WO2017078618A1

WO2017078618A1 - An electrostatic precipitator

Info

Publication number: WO2017078618A1
Application number: PCT/SG2016/050160
Authority: WO
Inventors: Kim Lui So
Original assignee: Blue Sky Engineering & Trading Pte Ltd
Priority date: 2015-11-04
Filing date: 2016-03-31
Publication date: 2017-05-11
Also published as: WO2017078614A1

Abstract

An electrostatic precipitator for removing particles from an air stream, the electrostatic precipitator comprising: at least one ionizing electrode configured to charge the particles in the air stream during electrostatic precipitation; collectors configured to collect thereon charged particles from the air stream, a housing configured to house the collectors and the at least one ionizing electrode assembled therein and to allow passage of the air stream therethrough; and a washing fluid supply configured to provide washing fluid for washing collected particles off the collectors; wherein each collector is provided with through holes to allow passage of the washing fluid therethrough during washing of the collectors by the washing fluid while the collectors are assembled within the housing.

Description

AN ELECTROSTATIC PRECIPITATOR

FIELD OF THE INVENTION

This invention relates to an electrostatic precipitator and in particular, to a self-cleaning electrostatic precipitator.

BACKGROUND OF THE INVENTION

Electrostatic precipitators are particulate collection devices that clean air by removing particles from an air stream using an electrostatic charge. As shown in FIG. 1 (prior art), a conventional plate-type electrostatic precipitator typically comprises a stack of flat metal plates 200 spaced apart from each other to allow the air stream 202 to flow in the spaces there between. At least one ionizing electrode 300 is provided spaced apart from the metal plates 200. Each metal plate 200 serves as a collector 200 for aerosol particles carried in the air stream 202. Each ionizing electrode 300 serves as an electrode for at least one collector 200. When a voltage is applied between the ionizing electrode 300 and a collector 200, air around the electrode 300 in the stream 202 flowing through the space between the collectors 200 is ionized such that aerosol particles in the air stream are also ionized, or charged. Following the electric field created by the applied voltage, the charged particles are attracted to and move towards the collectors 200. The charged particles collect on the collectors 200 to form a layer that stays on the collectors 200. The exiting air stream 204 is thus cleaned from the charged particles that have collected on the collectors 200.

Since flow of the air stream 202 is minimally impeded and electrical energy is applied only to the particulate matter being collected, unlike wet scrubber filtration devices that apply energy directly to the flowing fluid medium, electrostatic precipitators are highly efficient in energy consumption and are highly efficient in removing fine particulate matter such as dust, smoke, oil and other particulate contaminants from the air stream. Electrostatic precipitators may thus be used in power plants, cement plants or kitchen exhaust systems to clean air containing particles such as smoke and oil fumes before discharging cleaned air into the outside environment.

However, it is well known that the efficiency of an electrostatic precipitator falls dramatically once the collectors have been coated with a layer of the collected particles. Cleaning of the collectors is therefore an important aspect in the use of electrostatic precipitators.

When large amounts of particles have accumulated as a layer on the collectors, vigorous washing and scrubbing may be needed to thoroughly clean the collectors because the collected layer may have become very tightly bonded to the collectors. Cleaning the collectors is usually a laborious and difficult process because close spacing between the collectors that is necessary for efficient precipitation gives rise to difficulty accessing the areas to be cleaned. Also, the stack of collectors may not be easily disassembled to facilitate cleaning.

Attempts to facilitate cleaning of the collectors include using special soaking solutions where the entire stack of collectors is removed en bloc from the electrostatic precipitator and soaked in a container of the soaking solution for a period of time, for example overnight, to loosen the layer that has become tightly bonded to the collectors. Other solutions include providing jets of washing fluid such as water or detergent directed at the collectors to spray off the collected layer, where the spray nozzles that are specially designed for this purpose are included as part of a self-cleaning feature of the electrostatic precipitator. However, due to close spacing between the collectors, it is still difficult to effect thorough cleaning of the inner parts of the collectors with externally applied jets of washing fluid.

SUMMARY OF INVENTION

According to a first aspect, there is provided an electrostatic precipitator for removing particles from an air stream, the electrostatic precipitator comprising: at least one ionizing electrode configured to charge the particles in the air stream during electrostatic precipitation; collectors configured to collect thereon charged particles from the air stream, a housing configured to house the collectors and the at least one ionizing electrode assembled therein and to allow passage of the air stream therethrough; and a washing fluid supply configured to provide washing fluid for washing collected particles off the collectors; wherein each collector is provided with through holes to allow passage of the washing fluid therethrough during washing of the collectors by the washing fluid while the collectors are assembled within the housing. Each collector may be made of one of: expanded metal, wire mesh, and perforated metal.

Each collector may have a form of a conductive sheet. Alternatively, each collector may have a form of a hollow tube, and wherein an ionizing electrode is provided within each collector.

The electrostatic precipitator may further comprise a heater provided in the housing and configured to generate heat for drying the electrostatic precipitator after washing of the collectors by the washing fluid.

The heater provided in the housing may be further configured to heat the collectors during washing of the collectors by the washing fluid. The electrostatic precipitator may further comprise a control system configured to activate a cleaning routine of the collectors at predetermined time intervals, the cleaning routine comprising spraying the washing fluid onto the collectors for a period of time.

The cleaning routine may further comprise halting passage of the air stream into the housing during the cleaning routine.

The cleaning routine may further comprise cutting off power supply to the at least one ionizing electrode and the collectors during the cleaning routine. The cleaning routine may further comprise switching on the heater provided in the housing for a further period of time after spraying the washing fluid onto the collectors for the period of time.

The cleaning routine may further comprise switching on the heater provided in the housing prior to spraying of the washing fluid onto the collectors.

Further collectors configured to collect charged particles from the airstream thereon may be provided downstream of the at least one ionizing electrode, the further collectors comprising charged collectors alternated with grounded collectors, wherein an electric field is generated between the charged collectors and the grounded collectors during electrostatic precipitation, and wherein the further collectors are each provided with through holes to allow passage of the washing fluid therethrough during washing of the further collectors by the washing fluid while the further collectors are assembled within the housing.

BRIEF DESCRIPTION OF FIGURES

In order that the invention may be fully understood and readily put into practical effect there shall now be described by way of non-limitative example only exemplary embodiments of the present invention, the description being with reference to the accompanying illustrative drawings.

FIG. 1 (prior art) is a schematic illustration of the working principle of electrostatic

precipitation.

FIG. 2 is a schematic illustration of a first exemplary embodiment of an electrostatic

precipitator during electrostatic precipitation.

FIG. 3 is a schematic illustration of the electrostatic precipitator of FIG. 2 during washing. FIG. 4 is a photograph of a first exemplary collector comprising a conductive sheet provided with through holes in the form of an expanded metal sheet.

FIG. 5 is a photograph of a second exemplary collector comprising a conductive sheet

provided with through holes in the form of a wire mesh.

FIG. 6 is a photograph of a second exemplary collector comprising a conductive sheet

provided with through holes in the form of a perforated metal sheet.

FIG. 7 is a schematic illustration of a second exemplary embodiment of an electrostatic

precipitator during washing.

FIG. 8 is a schematic illustration of a third exemplary embodiment of an electrostatic

precipitator during electrostatic precipitation.

DETAILED DESCRIPTION

Exemplary embodiments of the electrostatic precipitator will be described with reference to FIGS. 2 to 10 below in which the same reference numerals are used to denote the same or similar parts.

As shown in FIG. 2, a first exemplary embodiment of the electrostatic precipitator 10 for removing particles from an air stream 100 comprises collectors 20 configured for collecting charged particles thereon. At least one ionizing electrode 30 is provided between adjacent collectors 20 in order for a voltage to be applied between the collectors 20 and the at least one ionizing electrode 30 during electrostatic precipitation to generate an electric field and ionise the air around the ionizing electrode 30 which causes particles in the air stream 100 to become charged particles that are attracted to the collectors 20. The charged particles migrate to the collectors 20 and collect on the collectors 20 to form a layer of collected particles on each collector 20. The ionizing electrodes 30 may be provided in the form of plates or wires. The electrostatic precipitator 10 also comprises a housing 90 configured to house the collectors 20 and the at least one electrode 30 therein. The housing 90 is configured to allow passage of the air stream 100 therethrough, and thus may be configured to be placed within an air path through which the air stream 100 is passed normally passed, or the housing 90 may be configured to form part of any cleaning device, for example such as an air cleaner, dust collector, fume chamber or kitchen exhaust hood, as may be desired.

In the first embodiment, as shown in FIG. 3, each of the collectors 20 comprises a conductive sheet 20 configured to be washable by a washing fluid 66, the conductive sheet 20 being provided with through holes to allow passage of the washing fluid 66 therethrough while the collectors 20 are assembled in the housing 90. The conductive sheet 20 may be made of expanded metal (FIG. 4), wire mesh (FIG. 5), perforated metal (FIG. 6) and the like. The electrostatic precipitator 10 also comprises a washing fluid supply 60 that is configured to provide the washing fluid 66 for washing the collected particles off the collectors 20. In a preferred embodiment, at least one outlet of the washing fluid supply 60 comprises a spray nozzle configured to spray the washing fluid 66 onto the collectors 20. Configuring each collector 20 to be in the form of a conductive sheet provided with through holes 20 allows the washing fluid 66 to wash not only the collectors 20 that are nearest to outlets of the washing fluid supply 60, but also allows the washing fluid 66 to pass through the through holes of each collector 20 so as to reach and wash all the collectors 20 in the electrostatic precipitator 10. In this way, all areas of all the collectors 20 can be effectively and thoroughly washed and cleaned by the washing fluid 66 sprayed therethrough.

In a second embodiment as shown in FIG. 7, the electrostatic precipitator 10 is the same as the first embodiment except that each collector 20 is in the form of a hollow tube instead of a conductive sheet, and an ionizing electrode 30 is provided within each collector 20. Each hollow tube 20 may similarly be made of expanded metal (FIG. 5), wire mesh (FIG. 6), perforated metal (FIG. 7) and the like that has been shaped into the form of a hollow tube 20. In this way, the hollow tube collector 20 is provided with through holes to allow passage of the washing fluid 66 therethrough while the collectors 20 are assembled in the housing 90, as shown in FIG. 8. The hollow tube collectors 20 are preferably all oriented in a same direction. In one embodiment, the hollow tube collectors 20 have circular cross-sections to be in the form of hollow cylinders.

In a third embodiment as shown in FIG. 8, the electrostatic precipitator 10 comprises a first section 101 having a plurality of first collectors 20-1 alternated with a plurality of ionizing electrodes 30, in order for a voltage to be applied between the collectors 20 and the ionizing electrodes 30 during electrostatic precipitation to generate an electric field and ionise the air around the ionizing electrodes 30 which causes particles in the air stream 100 to become charged particles that are attracted to the collectors 20-1. The ionizing electrodes 30 may be provided in the form of plates or wires. The electrostatic precipitator 10 also comprises a second section 102 provided downstream of the first section 101 , both the first and second sections 101, 102 being provided in a housing 90 configured to allow passage of the air stream 100 therethrough. The second section 102 comprises further collectors 20-2, 20-G configured to collect charged particles from the airstream 100. The further collectors comprise a plurality of charged collectors 20-2 and a plurality of grounded collectors 20-G that are alternated and spaced apart from each other. An electric field is generated between the charged collectors 20-2 and the grounded collectors 20-G by applying a voltage to the charged collectors 20-2 during electrostatic precipitation. In one configuration, the voltage applied to the charged collectors 20-2 may be half the voltage applied between the ionizing electrodes 30 and the first collectors 20-1. For example, the voltage between the ionizing electrodes 30 and the first collectors 20-1 may be 13kV while a voltage of 6.5 kV is applied to the charged collectors 20-2.

It is observed that by generating an electric field between the charged collectors 20-2 and the grounded collectors 20-G during electrostatic precipitation, collection of charged particles on the grounded collectors 20-G is enhanced, thereby improving efficiency of removal of particles from the air stream 100. In use, it can be expected that some particles in the air stream 100 also adhere to the charged collectors 20-2. By providing the second section 102 with additional collectors 20-2, 20-G, more particles can be removed from the air stream 100 to improve air cleaning efficiency of the electrostatic precipitator 10.

All the first collectors 20-1 and further collectors 20-2, 20-G in the third embodiment are provided with through holes to allow passage of the washing fluid 66 therethrough while the first and further collectors 20-1 , 20-2, 20-G are assembled in the housing 90. In one configuration, each of the collectors 20-1 , 20-2, 20-G comprises a conductive sheet that may be made of expanded metal (FIG. 5), wire mesh (FIG. 6), perforated metal (FIG. 7) and the like.

For all embodiments, the electrostatic precipitator 10 preferably comprises a control system (not shown) configured to activate a cleaning routine at predetermined time intervals. The cleaning routine comprises turning on the washing fluid supply 60 and spraying the washing fluid 66 onto the collectors 20 for a period of time so as to remove the collected particles from the collectors 20.

Preferably, during the cleaning routine, passage of the air stream 100 through the housing 90 and the collectors 20 is halted. In addition, power supply to the at least one ionizing electrode 30 and the collectors 20 is preferably cut off for the duration of the cleaning routine.

Optionally, the electrostatic precipitator 10 may also comprises a heater 70 provided in the housing 90. The heater 70 provided in the housing 90 is configured to be switched on after the collectors 20 have been washed with washing fluid 66 so that heat generated by the heater 70 dries the collectors 20 and the ionizing electrodes 30 and any other parts of the electrostatic precipitator 10 that have been wet by the washing fluid 66. Switching on the heater 70 provided in the housing for a period of time may thus be incorporated into the cleaning routine described above as a final step after washing of the collectors 20 with the washing fluid 66 has been completed.

In addition to being switched on to dry the electrostatic precipitator after washing of the collectors 20 with the washing fluid 66, the heater 70 provided in the housing 90 may also be switched on to heat the collectors 20 for washing, for example, just prior to spraying the washing fluid 66 onto the collectors 20. This is particularly intended for washing the collectors 20 with heated washing fluid 66. Heating the collectors 20 minimizes cooling of the washing fluid 66 upon contact with the collectors 20, in order to maintain cleaning efficiency of the heated washing fluid 66. Besides providing a heater 70 in the housing 90 for drying the electrostatic precipitator 10 after washing, drying may additionally or alternatively be performed by ventilation drying means, such as by using a fan or channelling dry air into the electrostatic precipitator 10.

By configuring the electrostatic precipitator 10 to comprise collectors 20 provided with through holes, washing of the collectors 20 can be effectively performed in situ without requiring the collectors 20 to be removed or disassembled from the housing for washing, and without requiring the entire electrostatic precipitator 10 to be removed for cleaning. Preferably, the through holes have a diameter of about 3.5 mm to avoid surface tension across the through holes preventing the washing fluid 66 from passing through the through holes.

The present invention not only simplifies construction of the electrostatic precipitator 10 and reduces its production and maintenance costs, the simplicity and speed of in situ cleaning also allows washing of the collectors 20 to take place far more frequently when compared to prior art cleaning methods. The present electrostatic precipitator 10 is thus able to continually function at a high level of collection efficiency at a minimal operating and maintenance cost. This makes it especially suited for use in applications such as industrial kitchens of restaurants and commercial facilities to remove oil and smoke aerosol particles from cooking fumes in the kitchen exhaust before discharging the kitchen exhaust into the atmosphere. Since these kitchens are in frequent and heavy use, the electrostatic precipitator 10 needs to operate continually at high efficiency, it is important not to allow accumulation of a greasy layer on the collectors 20 as it is well known that long accumulated oil and smoke residue are particularly difficult. Thus, configuring the electrostatic precipitator 10 with collectors having through holes 20 that can be readily washed in situ allows the collectors 20 to be cleaned very frequently, on a daily basis if necessary, when the kitchen has closed for the day.

Whilst there has been described in the foregoing description exemplary embodiments of the present invention, it will be understood by those skilled in the technology concerned that many variations in details of design, construction and/or operation may be made without departing from the present invention. For example, the washing fluid 66 may be of any suitable type, and more than one type of washing fluid may be used to wash the collectors 20. For example, the washing fluid 66 may comprise water or water with a detergent or degreaser or any other appropriate cleaning agents. Furthermore, a first cycle of the cleaning routine may include a detergent in the washing fluid, while a second cycle of the cleaning routine may use clear water as the washing fluid to remove residual detergent from the collectors. In addition to or alternative to the top down spray of washing fluid as depicted in FIGS. 3 and 7, the washing fluid supply may have any other suitable configuration Besides conductive sheets and hollow tubes as described and depicted, the collectors provided with through holes may have any other desired shape or configuration for collecting particles charged by the ionizing electrodes. For example, where the collectors are hollow tubes, instead of cylinders, the collectors may have cross-sections that are rectangular or hexagonal or any other shape as may be desired, for example to optimize surface area and volume of the collectors within the housing.

Claims

1. An electrostatic precipitator for removing particles from an air stream, the electrostatic precipitator comprising:

at least one ionizing electrode configured to charge the particles in the air stream during electrostatic precipitation;

collectors configured to collect thereon charged particles from the air stream, a housing configured to house the collectors and the at least one ionizing electrode assembled therein and to allow passage of the air stream therethrough; and

a washing fluid supply configured to provide washing fluid for washing collected particles off the collectors;

wherein each collector is provided with through holes to allow passage of the washing fluid therethrough during washing of the collectors by the washing fluid while the collectors are assembled within the housing.

2. The electrostatic precipitator of claim 1, wherein each collector is made of one of: expanded metal, wire mesh, and perforated metal.

3. The electrostatic precipitator of claim 1 or claim 2, wherein each collector has a form of a conductive sheet.

4. The electrostatic precipitator of claim 1 or claim 2, wherein each collector has a form of a hollow tube, and wherein an ionizing electrode is provided within each collector.

5. The electrostatic precipitator of any preceding claim, further comprising a heater provided in the housing and configured to generate heat for drying the electrostatic precipitator after washing of the collectors by the washing fluid.

6. The electrostatic precipitator of claim 5, wherein the heater provided in the housing is further configured to heat the collectors during washing of the collectors by the washing fluid.

7. The electrostatic precipitator of any preceding claim, further comprising a control system configured to activate a cleaning routine of the collectors at predetermined time intervals, the cleaning routine comprising spraying the washing fluid onto the collectors for a period of time.

8. The electrostatic precipitator of claim 7, wherein the cleaning routine further comprises halting passage of the air stream into the housing during the cleaning routine.

9. The electrostatic precipitator of claim 7 or claim 8, wherein the cleaning routine further comprises cutting off power supply to the at least one ionizing electrode and the collectors during the cleaning routine.

10. The electrostatic precipitator of any one of claims 7 to 9 when dependent on any one of claims 5 or 6, wherein the cleaning routine further comprises switching on the heater provided in the housing for a further period of time after spraying the washing fluid onto the collectors for the period of time.

1 1. The electrostatic precipitator of any one of claims 7 to 10 when dependent on any one of claims 5 or 6, wherein the cleaning routine further comprises switching on the heater provided in the housing prior to spraying of the washing fluid onto the collectors.

12. The electrostatic precipitator of any preceding claim, wherein further collectors configured to collect charged particles from the airstream thereon are provided downstream of the at least one ionizing electrode, the further collectors comprising charged collectors alternated with grounded collectors, wherein an electric field is generated between the charged collectors and the grounded collectors during electrostatic precipitation, and wherein the further collectors are each provided with through holes to allow passage of the washing fluid therethrough during washing of the further collectors by the washing fluid while the further collectors are assembled within the housing.