Compositions: coating or plastic – Coating or plastic compositions – Inorganic settable ingredient containing
Reexamination Certificate
1999-07-20
2002-01-01
Marcantoni, Paul (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Inorganic settable ingredient containing
C106SDIG001, C264S049000
Reexamination Certificate
active
06334895
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a system for the treatment of ashes or residues from the combustion of carbonaceous fuels, such as coal. The invention discloses both methods and apparatus to control various physical and chemical characteristics of combustion ash as they relate to cold bonding processes, and as they relate to the cured consolidated materials which result from these processes. Specifically, this invention relates to cured consolidated combustion ash materials which have been standardized for use as normal weight and light weight aggregate for use in structural and landfill applications.
The combustion of carbonaceous fuels for the production of electricity or process steam by the utility and industrial sectors is a major generator of combustion ash. Combustion technologies such as fluidized bed combustion (FBC) and pressurized fluid bed combustion (PFBC) are widely implemented. Apprehension about pollution from the smoke stack industries and utilities has led to the implementation of clean coal technologies that addresses flue gas contaminants, not only for particulate, but also gaseous emission, such as sulfur oxides. These flue gas desulfurization (FGD) technologies are widespread and cover a range of techniques including wet scrubbers or wet FGD; dry scrubber FGD (i.e., spray driers); sorbent injection technologies; and fluidized bed combustion (FBC) technologies each of which produce a particular type of ash as a by-product.
The development of re-use technologies for each of these ashes, as well as those that result from the combustion of carbonaceous fuels without FGD technologies, has been slow. The obstacles are both technical, as well as regulatory and legislative. One of the prominent technical issues is the inability to produce ash-based products which have certain required engineering properties or meet particular standardards in the industry.
There are a number of ashes, for example FBC ashes, which contain large amounts of free lime and other oxides, such as those of magnesium, iron, sodium and potassium, which heat and expand upon combination with water. These exothermic and expansive hydration reactions can be detrimental to the dimensional stability of the conditioned, consolidated, or compacted ash in either landfill disposal or in other re-use applications. FBC and FGD combustion ashes are examples of ashes which tend to exhibit expansion sufficient to limit their options for use and often cause difficulty in the construction of stable landfills as discussed in “Ash Management Options For AFBC”, A. E. Bland and C. E. Jones which is hereby incorporated by reference. An approach to dealing with the problem of expansion in oxide rich combustion ash is disclosed by U.S. Pat. Nos. 5,364,572; 5,100,473; 4,250,134; 4,344,796 and by “A New Approach To Hydration Of FBC Residues” by J. Blodin and E. J. Anthony. Each teaches that all the free lime or other oxides must be initially slaked or nearly completely converted to a non-expansive hydrate prior to further processing steps. However, several problems are associated with using sufficient water to slake or nearly completely convert oxides to the corresponding hydrates which relate to handling problems and reduced early strength development in the cured consolidated combustion ash materials.
Another primary concern related to the production of construction related materials from certain lime and sulfate containing ashes, such as FBC ashes, is the subsequent formation of the minerals such as calcium sulfo-aluminate hydrate (ettringite), calcium sulfate di-hydrate (gypsum), calcium silicate hydrates and calcium aluminate hydrates as disclosed in “Effect of Curing Conditions on the Geotechnical and Geochemical Properties of CFBC Ashes”, Proceedings of the 15th International Conference on Fluidized Bed Combustion, A. Bland, 1999 which is hereby incorporated by reference. The slow formation of these compounds has been linked to the observed expansion in FBC and other ashes, poor strength development in consolidated combustion ash materials and with the disintegration of cured consolidated materials. As cured consolidated combustion ash materials age, the formation of such minerals may continue and subsequently a portion of the pore volume within the material. The deposition of these minerals in the pores of the cured consolidated combustion ash material, left unchecked, may ultimately create enough force to crack the cured material adjacent to the pore. These micro-cracks may lead to a substantial loss of strength and abrasion resistance in the cured consolidated combustion ash material. A number of researchers have shown the benefit of soluble silicate addition to ashes containing free lime, such as FBC ashes. For example, as disclosed by U.S. Pat. Nos. 5,002,611 and 5,152,837 which focus on the addition of other ashes having soluble silicates to FBC ash. The soluble silicates in the ash react with the free lime in the FBC ash and form calcium silicates preferentially to the compound ettringite. This approach, however, has at least two problems associated with it. First, it is applicable to only certain ashes, and secondly it is costly because it requires additional steps related to procuring fly ash with a suitable amounts of soluble silicate and the additional steps of processing the fly ash with the FBC ash.
Another significant problem in the field is the increasing use of self cementing combustion ashes, such as FBC ash, which contain large amounts of free lime and other oxides to replace the use of costly cement and lime additives in external cold bonding processes as disclosed by U.S. Pat. Nos. 4,624,711; 5,512,837; and 5,766,338 to increase the strength of the cured consolidation combustion ash product. As the use of self cementing ashes in other processes has increased, there has been an increased and unresolved need for effective and economic processes for controlling the expansion in conditioned and consolidated combustion ash due to hydrate or mineral formation.
Another basic problem which exists with regard to processing FBC and other dry ash relates to the existing practice of combining the dry combustion ash, the water and other additives. Cured consolidation materials which result from existing apparatus and methods which combine dry combustion ash, water and other additives at low energy may not develop optimum strength, may have high permeability, or may also have increased amounts of expansion. The amount of energy used to combine these components can be quantified with reference to “Standard Method For Mechanical Mixing Of Hydraulic Cement Pastes and Mortars of Plastic Consistency”, ASTM C305-82 which is hereby incorporated by reference. In actual practice, this standard has been used to quantify the amount of energy with which wet flue gas desulferization sludge (FGD sludge) is processed as disclosed in U.S. Pat. No. 4,613,374. Blending FGD sludge in a pug mill for about 20 to about 40 seconds is a common commercial processing practice and has been equated to about eight seconds of mixing in a Hobart N-50 mixer set at speed level 1. U.S. Pat. Nos. 4,613,374 and 5,211,750 disclose that the manner of can be beneficial with regard to processing FGD sludge and perhaps other materials that have thixotropic properties. Materials, such as FBC and other dry ashes, are not thixotropic and yet an unexpected relationship exists with regard to how dry ash is combined with water and the enhancement of various characteristics of cured consolidated combustion ash materials.
Another problem related to combining combustion ash with water and other additives is the ability to disperse the water through out the combustion ash solids evenly at low water to solids ratios. However, water to combustion ash solids ratios which are above about 0.30 may not achieve the level of strength which may be achieved using identical types of combustion ash at water to combustion ash solids ratios less than about 0.30.
From the commercial manufacturing perspective there remain several significant probl
Marcantoni Paul
Santangelo Law Offices P.C.
The University of Wyoming Research Corporation
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