Evaporating Pan or Steam Jacketed Kettle
Principle
The steam jacketed kettle or evaporating pan is an evaporator that can be used for the bulk evaporation of water from aqueous liquids. It is constructed in the form of a hemispherical shaped shell usually made of stainless steel that is comprised of an inner pan or ‘kettle’ and an outer pan or ‘jacket’. Steam flows through the space between the outer and inner pans at a slightly elevated pressure. The hot steam causes heat to pass through the inner pan, by conduction, to the solution that is to be evaporated. As the temperature of the solution rises, so solvent molecules are evaporated. The pan can be permanent mounted and the product is emptied through an outlet at the bottom of the pan, or the pan can be mounted in such a way that it can be tilted so that the product can be poured out.
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Construction and operation
Copper, which has good thermal conductivity may be used used for the construction of an evaporating pan or steam jacketed kettle. Tinned copper is preferred since acidic materials tend to react with untreated copper. Similarly iron may be used in the construction of the outer kettle providing it is coated on the inner surface with enamel or a protective metal. Stainless steel is, however, the preferred material for construction of evaporators used in the pharmaceutical industry on account of its versatility with a range of aqueous and non-aqueous solutions. An inlet for the steam and an outlet or vent for the non condensed gases is provided near the top of the jacket. Condensed steam accumulates at the bottom of the jacket where an outlet is provided for the condensate. The evaporated solvent exits the top of the evaporator. In the case of aqueous solutions the evaporated material is simply steam which may be allowed to discharge into the room. To prevent fog formation of condensed vapor in the area, good ventilation is important as it helps remove the vapor. Fans may be fitted to allow vapor to clear and prevent condensation in the area. For organic solvents, the evaporator is sealed with a lid which incorporates a vent hole through which the solvent is discharged to safety. A plugged hole is provided at the bottom of the evaporator for the discharge of product.
Smaller amounts of aqueous material can be stirred manually whereas large volumes or non-aqueous solutions require the provision of an automated stirrer. In the initial stages, the evaporation rate is rapid.
Pharmaceutical Applications
- Concentrating aqueous liquids
- Concentrating thermo stable liquors (ex. Liquorice extracts)
Features
- Pans can be constructed for small to large batch operations
- Easy to operate, maintain and has simple construction
- Low cost of installation and maintenance
- Wide variety of materials of construction (e.g., Copper, aluminum, stainless steel)
- Can be manually stirred and product removal is fast and easy
Disadvantages
- Unless mechanically stirred, the natural circulation of the product results in poor heat transfer resulting in solids being deposited out of solution and possible decomposition of the product.
- There is a limited heated surface is limited and this is proportionately reduced as the pan size is increased.
- It is not ideal for thermolabile materials as the liquid matter is heated constantly and is normally open to the atmosphere atmosphere. Note that some systems can be provided with a lid which may enable to evaporated solution to be vented to safety.
- With an open pan is open the solvent vapours can move around the room causing discomfort among workers and because the vapours are not force vented, this may slow down the evaporation process.
LFA does not manufacture any of this type of equipment. We specialise in Tablet Presses and capsule fillers but can source equipment such as evaporating pans/steam jacketed kettles not on our website or recommend a supplier. Please do not hesitate to contact us if you are interested in this type of product.