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Shell And Tube crystal precipitates settle in the bottom of the tank . After washing , they are transferred to a kiln for calcining ( heating to release the water molecules that are chemically bonded to the aluminium oxide molecules ). After calcining , the crystals are passed through the coolers and stored as shown in figure- [ 1 ].
The Hall-Heroult Process The Hall-Heroult Electrolysis Process is the process where the aluminium oxide reacts with carbon to give aluminium releasing carbon dioxide as shown in the equation below .
2Al 2
O 3
+ 3C 4Al + 3CO 2
The role of the heat exchanger In the Bayer process , a heat exchanger plays a vital role in digestion operation . In this process , bauxite ore is digested in caustic soda ( NaOH ) solutions and a heat exchanger is used to heat the solution using steam . After appropriate digestion and filtration steps to separate the insoluble materials , the supersaturated solution is cooled down to 65 ° C in order to accelerate crystallization . The product is then separated and calcined to obtain pure aluminium oxide ( Al 2
O 3
). Since the caustic solution is continuously supersaturated with sodium aluminate and silicate , scaling is present in every part of the process especially in heat exchangers because of its harmful effects on energy consumption . Since the solution is repeatedly heated up and cooled down in the Bayer process circuit , the heat exchanger is extremely important in terms of energy costs . The heat exchangers used for heating sodium aluminate solution are unique , and the criticality of these exchangers are listed as below :
• They have a multi pass radial tube layout with larger tube sizes . The main purpose of radial tube layout is to achieve turbulent flow with high viscosity slurries . It will help in reducing fouling on the tube side
• Expansion bellow on the shell side
• The channel cover assembly with channel is very intricate as the planarity has to be maintained to avoid leakages in pass partition plate .
Special closure assembly for radial tube bundle assembly .
Precision Equipments has hands-on experience in handling such critical equipment with in-house engineering including FEA and machining facility for intricate machining , assembly and testing . Through this experience Precision Equipments is confident in its ability to provide heat exchangers of high quality and performance for critical projects in mining sectors .
References :
•• https :// mobilityforesights . com / product / indiaaluminium-market /
•• https :// www . metallurgyfordummies . com / thebayer-and-hall-heroult-process . html
••
Bayer Process Heat Exchangers Cleaning Efficiency : Optimizing the Acid Dissolution of Sodalite Scale ( engconfintl . org )
Exchanger dispatched for an aluminium refinery .
About the authors
Prabhu Bala – Company Director is a post graduate mechanical engineer ( specialization in heat and mass transfer ) from RIT , New York . He is responsible for Precision Equipments ’ business development . Before joining Precision , Mr Bala worked in MIT Micro Fuel Cell , New York as a design engineer . He has published two of his research papers in the ASME International Journal of Heat and Mass Transfer . Ganesh Prasad – Technical Sales is a post graduate mechanical engineer specialised in thermal engineering with extensive research work in cryogenic & critical equipment . Much of his research work has been published in international journals . www . heat-exchanger-world . com Heat Exchanger World September 2022
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