Robertas Poskas

Investigation of sewage sludge treatment using air plasma assisted gasification

This study presents an experimental investigation of downdraft gasification process coupled with a secondary thermal plasma reactor in order to perform experimental investigations of sewage sludge gasification, and compare process parameters running the system with and without the secondary thermal plasma reactor. The experimental investigation were performed with non-pelletized mixture of dried sewage sludge and wood pellets. To estimate the process performance, the composition of the producer gas, tars, particle matter, producer gas and char yield were measured at the exit of the gasification and plasma reactor. The research revealed the distribution of selected metals and chlorine in the process products and examined a possible formation of hexachlorobenzene. It determined that the plasma assisted processing of gaseous products changes the composition of the tars and the producer gas, mostly by destruction of hydrocarbon species, such as methane, acetylene, ethane or propane. Plasma processing of the producer gas reduces their calorific value but increases the gas yield and the total produced energy amount. The presented technology demonstrated capability both for applying to reduce the accumulation of the sewage sludge and production of substitute gas for drying of sewage sludge and electrical power.

Investigation of Air Flow Distribution in Small-Scale Food Products Dryer

Experimental and numerical investigations showed that the air flow velocity distribution between the shelves with identical inlet cross sections is nonuniform; in the gaps between the shelves located in the bottom part of the dryer the velocity is rather high and in the gaps between the shelves located in the middle and at the top of the dryer the velocity is low. A nonuniform air flow distribution causes unequal drying of the product; therefore, the position of shelves with the products must be periodically changed; that is, operation of the dryer is not optimal. It was revealed during numerical investigations that the use of variable inlet cross sections between the shelves gives more uniform air flow distribution. Numerically obtained air flow velocity distribution results between the shelves with the use of variable inlet cross sections were also justified experimentally.

Opposing Mixed Convection Heat Transfer in the Inclined Flat Channel in a Laminar-Turbulent Transition Region

In this paper we present the results on experimental and numerical investigations of the local opposing mixed convection heat transfer in an inclined flat channel (φ = 60° from horizontal position) with symmetrical heating in the laminar-turbulent transition region. The experiments were performed in airflow (p = 0.2 and 0.4 MPa) in the range of Re from 1.5 · 103 to 5.3 · 104 and Grq up to 1.5 · 1010 and at the limiting condition qw1 ≈ qw2 ≈ const. The experimental data show similar tendencies in the heat transfer as it was revealed in vertical channel. It is already some difference in the local heat transfer for upper (stable density stratification) and bottom (unstable density stratification) walls. The data of the experimental investigations have been compared with the results of numerical modelling using Ansys Fluent 12.0 code. The modelling was performed using laminar and transition models for Rein = 3.1 · 103 and Grqin = 1.9 · 109 for the same conditions as during the experiment, i.e. with the same airflow pressure (0.4 MPa), velocity, and temperature at the inlet and heat flux at the walls of the flat channel with the same geometrical characteristics.Copyright