Method of managing the operation of a refrigerated truck for transporting heat-sensitive products by modifying the refrigeration power

Abstract

A method for managing the operation of a refrigerated truck for transporting heat-sensitive products, of the indirect-injection type, in which the parameter T=.sub.Tair inletT.sub.setpoint(T.sub.air inlet: temperature of the air coming into contact with the heat exchanger internal to the truck as a result of the action of the fan, T.sub.setpoint: temperature to be set in the chamber inside the truck) is determined in real time and in which if T is greater than an upper setpoint value T.sub.setpoint H, a rapid-pressurization (RMP) circuit is activated to vaporize some cryogen and thus increase the pressure in the head of gas above the reserve of cryogen of the truck.

Claims

1. A method for managing the operation of a refrigerated truck for transporting heat-sensitive products, of the indirect injection type, where the truck includes at least one chamber for storing the products, a reserve of cryogenic fluid, a heat exchanger, a fan, at least one temperature sensor, the heat exchanger disposed inside said at least one chamber, cryogenic fluid flowing through said heat exchanger system, and a circuit for pressurization of said reserve, said circuit comprising a line with an upstream portion that is connected to a liquid phase of said cryogenic fluid stored in said reserve and a downstream portion that is connected to gas phase of said cryogenic fluid stored in said reserve, said line including a heater, a valve (EV Rp), and a backpressure regulator (Rp), said method comprising the steps of: using said fan to bring air inside said at least one chamber into contact with cold walls of said heat exchanger system, determining, with said at least one temperature sensor, a temperature (T.sub.iniet air) of air coming into contact with said cold walls on account of said use of said fan; regulating an internal temperature (T.sub.int) of said at least one chamber to a setpoint value (T.sub.setpoint) by: determining, in real time a value T equal to the difference between the temperature (T.sub.inlet air) of air coming into contact with said cold walls on account of said use of said fan and the setpoint value (T.sub.setpoint), and activating said pressurization circuit by opening said valve so as to vaporize some of the liquid phase of said cryogenic fluid inside said heater if T is greater than a top setpoint value (T.sub.setpoint H), the vaporization of said liquid phase causing an increase in a pressure of a gas phase in said reserve.

2. The management method of claim 1, wherein: the truck includes a gas line having an upstream portion connected to the gas phase of said reserve and a downstream portion connected to a liquid line that feeds a liquid phase of said cryogenic fluid to said heat exchanger system, said gas line including a gas valve (EV Gas CTI); and when T drops below a bottom setpoint value (T.sub.setpoint B), said rapid pressurization circuit is deactivated and said gas circuit is activated by opening said gas valve (EV Gas CTI) of said gas line so as to feed gaseous cryogen to said heat exchanger system and maintain said gaseous cryogen feed until the pressure in the vessel drops to a specified level is obtained in said reserve.

3. The management method of claim 1, wherein when T drops below a bottom setpoint value (T.sub.setpoint B), said rapid pressurization circuit is deactivated by closing said valve (EV Rp) of said pressurization circuit.

4. The management method of claim 1, wherein the cryogenic fluid is nitrogen.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1 shows the variation in refrigeration needs of a truck depending on its operating phases.

(2) FIG. 2 illustrates the schematic diagram of pressure regulation of the reservoir as is currently used in this field.

(3) FIG. 3 shows the variation in refrigeration power depending on the pressure in the reservoir.

(4) FIG. 4 provides the schematic diagram of an exemplary embodiment of the pressure regulation of the reservoir according to the invention.

(5) FIG. 5 shows the variation in pressure in the reservoir depending on the operating mode of the refrigeration system, i.e. on the need for refrigeration power.

DETAILED DESCRIPTION

(6) As will become more clearly apparent from the following text, the invention proposes modifying the operating conditions of the reservoir that are currently used, so as to allow it to operate at a variable pressure which adapts automatically to the refrigeration needs of the truck. To this end, the work carried out by the Applicant company has revealed that two modifications prove to be very particularly advantageous:

(7) 1lowering the nominal pressure in the on-board reservoir to a pressure of no more than 2 barg, and preferably to 1.5 barg for cryogenic units involving indirect injection and to 1 barg for cryogenic units involving direct injection. This first modification is easy to carry out, for example by modifying the calibration of a backpressure regulator to the desired value, said backpressure regulator being positioned correctly on a connected line.

(8) 2connecting a system for rapid pressurization of the reservoir, 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 coming from this reservoir, resulting in a greater refrigeration power.

(9) Since the need for power by the system 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.

(10) The appended FIG. 4 illustrates an embodiment of the invention.

(11) By default, the pressure in the reservoir is kept at what is known as nominal pressure, that is to say a low pressure, for example between 1.5 barg and 2 barg. This pressure is maintained by the backpressure regulator RL equipped on its upstream side with a normally open solenoid valve (EV RL).

(12) When the demand for pressure to be supplied is high (notably during the pull-down phase or after the opening of doors), the rapid pressurization circuit RMP is activated. The solenoid valve EV Rp opens and the solenoid valve EV RL closes. A quantity of cryogen is vaporized via the pressurization heater RMP, which has the effect of increasing the pressure in the gaseous atmosphere of the reservoir. The backpressure regulator Rp is regulated to remain open up to a pressure setting for example around 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.

(13) This pressurization circuit is activated for as long as the demand for power is high.

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

(15) At this stage, the pressure in the reservoir is at a peak, for example around 4 barg.

(16) Under these conditions, the need for power is low, it can then be advantageous to use the available sensible heat of the gas to partially provide the power to the cooling system, the circuit EV gas is then activated. The pressurized 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 obtained. This valve EV Gas CTI is then closed and the valve EV LIN CTI is opened.

(17) This manner of operation makes it possible to combine two functions and to increase the efficiency of the solution: 1The depressurization of the reservoir in the heat exchanger without loss of enthalpy, and without venting; 2The use of the sensible heat of the gas in the partial load phase.

(18) The automatic management of regulation is carried out by suitable method control that a person skilled in the art will understand here without the need for more details. The pressure thresholds are determined in order to optimize the need for refrigeration power to be supplied and to ensure the integrity of the reservoir and that the consumption of the system is optimized.

(19) 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:
T=T.sub.inlet airT.sub.setpoint (T.sub.inlet air: the temperature within the air coming into contact with the heat exchanger on account of the action of the ventilation) (T.sub.setpoint: desired temperature inside the product storage chamber)

(20) The full load mode is characterized by a high value of T, typically greater than 5K. In this mode, the pressure should be at its maximum level in order to deliver the maximum refrigeration power.

(21) When this difference T 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.

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

(23) FIG. 5 shows a schematic depiction of these three operating modes, the temperature difference and the associated pressure level.

(24) Depending on the pressure in the reservoir and the temperature difference measured in real time, the rapid pressurization system is then activated, or not, until the desired pressure is obtained as indicated 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.

(25) If, by contrast, the pressure in the reservoir is above that which is required, the reservoir is depressurized by using the saturated vapor in its gaseous atmosphere 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. This valve EV Gas CTI is then closed and the valve EV LIN CTI is opened again.

(26) Thus, by providing all the operational flexibility that is desired, as explained above, the system proposed by the present invention is easy to use compared with the system currently used in this field as illustrated in FIG. 2: it only requires the installation of two additional solenoid valves controlled by the same control system that is already present on existing installations. The cost incurred by this modification is raised very little compared with the savings in consumption that are obtained.

(27) The present invention thus relates to a method for managing the operation of a refrigerated truck for transporting heat-sensitive products, of the indirect injection type, where the truck is provided: with at least one chamber for storing the products, with a reserve of cryogenic fluid such as liquid nitrogen, with a heat exchanger system inside said at least one chamber, the cryogenic fluid flowing through said heat exchanger system, with an air circulation system, for example of the fan type, that is able to bring the air inside the chamber into contact with the cold walls of the heat exchanger system, with temperature sensors that are able to determine the temperature of the atmosphere inside said at least one chamber (T.sub.int) for the one part and that of the air coming into contact with the internal heat exchanger on account of the action of the ventilation (T.sub.inlet air), with a circuit for rapid pressurization (RMP) of said reserve, said circuit comprising a line that is connected in its upstream part to the liquid phase stored in said reserve and in its downstream part to the gas phase stored in said reserve, said line comprising a heat exchanger/heater (RMP), a valve (EV Rp) and a backpressure regulator (Rp); and also with a management and control unit which is able to regulate the internal temperature T.sub.int to a setpoint value T.sub.setpoint,

(28) characterized by the implementation of the following measures: the value T=T.sub.inlet airT.sub.setpoint is determined in real time; if T is greater than a top setpoint value T.sub.setpoint H, the rapid pressurization circuit RMP is activated by opening said valve of the pressurization circuit (EV Rp) so as to vaporize some of the cryogen in said heat exchanger/heater and thereby increase the pressure in the gaseous atmosphere in the reserve.

(29) According to one of the aspects of the invention, when T drops below a bottom setpoint value T.sub.setpoint B, the rapid pressurization circuit RMP is then deactivated by closing said valve of the pressurization circuit (EV Rp).

(30) According to another of the embodiments of the invention, provision is made of a gas circuit, said circuit comprising a gas line connected in its upstream part to the gas phase stored in said reserve and in its downstream part to a line that feeds said heat exchanger inside the chamber, said line comprising a gas valve (EV Gas CTI), and when T drops below a bottom setpoint value T.sub.setpoint B, the rapid pressurization circuit RMP is deactivated and the gas circuit is activated by opening said gas valve (EV Gas CTI) so as to feed gas to said heat exchanger inside the chamber, said gas feed being maintained until a low pressure level is obtained in said reserve.

(31) While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations as fall within the spirit and broad scope of the appended claims. The present invention may suitably comprise, consist or consist essentially of the elements disclosed and may be practiced in the absence of an element not disclosed. Furthermore, if there is language referring to order, such as first and second, it should be understood in an exemplary sense and not in a limiting sense. For example, it can be recognized by those skilled in the art that certain steps can be combined into a single step.

(32) The singular forms a, an and the include plural referents, unless the context clearly dictates otherwise.

(33) Comprising in a claim is an open transitional term which means the subsequently identified claim elements are a nonexclusive listing i.e. anything else may be additionally included and remain within the scope of comprising. Comprising is defined herein as necessarily encompassing the more limited transitional terms consisting essentially of and consisting of; comprising may therefore be replaced by consisting essentially of or consisting of and remain within the expressly defined scope of comprising.

(34) Providing in a claim is defined to mean furnishing, supplying, making available, or preparing something. The step may be performed by any actor in the absence of express language in the claim to the contrary.

(35) Optional or optionally means that the subsequently described event or circumstances may or may not occur. The description includes instances where the event or circumstance occurs and instances where it does not occur.

(36) Ranges may be expressed herein as from about one particular value, and/or to about another particular value. When such a range is expressed, it is to be understood that another embodiment is from the one particular value and/or to the other particular value, along with all combinations within said range.

(37) All references identified herein are each hereby incorporated by reference into this application in their entireties, as well as for the specific information for which each is cited.