Thread Content
1. Ash and slag factors: Due to the complex composition of waste, the deposition of ash and slag on the pipe walls occurs through two distinct processes. One is the formation of an initial deposition layer, which is a thin layer of ash with high chemical activity and is composed of very small ash particles. It is primarily formed by the condensation of volatile ash components on the water-cooled walls and the deposition due to the thermal migration of fine particles, resulting in a very strong coating generated through adhesion and chemical reactions with the tubes. The initial deposition layer contains high levels of alkali and alkaline earth metal sulfates; these tiny particles adhere to the furnace walls. The initial deposition layer has good thermal insulation properties, and its formation causes the temperature of the outer surface of the tube wall to rise. Another deposition process involves larger ash particles impacting the initial deposit layer on the tube wall under the effect of inertial forces; when the initial deposit layer is viscous, it captures the ash particles carried by these inertial forces, resulting in a rapid increase in the thickness of the slag layer. Since the initial deposition layer is mainly caused by the condensation of volatile ash components and the thermal migration of fine particles, it is difficult to prevent its formation during actual operation. The main factor causing a rapid increase in slag formation inside the furnace and posing a threat to the safe operation of the boiler is inertial deposition. The adhesion of ash particles transported by inertia to the initial deposition layer depends not only on the properties of that initial layer but also on the temperature of the impacting ash particles. When the temperature of the impacting ash particles is very high, causing them to be in a molten liquid state, adhesion occurs easily, thereby accelerating the slagging process. The thickness of the ash layer is usually uneven, and it is related to the structure of the furnace, the location of the combustion center, the aerodynamic properties, the temperature characteristics of the furnace, as well as the physicochemical properties of the fuel. At different locations within the furnace, the thickness and structure of the ash will vary significantly. In terms of the actual ash fusion characteristics of waste fly ash, its deformation, softening, and melting temperatures are significantly lower than those of coal ash; it begins to soften at around 1050°C, which is about 200°C lower than that of coal ash. Tests have shown that there is little difference between these three temperature points, with no clear boundary between them. It can be said that the inherent properties of waste itself determine the tendency of waste incinerators to clog. 2. Furnace temperature: To ensure thorough decomposition of dioxins in the flue gases and to allow the boiler to handle higher loads, the furnace temperature of the boiler is generally kept around 1000°C during operation; in some cases it can even reach 1100°C. The temperature at the center of the flame is even higher, and the fly ash may already be at a temperature where it becomes softened or even melted. This situation poses a risk of coking in the boiler and is one of the main factors contributing to this issue. During subsequent operations, although strict control is exercised over the furnace temperature, certain deviations occur in the accuracy of the temperature measurements due to the accumulation of coke and ash at those measurement points. 3. Boiler structure: To ensure that waste with a low calorific value can ignite and burn more easily, the incinerator is designed with an insulated combustion system. Apart from the wall cooling air provided to protect the furnace walls as necessary, no heating surfaces are included in the design of the incinerator. At the same time, in order to guide the flue gas properly (similar to the flame deflection angle in coal-fired boilers) and to dry the waste material entering the furnace more effectively, front and rear arches have been designed at the flue gas outlet of the incinerator. This creates a structure similar to a cold ash hopper at the outlet of the incinerator. On one hand, during boiler operation at rated load, all of the boiler’s heat load is transferred through this area to the waste heat boiler; as a result, the heat load at this throat section reaches its maximum value. On the other hand, after passing through this throat, the flue gas expands, causing its velocity to decrease as it exits the furnace chamber. Some of the dust in the flue gas settles down, with most of it flowing downward along the walls of the furnace. The angle of the front arch creates significant resistance to this downward flow of dust, causing it to remain attached to the walls of the arch, where it fuses with new dust particles. The dust on the inner layers then cools and solidifies. Due to the unstable combustion characteristics of waste incinerators, when the boiler load is unstable, it is easier for layered masses of coke to form. At high loads and high flue gas temperatures, these loose masses of coke may melt deeply and fall off under their own weight, or they may solidify again into more compact masses when the furnace temperature drops once more. In addition, the fly ash in the ash hoppers of the second and third flues returns to the furnace, and carried by the primary air, it enters the flue gas once again, increasing the dust content in the flue gas. 4. Air volume: During operation, the amount of air supplied was significantly less than what was required for the boiler to function; the secondary fan was not in use, as can be seen from the high C0 level detected in subsequent flue gas tests. Due to insufficient oxygen supply under conditions of oxygen-deficient combustion, which creates a reducing or semi-reducing atmosphere, the melting point of inorganic ash and slag is further reduced, leading to their melting. Meanwhile, during oxygen-deficient combustion, especially when the secondary fan is not in operation, some unburned particles in the waste can easily settle back above the throat area after passing through the outlet of the incinerator; due to their heavy weight, they cause slag formation and coking. Furthermore, without the secondary air in operation, no disturbance can be created at the outlet throat of the incinerator, which would reduce the deposition of fly ash in that area. 5. Calorific value of waste: Changes in the calorific value of waste have a significant impact on the stable operation of incinerators; therefore, it is crucial to ensure proper stacking of waste in the storage areas, as well as proper mixing and feeding of the waste into the furnace, from the very beginning. When the automatic system is not in use, requirements and guidelines for the stacking, mixing, and feeding of waste are established primarily through intuitive qualitative methods, thereby forming a fixed cyclic operation pattern. Once the crane is fully automated, it is possible to increase the amount of waste mixed together, as well as the quality of the waste pile. Furthermore, in waste bin management, it is necessary to gain experience as the climate and seasons change, and make timely adjustments. The Zs-1021 high-temperature resistant, sealed anti-oxidation coating uses inorganic-organic silicone resin as its film-forming substance, with a certain amount of nano-graphite flakes, nano-alumina powder, ultra-fine rare earth powders, etc., added to it. The coating is environmentally friendly, easy to apply, requires little treatment of the substrate, and no additional coatings are needed for a single application. The cured coating has a high temperature resistance, capable of withstanding temperatures up to 1200°C. It maintains good stability when used at high temperatures for extended periods, features strong adhesion so as not to peel or flake off, exhibits excellent resistance to acids and alkalis, has good wear resistance, and high impact strength. It can be used for anti-corrosion and anti-coking of boiler water walls. ZS-1041 flue gas anti-corrosion coating uses an interpenetrating network polymer based on inorganic polymers as its film-forming substance. A silicon-containing inorganic polymer forms the main chain in this solution, while organic polymer-modified resins are grafted at high temperatures, resulting in a multiblock grafted inorganic-organic chelating polymer with an alternating structure. This coating features good film-forming properties, strong adhesion, a smooth surface that is self-cleaning, high temperature resistance, and a dense film structure that reduces dielectric loss. The main components of the pigments are inorganic corrosion-resistant and wear-resistant materials such as nano-silicon powder, silicon carbide, boron nitride, fine-grained aluminum oxide, graphite, ultra-fine zinc oxide, titanium oxide, ceramic microspheres, and zirconium oxide powder. These materials are used to create wear-resistant ceramic functional fillers under high-temperature sealing conditions, thereby enhancing the hardness, wear resistance, corrosion resistance, high-temperature tolerance, impact resistance, and good ductility of the coating. Suitable for various equipment such as flues, chimneys, desulfurization and denitration systems, dust collectors, exhaust gas pipelines, waste heat recovery systems, heat exchangers, economizers, and air preheaters.