Steel production generates dust from the use of electric arc furnaces. Because the electric arc furnace (EAF) dust is a hazardous material, it requires special processing for safe disposal and to create a product that can be reused.
Pontenossa utilizes the Waelz process to recover zinc oxide from EAF or steel dust.
In this process, the steel dust is combined with coal and lime and fed into a rotary kiln. The high temperature produces zinc and lead vapors that are re-oxidized and filtered. After cooling and filtration, the resulting Waelz oxide is washed and dried.
After washing, the material requires dewatering to remove as much moisture as possible.
“The oxide needs to reach a moisture level so low that it requires less energy to dry in the subsequent steps of the recovery process,” explained Dario Bonaldi, the environmental manager at Pontenossa.
Diefenbach supplied Pontenossa with a series of Filter Presses that were the perfect solution for dewatering the liquid-solid slurry.
Pontenossa purchased two Diefenbach Overhead Beam Filter Presses and a bespoke Side Beam Filter Press, with 222 filter plates between all three presses.
Diefenbach Filter Presses guarantee the lowest moisture content possible within a material, reducing energy use in the downstream process.
Diefenbach’s Filter Presses operate in a batch cycle. These machines utilize a series of plates suspended on an overhead beam or between two side beams. Each plate is recessed on both sides.
The filtration cycle begins as the plates are pushed and held together by the hydraulic mechanism, forming a series of chambers between each plate. The liquid-solid slurry is pumped into both sides of the Filter Press, filling the chambers.
The liquid in the slurry passes through the filter cloths on the plates and exits the filter press. The solid material is captured on the filter cloths as filter cakes.
After a core blowing of the central feed port to clear any remaining slurry from the channel, the hydraulic mechanism opens the plates and releases the filter cakes. After each cake is released, another filtration cycle begins.
The Filter Presses at Pontenossa were tailored to include an automatic cloth washing feature that prevents buildup on the filter plates, extending cloth wear life.
“The auto-wash is fundamental to maintain the filter presses,” explained Bonaldi.
Diefenbach’s Filter Presses allow Pontenossa to efficiently and effectively dewater the washed zinc oxide, producing a material with low-moisture content.
“Filtration is a fundamental step within the Waelz process. It guarantees the maximum removal of the liquid used to wash and process the Waelz oxide and gives us the minimum content of residual humidity within the product,” explained Tito.
Diefenbach and Pontenossa’s partnership has proven successful.
“We have been collaborating with Diefenbach for almost 30 years now,” explained Tito. “The compatibility between the machines and our product provides an almost total recovery of the product. The average residual humidity level is about 21-22%.”
Diefenbach’s Filter Presses provide a dewatering solution for Pontenossa, as well as easy operation and maintenance.
“The Diefenbach Filter Presses are machines with excellent performance – They’re relatively simple machines to operate and maintain. They’re reliable and robust, with a good level of automation,” said Tito.
Diefenbach also supplied Pontenossa’s team with proper training on how to operate the machines and perform routine maintenance.
“Basic maintenance is carried out about once a month. More heavy maintenance is done about every five to six months,” Bonaldi said. “Maintenance of the Filter Presses is quite easy to conduct.”
The auto-wash feature provides preventative measures to ensure the long life of the machines.
“The Waelz oxide is a sticky material,” Bonaldi explained. “We run the auto-wash every six or seven treatment cycles, otherwise the plates fill up with solid material.”
Not only do the Filter Presses provide Pontenossa with the means to process the zinc oxide efficiently, but they also help Pontenossa follow regulated safety and sustainability practices.
Bonaldi explained, “The water recovered by the Filter Press goes through the Pontenossa water treatment circuit. Since the water that washes the Waelz oxide contains pollutants, it’s circulated in the water treatment plant to remove the contained pollutants.”
Pontenossa is dedicated to producing zinc oxide safely, efficiently and effectively. Diefenbach’s Filter Presses help the company achieve these goals.
“Through the use of the Diefenbach Filter Presses, we can reach the production quality and safety standards of our product,” Tito explained.