Fly ash sorting technology

1、 Overview:

With the development of science and technology and the needs of modern industrial construction, the use of Class I and II fly ash in China is becoming increasingly widespread, especially in the building materials industry and concrete engineering construction. Adding grade I and II fly ash to large volume concrete can reduce hydration heat, improve later strength, replace cement, turn waste into treasure, reduce costs, and improve economic benefits.

Practice has proven that the fineness of fly ash is an important indicator for measuring its physical and chemical activity. The finer the fly ash particles, the higher the physical activity, the greater the density, and the lower the water requirement for standard consistency.

Fine grade fly ash that meets certain quality standards is an excellent concrete admixture. Through morphological effects, activity effects, and micro aggregate effects, it can improve the workability, facilitate pouring, and enhance the density of concrete. At the same time, it can also improve the impermeability and sulfate corrosion resistance of concrete, reduce the water demand of concrete, improve strength, and reduce cracks caused by shrinkage, as well as the alkali aggregate reaction in the later stage of concrete components.

According to the national standard GB/T 1596-2005, fly ash used in cement and concrete is classified into three grades based on fineness. Grade I ash has a fineness of 45 μ m and a sieve residue of no more than 12%, while Grade II ash has a fineness of 45 μ m and a sieve residue of no more than 25%.

In the development and application of the complete set of equipment for fly ash classification and sorting, we have worked hard for many years to develop two different forms of sorting machines:

The WX type eddy current sorting machine is a specialized equipment (patent number: ZL 94242462. X) developed based on the principle of low-speed cyclone separation and long-term extensive testing, with reference to the Boolean classifier technology of GE in the United States. It is more suitable for fly ash sorting. Due to the use of reasonable gas-solid two-phase flow velocity field control technology, this device solves the disadvantages of high resistance, high energy consumption, and severe wear of general sorting machines by adopting unique processes and novel structures. At the same time, it has the advantages of simple structure, easy operation and maintenance, low operation and maintenance costs, high sorting efficiency, and long service life. In addition, the equipment has strong adaptability to fly ash, a wide range of particle size segmentation, and simple adjustment methods. The eddy current sorting machine is an ideal equipment for separating fly ash, but it is more suitable for processing relatively fine raw ash (raw ash with a 45 μ m square hole sieve residue ≤ 45)

The WL turbine type sorting machine (Onoda Technology, Japan) has been proven through extensive practice to have special adaptability for coarser raw ash (raw ash with a 45 μ m square hole sieve residue ≤ 45-65), and is suitable for sorting systems with high processing capacity (greater than 50-70 tons/hour).

When users choose a sorting system, we provide a definition for the selection of the sorting machine form in the sorting system. The definition mainly depends on the user's supply and use of sorting ash, that is, the grade of finished ash supplied by the market, as well as the grade of raw ash in the power plant. Through the comprehensive selection of the above factors, the optimal sorting configuration is achieved.

When selecting sorting equipment, the following aspects were given special consideration:

1) Mature technology and products must be adopted.

2) Must adapt to the variability of coal types, boiler equipment operating conditions, and ash performance in power plants.

3) Must meet the operating habits and requirements of the operators.

4) The need for structural adjustment of fly ash products must be met.

The WX and WL dry classification machines for fly ash provide favorable conditions for the large-scale use of fly ash as an admixture for cement and concrete, expanding its application in building materials, construction, and material filling, and other fields. They have a great promoting effect on the comprehensive utilization of fly ash. This machine can be used for power plants to classify fly ash and recycle and sort Grade I and Grade II ash according to requirements. At present, many users (manufacturers) in China have adopted this type of sorting machine.

2、 Principle of Sorting Machine:

1. Working principle of snail shell sorting machine

The airflow carrying materials enters the sorting machine through the feeding port (1), and is initially separated by the centrifugal force at the sharp turn (2) and the action of the baffle (3). The secondary air is fed in from the bottom inlet (11), and coarse particles settle at the bottom of the sorting machine due to gravity. Medium sized particles follow the vortex spiral trajectory, and the combined force of centrifugal force Fc (proportional to the cube of particle diameter) and drag force Fd (proportional to particle diameter) is different. Finer particles move inward due to Fd>Fc, and are discharged from the two sides (5) in the middle of the sorting machine. They are collected by the collector and become fine products (products required by the user); Coarse particles move outward due to Fc>Fd, decelerate at the periphery, and settle at the bottom of the sorting machine (10) under the action of gravity, thus achieving the classification effect.

2. Turbine sorting machine

WL type dry classification machine for fly ash is mainly used for dry classification of fly ash, and can also be widely used for classification of other powdery dry materials (such as cement, limestone, coal powder, etc.). We can produce various grades of ash products that meet national standard requirements.

Working principle and characteristics:

This product consists of components such as an intake volute, a rotating body, an upper structure, and a lower structure.

Working principle: Mainly based on the balance between the centrifugal force of the snail airflow and the centripetal force of the rotating airflow, it effectively separates coarse and fine particles.

Powdered materials enter the sorting machine through the inlet of the volute with the airflow. Under the action of centrifugal force, coarse and fine particles are initially separated, and the dust particles are forcibly separated again by the rotating body. The separated coarse particles fall down along the inner ash hopper in the lower structure, and the fine particles are blown back into the volute body for separation by the secondary air set. The separated coarse particles are collected and discharged by the outer ash hopper of the lower structure, while the fine particles enter the lower collection device of the system through the outlet of the upper structure for collection.

3. Main features:

a. By adopting a rotating body and secondary air structure, the sorting recovery rate is improved, and it can be easily adjusted according to product requirements.

b. The snail shell is lined with wear-resistant corundum, and the rotating body is treated with overall wear-resistant spraying to improve its service life.

c. Compact structure, easy installation, convenient maintenance, and reliable operation.

4. Selection of sorting machines in the sorting system:

There are two options for selecting sorting machines in the design of sorting system schemes, namely vortex shell and turbine type. The two types of sorting machines have different adaptations to raw ash and system operation, which are briefly described as follows:

There are two main types of sorting machines in China: eddy current sorting machines (based on GE's Boolean classifier technology in the United States) and turbine sorting machines (based on Onoda's technology in Japan). Both technologies have been accepted by the market in practice. Generally, vortex shell sorting machines are easier to operate and more reliable than turbine type sorting machines, with lower energy consumption, maintenance, and failure rates. They have a market share of over 85% in China and are generally the preferred models in sorting systems. However, the adaptability of these two forms of sorting machines to undisturbed fly ash is slightly different. The vortex shell sorting machine is suitable for processing relatively fine raw ash (raw ash with a 45 μ m square hole sieve residue ≤ 45), while the advantage of the vortex wheel sorting machine is reflected in adapting to coarser raw ash (raw ash with a 45 μ m square hole sieve residue ≤ 65), and the resistance is lower than the upper one. In the case of finer raw ash, the sorting efficiency of the turbine sorting machine is lower than that of the upper one, while the energy consumption, vibration, wear, and maintenance of this type of sorting machine are higher than those of the upper one.

3、 System process flow:

Under the negative pressure of the induced draft fan, the material is fed into the sorting machine through the feeding device along with the airflow. After being classified by the sorting machine, coarse ash is discharged from the lower part, while fine particles (products) are discharged from the vortex shell along with the airflow and collected by the collector and dust removal (bag) equipment. The gas discharged by the fan should meet the environmental requirements on site.

Coarse ash is discharged into the coarse ash silo by the unloader, while fine ash is discharged from the lower part of the collector and discharged into the fine ash silo by the unloader. The ultra-fine fly ash is collected by the dust removal equipment. Coarse ash, fine ash, and ultrafine ash can be transported out through methods such as water flushing discharge, canned truck loading, and manual bagging.

4、 Performance parameters:
The developed models of vortex shell fly ash dry classifier are shown in the table above:

5、 System supporting equipment and application situation:

Based on the characteristics of fly ash and its sorting, various systems and process flows have been developed in terms of system design, including fully closed, semi closed, fully open, single sorting, and integrated dry ash conveying sorting, according to the on-site situation. In terms of equipment configuration, taking advantage of the comprehensive research and development of multiple specialties in the thermal engineering institute, efficient downward suction cyclone collectors have been developed for the sorting system, and a utility model patent (01142053.7) has been obtained, which has been adopted in multiple projects. Specialized high-pressure vertical and imported high-efficiency bag filter dust collectors, high-pressure energy-saving wear-resistant fans, and high-performance ball type air locks (patent number ZL972261354) have been researched and developed. Tongue type air locks have been widely used in engineering, with nearly 2000 units sold since 1997, as well as controllable sealed unloaders. And optimized the selection of air distribution structure and wear-resistant components in the flow chamber of the sorting machine, installed a flow equalizer and wear-resistant (corundum) lining, and equipped an online ash sample collector and wind pressure and air volume monitoring system, which significantly improved the service life of the equipment and the reliability of the system operation.

Since the WX/WL fly ash sorting machine was utilized in China in 1994, our company's personnel have personally completed and are currently completing a total of 118 fly ash sorting projects, using 135 sets of WX/WL fly ash sorting machines (see sorting project performance table), distributed in 20 provinces and municipalities directly under the central government in China (see domestic distribution map of fly ash sorting projects)

Among them, two sets of sorting devices were installed simultaneously in Zhuzhou, Tangshan, Pingwei Phase I, and Macun Phase II, totaling 135 sets. As of now, there are 118 engineering projects and 135 sets of commercial ash that have been put into operation, and the sorting fineness has reached the national level I ash index.

In the sorting devices that have been put into operation, the sorting fineness of commercial ash reaches the national level I ash index. These devices (partially) are:

Among them, the more representative ones are:

Shenzhen Mawan Power Plant has been in continuous production for over 12 years

2. Zhenjiang Jianbi Power Plant has accumulated 11 years of production

Xiamen Songyu Power Plant has been in continuous production for over 10 years

4. The Tiandong Power Plant in Guangxi has been in production for over 10 years

Wuhan Yangluo Power Plant has been in production for over 10 years

6. Jinling Petrochemical's self owned power plant has accumulated production for 10 years

7. Anhui Pingwei Power Plant has been in continuous production for over 9 years

8. Luohuang Power Plant has accumulated 7 years of production

9. Huaneng Dalian Power Plant

10. Shandong Zouxian Power Plant

11. Huaneng Dezhou Power Plant
 

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