	US 12,145,869 B2
	Hollow fiber nanofiltration membrane system and control method thereof
Mu Liu, Beijing (CN); Yingqiang Su, Beijing (CN); Zehua Li, Beijing (CN); Mengyuan Duan, Beijing (CN); Kai Sun, Beijing (CN); Xikun Zhu, Beijing (CN); Liyan Zhang, Beijing (CN); Cong Xiao, Beijing (CN); and Huiming Han, Beijing (CN)
Assigned to Greentech Environment Co., Ltd., Beijing (CN)
Filed by Greentech Environment Co., Ltd., Beijing (CN)
Filed on May 23, 2024, as Appl. No. 18/672,395.
Claims priority of application No. 202310694549.4 (CN), filed on Jun. 13, 2023.
Prior Publication US 2024/0308883 A1, Sep. 19, 2024
Int. Cl. C02F 1/44 (2023.01)

CPC C02F 1/442 (2013.01) [C02F 2209/001 (2013.01); C02F 2209/003 (2013.01); C02F 2209/03 (2013.01); C02F 2301/04 (2013.01); C02F 2303/20 (2013.01)]

5 Claims

1. A control method of a hollow fiber nanofiltration membrane system, the hollow fiber nanofiltration membrane system comprising a water feeding system, a return system, a hollow fiber nanofiltration membrane group, a water production system, a cleaning system, a dosing system and a program control system; the water feeding system being connected with the hollow fiber nanofiltration membrane group through a first pipe, and being configured to provide a feedwater pressure required by operation of the hollow fiber nanofiltration membrane group;

the return system being connected with the first pipe, and being configured to provide a concentrated water return flow required by the operation of the hollow fiber nanofiltration membrane group;

the hollow fiber nanofiltration membrane group being configured to perform solid-liquid separation for a raw water sample to trap foulants and produce clear water;

the water production system being connected with the hollow fiber nanofiltration membrane group, and being configured to provide a water storage tank or a water box to store produced water from the hollow fiber nanofiltration membrane group and provide a discharge destination for the produced water from the hollow fiber nanofiltration membrane group;

the cleaning system being connected with the water production system and the hollow fiber nanofiltration membrane group, and being configured to provide physical cleaning and chemical cleaning for the hollow fiber nanofiltration membrane group;

the dosing system comprising a first dosing device and a second dosing device; the first dosing device being connected with the first pipe, and being configured to provide selective and simultaneous dosing of a scale inhibitor at an inlet end of the hollow fiber nanofiltration membrane group; the second dosing device being connected with the cleaning system, and being configured to feed an acid, an alkali or a disinfectant to the cleaning system;

the program control system being connected with the water feeding system, the return system, the water production system, the cleaning system and the dosing system, and being configured to control operation of the water feeding system, the return system, the water production system, the cleaning system and the dosing system; and the program control system being also configured for simultaneous monitoring, observation and feedback record of operation data or state and fault or alarm, and real-time analysis and calculation to adjust a working condition parameter; and

the control method comprising:

presetting, by the program control system, an operation mode according to a preset working condition and an inlet water quality obtained in real time, and automatically selecting, by the program control system, whether to add the scale inhibitor or perform concentrated water return at a beginning of filtration;

automatically outputting, by the program control system, a dosage of the scale inhibitor or the concentrated water return flow to perform dosing of the scale inhibitor or the concentrated water return in response to a requirement to add the scale inhibitor or perform the concentrated water return;

monitoring, by the program control system, a change of the inlet water quality, and the feedwater pressure or a transmembrane pressure in real time during the operation of the hollow fiber nanofiltration membrane group; and

adjusting, by the program control system, the dosing of the scale inhibitor or the concentrated water return flow according to a calculation result in response to a case that the feedwater pressure or the transmembrane pressure exceeds a set limit value; wherein the preset working condition comprises a membrane flux and a recovery rate; and the inlet water quality comprises water temperature, electrical conductivity and turbidity;

the membrane flux is represented as J; the recovery rate is represented as y; the water temperature is represented as t; the electrical conductivity is represented as E; and the turbidity is represented as T_U;

wherein a=0.5E/(1−y)/1000;

b=(T_U/3)×(J/25)×(y/80%); and

c=t/15;

when a<1 and b<1, neither the dosing of the scale inhibitor nor the concentrated water return is performed;

when a≥1 and b<1, only the scale inhibitor is added, and the concentrated water return is not performed; and at this time, the dosage of the scale inhibitor is represented as D, when c≥1, D=0.3a−0.1; and when 0<c<1, D=0.3a;

when a<1 and b≥1, the scale inhibitor is not added, and only the concentrated water return is performed; and at this time, a ratio of the concentrated water return is represented as F, when c≥1, F=2.1b-0.5; and when 0<c<1, F=2.1b;

the number of filtration-flushing operations in a single chemically enhanced backwash (CEB) cycle is set as M, a limit of the feedwater pressure and a limit of the transmembrane pressure at an end of an M-th filtration before an M-th flushing are set to 6 bar and 5.5 bar, respectively, and the feedwater pressure and the transmembrane pressure at a beginning of a first filtration are respectively represented as P1_1beginningand P2_1beginning, such that a limit of the feedwater pressure and a limit of the transmembrane pressure at an end of an N-th filtration before an N-th flushing are P1_Nend=P1_1beginning+(6−P1_1beginning)×N/M, and P2_Nend=P2_1beginning+(6−P2_1beginning)×N/M, wherein 1≤N≤M; and

during the N-th filtration, an actual feedwater pressure and an actual transmembrane pressure of the hollow fiber nanofiltration membrane group are respectively represented as P1_Nand P2_N, and the feedwater pressure and the transmembrane pressure at a beginning of the N-th filtration are respectively expressed as P1_Nbeginning, and P2_Nbeginning, such that an increase of the feedwater pressure is expressed as ΔP1=P1_N−P1_Nbeginning, and an increase of the transmembrane pressure is expressed as ΔP2=P2_N−P2_Nbeginning; and if P1_N>P1_Nendor P2_N>P2_Nend, the dosing of the scale inhibitor or the concentrated water return is adjusted as follows:

when only P1_N>P1_Nendoccurs, the ratio of the concentrated water return is increased by 0.5;

when only P2_N>P2_Nendoccurs, the dosage of the scale inhibitor is increased by 0.2 ppm; and

when P1_N>P1_Nendand P2_N>P2_Nendboth occur, if ΔP1≥ΔP2, the ratio of the concentrated water return is increased by 0.5; and if ΔP1<ΔP2, the dosage of the scale inhibitor is increased by 0.2 ppm.