Problems, troubles in catalytic reactors. General guidelines for reactors operation optimization.

1. Trouble Shooting of Catalytic
Reactors
BY: NASIR HUSSAIN
PROCESS OPERATIONS ENGINEER REFINERY
CONTACT: NASIR.MUGHAL3010@GMAIL.COM

2. Introduction
Catalyst: “A catalyst is a substance that changes the rate of chemical reaction
without itself appearing in the products.” A catalyst changes the rate of a
reaction by altering the free energy of activation (or activation energy) without
altering the thermodynamic aspects of the reaction.

3. Catalysts at My Refinery
Sr. No Area Catalyst Process Reactions
01 Hydrocracker Ni Mo/Co Mo Hydrocracking
02 Platforming Platinum, R134 Naphtha Reforming
03 DHT Ni Mo/Co Mo Hydro treating
04 Isomerization Platinum Isomerization

4. Important Terms
1. Catalyst
2. Activity
3. Selectivity
4. Sintering
5. Channeling
6. Temperature runaway
7. Chemisorption
8. Cocking or carbon laydown

5. Definitions
Activation Energy: Activation energy, in chemistry,
the minimum amount of energy that is required to
activate atoms or molecules to a condition in which
they can undergo chemical transformation.
2.Activity: It is the extent to which the catalyst
influence the rate of reactions as measured by the
disappearance of the reactions. It is often expressed
as rate per unit volume.
3. Selectivity: It is the ability to promote the
particular reaction while minimizing the production
of unwanted compounds.
4. Catalyst Life: It is the period during which the
catalyst provide the required product at required
degree of selectivity and activity.

6. Catalyst Sintering:
Sintering is the process of compacting and forming a solid mass of material by
heat or pressure without melting it to the point of liquefaction. The atoms in
the materials diffuse across the boundaries of the particles, fusing the
particles together and creating one solid piece. Thermally induced loss of
catalytic surface area, support area, and active phase–support reactions.
Sintering on bulk catalysts is normally physical (Thermal) rather than
chemical phenomena. Sintering is strongly temperature-dependent. The rate
of sintering increases exponentially with temperature. Sintering may
result; Agglomeration, the sticking of particles to one another or to solid
surfaces, is a natural phenomenon. For powders and bulk solids,
agglomeration can be unwanted, resulting in uncontrolled buildup, caking,
bridging, or lumping.

7. Catalyst Channeling
It is the formation of specific flow path by process fluid through the catalyst bed.
Channeling can either result in an increase in DP or a decrease in DP depending on what
is causing it. If there is coking in the bed, then flow will be forced through paths that are
not coked. The reduction in flow area will cause a net increase in DP. If there are voids
in the catalyst bed due to poor loading of the catalyst into the reactor, then the void
spaces in the bed provide more open channels for flow. Flow takes the path of least
resistance and much of the catalyst bed is effectively bypassed.
If you have coking going on you will see a higher than expected reactor DP. It may or
may not be accompanied by erratic radial temperature profiles and/or difficulty
meeting product specs (if coking is uniform across the top of the bed then it may only
show up as higher than expected DP). If you have channeling due to poor catalyst
loading it will show up as lower than normal DP, difficulty meeting product sulfur specs,
and likely an erratic radial temperature profile.

8. Channeling
Channeling may be confirmed by checking radial temperature variations across reactor at
various levels. If the temperature variation is more than 6-10 deg C, there is a channeling. On
the question of “how to tell,” a well-designed pattern of radial bed thermocouples and the luck
of having them read accurately throughout the run are the best means of determining
channeling .

9. Definitions
Adsorption is the adhesion of atoms, ions or molecules from a gas, liquid or dissolved
solid to a surface.[1] This process creates a film of the adsorbate on the surface of
the adsorbent. This process differs from absorption, in which a fluid (the absorbate)
is dissolved by or permeates a liquid or solid (the absorbent), respectively.
Adsorption is a surface phenomenon, while absorption involves the whole volume of
the material. The term sorption encompasses both processes, while desorption is the
reverse of it.
Chemisorption is a kind of adsorption which involves a chemical reaction between
the surface and the adsorbate. New chemical bonds are generated at the adsorbant
surface. Examples include macroscopic phenomena that can be very obvious, like
corrosion, and subtler effects associated with heterogeneous catalysis. The strong
interaction between the adsorbate and the substrate surface creates new types of
electronic bonds.

10. Definitions:
Temperature runaway: Thermal runaway occurs in situations where an increase in temperature
changes the conditions in a way that causes a further increase in temperature, often leading to a
destructive result. It is a kind of uncontrolled positive feedback.
In other words, "thermal runaway" describes a process which is accelerated by increased
temperature, in turn releasing energy that further increases temperature. In chemistry (and chemical
engineering), it is associated with strongly exothermic reactions that are accelerated by temperature
rise. Typical causes of temperature runaway;
1. Loss of quench gas
2. uncontrolled firing in feed heater
3.Loss of cooling media
4. Sudden change in feed quality
5. Maldistribution of flows across the reactor causing hot spots.

11. Catalyst Deactivation
The loss overtime of catalytic activity or selectivity of the catalyst is called
deactivation. Loss in catalytic activity due to chemical, mechanical or thermal
processes.
Catalyst deactivation, the loss over time of catalytic activity and/or selectivity, is
a problem of great and continuing concern in the practice of industrial catalytic
processes.
Typically, the loss of activity in a well-controlled process occurs slowly. However,
process upsets or poorly designed hardware can bring about catastrophic
failure.

12. Types of Deactivation
1. Thermal
2. Chemical
3. Mechanical

13. Thermal
Thermally induced loss of catalytic surface area, support area, and active phase–
support reactions. Thermal degradation is the catalyst deactivation due to high
temperatures. This include normal or routine deactivation due to aging and also
due to plant upsets or thermal shocks. Following are the types of Thermal
degradation;
1. Sintering
2. Coking

14. Mechanical
Physical deposition of species (metals) from fluid phase onto the catalytic
surface and in catalyst pores. In addition, loss of catalyst surface or any other
problem due to high velocity of fluid is mechanical loss.
Moreover, any damage due to mechanical parts problem also comes in this
category.
1. Fouling due to heavy metals
2. Attrition/Crushing

15. Chemical
Deactivation of catalyst due to chemical reactions on the catalyst surface is
Chemical deactivation. It can permanent or temporary. Following are examples of
Chemical deactivations;
1. Poisoning
2. Chemical reactions; and Phase transformations
3. Coking can also come in this category.

16. Mechanisms of Catalyst Deactivation

17. Catalyst Poisoning

18. Poisoning
Poisoning basically involve chemisorption of reactants or products or feed
impurities on the active sites of the catalyst surface, thereby decreasing
the number of active sites available for catalytic reactions. Since poisoning
involves chemisorption, it is known as chemical deactivation. This process
can be reversible or irreversible. Compound of sulphur and other
materials are frequently chemisorbed on nickel, copper and Pt catalysts.
In reversible poisoning, the strength of adsorption bond is not great and
activity is regained when the poison is removed from the feed. When the
adsorbed material is tightly held on the active sites, poisoning is
irreversible and permanent.

19. Troubleshooting of catalytic Reactors
Symptoms Causes
DP higher>design Catalyst degradation/ instrument error/ high gas flow/ sudden coking/ problem left in from
construction or revamp, internal damage.
Rapid decline in
conversion
unfavorable shift in equilibrium at operating temperature, for exothermic reactions/
[sintering]*/ [agglomeration], poisons in feed, temperature runaway
Gradual decline in
conversion
Sample error/ analysis error/ temperature sensor error/ [catalyst activity lost]*/
[maldistribution]*/ [unacceptable temperature profiles]*/ [inadequate heat transfer]*/ wrong
locations of feed, discharge or recycle lines/ faulty design of feed and discharge ports/ wrong
internal baffles and internals/ faulty bed-voidage profiles
Temperature runaways Change in feed composition, furnace controlled firing, uncontrolled reactions. feed
temperature too high/ [temperature hot spot]*/ cooling water too hot, failure of cooling
media
Local high
temperature/hot spot
[misdistribution of gas flow]*/ instrument error/ extraneous feed component that reacts
exothermically
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20. Troubleshooting of catalytic Reactors
Local low temperature within the
bed
[maldistribution of gas flow]*/ instrument error/ extraneous feed
component that reacts endothermic ally
Exit gas temperature too high instrument error/ control-system malfunction/ fouled reactor coolant
tubes.
Temperature varies axially across
bed
[maldistribution}
Symptom: Soon after startup, temperature of tubewall near top>usual and increasing and perhaps Dp increase
and less conversion than expected or operating temperatures>usual to obtain expected conversion
Cause: inadequate catalyst regeneration/ contamination in feed; for steam reforming sulfur
concentration>specifications/ wrong feed composition; for steam reforming: steam/CH4<7 to 10
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21. Troubleshooting of catalytic Reactors
Symptoms Causes
conversions<standard Reduction faulty, bad batch of catalyst/ preconditioning of catalyst faulty/
temperature and pressures incorrectly set/ instrument error for pressure or
temperature
poor selectivity bad batch of catalyst/ preconditioning of catalyst faulty/ temperature and
pressures incorrectly set/ instrument error for pressure or temperature
Dp<expected and conversion<standard maldistribution and axial variation in temperature/ larger size catalyst.
conversion<standard and Dp increasing maldistribution and axial temperatures different]*/ feed precursors present
for polymerization or coking
Dp for this batch of catalyst>previous batch catalyst fines produced during loading/ poor loading
conversion<specifications per unit mass of
catalyst and more side reactions
maldistribution/ faulty inlet distributor/ faulty exit distributor
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22. Troubleshooting of catalytic Reactors
increased side reactions and
conversion<specification
Catalyst loading not the same in all tubes.
Active species volatized [regeneration faulty]*/ faulty catalyst design for typical reaction temperature/
[hot spots]*.
Agglomeration of packing or catalyst
particles
[temperature hot spots
Carbon buildup inadequate regeneration]*/ [excessive carbon formed]*. [Catalyst selectivity
changes]*: [poisoned catalyst]*/ feed contaminants/ change in feed/ change
in temperature settings
Catalyst activity lost carbon buildup]*/[regeneration faulty]*/ [sintered catalyst]*/ excessive
regeneration temperature/ [poisoned catalyst]*/ [loss of surface area]*/
[agglomeration]*/ [active species volatized
Excessive carbon formed operating intensity above usual/ feed changes/ temperature hot spots.
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23. Troubleshooting of catalytic Reactors
Symptoms Causes
Dust or corrosive products
from upstream processes
in-line filters not working or not installed/ dust in the atmosphere brought in with air/ air
filters not working or not installed.
Loss of surface area [sintered catalyst]*/ [carbon buildup]*/ [agglomeration
Maldistribution faulty flow-distributor design/ plugging of flow distributors with fine solids, sticky byproducts
or trace polymers/ [sintered catalyst particles]*/ [agglomeration of packing or catalyst
particles]*/ fluid feed velocity too high/ faulty loading of catalyst bed/ incorrect flow collector
at outlet.
Poisoned catalyst Poisons in feed/ flowrate of “counter poison” insufficient/ poison formed from unwanted
reactions.
Reactor instability Control fault/ poor controller tuning/ wrong type of control/ insufficient heat transfer area/
feed temperature exceeds threshold/ coolant temperature exceeds threshold/ coolant
flowrate<threshold/ tube diameter too large
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24. Case Study
At 0200 hours on April 2, one of the six continuous
polymerization reactors experienced a temperature runaway.
That is, the reactor temperature rose exponentially from a
normal temperature of 150 to 175 ° F in a 30 – minute period.
Polymerization is an exothermic reaction that generates a signifi
cant amount of heat for each pound of polymer produced. The
heat of reaction is removed by circulating cooling water.
Polymerization reaction rates generally double with every 20 ° F
increase in temperature. When the reactor in question reached
175 ° F, the reaction was terminated by injection of a quench
agent.

25. Case Study
All the other reactors were operating normally. The temperature
control system on the reactor was such that an increase in
temperature caused an immediate increase in the cooling water
supply fl owIt was known that a small increase in catalyst rate
occurred right before the temperature began increasing. However in
the past, catalyst rate increases of this magnitude only resulted in a
slight temperature increase. Following this slight increase, the
reactor temperature very quickly returned to normal as the cooling
water control system responded. The heat exchanger that is used to
remove the heat of polymerization is periodically removed for
cleaning. OnApril 1, the exchanger seemed to be “ ok ”.

26. Case Study
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27. The End