Chemical apparatus and process disinfecting – deodorizing – preser – Process disinfecting – preserving – deodorizing – or sterilizing – Process control in response to analysis
Reexamination Certificate
1998-11-06
2002-08-27
Thornton, Krisanne (Department: 1744)
Chemical apparatus and process disinfecting, deodorizing, preser
Process disinfecting, preserving, deodorizing, or sterilizing
Process control in response to analysis
C099S467000, C099S468000, C099S483000, C422S105000, C422S108000, C422S109000, C426S231000, C426S232000, C426S407000, C426S521000
Reexamination Certificate
active
06440361
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates generally to a controller for administering a hydrostatic sterilization process being performed on line of carriers that each carry a set of containers. In particular, it pertains to such a controller that also provides on-line handling of a deviation in a scheduled parameter during the process by identifying any carriers with under processed containers as a result of the deviation.
BACKGROUND OF THE INVENTION
A hydrostatic sterilization system is a continuous source processing system. It is widely used in the canning industry to sterilize a shelf stable food product packaged in containers. It is used most often for sterilizing a food product that does not benefit from mechanical agitation of containers, as is performed in a rotary sterilization system.
A hydrostatic sterilization system comprises a hydrostatic sterilizer that has a conveyor (or chain) and a line of carriers {1, . . . , i, . . . , I}
line
conveyed by the conveyor. Each carrier i carries a set of containers and is conveyed through the hydrostatic sterilizer by the conveyor. The conveyor has a scheduled conveyor speed for conveying the carriers through the hydrostatic sterilizer. Moreover, the containers carried by each carrier are treated with scheduled retort temperatures in the hydrostatic sterilizer.
In order for the food product in the containers of each carrier i to be commercially sterilized, a total lethality F
i
over a total time interval [t
f,i
, t
d,i
] that satisfies a predefined target total lethality F
targ
must be delivered during the hydrostatic sterilization process to the product cold spot of each container of the carrier. Here, t
f,i
and t
d,i
are the loading and unloading times when the carrier is loaded into and unloaded from the hydrostatic sterilizer. The target total lethality is set by the USDA (U.S. Department of Agriculture), the FDA (Food and Drug Administration), and/or a suitable food processing authority for destroying certain microorganisms. The conveyor speed and the retort temperatures are then scheduled so that the containers of each carrier will receive a time-temperature treatment according to a scheduled time-temperature profile that delivers a total lethality to the containers which satisfies the target total lethality.
As is well known, the lethality F
i
delivered to each container in a carrier i over a particular time interval [t
m
, t
k
] is given by the lethality equation:
F
i
=
∫
t
m
t
k
10
(
T
cs
(
t
)
i
-
T
REF
)
/
z
ⅆ
t
where t
m
and t
k
are respectively the begin and end times of the time interval [t
m
, t
k
], T
CS
(t)
i
is the product cold spot time-temperature profile for the container, z is the thermal characteristic of a particular microorganism to be destroyed in the sterilization process, and T
REF
is a reference temperature for destroying the organism. Thus, the total lethality F
i
delivered to the container over the total time interval [t
f,i
, t
d,i
] due to the scheduled retort temperatures is given by this lethality equation, where t
m
=t
f,i
and t
k
=t
d,i
.
The total time interval [t
f,i
, t
d,i
9
and the product cold spot time-time-temperature profile T
CS
(t)
i
must be such that the total lethality F
i
over [t
f,i
, t
d,i
] satisfies the target total lethality F
targ
. In order to ensure that this occurs, various mathematical simulation models have been developed for simulating the product cold spot time-temperature profile based on the scheduled retort temperatures. These models include those described in Ball, C. O. and Olson, F. C. W.,
Sterilization in Food Technology; Theory, Practice and Calculations
, McGraw-Hill Book Company, Inc., 1957; Hayakawa, K.,
Experimental Formulas for Accurate Estimation of Transient Temperature of Food and Their Application to thermal Process Evaluation
, Food Technology, vol. 24, no. 12, pp. 89 to 99, 1970;
Thermobacteriology in Food Processing
, Academic Press, New York, 1965; Teixeira, A. A.,
Innovative Heat Transfer Models: From Research Lab to On
-
Line Implementation in Food Processing Automation II,
ASAE, p. 177-184, 1992; Lanoiselle, J. L., Candau, Y., and Debray E.,
Predicting Internal Temperatures of Canned Foods During Thermal Processing Using a Linear Recursive Model
, J. Food Sci., Vol. 60, No. 4, 1995; Teixeira, A. A., Dixon, J. R., Zahradnik, J. W., and Zinsmeister, G. E.,
Computer Optimization of Nutrient Retention in Thermal Processing of Conduction Heated Foods
, Food Technology, 23:137-142, 1969; Kan-Ichi Hayakawa,
Estimating Food Temperatures During Various Processing or Handling Treatments
, J. of Food Science, 36:378-385, 1971; Manson, J. E., Zahradnik, J. W., and Stumbo, C. R.,
Evaluation of Lethality and Nutrient Retentions of Conduction
-
Heating Foods in Rectangular Containers
, Food Technology, 24(11):109-113, 1970; Noronha, J., Hendrickx, M., Van Loeg, A., and Tobback, P.,
New Semi
-
empirical Approach to Handle Time-Variable Boundary Conditions During Sterilization of Non
-
Conductive Heating Foods
, J. Food Eng., 24:249-268, 1995; and the NumeriCAL model developed by Dr. John Manson of CALWEST Technologies, licensed to FMC Corporation, and used in FMC Corporation's LOG-TEC controller.
However, if any of the actual retort temperatures in the hydrostatic sterilizer drops below a corresponding scheduled retort temperature, a temperature deviation occurs. Traditionally, when such a deviation occurs, the controller stops the conveyor and prevents any of the carriers {1, . . . , i, . . . , I}
line
from being loaded into or unloaded from the hydrostatic sterilizer until the deviation is cleared. But, this approach causes numerous problems. For example, significant production down time will result. And, many carriers { . . . , i, . . . }
ovrpr
will have over processed containers since the total lethalities { . . . , F
i
over [t
f,i
, t
d,i
], . . . }
over
actually delivered to these containers will significantly exceed the target total lethality F
targ
. All of these problems may result in severe economic loss to the operator of the hydrostatic sterilization system.
In order to prevent such loss, a number of approaches have been discussed and proposed for on-line control of sterilization processes. However, all of these approaches concern control of batch sterilization processes performed on a batch of containers {1, . . . , i, . . . , I}
batch
. In a batch sterilization process, all of the containers generally receive the same time-temperature treatment whether or not a temperature deviation occurs. Thus, when a deviation does occur, a correction to the process can be made which simultaneously effects all of the containers so that a minimum total lethality F
i
over [t
b
, t
e
] will be delivered to each container i, where t
b
and t
e
are the begin and end times of the batch sterilization process. An example of such an approach is described in concurrently filed and co-pending U.S. patent application Ser. No. 09/187,333, entitled Controller and Method for Administering and Providing On-Line Correction of a Batch Sterilization Process , filed on Nov. 6, 1998, with Weng, Z. as named inventor. This patent application is hereby explicitly incorporated by reference.
In contrast, each carrier i in a hydrostatic sterilization process will receive a unique time-temperature treatment. Thus, the total lethality F
i
over [t
f,i
, t
d,i
] actually delivered to each carrier's containers is different. This makes it difficult to identify, while on-line and in real time, each carrier that will have a total lethality predicted to be delivered to its carriers that is below the target total lethality F
targ
. As a result, the development of a controller that provides on-line handling of a temperature deviation in a hydrostatic sterilization process without stopping the conveyor has been inhibited.
However, in Weng, Z., Park, D. K., a
Dorsey & Whitney LLP
FMC Technologies Inc.
Mendenhall Larry
Thornton Krisanne
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