2. CO Boilers
Furnace Improvement Services (FIS) is a full service engineering and consulting
company, having completed over 300 engineering studies and projects. FIS currently has a
team of 40 skilled engineers on board with offices in Sugar Land, TX and in New Delhi, India.
We have experience in design and revamp of all types of CO boilers
CO Boilers
Most of the fluid catalytic cracking (FCC) units produce gases rich in carbon monoxide (CO).
This gas is burnt in a CO boiler to recover heat and produce steam.
The supply of CO gas is normally not sufficient to ensure destruction of CO. Supplementary
fuel raises the temperature of the CO gases to the ignition point and assures the complete burn-
ing of the combustibles in the CO gas stream . There are two types of CO boilers prevalent in
the industry. One design has a separate combustion chamber for CO burning and is followed by
a convection section for heat recovery. The other type is a water wall type boiler which is modi-
fied to burn CO gas.
Our Expertise
Furnace Improvements has worked on several CO Boilers in the past 15 years.
Scope of Services include:
♦ Increasing Capacity
♦ Improving Boiler efficiency
♦ Eliminate flow distribution problems
♦ Tube Failure analysis
♦ CFD Modeling
♦ NOx Reduction
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3. CO Boilers
Case Study - CO Boiler Revamp
An Illinois refinery had a carbon monoxide (CO) boiler in their Fluid Catalytic Cracking (FCC)
Unit. The CO boiler was more than 40 years old. The CO boiler’s convection section is used to
preheat the FCC charge and also generate superheated steam at 600 psig/710°F.
The boiler had three main problems:
♦ low economizer tube metal temperatures were reaching dew point levels
♦ high super heated steam temperature
♦ problems with tube supports in the hottest zones
The refinery approached FIS to provide thermal design for replacing the convection section of
the CO boiler. Furnace Improvements carried out the engineering study for replacing the con-
vection section. We conducted a detailed operation analysis of the existing CO boiler and built
a model of the existing design. With the model built, we were able to simulate the current oper-
ating conditions and predict the heater performance for the future operating conditions.
The convection section was redesigned to: Item Units Before Revamp After Revamp
Heat Duty
♦ Increase FCC feed flow rate MMBtu/hr 182.45 220.83
Total
Process Heat
MMBtu/hr 81.55 104.91
♦ Improve CO Boiler efficiency Duty
Process Flow BPD 41,995 48,000
♦ Prevent cold end corrosion of economizer
Process ∆T °F 674 - 459 694 – 459
♦ Eliminate flow distribution problems Steam Heat
MMBtu/hr 100.90 115.92
Duty
Steam Flow lb/hr 155,170 190,000
The new design was developed retaining the ex- Steam Outlet
°F 765 714
Temp.
isting soot blower locations, same platform eleva-
Economizer
tions, and without any additional firing require- TMT
°F 301 318
ment. The detailed engineering drawings of the Stack Temp. °F 636 577
convection section vendor were also reviewed. Efficiency % 68.0 72.6
0.55 Million*
Fuel Savings $ / annum
* Based on $3.0 / MM Btu
Savings
The proposed revamp took care of all the operating issues with the existing CO boiler. It was
estimated to save the client almost $550,000 per year. The boiler was commissioned in March
2003.
Revamping - Training - Troubleshooting
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4. CO Boilers
Case Study - NOx Reduction
A Texas refinery’s CO boiler was originally designed to generate 450,000 lb/hr steam @ 600
psig / 750°F by firing a combination of CO gas and refinery fuel gas.
Furnace Improvements (FIS) was approached to convert the CO boiler to a refinery fuel gas
fired boiler only and reduce the NOx emissions to 0.02 lb/MMBtu (15 ppm).
Case Study Results
FIS conducted a study and provided the client with various options for NOx reduction. Conoco-
Phillips selected the option of Ultra Low NOx Burners with flue gas recirculation for detail en-
gineering. FIS’ scope of services was comprised of the following:
♦ Ultra Low NOx Burners with steam injection
♦ Flue gas Recirculation
♦ New economizer to increase the efficiency by 3%
♦ Design of additional rows of super heater coil
♦ Remove CO burners from firebox and seal the CO ports with additional heat transfer
surface
♦ Computational fluid dynamics (CFD) modeling of the existing and new burners to pre-
dict the combustion scenario
The project was completed and commissioned successfully in December 2007 by FIS
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5. CO Boilers
Case Study - CO Slippage
ConocoPhillips Wood River Refinery has a CO heater (CCU-1) in their FCC unit. It is used to
combust the FCC off gas (mainly CO gas) from the spent catalyst regenerator unit. The hot flue
gases generated from combustion of FCC off gas are used to preheat the oil and generate super
heated steam @ 600 psig / 700ºF.
ConocoPhillips was installing a new SCR unit downstream of the CO
Heater as a part of the consent decree agreement to reduce the NOx
emissions. The new SCR requires a flue gas inlet temperature in the
range of 680-700 °F, which required reconfiguring the heat transfer
surface in the convection section. FIS modeled the convection section
for 5 proposed cases and provided a revised design.
FIS developed a CFD model of the existing combustion chamber and
found out that mixing of FCC off gas and air was very poor in the
combustion chamber leading to incomplete combustion in the firebox
and post combustion in the convection section. FIS also found out
that the burners were oversized and they were operating at a very low
fuel gas pressure.
CFD Models
FIG. 1 FIG. 2
Contour of CO Mass Fraction Contour of Temperature Distribution
FIS proposed modifications to the combustion chamber and verified the modifications with the
CFD. As shown in figure 2, CO is burned completely compared to the existing case. The flue
gas temperature pattern inside the combustion chamber is uniform compared to the existing
case.
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6. CO Boilers
Case Study Cont.
The CFD model predicted the following:
♦ Mixing of the FCC off gas and air in the combustion chamber is very poor. The CO enter-
ing the chamber sweeps along the floor and exit, which results in incomplete combustion
of CO. The flue gas temperature distribution is not uniform.
♦ FIS observed misdistribution of FCC off gas to the nine burners.
FIS proposed modifications to the CO plenum, the misdistribution is calculated via CFD model.
As shown in figure 3, the proposed modification ensured uniform distribution of FCC off gas to
all the burners. This coupled with the modifications made to the combustion chamber ensured
complete combustion of CO gas and reduced the CO emissions.
FIG.3
After FIS developed a CFD model of the proposed design and the model suggested a marked
improvement in the combustion of CO. Some of the modifications FIS suggested are as fol-
lows:
♦ Install correct size burners
♦ Install a baffle wall in the combustion chamber
♦ Inject FCC off gas in the flame zone.
♦ Increase the air velocity through over fire air port
All modifications to CO Heater (CCU-1) have been completed and it has been in
operation since February 2008.
Revamping - Training - Troubleshooting
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7. CO Boilers
Project Reference List
Mobil - (FIS 152) ConocoPhillips - (FIS 188)
Location: Beaumont, TX Location: Roxana, IL
Scope of Work: Rating of a CO Boiler Scope of Work: Performance improvement
study on CO Heater Convection Section
Citgo - (FIS 207) Citgo - (FIS 214)
Location: Corpus Christi, TX Location: Corpus Christi, TX
Scope Of Work: Performance Improvement Scope Of Work: CO Boiler Burner Inspection
Study for CO Boiler
ConocoPhillips - (FIS 243) ConocoPhillips - (FIS 263)
Location: Corpus Christi, TX Location: Borger,TX
Scope Of Work: CFD Modeling of BFW Dis- Scope Of Work: Design, Engineering and
tribution in CO Boiler Economizer Coils supply and erection services for conversion of
Unit No. 40 CO Boiler to Fuel Gas Fired
Boiler.
Citgo - (FIS 267) ConocoPhillips - (FIS 276)
Location: Corpus Christi, TX Location: Roxana, IL
Scope Of Work: CO Boiler Re-rating report Scope Of Work: CO Boiler Engineering
as a Flue gas cooler Study, Tuning and CFD modeling
ConocoPhillips - (FIS 299) Citgo - (FIS 349)
Location: Roxana, IL Location: Lemont, IL
Scope Of Work: CCU -2 CO Boiler H -2 Scope Of Work: Engineering Study for in-
Modification Re-rating study creasing steam production in CO Boiler
Revamping - Training - Troubleshooting
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8. Low Cost Value Added Solutions for Fired Heaters
Our Clients We have an Agent near You.
AUSTRALIA, SINGAPORE, TAIWAN
NEWZEALAND, INDONESIA Douglas Chang
& MALAYSIA Tel: +8862-2706-1544
Kate Gimblett Mobile: +8869-2106-9827
Tel: +61 (0) 7 5435 2205 china.abc@msa.hinet.net
Mobile: +61 (0) 417 087 129
kate@energysolutions.com.au
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Jose Fleischmann David P. Diggins
Tel: (+55) 11-5641-4361 Tel: +94-9497-6551
Fax: (+55) 11-5641-4361 Mobile:+94-9463-8591
jofleis@attglobal.net digginsinc@cox.net
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Paul Henry ARGENTINA & ARUBA
Tel: +450-676-3222 Carlos Alarcon
Fax: +450-676-5997 Tel: +58-441-6609-3444
bjuren@bellnet.ca Fax: +58-441-4366-8406
caav-ramasco@cantv.net
INDIA INDIA
Vijay Thiruvady R. Rajamani
Tel: 080-25530671 Tel: + 91 94483 79108
Tel: 080-25521125 Tel: +91 80 65971113
vrt@bgl.vsnl.net.in rajamani@iprefining.com
INDIA LOUISIANA, USA
Ajai Agarwal Charles H. Thatcher
Tel: +9111-4214-3751 Tel: 985-892-4224
Mobile:+9198-1015-9901 Mobile: 985-966-5513
aqology@gmail.com cht@bellsouth.net
MEXICO SOUTHEAST, USA
Jorge Ruiz Silva David Gangle
Cel: 1+52 55 54 62 04 09 Tel: +20-5437-1702
scubasha@hotmail.com Mobile:+20-5542-7006
dgangle@gancoheat.com
KUWAIT TEXAS, USA
Alex Ambi Stan McHugh
Tel: +965-2482-9160 ext.126 Tel: +713-839-8788
Mobile: +965-3384-1712 Mobile:+713-703-8907
alex@alzahemgroup.com sam.co@sbcglobal.net
UTAH, MONTANA, NEVADA,
IDAHO, WYOMING;
Allan Woodbury
Tel: +801-274-3333
Mobile: +801 918-4826
Northassociates@yahoo.com
Furnace Improvements Services Inc. A.G. Furnace Improvements Pvt. Ltd.
1600 Highway 6 South, Suite 480 K-33, Ground Floor
Sugar Land, Texas 77478 USA Opp. Balaji Estate, Kalkaji
Tel: (281) 980-0325 New Delhi, India 110019
Fax: (1877) 395-0760 Tel: 91-11-405-8-8696
Email: info@heatflux.com
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