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Improving Steam Methane Reformer Performance with the ZoloSCAN-SMR
The global demand for hydrogen continues to increase as heavier crudes are processed and stricter
governmental mandates require reductions in sulfur content for transportation fuels. This higher hydrogen
demand has resulted in refiner’s interest in maintaining or even increasing hydrogen production from existing
units. Combustion monitoring directly in the reformer can achieve higher process efficiency and greater
availability to meet the higher hydrogen demand.
Combustion Monitoring and Balancing
The steam reforming process requires a very tight temperature control and uniformity for optimum
performance. A typical hydrogen plant has many sensors installed in many different areas of the steam
methane reformer (SMR) for the purpose of monitoring and controlling the combustion and reforming
processes. However, the number of sensors available for use directly inside the firebox are very limited
(Figure 1). This lack of measurement data directly in the combustion area makes it very difficult to maintain
the optimum temperatures and a uniform combustion profile. The ZoloSCAN-SMR, however, measures the
temperature, O2, H2O and CO in real-time, directly inside the firebox. It delivers quantitative, actionable
information that can be used for combustion monitoring and balancing to improve SMR performance and
reliability.
Figure 1: Diagram of many of the typical sensors on and SMR. The ZoloSCAN is the only quantitative sensor for use directly inside the furnace.
Benefits of Balanced Combustion in an SMR
Improved Efficiency: Reducing the spread of tube wall temperatures allows the overall process
temperature to be increased without pushing some tubes above the desired maximum operating
temperature. This improves the radiant efficiency and allows a reduction in methane slip without a
decrease in reliability. In addition, for plants that do not produce large amounts of steam, efficiency
improvements can be obtained by reducing excess oxygen to the desired optimal levels. ZoloSCAN allows
operators to bring the entire furnace into the optimal excess oxygen range, rather than simply the limited
regions measured by the conventional plant sensors, leaving the risk that other regions are operating
either above or below the optimal range.
Based on industry standards, a 30-50°F reduction in the tube temperature spread through better balance
can allow the plant to operate at a 15-30°F increase in reformer outlet temperature (ROT) without
damaging tube life or impacting reliability. As a result, a process efficiency gain of 1.5-2.5 btu/scf can be
achieved, which provides $200,000 to $350,000 per year in savings for a 100 MMscfd reformer.
Longer Tube Life: The high performance process tubes installed in SMRs have a lifetime that is highly
temperature dependent as illustrated by the Larson-Miller relationship. It is generally accepted that a
10°C increase in the operating temperature can reduce the tube life up to 50%. Therefore, reducing the
tube wall temperature spread by balancing the flue gas temperature can eliminate the need to inspect
and replace individual tubes that are prematurely approaching their design life. Eliminating the high
temperatures on only 10-15% of the tubes can reduce maintenance costs (i.e. tube replacement) by over
$100,000 per year on a 100 MMscfd reformer.
Increased Catalyst Life: Narrowing the spread in tube temperatures has an added benefit in that it
reduces premature catalyst degradation that results from overheating. Reducing the temperature spread
for catalyst in different tubes will produce more consistent utilization and increase the overall catalyst life.
Savings of up to $50,000 per year may be achieved by less frequent catalyst changes.
Remote Monitoring: Typical steam methane reformers have a wide array of sensors located on the fuel
and air lines both before and after the combustion region, but there are very few sensors available for
directly inside the furnace. The ZoloSCAN combustion sensor provides the first quantitative sensor that
measures real-time and directly in the furnace, where the process is taking place, to compliment operator
observation and pyrometer measurements of tube temperatures. As an example, a sudden increase in the
Temperature and H2O as measured by ZoloSCAN can provide an early warning of a tube leak which could
prevent further damage to adjacent tubes.
Safety: The real-time measurement capability of ZoloSCAN provides real-time status of the furnace so
operators can identify poor combustion conditions or dangerous situations in the safety of the control
room. For example, excessive CO levels measured in-situ by ZoloSCAN can be a signal of a dangerous
combustion condition. Quantitative measurements can be configured to trigger alarms if certain limits are
exceeded.
Node BoxNode Box
Sensor Heads
Control Rack
J-boxes
Purge air
The ZoloSCAN Combustion Monitoring System
The ZoloSCAN-SMR™ is an innovative laser-based combustion diagnostic system which simultaneously measures
temperature, O2, CO and H2O in real-time, directly in the furnace of a steam methane reformer. There are no
probes to insert, no sensitive electronics near the reformer and no regular field calibration. ZoloSCAN utilizes a
well proven technique known as Tunable Diode Laser Absorption Spectroscopy (TDLAS). Developed in
collaboration with Stanford University, TDLAS uses lasers tuned to the unique absorption wavelengths for each
constituent. ZoloSCAN is designed for ultra-harsh combustion environments and has been successfully installed
on steam methane reformers and over 50 coal-fired boilers around the world.
ZoloSCAN combines several lasers onto a single
optical fiber and then transmits the light across
the furnace. Light is collected by a receiver and
transmitted back to the control rack where the
ratio of unabsorbed light to absorbed light is
measured to determine the average
concentrations for each constituent along the
laser path. Each path simultaneously measures
an average temperature and concentrations of
O2, CO and H2O. Multiple paths are arranged to
provide combustion information corresponding
to the burner configuration.
Figure 2: Diagram of a typical ZoloSCAN-SMR configuration
The Control Rack (NEC Class 1, Div 2 compliant) houses all of the critical electronics but is located away from
the reformer. Only small port openings and a line of sight across the reformer are required for each laser path.
A simple tube and flange are used to mount the ZoloSCAN heads as shown in Figures 3 and 4. Each head also
has an automatic alignment mechanism to maintain laser alignment through ambient and process
temperature changes.
Figure 3: ZoloSCAN head mounted on flange Figure 4: ZoloSCAN heads mounted on side of SMR
The layout of the ZoloSCAN paths in an SMR will depend upon the burner configuration of the SMR; access
through the process tubes and the optimization objectives. The ZoloSCAN-SMR interface provides actionable
information based on the path layout. Below are two potential layouts:
Figure 5: Iso-metric ZoloSCAN layout with “Cells” (left), plan view (center) and ZoloSCAN-SMR interface (right)
Figure 6: Iso-metric ZoloSCAN layout with orthogonal paths (left), plan view (center) and ZoloSCAN-SMR interface
(right)
1 2 4 5 63 7
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A B C D E F G H
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8
1 2 4 5 63 7
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10
9
A B C D E F G H
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ZoloSCAN-SMR Interface
ZoloSCAN-SMR Interface
Plan View w/ Path Layout
Plan View w/ Path Layout
Zolo Experience on Steam Methane Reformers
ZoloSCAN Correlates with Traditional Sensors The ZoloSCAN data correlates very well with traditional plant sensors. In Figure 7 below, the average
ZoloSCAN temperature measurements are shown over time compared to traditional downstream
temperature measurements (downstream of the firebox). The temperature offset (between the ZoloSCAN
measurements and the traditional tempo-couples) represents the changes in the temperature profile in the
firebox versus in the crossover downstream. ZoloSCAN is also much more sensitive to the small changes in
temperature than the traditional temperature sensors.
Figure 7: ZoloSCAN Path Temp vs Plant Sensors
The ZoloSCAN average O2 measurement trends also compare favorably to the plant O2 sensors (zirconium
oxide) as shown in Figure 8. However, the ZoloSCAN measurements are obtained directly in the furnace and
represent a broader sample (path averages of 7 paths) and more stable when compared to the scatter of the
traditional O2 which only represent two “point” measurements but are used for excess O2 control.
Figure 8: ZoloSCAN Path O2 vs Plant Sensors
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12:00 AM 12:00 AM 12:00 AM 12:00 AM 12:00 AM 12:00 AM 12:00 AM 12:00 AM 12:00 AM
Zolo Temperature vs. Plant Sensors Avg temp (Zolo)
Local temp (Plant sensor 1)
Local temp (Plant sensor 2)
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0
Rel
ativ
e te
mpe
ratu
re (
F)
Time stampDay 1 Day 2 Day 3 Day 4 Day 5 Day 6 Day 7 Day 8 Day 9
1.0
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5.0
6.0
7.0
12:00 AM 12:00 PM 12:00 AM 12:00 PM 12:00 AM 12:00 PM 12:00 AM
Oxy
gen
(%)
Zolo O2 vs. Plant Sensors Avg O2 (Zolo)
Local O2 (Plant sensor 1)
Local O2 (Plant sensor 2)
Time stampDay 1 Day 2 Day 3 Day 4
ZoloSCAN Shows Real-time Process Changes: When operated in Real Time Mode ZoloSCAN can measure process variations due to effects such as the PSA
operation. Every path showed a strong semi-periodic PSA signature in both temperature and oxygen. The PSA
cycle is illustrated in Figure 9 and shows the data recorded on a single ZoloSCAN path located in the center of
the firebox. Note the very strong correlation between the temperature and excess oxygen due to the
variations in the PSA purge gas.
Figure 9: ZoloSCAN Temperature and O2 measurement in the center of firebox over PSA cycles for a single path
ZoloSCAN Identifies Imbalances & Gives Actionable Information to Improve Balance The ZoloSCAN-SMR interface can identify areas or “cells” with high temperature or O2 concentrations. These
“cells” can be correlated to specific groups of burners to make actionable changes to burner settings to
improve combustion balance. Small changes to air/fuel settings on groups of burners reduced the
temperature spread by 75% from 126°F to only 32°F in the center of the furnace as shown in Figure 10 below.
Figure 10: ZoloSCAN-SMR interface showing imbalanced profile (left) and balanced profile (right)
150 F
Spread in center rows = 129°F
110 F
Spread in center rows = 32°F (75% reduction)
ZoloSCAN Gas Temperatures Correlate with Tube Wall Temperatures (TWT) SMR operators are very concerned about the TWT of the process tubes. Various methods are used to measure
the temperature of the tubes in-situ to maintain an acceptable temperature spread across the reformer
(typically 50-100°F). This manual process is performed periodically (daily to monthly). ZoloSCAN measures the
average flue gas temperature along each path in real-time and all of the time. There is a good correlation
between the flue gas temperatures as measured by ZoloSCAN and the TWT as measured by traditional means
(infrared pyrometer). Figure 11 below shows the correlation between the ZoloSCAN paths (P1 to P4) and the
average TWT on each tube row (Rows 1-3). Notice how both methods show the same general profile (higher
on the East-West walls and cooler in the middle). The ZoloSCAN measurements also correlate with the
individual TWT profiles for each row as shown in Figure 12. The temperatures are higher in the center of the
firebox (tube Row 2 and ZoloSCAN Path 6) than against the North and South walls.
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Tube Temps vs. East-West Zolo Paths
Flue gas temp (ZoloSCAN)
Tube row avg temp
Zolo
Path 1
Zolo
Path 2
Zolo
Path 3
Zolo
Path 4TubeRow 1
TubeRow 2
TubeRow 3
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Tube temps vs. North-South Zolo PathsFlue gas temp (ZoloSCAN) Tube Row 1
Tube Row 2 Tube Row 3
ZoloPath 5
ZoloPath 6
ZoloPath 7
Figure 11: TWT and ZoloSCAN flue gas comparison (East-West)
Figure 12: TWT and ZoloSCAN flue gas comparison (East-West)
Figure 13: Burner, process tube, and ZoloSCAN path layout
P5 P6 P7
P1
P2
P3
P4
Row 1
Row 2
Row 3
No
rthN
orth
We
stN
orth
Shape of TWT Profiles MatchFlue Gas Profiles Across Tube Rows
Shape of TWT Profiles MatchFlue Gas Profiles Along Tube Rows
Burners
Process tubes
ZoloSCAN Gas Temperatures Used to Balance Tube Wall Temperatures (TWT) Once a correlation is developed between the ZoloSCAN gas temperatures and the TWTs, ZoloSCAN can be
used by operators to adjust the flue gas balance and reduce the spread of the tube wall temperatures to
improve process efficiency and tube life. Figure 12 shows how the flue gas spread was significantly reduced
(140°F to 7°F) to by using ZoloSCAN to make changes to groups of burners from the initial imbalanced
conditioned. Once the flue gas was balanced, the resulting tube wall temperatures spread was consequently
reduced from 97°F to 51°F.
Figure 14: TWT can be balanced using flue gas temperatures
Conclusions The ZoloSCAN-SMR combustion monitoring system can assist steam methane reformer operators to improve
process efficiency and reliability through longer tube and catalyst life. ZoloSCAN provides real-time,
temperature, H20, O2 and CO measurement directly in the furnace which can be used to balance the
combustion flue gas profiles. The ability to control the flue gas profile by making small changes to the burners
based on the ZoloSCAN measurements influences the tube wall temperatures in the reformer. Operators can
therefore maintain an acceptable TWT spread using the flue gas measurements in order to optimize efficiency
and reliability.
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Tube temps vs. North-South Zolo PathsFlue gas temp (ZoloSCAN) Tube Row 1
Tube Row 2 Tube Row 3
ZoloPath 5
ZoloPath 6
ZoloPath 7
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Tube temps vs. North-South Zolo PathsFlue gas temp (ZoloSCAN) Tube Row 1
Tube Row 2 Tube Row 3
ZoloPath 5
ZoloPath 6
ZoloPath 7
Unbalanced Flue GasTWT Spread: 97°F
Flue Gas Spread: 140°F
Balanced Flue GasTWT Spread: 51°F
Flue Gas Spread: 7°F
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