A new Yankee hood and air system installed in August 2013 has resulted in substantial energy savings, according to Wepa mill director Maurizio Lattanzi. Here he discusses the potential that exists throughout the industry to increase efficiency with targeted investments in drying. A TW report.
Wepa Cassino’s 60,000tpy mill based in Rome, Italy, has seen a significant impact in terms of its energy efficiencies following an investment in a Yankee hood and air system in August 2013. The site has one tissue machine and converting facilities, and mill director Maurizio Lattanzi says there has been a 10% drop in electrical energy for the hood fans, a 4% drop in steam consumption, but significantly, a 20% reduction in gas consumption by the hood.
The Milltech-supplied system has also increased the site’s capacity and improved its paper quality, and all within the existing tissue machine.
The mill uses virgin pulp to produce branded and private label roll products, including toilet tissue and kitchen towel (some printed), and folded products, namely napkins. Its double-sided De Pretto Escher Weiss tissue machine started up in 1989 and has since been upgraded from twin-wire to crescent former format by Toscotec. Lattanzi says the tissue production line has evolved gradually over the years; stock preparation has benefited from the modification of the refiner installation to reduce energy and more efficient motors for the tank propellers. But he says the replacement of the 25-year-old hood is “a comparatively radical” step.
The key technologies responsible for the new hood’s performance are the fans, burners (for which a custom solution was found) and control of the exhaust process. A key improvement was also a significant reduction in the distance between the Yankee and the hood. An increase in the dryable width of the web to 5.42m meant production increased by 4% across all product categories and the desired safety improvement was achieved by moving the air system from its cramped situation within the mill to outside, thereby reducing fire risk. The project also includes replacement of DC drives and motors with AC, bringing greater reliability and efficiency.
The Computational Fluid Dynamic Software (CFD) used to develop SMART-eMT has been tailored to predict process parameters such as heat transfer capacity and efficiency, airflow distribution through the nozzle boxes and the exhaust slots, as well as air flow through the supply ducts. Optimised layout of fans, burner and ductwork improves drying efficiency, prevents stratification and improves air distribution.
According to Lattanzi, the nozzle pattern ensures uniform air distribution over the paper sheet, and round-hole nozzle boxes allow maximum drying efficiency and provide energy savings. Appropriately dimensioned exhaust slots allow maximum removal of water and ensure uniform exhaust air flow with low pressure drop.
The Yankee Hood is supplied with a fully functional, pneumatically actuated retraction system with cross profile and edge control.
‘The nozzle pattern ensures uniform air distribution over the paper sheet, and round-hole nozzle boxes allow maximum drying efficiency and provide energy savings.’
The hood’s dimensions take into account the fact that space is often limited at the customer’s premises, and each hood is manufactured in large segments in order to facilitate and reduce transport costs.
“All these factors contribute to the drying efficiency of the line, output, reduced environmental impact and the quality of the end product,” says Lattanzi. “As such we have met our targets in every respect, which, in a competitive market makes this a timely and highly effective investment.”