Disposal of hydrocarbon condensate with LEWA process diaphragm pumps

Hydrocarbon condensate (HCC) is a waste product during the production of natural gas, offshore and onshore.

The disposal of HCC is difficult, because of its toxic, corrosive, abrasive and partially high boiling nature. With these contents, the material selection for the pumps requires particular competence.

Solution

Advantages of diaphragm pumps in offshore applications:

  • Absolutely resistant PTFE diaphragms
  • Safe sandwich diaphragm with monitoring
  • Hermetically tight, no leakage of toxic and environmentally polluting components
  • Fast and easy diaphragm replacement
  • No wetted piston sealing
  • Diaphragm pump body made of resistant solid material
  • Optimum valve layout using a modular system
  • Service life of over 10,000 hours is normal
  • Optimum lifetime with very low service costs

The stand-by pump can be started directly and remains switched on under suction or discharge pressure in the system.

Background

Onshore disposal is really not a problem because of the storage options. Offshore, HCC is separated from gas and intermediately stored in what are called knock-out drums. Reinjection or transport runs to a central collection point for further pumping onshore and for processing at the knock-out drums.

The quantity in this process is variable; pressure and availability are important aspects: The pump must withdraw a sufficient volume to avoid triggering the LSHH of the knock-out drum, since otherwise production must be stopped.

The mixing of corrosive and abrasive contents means the selection of wetted parts is highly important, especially for valves that need matching hardness and corrosion resistance.

The various components of HCC are listed in the table:

HCCFormulaMelting point °CBoiling point °CState at 25°C
MethaneCH4-183-164gaseous
EthaneC2H6-183  -89gaseous
PropaneC3H9-190  -42gaseous
ButaneC4H10-138  -0.5gaseous
PentaneC5H12-130  +36gaseous
HexaneC6H14  -95  +69gaseous
HeptaneC7H16  -91  +98gaseous
OctaneC8H18  -57+125gaseous
NonaneC9H20  -51+151liquid
DecaneC10H22  -30+174liquid
UndecaneC11H24  -25+196liquid
DodecaneC12H26  -10+216liquid
EicosaneC12H42 +37+343liquid
TriacontaneC30H62 +66+450solid

Important points for a proper layout:

  • Design of the piping system
  • Sizing of the piping system
  • Filter data
  • Pressure drop and mesh size (filter surface, double filter with switch-over and differential pressure display/signal)
  • Shut-off valves with full area
  • Pulsation damper and their installation location
  • Position of the knock-out drum (over the pump, if possible, so that there is a feed)

In addition it includes the following substances:

  • H2S: corrosive and highly toxic
  • CO2: high vapor pressure, non-lubricating, freezes when decompressed
  • Mercury: highly toxic and water contaminating
  • Water, that is also separated from gas and combined with H2S is very corrosive
  • Diesel portions (low): not dangerous, other than possible water contamination
  • Water + H2SO4: acid, very corrosive
  • Sand portions in HCC (low): highly abrasive in the predominant operating pressures up to 250/300 bar

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