1. Dealing with Impurities in Processes and Process Simulators ChEN 5253 Design II Terry A. Ring There is not chapter in the book on this subject

2. Impurity Effects Heat Exchange Reactors Separation Systems Recycle Loops

3. Impurities in Heat Exchange Impurities effect heat capacity –Lower C p Various options –Raise C p Increase H 2 Impurities effect the enthalpy of stream –Total heat of condensation is less due to impurity –Total heat of vaporization is less due to impurity

4. Impurities in Heat Exchange Impurities in Steam – Trouble shooting (MicroPlant) Lecture –Heat exchanger with Steam Trap –Build up of Impurity with Time Kills Heat Exchange with Time. –To Overcome This Problem Clean up steam Purge to remove impurity build up How to determine the purge flow rate?

5. Impurities in Heat Exchange Impurities in Fuel –Vanadium in Venezuelan Crude Oil Vanadium follows the heavy oil product that is burned to supply heat for the refinery Vanadium gives low temperature eutectic in weld beads –Welds failed in process heaters –Welds failed in process boiler –Crude Processing (desalting & hydrotreating) to remove heavy metals before entering the refinery

6. Impurities in Heat Exchange Impurities that lead to high corrosion rates –e.g. HCl in steam –Heat exchangers are hot so corrosion is fast –Corrosion of Heat Exchanger surfaces Decreases heat transfer coefficients in U Heat Exchange is not as effective with time –Cooling towers are easily corroded Lower heat transfer coefficients Heat Exchange is not as effective with time

7. Corrosion Pitting Corrosion Galvanic Corrosion Corrosion in General

8. Galvanic Series Least Noble metal corrodes when two metals are in contact

9. Galvanic Corrosion Two metals are connected together Exposed to water with dissolved salts Less Noble metal is dissolved away –Aluminum is less noble to steel Higher salt content and higher pH leads to higher dissolution rate Solution

10. Corrosion Products Fe2+(aq) + 2e− → Fe(s) −0.44 V Fe with Stainless Steel –Corrosion Potential = + 0.14 V Fe with Copper –Corrosion Potential = + 0.3 V Pourbaix diagram

11. Corrosion Rates-OLI Corrosion Analyzer Pipe Flow D= 0.1m

12. Aluminum Corrosion Al3+(aq) + 3e− → Al(s) −1.68 V Connection with Iron Corrosion Potential = + 1.2 V

13. Aluminum Corrosion Rates Increase with salt concentration Increase with temperature Increase with decrease in pH

14. Galvanic Corrosion Two metals are connected together Exposed to water with dissolved salts Less Noble metal is dissolved away –Aluminum is less noble to steel Higher salt content and higher pH leads to higher dissolution rate Solution

15. Steam Plants Water is recycled in Stream Plant –Steam Generator –Process –Return Condensed Steam –Makeup water is DI water to eliminate impurites Steam Generator –Chemical Treatment to prevent corrosion –Phosphates, pH control (buffers), other chemicals

16. Cathodic Protection Zinc Protection Zn-Fe –1 mm/yr Zn loss Al SS Fe