Furnaces – Process – Treating fuel constituent or combustion product
Reexamination Certificate
2000-08-01
2001-06-26
Ferensic, Denise L. (Department: 3749)
Furnaces
Process
Treating fuel constituent or combustion product
C110S218000, C110S346000, C110S347000, C110S345000
Reexamination Certificate
active
06250235
ABSTRACT:
FIELD
The present invention relates to a method of fossil fuel combustion.
BACKGROUND
Acid rain is a problem throughout the world. Acid rain affects the environment by reducing air quality, rendering lakes acid and killing vegetation, particularly trees. It has been the subject of international dispute. Canada and the United States have argued over the production of acid rain. European countries are other antagonists.
In the main, acid rain stems from sulphur dioxide produced in smoke stacks. The sulphur dioxide typically originates from the sulphur containing fuel, for example coal. The sulphur dioxide is oxidized in the atmosphere to sulphur trioxide and the sulphur trioxide is dissolved to form sulphuric acid. The rain is thus made acidic. The oxides of nitrogen are also a factor in producing acid in the atmosphere. Millions of tons of oxides of nitrogen are fed to the atmosphere each year.
With the passage of international clean air acts, such as issued in the United States in 1990, the reduction of acid emissions has become a priority. Planners for electrical utilities in particular are developing strategies for reducing emissions of sulphur dioxide and nitrogen oxides in the production of electrical and thermal power. The majority of fossil fuel used in power production contains sulphur which produces sulphur dioxide and hydrogen sulphide during combustion.
In an effort to improve economics for electric power production from coal and production of concrete, as well as eliminate metal containing solid waste discharges to landfills, there is an increasing desire to recycle the ash combustion products of fossil fuel combustion, especially that related to char or coal combustion.
Naik et al (ref. 14) describes the beneficial effects of low carbon content coal ash on the performance of concrete. High calcium containing coal ash was successfully used to replace up to 50% of Portland cement in concretes with a variety of enhanced properties including improved durability such as cracking resistance.
Malhotra and Mehta (ref. 11) indicated that “Portland cement is the most energy-intensive component of a concrete mixture, whereas pozzolanic and cementitious by-products from thermal power production and metallurgical operations require little or no expenditure of energy. Therefore, as a cement substitute, typically from 20% to 60% cement replacement by mass, the use of such by-products in the cement and concrete industry can result in substantial energy savings. Concrete mixtures containing pozzolanic and cementitious materials exhibit superior durability to thermal cracking and aggressive chemicals. This explains the increasing worldwide trend toward utilization of pozzolanic and cementitious materials either in the form of blended portland cements or as direct additions to portland cement concrete during the mixing operation.” These authors classify ash products as follows:
Pozzolans—“A pozzolan is a siliceous or siliceous and aluminous material, which itself possesses little or no cementitious property but which will in finely divided form and in the presence of moisture, chemically react with calcium hydroxide at ordinary temperature to form compounds possessing cementing properties.”
Cementitious—“there are some finely divided and non-crystalline or poorly crystalline materials similar to pozzolans but containing sufficient calcium to form compounds which possess cementing properties after interaction with water. These materials are classified as cementitious.”
Ramme in U.S. Pat. No. 5,992,336 (ref. 15) indicated that “a principal reason for the lack of commercial value for coal ash is the presence of unburned carbon in the ash (page 1, lines 18-20). He describes “reburning” of coal ash as the only cost effective alternative to reducing carbon content of coal ash.
Frady et al (ref. 7) also describe a process for upgrading the pozzolanic value of ash using a fluidized bed ash reburning process to reduce its carbon content. They acknowledged a desire to promote the use of coal ash in concrete production. They indicated that without their ash reburning technology “ash carbon content was marginal at best and non-saleable to the concrete market at worst”. In addition they “recognized that changes in combustion conditions designed to meet low NOx regulations would lead to a further diminishment in fly ash quality. As quality was already marginal at several stations, further diminishment would essentially shut this fly ash out of the local concrete market, which was strong and growing.”
Gas desulphurization systems are known. The majority rely on simple basic compounds such as calcium carbonate, calcium oxide or calcium hydroxide, to react with the acidic sulphur containing species to produce non-volatile products such as calcium sulphite and calcium sulphate.
Conventional alkaline adsorbents such as calcium carbonate and calcium hydroxide undergo thermal decomposition to calcium oxide at high temperature, which results in the chemical reaction of calcium oxide with sulphur dioxide. However, the adsorbents suffer from a number of problems:
a) Fouling of exterior solid surfaces by calcium sulphite or calcium sulphate;
b) Absorption of heat due to evolution of carbon dioxide (from calcium carbonate) or steam (from calcium hydroxide) resulting in lower furnace temperatures, reduced rates of fossil fuel burning, reduction of furnace power output per unit of fuel input;
c) Desulphurization is restricted to the “post flame combustion region” which is associated with the “sintering” or “collapse” of calcium oxide crystals at temperatures of about 1200° C. resulting in a loss of their porosity. Loss of lime porosity is clearly identified by the Simons reference (see ref. 17) as highly detrimental to sulphur dioxide adsorption;
d) The desulphurization is restricted to the formation of calcium sulphate or calcium sulphite;
e) The lime/sulphur reaction which occurs in the gas-solid state, in the post combustion zone is slow, resulting in inadequate sulphur dioxide removal and inadequate residence times for sulphur dioxide removal. The lime sintering problem therefore requires precise narrow temperature region injection of the reagent e.g. <1200° C.; and
f) No byproduct ash recycling in a value-added form is possible. In fact the ash is contaminated with a calcium sulphate byproduct contaminated with unreacted internal lime which results in an undesirable landfill problem due to residue alkalinity.
This technique for desulphurization has not been accepted to any degree by the coal-fired power industry.
The prior art has described laboratory experiments with respect to catalytic destruction of NOx. For instance, Illán-Gómez et al. (ref. 10) investigated the catalytic destruction of NO on carbon surfaces in the presence of Cao. They indicated that well dispersed CaO formed upon pyrolysis of lignite coals was found to be efficient in both in-situ sulphur capture and NOx reduction. They described the effectiveness of calcium loaded carbon in NOx reduction in the presence of molecular oxygen O
2
. The catalytic role of calcium was found to be analogous to the role it has in carbon gasification, that of increasing the concentration of carbon-oxygen complexes on the carbon surface.
Aarna and Suuberg (ref. 1) demonstrated the enhancement of NO reduction on coal char by CO. They described reports concerning the catalysis of the following reaction by various types of surfaces including calcined limestone (CaO) and CaO used in sulphur retention:
NO+CO=½N
2
+CO
2
The steel industry has described techniques for desulphurization in molten alkaline CaO environments.
For instance, Ward (ref. 20) summarized conditions for optimum desulphurization via oxide melts:
a) High CaO content;
b) Low temperature;
c) A fluid slag this is promoted by CaF
2
additions and avoiding excessively high slag acidities or operation below the melting point of the slag;
d) CaF
2
additions—these not only increase fluidity, but also increase the fundamental rate of the desulphurization reaction; and
e) Sti
Oehr Klaus H.
Yao Felix Z.
Ferensic Denise L.
Global New Energy Technology Corporation
Hall Priddy Myers & Vande Sande
Rinehart K. B.
LandOfFree
Method and product for improved fossil fuel combustion does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and product for improved fossil fuel combustion, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and product for improved fossil fuel combustion will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2509528