Fuel properties and incineration behavior of poultry litter blended with sweet sorghum bagasse and pyrolysis oil

Poultry litter (PL) waste is produced from large-scale commercial broiler chicken rearing in rural areas. With the increasing demand for poultry meat and eggs, the volume of PL generated has also risen. Traditionally, PL has been used as fertilizer on small and mid-size farms. However, as poultry production has become more centralized and farm sizes have grown, there are significant concerns about water, land, and air pollution. The large-scale accumulation of waste outside of the cropping season and inadequate PL waste management can lead to health and welfare issues in flocks, increased fly breeding, air pollution, unpleasant odors, and land and water contamination. Currently, PL is disposed of through direct land application during the cropping season and through energy applications for the rest of the year. Various energy recovery methods and techniques have been employed for PL; among them, co-combustion with various renewable or nonrenewable fuels has been identified as the most effective from both technical and environmental standpoints. Incineration is considered the quickest option for disposing of PL due to the substantial waste accumulation. The incineration of poultry litter is an effective method for reducing waste volume, aligning with the United Nations Sustainable Development Goal of "affordable and clean energy." However, mono-incineration presents significant challenges due to the varying moisture, structural and chemical composition, and low energy yield of the litter. While poultry litter contains lignocellulosic bedding and energy-rich manure- like components, direct incineration experiments have not been successful due to the presence of moisture, ash, and the chemical composition of ash, which degrade fuel quality and combustion performance. Additionally, ash deposits caused by alkaline minerals in the ash further complicate the incineration process. Therefore, blending poultry litter with auxiliary fuels is necessary to achieve uniform combustion. Biomass, as a renewable resource, contains high levels of organic compounds, resulting in a high calorific value that can aid in fueling poultry litter. Mixing poultry litter with lignocellulosic biomass can enhance the heating value of the blends. Furthermore, biomass exhibits different combustion characteristics compared to poultry litter, with higher volatility and lower ash content. This blending process can influence the overall combustion process, leading to improved combustion efficiency, reduced carbon monoxide emissions, and lower unburned carbon content in ash. The increase in poultry production leads to a significant amount of poultry litter (PL), mainly consisting of manure and litter materials. Disposing of this waste safely and efficiently is a challenging task. The higher heating value (HHV) of this animal origin waste is 19.0 MJ kg-1, making it a promising renewable energy source. Due to the high prices of fossil fuels, there is growing interest in using PL for combustion in specialized furnaces designed for heating poultry houses. The circular economy approach and regulations promoting the use of farmed animal manure as a fuel in combustion plants further encourage the use of PL as a fuel for direct combustion to heat poultry houses on site. However, PL is considered a challenging fuel because it decomposes quickly, causing the HHV to drop from 19.0 to 9.0-13.5 MJ kg-1 within a few days due to higher moisture content. This hinders combustion and leads to ash- related problems when mono combustion is applied. Therefore, pre-mixing or pretreatment is necessary to improve the properties for combustion in a power plant or direct combustion on a farm for space heating. Some biofuel feedstocks have high HHV, low ash content, low ignition point, and optimal fouling, slagging, and high ash melting temperatures, making them suitable for combustion. It's generally recommended to blend more than two feedstocks after analyzing combustion characteristics to optimize combustion problems and minimize gas emissions and ash- related issues. Previous research indicates the synergistic effect of additional biomass fuels on PL in relation to combustion parameters such as flame characteristics and ash element index. The study examines a practical method to enhance the combustion characteristics of PL by using a blend of sweet sorghum bagasse (SS) and pyrolysis oil (PO). The research analyzes the combustion behaviors of PL, SS, their mixture, and the addition of PO using standard fuel analysis and image analysis. Additionally, the study investigates the ash composition to compare the blended fuel's propensity for fouling and slagging in the boiler system. The aim of the study is to investigate how SS and PO can improve the fuel properties of PL and reduce ash-related issues during combustion. Different biomass combinations were created by blending PL with sweet sorghum bagasse at various percentages (0.0%, 25%, 50%, 75%) and compared with 100% sweet sorghum bagasse. To maximize energy potential and minimize ash deposition, some samples were also mixed with 10% pyrolysis oil. The experimental results indicate that increasing the proportion of SS and adding pyrolysis oil (PO) to the mixtures raises the volatile matter and lowers the moisture and ash content. The results from the proximate analysis on a dry basis for ash content, volatile matter, and fixed carbon confirm our hypothesis that both pyrolysis oil and SS proportions reduce ash content and increase volatile matter, making the mixtures more suitable for combustion due to their high volatile matter, low ash content, and low fixed carbon. According to the data, the pyrolysis oil used in the experiments contains 64% volatile material, showing reasonable combustibility. The addition of SS to PL significantly increased volatile matter by 67%, 68%, and 71.50% with 25% (T1), 50% (T2), and 75% (T3) SS addition, respectively. Furthermore, pyrolysis oil addition further increased the volatile matter to 68%, 70%, and 73%, respectively. Similarly, SS and PO significantly reduced ash content from 12.85% to 7.10% on a dry matter basis, suggesting that most of the material resulting from burning are products that do not contribute to fouling, slagging, and agglomeration during combustion. The ignitability index is a useful indicator of how well biomass will perform in boiler conditions. When SS is added to PL, the ignitability index of the pellet shifts in a 25% mixture and remains almost constant (41.94 - 42.02) with further increases of SS in the mixture. The addition of PO to PL:SS blends significantly improves the ignitability index from 41.75 to 43.74. All the estimated ignitability index values were above 35, indicating efficient use in a boiler. The high volatile content of SS is beneficial for rapid ignition at low temperatures, avoiding prevalent problems with ash at higher temperatures. The calorific content increases as the proportion of SS in the poultry litter mixture increases. By increasing the proportion of SS from 25% to 100%, the higher heating values (HHV) increase from 4295 ± 12 Kcal kg-1 to 4404 ± 9 Kcal kg-1. Additionally, the HHV values of PL:SS blends further increased in the 0.5-2.6% range when the blends were mixed with 10% PO in fuel blends. The increasing trend in lower heating value (LHV) and HHV values can be attributed to the chemical structure of both SS and PO materials, as poultry litter contains relatively high moisture and ash minerals, which reduce the LHV. The addition of SS and PO improved the flame volume and red color intensity of the PL blends based on image analysis. When compared to pure PL, the size and brightness of the flame area and red color intensity of images increased with a higher percentage of SS in the mixture. The flame area and red color intensity were further increased by the addition of PO to the biomass pellets. These results support our hypothesis that sweet sorghum bagasse and pyrolysis oil have a more potent effect on PL combustion. The volatile flame's area and red color intensity for SS and PO were larger and more robust than for pure PL. It is worth noting that SS alone and in combination with PO exhibited a shorter time to ignition compared to PL. Therefore, the ignition delay times of the prepared pellets were 75, 29, and 38 seconds for pure PL, SS, and their 50-50% mixture, respectively. When 10% pyrolysis oil was added to the pellets, the ignition delay times were shortened to 49, 28, and 33 seconds, respectively. These results are consistent with the phenomenon that more volatiles provided by SS and PO affect dehydration, devolatilization, and positively contribute to burning. To better understand the impact of changing biomass fuel parameters on flame red color intensity, Pearson correlations were performed using proximate composition parameters and ignition index values obtained from prepared biofuel pellets. The results showed the significant positive contribution of volatile matter and organic matter content on flame red color intensity. Higher Heating Value (HHV) and ignitability index (Ii) also positively affect red color intensity. On the other hand, the ash content and fixed carbon contributed by PL had significant adverse effects on the red color intensity. PL had the highest fouling index value (FI < 40) and was classified as extremely high due to the presence of potassium, sodium, and phosphorus in ash. On the other hand, the index value of SS was in the medium range (FI 0.6-40). The fouling index results of the 50% PL and 50% SS mixture reduced the overall index value. However, neither SS nor PO in the mixture showed a low tendency to ash fouling. The presence of SS and PO did not sufficiently improve the ash-related index values, which necessitates further investigation.