DYNAMIC SIMULATION OF THEDYNAMIC SIMULATION OF THE COMPRESSIONCOMPRESSIONSYSTEM OF A DELAYED COKING UNITSYSTEM OF A DELAYED COKING UNIT
AuthorsAuthors::André Gonçalves OliveiraAndré Gonçalves Oliveira
Barbara Damásio de CastroBarbara Damásio de Castro CioquetaCioquetaNeydeNeyde Alexandra Fraga MarquesAlexandra Fraga Marques
SS SIM-02, Part 1
October // 2013
AuthorsAuthors::André Gonçalves OliveiraAndré Gonçalves Oliveira
Barbara Damásio de CastroBarbara Damásio de Castro CioquetaCioquetaNeydeNeyde Alexandra Fraga MarquesAlexandra Fraga Marques
AGENDA
Introduction
Process Description
Delayed Coking Unit
Gas Compression System
Dynamic Simulation
Cases Study
Solutions
Conclusion
Introduction
Process Description
Delayed Coking Unit
Gas Compression System
Dynamic Simulation
Cases Study
Solutions
Conclusion
INTRODUCTIONINTRODUCTION
INTRODUCTION
During a Throughput Test of a Delayed Coking Unit(DCU), it was identified operational bottlenecks insome systems, among them Pressure Safety Valves(PSV)
An evaluation of the PSV installed in the interstagedrum of the Compression System was done using theDYNSIM, considering some emergency scenarios toanalyze the PSV relief capacity and the safety of theDCU
The simulation extended from the top of the mainfractionator to the high pressure drum, downstreamthe compressor, including the anti-surge system
During a Throughput Test of a Delayed Coking Unit(DCU), it was identified operational bottlenecks insome systems, among them Pressure Safety Valves(PSV)
An evaluation of the PSV installed in the interstagedrum of the Compression System was done using theDYNSIM, considering some emergency scenarios toanalyze the PSV relief capacity and the safety of theDCU
The simulation extended from the top of the mainfractionator to the high pressure drum, downstreamthe compressor, including the anti-surge system
PROCESS DESCRIPTIONPROCESS DESCRIPTION
DELAYED COKING UNIT (DCU)
The DCU is one of the most profitable units in arefinery once it converts the residue from thevacuum unit into products with high value, such asLPG, Naphtha, Gas Oil and Coke
Residue from the vacuum distillation is heated in afurnace and sent to a coking reactor wherethermal cracking reactions process, convertinghydrocarbon charge into lighter products and coke.
Light hydrocarbons are sent to the mainfractionator unit, where they are separated, andcoke is retained in the reactor, which must bedecoked.
The DCU is one of the most profitable units in arefinery once it converts the residue from thevacuum unit into products with high value, such asLPG, Naphtha, Gas Oil and Coke
Residue from the vacuum distillation is heated in afurnace and sent to a coking reactor wherethermal cracking reactions process, convertinghydrocarbon charge into lighter products and coke.
Light hydrocarbons are sent to the mainfractionator unit, where they are separated, andcoke is retained in the reactor, which must bedecoked.
DELAYED COKING UNIT (DCU)
GAS COMPRESSION SYSTEM
Gases from the top of the fractionator are sentto the gas recovery section in order to separateLPG, Naphtha and Fuel Gas.
Before the separation process, these gases mustbe compressed.
The compression system is usually composed ofa compressor with two compression stages anda intermediate cooling.
Gases from the top of the fractionator are sentto the gas recovery section in order to separateLPG, Naphtha and Fuel Gas.
Before the separation process, these gases mustbe compressed.
The compression system is usually composed ofa compressor with two compression stages anda intermediate cooling.
GAS COMPRESSION SYSTEM
DYNAMIC SIMULATIONDYNAMIC SIMULATION
SCOPE OF SIMULATION
Top of the Fractionator
Fractionator PrimaryCondenser
Fractionator SecondaryCondenser
Fractionator Overhead Drum
First Stage Knockout Drum
First Stage Compressor
Intercooler
Interstage Knockout Drum
Second Stage Compressor
High Pressure Condenser
High Pressure Drum
Primary Absorber (simplified)
Naphtha Stripper (simplified)
PSV’s
Pumps
Compressor Turbine
Anti-surge Valves
Main Control Valves
The following equipment were simulated in DYNSIM:
Top of the Fractionator
Fractionator PrimaryCondenser
Fractionator SecondaryCondenser
Fractionator Overhead Drum
First Stage Knockout Drum
First Stage Compressor
Intercooler
Interstage Knockout Drum
Second Stage Compressor
High Pressure Condenser
High Pressure Drum
Primary Absorber (simplified)
Naphtha Stripper (simplified)
PSV’s
Pumps
Compressor Turbine
Anti-surge Valves
Main Control Valves
METODOLOGY
Dynamic Simulation using DYNSIM
Input: Overhead gas stream characterization according to the
Basic Design
Operational data (temperature, pressure, flow rate)obtained from plant at normal operating condition
“As-built” equipment and piping data
PID controller’s tuning
Steady State adjustment for current feed flow and forthe future feed flow
Dynamic Simulation using DYNSIM
Input: Overhead gas stream characterization according to the
Basic Design
Operational data (temperature, pressure, flow rate)obtained from plant at normal operating condition
“As-built” equipment and piping data
PID controller’s tuning
Steady State adjustment for current feed flow and forthe future feed flow
DYNSIM FLOWSHEET
FLOWSHEET DETAILS
FLOWSHEET DETAILS
CASES STUDYCASES STUDY
EMERGENCY SCENARIOS
For the future feed flow, the emergency scenariosbelow was studied:
Lack of Cooling Water in Intercooler
Closed Outlets:
First Stage Blocking Valve
Second Stage Blocking Valve
Inadvertent anti-surge opening
Second Stage Check Valve failure during compressor trip
For the future feed flow, the emergency scenariosbelow was studied:
Lack of Cooling Water in Intercooler
Closed Outlets:
First Stage Blocking Valve
Second Stage Blocking Valve
Inadvertent anti-surge opening
Second Stage Check Valve failure during compressor trip
FLOWSHEET DETAILS
First StageBlocking Valve
Anti-surge ValvePSV
Intercooler
Second StageBlocking Valve
LACK OF COOLING WATER IN INTERCOOLER The lack of cooling water in Intercooler causes:
Increase of the Intercooler outlet temperature
Increase of the Interstage Drum pressure
The Interstage Drum PSV didn’t open, because the Intercooler pressuredidn’t overcome the maximum allowable pressure (6.5 kgf/cm2)
FIRST STAGE BLOCKING Closing the First Stage Blocking Valve causes:
Interstage Drum PSV opening. The relief flow rate was not high enough tokeep the Intercooler pressure above the PSV relief pressure (6.5 kgf/cm2)
The pressure remained at 6.5 kgf/cm2 after the compressor shutdown
Closing the First Stage Blocking Valve causes:
Interstage Drum PSV opening. The relief flow rate was not high enough tokeep the Intercooler pressure above the PSV relief pressure (6.5 kgf/cm2)
The pressure remained at 6.5 kgf/cm2 after the compressor shutdown
SECOND STAGE BLOCKING Closing of Second Stage Blocking Valve causes:
Interstage Drum PSV opening. The relief flow rate was not high enough tokeep the Intercooler pressure above the PSV relief pressure (6.5 kgf/cm2)
The pressure remained at 6.5 kgf/cm2 after the compressor shutdown
INADVERTENT ANTISURGE OPENING
Opening totally the Second Stage Anti-surge Valvecauses the same impacts as the blocking of theDischarge Compressor Valves described in previouscases
Opening totally the Second Stage Anti-surge Valvecauses the same impacts as the blocking of theDischarge Compressor Valves described in previouscases
SECOND STAGE CHECK VALVE FAILURE There is one Check Valve in the first stage discharge and one in the
second stage discharge During the compressor trip, there would be reverse flow passing
through the compressor in case of failure in the Second Stage CheckValve
In spite of the Interstage Drum PSV opening, the pressure reached highvalues above the PSV relief pressure
RESULTS
The emergency scenarios studies for the futurecondition of the DCU showed that: The Interstage Drum PSV doesn’t open in case of lack of
cooling water for the Intercooler.
The Interstage Drum PSV doesn’t have relief capacity forthe events: closing the First and Second Stage BlockingValves, inadvertent anti-surge valve opening and SecondStage Check Valve failure for the new process condition.
The PSV needs to be redesigned to meet a futureDCU revamp.
The emergency scenarios studies for the futurecondition of the DCU showed that: The Interstage Drum PSV doesn’t open in case of lack of
cooling water for the Intercooler.
The Interstage Drum PSV doesn’t have relief capacity forthe events: closing the First and Second Stage BlockingValves, inadvertent anti-surge valve opening and SecondStage Check Valve failure for the new process condition.
The PSV needs to be redesigned to meet a futureDCU revamp.
SOLUTION
A new PSV with a larger area orifice wascalculated based on static analysis
The Dynamic Simulation was used to check if thecalculated orifice area has a relief capacity for theemergency scenarios such as: closing the First andSecond Stage Blocking Valve, opening SecondStage Anti-surge Valve and Second StageDischarge Check Valve failure
A new PSV with a larger area orifice wascalculated based on static analysis
The Dynamic Simulation was used to check if thecalculated orifice area has a relief capacity for theemergency scenarios such as: closing the First andSecond Stage Blocking Valve, opening SecondStage Anti-surge Valve and Second StageDischarge Check Valve failure
SOLUTION Blocking the First Stage Blocking Valve:
The new PSV opens and the Intercooler Pressure doesn’tovercome 6.5 kgf/cm2.
SOLUTION Blocking the Second Stage Blocking Valve:
The new PSV opens and the Intercooler Pressure doesn’tovercome 6.5 kgf/cm2.
SOLUTION Anti-surge valve opening:
The new PSV opens and the Intercooler Pressuredoesn’t overcome 6.5 kgf/cm2.
SOLUTION Second Stage Check Valve failure during a compressor trip:
Changing only the PSV was not enough to avoid pressurization of thevessel above 6.5 kgf/cm2
If the First Stage Check Valve is removed, the pressure doesn´tovercome 6.5 kgf/cm2, because the gas expands until the fractionatortop section. The graphic bellow shows the scenario without the FirstStage Check Valve
CONCLUSIONCONCLUSION
CONCLUSION
Dynamic Simulation was important to complementthe static analysis of the PSV relief capacity. Itprovided additional information regarding systembehavior during emergency scenarios.
The results confirm the necessity of changing theexistent PSV for another one with a larger orificearea to increase the DCU feed flow rate.
Dynamic Simulation was important to complementthe static analysis of the PSV relief capacity. Itprovided additional information regarding systembehavior during emergency scenarios.
The results confirm the necessity of changing theexistent PSV for another one with a larger orificearea to increase the DCU feed flow rate.
Thank you