Abstract: The heat exchanger tube comprises a cylindrical, smooth walled outer tube (1) of steel into which a profiled insert (2) of aluminium is inserted. The profiled insert is constituted by two half shells (3,4) which engage in one another at their longitudinal edges with groove-shaped recesses (7) and rib-like projections (8). Both half shells (3,4) carry longitudinally extending ribs (5) on their internal surface which are so aligned that each half shell with its ribs constitutes a profile which is open on one side.

Abstract: A track system for a track vehicle which has a crawler chain and a driving sprocket wheel. The chain has links each of which has a pin assembly with a bushing or one piece bolt the outer periphery of which at least is composed of a material consisting of Si.sub.3 N.sub.4 silicon nitride or a zirconium oxide with at most 15% of sintering additives. The driving sprocket wheel can have segments formed with the teeth and bolted to a disk, the segments being composed of a material consisting of Si.sub.3 N.sub.4 silicon nitride or zirconium oxide with less than 15% of sintering additives.

Abstract: A method is shown for the separation of catalyst-free working solution from working solution, containing noble-metal black, especially palladium black as catalyst, of the hydrogenation cycle of the so-called anthraquinone method for the production of hydrogen peroxide by filtration of the catalyst-containing working solution using filter candles. The filter candles are formed of an open-pore support body based on a carbon material or metallic or ceramic material with an average pore width in a range of 5 to 100 .mu.m and of a single-layer or multi-layer membrane of ceramic material with an average pore width in a range of at least about 1 up to 10 .mu.m located on the outside surface of the support body.

Abstract: An aqueous hydrogen peroxide extract which contains small amounts of dispersed working solution and a working solution which contains small amounts of dispersed aqueous hydrogen peroxide are collected in the extraction stage of the anthraquinone method for preparing hydrogen peroxide. In order to purify these solutions, the working solution is compounded with aqueous hydrogen peroxide or preferably with water and the hydrogen peroxide extract is compounded with an organic dissolving mixture, preferably a quinone dissolver, and the respective dispersed phase is separated out with the aid of coalescers in a separator unit. It is especially preferable to add 1-3% by volume water or 1-3% quinone dissolver before the coalescer stages and to use coalescers with a drop-enlarging design and filter layers consisting of thermally desized glass filament yarn.

Abstract: There is provided a continuous parallel current flow process for carrying out the catalytic hydrogenation with hydrogen or a hydrogen containing gas for the production of hydrogen peroxide in the anthraquinone process using palladium black suspended in the working solution at a temperature up to 100.degree. C. and a pressure up to 15 bar absolute in a reaction space constructed as a meandering tube system in which the hydrogenation is carried out in a loop reactor made of tubes of the same nominal diameter and arranged either vertically or horizontally and connected by curving tubes (tube elbows) at flow velocities in the tubes of more than 3 m/sec.

Abstract: Tetra substituted ureas wherein at least one substituent is an aryl group have proven very oxidation resistant in the anthraquinone process for making hydrogen peroxide. The urea nitrogen is directly attached to the aryl group. These ureas can be used as a single solvent or as a component of a mixture of solvents.

Abstract: A fire tube for a heating boiler comprising two metal tube halves each having a base portion and two leg portions projecting at an angle from the base portion, the tube halves being disposed relative to one another such that the terminating ends of the leg portions abut one another and are joined by welding. A plurality of substantially U-shaped elements extend longitudinally within the fire tube, each of the U-shaped elements having a base section and projecting leg sections, the base sections being welded to the base portion of one of the tube halves, the leg sections being parallel to one another and extending substantially across the width of the fire tube.

Abstract: A double-fired heating boiler includes first and second combustion chambers positioned within a common boiler water chamber and adapted to be fired respectively by gas or oil and by solid fuel. A collector for the combustion gases produced by the burning of the fluid and solid fuel is provided. Separate exhaust conduit systems having ancillary heat exchange surfaces are connected to the respective combustion chambers and to the collector.

Abstract: A boiler having a hot gas generator for burning liquid or gaseous fuels. The hot gas generator comprises a combustion chamber unit, into the combustion chamber of which the fuel and air for combustion are introduced and in which the combustion of the fuel takes place. The combustion gases are conveyed out of the combustion chamber into a water cooled boiler firebox. A compressor supplies the air for combustion into the combustion chamber unit. A flue gas conduit, which leads to the flue gas vent of the boiler, at its inlet end, which is connected with the boiler firebox, is connected with the air intake of the compressor of the hot gas generator for recirculating a regulatable amount of flue gases into the combustion chamber unit of the hot gas generator. The flue gas conduit offers a resistance to the flow of flue gas therein, which resistance is greater than the chimney draft force present in the flue gas vent of the boiler.