The present invention relates to an apparatus and method for automatically controlling the flow of gas in a system. In particular, the invention relates to controlling the flow of inert gas to a silo in which biomass fuel is stored prior to combustion and thereby preventing fires and/or explosions in the silo, via sudden dust cloud formation and associated static risk.

The burning of biomass as a fuel in power stations has become more prevalent in recent years and the volume of biomass used and stored at power stations has correspondingly increased. In general terms, biomass comprises plant matter, which may be in the form of wood, a fluff material or pellets formed from material which has been shredded and compacted. The biomass material is stored in large silos to keep the material dry and reduce loss of the material prior to being conveyed for use in boilers. Such silos can range from hundreds to thousands of cubic meters in volume. Biomass dust may be generated from the biomass during storage and handling. The dust is drawn off in an air stream which is filtered to remove the dust.

Fires may occur in both biomass storage silos and dust storage silos, and the factors which cause fires in both cases are broadly the same. Fires in biomass storage silos can come about as a result of bacterial and fungal activity which generate heat and produce methane, carbon monoxide and carbon dioxide. Heat accumulates to over 50°C leading to thermal oxidation of the biomass. Due to the thermal insulating properties of the biomass, the rate of heat generation may exceed the rate of heat loss, leading to a temperature rise, and may eventually lead to ignition. Fires may also be imported into silos, for example through hot product, or from hot bearings within the conveying system. Although water is the best medium for removing heat from smouldering fires, the use of water sprinklers would destroy the biomass product and cause significant damage to the storage silos due to the expansion of the wet pellets. It is known in the art that smouldering fires can be controlled and extinguished by providing an inert atmosphere within the silo. This is commonly achieved by providing a nitrogen and/or carbon dioxide atmosphere within the silo, although other gases such as argon can also be used. Accordingly, inert gas can be injected into the headspace to minimise the risk of self heating, to inert the headspace in the event of a surface fire or to provide an inert atmosphere in the event of a high risk of imminent explosion. In large silos, the top may be about 40 to 60 metres above ground level. Accordingly, to minimise the use of materials, the most efficient way of piping an inert gas into the headspace of a large silo is to pipe the gas in a relatively small bore pipe at a relatively high pressure (approximately 5-10 barg) and at a velocity of approximately 10-30 m/s, and then pass the gas through an orifice on a nozzle into the silo. As the gas passes through the nozzle, a critical pressure drop takes place, reducing the gas to effectively atmospheric pressure, thereby causing the velocity of the gas to increase further. A problem with high velocity gas is that it can disturb any dust present in the silo, thereby creating a dust cloud. A problem resulting from the dust cloud is that it can cause the nozzle to become blocked, and sudden dust cloud movement can lead to static electricity which can create sparks, which increase the risk of fires and/or explosions in the silo.

Accordingly, to overcome this problem the inert gas is often introduced slowly at first. This slowly increases the inert atmosphere in the headspace and the velocity of the inert gas can gradually be increased as the risk of static from dusts around the nozzle is reduced due to the reduced oxygen content.

To slowly increase the flow of gas in a system from zero, to the desired design flow, may be done at present by a control valve (either on flow or pressure), and slowly opened at a defined rate by an operator or programmed via a programmable logic controller. Both of these solutions have associated cost implications and are prone to errors occurring. Alternatively, actuators for on/off valves may be tweaked to delay the opening of the valve through spring adjustment or a throttling valve. However, the delays in opening are not sufficiently long from being in the closed position to being in the open position.

The present invention arises from the inventor's work in trying to overcome the problems associated with the prior art. In accordance with a first aspect of the invention, there is provided an apparatus for controlling the flow of gas into a container, the apparatus comprising: a primary gas conduit configured to feed inert gas from an inert gas source at a pressure greater than atmospheric pressure to a container configured to receive flammable material;

a first gas flow regulating means operably connected to the primary gas conduit, and configured to regulate the flow of gas flowing therethrough; a secondary gas conduit in fluid communication with the primary gas conduit, and disposed upstream of the first gas flow regulating means;

gas storage means operably connected to the secondary gas conduit, and configured to store a volume of inert gas; and

- a first valve operably connected to the primary or secondary gas conduit, and disposed upstream of the gas storage means,

characterised in that the apparatus is configured to switch between a standby mode in which the storage means is not in fluid communication with the inert gas source, and an activated mode in which the storage means is in fluid communication with the inert gas source, and wherein the first flow regulating means is configured to prevent the pressure of the inert gas downstream of the first flow regulating means from exceeding the pressure of the inert gas in the storage means.

Advantageously, by preventing the pressure of the gas downstream of the regulating means from exceeding the pressure in the storage means, the apparatus of the invention enables the inert gas to be automatically introduced into the container (for example, the headspace of a storage silo) in a very controlled manner such that the flow rate of the gas increases gradually. The result is that the apparatus reduces the risk of a dust cloud forming in the container, and will therefore reduce the risk of fires or explosions occurring therein. The apparatus of the invention is not prone to the errors inherent in prior art systems, and does not involve the same cost implications.

Preferably, the container is a storage silo. The flammable material preferably comprises a biomass substance, for example plant material. The flammable material may be in the form of pellets and/ or dust. The flammable material may be a fuel source.

The inert gas source may comprise a liquid gas store, a Pressure Swing Adsorption (PSA) unit, a membrane gas generation plant, or any other appropriate inert gas source. However, in a preferred embodiment, the inert gas source comprises a liquid gas store. Preferably, the inert gas comprises carbon dioxide, nitrogen gas and/or argon. The apparatus may comprise a restriction orifice operably connected to the primary gas conduit, and disposed downstream of the first flow regulating means, wherein the orifice is configured to reduce the pressure of gas flowing therethrough. The restriction orifice may have a diameter which is at least 30% less than the diameter of the primary gas conduit upstream thereof. Preferably, the restriction orifice has a diameter which is at least 40% less, 50% less, 60% less, 70% less, 80% less or 90% less than the diameter of the conduit upstream thereof. Preferably, the apparatus comprises control means configured to switch the apparatus between the standby mode and the activated mode. Preferably, the control means is configured to send a signal (which is preferably a digital signal) to the first valve to switch the apparatus between standby and activated modes. The first valve may be operably connected to the secondary gas conduit, and is preferably disposed upstream of the gas storage means. The first valve can be any type of valve known in the art. Preferably, however, the first valve comprises a solenoid valve, and is arranged to receive the signal from the control means.

In one embodiment, the first valve may comprise a two-port valve in which first and second ports are operably connected to the secondary gas conduit. Accordingly, when the apparatus is in standby mode, the first valve is configured so that the storage means is not in fluid communication with the inert gas source such that inert gas cannot flow therethrough, and when the apparatus is activated, the first valve is configured such that the storage means is in fluid communication with the inert gas source such that inert gas can flow therethrough.

However, in a preferred embodiment, the first valve comprises a three-port valve, in which first and second ports are operably connected to the secondary gas conduit, and a third port is operably connected to a first vent line. Accordingly, when the apparatus is in standby mode, the storage means is in fluid communication with the first vent line, and when the apparatus is activated the storage means is not in fluid communication with the first vent line.

The first gas flow regulating means may comprise a gas regulator, and preferably a forward pressure regulator comprising a loading mechanism, a sensing element and a control element. Preferably, the forward pressure regulator comprises a dome-loaded regulator. Preferably, the loading mechanism is configured to determine the gas regulator's outlet pressure, i.e. the pressure downstream of the dome loaded regulator. Preferably, the sensing element is adapted to sense changes in the outlet pressure and allows the regulator to react to these changes. Preferably, the control element is configured to reduce the inlet pressure to the desired outlet pressure and maintains it by increasing or decreasing an orifice area as the control element moves away or towards a regulator seat.

In a preferred embodiment, the first gas flow regulating means comprises a dome loaded regulator, wherein the loading mechanism comprises a dome in fluid

communication with the gas storage means. The sensing element may comprise a diagram sensing element, a piston sensing element or a bellows sensing element. The control element may comprise an unbalanced control element or a balanced control element.

Preferably, the apparatus comprises a second gas flow regulating means in operable communication with the secondary gas conduit, and disposed upstream of the gas storage means, and configured to restrict the flow of the inert gas into the storage means. In embodiments in which the first valve is operably connected to the secondary gas conduit, the second flow regulating means may be disposed upstream of the first valve. However, the second flow regulating means is preferably disposed downstream of the first valve.

Preferably, the second flow regulating means has a flow coefficient (Cv) of less than o.i, and more preferably less than o.oi. Preferably, the second flow regulating means has a flow coefficient (Cv) of less than 0.005, and most preferably less than 0.002.

Preferably, the second flow regulating means has a flow coefficient (Cv) of about 0.001.

In one embodiment, the second flow regulating means may comprise a restriction orifice. However, in a preferred embodiment, the second flow regulating means comprises a metering needle valve. Advantageously, a metering needle valve allows the flow coefficient (Cv) to be varied.

The apparatus may comprise a second vent line operably connected to the secondary gas conduit and/or storage means, and disposed downstream of the first valve. In embodiments in which the second flow regulating means is present, the second vent line is preferably disposed downstream of the second flow regulating means. The apparatus preferably comprises a vent valve operably connected to the second vent line. The vent valve may comprise a pressure safety valve configured to prevent the pressure in the gas storage means from exceeding a predetermined pressure. Alternatively, the vent valve may comprise a solenoid valve wherein when the apparatus is activated, the storage means is not in fluid communication with the second vent line, and when the apparatus is in standby mode, the storage means is in fluid communication with the second vent line.

In a preferred embodiment, the first valve is operably connected to the secondary gas conduit, and disposed upstream of the gas storage means, and the apparatus comprises a second valve operably connected to the primary gas conduit, and disposed upstream of the first flow regulating means. Preferably, when the apparatus is in standby mode, the first gas flow regulating means is not in fluid communication with the inert gas source, and when the apparatus is in activated mode, the first gas flow regulating means is in fluid communication with the inert gas source.

In one embodiment, the second valve may be disposed upstream of where the secondary gas conduit is in fluid communication with the main gas conduit.

Alternatively, in another embodiment, the second valve may be disposed downstream of where the secondary gas conduit is in fluid communication with the main gas conduit.

In a preferred embodiment, the second valve comprises an actuated isolation valve system.

The further valve may comprise a further solenoid valve. Preferably, the control means is configured to send a digital signal to the further solenoid valve to switch the apparatus from standby mode to activated mode and from activated mode to standby mode.

Preferably, the apparatus comprises a further flow regulating means operably connected to the secondary gas conduit, and configured to limit the pressure of the inert gas downstream thereof. Preferably, the further flow regulating means comprises a pilot regulator. Preferably, the further flow regulating means is disposed upstream of the gas storage means. It will be appreciated that the apparatus of the invention has several important uses.

Thus, in a second aspect, there is provided use of the apparatus of the first aspect to control the flow of gas into a container.

The gas is preferably inert, and the container is preferably a storage silo.

Thus, the apparatus is used to control the flow of inert gas into the container in order to:- (i) inert the atmosphere in a container's headspace to minimise the risk of its contents from self-heating,

(ii) inert a container's headspace in the event of a fire occurring at the surface of the container's contents, and/or

(iii) provide an inert atmosphere in a container in the event of a high risk of imminent explosion therein.

Furthermore, in accordance with a third aspect, there is provided a method of controlling the flow of gas into a container from an inert gas source, the method comprising:

- splitting a flow of gas from an inert gas source into a primary stream and a secondary stream;

feeding the secondary stream into a storage means thereby gradually increasing the pressure therein;

feeding the primary stream passed a restriction point at a rate configured to prevent the pressure of the inert gas downstream of the restriction point from exceeding the pressure of the inert gas in the storage means; and releasing the primary stream into the container.

The method of the third aspect comprises the use of the apparatus of the first aspect.

Preferably, the method comprises controlling the rate at which the secondary stream is fed into the storage means.

Preferably, the method comprises an additional step, carried out subsequent to the step of feeding the primary stream passed the restriction point and prior to releasing the primary stream into the headspace, comprising reducing the pressure of the primary stream. Preferably, the pressure of the primary stream is reduced to approximately atmospheric pressure.

Preferably, the method comprises an initial step of switching the ports of a first valve, causing the inert gas source to be in fluid communication with the storage means. Preferably, the step of switching the ports of a first valve comprises sending a digital signal to a first solenoid valve.

Preferably, the initial step also comprises switching the ports of a second valve thereby causing the restriction point to be in fluid communication with the inert gas source. Preferably, the step of switching the ports of the second valve comprises sending a digital signal to a second solenoid valve.

Preferably, the method comprises preventing the pressure of the inert gas in the storage means from exceeding a predetermined pressure.

Preferably, the method comprises allowing a desired volume of inert gas to be released into the container, and preferably a headspace thereof. Preferably, once the desired volume of inert gas has been released into the container, the method comprises:

- stopping the flow of the secondary stream into the storage means; and

venting inert gas from the storage means.

The step of stopping the flow of the secondary stream into the storage means may comprise switching the ports of a first valve causing the inert gas source to not be in fluid communication with the storage means.

In one embodiment, the step of switching the ports of the first valve causing the inert gas source to not be in fluid communication with the storage means also causes the storage means to be in fluid communication with a first vent line.

Preferably, the step of switching the ports of a first valve comprises sending a digital signal to the first solenoid valve.

Once the desired volume of inert gas has been released into the headspace the method may also comprise switching the ports of the second valve causing the restriction point to not be in fluid communication with the inert gas source. Preferably, the step of switching the ports of the second valve comprises sending a digital signal to the second solenoid valve. In one embodiment, the step of venting the inert gas from the storage means comprises switching the ports of a third valve thereby causing the storage means to be in fluid communication with a second vent line. Preferably, the step of switching the ports of the third valve comprises sending a digital signal to a third solenoid valve. All features described herein (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined with any of the above aspects in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. For a better understanding of the invention, and to show how embodiments of the same may be carried into effect, reference will now be made, by way of example, to the accompanying Figures, in which:-

Figure 1 is a schematic diagram showing a first embodiment of an apparatus for automatically increasing the flow of inert gas to a silo;

Figure 2 is a schematic diagram showing a second embodiment of the apparatus of Figure 1;

Figure 3 is a schematic diagram showing a third embodiment of the apparatus for automatically increasing the flow of inert gas to a silo; and

Figure 4 is a schematic diagram showing a fourth embodiment of the apparatus for automatically increasing the flow of inert gas to a silo.

Example 1

Inert gas 2 is often used to inert the headspace 3 of a silo (not shown) which is used to store flammable biomass. The purpose of the gas 2 is:- (i) to inert the atmosphere in the headspace 3 to minimise the risk of the contents of the silo from self-heating, (ii) to inert the headspace 3 in the event of a fire occurring at the surface of the silo's contents, or (iii) to provide an inert atmosphere in the event of a high risk of imminent explosion in the silo. To avoid explosions caused by static electricity, the inert gas 2 is often introduced slowly at first, and the flow is gradually increased as the ignition risk is reduced due to the reduced oxygen content of the gases in the headspace. A first embodiment of an apparatus 4 shown in Figure 1 is used to automatically increase the flow of the inert gas 2 into the silo's headspace 3. The inert gas 2, in this case nitrogen, is piped from an inert gas source (not shown). It will be understood that the inert gas source may be a liquid gas store, a Pressure Swing Adsorption (PSA) unit or a membrane gas generation plant. Inert gas 2 from the inert gas source will generally be provided at a pressure of between about 5 to 10 barg. In the present example, the inert gas 2 is provided at a pressure of 8 barg.

The inert gas 2 is piped from the inert gas source to the silo's headspace 3 by a main gas conduit 6. In the present example the main gas conduit 6 is an 80 mm nominal diameter pipe. A dome loaded regulator 8 is disposed further downstream on the main gas conduit 6, and is provided to regulate the flow of the inert gas 2 therealong. A restriction orifice 9 is disposed downstream of the dome loaded regulator 8 in the gas conduit 6 and adjacent to the headspace 3 of the silo. The restriction orifice 9 causes a pressure drop in the inert gas 2 that passes therethrough. Accordingly, the inert gas 2 downstream of the restriction orifice 9 will be at about atmospheric pressure, which is the pressure of the atmosphere within the silo.

Upstream of the dome loaded regulator 8, the main gas conduit 6 branches off to create a secondary line 10 which forms a loop between upstream and downstream branch points. Adjacent to the upstream branch point, the secondary line 10 narrows at a narrowing point 12 from about 80 mm to about 6 mm. Downstream of the narrowing point 12, a first solenoid valve 14 is disposed in the secondary line 10 for controlling whether or not gas flows along the secondary line 10. In one embodiment, the solenoid valve 14 is a three-port valve having first, second and third ports 15, 16, 17. The first port 15 is connected to the upstream portion of the secondary line 10, the second port

16 is connected to the downstream portion of the secondary line 10, and the third port

17 is connected to a first vent line 18. However, it will be appreciated that a two-port valve could also be used where both ports were connected to the secondary line 10.

A metering needle valve 19 is disposed downstream of the first solenoid valve 14 in the secondary line 10. When the first solenoid valve 14 allows inert gas 2 to flow along the secondary line 10, the metering needle valve 19 controls the rate at which the inert gas 2 can flow. In one embodiment, the metering needle valve 19 is a Swagelok SS-SS6MM valve set with a flow coefficient (Cv) of 0.001. It will be readily understood that a restriction orifice with a low flow coefficient could be used instead of the metering needle valve 19 to control the gas flow rate through along the secondary line 10.

Alternatively, in another embodiment, it is possible to use the apparatus 4 without any metering needle valve 19 or restriction orifice being provided in the secondary line 10. However, a preferred embodiment of the invention, as shown in Figure 1, includes the metering needle valve 19 as it allows the flow coefficient to be varied.

Downstream of the metering needle valve 19 there is disposed a gas receiver 20, which is a two litre gas receiver capable of containing inert gas at a pressure of at least 8 barg (the pressure of the inert gas 2 in the main gas conduit 6). The receiver 20 is provided with a second vent line 21 which includes a pressure safety valve 22, which is a two-port valve. The pressure safety valve 22 is configured to allow the gas stored in the receiver 20 to vent if it exceeds a predetermined pressure, and thereby prevents inadvertent overpressure of the receiver 20. Downstream of the receiver 20, the secondary line 10 is connected to a dome 24 of the dome loaded regulator 8 which is provided on the main gas conduit 6.

It will be understood that the dome 24 comprises the loading mechanism of the dome loaded regulator 8. The pressure in the dome 24 determines the regulator's outlet pressure, i.e. the pressure downstream of the dome loaded regulator. In addition to the loading mechanism, the dome loaded regulator 8 will also comprise a sensing element, which senses the changes in the outlet pressure and allows the regulator to react to these changes, and a control element, which acts to reduce the inlet pressure to the desired outlet pressure and maintains it by increasing or decreasing the orifice area as the control element moves away or towards a regulator seat. It will be understood that the sensing element may comprise a diagram sensing element, a piston sensing element or a bellows sensing element. In the present system the inventor has used a diaphragm sensing element.

In use, when the apparatus 4 is in standby mode, the first solenoid valve 14 allows flow between the second port 16 and the third port 17, and the pressure in the receiver 20 is at atmospheric pressure. Accordingly, the dome 24 of the dome loaded regulator 8 is also at atmospheric pressure. Since the pressure in the main gas conduit 6 immediately downstream of the dome loaded regulator 8 will not drop below atmospheric pressure, no inert gas 2 flows into the silo. However, when the apparatus 4 is activated, a digital signal (e.g. a 24V direct current signal) is sent from a control system 26 to the first solenoid valve 14. It will be understood that this signal could be triggered automatically or could be sent manually. The digital signal causes the ports of the first solenoid valve 14 to switch, so that flow is allowed between the first port 15 and second port 16, thereby allowing the inert gas 2 to flow along the secondary line 10, at a rate controlled by the metering needle valve 19. The flow of inert gas 2 into the receiver 20 causes the pressure in the receiver 20 to gradually increase until it reaches 8 barg. This is shown in Table 1 in which all values have been calculated assuming the temperature is 288 K.

Table 1: Pressure in the receiver and at point A (shown on Figure 1) and flow rate of the inert gas at point B (shown on Figure 1) as a function of time

It will be noted that the flow rate of the inert gas 2 into the receiver 20 is initially constant, but then decreases as the pressure into the receiver 20 increases. After ten minutes, the pressure in the receiver 20 is 8 barg, which is the same as the pressure of the inert gas in the main gas conduit 6 upstream of the dome loaded regulator 8.

Accordingly, after 10 minutes the pressure in the receiver 20 will remain at 8 barg until the apparatus 4 is switched to standby mode.

The pressure in the receiver 20 will be the same as the pressure in the dome 24 of the dome loaded regulator 8. Accordingly, as the pressure in the receiver 20 increases, it allows the flow of the inert gas 4 through the dome loaded regulator 8, restriction orifice 9 and subsequently into the silo headspace 3 to also increase, as shown in Table 2. Table 2: The pressure and flow rate of the inert gas in the main gas conduit 6 at point C

(shown on Figure 1) as a function of time

Since the pressure in the receiver 20 will remain constant after 10 minutes, the flow rate of the inert gas 2 along the main gas conduit 6, passed the dome loaded regulator 8 and into the silo headspace 3 will remain at 4449.71 sm3/hr until the apparatus 4 is switched to standby mode. The rate at which the pressure in the receiver 20 (and therefore the flow into the silo) increases can be varied by modifying the flow which the metering needle valve 19 allows along the secondary line 10 and/or by modifying the size of the receiver 20.

When a sufficient quantity of the inert gas 2 has been fed to the silo headspace 3 it will be necessary to return the apparatus 4 to standby mode, and this can be achieved by sending a digital signal from the control system 26 to the first solenoid valve 14. Again, it will be appreciated that this signal could be triggered automatically or could be sent manually. This signal will cause the ports 15, 16, 17 of the first solenoid valve 14 to switch to once again allowing flow between the second port 16 and the third port 17, and preventing any more of the inert gas 4 from flowing into the first port 15 and out of the second port 16.

Instead, the inert gas 2 stored in the receiver 20 will start to flow out of the first vent line 18 decreasing the pressure of the inert gas 2 in the receiver 20. Due to the presence of the metering needle valve 19, the rate at which the receiver 20 is able to vent is restricted. Accordingly, the pressure of the inert gas 2 in the receiver 20 and the flow rate of the inert gas 2 into the silo headspace 3 will both decrease gradually over time, as shown in Table 3.

Table 3: Pressure in the receiver and at point A flow rate of the inert gas at point B

(shown on Figure 1) as a function of time

Accordingly, it will be appreciated that it will take nineteen minutes to vent the receiver 20, and thereby to stop the flow of the inert gas 2 into the silo headspace 3. However, in some situations, it might be beneficial to vent the receiver 20, and prevent the flow of inert gas 2 into the silo headspace 3 much more quickly. Alternatively, in an alternative embodiment of the apparatus, the receiver 20 could be provided with a further vent line including a further solenoid valve (not shown). It will be appreciated that this vent line could be provided in addition to, or instead of, the second vent line 21 with the pressure safety valve 22 which is shown in Figure 1. Accordingly, in addition to switching the ports of the first solenoid valve 14, a further digital signal can be sent from the control system 26 to the further solenoid valve. This further signal will switch the flow on in the further solenoid valve, allowing the inert gas 2 in the receiver 20 to also vent along the further vent line 21. Since a metering needle device 19 is not present on the further vent line, the inert gas 2 is able to vent much more quickly. Accordingly, the pressure in the receiver 20 and the flow rate of the inert gas 2 into the silo headspace 3 will both decrease rapidly. Where the solenoid valve has flow coefficient (Cv) of 0.1 then the pressure in the receiver would decrease to atmospheric pressure in about 10 seconds.

Alternatively, it will be understood that if the first solenoid valve 14 is disposed downstream of the metering needle valve 19 (as shown in a second embodiment of the apparatus 4, as depicted in Figure 2), then the metering needle valve 19 will not affect the rate at which the receiver 20 is able to vent. Accordingly, it is not necessary to provide the embodiment of the apparatus 4 shown in Figure 2 with a second vent line 21. However, with this embodiment, when the apparatus 4 is activated, a small volume of inert gas 2 which has built up in the secondary gas conduit 10 between the metering needle valve 19 and the first solenoid valve 14 will immediately be released into the receiver 20, but to be of such little volume so as to have negligible impact on the efficacy of said invention. Example 2

The apparatus 4 shown in Figure 1 and discussed in Example 1 can be modified by adding additional elements thereto, and a third embodiment is shown in Figure 3. The apparatus 4' shown in Figure 3 includes all of the elements which were present in the apparatus 4 shown in Figure 1, namely a main gas conduit 6' provided with a dome loaded regulator 8', and a restriction orifice 9' provided downstream of dome loaded regulator 8'. The apparatus 4' also includes a secondary line 10' which is taken off the main gas conduit 6' and which is connected to the dome 24' of the dome loaded regulator 8'. The secondary line 10' includes a narrowing point 12', a first solenoid valve 14' provided with a first vent line 18', a metering needle valve 19' and a receiver 20' provided with a second vent line 21' which includes a pressure safety valve 22'. Similarly, the apparatus 4' includes a control system 26' which can send an electrical signal to activate and deactivate the apparatus 4'.

In addition to these elements, the apparatus 4' shown in Figure 3 also includes an actuated isolation valve system 28' which comprises a second solenoid valve 30' disposed on a further gas line 32' which is connected to the main gas conduit 6' via an actuated valve 42'. The second solenoid valve 30' controls whether or not gas can flow along the further gas line 32', which may for example be taken from a site instrument gas supply. In this embodiment, the second solenoid valve 30' is a three-port valve with the first port 34' being connected to the upstream portion of the further gas line 32', the second port 36' being connected to the downstream portion of the further gas line 32', and the third port 38' being connected to a third vent line 40'.

In use, when the apparatus 4' is in standby mode, the second solenoid valve 30' is set to allow a flow of gas through the second port 36' and the third port 38', and along the third vent line 40'. Accordingly, gas is unable to flow along the further gas line 32'.

When the second solenoid valve 30' is configured in this manner, the actuated valve 42' does not allow gas flow along the main gas conduit 6'.

As with the apparatus 4 discussed in Example 1, when the apparatus 4' is activated, a digital signal (e.g. a 24V direct current signal) is sent from the control system 26' to the first solenoid valve 14', which switches the ports of the first solenoid valve 14', as discussed in Example 1. At the same time, the control system 26' sends a digital signal to the third solenoid valve 30', which causes the ports of the third solenoid valve 30' to switch, so that gas flows between the first port 34' and second port 36' and along the further gas line 32'. The pressure caused by this gas flow causes the actuated valve 42' to allow flow along the main gas conduit 6'. This will not have any noticeable effect when the apparatus 4' is activated. However, the difference is noticed when the apparatus 4' is switched from on to standby mode. Again, this can be carried out by sending a digital signal from the control system 26' to both the first solenoid valve 14' and the third solenoid valve 30'. This switches the ports of the first solenoid valve 14' as discussed in Example 1, and causes the ports 34', 36' and 38' of the third solenoid valve 30' to switch to once again allow flow between the second port 36' and the third port 38'. This immediately stops the flow of the inert gas 4 through the actuated valve 42'. Accordingly, unlike the apparatus 4 discussed in Example 1, when apparatus 4' is switched to standby mode, the flow of the inert gas 4 into the silo headspace 3 stops almost immediately.

It will be appreciated that the apparatus 4' shown in Figure 3 would also function if it was not provided with the first solenoid valve 14'. In this embodiment the actuated isolation valve system 28' would be the only valve configured to control whether or not the inert gas 2 could flow from the inert gas source to the receiver 20'. Example 3

A fourth embodiment of the apparatus is shown in Figure 4, which includes all of the elements which were present in the apparatus 4 shown in Figure 1. Unlike the apparatus 4' shown in Figure 3, the apparatus 4" shown in Figure 4 does not include an actuated isolation valve system 28'. However, it will be understood that a further embodiment could include this feature.

In addition, the apparatus 4" shown in Figure 4 includes a pilot regulator 44" disposed on the secondary line 10" between the narrowing line 12" and the first solenoid valve 14". The pilot regulator 44" restricts the pressure of the inert gas 2 downstream thereof as it feed through the secondary line 10". The pressure of the inert gas 2 in the receiver 20" and at the dome 24" cannot exceed a pre-set maximum, which means that the pressure of the inert gas 2 in the main gas conduit 6" downstream of the dome loaded regulator 8" cannot exceed the pre-set maximum. Accordingly, the embodiment of the apparatus 4" shown in Figure 4 is a combined slow opening and flow limiting device.

It will be understood that a similar effect may be achieved if the pilot regulator 44" were disposed on the secondary line 10" downstream of the gas receiver 20". However, in such an embodiment, the pilot regulator 44" would not limit the rate at which the receiver 20" fills with gas. Accordingly, the preferred embodiment is when the pilot regulator 44" is positioned upstream of the receiver 20" as shown in Figure 4.

Summary

Each embodiment of the apparatus 4, 4', 4" shown in the Figures may be retrofitted to existing silos, or included in new silos and enable inert gas to be automatically introduced to the headspace 3 of the silo in a controlled way where the flow rate of the gas increases gradually. The apparatus 4, 4', 4" is not prone to the errors of prior art systems and does not involve the same cost implications. In addition, the apparatus 4, 4', 4" reduces the risk of a dust cloud forming in the silo and will therefore reduce the risk of fires or explosions occurring therein.