Sandwich gasification process for high-efficiency conversion of carbonaceous fuels to clean syngas with zero residual carbon discharge
The present invention discloses a gasifier and/or a gasification process that provides a long, uniform temperature zone in the gasifier, regardless of the particle size, chemical composition, and moisture content of the fuel by sandwiching a reduction zones between two oxidation zones. The gasifier and/or gasification process has a char that is more energy-dense and almost devoid of moisture that affords for an additional (or char) oxidation zone with a temperature that is higher than a first oxidation zone which is closer to an evaporation and devolatilization zone. As such, the additional (or char) oxidation zone contributes to augmenting the reduction zone temperature, thereby providing a favorable dual impact in improving syngas composition and near-complete conversion of the tar.
1. A mixed-mode gasification process for producing syngas comprising:
providing a fuel;
providing a gasifier having a fuel injection port, an ash or residue extraction port, an outer periphery, and at least the following zones: an evaporation and devolatilization zone, a first exothermic oxidation zone, a second exothermic oxidation zone, a third exothermic oxidation zone, a first endothermic reduction zone located directly next to and sandwiched between the first and second exothermic oxidation zones, and a second endothermic reduction zone located directly next to and sandwiched between the first and third exothermic oxidation zones, the first exothermic oxidation zone located on a side of the gasifier next to the fuel injection port and upstream from the first and second endothermic reduction zones, the second and third exothermic oxidation zones located on a side of the gasifier next to the ash or residue extraction port; and
providing an aerodynamic propulsive device to transfer devolatilized products from the evaporation and devolatilization zone to the second and third exothermic oxidation zones.
2. The process of claim 1 , wherein the evaporation and devolatilization zone is disposed in direct flow communication with the fuel injection port.
3. The process of claim 1 , wherein the evaporation and devolatilization zone is located upstream of the first exothermic oxidation zone.
4. The process of claim 1 , wherein the aerodynamic propulsive device is an ejector.
5. The process of claim 1 , wherein an oxidizer or a carrier gas is used in the aerodynamic propulsive device to convey the devolatilized products.
6. The process of claim 5 , wherein the oxidizer or the carrier gas is a hot gaseous product obtained from combusting of an auxiliary fuel.
7. The process of claim 5 , wherein the oxidizer or the carrier gas is an oxidizer, and wherein the oxidizer is used to control a temperature of the second and/or the third exothermic oxidation zones to increase fuel conversion.
8. The process of claim 1 , wherein a temperature of the second and the third exothermic oxidation zones is higher than a temperature of the first oxidation zone.
9. The process of claim 1 , wherein the devolatilized products include volatiles and/or char.
10. The process of claim 1 , wherein char particles are injected as a secondary fuel into the gasifier.
11. The process of claim 10 , the process further comprising fluidizing the char particles above one or more grates disposed in flow communication with the second and/or the third exothermic oxidation zones.
12. The process of claim 1 , wherein the fuel is selected from the group consisting of coal, biomass, black liquor, animal waste, food waste, industrial waste, automotive waste, and combinations thereof.
13. The process of claim 1 , wherein char is extracted from the second and the third exothermic oxidation zones, and wherein the char is used as a sorbent in a packed bed for syngas contaminant removal.
14. The process of claim 13 , wherein spent or contaminated char removed from the packed bed is used as at least a portion of the fuel.
15. The process of claim 1 , wherein the process is characterized by zero residual carbon discharge.
16. The process of claim 1 , the process further comprising recovering syngas, wherein the syngas is optionally utilized for the production of heat, electricity, gaseous fuels, liquid fuels, chemicals, or a combination thereof.
17. A mixed-mode gasification system comprising:
a gasifier having a fuel injection port, an ash or residue extraction port, an outer periphery, and at least the following zones: an evaporation and devolatilization zone, a first exothermic oxidation zone, a second exothermic oxidation zone, a third exothermic oxidation zone, a first endothermic reduction zone located directly next to and sandwiched between the first and second exothermic oxidation zones, and a second endothermic reduction zone located directly next to and sandwiched between the first and third exothermic oxidation zones, the first exothermic oxidation zone located on a side of the gasifier next to the fuel injection port and upstream from the first and second endothermic reduction zones, the second and third exothermic oxidation zones located on a side of the gasifier next to the ash or residue extraction port; and
an aerodynamic propulsive device configured to transfer devolatilized products from the evaporation and devolatilization zone to the second and third exothermic oxidation zones.
18. The system of claim 17 , wherein the aerodynamic propulsive device is an ejector.
19. The system of claim 17 , the system further comprising one or more grates disposed in flow communication with the second and/or the third exothermic oxidation zones.