•Thermal analysis of coal, biomass and sewage sludge were studied.•Biomass and sewage sludge are good candidates for co-combustion with coal.•Exhaust gases emitted during combustion were analysed by ...mass spectrometry.•TGA and MS techniques are very useful tool for the investigation combustion process.
The main aim of the paper was presentation of TG, DTG, and DTA results on the combustion of two different biomasses, sewage sludge and coal and their co-combustion when the biomass and sludge are mixed with coal. The products of the combustion were identified by mass spectrometry and the composition of ash of the fuels evaluated. Thermal analysis has been generally used to characterise the thermal decomposition of biomass, coal and, more recently, sewage sludge. Thermogravimetric analysis is the easiest and the most effective technique to observe the combustion profile of a fuel. The advantage of this analysis is its rapid assessment of the fuel value, the temperatures at which combustion starts and ends and other characteristics, such as maximum reactivity temperature, ash amount and total combustion time. The materials were characterised in terms of their proximate and ultimate analysis and calorific value. The performed investigation of studied fuels combustion and gas composition analysis from TG/DTG and MS experiments have confirmed the variety of their combustion behaviour.
The most important results focus on the temperature of maximum weight loss rate and the effect of heating rate. The temperature of maximum weight loss rate were dissimilar (DTG profiles) for studied fuels and the effect of heating rate significantly influenced the TG/DTG curves profiles, too. The co-combustion of coal and sewage sludge or biomass results have shown that coal can be burned with biomass and sewage sludge beneficially.
Hydrothermal carbonization is an innovative method of sewage sludge disposal. The solid product hydrochar (c.a.10%), may be converted to a fuel or fertilizer. Gaseous products (less than 10%) are ...mainly CO2 and nitrogen, but c.a. 80% of post-processing liquid presents as a challenging issue due to its high toxicity. Therefore, the main aim of this study was to determine the potentiality of hydrochars derived from sewage sludge as a fuel, at two temperatures: 200 and 220 °C, and 2 h of residence time, and successfully utilize the filtrates after the implementation of an adequate purification process. The results of hydrochars depicted better energy properties and dewaterability than in the case of raw sewage sludge, including improved chemical composition, a higher fixed carbon content and fuel ratio, and it also gained more effective filtration. The comprehensive analysis of the Thermal Analysis data proved that hydrochar can be combusted, but based on X-ray Fluorescence data a high tendency to slagging and contamination is expected. The highly toxic processing liquids indicated a great need for an appropriate treatment. Accordingly, distillation and the preliminary study of wet oxidation processes were applied. In both methods the chemical oxygen demand, an indicator of organic pollution, was significantly reduced.
This paper presents chemical properties of sewage sludge ashes required for determining their thermal characteristics. A novel approach, linking selected advanced analytical techniques with FactSage ...modelling, was developed and applied to obtain new information on deposit formation mechanisms that contribute to fouling and slagging. The mineral matter and fusion temperatures were investigated using a variety of analytical techniques including XRF, ICP-MS, XRD, SEM-EDX and AFT. The slagging and fouling indices were calculated and the sintering properties were predicted. The studied ashes were rich in P2O5, CaO, SiO2 and Fe2O3, but their concentrations slightly differed. Phase analyses suggested the existence of calcium and phosphorus as main phases. Thermal behaviour of ashes was studied focusing on the mass loss, temperature peaks and thermic effects with the increasing of temperature up to 1200 °C under air atmosphere. The changes in concentration of ash compounds contributed to differences in ash fusion temperatures. FactSage thermochemical equilibrium calculations were used to predict the amount of liquid slag and solid phases, giving information about slagging properties of ashes. The general conclusion based on experimental studies is that sewage sludge ashes cause the slagging and fouling hazard while they reveal low corrosive effect.
•Characterisation of sewage sludge ashes were given.•Transformation of inorganic components was determined using XRD and FTIR.•The ash fusion behaviour of ashes was studied experimentally.•Empirical indices were calculated indicating slagging and fouling propensities.•Thermodynamic equilibrium calculation was used.
Hydrochars (HTCD) derived from digestates, namely D1 and D2 (from two plants) of sewage sludge, were examined with respect to their fuel properties. The hydrothermal carbonization (HTC) tests were ...performed at temperatures of 200 and 220 °C, for 2 and 4 h of residence times, and with 1:10 and 1:8 digestate to water ratios (D/W), causing an increase of ash content (max. 55.8%), and a decrease c.a. 20% of the higher heating value except for a slight increase to 15 kJ/kg at 200 °C and 4 h in hydrochars. Conversely, the combustion profiles of hydrochars moved towards higher temperatures (225–257 °C) and finished earlier at lower temperatures (423–438 °C). The HTCD from D1 and D2 showed very similar properties under the same conditions (200 °C, 4 h, 1:8 D/W) for combustion characteristic temperatures, indices and profiles. The best efficiency was found for HTCD2. In addition, the polluted post-processing liquid phase was treated by a distillation process providing 30% higher pH, 50% lower BOD values, up to 15 times lower COD values, and c.a. three times lower conductivity.
One of the by-products of a mechanical-biological waste treatment plant is the under-sieve fraction, which requires separation prior to further processing of municipal mixed waste. This stream ...usually follows the fate of landfilling. Instead, it could be introduced to the hydrothermal carbonization (HTC) process to improve its fuel properties and become solid recovered fuel. The organic fraction and high moisture content (approximately 26%) of under-sieve fraction are favorable properties for the HTC process. In this study, hydrochars, the solid product of HTC, were produced at 200 and 220 °C with residence times of 1, 4, and 8 h. The main aim of this investigation was to establish the influence of different process parameters on hydrochars’ fuel properties. Thermogravimetric analysis (TGA), Fourier-transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM) were employed in the analyses. The results confirmed the positive effects of hydrothermal carbonization on the under-sieve fraction of municipal mixed waste properties. The ignition temperature increased from 247 °C to 288 °C and burnout temperature decreased to 443 °C from 489 °C after hydrothermal carbonization, causing a shorter combustion process. The determined key combustion parameters were: S = 12.4 × 10−8%·min−2·°C−3, Hf = 1174.9 °C and Di = 0.0075%·min−3, which in comparison to USF decreased by 44%, increased by 33%, and decreased by 29%, respectively, and became closer to those of coal. Furthermore, the identified structural changes indicate that hydrochars could be successfully used in energy production. The most promising results were found for hydrochar produced at 220 °C for 1 h, leading to a better combustion performance and providing a more stable and a less violent flame.
Since the very beginning of the COVID-19 pandemic, control policies and restrictions have been the hope for containing the rapid spread of the virus. However, the psychological and economic toll they ...take on society entails the necessity to develop an optimal control strategy. Assessment of the effectiveness of these interventions aided with mathematical modelling remains a non-trivial issue in terms of numerical conditioning due to the high number of parameters to estimate from a highly noisy dataset and significant correlations between policy timings. We propose a solution to the problem of parameter non-estimability utilizing data from a set of European countries. Treating a subset of parameters as common for all countries and the rest as country-specific, we construct a set of individualized models incorporating 13 different pandemic control measures, and estimate their parameters without prior assumptions. We demonstrate high predictive abilities of these models on an independent validation set and rank the policies by their effectiveness in reducing transmission rates. We show that raising awareness through information campaigns, providing income support, closing schools and workplaces, cancelling public events, and maintaining an open testing policy have the highest potential to mitigate the pandemic.
The optimal process conditions concerning the hydrothermal carbonization of digested sewage sludge are crucial to the economically effective technology needed to produce a solid product, hydrochar, ...for energy purposes. Accordingly, different residence times, 0.5 h, 1 h and 2 h, were investigated in order to understand the effect of residence time on the process. Furthermore, the physical and chemical properties of hydrochar were investigated and compared to the raw material. For these reasons, analyses describing fuel properties were performed, including ultimate and proximate analyses, HHV, and TGA analysis. The latter method was employed to study the combustion process of solid samples. In addition, the oxide content of different elements within the ash of solid samples was determined using the XRF method to calculate indices related to operational problems during the combustion process. The results confirmed that time did not matter significantly and the physical and chemical properties of hydrochar were very similar to each other. However, the contact angle for 2 h of residence time confirmed that a longer processing time resulted in a more hydrophobic character of hydrochar and enabled more effective dewaterability of hydrothermal slurry. It was also noted that the hydrothermal carbonization process affected the sewage sludge in a positive way. In brief, the results confirmed that the hydrochar was a brittle, moderately hydrophilic, solid carbon-containing product that provided a different combustion performance than the raw sewage sludge.
The main aim of the paper is to analyze the effect of different pretreatment processes (HTC, torrefaction and slow pyrolysis) on the properties of Miscanthus giganteus. In this study, the HTC process ...was conducted in a Zipperclave Stirred Reactor under following parameters: temperature (180, 200 and 220 °C), pressure (<2.5 MPa) and residence time (2, 3, 4, 6, and 12 h). The effect of temperature and residence time of torrefaction and slow pyrolysis were studied in specially designed laboratory apparatus. Torrefaction temperature was held at 230, 260, and 290 °C, and residence time was specified for 0.5, 1.0 and 1.5 h. The preliminary study for slow pyrolysis processes were performed at 350, 400, 450 and 500 °C for 0.5, 1.0 and 1.5 h. The thermal behaviour of raw and pretreated Miscanthus was investigated by TGA analysis. Finally, HTC, torrefaction and slow pyrolysis processes proved an improvement in the combustible characteristics of the obtained biochars compared to raw biomass by the spectacular increase of carbon content 36%, 34% and 80%, respectively.
•The pre-treatment processes of Miscanthus x giganteus were investigated.•The effect of temperature and residence time on hydrothermal carbonization, torrefaction and slow pyrolysis was studied.•The physical and chemical properties of raw, hydrochars, torrefied Miscanthus and pyrochars were determined.•The thermal behaviour of raw and pretreated Miscanthus was investigated by TGA analysis.
In agricultural biogas plants, besides biogas, the by-product digestate is also produced. Due to its high moisture content and organic origin, it can successfully be applied in the hydrothermal ...carbonization process to avoid the fate of landfilling. This paper reviews the properties of agricultural digestate and its hydrothermal conversion (HTC) into hydrochar and process water. The type of feedstock and the parameters of the HTC process, such as temperature, pressure and residence time, affects the physical and chemical characteristics of hydrochar. Therefore, its possible application might be as a biofuel, fertilizer, soil improver, adsorber, or catalyst. In this paper, the properties of hydrochar derived from agricultural digestate are widely discussed.
Rigid polyurethane foams (RPUFs) are characterized by their excellent viable properties; thus, these materials can be successfully used as thermal insulation materials. The main problem, the solution ...of which is partly indicated in this paper, is that the products for the synthesis of RPUFs are produced from petrochemicals. Due to this, the use of natural fillers in the form of waste biomass is introduced for the synthesis of RPUFs. The biodegradable biomass waste used in the RPUF production process plays multiple roles: it becomes an activator of the RPUF foaming process, improves selected properties of RPUF materials and reduces the production costs of insulating materials. The paper presents the results of the foaming process with the use of six different fillers: sunflower husk (SH), rice husk (RH), buckwheat husk (BH), sunflower husk ash (SHA), rice husk ash (RHA) and buckwheat husk ash (BHA). In all cases, composites of rigid polyurethane foam with 10 wt.% of filler were produced. New foams were compared with polyurethane materials without the addition of a modifier. Moreover, the paper presents the results of the fillers’ analysis used in the tests and the effects of the fillers’ addition as activators of the RPUF foaming process. Promising results were obtained for two of the fillers, BHA and SHA, as activators of the foaming process and confirmed by the volumetric results, where the named samples reached their maximum value in half the time compared to the remaining samples. In addition, the expansion rate for PU_10BHA was a maximum of approximately 11 cm3/s and PU_10SHA was a maximum of approximately 9 cm3/s, whereas the remaining samples showed this parameter at about 3 cm3/s. During the research, the scanning electron microscopy method and infrared camera technique were used.
