Project background:
In May 2009, the Shanghai City Government forwarded the "Implementation Plan for Comprehensive Utilization and Safe Disposal of Desulfurized Gypsum in Shanghai City" formulated by the Municipal Development and Reform Commission with Shanghai Government Office (2009) No. 56. The "Plan" requires the start of the construction of two demonstration lines of 100,000 tons of building gypsum powder with an annual output of 100,000 tons using desulfurization gypsum from power plants in Shanghai in 2009; One of them is a 100,000-ton construction gypsum powder demonstration line for Huaneng Shanghai Shidongkou Plant No. 1, which is a supporting demonstration line for energy conservation and environmental protection for the World Expo Year of the Shanghai City Government.

Project tasks:
Solve the problem of comprehensive utilization of gypsum (CaSO4.2H2O), a by-product of flue gas desulfurization in power plants, and use the waste heat of auxiliary steam in power plants to convert desulfurized gypsum into renewable resources (construction gypsum powder, cement retarder), which not only improves comprehensive utilization rate, saves social resources, but also improves the urban environment.

Introduction to gypsum drying and calcination process:
At present, desulfurized gypsum is mainly used in the following fields after treatment: (1) production of building gypsum powder-β hemihydrate gypsum (β-CaSO4·0.5H2O);(2) cement retarder-the desulfurized gypsum is used to dry free water on the surface to about 2%. Among them, beta hemihydrate gypsum is used in the largest amount and can be made into gypsum boards, gypsum blocks, gypsum ceilings, etc.
At present, the main technical solutions used in the desulfurized gypsum drying and calcination line include:1. High-temperature and short-term flash evaporation process. Lafarge, the world's largest gypsum board manufacturer, uses natural gas as energy and 600 ° C high-temperature gas to desulfurize gypsum. Short-term calcination into beta hemihydrate gypsum, with a residence time of about 6 seconds. 2. The one-step process of low-temperature and long-term drying and calcination generally uses steam as the heat source, and uses the latent heat released by the steam to dry and calcined desulfurized gypsum. The drying and calcination processes are completed in one equipment, and the residence time is generally 15.~More than 20 minutes. Rotary kiln technology is mainly used, such as Jason Company, the world's third largest gypsum board manufacturer, adopts this technology. 3. The two-step process of low-temperature long-term drying and calcination uses steam as the heat source to divide drying and calcination into two stages, which are completed in different equipment. Two products can be produced, one cement retarder that only goes through the drying process, and the other is building gypsum powder (β-CaSO4·0.5H2O) that goes through the drying and calcination process. The main process includes the pilot production line of Side dryer + fluidized calciner of Huaneng Yangluo Power Plant. However, due to the large fluctuations in the surface moisture of desulfurized gypsum and the strong adhesion of gypsum, the heat exchange effect of the Side dryer is poor, and the system consumes energy. Due to the large energy, large-scale production and application cannot be applied.
Taking advantage of the current situation that the power plant has a large amount of auxiliary steam waste heat, combined with the characteristics of large fluctuations in moisture content and strong adhesion of desulfurized gypsum, the experience and lessons of the gypsum powder production line of Huaneng Yangluo Power Plant were carefully summarized (the materials in the drying process have poor fluidity and adhesion are strong). This project proposes and applies a step-by-step desulfurization gypsum drying and calcination process for the first time, that is, the drying process adopts a secondary drying system + a primary calcination process system. The advantages of the system are: adapting to the large fluctuations in raw material moisture content, stable product quality, using power plant auxiliary steam as the heat source, and utilizing energy step by step to achieve low-temperature drying and low-temperature calcination. The system energy consumption is low, and two products can be produced at the same time (1. Cement retarder;2β hemihydrate gypsum).
Introduction to step-by-step drying and calcination process:
Drying process: The first stage: double blade dryer, the second stage: tray dryer. Calcination process: fluidized calciner.
Process flow: The desulfurized gypsum dehydrated by the vacuum belt conveyor is transported to the raw material warehouse for storage by the belt conveyor, poured into the upper hopper by a forklift, measured by the belt, and sent to the drying system; after passing through a twin-blade and disc dryer, it is transported to the fluidized bed furnace for calcination, which can be transported to the bin pump through a modified mill or direct screw, and pneumatically transported to the silo for storage; the silo can be loaded on a bulk machine or packed and taken out by a packaging machine.
Steam energy is utilized in steps. High-pressure steam is first used in the calcination process, and the saturated water after calcination is aerated again and used as the heat source for drying. Take out water in the drainage tank (as domestic hot water).