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The term “kettle”, as used in the packaging and processing industry, means a vessel capable of holding a liquid. It usually implies a round bottom and a means of heating or cooling. Sizes may range from a couple liters to a couple hundred gallons.
Most kettles today are stainless steel though copper kettles are still found. Copper kettles have the advantage of more even heat distribution. They have the disadvantage of being incompatible with some products.
Many kettles have jackets into which steam, hot or chilled water or other heating or cooling fluid may be circulated. A temperature control commonly regulates the flow to maintain a desired temperature. PLCs or other controllers may be used to drive a sophisticated heating and cooling profile. For example, heat the base material quickly to 150 degrees, after adding a flavor heat rapidly to 200 degrees and hole for 1 hour, then cool slowly to 80 degrees for packaging.
Not all plants have steam for heating. Gas fired and electrically heated kettles are also available when necessary.
Kettles are often open topped or have a loose fitting lid. Some kettles have a sealed top to withstand internal pressure or vacuum. Pressurization and/or vacuum may be useful in “cooking” some types of food, pharmaceutical or chemical products. Pressure allows a water-based product to achieve temperatures above boiling without evaporating. Vacuum allows liquid to be boiled off at while keeping the product at a lower temperature than would be possible in an open kettle.
Some non-viscous products will circulate sufficiently by natural convection to heat evenly. Most product will require some type of mixer. Products with suspended solids will also require a mixer to prevent the particles from settling. Mixers can range from a simple propeller mixer to aid natural convection in a non-viscous product to counterrotating paddles with scrapers in the case of a viscous product. The scrapers are required to prevent the product sticking to the kettle walls.
Kettles are often top loaded by opening the hinged top or through a handhole in a pressurized kettle. Some kettles have piping connections that permit the liquid components to be injected directly. This can be useful to prevent splashing, foaming or air entrainment.
Some kettles are designed to be drained from the bottom. These may have a simple fitting with ball valve on the bottom. This is generally undesirable unless the diameter of the discharge is fairly large in relation to its length. If not, it forms a “dead leg” in which product does not circulate well. Particles in suspension may also settle into this deadleg. Kettles with a bottom discharge should have a special, flush, valve to eliminate this deadleg.
Other kettles have no opening in the bottom and are mounted on gimbles. The kettle is emptied by rotating it and dumping the product. This is useful when the process requires rapid dumping or when the product has a lot of solids that will not flow well in piping.
Industrial liquid silos are a type of tank used for bulk storage of liquids and semi-liquids. They are commonly storage, as opposed to processing or transport tanks. Their high aspect ratio (height relative to diameter) and non-openable top is what makes them “silos” rather than “tanks”. Silos are often located outdoors though they can be located indoors ceiling height permitting.
Construction is commonly stainless steel though silos can be build of fiberglass, plastic, lined or unlined steel or other materials. The liquid in a tall silo can exert considerable lateral pressure, especially at the bottom of the tank. This would deform a square or rectangular silo so almost all liquid silos are round. Ends can be dished, conical or flat. If flat, it may be desirable for the head to be at an angle for ease of drainage (bottom) and to avoid accumulation of dirt and debris (top head) Outer coverings for physical protection or insulation to avoid large temperature swings may be required for outdoor silos. Silos may be jacketed to allow circulation of steam, hot or cold water or even nitrogen to maintain a constant product temperature.
Suitable fittings and connectors must be provided for filling and draining the silo. Level sensors are required to show how much product is in the silo. Several types are available:
Internal spray balls or nozzles may be fitted for automated cleaning if needed.
Manholes are common to allow access to the silo interior if required for cleaning or maintenance.
CAUTION: Confined spaces such as silos are dangerous. Never enter a silo without taking all safety precautions as well as having a second person outside the silo.
Most silos are not built to withstand vacuum. If the silo is emptied without adequate venting, sufficient vacuum can build up which will collapse the silo. If silos are steam cleaned or sterilized, the condensing steam will create enough vacuum to collapse any silo. All silos must have sufficient venting for the worst case scenario. In addition to proper venting, rupture disks are recommended. In the event of excess vacuum, these break allowing emergency venting.
Selecting the proper tank for the intended purpose is critical to proper processing, handling and manufacturing. Tanks can be used for storage, shipping, mixing 2 liquids, mixing a liquid and a powder, heating, cooling, cooking, reacting and dozens of other uses. Here are some things you need to know about them.
There is a lot more to know about tanks. Be sure to match product, tank and application.
Discuss your application directly with our qualified engineers.
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