Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CASE 2~31
"PROCESS FOR PUMPING A MULTI-PHASE GAS-LI~UID MIXTURE BY
MEANS OF TME USE OF A PUMP"
The present invention relates to a process for
suppling pressure energy to a multi-phase gas-Liquid
mixture~ and in particular to a multi-phase fluid com;ng
from a petroleum well, by means of the use of a pump as
the thrust-supplying machine. The system can handle
fluids also containing small amounts of solid particles,
as a -function of the amount of solids ~hicl1 is acceptable
for the pump~ The use of the present invention is above
all referred to scenarios wherein a high reliability is
required in the absence of attending personnel, and with
a low maintenance frequency. Such scenarios may relate to
submarine applications, or applications on non-attended
offshore platforms, as well as to situations on land,
with hostile environments, or environments which are
difficult ~rom a logistic vieilpoint~
The presently available methods and systems for
pumping a mult;-phase gas-liquid m;xture may be
reconducted to the following categories
A) methods and systems based on the separation of the
2G phases, followed by a ma~hine (a pump) operating on
the liquid phase only, and a machine (a compressor)
operating on the cJas phase only;
B~ methods and systems based on the use of machines
(mulSi-phase "pumps"), directly capable of handling
the multi-phase mixture itself.
The systems belonging to the tA) category require
the use of two machine types, one of which (the
compressor) is characterized by a certain mechanical
clelicacy, and poor reliability.
The machines belonging to the (B) category are
presently in an experimentaL stage. They require
considerable development work and tests to be carried out
before being able ~o reach an effic;ency and a
reliability at an industrial level.
We have found now a pumping process by means of the
use of a conventional pump, which makes it possible the
drawbacks whlch affect the prior art, as hereinabove
mentioned, to be overcome.
The process for pumping a multi-phase gas-liquid
mixture, according to the present invention, is
characterized in that it uses a pump as the thrust-
supplying machine, and at least two pumpiny vessels,
which alternatively perform Functions of intake and
functions of ~ompression and/or delivery.
Since the pump must only handle the liquid phase, it
can be selected from among the conventional pumps, and in
particular it can be a centrifugal pump.
In case only two vessels are used, they perform,
always alternatively, functions of intake and functions
of compression/delivery.
In case more than two YesSels are used~ a further
stand-by function can be performed~
The present process is disclosed now, by referring
~o two particular operating modes.
The first operating mode uses two pumping vessels
only~ which a~ternat;vely perform functions of intake and
functions of compress;on/delivery; and more than two
vessels, which alterna~ively perform functions of intake~
functions oF compression/delivery, and standby functions.
Said first operating mode comprises the following
3.
steps:
a) feeeding the multi-phase mixture, under the pressure
of the intake line, to the vessel performing the
intake functions, and acting as the gas-liquid phase
separator;
b) sending the liquid separated inside the vesseL
performing intake functions, to the pump, hy means of
which it is pumped into the vessel, full of gas under
the intake pressure, which performs functions o~
compression/delivery, caus;ng the gas contained lnside
said vessel to be compressed, until it reaches the
same pressure as of the delivery line;
c) causing the compressed gas to Leave the vessel
performing compression/delivery functions, ~ollowed by
an amount of liqu;d, which is the same as of the
system-entering liquid, with them being fed to the
delivery! line.
For such a process type, the sequence, for each
vesse~, in case more than two vessels are used, can be;
intake, stand-by, compression/delivery; or intake,
compression/del;very, stand-by.
The second operating mode only uses more than two
pumping vessels~ wh;ch ~iLl aLternatively perform
functions of ;ntake, func~ions of compression/stand-by~
and functions of deLiveryO
Said second operating mode comprises the following
steps:
a) Feeeding the multi-phase mixture, under the pressure
of the intake line, to the vessel performing intake
functions~ and acting as the gas-liquld phase
separator;
~ 3
4.
b) sending ~he liquid separated inside the vessel
performing intake functions, to the pump, by means o~
which it is pumped ;nto the vessel, full of gas
co~pressed at the delivery pressure, performing
functions of delivery, causing the compressed gas
contained ;nside said vessel to leave, followed by an
amount of liquid, wh;ch ;s the same as of the system-
enter;ng liquid, with sa;d compressed gas and said
liquid be;ng fed, after that a portion of the
compressed gas ;s subtracted and is fed into the
vessel performing compression/stand-by functions, to
the delivery line.
c) feeding to the vessel full of gas under the intake
pressure, peforming functions of compression/stand-by,
a portion of the already compressed gas, w;thdrawn
from the vessel performing delivery functions, causing
the contained inside said vesssl gas to be compressed,
until the same pressure as of the delivery line is
reached
For such an operat;ng mode, the sequence, for each
vessel is the following: intake, compressionlstand-by,
delivery.
In case a centrifugal pump is used, the use of
(either pressure or flowrate controlling) regulation
valves is necessary, in order to render the pump
operating conditions as constant as possible.
The invention will be better d;sclosed w;th the a;d
of the d;agrams of F;gures 1, 2 and 3~ which represent
preferred forms of practical embodiments, using 3 pumping
vessels and one centrifugal pump, and which are not to be
considered as limitative of the same invention.
The status of thee pumping vessels (1, 2 and 3) is
determined by the status of the on/off valves ~4~ S~ 6,
7, 8, 9), wh;ch i5 governed by a dedicated electronic
logic system.
Referring to Figure 1, let us consider, e.g., the
case in which a vessel (1) is in its intake stage, the
vessel ~2) is in its stand-by stage, and the vessel t3)
is in its compression/delivery stage~ Under such
conditions, the multi-phase fluid t10) enters the vessel
(1~ (through 11; the other valves 12, 13, 14, 15, 16 are
closed), which acts as the gas/liqu;d separator, wh;lst
the "liquid piston" through the valve (4) comes to the
centrifugal pump ~17) from which, through the flow-rate
regulation or pressure regulation valve (18) and the
valve ~9), is pumped into the vesseL (3) (initially full
of gas under the intake pressure). The "liqu;d piston"
entering the vessel (3) causes the therein contained gas
to be compressed, until a same pressure as of the system
delivery line ;s reachedn Now, the valve (16) is opened,
and the gas is sent to the delivery line (19)r followed
by an a~ounc of liquid, which is the same as of the
system-entering liquid~ ~hen the level of the liquid
inside the vessel (1) reaches a suitable minimum value,
the control logic will switch the status of the on/off
valves. The vessel 1 turns into a stand-by status (valve
4 ;s closed), the vessel (3) swiSches into its intake
condition (valve 8 is opened; valve 9 i5 closed), the
vessel (2) switches into compression/delivery conditions
(valv~ 7 is opened~. Such a sequence is repeated, thus
making it possible a continuous stream of liquid to flow
through the pump (17) which, thanks to the action of the
regulation valve, (18), operates under nearly steady
conditions~ No diaphragms or separation bodies are
provided between the "liquid piston" and the multi-phase
fluid.
The system can also work according to a different
operating cycle, which, instead of the intakeistand-
by/compression-delivery sequence tfor each vessel)
accomplishes the intake/compression-delivery/stand-by
sequence.
An alternative configuration of the system of Figure
1 is depicted in Figure 2.
Let us consider, e.g., ~he case in which the vessel
(1~ is in its intake stage, ~he vessel t2) is in its
del;very stage and the vessel t3) is in its
compression/stand-by stage~
The multi-phase fluid t1l0) enters the vessel t1)
tthrough the valve 11: the other valves 12, 13, 14, 15
and 16 are closed), wh;ch acts as the gasiliquid
separator, whilst the "liquid piston" through the valve
~4) comes to the centrifugal pump (17), the correct
operation of which is ensured by the regulator valves
(20), (21) and t22), wh;ch maintain cons$ant the delivery
pressure of the pump~
The compression step is accomplished by means of the
delivery of a portion of the gas phase from the delivery
vessel t2) through the regulation valve t21), to the
vessel in the compression stage t3), until inside this
latter vessel the delivery pressure is reached.
The "liquid p;ston" is pumped into (2) ~hrough the
valve t7), and in this stage it performs the function of
sending a portion of the compressed gas to the vessel t3)
s
through (21), and the remainder portion thereof to the
delivery line tl9) through the vaLve (14~, followed by an
amount of liquid, ~hich the same as of the system-
entering liquid.
When the level of the liquid inside the vessel (1)
reaches a suitable minimum value, the control logic will
switch the status of the on/off valves. The vessel (1~
turns into its compression/stand-by status ~valves 4 and
11 are closed); the vessel ~2) switches into intake
condition ~valves 13 and 6 are open, 14 and 7 are
closed); the vessel ~3) turns into its delivery status.
A further alternative configura~;on is shown in the
simplified diagram of Figure 3~
In such a diagram~ a gas~liquid separator t23) is
added.
This makes it possible only gas to be sent to the
upper inlet of pumping vessels, ~hilst the liquid is
directly sent to the intake port of the centrifugal pump
~17).
As for the rest, the operation of the diagram sho~n
in Figure 3 is similar to as disclosed for the diagram
shown in Figure 1~
The configuration shown in F;gure 3 transfers the
function of phase ~gas/liquid) separation from the
pumping vessels t1, 2 and 3) to the separator ~23)~
An alternatlve possibility, valid for both of the
diagrams of Figure 1 and Figure 3, consists in using,
instead of one single regulation valve, three regulation
valves tone valve per each pumping vessel), installed in
cascade to the on/off valves ~5, 7, 9).
One should observe that the pumping vessels can be
given various configurations (horizontal, verticaL
vessel, and so forth), according to the process plan
adopted (and consequently of the functions which the same
vessels are reguired to perform), and of the
characteristics of the processed fluids. For example, for
the diagram of Figure 3, since the pumping vessel must
not act as a phase separator too, its reference
configura-tion is that of a vertical vessel.
The number of the pump;ng vessels can be both
increased and reduced ~to two vessels), in this latter
case 3 h;gher funct;onal irregularity having to be
accepted~
