A Research Of The On-line Monitoring System For The Inner Leakage Of Water Cooler

Heat exchangers are important equipment in the petrochemical industry. There exist many defects in them, which result from manufacture, installation and so on. It is impossible to avoid such defects entirely from the viewpoint of technology and economy. During operation, the cracking and micro-hole are usually found in the tube sheets and tubes of a well-manufactured heat exchanger, owning to the change of operation condition such as temperature, pressure, process media etc. The cracking grows slowly under the high-temperature and corrosive environments, and the disastrous accidents would occur ultimately. Once the accidents occur, not only the normal operating state is disturbed, which lead to considerable losses of properties, but also the leakage will pollute the environment and erode the equipments. In order to avoid the unnecessary losses and risk, it is essential to detect the heat exchanger in operation and find out any leakage immediately and locate the exact leaking position.In petrochemical industry, the cycling water is often used as cooling medium, and the leakage is a ubiquitous problem. According to statistical date, the leakage accident rate in the petroleum refinery units in china can reach more than 85%. The objective of this thesis is to offer a simple and convenient on-line monitoring and alarm device for cooler leakage. A leakage detecting system based on potentiometer is presented and the on-line monitoring technology based on electrochemical sensor is developed. By analyzing and processing the electric signal, a real-time detecting system is set up, which could detect and locate the leakage of the cooler quickly and precisely. Also, no mathematical model and complicated equipment are needed.There is often H₂S in the petroleum and the petrochemical products.H₂S is reducing matter which could produce S2" ion and consequently build electric potential in water. According to Nernst equation, the value of electric potential reflects the solution concentration. Once there is leakage in the water, the electro-motive force of the cell changes immediately and shows whether there is H₂S in the water. So the system can detect the leakage of coolers and locate it in water cooler. The optimal measuring form is determined by experimental evaluation. The experimental results show that the optimal electrochemical cell should be made up of platinum electrode for the selective electrode and double junction electrode calomel one for the reference electrode. There are scale Inhibitor, corrosion inhibitor and fungicide in the industrial cycling water, so the effects of them on the potentiometer are studied in this article. Both of them produce no effect on the potentiometer. The systems can precisely give the alarm when hydrogen sulfide content in water is more than 100 ppm.The sensor that be made up of platinum electrode and calomel electrode transforms the hydrogen sulfide concentration into electric signal of -1 1V, which is sent to the monitoring system. After being handled and analyzed by the monitoring system which is made up of single chip, the hydrogen sulfide concentration in the cycling water is displayed digitally. If the concentration overruns the tolerance, the monitoring system will alarm at the abnormal state. The practical application to the industrial equipment shows that this system is sensitive and reliable, and could be applied broadly.