NL8901071A - METHOD FOR MELTING INDUSTRIAL RESIDUES - Google Patents

Description

APPLICANT: Project Office for Industrial Waste e.g. (PBI) Hertogsingel 83 6211 NE MAASTRICHT AGENT: None

METHOD FOR MELTING INDUSTRIAL RESIDUES

The invention relates to a method for preparing a substance with industrially applicable properties by melting, to a certain extent, environmentally unfriendly substances in a first oven and draining the melt, optionally with the addition of other substances, and until to process a usable product.

STATE OF THE ART

A much-appreciated work-up to reuse environmentally unfriendly substances in a less unfriendly form is the melting of one or more of these substances and then reuse them in solid form, after possibly adding other substances.

An example of this is described in EU-0 014 338, in that non-damage fly ash per se is melted and, after adding additives, is tapped and processed into a powdery binder. Incidentally, this described method is not limited to fly ash.

Fly ash, as well as many other materials to be melted, supply, in addition to what is achieved with the melt, under heating to high temperatures, substances which escape from that melt or the melt to be formed, in volatile or dust-like form . These can sometimes be very environmentally unfriendly substances.

PURPOSE OF THE INVENTION

With the prior art described, the ultimate object, namely to render one or more substances "harmless" by melting and further processing, is in many cases only partly achieved. A substance or mixture of substances volatilized in the melt in some way is left over, which in itself can be (or may have) an even more environmentally unfriendly character than the original substance or substances.

According to the invention, substances which emanate from the first furnace are captured from the melt at a temperature in which they are in the solid phase and subsequently melted in a second furnace at a temperature lower than that of the first melt, drained and for a determined purpose or deposited in a suitable place, without the need for perpetual aftercare. This object will be different from that envisaged with the first melt.

The melting of a substance evaded from an oven is known per se, in particular the fly ash, originating from a (coal) incinerator.

The present invention is particularly directed to the melting of substances that elude from another melt, mainly in the gaseous phase and containing little or no ash from the initially melted or melted substance. With little or no is meant here a maximum amount of up to about 5%.

The invention is therefore to be regarded as an addition to that of, for example, EU-0 014 338.

Preferably, a substance is added to the melt which gives the mixture a glass-like character after draining and cooling. When depositing this glassy substance, the chance of leaching by water is greatly reduced.

DESCRIPTION OF THE INVENTION

The capture of all substances which have escaped from the first melt takes place in any case at a temperature at which volatiles are again in the solid phase. All conventional filters suitable for capturing the specific substance are suitable as filters. Examples are electro filters, cloth filters, cyclones and the like.

From these filters, the captured material is placed in a second melting furnace and heated in this furnace to just above their melting point, but below the temperature at which they volatilize. As a rule, this will be 200 ° C to 400 ° C lower than the temperature of the first oven.

In order to obtain a manageable melt, the use of additives will be necessary. If this is not to obtain a melt which has certain useful properties after tapping, then to give the tapped melt glass-like properties. As already mentioned, the leaching behavior upon deposition can be greatly reduced in this way.

A very obvious additive, for example, will be old glass, but other materials, even metals, will sometimes be suitable. Examples include hydroxide sludges, asbestos, limestone and sewage sludge.

Substances which lend themselves to be melted in the first furnace and processed into an industrially usable product, as well as the substances which escape them, are shown in the following table with the corresponding melting temperatures, without being limited to these substances:

First oven

Substance Addition Melting temperature AVI slag aluminum-containing waste + limestone approx. 1,500 ° C Blasting grit aluminum-containing

waste + limestone approx. 1,600 ° C Dredge spoil limestone approx. 1,500 ° C

Second oven

Substance Addition Melting temperature

Sublimate old glass, sludges containing silicon-containing substances, which are called above hydroxide

waste materials approximately 1,200 ° C

Hydroxide sludge old glass containing silicon

waste materials approximately 1,200 ° C

The invention is briefly described by choosing one of the substances from the above table:

Blasting grit with approximately 6% heavy metals is mixed with crushed limestone and possibly other additives, so that the composition of the mixture corresponds to that of a good cement and, optionally after preheating to 1,000 ° C, is fed in an electrically heated melting furnace at a temperature of 1,600 ° C. Approximately 80% of the more volatile metals, such as lead and zinc, sublimate and are collected in a suitable system together with the released melt ash.

The molten material is converted into slag by pouring into water or by (indirect) cooling with water-cooled rollers, after which the glass plate obtained therewith is broken, as described in the Dutch patent application EU-0 014 338. The fully glazed slag obtained used after grinding as an alkali slag cement.

The collected sublimated metals are mixed with siliceous residues or other additives such that the melting temperature is approximately 1,250 ° C. The mixture is then melted at about 1,250 ° C and the heavy metals hardly sublimate. The resulting melt with up to 5% heavy metals is cooled and converted into a slag. This slag is chemically inert and the heavy metals present in it are in the glass phase and do not leach. The slag can be used in low-value applications such as civil engineering fill-up material or aggregate in concrete or, if desired, be deposited without perpetual aftercare.

Claims (4)

Method for preparing a substance with industrially applicable properties by melting to some extent environmentally unsatisfactory substance or substances in a first oven and draining the melt, optionally with the addition of other substances, and until a usable product, characterized in that substances eluding from the melt of the first furnace are captured in known manner at a temperature at which those substances are in the solid phase and subsequently at a temperature lower than that of the first melt in a second oven melted, drained, or used for a specific purpose without the need for perpetual aftercare. 2. A method as claimed in Claim 1, characterized in that additives are added to the second melting additives, so that the melt has a glassy character after tapping and cooling and solidifying. Method according to claim 1 and 2, characterized in that waste glass or another waste material containing silicon (hydroxide sludges, asbestos, etc.) is added to the second oven as an additive. 4. A method for converting melt avoidants into environmentally friendly form or into industrially useful form, according to the description, the example and summarized in the claims.