Economical Ozone Treatment for Quality Fly Ash with Improved Performance (Case 1363)

Principal Investigators:

 

Robert Hurt, PhD, Professor
School of Engineering

 

Eric Suuberg, PhD, Professor
School of Engineering


Brown University

Providence, RI

 

Brief Description:

 

Coal combustion fly ash is a useful additive in concrete due to its pozzolanic property or ability to react with calcium in concrete mixes and contribute to the formation of the cementitious matrix.  Fly ash serves as a partial replacement for Portland cement, yielding cost savings as well as a variety of concrete property enhancements, which may include reduced permeability, improved workability, increased long-term strength, and reduced threat of long-term failure due to alkali-silica reactions.  A practical problem with this additive, recycling technology is the tendency of residual carbon in ash to interfere with the manufacturing process of concrete, thereby weakening the material and resulting in an inferior concrete.  Furthermore, fly ash samples show great variability in terms of absorptivity, an important property based on carbon in the ash, and thus a determinant of fly ash quality. 

 

Oxidation of carbon surfaces in the fly ash can address this carbon problem.  Existing wet or dry oxidative treatments have practical disadvantages including high costs, the need for extremely high temperatures, self-cementation, or loss of pozzolanic activity, while other commercial combustion-based methods remove the carbon altogether at modest temperatures, but at greater expense and are heavily polluting.  An oxidative treatment is needed that is capable of attacking carbon surfaces – to deactivate – in fly ash in the dry state and at ambient temperature.

 

The invention is a novel method for efficient, economical and homogenous treatment of carbon-containing fly ash, with optimum amounts of ozone and no oversaturation.  The fly ash can be derived from any fuel source.  This technology achieves a higher quality of uniform fly ash for improved performance as an additive in air-entrained concrete, pozzolanic admixture in Portland cement concrete, or related construction products.  Desired ozone consumption ranges for class C and class F fly ash of 30-300 g-ozone/kg-carbon and 10-100 g-ozone/kg-carbon, respectively, are achieved.  During treatment no portion of the fly ash results in ozone consumption of greater than 300 gram-ozone/kg-carbon for class C ashes or greater than 100 gram-ozone/kg-carbon for class F ashes. 

 

This innovative method involves continuous mixing of fly ash with ozone and alternating cycles of two minutes of ozone exposure followed by three minutes of purging with ozone-free air.  There is no opportunity for ozone overexposure of any part of the fly ash, and the process is cost effective in that it uses the minimum amount of ozone to achieve the desired affect.  A stirring element is designed to provide maximum radial, with little axial, mixing to minimize exposure time of any ash portion to fresh ozone at nozzle exits.  To expose the fly ash to ozone, three different contacting/mixing schemes to create agitation can be employed: a mechanical device such as a solids blender, screw conveyor or ash conditioner; an aerodynamic device that incorporates a fluid, spouted, or circulating fluid bed, or a transport reactor; or a pneumatic conveying system that meters and controls the ratio of ash to ozone.

 

The market is in construction products, with market niches in additives, cement, concrete and/or other related construction/building materials.  Applications are in the production of fly ash additives, and in the manufacture of cement, concrete, or related construction products.

 

Information:

 

US patent 6,890,507 is issued (05/10/2005)

Patent Information:
For Information, Contact:
Margaret Shabashevich,
Manager of Operations
Technology Ventures Office
Brown University
401-863-7499 TVO_Patents@brown.edu
Inventors:
Eric Suuberg
Robert Hurt
Yu-Ming Gao
Keywords:
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