This invention relates to an arrangement for heating material in a conveying pipe. The material consists preferably of fibre material in the form of cellulose pulp, and the heating medium is steam.

In a cellulose process it is necessary in many places to heat the pulp, for example in order to cause different chemical reactions and treatments to start and to continue. This applies, for example, in many bleaching steps. In order to ensure this heating, steam of different pressures is used, depending on the pressure level required by the process in the installation in question.

The heating of the pulp with steam preferably takes place in a pulp conveying pipe to the treatment step in question. The pulp concentration can be 3-20% and preferably 5-15%. Hereby a relatively rapid and uniform heating can be achieved. The steam normally is supplied through one or several steam pipes connected to the pulp pipe. Such so-called steam extension pipes to the pipe system can be designed in different ways, whereby the result concerning temperature increase of the pulp can vary and the functioning of subsequent machines will be more or less good.

In earlier used systems/arrangements problems have often arisen with large steam bubbles developing on the inside of the pulp pipe. When these steam bubbles condense rapidly, condensate bangs occur which cause harmful cavitations in the pipe system and surrounding components. It is difficult, furthermore, to achieve an entirely uniform temperature profile in the pulp. It is certainly possible to improve the temperature profile by inserting the steam pipes into the pulp pipe, but this implies very much deteriorated flow in the pulp pipe and also difficulties in cleaning the pulp pipe and steam pipes in cases of plugging.

The aforesaid problems are solved by the present invention. Due to it, the steam heating can take place effectively and uniformly in that the steam is exposed to a large volume/surface of the passing pulp flow. The steam, furthermore, is supplied without any condensate bangs and

without objecting the pulp flow. The arrangement according to the invention, besides, is designed so that it can be cleaned easily when plugging of pulp occurs.

The characterizing features of the invention are apparent from the claims.

The invention is described in greater detail in the following, with reference to the accompanying drawings, in which:

Fig. 1 is a lateral view of the arrangement according to the invention;

Fig. 2 is a cross-section of the conveying pipe; Fig. 3 shows a detail according to the section III-III in Fig. 1;

Fig. 4 shows an installation of the arrangment according to the invention.

In Fig. 1 a portion of a conveying pipe 1 for pulp is shown. To the pipe a number of fittings 2 are attached, prefer¬ ably by welding. The fittings preferably have a semicircular cross-section and are arranged in a helical curve on the conveying pipe 1. The fittings form an angle of between 15 and 75 degrees, preferably 30 to 60 degrees, with the longitudinal direction of the conveying pipe. The number of fittings and the angles thereof are adapted so that the fittings together extend about the entire circumference of the conveying pipe. According to the embodiment shown, the fittings are four in number and the angle is about 45 degrees.

In the wall of the conveying pipe a plurality of small inlet holes 3 for the steam are arranged in each fitting 2. These holes are located along the length of the fitting. The holes 3 are formed so as to widen toward the inside of the conveying pipe 1. The holes preferably have cone shape, with a cone angle of 75-120 degrees. The hole size can be, for example, about 10 mm in the narrowest portion. Alternatively, the holes can be arranged obliquely inward in the flow direction of the pulp.

A steam pipe 4 for the supply of steam is connected to the end of the fittings located up-stream, counted in the flow direction of the pulp. To the other end of the fittings 2,

cleaning pipes 5 are connected which are closed when the arrangement is in operation.

The steam supplied through the steam pipes 4 is distributed along the fittings 2 and flows into the conveying pipe 1 through the inlet holes 3. Due to the configuration of the arrangement, the steam is exposed against the circumference of the entire pulp flow, and at the same time the steam supply is distributed in the flow direction of the pulp. This implies, that the temperature of the pulp can be increased on a short distance of the conveying pipe, and at the same time the small inlet holes 3 prevent the development of large steam bubbles and resulting detrimental cavitationε. The heating has a uniform temperature profile, and the pulp flow is not objected.

Due to the conical shape of the holes, with inwardly increasing diameter, the steam jets will reach the center of the conveying pipe and the risk of plugging with pulp is eliminated to the greatest possible extent. At a possible pressure drop in the steam supply, the pulp tends to pierce out through the holes 3. The shape of the holes renders it difficult for the pulp to get out through the holes. If holes and fittings yet are plugged, cleaning can take place simply by blowing steam through the cleaning pipes 5.

The installation shown in Fig. 4 comprises a conveying pipe 1 where the steam pipes 4 are connected to a steam supply pipe 6. The cleaning pipes 5 are connected to a cyclone 7 for separating fibres from the steam. In the cleaning pipes 5, stop valves 8 are located. The pulp is heated, as described above, by steam supply via the steam pipes 4. If, after all, pulp should penetrate out through the inlet holes 3 to the fittings 2, cleaning can be effected by opening one or several of the valves 8. The supplied steam then flows through the corresponding fitting 2 out through the cleaning pipe 5 to the cyclone 7. The pulp thereby follows along, and the inlet holes 3 are exposed. In the cyclone the pulp then is separated from the steam. The cyclone 7, thus, starts to operate only at the cleaning of the arrangement by blowing.

This installation renders it easily possible to clean the arrangment even when it is in operation. The stop valves 8 for example, can be opened one at a time for cleaning as soon as there is a tendency of plugging, thereby reducing inter¬ ruption of the operation to the smallest possible extent.

The invention is not restricted to the embodiment shown, but can be varied within the scope of the invention idea.