Brazil 2014ugm Performance of Hydrotreating High Pressure Heat Exchanger

8/10/2019 Brazil 2014ugm Performance of Hydrotreating High Pressure Heat Exchanger

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Internal Sealing Performance of a

Hydrotreating High Pressure Heat Exchanger

Rafael Pavan Bagagli

21/05/2014


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Summary

Company Overview;

Problem Description;

Methodology;

Goals;

Conclusions.


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Company Overview

REPLAN Paulnia Refinery

Capacity: 420 mbpd

Location: Paulnia - SP


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Problem Description

HDT Reaction Section simplified flowchart:

Feed

(S2000)

HDD

(S10/S500)

HHPHE

Furnace

Reactor

#1

Reactor

#2

H2

H2 H2


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Problem Description

What is a HPHE?


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Problem Description

Why contamination of hydrotreated Diesel

occurs?

Loss of internal gasket

sealing


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Problem Description

Main questions:

Why gasket looses sealing?

How can we fix it?

LETS CREATE A NUMERICAL MODELAND EVALUATE!


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Methodology: Physical Model

Physical model of HHPE is similar to springs in

series:


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Balancing the forces:

SgT is the THEORETICAL gasket stressconsidering uniform distribuiton of Won gasket

surface.

FGFH


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Bolt assembly selection criteria:

ASME: 1,8 ksi (12,5MPa) Min: 6,0 ksi (40MPa) Max: 60,0 ksi (420MPa)


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And how about diferential thermal expansion?

Operation temperature: 360C;

Heat expansion coeff. of internals (300SS)

greater than channel (1 1/4Cr1/2Mo);

Diferential thermal expansion (~1,79mm) will

tension the channel and compress internals.


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Diferential thermal expansion force (FDTE) IS

NOT ADDEDto initial bolt load (W);

Internals behave like springs in series, so the

GREATERof them (W or FDTE) predominate;

Then, how define the sealing force? WILL

SEE BEFORE.


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Methodology: Numerical Model

The numerical model was developed

considering solid elements and geometry,

material and contact nonlinearities;

Were modeled only the gasket, tubesheet,

partition and internal jack screws;


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Components modeled:

Gasket

Partition BoxJack

Screws

Tubesheet


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Geometry and mesh:


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Stiffness of non-modeled componetsconsidering linear elastic materials and no

bending:

It was computed changing jack screw Young

Modulus:


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Details of material models:

* Modified Ey considering non-modeled components rigidity

Material SA-240 TP 347 SA-387 Gr11 SA-453 660B

Model EP kinematic hardening EP kinematic hardening Linear-elastic

Temperature (C) 22 360 22 360 22 360

Yield StrenghtSy (MPa) 276 185 380 316 655 601

Tensile Strenght Su

(MPa)586 480 586 505 965 922

Young Modulus

Ey (MPa) 194994 171358 204084 181844 65281* 57644*

Poisson Ratio 0,3 0,3 0,3 0,3 0,3 0,3


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Stress-Strain curves (Ramberg-Oosgod model):


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Supports:

Frict ionlesson symmetry surfaces;

Frict ionlesson gasket surface oposite to the

tubesheet;

Fixed Suppo rton jack screw surfaces

oposite to the partition.


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Boundary conditions visualization:


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Goals: Part 1 Gasket Loads Evaluation

Object ive:

Evaluate influence of Wand FETDon gasket

stress.

Methodology:

Evaluation of Load x deflection (response)

curve


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After heating up FETDpredominate over W;

Maximum load (GPD) is about 2,15e7N,

resulting ~ 23ksigasket stress (theoretical);

Increase W

Use ferritic materialCounter Measure

Reduce gasket widthCounter Measure


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Goals: Part 2 Gasket Stress Distribution

Object ive:

Evaluate gasket stress distribution on gasket

surface

Methodology:

Evaluation of pressure on gasket x tubesheet

contact pair


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Load sequence:

Determ ined from Load x Def. Curve


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Resultant gasket stress:

DISTRIBUTION

IS IRREGULAR


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Reduced stiffness on holes area promote:

Bending of partition;

Loss of partition x tubesheet contact areas;

Reinforce partition holesCounter measure


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Proposals for project improvement:

1. Reduce gasket width + increase W;

2. Change partition material to 1 1/4Cr1/2Mo;

3. Insert reinforcement on partition holes;

Increase gasket s tress

Reduce temp. inf luence

Improve gasket s tress dist r ibut ion


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New geometry:

Original Partition

New Partition


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New load sequence:

Sg= 30 ks i (Theo retical)


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New gasket stress distribution:

Mn. OK

Mx. OK

Stress distribution along gasket width (0):


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Conclusions

For low bolt loads (W) diferential thermalexpansion load predominates and increase

gasket stress(Sg);

However sealing performance depends on

Top, wich is not uniform for all exchangers and

can vary with process conditions;


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Conclusions

Changing partition material to ferritic,reducing gasket width and increasing W,

eliminate Top dependence;

However gasket stress distribution is

irregular, wich decrease sealing performance

in some areas;


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Conclusions

Inserting a reinforcement on partition holesand increasing shell thickness improve gasket

stress distribution;

Thus, a minimum of 6ksi gasket stress is

achieved in critical regions and leaking

probability during operation is quite reduced.


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Conclusions

QUESTIONS?

THANK YOU!

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Brazil 2014ugm Performance of Hydrotreating High Pressure Heat Exchanger

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