Research On Scaling Mechanism Of High Temperature Flue Gas In Energy Recovery System Used For Fluid Catalytic Cracking Unit

Energy Recovery System (ERS) used for Fluid Catalytic Cracking (FCC) unit plays animportant part in energy saving and emission reducing in the oil-refining industry. It also hasadvantages of good economic benefits to the society. However, there appears the increase ofequipments breakdown rates, low energy recycling efficiency, downtime and even stoppingproduction because of the equipments scaling in the actual factory running process.Nowadays people are short of sufficient knowledge about the scaling of high temperature fluegas in ERS used for FCC unit. The live conclusions are burdensome and are of pooruniversalities. Not to metion that it lacks of adequate awareness of the scaling mechanism ofhigh temperature flue gas in ERS used for FCC unit. In this article, with combination of thetheoretical analysis, experimental research, numerical calculation and the advanced fluiddynamic technology, the influence of gas-solid phases flow on the scaling of low and highslip speed equipments were studied. Besides, the scaling mechanism of high temperature fluegas were deeply investigated.Firstly, the influence factors of high temperature flue gas scaling were general improved,and the influence rules were also summarized and analysised. Based on lots of on-siteinvestigations and mathematical statistic analyses, also with the supplemented and improvedlaboratory thermal state experiments, we find that the overall influence high temperature fluegas scaling factors (particle sizes, particle concentrations, metal contents, thermal pressuresbetween particles and walls, water vapor contents, temperatures and handling amounts are inorder). We seriatim discuss the influence rules of each factor on scaling, detailed descript thephenomena of scaling and thereafter find out there is a close link between scaling andgas-solid two-phase fluid flow situations.Secondly, we transfer the flue gas scaling problem to the deposition and adhesion behaviorsof the particles in the boundary layer. Besides, the fundamental theories of deposition andadhesion models between particles and wall were introduced, also based on theJohnson-Kendall-Roberts (JKR) contact theory, the deposition and adhesion peocess of the interreactions between the particles and wall was devided into two steps, one is the initialadhesion of the particles near the walls under the pure colliding actions, and the other is theseparating process of the particles in the edge of walls under the fluid dynamic actions,thereafter, the reasonable rebound coefficient was set along with the flow features of eachequipment in ERS, and finally the suitable deposition and adhesion models between theparticles and wall were established. The calculated conclusions through Computational FluidDynamics (CFD) softwares about particles adhension and scaling used in this model agreewell with the experimental phenomena.Thirdly, the ERS equipments were classified into low slip speed and high slip speedequipments according to the relative motions between particles and walls. The influence lawof scaling of two types of typical equipments with different high temperature flue gasoperation parameters (operation contents, temperatures, operation pressures and water vaporcontents) and different physical parameters (particles concentrations, granularity and metalelements contents) were deeply researched, which supplys data supports for the establishmentof calculation model of high temperature flue gas scaling, and also provides theorticalguidance for effective steps to prevent scaling for further research.Finally, the calculation model was built to study the high temperature flue gas scaling inhigh slip speed equipments. It is found that: the essence of high temperature flue gas scalingis kind of dense and hard material after flue gas’ sintering. Besides, the effective steps ofcontrolling particles scaling were put forward based on the scaling production process.Thesesteps includ: taking appropriate hood operating temperatures, avoiding emerging condensedwater, avoiding emerging the low melting point compounds’ temperature range, reducingthe paticles concentrations in the equipments and preventing from emerging minimumparticles, avoding the harmful metals contents in the balance agent and adding appropriateadmixtures to hinder particles contacting with each other, choosing appropriate atmospheres,reducing the sources of generation of hot pressure as far as possible.The research results supply theoretical foundation and evidence for further perfecting andoptimizing process operation of ERS, and play important parts in safeguarding catalyticcracking unit for long period running. So this research is of great both theoretical andpractical significance.