Difference between short type vertical evaporators and basket type evaporator
Answers
Answered by
1
Short-tube vertical evaporators — These are often referred to as calandria or standard evaporators, the latter because of earlier popularity with users. Units consist of short tubes, 4-6 ft long, and 2-4 in. dia., set between two horizontal tubesheets that span the evaporator-body diameter. The tube bundle contains a large circular downcomer that returns concentrated liquor above the top tubesheet to below the bottom tubesheet for product withdrawal. The driving force for flow of liquid through the tubes is the difference in density between the liquid in the downcomer and two-phase mixture in the tubes.
Advantages: these evaporators can be used with scaling liquids, since evaporation takes place inside the tubes, which are accessible for cleaning. Fairly high heat-transfer coefficients are obtained with thin liquors (i.e., water or dilute solutions of 1-5 cP). Units are relatively inexpensive, provided that they are made of carbon steel or cast iron.
Disadvantages: a large area is required since the units are squat. Heat-transfer coefficients are sensitive to the temperature difference and liquor viscosity, and, due to large liquid holdup, these evaporators cannot be used with heat-sensitive materials. Turndown and flexibility are low — turndown being <2:1.
Also, such evaporators are unsuitable for crystalline products, unless a propeller is used to produce forced circulation.
Industrial applications: these short-tube vertical evaporators are suitable for noncorrosive (e.g., cane sugar), clear and noncrystallizing liquors.
Basket-type evaporators — These are similar to calandria-type units except that the tube bundle is removable and the liquor downtake occurs between the bundle and the shell, instead of in a central downcomer.
Advantages: The heating surface is removable, allowing easy cleaning and maintenance. Also, due to the construction, differential thermal expansion is not a problem.
Disadvantages: These are the same as for short-tube evaporators.
Industrial applications: These are the same as for short-tube evaporators. Basket types can also be used when the liquor may result in scale.
Advantages: these evaporators can be used with scaling liquids, since evaporation takes place inside the tubes, which are accessible for cleaning. Fairly high heat-transfer coefficients are obtained with thin liquors (i.e., water or dilute solutions of 1-5 cP). Units are relatively inexpensive, provided that they are made of carbon steel or cast iron.
Disadvantages: a large area is required since the units are squat. Heat-transfer coefficients are sensitive to the temperature difference and liquor viscosity, and, due to large liquid holdup, these evaporators cannot be used with heat-sensitive materials. Turndown and flexibility are low — turndown being <2:1.
Also, such evaporators are unsuitable for crystalline products, unless a propeller is used to produce forced circulation.
Industrial applications: these short-tube vertical evaporators are suitable for noncorrosive (e.g., cane sugar), clear and noncrystallizing liquors.
Basket-type evaporators — These are similar to calandria-type units except that the tube bundle is removable and the liquor downtake occurs between the bundle and the shell, instead of in a central downcomer.
Advantages: The heating surface is removable, allowing easy cleaning and maintenance. Also, due to the construction, differential thermal expansion is not a problem.
Disadvantages: These are the same as for short-tube evaporators.
Industrial applications: These are the same as for short-tube evaporators. Basket types can also be used when the liquor may result in scale.
Answered by
2
Answer:
Basket-type evaporators — These are similar to calandria-type units except that the tube bundle is removable and the liquor downtake occurs between the bundle and the shell, instead of in a central downcomer. ... Industrial applications: These are the same as for short-tube evaporators.
Similar questions