FI56867C - SAETTING THE ORGANIZATION FOR THE DEVELOPMENT OF A VAERMEYTOR TAECKTA AV ETT SMAELT SKIKT - Google Patents

Description

fBl advertisement publication rcnC7 jmBrg LBJ (”) UTLÄGGNINGSSKRIFT 5606 / C Patent granted 10 .'4 1030 V% ^ 7 Patent cteddelat v (5f) Kv.ik. * / Int.ci. * D 21 0 11/12 FINLAND — FINLAND ( 21) 782391 (22) Htkamispllvi - Aiwdicnlnitdig 03.08.78 (23) Alkupllvl - GHtl | h «t * d * i 03.08.78 (41) Tullut fulklMktl - Bllvlt oflfaitllf

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Patent and registration authorities Anaekan utltgd och utl. «Knft« i publkarad 31.12.79 (32) (33) (31) Privilege requested - B «gird prloritet (71) A. Ahlström Osakeyhtiö, Noormarkku, Suomi-Finland (Fl) ( 72) Jukka Sainiemi, Helsinki, Seppo Ruottu, Karhula, Finland-Finland (FI) (5H) Method and apparatus for cleaning thermal surfaces covered by molten bed - Sätt och anordning för ringörning av värmeytor täckta av ett smält skikt

The present invention relates to a method and apparatus for removing molten deposits from heating surfaces, intended in particular for use in waste liquor boilers in which the waste liquor of a cellulose broth is incinerated to recover heat and chemicals.

It is known that in the steam boiler, which is rich in inorganic broths containing salts melting at the combustion temperature, it is known that at the solidification temperature of the salts it is particularly difficult to keep the heating surfaces clean. The layer covered by the melt is tough and as such difficult to remove from the heat surfaces. In addition, as the flue gases asymptotically approach the solidification temperature of the melt, all the heating surfaces at the end of the boiler tend to be covered by a layer of melt under which a thick, solid layer of dirt accumulates. The thickness of the solid layer is determined by the according to the heat transfer properties and heat flux density of the ash. As the temperature difference T. - T .. approaches zero, the solid layer can become very thick and even completely block the flue gas ducts.

2 56867

Currently known equipment for cleaning wet surfaces are gas, steam and liquid scavengers as well as various mechanical shock and contact scavengers. What all of these have in common is that their cleaning effect is based directly on the shear stress caused to the dirt layer. The use of compressed gas, vapor or liquid causes the need for high power of the extractors as well as erosion problems. Impact absorbers, on the other hand, cause mechanical stresses on boiler structures and are quite poor in their efficiency when cleaning molten surfaces.

It has now surprisingly been found that the deposit accumulated on the heating surfaces can be removed by cooling the deposit so that the molten layer solidifies, whereby the deposit ruptures and detaches under the effect of the thermal stresses generated. Preferably, the cooling is provided by cold air which is blown so that the cooling effect of the air extends transversely over the heating surface. The detachment of the dirt layer, which has been converted to an easily detachable form by cooling, can be enhanced by simultaneous mechanical sooting.

The advantages of the proposed new sooting method compared to known methods are e.g. the following features: - surfaces are cleaned efficiently - sooting does not cause erosion - negligible power requirements - cheap equipment, as air from a combustion air fan can be used, for example

The invention will now be described in more detail with reference to the accompanying drawings, in which Figure 1 shows a vertical section of a waste liquor boiler to which the invention has been applied.

Fig. 2 shows a section of Fig. 1 along the line A-A, Fig. 3 shows an alternative embodiment and Fig. H shows a section of Fig. 3 along the line B-B.

In the waste liquor boiler shown in Figs. 1 and 2, reference numeral 1 denotes a combustion chamber into which combustible material and combustion air are fed in a manner not shown in more detail. The melt is separated from the flue gases by a separator 2 and flows along the sloping bottom 3 of the flue gas duct to the elbow k, from which it is removed. For heat recovery, the boiler has a plurality of adjacent vertical heating surfaces 5 »formed of parallel pipes, between which the flue gases flow into the outlet duct 6. Although most of the molten components in the flue gases are separated before the flue gases come into contact with the heat recovery device salts in the space that accumulate on heat surfaces. To clean the heating surfaces, transverse air supply pipes 7 * with several adjacent openings or nozzles 8 are arranged at their lower end, through which cooling air can be supplied to the spaces between the heating surfaces 9.

The openings or nozzles are arranged so that their cooling effect extends over the entire heating surface. The amount of air supplied is chosen so large that its cooling effect covers the entire heating surface and that the entire melt layer is solidified.

The embodiment shown in Figures 3 and k has air supply pipes 10 arranged perpendicular to the heating surfaces 5. By rotating the supply pipe alternately in opposite directions, a cooling effect extending over the heating surface is created.

It is clear that in the embodiment shown in Figures 1 and 2, the supply pipe 7 can be reciprocating. Each space 9 between the heating surfaces can have several supply pipes.

The method and device according to the invention are best suited for combustion plants in which the heat surfaces of the heat recovery devices are vertical, but it can also be used in other types of structures.

Example Cooling soot was practically tested in a prototype boiler where sulphate black liquor was burned. The dry matter capacity of the boiler was 0.3 kg / s (1.1 t / h) and the steam production was 1 kg / s (3.6 t / h). The steam produced was saturated, pressure 11 bar. After the melt separation section of the boiler, before the hanging, curtain-like heating surfaces, the flue gas temperature was about 1120 ... 11U0 ° K and the mass flow was 1.8 kg / s. The melting temperature of the 56867 h dust contained in the gases was measured to be 1070 ° K. The flue gas duct, with cross-sectional dimensions of 1200 mm / 1000 mm and a height of h meters, was divided by vertical heating surfaces into six sub-ducts, each of which received an equal flue gas flow. The distance between the heating surfaces was 200 mm. The temperature of the cooling air used was 300 ° K and the mass flow was 30 g / s, which was divided into six supply pipes, whereby effective sooting of the heating surfaces was achieved.

Claims (7)

5,56867 A method for removing a melt-covered deposit from the thermal surfaces of a heat recovery device of a combustion plant, characterized in that the molten layer is cooled to a solid state by an air jet applied to its surface so that the deposit breaks and is released. Method according to Claim 1, characterized in that the molten layer is cooled by low-pressure air from a combustion air blower. Device for carrying out the method according to claim 1 or 2, characterized in that it comprises nozzles (8) for the cooling line arranged close to the heating surfaces (5) formed of parallel pipes, located at the inlet end of the spaces (9) between the heating surfaces and arranged so that the cooling air extends transversely over the heating surfaces. Device according to Claim 3, characterized in that the nozzles (δ) are arranged in supply pipes (7) which extend transversely over the heating surfaces (5). Device according to Claim k, characterized in that the supply pipes (7) are arranged to reciprocate. Device according to Claim 3, characterized in that the nozzles (8) are arranged perpendicular to the supply pipe (10) opposite the heating surfaces (5). Device according to Claim 6, characterized in that the supply pipe (10) is arranged to rotate alternately in opposite directions.