Contemporary Problems in Combustion—Fuels, Their Valorisation, Emissions, Flexibility and Auxiliary Systems

This Special Issue is dedicated to the XXIV Symposium on Combustion Processes (23–25 September 2019, Wrocław, Poland), which is an official symposium of the Polish Section of the Combustion Institute that takes place every two years [...

Experimental Investigation of Thermoacoustics and High-Frequency Combustion Dynamics with Band Stop Characteristics in a Pressurized Combustor

In combustor systems, thermoacoustic instabilities may occur and must be avoided for reliable operation. An acoustic network model can be used to predict the eigenfrequencies of the instabilities and the growth rate by incorporating the combustion dynamics with a flame transfer function (FTF). The FTF defines the interconnection between burner aerodynamics and the rate of combustion. In the current study, the method to measure the FTF in a pressurized combustor is explored. A siren unit, mounted in the fuel line, induced a fuel flow excitation of variable amplitude and high maximum frequency. This was performed here for pressurized conditions at 1.5 bar and 3 bar and at a thermal power of 125 kW and 250 kW. In addition to the experimental investigation, a 1-D acoustic network model approach is used. In the model, thermoviscous damping effects and reflection coefficients are incorporated. The model results compare well with experimental data, indicating that the proposed method to determine the FTF is reliable. In the approach, a combination of an FTF with a band stop approach and a network modeling approach was applied. The method provides a good match between experimentally observed behavior and an analytical approach and can be used for instability analysis

Computational fluid dynamic model for glycerol gasification in supercritical water in a tee junction shaped cylindrical reactor

Gasification in supercritical water is a very promising technology to process wet biomass into a valuable gas. Providing insight of the process behavior is therefore very important. In this research a computational fluid dynamic model is developed to investigate glycerol gasification in supercritical water, which takes place in a cylindrical reactor with a tee junction. The performance of the developed model is validated against experiment, and it shows that the model is able to describe the process very well. The experimental validation shows that the model slightly overestimates the outlet temperature on average by 6% and underestimates the carbon gasification efficiency on average by 16%. The flow behavior in the supercritical water gasification process is successfully described and a sensitivity analysis is conducted. It is revealed that the flow pattern of the process is heavily influenced by gravitational forces which significantly influences mixing and heat transfer

Recovery of chemical energy from retentates from cascade membrane filtration of hydrothermal carbonisation effluent

Organic fraction of municipal solid waste is a type of biomass that is attractive due to its marginal cost and suitability for biogas production. The residual product of organic waste digestion is digestate, the high moisture content of which is a problem, even after mechanical dewatering, due to the significant heat requirement for drying. Hydrothermal carbonisation is a process that can potentially offer great benefits by improved mechanical dewatering and valorisation of the digestate into a better-quality solid fuel. However, such valorisation produces liquid by-product effluent rich in organic compounds. Membrane separation could be used to treat such effluent and increase the concentration of the organic compounds while at the same time facilitating the recovery of clean water in the permeate. This work presents the results of the investigation performed using polymeric membranes. The study showed that membrane separation keeps a significant fraction of organics in the retentate. Such concentration significantly increases the biomethane potential of such effluent as well as the energy that could be theoretically used for the generation of process heat using the concentrated retentate in the wet oxidation process.Web of Science284art. no. 12852

Hydrothermal Carbonisation as Treatment for Effective Moisture Removal from Digestate—Mechanical Dewatering, Flashing-Off, and Condensates’ Processing

One of the processes that can serve to valorise low-quality biomass and organic waste is hydrothermal carbonization (HTC). It is a thermochemical process that transpires in the presence of water and uses heat to convert wet feedstocks into hydrochar (the solid product of hydrothermal carbonization). In the present experimental study, an improvement consisting of an increased hydrophobic character of HTC-treated biomass is demonstrated through the presentation of enhanced mechanical dewatering at different pressures due to HTC valorisation. As part of this work’s scope, flashing-off of low-quality steam is additionally explored, allowing for the recovery of the physical enthalpy of hot hydrochar slurry. The flashing-off vapours, apart from steam, contain condensable hydrocarbons. Accordingly, a membrane system that purifies such effluent and the subsequent recovery of chemical energy from the retentate are taken into account. Moreover, the biomethane potential is calculated for the condensates, presenting the possibility for the chemical energy recovery of the condensates.Web of Science1613art. no. 510

Estimating droplet charge in numerical simulations of charged sprays

A novel method for estimating droplet charge in numerical simulations of conductively and inductively charged sprays is presented. This method is based on balancing the effective electric field at the sprayer nozzle with the global electric field induced by the charged droplets. The global approach avoids the need for computationally expensive local resolution of the spray formation region, allowing it to be used in Eulerian–Lagrangian simulations of high-flowrate sprays. The method is validated against experimental data from literature, proving it can predict droplet charge with reasonable engineering accuracy, over a wide range of spray parameters, for conductive spray liquids

Numerical simulation of evaporating charged sprays in spray chilling

In this research we investigate whether charged sprays offer any improvements over conventional spray in the spray-chilling of meat. A Eulerian-Lagrangian CFD modelling approach is developed and validated with results from automotive spray painting. The model is then extended to include evaporation and the transport of evaporation products. The simulation results show doubling of the spray transfer efficiency as well as a notable increase in the rate of cooling when electric charge is applied to the spray. Furthermore, the presented modelling approach yields consistent results at low computational costs, making it suitable for use in future design optimisation studies

Spray characteristics of an air-assisted electrostatic atomiser

The spray characteristics of an air-assisted electrostatic atomiser are experimentally investigated using a shadowgraphy particle/droplet image analysis (PDIA) technique. Tests are conducted for varied rates of liquid- and airflow, with and without a voltage applied to the nozzle electrode. The found droplet sizes neatly match the Rosin–Rammler distribution, and an expression for the mean diameter as a function of the flow rates is given. Notably, the electrode voltage (up to 40 kV) has no measurable impact on the droplet size and velocity, and the energy efficiency of the sprayer is found to decrease with increases in both liquid- and airflow

Numerical Study and Experimental Validation of Skim Milk Drying in a Process Intensified Counter Flow Spray Dryer

This research presents 3D steady‐state simulations of a skim milk spray drying process in a counter‐current configuration dryer. A two‐phase flow involving gas and discrete phase is modeled using the Eulerian–Lagrangian model with two‐way coupling between phases. The drying kinetics of skim milk is incorporated using the Reaction Engineering Approach. The model predictions are found to be in accordance with the experimental temperature measurements with a maximum average error of 5%. The validated computational model is employed further to study the effects of nozzle position, initial spray Sauter Mean Diameter (SMD), air inlet temperature, and feed rate on the temperature and moisture profiles, particle impact positions, drying histories, and product recovery at the outlet. The location of the nozzle upwards (≈23 cm) resulted in maximum product recovery and increased the mean particle residence time at the outlet. A similar trend was observed for the highest feed rate of 26 kg/h owing to the increased spray penetration upstream in the chamber. The maximum evaporation zone was detected close to the atomizer (0–10 cm) when the spray SMD is 38 μm, whereas it shifts upstream (40–50 cm) of the dryer for an SMD of 58 μm. The high air inlet temperature resulted in enhanced evaporation rates only in the initial 10–20 cm distance from the atomizer. The results obtained in this study are beneficial for the development of the novel vortex chamber‐based reactors with a counter flow mechanism

Experimental analysis of spray drying in a process intensified counter flow dryer

This research presents an experimental analysis of a counter flow spray drying process using water and skim milk as a feed. The study was performed by examining the droplet size distribution of sprays and the temperature profiles in the dryer. The influence of air inlet temperature, air mass flow rate, feed flow rate, and droplet size on air temperatures in the dryer was evaluated. The evaporation and deposition zones were found to be highly dependent on the droplet size. The obtained results show that it is possible to achieve efficient contact between hot air and spray in a small volume using a counter-current mechanism