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Showing posts with label Furnace lining. Show all posts
Showing posts with label Furnace lining. Show all posts

Refractory Installation Procedure and Heating Schedule to be followed after starting an Induction Furnace

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Installation of refractories in any furnace is a tricky process and after the lining is done the most important thing is the heating schedule. That means how the furnace after repairing or with new refractory lining should be started, what should be the rate of heating (rising temperature) and holding time at any particular temperature. You cannot start the furnace by raising its temperature to peak at one go, as otherwise the refractories will be damaged or even the refractory lining may fall apart. The furnace starting heating schedule depends on various aspects including, thermal conductivity of the refractories used.


Here is a step-by-step guide for installation of Refractories (Ramming Masses, etc.) in Induction Furnace also the heating schedule that should be followed after starting the furnace:


Read: Refractory Lining Installation of Pipes and Chutes in a Furnace


1. Scrub all loose materials and clean the furnace.

2. Before using heat the refractory material (Ramming mass) at about 100OC to make it free from moisture. Spread the material at the furnace bottom to about 50 - 60 mm thick layer at each time. Then ram the layer uniformly using a suitable rammer. The material has to be rammed layer by layer to get maximum compaction. Before ramming, little bit poking with a rod help to drive away the air-pockets trapped within the loose refractory material spread.

3. Place the steel former on the rammed bottom. Then fix the steel iron block at the center of the steel former to get uniform thickness throughout the furnace wall.

4. For ramming the upper portion of the side-wall just above the induction coil, mix the dry refractory material with 1-1.5% Sodium Silicate solution and 3-4% water.

5. Best results can be achieved by following the heating schedule for the furnace as mentioned hereunder -

Furnace Heating Schedule

Furnace Temperature

Rate of Heating with Holding Time

Ambient temp to 100OC

@ 30OC / hr.

Hold at 100OC.

4-6 hr depending upon the lining thickness.

100O - 800OC.

@ 50OC / hr.

Hold at 800OC.

2 - 3 hr.

800O - 1400OC.

@ 100OC / hr.

Hold at 1400OC.

4 - 6 hr.

1400OC to furnace operating temperature.

@ 100OC / hr.

Refractory Lining Installation of Pipes and Chutes in a Furnace

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7-July-2020
‘Piping’ and ‘Chutes’ are used in furnaces for the purpose of transporting hot air, gases or solid usually accompanied with fine, hot dust particles. Depending on the existing stress, the piping is lined with single layer or multilayer insulating refractory materials. 

Examples for piping with diameters up to 2000 mm are gas piping for Reformers and metal slides in Preheaters of Cement Plants. Examples for piping with diameters above 2000 mm are recirculation shafts in Lignite Power Plants and Hot Blast Mains in Blast Furnace of Steel Plants.

Below given are certain points (rules) must be taken care of while doing refractory lining of pipes, chutes and circular or curved structures in a furnace:

=> Material and personal transport must be coordinated with the piping designer during the planning phase. Manholes, equipment for scaffolds and material transport must be determined.
=> If the refractory lining consists of several layers, each layer should be installed separately or section by section in order to prevent material mix-up.
=> Expansion joints may not be smaller or larger than what is indicated in the drawings. Mortar residue or other contamination (dust etc.) must not get into the expansion joints.
=> Expansion joint bricks, closed bricks and bricks for bevel areas must be measured, finished and installed precisely. Hollow spaces must be avoided due to danger of background currents.
=> If piping is lined on the ground, a trial installation of the closer piece to be fitted into each stand of pipes must be undertaken or it must be lined on site.
=> The lining on the ground is only possible if both piping and refractory designer have already determined length and weight of the pipe chutes. This will help prevent undesired deformations of the lined pipes.
=> In order to prevent transportation damages the lining of pipe chutes having larger diameters should be protected by braces. These braces must be of such a design and make that they can be securely transported and can be easily removed without damaging the lining.
=> The refractory lining dimensions, especially at the ends of pipe chutes, must be precisely observed. Crowding and damage to the refractory lining during assembly should be prevented.                
=> Below expansion joints must be approved and cleared by the piping designer before refractory lining work starts. Special attention must be given to observance of the cold dimensions (initial tension / stress) and flow direction.



The Function of a Furnace and Kiln used in Ceramic and other Industries

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Difference between Kiln and Furnace

There are so many definitions for Kiln and Furnace. Actually kilns are an integral part of the manufacture of all ceramics, which require heat treatment, often at high temperature. The distinction of a Kiln and a Furnace is often done on the basis of user industry than on the design of the device. Generally the term kiln is used when referring to high temperature treatment of non-metallic materials such as in the ceramic, cement (cement rotary kiln), lime (lime kiln) industries etc. When melting is involved the term furnace is used as in steel manufacture (Blast Furnace, Basic Oxygen Furnace, Ladle Furnace), glass industries (Glass Melting Tank Furnace) etc.


Definition and Function
As a practical working definition, it has been proposed to restrict the term Furnace (or Kiln) to an industrial appliance, constructed to heat a material through a cycle involving temperatures exceeding 400OC. This temperature has been chosen in order to exclude a large number of industrial process in which steam is used as a medium of transferring heat. It is essential that the heat released in the space of the furnace should be so utilized that the maximum heat economy is effected. A good working furnace must therefore -
  • have very good control of temperature.
  • require a minimum amount of fuel or other energy sources and other auxiliary materials.
  • require minimum capital and maintenance costs.
It is felt that a greater use of thermodynamics in furnace design and refractory lining can lead to more accurate and closer way of thinking about such problems as those of preheat, utilization of waste heat, recirculation of the flue gases and different qualities of energy sources, etc.

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