1

Paper for ASME JERT

Design and Performance of Passive Control System forGas-Liquid Cylindrical Cyclone Separators

byRam Mohan, Shoubo Wang, & Ovadia Shoham, The University of Tulsa and

Gene Kouba, Chevron Petroleum Technology CompanyAbstract:

The performance of Gas Liquid Cylindrical Cyclone (GLCC) separators can be improvedby reducing or eliminating liquid carry-over into the gas stream or gas carry-under through theliquid stream, utilizing a suitable liquid level control. In this study, a new passive control systemhas been developed for the GLCC, in which the control is achieved by utilizing only the liquidflow energy. A passive control system is highly desirable for remote, unmanned locationsoperated with no external power source. Salient features of this design are presented here.Detailed experimental and modeling studies have been conducted to evaluate the improvement inthe GLCC operational envelope for liquid carry-over with the passive control system. The resultsdemonstrate that a passive control system is feasible for operation in normal slug flow conditions.The advantage of the dual inlet configuration of the GLCC is quantified for comparativeevaluation of the passive control system. The results of this study could form the basis for futuredevelopment of active control systems using a classical control approach.

INTRODUCTION

For many years, the Petroleum Industry has relied mainly on conventional vessel-type

separators. They are bulky, heavy and expensive in capital, installation and operation. Due to

economic and operational pressures, the petroleum industry has recently shown interest in the

development of innovative alternatives to conventional separators. One such alternative is the

Gas-liquid Cylindrical Cyclone (GLCC). Unlike conventional vessel type separators, the GLCC

is simple, compact, low weight, low-cost, requires little maintenance, and is easy to install and

operate. It is therefore gaining popularity as an easy-to-operate, economically attractive

alternative to the conventional separator.

The development ranking of the various separation technology alternatives is shown

schematically in Fig. 1 (Kouba et al., 1995). As shown in this figure, conventional vessel-type

separators have reached their maturity, except for some minor improvements that are being

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incorporated, such as new developments of internal devices and control systems. Large diameter

vertical cyclones and hydro-cyclones have also been used by the industry for some time.

However, recent trends in development are focused towards new types of compact separators,

such as the GLCC. The compact dimensions, smaller footprint and lower weight of the GLCC

offer a potential for cost savings to the industry, especially in offshore applications. Also, the

GLCC reduces the inventory of hydrocarbons significantly, which is critical for environmental

and safety considerations.

A schematic of the GLCC separator is shown in Fig. 2. It is a vertically installed pipe

mounted with a downward inclined tangential inlet, with outlets provided at the top and bottom of

the pipe. It has neither moving parts nor internal devices. Due to the tangential inlet, the flow

forms a swirling motion, producing centrifugal forces. The two phases of the incoming mixture

are separated due to centrifugal and gravity forces. The liquid is forced radially towards the walls

of the cylinder and is collected from the bottom, while the gas moves to the center of the cyclone

and is taken out from the top. Currently, the GLCC finds potential application as a gas knockout

system, upstream of production equipment. Through the control of gas liquid ratio (GLR), it

enhances the performance of multiphase meters, multiphase flow pumps, and de-sanders. Other

applications are portable well testing equipment, flare gas scrubbers, and slug catchers. The

GLCC is also being considered for down hole separation, primary surface separation (onshore and

offshore) and sub sea separation.

The strength and weakness of the GLCC are its compactness. Its strength is primarily due

to its compact dimensions where centrifugal forces are used for separation. However, its inherent

disadvantages are that it does not offer large residence time and it cannot tolerate large surges in

flow conditions. Previous studies of GLCCs have been carried out for loop configurations,

characterized by recombination of the gas and liquid streams at the outlet. The significance of this

configuration lies in the fact that it is self-regulating for small flow rate variations. However, for

large flow variations, there is an increasing need for liquid level control to improve the GLCC

loop operation so as to prevent liquid carry-over or gas carry-under. Also, for field applications

other than metering, separate outlet gas and liquid streams are needed for the GLCC. This

configuration must have liquid level control for efficient operation.

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GLCC control philosophy should be aimed at developing suitable control strategies

appropriate for field applications. The different strategies which could be adopted in the field are

passive control, active control using classical control theory and robust control using modern

control theory. Passive control is the simplest form of control, which does not need any external

power source, is easy to use and is cheap. Passive control is ideal for offshore applications and

remote oil fields where electric power is very scarce or expensive. Active control developed

using classical control theory, even though more expensive, is relatively accurate and reliable for

field operation. Modern control techniques such as fuzzy logic control and neural network

control could be adopted for GLCCs which need more robust, fast acting, and predictable

controllers. In this investigation, it is proposed to design, develop and evaluate a GLCC passive

control system which is capable of controlling the GLCC liquid level, eliminating liquid carry-over

and gas carry-under. The specific objectives of this investigation are given below.

♦ Develop a steady-state model for GLCC control of liquid level and pressure and

perform a system sensitivity analysis.

♦ Conduct experimental investigations to establish the GLCC operational envelope for

liquid carry-over and to determine the liquid level sensitivity. The experimental data

are compared with a mechanistic model.

♦ Design and develop a new 3-in. inner diameter (ID) GLCC with a passive control

system. The passive control is carried out by means of a dual edge float with

throttle/orifice assembly for controlling the liquid level in the GLCC.

♦ Conduct an experimental study to investigate the feasibility of passive control of the

liquid level in the GLCC.

A brief review of the relevant literature pertaining to this area is provided in the next

section.

LITERATURE REVIEW

A detailed review of the literature on separation technology presented by Arpandi et al.

(1996) reveals that very little information is available about the optimum design and performance

of the GLCC. Furthermore, existing mathematical models for cyclone separators have been

limited to single-phase flow with low concentration of a dispersed phase. No reliable models are

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available (Motta et al., 1997) for cyclones (conical or cylindrical) that are capable of simulating a

full range of multiphase flows entering and separating in a cyclone.

Even though several investigators have realized that the performance of compact

separators could be improved by incorporating suitable control systems, only a few control studies

have been conducted. Kolpak (1994) developed a hydrostatic model for passive control of

compact separators in a metering loop configuration. This model provides the sensitivity of the

liquid level to the gas and liquid inflow rates. Genceli et al. (1988) developed a dynamic model

for a slug catcher. Roy et al. (1995) discussed the control algorithms in digital controllers and

Galichet et al. (1994) presented the development of a fuzzy logic controller for liquid level

control. Both of the cases dealt with only single-phase liquid flow.

From the above, it could be noted that compact multiphase separation technology research

remains a critical issue for the petroleum industry. The performance of compact separators could

be enhanced considerably by incorporating suitable control systems. An overview of the steady-

state model developed for the GLCC is presented below, followed by a discussion of the

experimental results. A more detailed discussion of the subject is available in Wang (1997) and

Wang et al. (1998).

STEADY-STATE MODELING AND SENSITIVITY ANALYSIS

Equilibrium Liquid Level

The GLCC geometrical parameters and nomenclature are shown in Fig. 3. The liquid level

can be determined for the metering loop configuration by balancing the pressure drops in the gas

and liquid legs between the gas-liquid interface and the outlet of the GLCC.

The pressure drops in the liquid and gas legs are given respectively by:

P PC Q gH

gL L L L

c1 2

2

− =−ρ ρ

(1)

P PC Q gH

g1 2G G G

2G

c− =

−ρ ρ (2)

where, the liquid and gas leg coefficients are given respectively by :

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L

n

1i

m

1i4i

2i25i

iiL d

8K

dLf8

C

π+

π= ∑ ∑

= = (3)

G

n

1i

m

1i4i

2i25i

iiG d

8K

dLf8

C

π+

π= ∑ ∑

= = (4)

Here, n and m are the number of pipe segments and the number of valves and fittings,

respectively. Equating the pressure drop in the liquid and gas legs, as given by Eqs. (1) and (2),

the liquid level relative to the recombination outlet, can be solved as follows:

HC Q C Q

gL L L G G G

L G=

−−

( )( )

ρ ρρ ρ

2 2

(5)

Liquid Level Sensitivity To Inflow Rates

From Eqs. (1) and (2), solving for CL and CG at the initial conditions (set-point):

2LSLSLcSLS Q/)gHgP(C ρρ+∆= (6)

2GSGSGcSGS Q/)gHgP(C ρρ+∆= (7)

in which QGs , QLs , ∆Ps and H s are values of gas and liquid inflow rates, pressure drop across the

gas or liquid leg and liquid level, respectively corresponding to the set point.

Note that adjusting the valves changes the C values. However, changing the inflow rates

does not change the C values, unless the flow regime changes from turbulent to transition or

laminar. Eq (5) may be simplified for the purpose of expressing level sensitivity to inflow rates by

substituting constants LSφ and GSφ as defined by:

)(g/)gHgP()(g/QC GLSLcSGL2LSLLSLS ρ−ρρ+∆=ρ−ρρ=φ (8)

)(g/)gHgP()(g/QC GLSGcSGL2GSGGSGS ρ−ρρ+∆=ρ−ρρ=φ (9)

LSφ and GSφ are the equivalent hydrostatic heads corresponding to the liquid and gas leg frictional

losses, respectively, for the set point conditions. Substituting Eqs. (8) and (9) in Eq. (5) yields:

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HH)Q/Q)(C/C()Q/Q)(C/C( S2

GsGGSGGS2

LsLLSLLS ∆+=φ−φ (10)

Equation (10) shows the response of liquid level in the GLCC to changes in both gas and liquid

inflow rates as well as the gas and liquid leg flow coefficients. It is clear that for constant flow

coefficients, (i.e. CL/CLS = 1 and CG/CGS = 1) there exists a family of ( LSL Q/Q ) and ( GSG Q/Q )

pairs for which there is constant level change ( H∆ = constant).

The sensitivity of the liquid level to liquid flow rate can be obtained by considering the

liquid and gas flow coefficients and the gas flow rate to be constant (i.e. CL/CLS = 1, CG/CGS = 1

and QG/QGS = 1) in Eq. (10). Also, ( ) 1/H LSSGS =φ+φ could be considered as an identity as

HS=( LSφ - GSφ ). Then, the liquid level sensitivity to liquid flow rate is given by:

( )[ ]1Q/QH 2LSLLS −φ=∆ (11)

From Eqns.(8) and (11) it is clear that the lower the set point pressure drop and/or set point liquid

level across the GLCC (indicated by lower LSφ ), the less the sensitivity of the liquid level to the

liquid flow rate. This observation is very significant, especially for a GLCC characterized by

recombined outlet.

Proceeding along similar lines, the liquid level sensitivity to gas flow rate is given as:

( )[ ]2GSGGS Q/Q1H −φ=∆ (12)

From Eqns.(9) and (12), it is clear that the lower the set point pressure drop across the GLCC

(indicated by lower GSφ ), the less the sensitivity of the liquid level to the gas flow rate. It may

also be noted that the sensitivity of the liquid level to the liquid flow rate is higher than that of the

gas flow rate.

Liquid Level Sensitivity To Flow Coefficients

Similar to the inflow rates, the sensitivity of the liquid level to the gas and liquid leg flow

coefficients as a function of their corresponding valve openings is also an important GLCC liquid

level control parameter. For constant inflow rate conditions, QL/QLS = 1 and QG/QGS = 1.

Substituting these conditions in Eq. (10) yields,

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HH)C/C()C/C( SGSGGSLSLLS ∆+=φ−φ (13)

The sensitivity of the liquid level to liquid leg flow coefficient can be obtained by

considering gas valve opening remaining constant, i.e. CG/CGS = 1. As ( ) 1/H LSSGS =φ+φ , the

liquid level sensitivity to liquid leg flow coefficient is given by:

( )[ ]1C/CH LSLLS −φ=∆ (14)

Equation (14) indicates that the change in liquid level is directly proportional to the change in

liquid leg flow coefficient. From Eqs. (8) and (14), it may also be noted that the higher the set

point pressure drop across the GLCC, the higher the sensitivity of the liquid level to liquid leg

flow coefficient.

Similarly, the liquid level sensitivity to gas leg flow coefficient is given as:

( )[ ]GSGGS C/C1H −φ=∆ (15)

Note that, the sensitivity of the liquid level to liquid leg flow coefficient is higher than that of the

gas leg flow coefficient.

Sensitivity Of GLCC Pressure To Inflow Gas Rate And Gas Leg Flow Coefficient

Neglecting the hydrostatic head of the gas column, (as ρG << 1), the pressure drop across

the GLCC (∆P) can be solved from Eq. (2) as:

( )( )2GSGGSGGS

c

2GGG Q/QC/C

gQC

P φ′=ρ=∆ (16)

where, GSφ′ is a constant and is the set point pressure drop in the GLCC given by:

Sc

2GSGGS

GS Pg

QC ∆=ρ=φ′

Equation (16) shows that the higher the gas flow rate above the set point, the higher is the

sensitivity of the GLCC pressure drop. It may be noted that the sensitivity of GLCC pressure

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drop to gas flow rate is higher for higher set point pressure. Similarly, the GLCC pressure drop is

directly proportional to the gas-leg flow coefficient.

EXPERIMENTAL RESULTS

In this study, a GLCC equipped with a passive control system was fabricated and used for

the experimental investigation. This section discusses the specific details of the experimental

facility, experimental setup and procedure, and the experimental results. The experimental results

are used to compare salient modeling predictions.

Experimental Test Facility

The experimental two-phase flow loop consists of a metering section to measure the single-phase

gas and liquid flow rates, and a GLCC test section where all the experimental data are acquired.

A standard metering section was used for the experimental investigations. Details are given

below.

Metering Section

The metering section is comprised of two parallel, single-phase feeder lines to measure

single-phase gas and liquid flow rates. A two-phase mixture is formed at the mixing tee and is

delivered to the test section. Air is used as the gas phase, which is supplied to a gas tank by an air

compressor with a capacity of 250 cfm at 120 psig. The gas flow rate into the loop is controlled

by a regulating valve and metered utilizing a combination of a mass flow meter and an orifice flow

meter.

The liquid phase is supplied from a 40 gallon storage tank at atmospheric pressure and is

pumped to the liquid feeder line with a centrifugal pump. Similar to the gas phase, the liquid flow

rate is controlled by a separate regulating valve and is metered using orifice and mass flow meters.

The single-phase gas and liquid streams are combined at the mixing tee. Check valves, located

downstream of each feeder, are provided to prevent the occurrence of back flow. The two-phase

mixture downstream of the test section is separated utilizing a conventional separator. The gas is

vented to the atmosphere and liquid is returned to the storage tank to complete the cycle.

GLCC Test Section

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A schematic of the design of the GLCC equipped with passive control is given in Fig. 4.

The test facility is divided into 4 parts:

1. The 3-in. ID GLCC with the dual inlet configuration, as shown on the left hand side;

2. The passive control system, shown in the center;

3. Liquid carry-over trap on the gas leg; and

4. The recombination section, as shown on the right hand side.

The dual inlet of the GLCC consists of a lower inlet and an upper inlet (refer to Fig. 4).

The lower inlet is 3-in. diameter pipe, terminating at the GLCC with an inlet having a slot/plate

configuration with an area of 25% of the inlet pipe cross-sectional area. The upper inlet is simply

a reduced pipe with a full bore 1.5-in. ID “slot” into the GLCC. The area of the cross-section of

the inlet pipe is also 25% of that of the inlet pipe.

A passive control system is designed for the lower inlet to throttle the flow at either of the

GLCC outlets by the movement of a float controlled by the liquid level. The response of such a

passive control system could be considered to be similar to that of a control valve with quick-

response characteristics. Table 1 illustrates the gas and liquid throttle valve response as the liquid

level changes. The passive control system consists of a float chamber and a float assembly. The

float assembly consists of a float, two throttles and a connecting rod between the float and the

throttles. For high liquid and low gas rates the liquid level in the GLCC will increase, pushing the

float upwards. The upper throttle will engage into the upper orifice, blocking the passage of the

gas and avoiding liquid carry-over. As a result of the pressure increase, the liquid level is pushed

downwards. On the other hand, for high gas and low liquid rates, the liquid level in the GLCC

decreases. This will result in the float moving downwards, and the lower throttle engaging with

the lower orifice. Thus, the passage of the liquid will be blocked, avoiding gas carry-under and

increasing the liquid level in the GLCC. The float assembly design includes buoyancy force and

gravity force calculations. In order to make the float assembly move up and down with the liquid

level in the float chamber, the total weight of the float assembly should be less than the buoyancy

force applied on the float.

The GLCC is equipped with a level indicator (sight gauge) installed in parallel to the body

of the separator, and a differential pressure transducer, which gives a measure of the liquid level.

The separated gas and liquid phases are metered by means of a gas vortex shedding meter

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(located in the gas leg) and a mass flow meter (in the liquid leg). The average pressure of the

GLCC is measured by an absolute pressure transducer located in the GLCC. The temperature

and density of the liquid phase are also measured by the mass flow meter.

All output signals from the sensors, transducers and metering devices are terminated at a

central panel, which in turn is connected to the computer through an A/D converter. A data

acquisition setup is built in to the computer using suitable software, to acquire data from the

instrumentation. This setup is capable of fixing the sampling frequency at specific rates, as

desired. The sampling rate was set at 2 Hz for the flow meter and 50 Hz for the differential

pressure transducer. Once the steady condition is established, an arithmetic average of data

collected for two minutes duration is computed as the final value of the quantity measured.

A regular calibration procedure, employing a high-precision pressure pump, has been

performed on each pressure transducer on a regular schedule, to guarantee the precision of

measurements. The temperature transducers consist of a Resistive Temperature Detector (RTD)

sensor, and an electronic transmitter module calibrated with an ice bath.

Experimental Results And Model Predictions

In this section, the experimental results on the GLCC performance, including the

operational envelope for liquid carry-over, passive control system performance, and dual inlet

performance are compared with the model prediction.

Operational Envelope for Liquid Carry-Over

Liquid carry-over is the initiation of liquid entrainment into the discharged gas stream at

the top of the GLCC. It occurs under extreme operating conditions of high gas and/or high liquid

flow rates. Plotting the locus of the liquid and gas flow rates at which liquid carry-over is

initiated provides the operational envelope for liquid-carry over. The area below the envelope is

the region of normal operating condition. In this region, no liquid carry-over is experienced in the

separator. The region above the operational envelope represents the flow conditions for

continuous liquid carry-over .

Single Inlet: Figure 5 illustrates the operational envelopes for liquid carry-over and the

corresponding liquid level in the GLCC for single lower inlet without control. The experimental

results are presented as scattered points. The single inlet operational envelope is characterized by

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three regions, namely churn, annular and transition. The mechanistic model predictions are shown

as a solid line. In the churn region, characterized by Vsg < 10 ft/s, the liquid level in the GLCC is

above the inlet and the mechanism of liquid carry-over is by churn flow. Here, as the liquid level

is above the inlet, it is easier for the liquid to be blown out by incoming gas flow. The liquid level

in the annular region, characterized by Vsg > 18 ft/s, is below the inlet and the mechanism of

liquid carry-over is by droplets carried in a high velocity gas stream. The liquid flow rate for the

onset of liquid carry-over has a linear trend with the gas flow rate in this region. Between the

churn and annular regions is the transition region, characterized by 10 ft/s < Vsg < 18 ft/s, in which

the liquid level is around the inlet. The mechanism of liquid carry-over is churn flow or annular

flow. In this region, the liquid flow rate for the onset of liquid carry-over is fairly constant for

increase in gas flow rate. This is because the liquid level shifts from above the inlet to below the

inlet as the gas flow rate increases.

The mechanistic model used for predicting the operational envelope for liquid carry-over is

a revised version of the model presented by Arpandi et al. (1996). Details of the model are

available in Movafaghian (1997). As illustrated in Fig. 5, the liquid level and the operational

envelope predicted by the model match very closely with the experimental results. The marginal

deviation of the operational envelope from the model at the annular flow region could be due to

the unpredictable behavior of the gas trap added in the liquid leg of the GLCC.

Passive Control: One can intuitively expect that, when the passive control system is

activated, liquid level will be maintained around the inlet (lower inlet). Thus, the operational

envelope for the onset of liquid carry-over can be improved in the churn region because of the

lower liquid level compared to that of the single inlet without control. The operational envelope

for passive control is shown in Fig. 6. The operational envelope is expanded in the churn region.

For very high liquid flow rates, the passive control system fails to work, as it blocks the liquid

outlet. At this condition, the momentum force of the liquid acting on the throttle at the liquid leg

is larger than the buoyancy force of the float, which causes the throttle to block the liquid orifice.

This problem could be compensated by opening the liquid leg valve to bypass the liquid to the

downstream, which could provide an operational point (point 'A' in Fig. 6) for liquid carry-over at

larger liquid flow rates. The passive control system fails to work for high gas flow rate

conditions, as it blocks the gas outlet. At this condition, the momentum force of the gas acting on

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the throttle at the gas leg is larger than the gravity force of the float, which causes the throttle to

block the gas orifice. This problem could be compensated by opening the gas leg valve so as to

bypass the gas to the downstream. At slug flow conditions, due to its quick response

characteristics, the passive control system was exhibiting oscillatory response, causing marginal

instability. The performance of the passive control system could be improved further (as a future

activity) through suitable modifications of the float chamber.

Dual Inlet: A dual inlet configuration significantly improves the performance of the GLCC

for liquid carry-over, as shown in Fig. 6 by the upper most curve. The operational envelope is

almost parallel to that for a single inlet. The operational envelope is improved in all the three

regions, namely, churn, annular and transition. Note that in the churn region, for 7 ft/s<Vsg<10

ft/s, the performance of the dual inlet is better than the performance of the passive control system.

The significant advantage of the dual inlet is the effect of pre-separation. Stratified flow occurs in

the inclined inlet pipe; the upper inlet takes the gas flow to the top of the GLCC, while the liquid

flow through the lower inlet. For high gas flow rates, annular flow occurs in the inlet pipe. Both

inlets take the mixture of gas and liquid. The lower inlet is rich in liquid, and the upper inlet is

rich in gas, which increases the efficiency of separation for liquid carry-over. Thus, the

operational envelope can be improved with a dual inlet for all flow regimes.

GLCC Liquid Level and Pressure: Figure 6 presents a plot of GLCC equilibrium liquid level

corresponding to the operational envelopes for single inlet, dual inlet and single inlet with a

passive control system. The equilibrium liquid level corresponding to the dual inlet shows a linear

trend with increase in the gas flow rate and is found to be marginally higher than the liquid level

corresponding to the operational envelope of the GLCC with a single inlet. However, the

equilibrium liquid level of the GLCC operated with a passive control system is maintained around

the inlet. Figure 7 shows a plot of GLCC pressures corresponding to the operational envelopes

for single inlet, dual inlet and single inlet with passive control system. The GLCC pressure is

found to be higher for higher gas flow rates. The GLCC pressure for passive control is higher

than that for single inlet without control. This is because more pressure drop occurs at the

orifices and the throttles in the gas and liquid legs. Compared to the single inlet, the dual inlet can

tolerate higher liquid flow rates for the same gas flow rate for the onset of liquid carry-over.

Hence, the GLCC pressure is higher for dual inlet configuration.

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Liquid Level Sensitivity to Inflow Rates

For a given system, the liquid level is a function of inlet gas and liquid flow rates. By

balancing the pressure drop across the gas and liquid legs, the liquid level can be maintained at the

same level for a combination of gas and liquid flow rate conditions. Figure 8 illustrates the

combinations of gas and liquid flow rates for three different liquid levels (set point, 6-in. below,

and 6-in. above the set point). The X-axis of Fig. 8 gives the ratio of the in-situ gas flow rate to

the set point gas flow rate and the Y-axis gives the ratio of the in-situ liquid flow rate to the set

point liquid flow rate. This figure provides a measure of the sensitivity of the liquid level to the

inflow rate conditions. The solid lines correspond to the model predictions (see, Eq. (10)) and the

broken lines show the experimental results. Given a specific liquid flow rate ratio (say, QL/QLS =

0.8), the change in the gas flow rate ratio which causes the liquid level to increase 6-in. above the

set point is a 44% reduction of the initial gas flow rate. For a decrease 6-in. below the set point,

an increase of 131% of the initial flow rate is required. Given a specific gas flow rate, the liquid

flow rate change can also be similarly determined. For lower gas flow rate conditions, the model

shows good conformance with the experimental results; whereas, for higher gas flow rate

conditions, the prediction shows some deviations. This is because the liquid trap in the gas leg

creates significant pressure drop, which pushes the liquid very low. In this case, the operational

envelope is extended for high gas flow rates.

CONCLUSIONS

The specific conclusions derived from this investigation are given below:

1. A steady-state model for control of the GLCC loop configuration has been developed which

can predict the equilibrium liquid level and GLCC pressure.

2. Detailed analysis of the system sensitivity indicates that the equilibrium liquid level is more

sensitive to the liquid flow rate and the GLCC pressure is more sensitive to the gas flow rate.

Hence, liquid level control could be achieved effectively by a control valve in the liquid outlet

and GLCC pressure control could be achieved by a control valve in the gas outlet.

3. GLCC pressure is less sensitive to inlet gas flow rate when lower friction losses exist in the

gas leg. Similarly, equilibrium liquid level is less sensitive to liquid flow rate in the presence of

lower friction losses in the liquid leg. Thus, for GLCCs characterized by higher friction losses

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in the gas and the liquid legs, and GLCCs in which the gas and liquid outlets are not

recombined, active control systems are needed for GLCC pressure and liquid level control.

4. Detailed experimental data were acquired to establish the GLCC operational envelope for

liquid carry-over and to determine the liquid level sensitivity. The data have been compared

with the predictions of the modified mechanistic model by Arpandi et al. (1996). A new 3-in.

GLCC equipped with a passive control system has been designed and fabricated.

5. Experimental results showed that the passive control system considered does improve the

GLCC performance for liquid carry-over, but worked in a restricted range of flow conditions.

The passive control system could be extended for large liquid flow rates by bypassing the

liquid using a by-pass valve.

6. The dual inlet configuration of the GLCC, characterized by a reduced pipe slot upper inlet and

a sector slot/plate lower inlet, provides significant merit in terms of a wider operational

envelope for liquid carry-over, compared to a single inlet configuration or passive control

configuration.

ACKNOWLEDGMENTS

The authors wish to thank Chevron Petroleum Technology Co. and the other member companies

of the Tulsa University Separation Technology Projects (TUSTP) for supporting this project.

REFERENCES

1. Arpandi, I., Joshi, A. Shirazi, S., Shoham, O. and Kouba, G.: "Hydrodynamics of Two-Phase

Flow in Gas-Liquid Cylindrical Cyclone Separators", SPE 30683, presented at the SPE 70th

Annual Meeting, Dallas, October 22-25 (1995), SPE Journal, December 1996, p. 427-436.

2. Galichet et al. “Fuzzy Logic Control of a Floating Level in a Refinery Tank,” LAMII 41,

Avenue de la plaine, BP 806, 74016 Annecy Cedex, France, 1994.

3. Genceli, H., Kuenhold, K., Shoham, O. and Brill, J.P.: “Dynamic Simulation of Slug Catcher

Behavior,” presented at the SPE 63rd Annual Meeting, Houston, October 2-5, 1988.

4. Kolpak, M. M.: “Passive Level Control in Two-Phase Separator,” Arco Exploration and

Production Technology, 1994.

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5. Kouba, G., Shoham, O. and Shirazi, S.: "Design and Performance of Gas-Liquid Cylindrical

Cyclone Separators", presented at the BHR Group 7th International Meeting on Multiphase

Flow, Cannes, France, June 7-9, 1995.

6. Motta, B., R., F., Erdal, F. M., Shirazi, S., A., Shoham, O. and Rhyne, L., D.: “Simulation of

Single-phase and Two-Phase Flow in Gas-Liquid Cylindrical Cyclone Separators”, presented

at the ASME Summer Meeting, Fluid Eng. Division, Vancouver, Canada, June 22-26, 1997.

7. Movafaghian, S.: “The Effects of Geometry, Fluid Properties and Pressure on the Flow

Hydrodynamics in Gas-Liquid Cylindrical Cyclone Separators,” M.S. Thesis, The University

of Tulsa, 1995.

8. Roy et al. “Better Than Averaging Level Control,” University of South Florida, 1995.

9. Wang, S.: “Control System Analysis of Gas-Liquid Cylindrical Cyclone Separators,” M.S.

Thesis, The University of Tulsa, 1997.

10. Wang, S., Mohan, R., Shoham, O. and Kouba, G.: “Performance Improvement of Gas-Liquid

Cylindrical Cyclone Separators Using Passive Control System,” to be presented in the ASME

Energy Sources Technology Conference and Exhibition, ETCE ’98, Houston, TX, Feb. 2-4,

1998.

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Table 1-Valve response to the liquid level

LIQUID LEVEL

GAS VALVE

(ORIFICE)

LIQUID VALVE

(ORIFICE)

abovemaxS HH ∆+ fully closed fully open

SH half open half open

belowmaxS HH ∆− fully open fully closed

Where SH = mid-way between the highest and lowest acceptable level

∆H max = largest allowable deviation in liquid level

17

Dev

elop

men

t

GLCC’s

FWKOCyclones

Emerging

Gas Cyclones

Conventional Horizontal and Vertical Separators

Growth

Finger Storage Slug Catcher

Vessel TypeSlug Catcher

Maturity

Time

Hydrocyclones

Fig. 1 - ‘S’ Curve for Developmental Ranking of Separation Technology

Fig. 2 - Gas-Liquid Cylindrical Cyclone Configuration

18

GasMeter

Liquid Meter

Inlet Flow

OutletFlow

Liquid Leg

Gas Leg

H

LG1

LG2

LG3

LL1

LL2

LL3

Gas-Liquid Interface

Fig. 3 -Schematics and Nomenclature of GLCCLoop Configuration

P1

P2

d1

d 3

d 2

19

3”

3”

6”

3”

1/8” 3/8”

Fig. 4 -Schematics of GLCC Loop With Passive Control

26”

21”

6”

24”

24”

48”

60”

6”

24”

12”

2”

1”or 2”

1.5”

8”

30”

8”

24” 43”

111”

5”

27”

9”

24”

26”

24” 23” 16” 38” 3” 10” 61”

79”

27”8”5”

10”

1.5”

8”6”

21”

MM

5” 3”

#2

#1

3”10”

20”

20”

4”

2.5”

Flat plate tangent (top view of inlet)

3”

2”

0.75”

1”

10”

3”

Nozzle tangential inlet

1.5”

gas leg

liquid leg

liquidcarry-over trap

floatchamber

Recomb-inationSectionGLCC

20

Fig. 5-Comparison of Operational Envelope With Model PredictionFor Liquid Carry-Over

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

0 5 10 15 20 25 30

Vsg (ft/s)

Vsl

(ft/s

)

0

2

4

6

8

10

12

14

16

18

20

Liqu

id L

evel

(ft)

ModelData

Operational Envelope

Liquid Level

21

Fig. 6 - Liquid Level Corresponding to Operational Envelopenvelope

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

0 5 10 15 20 25 30

Vsg (ft/s)

Vsl(ft/s)

-1

1

3

5

7

9

11

13

15

Single Inlet (no control)

Single Inlet (passive control)

Dual Inlet (no control)

LiquidLevel(ft)

Vsl

LL

22

Fig. 7 - GLCC Pressure Corresponding to Operational Envelope

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

0 5 10 15 20 25 30

Vsg (ft/s)

Vsl(ft/s)

0

10

20

30

40

50

60

70

80

90

100

Single Inlet (no control)

Single Inlet (passive control)

Dual Inlet (no control)

Pressure(psi)

Pressure

23

QGs=0.886 (ft /s)3

Q

∆ H ft= 0 ( )∆H ft= − 0 5. ( )

∆H ft= + 0 5. ( )

Ls=0.05 (ft /s)3

Fig. 8 - Liquid Level Sensitivity to Inflow Rates

0

0.2

0.4

0.6

0.8

1

1.2

0 0.2 0.4 0.6 0.8 1 1.2

Data

Model

QG / QGS

QL / QLS

QGS = 0.886 (ft3/s)QLS = 0.05 (ft3/s)

24

NOMENCLATURE

C = flow coefficient (1/ft4)

d = diameter (ft)

f = friction factor

g = acceleration due to gravity (ft/s2)

gc = units conversion constant (lbm.ft/lbf.s2)

H = liquid level relative to recombined outlet (ft)

K = fitting resistance coefficient

L = length (ft)

m = number of valves and fittings

n = number of pipe segments

P = pressure (lb/ft2)

Q = volumetric flow rate (ft3/s)

V = velocity (ft/s)

∆ = incremental deviation

φ = frictional loss coefficient

ρ = density (lbm/ft3)

π = 3.141592654

Subscripts

G = gas

L = liquid

max = maximum

s = set point value

sg = superficial gas

sl = superficial liquid