I. Application of GYLM Generalized Vertical Mill in Coal Powder Preparation 1. Characteristics of Coal Grinding: ● Due to differences in coal quality and boiler conditions, the particle size requirements for coal vary. Generally, a passing rate of around 90% for 200 mesh is required, and the grinding equipment must be able to adjust the fineness. ● Coal generally contains more than 15% moisture, with lignite reaching as high as 45%. Therefore, the grinding equipment must be suitable for high moisture content and ideally, it should be able to dry the material simultaneously with grinding, eliminating the need for a separate dryer and additional drying process. ● Coal contains flammable volatile moisture, and given that coal itself is combustible, flame-retardant and explosion-proof measures are necessary during grinding. ● Coal contains hard, difficult-to-grind impurities, requiring the grinding process to accommodate these hard impurities. ● The ground dry powder must be suitable for pneumatic conveying. Currently, power plants mostly use ball mills and Raymond mills for coal grinding. These are familiar to most and will not be elaborated upon here. Many power plants, for energy conservation and environmental protection purposes, have selected or upgraded to more advanced vertical mill (also known as medium-speed mill) systems for pulverized coal preparation. A vertical mill coal grinding system generally consists of a vertical mill main unit, a fine powder collection device, a blower, and pipelines. The working process involves raw coal entering the vertical mill for grinding, then being carried by air (or hot air) to a classifier. Fine powder is collected by the fine powder collection device and then sent to a pulverized coal silo or pulverized coal conveying device. The GYLM (Glass Mill) vertical mill is a type of vertical mill, and its system layout and characteristics are adaptable to the aforementioned pulverized coal mills. The following section focuses on the differences between it and a general vertical mill. [b]2. Working Principle and Process of GYLM Generalized Vertical Mill[/b] Vertical mills, commonly used in industry, are a type of roller mill. Their basic principle is to place the material to be ground between the grinding rollers and the grinding disc, utilizing mechanical forces such as spring force, hydraulic pressure, or centrifugal force generated by rotation to crush and pulverize it. This type of grinding equipment, which utilizes the principle of material bed extrusion crushing, has advantages over grinding equipment that utilizes shearing and impact forces, such as higher grinding efficiency, lower power consumption, and less wear. There are many types of vertical mills; a typical example is the widely used MPS vertical mill, where the grinding disc rotates while the grinding rollers remain relatively stationary (do not revolve around a vertical line). The MPS vertical mill mainly consists of a feeding device, grinding roller device, hydraulic device, grinding disc, vertical mill reducer, classifying device, and base. The reducer is installed on the ground, and the grinding disc is mounted on it. The motor drives the reducer, causing the grinding disc to rotate around a vertical line from the ground. The grinding rollers, under the hydraulic pressure generated by the hydraulic device, crush the material placed on the grinding disc. The grinding rollers do not revolve around a vertical line from the ground, but rotate around their own axes under the resistance of the material. The ground material is carried by an upward airflow in the annular area at the edge of the grinding disc to the classifying device located above. The fine powder passing through the classifying device is discharged from the upper discharge pipe to the fine powder collection device. Because the grinding disc is directly mounted on the reducer, the grinding force is entirely borne by the reducer. The reducer must withstand the axial force from above, as well as the bending moment caused by uneven force on the grinding disc and the torque that drives the grinding disc to rotate. Therefore, the vertical mill reducer has high performance requirements, a complex structure, is difficult to manufacture, and is expensive, generally accounting for about 1/3 of the total machine cost. The GYLM general-purpose vertical mill is manufactured using patented technologies ZL200520050036.7 and ZL200510031126.6 from Hunan Guangyi Technology Co., Ltd. Its greatest innovation lies in overcoming the aforementioned defects of existing vertical mills. The grinding disc directly transmits various grinding forces to the equipment foundation via a rotary bearing. The reduction gear only needs to bear the torque that drives the grinding disc to rotate. The machine has a simple structure, reliable operation, and low cost. The GYLM general-purpose vertical mill is characterized by a rotary bearing and bearing support. The grinding disc is mounted on the bearing support via the rotary bearing, and the bearing support is directly mounted on the ground. The weight of the grinding disc, the grinding force applied to the grinding disc by the grinding rollers, and the deflection torque caused by uneven force are all transmitted to the rotary bearing, then to the bearing support, and finally to the foundation. The reduction gear is directly mounted on the ground, maintaining a fixed position relative to the rotary bearing. Thus, the reduction gear only transmits torque and does not need to bear the grinding normal pressure and tilting torque. [b]3. Key Advantages of GYLM Generalized Vertical Mill[/b] Compared to ordinary vertical mills, the GYLM generalized vertical mill has the following key advantages: Superior Structure and Lower Investment Compared to conventional vertical mills, the generalized vertical mill has a significantly improved structure: it adopts a simple and reliable reducer, improving reliability and facilitating maintenance; and it uses thin oil circulating lubrication to improve bearing life. Good Wear Resistance and Long Life of Wear Parts Wear is related to three factors: grinding force, grinding media material, and grinding method. Of these three factors, the grinding force is determined by the material crushing ratio, and generally, the grinding effect cannot be reduced by decreasing the grinding force. The material of the grinding media is an important adjustable factor. Guangyi Company has expertise in the research and application of wear-resistant materials. Guangyi vertical mills use high-chromium high-alloy steel to manufacture grinding rollers and wear-resistant liners. Its crystal phase structure consists of a martensitic body with embedded high-wear-resistant carbide (WC, TiC, etc.) hard phases. In addition to containing more than 20% Cr, it also contains valuable alloying elements such as W, V, Ti, Mo, Mn, and Cu, which makes the wear-resistant parts have a long service life. For highly abrasive materials such as manganese ore, the service life of grinding rollers and wear-resistant liners can also be more than six months. Among the grinding methods, only extrusion crushing has the highest efficiency and the least media wear. An important point in designing the grinding working chamber is to use grinding rollers with special cross-sections to reduce sliding wear and extend the service life of vulnerable parts. Guangyi vertical mills have fully achieved this. Long air ring life: The use of dynamic air rings reduces air resistance, makes airflow uniform, and reduces wear. Compared with static air rings, the service life of the air ring is more than twice that of static air rings. **II. Application of GY Generalized Mill in Desulfurization Limestone Grinding** **1. Working Principle of GY Generalized Mill** The GY generalized mill has a vertical structure, with the main shaft perpendicular to the ground. It consists of a feed inlet, transmission device (including rotor components), machine body, grinding working chamber, and discharge outlet. A rocker arm crushing roller is mounted on the main shaft via a disc. The rocker arm shaft and the rocker arm maintain a relationship of synchronous revolution around the main shaft and mutual rotation. During operation, the transmission device rotates the main shaft, which drives the feed disc, disc, rocker arm, and other rotor components to rotate synchronously. After entering from the top, the material is spread onto the inner wall of the machine body by the feed disc, and then falls between the wear-resistant liner and the crushing roller under gravity. The crushing roller crushes the material under the action of centrifugal force and spring force. After being repeatedly crushed and pulverized, the material is discharged from the bottom discharge outlet. Therefore, the crushing ratio is large, and the output is uniform. Meanwhile, due to the adjustable gap between the grinding roller and the wear-resistant liner, the relative sliding between the material and the wear-resistant material is small, resulting in a long service life of vulnerable parts, up to 1.5 years or more, which is unmatched by other pre-grinding equipment. [b]2. Main advantages of the GY generalized mill:[/b] Energy saving: Low power consumption, only about 50% of that of a Raymond mill or ball mill. Environmental protection: No dust, low noise, saving environmental protection costs. Long service life of vulnerable parts: Wear-resistant parts can last up to two years; the internal lubrication of the mill with thin oil circulation can improve bearing life and provide cooling and chip removal functions. [b]3. Application of the GY generalized mill in limestone grinding for wet desulfurization[/b] Currently, wet desulfurization devices require limestone powder with a fineness of approximately -325 mesh (90%), employing both dry and wet grinding methods. Dry grinding uses vertical mills and dry ball mills, while wet grinding uses wet ball mills to grind the slurry, which is then pumped into the absorption tower. The GY GY generalized mill adopts dry grinding, and its grinding system consists of three pieces of equipment: the generalized mill main unit, the classifier, and the bucket elevator (see Appendix 1). The working process is as follows: after the material is ground by the generalized mill, it is lifted by the elevator to the classifier. The qualified fine powder selected by the classifier is directly stored for later use, while the coarse powder that does not meet the fineness requirements is fed back into the mill for regrinding via a chute. Its system features external classification, high classification efficiency, and no need for pneumatic lifting and conveying, resulting in energy consumption far lower than vertical mills and ball mills. The system is simple and reliable in operation. Our company has extensive experience in the design, equipment supply, and installation of gypsum powder production lines for the comprehensive utilization of gypsum, including natural gypsum, phosphogypsum, and the aforementioned desulfurized gypsum. We can undertake turnkey projects for desulfurized gypsum powder production lines. [b]4. Application of the Generalized Mill in the Limestone Powder Preparation System for Circulating Fluidized Bed Boiler Desulfurization[/b] Circulating fluidized bed boiler desulfurization, characterized by low power plant investment and quick results, has gained increasingly widespread application. Its limestone powder preparation system generally maintains a uniform limestone particle size distribution. Below is a brief introduction using our company's application example in the limestone powder preparation system of the Meixian Heshuyuan Power Plant desulfurization project of Guangdong Baolihua Power Co., Ltd. This limestone powder preparation system was designed by Guangdong Electric Power Design Institute, and the key equipment—the limestone mill—uses the GY-1250 generalized mill. The table below lists its main technical parameters. Limestone Mill (GY-1250 Generalized Mill) Technical Parameters: [table][tr][td=1,1,48]Serial Number[/td][td=1,1,192]Item[/td][td=1,1,60]Unit[/td][td=1,1,300]Specifications or Values[/td][/tr][tr][td=1,1,48]1[/td][td=1,1,192]Equipment Model[/td][td=1,1,60][/td][td=1,1,300]GY-1250[/td][/tr][tr][td=1,1,48]2[/td][td=1,1,192]Equipment Capacity[/td][td=1,1,60]t 80-100 (throughput), 35-45 (finished product output) 3 Equipment dimensions (mm): 2640×3899 4 Feed size (mm): 35 35 300 (td=1,1,300) 5. Discharge particle size (after grading) mm D50 = 450µm dmax = 1.5mm Lifespan of liner plates: 8 hours, 13000 hours, 9 hours, 11192 hours, 13000 hours. Due to its structural characteristics, the GY general-purpose mill has a low rotational speed (80-90 rpm), allowing for control of fine powder content, long service life of wearing parts, high operational reliability, low power consumption, and small footprint, making it an ideal grinding equipment for desulfurized limestone powder. [b]III. Application of General-Purpose Mills in Fly Ash Grinding and Sorting[/b] After sorting, the coarse fly ash must be ground to at least reach the particle size requirement of grade II ash to have commercial value. Currently, ball mills are mainly used for grinding coarse fly ash. In 2003, our company initiated a project with the Hunan Provincial Economic Commission to study the grinding of coarse fly ash and conducted industrial trials using general-purpose mills such as GY and GL. Because fly ash has good fluidity, low moisture content, fine initial particle size, high microhardness, and high abrasion, using a ball mill with microspheres and microsegments for open-circuit grinding or using a classifier to form a closed-circuit process is a feasible solution at present, but it suffers from high power consumption and high steel consumption. The following is a brief description of the working process of a typical GYLM generalized vertical mill system integrating grinding and sorting of fly ash. Raw fly ash is metered from the raw ash silo by an electronic screw scale and conveyed to the mill head hopper. It is then evenly fed into the GYLM generalized vertical mill via a star feeder for grinding. Selected air enters the mill cavity from the bottom, carrying the ground fly ash to the classifying device at the top of the mill. The classifying device separates the gas-solid mixture that meets the fineness requirements into a high-concentration air-box pulse dust collector (i.e., a bag filter dust collector), separating the product from the gas. The finished product is discharged by a screw conveyor into a bucket elevator and enters the powder silo. Adjusting the speed of the classifying device allows for convenient adjustment of the product fineness. From a technical and equipment perspective, the aforementioned GYLM generalized vertical mill is the most suitable grinding equipment. However, equipment modifications must be made to address the specific grinding characteristics of fly ash, and there are also technical issues that must be resolved when using the GYLM generalized mill closed-circuit system.