fluidized bed reactors is simpler. It has many advantages, such as good gas solid contact, excellent heat transfer properties, better temperature control and large heat storage capacity. Fluid bed pyrolysis offers good and consistent performance from wood, usually with a high liquid product efficiency of 60-75% by weight [58].
1.4.2.2 Circulating Fluidized Bed and Transport Bed Reactor
Circulating fluidized bed pyrolysis reactors have similar properties as bubble pyrolysis reactors. Compared to the bubbling fluidized bed pyrolysis reactor, steam and char are formed faster due to higher gas velocities. Thus, the char content in bio-oil is higher. Circulating fluidized bed pyrolysis reactor should provide higher process capacity, better gas solid contact [59].
Table 1.2 Types of reactors used in pyrolysis.
| Reactor Type | Biomass | Temperature (°C) | Pressure (atm) | Biofuel Yield (%) | Reference |
|---|---|---|---|---|---|
| Circulating fluidized bed | Wood chips | 250 | 138 | 49.9 | [61] |
| Tubular quartz | Arthrospira platensis | 450 | NA | 29.9 | [62] |
| Circulating fluid bed reactor | Lignocellulosic biomass | 400-600 | 1.6-3.3 | 72 | [63] |
| Stirred semi-batch reactor | Municipal plastic wastes | 400 | 1 | 76 | [64] |
| Fluidized bed reactor | Coal and beechwood | 600 | NA | 46 | [65] |
| Double auger reactor | Hardwood | 1061 | NA | 62 | [66] |
| Downer fluidizer bed reactor | Lignocellulosic biomass | 500 | 1 | 49.9 | [67] |
| Spouted bed reactor | Lignocellulosic biomass | 450 | NA | 58.7 | [68] |
1.4.2.3 Ablative Pyrolysis Reactor
The heat transferred from the hot reactor wall softens the raw material it contacts with under pressure. Pyrolysis moves in one direction between the biomass particles. Since the raw material is mechanically pushed forward, the remaining liquid film creates lubrication for the biomass particles. It also evaporates quickly to collect pyrolysis vapors. Pressure significantly affects the reaction rate. The advantages of the ablative pyrolysis reactor are that the particles create high pressure on the hot reactor wall due to the high relative motion and mechanical strength between the particle and the reactor wall [58].
1.4.2.4 Rotary Cone Reactor
Gas-solid contact was provided in the rotating conical reactor. At room temperature, biomass particles and hot sand particles are contacted near the bottom of the cone when the solids are mixed and carried up by the rotational motion of the cone. In such reactors, rapid heating and short gas retention time should be provided. Pressure is just above atmospheric levels. The initially entrained biomass enters the reactor superficially so that the particles are centrifuged against the cyclone wall, which is electrically heated to 1000 °C [59].
1.4.3 Chemical Conversion
Basically, acid hydrolysis of hexoses, pentoses and lignin is called chemical conversion processes. Various studies are carried out on the transformation of biomass with chemical processes. Hydrolysis reactions of biomass with enzymes are rather slow compared to hydrolysis reactions with acids. Acids used in hydrolysis process are examined in two parts. The first is hydrolysis in dilute acid medium, and the second is hydrolysis using sulfuric acid [69]. In Table 1.3, the yield of biofuels obtained under different chemicals and different biomass are indicated.
1.4.4 Electrochemical Conversion
Biomass can be converted into electrical energy by electrochemical (electrocatalytic) oxidation of the material. This can be performed in a carbon fuel cell, using an ethanol fuel cell, a methanol fuel cell and a microbial fuel cell. Fuel can also be consumed indirectly through a fuel cell system that includes a reformer that converts biomass into a mixture of CO and H2 before being consumed in the fuel cell [78].
Table 1.3 Biofuels as a result of chemical conversion of different chemicals and different biomass.
| Biomass | Reactor Type | Temperature (°C) | Chemical | Biofuel Yield (%) | Reference |
|---|---|---|---|---|---|
| Tea factory waste | Fixed bed | 400-700 | KOH | 24.7 | [70] |
| Chlorella pyrenoidosa | Mini autoclave | 400 | Freshly deionized water | 43.8 | [71] |
| Soybean oil | 5L home-made reactor | 40 | SnO | 60 | [72] |
| Pinewood | Autoclave | 280 | Pt/C | 33 | [73] |
| Empty fruit bunches | Autoclave | 300 | Metal chloride | 22.8 | [74] |
