537 posts
Re: brown core in clinker
dry process:
I am very interested in your last answer. We very often have 4 or 5 times per day free lime. According to your answer I can make conclusion that generally free lime in clinker appear (if raw meal was ok in chemical composition) from large lumps or slabs? But what are the reasons of it? How to avoid it?
The reason for the kiln inlet slabs is invariably lack of oxygen in the kiln inlet (reducing conditions). This situation results in the local volatilisation of large amounts of sulphur which cause large buildups in and around the kiln inlet, bottom cyclones and riser duct. If you don't have a kiln inlet oxygen or CO analyser you can get an indication of the degree of reducing conditions by checking the SO3 content of the hot meal exiting the bottom cyclones. It depends on your kiln but a good guide is that you will probably start to experience periodic slabs and/or cyclone blockages if you operate with hot meal SO3 values which are continuously >2%. The lower you can get your hot meal SO3 the better, (0.5 to 1.5% is fairly typical).
Increasing the oxygen in the kiln inlet can be achieved in two ways, either increasing the kiln draught or decreasing the coal to the main burner. Which one you choose depends on the condition of the rest of the kiln system at the time.
Sometimes if the slabs are large enough, they will temporarily block gas flow at the kiln inlet and you may see the kiln inlet pressure suddenly become more negative. Often this returns to normal as the slab breaks up, but within about an hour (as the lumps pass through the kiln and cooler) you will always see a large and sudden increase in free lime in your clinker samples. I have seen free lime contents in excess of 10% for a couple of hours in the very worst cases, with 'soft brown centre' clinker nodules the size of grapefruit! The centres of these nodules were composed of completely unburnt soft buildup.
Another way to combat these slabs is to perform regular thermal imaging of the kiln inlet, bottom cyclones and riser duct using a digital infrared camera. This can help to locate where these buildups are forming and where to install future CARDOX or air blaster points.
Last week we have ‘hard brown centres’. We made chemical test and it showed 0,12% Fe +2.
0.12% Fe+2 is VERY high and indicates severe reducing conditions in the burning zone. I doubt if this was caused by hard burning. It is much more likely that you have nowhere near enough oxygen in the burning zone.
That time the 4-th cyclone outlet temperature was 900-910oC. What it was? How we can measure temperature in the burning zone and make decision that it was too much?
Don't you have any temperature measurement in your burning zone at all? These days BZT measurement is pretty much a standard tool (using pyrometers, infrared cameras etc) If you don't have any temperature measurement in your burning zone your clinker free lime can be a very rough indicator. If your free lime is <0.5% you are burning far too hard. However, I suggest you invest in some suitable temperature measuring hardware.
Hope this helps,
Regards,
Ted.
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5 posts
Re: brown core in clinker
Ted,
That is good idea! We haven't bypass and therefore during 2-3 days after starts the kiln we haven't any problem with free lime and chemical analysis show SO3 in hot meal 0,3-0,7%. But after a couple of days it increase to 2-3% and we have problem.
We can’t decrease coal on main burner because there we supply 40% of fuel and 60% at the calciner. Can SO3 from burning coal made influence on the reason for the kiln inlet slabs? Because now we started to use different type of coal which have SO3 from 0,5% to 4%. We have gas kiln inlet analysis and it shows 1,5-2%O2
On our plant we use only thermo couples at all cyclone stage, inlet kiln, discharge kiln, second and third air. Also we use thermo scanner along kiln shell, but I have never seen using thermo cameras for measuring burning zone temperature. Should you give me some infrared cameras producers name?
Also we use air blaster points on bottom cyclone and inlet kiln. The frequency of it is half an hour. Maybe we should use it more frequently, for example every 15 minutes? And then we can avoid slabs build up.
537 posts
Re: brown core in clinker
We can’t decrease coal on main burner because there we supply 40% of fuel and 60% at the calciner. Can SO3 from burning coal made influence on the reason for the kiln inlet slabs? Because now we started to use different type of coal which have SO3 from 0,5% to 4%. We have gas kiln inlet analysis and it shows 1,5-2%O2
The amount of extra SO3 input (from either fuels or raw materials) that your kiln can tolerate before buildups become a problem depends on two things;-
1. Your Alkali/Sulphur balance, which determines whether you have sufficient alkalis to offset the extra SO3.
and
2. The kiln inlet O2, which determines whether the extra sulphur will be converted to the less volatile alkali sulphates (SO4), rather than the problematic SO3.
These two factors go critically hand-in-hand. BOTH must be optimal to prevent slabs and buildups in the kiln inlet area.
In your case, changing the SO3 input from the coal from 0.5% to 4% is a fairly big step. You need to check your new Alkali/Sulphur ratio, taking into account all of your raw materials and fuel inputs.
With respect to the kiln inlet O2 level, 2% is probably the minimum I would operate at. Some kilns require 4-5% to eliminate these sorts of kiln inlet slabs and buildups.
On our plant we use only thermo couples at all cyclone stage, inlet kiln, discharge kiln, second and third air. Also we use thermo scanner along kiln shell, but I have never seen using thermo cameras for measuring burning zone temperature. Should you give me some infrared cameras producers name?
The following are just a few of the suppliers I know about, you can find more Online;-
Also we use air blaster points on bottom cyclone and inlet kiln. The frequency of it is half an hour. Maybe we should use it more frequently, for example every 15 minutes? And then we can avoid slabs build up.
Yes, I would consider trialling that. If you are experiencing slabs falling several times a day, then air blasting more frequently in that area is a good idea... if only to see if that improves the situation.
Also, hand-held digital infrared cameras for identifying the areas where slabs are building up can be obrained from a company called FLIR... more info can be found here;-
http://www.flir.com/thermography/APAC/au/products/?id=13936
Regards,
Ted.
5 posts
Re: brown core in clinker
1. Your Alkali/Sulphur balance, which determines whether you have sufficient alkalis to offset the extra SO3.
Which is the Alkali/Sulfur balance must be? What is the relation between it? Is there any formula? What kind of material we can use to increase Alkali?
2. The kiln inlet O2, which determines whether the extra sulphur will be converted to the less volatile alkali sulphates (SO4), rather than the problematic SO3.
What is the relation of conversion from SO3 to SO4 according to inlet kiln O2 concentration? Is there any models or formulas which describe it? If we have less O2 that mean we will have more SO3 than SO4, isn't it?
How
we can determine the optimum kiln inlet O2, only increase it and watching what
will happen?
Also, hand-held digital infrared cameras for identifying the areas where slabs are building up can be obrained from a company called FLIR... more info can be found here;-
Hand-held digital infrared cameras use for determining outside cyclone, kiln and so on temperature and if in any place where all other parts should have the same temperature it will have less temperature that means there we have buildups and we must install there blast point. Isn't it?
Regards,
Vladimir