Next Generation Reheat Furnace Control: ZoloSCAN Laser Combustion Diagnostics

Transcription

1 Next Generation Reheat Furnace Control: ZoloSCAN Laser Combustion Diagnostics Ken Grieshaber 1, David M. Giltner 1, James R. Phillips 2, Terence L. Choncoff 2, and Rajko Vukobrat 2 1 Zolo Technologies, Inc North 63 St, Boulder, Co Phone kgrieshaber@zolotech.com 2 US Steel Corporation, Gary Works-MS 184, One North Broadway, Gary, IN Keywords: Sensor, laser, reheat, process control, analysis, efficiency, scale, oxygen INTRODUCTION Zolo Technologies Laser (TDLAS) Diagnostic System measures temperature, oxygen, carbon monoxide and water across a wall to wall laser path inside high temperature combustion furnaces. Having proven its value and durability over the past seven (7) years in coal fired boilers, it has recently been introduced to the steel industry. A ZoloSCAN-RHT system was installed in a five (5) zone slab pusher reheat furnace at US Steel, Gary Work in mid A laser was positioned at the exit (convergence) of each zone. Commissioning was completed in less than one week and data flowed uninterrupted for the duration of the study period (over 33 weeks), reporting T, O 2, CO, H 2 O for each zone. The continuous reporting of combustion gases is a first of its kind and allowed the operators to tune burner controls to achieve fuel savings, lower CO and maintain a preferred atmosphere for optimum scale formation. Automation of air to fuel ratios was successfully implemented allowing feedback to direct the flow of products of combustion in the furnace as a whole instead of preset values in each zone determined in isolation. Zolo Technologies has been providing laser based combustion monitoring systems to a variety of industries since 2006, with over 50 systems installed globally. Early focus was on the coal fired power industry, but recent years have shown significant interest from the petrochemical and steel industries in using the technology to optimize process heaters and furnaces. The ZoloSCAN platform was developed specifically for the steel industry, including the ZoloSCAN-RHT for steel reheat furnaces and ZoloSCAN-EAF for Electric Arc Furnaces (EAFs). Here we describe results from the installation of a ZoloSCAN system on a reheat furnace at US Steel s Gary Works 84 HSM in Gary, IN. Information will be presented showing ZoloSCAN correlation to thermocouples and air fuel ratios, along with the surprising relationship between CO and O 2 levels at various fuel settings. Conclusions are drawn revealing how savings have been achieved.

2 BACKGROUND The reheat furnaces in a typical hot strip mill consume a large share of the energy required to operate a steel plant. Because of this, steel mill plant managers are looking for ways of reducing costs by improving the fuel efficiency of these furnaces. However, the multi-zone construction of many reheat furnaces makes combustion optimization very difficult using conventional sensors because of zone interaction, constantly changing product requirements, changing speed of extraction, and the act of extracting bars itself. Monitoring the combustion process directly inside the furnace using Zolo s Tunable Diode Laser Absorption Spectroscopy (TDLAS) technology provides significant opportunities for improving efficiency, lowering emissions, and improving the safety of these furnaces. Zolo s TDLAS technology provides simultaneous analysis of multiple gas species required for combustion optimization, along with temperature, all along a single laser path. Zolo s unique system architecture allows for monitoring of combustion parameters along multiple paths using a single set of lasers and detectors, and calculate two-dimensional (2D) species concentration and temperature profiles. The resulting 2D data provides the operator with the information required to homogenize combustion and reducing excess air while better optimizing operating temperatures. Elimination of hot spots typically improves asset run time between unplanned outages. The Problem There are many types of reheat furnaces in operation in the steel industry. Most furnaces are designed with multiple heating zones (Figure 1). Each zone has a different purpose and the zones typically have independent burner controls even though the products of combustion move through the previous zones to exit the flue. The air-to-fuel ratio (air/fuel) is typically set with the intention of producing a desired level of excess oxygen in the flue gas. The objective is to insure that all the fuel is combusted but avoid excessive combustion air that will reduce efficiency. Stack Recuperator Thermocouples Charge end Few sensors are available for use here Skid line Hearth Discharge end Figure 1: Few sensors are available for use directly inside the furnace Based on burner capabilities and desired levels of excess oxygen, fixed stoichiometric ratio tables are programmed for each zone. The ratios may differ from zone to zone for two reasons: 1. The desired excess oxygen may be different for each zone due to the relationship between oxygen level, temperature and scale formation 2. Stoichiometry may need to be adjusted for different burner turndown rates because of the mixing capabilities of the burners. Traditionally, the only real time process feedback for reheat furnace operators is temperature from thermocouples located near the refractory surface (see Figure 1). Typically, no process information regarding the amount of unburned fuel or excess oxygen has been available. This leaves the operator with no choice but to preset a stoichiometric ratio and hope the

3 system delivers it correctly despite inevitable changes in fuel and combustion air conditions. A calculation is programmed into the controller which targets a specific air to fuel ratio with the goal of having excess oxygen in the products of combustion in the range of 1 to 2%. While the calculation method may be sound, many issues can cause a drift in the end result, such as: Inaccurate metering of gas or air Changes in humidity of the air Significant amounts of fuel or oxygen migrating from another zone of the furnace In the case of preheated air via recuperators o o o Leaks in piping or recuperators Temperature correction factors out of calibration Seasonal variations Wear or damage to valve and actuators Leaks in furnace Historically, the operator does not know whether the oxygen is at or near the desired set point because there is no real-time process feedback. The consequences of operating a furnace with this level of uncertainty can be significant. Considering the burner reactions and theoretical products of combustion shown in Figure 2, issues arise when the stoichiometry varies off of set point. If the actual oxygen level in the flue gas exceeds the set point, efficiency is reduced adding unnecessary fuel costs. If the actual oxygen level is lower than the set point, CO levels will increase creating both an unsafe operating condition as well as reduced efficiency due to unburned fuel exiting the furnace. In addition, ratio controllers are continuous adjusting their set points in order to meet changing furnace demands and thus the state of oxidation is also always changing. In practice all furnaces experience some degree of incomplete combustion. A number of issues contribute to poor mixing: Burner efficiency Turndown Air and fuel velocities unmatched Ratio control out of adjustment Furnace leaks Incomplete combustion due to poor mixing can also result in the co-existence of carbon monoxide and oxygen. While Figure 2 shows the results of a well-mixed (equilibrium) situation, in practice it is common to have both carbon monoxide and oxygen present. Therefore, optimal operation of a reheat furnace requires real-time combustion product data. Suitable sensors for collecting this data are very limited, however.

4 Figure 2: The relationship of combustion products to excess air 1 Oxygen Sensors Oxygen analysis is typically done by Zirconia oxygen analyzers. These are most commonly used in flue stacks to measure fully combusted gases exiting furnaces. In this location they only provide information about the furnace as a whole, not the combustion performance of the individual zones. A few manufacturers have recently introduced Zirconia oxygen systems which can operate in higher temperature environments. These pose limitations, however, and require a lot of attention by the operators. Some of the issues to deal with when using Zirconia sensors are: Ceramic probes are brittle and sensitive to breakage on thermal cycling A constant reference gas (usually clean, dry compressed air) must be added into the probe at a fixed flow rate A span gas (stored in a high pressure cylinder) must be attached to the system for regular calibration Oxygen accuracy is lost when combustibles are still present in the furnace atmosphere gas The reading represents a single point in the furnace, at or near a refractory surface which is not representative of the entire furnace chamber High furnace temperatures lead to more rapid deterioration of the probes CO Analyzers Some furnace operators use portable Carbon Monoxide (CO) Analyzers to determine if combustibles remain in the products of combustion at or near the flue. If equilibrium conditions exist at the flue, one would not expect to find both CO and O 2 present; however, they often do coexist because of poor mixing, furnace leaks, burner problems, etc. While well intended, there are limitations to the use of CO analyzers which should also be understood: Cannot handle furnace temperatures During sample cooling CO will react with any oxygen present in the sample stream when temperature is over the lower ignition temperature (this can consume as much as 90% of the actual CO present) 2 The CO concentration inside the furnace exceeds the limits of many CO analyzers A span gas (stored in a high pressure cylinder) must be attached to the system for regular zero and calibration

5 Extractive Analyzers The state of the art for taking combustion gas measurements inside the furnace is through the use of extractive gas analyzers. These analyzers can measure a variety of species and can in principle be placed in many regions inside a furnace. Furnace gas analysis is currently done with spot monitoring of a single gas by a single analyzer probe. While some units are mounted permanently, periodic furnace calibration testing is more common. This type of combustion supervision cannot optimize furnace control because it is not continuous and the spots being checked are not representative of overall furnace activity. In addition, accuracy can be questioned due to pre-combustion of CO gas samples drawn, along with calibration of both instruments. Finally, neither CO nor O 2 conventional analyzers can report data in critical furnace areas that are near both burners and products. The Solution The ZoloSCAN laser-based combustion monitoring system is capable of measuring directly inside the reheat furnace where the flue gas temperatures are high. Laser paths were placed in multiple locations around the furnace where they can measure flue gas at the exit of each zone or within the zones (Figure 3). Each path measures temperature, O 2, H 2 O and CO in realtime, and delivers quantitative, actionable information that is used for combustion monitoring and control to improve reheat furnace performance and reliability. Preheat Zone Exit Heat Zone Exit Soak Zone Exit Soak Zone Skid line Hearth Zolo SensAlign Heads Laser path Figure 3: Locations for ZoloSCAN paths Tunable Diode Laser Absorption Spectroscopy (TDLAS) The TDLAS technology used by Zolo to measure flue gas temperature and concentrations is based on the fact that each molecule has a unique set of wavelengths at which it absorbs light. Lasers are then selected to match one unique wavelength for each molecule to be measured and the laser light is sent across the furnace in a single collimated beam. TDLAS measures the light absorbed by the molecules along the laser path and calculates gas concentration using an algorithm based on Beer s Law: I/I o = e -[σln] where (1) I/I o = Ratio of (received light/transmitted light)

6 N = Density of particles along light path σ = Absorption cross section L = Length of path through furnace The unknown in the above equation is N, which directly correlates to the concentration of that particular molecule in the gas stream being measured. The absorption cross section is a constant for each molecule and these values are very well characterized. By measuring the light transmitted into the furnace, the light received at the other end, and by knowing the path length across the furnace, the molecular concentration can be calculated. 3 It is worth noting that because the absorption cross section, the only parameter that is not directly measurable, is constant; the ZoloSCAN does not drift and therefore does not require periodic calibration. ZoloSCAN-RHT Architecture The ZoloSCAN includes a centralized instrument rack (NEC Class 1, Div 2 compliant) which houses the components that are the heart of the system such as lasers, detectors, a computer, and various control electronics (Figure 4). Inside this rack, the ZoloSCAN uses a proprietary technology to combine multiple lasers onto a single optical fiber. A fiber optic switching network allows the selection of any one of the paths mounted on the furnace, and fiber optic cable transmits the light to the pitch head. From here the laser signal is projected across the furnace, directly through the flames and dirty combustion atmosphere. Light is collected by a catch head on the opposite side of the furnace, and the received light is transmitted back to the instrument rack via fiber optics. Back inside the rack, detectors measure the received light for each laser wavelength and a computer simultaneously measures an average gas temperature and concentrations of O 2, CO and H 2 O along the selected path. The switching network then selects the next path in the sequence and the measurements are repeated. The instrument rack houses a single set of lasers and detectors, and a switching network that can supply as many as 30 laser paths, making expansion a low cost, efficient process. Zolo s fiber-coupled architecture allows for the critical components in the instrument rack to be located in a cooler, safer environment away from the furnace. Junction boxes SensAlign heads Node box Node box Purge air Control Rack Figure 4: Schematic of a typical ZoloSCAN-RHT system SensAlign Heads are mounted on sight tubes which are inserted through the furnace wall and refractory and attached directly to the furnace steelwork. Sight tubes are aligned with a laser prior to head mounting in order to ensure optimal signal power for maximum sensitivity. Since furnaces in operation move due to thermal expansion and vibration, each SensAlign Head is equipped with servo motors to provide small alignment adjustments via instructions from an algorithm in the control rack computer.

7 Determining Path Locations The decision as to where to install paths and how many to install is important to assure the data collected is most relevant to the process. While the final decision on path location is made by the furnace operations team, guidelines for locations are as follows: All pitch/catch head pairs must have a clear line of sight The closer to the burner, the higher level of unburned gas Paths may be located very near the work surface for best analysis of the atmosphere and temperature the products are experiencing Paths may be located near the exit of heating zones to isolate data for each zone Multiple paths can be located in the most critical heating or product quality areas Path can also be located in the flue to get the overall furnace efficiency data in real time The objective of any Zolo installation is to provide information that can be directly matched to the furnace controls in order to guide the operators to a clear action to improve performance. On a typical steel reheat furnace, combustion air and fuel are controlled separately for each zone, so a typical ZoloSCAN-RHT installation will have a path at the exit of each zone. ZOLO - US STEEL PROJECT Zolo approached USS Gary 84 HSM personnel about installing a ZoloSCAN system in early USS was interested in improving fuel efficiency because the reheat furnaces are the largest consumers of energy in the Gary Works facility. They were also interested in exploring the source of occasional CO measured in the working areas around the furnaces. ZoloSCAN was determined to be the ideal system for addressing both of these issues. Installation Details USS operates four (4) identical pusher reheat furnaces at the Gary 84 HSM complex. Each furnace has top and bottom preheat and heating zones, and side by side soak zones (for this demonstration the soak zones were considered to be a single zone). In June 2013 it was agreed to install a ZoloSCAN system with five (5) paths on No. 1 Reheat Furnace, as shown in Figure 5. The lasers were located to measure flue gas properties as the gas exits each zone. This enabled the combustion products of each zone to be analyzed and optimized independently. Prior to installation of the ZoloSCAN system, the only process information available was temperature reported by thermocouples located near the top and bottom refractory surfaces in each zone. No information about efficiency or emissions had been available on a real time basis. Photos of the ZoloSCAN heads installed on the furnace are shown in Figure 6. Figure 5: Side view of the ZoloSCAN layout for the reheat furnace demonstration

8 Figure 6: ZoloSCAN heads mounted on side of a reheat furnace The instrument rack, Figure 8 was located between two furnaces to allow for future expansion. Five (5) paths were installed on No. 1 Reheat furnace for the demonstration. The instrument rack installed at Gary Works has the capacity to handle an additional five paths which can be installed on No. 2 Reheat furnace in the future. The only requirement for this expansion is field wiring of the fiber optics and installation of the SensAlign Heads as shown in Figure 7. The unique architecture of the Zolo system enables this significant capital cost benefit by allowing a single system to monitor two furnaces. (As of the writing of this article, paths have been installed on No. 2 furnace as a result of this successful demonstration) SensAlign heads Junction boxes Node box Node box Purge air Control Rack Figure 7: Diagram of single ZoloSCAN instrument rack located to support two furnaces Figure 8: ZoloSCAN instrument rack located between furnace #1 and #2 ZoloSCAN Provides Zone-by-Zone Combustion Information The ZoloSCAN-RHT HMI is shown in Figure 9. The data displayed shows a typical operating condition for No. 1 furnace before any optimization was performed. Note that the excess O 2 values measured for the five zones ranged from 1.3% to

9 Bottom Heat Zone ( F) Top Heat Zone ( F) 4.6%. This is a very wide spread, and is a clear indication of how difficult it was to optimize the individual zones properly before the Zolo system was installed. Zone temperatures vary widely depending on product in furnace. This is normal Reheat Furnace #1 Excess O 2 varies from 1.3% to 4.6% - this is not desirable CO varies with firing rate and O 2 levels Figure 9: ZoloSCAN-RHT User Interface for steel reheat furnaces, showing flue gas temperature, oxygen, and carbon monoxide concentrations BEFORE optimization ZoloSCAN Measures Process Variations The ZoloSCAN system is a great tool for measuring and tracking changes in the combustion process in real-time. In Figure 10 below, the flue gas temperature measured by ZoloSCAN is compared to the average value of the thermocouples mounted in the furnace walls. ZoloSCAN tracks the frequent temperature changes as precisely as the thermocouples. The temperature offset between the ZoloSCAN measurements and the thermocouples arises from the fact that the thermocouples are located near the burners and the ZoloSCAN paths are located at the zone exit, where the flue gas temperature is lower. Average Thermocouple TPHZ BPHZ THZ BHZ SZ ZoloSCAN-RHT Average Thermocouple TPHZ BPHZ THZ BHZ SZ ZoloSCAN-RHT Timestamp Figure 10: ZoloSCAN temperature measurements vs. plant thermocouples

10 As is typical of many reheat furnaces, this reheat furnace did not have either O 2 or CO sensors installed. Therefore, the ZoloSCAN data provided the operations team with their first look at the variation of the CO and excess O 2 over time as the furnace was adjusted to process a wide variety of steel products. Figure 11 shows the variation in the O 2 and CO in the bottom preheat zone for normal operation over approximately a day and a half. Note that there are a number of periods where the excess O 2 is very high, leading to reduced combustion efficiency. There are also frequent periods where the CO is very high, above 10,000 ppm, which can present a safety hazard if the CO escapes through the charging door and into the surrounding work areas. Figure 11: ZoloSCAN O 2 and CO data for the bottom preheat zone showing the wide variation in excess air and CO emissions BENEFITS OF ZOLOSCAN-RHT AT GARY WORKS ZoloSCAN Identifies Furnace Problems The first benefits realized by the ZoloSCAN system installed at Gary Works were unexpected. When the excess O 2 measured in the bottom heat zone (BHZ) by the ZoloSCAN system did not respond to combustion air changes as expected, it was determined that there was a large air leak in the BHZ burner wall. This leak was validated by the exceptionally high O 2 value measured in the BHZ in the data in Figure 12. Operators were not aware of this leak prior to the installation of ZoloSCAN. It was only identified as a concern because the ZoloSCAN data provided real time feedback of actual oxygen levels, which were far outside the expected range. After the ZoloSCAN system was installed, operators were able to safely reduce the combustion air flow to bring the excess O 2 closer to the desired level, while monitoring CO to ensure safe operation until the leak could be repaired. Because the furnace gases move between zones, improvements to the BHZ reduced the amount of O 2 in the top heat zone (THZ) and the bottom preheat zone (BPHZ) as well. ZoloSCAN provided the information to identify these trends and helped operators adjust their heating strategy accordingly. In another case, ZoloSCAN indicated that the changes in excess O 2 and CO in the top pre-heat zone (TPHZ) were not consistent with the combustion air changes reported by the DCS. A physical inspection of the gas delivery systems revealed a component in the combustion air control had failed and the air/fuel was not being reported properly. Without ZoloSCAN, this inefficient operating condition would have continued for a long time. ZoloSCAN Enables Zone-by-Zone Furnace Optimization ZoloSCAN provides measurements of the products of combustion directly in each zone, allowing the operator to adjust the air/fuel ratios for each zone to optimize the excess O 2, while monitoring the CO to ensure combustion stays in a safe operating condition. While operators can improve combustion efficiency by adjusting the air/fuel ratios manually or by utilizing air/fuel ratio vs. firing rate lookup tables, far greater improvements are obtained with closed-loop control to maintain

11 the desired excess O 2 levels measured by ZoloSCAN. Closed-loop control ensures that the most efficient combustion conditions are maintained in each zone, over the entire firing rate range, as well as over varying fuel composition and ambient temperature, pressure, and humidity conditions. In addition, as burner performance and air-fuel mixing change over time, closed loop O 2 control ensures the proper air/fuel ratio is maintained for best efficiency. Closed-loop O 2 control utilizing the ZoloSCAN data was added to Gary Works No. 1 furnace as part of this demonstration. The ZoloSCAN-RHT interface screenshots in Figure 12 show the significant improvement that closed-loop O 2 control provided. Before closed-loop control the O 2 values vary greatly between zones, and it is particularly high in the BHZ due to the air leak that ZoloSCAN identified. After closed loop control was implemented, the O 2 levels were lower and more consistent between zones, resulting in a dramatic improvement in efficiency. It was also observed that the O 2 levels were more consistent as the firing rates changed to accommodate varying steel product. Prior to ZoloSCAN, operators were often running the furnace in the manual mode because all they could respond to was furnace temperature and had no information as to the state of combustion. After the installation of ZoloSCAN the furnace operates almost entirely on automatic. This improvement provides much more consistent shift to shift operations. Installing ZoloSCAN on all four furnaces will lead to much more consistent operation across the entire shop. Note that closed loop control was also able to greatly mitigate the impact of the BHZ air leak. The air leak was large enough that the excess O 2 could not be reduced to the target value, in line with the other zones, but it was reduced significantly from the original value. The increase in CO was minimal, indicating that combustion was still operating in a safe but much more efficient condition. This improvement saved the plant significant fuel costs for several months until the furnace could be shut down to make proper repairs. The performance of the adjacent zones were impacted by the leak as well. The THZ and the BPHZ were also improved because the furnace was controlled to the current condition reported by ZoloSCAN instead of unverified predicted values. Indicates large air leak Leak impact greatly reduced a) Before O 2 control with ZoloSCAN: High and varied O 2 High O 2 in BHZ due to leak b) After O 2 control with ZoloSCAN: Lower O 2, similar CO BHZ leak compensated Figure 12: ZoloSCAN O 2 and CO data for the demonstration furnace a) before and b) after optimization and closed-loop O 2 control ZoloSCAN Improves Furnace Efficiency Fuel savings is the most quantitative measurement of success in combustion optimization. Using actual oxygen on a real time basis for ratio control improves fuel efficiency by limiting excess combustion air and limiting unburned fuel. Gradually, excess oxygen was lowered in each zone to stay below 2.0% over most of the firing ranges for each zone. The goal was to lower the oxygen while maintaining CO at safe operating levels. By maintaining optimal O 2 levels in each zone over all

12 Furnace energy use per ton (Normalized) operating conditions with real-time closed-loop control during the months of September 2013 through December 2013, fuel use was reduced by more than 5.2%. Figure 13 shows the fuel savings achieved by actively controlling air/fuel based using the O 2 values reported by ZoloSCAN. The savings presented here support a payback on the ZoloSCAN-RHT system of approximately 6 months. US Steel is developing a process to tune their furnace temperature model predictions using the ZoloSCAN. This is possible because of the close proximity of three laser paths to the surface of an identified bar at three locations in the furnace. The ability to evaluate this information on a majority of the bars passing through the reheat furnaces is unprecedented. No O 2 control O 2 control July-Aug average 5.2% Zolo enabled reduction in fuel usage Sept-Dec average July 2013 Aug 2013 Sept 2013 Oct 2013 Nov 2013 Dec 2013 Figure 13: Fuel savings measured for USS Gary Works furnace #1 after implementation of O 2 control using ZoloSCAN ZoloSCAN Improves Safety Control of Carbon Monoxide was a major concern for USS Gary. Due to random excursions of CO, personal monitors have been required for personnel working around the furnaces, and fixed CO monitors have been installed in the working areas around the furnace. Prior to the installation of ZoloSCAN no correlation could be made between high CO measured outside the furnace and any particular furnace operating condition. Data from ZoloSCAN showed that the high CO in the working areas only occurred when the CO was high in the preheat zones (Figure 14). Optimization of the preheat zone combustion to minimize CO at the zone exit would dramatically reduce the incidents of high CO in the working areas, and ZoloSCAN could be used to trigger an alarm when CO levels exceed a specified target.

13 CO CO next outside to Furnace Furnace 1 CO next to Furnace 1 CO next to Furnace 1 CO CO next outside to Furnace Furnace 1 Safe operating range CO in BPHZ CO CO at in TPHZ exit Charging door Safe operating range CO CO at in BPHZ BPHZexit CO in TPHZ Figure 14: Measured CO adjacent to furnace compared to CO measured inside preheat zone CONCLUSION The ZoloSCAN-RHT combustion monitoring system can assist steel reheat furnace operators to improve process efficiency and safety through controlling air/fuel ratios based on the products of combustion rather than the input fuel and air. Measurements of temperature, H 2 O, O 2 and CO directly in the furnace allow optimization of each zone individually for maximum performance. Zone-by-zone combustion tuning to control excess O 2 and limit CO ensures maximum efficiency, improved safety, and provides conditions for optimum scale formation. Real time data enables the operator to identify combustion problems and take action right way, rather than waiting for the problem to show up in increased fuel consumption over time. Improvements like those observed on the Gary Works furnace can be recognized on other reheat furnaces as well. We estimate that ZoloSCAN can enable typical large steel reheat furnaces to improve fuel efficiency by 4-8% yielding capital payback in well under one year. ACKNOWLEDGEMENTS We wish to thank the US Steel 84 Mill operating and maintenance departments for their cooperation and enthusiasm during this project along with Mr. Mark Urda, President of Synergy Systems, Inc for his work on integration of level 1 control. REFERENCES 1. Engineeringtoolbox.com: 2. S. Sandlobes, D. Senk, L. Sancho, A. Diaz, In-Situ Measurement of CO- and CO 2 -Concentrations in BOF Off-Gas, Steel Research International, 3. A. Sappey, J. Howel, P. Masterson, H. Hofvander, J. Jeffries. X. Zhou, R. Hanson Determinations of O 2, CO and H 2 O Concentrations and Gas Temperature in a Coal Fired Utility Boiler using a Wavelength-Multiplexed Tunable Diode Laser Sensor, poster at 30th Int. Combustion Symp., Chicago, July 2004