· Example 3 – Waste Activated Sludge Thickening With DAF Design Steps
1. Define the problem.
2. Calculate the total weight of sludge to be removed, assuming 100 percent removal of incoming solids.
3. Calculate the flotator tank area using an SLR = 2 lb/hr/ft2 (10 kg/hr/m2), if pilot plant data is not available.
4. Calculate the flotator tank area based on HLR:
a. From Figure 11 obtain the solubility of air based on: 1 atm and influent feed temperature.
b. Determine pressurization pressure in atm.
c. Determine the recycle ratio using Eq. (2) and calculate recycle flowrate. The recycle rate must be at least 100 percent.
d. Calculate the total flowrate as: fresh feed flowrate + recycle rate.
e. Calculate the flotator tank area using an HLR = 2.0 gpm/ft2 (1.4 l/sec/m2), if pilot plant data is not available.
This information is considered CONFIDENTIAL and shall not be released to or discussed with any persons except (a) employees of ExxonMobil 5. Select the larger of (3) and (4e).
6. Calculate the design area by multiplying the area in (5) by a safety factor of 1.1 to 1.25.
7. Specify a unit with the design size calculated in (6). Spare or parallel waste activated sludge thickeners are typically not specified.
Example
Step 1 – Define the problem
A DAF with pressurized recycle is to be designed to thicken the solids in waste activated sludge from 8000 mg/L to about 4wt%. The sludge flowrate is 70 gpm (260 Ipm) at 68°F (20°C). The sludge settles very well with an SVl of about 60, therefore, alum and flocculant are not used. Pilot data is not available and a saturation drum pressure of 75 psig (500 kPa) is assumed.
Step 2 – Calculate the solids loading to the DAF at 100 percent solids removal
(70 gal/min) (3.785 liters/gal) (8000 mg/L) (1 gm/1000 mg) (lb/453.6 gms) (60 min/hr) = 280 Ib/hr (127 kg/hr)
Step 3 – Calculate the flotator area using solids loading rate determined from pilot plant testing. In the absence of pilot plant data, use an SLR = 2 Ib/hr/ft2 (10 kg/hr/m2)
(280 lb/hr) / (2 lb/hr/ft2) = 140 ft2 (13 m2) Step 4 – Calculate the area based on HLR:
a. From Figure 11 obtain the solubility of air at 14.7 psia and 20°C sg = 18.7 mg/l
b. Determine saturation drum pressure in atm P = (75 + 14.7) / 14.7 = 6.1 atm
c. Determine the recycle ratio using Eq. (2) and calculate recycle flowrate. The recycle rate must be at least 100 percent. Use A/S = 0.2 in absence of pilot data.
A/S = 1.3 (sg / Sa) (f P - 1) (R/Q)
0.02 = 1.3 (18.7/8000) [0.8 (6.1) - 1] (R/Q)
1.7 = (R/Q)
R/Q = 1.7, which is 170 percent of fresh wastewater feed flow rate and greater than 100 percent R = (1.7) (70 gpm) = 120 gpm (0.45 m3/min)
d. Calculate the total flowrate as: fresh feed flowrate + recycle rate 70 + 120 = 190 gpm (0.72 m3/min)
e. Calculate the flotator tank area using an HLR = 2.0 gpm/ft2 (1.4 l/sec/m2), since pilot plant data is not available (190 gpm) / (2 gpm/ft2) = 95 ft2 (8.8 m2)
Step 5 – Select the larger of (3) and (4e) 140 ft2 (13 m2)
Step 6 – Calculate the design area by multiplying the area in (5) by 1.2 (no pilot data) (140 ft2) (1.2) = 168 ft2 (15.3 m2)
Step 7 – Specify one unit with an area of 168 ft2 (15.3 m2)
9 OPERATING / CONTROL STRATEGY
A cost-effective operating / control strategy should contain not only procedures for proper operation of the flotation equipment but also elements for load minimization. Methods for minimizing load to the flotation equipment should include keeping upstream equipment operating efficiently and minimizing ingress of oil and suspended solids to the sewers. These upstream controls will help ensure consistently good removal performance and also less solid waste generation from flotation units.
Reference 19 provides guidelines for formulating improved control / operating strategies to reduce operating costs for flotation units and the overall WWTP. In addition, the following should be considered in the operating / control strategies:
· Periodic Optimization of Flotation Aids – Flotation aids are used to enhance the performance of a flotation system. To ensure that effluent quality is maintained, periodic testing should be conducted since the influent wastewater characteristics can fluctuate significantly and a change of flotation aid and/or dosage rate may be needed. Also, dosage rate adjustment may be needed when upstream separators are not performing as designed. Optimization also minimizes over treatment with relatively expensive flotation aids. Over treatment tends to degrade effluent quality and can be costly. If an inorganic coagulant, e.g., alum, is being used, testing with several chemical vendors is recommended to find an organic coagulant with equal performance to reduce sludge volume.
· Periodic Cleaning of Nozzle / Striker Plate Gas Inductors – The bubble size generated by the nozzles in nozzle / striker plate gas inductors influences oil removal performance. The shear imparted by the nozzles on the bubbles causes the formation of minute bubbles. Although there is an optimum bubble size below which improvement becomes insignificant, the smaller the bubble size the better the oil removal performance will be. Maintenance of high nozzle shear is important.
Therefore, periodic maintenance of the nozzles is required, since they tend to plug with scale or solid deposits. For cleaning the nozzles, one refinery has good experience with 1% EDTA (a chelating chemical). During scheduled maintenance, this solution is pumped around with the recycle pump. The nozzles are cleaned one at a time. Cleaning with inhibited acid is another option provided the acid is compatible with all internals and coatings.
· Maintenance of Key Components – Vendor's maintenance recommendations for critical parts of the system, such as pumps, nozzles, skimmers, and saturation-drum, should be implemented.
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This information is considered CONFIDENTIAL and shall not be released to or discussed with any persons except (a) employees of ExxonMobil TABLE 1A
CHARACTERISTICS OF EXXONMOBIL DISSOLVED AIR FLOTATION UNITS
LOCATION INGOLSTADT REFINERY TRECATE REFINERY
Pretreatment Equalization Tank API Separator, Equalization Tank
Type of Service Oil/solids removal upstream of BIOX Oil/solids removal upstream of Biox
Number of Units 2 1
OPERATIONAL PARAMETERS DAF 1 DAF 2
Size, ft (m) 23' diameter x
8' depth (7 x 2.5)
Dosage, mg/L 12 mg/l (AlCl3), 1 mg/l (polymer),
Fe2(SO4)3 as needed PERFORMANCE PARAMETERS
Influent Quality, mg/l
· Oil 75 75 50
· Suspended Solids 100 100 45
· pH
Effluent Quality, mg/l
· Oil 10 10 15
· Suspended Solids 30 30 22
· pH 8.5 – 9 8.5 – 9 8.5
Air-to-Solids Ratio
Rise Rate (HLR), gpm/ft2 (m3/h/m2) 0.6 (1.4) 0.8 (1.9) Normal: 1.2 (2.9) Design: 1.8 (4.4) PRESSURIZATION DRUM
Operating Pressure, Psig (barg) 70 (4.8) 58 (4) 41 (2.8)
Operating Temp, °F (°C) 77 (25) 77 (25)
Retention Capacity, min Normal Flow: 7 Normal Flow: 4 1.7
Saturation efficiency, % Baffles (yes/no)
FLASH MIX TANK None None None
Baffles (yes/no)
Dewatering Filter Filter Plate and Frame Filter
Disposal Return to crude oil
tankage
Return to crude oil
tankage Land
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TABLE 1A (Cont)
CHARACTERISTICS OF EXXONMOBIL DISSOLVED AIR FLOTATION UNITS
LOCATION PORT JEROME REFINERY FAWLEY REFINERY BATON ROUGE REFINERY
Pretreatment API (~80%) or Biox (~20%) None API, CPS, Pre-Biox ABT
(Aggressive Biological Treatment)
Type of Service Clarification Thickening
Downstream of ABT for
Feed Rate, gpm (m3/hr) 4400 (1000) 400 (90) 10,000 (2270)
Recycle Rate, gpm (m3/hr) 440 (100) 1800 – 2200 (410 – 500)
Retention Time, min (including recycle) 26 44
Float Quality
Oil + Suspended Solids, wt% 10 4 – 6
Flotation Aid(s) Alum (wastewater from
chemical plant) and polymer None (but planned)
Cationic prior to flash mix tank, cationic emulsion polymer added
in flocculation tank
Dosage, mg/L Alum ~ 180
Polymer ~0.7 (dry)
Cationic prior to flash mix: 80 cationic emulsion in floc tank: 1.5 PERFORMANCE PARAMETERS
Influent Quality, mg/l
· Oil 350 (as TOC) 100
· Suspended Solids <70 1000 110
· pH 7 8 7.5
Effluent Quality, mg/l
· Oil 2 200 (100 with polymer)
(as TOC) 50
· Suspended Solids 14 400 (200 with polymer)
(as TOC) 55
Dewatering Centrifugation Gravity Belt Filter then Drying
Disposal Offsite Incineration Land Non-Hazardous Offsite Landfill
This information is considered CONFIDENTIAL and shall not be released to or discussed with any persons except (a) employees of ExxonMobil TABLE 1A (Cont)
CHARACTERISTICS OF EXXONMOBIL DISSOLVED AIR FLOTATION UNITS
LOCATION BATON ROUGE
CHEMICAL PLANT
JOLIET REFINERY
OKINAWA REFINERY
Pretreatment API Separator API Separator Desalter effluent through API
Type of Service Flocculation BIOX pretreatment
Clarification
Feed Rate, gpm (m3/hr) 3000 (681) 1250 (284) 220 (50) (design)
Recycle Rate, gpm (m3/hr) None 415 (94)
Retention Time, min (including
recycle) 26
Float Quality
Oil + Suspended Solids, wt%
Flotation Aid(s) Coagulants Nalco 7134 Poly aluminum chloride
Dosage, mg/L 2.3 (5 – 7 average)
· Suspended Solids 14 75
· pH 8-9
Air-to-Solids Ratio
Rise Rate (HLR), gpm/ft2 (m3/h/m2) 4 (9.8) PRESSURIZATION DRUM 1200 gal (254 m3)
Operating Pressure, Psig (barg) 135 (9.3) 40 (2.7)
Operating Temp, °F (°C)
Retention Capacity, min 0.4
Saturation efficiency, %
Baffles (yes/no) Yes Yes
FLASH MIX TANK 26,500 gal (5615 m3) Flash mix and Flocculation
Tank combined
Baffles (yes/no) Yes
Agitator Size, HP 3
FLOCCULATION TANK 51,500 gal (10,910 m3) None Flash mix and Flocculation Tank combined
Mixer (yes/no) Yes Yes
Baffles (yes/no) No
FLOAT TREATMENT
Dewatering Drying and Presses None Centrifuge
Disposal Incinerator/Land Reuse in Delayed Coker
TABLE 1A (Cont)
CHARACTERISTICS OF EXXONMOBIL DISSOLVED AIR FLOTATION UNITS
LOCATION ANTWERP REFINERY CERRO NEGRO
Pretreatment Separator, Equalization or Ballast Tank API Separator
Type of Service Clarification, Control of pH , H2S, P BIOX Pretreatment
Number of Units 2 (each unit same) 2
OPERATIONAL PARAMETERS
Size, ft (m) 53' diameter x 10' depth
(16 x 3)
Flotation: 8 x 35 x 4 (2.4 x 10.7 x 1.2) Flocculation: 8 x 8.5 x 8 (2.4 x 2.6 x 2.4)
Shape Circular Rectangular
Feed Rate, gpm (m3/hr) Normal: 1540 (350)
Design: 2600 (590) 300 (68) each
Recycle Rate, gpm (m3/hr) 75 % of Feedrate
1100 – 1230 (250 – 280) 60 (14) each
Retention Time, min (including recycle) Normal: 63, Design: 43 23
Float Quality
Oil + Suspended Solids, wt%
1 – 2
N/A
Flotation Aid(s) Polyelectrolytes Polyaluminum chloride / Cationic Polymer
Dosage, mg/L Cation : 5, Anion: 0.5 20 ppm / 4 ppm
PERFORMANCE PARAMETERS Influent Quality, mg/l
· Oil 15-150 300
· Suspended Solids 60 200
· pH 8.5 – 9 6-9
Effluent Quality, mg/l
· Oil 10 – 15 < 120 (Petroleum Hydrocarbon < 50 mg/l)
· Suspended Solids 20 < 50
· pH 6-9
Air-to-Solids Ratio 0.013
Rise Rate (HLR), gpm/ft2 (m3/h/m2) Normal: 1.2 (2.9)
Design: 1.7 (4.2) 1.3 (3.2)
PRESSURIZATION DRUM
Operating Pressure, Psig (barg) 94 - 102 (6.5 – 7) 50 (3.4)
Operating Temp, °F (°C) Ambient 68 – 95 (20 – 35) 72 - 97 (22 - 36)
Retention Capacity, min Normal flow: 103
Max flow: 64 2.3
Saturation efficiency, % 100 N/A
Baffles (yes/no) No, splash plate Yes
FLASH MIX TANK
Disposal Incinerator, Future: Rotterdam coker Recycle to Coker
This information is considered CONFIDENTIAL and shall not be released to or discussed with any persons except (a) employees of ExxonMobil
Post-Treatment Biox Tilted Plate Interceptor (TPI)
Thickening Tank (UTK-78)
Fuel Gas Stripper (UT-75) TPI (UX-89)
Number of Units 1 2 1
Inductor Type Hydraulic (eductor) Mechanical Mechanical
Type of Service Oil/TSS removal of total plant wastewater stream
Oil/TSS removal
Oil/TSS removal
Air/Gas Used for Flotation Nitrogen Air Fuel Gas
Number of Compartments 4 6 6
OPERATIONAL PARAMETERS
Feed Rate, gpm (m3/hr) 240 (55) 120 (27) Maximum: 26 (6)
Retention Time, min 12 15 30
Flotation Aid Cationic polymer
· Suspended Solids 10 – 20 (designed for 90-97%
removal)
30 30
FLOAT QUALITY/TREATMENT
Suspended solids, wt% Design: 3 1 1
Thickening None Gravity Gravity
Dewatering Decanting None None
Disposal Incinerator Off-site Incinerator Off-site Incinerator
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TABLE 1B (Cont)
CHARACTERISTICS OF EXXONMOBIL INDUCED GAS (AIR) FLOTATION UNITS
LOCATION BILLINGS REFINERY CHALMETTE REFINERY
Pre-Treatment API API
Post-Treatment Biological Oxidation Ponds BIOX (Water)
CPI Concentrator (Float)
Type of Service Oil/TSS removal in
refinery wastewater
Oil / TSS Removal in Refinery Wastewater
Air/Gas Used for Flotation Air Air
Number of Compartments 2
US Filter - 7 compartments (6 w/
aerators, 1 effluent bay) Wemco - 5 compartments (4 w/
aerators, 1 effluent bay) OPERATIONAL PARAMETERS
Feed Rate, gpm (m3/hr) Normal: 700 (160) Maximum: 1400 (320)
Normal Flow - 2250 (511) Maximum Flow - 5900 (1340)
(Flow is split between units)
Retention Time, min Normal flow: 5 min
US Filter-6 min at max flow (4000 gpm)
Wemco-4 min at max flow (3000 gpm)
Flotation Aid Nalco EC 2338A Flocculant Cationic Solution Polymer (GEBETZ Klaraid PC1192)
Dosage, mg/L 4 10 - 25
Operating Temp, °F (°C) 90 – 110 (32 – 43) 100 - 120 (38 - 49)
Recirculating Pump Capacity: None N/A
% of WW flowrate N/A
· Suspended Solids N/A Target <50
FLOAT QUALITY/TREATMENT recycled to head of IAF;
Thickened solids, 40-50wt%, to thickener tank )
Dewatering N/A
Disposal Coker MOSC
This information is considered CONFIDENTIAL and shall not be released to or discussed with any persons except (a) employees of ExxonMobil
Pre-Treatment Skim Tanks Skim Tanks Skim Tanks
Post-Treatment None None None
Number of Units 3 2 1
Inductor Type Mechanical Mechanical Hydraulic (eductors)
Type of Service Heavy Oil Removal from
Produced Water
Heavy Oil Removal from Produced Water
Heavy Oil Removal from Produced Water
Air/Gas Used for Flotation Fuel Gas Fuel Gas Fuel Gas
Number of Compartments 4 4 6
OPERATIONAL PARAMETERS
Feed Rate, gpm (m3/hr) 2050 (465) each 2380 (541) each 4380 (995) each
Retention Time, min 6 8 6
Flotation Aid Nil Nil Nil
Dosage, mg/L N/A N/A N/A
Operating Temp, °F (°C) 185 (85) 185 (85) 185 (85)
Recirculating Pump Capacity: N / A N / A Eductor Supply Pumps: 2 x
100% at (249 m3/hr) each
% of WW flowrate N / A N / A N / A
PERFORMANCE PARAMETERS Influent Quality, mg/L
· Oil 200 200 200
· Suspended Solids Negligible Negligible Negligible
· pH 6.8 (controlled by sweep gas
rate)
Disposal Recycle to Oil Production Recycle to Oil Production Recycle to Oil Production
TABLE 2
COMPARISON OF IGF AND DAF
ITEM IGF vs. DAF
A. Capital Investment
1. Flotation Unit IGF has shorter residence time, thus smaller and less complex.
2. Auxiliary Equipment IGF requires a small thickener. DAF requires flash-mix tank and air/water mix drum.
3. Installed Cost IGF including thickener is less than DAF.
B. Operating Cost
1. Utilities IGF (mechanical type inductor) has higher power requirement.
2. Chemicals Depends on feed quality, but IGF does not generally require a coagulant. Similar addition rate for cationic flotation aid.
3. Sludge Disposal Same.
4. Oil Recovery Both floats require further processing if oil recovery is desired.
C. Operating Characteristics
1. Oil and TSS Removal IGF is less resilient to feed quality and flow surges. Surge capacity is required, especially when Oil and TSS concentrations are high (above 200 mg/L). DAF produces a more consistent effluent quality. IGF may not be as effective on difficult wastewaters due to high energy system and lack of flash mix and floc tanks.
2. Time Required to Correct IGF response to operating adjustment is quicker than DAF due to shorter residence time.
3. Feed pH Control Same.
4. Coagulant Depends on feed quality, but less coagulant is generally required in IGF.
5. Polyelectrolyte Required Cationic polyelectrolyte is used in both processes.
6. Recovery from Upsets IGF recovers faster due to shorter residence time.
7. Operating Adjustments IGF has a simple skimmer; no air saturation drum.
8. H2S Removal Similar but more convenient in DAF with FeSO4. 9. VOC Stripping Occurs in both but higher in IGF due to higher gas rate.
10. Float Handling IGF float is less concentrated at 1 to 2 % solids versus 2 to 6% in DAF. IGF requires a float thickener. (Note that IAF produces a higher total volume of float than IGF.)
D. Operating Performance
1. Effluent Quality DAF will produce a slightly higher quality and more consistent effluent.
2. Removal Efficiency DAF is higher because of smaller bubbles and longer residence time. DAF oil removal efficiency should range from 80 to 90 percent and IGF oil efficiency should range from 75 to 85 percent at design conditions. Solids removal efficiencies are usually slightly lower (~ 5 percent) for both DAF 75- 85 and IGF 70 - 80.
3. Bubble Size DAF bubble size range is 30 mm to 120 mm compared to up to 1000 mm in IGF 4. Floc Carry Over Low turbulence and longer retention time in DAF reduces floc carryover; high energy
and shear tends to increase floc carryover in IGF.
E. Other
1. Plot Area IGF is smaller, about 1/4 size of DAF tank.
2. Winterization IGF is usually a closed unit.
3. Air Emissions Easier to control in IGF with seals or pressure vessel design. DAF requires a cover.
For grassroots designs where air emissions are a concern, IGF is generally the best option.
4. ExxonMobil Experience More extensive ExxonMobil experience in designing and operating DAF units.
5. Reliability IGF (hydraulic type inductor) striker plate can foul with salts and require cleaning.
DAF more susceptible to solids buildup. IAF loss of any one inductor usually requires a vessel shutdown to fix.
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This information is considered CONFIDENTIAL and shall not be released to or discussed with any persons except (a) employees of ExxonMobil TABLE 3
SAMPLE DUTY SPECIFICATION FOR DISSOLVED AIR FLOTATION
EQUIPMENT SYMBOL TK-
TK-Service Wastewater clarification by the
removal of oil and suspended solids from API Separator effluent
Waste activated sludge thickening
Number of Units 2 at 60 percent of design 1
Type of Unit (Rectangular or Circular) Rectangular Circular
Feed Rate, gpm (m3/hr)
Max 2,800 (635) 85 (19)
Design 2,500 (570) 70 (16)
Influent Quality
Oil, mg/L 180 Max.; 150 Design 20 Max.
pH 7.0 - 8.5 6.0 - 9.0
Suspended Solids, mg/L 150 Max.; 100 Design 8000 Design
Effluent Quality
Oil, mg/L 25 Max.; 20 Design –
Suspended Solids, mg/L 25 Max.; 20 Design 400 Max.
Float Quality
Oil + Suspended Solids, wt % 2 Min. 4 Min.
Area Classification Class 1, Group D, Division 1 Class 1, Group D, Division 1
Electrical Enclosure NEMA7 NEMA 7
Power Available 460 volt/3 phase/ 60 Hz 460 volt/3 phase/ 60 Hz
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TABLE 3 (Cont)
SAMPLE DUTY SPECIFICATION FOR DISSOLVED AIR FLOTATION Proposed Design Parameters (Vedor to Verify):
Recycle Rate, gpm (m3/hr)
Max 1120 (255) 150 (34)
Design 1000 (227) 120 (27)
Percent (%) 40 170
Air-to-Solids Ratio 0.04 0.02
Rise Rate (HLR), gpm/ft2 2.4 Design, 2.0 Min. –
Solids Loading Rate (SLR), lbs/hr/ft2 – 2.0 Design
Pressurization Drum
Operating Pressure, psig (kPa)
Design 65 (450) 75 (517)
Max. Design 80 (550) 90 (620)
Operating Temperature, °C (°F)
Max. Design 40 (105) 20 (68)
Retention Capacity, minutes 2 2
Saturation Efficiency, % 80 Min. 80 Min.
Retention Capacity 2 minutes total capacity, 30 seconds normal level
2 minutes total capacity, 30 seconds normal level
Baffles Yes Yes
Flash Mix Tank Not Required
Retention Time, minutes 2
Baffles Yes
Agitator Size 15 hp
Vessel Shape (Note 1)
Flocculation Tank Not Required
Retention Time, minutes 22
Mixer Yes (Note 2)
Baffles Yes
Miscellaneous
Vendor shall supply the air-water mix drums including internals, inlet distributors, and let-down valves, all of proven design. Let-down valves shall be located as close as feasible to the inlet distributors and installed horizontally.
Vendor shall supply float skimmers and sludge scrapers of proven design.
The float skimming device shall be designed to minimize the amount of water skimmed with the float. The float shall be transferred to a float transfer vessel provided by others.
The DAF equipment vendor shall provide the beach/trough that the float skimming device discharges into.
The design of the pressurization drum, inlet distributor, let-down valve location, float skimmer, and sludge scraper must be submitted to the Owner's Engineer for approval.
Reference Design Guide 11-7-1 for more information for DAF Duty Specifications.
This information is considered CONFIDENTIAL and shall not be released to or discussed with any persons except (a) employees of ExxonMobil TABLE 3 (Cont)
SAMPLE DUTY SPECIFICATION FOR DISSOLVED AIR FLOTATION Materials3
Vessels Carbon steel with corrosion resistant lining4 or concrete
Drums Carbon steel with corrosion resistant lining4
Lines and Accessories Contacting Aerated Water Carbon steel with corrosion resistant lining4
Internals Carbon steel with corrosion resistant lining4
Other Lines and Accessories Carbon steel
Notes:
(1) Length = width = depth or diameter = depth
(2) Mixer to be slow speed type with maximum tip speed of 2 ft/sec.
(3) The materials selection must be submitted to Owner's Engineer for approval.
(4) In accordance with Owner's approved coating system.
TABLE 4
SAMPLE DUTY SPECIFICATION FOR INDUCED GAS FLOTATION
EQUIPMENT SYMBOL D–
Service Wastewater clarification for the removal of oil and suspended
solids from API Separator effluent
Number Required Two (2) at 60 percent of design.
Fluid Handled Refinery wastewater
Upstream Treatment API separator and the addition of cationic polymer Feed Rate, gpm (m3/hr)
Max. 2,800 (635)
Design 2,500 (570)
Influent Quality
Oil, mg/L 180 Max.; 150 Design
Suspended Solids, mg/L 150 Max.; 100 Design
pH 6 – 9
Effluent Quality
Oil, mg/L 25 Max.; 20 Design
Suspended Solids, mg/L 25 Max.; 20 Design
Retention Time 4 minutes at design rate
Operating Temperature, °C (°F)
Design 35 (95)
Max. 40 (102)
Recirculation Pump Capacity
Percent (%) of Design Wastewater Flowrate 20; provide common spare Float Quality
Suspended Solids, wt% 0.75 Min.
Educting Gas Nitrogen
Area Classification Class 1, Group D, Division 1
Electrical Enclosure NEMA 7
Power Available 460 volt/3 phase/ 60 Hz
Type and Description
Totally enclosed, induced gas flotation unit complete with four active cells, degassing cell, internal skim cell, internal skimmer (adjustable), internal eductors, eductor water supply header, eductor gas supply header, primary skim trough, inspection hatches, access hatch, eductor gas return line, purge gas lines, skim outlet, internal baffles, automatic cycle timer, drain, support skid, outlet level controller, interconnecting piping and valves, instrument controls, recycle pump and motor, isolation valves, check valves, external T-bar adjusting tool. Motor control station, motor starters, external piping, wiring and erection shall be provided by others.
Materials and Details of Construction
The materials shall be manufacturer's standard for the specified service unless noted otherwise.
The vessel shall be of carbon steel construction with a corrosion resistant coating (epoxy lining or equivalent), and with mechanical design pressure of 30 psig (206 kPa) at 170°F (77°C); the vessel shall be ASME coded. An allowance of 1/16 in. (1.6 mm) for corrosion shall be included.
The vessel internals shall be constructed of corrosion resistant materials suitable for the intended service. Eductor / nozzle shall be 316 stainless steel.
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This information is considered CONFIDENTIAL and shall not be released to or discussed with any persons except (a) employees of ExxonMobil TABLE 4 (Cont)
SAMPLE DUTY SPECIFICATION FOR INDUCED GAS FLOTATION
All vessel internals that are not corrosion resistant materials shall be protectively coated in accordance with Owner’s approved coating system.
All nozzles shall have ASME Class 150 raised face (RF) flanges.
Manufacturer shall provide all necessary connecting and interconnecting piping, fittings and valves. The piping shall be suitably designed to ensure equal flow to each vessel. All piping shall be carbon steel.
Skimming cycle time sequences shall be initiated by the control timer within the control panel. The level transmitter / controller shall control the level to insure proper operation of non-skim (nominal mode) and skimming mode.
All pressure control devices shall be furnished by the manufacturer.
Manufacturer to provide capability to relevel the internal float trough as well as the vessel itself.
Manufacturer to provide capability to relevel the internal float trough as well as the vessel itself.