Hyungseok Nam

Influence of biochemical composition during hydrothermal liquefaction of algae on product yields and fuel properties

Hydrothermal liquefaction (HTL) of nine algae species were performed at two reaction temperatures (280 and 320°C) to compare the effect of their biomass composition on product yields and properties. Results obtained after HTL indicate large variations in terms of bio-oil yields and its properties. The maximum bio-oil yield (66wt%) was obtained at 320°C with a high lipid containing algae Nannochloropsis. The higher heating value of bio-oils ranged from 31 to 36MJ/kg and around 50% of the bio-oils was in the vacuum gas oil range while high lipid containing algae Nannochloropsis contained a significant portion (33-42%) in the diesel range. A predictive relationship between bio-oil yields and biochemical compositions was developed and showed a broad agreement between predictive and experimental yields. The aqueous phases obtained had high amount of TOC (12-43g/L), COD (35-160g/L), TN (1-18g/L), ammonium (0.34-12g/L) and phosphate (0.7-12g/L).

Decentralized biorefinery for lignocellulosic biomass: Integrating anaerobic digestion with thermochemical conversion

Anaerobic digestion (AD) of lignocellulosic biomass i.e. Napier grass (Pennisetum purpureum), was investigated via a series of batch and bench-scale experiments. Two semi-continuous bench-scale horizontal bioreactors were operated in parallel for nearly 300 days, and the reactors were able to handle the organic loading rate (OLR) up to 6 kg volatile solids (VS)/m3-d, which was among the highest OLR reported in the literature for lignocellulosic biomass. Hemicellulose was the main structural carbohydrate of lignocellulosic biomass per unit respective mass (dry weight) basis contributing to methane production. The cellulose- and lignin-rich digestate was further examined for its bioenergy potential via torrefaction and hydrothermal carbonization, and was found to have higher mass and energy yield compared with those of raw Napier grass. The produced solid char has energy content similar to bituminous coal with low ash content. Thus, this study provided a successful integration of anaerobic digestion with thermochemical conversion representing a biorefinery concept for lignocellulosic feedstocks.

Fluidized Bed Air Gasification Using Low Heating Value Sand-Bedded Dairy Manure and Sludge Pellets

Solid manure handling is a major environmental issue confronting animal facilities in the United States. One difficulty in using dairy manure as a fuel source is the presence of sand bedding used for lactating dairy cows. More than 30% of dairy farms use sand beds for a dry and clean environment that prevents bacterial growth [1]. In this study, dairy animal manure obtained directly from waste lagoons was used for the air gasification process. The manure was dried to reduce the moisture down to 5% and a sand separating system was designed to remove some sand bedding materials. Preliminary air gasification experiments showed that the direct use of dairy manure containing 75% ash content, that reflect high sand content, reduced the temperature of the reactor. The study is also aimed at handling unprocessed dairy manure and generating electric power for the on-site use. A high heating value manure is needed to run the gasifier and the produced synthesis gas (or syngas) is fed to an engine coupled with a generator. Some dairy manure gasification work were done using fresh dairy manure. The highest heating value from the dairy manure biomass was found to be 4.5MJ/kg in a fixed-bed gasifier [2]. Another gasification study using a fluidized-bed reactor could produce syngas heating value as high as 4.7MJ/m3 from dairy manure [3]. A bench-scale fluidized bed containing a 3-inch diameter reactor tube with a cyclone and a scrubber was used to gasify dairy manure using air at different temperatures. The sand separated dairy manure used in this study contained approximately 45% ash content. The maximum heating value of the synthesis gas was 3.8MJ/m3 at an operating temperature of 750°C. The syngas will need to be upgraded. To upgrade the synthesis gas heating value, sludge pellets of 18.7MJ/kg were mixed with the dairy manure in different ratios of 10% and 30%. The syngas heating values from mixed manure with sludge pellet were increased to 5MJ/m3 with 10% sludge, and 5.7MJ/m3 with 30% sludge. The sludge used has higher heating value resulting in higher gas HV. The cold gasification efficiency was achieved as high as 36±5% with dairy manure mixed with sludge pellet. At a higher operating temperature, higher efficiency was obtained with increased gas composition of hydrogen and carbon monoxide. This syngas may then be used for power generation as well as possible input gas for the Fisher Tropsch process for liquid biofuel production. The result of the experiments will be a cornerstone for the widespread application of low heating value animal waste for producing high heating value syngas that may be used for electric power generation as a result of various upgrading processes.Copyright

Optimising Pyrolysis Conditions for Thermal Conversion of Beauty Leaf Tree (Calophyllum inophyllum L.) Press Cake

Beauty leaf tree (BLT) has been recognised as one of the potential species for biodiesel production in the tropics as it can produce up to 3800 L of non-edible oil which can be converted to biodiesel. The BLT is also resilient to stress conditions so it can be cultivated on degraded lands such as salt- and drought-affected soils. Biodiesel production from BLT, however, generates wastes such as the husk, press cake and glycerol. These wastes will increase the cost of producing biodiesel, and they can also add waste management issues. The current study investigated conversion of BLT biodiesel production wastes into other forms of biofuels. Oven-dried press cake samples were pyrolysed using a batch reactor at 300, 400 or 500 °C, with a residence time of 30, 60 or 90 min. The gas generated from this process was condensed to produce bioliquor and biooil, and the uncondensed gas was quantified as syngas. The pyrolysed biomass residue was collected as biochar and quantified. Energy content of these four products was determined, and the results showed that more than 90% of the energy contained in the BLT press cake can be recovered as other forms of biofuel. It was also found that the temperature had greater influence on the conversion process than on residence time. Furthermore, the biochar yield decreased with an increase in temperature, in contrast to biooil and syngas yields. The optimum conditions for thermal conversion of BLT press cake were found to be 500 °C, with a residence time of 30 min. This study demonstrates that the wastes resulting from biodiesel production process can be used as the feedstocks for producing other forms of biofuels. This approach will not only solve the environmental issues, but it will also improve economic viability of BLT biodiesel production process. Based on these results and the additional tests, a portable and continuous feeding auger pyrolysis reactor is recommended for converting BLT whole fruits, press cake or husks into biofuels.

Biomass gasification producer gas cleanup

Abstract In addition to primary gases, biomass-derived producer gas contains nonnegligible concentrations of undesirable byproducts collectively known as contaminants. Syngas contaminants are composed of tar-, nitrogen-, and sulfur-based compounds and halides and other trace metals that must be minimize their negative impacts on downstream processes or to adhere to environmental regulations. The producer gas cleanup consists of all processes that are employed to reduce the concentration of contaminants in raw producer gas prior to conditioning and utilization in downstream applications. This chapter discusses primary contaminants, the impact of operating conditions on them, their mitigation and regulations governing their emissions. Additionally, best of available technology (BAT) are discussed for select contaminants.

Experimental Investigation of Microexplosion Phenomena in Emulsified Vegetable Oil-Methanol Blends

Secondary atomization is one of the most attractive and misunderstood effects in the combustion of microemulsified fuel blends. The occurrence of secondary atomization has been studied to determine its effects on improved combustion efficiency especially when low vapor pressure fuels are used. Several methods to detect microexplosion as alternative to secondary atomization have been considered including acoustic signal processing. As part of the physical characterization of an emulsified vegetable oil-methanol blend, microexplosion behavior of fuel blend droplets has been observed to take place under certain environmental conditions. Droplets microexplode as methanol surrounded by vegetable oil molecules flashes or microexplodes under intense temperature and intense droplet pressure. The droplets of emulsified methanol-in-oil break up forming tiny droplets with greater surface-to-volume ratio in the process. To understand the effects of emulsification on microexplosion, characterization of secondary atomization has been performed using a temperature probe, a high-speed camera and an acoustic sound signal processor. Experiments have been conducted at temperatures similar to those encountered in liquid fuel boilers. The acoustic signal data were analyzed using Fast Fourier Transform (FFT) to define and understand the overall microexplosion process. Also, the effect of temperature, droplet sizes and the percentage of methanol in the vegetable oil blend have been studied to understand what leads to a higher probability of microexplosion occurrence. A correlation between the analyzed acoustic signal data and high speed images were used to differentiate between the different microexplosion events. The results of the study can be useful in predicting the occurrence of microxplosion in liquid fuel boiler which should result in more complete combustion processes, reducing contaminant levels significantly.Copyright