by Amanda Gogates, Cascade Global Product Manager, Emerson
Nitrogen oxides are powerful pollutants that can cause smog and acid rain and contribute to the development of tropospheric ozone. It’s critical to control nitrogen oxide (NOx) emissions to protect the environment and meet environmental regulatory requirements. NOx occurs as a result of combustion occurring in the presence of nitrogen and results from combustion processes in turbines, crackers, combustion engines, boilers, and other locations within a plant.
Ammonia can be used to react with NOx at high temperatures in order to turn it into molecular nitrogen and water vapor. Both selective catalytic and selective non-catalytic reduction (SCR and SNCR) are techniques used worldwide to remove NOx in DeNOx reactors.
However, this process can result in a byproduct of unreacted ammonia, or ammonia slip. Operators must use the precise amount of ammonia since either too much or too little can be problematic. Not enough ammonia will result in emissions, while too much ammonia can lead to waste.
As a result, continuous measurement and monitoring of ammonia slip is needed. However, such measurement can be challenging, especially in high-dust, high-temperature environments.
The video describes the Emerson DeNOx Optimization Solution, a unique system using the Quantum Cascade Laser. I think you’ll find this solution interesting and maybe a bit surprising.
For questions on how this system can both optimize DeNOx and maintain precise measurement of ammonia slip, please contact me at firstname.lastname@example.org. Or get more information on the Quantum Cascade Laser analyzer technology here.
by Sara Wiederoder, Product Manager, Rosemount Combustion Products, Emerson
Hello. My name is Sara Wiederoder and I’m your Analytic Expert for today. I’d like to share an interesting and innovative waste-to-energy application in which a number of Emerson products are used including the Rosemount OCX8800. The company in this application is Sustainable Waste Power Systems (SWPS) and they’re building a garbage in/power out (GIPO) system, or more specifically, a two-stage, wet, thermal conversion of wet carbon-based waste into synthesis fuel gas (SynFuel). In the system, a devolitization stage reduces the wet feedstock into a bio-char and light volatiles. A large pressure drop between the stages causes fluidization and pulverization of the flow. Gasification completes the fuel synthesis through the water-gas shift and cooling of hot oil and process systems provides thermal power to the customer.
One of the key challenges of the system is to provide stable burner and air control. In general, it can be said that the concentration of excess oxygen is one of the best indicators of how efficient a combustion process is. Industry quickly discovered that if you do not have excess oxygen in your flue gas (indicating there is too much fuel), there is a good chance your boiler will explode, so excess air/oxygen is required. Adding too much air/oxygen will cool down the combustion process, which is undesirable since combustion is being used to produce thermal energy, and the more you cool it, the less heat you can get out of it. Typically, combustion processes are controlled between 2-5% excess oxygen. The actual value varies upon the type of fuel. Gaseous fuels combust very efficiently and quickly, so there is less excess oxygen required for optimal efficiency. However, solid fuels don’t combust as well, so adding extra oxygen ensures the solid particles are fully combusted. Having a continuous measurement of oxygen, and inputting this data into a control system that automatically controls air flow to the combustion burner, ensures the combustion process is operating at optimal efficiency.
The Rosemount OCX8800 Combustion Flue Gas Transmitter provides a continuous, accurate measurement of not only the oxygen, but also the combustibles remaining in flue gases from a combustion process. The renowned zirconium oxide sensor is the basis for the oxygen measurement. This, combined with the combustibles sensor, detects oxygen and combustibles concentrations in flue gases with temperatures up to 2,600°F (1,427°C).
For this application, complete and efficient combustion within a very tight set point was crucial. So in addition to oxygen, carbon monoxide (CO) measurements give greater detail into the current condition of a combustion process. CO is an indicator of un-combusted fuel. When processes are short on oxygen it’s usual to see a lot of CO, but it’s normal to have small concentrations of CO right near the optimal combustion set point. Right around the point of greatest efficiency, it’s typical to see trace amounts of CO around 200 ppm. Using both CO and oxygen measurements gives the user greater control over their combustion process.
The solution in the SWPS application included:
Ultimately, the commercial scalability of the GIPO was proven including:
While your application may not resemble this unique GIPO system, talk to our analytic experts about achieving efficient combustion in your demanding applications.
Hi. I’m Bonnie Crossland, Rosemount product manager for gas chromatograph (GC) technology and I’ll be your analytic expert today. I recently had an opportunity to write an article for InTech magazine and I’d like to share with you some of the ideas from that article.
You may be aware that glass production is one of the most energy intensive industries, with energy costs topping 14% of total production costs. The bulk of energy consumed comes from natural gas combustion for heating furnaces to melt raw materials, which are then transformed into glass. Additionally, glass manufacturing is sensitive to the combustion processes, which can affect the quality of the glass and shorten the lifespan of the melting tanks if not managed properly. Historically, the composition of natural gas has been relatively stable. However, dramatic changes in the supply of natural gas (including shale gas and liquefied natural gas imports) are causing end users to experience rapid and pronounced fluctuations in gas quality.
You may not have anything to do with glass manufacturing, however, this application is an excellent example of the impact of the combustion process on energy consumption in any industry – and the best ways to measure and control that process. Many companies in a wide range of industries faced with the problems of inconsistent quality in natural gas may not have considered gas chromatography as a viable solution for balancing air/fuel ratio due to the traditional complexities of the measurement. It’s time to look again. New developments in gas chromatography technology may make this approach the first choice for improving energy efficiency, and ultimately, process quality.
The efficiency of the furnace can be optimized for the air/fuel ratio when the composition of the incoming gas changes. This can significantly reduce energy consumption and provide substantial savings to the business in product quality and equipment life. Optimizing the furnace efficiency has traditionally been complex and costly. Next-generation gas chromatography, however, is changing that paradigm, providing a cost-effective, task-focused methodology that can be carried out by less technically proficient personnel than were traditionally required.
A major glass company in the southeastern U.S. is a heavy user of natural gas. However, the gas comes from multiple locations, causing a constant fluctuation of the BTU value. Because gas flow is adjusted based on the BTU value, knowing the precise measurement is essential. In addition, because gases with the same BTU operate differently through a burner, knowing the Wobbe Index is critical to quality.
When the company began employing a gas chromatograph to optimize its fuel quality, it found the traditional intricacies of gas chromatographs inappropriate for its application. Despite repeated training, its staff was unable to calibrate the instrument. New GC technologies designed specifically for natural gas optimization significantly reduced the complexity of operation. In new designs, all of the complex analytical functions of the gas chromatograph may be contained in a replaceable module, greatly simplifying maintenance. Features like auto-calibration make operation easier and more accurate, even for novice users. And unlike other analyzers that change the air/fuel ratio based on feedback after combustion, the GC offers a feed-forward control, where the air/fuel ratio can be changed based on the composition before combustion occurs in the flue. This can help stay in emission compliance and maintain energy efficiency with the GC.
The InTech article has a lot of other details on the need and process of optimizing combustion and the effectiveness of new generation GCs in meeting those needs. Gas chromatographs are used throughout the natural gas chain of custody (from wellhead to burner tip) to determine the gas composition for quality monitoring and energy content. For pipeline quality natural gas, the industry standard is the C6+ measurement method. If your company is a user of natural gas, you may already have GCs involved in your process. Using them to ensure the efficiency of your combustion and the ultimate quality of the product is just another vital addition. If you aren’t currently using GCs, let me know if you have any questions, or would like a demonstration, by leaving a comment HERE, or emailing me HERE.
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).
Flue 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.
The 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.
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.
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?