30 Power Engineering International February 2018 www.PowerEngineeringInt.com
components in the classic processes of
feedwater treatment, steam generation, turbine
injection, flue gas cleaning, and district heating
networks, just as they are in conventional power
and cogeneration plants. And, as with
conventional plants, high temperatures, high
pressures, and vibration all test the durability of
valves and actuators. However, the complex
and variable nature of biofuels introduces some
challenges, as the following examples show.
The straw-fired Lisbjerg power plant,
commissioned in 2016, is one of the largest of
its kind in Denmark.
With its output of 38 MW of electricity and
78 MW of heat, the plant supplies 20 per cent
of the district heating demand of Aarhus, the
second largest city in Denmark. Aarhus plans
to source all its district heating from CO2-neutral
energy sources by 2030.
Lisbjerg power plant burns up to
240,000 tonnes per year of straw from nearby
farms. To increase its flexibility, the plant can also
burn up to 50 per cent woodchips. Four parallel
conveying lanes and feeders supply straw to
the boiler. Combustion takes place on a water-cooled vibrating grate.
Approximately 50 of AUMA’s latest-generation
SA and SAR electric actuators automate valves
in the Lisbjerg plant. Equipped with AC intelligent
controls, all the actuators are centrally controlled
via a Profibus DP V1 interface. Notable is the
actuator on the condenser bypass damper,
which has special safety requirements.
To make full use of its residual heat, the flue
gas passes through a condenser. In case this
needs to be taken offline for maintenance, the
plant has a large bypass damper that allows
the flue gas to be routed directly to the chimney.
Failure of the damper to open when required
could lead to a plant shutdown.
The contractor of the plant contacted Kolster,
a Danish damper manufacturer that is part of
engineering company KSM Kragelund. Kolster
has a long history of working with Grønbech &
Sønner, AUMA’s representative in Denmark.
Together, Kolster and Grønbech & Sønner
decided on the most suitable combination of
actuator, control unit and gearbox for this
The designers specified that the actuator
must meet the requirements of at least Safety
Integrity Level (SIL) 1, as specified by IEC 61508
edition 2. They chose a Kolster KLS 1500 × 2750
mm damper with an AUMA SA 14. 6 actuator,
AC 01.2 SIL actuator controls, and GS 250.3
gearbox. This actuator combination is designed
for applications requiring a high degree of
safety, and meets SIL 2 requirements. At Lisbjerg
it is used for both normal and safety-critical
First German straw-fired plant
The BEKW power plant in Emlichheim is the first
in Germany to rely on straw as a fuel. This
cogeneration plant ( 10. 2 MWe/49.8 MWth)
started up in 2013 and burns approximately
70,000 tonnes per year of straw from surrounding
farms. It achieves a record primary energy
efficiency of approximately 90 per cent.
Technical availability is 98 per cent, which is
excellent for this type of plant.
AUMA electric actuators contribute to both
the efficiency and the reliability of the
Emlichheim plant. In use are around 30 SA
actuators for open-close duty and SAR
actuators for modulating duty, all equipped
with AC intelligent actuator controls.
An example application is the control of
water flow to the spray attemperators located
after the superheaters.Variations in the quality
of the straw fuel, and the continuously changing
demand for district heat, make this a
challenging task that the AUMA actuators are
well placed to handle.
Skaerbaek power plant near Fredericia,
Denmark, is one of three power plants operated
by energy giant Ørsted (formerly DONG Energy)
that have recently been converted to biomass.
Originally built for natural gas, the plant was
converted to dual-fuel cogeneration in 2017.
Two new highly efficient 140 MW wood chip
boilers were installed during the refurbishment.
Wood chips are the primary fuel, with natural
gas as a backup.
The main purpose of the plant is to provide
district heating for roughly 200,000 people.
However, the new wood chip boilers can also
supply steam to the existing turbine, to the extent
that the plant can be dedicated entirely to
electricity generation. This ensures maximum
flexibility in the summer, and during periods
when wind or solar electricity production drops.
The plant also has a 5500 GJ heat storage
system that covers approximately eight hours
of heat consumption on a winter’s day.
Installing the wood chip boilers required new
pipelines for water and steam to be installed
and linked to the original gas-fired plant.
Approximately 100 SIPOS SEVEN actuators were
The SIPOS SEVEN actuators, which are
engineered and manufactured by AUMA Group
company SIPOS Aktorik, incorporate frequency
converters that allow their operating speeds to
be adjusted during the valve travel. Variable
speed offers significant advantages in a wide
variety of closed-loop and open-loop control
applications, since each change of valve
position can be matched to its optimum
Variable-speed operation also makes SIPOS
SEVEN actuators very versatile, since a single
size of actuator typically covers eight different
torque settings and seven operating speeds.
This reduces the number of actuator variants
required across the plant, and so simplifies
inventory management. Torques and speeds
can be adjusted at any time to optimize the
process or accommodate process changes.
The new HOFOR Bio 4 cogeneration unit at
Amagervaerket power plant in Copenhagen,
Denmark, is another example of challenging
requirements for valve automation. The plant is
SIPOS SEVEN actuators with Profibus interface
(V2 services as standard) in Skaerbaek power plant