aspen dynamics diers benchmarks

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Modeling Pressure Relief in Aspen Dynamics the DIERS Benchmark Examples 1

Modeling Pressure Relief inAspen Dynamics the DIERSBenchmark Examples

Pressure Relief in Aspen DynamicsThe pressure relief capability in Aspen Dynamics is provided

by a collection of specialized pressure relief models togetherwith a number of unit operation models with pressure reliefsupport. All models use Aspen Properties for accurate andreliable estimation of physical properties.

Pressure relief models can be added to a dynamic flowsheet andconfigured as necessary to define a relief system. This approach

allows you to model and simulate pressure relief from entireflowsheets, including the control system, rather than justindividual unit operations.

The combination of equation-based solution strategy, rigorousphysical property estimation and an extensive library of unitoperation models gives Aspen Dynamics a unique and flexiblecapability for solving a wide variety of pressure relief

problems, from steady state (rating) calculations through todynamic simulation of relief events such as blocked-inoperation or runaway reactions.

Formed in 1976 under the auspices of AIChE, the Design Institutefor Emergency Relief Systems (DIERS) was originally aconsortium of 29 companies to develop methods for the design ofemergency relief systems to handle runaway reactions. DIERS

became a user group in 1985. Presently, over 120 companies haveformed the DIERS Users Group to cooperatively assimilate,implement, maintain and upgrade the DIERS methodology. The

purpose of the group is:

to reduce the frequency, severity and consequences ofpressure producing accidents, and;

to develop new techniques which will improve the designof emergency relief systems.

The DIERSConsortium


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Of particular interest to DIERS is the prediction of two-phaseflow venting and the applicability of various sizing methods fortwo-phase vapor-liquid flashing flow. DIERS has spent $1.6million to investigate the two-phase vapor-liquidonset/disengagement dynamics and the hydrodynamics of

emergency relief systems. Aspen Technology is a member ofthe DIERS Users Group.

The Aspen Dynamics pressure relief models include methodsand principles developed by DIERS for calculating two-phasevessel onset/disengagement dynamics and relief systemhydrodynamics (Fisher et. al., 1992; CCPS, 1998). Theaccuracy and validity of these models for rating pressure reliefsystems in Aspen Dynamics has been demonstrated throughsolution of the DIERS benchmark examples. These examples

include various cases of compressible and incompressiblesingle phase flows and flashing, hybrid and frozen two-phaseflows through (i) a safety relief valve system and (ii)combinations of nozzles and horizontal and vertical pipingarrangements. Solutions obtained with Aspen Dynamics givegood agreement with consensus results.

DIERS Benchmark ExamplesThe DIERS benchmark examples are a set of case studies that

serve to validate computer software for rating pressure reliefsystems. Successful solution of the benchmark examples isdemonstrated by attainment of consensus results with thosereported by other members of the users group (Adair and Fisher,1999).

There are two categories of benchmark examples:

safety relief valve case studies

pipe benchmark studies

Full details of the DIERS benchmark examples and results areavailable in the open literature (Adair and Fisher, 1999).

The safety valve problem was formulated to illustrate the effect ofviscosity, the presence of non-condensable gas and inlet quality(disengagement) assumptions on safety relief valve (nozzle) massflow rate, inlet pipe irreversible pressure loss and discharge pipe

back pressure calculations, for a relief system venting toatmosphere. The relief system comprises an inlet line, a safetyrelief valve and a discharge line.

DIERS Methodology

Safety Relief ValveCase Studies


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A summary of the safety relief valve case studies is given inTable 2.1.

Case Flow Viscosity Inlet Quality Comments

1 Vapor Low 1.02 Flashing

LiquidLow 0.01

3 Hybrid Low 0.01

4 FlashingLiquid

Moderate 0.01

5 Hybrid Moderate 0.01

6 FlashingLiquid

Low Churn-Turbulentonset/disengagement

7 Flashing

Liquid

Low Homogenous

onset/disengagement8 Liquid

(water)Low 0.0

9 Liquid(water)

High 0.0

10 Frozentwo-

phase

Low 0.01

11 Frozentwo-

phase

High 0.01

12 Flashingliquid

High 0.01

13 Flashingliquid

Veryhigh

14 Hybrid High 0.01

15 Hybrid Veryhigh

0.01

16a Flashingliquid

Veryhigh

0.01 Constant viscositynozzle flow

16b Flashing

liquid

High 0.01 Constant viscosity

nozzle flow16c Flashing

liquidModerate 0.01 Constant viscosity

nozzle flow

17 Frozentwo-

phase

Veryhigh

0.01

Tabl e 2.1: Safety Val ve Case Studies


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Running the Safety Relief Valve Case Studies

To run one of the safety relief valve case studies:

1. Copy the relevant Aspen Dynamics input file (.dynf) andthe appropriate Aspen Plus backup file (.bkp) to a

convenient working folder. There is one Aspen Dynamicsinput file for each case study (named accordingly) and twoAspen Plus backup files; SafetyReliefValve.bkp is usedfor Cases 1-9 and 12-16,SafetyReliefValveFrozenFlow.bkp is used for Cases 10,11 and 17.

2. Load the .bkp file into Aspen Plus and run it. Note that the.bkp file is used to create a properties input file, so youwill not see a flowsheet within Aspen Plus.

3. To create an Aspen Plus Problem Definition file (.appdf),

save the simulation as an Aspen Plus Document (.apwfile) and exit Aspen Plus. The .appdf file contains all ofthe physical properties data required for the dynamicsimulation. The .apw file is not required, and can bedeleted.

4. Open the Aspen Dynamics simulation.

5. From the Tools menu, click Snapshots.

6. Select the converged snapshot that is marked as kept, thenclick Copy Values.

Ensure the Run Mode is set to Initialization and Run the

simulation.

Once you have run the simulation, you can use the forms andplots for the streams and blocks to see the results.

Results

Results of the safety relief valve examples are summarized inthe attached spreadsheet (click on icon to open):

AD121SafetyValveR

esults.xls

The key results reported for each case are:

the relief mass flow rate,

the irreversible inlet pressure drop (the difference betweenthe inlet stagnation pressure and the stagnation pressure atthe valve inlet, less any pressure drop due to inlet pipeelevation),

the discharge pipe back pressure (the difference betweenthe exit pressure of the valve and the relief systemdischarge pressure).
http://ad121safetyvalveresults.pdf/http://ad121safetyvalveresults.pdf/http://ad121safetyvalveresults.pdf/


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Other results, including the choke conditions at the nozzlethroat, are also reported.

The pipe benchmark cases were formulated to illustrate the effect

of viscosity, the presence of non-condensable gas and inletquality, and the pipe orientation on the mass flow rate throughpiping systems.

A summary of the pipe benchmark cases is given in table 2.2.

Case Flow Viscosity InletQuality

Comments

1 Liquid Low 0.0 Horizontal anddown flow

2 Two-phaseflashing

Low 0.001 Horizontal anddown flow

3 Two-phaseflashing

Low 0.001 Horizontal/verticalandvertical/horizontal

4 Hybrid Low 0.001 Horizontal andvertical andinclined downflow

4a Hybrid Low 0.01 Horizontal andvertical andinclined down

flow5 Initially

subcooled/two-phase flashing

Low 0.0 Nozzle flow

6 Initiallysubcooled/two-phase flashing

Low 0.0 Pipe flow

7 Two-phaseflashing

V. high 0.001 Horizontal anddown flow

8 Two-phase

flashing

High 0.001 Horizontal and

down flow

9 Two-phaseflashing

Moderate 0.001 Horizontal anddown flow

10 Cold Liquidflow and hotinitiallysubcooled/two-phase flashingflow

Low 0.0 Horizontal anddown flow

Table 2.2: Pipe Benchmark Cases

Pipe Benchmark

Cases


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Running the Pipe Benchmark Examples

To run one of the pipe benchmark examples:

1. Copy the Aspen Plus backup file pipebench1.bkp and therelevant Aspen Dynamics input file (.dynf) to aconvenient working folder. There is one Aspen Dynamicsinput file for each benchmark example (namedaccordingly).

2. Load the .bkp file into Aspen Plus and run it. Note that the.bkp file is used to create a properties input file, so youwill not see a flowsheet within Aspen Plus.

3. To create an Aspen Plus Problem Definition file (.appdf),save the simulation as an Aspen Plus Document (.apwfile) and exit Aspen Plus. The .appdf file contains all of

the physical properties data required for the dynamicsimulation. The .apw file is not required, and can bedeleted.

4. Open the Aspen Dynamics simulation.

5. From the Tools menu, click Snapshots.

6. Select the converged snapshot that is marked as kept, thenclick Copy Values. Note that many of the pipe benchmarkexamples include several sub-cases. Table 2.3 identifiesthe kept snapshots for each case.

7. Ensure the Run Mode is set to Initialization and Run thesimulation.


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Once you have run the simulation, you can use the forms andplots for the streams and blocks to see the results.

Case Snapshot Name Description

Pipe2x16_4 2 ID, 16.4 pipe

Pipe2x160_4 2 ID, 160.4 pipe

Pipe2x1600_4 2 ID, 1600.4 pipe

Pipe8x16_4 8 ID, 16.4 pipe

Pipe8x160_4 8 ID, 160.4 pipe

1

Pipe8x1600_4 8 ID, 1600.4 pipe

H16_4 Horizontal 16.4 pipe


2


V16_4 Vertical 16.4 down pipeV160_4 Vertical 160.4 down pipe

V1600_4 Vertical 160.4 down pipe

HV16_4 Horizontal 16.4 pipe



VH16_4 Vertical 16.4 down pipe


3


H16_4 Horizontal 16.4 pipeH160_4 Horizontal 160.4 pipe





DEG45_16_4 45 degree 16.4 down pipe


4



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Case Snapshot Name Description



H1600_4 Horizontal 1600.4 pipeV16_4 Vertical 16.4 down pipe





4a


N2_0psi 0 psi of N2 subcooling

N2_1psi 1 psi of N2 subcooling

5

N2_2psi 2 psi of N2 subcoolingID0_417 0.417 ID pipe

ID1_291 1.291 ID pipe

6

ID3_146 3.146 ID pipe



7










8







9


H_cold Horizontal pipe, cold water

H_hot Horizontal pipe, hot water

V_cold Vertical down pipe, cold water

10

V_hot Vertical down pipe, hot water

Table 2.3: Snapshots for Pipe benchmark examples.


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Results

Results of the pipe benchmark examples are summarized in theattached spreadsheet (click on icon to open):

AD121PipeBenchmarkResults.xls

The key result reported for each case is the relief mass flowrate.

ReferencesFisher, H.G., Forrest, H. S., Grossel, S. S., Huff, J. E., Muller, A.R., Noronha, J. A., Shaw, D. A. and Tilley, B. J. (1992).

Emergency Relief Systems Design Using DIERS Technology: theDesign Institute for Emergency Relief Systems (DIERS) projectmanual. AIChE.

Center for Chemical Process Safety (CCPS). (1998). PressureRelief and Effluent Handling Guidelines. AIChE.

S. P. Adair and H. G. Fisher (1999). Benchmarking of two-phase flow through safety relief valves and pipes. Journal ofLoss Prevention in the Process Industries. 12,pp.269-297.
http://ad121pipebenchmarkresults.pdf/http://ad121pipebenchmarkresults.pdf/http://ad121pipebenchmarkresults.pdf/

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