THE INFLUENCE OF THE SOLVENT QUANTITY ON THE SEPARATION OF LIGHT HYDROCARBON FRACTIONS

ABSTRACT

The article an appropriate solvent and optimal solvent quantity were determined. It was established that light naphtha as a solvent at a concentration of 30% is more optimal compared to other solvents at a temperature of 20°C. As a result of the conducted research on cleaning oil sludge from mechanical impurities, the most suitable diluent – light naphtha, was chosen. The optimal amount of light naphtha is determined to be 30% for cleaning oil sludge. The influence of these diluents on the density and viscosity of various oil sludges has been studied, as the indicators of these properties decrease from 1200 kg/m³ to 910 kg/m³ for density and from 960 mm²/s to 935 mm²/s for viscosity. In the process of oil sludge processing, a mixer is used to mix the mixture. Additionally, the process of oil sludge processing is influenced by the design parameters of this mixer, i.e., the optimal number (6 pieces) of mixer blades for mixing has been determined. As a result, the mixing efficiency reached 99.87%.

АННОТАЦИЯ

В статье был определен подходящий растворитель и оптимальное количество растворителя. Было установлено, что легкая нафта в качестве растворителя при концентрации 30% является более оптимальной по сравнению с другими растворителями при температуре 20°C. В результате проведенных исследований по очистке нефтяного шлама от механических примесей был выбран наиболее подходящий растворитель – легкая нафта. Оптимальное количество легкой нафты составляет 30% для очистки нефтяного шлама от механических примесей. Было изучено влияние этих растворителей на плотность и вязкость различных нефтяных шламов, при этом показатели этих свойств снижаются с 1200 кг/м³ до 910 кг/м³ для плотности и с 960 мм²/с до 935 мм²/с для вязкости. В процессе переработки нефтяного шлама используется мешалка для смешивания смеси. Кроме того, на процесс переработки нефтяного шлама влияют конструктивные параметры этой мешалки, а именно, было определено оптимальное количество лопастей мешалки (6 штук) для смешивания. В результате эффективность перемештвания достигла 99,87%.

Keywords: oil sludge, reformate, kerosene, light naphtha, viscosity, density.

Ключевые слова: нефтяной шлам, реформат, керосин, легкая нафта, вязкость, плотность.

Introduction. The process of oil sludge processing is a complex and multi-component process that is subject to the influence of various factors. The impact of these factors may vary depending on the technologies and methods of processing used, as well as the characteristics of the oil sludge itself [1].

In [2], a technology for processing emulsified oil sludge with an emulsified water content of up to 50% was developed, which includes filtration and evaporation of water and low-boiling hydrocarbons from the emulsified oil sludge. The dynamics of the thermal dehydration process of emulsified oil sludge were studied. It was found that complete water evaporation from the oil sludge occurs at temperatures of 150-170°C. The authors of this article stated that innovative solutions include replacing mixed reservoirs with more efficient devices, using gravity separators instead of decanters, and applying "sludge thinners" to reduce the viscosity of oil sludge [3].

The results of data analysis from [4] demonstrate that during the processing of thousands of tons of oil at oil refineries, from 1 to 5 tons of oil sludge is generated. Due to the fact that existing technologies for waste oil utilization are insufficiently effective, refineries are forced to accumulate sludges and constantly increase the volumes of sludge storage facilities. Some of the key influencing factors include the density and viscosity of oil sludge, the various solvents used and their ratios, as well as the design of the decanter centrifuge used to separate oil sludge into water, organic matter, and solid substances. Temperature and pressure during the processing also play a significant role [5].

The processing of oil sludges using biochemical methods relies on the capabilities of microorganisms, which oxidize the oil sludge and degrade the hydrocarbon products [6]. This process facilitates soil remediation through the utilization of microorganisms. However, this method has its drawbacks. Firstly, it primarily decomposes the light organic components of oil waste, subsequently transforming them into other organic compounds. Meanwhile, the role of microorganisms in the natural decomposition chain has not yet been fully studied. Additionally, the temporal framework is a significant factor, meaning the duration of the decomposition process and the narrow temperature range within which microorganisms operate are important considerations. A key requirement of this technology is the composition of the oil waste, which should have low hydrocarbon content [7].

The presented technology is relevant for the final disposal after other processing methods.

Methods and Materials. To achieve this, experiments were conducted to study the changes in the densities of waste oil sludges when three types of solvents (light naphtha, kerosene, reformate) were added at concentrations ranging from 5 to 30 percent, as shown in Figure 1.

Figure 1. Changes in the densities of waste oil sludges depending on the quantity of different solvents added

From Fig. 1, it can be observed that the addition of solvents to waste oil sludge, ranging from 5% to 30%, reduces the density from 1200 kg/m³ to 910 kg/m³. The density of regular waste oil sludge without added solvent is 1200 kg/m³. When 5% of light naphtha solvent is added, the density of the oil sludge is 1160 kg/m³. If the quantity of solvent reaches 10%, then the oil sludge has a density of 1090 kg/m³. With 15% solvent added, the density of the oil sludge is 1020 kg/m³. If the quantity of solvent reaches 20%, then the oil sludge has a density of 980 kg/m³. The density of waste oil sludge is 950 kg/m³ when 25% solvent is added. If the quantity of light naphtha solvent reaches 30%, then the oil sludge has a density of 910 kg/m³. This is because the solvent dissolves the organic components of the oil sludge (e.g., heavy oil hydrocarbons), which naturally affects their density. Therefore, it can be concluded that light naphtha is the most optimal solvent for reducing the density of oil sludges.

Similarly, experiments were conducted to study the changes in the densities of oil sludges formed during the purification of technical water when solvents were added in concentrations ranging from 5 to 30 percent, as shown in Fig.2.

Figure 2. Changes in the densities of oil sludges formed during the purification of technical water depending on the quantity of different solvents added

From Fig. 2, it can be observed that the addition of solvents to the oil sludges formed during the purification of technical water, ranging from 5% to 30%, reduces the density from 1060 kg/m³ to 875 kg/m³. The density of regular waste oil sludge without added solvent is 1060 kg/m³. When 5% of light naphtha solvent is added, the density of the oil sludge is 1020 kg/m³. If the quantity of solvent reaches 10%, then the oil sludge has a density of 1000 kg/m³. With 15% solvent added, the density of the oil sludge is 970 kg/m³. If the quantity of solvent reaches 20%, then the oil sludge has a density of 930 kg/m³. The density of oil sludge formed during the purification of technical water is 900 kg/m³ when 25% solvent is added. If the quantity of solvent reaches 30%, then the oil sludge has a density of 875 kg/m³.

During the experiments, tests were conducted to study the changes in the densities of tank oil sludges when solvents were added in concentrations ranging from 5 to 30 percent, as shown in Fig. 3.

Figure 3. Changes in the densities of tank oil sludges depending on the quantity of different solvents added

From Fig. 3, it can be observed that the addition of solvents to the oil sludges formed during the purification of technical water, ranging from 5% to 30%, reduces the density from 909 kg/m³ to 855 kg/m³. The density of regular waste oil sludge without added solvent is 909 kg/m³. When 5% of solvent is added, the density of the oil sludge is 895 kg/m³. If the quantity of solvent reaches 10%, then the oil sludge has a density of 885 kg/m³. With 15% solvent added, the density of the oil sludge is 870 kg/m³. If the quantity of solvent reaches 20%, then the oil sludge has a density of 860 kg/m³. The density of oil sludge formed during the purification of technical water is 858 kg/m³ when 25% solvent is added. If the quantity of solvent reaches 30%, then the oil sludge has a density of 855 kg/m³.

Viscosity is an important parameter to consider in the processing of oil sludges. Oil sludges, such as oil tank bottoms, contain a mixture of various hydrocarbon compounds, including heavy fractions, which can be viscous and difficult to process. Here are several ways in which viscosity can affect the processes of oil sludge processing.

Transport and Mixing: High viscosity can hinder the transportation and mixing of oil sludges during processing. This may require the use of more powerful equipment for effective raw material preparation for processing. Thermal Treatment: Some processing methods, such as thermocatalytic cracking or thermal destruction, may be used for the decomposition of heavy hydrocarbons. However, high viscosity can create difficulties in achieving the required temperature and efficient heat exchange. Dissolution: Processes based on the dissolution of heavy oil components, such as solvent extraction, may be hindered by high viscosity, as it can slow down diffusion and mixing processes. Oil Refining Processes: In oil refining processes such as hydrocracking and hydrotreating, high viscosity may require higher temperatures and pressures to achieve optimal results [8].

Innovations in technology and processing methods are constantly being developed to overcome the difficulties caused by viscosity and to increase the efficiency of oil sludge processing processes [9].

We have conducted a series of experiments to reduce the viscosity of oil sludges using solvents. Solvents can have a significant impact on the viscosity of oil sludges. This is due to their ability to disrupt or reduce the viscosity of heavy hydrocarbon components present in oil sludges. Here's how solvents can affect the viscosity of oil sludges.

Dissolution of heavy components: Solvents such as various organic solvents or supercritical fluids can interact with heavy hydrocarbons, leading to their dissolution. This can reduce the content of viscous components in the sludges, thereby reducing their overall viscosity. Improvement of fluidity: Solvents can improve the fluidity of oil sludges by helping to disrupt the structure and reduce the cohesion between hydrocarbon molecules. This can result in easier processing and transportation of the sludges. Phase modification: Introducing solvents can change the phase composition of oil sludges, reducing the amount of solid particles and decreasing viscosity due to the change in the system's structure. Temperature effect: Some solvents can lower the freezing temperature of components in oil sludges, which can also affect their viscosity. Chemical composition alteration: Solvents can interact with specific chemical groups in the sludge composition, leading to changes in their structure and properties, including viscosity [10].

However, it should be noted that the choice of solvent should consider not only the desired effect on viscosity but also environmental and economic aspects, as well as the safety of the processing process.

The centrifugal force developed during centrifugation, denoted as C (in H), was determined using the equation [11]:

                                      (1)

where, M- is the mass of the liquid and sediment in the centrifuge drum, in kilograms; ω- is the angular velocity in radians per second; D = 2R is the diameter of the centrifuge drum, in meters; n- is the rotation frequency of the centrifuge, in hertz.

The separation factor in centrifuges is the ratio of the centrifugal force acceleration to the acceleration due to gravity.

                                  (2)

                                             (3)

where R is the radius of the drum, in meters; ω is the angular velocity, in radians per second.

The quality of mixing is characterized by the degree of phase mixing.

The degree of phase mixing in the entire volume of the mixing device I can be determined by the following equation [12]:

                                                     (4)

here, m - is the sample for analysis,  > 0; x’ - the difference in concentrations in the mixer, and is calculated by the formula x’ = x - x_ap;  x_ap - the concentration of particles in the mixture under ideal mixing conditions, which is determined by the following formula:

                                                            (5)

here, V_c is the volume of liquid; V_k​ is the volume of solid particles distributed in the main mass (liquid); r_к and r_с  are the densities of solid particles and liquid in the mixture, respectively; n - is the number of samples taken for analysis; x” < 0; x” - represents the difference in concentrations x” = x – x₀, calculated by the following formula:

The degree of phase mixing can vary from 0 to 1. In our mixer, the components are perfectly mixed, so I=1.

Results and discussion. During the experiments, various amounts of solvent were added to the oil sludge in ratios ranging from 5% to 30%. Subsequently, the optimal ratio was determined based on the observed effects on viscosity. The influence of different amounts of solvent on the viscosity of the oil sludge was thoroughly investigated.

Table 1.

Changes in the viscosity of oil sludges depending on the amount of solvent

From Table 1, it can be observed that the addition of solvent in various ratios results in different viscosities of oil sludge of different origins. Without the addition of solvent, oil sludge derived from the purification of technical water has a viscosity of 960 mm²/s. With the addition of 5% solvent, the viscosity of oil sludges of this type decreases to 950 mm²/s. Further increasing the amount of solvent reduces the viscosity of the oil sludges. Throughout the experiments, we selected the optimal ratio of solvent and oil sludge, which plays a crucial role in the processing of these wastes. A mixture of 30% solvent and 70% oil sludge allows us to utilize the oil sludge for obtaining secondary materials.

Indeed, among these solvents, light naphtha appears to be the most optimal in composition. It effectively dissolves solid and resinous components of oil sludge.

In addition to the diluent, the processing of oil sludge is also influenced by the regime and design parameters of the apparatus, such as the geometric dimensions of the tank with the agitator, the number of agitator blades, the rotation frequency of the blades, the length of the blades, and so on. For example, the diameter of the tank is 0.4 m. Table 1 shows the results of the impact of the blade diameter ratio d (D/d) on mixing efficiency.

Table 2.

The influence of structural parameters of the agitator on mixing efficiency

From table 2, it can be seen that at a ratio of tank diameter to impeller diameter of 2.8 (D/d) and a rotational speed of 60 rpm, the mixing efficiency is 71%, with 2 blades. At a blade diameter ratio of 2.8 (D/d) and 3 blades, the mixing efficiency was 78%. Further increasing the number of blades to 4, with a rotational speed of 60 rpm, the mixing efficiency reached 86%. As a result, the optimal design for the tank with the impeller is at a blade diameter ratio (D/d) of 2.8 to the tank diameter, with a rotational speed of 60 rpm, 6 blades, and a mixing efficiency of 99.87% for the oil sludge with the diluent.

Thus, as a result of the conducted research on cleaning oil sludge from mechanical impurities, the most suitable diluent – light naphtha, was chosen. The optimal amount of light naphtha is determined to be 30% for cleaning oil sludge. The influence of these diluents on the density and viscosity of various oil sludges has been studied, as the indicators of these properties decrease from 1200 kg/m³ to 910 kg/m³ for density and from 960 mm²/s to 935 mm²/s for viscosity. In the process of oil sludge processing, a mixer is used to mix the mixture. Additionally, the process of oil sludge processing is influenced by the design parameters of this mixer, i.e., the optimal number (6 pieces) of mixer blades for mixing has been determined. As a result, the mixing efficiency reached 99.87%.

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