Thermal insulation riser is a riser made of low thermal conductivity material. In the process of casting and smelting, the temperature of the insulated riser is not constant, but in a state of continuous heating, which may lead to the deterioration of the thermal stability of the riser covering agent, so it is easy to be destroyed by drastic temperature changes. In general, the reaction temperature of the melting furnace is high, and the riser covering agent is in a high temperature state for a long time, which leads to the gradual change of the crystal phase and grain decomposition degree of the riser covering agent, which destroys the original structure and organization and makes the covering agent ineffective.
Potassium oxide, iron oxide and sodium oxide are harmful impurities in riser heating agent, and their influence may lead to the failure of riser heating agent. The active surface of the riser covering agent is easy to be covered and the pores of the riser covering agent are easy to be blocked due to impurity pollution and reactant coking carried by the feed gas. The covering agent of riser sticks together, which causes the local resistance in the bed to rise and the reaction gas to be short-circuited, which directly leads to the reduction of the utilization rate of covering agent of riser and the shortening of service life. If it contains volatile iron compounds, it will decompose into iron oxide on the riser covering agent, covering the surface and destroying its activity. Moreover, the surface of the catalyst is covered with fine iron oxide particles, which will accelerate the complete combustion reaction of the covering agent and release a lot of heat at the same time, which will make the reaction temperature rise rapidly or even out of control, thus affecting the performance of the covering agent for the riser and leading to the increase of side reactions. Therefore, the existence of harmful impurities such as potassium oxide, iron oxide and sodium oxide will lead to the failure of riser heating agent.