Wet Torrefaction Process Research Articles

Wet torrefaction pre-treatment of yard waste to improve the fuel properties

The utilization of biomass has emerged as an attainable alternative for energy production. However, the intrinsic properties of biomass including hygroscopic behaviour, heterogeneity in structure and high moisture content constraint the usage of biomass in bioenergy applications. Wet torrefaction enhance the fuel properties of the lignocellulosic biomass by treating in hot compressed water. The present study aimed to identify the effectiveness of wet torrefaction to improve the properties of yard waste as an energy resource. Wet torrefaction operating parameters investigated in this study were water-to-biomass ratio (10:1–30:1) and reaction temperature (180–220 °C). The energy yield varies from 63.9% - 74.4% in these operating conditions. Temperature was found to have greater impacts on the fuel properties of biomass compared to water-to-biomass ratio. The higher heating value (HHV) of yard waste achieved was 24.2 MJ/kg after undergoing the wet torrefaction process at 220 °C with water-to-biomass ratio of 10:1. The enhanced properties for wet-torrefied biomass were observed as lower moisture content, lower ash content, higher fixed carbon content and higher heating value in relative to raw yard waste. Torrefied biomass had reduced oxygen content and higher carbon content in comparison with raw biomass, which implied that wet torrefaction is capable in improving the fuel properties.

Co-processing textile sludge and lignocellulose biowaste for biofuel production through microwave-assisted wet torrefaction

Microwave-assisted wet torrefaction was adopted in this study for co-processing textile sludge (TS) and biowaste. Key operating parameters, including different temperatures (120–180 °C) and reaction times (10–30 min), for the torrefaction of legally recyclable TS (R-0906 in Taiwan) were evaluated. Furthermore, TS was blended with six widely produced types of lignocellulose biowaste at different blending ratios for improving the biochar quality and combustion characteristics. The results indicated that the optimal temperature and reaction time for TS torrefaction were 180 °C and 20 min, respectively, beyond which the fixed carbon content and higher heating values (HHVs) of biochar increased from 1.7% to 5.1% and 13.0–18.7 MJ/kg, respectively. However, biochar produced through the torrefaction of TS and macadamia husk with a blending ratio of 30/70 (db%) exhibited the highest fixed carbon content (29.8%) and HHV (19.7 MJ/kg) among the six tested lignocellulose biowaste samples with the atomic H/C and O/C ratios close to those of peat. The thermal stability, activation energy, frequency factor, and ignition and combustion temperatures of the biochar produced through microwave-assisted wet torrefaction co-processing were higher than those produced using raw TS or biowaste. The energy return on investment of the biochar system reached 10.9. Greenhouse gas emissions can be decreased by 57.5% if biochar is used as a bituminous coal substitute. Therefore, microwave-assisted wet torrefaction is a sustainable approach for mitigating the disposal problems of TS and lignocellulose biowaste as well as improving the energy performance and environmental friendliness of biochar-to-energy systems. Besides, the protein and carbohydrate contents in the supernatant of TS co-torrefied with biowaste at different blending ratios increased by 1.0–4.1 and 1.2–5.9 times, respectively. These contents can be recycled back to the activated sludge unit as a nutrient source. Overall, the microwave-assisted wet torrefaction process is green and economically beneficial.

Microwave-assisted wet torrefaction of microalgae under various acids for coproduction of biochar and sugar

Wet torrefaction is a promising method to converts the high moisture microalgae to biofuel. In this study, the microalgae were torrefied in water or dilute acid solutions with the aid of microwaves irradiation. The reaction temperature and heating time were fixed at 160 °C and 10 min. The effects of sulfuric, phosphorus, and succinic acids on two different microalgae species (Chlorella vulgaris ESP-31 and FSP-E) were investigated. As a result, the disruption of the microalga FSP-E (high protein) was not notable in the acidic solution. The higher heating value of wet torrefied microalga ESP-31 (high carbohydrate) in succinic acid was enhanced up to 40% with at least 45% of energy yield. The use of 0.1 M of phosphorus acid in wet torrefaction produced the highest ash content of 1.61 and 11.60 wt% for microalgae ESP-31 and FSP-E, respectively. Thermogravimetric analysis revealed that the carbohydrate content of microalga ESP-31 has the highest degradation in sulfuric acid solution. In contrast, crystalline cellulose in the microalgae is hardly affected by the wet torrefaction process in low-temperature acidic solution. In terms of liquid product, a maximum glucose extraction of 35.39 g/L occurred with the use of 0.1 M of sulfuric acid. In conclusion, biochar produced using organic acid is desirable as solid fuel, whereas the use of sulfuric acid is more suitable to produce sugar for bioethanol production.

Upgrading almond-tree pruning as a biofuel via wet torrefaction

Two series of six wet torrefaction tests were performed using a pressurized batch reactor in order to upgrade almond-tree pruning (a largely available agricultural waste in Mediterranean areas) as a fuel. The assayed maximum temperatures were in the range of 175–300 °C, held for either 10 or 60 min. Raw almond-tree pruning and wet-torrefied solid products were systematically characterized through a wide range of analytical procedures, such as bulk density, particle size, structural and elemental composition, ash content, heating values, moisture uptake, FTIR spectra and SEM micrographs. The effects of temperature and time on the wet torrefaction process of almond-tree pruning were simultaneously evaluated through the severity factor. Higher temperatures and longer holding times brought the fuel properties of wet-torrefied solid products closer to those of sub-bituminous coal. The most severe operating conditions (i.e., 300 °C held for 60 min, or a severity factor equal to 7.68) allowed achieving an energy densification ratio of 1.67. However, the optimal processing conditions in terms of energy yield, which were found at a severity factor of 5.78, led to 57.1 wt% solid yields, with a higher heating value of 24.0 MJ/kg and an energy densification ratio of 1.36.

Utilization of mixed organic-plastic municipal solid waste as renewable solid fuel employing wet torrefaction

The largest obstacles in the utilization of municipal solid waste (MSW) as solid fuel in developing countries such as Indonesia are its high water content, irregular size and shape, and difficulty-to-sort due to the mix of plastic and organic waste. Based on literature study, wet torrefaction could be an appropriate pre-treatment process for mixed MSW because it requires no initial drying and mixed organic-plastic MSW can be processed without initial sorting. In this research, experiments were conducted to investigate the effect of wet torrefaction on increasing the fuel properties of mixed MSW. Based on field survey, the composition of the analyzed sample was: leaf litter (34.67%), food waste (23.33%), vegetable waste (14.33%), fruit waste (11.00%), and non-recycled plastic (16.67%). The experiments were conducted in a 2.5-L stirring reactor temperature variation (150, 175, 200 and 225 °C) with several holding times and solid loads. The result showed that wet torrefaction at a temperature of 200 °C with holding time of 30 min and solid load of 1:2.5 was the optimum condition, producing solid product with uniform physical shape, small particles and homogeneous particle size distribution, HHV of 33.01 MJ/kg and energy yield of 89%. The wet torrefaction process is not only suitable to convert the mixed MSW into renewable high energy density solid fuel, but it can also be used to produce separate organic product that can be used as solid fuel and plastic product that can be prepared for other treatments, such as pyrolysis to produce liquid fuel or recycling.

Experimental Study on Utilization of Indonesian Non-Recycled Organic Waste as Renewable Solid Fuel Using Wet Torrefaction Process

Municipal solid waste (MSW) is a complex problem in major cities in Indonesia that has not been resolved. MSW is currently only collected and disposed to final landfill. On the other hand, national energy security is also an issue to be solved. Utilization of MSW, which is dominated by organic waste, as solid fuel can be a solution for both problems. This paper discusses an experimental study on utilization of organic waste as renewable solid fuel using a wet torrefaction process. Four types of samples were chosen to represent the four types of organic waste in MSW with the highest mass fraction found in a field survey: leaf litter, food waste, vegetable waste and fruit waste. Each sample was treated with wet torrefaction under four conditions: 150, 175, 200 and 225 oC with holding time 30 minutes. The experimental results showed that the optimum wet torrefaction temperature for mixed organic waste is between 200 and 225 °C, which is predicted to produce a solid product with a heating value (db) of 23.22-24.44 MJ/kg, volatile matter content of 61.18-66.00%, fixed carbon content of 26.04-31.35%, ash content of 7.47-7.96%, and energy yield equal to 58%. A higher operating temperature will increase the calorific value, followed by a decrease in mass yield as a consequence of the process severity degree. However, food waste torrefaction showed different characterisics: the increase in calorific value was followed by an increase in mass yield. This is unique and different from the results of wet torrefaction on other organic wastes. Keywords: Indonesian organic MSW, national energy security, wet torrefaction, renewable solid fuel.

Municipal solid waste processing and separation employing wet torrefaction for alternative fuel production and aluminum reclamation

This study employs wet torrefaction process (also known as hydrothermal) at low temperature. This process simultaneously acts as waste processing and separation of mixed waste, for subsequent utilization as an alternative fuel. The process is also applied for the delamination and separation of non-recyclable laminated aluminum waste into separable aluminum and plastic. A 2.5-L reactor was used to examine the wet torrefaction process at temperatures below 200°C. It was observed that the processed mixed waste was converted into two different products: a mushy organic part and a bulky plastic part. Using mechanical separation, the two products can be separated into a granular organic product and a plastic bulk for further treatment. TGA analysis showed that no changes in the plastic composition and no intrusion from plastic fraction to the organic fraction. It can be proclaimed that both fractions have been completely separated by wet torrefaction. The separated plastic fraction product obtained from the wet torrefaction treatment also contained relatively high calorific value (approximately 44MJ/kg), therefore, justifying its use as an alternative fuel.The non-recyclable plastic fraction of laminated aluminum was observed to be delaminated and separated from its aluminum counterpart at a temperature of 170°C using an additional acetic acid concentration of 3%, leaving less than 25% of the plastic content in the aluminum part. Plastic products from both samples had high calorific values of more than 30MJ/kg, which is sufficient to be converted and used as a fuel.

A pilot-scale study of wet torrefaction treatment for upgrading palm oil empty fruit bunches as clean solid fuel

Less utilized empty fruit bunch (EFB) is seldom used as solid biofuel due to its high alkali content that potentially cause ash deposit called slagging and fouling. This phenomenon could harm biomass-fired power plant equipment. Some pre-treatment of EFB is needed to reduce EFB ash deposit potential. The effect of wet torrefaction pre-treatment in laboratory scale was successfully proven in decreasing slagging and fouling potential while increasing EFB calorific value that could fulfill clean solid fuel criteria. This research focuses on wet torrefaction process that conducted on a pilot scale with the capacity of 250 liters. It was found that wet torrefaction process can improve the product’s calorific value up to 9.41% while reduce its ash content down to 1.01% comparing to the raw EFB. The reduction of ash content also leads to the reduction of slagging and fouling tendency that presents in terms of alkali index. Alkali index is a quantitative method that can be calculated after obtaining metal oxides fraction on solid fuel. Metal oxides could be obtained by using energy dispersive x-ray spectroscopy.

Thermal pretreatment of lignocellulosic biomass

AbstractTorrefaction is a process to convert diverse lignocellulosic biomass feedstocks into an energy dense homogeneous solid, a pretreatment for subsequent thermochemical conversion. Loblolly pine was treated by wet torrefaction (hot compressed water, 200–260°C) and dry torrefaction (nitrogen, 250–300°C), with mass yield of solid product ranging between 57 and 89%, and energy densification to 108–136% of the original feedstock. The solid product has been characterized, including proximate analysis, fiber analysis, ultimate analysis, and equilibrium moisture. In both dry and wet torrefaction, increasing temperature results in decreased mass yield and increased energy densification, and results in a solid with increased carbon content, decreased oxygen content, and decreased volatiles. The biomass is transformed into a fuel similar to a low‐rank coal. Generally, the wet torrefaction process produces a solid with greater energy density than dry torrefaction, with the same mass yield. The fiber analysis indicates that hemicellulose is quickly removed during wet torrefaction, and the solid product contains substantial quantities of aqueous soluble compounds. The equilibrium moisture content of solids produced by both processes is somewhat decreased from that of the biomass feedstock, indicating a hydrophobic solid suitable for storage and transportation. © 2009 American Institute of Chemical Engineers Environ Prog, 2009