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
Temperature(°C)
Temperature(°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
TEMPERATURE,°C
Dec-02
Jan-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

Catalyst Catastrophes in Syngas Production - I

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