See discussions, stats, and author profiles for this publication at: https://www.researchgate.

net/publication/232948832

Key development phases of condebelt: Long journey from idea to commercial

product

Article in Drying Technology · August 2006

DOI: 10.1081/DRT-100108248

CITATIONS READS

8 1,007

1 author:

Elias Retulainen
Fiber and Fibril
116 PUBLICATIONS 1,500 CITATIONS

SEE PROFILE

All content following this page was uploaded by Elias Retulainen on 16 April 2018.

The user has requested enhancement of the downloaded file.

Keynote lecture at the 12th International dying symposium. Advances in Paper Dewatering, AIPD 2000;
Noordwijkerhout, Netherlands, Aug 28-31, 2000.

KEY DEVELOPMENT PHASES OF CONDEBELT,

LONG JOURNEY FROM IDEA TO COMMERCIAL PRODUCT

Elias Retulainen

Asian Institute of Technology, Pulp and Paper Technology, P.O. Box , Klongluang,
Pathumthani 12120 Thailand, E-mail elias@iki.fi

Keywords; paper drying, press drying, product development, paper properties, drying rate

ABSTRACT

The development of Condebelt from idea to a commercial product took twenty one years. The first patent
was issued 1975 and the start-up of the first mill scale installation was 1996. The results obtained from
the first mills scale applications have clearly exceeded the early expectations put on the paper properties.
The progression of the development work was not a continuos and steady. The development work was
even halted for nearly three years in early 80's. However, since the late 80's extensive efforts were made
to commercialize the process. Several static test dryers and two dynamic pilot machines were built. The
second pilot machine especially offers versatile capabilities to study the drying process and it’s effects on
commercial paper and board grades. Recent efforts have concentrated in applying the concept to
increasingly wider machines and higher speeds. Technically Condebelt has been a success, a brilliant
example of perseverance and ingenuity. However, the extent of work needed to overcome the
encountered problems probably was seriously underestimated. Commercially it has not become a success
story, yet. But it has all the possibilities to become a one.

INTRODUCTION

Condebelt process has been applied in commercial scale since May 1996. At the moment two mills
are applying this technology for board grades. The process brings excellent improvements in board
properties. The best improvements have been obtained with grades where high z-pressures can be
applied, like with core board and linerboard. Recently the process has been applied also for drying bulky
board grades as well (Retulainen et al., 2000). With a narrow machine the energy economy has been same
or better than with conventional machine. With wider machines the economy is clearly better.
Any development project contains ups and downs, periods of success and failure. The Condebelt
development is not an exception. It has been an exceptionally large development project which, in terms
of efforts, time and money, has very few equal in extent.
The objective of this presentation is to give a general view of development history of this interesting
invention. Unfortunately, there are very few persons who have been involved with the development of
Condebelt for more that 5-10 years. The only person who would have known the full history of the
invention - Dr. Jukka Lehtinen - cannot be asked anymore. This restriction makes this presentation
imperfect and subjective.
Keynote lecture at the 12th International dying symposium. Advances in Paper Dewatering, AIPD 2000;
Noordwijkerhout, Netherlands, Aug 28-31, 2000.

THE INVENTOR AND HIS BACKGROUND

When we are looking closer at the development of the product that we today know by the name
Condebelt, we cannot underestimate the role of Dr. Jukka Lehtinen as the inventor and key driving force
in the development work. This invention is, no doubt, one of those where the inventor can be clearly
identified and were inventor's interest, enthusiasm and large knowledge could be utilized in putting the
invention into practice.
Dr. Lehtinen got his main education in US where his father served at the Embassy of Finland. After
graduating from high school he was enrolled at Massachusetts Institute of Technology where he studied
thermodynamics reaching doctor's degree 1957.
One of his first employers was Westinghouse Electric Corporation, where he already was planning
thermal processes. Later he served as professor in Finland and in Brazil. In the year 1973 he was
employed by Tampella Corporation. Tampella was a company that had both paper and board production
and machine construction, including grinders, paper and board machines. In Tampella dr. Lehtinen was
deeply involved with paper machinery and paper production. Among many other ideas he started to
develop ideas to apply heat pipe process in paper and board drying.

HEAT PIPE PROCESS

It seems that Dr. Lehtinen was attracted to this phenomenon since his student years. At those days
student dormitories had steam heating. The steam heating was complex and clumsy for this purpose but it
is easy to think that a student studying thermodynamics and listening to the banging of steam pipes easily
got involved with the “mental life and behavior” of steam and condensate.
Heat pipe phenomenon is
illustrated in the Figure 1. An
airless chamber, a pipe,
contains liquid in equilibrium
with vapor phase. When the
liquid is heated by external
heat source and thermal energy
(T1) is brought to the system,
vapor is produced and the
latent heat of the vapor is
transmitted to the top of the
pipe, which is coolest part of
the heat pipe. The vapor
condenses there rendering the
latent heat (T2) to the end wall
of the pipe. The condensate
flows back to the liquid
reservoir and the process can
be repeated indefinitely for
heat conveyance. This process Figure 1 A schematic illustration of heat pipe process and the Condebelt
has high energy transfer rate process.
and the process can continue
indefinitely.
Keynote lecture at the 12th International dying symposium. Advances in Paper Dewatering, AIPD 2000;
Noordwijkerhout, Netherlands, Aug 28-31, 2000.

THE INNOVATION AND THE FIRST EXPERIMENTS

First patent

How the heat pipe process could then be applied in paper drying? On the right side of the Figure 1. we
can see that in Condebelt thermal energy T1 is brought to a closed chamber formed between a cold and a
hot steel belt. Water is evaporated from the web and the vapor traverses through the web and wires to
the cold steel belt and condenses there. The latent heat is conveyed to the steel belt and further to the
cooling water where it can be Basically this is a heat pipe process, but the water is located in the web
and the condensate is not allowed to move back to the evaporation zone. Due to this the process slows
down with the reducing moisture content in the web and finally the process stops. Additionally on micro
scale heat pipe process occurs in the web during the initial stages of the drying. The evaporation
condensation cycle takes place in the conduits of web, and the web moisture traverses toward the hot
surface. This process is responsible for the quick warming-up of the web in the beginning of drying
process.
In Fig . 2 we can see diagram of the first
patent filed in December 1975 (Lehtinen, 1975).
The basic design of the equipment is
surprisingly similar with the process applied
today. The use of vacuum – which was
considered necessary - probably was the reason
that impermeable heat conductive belts were
considered from the beginning.
The main advantages of the process was
expected to be in the area of improved drying
rate and heat economy. The main assets of the
process were considered to be the high
evaporation speed at relatively low temperature,
simplicity of the process and evenness of the
process conditions. The equipment was
considered to be "a low cost one", "small in size"
and "low in energy costs, noiseless and safe
without any basis weight, speed or quality Figure 2 Condebelt process as illustrated in the first
restrictions". The patent implies that suitable patent (Lehtinen 1975).
temperature of the hot side was assumed to be
not much over 100oC and cold side temperature from 10 to 40oC for the cooling side. (As we know, today
the cooling side temperature is around 80 oC and the heating side from 120 to 160 oC.) The patent
contained no reference to potential improvements in paper properties.

Experimental results obtained with static laboratory dryer

The laboratory scale tests were started in the year 1976 and results were very promising. The first
results were however not published earlier than 1980 (Lehtinen, 1980). The drying speed clearly
exceeded that obtained with conventional methods and improvements in paper properties were also
obtained. Most improvements were in strength properties. Tensile strength of newsprint was found to
improve from 7 to 14%. Some improvements in smoothness were also recorded. The hot surface
temperatures were around 170oC. The main advantages obtained were in the improved drying rate, which
was estimated to be even 12 times that of conventional drying. In the first static devices the sheet
experienced an external pressure of 0.1 MPa (1 bar) or less due to the vacuum created in the drying
Keynote lecture at the 12th International dying symposium. Advances in Paper Dewatering, AIPD 2000;
Noordwijkerhout, Netherlands, Aug 28-31, 2000.
space. This process was called CONVAC, referring to the process of maintaining the vacuum by
condensation.
The vision of commercial Convac process was in the first publication based on drying the web
between a large diameter cylinder and a cooled belt (Fig. 3) . This construction, however, was later
abandoned due to anticipated problems in belt steering, unsufficient heat flux through the cylinder shell
in order to reach 170 oC surface temperature and the high steam pressures needed.

Figure 3 Proposed commercial cylinder Convac dryer

(Lehtinen, 1980).
OTHER PARALLEL DEVELOPMENTS IN THE FIELD OF PRESSING AND DRYING

In early 70's oil crisis promoted research on new drying methods. Independently at STFI in Stockholm,
Sweden and in Forest product laboratory in Madison, Wisconsin, similar ideas were developed. Their
main objectives were to improve paper and board properties by effectively softening chemical
components of wood and pulp fibers in order to use high yield pulps and hardwood raw material.
In both processes the laboratory experiments showed excellent improvements in several paper
properties like compression strength, tensile strength and internal bond strength (Anderson & Back, 1976;
Setterholm, 1979). Later improvements were also found in the wet strength, dimensional stability and
humidity resistance of press dried sheets. The effect of increased drying pressure and temperature on
paper properties was clearly demonstrated.
Press drying was not completely new type of process in forest industry. Similar process has been
applied in hardboard manufacture where belt-based processes were utilized. However, in paper drying
the applications of press drying were was mostly considered to be take place using press nips.
In early 80's a new process innovation called impulse drying came up (Wahren, 1982). It seemed most
promising. Vast possibilities to reduce energy consumption were reported. Also improvements in paper
properties were found. Also serious problems were encountered, delamination of the sheet at high roll
temperatures and sticking at lower temperatures. This process got very much attention and it was
competing with press drying process for the interest of paper makers.
Press drying and impulse drying were revolutionary developments, but a parallel evolutionary
development took place in wet pressing where increased web temperature, longer nips and double felted
presses were utilized. The solids content of the web could be increased several percentage points with
corresponding effects on paper properties.
Keynote lecture at the 12th International dying symposium. Advances in Paper Dewatering, AIPD 2000;
Noordwijkerhout, Netherlands, Aug 28-31, 2000.
INCREASING THE CONVAC DRYING PRESSURE

The development of Convac/Condebelt benefited greatly from the press drying studies. Several
reports showed that raising the z-pressure to a level above 0.1 MPa (1 bar) improves considerably the
strength characteristics of the sheet. This increased the interest to test the effect of higher pressure in
Convac drying. In Table 1 we can see results obtained using a static Convac rig at Helsinki University of
Technology. The Convac drying improved kraftliner properties distinctly but increasing the z-pressure
from about 0.1 MPa( 1bar) to 1.2 MPa (12 bar) is clearly beneficial to both strength and smoothness of
the sheet. Tensile and Ring Crush compression strengths were improved by 36-38%, while Convac drying
at lower z-pressure gave improvements of 12-18%. These and other similar results suggested that Convac
suits well to board grades and better results are obtained at higher z-compression pressures.

Table 1 Effect of normal Convac drying and Convac press drying on kraftliner handsheets (200 g/m2) (Jokio et
al., 1982)

Density Roughness, Tensile index Elongation Tensile stiff. RCT index

Sample kg/m3 (Bendtsen) ml/min Nm/g % index, Nm/g Nm/g
Drum drying 626 2050 61 4,5 4597 13,3
Plate drying 679 625 64 4 4554 15,5
Convac 140C 681 600 72 2,9 5814 15,0
Convac180C 672 925 69 2,9 5581 15,1
Press drying 0.6 MPa, 140C 754 215 84 3 6066 18,2
Press drying 1.2MPa, 140C 793 170 83 3 6075 18,2

Tests undertaken with the static dryer suggested that main economic incentives to develop
Convac/Condebelt further to a production machine stage were:
1) Improved strength and other quality characteristics
2) Increased drying rates
3) Possible energy savings

Some papermaking companies became interested in this new method already at the early stages.
However, in order to have significant progress the support of machine manufacturers was essential. In the
year 1978 a cooperation between Tampella and Valmet was initiated in order to further develop Convac
process. Valmet had plans to build a pilot unit. However, Valmet's interests were greatly diminished
when the experimental results suggested that the method suits best for board grades. Additionally, a
world wide depression in paper and board machine business started and Tampella had to cut down
development projects. The development work of Convac was halted for three years.

THE FIRST DYNAMIC CONDEBELT DRYER

In 1985 the development work was restarted within Tampella. New winds were blowing in the
company and great visions for the future were painted. The development of Convac started from the
original idea of using two horizontal belts. The static test results were good but there were a number of
uncertainties: Does the process function under dynamic conditions? Do the belts, seals and other
mechanical parts stand under the demanding thermo-mechanical conditions? A small dynamic test
device was built to check these questions. First version had only one belt to test the controllability of the
belt rotation and other mechanical functions. Soon the second belt was installed. The belt width was 150
mm and the length of the drying zone was 1 meter (Fig 4). This machine was run at various speed
Keynote lecture at the 12th International dying symposium. Advances in Paper Dewatering, AIPD 2000;
Noordwijkerhout, Netherlands, Aug 28-31, 2000.
ranging from 0.4 to 20 m/s. Intensive testing period of three months took place. These dynamic test
results verified the earlier results with static rigs. The basic assumptions were correct and properties of
the dried web were equivalent to those obtained with the static rig. A special reason contributed to the
short trial period. The experiments took place in a power house where steam was readily available.
However no proper sealing was not constructed for the device and the steam leakage from the test device
was so extensive that considerable corrosion started in all machines in the neighborhood. No further tests
were allowed to take place in the power house. The tests had, however, shown that the dryer both the
mechanical and thermal processes work even at high speed and the drying process possesses a
considerable potential for drying paper and board grades. But there were also many details to be
improved.
Since the emphasis in the development work has clearly shifted towards higher steam pressures and
temperatures, Dr. Lehtinen renamed the process. The new name was CONDEBELT, implying that an
essential feature of the process is the use of a cool belt which acts as a condensing belt.

Figure 4 The first dynamic Condebelt unit. (Lehtinen, 1988)

THE FIRST LARGE SCALE PILOT MACHINE

Based on the encouraging results from the first dynamic pilot dryer the designing and planning of a
new larger scale pilot machine was started in 1987. The final decision to build the pilot machine was done
in May 1988. It was to be the so called high pressure version, although ideas related to the low pressure
version were also developed. Two years later 1990 the first experiments were conducted with the new
machine. There were large number of details that were to be solved in order to find the most suitable
solutions in the dynamic process. Special attention was needed in designing the seals and choosing their
material. The most demanding area was the steam chamber/hot belt interface, and the edge seals the
drying chamber. The wire structure, filament materials and the edge seals were to be developed. The
development was boosted when the wire manufacturers became interested in the process. With further
tests with the pilot machine several details could be improved and the runnability of the machine was
improved. Also special attention has to be put in the driving and guiding system of the belts.
Considerable change took place on the corporate level when Valmet 1993 acquired the paper and board
machinery business of Tampella. However, the development work continued uninterruptedly.
Keynote lecture at the 12th International dying symposium. Advances in Paper Dewatering, AIPD 2000;
Noordwijkerhout, Netherlands, Aug 28-31, 2000.

Figure 5 The pilot board machine and dynamic pilot Condebelt dryer at Valmet Inkeroinen Research Center.

The final construction of the pilot dryer can be seen in Fig. 5. The drying zone is 18 m long, 700 mm
wide web can be dried. Speed of the dryer is over 600 m/min and maximum steam pressure is 0,5 MPa
(gauge) The pilot Condebelt can be used for “on-line” drying of wet web taken from the pilot board
machine or for “off line“ drying of wet rolls made in commercial board machines. This was a crucial step
in commercialization of the process. The papermakers started to show serious interest in this new process.
In addition to the new dynamic dryer, an improved static test rig was developed and used alongside the
dynamic dryer. The drying results were identical under corresponding drying conditions, but in the static
rig drying conditions could be controlled in a wider range than in the dynamic dryer, which was important
for understanding the basic phenomena involved. Dr. Lehtinen developed also computer models to
predict the temperature distributions within the hot belt and to evaluate the factors affecting the drying
rate (Lehtinen, 1992). These models were very helpful when later predicting the outlet dryness of
different board grades.

FINALLY THE FIRST COMMERCIAL MILL SCALE CONDEBELT

One of the first companies interested in Condebelt was Enso (now Stora Enso). Enso had two small board
machines at Pankakoski mill. The demand of the main products of Pankakoski had almost disappeared
due to the collapse of the former Soviet Union. In order to survive they badly needed improvement in
product quality. Condebelt was an attractive option for their BM3 machine. Intensive series of pilot
scale test runs were started in the year 1993. In most test runs the web was taken from the BM3. The
BM3 was producing board grades where the strength properties were important. The machine was rather
narrow (2,2 m) and slow (240 m/min) so that the step from the pilot machine to the first mill application
was not excessively long. The purchase contract was signed in February 1995 and the new, first
production scale Condebelt dryer started up fifteen months later in May 1996.
Keynote lecture at the 12th International dying symposium. Advances in Paper Dewatering, AIPD 2000;
Noordwijkerhout, Netherlands, Aug 28-31, 2000.

Figure 6 The first commercial Condebelt dryer installed at the Stora Enso Pankakoski mill.

Several new solutions were needed in designing the first installation. One of the first questions was:
Were to locate the new dryer? An important innovation was to put the Condebelt on the second floor
above the existing dryer. This gave many advantages:
- The drying capacity could be increased considerably.
- The whole assembly work could be done almost independently from the conventional drying
section. The total shut down time needed was less than 10 days.
- It was possible to run the machine “the old way”, using only the conventional drying cylinders.
This made it possible to produce the conventional grades and reduce the risks involved with the
application of the new technology.
- Two different drying modes with the condensing belt process were made possible:
1) The web can be taken directly from the press section and fed into the condensing belt dryer,
from which it is brought back to the 4th cylinder group.
2) The web can be predried with three cylinder groups before going into condensing belt dryer and
returning to 4th cylinder group. This alternative has become the dominant mode.
- The amount of predrying and final drying could be optimized according to quality requirements.
The machine became very flexible and suitable for producing multiple grades and utilizing a wide
range of raw materials: old corrugated containers, bleached kraft, spruce groundwood,
newspapers and recycled liquid packages.
A great amount of valuable information was obtained from this first installation. In addition to
verification of the mechanical solutions, also the potential of Condebelt dryer as an addition to an existing
cylinder drying section was demonstrated. The optimum inlet and outlet dryness levels were determined,
and the role of steam pressures were established for the produced board grades. The best improvements
were received with the core boards which is a high basis weight board made from old corrugated
containers. Important strength properties could be improved from 30 to 100% compared with the
cylinder dried grades ( Table 2).

Table 2 Effect of Condebelt Drying on Core Board (300 - 550 g/m2)

• Density increased 20%

• Scott bond increased 60 -100%
• Burst strength increased 60%
• RCT (CD) increased 30%
• SCT /STFI (CD) increased 60%
Keynote lecture at the 12th International dying symposium. Advances in Paper Dewatering, AIPD 2000;
Noordwijkerhout, Netherlands, Aug 28-31, 2000.
The versatility of the machine was shown in production of low density board grades for which good
smoothness/ bulk combination is important. The quality results were better than obtained with the BM2 ,
which has an Yankee cylinder. In nearly all cases the commercial dryer gave results that already were
obtained with the pilot and even static laboratory scale dryers. Some positive surprises were also
experienced: less drying and water removal in Condebelt was needed to give good improvements in
board properties especially in smoothness. Another important observation was that the wire structure was
crucial for high basis weight boards. If the water volume in the wire is not high enough the drying rate is
seriously reduced, which can lead even to web delamination in Condebelt's 22m long " nip". This
predicts bleak future for shorter nips.
Second commercial installation was started in January 1999 at the Ansan mill of Dong Il in South Korea.
Their wider (over 4 m) and faster (700 m/min) machine was again a new challenge for the designers, but
the Pankakoski experience gave a valuable help in this respect. This machine could fully utilize the extra
drying capacity brought about by the new dryer. Main products were linerboard and fluting which were
made from recycled raw material. Due to the speed and pressure level used the importance of thermo-
mechanical stresses in the system and the dynamic of the drying process were to be considered. The
quality results were excellent.

TWO DECADES OF DEVELOPMENT WORK

The development of Condebelt dryer started 25 years ago. The development was not fast if we
compare it with the development in the electronic industry. It took 21 years from the first patent to the
first commercial installation.
The development can period can be divided into three phases based on the type of research and
development conducted:
1) Basic research and development period (1975-1984)
2) Research and development related to dynamic process (1985-1992) and
3) Research and development related to practical applications in the mills (1993- 1998).

The first nearly 10 years research was conducted with the static rig mainly concentrating in mapping
the potential of the new invention and finding the main application areas. Development work contained
theoretical calculations and planning of the laboratory scale test rigs. The total number of patents granted
during the first 10 years was 5.

35
Cumulative number of patents

30

25

20

15

10

0
1970 1975 1980 1985 1990 1995 2000

Figure 7 Cumulative number of Condebelt patents granted in Finland

Keynote lecture at the 12th International dying symposium. Advances in Paper Dewatering, AIPD 2000;
Noordwijkerhout, Netherlands, Aug 28-31, 2000.
The development of the first dynamic pilot dryer and related research efforts doubled the number of
patents in two years. The design and construction of the second dryer followed the first one. But the
development took clearly more than expected, nearly 7 years.
In the third phase customers were involved and the research and development work concentrated in
specific board grades and specific mills. This activated and motivated a remarkable increase in the
number of patents which again doubled in a couple of years.
The number of patents is indicative for the development work. It reflects the activity, the amount of
resources, both economical and human resources, allocated in the development work. The Figure 7
would closely correlate with the number of engineers involved with the development project.
The experience with Condebelt shows that the path of a revolutionary technology is not smooth,
especially in paper industry. A serious limiting factor is the conservativeness of the industry combined
with it's strong dependency on the economic cycles. These factors strongly hit the product development
resources in any company involved with paper machine construction business. The new innovations may
have difficulties to survive over the recessions.

FUTURE OF CONDEBELT

Condebelt has now established itself as an important alternative to the conventional cylinder drying in
certain board grades. Practical mill scale experience suggests that the dryer will win several new
applications in the board drying area. Technically Condebelt has been a success, a brilliant example of
perseverance and ingenuity. However, the extent of work needed to overcome the encountered problems
probably was seriously underestimated. Commercially it has not become a success story, yet. But it has
all the possibilities to become a one.

As process based on completely new kind of operation principles, Condebelt may also contribute to
the application of belt technology in drying section. The same technology may also find applications in
other parts of paper machine. Pilot scale experiments have indicated that this technology has potential in
combining wet pressing, drying and calendering into a single process. This suggests that Condebelt based
technology can bring new solutions for future paper and board machines.

ACKNOWLEDGEMENT

Author is grateful for several persons for valuable information regarding the Convac /Condebelt
development within Tampella and Valmet Corporations. Thanks are due to Mssrs. Johan von Pfaler,
Olli-Pekka Sorma, Paavo Rautakorpi, Harri Vainio, Timo Ojala, Antti Palokangas and several others.

LITERATURE

Anderson, R.G., Back, E.L., (1976) The effect of single nip press drying on properties of liner of high
yield kraft pulp. Pulp&Paper Canada Vol 13, no. 12, T260-263.

Jokio, M. and Retulainen E., (1982) The suitability of Convac vacuum drying and press drying for
linerboard. Special study. Helsinki University of Technology, Laboratory of Paper Technology, Nov
11, 37 p.
Keynote lecture at the 12th International dying symposium. Advances in Paper Dewatering, AIPD 2000;
Noordwijkerhout, Netherlands, Aug 28-31, 2000.
Lehtinen, J., (1988) The Tampella Condebelt process: A versatile web drying and consolidation method
under development. Paper ja Puu (1988)4, 310-313.

Lehtinen, J., (1992) Further development of a computer program simulating heat pipe functioning in
Condebelt paper drying. Drying Technology 10(1992)4, 1037-1062.

Lehtinen, J., Oy Tampella Ab, (1975) A method for drying board and paper web and equipment for
application of this method (In Finnish). A Finnish patent, December 30, 1975.

Lehtinen, J.,(1980) A new vacuum drying method for paper, board and other permeable mats. In
Mujumdar (ed.) DRYING ‘80, Vol 2 . Proceedings of the second International Symposium held July
6-9, Montreal Canada, 347-354.

Retulainen, E. and Hämäläinen, A., (2000), Three Years of Condebelt Drying at Stora Enso's Pankakoski
Mill. Tappi Journal 83(2000)5, 84.

Setterhom, V.C.(1979), Press drying overview. 1979 Tappi Annual Conference, New York, p. 5-7.

Wahren, D., (1982) Methods and apparathus for the rapid consolidation of moist porous webs, US Patent
4,324,613, April 13,

View publication stats