Pumps – Motor driven – Including means utilizing pump fluid for augmenting cooling,...
Reexamination Certificate
1999-07-30
2001-07-17
Walberg, Teresa (Department: 3742)
Pumps
Motor driven
Including means utilizing pump fluid for augmenting cooling,...
Reexamination Certificate
active
06261070
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to the field of gas compressor systems. In particular, it relates to compressor systems for transporting natural gas to compressor systems using an in-line compressor. In addition to natural gas, the invention relates to the compression of any clean, dry gas service, i.e., air, nitrogen, hydrogen, etc.
BACKGROUND OF THE INVENTION
The gas pipelines in use throughout the world transport billions of cubic feet of natural gas every day, at pressures in excess of 750 PSIG. As the gas is forced through these pipelines, friction occurs. Friction results in pressure loss, which results in a loss of capacity and lost sales opportunities. To minimize the loss due to frictional pressure drop, traditional pipeline companies install large booster compressor stations.
The natural gas transmission systems were originally designed with thousands of miles of pipe, utilizing compressor stations at 80 mile intervals to boost the gas pressure. As system capacity requirements increased, intermediate stations were installed, shortening the distance between stations to 40 miles. The distance between stations represents the industry's attempt to balance compressor station costs, pipeline costs, and available capacity. With costs exceeding $40 million for a typical station, most companies could not economically justify locating their stations closer together.
Compressor stations boost a pipeline's capacity by increasing the pressure. Increasing pressure increases the gas density, which allows the same quantity of energy to occupy less space. Maintaining high pressure helps in two ways: higher pressures create denser gas that requires less space and flows at a lower velocity, thus introducing less friction in the pipeline and lessening the pressure drop for equivalent gas energy packets; and denser gas allows more gas to be packed into the pipeline.
Packing is very important to pipelines. If a pipeline operator knows that the demand in the morning is going to be higher than what the company can normally deliver, the operator can “pack” the line the night before, storing extra gas in the line. This pack allows the customer to draw down the pressure. Therefore, it is advantageous to keep the pressure as high as possible for as long as possible.
Due to the pressure losses that occur along the length of a natural gas pipeline, compressor stations are needed at various intervals to maintain the pressure and flow of natural gas through the pipeline. Typical compressor stations use gas power engines to drive the compressors. These compressor stations suffer from numerous disadvantages. For example, compressors are not efficient when partially loaded and tend to generate significant amounts of noise in the surrounding environment. Additionally, conventional compressors are very sensitive to stops and starts. Therefore, numerous starts and stops can significantly reduce the useful life of the unit.
Moreover, conventional compressors are difficult to replace in the event of a failure. During an outage, pipeline companies tend to repair engines in place, causing down time for the pipeline. Furthermore, conventional compressors are rarely interchangeable. If the pipeline operator chooses to change equipment or modify the plant's piping, the operator is usually limited to the unique footprint of that equipment. Thus, unless the operator is willing to scrap the existing equipment, it would be impractical to modify or change conventional compressors. In addition, emissions from gas-driven compressors continue to be an increasingly greater problem when trying to comply with increasingly strenuous environmental regulations.
FIG. 5
is an example of a conventional compressor station. The compressor station comprises underground gas pipeline
100
through which gas flows from left to right as indicated by the arrow. Blocking valve
102
is provided to prevent the gas from flowing in a circular pattern. and is normally closed when the station is operating. On the upstream side of pipeline
100
is a suction header
104
. The suction header
104
contains various piping components that are conventional in the art such as station block valve
105
and scrubber
107
. The suction header
104
supplies gas to the centrifugal compressor
116
which is driven by motor
114
. In order to duct the gas to the compressor
116
, there is provided a 45° elbow
106
which feeds a rolled 90° elbow
108
. On the output side of compressor
116
similar piping is provided. The output flows through rolled 90° elbow
110
and then through 45° elbow
112
in the discharge header
118
and finally reenters the pipeline
100
. One problem with the conventional compressor station shown in
FIG. 5
is that there is a pressure loss due to the friction of the gas in the pipelines going through bends, such as the 90 and 45° elbows. Therefore, it is desirable to eliminate these elbows in a compressor station. Also, since the gas enters the compressor
116
at a right angle to the shaft of motor
114
there is a chance that piping forces could be imparted on the intake or output nozzles of the compressor
116
. This can cause casing distortion to the compressor
116
and damage the compressor and motor
114
. It can also cause misalignment of the motor
114
and the compressor
116
which causes vibration in the compressor station. This vibration can, in turn, cause the compressor to shut down and wear out mechanical components prematurely. Further, this misalignment makes it difficult to adequately seal the compressor
116
. Because of maintenance issues, conventional compressor stations are typically constructed in buildings above ground which require additional space and costs for the station. The building also must be insulated to reduce noise. The same problems occur in a variety of gas compression systems and are not limited to natural gas compressor stations.
Though the previous examples represent some of the major deficiencies of conventional compressor stations, this list is by no means exhaustive.
The present invention overcomes these deficiencies and provides further improvements and advantages which will become apparent in view of the following disclosure.
SUMMARY OF THE INVENTION
One aspect of the present invention relates to In-line electric motor driven compressor stations that use In-line Electric Motor Driven Compressors (“IEMDCs”) to transport gas through a pipeline. This avoids the piping bends in conventional compressor stations that cause pressure loss and other problems discussed earlier. The compressor can be either axial, centrifugal, or fan. Also, the In-line compressor can be mounted above or below ground. In one advantageous embodiment, the compressor is optimized for a compression ratio of about 1.1:1 to about 1.3:1. The motor can be immersed in the gas stream, thus cooled by the flowing gas, or can be mounted outside the gas stream, and cooled by air. If the motor is mounted in the gas stream, both the motor and the compressor can have a plurality of magnetic bearings, which make the compressor station virtually maintenance free and environmentally friendly because there are no conventional compressor seals to leak gas to the atmosphere.
IEMDCs as used in conjunction with the teachings of the invention overcome a variety of the deficiencies in the conventional compressor stations. First, an IEMDC is less sensitive to stops and starts. The operator can run the system only when required and shut it down without worry of significantly shortening the life of the unit. Additionally, because a failed unit can be quickly removed and replaced with a spare or a pipe spool, pipelines will not suffer the significant outages caused by repairing conventional compressors in place. Moreover, pipeline companies will have the option to choose from a variety of vendors' compressors, allowing them to modify equipment or insert a pipe spool. In addition, In-line compressor stations offer reduced emissions, full automation, quieter operation, improved safety, a reduc
El Paso Natural Gas Company
Locke Liddell & Sapp LLP
Patel Vinod D
Walberg Teresa
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