EP0583692B1 - Gefriereinrichtung - Google Patents

Gefriereinrichtung Download PDF

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Publication number
EP0583692B1
EP0583692B1 EP19930112539 EP93112539A EP0583692B1 EP 0583692 B1 EP0583692 B1 EP 0583692B1 EP 19930112539 EP19930112539 EP 19930112539 EP 93112539 A EP93112539 A EP 93112539A EP 0583692 B1 EP0583692 B1 EP 0583692B1
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EP
European Patent Office
Prior art keywords
freezer
exhaust duct
vapour
tunnel
flow
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
EP19930112539
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English (en)
French (fr)
Other versions
EP0583692A1 (de
Inventor
Jeremy Paul Miller
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Air Products and Chemicals Inc
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Air Products and Chemicals Inc
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Filing date
Publication date
Application filed by Air Products and Chemicals Inc filed Critical Air Products and Chemicals Inc
Publication of EP0583692A1 publication Critical patent/EP0583692A1/de
Application granted granted Critical
Publication of EP0583692B1 publication Critical patent/EP0583692B1/de
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25D—REFRIGERATORS; COLD ROOMS; ICE-BOXES; COOLING OR FREEZING APPARATUS NOT OTHERWISE PROVIDED FOR
    • F25D3/00—Devices using other cold materials; Devices using cold-storage bodies
    • F25D3/10—Devices using other cold materials; Devices using cold-storage bodies using liquefied gases, e.g. liquid air
    • F25D3/11—Devices using other cold materials; Devices using cold-storage bodies using liquefied gases, e.g. liquid air with conveyors carrying articles to be cooled through the cooling space
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25D—REFRIGERATORS; COLD ROOMS; ICE-BOXES; COOLING OR FREEZING APPARATUS NOT OTHERWISE PROVIDED FOR
    • F25D29/00—Arrangement or mounting of control or safety devices
    • F25D29/001—Arrangement or mounting of control or safety devices for cryogenic fluid systems

Definitions

  • This invention relates to a freezer as defined in the preamble of claim 1.
  • a freezer is shown, for example, in US-A-4 276 753 or US-A-3 277 657.
  • liquid nitrogen which is at -196°C, rapidly cools the foodstuffs whilst substantially preserving their colour, flavour and appearance.
  • tunnel freezers are provided with an exhaust duct and an exhaust fan for sucking nitrogen out of the tunnel freezer and venting it into the atmosphere remote from the workplace.
  • the amount of gaseous nitrogen vented should exactly correspond to the amount of liquid nitrogen introduced into the tunnel freezer.
  • the exhaust fan is operated so that all the nitrogen resulting from the vaporization of the liquid nitrogen is vented together with a small volume of air which is inevitably drawn into the freezer.
  • Control of the exhaust fan is important to both the safety and the economics of the process. Under-extraction could result in an asphyxiating atmosphere whilst over-extraction will result in excess air being drawn into the tunnel freezer via the product inlet and outlet thereby increasing thermal load from the cooling of the air and depositing frost from the water vapour in the air within the freezer. In extreme conditions this frost can build up to prevent efficient operation of the freezer, necessitating a lengthy defrost before freezing can be resumed.
  • the present invention at least in its preferred embodiments, aims to overcome or at least reduce the problems associated with the prior art.
  • EP-A-0 159 858 is primarily concerned with determining the consumption of cryogenic fluid in a freezer.
  • the specification contains a reference to controlling the speed of the exhaust fan as a function of the concentration of oxygen in the exhaust duct. However, there is no indication as to how such a modification would be implemented in an overall control system.
  • said means responsive to said second signal to control the flow of vapour through said exhaust duct is arranged to vary at least one of:
  • said gas sensor is an oxygen sensor.
  • the present invention is applicable to all freezers which use a liquid cryogen for freezing it is particularly applicable to freezers in which the freezing section is a tunnel having a conveyor extending through openings at opposite ends thereof.
  • said freezing section comprises at least one circulation fan for blowing cryogenic fluid towards said exhaust duct, a second gas sensor for sensing the concentration of gas adjacent the opening remote from said exhaust duct, and means responsive to said second gas sensor to vary the output of said circulation fan.
  • said second gas sensor is disposed outside said freezing section.
  • FIG. 1 there is shown a conventional tunnel freezer which is generally identified by reference numeral 1.
  • the tunnel freezer 1 comprises a conveyor 2 which carries hamburgers 3 (or other items to be frozen) in the direction of arrow A.
  • Liquid nitrogen is introduced into the tunnel 4 through a spray bar via an inlet pipe 5 and heat transfer between the cold evaporating nitrogen and the hamburgers 3 is enhanced by scroll fans 6, 7 which suck the cold evaporating nitrogen (which tends to settle in the bottom of the tunnel 4) upwardly and blow it horizontally in counter-current flow to the hamburgers 3.
  • An exhaust fan 8 withdraws nitrogen vapour from the tunnel 4 and exhausts it through the roof of the factory via an exhaust duct 9.
  • the flow through the exhaust duct 9 is important. If it is too low then nitrogen will escape through the openings 10, 11 at either end of the tunnel 4. A build-up of nitrogen in this area could result in asphyxiation of staff and is thus unacceptable. On the other hand, if the flow through the exhaust duct 9 is too high nitrogen will be wasted and, more importantly, air will enter the tunnel 4 through the openings 10, 11. The moisture in this air will condense and freeze in the tunnel 4 and will continue to build up on the inside of the tunnel 4 and scroll fans 6 and 7 and exhaust fan 8 progressively impairing the efficiency of the tunnel 4.
  • a first temperature sensor 101 is located in the tunnel 4 and a second temperature sensor 102 is located in the exhaust duct 9.
  • the signals from the two temperature sensors 101, 102 are compared in a control unit 103 and a signal 104 is generated which is a function of the difference between the temperatures at the two temperature sensors 101, 102.
  • This signal 104 is then used to control the speed of the exhaust fan 8 in the exhaust duct 9.
  • the object of the control system is to ensure that the difference in temperature between the two temperature sensors 101, 102 is maintained at a constant, predetermined level.
  • the underlying principle behind this control system is that in order to ensure that nitrogen does not escape into the workplace the exhaust fan 8 is operated so that there is a small steady flow of air 105 into the tunnel 4 through the opening 11.
  • the air 105 mixes with nitrogen vapour 106 and the mixture passes up the exhaust duct 9 where the temperature of the mixture is sensed by second temperature sensor 102.
  • the temperature at the temperature sensor 101 is kept substantially constant by varying the supply of liquid nitrogen through inlet pipe 5 to the spray bar through control valve 108 in accordance with the temperature sensed at temperature sensor 101. Accordingly, the difference in temperature between the temperature sensors 102 and 101 is considered a measure of the proportion of air passing through the opening 11.
  • the disadvantages of this arrangement are that the two temperature sensors 101, 102 (and particularly the temperature sensor 102) are sensitive to ice build-up.
  • a hot product for example a hot hamburger 104 enters the tunnel 4 through opening 11 it heats the local atmosphere which is sucked up through exhaust duct 9 raising the temperature at temperature sensor 102.
  • the control system interprets this influx of heat as indicating a high proportion of air and reacts by reducing the speed of the exhaust fan 8 in an attempt to lower the temperature at temperature sensor 102 and thus restore the preset temperature differential. It can clearly be seen that this response may result in excess nitrogen passing through openings 10, 11 into the area surrounding the tunnel freezer 1. It should perhaps be emphasised that whilst the signal 104 could easily be compensated for a steady supply of hot items problems arise because the supply of product is rarely steady and, in practice, excess nitrogen is vented through exhaust duct 9.
  • the temperature at a temperature sensor 201 is measured and a signal transmitter to a control unit 203.
  • a signal 207 is then sent to the control valve 208 to open or close the control valve 208 with a view to maintaining the temperature at the temperature sensor 201 substantially constant.
  • a signal 209 is sent to exhaust fan 8 to vary the speed of the exhaust fan 8 as a function of the liquid nitrogen entering the tunnel freezer 1.
  • control unit 203 also regulates the speed of scroll fans 6 and 7 to blow the nitrogen from the spray bar towards the exhaust duct 9.
  • an oxygen sensor is disposed in the exhaust duct 9 upstream of the exhaust fan 8.
  • the signal from oxygen sensor 310 is transmitted to control unit 313 which generates a signal 311 which controls the exhaust fan 8 so that the concentration of oxygen at the oxygen sensor 310 is at a constant predetermined level.
  • the flow of liquid nitrogen to the tunnel freezer 1 is controlled in response to the temperature sensed by temperature sensor 301.
  • the temperature sensor 301 generates a signal representative of the temperature at the temperature sensor 301.
  • the signal is then sent to a control unit 303 which opens and closes control valve 308 with the aim of maintaining the temperature at temperature sensor 301 constant at a predetermined level.
  • the tunnel freezer 1 is in equilibrium with a steady stream of liquid nitrogen being dispensed from the spray bar to maintain a steady temperature at temperature sensor 301.
  • the exhaust fan 8 is operating at a steady speed and a small amount of air is being drawn in through opening 11 so that the concentration of oxygen at the oxygen sensor 310 is about 10.5% (by volume).
  • Control unit 303 opens valve 308 to admit more liquid nitrogen through the inlet pipe 5 to the spray bar. As the liquid nitrogen vaporizes it expands and has the effect of inhibiting the flow of air into the tunnel 4 through the opening 11. This causes the concentration of oxygen detected by oxygen sensor 310 to fall and control unit 313 to generate a signal 311 to increase the speed of exhaust fan 8 until sufficient air is sucked through opening 11 to return the concentration of oxygen at oxygen sensor 310 to its desired level.
  • control unit 303 If the heat load decreases the signal from temperature sensor 301 causes control unit 303 to close control valve 308. As the flow of liquid nitrogen through spray bar 5 decreases the volume of nitrogen travelling along the tunnel 4 decreases. As a consequence more air is sucked in through opening 11 and the concentration of oxygen at oxygen sensor 310 rises. The signal from oxygen sensor 310 is processed by control unit 313 which lowers the speed of the exhaust fan 8 until the oxygen concentration at oxygen sensor 310 returns to its desired level.
  • a second oxygen sensor 410 is disposed between the opening 10 and the spray bar.
  • the oxygen sensor 410 transmits a signal to a control unit 411 which controls the speed of scroll fans 6 and 7 to maintain the concentration of oxygen at the oxygen sensor 410 substantially constant.
  • the speed of the exhaust fan 8 is varied to control the flow through the exhaust duct 9 various alternatives are available, for example the pitch of the blades of the fan could be varied. Alternatively, the speed of the exhaust fan 8 could be kept constant and the effective diameter of the exhaust duct varied by, for example varying the setting of a butterfly valve or a variable shutter in the exhaust duct 9.

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Physics & Mathematics (AREA)
  • Mechanical Engineering (AREA)
  • Thermal Sciences (AREA)
  • General Engineering & Computer Science (AREA)

Claims (6)

  1. Gefriervorrichtung, mit einem Gefrierabschnitt (4), einem Einlaß (5) für die Zufuhr von Tiefsttemperaturfluid zum Gefrierabschnitt (4), einem Abgasrohr (9) für den Transport von Dampf vom Gefrierabschnitt (4), einem Abgasgebläse (8) für die Abführung von Dampf vom Gefrierabschnitt (4) durch das Abgasrohr (9) und einem Steuersystem für die Steuerung der Strömung des Tiefsttemperaturfluids durch den Einlaß (5) und der Strömung des Dampfes durch das Abgasrohr (9), wobei das Steuersystem enthält:
    (a) einen Temperatursensor (301), der ein erstes Signal erzeugt, das die Temperatur im Gefrierabschnitt (4) angibt
    (b) ein Mittel (308), das auf das erste Signal anspricht und die Strömung des Tiefsttemperaturfluids durch den Einlaß (5) steuert;
    wobei die Gefriervorrichtung gekennzeichnet ist durch
    (c) einen Gassensor (310), der ein zweites Signal erzeugt, das die Gaskonzentration im Abgasrohr (9) angibt und
    (d) ein Steuermittel, das auf das zweite Signal anspricht und die Strömung des Dampfes durch das Abgasrohr (9) steuert;
    wobei die Anordnung von der Art ist, daß im Gebrauch das Volumen des dem Gefrierabschnitt (4) zugeführten Tiefsttemperaturfluids durch den Temperatursensor (301) bestimmt wird und das Volumen des vom Gefrierabschnitt (4) abgeführten Dampfes durch den Gassensor (310) gesteuert wird, um so eine zu geringe Abführung, die eine erstikkende Atmosphäre im Arbeitsbereich um die Gefriervorrichtung zur Folge haben könnte, sowie eine zu große Abführung zu verhindern, die zur Folge haben könnte, daß überschüssige Luft in die Gefriervorrichtung eingesaugt wird und in der Gefriervorrichtung von dem in der Luft vorhandenen Wasserdampf Frost abgelagert wird.
  2. Gefriervorrichtung nach Anspruch 1, dadurch gekennzeichnet, daß die Steuermittel, die auf das zweite Signal ansprechen, um die Strömung des Dampfes durch das Abgasrohr (9) zu steuern, so beschaffen sind, daß sie wenigstens einen der drei folgenden Parameter verändern:
    (a) die Drehzahl des Abgasgebläses (8);
    (b) die Neigung der Schaufeln des Abgasgebläses (8); und
    (c) den Verschluß eines Elements, das die Strömung durch das Abgasrohr (9) sperrt.
  3. Gefriervorrichtung nach Anspruch 1 oder 2, dadurch gekennzeichnet, daß der Gassensor (310) ein Sauerstoffsensor ist.
  4. Gefriervorrichtung nach Anspruch 1 oder 2, dadurch gekennzeichnet, daß der Gefrierabschnitt ein Tunnel (4) ist, der eine Fördereinrichtung enthält, die durch an dessen gegenüberliegenden Enden befindliche Öffnungen (10, 11) verläuft.
  5. Gefriervorrichtung nach Anspruch 4, dadurch gekennzeichnet, daß der Tunnel (4) wenigstens ein Umwälzgebläse (6, 7), das Tiefsttemperaturfluid zum Abgasrohr (9) bläst, einen zweiten Gassensor (410), der die Gaskonzentration in der Nähe der vom Abgasrohr (9) entfernten Öffnung (10) erfaßt, sowie Mittel enthält, die auf den zweiten Gassensor (410) ansprechen, um den Ausgang des Umwälzgebläses (6, 7) zu verändern.
  6. Gefriervorrichtung nach Anspruch 5, dadurch gekennzeichnet, daß der zweite Gassensor (410) außerhalb des Tunnels (4) angeordnet ist.
EP19930112539 1992-08-13 1993-08-05 Gefriereinrichtung Expired - Lifetime EP0583692B1 (de)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB9217189 1992-08-13
GB929217189A GB9217189D0 (en) 1992-08-13 1992-08-13 Control system for freezer

Publications (2)

Publication Number Publication Date
EP0583692A1 EP0583692A1 (de) 1994-02-23
EP0583692B1 true EP0583692B1 (de) 1995-10-18

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EP19930112539 Expired - Lifetime EP0583692B1 (de) 1992-08-13 1993-08-05 Gefriereinrichtung

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EP (1) EP0583692B1 (de)
DE (1) DE69300669T2 (de)
GB (1) GB9217189D0 (de)

Families Citing this family (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
BE1009212A6 (nl) * 1995-03-16 1996-12-03 Oxhydrique Internationale L Werkwijze en inrichting voor het controleren van de temperatuur van een poeder- en/of korrelvormige grondstof.
FR2765674B1 (fr) * 1997-07-03 1999-08-06 Air Liquide Procede de commande du regime d'extraction d'un extracteur de gaz d'une enceinte d'un appareil cryogenique et appareil pour sa mise en oeuvre
FR2808584B1 (fr) * 2000-05-03 2002-08-30 Carboxyque Francaise Procede et dispositif de controle et de commande d'injection de fluide regrigerant dans une enceinte de malaxage
FR2959139B1 (fr) * 2010-04-27 2013-06-07 Air Liquide Procede de regulation du fonctionnement d'enceintes de type malaxeurs ou broyeurs
CN115218578A (zh) * 2022-07-25 2022-10-21 浙江铭元食品科技有限公司 用于食品生产的穿梭渐进式液氮速冻系统

Family Cites Families (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3277657A (en) * 1965-09-15 1966-10-11 Integral Process Syst Inc Method and apparatus for flash freezing various products
US3728869A (en) * 1971-12-27 1973-04-24 H Schmidt Coolant system for heat removal apparatus
US3892104A (en) * 1973-09-20 1975-07-01 David J Klee Cryogenic freezer with variable speed gas control system
US4142376A (en) * 1977-11-02 1979-03-06 Formax, Inc. Control for cryogenic freezing tunnel
US4276753A (en) * 1980-05-19 1981-07-07 Formax, Inc. Cryogenic freezing tunnel control system
US4627244A (en) * 1984-04-13 1986-12-09 Willhoft Edward Max Adolf Cryogenic cooling
US4800728A (en) * 1987-09-18 1989-01-31 Air Products And Chemicals, Inc. Method and apparatus for gas flow control in a cryogenic freezer
US4955206A (en) * 1989-11-30 1990-09-11 Liquid Carbonic Corporation Liquid cryogen freezer with improved vapor balance control

Also Published As

Publication number Publication date
DE69300669T2 (de) 1996-03-21
DE69300669D1 (de) 1995-11-23
EP0583692A1 (de) 1994-02-23
GB9217189D0 (en) 1992-09-23

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