The present invention relates to an activated carbon fibre filter for example for indoor air purification.
In 2001, Subremat et al. in Carbon, volume 39, pages 707-716 reported the desorption by Joule effect heating of volatile organic compounds (VOCs) adsorbed on activated carbon cloth and established that the electrical resistance of activated carbon cloth could be determined from the geometrical size of the piece and the electrical resistivity of the fabric.
In 2009 Yao et al. in Journal of the Air & Waste Management Association, volume 59, pages 31-36 reported the application of activated carbon fibre cloth (ACFC) as a regenerative adsorbent for the removal of VOCs from indoor air, with single layer ACFC exhibiting remarkable adsorption and regenerative properties using 100 parts per billion by volume (ppbv) toluene as the indoor contaminant. They also reported that Joule heating regeneration of the ACFC was rapid and showed very good performance even after 300 heating and cooling cycles.
In 2019 Roegiers et al. in Chemical Engineering Journal, volume 365, pages 80-87 reported the investigation of activated carbon fibers for indoor air purification by means of pressure drop and adsorption capacity, the Darcy-Forchheimer law combined with Computational Fluid Dynamics (CFD) modelling being deployed to simulate the pressure drop over an FM10 (Calgon Corp) activated carbon fiber cloth (ACFC) filter disposed perpendicularly to the air flow with varying filter thickness (single layer, two layer, three layer and four layer) and Joule effect heating to 150° C. in combination with a clean air flow of 2000 cm3/min being used to regenerate the filter by desorbing the acetaldehyde used as a model pollutant.
WO 2017/140967A1 discloses a regenerable filter comprising: a filtering matrix, adapted to allow the circulation of a flow of fluid therein, from an inlet to an outlet of said filter matrix, so as to filter said fluid, and at least one heating element comprising at least a first and a second electrode, positioned at a defined distance from each other and connected to each other via a conductive material, said conductive material being a positive temperature coefficient material, adapted to function as a heating resistor and allow the electrical connection to be cut between said first and second electrodes when the temperature of said conductive material reaches a threshold temperature; a method for regenerating said filter and the use of said method.
US 20020170435A1 discloses an air filtration system for placing in an air stream comprising: 1) a pleated, air permeable filter medium of electrically insulative material having folded edges present along both an up-stream side and a down-stream side of said filter medium with respect to the direction of airflow to be passed therethrough; 2) exposed, conductive, fiber ends located at least along the up-stream side of said filter medium; 3) an ion-inducing conductive array positioned along the downstream side of the filter medium; and 4) coupling means for connecting a high voltage power supply between said fiber ends and conductive array to create an electric field between them, whereby said conductive fiber ends, when provided with an ionizing voltage potential, will emit ions that charge dust particles to increase the trapping efficiency of the air filtration system. This differs from the present invention in that the filter consists of an electrically insulating (fibrous) material (only the tips of the pleats are electrically charged), whereas in the present application the electrical current must pass through the filter in order to induce the Joule effect i.e. the filter itself is conducting.
WO 02-09847A1 discloses a regenerable air cleaning device comprising: a filter holder supporting a regenerable filter that includes activated carbon fibers (ACF); and a control system that is adapted to determine when to regenerate the regenerable filter. In the device therein disclosed, the supporting system for the pleated ACF consists of non-conducting pleating bars, installed in a rectangular housing and two electrodes are present on opposite sides of the ACF filter, whereas in the present invention the electrodes are present in the pleated tips and hence form the supporting system and the electrical circuit consists of a number of resistances in parallel.
In 2019 Roegiers et al. in Chemical Engineering Journal, volume 365, pages 80-87 showed that an increase in filter thickness of ACF cloth was found to increase acetaldehyde adsorption, but at the expense of pressure drop, which scaled with filter thickness, illustrating the perceived trade-off in filtering systems between adsorption capacity and pressure drop across the filter medium, the experimental data for pressure drop followed the predictions from Computational Fluid Dynamics (CFD) modelling. It is known from HEPA technology that pleated filters have the advantage that pressure loss can be lowered by increasing the surface area. With pleating, pressure drop is not only generated by the filter medium, but also by viscous drag in the pleat spacings. Here CFD modelling predicted a significantly lower pressure drop for a particular increase in available surface area for adsorption which was borne out experimentally, thereby reducing the trade-off between adsorption and pressure drop.
It is an objective technical problem realized by the regenerable gas filter of the present invention to reduce the power consumption required for regeneration of a pleated filter.
A further advantage of the present invention is the use of such a filter for the purification of air in a Heating, Ventilation and Air Conditioning (HVAC) system.
According to a first aspect of the present invention, a regenerable gas filter is provided, said regenerable gas filter comprising a housing having in-line an entrance and an exit, a pleated activated carbon fibre sheet or tube, each pleat having two substantially rectangular elements, with electrical conductors in the tip of each pleat and further electrical conductors being optionally attached to the ends of said sheet, said conductors being disposed substantially perpendicularly to the gas flow through said housing and said conductors on one side of said pleated sheet being connected to a single central conductor, which in turn was coupled to an electrical DC power source, this being repeated for the conductors on the other side of said pleated sheet, said sheet being stretched over and in electrical contact with said conductors and said pleated sheet or tube being provided with a sealing means to said housing.
According to a second aspect of the present invention said regenerable gas filter is used for the purification of air in a Heating, Ventilation and Air Conditioning (HVAC) system.
Particular and preferred aspects of the invention are set out in the accompanying independent and dependent claims. Features from the dependent claims may be combined with features of the independent claims and with features of other dependent claims as appropriate and not merely as explicitly set out in the claims.
Although there has been constant improvement, change and evolution of devices in this field, the present concepts are believed to represent substantial new and novel improvements, including departures from prior practices, resulting in the provision of more efficient, stable and reliable devices of this nature.
The above and other characteristics, features and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. This description is given for the sake of example only, without limiting the scope of the invention. The reference figures quoted below refer to the attached drawings.
In the different figures, the same reference signs refer to the same or analogous elements.
The present invention will be described with respect to particular embodiments and with reference to certain drawings but the invention is not limited thereto but only by the claims. The drawings described are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn on scale for illustrative purposes. The dimensions and the relative dimensions do not correspond to actual reductions to practice of the invention.
Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequence, either temporally, spatially, in ranking or in any other manner. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein.
Moreover, the terms top, bottom, over, under and the like in the description and the claims are used for descriptive purposes and not necessarily for describing relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other orientations than described or illustrated herein.
It is to be noticed that the term “comprising”, used in the claims, should not be interpreted as being restricted to the means listed thereafter; it does not exclude other elements or steps. It is thus to be interpreted as specifying the presence of the stated features, integers, steps or components as referred to, but does not preclude the presence or addition of one or more other features, integers, steps or components, or groups thereof. Thus, the scope of the expression “a device comprising means A and B” should not be limited to devices consisting only of components A and B. It means that with respect to the present invention, the only relevant components of the device are A and B.
Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment, but may. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner, as would be apparent to one of ordinary skill in the art from this disclosure, in one or more embodiments.
Similarly, it should be appreciated that in the description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various inventive aspects. This method of disclosure, however, is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the claims following the detailed description are hereby expressly incorporated into this detailed description, with each claim standing on its own as a separate embodiment of this invention.
Furthermore, while some embodiments described herein include some but not other features included in other embodiments, combinations of features of different embodiments are meant to be within the scope of the invention, and form different embodiments, as would be understood by those in the art. For example, in the following claims, any of the claimed embodiments can be used in any combination.
In the description provided herein, numerous specific details are set forth. However, it is understood that embodiments of the invention may be practiced without these specific details. In other instances, well-known methods, structures and techniques have not been shown in detail in order not to obscure an understanding of this description.
The following terms are provided solely to aid in the understanding of the invention.
ACF, as used in disclosing the present invention, is an abbreviation of activated carbon fibre, which is a microporous activated carbon material with a fibre shape and a well-defined porous structure.
A pleated activated carbon fibre tube, as used in disclosing the present invention, is a pleated activated carbon fibre continuous sheet without ends, which may be cylindrical in shape.
A non-end pleat, as used in disclosing the present invention, has two elements, which are each part of two pleats each having a conductor at its tip, an element being the substantially rectangular part of ACF sheet between two of the conductors, see
An end pleat, as used in disclosing the present invention, has two elements with a conductor at the tip thereof with an element between two conductors, which is also part of the adjacent pleat non-end pleat, and a second element between the conductor at the tip of the end pleat and the end of the ACF sheet, see
The term element, as used in disclosing the present invention, is, in the case of an ACF tube, that part between conductors in the tips of adjacent pleats and, in the case of an ACF sheet, that part between conductors in the tips of adjacent pleats and that part between the end of the sheet and the conductor in the tip of the adjacent end pleat. The dimensions of these elements may be the same or different.
ACFC, as used in disclosing the present invention, is an abbreviation of activated carbon fibre cloth.
ACFF, as used in disclosing the present invention, is an abbreviation of activated carbon fibre felt.
PCO, as used in disclosing the present invention, is an abbreviation of photocatalytic oxidation.
VOC, as used in disclosing the present invention, is an abbreviation of volatile organic compound.
HVAC, as used in disclosing the present invention, is an abbreviation of Heating, Ventilation and Air Conditioning.
The expression “in electrical contact with”, as used in disclosing the present invention, means that the tension of the ACF sheet or tube stretched over the conductors is sufficient to provide optimal electrical contact. The tension force required, for example, with a woven 0.5 mm thick ACF sheet is 38 Nm−1 and can be determined at constant voltage by measuring the current between two conductors upon applying different weights to one end of the ACF sheet.
The expression ‘further conductor”, as used in disclosing the present invention, only refers to the conductors optionally attached to one or both ends of the ACF sheet and is thereby distinguished from the conductors at the tips of the pleats.
The invention will now be described by a detailed description of several embodiments of the invention. It is clear that other embodiments of the invention can be configured according to the knowledge of persons skilled in the art without departing from the true spirit or technical teaching of the invention, the invention being limited only by the terms of the appended claims.
Regenerable Gas Filter
According to a first aspect of the present invention, a regenerable gas filter is provided, said regenerable gas filter comprising a housing having in-line an entrance and an exit, a pleated activated carbon fibre (ACF) sheet or tube, each pleat having two substantially rectangular elements, with electrical conductors in the tip of each pleat and further electrical conductors being optionally attached to the ends of said sheet, said conductors being disposed substantially perpendicularly to the gas flow through said housing and said conductors on one side of said pleated sheet being connected to a single central conductor, which in turn was coupled to an electrical DC power source, this being repeated for the conductors on the other side of said pleated sheet, said sheet being stretched over and in electrical contact with said conductors and said pleated sheet or tube being provided with a sealing means to said housing.
According to a preferred embodiment of the first aspect of the present invention, the gas is polluted air.
According to another preferred embodiment of the first aspect of the present invention, the activated carbon fibre sheet or tube is woven i.e. an activated carbon fibre cloth (ACFC).
According to yet another preferred embodiment of the first aspect of the present invention, the activated carbon fibre sheet or tube is non-woven i.e. an activated carbon fibre felt (ACFF).
According to yet another preferred embodiment of the first aspect of the present invention, the sealing means is a rubber sealing means.
With a pleated ACF tube the number of pleats, conductors and electrically-active elements is identical, whereas with a pleated ACF sheet the number of pleats and conductors is identical, but in the absence of further conductors there is one less electrically-active element to which one electrically active element is to be added for each optional further conductor.
The use of a pleated activated carbon fibre (ACF) sheet or tube results in a lower pressure drop at a given air velocity and a reduced dependence of pressure drop with increasing air velocity compared with a planar filter, as shown in
The conductors must be rigid enough to withstand the tensional force required to obtain optimal contact between the ACF sheet and the conductors, with steel conductors being preferred. According to yet another preferred embodiment of the first aspect of the present invention, the conductors have a cross-sectional area of at least 6 mm2.
To obtain the maximum contact breadth of the conductor with the ACF-material, the part of the conductor in contact with the ACF sheet should preferably have some curvature, with rods being particularly preferred. According to yet another preferred embodiment of the first aspect of the present invention, the conductors are rods. Rods combine maximum strength for a given cross-sectional area with curvature with steel rods being preferred.
The maximum number of pleats with conductors with a cross-sectional area of 6 mm2 (diameter 2.75 mm) and the elements stacked horizontally is 307 pleats/m. This provides a maximum current of 52 A, whereas a typical current is 1 A.
The optimum operating conditions in respect of the number of pleats and the pleat height is determined by the flow conditions, there being a trade-off between the pressure drop and the amount of contaminant adsorbed. Set-up 2 has 7 pleats over 185 mm or 37.8 pleats/m and Set-up 3 has 14 pleats over 185 mm or 75.7 pleats/m.
According to yet another preferred embodiment of the first aspect of the present invention, the housing segment accommodating said pleated activated carbon fibre sheet or tube is cylindrical.
According to yet another preferred embodiment of the present invention, the housing segment accommodating said pleated activated carbon fibre sheet or tube has a rectangular profile.
Use of the Regenerable Gas Filter
According to a second aspect of the present invention, said regenerable gas filter is used for the purification of air in a Heating, Ventilation and Air Conditioning (HVAC) system.
According to a preferred embodiment of the second aspect of the present invention, the ACF sheet or tube is regenerated by resistively heating the elements of the pleated ACF tube or sheet between said conductors.
According to another preferred embodiment of the second aspect of the present invention, the ACF sheet is regenerated by resistively heating the elements of the pleated ACF sheet between the conductors and resistively heating the elements between the adjacent conductors and the further conductors attached to the ends of the ACF sheet.
According to a yet another preferred embodiment of the second aspect of the present invention, the Heating, Ventilation and Air Conditioning (HVAC) system comprises the combination of photocatalytic oxidation (PCO) and activated carbon fibre (ACF) units in a hybrid system.
The filter device in the examples is shown in
The performance of three experimental set-ups was evaluated. The characteristics of these arrangements are summarised in Table 1 below.
In set-up 1 the ACFC cloth was stretched across the 185×185 mm2 opening and electrical contact was made at either end with brass electrodes, as described by Roegiers et al. in 2019 in Chemical Engineering Journal, volume 365, pages 80-87. In set-ups 2 and 3, according to the present invention, the pleats mentioned in Table 1 for these set-ups were formed by stretching the ACFC cloth over steel conductors (cross-sectional area 12 mm2) as shown schematically for five pleats in
According to Ohm's law, the electrical current flowing through the entire pleated ACF sheet can be calculated as:
With Rpar the parallel electrical resistance (Ω), Rsheet,i the electrical resistance of an individual pleat of ACF (n), i.e. one planar ACF element between two conductors, and n the total number of ACF elements in the filter device. Based on the assumption that the electrical current is uniformly distributed and that the resistance of each ACF element is identical, theoretically:
Furthermore, the electrical resistance can be described as:
Wherein, represents the electrical resistivity (Ωm), l the width of the ACF pleat (m), i.e. the distance from conductor to conductor, t the sheet thickness and w the breadth of that part of the ACF sheet in direct contact with the conductor. The electrical resistivity is in turn a temperature dependent property, often described as:
In which ρ0 is the electrical resistivity (Ωm) at temperature T0 (K), T is the average temperature of the ACF sheet (K) and α0 is the thermal coefficient at temperature T0(K). If the values of ρ0 and α0 can be determined, it is possible to calculate the total resistance of the ACF sheet Rpar and hence the electrical power required to heat the ACF sheet to a certain temperature for regeneration purposes. The values of ρ0 and α0 were determined by measuring the surface temperature of the ACF sheet with a thermocouple (TC Direct, Type K), in setups with different element heights and by varying the voltage and DC current.
The thermo-electric properties of pleated ACF sheets were investigated for the three setups listed in Table 1. The goal was to derive the electrical resistivity of the ACF sheet in order to estimate the ACF sheet temperature when a particular electrical power is supplied. Therefore, voltages ranging from 0 to 25V were applied to all setups and from the amperage, the total resistance Rpar was determined, according to equation 1. Equations 2 and 3 were then used to determine the electrical resistivity and the results for all setups are shown in
It is clear from
wherein ρ represents the air density (1.2041 kg/m3), u the velocity vector (m/s), I the identity matrix, p the pressure (Pa), μ the dynamic viscosity (Pa·s) and μT the eddy viscosity (Pa·s), derived by the k-ε turbulence model. A parametric sweep of velocity inputs was performed ranging from 0 to 4.5 m/s with 0.1 m/s intervals in order to obtain a smooth pressure-velocity curve in the same range as the experimental pressure-velocity curves.
The good fits with the CFD model means that the CFD model can be used to perform a sensitivity analysis of the pressure drop with respect to filter thickness (0.5, 1.0 and 1.5 mm), pleat height (2.76 mm and 3.90 mm, corresponding to typical conductor dimensions of 6 mm2 and 12 mm2 respectively) and length of the filter module (0.3 m and 0.6 m), each of the twelve configurations containing a maximum number of pleats (so the elements are stacked horizontally), but the number of pleats differing due to variations in filter thickness and conductor diameter. The characteristics of the twelve configurations are given in Table 2 below:
The pressure drop, ΔP vs adsorbent mass i.e. of ACF sheet in kg was studied to find an optimal number of pleats, for a flow rate of 2.5 m/s and is shown in
On the other hand, configuration 12 contains the most activated carbon of all tested setups. Remarkably, the remaining configurations all show a similar pressure drop of 100-150 Pa, while the amount of adsorbent mass is highly divergent. In general terms, it is more profitable to increase the length of the device, as this means more adsorbent mass while retaining more or less the same pressure drop. This can be explained by the fact that an increase in pressure drop is expected in elongated pleats due to more viscous drag, but also a counteracting decrease in pressure drop because of a higher filter surface area and thus a lower facial velocity. Obviously, continuously elongating the filter device is restricted by practical limitations and requires a high electrical power consumption for regeneration purposes. The same reasoning holds when analyzing the pleat height. For example, when configurations 10 and 11 are compared, a similar pressure drop is observed. Configuration 10 has a pleat of height of 2.76 mm, while configuration 11 has a pleat height of 3.9 mm. Thus, configuration 10 is subject to higher viscous drag, but due to a thinner filter layer of 1 mm, the pressure drop is very similar to setup 11 with a filter thickness of 1.5 mm. Moreover, Configuration 10 contains more pleats within the same volume, but the pleats contain less activated carbon per pleat, resulting in a similar amount of activated carbon. The best choice of filter configuration depends on the application and customer needs. One can argue that configuration 12 is favorable because it has the highest amount of activated carbon per unit of volume. But one can also argue that configuration 11 is more favorable because it decreases the pressure drop by 67.9%, while losing only 22.4% of adsorbent mass.
At a flow rate of 2.5 m/s configuration 11 provides the best performance, but if the filter is required to have a maximum adsorbent mass in a given volume, regardless of the pressure drop, configuration 12 is the best. Configuration 1 is best, if pressure drop is a big issue. However, a different outcome is possible at different face velocities. There is therefore no particular optimal configuration, there always being a trade-off between pressure drop and adsorbent mass and user demands.
It is to be understood that although preferred embodiments, specific constructions and configurations, as well as materials, have been discussed herein for devices according to the present invention, various changes or modifications in form and detail may be made without departing from the scope and spirit of this invention.
Number | Date | Country | Kind |
---|---|---|---|
20193505.3 | Aug 2020 | EP | regional |
Filing Document | Filing Date | Country | Kind |
---|---|---|---|
PCT/EP2021/073812 | 8/27/2021 | WO |