Yongwoon Lee

Comparison of biochar properties from biomass residues produced by slow pyrolysis at 500°C

Application of biochar from biomass pyrolysis to soil is gaining greater interest; this can ameliorate the soil quality, reduce fertilizer consumption, and sequestrate carbon. This study compares the characteristics of biochar produced by slow pyrolysis at 500°C for agricultural residues: sugarcane bagasse, cocopeat, paddy straw, palm kernel shell (PKS) and umbrella tree. In the biochar yield, the influence of the inert and lignin contents was significant. The wood stem, bagasse and paddy straw had biochar yields of 24-28 wt.% from the organic fraction while cocopeat had 46 wt.%. The carbon content of biochar ranged from 84 wt.% to 89 wt.%, which corresponded to 43-63% of carbon in the biomass. The biochar from wood stem and bagasse had well-developed pores of various sizes with large surface areas. Although the surface area was significant, PKS biochar had dense matrix with few large pores. The elemental composition and pH of biochars were also compared.

Slow pyrolysis of rice straw: analysis of products properties, carbon and energy yields.

Among many uses of rice straw, application of its biochar from pyrolysis to the soil is receiving greater interest for increased crop productivity and sequestration of CO2. This study investigated slow pyrolysis of rice straw at 300-700°C to characterize the yields and detailed composition of the biochar, bio-oil and non-condensable gases. Biochar was analyzed for pH, microscopic surface area and pore volume distribution. Although the mass yield for the organic fraction was only about 25% above 500°C, biochar was the primary product of pyrolysis containing 40% of energy and 45% of carbon from the straw. The utilization of by-products (bio-oil and gases) as energy resources was essential, since the sum of energy yield was about 60%. The gases could be burned to produce the heat for an auto-thermal pyrolysis process, but the heat balance was significantly influenced by the moisture content of the raw material.

Characteristics of biochar produced from slow pyrolysis of Geodae-Uksae 1

This study investigated producing biochar from Geodae-Uksae 1 for soil applications to sequestrate carbon from the atmosphere and improve the productivity of crops. Using a lab-scale packed bed reactor, pyrolysis products of Geodae-Uksae 1 were produced over a temperature range of 300-700°C with a heating rate of 10°C/min. Pyrolysis at 500°C was found appropriate for biochar production considering the properties of char and the amount of heat required. It yielded biochar of 27.2wt.% that contained approximately 48% carbon in the raw biomass. The surface area of the biochar rapidly increased to 181m(2)/g. Large cylindrical pores with diameters of 5-40μm developed within the biochar due to the vascular cell structure of the parent biomass. The byproducts (bio-oil and gases) were also analyzed for use as fuel.

High temperature oxidation of TiCrN coatings deposited on a steel substrate by ion plating

Abstract The oxidation behavior of TiCrN coatings having compositions of Ti 36 Cr 26 N 38 , Ti 31 Cr 35 N 34 and Ti 14 Cr 52 N 34 was studied between 700 and 1000°C in atmospheric air. The oxidation resistance of TiCrN coatings which were composed of TiN and CrN phases increased in the order of Ti 36 Cr 26 N 38 , Ti 31 Cr 35 N 34 and Ti 14 Cr 52 N 34 , implying that chromium within the coating played a decisive role in providing the oxidation protection. The oxides formed always consisted of TiO 2 and Cr 2 O 3 . During oxidation, all the involved elements diffused either outwardly or inwardly, depending on the concentration gradients. The substrate elements diffused outwardly toward the oxide-gas interface, oxygen from the atmosphere diffused inwardly and the coating elements diffused predominantly outward.

Low-temperature reactivity of coals for evaluation of spontaneous combustion propensity

Low rank coals are more reactive at low temperatures than high rank coals, which leads to spontaneous combustion if not controlled. Due to the increased use of low rank coals, preventing spontaneous combustion during storage and size reduction has become an important issue in power plants. The present study evaluates the low-temperature reactivity for various coals in terms of their rank and country of origin. The experimental method determined the temperature and its gradient for coals in a small fixed bed at the point surpassing that of input oxygen, which were defined as the crossing-point temperature (CPT) and slope (CPS), respectively. Combining the two parameters, a low-temperature reactivity index (LTR index) was proposed. The method tested 17 coals collected from a power plant that yielded CPTs ranging between 168–190 °C and CPSs between 0.862–1.228 °C/min. The LTR index for the coals was calculated to be 0.696 to 1.542. The LTR index was positively correlated with the moisture content and volatile matter/fixed carbon (VM/FC) ratio, and inversely correlated with the ash content. The ignition temperature, measured by thermogravimetric tests, also exhibited a positive relationship with the LTR index. However, no single property of coal was sufficiently correlated with the self-heating propensity for all the coals tested, illustrating the complex mechanisms involved.

Partial oxidation of sewage sludge briquettes in a updraft fixed bed.

The fixed bed reaction of sewage sludge briquettes was investigated to evaluate the potential applications to gasification, combustion, or production of biochar as soil ameliorator. The reaction had two distinctive stages: ignition propagation and char oxidation. The ignition front of the sludge briquettes propagated at a lower speed, which significantly increased the stoichiometric ratio of overall combustion reaction and peak temperatures. The ignition front also had irregular shapes due to the channeling effects. During the char oxidation stage, the sludge ash agglomerated because of the slow reaction rate and increased CO2 formation. Because of low energy content in the product gas, the large briquettes were not favorable for syngas production. In addition, the low burning rates and ash agglomeration could cause problems in the operation of a grate-type furnace for combustion. However, the char accumulated above the ignition front had similar properties with that from pyrolysis under inert atmosphere. Therefore, the fixed bed reaction under partial oxidation conditions can be applied to produce biochar as soil ameliorator from the sludge briquettes without external heat supply.

Experimental study on moisture re-adsorption characteristics of dried coal

Recently, Korean coal-fired power plants have used sub-bituminous coals with moisture and volatile contents higher than design coal of those plants. This causes a decrease in the efficiency of boil...