KAUSAR AHMAD KULLIYYAH OF PHARMACY PHM3133 Dosage Design 1 2010/11 1 Steam as a heating medium

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

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

Requirement of a heating medium

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High specific heat capacity

Inert

Why is steam popular?

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Cheap

Abundance

No residue (compare with water)

Easy to clean

Equipment to produce steam

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BOILER

Boiler System

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Deaerator tankIon-exchanger

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

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

Boiler Room

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Would this be good enough for a steam

bath?deaerato

r

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.

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

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

.

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

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)

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

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

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

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

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

Exercise

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1. What is the heat content of steam?

2. What is the effect of pressure on steam properties?

Conclusion: Steam as a choice

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Cheap

Non-hazardous

Well-researched

Simple operation

Easy to maintain if proper procedures are followed

Reference

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Aulton, M. (1988). Pharmaceutics. London: Churchill

Livingstone.

Rawlins, EA (1977). Bentley’s Textbook of

Pharmaceutics. East Sussex: Bailliere Tindall