Technology of Coal-based Direct Reduction Iron(1)

Keywords:

DRI,RHF

Source: internal company

1. Background Technique

1.1 Basic introduction

At present, there are mainly the following technical routes for direct reduced iron. Coal-based direct reduced iron and gas-based direct reduced iron, among them, gas-based reduction technologies include: COREX, Midrex, FINEX, HIsmelt, etc.Among them, coal-based reduction technologies include: tunnel kiln, RHF, rotary kiln, etc. Gas-based reduction technology can achieve large-volume industrial production. The comprehensive economic indicators are good, but the investment is relatively large. Coal-based reduction technology generally has low output and relatively low investment.

Based on the above reasons and according to the current actual situation, we believe that coal-based reduction technology should be selected first.

1.2 The advantages and disadvantages of several coal-based reduction processes

Process Category	Advantages	Disadvantages
Tunnel kiln	1. Mature technology 2. Obtain high-quality DRI, metallization rate ≥92% 3. Simple process 4. Raw material does not require briquette	1. Low degree of automation 2. When the degree of automation is high, the investment is larger 3. High energy consumption and high operating costs，Natural gas demand is about 160Nm³/T DRI 4. Silicon carbide tanks are more expensive 5. Large production area 6. Small scale of single production line
RHF	1. Mature technology 2. Less energy consumption and lower operating costs.Natural gas demand is about 120Nm³/T DRI 3. High degree of automation, environmentally friendly 4. Moderate investment 5. Fast and direct reduction, the reduction time is about 20-25Min	1. necessary laboratory research is required for specific raw materials 2. Low metallization rate and low product purity
Rotary kiln	1. Mature technology 2. Lower investment	1. Need to prepare oxidized pellets first 2. Strict requirements on coal 3. There should be no scale mill in the raw materials

Based on the above analysis, we believe that the RHF process should be more suitable.

1.3 Comparison of different direct iron reduction processes

Note: The following information is from a university in China

1.3.1 Comparison of energy consumption of different processes

Process method	Energy consumption in kind	Equivalent energy consumption,kgce/t
Natural gas shaft furnace (HYL-ZR)	300~350Nm³ Natural gas /t, 10.4~11.5GJ/t	355.3~392.9
Natural gas shaft furnace (MIDREX)	350~400 Nm³ Natural gas /t, 11.0~12.5 GJ/t	375.8~427.1
Coal to gas - shaft furnace	600~750kgThermal coal/t, 11.0~12.5 GJ/t	375.8~427.1
Rotary kiln	850~950kg lignite/t,17.8~21.3GJ/t	650.0~750.0
Tunnel kiln	250~400kg Burning coal+460~600kg Reduced coal/t	700.0~800.0

1.3.2 Comparison of energy consumption and production capacity of existing main direct reduction processes

Name	Reducing agent	Energy consumption (GJ/t)	Converted standard coal energy consumption (kg/t DRI)
MIDREX	Natural gas/ syngas	11	342
HYL-Ⅲ	Natural gas/ syngas	11	342
RHF	coal/Natural gas	15	410
SL/RN Rotary kiln	coal	18	683
Tunnel kiln	coal	25~30	854~1025

1.3.3 Productivity index comparison of existing main direct reduction processes

Name	HYL-Ⅲ shaft furnace	MIDREX shaft furnace	SL/RN Rotary kiln	Tunnel kiln	RHF
Pressure of work	0.8MPa	0.3 MPa	-25±15Pa		3000Pa (Air pressure before burner)
Maximum utilization factor (t/m³d)	162	112	0.43		1.33