine concentration, T B Indicating the flash brine temperature. h is a total of v Representing the enthalpy of the steam, T S Is the steam temperature. h is a total of B Indicating the enthalpy of the brine. h is D Represents the enthalpy value, T, of fresh water D Representing 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 j Denotes the flash brine level, w j Denotes the width, Δ T, of the condensing tube of the j-th stage flash chamber B Representing 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 flow rate in the tubes, brine temperature and diameter in the condenser tubes, 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. v represents the flow velocity in the tube, D i Denotes the internal diameter of the condenser tube and T denotes the temperature of the brine at the outlet of the heat exchanger. W DN The 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 apparatus, C3 represents the maintenance and idling cost, C4 represents the pretreatment cost, C5 represents the labor cost, and TOC represents the daily operation cost of the system. D N Representing the total fresh water production, p w Denotes the pure water density, ρ b Represents 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 BH Heat and steamRecovery section and heat discharge section flash chamber scaling factor f j The 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) 1 ,x 2 ,…,x p ) T ，G＝(g 1 ,g 2 ,…,g q ) T ，g i (i＝1,2,…,q):R n →R。
Wherein x is 1 ,x 2 ,…,x p P 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. g 1 ,g 2 ,…,g q Q 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.
And step B2: let initial iteration number k =0, set initial value x 0 ∈R n Initial quasi-Newton matrix B k The 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.
And step B3: calculating search direction vector d under iteration times k k To get the value of the next point:
x k+1 ＝x k +d k (41)；
d k ＝-B k ΔG(x k ) (42)；
and step B4: calculate G (x) k ) And G (x) k+1 ) If G (x) k+1 ) | | < epsilon or | | | x k+1 -x k If | | < delta, terminating the iteration to obtain the solution of the nonlinear equation set and the scaling coefficient f of the brine heater BH Fouling factor f of flash chamber j GOR water making ratio and daily operationCost TOC; otherwise, go to step B5.
And step B5: by modifying B k To obtain B k+1 ：
Wherein s is k ＝x k+1 -x k ，y k ＝ΔG(x k+1 )-ΔG(x k )。x k Denotes the value, x, evaluated at the k-th iteration k+1 Denotes the value, s, evaluated in the (k + 1) th iteration k The 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 k The gradient vector difference for the (k + 1) th iteration and the k iterations is expressed.
Step B6: and (5) enabling k = k +1, and turning to the 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 BH Fouling factor f of flash chamber j The 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 BH Fouling factor f of flash chamber j GOR water production ratio and TOC daily operating cost, and scaling factor f for brine heater BH Setting the upper limit H 1 Fouling factor f of flash chamber j Setting the upper limit H 2 The water making ratio GOR sets the lower limit X 1 Daily operating cost TOC setting upper limit X 2 。
And step C2: dividing the data into four parts to be fitted respectively, and firstly, fitting the scaling coefficient f of the brine heater BH And (4) performing curve fitting by using a least square method. Suppose that a given collected data point (xx) i ,yy i )(i＝0,1,…,m)，xx i Representing data acquisition time points T i ，yy i Represents 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 calculates the speed, the polynomial order nn =3, such that
Wherein I is a 0 ,a 1 ,a 2 ,a 3 So the above problem is to find I = I (a) 0 ,a 1 ,a 2 ,a 3 ) The extreme value problem of (2).
And C3: obtaining the necessary condition of extremum by multivariate function
Namely, it is
And 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 BH Fouling factor f of flash chamber j The 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 P 1 (t)、P 2 (t)、P 3 (t) and P 4 (t), wherein t represents time.
And 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 equation 1 、Tim 2 、Tim 3 、Tim 4 。
Step C7: mixing Tim 1 、Tim 2 、Tim 3 、Tim 4 And 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.
And C8: fouling factor f for brine heater BH Fouling factor f of flash chamber j The scale degree 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 (2)
1. 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 structural parameters of a multistage flash seawater desalination system through a man-machine interaction module, and sets an operation period; then the scaling cleaning device of the multi-stage flash seawater desalination system collects required data in a given period and sends the data to the central processing module through the A/D and D/A conversion modules, 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 BH And fouling factor f of flash chamber j GOR (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; repeating the data acquisition, simulation calculation and comparative analysis processes in the next operation period of the scaling cleaning device of the multistage flash seawater desalination system, and continuously estimating the scaling degree of the system 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 F Flow rate W of circulating seawater Re Heating steam flow rate W steam Flow rate W of flash brine B Flash evaporation fresh water flow W D Temperature T of feed seawater sea Temperature T of heating steam steam Temperature of flash brine T B Flash fresh water temperature T D Feed brine concentration C F Concentration of flash brine C B (ii) a Recording the current time, making the variable T1 equal to the current time, and then sending the parameters to the central processing module through the A/D and D/A conversion modules;
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 multistage flash seawater desalination device, so as to calculate the scaling coefficient f of the brine heater at the current T1 moment BH Fouling factor f of flash chamber j The water making ratio GOR and the daily running cost TOC, and then the parameters are sent to a parameter decision module;
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-1 C Bj-1 ＝W Bj C Bj (2)；
W Bj-1 h Bj-1 ＝W Bj h Bj +V Bj h Vj (3)；
W Bj-1 -W Bj ＝V Bj (4)；
wherein, W Bj Represents the mass flow of flashed brine, W, of the j stage Bj-1 Denotes the mass flow of the flashed brine, W, of the j-1 stage Dj The mass flow of fresh water W representing the j-th output Dj-1 Represents the mass flow of the flash brine of the j-1 stage; c Bj Denotes the flash brine concentration of the j stage, C Bj-1 Represents the flash brine concentration of the j-1 stage; h is Bj Represents the specific enthalpy, h, of the j-th stage flash brine Bj-1 Represents the specific enthalpy, h, of the j-1 th stage flash brine Vj Specific enthalpy, V, of the j-th stage flash steam Bj Expressing the evaporation amount of the brine in the j-stage flash chamber; w is a group of F Indicating the mass flow, CP, of the chilled brine entering the hot discharge section Rj Denotes the heat capacity, CP, of the cooled brine leaving the j-th stage flash chamber Dj Denotes the specific heat capacity, CP, of fresh water leaving the j-th stage flash chamber Dj-1 Denotes the specific heat capacity, CP, of fresh water leaving the j-1 stage flash chamber Bj Denotes the specific heat capacity, CP, of the flashed brine leaving the j-th stage flash chamber Bj-1 Represents the specific heat capacity, T, of the flashed brine leaving the j-1 stage flash chamber Fj Indicating the temperature, T, of the cooled brine leaving the j-th stage flash chamber Fj+1 Indicating the temperature, T, of the chilled brine entering the j-th stage flash chamber Bj To representBrine temperature, T, leaving the j-stage flash chamber Bj-1 Indicating the temperature, T, of the brine leaving the j-1 stage flash chamber Dj Indicating the temperature, T, of the fresh water leaving the j-stage flash chamber Dj-1 The temperature of the fresh water leaving the flash chamber of the j-1 stage is shown, and T denotes the flash reference temperature in an ideal state; a. The j The heat transfer area of the j-th stage flash chamber is shown,
denotes the heat transfer coefficient of the j-th stage flash chamber, where W denotes the feed flow to the j-th stage flash chamber, W = W for the heat discharge section F Denotes the feed seawater flow rate, whereas W = W for the heat recovery section R The 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, D i The 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 j Denotes the boiling point rise of the j-th brine, Δ NETD j Denotes the unbalance margin, Δ TL j Represents the temperature loss through the demister and condenser; t is Vj Indicating 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 R CP RH (T B0 -T F1 )＝W steam λ s (11)；
wherein the content of the first and second substances,
wherein, W B0 Represents the mass flow of flashed brine, W, exiting the brine heater R Represents the mass flow of chilled brine entering the heat recovery section; c B0 Represents the concentration of the flashed brine, C, entering the brine heater R Represents the concentration of chilled brine entering the heat recovery section; CP (CP) RH Indicating the cooling brine heat capacity, T, into the brine heater B0 Represents the temperature of the flashed brine, W, exiting the brine heater steam Expressed as heating steam mass flow, lambda s Representing the latent heat of vapour, T steam Expressed as brine heater steam temperature; a. The H The 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 equations (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)；
W F ·h WF ＝S·h S +W S ·h WS (20)；
wherein W BD Represents the mass flow of the waste seawater, W BN Representing the mass flow of brine, W, leaving the last stage flash chamber Re Represents the circulating brine mass flow; w m Represents the mass flow of make-up brine, W r Representing the hot discharge seawater mass flow; s represents the return flow rate of the hot discharge section, C w Representing the mass flow of brine discharged from the hot discharge section; c Re Denotes circulating brine concentration, C m Indicates make-up brine concentration; h is R Represents the specific enthalpy of the brine entering the heat recovery section, h Re Denotes the specific enthalpy of the circulating brine, h m Represents the specific enthalpy of make-up brine; w S Representing the feed seawater mass flow;
represents the specific enthalpy of the brine at the inlet of the heat discharge section, h S Representing 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 -5 T 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 B Represents the flash brine concentration;
wherein, ω is j ＝W F /w j ，ω j Denotes the mass flow per unit length of the cooled brine entering the hot discharge section of the j-th stage, w j The 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×D i ) 0.2 ]/[(0.2018+0.0031×T)v] (30)；
GOR＝W DN /W steam (32)；
wherein CP D The specific heat capacity of the fresh water in the flash chamber is represented; CP (CP) B Indicating the specific heat capacity of brine in the flash chamber, C B Denotes the flash brine concentration, T B Represents the flash brine temperature; h is v Represents the enthalpy of the steam, T S Is the steam temperature; h is B Represents the enthalpy of the brine; h is D Represents the enthalpy value, T, of fresh water D Represents the fresh water temperature; BPE represents the brine boiling point rise, where T represents the brine temperature in the flash chamber or the brine heater;NETD denotes the non-equilibrium temperature difference, H j Denotes the flash brine level, w j Denotes the width, Δ T, of the condensing tube of the j-th stage flash chamber B Representing 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 related to the flow velocity in the pipe, the temperature of the brine and the diameter in the condensing pipe, z is an intermediate expression related to the fresh water temperature of the flash chamber, y and z are only simplified calculation, and f is the scaling coefficient of the brine heater or the flash chamber; v represents the flow velocity in the tube, D i Represents the internal diameter of the condenser tube, T represents the temperature of the brine at the outlet of the heat exchanger; w DN The 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 operation cost of the system; d N Representing the total fresh water production, p w Denotes the pure water density, ρ b Represents 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 BH Fouling factor f of flash chamber in heat recovery section and heat discharge section j The 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) 1 ,x 2 ,…,x p ) T ，G＝(g 1 ,g 2 ,…,g q ) T ，g i (i＝1,2,…,q):R n →R；
Wherein x is 1 ,x 2 ,…,x p P 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; g is a radical of formula 1 ,g 2 ,…,g q Representing 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;
and step B2: let initial iteration number k =0, set initial value x 0 ∈R n Initial quasi-Newton matrix B k The 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;
and step B3: calculating search direction vector d under iteration times k k To get the value of the next point:
x k+1 ＝x k +d k (41)；
d k ＝-B k ΔG(x k ) (42)；
and step B4: calculate G (x) k ) And G (x) k+1 ) If G (x) k+1 ) | | < epsilon or | | | x k+1 -x k If | | < delta, terminating the iteration to obtain the solution of the nonlinear equation set and the scaling coefficient f of the brine heater BH Fouling factor f of flash chamber j GOR (water production ratio), TOC (total organic carbon) of daily operation cost; otherwise, go to step B5;
and step B5: by correcting for B k To obtain B k+1 ：
Wherein s is k ＝x k+1 -x k ，y k ＝ΔG(x k+1 )-ΔG(x k )；x k Denotes the value, x, evaluated at the k-th iteration k+1 Denotes the value, s, evaluated in the (k + 1) th iteration k Representing the difference between the two evaluated values; 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 k Expressing the gradient vector difference of the (k + 1) th iteration and the (k) th iteration;
step B6: enabling k = k +1, and turning to the step B3 for calculation;
step A4: the parameter decision module makes the parameter set L obtained in the period 1 (f BH ,f j GOR, TOC) and the parameter set L obtained in the previous cycles i (f BH ,f j GOR, TOC), i =1,2, …, m and m are current cycle numbers, comparison analysis is carried out, the scaling degree of the current system and the next cleaning time of the system are obtained through estimation, and a simulation calculation module and a parameter decision module send the calculation data to a 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 BH Fouling factor f of flash chamber j The 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, turning to the step A2 and carrying out data acquisition again.
2. The method for cleaning the scale in the multi-stage flash evaporation seawater desalination system as claimed in claim 1, 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 BH Fouling factor f of flash chamber j The water making ratio GOR and the daily running cost TOC are carried out by adopting a least square methodFitting and analyzing, and reasonably judging the system scaling degree, wherein 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 BH Fouling factor f of flash chamber j GOR (water production ratio), TOC (total organic carbon) of daily operating cost and scaling coefficient f of brine heater BH Setting the upper limit H 1 Fouling factor f of flash chamber j Setting the upper limit H 2 A lower limit X is set for a water generation ratio GOR 1 Daily operating cost TOC setting upper limit X 2 ；
And step C2: dividing the data into four parts to be fitted respectively, and firstly, fitting the scaling coefficient f of the brine heater BH Performing curve fitting by adopting a least square method; suppose a given collected data point (xx) i ,yy i )，i＝0,1,…,m，xx i Representing data acquisition time points T i ，yy i Represents 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 calculates the speed, the polynomial order nn =3, is such that:
wherein I is a 0 ,a 1 ,a 2 ,a 3 Is thus the solution I = I (a) 0 ,a 1 ,a 2 ,a 3 ) The problem of extreme values of (a);
and C3: the necessary condition of extreme value is solved by a multivariate function, and the following results are obtained:
namely, it is
And C4: rewrite equation (46) to normal equation set form:
the coefficient matrix of the normal equation set (47) can be proved to be a symmetric positive definite matrix, so that a unique solution exists; is solved from formula (47) to obtain a kk (kk =0,1, …, 3), thereby obtaining a polynomial:
and C5: repeating the steps C2 to C4 to respectively obtain the scaling coefficient f of the brine heater BH Fouling factor f of flash chamber j The 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 P 1 (t)、P 2 (t)、P 3 (t) and P 4 (t), wherein t represents time;
and 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 parameters according to a fitted equation 1 、Tim 2 、Tim 3 、Tim 4 ；
Step C7: mixing Tim 1 、Tim 2 、Tim 3 、Tim 4 Comparing to obtain the latest time node which is marked as Tim and is the time point to be cleaned next time;
and C8: fouling factor f for brine heater BH Fouling factor f of flash chamber j The scale degree of the system can be obtained according to the numerical value of the current data acquisition point.
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