Emissions Testing of Pressure Assisted Flare Burners

Transcription

1 Emissions Testing of Pressure Assisted Flare Burners 2014 Industrial Combustion Symposium American Flame Research Committee Houston, Texas September 7, 2014 Vance Varner Global Flare Subject Matter Expert The Dow Chemical Company Zach Kodesh Technology Manager - Flare Systems Group John Zink-Hamworthy Combustion INTRODUCTION Since their introduction in the 1940 s, flares and flare technology has progressed through the years: pipe flares, steam assisted, air assisted, fuel assisted, and so on. One specific type which can be used with high pressure gas feeding the flare is known as a pressure assisted (PA) flare burner. There are a number of features, advantages, and disadvantages to utilizing this type 1, and the technology has been used for over 40 years. Unfortunately, the design feature critical for the operation of these flares, high exit velocity, is above the maximum limits set by the current EPA regulations found in 40CFR60.18 and 40CFR EPA regulations govern flare burner exit velocity depending on the gas heating value and type of flare, ranging from 60 to 400 feet per second. In contrast, PA flare burners often have exit velocities at or near the sonic velocity or Mach 1. As a reference, sonic velocity ranges from 700 to 1400 feet per second for common paraffinic or olefinic hydrocarbon gases. Pressure assisted flares are commonly utilized in the following types of facilities: Pipeline pumping stations LNG processing plants Ethylene / other olefins units Oil platforms Aromatic production These facilities are located all over the world, but mostly outside the USA. Some PA units are elevated, but the majority of the units are designed with near ground level burners, and they are situated behind a barrier or fence. This style is known as a multipoint ground flare (MPGF), and MPGF is the focus of this paper. 1 Varner, V. (2012), Pressure Assisted Flares A User s Perspective, American Flame Research Committee Combustion Symposium, Sept. 2012, Salt Lake City, UT 2 Code of Federal Regulations Title 40: Protection of Environment, PART 60 STANDARDS OF PERFORMANCE FOR NEW STATIONARY SOURCES / PART 63 NATIONAL EMISSION STANDARDS FOR HAZARDOUS AIR POLLUTANTS FOR SOURCE CATEGORIES Approved for External Release 1

2 NEW INSTALLATION OF MPGF WITHIN DOW The Dow Chemical Company (Dow) is currently investing capital in the US Gulf Coast region taking advantage of low cost feed and an existing facility infrastructure base. Included in this investment are two production units which will incorporate MPGFs as part of the safety system. The propylene production unit, known as PDH-1, will come on-stream in 2015, and the ethylene production unit, LHC-9, in The PDH-1 plant utilizes the UOP OLEFLEX process 3 : it converts propane feed, splitting it to propylene (primary product) and hydrogen. By products include small amounts of methane, C2 s, C4 s. The PDH-1 MPGF will have an ultimate capacity of approximately 2,000,000 pounds per hour of a propylene / propane mixture. This system will be set up as a typical MPGF: Burners are in a staged sequence. First stage is steam assist / designed to operate at low pressure / will meet 40CFR requirements. All other stages utilize high pressure / high exit velocity to induce combustion air and avoid smoke production. Radiant heat fence designed to hide the flames. Layout is about the size of a football field. Staging valves open / closed based on the flare header pressure. This is easier to monitor and control rather than flow. The MPGF system was selected based on lower long term cost of ownership, though higher initial cost, and the improved operation related to environment issues: Lower maintenance cost Lower utility cost No smoke through the entire flow range Equivalent or better destruction (DRE) and combustion efficiency (CE) compared to typical assisted flares For the sake of comparison, the alternative to the MPGF system would have been an elevated steam assisted flare, approximately 350 feet tall, with a smokeless capacity of no more than 300,000 lb/hr. REGULATORY LIMITATIONS One of the main issues with the use of pressure assisted flare burners is the concept that allows them to operate as well as they do high exit velocity. For reference, the maximum exit velocity limits set in 40CFR are on a sliding scale based on flare inlet gas net heating value. For steam assisted, at the minimum heating value of 300 Btu per standard cubic foot (SCF), the maximum velocity is 60 feet / sec. At or above 1000 Btu / SCF, the maximum velocity is 400 feet / sec. As noted previously, the PA flare burners have exit velocities near sonic velocity. Due to the 3 Open literature / public announcement reference Approved for External Release 2

3 operation requirements, performance of pressure assisted flare burners is not as easily described as the heating value velocity guidance provided for other flare types. Since the pressure assisted burners operate outside the velocity limits set by 40CFR, the use of an Alternative Means of Control (AMOC) request for regulatory approval has been used. The ability to operate outside these limits and utilize these burners requires proof that the expected emissions will be no worse than those from a well-designed steam or air assisted flare burner. The proof was accomplished with emissions testing of a single burner from the flare design. EMISSIONS TESTING PLANNING / EXECUTION The John Zink Hamworthy Combustion Company (Zink) was selected to supply the MPGF system for PDH-1. As part of the purchase agreement, the emissions testing protocol was developed for execution at the John Zink Research and Testing facility in Tulsa, Oklahoma. The Zink personnel were responsible for leading / coordinating this testing. Note that multiple other emissions tests have been performed at this same facility, which is set up to capture appropriate data: operational (flows, temperature, pressure, heating value, etc.) and meteorological. Figure 1 - Test Equipment Set Up Approved for External Release 3

4 Key points of the testing protocol and execution include the following: 1. The primary emission tests were performed utilizing a single LRGO (Zink designation) burner. This burner was the same design (shape, number of holes, size) as the entire set of PA burners as designed for PDH The emissions were measured utilizing a gas scoop that captured a portion the flue gas and utilized tubing to send the gas to separate analytical equipment. This equipment was operated by an independent contractor. 3. A Passive Fourier Transform Infrared Spectroscopy (PFTIR) system was also used in parallel to evaluate / corroborate the analytical emission data. 4. The testing for the LRGO burner utilized several different gas mixtures, as well as operating at the maximum (H) and minimum (L) expected operating pressure (staging and de-staging). a. Test P1H / P1L: 100% propylene b. Test P2H / P2L: Mixture of propylene and nitrogen c. Test P3H / P3L: Mixture of propylene, natural gas, and nitrogen 5. Each gas / pressure combination for tests P1-3 operated for 20 minutes to capture data over an extended period. Each 20 minute test was replicated twice to demonstrate repeatability. 6. There was a secondary set of testing, this time utilizing the SKEC (Zink designation) design for first stage burner. This burner was a steam assisted burner consisting of a central gas flow area and steam nozzles on the arms projecting outward from this. The test burner also matched the field design of the stage one burners for PDH The gas mixtures for the SKEC burner testing were propylene and nitrogen, adjusted to the minimum heating value which produced a stable flame. a. Test S1: Operating at high pressure / sonic velocity / steam at design flow b. Test S2: Same as test S1 without steam c. Test S3: Low flare gas pressure, low heating value (300 Btu/SCF), steam as needed for smokeless operation d. Test S4: Low flare gas pressure, mid-level heating value (700 Btu/SCF), steam as needed for smokeless operation e. Test S5: Low flare gas pressure, low heating value, steam at 10 psig (higher steam flow) f. Test S6: Low flare gas pressure, mid-level heating value, steam at 10 psig 8. Tests S1 and S2 were done to demonstrate high DRE without steam being necessary, and that this burner design could operate as a pressure assisted burner if required. 9. Tests S3 through S6 helped to define the matrix of stability related to fuel heating value, fuel exit velocity, and steam rate. Each of these tests consisted of a single, 20 minute run. Approved for External Release 4

5 10. A final test (designated P4) was run on the LRGO burner with a stream of 90 mole percent hydrogen and 10 percent methane. The purpose was to show flame stability at high velocity and high hydrogen content. There was no flue gas collection for this test; consequently no emission results reported. 11. For all tests (P and S), once the burner had the main flame ignition, the pilot used for ignition was turned off to prove flame stability. 12. The tests were witnessed by the Zink team, the PDH project team, and Dow environmental specialists. The regulatory agencies (TCEQ / EPA) were invited to attend, but were unable to. Figure 2 - Test Burners Set Up Figure 3 - Flue Gas Capture Scoop Approved for External Release 5

6 Zink personnel coordinated the following activities / sub-suppliers for the tests: Analysis of fuel and combustion gases TRC PFTIR camera and videography (visible and IR) Clean Air Engineering Industrial gas supply Propylene, Nitrogen, Hydrogen via tanker trucks Crane operation Test area operations via Zink staff o Video camera o Gas handling / metering equipment o Data collection o Pilot ignition o Communications The actual testing of the burners occurred on four consecutive days starting November 19, The weather conditions were acceptable except for the final day. The wind on November 22 mostly exceeded 20 mph, making sample collection with the scoop system very difficult due to flame lean. Figure 4 SKEC Burner Operation / Flame Figure 5 - LRGO Burner Operation / Flame Approved for External Release 6

7 Figure 6 - Full Propylene Flame CALCULATION METHODOLOGY The calculation of flare destruction removal efficiency (DRE) was determined using the calculation techniques from EPA Reference Method Knowing the composition of the fuel, a fuel specific F factor (standard cubic feet of combustion products / million (MM) Btu of fuel burned) was determined by the equations shown in Section of EPA Reference Method 19. The F factor was used to calculate the mass emission rate of the exhaust hydrocarbons as sampled from the gas collection apparatus. Both O 2 and CO 2 concentrations were used to calculate dilution ratios resulting in the calculation of two DRE s. Using the total hydrocarbon (THC) measurement, equations 19-4 and 19-8 of Method 19 was used to calculate the mass of unburned hydrocarbons on a pound per MM Btu fired basis. Multiplying these numbers by the heat release of the hydrocarbon flowing to the burner yielded the pounds per hour of unburned hydrocarbons exiting the flare flame. Knowing the mass flow rate of hydrocarbon sent to the flare and the mass of unburned hydrocarbon exiting the flame, the destruction efficiency was determined as follows: Mass of THC to flare Mass of THC in exhaust gas THC DRE % = 100 Mass of THC to flare 4 Code of Federal Regulations Title 40: Protection of Environment, PART 60 STANDARDS OF PERFORMANCE FOR NEW STATIONARY SOURCES, Appendix A Approved for External Release 7

8 The advantage of using this method is that all of the burner exhaust does not have to be captured. If the exhaust plume is diluted by ambient air (hydrocarbon concentrations biased low), the increased O 2 or decreased CO 2 in the exhaust sample will correct this bias by means of the dilution ratio component of the respective equations. These same calculations were repeated but instead of using the total hydrocarbon measurement, the propylene measurements from the GC were added and used to determine destruction efficiency. C 3 H 6 DRE % = Mass of C 3H 6 to flare Mass of C 3 H 6 in exhaust gas 100 Mass of C 3 H 6 to flare The combustion efficiency (CE) of the flare was also calculated using the following equation: CO 2 CE % = 100 CO 2 + CO + THC d Where CO 2, CO, and THC d are the volume fractions of the components on a dry basis. OVERALL OBSERVATIONS There were no unexpected results from these tests. The main focus was the LRGO burners during the high pressure / high exit velocity conditions. The following tables reflect the overall results of the testing: Parameter Pressure Assisted Tests Test ID P1H P1L P2H P2L P3H P3L Combustion Efficiency (%) THC DE (%) (Based on O2 F-Factor) Propylene DE Direct (%) (Based on O2 F-Factor) Propylene DE Bag (%) (Based on O2 F-Factor) Critical Pressure (psig) Pressure at Flare Tip (psig) Exit Velocity at Flare Tip (ft/s) , , Fuel Gas LHV (BTU/SCF) (GC Analysis) 2,145 2, Fuel Gas Flow Rate (lb/hr) 8,307 5,422 7,914 4,898 7,512 4,592 Combustion Efficiency (%) via PFTIR Tables JZ-2 and JZ-4, Report on Emissions Testing of Pressure Assisted LRGO-HC and Steam Assisted SKEC Burners, Document: GP0-P , Rev 0 Approved for External Release 8

9 Parameter Steam Assisted Tests Test ID S1 S2 S3 S4 S5 S6 Combustion Efficiency (%) THC DE (%) (Based on O2 F-Factor) Propylene DE Direct (%) (Based on O2 F-Factor) Propylene DE Bag (%) (Based on O2 F-Factor) Critical Pressure (psig) Pressure at Flare Tip (psig) Exit Velocity at Flare Tip (ft/s) Fuel Gas LHV (BTU/SCF) (GC Analysis) 1,015 1, ,136 Fuel Gas Flow Rate (lb/hr) 10,758 10,711 1,597 4,169 1,836 1,970 Steam Flow Rate (lb/hr) Net Heating Value in Combustion Zone (BTU/SCF) Combustion Efficiency (%) via PFTIR During the testing, it was shown that a stable flame, while not always attached to the burner, can remain stable. The testing confirmed that as long as there is a stable flame, the CE / DRE remained high. 6 Tables JZ-1 and JZ-4, Report on Emissions Testing of Pressure Assisted LRGO-HC and Steam Assisted SKEC Burners, Document: GP0-P , Rev 0 Approved for External Release 9

10 Figure 7 Detached Stable Flame For the single LRGO test with a hydrogen rich stream, the flame was very stable and attached throughout the flow / velocity range. Figure 8 - Stable Hydrogen Flame Approved for External Release 10

11 In addition, the SKEC burner test results showed that these burners can operate efficiently as either a steam assisted or pressure assisted burner. Steam is not required to provide assistance at the higher exit velocity. PA burners have been tested for emissions at least three other times in the last eight years and once in the EPA/CMA test program in In all these previous tests, pressure assisted flares performed with very high CE and DRE. As expected, the results from this round of testing showed close agreement with these past tests. In addition to the CE / DRE determination, this test program sought to determine the minimum heating value of fuel required for good combustion. Three of the initial pressure assisted test runs (P2H, P2L, and P3L) developed instability and extinguished during the test. When this occurred, the test was stopped, the fuel composition adjusted to achieve a higher heating value and the test started over. On two of those runs, a reasonable amount of emissions data was collected. While the data from those aborted tests were not used in the final results, the fact that those tests extinguished indicates that the burner was on the very edge of stability. The results from those aborted tests indicate that the combustion and destruction efficiency remained high at 99+% as long as the flame was present. Approved for External Release 11

12 CONCLUSIONS The very high combustion and destruction efficiencies achieved during this test program, together with the results of previous testing demonstrate the ability of the pressure assist flare burner design to deliver high efficiencies when operating over a range of gas heating values and a range of gas exit velocities up to Mach 1. The minimum heating value at high exit velocities is higher than required in 40CFR to maintain the stable flame. The results from these tests show that the minimum heating value appears to be around 690 Btu/SCF. Any future testing should focus on flame stability rather than emission / flue gas capture and analysis. Future regulations should include provisions for use / operation of pressure assisted flare burners within the petrochemical / refinery / oil production industries. While not the primary purpose, the results from the PFTIR device showed reasonable matching of the analytical results, with one exception (S5). Use of this and other technology will be critical for remote monitoring of operating flares in industry, when it is impractical to capture / analyze flare flue gas. These technologies should continue to be developed. Results with the PFTIR: Approved for External Release 12

13 ACKNOWLEDGEMENTS Special thanks to all that participated and made the testing a success: Vivek Sundaram Mechanical Engineering, Fluor Jim Barufaldi Extractive Gas Analysis, TRC David Murray Extractive Gas Analysis, TRC Gabriel Gonzales Extractive Gas Analysis, TRC Daniel Pearson PFTIR Plume Analysis and Videography, CleanAir Engineering Scott Evans PFTIR Plume Analysis and Videography, CleanAir Engineering Mark Sloss PFTIR Plume Analysis, IMACC John Beavers Nitrogen Supply, CUDD Danny Allen Nitrogen Supply, CUDD John Roberts Nitrogen Supply, CUDD Beryl Hart Crane Operator, Belger Cartage Services Inc. Cliff Pugh Technician, John Zink Hamworthy Combustion Richard Lawhead Technician, John Zink Hamworthy Combustion Craig Ware Technician, John Zink Hamworthy Combustion Grady Dungan Technician, John Zink Hamworthy Combustion Craig Skaggs Instrumentation, John Zink Hamworthy Combustion Charlie Crown Instrumentation, John Zink Hamworthy Combustion Zach Kodesh Engineer, John Zink Hamworthy Combustion Approved for External Release 13