Control of dust

Details Control of dust Control of dust

2002-10-07

2004-09-14

Smith, Duane S. (Department: 1724)

Fuel and related compositions

With antidusting additive

C252S088100

Reexamination Certificate

active

06790245

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to short term residual dust suppression, and more particularly to such suppression by application of a dust suppressant composition to a dust-bearing material.
2. Description of the Prior Art
Dust formation from a variety of sources has been a continuing cause of environmental and health concerns. Particular attention has been paid to the dust developed from the handling of coal, but such sources also include, for example, petroleum coke, recycled glass dust, bauxite, and mined minerals such as iron ore, aluminum ore, copper ore, and limestone. Thus, while this specification may refer at times to coal, it should be understood that this discussion is applicable to numerous other dust sources as well.
Various industries affected by such dust formation have engaged in many efforts to avoid or to alleviate the problem of dust formation that results during handling, conveyance, transportation and even storage of coal and the other dust sources. Typically, such efforts involve the use of water incorporated into a chemical dust suppressant that is applied to the coal or other dust source. Although the categories of dust suppressants have overlapped to some extent in that certain types of suppressants may be reformulated to be applied through a system designed for another type, conventionally a suppressant may fall into the category of a short term dust suppressant, which may be a wet suppressant or a foam suppressant, or a long term residual dust control suppressant. Short term dust suppressants function by coating the source and dust with water. Thus, such suppressants lose their effectiveness upon evaporation of the water. Moreover, their effectiveness generally does not persist beyond one to two impact points; that is, points at which dust is generated during handling or movement of the coal or other source. Examples of wet and foam suppressants are discussed in U.S. Pat. No. 4,737,305 to Dohner, U.S. Pat. No. 4,836,945 to Kestner, U.S. Pat. No. 4,971,720 to Roe, and U.S. Pat. No. 5,409,626 to Muth, and in Surfactants and Interfacial Phenomena, 2d Edition, by Milton J. Rosen, Wiley Interscience Publications (1989), all of which are incorporated herein by reference. Conventionally, long term residual dust suppressants control dust by means of the formation of a polymer or binder film over the dust source and thereby persist even after evaporation of water in the suppressant. Such suppressant compositions typically contain a binder composition such as lignosulfonate and a polymeric dispersant. For example, U.S. Pat. No. 5,436,429 to Bennett describes such a long term dust suppressant and mentions in apssing that certain sugar by-products may be as a binder or tackifier. However, binders such as lignosulfonates and polymeric binders or dispersants are costly and create waste disposal problems.
Wet suppression is based on what is called “wet technology”. This suppression can be as simple as spraying large amounts of water on the coal (or other source) as it travels along a conveyor or drops to a storage pile or transfer bin. However, although water is an effective dust suppressant, its use involves a number of drawbacks, such as adding weight to the coal or other source (which can result in higher costs for transporting the source), development of substantial vapor pressure when the coal or other source is heated or burned, and the absorption and thus wasting of substantial energy as the water vaporizes when the coal or other source is heated or burned.
As a result, surfactants or “wetters” often are added to the water to reduce the amount of the water needed for dust suppression. Conventional wetters include nonionic epoxide (e.g., ethylene oxide or propylene oxide) derived block co-polymers, alcohols of from about eight to about sixteen carbons ethoxylated with from about four to about ten moles of ethylene oxide (wherein the alcohol may be an aromatic such as alkyl phenol, preferably nonylphenol, which can be ethoxylated with, for example, ten moles ethylene oxide), and branched nonionic surfactants such as branched alpha sulfo ester salts comprising an acid chain and an alcohol chain of from about six to about twelve carbons each, and highly branched alcohol sulfate and alcohol ether sulfate detergents. Generally, the wetter is added to the water in a weight proportion of from about 0.2 to about 5 parts of the wetter to about one thousand parts of water. As this concentration, the wetter acts at the interface between the coal (or other source) and the water to increase the affinity of the coal and water, thereby decreasing the amount of water needed to soak the coal as well as decreasing the time required for the water to penetrate the coal stream.
Typically, such wet technology is employed to suppress dust Generated at transfer points, areas where the coal falls freely from one point to another (free falls) such as loading points where the coal is dropped into a vessel for transportation, impact points where the coal strikes a surface, and storage areas. The water is applied at the point of dust generation and is applied to the air-borne dust as well as to the source of the dust. If the amount of water added to the coal is sufficiently great, the coal can be prevented from dusting significantly on impact. For such benefits, the water should be added in an amount sufficient to result in a proportion of one to three parts by weight water per one hundred parts by weight wetted coal. However, because the suppressant is effective only through one or two impact points where dust could be generated, repeated applications are necessary, thereby increasing the water content of the wetted coal quickly to seven or eight percent.
Foam suppressants are applied to form a blanket over the coal or other source to capture and smother dust. Bubbles in the foam suppressant catch the dust particles and so the foam suppressant is effective only until the bubbles break or the layer of foam becomes discontinuous. The foam suppressant is formed by addition of a roamer to water. Conventional foamers include alpha-olefin sulfonates, alkylphenyl sulfonates with long alkyl chains (e.g., eight to sixteen carbons) such as sodium lauryl benzene sulfonate, alcohol sulfates, alcohol ether sulfates, alpha sulfo esters and mixtures of such compounds. Under standard conditions, from about one to about twenty parts by weight roamer is added to about one thousand parts by weight water. The resulting foam has about five to ten percent of the density of the water used in wet technology and so much less water is needed for a foam to provide the same volume of applied dust suppressant as the wet suppressant. Thus, the foam suppressant can be added to the coal in a proportion such that the wetted coal contains 0.2 to 0.5 parts by weight added water per one hundred parts by weight wetted coal. However, as with the wet suppressant, the foam suppressant is effective only through one or two impact points where dust could be generated. Thus, repeated applications are necessary and the water content of the wetted coal increases quickly to several percent.
As with wet suppressants, the foam suppressants are employed to suppress dust Generated at impact or transfer points, areas where the coal falls freely from one point to another (free falls) such as loading points where the coal is dropped into a vessel for transportation, impact points where the coal strikes a surface, and storage areas. The foam is applied as a curtain or barrier to capture Generated dust. The foam applicator nozzles are located in such a way that the remaining foam and the captured dust are deposited back onto the moving coal stream. This orientation not only prevents dust from escaping into the environment, but also places at least a partial blanket of foam onto the deposited coal, which may prevent dust Generation until bubbles are broken or disrupted by another transfer point. The dust suppression effects of normal foam does not carry over from a previous application poi

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