Method for heat treatment of articles and arrangement for carrying out the method

In a chamber (24) in a pressure vessel, e.g. an autoclave (10), articles (26) are heat-treated by water, which is sprayed over the articles through nozzles (20) and supplies heat to or removes heat from the articles. Simultaneously, a gaseous medium, e.g. a mixture of steam and air, is forced by an impeller (34) to flow through the articles in countercurrent to the water. By this a very even temperature distribution of the articles in the chamber (24) is obtained.

The present invention relates to a method for heat treatment of articles 
which are placed in a chamber in a pressure vessel, heat being supplied to 
and heat being removed from, respectively, the articles via water 
circulated in a closed circulation circuit and sprayed over the articles, 
which water during a heating period is heated by steam being introduced 
into the vessel and during a cooling period cooled by a first heat 
exchanger in the circulation circuit. 
The invention furthermore relates to an arrangement for heat treatment of 
articles which are placed in a chamber in a pressure vessel for carrying 
out the method, which arrangement comprises a closed circulation circuit 
for water including a bottom outlet in the pressure vessel, a pump, a 
first heat exchanger and nozzles which spray the water over the articles 
in the chamber, and means for supplying steam to the vessel. 
It is known to sterilize articles, e.g. liquids in glass- or plastic 
packages, in a pressure vessel. The packages are placed in the vessel, 
which is then closed, and the articles are heated to sterilizing 
temperature by water being sprayed through nozzles over the articles. This 
water is collected at the bottom of the vessel and pumped through a return 
conduit back to the nozzles. The water is heated by steam supplied to the 
vessel. When the sterilizing temperature has been reached and the articles 
have been kept at this temperature a certain time, the articles are cooled 
by water, which has been cooled in a heat exchanger in the return conduit, 
being sprayed over the articles. After that the vessel is opened and the 
sterilized articles can be taken out. 
The drawback of the known method is that the articles in different parts of 
the vessel are unevenly heated and cooled, respectively, which is 
detrimental to the sterilizing result. 
It is also known to sterilize articles, e.g. liquids in glass- or plastic 
packages, by exposing them to a flow of gaseous medium, which flow is 
generated by an impeller inside the pressure vessel. The gaseous medium 
can for example be composed by a mixture of air and steam. During heating 
steam is supplied to the vessel and circulated together with the air 
through the articles by the impeller. Inside the vessel a heat exchanger 
is arranged in the flow of gaseous medium to cool the gaseous medium 
during cooling of the articles. 
This method also has the drawback, that articles in different parts of the 
vessel are unevenly heated and cooled, respectively. 
The object of the invention is to eliminate said drawback and provide a 
temperature distribution of the articles in the chamber which is as even 
as possible. This object is attained by the method according to the 
invention thereby that simultaneously as the water is sprayed over the 
articles and flows downwards through them gaseous medium in the vessel is 
forced to flow upwards through the articles, and by the arrangement 
according to the invention thereby that an impeller is arranged in the 
vessel for generating a force circulating flow of gaseous medium through 
the articles in countercurrent to the water flowing downwards through the 
articles and that means are arranged for driving the impeller and the pump 
simultaneously.

The numeral 10 designates a pressure vessel in the form of an insulated 
cylinder 12 with end walls (not shown). In the lower part of the vessel is 
an outlet 14, which communicates with a pump 16. The pressure side of the 
pump is connected to the inlet of a heat exchanger 18, the outlet of which 
is connected to several spray nozzles 20 positioned in the top wall 22 of 
a chamber 24, into which the articles to be sterilized, e.g. glass 
packages 26, are inserted. By the chamber 24 comprising vertical walls 28, 
the vessel obtains double-walled form. Heat exchangers 32 are arranged in 
ducts 30 located outside the walls 28. 
In the upper part of the vessel there is an impeller 34, the inlet of which 
is located in the top wall 22 of the chamber 24. The outlet of the 
impeller is directed radially and communicates with the chamber via the 
ducts 30 and an opening 36 in the bottom of the chamber 24. In the vessel 
there are furthermore one or more steam inlets 38. 
The arrangement works in the following way. After the articles to be 
heat-treated have been inserted into the chamber 24, the door (not shown) 
of the vessel is closed. A quantity of water is supplied to the lower part 
of the vessel via a valve 58. The treatment is thereafter started by a 
control means 40, which simultaneously starts the pump 16, so that water 
will be sprayed over the articles, the impeller 34, so that gaseous 
medium, at the beginning only air, will flow through the articles, and 
opens a valve 42 to the steam inlet, so that steam will flow into the 
vessel. The steam heats the air and water flowing through the articles, 
the water being heated by the steam condensing in it. The circulating air 
is mixed whith the steam and brings about an intense mixing and heating 
effect inside the chamber 24 on the water which is sprayed over the 
articles and flows downwards through them, so that all parts of the 
articles will be heated evenly and rapidly. 
A temperature sensor 44 senses the temperatures in the chamber 24 and 
regulates via the steam valve 42 the steam supply to the vessel in 
dependence of the temperature in the chamber 24. 
When another temperature sensor 46 located in a representative glass 
package in the chamber 24, senses that the desired treatment temperature 
has been reached in the package, it gives a signal to a timer 48 of the 
control means to start. When the timer has run the time, during which the 
desired heat treatment shall take place, it initiates simultaneous closing 
of the steam valve 42 and opening of the valves 50 and 52 of the heat 
exchangers 18 and 32, respectively, so that cooling water will flow 
through them and cool them both the water being sprayed over the articles 
and the gas mixture circulated through the articles. The circulating gas 
mixture brings about an intense mixing and cooling effect inside the 
chamber 24 on the water which is sprayed over the articles and flows 
downwards through them, so that all parts of the articles will be cooled 
evenly and rapidly. 
When the articles are cooled to the desired temperature the pump 16 and the 
impeller 34 are stopped and the valves 50 and 52 are closed, after which 
the water is discharged through a valve 60 and the pressure in the vessel 
10 is equalized against the surrounding atmosphere pressure by opening of 
a valve 54. The vessel can then be opened and the heat treated, e.g. 
sterilized, articles be taken out. 
During the whole process the desired pressure in the vessel is controlled 
by supplying sterile compressed air through a valve 56 or by discharging 
gaseous medium through the valve 54. 
Tests have been made which show the difference in result between the two 
said known methods and the method according to the invention. The chamber 
24 in an arrangement according to the drawing was filled with glass 
packages 26. The temperatures T1, T2 and T3 were measured in three 
different packages. 
The first known method described in the description was carried out on the 
packages. The impeller 34 was standing still while the pump 16 was 
running, spraying water over the packages. Heating was effected by steam 
only from the steam inlet 38. Cooling was effected by the heat exchanger 
18 only. The result is evident from Table 1. 
Without moving the packages in the chamber 24 the second known method 
described in the description was carried out on the packages. The pump 16 
was standing still while the impeller 34 was running and circulated 
gaseous medium between the packages. Heating was effected by steam only 
from the steam inlet 38. Cooling was effected by the heat exchangers 32 
only. The result is evident from Table 2. 
The packages were furthermore subjected to the method according to the 
invention. The pump 16 as well as the impeller 34 were running. Heating 
was effected by steam only from the steam inlet 38. Cooling was effected 
by as well the heat exchanger 18 as by the heat exchangers 32. The result 
is evident from Table 3. 
TABLE 1 
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Circulating water only 
Time T1 T2 T3 
min., sec. 
.degree.C. .degree.C. 
.degree.C. 
______________________________________ 
Heating 0'00" 42,1 37,8 
36,6 
2'00" 84,9 90,4 
84,7 
4'00" 113,4 118,0 
114,5 
6'00" 127,5 128,7 
127,9 
Sterilizing 
6'00" 127,5 128,7 
127,9 
7'00" 127,8 127,9 
127,8 
8'00" 127,9 128,0 
127,9 
Cooling 8'00" 127,9 128,0 
127,9 
9'00" 100,6 97,5 
98,2 
10'00" 76,1 74,2 
74,2 
11'45" 48,0 47,6 
47,5 
______________________________________ 
TABLE 2 
______________________________________ 
Circulating gaseous medium only 
Time T1 T2 T3 
min., sec. 
.degree.C. .degree.C. 
.degree.C. 
______________________________________ 
Heating 0'00" 36,0 28,7 
35,8 
1'00" 94,5 89,6 
88,8 
2'00" 123,1 121,9 
119,6 
2'30" 129,0 128,8 
127,2 
Sterilizing 
2'30" 129,0 128,8 
127,2 
3'30" 128,0 128,0 
127,7 
4'30" 128,1 128,0 
127,9 
Cooling 4'30" 128,1 128,0 
127,9 
5'30" 90,4 89,0 
99,3 
9'30" 67,2 52,7 
65,5 
13'15" 49,5 34,5 
45,7 
______________________________________ 
TABLE 3 
______________________________________ 
Both circulating water and 
circulating gaseous medium 
Time T1 T2 T3 
min., sec. 
.degree.C. .degree.C. 
.degree.C. 
______________________________________ 
Heating 0'00" 37,5 35,0 
36,4 
2'00" 79,4 78,0 
78,5 
4'00" 110,5 110,0 
109,8 
6'00" 128,0 127,8 
127,8 
Sterilizing 
6'00" 128,0 127,8 
127,8 
7'00" 127,8 127,8 
127,8 
8'00" 127,8 127,8 
127,8 
Cooling 8'00" 127,8 127,8 
127,8 
9'00' 100,2 97,0 
98,1 
10'00" 74,2 73,6 
73,6 
11'30" 48,9 49,2 
49,2 
______________________________________ 
From the above tables it is evident that the method and the arrangement 
according to the invention result in that the heat treatment of the 
articles takes place rapidly and simultaneously homogeneously, so that the 
articles at each moment during the treatment show an extraordinary even 
temperature distribution over the whole chamber 24. All the articles reach 
rapidly and simultaneously the desired treatment temperature during the 
heating without any part of the articles lagging in temperature respect, 
which would imply a harmful under-treatment of this part of the articles 
during the subsequent heat treatment. After that, all the articles keep at 
the desired treatment temperature without any part being neither colder 
nor warmer, which would be harmful to the treatment result. During the 
cooling the temperature of the articles sinks rapidly and simultaneously 
with the advantage that no part of the articles is staying at a higher 
temperature, which would imply a harmful over-treatment of the articles. 
A cause contributing to the even temperature distribution during the 
heating is that the articles then are exposed to warm medium from two 
directions simultaneously, viz. partly by warm gas mixture which flows 
upwards through the articles from below and is cooled by the articles on 
its way upwards through the articles, and partly by warm water which flows 
downwards through the articles from above and is cooled by the articles on 
its way downwards through them. 
A cause contributing to the even temperature distributing during the 
cooling is that the articles then are exposed to cold medium from two 
directions simultaneously, viz. partly by cold gas mixture, cooled by the 
heat exchangers 32, which gas mixture flows upwards through the articles 
from below and is heated by the articles on its way upwards through them 
and partly by cold water, cooled by the heat exchanger 18, which water 
flows downwards through the articles from above and is heated by the 
articles on its way downwards through the them. 
Besides being applicable to sterilization the invention is also with 
advantage applicable to other kinds of heat treatments in order to kill 
micro-organisms, e.g. pasteurizing and tyndalizing.