System and method for low-temperature treatment of heavy metals and dioxins in fly ash

Patent metadata

Field	Value
Publication number	US-2023398587-A1
Application number	US-202318195174-A
Country	US
Kind code	A1
Filing date	May 9, 2023
Priority date	Jun 13, 2022
Publication date	Dec 14, 2023
Grant date	—

Abstract

Provided is a system and a method for low-temperature treatment of heavy metals and dioxins in fly ash. In the present disclosure, the fly ash is subjected to tertiary water washing and then separation by pressure filtration with a plate and frame filter press to obtain fly ash after the tertiary water washing. A low-temperature heat treatment is conducted on the fly ash after the tertiary water washing in a stirring reactor by adding an additive combination. Chlorine salts in the fly ash can be effectively removed by the tertiary water washing, which avoids the chlorination of a precursor in the fly ash to form dioxins during the low-temperature pyrolysis, thereby improving a heat reduction efficiency of the dioxins in the fly ash. Moreover, the reduction of a chlorine content in the fly ash can also avoid deactivation of the additives and improve a solidification effect of the heavy metals.

First claim

What is claimed is:

1 . An additive combination for treatment of heavy metals and dioxins in fly ash, comprising a high-temperature section-targeted pyrolysis additive and a low-temperature section-targeted pyrolysis additive; wherein the high-temperature section-targeted pyrolysis additive is a calcium-based additive for a reaction at 300° C. to 350° C.; and the low-temperature section-targeted pyrolysis additive is obtained by mixing a phosphate and a ferric salt at a mass ratio of (3-5):1, and is used for a reaction at less than or equal to 250° C.

2 . The additive combination according to claim 1 , wherein the calcium-based additive is obtained by mixing CaO and CaSO 4 at a mass ratio of 1:(1-3); the phosphate is selected from the group consisting of Ca 3 (PO 4 ) 2 , Ca(H 2 PO 4 ) 2 , and NaH 2 PO 4 ; and the ferric salt is selected from the group consisting of Fe 2 (SO 4 ) 3 and Fe(NO 3 ) 3 .

3 . A system for low-temperature treatment of heavy metals and dioxins in fly ash, comprising:
a water washing tank configured to receive fly ash and water, and wash the fly ash; a plate and frame filter press connected to the water washing tank, and configured to conduct solid-liquid separation on an obtained water-washed fly ash, and then transport an obtained fly ash slurry to the water washing tank using a diaphragm pump to repeat three times of water washing; a buffer tank connected to the plate and frame filter press and the water washing tank, and configured to store an obtained fly ash water washing solution after pressure filtration, and pump the fly ash water washing solution to the water washing tank for secondary use; a single-cylinder dryer connected to the plate and frame filter press, and configured to dry an obtained tertiary fly ash slurry after tertiary water washing and pressure filtration; a stirring reactor connected to the single-cylinder dryer, and configured to conduct a heat treatment at 300° C. to 350° C. and a low-temperature heat treatment at 200° C. to 250° C. on the fly ash; a metering feeder connected to the stirring reactor, and configured to separately deliver the calcium-based additive for the reaction at 300° C. to 350° C. and the low-temperature section-targeted pyrolysis additive for the reaction at 200° C. to 250° C. according to claim 1 to the stirring reactor; and a nitrogen generator connected to the stirring reactor, and configured to supply nitrogen to the stirring reactor.

4 . The system for low-temperature treatment of heavy metals and dioxins in fly ash according to claim 3 , further comprising a natural gas burner connected to the stirring reactor, wherein the natural gas burner is configured to provide a heat source for a heating layer of the stirring reactor by burning natural gas.

5 . The system for low-temperature treatment of heavy metals and dioxins in fly ash according to claim 3 , wherein the buffer tank comprises a primary buffer tank, a secondary buffer tank, and a tertiary buffer tank; the primary buffer tank is connected to the plate and frame filter press, and is configured to store a resulting primary fly ash water washing solution after first pressure filtration; the secondary buffer tank is connected to the plate and frame filter press and the water washing tank, and is configured to store a resulting secondary fly ash water washing solution after second pressure filtration; and the tertiary buffer tank is connected to the plate and frame filter press and the water washing tank, and is configured to store a resulting tertiary fly ash water washing solution after third pressure filtration.

6 . A method for low-temperature treatment of heavy metals and dioxins in fly ash using the system for low-temperature treatment according to claim 3 , comprising the following steps:
S1, receiving fly ash and water with the water washing tank, and conducting water washing; S2, conducting pressure filtration on a water-washed fly ash obtained in step S1 with the plate and frame filter press to obtain a fly ash slurry and a primary water washing solution; transporting the fly ash slurry to the water washing tank with the diaphragm pump to conduct secondary water washing, and repeating the water washing twice to obtain fly ash after tertiary water washing; S3, drying the fly ash after tertiary water washing with the single-cylinder dryer; S4, crushing dried fly ash obtained in step S3 with the stirring reactor; S5, evacuating air in the stirring reactor with nitrogen generated by the nitrogen generator; and when an oxygen content in the stirring reactor is less than 1%, providing a heat source for the stirring reactor with a natural gas burner; S6, when the stirring reactor reaches 300° C. to 350° C., adding the calcium-based additive to the stirring reactor with the metering feeder; and S7, when the stirring reactor is cooled to 200° C. to 250° C., adding the low-temperature section-targeted pyrolysis additive to the stirring reactor after step S6 with the metering feeder, and conducting low-temperature pyrolysis; wherein the low-temperature section-targeted pyrolysis additive is added at 5% to 10% of a mass of the fly ash.

7 . The method for low-temperature treatment of heavy metals and dioxins in fly ash according to claim 6 , wherein in step S1, the fly ash and the water are mixed at a liquid-to-solid ratio of 3 mL: 1 g.

8 . The method for low-temperature treatment of heavy metals and dioxins in fly ash according to claim 6 , wherein in step S3, the single-cylinder dryer has an operating temperature of 100° C. to 180° C.

9 . The method for low-temperature treatment of heavy metals and dioxins in fly ash according to claim 6 , wherein in step S6, the calcium-based additive is added at 5% to 10% of a mass of the fly ash.

Assignees

• Univ Zhejiang

Inventors

• Peng Yaqi
• Lu Shengyong
• Zhang Chengbo
• Wang Shuai
• Jin Lizheng
• Ding Jiamin
• Li Xiaodong
• Yan Jianhua

Classifications

• B09B3/80 Primary

  involving an extraction step · CPC title

• C02F1/001

  Processes for the treatment of water whereby the filtration technique is of importance (C02F1/44 takes precedence; construction of filters in general B01D24/00 - B01D41/00) · CPC title

• C02F1/04

  by distillation or evaporation · CPC title

• C02F1/283

  using coal, charred products, or inorganic mixtures containing them · CPC title

• C02F1/5236

  using inorganic agents · CPC title