A METHOD OF RECIRCULATING FINE WASTE PRODUCTS

WIPO Patent Application WO/1992/007964

A1

In ore based steel making, the dust and sludge from the blast furnace and converters is mixed and the mixture is added to the stream of converter slag when the slag is poured into a ladle. The stream of slag draws the mixture down into the slag. Zinc is collected from the fumes and when the resulting slag has solidified, it is crushed and a major part of it is recycled to the blast furnace.

JP2000355711	TREATMENT OF SLAG
JP57051142	PREPARATION OF SLAG FIBER
JP52129671	IMPROVEMENT IN PROPERTIES OF SLAG

Eriksson
Lars
Erik

PCT/SE1991/000728

May 14, 1992

October 30, 1991

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SSAB TUNNPLÅT AB ERIKSSON
Lars
Erik

C21B3/06; C21B5/00; C22B7/02; C22B7/04; (IPC1-7): C21B5/00; C22B7/02

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CLAIMS

1.

A method of recirculating fine waste products of the iron and steel making processes c h a r a c t e r i z e d in that said products are mixed f with liquid slag to smelt therein, the resulting slag is 5 then solidified and crushed, and at least a part of the crushed slag is added to a blast furnace charge. A method according to claim 1, c h a r a c t e r i z e d in that said waste products are added to the slag adjacent the stream of slag when the slag 10 is poured into a vessel such that the stream of slag draws the waste products into the slag. A method according to claim 1 or 2, c h a r a c t e r i z e d in that the waste products contain zinc, and zinc is separated from the exhaust fumes. 15 4 A method according to any one of the preceding claims, c h a r a c t e r i z e d in that said waste products is a mixture of sludge and dust. 5 A method according to any one of the preceding claims, c h a r a c t e r i z e d in that a major part of the 20 crushed resulting slag is utilized as a blast furnace charge additive. 6 A method according to any one of the preceding claims c h a r a c t e r i z e d in that said waste products contain sludge and/or dust from the blast furnace and from 25 converters. 7 A method according to any one of the preceding claims c h a r a c t e r i z e d in that the fines is removed from the crushed resulting slag and recirculated by being added to the fine waste products. *& 30.

2.

_• ft.

A METHOD OF RECIRCULATING FINE WASTE PRODUCTS This invention relates to a method of recirculating fine waste products of the iron and steel making processes. In ore based iron and steel making, dust and sludge are collected at various places. Dust as well as sludge is 5 usually collected from the cleaning of the blast furnace top gas and from the LD converter gas. There are also other filters that collect dust. The fines is also removed from the slag formers for the blast furnace since the fines cannot be allowed in the charge. -0 US 4711662 A describes a way of mixing dust and sludge with liquid metallurgical slag by first making lumps of the dust and sludge and then adding the lumps to the liquid slag. The resulting slag is not recirculated but it is used as a material for civil engineering works. ¹⁵ DE 3906869 C describes a method of blowing zinc containing dust into a liquid slag. Nitrogen is used as a bearer gas and the evaporated zinc is recovered. A similar method is also described in JP 59153848. The resulting slag is not recirculated. - ^Q It is objects of the invention to recover iron from the waste products, to reduce the amount of slag formers needed and to reduce the amount of slag and fine waste products that has to be dumped or disposed of in any other way. According to the invention, the various fine waste -~ products are mixed with liquid slag to smelt therein. The solidified slag is then crushed and a major part of the crushed slag is recycled by being added to a blast furnace charge.

A test has been carried out in which the fine waste ~ ~ products from ore-based steel making were mixed, that is both sludge and dust from the blast furnace and from the converters. The water content of the mixture was 8-9 weight %

Liquid converter slag from a LD converter was poured into a ladle and the mixture was poured against the stream of slag -~ so that the stream drew the fine waste mixture into the liquid. About 20 weight % mixture was added to the liquid slag. The reaction was violent and the mixing was effective. When the resulting slag had solidified, it was crushed. Its

analysis proved that it could be added to the charge of a blast furnace. Its Fe content was about 5 % higher than the Fe content in the original slag and its zinc content was low. The carbon of the blast furnace dust and sludge had reduced the zinc oxide to metallic zinc which had evaporated as a white smoke.

In production, the evaporated zinc can be collected from the exhaust fumes. When crushing the final slag, the fine fraction (-5 mm) must be removed before the slag can be added to the blast furnace charge. This fine fraction can be added to the fine waste mixture and recycled.

The invention is particulary suitable for processes in which the blast furnace is charged with pelletized ore.

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