The mass recovery from various waste thermochemical conversions through different reactors were balanced. An auger, batch, and fluidized bed reactors were used for pyrolysis at 500 oC. A batch reactor was utilized for the torrefaction process at 250 oC and 290 oC. Figure 6.1 shows the mass recovery of a solid bio-char, a liquid bio-oil and aqueous phase, and gas products. Two other pyrolysis studies of corn stover [119] and sorghum [183] were also referenced for comparison purposes. As a lower
temperature was used in the torrefaction process, the mass yields of bio-char ranged from 68% to 71%, which were higher yields than the bio-char from pyrolysis at the constant temperature of 500 oC ranging from 23% to 63%. A higher product mass yield of microalgae bio-char than other wastes through an auger reactor was caused by not enough residence time for the wastes to be fully volatilized and its larger amount of ash content. The production of bio-char from batch and auger reactors showed a similar amount regardless of the biomass types. On the other hand, the oil crop of BLT (beauty leaf tree) seed cake (48%), sludge pellet (54%) and corn stover (32%) produced a high mass yield of bio-oil even in a slow pyrolysis, which was comparable to the mass yields from fast fluidized bed pyrolysis (32 – 42%).
Figure 6.1. Mass recovery of bio-char, bio-oil and gas from various pyrolysis experiments.
Figure 6.2 shows the energy recovery of products produced from torrefaction and pyrolysis through various reactors. Some process products showed a similar distribution of mass and energy yields, while others did not. The energy from torrefied bio-char products recovered over 80%, while no energy was recovered in bio-oil and gas products as they included mostly water in bio-oil and non-combustible gases in gas products. In contrast, a high yield of bio-oil was obtained from a lignocellulosic fluidized bed pyrolysis (44 – 48%) and a microalgae slow pyrolysis (50%), which was a much larger amount of bio-oil than other feedstock (5 – 18%). It can be concluded that a slow
pyrolysis is not recommended for producing bio-oil if considering only energy recovery. However, the HHV of bio-oil produced from a slow pyrolysis showed a much higher value than that produced from fast pyrolysis as shown in Figure 6.3. As was discussed in Chapter 4, a higher HHV for rice straw bio-oil was obtained from a slow and
Another classification of biomass can be based on the protein content as wastes including a large amount of protein such as microalgae, BLT cake and sludge pellet showed a relatively higher HHV of bio-oil (over 34 MJ/kg) compared to other
lignocellulosic wastes (29 – 32 MJ/kg). The HHV of torrefied bio-char ranged from 21 to 24 MJ/kg, while most of the pyrolytic bio-char showed from 7 to 19 MJ/kg except for that of corn stover (23 MJ/kg) and BLT de-oiled cake (28 MJ/kg). A high HHV for bio- char can be inferred from the existence of a high VCM content and oil. The highest HHV of bio-char obtained from the current study was 29 MJ/kg for rice straw torrefaction at the condition of 290 oC and 60 min.
Figure 6.2. Energy recovery of bio-char, bio-oil and gas from various pyrolysis experiments.
Figure 6.3. Higher heating value of bio-char and bio-oil from different reactors, biomass and temperatures.
Figure 6.4 shows a Van Krevelen diagram that helps in understanding the elemental compositions of bio-char and bio-oil products. As discussed in Chapter 5, the O/C and H/C ratios of bio-oil and bio-char products were gathered in at designated ratios. The high oxygen content in a bio-oil produced from a fluidized bed reactor caused a higher O/C ratio (0.6 – 0.9), while the bio-oil from a batch and an auger reactor
showed O/C ratios of 0.1 – 0.15 and 0.22 – 0.33, respectively. However, the H/C of bio- oil produced from different reactors showed more or less similar ranges between 1.4 and 1.8, which is close to the H/C ratio of petro fuel (1.65 – 2.0). The bio-oil with the lowest H/C ratio (1.0) was produced from BLT de-oiled cake in a batch reactor as the hydrogen content (6.1%) was the least compared to other bio-oils, while the most nitrogen content (8.8%) and the second most sulfur content (1.6%) were found from BLT cake bio-oil. The highest sulfur content was from sludge pellet pyrolytic bio-oil (2.4%). The different
in the bio-oil of 11 – 15% from a batch, 20 – 26% from an auger, and 41 – 50% from a fluidized bed reactor. As the dotted lines of dehydration and decarboxylation show, the bio-oil elemental property from a fluidized bed to a batch reactor can be expected to produce CO2 and CO gas through decarboxylation (loss of carboxyl groups, -COOH) and H2O through dehydration reactions (loss of hydroxyl groups, -OH). The
decarboxylation reaction is preferred so that the bio-oil is close to the petro fuels.
Figure 6.4. Van Krevelen diagram for the various feedstocks and its pyrolysis (or torrefaction) solid and liquid products.
The ratio ranges of solid product were separated depending on the temperature or feedstocks. The initial ratios of lignocellulosic biomass wastes locates in 1.4 – 1.62 of H/C and 0.6 – 0.75 of O/C, whereas N. Oculata microalgae located at around 1.9 of H/C
degradable than the less O/C and H/C ratios of bio-char as the higher amount of oxygen and hydrogen leads to more chemical reactivity against stability of bio-char in soils. Most of the pyrolytic bio-chars were represented in the range of 0.4 – 1.0 of H/C and 0.02 – 0.1 of O/C, similar to bituminous coal ranges. Some were located in a range of desirable ratios for soil amendment. The square box was imported from
Schimmelpfennig et al. [64] in that the high C content was caused by the substantial amount of aromatic C with low functional groups, and they suggested that the carbon contents close to 100% can be classified as hardly degradable in the environment. The bio-char defined from Kuhlbusch and Cruten [208] had an H/C ratio less than 0.2, which should be recalcitrant to degradation in soils due to C sequestration. The utilization of bio-char in soil was positively proved because of its characteristics of nutrient retention, water-holding capacity, and microbial growth, which helped product yields and growths [209,210].
Figure 6.5. Proximate analysis of bio-chars from various samples, reactors and reaction temperatures.
The proximate analysis of the torrefaction pyrolysis solid products are compared in Figure 6.5. As a lower temperature was used in torrefaction, more VCM (volatile combustible matter) ranging from 65 to 82% were obtained at the operating temperature from 250 to 290 oC. Because of the discrepancy in weight loss of hemicellulose,
cellulose, and lignin contents, the solid yield and VCM content at different temperatures and biomass types resulted accordingly. However, at a higher temperature of 500 oC, the highest amount of ash content was found at 42 – 65% from most biomass wastes. Only the wastes of corn stover and BLT cake obtained the most fixed carbon at about 64%.