• When do you use a centrifuge?
• What is pre-thickening or de-watering?
• Why are the machines called Decanters?
• What is sedimentation?
• What is centrifugation?
• How does centrifugation work?
• What does the centrifuge’s performance depend on?
• How does the supply feed rate affect yield?
• What is polymer and fossil flour used for?
• What is an Inverter?
• What are the advantges of a centrifuge in relation to a filter-press?
When do you use a centrifuge?
The centrifuge is used to separate a sludge or a slurry into a solid part and a liquid part. The slurry treatment and disposal plants generate a final residue though the various process stages (equalisation, neutralisation, coagulation, sedimentation, floatation, biological treatment etc.). This residue is generally subjected to a further series of treatments, before final disposal. It is in one of these processes, thickening or de-watering, that the centrifuge is used.
What is pre-thickening or de-watering?
They are processes through which effluent slurry is generated (output slurry), more concentrated than the influent (input slurry).
Why are the machines called Decanters?
This name comes from the word DECANTATION which means the clarification of a liquid obtained through the separation of suspended particles (sedimentation).
What is sedimentation?
This is a process in which solid particles in a liquid undergo the effect of the force of gravity and deposit on the bottom, separating themselves in this way from the liquid itself. In some cases (biological fluids) the time for spontaneous sedimentation would be too long and some particles would take years for a sedimentation process. It’s in these cases centrifugation is used.
What is centrifugation?
With centrifugation it is possible to generate an increase of gravity with respect to the earth’s gravity, thus accelerating the sedimentation process. The container of the product that must be treated is made to rotate. The solution is thus subjected to an artificial force of gravity (centrifugal force) proportional to the distance from the centre of rotation and to the square of the rotation speed.
How does centrifugation work?
The centrifuge is made up from a cylindrical-conical container (drum) containing a worm screw mechanism (auger) for the removal of the sludge. The slurry is fed into the unit through the auger support axle. The centrifugal force acting, generated by drum rotation, makes the sludge compact against the walls of the container and the dragging action of the worm screw, which turns at a slightly lower speed, makes the compacted sludge advance along the container and towards the conical section of the same, from where it is extracted.
What does the centrifuge’s performance depend on?
The yield is affected by the construction of the centrifuge itself and by the operational parameters of the process. The variables due to construction are: rotation speed, volume available and sludge extraction speed. The process variables are: product feeding speed, characteristics of the solids, dosing of chemical additives (polyelectrolyte for the ecology sector and fossil flours for the food sector) and operational temperature.
How does the supply feed rate affect yield?
By increasing the supply flow rate at a certain centrifuge, decreases the retention time (product preservation in the centrifuge) and decreases the recovery of solids.
What is polymer and fossil flour used for?
The polyelectrolyte (ecology sector) increases the structural resistance of the solids and causes the formation of flakes even starting from the finest particles. The fossil flours (food sector) allow to weigh down the solid. The use of these substances allows to facilitate the separation and increase the recovery of the solids.
What is an Inverter?
It is an electronic appliance that produces a three-phase signal used for start-up of the electric motor.
What are the advantges of a centrifuge in relation to a filter-press?
The centrifuge works in closed circuit and in continuous cycle. The product to be treated enters the centrifuge through a feeding tube and the solids and liquid are to the outside through pipes and evacuation auger, keeping the working environment clean and uncontaminated by residues and odours of sludge or slurry. Furthermore, the downtimes of the typical filter press are eliminated, necessary for unloading and cleaning. The centrifuge is very compact and space-saving in relation to the volume of slurry that it can treat and occupies much less space than a filter-press with the same flow rate. To ensure good operation of the centrifuge it only needs cleaning and maintenance at regular intervals (e.g. greasing the bearings), thus saving large amounts of consumables, such as filters and cloths, which a filter-press requires.
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