RU2464067C2 - Method of air cleaning from aerosols in enclosed spaces - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to methods of air cleaning. It may be used in any industry, medicine, aviation etc. Proposed method consists in that indoor air is cleaned of coarse dust with particle size exceeding 4 mcm by known procedures. Then, air if forced through fluoroplastic diaphragm at leaner velocity not exceeding 4 cm/s in single step not exceeding 1.5 h. Said step over, filtered airflow is switched over to sort-term discharge of accumulated fine dust with particle size smaller than 4 mcm for 3-10 s into external atmosphere. Thus, cleaned filter does not accumulate whatever dust, nor increase airflow drag and stays available for next cleaning step.

EFFECT: expendables are completely withdrawn from process.

Description

The invention relates to methods for air purification. It is intended for use in various industries, in medicine, aviation, for air conditioning of residential and industrial buildings, closed facilities. The proposed method can be used, for example, for air purification in residential premises.

The main directions for improving indoor air purification facilities are related to the exclusion of the use of consumables in the process of air purification; reducing energy consumption in the process of indoor air purification and improving the quality of air purification.

Coarse dust (particle size greater than 4 microns) is retained by known cleaning agents (cloth bags, cyclones, containers, etc.). These tools provide air purification to a level of 90-95%. Coarse dust settles in this case in a specially designed container (dust collector) with its subsequent dumping into the garbage container after the end of the cleaning session. Fine filters installed at the outlet of the air stream are designed to delay fine dust with particle sizes less than 4 microns, allergens and microorganisms, including viruses. It should be noted that it is this part of the dust that is most harmful to humans. For people with allergies or asthma, air purification is required not lower than the class HEPA N 12 (dust retention of at least 99.5%). But such filters work in cumulative mode.

Known means of air purification based on the sparging of the air flow through a layer of water (aquafilters). For example, patent RU 2321329, A47L 9/10, 2008, patent RU 2249425, A47L 9/10, 2005, patent RU 2286710, A47L 7/00, 2006. However, the efficiency of air purification with water filters is largely determined by the chemical and physical nature of the captured particles , namely their ability to wet. In most cases, fine dust is poorly wetted during the contact of the stream with water. As a result, very often there is a slip of this dust into the atmosphere to be cleaned.

Known methods for fine purification of air at the final stage of purification using electrostatic microfilters and filter materials class HEPA (High Efficiency Particutate Air - high-efficiency particle retention), as well as S-class filters. An S-class filter can be any filter that provides a filtration efficiency of 99.97% or more (particle delay larger than 0.3 microns). These filters are distinguished from each other by particle retention efficiency and service life.

Electrostatic microfilters are made of electrified microfiber cellulose or propylene (patent RU 2334449, A47L 9/10, 2008). They are disposable or reusable and differ from each other in work efficiency, service life, presence or absence of a frame and gaskets. Electrostatic microfilters are recommended to be replaced every 5 paper dust collectors. The efficiency of air purification using such filters ranges from 80 to 99.9% (particle delay with a size of more than 0.3 microns). But they are usually complex and require subsequent additional post-treatment.

Known methods for fine purification of air at the final stage of purification using 3-class fiber volumetric filters and HEPA filters that provide high delay efficiency of the smallest particles and allergens (see patent RU 22571129, A47L 9/12, 2002; patent RU 2257831, A47L 9/10, 2003; patent RU 2200615, B01D 39/16, 2001).

As a prototype of the invention, the method proposed in the patent RU 22571129, A47L 9/12, 2002 is selected. Initially, dusty air is passed through a cyclone and it is cleaned of coarse dust. Then air is passed through a fine filter (HEPA filter). The theoretical life of such filters is about 50 hours of operation, if the filter can be washed with water. In addition, HEPA filters are quite compact.

HEPA filters can be washable and simply replaceable. If the washable filter is dirty, it can be washed, dried and put back. But, it is important to note that they always work in accumulation mode. The disadvantage of this HEPA filter is the impossibility of its complete regeneration (full recovery) and the gradual irreversible accumulation of dust in the filter volume. Any HEPA filters are gradually clogged irreversibly and must be replaced periodically (consumable).

Clogged HEPA filters create high airflow resistance and therefore increase energy consumption. It should also be noted that replaceable HEPA filters are of high cost.

There is another important drawback of such filters, which are usually silent. This is the possibility of the accumulation of toxic substances (including radioactive ones) or the formation of an environment for the cultivation of microorganisms (bacteria, viruses) in the volume of the HEPA filter. During storage, it is possible to redistribute these substances in the filter volume with subsequent partial release of them back into the medium to be cleaned.

These are the main disadvantages of filter media, including HEPA filters.

The objectives of the invention is:

- eliminating the need to use consumables in the process of air purification;

- elimination of the possibility of accumulation of toxic substances and microorganisms in the filter volume;

- reduction of resistance (power consumption) in the process of purifying indoor air.

The above problems are solved by the method of air purification from aerosols in enclosed spaces, namely, that the air of the room is preliminarily cleaned of coarse dust with a particle size of more than 4 microns by known methods, and characterized in that the air is then passed through a fluoroplastic membrane with a linear velocity of not more than 4 cm / sec, during a one-time work session lasting no more than 1.5 hours, and at the end of the work session, the filtered air flow is switched to a short-term discharge of accumulated a session of fine dust with a particle size less than 4 microns and retained for a session fine dust shed for 3-10 sec in the atmosphere of the external environment.

The first feature of the method (the first distinguishing feature) is that after air passes through the cyclones and separates coarse dust, it enters the fluoroplastic membrane filter selected as the HEPA filter. A distinctive feature of the fluoroplastic filter as a material is its excellent release properties, a low coefficient of friction of its surface with other materials, high chemical inertness and high hydrophobicity. The use of fluoroplastic as a filter material, thus, virtually eliminates the possibility of adhesion of dust to the surface of the material.

The second feature of the method (the second distinguishing feature) is that the linear velocity of air flow through the filter material is not more than 4 cm / s. In the proposed method, the air flow through the filter is 10-20 times less than through a conventional HEPA filter. It also reduces the possibility of dust adhering to the filter surface. In addition, the dust remains on the surface of the filter, while not penetrating into its volume, as is the case with replaceable HEPA filters. Aerosol particles (up to 0.01 μm) are retained on the surface of such a filter not only and not so much due to the small size of the holes in the filter, but rather due to the electrostatic potential that appears due to air friction when passing through the membrane. In this case, the filtering surface of the fluoroplastic filter should be significantly larger (about an order of magnitude) compared with the total surface of the HEPA filter.

Thus, in contrast to the usual HEPA filter, the fluoroplastic material does not absorb dust, but rather rejects it. The listed features of the proposed cleaning method (the choice of fluoroplastic and the choice of a low linear flow rate) provide the ultimate reversibility of the filtration - regeneration process at the final stage.

The third feature of the method (the third distinguishing feature) is that finely dispersed dust (about 1% of the total mass of dust) of air concentrated during the filtering session is discharged into the atmosphere. At the end of the session (approximately 1 hour), the filtered air stream is switched to a short-term (5-10 sec) discharge of fine dust accumulated during the session with a particle size of less than 4 microns into the atmosphere (outside the cleaned room). The air flow in this case can be reverse or directed parallel to the surface of the filter material. In this case, the electrostatic voltage on the surface of the filter (air friction with the filter material actually stops) drops within 3-8 seconds. Fine dust accumulated during the session is discharged into the atmosphere for 3-10 seconds, and large dust remains in the garbage container (99% of the total mass of dust).

Thus, at the final stage of cleaning, an extremely small fraction of dust (not more than 1%) falls on the filter. In fact, this is a part of the dust invisible to the naked eye, although it is the most hazardous to health. As a rule, the concentration of discharged dust does not exceed the background concentration of the external environment. And finally, the microorganisms of the dust discharged by the specific environment of the enclosed space die when discharged into a foreign environment.

The accumulation of fine dust insignificant in mass and volume, at least for 1-1.5 hours, does not lead to a significant increase in the resistance of the fluoroplastic filter (about 1-2 kPa).

Distinctive features of the method is that a fluoroplastic membrane is selected as the HEPA material, through which fine dust is passed at a speed of 1-4 cm / s and concentrated fine air dust is discharged into the atmosphere.

In the totality of the above distinguishing features, the essence of the invention is expressed. The exclusion of any of these signs does not allow to solve the above tasks, that is, to achieve the desired technical result.

Thus, the cleaned filter does not accumulate any dust, does not increase resistance to air flow and becomes fully prepared for the next session. Consumables are excluded from circulation completely.

The discharge of 1% fine dust is most expedient directly into the atmosphere by blowing, but if this is not possible, concentrated dust can be planted on a one-time, cheap filter material, followed by washing off the dust. The direct dust discharge operation takes about 5-10 seconds. This is due to the absence of any adherence of dust to the filter material, the possibility of simple regeneration of the filter. The filter operating time in the filtration stage is incomparably longer than its regeneration time.

The proposed method in General is as follows. Initially, dusty air is passed through coarse dust separation means (with a particle size of more than 4 microns), for example, through a small diameter cyclone battery. Coarse dust is transferred to a dust collector if cleaning is carried out indoors, or discharged back into the external environment if air is taken from the external atmosphere into the room (for example, when cleaning external air contaminated with toxic or radioactive substances). Then, the air purified from coarse dust is passed through a fluoroplastic membrane with a linear speed of 1-4 cm / s, during a work session lasting no more than 1.5 hours, and at the end of the work session, the filtered air flow is switched to short-term discharge of fine dust accumulated during the session ( with a particle size of less than 4 microns), and the fine dust accumulated during the session is discharged within 5-10 seconds into the atmosphere of the environment.

The air purification method proposed above has been tested on prototype filter systems. After air passed through the battery (five) of small diameter cyclones (25 mm), air entered the fluoroplastic membrane filter element. Through the hydrophobic fluoroplastic (F42L) membrane of the MFK-3 brand (TU-6-55-221-1413-01), a stream of air was passed into one layer at a speed of 4 cm / s. The pore size of the membrane is 0.65 microns. The holding capacity for aerosol particles of 0.3 microns in size at a speed of 1 cm / s is at least 99.00%. The indicated particle delay efficiency corresponds approximately to the class of PER NI. In the experiments we used fluoroplastic membranes of the MFFK brand manufactured by NPP Vladipor LLC. BS-120 white soot (GOST 18307-78) was used as model dust. The average particle size of the soot BS-120 brand is 19-27 nm. Air was "sparged" through a layer of dried white soot. The concentration of supplied dust is 10 g / m ³ .

For comparison, filter paper hydrophobic type BFB-G (TU 13-00281097-34-95) was used as a HEPA type material. The duration of the working cycle was 45 minutes The regeneration of the filter surface was carried out by reverse purging for 10 seconds after each cycle. The results of the experiments are presented in the table.

Table Comparative characteristics of air purification devices made according to the known and proposed methods The characteristics of the device and method A device made by a known method The device made by the proposed method - The first stage of cleaning Small diameter cyclone battery Small diameter cyclone battery - Second stage of cleaning PERA type filter media Fluoroplastic (F42L) membrane - Permeability coefficient,%, no more 1.10 ^-4 1.10 ^-4 - Productivity by air, m ³ / hour 40 40 - Filtration rate, cm / s 72 four - The working area of filtration, cm ² 154 2500 - Resistance at the end of duty cycle 1, KPa 6 6 - Resistance at the end of the operating cycle 50, KPa 8 6 - A way to restore the filter (dust removal) Periodic washing of the filter material (the filter is not completely regenerated) Dust discharge into the environment after each cycle (the filter is completely regenerated) - The possibility of accumulation of dust in the filter material Saved Absent - The need to change the filter of the second stage (availability of consumables) Saved Absent

As can be seen from the comparative data in the table, the need to use consumables in the air purification process is eliminated, the resistance (energy consumption) in the process of air purification in the room is reduced, and finally, the possibility of accumulation of toxic substances and microorganisms in the HEPA filter is eliminated. The latter circumstance gives this method a new important quality.

The compactness of the air purification devices operating by this method does not actually decrease, since the dimensions of the filtering systems as a whole are determined by means of rough cleaning (a set of cyclones). To ensure compactness, the filter is corrugated (corrugated).

Claims (1)

The method of air purification from aerosols in enclosed spaces, which consists in the fact that the room air is preliminarily cleaned of coarse dust with a particle size of more than 4 μm by known methods, characterized in that the air is then passed through a fluoroplastic membrane with a linear velocity of not more than 4 cm / s, during a one-time work session lasting no more than 1.5 hours, and at the end of the work session, the filtered air flow is switched to a short-term discharge of fine dust accumulated during the session with a particle size of less than 4 microns and fine dust accumulated during the session are discharged into the atmosphere of the environment for 3-10 s.