• Energy Research

Abstract Two systems of hydraulic mixing in a vertical cylindrical anaerobic digester: standard and modernised are discussed in the paper. Numerical investigations that were carried out are focused on a study of hydrodynamic processes in an aerobic digester using two various systems of hydraulic mixing as well as on analysis of the efficiency of methane fermentation process accomplished under different geometric parameters of an anaerobic digester and systems of hydraulic mixing.

Amaranthus retroflexus or redroot pigweed is a second generation lignocellulosic fuel. Each biomass sample (leaves, inflorescences and stems) was pyrolyzed in a lab-scale furnace, in a nitrogen atmosphere under non-isothermal conditions at heating rates of 10 °C/min until the furnace temperature reached 550 °C. The pyrolysis characteristics of the three major components were also studied through thermogravimetric analysis. The thermal decomposition of the biomass samples is similar to the process of pyrolysis of lignocellulosic materials and proceeds in three main stages: dehydration, devolatilization, and carbonation. The highest bio-oil yield was obtained for inflorescences (55%) and leaves (45%). Gas chromatography—mass spectrometry analysis was carried out for oil fractions of the pyrolysis liquid from Amaranthus retroflexus. The composition of the pyrolysis oil fraction from the leaves had an overbearing aliphatic hydrocarbon nature whereas the oil fraction from inflorescences and stems was composed mainly of oxygen-containing components. The use of Amaranthus retroflexus biochars can lead to slag formation in power equipment, so it is advisable to use them to produce composite fuel, for example, mixed with coal. The results would help to better understand the thermal behavior of Amaranthus retroflexus biomass and its utilization for fuels or chemicals.

One of the methods of influence on rheological properties of heavy high-viscosity crude oils is ultrasonic treatment. Ultrasonic treatment allows reducing the viscosity of crude oil and, therefore, reducing the costs of its production and transportation. In this paper, the influence of ultrasonic treatment on the rheological characteristics of crude oil (sample No. 1 API = 29.1, sample No. 2 API = 15.9) was investigated. An experimental method was developed. Experimental studies were carried out using the Physica MCR 102 rheometer. The influence of the intensity and duration of ultrasonic treatment on the viscosity of the initial crude oils was studied for 24 h. In addition, the rheological characteristics of the treated oil were investigated after its natural cooling to 293 K. The results are compared with similar results for thermal heating.

Introduction. The use of biomass allows increasing the rate of biogas formation and its specific yield. This work aims to study the kinetics of methanogenesis and determine the optimal duration of digestion and organic load, which are the main indicators of the technological process of biogas formation. Materials and Methods. The substrate (dairy manure, biomass of amaranth) was the study object. Experimental studies were carried out using a laboratory biogas plant. The computer program (certificate No. 2018662045) was used to obtain modified Gompertz models describing the kinetics of biogas formation. Based on the obtained data, the hydraulic retention time and organic loading rate (the key parameters in the design of biogas plants were determined). Results. The paper presents the experimental studies results of the biogas formation kinetics when using dry amaranth biomass. The Gompertz mathematical models were obtained. Methane-tank control parameters (hydraulic retention time and organic loading rate) were obtained for anaerobic digestion of a new substrate. Discussion and Conclusion. The use of new co-substrate Amaranthus retroflexus L. allowed increasing the specific biogas yield from dairy manure by 52.2 % and the ultrasonic pre-treatment in combination with the herbal supplement by 89.1 %. The optimal hydraulic retention time value was 10 days and organic loading rate was 4.1 kg of volatile solids per m3 of digester per day.

Abstract The paper presents the mathematical model and the numerical studies results of heat transfer and hydrodynamics at circulatory heating of the M100 fuel oil in the RVS-3000 tank. Calculations for various inclination angles of the nozzle in the range of 40° to -40° in increments of 10° were made. The winter storage period of fuel oil in the fuel tank is considered. Comparison of the tank heating time up to the hot storage temperature (60°C) and up to the fuel temperature before feeding to the nozzles for combustion (90°C) is performed.

The combustion of sunflower husk pellets was investigated by kinetic analysis supplemented by the Kriging method. The nonisothermal thermogravimetric experiments in air were carried out at the temperatures from 20 to 700 °C and heating rates of 5, 10, and 20 °C/min. Kinetic analysis was carried out using the model-free OFW (Ozawa–Flynn–Wall) method and Coats–Redfern (CR) method. The activation energy values, calculated by the OFW method, ranged from 116.44 to 249.94 kJ/mol. These data were used to determine the combustion mechanism by the CR method. The kinetic triplet (Eα, A, g(α)) was determined in the conversion interval 0.2 to 0.8. The model of the chemical reaction F8 was recommended to describe the mechanism of the thermochemical conversion process. The relationship between the kinetic parameters was analyzed using the Kriging method. The patterns between the kinetic parameters were represented as three-dimensional surfaces and two-dimensional projections. The distribution’s surfaces were uniform; there were local extremes as well as linear regions. A new approach to the data analysis will allow predicting parameters of a thermochemical conversion of the various raw materials and contributes to a deeper understanding of the characteristics and mechanism of biomass combustion.

A new criterion of mixing quality in anaerobic digester based on the most important process parameters of methane fermentation is proposed. A set of numerical studies of mixing quality in anaerobic digesters of cylindrical shape with various systems of hydraulic mixing was carried out. Comparative analysis using the proposed criterion as well as other known methods of evaluation of mixing quality showed that results of evaluation of mixing quality in anaerobic digester using different methods are consistent with each other and are not contradictory.

This paper describes the experimental results of the thermal decomposition of the digestate obtained as a result of anaerobic digestion of dairy manure and dry biomass of Amaranthus retroflexus L. The high yield of Amaranth green mass in the main soil and climate zones of Russia is its advantage over other crops. The ratio of amaranth stems, amaranth leaves, and dairy manure for volatile solids was equal to 1:5:16. Amaranthus retroflexus L. is a weed; therefore, a thermochemical digestate processing is proposed to avoid the seed integrity. The higher heating value (HHV) of digestate was 18.6 MJ/kg. The HHV of the char residue was 19 MJ/kg. In the inorganic part of the digestate sample, the oxides CaO, SiO2, and K2O are prevailed. Thermal decomposition of digestate was studied in the temperature range 25–1000 °C in an inert atmosphere using thermogravimetric and differential scanning calorimetry (TG-DSC) at the heating rates of 5, 10, and 20 °C/min. Char residue mass was ranged from 39.8 to 41.08%. Consequently, the rest of the organic matter components pass into the pyrolysis gas and liquid phase. Additionally, studies of the digestate pyrolysis process were carried out in a laboratory setup (in an inert atmosphere) at the heating rate of 10 °C/min and the temperature of 550 °C. As a result, 31% of pyrolysis liquid, 28% of gas, and 41% of char residue were obtained. The HHV of the char residue increased on 4.8% compared with the initial value of digestate. The main components of the pyrolysis liquid are acetic acid (71.44%) and propionic acid (6.12%).