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Fired Heater - Question Review - Final in
Analysis and Design of Algorithms (Đại học Đà Nẵng)
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FIRED HEATER - QUESTION REVIEW
Chapter 1
Question
Answer
1. In the fired heater, heat is produced by burning …….?
Fuel
2. What is happen when velocity in tube is too low?
Undesirable flow regime, Poor inside heat transfer coefficient,
Degrade or Depositing coke material in tube
3. What will happen when velocity in tube is too high?
Pressure drop may be high, Cost of operation high
4. How many method of heat transfer?
3 method (Conduction, Radiation, Convection
5. ________ Is enclosure in which flue gas is collected after
the last convection coil for transfer to stack of outlet duct
work.
Breeching
6. ________ connect tube in the same coil.
Headers or Return bends
7. __________ is the piping connecting two different tube
coil.
Crossover
8. The first two rows of convective tubes (in the direction of
flue gas flow) are called ?
Shock or shield tubes
9. How many requirement of design considerations?
8
10. Which zone is the highest temperature?
Radiant section
11. What kind of burners will help to improve the heat
uniformity in the firebox?
Small burner
12. Which is one of factor affect to the heat efficiency ?
Excess air
13. A device regulate draft through the stack is :
Damper
14. Where is a burner mounted in the fired heater?
On floor or wall
15. Which is received most of heat from the burner in the
fired heater ?
Radiant tubes
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Chapter 2
Question
Answer
1. Can be classified fired heaters according to : 5 ways
Note
a/ Phase behavior of process fluid
b/ Firedbox shape
c/ Tube coil layout
d/ Firing of radiant coil
e/ Draft
2. According to fluid phase behavior, classified fired heaters a/ Liquid phase only
into 4 types
b/ Vapor phase only
c/ Vaporrizing
d/ Other two-phase
3. According to firebox shape, classified fired heaters into 5
basic shapes:
a/ Vertical cylindrical
b/ Horizontal cylindrical
c/ Box
d/ Terrace wall
e/ Cabin or A-flame
4. According to tube coil layout, classified fired heaters into 4 a/ Vertical in series
types:
b/ Vertical in parallel
c/ Horizontal in series
d/ Horizontal in parallel
5. According to firing of the radiant coil, classified fired
heaters into 3 types:
a/ Single fired with process fluid in tubes
b/ Double fired with process fluid in tubes
c/ With the fire in a submerged "fire tube"
6. According to draft, classified fired heaters into 3 types:
a/ Natural draft
b/ Forced and Induced
c/ Forced only
7. In case of two-phase flow (fluid behavior), which is the
preferred tube coil layout?
a/ Horizontal in series
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8. In case of single fired with process fluid in tubes, the
advantage and the disadvantage are?
Chapter 3
1.Process and
economic
consideration
a/ The advantage is an economical arrangement and is used in
most heaters
The disadvantage is the ratio of peak to average flux is high
9. Typical of fired heater in Fig 3 (page 15), Fig 5 (page 17),
Fig 7 (page 18), Fig 8 (page 19) are?
a/ Fig 3: Box heater, horizontal in series
Fig 5: Terrace wall, vertical in parallel ( reformer heater)
Fig 7: Box heater, vertical in parallel ( steam-hydrocarbon
reforming heater)
Fig 8: Box heater, vertical in parallel ( catalytic reformer heater)
10. What heater in refinery are common use the vaporizing
fired heater:
a/ Crude oil, visbreaker and coker heater.
11. Choose the correct answer:
- Catalytic reforming unit uses vapor phase only fired
- Hydroprocessing plant uses other two phase fired heater
- Coking unit uses vaporizing fired heater
Question
1.Procedure of flue gas in fired heater follow as:
Answer
A. Fuel gas after burn become flue gas, then passes through
the radiant and convection section and up the stack
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Note
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2.Main part of heat exchange in fired heater?
A. Convection section and radiant section
3.Procedure for designing a fired heater tube coil is base on? A. Fix the process condition ( fluid flowrate, inlet and outlet
temperature of feed, absorbed heat duty), set the average heat
flux, tube size and layout
a.Heat flux and
temperature
4. What is unit of heat flux?
A . Btu/hr
5. Difination of average flux in fired heater?
A. Average Flux = duty of radiant section / total absorbed
head duty ( include convection and radiant)
A. Reduce the firing rate
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A. The hottest point on the tube will be on the side toward the
flame, where the surface is at a right angle to the flux
A: In the case of single firing, the ratio is 1.8, In the case of
double firing, the ratio is 1.2
A. This is the maximum temprerature that the process fluid sees.
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6.If the average flux is too high in the radiant section of an
heater , how to decrease this value?
7.Difination of Peak / Maximum flux in fired heater?
8.The ratio of peak to average flux ?
9.what is inside film temparature?
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10. About fired heater, the fouling parameter have
meaning:
11. Volumetric heat release is defined as:
A. The fifference between the inside tube metal temperature
and the maximum inside film temperature.
(Fouling temperature allowances are in the range 50 to 100 độ
F)
A. This is total heat release divided by firebox volume.
12.The temperature begins to decompose(crack) petroleum A. 700 độ F
hydrocarbon is?
13. How to minimize cracking to the extent that is
A. Choose process fluid velocities and flow regimes that will
economical.
result in good heat transfer coefficients
B. Minimize process fluid residence time at high temprature.
C. both using A and B
b.Velocity,
14. The tube diameter and number of parallel are
A. Velocity, flow regime , or pressure drop
Pressure Drop, determined by :?
and flow regime 15. Benefit of high velocity (flow rate) in tube is:
A.- Improves the inside heat transfer coefficient.
- It may result in a better flow regime for two phase process
fluids.
- It increase the shear rate at the tube wall, which may decrease
the rate of coke deposition.
16. Purpose of injecting steam or water into process coils?
A. Increase velocity, improve flow regime, and reduce coking
tendency.
c.Parallel tube
passes
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Answer: C
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17. What are unexpect results when using parallel tube
passes?
A. It lead to the possibility of unequal flow in passes.
pass staling mean: a
And requires additional and constant operator attention to
sudden decrease or loss
maintain the balance.
of flow in one pass
Unbalance flow ( Overheating tube pass, coking, pass staling)
18.why we shoud not split a two-phase process stream into A. It can't ensure equal vapor/liquid ratios in the various passes.
multiple passes?
d.Turndown
e.Natural vs
forced/induced
19. When we turndown operate of fired heat, it mean?
A: Operate fired heater at lower than design rate.
20. Fired heater with fuel oil burners can turndown
howmany percent of design capacity?
A. 33%
21. Fired heater with gas burners can turndown howmany
percent of design capacity?
A. 10%
22. Classification of fired heater base on draft?
A. Nature and forced/induced draft
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23.Disincentives when using forced/induced draft are:
f.Direct vs
indirect heating
24. Difination of direct heating:
25. Difination of indirect heating:
Combustion and 26. Difination of heating value:
fuels
a.Heat value
27. Difination of higher ( gross) heat value?
A. (1)Capital cost of fans, ducting, and control system;
(2) Operating cost of fans;
(3) Potential for shutdown due to failure of fans
(4) Potential for explosion hazard caused by failure of fans or
control systems
A. In a heating system , heat is transferred from flame or hot
flue gas directly to the process fluid, the two being separated by
a single tube wall.
A. In an indirect system, an intermidiate heat transfer fluid
carres heat from the fired coils to the ultimate users.
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A. Heat value is
A. The higher or gross heating value is that obtained with the
product water present as a liquid.
A. The lower or net heating value assumes the water remains in
the vapor state.
28. Difination of lower ( net) heat value?
b.Complete
29. Difination of complete combution?
Complete combustion that carbon may burn completely to
carbon dioxide, water vapor and sulfur dioxide.
Incomplete combustion that carbon burn incompletely, the
product contain unburned carbon or combustible gases such as
carbon monoxide, hydrogen, methance or other hydrocarbons.
30. Difination of incomplete combution?
31.Product of incomplete combustion process in fired
heater?
c.Flame color
d.Gas or oil?
the product contain unburned carbon or combustible gases such
as carbon monoxide, hydrogen, methance or other
hydrocarbons.
32.The different of the flame when burn liquid fuel and gas A, Flame is more luminous and longer and less predictalble
fuel?
shape than gas flame.
33. When burn fuel inside fired heater, the flame have
A.
yellow color, it mean :
- Fuel dissociate
- Higher Hydro/Carbon ratio
- Lower molecular weight in the same series of compounds.
34. why oil flame are typically characterized by a very bright A.
yellow ?
Because in the oil, there is so much free carbon around.
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35. Benefit of using gas for burning in fired heater?
A.
It is easier to handle ( control) , burns cleaner, less expensive,
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36. Choosen burner materials for fired heater depend on :
37. What are attention point when using oil for fired heat.
Heat transfer
A.
- The source reliability
- Operator attention
- Response time
A. - Requires separate oil guns and steam for atomization
The flame for a given heat release is longer and less predictable
shape than the flame in gas fired heater
- Oil burning produces ash and soot, design of heater's
convection should include provision for tube cleaning by on
tream water washing or soot blowing.
38. How many way of heat transfer using in fired heater.
a. Radiation
b. Convection
c. Conduction
A. Is defined as the total heat absored divided by the total heat
input.
Thermal
efficiency
39. Defination of Fired heater thermal efficiency
a.General
40. Defination of heat absored of fired heater?
A. Heat absored is heat transferred to process streams, to steam
generation and super heating coils, to boiler feedwater, etc…
41. Heat in put of fired heate is:
A. Heat input consists mainly of the net or low heating value of
the fuel burned.
A. 300 to 400 độ F
b.Definations
42. when efficiency of fired heater is around 90%,
temperature of cooling stack gas is in the range of:
43. Total heat input of fired heater include:
Draft
a.Defination
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44. Total heat absorbed of a fired heater is:
A. This is the net heat of combusion of the fuel plus the sensible
heat of the air, fuel and fuel atomizing medium.
A. The heat transferred to the process coils and to utility coils.
45. Total heat loss of a fired heater is know as:
A. It is the sum of radiation heat loss and stack gas heat loss.
46. Definition of the positive draft?
A. It is disired condition where absolute pressure inside the
heater is lower than that outside.
b.Scale, Units,
c. Adjustment of 47. Adjustment of draft depend on what factors of fired
draft
heater?
48. The minimum value of pressure in draft?
A. - Burner air registers
- Damper
A. 0.05 - 0.1 inch of water column
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Chapter 4
Question
Answer
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Note
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1 Where is the most heating loss in refinery
2 what are the causes of unsafe fired heater
3 what are the losses of fired heater incident
4 the production loss can be… sinigficant than the actual fire
loss
5 what are the main reasons of fires
6
7
8
9
how does the tube failure contribute to the fires
what are the factors for tube failure
what are the causes of tube overheating
the causes of lost flow
10 what are the main causes of coking/fouling
11 how can we measure the corrosion rate
12 the ways to reduce tube rupture due to corrosion
13 why feed stock switch can cause corrosion and coking
14 why firebox can be exploded
15 how does the firebox explosion happen
16 what the most common causes of firebox explosion
17 what are the causes of external fires
18 what if the fuel gas supplies are unreliable
19 what factors do we concern about unreliable fuel gas
20 what if the heating value too low
21 what if the heating value too high
22
23
24
25
26
dewpoint must be keep… the piping's lowest temperature
reliable fuel oil requires careful design to cope with…
why must we automize the fuel oil before burning
how burner's pressure are controlled
why and when have we to isolate the burners
27 how many ways do we have to isolate the burners
90% heating loss occured on fire heater
improper design, inadequate inspection or maintenace, and
operating procedure misuse
both financial cost and human loss
much more!
tube failure,explosion of unburned fuel from ignition, and
external fires
approximately 20 percent
overheating, and corrosion/mentallurgy
low flow or internal coking/fouling
pump, compressor failure, improper valve operating, process
turndown…
unanticipated type of stock , overheating the feed
generally based on operating experience, plus unanticipated
change
appropriate material selection, inspection strategies, and
carefully look at any unanticipated change
because new feed may contain new components incompatible
with existing tube design
accumulation and ignition of unburned fuel in the firebox
unburned fuel mixs with air plus ignition source such as hot
brickwall, lighting tourch…in firebox
improper light-off( ignition for startup) or equipment failure
leaks in fuel gas piping to the buners, leaks on the process piping
on furnace, and fires from outside firebox
burner plugging, flame impingement
heating value, the dewpoint, gas purity(or clean), and gas
pressure
make very large flame impinged on tubes that can not
withstand
can cause unstable burner operation due to velocities adjusted
through the burners
below
high pour-point stock,and dirty stock
keep fuel's viscosity controlled within the limit of burner
by adjusting the number of operating burner
to prevent unburned fuel entering the firebox in case of burners
not being lit-off
using blind of single block valve, or double block system
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28 in case of furnace having more than 100 burners, how can
we do to isolate the burner
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32
why oil fuel burner do not need to blind
what is the function of single block valve
can we use block valve to balance the firing
what is the main function of minimum fire bypass/pilot
33 what is the pilot burner
34 why and where have we to control the pressure of fuel oil
35 for large funace operating what shall we do first: incsrease
the air or oil fuel
36 what is the main function of tube skin temperature Tis
37 why must we design the minimum stop on pass control
valve
38 what is the main fucntion of purging
39 what are the diffirent between forced/induced and natural
darft purging
40 how to know the purging is sufficient
41 why do we need view port
42 why do we need to install Tis( temperature indicators) on
stack and arch of firebox
43 why is the minimum stop of damper used
44 what are the main purposes of using O2 combustion
analyzers
45 in which case should we use the CO analyzers
Chapter 5
Question
1. What are the goals of Furnace tuning ?
approved by operation manager to use ball valve at burner
header to block buners( burner header allow us to close group of
burners)
oil gun easily to remove away
to block immediately the upstream oil fuel
absolutely not, it can cause flame out in the firebox
prevent unburn fuel enter hot firebox by returning it through
bypass/pilot line
is the alternative way to re-light the burners
because it provide stable source of fuel to furnace, pressure
control valve installed on the main header upstream
increase the air first
to indicate the internal coking and flow condition
to prevent full closure of flow
to remove flammable vapor in the firebox at starup process
natural draft using steam, otherwise forced/induce using air to
purge
using gas detector to read the zero percent of gas
online observe the conditions of firebox and radiant section
operator can determine whether the firebox begin to go trouble
or the tube rupture in convection section
to prevent full closure of the stack causes flame-out in the
firebox
to monitor the combustion process, optimize fuel efficiency
in case of heat duty of furnace equal or greater than 50MM
BTU/H
Answer
- Safe and incident free operation
- Satify specific process goals and local operating constraints
- optimize efficency
2. What are the steps to accomplish Furnace tuning and
Three steps:
efficiency ?
'- Furnace assessment
- Determining an O2 target range
Furnace monitoring and tuning.
3. What are the main reason of the actual optimum O2 for a -Air leaks in the furnace
real furnace > 0.5%?
- Burner
imbalance
or bad
burners
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4. What is the theoretical optimum level for efficiency ?
250 ppm CO and 0.5 % combustion O2
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5. What are the causes of burner imbalance?
6. What is the Lower limit of O2?
7. What is the Upper limit of O2?
8. Why we has to determine an O2 target range?
9. What are the causes of hotspot ?
10. What is the most frequent cause of hot spots?
11. How to monitor hot spots ?
12. How to correct phase separation problem?
13. What will you do when overfiring occur?
14. What will you do when daft is high and the O2 is above
upper limit?
15. What will you do when daft is low and the O2 is above
upper limit?
16. what ways are used to keep convection section tubes
clean?
17. what is the reason lead to overfiring?
18. how to increasing the flow velocity when the phase
separation or the coking occur?
19. what will you do when the coking occur?
20. what are the causes of increased coking rates?
-Differences in air register setting
- Corrosion or plugging of burner tips or holes
- Improper maintenance of burner tips
differences in fuel pressure
O2 level at the point of CO breakthrough plus the size of sudden
downward changes
The Lower limit of O2 plus the size of swing or variation in O2
reading that occur during normal steady operation.
O2 target range is used to tune excess air that improve
efficiency.
External causes :
'- Flame impingement
- Overfiring
Internal causes:
- Loss of flow
- Phase separation
- Coking
Loss of flow
Visual checks, thermocouples on tube skin and infrared (IR)
thermograpphy.
Icreasing he flow velocity
Back off on the firing rate or increase the charge rate.
Close damper more
Close registers more
-soot blowing
- onstream water washing
when we try to transfer more heat than the tube surface can
absorb
-injecting steam
- reducing the tube size
- reducing the number of parallel passes
- increasing the hydrogen circulation rate - in reforming or
hydroprocessing units
-altering the charge mix
increase the flow velocity
-change to a charge stock with a higher coking propensity or one
that requires more heating at the same charge rate
-flow rates are too low
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