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Article

Pyrolysis as a Method for Processing of Waste from Production of Cultivated Tobacco (Nicotiana tabacum L.)

by
Bogdan Saletnik
*,
Marcin Fiedur
,
Radosław Kwarciany
,
Grzegorz Zaguła
and
Marcin Bajcar
Department of Bioenergetics, Food Analysis and Microbiology, Institute of Food Technology and Nutrition, College of Natural Science, Rzeszow University, Ćwiklińskiej 2D, 35-601 Rzeszów, Poland
*
Author to whom correspondence should be addressed.
Sustainability 2024, 16(7), 2749; https://doi.org/10.3390/su16072749
Submission received: 27 February 2024 / Revised: 22 March 2024 / Accepted: 23 March 2024 / Published: 26 March 2024
(This article belongs to the Special Issue Sustainable and Innovative Agriculture in Issues of Energy Production and Food Safety)
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Abstract

:
Because of the current energy crisis, researchers are looking into new potential substrates for production of biofuels and for possible ways to enhance their parameters. In line with such efforts, the current study focuses on the feasibility of processing waste from the production of cultivated tobacco. The aim of this study was to assess the potential of tobacco waste as a raw material for the production of solid biofuels, such as biochar produced through pyrolysis, and to determine its basic physicochemical properties, compared to other materials used for the production of green fuels. The analyses showed calorific values of 16.16 MJ kg−1 for the raw biomass and those in the range of 24.16–27.32 MJ kg−1 for the products of pyrolysis conducted at temperatures of 400–500 °C and with a heating time in the range of 5 to 15 min. To address the safety-related issues, the study also measured the explosion index (Kst max), which, in the raw biomass, amounted to 72.62 bar s−1 and in the biochar was in the range between 82.42 and 88.11 bar s−1. The registered maximum explosion pressure was 7.37 bar in the case of raw biomass, whereas in the biochars, the value ranged from 8.09 to 8.94 bar. The findings show that tobacco waste has parameters comparable to those identified in the case of other solid biofuels, whereas the process of pyrolysis enhances the energy-related parameters without increasing the explosion class of the product.

1. Introduction

Economic development has contributed to a significant increase in energy demand. Over the past 20 years, the available non-renewable energy resources have decreased significantly. In addition, obtaining energy from non-renewable sources is becoming increasingly expensive and has a negative impact on the environment. In the face of these changes, there is an increasing focus on finding new solutions for renewable energy [1]. It should also be emphasised that there has been rapid population growth over the years, and this has contributed to an increase in the amount of waste produced, which has become a major problem in cities of economically advanced countries. As a result, well-designed management of waste and its conversion into energy has been gaining importance worldwide [2,3,4]. As a result of waste management, it is possible to decrease the demand for fossil fuels. Furthermore, research shows that production of energy from reviewable sources will increase at the most rapid rate in the coming years in relation to the growing consumption of energy [5]. Solid waste management is an important issue worldwide, and efforts are needed to achieve progress in this area, to identify other sources of energy and to develop clean technologies in order to address problems connected with global warming and climate change [6]. Biomass is a highly feasible resource for energy production, and it can be used directly as a fuel or indirectly as a raw material for fuel production [7,8]. Alternative fuels may vary in terms of their source and production process, but what they have in common is that their production is sustainable and clean, with no additional emissions of carbon dioxide [9]. Biofuels have better combustion properties, are easier to handle and distribute and, last but not least, they can be produced from waste biomass residues. Biomass resources, such as agricultural waste, are multiple by-products, but most importantly, they can be effectively used in the form of biofuels. Finally, the concerns about global climate change, acid rain and fossil fuel-related air pollution as well as the emerging advances in biomass technology have revived interest in biomass energy as a renewable and sustainable energy source [10]. Therefore, alternatives are being sought to meet the principles of sustainability and environment conservation by exploiting the potential of biochar as a possible resource for long-term carbon storage to reduce emissions of CO2 [11,12]. Biomass is acquired, for instance, as a residue from the whole agricultural production process [13]. In crop production, biomass residues are directly associated with the yield. A higher yield corresponds to more post-harvest residues, as these represent a certain percentage of the crop. These are the residues from the cutting of stems, grasses, leaves, branches, etc., after the harvest of the main crops in agriculture [14].
Biochar is a renewable resource taking a form of a solid fuel similar to charcoal. It is produced by pyrolysis of plant biomass and organic waste, a process, which, in addition to biochar, generates liquid and gaseous products with high calorific value [15]. Pyrolysis is a thermal decomposition process carried out under aerobic conditions in a temperature ranging from 400 °C to 900 °C. The process itself is complex and consists of simultaneous as well as sequential reactions [16]. As a result of the thermal processes, the substrates decompose into compounds with lower molecular weight or elements. The products of the process include various substances, including gaseous, liquid (pyrolysis oil) and solid (carbonisate) materials [17,18]. At the current level of research, it is believed that pyrolysis of lignocellulosic biomass yields products that can also be obtained during a separate thermal decomposition of its components, i.e., lignin, cellulose and hemicellulose [19]. Current research shows that decomposition into individual components can be carried out through the hydrolysis process with fraction fragmentation, which allows us to obtain cellulose from post-production raw materials more effectively [20]. As a result of cellulose and hemicellulose decomposition, volatile compounds are produced, whereas decomposition of lignin, which is a natural polymer, produces a solid residue [21]. Decomposition of the components takes place at different temperatures, i.e., hemicellulose decomposes at 200–260 °C, cellulose at 240–350 °C and lignin at 280–500 °C [22,23]. The proportions of the products depend on the pyrolysis method itself, the properties and characteristics of the biomass and the reaction parameters. The quality of biochar depends on a number of factors, such as the type of biomass, its chemical composition and moisture content as well as the process used during the production of biochar. The final quality of the biochar is of key importance for its performance and use for various purposes [24].
Biochar produced in a process of pyrolysis contains stable organic carbon, aromatic and aliphatic compounds as well as ash [25]. However, the chemical composition of biochar largely depends on the composition of the substrate. Biochar can be regarded as a high-quality fuel, enabling recovery of energy from waste, and it can also be used in agriculture as a soil amendment or as a sorbent for soil and water contaminants [26].
When investigating the potential of tobacco waste for production of energy, it should be emphasised that in 2021, tobacco production in Poland covered 9566 ha, which means that Poland is among the top producers in Europe [27]. However, compared to previous years, there was a significant decrease in the area designated for tobacco cultivation. The structure of farms changed as well. Plantations with an area of less than 1 ha were replaced by those with an area of 2–5 ha or more, and the production of this crop is largely concentrated in one region. The farms specialising in tobacco cultivation, which are mainly located in the Lubelskie Region, account for 66.8% of the total production of the crop in Poland [27]. The largest tobacco producer worldwide is China, with the area designated for cultivation of the crop amounting to 938,468 ha, which accounts for 29.6% of the global tobacco production covering an area of 3,132,322 ha [28]. Globally, the area under cultivation decreased in 2020–2021; however, the volume of tobacco produced increased as a result of the facts that novel tobacco varieties were introduced worldwide and the tobacco production area was more concentrated. It should be emphasised that tobacco production generates post-harvest waste, which, if left in the field, requires adequate treatment, i.e., refining and mixing with the soil to avoid the development of plant diseases. Additionally, a high proportion of woody parts means that such waste requires considerable time for microbiological decomposition. It therefore seems reasonable to make attempts to convert such waste, for instance, into biochar materials. Tobacco waste left in the field after the harvest largely loses the water accumulated in the plants, which means that there is no need for additional energy inputs to achieve an air-dry state. This significantly increases the attractiveness of this raw material as a component for production of high-quality biofuel.
The quality of biochar can be enhanced by improving the technological processes, selecting the right raw materials and defining the most effective pyrolysis technique [29]. As a result, biochar has a potential to become an alternative to fossil fuels, which would help to reduce greenhouse gas emissions and improve air quality. Safety of biochar materials is a key issue due to the potential risks they may pose to humans and the environment. These materials are usually made from natural organic products such as wood, straw, sawdust, sugar cane as well as plant and animal waste. The main risks associated with biochar materials include fires, which can lead to the emission of hazardous substances such as smoke, toxins and fumes. To ensure an adequate level of safety in the processes of biochar production and storage, biochar materials should be produced in compliance with strictly defined norms and standards [30,31]. All components used to produce biochars should be carefully selected and approved by the applicable regulatory authorities, and all the production processes should be controlled and monitored to prevent any risks or hazards [32]. The initial processing of biomass through refining the material into smaller fractions generates significant quantities of dust, which can be associated with increased hazards in the production area [33]. Significant levels of dust lead to increased risk of explosion or spontaneous combustion, consequently constituting a fire hazard [34]. There are a number of factors that are necessary conditions for a dust explosion to occur, namely the presence of fuel in particulate form, an oxidant and an ignition source, as well as mixing of the components and confinement of the mixture [35,36]. The hazards that increase the risk of ignition include contact of dust with hot air, heated components such as engines and moving parts of machinery. In the case of lignocellulosic biomass, important risk factors include electrostatic discharges, which occur during mechanical processing, transport and storage of the biomass [37,38,39].
The literature related to this subject matter does not contain detailed information on the production of biochar from tobacco waste. Therefore, this study was designed to evaluate the energy-related potential of tobacco waste biomass and the product refined through pyrolysis. In addition, the aim of this study was to assess the safety and explosivity levels of biomass and biochar dust. The above research will allow maintaining all safety standards during the transport and storage of biocarbon materials and the spread of post-production biomass in the field of professional energy and heating.

2. Materials and Methods

2.1. Research Object

Waste from the cultivation of Nicotiana tabacum was used in the production of biochar. The material comprised tobacco stems, residues from plantation operations as well as leaves, which were unsuitable for industrial purposes. Detailed quantitative and qualitative analyses were performed for each material. The material for the study was acquired during the 2021/2022 growing season from a farm, located in Korchów Pierwszy, a village in the Lubelskie Region and specialising in tobacco production since 2001. The material was acquired from a one-hectare area by random sampling. Subsequently, the biomass was dried to an air-dry state, finely crushed to particles < 10 mm and processed to prepare it for further treatment.

2.2. Pyrolysis Process

The pyrolysis process was conducted in a retort furnace FCF 2R, enabling thermal treatment in an atmosphere of inert gas and equipped with a post-process gas cooler with water well (CZYLOK, Jastrzębie-Zdrój, Poland) (Leco, St. Joseph, MI, USA) (Figure 1).
Pyrolysis experiments aiming to produce test pellet samples were performed at temperatures of 400, 450 and 500 °C, with a maintenance time of 5, 10 and 15 min, in a nitrogen atmosphere of 99.99% purity and with a gas flow of 10 L/min (Figure 1). The products of pyrolysis were sifted through a sieve with 1 mm holes. The samples were rinsed a few times with distilled water to remove possible contaminants and then dried for 12 h (at 80 °C).

2.3. Analysis of Samples

Measurements were performed to assess the basic physicochemical parameters of the materials, i.e., the contents of total carbon, nitrogen, hydrogen, ash and volatile substances as well as the calorific value. The contents of ash and volatile substances in the specific samples were measured using a thermogravimetric method, with a TGA 701 apparatus from LECO (LECO Corporation, Saint Joseph, MI, USA). Measurements of total carbon, hydrogen and nitrogen were performed using a TrueSpec CHN analyser (LECO Corporation, Saint Joseph, MI, USA). The calorific value of the samples was assessed using an AC500 calorimeter (LECO Corporation, Saint Joseph, MI, USA).
Dust explosibility was measured using a KSEP20 instrument equipped with KSEP 310 control unit (Kuhner AG, Basel, Switzerland). The instrument comprises a spherical testing chamber with a capacity of 20 dm3. A surrounding water jacket provides thermostatically controlled temperatures and dissipates explosion heat (Figure 2).
During the testing process, the dust is dispersed under pressure through an inlet valve, opened and closed pneumatically. The source of ignition, designed as two chemical igniters with an energy of 5 kJ each, is located centrally within the spherical chamber. Kistler pressure piezoelectric sensors record the parameters during the process. During the assessment, the maximum explosion pressure (Pmax) is determined as the highest recorded explosion pressure of the combustible mixture, consisting of a combustible material and air. Pmax, and the value of the maximum pressure rise over time, (dp/dt)max, provide the basis for determining the explosibility class Kst max for the material. The latter parameter is applied in European standards defining categorisation of combustible dust according to EN14034 [40]. The parameter was calculated from the formula:
K max ⁡ = K s t = V ( d p d t 3 ) max ⁡ = 0.271 ( d p d t ) max ⁡ [ m b a r s − 1 ]
  • Kst max—explosibility index
  • V—volume of the testing chamber
  • (dp/dt) max—indicator of maximum explosion pressure rise.
The explosibility index is classified according to the values listed in Table 1, class St1 corresponding to low explosibility, class St2 meaning moderate explosion hazard and class St3 reflecting high explosion hazard.
The biomass and biochar samples were subjected to laboratory testing in line with current analytical standards (Table 2).

2.4. Names of Samples

For further identification, the tobacco biomass samples were marked as follows:
  • TS—material subjected to no thermal processing;
  • TS400/5—pyrolysis (400 °C; 5 min);
  • TS400/10—pyrolysis (400 °C; 10 min);
  • TS400/15—pyrolysis (400 °C; 15 min);
  • TS450/5—pyrolysis (450 °C; 5 min);
  • TS450/10—pyrolysis (450 °C; 10 min);
  • TS450/15—pyrolysis (450 °C; 15 min);
  • TS500/5—pyrolysis (500 °C; 5 min);
  • TS500/10—pyrolysis (500 °C; 10 min);
  • TS500/15—pyrolysis (500 °C; 15 min).

2.5. Statistical Analysis

Analysis of variance (ANOVA) was performed using the Duncan test to assess the effects of the experimental factors on the relevant parameters and the correlations between these. The statistical analyses were performed using Statistica 12 software. A significance threshold of ≤0.05 was set for all analyses. The analyses were carried out separately for each type of material [46,47].

3. Results

In all the samples, the nitrogen level was lower than the detection level of the instrument, and the hydrogen content of the samples decreased with growing temperature and duration of thermal treatment; the lowest result was obtained for a temperature of 500 °C and thermal treatment time of 15 min and was 3.91%. The content of carbon successively increased with growing temperature and duration of the treatment; the highest result of 63.13% was observed in TS500/15, i.e., the sample subjected to pyrolysis at 500 °C with a heating time of 15 min. Increase in the temperature and the duration of thermal treatment was also reflected in the contents of volatile substances. Both the temperature and the duration of the thermal treatment produced a significant effect reflected by a decrease in the contents of volatile substances, from 76.06% in raw biomass to 22.81% in the sample treated at 500 °C for a duration of 15 min. Conversely, the content of ash was found to increase and reached a value of 9.55% in the sample with the highest temperature and duration of the processing (Table 3).
The calorific value of the specific samples varied in relation to the thermal treatment parameters applied; the important parameter was the duration of the process since the increase in the calorific value corresponded to longer duration of the thermal treatment. The calorific value of the raw biomass on average was 16.16 MJ kg−1, whereas the highest mean results of 27.04 MJ kg−1 were achieved at a temperature of 500 °C and process duration of 15 min. The effects corresponded to a mean increase in the calorific value of the biochar relative to the raw biomass amounting to 9.73 MJ kg−1, which is an increase of 60.2% (Figure 3).
Table 4 shows the increase in the maximum explosion pressure, Pmax, and the maximum rate of the pressure rise of the dust, (dp/dt)max, where both the former and the latter parameters increased with higher temperature and longer duration of the pyrolysis process. These respective parameters were in the range of 7.37–8.94 bar and 267.71–326.69 bar s−1. These correlations are consistent with data reported in the literature [48].
The data presented in Figure 4 are related to Kst max, a parameter describing an actual risk of dust explosion. Relative to the raw biomass, the values were higher in the products of pyrolysis, with the mean results for the specific temperatures amounting to 84.04, 85.34 and 86.83 bar s−1, respectively, whereas in the raw biomass, the value of the parameter was 72.62 bar s−1. Consequently, the risk of explosion increased with higher temperature and longer duration of the pyrolysis process. Analysis of these findings made it possible to assign the materials to one of the four classes St0–St3 [15,49,50,51] reflecting the safety of handling and storage of the material.
Figure 5 shows the trends in the changes of the explosion pressure distribution per unit time in the tested material. The analysis showed that the observed changes in explosion pressure show similar trends, which is due to the significant effect of the varying thermal treatment conditions. Increasing the temperature of the process proved to be a particularly important factor, which significantly affected the investigated phenomenon. The maximum explosion pressures were measured in the tobacco stalks and the biochar produced from these, and the values were recorded 5 ms after the explosion was initiated. The findings also show a relationship between increase in dust explosion pressure and higher parameters of the pyrolysis process. The highest explosion pressure of 8.94 bar was identified in the samples of biochar produced at a temperature of 500 °C with the thermal treatment applied for 15 min, whereas the lowest explosion pressure of 7.37 bar was found in the samples of raw biomass which were not subjected to pyrolysis.

4. Discussion

At present, there are a number of methods and processes designed to improve the quality of organic material as a resource for energy-related purposes. All of these processes are necessary because of the parameters of raw biomass, such as the low feedstock value and the high proportional content of water in the material, due to which there is a high risk of decomposition during storage of the material. Therefore, biomass must be subjected to processes designed to reduce the water content and increase density of the material in order to improve the parameters of the fuel. Various methods are applied to improve the biomass parameters, e.g., drying, pelletisation or briquetting, and to significantly enhance the quality of the biomass, e.g., torrefaction or pyrolysis [23,52,53]. According to the Act on Renewable Energy sources (Journal of Laws from 2015, item 478) [54], biochar materials must exceed a calorific value of 21 GJ t−1 and they must be produced from plant materials or animal by-products, in course of biomass conversion processes carried out at temperatures in the range of 320–700 °C, in an anaerobic atmosphere or under extreme oxygen deficiency and at a pressure similar to atmospheric, without the use of catalysts and foreign substances [55]. Such parameters as the proportional contents of carbon, nitrogen, water and volatile substances are mainly defined by the raw material from which the biochar is produced, hence by adequately selecting the raw materials for biochar production, it is possible to obtain a material with very good properties. The contents of the components of biochar should be as follows: carbon in the range of 50–90%, water 1–15% and volatile substances should not exceed 40%. By altering the parameters of pyrolysis, it is possible to modify the properties of the product and this way determine the designation of the biochar to be used not only for energy-related purposes but also as a material for production of briquettes, in which, as a component, it significantly improves the calorific value and mechanical strength of the product obtained [56]. Furthermore, owing to its properties, biochar can improve the sorption structure of soils and contribute to an increase in soil pH [26].
Tobacco cultivation is an important branch of agriculture in many countries worldwide, including Poland. In 2022, the area designated for tobacco farming in Poland was 10,200 ha, and raw tobacco production totalled at 15,200 tonnes [27]. In 2022, the area designated for tobacco farming globally amounted to 7.2 million hectares, and raw tobacco production totalled 6.5 million tonnes [57]. However, tobacco production generates significant amounts of waste, which poses a challenge to the environment if the waste is not managed properly. The most substantial amounts of waste are generated during the harvesting of tobacco leaves. After harvest, tobacco leaves are sorted, and those that are not suitable for further processing are disposed of as waste. Waste from tobacco production also includes tobacco stalks left behind after leaves are harvested, tobacco seeds that are not suitable for further use and organic waste from tobacco factories, generated during fermentation, drying as well as cigarette production. In the case of the tobacco stalks presented in the table below (Table 4), a calorific value of 16 MJ∙kg−1 was identified in the raw biomass. This high value was similar to the results reported for other popular raw materials used as a source of energy. According to one study [58], the correct planting rate is between 23,000 and 25,000 plants per hectare. Further research estimated that the yield of the by-product in the form of stalks left over from tobacco farming amounts to 2.3 t/ha of dry waste to be burnt directly or subjected to enhancement treatments. Based on the evidence presented by researchers [57,58], the overall yield of the by-product in Poland can be estimated at 23,460 t, with an energy potential close to 375,360 GJ.
The calorific value of biochar is an important property of this material. By subjecting the raw biomass to a thermal decomposition process, i.e., pyrolysis, it was possible to obtain the calorific values comparable to other solid fuels such as coal, lignite or wood. Similar calorific values of biochars produced have been reported by other authors, as shown in Table 5 [59,60,61].
The analyses showed no content of total nitrogen in the samples assessed, and the processes of pyrolysis did not produce any change in this parameter. Similar conclusions were reported by Yuan et al., who investigated materials obtained from sewage sludge [48], and by Saletnik et al., who did not find a relationship between pyrolysis and changes in this parameter in biochar produced from pellets [64]. In the case of pyrolysis conducted at 400–500 °C for a duration of 5–15 min, a significant increase in carbon contents was observed in the samples, with the highest value of 63.16% obtained as a result of pyrolysis conducted at a temperature of 500 °C for a duration of 15 min. The findings also show a decrease in hydrogen contents, with the most significant change, and the lowest water content of 3.91%, also resulting from the treatment at 500 °C for a duration of 15 min. The current study also showed significant changes in the contents of volatile substances. The best values of this parameter were also observed in the case of pyrolysis conducted at 500 °C for a duration of 15 min. Similar results were reported by Saletnik et al. (2022) [64] in a study assessing such materials as wood, bark, brushwood, leaves and acorns subjected to pyrolysis to produce biochar. The authors observed that the changes in the contents of volatile substances were related to the pyrolysis method applied [48]. The duration and temperature of the pyrolysis process applied to biomass significantly impact the effectiveness of charring. The cracking of hydrocarbons with an increase in the contents of hydrogen is promoted by higher temperatures and the use of smaller particles, as demonstrated in the work by Zanzi et al. [65]. Biocarbon materials acquired from by-products of tobacco farming have a maximum explosion pressure which is 21.3% higher compared to the untreated samples. This change is associated with higher brittleness of the biochar, as well as higher contents of carbon and volatile matter. Similar trends were also observed with regards the maximum rate of pressure rise, with the largest values, on average 22.03% higher, identified in the case of biochar samples produced at 500 °C with treatment time of 15 min. Despite the slight increase in explosion pressure (the mean of 302.51 bar s−1), the classification of dusts did not change. The mean explosion index for the investigated biochar samples was 87.13. As a result, they can be assigned to Class St1, comprising materials with low explosion hazard [29,40]. The findings show an increase in explosion index following the thermal treatment, compared to raw biomass. Similar conclusions were presented by Bajcar et al. [29]. Many researchers suggest that these changes may be linked to differences in emissivity of the specific materials as well as the shape and size of the specific particles [35,37,55,66]. Studies by Dobashi et al. and Yuan et al. [48,67] demonstrated a significant correlation between Pmax and a decrease in particle size. They also showed that the maximum rate of rise increases exponentially with decreasing size of the dusts examined. In their studies, the researchers also focused on understanding the relationship between flammability and chemical activation levels of dusts and their particle size. Further analyses conducted by Yuan et al. [48] demonstrated that the value of Pmax decreases with higher content of moisture in dust.

5. Conclusions

Tobacco waste has a good potential for energy production, as the findings show that raw biomass from tobacco stalks reaches calorific value of 16.16 MJ kg−1. The research assessing the feasibility of using tobacco waste showed that, as a result of pyrolysis, it was possible to obtain high-quality solid fuel, i.e., biochar with calorific value of 25.79 MJ∙kg−1, a property similar to that observed in conventional fuels. Biochar has a high potential for production of energy; however, there are some barriers that need to be overcome in order to utilise that potential. The technologies and solutions designed to enable efficient use of biochars should be developed in such a way as to minimise the cost of biochar production; it is also necessary to increase availability of biomass and improve the technical options for using this type of material.
Continued research assessing effectiveness of pyrolysis applied to a variety of materials provides important information about potential green and renewable sources of energy; as a result, it will be possible to create a database presenting feasible sources of biomass to be used in biochar production. Furthermore, the related studies make it possible to define the optimum parameters of the process to enable production of the most effective fuel from each type of raw biomass. They also provide evidence showing safety class of the materials, which is necessary to minimise the risk of any hazardous incidents due to dust explosion.
Prior to the thermal treatment process, the material was found with mean Kst value of 72.62 bar s−1. Following the pyrolysis process, the measure increased to the maximum value of 86.83 62 bar s−1, which corresponds to Class St1 materials with low explosion hazard and shows no significant differences in the increase in the level of explosivity. Biochar dusts exhibit relatively low explosibility but can still pose a risk. Despite the low hazard, it is still important to remember to follow safety rules to prevent biochar dust explosions and similar incidents.
Given the distribution of farms, tobacco waste, prior to the pyrolysis process, could provide an alternative source of energy for farms specialising in this crop as a feedstock for solid fuel boilers. This would significantly reduce the costs associated with transport of the waste and increase the proportion of renewable energy sources used by farms. This study showed a relationship between the selected methods of pyrolysis and proportional contents of the elements in the samples investigated; the best values are achieved by the samples produced through pyrolysis at 500 °C with treatment time of 15 min.

Author Contributions

Conceptualisation, B.S., M.F. and R.K.; methodology, B.S., M.F., R.K., G.Z. and M.B.; formal analysis, B.S., M.F. and R.K.; data curation, B.S., M.F. and R.K.; writing—original draft preparation, B.S., M.F. and R.K.; writing—review and editing, B.S.; supervision, B.S.; project administration, B.S.; funding acquisition, B.S. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The data presented in this study are available on request from the corresponding author.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. The retort furnace used for the pyrolysis process.
Figure 1. The retort furnace used for the pyrolysis process.
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Figure 2. Explosivity analyser KSEP 310.
Figure 2. Explosivity analyser KSEP 310.
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Figure 3. Calorific value (MJ kg−1) of the samples relative to the temperature and duration of the pyrolysis process. Statistically significant differences are marked by different letters (p ≤ 0.05). Differences between average values marked with the same letters are not statistically significant at the level of p ≤ 0.05 according to the Duncan test. The data were analysed separately for each type of material.
Figure 3. Calorific value (MJ kg−1) of the samples relative to the temperature and duration of the pyrolysis process. Statistically significant differences are marked by different letters (p ≤ 0.05). Differences between average values marked with the same letters are not statistically significant at the level of p ≤ 0.05 according to the Duncan test. The data were analysed separately for each type of material.
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Figure 4. Dust explosion index (bar s−1) in the materials investigated relative to the parameters of the processing. Statistically significant differences are marked by different letters (p ≤ 0.05). Differences between average values marked with the same letters are not statistically significant at the level of p ≤ 0.05 according to the Duncan test. The data were analysed separately for each type of material.
Figure 4. Dust explosion index (bar s−1) in the materials investigated relative to the parameters of the processing. Statistically significant differences are marked by different letters (p ≤ 0.05). Differences between average values marked with the same letters are not statistically significant at the level of p ≤ 0.05 according to the Duncan test. The data were analysed separately for each type of material.
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Figure 5. Distributions of explosion pressure in the dust of tobacco stalks and charcoal produced from these.
Figure 5. Distributions of explosion pressure in the dust of tobacco stalks and charcoal produced from these.
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Table 1. Dust explosion classes [41].
Table 1. Dust explosion classes [41].
Explosibility ClassKst max Value [bar s−1]
St1≤200
St2200–300
St3>300
Table 2. Research methods applied in the analysis of the parameters.
Table 2. Research methods applied in the analysis of the parameters.
ParameterResearch Method
Carbon, nitrogen and hydrogen contentsPN-EN 15104:2011 [42]
Ash contentPN-EN 14775:2010 [43]
Content of volatile substancesPN-EN 15402:2011 [44]
Calorific valuePN-EN 14918:2010 [45]
Explosibility index Kst maxPN-EN 14034-2 [40]
Table 3. Contents of nitrogen, carbon and hydrogen, as well as ash and volatile substances relative to the temperature and duration of the pyrolysis process.
Table 3. Contents of nitrogen, carbon and hydrogen, as well as ash and volatile substances relative to the temperature and duration of the pyrolysis process.
NCHAshVolatile Substances
%
TS<0.04 *40.62 a ± 0.086.52 d ± 0.045.04 a ± 0.176.06 d ± 0.19
TS400/556.95 b ± 0.325.07 c ± 0.016.67 b ± 0.0231.49 c ± 0.04
TS400/1059.46 b ± 0.364.89 c ± 0.026.73 b ± 0.0330.58 bc ± 0.09
TS400/1559.7 b ± 0.174.99 c ± 0.017.4 c ± 0.0729.83 bc ± 0.1
TS450/557.34 b ± 0.054.56 bc ± 0.018.47 d ± 0.0729.22 bc ± 0.09
TS450/1060.34 b ± 0.124.54 bc ± 0.019.23 e ± 0.0527.11 b ± 0.07
TS450/1560.96 b ± 0.144.51 bc ± 0.049.51 e ± 0.0525.51 ab ± 0.15
TS500/557.31 b ± 0.074.23 b± 0.018.67 d ± 0.0425.42 ab ± 0.06
TS500/1063.03 b ± 0.074.22 b ± 0.038.74 d± 0.0123.89 a ± 0.02
TS500/1563.13 b ± 0.163.91 a ± 0.019.55 e ± 0.0622.81 a ± 0.07
* below the detection level of the instrument. Statistically significant differences are marked by different letters (p ≤ 0.05). Differences between average values marked with the same letters are not statistically significant at the level of p ≤ 0.05 according to the Duncan test. The data were analysed separately for each type of material.
Table 4. Maximum explosion pressure and maximum rate of the pressure rise of the dust in the tobacco samples and in the products of pyrolysis.
Table 4. Maximum explosion pressure and maximum rate of the pressure rise of the dust in the tobacco samples and in the products of pyrolysis.
Pmax(dp/dt) max
BarBar s−1
TS7.37 ± 0.16267.71 ± 3.79
TS400/58.09 ± 0.12277.46 ± 3.64
TS400/108.33 ± 0.09279.07 ± 3.95
TS400/158.56 ± 0.13281.66 ± 3.35
TS450/58.33 ± 0.15296.17 ± 3.52
TS450/108.64 ± 0.11316.76 ± 3.54
TS450/158.74 ± 0.14324.09 ± 3.52
TS500/58.58 ± 0.18302.96 ± 3.66
TS500/108.78 ± 0.16317.69 ± 3.62
TS500/158.94 ± 0.15326.69 ± 3.42
Table 5. Comparison of the calorific value and physicochemical properties of different types of conventional fuels, biomass and biochar.
Table 5. Comparison of the calorific value and physicochemical properties of different types of conventional fuels, biomass and biochar.
Calorific ValueTotal CarbonVolatile SubstancesAshReferences
MaterialMJ kg−1%
Natural gas48.075.0100.00.0[15]
Coal25.060.035.05.7[49,50]
Lignite22.9367.4046.44.1[50]
Wood18.1949.6183.300.75[50]
Straw16.815.7275.106.69[50]
Rape15.31478.77.3[60]
Sunflower15.717.274.58.3[59]
Tobacco stalks16.16–18.440.96–43.9776.075.04–5.49[51,62,63]
Tobacco leaves15.6–17.2--[62,63]
Rape straw biochar23.472.713.621.8[15]
Sunflower biochar20.563.413.428.9
Biochar from oil palm empty fruit bunches 17.153.881.93.1[60]
Cherry wood biochar27.759.522.29.1[61]
Tobacco biochar27.0463.823.359.15-
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Saletnik, B.; Fiedur, M.; Kwarciany, R.; Zaguła, G.; Bajcar, M. Pyrolysis as a Method for Processing of Waste from Production of Cultivated Tobacco (Nicotiana tabacum L.). Sustainability 2024, 16, 2749. https://doi.org/10.3390/su16072749

AMA Style

Saletnik B, Fiedur M, Kwarciany R, Zaguła G, Bajcar M. Pyrolysis as a Method for Processing of Waste from Production of Cultivated Tobacco (Nicotiana tabacum L.). Sustainability. 2024; 16(7):2749. https://doi.org/10.3390/su16072749

Chicago/Turabian Style

Saletnik, Bogdan, Marcin Fiedur, Radosław Kwarciany, Grzegorz Zaguła, and Marcin Bajcar. 2024. "Pyrolysis as a Method for Processing of Waste from Production of Cultivated Tobacco (Nicotiana tabacum L.)" Sustainability 16, no. 7: 2749. https://doi.org/10.3390/su16072749

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