Drying in fluidized beds with immersed heating elements

Sludge low-temperature drying with mainly non-phase change in mere seconds based on particle high-speed self-rotation in cyclone

Improper sludge treatment will cause serious environmental problems, and sludge drying is the key to effective treatment. Almost all the existing sludge drying technologies use heating to overcome the great latent heat of moisture vaporization, which leads to high drying energy consumption. In this study, based on the particle high-speed self-rotation in the cyclone and micro-interface oscillations, the cyclone self-rotation drying (CSRD) technology was developed. It can realize drying of the dewatered landfill sludge (DLS) and the urban sewage dewatered sludge (UDSS) with mainly non-phase change. The obtained results reveal that at low carrier gas temperatures (< 100 °C) and very short residence time (< 15 s), the moisture content of the DLS decreased from 53% to 6.85%, and that of the UDSS decreased from 67% to 18.92%. Through calculation, the proportions of moisture non-phase change removal during the CSRD process touched 68.94% and 63.39%, respectively. Based on the experimental studies, we proposed an enlarged industrial application program (50 t/d) for the UDSS drying by employing the CSRD technology. The operating cost was 159.69 CNY/t H₂O, showing prominent advantages. This study can provide guidelines for the practical application of CSRD technology and fill the scientific gap in the field of moisture non-phase change separation for sludge drying.

Parameter Identification For Continuous Fluidized Bed Spray Agglomeration

Agglomeration represents an important particle formation process used in many industries. One particularly attractive process setup is continuous fluidized bed spray agglomeration, which features good mixing as well as high heat and mass transfer on the one hand and constant product throughput with constant quality as well as high flow rates compared to batch mode on the other hand. Particle properties such as agglomerate size or porosity significantly affect overall product properties such as re-hydration behavior and dissolubility. These can be influenced by different operating parameters. In this manuscript, a population balance model for a continuous fluidized bed spray agglomeration is presented and adapted to experimental data. Focus is on the description of the dynamic behavior in continuous operation mode in a certain neighborhood around steady-state. Different kernel candidates are evaluated and it is shown that none of the kernels are able to match the first six minutes with time independent parameters. Afterwards, a good fit can be obtained, where the Brownian and the volume independent kernel models match best with the experimental data. Model fit is improved for identification on a shifted time domain neglecting the initial start-up phase. Here, model identifiability is shown and parameter confidence intervals are computed via parametric bootstrap.

A new setup for the quantitative analysis of drying by the use of gas-phase FTIR-spectroscopy

Drying rates are important for the manufacture of thin films and in specific for the production of electrodes used in electrochemical devices such as fuel cells and electrolyzers. The known procedures to investigate time-dependent sample compositions and selective evaporation rates are insufficient to obtain mean information about the full area instead of a single point analysis. Therefore, a new setup is presented using gas-phase Fourier-transform infrared spectroscopy. This method analyzes the gas-phase composition to recalculate the layer composition in electrode fabrication at any time during drying. According to the golden rule of measurement technology, manufacturer specifications are often overestimated. Therefore, our alternative procedures were used to evaluate the precision of devices used. The calculated measurement precision is confirmed by validation. The expected deviation is quantified to be less than 2% for the common application. Further on, the relative test-retest standard deviation is determined to be 0.3%-0.4%. As a result of the error propagation, the measurement precision is limited by the background gas flow rate precision for common application. At low volume fractions, the influence of the substance flow rate deviations becomes significant. However, further studies will focus on increasing the gas flow rate precision.