Conveyors: power-driven – Conveyor frame or casing – Casing – cover – shield or load supporting surface
Reexamination Certificate
1999-11-05
2001-01-23
Bidwell, James R. (Department: 3651)
Conveyors: power-driven
Conveyor frame or casing
Casing, cover, shield or load supporting surface
C198S860300
Reexamination Certificate
active
06176368
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the provision of a dust containment housing that passively prevents dust from escaping from the housing during a transfer of bulk material from a first station to a second station. More particularly, the present invention relates to providing a region of low air pressure in a dust containment housing to cause air to flow from a region of high air pressure generated by a transfer of bulk material to the region of low air pressure inside the housing. Still more particularly, the present invention relates to the provision of a circulation compartment inside the housing to create a circulation path for the induced air flow inside the housing from a termination area of the transfer back to the first station.
PROBLEM
One of the most significant problems facing today's industrial society is air pollution. It is commonly known that air pollution is among the causes of many environmental problems, such as the greenhouse effect, and many health problems, such as silicosis and pneumoconiosis. As society has become aware of these environmental and health problems caused by air pollution, methods have been sought to reduce the amount of pollution released into the air.
One type of air pollution is dust emitted into the atmosphere. Dust is comprised of particles of a bulk material, such as hard or soft ores, that are suspended in the air. One cause of dust emissions is the transfer of a bulk material from a first station to a second station. The bulk material is typically transferred from the first station to the second station by causing the bulk material to fall from the first station to the second station or by projecting the bulk material from the first station to the second station.
A stream of bulk material is formed by the material falling or being projected from the first station to the second station. The individual particles in the stream of bulk materials impart a frictional drag on the surrounding air. The surrounding air begins to flow in the direction of the material stream and attains a velocity approaching the velocity of the material stream. This is called an induced air flow. At the end of the fall, the bulk material is suddenly stopped and compacted the material caused by impact of the material stream within the area of the second station. The velocity pressure of the induced air flow is converted to static pressure by the impact of the bulk material. A region of high air pressure is created by the static pressure. Air in the region of high air pressure must flow to a region of lower air pressure. As the air flows from the region of high air pressure to the region of lower air pressure, small particles of the bulk material are suspended in the air. In an open system, the movement of the air is from high pressure to low pressure is evidenced by a dust cloud billowing from the termination area of the second station.
One common dust control system is a housing enclosing a first station, a second station, and the material stream between the first and second stations. The housing guides the bulk material and prevents dust from escaping. A typical housing has an inlet near the first station to receive the bulk material at the first station and an outlet near the second station to transport the bulk material from the second station out of the housing. In addition to the inlet and outlet, a dust containment housing typically has several tolerance openings around moving and vibrating components of the first and second stations.
It is a problem that the primary function of the housing is to guide flowing bulk material from the first station to the second station and not to prevent dust emissions. When a region of high air pressure is generated proximate the second station by the impact of the bulk material terminating the induced air flow, the dust laden air in the region of high air pressure flows through openings, such as the outlet, near the second station to a region of lower air pressure outside the housing. The air flowing out an opening carries the suspended particles of bulk material out of the opening.
One method for preventing air from carrying dust out of openings in the housing is to exhaust the induced air flow to a filtration system. A filtration system has a vacuum or fan to create a negative air pressure in a duct leading to the filtration system. An entry to the duct is attached to the housing. The air flows from the region of high air pressure flows into the duct having a negative air pressure and to the filtration system instead of out of the openings in the housing. In the filtration system, the air passes through a filter which removes the suspended particles from the flowing air. The filtered air is then released to the outside environment.
Filtration systems are not desirable for several reasons. A first reason that a filtration system is undesirable is the capital cost required to add the filtration system to a housing. One factor in the prohibitive capital cost of a filtration system is the need to incorporate a duct system to the filtration system from the housing. This increases the cost of the housing and causes many design and operation problems.
A second reason that filtration systems are not desirable is the high maintenance required to maintain the filtration system in proper working order. One cause of the need for high maintenance is that the bulk material caught by the filter must be removed from the filter using a shaker or other device. A second cause of the high maintenance is that the entire filter must be periodically replaced in order to maintain the same efficiency level for the filtration system.
A third reason that filtration systems are not desirable is the high energy consumption by the filtration systems. A great amount of energy is needed to create a region of negative air pressure in the ducts that will cause the air to flow through the filtration system. A further reason that filtration systems are undesirable is that an improperly working filter system will emit dust.
A second form of dust emission control is a dust suppression system. A dust suppression system can be used either in an open or a closed bulk material transfer system. In a dust suppression system, the bulk material is wetted with a surfactant such as foam or water. The surfactant agglomerates with the fine particles of the bulk materials. The agglomeration of the fine particles and surfactant increases the weight of the fine particles. The increased weight prevents the particles from being suspended in the air flowing from the region of high air pressure to the region of low air pressure. It is a problem that dust suppression systems are typically not as effective as filtration systems in preventing dust from being emitted. Further, the capital cost of a dust suppression system is comparable to the capital cost of a filtration system that has a comparable emission control performance.
Dust suppression systems that are as effective as filtration systems wet the bulk material with a mist having droplets approaching the size of the dust particles. However, these efficient dust suppression systems are as expensive to install as are the filtration systems and typically have higher maintenance costs. A high level of maintenance is needed to maintain production of the particle sized droplets in the mist and to assure that even very small particles of bulk material are agglomerated.
One disadvantage of a dust suppression system is that dust suppression systems have numerous problems in cold temperatures. In order to keep the surfactant from freezing, a dust suppression system must be heated or well insulated. The wetted bulk material can also freeze which causes plugging in the transfer system. These problems lead to excessive maintenance and extra cost to maintain efficiency in the dust suppression system in cold temperatures.
There is a long felt need in the art for an inexpensive and maintenance-free dust control system.
SOLUTION
The above and other problems are solved and an advance in the art is made by the p
Bradbury Steven Arthur
Tooker Garren Ewers
Air Control Science, Inc.
Bidwell James R.
Duft, Graziano & Forest, P.C.
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