This document discusses the driving factors for fuel flexibility in power plants, including power purchase agreements, fuel purchase agreements, and merchant energy sales. It outlines technical challenges around changing fuels, such as ensuring combustion stability and meeting emissions limits. Environmental issues related to liquid fuels are also examined. The document recommends taking care when specifying secondary fuel systems, developing a methodology to evaluate costs and benefits, and ensuring operations and maintenance focus on secondary fuel systems.

2. Outline
( Fuel-flexibility - Nhat benefit?
c
The driving factors influencing the need
" Fuels issues
'- Environmental factors
r
Technical challenges
' O&M
Project decisions
Conclusions and recommendations
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National Power
C National Power PLC, 1999

6. Driving Factors
,. Povver purchase agreement
often based on availability payments
'~·
Fuel purchase agreement
interruptible fuel agreements
,. Merchant plant energy sales
'pool' price is often volatile for gas and
electricity
may want to trade gas
increased plant value with 'black' start
0
National Power
0 National Power PLC. 1999

8. 1
Other Important Fuel' Flexibility
Issues
t
Over-firing
for grid compliance
additional capacity
*
-
Power augmentation
for additional capacity
( Operation use
when the pool purchase price is high
hot summer's day to maintain output
'Black' start
0
National Power
C National Power PLC. 1999

10. Fuel Factors
f
Changing fuel is not a trivial matter
changing from one natural gas to another
•
requires care
- CV, dew-point and Wobbe index may all be
within specification but the gas turbine may
encounter emissions or pulsation problems
( Cost implications of fuel sNitching must
be assessed in terms of:
capital; operational; fuel; plant output and
availability
0
National Power
I!:> National Power PLC. 1999

12. Fuel Quality and Variability
- Natural gas is not 100% methane
{ Gas composition will change as the well
'matures'
( Gas may be from two different sources
gas A has a CH 4 content of 82 % , CV of
9,260kCal m- 3 ± 8%
gas B has a CH 4 content of 84%, CV of
9,SSOkCal m-3 ± 9%
but the station cannot control the source
0
National Power
C National Power PLC, 1999

14. Fuel Quality and Variability
{ Delivery pressure
pressure can vary over the day and has been
seen to cause combustion problems
( Relative fuel density
- again this can vary on a daily basis has been
seen to cause combustion problems
Level of longer-chain hydrocarbons
increased levels of CG+ in the gas stream has
been seen to cause combustion problems
0
National Power
C National Power PLC. 1999

17. Environmental Issues
f
Liquid fuels
storage
- spills
- contaminated water from washing of heavy
fuel oil
fire hazard
drain oil from failed starts
0
National Power
IO National Power PLC. 1999

18. Environmental Issues
( It may be possible to get exceptions
from the strictest emissions limits vvhile
burning 'alternative' fuels, vvhere it can
be shovvn that:
- the fuel is being burnt in the most
environmental way
all efforts are being made to keep emissions
to best achievable levels
where local air quality is not an issue
0
National Power
<O National Power PLC. 1999

20. Maintenance
c
Need to ensure that fuel {and vvater)
distribution is optimal for~ fuels
c
Control system must be 'intelligent' to
be able to handle the range of fuels
-~
adaptive?
'· Regular maintenance is required on all
fuel systems but especially liquid fuel
systems
0
National Power
~National
Power PLC, 1999

22. Operations
( l
It is important to regularly exercise all of
the fuel systems
but risk of tripping machine
reduced availability
( J
Fuel svvitching on gas fuel in DLN
machines is not seamless
emissions limits may be exceeded
combustion pulsations may occur
load swings
the Change-over needs tO be SeamleSS
C National Power PLC. 1999
0
NationalPower

24. NG only - may need to
renegotiate PPA
NG + DFO ~t option

25. Conclusions
. _ Fuel flexibility can offer improved
profitability
~·
Fuel flexibility must include the ability to
handle natural gases of differing
properties
The technical challenges to improve
secondary fuel availability exist
0
Flexibility should also include options
for povver augmentation
National Power
at10nal Power PLC , 1999

26. Recommendations
( Take care when specifying secondary
fuel handling systems if you need high
availability
' Develop a methodology to identify the
value and costs of a back-up fuel system
to see if you really do need it
Ensure that sufficient interest from both
operations and maintenance is focused
on the secondary fuel system
O
National Power
ional Power PLC , 1999