Gas separation: processes – Electric or electrostatic field – With cleaning of collector electrode
Reexamination Certificate
1999-05-19
2001-05-08
Chiesa, Richard L. (Department: 1724)
Gas separation: processes
Electric or electrostatic field
With cleaning of collector electrode
C055S431000, C095S075000, C095S078000, C096S044000, C096S050000, C096S061000, C096S097000, C096S228000
Reexamination Certificate
active
06228148
ABSTRACT:
BACKGROUND AND SUMMARY OF THE INVENTION
The object of the present invention is a method and an apparatus according to the introductory parts of the independent claims presented below for separating solid or drop-like particles from air flows to be purified.
Then the invention relates particularly to a method and an apparatus where particles are separated from an air flow or a corresponding gas flow in a separator chamber or similar, by electrically charging the particles to be separated, e.g. by conventional high voltage techniques or ionisation, and by separating these electrically charged particles with the aid of a grounded collector surface or similar. Typically the separation occurs in an elongated cylindrical chamber, where at one end there is formed an air flow inlet and at the other end there is formed an outlet for the purified air flow which is separated from the particles. The electrode, ion generating means or similar which charges the particles is typically arranged in the central part of the separator chamber, so that it extends generally from the air flow inlet end to the purified air flow outlet end.
In conventional separators based on the electrical charge of the particles, as well as in electrical filters, the aim has been to obtain as low air flow velocities and as little turbulence as possible, so that the dust particles can be separated from the air flow in a smooth and controlled manner, and so that they are prevented from re-mixing with the air flow. The air flow is typically directed to the separator chamber via an inlet opening at the centre at one end of the chamber, and then the air flow is allowed to pass smoothly in the axial direction through the separator chamber, whereby the air flow and the separated particles uniformly fill the whole chamber, both at the centre and in the peripheral regions. Such conventional purification equipment must be made relatively large in order to provide the desired purification effect.
In conventional separators particles are separated from the air to be purified on all separator surfaces being in the way of the flow, both on the electrodes, on the structures supporting the electrodes and on the isolators arranged between the electrodes and the grounded collector surfaces. The particles accumulated on the surfaces will easily cause blockages which interfere with the free air flow through the separator chamber. On the other hand, piles of dry particles accumulated on the surfaces may from time to time begin to move again, as dust clouds, and form dusty air mixtures which impair the desired purification result. Further, layers accumulated particularly on the isolators may cause a short circuit between the electrodes and the grounded collector surfaces, which interferes with the operation of the isolator. Thus, due to the particles accumulated on the surfaces, the manageability and control of conventional purification equipment has often been difficult.
In addition to the small dust particles the air flow to be purified which flows through the separator chamber can sometimes also contain large particles or bodies which, when they hit the electrodes and stick to the electrode support structures, can both damage the structures and cause blockage.
Previously it has been proposed to use water spraying to wet the dust particles and bind them to each other in order to provide a better separation. However, the water will evaporate relatively rapidly from the moistened dust fog, and thus this wetting has not provided the desired result.
The American patent publication U.S. Pat. No. 4,388,089 presents an improved separator into which the gas to be purified is supplied in the tangential direction from above, so that the gas is made to pass through the separator in a generally spiral path around a smooth and simple wire electrode on the central axis of the separator whereby the centrifugal force automatically directs a part of the particles toward the grounded walls of the separator. There is further arranged a water film on the separator walls which flows from the top downwards, and with this film the aim is to lead in a controlled manner the particles which have separated on the separator walls away from the separator, and another aim is to prevent the particles from being re-mixed with the gas flow.
The capacity of a separator provided with a simple wire electrode is relatively low. In the above described case the use of other more efficient electrodes is limited i.a. by the fact that particles are more easily accumulated on their surfaces, which causes above mentioned blockage problems, or that the electrical field in their central part can be so low that the dust containing air flowing downwards in the central part will pass through without being purified. Particularly when the gas flow to be purified is large it may be difficult to prevent the particles in the central part of the separator, and at a distance from the water film to follow the gas downwards into the purified gas discharge at the bottom of the separator. Already due to the gravity force the particles tend to propagate directly downwards.
The objective of the present invention is thus to provide a new method and apparatus which are better than the previously known, in order to separate particles from an air flow.
The objective is to provide a method and an apparatus, where particularly the above mentioned drawbacks are minimised. Then an objective is particularly to provide a method and apparatus which minimise the accumulation of particles separated from the air flow on the electrodes, on the structures supporting the electrodes and on the isolators, and which minimise the problems caused by the accumulation.
An objective is to provide a method and an apparatus which enable the use of effective electrodes for charging the particles in the separator.
In order to achieve the above mentioned objectives the method and the apparatus according to the present invention are characterised in what is presented below in the characterising clauses of the independent claims.
The invention is particularly well suited for separating solid and drop-like particles from air flows to be purified in connection with the manufacturing of paper, paperboard, pulp or similar.
In a typical solution according to the invention the air flow to be purified is arranged to travel along a spiral path through an elongated vertical separator chamber, from an inlet at its bottom end to an outlet at its upper end, whereby the separator chamber acts as a separator where both electrical forces and the centrifugal force act on the particles and direct the particles toward a grounded collector surface at the periphery of the chamber. The collector surface is typically formed by the wall of the separator chamber, and the wall is grounded.
A typical separator according to the invention comprises a vertical cylindrical separator chamber, into whose central part an elongated electrode, ionising means or similar means with an open structure is arranged axially, which means can electrically charge the particles to be separated. The most different such electrodes can come into question where the electrode's horizontal open section has a large area, preferably over 90%. The electrode can be formed for instance of vertical wire electrodes or similar which are placed adjacent each other at short mutual distances in the form of a circle, of a net formed by wire electrodes which is bent into the shape of a cylinder, or of a smooth narrow cylinder, which is provided with sharp points or pins which initiate the discharge.
According to the invention the air flow to be purified is arranged to travel around an electrode or similar along a spiral path directed upward from the bottom. Then particles are separated from the air flow when they are exposed to the action of the centrifugal force and/or when they are electrically charged and directed toward the walls of the separator chamber. In a preferred solution according to the invention the air flow is arranged to pass spirally upwards along the walls of the sepa
Aaltonen Rami
Leimu Juha
Norri Petri
Chiesa Richard L.
Nixon & Vanderhye P.C.
Velmet Corporation
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