Influence of the Heat Loss on the Performance of a Two-stage Gasification Reactor

This paper investigates the gasification efficiency of a two stage gasifier, described in all detail in previous works, as a function of the heat loss across the reactor walls. The behaviour of the reactor was simulated using a simple mathematical model already reported in previous papers. The examined heat loss ranges from 0% of the heat produced by the exothermic reactions into the reactor, up to 20%. Calculations have been performed by keeping constant both the injected total oxygen and its partition between the two stages, while different feedstocks have been used, such as landfill gas, municipal solid waste (MWS), willow and rice straw. The results of calculation show that the gasification efficiency at fixed oxygen injection is greatly influenced by the feedstock. The elaboration of the obtained data indicates also that the trend of the gasification efficiency vs. heat loss is a function of the high heating value of the feedstock and of the ratio between the oxygen present into the reactor (injected + the one of the feedstock) and the stoichiometric oxygen necessary to transform the feeding into carbon dioxide and steam.

Modeling and Simulation of Janus-like Nanoparticles Formation by Solid-Gas Exothermic Reactions

Theoretical model for the simulation of synthesis of Janus-like particles (JP) consisting two different phases using the Carbon Combustion Synthesis of Oxides (CCSO) is presented. The model includes the variation of sample initial porosity, carbon concentration and oxygen flow rate used to predict the formation of JP features. The two temperature (2T) combustion model of chemically active submicron-dispersed mixture of two phases including ferroelectric and ferromagnetic was implemented and assessed by using the experimentally estimated activation energy of 112±3.3 kJ/mol and combustion temperature. The experimental values allowed to account the thermal and concentration expansion effect along with the dispersion by the slip-jump simulation for high Knudsen numbers. The model predicted that the smaller initial porosity of the combustion media creates higher formation rate of Janus-like particles. The simulation of slippage and jumps of the gas temperature allowed the scale-bridging between macro- and micro- structures.

Thermochemistry

Thermochemistry explores the basic principles of energy changes in chemical reactions. Calorimetry is described as a tool to measure the quantity of heat involved in a chemical or physical change. Quantitative overviews of enthalpy and the stoichiometry of thermochemical equations are provided, including the concepts of endothermic and exothermic reactions. Standard conditions are defined to allow comparison of enthalpies of reactions and determine how the enthalpy change for any reaction can be obtained. Hess"s Law, which allows the enthalpy change of any reaction to be calculated, is discussed with illustrative examples. A presentation of bond energies and bond dissociation enthalpies is offered along with the use of bond enthalpy to estimate heats of reactions.

Mathematical modelling of the thermal regime of a ladle- furnace unit considering internal heat sources

We apply mathematical modelling to study heat transfer processes during fire refining of blister copper in a ladle-furnace unit. A ladle-furnace unit was designed to test the refining technology using bottom blowing in a bubble mode by gaseous reducing agents (hydrocarbons) and an oxidiser. Mathematical modelling allows the properties of a real process to be described based on mathematical formalisation of physical laws and regularities. It was proposed to use gaseous reducing agents, rather than expensive residual fuel, as a liquid-reducing agent. The use of gaseous reducing agents in the bottom blowing mode produces higher technical and economic indicators of the process. In addition, some technological operations were transferred directly to the ladle, thereby eliminating the need for re-melting and heating of refined copper. One of the identified problems was the need to maintain the predetermined thermal regime, which provides the very possibility of both performing refining operations and introducing a gaseous reagent (determining the hydro-gas-dynamic parameters) into the melt during bottom blowing. An original method for considering the thermal effects of chemical reactions in mathematical models was presented using an example of exothermic reactions during oxidative refining. The use of two different methods of analysis allowed a comprehensive assessment of the influence of the main exothermic reactions on the thermal regime of the refining process. The presented mathematical models can be used for determining the specific effect of various technological parameters (composition and fuel consumption, temperature and degree of blast enrichment, lining design, etc.) on the dynamics of changes in the temperature field of the melt and the technical and economic parameters of melting as a whole.

Energetic Materials Based on W/PTFE/Al: Thermal and Shock-Wave Initiation of Exothermic Reactions

The parameters of combustion synthesis and shock-wave initiation of reactive W/PTFE/Al compacts are investigated. Preliminary thermodynamic calculations showed the possibility of combustion of the W/PTFE/Al system at high adiabatic temperatures (up to 2776 °C) and a large proportion of condensed combustion products. The effect of the Al content (5, 10, 20, and 30 wt%) in the W/PTFE/Al system on the ignition and development of exothermic reactions was determined. Ignition temperatures and combustion rates were measured in argon, air, and rarefied air. A correlation between the gas medium, rate, and temperature of combustion was found. The shock initiation in W/PTFE/Al compacts with different Al content was examined. The extent of reaction in all compacts was studied by X-ray diffraction. The compositions with 10 and 20 wt% Al showed the highest completeness of synthesis after combustion and shock-wave initiation.

Rice Husk Research: From Environmental Pollutant to a Promising Source of Organo-Mineral Raw Materials

Rice husk is a large-tonnage waste left from rice production. It is not subject to humification and therefore becomes a serious environmental pollutant. Due to the presence of two essential elements—carbon and silicon—in its composition, rice husk is a promising organo-mineral raw material. The known methods for processing of rice husk are associated with the formation of even more aggressive waste. The creation of a waste-free technology for processing this plant material requires a detailed study. Rice husk of yzylorda oblast was studied using IR, SEM, TA, TPD-MS, EPR, and TEM methods. It was determined that under a temperature up to 500 °C, the ligno-carbohydrate component of rice husk decomposes almost completely. Three main peaks are recorded during the decomposition: hemicellulose at 200 °C, cellulose at 265 °C, and lignin at 350–360 °C. This process is endothermic. However, above of 300 °C the exothermic reactions associated with the formation of new substances and condensation processes in the solid residue begin to prevail. This explains the increase in the concentration of paramagnetic centers (PMCs) in products of rice husk carbonization in the range of up to 450 °C. Further increase in temperature leads to a decrease in the number of PMCs as a result of carbon graphite-like structures formation. The silicon–carbon product of rice husk carbonization (nanocomposite) is formed by interconnected nanoscale particles of carbon and silicon dioxide, the modification of which depends on the temperature of carbonization. The obtained data allow management of the rice husk utilization process while manufacturing products in demand based on ecofriendly technologies.

Formation and hydration of eco-friendly cement using industrial wastes as raw materials

In this work, the optimal conditions of the synthesis of eco-friendly cement by using industrial wastes as well as the peculiarities of its early stage hydration were investigated. The eco-friendly cement was synthesized within the 1000–1250 °C temperature range when the targeted composition was 60% of belite, 20% of ye’elimite, and 20% of brownmillerite. It was determined that the optimal sintering temperature for eco-friendly cement is 1100 °C because the primary compounds were fully reacted, and hydraulic active compounds were dominant in the products. Microcalorimetry analysis was performed for the investigation of early stage hydration. The best results of hydration were obtained with the eco-friendly cement which was produced by using mixtures with silica gel waste: three exothermic reactions were observed in the heat evolution curve, while the cumulative heat was equal to 264 J/g after 72 h. Additionally, the sequence of compounds formation during the first day of hydration was analyzed. It was determined that the composition of the initial mixture impacts the hydration rate of synthetic eco-friendly cement; however, it did not affect the mineralogical composition of the hydration products. These results were confirmed by XRD, STA, and SEM analysis.