Use of rice hull ash in steelmaking

Details Use of rice hull ash in steelmaking Use of rice hull ash in steelmaking

2002-08-27

2004-08-10

Andrews, Melvyn (Department: 1742)

Specialized metallurgical processes, compositions for use therei

Processes

Free metal or alloy reductant contains magnesium

C075S751000, C075S764000, C075S773000

Reexamination Certificate

active

06773486

ABSTRACT:

This invention relates to the steelmaking industry, and has to do particularly with the use of rice hull ash for certain purposes relating to steelmaking.
BACKGROUND OF THIS INVENTION
Rice hull ash, a by-product of the combustion of rice hull, is used in the steel industry to insulate liquid steel (temperature of liquid steel: 1560° C.).
Rice hull ash is composed of:
amorphous silica
85-95%
Crystalline silica
 5-10%
Carbon
 0-10%
Crystalline silica is a known health hazard.
Rice hull ash comes in a fine powder form, and a substantial portion thereof is respirable particles (<10 micron).
Typically, rice hull ash is used at temperatures exceeding 1500° C., well above the temperature (1350° C.) at which the amorphous silica changes into crystalline silica, mainly in the form of quartz and/or cristobolite
Pelletizing the powdered rice hull ash will alleviate the problem of respirable crystalline silica, but not the fact that crystalline silica has been created. In addition, the type of binder used to hold the dust in the pellet form, such as molasses, will generally decompose at steelmaking temperatures, or if sodium silicate is used it will flux the ash at a temperature of approximately 1150-1200° C. and therefore will create a molten mash with no insulating properties.
GENERAL DESCRIPTION OF THE INVENTION
An object of one aspect of this invention is to change the nature of the hazardous silica (crystalline form) by creating compounds like calcium silicate or calcium magnesium silicate, neither of which is hazardous at room temperature or steelmaking temperatures.
An object of another aspect of this invention relates to the pelletizing or granulating of the rice hull ash. By the process of pelletizing or granulating, there is no change in the porosity which is natural to rice hull ash, allowing the material to retain its insulating properties as well as its floatability.
More particularly, this invention proves a method of using rice hull ash in steelmaking, comprising the steps of:
blending the rice hull ash with one or more of i) lime, or ii) dolime, and with a mixture of water and molasses, thus
generating heat as the lime and water react to form lime hydroxide, which is a known binder, and
pelletizing the resulting blend, such that the heat generated by the lime/water reaction reduces the energy required for drying the pellets.


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