Is slag removal required every time the space furnace is started up?

Personal opinion: 1. In fact, the effective load for slag scraping in coal-fired boilers with a water wall structure lies within the range of 2.0–2.4 MPa; at this load level, the gasification chamber can maintain an adequate temperature, and the heat generated by the combustion reaction is sufficient to melt the ash present in the newly added coal. In the 1.0~2.0 MPa range, the calorific value is insufficient; therefore, the pressure increase rate at this stage is relatively higher. 2. If conditions permit, coal with a relatively higher ash melting point can be used for the initial slag formation on the water wall. When the operation is stable, the underlying solid slag layer generally remains intact, which helps to reduce the impact of operational fluctuations. 3. When the plant is at rest, and there are no large-scale leaks in the water wall coils, the slag layer is generally not intentionally disrupted. Therefore, during the restart phase, there is no need to consider replenishing slag. Conversely, if the slag layer is damaged before shutdown due to operations, maintenance, or replacement, care must be taken to maintain it for a period of time and replenish the slag when the pressure is raised to around 2.4 MPa; however, loading operations should be carried out only after the temperature measurement points in the gasification chamber have stabilized and reached equilibrium (i.e., after dynamic equilibrium of the slag layer is established).

The heating surface of the water wall is coated with an SIC refractory lining (it’s been some time since I last checked, so I can’t remember the exact thickness). At the beginning of operation of the gasifier, this lining affects the heat transfer coefficient of the membrane wall and leads to the formation of a slag layer; eventually, a balance is established between the thickness of the solid slag layer and that of the liquid slag layer. Therefore, in my opinion, there is no need to deliberately allow slag to accumulate on the water wall during operation. If there are concerns regarding an unsatisfactory level of slag accumulation, it is possible to increase the thickness of the refractory lining during the initial drying phase of the gasifier.