Increase In Torrefaction Temperature Research Articles

Thermal characterization of oil palm fiber and eucalyptus in torrefaction

Thermal behavior of biomass in torrefaction plays an important role in the operation of pretreatment. To understand the endothermic and/or exothermic characteristics of biomass in the course of torrefaction, an experimental system is conducted and two kinds of biomass (oil palm fiber and eucalyptus) are investigated. The results indicate that the thermal behavior is significantly influenced by the lignocellulosic composition in biomass and the torrefaction temperature. The thermal decomposition of hemicellulose is the dominant mechanism for oil palm fiber torrefied at 200 and 250 °C, whereas the thermal degradation of cellulose is crucial when the biomass is torrefied at 300 °C. Therefore, the heat of reaction of oil palm fiber increases with increasing torrefaction temperature. The torrefaction of eucalyptus is always endothermic, as a consequence of high cellulose contained in the biomass. It is less endothermic when the torrefaction temperature increases, presumably due to the char formation from cellulose thermal degradation and the exothermic lignin decomposition. As a whole, the values of the heat of reaction of the two samples are between −3.50 and 2.23 MJ/kg. The obtained results have provided a useful insight into the control of torrefaction operation and the design of torrefaction reactor.

백합나무의 반탄화 처리를 이용한 고체연료화 가능성 조사

This study was performed to investigate the potential of torrefied tulip tree (TT) for the production of pellets. For this purpose, chemical composition and fuel characteristics of torrefied TT were examined. In addition, pellets were fabricated by using sawdust of torrefied TT chip, and durability of the pellet was measured. Lignin content of torrefied TT was higher than that of non-torrefied TT, and increased with the increases of torrefaction temperature and time. Fuel characteristics of torrefied TT were affected by torrefied conditions, and the characteristics were influenced more by torrefaction temperature than by torrefaction time. Higher heating value (HHV) and ash content (AC) of torrefied tulip tree increased with increasing torrefaction temperature, and the values were much higher than HHV and AC values of non-torrefied TT. Durability of pellets fabricated with <TEX>$230^{\circ}C$</TEX>- and <TEX>$250^{\circ}C$</TEX>-torrefied TT was higher than that of <TEX>$270^{\circ}C$</TEX>-torrefied TT, and the value exceeded the minimum requirement (-97.50%) of the 1st-grade pellet standard designated by Korea Forest Research Institute. Based on the results, torrefaction treatment of <TEX>$250^{\circ}C/50min$</TEX> to TT might be a optimal condition for the production of TT pellets considering the mass balance and fuel characteristics of TT as well as the durability of the pellets. Thus, it is confirmed that torrefied TT can be used as a raw material for the production of bio-pellets.

Thermal behaviour and kinetic study for woody biomass torrefaction and torrefied biomass pyrolysis by TGA

The thermal decomposition behaviour and kinetics of Douglas fir sawdust torrefaction and torrefied sawdust pyrolysis were investigated using a thermogravimetric analyser (TGA). The mass loss of samples in torrefaction was highly related to the torrefaction temperature. The two-step reaction model fitted well for Douglas fir sawdust torrefaction. The activation energies of the first and second reaction stages were 112 kJ mol−1 and 150 kJ mol−1, respectively. Torrefied biomass exhibited different thermo decomposition behaviours compared to untreated biomass. The start point of torrefied biomass decomposition was shifted and the degree of shift increased with the severity of torrefaction. The final biochar yield of torrefied biomass was also increased with the increase of torrefaction temperature. Derivative thermogravimetric (DTG) curves showed that the shoulder of hemicelluloses decomposition in torrefied biomass pyrolysis was eliminated. The decomposition rate of torrefied biomass has a decreasing trend due to the mass depletion in torrefaction. A first-order one-step global model with the average activation energies in the range of 195–204 kJ mol−1 can describe the raw and torrefied biomass pyrolysis. The kinetic analysis also showed that the torrefied biomass pyrolysis from high torrefaction temperature might be multiple-step reactions.

Effects of torrefaction on the physiochemical properties of oil palm empty fruit bunches, mesocarp fiber and kernel shell

In this work, the effects of torrefaction on the physiochemical properties of empty fruit bunches (EFB), palm mesocarp fiber (PMF) and palm kernel shell (PKS) are investigated. The change of properties of these biomass residues such as CHNS mass fraction, gross calorific value (GCV), mass and energy yields and surface structure when subjected to torrefaction process are studied. In this work, these materials with particle size in the range of 355–500 μm are torrefied under light torrefaction conditions (200, 220 and 240 °C) and severe torrefaction conditions (260, 280 and 300 °C). TGA is used to monitor the mass loss during torrefaction while tube furnace is used to produce significant amount of products for chemical analyses. In general, the study reveals torrefaction process of palm oil biomass can be divided into two main stages through the observation on the mass loss distribution. The first stage is the dehydration process at the temperature below than 105 °C where the mass loss is in the range of 3–5%. In the second stage, the decomposition reaction takes place at temperature of 200–300 °C. Furthermore, the study reveals that carbon mass fraction and gross calorific value (GCV) increase with the increase of torrefaction temperature but the O/C ratio, hydrogen and oxygen mass fractions decrease for all biomass. Among the biomass, torrefied PKS has the highest carbon mass fraction of 55.6% when torrefied at 300 °C while PMF has the highest GCV of 23.73 MJ kg−1 when torrefied at the same temperature. Both EFB and PMF produce lower mass fraction than PKS when subjected to same torrefaction temperature. In terms of energy yield, PKS produces 86–92% yield when torrefied at light to severe torrefaction conditions, until 280 °C. However, both EFB and PMF only produce 70–78% yield at light torrefaction conditions, until 240 °C. Overall, the mass loss of 45–55% of these biomasses is observed when subjected to torrefaction process. Moreover, SEM images reveal that torrefaction has more severe impact on surface structure of EFB and PMF than that of PKS especially under severe torrefaction conditions. The study concludes that the torrefaction process of these biomass has to be optimized based on the type of the biomass in order to offset the mass loss of these materials through the process and increase the energy value of the solid product.

Synthetic indicator on the severity of torrefaction of oil palm biomass residues through mass loss measurement

In this work, the change of properties of empty fruit bunches (EFB), mesocarp fiber (PMF) and kernel shell (PKS) of oil palm when subjected to torrefaction process is reported. The properties include CHNS content, gross calorific value (GCV), mass and energy yields. These oil palm residues are torrefied at 200, 220 and 240, 260, 280 and 300°C, respectively for duration of 2h. In general, it has been found that the GCV and carbon content increase with the increase of torrefaction temperature but the O/C ratio, H and O content decrease for all residues. Also, we have shown that there are linear relationships between the mass loss with GCV and C content suggesting that it can be used as an indicator to monitor the severity of torrefaction process on these oil palm residues.

Reprint of: Pelletizing properties of torrefied wheat straw

Combined torrefaction and pelletization are used to increase the fuel value of biomass by increasing its energy density and improving its handling and combustion properties. However, pelletization of torrefied biomass can be challenging and in this study the torrefaction and pelletizing properties of wheat straw have been analyzed. Laboratory equipment has been used to investigate the pelletizing properties of wheat straw torrefied at temperatures between 150 and 300 °C. IR spectroscopy and chemical analyses have shown that high torrefaction temperatures change the chemical properties of the wheat straw significantly, and the pelletizing analyses have shown that these changes correlate to changes in the pelletizing properties. Torrefaction increase the friction in the press channel and pellet strength and density decrease with an increase in torrefaction temperature.

Change in particle size distribution of Torrefied biomass during cold fluidization

Torrefaction is a thermo-chemical process for upgrading biomass that is usually run at temperatures ranging from 200 to more than 300 °C in an oxygen-free atmosphere and at ambient pressure. It is a useful pre-treatment technology for biomass that significantly alters its physical and chemical composition, making it more efficient in pulverized systems. This paper investigates the grindability of eucalyptus chips torrefied at temperatures ranging from 210 °C to 270 °C for a 15 min residence time, compared to raw material before and after fluidization. The tests were carried out in a cold flow fluidization bed chamber with an internal diameter of 150 mm, with air as the fluidizing medium and a chamber height of up to 750 mm. Biomass grindability was assessed by evaluating the change in particle size distribution. The results showed that the degree of thermal degradation depended on the temperature and was also influenced by particle size. The mean particle size of ground torrefied biomass decreased with an increase in torrefaction temperature. Lastly, for larger particles, it was possible to correlate the size distribution with the severity of the heat treatment by a simple linear equation in our experimental conditions.

Pelletizing properties of torrefied wheat straw

Combined torrefaction and pelletization are used to increase the fuel value of biomass by increasing its energy density and improving its handling and combustion properties. However, pelletization of torrefied biomass can be challenging and in this study the torrefaction and pelletizing properties of wheat straw have been analyzed. Laboratory equipment has been used to investigate the pelletizing properties of wheat straw torrefied at temperatures between 150 and 300 °C. IR spectroscopy and chemical analyses have shown that high torrefaction temperatures change the chemical properties of the wheat straw significantly, and the pelletizing analyses have shown that these changes correlate to changes in the pelletizing properties. Torrefaction increase the friction in the press channel and pellet strength and density decrease with an increase in torrefaction temperature.

Physical and chemical characteristics of products from the torrefaction of yellow poplar (Liriodendron tulipifera)

We investigated the characteristics of torrefied yellow poplar (Liriodendron tulipifera) depending on reaction time (30min) and temperature (240–280°C). The thermogravimetric, grindability and calorific value of torrefied biomass were analyzed. As the torrefaction temperature increased, the carbon content of torrefied biomass increased from 49.50% to 54.42%, while the hydrogen and oxygen contents decreased from 6.09% to 5.65% and 28.71% to 26.61%, respectively. The highest calorific value was 1233kJ/kg when torrefaction was performed at 280°C for 30min. An overall increase in energy density and decrease in mass and energy yield was observed with the increase in torrefaction temperature. The analysis of thermal decomposition demonstrated that the hemicelluloses contained in torrefied biomass decreased with increasing torrefaction temperature, whereas cellulose and lignin were only slightly affected. The grindability of torrefied biomass was significantly improved when torrefaction was performed at high temperature. Torrefaction of yellow poplar improved the chemical and physical fuel properties of the biomass.

Upgrading of woody biomass by torrefaction under pressure

In this study, the upgrading by torrefaction of leucaena, woody biomass, at 200–250°C under volumetric pressure up to 4MPa was examined. It was found that the yield of torrefied leucaena decreased with the increase in torrefaction temperature, whereas at the same temperature the yield of torrefied leucaena increased with the increase in torrefaction pressure. From the elemental analyses, the higher carbon content in torrefied leucaena can be achieved by the rising of torrefaction pressure. As large as 92.6% of carbon was recovered in the torrefied leucaena prepared at 250°C and 4MPa. On the other hand, the oxygen content decreased to 31.1% for the leucaena torrefied at 250°C and 4MPa. The higher heating value (HHV) of leucaena torrefied at high pressure increased significantly when compared to that of leucaena torrefied at atmospheric pressure. As large as 94.3% of energy yield was achieved with the mass yield of 74.4% for the torrefaction at 250°C and 4MPa. From the subsequent pyrolysis and combustion in TGA, leucaena torrefied under pressure showed the difference of weight decreasing curves comparing to that of leucaena torrefied at atmospheric pressure. It was found that the weight of leucaena torrefied at high pressure started to decrease at temperature lower than 200°C. The char yield at 800°C for the leucaena torrefied at high pressure increased with the increase in torrefaction pressure. These results suggested that the structure of leucaena was changed by the torrefaction under pressure and the cross-linking reactions during the pyrolysis were enhanced by the pressure during the torrefaction resulting in increase in char yields. The substantial increase in char combustion rate was also found for leucaena torrefied under pressure.

Changes of chemical and mechanical behavior of torrefied wheat straw

The purpose of the study was to investigate the influence of torrefaction on the grindability of wheat straw. Straw samples were torrefied at temperatures between 200 °C and 300 °C and with residence times between 0.5 and 3 h. Spectroscopic information obtained from ATR-FTIR indicated that below 200 °C there was no obvious structural change of the wheat straw. At 200–250 °C hemicelluloses started to decompose and were totally degraded when torrefied at 300 °C for 2 h, while cellulose and lignin began to decompose at about 270–300 °C. Tensile failure strength and strain energy of oven dried wheat straw and torrefied wheat straw showed a clear reduction with increasing torrefaction temperature. In addition, Hardgrove Grindability Index (HGI) of wheat straw torrefied at different conditions was determined on a standard Hardgrove grinder. Both results showed an improvement of grindability in the torrefaction temperature range 250–300 °C, which can be well explained by the findings from FTIR analysis. At a torrefaction temperature of 260 °C and with a residence time of 2 h, wheat straw samples produced similar HGI values as coal (RUKUZN) with 0% moisture content. Under this condition, the Anhydrous Weight Loss (AWL%) of the wheat straw sample was 30% on dry and ash free basis (daf), and the higher heating value of the torrefied wheat straw was 24.2 MJ kg −1 (daf). The energy loss compared to the original material was 15% (daf). ► The influence of torrefaction on wheat straw’s grindability. ► Degradation temperatures of hemicelluloses, lignin and cellulose are suggested. ► Both tensile test and HGI show reduction when increasing torrefaction temperature. ► The energy loss increases faster than the weight loss.

Impact of torrefaction on the grindability and fuel characteristics of forest biomass

Thermal pretreatment or torrefaction of biomass under anoxic condition can produce an energy dense and consistent quality solid biomass fuel for combustion and co-firing applications. This paper investigates the fuel characteristics and grindability of pine chips and logging residues torrefied at temperatures ranging from 225 °C to 300 °C and 30 min residence time. Grinding performance of torrefied biomass evaluated by determining energy required for grinding, particle size distribution and average particle size were compared with raw biomass and coal. Specific energy required for grinding of torrefied biomass decreased significantly with increase in torrefaction temperatures. The grinding energy of torrefied biomass was reduced to as low as 24 kW h/t at 300 °C torrefaction temperature. The gross calorific value of torrefied chips increased with increase in torrefaction temperature. Torrefaction of biomass clearly showed the improved fuel characteristics and grinding properties closer to coal.

Pretreatment of agricultural residues for co-gasification via torrefaction

Torrefaction is a main pretreatment technology for improving the properties of agricultural biomass in order to deal with such problems as high bulk volume, high moisture content and poor grindability. Two typical agricultural residues, rice straw and rape stalk were torrefied in a vertical reactor at 200 °C, 250 °C and 300 °C for 30 min, under inert atmosphere. The product distribution profiles of solid, liquid and gases were obtained. The grindability of the torrefied biomass was evaluated by the particle size distribution after being milled in a ball mill. It was found that temperature strongly affected the torrefied biomass and the type of feedstock influenced the conversion rate due to the different volatile content in raw biomass. An increase of torrefaction temperature leads to a decrease in solid bio-char yield and an increasing yield in the volatile matters including liquid and non-condensable gases. The maximum increase of the heating value of the torrefied residue compared with the raw material is 17% for the rice straw and 15% for the rape stalk, respectively. On the other hand, the torrefied residues are liable to be pulverized. A kinetic study on the generation of main non-condensable gases was accomplished, which shows that the gases are formed through parallel independent first-order reactions. The kinetic characteristic parameters for the generation of each gas were determined. A novel method which combined torrefaction with co-gasification to improve the efficiency of biomass utilization is promising.

97/03523 Operating experience of Mitsubishi ultrafine mill for various slurry applications

The purpose of the study was to investigate the influence of torrefaction on the grindability of wheat straw. Straw samples were torrefied at temperatures between 200 °C and 300 °C and with residence times between 0.5 and 3 h. Spectroscopic information obtained from ATR-FTIR indicated that below 200 °C there was no obvious structural change of the wheat straw. At 200–250 °C hemicelluloses started to decompose and were totally degraded when torrefied at 300 °C for 2 h, while cellulose and lignin began to decompose at about 270–300 °C. Tensile failure strength and strain energy of oven dried wheat straw and torrefied wheat straw showed a clear reduction with increasing torrefaction temperature. In addition, Hardgrove Grindability Index (HGI) of wheat straw torrefied at different conditions was determined on a standard Hardgrove grinder. Both results showed an improvement of grindability in the torrefaction temperature range 250–300 °C, which can be well explained by the findings from FTIR analysis. At a torrefaction temperature of 260 °C and with a residence time of 2 h, wheat straw samples produced similar HGI values as coal (RUKUZN) with 0% moisture content. Under this condition, the Anhydrous Weight Loss (AWL%) of the wheat straw sample was 30% on dry and ash free basis (daf), and the higher heating value of the torrefied wheat straw was 24.2 MJ kg−1 (daf). The energy loss compared to the original material was 15% (daf).