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Application of Ceramic Ultrafiltration Membrane in Reform of Chemical Water Treatment System in Power Plant

来源:工业水处理 作者: 李新望,等 阅读:2925 网友评论0 Updated: 2019-09-23 11:18 Source: industrial water treatment Author: Li Xin Wang, etc. Read: 2925 2010 0 comments

This paper introduces the pilot test and application of CM large-area block-type ceramic ultrafiltration membranes in chemical water treatment systems of power plants. The pilot test results show that for river water pretreated by coagulation filtration, the CM ceramic ultrafiltration membrane can run stably at a high operating flux of 333L / (m2 , h) and a filtration time of 50min; for untreated river water, ceramics The ultrafiltration membrane also achieves stable operation under direct filtration of raw water. CM-151TM ceramic ultrafiltration membrane was used to replace the original organic hollow fiber membrane during the ultrafiltration transformation. The actual operating flux of the CM ceramic ultrafiltration membrane was higher than 260 L / (m2 , h). The amount of backwash water and chemically enhanced backwashing (CEB ) The frequency is reduced by half compared with the original organic ultrafiltration membrane, turbidity <0.1NTU, SDI <2, which fully meets the water inlet requirements of subsequent reverse osmosis systems.

A Zhejiang combined heat and power plant takes the Yangtze River tributary as the source of circulating cooling water and boiler make-up water, and is equipped with a chemical water treatment system for advanced treatment of river water. Its treatment process is raw water dosing, coagulation clarification, multi-media filtration, ultrafiltration, desalination (including reverse osmosis) and acid-base regeneration.

This system originally used external pressure hollow fiber organic ultrafiltration membrane as the front-end process of the reverse osmosis device. After running for a period of time, problems such as broken wires, fouling and high SDI in the water outlet caused the subsequent reverse osmosis system to be difficult to run stably. The normal production of the entire power plant poses great risks. After trying various measures, the power plant decided to replace the organic ultrafiltration membrane with the CM-151TM large-area block ceramic ultrafiltration membrane. The author discussed the characteristics of the ceramic ultrafiltration membrane, pilot data, and engineering performance.

I. Project Introduction

01 Raw water quality

The raw water of the chemical water treatment system is taken from river water. As the river flows through the industrial area and is injected with seawater, the water quality fluctuates greatly. See Table 1 for specific water quality. The raw water is treated to meet the water quality requirements of the power plant for circulating cooling water and boiler make-up water.

02 Pretreatment process

The pretreatment process before the reverse osmosis of the chemical water treatment system is river water → coagulation clarification → multimedia filter → mesh filter → ultrafiltration. Among them, PAC (10 mg / L) and NaClO (1 mg / L) were added to the coagulation clarification tank.

Organic ultrafiltration membrane is the core of the pre-salting system in the full (dual) membrane separation technology of the chemical water treatment system of the power plant. In actual use, problems such as the quality of produced water not meeting the requirements and broken wires have been repeatedly reported. In this project, the original organic ultrafiltration system had broken wires and fouling after a period of operation. The single set of water production decreased from 90 m3 / h to 45 m3 / h and the effluent SDI reached 4-5, resulting in subsequent reverse osmosis systems. Difficult to run stably. To solve this problem, the power plant used a new organic ultrafiltration membrane of the same brand to completely replace the old membrane, but the new membrane after the replacement had the same problem. After that, the owner tried to add polymer flocculant to the water in the multi-media filter to improve the treatment effect. This measure increased the cost of additional medicaments, but still failed to provide SDI-qualified inlet water for the RO system. The pilot test conducted by the author on site confirmed that the ceramic ultrafiltration membrane can run stably at an unexpectedly high flux of 333 L / (m2 , h).

03 CM ceramic ultrafiltration membrane

The cross section of the CM ceramic ultrafiltration membrane has a porous asymmetric structure. The support layer is made of aluminum oxide (A2O3), and the filter layer is made of α-type aluminum oxide. They are tightly fused by high temperature sintering. The pore diameter of the formed film is stable in the range of 30 nm, the pore diameter distribution is very uniform, and it has a more narrow and concentrated normal distribution curve. The membrane material is made of inorganic ceramic material, which has better hydrophilicity and higher filtration flux. The mechanical strength and chemical stability of ceramic itself make the ceramic ultrafiltration membrane resistant to pressure, temperature, corrosion and oil. In terms of performance and resistance to chemical cleaning, it is superior to organic hollow fiber ultrafiltration membranes.

The performance comparison between CM ceramic ultrafiltration membrane and organic hollow fiber ultrafiltration membrane can be found in the literature.

04 Pilot equipment and operating parameters

The pilot test is divided into 3 test phases, see "5 Existing Problems and Discussion". The pilot plant uses Nanostone Water's integrated experimental device. The ceramic ultrafiltration membrane element has a membrane area of 3 m2, a filtration accuracy of 30 nm, a filtration cycle of 30 to 60 minutes, and a backwash time of 40 s.

05 Problems and discussions

(1) Stage 1: River water enters ceramic ultrafiltration membrane after coagulation and clarification and multi-media filter, and the operating flux is 300 ~ 330 L / (m2 , h). The operation effect of CM ceramic ultrafiltration membrane at this stage is shown in Figure 1.

First, test the target operating flux of 300 L / (m2 , h) (13 d in total), the filtration period is 30 minutes, and the ceramic UF membrane feed water PAC dosage is 1.4 mg / L. It can be seen from Figure 1 that the transmembrane pressure differential shows a cyclical change from 0.04 to 0.08 MPa, and the later transmembrane pressure difference (0.04 to 0.06 MPa) is significantly lower than the previous transmembrane pressure difference, which is mainly due to the optimization measures adopted in the later stage Such as adjusting chemical enhanced backwash (CEB) parameter settings. This set of operating data confirms that the ceramic ultrafiltration membrane operates stably at a target flux of 300 L / (m2 , h). After that, the operating flux was increased to 316 L / (m2 , h). It can be seen that the transmembrane pressure difference changes regularly in a more stable and narrower interval during the 7d operation time, and the operation of the ceramic ultrafiltration membrane is stable. By further increasing the operating flux to 330 L / (m2 , h) and operating for 5 d, the ceramic ultrafiltration membrane remained stable.

(2) Adjust the filtration time. The operating flux is 316 ~ 333 L / (m2 , h). Combined with the data of stage 1, the pretreatment process (coagulation clarification and multi-media filtration) of stage 1 is used to carry out the optimization test of the filtration time. The results are shown in Figure 2.

It can be seen from Figure 2 that under the operating fluxes of 316 and 333 L / (m2 , h), the filtration time is adjusted to 40 and 50 min, respectively, and the change trend of the transmembrane pressure difference is still stable and regular (0.04 ~ 0.06 MPa). Under the operating flux of 333 L / (m2 , h), the filtration time was continued to extend to 60 min, the transmembrane pressure difference increased slightly, and the upward trend in the later period (extended CEB cycle) was more obvious, but it still recovered well after CEB cleaning. .

(3) The river water directly enters the ceramic ultrafiltration membrane, and the running flux is 167 ~ 366 L / (m2 , h). At this stage, the river water without coagulation clarification and multi-media filter pretreatment is directly entered into the ceramic ultrafiltration membrane to further verify the pollution resistance and cleaning recovery of the ceramic ultrafiltration membrane. The filtration time is 30min, the dosage of PAC is 8mg / L, and the operation is 4d. The operation data is shown in Figure 3.

At operating fluxes of 167 and 250 L / (m2 , h), the transmembrane pressure difference fluctuates between 0.02 ~ 0.03 and 0.03 ~ 0.04 MPa, respectively, and the ceramic ultrafiltration membrane runs smoothly. The operating flux increased to 330 L / (m2 , h), and the fluctuation of the transmembrane pressure difference increased. After 366 L / (m2 , h), the fluctuation of the transmembrane pressure difference increased further, but all recovered after CEB. To near the starting value. Pollution resistance and cleaning recoverability of ceramic ultrafiltration membranes have been verified. At the same time, the feasibility of the river water directly entering the ceramic ultrafiltration membrane without pretreatment has been verified, and the recommended operating flux is not higher than 250 L / (m2 , h). There is no need for restoring chemical cleaning (CIP) during the entire pilot period.

See Figure 4 for the turbidity of the ceramic ultrafiltration membrane during the pilot test.

It can be seen from Figure 4 that the turbidity of the water after the pretreatment of the ceramic ultrafiltration membrane fluctuates between 0.2 and 0.4 NTU, and the turbidity of the produced water is between 0.046 and 0.093 NTU, which is stable <0.1 NTU, which is better than subsequent reverse osmosis systems. Requirements for turbidity of incoming water.

Introduction to Engineering Application and Operation

On the premise of meeting the economic requirements of the project, the original organic ultrafiltration system was retrofitted with an operating flux of 260 L / (m2 , h) as the design value. The reconstruction project uses Nanostone Water's third-generation CM-151TM ultrafiltration membrane module. The main parameters of the modified ceramic membrane ultrafiltration system and the original organic ultrafiltration system are compared in Table 2.

The original single set of organic ultrafiltration required 28 membranes. Due to the greatly increased operating throughput, only 14 CM-151TM ceramic ultrafiltration membranes were required for a single set after the transformation. The renovation process made full use of the original facilities. The original organic ultrafiltration system's water inlet pump, self-cleaning filter, backwash water pump and CEB system were all continued to be used. The transformation only involves a small number of pipelines on the original membrane group frame, that is, the PVC pipelines on the original membrane group frame are transformed into ceramic ultrafiltration membranes and connected with the original valve group pipeline and the original main pipe.

The renovation project was commissioned in December 2017 and has been operating steadily so far. It has continuously provided high-quality water with SDI <2 and turbidity <0.1 NTU. See Figure 5 for the transmembrane pressure difference data of the 1 # unit in the 4 sets of ceramic membrane ultrafiltration units running for 1 month.

Figure 5 shows that the transmembrane pressure difference of the ceramic membrane ultrafiltration system mainly fluctuates between 0.04 and 0.07 MPa, which does not exceed 0.1 MPa, and the operation is stable. After the transformation, no additional polymer flocculant needs to be fed into the multi-media filter. In addition, the backwash water volume and CEB frequency of the ceramic membrane ultrafiltration system are both reduced to 50% of the original organic ultrafiltration system, and the CIP cycle is> 2 months, which greatly saves the cost of chemicals and reduces operating costs and improves the system recovery rate.

Third, the conclusion

(1) River water enters the ceramic ultrafiltration membrane after coagulation and clarification, multi-media filter treatment and dosing of 1.4 mg / L PAC. The ceramic ultrafiltration membrane runs smoothly at a running flux of 300 ~ 330 L / (m2 , h). (Filtration time 30 min).

(2) Pilot stage 2 ceramic ultrafiltration membrane runs stably at a running flux of 333 L / (m2 , h) and a filtration time of 50 min, only at a running flux of 333 L / (m2 , h) and a filtration time of 60 Under the conditions of min and prolonged CEB cycle, the transmembrane pressure difference increased significantly, but still recovered well after CEB cleaning.

(3) The feasibility of the river water directly entering the ceramic ultrafiltration membrane has been verified, and the recommended operating flux is not higher than 250 L / (m2 , h).

(4) The original organic ultrafiltration membrane system was transformed with a ceramic ultrafiltration membrane, with a small amount of reconstruction work, and the original supporting systems and facilities were fully utilized. The actual operating flux is higher than 260 L / (m2 , h), the amount of backwash water and the CEB frequency are halved, and no additional polymer flocculant is required to be fed into the multi-media filter, which saves pharmaceutical costs and operating costs. Increased recovery.

(5) The pilot-scale and actual operation of ceramic ultrafiltration membranes produce continuous, stable, high-quality water with a turbidity <0.1 NTU and SDI <2, which fully meets the water inlet requirements of subsequent reverse osmosis systems. This project provides a reference for the popularization and application of ceramic ultrafiltration membranes in similar water treatment.

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