TECHNICAL FIELD

[0001] The present invention relates to systems for supply of a gas and, more particularly, systems for supply of a gas mixture. In some forms the system may be applied, although not exclusively, to the control of insects in food storage facilities. More generally in some forms the system may be applied, although not exclusively, to the fumigation of sealed and unsealed grain storage facilities.

BACKGROUND

[0002] Industrial phosphine mix has been generated by heating phosphorus in an aqueous solution of potash (Gengembre 1783). Industrial phosphine mix produced from metallic phosphides (e.g.; aluminium phosphide, A1P; calcium phosphide, Ca ₃ P ₂ ; magnesium phosphide, Mg ₃ P ₂ ; zinc phosphide, Zn ₃ P2) is currently the major source of industrial phosphine mix forfumigation use. Hydrolysis of aluminium phosphide is the most suitable for laboratory preparation of industrial phosphine mix however high purity aluminium phosphide is required with this method if one is to avoid the formation of spontaneously flammable industrial phosphine mix. The presence of small amounts of diphosphine and also higher phosphines in the industrial phosphine mix (mixed together with the phosphine) are responsible for this spontaneous flammability. It appears that these are formed when P-P bonds are present in the aluminium phosphide (which may be avoided by using excess phosphorus in preparation of the phosphide). The hydrolysis of calcium phosphide generates phosphine and noticeable amounts of diphosphine (P ₂ H ₄ ) and other higher phosphines so this reaction can be used for the preparation of such compounds (Fluck 1973).

[0003] In another process a cold trap was used to separate diphosphine (P ₂ H ₄ ) from phosphine (PH ₃ ) generated from calcium phosphide (Ca ₃ P ₂ ), demonstrating P ₂ H ₄ is responsible for

spontaneous flammability associated with PH ₃ (Thenard 1844).

[0004] The pure compound phosphine [PH ₃ ] has many of the properties desirable for a fumigant (e.g. high penetrant ability, low sorption on foodstuffs, very low residue formation). However PH ₃ has a major disadvantage: it is flammable and explosive in mixtures with air. The published literature give the flammability of PH ₃ in air: 1.8% to 98%. The initial industrial phosphine mix product for fumigation of grain was metallic phosphides (e.g. aluminium phosphide, A1P) which slowly generated PH ₃ on exposure to atmospheric moisture. The initial industrial phosphine mix formulation in industrial gas cylinders was a non-flammable mixture of 2% PH ₃ in CO2 which allow rapid dispensing of the PH ₃ into the grain storage to be fumigated. The more recent rapid on-site mixing of 99% industrial phosphine mix with air has advantages of lower costs and reduction in the number of gas cylinders required.

[0005] A method of using normally available, pyrophoric and flammable phosphine gas in fumigation applications, is disclosed in AU779235 in which the phosphine gas is injected into a turbulent air stream flowing at a rate said to be sufficient to dilute the phosphine to a level below its flammability limit. The disadvantage of using a pyrophoric gas is that it can auto-ignite anywhere within the flammability range during the dilution process.

[0006] Scientific literature reports pure PH ₃ gas is not pyrophoric however specific impurities can change this status. These specific impurities include the pyrophoric white phosphorus (P ₄ ) and diphosphine (P ₂ H ₄ ). As white phosphorous (P ₄ ) is the common raw material in the manufacture of both solid and gaseous PH ₃ products, P ₄ has a high probability of causing ignition issues. The pyrophoric P ₄ solid can also deposit in dispensing equipment resulting in ignition on exposure to air. The relative high vapour pressure (lOPa @ 34°C) allows the transfer of P ₄ as a vapour throughout dispensing systems. Trace deposits of P ₄ can ignite deposits of PH ₃ polymer resulting in a more significant fire incident.

[0007] According to General & Inorganic Chemistry by P.J Durant, Longmans, Grenn & Co, London, pure phosphine is not pyrophoric unless diphosphine (P ₂ H ₄ ) is present. Durant further has it that white phosphorus can spontaneously ignite at the low temperature of 35 degrees Celsius.

[0008] Professor E.Fluck of University of Stuttgart considers that phosphine with P ₂ H ₄ present at levels of <1% is not pyrophoric while other scientific literature state <0.2%.

[0009] The reaction of pure PH ₃ with oxygen to form polymers is an issue in dispensing equipment and requires pre- and post-purging of gaseous PH ₃ dispensing systems with an inert gas. The polymer dust and associated oily phosphoric acid negatively effects gas flow control equipment (Schonstein et al. Controlled release of phosphine - an update. Proceedings of the 6 ^th International Working Conference on Stored-Product Protection, 1994, Canberra, Australia)

[00010] It is an object of the present invention to address or at least ameliorate some of the above disadvantages. Notes

[00011] The term“comprising” (and grammatical variations thereof) is used in this specification in the inclusive sense of“having” or“including”, and not in the exclusive sense of“consisting only of’.

[00012] The above discussion of the prior art in the Background of the invention, is not an admission that any information discussed therein is citable prior art or part of the common general knowledge of persons skilled in the art in any country.

SUMMARY OF INVENTION

Definitions

[00013] ‘Flammable’: a flammable substance is a substance which will bum if a source of ignition is applied.

[00014] ‘Pyrophoric’ a pyrophoric substance is a substance which will spontaneously bum if mixed with an effective amount of an oxidizing agent.

[00015] ‘Phosphine (PH ₃ )’: is a compound which is flammable but, in its pure form, is not pyrophoric. In the specification the term phosphine used on its own means phosphine in its pure form.

[00016] ‘Industrial phosphine mix’: in this specification an‘industrial phosphine mix’ is a mixture of compounds including a predominant compound and impurities, usually all in gaseous form at room temperature, where the predominant compound by volume is phosphine. Industrial phosphine mix is utilised in various industries including agricultural fumigation, electronics production and as an intermediary in organophosphoms chemistry.

[00017] In one broad form of the present invention, there is provided a method of providing a gaseous mixture for fumigation of a grain storage facility; the gaseous mixture comprising a non- pyrophoric gas and air; the non-pyrophoric gas injected into an air stream passing through a gas control manifold block thereby to produce the gaseous mixture; the non-pyrophoric gas including impurities at a sufficiently low level to cause the gas to be non-pyrophoric.

[00018] Preferably, the non-pyrophoric gas is a non-pyrophoric industrial phosphine mix wherein impurities are at sufficiently low levels or are not present in the non-pyrophoric industrial phosphine mix so as to render the industrial phosphine mix non-pyrophoric. [00019] Preferably, the non-pyrophoric industrial phosphine mix has no residual white phosphorus (P4) carried over into the phosphine gas.

[00020] Preferably, trace elements of diphosphine (P ₂ H ₄ ) in the industrial phosphine mix are not present or at levels sufficiently low to cause the industrial phosphine mix to be non-pyrophoric.

[00021] Preferably, the air stream is an accelerated air stream passing through a venturi- shaped passage in the gas control manifold block; the non-pyrophoric gas being injected into the accelerated air stream at a narrowest section of the venturi- shaped passage.

[00022] Preferably, the gas control manifold block includes three gas entry orifices; a first and a second industrial phosphine mix gas entry orifice and a third purging gas entry orifice.

[00023] Preferably, the gas control manifold block includes two main internal gas passages; a first main gas passage extending between the first industrial phosphine mix gas inlet orifices and the purging gas entry orifice; a second main gas passage extending from the second industrial phosphine mix entry orifice to an end point within the block past the narrowest section of the venturi- shaped passage.

[00024] Preferably, the gas control manifold block further includes transverse gas passages; a first and a second transverse gas passage interconnecting the first and second main gas passages; the first transverse gas passage extending from the end point of the second main gas passage to intersect the first main gas passage; a second transverse gas passage located downstream of a first gas control valve on the second main gas passage; a third transverse gas passage extending from the first main gas passage to an injection orifice at a narrowest section of the venturi- shaped passage.

[00025] In another broad form of the present invention, there is also provided a gas control manifold block controlling injection of a non-pyrophoric gas into an air stream passing through the gas control manifold block; the non-pyrophoric gas comprising an industrial phosphine mix manufactured with impurities at levels sufficiently low to cause the industrial phosphine mix to be non-pyrophoric.

[00026] Preferably, all interconnections between one or more cylinders of the non-pyrophoric gas and a cylinder of purging purging gas as well as valves controlling flows of the respective gases are encapsulated within the gas control manifold block.

[00027] Preferably, the non-pyrophoric industrial phosphine mix has no residual white phosphorus (P4) carried over into the phosphine gas. [00028] Preferably, trace elements of diphosphine (P ₂ H ₄ ) in the industrial phosphine mix are not present or at levels sufficiently low to cause the industrial phosphine mix to be non-pyrophoric.

[00029] Preferably, two or more sources of non-pyrophoric industrial phosphine mix are connected to the manifold block.

[00030] Preferably, a source of purging gas is connected to the manifold block.

[00031] Preferably, an air stream under pressure is injected into a venturi- shaped through passage of the manifold block.

[00032] Preferably, gas passages and gas control valves within the manifold block allow the gas sources in isolation or in combination to be injected into the air stream as it passes through the venturi shaped through passage.

[00033] In yet another broad form of the present invention, there is also provided a manifold block for control of at least one gas from at least one gas source; the manifold block including a venturi shaped passage extending through the manifold block; the venturi- shaped passage conducting an accelerated air flow in which gas from the at least one gas source may be entrained; the manifold block further including at least one gas conducting passage extending from one or more entry orifices; at least one gas conduction passage and leading to an outlet orifice at a narrowest section of the venturi shaped passage; the manifold block incorporating one or more control valves for control of gas flow through the at least one gas conducting passage.

[00034] In yet another broad form of the present invention, there is also provided a unitary manifold block for controllable introduction of a gas flow of at least one gas from at least one gas source into an air stream; the manifold block including a venturi- shaped passage extending through the manifold block from an air entry to an air exit; the venturi- shaped passage causing an accelerated air flow within the passage relative to the air flow at the air entry and in which the gas from the at least one gas source may be entrained; the manifold block further including at least one gas conducting passage extending from one or more entry orifices; the at least one gas conducting passage leading to an outlet orifice at a narrowest section of the venturi- shaped passage; the manifold block incorporating one or more control valves for control of the gas flow through the at least one gas conducting passage thereby to control the proportion of the at least one gas entrained in the air flow at the air exit.

[00035] In yet another broad form of the present invention, there is also provided a method of providing a gaseous mixture; the gaseous mixture comprising a non-pyrophoric gas and air; the non- pyrophoric gas injected into an air stream passing through a gas control manifold block; the method including a gas with impurities at a sufficiently low level to cause the gas to be non-pyrophoric.

[00036] Preferably, the gas from which pyrophoric impurities are at sufficiently low levels or are not present in the non-pyrophoric gas is phosphine gas.

[00037] Preferably, the non-pyrophoric gas has no residual white phosphorus (P ₄ ) carried over into the phosphine gas.

[00038] Preferably, trace elements of diphosphine (P ₂ H ₄ ) in the phosphine gas are not present or at levels sufficiently low to cause the phosphine gas to be non-pyrophoric.

[00039] Preferably, the air stream is an accelerated air stream passing through a venturi- shaped passage in the gas control manifold block; the non-pyrophoric gas being injected into the accelerated air stream at a narrowest section of the venturi- shaped passage.

[00040] Preferably, the air stream passes through a passage in the gas control manifold block; the passage being of substantially constant diameter throughout.

[00041] Preferably, the gas control manifold block includes three gas entry orifices; a first and a second phosphine gas entry orifice and a third purging gas entry orifice.

[00042] Preferably, the gas control manifold block includes two main internal gas passages; a first main gas passage extending between the first phosphine gas inlet orifices and the purging gas entry orifice; a second main gas passage extending from the second phosphine entry orifice to an end point within the block past the narrowest section of the venturi- shaped passage.

[00043] Preferably, the gas control manifold block further includes transverse gas passages; a first and a second transverse gas passage interconnecting the first and second main gas passages; the first transverse gas passage extending from the end point of the second main gas passage to intersect the first main gas passage; a second transverse gas passage located downstream of a first gas control valve on the second main gas passage; a third transverse gas passage extending from the first main gas passage to an injection orifice at a narrowest section of the venturi- shaped passage.

[00044] Preferably, the gas control manifold block further includes transverse gas passages; a first and a second transverse gas passage interconnecting the first and second main gas passages; the first transverse gas passage extending from the end point of the second main gas passage to intersect the first main gas passage; a second transverse gas passage located downstream of a first gas control valve on the second main gas passage; a third transverse gas passage extending from the first main gas passage to an injection orifice at an intermediate point along the passage of constant diameter.

[00045] In yet another broad form of the present invention, there is also provided an industrial phosphine mix for agricultural use; the industrial phosphine mix including impurities at a sufficiently low level to render the industrial phosphine mix non-pyrophoric; the impurities including one or both of diphosphine P ₂ H ₄ and white phosphorus P ₄ ; supply of the industrial phosphine mix added to an air stream passing through a manifold block.

[00046] Preferably, the impurity of diphosphine P ₂ H ₄ is not present or at sufficiently low level to cause the industrial phosphine mix to be non-pyrophoric.

[00047] Preferably, the impurities are a residual effect of a process producing the industrial phosphine mix.

[00048] Preferably, the non-pyrophoric industrial phosphine mix has no residual white phosphorus (P4) carried over into the industrial phosphine mix.

[00049] Preferably, the industrial phosphine mix is entrained in an air stream passing through a passage in a gas control manifold block; the industrial phosphine mix being injected into the air stream at an intermediate point in an air passage through the gas control manifold block.

[00050] Preferably, the industrial phosphine mix is entrained in an accelerated air stream passing through a venturi-shaped passage in a gas control manifold block; the industrial phosphine mix being injected into the accelerated air stream at a narrowest section of a venturi-shaped passage in the gas control manifold block.

[00051] Preferably, the gas control manifold block includes three gas entry orifices; a first and a second industrial phosphine mix entry orifice and a third purging gas entry orifice.

[00052] Preferably, the gas control manifold block includes two main internal gas passages; a first main gas passage extending between the first phosphine gas inlet orifices and the purging gas entry orifice; a second main gas passage extending from the second phosphine entry orifice to an end point within the block past the narrowest section of the venturi- shaped passage.

[00053] Preferably, the gas control manifold block further includes transverse gas passages; a first and a second transverse gas passage interconnecting the first and second main gas passages; the first transverse gas passage extending from the end point of the second main gas passage to intersect the first main gas passage; a second transverse gas passage located downstream of a first gas control valve on the second main gas passage; a third transverse gas passage extending from the first main gas passage to an injection orifice at the intermediate point in the air passage or at the narrowest section of the venturi-shaped passage.

BRIEF DESCRIPTION OF DRAWINGS

[00054] Embodiments of the present invention will now be described with reference to the accompanying drawings wherein:

[00055] Figure 1 is a schematic representation of a grain storage facility fumigation system according to a preferred embodiment of the invention;

[00056] Figure 2 is an enlarged schematic representation of a gas control manifold with venturi of the system of Figure 1 ;

[00057] Figure 3 is a further enlarged schematic representation of a gas control manifold without venturi of the system of Figure 1.

DESCRIPTION OF EMBODIMENTS

[00058] The present invention provides for a method and gas treatment system 10 utilising industrial phosphine mix in which pyrophoric inducing impurities are at a level at which the industrial phosphine mix is non-pyrophoric and may be injected into an air stream and not auto- ignite.

Production of industrial phosphine mix First Preferred Method

[00059] Phosphorus is reacted with a sodium hydroxide slurry to produce phosphine gas and sodium hypophosphite.

4P + 3NaOH + 4H ₂ 0 => 3NaH ₂ P0 ₂ + 3H ₂ 0 + PH ₃

[00060] The reaction takes place in a specially designed reactor and at elevated temperatures. The main by-product of the process is hydrogen.

4P + 4NaOH + 4H ₂ 0 ®4NaH ₂ P0 ₂ + 2H ₂ [00061] Water is removed and the product gaseous mixture is then purified through a series of columns and finally liquefied under pressure and reduced temperature. The liquefied phosphine is then stored in the form of industrial phosphine mix for filling into cylinders.

[00062] Phosphorus is reacted with excess sodium hydroxide to ensure all phosphorus is consumed during the reaction and no residual phosphorus is carried over into the product gaseous mixture which could cause the industrial phosphine mix to become pyrophoric. Trace levels of diphosphine (P ₂ H ₄ ) may exist in the industrial phosphine mix but these are at sufficiently low levels not to cause the industrial phosphine mix to be pyrophoric.

[00063] Phosphine gas, PH ₃ , in the form of a non-pyrophoric industrial phosphine mix produced by the above process is fed to a gas control manifold block 22 of the system 10 shown, schematically in Figure 1, of a grain storage fumigation system 14. The system 10 includes phosphine gas sources 16 in the form of at least one, preferably two or more pressurized phosphine gas cylinders 16A and 16B containing non-pyrophoric industrial phosphine mix able to feed phosphine gas in the mix manufactured by the process described above, to the control manifold block 22. In the case of two phosphine gas sources, both may be in service simultaneously. The system further includes a source of purging gas. In one form the purging gas source may be a nitrogen gas source comprising of at least one pressurized nitrogen gas cylinder 18. In a preferred form the purging gas source may also be connected to the control manifold block 22. Alternatively, C0 ₂ may be used instead of nitrogen as a purging gas.

[00064] A fan 24 supplies air under pressure also to the gas control manifold block 22 to pass through a venturi- shaped passage 26 within the gas control manifold block to provide an accelerated air flow through the passage 26. A gaseous mixture comprising phosphine laden air is then fed from the manifold block via a delivery conduit 30 to a gas distributor 32 in the grain storage facility 34. The functions of the manifold block 22 are controlled by a programmable logic controller 36.

Second Preferred Method

[00065] Another of the methods by means of which industrial phosphine mix can be produced (Troy 1973) includes the following steps:

White phosphorous converted to red phosphorus and then reacted with steam and phosphoric acid is the preferred method if further reaction of the phosphine to substituted phosphines is needed. The acid route requires purification of PH ₃ : 8P + 12H ₂ 0 - >PH ₃ + 3H ₃ P0 ₄ Further Preferred Methods

[00066] Other preparations of industrial phosphine mix reported (Fluck 1973) include:

Pyrolysis of phosphorous acid.

Hydrolysis of phosphonium iodide with water or dilute bases.

Reduction of phosphorous trichloride with lithium in diethyl ether.

Reaction of PCI ₃ with finely divided sodium in toluene.

Treatment of phosphorous with steam in phosphoric acid at 275-285°C.

Reaction of phosphorous in aqueous acid in contact with mercury or zinc amalgam.

Reaction of mix of phosphorous and granulated zinc with acids plus methanol.

Electrolysis of phosphorous and hypophosphorous acid at mercury or lead cathodes

Industrial phosphine mix purification

[00067] The above described preferred methods may require additional processing of the industrial phosphine mix they produce in order to render the resulting industrial phosphine mix to be non-pyrophoric. The pyrophoric inducing impurities of interest (diphosphine, P ₂ H ₄ ; and white phosphorus, P ₄ ) need to be of significant concentration to be of concern. Unlike purification levels, part per billion, ppb, required for electronic grade gases which require sophisticated purification techniques such as SAES Getters, traditional low temperature/molecular sieve techniques should give acceptable purity for agricultural grade phosphine. A cold trap may be used to separate diphosphane from phosphine (Thenard 1844).

[00068] Note P ₂ H ₄ is a liquid (boiling point = 65°C) and P ₄ is a solid (melting point = 44°C).

Industrial phosphine mix in the system of the invention

[00069] Samples of the industrial phosphine mix used in the system of the present application prepared by the first preferred method as described above, were analysed for residual phosphorous and diphosphine using Nuclear Magnetic Resonance (NMR) technique. The pyrophoric inducing impurities were at such levels that it confirmed the observations that the industrial phosphine mix for use in the system below is non-pyrophoric.

The Gas Control Manifold Block

[00070] Turning now to the detailed schematic view of the gas control manifold block 22 shown in Figure 2, in addition to the venturi- shaped through passage 26 into which air is injected under pressure, the control manifold block 22 includes two main gas passages 42 and 44, preferably parallel to the venturi- shaped through passage 26. The first one of these passages 42 extending the full width of the control manifold block 22 between an entry orifice 46 for industrial phosphine mix from one of the two cylinders, for example from cylinder 16B at a first, for example, the air entry end of the block, and an entry orifice 48 for N ₂ from cylinder 18 at the opposite end. The second one of the two main gas passages 44 extends from an entry orifice 49 for industrial phosphine mix from cylinder 16A also at the air entry side of the block to a point some distance past the narrowest portion of the venturi- shaped passage 26.

[00071] Two transverse gas passages 50 and 52 interconnect the first and second main gas passages 42 and 44; a first transverse gas passage 50 extending from the end of the second main gas passage 44 to intersect the first main gas passage 42 and with the second transverse gas passage 52 extending between the two main gas passages at some distance from the entry orifices for industrial phosphine mix from cylinders 16A and 16B and downstream of a first gas control valve 58 on the first main gas passage 42. A third transverse gas passage 54 extends from the first main gas passage 42 to an outlet orifice 56 at the narrowest section of the venturi- shaped passage 26. In a preferred form the diameter 71 of the outlet orifice 56 where it meets with the venturi- shaped passage 26 is greater than l/25 ^th of the diameter of the narrowest section 70 of the venturi passage 26. In a preferred form the narrowest section 70 is in line with the outlet orifice 56 of the third transverse gas passage 54.

[00072] In a preferred form the valves including the first gas control valve 58, are screwed into sockets provided in the control manifold block 22. In a preferred form the valves are controlled by pneumatic spring return, normally closed actuators. The control manifold block 22 incorporates gas ports, seals and stainless steel diaphragms. In a preferred form_the valves are located along the two main gas passages and control the flows of industrial phosphine mix from the two phosphine cylinders, 16A and 16B, and nitrogen N ₂ from cylinder 18, and so determine the constitution of the gas injected through orifice 56 into the air stream passing through the venturi- shaped passage 26.

[00073] The first gas control valve 58 is located on the first main gas passage proximate the entry orifice 46 thus controlling the entry into the manifold block of the industrial phosphine mix from cylinder 16B.

[00074] A second valve 60 is located on the second main gas passage 44 between the entry orifice 49 and the second transverse gas passage 52, thus controlling the entry into the manifold block of the industrial phosphine mix from cylinder 16A. [00075] A third valve 62 is located along the first main gas passage between the second transverse gas passage 52 and the third transverse gas passage 54.

[00076] A fourth valve 64 is located on the main gas passage 42 between the first and the third transverse gas passages 50, 54.

[00077] A fifth valve 66 is located near the end of the second main gas passage 44.

[00078] With only the first and the third valves 58, 62 open, industrial phosphine mix 16B gas only would flow to the outlet orifice 56. With only the second and the third valves 60, 62 open, only industrial phosphine mix 16A gas would flow to the outlet orifice.

[00079] A table of possible combinations is shown below:

[00080] It will be understood that the connections of the industrial phosphine mix and N ₂ cylinders, the gas passages and control valves within the control manifold block shown in Figure 2 are exemplary only and that these features may be arranged in a number of different ways. The important feature of the control manifold block is that it provides a compact leak proof block minimizing external piping and in which all interconnections between the cylinders of non- pyrophoric gas and nitrogen gas along with the valves controlling the flow of these gases, are completely encapsulated within the block. Moreover, the control manifold block and the solenoids may be separated from an enclosure containing the programmable logic controller and other electrical systems.

[00081] The control manifold block 22 thus provides for control of each of the sources of gases which are connected to the manifold block.

[00082] A feature of the gas supply and treatment system in at least some preferred forms of the invention is that long periods of operation without interruption are provided for by a novel system of nitrogen purging of the industrial phosphine mix and air passages within the gas control manifold block 22. This purging may assist in minimizing if not preventing_the build-up of polymer within the main and transfer passages and at the gas outlet orifice 56.

[00083] Preferably the purging regime includes two purging cycles; firstly, a full system purge of all internal passages by suitable settings of the control valves, and secondly purges of the gas outlet orifice 56. It can be seen from the disposition of the gas control valves as shown in Figure 2, that for example, the third transverse passage 54 and thus gas outlet orifice 56, can be purged if gas control valves 62 and 66 are closed with gas control valve 64 open.

[00084] A full system purge may be conducted by the system before a duty cycle, and at the conclusion of that cycle. That is, a full system purge is conducted when the system is initially installed at a grain storage facility after connection of the PH ₃ cylinders in preparation for use and before disconnection of the PH ₃ cylinders after use.

[00085] Preferably, outlet orifice purges are provided at predetermined intervals throughout a duty cycle, for example every 6 hours of operation. Nitrogen is injected into the gas control manifold at high pressure, at least at 30bar, and may be regularly pulsed under control of the PLC.

[00086] Various sensors report to the PLC to monitor correct operation of the system. The system will not operate and shuts down if a range of adverse operating conditions are encountered. A touch screen (not shown) can display any of the above alarm conditions as well as providing for the setting of preferred operating parameters. The operation parameters may include fumigation time for which the system is to operate. The operating parameters may include purging frequency. Particularly for large installations, the operating parameters may include the PH ₃ in kilograms required, rather than the fumigation time. The operating parameters may include a specified flow rate of the phosphine- mix.

[00087] In an alternative arrangement with reference to Figure 3, the control manifold block again includes all the gas passages and control valves as well as their functions, as described above, but in this arrangement the air passage 26 does not include the narrowing venturi section of Figure 2 but maintains a substantially constant diameter throughout its length.

In Use

[00088] Air in the form of an air stream 74 is injected at air entry 72 into the venturi-shaped passage 26. The velocity of the air stream 74 will increase as it passes through the narrowest section 70 of the venturi passage 26. When valves 60 and 62 are opened a gas from cylinder 16A passes through entry orifice 49 through passage 52, passage 42 and passage 54 to outlet orifice 56 where it is injected into air stream 74 at a point of high air stream velocity.

[00089] When valves 58 and 62 are opened a gas from cylinder 16B passes through entry orifice 46 through passage 42 and passage 54 to outlet orifice 56 where it is injected into air stream 74 at a point of high air stream velocity.

[00090] For purpose of purging, valve 64 may be opened and a purging gas passes through entry orifice 48 through passage 42 and passage 54 to outlet orifice 56 for the purpose of purging at least passage 54 and orifice 56. Passage 44 up to the supply cylinder 16A can be purged when the valves 66 and 60 are opened. Passage 42 up to the supply cylinder 16B can be purged when valves 60 and 58 are opened.

Industrial Applicability

[00091] The system of the invention, utilizing as it does, non-pyrophoric phosphine gas injected into an air stream, provides for considerable improvement in the effectiveness of the phosphine/air mixture introduced into a grain storage facility.

[00092] The features and benefits of at least some preferred forms of the system of the invention may be summarized in the table below: