3.4　Slab Reheating Furnace of Stainless Steel and Silicon Steel

3.4.1　The choice of furnace type should comply with the following rules:

1　Slab reheating furnace of stainless steel and silicon steel should be walking beam reheating furnace with upper-heating and lower-heating means.

2　For slab reheating furnace heating high temperature orientation silicon steel，side heat supply shall be adopted for lower heating section while flat flame radiant type burners for the upper heating section，or otherwise flame radiant type burners for the soaking section，side burners or end burners for the other section which are used for axial heating.

3　When the reheating furnace is used for heating carbon steel and also heating high temperature orientation silicon steel plus stainless steel，6-section or more section heat supply and automatic control system are recommeded.

3.4.2　Heating capability and number of the reheating furnace should comply with the following principles:

1　Heating capability of the reheating furnace should be based on annual yield and requirement of rolling mill，and at the same time，room shall be reserved to give further play of the mill.

2　Heating capability and number of reheating furnace should be based on thermal efficiency，maintenance，leveling of production and utilization rate of furnace，etc.

3　Hearth intensity of stainless steel and silicon steel slab reheating furnace can be defined following the Table 3.4.2.

3.4.3　The choice of fuel type shall comply with the following principles:

1　When liquid fuels are used as the main fuel of reheating furnace，a given quantity of gas fuel should be considered for soaking zone.

2　When the reheating furnace is used for heating austenitic stainless steel，the sulphur content in liquid fuel should be less than 0.8%，the hydrogen sulfide content in mixed fuel should be less than 200mg/m3.

3　When the reheating furnace is used for heating high temperature orientation silicon steel，the calorific value of mixed gas（blast furnace gas and coke-oven gas）should be greater than 10000kJ/m3；when the silicon steel reheating furnace adopts water slag tapping，the calorific value of fuel should be no less than 11700kJ/m3，the fuel can be used for clinkering of hearth and flame seal of slag hole；when the gas fuel calorific value for the main burners is 17300kJ/m3 or above，we can cancel the clinkering burners of hearth.

4　Heat generation value of gas should be stable，with fluctuation between 5%and 8%；calorimeter may be provided for modifying the air-fuel ratio.

5　Tar content in gas should not be greater than 10mg/m3，the dust content in mixed gas should not be greater than 10mg/m3.

6　Measures shall be taken to stabilize gas supply pressure to maintain fluctuation between-5% and+5%.

3.4.4　Layout of longitudinal water beams in furnace bottom shall comply with the following principles:

1　Under the premises of meeting requirements of production process，the number of longitudinal water beams should be reduced as far as possible，the longitudinal water beams layout at the discharge end should be staggered in arrangement.

2　When the carbon steel and high temperature orientation silicon steel are reheated，the spacing interval between the adjacent longitudinal water beams should be less than 900mm，with end jibarm around 150-350mm.

3　When high temperature orientation silicon steel is reheated，surface pressure intensity of hot skid on longitudinal beams for support of slab shall be no greater than 50% of that for the carbon steel reheated.

4　When the ferritic stainless steel and martensitic stainless steel are reheated，the spacing interval between the adjacent longitudinal water beams should be less than that for the carbon steel reheated.

5　The strength and rigidity of supporting columns and translation frame should be ensured.

6　Material for seamless steel pipe of longitudinal water beam and supporting column should be according to the 6th paragraph of article 3.7.4.

3.4.5　Design of walking machinery should comply with the following principles:

1　Large slab reheating furnace should adopt the roller skew table hydraulic drive stepper machine，also can use the wheel crank connecting rod type or electric eccentric wheel type stepping machine.

2　When the reheating furnace is used for reheating carbon steel and stainless steel，walking distance can be fixed step of 500-600mm；if the reheating furnace is used for reheating high temperature orientation silicon steel，translational stroke can be of 400-600mm adjustable step pitch.With fixed beam as reference，lifting stroke can be of 100mm upwards or downwards.

3　Walking movement cycle can be 45-55s for reheating carbon steel and stainless steel，and 70s for reheating high temperature orientation silicon steel.

4　When the high temperature orientation silicon steel is reheated，and the water beam adjacent to furnace wall is a movement beam，walking beam should have the function of stop at the middle position.

5　Hydraulic station should be set up with ventilation，fire fighting and automatic fire alarm system.

3.4.6　Composite lining masonry material should comply with the following principles:

1　For high temperature silicon orientation reheating furnace，structure and material of lining mansory of low temperature section（preheating section）and flue duct can be of the same kind as that for ordinary reheating furnace.

2　For high temperature section（heating section）of high temperature orientation silicon steel reheating furnace with water slag system，maximum operation temperature of slag hole refractory layer should be greater than 1650℃，and the refractory layer should have a good resistance to slag corrosion.

3　When silicon steel reheating furnace adopts dry slag system，the upper surface of furnace hearth should be level，the embankment of waking column should be 400-500mm higher than the upper masonry surface of furnace hearth；the surface around fixed column should be 150-200mm higher than the upper masonry surface of furnace hearth.

When silicon steel reheating furnace adopts water slag system，the upper surface of furnace hearth masonry should be inclined 4.7° to two sides with reference to furnace center line；the high embankment of waking column and fixed column should be 280-300mm higher than the highest surface on the top of furnace center line.

3.4.7　Combustion devices should comply with the following principles:

1　When the upper of soaking section adopts flat flame radiant type burner，heat supply capacity shall be reserved with quite some excess.

2　The low-NOx adjustable flame burner should be used for other section when side burner or longitudinal burner is applied for their heat supply.

3　The air for fuel combustion should be preheated to no less than 550℃.

3.4.8　The slag system should comply with the following principles:

1　The hearth slag system for stainless steel reheating furnace should adopt dry slag system each half year or one year on regular basis with reheating furnace being shut down.

2　When water slag system is applied，the water slag should be granulated.Water used for slag granulation system should be turbid recirculaitng water，with total hardness of water no greater than 150mg/L（CaCO3），suspended matter no greater than 20mg/L.Water consumption of slag granulation is 1.2t/t（billet）.