Puigjaner L. (ed.) Syngas from Waste - Emerging Technologies
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CIUDEN Energy City Foundation (Fundación Ciudad de la Energía)
HP High pressure
HRSG Heat recovery steam generator
IGCC Integrated gasification combined cycle
IGME Geological and Mining Institute (Instituto Geológico y Minero de
España)
IPCC Intergovernmental Panel on Climate Change
INCAR Coal Spanish Research Centre (Instituto Nacional del Carbón)
ISO International Standards Organisation
LLB Lurgi Lentjes Babcok
MBM Meat and bone meal
aMDEA Active methyl diethanol amine
MWe Electrical mega Watt
MWh Mega Watt-hours
MW
th
Thermal mega Watt
NGCC Natural gas combined cycle
O&M Operation and maintenance
Petcoke Petroleum coke
PSA Pressure swing adsorption
R&D Ressearch and development
Syngas Synthetic gas
UCLM University of Castilla-La Mancha
VI FP Sixth Framework Programme
1 ELCOGAS Description
1.1 The Company
ELCOGAS, S.A., the owner company of the Puertollano IGCC power plant was
founded on 8th April 1992, as a mercantile company subject to Spanish legislation,
with the objective of the construction and exploitation of the Puertollano inte-
grated gasification combined cycle (IGCC) plant (Fig. 1).
This power plant is the largest IGCC plant in the world using solid fuel in a
single pressurised entrained flow gasifier and is in commercial operation since
1998 with synthetic gas. Its design fuel is a mixture 50:50 of poor quality coal
(high content of ash) and petcoke (high content of sulphur).
The founding members were European electrical companies along with the
main combined cycle and gasification plant suppliers, Krupp Koppers and Siemens
from Germany, in association with Babcock Wilcox Española, from Spain as
manufacturer. The current members and their percentage of shares are shown
graphically in the following Fig. 2.
278 P. Coca et al.
1.2 Process and Integration Description
Table 1 summarises the principal data for the ELCOGAS IGCC power plant.
The Puertollano IGCC power plant consists of three main units: (i) the gasification
unit (generating the synthetic gas) supplied by Krupp Koppers, (ii) the air sepa-
ration unit (ASU) that produces nitrogen and oxygen supplied by Air Liquide and
(iii) the combined cycle (CC) (producing electricity) supplied by Siemens.
These main units division is analogous to the considered approach in chapter
Modelling Superstructure for Conceptual Design of Syngas Generation and
Treatment for superstructure conception. The solid fuel is dried, mixed and milled
in the coal preparation system and then sent with pure nitrogen to the gasifier to
produce synthetic gas. Then, the syngas obtained in the pressurised entrained flow
gasifier is cooled down, cleaned and subsequently burnt as fuel in the gas turbine
Fig. 1 The Puertollano IGCC power plant view
Fig. 2 ELCOGAS capital
share (at 31st December
2010)
Examples of Industrial Applications 279
of the combined cycle plant. The synthetic gas is the result of several reactions
between fuel (a mix of coal and petroleum coke) with oxygen/steam at high
temperatures of up to 1,600C. The required oxygen for the gasification process is
produced in an integrated ASU (based on a cryogenic process), which also pro-
duces pure nitrogen for drying the pulverised fuel, for fuel transportation and for
the safety inertisation of the different circuits with a purity of 99.99% and waste
nitrogen with 98% purity to dilute clean gas from gasification unit before being
burnt in the gas turbine combustion chamber. Figure 3 shows the ELCOGAS
IGCC simplified flow diagram.
The synthetic gas obtained, which basically consists of CO and H
2
, is subse-
quently subjected to an exhaustive cleaning process to eliminate the small parts of
pollutants, fly ash, halogens, cyanides, sulphur compounds, etc. Then, the so-called
clean gas, free of pollutants, is saturated, mixed with waste nitrogen (to reduce
NO
x
formation) and burnt, with a high-efficiency level, in the gas turbine of the CC
electricity-generating unit. The gas turbine (model V94.3, 200 MW
e
under ISO
conditions) is capable of operating with both synthetic and natural gases. The gas
turbine exhaust gases with residual heat are fed into a heat recovery steam
generator (HRSG), producing steam that is used together with the steam produced
in the gasification process to generate additional electricity in a conventional steam
turbine (135 MW
e
under ISO conditions) with condensation cycle. The demon-
strated plant net efficiency is 42.2% under ISO conditions.
The design of the heat exchangers battery is particularly relevant in terms of
efficiency, basically as regard steam production and consumption, incorporating
two heat recovery boilers, one for the raw gas produced in the gasifier and the
other for the turbine exhaust gases. Furthermore, the steam acts as a heat conductor
for several uses in gasification, desulphurisation and air separation processes.
The Puertollano power plant was designed with a high-integration level that
involves the integration of the three previously mentioned units:
• Integration of the gasification island and combined cycle water–steam systems:
The water fed to the steam generators is pre-heated in a section of the combined
Table 1 Summary of the ELCOGAS IGCC power plant main data
Design fuel: coal and petcoke (50 wt%.)
Coal Petcoke Mix
LHV (MJ/kg) 13.10 31.99 22.55
Electrical output
Gas turbine (MW) Steam turbine (MW) Total gross (MW) Total net (MW)
ISO conditions 200 135 335 300
Site conditions 182.3 135.4 317.7 282.7
Efficiency (LHV)
Gross Net
Thermal efficiency 47.12% 42.2%
Heat rate 7,647 kJ/kWh 8,538 kJ/kWh
280 P. Coca et al.
cycle’s HRSG and is sent to gasification where a saturated steam is produced
as a result of the exchange of heat with the raw gas. This saturated steam is
exported to the HRSG for superheating and expansion inside the steam turbine,
generating additional electricity.
• Nitrogen-side integration between ASU and combined cycle: The waste N
2
,a
by-product of the ASU, is compressed and mixed with the syngas to reduce NO
x
emissions and to increase the capacity of the gas turbine.
• Air-side integration between ASU and combined cycle: The compressed air
required by the ASU is totally extracted from the gas turbine compressor.
The integration of water–steam systems is normal in all IGCC power plants in
operation. On the other hand, integration between the ASU and CC is an option,
which is much more frequently discussed. The highly integrated designs mean
greater power plant efficiency, because the consumption of auxiliary systems for
air compressors and ASU products is reduced. Nevertheless, these involve longer
start-up times during which time, the back-up fuel (natural gas in most cases) is
used. With regard to the IGCC power plants using coal that are in operation in
Europe, highly integrated design has predominated because of its increased effi-
ciency, whereas in the United States, with lower fuel prices, increased availability
and flexibility, which a non-integrated design offers, has been preferred. Currently,
the tendency is towards designs where the air required by the ASU comes in
part from the gas turbine compressor and in part from a separate compressor.
This provides the necessary flexibility for faster start-ups and an intermediate
auxiliary consumption between the two options.
Sulphur
Sulphur
Sulphur
Fig. 3 Simplified flow diagram of the Puertollano power plant
Examples of Industrial Applications 281
1.3 Fuel and Clean Gas Data
Main parameters of ELCOGAS fuel components, coal, petcoke and mixture are
shown in Table 2.
Coal comes from the ENCASUR mine and the petcoke from REPSOL-YPF
refinery being both of them located very close to the power plant and transported
by trucks. It must be noted that the main features of mixture are its high content in
ash and sulphur approximately 21 and 3.5%, respectively.
The composition of obtained syngas before and after the cleaning-up pro-
cesses—dry dedusting, washing and desulphurisation systems—(called raw and
clean gas, respectively) is shown in Table 3.
1.4 Environmental Advantages
ELCOGAS IGCC power plant can meet all projected environmental legislation,
solving the compliance problems of electric power generation. Because it
operates at higher efficiency levels than conventional fossil-fuelled power plants,
ELCOGAS emits less CO
2
per unit of energy.
Table 2 Fuel characteristics
(design data)
Coal Coke Mix
(50/50 wt/wt%)
Humidity (wt%) 11.8 7.00 9.40
Ashes (wt%) 41.10 0.26 20.68
Carbon (wt%) 36.27 82.21 59.21
Hydrogen (wt%) 2.48 3.11 2.80
Nitrogen (wt%) 0.81 1.90 1.36
Oxygen (wt%) 6.62 0.02 3.32
Sulphur (wt%) 0.93 5.50 3.21
LHV (MJ/kg) 13.10 31.99 22.55
HHV (MJ/kg) 13.58 32.65 23.12
Table 3 Syngas composition
Raw gas Clean gas
Average design Design Average design Design
CO (%) 59.26 61.25 CO (%) 59.30 60.51
H
2
(%) 21.44 22.33 H
2
(%) 21.95 22.08
CO (%) 2.84 3.70 CO (%) 2.41 3.87
N
2
(%) 14.32 10.50 N
2
(%) 14.76 12.5
Ar (%) 0.90 1.02 Ar (%) 1.18 1.03
H
2
S (%) 0.83 1.01 H
2
S (ppm) 3 6
COS (%) 0.31 0.17 COS (ppm) 9 6
HCN (ppmv) 23 38 HCN (ppmv) – 3
282 P. Coca et al.
ELCOGAS gaseous emissions (SO
2
,NO
x
) are small fraction of allowable
limits, being NO
x
emissions lower in IGCC operation than in NGCC (Natural Gas
Combined Cycle) mode.
The water required to operate it is less than half of that required for pulverised
coal plant with a flue gas scrubbing system. In addition, a complex wastewater
treatment plant permits and meets European and Spanish legislation (European
Union Directive [1] and AAI-CR21 [2], respectively).
The solid residues are, in its majority, vitrified (no leachable), resulting in
useable by-products for construction industry. Sulphur recovery is approximately
99.9% because of tail gas recycling system.
1.5 Main Milestones
Since order of main contracts, up to more than 14 million of electrical MWh has
been produced as IGCC, the main milestones can be summarised as follows in
Table 4.
1.6 Operating Data: Power Production and Emissions
1.6.1 Power Production
A graphical summary of historical power production data is presented in the
following figures and tables. Figure 4 presents the annual power production
using syngas (mode IGCC) and natural gas (mode NGCC), as well as, the total
gross power production, showing a great improvement since 1998 up to 2002.
In the year 2003 and 2006, two gas turbine major overhauls (50,000 and 75,000
equivalent operating hours) were carried out, reducing the annual production.
Other main causes of reduction of energy production were in 2004 and 2005
because of a gas turbine main generation transformer isolation fault, and in 2007
and 2008 because of the ASU waste nitrogen compressor coupling fault and poor
Table 4 ELCOGAS power plant milestones
1992 Main contracts
1993 Start of civil works at site
June 1996 First synchronisation of gas turbine
October 1996 Commercial operation of combined cycle with natural gas
June 1997 Performance test of air separation unit
March 1998 First switch over from natural gas to syngas in the gas turbine
November 2000 First 1,000,000 MWh produced with coal gas as IGCC
December 2010 Total: 21,052 GWh, IGCC: 14,437 GWh
Examples of Industrial Applications 283
repair of MAN TURBO. A new increase in power production was produced in
2009. Table 5 shows the main operational achievements for the ELCOGAS
power plant.
1.6.2 Emissions
The Puertollano power plant atmospheric emissions of SO
2
,NO
x
and particles
comply with the European Union Directive 2001/80 EEC [1], which for the IGCC
operations is much more restrictive than that applied to all other coal-fired power
plant, as well as the ELCOGAS specific power plant regulation, as Fig. 5 shows
including real average data from 2010.
2 Lessons Learnt in the Early Operating Years
The following can be highlighted as main lessons learnt in relation to the
ELCOGAS operating experience achieved in the early years.
Fig. 4 IGCC, NGCC and
total gross power production
Table 5 ELCOGAS main
operational achievements
Total maximum
power
IGCC
mode
Gas turbine (MW) 225.2 201.6
Steam turbine (MW) 147.1 147.1
Total gross (MW) 359.5 359.5
Maximum continuous
operation of the
ELCOGAS power plant
1,300.0 (h) 954.0 (h)
284 P. Coca et al.
2.1 Inflexibility of the Operation Because of the Design
Including Total Integration
Although its advantages in relation to plant efficiency have been demonstrated, the
total integration between the ASU and combined cycle involves, besides a greater
level of complexity, a long and costly start-up sequence. In practice, these result in
it operating as a base load power plant, maintaining a high-minimum technical
load (60%). The regulation of the load being around 60–100% is indeed viable,
with it being possible to offer a competitive response in relation to reaction times
(3% load variation per minute).
Bearing in mind the additional cost involved in the high level of N
2
required
during the commissioning process, one reaches the conclusion that an important
saving can be made if in the new designs the concept of total integration is
reconsidered in favour of an ASU capable of producing pure N
2
independently of
the combined cycle operation.
2.2 Main Causes of Limitations in Availability During First
Operating Years
Availability has not been substantially affected by problems that are intrinsic to the
gasification process, but by the low level of reliability of more conventional units
in any coal-fired thermal power plant.
Fig. 5 ELCOGAS power
plant emissions in IGCC and
NGCC modes including 2009
average emissions data
Examples of Industrial Applications 285
At a global level, the most significant problem was related to the gas turbine,
because of the burner overheating and the refractory tiles on the combustion
chamber what implied an overhaul every 500 operating hours. Both problems
were solved by burners modifications—carried jointly between ELCOGAS and
Siemens—and after their implementation in 2003, overhauls are every 4,000
operating hours.
Other main problems were related to water leakages of gasifier membrane wall
because of flow blockages, local erosion and distributors design, solids handling
(slag and fly ash) because of erosion of components by local high velocities that
were substituted by abrasion resistant materials and design and operating proce-
dures were revised, pressure control and fluidisation stability of fuel dust con-
veying and feeding systems, candle filter performance because of poor engineering
from LLB (Lurgi Lentjes Babcok) and COS hydrolysis alumina-based catalyst
water carryover that were solved changing the catalyst by other one based on
titanium oxide.
2.3 Alternative Fuels
Different tests were undertaken during early operating years to demonstrate IGCC
fuel flexibility (see Sect. 3.2 for additional fuel tests). So in 2000, different ratios
of coal and petcoke were tested modifying their design percentage (50/50 wt/wt %)
to 54–46%, 58–42%, 45–55% and 39–61% whose main results were:
• Carbon conversion ranges varied between 98.4 and 99.7%.
• Clean gas composition was kept very stable during the tests.
• The higher mixture ash content, the higher slag/ash separation.
• Emissions fulfilled European and Spanish legislative limits and ELCOGAS
emission permit in the whole range of tested mixture.
In addition, in 2000, some tests with meat and bone meal (MBM) were
undertaken, using a total of 93 tons of MBM. The main conclusions obtained from
these tests were:
• Co-gasification IGCC technology is the best to eliminate MBM, without envi-
ronmental impact in emissions and with high energy efficiency
• A method for controlled dosage of MBM to the gasifier was defined, checking
that the method was valid for inserting a material different from usual fuel in the
gasifier.
• Protection of MBM from humidity during storage and handling is the most
important factor for preventing problems of transport in grinding train.
• There were not great differences with usual operation in fuel preparation,
sluicing systems, fly ash dedusting systems and slag discharge system. The
expected behaviour of MBM as fusion agent (because of its high Ca content)
could not be confirmed.
286 P. Coca et al.
• Two effects were clear: The chloride concentration increased with MBM per-
centage increase and the fouling of HP boiler gasifier tended to decrease.
2.4 Improvements for Future Designs
The large amount of knowledge acquired during the design, construction and
operation of the Puertollano IGCC power plant enables ELCOGAS to define a
series of improvements to be incorporated in the design of a new IGCC plant.
Those with a high financial value, which enable substantial cost reductions to be
made, are summarised in Table 6.
If a new and optimised design for the ELCOGAS IGCC plant was to be created,
using the same combined cycle technology, but incorporating the above-men-
tioned improvements and other less significant improvements resulting from the
operating experience of the first operating years, a saving in terms of the invest-
ment cost of between 20 and 25% would be made in relation to the cost of the
current power plant.
However, the improvement that would have the greatest impact on the installed
cost would be the use of more advanced gas turbines, which would enable IGCC units
with larger capacities and higher efficiency levels to be developed, with a significant
Table 6 Summary of possible improvements in new IGCC designs
System/
equipment
Reduction in production variable
cost
Reduction in investment cost
Coal preparation Hot gas generator fed with
synthesis gas
Mixing equipment removal
Pressurised coal
dust feeding
Fluidification vessel optimisation
for N
2
consumption reduction
Concrete building for coal storage and
lock hopper system removal
Gasifier Fine slag recycle Auxiliary burner removal
HP surfaces decrease, increasing raw
gas speed
Slag extraction Filtration system replacement by
settling system
Slag water circuit simplification. One
lock hopper and extractor removal
Dry filtration Design, material and candle filter
cleaning system improvement
Fly ash recycle removal (lock hoppers,
distribution and discharge systems)
Fly ash
extraction
Watery system removal Conveying vessel removal
Gas washing and
gas stripping
– Controlling filter removal
Sulphur removal SuperClaus plant assessment Equipment dimension decrease by using
enriched air
Air separation
unit
Storage capacity increase for liquid
N
2
Liquid O
2
storage removal. O
2
purity
control flexibility
Gas turbine New gas turbine with higher
efficiency
Higher output gas turbine, scale benefits
Examples of Industrial Applications 287