ZoloBOSS™ FAQ

What is TDLAS?
What can be measured with the ZoloBOSS?
Is the ZoloBOSS accurate?
How can the ZoloBOSS measure through coal dust and turbulence in the boiler?
Where in the plant is the system installed?
What is the update time for each path?
What DCS input(s) are available to help in control of the various species measured by the ZoloBOSS?
What is tomography and how does the ZoloBOSS create the tomography images from path average data? Is it accurate?
Can I display the tomography data in my software and can I also get point measurements?
What reference gases are required for calibration?
How does the ZoloBOSS maintain alignment?
How does the ZoloBOSS keep the port opening clear?
What is the life of the key electronic equipment, such as lasers?
How much maintenance is required?
Can the ZoloBOSS be installed in all types of boilers?
What types of fuels can be used with the ZoloBOSS?

What is TDLAS?
Tunable diode-laser absorption spectroscopy is a proven technique that uses lasers to measure combustion constituents. An industry standard diode-laser is tuned in wavelength across a tiny portion of the optical spectrum. Light at the chosen wavelength is absorbed by a given combustion constituent and the relative amount of absorption is proportional to the concentration. The ZoloBOSS transmits multiple laser wavelengths, simultaneously along a single path and measures an average of each concentration.
For more information see wikipedia's entry on TDLAS.
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What can be measured with the ZoloBOSS?
The ZoloBOSS can measure O₂, CO, CO₂, H₂O, and temperature all simultaneously and directly in the combustion zone, back-pass or anywhere with a line-of-sight in the boiler.
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Is the ZoloBOSS accurate?

The ZoloBOSS provides accurate and repeatable measurements of combustion constituents and temperature directly in the furnance.

The measurement techniques employed by the ZoloBOSS are based on over 25 years of well-established and documented research on spectral absorption characteristics of specific constituents. A detailed database of absorption profiles for each constituent has been established through work performed at Stanford University and the Harvard-Smithsonian Center for Astrophysics. Zolo Technologies has validated the accuracy of these profiles in boiler-simulated conditions with known concentrations of gases in its own state-of-the-art test furnace.

In-situ field comparisons with traditional measurement devices are more difficult, as the ZoloBOSS is the only measurement device capable of measuring multiple constituents plus temperature directly in the furnace. Currently, the accepted measurement method in a boiler is gas extraction with a high velocity thermocouple (HVT) probe. Sample extraction from an ongoing reaction zone, such as the fireball, leads to significant errors in concentration measurements. In particular, the sample cannot be quenched quickly enough to prevent further reaction in the probe before measurements are completed (without condensing water). This is especially true when using HVT in the combustion zone as opposed to downstream or even in the back-pass where combustion is completed. Using an HVT probe to obtain temperature measurements often leads to measurement uncertainties due to issues of heat transfer, radiation effects and difficulties of proper and repeatable sampling practices. Even experienced practitioners of HVT testing concede that HVT probes will under-report temperature, in some cases by several hundred degrees. While they strive to minimize these problems, they cannot be completely eliminated. These challenges with current HVT practices create a need for a better measurement device to measure accurately where it counts—in the combustion zone.

In addition to the obstacles facing accurate HVT measurements, differences in the measurement acquisition methods hinder a direct comparison of HVT information with ZoloBOSS data. For example, the HVT data is obtained at specific points across the boiler. As a result, there can be significant time delays as the data is acquired via HVT across the entire boiler for each point; HVT only captures the constituent concentration at a single point in time; or the test probe can miss pockets of high concentrations or temperature across the boiler. Obtaining data in the middle of large furnaces can be impossible since HVT probes may not be sufficiently long. Also, while care is usually exercised to attain a steady-state condition during the HVT test period, it is very difficult to achieve in practice. In contrast, the ZoloBOSS system obtains measurement data in real-time, for all constituents, based on a path-average across the boiler. This method captures all of the information across the boiler length and eliminates the impact of any operational changes that may occur during data acquisition. Meanwhile, a two-dimensional tomography grid offered by the ZoloBOSS system can also provide derived discrete point data across the measurement plane.

Despite differences and limitations, it is still instructive to compare HVT data with data from the ZoloBOSS. Indeed, if sufficient care is taken and the HVT temperature measurements are made in exactly the same location as our ZoloBOSS temperature measurements, it is possible to make a comparison of data. Zolo Technologies has completed numerous measurement campaigns and the results show agreement between the ZoloBOSS temperature measurements and HVT measurements with HVT temperature data reported 10 – 40 °F below the ZoloBOSS measurements, well within the prescribed accuracy of both instruments. These tests confirms that the ZoloBOSS readings are comparable to traditional methods in a boiler under real operating conditions. Not surprisingly, the HVT reads low, despite being operated with standard radiance shielding and the great care taken to verify that adequate gas flow rates were maintained across the flow tip to balance inevitable radiance losses.

A similar comparison can be made between the level of O₂ obtained with the ZoloBOSS and traditional extractive methods for oxygen. While such a comparison should provide comparable values, it should be noted that the extractive measurements are made at a single point, but the laser measures a path average along the entire path. Whereas the laser makes nearly instantaneous measurements along the measurement path, it can take up to an hour to do an extractive traverse along the line of sight in the boiler, depending upon the number of measurement points being obtained. As a consequence, comparisons of the two different measurement approaches cannot be exact and can differ based on the degree of temporal and spatial variability exhibited by the parameter being measured during the two different measurement time periods. Secondly, it should also be noted that the ZoloBOSS measurement is made on an in situ basis in the presence of moisture. Thus, it is a “wet” measurement. Extractive gaseous measurements, on the other hand, remove the moisture prior to the gaseous sample reaching the analyzer and are conducted on a “dry” basis.

Finally, traditional measurement methods, such as HVT probes or zirconium oxide probes, typically exhibit a random measurement error for each reading and each device. Even with multiple points or probes, this random error can often mask small changes or trends in the combustion process. Conversely, the ZoloBOSS system uses the same laser and same signal processing on each path, which eliminate most of this random error. This results in significantly more consistent and repeatable measurements. In comparative tests conducted both in the furnace and backpass areas, the ZoloBOSS measurements read higher than extractive measurements by about 0.5%. This can be largely attributed to the ongoing reaction between O₂ and CO within the extractive probe
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How can the ZoloBOSS measure through coal dust and turbulence in the boiler?
Each laser in the ZoloBOSS system is tuned for a very specific wavelength of light that coincides with the absorption feature of a certain constituent (such as O₂ or CO). Light will only absorb at this certain wavelength–not above or below. The laser is then scanned over a narrow wavelength range around this absorption feature (slightly above and below the wavelength of the absorption feature). The ZoloBOSS measures the ratio of light absorbed by the constituent compared with the light that is not absorbed (because it is either just above or below the absorption feature wavelength). This ratio-metric measurement is a function of the concentrations of the constituent. Since we are only interested in this ratio of absorption and not the absolute absorption, we are indifferent if some of the light gets blocked by excess coal-dust and ash. Due to fiber-coupled lasers for transmission and detection, the ZoloBOSS is extremely sensitive. As a result, if less than one one-hundredth of the light sent across the boiler makes it through the turbulence, coal-dust and ash, measurements can still be obtained.
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Where in the plant is the system installed?
The ZoloBOSS instrument consists of a control rack, distribution cabinet, distribution nodes and transmitter and receiver heads. The control rack contains lasers and sensitive instruments and is located in or near the plant control room up to a kilometer from the boiler.
One cable bundle is sent to the distribution cabinet, located somewhere near the boiler, where it the optical fiber is switched and sent serially to each distribution node at each measurement level. Distribution nodes are specific for each installation with one or more per measurement level. From here the light is sent to each head and collected on the other side and brought back to a distribution node. The heads are mounted directly on the boiler.
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What is the update time for each path?
A complete system, and depending on opacity in the boiler, updates take 10-15 seconds per path for a total of 150 to 225 seconds for a complete round. However, since the system is fully user-customizable, the user could cycle faster at the economizer outlet by repeating those measurements for a number of cycles, then go back to a full cycle. The user can select how often to sample in a specific area.
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What DCS input(s) are available to help in control of the various species measured by the ZoloBOSS?
The ZoloBOSS provides an OPC server that can be used to communicate data to a DCS. Alternately, data can be sent to a “slave” server to maintain the utility's firewall.
A MODBUS program is also available and any data can be collected. Average concentration on a path, or even an arbitrary point on a tomographic map for a level. For example, O₂ viewed at any point on the tomographic map can be digitized and pulled as a data point for DCS or Neural Net biasing. One point, or two hundred points, whatever X/Y data the user requires.
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What is tomography and how does the ZoloBOSS create the tomography images from path average data? Is it accurate?

Each ZoloBOSS path measures an average value. By using the intersection of multiple crossing paths and creating a grid of laser beams through the combustion zone, Zolo Technologies can create a concentration map for each measured constituent simultaneously. This technique creates a rough image (due to far fewer paths) similar to computed axial tomography, or CAT scans. For this reason, we call this combustion CAT scanning. Paths do not have to be equally spaced and are not required to be rectilinear. Installing more paths increases the resolution and usefulness of a given tomographic map, but as little as four paths can provide valuable information used for tuning and balancing boiler performance.
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Can I display the tomography data in my software and can I also get point measurements?

The ZoloBOSS measures the concentration of each constituent across a line-of-site path from one side of the furnace to the other. Path averages are less sensitive to local variation, gradients, and turbulence as compared to single point measurements. Furthermore, whereas the ZoloBOSS makes instantaneous measurements along the measurement path, it can take up to an hour to do an extractive traverse along the line of sight in the boiler, depending upon the number of measurement points being obtained. As a consequence, comparisons of the two different measurement approaches cannot be exact and can differ based on the degree of temporal and spatial variability exhibited by the parameter being measured during the two different measurement periods.

Tomography is calculated in real-time from the data supplied using our proprietary software and algorithms. We can supply all the data necessary to calculate the tomography in various other software or supply the tomographic map as a static picture (bitmapped or jpeg image) that can be used in presentations or other applications.
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What reference gases are required for calibration?
None. The ZoloBOSS does not use any reference gas at the plant. The values necessary for calibration are generated for each system in our laboratory at Zolo Technologies. From that point on, the system requires no further, ongoing calibration to maintain accurate measurements. As power fluctuates either in the system or due to the changes in the boiler, the system's ratio-metric measurements ensure that, whenever a measurement is made, it is an accurate one.
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How does the ZoloBOSS maintain alignment?

Utility boilers operate in one of the worst environments in the power business; they warp, they grow, they shrink and they twist. Zolo Technologies' SensAlign system is designed to perform in this challenging environment. No sensitive electronics are located in the measurement heads. Instead, lasers and detectors are installed in the control rack and connected to the heads with fiber-optic cables. High temperature servos in the measurement heads are controlled from the control rack and actuate output and collection optics inside the SensAlign head. As the boiler conditions change, the heads actively maintain alignment for each measurement to ensure optimum laser signal across the furnace.
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How does the ZoloBOSS keep the port opening clear?

Each port has a low volume of plant air, which both keeps light dust and ash from collecting and the window free of condensation. Heads located in the combustion zone also include the ClearView port-rodding system to automatically clear a path of dust, ash or slag that may block the port opening. Air-actuated cylinders rapidly extend a sleeve into the furnace and quickly retract, removing slag or popcorn ash from the port before measurement takes place. The ClearView system is controlled by the system software and requires no user intervention to operate. If these methods fail, each head is removable and port openings can easily be easily accessed in order to be manually cleaned.
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What is the life of the key electronic equipment, such as lasers?

Much of the technology used in the ZoloBOSS system was developed for the telecom market and is designed to for harsh environments such as buried undersea and still operate reliably, completely free of maintenance for up to 20 years at a time. These robust components are well-suited to the power plant environment. The lasers used in the ZoloBOSS system, for example, are designed for a mean life of 100,000 hours of operation.
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How much maintenance is required?

The ZoloBOSS requires no on-site calibration, requires no reference gases and does not exhibit drift. Primary maintenance is cleaning the transmit and receive head windows with a soft cloth. Cleaning frequency depends on the path location, for example near soot blowers, conditions in the boiler, for example high ash fuels, and the cleanliness of the purge air. Typical cleaning schedules amount to approximately one hour per week to clean all paths and ensure ports are clear.
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Can the ZoloBOSS be installed in all types of boilers?

The ZoloBOSS can be installed in on most types of boilers including wall-fired, tangentially-fired, downshot or cyclone-fired. The ZoloBOSS can not be installed on circulating fluidized bed boilers. The specific configuration will depend upon the specific objectives of the operator and sufficient access to the ports and clear lines-of-sight for measurement paths across the furnace. Furnace division walls and other obstructions can limit path location possibilities, however, depending on the application, careful arrangement of paths can yield valuable results on a wide range of burner configurations and boiler geometries.
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What types of fuels can be used with the ZoloBOSS?

The ZoloBOSS can measure nearly any form of combustion including coal, oil and gas fired boilers. With respect to coals, current installations include bituminous, sub-bituminous, lignite and biomass. The ZoloBOSS can collect data in extremely challenging environments but some very high opacity conditions can limit how much data is collected. Contact Zolo Technologies to arrange an appointment to look at your application to learn more.
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Zolo Technologies, Inc.

ZoloBOSS™ FAQ