Technical Field

The present invention relates to expired fire extinguisher powder processing methods and apparatus.

Background

Fire extinguisher powder (hereinafter referred to as “FEP”) is used in certain types of fire extinguishers. The requirement for the powder is stringent in that, although the fire extinguisher may never be used, if required, it must operate satisfactorily. Fire regulations stipulate the regular checking of fire extinguishers and an expiry date is assigned to the fire extinguisher.

FEP comprises two main components: mono ammonium phosphate (“MAP”) and ammonium sulphate (“AS”). To ensure that the FEP remains free flowing and available for use after long periods of non-use, FEP particles are coated with silicone oil. The silicone oil is hydrophobic and prevents moisture uptake by the FEP which could lead to agglomeration of the FEP and cause operational failure. The FEP may also comprise small amounts of insoluble ingredients such as Fuller’s Earth, mica, calcium carbonate and amorphous silica.

After expiry, the FEP requires disposal. MAP and AS can be utilised as fertiliser but the presence of silicone oil prevents this, since it affects the handling and solubility of the MAP and AS particles. Removing the silicone oil to a sufficient extent at an economic cost has proved problematic. Hence most FEP has traditionally been sent to landfill, which is increasingly expensive and environmentally unfriendly. Some methods have been proposed for processing FEP for re-use, but these have utilised volatile organic solvents, such as acetone, as solvents for the silicone oil. Such solvents pose health, safety and disposal risks.

Statements of Invention

According to a first aspect of the present invention, there is provided an expired fire extinguisher powder (“FEP”) processing method, the FEP comprising mono-ammonium phosphate (“MAP”), ammonium sulphate (“AS”) and silicone oil, the method including: mixing the FEP with a solvent under agitation for a predetermined mixing time; the mixing resulting in a mixed material which comprises solid components and a liquid component; the mixed material then being separated into the solid components and the liquid component; the solid components comprising insoluble FEP components, the insoluble FEP components including a major proportion of the silicone oil, the liquid component comprising soluble FEP components in solution, the soluble FEP components including a major proportion of the MAP and the AS, wherein the solvent comprises water.

Possibly, the expired FEP processing method is carried out in expired FEP processing apparatus. Possibly, the processing apparatus includes a mixing vessel, in which the mixing takes place. The mixing vessel may include an agitator.

Possibly, the mixed material is substantially homogeneous in appearance. Possibly, the predetermined mixing time is at least 10 minutes and may be less than 30 minutes. Possibly, the predetermined mixing time is at least 15 minutes and may be less than 25 minutes. Optimally, the predetermined mixing time is approximately 20 minutes.

Possibly, the mixing takes place at a predetermined temperature, which may be in the region of 10° to 45° C.

Possibly, the solvent comprises at least 80% w/w water and may comprise 90% w/w, more preferably 95% w/w and possibly 100% w/w.

Possibly, the water comprises deionised water.

Possibly, the solvent comprises an organic solvent and may comprise alcohol, and may comprise methanol.

Possibly, the solvent comprises no more than 20% w/w methanol, may comprise no more than 10% w/w and possibly no more than 5% w/w.

Possibly, the ratio of FEP to solvent by weight is at least 1 :10, may be at least 1 :3 and possibly is at least 1 :2.

Possibly, the processing apparatus includes separation apparatus in which the mixed material is separated into the solid components and the liquid component.

Possibly, the mixed material is separated by filtering. Possibly, the separation apparatus includes filtration apparatus, which may comprise a filter screen.

Possibly, the liquid component is subjected to a solvent removal step. Possibly, the processing apparatus includes solvent removal apparatus for carrying out the solvent removal step. The solvent removal step may comprise a concentrating step, in which the liquid component is heated, possibly to cause evaporation of solvent vapour from the liquid component. Possibly, the solvent removal apparatus includes concentration apparatus, in which the liquid component is subjected to the concentration step.

Possibly, in the concentration step, the liquid component is heated to an elevated temperature, which may be greater than 50°C and may be greater than 55°C. Possibly, the elevated temperature is no greater than 70°C and may be no greater than 65°C. Possibly, the elevated temperature is approximately 60°C.

Possibly, in the concentration step, the liquid component is under vacuum. Possibly, the vacuum has a pressure of no more than 200mbA (where mbA is millibar absolute pressure), possibly no more than 150mbA and desirably of approximately 100m BA.

Possibly, the processing apparatus includes a vacuum pump to create and maintain the vacuum.

The solvent removal step may include a crystallising step, in which the liquid component undergoes crystallisation. Possibly, the solvent removal apparatus includes crystallisation apparatus, in which the liquid component undergoes the crystallisation step.

Possibly, in the crystallisation step, the liquid component is cooled.

Possibly, the solvent removal apparatus includes a concentration and crystallisation vessel, which comprises the concentration apparatus and the crystallisation apparatus, and in which the liquid component may undergo the concentration step and the crystallisation step, possibly in sequence. Possibly, the solvent removal process includes filtering and may include drying. Possibly, the solvent removal apparatus includes a filter-dryer in which the liquid component may be filtered and dried.

Possibly, the solvent removal process results in formation of solid materials which may comprise recovered soluble FEP components. Possibly, the solid materials are in crystalline form, and may comprise MAP and AS.

Possibly, the filtering results in the formation of liquid recovered solvent. Possibly, the drying results in the formation of solvent vapour.

Possibly, the solvent vapour is subjected to a solvent recovery step, which may result in the formation of liquid solvent. Possibly, the processing apparatus includes solvent recovery apparatus, which may carry out the solvent recovery step.

Possibly, the solvent recovery step includes a condensing step, in which the solvent vapour is condensed to the liquid solvent. Possibly, the solvent recovery apparatus includes a condenser, which may carry out the condensing step.

Possibly, the solid components are heated and dried, and may comprise recovered insoluble FEP components, which may include the major proportion of the silicone oil. Possibly, the insoluble components include any of the group containing: Fuller’s Earth, mica, calcium carbonate and amorphous silica.

Possibly, the method includes a pre-mixing step, which may precede the mixing step, and may comprise a contacting step. Possibly, in the contacting step, solid FEP is contacted with a liquid catalyst, which may comprise a solvent, which may comprise alcohol or acetone. Possibly, in the contacting step, the FEP is only briefly brought into contact with the liquid catalyst, possibly for less than ten minutes on average. Possibly, in the contacting step, the liquid catalyst is sprayed into or onto the FEP, possibly in a fluidised bed. Possibly, the pre-mixing step includes an evaporating step after the contacting step, in which the liquid catalyst may evaporate from the FEP.

According to a second aspect of the present invention, there is provided expired fire extinguisher powder (FEP) processing apparatus for carrying out the method described in any of the above statements.

According to a third aspect of the present invention, there is provided expired fire extinguisher powder (FEP) processing apparatus, the FEP comprising mono-ammonium phosphate (“MAP”), ammonium sulphate (“AS”) and silicone oil, the processing apparatus including: a mixer for mixing the FEP with a solvent under agitation for a predetermined mixing time; the mixing resulting in a mixed material which comprises solid components and a liquid component; separation apparatus for separating the mixed material into the solid components and the liquid component; the solid components comprising insoluble FEP components, the insoluble FEP components including a major proportion of the silicone oil, the liquid component comprising soluble FEP components in solution, the soluble FEP components including a major proportion of the MAP and the AS, wherein the solvent comprises water.

Possibly, the apparatus includes any of the features shown or described in any of the preceding statements, following description or accompanying drawings. Possibly, the method includes any of the steps shown or described in any of the preceding statements, following description or accompanying drawings. Embodiments of the present invention will now be described, by way of example only, and with reference to the accompanying drawings, in which:-

Fig. 1 is a schematic block diagram of an expired fire extinguisher powder (FEP) processing method;

Fig. 2 is a schematic block diagram of apparatus for carrying out the method shown in Fig. 1 ;

Fig. 3 is a schematic process flow diagram of the expired fire extinguisher powder (FEP) processing apparatus;

Fig. 4 is a schematic block diagram of a pre-mixing step; and

Fig. 5 is a schematic block diagram of apparatus for carrying out the method shown in Fig. 4.

Fig. 1 shows an expired fire extinguisher powder (“FEP”) processing method, the FEP comprising mono-ammonium phosphate (“MAP”), ammonium sulphate (“AS”) and silicone oil, the method including: mixing the FEP with a solvent under agitation for a predetermined mixing time; the mixing resulting in a mixed material which comprises solid components and a liquid component; the mixed material then being separated into the solid components and the liquid component; the solid components comprising insoluble FEP components, the insoluble FEP components including a major proportion of the silicone oil, the liquid component comprising soluble FEP components in solution, the soluble FEP components including a major proportion of the MAP and the AS, wherein the solvent comprises water. The expired FEP processing method is carried out in expired FEP processing apparatus, which is shown in Figs. 2 and 3.

The processing apparatus includes a mixing vessel, in which the mixing takes place. The mixing vessel could include an agitator.

The mixed material is substantially homogeneous in appearance.

In one example, the predetermined mixing time could be at least 10 minutes and could be less than 30 minutes. In another example, the predetermined mixing time could be at least 15 minutes and could be less than 25 minutes. Optimally, the predetermined mixing time is approximately 20 minutes.

In one example, the mixer is located inside the mixing vessel. In another example the mixer is located on a recirculation loop outside the mixing vessel (as shown in Fig. 2 in dashed lines).

The mixing takes place at a predetermined temperature, which could be in the region of 10° to 45° C and more desirably in the region of 20 to 35°C.

In one example, the solvent comprises at least 80% w/w water. In other examples, the solvent could comprise higher percentages, such as 90% w/w, 95% w/w and 100% w/w.

In one example, the water comprises deionised water.

In other examples, the solvent could comprise an organic solvent, preferably could comprise alcohol, and desirably could comprise methanol. In one example, the solvent comprises no more than 20% w/w methanol. In other examples, the solvent could comprise no more than 10% w/w, and could comprise no more than 5% w/w.

In one example, the ratio of FEP to solvent by weight could be at least 1 :10. In other examples, the ratio of FEP to solvent by weight could be at least 1 :3 and could be at least 1 :2.

The processing apparatus includes separation apparatus in which the mixed material is separated into the solid components and the liquid component. In one example, the mixed material is separated by filtering and the separation apparatus comprises filtration apparatus which comprises a filter screen.

The liquid component is then subjected to a solvent removal step. The processing apparatus includes solvent removal apparatus for carrying out the solvent removal step.

The solvent removal step comprises a concentrating step, in which the liquid component is heated to cause evaporation of solvent vapour from the liquid component. The solvent removal apparatus includes concentration apparatus, in which the liquid component is subjected to the concentration step.

In the concentration step, the liquid component is heated to an elevated temperature. In one example, the elevated temperature could be greater than 50°C and could be greater than 55°C. In one example, the elevated temperature could be no greater than 70°C and could be no greater than 65°C. Desirably, the elevated temperature could be approximately 60°C.

In the concentration step, the liquid component is under vacuum. In one example, the vacuum could have a pressure of no more than 200mbA (where mbA is millibar absolute pressure), preferably no more than 150mbA and desirably of approximately 100m BA. The processing apparatus includes a vacuum pump to create and maintain the vacuum.

The solvent removal step includes a crystallising step, in which the liquid component undergoes crystallisation. The solvent removal apparatus includes crystallisation apparatus, in which the liquid component undergoes the crystallisation step.

In the crystallisation step, the liquid component is cooled.

In one example, the solvent removal apparatus includes a concentration and crystallisation vessel, which comprises the concentration apparatus and the crystallisation apparatus, and in which the liquid component undergoes the concentration step (heating) and then the crystallisation step (cooling) in sequence.

The solvent removal process includes filtering and drying. In one example, the solvent removal apparatus includes a filter-dryer in which the liquid component is filtered and dried.

The filtering and drying results in solid materials which comprise solid recovered soluble FEP components. The solid materials are in crystalline form, and comprise MAP and AS.

The filtering results in the formation of liquid recovered solvent.

The drying could result in the formation of solvent vapour.

The solvent vapour is subjected to a solvent recovery step, which results in the formation of liquid recovered solvent. The processing apparatus includes solvent recovery apparatus, which carries out the solvent recovery step. The solvent recovery step includes a condensing step, in which the solvent vapour is condensed to the liquid solvent. The solvent recovery apparatus includes a condenser, which carries out the condensing step.

In one example, the solid components from the separation step are heated and dried. The solid components comprise recovered insoluble FEP components, and include the major proportion of the silicone oil. The insoluble components could include any of the group containing: Fuller’s Earth (comprising magnesium aluminium silicate), mica (comprising potassium aluminium silicate), calcium carbonate and amorphous silica (comprising precipitated synthetic zeolite).

Experimental Background

In devising the process above, the Applicant undertook a number of experiments, as follows:

1 . Using organic solvents only

Following the guidance of the prior art, attempts were made to use organic solvents such as methanol and ethanol as the solvent but surprisingly these were unsuccessful and no salts (MAP and AS) were extracted by these methods. It was theorised that for the extraction of inorganic salts (ie MAP and AS), the solvent must comprise water to dissolve the salts, since inorganic salts are not soluble in an organic solvent and therefore using only methanol or only ethanol does not work in this case.

2. Using methanol and water solutions as the solvent

Extraction experiments of MAP and AS using 5%, 10% and 20% MeOH solution: 3 batches of methanol solution with 5% (A), 10% (B) and 20% (C) concentration were prepared. 2 g of mixed FEP was added in each batch, sealed, and stirred for 20 min at room temperature (20° C) and at the same conditions. The solid components were filtered off and dried. The liquid components were dried at 60°C. The dried solid components from experiments A, B and C were named AS5, BS10, and CS20 respectively. The solid recovered soluble FEP components from experiments A, B and C were named AF5, BF10 and CF20 respectively. The results of the mass of each sample are reported below:

Mass of dried solid components (g):

AS5: 0.363 g BS10: 0.368 g CS20: 0.3167 g

Mass of solid recovered soluble FEP components (g):

AF5: 1.6158 g (80.8% of original FEP) BF10: 1.6022 g (80.1 % of original FEP) CF20: 1.6072 g (80.4% of original FEP)

X-ray fluorescence (XRF) testing was performed on the dried solid components (AS5, BS10, CS20) and the solid recovered soluble FEP components (AF5, BF10, CF20) with the following results:

SI02 is a measure of the amount of silicone oil present.

P2O5 is a measure of the amount of MAP present. S03 is a measure of the amount of AS present.

The XRF results show that there is almost no silicone oil in the solid recovered soluble FEP components.

Increasing the methanol proportion appeared to make no significant difference to the overall amount of the solid recovered soluble FEP components.

3. Using only de-ionised water as the solvent

3(a) Extraction experiments on a mixture of expired FEPs using only deionised water as the solvent, with mixing using magnet stirrer/agitator:

2 g of FEP was added in 10 ml de-ionised water (ratio FEP:solvent 1 :5), sealed and stirred for 20 min at room temperature and at the same conditions as with the previous extraction experiments. The undissolved solid components were filtered off and dried. The liquid component was dried at 60°C gradually to form MAP and AS crystals.

Mass of dried solid components: 0.3714 g

Mass of solid recovered soluble FEP components: 1 .6075 g (80.4% of original FEP).

This experiment gave the surprising result that just water as the solvent gave as good a result as using a combination of methanol and water.

3(b) Extraction experiment on a mixture of a number of expired FEPs from different manufacturers:

100g of mixed FEP (M2) was added in 500g of de-ionised water in a 1 L beaker (ratio FEP:solvent 1 :5). The mixture was mixed with the mixer for 2 min at room temperature. The solid components were filtered off and the liquid component was dried at 60°C to form the solid recovered soluble FEP components. The mass of the solid recovered soluble FEP components was measured to be about 79g (79% of original FEP mixture).

To check the solubility of the solid recovered soluble FEP components, 1 g of the solid recovered soluble FEP components was added to 10 ml of water. After 5 min, all of the soluble FEP components were completely dissolved in water, indicating that the recovered soluble FEP components were of high purity, ie did not substantially comprise any of the insoluble FEP components and in particular substantially did not comprise any silicone oil.

3(c) Extraction experiments on individual expired FEP from 5 different manufacturers:

These experiments were performed on 5 different manufacturers’ products, coded R1 to R5. In 5 batches (glass beakers), 2 g of each FEP was added in 10 ml of de-ionised water (ie ratio FEP:solvent 1 :5). Each batch was sealed and kept under stirring (magnet stirrer) for 20 min at room temperature (at the same condition of previous experiments). The filtration was performed through vacuum filtration (with Buchner funnel). The mass of each filter paper used empty dish (for the solid components) and empty beaker (for the liquid component) was measured by isolated balance to report the final mass more precisely.

After filtration, the separated solid components and the liquid component of each experiment were placed in an oven at 60°C to achieve well dried samples of the solid insoluble FEP components and the solid recovered soluble FEP components. The recovered solid insoluble components were labelled as R1 S, R2S, R3S, R4S and R5S respectively. The recovered soluble FEP components were labelled as R1 F, R2F, R3F, R4F and R5F respectively. The following tables show the mass of the dried recovered solid insoluble components and the dried solid recovered soluble FEP components in grams.

These results show good levels of recovery of the soluble FEP components for each of the different manufacturer’s FEP products. The variation may be due to differing FEP formulations used by different manufacturers.

XRF tests were carried out on the recovered products from R1 , R2 and R3 with the results shown below.

These tests show that no silicone oil was present in the solid recovered soluble FEP components R1 F, R2F and R3F. For comparison, XRF tests were performed on unprocessed FEP powders with the following results:

These results show the variability of the formulations between different manufacturers.

Summarising these results, the Applicant has surprisingly found that it is possible to recover high levels of MAP and AS which are substantially free of silicone oil from expired FEP using only water as the solvent. This means that secondary processes such as washing with solvent after crystallisation to increase purity is not required

Advantageously and again surprisingly, the results suggest that a ratio of 1 :5 FEP to solvent is sufficient to achieve good results.

An Example of the Expired Fire Extinguisher Powder (FEP) Processing Apparatus at Plant Scale

Fig. 3 diagrammatically shows an example of the expired fire extinguisher powder (FEP) processing apparatus at plant scale.

The processing apparatus includes a mixing vessel K-002. Solvent is fed in at the location labelled Solvent Feed and dispensed into the mixing vessel K-002. Pump P-001 will be used to pump the solvent into the vessel.

FEP is fed in at the location labelled FEP Feed to powder hopper K-001 positioned directly above a rotary valve X-001 which meters FEP into the mixing vessel K-002. In this example, a recirculation loop from an outlet of K-002 moves through the mixing pump P-002 then through a flow indicator Fl-002 before re-entering vessel K-002 at the top.

Once sufficient mixing of the solvent and the FEP has been achieved via the recirculation loop, the mixed material is pumped via a pump P-003 through filtration apparatus comprising a screen filter F-001 to remove the solid components (indicated by the label Solid Components) which comprise undissolved silicon and impurities. It is possible to isolate F-001 to allow removal of solids build up from the screen.

The liquid component is fed to solvent removal apparatus which comprises a concentration and crystallisation vessel K-003, which is temperature controlled via an external jacket and agitated. When the liquid component has been pumped into K-003, the concentration step is performed under vacuum to remove the solvent.

The processing apparatus includes a vacuum pump C-001 . Once a vacuum is pulled within K-003 (in the order of 100 mbarA) the jacket is heated to raise the temperature such that the solvent evaporates as solvent vapour (indicated by the label Solvent Vapour).

Once the liquid component has been concentrated sufficiently, the mixture is cooled to allow crystals to form. After the required period of crystallisation, the concentrated liquid component can be pumped to the drying stage via pump P- 004.

The solvent removal apparatus includes a filter dryer F-004. In one example, this could comprise a perforated plate, over which a filter mesh can be fitted designed to filter the remaining solvent from the produced crystals. The separated solvent which flows through the filter plate can be pumped back into the crystalliser K-003 via pump P-005 (as indicated by the label Solvent Liquid below filter-dryer F-004) to use as a wash for the crystalliser to maximise the amount of solids transported to the filter dryer.

The filter dryer could be temperature controlled via an external jacket, and could be connected to the vacuum pump C-001 to lower the required temperature to drive off remaining solvent (indicated by the label Solvent Vapour above the filter-dryer F-004.

The filter dryer includes an agitator which can be used either to smooth the dried solid recovered soluble FEP components during drying or can be used to break up the dried solid recovered soluble FEP components for discharge. The location of the discharge of the dried solid recovered soluble FEP components is indicated by the label Solid Recovered Soluble FEP components.

The solvent vapour from the concentration and crystallisation vessel K-003 and the filter-dryer F-004 moves through the solvent recovery apparatus comprising a condenser W-005. The condensed solvent liquid drains into collection vessel K-005 with remaining vapour moving through a coalescing filter F-001 before moving through the vacuum pump C-001 and to vent. The purpose of F-001 is to protect the vacuum pump C-001 from any remaining entrained liquid within the gas stream.

Liquid recovered solvent could be fed from the collection vessel K-005 to the Solvent Feed as indicated by the label Solvent Liquid below the vessel K-005.

The processing apparatus could include a recirculating, refrigerated water chiller which would re-circulate and cool water from an internal reservoir to approximately 5°C to act as a cooling medium for the condenser W-005, the crystalliser jacket cooler W-002 and the filter dryer jacket W-004.

For both the crystalliser K-003 and the filter dryer F-004, the jacket temperature would be controlled to a set point using either a heater (W-001 and W-003 respectively) or via a cooler (W-002 and W-004 respectively. The outlet temperature of the heat transfer medium (determined by TE-008 or TE-013 respectively) versus the set temperature for the jacket would determine if heating or cooling was required.

For heaters W-001 and W-003, the heating element could be controlled based on the outlet temperature of the jacket fluid versus the set point.

For coolers W-002, W-004 and W-005 the flow of cooling water into the heat exchanger could be controlled based on the outlet temperature of the jacket fluid or condensed solvent.

Final Remarks

Various other modifications could be made without departing from the scope of the invention.

In Figs. 4 and 5, the method includes a pre-mixing step, which precedes the mixing step of Figs. 1 and 2. The pre-mixing step comprises a contacting step. In the contacting step, solid FEP is contacted with a liquid catalyst in a contactor. The liquid catalyst comprises a solvent, which could comprise alcohol or acetone. In the contacting step, the FEP is only briefly brought into contact with the liquid catalyst. In one example, the FEP is brought into contact with the liquid catalyst for less than ten minutes on average. In the contacting step, the liquid catalyst is sprayed into or onto the FEP, for example, in a fluidised bed. The contactor could include a spray arrangement and could include a fluidised bed.

The pre-mixing step includes an evaporating step after the contacting step, in which the liquid catalyst is evaporated from the FEP in a evaporator. The evaporating step could also be carried out in a fluidised bed. In the evaporating step, the evaporation could be carried out over a time period of approximately 30 minutes. Advantageously, the Applicant has found that briefly contacting the FEP with the liquid catalyst softens the FEP and surprisingly this reduces the overall process time markedly and hence reduces cost.

Any of the features or steps of any of the embodiments shown or described could be combined in any suitable way, within the scope of the overall disclosure of this document.

There are thus provided an expired fire extinguisher powder (FEP) processing method and apparatus with a number of advantages over conventional methods and apparatus. In particular, the methods and apparatus of the invention provide solid recovered soluble FEP components of high purity at low cost and low energy consumption without the use of volatile organic solvents which pose health, safety and disposal risks.