Note: Descriptions are shown in the official language in which they were submitted.
Z
METHOD AND APPARATUS FOR DETEKMINING
MASS FLOW RATE AND OUALITY IN A STEAM LINE
(D#77,996-f)
BACKGROUND OF THE INVENTION
Field of the Invention
This invention concerns measurement of steam
quality in general. More specifically, the method
concerns a system and/or method which may determine the
mass flow rate and the quality of steam in a flow line
without prior knowledge of either.
In oil-field steam injection projects and
procedures it has been well known that an important
aspect is the knowledge of steam mass flow rate and
quality at an individual injection well. Heretofore
known methods generally require prior knowledge of either
mass flow rate or quality in order to determine the
other. Consequently, the prior procedures fail when
neither quality nor mass flow rate is known and such is
the case where two or more injection wells are being
supplied by one steam source.
SUMMARY OF THE INVENTION
Briefly, the invention is in relation to a
steam transmission line and in particular to a method for
measuring particular characteristics of steam comprising
water and vapor, flowing in a line which communicates an
apparatus in which said steam is generated to the point
of use thereof, toward determining the steam mass flow
rate and quality. The method comprises the steps of
diverting the total steam flow from said line into a
liquid-vapor separator having a liquid holding
reservoir, and in which separator discrete streams of
liquid and vapor are formed; directing the discrete
streams of vapor and liquid through separate flow meters,
each flow meter being capable of measuring the rate at
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which fluid is passing therethrough; adjusting the
rate at which vapor is flowing through said one flow
meter until the amount of liquid held in said separator
reservoir remains at a constant level; measuring the
respective flow rates, pressures, and temperatures of
each of said discrete liquid and vapor streams while said
liquid level in said reservoir remains constant.
Again, briefly, the invention is in combination
with a steam line for supplying a steam injection well or
the like, and it concerns a system for determining both
steam mass flow rate and quality where neither of these
is known. It comprises means for diverting total steam
flow from said line to a liquid-vapor separator having a
liquid reservoir, and means for passing separated vapor
and liquid streams through single-phase flow meters for
measuring vapor and liquid flow rates. The said single-
phase flow meters comprise an orifice-plate vapor flow
meter and a liquid dump-meter, respectively. It also
comprises means for measuring pressure and temperature of
said separated vapor and liquid streams, and means for
throttling at least one of said separated streams for
maintaining the level of said liquid reservoir constant.
The said means for throttling comprises throttle valves
in said separated streams located downstream from said
meters. The system also comprises means for rejoining
said separated streams after said throttling, all whereby
said total mass flow rate and quality may be determined.
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing and other objects and benefits of
the invention will be more fully set forth below in
connection with the best mode contemplated by the
inventors of carrying out the invention, and in
connection with which there are illustrations provided
in the drawings, wherein:
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the figure of drawing shows a schematic system
illustrating the apparatus necessary for carrying out the
invention.
DESCRIPTION OF THE PREFERRED E~30DIMENT
_ _
The drawing illustrates a system for carrying out the
invention and it will be observed that there is a steam line
conduit 11 through which the steam is flowing. The steam is
being directed to an injection well (as indic e ) or the like.
The steam line l1 connects directly to a valve 12 in the line.
This valve 12 will be closed during the determination
concerning mass flow rate and quality.
There is a branching conduit 15 which carries the
entire flow from conduit 11 when the system is in operation.
There is another valve 16 in the conduit 15 which will remain
fully open during the system's operation. A conduit 17
continues from the other side of the valve 16 and connects with
20~ the input of a cyclone separator 20. It will be understood
that other and different types of separators might be employed,
so long as the separation obtained is substantially complete,
viz-a-viz v~por and liquid. At the bottom of the cyclone
separator 20 there is a reservoir 21 where the separated liquid
gathers. Near the bottom of the reservoir 21 there is an
outlet pipe or conduit 24 that connects to a liquid flow meter
25. It will be understood that any feasible single phase
liquid flow meter might be employed. However, preferably it is
- of a type called a liquid dump-meter.
There is an outlet pipe 28 from the liquid flow meter
25 to a throttle valve 29. From the throttle valve 29, a pipe
or conduit 30 connects to another valve 31 which will normally
be open during the operation of the system. On the other side
of valve 31, a pipe 34 connects into an outlet pipe 35 that
carries the flowing steam to the injection well or other use
for the steam.
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At the top of the cyclone separator 20 there is an
outlet conduit 38 that carries the separated vapor phase to a
vapor flow meter 39. This flow meter may be any feasible
single phase vapor meter, such as an orifice-plate vapor flow
meter. There is a conduit 42 from the outlet side of flow
meter 39 that goes to a throttle valve 43. On the outlet side
of valve 43 there is a conduit 44 that connects into the pipe
30.
There is a pressure meter 47 and a temperature
indicator 48 that both connect into the line or pipe 38 between
the vapor flow meter 39 and the outlet from the cyclone
separator 20. Similarly, there is a pressure meter 49 and a
temperature indicator 50 that are connected into the line o~
pipe 24 which goes from the bottom of the cyclone separator 20
and is carrying the liquid phase fluid.
There is a measurement and control panel 53
illustrated. It has connections to the flow meters and
throttle valves, as well as to a iiquid level sensor 54. As
will appear more fully below, the measurement and control may
be carried out manually or could be performed automatically
using any feasible system, e.g., a computerized system. In
operation, one or both of the throttle valves 29 and 43 are
controlled in order to maintain the liquid level in reservoir
21 constant, as determined by the liquid level sensor 54. When
steady-state conditions have been established, the measurements
of flow rates by flow meters 25 and 39 plus the pressures and
temperatures of each of the separated streams, are determined.
The total mass flow rate and quality of the steam may then be
calculated from those measurements in accordance with the more
complete explanation which follows.
It may be noted that the total mass flow rate remains
the same throughout the flow system. The steam quality will,
of course, decrease, but only by a negligible amount which
would be determined by the amount of heat loss from the system
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to the environment. However, it will be noted that the system
is well insulated throughout in order to minimize that aspect.
Thus, the total mass flow rate remains the same in accordance
with the following expression:
ml m2 + m3 ~1 )
where: m1 is the total mass flow rate of the stream being
measured;
10m2 is the mass flow rate of the ~ r; and
m3 is the mass flow rate of the liquid.
Equation (1) may be expanded to
151 [Xlhgl + (1-xl)hfl] = m2h 2 + m3hf + Q (2)
wherein:
ml is the mass flow rate at conduit 15,
hf1 hg1 are the enthalpies of the saturated liquid
and vapor, respectively, at conduit 15,
xl is the steam quality at conduit 15, and
QL is the heat loss from the separator system.
For a well-insulated flow system, the heat loss is
small compared to the flow enthalpy and can be neglected.
Therefore
301 [xlhgl + (l-xl)hfl] = m2hg2 + m3hf3 (3)
Example
In accordance with the foregoing relationships, the
determination of mass flow rate and quality of the total steam
flow being measured may be determined in accordance with the
following example. At steady-state conditions, the following
measurements are obtained:
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m2 = 12,000 lbs./hr.
m3 = 3,000 lbs./hr.
Pl 960 psia (at conduit 15)
P2 = 940 psia (at conduit 38)
P3 940 psia (at conduit 24)
Then, from equation (1) we have the following
ml = 12,000 + 3,000 = 15,000 lbs./hr.
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And, from standard steam tables, the
saturation enthalpies may be ascertained for the stations at
conduit 15 (1), conduit 38 (2) and conduit 24 (3) as follows:
hfl = 536.2 Btu/lb.
hgl = 1193.9 Btu/lb.
hg2 = 1194.6 Btu/lb.
hf3 = 533.0 Btu/lb.
Then solving for xl in Equation (3) we get
xl = 80%
It may be noted that a variation of the described
system and operation in the foregoing, might be employed.
Under certain operating conditions it might improve the
results. Thus, by collecting the separated liquid in a holding
tank (not shown) for the duration of a test, the accumulated
liquid volume divided by the duration of test will also provide
tile average liquid flow rate.
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While the foregoing explanation and description has
described the invention in considerable detail in accordance
with the applicable statutes, this is not to be taken in any
way limiting the invention but merely as being descriptive
thereof.
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