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Oil & Gas Separation Book 2 > Oil & Gas Separation Book 2 > Flashcards

Oil & Gas Separation Book 2 Flashcards

1
Q

What 2 major controls do separators have in order to maintain optimum separation and this production? (2)

A
  • Liquid level control

- Pressure control

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2
Q

In any continuous process such as oil and gas separation there are a number of factors which must be kept within certain limits.

(a) What are these factors referred to as? (1)
(b) What are the 4 factors that must be kept within certain limits?

A

(a)

Process Variables

(b)

  • Liquid Level
  • Pressure
  • Temperature
  • Fluid Flow
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3
Q

What does an oil and gas separation system rely on having built into it to achieve the desired control for optimum separation? (1)

A
  • Control Loop
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4
Q

Describe:

(a) Closed Control Loop
(b) Open Control Loop

A

(a) An AUTOMATIC system which controls the separation parameters for optimum separation.
(b) An open control loop has a MANUAL input to control a system variable.

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5
Q

What are the four main elements in a closed control loop? (4)

A
  • The Process Variable (Liquid, Pressure, Temperature, Flow)
  • The Measuring Unit (Displacer Mechanism, LI, PI, PT)
  • The Controller (Pneumatic)
  • The Correcting Unit (Valve)
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6
Q

In a closed control loop we have 4 main elements listed below. Describe what each element is:

(a) - The Process Variable (1)
(b) - The Measuring Unit (2)
(c) - The Controller (2)
(d) - The Correcting Unit (3)

A

(a) - The Process Variable:
- Is the part of the process which has to be controlled within certain limits (i.e. level, pressure etc).
(b) - The Measuring Unit:
- DEVICE (such as a pressure transmitter, or level indicator) which MEASURES THE ACTUAL VALUE of the variable such as pressure or flow)
- Obtains the MEASURED VALUE
(c) - The Controller:
- The MEASURED VALUE of the process variable is COMPARED against the DESIRED VALUE.
- If it senses a deviation between the two, it sends a SIGNAL to the CORRECTING UNIT
(d) - The Correcting Unit:
- This part of the control loop is usually a VALVE
- RECEIVES SIGNAL from correcting unit
- MEASURED VALUE returns to DESIRED VALUE

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7
Q

Separator liquid level control is required for:? (5)

A
  • To prevent liquids being carried out with the gas (known as carry-
    over)
  • To prevent gas from leaving the separator through the liquid outlet. This is known as blow by or blow round
  • To help maintain the pressure on the vessel (Fluctuating levels affect the pressure)
  • In a three phase separator, to prevent oil from leaving through the water outlet or vice versa
  • To ensure optimum retention time
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8
Q

What does ‘Blow By’ or Blow round mean? (1)

A
  • When gas leaves a separator through the liquid outlet due to the levels not being maintained to the desired value.
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9
Q

What could fluctuating levels of liquid alter in side a separator? (1)

A
  • Fluctuating liquid levels affect the pressure inside the vessel)
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10
Q

Draw a diagram showing a simple Oil Level Control System for a two phase horizontal separator (5)

Showing:

  • Separator with corrects inlets/outlets (3)
  • Displacer Mechanism (Measuring Unit)
  • Level Controller
  • Level Control Valve
  • Process Flow
A

Shows:

  • Separator with corrects inlets/outlets (3)
  • Displacer Mechanism (Measuring Unit)
  • Level Controller
  • Level Control Valve
  • Process Flow
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11
Q

What is

a) Displacer Mechanism? (2
(b) How does it operate? (5)

A

(a)

  • Piece of equipment which measures liquid level by a method which is:
  • Based on the principle of Archimedes

(b)

  • Usually a cylindrical weight partially submerged in a liquid
  • If the levels rise and fall, more or less of the cylinder will be submerged. Its apparent weight will therefore vary.
  • The weight can then be measured to give an indication of the level of the liquid.
  • The loss or gain of apparent weight is transmitted to the controller as a signal which is proportional to the increase or decrease in liquid level.
  • Signal transmission is achieved by means of a torque tube assembly
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12
Q

What are:

(a) The basic components of a torque tube assembly? (6)
(b) Describe what each component is/does (6)
(c)
(i) What is the rotation of the torque tube transmitted to?
(ii) How is the

A

(a):

  • Float Rod
  • Knife Edged Bearing
  • Torque Tube
  • Torque Tube Plate
  • Outer Flange
  • Torque Tube Rod

(b) :
- Float Rod: - What the displacer is attached to. As the liquid level inside the vessel goes down the weight on the float rod will increase, the increased weight hanging on the torque tube will twist the torque rod which is connected to the level controller.
- Knife Edged Bearing: - The component which the Float rod is resting on, its in the shape of a triangle allowing the rod to rock up or down on the knife edge of the bearing.
- Torque Tube: - A hollow rod which the torque tube rod fits inside.
- Torque Tube Rod: - Fits inside the torque tube and is welded at the torque tube plate
- Torque Tube Plate: - The component which the displacer is attached to and the torque tube rod is welded to
- Outer Flange: - The housing in which all the components fit inside.

(c)

(i) To the next element in the control loop - The Controller
(ii) Rotation transmitted via linkage

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13
Q

What is the job of The Controller (2)

A
  • To compare two values, the measured value signal and the desired value signal
  • If a deviation exists, it sends a correcting signal to the control valve
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14
Q

In a Pneumatic Controller, what are the four separate but interconnected units?

A
  • The Differential Mechanism
  • The Flapper/Nozzle Assembly
  • The Feedback Unit
  • The Pilot Relay
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15
Q

Draw a block diagram showing the four units of a pneumatic level controller (10)

A

Shows:

  • Four Units of Controller (4)
  • Measured Value Input (1)
  • Desired Value Input (1)
  • Route to Correcting Element (valve) (1)
  • Air in and correct pressure (2)
  • Controller Limits (1)
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16
Q

What two types of Differential Mechanism exist? (2)

A
  • The Motion Balance Mechanism

- The Force Balance Mechanism

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17
Q

Inside a level controller What is the job of the Differential Mechanism? (2)

A
  • Compare the desired value against the measured value
  • If a deviation exists between the two, the Differential Mechanism feeds the information to the next unit in the controller: The Flapper/Nozzle Assembly
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18
Q

How does a Motion Balanced Differential Mechanism Operate? (3)

A
  • Uses 2 mechanical linkages to compare the MV & DV.
  • One end of The MV Link DV Link are attached to the Differential Arm which is connected to the Deviation Link
  • The Deviation Link transmits any motion of the Differential Arm to the Flapper/Nozzle Assembly.
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19
Q

Draw a diagram of a Motion Balanced Differential Mechanism (1)

A

Shows:

  • MV Link
  • DV Link
  • Differential Arm
  • Deviation Link
  • Movement Direction & Interaction
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20
Q

(a) - How does a Force Balance Differential Mechanism Operate? (5)
(b) - Describe the action of this mechanism (3)

A

(a)
- Uses pressure applied to bellows to compare desired and measured values
- Output from the measuring element fed as a pressure to the Measured Value Bellows
- Movement of bellows is opposed by a second set of bellows
- The Desired Value Bellows are pressurised by a signal which relates to the desired value of the process variable.
- Between the two bellows is one end of a bar known as a Force Bar. The bar is pivoted using a fulcrum. The other end from the bellows is free to move.

(b)

  • If the measuring element output gave an increased signal, the MV bellows would expand against the DV bellows
  • This movement would cause the free end of the force bar to move
  • Movement then fed to the flapper/nozzle assembly as a deviation
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21
Q

Which type of Mechanism is most commonly used in pneumatic controllers? (1)

A
  • Force Balance Mechanism
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22
Q

What are the main components of a flapper assembly? (3)

A
  • The Flapper
  • The Nozzle
  • The Restrictor
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23
Q

Draw a diagram of a flapper assembly (6)

A

Shows:

  • 20 PSI Air Supply
  • Restrictor
  • Nozzle
  • Flapper
  • Back Pressure Outlet
  • Movement of link from differential unit
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24
Q

What is the job of the flapper assembly (1)

A
  • Send correcting pressure signal from the controller to the final element in the control loop - The Control Valve
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25
Describe how a flapper assembly works (
- Air supply fed to line upstream of restrictor, typically at a pressure of 1.3 bar. - The air can pass through the restrictor to the nozzle outlet and also through the variable back pressure outlet - When flapper is positioned away from nozzle air can pass through the restrictor and out through the nozzle. - Because the diameter of the restrictor is small compared to that of the nozzle there will be very little pressure build up in the space between the restrictor and the nozzle meaning there will be no pressure build up in the back pressure line. - If the flapper is moved towards the nozzle, the area of nozzle through which the air can pass is reduced. This means that the nozzle back pressure will increase. - If the nozzle is completely covered then the back pressure would build up to the supply pressure of 1.3 bar.
26
Draw a graph showing the back pressure against position of flapper relative to the nozzle in a Flapper Nozzle Assembly
Draw from Memory
27
What typical pressure range will pneumatic instruments record, transmit and control in? (1)
- 0.2 to 1 Bar
28
If the movement from a differential unit is linked to the flapper what will occur? (2)
- A varying back pressure signal will be obtained from the nozzle - This signal will be proportional to the deviation between measured and desired values of the process variable
29
What is a feedback unit? (1)
- Feedback simply means feeding back the output signal of the controller to the input of the same unit
30
Describe how a feedback unit works? (5)
- Pivot point of flapper attached to movable end of set of bellows. The movement of bellows is opposed by a spring. - Nozzle back pressure fed to these bellows in addition to being the controller output signal to the correcting unit. - When a deviation occurs, the flapper moves towards the nozzle and causes an increase in back pressure. - The increased bellows pressure will move the pivot point of the flapper against the spring until the spring and bellows forces are balanced - when this happens the flapper moves away from the nozzle until a steady state is reached - When steady state is reached, flapper will have moved very slightly neared to the nozzle — just enough to increase the output to the correcting unit.
31
Draw a digram of a feedback unit (6)
Shows: - Bellows - Spring - Nozzle back pressure line - Nozzle - Flapper - Differential unit arm
32
(a) What is a Pilot Relay? (1) (b) What is its function? (1)
(a) A device which is connected to the nozzle back pressure line. (b) - Its function is to act as a signal amplifier.
33
Draw a block diagram of a closed control loop (7)
Shows: - Process Variable (1) - Measuring Unit (1) - Controller (1) - Correcting Unit (1) - Correcting Signal (1) - Desired Value (1) - Measured Value (1)
34
What is the principle of Archimedes (1)
- The principle states that, if a body is immersed in a liquid, it will apparently lose weight equal to the amount of liquid it displaces.
35
In closed control loop, what is used as the measuring unit? (1)
- Displacer Mechanism
36
What is the function of a control valve?
- To throttle or regulate the rate of flow of a fluid
37
(a) In a Pneumatic Automatic Closed Loop control system, how is the final element in the control loop operated? (1) (b) What is the typical air pressure range of this signal?
- A signal from the controller - In the case of a pneumatic system, the signal is air pressure - 0.2 to 1 bar
38
What components does a diaphragm motor control valve consist of? (6)
- Diaphragm - Actuator Spring - Valve Stem - Valve Body - Valve Plug - Valve Seat
39
How does a diaphragm motor control valve operate? (3)
- Actuator spring holds the valve open (Normally Open Valve) - Control signal (air pressure) applied to the top of the diaphragm as the pressure increases it overcomes the resistance of the actuator spring and closes the valve - 3 PSI will start to close the valve. 15 PSI the valve will be fully closed
40
What is a Fail Open Actuated Valve? (1)
- If there is a complete loss of pressure, the actuator spring will cause the valve to move into the fully open position.
41
What is a Fail Open Closed Valve? (1)
- If there is a complete loss of pressure, the actuator spring will cause the valve to move into the fully closed position
42
What is a Double Ported Valve? (1)
- A valve which has 2 valve plugs and seats
43
Draw a diagram of a Level Control Valve (7)
Shows: - Control signal coming in - Diaphragm - Actuator Spring - Valve Stem - Valve Body - Valve Plug - Valve Seat
44
To which part of the control loop does the Pilot Relay belong? (1)
- Level Controller
45
To which part of the control loop does the Differential Mechanism belong to? (1)
- The Controller
46
To which part of the control loop does the Differential Mechanism belong to? (1)
- The Controller
47
To which part of the control loop does the Flapper/Nozzle Assembly belong to? (1)
- The Controller
48
To which part of the control loop does the Feedback Unit belong to? (1)
- The Controller
49
Which piece of equipment would you find the back pressure outlet on? (1)
- Flapper/Nozzle Unit Assembly
50
Which piece of equipment would you find the MV Bellows and the DV Bellows? (1)
- Force Balanced Mechanism inside a pneumatic controller
51
Which piece of equipment would you find the restrictor on? (1)
- Flapper Nozzle Unit
52
Which piece of equipment would you find a fulcrum on? (1)
- Force Balanced Mechanism inside a pneumatic controller
53
To which part of the control loop does the Torque Tube Rod belong to?
- Measuring Unit
54
To which part of the control loop does the Actuator Spring belong to?
- Correcting Unit Level (Control Valve)
55
To which part of the control loop does the Valve Plug belong to?
- Correcting Unit Level (Control Valve)
56
To which part of the control loop does the Flapper/Nozzle Assembly belong to?
- The Controller
57
To which part of the control loop does the Diaphragm belong to?
- Correcting Unit Level (Control Valve)
58
To which part of the control loop does the Feedback Unit belong to?
- Correcting Unit Level (Control Valve)
59
To which part of the control loop does the Float Rod belong to?
- Measuring Unit
60
To which part of the control loop does the Valve Stem belong to?
- Correcting Unit Level (Control Valve)
61
How would Separator Pressure be controlled with a pressure control loop (
- Bourdon Tube connected via a linkage to the flapper/nozzle assembly - If the pressure rises/falls the Bourden Tube tries to straighten/retract pushing/pulling the flapper away/closer to the nozzle
62
What might result from the following separator malfunctions (6) (a) Oil level goes too high (1) (b) Oil level goes too low (2) (c) Pressure continues to increase (d) Pressure continues to decrease (e) Water level goes too high (f) Water level goes too low.
(a) - Oil gets carried over with the gas, causing problems downstream (b) - Danger of gas leaving the separator through the oil outlet, this is called gas blowby. (c) - Risk of exceeding the safe working pressure of the separator (d) - Insufficient pressure to push the liquids from the separator (e) - If the water level rises above the weir, water will contaminate the oil leaving the vessel (f) - Should the water level go too low, oil will flow from the separator through the water outlet
63
With regards to Level Control & Safety, what components would be connected to the level controller apart from the correction unit? (2)
- LAH | - LAL
64
What would happen if a LAH was activated due to separator liquid levels rising too much? (1)
- An audio/ visual alarm would be generated.
65
How does a separator Level Control Safety System operate?
- LSH Activation (audio/ visual alarm) - LSL Activation (audio/ visual alarm) If the Situation is not rectified after the above coming into alarm: - LSHH or LSLL are activated, these are CONNECTED to the separator INDEPENDENTLY of the level controller if they are activated a signal is sent to the ESD system.
66
What would happen if a LSLL/LSHH are activated on a separator? (1)
- A signal is sent to the ESD system which automatically isolates the vessel and makes it safe, by activating the appropriate ESD valves.
67
What are (a) (i) LSLL & LSHH? (2) (ii) Where are they normally found? (1) (b) What is their function? (2)
(a) (i) - Level Switch Low Low & Level Switch High High (ii) - Connected to the separator independently of the level controller. (b) - If Separator fluid levels continue to rise after the LAH or LAL are activated. - The LSLL or LSHH sends a signal to the ESD valves which automatically isolate the vessel, making it safe
68
Where would the instrumentation relating to Separator Level Control Safety be located? (2)
- Located externally to the vessel | - Mounted on pipework sometimes referred to as an instrument bridle.
69
Draw a diagram on a typical Instrument Bridle of a 3 Phase Horizontal Separator (8)
Shows: - Separator (weirs, oil, water, outlet) - Bridle itself - Level Alarms - Level Switches - Sight Glass 1 - Sight Glass 2 - Overlap of Sight Glasses - Valves in correct position
70
What components would be found on a Level Control Safety System on a Separator? (5)
- LAH - (Level Alarm High) - LAL - (Level Alarm Low) - LSLL - (Level Switch Low Low) - LSHH - (Level Switch High High) - LCV - (Level Control Valve)
71
What components would be found on a Pressure Control Safety System on a Separator? (5)
- PAH - (Pressure Alarm High) - PAL - (Pressure Alarm Low) - PSLL - (Pressure Switch Low Low) - PSHH - (Pressure Switch High High) - PCV - (Pressure Control Valve)
72
How does a separator Pressure Control Safety System operate?
- The Pressure Controller activates the Pressure Control Valve - Pressure Controller generates pressure alarm signals (PAL, PAL) if the pressure goes too high or low. - If the pressure continues to rise/fall after the PAL & PAH have came in, (i.e. a malfunction with the PCV) PSLL or PSHH are activated - these switches are linked to the ESD system - the Separator is then isolated via the ESD valves
73
If the pressure in a separator went to high, it could rupture. What further level of protection against excessive pressure can be fitted to Separators? (1)
- PSV's (Pressure Safety Valves)
74
As part of a separator pressure safety system, you will find PSV,s. (a) - Identify the key information with regards to PSV's being part of a separator Pressure Safety System (5)
- Fitted to the top, or gas section, of the separator Upstream of any de-mister pad. (This is to ensure that, should the de-mister pad become blocked, then the PSVs will still function properly.) - At a pre-determined pressure, which is higher than the set pressure of PSHH - Sizing of the PSVs is determined by the maximum amount of gas which may be required to be vented. - Separators are fitted with two PSVs, either one of which will cope with the full pressure relief requirements of the vessel. - Usual method of operation is that one PSV is ‘on-line’ whilst the other PSV is isolated and on ‘standby’. - An Interlock system, incorporated into the PSV setup in order to prevent both PSV's being put on 'Standby'.
75
(a) What is incorporated into the PSV setup in order to prevent both PSV's being put on 'Standby'. (1) (b) - What does the interlock system allow? (3)
(a) An Interlock system (b) - Both PSVs may be on-line - PSV A may be on-line, or - PSV B may be on-line.

Oil & Gas Separation Book 2 (1 decks)

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