Sludge dewatering machine
The sludge dewatering machine is designed to remove most of the moisture in mud cake, eliminate harmful toxic substances, and provide conditions for subsequent processing, utilization and transportation. The sludge after treatment is used as a fertilizer in soils such as farmland and greening, or be utilized in resources to form useful materials such as paving slag, cement, bricks, etc, or landfill.
High water content is the main feature of sludge as a solid waste pollutant. Just because of the large amount of water that sludge is more serious than other forms of solid waste. Even after concentration and digestion, the water content is still as high as 96%, which is very bulky and difficult to dispose of. It must be dehydrated to increase the solid content of mud cake and reduce the footprint of the sludge. In general, mechanical dewatering can achieve a solids content of 20% to 30%, and the sludge formed is also called a mud cake.
Generally, mechanical dehydration are adopted in large and medium-sized sewage treatment plants. There are many kinds of sludge dewatering equipment, which can be divided into vacuum filtration dehydration, pressure filtration dehydration and centrifugal dehydration according to the principle of dehydration. This paper will introduce the commonly used belt filter press, plate and frame filter press and centrifugal dewatering machine in sewage treatment plants in terms of working principle, equipment selection, maintenance and operation.
1. Belt filter press
The belt type filter press dewatering machine is composed of a sludge layer sandwiched by two upper and lower tensioned filter belts, and passes through a series of regularly arranged roller cylinders in an S shape, and relies on the tension of the filter belt itself to form a squeeze layer on the sludge layer. The shearing force squeezes the capillary water in the sludge layer to obtain a mud cake with a high solid content, thereby realizing sludge dewatering.
The belt filter press is composed of a filter belt, a roller cylinder, a filter belt tensioning system, a filter belt deflection system, a filter belt washing system and a filter belt drive system. When choosing a model, it should be considered from the following aspects:
(1). Filter belt
The high tensile strength, bending resistance, acid and alkali resistance, temperature resistance and other characteristics.
(2). Adjustment system of roller cylinder
Usually done by pneumatic means.
(3). Filter belt tensioning system
Also generally controlled by a pneumatic system. The filter belt tension is generally controlled at 0.3-0.7 MPa, and the usual value is 0.5 MPa.
(4). Belt speed control
Different types of sludge have different requirements on the belt speed, that is, there is an optimal belt speed control range for any particular sludge. Within this range, the dewatering system can guarantee a certain processing capacity, and Can get high quality mud cake.
2. Plate and frame filter press
Plate and frame filter press is mainly composed of concave man filter plate, frame, automatic-pneumatic closed system measuring plate suspension system, filter plate vibration system, air compression device, filter cloth high-pressure flushing device and fuselage side photoelectric protection device. The sludge is extruded through the plate frame, so that the water in sludge is discharged through filter cloth to achieve the purpose of dehydration. When choosing a model, it should be considered from the following aspects:
(1). Solid content of mud cake
Compared with other types of dewatering machines, the plate and frame filter press has the highest solid content rate of up to 30%. If considering the factors of reducing the sludge pile occupation, the plate and frame filter press should be the preferred solution.
(2). The material of frame, filter plate and filter cloth
Corrosion resistance is required, and the filter cloth must have a certain tensile strength.
(3). How the filter plate moves
Automatically or not.
(4). Filter cloth oscillating device
To make the filter cake is easily peeled off.
3. Centrifugal dewatering machine
The centrifugal dewatering machine is mainly composed of a reloading and a screw conveyor with a hollow shaft. After the sludge is sent into the drum by hollow shaft, it is broken into the cavity of the hub under the centrifugal force generated by the high-speed rotation. The sludge particles have a large specific gravity, and thus the centrifugal force is also large, and is attached to the inner wall of the rotating hub to form a solid layer; the water density is small, the centrifugal force is also small, and only a liquid layer is generated inside the solid layer. The sludge in solid layer is transported to the cone end of the transfer under the slow push of the screw conveyor, and is continuously discharged through the outlet around the transfer. The liquid is discharged from the overflow to the transfer, and is discharged to the dewatering machine.
The most critical component of centrifugal dewatering machine is the hub. The larger the diameter of the hub, the greater the dewatering capacity, but the manufacturing and operating costs are quite high and uneconomical.