replacement of a 22 years old secondary reformer - gpic's .../fileser… · process licensor...

Replacement of a 22 years old Secondary Reformer - GPIC’s

experience This paper discusses the reason for replacing a 22 years old Secondary Reformer, the improvements

that were made in the new Secondary Reformer, the proactive measures that were taken for

successful replacement and the actual operational performance after replacement.

Samih Al Alawi and Cholaperumal Subramanian

Gulf Petrochemical Industries Company, Kingdom of Bahrain

K. Schmalstieg and M. Wolske

KARRENA GmbH, Germany

1.0 Introduction

ulf Petrochemical Industries Co.

(GPIC), Bahrain was established in

1979 as a joint venture with equal

participation by Government of Bahrain,

Petrochemical Industries Company (PIC)

Kuwait and Saudi Basic Industries Company

(SABIC) Saudi Arabia. GPIC is a fine example

of a successful joint venture between Arab Gulf

companies in the Arabian Gulf.

GPIC operates a complex comprising of single

stream Ammonia and Methanol Plants, each of a

capacity of 1200 MTPD and a single stream of

1700 MTPD Urea Plant (Granulation route)

along with associated utilities, off-site and

material handling units. The Ammonia and

Methanol Plants are in operation since 1985

while the Urea Plant was commissioned in

January 1998 and is in operation since then.

Process licensor for Ammonia and Methanol

plants is Uhde GmbH, Germany and the process

licensor for Urea Plant is Snamprogetti, Italy. In

just over two decades GPIC has grown to

become a major petrochemical venture. It has

earned a reputation for reliability, quality,

safety, health and care for the environment on an

international scale. Its achievement in terms of

plant reliability is spectacular and proven by

many benchmarking studies with similar plants

throughout the world. The company has earned

an outstanding reputation not only within the

region but in the international arena too, for its

continuous on stream record of 738 days, 941

days and 931 days of Ammonia, Urea and

Methanol plants respectively. The Company

remains fully committed to complying with, and

wherever possible, exceeding all national and

international safety and health laws and

regulations. GPIC continues to place a top

priority on its excellent management of safety,

health and environment. The many awards

received from highly recognized international

institutions are a proof of this commitment.

The Ammonia Process is a conventional steam

reforming process for synthesis gas generation

and an axial bed converter for ammonia

G

187 AMMONIA TECHNICAL MANUAL2008

synthesis followed by the ammonia recovery

step.

One of the most critical equipment items in an

Ammonia Plant is the Secondary Reformer.

During the turnaround of the Plant in November

2007, GPIC replaced the 22-year-old Secondary

Reformer with the new one with improved

design features.

2.0 Design features of the old Secondary Reformer.

The Secondary Reformer is a standard Uhde

design where the process gas enters from the

bottom through the central riser and mixes with

the hot air introduced through a ring shaped

burner and the combustion takes place. The gas

then flows through the catalyst bed axially and

exits the Secondary Reformer from where it is

routed to the Process Gas Cooler. The detail of

the old Secondary Reformer arrangement is

provided in Figure 1. The pressure shell of the

Secondary Reformer is lined internally with

refractory lining. The design temperature of the

hot face of the refractory lining above the

catalyst bed is 1800 oC (3272

oF). The pressure

shell is designed for 150 oC (302

oF). In order to

keep the pressure shell within its design

temperature, the external surface of the

complete vessel is provided with a non-

pressurised water jacket. The hot face lining of

the combustion zone (inner layer) in contact

with the hot gasses is of high alumina type

bricks and the outer insulating layer is of high

silica based refractory concrete. (Figure 2)

2.1 Observations made during Refractory inspection in 2005 turnaround

The most effective check of the refractory lining

is possible only during shut downs when

inspections enable the evaluation of the

conditions of the hot face skin.

During the regular shut down of the plant in

2005 an inspection of the Secondary Reformer

lining was done at the dome area and the

cylinder wall above the catalyst bed. The

following observations were made.

• The brick lining of the dome and first part of

the cylindrical wall area was so far in

acceptable condition taking into

consideration the operation time of 20 years.

(Picture 1)

Picture 1: Brick lining of dome after 20 years

Picture 2: Brick lining above catalyst bed

• Several larger cracks that were filled up with

a mixture of Saffil fibre and mortar during

the previous shutdowns were observed to be

in a satisfactory condition. (Picture 2).

• The mortar joints and the brick shapes had

eroded strongly due to the hot process gas.

188AMMONIA TECHNICAL MANUAL 2008

The hot face of the bricks was glazy caused

by the advanced operation time period and

the hot process gas. The mortar at the joint

was also observed to be partly eroded.

(Picture 3).

Picture 3: Cracks and eroded joints

• The expansion gaps at the expansion joints

were found to have increased and might not

close completely during operation.

Furthermore they must be cleaned to allow

for free expansion before next heating up

(Picture 4).

Picture 4: The expansion joint is extended

The refractory lining of the dome and upper

cylindrical part seemed to limit seriously the

lifetime of the lining. Due to the joint conditions

a potential risk for gas bypassing could not be

excluded. This may cause higher temperatures

of the steel shell, which will not be immediately

obvious because of the water jacket.

2.2 Merits and Demerits of Silica based Refractory:

Silica based refractory material has good

insulating property. Hence the former designs of

Secondary Reformer refractory lining were

based on using insulating products containing

Silica. The refractory lining of the old

Secondary Reformer was designed for a skin

temperature of 170 oC (338 oF) at the pressure

shell (without water jacket).

However, it is now well known that Hydrogen

rich process gas considerably affects Silica at

higher temperatures in reducing atmospheres.

Hydrogen can remove Silica as per the

following chemical reaction:

SiO2 (solid) + H2 (gas) ��SiO (gas) + H2O (gas)

This chemical reaction depends on the process

gas temperature and pressure.

If condensation of gaseous SiO will take place

later in the process, fouling at downstream heat

exchanger tubes could be a typical result of this

chemical reaction.

GPIC had observed voids behind the hot face

refractory brick lining in the shutdowns prior to

2005. GPIC had also been experiencing fouling

phenomenon of the downstream Process Gas

Cooler due to silica migration from the

refractory lining corroborating with the above

theory.

Based on the above findings, GPIC decided to

change the refractory lining of the Secondary

Reformer. Uhde recommended to change the

refractory from silica based to alumina-based

refractory to overcome the refractory

deterioration due to silica migration, as has been

carried out in the Secondary Reformer of the

recent Uhde Ammonia Plants.


3.0 Reason for GPIC to replace the entire equipment

Two options towards replacement of the

refractory lining were considered and evaluated.

• Replacement of the whole refractory during

a turnaround:

The cost of this option will be low.

However, it would have required a 50 days

plant outage for the repair works, costing in

terms of lost production.

• Replacement of the Secondary Reformer

during a turnaround:

GPIC would have to incur cost of new

equipment, but the number of days required

for restoring production would reduce, thus

minimizing the costs in terms of lost

production.

This option also offered an opportunity to take

advantage of the latest design improvements in

the Secondary Reformer technology.

Cost incurred in the replacement of the

refractory during Turnaround and the lost

revenue in terms of production (Option 1) was

Figure 1: New Secondary Reformer with air ring header and air inlet

nozzles arrangement. Old Secondary Reformer with air ring burner

arrangement.

New Secondary

Reformer

Old Secondary

Reformer

Catalyst

Bed

Gas Outlet

Gas

Inlet

Combustion

Zone

Water

Jacket

Air Nozzle with

ring header

outside

Air ring

burner inside

Gas Outlet


estimated to be USD 25.3 million. Cost of

procurement of the new Secondary Reformer

and its installation during Turnaround (Option

2) was estimated as USD 15.1 million. Option 2

was found to be a competitive choice. A

conscious decision was taken to pursue Option 2

(i.e. procurement of a new Secondary

Reformer).

4.0 Design features of the new Secondary Reformer & Refractory

Basic Engineering and procurement

specification for the new Secondary Reformer

was provided by Uhde. Uhde also provided their

services for approval of the vendor's drawings &

documents, inspection during fabrication of the

equipment and during erection of the equipment

at site.

4.1 Features of new Secondary Reformer (Steel)

In the new Secondary Reformer design, the

internal ring burner is removed and instead a

ring shaped air header is provided on the outside

of the vessel. The inlet air then passes through

the flexible pigtails and is released at high

velocity into the Secondary Reformer through

the nozzles oriented at an angle. The angular

orientation of the nozzles creates a vortex flow,

which enables better mixing of gas and air and

also prevents the flames to come in contact with

the central riser pipe or the refractory on the

shell. The height of the combustion zone has

been increased in the new Secondary Reformer

in order to have sufficient residence time to

achieve uniform temperature before entry into

the catalyst bed. Due to this the height of the

new Secondary Reformer is 16.8 metres (55.12

ft) which is 2.35 metres (7.71 ft) more than the

old one. The details of the new Secondary

reformer arrangement are provided in Figure 1.

The main advantages of the new design are

• better mixing of gas and air by creating a

vortex flow (lower methane slip)

• sufficient residence time to achieve a

uniform temperature before the gas enters

the catalyst bed.

• avoidance of flame impingement on the

refractory or catalyst

• no metallic burner in the combustion zone

(no replacement of the burner ring

required)

The weight of the new Secondary Reformer

steel is 120 tons, which is 30 tons more than the

old one. The operating weight of the new

Secondary Reformer is 371 tons as compared to

the operating weight of 295 tons for the Old

Secondary Reformer. The ex-works delivery of

the Secondary Reformer was 14 months from

the date of Purchase Order. The equipment was

received at site 15 months after Purchase Order

date.

4.2 Features of Refractory of new Secondary Reformer

The basic concept for the refractory design of

the new Secondary Reformer is Silica free lining

and installation of the refractory under hot

climate conditions in Bahrain. Bubble alumina

is used as back-up lining in the new design

instead of silica based lining. The Silica free

refractory lining will reduce the potential risk

for fouling in heat exchanger tubes of

downstream Process Gas Cooler due to

condensation of gaseous SiO. Since the

insulation properties of bubble alumina are not

as good as the silica-based material, the heat

transferred to the water jacket will rise. The

refractory lining of the new Secondary Reformer

is designed for a skin temperature of 260 oC

(500 o

F) at the pressure shell (without water

jacket) as against 170 oC (338

oF) for the old

one.


The installation, which was scheduled in

Bahrain under hot climate conditions, is the

reason to use Bubble Alumina pre cast shapes in

the second layer of Secondary Reformer lining

instead of casting both insulation layers. The

benefits of using pre cast shapes are:

� Less water in the refractory lining and

therefore safer dry out.

� Less working period with castable

which is of particular importance under

hot climate conditions

New Secondary Reformer

Modern Refractory design

Figure 2: Secondary Reformer of different designs

� The time period for installation will be

reduced.

� More economical because of avoiding

solid steel shuttering.

The details of new refractory design of

secondary reformer compared to the former one

together with main characteristics of the

refractory materials are provided in Figure 2 and

Table 1.

Old Secondary Reformer

Former refractory design

Bubble Alumina

shapes

High Alumina

Refractory Bricks

Bubble Alumina

shapes

Bubble Alumina

Insulating Layer

Insulating Firebrick

ASTM-Group 23

Insulating Layer with

approx. 30% SiO2

Synthesis gas

flow

High Alumina Castable


5.0 Planning of Replacement

The Secondary Reformer replacement site

activities had to undergo careful planning

because of the criticality and complexity

associated with it. The planning for the

replacement activities at site started at the same

time the Specification for the new Secondary

Reformer was finalized. Extensive consultations

were held with Uhde, Karrena and the erection

contractor for execution of the project in a safe

manner and in the shortest possible time.

The new Secondary Reformer was supplied by

the vendor with the water jacket and the air inlet

ring header pre-installed in the vendor

workshop. To prevent any damage to the air

inlet pigtails during transport, the pigtail

connection between the air inlet header and the

inlet nozzles were carried out at site before the

shutdown.

To reduce the activities and time during the

plant shutdown, it was decided to carryout

installation of the refractory lining and dry out

of the lining prior to the start of the plant

shutdown. In order to reduce the lifting and

shifting activities of the new Secondary

Reformer after installation of the refractory

lining, the new equipment was erected on a

temporary foundation closer to the existing

Secondary Reformer (19.35 metres [63.48 ft]

from the existing reformer) (Picture 5 and

Picture 7).

The following activities carried out on a

proactive basis helped in the smooth execution

of the replacement work.

a. Based on the technical specification for

the new Secondary Reformer prepared by Uhde,

increase in weight of the new Secondary

Reformer due to the increased height was

envisaged. The maximum load bearing capacity

of the existing foundation was checked and

calculated prior to floating of enquiry. Vendors

were informed of this foundation load capacity

limitation during the enquiry stage itself thereby

ensuring the weight of the new equipment to be

within the load capacity limit of the foundation.

b. The new Secondary Reformer had to be

erected on the existing foundation bolts and

connected to the existing inlet and outlet

connection on the gas side. Hence it is of utmost

important that the bolt circle diameter of the

base ring bolt holes, base bolt hole pitch,

Description UOM

Karrena material no. 2037 5016 2037 4006 4001 5206

Product description

High Alumina

brick

High Alumina

shapes or castableHigh Alumina brick

Bubble Alumina

brick

Insulating fire brick

ASTM Group 23

Insulating castable

layer

Main raw material

Fused

CorundumBubble Alumina Fused Corundum Bubble Alumina Fireclay

Light weight

aggregates

Max. service temperature °C (°F) 1600 (2912) 1800 (3272) 1600 (2912) 1700 (3092) 1150 (2102) 1250 (2282)

Chemical composition

AL2O3 %wt. 99 96 99 98.5 37 50

SiO2 %wt. 0.1 0.5 0.1 0.7 46 31

CaO %wt. 3 14 16

Fe2O3 %wt. 0.1 0.2 0.1 0.1 1 0.7

Bonding system ceramic hydraulic ceramic ceramic ceramic hydraulic

Apparent porosity % 16 48 16 64 82 45

Bulk density g/cm³ 3.32 1.55 3.32 1.45 0.55 1.1

CCS after heating at 110°C (230°F) Mpa (psi) 95 (13778) 10 (1450) 95 (13778) 8 (1160) 0.8 (116) 3 (435)

Thermal conductivity @ 400°C (752 °F) W/mK 7.5 1 7.5 17 0.15 0.24

Thermal conductivity @ 800°C (1472 °F) W/mK 4.5 0.8 4.5 1.3 0.21 0.3

Table 1 : Comparison of Refractory Material Properties of Old and New Secondary Reformer

New Secondary Reformer Old Secondary Reformer


angular orientation of the base bolts, elevation

& angular orientation of the gas inlet and outlet

nozzles for the new Secondary Reformer are the

same as that of the existing Secondary Reformer

at site.

Picture 5: New Secondary Reformer as received

at site and ready for erection on temporary

foundation.

As-built dimension measurement of the old

Secondary Reformer was carried out before the

start of actual shop fabrication of the new one.

The as-built dimensions of the old Secondary

Reformer were checked with the aid of 'Total

Station' survey equipment. Dimensional

difference was noted in the bolt circle diameter

and the pitch of the base bolts from the

dimensions indicated on the drawing. The pitch

of the base bolts was observed to be not

uniform. These dimensions were incorporated

into the fabrication of the new Secondary

Reformer. The bolthole diameter of the base

plate of the new Secondary Reformer was

increased to accommodate the variation in the

base bolt pitch observed at site. This proactive

approach eliminated the problems that would

have been encountered if dimensional

corrections had not been incorporated in the new

equipment.

c. The air inlet piping of the new

Secondary Reformer had to be modified due to

the increased height of the new equipment and

also due to the change in design to air ring

header type. Uhde carried out stress analysis for

the modified piping arrangement. The existing

pipe supports and spring hangers of the air inlet

piping were observed to be adequate for the new

piping arrangement.

d. Experience of other plants with the Uhde

designed Secondary Reformer similar to our

new Secondary Reformer indicated higher jacket

water consumption due to the poor insulating

property of silica free type of refractory lining

and also due to the many air inlet nozzles cooled

by the jacket water. Hence the number of water

jacket vent pipes was increased from 2 to 4 to

handle the increased steam generated from the

water jacket. This will prevent the jacket water

from splashing out from the top seals of the

water jacket.

e. The Transfer Line (Gas outlet header)

from the Primary Reformer is welded to the gas

inlet nozzle of the Secondary Reformer. The

inside of the Transfer Line and the gas inlet

nozzle are refractory lined with Incoloy 800H

sleeve on the inner bore. The refractory joint

between the Transfer Line and the inlet nozzle

of the Secondary Reformer at the site weld is a

Z-joint with the inner sleeve overlapping the

sections with a sliding arrangement. This is to

allow for thermal expansion of the refractory

lining and the inner Incoloy Liner. (Figure 3).

Due to this arrangement, lifting out of the

Secondary Reformer without sufficient gap

between the Transfer Line and inlet nozzle of

the Secondary Reformer will damage the

internal refractory and the Incoloy liner of the

Transfer Line. Hence, the Transfer Line has to

be pulled away from the Secondary Reformer

after cutting of the site weld. (Picture 6)


Picture 6: Transfer Line pulling arrangement

The pulling away of the Transfer Line will also

result in movement of all the five sub-headers

welded to the Transfer Line and the Primary

Reformer tubes welded to the sub-headers.

Expansion gaps are provided around the

Catalyst tubes at Primary Reformer floor. These

gaps were also physically verified and checked

at site soon after the plant shutdown.

Extensive dimensional measurements were also

carried out on the inlet and outlet nozzles of the

new and old units to decide the exact cutting

location.

The edges of the refractory at the Transfer Line

end and the gas inlet nozzle end have to be

properly made to ensure correct Z-joint fit

between them after erection.

Any problem in this connection can lead to hot

spots at this site weld joint during plant

operation.

f. The Secondary Reformer gas outlet

nozzle is welded to the inlet nozzle of the

Process Gas Cooler (PGC), which is of

horizontal, double compartment design. Extra

precaution was taken to maintain the position

and level of the PGC inlet nozzle after cutting of

the Secondary reformer outlet nozzle

connection. Adequate hold down and movement

arresting temporary clamps were welded to the

support saddles of the PGC to prevent possible

cold pull back of the PGC or change in elevation

and position of the PGC inlet nozzle, after

cutting of the Secondary Reformer nozzle

connection.

Figure3: Old Secondary Reformer to transfer line joint Figure4: New Secondary Reformer to transfer line

joint


6.0 Site Erection

The erection activities can be divided into the

following activities.

1. Temporary foundation and erection of

new Secondary Reformer on it.

2. Installation of refractory lining and dry

out of refractory before turnaround.

3. Removal of old Secondary Reformer and

erection of new Secondary Reformer.

6.1 Temporary foundation and erection of new Secondary Reformer:

The temporary foundation was made on the road

closer to the Secondary Reformer due to site

limitation. The anchor bolts locations were fixed

with the help of the base ring template supplied

by the vessel manufacturer. The new Secondary

Reformer received at site was directly erected on

the temporary foundation and aligned vertically.

Perfect vertical alignment of the equipment on

the temporary foundation is of utmost

importance for later installation of the refractory

lining (Picture 7).

Picture 7: New Secondary Reformer erected and

aligned on temporary foundation.

6.2 Installation of refractory lining and dryout of refractory before turnaround:

Scaffolding was build around the vessel and

covered with tarpaulin to avoid overheating of

the steel surface by the sun. A platform was

built in front of outlet nozzle for material

transport and in between storage (Picture 8).

Furthermore a transportable air condition system

was used for best working conditions inside the

vessel.

The refractory installation was started with

casting of gas inlet nozzle at the bottom of

Secondary Reformer (Picture 9).

Picture 8: Platform in front of Secondary Reformer

Picture 9: Casting of inlet nozzle


In the next step the first brick rings made of high

alumina were placed on the bottom of secondary

reformer, which is the foundation of the whole

brick lining (Picture 10).

Picture 10: First bricks placed

After completion of the bottom, which is

designed with bubble alumina castable and one

layer high alumina castable on the top, the main

brick laying activity started (Picture 11 &

Picture 12).

Picture 11: Placing of brick in area of catalyst

dome

Until finish of refractory lining activities

Karrena had worked 30 days continuously in

day and night shift. 60 tons High Alumina

bricks, 30 tons High Alumina concrete and 60

tons Bubble alumina concrete were installed

during that time period (Picture 13).

Picture 12: Casting of secondary reformer neck.

Picture 13: Completed refractory lining

Shortly after finish of lining activities the dry

out equipment was installed and the dry out was

started. The heating of the vessel was performed

by using a high velocity gas burner and

combustion air fan. To provide a clear space for

the burner flame and ensure no possibility of

flame impingement to the internal Incoloy liner,

a temporary extension pipe was installed

(Picture 14).

The time period for dry out was 6 days with a

maximum temperature of 550 °C (1022

oF).

The complete activity was finished in the time

period as scheduled.


Picture 14: Dry out of refractory lining

6.3 Removal of old Secondary Reformer and erection of New Secondary Reformer

The gas inlet and outlet nozzle projection

measurements of the new Secondary Reformer

were transferred to the old one to mark the exact

cutting location at site. Cutting of the inlet and

outlet nozzle connections of the old Secondary

Reformer was carried out by rotary cutting

machine. This machine was also used to bevel

the nozzle edges for welding. The transfer line

was pulled away from the Secondary Reformer

by 40 mm (1.57”). (Picture 15)

Picture 15: Gap of 40 mm (1.57”) between transfer

line and Secondary Reformer inlet nozzle after

pulling.

Several site measurements in cold condition

with respect to fixed reference marks were taken

before the pulling process to confirm that the

transfer line, sub-headers connected to the

transfer line and the Primary Reformer tubes

also move along with it. These measurements

also helped in verifying that these items went

back to their original location after pushing in of

the transfer line.

A large tracked crane with lifting capacity of

600 tons was installed closer to both Secondary

Reformers. Land preparing and compaction was

done to protect the underground cables from

damage due to the high load of the crane

(Picture 16).

Picture 16: Crane positioned between the old

and new Secondary reformers.

The old Secondary Reformer was lifted out and

rested on compacted / levelled area closer to the

temporary foundation. The integrity of the gas

barrier closer to the cut edge inside the transfer

line was verified. The transfer line was edge

prepared and the internal refractory joint was

prepared to match the joint shape and dimension

of the refractory at the Secondary Reformer gas

inlet nozzle end (Picture 17, Picture 18 and

Figure 4).


Picture 17: Gas inlet nozzle refractory joint.

The new Secondary Reformer was shifted to the

original foundation (Picture 19) and the transfer

line was pushed back. The old Secondary

Reformer was then erected on the temporary

foundation for later dismantling of the refractory

lining before shifting it horizontally to the

storage yard.

Actual erection activities from start of cutting of

the inlet and outlet nozzles, refractory repair at

the nozzle connections and welding back the

nozzle connections were completed within a

period of 8 days.

Picture 18: Transfer line refractory joint.

Picture 19: Erection of new Secondary

Reformer.

The modification to the air inlet piping was

carried out in parallel to the other erection

activities. Hydrotest of the air inlet piping along

with the ring header and the air inlet pigtails was

carried out. Loading of the catalyst was

completed in one day and the plugs welded to

the air inlet nozzles were cut and removed after

completion of catalyst loading.

7.0 Actual performance

After the installation in Turnaround 2007, the

new Secondary Reformer was put in service in

December 2007.

Performance of the new Secondary Reformer is

satisfactory. After installation of the new

equipment there has been no observation of

fouling in the Process Gas Cooler till date.

After the 2007 Turnaround, due to improvement

in the downstream equipment the air to the

Secondary Reformer could be increased. In the

Secondary Reformer with the old design, this

would have led to an impingement of flame on

the catalyst, which was detrimental for the

catalyst. With the improved design there is a

margin for increasing air into the Secondary

Reformer. This has helped in increasing the

ammonia production by processing additional

amount of hydrogen received from the PSA

Hydrogen Recovery Unit of Methanol Plant.


This additional hydrogen is introduced upstream

of the Methanator.

The methane slip from the new Secondary

Reformer is 0.18% as compared to 0.35%

earlier.

8.0 Conclusion

The new design of the Secondary Reformer has

helped in reducing the methane slip and has

facilitated a higher throughput. This has resulted

in an increase of Ammonia production by

approximately 4 %.

Careful and thorough pre-planning and

proactive measures taken during engineering,

procurement and equipment fabrication as well

as during the plant shutdown helped in the

smooth replacement of the Secondary Reformer

in shortest time.


replacement of a 22 years old secondary reformer - gpic's .../fileser… · process licensor...

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