Title:
Apparatus for heating and controlling the temperature in a continuously operating digester
United States Patent 2414062


Abstract:
The present invention relates to an apparatus for heating and for controlling the temperature of the contents of a continuously operating digester for digestion of fibrous material, of the type which is provided at one end with a device for feeding raw material into the digester, and at its...



Inventors:
Carl, Richter Johan Christoffer
Application Number:
US60769645A
Publication Date:
01/07/1947
Filing Date:
07/30/1945
Assignee:
KAMYR AB
Primary Class:
Other Classes:
162/249, 165/61
International Classes:
D21C7/12
View Patent Images:



Other References:
None
Description:

The present invention relates to an apparatus for heating and for controlling the temperature of the contents of a continuously operating digester for digestion of fibrous material, of the type which is provided at one end with a device for feeding raw material into the digester, and at its other end with a device for discharging the digested product, and through which digester the contents thereof, that is to say, the material charged into the digester, and the digestion liquor, thus move continuously from the feeding end to the discharge end. The contents of the digester may, but need not necessarily, be maintained at a pressure which exceeds the vaporization pressure of the digestion liquor at the maximum temperature prevailing in the digester.

It is the purpose of the present invention to provide an apparatus which renders it possible easily to attain and maintain the desired temperature or temperatures at desired points or in predetermined zones between the feeding end and the discharge end of the digester, in such manner that at such points or zones the temperature becomes as uniform as possible over the entire cross section of the digester.

According to the present invention there are connected to the digester, at a point between the feeding end and the discharge end thereof, or at several such points, two or more circulation conduits located outside the digester, in such manner that the outlet or outlets from the digester of each circulation conduit, which outlet or outlets are suitably covered by a sieve provided in the wall of the digester, and the inlet or inlets into the digester of each circulation conduit are positioned substantially diametrically opposite to one another. The outlets and inlets of all circulation conduits are located in one and the same transverse plane through the digester, or substantially in such a plane, and the several circulation conduits are displaced, as far as their outlets and inlets are concerned, relatively to one another around the circumference of the digester, preferably at an angular distance corresponding to 3600 divided by the number of circulation conduits, that is to say, in such manner that the outlets as well as the inlets are distributed at preferably equal angular distances from one another around the circumference of the digester. The circulation conduits are connected with a pump and with a heat exchanger or the like located outside the digester, by means of a reversing valve of such construction that by means of said valve any of the circulation conduits may be connected to the pump and to the heat exchanger.

By allowing liquor to circulate alternately through the several circulation conduits at suitable intervals of time, and by supplying to the liquor or removing from the same the necessary amount of heat, the desired temperature control, that is, heating or cooling, may easily be effected in the digester, and by alternately introducing the circulating liquor from various points of the circumference, thus causing it to flow in various directions through the digester transversely thereof, an as uniform heating or cooling as possible is obtained over the entire cross section of the digester. The supply of the required amount of heat to the circulating liquor may be effected either directly, as for instance by introducing fresh steam into the liquor, or indirectly through the heat exchanger, and by means of the latter it is also possible to remove heat from the circulating liquor and thus from the digester.

The accompanying drawing illustrates by way of example and schematically an apparatus according to the present invention. Fig. 1 is a schematic showing of the apparatus with a portion of the digester in axial section, and Fig. 2 shows schematically the apparatus with the digester in cross section.

The circulating liquor is drawn through an outlet from the digester covered by a sieve I by a circulation pump 2 which pumps it through a heat exchanger 3 back to the digester through an inlet 4, or several inlets, arranged diametrically opposite the sieve I. The latter has suitably a peripheral extension of 1200, since in such case the circulation liquor is distributed in the best possible manner over the entire cross section of the digester, as indicated by the arrows in Fig. 2.

The digester is further provided with a similar sieve 5 and an outlet diametrically opposite to the sieve I, and with an inlet 6 diametrically opposite the inlet 4. By a simple reversal of the direction of flow by means of the slide 7 of a reversing valve, such reversal being indicated by the dotted lines in the drawing, the required equalization of the temperature over the cross section of the digester may be easily effected.

In the position of the slide 7 of the valve that is illustrated with full drawn lines in Figs. 1 and 2, the pump 2 draws the circulating liquor from the digester through the sieve I and forces it through the heat exchanger 3 to the inlet or inlets 4. If the slide 7 is moved to the position shown with dotted lines, then the pump 2 draws the circulating liquor through the sieve 5 and forces it through the heat exchanger 3 to the inlet or inlets 6. It is of course possible to use three sieves, each having a peripheral extension of 1200, and a, corresponding number of inlets, but the arrangement above described using two sieves I and 5 has been found efficient for practical purposes.

In addition to supplying heat by the aid of a heat exchanger, as above described, it is also possible by means of a heat exchanger in a similar circulation system at another stage of the digestion, for instance at a further point on the path of travel of the mass through the digester, to remove heat in order to lower the temperature within a certain limited zone.

In addition to effecting control Of the temperature by supplying or removing heat, the apparatus according to the invention may, of course, be utilized for introducing into the digester, simultaneously or separately, the chemicals that are required for the digestion, such as acid, alkali, S02, and so forth. It is also possible by means of the arrangement to remove, for intance, SO2 from the digester, by lowering the pressure of the circulating liquor outside the digester in order to partially free the liquor from SOS, after which the liquor is returned to the circulation system.

It will be understood that the several circulation conduits should preferably lie as nearly as possible in one and the same plane as far as their inlets into and outlets, from the digester are concerned. Usually, however, digesters used for continuous digestion have a considerable length such as twenty meters or more, between the feeding end and the discharge end, and in view hereof it is, of course, of less importance if the inlets and outlets of the several circulation con. duits lie at a distance of, say, one meter fron one another in the longitudinal direction of thi digester.

I claim: 1. In an apparatus for heating and controlling the temperature in a continuously operating digester for digesting fibrous material, the combination of means for charging raw material into the digester at one end thereof, means for discharging digested product from the digester at the other end thereof, at least two circulation conduits located outside the digester and connected to the digester at a point intermediate the feeding end and the discharge'end thereof, each circulation conduit having its outlet from the digester and its inlet into the digester positioned substantially diametrically opposite to one another, the outlets and inlets of all circulation conduits being located substantially in one and the same transverse plane through the digester, the outlets and the inlets of the several circulation conduits being respectively spaced relatively to one another around the circumference of said digester, a pump, a heat exchanger, and a reversing valve connecting said pump and said heat exchanger to said circulation conduits in such manner that said conduits may be selectively connected to said pump and said heat exchanger by means of said reversing valve.

2. An apparatus as defined in claim 1, wherein the outlet from the digester of each circulation conduit has a peripheral extension of 1200 along the circumferencpef the digester.

3. An apparatus as defined in claim 1, wherein the outlet from the digester of each circulation conduit is covered by a sieve in the wall of the digester.

4. An apparatus as defined in claim 1, wherein S35 the outlets from the digester and the inlets into S the digester of the several circulation conduits S are respectively spaced at equal angular distances S from one another around the circumference of 1 the digester.

S40 JOHAN CHRISTOFFER FREDRIK CARL RICHTER.