This invention relates generally to conveying systems and, more specifically, to a conveying system and a low energy method of maintaining a flow of conveyable material that is subject to bridging.
In conveying solid materials, which may comprise a variety of solid materials or particles, the conveyable materials are typically delivered to a gravity hopper, which contains a cone shaped base that directs the conveyable material to an outlet at the bottom of the gravity feeder. Typically, the outlet connects to a conveying line such as a pneumatic or mechanical conveying line, which conveys the material to a different location. One of the difficulties with delivering conveyable materials through a gravity hopper is that often times the particles of the conveyable materials may adhere to one another and form a self supporting bridge over the outlet in the gravity hopper thus preventing flow of the conveyable materials through the hopper outlet. Numerous devices and methods have been proposed to eliminate the tendency of the conveyable materials to form a material bridge in the hopper or to break up a bridge of conveyable material in the hopper.
U.S. Pat. No. 3,195,775 shows an example of a device that vibrates a hopper to break a material bridge in a hopper, unfortunately vibration of the hopper can prematurely decrease the life of the system as well as consume a large amount of energy.
U.S. patent publication 2003/0017012 shows an air knocker that is mounted on the side of a storage tank with the air knocker having an elastic sheet or diaphragm that attaches to the side of the storage tank for blasting pulsed air. A permanent magnet holds the valve in a closed state until the magnetic force is overcome, which enables one to blast air into the side of the storage tank or the bottom of the tank in order to fluidize the material in the tank. In one embodiment air is blasted past an elastic member that is mounted on the sidewall of the hopper.
U.S. Pat. Nos. 3,788,527, 4,767,024 and 4,496,076 show the use of air blasters that inject air through the sidewall of a hopper. The air blasters are mounted on a hopper with the air blasters containing a relatively large volume of air under significant pressure and a quick release valve for suddenly blasting the volume of air directly into the conveyable material. U.S. Pat. No. 4,496,076 shows examples of air blasters mounted to cone of the hopper and with the air blasters directing a blast of air downward or tangentially with respect to the wall of the hopper in order to break up a bridge of conveyable material.
This type of device requires a large amount of energy to break up the bridge and has been referred to as the creation of a “dull explosion” in the material.
U.S. Pat. No. 6,007,234 shows a fluid injector that directs air along a surface wall of the hopper to dislodge materials located along the sidewalls of the hopper. This type of device minimizes bridging by inhibiting materials from adhering to the sidewall of the hopper. In this type of apparatus multiple fluid injectors may be mounted in the hopper sidewall to keep material from adhering to the sidewall of the hopper and thus inhibiting bridging.
U.S. Pat. No. 4,826,051 disclose another high energy manifold blaster that attaches to the side of the hopper to pulverize the particulate matter in the hopper so the material can flow through the hopper. Generally, multiple units are mounted in the hopper sidewall.
As can be seen from the above prior art it is difficult to continuously convey bridgeable materials due to the problem of bridging of conveyable materials, which has given rise to numerous methods and apparatus. Some methods employ brute force by shaking the bin or blasting air through a sidewall of the hopper and into the side of the bridged material to break up a bridge while other methods and apparatuses attempt to prevent a bridge of conveyable material from forming in the hopper by directing air along a sidewall of the hopper through a plurality of openings in the sidewall. Compounding the problem of conveyable materials, which may bridge, is that some bridges within the hopper may be broken easily while others are extremely difficult to break up.
The prior methods have certain disadvantages in that some methods may substantially increase noise level proximate the hopper, some may shorten the life of the system, some may require large amounts of energy or some require multiple air blasters or bin aerators mounted to the sides of the hopper, which increases both the complexity and costs of the system. In some cases the prior art methods are simply ineffective and instead of dislodging bridged material an air blaster may form a “rat hole” in the bridged material, which is a passageway from the blaster to the hopper outlet that does not break up the bridge but prevents the bridged material from falling into the hopper outlet.