Pumps – Processes
Reexamination Certificate
2000-07-24
2001-07-31
Walberg, Teresa (Department: 3742)
Pumps
Processes
C095S190000
Reexamination Certificate
active
06267560
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a wet gas compression device comprising a gas compressor associated with a separator and with a heat exchanger upstream from the compressor.
In the present application, what is understood to be a wet gas is a mainly gaseous fluid comprising a liquid phase in such a proportion that it can be evaporated using the enthalpy increase resulting from gas compression.
BACKGROUND OF THE INVENTION
Various multiphase pump types allow compression of a two-phase mixture. However, rotodynamic type machines are limited to GLR ratios hardly greater than 20 and positive-displacement machines are relatively bulky for compression of a wet gas.
It is difficult to use conventional centrifugal or axial gas compressors to compress a gaseous fluid comprising a liquid phase because of the erosion due to the liquid droplets on the blades of the impellers, of the embrittlement of the blades and of the rotor unbalance resulting therefrom.
A first primary separation stage (working under the action of the terrestrial gravity) is therefore used more generally upstream from a gas compressor for rough separation of the gas and the liquid, then a second, secondary (for example sieve) separation stage is used for finer separation of the droplets contained in the gas. This layout also requires a single-phase pump for transfer of the liquid from the input pressure to the discharge pressure. These equipments are heavy and bulky.
The volume of the static separators can be reduced while maintaining the same degree of separation of the liquid droplets and of the gas, by generating great centrifugal forces produced only by using the energy of the fluid (without external energy supply). This is for example the working principle of cyclone separators.
The volume of the separators can be reduced further yet, while maintaining the same degree of separation of the liquid droplets and of the gas, by generating very great centrifugal forces produced from an external energy (separators known as dynamic separators). It is for example the working principle of the dynamic separator described in the Bertin patent No. WO-87/03051. While this separator has the advantage of being relatively compact, it constitutes a second rotating machine when it is mounted outside the compressor, and it reduces the number of impellers of the compressor by about 30% when mounted inside the compressor.
SUMMARY OF THE INVENTION
The object of the invention is a wet gas compression device that overcomes the drawbacks of the prior art.
The present invention relates to a wet gas compression device comprising in combination at least the following elements:
a compression device suited to compress a gas, said compression device comprising at least one gas delivery line and at least one compressed gas discharge line, and one or more lines allowing withdrawal or reinjection of at least a fraction of the gas circulating in the compressor,
at least one wet gas delivery line,
a circuit comprising at least the following elements:
a separator separating the liquid phase from the gas phase, said separator being connected to the line,
a liquid phase discharge line and a gas phase discharge line,
a heat exchanger,
the heat exchanger is connected at least to the following lines:
a delivery line for the mainly liquid phase,
a delivery line for a compressed gas, which can be a line for withdrawing compressed gas from the compressor,
a line allowing to send the compressed gas back to a compression stage after heat exchange with the liquid fraction,
a discharge line for the liquid fraction vaporized by heat exchange. The liquid fraction can be sent to the compressor or to any other destination.
The device can also comprise several temperature detectors C
T
placed for example at the level of the lines.
The rank i of the stage Ei of the compressor equipped with the withdrawal line and/or the line designed to send the gas back to a stage of the compressor is for example determined so as to satisfy the relation:
Q
g
>Q
12
with
Q
12
=L
1
M
1
+C
1
(
T
2
−T
1
)
M
1
+Cp
g1
(
T
3
−T
2
)
M
1
Q
g
=Cp
g2
(
T
5
−T
4
)
M
g
and
L
1
, C
1
, Cp
g1
, Cp
g2
, M
1
, M
g
, which respectively correspond to the latent heat of the liquid, to the specific heats of the liquid, of the vapour and of the gas, and to the mass flow rates of the liquid and of the gas, and
T
1
, T
3
, T
4
and T
5
represent the temperatures measured on lines
11
,
14
,
6
and
5
respectively; T
2
represents the evaporation temperature of the liquid at the input pressure of the wet gas.
The device can comprise a pressure control device placed downstream from the separator.
The device according to the invention comprises for example a bypass line allowing to divert part of the main gas flow withdrawn from the compressor before it passes into the heat exchanger, the bypass line being equipped with a gas flow control valve.
The line allowing to send the diverted gas flow back to a compression stage after heat exchange with the liquid fraction can be equipped with a control valve placed downstream from said heat exchanger.
The withdrawal line can be the main compressed gas discharge line and it can divide into two lines. A first line allows discharge of a first compressed gas fraction and a second line allows recycle of a second compressed gas fraction to the compressor, the second line being equipped with a control valve and the second line being connected to the compressor inlet or to the static mixer placed upstream from the compressor inlet, the recycled gas amount being so determined that Q
g
>Q
12
.
The withdrawal line is for example the discharge line and it can be divided into two lines. A first line allows discharge of a first compressed gas fraction and a second line allows recycle of a second compressed gas fraction to the compressor, the second line being equipped with a control valve and said second line being connected to a stage of the compressor.
The present invention also relates to a method for compressing a wet gas comprising at least one gas phase and at least one liquid phase.
It is characterized in that it comprises in combination at least the following stages:
(a) a separation stage at the end of which a mainly gas phase and a mainly liquid phase are obtained,
(b) a stage of conversion of said mainly liquid phase from separation phase (a) to a vapour phase by heat exchange,
(c) a stage of compression of the gas phases from stages (a) and (b).
Conversion stage (b) consists for example in:
(d) withdrawing at least part of the gas phase during a compression stage,
(e) sending the mainly liquid phase from the separation stage to a heat exchanger,
(f) carrying out the conversion of the mainly liquid phase to vapour by heat exchange with the gas phase withdrawn (stage (d)).
The amount of gas phase withdrawn for stage (f) can be controlled.
All of the gas phase is for example withdrawn at the end of the compression stage, said withdrawn part is used for carrying out stage (f) and part of the gas phase is recycled to a compression stage.
All of the gas phase can also be withdrawn at the end of the compression stage, said withdrawn part is used for carrying out stage (f) and part of the gas phase is recycled before the first compression stage.
The compression device according to the invention will be advantageously used for desiccating a wet gas in petroleum production.
The compression device according to the invention notably has the following advantages:
it requires a single rotating machine instead of two in a conventional production program (single-phase compressor and pump), hence a mechanics simplification and an improvement in the equipment reliability,
it is compact and not very bulky,
it allows to decrease the power absorbed by the gas for a flow rate Mg on account of the gas temperature decrease at the exchanger outlet. This advantage exists only provided that evaporation of the liquid can be achieved from a gas withdrawn at a lower pressure than the discharge pressure, since the temperature re
Antonelli Terry Stout & Kraus LLP
Fastovsky Leonid
Institut Francais du Pe'trole
Walberg Teresa
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