Structure and operation principle of filter press

What is the Filter Press

Filter press is a kind of mechanical equipment using a special filter medium to exert a certain pressure on the object to make the liquid dialysis out. Separate the solid from the liquid.

Used in tailings treatment, sewage treatment, chemical industry, pharmacy, metallurgy, dyes, food, ceramics, oil refining, and other environmental protection industries, filter press can participate in the production of all walks of life.

How does the Filter Press Work?

The filter press is generally composed of HEAD PLATE, TAIL PLATE, FILTER PLATE, HYDRAULIC CYLINDER, MAIN BEAM, TRANSMISSION and PULLING DEVICE, etc. The piston of the hydraulic cylinder pushes the head plate to make the adjacent filter plates pressed to form a filter chamber; The mud is sent to the filter chamber by the mud pump, and the water is discharged through the filter cloth through the drain port. The solid mud forms a filter cake in the chamber. When the mud fills the chamber, the high-pressure pump is used to continue the pressure filtration of the mud to separate the solid and liquid in the filter chamber.

There are four steps of how to use a filter press.

STEP ONE: Operate the hydraulic system to move the tail plate towards the head plate and press all the filter plates between the head plate and the tail plate. Thus, a hollow sealed filter chamber is formed between adjacent filter plates.

STEP TWO: The feed pump transports the mud from the feed hole of the tail plate to the filter chamber. When the chamber is filled with mud, the pressure filtration process is being started, and the mud carries out solid-liquid separation with the help of the pressure of the feed pump.

At the initial stage of pressure filtration, the filter cake of the mud in the chamber is not to thick, thus the resistance of the filter cake is small, and the dehydration speed is fast. Usually, a pump is used at this time, which can lift the water to a very low height but with a large flow. With the increase of filter cake thickness and resistance, the pressure filtration speed decreases. At this time, the pump shall be used which can lift the water to a very high height but with a small flow. The time required for the pressure filtration process is determined according to the filtration characteristics and process requirements of the mud. When the specified pressure filtration time is reached, the feeding is stopped and the pressure filtration process is completed. 

STEP THREE: Loosen the filter plate. Operate the hydraulic system and return the head plate to its original position. 

STEP FOUR: Discharge the filter plate. The transmission chain on the transmission and pulling device successively pulls apart the filter plate, and the filter cake falls off with the help of its own weight and is transported away by the lower conveyor.

How to Select the Filter Press?

Filter press models are generally calculated by square, such as 50 square filter press and 100 square filter press. This square is the model of the filter press, which is the standard representation of the filter press.

For example, a sewage treatment plant is designed to treat 1000 tons of sewage with a solid content of 1% (this parameter is very important). It is planned to work 8 hours a day. The nature of sewage is municipal sewage. Then how do we calculate the size of the filter press?

First, calculate the amount of absolute dry sludge in the sewage on that day (absolute dry sludge is the sludge without any water)

Calculation formula: total sewage × Solid content 1% = absolutely dry sludge (1000 tons) × 1% = 10 tons)

Second, 10 tons of absolutely dry sludge were obtained. The sludge from the filter press is not absolute dry sludge. The moisture content of municipal sludge treated by the normal filter press is about 75%. The absolute dry sludge shall be converted into the sludge volume with water content of 75%. Next, calculate the sludge volume with 75% water content. Absolute dry sludge volume × 1.75 = sludge with 75% water content (10 tons) × 1.75 = 17.5 tons), that is to add 75% of the total weight of water to the absolutely dry sludge, which is 17.5 tons in total. It is concluded that the sludge with water content of 75% has 17.5 tons a day.

The third step is to add the factor of the working time of the filter press. We plan to work eight hours a day (of course, the length can be arbitrary). Then we use the total amount of sludge with water content of 75% ÷ 8 hours = the amount of sludge with water content of 75% per hour (17.5 tons ÷ 8 = 2.1875 tons), and we need to treat about 2.2 tons of sludge per hour. The cycle of our filter press to treat municipal sewage is usually once every 4 hours, so we can get the single treatment capacity of a machine × 2.2t = 8.8t. Then divide by the planned use of several filter presses. Here we only choose one filter press, that is, 8.8 tons ÷ 1. We need a filter press that can process 8.8 tons of sludge at a single time. If the volume of one square meter of filter press is 15L, then 8.8 tons ÷ 15L will get a filter press with an area of about 586 square meters. Then multiply it by 1.2 times (appropriate magnification). Such a filter press basically meets the production needs and is just right.