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