The document discusses ring formation and accretion build up in direct reduction kilns, which adversely impact kiln operation. It notes that many direct reduction units have campaign lives as low as 30-50 days. Key questions raised include the optimal campaign life and how to increase it, as well as why rings and accretion form in particular zones of kilns. The discussion that follows involves comments and questions from industry professionals about factors influencing ring formation like raw material quality, process parameters, and kiln design features.

1. Ring formation, accretion build up in DR kilns
Above phenomena adversely affect kiln operation,
productivity, kiln avilability per year, maintenance
cost etc. Yet, many / most DR units are perhaps not
so serious on the issue - plants of various capacities
(100 tpd-500 tpd) are often having average campaign
life as low as 30-50 days. Important points are:
(a) what should be the minimum / maximum /
optimum campaign life
(b) how to increase campaign life
(c) why does ring / accretion form in particular zones
- it is even observed that rings / build up form around
zones say 30-50% from inlet.
May we start a discussion.
May I expect owners / key management / production
personnel to take active part in the discussion.
6 months ago
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2. vishnu K. • Generally when there is a large amount of
Fines going in the kiln you shall find ring formation in
the initial zones of the kiln.
But generally when observed the ring formation
generally takes place in the later part of the kiln i.e.
near the outlet.
Moreover now a days many of the plants are using
iron ore pellets which is a much processed form of
iron ore, here i have a major question arising should
there actually be any accretion formation / ring
formation in a kiln using pellets because there is no
contamination entering the kiln
6 months ago
vishnu K. • Can you let us know the material that
was being run during the 230 days campaign
6 months ago
vishnu K. • Does modified process conditions relate
only to better process engineering or also to any
changes in the kiln design, and also would like to

3. know is there any benefit if having corse size of coal
seperately for feeding from outlet and inlet side
6 months ago
Pabitra M. • (a) Modified process conditions are
arrived at after process analysis which is based on
prevailing design - so, modified conditions are
advised on the basis of prevailing design. Normally,
change in design is not a very logical step - it calls
for additional investment too. A process engineer's
job is to understand and analyse the problem, and
advice changes in process conditions within the
restricted framework of design, raw materials etc.
Anyone will love to have ore/pellet with 65%+ FeT,
and so on, coal with min 35 FC, ash 25 max and so
on, etc etc - let us think of the reality! Where/how to
get that ore/coal and at what price? Much better is
to suggest conditions under which best techno-
economical results are achieved.
(b) Coal size distribution is important - but again a
reality - can anyone have desired coal size
distribution when coal varies from truck-to-truck,
wagon-to-wagon, rake-to-rake?
6 months ago

4. Sanjay C. • As per my experience, I can say Oxygen
enrichment from Outlet end can enhance kiln
operating days. As the more coal we feed, the more
ash we are feeding into the kiln. These fused ash are
the main culprit in ring formation. Oxygen
enrichment reduces coal consumption as well as
specific cost too. Can anybody enlighten some more
on it?
5 months ago
Pabitra M. • (a) "Oxygen enrichment reduces coal
consumption" - how and why plz?
(b) "These fused ash are the main culprit in ring
formation" - does chemical analysis of ring/accretion
say that?
5 months ago
Thomas j C. • On the long running plant, can you give
the details on placement of on-board burners if any,
details of length of kiln and dia., physical and
chemical analysis of raw material feed for iron ore

5. and for coal?
Is supplemental fuel used?
Do you have monitors/on-boared thermocouples and
at what locations? As compared to burners?
Need to know the design of dam on discharge.
Type of refractory? chemistry and brick or castable?
5 months ago
jai V. • actually i am working in 100 tpd kiln.
i have seen that mostly ring formation occur at
outlet side of kiln and mosty 10 metre away frm the
outlet.
our 100 tpd kiln length is 42 metre and mostly ring
formation is outtlet.
inlet is fresh.but due to ring formation we are unable
to control the outlet hood pressure which result
sometime burning of bellow of CB pipe.
coming to raw material we feed 58-60 Fe(T) iron ore
with maintaing C/Fe at 0.39.but then again we exp.
shorther campain.
plz suggest how to overcome and reduce ring
formation at outlet and increace the campaign life..
4 months ago

6. Pabitra M. • jai
ring formation around 20-30% from outlet is very
common. the most difficult job in DR is to reduce the
wustite to Fe - if that can be controlled properly,
control of other aspects becomes easier - it is like
the old saying [re: saving] "if we can take care of
paisas, rupees will take care of themselves". in
most, if not all cases, to reduce the wustite, the
temperature around outlet [20-30%] is increased. it
is encouraging to note that you feed 58-60 FeT ore
and achieve C/Fe 0.4 max - although you have not
mentioned the coal FC. it appears to me, in the
absence of details, your coal distribution
(inlet/outlet) vis-a-vis air profile need to be assessed
and modified if necessary. i tend to guess at this
stage that temperature profile (hence metallisation
profile) is having bumpy and/or pretty steep (rising)
gradient (towards outlet), after say 60/70% kiln
length from inlet - that is in the last 30-40% length.
4 months ago
P.R.K.Raju C. • Most of the times ring formation is
due to manual errors like not maintaiing
temperatures and keeping process engineering with
out knowledge. My observation is most of the times

7. the night time process perameters are controlled
from control room with out checking physically.
Many DR plants donot have the process engineers
with proper knowledge.
4 months ago
Pabitra M. • PRKR: Amazing observation (night time
process perameters are controlled - - ) indeed! hah!
hah! hah! Looking at the 'C' shift log sheets of some
units, I have observed in some cases, that between
12 midnight and 4 am [particularly during cold
winter], the bed/gas QRT temperatures are virtually
the same as those of say 12 noon and 4pm ('A'/'B'
shift). For data analysis, such data is to be
filtered/eliminated as "noise". However, that is
definitely NOT THE cause for accretion/ring
formation. Rather, lack of process engineering is
responsible.
4 months ago
yu W. • hi all, i'm a student, we research the effect of
rank and particle size of coal on the melting behavior
of low grade(43%Fe) of hematite in the temperature

8. range of 1100 to 1200°C, it seems relate to ring
formation
3 months ago
P.R.K.Raju C. • Dear Wen, In the rotary kiln the iron
ore used will be mostly above 60% Fe. Please do a
research for the iron ore from 55% fe to 60% fe. That
will be more useful.
3 months ago
yu W. • Dear Raju, thank you for your advice, in fact,
we use a new method to extract metallic iron from
difficult-to-process ores, namely coal-based direct
reduction-magnetic separation, the hematite was
reduced to metallic iron and iron grain aggregation in
roasted stage, and then the reduced composite
pellet was ground to liberation size and separated by
magnetic separation. The type and particle size of
coal present a important effect on the smelting
behavior of the pellet, as you know, the smelting
behavior relate to the growth of metallic iron which
affecting the separation of iron from slag. Sorry my
english is very poor, is my pleasure to talk with you!
3 months ago

9. Thomas j C. • Oh well, I guess noone is willing to part
with details of their process or design in order for us
to assist in the mystery of accretions. So we can
continue this speculative discussion on the subject
without any real answers or experience? Let me
know when you are willing to part with something!
tcinc002@aol.com
3 months ago
P.R.K.Raju C. • Mr.wen please send your address and
mobile number to me . iam visiting Beijing next
month. we meet and discuss more.
prksouth@gmail.com