Improving Steam Methane Reformer Performance with the ZoloSCAN-SMR

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1 Improving Steam Methane Reformer Performance with the SCAN-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 SCAN-SMR, however, measures the temperature, O 2, H 2 O 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 SCAN is the only quantitative sensor for use directly inside the furnace.

2 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. SCAN 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 F reduction in the tube temperature spread through better balance can allow the plant to operate at a F increase in reformer outlet temperature (ROT) without damaging tube life or impacting reliability. As a result, a process efficiency gain of 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 SCAN 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 H 2 O as measured by SCAN can provide an early warning of a tube leak which could prevent further damage to adjacent tubes. Safety: The real-time measurement capability of SCAN 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 SCAN can be a signal of a dangerous combustion condition. Quantitative measurements can be configured to trigger alarms if certain limits are exceeded.

3 The SCAN Combustion Monitoring System The SCAN-SMR is an innovative laser-based combustion diagnostic system which simultaneously measures temperature, O 2, CO and H 2 O 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. SCAN 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. SCAN 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. SCAN 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 Node Box Sensor Heads J-boxes Node Box laser path. Each path simultaneously measures an average temperature and concentrations of O 2, CO and H 2 O. Multiple paths are arranged to provide combustion information corresponding Purge air to the burner configuration. Control Rack Figure 2: Diagram of a typical SCAN-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 SCAN 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: SCAN head mounted on flange Figure 4: SCAN heads mounted on side of SMR

4 The layout of the SCAN paths in an SMR will depend upon the burner configuration of the SMR; access through the process tubes and the optimization objectives. The SCAN-SMR interface provides actionable information based on the path layout. Below are two potential layouts: Plan View w/ Path Layout SCAN-SMR Interface Figure 5: Iso-metric SCAN layout with Cells (left), plan view (center) and SCAN-SMR interface (right) A B C D Plan EA View F B w/ Path G C Layout HD E F G H SCAN-SMR Interface N N C C S S Figure 6: Iso-metric SCAN layout with orthogonal paths (left), plan view (center) and SCAN-SMR interface (right)

5 Oxygen (%) Relative temperature (F) Experience on Steam Methane Reformers SCAN Correlates with Traditional Sensors The SCAN data correlates very well with traditional plant sensors. In Figure 7 below, the average SCAN temperature measurements are shown over time compared to traditional downstream temperature measurements (downstream of the firebox). The temperature offset (between the SCAN measurements and the traditional tempo-couples) represents the changes in the temperature profile in the firebox versus in the crossover downstream. SCAN is also much more sensitive to the small changes in temperature than the traditional temperature sensors Temperature vs. Plant Sensors Avg temp () Local temp (Plant sensor 1) Local temp (Plant sensor 2) :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 Day 1 Day 2 Day 3 Day 4 Time Day stamp 5 Day 6 Day 7 Day 8 Day 9 Figure 7: SCAN Path Temp vs Plant Sensors The SCAN average O 2 measurement trends also compare favorably to the plant O 2 sensors (zirconium oxide) as shown in Figure 8. However, the SCAN 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 O 2 which only represent two point measurements but are used for excess O 2 control. 7.0 O2 vs. Plant Sensors Avg O2 () Local O2 (Plant sensor 1) Local O2 (Plant sensor 2) :00 AM 12:00 PM 12:00 AM 12:00 PM 12:00 AM 12:00 PM 12:00 AM Day 1 Day 2 Time stamp Day 3 Day 4 Figure 8: SCAN Path O 2 vs Plant Sensors

6 SCAN Shows Real-time Process Changes: When operated in Real Time Mode SCAN 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 SCAN 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: SCAN Temperature and O 2 measurement in the center of firebox over PSA cycles for a single path SCAN Identifies Imbalances & Gives Actionable Information to Improve Balance The SCAN-SMR interface can identify areas or cells with high temperature or O 2 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. Spread in center rows = 129 F Spread in center rows = 32 F (75% reduction) 150 F 110 F Figure 10: SCAN-SMR interface showing imbalanced profile (left) and balanced profile (right)

7 SCAN 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 F). This manual process is performed periodically (daily to monthly). SCAN 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 SCAN and the TWT as measured by traditional means (infrared pyrometer). Figure 11 below shows the correlation between the SCAN 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 SCAN 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 SCAN Path 6) than against the North and South walls. Tube Temps vs. East-West Paths Flue gas temp (SCAN) Tube row avg temp Shape of TWT Profiles Match Flue Gas Profiles Across Tube Rows Path 1 Tube Row 1 Path 2 Tube Row 2 Path 3 Tube Row 3 Path 4 Figure 11: TWT and SCAN flue gas comparison (East-West) Tube temps vs. North-South Paths Flue gas temp (SCAN) Tube Row 1 Tube Row 2 Tube Row West North P1 P2 P3 P4 P5 P6 P7 Burners Process tubes Row 1 Row 2 Row 3 Figure 13: Burner, process tube, and SCAN path layout North North 1660 Shape of TWT Profiles Match Flue Gas Profiles Along Tube Rows Path 5 Path 6 Path Figure 12: TWT and SCAN flue gas comparison (East-West)

8 SCAN Gas Temperatures Used to Balance Tube Wall Temperatures (TWT) Once a correlation is developed between the SCAN gas temperatures and the TWTs, SCAN 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 SCAN 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. Unbalanced Flue Gas TWT Spread: 97 F Flue Gas Spread: 140 F Balanced Flue Gas TWT Spread: 51 F Flue Gas Spread: 7 F 2050 Tube temps vs. North-South Paths Flue gas temp (SCAN) Tube Row 1 Tube Row 2 Tube Row Tube temps vs. North-South Paths Flue gas temp (SCAN) Tube Row 1 Tube Row 2 Tube Row Path 5 Path 6 Path Path 5 Path 6 Path Figure 14: TWT can be balanced using flue gas temperatures Conclusions The SCAN-SMR combustion monitoring system can assist steam methane reformer operators to improve process efficiency and reliability through longer tube and catalyst life. SCAN provides real-time, temperature, H 2 0, O 2 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 SCAN 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.