What are the uses of periodic blowdown expansion tanks and continuous blowdown expansion tanks?

Both make use of secondary steam and waste heat water as heat sources, enabling the recovery of some of the heat lost through continuous boiler blowdown and thereby improving boiler efficiency. The difference lies between fixed-discharge and continuous-discharge; continuous-discharge and fixed-discharge are abbreviations for discharge on a continuous basis and discharge at regular intervals, respectively. Waste discharge is an operation carried out to ensure that the boiler water meets certain standards, to prevent scaling, to maintain steam quality, and to avoid foaming in the steam. There are two meanings to \"serial arrangement\" and \"fixed arrangement\"; one refers to the operation ； Secondly, in terms of process design, it is commonly used to refer to the continuous blowdown expansion vessel and the periodic blowdown expansion vessel as \"continuous blowdown\" and \"periodic blowdown\" respectively. When a boiler is started for the first time, all the water in it is new; during operation, a significant amount of wastewater that does not meet the required standards is generated. Therefore, a boiler drain system is installed to remove this wastewater. After the boiler has been operating normally for a while, it is only necessary to add water periodically; since there is less wastewater of poor quality, a regular drainage method is used to discharge it at set intervals. Continuous discharge constitutes a type of surface discharge; it involves releasing boiler water with a high salt concentration from the surface, thereby keeping the salt content of the boiler water within acceptable limits. This helps to reduce boiler water expansion and foaming, as well as the humidity and salt content of the steam, and it can also minimize scaling in the evaporation tubes ； Regular sludge discharge is primarily aimed at removing the sediment formed in the water due to the hardness salts generated after chemical addition.

We carry out regular discharge three times a week, discharging 10% of the liquid level each time； The discharge volume of continuous wastewater discharge is controlled at 1%

What materials are generally used for expansion vessels?