Measuring and testing – Gas content of a liquid or a solid – By pressure of the gas
Reexamination Certificate
2002-01-16
2004-07-27
Williams, Herzon E. (Department: 2856)
Measuring and testing
Gas content of a liquid or a solid
By pressure of the gas
C073S019010, C073S019100, C073S023330, C073S025040, C073S029010
Reexamination Certificate
active
06766680
ABSTRACT:
FIELD OF THE INVENTION
This invention provides means for improving control of continuous processes that handle liquids, and therefore provides benefits to manufacturers by enabling them to effectively monitor and operate their processes. Data generated by this invention can be used to control the gas contents of liquids within optimum ranges, for instance in paper coating processes and in the manufacture of such products as food products (ketchup, mayonnaise, syrup), personal care products (skin cream, shampoo), pharmaceutical products, paints, petroleum blends, and the like. This invention is useful in any industry where information on entrained and/or dissolved air and other gases, and related parameters such as true density of and gas solubility in process liquids, is employed to optimize processing.
BACKGROUND OF THE INVENTION
Those skilled in the arts of processing liquids desire to know how much air and/or other gases are entrapped and dissolved therein for a variety of reasons. Entrapped air can cause undesired foaming during processing, e.g. in papermaking and in the preparation of foodstuffs, and can result in disruption of film products, e.g. from paints. Entrained gases distort such processing parameters as density, making precise control of processes impossible. Those skilled in the art know that, generally, the more viscous a fluid being processed, the more difficult it is for any entrained air to escape from it and consequently the greater the amount of air bubbles likely to be accumulated therein. Also, as pressure on a fluid is lowered, dissolved air or other gas therein tends to leave solution and form bubbles in the fluid.
There are a number of instruments that are currently commercially available for measuring the air or gas content in a liquid. Such instruments include Valmet's COLORMAT, Mütek's GAS-60, Papec's PULSE))))AIR, Capella Technology's CAPTAIR, Anton-Paar's CARBO 2100 CO
2
analyzer, and CyberMetrics' AIR TESTER.
Mütek's GAS-60, for instance, is said to be useful in the context of minimizing pinholes (voids) in papermaking processes. Pinholes develop when pressure is reduced and dissolved gases—which accumulate in the papermaking process due to mechanical effects and chemical and biological reactions—are released. The GAS 60 is installed on line and is used to determine the gas content of entrained and dissolved gases in pulp suspensions. Having determined gas content, process engineers are able to calculate how much (expensive) deaerating additive should be used, and thus to avoid unnecessarily increased manufacturing costs due to employing too much deaerating additive.
Papec's PULSE))))AIR_V3 is a sensor for the measurement of entrained air and gases in process fluids. It is said to be useful in the pulp and paper industry in connection with machine headboxes and white water systems, coatings, and brownstock washers, in the secondary fiber industry (for effluent treatment), in the paint industry, in oil bottling processes, in the processing of well drilling muds, and in general in any application needing entrained air information.
Anton-Paar's CARBO 2100 CO
2
analyzer employs a patented impeller method which is said to make it significantly faster that other commercially available systems for measuring and monitoring tasks and also for regulating the CO
2
content of process liquids during production runs in the beer and soft drink industry.
It is believed that all of these instruments adopt a common approach, using Boyle's Law. Boyle's law is given by the formula
P
1
V
1
=P
2
V
2
(1)
where V
1
and V
2
are the volumes of the free gas in the liquid at two different pressures, P
1
and P
2
, respectively. Being a “two-point measurement”, this common approach measures the volume difference &Dgr;V=V
1
−V
2
between P
1
and P
2
, and calculates the volumes of free gas, V
1
and V
2
, from Boyle's Law as
V
1
=
P
2
Δ
V
P
2
-
P
1
and
V
2
=
P
1
Δ
V
P
2
-
P
1
(
2
)
More general formulas, which correlate the volumes of free gas with the pressures being acted upon, can be derived from the Ideal Gas Law as
P
1
V
1
=n
1
RT
1
(3)
and
P
2
V
2
=n
2
RT
2
(4)
where R is the gas constant, and n
1
, T
1
and n
2
, T
2
are moles of free gas and temperatures at P
1
and P
2
, respectively. In the case of n
1
=n
2
and T
1
=T
2
, equations (3) and (4) can be simplified to the equation of Boyle's Law given in (1). Hence, Boyle's Law is, in fact, a special case of the Ideal Gas Law and is valid only if the moles of free gas and temperatures at P
1
and P
2
are kept constant.
In practice, a portion of free gas, however, will be dissolved into the liquid. The solubility of gas is, as a general rule, proportional to the gas pressure as stated in Henry's Law
P=Hn
d
(5)
where P, H, n
d
are the pressure of the gas being dissolved, the constant of Henry's Law, and moles of dissolved gas, respectively. This unquestionably makes n
1
≠n
2
between P
1
and P
2
, causing a violation of Boyle's Law. Therefore, using Boyle's Law for a “two-point measurement” is an unreliable approximation and can cause a significant amount of error, especially when the pressure difference between the two points becomes large.
To cure this error, there have been some attempts to use Henry's Law to compensate for the amount of the dissolved gas. This approach, however, is generally impractical, inasmuch as the constants of Henry's Law are not available for many process liquids, particularly for those containing multiple-components such as coating slurries. Using the known constant of one liquid to approximate the constant of the others may potentially introduce a considerable amount of error, because the solubility of gases such as air changes dramatically from liquid to liquid. The solubility of air in isooctane at standard temperature and pressure, for example, is more than 100 times higher than the solubility of air in water.
SUMMARY OF THE INVENTION
The present invention provides methods and apparatuses for determining the entrained gas content and/or the dissolved gas content of liquids. This invention provides means for improving control of continuous processes that handle liquids, and therefore provides benefits to manufacturers by enabling them to effectively monitor and operate their processes. Data generated by this invention can be used for instance to control the gas contents of liquids within optimum ranges, for instance in the processing of foam such as shaving cream or ice cream and to minimize gas contents, for instance in paper coating processes and in the manufacture of such products as food products (ketchup, mayonnaise, syrups, various sauces), personal care products (skin cream, shampoo, lotions, toothpaste), pharmaceutical products, herbicides, paints, lubricating greases, petroleum blends, water softeners, and the like. This invention is useful in any industry where information on entrained and/or dissolved gas, and related parameters such as true density and solubility of process liquids, is employed.
In one embodiment, this invention provides a method for controlling the entrained gas content of a liquid or slurry being flow-processed. The liquid or slurry being flow-processed may be—without limitation—a slurry of kaolin clay, calcium carbonate, titanium dioxide, or alumina trihydrate being supplied as a coating to a paper substrate. Alternatively—again without limitation—the liquid or slurry being flow-processed is ointment, cream, lotion, toothpaste, mayonnaise, ketchup, or lubricating grease being packaged into a retail container. The method comprises: a.) setting a quantitative target for the free gas content of said liquid or slurry; b.) continuously flowing said liquid or slurry and mixing an antifoam agent therewith; c.) determining the volume percentage of free gas,
Chen Qingyuan
Franda Robert Josef
Appleton Papers Inc.
Birch & Stewart Kolasch & Birch, LLP
Rogers David A.
Williams Herzon E.
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