Energy consumption reduction in tissue drying methodology
Author
D
Mainardi TO Italy
Product
Manager
T ssue
L nes
PMT Italia
A p S
Pinerolo
AbstraCt It is well known that drying tissue paper using high temperature and high drying rates is very inefficient process In order to reduce the cost of the tissue
plants
the
drying
many
attempts
to increase the efficiencies in this
For this purpose different state of the art
part of the process methodology for reducing energy
a
have been made in
costs
are
analyzed
from
the author
In betwwen these
methodologies a cogeneration system which feeds the mach nery and equipment reducing energy A similar system has been supplied by PMT Italia and started up with the aim of reducing thermal costs in a tissue plant Cogeneration or Combined Heat and Power CHP generation is the sequential use of the primary energy source to produce two forms of energy at the same time namely heat and Power The author analyzes and comments on the results from the recent example based on the experiente of the design installation up and running of a state of the art tissue machine fed with gases start coming from a brand new cogeneration plant supplied for this purpose is
a
good
Key
tool for
words tissue plant dryness cogeneration shoe press re nforced
or high n p
load
Yankee
D ryer
Palavra
Chave
Fabrica
de
Cilindro Papel Tissue Secagem gera Co ªo
Secador Yankee
refor ado Exclu do
1 INTRODUCTION the beg nn ng of 2006 PMT Italia t started up jointly Hayat w th Group n Izmit Turkey plant new for a the production of high quality bulky tissue to be converted and sold in the large demanding tissue areal of the Turkish region 1 The project has been developed as a greenfield mill in a 18 months span iointly time between th tw o e companies The plant that s cons dered one of the most modern in the nation includes a Crescent Former PMT Italia tissue machine for high quality tissue paper four unwind stations and one PMT Italia winding stat on for the production of multi layered types of tissue The plant also includes two PMT Italia stock preparation l nes w th the auxiliary systems necessary for the operation of the machine steam system high performance cogeneration hood lubrication system DCS etc The main technical
parameters are 000 converting 60 tpy
Production at
AD
Average daily production 180 tpd AD Max daiy production 230 tpd AD 200 mpm Design speed 2 Max speed 2 000 mpm 600 mpm Average speed 1 28 g Range of basis weights at reel 14 mZ The types of paper produced are mainly toilet tissue The
9
Exclu do
Exclu do
nas
Exclu do
ing
Exclu do
together
Exclu do
s
and kitchen towel
unique featurer of the Hayat plant is that the design of the machinery has been done in or o t r de optimize the production cycle the quality of the tissue produced and the energy savings factors
2 COGENERATION IN HAYAT TISSUE MILL
prying
tissue
as
purpose HAYAT
indicated
Yenikoy
The electr cal
and high dry ng is a very inefficient process In rates order dry ng process many attempts have been dope in the tissue plants For this cogeneration system has been designed for reduc ng thermal energy cost n
temperature us ng paper high
to reduce the cost of the a
The
as
q
Exclu do
canceuing
Exclu do
is
Exclu do
is
Tissue Plant
7percent and 66 3percent of energy nput is Hayat Yenikoy plant is 33 coming from the turbines These Ovaste gases having a sign ficant temperature about 500 C and at high flow rates can easily be used in a special design Yankee hood reduc ng and even their air systems depend ng on liminating the gas consumption n the production rates considered High temperature Ovaste gases are utilized to dry the tissue then to generate steam and cold water at a constant temperature levei Electrical equipment is needed to distribute the electricity or to produce it in parallel with the utility grid Hydraulic interconnections are needed to transport cold water or steam wherever it is required released
Exclu do
efficiency
n
residual heat in the Ovaste gases
in HAYAT Tissue Plant consists of six basic elements
cogeneration system Two 7 5MW gas
turbines natural gas fired
BRUNNSCHWEILER Yankee Hood Two steam boilers Four duct burners steam
two
reserve
burners for the hood
boilers ali to be used when the turbines
are
systems off
Absorption chillers New adapted control system in hood air circuits for operation of the hoods and the turbines The gas turbine is
designed
for cont nuous
operation
from
and two
the perfect
reserve
ntegration
burners for the
between the
idle to full load The turbines feature the
SoLoNO system that is a lean premix low emission combustion system for NOx control designed to achieve low NO and CO Selected turbine exhaust
necessities of mass gas flows and temperatures are suitable for the dry ng grades Full use of cogeneration gases is desired cogeneration gases flow calculated have minimum gas consumption in hood burners Fans burners hood boilers and chillers are designed according to the new air flows and temperatures As a comparison with tradit onal systems involving a conventional gas heated hood Ove can verify the ma n difference in the operation of a new system In fact Ove can see that the Ovaste energy flows delivered to the atmosphere re the n with reduced tissue dry ng and steam complete ntegration of the three processes Electricity generat on generat on which means that the total energetic efficiency of the system is improved We will quant fy this improvement with the actual efficiency parameters normally used in the next chapter Calculations various tissue
The ma n
advantages
of the system
are
Better gas energy
saving as no gas is consumed in the hood burners Minimum gas energy loss through ch mney because of use of residual cogeneration gases for dry ng and steam generat on
thermal energy from
3 CALCULATIONS The ma n
features of relevance to the case
under considerat on study
are
I
Exclu do 9
Yankee Diameter 5486 Yankee Yankee Yankee
Creping
mm
Paper Width 5600 mm Speed 2000 mpm Product on 7321 kg h Ratio 16
percent Weight 13 g m2 Energy Product on turbine efficiency
Reel Basis Electrical
7 33 percent
f
There
315 kW @ 15 C and 97 000 kg producing 7 hof Ovaste as in most countries the ratio between electricity unit in cost and thermal unit cost is very attractive for optimisat on About 3 kW of electrical energy can be h of Natural gas The rest of the energy will be util sed for the steam generation produced using 1 Nm3 and ch lled water production apart from the use of the Ovaste gases n the BRUNNSCHWEILER Yankee hoods Due to the electrical balance of the Hayat Site the generat on of electrical energy exceeds the requirements for the HAYAT Tissue plant n excess electrical energy will be For th s reaso used in a possible other HAYAT plant or can be sold to the grid Every tissue plant cogeneration system should be designed according to the r own necessities are
gases at
In this
two gas turbines and each
C 490
one
is
In the Turkish energy scenario
are designed to cover only around 78 of capacity what this means is that for an average production rate of the machine the gas consumption in the hoods is totally liminated The missing 20 thermal energy for the attainment of the maximum production capacity for high grammage tissue max drying capability in the machine will be supplied by the standby duct type burner in the hoods circuits For that case consumed Natural Gas amount is 2300 Nm3 h @ 15 C in every gas turbine h in every reserve hood burners always for maximum capacity See the following plus about 210 Nm3 graph case
Ovaste gases
the hood thermal energy
flowing from requirement
Total Natural gas consumed for both electrical and thermal energy
But
IN
In
on
Plant is 2300 Nm3 h x 2
210
the other hand in this way Ove
are
h Nm3
capable
4810
to sell
in the tissue
production
and
plant
h at full capacity in the tissue machine Nm3
an excess
of
electricity
to the net of
6 MW 3
COVENTIONAL MODE
the
case
conventional
of the
hood
typical
being
stopped
rec rculation
reduced flow in exhaust
consequently tine will be in
turbines in
operat on
Hood air circuits is not
in order to
enough
an
the Yankee Hood
mode
with
h gher standby
In this case the
produce required
amount of
additional externa air is
air
circuits
moisture
w ll
content
operate at
as
an
and
exhaust
burners installed in the exhaust air
steam but
as
the flow
given by
the
needed to compensate the missing flow in
the steam boilers In
this
h Nm3
case
the total natural gas
but no
So the energy
excess
electricity
consumed
is less
f
compared
is available to be used in the mil
cost balance in the two
capacity production
is summarized
n
exclu do
canceued
at maximum
IN COGENERATION MODE
Hayat 230 tpd
ed
the turbine exhaust
FOR FULL CAPACITY IN TISSUE MACHINE OF 230 TPD
other
exclu do
cases
conventional
the hereunder table
and
or
with the
cogeneration
mode
959
sold
cogeneration mode
for machine
full
FOR MAXIMUM PRODUCTION CAPACITY 230 TPD GOGENERATION HOOD Net production at reel
Prod uc ion
CONVENTIONAL
58 9
h ton
Net
production
HOOD
at reel
58 9
0 230 day ton anil cost
anil cost
32 0
Nm3 USD
HHV
80 10
Nm3 kWh
Natural HHV gas
Energy cosi
Gas
Electricity
80 kW hIN m3 10
cost
63 29
MWh USD
unlt cos when bu In
00 80
USDIMWh
unlt cost when bu
unir cost when
00 90
MWh USD
unir cost when
00 32
ton USD
ower
selling
unlt cost Steam
Latent heat at 8 bar Steam power
76 56
Gas
as
densit V
cost
ower
In
00 80 00 32
cost
Latent heat at 8 bar
USDIMWh
00 USD 90 MWh
selling
unlt
MWh USD
63 USD 29 MWh
ton USD
50 kJlkg 2029
Steam gower cost
steam
76 USD 56 MWh
3772 kc h
mc as
Turbines
Gas
steam
50 kJlkg 2029
cost
h ton
0 230 day ton
32 USD 0 Nm3
0 8 2 k INm3 4600 Nm3 h
as
Cost
1472 USD h
Natural gas 172 kg h 82 Nm3 0 kg
mgas Yankee
gas
denslty
hoods
V
210
as
Cost Total elect
ower
consumed
atlhe
Cost
67
lant
h USD
as
Cost Total elec
ower
consumed
at
0USD MWh
Cost
denslty V
0MW 11
unlt cost
786 kg h 82 kglN 0
mgas gas
h Nm3
lhe lant
unlt
0USD h
m3
959
h Nm3
307
h USD
0MW 10
cost
0 80 MWh USD
Cost
0 800 h USD
Electricit y Total Income
electricity produced at lhe plant electrlcity sold to lhe net
6 14
Excess of
Steam Steam
7 326 h USD 0ton 9 h
consumption
Cost
unlt cost
In lhe table paper
we can see
lhe reei of
on
In this table
we
produce
0
ton of paper at reel
a
that there is
Steam
unlt cost
h USD
5 126 ton USD
Cost to
0USD 19 tonof paper
have not considered lhe ncome
0 32 ton USD
Cost
produce
a
on
related to lhe
lhe reei Soa
excess
288
ton of paper at reel
net reduction in lhe energy cost consumed to
a
5 126 145 5
0toNh 9
consumption
0USDIton
Cost
Cost to
MW
6MW 3
Income
of steam
h USD
5 145 ton USD
produce
a
ton of
13 of reduction
produced
for
anc llary
equipment For 8000 noted
yr we h
that
equipment
no or
would have 19 0USD tonx
consideration
chilled water
of
lhe
58 ton 9 h x 8000
Income
related
to
lhe
456 USD 1 yr 160 h yrIt should be steam produced for ancillary
excess
has been mad
production
FOR A REDUCED CAPACITY IN TISSUE MACHINE TO 192 TPD
If
we now repeat lhe consumption required
same
comparison for a reduced capacity of 192 TPD and no additional burners we obtain lhe data summarized in lhe following table
gas
in hood
FOR A REDUCED PRODUCTION CAPACITY 192 TPD GOGENERATION H OOD Neproduction at
Production
reel
CONVENTIONAL HOOD
00 8
h ton
Net production at reel
00 8
0 192 day ton
N
a
t
anil cost
32 0
USDINm3
HHV
80 10
Nm3 kWh
ura l
gas
Gas
powercost
when cos uni E
ergy costa
Electricity
anil cost when
buying selling
anil cost Steam
Latent heat atØ bar eam powercost S mgas
Gas
gas
density
Turbines
Vgas Cost
N
tural gas mgas Yankee
gas
denslty
hoods
Total elect
Total olectricity Income
Income
Steam
Costa
consumption anil cost Cost
Cost to
produce
0 kg h 82 kgMm3 0
0 11
a
ton of papor at rcl
MW
mgas gas
density Vgas Cost
Total elec power consumed at thc
plane cost unl
0USD MWh
6 14
Stcam
powercost
MWh USD
ton 00 USD 32 2029 kJlkg stcam 5
76 56
MWh USD
82 kgMm3 0
produced alhe plan sold to tho net
Stoam
MWh USD
1472 USD h
0
Excess of clectricit
MWh USD
80 00 00 90
4600 Nm3 h
Cost lectricity
Latent hcatat8 bar
69 USD 29 MWh
h kg
0 USD h
cost
buying when selling cos anil cost
steam
0 Nm3 h
unlt
Nm9 kWh
anil
Cost
plant
Nm9 USD
80 10
MWh USD
00 32 2029 kJ 5 kg
3772
32 0
HHV
costwhen uni
ton USD
76 56
unir cost
Gas power cost
USDIMWh
Vgas
power consumed at lhe
Costa
69 USD 29 MWh
80 00 00 90
h ton
0 192 day ton
h USD
Cost
615 kglh kg Q82 Nm3 750 Nm3 h 240 USD h
1Q0
MW
0 80 MWh USD
0 800
h USD
MW
3MW 6
7 326 0 9
h USD h on
Steam
0USD ton
2 USD 143 ton
consumption unir cost
h 0 USD
Cost
Cost to
produce
a
ton of paper at reel
0 9 32 0
h ton ton USD
h 288 USD
0 166
ton USD
The reduction in the energy cost consumed to
2 ton 143 USD a 14 8 2 So
Jn
this table
have we
produce
one
ton of paper
on
the reei is
now
0 1
Exclu do
of reduction
Exclu do
not considered the incorre
tothe excess of related
steam
produced
for
ancillary
equipment
72 8
Exclu do Exclu do
For 8000
00 ton 8USD 2 x8 ton hx 800 0h yr 1 200 59It 4 yr USD should be noted that no consideration of the ncome related to the excess steam produced for ancillary equipment or chilled water production has been made
yr we h
would have
FFICIENCY COMPARISON
Exclu do
8
Exclu do
843
Exclu do 4
A
n
comparison effic ency
between the two different
Hereunder you find this kind of
drying approaches
could be
interesting
4
also in terms of
4 4 4
comparison
4 4 4
Energv efficiencv parameters CONVENTIONAL HOOD a 4 M r
hood evap
x
4 4
7171 kW
hfg
8
DRY NG M f
x
LHV
10526 kW
4 4 4
Enerav efficiencv Darameters COGENERATION HOOD b M r
hood x vap
hfgx hfg am Mst net Wx
DRY NG gOILER GENERATIONS
M
LHV
x r
7150 kW 2x7315 kW 2x6800 kW 74 3650 kW 2x22110 kW
Energv efficiencv parameters COGENERATION HOOD WITH CHILLERS c
vap x x M hood Msthfg t n Wx hfg 0ans r
g GEN DRYING AgS O CHILLER
M
x i fu
LHV
7150 kW 2x7315 kW 2x6800 kW 1x4650 kW 83
when
we use
only one chiller
3650 kW 2x22110 kW
hood x hfg Mevap Xhfg Qabs cam Ms net Wx r
DRY NG Ag gO GEN C H LLER S
M r
x
LHV
7150 kW 2x7315 kW 2x6800 kW 2x4650 kW 93
when
we use
two chillers
3650 kW 2x22110 kW
W here
vap hood evaporation kg M d h s of water evaporation at balance temperature nnet power produced by generator kW Wx am steam mass created in the boiler house kg Mst s Qabs Equivalent heat to chilled water kW
hfg enthalpy
kg kJ
5
quant ty to the conventional case s kg LHV gas low heat ng value i gas Mru
turbine
burners
cogeneration case
or
to
the hood
halves
kg kJ
COGENERATION FEATURES 4
pesired operation ofthe explained before as system cogeneration installations which
Parallel
are
is based
on
the
simplified
control
of
listed below
arrangement
to
simplify
controls and
enable easy
integration
between gas
turbines
and Yankee hoods Control of available pressure in the turbine exhaust Control of balance in the hoods Control of
supply temperature
Control of
0p
No
reason
in combustion fans
for moisture control
n
the exhaust from the Yankee hood
Bypass arrangement Control of pressure in Ovaste heat boiler
In the followinq
figure
a
schematic process
STEAM GENERATOR
diagram is shown
t
STEAM GENERATOR
RESERVE
RESERVE
BURNER
BURNER
1
EXHAUST FAN
Fig
1
Integration
of gas
exclu do 4
EXHAUST OFF
OFF
FAN
turbines Yankee hoods and Ovaste heat boilers for steam generation
6
q
SHOE PRESS SYSTEM FEATURES 5 As
already indicated before another implementation on the machine that might affect the energy consumpt on reduction s that the des gn has been prov ded in order to be easily retrofitted with shoe press technology For this reason the follow ng features have been appl ed to the press and YD sections The des gn of the felt run has been carried out with one press solution with the possibility to nstall the shoe press in a short shut down period The large diameter press has been supplied with no driven configuration The SPR can be re used for felt condit on ng in the shoe press configuration The YD prov ded PMT Italia sfully owned UK subs diary by PMT INDUSTRIES LIMITED has been supplied as h gh load dryer allowing to work up to 170 KN m nip The des gn of this solution allows to have versatility in the requirement for the t ssue manufacturer In fact a shoe press can be used aga nst the Yankee to increase post press dryness by ut lising h gher line loads than a conventional suction pressure roll in this way the energy consumpt on is reduced having h gher dryness at the hood inlet or by reducing the line load can reduce the loss in bulk associated with pressing as indicated in Fig 3 Erro V nculo In any atile to
case
w th
operate
nªo vÆlido
the introduction of the shoe press to with
But there must be
an
no
external line load of up to 170
loss n
drying capacity
as
t ssue machines the Yankee dryer needs to be m mas opposed to the conventional 90 kN kN
the Yankee may still be used with the conventional 90
m suction presser roll kN Th s
potential problems H gh external l ne loads create h gh fatigue stresses n the an acceptable leve the shell strength has to be ncreased However an increase in shell thickness the conventional way to increase shell strength reduces heat transfer flux and this results in less drying It also increases the possibility of shrinkage porosity reducing the tensile strength and quality of the casting Both these potential problems have to be addressed presents
some
shell to reduce the stresses to
1 Design 5
of
The heat transfer
h gh
load Yankee
problem through
was
compare the heat flux
condit ons model
the ribbed bore
is
plain h gher a
to show the distribution
producing
t ssue
Dryers
solved 40 years ago with the bore shell Th s
can
of heat flow
vs
a
ribbed
be illustrated
flux through
development
bore for the
by using a
FEA
section of
of the ribbed shell
same
a
pressure and l ne
Finite
Element
If
we
load
Analysis
Yankee shell when it is
HF1xX
HFlx
26m
260
2 38
239
298
zmm
9 1
iam
1a9
iam
119
iim
m sm
m sm
9 s9
m sm
9 29
9 29
F gure The model in
figure
3 Heat Flow
4 shows
a
through
section of
a
On the inside of the plain bore shell there is flow thus
a
Plain Bore Ribbed Bore Yankee Shell
plain Bore a layer of
shell
on
the left and
a
ribbed bore
condensate which acts
as
on
the
right
barrier to the heat
drying capacity The ribbed bore only has the layer at the bottom of the grooves with the rest of the rib in direct contact with the steam The heat flow pattern on the ribbed shell shows that most of the heat transfers from the side of the r b just above the condensate layer th s is because there s no condensate layer to insulate and restrict the heat transfer and there is less iron shell material to pass through than the rest of the rib On average the rib design has approximately 30 larger heat transfer than a corresponding pla n bore design with turbulator bars and approximately 50 larger heat transfer than a corresponding plain bore design w thout turbulator bars But with the increase in line loads further developments are needed For a high externa tine load the shell second moment of area needs to be increased to ma ntain acceptable shell stress leveis Th s can be done in two ways figure 5 insulating
i ii
reducing
the overall heat transfer and therefore
a
condensate
by increasing by increasing
the rib
he ght
or
the root thickness
Figure
4 Alternative
Design
Ribbed Bore Yankee Shells
The increased rib
height option has the disadvantages of a greater overall machining however it has the advantage of higher heat transfer
cost of
thickness and
HFixx
HFixx
00 430
08 439
2s 376
2s 376
50 322
59 322
75 268
7s 268
mm zis
mm 2is
Figure
5 Heat Flow
zs isi
2s isi
sm im7
sm im7
759 s3
7s0 s3
mmmm m
mmmm m
through
increased
Alternative
Design
Ribbed Bore Yankee Shells
The model
n figure 6 shows a section of the increased r b option on the left and the increased root option on the right As shown before most of the heat flows through the r b just above the condensate layer however in the case of the deep r b design the heat flow is larger because there is less metal between th s the
area
and the outs de
of the shell It should be noted that there
s
little
or no
heat flow
deep rib the add tional height of the rib provides strength only by ncreasing the second moment of area t is the reduction of root thickness that increases the heat flow The similarity of root thickness makes the deep rib design comparable in drying to a conventional low tine through
of the
top
load Yankee
2 Casting 5
of
high
load Yankee
The cast thickness of the shell for
casting quality
high
Dryers
load YD is
50 thicker than
a
conventional ribbed shell and
must be maintained
Over the last 50 years the
quality of PMT Ind castings has been improved dramatically Specially developed Class 60 shell material and optimised foundry practice ensure that Yankee dryers have the optimum strength conductivity and wear corrosion resistance character stics with m nimal var ation along the length of the shell As a result of these developments the Yankee castings have less surface defects less
through shell leaks radiographs which along Qual ty control assessment better
shell ultrason c
examination
are
part
of
a
r gorous
experiente and ongoing development PMT Ind now has another sophisticated gives an advantage over the predecessors the computer A recent investment in a state of the art casting software package now gives PMT Ind the chance to model a casting without the time and expense of making a casting This in conjunction with the acquired experiente has enabled us to predict the quality of a casting before any metal is poured Today
in addition to the
with 100
tool which
Figure
The
example shows a liquid The Hayat high
Example
section of load YD
November 2003 the first
3 5
6
deep
rib
PMT Italia shoe press
The PMT shoe presses
family
All the PMT solutions feature m up to range between 80 KN
an
was
of
Casting
Software
Modelling
Yankee Shell
18ft Yankee shell where the metal has frozen and where it is still the fourth
design
cast in this range of
Yankee shell
was
product by
PMT Ind On the 7th
0m cast 18ft diameter 6
long
design
varies from standard shoe press size to
patented SMARNIPTM solution edge relieving system and shoe tilting and can operate n a force line 170 KN m Shoe length s defined accord ng to the different shoe press
adoption Shoe presses main features
Machine direction
Long nip Possible
are
elongated nip
residence Time
high Press Impulse specific pressure peak intensity D specif c pressure development in M
Control of Gradual
Uniform Cross Machine
Nip propert es
10
Effect of shoe presses
on
tissue
grade
could be defined
Higher Bulk at same Dryness H gher Dryness at same Bulk Flex ble Nip no more crown issues poss bil ty
as
Or
Better adhesion of sheet Better moisture Better
Yankee
to
run
any
nip
dryer
profile
creping
The shoe press solution for easy retrofit in mach ne
on
a
new
proposed by PMT can be offered in three different ways for new machines machine prepared for l ke the case of Hayat and finally for major tissue
rebuilds
CONCLUSIONS 6
The authors have
presented with a practical case the innovation that can allow in a modern tissue consumptions costs For the total efficiency point of view cogeneration type drying is clearly the right choice and it opens a new field in the use of residual energies in the drying processes where very modest attempts jn this respect have been carried out in the past The main innovation of the Hayat project now a reality lies in the fact that no one ver undertaken an integration at this exten has Further considerations than could be done case by case adopting other different turbines design and plant
to reduce the energy
features Furthermore shoe press reliable
h gh
load YD s
Amendments
technology ava lable among PMT Italia tissue range products combined ght additional tool to implement energy consumption reduction
The author would
from Brunnschweiller
with
the r
Spa n
A S
like to thank
you the
Hayat Group management
and
to O
Lopez
for the contribution to the paper
Bibl ography D
1
s Article Mainardi Tissue World
reducition in tissue Energy consumption drying methodology Magazine July June 2007 by A Isiklar L Aydin D Mainardi and O Lopez Hayat
cogen cuts costs
2 O
2th APPITA
Lopez
A
23 2008 by D Mainardi G Gianlorenzi Conferente Rotorua New Zealand April 21 Emmanuel Energy consumption reduction in tissue drying methodology