CONTROL VALVES IN SPLIT RANGES

For certain control strategies some valve need to be operated in split range ,i.e, from 0 to 100 % signal two valves operate to maintain the parameter. Inthese cases valves may operate in either of following manner

% SIGNAL

The above figure shows opening of both valves as signal varies from 0 to 100 %

SIGNAL OPEN. OF VALVES% VALVE 1 VALVE 20 100 0

25 50 050 0 075 0 50100 0 100

Example LV - 5 A & B :LV - 5A is the condensate import valve of the carbamate condenser shell sideLV - 5B is the condensate export valve of the carbamate condenser shell side At 50 % output both valves are closedAt 0 % output LV - 5A valve is full open & LV - 5B full closedAt 100 % output LV - 5A valve is full closed & LV - 5B full open

CASE A

25 50 1000

VALVE 1 VALVE 2

CASE B

VALVE 1 VALVE 2

% SIGNAL

The above figure shows opening of both valves as signal varies from 0 to 100 %

SIGNAL OPEN. OF VALVES% VALVE 1 VALVE 20 0 0

25 50 050 100 075 100 50100 100 100

Example PV - 7 A & B .

PV - 5A is the condensate import valve of the carbamate condenser shell side& LV - 5B is the condensate export valve of the carbamate condenser shellside At 50 % output both valves are closedAt 0 % output LV - 5A valve is full open & LV - 5B full closedAt 100 % output LV - 5A valve is full closed & LV - 5B full open

TRIP LOGICS FOR UREA PLANT

The plant operates on fail safe principle which means that in case of an emergency orany undesirable event the plant should move to safe conditions.For this to happen all

critical equipments have been provided with tripping logics so that a particularequipment would be stopped automatically in case of an emergency

IS - 01 TRIP LOGIC FOR TK - 01 / K - 01

IS - 02 TRIP LOGIC FOR H.P SYNTHESIS LOOP

IS - 03 TRIP LOGIC FOR H.P AMMONIA PUMP , P - 01

25 50 1000

IS - 04 TRIP LOGIC FOR H.P CARBAMATE PUMP , P - 02

IS - 05 TRIP LOGIC FOR UREA MELT

IS - 06 TRIP LOGIC FOR INSTRUMENT AIR FAILURE

IS - 08 TRIP LOGIC FOR DRAIN RECOVERY PUMPS P-12A/B

IS - 09 TRIP LOGIC FOR HYDROLYZER TRIP CIRCUIT

IS - 10 TRIP LOGIC FOR HYDROLYZER FEED PUMP

IS - 11 TRIP LOGIC FOR COND. EXTACTION PUMP TRIP

IS - 12 TRIP LOGIC FOR PURIFIED WASTE WATER IS - 16 TRIP LOGIC FOR DEMISTER FLUSHING

TERMS ASSOCIATED WITH TRIP LOGICS

1

2for starting the M/C

3particular tripping cause so that actual tripping occurs onlywhen atleast 2 out of 3 switches for a particular reason actuatesimultaneously

4actuated will cause tripping whereas inactive switch will notcause tripping even on actuation of the switch

5than one tripping switches

6tripping even in case of actual actuation of switch

7knobs to bypass the trip switches

8

DESCRIPTION OF TRIP LOGICS

IS - 1

This trip logic relates to TK - 1/K - 1. All the trip reasons are listed below

PSXL 601

PSXL 02

PSXH 01LSXH 641 High level in surface condenser E - 28PSXH645 High extraction steam pressure

DELAY: Minimum time for which a switch has to remain actuated to cause tripping

READY TO RESET: Condition indicating fullfilment of certain requirements

VOTING LOGIC: Provision of more than one usually three switches for a

ACTIVE / INACTIVE: Indicates the state of switches. An active switch if

FIRST OUT: First reason (switch) on which a m/c trips on actuation of more

BYPASS: Physical condition of a trip cause which will not lead to

HARDWARE SWITCH : Switches provided on DCS consoles in form of

SOFTWARE SWITCH : Switches which can be bypassed from LM only

CO2 Compressor low suction pressure

CO2 Compressor low discharge pressure

CO2 Compressor high discharge pressure

PSXH 648 Turbine exhaust pressure very high

LSXH62ZSXH 650 Compressor,Turbine, Gear box high axial displacementXSXH 650 Compressor, Turbine, Gear box high vibrationSH 650 Turbine high speedPSXL677 Lube oil header pressure lowPSXL690 Lube control oil pressurePSXL 691 Low trip oil pressureLSXH606 High level in 1st interstage separator MV - 16LSXH 609 High level in 2nd interstage separator MV - 17LSXH 612 High level in 3rd interstage separator MV - 18IS 06 Emergency trip: instrument air failure.

On the trip , following actions will be taken by the system automatically.- ESV closes- passivation air flow control valve FV 61 closes- anti surge valve FV 602 opens- Interstage vent valve opens- HV 01 closes

Barring device gets permissive to start only after the following- Normal lube oil pressure- Turbine zero speed achieved- Trip oil pressure switch actuated (PXL 691)

IS 01 restting is permitted only after following :- All the trips switches are in healthy condition- Trip oil switch (PSXL 691) bypassed- Barring device disengaged- Interstage vent valve open indication switch bypassed- FV 602 open- HV 601 open- Overhead tank normal level

IS - 2

This trip logic relates to HP Loop. All the trip reasons are listed below

Trip actuation is on the following- PSXH 06 Reactor high pressure- IS 03 P 1 trip- IS 06 Emergency trip actuation

On the trip , following actions will be taken by the system automatically.- HV 02 closes- FV 34 opens- HV 06 closes- P 1 tripping

High level CO2 knock out drum MV -9

IS 02 restting is permitted only after following :All the trips switches are in healthy conditionP 1 running

IS -3

This trip logic relates to HP AMMONIA PUMP P-1. All the trip reasons are listed below

- PLL 98 Low lube oil pressure in torque convertor- PLL 97 Low lube oil pressure in Gear box- PLL 96 Low lube oil pressure in Crank case- PSXH 31 High dicharge pressure- WSXH 51 Crank case overload protection- IS 02 On the actuation of IS 02

On actuation of pump overspeed switch (SXH 51) , the pump return to minimumspeed. It can be restted only with the help of local hardware push button switchprovided.

IS - 4

This trip logic relates to HP CARBAMATE PUMP P-2. All the trip reasons are listed below

IXL 02 Low current consumptionZXH 501 High axial displacementXXH 501 High vibrationTH 509 High 1st stage thrust bearing temperatureTH 510 High first stage journal bearing tempTH 512 High first stage journal bearing tempTH 516 High second stage journal bearing tempTH 518 High second stage journal bearing tempTH 515 High second stage thrust bearing tempPLL 522 Low lube oil pressurePLL 527 Low seal flush suction pressurePLL 508 Low seal flush flow

IS 04 restting is permitted only after following :

All the trips switches are in healthy conditionPLL 508 Noramal seal flush flowPH521 Normal lube oil pressureTL 503 Normal lube oil tempLL 504 Normal level in lube oil console

IS - 5

This trip is actuated only when for following reasons

- Belt conveyors not running- Scrapper not running- Bucket not running

On the trip , following actions will be taken by the system automatically.

- 11 HS 132 11 Unit prilling diversion to V5- 21 HS 132 21 Unit prilling diversion to V5- HS 137 Flushing steam to bucket side will open

IS - 6

In case of instrument air failure PSXL 301 will actuate, the IS 06 will activate, and this will

IS - 8

The actuation of this trip will give start / off command to P 12 A/B.

IS - 9

This trip will be actuated only when hydrolyser temp goes very high (TXH 160 )And this will result in closing HS inlet to R 02 (FV 165)

IS - 10

This trip will be actuated on following:

IXL 14 Low current consumptionFXL 158 / 159 Low seal flush flow

This will result in the tripping of P 14.

IS - 11

The actuation of this trip will give start / off command to P 23 A/B.

IS - 12

This trip will actuate only when 11AH 161 A (high conc of urea in treated wastewater) actuate.The actuation of this trip will close HV 163 (condensate to DM plant) and open HV 162(recycle to V 6).

IS - 16

This opens the demister pad flushing water valve HV 173 after every 15 mins for aduration of 15 sec

result in the tripping of CO2 compressor (IS 01) and IS 02