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Fig. 10 Effectiveness data of selected products at 8°C and 22°C on a stable crude oil emulsion (Lode, 1981).

Recovered oil, emulsion and water

Recovery of water and oil residue is governed by skimmer effectiveness and capacity, and by water content in the emulsion. Skimmer effectiveness will vary dependent on oil properties, skimming principle, sea state, and oil thickness (Nordvik, 1995 and Nordvik et al., 1995). Table 3 presents mass balance calculations of total water including free water and emulsified water (H20), emulsion (Emu.) and oil residue rates (Oil) at selected skimmer capacities and effectiveness of skimmers. Note: 80% water content in the emulsion has been used to calculate total recovered water and oil residue.

The data illustrate the high volume of water being recovered, due to emulsification and changes in skimmer effectiveness. The potential for improvement of oil recovery capacity by use of enhanced separation techniques is large. These calculations demonstrate the importance of using high capacity skimmer systems and separation technologies to increase recovery of oil. A doubling of skimmer capacity has the potential to Spill Science & Technology Bulletin 3(3)

double the oil residuc capacity. To compensate for low skimmer effectiveness and high water content in an emulsion, vessel of opportunity recovery systems most likely need a skimmer capacity of 100 mph-.

The following calculations quantify the potential gains in operational efficiency by optimizing productive time and utilization of advanced separation technologies. The 100 m'h-' skimmer and 200 m storage capacity systems have been elected to demonstrate the effect of integration of separation technologies. For these calculations, the duration of daily recovery operations is limited to 12 h, in keeping with the current practice of not recovering oil during night-time because of problems of accurately finding and working in the spilled oil.

Optimizing time of skimming operations

The following calculations quantify the potential gains in operational efficiency and cost effectiveness by optimizing productive time and utilization of

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Fig. 11 Effect of separation by use of a selected emulsion breaker in combination with heat on a SOI SO w/o emulsion of Bunker Oil IF 80 (Strom-Kristiansen et al., 1994b).

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Fig. 12 Reduction in emulsion viscosity of Bunker Oil IF-80 emulsion (pre-mixed with emulsion breaker) as a function of time during heating from 10°C up to an average emulsion temperature of 40°C (Strom-Kristiansen et al., 1994b).

advanced separation technologies. The 100 m n skimmer and 200 m storage capacity systems have been elected to demonstrate the effect of integration of separation technologies. For these calculations, the duration of daily recovery operations is limited to 12 h, in keeping with the current practice of not

110

Time (hours)

recovering oil during night-time because of problems of accurately finding and working in the spilled oil.

Time available for effective skimming operations will vary depending on storage and skimmer capacity. the effectiveness of skimmers and separation and discharge of free water and emulsified water. In the

Spill Scorner & Technudeegt Butkom is

LINDMATER SEPARATION

RESEARCH

Table J Capacity of entire water (H:0), emulsion (Emu.) and oil residue (Oil) at different skimmer capacities and skimmer effectiveness, when summing an emulsion with 80% water content

Capacity (m') for vanous skimmer effectiveness levels

25%

50%

75%

100%

Skimmer capacity (m'n')

HO

Oil

H,0

Emu.

Oul

HO

Emu.

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H,0

Oil

5 10 15

42.5 85 127.5

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The potential for improvement of oil residue recovery is large. The volume of oil residue recovered during a 12 h day of operation may increase from 30 to 60 m.

Table 5 presents mass balance calculations using productive skimming time for 12 h of operation as developed in Table 4. The three separation alter. natives, no separation, free water separation and separation of free and emulsified water, are marked respectively A, B, and C. Water content and oil residue in the emulsion is calculated for an emulsion with 80% water content.

Effect of Separation on Cost Savings and Disposal Costs

Table 6 presents a summary of potential cost savings/disposal costs for the three alternatives, no separation, free water, and total water and discharge in the field. Calculations of oily waste savings and

Emu.

SO 100 150

47.5 95 142.5

12.5
25
37.5

2.5
S
7.5

45
90
135

25
So
75

•The H2O includes free water and water content of the emulsion. The data has been calculated using selected levels of skimmer effectiveness (25. 50. 75. and 100%).

Interpretative note when the skimmer effectiveness is 25% and the skimmer capacity is 100 m'b', the recovered volumes will be as follows: 25 m' of emulsion which will contains mor oil and 20 m' of water, and 75 ml of free water, yielding a total of 95 m' of water and only s m'of ou being recovered in 1h of separation. Even though the skimmer effectiveness can be increased (four times) to 100%. only 20% of the 100 m'hi of recovered fluid will be oil and 80% will be water

Table 4 Productive skimming time (hours) in a 12 b day of operation at different
separation and discharge alternatives and skimmer effectiveness levels, for 100 m'h!
skimmer capacity and 200 m storage capaaty. Numbers in parentheses represent the
estimated hours to kill a storage tank or bladder before discharge is required

Skimmer effectiveness level
No separation (h)
Separation of free water (h)
Separation of total water (h)

25%
6 (2)
9 (8)
12 (40)

following example, water, emulsion and oil data for
100 m'h-skimmer capacity from Table 3 has been
used to calculate productive skimming time for a 12 h
day of operation. Productive skimming time is reduced
for handling and transfer of recovered fluid by a fixed
3 h time period every time unloading is required.
Table 4 presents net productive skimming time
calculated in hours for three different separation and
discharge alternatives and four assumed skimmer
effectiveness.

The most significant increase in productive skimming time, before discharge of oil residue is needed, is demonstrated for total water separation at 25% skimmer effectiveness, with an increase from 2 to 40 h, and recovery of oil residue from 10 to 200 m'. Discharge of separated free and emulsified water during the 40 h is 3800 m'. Only complete separation of free water and water in the emulsion will allow for an optimal 12 h day of skimming operation before transfer is required. The productive time will decrease to 10 h when the skimmer effectiveness reaches 100%. Separation of free water only does not increase productive time in operation compared with no separation when the skimmer effectiveness exceeds 75%. Implementation of remote sensing and down link systems may extend net productive time in operation from 6 to 12 h in a

Spill Science & Technology Bulletin (3)

119

RESEARCH

A B NORDVIK el d.

Tables Mass balance of recovered fluid (in m') and total oily waste recovered (in m) in a 12 h working day, for 100 min-skimmer capacity and 200 m' storage capacity

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Table 6 Summary of, in a 12 h working day. cost savings and disposal cost ia parentheses for no separation,
free water separation and toul water separation and overboard discharge u selected different (25, 50, 75, and
100%) skimmer efficiencies for skimmer with 100 min-1 capacity and with 200 m' storage capacity

Skimmer effectiveness level
No separation (S)
Separation of free water (5)
Separation of total water (5)

25% O (22,500) 25,312 (8438) 42,750 (2250)

50% 0 (22,500) 15,000 (15,000) 40.500 (6500)

75% O (22,500) 5625 (16,875) 38.250 (6750)

100%
0 (22,500)

0 (22.500) 36,000 (7500)

urgent need for rapid recovery and control of the oil spill because of resource damage risk, might warrant the use of such response actions which would currently be considered as unorthodox.

disposal costs are based upon the nominal value of $37.50 per m', derived from the personal experience of the authors, for disposal of oily waste at U.S. facilities. Disposal costs do not include transportation and handling costs to the disposal facility.

The potential for improvements of net productive time in operation by use of enhanced separators is great. Enhanced separation might reduce oily waste disposa) costs by a factor of 10 compared with no separation when skimmer effectiveness is 25%. The reduction of oily waste disposal cost for 25% skimmer effectiveness is 542,750. Oily waste facilities might pay approximately $10/moto buy water free oil residue. In such a scenario, using this cost offset, the disposal cost can be eliminated if total separated water is discharged overboard.

When water is removed from an emulsion, the window-of-opportunity for use of in situ burning and dispersant may reopen, providing an opportunity for combination of alternative response methods such as burning or chemical dispersion (Nordvik, 1995 and Nordvik et al., 1995). While the application of these methods are normally considered when the spilled oil is still on the surface, there is a second opportunity to use these techniques after emulsion breaking and oilwater separation. Assuming that both operational and regulatory conditions allowed discharge of the water. free oil residue, the product might be discharged into a fire resistant boom and burned there, or perhaps mixed with a chemical dispersant to enhance natural dispersion and removal from the sea surface into the water column. Operational limitations such as a shortage of oil storage capacity, or a particularly

Conclusions

120

Implementation of enhanced (separation of free water and water from the emulsion) separation technologies has a large potential to increase net productive skimming time, and improve cost and clean up effectiveness. Discharge of separated water will increase recovery capacity of oil residue, reduce oily waste disposal costs, and facilitate oily waste disposal. Improved recovery of oil residue might reduce resources needed to clean up an oil spill with consequent reduction of logistic requirements and investment costs of skimmers, booms and temporary storage bladders. This will also reduce basic maintenance and stand-by operating costs for a spill response organization. In general, it can be concluded that:

• Separators function because of the difference in

density between oil and seawater. As an oil evaporates this difference decreases, because the oil density increases. The density also increases as the oil incorporates water to form a w/o emulsion. These changes occur simultaneously during weath

ering and reduce the effectiveness of separators. • The emulsification process is partly or fully

reversible by use of heat and/or chemical treatment

Spill Science & Technolog Bulletin (3) OIL AND WATER SEPARATION

RESEARCH

References

Abbot, I A. McDonagh, M. Tookey. D. Gascoigne. J. Dunn R,

Swannell. R. Martin, I. Rampling. T. Gundlach. E. Won W. and Nordvik, A B. (1994) Recovered oil and oily debris handhng to facilitate disposal. MSRC Technical Report Series 93-031

Manne Spull Response Corporation. Washington, DC. pp. 218 Bobra, M. (1992). A study of water-in-oil emulsification. Report EE.

132. Environment Canada, Environment Protection Directorate,

Ottawa, Canada, 63 pp. Bitting. KR, Nordvik, A B. and Murdoch, M. A. (1993) Tests of

oil/water separators for spilled oil recovery operations in Proceedings of the Marine Technology Society Conference 1993.

Washington DC. pp. 222-228. Bitting. KR, Nordvik, A. B. and Fickel. M. (1995) (in press). Test

of lightweight oil/water separators for spilled oil recovery operations. Paper presented at the Second International Research and Development Forum, International Manlime Organization,

London, England, 23-26 May 1995 Daling. P. S., Brandvik, P. J., Mackay. D. and Johansen. 6. (1990).

Characterization of crude oil for environmental purposes. Oil &

Chemical Pollution 7, 199-224. Daling. P. S. and Nerbe Hokstad, J. (1991). Weathering properties

of Balder crude oil at sea. IKU Report No. 22 00102/91, 18 pp Fleischer, A. (1984). Separation of oily wastewaters the state-of-the

art. Paper presented at the Annual Technical Conference Canadian Institute of Marine Engineers. MARI-TECH 84,

Ottawa, May 25 1984, 11 pp. Giammona, C.P., Binkley, K. S., Engelhardt, F R., Nichols, J. D.

and Buechel, S. (1995). Aenal image processing technology for

emergency response. Spill Sci. Technol. Bull. 21. 47-54 Hokstad, J., Daling, P. S. Lewis, A. and Strom-Kristiansen. T

(1991). Formation and breaking of water-in-oil emulsions. Workshop Proceedings MSRC Technical Report Senes 93-018.

Manne Spill Response Corporation, Washington, DC, 300 pp Knapstad, A. (1981). Emulsion breaker experiments at Fusa, 6-9

April 1981, IKU Report No. 0-34318112. Trondheim, Norway, 28

PP. Lee, R. (1995). Isolation and identification of compounds and

mixtures which promote and stabilize water-in-oil emulsions, MSRC Technical Report Series 95-002, Manne Spill Response

Corporation, Washington, DC, 62 pp. Lewis, A., Daling, P. S., Strem-Knistiansen, T. Singsaas, I., Fiocco. RJ, and Nordvik, A. B. (1994). Chemical dispersion of oil and water-in-oil emulsions—a companson os bench scale test methods and dispersant treatment in meso-scale fume In Proceedings of the Seventeenth Arctic and Marine Oil Spill Program. Environ.

ment Canada, Ottawa, Ontano, Canada, Vol. 2, pp 979-1010 Lewis, A., Singsaas, I., Johannesen, B. O and Nordvik, A B

(1995a). Key factors that control the efficiency of oil spill mechanical recovery methods. MSRC Technical Report Series 95-038. Manne Spill Response Corporation, Washington, DC, 54

PP. Lewis, A., Singsaas, I., Johannesen, B. O., Jensen, H., Lorenzo, T.

and Nordvik, A. B. (1995b). Large scale testing of the effect of demulsifier addition to improve oil recovery efficiency. MSRC Technical Report Senes 95-033. Manne Spill Response Corpora

tion, Washington, DC, 54 pp. Lode, T. (1981). Offshore emulsion breaking while recovering crude

oil spills. Norwegian Clean Seas Association for Operating Companies (NOFO). Emulsion Breaker Work Group. Lever.

igsveien 32, P. O. Box 133, N-4001 Stavanger, Norway, 25 pp McGraw-Hill Dictionary of Scientific and Technical Terms (1974)

(Ed. in Chief D. N. Lapeds). McGraw-Hill, New York, 1634 pp. Murdoch, M. (1993a) (In Draft). Oil/water separator test and

evaluation. Naval Facilities Engineering Service Center. 560

Laboratory Drive, Port Hueneme, CA, 200 pp. Murdoch, M. (1993). Evaluating oil/water separators. In Proceed.

ings of the Sixteenth Arctic and Marine Oil Spill Program Technical Seminar. Environment Canada, Ottawa, Ontano,

Canada. Vol. I., pp. 435 449. Nordvik, A, B., Simmons, L. L., Engelhardt, F. R. and Hudon, T.

(1993). The effect of the environment on oil properties and the subsequent impact on response technology A need

with subsequent reductions in emulsion viscosity and density. This may also improve pumpability and discharge capacity, reduce transfer and discharge time, and enhance the potential for sale and reuse of

recovered oil. • The greatest increase in productive skimming time,

before discharge of oil residue was demonstrated for total water separation at 25% skimmer effectiveness, with an increase from 2 to 40 h, and recovery of oil

residue from 10 to 200 m'. • Separation of free water only, has limited effect on

productive skimming time when skimmer effective

ness is above 75%. • Separation of oil contaminated free water has its

largest effect on effective skimming time and recovery of oil residue, when skimmer effectiveness

is less than 50%. . Separation of w/o emulsions has the greatest

potential to increase effective skimming ume, recovery of oil residue and to decrease or eliminate disposal costs, making the selection of high effectiveness skimmers (>75%) less important.

Recommendations • Continue development of enhanced separation

processes for use in marine oil spills. • Development of data on oil and emulsion droplet

sizes when a mixture enters an oil-water separator, formed by skimmers, pumps and transfer hoses at

different oil weathering stages. • Implementation of an internationally accepted

laboratory standard for performance testing of emulsion breakers at different degrees of oil weathering is required for evaluation, comparison and

interpretation of results generated world wide. • Test standards for marine oil spill separators need to

include oil characteristics and maximum water

content in oil effluent and oil in water effluent. • Meso and full scale experiments of separation

capabilities of recovery systems (skimmers, injection of emulsion breakers and on-line separators) are required for system optimization and improved

contingency planning and response. • Use of emulsion breakers might be a rapid and cost

effective method to separate emulsions. However, effective use of emulsion breakers is related to product, time, environmental conditions and is oil dependant. A combination of heat and emulsion breakers is recommended for separation of high viscosity fuel oils.

AcknowledgementThis work was initiated when the senior author was Director of Applied Engineering in Research & Development at the Marine Spill Response Corporation (MSRC) in Washington, DC.

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