When a severe water carryover problem occurs in the gasifier, it is usually due to an excessive heat load on the gasifier, causing heat transfer to become inefficient in a film-like manner

The heat transfer process in the upper half of the downcomer is very intense; most of the cooling of the syngas takes place in this upper section. As a result, the operating conditions in this upper part of the downcomer are the most severe, making it the most prone to damage. Failures that occur in chemical plants confirm this finding. There is a significant temperature difference between the wall surface and the center. Heat transfer due to liquid boiling is a complex process. According to the theory of heat transfer during liquid boiling, the degree of superheating of the liquid depends on the difference between the temperature of the heating surface, tw, and the temperature of saturated steam, ts, namely Δt = tw – ts. The heat load Q is given by Q = α•F•Δt, and thus the heat flux intensity Q/F is equal to α•Δt. When △t is small, Q/F is not large, and the liquid undergoes only slight boiling; this stage is characterized by natural convection heat transfer, and the value of α is also low. As △t increases, both Q/F and the α value increase as well; this stage is nucleate boiling. As △t continues to increase, more steam bubbles are formed; these bubbles gather together to create a layer of steam on the heating surface. The value of α drops sharply, and a large amount of water film is carried in the gas phase (in other words, the quenching chamber becomes saturated with water). At this point, the values of Q/F and α reach their extremes, which are known as critical values. The stage that follows is referred to as film boiling. In boiling operations, film boiling should be avoided, as it otherwise undermines the efficient heat transfer through boiling. Based on the above heat transfer theory, in order to prevent water from entering the quenching chamber, its boiling condition should be maintained at nucleate boiling, that is, the heat flux density Q/F in the quenching chamber should be kept below the critical heat flux density. (1) The deterioration of the heat transfer conditions is the main cause of water carryover in the quench chamber; to eliminate this phenomenon, it is necessary to adjust the heat transfer conditions within the quench chamber. (2) Preventive measures against water in the quench chamber include: ① When designing the quench chamber, as pressure and coal feeding rate increase, its dimensions should be enlarged to ensure an adequate heat transfer area within the chamber as well as sufficient space for gas-liquid separation. ②Once the design is finalized, in terms of operation, increasing the amount of cooling water or reducing the inlet temperature of the cooling water can be used to reduce △t and mitigate the deterioration of operating conditions. ③ Ensure the proper operation of the lock hopper and prevent excessive solid content in the liquid phase of the quench chamber. In actual production, the specific factors include: ① An excessively high operating temperature in the quench chamber of the gasification furnace. ②The system load is too high, and the amount of syngas is excessive. ③System pressure fluctuations, or fluctuations in the pressure downstream of the system, with low values. ④The internal components of the quench chamber are damaged and fall off, such as the downward tubes and upward tubes becoming deformed. ⑤The liquid level in the quench chamber is too high or too low.