No. 067


Classification of Technology:

Air Pollution Control

Type of Industry:

Steel
(Coke-making)

Subject:

Coke Oven Gas Desulfurization Equipment
( TAKAHAX - Sulfuric acid manufacturing process )



1. Purpose
Desulfurization of coke oven gas ( hereafter called COG ), and processing of desulfurization waste fluid to prevent secondary pollution and effective use of the recovered sulfur.

2. Details and the Time of Introduction
The COG desulfurization system was completed in May of 1977 as a composite system, composed of TAKAHAX desulfurization method and sulfuric acid manufacturing method towards (1) assuring high desulfurization rate, (2) stable operation, (3) no generation of secondary pollution and (4) low cost operation.

3. Principle
(1)Desulfurization process ( TAKAHAX method )
1) H2S is absorbed in alkali solution in the absorption column, air oxidation is carried out in the oxidation column with naphthoquinone sulfonic soda as the catalyst, and is recovered by changing it to free ion.
2) Reaction formula ; 4NO + 4NH3 + O2 -> 4N2 + 6H2O
Absorption : H2S + Na2CO3 -> NaHS + NaHCO3
Oxidation of sulfates : NaHS + Q1 - SO3Na + H2O -> NaOH + Q2 - SO3Na + S
Oxidation of catalyst : Q2 - SO3Na + 1/2 O2 -> Q1 - SO3Na + H2O
3) When reclaiming, thiosulfate, sulfate and rhodanate are formed as byproducts.
(2) Waste liquid treating process ( Reducing decomposition method )
1) Carry out combustion decomposition in reduction atmosphere of waste liquid by partial combustion of COG, and obtain hydrogen sulfide and sodium carbonate.
2) Sodium carbonate is circulated for absorption use and hydrogen sulfide is sent to the sulfuric acid manufacturing equipment as raw material.
(3) Sulfuric acid manufacturing process
1) Sulfur generated in the desulfurization process and hydrogen sulfide generated in the waste liquid treating process are burned to form SO2.
2) SO2 is caused to react with steam to form dilute sulfuric acid ( concentration 60wt% ) and the total amount is recycled and used in the ammonium sulfate recovery equipment to remove ammonia in COG.

4. Effect and Achievement
(1) Desulfurization Facilities
Item
Specifications
Achievement
1) Gas Treating Capacity [1] -A : 54,500 mN3/H
-B : 54,500 mN3/H		Same as Left
2) Desulfurization Rate[2] : 71,500 mN3/H
H2S Concentration
Inlet = 7.3 g/mN3 ( max. )
Outlet = 0.3 ( 96% )
HCN Concentration
Inlet = 2.3 g/mN3
Outlet = 0.1 ( 96% )		5.0
0.1 ( Over 98% )

3.5
< 0.1 ( Over 98% )

(2) Waste Liquid Treating Facilities ( Normally 1/3 unit Operation )
Item
Specifications
Achievement
1) Amount of COG Burned 3,500 mN³/H x 3 Unit1,000 ~ 1,800
2) Amount of Waste Liquid Treatment 7 m³/H x 3 Unit5 ~ 7
3) Amount of Decomposed Gas ( Outlet ) 12,600 mN³/H x 3 Unit8,000 ~ 10,000
4) Rate of Waste Liquid DecompositionNa2S2O3 : Over 90%
Na2SO4 : Over 80%
Na2SCN : Over 95%		Over 99%
Over 95%
Over 99%

(3) Sulfuric Acid Manufacturing Facilities
Item
Specifications of the Facilities
Achievement
1) Amount of COG Burned1,500 mN³/H~ 500
2) Amount of S Burned1.5 t/H~ 800kg/H
3) Amount of Sulfuric Acid104 t/Day
( 100% converted )		~ 95
4) Concentration of Sulfuric Acid40 ~ 65 %60 ~ 63
5) Amount of Flue Gas ( Dry )82,000 m³/H ( MAX )20,000 ~ 38,000
6) Outlet SOxbelow 70 ppmbelow 10ppm
7) Outlet NOxbelow 65 ppm
( O2 = 14% Converted )		below 60ppm





Implementing company:

Nippon Steel Corporation


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