Oilfield Produced Water Treatment by Coagulation ...

The Second Conference of Post Graduate Researches (CPGR'2017) College of Engineering, Al-Nahrain Univ., Baghdad, Iraq - 4th Oct. 2017

Oilfield Produced Water Treatment by Coagulation /Flocculation Processes Khalid M. Mousa Chemical Eng. Dep. Nahrain University [email protected]

Ali. A. Al-Hasan Chemical Eng. Dep. Nahrain University [email protected] dispersed fine oil particles being converted into large agglomerated flocks can be separated from water due to sedimentation and filtration [7]. This method has a preference in the primary purification processes mainly due to the ease of operation, cost effective, high efficiency , also, it uses less energy than alternative treatment [8]. Essentially, coagulation is divided in two categories, according to their application: Aluminum salts (alum) and Ferric salts. These compounds often produce good coagulation when conditions are too acidic for best results with alum. Sometimes the particles are best removed under acidic conditions with iron, at around neutral pH, ferric has limited solubility, because of the precipitation of an amorphous hydroxide, which can play a very important role in practical coagulation and flocculation processes. Positively charged precipitate particles may deposit on contaminant particles (hetero coagulation), again giving the possibility of charge neutralization [9]. Many researchers studied the coagulation /flocculation process on waste water treatment. N. D. Tzoupanos et al.; 2008 show that the implication of coagulation – flocculation in the area of water and wastewater treatment is studied and evaluated, emphasizing on the sequence of requests employed [10]. Sawain et al.; 2009 investigated the effect of pH by acids adjustment and using coagulant and coagulant aid in combination with pH control on grease and oil removal in wastewater from biodiesel process. [11]. Santa et al.; 2010 investigated the assessment of the coagulation/flocculation of produced water, using seeds of Moringa oleifera Lam. as coagulant and study the interaction of coagulant agent with the other components of the Synthetic Produced Water. [12]. Hamidreza et al.; 2012 studied the probability of using poly aluminum chloride instead of ferric chloride in petrochemical wastewater treatment [13]. Zawawi et al.; 2015 studied the efficiency of coagulation and flocculation processes for eliminating suspended solid (SS), COD ,color and oil and grease from biodiesel wastewater [14]. Mousa et al.; 2016 was used three coagulant materials. Klaraid CDP1326, klaraid PC1195 and klaraid IC1176 and Zetag8140 as flocculent material The results showed that klaraid CDP1326 had superior efficiency in removing turbidity compared with other coagulants at the same conditions and the

Abstract In this work ferric sulphate and klaraid CDP1326 were used as the coagulant, and polyelectrolyte (polyacrylamide) as the flocculant as first step to treatment the oily water produced from ALAhdab oil field. The addition of coagulant and flocculant led to the optimal elimination of total suspended solids and oil content. It was found that the oil removal reached 86% when using 30 mg/L ferric sulphate and 2.5 mg/L polyacrylamide and the oil removal reached 84.4% when using 60 mg/L klaraid CDP1326 and 2.5 mg/L polyacrylamide at pH = 6.86 and room temperature (25 oC). Generally ferric sulphate is high ability to adsorb oil and suspended solids from produced water, additionally, reduces the economic cost of water treatment. Keyword: produced water, oil/water separation and coagulation and flocculation treatment.

1.

Introduction

Produced water is the huge volume by-product or waste stream related with oil and gas exploration and production. It is the water found in the same constructions as oil and gas in the fields [1]. The physical and chemical properties differ significantly depending on the type of hydrocarbon product being produced, the geological formation from where the water was produced and the location of the field [2] .The oily wastewater is generated by various oil fields, oil refineries, petroleum industries, chemical and metal working plants, petrochemical plants, oil terminals during washing of storing tanks [3]. Produced water is very complex and can include several thousand compounds that differ in concentration between wells and over the lifetime of a well. [4].Treatment is necessary before disposal, treatment of these effluents may result in improved oil /water separation, oil recovery, improved water quality, water reuse, protection of downstream facilities and environmental permit compliance [5,6].The most common treatment methods for treating produced water are sedimentation, centrifugal separation, coagulation and flocculation, sorption, flotation, filtration ultra-filtration, and reverse osmosis. These methods can be used separately or in combinations [6]. One of the effective methods of oil removal is coagulation. In this process,

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(CPGR'2017) College of Engineering, Al-Nahrain Univ., Baghdad, Iraq Mousa& Al-Hasan, pp.75-79

best turbidity removal was achieved [15]. Zawawi et al.; 2016 stated that the coagulation and flocculation is a valuable method as a pretreatment of biodiesel wastewater. [16]. This study interested on removal suspended solid pollution and oil content from produced water using coagulation -flocculation treatment, studying the capacity of two coagulant materials (klaraid CDP1326, and ferric sulphate) and polyelectrolyte polyacrylamide flocculent material.

turbidity (210 NTU). Different doses of coagulants (10, 20, 30 and 40) ppm from ferric sulphate, (15,30,45 and 60) ppm from klaraid CDP1326 and flocculent (1,1.5,2,2.5 and 3) ppm from polyacrylamide reagent were added to the beaker. The beaker was agitated at various mixing time and speed, which consists of fast mixing (120 rpm) after added coagulant for 2 minutes and slow mixing (50 rpm) after added flocculant for 20 minutes. After the agitation being stopped, the suspension was allowable to settle for 20 minutes. Lastly, a sample was withdrawn using a pipette from the top of supernatant to analyze for turbidity and oil content in the produced water.

2. Materials and Methods 2.1Chemicals FeSO4-7H2O (India 99 % purity), H2SO4 (SDFCL 98 % purity) and Sodium hydroxide (Thomsas Baker). Two coagulant materials used in the study are: klaraid CDP1326 is a powerfully cationic, high charge and molecular weight, liquid coagulant. Its chemical name is N, N-DimethylN2.propenyl2propen1amoniumchloridehomopolym erize, ferric sulphate (25%) and Ferric sulphate is a powerfully cationic, high and molecular weight solid coagulant. The polyelectrolyte (C3H5NO) n (France (99%). It is high molecular weight polyacrylamide with a bulk specific gravity of approximately 0.6, while its grade of charge varies from low to medium to high.

3.2 Turbidimeter Sample analyses After using magnetic stirrer, Pipet water out of the beaker and place it in a sample tube, making sure that no air bubbles are present in the sample. Place the sample tube in a calibrated turbidimeter and read the turbidity.

3.3 Determination of oil concentration using UV-spectrophotometer 0.25 gm of NaCl was added to 50 mL produced water in the separating funnel in order to break the emulsion of oil. 5 ml of carbon tetra chloride was added and followed by vigorous shaking for 2 min. After 20 min, when the solution separated into two distinct layers, the lower (organic) layer was taken for the absorbance measurement, and from the calibration curve, concentration of oil was obtained.

2.2 Produced water Produced water samples were collected from Al-Ahdab oil field at Wassit governorate, Iraq. Table 1 shows the properties of the produced water used in this study. Table 1: - Properties of the produced water used in this study Parameter

value

Oil

422.8667 (mg/l)

Turbidity

210 NTU

pH

6.86

Solution oxygen content

0.07 (mg/l)

Specific gravity

1.046

conductivity

172500 μs/cm

TDS

110400 (mg/l)

4. Results and Discussion 4.1 Analytical Analysis The percent of oil removal in produced water was determined through the following equation (1): − C treated C η = initial x100% C initial where η, percentage of oil removal; Cinitial, measured concentration before the treatment (mg oil/L); Ctreated, concentration value after treatment (mg oil/L).

4.2 Comparison of Different Coagulants To find out the best coagulant that can be used to reduce turbidity to the allowable level for produced water, series of experiment were conducted. The value of turbidity varies with the colloid concentration in produced water, it could be used as the indicator of oil residual in produced water[11]. The turbidity of produced water used in this study is 210 NTU, a two substance of coagulants were used, which are ferrous sulfate and klaraid CDP1326 to reduce the turbidity to

3. Experimental work 3.1Dosage of coagulant and flocculent Coagulation-flocculation experiments were performed in a beaker of 250 mL capacity with Magnetic stirrer apparatus. The beaker was filled with 150 mL of produced water with identical

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the permitted value. It is well known that the performance of coagulant may change from produced water to another[8]. Figures 1 and 2 show the comparison between the ferrous sulfate and klaraid CDP1326 using 10 and 20 ppm of them and different polyacrylamide dose in the range 1-3 ppm.

dose in the range (1-3 mg/L) was used of polyacrylamide as shown in Figs. 3 and 4. Coagulant dose also gives the impression to have an impact on turbidity as can be seen in Fig.3. The coagulant dose (30 mg/L) of ferric sulfate gave better turbidity removal (up to 17.3 NTU) than the lower coagulant dose (10 mg/L; up to 39.9 NTU) through flocculant dose 2.5 mg/L, pH =6.86 in room temperature.

Figure 1 The effect of ferric sulphate and klaraid CDP1326 on turbidity.

Figure 3 The effect of ferric sulphate and flocculent dosage on turbidity. The coagulant dose (60 mg/L) of klaraid CDP1326 gave better turbidity removal (up to 21.5 NTU) than the lower coagulant dose (15mg/L; up to 66.8 NTU) and flocculant dose 2.5 mg/L, pH=6.86 in room temperature as shown in Fig. 4. This may well approve with the zones of coagulant dose recommended by Duan and Gregory.,2003 [18]. The low dose of coagulant possibly will have just been sufficient enough to provide charge neutralization for coagulation to occur.

Figure 2 The effect of ferric sulphate and klaraid CDP1326 on turbidity. The main purpose of this step was to confirm the existence of a point of maximal efficiency of coagulant in the suspensions. After the concentrations were well-known and tested, ferrous sulfate could observe that the same concentration of klaraid CDP1326 provided the best percentage of turbidity for the emulsion [12].

4.3 Effect of different Dose of Coagulant and Flocculant on Turbidity

Figure 4 The effect of klaraid CDP1326 and flocculent dosage on turbidity.

The dosage was one of the most important parameters that be used to determine the best condition for the performance of coagulant and flocculent in primary treatment. Mostly, insufficient amount or overdosing would result in the poor performance in coagulation/flocculation treatment. Consequently, it was critical on the way to determine the optimum dosage in order to lessen the dosing cost and obtain the optimum performance in treatment [17]. To estimate the effect of coagulant and flocculant dosages on turbidity of produced water, different coagulants were used ferrous sulfate in the range (10-40 mg/L) and different dose of klaraid CDP1326 in the range (15- 60 mg/L), different of flocculant

Figures 3 and 4 showed that, coagulant combining with a flocculant, these combinations increased the removal of turbidity with the increasing of dosage except 30 mg/L of ferrous sulfate, 60 mg/L of klaraid CDP1326 and 3 mg/L of polyacrylamide for both coagulants. The turbidity increased graduated to 21.5 and 28.1 NTU respectively. This singularity could be illuminated based on the charge of density. If compared to the other coagulants, the charge density of coagulant is high. Furthermore, polymer adsorption increased when the charge density of the polymer increased. Consequently, this signifies the rapid destabilization of the

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particles. In another word, it can be well-defined as ferric sulphate and klaraid CDP1326, a coagulant which has a high charge density need less quantity of the coagulant to destabilize the particles [19]. Adding 40 mg/L of ferrous sulfate, the oil removal is increased and the turbidity is increased. the coagulant amount rise, remaining turbidity reduced until reaching the smaller value at the finest coagulant quantity, then the enlarged due to high positive charge results from higher coagulant dose add [13,15].

mg/L, the oil removal is increased to 93.77% while the turbidity is increased to 28.1NTU as shown in figure previously. Figures 5 and 6 shows that the removal efficiency of oil increases with coagulation and flocculation does Increases [6]. Thus, the amount of coagulant and flocculent indicated rest on the turbidity of produced water, therefore, it was key to determine the optimum dosage so as to minimize the dosing cost and obtain the optimum performance in produced water treatment [21].

4.4 Effect of different Dose of Coagulant and Flocculent on Removal Efficiency The optimal dose of a coagulant or flocculant is well-defined as the value overhead or lower which there is no significant change in the increase in efficiency of removal with a further addition of coagulant or flocculant [17]. Inorganic coagulants are frequently based on multivalent cations such as (ferrous or ferric). This positive charge of molecules relates with negatively charged particles of produced water to assist in charge aggregation [20]. With the aim of improving the effectiveness of coagulation in other cases (e.g., at lesser coagulant doses), the polyacrylamide was added [7] . The amount of flocculant was varied from 1 to 3 mg/L and the ferrous sulfate dose was made constant of concentration in the range (10-40) mg/L. In order to determine the optimal dose of the polyacrylamide and the percentage removal of oil was measured. From these results below in Fig.5, the good ability of specific ferrous sulfate to reduce oil removal in produced water is demonstrated, in that way the ability of adding 30 mg/L of ferrous sulfate and 2.5 mg/L of polyacrylamide removal oil increased to 86 %, after increasing the flocculant dosage to 3 mg/L, the oil removal is increased to 97% while the turbidity is increased to 23.1 NTU as shown in figure previously.

Figure 6 The effect of klaraid CDP1326and flocculant dosage on oil removal.

5. Conclusion The ability of ferric sulphate on remove oil increased after adding different coagulant ratios especially with both ferric sulphate and polyacrylamide or klaraid CDP1326 and polyacrylamide. The highest removal efficiency of ferric sulphate / polyacrylamide is 86% at (30 mg/L ferric sulphate, 2.5 mg/L Polyacrylamide) and the highest removal efficiency of klaraid CDP1326 / polyacrylamide is 84.4% at (60 mg/L klaraid CDP1326, 2.5mg/L Polyacrylamide). Generally ferric sulphate is characterized significantly by its high ability to adsorb oil and suspended solids from produce water.

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Figure 5 The effect of ferric sulphate and flocculent dosage on oil removal. Figure 6 shows the results when using klaraid CDP1326 as coagulant and found that when adding 60 mg/L of klaraid CDP1326 and 2.5 mg/L of polyacrylamide removal oil increased to 84.4%, after increasing the flocculant dosage to 3

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