steam as a heating medium
DESCRIPTION
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. - PowerPoint PPT PresentationTRANSCRIPT
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KAUSAR AHMADKULLIYYAH OF PHARMACY
PHM3133 Dosage Design 1 2010/11
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Steam as a heating medium
http://staff.iiu.edu.my/akausar
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Contents
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Steam generation and use
Water treatment
Adverse effects of air in steam
Heat content of steam
Effect of pressure on steam properties
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Requirement of a heating medium
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High specific heat capacity
Inert
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Why is steam popular?
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Cheap
Abundance
No residue (compare with water)
Easy to clean
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Equipment to produce steam
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BOILER
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Boiler System
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Deaerator tankIon-exchanger
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BOILER
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Type: water-tube OR fire-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
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Components of a boiler
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Boiler feedwater
Ion exchanger
Feedwater
Deaerator
STEAM
Chemicals
Heat transfer applications:
Heating of waterDrying of solids
Blowdown (- TDS*)
Brine (NaCl)
* Total Dissolved Solids
BOILER
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Boiler Room
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Would this be good enough for a steam
bath?deaerato
r
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Feedwater treatment
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1. Removal of scale-producing elements such as calcium, magnesium & silica
2. Removal of dissolved oxygen and carbon dioxide that can cause corrosion in the boiler, piping and other components.
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Type of feedwater treatment
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1. Mechanical treatment Deaerator: a certain amount of oxygen and
carbon dioxide are removed by introducing steam into the tank.
2. Chemical treatment Addition of chemicals
Prevent scalingReduce hardness: Ca2+, Mg2+
Scale acts as insulator
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Mechanical treatment: Function of deaerator
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To remove oxygenHow?
The solubility of oxygen in water decreases with increasing temperature
Steam is introduced into the deaerator to increase the temperature of the deaerator to e.g. ca. 50ºC
.
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Chemical treatment programs
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Coagulation - obsolete Add sodium
carbonate
Phosphate program - cheap Add sodium
phosphate Require addition of
dispersant
Chelant program - expensive EDTA
Complexation/dispersion polymers
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Chemical Treatment
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• precipitates Ca2+, Mg2+, SiO2 sodium
phosphate
• bridging flocculationpolymer
(polyacrylic acid)
• remove oxygen: 2SO32- + O2 =
2SO42-sodium sulfite
• control alkalinity• maintains solids in suspension
(high ζ-potential)
caustic soda (NaOH)
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Maintenance
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1. General maintenance due to corrosion e.g.
tube replacement
condensate pumps
steam traps
2. Water treatment equipment
3. Ion-exchange resin
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Disadvantages of steam boiler
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Need water treatment to minimise corrosion
Regular maintenance to maintain heat transfer efficiency
blowdown
water pre-treatment facilities
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Effect of scale on heat transfer
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Equipment failure
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Adverse effects of air in steam
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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
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How to calculate amount of heat transfer
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PROBLEM:To heat 50 litres of water at 30ºC, how much energy is required? How much steam is required?
Q = mcTQ : energy required (J)m : mass (kg)c : specific heat capacity (J/kg.ºC)T : change in temperature
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Types of Steam
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AUTOCLAVE
Saturated steam(good for sterilisation)
Superheated steam(not desirable)
BOILER
Wet steam(not desirable)
dry steam(good for sterilisation)
Separator to remove moisture
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Exercise
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1. What is the heat content of steam?
2. What is the effect of pressure on steam properties?
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Conclusion: Steam as a choice
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Cheap
Non-hazardous
Well-researched
Simple operation
Easy to maintain if proper procedures are followed
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Reference
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Aulton, M. (1988). Pharmaceutics. London: Churchill
Livingstone.
Rawlins, EA (1977). Bentley’s Textbook of
Pharmaceutics. East Sussex: Bailliere Tindall