Flue gas purification and waste heat utilization system and method

Patent metadata

Field	Value
Publication number	US-11617985-B2
Application number	US-202017779590-A
Country	US
Kind code	B2
Filing date	Mar 5, 2020
Priority date	Nov 29, 2019
Publication date	Apr 4, 2023
Grant date	Apr 4, 2023

Abstract

Disclosed are a flue gas purification and waste heat utilization system and method. The system comprises a flue gas exhaust unit, a primary waste heat utilization unit, a primary flue gas purification unit, a secondary waste heat utilization unit and a secondary flue gas purification unit that are sequentially connected in a flue gas flow direction, wherein the primary flue gas purification unit is configured for removing NOx, large particles and CO in the flue gas, the secondary flue gas purification unit is configured for removing NOx and dioxin in the flue gas, an ammonia-spraying device is externally connected between the flue gas exhaust unit and the primary waste heat utilization unit, and the ammonia-spraying device is configured for injecting ammonia gas into the flue gas exhausted from the flue gas exhaust unit.

First claim

What is claimed is:

1. A flue gas purification and waste heat utilization system, comprising a flue gas exhaust unit, a primary waste heat utilization unit, a primary flue gas purification unit, a secondary waste heat utilization unit, and a secondary flue gas purification unit sequentially connected in a flue gas flow direction, wherein the primary flue gas purification unit is used for removing NO x , large particles and CO in the flue gas, and the secondary flue gas purification unit is used for removing NO x and dioxin in the flue gas;
an ammonia-injecting device is externally connected between the flue gas exhaust unit and the primary waste heat utilization unit, wherein the ammonia-injecting device is used for injecting ammonia gas into the flue gas exhausted from the flue gas exhaust unit.

2. The flue gas purification and waste heat utilization system according to claim 1 , wherein the flue gas exhaust unit comprises an EAF;
optionally, the primary waste heat utilization unit comprises a scrap steel preheating device;
optionally, the primary flue gas purification unit comprises a combustion settling chamber;
optionally, the secondary waste heat utilization unit comprises a waste heat boiler;
optionally, the secondary flue gas purification unit comprises a catalytic reaction device.

3. The flue gas purification and waste heat utilization system according to claim 1 , wherein the system further comprises a dust removal device, a wind drawing device and a chimney sequentially connected to the catalytic reaction device;
optionally, the dust removal device is a bag dust filter.

4. The flue gas purification and waste heat utilization system according to claim 1 , wherein the flue gas purification and waste heat utilization system comprises an EAF, a scrap steel preheating device, a combustion settling chamber, a waste heat boiler, a catalytic reaction device, a dust removal device, a wind drawing device and a chimney sequentially connected in a flue gas flow direction;
optionally, the scrap steel preheating device is connected to a fourth hole of the EAF.

5. The flue gas purification and waste heat utilization system according to claim 1 , wherein a flue gas cover is arranged over the EAF, wherein the flue gas cover is used for collecting flue gas escaping from the EAF;
optionally, the flue gas cover is connected to an escaped flue gas pipeline, and an outlet end of the escaped flue gas pipeline is connected between the catalytic reaction device and the dust removal device, wherein the escaped flue gas from the EAF is collected by the flue gas cover, passes through the escaped flue gas pipeline, mixed with the purified flue gas exhausted from the catalytic reaction device and then enters the dust removal device.

6. A flue gas purification and waste heat utilization method, which uses the flue gas purification and waste heat utilization system according to claim 1 to perform deep purification on the flue gas and perform multi-effect utilization on the waste heat of the flue gas.

7. The flue gas purification and waste heat utilization method according to claim 6 , wherein the method comprises:
injecting ammonia gas into the flue gas drawn from the flue gas exhaust unit by the ammonia-injecting device, performing a reaction for removing NO x in the flue gas, and then subjecting the flue gas to processes of the primary waste heat unit, the primary flue gas purification unit, the secondary waste heat utilization unit and the secondary flue gas purification unit in sequence, so as to remove CO, NO x , large particles, dioxin and dust in the flue gas and realize multi-effect utilization of the waste heat of the flue gas.

8. The flue gas purification and waste heat utilization method according to claim 6 , wherein the method specifically comprises the following steps:
S1 drawing the flue gas generated from the EAF by the wind drawing device, injecting ammonia gas into the flue gas by the ammonia-injecting device to perform SNCR reaction for removing part of NO x in the flue gas, and introducing the unreacted ammonia gas to the scrap steel preheating device with the flue gas;
S2 in the scrap steel preheating device, subjecting the flue gas to heat exchange with the scrap steel, wherein the scrap steel is heated, so as to realize primary utilization of the waste heat of the flue gas, and introducing the cooled flue gas to the combustion settling chamber;
S3 in the combustion settling chamber, subjecting the flue gas to combustion for removing CO, wherein large particles in the flue gas settle down under gravity, and introducing the heated flue gas to the waste heat boiler;
S4 in the waste heat boiler, using the heat from the flue gas to heat the medium of the waste heat boiler, so as to realize secondary utilization of the waste heat of the flue gas, wherein the synthesis of dioxin is inhibited by the unreacted ammonia gas injected upstream, and introducing the cooled flue gas to the catalytic reaction device;
S5 in the catalytic reaction device, subjecting NO x in the flue gas and the unreacted ammonia gas injected upstream to SCR reaction, and simultaneously subjecting dioxin in the flue gas to catalytic decomposition, so as to realize deep purification of the flue gas; and
S6 mixing the purified flue gas and the escaped flue gas which the flue gas cover collects from the boiler, then removing the particles in the mixture by the dust removal device, and finally discharging the flue gas through the chimney.

9. The flue gas purification and waste heat utilization method according to claim 8 , wherein, in step S1, the flue gas drawn by the wind drawing device is generated from a fourth hole of the EAF;
optionally, a temperature of the flue gas is 1200° C. to 1400° C.;
optionally, a flow rate of the flue gas is 200000 m 3 /h to 500000 m 3 /h;
optionally, the flue gas comprises one or a combination of at least two of dust, CO, NO x or dioxin;
optionally, a dust concentration in the flue gas is 10 g/m 3 to 20 g/m 3 ;
optionally, a CO concentration in the flue gas is 0% to 20%;
optionally, a dioxin content in the flue gas is 0 ng-TEQ/m 3 to 10 ng-TEQ/m 3 ;
optionally, a NO x content in the flue gas is 0 ppm to 2800 ppm;
optionally, a ratio of the injected ammonia gas to NO x in the flue gas is controlled within 1.4 to 1.6;
optionally, a removal rate of NO x is 50% to 70% after the SNCR reaction;
optionally, in step S2, after the heat exchange between the flue gas and the scrap steel, the scrap steel is heated to a temperature of 400° C. to 600° C.;
optionally, in step S3, a combustion temperature of the flue gas is 500° C. to 700° C. in the combustion settling chamber;
optionally, in step S4, the flue gas is cooled to a temperature of 200° C. to 250° C. in the waste heat boiler;
optionally, in step S5, after the SCR reaction, a removal rate of NO x is 80% to 90% in the flue gas;
optionally, in step S6, the escaped flue gas escapes through an electrode hole, a furnace door or an observation opening of the EAF;
optionally, a flow rate of the escaped flue gas is 500000 m 3 /h to 1500000 m 3 /h;
optionally, a temperature of the escaped flue gas is 60° C. to 100° C.;
optionally, a dust concentration in the escaped flue gas is 0 g/m 3 to 5 g/m 3 ;
optionally, a dioxin content in the escaped flue gas is 0 ng-TEQ/m 3 to 0.5 ng-TEQ/m 3 .

10. The flue gas purification and waste heat utilization method according to claim 8 , wherein the method specifically comprises the following steps:
S1 drawing the flue gas generated from the fourth hole of the EAF by the wind drawing device, wherein the flow rate of the flue gas is 200000 m 3 /h to 500000 m 3 /h, the temperature of the flue gas is 1

Assignees

• Inst Process Eng Cas

Inventors

• Zhu Tingyu
• Yang Yang
• Xu Wenqing

Classifications

• F27D17/30 Primary

  Arrangements for extraction or collection of waste gases; Hoods therefor · CPC title

• F27D17/10 Primary

  Arrangements for using waste heat · CPC title

• F27D17/20

  Arrangements for treatment or cleaning of waste gases · CPC title

• F27D17/15

  using boilers · CPC title

• F27D17/304

  specially adapted for electric arc furnaces · CPC title