Development Of Coating Process Optimization And Performance Online Evaluation System For Flue Gas Heat Exchange Tubes

The heat exchanger of the flue gas system of thermal power plants is an important equipment for waste heat utilization.The accumulation of ash causes low heat transfer efficiency,low-temperature acid dew point corrosion causes equipment damage and high replacement rate,which has long been a difficult problem in the industry.The use of coating technology to change the surface properties of materials is an important development direction and research hotspot to solve this problem.The different performance requirements of various application scenarios,repeated process optimization processes and long R&D cycles have seriously affected the molding and field application of the new coating process.In this paper,the coating process optimization research and the development of laboratory test platform for flue gas heat exchange tubes have important research value and practical significance for promoting the development of new processes and shortening the research and development cycle.Based on the theory of atomic hydrogen evolution,the reaction principle of electroless Ni-P alloy plating was analyzed,the influence of plating substrate pretreatment and plating process on the coating was explored.Based on this,the electro-degreasing and pre-nickel plating process was designed to optimize the Ni-P application of ND steel substrate.Plating process,using this process to prepare Ni-P coating on ND steel substrate;According to the deposition mechanism of nanoparticles and the three-stage process of co-deposition with Ni-P alloy,the influences of the types,contents and dispersion methods of nanoparticles on the coating were analyzed.Furthermore,based on the Ni-P plating process,the preparation process of Ni-P-PTFE was developed by designing the procedures of adding surfactant,magnetic stirring and ultrasonic dispersion.Finally,two electroless coatings of Ni-P-PTFE(5m L/L)and Ni-P-PTFE(10m L/L)on ND steel substrate were prepared.The surface of the above-mentioned three coating materials was evaluated by scanning electron microscope and X-ray energy spectrometer,it was found that the coating was evenly distributed and the surface was flat and smooth.The F element content in Ni-P-PTFE(5m L/L)and Ni-P-PTFE(10m L/L)coatings were 9.67%and 14.13%,indicating that the electroless composite coatings were successfully prepared;The contact angle and polarization curve of 8materials were measured,the surface energy and corrosion current density analysis results showed that Ni-P,Ni-P-PTFE(5m L/L)and Ni-P-PTFE(10m L/L)have excellent anti-corrosion and anti-scaling performance.Among them,the Ni-P coating has the best anti-corrosion effect,with a corrosion current density of 0.03928m A/cm~2,and the Ni-P-PTFE(10m L/L)coating has the best anti-scaling performance,with a surface energy of 21.047m J/m~2.In order to effectively shorten the research and development cycle,an online evaluation system for the anti-corrosion and anti-scaling performance of the flue-air heat exchange tube was developed.The system hardware device is composed of boiler coal burning system,flue system,heat exchange system,water circulation system and data acquisition system.The software part has data acquisition,analysis,display and storage functions.Based on this system,online experimental research of the above-mentioned 8 materials was carried out.The results show that the system can run for 72 hours to obtain significantly different test results,which greatly improves the test efficiency and effectively reduces the test cost compared with the field experiment,and can realize the online analysis of the anti-corrosion performance of the pipe;The corrosion current density of Ni-P coating is 0.03583m A/cm~2,which is much lower than other materials,indicating that its anti-corrosion performance is the best,which is consistent with the static test analysis results;Because the corrosion resistance of Ni-P-PTFE(10m L/L)coating is lower than Ni-P-PTFE(5m L/L)coating,so in the low temperature dew point corrosion on-line experimental environment,the change rate of the heat transfer coefficient of Ni-P-PTFE(5m L/L)coating with time is the smallest,only 3.39%,which represents the best scale inhibition performance.The simulation scenarios provided by the online evaluation system effectively make up for the shortcomings of static test analysis.