trueblue1
Chemical
- Aug 26, 2009
- 2
I have been tasked with sizing a sump pile that collects all the open drains water from the deck of an oil production platform. Any oil that is washed from the deck should be separated in the pile and pumped back to topsides. I have done my sizing based on the equations (9-26b and 9-27b) in Surface Production Operations by K. Arnold and M. Stewart. The calculated sizes are significantly bigger than what I have seen on my travels offshore and I am wondering if I have made a mistake or if there is a better method for sizing the caisson? My workings:
Diameter:
The following equation is based on separation of droplets 150micron and larger, is this a reasonable droplet diameter to pick?
d=(28,289(Qw+0.001Ad.Rw+Qwd)/DSG)^0.5
d=3024mm based on:
Qw=0 as no produced water enters the pile
Ad=deck area - 2800m2 based on a 40mx70m deck
Rw=rainfall rate - 23mm/h
Qw=washdown rate - 0 as don't wash deck during storm
DSG=difference in SG between oil 0.8 and water 1.02
I have checked this by doing a stokes law type calculation (for a 150micron droplet) and get a similar value so have some confidence in the answer. I am also assuming that I could reduce the diameter by having some hold-up volume in the pile however sizing the length is causing me a problem.
Length below mean water level (MWL):
L=(Ht+Hs+Ha+Hsd)SGo/DSG+0.6
L=106m - which seems a bit long especially if I add some hold up volume plus the section above MWL
Ht=normal tide range
Hs=design annual storm surge
Metocean report gives Hmax for 100y return period of 27.9m which I assume is Ht+Hs
Ha=alarm level 0.6m
Hsd=shutdown level 0.6m
SGo=specific gravity of the oil 0.8
Do I have to live with this huge sump pile or is there a better sizing method?
There is no detailed design information in surface production operations, so where do I set alarm levels, position oil return pumps, do I need a wier and trough to collect the oil?
Thanks in advance
TB1
Diameter:
The following equation is based on separation of droplets 150micron and larger, is this a reasonable droplet diameter to pick?
d=(28,289(Qw+0.001Ad.Rw+Qwd)/DSG)^0.5
d=3024mm based on:
Qw=0 as no produced water enters the pile
Ad=deck area - 2800m2 based on a 40mx70m deck
Rw=rainfall rate - 23mm/h
Qw=washdown rate - 0 as don't wash deck during storm
DSG=difference in SG between oil 0.8 and water 1.02
I have checked this by doing a stokes law type calculation (for a 150micron droplet) and get a similar value so have some confidence in the answer. I am also assuming that I could reduce the diameter by having some hold-up volume in the pile however sizing the length is causing me a problem.
Length below mean water level (MWL):
L=(Ht+Hs+Ha+Hsd)SGo/DSG+0.6
L=106m - which seems a bit long especially if I add some hold up volume plus the section above MWL
Ht=normal tide range
Hs=design annual storm surge
Metocean report gives Hmax for 100y return period of 27.9m which I assume is Ht+Hs
Ha=alarm level 0.6m
Hsd=shutdown level 0.6m
SGo=specific gravity of the oil 0.8
Do I have to live with this huge sump pile or is there a better sizing method?
There is no detailed design information in surface production operations, so where do I set alarm levels, position oil return pumps, do I need a wier and trough to collect the oil?
Thanks in advance
TB1
