Pumps – With signal – indicator – or inspection means
Reexamination Certificate
1999-09-01
2001-04-10
Freay, Charles G. (Department: 3746)
Pumps
With signal, indicator, or inspection means
C417S018000, C417S053000, C417S043000
Reexamination Certificate
active
06213724
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention generally relates to centrifugal compressors and more particularly to an improved method for electronically detecting the occurrence of surge in a centrifugal compressor driven by an electric motor, based on the measured rates of change of the discharge pressure and motor current.
Surge is an unwanted phenomenon in centrifugal compressors which occurs when the fluid flow rate through the compressor is suddenly reduced. When the flow rate is reduced to a point below a predetermined required minimum flow rate, fluid collects at the compressor discharge port and as the fluid collects, the fluid pressure at the discharge port increases until surge occurs. During the occurrence of surge, the direction of fluid flow is reversed and the built up fluid is flowed back into the compressor.
Surge is undesirable for a number of reasons. Compressor surge produces unstable fluid flow within the compressor and loud noise, and also increases the amount of heat generated by the compressor. Frequently, one of the consequences of surge is damage to compressor component parts.
One conventional way of avoiding surge is by increasing the fluid flow rate through the compressor inlet. Although surge is avoided by increasing the flow rate through the compressor inlet, such increased capacity for this compressor operation negatively affects the cost of compressor operation.
As an alternative to sacrificing compressor efficiency by increasing the inlet flow rate, mechanical means for avoiding the occurrence of surge have been developed. One such conventional mechanical means for avoiding the occurrence of surge is a mechanical differential pressure switch located in a switch tube or housing. Such known pressure differential switches include a pair of spaced apart contacts located in the housing. When the pressure differential between the ends of the switch housing is at a pressure level indicative of the occurrence of surge, the pressure differential causes the contacts to close and thereby provide an indication to a compressor operator that a surge condition is present. When the compressor surges, a valve is opened to adjust the fluid flow through the compressor and thereby take the compressor out of surge.
It is difficult for compressor operators to precisely set the gap between the contacts in known pressure differential switches. Additionally, the sensitivity of the contacts decreases over time. Moreover, such differential switches and other mechanically actuated surge detection means, usually do not prevent the compressor from going into deep surge once surge is detected.
The foregoing illustrates limitations known to exist in present devices and methods. Thus, it is apparent that it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. It is important to provide a reliable method for taking a compressor out of the surge condition to prevent compressor damage. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.
SUMMARY OF THE INVENTION
In one aspect of the present invention, this is accomplished by providing a method for
A method for controlling working fluid surge in a centrifugal compressor. According to the method, surge detection is accomplished by calculating the change in the compressible fluid mass flow rate that accompanies surge in a compressor. The compressor includes means for sensing a first fluid temperature, means for sensing a first pressure, means for sensing a second pressure, and means for measuring current drawn by a compressor prime mover, the method comprising the steps of: calculating the time rate of change of the first fluid temperature; calculating the time rate of change of the first fluid pressure; calculating the time rate of change of the second fluid pressure; calculating the time rate of change of current drawn by the compressor prime mover; calculating the mass flow rate by combining the calculated rates of change; and comparing the calculated mass flow rate to a predetermined acceptable mass flow rate to determine if surge is present.
REFERENCES:
patent: 3876326 (1975-04-01), Weitz
patent: 4137710 (1979-02-01), Preti et al.
patent: 4164033 (1979-08-01), Glennon et al.
patent: 4164034 (1979-08-01), Glennon et al.
patent: 4164035 (1979-08-01), Glennon et al.
patent: 4420947 (1983-12-01), Yoshino
patent: 4464720 (1984-08-01), Agarwal
patent: 4581900 (1986-04-01), Lowe et al.
patent: 4586870 (1986-05-01), Hohlweg et al.
patent: 4608833 (1986-09-01), Kountz
patent: 4686834 (1987-08-01), Haley et al.
patent: 4831534 (1989-05-01), Blotenberg
patent: 4831535 (1989-05-01), Blotenberg
patent: 4936741 (1990-06-01), Blotenberg
patent: 4949276 (1990-08-01), Staroselsky et al.
patent: 4971516 (1990-11-01), Lawless et al.
patent: 5195875 (1993-03-01), Gaston
patent: 5306116 (1994-04-01), Gunn et al.
patent: 5396779 (1995-03-01), Voss
patent: 5508943 (1996-04-01), Batson et al.
patent: 5873257 (1999-02-01), Peterson
patent: 6070404 (2000-06-01), Bosley et al.
Developments in Centrifugal Compressor Surgontrol-A Technology Assessment; K.K. Botros, J.F. Henderson; Novacor Research & Technology;Apr. 1994, vol. 116, pp. 240-249.
Haugen Ronald L.
Kann Meng Jeng
Evora Robert Z.
Freay Charles G.
Gnibus Michael M.
Ingersoll-Rand Company
LandOfFree
Method for detecting the occurrence of surge in a... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for detecting the occurrence of surge in a..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for detecting the occurrence of surge in a... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2534492