"Oil prices
have risen by over 420% in the last decade, gas by 310% and coal by 210% (source:
IMF). Further price rises are likely as current reserves are exhausted and
demand continues to grow, with no end in sight."
This is a typical statement from the internet in 2008. The important part
is "with no end in sight". This means that the energy cost situation
is not going to get better, only worse. In addition, carbon labelling will
become part of the packaging on tissue products in the near future, meaning
that manufacturers will have to declare the carbon emissions used to make the
product. This will put more pressure on the manufacture to reduce the specific
energy used in tissue products.
Reducing the specific energy (kWh/ton of paper produced) means reducing losses.
There are two major losses of energy on a yankee dryer: energy loss to the
pressure roll and energy loss to the machine hall via the heads of the yankee
dryer. Only the head insulation is under the control of the yankee manufacturer.
PMT Industries Ltd has designed a head insulation system to reduce the energy
leakage from the yankee heads for both new and installed yankee dryers. The
design (shown in the cutaway) consists of 12 stainless steel segments on each
end of the yankee with insulation attached to the inside; separate panels are
provided for rapid manhole access, although the segments are easily removed
for access to UT bolts.
Recently, PMT manufactured a 15ft yankee dryer for a tissue machine in China
and a 20ft MG dryer for a board machine in India. Both dryers have insulated
heads.
Tests were carried out during the manufacturing process to quantify the energy
saving the insulation gives. By measuring gas consumption of the boiler with
and without the head insulation, the resulting difference was 120 kW on the
15ft steamed 8.0 barg steam pressure.
Assuming boiler efficiencies, etc are similar, this would be a substantial
energy saving in a mill's operation, reducing the bottom line costs and their
carbon footprint.
In addition to the obvious, there are several advantages to insulated heads:
lower operating costs and carbon footprint; safer fire fighting and cleaning;
less dust build-up and cleaned environment; more comfortable environment for
operators.
There are also some disadvantages: additional capital cost; sections need
to be removed for bolt inspections; yankee operational shape changes, so on
retrofits a new crown system may be required.
To quantify the change in shape of the yankee shell, a finite element analysis
was made of the two systems. The results, shown in the graph, show that
the difference in shape of the 15-ft yankee was 0.2 mm at the edge of
the shell and less than 0.1 mm at the edge of the sheet. This is an insignificant
difference and concluded that there is no need for a change in the crown
system. TW
