Discussion on Deep Processing Technology of Lime Industry

2021-05-07

Summary:1. The Status Quo And Development Of Domestic Lime Deep ProcessingChina's annual lime output is over 300 million tons, accounting for more than half of the

1. The Status Quo And Development Of Domestic Lime Deep Processing

China's annual lime output is over 300 million tons, accounting for more than half of the world's total. But compared with the world's lime industry, especially the calcination technology, production environment and deep processing of developed countries, there is still a certain gap. The quality of most domestic limestone is not inferior to that of foreign countries, and some foreign deep-processing companies purchase lime from China and sell them back to China after deep processing, and the price increases several times. This shows that my country's lime deep processing technology is relatively backward and needs to be developed.

At present, lime deep processing products include: nanometer calcium, light calcium, calcium hydroxide, ash calcium powder, desiccant, food calcium, medical calcium, calcium oxide powder and lime products with high activity, high content and high specific surface area. In recent years, products for environmental protection have developed rapidly, and have developed from extensive processing to refinement, and from scattered small chaos to large-scale development. Therefore, the development of high-end products for deep processing of lime is a trend in the development of China's lime industry.

2. Requirements For Raw Material Lime

Deep-processed lime is different from other uses, such as metallurgical ash and road ash. The higher its calcium oxide content, the better, and the lower its silicon, magnesium and other heavy metal content, the better. Because the content of deep-processed products is the main factor determining the price. The calcining process is also different, its cost has also changed, and the output and energy consumption have also changed. The cost of calcining limestone with high calcium content is relatively low, and the price of processed products will be higher. It is generally required that the calcium content in the limestone should be above 54%. Because the content of limestone in the north and south is quite different from that of the whole country, the north is high and the north is low. Therefore, the northern limestone is mainly metallurgical lime and highway ash. Generally, high-end deep processing is mainly in the south. However, the quality of limestone in the same area in the southern regions is also quite different. Therefore, a lime company is very important for the quality of limestone and the market in this area.

Because the proportion of deep-processed lime must be overburned (older) during the calcination process, the requirements for raw materials are particularly high. ①The size of the limestone block should be uniform, ②The silicon content should not be too high, ③The limestone should be washed with water, ④ Coal must have low volatility, and calcination must be run dynamically. The above five points are for the purpose of deep processing of lime to achieve uniform calcination and not too much raw calcination. Increase the content of the product. In particular, the production of high-end products must have good raw materials and good calcining in order to have higher added value. The positioning of products in the market is the key to determining the choice of equipment.

3. Calcium Oxide Production

Lime is used in iron and steel, pesticides, medicine, desiccant, food tanning and alcohol dehydration. Calcium oxide has a wide range of uses.

Calcium oxide production equipment mainly includes: ball mill, superfine mill, Raymond mill, vertical mill, jet mill, etc. These models have their own characteristics. According to a company's main product and market to position and choose which equipment.

Ball mill: an extensive product, featuring high output, low loss, and simple operation. However, the noise exceeds the standard, which takes up a lot of space and is expensive. Generally, environmental protection fails, and the adaptability is below 200 mesh. The production process will also reduce the calcium oxide content.

Ring roller ultra-fine grinding: crushing and grinding to meet general ultra-fine requirements. Features: small output of single machine. Suitable for deep processing of general requirements. The fineness is between 800 and 1200 mesh.

Raymond mill: The most traditional mill, which belongs to the rough grinding equipment. It is the most cost-effective device among many devices.

(1) High Reliability

(New technology) Plum blossom frame and vertical pendulum grinding roller device, advanced and reasonable structure. The machine has very small vibration, low noise, stable mechanical operation and reliable performance. Through the practical application of the market, excellent social and economic benefits have been obtained.

(2) High Efficiency And Energy Saving

The processing capacity and efficiency of materials per unit grinding time are greater. Under the condition that the total power of the R-type mill is unchanged, the output is increased by more than 40% year-on-year, and the unit power consumption cost is saved by more than 30%. It is a real high-efficiency and energy-saving mill product.

(3) Environmental Protection

The remaining air outlet of the mill is equipped with a pulse dust collector, and its dust collection efficiency reaches 99.9%. All the positive pressure parts of the main engine are sealed, and a dust-free processing workshop is basically realized.

Vertical mill is an ideal large-scale grinding equipment. High cost and low maintenance. It can be used from coarse powder to ultra-fine powder. The fineness is from 200 mesh to 2500 mesh. Large investment, generally large enterprises can choose.

(1) Low Comprehensive Investment Cost

It integrates crushing, drying, grinding, grading, and conveying. The process flow is simple, the system equipment is small, the structure layout is compact, and the floor space is only 50% of the ball mill. The north can be arranged in the open air, and the construction cost is low, which directly reduces Enterprise investment expenses.

(2) High Grinding Efficiency

The grinding efficiency is high and the energy consumption is low. Compared with the ball mill, the energy consumption is 40%-50% lower; the single machine has a large production capacity and can use low-voltage electricity.

(3) Convenient Maintenance And Low Operating Cost

The grinding roller can be turned out of the machine with a hydraulic device, the replacement of the roller sleeve liner and the grinding machine have a large maintenance space, and the maintenance operation is very convenient; the grinding roller sleeve can be turned over and used, which prolongs the service life of wear-resistant materials; there is no need to use the grinding table before starting the machine. The cloth is loaded, and the mill can be started without load to avoid the trouble of starting up; the wear is low, the grinding roller and the grinding disc liner are made of special materials, and the service life is long.

(4) Stable Product Quality

The material stays in the mill for a short time, which is easy to detect the particle size distribution and chemical composition of the product, reduces repeated grinding, and the product quality is stable; the product particle shape is uniform, the particle size distribution is narrow, the fluidity is good, and the product adaptability is strong; The iron content in the medium is very small, and the mechanically worn iron contained is easy to remove. When used for grinding white or transparent materials, the product has high whiteness and purity.

(5) High Reliability

The roller limit device is adopted to avoid the severe vibration caused by the material interruption during the working hours of the mill. The use of a new type of grinding roller sealing device makes the sealing more reliable and does not require a sealed fan, which further reduces the oxygen content in the mill and has more excellent anti-explosion performance.

(6) Environmental Protection

The whole system of HLM vertical mill has small vibration and low noise; the whole system is sealed and operated under negative pressure, and there is no dust overflow, which can basically realize a dust-free workshop; vertical mill technology and equipment are new energy-saving and consumption-reducing technologies strongly advocated by the country, which are beneficial to upgrade The competitive strength of the company in the area and even the national powder industry.

(7) High Degree Of Automation

It adopts PLC automatic control system, and can realize remote control, which is easy to operate, convenient to maintain and reduce labor costs.

For the production of calcium oxide by the above-mentioned various equipment, the auxiliary equipment must be selected according to the selection, and the conveying dragon, hoist and feeder must be strictly sealed. Prevent a large amount of natural wind from entering and affecting the calcium oxide content, and the remaining products must be cleaned up each time before stopping processing to prevent calcium oxide from absorbing moisture in the air and becoming calcium hydroxide mixed with serious products that affect the quality of calcium hydroxide under static conditions.

4.The Requirements Of Deep Processing Lime Kiln

Because the lime needs to be too old, nodulation will appear accidentally, so all aspects of it must be accurately in place, controllable and adjustable, such as metering, cloth, and discharging, in the design of the kiln. Give full consideration to the situation and treatment methods caused by the occurrence of nodules. And between the ash outlet and the material warehouse, a material selection belt must be installed, which can sort the raw burned, over burned, and cinder. Due to the calcination of lime, there are many uncertain factors, and there are differences in the ash produced each time, so the lime bank requires at least four or more. It can be divided into normal ash, under-burned ash, over-burned ash and sieved powder. To produce a variety of products for various qualities, such as placing raw materials in a warehouse, it is difficult to classify and classify downstream products. Therefore, graded raw materials are very important to lay a solid foundation for the quality and grade of downstream products and realize product diversification.

5.Calcium Hydroxide

The calcium hydroxide production line mainly adds water to calcium oxide to enter the digestion and reprocessing process. The main problem in this process is how to achieve complete digestion to minimize free calcium, maximize powdering rate, and ensure smooth production. Restart the machine in the event of a power outage or mechanical failure. It is no longer necessary to manually clean up the materials in the digester to restart the machine. The environment is seriously polluted, dust is everywhere, and high temperature poses a safety hazard.

The selection of digesters should be equipped with: timely digestion with hot water, reducing the content of free calcium, calcium carbonate, and acid insoluble matter, and the process of uniform water content in the product. It is not possible to use "grinding" in the process of making the fineness of medium and high-grade calcium hydroxide products, because the method of making calcium hydroxide by grinding will greatly reduce the grade of calcium hydroxide. Ordinary and low-grade products can be replaced by any equipment. The equipment of the entire production line must be designed and constructed by a team with experience in production technology, and smooth production must be achieved.

At present, calcium hydroxide production mainly uses powder separators. There are many domestic manufacturers of powder separators. When choosing powder separators, you must choose ultra-fine type of fish-eye mixed beads. Because ultra-fine equipment is easy to make ordinary, but ordinary equipment It is difficult to produce ultra-fine ones. Therefore, the selection of powder separator should consider the characteristics of light specific gravity and high viscosity of calcium hydroxide. A large fan must be used for efficient collection and separation, and the spreader adopts an inclined screen structure to improve the sealing performance to adapt to the production of calcium hydroxide.

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