Disposal piles

Disposal piles. Disposal piles are large-diameter (24 to 48-in.), open-ended pipes attached to the platform and extending below the surface of the water. Their main uses arc to consolidate platform discharges into one location to provide a conduit protected from wave action so that discharges can... 

By regulation, produced water must be treated (i r, passed through a skimmer tank, cualcscer or flotation unit) prior to disposal. Disposal piles are permitted to collect treated produced water, treated sand, liquids from drip pans and deck drains and as a final trap for hydrocarbon liquid in event of equipment upsets. 

Disposal pile sizing. Produced water entering the pile has already been treated in vessels capable of separating smaller droplets than those predicted to settle out in the relatively slender disposal pile. Small amounts of separation will occur in the disposal pile due to coalescence in the inlet piping and in the pile itself. However, no significant treating of produced water can be expected. 

EPA requires that deck drainage be disposed of with no free oil." If the drainage is merely contaminated rainwater, disposal-pile diameter can be estimated from the following equation which assumes the need to separate 150-micron droplets ... 

Produced water rate in disposal pile, bpu Plan area of deck, ft2... 

The disposal pile should be as long as water depth permits in shallow water to provide maximum oil containment in event of malfunction and to minimize the possibility of sheen. In deep water, length is set to provide a safety- margin of reserve capacity after alarm and shutdown signals activate. 

A skim pile is a type of disposal pile. As shown in Fig. 9, flow through a scries of baffle plates creates quiescent wines that reduce the distance which a given oil droplet must rise to be separated from the main flow. Once in the quiescent zone, there is ample time for coalescence and gravity separation. Larger droplets then migrate up the underside of the baffle to an oil collection system... 

Besides being more efficient titan standard disposal piles from an oil-separation standpoint, skim piles have the added benefit of providing for some degree of sand cleaning. EPA requirements stale that produced sand must be disposed of without free oil. It is doubtful that sand from a vessel drain meets rhi< criteria when disposed of in a standard disposal pile. 

The determination of skim pile length is the same as for other disposal piles. Because of the complex flow regime, a suitable equation has yet to be developed to size skim piles for Hrrk drainage However, field exjv-rienee ha indicated that acceptable effluent is obtained with a 20-min retention time in the baffled section. 

Long-standing refinery practice is to size drain water treating equipment to remove oil droplets 150 microns in diameter or larger. If no other data are available, it is recommended that this be used in sizing sumps and disposal piles... 

It is desirable to bring information included in earlier installments of this series into a format that can be used in selecting and sizing individual pieces of equipment needed for a complete water treating system. Federal regulations require that produced water from the free water knockout receive at least some form of primary treatment before being sent to a disposal or skim pile. Deck drainage may be routed to a properly sized disposal pile that will remove free oil. 

Disposal pile. Internal diameter and tength of the baffle section can he determined. 

Disposal pile ID is excessive. A sump tank in conjunction with a disposal pile or skim pile is required. 

Figure 1.60 One of SQM s salt (halite) solar ponds, with a salt disposal pile in the background (courtesy of SQM SA).

Offshore, produced water can be piped directly overboard after treating, or it can be routed through a disposal pile or a skim pile. Water from the deck drains must be treated for removal of "free" oil. This is normally done in a skim vessel called a sump tank. Water from the sump tank is either combined with the produced water or routed separately for disposal overboard. 

EQUIPMENT TYPES Disposal Pile Skim Pile Reinjection Disposal Wells... 

SP Packs can also be used as retrofit components to improve the performance of existing water treating systems. Deck drainage may also be routed through an SP Pack prior to the drain sump or disposal pile. 

However, this is not recommended where water depth permits a longer pile. To minimize wave action effects a minimum pile length of about 50 ft is required. Figure 3.54 is a schematic showing disposal pile length. 

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