- When traditional bag filters cannot be employed -
Self-cleaning bag filters are the most employed dust removers, these equipments are largely widespread because they remove dust from a contaminated airflow and their filters don’t need to be replaced, in fact they are self-regenerated by a flow of compressed air.
In certain cases bag self-regenerating system is not applicable, for example when dust to be removed is not dry, airflow is too much damp or there are large changes of temperature in the airstream or if highly explosive fine powders are present.
In all these cases self-cleaning bag filter get into a crisis and it is necessary to find an alternative purification technology.
WHAT IS A VENTURI SCRUBBER
Venturi scrubber is an air purification system that enables, by mixing water with the gaseous flow to be treated, removing of water soluble substances and dust at the same time.
PRINCIPLE OF OPERATION
The polluted airflow is forced to flow through a set course (venturi pipe) where it takes an high speed, inside the same course scrubbing water is atomized by means of a nozzle.
In these conditions an intimate contact takes place between the air and scrubbing liquid (just water or water + additive) so that contaminants are transferred from the air to the scrubbing liquid.
OPERATION OF VENTURI SCRUBBER
Venturi scrubber consists of:
- water collecting tank;
- set of venturis;
- water recirculating pump/pumps;
- drop stop;
- suction fan.
Referring to the scheme below, airstream coming from industrial processes passes through one or more venturis, licks the surface of the water in the tank, flows through the drop stop and it is sent to the stack by the suction fan.
The water collected in the tank is sucked by the pump and injected in venturi’s throat where also air passes through, after that it falls again inside the collecting tank.
It is exactly in the venturi that, in virtue of high speed (both of the air and the injected water) and turbulence, air and water come into intimate contact and the transfer of pollutants from the air to the water takes place.
ADVANTAGES OF VENTURI SCRUBBER
Venturi scrubber is recommended in those cases when dry collection is difficult, that is when these conditions occur:
- Very damp air
When the airstream to be treated is very damp, bag-filter could meet some obstruction problem, humidity together with dust causes the irreversible obstruction of filter bags, this is impossible for venturi scrubber because the purifying “media” is exactly water.
- Dust that tend to “stick” oneself
In certain industrial fields (chemical, pharmaceutical, food industry, etc.) is possible that dust is not dry, dust can be damp or even stick oneself on filter media, in this case bag filters or cartridge filter will become obstructed quickly and compressed air won’t be enough to regenerate them.
In venturi scrubber this phenomenon doesn’t take place because the water wash constantly the internal surfaces of the equipment.
- Air with high temperature and high humidity percentage
In case of hot and damp fumes (e.g. combustion smokes), condensation can occur, those phenomenon arise in starting and shutdown phases. In these phases water condensation and dusts combine, obstructing bag filters or cartridge filters.
Venturi scrubber doesn’t suffer this kind of problem.
- Non-dusty substances absorption
Being a wet collector to all effects, venturi scrubber allows to purify, by absorbing, the water soluble gaseous substances (ammonia, acids, alcohol, etc.).
The venturi scrubber is an alternative solution in all those situations where dry dedusting systems present regeneration problems, it also offers the possibility of purify substances that are not dusty but soluble in water.