Abstract: In a cooling surface cladding for polygonal chambers of steam generators with a hopper-shaped floor and fired on the circulating fluidised bed principle, which consists partially of substantially vertical finned tubes extending in the manner of walls between manifolds and converging curves in the floor region to form a hopper, two opposite finned tube walls (1) in the hopper region, viewed from top to bottom, first form a hopper wall (1') inclined from the vertical over their entire width and then form at least one vertical hopper wall (1") of decreasing width and with partially oblique manifolds (2). In the region of the hopper, viewed from top to bottom, the adjacent tube wall (3) and the tube wall (3') opposite it form first a vertical hopper wall of diminishing width and with oblique manifolds (4) and then an inclined side wall (3") of the hopper of constantly reducing width.

Abstract: To recover the sodium-sulphur compounds following sodium-based pulp processing, e.g. the ASAM process or basic or acidic sodium sulphite processes, the waste liquor is burnt in a lye burning vat (1) with liquid slag extraction and the exhaust gases are subjected to multi-stage purification with dry fly-ash recovery and the gaseous sulphur compounds are also separated in a multi-stage washing process. The water-soluble components of the fly-ash are taken to the waste liquor to be burnt and thus the sulphur to be recovered in the slag is increased. The slag is dissolved in water and the dissolved sodium compounds are converted by multi-stage carbonisation with a part of the purified flue gas into sodium bicarbonate and H.sub.2 S. The H.sub.2 S is burnt and finally converted into sodium sulphite so that the desired lye for pulping cellulose can be made up from sodium sulphite and carbonate.

Abstract: A process is disclosed for extracting pure, coarse-grain silicic acid crystals from silicic acid-containing spent lye in cellulose production, comprising adding coarse-grain silicic acid to alkalized spent lye, lowering the pH of the alkalized spent lye to about 9 such that a sediment is formed, separating the sediment formed into coarse grain and fine grain silicic acid with little lignin and lignin-containing spent lye free from silicic acid, and separating the coarse grain and fine grain silicic acid with little lignin into course grain silicic acid and lignin. At least part of the course grain silicic acid separated is fed back to the alkalinized spent lye to be desilicified.

Abstract: A method for incinerating excess sludge from biological waste water treatment plants, in particular sludges arising from the manufacture of paper or paper pulp, preferably using the magnesium fusion process. Before incineration, the excess sludge is neutralized with the same base as used in the paper pulp process and the dust entrained by the combustion gas is precipitated to recover the base.

Abstract: The present invention is directed to a process for preventing the formation of dioxin and/or furan during combustion of composite combustible materials in a combustion chamber. The process includes passing the generated combustion gas in a flow from the combustion chamber to a dedusting device, cooled and purified while maintaining the SO.sub.3 content in the combustion gas flow from about 7 to about 500 mg/m.sup.3 and at a temperature of from about 300 .degree. to about 800.degree. C., The process allows at least surface regions of particles of meal dusts contained in the combustion gas to be converted to sulfates and thereby prevent formation of dioxins and furan. The invention also includes a steam generator for carrying out the process whose steel structures coming into contact with the combustion gases are either alloyed or coated with tungsten and/or vanadium on the combustion-gas side.

Abstract: In a two-stage activation plant, part of the activated sludge (sludge circuit (1)) from the first stage (11) is transferred to the second stage (12) and part of the activated sludge (sludge circuit (2)) from the second stage (12) is transferred to the first stage (11), so that mixed biocenoses are formed in both stages (11 and 12). The biomass to be denitrified from the first stage is transferred to the second stage by the sludge circuit (1) and the biomass to be nitrified from the second stage is transferred to the first stage by the sludge circuit (2), so that not only carbon compounds are decomposed but nitrogen compounds may be removed by nitrification and denitrification in both stages (11 and 12).

Abstract: A rotating tube heat treatment installation, for example a rotating tubular kiln for the thermal splitting of MgSO.sub.3, or a slag cooler for the separation of salts and aluminum, comprises as the main replaceable component, a rotating tube (1) which is surrounded by a tubular jacket (2) and separated therefrom by a gap. The tubular jacket (2) is linked to the rotating tube (1) by means of a carrier system, and has drive (8) and possible bearing races and bandings (9) mounted externally. The connections (3, 4) for the heat exchange fluid are disposed at its ends, and thermal insulation, in particular light insulation (7), is fitted internally. In this way the rotating tube, which is exposed to corrosion and thermal stresses, is simplified structurally and can be readily replaced.