Blast Furnace Gas Washer Removes
Cyanides, Ammonia, Iron and Phenol
ROGER A. DECAIGNY, Works Metallurgist
FRED G. KRIKAU, Engineer
Interlake Steel Corporation
Riverdale, Illinois
INTRODUCTION
Basic to the iron and steel industry is the blast furnace which converts iron ore
into molten iron and is the beginning of the process in the manufacturing of steel.
During the operation of a blast furnace, great quantities of gas are generated. This
gas, being rich in carbon monoxide, is used further in the steel making process as a
source of fuel. Gases leaving the blast furnace are contaminated with very fine
particles of dust and other contaminets which must be removed, not only to allow
the gas to be used as a fuel, but to prevent air pollution.
The gas is cleaned by high-energy scrubbers, which use water in great quantities
as the cleaning media.
BLAST FURNACE GAS CLEANING SYSTEM
A typical blast furnace gas cleaning system is currently utilized by most steel
producers. Water is pumped out of a nearby river or stream, through the gas scrubber
and gas cooler, and then into a clarifier. These clarifiers or thickeners do a fair job of
removing the flue dust, but, in order to meet today's water pollution laws this system
is no longer good enough. The water, after passing through the clarifier, is simply
dumped back to the river. Because the raw materials fed to a blast furnace contain
such things as iron ore, limestone, and coke, blast furnace gas contains quantities of
ammonia, phenol, and cyanide. The waters used in the gas scrubbers and gas coolers
absorb these compounds which become part of the dissolved solids content of the
water.
Table I is a typical analysis of the waters coming from the gas scrubbers, the
gas cooler and the water that is returned to the river. Using this information, Interlake began to study the methods available to further treat this water before it was
returned to the river. We evaluated such systems as chlorine additives at controlled
pH to disassociate the cyanide. We evaluated bacteria systems to assimilate the
ammonia and phenol. It became apparent during this evaluation that, since we were
required to clean the water to such a high extent, it would be foolish to discharge it
back to the river. For this reason, we felt that a system for recycling the clarifier
effluent back to the gas cleaning system would provide the best means for alleviating
the effluent problem. A number of plants were using such recycling systems and
operating information was collected from as many as possible. A wide variety of
results were reported, and it generally appeared that systems had been put into
operation and then made to work under conditions peculiar to each individual installation. A number of questions basic to the procedure remained unanswered.
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