The dust removal system of power plant is composed of the ash collection, processing and transportation equipment, pipes and their accessories. There are three types of dust removal: hydraulic, pneumatic and mechanical power. How to choose the type of dust removal type? Generally, it should be determined by ash comprehensive utilization requirement, water amount and the distance of ash storage yard. If one method cannot meet the requirement of ash removal, it requires the combined ash removal system by two methods. 

One. Hydraulic ash removal method

Hydraulic ash removal is a typical way of coal-fired ash conveying in power plant, with water as the medium, through part of the equipment and pipeline to complete the ash conveying.

Hydraulic ash removal has a strong adaptability for conveying different ashes. Each system device has the advantages of simple structure, mature, safe and reliable operation, easy and simple maintenance. In the conveying process, the clinker is not easy to scatter, and is beneficial to the environment cleaning, thus it can realize the long-distance transmission of mortar.

However, the hydraulic ash removal method also has the following disadvantages:

1. It is not conducive to the comprehensive utilization of ash and slag.

    2. It’s easy to scaling in the ash pipe wall, plug ash tube and not easy to remove, when the calcium oxide content in the slurry is high. 

3. Water consumption is relatively large.

4. After the ash sluicing water and ash mixed, it shows alkaline. PH value is more than the industrial "three wastes" emissions regulations.

In South area, the majority use the low concentration of ash transport system with the gray water ratio of 1:15. In North area, it adopts the high concentration ash transport system with the ratio of 1:1 ~ 1:2.5.  

Hydraulic ash removal system generally consists of several or all of its components among the following system: unloading ash device, ash sluicing pump system, slurry pump system, concentrator systems, recovery water system, long-distance transportation power device, transmission ash pipe.

 The main equipment in the internal dust removal system of the boiler has slag extractor, slag crusher and jet pump, while the main equipment of external system has mortar pump, backwater pump (slag water recycling pump, ash water recycling pump), concentrated pool, stirring groove or wet mixer, volumetric (including water isolation pump, uranium isolation pump, ram pump, box type ash device etc..

Two. Pneumatic ash removal system

Pneumatic ash disposal is a way that conveying the powder materials with the help of a certain kind of pressure (positive pressure or negative pressure) and pipe system, using a kind of air as the carrier. Ash removal system of coal power plant is a kind of advanced, economic and environmental protection technology.

Pneumatic ash disposal has an incomparable advantages on the environmental protection, water resources, water resources saving, automatic control and other aspects compared with the traditional hydraulic ash transport and conventional mechanical transmission modes, but there are also the following deficiencies:

1. The wear resistance of some equipment and components is difficult to meet the requirements of the working conditions, which will affect the reliability of the operation.

2. The coarse particles, viscosity of powder and wet powder is not suitable to convey by pneumatic. The transmission distance and throughput are subject to certain restrictions.

Three. Boiler slag removal system

The slag removal system of coal fired generating units generally has two types: hydraulic and mechanical slag removal.

Hydraulic slag system has the advantage: strong adaptability of transporting different ashes, safe and reliable operation, easy and convenient operation and maintenance, mature technology and no scattering in the transport process, which is a traditional and mature ash conveying form.

The main existing problems of hydraulic slag removal:

1. The water consumption of the slag is relatively large.

2. It will form scale in ash tube easily if the calcium oxide content is high, thus it will block the ash pipe and will be difficult to remove.

3. After the hydraulic ash-moving and ash mixed, it shows alkaline. PH value is more than the industrial "three wastes" emissions regulations. Or it’s not allowed to randomly discharge outward from the ash field. No matter take recycling or take processing measures, it needs a very high equipment investment and operating costs.

Compared with the hydraulic slag removal, mechanical solid slag has the following characteristics and advantages:

1. The mechanical slag does not need artesian ditch for the hydraulic slag removal, and the underground facilities (trench, pipe, nozzle) are simplified. 

2. The processing of mechanical slag removal is relatively simple, which can reduce the difficulty of outward discharge and with convenient transportation. It is conducive to the comprehensive utilization of slag.

3. Mechanical slag removal has no problem of ash sluicing water emission and recycling. 

Due to these advantages, now more and more new power plants adopts slag adopt the solid mechanical deslagging design, which is a modern coal-fired generating units ash conveying the development trend.

The slag method can run continuously with less water consuming, which can determines the revolving speed of chain according to the slag amount, with low power consumption. It is suitable for long distances transportation. But the structure of bottom is complex, with a large maintenance workload.