Catalyst Catastrophes in Syngas Production - I

Gerard B. Hawkins, Managing Director

The Hazards Review incidents by reactor ◦ Purification…. ◦ Through the various unit operations to ◦ Ammonia synthesis

Nickel Carbonyl Pre-reduced catalysts Discharging catalysts Conclusion

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Catalysts are pretty reactive! They are designed to be so!

Under normal conditions they get on and do the job they were designed to do

However if we give them the opportunity they will also perform other reactions ◦ many of which generate large amounts of heat ◦ others produce toxic materials ◦ or other dangers to life/equipment


Hydrodesulfurization (CoMo NiMo) ◦ can hydro-crack higher hydrocarbons - exothermic ◦ can form carbon from CO2 via reverse shift to CO and

carbon via the Boudourd reaction

Ultra-purification ◦ similar hazards to other copper catalysts exothermic reduction exothermic oxidation (both Cu and CuS)


Hydrogen plant with two low sulfur feeds: ◦ high hydrogen content ◦ butane

HDS heated to 350°C(662°F) with hydrogen feed 50°C(90°F) exotherm observed – reduction? Then butane was commissioned Exotherm developed, went off-scale ◦ ruined catalyst, covered with carbon ◦ could have reached 700°C(1292°F)


Avoid high partial pressures of hydrogen on unsulfided HDS catalysts above 200-300°C(392-572°F)

Recognize the potential for hydrocracking of higher

hydrocarbons with hydrogen ◦ particularly if HDS catalysts are reduced


Nickel carbonyl Oxidation – exothermic Can break up when wetted causing high pressure

drop ◦ Note potential damage from rapid drying


Tube failures during start-up Catastrophic carbon formation Catalyst wetting (drying) Nickel carbonyl


Significant loss of tubes on start-up ◦ happens every year

Invariably firing > heat removal

Usually deviation from normal start-up procedures ◦ e.g quick recovery from trip condition

Low flow means tube temperature measurements

are unreliable


Be super vigilant during start-ups Have a look (carefully) ‘Stop and Think’ if you deviate from established

procedures Establish steam flow before flue-gas temperatures

reach 500°C(932°F) to provide heat-sink and improved temperature indication


Above 500°C (932°F) the Boudouard reaction will go quickly! 2CO → C + CO2

Do not allow steam ratio below 2.5/1.5 Whisker carbon can form within the pores and

cause the outer layer of catalyst to break off - similar to metal dusting but much faster


Lesson ◦ do not run with low S/C ratio trip bypassed


Wetting is unusual - although some older plants loaded catalyst into tubes full of water

Rapid drying is a problem for all catalysts as steam pressure generated within the pellet can break it apart

Also if one can break reforming catalysts this way then all other catalysts are more susceptible


A plant underestimated the extent of condensation in the early part of their start-up and then continued as normal assuming normal rates of heating would dry the catalyst

The net effect was a pressure drop build up due to broken catalyst - particularly in the bottom of the tubes where catalyst had been flooded with condensate


If you get catalyst wet - dry it carefully


In addition to the obvious explosion hazard - Air addition without combustion can lead to vessel damage from exotherms in high/low temperature shift ◦ Air oxidation of HTS catalysts can generate temperatures

of 800°C(1472°F) Lessons ◦ Prevent air feed until secondary temperature is above the

auto-ignition temperature around 650°C(1202°F) ◦ Review quality of air isolation most secure philosophy - double block with high pressure

steam between the valves


Burner misalignment/failure can generate hot spots on vessel walls and catalyst damage


JMC Secondary Burner


Start-up exotherms

Boiler leaks

Oxidation (covered with secondary reformer)


Caused by dehydration - usually due to extended nitrogen circulation during plant commissioning

Lesson ◦ If you hold fresh HTS under dry nitrogen for an extended

period (days) introduce steam gradually

1st Steam Introduced

0 20 40 60 80 100

250

300

350

400

450

500

600

700

800

Time, minutes

Tem

pera

ture

(°C

)

Tem

pera

ture

(°F)

Inlet

Top

Mid

Bot


Lesson ◦ if you have a severe boiler leak dry the catalyst carefully

before going back on line

HTS TEMPERATURE PROFILE BEFORE/AFTER WETTING

360

380

400

420

440

0.0 20.0 40.0 60.0 80.0 100.0

% BED DEPTH

TEM

PERA

TURE

, °C

Dec-02Jan-03

Pressure drop after = same as before


Reduction - Exothermic

Oxidation – Exothermic

Condensation


N2 carrier - temperature rise 30°C(54°F) per % hydrogen

NG carrier - temperature rise 20°C(36°F) per % hydrogen

NG carrier - additional hazard from catalytic oxidation of natural gas

Lessons ◦ Closely monitor temperature/hydrogen concentration ◦ With NG carrier keep temperatures below 230°C(450°F)


Has the potential to generate temperatures over 900°C(1652°F)

Lesson ◦ Ensure process air cannot reach LTS


Some catalysts will break up on contact with water Water will also wash chlorides down the bed

shortening catalyst lives

Lessons ◦ Ensure quench systems working properly ◦ Ensure secure isolation from process gas during

start-up when LTS is cold


Nickel carbonyl (see later) Overheating ◦ temperature rise 74°C(133°F)/ %CO, 60°C(108°F)/

%CO2 ◦ around 4% carbon oxides will raise temperature to vessel

limit ◦ First line of protection is LTS and CO2 removal LTS failure is probably OK if HTS working CO2 removal failure can quickly generate temperatures over

700°C(1292°F)


◦ Final protection is the high temperature trip note thermocouple must be set in relation to exotherm if thermocouple too near inlet or catalyst deactivated may not

respond if too far down the bed may respond too late

Lesson ◦ Ensure CO2 removal and methanator trips are working

and the trip thermocouple is in the correct position


Hydrogen plant tripped - due to cat in switch-house

Cause was clearly identified, quickly remedied Priority is to get the plant back on line All reactors are still hot so should be able to turn

all back on and recover quickly OK? Is this a familiar or unfamiliar task? What happens next?


Methanator temperature goes off-scale Vessel ruptures, catalyst pouring out of the hole

Cause believed to be delay is establishing liquid

hold-up in CO2 absorber


Oxidation can generate temperatures above 1600°C(2900°F) - see later

During shutdowns loop boilers can be at higher

pressures and leak into the loop ◦ Water/oxygen deactivates these catalysts

Lesson ◦ During shutdowns isolate and drain loop equipment

containing water


Odorless, colorless, OEL/PEL 0.001ppm Will form on any Nickel catalyst in the presence of

CO at low temperature Key rule - never expose nickel catalysts to CO

below 200°C(392°F)


A CO plant was shut down, the reformer depressurized and a CO containing feed isolated

The reformer pressure was seen to rise ◦ passing isolation valve

When the pressure was vented to flare the flame went black

Fortunately those involved realised that Nickel Carbonyl was a likely cause

This was confirmed and led to a costly decontamination process


Early days of ammonia manufacture in Europe 6 men were injured by Nickel carbonyl

The plant was forced to shut down due to a severe leak in the waste heat boiler after the secondary ◦ the HTS stopped reacting (too cold) so the process gas

was blown off and methanator isolated under N2

It then became necessary to fit a slip plate into the methanator exit line ◦ So the N2 purge was stopped ◦ temperature is now 25°C(77°F)


While work was progressing it is believed that process gas entered the methanator via a passing isolation valve and formed carbonyl

The 6 men injured were working on the joint or in the immediate vicinity

One analysis showed a carbonyl concentration of 5800ppm - 5 million times the OEL

Lesson ◦ consider using breathing apparatus when breaking into

lines close to the methanator


The stabilization of pre-reduced catalysts is only retained at low temperatures.

For transport drum sizes are limited ◦ natural heat losses help limit accumulation of heat ◦ drums also limit availability of oxygen

Reactors are very large drums! ◦ heat can accumulate ◦ we should limit the access to oxygen ◦ also moisture can destabilize pre-reduced catalysts


Ammonia converter, just loaded and under nitrogen needed some welding on the exit pipe work

With the exit and the top manway open a chimney effect allowed fresh air into the vessel

Self heating started - creating temperatures over 700°C(1292°F)

Lesson ◦ keep pre-reduced catalysts under nitrogen when loaded


Catalysts can remove oxygen from air - asphyxiation risk

Contact with water can generate hydrogen Carbon and sulfides can self ignite Absorbed gases can be evolved In-situ oxidation/ passivation can generate very

high local temperatures


This requires high gas flow to quench hot spots that develop ◦ otherwise local hotspots suck oxygen from the

surroundings Particularly risky if there has been an

upset/mechanical problem damaging the catalyst and affecting the flow


An ammonia converter catalyst was oxidized in-situ before discharge

There was no indication of high temperatures during this process

But local areas had got hotter than 1600°C(2912°F)


Lesson ◦ must achieve good flow distribution for in-situ oxidation


Most of these incidents occurred during a ‘non-routine’ or ‘unfamiliar’ activity

A short ‘Stop and Think’ can save lives, equipment and business

I have used an ‘Unfamiliar Tasks Procedure’ with a one page form to encourage a ‘Stop and Think’ when anyone got into unfamiliar territory

My personal experience plus the fact that this procedure is still in use today suggests that it is worthwhile


Catalyst Catastrophes in Syngas Production - I

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