As with many energy intensive industries these days,
the tissue products industry is facing increasing pressure from
rising energy costs. Andritz addresses this challenge with the
development of components and systems for tissue production that
not only reduce energy consumption, but also the amount of emissions.
In the case of the EconoFit project, state-of-theart components
have been developed and existing machine concepts optimized.
The selection of the right application for the tissue
making process is a major decision. The available energy resources
and their 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 optimization, namely conceptual
solutions, specific equipment design for more efficient energy
use, as well as operational optimization and adjustments of the
equipment.
CONCEPTUAL SOLUTION
The ShortFlow™ 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 different mill environments and production requirements.
The ShortFlow™ process
speeds up grade change times and improves the controllability
of the total process. Furthermore, it creates opportunities to
develop the basic process in a new, reliable and exceptionally
useful way.
Strongly supported by the ShortFlow™ concept
is the PrimeLineCompact tissue machine that was launched approximately
two years ago. Based on its design and idea of modularization
a new overall Compact concept was created that considers both
economic and the ecological impacts.
Investment decisions will typically be made on the
expected overall costs (CapEx and OpEx). Machinery suppliers are
therefore required to consider not only the machine costs, as
in the past, but must instead consider the complete plant.
The machine is naturally the heart of the concept
with the highest level of modularization and standardization possible
considered. The stock preparation, energy utilization and building
concepts have also been incorporated into this modular design.
In the machine itself, a single platform former has been designed
for all speed ranges from 1600-2000 m/min.
The drying section is likewise modular. The PrimeDry
steel yankee and the modular high temperature hood (HTH) are optimized
from an energy standpoint. The possibility of considering re-evaporation
can deliver (under optimal operation) a potential for up to a
25% savings in the drying steam requirements.
Through the generation of steam recovered from the
HTH exhaust, it is possible to install a smaller steam boiler,
meaning a smaller water softening system and smaller steam piping,
as well as the logically smaller boiler house.
The standardization concept also allows operations
and mill processes to be performed at the highest degree of standardization.
This together with a shorter delivery time and an accelerated
start-up curve leads to a much shorter payback time and improved
ROI.
The successful start-up of the first PrimeLineCompact
in Europe proves the concept's success. In March 2008 at Fripa
Miltenberg in Germany the PrimeLineCompact successfully went on
stream. On 2 April 2008 a machine speed of 1800 m/min was reached
and two weeks after continuous operation started, 84 tons/day
was achieved. The machine has also operated in excess of 2000
m/min.
PrimePress XT: The new generation of shoe presses
has demonstrated its potential. One main feature is the increased
operational flexibility, meaning that the nip pressure profile
can be adjusted online. There is no need for machine downtime
and press reconfiguration to allow for either gentle and bulk-conserving
dewatering of the sheet or highest post-press dryness. The design
with its tandem hydraulic cylinders makes it possible to adjust
the MD pressure profile on the run. Less re-wetting is needed
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 the post press dryness. Extensive finite element analysis
of the belt stresses and the parallel static and dynamic lubrication
between belt and shoe allow for extended run-times and trouble-free
operation.
Field trials have been carried out on a commercial,
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 g/m2 sheet was observed. This clearly
shows the high potential of the PrimePress XT for energy savings.
Compared to a conventional single press in operation, the PrimePress
XT results in 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.
ReEvaporation: In an effort to use the exhaust air
of the hood to generate steam for the yankee, Andritz has developed
the so-called ReEvaporation system. It re-uses a large amount
of exhaust heat within the drying process. A part of the condensate
out of the yankee is reevaporated within the system and used as
steam in the yankee for drying. The system can be retrofitted
into existing hood systems or supplied with a new hood system.
Based on typical steam costs and operational conditions the payback
time of the investment is rather short.
PrimeDry steel yankee: Compared to cast yankees,
steel yankees have numerous advantages. Due to their lower wall
thickness, steel yankees have a 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
the first day on.
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). The higher performance of the steel yankee compared to cast
yankees can also be used for energy savings. 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 at the same production
level. This results in a reduction of the gas and electricity
consumed. Based on the energy prices shown in Figure 4, a reduction
of 4% of the energy costs can be realized. This amounts to cost
savings of €116,500/yr.
The tissue industry is one of the major energy-intensive
industries in the world, and energy is a key cost element driving
competitiveness of individual companies. With the EconoFit project,
its concepts and equipment solutions, Andritz offers a wide range
of possibilities for energy savings during the tissue making process.
