DK3046788T3 - Fremgangsmåde til styring af driften af en kølebil til transport af varmesensitive produkter ved at modificere køleeffekten - Google Patents

Description

METHOD OF MANAGING THE OPERATION OF A REFRIGERATED TRUCK FOR TRANSPORTING HEAT-SENSITIVE PRODUCTS BY MODIFYING THE REFRIGERATION POWER

This invention relates to the field of the transport and distribution of heat-sensitive products, such as pharmaceutical products and foods, and more particularly relates to technologies where the cold required to maintain the temperature of the products is supplied by a cryogenic unit that operates in an open loop and implementing: - a direct injection of a cryogenic fluid into the transport case (very often liquid nitrogen); or - a so-called "indirect" injection of a cryogenic fluid into the transport case (very often liquid nitrogen), said "indirect" technique often being referred to as "CTI" and employing one or more heat exchangers in the internal enclosure in which the products are transported (also known as a "chamber", "box", or isothermal "case", etc.), the cryogenic fluid (such as liquid nitrogen or liquid C02) flowing within said heat exchanger, the enclosure furthermore being provided with an airflow system (fans) that brings this air into contact with the cold walls of the heat exchanger, thereby making it possible to cool the air inside the cold chamber of the truck, the cryogenic fluid that supplies the one or more heat exchangers originating from a cryogen reservoir that is conventionally situated under the truck (the reservoir itself being supplied, when necessary, by an upstream reservoir that is fixed or movable but in any case not attached to the vehicle). A method of managing a refrigerated truck of a known type is disclosed in the document EP 0 599 610.

The term "reservoir" used herein below is understood to denote the on-board cryogen reservoir, unless a precision such as "upstream" or "fixed" is made to denote a different reservoir.

The atmospheres maintained inside the cold chamber can be provided both for fresh produce (typically a temperature of around 4 °C) and for frozen foods (typically a temperature of around -20 °C).

This invention more particularly relates to cryogenic solutions involving indirect injection, however the solutions proposed can be applied very advantageously to cryogenic units involving the direction injection of nitrogen, CO2 or any other cryogen.

In the case of indirect injections, the heat extracted from the air firstly allows for the complete evaporation of the cryogenic fluid flowing within the heat exchanger, then a rise in the temperature thereof until it reaches a temperature close to that of the enclosure. The cryogenic fluid is then discharged to the outside after having transferred a maximum quantity of cooling energy.

The following method control process is the most common typically implemented in such trucks that operate with direct or indirect injection: 1- when starting up the refrigeration system of the truck (for example when beginning a round or after an extended shutdown period of the refrigeration system for any reason) or after opening a door, a rapid temperature-drop mode is adopted (this is known as the "pull-down" phase in this industry). 2- Once the setpoint temperature has been reached in the product storage chamber, a control/regulation mode is adopted, making it possible to maintain the temperature in the product storage chamber at the setpoint value ("holding" phase).

However, the refrigeration needs in each of these two phases, in terms of the refrigeration power required, are extremely different.

More specifically, during the "pull-down" phase, there is often a need for the temperature of the air in the chamber to drop rapidly. In order to obtain this effect, a high refrigeration power must be provided, capable of overcoming the thermal inertia of the entire system (air, cryogenic unit, truck walls) and the heat intake through the truck walls and when opening the truck doors. These refrigeration needs drop dramatically in the holding phase, given that only the heat intake through the walls remains.

In other words, the refrigeration needs of a truck during a given round fluctuate between two levels that can be referred to as "full load" and "partial load", as clearly shown in the accompanying Fig. 1.

Although the refrigeration power during the holding phase must reach a required minimum level, that corresponding to the full load phase remains at the discretion of the refrigeration system designer within the limits laid down by the standards applied in this field (ATP, DIN, etc.) that recommend a power of the installed refrigeration unit that is at least equal to 1.75 times the power at partial load, this power mainly being dictated by the heat input through the walls (KSAT). It stands to reason that the greater the full load power, the more a drop and rapid return of the air temperature inside the chamber to the setpoint temperature can be ensured.

Existing cryogenic systems operate for example with "nominal" pressure in the reservoir at a virtually fixed level of around 3.2 barg. Operational modularity is currently most frequently obtained through regulation of the valves for injecting liquid in the all or nothing ("AON") mode or in the proportional mode.

The accompanying Fig. 2 shows the schematic diagram for a pressure regulation operation on the reservoir as commonly carried out today in this field.

It shows what one of ordinary skill in the art is familiar with: the line EV LIN CTI for supplying liquid from the one or more internal heat exchanger(s) to the chamber of the truck, and a so-called "RMP" ("rapid pressurisation") line for repressurising the ullage space of the reservoir.

This operation has several drawbacks: 1- If the pressure level is lower than the required level when filling the reservoir (which often occurs in practice), the power that the cryogenic unit is supposed to produce decreases rapidly. This results in a fairly long "pull-down" time and overconsumption that is detrimental to the economic performance of the system. The accompanying Fig. 3 shows these phenomena and gives experimental results that show this power variation as a product of the pressure variation within the reservoir; 2- Due to the fact that operation takes place at a fixed reservoir pressure, the level of modularity (the difference between the full load power and partial load power) remains limited with overconsumption of the cryogen as a result of the effects of thermal inertia in the system. In other words, it is very difficult to achieve a "boost" mode in which a very high refrigeration power is sought; 3- The nominal pressure of the reservoir as is conventionally used today (for example 3.2 barg) extends the filling time from the upstream large fixed reserve (source), which is generally kept at about 4 barg. This results in a loss of cryogen during filling in gas form (gas flash), as the difference in pressure between the fixed and movable reservoirs remains low, resulting in a long filling time (typically from 10 to 15 min).

This invention therefore proposes modifying the configuration of the reservoir of the truck, and in particular what is conventionally referred in the gas trade as the "valve box" thereof, so as to provide greater modularity in terms of the refrigeration power of the cryogenic units while optimising the cryogen consumption thereof.

As will become more clearly apparent from the following text, the invention proposes to modify the operating conditions of the reservoir that are currently in practice, so as to allow it to operate at a variable pressure which automatically adapts to suit the refrigeration needs of the truck. To this end, the works carried out by the Applicant have revealed that two modifications prove to be very particularly advantageous: 1- lowering the "nominal" pressure of the on-board reservoir to a pressure not exceeding 2 barg, and preferably to a pressure of 1.5 barg for cryogenic units involving indirect injection and 1 barg for cryogenic units involving direct injection. This first modification is easy to carry out, for example by modifying the calibration of a regulator to the desired value, said regulator being positioned correctly on a connected line. 2-connecting a rapid reservoir pressurisation system, which is activated when required, making it possible to increase the pressure in the reservoir when required by the procedure, and thus to ensure a higher flow rate of cryogen originating from said reservoir, resulting in a greater refrigeration power.

Given that the system's need for power is variable and directly linked to the operating phase (full load or partial load), the device proposed should allow variable use of the cryogen pressure in the reservoir in an optimal manner.

The appended Fig. 4 shows one embodiment of the invention.

By default, the pressure in the reservoir is kept at a so-called nominal pressure, that is to say at a low pressure, for example between 1.5 barg and 2 barg. This pressure is maintained by the regulator RL, the upstream side of which is equipped with a normally open solenoid valve (EV RL).

When the demand for power to be supplied is high (in particular during the "pull-down" phase or after opening the doors), the rapid pressurisation circuit RMP is activated. The solenoid valve EV Rp opens and the solenoid valve EV RL closes. A quantity of cryogen is vaporised via the pressurisation heater RMP, which increases the pressure in the ullage space of the reservoir. The upstream pressure regulator (regulator) Rp is configured so as to remain open up to a pressure setting, for example of about 4 barg. The circuit RMP is designed to ensure an increase in pressure in the reservoir over a time compatible with the "pull-down" time of the chamber to be cooled.

This pressurisation circuit is activated for as long as the demand for power is high.

When the demand for power decreases, i.e. either in the final "pull down" phase or in the "partial load" (holding) phase, the circuit RMP is deactivated.

At this stage, the pressure in the reservoir is at its peak, for example at about 4 barg.

Under such conditions, the need for power is low; in this case, it can be advantageous to use the available sensible heat of the gas to partially provide power to the cooling system, whereby the gas circuit EV is thus activated. The pressurised gas is injected into the heat exchanger: EV Rp is closed, EV LIN CTI is closed and EV Gas CTI is opened until the low-pressure level is reached. Said valve EV Gas CTI is then closed and the valve EV LIN CTI is opened.

This operating mode makes it possible to combine two functions and increase the efficiency of the solution: 1- The depressurisation of the reservoir in the heat exchanger without loss of enthalpy, and without venting; 2- The use of the sensible heat of the gas in the partial load phase.

The regulation process is automatically managed by a suitable method control process that one of ordinary skill in the art will understand here without the need for more details. The pressure thresholds are determined in order to optimise the need for refrigeration power to be supplied and to ensure the integrity of the reservoir and optimisation of the consumption level of the system.

To this end, the temperature for example will be used as an indicator of the operating phase. More specifically, the temperature difference between the air intake temperature (at the inlet of the heat exchanger CTI) and the desired setpoint temperature will be monitored for example continuously: ΔΤ = Tair inlet" Tsetpoint (Tair inlet being the internal temperature of the air coming into contact with the heat exchanger as a result of the action of the fan); (Tsetpoint being the desired internal temperature of the chamber for storing products).

The full load mode is characterised by a high ΔΤ value, typically greater than 5K. In this mode, the pressure must be at its maximum level in order to provide the maximum refrigeration power.

When this difference ΔΤ is, for example, strictly less than 2K, the system is considered to be in partial load operation. In this mode, the pressure can be at its minimum level, i.e. a minimum flow rate of liquid cryogen and a minimum refrigeration power.

Between the two temperature difference levels, the system is considered to be in transition from one mode to another, whereby the pressure can also be at an intermediate level between the two high and low-pressure levels.

Fig. 5 shows a diagrammatic view of these three operating modes, the temperature difference and the pressure level associated thereto.

Depending on the pressure of the reservoir and the temperature difference measured in real time, the rapid pressurisation system is then either activated or not, until the desired pressure is obtained, as shown in Fig. 3: in accordance with the diagram in Fig. 4, the solenoid valve EV Rp is open and the solenoid valve EV RL is closed.

If, by contrast, the pressure in the reservoir is above that which is required, the reservoir is depressurised while using the saturated vapour in its ullage space to feed the heat exchangers CTI: in accordance with the diagram in Fig. 4, EV Rp is closed and EV Gas CTI is opened until the low-pressure level required is obtained. Said valve EV Gas CTI is then closed and the valve EV LIN CTI is re-opened.

Therefore, by providing the operational flexibility desired, as explained hereinabove, the system proposed by this invention is easy to use in relation to the system currently used in this field as shown in Fig. 2: it only requires the installation of two additional solenoid valves controlled by the same control system already present on the existing systems. The cost incurred by this modification is not very high when compared to the consumption-related savings produced.

The paragraphs hereinabove make reference to the following accompanying figures: - Fig. 1 shows the variation in refrigeration needs of a truck according to the operating phases thereof. - Fig. 2 shows the schematic diagram of a pressure regulation of the reservoir as is routinely used today in this field. - Fig. 3 shows the variation in refrigeration power according to the pressure in the reservoir. - Fig. 4 provides the schematic diagram of one example embodiment of the pressure regulation of the reservoir according to the invention. - Fig. 5 shows the variation in pressure in the reservoir according to the operating mode of the refrigeration system, i.e. according to the need for refrigeration power.

This invention therefore relates to a method of managing the operation of a refrigerated truck for transporting heat-sensitive products, of the indirect-injection type, in which the truck is provided with: - at least one chamber for storing the products, - a reserve of a cryogenic fluid, such as liquid nitrogen, - a heat exchanger system inside said at least one chamber, in which the cryogenic fluid flows, - an airflow system, such as fans, capable of bringing the air inside the chamber into contact with the cold walls of the heat exchanger system, - temperature sensors capable of determining the temperature of the atmosphere inside said at least one chamber (Tint) on the one hand, and that of the air coming into contact with the internal heat exchanger as a result of the action of the fan (Tair inlet). - a rapid pressurisation circuit (RMP) of said reserve, said circuit comprising a line having an upstream portion connected to the liquid phase stored in said reserve and a downstream portion connected to the gas phase stored in said reserve, said line successively comprising an exchanger/heater (RMP), a valve (EV Rp) and a regulator (Rp); - in addition to a management and control unit capable of regulating the internal temperature Tint to a setpoint value Tsetpoint, characterised by the implementation of the following measures: -- the magnitude ΔΤ = Tair inlet - Tsetpoint is determined in real time; - if ΔΤ is greater than an upper setpoint value ΔΤυ setpoint, the rapid pressurisation circuit RMP is activated by opening said pressurisation circuit valve (EV Rp) so as to vaporise cryogen inside said exchanger/heater and thus increase the pressure in the ullage space of the reserve.

According to one aspect of the invention, when ΔΤ falls below a lower setpoint value ATL setpoint, the rapid pressurisation circuit RMP is deactivated by closing said valve of the pressurisation circuit (EV Rp).

According to another embodiment of the invention, a gas circuit is provided, said circuit comprising a gas line having an upstream portion connected to the gas phase stored in said reserve and a downstream portion connected to a line supplying said heat exchanger inside the chamber, said line comprising a gas valve (EV Gas CTI), and when ΔΤ falls below a lower setpoint value ATL setpoint, the rapid pressurisation circuit RMP is deactivated and the gas circuit is activated, by opening said gas valve (EV Gas CTI) so as to supply gas to said heat exchanger inside the chamber, said gas supply being maintained until a low pressure level is obtained within said reserve.

Claims (3)

1. Fremgangsmåde til styring afdriften afen kølebil til transport af varmesensitive produkter, af indirekte-indsprøjtning-typen, hvor bilen er forsynet med: - mindst et rum til lagring af produkterne, - en reservebeholdning afen kryogenfluid, såsom flydende nitrogen, - et varmevekslersystem inden i det mindst ene rum, i hvilket kryogenfluiden strømmer, - et luftstrømsystem, såsom blæsere, i stand til at bringe luften inden i rummet i kontakt med de kolde vægge af varmevekslersystemet, - temperatursensorer i stand til at bestemme temperaturen dels af atmosfæren inden i det mindst ene rum (Tint), og dels af luften, der kommer i kontakt med den indre varmeveksler som et resultat af virkningen af blæseren (Tiuftindiøb), - et kredsløb (RMP) til hurtig tryksætning af reservebeholdningen, hvilket kredsløb omfatter en ledning med en opstrøms del forbundet til væskefasen lagret i reservebeholdningen og en nedstrøms del forbundet til gasfasen lagret i reservebeholdningen, hvilken ledning successivt omfatter en veksler/varmer (RMP), en ventil (EV Rp) og en regulator (Rp); - endvidere en håndterings- og styringsenhed i stand til at regulere den indre temperatur Tint til en referenceværdi Treferenceværdi, kendetegnet ved implementeringen af de følgende forhold: - størrelsen ΔΤ = Tiuftindiøb — Treferenceværdi bestemmes i realtidj - hvis ΔΤ er større end en øvre referenceværdi ΔΤ0 referenceværdi, aktiveres styringskredsløbet RMP til hurtig tryksætning ved at åbne trykkredsventilen (EV Rp) til at fordampe kryogen inden i veksleren/varmeren og derved øge trykket i gasvolumenet af reservebeholdningen.

2. Fremgangsmåde ifølge krav 1, kendetegnet ved at den har et gaskredsløb, hvilket kredsløb omfatter en gasledning, der har en opstrøms del forbundet til gasfasen lagret i reservebeholdningen og en nedstrøms del forbundet til en ledning, der forsyner varmeveksleren inden i kammeret, hvilken ledning omfatter en gasventil (EV Gas CTI), og ved at når ΔΤ falder under en nedre referenceværdi ΔΤν referenceværdi, deaktiveres styringskredsløbet RMP til hurtig tryksætning, og gaskredsløbet aktiveres ved at åbne gasventilen (EV Gas CTI) for at forsyne gas til varmeveksleren inden i kammeret, hvor gasforsyningen vedligeholdes, indtil et lavt trykniveau opnås i reservebeholdningen.

3. Fremgangsmåde ifølge krav 1, kendetegnet ved at når ΔΤ falder under en nedre referenceværdi ΔΤν referenceværdi, deaktiveres styringskredsløbet RMP til hurtig tryksætning ved at lukke ventilen aftrykkredsløbet (EV Rp).