JPS60233476A - Improvement in cryogenic cooling - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides low temperature cooling (cryogenic cool%
g), particularly a device for use in low-temperature cooling, and a method for carrying out low-temperature cooling.

Many ingredients are frozen (fre) to preserve them.
eze) or chill. Such materials include foodstuffs (processed or raw), pharmaceuticals,
Blood and its components and biological specimens (bio-1ogi)
cal specimen). Most such materials are frozen or refrigerated using blast freezers. However, mechanical blast refrigeration often results in product damage. Such damage is of two types: freezer burn.
rn) and drip losses that occur once the frozen product is thawed (thaw out) for direct consumption or cooking.

Freezer burn is caused by forced turbulence associated with blast freezing.
turbulence). Dripping loss occurs when the product reaches freezing temperature (freezi).
ngtemperature). The faster the temperature decreases, the less chance of cell damage due to osmotic effects and minimization of ice crystal size.

Freezing agents such as liquid nitrogen and carbon dioxide (cryo-ge)
ns) using cryogenic freezing (crygenic f
It is generally accepted that the original product quality is better preserved by relying on re-ezing.

An important characteristic of cryogenic refrigeration is the rate at which temperature reduction can be achieved without a high degree of turbulence.

During cryogenic freezing, the liquid refrigerant is generally transported on a conveyor belt, typically 5 to 25 meters long and 0.75
~2 meter wide “inline 1 tunnel” (“inl”)
The material moving through the ine “tunnel”
It is sprayed just before it emerges from the tunnel for filling and storage in cold storage. Liquid refrigerant supply + (ttrbpply rαte
) is usually a cryogenic tunnel A/ (cryogenic t
thermal requirements as determined by the temperature within the tunnel. The vapor or gas originating from the liquid refrigerant is relatively gently turbulent to blast refrigeration.
The maximum amount of "Cold" is extracted from the liquid refrigerant by passing it in countercurrent flow over the material passing through a cold tunnel (e.g., U.S. Pat. No. 3,871,186, 414).
2376 and 4278753). The countercurrent flow of gas or vapor precools the material before it is contacted with the liquid refrigerant. This avoids damage to the material to be cooled if it is susceptible to the effects of excessive temperature gradients which could cause it to crack and fracture. This as well as the use of countercurrent heat transfer maximizes the efficiency of the cooling effect achieved by using liquid refrigerant. When liquid nitrogen is used as a freezing agent, about 50% of the "cold food" comes from the latent heat of vaporization during the transition from the liquid phase to the gas phase. During the period of countercurrent gas movement through the cold tunnel there is a sharp heat
le heat ) will be available. In the case of carbon dioxide refrigerant, 90% of the cold food comes from latent heat. The carbon dioxide cryogen was stored at a pressure above the critical point and at a temperature close to 0°C (typically in a vacuum-lined cylinder at about -196° at pressures as low as 1 to 10 atm).
vat, rubum-ined cylinder)
Although it starts out as a liquid (unlike the liquid nitrogen stored in it), it solidifies as soon as it is blown out of the sparger into the cold tunnel. Obtained snow (sn
ow) cools the product mostly by conduction at a temperature of about -78°C. For the reason mentioned above, low-temperature tunnels that use carbon dioxide as a refrigerant require countercurrent quenching (counter-current quenching).
(current chilling) is not required.

To improve the thermal efficiency of the tunnel, liquid refrigerant that does not evaporate when in contact with the material to be cooled can be collected from below the conveyor and optionally put to full use in cooling the material. more dense than steam or gas (
It can be recycled along with the cooler steam or gas that has not released its weight, which tends to settle at the lower heights of the tunnel below the denser) conveyor.

The effluent gas (e
It is important for safety reasons to guide the ffluent gasea) out of the tunnel and into the outside atmosphere, ie outside the factory environment. If this were not done, the oxygen content in the factory environment would decrease and
Including anoxia (anoxia). There will be possible adverse consequences for the people in the factory. Conventionally, it has been common practice not to monitor outflow gas.

The performance of a cryotunnel can be expressed by the liquid refrigerant used to product weight ratio. In most preferred cases, the ratio depends on the product and is strongly influenced by the water content, but can be as low as 0.7:1. In other words, for this ratio, 0.7 kg of liquid nitrogen is required to freeze 1 kg of product. In refrigeration operations, the consumption of liquid refrigerant primarily determines the cost of freezing or refrigeration and, during the performance period, the ratio of liquid refrigerant used to product should be kept as low as possible, consistent with optimal refrigeration from the point of view of quality and temperature. It is desirable to have information available that allows it to be kept small.

In general principle, it is possible to monitor the consumption of liquid refrigerant gravimetrically by placing a load cell under the storage tank for the liquid refrigerant. However, the considerable weight of the tank and its contents makes it difficult to obtain accurate consumption quantities for less than one day's production, and this limits the production time with a view to controlling the performance of the cryotunnel. Relaxation for making medium-continuous information available (Mittga-TG). Again, in general principle it is possible to monitor the consumption of liquid refrigerant by monitoring the rate of flow of the refrigerant, but in practice this is very difficult. This is because it requires measuring the flow rate of a very cold liquid at its boiling point. In other words, accurate measurements are
Requires phase separation, which is difficult to achieve for rapidly boiling liquids. Consumption of liquid refrigerant under operating conditions J
Another method for determining the rate of consumption is to determine the absolute gas flow rate (5 pent gas) of spent gas (5 pent gas) piped into the outside environment.
The aim was to focus all efforts on measuring the absolute gas flow. This method can be suitable if snow or frost formation does not occur in the discharge duct due to the high efficiency of the tunnel (the higher the spent gas temperature, the better the performance of the tunnel. (This is because clearly more "cold food" was delivered to the product being cooled by the liquid refrigerant.)
. Another problem with this method is dilution of the spent refrigerant by atmospheric air entering the tunnel with the product.

The present invention provides the basis for a totally computer-controlled method of cooling, for example by freezing or refrigeration.
io? The purpose is to monitor L). According to the invention, the consumption rate of gas originating from the liquid refrigerant is determined, thereby determining the rate of production of the frozen product.
If the production) is known [this can be done by a gravimetric method as described above, for example a weight "in-line check" (1n-1ine checklDeig).
By placing a weight-sensitive conveyor just before entering the tunnel, as is often done in
or by measuring the weight of the frozen product immediately after it leaves the tunnel], the consumed liquid refrigerant/product weight ratio can be easily calculated from the process data. I can do it. The information can be fed to a microprocessor or an in-line computer, the former ultimately setting up the control loop for automatic operation, and the latter for remote monitoring as desired or necessary.

According to the invention, the material to be cooled is introduced into an elongated cold tunnel housing by means for conveying the material from the inlet end to the outlet end, and a liquid refrigerant, preferably liquid nitrogen, is introduced into the elongated cold tunnel housing. spraying onto the material at a location near the exit end as the material moves through the tunnel; and directing vapor or gas from the liquid refrigerant over the material passing through the tunnel. passing in a countercurrent flow; an exhaust comprising said vapor or gas and atmospheric air entrained through said inlet end;
t) from the tunnel near the inlet end; determining the flow rate (Vαte offflow) of the exhaust gas and the content of molecular oxygen in the exhaust gas; A method of performing cryogenic cooling of a material is provided that includes calculating a rate of consumption of the liquid refrigerant from its content.

Preferably, the consumption of vapor or gas derived from the liquid refrigerant is controlled to optimize the production of cooled material and the weight ratio of liquid refrigerant consumed/cooled material. related to the information used to

Absolute gas flow rate through the exhaust duct (αbsoluteg
αsflow) is determined by its concentration (if a mixture of gases passes through the duct), temperature and apparent flow rate (appart
tnt rate of flow). The apparent flow rate of gas is measured using an anemometer (αne
mometer) or similar equipment. To keep the system as simple as possible this is preferably of the hot wire type, rather than the preferred type being a spinning head type instrument (vans).
, 5pin%ing sad instrrs-men
) or portex sieving meter (vo
rtex-shedding tnater).

If the exhaust from the tunnel is derived predominantly from refrigerant, i.e. molecular nitrogen, in other words if no atmospheric gases are entrained, then the apparent flow velocity can be determined by a temperature measuring device such as a thermocouple. and in combination with a pressure measuring device, for example an absolute pressure r-di, it will be possible to estimate the amount of refrigerant consumed by simple calculations.

However, in reality, some entrainment of atmospheric air always occurs. This is intentional (frosting up of the exhaust duct by reducing the exhaust temperature).
)] or unintentionally. With entrainment, it is necessary to determine the composition of the gas exhausted through the exhaust duct in order to obtain meaningful figures for refrigerant consumption.

Due to the chemical inertness of nitrogen, it is difficult to monitor the nitrogen content of gas mixtures in-line.

The same does not apply to oxygen, whose content is approximately constant in atmospheric air. By determining the deviation of the oxygen content of the exhaust gas from the cold tunnel from the oxygen content of the surrounding atmospheric air, the gas content derived from the liquid refrigerant can be quantified. The oxygen content of the air in the surrounding atmosphere is 21 volumes (more precisely 20
．． The greater the reduction in the oxygen content of the exhaust gas from the cold tunnel from 21 cm, the less air will be entrained into the tunnel.

Once the amount of entrained air is estimated from the oxygen content in the exhaust gas, it is a relatively simple matter to calculate the amount of gas resulting from evaporation of the liquid refrigerant passing through the tunnel.

While it is possible to assume a constant oxygen level in the ambient atmospheric air and still obtain accurate results,
It is also possible to monitor the oxygen content in the ir);
) Preferably simultaneously with the measurement of the oxygen content in the exhaust gas it is also possible to monitor the oxygen content in the air at the entrance end of the tunnel. If desired, the atmospheric oxygen content of the surrounding atmosphere and the exhaust gas
The oxygen content in es) can be measured using commercially available oxygen measurement probes. data, i.e., oxygen levels in the surrounding atmosphere and exhaust gases, voltage measurements from thermocouples or similar devices to determine the temperature of the exhaust gases, measured gas flow rates,
e), absolute pressure and product refrigeration amount (product f
The reezing rate) can be optionally supplied to a computer or microprocessor to remotely display the performance level of the cryogenic refrigeration tunnel or control the operation of the tunnel, such as in a factory manager's office.

If desired, other useful in-line parameters may be included, such as outside product temperature (ext
ernal product temperature
s) can also be monitored.

In addition to optimizing the liquid refrigerant/product ratio used, it is desirable to achieve substantially quantitative removal of refrigerant gas from the refrigerating tunnel. There are various reasons for favoring the quantitative removal of refrigerant gas, including safety, accuracy in deriving the proportion of liquid refrigerant/product used, and the economical capabilities of the cryogenic equipment. .

According to the invention, the analytical composition of a mixture of exhaust gases from a cryogenic device is monitored and the analytical composition of said mixture is determined, for example by forming a control loop, to determine the rate of expulsion of gas or vapor originating from the liquid refrigerant. αcti
extraction of refrigerant gas through the exhaust duct of the cryostat by associating it with a
A method is also provided for continuously regulating and controlling the refrigerant gas, thus ensuring substantially quantitative withdrawal of refrigerant gas to the outside atmosphere and maximizing refrigerant utilization. The amount of refrigerant gas withdrawn depends, for example, on the rate at which the exhaust gas mixture is withdrawn from the cryostat by an exhaust fan or other suitable means.
ction ) and/or by changing the amount of air entrained through the entrance end of the tunnel, for example by changing the position of the exhaust gas inlet. This aspect of the invention provides that the amount of refrigeration gas withdrawn which can be varied at any time is introduced either by atmospheric air (deliberately (to prevent knotting of the exhaust duct) or by entrainment with the product to be frozen). ) provides yet another control aspect.

Liquid nitrogen consumption
onsx-mption rate) (LNC
) is the formula [in which there are inducible constants, F is the measured flow rate of the gas in the exhaust duct at a temperature of 10 Kelvin, OA is the oxygen concentration in the atmosphere, and OD is the is the absolute oxygen concentration in the atmosphere, and P is the pressure relative to the standard atmosphere.
101.3skpa or 760mHg).

By coupling the value of OD to the speed of the exhaust fan (or some other gas extraction control system, which may include, for example, a variable-sized opening to control the intake of cold gas into the exhaust duct), that amount can be reduced to It is possible to automate the cryogenic process to ensure substantially quantitative withdrawal of wasteable refrigerant gas during the process.

There are no specific limitations to the method of measuring the various physical parameters outlined and the use of a wide variety of measuring devices is possible in accordance with the present invention.

The apparatus according to the invention thus comprises a cryogenic tunnel, means for passing material to be cooled at low temperature through the tunnel, and a liquid cryogen in the tunnel such that evaporation of the liquid cryogen cools the material passing through the tunnel. means for measuring the flow rate of the exhaust gas exiting the tunnel; means for measuring the temperature and pressure of the exhaust gas exiting the tunnel; and means for measuring the oxygen content of the exhaust gas exiting the tunnel. means for determining the rate at which material passes through the tunnel; optional means for determining the oxygen content of the atmosphere surrounding the cryogenic tunnel; and means for determining or monitoring the rate at which material passes through the tunnel. can be equipped with.

The invention is based on the analysis of the exhaust gas, in which the oxygen content of the exhaust gas is determined using an oxygen probe. However, it should be recognized that other methods can be used. For example, a gas chromatograph or mass spectrometer can be used. Other possible physical measurements of exhaust gas composition or even flow rates are characterized by infrared analysis of exhaust gases Patent applicant Nidward Jaczkus Adolf Willhoft

Claims (1)

Claims: 1. Introducing the material to be cooled into an elongated cold tunnel housing by means of a roll conveying the material from the inlet end to the outlet end; spraying onto the material at a location proximate to the exit end as it travels through the tunnel, and passing vapor or gas originating from the liquid refrigerant in a countercurrent flow over the material passing through the tunnel. extracting from the tunnel proximate the inlet end an exhaust comprising the vapor orifice and atmospheric air entrained through the inlet end; and a flow rate of the exhaust. and determining the content of molecular oxygen in the exhaust gas and calculating the consumption of the liquid refrigerant from the flow rate of the exhaust gas and its oxygen content. 2. A cryo-tunnel, means for passing the material to be cooled at low temperatures through the tunnel, and for supplying the tunnel with a liquid cryogen such that evaporation of the liquid cryogen cools the material passing through the tunnel. means for measuring the flow rate of the exhaust gas exiting the tunnel; means for measuring the temperature and pressure of the exhaust gas exiting the tunnel; and determining the oxygen content of the exhaust gas exiting the tunnel. means for determining the oxygen content of the atmosphere surrounding the cryogenic tunnel; and an optional means for determining the oxygen content of the atmosphere surrounding the cryogenic tunnel;
and means for determining or monitoring the cooling rate of a material.