What are the factors that cause coking in tar heaters? I would like to ask the experts here

(1) Inadequate coking removal from the furnace tubes during shutdown for maintenance； (2) Significant changes in steam injection volume and feed volume lead to a substantial decrease in flow velocity inside the furnace tubes ； (3) Unstable combustion, with flames of varying lengths or shooting directly at the furnace tubes, resulting in localized overheating and coking of the furnace tubes ； (4) The temperature at the convective outlet is excessively high, exceeding 420°C – above the critical reaction temperature – and the flow rate is low, resulting in coking ； (5) Furnace inlet flow, long-term deviation in the two branches ； (6) Excessive changes in the properties of the raw materials, high residual carbon content, or high salt content ； (7) Inaccurate instrument readings result in a high temperature at the furnace outlet ； (8) Illusions from control and indication instruments, leading to incorrect judgments.