Kinetics of the Reduction of Hematite Concentrate Particles by Carbon Monoxide Relevant to a Novel Flash Ironmaking Process

Abstract

A novel ironmaking process is under development at the University of Utah to produce iron directly from iron oxides concentrates by the gas–solid flash reaction using gaseous fuels and reductants. This process will reduce energy consumption and minimize carbon dioxide emissions. Having investigated the hydrogen reduction kinetics of magnetite and hematite concentrate particles relevant to the novel flash ironmaking process, the carbon monoxide reduction kinetics of hematite concentrate particles (average particle size 21 µm) was determined in the temperature range 1473 K to 1623 K (1200 °C to 1350 °C) under various carbon monoxide partial pressures. At 1623 K (1350 °C) and residence time 5 seconds, the reduction degree of hematite concentrate particles was more than 90 pct under a pure carbon monoxide. This is slower than reduction by hydrogen but still significant, indicating that CO will contribute to the reduction of hematite concentrate in the flash process. The kinetics of CO reduction separately from hydrogen is important for understanding and analyzing the complex kinetics of hematite reduction by the H₂ + CO mixtures. The nucleation and growth rate equation with the Avrami parameter n = 1.0 adequately described the carbon monoxide reduction kinetics of hematite concentrate particles. The reduction rate is of 1st order with respect to the partial pressure of carbon monoxide and the activation energy of the reaction was 231 kJ/mol, indicating strong temperature dependence. The following complete rate equation was developed that can satisfactorily predict the carbon monoxide reduction kinetics of hematite concentrate particles and is suitable for the design of a flash reactor $\frac{{{\text{d}}X}}{{{\text{d}}t}} = 1.91 \times 10^{7} \times e^{{\frac{ - 231000}{\text{RT}}}} \times \left( {p{\text{CO}} - \frac{{p{\text{CO}}_{2} }}{K}} \right) \times (1 - X),$ where X is the fraction of oxygen removed from iron oxide, R is 8.314 J/mol K, T is in K, p is in atm, and t is in seconds.

Appendix: Complete Experimental Data (Excess Carbon Monoxide > 500 pct)

Temp. [K (°C)]	K of Fe0.947O Reduction*	pCO (atm)	pCO2 (atm)	Residence Time (s)	Solid Feeding Rate (mg/min)	CO Flow Rate (L/min)**	Fractional Reduction Degree
1473 (1200)	0.3109	0.45	0.007	9.1	49	0.7	0.45
			0.006	6.3	84	1.1	0.36
			0.004	4.3	115	1.7	0.29
		0.60	0.012	8.6	85	1.0	0.46
			0.007	6.1	102	1.5	0.34
			0.007	4.6	143	2.1	0.37
			0.003	3.3	177	3.0	0.18
		0.85	0.015	8.7	97	1.4	0.51
			0.011	6.0	143	2.2	0.42
			0.011	4.5	221	3.0	0.35
1523 (1250)	0.2941	0.30	0.002	6.5	42	0.7	0.26
			0.003	4.8	75	1.0	0.28
			0.002	2.2	143	2.3	0.18
		0.45	0.006	9.1	49	0.7	0.40
			0.007	6.3	100	1.1	0.37
			0.005	4.3	126	1.7	0.28
			0.004	2.5	212	3.0	0.26
		0.60	0.011	8.6	70	1.0	0.52
			0.011	6.1	122	1.5	0.45
			0.007	4.8	128	2.0	0.38
			0.003	3.3	121	3.0	0.28
		0.85	0.013	8.7	74	1.4	0.59
			0.017	6.0	173	2.2	0.53
			0.016	4.5	255	3.0	0.45
			0.012	3.1	376	4.5	0.35
1573 (1300)	0.2792	0.30	0.005	6.3	56	0.7	0.39
			0.005	4.6	84	1.0	0.41
			0.002	2.1	120	2.3	0.20
		0.45	0.011	8.8	47	0.7	0.73
			0.011	6.0	85	1.1	0.64
			0.009	4.1	118	1.7	0.55
			0.007	2.4	228	3.0	0.44
		0.60	0.018	8.4	75	1.0	0.80
			0.016	5.9	109	1.5	0.74
			0.014	4.2	166	2.2	0.64
			0.012	3.2	221	3.0	0.55
		0.85	0.026	8.0	109	1.4	0.78
			0.027	5.8	163	2.2	0.88
			0.022	4.4	197	3.0	0.80
			0.019	3.0	308	4.5	0.66
1623 (1350)	0.2657	0.30	0.006	6.2	49	0.7	0.63
			0.006	4.5	69	1.0	0.58
			0.004	2.1	164	2.3	0.35
		0.45	0.012	8.8	44	0.7	0.85
			0.014	6.0	85	1.1	0.80
			0.011	4.0	117	1.7	0.71
			0.010	2.4	223	3.0	0.59
		0.85	0.023	7.9	85	1.4	0.91
			0.030	5.7	172	2.2	0.91
			0.032	4.3	255	3.0	0.89
			0.026	3.0	356	4.5	0.78

1. ^* HSC 5.11[24] was used to calculate equilibrium constants
2. ^** Flow rates were calculated at 298 K (25 °C) and 0.85 atm (1 atm = 101.32 kPa)