Frequently Asked Questions
- Is the ZoloSCAN accurate and repeatable?
- Is the ZoloSCAN system reliable?
- Does the ZoloSCAN need regular in-field calibration?
- How much maintenance is required?
- How does the ZoloSCAN maintain alignment?
- How does the ZoloBOSS keep the port opening clear?
- How does the ZoloBOSS laser penetrate the ash and dust in the furnace?
The ZoloSCANprovides accurate and repeatable measurements of combustion constituents plus temperature directly in the furnace.
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 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 over the typical range found in combustion.
The ZoloSCANis designed to operate in ultra-harsh combustion environments. The reliability of the ZoloBOSS system is enhanced by the system architecture and the component selection:
The ZoloSCAN is designed around a central control rack that contains all of the critical electronic components including the lasers and control computer. The control rack is typically located in an environmentally controlled area (relay room) to maintain acceptable operating conditions. The laser signal is transmitted to each measurement location via optical fiber cable where each path is measured in series. This central design architecture keeps the critical components well protected and not exposed to the harsh furnace environment. The heads which are mounted on the furnace wall only contain fiber optics, a collimating lens and high temperature alignment motors. If a failure occurs on an individual head, it will not impact the performance of the other heads and the ZoloSCAN still provides adequate data to continue to balance combustion.
Much of the technology used in the ZoloSCAN system was developed for the telecommunications market. As such, it has to meet stringent reliability requirements under rigorous environmental conditions. For example, the lasers used in the ZoloSCAN system are designed for a mean life of 100,000 hours of operation. Many industrial-grade components are used (such as computers and Uninterrupted Power Supply (UPS)) to further enhance the system reliability.
The ZoloSCAN requires no in-field calibration. Once the system is set up in the plant there is no measurement drift as with other types of sensors. The TDLAS measurement technique uses the absorption characteristics of light. These absorption characteristics do not change over time. Also, since our measurement method is based on the ratio of absorbed versus non-absorbed (baseline) light over a very narrow wavelength range, the measurements are not impacted by dust or particulates in the flue gas. Only about 1/1000th of laser light needs to make it across the furnace in order to get a valid measurement. However, if the ash content is too high, the ash (particles) will block 100% of the laser light and no measurements are possible.
The ZoloSCAN is designed for low maintenance and to operate in ultra-harsh environments. The critical electronic components, such as lasers, are “tele-com grade” and are designed for over 10 years of life. Mechanical components, such as the port rodder and associated linkages (if applicable with the ZoloBOSS), are also designed for the harsh environment but will exhibit normal wear over time and can be easily replaced or repaired if necessary while the furnace is operating. In general, no outage is required to maintain or repair the ZoloBOSS system as nothing is located directly in the furnace.
Primary maintenance requires cleaning transmit and receive head windows with a soft cloth. Cleaning frequency depends on the path location. For example locations near soot blowers may cause windows to foul more frequently. Other variables include: conditions in the boiler; high ash fuels; and the cleanliness of the purge air. Typical cleaning requires approximately one hour to clean all paths and ensure ports are clear. Some plants only need to clean the windows once every week but others once a month. For plants firing natural gas, maintenance requirements are greatly reduced and operation over six months between cleaning is normal. The ZoloSCAN provides a “signal indicator” for each path which can be used to alert operators of a weak performing path which may require more frequent cleaning.
Large furnaces represent one of the worst environments imaginable for optical sensors; 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 automatically controlled from the control rack to actively maintain laser alignment for each measurement to ensure optimal laser signal across the furnace.
In coal-fired applications using the ZoloBOSS, each port is purged by a low volume of plant air, which both keeps light dust and ash from collecting in the port and the window free of condensation. For coal applications, all SensAlign heads 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 “rodder” into the furnace and quickly retract, removing slag or 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 can be easily removed and port openings can be manually cleaned.
Each laser in the ZoloSCAN and ZoloBOSS systems is tuned to a very specific wavelength of light that coincides with the absorption feature of a certain constituent (such as O2 or CO). Light will only be absorbed at this wavelength – not at surrounding wavelengths. 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 ZoloSCAN measures the ratio of light absorbed (on resonance) versus the light that is not absorbed (off resonance). This ratio-metric measurement is a function of the concentration of the constituent. Since the ZoloBOSS uses the ratio of absorption on and off resonance and not the absolute transmission through the measurement zone, the measurements are unaffected by excess coal-dust and ash. Due to the laser-based architecture and carefully developed algorithms, the ZoloSCAN is extremely sensitive. As a result, if less than one one-thousandth of the light is transmitted across the boiler makes it through the turbulence, coal-dust and ash, measurements can still be obtained.