The increase in Silicon (Si) content in iron ore and coal, which are the raw materials used in the blast furnace, leads to an increase in the hot metal temperature in the blast furnace. This is because Silicon has a high affinity for oxygen, and as it reacts with oxygen during the reduction process, it liberates a significant amount of heat.

When the Si content in the charge material increases, the amount of heat liberated due to the reaction with oxygen also increases. This heat helps in raising the temperature of the hot metal in the blast furnace. Hence, an increase in Si content always attributes to an increase in hot metal temperature in the blast furnace.

When silicon is added to the blast furnace charge, it reacts with the oxygen present in the iron oxide to form silica (SiO2) and metallic iron (Fe). This exothermic reaction releases heat, which contributes to the increase in the hot metal temperature.

@Raghd Muhi Al-Deen Jassim sir as you said it forms SiO2 thus liberating heat , then it will join the slag phase, but why at that temperature if we test the sample the silicon content is high in the hot metal?

Because 2 main recievers of excessive heat in BF exist: Si reduction and Hot metal/slag/gas temperature increase - usually (in normal BF condition) they work parralel.

High HM Si and High HMT are not related. HM can have high Si but still be cold, for example during revival of furnaces from chilled conditions or other abnormal situations. Generally, silicon in HM increases for 2 reasons:

1. High input of Silica containing fuels (coke or PCI)

2. Slow furnace movement leading to high residence time in cohesive zone and trickling zone or More retention of HM in hearth due to del;ayed tapping or other reasons due to which silicon transfer increases to HM