As the state pays more attention to and invests more in environmental protection industry, New flue gas desulfurization projects are increasing rapidly, and correspondingly flue gas desulfurization gypsum is also growing rapidly. According to statistics, nearly 10 million tons of desulfurization gypsum were produced nationwide in 2010. The development of the domestic desulfurization gypsum market provides an excellent opportunity, and at the same time it also brings difficulties to power companies simply selling digested desulfurization gypsum. 

Process Necessity 
After vacuum dehydration, desulfurized gypsum in power plants often contains 10%-15% free water, which is wet and fine powder. If it is directly used in cement production, blockage, caking, feeding and metering difficulties will occur. As most cement plant now use natural gypsum as cement retarder, Its production equipment is designed according to massive gypsum raw materials in the early stage. If the above-mentioned special physical properties of desulfurized gypsum are not pretreated, caking, scale accumulation, material blocking, dust pollution and other phenomena will inevitably occur in all links of cement production process from transportation, storage, batching to feeding, resulting in limited use of cement enterprises. The solution to this technical problem is to adopt desulfurization gypsum granulation technology. 

Process Overview 
The granulation technology we have chosen mainly includes two major technological processes, dehydration and granulation. 

There are two kinds of granulation technologies in China: wet granulation and dry granulation. Wet granulation is to pre-process wet desulfurized gypsum into lumps or spheres, but the initial strength of spheres in this granulation process is often relatively low, and when drying later, the drying efficiency and heat energy utilization are relatively low. Dry granulation is to remove part of free water before extrusion granulation. According to the actual operation of some domestic technologies that dry desulfurized gypsum and then use dry roller pressing to pelletize, the pelletized desulfurized gypsum balls have higher strength and can be directly used as retarder on the existing production lines of cement enterprises instead of natural gypsum. The drying efficiency and heat energy utilization of the dry granulation process are relatively high, and the strength of the pellets made can meet the requirements of transportation and cement production. 

Desulfurization gypsum free water is dried and dehydrated to between 3% and 5%, and then extruded and granulated, i.e. Dried before granulation. The thermal energy used for drying adopts the steam potential of power plant boilers. Supersaturated steam from the steam pipeline of the power plant enters the rotating steam joint of the steam rotary dryer, enters the heating pipe through the steam chamber, and through heat exchange between the heating pipe wall and materials, the condensed condensed water flows to the low end under the action of gravity, and then enters the condensing pipe and drain valve to the condensing pool. 

The original desulfurized gypsum is fed into the steam rotary dryer by the feeder. The main body of the steam rotary dryer is a rotary cylinder, and 3-5 turns of heating pipes penetrating through the dryer are arranged in concentric circles in the barrel. Steam is introduced into the pipes to provide heat required for drying and calcination. With the rotation of the cylinder body, the material is lifted and sprinkled by the heating pipe, and the material is dried by various heat exchange modes such as convection, conduction and radiation, and moves from the higher end to the lower end by means of the inclination of the dryer, and finally is discharged by the discharge air lock valve at the tail of the dryer. The moisture removed by drying is carried by the moisture discharge carrier gas and discharged out of the dryer under the action of the fan. After heat exchange, the steam becomes condensed water, which is used for heating. The dried retarder powder is sent into the retarder powder bin through a screw conveyor and a hoist. 

After the retarder powder is fed into the retarder powder bin, the retarder powder is naturally cooled, compressed air is introduced into the bottom gas plate of the bin, the bottom discharge valve of the bin is opened, and the retarder powder is fed into the feed port of the granulator through a tubular screw conveyor. The powder is made into peach core retarder by strong extrusion of two rollers of a double-roll granulator, and is discharged out of the granulator by gravity, and is sent to the silo for storage by a belt conveyor and a hoist.