Fluid sprinkling – spraying – and diffusing – With heating or cooling means for the system or system fluid
Reexamination Certificate
2000-06-14
2002-03-12
Silverman, Stanley S. (Department: 1731)
Fluid sprinkling, spraying, and diffusing
With heating or cooling means for the system or system fluid
C239S075000, C239S500000, C162S057000, C162S056000, C165S174000, C165S175000, C138S038000
Reexamination Certificate
active
06354514
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION
This application is a U.S. national phase of International application no. PCT/ FI99/00054 filed Jan. 28, 1999.
BACKGROUND AND SUMMARY OF THE INVENTION
The present invention relates to a method and apparatus for treating material having poor thermal conductivity. The method and apparatus according to the invention are especially well applicable to heating or cooling of medium-consistency fiber suspensions within wood-processing industry, or in more general terms to treatment of pulp. In particular, the method and apparatus according to the invention are applied to heating pulp having a consistency of 5-20%, preferably 6-16%, or to recovery of heat from the pulp. The method according to the invention is suitable for treating pulp for the bleaching process at a raised temperature, for example. Bleaching processes using high temperatures include for instance oxygen and peroxide bleaching. Naturally, the method and apparatus for the invention are also applicable to recovering heat from the pulp or cooling the pulp.
It is known from the prior art that vapor is used for the above-mentioned purposes, i.e. for heating the pulp for bleaching, whereby the pulp is heated directly with the vapor. A process like this operates in such a way that the pulp is supplied by means of a pump into a vapor feeding device, in which it is possible by feeding vapor directly into the pulp to raise the temperature of the pulp as desired. Subsequent to the mixing of vapor, the pulp is directed into a mixer, by means of which the temperature differences brought about in the mixing process are evened out and the desired bleaching chemical/s is/are mixed into the pulp. From the mixer, the pulp is directed further into a reactor tower, in which the bleaching process itself takes place. In peroxide bleaching, for example, the temperature in the tower is maintained at about 100° C. and the pressure in the lower part of the tower at about 10-8 bar and in the upper part of the tower at about 5-3 bar. The pulp is removed from the tower by means of a removing device into a blow tank, where the vapor still in the pulp is separated from the pulp to the upper part of the blow tank and from which the pulp is removed by means of a pump. The vapor separated to the upper part of the blow tank is guided to a condenser, in which the heat still in the vapor is recovered from the vapor, the result being condensation water.
However, the process described above involves some disadvantages.
Firstly, a large part of the vapor is condensated into the pulp, whereby the consistency of the pulp is no longer the same as it was when exiting from the pump. For example, raising the temperature by 20° C. with direct vapor makes the consistency fall about 0.5%, which in some cases causes obvious problems in the process.
Secondly, the pressure in the vapor feeding device has to be limited to about 9-10 bar, as (depending on the mill conditions) there might not be vapor at a higher pressure available, or at least not in such a way that it could be easily directed to the bleaching plant.
Thirdly, a large combination of a blow tank, a pump and a condenser is required for recovering heat and guiding the pulp to the following process stage.
Fourthly, the highest temperature of the condenser is 100° C., because the pressure is lowered to the outer air pressure.
Fifthly, the condensate water from the condenser is foul, because it contains residues of bleaching chemicals and reaction products of the bleaching.
Sixthly, the high-pressure vapor means costs to the cellulose pulp mill. If there were less need for high-pressure vapor, a corresponding amount of energy could be sold to power plants, for example.
It was believed that all the above-mentioned problems would be solved if it were possible to develop an indirect heat exchanger that would be suitable for use with consistent pulp. In other words, it would be a device that would efficiently be able to both heat and cool consistent pulp having a tendency to flow as a uniform fiber net, i.e. as a so called plug. These so called MC heat exchangers are described at least in FI patent applications 781789, 943001, 945783, 953064, 954185, 955007 as well as in international patent application PCT/FI96/00330 and FI patents 67584 and 78131.
FI patent application 781789 discloses a large number of apparatus arrangements exploiting and applying fluidization of consistent pulp. This 1970's publication is based on the fluidization theory, which has not been further developed until recently. Over the past two decades, it has been discovered that the theory forms a sound basis for further development, but at that time, i.e. at the end of the 1970's, it did not yet lead to any other practical applications than the so called MC pump. In other words, the various objects of use described were at a stage of elementary ideas and have required a great deal of further study in the case of each individual apparatus. Further investigations have, depending on the case, led to the development of the apparatus to a commercial product or the rejection of the idea as unfeasible. The operating idea of the indirect heat exchanger described in the above-mentioned patent application is that the casing of a tubular apparatus is encircled by heat exchange channels, the casing of the apparatus forming the heat exchange surface. Inside the tube, at the location of the heat exchange surfaces, there is a rotor, by means of which the fiber suspension flowing in the tube is fluidized. The idea is that an intense turbulence is able to circulate each pulp particle so dose to the heat exchange surface that the temperature thereof would be able to change in a way depending on whether it is desirable to recover heat from the pulp or to heat the pulp. It is not known to us whether this kind of apparatus has ever been experimented. In the light of contemporary knowledge, it is obvious that the apparatus does work if the flow rate in the tube is sufficiently slow. However, the idea has two weaknesses. Firstly, treating the pulp for a long time by means of a fluidizator inevitably affects the paper technical properties of the pulp, such as the strength or average length of the fibers. Secondly, fluidization consumes such a great deal of energy that a heat exchanger based on the operation of a mechanical fluidizator will never become a product that would be accepted by cellulose pulp mills.
The heat exchanger according to FI patent 78131 is relatively small in size and intended to be positioned for example before the bleaching tower or after it, either to heat pulp or to recover heat from it. The essential thing in the apparatus described in the patent is that on the inlet side of the heat exchange elements, there is a fluidizing device, by means of which the pulp is made flow through the relatively narrow passes of the compact heat exchanger. However, the fluidizator, which is a prerequisite for the operation of the exchanger, is in fact a problem, as it consumes a large amount of energy. Also, the structure is not applicable to a large bleaching tower, the diameter of which would be in the order of 5-10 meters, for example. It is not even imaginable that in such a large tank, the pulp could be fluidized over the whole cross section area thereof, as described in the FI patent. The energy consumption would be enormous, and on the other hand, several fluidizators would have to be used, whereby there would inevitably be problems with structures. An apparent problem is also that since the publication does not present any precise dimensioning instructions for the heat exchanger, the pulp in the heat exchange channels forms a fiber net and the pulp will not be able to discharge from the apparatus, or that it may not be possible to heat the pulp in the apparatus as desired.
The greatest disadvantage of both above-mentioned apparatus is the energy consumption due to the fluidizator that would have to be continuously used in the apparatus. To eliminate the problem, the operation of the apparatus should, at l
Henricson Kaj
Peltonen Kari
Andritz-Ahlstrom Oy
Halpern Mark
Nixon & Vanderhye P.C.
Silverman Stanley S.
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