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KEYS TO SUCCESSFUL INTERNAL GAS-GAS HEAT EXCHAGNER

REPLACEMENT, A CASE STUDY

FINAL REPORT

Jesse, Huebsch, P.Eng., Bill Jones (Lucite), Grant Harding, P.Eng., and Jean-

Philippe Hudon, EIT.

Presented by:

Jesse Huebsch, P.Eng.

CHEMETICS INC.

Suite 200 – 2930 Virtual Way

Vancouver, BC, Canada

Presented at the

American Institute of Chemical Engineers

Central Florida Section

4798 S. Florida Avenue, #253

Clearwater Conference

June 10 – 11, 2016

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TABLE OF CONTENTS

ABSTRACT ............................................................................................................ 4

INTRODUCTION .................................................................................................. 5 PLANNING ............................................................................................................ 6 PRE-SHUTDOWN WORK .................................................................................... 9 SHUTDOWN ACTIVITES .................................................................................... 9 RESULTS ............................................................................................................. 19

SUMMARY .......................................................................................................... 19

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LIST OF FIGURES

Figure 1: 1st pass tube condition of the HHX ......................................................... 5 Figure 2: Schematic overview of the HHX replacement ........................................ 8

Figure 3: External ducting and insulation removed. ............................................. 10 Figure 4: External ducting and insulation removed .............................................. 10 Figure 5: Core duct section being removed .......................................................... 11 Figure 6: HHX exchanger preparation for removal .............................................. 12 Figure 7: HHX Bundle lifting lugs ....................................................................... 13

Figure 8: Removal of the original HHX ............................................................... 14 Figure 9: Converter core open for inspection with marked “foot print”............... 15 Figure 10: Staged prefabricated seal plate pieces ................................................. 15

Figure 11: Lift of the replacement HHX............................................................... 16 Figure 12: Aligning the new HHX........................................................................ 17 Figure 13: New HHX in place .............................................................................. 17

Figure 14: Welding in the annulus ........................................................................ 18

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ABSTRACT

Internal gas-gas heat exchangers provide numerous benefits over external

exchangers. These include reduced installation cost, simplified layout, improved energy

efficiency and elimination of gas leaks by eliminating nozzles, ducting and expansion

joints. One question that remained unanswered until now was how to replace the

exchanger should this become necessary during the lifetime of the plant.

This paper discusses the key issues that need to be considered before the start of

the turnaround; engineering, step-by-step sequence planning, maximizing prefabrication,

access requirements, safety considerations, and points specific to the installation and

removal of an exchanger.

A case study of a successful internal gas-gas heat exchanger replacement during a

standard plant turnaround will be presented, including key learnings in logistical and

construction challenges to achieve on-schedule completion.

In conclusion replacing an internal gas-gas heat exchanger has proven to be only

marginally more difficult than replacing an external unit.

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INTRODUCTION

In 2005 Chemetics was the technology vendor for a double contact conversion for

the Lucite Sulphuric Acid Regeneration (SAR) plant in Memphis, TN. This project

included a new converter with an internal Hot Gas-Gas Heat Exchanger (HHX).

In 2014 Lucite inspected the HHX and determined that the tubes on the hot end

were badly thinned and leaking, and that the exchanger would need to be replaced. See

“Figure 1: 1st pass tube condition of the HHX” for an example of the tube condition.

For the replacement unit an analysis was done of the performance of other

metallurgies in this plant’s environment the same gas space to select an alloy that would

provide better resistance to the aggressive gas at the exit of Bed 1. 310 SS was ultimately

selected to replace 304H SS for this application, based on both technical and economic

considerations.

To Chemetics knowledge this is the first time an internal gas-gas heat exchanger

has been replaced. Chemetics provided Lucite assistance in planning, coordinating and

executing the replacement, as well as provided the new fabricated internal HHX. Since

this was the first time for such a replacement, extensive pre-planning was done to

mitigate the risks inherent in a new procedure.

Figure 1: 1st pass tube condition of the HHX

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PLANNING

In the original construction of the converter, the HHX was supplied as a complete

unit that was incorporated into the structure of the converter. In particular, the shell of the

exchanger became part of the structural converter core. Due to this arrangement, the

exchanger bundle needed to be removed without replacing the exchanger shell / converter

core. There are a number of baffles and seal plates that connect the bundle to the shell.

A detailed sequence was developed to aid the shutdown planning. The sequence

considered:

Develop a drawing to determine the best cutting and re-welding locations

and define the components to be removed, replaced and required new or

modified.

The order in which major components would need to be removed and re-

installed.

Which baffles / seal plates / etc. would interfere with the lifts of the major

components.

What other items would need to be completed to get access to remove

baffles, the exchanger etc.

Where to cut the connecting parts to provide enough clearance for a safe

lift, and where to install locating clips and backing strips to aid re-

installation of the connecting pieces after the new exchanger bundle is

positioned inside.

The access and welding positions for welders to join the new parts during

re-installation.

What temporary attachments, braces and lifting lugs would be needed and

their locations. In particular, reinforcing the exchanger bundle with tie

rods to ensure that the compromised tubes would not break under the

lifting load brought by the bottom skirt and the tubesheet of the HHX.

Support saddles for the removed duct / pipe sections while waiting to be

re-installed.

The types of welds by location and the cuts requiring high precision where

they need to be reattached by butt welding.

The basic sequence was:

Remove insulation.

Layout cutting points on the vessel and ducting.

Lock duct supports and expansion joints to prevent movements during

removal.

Cut and remove external ducting.

Complete catalyst removal*

Brace the internal core’s ductwork.

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Cut and remove the internal core duct section above the HHX.

Remove baffles and seal plates from the HHX.

Install lifting lugs and tie rods in the HHX.

Remove the HHX bundle.

Clean deposits from interfacial/attachment areas.

Inspect the converter core (UT measurements).

Prepare backing bars on the inner core.

Stage baffle and seal plate petals in the converter.

Install the new HHX bundle.

Install new seal plates and baffles.

Re-install the core duct section.

Re-install external ducting.

Re-install catalyst.

Re-insulate.

* Note: Catalyst removal was required in 3 of 4 beds for other shutdown work.

The replacement could be have been completed without removing the catalyst with

reduced overall shutdown schedule. However, removing the catalyst was beneficial by

eliminating the risk of contaminating the catalyst during the work, and minimizing

contaminating workers with catalyst dust.

“Figure 2: Schematic overview of the HHX replacement” shows the major

components and how they connect. ‘Key Cuts’ shows where the gas barrier needs to be

cut and reattached to separate the parts. The “Core Duct Assembly” is removed to

provide access to the “Hot Gas Exchanger”, but it is then reinstalled after the new HHX

is replaced.

This sequence was then used to plan pre-fabricated materials, weld consumables

required, laydown areas and saddles / supports, shutdown work crews and other resources

such as cranes.

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Figure 2: Schematic overview of the HHX replacement

Core Duct

Assembly

Key Cuts

Hot Heat

Exchanger

Converter

Shell

(unmodified)

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PRE-SHUTDOWN WORK

To avoid delays in field installing the components, the baffle extensions and seal

plates were fabricated in sections chosen to be small enough to maneuver in the tight

spaces inside the converter. In some cases engineering was required to modify

arrangements making them more retro-fit friendly (for example, the HHX top expansion

plate was relocated). Weld bands were fabricated to reattach duct sections to avoid field

butt welds.

Insulation was removed while the plant was cooling down along with pre marking

key external cut lines. Laydown areas and removed core duct assembly support were

sorted out.

SHUTDOWN ACTIVITES

Remove Insulation and External Ducts

While the plant was cooling down, work was started to remove the insulation and

mark cut-lines on the external ducts. When the cool down was complete, the external

ducts were removed while screening was being done on the catalyst. See Figures “Figure

3: External ducting and insulation removed.” and “Figure 4: External ducting and

insulation removed” for an overview of the removed sections.

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Figure 3: External ducting and insulation removed.

Figure 4: External ducting and insulation removed

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Remove Core Ducts

The core duct assembly consists of 4 concentric ducts that direct the main gas

flow and bypass to the HHX as well as the gas flows to Beds 3 and 4. This assembly is

positioned on top of the HHX and needed to be removed to provide access to the HHX,

but needed to be retained to be re-installed. The ducts were cut at marked locations. The

uppermost large diameter cut’s accuracy was critical to ensure that a butt weld could be

done to re-assemble the converter at the original orientation and elevation, restoring the

original integrity. The core innermost ducts were braced to ensure minimal movement

within the assembly during lift.

After removal of the core duct assembly “Figure 5: Core duct section being

removed”, it was placed on cradles, and additional bracing was installed to ensure that the

concentric duct sections retained alignment after reinstalling it. Ideally, bracing would

have been installed before removal, but access restrictions to this duct area prevented

installation until after removal.

Figure 5: Core duct section being removed

HHX Bundle Preparation

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After the Core duct assembly was removed, the upper conical vestibule on the

HHX was removed to provide better access to the top tubesheet “Figure 6: HHX

exchanger preparation for removal”. 8 tie rods were installed to support the bottom

tubesheet in the event that the corroded tubes did not have sufficient structural integrity to

hold the weight themselves.

4 lifting lugs were welded onto the top tubesheet “Figure 7: HHX Bundle lifting

lugs”. Quality control was done by dye penetrant testing on all welds.

The seal plates between the tubesheets and the core were removed, In addition,

the two baffles that extended from the bundle to the core were trimmed back to provide

enough clearance to lift the HHX bundle out of the core.

The location of the ‘feet’ of the HHX was marked, and the wall to tubesheet gaps

were noted for later alignment of the new HHX.

Figure 6: HHX exchanger preparation for removal

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Figure 7: HHX Bundle lifting lugs

HHX Removal

The HHX bundle was lifted without incident to a waiting trailer for analysis and

disposal “Figure 8: Removal of the original HHX”. By providing a few inches of

clearance on each side and careful guidance, snags were avoided.

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Figure 8: Removal of the original HHX

Converter Core Inspection and Preparation

With the core of the converter completely empty “Figure 9: Converter core open

for inspection with marked” Wall thickness UT inspections were done. Minimal thinning

was found in the areas adjacent to Bed 1 exit consistent with the amount of tube thinning,

but due to the much thicker initial material in this location, the loss of thickness was

structurally insignificant and not a current issue.

The loose sections to be installed were pre laid out, numbered, and staged at the

appropriate converter levels while they could be lifted in place by the crane. “Figure 10:

Staged prefabricated seal plate pieces”.

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Figure 9: Converter core open for inspection with marked “foot print”.

Figure 10: Staged prefabricated seal plate pieces

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Install the New Exchanger Bundle

The new HHX had been pre-staged ahead of the job to ensure availability. It was

put upright “Figure 11: Lift of the replacement HHX” and lifted into place. The

exchanger was stopped slightly above its final position to adjust the orientation and

ensure that the feet landed in the same position as the original’s had been in.

Figure 11: Lift of the replacement HHX

The top was then aligned with chain falls to match the original tubesheet to wall

gap on each side. “Figure 12: Aligning the new HHX”. With the HHX now in place, the

seal plates and baffle extensions were installed. A sequence was set to minimize the risk

of any parts falling on workers below, and to ensure that if a part fell, there would still be

access to remove or recover it. A view from a bed provides a stark contrast between new

and old “Figure 13: New HHX in place”.

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Figure 12: Aligning the new HHX

Figure 13: New HHX in place

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Reinstall the Core Ducts and Completion

With the new HHX in place, the Core Duct Assembly was lifted back up and re-

installed. Weld bands were provided for each of the internal and external duct

connections, leaving just one butt-weld on the top vessel shell. The remaining parts were

welded in, with some tight squeezes required “Figure 14: Welding in the annulus”. As

part of the planning, the distances and access angles were checked to ensure that all

required welds would be possible to complete.

Figure 14: Welding in the annulus

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RESULTS

The replacement of the HHX was achieved in 21 days in a planned 35 day (feeds

off to feeds on) shutdown. The HHX replacement job did not become a critical path item

for the completion of the shutdown. Note that as one job in a large scope, long duration

shutdown, the HHX replacement was staffed with that in mind. The 21 day duration

included a minimal night shift (without crane support) and some resources, such as

insulators, were shared with other jobs.

Upon startup the plant was restored to normal operating conditions, with no

evidence of gas leaks or bypassing.

Differences from a “standard” external Gas Exchanger replacement/installation

are that additional cleaning for fitting and welding is required, there is an increased

amount of confined space work and a reduced amount of scaffolding/staging as the

converter vessel itself is a stable work platform.

SUMMARY

The first internal Gas-Gas Heat exchanger replacement was completed

successfully, within a standard shutdown. While slightly more complex than an external

Gas-Gas heat exchanger replacement, the schedule time and effort required were not

excessive and well controlled with careful pre-planning and site support.