By J. Patrick Tiongson, Product Manager, Emerson

At first glance, calibrating conductivity sensors may seem straightforward; however, many times, this is not the case. I’d like to share with you some of the various methods for calibrating contacting conductivity sensors and outline some of the potential issues that can accompany such procedures.

There are three main methods for going about calibrating contacting conductivity sensors: 1) with a standard solution, 2) directly in process against a calibrated referee instrument and sensor, and 3) by grab sample analysis. Understanding the fundamentals of each method, and the issues associated with each, can help make the decision on how best to calibrate a sensor.

Calibration with a standard solution consists of adjusting the transmitter reading to match the value of a solution of known conductivity at a specified temperature. This method is best when dealing with process conductivities greater than 100 µS/cm. Use of standard solutions less than 100 µS/cm can be problematic as you run into the issue of contaminating the standard with atmospheric carbon dioxide, thereby changing the actual conductivity value of the standard. For maximum accuracy, a calibrated thermometer should be used to measure the temperature of the standard solution.

If dealing with low conductivity applications (less than 100 µS/cm), in-process calibration against a referee instrument is the preferred method. This method requires adjusting the transmitter reading to match the conductivity value read by a referee sensor and transmitter. The referee instrument should be installed close to the sensor being calibrated to ensure you are getting a representative sample. Best practices for attaining a representative sample across both the process and referee sensors include using short tubing runs between sensors and increasing sample flow. Though usually not as accurate as calibrating against a standard solution, this method eliminates the need to have to remove your sensor from process, and removes any risk associated with contamination from atmospheric carbon dioxide.

The least preferred method of calibrating a contacting conductivity sensor is by analyzing a grab sample. This method entails collecting a sample from process and measuring its conductivity in a lab or shop using a referee instrument. Calibration via grab sample analysis is only ever recommended if calibration with a standard solution is not possible or if there are issues with installing a referee instrument directly in process. The collected grab sample is subject to contamination from atmospheric carbon dioxide and is also subject to changes in temperature when being transported. In other words, there are many potential sources for error in the final calibration results.

More information regarding calibrating conductivity sensors can be found HERE.

Have you been utilizing the best method for calibrating your sensors? Are there any challenges that you run into?


By Neil Widmer, Business Development Manager, Emerson Process Management

Sulfur plant tail gas incinerators are used to oxidize sulfur compounds that cannot be released directly into the atmosphere. These sulfur compounds include H2S, COS and CS2. Incinerators are operated at temperatures that are sufficient for oxidation of the sulfur compounds to SO2, as well as providing the required mechanism for proper plume dispersion. Sulfur plant incinerator control is typically based on a closed loop control on the fuel gas flow to achieve the required incinerator temperature. Natural draft dampers that are manually opened or closed, traditionally supply combustion air. Modern incinerator design incorporates forced draft combustion air. This allows closed loop temperature control where combustion air is provided based on the required ratio to fuel gas. Closed loop control based on excess oxygen can be used to optimize fuel gas control.

Optimizing Sulfur Incinerator Operation with an In-Situ Oxygen Analyzer

Figure1blogIdeal operation of these incinerators is to provide an excess of oxygen in the flue gas stream that ensures complete oxidation of all sulfur compounds to SO2. Sulfur plant incinerators are typically operated with excess oxygen levels of 6 to 10 percent. The recommended operating range for excess oxygen is 2 to 5 percent. Operating below 2 percent may result in insufficient oxidation of the sulfur compounds to SO2. This may result in a violation of the allowable concentrations of H2S, COS and CS2 allowed in the incinerator effluent. Operating above 5 percent excess oxygen will result in an excessive use of incinerator fuel gas. Figure 1 to the right illustrates the relationship between relative fuel demand, stack temperature and excess oxygen concentration.

RA.4000The most significant advantage of operating within the recommended range is two-fold: Operating above the minimum recommended 2 percent excess oxygen would ensure proper oxidation of sulfur compounds. Operating below the maximum recommended value of 5 percent excess oxygen will provide a reduction in fuel gas usage. An added bonus of operating with a decrease in excess oxygen is the reduction of CO2 (a greenhouse gas) emissions associated with a decrease in fuel gas consumption.

It’s possible to monitor excess oxygen concentrations within the sulfur plant incinerator by using the zirconium-oxide measurement principle. Zirconium oxide is an in situ measurement that provides a fast and reliable measurement of excess oxygen in the sulfur plant incinerator exhaust gas. To counteract the poisoning affect that SO2 has on standard zirconium-oxide sample cells, new sulfur resistant cells are available.

Summary of economic and environmental benefits:

  • Reduction in greenhouse gas emissions
  • Reduction of fuel gas consumption
  • Reduction in combustion air blower requirements

Analyzer Performance:

  • Accuracy 0.75% of reading or 0.05% O2
  • Withstands high sulfur process gases

To learn more about instrumentation that can optimize incinerator operation, click HERE.

How do you optimize oxygen levels in your combustion applications?


 

Hi. I’m Ruth Lindley and I’m happy to get the chance to tell you how to solve a significant problem in refining in a relatively simple and straightforward manner. The problem is ammonia slip.

TypicalNOxNitrogen oxides result from the combustion process in turbines, crackers, combustion engines, boilers, and other locations within a plant. NOX is a powerful pollutant, so it is important to control and contain NOX emissions. Both selective catalytic and selective non-catalytic reduction (SCR and SNCR) are techniques used worldwide to remove NOX. However, this process can result in a byproduct of unreacted ammonia, or ammonia slip. Continuous measurement and monitoring of ammonia slip can be a challenge to ensure sample integrity is maintained, especially in high-dust, high-temperature applications. But regardless of the complexity, to adhere to environmental guidelines, operators must balance using the precise amount of ammonia – not enough ammonia results in waste, too much can lead to emissions.

So how to solve the ammonia slip problem? The answer is QCL/TDL laser technology. (You may not have been expecting that!) In fact, capable, fast Rosemount QCL/TDL technology delivers the needed measurement precision (0–100 ppm) to ensure production is at its optimum and avoid overdosing issues that result in both economic and environmental problems and cost.

Quantum Cascade Lasers monitor ammonia slip to avoid the formation of damaging ammonia salts downstream or emission of 5100captionammonium chloride or gaseous ammonia, and the regulator fines and penalties that result. Here are some of the benefits of Quantum Cascade Lasers in this challenging application –

  • Interference-free monitoring of the presence of ammonia slip in the toughest environments
  • Thousands of measurements per second are recorded using patented laser chirp techniques to ensure identification of even trace levels of ammonia
  • Ammonia slip detection and insight into the efficiency of the plant’s NOX reduction system resulting from real-time measurement and analysis
  • Rugged, modular design delivers outstanding reliability and measurement stability in extreme operations
  • Monitoring of up to twelve critical component gases for all industrial applications, toxic gas detection, and plant-wide emissions monitoring
  • No consumables, no calibration, and no in-field enclosure or shelters reduce cost and simplify maintenance and upgrades

For additional information on the specific QCL/TDL laser products that might work for you, click HERE.

The QCL/TDL laser solution to ammonia slip may seem almost too good to be true – but it’s real and operating in plants worldwide. It’s time for all of us to adjust our thinking on the ammonia slip issue, accepting that there is a better way to overcome it efficiently, reliably, and cost-effectively.

Have thoughts or questions about QCL/TDL laser technology? Post them HERE!


By Amanda Gogates, Product Manager for Quantum Cascade Laser Analyzers, Emerson Process Management

You may have seen a few stories already on the innovative QCL laser technology. That technology has now been successfully implemented in Emerson’s Rosemount™ CT5100 continuous gas analyzer. It is the world’s only hybrid analyzer to combine Tunable Diode Laser (TDL) and Quantum Cascade Laser (QCL) measurement technologies for process gas analysis and emissions monitoring. The CT5100 provides the most comprehensive analysis available (down to sub ppm) for detecting a range of components, while simplifying operation and significantly reducing costs. The CT5100 can measure up to 12 critical component gases and potential pollutants in a single system – meeting local, state, national, and international regulatory requirements.

But if you’re thinking that the CT5100 is remarkable but “bleeding edge” technology that your application can’t afford – think again. The Rosemount CT5100 operates reliably with no consumables, no in-field enclosure, and a simplified sampling system that does not require any gas conditioning to remove moisture – truly “next generation” technology which chartsaves you money at every turn. The CT5100 is a unique combination of advanced technology and rugged design, and is highly reliable. Its patented laser chirp technique expands gas analysis in both the near- and mid-infrared range, enhancing process insight, improving overall gas analysis sensitivity and selectivity, removing cross interference, and reducing response time. This laser chirp technique produces sharp, well-defined peaks from high resolution spectroscopy that enables specificity of identified components with minimum interference and without filtration, reference cells, or chemometric manipulations.

The rugged Rosemount CT5100 analyzer features –

QCL-Image-CT5100-Ex-160420

  • Multi-laser, hybrid QCL/TDL configuration for up to 12 measurements simultaneously per analyzer
  • Accurate and sensitive gas measurement
  • Excellent linearity of response and repeatability
  • Fast and continuous gas measurements using the patented chirp technique
  • Low maintenance and low lifetime costs
  • No long-term drift due to inherent stability of spectroscopic measurement technique
  • Continuous health diagnostic reporting
  • Embedded ARM processor for fully autonomous operation
  • Modular architecture is easily serviceable and upgradeable in the field
  • Superior spectral analysis to eliminate cross-interference and improve measurement accuracy
  • Intuitive, simple front-panel user interface allows access to all instrument functions

Give your Emerson representative a call and discuss the potential of the CT5100 in your process gas analysis, continuous emissions monitoring, and ammonia slip applications. This could be a whole new solution to some costly problems. Click HERE for more information on the CT5100.

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.