Treatment Of Oily Water

Water from desalters is cooled from 225°F to approximately 130°F in exchanger E-101 to prevent thermal damage to CPI oil/water separator plates (see Figure 9-6). The cool effluent next joins all other potentially contaminated water streams for removal of oil in CPI-type API separators CPI-101A and CPI-10IB. CPI separators remove most of the free oil and some of the settleable solids associated with influent streams (Table 9-6). They do not reduce emulsified oil, H2S, or NH3. Oil removed from the CPI units is sent to a wet slop oil tank for oil recovery by pump P-101. The effluent water from CPIs is pumped to DAF surge tank TK-101. The oily sludge that settles to the bottom of the CPI units is drawn off periodically by a vacuum truck and taken to a sludge dump.

Waste treatment processes require a relatively steady-state operation to function optimally. Normal and emergency flows fluctuate dramatically throughout a normal operating day. These flows vary from periods of little or no flow to periods of flow approaching the design capacities of the lines. Surge tank TK-101 is therefore located prior to dissolved air flotation units to minimize erratic peak of flows and ensure optimum operation.

DAF units DAF-101A and DAF-101B treat all wastewater from the DAF surge tank. Wastewater is drawn from the surge tank using two pumps operating simultaneously. The flow from the tank is controlled using a manually operated control valve. The DAF unit reduces the oil

Thickened Sludge Sump Plan

SLUDGE REMOVAL BYVACUUM TRUCKS

FLOAT AND SLUDGE TO THiCKNENERS DAF EFFLUENT TO MIXING BASIN

DAF EFFLUENT SUMP

DAF FLOAT AND SLUDGE SUMP

Figure 9-6. Primary oil separation from water. M = motor (pump driver).

SKIMMED OIL TO WET SLOP TANK

SLUDGE REMOVAL BYVACUUM TRUCKS

FLOAT AND SLUDGE TO THiCKNENERS DAF EFFLUENT TO MIXING BASIN

DAF EFFLUENT SUMP

DAF FLOAT AND SLUDGE SUMP

Figure 9-6. Primary oil separation from water. M = motor (pump driver).

Table 9-6

Operating Data of an API Separator (CPI type) PARAMETERS UNITS INFLUENT EFFLUENT

DESALTED WASHWATER FEED

SUSPENDED SOILDS

ppm

500

500

TOTAL SOLIDS

ppm

750

750

FREE OIL

ppm

250

20

EMULSIFIED OIL

ppm

160

160

TOTAL OIL

ppm

410

180

COD

ppm

1000

500

BOD

ppm

620

310

PHENOLS

ppm

3

3

SULFIDES AS H2S

ppm

10

10

NITROGEN AS AMMONIA

ppm

35

35

TEMPERATURE

op

225

TOTAL OIL ppm 2200 190

OILY WATER FEED

TOTAL OIL ppm 2200 190

content of wastewater (emulsified plus free oil) to about 15ppm. De-emulsifying agents, such as polyelectrolytes or alum, are added to DAF influent in inline mixer MX-101 to increase the oil removal efficiency of éach DAF unit. Typical operating conditions and effluent qualities from a DAF unit are shown in Tables 9-7 and 9-8. Three DAF units are normally provided, each sized with 50% of the design capacity, to permit routine maintenance and cope with wide fluctuations in flow.

Sludge management consists of mechanical thickening, dewatering, and sludge storage. The sludge originates from the CPI system and DAF

Table 9-7

DAF Unit Influent and Effluent Quality

Table 9-7

DAF Unit Influent and Effluent Quality

PARAMETERS

UNITS

INFLUENT

EFFLUENT

SUSPENDED SOILDS

ppm

<500

20

FREE OIL

ppm

50

3

EMULSIFIED OIL

ppm

160

10

TOTAL OIL

ppm

210

13

COD

ppm

640

300

BOD

ppm

320

150

PHENOLS

ppm

1.8

1.8

SULFIDES AS H2S

ppm

10

8

NITROGEN AS AMMONIA

ppm

35

15

pH

6.5-7.5

6.0-7.0

Table 9-8 DAF Unit Operating Conditions

PARAMETERS

UNITS

FLOW RATE/UNIT

gpm

240

RECYCLE RATE, % FEED

50

AIR TO SOLID RATIO

0.1-0.3

AIR PRESSURE

psig

75

AIR FLOW RATE

scfm

2.0-5.0

FLOTATION DETENTION TIME

min

40

HYDRAULIC LOADING

gpm/ft2

0.5-2.0

COAGULATING CHEMICAL

ALUM (10% SOLUTION) DOSAGE

ppm

10-20

FLOCCULATING CHEMICAL

POLYMER SOLUTION

ppm

0.5

units. The sludge contains considerable water, oil, and some solids, which may be considered hazardous or toxic. Thickening is done in a thickener, followed by dewatering by a belt press to reduce sludge volume. The decanted or released water is returned to CPI system. The dewatered sludge, rich in solids and oil, is conveyed to a sludge storage area by conveyer belt to await disposal as landfill. Polyelectrolytes are added to the sludge as thickener and in the belt press influent to increase solid removal efficiency for both thickener and belt presses.

Effluent from the DAF units is combined with nonoily wastewater streams and cooling water return in a mixing basin and discharged to the sea or other water body.

The slop oil streams from sour water stripper, wastewater treatment, the oil terminal, and such contain large quantities of water, which need to be separated, using heating, settling, and by adding oil/water-emulsion-breaking chemicals (see Figure 9-7).

Wet slop treatment is a batch operation. All the wet slop produced is pumped to two wet slop tanks, T-101A and T-101B. Each tank is provided with a floating roof and a swing arm suction line. The tanks are in service alternately. When a tank gets full, its contents are heated and mixed by pumping the liquid through wet slop heater E-101 and back to the tank. LP steam is used to raise and maintain the wet slop temperature to 120°F. To

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