014_017mps1112franke:1 31/10/12 09:21 Page 14

FOCUS ON INDIA

Supercritical CFB boilers,

why they make sense for India
The supercritical CFB combines high efficiency with low emissions and considerable tolerance of lower quality
fuels. This provides an excellent fit with Indian power generation technology requirements.

Joachim Franke and Lakshmanan Srinivasan, Cethar Ltd, India

n a developing nation like India, the power and hydroelectricity) to usurp coal as the Limited has projected an 80% shortfall in its

I sector plays a pivotal role as an increase in

per capita consumption of power directly
translates into increased national
productivity. The Indian utility power sector
is expected to grow at the rate of 6-7%
major source of power.
Coal is also abundant in India, which has
the fourth largest coal reserves in the world,
but the true potential of this huge indigenous
asset is not being fully realised. This is largely
coal supply commitment for financial year
2012 (see Figure 2).
There has been heavy investment in the coal
mining sector to increase the pace of domestic
coal production, but India's coal supply is
annually, with coal the dominant fuel due to the quality of coal available in India, inadequate. Therefore, in order to tackle the
(currently accounting for over 57% of installed which is either lignite or high ash bituminous. deficit, Indian power producers are left with
capacity, see Figure 1). Therefore, it is necessary to locate power little choice but to import coal. Coal imports
Projections show that coal based power plants in the vicinity of coal extraction sites are therefore projected to significantly
generation will continue to dominate the (pit heads) as transporting this poor quality increase in the next 20-25 years (see Figure 3),
power sector in years to come. Other resources fuel over long distances is not economic. which may have direct implications for India's
are either uneconomic, unreliable (as in the Neither coal production nor electricity energy and financial security.
case of renewable sources of energy) or are generation has been able to keep up with the Reforms to address coal availability are one
simply too complex and expensive (nuclear needs of this power hungry nation. Coal India way of tackling the situation. But, if there is
no improvement in coal use technology and
Figure 1. Share of electricity generation in India for various technologies economics, India could end up reducing the
(Source: Central Electricity Authority). Total installed capacity around 203 GWe (as of 31/5/12) life time of its coal resources from 40-50 years
to a mere 10-15 years.
Nuclear Hydro Investment in more efficient power
2% 19% generating plant – in particular supercritical
technology – assumes great importance as it
Diesel Renewables offers fuel savings as well as emissions
1% 12% reduction.
Gas Coal
9% 57% Government policies
The Indian government is under enormous
pressure to cater to the growing demand for
power and the coal deficit is only aggravating
the situation.
In order to partly address this issue, the
Indian government has mandated that power
plant equipment is to be designed for burning
at least 30% imported coal. This calls for either
a blending of imported and Indian coals or
100% imported coals.
Another major policy framed by the
government is that power plants must use coal
Figure 2. India's coal supply deficit (LOA = "letter of assurance") with less than 34% ash if they are located more
than 1000 km from the mine sites or in
1000 100
critically polluted areas, urban areas, and
92% ecologically sensitive areas. This reflects the
Total commitment based
on LOAs fact that transportation of high ash coals over
80% long distances adversely affects power plant
800 Projected production 80
economics.
Ratio of coal defici In addition to these policies, there is a push
Ratio of coal defici

600 60
for efficient power producing technology,
Million tons

with preference given to supercritical plants.

400 40
Concerns for the Indian power
33%
producer
Given the above policy framework established
200 20
by the Indian government, certain key areas
of concern arise for the Indian power
producer.
0 0
When it comes to importing coal, Indonesia
FY2011 FY2012 FY2013 has been the prime supplier of coal to India in
the recent past. But now the Indonesian

14 Modern Power Systems November 2012 www.modernpowersystems.com

014_017mps1112franke:1 31/10/12 09:22 Page 15

FOCUS ON INDIA

government has announced a 25% tax on coal

exports, adding to the complexity of the Figure 3. Indian coal import status Figure 4. The CFB Flue gas
situation. (source: Coal India Limited) process 850 - 950ºC
A closer look at Indonesia's coal export 300
0
patterns reveals that it is prioritising the export
of low rank coals having high moisture (in the
range of 35 to 45%). Indonesian coal also has 250
0
250
a somewhat higher sulphur content than
Indian coal.
200
0
High moisture coals present challenges to
power plant owners, from handling issues to 850 - 950ºC

Million tons
efficiency of burning in the boilers. Also, 0
150
importing coal with higher sulphur content
requires additional downstream flue gas
desulphurisation equipment to comply with 100
0 108
the emission norms laid down by the
government.
On the other hand, the requirement that 50
0
only coal with ash quantity less than 34% can
be transported over distances of over1000 km 25
0 11
creates the need for coal washing plants, 9th 10th 11th 12th 4.5 - 6.5m/sec
which, in turn, produces vast amounts of coal plan plan plan plan
rejects. This could still be used to generate
Air
power in the vicinity of the washeries. But the
burning of washery rejects poses many further coal technology this has matured to utility Fuel
challenges to power producers if they plan to scale.
use conventional pulverised coal (PC) fired In a CFB boiler (Figure 4) a bed of fine solids Limestone
boiler technology. is fluidised in the furnace using high pressure air.
The solids elutriate from the bed owing to the
Circulating fluidised bed (CFB) high velocity maintained in the furnace. Loss of Air
technology solids causes non uniform temperature
However, there is another approach to coal distribution in the furnace. So to capture and
burning, the circulating fluidised bed, which recirculate the coarser solids back to the furnace
has become well established over the last 30 a cyclone or U-beam separator is used. The high The efficiency of a CFB boiler is comparable
years and which could address a number of the pressure air imparts fluid-like properties to the with that of a PC fired boiler.
issues arising in India. Also, like pulverised bed and the turbulence in the bed causes effective The strongest selling point of CFB
mixing and efficient combustion, technology is that it offers a high degree of fuel
producing low levels of unburnt flexibility, which minimises fuel related risks
Cyclone
outlet
carbon at optimum levels of excess for the plant owners. Features of the CFB
chamber air. Limestone can be added to the boiler, such as multi fuel firing, ability to burn
furnace as required to capture the a wide range of fuels, in situ sulphur capture
SOx within furnace and reduce the and staged combustion for reducing NOx
RH–II
emissions from the plant. emission levels, have the potential to provide
RH–I
PSH

Figure 5a (left) and 5b (below). Boiler cross

Bank II section and photograph of the 2 x 150 MW Shree
Bank I Mega CFB-based power plant in Beawar,
Rajasthan (courtesy: Cethar Limited). This
Economiser constitutes the first 300 MW CFB plant in India.
Design fuels include petcoke, lignite + fly ash,
Block IV plus Indian, Indonesian and South African coals.
Cyclone Cethar was the EPC contractor. Unit 1 started up
Block III
Block II
in July 2011 and unit 2 in December 2011. Unit
steam flow: SH/RH, 495/406.55 t/h. Unit steam
Block I
pressure: SH/RH, 147/25.09 kg/cm2. Steam
temperature, 540°C
Furnace Air heater

SA fans

www.modernpowersystems.com November 2012 Modern Power Systems 15

014_017mps1112franke:1 31/10/12 09:23 Page 16

FOCUS ON INDIA

customised solutions to the set of unique furnace height, with, for example,
Figure 6. How heat flux varies with furnace challenges faced by the Indian power implications for reliable cooling of the furnace
height producer. waterwall.
50.0
0 There are already CFB units operating in These variations in heat flux are much less
CFB furnace India, see Figures 5a and 5b. of a concern for the CFB boiler, which
0
45.0 operates with heat fluxes that are reasonably
PC furnace and
(comparable) Integration of supercritical and CFB uniform over the height (Figure 6) and around
0
40.0
downshot firing fo technologies the periphery of the furnace. Hence, a CFB
0
35.0 anthracite coal It is a well established fact that overall plant boiler is inherently more suited to the once
efficiency increases when a power plant through configuration.
Furnace height (m)

0
30.0 operates at supercritical parameters, with the Unlike supercritical PC boilers CFB
attendant benefits of cost and fuel savings and technology can achieve emissions levels that
0
25.0
lower emissions of the greenhouse gases and comply with stringent pollution standards for
0
20.0 other pollutants. Integration of supercritical almost any fuel without any downstream
and CFB technologies gives us the best equipment. Integration with CFB brings these
0
15.0 features of both these technologies. The high emissions benefits to supercritical boiler
degree of fuel flexibility coupled with the lower technology.
0
10.0
plant heat rate is indeed proving very Supercritical turbines are not available
0
5.0 attractive for power producers. below the size of about 300 MW as they would
One of the critical areas of concern not be economic at capacities less than this.
0
0.0 associated with pulverised coal firing in a This dictates a minimum size for the integrated
0 100 200 300 400
Heat flux ( verage) (kW/m2) supercritical boiler employing the once supercritical and CFB plant, which can be
through concept is variation in heat flux with achieved by using a suitably scaled up CFB
boiler or by using two smaller supercritical
Figure 7. Commercial maturity of CFB technology CFB boilers connected to one turbine.

Supercritical CFB Scale up of CFB boilers to

600 Under supercritical sizes
construction Over the years, circulating fluidised bed boiler
Over 70 000 MWe and more than 1000 units 550 technology has been scaled up (Figure 7), with
(Excluding China) a supercritical CFB unit of 460 MWe now in
500 operation (the Lagisza plant), and a total
460
world CFB installed generating capacity of
some 200 GW. Thus, the circulating fluidised
400 bed has established itself as a utility scale boiler
Natural circulation technology.
MWe

350 Subcritical units of up to 350 MWe are

300 already in operation today, while a 330 MWe
300
supercritical CFB is under construction in
235 240
Russia, a supercritical CFB plant with four
200 550 MWe units is under construction in Korea
180
and a 600 MWe supercritical CFB unit –
125 currently the world's largest CFB – is being
built at the Baima power plant in China, due
100 85
to be commissioned this year. Looking to the
55
40 future, supercritical CFB designs with a unit
20 size of 800 MWe are on offer.
0.05 5
0 All these supercritical units employ a low
1976 1979 1981 1984 1987 1989 1990 1993 1998 2001 2002 2007 2009 2014
Year mass flux BENSON technology with a special
design of vertical wall tubes for the evaporator
section, developed by Siemens.
Figure 8. Modular approach – no scale up risk. Left, 150 MW boiler, already in operation. Right, So large scale CFB is a reality. But among
proposed supercritical 350 MW CFB boiler. Image courtesy Cethar Limited Indian power producers there is a mindset that
Furnace Furnace CFB boilers are only proven at industrial sizes
and at the lower end of the utility size range,
Cyclone CL/CL
Cyclone CL/CL 7 unlike PC technology, which of course has well
70 39 ø7600
179 ø7340 29 established credentials in large capacity
supercritical plants.
In reality, there is no technological barrier
preventing scale up of CFB technology to
Cyclone supercritical sizes. The only barrier is the size
Cyclone of the market. Nevertheless, when scaling up
Cyclone CFB boilers, a modular approach is
32000

Cyclone recommended to minimise the technology

risks (Figure 8).
Cyclone
41000

This can be done by adding additional modules

in the boiler, eg by increasing the number of
cyclones, bunkers, feeders etc, and by changing
the width to depth ratio of the furnace. Such a
modular approach minimises the changes made
to the configuration of the boiler from the well
proven existing designs and guarantees
performance at the increased capacity.
74
82 While the modular approach can be used to
97 scale up the boiler, the concept of two boilers
74
connected to a single turbine can be used to
scale up the power plant size (Figure 9). The

16 Modern Power Systems November 2012 www.modernpowersystems.com

014_017mps1112franke:1 31/10/12 09:25 Page 18

FOCUS ON INDIA

integration of two boilers to power a single

turbine requires boilers half the capacity of the Figure 9. Two boilers
turbine and hence mitigates all cause for powering a single turbine
Superheater
concern and risks related to the scale up.
Also, a single turbine used in the place of
two, enhances the economics of the plant.
With this scheme, overall plant availability is Reheater
not compromised when one of the two boilers
trips. This is not the case when a single boiler
Boiler-I
is used to power a turbine.
HP IP
However, two boilers connected to a single turbine turbine
turbine is not without its downsides as well.
The scheme requires a dedicated control
system designed specially for this mode of
operation. In addition, the outage of one of
the two boilers causes the turbine to operate Superheater
at lowered efficiency due to part load
conditions. However, it can be seen that the
merits of this scheme make it a commercially Reheater
viable proposition.
Boiler-II
Supercritical CFB boilers – tailor-
made for India
The supercritical CFB boiler combines the
best of both worlds, providing better efficiency norms in future without any additional modular approach towards scale up and the
and a high degree of fuel flexibility thus investment. concept of two boilers powering a single
directly addressing the complex challenges Such an integration of the technologies turbine answers these concerns.
faced today by power producers in India. offers a very attractive way to produce power The supercritical circulating fluidised bed
It meets the government's initiative to in the 300 to 800 MWe size range. boiler promises to have a major impact on the
promote supercritical technology and has the There are certain concerns about the scale future of the power generation business in
potential to meet stringent pollution control up of power plants using CFB boilers. But a India. MPS

Q&A with Dr Joachim Franke, for many years Senior Principal and Head of
Siemens BENSON boiler technology, now executive director, technical,
supercritical boilers, Cethar Ltd, an Indian boiler OEM.
What, in your opinion, are the most technology for utility capacity additions and
significant challenges the Indian power the requirement that plants should be
industry is facing? designed to burn a minimum of 30% of
I would say the most significant challenge to imported coal are, in my view, steps in the
the industry is related to fuel. India's coal right direction. But, I would not say it is the
production is far below current requirements complete solution.
and this gap is expected to get wider still. This Environmental concerns cannot be
situation makes coal imports inevitable. But confined just to CO2 abatement. Most
experience tells us that burning blended countries aim to reduce SOx and NOx too. But,
imported coal has its own risks and this has not been the case in India.
complications. In fact, most Indian utility The increase in plant efficiency achieved by
plants are designed to burn only a specific using a supercritical boiler certainly helps, but
fuel, with a narrow band of variation. As the there is a still a need for significant reduction
quality of the fuel changes over the years, of other emissions, most probably by
either plant performance is compromised or adopting FGD and SCR for PC boilers.
the required fuel must be purchased at higher There has always been an argument that
cost. In existing projects this erodes the profit Indian coals have low sulphur and hence
margin of the developers and for new plants there is no need for any SOx control. This is that perfectly fit the Indian grid system, and
this becomes a huge risk even affecting the not really true, particularly considering the having features that are inherently very
very viability of the project. low heating value of Indian coals. CO2 suitable for supercritical applications.
emissions are harmful, no doubt, but in the
What could be done at the generating end longer term, whereas SOx and NOx have India is a country with a huge power
to avert grid blackouts similar to those that imminent harmful effects. The current policy demand, but a number of obstacles in the
occurred in July? in India allows developers to merely provide way of meeting it, not least "Coal-gate".
Overdrawing of power can be managed only space for future addition of emission control How positive are you about the future?
by operating with sufficient operating equipment, but that is not enough. India has undergone a major shift from a
reserves. Operating reserves can be created protected to liberalised economy and such
by adding new plants. But the larger the units What you would suggest as an alternative? changes are inevitably problematic. This is
the more severe the impact when if they fail. I would advocate the integration of CFB and common to any economy and India is no
One needs to build the grid with midsized supercritical technologies. It is a exception. Issues such as "Coal-gate" are, in
units, preferably in the 500 MW range. comprehensive solution that can address my view, just short term road blocks. The
Furthermore, the superior dynamic load both the fuel related challenges as well as the biggest positive for India remains its
response of supercritical units can contribute commitment to provide environmentally commitment to delivering power. There are
towards grid stability. responsible power. The big advantage is that clear policies defining the drivers. The country
this can be done without the installation of anticipates a capacity addition of 85 GW in
Is supercritical technology the way ahead space and power intensive equipment like the 12th five-year plan, providing huge
for India? FGD and SCR downstream of the boiler. CFB is opportunities for power developers and their
The policy decision to adopt supercritical a mature technology now, available in sizes suppliers.

18 Modern Power Systems November 2012 www.modernpowersystems.com