Method of removing particles and fluids from a gas stream by charged droplets

• US 3,958,959 A
• Filed: 08/05/1974
• Issued: 05/25/1976
• Est. Priority Date: 11/02/1972
• Status: Expired due to Term

• Current Assignee: TRW Limited (Zeppelin - Stiftung der Stadt Friedrichshafen)
• Original Assignee: TRW Limited (Zeppelin - Stiftung der Stadt Friedrichshafen)
• Inventors: Cohen, Ernest, Lear, Charles W., Huberman, Marshall N., Krieve, Walter F.
• Primary Examiner(s): Nozick, Bernard
• Application Number:
  US05/495,013
• Time in Patent Office: 659 Days
• Field of Search: 55/10, 55/107, 55/122, 239/15, 261/116, 261/117
• US Class Current: 95/64
• CPC Class Codes: B03C 3/00 Separating dispersed particles from gases or vapour, e.g. air, by electrostatic effect
• CPC Class Codes: B03C 3/01 Pretreatment of the gases prior to electrostatic precipitation

Abstract

A method for the removal of particulate matter as well as noxious gases and vapors from a gas stream. This is accomplished by means of charged droplets having a size between 60 and 250 microns and preferably between 80 and 120 microns. The droplets are generated by first ejecting a stable jet of liquid such as water. The liquid jet is broken up into charged droplets by applying an electric potential between the jet and the collecting walls of the scrubber. Since most gases are electronegative the droplets are preferably charged positively by the resultant electrostatic field. However, in case some of the particles are already charged it is preferred to generate charged droplets having a polarity which is the same as that of the particles. The method works well with particles having a diameter of approximately 0.01 micron or more and the droplets are preferably moved at an angle to the direction of movement of the gas stream to increase the relative velocity between the droplets and the particles. The droplets may include a chemical agent which chemically reacts with an undesirable fluid in the gas stream to remove it. The collector wall may be sprayed to flush particulate matter which may have been collected by the wall.

Claims

1. The method of removing from a gas stream undesirable fluid components and particulate matter entrained thereby, by utilizing spaced, conducting elements and a spray tube disposed between the elements, the method comprising the steps of:

a. causing the gas stream to flow between the elements and past the spray tube;

b. forcing a liquid through the spray tube into the gas stream at substantially atmospheric pressure to generate a liquid jet;

c. applying a steady electric potential of substantially 50 kilovolts to 60 kilovolts between the liquid jet and the spaced elements, the potential being sufficiently large to break up the liquid jet by the resultant electrostatic field into individual droplets having a diameter between aproximately 60 microns and approximately 250 microns, each droplet having a high surface charge density;

d. causing the charged droplets to flow toward the elements at an angle with respect to the direction of flow of the gas stream to provide a relative velocity between the gas stream and the droplets, whereby the droplets will collide with individual particles or undesirable fluids to remove them; and

e. eventually causing the droplets to move toward the elements due to the electrostatic field where they collide and collect.

2. The method defined in claim 1 wherein the liquid jet has such a diameter and the electrostatic field has such a value that the jet is broken up into droplets having a diameter on the order of between 80 and 120 microns.

3. The method defined in claim 1 wherein the droplets are formed while moving in a generally downward direction and are then caused to move under the influence of the electrostatic field and including the step of moving the gas stream at an angle to the direction of movement of the droplets.

4. The method defined in claim 1 wherein the gas stream contains predominantly electronegative gases and wherein the electric field is such that the droplets are charged positively, thereby to minimize the formation of ions from the gas stream.

5. The method defined in claim 1 wherein the liquid jet includes a chemical agent which will chemically react with at least one undesirable fluid of the gas stream.

6. The method defined in claim 1 wherein the viscosity of the gas stream and the magnitude of the electrostatic field are so related that the droplets move toward the elements at a substantially constant speed.

7. The method defined in claim 1 wherein a droplet is capable of multiple collisions with successive particles to collect them one by one.

8. The method of removing particulate matter entrained by a gas stream by utilizing spaced, conductive walls and a spray tube disposed between the spaced walls, the method comprising the steps of:

a. causing the gas stream to flow between the spaced walls and the spray tube;

b. ejecting a stable liquid jet from the spray tube at substantially atmospheric pressure insufficient to break up the jet into droplets;

c. applying a direct-current electric potential of substantially 50 kilovolts to 60 kilovolts between the spray tube and the walls, the resultant electrostatic field being strong enough to break up the liquid jet some distance from its origin into charged droplets having a diameter between approximately 60 microns and approximately 150 microns; and

d. moving the thus formed charged droplets under the influence of the resultant electrostatic field toward the walls, whereby the droplets encounter particulate matter and remove it from the gas stream when they collide with the walls.

9. The method defined in claim 8 wherein the diameter of the particulate matter is no less than approximately 0.01 micron.

10. The method defined in claim 8 wherein the droplets are capable of supplying an electric charge by induction to the particulate matter of the same polarity as that of the droplets, whereby a thus charged particle is attracted by the electrostatic field toward the walls and is eventually removed.

11. The method defined in claim 8 wherein a plurality of closely adjacent liquid jets are generated so that the resulting droplets fill substantially the entire space between the walls, whereby the probability of a droplet encountering a particle is increased.

12. The method of removing particles entrained by a gas stream flowing between spaced, conductive walls and by utilizing a spray tube disposed between the walls, some of the particles being electrically charged and having a predetermined polarity, the method comprising the steps of:

a. causing the gas stream to flow between the spaced walls and past the spray tube, the gas stream containing both charged and uncharged particles;

b. ejecting a stable liquid jet from the spray tube at substantially atmospheric pressure insufficient to break up the jet into droplets;

c. applying a direct-current electric potential of substantially 50 kilovolts to 60 kilovolts between the spray tube and the walls, the spray tube having a polarity which is the same as that of the charged particles and the resultant electrostatic field being strong enough to break up the liquid jet some distance from its origin into droplets having a charge of a polarity which is the same as that of the spray tube, each droplet having a high surface charge density and a polarity equal to that of the particles; and

d. moving the thus formed charged droplets under the influence of the electrostatic field toward the walls, whereby the droplets encounter both uncharged and charged particles, engulf the particles and remove them from the gas stream when the droplets collide with the walls, and whereby charged particles which are not so engulfed are similarly moved under the influence of the electrostatic field toward the walls, and thereby removed from the gas stream.