Elsevier

Chemical Engineering Science

Volume 91, 22 March 2013, Pages 122-129
Chemical Engineering Science

Removal of emulsion oil from oilfield ASP wastewater by internal circulation flotation and kinetic models

https://doi.org/10.1016/j.ces.2013.01.020Get rights and content

Abstract

The use of alkali/surfactant/polymer (ASP) in oil exploration results in wastewater from oilfields that is more difficult to treat. In this study, emulsion ASP wastewater was treated using loop-flow flotation technology. The impact of several process variables on the removal rate of oil from wastewater was analyzed, including the concentration of partially hydrolyzed polyacrylamide (HPAM) (0–228 mg/l), temperature (10–40 °C), volumetric flow rate of the flotation gas, concentration of sodium dodecyl benzene sulfonate (SDBS) (5–27 mg/l), and alkali. A collection model was used to determine the oil removal rate. Data gathered using a factorial design revealed that the reactor efficiency was highly dependent on the performance parameters and water quality, especially the alkali/surfactant/polymer (ASP) concentration in the oilfield wastewater. The removal efficiency of the emulsion oil and the rate constant initially decreases when the HPAM concentration CHPAM is below 88 mg/l and above 164 mg/l and is stable for HPAM concentrations between 88 and 164 mg/l. The removal rate of oil greatly improves with the increase in temperature. The removal rate reaches its maximum when the volumetric flow rate of the flotation gas is at 10–15 m3/(h m3). The removal rate decreases continuously with an increase in the SDBS concentration. Because the surfactant increases the stability of the oil droplets, the removal rate decreases continuously with an increase in the SDBS concentration. The oil droplets form floc when HPAM is present in the wastewater. However, the oil droplets do not coalesce and the removal rate does not change with alkali addition. Finally, empirical equations reveal the coded factors for oil droplet removal when alkali/surfactant/polymer exist simultaneously.

Highlights

► Emulsion ASP wastewater was treated based on loop flow flotation and the coarse-graining technology. ► The removal efficiency of the emulsion oil decreases as the HPAM concentration increases. ► The removal rate of the reactor greatly improves with the increase in temperature. ► When the volumetric flow rate of the flotation gas is at 10–15 m3/(h m3), the efficiency is highest. ► Alkaline/surfactant/polymer can react with each other which affect the flotation.

Introduction

For oil exploration in China, chemical enhanced oil recovery operations have become an important means to enhance petroleum recovery. Three types of chemical substances, alkali/surfactant/polymer (ASP), are prepared in an aqueous solution and injected into the stratum in a specific proportion, and the substances can be mined together with crude oil. Although ASP flooding technology has been found to increase oil recovery by over 20% (Li et al., 2000), phenol and phenolic derivatives in petroleum refinery effluents pose a significant threat to the environment because of their extreme toxicity, stability, poor biodegradability and ability to remain in the environment for long periods of time. Thus, there is an urgent need for efficient and economical methods that can remove these pollutants from petroleum refinery effluent (Wang et al., 2011b, Shahrezaei et al., 2012).

Deng and co-workers have previously investigated the properties of oil-in-water emulsions based on the Daqing crude oil. ASP is able to greatly decrease the interfacial tension (IFT) between the water and the oil droplets. Surfactants tend to decrease the oil/water interfacial tension; alkali saponifies indigenous acidic components in the crude mixture, resulting in higher water solubility and lower IFT; and polymers increase the viscosity of the aqueous phase (Deng et al., 2002a, Deng et al., 2002b). These studies have provided insight into the potential problems related to the emulsion stability and the treatment of produced water from ASP flooding (Dalmazzone et al., 2012). Thus, the water produced from ASP flooding forms a complex and stable emulsion system that is more difficult to treat than that formed from water flooding (Foyeke and Diane, 1998, Wang et al., 2011a).

Various separation techniques for oil–water cleaning have been proposed over the last few decades. Shpiner et al. (2009) evaluated the biological treatability of produced water at an HRT of 6 days; Ji et al. (2002) constructed a pilot-scale subsurface flow-constructed wetland in the Liaohe Delta, China, to treat water produced by heavy oil with mineral oil; Wang et al. (2011b) used the ultrafiltration membrane technique to treat synthetic oilfield poly-flooding wastewater.

However, none of these traditional separation techniques meets the complex demands for purifying the polymer-flooding wastewater from tertiary oil extraction (Dalmazzone et al., 2012). Some separation methods are limited by the critical diameter of the oil droplets being treated (Gu, 1998, Li et al., 2000, Maruyama et al., 2012). Many high efficiency oil removal technologies have been combined into one technology. The loop flotation and coarse-graining technologies are generally considered the most efficient oil removal technologies currently available. These technologies are mostly used in distillation, absorption and other related applications (Haghshenas Fard et al., 2007). The accurate design of these columns can be very effective in increasing separation efficiency and decreasing cost (Fernandes et al., 2008).

The progress of flotation technology was influenced by a large number of factors. Most of these factors disturb the flotation process, and only some can be controlled (Niemi, 1995). In this study, the single factor test and the model kinetics methodology were applied to study the five important variables: polymer, temperature, volumetric flow rate of the flotation gas, sulfonate and alkali. These tests contribute to the formation of a more detailed and quantitative picture of industrial flotation processes. The resulting models can contribute to the scale-up of flotation from the laboratory to a full-scale plant, and they can also be expanded to models of larger flotation plants for the development of appropriate controls.

Section snippets

Equipment

A two-stage flotation reactor is shown in Fig. 1, including the flotation and separator stages (similar to the two distinct phases in a flotation cell: pulp and froth phases). Air was introduced into the bottom of the flotation stage after passing through a sparger. A stable, simulated oil–water emulsion was pumped into the bottom of the separator stage. The treated, clean water left the column from the flotation discharge pipe, while the oil-laden foam overflowed from the top of the separator

Results

The results from this experiment are listed in Table 2; Fig. 4 shows the impact of HPAM, temperature, volumetric flow rate of the flotation gas and SDBS on the oil removal rate R and the rate constant k. Substituting the results from Eq. (2) into Fig. 4 reveals that the model can adequately be used to describe the oil removal rate under a wide range of operating conditions.

The removal efficiency of the oil droplets and k initially decrease when the HPAM concentration CHPAM is either below 88 

HPAM concentration

The polymer increases the viscosity of the aqueous phase and the interfacial elasticity and stabilizes the oil droplets. The wastewater's viscosity rises with an increase in HPAM concentration. Overall, the change in the viscosity of the water produced due to HPAM is the main factor influencing the emulsion stability, and the removal rate decreases as the HPAM concentration increased.

On the other hand, the emulsion viscosity increases as the HPAM concentration increases; the sparger produce

Conclusions

  • (1)

    The polymer increases the viscosity of the aqueous phase and the interfacial elasticity and stabilizes the oil droplets. The removal efficiency of the emulsion oil and the rate constant initially decreases when the HPAM concentration is below 88 mg/l or above 164 mg/l. On the other hand, the polymer not only increases the number of bubbles but also strengthens the stability of the bubbles. The flotation efficiency is stable if the HPAM concentration is 88–164 mg/L.

  • (2)

    The elasticity and viscosity of

Notation

    C(t)

    emulsion oil concentration (mg/l3)

    C0

    initial emulsion oil concentration (mg/l3)

    C

    asymptote emulsion oil concentration (mg/l3)

    CHPAM

    HPAM concentration (mg/l3)

    CSDBS

    SDBS concentration (mg/l3)

    Q

    volumetric flow rate of gas (m3/h)

    k

    removal rate constant

    R(t)

    removal rate (%)

    R

    asymptote removal rate (%)

    t

    time (h)

    T

    temperature (°C)

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