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Steam as a heating medium

Steam as a heating medium. Kausar Ahmad Kulliyyah of Pharmacy. http://staff.iiu.edu.my/akausar. Contents. Steam generation and use Water treatment Adverse effects of air in steam Heat content of steam Effect of pressure on steam properties. Requirement of a heating medium.

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Steam as a heating medium

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  1. Steam as a heating medium Kausar Ahmad Kulliyyah of Pharmacy http://staff.iiu.edu.my/akausar PHM3133 Dosage Design 1 2010/11

  2. Contents • Steam generation and use • Water treatment • Adverse effects of air in steam • Heat content of steam • Effect of pressure on steam properties PHM3133 Dosage Design 1 2010/11

  3. Requirement of a heating medium High specific heat capacity Inert PHM3133 Dosage Design 1 2010/11

  4. Why is steam popular? Cheap Abundance No residue (compare with water) Easy to clean PHM3133 Dosage Design 1 2010/11

  5. Equipment to produce steam BOILER PHM3133 Dosage Design 1 2010/11

  6. Boiler System Ion-exchanger Deaerator tank PHM3133 Dosage Design 1 2010/11

  7. BOILER • Type: water-tube ORfire-tube • Fired by fossil fuel or electricity • Specified by the capacity e.g. 5 barg or 20 barg • Requirement • Maintenance system • Water treatment system • Corrosion control PHM3133 Dosage Design 1 2010/11

  8. Components of a boiler Blowdown (- TDS*) BOILER Boiler feedwater STEAM Deaerator Chemicals Ion exchanger Brine (NaCl) Heat transfer applications: Heating of water Drying of solids * Total Dissolved Solids Feedwater PHM3133 Dosage Design 1 2010/11

  9. Boiler Room Would this be good enough for a steam bath? deaerator PHM3133 Dosage Design 1 2010/11

  10. Feedwater treatment • Removal of scale-producing elements such as calcium, magnesium & silica • Removal of dissolved oxygen and carbon dioxide that can cause corrosion in the boiler, piping and other components. PHM3133 Dosage Design 1 2010/11

  11. Type of feedwater treatment • Mechanical treatment • Deaerator: a certain amount of oxygen and carbon dioxide are removed by introducing steam into the tank. • Chemical treatment • Addition of chemicals • Prevent scaling • Reduce hardness: Ca2+, Mg2+ • Scale acts as insulator PHM3133 Dosage Design 1 2010/11

  12. Mechanical treatment: Function of deaerator To remove oxygen How? • The solubility of oxygen in water decreases with increasing temperature • Steam is introduced into the deaeratorto increase the temperature of the deaerator to e.g. ca. 50ºC . PHM3133 Dosage Design 1 2010/11

  13. Chemical treatment programs • Coagulation - obsolete • Add sodium carbonate • Phosphate program - cheap • Add sodium phosphate • Require addition of dispersant • Chelant program - expensive • EDTA • Complexation/dispersion • polymers PHM3133 Dosage Design 1 2010/11

  14. Chemical Treatment PHM3133 Dosage Design 1 2010/11

  15. Maintenance • General maintenance due to corrosion e.g. • tube replacement • condensate pumps • steam traps • Water treatment equipment • Ion-exchange resin PHM3133 Dosage Design 1 2010/11

  16. Disadvantages of steam boiler • Need water treatment to minimise corrosion • Regular maintenance to maintain heat transfer efficiency • blowdown • water pre-treatment facilities PHM3133 Dosage Design 1 2010/11

  17. Effect of scale on heat transfer PHM3133 Dosage Design 1 2010/11

  18. Equipment failure PHM3133 Dosage Design 1 2010/11

  19. Adverse effects of air in steam • Corrosion • How long can the boiler last? • Lower heat transfer efficiency • Air is an insulator • Knocking • Bad for structure of the boiler system • Quality • May affect product if in direct contact PHM3133 Dosage Design 1 2010/11

  20. How to calculate amount of heat transfer PROBLEM: To heat 50 litres of water at 30ºC, how much energy is required? How much steam is required? Q = mcT Q : energy required (J) m : mass (kg) c : specific heat capacity (J/kg.ºC) T: change in temperature PHM3133 Dosage Design 1 2010/11

  21. Types of Steam AUTOCLAVE Saturated steam (good for sterilisation) Superheated steam (not desirable) BOILER Wet steam (not desirable) dry steam (good for sterilisation) Separator to remove moisture PHM3133 Dosage Design 1 2010/11

  22. Exercise • What is the heat content of steam? • What is the effect of pressure on steam properties? PHM3133 Dosage Design 1 2010/11

  23. Conclusion: Steam as a choice • Cheap • Non-hazardous • Well-researched • Simple operation • Easy to maintain if proper procedures are followed PHM3133 Dosage Design 1 2010/11

  24. Reference Aulton, M. (1988). Pharmaceutics. London: Churchill Livingstone. Rawlins, EA (1977). Bentley’s Textbook of Pharmaceutics. East Sussex: Bailliere Tindall PHM3133 Dosage Design 1 2010/11

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