Using Hydrogen as a Reductant in Fire Refining at Aurubis Hamburg’s “Down-town” Smelter

Abstract.

The deoxidation of copper or “poling” is the final step in the pyrometallurgical process of primary and secondary copper extraction. The deoxidation generates CO₂ since gaseous and liquid hydrocarbons (natural gas) are the common choice for reducing agents. Previous energy and cost-saving measures increased the efficiency of the process, but the inherent production of CO₂ cannot be avoided. The use of hydrogen as a reductant may decarbonize a core process of copper production, which is a desirable target for the metal industry in general and Aurubis in particular.

The primary smelter in Hamburg runs two anode furnaces with a capacity of 270 t per batch each. From September to December 2021, the anode furnaces were provisionally supplied with hydrogen and 14 batches were poled using hydrogen. These experiments were designed to determine in full-scale operational tests the properties of the poling with hydrogen in terms of efficiency and process control.

The average efficiency of poling with hydrogen was higher than poling with natural gas. The adjustment of the volume flows and the temperature of the process were always controllable. The endpoint of the poling with hydrogen could be determined similarly to the poling with natural gas based on the temperature curve.

The tests showed the importance of nitrogen addition for stable jetting conditions where clogging of the tuyeres was a phenomenon observed when pure hydrogen was used. An important observation from the tests was that the efficiency of the reduction was not affected by the addition of nitrogen.

Notation

d	tuyere diameter	mm
g	gravitational constant	m/s2
M	Mach number
M´	nominal Mach number	at standard conditions
M	molar mass	mol
m	mass	kg or t
P	pressure	Pa
R	gas constant	J/mol K
Ri	gas constant of i	J/kg K
T	temperature	K or °C
t	time	minutes
u	velocity	m/s
V	volume	Nm3 aka standard cubic meter aka scm at P = 101,325 Pa and T = 273 K
Subscripts:
exp		expanded conditions, does not reflect the true conditions, but a hypothetical situation where the gas jet can expand freely. It therefore indicates how strongly the jet is under-expanded
g		gas
inlet		conditions at tuyere inlet
l		liquid or molten metal
outlet		conditions at tuyere inlet
Greek
η	efficiency	%
λ	air ratio	indicates lean, rich, or stoichiometric burner operation
ρ	density	kg/m3

1.1 Abbreviations

AES:

Atomic emission spectroscopy

AF:

Anode furnace for the fire refining of blister copper

NG:

Natural gas, mostly methane

PSC:

Peirce–Smith converter

Q-BOP:

Bottom-blown basic oxygen process – Steel converter