Fluidized bed biogasifier and method for gasifying biosolids
A fluidized bed biogasifier is provided for gasifying biosolids. The biogasifier includes a reactor vessel and a feeder for feeding biosolids into the reactor vessel at a desired feed rate during steady-state operation of the biogasifier. A fluidized bed in the base of the reactor vessel has a cross-sectional area that is proportional to at least the fuel feed rate such that the superficial velocity of gas is in the range of 0.1 m/s (0.33 ft/s) to 3 m/s (9.84 ft/s). In a method for gasifying biosolids, biosolids are fed into a fluidized bed reactor. Oxidant gases are applied to the fluidized bed reactor to produce a superficial velocity of producer gas in the range of 0.1 m/s (0.33 ft/s) to 3 m/s (9.84 ft/s). The biosolids are heated inside the fluidized bed reactor to a temperature range between 900° F. (482.2° C.) and 1700° F. (926.7° C.) in an oxygen-starved environment having a sub-stoichiometric oxygen level, whereby the biosolids are gasified.
1. A method for gasifying biosolids obtained from sewage sludge, comprising:
receiving biosolids in a fluidized bed biogasifier, the biogasifier having:
a reactor vessel;
a freeboard section having a diameter of at least 57 inches and a height of at least 10 feet;
a feeder for feeding biosolids into said reactor vessel, said feeder being configured to feed said biosolids into said reactor vessel at a biosolids fuel feed rate during steady-state operation of the biogasifier; and
a fluidized bed in a bed section of said reactor vessel, said fluidized bed having a diameter of at least 45 inches;
wherein the freeboard section has a greater diameter than the fluidized bed,
wherein the ratio of the freeboard section diameter to the fluidized bed diameter is at least 57:45;
and further wherein a ratio of a height of the bed section of the reactor vessel to a depth of the fluidized bed is 1.5;
introducing gas to said fluidized bed reactor; and
heating and reacting said biosolids inside said biogasifier, whereby biosolids are gasified.
2. The method for gasifying biosolids in accordance with claim 1 , wherein a superficial velocity of producer gas inside the freeboard section during steady state operation is between 0.1 m/s (0.33 ft/s) and 3 m/s (9.84 ft/s).
3. The method for gasifying biosolids in accordance with claim 1 , wherein a thermochemical conversion process occurs within the biogasifier at a temperature between 900° F. (482.2° C.) and 1700° F. (926.7° C.).
4. The method for gasifying biosolids in accordance with claim 1 , wherein said fluidized bed reactor comprises a bubbling fluidized bed reactor.
5. The method for gasifying biosolids in accordance with claim 3 , wherein said temperature range is between 1150° F. (621.1° C.) and 1600° F. (871.1° C.).
6. The method for gasifying biosolids in accordance with claim 1 , wherein a superficial velocity of the producer gas inside the freeboard section during steady state operation is between 0.5 m/s and 2.5 m/s.
7. The method for gasifying biosolids in accordance with claim 1 , further comprising the step of using a cyclone separator to separate material exhausted from said fluidized bed reactor into producer gas and ash.
8. The method for gasifying biosolids in accordance with claim 3 , wherein the thermochemical conversion process occurs with an oxygen-to-fuel equivalence ratio between 0.1 and 0.5.
9. The method for gasifying biosolids in accordance with claim 3 , wherein the thermochemical conversion process occurs with an oxygen-to-fuel equivalence ratio between 0.15 and 0.35.
10. A method for gasifying biosolids obtained from sewage sludge, comprising:
receiving biosolids in a biogasifier apparatus, the apparatus having:
a fluidized bed biogasifier for gasifying biosolids to produce a producer gas;
a staged-combustion thermal oxidizer for thermally oxidizing said producer gas; and
a recycle flue gas loop connecting the staged-combustion thermal oxidizer to the fluidized bed biogasifier;
wherein the fluidized bed gasifier comprises:
a reactor vessel;
a freeboard section having a diameter of at least 57 inches and a height of at least 10 feet;
a feeder for feeding biosolids into said reactor vessel, said feeder being configured to feed said biosolids into said reactor vessel at a biosolids fuel feed rate during steady-state operation of the biogasifier; and
a fluidized bed in a bed section of said reactor vessel, said fluidized bed having a diameter of at least 45 inches;
wherein the freeboard section has a greater diameter than the fluidized bed;
wherein the ratio of the freeboard section diameter to the fluidized bed diameter is at least 57:45;
and further wherein the recycle flue gas loop is configured to recycle flue gas to the fluidized bed biogasifier;
introducing gas to said fluidized bed reactor; and
heating and reacting said biosolids inside said biogasifier, whereby biosolids are gasified.
11. The method for gasifying biosolids in accordance with claim 10 , wherein a superficial velocity of producer gas inside the freeboard section during steady state operation is between 0.1 m/s (0.33 ft/s) and 3 m/s (9.84 ft/s).
12. The method for gasifying biosolids in accordance with claim 10 , wherein a thermochemical conversion process occurs within the biogasifier at a temperature between 900° F. (482.2° C.) and 1700° F. (926.7° C.).
13. The method for gasifying biosolids in accordance with claim 10 , wherein said fluidized bed reactor comprises a bubbling fluidized bed reactor.
14. The method for gasifying biosolids in accordance with claim 12 , wherein said temperature range is between 1150° F. (621.1° C.) and 1600° F. (871.1° C.).
15. The method for gasifying biosolids in accordance with claim 10 , wherein a superficial velocity of the producer gas inside the freeboard section during steady state operation is between 0.5 m/s and 2.5 m/s.
16. The method for gasifying biosolids in accordance with claim 10 , further comprising the step of using a cyclone separator to separate material exhausted from said fluidized bed reactor into producer gas and ash.
17. The method for gasifying biosolids in accordance with claim 12 , wherein the thermochemical conversion process occurs with an oxygen-to-fuel equivalence ratio between 0.1 and 0.5.
18. The method for gasifying biosolids in accordance with claim 12 , wherein the thermochemical conversion process occurs with an oxygen-to-fuel equivalence ratio between 0.15 and 0.35.