Hydrodynamic Cavitation Reactor Research Articles

Ultra-high efficient hydrodynamic cavitation enhanced oxidation of nitric oxide with chlorine dioxide

Ships carry over 80% of the world’s trade, and in the meantime, they cause severe air pollution. Nitrogen oxide (NOx) is one of the most difficult items to be treated among ship’s air pollutants. In this paper, a novel treatment of gaseous pollutants based on hydrodynamic cavitation is proposed and systematically investigated. In comparison with the bubbling reactor, the hydrodynamic cavitation reactor (HC reactor) expanded the gas-liquid contact area by more than 37.5 times through generating microbubbles (about 0.50 mm) filled with the nitric oxide mixture (Gas-Filled-Bubbles). The small space inside the Gas-Filled-Bubble facilitated collisions of gas molecules, and thus accelerated the rate of gas phase chemical reactions. Furthermore, the collapse of cavitation bubbles (Cavities) may result in highly reactive free radicals and microjets, and the microjets helped to enhance gas-liquid mass transfer. The HC reactor had a longer duration for NOx removal rate over 90% than the bubbling reactor. When 1.0 mg/L chlorine dioxide (ClO2) solution was used, the duration for NOx removal rate over 90% was 100 s in the HC reactor, whereas in the bubbling reactor the duration was 0 s. Comparatively high ClO2 concentration contributed to prolonged high NOx removal rate (≥90%) duration, however, the escape of ClO2 would lead to more nitrogen dioxide (NO2) production, and poor ClO2 utilization. The effects of the inlet and outlet pressures of the HC reactor on the denitrification effect were studied, and the cost-effectiveness of the proposed method was assessed. The results showed that the inlet pressure of 3.00 bar and the outlet pressure of 0.30 bar were reasonable options for HC reactor’s denitration when both cost benefit and application conditions were taken into account.

Efficient production of biodiesel from Cannabis sativa oil using intensified transesterification (hydrodynamic cavitation) method

ABSTRACT In order to commercialize and maximize biodiesel production, there is an evident need to search contemporary and evidently efficient technique for its mass production, which lowers the reaction time and manufacturing cost as well as save the energy. This paper is basically an investigation of a brand new method for successful conversion of biodiesel derived through alkali-catalyzed transesterification of Cannabis sativa L. oil using a hydrodynamic cavitation reactor. The subsequent effects of the oil to methanol molar ratio (3:1–7:1), catalyst concentration (0.5–1.25 wt.%), and reaction temperature (50°C–65°C) have been studied by utilizing an optimized plate with seven holes of 3 mm diameter in a 10 L of hydrodynamic cavitation reactor. Optimal conversion of 97.5% was thoroughly achieved within 20 min in a hydrodynamic cavitation reactor with 6:1 molar ratio of oil to methanol, 1 wt. % of catalyst, 60°C of reaction temperature and 3 bar of upstream operating pressure. Further observations indicated a significant reduction in the optimum reaction time for transesterification from 90 min for mechanical stirring approach to 20 min for the hydrodynamic cavitation approach.

Valorization of Rendering Fats to Produce Biodiesel by Single and Multi Orifice Plate Cavitation Reactor

The aim of this work is focused on the valorization of category two rendering pig fats, to evaluate their use as source of biodiesel by hydrodynamic cavitation reactors. The optimum reaction conditions have been previously determined in laboratory, obtaining as optimum values 60 °C, 1 wt% of sodium hydroxide, fat to methanol molar ratio of 1:6. The design of the cavitation reactor orifice plates has been carried out taking into account these optimum conditions. The design is based on the cavitation number as a function of the degree of advancement of reaction, which ensures that cavitation occurs through the entire reaction time. Then, the cavitation reactor was used in a pilot plant to study different configurations of orifice plates. The results obtained indicate that it is more efficient to use cavitation reactors with consecutive orifice plates (9.05 g/kJ) instead of traditional stirring reactor (3.75 g/kJ) or single orifice plate reactors (6.7 g/kJ). This reactor also allows reaching higher FAME content (90%) compared to a stirring reactor (85%). It also allows reducing the residence time up to 5 min from 22 min of a stirring reactor or from 10 min of a single orifice plate reactor.

Sulfadiazine degradation using hybrid AOP of heterogeneous Fenton/persulfate system coupled with hydrodynamic cavitation

Sulfadiazine (SDZ) is a prominent antibiotic pollutant that appears in wastewater discharges from domestic, agricultural and pharmaceutical sectors. In this paper, we have reported studies in SDZ degradation using a novel hybrid AOP that coupled hydrodynamic cavitation with heterogeneous Fenton and persulfate. Two solid Fenton catalysts (α-Fe2O3 and Fe3O4) in the form of nanoparticles were synthesized. The composition of reaction mixture was optimized using statistical techniques. Effect of four operating parameters, viz. (1) SDZ initial concentration, (2) inlet pressure of cavitating flow, (3) pH and (4) type of heterogeneous Fenton catalyst (at optimum loading), on SDZ degradation was studied. A kinetic model for SDZ degradation was proposed based on homogeneous Fenton/persulfate system, and experimental degradation profiles were analyzed vis-à-vis simulated profiles. The highest degradation of SDZ (81%) was obtained for SDZ initial concn. = 20 ppm, pH = 4, inlet pressure = 10 atm, Na2S2O8 = 348.5 mg/L, H2O2 = 0.95 mL/L and α-Fe2O3 catalyst (181.8 mg/L). Kinetic model analysis showed best match between experimental and simulated profiles for [Fe2+]/[H2O2] initial ratio = 4. This indicated efficient catalytic activity of α-Fe2O3 nanoparticles – close to that of homogeneous catalyst. This is a consequence of high rate of mass transfer at surface of α-Fe2O3 particles due to intense turbulence and shear generated in cavitating flow in hydrodynamic cavitation reactor.

Improved rate of transesterification reaction in biodiesel synthesis using hydrodynamic cavitating devices of high throat perimeter to flow area ratios

The present study reports the process intensification of biodiesel synthesis from waste cooking oil using hydrodynamic cavitation (HC) which was achieved by increasing the ratio of the throat/hole perimeter to flow cross section area (α) (α: 1.33 to 13.33 mm−1) of the cavitating device. Initially, the optimization of process reaction parameters such as oil to alcohol molar ratio (1:6.8) and catalyst concentration (NaOH; 1 wt. % of oil) was carried out by response surface methodology (RSM). Thereafter, biodiesel synthesis was carried out in the HC reactor for optimization of cavitating devices (circular Venturi and three orifice plates). Maximum of 99% yield was obtained in 5 min of treatment time by using an orifice plate having 100 circular holes of 0.3 mm diameter each (α : 13.33 mm−1) at the optimum operating inlet pressure of 7 bar. LC–MS and FT-IR analysis of the biodiesel product confirmed the formation of fatty acid methyl esters (FAME). The energy efficiency evaluation of HC revealed that the intensification of HC using a cavitating device of higher α value significantly reduced the energy requirement for the synthesis of biodiesel as compared to the other conventional approaches of cavitation as well as increased the overall reaction rate.

Combined hydrodynamic cavitation based processes as an efficient treatment option for real industrial effluent

In the present work, hydrodynamic cavitation (HC) operated alone and in combination with chemical oxidants has been applied for the treatment of real industrial effluent obtained from a local industry. Initially, the analysis of literature related to the hybrid methods involving hydrodynamic cavitation has been presented along with recommendations for the selection of important operating conditions for the HC operated individually and in combination with oxidation processes based on hydrogen peroxide (H2O2), ozone (O3) and persulphate (KPS). Subsequently, the treatment of real industrial effluent has also been investigated in details using HC alone and in combined mode with other oxidation processes focusing on the main objective of COD reduction. The reduction in the COD achieved using individual treatment of HC under the optimized conditions of inlet pressure as 4 bar and pH as 4 was only 7.9%. The application of different hybrid approaches based on HC such as HC + H2O2, HC + O3, HC + KPS and HC + H2O2 + O3 established higher COD reduction as compared to only HC. The maximum extent of COD reduction as 60.8% was achieved using HC + H2O2 + O3 combination whereas, relatively lower extent of COD was achieved for operations of HC + H2O2, HC + O3 and HC + KPS with the actual COD reduction being 40.3%, 38.7% and 8.5% respectively. It was also observed that 30.4%, 28.2%, 15.6%, and 4.7% of TOC reduction was obtained for the combined process of HC + H2O2 + O3, HC + H2O2, HC + O3, and HC + KPS respectively. Based on the kinetic study, it was established that the degradation fitted the first order kinetics for all the approaches. The combined processes of HC with oxidants were also compared with ultrasound reactors (both individual and combined operation) in terms of COD reduction, cavitational yield calculations, and treatment cost. HC reactors were established to be more energy efficient and also yielded treatment costs significantly lower than ultrasonic reactors.

Application of Hydrodynamic Cavitation Reactors for Treatment of Wastewater Containing Organic Pollutants: Intensification Using Hybrid Approaches

The concentration of hazardous pollutants in the wastewater streams has to keep below a certain level in order to comply with the stringent environmental laws. The conventional technologies for wastewater treatment have drawbacks in terms of limited applicability and efficiency. Utilization of hydrodynamic cavitation (HC) reactors for the degradation of pollutants at large scale has shown considerable promise over last few years, due to higher energy efficiencies and low cost operation based on lower consumption of chemicals for the treatment. The present work overviews the degradation of different pollutants, such as pharmaceuticals, pesticide, phenolic derivatives and dyes, as well as the treatment of real industrial effluents using hybrid methods based on HC viz. HC/H2O2, HC/Ozone, HC/Fenton, HC/Ultraviolet irradiations (UV), and HC coupled with biological oxidation. Furthermore, based on the literature reports, recommendations for the selection of optimum operating parameters, such as inlet pressure, solution temperature, initial pH and initial pollutant concentration have been discussed in order to maximize the process intensification benefits. Moreover, hybrid methods based on HC has been demonstrated to show good synergism as compared to individual treatment approach. Overall, high energy efficient wastewater treatment can be achieved using a combined treatment approach based on HC under optimized conditions.

Degradation of refractory pollutants by hydrodynamic cavitation: Key parameters to degradation rates

Degradations of refractory pollutants by hydrodynamic cavitation were experimentally carried out in a self-developed hydrodynamic cavitation reactor with Venturi tubes, multi-orifice plates and their combinations. Effects of hydraulic elements of cavitation due to the Venturi tube on degradation of refractory hydrophobic pollutant were studied, and an optimal throat length corresponding to the maximum degradation rate was obtained. Effects of cavitation due to number, size and distribution of orifice for the multi-orifice plates on degradation of refractory hydrophilic pollutant were investigated, and comparisons and analyses were made. Effects of cavitation due to different combinations of the Venturi tubes with the triangular multi-orifice plates on degradation of hydrophilic and hydrophobic mixtures were studied, and an appropriate combination was determined. Also, effects of cavitation duration, pH value and initial concentration on the refractory pollutants were explored.

Cocoa bean shell waste valorisation; extraction from lab to pilot-scale cavitational reactors

The use of zero-waste processes to integrate food-waste valorisation into the circular economy equation is currently one of the hottest topics in sustainability research. This goal is still far from being fully achieved despite the release of a number of patents and papers that deal with the topic.The present work aims to valorise cocoa shells, one of the main by-product of the roasting process, in order to enhance the effective extraction of high added value compounds by means of green protocols. The high potential added value of the residual waste has been demonstrated via a direct analytical comparison of extracts and bean composition.A range of raw matrix extraction procedures have been investigated in order to define the best solvent and technology; ultrasound (US) and hydrodynamic cavitation (HC) were compared with conventional methods. The high-energy microenvironments generated by cavitation substantially promote fast biomass deconstruction with low energy consumption. The optimized protocol couples a HC reactor with a ternary water/ethanol/hexane mixture, simultaneously providing a hydrophilic product, which is rich in methylxanthines and polyphenols, and a lipid layer.Sequential milling and sieving pretreatment provided an enriched shell fraction via the partial removal of husk fibres (54.45 vs. 81.36 w/w % total fibres). The disposal of the latter reduces mass balance, but is rerouted into animal feedstock components and crop mulching.The protocols herein reported produce valuable extracts, which are rich in antioxidant flavanols (catechins and epicatechins), theobromine (32.7 ± 0.12 mg/g shells), caffeine (1.76 ± 0.08 mg/g shells) and cocoa butter, in a simple and easy manner. This new valorisation process afforded 20.5 w/w % and 15.8 w/w % hydrophilic and lipophilic fractions, respectively, when scaled up to function in a pilot flow reactor. The fatty acids, obtained in remarkable yield (forming the 96.4 w/w % of the total light part) well match the commercial cocoa butter profile. The antioxidant extract shows an impressive total phenolic content of 197.4 mg/g extract (gallic acid eq.), with a radical scavenging activity of 62.0 ± 3.1 μg/mL (expressed in DPPH EC50). This work should facilitate industrial design for the convenient recovery of cocoa by-products as part of a zero-waste strategy.

Modelling of vortex based hydrodynamic cavitation reactors

Vortex based hydrodynamic cavitation reactors offer various advantages like early inception, less erosion and higher cavitational yield. No systematic modelling efforts have been reported to interpret the cavitation performance of these vortex based devices for cavitation. It is essential to develop a modelling framework for describing performance of cavitation reactors. We have addressed this need in the present work. A comprehensive modelling framework comprising three layers: per – pass performance models (overall process), computational fluid dynamics models (flow on reactor scale) and cavity dynamics models (cavity scale) is developed. The approach and computational models were evaluated using the experimental data on treatment of acetone-contaminated water. The presented models were successful in describing the experimental data using initial cavity size as an adjustable parameter. Efforts were made to quantify optimum operating conditions and scale-up. The developed approach, models and results will provide useful design guidelines for pollutant degradation using vortex based cavitation reactors. It will also provide a sound and useful basis for comprehensive multi-scale modelling of hydrodynamic cavitation reactors.

Pressure characteristics of hydrodynamic cavitation reactor due to the combination of Venturi tubes with multi-orifice plates

The pressure characteristics in the throats of Venturi tube and behind triangular multi-orifice plates were experimentally investigated by a pressure data acquisition system of SINOCERA-YE6263, and the effect of throat length of Venturi tube, different geometric parameters of multi-orifice plate and their combinations on the time-averaged pressure, cavitation number, and pressure frequency spectrum, correlation function calculated by FFT were analyzed. The experimental results showed that the throat length of L/R = 40 made for improving the fluctuation energy and promoting the uniform energy distribution, appropriately decreasing the size and increasing the number of orifice could accelerate the uniform distribution of the fluctuation energy in frequency domain. In the combination reactors, the cavitation number behind multi-orifice plates was lower and the fluctuation of correlation function was more intense.

Improvement in biological oxidation process for the removal of dichlorvos from aqueous solutions using pretreatment based on Hydrodynamic Cavitation

In the present work, the removal of Dichlorvos (DDVP) from aqueous solution was investigated using combined approach of Hydrodynamic cavitation (HC) as pretreatment followed by the biodegradation operated as per the OECD protocol, 301E. Initially, the efficiency of HC reactor based on slit venturi was optimized by varying the inlet pressure (range of 4–7 bar) and pH (range of 4–9). Under optimized conditions established as inlet pressure of 5 bar and pH of 4, subsequent studies for the degradation of DDVP using combined approaches of HC with Ozone (HC + O3) as intensified pretreatment were performed. It was established that the combined approach significantly enhanced the degradation to 84.8% with TOC reduction of 39.4%. Further, biodegradation analysis of HC and HC + O3 pretreated DDVP aqueous solution was performed. A maximum kinetic rate constant as 64.2 × 10−3 day−1 was obtained for pretreated DDVP solution using the HC + O3 combination, which was about 10 times higher as compared to the case where untreated solution of DDVP (kinetic rate constant as 5.3 × 10−3 day−1) was directly used for biological oxidation. Integral method of analysis revealed that the reduction follows the first order kinetics with maximum oxidation rate constant as 64.2 × 10−3 day−1 for the combined approach involving HC + O3 as the pretreatemnt followed by biological oxidation. Overall, it has been demonstrated that HC combined with ozone can be effectively used as pretreatment for improving the biodegradability of DDVP.

An experimental study on the thermal performance of a novel hydrodynamic cavitation reactor

The hydrodynamic cavitation technique has been widely considered to have great potential for many environmental, chemical, and biological industrial-scale applications. This paper presents an experimental investigation of the thermal performance, i.e., heat generation rate and thermal efficiency of a novel, advanced, rotational 15 kW class hydrodynamic cavitation reactor (HCR). The cavitation generation mechanism of the HCR was analyzed according to flow visualization. The thermal performance was tested in 20 experiments with various rotational speeds of the rotor (2700, 3000, 3300, and 3600 rpm) and pump pressure settings (0.0, 0.5, 0.7, 1.0, and 1.5 bar gauge pressure) without controlling the flow rate. The HCR achieved a maximum heat generation rate of 48.15 MJ/h (i.e., 13.375 kW) and a maximum thermal efficiency of 82.18%. To evaluate the independent effects of the operational conditions, the thermal performance was also evaluated under various flow rates (6, 8, and 10 L/min), pump pressure settings (0.5, 0.8, 1.1, and 1.4 bar), and inlet water temperatures (15, 25, 35, and 45 °C). The results showed that increasing the rotational speed, flow rate, and pump pressure setting gave rise to higher heat generation rate and thermal efficiency of the HCR. Moreover, the thermal performance decreased with increasing water temperature. Compared with the conventional and advanced rotational HCRs introduced in previous research, the HCR in this study provided more outstanding thermal performance and stable operational state and has great development potential for various large-scale applications.

Experimental investigation of the thermal and disinfection performances of a novel hydrodynamic cavitation reactor

In the present study, we proposed an effective, efficient, and economical approach to disinfect water using a novel, advanced, rotational hydrodynamic cavitation reactor (HCR). First, analyses of the flow field and cavitation generation mechanism in the HCR were conducted through visualization of the reactor flow field using a high-speed camera. Second, the thermal performance was tested in 20 experiments with various rotational speeds of the rotor (2700, 3000, 3300, and 3600 rpm) and pump pressure settings (0.0, 0.5, 0.7, 1.0, and 1.5 bar gauge pressure). The HCR maximally achieved a heat generation rate of 48.15 MJ/h and thermal efficiency of 82.18%. Then, the disinfection effect was evaluated using water that simulated an effluent containing Escherichia coli (E. coli) for various flow rates (8, 11, and 14 L/min), a pump pressure setting fixed at 0.5 bar, and a rotational speed of 3600 rpm. In addition, an economical assessment of the disinfection processes was performed by considering the measured electric consumption. The thermal effect generated by the HCR was the dominant factor affecting the concentration of E. coli. The HCR achieved a 100% disinfection rate with a 4.3 L/min treatment rate and a cost of US $ 3.019/m3 at the optimal flow rate. The effects of the pressure setting and rotational speed on the performance were discussed in detail. Finally, compared to the recent studies, the treatment rate of the HCR is several hundred times greater than that obtained by the HCRs utilized in those studies, and also has a reasonable cost.

Treatment of textile dyeing industry effluent using hydrodynamic cavitation in combination with advanced oxidation reagents

Treatment of textile dyeing industry (TDI) effluent was investigated using hydrodynamic cavitation (HC) and in combination with advanced oxidation reagents such as air, oxygen, ozone and Fenton’s reagent. Slit venturi was used as the cavitating device in HC reactor. The effects of process parameters such as inlet pressure, cavitation number, effluent concentration, ozone and oxygen flow rate, loading of H2O2 and Fenton’s reagent on the extent of reduction of TOC, COD and color were studied. Efficiency of the hybrid treatment processes were evaluated on the basis of their synergetic coefficient. It was observed that almost 17% TOC, 12% COD, and 25% color removal was obtained using HC alone at inlet pressure of 5bar and pH of 6.8. The rate of reduction of TOC and COD decreased with dilution of the samples. HC in combination with Fenton’s reagent (FeSO4·7H2O:H2O2 as 1:5) was most effective with reduction of 48%TOC and 38% COD in 15min and 120min respectively with almost complete decolorization (98%) of the TDI effluent. Whereas HC in combination with oxygen (2L/min) and ozone (3g/h) produced reduction of 48% TOC, 33% COD, 62% decolorization and 48% TOC, 23% COD, 88%, decolorization of TDI effluent respectively.

Intensified degumming of crude soybean oil using cavitational reactors

A novel cavitation assisted degumming approach for the purification of crude soybean oil in terms of the removal of the total phospholipid content has been reported in the work with a detailed study into the effect of operating parameters such as temperature, hydrogen peroxide loading and introduction of ozone gas at varying flow rate. Ultrasonic horn, ultrasonic bath and hydrodynamic cavitation reactors have been used for comparing the efficacy of different types of cavitational reactors. Initially, extent of degumming was quantified at different temperatures and 60 °C was established as optimum to give significant extent of degumming in terms of phospholipids removal. Degumming in the presence of ozone gas gave unsatisfactory results because of the specific physical and chemical properties of crude soybean oil. Combination of ultrasound and hydrogen peroxide resulted in complete phospholipid degradation at capacity of 250 ml at optimized temperature in 100 min of treatment. Ultrasonic horn and bath were also used at 1 L operating volume and the extent of degumming was found to be 90.81% and 93.50% respectively. For large scale studies, hydrodynamic cavitation was operated at 4 bar pressure using slit venturi as the cavitating device which gave 93.65% as the extent of degumming. Overall, intensified degumming approach for processing of crude soybean oil was demonstrated to yield high quality oil in terms of the reduced phospholipids content. Cavitation based degumming process can be an excellent alternative approach to the conventional method with major benefits like reduction in time and energy requirements as demonstrated in the present work.

Production and purification of biodiesel produced from used frying oil using hydrodynamic cavitation

This work describes the biodiesel production from used frying oil using a hydrodynamic cavitation reactor as well as separation and purification of fatty acid methyl esters (FAME). Under the optimized process conditions, i.e., methanol to oil molar ratio of 4.5:1 and catalyst (KOH) concentration of 0.55 wt%, the conversion achieved was 93.86 mol%. Higher conversion (93.6%) was obtained in only 20 min as compared to 88.5% in 1 h in stirred tank reactor. Due to the completion of transesterification reaction, the amount of intermediate diglycerides and monoglycerides present in the reaction mixture was less. It helps for the complete separation of methyl ester and glycerol layers without hindrance in 1 h. Small amount KOH catalyst used for completion of reaction reduces amount of KOH and soap in ester layer which further helps to form a less stable emulsion during water washing step. The complete separation was observed at 70 °C temperature in just 3 h. Thus, this study indicates that the increased production capacity can be achieved by shortening the time for the separation and purification.

Production and purification of biodiesel produced from used frying oil using hydrodynamic cavitation

This work describes the biodiesel production from used frying oil using a hydrodynamic cavitation reactor as well as separation and purification of fatty acid methyl esters (FAME). Under the optimized process conditions, i.e., methanol to oil molar ratio of 4.5:1 and catalyst (KOH) concentration of 0.55 wt%, the conversion achieved was 93.86 mol%. Higher conversion (93.6%) was obtained in only 20 min as compared to 88.5% in 1 h in stirred tank reactor. Due to the completion of transesterification reaction, the amount of intermediate diglycerides and monoglycerides present in the reaction mixture was less. It helps for the complete separation of methyl ester and glycerol layers without hindrance in 1 h. Small amount KOH catalyst used for completion of reaction reduces amount of KOH and soap in ester layer which further helps to form a less stable emulsion during water washing step. The complete separation was observed at 70 °C temperature in just 3 h. Thus, this study indicates that the increased production capacity can be achieved by shortening the time for the separation and purification.

Metal of cavitation erosion of a hydrodynamic reactor

Cavitation erosion is a major cause of the petroleum equipment hydraulic erosion, which leads to the metal weight loss of the equipment and its breakdown, which can be followed by the full stop of the plant or company work. The probability of the metal weight loss and equipment failure can be reduced by the use of special protective coatings or rivets, made of the sacrificial metals, the use of which significantly increases the service life and the production equipment reliability. The article investigates the cavitation erosion effect, occurred under the condition of the advanced hydrodynamic cavitation on the hydrodynamic cavitation reactor. This article presents the results of the experiments and recommendations for increasing the operational resource.

Harnessing hydroxyl radicals generated by hydrodynamic cavitation reactor in simultaneous removal of chlorpyrifos pesticide and COD from aqueous solution

Harnessing hydroxyl radicals generated by hydrodynamic cavitation reactor in simultaneous removal of chlorpyrifos pesticide and COD from aqueous solution