No manufactured product plays a more significant role in every area of human activity than
paper and paper products. Its importance in everyday life is obvious from its use in
recording, storage and dissemination of information. Virtually all writing and printing is
done on paper. It is the most widely used wrapping and packaging material, and is
important for structural applications. The uses and applications for pulp and paper
products are virtually limitless. Apart from the products and services that it provides, the
paper and pulp industry is one of the major manufacturing industries in the world
providing employment for vast number of people and contribute to national economy.
The paper making process is essentially a very large dewatering operation where a diluted
solution of pulp suspension with less than 0.5% fibre solid is used. The major sections of a
paper machine consist of: forming section, press section and dryer section. In the forming
section, the fibres present in the diluted pulp and water slurry form paper web through
drainage by gravity and applied suction below the forming fabric. In the press section
additional water in removed by mechanical pressure applied through the nips of a series of
presses or rotating rolls and the wet web is consolidated in this section. Most of the
remaining water is evaporated and inter-fibre binding developed as the paper contacts a
series of steam heated cylinder in the dryer section. Water removal from the wet web to the
final moisture level between 6% and 7% is a critical step of papermaking. Majority of the
functional properties of paper are developed in this section.
In spite of its key role in papermaking, large equipment size, and large capital and operating
costs, drying is arguably the least understood papermaking operation. Books on
papermaking technology generally devote fewer pages to drying than other papermaking
operations such as forming, pressing or calendaring. A similar situation is found in
papermaking courses, in which drying occupies a shorter time than the proportion of space
it takes in a paper machine. Furthermore, a large portion of that time is devoted to the
description of the equipment by its suppliers rather than to its operation by the
papermakers.
6. Backside
(Drive Side)
Frontside
(Tending Side)
Steam In
KC Stayed Head Yankee Dryer
Stay Bar
Blowthrough
Steam &
Condensate Out
Blowthrough
Steam &
Condensate Out
Shell
Journal
Head Head
Condensate
Removal Pipe
18. Dryer
Rotation
Movement in
Relation to Dryer
Shell
Condensate
Movement in
Relation to Dryer
Shell
Minimum Condensate
Thickness
Maximum
Condensate Thickness
GRAVITY
28. Identified Problems on B1
• Make-up air dampers closed
• This condition results in the hood not being
balanced (infiltration/exfiltration)
• This condition make the system less energy
efficient.
31. FEATURES SUITABLE FOR:
- New machines
- Rebuilds / replacements
- No limit for paper width
VALUES
- lower energy consumption
at same (competitors’)
performance
= Less cost per ton
TECHNICAL DATA
- Impingement speed up to 37400 fpm
- Impingement temp. up to 950 °F
- Specific evaporation up to 41 lb/hft2
Metso Paper Basic SC- Yankee Hood
39. Controlling Blowthrough Flow
•Stable condensate removal -
Annular flow velocity > 21 m/sec.
Reduces the density with more steam.
Makes condensate removal easier
•Pressure drop is not a reliable indicator of
blowthrough flow.
Blowthrough should be controlled by
controlling flow.
(Or in the case of B3 – Velocity)
40. Effect of Yankee Pressure
On Density and Blow-Through
•Steam density changes significantly with pressure
100 psig steam (7 bar) -- 0.24 m^3/kg
50 psig steam (3.5 bar) – 0.42 m^3/kg
•The higher the density the more blow-through
steam is required for good evacuation.
For consistent condensate removal if we
operate at various Yankee steam pressures
we need to have various blow through
(Velocity) set points.
50. Thermocompressor Sizing
The thermocompressor spindle can regulate
dryer steam pressure.
Changes in spindle opening also change suction
flow (blowthrough).
This can result in blowthrough flow instability
and problems with condensate removal.
Thermocompressors should be sized so that
they remain 100% open 100% of the time.
52. Three Main Control Parameters
• Air Temperature
– Temperature of the impingement air reaching the sheet
• Impingement Velocity
– Nozzle Velocity of the air reaching the sheet
• Return Humidity
– Humidity of the air at the entrance to the burner
53. Effect of these Parameters on Heat
Transfer Rate
Hood Drying Rate Impact
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
0 2 4 6 8 10 12 14 16 18 20
Hood Rw (# / hr-sq ft)
Normalizedvalueof
IdependentVariables
Effect of Humidity Effect of Temperature Effect of Nozzle Velocity
54. Effect of These Parameters on
Fuel Cost
Natural Gas Consumption Rate
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
Normalized Gas Consumption
Normalizedvalueof
IndependentVariables
Effect of Humidity Effect of Temperature Effect of Nozzle Velocity
56. Main Gas
Combustion Air
Main Gas
Combustion Air
TTTT
TC TCTV TV
Tissue Machine Hood System
Temperature Control
PT PT
57. TC TCTV TV
Tissue Machine Hood System
SC SC
Air Velocity (h ) Control
Dampers
a
58. Hood - Yankee Clearance
The hood must supply air in a way to:
•Penetrate the air boundary layer.
•Promote effective mass transfer.
Initial jet diameter depends on nozzle diameters
and the shapes of their edges.
As the jets travel farther from the nozzle exits,
they begin to break up.
Optimum heat transfer occurs when the nozzle
to sheet spacing is 4-7 nozzle diameters.
62. Current Best Practices
Hood System Performance
KPI-01
Hood
Performance
Fuel consumption is less than 3.0 MMBTU/MT
KPI-02
Hood
Performance
Pressure distribution difference between crescent headers in the same hood half,
with profiling dampers open, is maintained at less than plus or minus 5%.
Safety
HD-01 Safety Lockout and confined space entry procedures are in place and practiced.
HD-02 Safety
No water streams or sprays are used to contact high temperature or insulated surfaces of
the hood.
HD-03 Safety
Mechanical stops are checked annually to make sure the hood cannot contact the
Yankee.
HD-04 Safety Personal protective equipment is provided and used when working around hoods.
HD-05 Safety Air Nozzle Best Practices are in use when cleaning around hoods
HD-06 Safety
Burner management interlocks are checked annually. (Fuel High/Low Pressure Switch)
(Proof of Combustion Air Flow) (High Burner Temperature Shutdown)
63. Rate of Rise
1.) Put LIC in Manual
2.) Lower level in FV
3.) Close isolation
valves (manually)
4.) Measure time for
condensate to
rise a given height
Measurement Locations
LIC
Sight Glass
TT
PI
LICF.T.
Condensate
Dryer
DPI
5.) Restore system to
normal