WO2008145988A1

WO2008145988A1 - Filters

Info

Publication number: WO2008145988A1
Application number: PCT/GB2008/001807
Authority: WO
Inventors: Anthony Martin
Original assignee: Bioquell Uk Limited
Priority date: 2007-05-30
Filing date: 2008-05-29
Publication date: 2008-12-04
Also published as: GB0710338D0

Abstract

The disclosure relates to a filter (10) comprising an inlet (12),. an outlet (13), a body of a porous filtration medium through which a fluid (such as air) passes between the inlet and outlet for contaminant to be removed from the fluid. A porous probe (14) is located in the filtration medium at a location where a cavity is provided to enable fluid carrying contamination to enter the probe, and a sensor pack (16) is connected in a circuit (15) coupled to the probe cavity for assessing the level of contamination in the fluid received in the cavity.

Description

FILTERS

This invention relates to filters for removing chemicals from fluids such as air having means for determining the residual capability of the filters to remove chemicals.

US-A-5334237 discloses a method for predicting end- of-life of a system consumable in a fluid purification system in which a model consumable is coupled to the fluid purification system which has comparable characteristics but substantially less time capacity than the system consumable; a portion of an unpurified fluid which could otherwise flow into the system consumable is diverted into the model consumable; and the model consumable is analysed to predict the end-of-life of the system consumable.

WO-A-02/036233 discloses apparatus in fluid communication with a water leg portion of a hydrocarbon- contaminated water, e.g., a water leg portion of an offshore drilling or production platform sump tank for conveying water, separated from oil, into contact with organophilic media canisters such that the hydrocarbons and other organic materials commingled with the sump tank water will be adsorbed onto the organophilic media and detected by the embedded probe in selected canisters. The canisters are provided in a plurality of stacks and are in fluid communication with a header disposed at the bottom of the vessel housing the various stacks of canisters. Solids that do not pass through the canisters are accumulated at the bottom of the vessel and drained through a drain port. The water will pass through the media and will be conveyed back to the ocean water without contamination. At some point in time, the organophilic media will become "spent" and at a certain "spent level", the saturated condition of the organomedia will be electronically detected by an embedded probe linked to an alarm/control panel. The alarm indicates that the "spent" organophilic media should be replaced with fresh media or the spent media regenerated.

US-A-4095965 discloses an absorption filter for the purification of gas or air streams, especially gas or air streams which contain toxic or radioactive contaminants.

GB-A-1557821 discloses a filter element for fluids comprises at least one cylindrical sheet of non-woven micro-porous material impregnated with a binder and embodying a layer of glass fibres. The sheet is at least 0.73 mm thick and is formed with pleats over its entire area, and at least one supporting cylinder is formed with perforations substantially over its whole area providing support for the pleated sheet . Means are provided for providing warning indication when a filter element is saturated with oil. This may be achieved by applying a layer containing an oil soluble dye which changes the colour of the filter element to red in the presence of an oil.

The use of adsorbent materials in filter beds to remove unwanted chemicals from host fluid (gas and liquid) streams is widespread in the chemical, pharmaceutical, laboratory and health related industries. Adsorbents used are many and various typically but not necessarily, they include charcoal (sometimes referred to as carbon or simply coal) and Zeolite materials .

Removal of the unwanted chemicals by the adsorbents is generally by molecular attraction onto the adsorbent, but may also involve reaction with chemicals within the absorbent and may also be aided by catalytic processes. In many applications simultaneous removal of many different chemicals is carried out. The following discussion is written as for a single unwanted chemical in a gas stream, but applies equally for single or multiple unwanted chemicals in any fluid, albeit the parameters for each may be widely different.

The entrapment is not instantaneous and therefore requires the host stream to be in contact with the adsorbent for a period of time. The time required depends on many factors, but primarily the concentration of unwanted chemical in the host stream, the velocity of the host stream, the characteristics of the adsorbent and the acceptable level of unwanted chemical in the stream leaving the filter.

The need for the host fluid to be in contact with the adsorbent for a period of time necessitates that the adsorbent is held in a bed of sufficient thickness for that time to be achieved.

The resultant effect is that the concentration of unwanted chemical in the host fluid is progressively reduced as it passes through the adsorbent . Since the rate of adsorption at any point in the filter bed is proportional to the concentration at that point an infinite bed depth is necessary for the concentration to be reduced to zero.

The bed thickness used is therefore determined from the acceptable concentration of unwanted chemical in the fluid leaving the filter (known as the 'breakthrough concentration') and how long the filter is required to be used under given conditions before the breakthrough concentration occurs, known as 'filter life' .

It is normal for the concentration of unwanted chemical in the host stream leaving the filter to be monitored using a method appropriate to the unwanted chemical breakthrough concentration. The filter is then replaced when found necessary.

In some critical applications two separate filters are used in series with the unwanted chemical concentration being measured in the space between the two filters, thereby monitoring for both breakthrough and sealing failure. This approach may also be used if the threshold for practical detectors is above the acceptable breakthrough concentration, the second filter giving the necessary further reduction in concentration.

In some circumstances, particularly in fighting vehicles and aerospace applications, physical constraints preclude the use of the two filter system described above. Particularly where war gases are involved, it is highly desirable that a means is available for estimating how much longer the filter can continue to be used, known as residual life. This not only assures the users but can also result in significant cost and logistical advantage by avoiding unnecessary filter changing. The lack of sufficient sensitivity of present detectors precludes the use of detection levels greatly below the breakthrough concentration to forecast residual life.

In addition inlet concentrations are variable and the capability of the adsorbent is markedly affected by the natural variation in the condition of the host fluid, in this case the ambient atmosphere.

In a war gas situation determination of residual life may be necessary during an attack and thus needs to be quick and easy. Determination after an attack in anticipation of further attacks is also highly desirable, in which case simulants can be used if no actual threat is present.

Presently there are many methods of estimating residual life of a filler of which the following are examples :

JP-A-2006150299 proposes a method to pass fluid through small representative sample filters and use these to predict residual life of the main filter. KR-A-20050017974 utilises water quality of raw water (analogous to input concentration) and water flow rate to calculate when the known adsorbtion capacity of the filter will be occur and thus to predict when filter changing will be necessary (i.e. residual life) .

US-A-2002112605 oscillation frequency techniques are used on sample filters to determine their condition and thus residual life.

JP-A-200032121257 utilises similar principles but in a different manner. JP-A- 10258213 utilises varying concentrations of test gases to predict residual life.

JP-A-9105711 uses an 'acceleration test¹ (which appears to be a short dose of test gas) and other data to predict residual life.

W0-A-2005084507 utilises a separate sampling canister which then monitored. US-A-2003127040 utilises a reactive dye to monitor utilisation of the bed.

WO-A-183083 utilises embedded thermocouples to measure temperature change resulting from pulses of butane gas as a means of detecting progress of contamination through the bed.

JP-A-2000218158 also uses heat effects and a test gas but in a different manner . US2951156 Uses adsorption of Beta radiation at varying depths through a sample filter to determine its condition, and thus residual l i fe .

Whilst producing solutions for particular applications all of the methods either require a separate sample filter, are specific to single gases, require the use of a test gas, require the use of sophisticated and bulky test equipment or are not suitable for greatly varying ambient conditions.

According to the present invention measurement of the concentration of unwanted chemical in the host stream is carried out directly from within the adsorbent bed thereby permitting prediction of residual life.

This invention provides a filter comprising an inlet, an outlet, a body of a porous filtration medium through which a fluid (such as air) passes between the inlet and outlet for contaminant to be removed from the fluid and means for determining the effectiveness of the filtration medium at a location between the inlet and outlet to enable the future life of the filtration medium to be assessed, said means comprising a probe located in the filtration medium at a location where contamination is to be assessed, the probe having a perforated or porous wall and providing a cavity within the wall to enable fluid carrying contamination to enter the probe, and means for assessing the level of contamination in the fluid received in the cavity.

In one arrangement according to the invention the cavity in the probe may be connected in a circuit to receive fluid from the probe and the circuit includes means for determining the level of contamination in the fluid received from the cavity.

In the latter arrangement the circuit may be connected between the cavity to the probe and the inlet to the filter.

More specifically the circuit may include pump means to draw fluid from the cavity in the probe.

In any of the above arrangements a plurality of probes may be provided for determining the level of contamination in the fluid passing through the filtration medium at a plurality of positions spaced between the inlet and outlet to the filter.

Also in any of the above arrangements the filtration medium may be an adsorbent bed for the fluid to be filtered.

The following is a description of some specific embodiments of the invention, reference being made to the accompanying drawings, in which:

Figure 1 is a graph showing typical adsorption characteristics for a filter over different states; and

Figure 2 is a diagrammatic illustration of a filter in accordance with the invention.

The steps taken in performing the invention are as follows: Constructing filters as described in detail below with one or more sampling probes within the adsorbent bed at a distance from the outlet face of the filter determined by experiment according to the requirements of the application and the sensitivity of available detectors .

Continually or periodically determining the concentration of unwanted chemical in the host stream at the sampling point or sampling points.

Using the determined concentration and previous concentrations together with known characteristics of the adsorbent to predict the residual filter life. Typically, but not necessarily, this would be by computational techniques based on laboratory test results .

The invention can be employed when gas or liquid is the host stream, but the following description will be based on air as the host stream. The description will refer to cylindrical filters without particulate filtration elements, but the invention can be employed with filters in "flat bed" or "cylindrical bed" format, with or without particulate elements.

An embodiment of the filter in accordance with the invention will now be described by way of example with reference to Figure 2 of the accompanying drawings.

In Figure 2 there is shown a cylindrical filter 10 with an adsorbent bed 11. Contaminated air passes into the filter at a inlet 12 through the adsorbent bed 11 and exits through an outlet 13 as shown by the arrows on the Figure .

A probe 14 is installed within the adsorbent bed 11 of the filter 10. The probe 14 as shown is a blind ended tube perforated or porous along its length within the adsorbent bed. A sample of air is drawn from the cavity in the probe into a circuit 15 containing a sensor pack 16, by a pump 17 and is returned to the inlet 12 to the filter. This ensures that any retained unwanted chemical is subsequently filtered out.

Seals 17 and 18 serve to seal the filter from the surrounding environment and plates 19 and 20 serve to hold the filter in position in a conventional manner.

The twin lip seal 17 serves to provide a manifold to link the sensing probes if more than one is used.

Although shown with as twin lipped, the seal 17 may be two separate seals forming a similar manifold.

The sensor pack 16 utilises a method or methods appropriate to the unwanted chemical or chemicals and their associated concentrations and is used in conjunction with its own or associated remote predictive capabilities .

Claims

CLAIMS :

1. A filter comprising an inlet, an outlet, a body of a porous filtration medium through which a fluid (such as air) passes between the inlet and outlet for contaminant to be removed from the fluid and means for determining the effectiveness of the filtration medium at a location between the inlet and outlet to enable the future life of the filtration medium to be assessed, said means comprising a probe located in the filtration medium at a location where contamination is to be assessed, the probe having a perforated or porous wall and a cavity within the wall to enable fluid carrying contamination to enter the probe, and means for assessing the level of contamination in the fluid received in the cavity.

2. A filter as claimed in claim 1, wherein the cavity in the probe is connected in a circuit to receive fluid from the probe and the circuit includes means for determining the level of contamination in the fluid received from the cavity.

3. A filter as claimed in claim 2, wherein the circuit is connected between the cavity to the probe and the inlet to the filter.

4. A filter as claimed in claim 2 or claim 3, wherein the circuit includes pump means to draw fluid from the cavity in the probe .

5. A filter as claimed in any of the preceding claims, wherein a plurality of probes are provided for determining the level of contamination in the fluid passing through the filtration medium at a plurality of positions spaced between the inlet and outlet to the filter.

6. A filter as claimed in any of the preceding claims, wherein the filtration medium is an adsorbent bed for the fluid to be filtered.

926735; GCB; LMB