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)

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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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Zolo Temperature vs. Plant Sensors Avg temp (Zolo)

Local temp (Plant sensor 1)

Local temp (Plant sensor 2)

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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

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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

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P4

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Row 2

Row 3

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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

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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