THE ENERGY INDUSTRY TIMES - NOVEMBER 2017
requirements such as operational
load range and steam data, as well as
investment factors such as plant
availability.
The Teesside steam plant is designed
to operate in a sliding pressure mode
in order to maximize efficiency over
its load range and to allow the unit to
respond to rapid load changes when
operating at base load conditions. The
plant is designed to fulfil the frequency
response required by the United
Kingdom’s national grid.
Primary frequency control is 5 per
cent load change within 30 seconds.
Secondary frequency control requires
3-5 per cent of maximum continuous
rating near minimum and near maximum
load between 30 seconds and 15
minutes. Also, the plant must respond
to a 10 per cent load change in 10
Special Project Supplement
sufficiently clean biomass and a
state-of-the-art design, high availability
and acceptable lifetimes of
boiler pressure parts can be maintained
at the advanced steam pressures
and temperatures.
CFB boilers operating on 100 per
cent biomass have typically used
steam conditions of approximately
540°C and up to about 140 bara.
Steam conditions have been limited
by commonly identified corrosion issues
in the combustion of biomass and
waste derived fuels, attributed to ash
forming elements such as halogens
(notably chlorine), alkali metals
(mainly sodium and potassium),
phosphorous and heavy metals (e.g.
lead, zinc).
Sumitomo SHI FW’s ABC technology
has specific features which control
ash agglomeration, fouling, and
corrosion.
From the top of the furnace, flue gas
flows into steam-cooled high efficiency
solids separators. Separated
solids are conveyed to the return leg
and discharged into INTREX heat
exchangers, which contain high conduction
heat transfer coils submerged
in the bubbling hot solids. The INTREX
units serve as the final main
steam superheaters and extraction
steam reheaters and, as the coils are
submerged, they are protected from
corrosive elements in the flue gas.
The ABC technology not only addresses
the fuel issues related to biomass
firing, but also considers plant
seconds and maintain that load for
30-60 seconds.
For short-term transients, sufficient
steam pressure is maintained upstream
of the steam turbine control valves in
order to effectively respond to grid
frequency dips. For long-term transients,
the CFB firing rate changes in
order to respond to a grid transient.
Also, the Teesside CFB can use overfiring
to achieve a 10 per cent step
change in load in 10 seconds.
Teesside’s operational and fuel flexibility,
as well as its size, create more
opportunities for plant developers and
utilities looking to produce green,
more sustainable energy. But while it
is possible to build boilers of higher
output than Teesside, Sumitomo SHI
FW believes the real opportunities
still lie in the smaller units. The economics
of large biomass projects mean
that, currently, they still require subsidies.
And as governments seek to
balance budgets against high-cost environmental
solutions, financial support
for larger projects will reduce.
Giglio said: “There are other environmental
solutions that you could
select, like wind and solar with gas as
a backup. So we don’t see a lot of
strong support for the large units.
There is also the logistical issue of
getting the fuel, so most of the market
will continue to be in the smaller to
medium 50-100 MW range. A lot of
countries can source the biomass locally
in this range.”
He also noted that avoiding imports
means governments are less dependent
on other countries for their energy
needs. In addition, using locally
supplied fuels in CFBs presents the
opportunity for the development of
community-type schemes.
“A community can get together
with a developer and source fuel from
waste and biomass, or even locally
available coal which can be blended
in. What’s good about this model is
that they can source the fuel locally
as long as they have a flexible technology
that can adjust its fuel appetite;
and a CFB does that. That same
plant can then provide the community
with heat and power and even
steam for industrial plants. We see
this model becoming more viable on
a small scale,” said Giglio.
In the medium-scale 100 MW range,
Sumitomo SHI FW sees projects that
still work like the Teesside project,
i.e. they have to import some fuel but
most of the fuel is sourced locally. In
this case, to increase the scale of the
plant for better economics, a developer
would typically over-size the
plant so it can use the domestic fuel
first and then import the remainder.
South Korea is a good example of
this, where Sumitomo SHI FW executed
an interesting project called
the Dangjin 1 Biomass Power Plant.
When it began operation just over
two years ago the 105 MW plant,
owned by private utility GS EPS,
became the largest renewables power
plant in the country.
Giglio said: “It was originally designed
for coal with some wood
pellets and palm kernel shells but the
government has now said that no
coal can be burned in the plant. The
coal has therefore been replaced with
locally produced recycled wood
chips. Although we had to modify
the boiler at Dangjin 1, due to an increase
in debris in the waste fuel,
generally speaking the technology
allows you to do that.”
In situations where fuel flexibility
is key and greening the power sector
is crucial, CFB technology has an
important role to play and the startup
of Teesside will go a long way to
demonstrating what is possible.
A cross-sectional view of
Teesside
Dangjin 1 Biomass Power
Plant: South Korea’s largest
renewable energy project
Table 2. Design fuel data for both 100 per cent wood pellets
and a mixture of pellets and chips
Fuel component 100 per cent wood pellets Mixture __ per cent pellets,
__ per cent chips
Sulphur 0.02 per cent 0.03 per cent
Nitrogen 0.05 – 0.6 per cent 0.16 per cent
Moisture 5.0 per cent 18.5 per cent
Ash 1.0 per cent 1.0 per cent
Heating value (LHV) 17.8 MJ/kg 14.95 MJ/kg