Refinery Wastewater Treatment

College of Engineering

Refinery Wastewater Treatment: A true Technological Challenge Farid Benyahia, Department of Chemical and Petroleum Engineering, E-mail: [email protected] Mohamed Abdulkarim and Ahmed Embaby, Department of Chemical and Petroleum Engineering Madduri Rao, Department of Chemistry U.A.E. University, Al-Ain, P.O. Box: 17555, U.A.E. Abstract Crude oil and condensate refineries generate a large amount of wastewater that has both process and non-process origins. Depending on the type of crude oil, composition of condensate and treatment processes, the characteristics of refinery wastewater vary according to a complex pattern. The design and operation of modern refinery wastewater treatment plants are challenging and are essentially technology driven. In this investigation, the sources of wastewater pollutants have been traced to specific sources and operations, and suitable treatment technologies identified. Modern powerful tools such image analysis have been employed to characterize oil droplet sizes in oily wastewater and immobilized cell technology considered in biological reactor design for wide spectrum chemical pollutant degradation. A biomass extraction method was developed to harvest Pseudomonas P. and Baccili S. cells from a commercial biological product and acclimate them to a source of carbon rich in phenol, prior to immobilizing them in a suitable gel.

1. INTRODUCTION The petroleum refining industry converts crude oil into more than 2500 refined products, including liquefied petroleum gas, gasoline, kerosene, aviation fuel, diesel fuel, fuel oils, lubricating oils, and feedstocks for the petrochemical industry. Typically, petroleum refining activities start with receipt of crude oil for storage at the refinery, include all petroleum handling and refining operations, and they terminate with storage prior to shipping the refined products from the refinery. The petroleum refining industry employs a wide variety of physical and chemical treatment processes. A refinery processing flow scheme is largely determined by the composition of the crude oil feedstock and the chosen final petroleum products. Typical processing and auxiliary units in refineries are presented below [1]: 1. Separation processes a. Atmospheric distillation b. Vacuum distillation c. Light ends recovery (gas processing) 2. Petroleum conversion processes a. Cracking (thermal and catalytic) b. Reforming c. Alkylation d. Polymerization e. Isomerization f. Coking g. Visbreaking 3. Petroleum treating processes a. Hydrodesulfurization b. Hydrotreating c. Chemical sweetening d. Acid gas removal e. Deasphalting 4. Feedstock and product handling a. Storage b. Blending c. Loading d. Unloading 5. Auxiliary facilities a. Boilers b. Wastewater treatment c. Hydrogen production d. Sulfur recovery plant Large volumes of water are employed in refining processes, especially for cooling systems, distillation, hydrotreating, and desalting. Tank drains, equipment flushing, surface water runoff and sanitary wastewaters are also generated. It is therefore clear that refinery wastewater can be broadly categorized as process or nonprocess wastewater. In most modern refineries, these different wastewaters are channeled in separate sewer systems. At least two different independent sewers exist in most petroleum refineries: one that handles storm water and surface runoff and another that handles all process water and water produced from utilities units. However, in most efficient refineries, process water sewers are usually split in more than one sewer depending on the nature of wastewater, thus reducing the load on the wastewater treatment plants, increasing

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The Seventh Annual U.A.E. University Research Conference

College of Engineering the efficiency of each treatment unit and broadening the possibilities of wastewater reuse in different refining units. Clearly, there is no universal approach to handling and treating refinery wastewater streams. The quantity of wastewaters generated and their characteristics depend on the process configuration. As a general guide, approximately 3.5–5 cubic meters (m3) of wastewater per ton of crude are generated when cooling water is recycled. Refineries generate polluted wastewaters, containing biochemical oxygen demand (BOD) and chemical oxygen demand (COD) levels of approximately 150–250 milligrams per liter (mg/l) and 300–600 mg/l, respectively; phenol levels of 20–200 mg/l; oil levels of 100–300 mg/l in desalter water and up to 5,000 mg/l in tank bottoms; benzene levels of 1–100 mg/l; benzo(a)pyrene levels of less than 1 to 100 mg/l; heavy metals levels of 0.1–100 mg/l for chrome and 0.2–10 mg/l for lead; and other pollutants. Refineries also generate solid wastes and sludges (ranging from 3 to 5 kg per ton of crude processed), 80% of which may be considered hazardous because of the presence of toxic organics and heavy metals [2]. Given the complex and diverse nature of refinery wastewater pollutants, a combination of treatment methods is often the norm before discharge. Therefore separation of wastewater streams, such as storm water, cooling water, process water, sanitary, sewage, etc., is essential for minimizing treatment requirements.

2. OILY WASTEWATER TREATMENT TECHNOLOGIES Knowledge the oil droplet size distribution in refinery wastewater is paramount to understanding the wastewater behavior in an oil/water separator [3,4]. This size distribution is crucial for determining the proper oil/water separation system and its efficiency. Oil and grease present in the wastewater generated in the oil processing industries can be removed by various established or novel techniques. Many researchers tried to divide the oil droplets size spectrum and then propose an appropriate treatment technique for each section. The diagrams shown in Figure 1 represents such classifications.

Fig. 1: Oily water treatment techniques as a function of oil droplet sizes [5]. On a general basis, and in order to obtain an effluent that meets the current EPA (fairly stringent) effluent discharge guidelines, a refinery wastewater treatment plant should contain at least the units depicted in Figure 2. It should be stated that the configuration shown in Figure 2 is very basic and by no means definitive or complete.


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Fig. 2: Typical refinery oily wastewater treatment stages [6]. If a complete wastewater treatment plant that comprises the three treatment stages, namely primary, secondary and tertiary, is in operation, then we can achieve an effluent that can be recycled and if a reverse osmosis unit is supplemented, the treated wastewater can be reused in processing units. Removal efficiencies can reach 90-99 % of all wastewater parameters; COD, BOD, O&G, BTEX, SS, NH3, Heavy metals [7]. Since this project is in association with TAKREER (end user), and the objectives aim at developing wastewater treatment technologies that would enable recycling wastewater, a brief description of the refinery and its current wastewater system will be presented in the next sections.

3. RUWAIS REFINERY OVERVIEW 3.1 History and Processes Ruwais Industrial Complex was officially inaugurated in 1982. Soon after commissioning the original 120,000 barrels per day (bpd) Hydro skimming refinery in June 1981, plans were drawn up to add a 27,000 bpd Hydro cracker complex that was started in 1985. To consolidate operations, the General Utilities Plant, set up in 1982 to provide electricity and water for the area, was merged with the Refinery in 1986. A central Sulphur Handling and Granulation Plant was established in 1991 to handle all the liquid Sulphur recovered in the GASCO and ADGAS Natural Gas Liquefaction facilities. After its expansion in early 2001, the granulation capacity, at 7,650 tons per day, has become one of the largest in the world. Two 140,000 bpd condensate-processing trains were commissioned in year 2000-2002 to process condensate produced in the on-shore gas fields of Abu Dhabi. Currently these are two of the largest such condensate splitters in the world. Meanwhile, support facilities such as berths, power generation and water production facilities continued to be expanded to meet the growing needs of the industrial area. Today the range of refined products includes Liquefied Petroleum Gas, Premium Unleaded Gasoline (98 Octane), Special Unleaded Gasoline (95 Octane), Naphtha grades, Jet-A1 and Kerosene grades, Gas Oil grades, Straight run Residue, Bunker grades 180 and 380 cst and Granulated Sulphur. 3.2 Wastewater Treatment Plant The wastewater treatment facility in the Ruwais refinery belongs to the "Oil Movement Department". Figure 3 shows a schematic diagram of the complete water treatment plant and associated ancillary equipment. The wastewater treatment plant receives oily wastewater streams from the following three refinery sewer channels: § Existing Refinery Oily Water Sewer System § New Oily Sewer System § New Accidental Oily Sewer System

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Fig. 3: Ruwais refinery wastewater treatment flow diagram. These sewer channels are fed with wastewater from several sources: crude and condensate refining units, flare systems, crude oil storage tanks, laboratory drains and sanitary drains. In the latter source, the drains are fitted with septic tanks to retain solids and the liquid is directed to the sewer. The solids are collected periodically for treatment and disposal. The sewer channels network eventually converge into the mixing sump (247 F1) in the waste water treatment plant. The oily water sump (mixing sump 247 F1) consists of three separate sections, each being provided with a proper inlet pit. The three sections are connected together by bottom slide gates and receive the wastewater according to the following sources and entry point: (1) The wastewater streams from the new refinery (Condensate splitting unit) oily wastewater system, namely: § Accidental oily wastewater streams (AY) originate from the condensate unit and enter the sump 247-F001C. § Oily wastewater streams (SY) originate from the condensate unit and enter the sump 247-F001B. § Wastewater from the new flares and tank farm areas also enter the sump 247 F001B via the SY system. (2) The wastewater streams from the existing refinery oily wastewater system, namely: § Existing Hydroskimmer Unit oily wastewater stream § Existing Hydrocracker Unit oily wastewater stream § Existing tank farm oily wastewater stream § Sanitary and laboratory wastewater stream The streams described above are collected in the existing API separator (currently not in operation in its original function but used for another purpose) inlet pit (47 F 10) and then flow to 247 F001A. The mixing sump (247 F001) includes an oil settling compartment (247 F001E) that collects slop oil which is in turn pumped into tank 247 F003. The wastewater with residual oil from mixing sump (247 F001 A/B/C) is then pumped into the CPI separator (247 V1) where oil separation via coalescing plates occurs. The effluent water flows to water settling tank (247 F002) and the separated oil is recovered and routed to the slop oil settling tank (247 F003).


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College of Engineering Water from the settling tank (247 F002) is directed to two large tanks called "ballast tanks", working alternatively according to the liquid level (F01A/B), then proceeds to the mechanical flotators (V04 A/B) and finally to the final dilution pit (47 F20) that precedes discharge into the marine environment. The mechanical flotators aforementioned are not functional and used simply as a transition stage. The settling tank and ballast tanks have oil skimming weirs that discharge slop oil when a certain liquid level is reached. In the final dilution pit (47 F 20), dilution of discharge water with used cooling sea water occurs in the ratio of around 1:60. Wastewater streams that do not flow through the wastewater treatment unit (in this context, the CPI) are channeled directly to the final dilution pit (47 F 20). These streams are essentially pH adjusted spent caustic streams from LPG and Kerosene sweetening units, as well as spent caustic solutions from the condensate splitting unit. This brief description of the Ruwais refinery wastewater treatment facility indicates that only mechanical treatment followed by high dilution with seawater is employed before discharge into the marine environment. The refinery laboratory conducts routine analysis on samples of treated waste water after the water settling tanks (247 F01A) and possibly in other unspecified locations to ensure discharge compliance limits.

4. OBJECTIVES OF STUDY The objectives of this work include: • Characterization of wastewater generated at the Ruwais refinery, • Evaluation of the current treatment process performance • Design, development and evaluation of alternative treatment processes compatible with project resources. • Laboratory scale tests on the most promising treatment process with a view to improve the current process and enable recycling of wastewater for uses required by the end user, namely TAKREER. The project involves visits to the refinery to collect process data and wastewater samples for analyses. At some stage, wastewater treatment process simulation would play a major role in the advancement of the project, using real plant data from the Ruwais refinery wastewater unit and physical/chemical characteristics of its wastewater. Superpro Designer has been selected as the best simulation tool to conduct the simulation work owing to its rich library of biological process and cost models.

5.

EXPERIMENTAL

5.1 Sampling & wastewater characterization During two consecutive visits to the refinery premises in June 2005, wastewater samples from the wastewater treatment unit (247) were collected. Sampling points are shown in Figure 3 (points A to E). Most of the samples were collected again in a second visit to check the consistency of parameters measured and to verify the stability of the treatment process. Table 1 summarizes the parameters measured. At this stage no BOD/COD measurements were made as these would have required immediate processing and that was not possible at the time of sampling. Table 1: Wastewater analysis parameters. Sample location Code

Unit

A

B

3

177

Design Flow Rate

m /hr

175.5

Average Flow Rate

m3/hr

129

m3/hr

F

F

D

< 0.2

< 0.2

37.7

155

155

155

Max

3

m /hr

290

290

290

Min

mg/l

488

49

33

Max

mg/l

3714

339

124

Min Max

466 3428 306

253

89

Naphthalene

mg/l mg/l µg/l

334

220

< 0.22

Acenaphthylene

µg/l

0.18

ND

1.20

Acenaphthene

µg/l

21.2

7.4

Flourene

µg/l

1.80

114

Flow Rate TPH Oil & Grease

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Min

C

E

12.8

622

< 0.22

29.6

576 218

ND

ND

ND

< 0.18

0.8

< 0.05

< 0.05

0.30

2.60

88.2

0.07

ND

4.10

0.40


College of Engineering Phenanthrene

µg/l

236

164

Anthracene

µg/l

0.40

< 0.05

Fluoranthene

µg/l

34

12.0

Pyrene

µg/l

6.60

6.40

Benzo(a)anthracene

µg/l

19.8

Chrycene

µg/l

ND

Benzo(b)flouranthene

µg/l

ND

Benzo(k)flouranthene

µg/l

< .08

Benzo(a)pyrene

µg/l

0.60

0.20

Dibenzo(a,h)anthracene

µg/l

0.20

Benzo(g,h,i)perylene

µg/l

0.80

Indeno(1,2,3-cd)pyrene

µg/l

0.40

2,4-Dinitrophenol

mg/l

2-Methyl-4,5-dinitrophenol 2,4,6-Trichlorophenol

1.8

0.20

< 0.08

4.20

0.40

0.20

< 0.05

< 0.05

< .05

0.20

88.4

< 0.09

ND

3.20

20.6

46.6

0.10

< 0.05

0.80

< 0.05

17.4

11.4

< 0.05

ND

0.30

< 0.05

41.2

32.4

ND

ND

0.40

ND

0.20

4.00

< 0.10

< 0.10

0.10

< 0.1

0.20

1.60

ND

ND

< .08

ND

0.40

ND

ND

< .05

ND

ND

ND

ND

ND

0.20

ND

0.80

2.80

ND

ND

ND

ND

ND

2.00

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

mg/l

0.02

0.02

0.10

ND

ND

ND

8.98

mg/l

ND

ND

ND

ND

ND

ND

ND

2,4-Dichlorophenol

mg/l

ND

ND

ND

ND

ND

ND

ND

2,4,5-Trichlorophenol

mg/l

ND

ND

ND

ND

ND

ND

ND

Phenol

mg/l

0.20

0.19

0.24

ND

ND

0.17

5.75

m,p-Cresol *

mg/l

0.24

0.24

0.23

ND

ND

0.12

2.95

o-Cresol + 2-cyclohexyl-4,6-dinitrophenol*

mg/l

ND

ND

ND

ND

ND

ND

ND

2,3,4,6-Tetrachlorophenol

mg/l

0.18

0.11

0.32

ND

ND

0.18

0.38

4-Chloro-3-cresol

mg/l

0.06

0.06

0.10

ND

ND

0.07

0.23

2,4-Dimethylphenol

mg/l

ND

0.04

0.14

ND

ND

0.06

ND

o-Chlorophenol

mg/l

ND

ND

ND

ND

ND

ND

ND

2,6-Dichlorophenol

mg/l

ND

ND

ND

ND

ND

ND

ND

o-Nitrophenol

mg/l

0.14

0.11

0.10

ND

ND

0.07

0.09

p-Nitrophenol

mg/l

ND

ND

ND

ND

ND

ND

ND

Pentachlorophenol

mg/l

0.06

0.05

0.07

ND

ND

ND

0.10

Al

mg/l

0.89

0.28

0.09

0.02

0.02

0.05

0.85

As

mg/l

ND

ND

ND

ND

ND

ND

ND

Cd

mg/l

ND

ND

ND

ND

ND

ND

ND

Co

mg/l

ND

ND

ND

ND

ND

ND

1.05

Cr

mg/l

0.03

0.01

ND

ND

ND

ND

0.01

Fe

mg/l

11.7

3.42

0.68

ND

ND

0.97

0.33

Mn

mg/l

0.20

0.09

0.02

ND

ND

0.03