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Show AFRC 2017: Industrial Combustion Symposium Hyatt Regency Houston, Houston, Texas - September 17-20, 20017 Unmanned Aerial System Based Flare Emissions Monitoring Joseph D. Smith, Ph.D., Laufer Endowed Energy Chair Missouri University of Science and Technology, Rolla, MO Robert Jackson and Zachary Smith Elevated Analytics, Inc., Catoosa, OK Abstract Gas flares are an important safety and emission control device used by the petrochemical and chemical industries to dispose of large amounts of flammable hydrocarbon gases produced in various manufacturing and industrial processes. Previous work to characterize the efficiency of the flare combustion process and emissions emanating therefrom (i.e., CO, CO2, CH4, unburnt hydrocarbons, and soot) has focused on characterizing the performance of single point elevated flares using extractive sampling techniques together with sensor technology used in standard stack sampling (e.g., CMA 1983 and TCEQ 2010). More recent studies have extended the work by applying several different optical techniques including Open-Path Fourier Transform Infra-Red Spectroscopy (OPFTIR), the SKY-LOSA technique for Black Carbon (BC) emissions and passive FTIR (PFTIR) technique. Application of these techniques in previous tests have focused only on examining the performance of a non-assisted or assisted flare tip with samples collected from a single region above the flare combustion zone. The measured data were collected from a temporally and spatially varying plume with reported gas concentrations from the flare representing an averaged result. To this point, none of these techniques appear to have been applied to Multi-Point Ground Flares (MPGF) due to the sampling limitations. Current work by Elevated Analytics, Inc. makes use of unique carbon nanotube (CNT) based sensors to measure gas concentrations of CO, CO2, CH4. These sensors are ultra-lightweight which makes them well suited for use on Unmanned Aerial Systems (UAS) to make measurements in "hard-to-reach" locations. These sensors use very fast response time, coupled with the UAS based gps data, to monitor real-time CO, CO2 and CH4 concentrations, gas temperature and relative humidity. Real-time spatial position of time resolved data provides a "time-varying" contour map of regional air quality. This feature allows the system to function as an early warning device as well. Work presented in this paper describes application of this technology to monitoring gas flare plumes using special control technology that allows the UAS to automatically track the flare plume. Testing has been accomplished using full-scale industrial flares at Zeeco's flare test facility. Results demonstrate these UAS based sensors can accurately track flare emissions that can be used to determine actual real-time flare combustion efficiency. Unmanned Aerial System Based Flare Emissions Monitoring AFRC 2017: Industrial Combustion Symposium 1. Introduction and Background Regulatory requirements for flares are contained in 40 CFR §60.18 and §63.11. These requirements were developed from a series of flare emissions tests led by the United Stated Environmental Protection Agency (USEPA) from 1983 - 1986. [1], [2], [3] The requirements include maintaining a flare pilot, operating with a minimum net heating value of 300 BTU/scf in the vent gas, operating at exit velocities of less than 60 ft/s (or 400 ft/s depending upon the vent gas net heating value) and operating with a limited amount of visible emissions. However, a flare can be operated in compliance with these requirements and still be over-steamed. The Clean Air Act Section 114 requires steam assisted flares be tested to confirm they operate within established performance limits. Previous work by the USEPA and others have identified key operating metrics that help ensure efficient flare operation including: 1. Flare gas should have a lower heating value (LHV) of at least 200-300 BTU/scf, and 2. A steam flare should operate with a maximum steam/vent gas ratio of 3 when the flare gas lower heating value is at least 200 BTU/scf. Flare performance testing and routine flare operation rely on efficient analysis of flare combustion emissions. Earlier testing has quantified the impact of steam flow on flare performance in terms of combustion efficiency (CE) using equipment such as listed in Table 1. Some plants have implemented automatic control to optimize the amount of steam and educted air introduced into the combustion zone to promote combustion efficiency. The efficiency of a steam injection system with respect to smoke suppression can be measured by monitoring steam rates and visually observing smoking performance. Table 1- Common sensors to quantify flare performance In the past, measuring the combustion products from a flare was difficult and dangerous. Recent technological advances, however, have led to the development and application of remote sensing Page 2 of 9 Unmanned Aerial System Based Flare Emissions Monitoring AFRC 2017: Industrial Combustion Symposium technology capable of measuring combustion products (i.e., carbon dioxide, carbon monoxide and select hydrocarbons) without the safety hazards related to physically sampling a flare plume. However, the ability to measure or even identify excess emissions caused by over-steaming remains a more difficult challenge. The Texas Commission of Environmental Quality (TCEQ) evaluated PFTIR against extractive FTIR in 2004 [4] for Marathon's Texas City main flare. This test was the first time PFTIR was used on an operating industrial flare. Other land based remote sensing technologies (i.e., DIAL, LiDAR, etc.) have also been developed and demonstrated at additional sites since the 2004 PFTIR testing. However, these tests rely on tracking the flare plume subject to atmospheric conditions and wind. Plus, these tests require significant time to set up and execute and they are very expensive and disruptive to normal plant operation. These land-based optical techniques also present challenges for composite plumes from multi-burner flares, where conditions at different locations in the plume can vary. A technique that can be set up quickly and could remotely measure flare emissions without significant interruption to plant operation remains the goal for both industry and environmental agencies. This paper describes a novel approach to use advanced sensor technology mounted onboard an Unmanned Aerial System (UAS) that can fly into the flare plume and remotely measure flare emissions as a function of position and time which are wirelessly transmitted back to the ground. 2. Elevated Gas-Flare Emissions Three example applications of the Flare Emissions Airborne Sensor (FEAS) System illustrate the transformative nature of this new capability. Companies who want to optimize plant operations which require flaring are no longer subject to inaccurate emission estimates but can now link real time measurement of flare emissions in the plume to plant operations through the control room. Also, companies can now self-regulate and self-report during upset conditions involving unplanned flaring events which reduces their exposure to lawsuits. Finally, environmental agencies who must monitor operating flares can more easily set up and conduct tests to quantify specific release amounts which can help them set fines and penalties related to poor environmental performance associated with consent decrees. Application 1: Flares Elevated Steam and Air Assisted Elevated flares are the most common design used in the chemical and petrochemical industries (see Figure 1). Gas flares were pioneered by the John Zink Figure 1 - Steam assisted elevated flare Page 3 of 9 Unmanned Aerial System Based Flare Emissions Monitoring AFRC 2017: Industrial Combustion Symposium company in the mid-1950's to burn hydrocarbon fuels previously vented from plants to the atmosphere. [5] Figure 3 - Steam Flare with center and internal steam added to enhance combustion Figure 2 - Example of elevated assisted flare Application 2: Multi-Point Elevated Flare Combining several single elevated flares is possible to form a "multi-point" elevated flare as shown in Figure 4. This flare, originally designed by the John Zink Company, is based on the Kaldair "Tulip" Coanda flare and was operated by Statoil company at their Petroleums Process Plant at Kollsnes. Flares like this can fire thousands of tons of flare gas per hour but experience unique operating challenges which make it nearly impossible to quantify flare performance. The shape and height of the flame and smoking potential can be compared to images from the test flares to assess the magnitude and accuracy of sensing technology used. The UAS based sensor technology allows one to remotely monitor complex combustion and quantify flare performance. Page 4 of 9 Unmanned Aerial System Based Flare Emissions Monitoring AFRC 2017: Industrial Combustion Symposium Figure 4 - Multi-point elevated flare Application 3: Multi-Point Ground Flares Multi-Point Ground Flares combine numerous flare tips, numbering into the hundreds, into a field surrounded by a fence (see Figure 5). The fence provides safety to surrounding equipment and personnel by blocking the radiation from the flames but is porous to allow for ingress of air needed for good combustion efficiency. MPGFs typically will be staged so that only as many tips as are needed will be firing at any given time, thus allowing flexibility in operation. In this way, an MPGF can flare relatively small amounts a flare gas or up to thousands of tons per hour as needed. a. Image of Zeeco MPGF [6] Image of Honeywell UOP flare [7] Figure 5 - Multi-Point Ground Flares (MPGF) Page 5 of 9 Unmanned Aerial System Based Flare Emissions Monitoring AFRC 2017: Industrial Combustion Symposium Each tip in the MPGF has a separate flame, although depending on local availability of oxygen (from air) individual flames can at times merge; however, the plumes coming from an MPGF will most often merge into a single plume. An illustration of the difference in plumes for a Single Point Elevated flare and an MPGF is shown in Figure 6. MPGFs present unique challenges to understand emissions coming from the flare due to the size of the plumes and the various conditions at which they operate. The UAS based emissions monitoring system is particularly well suited to measure emissions from these flares. Figure 6 - Illustration of differences between plumes from single point elevated flare and MPGF 3. UAS Based Flare Emission Monitoring System A new UAS based flare emissions monitoring system is under development which has great promise due to its flexibility and low cost when compared to optical techniques such as PFTIR which have been developed in the past two decades. The UAS system is based on carbon nanotube (CNT) sensors. CNT sensors that can determine various properties in gases and liquids have been under development by various groups including NASA [8] and numerous patents have been submitted related to these types of sensors [9], [10], [11]. The current work is an extension of these CNT based sensors using a unique CNT sensor under development at Brewer Science [12], which provides for increased sensor selectivity and improved response times which can be on the order of 0.25 seconds. Current work is focused on the gases needed for combustion efficiency determination such as CO and CO2. Additional gases, such as NO, NO2, SO2 and general VOCs are also under development as well as properties such as radiation flux which can also be monitored with these CNT based sensors. The CNT sensors are extremely lightweight providing for small packages with associated electronics included (i.e., control system, wiring, batteries, wireless communicator, etc.) that can be mounted on a small unmanned aerial system (sUAS). Current prototypes are based on existing commercially available sUAS which have proven the concept but Page 6 of 9 Unmanned Aerial System Based Flare Emissions Monitoring AFRC 2017: Industrial Combustion Symposium temperature hardened sUAS are also under develop to extend the capability of the system to allow for measurements in hotter regions of the plume. These sUAS-CNT monitoring systems can be deployed rapidly in a very cost-effective manor to monitor any type of flare. This sUAS-CNT system can monitor even MPGFs well, as emissions in all areas of the plume can be determined. While a single sUAS-CNT device can be deployed and under quasi-steady state conditions can determine emissions throughout the plume, for larger plumes such as those from an MPGF, a swarm of multiple sUAS-CNT devices can also be used to make multiple measurements at the same time as is illustrated in Figure 7. Each sUAS-CNT device transmits the sensor input to a ground station data acquisition system (DAQ). The rapid response time of the sensors combined with the possibility of monitoring at multiple locations at the same time allows for levels of detail in data from flares that have hitherto been unavailable. This level of detail will allow for: improved flare operation, improvements to CFD based flare models due to increased availability of data for validation, and improved flare designs. Figure 7 - System of sUAS-CNT sensor devices to monitor emissions from MPGF 4. Conclusions and Recommendations New, small, light-weight CNT based sensors under development hold promise for monitoring emissions from flares with high accuracy and selectivity. Due to their small size, these CNT sensors can be mounted on sUAS devices and a sUAS-CNT monitoring system can be flown through the plumes of flares monitoring emissions at locations throughout the plume. Due to the relatively low cost of these sUAS-CNT systems, swarms of sUAS-CNT monitors can be deployed measuring emissions at multiple locations at the same time and all wirelessly transmitting to a central data acquisition system. These sUAS-CNT systems will provide the following improvements over existing devices such as land-based optical devices: • Improved flare emissions detail with data sampled from many locations throughout the plume ate relatively high rates (as much as 4 samples per second), Page 7 of 9 Unmanned Aerial System Based Flare Emissions Monitoring AFRC 2017: Industrial Combustion Symposium • Improvements to CFD flare models due to the detail of data available, • Improvements to flare operation due to the rapid response time of the sensors and the ability to monitor multiple locations in the plume at the same time, • Improvements to flare design, particularly MPGFs, because of the amount of data available showing where combustion efficacy is good and where proper entrainment of air may be lacking. Testing has been done for small flares. It is recommended that the next steps for this new technology would include testing on full scale flares both at flare manufacturer test facilities and at end user facilities. 5. References [1] United States Environmental Protection Agency-Office of Air Quality Planning and Standards, "EVALUATION OF THE EFFICIENCY OF INDUSTRIAL FLARES: TEST RESULTS," EPA-600/2-84-095, May 1984. [2] United States Environmental Protection Agency, Office of Air Quality Planning and Standards, "EVALUATION OF THE EFFICIENCY OF INDUSTRIAL FLARES: FLARE HEAD DESIGN AND GAS COMPOSITION," EPA-600/2-85-106, September 1985. [3] United States Environmental Protection Agency, Office of Air Quality Planning and Standards, "EVALUATION OF THE EFFICIENCY OF INDUSTRIAL FLARES: H2S GAS MIXTURES AND PILOT ASSISTED FLARES," EPA-600/2-86-080, September 1986. [4] Texas Commission on Environmental Quality, "PASSIVE FTIR PHASE 1 TESTING OF SIMULATED AND CONTROLLED FLARE SYSTEMS," June 2004. [5] C. Baukal and e. R.E. Schwartz, The John Zink Combustion Handbook, CRC Press, 2001. [6] Zeeco, "Zeeco MPGF Staged Flares," Zeeco, http://www.zeeco.com/flares/flares-ground-multi-point.php. [Online]. Available: [7] Honeywell, "Honeywell UOP flares," [Online]. Available: https://www.uop.com/equipment/callidus-combustion-equipment/uop-callidusflares/general-market-flares/multipoint/. [8] N. Ames, "Ames Technology Capabilities and Facilities," NASA, [Online]. Available: http://www.nasa.gov/centers/ames/research/technology-onepagers/gas_detection.html. [9] D. B. G. Ilia N. Ivanov, "Carbon nanotube temperature and pressure sensors Mar 3, 2011". US Patent US 20110051775 A1,, 3 Mar 2011. Page 8 of 9 Unmanned Aerial System Based Flare Emissions Monitoring AFRC 2017: Industrial Combustion Symposium [10] S. B. P. B. Michael S. Strano, "Sensors employing single-walled carbon nanotubes, Jul 1, 2014". US Patent US 8765488 B2, 1 Jul 2014. [11] C. LANDORF, "Highly soluble carbon nanotubes with enhanced conductivity". Patent WO 2012177975 A1, 27 Dec 2012. [12] R. E. Giedd, V. Kayastha, J. Fury and R. C. Cox, "Thin-Film Resisteive-Based Sensor". USA Patent US 2016/0025517 A1, 28 Jan 2016. Page 9 of 9 |
