The Fiber Accelerator - Pulp and Paper Canada

MACHINE DESIGN
The Fiber Accelerator:
A new device for energy recovery
in TMP and CTMP plants
By K.-G. Ryrberg, L. Obitz and R. Englund
Abstract: This paper describes the Fiber Accelerator, a new device suitable for replacing the pressure
cyclones in TMP systems, with a view to reducing the fibre content of refiner-generated steam
going to the heat-recovery system. In contrast to the performance of a pressure cyclone, this new
device accelerates the pulp above the blow-line velocity and decreases significantly the amount of
fibre carry-over to the heat-recovery unit. Operating data from a full-scale prototype unit as well as
from permanently installed commercial units are discussed in the paper.
K.-G. RYRBERG
Fiber Accelerator
Sweden AB
Hagersten, Sweden
k-g.ryrberg@bredband.net
R. ENGLUND
Fiber Accelerator
Sweden AB
Hagersten, Sweden
ANY OF the TMP and CTMP mills in
M
operation today are equipped with
heat-recovery systems for generating
clean steam from the substantial
amount of dirty steam generated during
the refining process. To enable the mill to make
better use of this steam and achieve real energy savings,
it is essential that the recovered steam is clean
and maintained at high pressure. The refiner-generated
steam is converted into clean steam with reasonable
efficiency in a reboiler, often of the falling
film type. To avoid fouling and achieve trouble-free
operation, the reboiler must be fed with processgenerated
steam that is not contaminated with fibre.
Separation of the fibre and steam after refining
was already an issue in the early commercial TMP
plants. Then, the main objective was to avoid excessively
high white-water temperatures. There was no
intention of energy recovery in these early systems,
and the separated steam was simply blown over the
roof. Then, cyclones were employed, probably as a
heritage from similar, earlier applications in the
fibre-processing industry. Some of these early installations
were plagued with fibre accumulation on
the roof, and quenching showers were often
installed in the steam exhaust to alleviate this problem.
Thus cyclones were not very efficient in separating
fibre and steam in TMP plants, and their performance
has not improved very much since they
were converted to pressurized operation as an
adaptation to energy-recovery systems.
Many of today’s energy recovery systems are built
around a reboiler of the falling film type to produce
clean steam from boiler feed-water using the contaminated
steam generated in the refining process.
Although such a reboiler is very forgiving with
regard to the presence of impurities, the presence of
excessive amounts of fibre will cause fouling. Generally,
the cure is to add water to the blow-line in order
to reduce carry-over, or to invest in the installation of
a scrubber in the system. In either case, the result is
a significant loss in energy. Additional problems arise
from an intermittent build-up of fibre in the body of
the cyclone, resulting in erratic discharge and problems
in subsequent refining stages.
All of these problems are well documented, suggesting
that there is a strong requirement for an
improved device for separating fibre and steam to
resolve the problems associated with this important
phase of TMP operation. This paper describes a new
device, the so called Fibre Accelerator, which has
been designed to replace the less efficient pressure
cyclones in use in TMP and CTMP plants and
reduce fibre carry-over to the heat-recovery system or
to the atmosphere. The flow diagram shown in Fig.
1 indicates a typical two-stage TMP system with Fiber
Accelerators installed to separate fibre from the contaminated
steam going to the heat-recovery unit.
DESCRIPTION OF THE
FIBER ACCELERATOR
The basic principle of the Fiber Accelerator is that
the fibres present in the dirty steam flowing through
the refiner blow-line are accelerated by a high-speed
rotating element inside the Fiber Accelerator so as to
achieve effective separation. This approach is in
direct contrast to the principle employed in the pressure
cyclone, where the fibre velocity decreases when
the fibre and steam mixture enters the cyclone relative
to their velocity in the refiner blow-line.
Figure 2 shows a side view of the Fiber Accelerator.
The fibre and steam inlet is located in the
outer radius of the device, the outlet for the separated
steam is located, as shown, on the same
side and the drive of the cantilevered rotor on the
opposite side. The fibre outlet is located on the
underside of the unit, allowing the separated
fibre to discharge vertically.
Figure 3 shows a cut-away section of the same
machine. The rotor is equipped with radial pockets,
which are dimensioned mathematically so that a fibre
entering a pocket close to the centre is thrown out to
the periphery after half a revolution of the rotor, and
before it has passed the length of the rotor. The
steam flow is reversed, passes the rotor once more
and discharges from the unit at the centre.
The theoretical principle of the Fiber Accelerator
is apparent from the sketch in Fig. 4.
THE PRINCIPLE OF FIBER
ACCELERATOR
Every individual installation is calculated involving
steam flow and velocity, steam pressure and
rotational speed.
There are two sizes of the Fiber Accelerator available:
the FA-1000 unit has a rotor diameter of 1,000
mm, and the FA-1100 unit has a rotor diameter of
1,100 mm. Both units are designed for a maximum
24 ❘❘❘ 105:2 (2004) T 26 Pulp & Paper Canada

MACHINE DESIGN
FIG. 1. A typical two-stage TMP system
with Fiber Accelerators.
FIG. 2. Side view of the Fiber Accelerator.
FIG. 3. Cut-away section of the Fiber
Accelerator.
FIG. 4. The theoretical principle of the
FA.
FIG. 5. Fiber Accelerator FA 1100
steam capacity at various operating
pressures or inlet velocities.
FIG. 6. Steam capacity at various
operating pressures for Fiber Accelerator
FA 1000.
Operating data prototype of
Fiber Accelerator FA-1000
at SCA Ortviken Paper Mill, Sweden
1000 rpm 1500 rpm
FIG. 7. Steam capacity at various
operating pressures for Fiber Accelerator
FA 1100.
operating pressure of 12 bar.
The smaller unit is driven by a 150- to
300-kW motor and the larger unit is driven
by a 200- to 600-kW motor. A typical
diagram illustrating the steam capacity of
the units at various operating pressures or
inlet velocities is shown in Fig. 5.
Figures 6 and 7 shows the steam capacity
for the two units at various operating pressures
and at a given inlet velocity of 40 m/s.
The specific energy required to drive
the rotor is between 5 and 20 kWh/bonedry
tonne (bdt) of pulp produced, the
exact amount depending on the speed of
rotation and the dryness of the pulp. The
pressure drop across the machine is low, of
the order of 0.1 to 0.3 bar, which is important
for efficient energy recovery. In addition,
the extremely short retention time of
the pulp, less than one second, at the high
temperature prevailing within the unit has
positive implications for pulp brightness.
PROTOTYPE UNIT
In order to evaluate the concept of the
Fiber Accelerator, a full scale prototype
FIG. 8. Prototype unit of Fiber Accelerator,
SCA, Ortviken Mill.
equipped with a 1,000-mm diameter rotor
was built. It was installed at the SCA
Ortviken paper mill in Sundsvall, Sweden,
as an integral part of a single-stage, double-disc
refiner line producing TMP for
newsprint and LWC paper. Although the
original intention was to run the unit for
a trial period of three weeks, the machine
performed so well that it remained in continuous
operation for eight months.
The installed prototype unit is shown
in Fig. 8, where it is evident that parts of
an old refiner were used for the frame of
the unit as well as for the rotor bearings.
Being a prototype, with a rotor housing
consisting of mild steel, this initial unit
was not built for permanent installation
and was eventually taken out operation.
Prior to this, a large number of trials were
carried out at rotational velocities of 1,000
rpm and 1,500 rpm.
Operating parameters are provided in
the table shown in Fig. 9, and some operating
results are plotted in Fig. 10.
As indicated, the observed fibre carryover
with the steam is extremely low, in the
range of 10 to 150 grams of fibre per tonne
of pulp produced, and independent of pulp
Spec. energy consumption kWh/ton pulp 10 19
Fiber carry-over g/ton pulp

MACHINE DESIGN
FIG. 10. Operating results, prototype
unit of Fiber Accelerator, SCA.
FIG. 11. Fiber Accelerator FA 1000,
Holmen Paper, Braviken Mill.
FIG. 12. Fiber Accelerator FA 1000,
Holmen.
Operating data
Fiber Accelerator FA-1000
at Holmen Paper Braviken Mill, Sweden
1000 rpm
Spec. energy consumption kWh/ton pulp 5-6
Fiber carry-over g/ton pulp

MACHINE DESIGN
Gain by operating Fiber Accelerator instead of pressure cyclone
or steam loss by blow line dilution (based on a real case)
Steam in blow line
q 1
20 t/h
Pressure 4 bar(a)
enthalpy 2738 kJ/kg
q 2
Blowline dilution 5 l/s
18,0 t/h
temp 35 °C
enthalpy 147,0 kJ/kg
Steam loss 3,8 t/h
Energy cost (operating cost Fiber accelarator)
q 3
16,2 t/h
q 4
enthalpy 602 kJ/kg
Specific energy consumption 6 KWh/ton, FA1000/1100
Pulp production 25 ton/h
Energy price 0,3 SEK/kWh
Operating time 350 days/year 378000 SEK/years
Energy saving/recover
Steam gain 3,8 t/h
Live steam cost 75 SEK/t 2418148 SEK/year
Generated steam Fiber accelerator
1260 t/year 94500 SEK/year
Fibre gain
Fibre loss pressure cyclone 5 kg/ton
Fibre loss FA 0,5 kg/ton
Wood price 300 SEK/ton 283500 SEK/year
Energy loss (energy used on loss fibre)
Spec. energy pulp 1100 KWh/ton
Energy price 300 SEK/ton steam generated (1MW=1ton steam)
Power on lost fibre 124 KW 233888 SEK/year
Cost 3788000 SEK/year Savings 3030036 SEK/year
Gain 2652036 SEK/year
FIG. 19. Example of energy balance and cost calculation fir a typical TMP system
to be equipped with Fiber Accelerator.
Since the start-up, almost two years ago, the Fiber Accelerator
has practically been in continuous operation with 100%
availability.
INSTALLATION OF THE
FA-1100 UNIT AT ORTVIKEN
A new FA-1100 Fiber Accelerator was installed after the primary
refiner on a new double-disc TMP line in the Ortviken mill of
the SCA Company during the fall of 2001. This line was started
up at the end of October 2001. Figures 15 and 16 shows photographs
of the installation.
And details of the operating parameters are provided in
Fig. 17.
EXPERIENCE WITH THE
FA-1100 UNIT AT ORTVIKEN
Since the presentation of the Fiber Accelerator at the PAPTAC
Annual Meeting 2002, the FA-1100 Unit at Ortviken has been
equipped with a “Frequency Control” Variable Speed Drive and
data has been collected at various speed.
The diagram, Fig. 18, shows the fibre carry-over in grams per
ton of pulp produced at various speeds of rotation and at two
different levels of pulp consistency in the blow-line.
When these data were collected the pulping capacity was 285
air-dried tonnes/day (adt/d), pulp freeness in the blow-line at
150 to 170 mL CSF and the steam flow 22 t/h.
The maximum capacity, so far, of this Unit at Ortviken has
been 355 adt/d with a steam flow of 27.5 t/h.
CONCLUSION
For each individual application a calculation should be made to
determine the optimal operating parameters with regard to
steam and pulp capacity, blow-line velocity, size of the Fiber
Accelerator unit, speed of rotation and motor size. It is also advisable
to make an energy balance and a cost calculation. Such a calculation
for a typical existing TMP system is shown in Fig. 19.
In this case the calculation clearly illustrates the energy losses
caused by blow-line dilution. In the upper section of the figure,
the calculated steam loss due to the dilution was 3.8 t/h.
The pulp production capacity of the plant was 25 t/h, the steam
flow from the refiner was 20 t/h and in this case the blow-line
dilution was 5 L/s, which is a rather normal figure.
The three lower sections shown in this figure deal with the
savings achieved by using a Fiber Accelerator instead of the pressure
cyclone. The first section shows the energy cost for running
the Fiber Accelerator with the specific energy consumption 6
kWh/t pulp. The middle section demonstrates the energy gain
by avoiding dilution, the gain from steam generated by the energy
input in the Fiber Accelerator and the gain from wood cost
due to reduced fibre losses with the Fiber Accelerator.
In this case there is no recovery of carried-over fibres and the
fibre loss is conservatively calculated at 5 kg/t pulp for the pressure
cyclone, and 500 g/t for the Fiber Accelerator. The third
section of the calculation shows the energy loss due to the fibres
which are lost from the system. The cost, the accrued savings
and the financial gain achieved by using the Fiber Accelerator
are summarised on the right side of the diagram. These relative
figures are illustrative but for comparison it may be noted that
the exchange rate at the time that this paper was prepared was
6.70 Swedish Kronor (SEK) to 1.00 Canadian Dollar.
In summary, the Fiber Accelerator is a new efficient device
capable of replacing conventional equipment for the effective
separation of steam and fibre in TMP and CTMP plants. Two
sizes are available, designed to meet the capacity requirements
of most existing TMP plants today. From the operating experience
gained to date, it is evident that the Fiber Accelerator will
solve many of the problems currently associated with energy
recovery. Some of the advantages are:
• Very little fibre carry-over, no fouling of reboiler, minimum
loss of fibres;
• No build-up of fibres in the system;
• Uniform feed through, undisturbed and consistent process;
• Short fibre retention time at high temperature, minimum of
fibre darkening;
• Low pressure drop, optimal energy recovery;
• No requirement for blow-line dilution and thus no energy loss;
• Immediate start-up of the system with heat recovery; and
• No requirement for a scrubber.
Résumé: La présente communication porte sur le Fiber Accelerator, un
nouveau dispositif pouvant remplacer les épurateurs sous pression dans les
circuits de PTM, afin de réduire la teneur en fibres de la vapeur produite par
les raffineurs et acheminée au récupérateur de chaleur. À l’opposé de l’épurateur
sous pression, ce nouveau dispositif permet à la pâte de circuler à une
vitesse supérieure à celle de la conduite de décharge et réduit considérablement
la quantité de fibres transportées au récupérateur de chaleur.
Les données opérationnelles d’un prototype en usine ainsi que d’une unité
commerciale installée en permanence font l’objet de discussion.
Reference: RYRBERG, K.-G., OBITZ, L., ENGLUND, R. The Fiber
Accelerator: A new device for energy recovery in TMP and CTMP
plants. Pulp & Paper Canada 105(2): T26-29 (February, 2004). Paper presented
at the 88th Annual Meeting in Montreal, QC, on January 28 to
31, 2002. Not to be reproduced without permission of PAPTAC.
Manuscript received on November 29, 2001. Revised manuscript
approved for publication by the Review Panel on December 4, 2002.
Keywords: THERMOMECHANICAL PULPING, MACHINE DE-
SIGN, STEAM, HEAT RECOVERY, FIBERS, ENTRAINMENT, VELOCI-
TY, ACCELERATION, BLOWLINE REFINING.
Pulp & Paper Canada T 29 105:2 (2004) ❘❘❘ 27