FEATURE: Energy optimisation
EconoFit – for tissue Economy and profit
Tissue production, like all papermaking processes, is energy-intensive. As producers face rising energy costs, ANDRITZ is developing components and systems that not only reduce energy consumption, but also the amount of emissions. In the case of EconoFit, state-of-the-art components are now available to optimise new or existing installations.
The selection of the right process and equipment for tissue making is a major decision. A current key part of that consideration is the availability of energy resources. Energy costs must be taken into consideration, with a strong focus on the specific end-product’s quality requirements. In general, there are three main areas for energy optimisation: conceptual solutions, specific energy-efficient equipment, and operational procedures which optimise and adjust the equipment.
The EconoFit programme for resource saving. Text in blue is highlighted in this article.
Conceptual solutions
ShortFlowTM stock preparation and approach system technology, part of the PrimeLineCOMPACT tissue concept, is a simple, space- and energy-saving solution that is applicable to a broad range of mill environments and production requirements. The ShortFlow™ process speeds up grade changes and improves the controllability of the total process. The PrimeLineCOMPACT tissue machine was launched by ANDRITZ approximately two years ago. Based on the idea of modularisation, the COMPACT concept considers both economic and the ecological impacts.
Investment decisions are typically based upon the economic return in excess of Overall Costs (CapEx and OpEx). Machinery suppliers must consider not only the machine costs, as in the past, but also the lifecycle costs of the complete plant.
Stock preparation, energy utilisation, and installation efficiency have also been incorporated into the COMPACT design.
The tissue machine is naturally the heart of the production line, so high levels of modularisation and standardisation of the machine generate significant economics. For the machine itself, a single platform former encompasses speed ranges from 1600 to 2000 m/min.
The drying section is likewise modular. The PrimeDry Steel Yankee and the modular High Temperature Hood (HTH) are optimised from an energy standpoint. The addition of ReEvaporation has the potential to deliver up to 25% savings in drying steam. With steam being recovered from the HTH exhaust, it is possible to install a smaller steam boiler, which requires a smaller house, smaller water softening system and smaller steam piping.
Standardisation allows operations and mill processes to be performed at the highest degree of efficiency. Higher efficiency, shortened delivery times, and an accelerated start-up curve leads to a much improved ROI.
PrimeLineCOMPACT drying packages – efficient due to modularization
The successful start-up of the first PrimeLineCOMPACT in Europe (March 2008 at Fripa Miltenberg in Germany) has proven the soundness of the concept. On April 2, 2008 the machine reached a speed of 1800 m/min. Two weeks after continuous operation, 84 t/d production was achieved. The machine has since operated in excess of 2000 m/min.
PrimePress XT
A new generation of shoe presses has demonstrated its potential for energy savings and improved product quality. One main feature of the new presses is increased operational flexibility, meaning that the nip pressure profile can be adjusted online. There is no need to take the machine down or to reconfigure the press in order to adjust for either gentle and bulk conserving dewatering or the highest post-press dryness.
The design of the PrimePress XT with its tandem hydraulic cylinders makes it possible to adjust the MD pressure profile on the run. Less re-wetting is achieved due to the rapid pressure release at the nip outlet and the fast separation of the sheet and the felt – a main benefit for the increase of post-press dryness. Extensive finite element analysis of the belt stresses and the parallel static and dynamic lubrication between belt and shoe have created a shoe press with extended run times and trouble-free operation.
Field trials have been conducted on a two-layer PrimeLine tissue machine to verify the potential of the post shoe press dryness. Up to 7% increased dryness relative to a defined bulk operation was achieved. A post-press dryness as high as 47.6% for a 23 gsm sheet was observed. This shows the high potential of the PrimePress XT for energy savings. Compared to a conventional single press in operation, the PrimePress XT requires approximately 12% less drying energy at comparable bulk. By increasing the line force to 160 kN/m, savings up to 20% are possible at slightly reduced bulk.
Energy savings with the PrimePress XT shoe press. Each column shows the drying energy required (a total of steam, gas, and electricity for the hood circulation fans) converted to kWh/t.
ReEvaporation
To use the exhaust air of the hood in generating steam for the Yankee, ANDRITZ developed its ReEvaporation system. It reuses a large amount of exhaust heat within the drying process. Part of condensate from the Yankee is re-evaporated within the system and used as steam in the Yankee for drying. The system can be retrofitted into existing hoods or supplied as part of a new hood system. Based on typical steam costs and operational conditions, the payback time of the investment is short.
PrimeDry Steel Yankee
Compared to cast Yankees, steel Yankees have numerous advantages. The higher performance of the steel Yankee compared to cast Yankees can contribute to energy savings. Due to their lower wall thickness, steel Yankees have higher evaporation performance at the same pressure. The wall thickness is constant over the cylinder lifespan due to the application of a metallic coating on the shell surface. Steel Yankees run at full performance from day one.
Assuming a 12 ft cast iron Yankee as the basis, a steel Yankee of the same size will have a 10% higher steam consumption when keeping the production level constant. But the Yankee hood impingement temperature and velocity requirements are considerably lower to keep the same production. This results in a reduction of the gas and electricity consumed. Based on the energy prices shown in the table, a reduction of 4% of energy costs can be realised (approx. € 116,500 per year).
The ANDRITZ PrimeDry Steel Yankee is available in diameters of 3658 mm (12 ft), 4572 mm (15 ft) and 4877 mm (16 ft) with shell length up to 6300 mm (maximum paper width 5800 mm).
Comparison of cast iron and steel Yankee diameter 3658 mm (12 ft
Path forward
The tissue industry is an extremely energy-intensive industry. Energy is a key cost element driving competitiveness of individual companies. With EconoFit solutions, ANDRITZ offers tissue producers a wide range of possibilities for energy savings during the tissue making process.
