The Feasibility of Flare Gas Recovery for Ethylene Plants Dr. John Joyce, PhD, PE

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Theodore West
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1 The Feasibility of Flare Gas Recovery for Ethylene Plants Dr. John Joyce, PhD, PE 3/7/16 Page 1

2 Flare Gas Recovery Concept and technology for flare gas recovery (FGR) has bloomed (especially compressor technology) FGR systems are presently installed at many US refineries However, FGR installs for refineries were CD and regulatorily driven without significant consideration for economic feasibility Largely driven by the requirement for emission reductions by mitigating/reducing flaring incidents And for refineries, almost in every circumstance, flare gas was ultimately routed to fuel gas systems And most refinery FGR systems are large in scale 3/7/16 Page 2

3 Flare Gas Recovery In refineries, flare gas composition can be variable and highly dependent on what part of the refinery may be flaring? Composition can be a mix of: Hydrogen Nitrogen H2S Methane Ethane Propane Butane Other Often predominated by hydrogen and nitrogen from sweep gas, vessel purging etc. In refinery FGR systems, there is no process value for the recovery of this gas volume So the destination for the recovered flare gas is the refinery fuel gas system Typically, many fired sources at a refinery 3/7/16 Page 3

Flare Gas Recovery A typical refinery flare gas recovery system looks like: Flare gas recovery is technically an air pollution control system Clearly technically feasible Mostly sunk cost

4 Flare Gas Recovery A typical refinery flare gas recovery system looks like: Flare gas recovery is technically an air pollution control system Clearly technically feasible Mostly sunk cost though More fuel gas that doesn t have real tangible cost/benefit And actually adds variability (BTU and composition) to the existing fuel gas system John Zink-Hamworthy Combustion 3/7/16 Page 4

5 If you are an ethylene plant or comparable chemical plant with flares and are facing potential flaring minimization..voluntary or otherwise: The consideration of FGR has more moving pieces to think through: Flare gas volumes (flow) are typically much smaller Flare gas composition is different Consideration of recoverable constituents, or not Presence of moisture in the flare gas The fuel gas system is generally more stable than in a refinery --- in some cases chemical plants are using natural gas --- the fuel gas systems are more sensitive to upsets 3/7/16 Page 5

6 So.when considering flare gas recovery for an ethylene plant. How often is flaring occurring? Is there truly recoverable ethylene, propylene, butylene in the flare gas? If there is, how do you recover it? Do you need a compressed gas after-cooler; distillation column? Can it be reasonably routed back to the cracking furnace effluent? Can a suitable compressor system be found for the smaller gas volumes? Will the compressor have enough turn down? Can the compressor have reasonable efficiency at lower turn down rates? 3/7/16 Page 6

7 Depending on your flare gas volumes the FGR compressor skid could be this size: 3/7/16 Page 7

8 Or the FGR compressor skid could be this size: The size/capacity of the compressor skid is one of the biggest single cost drivers to an FGR project Unfortunately, FGR compressor technology is still largely geared around large flare gas volumes 3/7/16 Page 8

9 And the choice of compressors can be: Sliding Vane Compressor Liquid Ring Compressor 3/7/16 Page 9

10 If there isn t recoverable ethylene, propylene, butylene.. Can the flare gas (some small level of C2, C3, C4, some hydrogen, and mostly nitrogen sweep gas) reasonably be routed to the fuel gas system without upset to furnaces, process heaters, and boiler burners? Can those fired source burners be tuned to accommodate the change in fuel gas composition and BTU value? It is possible that burners might have to be modified? New burner tips? Increase in H2 and N2 will most likely increase NOx emissions from those fired sources 3/7/16 Page 10

11 If there isn t recoverable ethylene, propylene, butylene.. Really..don t overlook the impact to the fuel gas system and heater, boiler, and furnace burners 3/7/16 Page 11

12 Even if there is recoverable ethylene or comparable C2 or C3 fractions, current spot market prices to sell recovered ethylene and propylene are low (propylene has higher margin than ethylene at the moment) Almost regardless of the flare gas volumes, the presence of nitrogen (N2) from the sweep gas is an unwanted constituent --- thus, Do you convert your sweep gas to natural gas? There is certainly a cost associated with the switch If you don t convert sweep gas, then a membrane or amine treatment system may be needed to eliminate the unwanted N2 3/7/16 Page 12

13 And inevitably, is the physical space or real estate available for an FGR system? Where do you tie in to the flare system For consideration of piping runs and related cost. Is it best closer to the flare? Closer to the cracking furnaces? And almost certainly your flare will need a new deep liquid seal as part of the FGR install for the flare 3/7/16 Page 13

14 And if you are doing N2 removal from your flare gas to facilitate product recovery or product purification. Membrane Purification Amine Treatment 3/7/16 Page 14

15 The Ethylene FGR System Compressors Flare Header Moisture Separators After-Cooler Phase Separator Recovery N2 Treat Fuel Gas 3/7/16 Page 15

16 When all is said and done. This is an installed and functional FGR system at an Ethylene Plant Not that many but there are a few existing Ethylene plants with flare gas recovery systems 3/7/16 Page 16

17 Would you invest in an FGR system if you didn t have to? Range of FGR Costs/ Flare** Total Mechanical Equipment & Piping: $4MM - $8MM Total Electrical & Controls: $0.8MM - $1.6MM Total Civil/Site/Structural: $0.3MM - $0.6MM Total All Other: $1MM - $2MM Total All $6.1MM MM/Flare (Capital only) **(capital costs only -- so purchase/install) 3/7/16 Page 17

18 Potential Costs Recovered: Spot market ethylene $0.24/lb (+/-) Spot market propylene $0.28/lb (+/-) So.you need to recover a whole lotta product to have any semblance of payback Additional new operating costs (electricity for compressors etc.; potential use of NG as sweep gas) Payback ranges from~ 6 to 10 years depending on system size and flare gas composition 3/7/16 Page 18

19 Is FGR for ethylene plants technically feasible? Yes, with caveats Is FGR economically feasible? Not in investment and payback terms Would you do FGR if you didn t have to. Probably not! Current FGR technology (compressors, coolers etc.) must become more scalable and efficient to fit the needs of a chemical plant 3/7/16 Page 19

20 THANK YOU!!! John M. Joyce, PhD, PE Sage Environmental Consulting, LP Kennesaw, GA /7/16 Page 20

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