1/2022
Zlata Mužíková, Pavel Šimáček
Over the last 25 years, the diesel fuel has undergone major changes in its composition, which have fundamentally affected its long-term storage possibilities. An oxidation stability is a main parameter characterising the storage of the diesel fuel and it is strongly affected by a diesel fuel composition. The oxidation stability decreases in a line saturated hydrocarbons – aromatic hydrocarbons – unsaturated hydrocarbons. The mandatory use of FAME as a biocomponent of the diesel fuel negatively affect its oxidation stability. The FAME contain unstable double bonds C=C and their mixtures with mineral diesel fuel cannot be storage for a long time. The use of antioxidants with FAME has not effect in the long time storage. A recommended usable life of diesel fuel with FAME accor-ding to ČSN 65 6500 is from 1 to 3 months according to the FAME content. However, in some cases it is ne-cessary to store diesel fuel for a long time. State material reserves or back-up diesel generators are examples, when the diesel fuel is stored for the long time.
The oxidation stability of the fuel expresses a resistance to an oxygen action. The oxygen, which is dissolved in the fuel, attacts molecules of the fuel and various oxidation products create. Hydroperoxides are the primary oxidation products. Secondary oxidation reactions give aldehydes, ketones, karboxylic acids and insoluble deposits. The oxidation products negatively affect the diesel fuel properties.
Besides the composition the oxidation stability of the fuel is negatively affected by a high temperature,a high content of dissolved oxygen, an UV radiation and a presence of metals with a catalytic effect.
An overview of methods used for the measuring or the observing oxidation stability was prepared in the article. It means not only the oxidation stability measuring but also a measuring of the content of different oxidation products which are related to the various oxidation degree .
The aim of the article was to summarize the possibilities of a predicting the storage time of the diesel fuel and to propose a procedure for the monitoring and the predicting its longterm durability. Only one standardized storage test according to the ASTM D4625 can be found in the literature. The test is based on the storage of 400 ml of the diesel fuel at 43 °C for periods of 4, 8, 12, and 24 weeks. After aging for a selected period, a sample is analyzed for insolubles. The correlation of the test results is: a week at 43 °C is roughly equivalent to a month of the storage at the temperature of 21 °C. The test is a time and material consuming and the correaltion was determined for diesel fuels made up to 1990´s.
The new shorter storage test based on the standard test according to ASTM D4625 was proposed to predict diesel storage stability. The temperature was rised and the the time was shortened up to one month. During the test short laboratory analyses can be used for monitoring oxidation of the diesel fuel for example: the oxidation stability by PetroOxy, the peroxide number, the oxidation index by infrared spectroscopy, the acid number, the bromine number or the antioxidant content. The sample consumption is about 100 ml according to the selected analyses.
Keywords: diesel fuel; oxidation stability; storageability
Markéta Kalivodová, Marek Baláš, Pavel Milčák, Hana Lisá, Martin Lisý, Jakub Lachman, Petr Kracík, Peter Križan, Karel Vejražka
Biomass has increasingly been used as a renewable energy source, and the possibility of using waste ma-terials for energy purposes has recently been highlighted. Therefore, it is necessary to know the properties of these fuels. The most important is the Higher Heating Value (HHV), and also the Lower Heating Value (LHV), which expresses the amount of energy stored in the fuel. These are determined by an experiment but can also be determined by calculation. This paper deals with the comparison of existing equations for the calculation of HHV with the value determined experimentally by a calorimetric method. The suitability of using the given equation for the given fuels is evaluated. Based on the results of the applied equations, some of them are selected and recommended for the calculation of certain fuels.
Keywords: higher heating value, lower heating value, biomass, calorific value
Karel Ciahotný
The use of activated carbon in environmental protection and other separation processes has expanded considerably in recent years in the technologically advanced countries of the world. World production of this interesting adsorbent material is currently approaching 1 million tons per year and is growing constantly. The largest use of activated carbon is in the field of drinking and wastewater treatment, waste gas treatment, chemical methods of gold mining and refining processes in industrial, pharmaceutical and food processing. The sorbent used needs to be regenerated in order to be able to continue to serve or to dispose of it ecologically if its regeneration or reactivation is not possible. The article deals with the possibilities of the restoration of sorption properties of used by regeneration and reactivation procedures, describes the differences between these processes, and also deals with evaluation of the sorption capacities of carbonaceous sorbents with restored sorption capacity.
The technologies that use integrated regeneration of the saturated adsorbent directly in the adsorption plant and technologies that replace the saturated adsorbent with new ones, which show more favorable investment costs, are currently used in the operational practice. The saturated adsorbent used with organic substances is usually not disposed of, but regenerated or reactivated in the regeneration / reactivation plant. Both of these technologies have also been introduced and operated in the Czech Republic in the past.
In the Czech Republic, there are currently two industrial facilities in operation designed to regenerate activated carbon saturated with organic substances.
In the case of regenerated / reactivated sorbents, it is important to have a suitable sorbent certificate with a restored structure, which determines the degree of restoration of the porous structure of the sorbent. Because of this, it is necessary to adjust the expected adsorption capacity of the sorbent with a restored porous structure for the captured substances, and subsequently also the sorbent exchange interval. Only in this way will the adsorption equipment meet the emission limits determined throughout the operation.
Keywords: adsorption; regeneration; reactivation; testing; activated carbon
František Skácel a Viktor Tekáč
During various modes of operation of the melting furnace, a large amount of aerosol particles consisting mainly of amorphous carbon is generated irregularly depending on the current state (especially during the loading of the return material), accompanied by the development of significant amounts of volatile organic compounds and methane. The resulting mixture of organic substances is not quantitatively eliminated in the afterburner chamber of the melting furnace. The VOC mass flow remains almost unchanged and only the methane mass flow decreases. The mass flux of aerosol particles, on the other hand, increases after passing through the afterburner chamber, with particles of aluminium metal contributing significantly to this increase. The aerosol particles trapped on the textile filter of the melting furnace are thus composed of particles of amorphous carbon and particles of inorganic origin (metallic aluminium and limestone). The structure and surface properties of the carbon particles pose a significant risk of textile filter ignition.
From the measurement results obtained, the following solution to the hazardous condition of the plant can be found:
(a) a change in the existing technology, for example: changing the design of the part of the melting furnace into which the return material is fed; changing the heat input and the mode of the gas burner and fan in this part of the furnace; a significant reduction of the flue gas flow in the A-gauge and afterburner chamber or change of machining emulsion;
(b) the installation of an additional gas burner in the newly installed afterburner chamber, to which the flue gases from the part of the melting furnace into which the return material is fed would be discharged in the existing return material inlet mode.
Keywords: amorphous carbon, black carbon, fire protection, aluminum foundry, textile filter
Karel Svoboda, Michael Pohořelý, Tomáš Ružovič, Václav Veselý, Jiří Brynda, Boleslav Zach, Michal Šyc
Emissions of toxic heavy metals (HMs), as Hg, As, Cd, Pb, etc., and some harmful compounds of F, Se, and B are related to waste streams from coal-fired power plants (CFPP). Coal/lignite combustion, due to relatively high content of ash, sulfur, and chlorine, generates in flue gas cleaning processes tremendous amount of fly ash, CaSO4 and CaCl2. Measures for minimization of Hg- and NOx-emissions (e.g. addition of bromides and NH3) change properties of fly ash, wastewater and speciation/partition of HMs. Wet flue gas desulfurization (FGD) consumes high amount of fresh water and generates harmful wastewater with water soluble salts. The planned, more stringent limits on emissions of dust, Hg, HCl, HF, SO2, etc. in CFPP will increase contents of polluting compounds in solid and liquid waste streams. We critically assess possibilities, measures and obstacles for higher efficiency of Hg and HMs removal from flue gas in CFPP, together with efficient removal of other pollutants including mutual influences and interrelations. The fates of mercury, selected harmful HMs, and some other pollutants in waste streams from wet FGD are critically analyzed and discussed. Non-toxic, stable forms of mercury (e.g. HgS) and other HMs in solid waste should be preferred. Schemes and measures for minimization of emissions and hazardous waste streams from air pollution control (APC) are compared and discussed for three selected technologies of coal combustion with different methods of gas cleaning.
Keywords: Coal combustion, Mercury removal, Hazardous waste, Heavy metals, Zero liquid discharge, Water recovery
