By Amanda Gogates, Cascade Global Product Manager, Emerson Automation Solutions
Precise and cost-effective measurement of gas purity significantly impacts the bottom line in a number of industrial applications. I’d like to share a new technology with you that will overcome many of the most common problems manufacturers face in this area, including poor sensitivity, costly consumables, and outmoded equipment requiring high levels of technician resourcing to operate and maintain. You may be aware of the Emerson line of Quantum Cascade Laser (QCL) technology for measurement applications such as Continuous Emission Monitoring or CEMS. Now, this remarkable technology has been extended to some of the most demanding markets in the world and is a quantum leap over previous generation solutions.
First, a little background on the technology. Emerson’s QCL technology offers fast, high-resolution spectroscopic detection to identify a range of compounds. QCLs operate in the mid-infrared spectral region, where molecules typically exhibit strong absorption bands that can be exploited to improve measurement sensitivity. Coupled with Tunable Diode Laser (TDL) spectroscopy, a single instrument is now able to broaden measurement capability and exploit both the near- and mid-infrared regions. The result is that a single analyzer is able to monitor an increased number of compounds compared to preceding technologies. The system uses what is called a laser chirp technique. In this technique, a QCL is pulsed with electrical energy and heats up and as the temperature increases, the wavelength of the emitted light also increases. A laser chirp lasts about one microsecond, and in this time a spectrum of between one and three wavenumbers is scanned, sufficient to detect unique absorption features from one or multiple gases. This data can then be interpreted in terms of absolute concentration, minimizing the need for complex and frequent instrument calibration. QCLs can be chirped at a frequency of up to 100 KHz, enabling many thousands of spectra to be gathered in a few seconds, resulting in a high signal-to-noise ratio, while maintaining a rapid response time.
As a result of this unique design, the new CT5800 enables highly accurate measurement of concentrations of impurities down to sub-ppm levels in a variety of gas streams. This makes it ideal for hydrogen purity, nitrogen purity, and ethylene purity applications. With up to six laser modules housed inside the same enclosure, the CT5800 analyzer can measure up to twelve components simultaneously, greatly reducing the need for multiple analyzers while still meeting the real-world analysis needs of these markets.
The key outcome of this new technology is that the combination of this measurement performance and analyzer capabilities has not been possible before – not with existing lasers or other measurement technologies. Of course, not every application needs this level of performance, but when taking the example of ethylene product quality, time and product contamination is money in this volatile industry. When multiple, highly sensitive measurements can be made in seconds by a QCL, excursions in the product quality can be rapidly detected, facilitating decisions to suitably manage plant operation, and minimize losses. QCL technology provides a speed and quality level never before possible. Likewise, the low levels of detection not only improve product quality for the user, but they also open up wider market options and help meet guidelines.
Over the next months, I’ll be sharing about ways to optimize gas analysis in different critical markets. For now, if you have questions about how QCL technology might work for you, please contact me at Amanda.gogates@Emerson.com.
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
Ideal 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.
The 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:
To learn more about instrumentation that can optimize incinerator operation, click HERE.
How do you optimize oxygen levels in your combustion applications?
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 saves 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 –
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.
By Iliana Colín, Emerson Gas Specialist for Analytical Measurements
Hello, I’m Iliana Colín and I’m your Analytic Expert today. I’d like to talk about some of the challenges associated with catalyst regeneration in catalytic cracking and how rethinking the approach to hydrocarbon monitoring in these processes can reduce risk and save you time and money.
Catalytic crackers have long been utilized to extract additional gasoline from heavier components resulting from the distillation process. The distillation process is the physical separation of a mixture of different molecules based upon the different boiling points of these molecules. The catalytic cracking process splits larger hydrocarbon molecules into lighter and higher value components such as gasoline by using a catalyst, which aids the reaction or “cracking” process. The cracking process produces carbon, or coke, which remains on the catalyst particle, reducing its effectiveness over time. Fluidized Catalytic Cracking Units (FCCU) will continuously route coked catalyst into a regenerator unit where oil remaining on the surface of the catalyst is stripped off with steam or solvent. The catalyst is then sent into the regenerator, where air is introduced to burn the coke off of the hot catalyst, usually in suspension. There are many different variations in the regeneration process: the semi-regenerative catalytic reformer and the continuous catalyst regeneration reformer (CCR). This last one is preferred because of the continuous regeneration of the catalyst, which allows plant operation for more than two years before a catalyst change is needed. This is important because the cost of the catalyst is very high.
One of the key parameters in the process is the purity of the nitrogen, which is required to move the catalyst from the reactor to the regenerator. The hydrogen content must be below 1% and total hydrocarbons must be below 15% in order to keep a non-explosive atmosphere in the process since high temperatures are needed. In addition, if hydrocarbons are burned they may lead to the formation of a coke lining over the catalyst, inhibiting its function, so monitoring is essential.
Challenges that arise in this application include the high quantities of dust due to the continuous flow of the catalyst that enables cracking. When older analyzers are used, it’s not uncommon for the dust to cause the sampling lines to plug, or even worse, damage the analyzer. This is often the result of a sampling system with inappropriate design for such a challenging environment. As a result, some plants use this as a reason to bypass the analyzer, and leave it without maintenance until it becomes useless. This is an extremely costly and dangerous approach, since the analyzer can signal a plant shut down, and if the signal is bypassed, the safety of the plant is threatened.
Also challenging is the fact that the area certification in these plants is classified as hazardous. This may drive users to install general purpose analyzers in high cost shelters that also require power supply, air conditioning, and safety devices. These shelters must be installed at floor level, representing larger tubing lines and the inherent time delay that affects the control of the application because the control system receives data with a delay of some minutes, and thus process safety is jeopardized.
Many analyzers currently installed on-site use analog outputs, and there is no way to know the status of the analyzer unless the tech is standing in front of it, which can be ill-advised in hazardous areas due to risks such as radioactive measurement of the flow rate of the catalyst moving bed, noise, height, and so on. New analyzers are able to send more information through a Modbus protocol to make the maintenance program of the analysis system easier.
A monitoring approach that can reduce risk and costs is to use an analyzer designed specifically for hazardous environments such as the X-STREAM Enhanced XEFD. Enclosed in a wall-mountable, flameproof housing certified for installation in CSA and ATEX hazardous areas, these modern analyzers offer communications protocols to keep the control room constantly informed of their condition as well as process feedback. The housing also means the analyzers do not require costly and space-intensive shelters, eliminating the need for additional utilities, such as power, air conditioning, etc. These systems offer the monitoring of both hydrogen and total hydrocarbons in a single analyzer, further reducing costs and time for installation, start up, maintenance and calibration. Because the systems are designed from the outset with very short sampling lines, which are far less likely to become plugged and have fewer fault points, analysis is faster and more reliable.
What kind of monitoring systems are you using in your catalytic regeneration processes? Have you experienced challenges?
By Edward Naranjo, Marketing Director, Emerson
Gas concentration is one of the most important determinants of a substance’s hazard potential. Flammability, toxicity, and oxygen deficiency are often determined by concentration. For combustible gas detectors, gas concentration is expressed as a volume fraction of combustible gas or vapor in air known as the lower explosive limit (LEL), while for toxic gas detectors, the signal output is read as a percent by volume (% vol.), parts per million by volume (ppm (vol.)), or mass per unit volume. Countries and jurisdictions use different units of measurement to define maximum permissible combustible and toxic gas concentrations in the workplace. The choice of the units to use depends on the chemical and its abundance under ambient conditions. As a result, it is necessary to become familiar with the units used and methods for converting between units of measurement.
Volume and Mole Fractions
Units of volume fraction and mole fractions are frequently used for gas concentration. The most common value fraction is ppm (vol.), defined as the ratio between the volume of a constituent Vi and the total volume Vtotal:
As an example, 10,000 ppm = 1% (v/v) or a volume fraction of 0.01. The volume fraction of a constituent φi is defined as the volume of constituent Vi divided by the volume of all constituents of the mixture Vtotal:
Similarly, the mole fraction of constituent Xi is the moles of a target substance n divided by the total number of moles in a mixture ntotal:
The values of volume fraction and mole fraction are identical under the ideal gas law:
The advantage of volume/volume or mol/mol units is that gas concentrations reported in these units do not change over temperature and pressure. By contrast, atmospheric concentrations like mass per unit volume (ex. mg/m3) decrease as gas is expanded since the component’s mass remains constant as the volume increases.
Mass Concentration Units
Concentration units based on mass include mass fraction (ex. mass chemical per total mass) and mass per unit volume. Like ppm (vol.), mass/mass concentrations are commonly expressed as parts per million, where mi is the mass of constituent i and mtotal is the total mass:
Note: Where a gas concentration is expressed simply as ppm, it is unclear whether a volume or mass basis is intended.
In the atmosphere, it is common to express concentrations of mass/volume air like milligrams per meter cubed (mg/m3). Thus, the United States’ National Institute for Occupational Safety and Health (NIOSH) Pocket Guide for Chemical Hazards reports worker exposure limits in ppm (vol.) and mg/m3. To convert from ppm (vol.) to mg/m3, it is assumed the ideal gas law applies under standard temperature and pressure where MW equals molecular weight:
Note that at standard conditions (p = 760 mmHg, T = 273°K), one mole of any pure gas occupies a volume of 22.4 L.
Another useful formula is one that converts from units of ppm (vol.) to ppm (m) at 760 mmHg and 25°C:
For convenience, NIOSH recommended exposure limits (REL’s) for several toxic gases are shown in Table 1 below.
Table 2 shows the LEL’s of several combustible gases in ppm (vol.), ppm(m), and volume fraction.
Last, conversion units for common industrial gases are illustrated in Table 3.
Situations Where Unit Conversions May Be Useful
It is tempting to think that converting units of measurement is hardly necessary. After all, in most countries, combustible gas concentrations are measured either in volume fractions or its derivatives, while toxic gas exposure limits are established in ppm (vol.) or mass volume units. Yet one cannot gauge a gas’ hazard potential without comparing attributes in a common plane. Consider that several toxic gases like ammonia and hydrogen sulfide are combustible. The graph in Figure 1 below showing gas concentration in ppm (vol.) gives a sense of toxic and combustible limits in relationship to one another.
Similarly, most hydrocarbons are harmful long before they are at combustible concentrations. As shown in Figure 2 below, the IDLH is often at approximately 10% LEL. Based on those results, an analysis of hydrocarbon toxicity recommended that alarm levels be set at 10% LEL to protect workers from hydrocarbon narcosis (Gardner 2012).
ISO 10156, Determination of Fire Potential and Oxidizing Ability for the Selection of Cylinder Valve Outlets. 2010. Geneva, Switzerland: ISO.
Gardner, R. 2012. Use of Reciprocal Calculation Procedures for Setting Workplace Emergency Action Levels for Hydrocarbon Mixtures and their Relationship to Lower Explosive Limits. Ann. Occup. Hyg. 56 (3): 326–339.