Elimination of Percent Level H 2 S Calibration Gas from Flare Gas Monitoring Systems Measuring Total Sulfur, H 2 S and BTU. Control Analytics, Inc 6017 Enterprise Dr Export, PA 15632 (724) 387 CEMS (2367) sales@controlanalytics.com www.controlanalytics.com Control Analytics, Inc Page 1
Application Note Elimination of Percent Level H 2 S Calibration Gas standards from Flare Gas Monitoring Systems Measuring Total Reduced Sulfur. What is the problem? In November 2015 most refineries were required to be in compliance with the USEPA NSPS Subpart Ja rules which mandate the continuous measurement of H 2 S and Total Reduced Sulfur or Total Sulfur in Flare Gas samples (Pending compliance regulations, will add BTU to this measurement requirement). The regulation established an emission limit for H 2 S of 162 ppm (3 hour rolling average) and established the span for the measurement at 0 300 ppm. The regulation also requires that a continuous TRS (or Total Sulfur) measurement be made during flaring events. Companies must establish the span of this Instrument based on "Maximum Anticipated Sulfur Concentration" in the flare gas. At many refineries, the flare gas, under certain flaring conditions, can contain sulfur in percent concentrations resulting in instrument span settings in percent concentrations, some at 0 100% by volume. The regulation also requires that the TRS/Total Sulfur Monitor follow USEPA Performance Specification 5 (TRS), which in turn references calibration drift requirements found in Performance Specification 2. PS 2 is familiar to most users as the daily calibration specification required by the NO X /O 2 priority pollutant CEMs operating in the plant. If the rule is followed as written, the TRS/TS instruments must be verified on daily span gas containing H 2 S concentrations between 50% 100% of the analyzer span. Companies employing these percent range analyzer spans are therefore required to operate H 2 S calibration gas cylinders, or liquid H 2 S standards, on a daily basis that are thousands or tens of thousands times more concentrated than the 100 ppm OSHA IDLH (Immediately Dangerous to Life and Health) limit for H 2 S. The use of these cylinders has created an extremely hazardous situation for engineers and technicians operating the CEMs, changing gas cylinders, as well as dangerous cylinder storage operations. What is the solution? The solution to the problem is to obtain from US EPA approval of an Alternative Monitoring Plan (AMP) that employs specific technology and methodology in such a manner that your system can be validated without the use of these dangerous high range H 2 S standards. The US EPA has approved such site specific AMPs which employ measurement techniques that are inherently linear and are accurate from ppm to percent levels. The AMP defines the verification methodology that provides validation of the analyzer ability to measure the components of interest in the flare from the low ppm levels to the high percent levels by using a combination of low levels of H 2 S in conjunction with surrogate gases for high range response. Control Analytics, Inc Page 2
In these applications, once approved, the use of the same daily gas for the 0 300 ppm measurement can also be employed for daily verification of the TRS/Total Sulfur measurement. Generally, the highest hazardous daily calibration gas that will be needed is 275 ppm H 2 S, which is being used routinely on fuel gas H 2 S CEMs throughout the plant. Not all instruments have the ability to be used in this application. In fact, the successful instrument must have some unique capabilities if it is intended to be used to support this an AMP method. The instrument capabilities must include: A detection technique that is inherently linear based on the physics of the measurement. Ability to measure the surrogate gas as well as the TRS/H 2 S found in these applications using the one sample path, sampling system and detector. A detection technique capable of measuring low ppm to high percent levels without applying changing sample volume (multiple sample loops), and using a common detector for all analysis. Ability to measure all constituents in the sample, including the sulfur species as well as the surrogate gas, with the same linearity and accuracy throughout the entire measurement range. The only analyzer that meets these stringent requirements and currently demonstrate the capability operating in an EPA AMP is the Extrel MAX 300 Mass Spectrometer. The reasons for the use of this instrument in flare gas applications where clients are seeking EPA AMP approval are: The Extrel IMAX 300 can detect H 2 S as well as the surrogate gas (CO 2 ) with a dynamic measurement range from 1ppm to 100% by volume. The Extrel IMAX 300 can detect all flare components, including the CO 2 surrogate gas as well as all sulfur species and all hydrocarbon species, and produce a measurement for the 0 300 H 2 S, 0 100% TRS and BTU, all with one instrument, on one sample using a single detector and sample system. The Extrel IMAX 300 is inherently linear in response across its entire dynamic range. How does the measurement work without high range gas validations? US EPA requires that all measurements for environmental compliance have a high degree of accuracy, defined by their performance specifications, and validated to insure correct readings to source gas concentrations. Techniques employed in the AMPs currently in use provide this assurance without validating the measurement on the high range H 2 S gas, and have obtained EPA AMP approval as such. The verification method is largely based upon the demonstrated linearity of the Mass Spec instrument methodology, and in particular the extensive H 2 S measurement data provided by Extrel on the method. This data includes multiple gas standards containing sulfur blends that simulate various flare gas conditions. The high degree of linearity demonstrated in the Extrel Mass Spec method ensures that a single point calibration will be accurate across the instrument's entire dynamic range, and it meets the requirement for an alternative validation method for the high H 2 S measurement using a low level H 2 S standard in place of dangerous, highpercent H 2 S blends. Due to the demonstrated linearity of the technique, an accurate validation at a low concentration validates the measurement at a high concentration as well. Control Analytics, Inc Page 3
Figure 1 In addition, Extrel has demonstrated the linearity and accuracy of a calibrated system is not component specific. This means that instrument accuracy can be validated at, or near, full range on the detector (100%) using any high concentration standard, regardless of chemical composition. For Subpart Ja, or any regulation requiring daily validations using dangerous high concentration sulfur standards, the mass spectrometer operation principle allows for an alternative approach using common, safe to handle gases like CO 2, nitrogen or argon to validate analysis at the high range, and has been approved by EPS as an alternative validation method. Control Analytics, Inc Page 4
Figure 2 Surrogate Gas Calibration: The use of the manufacturers verified and published linearity and response data provides the basis for low level verification of the entire measuring range of H 2 S using only low level H 2 S gas. The Surrogate Gas calibration provides a secondary validation of the instrument response and accuracy by verifying the response of the instrument system at both ppm and percent concentrations using a safe, surrogate gas such as CO 2. In this method the instrument is validated by a bottle of calibration gas of 270 ppm H 2 S and 270 PPM CO 2, and another validation using a bottle containing 20% by volume CO 2. This allows the validation of the H 2 S as well as a surrogate at ppm concentrations, and providing verification of the instrument response and linearity at high concentrations. The use of the inherent linearity of the Mass Spec, the data provided by the manufacturer, and the site validation of H 2 S response and system linearity and accuracy provides an alternative validation method that has been accepted by EPA. Control Analytics, Inc Page 5
Figure 3 Control Analytics, Inc Page 6
Figure 4 What is the response time of the Mass Spec compared to my existing systems? The Mass spec measurement is much faster than any comparative analyzer being employed on flare gas monitoring systems. The added value that can be realized in enhanced response time is dependent on the type of system you employ now for the H 2 S, TRS/TS measurements. The total analysis time of the Mass Spec is between 5 10 seconds. Typical GC H 2 S measurement cycle times are 5 6 minutes, while Oxidative Total Sulfur (Thermo Sola II type) measurement cycles are closer to 3 5 minutes. The response time of GC's and Oxidative Total Sulfur analyzers is longer when responding to a flaring event where sulfur concentrations are rising or falling quickly, as these instruments must switch injection sample loops to keep the measurement on scale, thereby requiring multiple injections before a stable reading is obtained. This delay while "chasing" rising or falling sulfur levels and can lead to improper assessment of flaring events and improper reporting. The Mass Spec can complete and output measurements on all components in 5 10 second intervals. Control Analytics, Inc Page 7
Can I measure BTU along with the H 2 S and TRS/TS measurements? Yes. The Mass Spectrometer can make a comprehensive hydrocarbon species and BTU measurement. In addition, the Mass Spectrometer cycle times are typically 100 times faster than the typical GC cycle time of 15 minutes. How difficult is it to modify my system? In most cases the modifications needed to convert a system which employs typical GC's and Thermo Sola type Total Sulfur instruments are straightforward and can be completed on site in a few days. The modifications vary depending upon the type of sampling system employed, the design of the calibration gas cabinet, and other details. Control Analytics can provide a detailed list of system specific modifications, as well as a budgetary proposal for the costs associated with purchasing the hardware and making the system modifications onsite. Alternatively, CAI can provide the engineering and material, and work with your site personnel to make the proper modifications to the system. CAI can provide startup and commissioning, as well as certification assistance for the system. What's my take away? There are a number of refineries in different EPA regions that have been EPA approved to operate their flare monitoring systems using an Alternative Monitoring Plan and this same alternative may be applicable to your plant and your flare monitoring application. AMP approval will allow you to operate your flare gas monitoring system using cal gas validation techniques that eliminate the need for dangerous, high concentration H 2 S calibration gases in your flare monitoring systems. This application of Mass Spectrometry to your flare application will also allow you to measure speciated hydrocarbons and BTU, and characterize your flare composition more accurately. Control Analytics has helped other clients engineer and modify their systems, and can support you should you choose implement this approach. Control Analytics, Inc Page 8
Control Analytics, Inc. is an analyzer engineering and system integrator of on line analyzers and systems for industrial use. Our product specialties include Continuous Emission Monitoring Systems (for EPA reporting), Flare Gas Monitoring Systems, on line process control monitoring, analyzer engineering, sample system design, and instrumentation enclosure and shelter integration. For more information on how we can assist in reducing H2S Calibration Gases at your facility, schedule a site walk down or any other process monitoring questions you may have, please contact: Control Analytics, Inc. 6017 Enterprise Drive Export, PA 15632 Phone: (724) 387 2367 Fax: (724) 327 4300 Email: Inside Sales www.controlanalytics.com Control Analytics, Inc Page 9