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.
Current issue
1/2024
Effects of thermal disposal of oil-water residues on operation heating plant boiler
Ondřej Hlaváček
Industrial zones are often the source of specifically polluted waters, depending on type of industry. These waters are usually not in the limits for outtake into public sewers and it is necessary to dispose them externally or build-up technologies for their pre-treatment. The article is about the real case of an industrial.
A separate sewage network is built for oily water. Solid impurities are separated from the oily water and oily water is treated by evaporation technology. The evaporator produces two types of products - condensate and concentrate. Condensate is a water with high organic content, and it is necessary to purified it by a chemical treatment plant in next step. Evaporator technology remove from water the most of metal content and significantly decrease organic and water content in concentrate. Concentrate is oily stream with lower water content. Water content in concentrate decreased in next technology steps to ca. 40-50 %. The final product is certificated technological fuel, and its final elimination is in the heating plant fluidized bed boiler.
The article is detailed focused on the influence of concentrate combustion. A local temperature increases around 10-15 °C extending across the combustion chamber was confirmed. There was also an increase in HF concentration in flue gas. CO concentrations were higher in the first moments of combustion, but the control system responded by increasing the combustion air supply, and CO concentrations were finally lower at the level of 3 mg·m-3. During combustion, there was no provable increase in concentrations of NOX or other substances, and the co-combustion did not have a significant effect on the operation of the boiler, so this way was evaluated like technically and economically effective.
Keywords: combustion, oil emulsion, evaporator, boiler
1/2024 - pages 1 - 8DOI: 10.35933/paliva.2024.01.01
Use of solid recovered fuels for heat production - analysis of Czech legislation
Ondřej Hlaváček
The article is about solid recovered fuel (SRF) and its legislation possibilities to use them as a fuel in heating plants. This solution is quite popular because it brings solution of two very problematic tasks – the decreasing of waste landfilling and the end of fossil fuel (especially coal) combustion. Due to these arguments are there many producers which offer SRF (often in the pellets form) to conventional heating plants. However heating plant have flue gas cleaning technologies, which are able to combustion SRF and keep current emissions limits, the usage of SRF is forbidden for them. The reason is in the classification of origin material as a waste and the permission and limits as a waste combustion is required. The criteria and limits for waste combustion are much stricter and for heating plants is very difficult to reach them if it is possible.
The article is about view of Czech legislation, where some of law had different interpretation about waste material and SRF combustion. Article compare requirements and results for SRF from waste and SRF from waste biomass. The interpretation is described from a view of waste, air protection, IPPC, EU ETS and support of renewable energy sources law based on Czech a EU law documents.
The most important is origin of SRF. When the SRF is made by waste (municipal or industrial) all laws must assess final combustion technology as waste combustion technology, the support for renewable energy sources is not allowed (except biodegradable municipal waste) and CO2 emission permit is not required. With new regulation No. 169/2023 Coll. is possible to combustion SRF, which is based on waste biomass from forestry and agriculture. The permits and limits for combustion plants are same as biomass combustion, support for renewably energy sources is possible and CO2 emission permits are not required.
Investment to SRF combustion technology is not advantageous, because purchase prize of SRF will be higher than standard waste but requirements for technology will be same. Meaning of the newest legislation was not in possibilities to use of more SRF in heating plant, but bring waste and air protection law into accord, because some of waste biomass was possible to combust, however it was waste by waste law.
Keywords: solid alternative fuels, legislation, waste, biomass
1/2024 - pages 9 - 15DOI: 10.35933/paliva.2024.01.02
Progress towards the standardization of test parameters and protocols for evaluating densified fuel products
Gratitude Charis, Bilal Patel, Charles Rashama, Benias C. Nyamunda
Densification technologies used in managing biomass and coal fines to produce fuel briquettes or pellets are gaining rapid acceptance and application due to the widespread uptake of renewable energy. This has resulted in the mushrooming of many standard and non-standard evaluation tests for densified solid fuels in this industry. These tests are sometimes inconsistently applied especially if the available options for evaluation, underlying assumptions and principles of the test methods chosen are misunderstood. A critical review of the fuel briquettes evaluation tests to understand their relevance, strengths and limitations is necessary to advance public and research knowledge. This study investigated current methods of standardization to identify best practices, inconsistencies, trends and gaps in the application of fuel briquettes testing protocols. Procedures for evaluating combustion or thermal properties include calorific value, burn rate, open air combustion test and water boiling test; ignition time; after-glow test; specific fuel combustion or thermal efficiency were discussed. Physical and chemical property evaluations involved densities and related ratios, proximate and ultimate analyses. Equally important are mechanical parameters frequently informed by tensile/compressive strength, impact resistance, friability and water resistance. As renewable densified fuels gain more global popularity, it is critical to have a uniform standard of evaluating their quality.
Keywords: Briquette, densification, biomass, solid biofuel, evaluation methods, analytical techniques
1/2024 - pages 16 - 29DOI: 10.35933/paliva.2024.01.03
Comparison of properties of brown coal and bio-mass-based substitute fuels
Ondřej Hlaváček, Zdeněk Beňo
Due to the EU climate change strategy, there are many coal-fired heating plants looking for new fuel. One of the possibilities is biomass-based fuels. This term is quite general because the final technology can be different because of properties of different types of biomasses. The sustainable solution can be the use of biomass residues. This article is about long-term monitoring of the properties of brown coal, agglomerated herbaceous biomass from agricultural residues, and wood chips from harvesting residues.
702 samples of brown coal, 715 samples of plant pellets and 607 samples of wood chips were analyzed, which were supplied do commercial heating plant between the years 2021-2023. The water and ash content, lower heating value (LHV) and higher heating value (HHV), were analyzed. The mineral composition of the fuels was determined quarterly from mixed samples.
In the case of water content, the lowest values were achieved for herbaceous pellets (11.35%), due to their previous drying. The moisture content of the wood chips fluctuated. The average was 36.34%, with a maximum deviation of up to 49.9%. The average water content in brown coal was around 28.63%. In detail, there is a seasonal influence of the weather.
In the case of ash content determination, the values for brown coal and herbaceous pellets are similar (slightly above 5%), wood chips contain less ash (2.2%). The results for the wood chip samples fluctuated again. There were samples consisting of chipped logs (0.33% ash) and samples with a large proportion of forest soil (4.37%).
The highest average HHV values were achieved for brown coal (18.98 MJ/kg), followed by herbaceous pellets (15.84 MJ/kg) and wood chips (11.02 MJ/kg). These differences may cause a decrease in steam output due to a limitation of space in the combustion chamber of the boiler after the retrofit.
In the case of the content of nonmetallic elements, a different character of the biomass is evident, consisting of a higher oxygen content (38% vs 19%) and a lower carbon content (48% vs 68%). Biomass also contains less sulfur, but the high chlorine content of 0.12% compared to 0.02% in wood chips was determined in herbaceous pellet samples. For a heating plant, this means intensive chlorine corrosion or exceeding the emission limits of HCl. The solution can be in DSI technology.
Brown coal contains more Ti, V, Li, Sr, Be, Na, Fe, and Al. The biomass contains more biogenic elements, especially Ca, K, P, and Zn, which allows the ash to be used for land application. For the combustion process, a significantly higher content of alkali has an adverse effect, causing a decrease of the melting temperature of ash, which can lead to technological problems, such as the formation of a material based on alkaline glass, which decreases heat transfer and combustion efficiency. Most often, this complication is solved by micro detonations and more frequent maintenance. The contents of Hg, Cd, and Tl in the samples were below the detection limit.
Keywords: lignite, biomass, pellets, wood chips
1/2024 - pages 30 - 36DOI: 10.35933/paliva.2024.01.04