DE4012158A1 - Fluidised bed for thermal regeneration of used foundry sand - has synthetic resin binder removed by heat and uses regenerated sand heat to warm used sand entering the bed - Google Patents

Abstract

Thermal regeneration of used foundary sand bound by synthetic resin involves combustion of the resin in a fluidised bed. The waste gases loaded with injurious materials are burnt in a combustion chamber (3). The waste gases are conducted over heat exchangers (4) through the fluidised bed such that a thermal transfer is acheived between the burnt waste gases and the layers of fluidised bed sand. In this way the sand is heated to the required temp. for regeneration. The sand is continuously fed through an inlet (1) into the chamber. Before the heated and regenerated sand leaves the unit, it is fed past plate-like esp. ribbed heat exchanger surfaces. This flow of sand runs in the opposite direction to that of the sand which is to be heated. ADVANTAGE - The meeting of heated regenerated sand with that to be heated, reduces the energy input and hence enables the former heat exchanger (4) to be of smaller dimensions. Furthermore, the cooling unit for the regenerated sand can be similarly reduced in size.

Description

The invention relates to a method for thermal regeneration Resin-bonded foundry sands for reuse instead of new sand.

The invention further relates to a device for carrying out a such regeneration, appropriate facility.

Due to the progressive mechanization in the foundry industry, with ever increasing demands on the molding material systems come alongside the usual clay-bound molding materials to an increasing extent Resin-bound molding sand for use.

In contrast to the clay-bound molding materials, in which the Bindeton only partially binds during the casting process loses, the bindability of the synthetic resin binders goes after everyone The molding and casting process is irreversibly lost. A reuse Formation of such old molding materials therefore presupposes that they are not more bindable synthetic resin casings are separated from the grain of sand. For this purpose, the foundry sand is subjected to a thermal treatment and subjected to a temperature exceeding 500 ° C heated, burning the synthetic resin casings.

A problem of thermal regeneration is that in the exhaust gas contained pollutants in the form of carbon monoxide and unburned hydrocarbons.

Known methods solve this problem so that the plants ent are not operated at very high temperatures (approx. 850 ° C), or the exhaust gases are subjected to post-combustion. This either has a high energy consumption or a high one apparatus-related expenditure for the use of waste heat.

The invention aims to be economical, powerful To create procedures and the associated facility at which the starting product resin-bound foundry sand so is treated that he is like new sand without restrictions can be used, and the process exhaust the prescribed limits fall below values for pollutants.  

This task is solved by the old sand after a mechani destruction of the sand bulbs and a separation Metal parts of a fluidized bed apparatus located in the sand fed and to the temperature required for regeneration is heated.

Fig. 1 shows a longitudinal section through the Appara tur,

Fig. 2 is a sectional plan.

The sand is continuously passed through the filler opening 1 and brought into a fluidized bed state by blowing air. This can be done either through a porous and / or through bottom openings, or through pipes provided with holes. The height of the fluidized bed is determined by the height of the outlet edge.

By placing the fluid in the fluidized bed state (fluidized) on the one hand you achieve a flow behavior similar to one Liquid, on the other hand you get a very good warmth transition between the heat in the fluidized bed exchangers and the fluidized sand bed.

The pollutant-laden exhaust gases from the fluidized bed 2 (represented by a dash-dotted line in FIG. 1) are fed to a combustion chamber 3 , where they are heated to a temperature with the supply of heat, which ensures complete combustion of the pollutants contained in the flue gas.

The heated gas flows through heat exchangers 4 , which are located in the fluidized bed, and emits a large part of its heat content to the sand, as a result of which it is heated to the temperature of regeneration. The fluidized sand flows in countercurrent to the gases flowing in the heat exchangers. Built-in baffles 5 preventing individual grains of sand through the apparatus to quickly and thereby riert deficient regene (the direction of flow of the sand is shown in Fig. 1 and Fig. 2 indicated by arrowed solid lines). Before the heated and regenerated sand leaves the apparatus, it flows through a plate-shaped, sensibly finned heat exchanger 6 , where it moves in countercurrent to the sand to be heated and thereby gives off heat to it. This has the effect that the energy consumption is reduced, the heat exchanger 4 can be dimensioned smaller, and the downstream cooling devices, in which the regenerate is cooled to processing temperature, can be made smaller.

Claims (2)

1. A process for the thermal regeneration of resin-bound foundry sands by burning the synthetic resin casings adhering to the grains of sand in a fluidized bed apparatus, characterized in that the pollutant-laden exhaust gases from the fluidized bed are re-burned in a combustion chamber ( 3 ) with the supply of heat and the post-burned exhaust gases via heat exchangers ( 4 ) are passed through the fluidized bed, with heat transfer between the afterburned exhaust gas and sand fluidized bed, whereby the sand is heated to the temperature required for regeneration. 2. Device for performing the method according to claim 1, characterized in that the fluidized bed, heated and separated from synthetic resins sand past plate-shaped, in particular finned, heat exchange surfaces ( 6 ), with a heat transfer between hot and separated from synthetic resin sand and also used sand to be heated in the fluidized bed state.