Solid Fuel

In the last decades, hybrid rocket engines have been increasingly studied and used in space vehicles. However, the low regression rates and specific impulses still represent major drawbacks to this technology. The objective of this study was to quantify the relative improvement of regression rate values with the use of a swirling flow injector in comparison to an axial injector. Seven tests were conducted with axial injection and seven with swirl injection. Regression rate results were compared, and it was found that swirl injection improved regression rates in 50% for mass fluxes higher than 45 kg • s –1 • m –2. It was possible to see radiation, kinetic and diffusion theory on the logarithmic plot of regression rate per oxidizer flux yielded by both injectors. A strong agreement with experimental findings of regression rates in the literature parameters is reported.

Microwave co-torrefaction (MCT) was performed on empty fruit bunch (the most abundant waste from oil palm industry) mixed with waste oil (used engine oil, used cooking oil) to simultaneously utilize these waste materials to produce better quality solid fuel product. The effect of temperature and types of waste oil on the product yield and fuel properties (high heating value (HHV), energy yield, and fuel ratio) were investigated. MCT provided a rapid heating (50-65 • C/min) and a shorter process time of 5-8 min than that shown by conventional torrefaction performed using furnace (> 30 min). The rapid heating could be attributed to the use of a cubical microwave cavity with helical lift for 2-dimensional movement (rotational and translational motion) that allows uniform distribution of microwave radiation for heating and torrefaction. The empty fruit bunch torrefied with used engine oil at 250 • C showed maximum energy yield of 100 wt% and produced solid fuel product with high mass yield (85.5 wt%), fuel ratio (1.8), carbon content (68.3 wt%) and fixed carbon content (62 wt%). Solid fuel product of high higher heating value (28.0 MJ/kg) was produced from microwave co-torrefaction of empty fruit bunch with used engine oil at 300 • C. Our results demonstrate that microwave-co-torrefaction represents a promising waste reduction approach to convert empty fruit bunch mixed with waste oil to produce solid fuel with improved properties.

The amount of Paper Board Mill Effluent Treatment Plant Sludge (PBM-ETPS) dumped from paper mills are huge and its conversion into hydrochar for the purpose of energy has broad prospects. this study investigated the optimum conditions for the production of PBM-ETPS derived hydrochar (PBM-ETPSH) through Reponse Surface Methodology (RSM) for more surface area and pore volume with minimal hydrogen to carbon (H/C) and oxygen to carbon (O/C) ratios. The PBM-ETPSH had higher heating value (HHV) of 18.39 MJ kg −1 with fixed carbon percentage of 15.6. Our results showed a reduction in H/C (35.05%) and O/C (43.7%) ratios confirming the coalification of optimized PBM-ETPSH. Thermogravimetric investigations of blending PBM-ETPSH with coal in 1:1 ratio increased its HHV to 22.25 MJ kg −1 making it suitable as an energy alternative for paper mills. The advent of industrial revolution has boosted an enormous generation of liquid and solid wastes leading to advanced treatment technologies. Hydrothermal carbonization (HTC) is an emerging method for the conversion of wet biomass at relatively mild reaction temperatures into a coal-like material called as hydrochar 1. Technically, the conversion process was performed in the temperature range of 180 °C-260 °C for 30 minutes to 10 h with biomass to water ratio of 1:9 2. The HTC process is governed by different process parameters such as temperature, time, biomass to water ratio, pH of the substrate and concentration of the catalyst, among which the temperature and time are significant. Higher temperature promoted lower solid yield production with higher quantity of gaseous compounds 3. In another study, the increase of HTC temperature from 180 °C to 300 °C has resulted in the solid yield reduction of hydrochar from 66.18% to 53.00% 4. The distribution and quality of solid, liquid and gaseous products are influenced by the residence time of the reaction and 12 h residence time resulted 60% increase in the solid yield of hydrochar per unit biomass due to the polymerization of fragments in the dissolved phase thereby forming secondary hydrochar with a polyaromatic structure 5. Being a carbon compound with good aromaticity, hydrochar has a potential application in the energy sector as an alternative source of energy due to the reduction of inorganic constituents and increased proportions of carbon compounds 6. Thus, conventional polluting energy sources can be replaced by hydrothermally car-bonized products thereby ensuring sustainability. The thermal behavior of hydrochar was found similar to the non-renewable energy sources such as coal, lignite and anthracite thus reducing the dependency on conventional energy sources 1. Hydrochar also possess more calorific value than any other carbon based material due to complete removal of volatile matter with an increase in the ash content thereby resulting in higher heat generation during combustion 7. Hence the hydrochar can be used as a coal substitute for heat production through co-combustion process at specific proportions. The global production of paper accounted for about 413 million tons in 2017 of which India contributed 3.18% through paper, paperboard and newsprint production per annum 8. The paper products were recycled after utilization through paper board mill industries thereby producing recycled paper and packaging materials with PBM-ETPS as the predominant solid waste. Since, the present study was taken to convert the PBM-ETPS into Hydrochar by HTC process, the optimization of process parameters are considered to be an important for producing hydrochar from PBM-ETPS with anticipated surface and fuel characteristics which was made ease by employing statistical tool named Response Surface Methodology (RSM). Investigations on thermal behavior of the hydrochar also paved way for its utilization as an alternate energy source.

Solid fuels are still widely used in rural China though the living standard has improved greatly. Energy poverty is an obvious indicator of poverty, which has serious effects on economic development, environment, and health. In this paper, we conducted a detailed analysis on fuel choice and usage behavior of different end-use activities in rural residential energy consumption. Using 717 household observations from micro-survey data in two counties of Shandong and Hebei province in 2016, we find that biomass is the dominant fuel used for cooking among all energy sources despite of obvious decreasing trend in recent years, accounting for 44%. Clean energy used to cook increased markedly with a proportion of nearly 50%. Solar energy is an ordinary fuel used for water heating except for biomass. Almost 90% of households rely on coal for space heating in winter, and one-third of households have space heating for fewer than two months. Ownership of home appliances for basic needs is higher than that for hedonistic needs, and usage behaviors of some appliances are economical. Fuel accessibility of commercial energy have improved noticeably in rural areas, and the high proportion usage of biomass is affected by family income, usage habits, local resources, environmental recognition, education, and age. Since the negative effects of using solid fuels, it is urgent to cleanse biomass, develop new energy, and improve residents' cognition about the consequences of using solid fuels.