Paliva (Fuels) is a scientific journal issued quarterly by the Faculty of Environmental Technology, ICT Prague. Fuels publishes papers on a broad range of topics covering exploitation, processing, upgrading, and utilization of various types of fuels, and power engineering.
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Hydrocracking of Fischer-Tropsch Wax

Olga Pleyer, Petr Straka, Dan Vrtiška, Jiří Hájek, Radek Černý

The low-temperature Fischer-Tropsch synthesis (LTFT) processing of renewable feedstocks combined with the hydrocracking of its solid product is an effective way to produce synthetic renewable engine fuels. The hydrocracking of an FT wax derived from natural gas using the LTFT synthesis was studied in this paper. The hydrocracking was carried out in a tubular fixed-bed reactor with a cocurrent flow of the feedstock and hydrogen. Reaction temperatures in the range of 305– 370 °C, a pressure of 8 MPa, an H2/feed ratio of 500 m3/m3 and weight hour space velocities (WHSV) of 1; 2 and 4 h-1 were tested. The naphtha fraction (boiling up to 200 °C) was the main product of the hydrocracking under all the tested reaction conditions. It could be used as a component into petroleum-derived gasoline in a neat form or the after processing by common refinery processes (isomerization and/or reforming). The production of low-sulfur and low-aromatic paraffinic solvent or the utilization as a feedstock for steam cracking could be some other options of the naphtha fraction utilization. The maximum yield of the gaseous products (depending on the reaction temperatures and WHSV) was 20 wt.%. They were primarily composed of n-alkanes and isoalkanes and could be, therefore, used as an optimal feedstock for steam cracking as well. The C3-C4 fraction of the gaseous products could be also utilized as an LPG fuel. Very low yields (up to 10.4 wt.%) of the middle distillates were obtained under all the tested reaction conditions. Due to their saturated nature, their densities were very low and, additionally, poor low-temperature properties can be expected.

Keywords: Fischer-Tropsch synthesis; hydrocracking; FT wax; synthetic fuels
2/2020 - pages 26 - 33DOI: 10.35933/paliva.2020.02.01

A review on short-range dispersion modelling of gaseous pollutants released from stationary sources

William R. Patiño, Van Minh Duong

The reliance on solid fuels for heat processing and power generation with low efficiency and inadequately control of gaseous pollutants is strongly related to health impacts and environmental pollution. Atmospheric dispersion modelling is an essential tool to assess the potential impacts of related stationary sources on local air quality. Advanced Gaussian plume models provide an up-to-date assemble of algorithms to estimate contaminant concentrations distributed at a variety of heights and distances. This review presented a comparative evaluation on ADMS and AERMOD performance in different validation scenarios considering SO2 emissions and the NOx chemistry scheme. Terrain, stack height and plume rise influence on emissions, along with modelling uncertainties and limitations were also discussed. Contour plots of maximum daily values and annual averages confirmed a remarkable similarity in patterns within simulations. By this approach, the study extended recent practical information and recommended a complementary instrument for the improvement of the reference model SYMOS´97 implemented in the Czech Republic.

Keywords: power plant, air dispersion modelling, Gaussian plume model, nitrogen oxides
2/2020 - pages 34 - 41DOI: 10.35933/paliva.2020.02.02

Effect of the hydrogen to feedstock ratio on the hydrotreating of the mixture of petroleum middle distillates and rapeseed oil

Josef Blažek, Daria Kochetkova, Bogdan Shumeiko, Veronika Váchová, Petr Straka

The hydrotreating of vegetable oils and animal fats is a possible way to produce a high-quality renewable diesel fuel component. It can be produced by processing the bio-raw material in new units or by the co-pro-cessing of the renewable raw material together with the petroleum middle distillates in existing hydrotreating units. This work was focused on investigating the effect of the hydrogen to the feedstock ratio on the hydrotreating of a mixture of petroleum middle distillates and rapeseed oil in a weight ratio of 8:2 in a tubular fixed-bed reactor. The hydrotreating was performed using a sulfided Ni-Mo/Al2O3 catalyst, a temperature of 345 °C, a WHSV of 1.0 h-1, a pressure of 4.0 MPa and a hydrogen to the feedstock ratio in the range of 120-600 m3∙m-3. The hydrogen to feedstock ratio of 120 m3∙m-3 was not sufficient to desulfurise the feedstock to the level of 10 mg∙kg-1. On the contrary, increasing the hydrogen to feedstock ratio to above 240 m3∙m-3 had no significant effect on the yield and quality of the obtained products. Therefore, the ratio of 240 m3∙m-3 was considered as sufficient for the hydrotreating of the mixture of the petroleum middle distillates and rapeseed oil.

Keywords: hydrotreating; vegetable oil; catalyst; renewable diesel; hydrogen to fuel
2/2020 - pages 42 - 52DOI: 10.35933/paliva.2020.02.03

Influence of engine and exhaust system condition on NOx emissions of petrol-powered personal cars

Libor Špička, Ondřej Červinka, Jitka Hegrová, Zdeněk Hejkal
The article is focused on the measurement of emissions in real traffic, where the concrete examples shows the impact of technical condition of vehicles on NOx, namely NO emissions production. The choice of vehicles was limited to vehicles with spark ignition engines. One vehicle had unsuitable condition of the engine. The other vehicle had insufficient efficiency of exhaust gas treatment components. The measurement results of both vehicles were compared with the reference vehicle, which was demonstrably in good condition. The condition of the vehicles was assessed on the basis of diagnostic trouble codes stored in the engine control unit and analysis of the engine oil sample by mass spectrometry or information from the vehicle owner. Emissions were measured using a mobile measuring device, where NO is determined by the electrochemical method. The experiment showed that the defective vehicles showed by one or two orders of magnitude higher emission factors. A vehicle with demonstrable defects in sphere of the preparation of fuel mixture and cylinders filling, produced approximately 18 - 167 times more nitric oxide in each type of operation than the selected car in good technical condition. A vehicle with a presumably inoperative catalytic converter emitted nitric oxide approximately 55 - 134 times more.
Keywords: emission; abrasion; metals; mass spectrometry; technical condition
2/2020 - pages 53 - 59DOI: 10.35933/paliva.2020.02.04

Microscopy as a Reliable Tool for the Evaluation of Marine Fuels Stability

Aleš Vráblík, Karolína Jaklová, Nikola Bringlerová, Dominik Schlehöfer, Radek Černý

The stability of marine fuels is traditionally a very hot topic, especially in the beginning of so-called sulphur cap. The sulphur cap is the process of reducing the maximum level of sulphur content (from 3.5 to 0.5 wt%) in marine fuels, which are being used on deep sea from the first of January 2020. After this change, the large amount of marine fuels will be produced as a mixture of two or more components to achieve required sulphur level. Higher amounts of cutter stocks will increase the likelihood of decreased stability or compatibility of the marine fuels. Therefore, a reliable stability tests or their combination will be very important for marine fuels evaluation. However, only total sediment after aging is defined as a standard method according to ISO 8217 for stability testing. This method is not suitable for all the analysed marine fuels, so we verified using of microscopy for this type of evaluation. The set of marine fuels samples was tested using microscopy, results were processed and correlated with other selected qualitative parameters. The microscopy was evaluated as a suitable method for testing of marine fuels stability. This method could be used for very fast evaluation in industrial as well as research laboratories in combination with standard methods.

Keywords: marine fuel; stability; microscopic analysis; total sediment
2/2020 - pages 60 - 65DOI: 10.35933/paliva.2020.02.05

Secondary utilization of the spent fly ashes-derived sorbents

Marek Staf, Barbora Miklová, Zuzana Strolená, Lukáš Anděl
In the years 2017-20, the research on the use of fly ashes and bottom ashes from power plants for the preparation of adsorbents for carbon dioxide capture from flue gases was carried out at the involved institutes. As part of the research, adsorbents were prepared by alkali fusion and hydrothermal processes. The obtained products were subjected to cyclic adsorption and desorption tests simulating their industrial use. One of the partial tasks was to evaluate how the worn adsorbents can be subsequently utilized.
In the study presented here, the materials collected after the adsorption testing were subjected to several procedures, which aim was to verify the applicability of these materials as substrates for the reclamation of excavated brown coal and lignite quarries. The basic property assessed was the ability to retain humidity and thus contribute to the water balance in the reclaimed landscape. A hydration test followed by slow drying of the sample in a thermogravimetric analyzer was proposed for this purpose.
With regard to the raw materials from which the adsorbents were prepared, attention was also paid to the risk of undesired leaching of toxic substances.
The last measured parameter was the course of CO2 desorption from the pores of the used adsorbent. It answers the question of whether the adsorbent is usable for terrain reclamations in the state after the last adsorption (i.e. CO2 saturated), or whether it requires thermal desorption as the final step.
Based on the results of hydration tests of the spent adsorbents, it can be concluded that they could be applied in the reclamation of closed lignite quarries, and these materials would allow a more sophisticated application than just as a stabilizer.
In the tested samples, the high retention of water and its slow release was confirmed by the TGA method, which (in the case of the mentioned use) could improve the management of soil humidity and its distribution to woody plants used in the biotechnical reclamation phase. Another, but as yet unproven, possibility is to use the porous structure of the materials as a suitable substrate for colonization by nitrifying bacteria. These bacteria would subsequently improve the self-cleaning ability of the water tank created in the case of the hydraulic reclamation method.
Due to the results of measurements of carbon dioxide desorption from saturated adsorbents, it is necessary to recommend that thermal desorption should be included in their preparation before the use in reclamation.
Tests of toxic elements leaching have not identified any potential risk from their mobilization into groundwater or surface water.
Keywords: adsorbent, fly ash, carbon dioxide, recultivation
2/2020 - pages 66 - 76DOI: 10.35933/paliva.2020.02.06

technical support editor-in-chief