Drying and gas or vapor contact with solids – Apparatus – With means to treat gas or vapor
Patent
1981-11-24
1984-08-21
Schwartz, Larry I.
Drying and gas or vapor contact with solids
Apparatus
With means to treat gas or vapor
34 57A, 34102, 34168, F26B 310, F26B 1710
Patent
active
044662009
DESCRIPTION:
BRIEF SUMMARY
A process for conveniently drying and optionally roasting and peeling/grinding a granular free-flowing bulk material and a device for carrying out the process.
The invention relates to a process for convectively drying a granular free-flowing bulk material, according to which the bulk material is passed into a silo and a vertically introduced, upwardly directed jet of hot drying gas is introduced into the silo via a jet nozzle or jet aperture (orifice), in such a way that granules are continously entrained by part of said gas jet along a straight upward path to above the bulk material and fall down as a fountain onto the surrounding bulk material which slowly descends in the silo, whereas another part of the gas jet is laterally deflected and flows downward as a recycle stream.
A similar process is known from U.S. Pat. No. 2,786,280. Therein the gas jet is freely blown into the bulk material present in the silo via a jet nozzle or jet aperture (orifice) disposed in the bottom of the silo. A portion of the gas jet flows upward along a straight path, entraining the bulk material granules being at its path and causes a cylindrical channel bounded by the surrounding slowly descending bulk material; another portion of the gas jet, as applicants' investigation taught, deflects laterally and then flows downward (recycle stream); the remainder of the introduced gas jet (in practice often half to three quarters of it) deflects laterally on its way up and flows away upward through the surrounding bulk material.
This process gives a high drying efficiency, especially thanks to the laterally deflected and upwardly flowing gas.
When this process is applied to bulk material where the resistance controlling the moisture transport is in the granules, for instance to granular agricultural products, it only gives a constant drying rate at the initial stage with as a result that with bulk material of this kind the granules can easily damage, for instance get cracked, in consequence of which the useful value of bulk material dried with this known process is strongly reduced.
Moreover, the system allows of little variation. The filling level of the silo for instance cannot be altered and alteration of the output of the air jet is hardly possible as well.
It has now been found that by controlling the amount of laterally deflected and upwardly flowing drying gas a constant drying rate can be achieved. This can be explained in that the granules which are entrained by the upward flowing portion of the gas jet along a straight path give up the moisture present in the outer layer to the driving gas, whilst--as the moisture transport controlling resistance is within the granules--the moisture distribution in the core of the granules hardly changes and that thereupon the granules when they have fallen to the surrounding bulk material and slowly descend steadily with this bulk material, get sufficient opportunity for levelling out the unequal distribution of moisture which has been obtained in the gas jet, and those granules are then reintroduced into the vertically introduced gas jet by means of the recycle stream and are entrained by the portion of the gas jet flowing upward along a straight path, whereupon the whole cycle is repeated. By controlling the amount of laterally deflected and upwardly flowing gas and the recycle stream, same can be attuned to the nature of the bulk material and the drying result aimed at.
The process according to the invention is characterized, in that during the drying of bulk material, where the moisture transport controlling resistance is within the granules, a tube having a wall closed along its entire length is inserted into the bulk material coaxially with the axis of the vertical gas jet, the tube being lowered up to a predetermined distance above the bottom of the silo, in such a way that continuously an amount of the descending bulk material is entrained by the recycling gas jet and is blown into the vertically introduced upwardly directed jet of hot drying gas, and the tube is of such a length t
REFERENCES:
patent: 2786280 (1957-03-01), Gishler et al.
patent: 3911594 (1975-10-01), McIntire et al.
patent: 4349967 (1982-09-01), Jones et al.
patent: 4373272 (1983-02-01), Jones et al.
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