On a tissue machine, the Yankee is a key component due to its consumption of energy and its impact on the quality of the final product. Therefore, it is essential to operate the Yankee in the most efficient and economic means possible. The critical parameters are air impingement speed, wet- and dry-hood temperatures, exhaust humidity, and steam pressure in cylinder.
With environmental sustainability and the cost of energy under consideration, PrimeDry Hood E uses the same air system as gas or steam-heated hoods, but electric heaters replace gas burners or steam heaters. The result is a system capable of achieving air temperatures of 400 - 450°C while increasing energy efficiency and reducing carbon dioxide emissions.
A high-performance hood is today a must on all Yankees in order to achieve maximum production at the lowest cost. It is estimated that the sheet contact with the Yankee itself accounts for about 30-50% of total drying, while the hot air impinged by the hood provides the remaining 50-70%. Depending upon the fuel source available, ANDRITZ supplies oil- or gas-heated hoods that typically operate in a range of 530° C (PrimeDry Hood HT) to 650° C (PrimeDry Hood TT).
When steam is available and cheaper, and preferred over oil or gas, ANDRITZ supplies the PrimeDry Hood ST, which is engineered with a steam-heated air system. The PrimeDry Hood ST operates in a temperature range around 200° C of impingement air temperature, which can provide an additional 15-25% of drying capacity compared to the Yankee cylinder alone.
The installation of systems to cogenerate electricity and heat is becoming more prevalent in the tissue industry, due to the availability of gas turbines of a suitable size and efficiency. The exhaust gas from
these turbines has sufficient enthalpy that it can be utilized to feed the PrimeDry Hood CHP for a Yankee dryer. Operating in a temperature range of 400-510° C, the PrimeDry Hood CHP can provide up to 60% of the drying capacity required.
To achieve maximum drying capacity and efficiency on a tissue or MG machine, the high-pressure steam introduced into the Yankee cylinder must be properly controlled. In addition, the condensate formed inside the Yankee must be removed and prepared for reuse in the mill. ANDRITZ supplies the PrimeDry SC system which regulates steam supply, properly distributes the steam inside the Yankee, removes the condensate, and controls reuse of the condensate and blow through steam. The system works in an integrated mode with the Yankee hood as well as a heat recovery system to result in an optimum solution for drying performance and energy usage.
Steam for tissue machines is typically produced by the mill’s boiler system. There are some technical issues with this arrangement: older, less energy-efficient steam production equipment, long steam piping layout, and excessive losses of steam pressure and energy. ANDRITZ’ solution to solve this problem is the PrimeDry YES steam generator that utilizes exhaust air from the Yankee hood. Depending from the application, the PrimeDry YES can produce in the range of 25-40% of the steam required for the Yankee, which can save up to 15% in energy costs.
Recovering and reusing the heat that is generated during the tissue drying process, which is often lost to the atmosphere, results in significant energy savings. ANDRITZ offers a range of heat recovery solutions: air-to-air indirect, air-to-water direct scrubbing, air-to-water indirect, and even a
sequential arrangement (tower) of two or more PrimeDry Heat Recovery units.
