3.3　Hot Rolled Strip/Slab Reheating Furnace

3.3.1　Walking beam reheating furnace should be adopted for newly-built wide strip mill，medium steel plate mill and steckel-mill.

3.3.2　The hourly output of the slab walking beam reheating furnace should accord with the following specifications:

1　The hourly output of a slab reheating furnace can be calculated on the basis of the following formula:

where，p—The hourly output of the reheating furnace（t/h）；

Q—The nominal annual output of the mill（t/a）；

h—The annual working hours of the reheating furnace（h/a）；

η—The utilization factor of the reheating furnace.

2　The annual working hours of the reheating furnace is better to be 6000-6500h；utilization factor of the reheating furnace is better to be 0.65-0.80.The above data can be determined according to the enterprise's management level and the number of reheating furnaces.In determining output of the reheating furnace，factors such as hot charging rate and the hot charging temperature should be taken into account.

3　The hourly output of the reheating furnace should be no less than the hourly output of the main product which was produced by the mill，nor less than the maximum hourly output of some kinds of the productions which were produced by the mill.

4　After the hourly output of the reheating furnace was determined preliminarily，the annual working hours of the reheating furnace should be verified when the mill produces other types of products.

5　The designed annual output of the reheating furnace shall be no less than the annual output of the mill.

3.3.3　Structure design of the slab walking beam reheating furnace should accord with following specifications:

1　If the charging machine is arranged and the plant span is big enough，charging atria can be arranged between the charging end and the charging roller table.Its width is equal to the inside furnace width，and its length should meet the requirement that two slabs can be stored in it.The effective furnace length of the reheating furnace can be calculated according to the following formula:

where，L—effective furnace length of the reheating furnace；

P—nominal production（kg/h）；

P0—furnace hearth intensity［kg/（m2·h）］；

l—reference slab length（m）；

n—the number of the reference slab columns.

2　The furnace hearth width should be determined according to the number of reference slab columns and the slab length.

3　The slab layout plan and the arrangement of the furnace hearth longitudinal beams should accord with following requirements:

1）The slabs in the furnace can be arranged with one side aligned，or with two sides aligned and staggered，or arranged symmetrically to the walking beam mechanism center line of the reheating furnace.

2）Minimum center distance between two longitudinal beams should not be less than 600mm.

3）Slab jiblength to the longitudinal beam center line and the headroom distance between the slab and the longitudinal beam center line are better to be no less than 150mm.

4）Maximum jiblength of the slab should be determined according to factors such as the slab thickness，heating temperature，stay time at high temperature，or be estimated according to the formula（3.3.3-2）.Maximum distance between centers of the movable beam or the fixed beam can be estimated according to the formula（3.3.3-3）.

where，L1—the most jiblength（m）；

L2—Maximum center distance of the movable beam or the fixed beam（m）；

S—slab thickness（m）.

5）The position of the charging machine and the discharging machine supporting rod should be given attention to in the slab layout plan.

6）The longitudinal beam strength should be calculated.Deflection of the movale beam at the burner passage of the slab reheating furnace with end heat supply and lower heating section should not be more than 1/800.

4　Arrangement of burners of lower heating zones shall avoid combustion flame impact to upright columns of the longitudinal beams.

5　The material and the height of the heat-resisting skid on the longitudinal beams should be selected according to the temperature of the skid in the furnace.

6　The steel structure of the reheating furnace is better to be designed as block prefabricated components.

7　Charging door，discharging door，peep hole on both sides，operation door and access door should be opened flexibly and closed tightly.

3.3.4　Heat supply of the slab walking beam reheating furnace should accord with following specifications:

1　The heat supply mode and equipment should be selected according to slab specification，output and heating quality of the reheating furnace.

2　The nominal specific consumption of the reheating furnace should be selected according to Table 3.1.4 in this specification.

3　The distribution of gas and capacity of the burners on each heating zone should meet the heating requirement in case of cold slab charge，and should meet the requirement of stable combustion and small flame length change in case of high heating capacity change of reheating furnace when the hot slab is charge.

3.3.5　The energy saving of the slab walking beam reheating furnace should accord with following requirements:

1　If there is enough space in the plant，the furnace length can be lengthened，and the heat recovery area where there is no heat supply is better to be set up.

2　The furnace structure and the heating mode should be facilitative to increasing hot charging rate and the hot charging temperature.

3　Waste heat of exhaust gas of the reheating furnace can be used to preheat air only，or preheat both air and gas.

4　The furnace longitudinal beams and upright columns should be arranged reasonably，and the cooling component should be insulated by double layers.

5　Energy-efficient hydraulic system is better to be adopted for walking mechanism.

3.3.6　The EIC control of the slab walking beam reheating furnace should accord with following requirements:

1　The function such as the location of the slab on the charging roller table，logical motion sequence，timing，interlock，and the counting of the charging door，the charging machine，the discharging door，the discharging machine and the walking beam should be realized by the programmable logic controller in the furnace area.The operation such as the location of the slab on the charging roller conveyor，the logical motion sequence，the timing，the interlock，and the counting of the charging door，the charging machine，the discharging door，the discharging machine and the walking beam should be realized on the charging console and discharging console respectively in the furnace area，and local manual console should be set up in the pit of the reheating furnaces.

2　Fine thermal automatic control system should be installed for the reheating furnaces.The optimum control of the each heating zone temperature through computer according to heating mathematic model should be promoted gradually for the reheating furnaces when possible.