Patent Application
20080145155
The invention pertains to a method for rendering vacuum conveyors inert, said vacuum conveyors featuring at least one intake device, a discharge device, a separating vessel, a vacuum pump device, and a means for feeding inert fluid into the separating vessel, and pertains to a correspondingly equipped vacuum conveyor which can be rendered inert.
A vacuum conveyor transports material powder, granulate, dust, tablets, small parts etc, in a suction gas flow, as a rule, air or inert gas.
Material is taken in from a feed location, e.g., with a hand-held suction line, feed funnel or similar, transported through a hose or pipe, and reaches the vacuum conveyor by means of an intake opening. In the vacuum conveyor, an inserted filter element, aided by centrifugal force and sedimentation, separates the transported material from the suction gas. The transported material is collected in the separating vessel of the vacuum conveyor. The filtered suction gas flow is diverted from the separating vessel to flow through the vacuum pump driving the conveying process. Said vacuum pump commonly is installed in a stationary manner directly on the upper part of the vacuum conveyor or in the immediate vicinity thereof and is to be protected—even independently of protecting the environment—from contamination. After the process of filling the separating vessel has been carried out, the vacuum pump is switched off or the suction gas flow between the separating vessel and vacuum pump is interrupted by means of a valve mounted on the filtered clean side or gas side
For a standard vacuum conveyor, a discharge valve mounted at the bottom of the separating vessel now opens and the transported material falls out of the separating vessel through the discharge opening
Bridging materials can be fluidized as an aid, or pushed out of the separating vessel with overpressure. The filter is cleaned of adhering filter residue by means of a counter blow from the clean gas side. The duration of individual intake and discharge cycles commonly is controlled by means of a sequence control system having adjustable intake and discharge times. Intake and discharge times for a vacuum conveyor commonly are relatively short and, as a rule, are only several seconds each. Since filter residue can be cleaned very frequently, this brief cycle time permits an extremely compact structure having extremely small filtering surfaces in comparison to the inflow velocity in a conventional air-filter installation.
If solid matter is conveyed in the suction gas flow, then a separation of electrical charge can occur due to contact of individual material particles with one another and also due to contact with the conveyor lines. In this connection, the material and also the contacted surfaces receive an electrostatic charge, resulting in the risk of ignition by means of various types of electric discharge for ignitable solid matter or present combustible gases as well as mixtures thereof. Said effect can be counteracted in a vacuum conveyor by means of suitable grounding measures. Gaining acceptance in particular are solutions featuring a completely, constantly electrically conductive separating vessel. Hose assemblies should be equipped with wire spirals grounded at both ends connected to the separating vessel via metal, for example, a clamp. In the conveyor itself, all electrically conductive parts are connected to one another in an electrically conductive manner and are grounded, so the risk of a spark discharge in the conveyor can be minimized and essentially ruled out.
However, conveyed material itself retains a charge that can be dissipated only slowly by means of the vessel wall of the separator or by means of atmospheric moisture. Also, a risk of explosion originates from the filter residue adhering to the filter of the separator—with sufficiently great quantities of charge, the surface charge can lead to so-called brush discharges.
According to current science, brush discharges for solid matter having a minimum ignition energy MIE greater than 1 mJ are not capable of ignition, such that a vacuum conveyor for solid matter having an MIE greater than 1 mJ generally can be utilized. However, for safety reasons, the quantity of matter per conveying cycle is limited to a mass of approximately 10 kg in order to prevent larger build-ups of charge.
However, if combustible gases or gases which support a combustion process, such as oxygen, are present in the surroundings, even lower energy levels are sufficient to ignite said gases. In said cases, inertization regularly is selected as a measure of explosion protection. In this connection, the oxygen content in particular is reduced to a non-critical level for the respective application and replaced by means of a suitable inert fluid. Examples include N2, CO2, or noble gases.
For an inertization process for vacuum conveyors known from the state of the art according to EP 0 937 004 B1, material is taken from a feed point into the separating vessel of a conveyor, the intake opening of the vacuum conveyor is closed and the separating vessel of the conveyor is evacuated to a sufficiently high vacuum. The vacuum pump device is then isolated from the separating vessel by means of a valve and the separating vessel is rendered inert from the clean gas side of the filter.
In order to ensure that a nearly complete gas exchange has occurred and the oxygen content thus reduced to a non-critical level, an inertization process occurring three times in succession has gained acceptance among known methods. This means that after the intake of material has taken place, the separating vessel is evacuated three times and rendered inert in order to ensure a gas exchange above the separated material, in particular. The material is subsequently discharged under a nitrogen blanketing. A disadvantage of the previous method therefore lies in the fact that in order to ensure non-critical oxygen content in the gas or fluid present in the separating vessel, time-intensive multiple inertizations must take place.
It now has been established that the inert fluid fed into a separating vessel above the separated material has little interaction with the volume of separated material and the risk exists that oxygen present in the gap volume and/or pore volume of the separated material is not exchanged at all or is only incompletely exchanged with the inert fluid with the aid of the aforementioned inertization process.
With this background, the underlying purpose of the invention is to make available a process and a device for rendering vacuum conveyors inert, which ensures that the entire separating vessel and the surroundings of the separated material in particular are nearly completely rendered inert.
In order to solve this problem, a method of the aforementioned type is proposed in which, during the process of inertization, an inert fluid is fed into the at least one separating vessel below the free surface of a separated material.
The root idea of flowing through the material present in a separating vessel with an inert fluid can be realized in multiple ways. In each case an exchange of the combustible gas or of the oxygen with the inert fluid is achieved not only above the separated material, but to the contrary, due to a difference in pressure in particular, inert gas flows through the separated material from below in an upward direction in particular, with the entire inertization process preferably being determined by means of a continuous feed as well as an evacuation of the inert fluid. Among other things, the invention can eliminate multiple cycles for rendering a separating vessel inert and the vacuum conveying process can be accelerated substantially.
In order to construct a suitable differential pressure and simultaneously to remove combustible gas and/or oxygen from the separating vessel, a pressure lower than the pressure of the inert fluid is generated or maintained in the at least one separating vessel during the inertization process by a vacuum pump device mounted, in particular, above the separated material, or else the feed pressure of the inertization device is selected to be sufficiently high that, for a vacuum pump device that is switched off and can be freely flowed through or for a bypass valve which is switched on, there is the presence of a sufficient flow-through or fluidization of the conveyed product.
In order to enable a space saving arrangement of the inert fluid feed and a particularly effective explosion protection, inert fluid is fed into the at least one separating vessel in the immediate proximity of and, in particular, above the discharge opening.
In order to ensure a nearly complete flow-through of the separated material and of the remaining volume of a separating vessel with inert fluid, as well as of the filter and of filter residue adhering to said filter, inert fluid fed into said separating vessel by means of a line, a valve-controlled line in particular, flows through the filter in the direction of the clean gas side where it exits the separating vessel.
In order to keep the time for inertization as brief as possible and in order to reduce the operating steps necessary for this, inertization can occur within the scope of a process characterized by means of a continuous feed of inert fluid and by means of the simultaneous, continuous evacuation of the separating vessel.
In order to constantly monitor the content of oxygen, in particular during inertization, and in order to use this information, if necessary, in order to control said inertization, the oxygen concentration of the fluid present in the at least one separating vessel is measured, in particular, in an area of the clean gas side.
In order to allow utilization in the most flexible way possible, the method according to the invention may be combined in a suitable manner with a conventional inertization step that, rather than conducting flow through the separated material, conducts flow through the filter in particular, from the direction of the clean gas side.
A further aspect of the invention consists in making available a vacuum conveyor which ensures a thorough inertization of the separating vessel and ensures that the separated material in particular is nearly completely subjected to inertization.
In order to solve this problem, a device of the aforementioned type is proposed for which the means for feeding inert fluid below the free surface of the material to be separated are provided on and/or in the at least one separating vessel.
In order to ensure a controlled and effective feed of inert fluid into the separating vessel, the means for feeding inert fluid are in the form of fluid nozzles.
In order to control the feed of inert fluid at any time and, if necessary, to be able to adjust the quantity of inert fluid, the lines which conduct the feeding means are controllable via valves.
In order to bring the feeding means for inert fluid into an optimal position with regard to a flowing through of the separated material and additionally, in this connection, in order to ensure a compact structure, the feeding means are provided in and/or on the vessel wall and/or in the discharge lid belonging to the discharge device.
In order to bring the inert fluid into the optimal position with regard to a flowing through of the separated material, the areas of the vessel wall in which the fluidizing nozzles are provided are arranged in a diagonal progression downward, preferably with an aperture angle of 30-75°. However, this funnel-shaped area can be omitted, with smaller vessel diameters of up to 450 mm in particular, such that a cylindrical surface is yielded on which are arranged the inertization devices. A discharge valve that seals the entire diameter of the vessel can close the vessel from below.
In order to ensure the most effective flow-through of the separated material, several feeding means are arranged in a structure, in a ring structure in particular, that corresponds to the geometry of the separating vessel, to the peripheral shape thereof in particular. For a small vessel diameter, an individual feeding means mounted only on one side is also possible according to the invention.
The aforementioned components as well as those claimed and described in the embodiments to be used according to the invention underlie no particular exceptional circumstances with regard to size, configuration, material selection or technical conception such that the selection criteria known in the sphere of application can find unlimited application.
Additional details, features and advantages of the method of the invention are given in the dependent claims and from the following description of the associated drawing in which is represented an example of an embodiment of the method according to the invention for rendering vacuum conveyors inert.
The drawing shows in detail:
The block diagram evident from
Within the separating vessel (100), a filter (50) filters the taken-up conveying fluid of dust or particles such that the latter cannot reach the vacuum pump device (20). Provided in the upper part of the separating vessel (100) is an additional opening, to which is joined a line (28), controlled by means of a valve (29); said line conducts the fluid within the separating vessel (100) further on to a corresponding measuring apparatus, with the aid of which, e.g., the oxygen content can be determined. Also sufficient is only one opening in the vessel lid, which connects all other devices by means of a collecting line. This can simplify maintenance and repair work on the separator (smaller masses to handle). Located in the lower region of the separating vessel is a discharge device (40), which in the embodiment represented in
A line (26) controlled by means of a valve (23′) can be used to clean the filter (50) by means of a counter blow at a given time. Said line can be used to feed optional additional inert fluid during the aforementioned inertization process.
Represented in
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2004 019 703.2 | Apr 2004 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2005/004229 | 4/20/2005 | WO | 00 | 9/5/2007 |
