vgbe energy journal 7 (2022) - International Journal for Generation and Storage of Electricity and Heat

mg
[ ]
mg
[ ]
Emission footprint analysis of dispatchable gas-based power generation technologies
1 Legislation overview
1.1 Utilization of g/kWh el as an
apples-to-apples metric for
environmental footprint
analyses
Regulations and scientific publications commonly
employ ppmvd 1 , mg/m N 3 , and also
non-SI units as metrics for quantifying emissions
from dispatchable gas-based power
generation technologies. Emission values
are typically normalized to a reference oxygen
content to account for dilution of pollutants
due to excess air and varying oxygen
contents in the exhaust gas. In most cases,
emissions from GT and RICE are normalized
to different oxygen contents 2 . As a result,
normalized emission values cannot be compared
directly. Furthermore, even when the
same reference oxygen content is utilized,
emissions reported in ppmvd or mg/m N ³ do
not account for power generation efficiency
associated with the emission release. The
present study uses g/kWh el as an apples-toapples
metric for GT and RICE emissions to
overcome these limitations. On the one
hand, this metric accounts for the massbased
emission release, which is essential for
environmental impact considerations. On
the other hand, it considers the electrical efficiency
of the investigated power generation
technology, which is a primary indicator for
a comprehensive technology comparison.
1.2 Comparison of major regulatory
frameworks of GT and RICE
As they impose binding constraints on power
plant operators, regulations have an important
impact on the emission footprint of
gas-based power generation technologies.
However, significant variations in scope and
strictness can be observed when considering
1
ppmvd: parts per million by volume (dry)
2
For example, the German 13 th BImSchV defines
a reference oxygen content of 15 vol.% for
GT and a reference oxygen content of 5 vol.%
for RICE [3].
3
Environmental, Health and Safety Guidelines
– Small Combustion Facilities Emission Guidelines
[5]
4
Best available techniques (BAT) conclusions
for large combustion plants [4]
5
Directive on the limitation of emissions from
certain pollutants into the air from medium
combustion plants (EMCP) [6]
6
Verordnung über Großfeuerungs-, Gasturbinen-
und Verbrennungsmotoranlagen (13.
BImSchV) [3]
7
Verordnung über mittelgroße Feuerungs- Gasturbinen-
und Verbrennungsmotoranlagen
(44. BImSchV) [7]
8
Exemplary Environmental Protection Agency
(EPA) site permit [8]
9
The EU BAT conclusions specify value ranges
instead of fixed emission limits. Therefore,
F i g u r e 1 considers the upper and lower
bound of the respective NO X value ranges
(BAT low and high).
kWh el
NO X emissions
800
700
600
500
400
300
200
100
GT-SC
RICE-SC
GT-CC
RICE-CC
0
30 35 40 45 50 55 60 65 70
el in %
Fig.1. Emission limits of major current NO X regulations for GT and RICE.
kWh el
CO emissions
1000
900
800
700
600
500
400
300
200
100
GT-SC
RICE-SC
GT-CC
RICE-CC
13 th BImSchV
WorldBank
BAT low
BAT high
EPA (exemplary)
EMCP
44 th BImSchV
13.BImSchV
BAT low
BAT high
EPA (exemplary)
44. BImSchV
0
30 35 40 45 50 55 60 65 70
el in %
Fig.2. Emission limits of the major current CO regulation for GT and RICE.
current emission regulations for GT and
RICE from a national to a global level. To account
for this variety, the present study examines
emission guidelines issued by the
World Bank 3 (WB), emission limits provided
by the EU 4,5 and emission limits defined by
national regulators in Germany 6,7 and the
United States 8 . Employing the previously introduced
metric of g/kWh el , Figure 1
shows an apples-to-apples comparison between
these regulations focusing on nitrogen
oxides (generally referred to as NO X )
emissions 9 depending on the net electrical
efficiency of the generating unit.
As most investigated regulations define
emission limits in ppmvd or mg/m N ³, the
conversion to g/kWh el requires information
regarding electrical efficiency. Differentiating
between single cycle (SC) and combined
cycle (CC) configurations, F i g u r e 1 accounts
for a range of efficiency values associated
with state-of-the-art GT and RICE 10 .
For RICE, even though the legislation does
not distinguish between SC and CC, the two
technologies are colored differently due to
their different electrical efficiencies. The
displayed data indicate that the more strict
regulations (i.e., EU BAT conclusions,
13 th BImSchV, an exemplary EPA permit for
gas turbines) result in comparable emission
limits in mass per generated energy output
for SC-GT and SC-RICE. In contrast, the
10
For a given emission limit defined in ppmvd or
mg/m N ³, an increase in electrical efficiency
results in a decreased value in g/kWh el .
Above certain efficiency thresholds for SCand
CC-GT configurations, the 13 th BImSchV
and the EU BAT conclusions stipulate a linear
increase in emission limits depending on the
electrical efficiency. As a result, F i g u r e 1
and F i g u r e 2 show constant emission limits
when these efficiency limits are surpassed.
vgbe energy journal 7 · 2022 | 33