POWER PLANT TECHNOLOGY

Gas Turbines

Hybrid Combustion Air Conditioning to as anti-icing by specialists. The

following methods and heat sources

A New Method to
are used for this:
• direct preheating of the intake air
by mixing with:

Optimise the Operation - warm air from the compressor

outlet
- warm exhaust air of the package

of Gas Turbines of the gas turbine

- warm exhaust gas (more rarely).
• indirect preheating of the intake
In steady-state operation, gas turbines serve to drive electrical gen- air with waste-heat exchangers in
erators, gas compressors and fluid pumps. Their advantage relates the intake air stream with:
- heat from a combined cycle.
to simple design, a very high power density, a long service life and However, intake air preheating, as al-
the option of operation with various calorific values, advantages ready mentioned, causes a reduction
not afforded by piston machines. In recent years, it has been pos- in the inducted volumetric air flow,
sible to increase the output and efficiency of gas turbines and re- output and efficiency of the gas tur-
duce pollutant gas emissions in the waste gases in line with more bine. This reduction is particularly
stringent legislation. However, secondary processes of gas turbines high if warm air from the compres-
sor outlet is used for anti-icing since
continue to have an important optimisation potential. this air is taken from the process
after compression has already oc-
curred and is no longer available for

T
he output and effectiveness - nozzle admission into the air performing work in the gas turbine
of gas turbines are greatly de- stream using binary blast con- and the steam process.
pendent on the temperature nections (additional air con-
of the process air at the compressor sumption) Part-load operation
inlet, owing to the use of an axial- - cascading or film humidification The intake air quantity through the
flow compressor. The air density with water on fitted cooling de- system is reduced with priority on
and, consequently, the quantity of vices (max. 65 to 80% relative gas turbines for operation at part
air inducted by the axial-flow com- humidity) load. This is done by actuation of
pressor drop with increasing intake - direct flow through ice banks. the fixed blades at the inlet of the
air temperature. The output and the • indirect cooling of the intake air axial-flow compressor. This increas-
efficiency of the gas turbine drop in by waste-heat exchanger, cooled es the pressure loss at the suction
proportion with this (figure 1). with: end and consequently reduces the
The inducted air quantity, the - absorption refrigerating units efficiency of the gas turbine. In ad-
output and the efficiency can be in- - adsorption refrigerating units dition, the air lost as the result of re-
creased again by artificial cooling of - compression refrigerating units. duced flow rate is then not available
the intake air in the summertime, Refrigerating units are costly in- in the downstream steam process of
and the following methods are al- vestments and are costly to operate. a combined gas and steam process,
ready used in practice for this: Compression refrigerating units re- thus leading to a reduction in the
• direct adiabatic cooling of the in- quire expensive electrical power to parameters in this sub-process as
take air with water: drive them. The drive energy con- well.
- nozzle injection into the air verted to heat and the heat absorbed
stream using unitary high-pres- from the intake air stream must be Secondary cooling circuit
sure blast connections (can hard- dissipated to the ambient air. This, Gas turbines are very effective
ly be controlled) in turn, necessitates large recoolers drives. Nevertheless, (waste) heat
that also consume water and elec- that must be dissipated to the en-
tricity. vironment via separate cooling
systems is produced in secondary
Remarkable optimisation processes. This includes the (waste)
potential heat of the generator, the waste heat
of the lube oil of the bearings and
Anti-icing any gearing mechanisms present
The risk of icing up of the intake and, depending on make, other
air filter and of the inlet diffuser of (waste) heat sources. In warmer re-
the axial-flow compressor occurs gions in particular and also as a con-
Dr.-Ing. Frank
Triesch, Managing
in cold regions in the wintertime at sequence of global warming, these
Director, high intake air relative humidities. coolers frequently pose a problem
Airtainer GmbH & This is counteracted by artificially in respect of operation of the gas
Co. KG, Leipzig/ reducing the relative humidity by air turbines. The lube oil temperature
Germany preheating. This process is referred can no longer be stabilised in the

EuroHeat&Power • English Edition • Vol. 13 III/2016 33

POWER PLANT TECHNOLOGY
Gas Turbines

Relative power output subject to ambient Relative efficiency subject to ambient

air temperature air temperature
1,30 1,04
1,02
1,20
1,00
1,10 0,98
0,96
1,00
0,94

/0
P/P0

0,90
0,92

0,80 0,90
0,88
0,70
0,86
0,60 0,84
–40 –30 –20 –10 0 10 20 30 °C 50 –40 –30 –20 –10 0 10 20 30 °C 50
–40 –20 0 20 40 60 °F 120 –40 –20 0 20 40 60 °F 120
Air temperature Air temperature

9856.1

Figure 1. Example of the dependence of output and efficiency of a gas turbine on ambient temperature

summertime and the gas turbine burning in the form of large droplets, • recooling of the secondary cooling
output must be reduced. In rare cas- this may cause the dreaded damage circuit (lube oil and generator)
es, it is also necessary to completely to the turbine blades, also known as • fuel preheating
discontinue operation temporarily. flashback. • combustion air conditioning of
The lube oil ages more quickly and Gas turbine manufacturers conse- the gas turbine:
other lube oil grades may need to quently demand a gas temperature - indirect preheating of the intake
be used. at the combustion chamber inlet air in the event of the risk of sub-
that is around 15 K above the hydro- zero temperatures
Fuel preheating carbon or water vapour dew point at - direct humidification of the in-
Fuel preheating is required on every operating point. This combus- take air in the case of positive
steady-state gas turbines operated tion gas preheating is performed in ambient temperature
with natural gas so as to compen- gas pressure reducing stations in a - indirect preheating of the intake
sate for the Joule-Thomson ef- separate heating building with a not air in order to achieve part-load
fect when reducing the pressure insignificant fuel gas consumption operation.
of the natural gas from pipeline from the turbine’s own fuel. This involves interconnecting the
pressure to combustion chamber Moreover, in power stations, (waste) heat sources of generator
pressure. The temperature reduc- the fuel gas is heated further, di- and lube oil etc. with a safety heat
tion of the natural gas occurring in rectly upstream of the gas turbine, exchanger to be installed in the fuel
the isenthalpic restriction process temporarily up to temperatures line and hybrid coolers to be in-
may also be so great – depending as high as approximately 200 °C. stalled in the intake air by the closed
on pressure ratio on regulator and This preheating is performed with secondary cooling circuit to form a
inlet temperature of the gas from heat from the combined cycle. This system of hybrid combustion air
the pipeline – that there is a risk of results in a saving in fuel gas cor- conditioning (figure 2).
the temperature dropping below responding to the heat equivalent
the water vapour dew point and and an almost proportional in- Hybrid cooler
consequently, icing up inside and crease in efficiency of combined Hybrid coolers have been used for
outside the gas pipe. cycle. recooling to date. They are operated
The effects on gas turbines can only dry up to outside tempera-
be at least just as far-reaching if the Connection between secondary tures of approximately 7 to 18 °C
actual temperature drops below the cooling, fuel preheating, anti- depending on design. Recooling is
carbon dew point in the natural gas. icing and air humidification then performed via a finned tube
Propane, butane and other higher matrix. If the outside temperature
hydrocarbons contained in natural A new system that performs the fol- is beyond these limits, it is humidi-
gas are precipitated to a certain ex- lowing tasks with few known and fied externally so that a water film
tent in liquid phase at low tempera- tried-and-tested components has wets the entire matrix with second-
tures and/or low pressures. If this been developed for conditioning the ary water. Partial evaporation of the
liquid phase enters the gas turbine, intake air on gas turbines: wetting water results in indirect ad-

34 EuroHeat&Power • English Edition • Vol. 13 III/2016

ditional cooling. The excess water
is caught in a sump beneath the
cooler and fed back to the wetting
circuit until the permitted concen-
tration is reached and automatic 1 Generator cooler
2 Lubricating oil cooler
blow-down/desludging occurs. 3 Fuel gas preheater
Wetting is performed with excess 4 Circulating pumps
5 Intermediate cooling circuit
water so as to reliably flush out 6 Hybrid cooler
contamination from the ambient 7 Air intake duct
8 Combustion air flo
air and in order to avoid drying of 9 Secondary water flow
10 Secondary water pump
the fins during wetting. Air is cir- 11 Demin-water supply
culated with variable-speed fans. 12 Blow-down valve
Hybrid coolers thus feature eco-
nomical use of water and electri- Third bank of
cal power. Cooler elements derived hybrid coolers
from the sector of hybrid cooler
construction are now also used for
combustion air conditioning and
are installed directly in the intake
air stream.
Air washing relieves the load on
the downstream air filters in hu-
midification mode, thus leading to
a far longer service life of the filter
elements. 9856.2

The hybrid heat exchangers are

designed on the basis of the permit-
Figure 2. Schematic of a hybrid combustion air conditioning system for gas
ted additional pressure loss in the
turbines
air-intake, e.g. 100 Pa. This means
that they are so generously dimen-
sioned that cooling of the intermedi-
ate cooling circuit is performed with
very slight temperature differences
between the air and the cooling wa-
1 Hybrid cooler bank
ter.
2 Pre-filter wall
A relative humidity of around 98 aaaaaaaaaaaaaaaaa
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to 99% is achieved at the inlet of the
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4 Air intake grille

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gas turbine in humidification mode

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5 Adapter
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6 Intake silencer
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with no appreciable discharge of

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droplets. Humidification mode is 1 2 34 5 6 7 7 Intake duct

possible as of an outside air tem-
perature between 5 and 8 °C. The
thermal output and the air tem-
perature at the outlet of the hybrid
coolers can be controlled to a certain
extent on the basis of the quantity of
wetting water approximately from
30 to 100%. No other humidification 1 Weather protection grille
method can be controlled as well or 2 Grille
3 Pre-filter wall
is as effective.
4 Hybrid cooler bank
As-rolled aluminium are electro- aaaaaaaaaaaaaaaaa
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phoretically coated and are therefore
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6 Air intake grille

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insensitive to corrosion and conse- 7 Adapter

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8 Intake silencer
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quently afford a long service life.

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1 2 3 4 56 7 8 9 9 Intake duct
Copper is used as the pipe materi-
al. Fully demineralised water should
be used to wet the hybrid coolers.
Desludging that is then required
far less frequently is controlled as a
function of the measured conductiv- 9856.3

ity in the secondary water circuit,

thus contributing towards economi- Figure 3. Options for arrangement of hybrid cooler elements in the intake
cal use of additional water. tract of a gas turbine

EuroHeat&Power • English Edition • Vol. 13 III/2016 35

POWER PLANT TECHNOLOGY
Gas Turbines

fuel preheating and combustion air

conditioning result in interesting
options for gas turbine construc-
tion overall:
• Very effective recooling of the
generator, the lube oil and other
(waste) heat sources without ad-
ditional demand for fan power or
secondary water, universally at
any outside air condition; con-
ventional recooling might be left
out.
• Boosting output and efficiency
of the gas turbine for long parts
of the year due to combustion
air humidification to approxi-
9856.4
mately 98 to 99% relative humid-
ity. This means that combustion
air humidification can also be
Figure 4. Integration of a hybrid combustion air conditioning system in a gas
used in moderate climatic zones
and steam process
and achieves operating times
> 5,000 h/a. The use of fully de-
Arrangement of the hybrid the result of the Joule-Thomson ef- mineralised water alone produces
cooler elements in the air intake fect. additional electrical power in this
of the gas turbine The use of safety heat exchangers case (water to electricity).
for fuel preheating means that there is • Boosting output and efficiency of
In desert regions subject to perma- absolute certainty that the fuel is un- the gas turbine in the case of anti-
nent sand contamination of the in- able to enter the intermediate cooling icing due to the use of (waste) heat.
take air, the hybrid cooler elements circuit in the event of any fuel leak- • Boosting the efficiency of combined
should be arranged between the age. Any fuel leakage is signalled by cycle system in part-load operation,
prefilters and fine filters of the gas a fail-safe leakage switch. Safety heat resulting from artificial combustion
turbine (figure 3). exchangers require no maintenance air preheating with (waste) heat.
and can also be operated for a limited This makes part-load operation of
Fuel preheating period after any leakage event owing gas and steam system efficient.
Fuel preheating with the (waste) to the pressure-resistant design. • Prefiltering of the intake air in the
heat of the gas turbine is practical hybrid cooler in the case of pre-
if the fuel itself has adequately low The benefits of hybrid humidification – this greatly pro-
temperatures. This will be the case combustion air conditioning longs the service life of the down-
with natural gas that is taken from stream air filter elements.
a pipeline at high pressure and that Benefits • Reduction in installation space re-
cools down substantially when re- Process-engineering coupling of quired by gas turbine installation
duced to combustion pressure as recooling for secondary processes, owing to the fact that there is no
recooler in the secondary cooling
circuit.
• Fuel saving due to fuel preheating
with (waste) heat – an additional
fuel saving of approximately 0.1%
per 20 K gas preheating, no need
for the conventional heating boiler
installation.
• Use of the fuel for indirect in-
take air cooling – the natural low
temperature of natural gas is the
cheapest refrigeration energy
available.
• Reduction in NOx emissions in the
case of combustion air humidifi-
cation.
• Online compressor washing, fog-
ging or wet compression in the
case of negative temperatures.
Figure 5. Air intake with hybrid combustion air conditioning and three-stage In the case of new installations, sav-
air filtration ings are possible with the invest-

36 EuroHeat&Power • English Edition • Vol. 13 III/2016

ment by comparison with conven-
tional solutions. The substantial
benefits achieved when operating Ambient air temperature Air temperature after HCAC

the installation must also be con- Ambient air RH Air RH after HCAC

sidered. The method of combustion 35 100

33.2 °C 98.9%
air conditioning thus represents an °C %
important advance in the sector of
gas turbine construction (figure 4). 30 80
70
Reference plant on the gas 25
–13.4K
60

Relative humidity
turbines at Potsdam South Temperature
CHP station +74.4% 50
20 40
The German utility Energie und 19.8 °C
Wasser Potsdam has been operat- 30
ing a combined cycle system as a 15 20
CHP plant using two Siemens SGT- 24.5% RH
600 (previously ABB/Alstom GT10B) 10
gas turbines at its southern site since 10 0
1996. 0:00 4:00 8:00 12:00 16:00 20:00 0:00
The following operating states time (15 min)
were examined in a survey, to deter- 28 July 2008
mine the cost-effectiveness of retro-
fitting a plant for hybrid combustion 9856.6

air conditioning (HCAC) to prevent

icing, increase output and improve Figure 6. Reducing the intake air temperature
efficiency:
• fuel gas preheating using waste was determined. The first hybrid identical system was installed on gas
heat combustion air conditioning sys- turbine 2 (figure 5) as early as 2008.
• anti-icing using waste heat tem was installed on gas turbine 1
> 300 h/a on this basis in 2007. This measure Anti-icing using cooling water
• increase in output using adiabatic was associated with the erection of a The hybrid coolers were integrated
air humidification > 5,205 h/a completely new filter enclosure with into the cooling system for the pur-
• reduction in output using waste three-stage air filtration, in which poses of anti-icing. This is sufficient
heat > 780 h/a. the hybrid cooling elements were a to preheat combustion air in critical
Ultimately, a return on investment crucial component. Initial operat- air states upstream of the turbine
in approximately 2.2 to 2.5 years ing experience was positive, so an from –5 to +5 °C and at a relative

Advertisement

EuroHeat&Power • English Edition • Vol. 13 III/2016 37

POWER PLANT TECHNOLOGY
Gas Turbines

As a result, output variability and

efficiency rose across a wide oper-
Without combustion air conditioning Part load with 650 kW heat input, dry ating range. At an ambient air tem-
With humidification and heat input Peak load with 100% humidification, cold
perature of 25 °C, the output of an
28
27.31 SGT-600 gas turbine can be varied
MW from 20.5 MW to about 23.7 MW,
26 26.77
i.e. by approximately 3.2 MW, if re-
25 24.80 quired, thus artificially reducing
Generator output

24.30
24 23.66 the standard output of 22.5 MW by
23.30
23 22.79 22.69
around –2 MW (–9.1%) by means of
22.49
22 air preheating, or increasing it by
21.44
21 approximately +1.2 MW (+5.3%) by
Increase in output and reduction in output = output variability 20.50
20 with hybrid combustion air conditioning air humidification (figure 7). Intake
19
Output Anti-icing air humidification increases the ef-
restriction
ficiency of the gas turbine by about
18
–15 –10 –5 0 5 10 15 20 25 °C 35 0.43% absolute at 25 °C (figure 8). A
Ambient air temperature maximum of 1.75 t of completely
demineralised water evaporates per
9856.7
hour in air humidification.
Complete replacement of the filter
Figure 7. Output variability by means of hybrid combustion air conditioning enclosures with hybrid combustion
on an SGT-600 air conditioning and three-stage air
filtration facilitated:
• reliable anti-icing operation
• reduction in intake pressure loss
Without combustion air conditioning Cold with humidification and heat input • high output variability
Peak load with 100% humidification With preheating, dry • no filter flushing requirement
0.345 • considerably longer filter life
• reduction in NOx emissions
• relief of the recooling system in
0.340 0.3390
both summer and winter.
0.3380
0.3386 0.3378 Alternatively, the combustion air can
0.3372 0.3367 be conditioned in stackable airtain-
Efficiency

0.335 0.3349
ers, which combine three-stage air
0.3328 0.3336
filtration and hybrid combustion air
0.3314
0.330
Output Anti-Icing 0.3306 conditioning within the dimensions
restriction
of a standardised unit. Compared to
0.3265 a filter enclosure with two-stage air
0.325 filtration, an airtainer conditioning
–15 –10 –5 0 5 10 15 20 25 °C 35
system is amortised in less than two
Ambient air temperature
years. 
9856.8

Figure 8. Increasing efficiency of an SGT-600 by hybrid combustion air con-

ditioning

humidity > 80% into a non-critical higher part-load combined cycle ef-
range. The dry cooler fans are now ficiency.
operated at a lower speed.
Increase in output using adiabatic
Artificial reduction in output using air humidification
waste heat The possibility exists of operating
A combined cycle system operating the gas turbine with intake air hu-
in combined heat and power is pre- midification from approximately
dominantly heat-led, but is nowa- March to November. The associated
days also subject to market demands natural cooling of the intake air sta-
for electrical energy. It is possible to bilises the gas turbine output. In the
reduce gas turbine output artificially hot months, intake air temperatures
by preheating air using waste heat. < 20 °C were measured consistently triesch@gmx.de
The elimination of throttling losses at ambient air temperatures of up to
and the waste heat input produce 34 °C (figure 6). www.thermointegral.de

38 EuroHeat&Power • English Edition • Vol. 13 III/2016