Boiler Burner Refractories

Refractories

A material in solid form which is capable of maintaining its shape at high tempo (furnace tempo as high as 1650^oC) have been recorded.

Purpose

                            i.  To protect blr casing from overheating and distortion and the possible resulting leakage of gasses into the machinery space.

                           ii.  To reduce heat loss and ensure acceptable cold faced temperature for operating personnel

                          iii.  To protect exposed parts of drum and headers which would otherwise become overheated. Some tubes are similarly protected.

                          iv.  Act as a heat reservoir.

                           v.  To be used to form baffles for protective purposes or for directing gas flow.

Properties

                            i.  Must have good insulating properties.

                           ii.  Must be able to withstand high tempo's

                          iii.  Must have the mechanical strength to resist the forces set up by the adjacent refractory.

                          iv.  Must be able to withstand vibration.

                           v.  Must be able to withstand the cutting and abrasive action of the flame and dust

                          vi.  Must be able to expand and contract without cracking Note: no one refractory can be used economically throughout the boiler

Types

                            i.  Acid materials- clay, silica, quartz , sandstone etc

                           ii.  Neutral materials-chromite, graphite, plumbago, alumina

                          iii.  Alkaline or base materials- lime, magnesia, zirconia

Forms

                            i.  Firebricks- these are made from natural clay containing alumina , silica and quartz. They are shaped into bricks and fired in a kiln

                           ii.  Monolithic refractories- These are supplied in the unfired state, installed in the boiler and fired in situ when the boiler is commissioned.

                          iii.  Mouldable refractory- This is used where direct exposure to radiant heat takes place. It must be pounded into place during installation . It is made from natural clay with added calcided fire clay which has been chrushed and graded.

                          iv.  Plastic chrome ore- This is bonded with clay and used for studded walls. It has little strength and hence stud provides the support.

                           v.  Castable refractory-This is placed over water walls and other parts of the boiler were it is protected from radiant heat . It is installed in a manner similar to concreteing in building

                          vi.  Insulating materials- Blocks, bricks , sheets and powder are usually second line refractories. I.E. Behind the furnace refractory which is exposed to the flame. Material; asbestos millboard, magnesia , calcined magnesia block, diatomite blocks, vermiculite etc. all having very low heat conductivity.