the feasibility of flare gas recovery for ethylene...

3/7/16 The Feasibility of Flare Gas Recovery for Ethylene Plants

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


Flare Gas RecoveryConcept 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


Flare Gas RecoveryIn 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


Flare Gas RecoveryA 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


Flare Gas Recovery – Ethylene PlantsIf 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”


Flare Gas Recovery – Ethylene PlantsSo….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?


Flare Gas Recovery – Ethylene PlantsDepending on your flare gas volumes……the FGR compressor skid could be this size:


Flare Gas Recovery – Ethylene PlantsOr……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 projectUnfortunately, FGR compressor technology is still largely geared around large flare gas volumes


Flare Gas Recovery – Ethylene PlantsAnd the choice of compressors can be:

Sliding Vane Compressor Liquid Ring Compressor


Flare Gas Recovery – Ethylene PlantsIf 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


Flare Gas Recovery – Ethylene PlantsIf there isn’t recoverable ethylene, propylene, butylene….….

• Really…..don’t overlook the impact to the fuel gas system and heater, boiler, and furnace burners


Flare Gas Recovery – Ethylene PlantsEven 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


Flare Gas Recovery – Ethylene PlantsAnd 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


Flare Gas Recovery – Ethylene PlantsAnd if you are doing N2 removal from your flare gas to facilitate product recovery or product purification….

Membrane Purification Amine Treatment


The Ethylene FGR System

PhaseSeparator

Recovery Fuel Gas

Moisture Separators

Compressors

After-Cooler

Flare Header

N2Treat


Flare Gas Recovery – Ethylene Plants• 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


Flare Gas Recovery – Ethylene PlantsWould 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 - $1.6MMTotal Civil/Site/Structural: $0.3MM - $0.6MM

Total All Other: $1MM - $2MM

Total All $6.1MM - 12.2MM/Flare (Capital only)

**(capital costs only -- so purchase/install)


Flare Gas Recovery – Ethylene PlantsPotential 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


Flare Gas Recovery – Ethylene PlantsIs FGR for ethylene plants technically feasible?

Yes, with caveatsIs FGR economically feasible?

Not in investment and payback termsWould 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


John M. Joyce, PhD, PESage Environmental Consulting, LP

Kennesaw, GA512-569-5473

[email protected]

THANK YOU!!!

the feasibility of flare gas recovery for ethylene...

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