17 May, 2016  |  Written by  |  under Boilers, Combustion


 

By Neil Widmer, Business Development Manager, Emerson Process Management

Recently, Bob Sabin of Emerson Process Management presented an article on “4 Key Measurements for Boiler Control Performance” in Flow Control. The purpose of boiler control is to achieve safe and reliable operation and optimized performance with respect to output, operational cost, and by-product emissions. His article emphasizes how the foundation of optimal control rests in the quality of measurement and actuation field devices as shown in Figure 1 below. The four keys of boiler control are drum level, fuel flow, air flow, and flue gas oxygen (O2).

Figure1goodFlue gas O2 measurement was suggested to be the most critical parameter for maintaining boiler safety, maximizing thermal efficiency, and minimizing emissions. With insufficient combustion air, indicated by low O2, incomplete combustion can occur and generate hazardous air pollutants and fuel conversion efficiency losses. On the other hand, excess combustion air, indicated by high O2, reduces thermal efficiency, can limit output and increase emissions of nitrogen oxides pollutants. Non-optimal O2 operation can also increase fouling and slagging, corrosion, erosion, thermal degradation, and other boiler reliability and availability losses.

An accurate and fast response time O2 measurement is ideal to support optimal combustion control. The industry standard O2 measurement technique is with a zirconia oxide (ZrO2) sensor. O2 sensors are housed in probes that can be inserted directly into high-temperature flue gas to provide a continuous and near instantaneous response to flue gas conditions. These probes are called in situ combustion O2 probes. Probes should be located close to the furnace exit to improve response time and, for induced draft boilers, to avoid air in-leakage that can occur at duct joints, air preheaters, air pollution control devices, and fans.

Figure2The O2 probe location is selected to measure a representative average O2 level exiting the furnace. Due to stratification of fuel and air within a burner and from burner to burner, a single measurement may not always provide adequate indication of the average furnace exit O2 levels. (See Figure 2) In highly stratified multi-burner facilities, multiple O2 probes can be used. Some large power generation boilers may have 20-24 O2 probes per boiler. However, on a single-burner industrial or commercial boiler, one O2 sensor may be sufficient as long as burner stratification is not an issue. Best practice however is to install a redundant O2, especially when O2 measurement is used to “trip” or shutdown the boiler.

With the importance of the flue gas O2 measurement, O2 probe reliability and accuracy is critical. Emerson’s Rosemount in situ O2 probes have set the standard in reliability and today’s products feature automatic calibration and other diagnostics to ensure reliability and accuracy for optimal boiler combustion control. More information on this technology can be found HERE.

To improve boiler control, it’s important to have a good base of instrumentation and actuations devices. The full article in Flow Control can be viewed HERE.


The global dairy industry is growing, and one of the dairy producers’ biggest challenges is to maintain high product quality, while also increasing efficiency and minimizing waste and downtime. Recently Philip Edwards wrote an article on this topic for What’s New in Food Technology and Manufacturing titled, “Conductivity Measurement: A Hidden Key to Dairy Industry Success.” Below is an excerpt from this piece:

NZCattle2_lessgreenTo ensure this consistent product quality, the equipment used in the manufacturing of dairy products is not only made from the highest grade of material, but also needs to be cleaned and maintained in such a way as to minimize any possible contamination when changing from one product to another or from one batch to another. This process is called CIP (clean-in-place).

To remain competitive, it is important to minimize production downtime without compromising on the safety and quality of the end product. In the CIP process, conductivity measurement is used to determine how effectively equipment has been cleaned and flushed. Conductivity in CIP picks up the change in the electric conductivity of a sample stream to indicate when a flushing process has started and ended. On a rinse cycle, for example, low conductivity indicates that all chemicals in the process stream have been flushed out and it’s ready for the next batch of product.

An Interesting Case History
A major global dairy company with plants around the world was experiencing challenges with its liquid analytical systems, particularly as related to CIP. CIP systems thoroughly clean wetted components such as tanks, vessels, fermenters, process lines and inline sensors. The CIP process controlled the flow of pre-rinse, wash and post-rinse cycles, which include caustic rinse, acid rinse and water rinse cycles.

Conductivity sensors are a critical component in the design of CIP systems. The various cleaning solutions have more conductivity than the water used for flushing and final rinse. Since many systems are a ‘re-used design,’ the sensor can monitor the strength of cleaning solutions as chemicals get used up through successive cleaning cycles. Conductivity measurements can indicate the need for replenishment.

Any sensors that have to withstand CIP and sterilization must be able to function under very harsh conditions — not a simple requirement for a sensitive analytical sensor. The dairy company was experiencing up to a 50% failure rate on sensors each year, at an approximate cost of $1,200 per sensor. Much worse, however, was the cost of plant downtime — up to $100,000 per hour. The significant failure rate called the reliability of every sensor into question after a short usage period. As a preventive measure, every conductivity sensor was replaced at the end of the season, which required another CIP cycle to be performed, adding even more costs and delay to production. It was preferable, however, to the possible dumping of milk product that would have to occur in the event of a sensor failure during processing.

To learn more about the unique solution the dairy producer implemented to overcome these challenges, click HERE to read the full story.


by Bonnie Crossland, product marketing manager – gas chromatographs, Rosemount Analytical

Whether your gas chromatograph (GC) is used for custody transfer measurement or process control, it is critical to know your GC is providing accurate data and operating as it should. Validation is the testing of the correct calibration and operation of the GC. Many times we have heard customers say they run the calibration gas as an unknown to validate the GC – however, this is not an effective method. This only shows that the GC is doing what it is told. The GC will always read what it was forced to read in the morning calibration run. If the GC is set up incorrectly, has an issue, or the calibration gas blend is bad, the daily calibration may hide the issue and result in inaccurate analysis for the sample stream.

The validation of the GC can be completed in three steps:

  1. Validate the operation of the GC for the previous period
  2. Validate the current accuracy of the GC
  3. Check for changes in operation that may affect future reliability

Validating the operation of the GC for the previous period is done by checking alarm logs, event logs, and un-normalized total trend for the past 30 days. Reviewing the logs will yield clues as to whether the GC was running correctly. All alarms during the period should be investigated and the cause determined before moving to step 2.

Validating the current accuracy of the GC is done by confirming that the As Found calibration is correct, and then observing the correct operation and repeatability of the GC. Check the latest calibration report to be sure that the calibration gas concentrations entered into the GC match the certificate of the calibration gas cylinder. For natural gas applications, you will check the calibration report for Response Factor Order, Response Factor Deviation, and Retention Time Deviation. Once the existing calibration of the GC is confirmed to be accurate, run the GC through a calibration cycle. Check the results of the analysis of the calibration gas before and after the calibration cycle for repeatability. If everything looks good, move onto step 3.

The third and last step is to check for changes in operation that may affect future reliability of the GC. This is best accomplished by checking the retention times of the individual components peaks over the last 30 days. Overtime, retention times gradually increase from contamination of the analytical flow path. This is called Retention Time Drift and it can cause two issues – incorrect peak detection and incorrect component separation. The current calibration chromatogram is compared to the chromatogram from 30 days ago to assess the amount of drift that has occurred. This information is used to make a judgment on the likely amount of drift to occur over the next 30 days. If the drift will not impact peak detection or component separation, validation is completed. If the drift will impact peak detection or component separation, the GC should undergo planned maintenance during the next 30 days.

For more information on validating the operation of your gas chromatograph, click HERE to view the recorded webinar, “Validating the Operation of Your Gas Chromatograph,” the first in a new series of FREE webinars from Rosemount that we’ve prepared to help you get optimum ROI from your gas chromatographs. This new educational webinar series is called “Maximizing Your Gas Chromatograph’s Capabilities” and is hosted by Emerson’s top analyzer experts who will be covering the most critical aspects of the GC, sharing best practices, and addressing users’ frequently asked questions and challenges faced in the field.

Click HERE to register for this FREE new webinar series today! Next ones up include:

  • Webinar #2 – April 21: “Communicating with Your Gas Chromatograph Through Modbus: RS-2332, RS-485, or Ethernet”
  • Webinar #3 – June 16: “Installation Considerations for the Rosemount™ 370XA Gas Chromatograph”
  • Webinar #4 – August 11: “Maintaining Your Gas Chromatograph at Optimal Performance Levels”
  • Webinar #5 – October 20: “Sample Handling System Considerations for Your Gas Chromatograph”

And if you end up missing any, recorded versions will be available for all.


Hi and welcome to Analytic Expert. I’m Neil Widmer. Recently on our Emerson Exchange 365 site, I’ve fielded some interesting questions from customers and I thought the answers could be useful to you. So here are some application solutions that may save you money and improve your boiler operations.

An engineer from JANSEN, a combustion and boiler engineering service company in the Western U.S., recently asked a question regarding a Rosemount O2 probe application. Their client operates several stoker coal-fired boilers. On each boiler they use a single 6888 O2 probe located downstream of the ID fan for fuel-air control. The service company encouraged the client to move the probe closer to the furnace due to air infiltration in the back passes. The concern is that air in-leakage can lead to inaccurate furnace excess oxygen measurement and boiler performance issues. The boiler operator said they tried the probes in locations closer to the furnace, but it “fouled” within months and they feel a clean stream downstream of the ID fan is a better option. The engineering service company asked if we are aware of conditions in a stoker coal fired application having a negative impact on the functionality of an oxygen instrument.

Rosemount 6888 O2 Transmitter Probe and 6888Xi Local Operator Interface

Rosemount 6888 O2 Transmitter Probe and 6888Xi Local Operator Interface

I responded that Rosemount agrees with the service company’s recommendation to move the probe to reduce boiler performance issues. In our experience, the probe should work very well upstream of the ID fan. Assuming that the fuel is typical bituminous stoker coal, there is no reason that our probe should not work perfectly when installed closer to the combustion process. Our probe can be located close to the boiler furnace exit and is often installed immediately downstream of the economizer convective pass. We have dozens of our probes in these exact stoker applications and they work very well.

For most of these stoker applications, the snubber diffuser works fine without ash fouling issues. If the flue gas chemistry plugs the snubber diffuser too quickly, then a ceramic or Hastelloy diffuser would be another option. Click HERE to learn more about the different diffuser options. I also mentioned that our latest model 6888A O2 system has a plugged diffuser diagnostic option which could help with predictive maintenance.

Another question came in asking about particulate or erosion due to ash content as a result of moving the probe closer to the point of combustion. There is more coal fly ash upstream and the fly ash will abrade the stainless steel probe over time. Rosemount offers two options to increase probe life: an abrasion resistant probe, or an abrasive shield which covers and protects the probe. Customers can also provide their own abrasion protection. The cost of abrasion protection and replacing probes is typically minor compared to damaging the boiler from operating at improper air-fuel ratios. Therefore we would not recommend installing the probes downstream of the ID fan to reduce abrasion.

An accurate measurement of furnace exhaust excess O2 level is critical to understanding the furnace air-fuel ratio. Some of the potential boiler losses associated with operating the furnace too fuel-rich include delayed heat release, high furnace exit gas temperatures (FEGT), and fuel-rich corrosive gases which can cause generator tubes erosion, corrosion, and excessive fouling and slagging. These impacts can result in lost availability due to tube leaks or slag and clinker build-up, lower efficiency, and increased emissions like opacity, CO, and hazardous air pollutants (HAPs). On the other hand operating too fuel-lean (i.e., with excessive combustion air) reduces efficiency and can increase emissions of oxides of nitrogen (NOx) and carry-over of particulate fly ash, as well as increase fan auxiliary power consumption and air pollution control device throughput, and last but not least, it can limit boiler output.

One advantage of stoker boilers is that the coal is relatively large; typically 50% between ¼” and 2” mesh size. The coal burns on the grate and results in lower ash carry-over than pulverized coal-fired boilers where coal is predominantly burned in suspension. We have thousands of probes and decades of experience in pulverized coal boiler applications too. For these applications, the Hastelloy or ceramic diffuser is always recommended to increase time between filter maintenance. 6888 O2 probes with these diffuser options have proven to be highly accurate and reliable in these harsh gas environments. Ultimately, the value of an accurate furnace O2 measurement far outweighs the lifetime cost of probe maintenance, repair, and operation.

Now it’s your turn. Do you have any questions on boiler operation I can help with?


We’d like to invite you to a new series of webinars that we’ve prepared to help you get optimum ROI from your gas chromatographs. The first of these webinars is coming right up – and they’re FREE – so sign up now so you don’t forget!

This new educational webinar series is called “Maximizing Your Gas Chromatograph’s Capabilities.”

Hosted by Emerson’s top analyzer experts, five webinars have been scheduled throughout the year to cover the most critical aspects of the gas chromatograph (GC), share best practices, and address users’ frequently asked questions and challenges you face in the field.

The first webinar, Validating the Operation of Your Gas Chromatograph is taking place on Feb 11th (details below), and will teach you how to verify the measurement accuracy of the analyzer at the time of testing and confirm that your GC continues to operate to the desired specifications between validation periods.

“Validating the Operation of Your Gas Chromatograph”
DATE: Thursday, February 11, 2016
TIME: 10:00am CST
DURATION: 60 minutes

Who should attend this webinar?
Measurement Engineers, Operations and Process Managers, Maintenance Technicians.

ADDITIONAL FOUR WEBINAR TOPICS AND DATES:

  • Webinar #2 – April 21, 2016
    Communicating with Your Gas Chromatograph through Modbus: RS-232, RS-485 or Ethernet
  • Webinar #3 – June 16, 2016
    Installation Considerations for the Rosemount™ 370XA Gas Chromatograph
  • Webinar #4 – August 11, 2016
    Maintaining Your Gas Chromatograph at Optimal Performance Levels
  • Webinar #5 – October 20, 2016
    Sample Handling System Considerations for Your Gas Chromatograph

We hope you’ll be able to join us for this first information-packed webinar and please feel free to pass on this information as well.

About the Presenter
Shane HaleShane Hale is the Director of Product Management for Rosemount Gas Chromatographs. With nearly 20 years of experience in the gas analysis industry, Shane is valued as one of the leading experts in his field, often invited to give lectures on chromatography.