This document discusses draft and excess oxygen control in fired heaters. It provides information on excess air, flue gas quantity, stack effect, combustion air preheaters, air leakage through openings, fuel saving, and typical values of draft and excess air. The document recommends designing heaters to minimize excess air and leakage, and maintaining heaters to optimize efficiency while meeting emissions regulations. Reducing excess air through proper control can increase heater efficiency and reduce fuel costs and CO2 emissions.
Key Thermo-Physical Properties of Light Crude OilsVijay Sarathy
Process facilities are equipped with protection measures, such as pressure safety valves (PSV) & as a minimum, PSVs are sized for a fire case. To do so for a pressure vessel containing crude oil a key parameter is the Latent heat of Vaporization [Hv].
For pure components, the Joback’s Method can be employed which uses basic structural information of the chemical molecule to estimate thermo-physical data. However it can be complex for equipment that contains crude oil because the plus fractions [C7+] can contain thousands of straight chain, cyclic & functional groups. Therefore by splitting and lumping the crude fractions, a smaller number of components are arrived at, to characterize and be able to apply Equation of State (EoS) correlations to estimate the fraction’s thermo-physical properties.
The presentation is for the engineers of HIRA POWER PLANT,. The complete calculations for calculation of boiler efficiency are described in the presentation
The presentation discusses the various factors which affect the performance of Power Boilers including the quality of coal, airheater performance, air ingress etc.
Key Thermo-Physical Properties of Light Crude OilsVijay Sarathy
Process facilities are equipped with protection measures, such as pressure safety valves (PSV) & as a minimum, PSVs are sized for a fire case. To do so for a pressure vessel containing crude oil a key parameter is the Latent heat of Vaporization [Hv].
For pure components, the Joback’s Method can be employed which uses basic structural information of the chemical molecule to estimate thermo-physical data. However it can be complex for equipment that contains crude oil because the plus fractions [C7+] can contain thousands of straight chain, cyclic & functional groups. Therefore by splitting and lumping the crude fractions, a smaller number of components are arrived at, to characterize and be able to apply Equation of State (EoS) correlations to estimate the fraction’s thermo-physical properties.
The presentation is for the engineers of HIRA POWER PLANT,. The complete calculations for calculation of boiler efficiency are described in the presentation
The presentation discusses the various factors which affect the performance of Power Boilers including the quality of coal, airheater performance, air ingress etc.
This is course on Plant Simulation will show you how to setup hypothetical compounds, oil assays, blends, and petroleum characterization using the Oil Manager of Aspen HYSYS.
You will learn about:
Hypothetical Compounds (Hypos)
Estimation of hypo compound data
Models via Chemical Structure UNIFAC Component Builder
Basis conversion/cloning of existing components
Input of Petroleum Assay and Crude Oils
Typical Bulk Properties (Molar Weight, Density, Viscosity)
Distillation curves such as TBP (Total Boiling Point)
ASTM (D86, D1160, D86-D1160, D2887)
Chromatography
Light End
Oil Characterization
Using the Petroleum Assay Manager or the Oil Manager
Importing Assays: Existing Database
Creating Assays: Manually / Model
Cutting: Pseudocomponent generation
Blending of crude oils
Installing oils into Aspen HYSYS flowsheets
Getting Results (Plots, Graphs, Tables)
Property and Composition Tables
Distribution Plot (Off Gas, Light Short Run, Naphtha, Kerosene, Light Diesel, Heavy Diesel, Gasoil, Residue)
Oil Properties
Proper
Boiling Point Curves
Viscosity, Density, Molecular Weight Curves
This is helpful for students, teachers, engineers and researchers in the area of R&D, specially those in the Oil and Gas or Petroleum Refining industry.
This is a "workshop-based" course, there is about 25% theory and about 75% work!
At the end of the course you will be able to handle crude oils for your fractionation, refining, petrochemical process simulations!
SAS Global Coal-Fired Power Diagnostic Testing and Combustion TuningJustin Bennett
Due to recent strict EPA regulations, more stringent burdens will continue to fall upon our industry. Coupled with increasing competition, fossil fueled power plants are struggling to comply with government regulations and
competing in a turbulent market. SAS Global Power is the only firm that has the experience to accurately assess
your current operating conditions and provide the technology for you to effectively and efficiently produce power without exceeding emissions standards.
The SAS Global Performance Testing and Combustion Tuning Group specializes in the reliable examination of your fuel flows to the boiler, backpass emission mapping, visual flame conditions inside boiler, fly ash and coal analysis. Utilizing the collected data, a comprehensive report detailing current operating assessment will be provided. The report will include recommendations designed to improve combustion stoichiometry, while enhancing auxiliary efficiencies and reducing emissions.
The scope of the test report will depend upon your predetermined goals and system imbalances, which will be
determined from your own custom test program.
Our service is unique to the specific requirements of each plant, price quotes are prepared on a location-by-location
basis. Please contact us for a custom tailored proposal that meets all of your specific needs.
Power Cycle Components/Processes and Compressible Flow Analysis WebinarEngineering Software
Engineering webinar material dealing with power cycle components/processes (compression, combustion and expansion) and compressible flow (nozzle, diffuser and thrust) when air, argon, helium and nitrogen are considered as the working fluid.
Coursework material provides the technical performance analysis of compression, stoichiometric combustion (carbon, hydrogen, sulfur, coal, oil and gas) and expansion.
Episode 60 : Pinch Diagram and Heat Integration
The optimal allocation of mass and energy within a unit operation, process and/or site.
Optimal allocation can be based on economic, environmental or other important objectives.
SAJJAD KHUDHUR ABBAS
Ceo , Founder & Head of SHacademy
Chemical Engineering , Al-Muthanna University, Iraq
Oil & Gas Safety and Health Professional – OSHACADEMY
Trainer of Trainers (TOT) - Canadian Center of Human
Development
This is a preliminary text for the chapter. The Oslo Group is invited to provide comments on the
general structure and coverage of the chapter (for example, if it covers the relevant aspects related to
measurement units and conversion factors, and if there are additional topics that should be covered in
this chapter), and on the recommendations to be contained in IRES.
The current text presents the recommendations from the UN Manual F.29 as well as some points that
were raised during the last OG meeting. The issue of “harmonization” of standard/default conversion
factors still needs to be addressed. It was suggested that tables be moved to an annex. Please provide
your views on which ones should be retained in the chapter.
OPTIMIZATION OF A TURBINE USED IN COAL FIRED THERMAL POWER PLANTS BASED ON IN...ijmech
The purpose of current study is to analyze the effect of inlet steam temperature coming from the boiler on
thermoeconomic performance of a steam turbine used in a coal fired thermal power plant. Second law of
thermodynamics is used to develop the thermoeconomic model for the turbine. Analyses based on exergetic
and exergoeconomic criteria are done for the turbine used in a 210 MW power plant. Methodology is
explained with the help of an example. Effect of inlet steam temperature on the exergetic efficiency of the
turbine, unit product cost of turbine and unit product boiler has been shown. Optimization has been done
for the turbine as a trade off between the unit product cost of inlet steam from the boiler and unit product
cost of the turbine.
This is course on Plant Simulation will show you how to setup hypothetical compounds, oil assays, blends, and petroleum characterization using the Oil Manager of Aspen HYSYS.
You will learn about:
Hypothetical Compounds (Hypos)
Estimation of hypo compound data
Models via Chemical Structure UNIFAC Component Builder
Basis conversion/cloning of existing components
Input of Petroleum Assay and Crude Oils
Typical Bulk Properties (Molar Weight, Density, Viscosity)
Distillation curves such as TBP (Total Boiling Point)
ASTM (D86, D1160, D86-D1160, D2887)
Chromatography
Light End
Oil Characterization
Using the Petroleum Assay Manager or the Oil Manager
Importing Assays: Existing Database
Creating Assays: Manually / Model
Cutting: Pseudocomponent generation
Blending of crude oils
Installing oils into Aspen HYSYS flowsheets
Getting Results (Plots, Graphs, Tables)
Property and Composition Tables
Distribution Plot (Off Gas, Light Short Run, Naphtha, Kerosene, Light Diesel, Heavy Diesel, Gasoil, Residue)
Oil Properties
Proper
Boiling Point Curves
Viscosity, Density, Molecular Weight Curves
This is helpful for students, teachers, engineers and researchers in the area of R&D, specially those in the Oil and Gas or Petroleum Refining industry.
This is a "workshop-based" course, there is about 25% theory and about 75% work!
At the end of the course you will be able to handle crude oils for your fractionation, refining, petrochemical process simulations!
SAS Global Coal-Fired Power Diagnostic Testing and Combustion TuningJustin Bennett
Due to recent strict EPA regulations, more stringent burdens will continue to fall upon our industry. Coupled with increasing competition, fossil fueled power plants are struggling to comply with government regulations and
competing in a turbulent market. SAS Global Power is the only firm that has the experience to accurately assess
your current operating conditions and provide the technology for you to effectively and efficiently produce power without exceeding emissions standards.
The SAS Global Performance Testing and Combustion Tuning Group specializes in the reliable examination of your fuel flows to the boiler, backpass emission mapping, visual flame conditions inside boiler, fly ash and coal analysis. Utilizing the collected data, a comprehensive report detailing current operating assessment will be provided. The report will include recommendations designed to improve combustion stoichiometry, while enhancing auxiliary efficiencies and reducing emissions.
The scope of the test report will depend upon your predetermined goals and system imbalances, which will be
determined from your own custom test program.
Our service is unique to the specific requirements of each plant, price quotes are prepared on a location-by-location
basis. Please contact us for a custom tailored proposal that meets all of your specific needs.
Power Cycle Components/Processes and Compressible Flow Analysis WebinarEngineering Software
Engineering webinar material dealing with power cycle components/processes (compression, combustion and expansion) and compressible flow (nozzle, diffuser and thrust) when air, argon, helium and nitrogen are considered as the working fluid.
Coursework material provides the technical performance analysis of compression, stoichiometric combustion (carbon, hydrogen, sulfur, coal, oil and gas) and expansion.
Episode 60 : Pinch Diagram and Heat Integration
The optimal allocation of mass and energy within a unit operation, process and/or site.
Optimal allocation can be based on economic, environmental or other important objectives.
SAJJAD KHUDHUR ABBAS
Ceo , Founder & Head of SHacademy
Chemical Engineering , Al-Muthanna University, Iraq
Oil & Gas Safety and Health Professional – OSHACADEMY
Trainer of Trainers (TOT) - Canadian Center of Human
Development
This is a preliminary text for the chapter. The Oslo Group is invited to provide comments on the
general structure and coverage of the chapter (for example, if it covers the relevant aspects related to
measurement units and conversion factors, and if there are additional topics that should be covered in
this chapter), and on the recommendations to be contained in IRES.
The current text presents the recommendations from the UN Manual F.29 as well as some points that
were raised during the last OG meeting. The issue of “harmonization” of standard/default conversion
factors still needs to be addressed. It was suggested that tables be moved to an annex. Please provide
your views on which ones should be retained in the chapter.
OPTIMIZATION OF A TURBINE USED IN COAL FIRED THERMAL POWER PLANTS BASED ON IN...ijmech
The purpose of current study is to analyze the effect of inlet steam temperature coming from the boiler on
thermoeconomic performance of a steam turbine used in a coal fired thermal power plant. Second law of
thermodynamics is used to develop the thermoeconomic model for the turbine. Analyses based on exergetic
and exergoeconomic criteria are done for the turbine used in a 210 MW power plant. Methodology is
explained with the help of an example. Effect of inlet steam temperature on the exergetic efficiency of the
turbine, unit product cost of turbine and unit product boiler has been shown. Optimization has been done
for the turbine as a trade off between the unit product cost of inlet steam from the boiler and unit product
cost of the turbine.
An air pre-heater is a general term to describe any device designed to heat air before another
process (for example, combustion in a boiler) with the primary objective of increasing the thermal efficiency of
the process of the flue gas in a regenerative pre-heater. This project analysis how operation parameters of a
regenerative air preheater can be optimized in order to increase its efficiency and consequently the overall
efficiency of a boiler. As mention in phase-1 project the case study of RAPH is implemented in this work for the
reduction in air leakage by 30% and in order to improve the efficiency of RAPH-2 in Unit-I, TPS-I (Expansion)
of the Regenerative Air Pre-Heater was improved by reducing the leakage of air into flue gas in the RAPH, and
i t is minimized by replacing the ordinary radial seals into “Flexible Seals” and also by proper maintenance of
the RAPH and it is implemented for the experimental analysis. For this purpose, the RAPH in thermal power
station -1 expansion at neyveli is considered and studied for a period and suitable remedies have been
suggested.
International Journal of Engineering and Science Invention (IJESI) is an international journal intended for professionals and researchers in all fields of computer science and electronics. IJESI publishes research articles and reviews within the whole field Engineering Science and Technology, new teaching methods, assessment, validation and the impact of new technologies and it will continue to provide information on the latest trends and developments in this ever-expanding subject. The publications of papers are selected through double peer reviewed to ensure originality, relevance, and readability. The articles published in our journal can be accessed online.
Simulation of the effects of turbine exhaust recirculationZin Eddine Dadach
For an effective carbon capture by an amine mixture, the molar percentage of CO2 in the flue gas should be at least equal to 10%. Moreover, in order to reduce technical problems due to amine oxidative degradation, the molar percentage of O2 in the flue gas should be limited to 5%. One possible option for increasing the concentration of CO2 and decreasing the amount of O2 in the flue gas from power plants using natural gas is recirculation of a part of the flue gas.
SIMULATION, EXERGY EFFICIENCY AND ENVIRONMENTAL IMPACT OF ELECTRICITY OF A 62...Zin Eddine Dadach
The first part of this study is to simulate a Natural Gas Combined Cycle (NGCC) for a production of about 620 MW of electricity using the commercial software Aspen Hysys V9.0 and the Soave-Redlich-Kwong (SRK) equation of state. The aim of the second part is to use exergy-based analyses in order to calculate its exergy efficiency and evaluate its environmental impact under standard conditions.
Packed Bed Reactor for Catalytic Cracking of Plasma Pyrolyzed Gasijsrd.com
Packed bed reactors play vital role in chemical industries for obtaining valuable product, like steam reforming of natural gas, ammonia synthesis, sulphuric acid production, methanol synthesis, methanol oxidation, butadiene production, styrene production. It is not only used for production but also used in separation process like adsorption, distillation and stripping section. Packed bed reactors are work horse of the chemical and petroleum industries. Its low cost, and simplicity makes it first choice to any chemical processes. In our experimental work vacuum residue is used as a feed which is pyrolyzed in the primary chamber with the help of plasma into hydrogen and hydrocarbon gases which is feed stream to the Ni catalyst containing packed bed reactor called catalytic cracker. Ni loading in the catalyst about 70 % is used to crack or decompose lower molecular hydrocarbon in to hydrogen to maximize the energy content per mass flow of gas steam and also to minimize the carbon dioxide equivalent gases at outlet of the reactor. Since cracking is surface phenomena so the catalyst play important role in designing of reactor shape. Parallel Catalytic packed bed with regeneration and deactivation can be used for commercial production of clean fuel.
International Journal of Engineering Research and DevelopmentIJERD Editor
Electrical, Electronics and Computer Engineering,
Information Engineering and Technology,
Mechanical, Industrial and Manufacturing Engineering,
Automation and Mechatronics Engineering,
Material and Chemical Engineering,
Civil and Architecture Engineering,
Biotechnology and Bio Engineering,
Environmental Engineering,
Petroleum and Mining Engineering,
Marine and Agriculture engineering,
Aerospace Engineering.
Design and Development of Small Scale VAR System by Using Exhaust Gas of IC E...
Draft & O2
1. Engr. M. Usman Saeed
E-III Visbreaking& Gas Concentration Unit
Email:ing.usmansaeed@gmail.com
Pak ArabRefineryLtd| QasbaGujrat MehmoodKot DistrictMuzaffarGarh
DRAFT AND O2 CONTROL IN FIRED HEATER
2. PAK ARAB REFINERY LTD Department: Process
Visbreaking& Gas ConcentrationUnit Area: 200 (U – 130 & 411)
Engr. Engr. M. Usman Saeed – 5509
CONTENTS
Draft & Excess O2 Control in Furnaces............................................................................................ 1
1 Introduction....................................................................................................................... 1
2 ExcessAir........................................................................................................................... 1
3 Flue Gas Quantity............................................................................................................... 1
4 Stack Effect........................................................................................................................ 2
5 Combustion Air Preheater...................................................................................................2
6 Air Leakage Through Openings............................................................................................ 3
7 Fuel Saving......................................................................................................................... 4
8 CO2 Emissions..................................................................................................................... 4
9 Typical Values of Draft and Excess Air .................................................................................. 5
10 Draft Adjustments...........................................................................................................5
10.1 Excessive Draft— Positive Pressure Created.................................................................5
10.2 Excessive Draft— Negative Pressure Created............................................................... 5
11 Recommendations..........................................................................................................7
11.1 Design Stage............................................................................................................... 7
11.2 Maintenance .............................................................................................................. 7
11.3 ExcessAir Control .......................................................................................................8
3. PAK ARAB REFINERY LTD Department: Process
Visbreaking& Gas ConcentrationUnit Area: 200 (U – 130 & 411)
Engr. M. Usman Saeed – 5509 1
DRAFT & EXCESS O2 CONTROL IN FURNACES
1 INTRODUCTION
Processheatersare the largestconsumersof energyinmostplants.A refinery,onaverage,burns
approximately2billionBtu/hrof fuel infiredheaters.The total quantityof fuel burned(heatreleased) isso
highthat any improvementwill resultinsignificantfuelsavings. Highenergycostsandtighteremissions
regulationsrequire increasedunderstandingandcontrol of excessair.Anyreductioninexcessairwill raise
the efficiencyof aheaterand reduce total emissions.NOX emissionsare of the highestconcernina fired
heater,althoughexcessaircontrol will alsoreduce refineryCO2 emissions andboostheaterefficiency.
It isrecommendedthatthe flue gastemperature approach(definedasflue gastemperature leaving
convection,minusprocessinlettemperature) be between50°Fand 100°F, dependingonheatertube
material andthe cost of fuel.However,heaterefficiencymaydeclinewiththe degradationof heater
components.The degree of degradationisdependentonthe qualityof the maintenance program
implementedatthe refinery.
2 EXCESS AIR
Excessair isdefinedasthe amountof air above the
stoichiometricairrequirementthatisneededtocompletethe
combustionprocess.Excessoxygen(O2) isthe amountof O2 inthe
incomingairnot usedduringcombustion.Inanoperatingplant,the
airflowrate can be adjustedata fixedabsorbed-heatduty(constantfeed
flowrate andinlet/outletconditions) untilanoptimumfuel-to-airratiois
achieved.Itisimportanttonote that there isa limitonminimum
possible excessO2.Below thislevel,combustiblescanenterthe flue gas,
whichposesa safetyhazard.Heaterandburnermanufacturersestablish
thisminimumlimitduringthe designstage.Operatorsshouldalsokeepa
safe marginfor upsetconditions.
HigherexcessO2 helpsachieve astable flame inthe firebox.At
the same time,itreducesthe efficiencyof the heater.Asageneral rule,
3% O2 influe gas isequivalentto15% excessair.
3 FLUE GAS QUANTITY
Flue gasquantityincreaseswitharise inexcessair,whichlowers
heatand increasesthe fuel requirement.Figure providesacorrelation
betweenfluegasgeneratedduringcombustion,andexcessair.The
followingequationcanbe usedto calculate approximateflue gasquantity
for natural gas: QF = 1 + 0.167 3 (100 + EA)
Where:EA = excessair,%; O2 = vol% of flue gasoxygen(dry); QF =
flue gasquantityinlb/lbof fuel.Asageneral rule,flue gasquantityis
approximately20 timesthe fuel quantity at15% excessair.
4. PAK ARAB REFINERY LTD Department: Process
Visbreaking& Gas ConcentrationUnit Area: 200 (U – 130 & 411)
Engr. M. Usman Saeed – 5509 2
4 STACK EFFECT
The net draftavailable isthe draftcreatedbythe stack effect,minusfrictional andvelocitylosses.
The net draftshouldbe sufficienttoobtaina negative pressure alongthe heaterfluegaspath.
It isimportantto maintainasafe draft level inafiredheatertoachieve the bestpossible efficiency
and operation.The targetdraftof 0.1 inchWC issetat the heaterarch. A highervalue of draftwill resultin
ingressof “tramp air” intothe heater.Trampair takesheat from the
combustionprocessandexitsthe stack,reducingheaterefficiency.The
flue gassample takenfromthe stack doesnotrepresentthe actual
volume of O2available forcombustion.Itisthe sumof unusedO2 from
the firebox (actual excessO2) andO2 fromtramp air.
A positive draftvalue will resultinthe leakage of hotflue gases
throughopeningsinthe heater.Thisisa hazardousoperationthatcan
overheatthe steel structure,refractoryandheatersupports,and,
consequently,shortenheaterlife.
Figure providesthe value of draftgeneratedinthe heaterfor
flue gastemperature andambientairtemperature.Itshouldbe noted
that stack effectdecreaseswithanincrease insite altitude.The
calculateddraftshouldbe amendedusingthe correction factorforsite
altitude.The followingequationcanbe usedtocalculate the draft generatedinaheater:
Where:H = Height,ft;PATM = Atmosphericpressure,psia; TAMB = Ambientairtemperature,°R; TFG =
Flue gastemperature,°R.Asa general rule,forevery10 ft of firebox height,the draftincreasesby0.1
inchWC:Draft at burner(inchWC) ≈ 0.1 + HFB ÷ 100 where:HFB = Firebox height,ft.
5 COMBUSTION AIR PREHEATER
The typical combustionairpreheater(APH) will increase the
heaterefficiencyby approximately10%.Fuel gasgenerallycontains
H2S or sulfur,whichconvertintoSO2 andthenintoSO3.The APH’s
heat-transfersurface issubjecttocold-endcorrosioncausedby
condensationof sulfurtrioxide(SO3),whichresultsinAPHleakage.Air
preheaterleakage isone of the mostcommonAPHoperating
problems,andanysuch leakage resultsinareductioninthe overall
efficiencyof the heater.
In APHoperation,the flue gasisgenerallyatnegativepressure,
and the air isat positive pressure.Therefore,leakageoccursfromair to
the flue gasside.Thisreducesthe quantityof airavailable for
combustion,anditincreasesthe quantityof flue gasleavingthe APH.
Thisleakage canbe detectedbymeasuringthe fluegasO2 contentat the APHinletandoutlet.Any
leakage will resultinhigherfluegasO2 at the APHexit,comparedtothe APH inlet.Generally,the APHisnot
5. PAK ARAB REFINERY LTD Department: Process
Visbreaking& Gas ConcentrationUnit Area: 200 (U – 130 & 411)
Engr. M. Usman Saeed – 5509 3
equippedwithaflue gasO2 analyzeratthe inletandthe outlet;however,the inclusionof 2-in.connections
at the APH’sinletandoutletwillenable operatorstomeasure O2 levelsusingaportable analyzer.
(M 3 CP ∆T)FLUE GAS = (M 3 CP ∆T)AIR
For a typical fuel gasat 15% excessair: MFLUE GAS ≈ 1.05 3 MAIR ; PFLUE GAS ≈ 1.15 3 CPAIR (7)
∆TAIR ≈ 1.2 3 ∆TFLUE GAS
Where:M = Flowrate CP = Specificheat∆T = Temperature difference acrossthe APH.
Anyleakage inthe APHwill reduce the ratioof ∆TAIR to ∆TFLUE GAS. For example,fora10% leakage in
the APH,the ratioof temperature differencewillbe around1.1.
Figure indicatesthe percentage of airleakage basedonthe ratioof ∆TAIR to ∆TFLUE GAS fora typical
natural gas firing.
6 AIR LEAKAGE THROUGH OPENINGS
A firedheaterisnota 100% sealedunit;
there are alwaysopeningsthroughwhichairingress
(trampair) can move. The volume of trampair
dependsonthe openingsize andthe draftat the
locationof the opening.Afterthe draftatthe
openinglocationisestimated,the followingequation
can be usedtoestimate the airleakage throughan
opening:
∆P = C 3 0.003 3 ρ 3 V2
Thisequationcanbe simplifiedforthe
leakage calculationpurposebasedonthe following
data:
Molecularweight(MW) of air = 28.96;
Atmosphericpressure(psia)=14.7; Velocityhead(C)
= 1
where:ΔP = Draft at openinglocation,inchWC;ρ =Density of air at ambienttemperature,lb/ft3
;V =
Velocityof airthroughopening,ft/s; C = Velocityhead;QL = Airleakage,lbperft2
/s;T = Ambientair
temperature,°R.
Figure providesthe quantityof airleakage perft2
of openingsize.Thisfigureisbasedonanambient
air temperature of 60°F.Once the openingsize isknown,the amountof airleakage canbe estimated.The
estimatedaircanbe translatedintothe additionalfiringrate required.
6. PAK ARAB REFINERY LTD Department: Process
Visbreaking& Gas ConcentrationUnit Area: 200 (U – 130 & 411)
Engr. M. Usman Saeed – 5509 4
7 FUEL SAVING
The absorbedheatdutyof the firedheateris
constant.Anyincrease inthe O2level will reduce the
efficiency,resultinginahigherfiringrate.Thisincrease in
the firingrate will leadtoa rise instack temperature,
whichresultsinanotherreductioninefficiency.This
reduction,inturn,demandsafurtherincrease inthe firing
rate.
The methodof efficiencycalculationforoff-design
operatingconditionspresentedinAPI-560Appendix Gcan
be usedto estimate the stacktemperature whenexcessair
ispresent.Thismethodcanbe simplifiedforexcessairas
follows:
Where:TS = Flue gasstack temperature,°R; EA =
Excessair,%; TF = Feedinlettemperature,°R(TF1 = TF2)
Φ = Excessair correctionfactor
Once the newflue gasstack temperature atexcessairisknown,thenthe heaterefficiencycanbe
estimated. Figure showsthe estimatedfuel savingsforareductioninthe O2 level to3%. Thisgraph isbased
on a fuel price of $6/MMBtu. The designflue gastemperaturelinesindicate the baseline stacktemperature
(i.e.,the flue gasstack temperature at3% O2).
8 CO2 EMISSIONS
The volume of CO2 emissionsgeneratedinafired
heaterisdirectlyproportional tothe firingrate.In
combustionprocesses,fuel carbonconvertsintoCO2.
Therefore,excessairreductionwill lowerCO2emissions.
Figure providesestimateddecreasesinCO2 emissions
througha reductioninthe O2 level to3%.
7. PAK ARAB REFINERY LTD Department: Process
Visbreaking& Gas ConcentrationUnit Area: 200 (U – 130 & 411)
Engr. M. Usman Saeed – 5509 5
9 TYPICAL VALUES OF DRAFT AND EXCESS AIR
Draft referstothe flowof gasesthrough the heatgenerating
equipment,beginningwiththe introductionof airat the back of the burner.
Once combustionoccurs,the heatedgasleavesthe combustionchamber,
passesheatexchangersandexitsthe exhauststack.
5 - 10% for natural gas, 5 - 20% for fuel oil, 15- 60% for coal
Carbondioxide - CO2 - is a productof the combustionandthe content
inthe flue gasisan importantindicationof the combustionefficiency.An
optimal contentof carbondioxide - CO2 - aftercombustionis
approximately 10% for natural gas and approximately 13% forlighteroils.
10 DRAFT ADJUSTMENTS
Stack dampersandsecondaryair registersaffectthe draftandboth
adjustmentsare related.The hotgaspushessothat the pressure isalways
greatestat the firewall.The stackdraftpullsandwhencorrectlybalanced
the pressure at the bridgewallshouldbe close tozeroorveryslightly
negative.A processheateroperatingproperlywill alsohave azero,or
slightlynegative draft,atthe shieldsection.The firebox will be slightly
positive (+0.5to +2.0 “watercolumn(wc)) andthe stack will have arange of
-0.5 to -1.0” wc. Excessive draft,eitherpositive pressure ornegative
pressure,canleadto severe problemsinthe convectionsection.
10.1 EXCESSIVE DRAFT — POSITIVE PRESSURE CREATED
In Figure 4, the air registersare wide openandthe dampermostlyclosed.Thisgeneratesapositive
pressure whichforcesflue gasesoutwardthroughleaksinthe convectionsectionleadingtoserious
structure damage,as well asheatloss.
10.2 EXCESSIVE DRAFT — NEGATIVE PRESSURE CREATED
In Figure 5, the air registersare mostlyclosedandthe stackdamperiswide openleadingtoahigh
negative pressure inthe convectionsection.Coldambientairissuckedinthroughleaksinthe convection
sectionleadingtoerroneousoxygenreadings,aswell asheatloss.Inadditionthe excessive draftcausestall
flameswhichcanreach the tubesresultinginseriousdamage.
8. PAK ARAB REFINERY LTD Department: Process
Visbreaking& Gas ConcentrationUnit Area: 200 (U – 130 & 411)
Engr. M. Usman Saeed – 5509 6
9. PAK ARAB REFINERY LTD Department: Process
Visbreaking& Gas ConcentrationUnit Area: 200 (U – 130 & 411)
Engr. M. Usman Saeed – 5509 7
11 RECOMMENDATIONS
Heaterexcessaircontrol starts at the designstage.Well-designedheatershave low trampair.There
are three stagesof excessaircontrol:
Designstage
Maintenance
Control
11.1 DESIGN STAGE
A heaterhasmany potential leakpointsforairingress:
Clearance aroundthe bottomcoil guide (spigots)
Sightdoorsand peepholes
Headerboxes,manholesandotheropeningsforviewingandaccess
Modules andduct splice joints
Terminalsandcrossovertubes
Weldjointsonthe heatercasing
Soot-blowersleeves
The APH.
These leakpointsmustbe designedforthe lowestpossibleleakage.Suggestionsfordesigningalow-
leakage heaterincludethe following:
Seal the clearance space aroundthe bottom tube guidesbyusingafloorsleeve withanend
cap, or seal boots
Use sightdoors,withsafetyglass,thatare equippedwithaninterlockcoverorflapper
Use a self-closingpeepholecoverinthe heaterfloor
Ensure that headerbox panelsandotheropeningsare airtight,anduse gasketsbetweenthe
gaps
Seal-weldall splice jointsbetweenmodulesfromthe inside,oruse high-temperature
sealant;also,use closer-boltspacing(6in.fromcenterto center)
Seal all terminalsandcrossoveropeningswithflexible seals
Ensure that all headerbox drainpointsare plugged
Ensure that no leakage isoccurringthroughinstrumentmountings
Limitleakage throughthe APHduringthe designstage,andperformanair-leakage testin
the shop.
11.2 MAINTENANCE
Routine maintenanceof the heatersisessential,since corrosiveagentscanbe presentinflue gases.
Deteriorationfromsulfuroxidesoccursmostlyoncoldsectionsof the steel casing.Climateconditionscan
alsoleadto rustingon exposedsurfacesof the heatercasing.Suggestedinspectionand
maintenance methodsincludethe following:
Checkfor heatercasingcorrosion;if anyleaksare discovered,theyshouldbe sealedtostop
air ingress
Ensure that observationdoors(generally locatedinthe bottomsectionof the radiantbox)
are closedaftertechniciansinspectthe heaterflame
10. PAK ARAB REFINERY LTD Department: Process
Visbreaking& Gas ConcentrationUnit Area: 200 (U – 130 & 411)
Engr. M. Usman Saeed – 5509 8
Checkpeepholes,accessdoors,etc.,forproperclosing
Checkflue gasO2 contentinthe convectionsectionandonthe APH; if there isany increase
inO2contentacross the flue gaspath,it indicatesleakage
Use a smoke testduringheatershutdowntodetectleakage
Use infraredscanning,while the heaterisinoperation,topinpointlocationswithair
leakage;these will have localized,lowerheatercasingtemperatures
To reduce leakage inburners,keepall burnersinoperation,evenduringloweroperating
loads;and close the airregisterwhenaburneris takenoutof service.
11.3 EXCESS AIR CONTROL
Knowingthe targetflue gasO2 contentisthe firststepin excessaircontrol.Each heaterisunique in
itsdesign.The O2 level requiredtoachieve ideal combustionmaybe anywhere from1%–4% or higher,
dependingonthe designandoperatingcharacteristicsof the heater.
The followingtwoinstrumentsare necessarytocontrol excessair:
Flue gas O2 analyzer. Thisis the mostimportantinstrumentonthe heater.Itis
recommendedtoinstall anO2 analyzeratthe radiantsectionarch.
Draft gauge.A draft gauge shouldbe installedatthe heaterarch. The arch isthe pointof the
highestflue gaspressure inthe heater.
HeaterO2 and draftat the radiantarch shouldbe checkedand,if necessary,adjustedatleastonce
pershiftand wheneverthere isachange in processload.All operatorsshouldbe familiarwiththe heater
controls.Often,heaterswithairregistersandstackdampersbecome jammedsimplybecause theyare not
used. Figprovidestacticsforcontrollingexcessairina natural draft heater.Forcontrollingexcessairinother
typesof heaters, Table 1 andTable 2.