Intelligent Sootblowing (ISB) In General
Q: What are the benefits for implementing intelligent boiler cleaning system?
A: A fully implemented intelligent and automated boiler cleaning system can typically achieve a wide variety of benefits. Some of the most important and obvious benefits possible are listed below:
- Efficiency improvements: 2% is fairly common
- Load gain: 10MW to 70MW per boiler has been achieved
- Elimination of outages: at least one per year
- Reduction of maintenance of previous hardware
- Reduction in NOx: typically 10-15%. Cases of 50% on record.
Q: How can intelligent boiler cleaning increase reliability and availablity?
A: Reliability and availability can be improved from three aspects:
- Continuous Load Generation
- As fouling increases in some areas and decreases in others, the system must be capable of recognizing these changes and responding automatically to these changes by having sufficient cleaning capability and range of control.
- Minimize Outages due to Tube Leaks
- Tube leaks are frequently caused from excessive sootblower operation, which can be minimized. The cleaning systemís capability to do this is largely dependant on the cleaning systems twin capabilities of being able to recognize reductions in fouling which dictate a reduction in required cleaning intensity and response and have the necessary controllability and flexibility to adjust the cleaning parameters to adjust to this reduction.
- Minimize De-rates or Pluggage due to Excessive Slagging
- Derating and outages due to excessive slagging should also be minimized or eliminated. This is achieved by responding prior to the accumulation of large quantities of deposit. This process can be automated using intelligent feedback and control.
Q: Why is intelligent boiler cleaning able to reduce NOx emission?
A: NOx emissions are a function of combustion temperature and amount of O2 in the combustion process. Typically Eldevich or thermal NOx production escalates at an exponential rate in areas where the local combustion temperature exceeds 2600 degrees Fahrenheit. The presence of hot and cold spots, such as indicated in the thermal profiles obtained from the HVT probes above will tend to indicate weak heat distribution in the combustion process and can be caused by a misdistribution of heat transfer in the furnace walls. This can be addressed by implementation of intelligent and dynamic boiler heat flux feedback mechanisms.
Q: Can intelligent boiler cleaning reduce SOx emission?
A: The combustion of sulfur results in SO2 formation. As SO2 emissions is a function of coal sulfur content and the quantity of coal burnt, the only method of reducing SO2 production from a boiler cleaning perspective is an increase in boiler efficiency, which can be achieved by intelligent boiler cleaning. In addition, as SO2 production is a permanent function of coal composition, a significant option to reduce its production is a switch to low sulfur coals, such as PRB. Methods for controlling slag formation on the use of such coals can be key to their successful adoption in a boiler, especially if it was originally designed for a higher grade coal. Intelligent biler cleaning is capable of effectively cleaning the furnace so that improve the flexibility of coal switch.
Q. How complicated it is to retrofit an existing boiler? Downtime, expenditures etc.
A. It is relatively easy compared to other installations in the power plant. Water Cannons and heat flux sensors are typically installed during a major outage. Installation could also be done in 1-2 weeks if sufficient labor available and the installation process are well managed. SmartGauge systems can be installed on line, depending on the temperature on the penthouse roof.
Q. Have you used this system on any Super Critical boilers or once-thru boilers?
A. Yes, we installed a number of systems on super critical and once-thru boilers such as Gavin and Michigan City.
Q. Has this been installed on any cyclone boilers?
A. Yes we have a number of cyclone boilers with water cannons installed. No strain gages have been installed on cyclone boilers yet.
Q. Does the soot blowing patterns change for units that use OFA during the ozone attainment season?
A. It would be possible to do this, but it is not part of our typical operation. The ISB system normally attempts to optimize boiler cleanliness, boiler efficiency, and maintain proper steam conditions.
Q. Is the ROI payback calculation based on assumptions about avoided outages/derates or based solely on Heat Rate improvements?
A. The ROI calculation is based on money saved from avoided outage, steam saved, heat rate improvements, fuel changes, and so forth. We can provide a detailed evaluation of the expected savings with an itemized list of the effect of each variable.
Q. What is a typical timeline for installation, and how much outage time is required? Also, how much time for optimization and what are overall load requirements during optimization?
A. The water cannon system can be installed within a normal planned outage. Minimum time required is 1 week. We need approximately 1-2 weeks for startup and optimization.
Q. How do you determine how to vary operation with varying load? What automatic options are available?
A. ISB system can adjust the clean and dirty setpoint automatically according to the load change.
Q. Do you need a tuning of the system during the boiler start-up? How about later in the operation?
A. We usually do a basic tune-up during startup. We will keep monitoring and fine tune system later in the boiler operation. For most installations, the monitoring is done remotely by modem.
Q. Can the ISB be installed on a blowing system by another manufacturer?
A. Certainly, ISB can be used for sootblowers from any manufacturer.
Q. How much back end instrumentation is required? i.e. economizer inlet and outlet gas and water temps, O2, etc.
A. For the typical boiler our system needs no additional instrumentation. We primarily use steam temperatures, pressures, spray flows, CEM data, O2, and unit load.
Q. Do you have any experience on biomass plants?
A. Yes we have an installation with water cannons in California.
Q. Does the ISB only use weight and heat flux monitor input to determine where to sootblow? Does it use any performance indices? That is does it look at any change in heat absorbed in backpass areas of the boiler to determine where to sootblow there?
A. ISB uses weight measured by SmartGauge and cleanliness factors calculated by thermodynamic model to determine the fouling condition in the pendants and backpass areas and direct the sootblower when and where to clean. The feedback from heat flux sensor is used to determine the operation of water cannon which cleans the water wall.
Q. What is the estimated $/KW range?
A. It is approximately 1.00 to 2.00 $/KW, it is relatively cheaper for larger size boiler than small size boiler in terms of $/KW.
Q. Have you implemented an ISB system for an entire boiler system (boiler, economizer, air preheater and/or dust collectors/precipitators, etc.) or has it been dedicated only to the boiler proper for now?
A. Our ISB system currently covers the furnace, convection pass, economizer, and air heater.
Q. Do you partner with controls systems integrators or is your product turnkey only?
A. We normally provide our own SmartControls open architecture platform for Intelligent Sootblowing. But we are also willing to collaborate with other system integrators.
Water Cannon Related
Q: How can water cannon minimize the process costs?
A: Costs of operation besides the cost of fuel include all other operational and maintenance costs. Maintenance of cleaning equipment, or any other equipment associated with cleaning activity can be directly affect. The following costs could be avoided or reduced by applying water cannon technology.
- Sootblower maintenance (labor and materials)
- Sootblower air compressor maintenance
- Cleaning media consumption
- MW lost used on cleaning with steam
- MW lost on running air compressors
- Fuel costs
Q: Will thermal impact from water cannon damage the tube?
A: Not in the expected boiler life expectancy. We use a thermocouples in the heat flux sensors to measure instant thermal shock and adjust the water jet progressive velocity and water pressure automatically to minimize thermal shock.A number of researches have been done for the thermal impact. Please refer to Mechanism of Thermal Tube Impact and this technical presentation for details.
Q. Does the cannon trace vertical or horizontal? and why?
A. The SmartCannon cleans the water wall horizontally. Vertical trace may cause water wall tube to be over cooled. We have extensive successful experience with horizontal cleaning.
Q. How close to the nose and convection section can the cannon clean without potential damage? Can you shoot the nose?
A. We usually keep a 2 to 3 foot off-set from the convection section. We can spray the bottom side of the nose, if the location of the cannon is high enough in the boiler.
Q. Do the water cannons cause damage to refractory when the refractory is hot?
A. We have some limited experience cleaning refractory without doing damage. However, our typical installation cleans tubes without refractory.
Q. Has Water Cannon operation caused loss of boiler fire?
A. We have never experienced this. We do not spray water into the burners. The cannons can clean a section of the furnace wall quickly. The time for cleaning a 30 feet by 30 feet area is only about 10 to 20 second. The amount of water added to the furnace is negligible.
Q. What is the typical quantity and make-up of the water for the water cannon?
A. The typical water flow through water cannon is 150 gallon/min to 250 gallon/min depending on the boiler size. Service water is commonly used as the water source. The typical water pressure in the system is between 250 and 350 PSI.
Q. How does the water cannon clean the walls?
A. Typically one water cannon is installed on each wall. The water cannon sprays water to the opposite water to remove the slag deposit. Each wall is divided into several clean zones. A heat flux sensor in each zone determines when to clean the zone. The water jet is accurately targeted to the dirty area and the zone is cleaned in 10 to 20 seconds.
Q. Do you have any water cannons at waste-to-energy plants?
A. Our sister company in Germany has many water cannon installations in European waste-to-energy plants. Although there are none currently installed in the U.S., we are currently working with waste-to-energy customers to design and install water cannons in this type of boiler.
Q. A water cannon typically replaces how many wall blowers?
A. One water cannon is able to clean the whole wall and replace all the wall blowers on that wall. Large boilers can have over 100 wall blowers, and the water cannons make them all obsolete.
Q. Are there programmable sequences with the water cannons so that you are not consistently blowing the same area?
A. Yes, we have 20 to 30 sequences stored in the system. There is also time delay setup for cleaning cycles so that the same zone will not be cleaned too frequently.
Q. What other equipment is included in a water cannon installation? What are the water supply requirements?
A. Other equipment includes heat flux sensors, variable speed pump, seal air fans and tube openings. Typical water supply is service water.
Q. Would a water cannon installation allow us to get rid of our current wall blower/water lance equipment?
A. Yes, many plants stop maintaining wallblowers and waterlances after the installation of water cannons.
Q. Do you require a recirc off the any speed pump during dwells between the next use?
A. Yes, we do have a small recirculation pipeline for water cannon system.
Q. Are you using your water cannon system on any oil-fired units?
A. Oil fired units usually has less slagging problem than coal fired unit, but we do have one application on oil fired unit.
Q. Does the use of a water cannon cause downstream boiler plugging due to higher moisture in flue gas?
A. No, water cannon use will not cause the plugging problem. Water cannons only run 10 to 20 second for a 30 ft by 30 ft cleaning zone, as a result, the amount of water added into the furnace is negligible.
Q. Have there been any documented tube failures caused by water canon erosion?
A. Erosion is not a problem with water cannons. Water cannon does not clean the wall by direct kinetic impact, which is applied by conventional air or steam sootblowers. Water cannon cleaning technology employs a two-step process. First, water sprays and penetrates into the slag, and second, water in the slag expansion as it converts from water to steam, providing the energy need for the slag to detach from water wall. The water jet speed is very low when it hits the water wall. In addition, a water cannon will only clean a zone when the water wall is covered by a layer of slag so that water will not impact wall tube directly. Therefore, the water erosion problem is non-existant for water cannon system.
Q. Do you have a system for removing eyebrows from top of burners?
A. Water cannon can be used to remove eyebrows but it is not its typical during normal operation. Some plants will program a sequence that includes zones that spray above the burners and target these zones prior to an outage, or at reduced loads with that particular row of burners out of service.
Q. How are the strain gauges protected from getting damaged after installation?
A. We cover the gauges with a mastic to eliminate moisture and enclose the gauges in a metal box to protect from physical damage.
Q. Can the ISB determines the location of slag or clinker buildup if it moves around on the pendants?
A. Yes, this is what strain gauge system designed to accomplish. We monitor the individual rods across the boiler and determine the location of severe slag or clinker build up laterally. With this information and variable speed control of the blowers we can bypass clean section of the pedant and target the specific clinker formation. Strain gauges can identify where the clinker buildup even if it moves.
Q. How many "smartguages" are required to properly identify problem areas and proper sootblowers to use?
A. It depends on how many superheater and reheater pendants need to be monitored. The minimum number is 18. We have installed 60 gauges in one large unit.
Q. On a boiler that exhibits a lot of Acoustic vibration at high unit loads. Will this interfere with the strain gages accuracy?
A. No, strain gauges measure the weight by voltage signal, acoustic signal will not affect its accuracy.
Q. What if you do not have a DCS? Do you have a stand-alone control system available?
A. Yes we can supply a completely stand alone system to automate the soot blowing system. It can incorporate the furnace cleaning and convection pass along with economizer and air heater cleaners.
Q. Do you have a preferred PLC vendor for your installations?
A. We typically use Allen-Bradley ControlLogic PLCís. However, we have built systems with other PLCís when requested by customers
Q. How many sequences can be stored? Can more than one sequence be active simultaneously? Can they be linked?
A. 20 to 30 sequences can be stored in the system. Multiple sequences can be active simultaneously and be linked.
Q. What happens when a strain gage or heat flux probe fails? How does the controller respond to this?
A. SmartControls generates and log the alarm when the sensor fails to respond to the system. The cleaning area associated with the failed sensor can be disabled for the automatic control. This area can be cleaned manually. The data from neighboring heat flux can also be used to direct the water cannon operation until the sensor is fixed. Each heat flux sensor is built with two spare thermocouples, so they can be repaired with a simple switch of the thermocouple lead out wires.
Q. Have you done applications where SB was limited by opacity emissions?
A. Yes. SmartControls was integrated with the opacity signal to generate warning / alarm to suspend sootblowing. Please contact factory for more information.
Q: Why do power generations switch to wester coals such as PRB? What are the advantages and challenges? What kind of solutions are available?
A: Please refer to the section Burning PRB coal.
Q: What is the mechanism for slagging and fouling? What is the advantages for different cleaning technologies?
A: Please refer to the section Mechanism of Slagging and Cleaning.
Q. What type of device do you have for measureing FEGT?
A. We use either AccuTemp or SpectraTemp to measure FEGT. The AccuTemp uses acoustic pyrometer technology. An acoustic signal generator transmits a sound across the furnace which is receives at the far side. The exact time of travel of the sound wave is recorded, and this accurately determines the mean temperature of the gas.
When more than one transmitter is coupled to more than one receiver, this system can be expanded to provide an accurate cross-sectional view of the temperatures across the entire gas path. SpectrTemp only provide a single point of FEGT. This device uses optical technology and monitors the radiation emission from the particulate matter in the flue gas path.
Q. We have a lot of problems with retractable soot blowers because our boilers run positive sometimes and the heat and ash destroy cables, etc. What makes your retractable soot blowers so superior?
A. Our retractable soot blowers were developed for the recovery boilers used in the pulp and paper industry. Recovery boilers burn black liquor, which has high ash concentrations. Thus the soot blowers must run almost continuously. The blowers that we designed for this difficulty duty have been adapted for power plant use.
Q. With the heat flux sensor being installed inside the tube, how is it hard wired to the outside and how is it sealed?
A. The heat flux sensor actually replaces a short part of wall tube. The thermocouples is wired to outside through the tube wall. The thermocouple sheath is enclosed with a weld overlay.
Q. Is your thermodynamic model generic? How long to customize between different boilers?
A. The thermodynamic model is not generic because every boiler is different. It typically takes 4 weeks for us to customize for different boilers.
Q. What is the availability of parts to keep up the system?
A. We have a complete warehouse in Atlanta, and two regional service center at Fort Collins, CO and Erie, PA. We can usually ship spare parts within 24 hours.
Q. What are the temperature limitations for the sensors?
A. Heat Flux sensors are installed in the water wall tubes. They are designed to withstand the furnace temperature. The strain gages have a design limitation of 200 oF. The high temperature strain gage system that we have recently installed in the penthouse and is exposed to temperature of over 1000 ?F.
Q. How many Flux devices would be necessary for a CE twin furnace 900 mw unit?
A. Typically 36.