ACARP Project Number: C3099
Philip Bennett, Don Holcombe
This commissioned review examines the current
status and future directions for pulverised coal injection (PCI)
into blast furnaces used in the production of pig iron. It has been
undertaken to assist the Australian coal industry to identify
possible future industry funded research. This research should aid
the coal industry in determining the advantages and disadvantages
of various types of coal for used as PCI coal.
Prior to starting the review of the literature a
wide spectrum of Australian coal producers were asked for their
views on research needs based on their efforts to market coal in
this developing market. All those actively selling coal in this
market expressed concerns on the level of understanding of the
value of their coal in the market and the impact of coal quality on
coal PCI performance. The information obtained was used to identify
the areas to be covered in this review.
An extensive review of the literature has been
conducted to determine the current level of understanding of the
impact of pulverised coal injection or granulated coal injection
(GCI) on the blast furnace process.
The subsequent impact on the whole steelworks
operation is examined, but not in detail as the overall impact is
in the area of reduced operating costs. These operating costs are
very dependent on a particular steelworks operation and this
information is not freely available in the literature.
Blast furnace technology is of critical
importance to the crude steel industry and is continually
undergoing refinements to improve productivity and reduce operating
costs. The past improvements in productivity, coke consumption and
fuel use within the steelworks have been hastened due to the
competition in the world steel markets.
Pulverised coal injection, while not new
technology, is one such process refinement that is being
implemented in steelworks around the world. Increased injection of
coal is also being driven by the need to extend the life of ageing
coke ovens and therefore reduce the need for newer higher cost coke
ovens. The injection of coal into the blast furnace has been shown
the productivity of the blast furnace, ie: the amount of hot metal
produced per day by the blast furnace;
the consumption of the more expensive coking coals by replacement
with cheaper soft coking or thermal coals;
in maintaining furnace stability; and
the consistency of the quality of hot metal and reduce the silicon
content of the pig iron.
The current rates of coal injection vary with
European steelworks achieving 180 to 215kg of coal per tonne of hot
metal (kg/tHM), while Japan's five major steel producers are
averaging around 83.5kg/tHM in 1993, down from 84.7kg/tHM in 1992,
with the maximum of 183kg/tHM achieved by Kobe Steel at the Kobe
The decline in PCI use in Japan was due to
reduced production demand leading to operators lowering the
productivity of blast furnaces. Currently, 25 out of 31 blast
furnaces operating in Japan are equipped for PCI.
By the year 2000 all Japanese blast furnaces will
be equipped for PCI, at which time the coal requirement for PCI in
Japan will approach 16 million tonne per year compared to current
requirements of 6 million tonne per year.
Pulverised coal injection, while not new
technology, is a process improvement that is being implemented in
steelworks around the world to improve the productivity of blast
furnaces and reduce operating costs. It has been demonstrated both
theoretically and in operating blast furnaces that injection rates
of over 200kg/tHM can be achieved.
At injection rates greater than about 160kg/tHM
special attention to burden charging is required to ensure furnace
stability and there is a requirement for greater oxygen enrichment
of the hot blast to maintain raceway temperatures and reduce gas
flow within the furnace.
The two main areas of concern to the Australian
coal industry relate toe the handleability of the coal, mainly
pulverised coal, and the combustibility of the coal.
Reports of handling problems, mostly blockages in
transfer lines, in dense phase transport systems are common.
Explanation of the mechanisms of dense phase transport blockages
are difficult as it is not always clear whether they occur
spontaneously or gradually.
Work done by ACIRL and Wollongong University did
indicate softer coals, due to the greater level fines in the
pulverised coal when milled under the same conditions of the
transfer system. Attention to the mill settings to match the
characteristics of the coal will greatly reduce these
Other mechanisms, such as those due to the
plastic nature of some coals which may lead to blockages, have not
been examined in the literature.
The perceived need for rapid combustion of the
injected coal has prompted some blast furnace operators in the past
to pulverise the coal very fine and to choose highly reactive
coals. It is now recognised that complete combustion of the coal is
not possible at high injection rates and in some cases low burnout
can be beneficial.
An example of this is lower blast momentum due to
a lower amount of combustion in the tuyere, and this lower momentum
reduces the degradation of coke in the deadman region.
The entry of unburnt coal char into the burden is
inevitable at high injection rates. It is desirable that this clear
participate in the ore reduction reactions in preference to the
coke, in order that bed permeability be maintained.
Limited research indicated that this may be the
case. A better understanding into the interactions of char with the
gases, liquid metal and fine coke around deadman region will be
obtained by examining the relative reactivates of coal char and
If coke reactivity is more than an order of
magnitude lower than char reactivity then the differences in coal
char reactivity due to coal types may not be significant to the
phenomena occurring in this region.
The chemical and physical phenomena that take
place within the blast furnace are complex. To understand the
impact of increasing PCI rates and coal quality on these phenomena
requires large scale tuyere combustion rigs, investigations on
operating blast furnaces and the use of powerful mathematical
These investigations are being conducted by most
steelworks around the world including Australia where BHP, at their
Newcastle laboratories, are in the early stages of their research