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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Halogenated polymers as a problematic component in the pyrolysis of waste plastics

Marek Staf, Gleb Petrenko

The study deals with the complications associated with the pyrolysis of a polymer releasing highly corrosive compounds and other products that are difficult to be utilized in practice. Poly(vinyl chloride-vinyl acetate) was chosen as a sample material. This copolymer was subjected to slow pyrolysis up to a temperature of 650 °C, which was achieved with a temperature ramp of 10 °C min‒1. Thermal decomposition took place in a batch apparatus in nitrogen atmosphere. The evaluation of the experiments included a mass balance using an online recording of gas and condensate formation, which was followed by an analysis of the obtained products. The tests showed very small yields of condensates (pyrolysis tar) in the range of 3.0 – 5.5% compared to gas production reaching 71.1 – 72.1% of the raw material weight. Within the discussion, the problem with the production of non-flammable gas consisting mainly of HCl in the initial stages of pyrolysis was highlighted. Under the given conditions, the release of acid gases, in which HCl was gradually replaced by also non-flammable CO2, continued up to about 400 °C. Only gases collected from this temperature above and having a calorific value of 33.5 MJ m‒3 (20 °C / 101.32 kPa) can be considered energetically usable. Condensates mainly represented by a mixture of aromatic hydrocarbons, acetic acid and chlorobenzene were also evaluated as problematic for possible use. The possibilities of physical activation of solid pyrolysis residues by steam at temperatures of 850 and 900 °C were also tested. All experiments led to obtaining products with very small specific surface areas in the range of 1 – 6 m2 g–1. The process loss during activation reached 25 – 33% of the pyrolysis residue weight, depending on the applied temperature and contact time with steam. These values show that the reaction of the activation medium with the sample took place more or less only on the outer surface of the particles and did not lead to the development of an internal porous structure. The achieved results were compared with the identically processed samples of waste tires, which were evaluated as promising in tests carried out in the past. The contrast be-tween the two materials clearly spoke against the discussed copolymer. The results of the experiments can be interpreted, among other things, as a certain warning against attempts at industrial pyrolysis processing of this type of plastic.

Keywords: pyrolysis, PVC, PVAC, bass balance, fhysical activation, surface area
3/2023 - pages 70 - 79DOI: 10.35933/paliva.2023.03.01

Long-term monitoring of the parameters of fuel wooden residues

Ondřej Hlaváček, Zdeněk Beňo
Due to European Union policy aimed at limiting the use of fossil fuels for the production of electricity and heat, there are many of producers looking for suitable substitutes. In 2022 in the Czech Republic coal-fired heating and power plants were almost 47.5% of the energy mix. One of the possibilities is the replacement of coal with wood chips or wood residues from the forest harvesting. But parameters of this material are fluctuating.
The article presents the results of the analysis of 403 samples representing deliveries of wood residues with a total weight of 17,473 t over a period of two years. Monitored parameters were moisture and ash content, LHV and HHV.
The average values were 36.02 % of moisture content, 2.28 % of ash content, 11.1 MJ·kg-1 LHV and 12.66 MJ·kg-1 HHV. There is an influence of the year period when the wood residues with better LHV were supplied during the summer months. There are some correlations between a moisture content and LHV as well as ash content and HHV. The sample with the highest moisture content (73.58%) had the lowest LHV (3.34 MJ·kg-1). The sample with the highest ash content (18.35%) had the lowest HHV (7.07 MJ·kg-1). In a few of supply were higher content of stones, asphalt or uncrushed parts of the tree which caused problems on heating plant technology.
Keywords: wood chips, biomass, calorific value, humidity, ash
3/2023 - pages 80 - 83DOI: 10.35933/paliva.2023.03.02

Storage of a mixture of natural gas and hydrogen in underground gas reservoirs

Dominik Tománek, Tomáš Hlinčík
In accordance with the document of the Ministry of Industry and Trade – Hydrogen Strategy of the Czech Republic, it can be expected that in the coming years, pressure will be exerted to inject hydrogen into the gas infrastructure, which is currently used mainly for natural gas. Injection of hydrogen into natural gas can have an effect not only on the transport and distribution system, but also on the storage of this mixture in underground reservoirs in CR. This article aims to describe the issue of storing a mixture of hydrogen and natural gas in underground reservoirs. In particular, the effect on the storage capacity and on the overall integrity of the reservoir, problems with the embrittlement of the metal parts of the probes, the effect on the rubber seal. The paper therefore describes not only the effects on the storage of a mixture of hydrogen and natural gas, but also on the devices that are located on surface technologies. The results of studies from foreign literature demonstrate that the addition of 10-15% by volume of hydrogen to natural gas will have a minimal effect on the operation of the underground reservoir.
The storage of a mixture of hydrogen and natural gas in the Czech Republic is currently a much-discussed topic, also regarding the experience with the storage of town gas (which contained a high proportion of hydrogen) in the Lobodice aquifer type underground gas storage.
Keywords: hydrogen, natural gas, underground storage
3/2023 - pages 84 - 91DOI: 10.35933/paliva.2023.03.03

Comparison of sorbents based on Ca(OH)2 for removing HCl from flue gas

Ondřej Hlaváček, Alice Vagenknechtová
Due to EU climate change policy are coal-fired heating and power plant switching their fuel to biomass one. Emissions of flue gas from biomass are more environmentally friendly in general, but emissions of HCl and HF are increasing, and BAT limits are quite low for them. The possible solution is installation of technology DSI (Dry sorbent injection), especially with connection with bag house filter flue gas treatment.
Powder of calcium hydroxide is one of suitable solution. Although the chemical composition is same, there are a huge differences in consumption between another types of Ca(OH)2. This article describes two most selling types of Ca(OH)2 in the Czech republic from the lime works in Štramberk (vz.1) and Čertovy schody (vz.2). This article is divided into laboratory part, where characterized both examples, and experimental part – operational test in the heating plant technology.
The results of laboratory part were same for both examples in their thermal characteristic (thermogravimetry and DTA) and real density. Elementary and matter composition were quite similar, only sample 1 was a little bit contaminated by CaCO3 from original material. There was big difference in BET specific area – 14.8 m2·g-1 by sample 1 example and 41.273 m2·g-1 by sample 2. Sample 1 had the most of pore volume in pores with diameter 20-80 nm, the second one on had a more developed pore structure through the whole particle,
Operational tests in same constructed CFB boilers were realized during two months in the same conditions. Control system of the heating plant mange cleaning technologies by emission limits, input fuel mixture was for both boilers same. Most of focused parameters were same, only data from DSI system were for each sorbent different. Efficiency of removing HF were for both sorbents same around 99%, for HCl around 85%. Consumption sample 1 was 80.63 m3 and 37.74 m3 of sample 2.
When comparing the laboratory and operational parts, higher consumption of sample 2 can be caused by more developed porous structure and a larger specific BET surface. This may be due to the purity of the original material (CaCO3), which was also higher in sample 2, as well as the production technology of the sorbents.
Keywords: Dry sorbent injection, Calcium hydroxide, flue gas
3/2023 - pages 92 - 100DOI: 10.35933/paliva.2023.03.04

Multivariate optimization of pyrolysis process parameters for biochar production

Kevin Nyoni, Leungo Kelebopile

Poultry litter is an abundant agricultural waste that poses a health risk when improperly disposed. To mitigate this problem, poultry litter can be used as fuel in combustion. The objective is to develop models that can optimize pyrolysis parameters for improved biochar quality and yield. Prior, the poultry litter is demineralized to reduce inorganic elements. RSM–CCD method developed models and optimized temperature, particle size, and reaction time to determine the outputs (biochar yield, higher heating value, H/C ratio, and energy yield). The developed models were significant with a p–value < 0.05. Maximum biochar yield (59.49%) was obtained at optimum pyrolysis parameters of 300 °C, 2.47mm, and 15 min. Maximum higher heating value (22.2MJKg–1) and energy yield (70.00%) were obtained at 300 °C, 4.04mm, and 15 min. Low H/C ratio was 0.03 at 550 °C, 1.17mm, and 15 min. ANOVA analysis verified the validity and degree of fitness of the developed models. Low standard deviation (< 7.00), small coefficient of variation (< 14.00%), high R2 (> 0.80), low difference of Adjusted R2 and Predicted R2 (< 0.20) and high adequate precision (> 4.00) verified the model’s adequacy for good precision. Models’ desirability function was satisfactory (> 4) with a 5.00% deviation from experimental values.

Keywords: Biochar, Central composite design, Demineralized poultry litter, Pyrolysis, Response surface methodology
3/2023 - pages 101 - 115DOI: 10.35933/paliva.2023.03.05

Possible Uses of Decommissioned Coke Batteries

Lenka Polívková, Karel Ciahotný, Jaroslav Kusý, Josef Valeš
Since the 80s of the 20th century, as a result of the reduction in demand for coke, economic crises and the availability of coking coal, the operations of coke plants in Europe have been ending. Furthermore, the pressure for using renewable energy sources continues to increase, including the production of fuels. In most cases, the current solution is to add biocomponents to fuels produced in the classical way from oil. There are considerations about reusing these coke batteries, this time for the production of liquid fuels. Therefore, this work is devoted to the processing of biomaterials mixed with brown coal by the pyrolytic process.
Extracted rapeseed meal, sunflower seed husks and dry distillery grain with solubles (DDGS) were selected as biomaterials. They are waste material from various productions, but these materials also show good energy potential. The brown coal came from the ČSA quarry, which is characterized by a low content of sulfur and ash and also improves the properties of liquid pyrolysis products, because it reduces polarity of organic phase, which enables easier separation of the aqueous and liquid phases of the product. Pyrolysis experiments were carried out in two different pyrolysis devices - i) in a micropyrolysis unit (sample loading: in the order of mg, heating rate: 100 °C s-1, fast removal of pyrolysis products); ii) in the pilot unit (sample weight: approx. 10 kg, heating rate: 5.2 °C min-1 and slower removal of pyrolysis products, cuboid shape of the pyrolysis retort simulating a coke oven battery). On the basis of mass balances and characteristics of micropyrolysis products, the pyrolysis temperature for pilot experiments was set at 650 °C. Behind the pyrolysis retort of the pilot unit, a thermic-catalytic reactor (catalyst: sulfurized aluminosilicate based on Ni-W) was connected in order to improve the quality of volatile pyrolysis products. The highest yields of organic phases of liquid products came from co-pyrolysis of coal and DDGS and coal with rapeseed meal. However, the characteristics of organic phases determined as the most advantageous material for the pyrolytic processing the rapeseed meal (specifically a higher proportion of aliphatic and aromatic hydrocarbons, a lower proportion of hydrocarbons with heteroatoms and a higher proportion of light fractions). The most beneficial pyrolysis mixture contained 35 % of rapeseed meal and the temperature in the catalytic part of the thermic-catalytic reactor was 300 °C.
Keywords: coke oven battery, coking industry, pyrolysis, co-pyrolysis, brown coal, biomass
3/2023 - pages 116 - 125DOI: 10.35933/paliva.2023.03.06

General Methods for the Analysis of Physical Properties of Fuels

Martin Staš, Hugo Kittel, Lukáš Matějovský, Lukáš Kejla, Pavel Šimáček
This article is another in a series of articles focused on introducing general methods for evaluating conventional and alternative fuels. The text presents an overview of the physical properties determined for liquid and gaseous fuels. Additionally, methods for determining these properties are presented. The significance of individual determinations is also discussed. Emphasis is placed particularly on standardized parameters and tests, but in some cases, tests that are not required by the relevant standards are also discussed. The main goal of the article is to provide a comprehensive overview of which physical properties are monitored for each fuel, why these properties are monitored, and what methods are used for this purpose.
The article provides an overview of monitored physical properties for liquid and gaseous alternative fuels. Regarding the physical properties, density at 15 °C is practically monitored for all discussed liquid fuels. Only for E95 fuel, the density at 20 °C is prescribed. Kinematic viscosity at 40 °C is monitored for all diesel engine fuels, while there are no prescribed viscosity limits for gasoline fuels. For Jet A-1 fuel, the relevant ASTM standard pre-scribes the maximum value of kinematic viscosity at -20 °C. Distillation characteristics are prescribed for all fuels except E85, E95, rapeseed oil, and FAME. It should be noted that for FAME and fuels based on vegetable oils, the simulated distillation method is often used as a complementary method. Vapor pressure is monitored for fuels containing volatile components, including E5 and E10 gasoline, E85 fuel, and LPG. Seasonal values for vapor pressure are prescribed for E5, E10, and LPG fuels, representing values for summer and winter periods. The vapor pressure of LPG is regulated by the ratio of C3 and C4 hydrocarbons in the mixture. Flash point characterizes the fuel from a fire safety perspective and is determined for petroleum-type fuels (B7-B30, FAME, SMN 30, and paraffinic diesel), as well as for rapeseed oil and E95 fuel. Except for E95 fuel, which is determined using an open cup method, all other fuels use closed cup methods. Lubricity is determined for aviation kerosene, motor diesel fuels B7 and B10, blended motor diesel fuel SMN 30, and paraffinic diesel. Low-temperature properties are determined for petroleum-type fuels, aviation kerosene, and marine fuels. The crystallization point is determined for aviation kerosene. For fuels B7-B30, FAME, SMN 30, and paraffinic diesel, prescribed values include the temperature of wax precipitation and CFPP (Cold Filter Plugging Point).
Keywords: conventional fuels, alternative fuels, physical properties, density, viscosity, distillation, vapor pressure, boiling point, calorific value, lubricity, low-temperature properties
3/2023 - pages 126 - 135DOI: 10.35933/paliva.2023.03.07

technical support editor-in-chief