Concentrating evaporators – Spray type – Gaseous current
Patent
1981-01-22
1983-01-18
Yudkoff, Norman
Concentrating evaporators
Spray type
Gaseous current
159 45, 159 4A, 159 481, B01D 116
Patent
active
043690912
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a method of spray drying a liquid product which is atomized in a drying chamber by means of a rotating atomizing wheel, a flow of warm drying gas being simultaneously directed towards the bottom side of the atomizing wheel from a first position located at a substantial distance below the same, in the presence of particulate solid material which under the present conditions tends to melt or become sticky in another way.
DESCRIPTION OF THE PRIOR ART
Applicants' U.S. Pat. No. 4,002,524 describes such a spray drying method, wherein the warm drying gas in the form of flue gas is caused to flow into the drying chamber through a gas supply tube arranged centrally therein and opening below the atomizing wheel, and the said patent also describes spray drying processes, wherein particulate material is introduced into the flue gas supply tube and is carried along with the warm flue gas.
It has been found that serious problems may arise in connection with such spray drying process, because particles which are present in the spray drying chamber and which have normally, but not necessarily, been introduced therein together with the drying gas, adhere to the atomizing wheel when due to the flow conditions prevailing in the drying chamber they come into contact with the bottom side of the atomizing wheel towards which the inflowing drying gas is directed. When deposits formed on the rotating atomizing wheel have reached a certain thickness the centrifugal forces acting thereon have become so great that the deposits are suddenly severed and flung outwardly against the walls of the drying chamber which at best are thereby subjected to a strong influence of wear and at worst damaged by the influence of impact. Such a severance of deposits from the rotating atomizing wheel may also cause that deposits remaining on the atomizing wheels give rise to an unbalance which may cause so serious vibrations that a permanent deflection or fracture of the spindle of the atomizing wheel occurs.
SUMMARY OF THE INVENTION
In order to solve these problems the present invention provides a method of spray drying a liquid product, said method comprising atomizing said liquid product in a spray drying chamber by means of a rotating atomizing wheel, directing from a first position below said atomizing wheel and spaced substantially therefrom a flow of hot drying gas towards the bottom side of said wheel in the presence of particulate solid matter tending to become sticky under the temperature conditions present, and simultaneously directing from a second position below the bottom side of said atomizing wheel, but substantially closer thereto than said first position, a flow of clearing or obstructing gas free of such solid matter so as to prevent said particulate solid matter from contacting said bottom side of the atomizing wheel.
The clearing or obstructing gas may be of any type provided that it does not contain particles which may adhere to the atomizing wheel. Thus, in principle it would be possible to use filtered gas from the drying chamber as clearing gas. However, it may be advantageous to use clearing gas, preferably atmospheric air, which is substantially colder than the drying gas because the clearing gas will then also cool the bottom side of the atomizing wheel and thereby contribute not only to increase the useful life of the wheel, but also to reduce the risk that particles which happen to come into contact therewith, adhere thereto.
The clearing or obstructing gas may be directed towards the bottom side of the atomizing wheel in any manner which substantially reduces the risk that particles of material floating in the air or gas in the drying chamber come into contact with the atomizing wheel. However, normally it is desired to limit the consumption of clearing gas to the smallest possible amount, with means to apply the clearing gas so that it becomes as effective as possible. Thus, the flow of clearing gas may be directed axially and centrally towards the atomizing wheel. When such axial flow of c
REFERENCES:
patent: 2475984 (1949-07-01), Owen
patent: 3460600 (1969-08-01), De Boer
patent: 3828837 (1974-08-01), Damgaard-Iversen et al.
A/S Niro Atomizer
Yudkoff Norman
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