This application is a U.S. National Phase entry under 35 U.S.C. § 371 of International application No. PCT/GB2018/050740, filed Mar. 21, 2018, which claims the benefit of Great Britain patent application No. 1706785.1, filed Apr. 28, 2017, the contents of each of which are incorporated herein by reference in their entireties.

This invention relates to a propellant conditioning assembly, a process plant including such an assembly, and a method of conditioning a propellant.

Drugs for treating illnesses such as respiratory disorders are frequently administered in aerosol formulations. Such aerosol drug formulations are typically delivered using a medical dosing device, e.g. a Metered Dose Inhaler (MDI), which contains the drug formulation along with a propellant. A nozzle or similar atomising outlet included within the dosing device is operated, e.g. depressed, to deliver the medication in an atomised form.

Example propellants for medical dosing devices include hydrofluorocarbons (HFCs) such as HFC 134a (1,1,1,2-tetrafluoroethane), HFC 227ea (1,1,1,2,3,3,3-heptafluoropropane) and HFC 152a (1,1-difluoroethane).

Conditioning a propellant, i.e. stabilising its liquid density by providing it at a constant pressure and temperature, is often essential prior to filling a dosing device with the propellant, especially when performing a dual fill of a dosing device with a concentrated drug suspension being added to the device prior to the propellant.

According to a first aspect of the invention there is provided a propellant conditioning assembly, for providing a propellant feed to a medical dosing device filling apparatus, the assembly comprising:an input conduit to receive a propellant at a constant pressure from a propellant reservoir;a bifurcation to divide the input conduit into first and second conditioning conduits, the first conditioning conduit including a cooler device to selectively cool a diverted first propellant stream flowing through the first conditioning conduit, and the second conditioning conduit including a heater device to selectively heat a diverted second propellant stream flowing through the second conditioning conduit; andan output conduit to receive the first and second propellant streams, the relative proportion of the first and second propellant streams merging in the output conduit being controlled to regulate the temperature of a merged constant pressure propellant feed exiting from the output conduit.

The ability to regulate the temperature of a constant pressure propellant feed exiting from an output conduit, i.e. the ability to condition the propellant in the foregoing manner is advantageous because it permits the continuous, inline conditioning of a propellant in real time. As a result, conditioned propellant is readily and consistently available, e.g. for a downstream medical dosing device filling apparatus, and there is no requirement to store large quantities of conditioned propellant.

This latter benefit is especially important with respect to flammable hydrofluorocarbon (HFC) propellants, such as HFC 152a (1,1-difluoroethane), as it avoids the associated fire and safety hazards.

Preferably the input conduit includes an input temperature sensor arranged to measure an input temperature of the propellant in the input conduit, the measured input temperature being used to control the selective operation of the cooler and heater devices.

The inclusion of such an input temperature sensor introduces a degree of feedback control to the propellant conditioning assembly of the invention, and allows relatively coarse changes to be made to the temperature of the respective propellant streams, which in turn allows for finer, subsequent regulation of the temperature of the merged propellant feed in the output conduit.

Optionally the cooler device is operated to cool the first propellant stream flowing through the first conditioning conduit when the measured input temperature is greater than a first temperature threshold.

Such an arrangement desirably cools the first propellant stream when the temperature of the propellant in the input conduit is higher than desired, and therefore makes available a cooled propellant stream for downstream merging in the output conduit with the second propellant stream.

The heater device may be operated to heat the second propellant stream flowing through the second conditioning conduit when the measured input temperature is less than a second temperature threshold.

Such an arrangement desirably heats the second propellant stream when the temperature of the propellant in the input conduit is lower than desired, and therefore makes available a heated propellant stream for downstream merging in the output conduit with the first propellant stream.

In a preferred embodiment of the invention the first and second temperature thresholds differ from one another.

Having differing first and second temperature thresholds helps to reduce the need to operate the cooler and heater devices, i.e. by causing one or other of them to operate only when the input temperature is outside the temperature range defined by the said first and second thresholds.

Preferably each of the cooler device and the heater device is or includes a heat exchanger.

Heat exchangers are able efficiently to remove or add heat to a respective propellant stream in a controlled and safe manner.

Optionally the first conditioning conduit includes a first flow control valve to control the flow rate through the first conditioning conduit and the second conditioning conduit includes a second flow control valve to control the flow rate through the second conditioning conduit.

The inclusion of such flow control valves permits the ready and effective control of the flow rate through each conditioning conduit, and hence helps also to control the relative proportion of first and second propellant streams that merge in the output conduit.

In another preferred embodiment of the invention the output conduit includes an output temperature sensor arranged to measure an output temperature of the merged constant pressure propellant feed in the output conduit, the measured output temperature being used to control the operation of the first and second flow control valves.

The inclusion of such an output temperature sensor introduces a further degree of feedback control to the propellant conditioning assembly of the invention and assists, via control of the first and second control valves, with close regulation of the temperature of the merged propellant feed in the output conduit.

In a still further preferred embodiment of the invention the first flow control valve is operated to increase the flow rate through the first conditioning conduit and/or the second flow control valve is operated to reduce the flow rate through the second conditioning conduit when the measured output temperature is above a first output threshold, and the first flow control valve is operated to reduce the flow rate through the first conditioning conduit and/or the second flow control valve is operated to increase the flow rate through the second conditioning conduit when the measured output temperature is below a second output threshold.

Such an arrangement permits fine control over the relative proportions of different temperature first and second propellant streams that merge in the output conduit, and hence similarly fine regulation of the temperature of the merged constant pressure propellant feed in the output conduit.

The input conduit may include an input flow rate sensor to measure the flow rate of the propellant through the input conduit.

The inclusion of such a flow rate sensor assists with controlling the relative proportion of first and second propellant streams that merge in the output conduit.

According to a second aspect of the invention there is provided a process plant, for providing a propellant feed to a medical device filling apparatus, comprising a propellant reservoir for a quantity of propellant and a supply line extending from the reservoir to a propellant conditioning assembly as described hereinabove, the supply line including a constant pressure pump to supply propellant at a constant pressure to the propellant conditioning assembly.

The process plant shares the benefits associated with the propellant conditioning assembly mentioned hereinabove.

According to a third aspect of the invention there is provided a method of conditioning a propellant, for feeding to a medical dosing device filling apparatus, comprising the steps of:(a) receiving in an input conduit a propellant at a constant pressure from a propellant reservoir;(b) dividing the input conduit into first and second conditioning conduits, the first conditioning conduit including a cooler device to selectively cool a diverted first propellant stream flowing through the first conditioning conduit, and the second conditioning conduit including a heater device to selectively heat a diverted second propellant stream flowing through the second conditioning conduit;(c) receiving the first and second propellant streams in an output conduit; and(d) controlling the relative proportion of the first and second propellant streams merging in the output conduit to regulate the temperature of a merged constant pressure propellant feed exiting from the output conduit.

The method of the invention similarly shares the benefits of the corresponding features of the propellant conditioning assembly of the invention.

