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Transcript of CombustionONE White Paper 13Oct10
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Application and Benefits of Combustion
Management to Fired Heaters
A White Paper
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Application and Benefits of Combustion Management to Fired Heaters
Sections
Introduction
Managing Combustion in Natural Draft Fired Heaters
How It Works
CASE STUDY: A Major Gulf Coast Refinery
The Recommended Best Industry Practice
The Technology
The Installation Process
Figures
Figure 1: Diagram of a Typical Fired Heater
Figure 2: Features and Benefits of TDLS Technology
Figure 3: TDLS Technology for Combustion Safety and Optimization
Figure 4: Basic Functional Capabilities of CombustionONE
Figure 5: Refiners Participating in the API 556 Task Team
Figure 6: CombustionONE - An Integrated Solution
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Application and Benefits of Combustion Management to Fired Heaters
CombustionONE solution unites a TDLS analyzer
with a dedicated control system and a safety system
certified to meet FM NFPA and SIL 2 standards.
The intrinsic value gained by adopting this newcombustion technology can be summarized by the
following:
Best Industry Practices
which can only be satisfied with new technology
Increased safety
because both air and fuel are continuously controlled
Improved thermal efficiency
as excess air is always optimized .............................
Longer fired heater life
(asset reliability) since heat is not concentrated at the
bottom of the convection section
Lower greenhouse gas emissions
through a more efficient use of fuel
Second only to raw materials costs, energy is
the leading cost pressure currently affecting
manufacturers. New analysis techniques, such
as tunable diode laser spectroscopy (TDLS),
can improve efficiency, maximize throughput,
reduce emissions, and improve safety and
reduce energy in combustion processes.
ARC INSIGHTS, INSIGHT# 2009-50MP,
November 2009
Introduction
While fired heaters are used throughout refining and
petrochemical processes as the source of process
heat, they carry inherent risks and costs that make
operating without current technologies problematic.
To address safety concerns, Industry standards
are upgrading their recommended practice for
Instrumentation, Control, and Protective Systems for
Fired Heaters and Steam Generators. While not yet
required by regulation, plants not meeting the best
Industry Practice guideline, will be at added risk in
the event of an incident on a fired heater. Since many
natural draft fired heaters do not meet this guideline
with existing instrumentation and control systems,
an upgraded system consisting of recommend
technologies will be needed. Further, since most
natural draft fired heaters have only automated control
of the fuel supply, not air, excess air is often applied to
the combustion process, reducing thermal efficiency.
According to ARC INSIGHTS, Second only to raw
materials costs, energy is the leading cost pressure
currently affecting manufacturers. New analysis
techniques, such as tunable diode laser spectroscopy(TDLS), can improve efficiency, maximize throughput,
reduce emissions, and improve safety and reduce
energy in combustion processes.
This paper highlights and describes the application
of a new combustion management system by
Yokogawa called CombustionONE. By incorporating
Tunable Diode Laser Spectroscopy (TDLS)
technology, this new system has the ability to
simultaneously control air and fuel supply to fired
heaters by measuring average gas concentrations
across the high temperature radiant section. Cross
sectional averages that measure O2and CO at high
temperatures has only recently become reliable
with the introduction of the TDLS technology. The
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Application and Benefits of Combustion Management to Fired Heaters
Managing Combustion in
Natural Draft Fired Heaters
The air supply for most fired heaters is natural
draft not forced air - and these heaters normally
lack the extent of automation as the other process
units in the plant. Natural draft fired heaters, as the
name implies, use flue gas buoyancy to support
combustion. These heaters can be either cylindrical
or box type (see Figure 1 below). The buoyancy of
the flue gas (combustion product) relative to the
surrounding air is determined by the product of the
average density of the flue gas and the height of the
heater. Furnaces are designed to run at a pressure
of -0.05 to -0.1 WC at the top of the radiant
section, whether a heater is natural draft, induced
draft or forced draft. Figure 1 provides a simplified
diagram of a typical fired heater.
Because of the lack of
air control, operators
will typically allow
excess air into the fired
heater, reducing its
thermal efficiency.
The low level of control on most fired heaters
is due, at least in part, to the historical lack of
reliable, effective instrumentation and automation
technology to simultaneously measure and controlthe fuel, gas concentrations, and the air/fuel ratio.
An oxygen (O2) sensor is typical ly required at the
stack base for thermal efficiency calculations, which
require total excess air. While operators attempt to
maintain excess O2in the furnace for safety, the
amount indicated from an existing sensor may be
incorrect due to tramp air. In fact, it is possible that
the burners may be starving for air, despite excess
oxygen at the stack base. Because of the lack of
air control, operators will typically allow excess air
Stack
Damper
Breeching
Process Fluid In
Process Fluid Out
Coil
Burner
Radiantsection
Shield section
Convectionsection
Natural Air Draft
Figure 1: Diagram of a Typical Fired Heater
Inefficient combustion can be attributed
to the air/feul ratio. Too much excess air
(air rich) results in loss of efficiency and
increased NOx emissions, while too little air
(fuel rich) is downright dangerous. Carbon
monoxide measurements provides an indi-
cation of fuel-rich conditions, while oxygen
measurements indiate air-rich conditions.
The optimal control point is the lowest pos-
sible excess air value that does not cause the
system to enter an unsafe condition or violate
emissions limits.
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Application and Benefits of Combustion Management to Fired Heaters
into the fired heater, reducing its thermal efficiency.
The lack of effective instrumentation to continuously
and rapidly measure O2and CO in the combustion
chamber of fired heater introduces considerable
safety risk. Apart from the simultaneous control offuel and air concentrations, it is possible for fuel-
rich conditions to arise which increases the potential
explosion risk. Note that under fuel-rich conditions,
temperature/fuel controllers no longer work properly.
The detection of combustibles - primarily CH4- in
the radiant section of the fired heater is recom-
mended by the American Petroleum Institute per API
556; however, traditional analyzer technology cannot
be installed in the radiant section due to the high
temperatures. As noted above, without accurate
measurements of CH4, O
2and CO concentrations,
operators tend to allow excess air than necessary
in the heater, reducing its thermal efficiency. To
properly control the combustion air, CH4and CO
must be measured at the top of the radiant section
where combustion is completed, regardless of the
burner loading. Note that O2and CO will coexist
within the flames, where the temperature may be as
high as 2,200 degrees F. Low NOx burners may use
delayed completion of combustion through staged
air/fuel mixing, or external recirculation of cooler
flue gas with combustion air, reducing peak flame
temperature. In either case, to effectively control the
combustion process it is essential to measure O2
Apart from the simultaneous control of
fuel and air concentrations, it is possible
for fuel-rich conditions to arise which
increases the potential explosion risk.
and CO at the top of the radiant section, ideally one
foot below the roof tubes. This is where combustion
reaction is expected to complete under all heater
operating loading. This is an ideal application of
CombustionONE, which employs new TDLS tech-nology. Using the TDLS in concert with a dedicated
controller, a cross section average O2and CO
density can be measured to determine the right air/
fuel ratio, rather than a localized spot measure-
ment of these gases. Using an average O2and CO
density produces safer burner control and greater
overall heater efficiency. Figure 2 lists the features
and benefits of TDLS technology, which has distinct
advantages over single point, in-situ analyzers that
may give false readings because of varying gas con-
centrations at different locations in the fired heater.
Fired heaters have two principal unsafe operating
conditions that must be avoided:
Fuel Rich - where air is reduced, CO will be
produced by the burners and excess O2will be
lower, which results in excess fuel (CH4) from
the burners
Flame Out where Loss of flame results in rapid
loss of gas temperature. O2levels are high as
burner air is not reduced by combustion, and
un-combusted fuel (CH4) is present
Figure 2: Features and Benefits of
TDLS Technology
Source: ARC INSIGHTS, INSIGHT# 2009-50MP, November 2009
Benefit
Sample conditioning not required
Real-time data for control
Interference-free analysis
Suitable for operations in harsh environments
In-situ analysis
Fast response
Tunable laser
Non-contact sensor
Feature
Low maintenanceOptical sensor
To properly control the combustion air,
CH4and CO must be measured at the
top of the radiant section where com-
bustion is completed, regardless of the
burner loading.
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Application and Benefits of Combustion Management to Fired Heaters
Higher costs as operators increase O2flow to
avoid a fuel rich atmosphere
Unexpected demand for fuel, leading to unsafe
combustion conditions
Greater risk during a process upset
Risk of inadequate air control may not be
assessed correctly for process upset
Wet steam introduced on start up, requiring a
steam purge, risking ignition failure
Shorter life of the finned convection section with
afterburning due to presence of combustibles
Before Combustion Management
of CombustionONETM, the embedded control and
safety systems will ensure that these conditions are
avoided or that combustion is extinguished and fuel
flow is interrupted automatically if these conditions
are detected. The TDLS analyzer technology willreliably respond to all O
2events, where conven-
tional sensor technology will miss most such events.
Reduced O2and lower operating costs as the
fuel-air mixture is controlled
Fuel is limited to the available air to prevent
unsafe fuel rich combustion
CO and O2concentrations are safely controlledat the optimum levels
Unburned fuel is detected readily, avoiding
unsafe combustion
Process upsets are handled with controlled
combustion conditions
Enforced drain removal from purge steam
prevents unsafe ignition attempt
After Combustion Management
Figure 3: TDLS Technology for Combustion
Safety and OptimizationBy optimizing air
flow control, O2
concentration is
typically reduced
from 6% to 2%,increasing thermal
efficiency of the
furnace
Consequently, continually measuring percent O2is
critical to improving heater efficiency and maintain-
ing safe operating conditions. When firebox con-
ditions are unacceptable, i.e. high levels of CO or
combustibles exist, the effective combustion man-agement solution must rapidly detect the condition
and initiate the appropriate response. In the case
Concentration
Variations
TDL Transmitter
Cool temperatures but CO reactionis nearing completion
Convection Tubing
TDL Receiver
Radiant Tubes
(Radiant Zone)
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Application and Benefits of Combustion Management to Fired Heaters
inputs directly from the furnace and operates the
heater steam purge valves and fuel trip valves when
necessary. The simplified architecture diagram
below illustrates the key components comprising the
solution. Because the TDLS is a non contactingmeasurement - never touching the flue gas - and
has no moving parts, the whole system enjoys very
high reliability. The TDLS analyzer technology within
CombustionONE has been operational on furnaces
since 2003 without incident and most of those units
have not required calibration. The analyzer has full
diagnostic capability, and if there is an issue, the
analyzer will alert the operator. Also, the measure-
ment signals from the TDLS are unaffected by the
Continuous measurements
of percent O2 is critical to
improving heater efficiency
and maintaining safe
operating conditions.
How It Works
Capable of measuring the average gas concentra-
tion across the radiant zone of the fired heater,
CombustionONE addresses both of the above less-
than-optimum conditions by simultaneously control-
ling the fuel and air (O2) supply based on 5 second
sample intervals. Measuring the gas concentration
in the radiant zone is also a requirement of API 556.
Measurements from the system include CO, CH4,
O2, H
2O and temperature. Using an average gas
concentration produces safer burner control and
greater overall heater efficiency. By optimizing air
flow control, O2concentration is typically reducedfrom 6% to 2%, increasing thermal efficiency of the
furnace.
The combustion management system manages fuel
flow and arch draft through the existing plant DCS
via Modbus, and combustion airflow directly.
The safety system with CombustionONE receives
(TDLS)
Gas Concentration
Measurement
Field
Instrument
Safety
System
CombustionONE
Control Systems
Control Element
Control Element
Burners
Burners
Refinery Heaters
Figure 4: Basic Functional Capabilities of CombustionONETM
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Application and Benefits of Combustion Management to Fired Heaters
6
be correlated to the output from the existing stack
gas analyzer to verify the results. Data collected
during this testing will be incorporated into the
future safety shutdown system. The modular proce-
dural automation capability in CombustionONE willenforce safe operating conditions during start-up
and shut-down. Once the Safety Interlock System is
in place, CombustionONE will be able to detect and
interdict any unsafe operating conditions.
Natural draft heaters lack the capability to use
air to purge the heater. Instead, steam is used. If
the steam is not dry water will accumulate on the
burners/igniters, preventing ignition. The start-up
sequence, part of the CombustionONE solution, will
purge the condensate from the steam line, thus pro-
viding dry steam to purge the heater before ignition.
Results
CombustionONE has been operational since June,
2010 and the TDLS analyzers continue to operate
reliably with no maintenance needed. The operators
have been able to reduce the percent O2by 1% to
1.5%, thus making the heater more efficient. Thefurnace is now near optimum operating point using
minimum excess air. The TDLS measurements have
been verified by the existing stack gas analyzers,
but with a percent O2reading of 1% to 1.5% lower
than the stack gas analysis because the measure-
ments are taken in the radiant section. Furnace con-
ditions can now be controlled (or shutdown) quicker
since CombustionONE is taking concentration
measurements at five second intervals in the radiant
section. If there were to be an excess concentra-
tion of CO or CH4in the furnace, these gases can
be detected earlier versus the conventional stack
gas analyzer, enabling the heater to be shut down
sooner and avoiding unsafe conditions.
presence of other gases in the flue gas, unlike sen-
sor based technology. TDLS uses a path average
measurement, as opposed to the traditional point
measurement, making the value of concentration
much more accurate.
CASE STUDY: A Major Gulf
Coast Refinery
Challenges
The most critical times of heater operation are at
start-up and shutdown. Recognizing that a much
faster, more reliable analyzer is required to measureO
2, CO and CH
4concentrations, a major Gulf Coast
refining operation has adopted the CombustionONE
solution for combustion management. Since
CombustionONE measures gas concentration in
the radiant section of the fired heater, the system
is expected to improve heater safety and overall
operational efficiency.
Solution
CombustionONE was installed with two Tunable
Diode Laser Spectroscopy (TDLS) analyzers for
measurement of O2, CO and CH
4concentrations
in the radiant section of the heater. A dedicated
CombustionONE controller uses these
measurements while feeding these values to an
existing DCS for monitoring and future control of the
heaters. The dedicated control hardware is equipped
to receive additional signals from the heater, which
will be used to control the airflow in the burners in
a subsequent phase of the project. Space has also
been allotted for a future safety shutdown system.
The CombustionONE system will be tested during
upset conditions and the response of combus-
tion gases will be analyzed to confirm the desired
response to unsafe conditions. This data can then
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Application and Benefits of Combustion Management to Fired Heaters
Composed of representatives from a cross-section
of the refining and petrochemicals industry, the API
Task Team continues to refine the API 556 guideline.
Figure 6 lists the refining companies who have pro-vided representatives to the API556 Task Team.
The Recommended Best Industry
Practice
Over two years in development, API 556, to be pub-lished by the American Petroleum Institute, is a rec-
ommended practice for Instrumentation, Control,
and Protective Systems for Fired Heaters and Steam
Generators. This guideline specifically applies to
gas fired heaters and steam generators in petroleum
refinery, hydrocarbon-processing, petrochemical,
and chemical plants. API 556 specifically states the
following regarding the use TDLS technology:
Not covered in this recommended practice are the
following:
Oil fired and combination fired heaters
Water tube boilers which consist of single or
multiple burners and are designed for utility
operation or where the primary purpose is steam
generation
Fired steam generators used to recover heat
from combustion turbines (HRSG)
Oven and furnaces used for the primary purpose
of incinerating, oxidizing, reduction or destruc-
tion of the process medium (covered by NFPA
86).
Water bath or oil bath indirect fired heaters.
CO boiler, ethylene furnace and other specialty
heaters
Laser based technology for combustioncontrol (oxygen trim to air or air/fuel ratio
controller) is a design consideration for
heater applications where a single sample
point will not provide a representative
sample. It has a response time of 5
seconds and can measure across a radi-
ant section up to 98.4 ft. (30 m). It is not
an ignition source to flue gas and requires
no reference air.
API 556
Figure 5: Refiners Participating in the API 556
Task Team
Valves
Analyzers
Protective System
Instrumentation
and Analytical
Analyzers Design
Burners
Control
Safety
Valves
Chairman SCOICS Combustion/general
General
Instrumentation
Chairman SCOICS
Heater Design Protective System Control, protective
General Instrumentation
Process Control
Heater Design
Analyzers Controls
General Instrumentation
Process Control
CITGO
BP
Chevron
ConocoPhillips
Valero Corp.
ExxonMobil
Company Contribution
Marathon Ashland
Petroleum
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Application and Benefits of Combustion Management to Fired Heaters
The CombustionONE combustion management
system is an integrated, self-contained system that
can be rapidly installed on any fired heater. Four
principal components that comprise the solution are
shown in Figures 7-10 and described as follows:
TDLS technology for gas concentration mea-
surements on 5 second intervals
A dedicated system for control of fuel and air
volumes based on a fired heater model
An OSHA compliant safety system to prevent
unsafe conditions from persisting
Sensing and actuation for additional measure-
ments and air flow control as needed
Two TDLS systems (transmitters and receivers)
are typically installed in the radiant section of the
fired heater, which is the most accurate location for
optimum combustion management. At minimum,
one unit measures O2and the other CO. AdditionalTDLS units can be installed to measure the products
of combustion, such as CH4. Since fired heaters
have differing configurations, capacities, environ-
mental and process conditions, custom mounting
brackets are built to hold and position the laser
across the radiant section. This is the best location
to obtain the most accurate gas concentration and
temperature measurements.
The dedicated controller is used to simultaneously
control fuel and air volumes based on five second
sampling measurements of average gas concentra-
tions across the radiant section from the TDLS.
The Technology
8
TDLS for Gas Concentration
Sensing and Actuation
Safety Interlock System
Dedicated ControllerClass 1, Division 2
Rated Enclosure
Figure 6: CombustionONE - An Integrated Solution
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Application and Benefits of Combustion Management to Fired Heaters
Since the combustion management solution
is completely self-contained and requires little
integration with existing control systems and
instrumentation, the installation phase is typically
straightforward. Where mechanical modificationsand/or upgrades to the fired heater are necessary,
Yokogawa acts as the prime contractor, partnering
with engineering companies and furnace
manufacturers to provide a single source for
the project. The installation and commissioning
processes occurs in 8 to 12 weeks, depending
on the size and complexity of the fired heater.
Installations on multiple fired heaters on a site or
across a fleet can also be easily accommodated.
A systematic installat ion plan that schedules the
installation across multiple fired heaters offers
greater economy of scale, while reducing the
time to realize the benefits from the combustion
management solution.
Embedded with the controller are proprietary fired
heater combustion strategies that direct fuel flow
at the valve and air volume through the burner
registers.
An OSHA compliant safety system is required on a
fired heater to meet regulatory requirements. The
safety system will safely shut down the fired heater
if the main controller fails or if unsafe conditions
persist in the fired heater. The embedded safety
system in CombustionONE is certified to meet
the requirements of NFPA, FM, ISA S84.01 and
IEC61508 and SIL3.
Smart (self diagnosing) multi-variable transmitters
and valve positioners provide reliable and accurate
performance and feedback of the combustion man-
agement solution. Additional SIL 2 transmitters are
sometimes added on the fired heater to provide air
flow measurements at multiple locations, ensuring
safety and optimum performance.
Asa best practice, Yokogawa recommends
commencing the installation of a combustion
management system with a discovery session that
includes a site review. The initial discovery session
will produce:
The specific fired heaters on-site where com-
bustion management can be of highest value
A note of the changes needed to each fired
heater that require detailed engineering
Order of installation for the combustion manage-
ment solution
A general project time-line and budget
The Installation Process
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What does Yokogawa vigilancemean to the future of your business? Quality. Through products that are built from the ground up and tested to the last hour, youre ensured continuous
operation and more uptime. Innovation. Your business will benefit from new insights andcapabilities, bringing true predictability to your process. Foresight. As the market changes
youll have solutions that give you the continuity and flexibility to plan ahead and grow. Oupartners know the difference. With Yokogawa, you can count on a lifetime of plant efficiency
from instrumentation to operation support. Let us be vigilant about your business.
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