Method For Managing Access To A Confined Space With Renewal Of The Atmosphere By Means Of Forced Ventilation/Extraction And The Use Of Physical Barriers That Can Be Opened In A Variable And Controlled Manner

Description

The present invention relates to the field of the carriage and distribution of heat-sensitive products and relates in particular to the case of pharmaceutical products and foodstuffs.

Observance of the cold chain and the sanitary quality of foodstuffs have actually become major stakes in logistic circuits. In the developed and developing countries, respect for the environment and reduction of noise nuisance are becoming increasingly important.

There is nowadays an alternative to mechanical cold for refrigerating enclosed spaces (for example trucks for transporting and refrigerating foodstuffs) and that alternative involves the use of cryogenic fluids. In the context of primary and secondary transport in refrigerated trucks, there are two solutions mentioned in this field of industry, using liquid nitrogen by way of cryogenic fluid.

The first technology involves injecting liquid nitrogen directly into the space (“direct injection”) and causing it to vaporize therein. The main advantage of this first technology is the refrigerating performance of the system; specifically, getting the space to the required temperature takes just a few minutes and the return to the low temperature after each opening of the door is near-instantaneous after the direct injection of liquid nitrogen into the space. However, it is necessary to bear in mind the risks associated with the direct injection of liquid nitrogen, these being anoxia, cold burns, hence the proposal to set in place timed ventilation systems that operate before the doors open and/or systems that detect a minimum oxygen content consistent with the legal requirements regarding personal safety.

The literature has proposed an alternative to liquid nitrogen, by using liquid air as the cryogenic fluid and injecting it directly into the enclosed space. It would nonetheless appear that storing a cryogenic mixture (in this instance liquid nitrogen and liquid oxygen) is a tricky operation because of the progressive enrichment of the liquid by its heaviest constituent, namely the oxygen.

The second technology (known as “indirect injection”) uses a heat exchanger (for example a simple serpentine coil) through which a cryogenic fluid flows, the space moreover being fitted with an air circulation system (fans) that bring this air into contact with the cold walls of the exchanger, thus allowing the air to become cooled. The problems associated with personal safety are thus eliminated but, on the other hand, the refrigerating performance has been questioned (particularly the reconditioning of the space after a door has been opened, which takes place far more slowly than in the case of its direct injection).

The present invention is concerned with the case of direct injection, and wishes to propose a new approach for managing access to such a confined space cooled by direct injection of a refrigerating gas, by controlling the renewal of the atmosphere in order to revert to an oxygen content that will allow an operator to enter this space.

In the prior art, this technical and safety problem was addressed using various approaches, including the following ones:

• • The alternative of using liquid air as cryogenic fluid instead of liquid nitrogen for direct injection into the space has already been mentioned hereinabove, but the difficulties that controlling the liquid air presents have also been mentioned.
  • The complete opening of the access door without ventilation and a recommendation (for example via an illuminated panel) not to enter the inert space until a given number of minutes have elapsed. This solution has been applied but has the disadvantage, according to the temperature difference between the gas inside the space and the external atmosphere, that it uses only the difference in density to bring about the renewal of the atmosphere, and this does not guarantee, when products are loaded in the space, that the desired renewal will be achieved at all points.
  • The complete opening of the door with forced ventilation and a recommendation (for example via an illuminated panel) not to enter the inert space until a given number of minutes have elapsed. This solution, through such a forced ventilation, allows the atmosphere to be renewed irrespective of the relative densities. However, this solution does have the disadvantage, in the absence of any physical barriers, that the operator is not prevented from entering the space (the operator might be distracted) even though the illuminated indicator is in the “do not enter” position.
  • Complete opening of the door without ventilation, but with one or more analyzers, and an automatic controller that manages the content information and issues a recommendation (for example via an illuminated panel) not to enter the inert space until the automated system, on receipt of an acceptable value for residual oxygen in the atmosphere, displays an illuminated signal indicating that it is safe to enter. As before, the lack of physical barriers does not make it possible for a distracted or risk-taking operator to be prevented from entering. In addition, installing oxygen sensors does allow measurements to be taken at various points but also presents a number of delicate questions, on the one hand, concerning the reliability of the measurement, and on the other hand concerning the distribution through the space particularly according to the way in which the load is configured in the space and concerning the reliability of these measurements in very cold spaces (typically of −20° C. or even of approaching −60° C.) and finally concerning the frequent need to calibrate.

It is known in particular that movements of the truck and potential knocks by the loads are factors which may lead to frequent malfunctions.

• • Complete opening of the door without ventilation, but with one or more analyzers, and formalized access denial (for example a cable stretched across at mid-height), together with an automatic controller that manages the content information and displays a recommendation (for example via an illuminated panel) not to enter the inert space until the automatic controller, on receipt of an acceptable value for the residual oxygen in the atmosphere displays an illuminated signal that it is safe to enter.
  • Here again, the use of oxygen sensors presents technical problems and the cable can hardly be considered to be a reliable physical barrier.

As will be seen in greater detail in what follows, the present invention proposes a new method for managing access to a confined space which is cooled by direct injection of a cryogenic fluid (for example of the truck or container type for transporting and/or refrigerating heat sensitive products such as pharmaceutical or food products), whereby the following steps are taken:

• • use is made of at least one system for closing the confined space, capable of denying access to this confined space,
  • use is made of a data acquisition and processing device capable:
• a) of controlling whether said closure system is open or closed;
• b) of ensuring, after each closure of said closure system, that a timed period (TP) is observed, at the end of which timed period injection of cryogenic fluid into the space is recommenced;
• c) and, at the demand of a user, of instigating the next cycle of opening said closure system:
  • i)the device evaluates the time elapsed (TE) in the closed position, that is to say the time that has elapsed since the last closure system closing cycle and compares TE against said timed period TP;
  • j)if TE<TP opening of said closure system is immediately authorized by the device, whereas if TE>TP the opening of said closure system is authorized by the device after a predefined waiting time.

Further, according to one of the preferred embodiments of the present invention:

• • the system for closing the confined space capable of denying access to this confined space has a degree of opening/closure which is variable and controllable, p1 said data acquisition and processing device is capable also of fixing and controlling the degree of opening/closing of said closure system.

As will be clearly evident to a person skilled in the art, during the “predefined waiting time”, the atmosphere in the confined space is renewed to make it breathable by an operator, notably using a ventilation and/or extraction system, preferably employing flow rate control.

The present invention therefore has the benefit of having proposed a new access control system that does not use an analytical check of the atmosphere internal to the confined space, uses forced ventilation and/or extraction and an associated predefined timed period that in a very novel manner takes account of the time elapsed (TE) in the closed position, that is to say of the time that has elapsed since the last closure system closure cycle.

As will be explained in greater detail hereinbelow using practical illustrations, the fact of adjusting the ventilation or extraction timed period to suit the time that has elapsed since the last door closure cycle notably makes it possible to adapt to the various logistic configurations encountered, and for example to adapt very effectively to the commonplace situations where a truck transporting products will, upon arrival at its destination (for example having arrived at the premises of a customer) offload in stages, the groups of products being offloaded and delivered in a number of goes.

As is stated hereinabove, for preference, this management employs an uncrossable barrier that forms an air intake in the part open condition.

• • In other words, according to a preferred embodiment of the invention, the physical barrier (the “opening/closure system”) that has variable (partial) opening here performs two functions: that of a physical barrier denying access when necessary, and that of an air intake for renewing the atmosphere because the barrier has a variable and controllable degree of opening (by way of illustration, the data acquisition and processing device may allow a partial opening of the door with an opening by 10 cm for example; air can thus circulate, but it is impossible for a person to enter, this of course being extremely safe).

The combination of these factors therefore makes it possible:

• • physically through correct management of the physical barrier, which preferably has variable and controlled opening (for example a roller door), to deny access to the space that has previously been cooled by a refrigerating gas until an atmosphere that presents no danger to the individual who is to enter this space is present again at all points;
  • for the atmosphere management and its impact on the surrounding space (unloading platform with airlock, etc.) to be adapted to all logistic and climatic situations and configurations encountered during the operations of loading/unloading the spaces;
  • for the atmosphere management to be adapted to suit the climatic conditions thus having the best possible efficiency for the renewal of the atmosphere;
  • for standard signals or accessories of the truck (action on the tail lift or pushbutton or the like) to be used as the demand to open or to close the door, thus making the method more acceptable to the operators and:
    • to increase or maintaining productivity (saving time),
    • to limit the consumption of refrigerant,
    • to improve temperature control in the space.
  • The fact that the ventilation or extraction timed period can be adjusted to suit the time that has elapsed since the last door closing cycle means that it is possible to adapt to the various logistic configurations encountered, to adjust the time taken to renew the atmosphere in complete safety and to limit the consumption of refrigerant;
  • to not rely on any analytical check of the atmosphere;
  • and to obtain a homogeneous atmosphere inside the confined space.

As will have been understood, the system for opening/closing the space, that constitutes the physical barrier, may be of a very variable nature: for example it may be a lift-up door (of the roller shutter type), or alternatively a door with leaves, and the system may constitute the insulating main door or the noninsulated secondary door.

According to the invention, following each closing of the door, the system starts a timed period TP. When this timed period has elapsed, injection of cryogenic fluid begins.

When the opening of a door is demanded by an operator, the system evaluates the time elapsed TE, and:

• • if the opening of the door has been demanded by the operator before this timed period has been completed (therefore when TE<TP), the atmosphere is still breathable because during the timed period no gas has been injected, and therefore the atmosphere does not present any risk to an operator and opening may be authorized immediately by the system,
  • if the opening of the door is demanded by the operator after this timed period has been completed (so when TE>TP), the system will have authorized an injection of cryogenic fluid, and the space will therefore at the time of this request be in a cooled or partially cooled state and the interior atmosphere will have a lower residual oxygen content connected with the injection time that has elapsed.

The case of TE>TP and TE<TP may for example be illustrated in greater detail using the following situation in which a truck transporting foodstuffs is going to unload its goods at the destination (for example the premises of a customer) in stages, the groups of products being unloaded and delivered in a number of goes:

• • i) the driver arrives at a customer and wishes to open the door. The door has been closed for around 30 minutes (TE=30 min greater than TP for example equal to 2 min), so the control system cannot authorize him to open the door until a predefined waiting time (dependent on the characteristics of the truck, on the time TE that has elapsed since the last door closing cycle, etc.) has elapsed.

From this door opening demand by the driver, the control system orders:

• • the closure of the valves that inject the refrigerant into the space (for example the nitrogen);
  • the partial opening of the door (this for example being controlled by a pneumatic actuator and an associated position controller and a controller that checks the degree of opening/closing of the door);
  • the starting of the renewal of the atmosphere in the space (the switching on of the fan(s)/extractor(s), the automatic choice via the control system as to whether to use fans and/or extractors is notably dependent on the interior temperature and on the exterior temperature, according to whether the ratio of these temperatures is greater than 1 or less than 1, the control system for managing the atmosphere will determine whether to operate in the extraction mode or in ventilation mode;
  • the starting of a predefined waiting time (the time to renew the atmosphere in the space), which waiting time will in particular take account of the time TE that has elapsed since the last door closing cycle (during this waiting time, the ventilation/extraction is in operation and its flow rate is controlled).
  • At the end of this waiting time, by way of example, the control system orders the illumination of a green illuminated indicator that indicates that access to the space is authorized, i.e. that indicates to the operator that he can proceed to open the door fully: action on the opening control button.
• j) on the tail lift, the driver can fit only four trolleys even though he has eight to deliver so he closes the door while he arranges the first four trolleys on the lift, and proceeds to deliver them.
• k) after 1 minute he returns to open the door and here, because TE=1 min<2 min=TP, he finds himself in the situation where the cryogenic fluid has not yet been reinjected into the space and the opening of the door is immediately authorized by the system allowing him to unload the remaining four trolleys before closing the door again.