Advances in Ma terials Physics and Che mist ry, 2012, 2, 169-172
doi:10.4236/ampc.2012.24B044 Published Online December 2012 (htt p://
Copyright © 2012 SciRes. AMPC
Progress of Modern P yrolysis Furn ac e Technology
Guotai Zhang, Bruce Evans
Technip USA Inc., Claremont, California, USA
Received 2012
This paper presents the fundamentals of thermal pyrolysis and discusses the modern ethylene furnace technology and its design
trends. Technip’s proprietary SPYRO® program is discussed for prediction of hydrocarbon cracking.
Keywords: E thylene Furnace; C racking Kineti cs ; Adiabatic Cracki ng; Non-Adiabatic Cracking; Radiant Coil; Convection Section;
Burn er and Select ive Catalytic Reduction
1. Introduction
Ethylene, the simplest of olefins, is used as a base product for
many syntheses in the petrochemical industry: plastics, solvents,
cosmetics, pneumatics, paints, p ackin g, etc. Today, the d emand
for ethylene is over 140 million tons per year with a growth rate
of 3.5% per year.
The production of ethylene has been dominated by the steam
cracking process since the end of World War II. The feed
stocks for steam cracking are hydrocarbons such as shale gas,
ethane, liquefied petroleum (LPG), naphtha, heavy gas con-
densat e, and gas oi l.
The cracking furnace is the heart of ethylene plant which
consists of the radiant section, the convection section and
transferline exchangers (TLE’s) for waste heat recovery. (See
Figure 1 ).
The objectives of this paper are to present the fundamentals
of thermal pyrolysis, to introduce different cracking types in the
furnace and to discuss the Technip modern furnace technology
and desig n t r e nds .
The variou s feedst ock cracking kin etics have been simulated
using Technip’s proprietary SPYRO® program which is widely
used by the industry for prediction of hydrocarbon cracking.
2. Fundamentals of Thermal Pyrolysis
Two scientific terminologies are used in the analysis below. [1]
Bond Energy
Bond energy is a measure of bond strength in a chemical
bond. The larger the bond energy, the stronger the bond and
hence t he higher t emperature required to break it.
Bond Length
Distance between centers of bounded atoms is called bond
length. There is a general trend in that the shorter the bond
length, the higher the bond energy.
The general t hermal cracking trend is listed belo w:
a) Th e H-H bond energy is higher than the C-H bond energy
and C-H bond energy is higher than the C-C bond energy. Thus,
the C-C bond is easier to break than H-H and H-C bonds, and
the H-C bond is easier to break than the H-H bond.
Table 1. Bond Length and Bond Energy.
Bond Type H-H H-C C-C C=C C≡C
Bond Length Picometers* 74 109 154 134 120
Bond Energy kcal/mol 104 99 83 147 200
* 1 Picometer = 10-12 m
Saturat ed
Cracked Gas
A ----- Non-Adiabatic Cracking-MFPH-2
A ----> B Crossover Piping Volume (Adiabatic Cracking) -CPV
B ----> C Firebox (Thermal Cracking) -FB
C ----> D Transferline Volume (Adiabatic Cracking) -TV
D ----> E Transferline Exchanger (Non-Adiabatic Cracking) -TLE
Steam Drum
Figure 1. Eth yl en e cr acking furna ce.
Copyright © 2012 SciRes. AMPC
b) The dehydrogenation ability of a hydrocarbon depends
upon its structure. Tertiary H is easily dehydrogenated and
Primary H is more difficult to dehydrogenate. The dehydroge-
nation ability is in the order of
Tertiary H > Secondary H > Primary H
c) Order of bond energy for Carbon-Carbon bonds is:
C≡C > C=C > C-C
d) Paraffin stability is lower with the molecular weight in-
crease or the longer carbon chain length. There is a general
trend in that the longer the carbon chain length the lower the
bond energy and h en ce the easier cr ackin g (breaki ng th e C-C o r
C-H bond) will occur. Therefore, the cracking temperature for
hydrocarbon molecules with long carbon chain length will be
e) Heat stability will be different for hydrocarbons with var-
ious structures. For hydrocarbons with the same numbers of
carbon atoms, the heat stability order is
Aromatics > Naphthene > Di-olefins > Olefin > Paraffin
3. Different Cracking Types in Pyrolysis Furna ce
Undesired cracking reactions can take place in the convection
coil MFPH-2, crossover piping, transfer line or Transfer Line
Exchanger ( TLE) as shown in Figure 1. The cracking react ion s
which take place in the convection section and TLE are
non-adiabatic cr acking. The cracking react ions in the crosso ver
piping and transfer line are adiabatic cracking reactions and
those that occur in the radiant box are thermal cracking. [2]
The extent of both the non-adiabatic cracking reactions and
the adiabatic cracking reactions depends on the hydrocarbon
feed type, st eam/ carb on mole rat io , mixed feed te mperat ure an d
pressure as well as mixed feed Residence Time (RT) in the
crossover piping or furnace effluent RT in the transfer line vo-
4. Modern Furnace Technology and Design
In this sectio n we descri be the state-of-art stea m cracki ng tech-
nology and its design trends.
4.1. Build Larger Ethylene Furnaces, Pl ants and
Toda y, the largest single cell gas cracking furnace produces 210
KTA ethylene, and the largest single cell liquid cracking fur-
nace produces 170 KTA ethylene. Limits of these technologies
have no t yet been reached.
The largest ethylene plant has 1500 KTA ethylene capacity.
New mega plants with 2000 KTA ethylene capacity are under
Currently, the world’s largest ethylene complex is Formosa
Petrochemical Corporation which produces about 3000 KTA
4.2. Develop Novel Radiant Coil
New radian t coils have b een develop ed to enhance heat t ransfer
and increase furnace run length, selectivity or operating capac-
a) SFT (It has been granted a patent)
Technip has developed a new coil, Swirl Flow Tube (SFT)
by bending tube process which can vary the amplitudes and
pitches of the tube swirl to reduce tube skin temperature or
increase run length and/or capacity.
For the same feed and feed rate with on-stream time of 50
days, the maximum Tube Metal Temperature (TMT) of SFT is
about 50 oC lower than that of bare tube. In other words, feed
rate can b e increased 23 % to reach maximu m TMT of 10 70 oC
at 50 days.
Similar comparisons can be made on run length impact at
constant capacity or on selectivity improvement with shorter
coil l ength and short resid ence time.
Swi r l Flow Tube (SFT)
New coils geometry to improve selectivit y and/or
longer run length and/or higher capacity
Recent Innovations:
Swirl Flow Tube s (SFT) with varying amplitudes
and pitches
b) GK-7 Coil (It has b een granted a patent)
A new coil called GK-7 has been developed by Technip,
which has an improved layout of the Technip GK-6. It has fol-
lowing features [3]:
Inlet tubes have an extra wide t ube spacing
Outlet t ubes have an IN-LINE layout
Small differ ence in TMT’s betwe en inlet/outlet passes
Symmetrical tube layout
Easier access for coil mai ntenance
A fur n a c e wi t h GK-7 coils is currently being constructed.
c) Crackin g t ube surface treat ments
Cracking furnace tub es can use a su rface treatment to redu ce
coking. For example, Kubota’s ANK 400 achieves unprece-
dented furnace run length by dramatically lowering coke for-
mation. The key to coke reduction is an inert, nanocrystalline
spinel surface which has been proven to reduce both catalytic
and pyrolytic coking.
d) Improved cracking tube alloys
Improved alloys can contain higher levels of chrome and
nickel, but can also contain other additives. For example, the
Schmidt + Clemens HT-E alloy, with a certain level of alumi-
nium (Al) addition, is claimed to significantly reduce the effect
of catalytic coking, while also offering protection against oxi-
dation and carburization.
The positive impact on run length has been verified for HT-E
compared to conventional 25/35 or 35/45 (Cr/Ni) alloys.
Copyright © 2012 SciRes. AMPC
4.3. Use DP Transfer Line Exchanger (TLE)
Direct coupled primary TLE (Double Pipe Type) is often used
for mega ethylene cracking furnace to cool down the furnace
effluent . DP pr imary TLE has following benefits:
Mechani cal cleaning is not r equired
No tube sheet erosion or tube plugging
Lower transf er line ( adiabatic) volume
Increase furnace availability
Fewer fittings at the radiant coil outlets
4.4. Optimiz e Burn ers an d Furnace Fir ing
Firebox program is used with the input of fuel gas/air data and
heat releas e pattern to si mulate t he furn ace firin g behavio r. The
burner input information may update after the Vendor’s burner
test results. Finally, CFD is used to model the burner fluid dy-
namics in th e firebox.
4.5. Reduce Flue Gas NOx Emission
There are two methods to reduce the amount of Oxides of Ni-
trogen (NOx) in the flue gas in order to meet US Environmental
Prot ection Agency (EPA) requirement s .
First is to use low NOx staged fuel or ultra low NOx staged
fuel burners to reduce the NOx in the range of 0.045-0.06
lb/MMBtu (HHV, High Heating Value) in the flue gas.
Secondly, Selective Catalytic Reduction (SCR) system can
be used to reduce the NOx down to 0.01 lb/MMBtu (HHV).
The SCR consists of SCR catalyst, an ammonia injection
grid, and an ammonia vaporization skid. SCR technology is
designed to react ammonia and NOx over a catal yst to produce
nitrogen and water vapor. Catalyst is titanium vanadium on
either a ceramic honeycomb type or corrugated type carrier.
The catalyst is located in the convection section at a region
where the temperatu r e is suitable for catalyst operation.
5. SPYRO® Y ield Pred ict ion Mod el
The first SPYRO® program was released in 1977, which has
been continuously developed over 30 years.
SPYRO® is a unique program for prediction of cracking fur-
nace effluent yields as well as overall performance of the fur-
nace. SP YRO® is the only program which is based on rigorous
fundamental mathematical equations representing reaction ki-
netics of almost all chemical, thermo-chemical reactions in the
pyrolysis furnace.
SPYRO® is now used by more than 85% of the ethylene
producing industry worldwide. The latest program version and
kinetic model SPYRO®-7 covers all hydrocarbon species from
C2 to C42 and more than 7000 reactions. This version also
allows better flexibility in establishing the furnace and heat
recover y flowsheet.
6. Conclusions
1. There are different crackin g modes at five vario us regions
in th e ethylene fur nace. Majo r t her mal crac king i s in th e radian t
2. Today, mega furnace sizes ar e 210 KTA ethylene and 170
KTA ethylene for sin gle cell gas an d liquid feedsto cks, respec-
SPYRO®Kinetic model for radiant coil
Coking / runlengthprediction
Feedstock selection / cocracking evalution
TES TransferlineExchanger Simulation
Coking / kinetics / runlength prediction
FIREBOX Combustion model coupled with SPYRO
Analysis of heat release patterns
CONVEC Convection section simulation, complete
process and steam/BFW system calculation
EFPS Complete furnace simu lation with steam
balance and feed / fuel flexibilit y analysis
CFD Computational Fluid Dynamics to analyze
combustion ai r / flue gas system, decoke
effluent to firebox and furnace effluent to
Primary TLE
3. Novel radiant coils, enhanced tube layout and new types
of tube metallurgy have been developed which enhance heat
transfer an d incr eas e r un length and/or capacity.
4. Double Pipe (DP) heat exchanger has been widely used as
the primary TLE to quench the furnace effluent and generate
high pressur e s team.
5. Ultra low NOx staged fuel burners incorporating primary
and seco ndar y tips are u sed to reduce th e NOx in th e flue gas to
0.045 lb/MMBtu (HHV). Furthermore, Selective Catalytic Re-
duction (SCR) system can be used for the reduction of NOx to
0.01 lb/MMBtu (HHV).
[1] “Optimization of Reformer Inlet Temperatu re based on Thermal
Cracking of Feedstocks” at 2011 World Congress on Engineer-
ing and Technology (CET 2011)”, Guotai Zhang and Sanjeev
Sekhri, Paper ID #23177, Oct. 28 Nov. 2, 2011, Shanghai,
[2] “Impact of Cracking at the Inlet and Outlet Transitions of Ethy-
lene Furnace Radiant Sections”, Guotai Zhang and Bruce Evans,
Presented at “Technip Ethylene Technology and SPYRO® Inter-
national Conference”, Jan. 30, 2008 in Abu Dhabi. “New Type
Copyright © 2012 SciRes. AMPC
of Cracking Furnace Radiant Coil”, Johan
[3] van der Eijk, Paper ID #173546 at the AIChE 2010 Spring Na-
tional Meeting, March, 21-25, 2010 in San Antonio, Texas,