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 February 4, 2016 - 11:59 AM EST
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Patent Issued for Method and Device for Controlling a Hot Restart of a Centrifugal Compressor (USPTO 9243644)

By a News Reporter-Staff News Editor at Journal of Engineering -- Nuovo Pignone, S.P.A. (

Florence
, IT) has been issued patent number 9243644, according to news reporting originating out of
Alexandria, Virginia
, by VerticalNews editors.

The patent's inventors are Bagni, Gianni (

Florence
, IT); Baldassarre, Antonio (
Florence
, IT); Baldassarre, Leonardo (Sesto Fiorentino, IT); Fontana, Michele (
Genoa
, IT).

This patent was filed on October 23, 2014 and was published online on January 26, 2016.

From the background information supplied by the inventors, news correspondents obtained the following quote: "Embodiments of the subject matter disclosed herein generally relate to methods and devices used to control a hot restart of a centrifugal compressor driven by a low speed shaft of a gas turbine.

"In natural gas processing systems, often a gas turbine 10 drives a centrifugal compressor 20. When a sudden shutdown occurs, a shaft (or rotor) of the centrifugal compressor 20 usually develops a thermal bow due to an asymmetric cooling (e.g., an upper side and a lower side of the centrifugal compressor 20 have different rates of cooling). If the cooling process is allowed to be completed, eventually, the thermal bow disappears. However, often it is necessary to restart the centrifugal compressor 20 sooner then the end of the cooling, while the thermal bow is still present. The restarting of the compressor 20 before the cooling is completed is named a hot restart.

"When the centrifugal compressor 20 is restarted while the thermal bow is still present, vibrations may occur. The vibrations usually have a maximum amplitude at a speed lower than operational speeds. Strong vibrations may result in rubbing and permanent damage to the compressor 20.

"A method of suppressing the thermal bow without waiting for complete cooling (which may last from several hours to several tens of hours depending on the compressor size and geometry) is to run the compressor 20 for a while at a low speed. This method is known as the slow roll method.

"Conventionally, the slow roll method is implemented by inserting a turning gear 60 that may be attached to the compressor 20 (as shown in FIG. 1) or to a gearbox 30, if present. The turning gear 60 is used to rotate the shaft 50 of the compressor 20 at a low speed until the bow is suppressed.

"However, adding a turning gear increases the cost of the system. Sometimes, a turning gear cannot be added to a system due to structural constraints. Additionally, the turning gear may fail, and, therefore, unintentionally, the compressor may be damaged by running at damaging speeds while still having a bow.

"Accordingly, it would be desirable to provide systems and methods that avoid the afore-described problems and drawbacks."

Supplementing the background information on this patent, VerticalNews reporters also obtained the inventors' summary information for this patent: "According to one exemplary embodiment, a system includes a compressor, a turbine and a controller. The turbine has a high speed shaft and a low speed shaft, the low speed shaft being configured to drive the compressor. The controller is connected to the compressor and the turbine. The controller is configured to perform, while the vibration amplitude remains smaller than a vibration limit, maintaining, for a predetermined time, the speed of the high speed shaft at a value at which the current speed of the low speed shaft is in a slow roll speed range, and, then, increasing the speed of the high speed shaft until the current speed of the low speed shaft exceeds a minimum operating speed.

"According to one exemplary embodiment, a method for controlling a hot restart of a compressor driven by a turbine having a high speed shaft and a low speed shaft, which is connected to the compressor, is provided. The method includes maintaining, for a predetermined time, a base speed of the high speed shaft at which a current speed of the low speed shaft is in a slow roll range. The method further includes comparing a vibration amplitude of vibrations of the compressor with a vibration limit, and, when the vibration amplitude is larger than the vibration limit, repeat the maintaining. The method also includes increasing a set speed of the high speed shaft until the current speed of the low speed shaft exceeds a minimum operating speed, while the vibration amplitude remains smaller than the vibration limit. When the amplitude of vibrations becomes larger than the vibration limit during the increasing, the maintaining is repeated.

"According to another exemplary embodiment, a controller configured to control a hot restart of a compressor driven by a turbine, which has a high speed shaft and a low speed shaft that is connected to the compressor is provided. The controller includes an interface and a processing unit. The interface is configured to receive information about a current speed of the low speed shaft and a vibration amplitude of vibrations of the compressor, and to transmit commands related to setting a speed of the high speed shaft. The processing unit is connected to the interface and is configured to generate the commands based on the information. The commands include a first sequence of commands to maintain, for a predetermined time, a base slow roll speed of the high speed shaft, and a second sequence of commands to increase a set speed of the high speed shaft until the current speed of the low speed shaft exceeds a minimum operating speed. A speed of the low speed shaft is within a slow roll range, when the high speed shaft has the base slow roll speed. The processing unit is configured to repeat sending the first sequence of commands to the interface, when, according to the information, the vibration amplitude is larger than a vibration limit."

For the URL and additional information on this patent, see: Bagni, Gianni; Baldassarre, Antonio; Baldassarre, Leonardo; Fontana, Michele. Method and Device for Controlling a Hot Restart of a Centrifugal Compressor.

U.S.
Patent Number 9243644, filed October 23, 2014, and published online on January 26, 2016. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=9243644.PN.&OS=PN/9243644RS=PN/9243644

Keywords for this news article include: Nuovo Pignone S.P.A..

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Source: Equities.com News (February 4, 2016 - 11:59 AM EST)

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