US 4,194,296 AGranted

Vacuum drying kiln

OwnerVincenzo Pagnozzi, Ernesto G. Pagnozziinventors

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Abstract

A vacuum drying kiln has a drying chamber in which, in use, is placed timber to be dried and around which is a surrounding water jacket through which is circulated a heat exchange fluid which derives its heat by flowing through the secondary circuit of a heat exchanger through the primary circuit of which is pumped a mixture of air and water vapor drawn by a vacuum pump from the interior of the drying chamber. The kiln is operated cyclically through successive heating and evacuation phases and the vacuum pump is one utilizing a secondary fluid to effect pumping, the characteristics of this secondary fluid being that it is immiscible with water and has a low specific heat so that it encourages the condensation of the water vapor in the primary circuit of the heat exchanger by undergoing large temperature variations for small changes in heat content.

Claims15

Dependent claims

In a vacuum drying kiln suitable for drying timber, comprising:

at least one drying chamber,
heating means including a primary fluid operable to transfer heat to the interior of said chamber,
a vacuum pump containing a secondary fluid and having an inlet and an outlet,
means selectively connected the inlet of said vacuum pump to said chamber whereby to produce in said chamber a pressure reduction for the purpose of evaporating water contained in the timber, and
heat pump means including condenser means connected to the outlet of said vacuum pump for receiving said water vapour and said secondary fluid, said condenser means being operable to extract from the water vapour drawn from the wood at the operating temperature in said chamber a quantity of the heat conveyed thereby from the chamber, and also to extract from the water vapour a quantity of heat corresponding to the thermal equivalent of the work done on the water vapour by the vacuum pump, and thereby raise the temperature of this extracted heat above the said operating temperature in the chamber and transfer means for transferring said heat back to the interior of the said chamber via the said heating means.

2 more elements

A method of drying timber using a vacuum drying kiln having first and second drying chambers, heating means including a primary fluid operable to transfer heat to the interior of said chambers, a vacuum pump containing a secondary fluid and having an inlet and an outlet, means for selectively connecting the inlet to one of said chambers, a heat exchanger having a primary and secondary circuit and conduit means for selectively connecting said chambers directly to each other, comprising the steps of:

(a)--heating the interior of at least the second drying chamber to raise the temperature of timber placed therein;
(b)--evacuating said second chamber with said vacuum pump and extracting the heat from the air and water vapour drawn therefrom by means of said heat exchanger and transferring this heat into said first chamber;
(c)--placing said first and second chambers into communication with one another through said conduit means and isolated from the atmosphere so that the pressures therein are equalised at a subatmospheric pressure;
(d)--evacuating said first chamber with said vacuum pump, extracting the heat contained in the air and water vapour drawn therefrom by means of said heat exchanger and transferring this heat into the second chamber;
and
(e)--repeating steps (b), (c), and (d) cyclically in this sequence until the moisture content of the timber in the two chambers has fallen to the required level.

3 more elements

Dependencies are inferred from the claim text.

Facts

Application: 05/902,632Filed 4 May 1978
Priority: IT 68116 A/7717 May 1977
Granted: 25 Mar 1980
Term ends: Not estimatedThe source records don’t support an estimate.

Classification9 codes

F26B 5/04
Drying solid materials or objects by processes not involving the application of heat: by evaporation or sublimation of moisture under reduced…
F26B 23/004
Recovered from dryer exhaust gases: by compressing and condensing vapour in exhaust gases, i.e. using an open cycle heat pump system
F26B 23/10
Heating arrangements: using tubes or passages containing heated fluids , e.g. acting as radiative elements; Closed-loop systems
F26B 2210/16
Drying processes and machines for solid objects characterised by the specific requirements of the drying goods: wood, e.g. lumber, timber