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Study of Microbial Corrosion in Central Air-conditioning Cooling Water System

Author: XuDanDan
Tutor: LiuHongFang
School: Huazhong University of Science and Technology
Course: Chemical Engineering
Keywords: Microbial corrosion Sulfate reducing bacteria Iron bacteria Total General Bacteria Electrochemical impedance spectroscopy Environmental scanning electron microscopy EDXA Electrochemical testing
CLC: TU831.4
Type: Master's thesis
Year: 2011
Downloads: 24
Quote: 0
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Abstract


The central air conditioning cooling water circulation system is an open wide circulation system. In this system, cooling water coming from the condenser of the refrigeration compressor, then sent through water pump to cooling towers, and flow back to the condenser at last. The central air conditioning cooling water circulation system can not only save a lot of water and also resuce its operation cost because of the cooling water recycle. But circulating water cooling is realized through the open cooling tower, when cooling water is spraying in the cooling tower, it will merge with a large amount of oxygen. Add in the air temperature ,dust impurities and suspended substance into the system through the cooling tower, water system water quality is very easy to breed aerobic microorganisms and resulting in the microbial corrosion of circulating cooling water system. In addition, the make-up water of cooling water system is tap water, its high impurity content can make cooling water enrichment ratio reach 810 times inside short time. Then plasma concentrations of Mg2+, Ca2+, and HCO3- in the water system will increase dramatically. They will not only to deposit in the surface of the heat exchanger, reducing the heat transfer efficiency of the heat exchanger, affecting the normal operation of the air conditioning, but also to provide a hotbed for anaerobic microbe, making the circulating cooling water system become a huge microorganism training device.The water temperature of the central air conditioning cooling water circulation is usually between 32℃to 42℃, and this temperature interval is very helpful in the various microbial growth and reproduction. In order to explore when the air-conditioning circulation cooling water system under different temperature, what kinds of bacteria grow, and the corrosion of the air conditioning water pipeline equipment , to provide theoretical foundation for actual situation of water circulation in air conditioning cooling water system of monitoring and water quality control, the subject combining site operation condition, to determine the corrosion test temperature 30℃,45℃,60℃and 70℃. The dynamic conditions of microbial corrosion affect almost negligible, namely the microbial corrosion usually happened in static environment. So the microbial expriments are static. The first experiment is in 30℃. It is based in Wuhan tap water, respectively add in 1/10 volume of sulfate-reducing bacteria （SRB）, iron bacteria （IB）, the general bacteria （TGB）. In the four different medium hangs in C1220 copper specimens and Q235B carbon steel specimens staticly under constant temperature for two weeks. Because these systems are wide open, and the most appropriate temperature for IB growth is from 25℃to 30℃, they are quite suitable for the growth of IB. Through the static hanging piece experiment and electrochemical corrosion test, in this subject we proved that corrosion of IB to copper and carbon steel specimens is most serious and far more than the water quality standard. Meanwhile, through the determination and contrast of COD and PH of corrosion water, combined with surface analysis technology SEM, EDXA analyzed main corrosion situation of copper and carbon steel material caused by SRB, TGB and IB of the water system .The second and the third experiment are about main microbial growth and the corrosion rule when circulation cooling water system under 45℃and 60℃. parts SRB required 55℃for growth, survival PH is 5-9. TGB is some kind of the general bacteria and its temperature 10℃ 45℃. So when medium temperature reach to 60℃from 30℃, producing mucus from TGB, iron and algae, to adhere to the air conditioning equipment, blocking pipe and causing oxygen strong bad battery corrosion, and the anaerobic environment under biofilms anaerobic can promote growth of SRB and other anaerobic microorganism and deepen the corrosion severity.Added explanation, because laboratory conditions can not completely imitate actual central air conditioning cooling water circulation system structure, namely we can not fully imitate its operation of circulating cooling water system, our experiment research contents primarily providing theoretical guidance and advice of microbial corrosion for air conditioning water circulating cooling water system .To the actual process must adjust measures to local conditions.

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CLC: > Industrial Technology > Building Science > Housing construction equipment > Air-conditioning, heating, ventilation,and its equipment > Air-conditioning > Air-conditioning machinery and equipment
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