Pawel Wawrzyniak | Technical University of Lodz (original) (raw)

Papers by Pawel Wawrzyniak

Energies

Drying is an extremely energy-intensive process. Superheated steam as a drying medium can improve... more Drying is an extremely energy-intensive process. Superheated steam as a drying medium can improve the energy efficiency of the drying processes. In superheated steam drying, waste heat can be recovered by condensing the exhaust steam or raising its specific enthalpy. Spray drying is widely used in industry, even though its energy efficiency is often low. Substitution of air by superheated steam as a drying medium in a spray dryer may reduce the energy consumption of the drying process by 20–30%; moreover, if excess steam generated by moisture evaporation is upgraded to a higher temperature level and reused for drying, the energy demand could be decreased by even 80%. A literature review showed that superheated steam spray drying was successfully applied for both thermally resistant and a wide range of thermally sensitive materials. Superheated steam drying gives a number of advantages in terms of product properties, i.e., higher particle porosity due to rapid moisture evaporation re...

Proceedings of the 22nd International Drying Symposium on Drying Technology - IDS '22

The paper presents the experiments of drying of skin forming material in counter-current pilot pl... more The paper presents the experiments of drying of skin forming material in counter-current pilot plant drying tower for the different distances between the nozzle and the air inlet. Laser Doppler Anemometry (LDA) experiments were performed to determine hydrodynamics in the tower for different mass air flow rates. Phase Doppler Anemometry (PDA) measurements carried out below and above a nozzle enabled to trace changes of particle size distribution and particle velocities in the tower as a function of nozzle position in the dryer. Experimental analysis of PSD of the powder proved the significant effect of nozzle position on product properties.

$Research paper thumbnail of Subcritical CO2 extraction of a volatile oil-rich fraction from the seeds of Nigella sativa for potential pharmaceutical and nutraceutical applications$

Journal of Essential Oil Research

Abstract Seeds of black cumin (Nigella sativa L.) were subjected to subcritical CO2 extraction (S... more Abstract Seeds of black cumin (Nigella sativa L.) were subjected to subcritical CO2 extraction (SbFE) at 70 bar and 30 °C for 2 h in a trial to isolate a volatile oil-rich fraction. That treatment led to obtaining an oleoresin which constituted 1.74 wt.% of the total seeds’ weight and was found to be rich in its volatile oil content (66.6 wt.%). Traditional methods of extracting the oleoresin using n-hexane at room temperature or at 60 °C led to much higher yields (23.6 and 32.9 wt.%), respectively. The volatile oils’ content of these oleoresins was 4.75 and 3.59 wt.%. GC-MS analysis showed that the volatile oil obtained after SbFE is characterized by the highest thymoquinone (TQ) content (60.5%) compared to that obtained after hexane extraction at room temperature (37.6%) or at 60 °C (41.6%). On the other hand, TQ content of the volatile oils isolated directly from the seeds by hydrodistillation and steam distillation was much lower (10.2 and 23.7%), respectively. Based on the above mentioned, SbFE of N. sativa seeds was found to be a useful green tool for obtaining a volatile oil-rich oleoresin with high TQ percentage which can be applied in pharmaceutical and nutraceutical products.

Proceedings of 21th International Drying Symposium, Sep 11, 2018

Drying is one of the most energy intensive unit operations. It easily accounts for up to 15% of a... more Drying is one of the most energy intensive unit operations. It easily accounts for up to 15% of all industrial energy consumption. In the most drying processes heat is required to evaporate moisture which is later removed with a flow of air. The hot, humid air leaving the dryer is often considered as a waste stream, and a large fraction of energy is lost. The aim of the theoretical and experimental concept study presented here was to evaluate a method of reclaiming energy from low temperature waste streams and converting it to useful in industry saturated steam of temperature from 120 to 150 °C. Chemical heat pump concept based on the dilution and concentration of phosphoric acid was used to test the method in the laboratory. Heat of dilution and energy needed for water evaporation from the acid solution were experimentally measured. The cycle of successive processes of dilution and concentration has been experimentally confirmed. Theoretical model of the chemical heat pump was tested and coefficient of performance measured. Energy balance of the drying system and efficiency increase of the dryer supported with chemical heat pump were calculated.

Drying Technology

Abstract The paper presents an experimental analysis of the spray drying conditions on the produc... more Abstract The paper presents an experimental analysis of the spray drying conditions on the product properties in a pilot plant counter-current spray dryer with swirling air flow. The influence of slurry – atomizing air ratio, drying air flow rate and swirl number on the product properties and the efficiency of the drying process was examined. The increase of the slurry – atomizing air ratio promotes agglomeration, ultimately leading to the development of wet, coarse granules. Through experimentation, the slurry-to-atomizing-air ratio can be optimized to maximize capacity ratio (i.e. acceptable product vs. total spray dried powder) and energy efficiency whilst achieving the desired product quality.

Advanced Powder Technology

Abstract In this study, CFD simulations of particle and droplet agglomeration in an industrial co... more Abstract In this study, CFD simulations of particle and droplet agglomeration in an industrial counter-current spray dryer are presented. For this purpose, a modified form of the stochastic collision agglomeration model is proposed. This model takes into account droplet–droplet collision as well as wet and dry particle interaction. These events are coupled with heat, mass and momentum transfer. A comprehensive moisture evaporation model based on the concept of characteristic drying curve (CDC) was applied to predict the drying kinetics of the detergent slurry. Due to high instability in air flow inside the drying chamber, simulations were carried out under transient condition. A comparison between time-averaged simulation results and measurements, which were performed on an industrial spray drying installation, shows a good agreement. This finding proves the correctness of the developed agglomeration and drying models. The presented methodology of CFD simulations of agglomeration can be used to design or optimise spray-drying installations and to predict the final particle size distribution of the product.

The verification of CFD modelling of particle and droplet agglomeration in an industrial counter-... more The verification of CFD modelling of particle and droplet agglomeration in an industrial counter-current spray dryer is presented. A comprehensive moisture evaporation model base on the concept of characteristic drying curve was applied into CFD solver. Model including coupling calculations of particle agglomeration and heat, mass and momentum transfer between phases. A comparison of simulation and measurements results shows good agreement of proposed agglomeration and drying model. Developed methodology of CFD simulations, shown in this work, can be used in optimization of spray drying installation and prediction of product properties and final particle size distribution.

The three-dimensional simulation of dust explosion in a closed volume is still one of the most ch... more The three-dimensional simulation of dust explosion in a closed volume is still one of the most challenging applications of CFD technique. Standard ANSYS software was selected to model dust explosion inside the spray drying tower. A typical approach replacing dust with a flammable gas-air mixture in the CFD calculations was used. Two sets of CFD calculations of dust explosion in the tower were carried out at uniform gas concentration, and variable concentration in the dryer which reflect distribution of wet and dry powder zone in spray dryer. The CFD calculation showed that dust explosion develops from the ignition point mostly to the upper part of the tower. The temperature, velocity and reaction profiles followed the same upward pattern. Results of calculations allow to determine position and parameters of venting devices which should be installed to minimize the risk of damages of the dryer construction.

Drying Technology, 2015

A 3D CFD model of agglomeration of droplets and particles based on the kinetic theory of gases to... more A 3D CFD model of agglomeration of droplets and particles based on the kinetic theory of gases to simulate a counter-current spray drying process in semiindustrial scale has been developed. The concept of characteristic drying curve was applied to model of particle moisture evaporation including coupling of particle agglomeration and heat, mass and momentum transfer between discrete and continuous phase. A comparison of calculated particle size distributions and experimental data obtained from PDA measurements in each cross-section of the dryer shows good agreement. The methodology developed in the frame of this work can be used to optimize the operation of spray towers and predict final product properties.

Journal of Non-Crystalline Solids, 1995

ABSTRACT A crucial stage in silica aerogel production in which extraction with liquid (or supercr... more ABSTRACT A crucial stage in silica aerogel production in which extraction with liquid (or supercritical) carbon dioxide is used is alcohol diffusion through alcogel to CO2. The quality of samples produced ranged from perfect monoliths (long diffusion times) to completely damaged specimens (the shortest diffusion times). In intermediate conditions, a non-transparent damaged zone was observed inside samples. On the basis of the dependence of damage size on diffusion time, the values of the diffusion coefficient of ethanol in the liquid CO2 inside the silica gel were identified for two temperatures.

Journal of Non-Crystalline Solids, 1998

Extraction of a primary solvent with liquid or supercritical carbon dioxide is the most difficult... more Extraction of a primary solvent with liquid or supercritical carbon dioxide is the most difficult to control stage in low-temperature silica aerogel production. Diffusion of primary ethanol through alcogel structure to surrounding CO was 2 investigated in carefully controlled experiments with cylindrical alcogel samples. Changes of the alcohol concentration in carbon dioxide leaving the autoclave were followed with on-line chromatograph analysis and experiments were repeated for temperatures around the critical point of carbon dioxide. On the basis of the concentration histories during the drying, the temperature dependence of diffusion coefficient in the ethanol-CO mixture inside the silica gel at constant pressure was 2 identified.

Journal of Non-Crystalline Solids, 2001

In low-temperature aerogel production, replacement of an original solvent with liquid or supercri... more In low-temperature aerogel production, replacement of an original solvent with liquid or supercritical carbon dioxide is the crucial stage, and it is one fully controlled by a diusional mechanism. The diusion of ethanol as the primary porē uid through an alcogel structure to the surrounding near-critical CO 2 was investigated in carefully controlled experiments with cylindrical alcogel samples. Changes of the alcohol concentration in carbon dioxide leaving the autoclave were followed with an online gas chromatographic analysis. The experiments covered the range of temperatures from 292 to 315 K and pressure from 6.9 to 9.1 MPa. On the basis of the concentration histories during the drying, the diusion coecient in the ethanol±CO 2 mixture inside the silica gel was identi®ed for each experiment. A comparison of measured concentrations with values derived from a mass transfer model is presented and discussed. The method for identifying an eective diusion coecient is described and the values of ethanol±CO 2 eective diusivity in a silica network are presented. The correlation of eective diusion coecient in the porous structure of silica gel with the Schmidt number ratio covering the entire investigated range of temperature and pressure is proposed.

Drying Technology, 2013

ABSTRACT

Drying Technology, 1996

ABSTRACT Gels dried in supercritical conditions give a new class of materials called aerogels. Th... more ABSTRACT Gels dried in supercritical conditions give a new class of materials called aerogels. The process of silica aerogel production in which extraction with liquid (or supercritical) carbon dioxide is used, consists of four main stages: elution, diffusion, heating and evacuation.Aerogel production from silica gels prepared from tetraethoxysilane is described. The autoclave process which started with alcohol-liquid carbon dioxide exchange was followed by supercritical evacuation. Some important technical aspects of the process are considered. The effect of elution rate, temperature and duration of diffusion is investigated.

Diamond and Related Materials, 1994

Journal of non-crystalline …, 1998

Developments in Chemical Engineering and Mineral Processing, 2008

ABSTRACT In this paper the need for innovative drying techniques is suggested. Pulse combustion a... more ABSTRACT In this paper the need for innovative drying techniques is suggested. Pulse combustion and supercritical fluid techniques which were developed in the drying laboratory of the Lodz Technical University are presented as examples. In the section concerned with pulse combustion, valved and valveless pulse combustors are described and several features of both types are identified. The advantages and drawbacks of the pulse combustor are presented. The selection of a pulse combustor, its geometry and atomizer as well as enhancement of drying rate are discussed. The importance of the high driving force in this process intensification is stressed. In the section dedicated to supercritical fluid techniques, high- and low-temperature procedures of drying are described. The most important aspects of the drying cycle are discussed with special reference made to the kinetics of diffusive solvent exchange inside a wet gel body.

Advanced Powder Technology, 2017

Abstract A methodology is presented here for the mathematical modelling of moisture evaporation i... more Abstract A methodology is presented here for the mathematical modelling of moisture evaporation in a dispersed system in an industrial tower. An empirical model using characteristic drying curves was applied to calculate moisture evaporation from a droplet and particle. A simple method was developed to calculate the agglomeration process of the dispersed phase in the drying towers, using transient functions between the initial and final particle size distributions, at the nozzle and in the final product. The developed model and simulation results were validated on the basis of industrial spray tower experiments. High instability of the airflow due to the geometry of the dryer and the construction of the air inlets was observed. The general methodology applied within this CFD model is universal, and can be applied to the scaling-up of installations for dewatering in dispersed systems in order to determine configurations of feeding systems and control the product quality and safety of the process.