Boiler Steam Drum Level Control

• Drum Level Control Systems are used extensively throughout the process industries and the Utilities to control the level of boiling water contained in boiler drums on process plant and help provide a constant supply of steam. 
• If the level is too high, flooding of steam purification equipment can occur. If the level is too low, reduction in efficiency of the treatment and re circulation function. Pressure can also build to dangerous levels. 
• A drum level control system tightly controls the level whatever the disturbances, level change, increase/ decrease of steam demand, feed water flow variations.

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Types of logic block algorithms ( gates)

1. Null (NULL)
2. AND Gate (AND)
3. OR Gate (OR)
4. NOT Gate (NOT)
5. NAND Gate (NAND)
6. NOR Gate (NOR)
7. XOR Gate (XOR)
8. Qualified OR Gate with 2 inputs On (QOR2)
9. Qualified OR Gate with 3 inputs On (QOR3)

1. Compare Equal with Deadband (EQ)
2. Compare Not Equal with Deadband (NE)
3. Compare Greater then with Deadband(GT)
4. Compare Greater then or Equal with Deadband(GE)
5. Compare Less then  with Deadband(LT)
6. Compare less then or Equal with Deadband(LE)  

• Check for Bad(CHECKBAD)

1. Fixed size bulse(PULSE)
2. Pulse with maximum Time Limit(MAXPULSE)
3. Pulse with Minimum Time Limit(MINPULSE)
4. Delay(DELAY)
5. On Delay(ONDLY)
6. Off Delay(OFFDLY)
7. Watchdog Timer(WATCHDOG)
8. Flipflop(FLIPFLOP)
9. Change Detect(CHDETECT)       

How to restart the GUS station ?

• start
• log in- administrator 
• LCN P windows status  under  status  column  power-ON  wait for 2 min
• open native windows 
• select Load button on right corner screen 
• screen will show WN 1,2,3........  then type N then press enter 
• wait 1 min 
• system status will be on screen 

other option 

•      start - enter 
•   select  program 
• select Honeywell TPS
• select native window 
• select control
• then load

screen will show WN 1,2,3........  then type N then press enter 

then screen will show OPR, UND X..  then type O then press enter 

load in progress wait for 2min 

SIL ( Safety Integrity Level )

                    SIL is defined as a relative level of risk reduction provided by a safety function or to specify a target level of risk reduction. In simple terms SIL is a measurement of performance required for a instrumental function.

                     SIL is the functional safety standards based on IEC 61508, SILs are defined,with SIL 4 is the most dependable and SIL 1 is being the least.

                      There are several methods are used to assign a SIL, these are normally used in combination, and may include,
 1. Risk matrices
 2. Risk graphs
 3. Layers of production analysis(LOPA)                
   this 3 are normally used

SIL level chart :

PFD(probability of failure demand ) and RRF(Risk reduction factor )

For Low demand operation:
SIL         PFD                                   PFD(power)                   RRF
  1          0.1-0.01                            10-1 to 10-2                   10-100
  2          0.01-0.001                        10-2 to 10-3                   100-1000
  3          0.001-0.0001                    10-3 to 10-4                   1000-1000
  4          0.0001-0.00001                10-4 to 10-5                   1000-10000

For Continuous  Operation 
SIL         PFD                                                 PFD(power)                    RRF
  1          0.00001-0.0000001                          10-5 to 10-6                  100,000-1,000,0000
  2          0.000001-0.00000001                      10-6 to 10-7                  100,000-10,000,0000
  3          0.0000001-0.000000001                  10-7 to 10-8                  10,000,000-100,000,000
  4          0.00000001-0.0000000001              10-8 to 10-9                  100,000,000-1,000,000,000

ESD(Emergency Shutdown ) System

                 ESD shutdown is required to perform a safe process shut down (trip) if any of the unsafe conditions occur .

                  By the safety standard IEC 61508 the functions of an ESD and a process control system cannot be shared -- the safety system must be separate. 

Layers of Protection