Measuring and testing – Liquid level or depth gauge – Hydrostatic pressure type
Reexamination Certificate
2003-09-17
2004-12-07
Williams, Hezron (Department: 2856)
Measuring and testing
Liquid level or depth gauge
Hydrostatic pressure type
C073S29000R, C073S298000
Reexamination Certificate
active
06826956
ABSTRACT:
TECHNICAL FIELD
This invention relates generally to systems and methods for monitoring the vertical level (height) of fluid contained in a container. More particularly, the invention concerns differential pressure level monitoring systems and methods.
BACKGROUND
Various systems and methods exist for monitoring the vertical level of fluid in a container. As used herein, a container generally refers to a structure for holding or transporting a fluid, such as a reservoir, an open or closed channel, a tank, or a reactor. These include visual measurement systems, microwave technologies, ultrasonic technologies, submerged pressure transducers, and differential pressure bubbler systems. Each of these includes various drawbacks. Visual measurement systems are not efficient. Ultrasonic technologies, microwave technologies, and submerged pressure transducer systems are expensive and they do not work well with turbulent processes, with fluids containing foam and/or suspended solids, or with corrosive fluids.
Existing differential pressure bubbler systems work well for measuring the vertical level of fluid in situations where turbulence, debris, foam, or corrosive substances make other systems impractical. However, conventional differential pressure bubbler systems suffer from a number of problems. For instance, they tend to become clogged often, which affects the accuracy of pressure measurements or prevents these measurements entirely. Further, they need frequent cleaning to remove build-up or clear clogs.
As an example,
FIG. 1
shows a typical differential pressure bubbler system
10
. As shown, bubbler system
10
includes a tank
12
containing fluid
14
, a small-diameter bubble tube
16
, an air supply
18
, and a differential pressure controller
20
. In general, bubbler system
10
measures the hydrostatic pressure in fluid
14
near the bottom of tank
12
by comparing atmospheric pressure with the pressure required to force air from bubble tube
16
. Bubble tube
16
is a small-diameter (less than 1.0 inch diameter) vertical tube about 15 feet long, which permits bubbles to flow from its opening
141
near the bottom of tank
12
. Air supply
18
provides air to bubble tube
16
at a pressure slightly greater than the hydrostatic pressure at the end
22
of bubble tube
16
. Small-diameter tubing is used for bubble tube
16
to reduce false readings and lag time in reading pressure changes, which can occur when a large volume of air is maintained in pressure tube
16
. Differential pressure controller
20
is connected to bubble tube
16
and includes one or more pressure sensors that sense atmospheric pressure and the air pressure in bubble tube
16
.
Differential pressure controller
20
calculates hydrostatic pressure, H, at the opening
22
of bubble tube
16
by comparing the atmospheric pressure and bubble tube pressure according to the following formula: H=&Dgr;P/Sg, where &Dgr;P=the difference between bubble tube pressure and atmospheric pressure, and Sg=specific gravity of fluid
14
. The vertical level of fluid
14
above the opening can be determined based on the hydrostatic pressure, H, at the opening
22
of bubble tube
16
. Further, if the vertical level of fluid
14
is known, the same system can be used to determine the specific gravity, Sg, of fluid
14
.
Such conventional differential pressure bubbler systems suffer from a number of problems. For example, bubble tube
16
periodically becomes clogged with build-up, scale, sludge, settlement and/or debris, which affects the accuracy of pressure measurements or prevents these measurements entirely. As such, bubble tube
16
often needs to be purged with high-pressure air to clear obstructions. Purging, however, does not completely remove scale or other build-up on the surfaces of bubble tube
16
and at opening
22
. Thus, bubble tube
16
is periodically removed from tank
12
to clean scale and other materials from the bubble tube
16
. Removing bubble tube
16
for cleaning is expensive and time-consuming. Further, such periodic removal and cleaning can be dangerous, depending on the type of fluid
14
in tank
12
.
Accordingly, there is a need for improved systems and methods for measuring the vertical level of fluid in a container. Further, a need exists for improved low-maintenance differential pressure bubbler systems and methods.
SUMMARY
In order to overcome the above-described problems and other problems that will become apparent when reading this specification, aspects of the present invention provide a method for measuring the vertical level (height) of fluid in a container. According to one aspect of the invention, a method for measuring the vertical level of fluid in a container includes moving air downward along the inside of a bubble tube at an angle of about 5 degrees to about 85 degrees from vertical into the fluid. According to another aspect, the method includes injecting a mixture of air and steam into fluid in a container via a bubble tube.
Aspects of the present invention further provide a differential pressure bubble tube system that includes a bubble tube mounted to a container at an angle of about 5 degrees to about 90 degrees. Aspects additionally provide a bubble tube having a diameter of about 1 inch to about 6 inches. Further aspects include a bubble tube having pressurized air and steam inputs. Other features and advantages of various aspects of the invention will become apparent with reference to the following detailed description and figures.
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patent: 5563584 (1996-10-01), Rader et al.
patent: 5791187 (1998-08-01), Chang
patent: 5901603 (1999-05-01), Fiedler
patent: 6510736 (2003-01-01), Van Ee
patent: 6527960 (2003-03-01), Bacon et al.
patent: 6647781 (2003-11-01), Su
patent: 02075933 (1990-03-01), None
“Chapter 11, Sulfunic and Phosphoric Acids”, Fertilizer Manual, Kluwer Academic Publishers, 1998, pp. 296-353.
I.A Series® Electric d/p Cell® Transmitters with HART Communication Protocol IDP10 Series for Differential Pressure Measurments, Foxboro Product Specifications, 1995, pp. 1-20.
“Series 62 Constant-Differential; Relays”, pp. 7.21-7.22, Siemens Energy & Automation, www.sea.siemens.com.
Banner & Witcoff , Ltd.
Cargill Inc.
Frank Rodney
Williams Hezron
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