Limestone powder selection millφ3.0×11mExploration of Stone Powder Grinding System Applications

Jiangsu Jidingda Environmental Protection Engineering Co., Ltd. - Wang Hua
     Hohhot Siprun Environmental Protection Co., Ltd. is a company that produces stone powder. In 2018, their powder grinding station established a stone powder production line. However, due to an incorrect selection of the classifier, frequent production failures occurred, and the produced stone powder failed to meet desulfurization requirements. After our company's technical reform, we successfully resolved the production difficulties for the powder grinding station. As a result, the company has decided to add another 350,000 tons per year stone powder production line. Our company is responsible for the full process design and equipment supply (except for the mill). The production line designed and supplied by our company has now been put into operation. The following is an introduction to the usage of our company's stone powder classifier:

Section 1: Stone Powder Performance and配套 Mill Selection Technology

1.1The poor fluidity of desulfurization stone powder often leads to clogging accidents due to easy accumulation of dust in the system. The low fluidity of materials demands a higher grading performance from the classifier. Because of the poor fluidity of stone powder, the friction coefficient increases, necessitating a strong throwing force to expel the powder after entering the classifier. To address this characteristic, our company's designed and produced stone powder classifier has modified the internal撒料 system, adding a material guidance zone and a double-layer撒料 system. The strong throwing performance allows the material to move towards the classification area in a jet-like manner, ensuring that the material undergoes wind cleaning before participating in the classifier's separation, thus maximizing the classifier's separation efficiency. The internal material collector and discharge pipeline of the classifier are both designed with large angles to prevent dust accumulation and to prevent clogging caused by excessive moisture in the stone powder.

1.2The stone powder used for desulfurization has high requirements for fineness and particle gradation uniformity. The stone powder classifier, catering to this characteristic, utilizes high-performance grading rotors and labyrinth-style sealing to ensure the adjustment effect of the finished product's fineness and the uniformity of the finished product's particles.

Section II: Main Production Process
    The company's mill specifications are φ3.0×11m, and it has chosen to use Jidingda's E-type stone powder separator and φ3.0×11m mill to form a closed-loop powder grinding system. After being weighed by a belt scale, the material is conveyed into the mill by a belt conveyor. The material exiting the mill is sent to the separator via a bucket elevator for classification. Coarse powder is returned to the mill via an air chute, while fine powder is transported to storage after being elevated through an air chute.
III. Technical Measures
Due to the closed-circuit grinding system being equipped with a stone powder separator, the material flow rate within the system needs to be accelerated, thus placing higher demands on the grinding mill's grinding efficiency and internal conditions. In response to this technical requirement, both parties' technical staff, based on the characteristics of the closed-circuit mill and considering the properties of the stone powder, have adopted the following technical measures for the grinding system:

3.1The mill employs a new two-layer separator baffle.
The separator plate plays a role in dividing compartments, controlling material discharge, and defining functional areas within the mill. If properly designed, it can enhance the mill's grinding efficiency. Therefore, we have adopted a forced feed double-sieve separator plate developed by Jidingda Company, which increases the material feeding power of the mill separator plate from a single lateral stacking pressure to two forces: gravity and lateral stacking pressure. This significantly accelerates the flow rate of materials inside the mill, making it particularly suitable for closed-circuit grinding. We have divided the mill into three compartments: one for crushing, one for coarse grinding, and one for fine grinding. On the φ3.0×11m mill, we use this type of separator plate, where the separator plate between the first and second compartments is a new double-sieve separator plate. The sieve gaps of the separator plate between the first and second compartments are appropriately widened to increase the opening rate and enhance ventilation. The sieve gaps in the separator plate between the first and second compartments are designed to be 6CM. When the material in the first compartment is crushed by steel balls into particles smaller than 6CM, the forced feeding device of the separator plate comes into play, promptly discharging particles smaller than 6CM to the second compartment. Larger particles are returned to the first compartment through a return feeder to be further crushed until they are smaller than 6CM, effectively reducing the coarse grinding pressure in the second compartment. The separator plate between the second and third compartments is also a strong double-sieve separator plate. However, the sieve gaps in the separator plate are designed to be 3CM. Following the same theory, this prevents coarse particles from entering the third compartment, maximizing the fine grinding function of the third compartment. This effectively controls the fineness of the product out of the mill, reduces the system's circulating load, and further improves the grinding efficiency.
3.2 Optimizing Ball Mill's Forge Grade Distribution
We have carefully studied the abrasiveness and moisture content of the stone, establishing reasonable ball diameters and appropriate filling rates. Therefore, based on the particle size characteristics of the stone to be ground, we have selected an appropriate average ball diameter to minimize the diameter of the grinding media in the medium and fine grinding bins. On this basis, we have also appropriately increased the load of the mill.
3.3 Utilizing state-of-the-art baghouse dust collectors to enhance internal mill ventilation
It is widely known that the ventilation condition of a mill directly affects its powder grinding efficiency. Insufficient air volume and pressure in the mill deduster can lead to poor internal ventilation, dust emissions from the mill head, severe over-grinding, and the inability to expel moisture from the mill in a timely manner, resulting in frequent occurrences of paste balling and grate clogging. This ultimately reduces the mill's output. Our company, recognizing the poor fluidity, high specific gravity, and high friction coefficient of stone powder, has chosen the high-efficiency 96-6 pulse jet dust collector from our Ji dingda company. We have also increased the air pressure appropriately. This dust collector retains the high efficiency of pulse cleaning while also employing a separate chamber structure, effectively preventing secondary dust adsorption. This significantly reduces the resistance in the dust collection system, enhancing the mill's ventilation performance.
Four: Production Effect
Upon the startup of the stone powder production line, thanks to the high efficiency of the JDD stone powder separator and the reasonable grading of the mill, the output has been increased from the designed 45T/H to 50T/H. The fineness is controlled above 325 mesh and remains stable, saving a significant amount of electricity for Suprun Company. The quality of the stone powder produced at the powder mill is excellent, and it has been exported to other power plants, where demand exceeds supply, creating substantial economic benefits for Suprun. The planning for the third production line is currently in progress, and our company will actively apply our new technologies and achievements to the third line to create greater economic and social benefits for our clients.