Cannon Bono Energia S.p.A. - part of the Cannon Group

Gravity self-backwashing filters


The filtration of make-up and side-stream water in closed cooling circuits, operated through cooling towers, is a fundamental step to ensure safe and continuous operations in a power plant. Water - required in large amounts for this application - should not be wasted, and the potential damages deriving from a poor treatment must be avoided at all cost.

BONO ARTES has developed a technical solution that combines the filtration capacity of the sand with the self-cleaning operation. The result is a very simple unit with very high efficiency and with very low costs. BONO ARTES is a company with more than 30 years of experience in providing solutions to cover the complete water and wastewater cycle related to the power production industry.

In the most recent years BONO ARTES has been granted several contracts relevant to the supply of large filtration systems to be installed in power plants. The application was the filtration of make-up and side-stream water in closed cooling circuits operated through cooling towers. The filters were “gravity-type self-backwashing”.

This technology is very well known by BONO ARTES, in terms of both its theoretical criteria and its applications. In a cooling circuit water is regularly added to compensate the losses due to the evaporation in the cooling tower.
Moreover water is regularly purged from the circuit to keep the chemical-physical characteristics of the circulating water into an acceptable range of pH, conductivity, dissolved salts, hardness.

In the purification of make-up water the target is to reduce to the maximum possible extent the presence of suspended solids coming from well or surface water. The circulating liquid is moreover contaminated by impurities due to the atmospheric air in contact with water.

A filtration of a partial stream of circulating water is therefore necessary to reduce the content of suspended solids and as a consequence the purging stream. In both applications, “make-up” and “side stream” filtrations, gravity type self-backwashing filters are mostly employed.

Unlike pressure-operated filters requiring backwashing pumps and blowers, backwashing is done by gravity and the required water is stored in a chamber included into the unit. No rotating parts are required and no spare parts are therefore needed, lowering the operating cost of the process. Due to the fact that no control equipment is required (automatic valves, flow-meter, regulating instruments, etc.) the filter is operated without supervisors.

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