CLEANING UP THE SLOP: PART II

Gordon K. Goldman, Avron Corporation, USA, A.B. Idzqandar, Sabah Shell Petroleum Co., East Malaysia, Cornelis Kasteleyn, ESP International, East Malaysia, and Andre Paille, Rubark Industrial Services, USA discuss waste minimisation and recovery of saleable oil from slop oil emulsion sludges achieving a BS&W of 0.00% for waxy crude.

The July/August 1999 issue of Hydrocarbon Engineering features an article describing a new chemical product that can liquefy slop oil bottoms (heavy paraffin waxes and asphaltenes) and disperse them in crude oil or any other hydrocarbon diluent. The final crude oil blend is stable at ambient temperature with no wax separation observed even after one year at 70°F.

The product is known as 505-SD Slop Oil Dispersant (patent pending) and is manufactured by Avron Corporation, USA. It was originally invented with only one purpose in mind: to develop a chemical product that, when added to slop oil (slope) tank bottoms, would be able to keep paraffin wax suspended in crude oil without separating out at ambient or lower temperatures.

Tests under varying conditions have found that 505-SD also acts as a demulsifier, degreaser, and pour point depressant. Other tests have shown that a modified form of the dispersant when used as an additive to lube oil base stocks can reduce the cloud point of the base stocks by as much as 15°C. These tests were carried out at concentrations as low as 500 ppm. Recently, two interesting applications have been found in waste minimisation:

• In the production of polyethylene a large amount of by-product wax is formed. This wax is normally treated as a waste product and disposed of in the usual manner (paying a disposal company to haul the by-product away). One large petrochemical company has found that, by mixing the by-product wax with 505-SD in concentrations as low as 0.5% and dispersing this mixture into fuel oil, they gain a new, inexpensive source of plant fuel (i.e. boiler feedstock). A more detailed article on this application will appear at a later date.
• Its second application, waste minimisation, is the subject of this article.

A tank cleaning contractor in Louisiana, Rubark Industrial Services (RIS), has developed a two step process whereby sludge emulsions from API separators at refineries and slop oil emulsion sludge tank bottoms from crude oil terminal tanks can be demulsified into three phases (an oil, wax and asphaltenes phase; a water phase, and a solid phase). Using Avron 505-SD and a demulsifying activating catalyst (Avron A-1000), emulsions from crude oil sludge bottoms have been broken. Recoveries of 95 to 99% of available hydrocarbon in the emulsion sludge oil have been observed using the RIS process. The oil recovered is usually wax, asphaltenes, and the heavy oil fractions.

The purpose of A-1000 is to activate the demulsification properties of 505-SD. Both of these are proprietary products and patents are presently pending on each; a patent has been applied for on the RIS separation process. In general terms the demulsification process is per- formed in the following manner;

• Step 1: Sludge emulsion from a crude oil slop tank is treated at elevated temperatures (ranging from 45 to 90°C) with a calculated amount of 505-SD, ranging from 1000 to 5000 ppm. The concentration used is temperature dependent.

• Step 2: An equal amount of water (based upon the amount of sludge emulsion used) is heated to the same temperature as the sludge emulsion in a second reactor. To this water solution is added an amount of A-1000 equal to 3 times the amount of 505-SD used (for example, if 1000 ppm of 505-SD were used, then 3000 ppm of A-1000 would be required). The quality of the water used is not limited to plant process water; tests have shown that effluent water from the demulsification process is acceptable for this purpose. Tests have also been per- formed using seawater (1.4% salt) and mixtures of sea- water and demulsification effluent water as process water in the separation process with excellent results.

• Step 3: When both mixtures have reached the same temperature and equilibrated for a period of at least 20 minutes, the water mixture is added to the sludge emulsion mixture continuously for a period of 30 minutes. At 50°C the emulsion break occurs in 30 to 40 minutes. At higher temperatures the emulsion breaks instantaneously.

• Step 4: After the emulsion is broken the two layers form.  The oil layer, consisting of wax, asphaltene and heavy crude, is separated from the mixture by pumping it out of the mixing reactor at a temperature above the wax melt temperature and into a tank containing light crude, or any crude that is present on site. In some cases heavy crudes have been used as the diluent. In one case, light cycle oil (LCO) and another middle distillate was used as the hydrocarbon diluent.

• Step 5: The light crude and the waxy recovered oil are mixed and allowed to cool down to ambient temperature.

The authors have found that the final blend of light crude oil and recovered oil is stable for periods as long as twelve months (no wax or asphaltene separation). The lower layer of water can be sent to the plant water treatment facility. The suspended solids (iron oxide, silica and other inorganics) are allowed to separate and are hauled to a disposal site.

The following test cases will illustrate in detail how the physical separation occurs. These examples are tests that were performed under varying conditions in the laboratory'.

Tank bottom emulsion sludge

The source of the sludge described in all case studies given below was from a tank designated as T-.101'. The sludge emulsion residues in tank T-101 had been in the tank for 6 to 7 years or more.

Water source

Effluent water from an earlier treatment was used as the water reactant. This water had a pH of 3.5 to 4.0. Unless specifically mentioned, all water used in these studies is effluent from previous treatments of sludge from tank T-101.

Case study one

• Step 1: 200 ml of oily emulsion sludge from T-101 was placed in a 400 ml glass beaker and heated to between 85 and 90°C with mixing (a magnetic stirring rod was used as the method of mixing). To the 200 ml of sludge was added 0.5 ml of 505-SD (0.25%) by volume of sludge emulsion treated. The mixture of sludge emulsion and dispersant was heated and mixed continuously for a period of 15 minutes.

• Step 2: 200 mi of water (effluent water from tank 1, the reactor tank used for treating previous batches of T-101 emulsion sludge) was heated to 85 to 90°C with mixing (a magnetic stirring hot plate was used as the mixing and heating mode). When the temperatures of the water reached 85°C, 2 ml of A-1000 was added. The mixture was allowed to continue mixing for an addition- al 10 minutes.

• Step 3: After both mixtures had been heated and stirred for a period of 10 minutes at 82 to 85 oC, the beaker containing the 200 ml of water and A-1000 was added to the beaker containing 200 ml of sludge emulsion and 505-SD. Immediately upon addition of the water/A-1000 solution to the sludge emulsion/505-SD mixture a sep- aration occurred. The initial solution separated into three layers: a black upper layer of oil, a brownish mid- die layer of water, and a dark brown lower layer of solids dispersed in the water.

• Step 4: After the three layers had cooled to 75°C, 50 ml of light crude was added to the mixture (400 ml of treated material). The blend of light crude, water, and demulsified sludge plus chemicals was heated up to 80°C and stirred for an additional 10 minutes. The total blend was allowed to cool to room temperature. At room temperature, two distinct layers were formed: the upper layer of light crude plus recovered hydro- carbon and a lower layer of water plus solids dispersed in the water. As the temperature reached room temperature (25°C) the solids began to settle out of the water.

The separation level of water and oil was as follows:

Total oil recovered = 215 ml
Less light crude added = 50 ml
Net amount of oil recovered = 165 mI
Percentage of oil recovered = 82.5%

In this example the ratio of light crude to recovered sludge crude is 0.3 to 1.0. In terms at barrels of light crude oil used to barrels of crude oil recovered the ratio is 0.3 bbls of light crude to 1.0 bbls of recovered emulsion crude.

Analysis of the crude oil blend

A sample of the final crude oil blend was sent to the terminal laboratory for testing. The two tests of interest were the BSRW (ASTM D4007-B1) and pour point (ASTM D97- 96a). The following results were obtained on the final crude oil blend:

Result                                    Acceptable limit
BS&W = 0.00%                    <2.00%
Pour point = 10°C               <15°C

* The acceptable limit is the standard set by the terminal for export grade crude oil.2

Case study two

• Step 1: 200 ml of oily emulsion sludge from T-101 was placed in a 400 ml glass beaker and heated to between 88 and 90°C with stirring (a magnetic stirring rod was used as the method of mixing). Ta the 200 ml of sludge was added 0.25 ml of 505-SD (0.25% by volume of sludge emulsion treated). The mixture of sludge emulsion and 505-SD was heated and mixed continuously for a period of 15 minutes.

• Step 2: 200 ml of water (seawater, salt content 1.4%) was heated to 85°C with mixing (a magnetic stirring hot plate was used as the mixing and heating mode). When the temperature of the water reached 85°C, 2 ml of A- 1000 was added. The mixture was allowed to continue mixing for an additional 10 minutes.

• Step 3: After both mixtures had been heated and stirred for a period of 10 minutes at 80 to 85°C, the beaker containing the 200 ml of sea water and A-1000 was added to the beaker containing 200 ml of sludge emulsion and 505-SD. Immediately upon addition of the water/A-1000 solution to the sludge emulsion/505-SD mixture a separation occurred. The initial solution separated into three layers: a black upper layer of oil, a light brownish middle layer of water, and a lighter brown lower layer of solids dispersed in the water.

• Step 4: After the three layers had cooled to 75°C, 50 ml of light crude was added to the mixture (400 ml of treated material). The blend of light crude, sea waters, and demulsified sludge plus chemicals was heated up to 80°C and stirred for an additional 10 minutes. The total blend was allowed to cool to room temperature. At room temperature, two distinct layers were formed: the upper layer of light crude plus recovered hydro- carbon and a lower layer of water plus solids dispersed in the water. As the temperature reached room temperature the solids began to settle out of the sea water mixture.

Using seawater as the water medium resulted in a much faster break of the emulsion and a cleaner water layer. As expected, the presence of seawater increases the speed at which the emulsion breaks.

The yield of oil recovered was as follows:
Total oil recovered = 140 ml
Less light crude added = 50 mI
Net amount of oil recovered = 90 ml
Percentage of oil recovered = 45%

In this example the ratio of light crude to recovered sludge crude is 0.5 to 1.0. In terms of barrels of light crude oil used to barrels of crude oil recovered the ratio is 0.55 bbls of light crude to 1.0 bbls of recovered emulsion crude.

Analysis of the crude oil blend

A sample of the final crude oil blend was sent to the terminal laboratory for testing. The two tests of interest performed were the BS&W (ASTM D4007-B1) and pour point (ASTM D97-96a). The following results were obtained:

Result	Acceptable limit
BS&W = 0.00%	<2.00%
Pour Point = 10°C	<15°C

*The acceptable limit is the standard set by the terminal for export grade crude oil2.

Laboratory experiments were repeated using mixtures of T-101 effluent water and seawater at different ratios. In all cases the sludge oil emulsion broke instantaneously. Initially the emulsion separated into three layers; after cooling down to 70 to 75°C, two distinct layers resulted.

Tests performed at lower temperatures such as 45 to 60°C paint to a lowering in the rate at which the emulsion breaks. Tests made under the same conditions as those described in Case Studies 1 and 2 but performed at these lower temperatures (45 to 60°C) took up to 40 minutes until a satisfactory break in the emulsion occurred.

Pilot plant batch test

In order to evaluate the commercial value of 505-SD and A-1000 a test was performed on the job site. At the job site the contractor treating the sludge emulsion from tank T-101 was asked to test the chemicals on a larger scale operation. In the past the best results the contractor had obtained using other manufacturers' chemicals were an emulsion break time of 24 hours and an oil recovery rate of not more than 30%. The contractor normally operated the treatment tanks at 85 to 90°C. This presented an excellent opportunity to evaluate the products.

A field test was carried out at the T-101 treatment area using 505-SD and A-1000 as fallows. The amount of T-101 sludge emulsion to be treated was 90 bbls.

The following process was utilised: the two reactor sys- tem used in the laboratory with success was used on site. The following procedure was used: two tanks located side by side on the site were used as reactors. Each tank had a maximum capacity of 250 bbls. Since a limited amount of the Avron chemicals were available (two 55 gallon drums of 505-SD and two 55 gallon drums of A-1000) it was decided to test 100 bbls of T-101 emulsion sludge. The two tanks used were T-10 and T-12. Mixing was by aeration and circulation was by pump. The heat source was steam coils, the source of the steam was an onsite mobile boiler.

• Step 1: Into tank T-12 was pumped 90 bbls of T-101 emulsion sludge residue. Prior to adding the 90 bbls of T-101 sludge, there were 10 bbls of water (effluent process water from an earlier run) at the bottom of the tank. One advantage in having the 10 bbls of effluent water in T-12 is that the water acts as a heat transfer medium and helps transfer the heat from the steam coils to the sludge. The sludge emulsion was heated for a period of 3 hours, the time it took to reach 80°C and equilibrate for a reasonable period. After T-12 reached 80°C, 10 gallons of 505-SD was added to the tank. The tank was mixed by recirculating the liquids present with a Wilden pump and by introducing air through an overhead aeration pipe.

• Step 2: Into tank T-10 was pumped 100 bbls of water (effluent water from previous batch runs) and heated in a manner similar to that used to heat tank T-12. After T- 10 reached 80°C, 32 gallons of A-1000 was added and allowed to mix in a manner similar to that used in tank T-12. After addition of chemicals both tanks T-10 and T- 12 were heated for an additional hour.

• Step 3: After tanks T-10 and T-12 were heated far an additional 1 hour, the contents of tank T-10 (effluent water plus A-1000) were pumped into tank T-12 (a mixture of water, emulsion sludge and 505-SD). The resulting mixture was allowed to mix and circulate through the tank for an additional hour.

The sampling of the final mixture began immediately after mixing followed by four additional samples taken every 15 minutes. The sample obtained immediately after mixing the contents of tank T-10 into tank T-12 required approximately 5 to 10 minutes before a good break in the emulsion occurred. All samples taken after that time gave an immediate break in the emulsion and on standing resulted in a two phase separation (an upper layer of oil and a lower layer of water plus suspended solids).

The separation into two layers of oil and water resulted in the following amounts of recovered oil (wax, oil, and asphaltenes) and water.
Oil layer = 60 bbls
Water + sediment = 140 bbls
Oil recovery rate = 66.6%
The recovered 60 bbls of oil was blended with 60 bbls of terminal light crude. The resulting blend of 120 bbls was sampled for testing in the terminal's analytical laboratory. The results are listed in Table 1.

Cost comparisons and economics

The recovery of 66% of the available hydrocarbon in the emulsion sludge presents a real challenge to the petroleum industry. It is important to note that the economics of the recovery of this oil from the sludge work in the favour of the oil producer in three ways:

The cost for disposal of the waste emulsion sludge is reduced immensely. Since the emulsion sludge is considered a hazardous waste the reduction in the quantities requiring disposal lowers the oil producer's overall cost by as much as 95%. The only wastes to be disposed of are the solids at the end of the process. These savings can be enormous depending upon the producer's location.

• The recovery of good crude that has a market value of at least US$20 to 25/bbl represents a good return to the producer. In this arrangement a plant recovering 10 bbls of oil (waxy) can now blend these 10 bbls with 10 bbls of good crude oil and the result will be 20 bbls of finished, blended product that has an overall cost af at most US$15/bbl of recovered oil. Based upon the total amount of oil sold the cost calculates out to US$ 7.50bbl. The final return overall, on the basis of 2 bbls of crude sold, gives the producer a profit of over two times his original cost (using US$ 25/bbl). For example, if a terminal processes 500 bpd in their ETP (emulsion treatment plant) and recovers 70% as saleable oil, their profit (at US$ 25/bbl) could be as much as US$ 5000 based on a chemical usage of 0.5%.

• The third, and most important, advantage to using these chemicals arises from never again having to cope with the problem of paraffin wax and Asphaltene separation. The ability of 505-SD to disperse paraffin wax in crude oil produces a tremendous advantage in future sales in that the wax separation problem is solved permanently (for at least 12 months). The bases for this last statement are not only the stability tests observed by various clients but also the laboratory results. The fact that a BS&W (bottoms, sediment and water) value of 0.00% has been attained through the use of this chemical is a major benefit to the petroleum industry.

Conclusion

The purpose of waste minimisation is to lower the amounts of hazardous and non-hazardous materials that have to be disposed of in an industrial environment. The fact that a process and a product now exist that give the industry (at least, the petroleum and petrochemical industries) a method to reduce waste, and at the same time make money from waste that it would normally have to pay to dispose of, is a major break- through in both economic and environmental terms. Probably the most important result of these tests is that, for the first time in the history of the petroleum industry, a BSRW of 0.00% has been achieved. This opens many new frontiers in the utilisation of wax and sludge oil waste deposits that in the past were regarded as a worthless, non-valued resource.

Acknowledgements 

The authors wish to thank Mr. F.P. Heisler, Jr., for assisting in the assembling, formatting, and arranging of the information described in this article; Mr. F.P. Heisler, Sr., for all of his support; Mr. Robert Herry, Lab Supervisor, Sabah Shell Petroleum, Ltd., Labuan Crude Oil Terminal (L.C.O.T.): the employees of ESP who conducted the pilot plant batch tests; and Mr. Marcel Degaldi ot 2MC SDN. BHD who arranged for the delivery of the Avron chemicals needed to conduct the pilot plant tests.

References

1.     Labuan Crude Oil Terminal (LCOT), Sarawak Shell Berhad, Sabah Shell Petroleum Co., Ltd., Labuan, F.T., East Malaysia, Laboratory facility, Labuan
2.    Specification for export oil at LCOT, Labuan Crude Oil Terminal, Labuan, F.T., East Malaysia
Enquiry no: 27