Analysis of the operation, maintenance and management of ultrafiltration-reverse osmosis system in the application of power plant water treatment

Abstract: This paper summarizes the power plant water treatment applications in the ultrafiltration - reverse osmosis system in the operation of a variety of factors affecting the author by summarizing their own many years of practical experience, for the system in the application of power plant water treatment operation and maintenance measures and the corresponding management experience for in-depth discussion.

Keywords: power plant; ultrafiltration; reverse osmosis; operation and maintenance with the development of social and economic, power plant water treatment technology has made a certain degree of progress, launched the development of ultrafiltration - reverse osmosis system. The system first originated in 2000, through the transformation of the primary desalination + mixed-bed ion exchange system. The modified system has strong applicability and brings great convenience to the operation of power plants, but there are still more or less problems in its operation, maintenance and management. In this context, in-depth analysis of the application of power plant water treatment ultrafiltration - reverse osmosis system operation and maintenance and management, has a vital role, and gradually become a new issue in front of the power plant managers and researchers need to be resolved.
I. Overview
Ultrafiltration - reverse osmosis system process mainly consists of industrial water pump outlet - unvalved filter tank - raw water pump - laminated filter - fresh water tank - fresh water pump - filter 20 μ - 4 groups of ultrafiltration - water purification tank - water purification pump - filter 5 μ - high-pressure pumps - 2 sets of reverse osmosis - fresh water tank - fresh water pumps - primary desalination + mixed bed ion exchange system. The system provides boiler make-up water for each unit of the power plant, and also shoulders the task of supplying water to the heating equipment of the power plant, which has a very important role and significance.
According to relevant surveys, with the ultrafiltration - reverse osmosis system in the permeate membrane running time increases greatly, the system water production decreases by about fifteen percent per year. Obviously, the power plant in the full use of the role of the system, achieved certain economic benefits, and greatly reduced the total amount of work of the power plant staff, reducing their burden.

Second, ultrafiltration - reverse osmosis system of stable operation measures
Power plant water treatment process, the application of reverse osmosis system, prompting the ultrafiltration device is installed in the near front pre-treatment equipment, so as to protect the safe operation of the water intake device, the ultrafiltration device is a key link in this system. In order to guarantee the economic, safe and reliable operation of the system, the original ion exchanger to maintain the optimal output of the system at 90 tons per hour. This places high demands on the water intake, requiring four UFs to provide no less than 140 tons of water supply, with an average of 35 tons of water output per UF. The operation of ultrafiltration and ultrafiltration pre-treatment technology is relatively simple, but it only has a valve-less filter tank. Therefore, it is subject to the influence of the external environment, and is very vulnerable to sudden abnormalities such as the rainy season. In order to solve this problem, it is imperative to ensure the stability of ultrafiltration operation.

(a) Determine the ultrafiltration operation index ultrafiltration - reverse osmosis system operation determines the ultrafiltration water output whether to meet the relevant standards, is effective to ensure that the ultrafiltration - reverse osmosis system is a prerequisite for normal operation. Membrane permeate flux is an important parameter, directly related to the separation performance of the ultrafiltration membrane, and changes with the pressure. Therefore. In the process of determining the ultrafiltration water output, the ultrafiltration retention rate should also be synthesized and the system provides the feed water, backwash pressure, etc., so as to determine the ultrafiltration operation index. In the process of determining the ultrafiltration operation index, the most important reference data that is the single ultrafiltration inlet operating pressure and low-limit water output.
(B) clarify the impact of ultrafiltration water output factors

1 Ultrafiltration process. Raw water in the pipeline or outside the pipeline flow, small molecules of solutes and solvents across the membrane gradually formed ultrafiltration solution, and reduce the concentration, become concentrated, so as to realize the separation and concentration of small molecules of solutes and solvents. The ultrafiltration process is dynamic, and the membrane is not easy to block, but with the increase in operating time, adsorption will occur, so that the ultrafiltration membrane surface residue and other substances. Therefore, the characteristics of ultrafiltration are necessary to ensure the water output.
2 Water quality changes. On the one hand, the feed water quality after 10μ filtration, to ensure that the turbidity is less than 1 NTV, the concentration is not greater than five percent, and the water temperature should be between 5 and 40 degrees Celsius, the pressure should not be greater than 0.2MPa, based on this, to ensure that the recovery rate of the feed water is more than 80%, the acidity and alkalinity is between 2 and 13. On the other hand, abnormal water quality is also an important condition affecting the ultrafiltration water output, including in the rainy season, the particulate matter and suspended solids contained in the raw water will increase, so that the turbidity will not meet the relevant requirements. In addition, the main source of feed water is surface water, containing more organic matter, in the case of pressure imbalance and poor connection will be mixed with a certain quality of raw water, is retained on the surface of the ultrafiltration membrane, making it difficult to maintain a regular cleaning, which directly leads to a reduction in the ultrafiltration water output. Indicators and current operating indicators, after normalization of its salt flux of up to 15%, cleaning should be carried out immediately.

(iii) Measures
1 In the process of system operation, backwashing is regularly carried out using reverse hydraulics to clean up the substances adsorbed or retained on the surface of the ultrafiltration membrane, and according to the quality of the incoming water, reasonably adjust the cleaning time and the system operating time.
2 Increase its investment, install water quality online monitoring instruments at the water intake, real-time monitoring of water intake quality, so as to timely and accurately grasp the water quality situation. At this stage, in the detection of whether there is surface water mixed into the water intake work, the use of more common is the raw water online DD table. The detection instrument will control the water pollution index within 2, when the incoming water exceeds this range, then the alarm is issued in a timely manner, so as to facilitate the duty personnel to analyze in a timely manner, and take appropriate measures. To a certain extent, to eliminate the phenomenon of lower water production due to increased turbidity.
3 For 20μm cartridge filter, should increase the supervision. The device as a security measure, shouldering the role of filtering suspended solids, but not the role of filtering load. Therefore, manufacturers should set the pressure drop limit value, so as to realize the timely replacement of cartridge filters.
4 Control of influent water quality by shutdown protection. This mainly refers to the presence of scale inhibitors to promote the formation of pressure-stabilized salt crystals, thus avoiding the propagation of organisms. Comprehensive ultrafiltration membrane materials and the operation of various devices, selective shutdown operation to achieve effective control of influent water quality.
5 Reverse osmosis membrane as a deep filtration element in ultrafiltration, the surface is bound to produce a large number of microorganisms, particulate matter and colloids and other substances. This puts forward high requirements for cleaning work, should pay attention to the timeliness of the cleaning work, in order to ensure that once a year on the basis of cleaning work, according to the cleaning standard of reverse osmosis membrane, compared to just put into operation when the indexes and the current operation indexes, after normalization of salt flux is as high as 15%, it should be cleaned immediately.

Third, the application of ultrafiltration - reverse osmosis system operation and maintenance and management priorities
(A) should be ultrafiltration operation in the stability of water output as the center of gravity of management, according to the actual operation of the power plant, the reasonable use of various types of operation and maintenance and management measures. On this basis, the safe and stable operation of pretreatment equipment is guaranteed to fully meet the feed water requirements in the operation of ultrafiltration-reverse osmosis system.
(ii) The extension and management of the service life of the ultrafiltration-reverse osmosis membrane should be taken as the primary task, and the corresponding operation and maintenance measures should be actively adopted to prevent the reverse osmosis membrane from being clogged or contaminated, so as to avoid the damage and deterioration of the ultrafiltration membrane.

Conclusion
In summary, ultrafiltration - reverse osmosis system in the application of power plant water treatment has a role that can not be underestimated, the demand for technicians to increase their attention to its focus on the day-to-day operation and maintenance of the system and management, in order to meet the specific requirements of the power plant water treatment. The author hopes that more professionals to devote to the study, for the shortcomings of the text, put forward corrective suggestions to promote the ultrafiltration - reverse osmosis system is fully applied to the power plant water treatment work.