HK1109753B - Rigid electrode ionization for packed bed scrubbers - Google Patents

Description

Rigid electrode ionization for packed bed scrubber

Technical Field

The present invention relates generally to systems and methods for enhancing particulate collection from an effluent stream of an industrial process, and more particularly to a system and method in which collection is improved by charging the particulates and increasing collection in a packed bed scrubber system using electric field forces.

Background

Many industrial processes, particularly the incineration of waste materials or high temperature generating materials such as glass fibers, for example, emit small or submicron particulates in their effluent streams, which are generally considered hazardous and limited by environmental protection agencies. Accordingly, systems and methods for removing such particulates from an exhaust stream prior to entry into the atmosphere have long been sought.

Various systems for electrostatically charging particles have been developed, for example, in the description of U.S. patent application No. 20040139853 entitled Bologa et al for the electrostatic cleaning of gases and methods for the operation therof, published in 2004 at 7/22, an Apparatus comprising three pipe sections is disclosed: an ionization and purification section in which particles contained in water-saturated air are ionized and then guided through a chamber having grounded walls so that a part of the particles are deposited on the walls; an additional purge section comprising a grounded hose through which gas passes to remove excess charged particles; and a filter section, wherein dry residual fines are removed from the gas stream.

It should be understood that such systems for electrostatically charging particulate matter have long been known in the art. For example, U.S. patent No. 5395430, "Electro-static precipitator assembly," issued by Lundgren et al on 5/7 1995 discloses an electrostatic precipitator device comprising a tubular collector and an electrode suspended therein, wherein the electrode comprises a substantially cylindrical collecting portion and a charging portion having a stem and a charging disk, and wherein a gap between the charging disk and the collector is at least as large as a gap between the collecting portion of the electrode and the collector.

Two other examples of Electrostatic purification systems are described in 5364457, "electric gas cleaning apparatus", issued to Cameron at 11/15/1994 and in 5282885, "electric gas cleaning process and apparatus", issued to Cameron at 2/1/1994, both of which disclose methods and apparatus for collecting particles or droplets in which charging devices and coalescing devices are combined to provide a purification apparatus that operates at a lower cost than conventional apparatus.

Another example is U.S. patent No. 4265641 entitled Method and apparatus for particle charging and collecting submicron particles issued on 5/1981 to natajan, which discloses a Method and apparatus for charging and collecting submicron particles whereby the particles are charged by a faller bar ionizer having offset rows of pins spaced from the bar. The charged particles are collected in a collection section having a deflection electrode and a pair of collection plates, wherein the deflection electrode comprises a conductor embedded in a dielectric material having a dielectric constant greater than 1 that inhibits the formation of an arc between the deflection electrode and the collection plates.

In yet another example, U.S. patent No. 4222748, "electrically assisted fiber bed and method of using," issued to Argo et al at 9/16 1980 discloses an apparatus comprising: a grounded fiber filter bed of 50-1000 micron average diameter fibers packed into a bed; an electrostatic or ionizing electric field device located upstream of the fiber filter bed to apply an electric charge to the particles; and a flushing means for the fiber filter bed and optionally a grounded electrostatic electrode means for flushing collected particulates away from the fiber filter bed and selectively from the grounded electrode. In operation, the particles are charged in the electrostatic device and the charged particles are collected in the fiber filter bed, where the charge is dissipated through the flushing liquid/particle mixture, whereby no significant space charge effects are created in the fibers of the fiber filter bed and re-entrainment of particles is avoided.

Increasing the velocity of the gas stream with venturi tubes is described in "Method for ionizing gases, ultrastatically charged particulates, and ultrastatically charged particulates or ionizing gases for removing contaminants from gas streams" in U.S. patent No. 4110086 issued to Schwab et al at 29/8 1978, which discloses using venturi tubes to increase the velocity of the contaminated gas and to direct the gas through an extremely dense, high electrostatic field perpendicular to the gas stream and extending radially outward between a centrally located and precisely sized disk electrode and the venturi surface. Downstream, the charged particles are collected by a wet cleaning process or electrostatic precipitator. The same device is disclosed in U.S. Pat. No. 4093430 issued to Schwab et al on 6.6.1978, "Apparatus for forming gaps, electrically converting gaps, and electrically converting gaps for removingcontaining from gap streams".

Similarly, U.S. patent No. 4072477, "Electrostatic precipitation process", issued to Hanson et al at 2.7.1978, discloses an Electrostatic precipitator which operates on the principle of repulsion of charged particles with grounded walls, wherein a gas stream laden with solid particles enters a collection section where additional particles, in the form of droplets, typically water, are injected into the gas stream laden with solid particles in the form of fine sprays, the solid particles and additional particles are electrostatically charged either by corona or by spraying droplets from a charge nozzle, and a portion of the water particles and solids are driven to the grounded walls by an electric field created by space charge as the charged particles pass through the grounded portion of the precipitator. The settled solid particles are entrained in the bound water flowing down the walls and drained by the settler.

In the 1970 s, Ceilcote APC developed an Ionizing Wet Scrubber (IWS) to remove submicron particulates from gaseous effluent streams. The IWS system is described in U.S. Pat. No. 3958958 issued to Klugman et al, 5/25/1976, as "Method for electronically removing a stream of particulate from a gas stream". This patent discloses a method comprising a packed wet scrubber through which scrubbing liquid, such as water, flows vertically downstream and through which the gas to be cleaned flows in a direction transverse to the direction of flow of the scrubbing liquid. The gas stream to be treated is ionized prior to flowing through the wet scrubber to provide particles in the gas stream with a charge of a given polarity, and once the gas stream flows through the wet scrubber, the charged particles in the gas stream approach and become attached to the scrubbing liquid and/or packing elements under the influence of attractive forces between the charged particles, the electrically neutral packing elements and the liquid. A similar device is disclosed in 3874858 issued to Klugman et al on 1/4 of 1975.

The IWS system incorporating the electrostatic charging section is followed by a packed bed collection system. The operation of the system is very complex and costly. Other electrostatic collection methods have been utilized, however they do not meet the requirements for collecting particles in the submicron size range. Tri-Mer developed a cloud chamber scrubber (patent #5147423, 5941465) that utilized ionization of particles in a mesh electrode and then collection on finely atomized droplets.

As will be appreciated, the prior art does not specifically address the problems and solutions achieved by the applicant.

Disclosure of Invention

The present invention aims to provide significant advantages over existing gas pollution control technologies and to provide advantages over ionized wet scrubber technologies.

With respect to the general air pollution control industry, the present invention provides the following aspects:

it is a primary object of the present invention to provide a system and method for enhancing particulate collection in a gaseous exhaust stream by charging the particulate and utilizing electric field forces to increase particulate collection in a packed bed scrubber system.

It is another object of the present invention to provide a system and method that is capable of collecting particles even in the sub-micron size.

It is a further object of the present invention to provide a system and method that can reduce installation costs as compared to conventional electrostatic scrubber devices.

It is a further object of this invention to provide such a system and method wherein the charging section is separate from the collecting section, thereby allowing for the simultaneous collection of particulates and other contaminants such as acid gases, condensable and soluble VOCs, etc. and the use of the same equipment when using a packed bed scrubber as the collecting section.

It is a further object of the present invention to provide a system and method that employs a concentric tube configuration for the charging section using a rigid screw electrode.

It is a further object of the present invention to provide a charging section with a short profile to minimize particulate collection that negatively impacts the performance of the charging section.

It is a further object of the present invention to provide a system and method that utilizes a vertical counterflow design that reduces the required coverage area.

With respect to existing ionizing wet scrubber technology, the present invention provides the following:

it is another object of the present invention to provide a system and method that can reduce operating costs compared to conventional ionized wet scrubber technology.

It is yet another object of the present invention to provide a system and method that can reduce the footprint of the equipment compared to conventional ionized wet scrubber technology.

It is a further object of the present invention to provide a system and method that reduces the continuous maintenance associated with multiple plate and wire designs currently used in ionized wet scrubber and some electrostatic scrubber technologies.

It is another object of the present invention to provide such a system and method that eliminates permanent washing of the plates with a cylindrical ground section instead of washing the plates to remove particulates and keep the charged sections dry and allow a more stable high voltage to be applied to the ionizer section.

It is yet another object of the present invention to provide a system and method for using a heavy screw electrode that does not require continuous tensioning in place of a wire electrode that is prone to breakage in certain situations.

It is a further object of the present invention to provide a system and method that employs self-cleaning fluid bed packing so that clogging does not occur when collecting particulates from a gas stream.

It is a further object of the present invention to provide a system and method that allows the collected solids to be collected in a slurry form and thereby minimize the liquid waste generated during operation.

It is another object of the present invention to provide high velocity ionization of gaseous fluids to minimize residence time in the charging section. This also minimizes particle collection in the charging region where high voltage input is to be reduced.

It is yet another object of the present invention to allow easy retrofitting of existing packed bed scrubbers by adding a charging section to enhance particulate removal.

To achieve the foregoing objects and advantages, the present invention broadly comprises, in brief, an ionizing particulate scrubber for removing particulates from a gaseous exhaust stream, the scrubber comprising two sections: a charging section and a collecting section. The charging or ionizing section includes one or more short cylindrical tubular ground chambers, each with a rigid threaded rod electrode through its center. A transformer/rectifier (T/R) is provided to supply high voltage DC energy to the electrodes to have the cylindrical wall as ground, thereby causing a corona to form on the screw electrode. Preferably, the transformer/rectifier is electrically connected to the rigid screw electrode by HV cables or bus bars. As the gas stream passes through the current flowing from the electrodes to the cylinder wall, the particles contained in the gas stream are electrostatically charged. The gas stream and charged particles are immediately sent from the charging section of the system to the collection section. The collection system comprises either a fixed bed or fluidized bed packed section that is continuously flushed from above using a liquid recirculation system and an integral settling tank. The packed bed provides an extended surface for particulate collection by a combination mechanism. Some of the larger particles are collected by inertial impaction on the filling surface. Smaller particles are collected by coulomb and image attraction of the neutral surface of the packing material. The ground rod in the filling and settling keeps the filling and recirculation liquid neutral to use the entire section as a grounded collector for charged particles. The clean gas is then passed through an entrainment separator section to remove liquid droplets. The clean gas is vented from the system to the atmosphere or for further processing. A structure in which collection is performed after multi-stage ionization can be constructed to achieve a higher particle collection effect.

Drawings

FIG. 1 is a schematic diagram of an ionizing particulate scrubber of the present invention showing two sections thereof;

FIG. 2 is a schematic diagram of the ionizer section of the ionizing particulate scrubber of the present invention;

FIG. 3 is a cross-sectional view showing a typical configuration of multiple charging tubes in the ionized particulate scrubber of the present invention;

detailed description of the preferred embodiments

Referring to the drawings, and more particularly to FIG. 1, an ionizing particulate scrubber is illustrated and generally designated by the reference numeral 10. The scrubber 10 includes a charging or ionizing section 12 and a collection section 14. The importance of having two separate sections 12, 14 need not be overemphasized because, provided the collection section 14 is a packed bed scrubber, particulate and other contaminants such as gases, water soluble and condensable VOGs, etc. can also be collected while using the same equipment. The charging section 12 includes an ionizer housing 28 with one or more cylindrical tubular ground chambers 34 each having a rigid threaded rod electrode 18 extending centrally therethrough. The screw electrode 18 provides an extremely long effective electrode length since the entire thread length is the actual ion emitter that charges the particles.

High voltage DC power is supplied to the electrodes 18 through a transformer/rectifier 20, which transformer/rectifier 20 is connected to the electrodes 18 by HV cables 22 through an insulator 24. An insulator 24 having a flux-through sleeve is provided to support an electrode which extends within the ionizer housing 28 and through a tubular ground chamber 34. In the preferred embodiment, the system 10 utilizes a high voltage DC transformer/rectifier 20 to provide power and commercial control components to control the high voltage and react to prevent or minimize flashover.

The electrode 18 and the tubular ground cavity 34 cooperate to form a corona on the threaded rod electrode 18 when DC energy is provided by the transformer/rectifier 20, with the tubular ground cavity 34 serving as ground. The tubular ground chamber 34 is connected to the external ground by a ground lug 35.

The gas inlet 30 is either formed in one side of the ionizer housing 28 or is disposed at the top of the ionizer housing as shown in figure 3. The inlet 30 is positioned to allow a flow of gas 32 containing particulate matter to flow through a tubular ground chamber 34 and past the rigid screw electrode 18. The particles contained in the gas stream 32 are electrostatically charged as the gas stream 32 passes through the current flowing from the electrode 18 to the tubular ground chamber 34 within the ionizer section 33 of the ionizer housing 28. In a preferred embodiment, the ionizer section 33 is relatively short (between 6 inches and 12 inches) to minimize the collection of any charged particles that adversely affect the performance of the ionizer section 33.

In the preferred embodiment, the inner diameter of the gas inlet 30 varies depending on the velocity and volume of the gas stream 32. The diameter of the tubular ground cavity 34 is approximately 12 inches; although it is understood that larger and smaller diameters may be used depending on the velocity and volume of the gas stream 32.

Once charged, the gas stream 32 exits the ionizer housing 28 through an outlet chamber or transition 36 and flows to a duct 38, the duct 38 leading to a collection inlet 40 of the collection section 14. The collection system 14 includes a stationary or fluidized bed filled section 42 that is constantly flushed from above. The washing liquid flows down through the packed portion 42 and is collected in the liquid sedimentation tank 45. A recirculation pump 44 and a regeneration pipe 43 are provided to continuously flush the packed section 42.

The filling part 42 and the liquid settling tank 45 are grounded via a grounding lug 46. This allows the entire packed section and the recycled liquid to be used as a grounded collector of charged particles in the gas stream 32. The gas stream 32 containing charged particles passes through the packed section 42 where the charged particles are removed from the gas stream 32 by inertial collisions, coulomb forces, and image force (image force) attraction of the charged particles to the grounded packing 48. The resulting clean gas 50 is then passed through an entrainment separator section 52 to remove liquid droplets. The clean gas is discharged from the collecting section 14 through a collecting discharge 54, and the gas at the collecting discharge 54 is discharged to the atmosphere or further processed. Multiple ionization stages can be configured after collection by connecting multiple charging sections 12 and collection sections 14 in series to achieve higher particulate collection efficiency.

In the preferred embodiment, the fill portion 42 uses a vertical counterflow design that reduces the required area or footprint. Also in the preferred embodiment, the vertical orientation of the collection system 14 gives the apparatus less footprint and improves collection efficiency. The system 10 also allows for high ionization rates and high collection rates, which further significantly reduces the overall footprint of the system. Fluidized bed packing 48 is preferred because it is self-cleaning and therefore does not clog due to solids collection. The packing 48 also allows the agglomerated solids to be collected in slurry form, thereby minimizing liquid waste generated during operation.

It will be apparent to those skilled in the art that separating the charging section 12 and the collecting section 14 as provided herein has additional advantages. For example, the ionizing section 12 may be easily retrofitted to existing packed bed collection systems, including the Ceilcote IWS systems that are currently installed. This will reduce the mechanical complexity of the system, improve performance and allow for increased capacity. The large installed bottom of a vertical or horizontal fluid-packed bed scrubber can also add an ionizing section to the chemical scrubber system to improve particulate collection. The ionizing portion 12 may be positioned with respect to vertical or horizontal flow to achieve optimal position condition advantages. The speed may be varied based on application requirements. The dwell time of the charging section can be varied based on the application by varying the diameter and length of the cylindrical ground cavity 34.

Claims (19)

1. An ionized particulate scrubber for removing particulates from a gaseous exhaust stream, the scrubber comprising:

a charging section comprising one or more cylindrical tubular cavities having a rigid screw electrode extending centrally therethrough, the entire thread length of the screw electrode being the actual ion emitter charging the particles, the screw electrode being supplied with high voltage DC energy to cause a corona to form thereon, wherein the cylindrical tubular cavities contained within the walls of the ionizer housing serve as ground terminals to form the corona; and

a collection portion comprising a flush fill portion.

2. The ionized particulate scrubber of claim 1, wherein the cylindrical tubular chamber includes an ionizing section in which the particulates in the gaseous exhaust stream are electrically charged.

3. The ionized particulate scrubber of claim 2, wherein the ionizing section is between 6 and 12 inches in length.

4. The ionized particulate scrubber of claim 1, wherein the high voltage DC energy is provided by a transformer/rectifier.

5. The ionized particulate scrubber of claim 4, wherein the transformer/rectifier provides high voltage DC energy.

6. The ionized particulate scrubber of claim 5, wherein the transformer/rectifier is electrically connected to the rigid threaded rod electrode by HV cables or bus bars.

7. The ionized particulate scrubber of claim 6, wherein the HV cable is connected to the rigid screw electrode with a flux insulator.

8. The ionized particulate scrubber of claim 1, wherein the cylindrical tubular chamber includes a gas inlet and a gas outlet, the gas outlet being located at an end opposite the chamber gas inlet.

9. The ionized particulate scrubber of claim 1, further comprising a conduit extending from the charging portion to the collecting portion.

10. The ionized particulate scrubber of claim 1, wherein the packed section is selected from the group consisting of a fixed bed and a fluidized bed.

11. The ionized particulate scrubber of claim 1, wherein the collecting section further comprises a recirculation pump.

12. The ionized particulate scrubber of claim 11, wherein the collection section comprises a flushed packed bed and a liquid settling tank, and further comprising a grounding rod connected to the flushed packed bed and the liquid settling tank.

13. The ionized particulate scrubber of claim 1, wherein the collecting section further comprises an entrainment separator.

14. The ionized particulate scrubber of claim 13, wherein the collecting section further comprises a collecting drain for draining clean gas.

15. The ionized particulate scrubber of claim 1, wherein the rinse fill section is vertically or horizontally disposed.

16. The ionized particulate scrubber of claim 1, wherein the wash fill section uses a vertical counter-flow design.

17. An ionized particulate scrubber for removing particulates from a gaseous exhaust stream, the scrubber comprising:

a high voltage transformer/rectifier capable of producing high voltage DC energy;

a charging section comprising one or more cylindrical tubular cavities having a rigid screw electrode extending centrally therethrough, the entire thread length of the screw electrode being the actual ion emitter charging the particles, the screw electrode being electrically connected to the transformer/rectifier by HV cables and insulators, and the electrode being supplied with the high voltage DC energy to cause a corona to form thereon, wherein the cylindrical tubular cavities comprise an inner cylindrical wall that serves as a ground to form the corona, the tubular cavities comprising an ionizing section in which the particles in the gaseous exhaust stream are charged, the tubular cavities further comprising a gas inlet and a gas outlet, the gas outlet being located at an end opposite the gas inlet of the cavity;

a collection section comprising a flushing fixed or fluidized bed packed section, an entrainment separator, a settling tank pump and a collection drain to remove any liquid droplets from the gaseous drain stream; and

a conduit extending from the charging portion to the collection portion.

18. A method of removing particulates from a gaseous exhaust stream, the method comprising the steps of:

providing an ionized particulate scrubber comprising:

a charging section comprising one or more cylindrical tubular cavities having a rigid screw electrode extending centrally therethrough, the entire thread length of the screw electrode being the actual ion emitter charging the particles, the screw electrode being supplied with high voltage DC energy to cause a corona to form thereon, wherein the cylindrical tubular cavities comprise an inner cylindrical wall that serves as a ground to form the corona; and

a collection portion comprising a flush fill portion;

charging the electrode to form the corona;

passing a gas stream containing said particles through said tubular cavity past said electrode to thereby electrostatically charge said particles;

flowing the gas stream from the charging section to the collection section;

passing the gas stream containing the charged particles through the purge fill portion to thereby remove the particles; and

discharging said gas stream without said particles from said collection portion.

19. The method of claim 18, further comprising the step of flowing the gas stream through a plurality of charging sections and collection sections.