why slagging in boiler

Without knowing any particulars about your boilers or fuel, clinkers and slag form when solid fossil fuels exhaust their metallic qualities in heat production and the change in temperature in the parts of the boiler farther away from the burn causes the remnant metal ore matrices to combine and coalesce.

By re-burning the initial combustion gases from non-fossil solid fuels --like cellulose-- at high heat, you may be able to avoid any ash at all.

Liquid and gas fuels don't, so far as I am aware, produce either clinkers or slag, although over a long period of time, incomplete combustion may cause liquid fuels to leave a fine white ash. Modern boilers try to overcome this by combining the fuel with misted water and spinning the combusted fuel in a vortex.

If you are using sold fossil fuel, I don't think that adjusting the burn in your boilers will help to make it more complete. If the clinkers and slag are strangely being caused by a somehow very saturated mineral-rich liquid fuel you are using, try enriching the air to the mix for a more complete combustion result that will produce smaller, less interfering clinkers and slag.

Mark

Slag from memory forms mostly around the burner due to it being a cool spots, this is over come by refractory cemented around the burner, there is also a correct procedure for curring the refectory to prevent its failure, there should be an small inspection viewing door near by for inspecting the burners? Also I believe that over spraying of ash in the pit can cause problems, if there is an accumulation of water when the hot clinker falls it gives off large amounts of steam, the burners can be a bit rich from a ball mill on pulling back the PA fans on initial load reduction, the coal feeder pulls back also and the balls give the coal in the mill an extra fine grind making for a rich mixture at the burner that can be put out by clinker generated steam? Its a long time since I retired from power station operation, so others made need to correct parts of the above.

Regards JD.

You are slagging because you are running oxygen starved or blower is not turbulent enough. If these are not problems, add 20% gypsum powder as a flux to percipatate slag out of flame front. You are using very dirty coal or a poor quality peat coal.

As someone has posted above, liquid and gaseous fuels don't normally clinker. Typically, clinker formation will occur when, at that location in the firing system, the temperature has exceeded the "ash fusion temperature" of the solid fuel (typically coals). This is a standard test used to identify the liquid/solid properties of the ash material; yes, it is impacted by the ash chemistry especially the metallic materials and content. Suggest you read/study the following text: "Chemistry of Coal Utilization" by H. H. Lowry (1945) National Research Council.

As already mentioned in one of the comments, slagging is caused due to combustion in reducing atm, and also burning low quality fuel such as lignite or peat. Try operating the Steam generator in an oxidising atm with boiler exit at 4% oxygen level max.

Slagging is because of the minerals present in coal. the temp of the boiler in the combustion zone is the order of 1400 deg C. The minerals present in coal ash bring down the ash fusion temperature and at low temps as low as 1200 Deg C the ash melts and fuses and causes slagging/clinker.

The clinkers formed are generally because of the unburnt coal particals fusing alongwith ash. Hence it is important that the coal particals burn totaly. The coal mills may also be responsible for this.

The clinkers are generally formed on the waterwalls which are removed by sootblowing. Sootblowing frequency also may decide the size of the clinkers.

If the clinkers are big then the 0022boiler tripping may occur when the clinker falls down. the clinker may fall down because of thermal shock when the load is reduced.

MANOHAR TATWAWADI, R-15, Laxminagar Nagpur. 440022

Coals have a very unconstant composition, every minute your mills will face a diferent ratio of ash, sulphur, water, carbon, volatiles and a diferent grindability. The origins of coals are various and diferent suppliers will never be able to respect the design qualities of coals. The dimensions of coal particles will not respect the optimal repartition.

For these reasons, your boiler management operations cannot respect a correct air excess and the various dimensins of coal particles will blow up in very diferent areas of the fire room, finding or not enough oxygen molecules for a correct oxydization.

A solution for your problem you may find in India to Cleantech Ecosystems www.cleantecheco.com.

I HAVE HEARD ABOUT ABHITECH COMPANY WHO SUPPLY PRODUCTS TO REDUCE IT

i heard about company abhitech which supply products to reduce this phenomenon, u can ctc them.

One of the reasons of slagging in boiler is character of coal that used as fuel to find the slagging and fouling behavior of coal visit COALspot.com. You can find some calculators which may indicate of slagging and fouling behavior of coal that you are using in plant. http://www.coalspot.com/calculator/slagging.php

You may want to reconsider modifying your burner design to improve the combustion efficiency and decrease peak temperatures as well as reducing zones of reduced conditions in your boiler. All these factors will reduce risk for slagging and particle depositions. CPS can help you to optimize your combustion process: http://www.creativepowersolutions.com

There is a new industry product, a coal catalyst, that not only solves the problem of slagging/fouling/clinkers in boilers but also improves the coal combustion (2-25%) depending on the efficiency of the boiler, reduces SOx and NOx up to 80% and reduces your boiler maintenance costs dramatically. We are looking for distributors throughout the world, please contact [email removed]

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Dear friend,

Your data is not sufficient to answer your question in full and it is not that simple.

The fuel character/analysis is to be informed such as non-combustibles, and the elements in it, volatile matter etc. Slag formation is due to over-heating/melting , and at what temp. slag forms is to be identified, and operate the furnace below the temp. This may give rise to some other problem, capacity fall etc.

Clinker is falling due to fall in temp. of furnace. Due to reduction in Load, the fuel burnt will come down, Heat released in to the Furnace is reduced.

The grate area, furnace volume, the Heat-Release rate, flue-gas flow and velocity, extent of volatile fuel combustion, flame character etc. to be examined.

I do not think, the Boiler Designer will give a bad design for this capacity of boiler mentioned by you. I have a doubt, the operating parameters have been changed from that of the design parameters. Pl. examine this and involve the Boiler designer.

DHAYANANDHAN.S