Conveyors: fluid current – Processes
Patent
1998-01-22
2000-05-16
Noland, Kenneth W.
Conveyors: fluid current
Processes
B65G 5300
Patent
active
060627743
DESCRIPTION:
BRIEF SUMMARY
The present invention is applicable in the field of monitoring the stability of operation in an installation designed for pneumatically conveying a substance in bulk, in dense phase. The invention relates to a method making it possible to detect automatically when such an installation is operating at the limit of stability, and also more generally to application thereof to automatically determining a limiting operating point between a zone of stability and a zone of instability.
In the field of processing substances in bulk on an industrial scale, it is known that the bulk substance to be processed can be conveyed in a leakproof conveyor duct by means of a flow of gas, e.g. for taking the substance directly from the outlet of an extruder and conveying it to storage silos for the purpose of subsequently processing the extruded substance, or indeed taking the substance from the outlet of a first storage silo to another industrial processing zone. To this end, a pneumatic conveyor installation is used which includes a member commonly referred to as a "lock" which has the function of injecting the carrying gas flow and the bulk substance simultaneously into the leakproof conveyor duct. In general, the lock is in the form of a chamber into which the bulk substance and the flow of carrier gas, generally air, are injected separately. Additionally, a certain type of lock advantageously includes a system for regulating the rate at which the bulk substance is injected into the chamber of the lock. More particularly, the regulation system consists, for example, in a rotary bladed wheel that rotates at a speed which is adjustable as a function of the desired flow rate of the bulk substance.
In the field of pneumatically conveying substances in bulk, there are at present two main families: is low, in practice less than 12 meters per second (m/s), and maybe as little as 0.5 m/s, with the concentration of the substance in the conveyor duct being high; and much higher travel speed, while the concentration of the bulk substance is much lower.
In practice, conveying in dense phase is characterized by pulsating operation, with the bulk substance moving inside the conveyor duct in the form of compact plugs of matter, separated from one another by pockets of gas.
The present trend is to develop pneumatic conveying in dense phase since that has the advantage not only of making it possible to work with lower rates of gas flow, but also of keeping down the wear of the conveyor ducts over time while conserving better quality in the conveyed substance, compared with conveying in dilute phase.
An installation for pneumatic conveying in dense phase is conventionally designed to operate at a predetermined load factor corresponding to the ratio of the flow rate of the bulk substance and the flow rate of the conveying gas at the inlet to the lock. To enable the conveyor installation to operate in stable manner while in dense phase, it is necessary for the load factor to remain within a narrow range of values. Varying the flow rate of the air or the flow rate of the bulk substance injected into the lock can lead very easily to causing the installation to operate in unstable manner, and in particular in a critical phase in which the installation oscillates between operating in dense phase and operating in dilute phase, and vice versa. It is absolutely essential to avoid this critical phase since it gives rise mechanically to hammering in the conveyor duct which leads to the installation being damaged very quickly.
In order to maintain the load factor of a given installation at a predetermined value, proposals have been made, for example in European patent application EP 490 174 in the name of the Buhler company, to keep the flow rate of the carrier gas and/or the flow rate of the bulk substance at the inlet of the lock constant on the basis of a measurement of pressure in the zone where the bulk substance is injected into the conveyor duct, so as to compensate for leakage of the carrier gas from the lock.
Nevertheless, maintaining a const
Destoop Thierry
Fourcroy Jean-Pierre
Guerra Thierry
Pacaux Patrick
Neu Transf'Air
Noland Kenneth W.
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