Council of the
European Union
Brussels, 10 October 2014
(OR. en)
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Interinstitutional File:
2013/0442 (COD)
LIMITE
ENV 788
ENER 410
IND 264
TRANS 452
ENT 207
SAN 361
PARLNAT 241
CODEC 1893
NOTE
From:
To:
General Secretariat of the Council
Delegations
No. prev. doc.:
13270/14 ENV 764 ENER 40 IND 249 TRANS 432 ENT 198 SAN 347
PARLNAT 231 CODEC 1832
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PARLNAT 326 CODEC 3089 - COM(2013) 919 final
No. Cion doc.:
Subject:
Proposal for a Directive of the European Parliament and of the Council on
the limitation of emissions of certain pollutants into the air from medium
combustion plants
- Comments from delegations
Delegations will find in the Annex a non-paper received from Belgium on the setting of an emission
limit value (ELV) for carbon monoxide (CO) under the proposal for an MCP Directive.
____________________
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ANNEX
BELGIUM
Non-paper from Belgium on the setting of an emission limit value (ELV)
for carbon monoxide (CO) under the proposal for an MCP Directive
Context
The proposal for an MCP directive concerns combustion plants, engines, and gas turbines with a
rated thermal equal to or greater than 1 MW and less than 50 MW. It strives to set new emission
limit values (ELVs) for three types of pollutant, namely, sulphur dioxide (SO2), nitrogen oxides
(NOx), and particulate matter (PM).
The meeting document of 19 September 2014 presents the latest developments in the emission limit
values per type of pollutant.
The emission limit value tables from this meeting document (annexed hereto) show that the
combustion plants, engines, and natural gas-fired turbines must comply with the ELVs for a
single pollutant (NOx or nitrogen oxides) only.
Basic principles of combustion
Natural gas is composed for the most part of hydrocarbon chains in the form of methane (CH4),
whereas the air supporting combustion (combustion air) is composed primarily of oxygen (close to
21%) and nitrogen (more than 78%).
In the presence of a spark or intense source of heat, methane reacts with oxygen to produce either a
flame that is then maintained and stabilized in the case of furnaces or gas turbines or an explosion in
the case of gas engines.
The fundamental equations of combustion are as follows: (1)
C + O2  CO2
H2 + 0.5 O2  H2O
S + O2  SO2
In the case of methane, CH4 + 202  CO2 + 2H2O.
The theoretical quantity of air is the exact quantity of air needed for the oxygen that it contains to
allow complete combustion. That means a perfect combustion air/fuel mixture.
Meeting the theoretical air requirement is not enough. In practice, the various types of combustion
plant require an additional air supply (excess air) for complete combustion. The consequence of this
excess air is the addition of more oxygen than necessary.
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The EEA (European Environmental Agency) gives a list of the main pollutants in the
EMEP/EEA Emission Inventory Guidebook 2013, to wit, “Relevant [combustion] polluants are
SO2, NOx, NMVOC, particulate matter (PM), black carbon (BC), heavy metals, PAH,
polychlorinated dibenzo-dioxins and furans (PCDD/F) and hexachlorobenzene (HCB).” (2)
The EPA (U.S. Environmental Protection Agency) specifies the pollutants that are generated by
certain types of natural gas-fired plant, as follows:
“The emissions from natural gas-fired boilers and furnaces include nitrogen oxides (NOx),
carbon monoxide (CO), carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), volatile
organic compounds (VOCs), trace amounts of sulfur dioxide (SO2), and particulate matter
(PM).” (3)
"The primary criteria pollutants from natural gas-fired reciprocating engines are oxides of
nitrogen (NOx), carbon monoxide (CO), and volatile organic compounds (VOC). The formation
of nitrogen oxides is exponentially related to combustion temperature in the engine cylinder. The
other pollutants, CO and VOC species, are primarily the result of incomplete combustion.
Particulate matter (PM) emissions include trace amounts of metals, non-combustible inorganic
material, and condensible, semi-volatile organics which result from volatized lubricating oil,
engine wear, or from products of incomplete combustion.” (4)
“The primary pollutants from gas turbine engines are nitrogen oxides (NOX), carbon monoxide
(CO), and to a lesser extent, volatile organic compounds (VOC). Particulate matter (PM) is also a
primary pollutant for gas turbines using liquid fuels. Nitrogen oxide formation is strongly
dependent on the high temperatures developed in the combustor. Carbon monoxide, VOC,
hazardous air pollutants (HAP), and PM are primarily the result of incomplete combustion.
Trace to low amounts of HAP and sulfur dioxide (SO2) are emitted from gas turbines. Ash and
metallic additives in the fuel may also contribute to PM in the exhaust.” (5)
When it comes to the pollutants in the NOx family, the mechanism of NOx formation is triggered
when the oxygen (02) in the combustion air reacts with the nitrogen (N2) under the effect of the
flame’s high temperature. In this case one speaks of thermal NOx.
Reduction of NOx emissions.
The simplest method for reducing NOx emissions is to reduce the excess air (see the figure below).
Another possibility is to opt for techniques that lower the temperature of the flame. NOx emissions
control systems such as low NOx burners and flue gas recirculation (FGR) are frequently installed
in combustion plants and appliances, either from the start or by retrofitting.
Reducing the excess air in order to reduce the NOx emissions can lead to incomplete combustion.
A reduced air supply usually also lowers the plant’s combustion efficiency and increases the
emissions of other pollutants, such as:
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“Carbon monoxide
The rate of CO emissions from boilers depends on the efficiency of natural gas combustion.
Improperly tuned boilers and boilers operating at off-design levels decrease combustion efficiency
resulting in increased CO emissions. In some cases, the addition of NOx control systems such as
low NOx burners and flue gas recirculation (FGR) may also reduce combustion efficiency,
resulting in higher CO emissions relative to uncontrolled burners.” (6)
Note: If carbon monoxide is present in large amounts in confined, unventilated spaces, it can have
detrimental health effects, to the point of being lethal in some cases. The types of plant that come
under the scope of the proposed MCP Directive are characterised by high input levels and thus
involve particularly high air flow and pollutant emissions levels compared with household
appliances and the internal combustion engines found in motor vehicles. The presence of
combustion plant in closed technical areas creates a risk that may be major if its carbon monoxide
(CO) emissions are not controlled.
“Volatile Organic Compounds
The rate of COV emissions from boilers and furnaces also depends on combustion efficiency. VOC
emissions are minimized by combustion practices that promote high combustion temperature,
long residence times at those temperatures, and turbulent mixing of fuel and combustion air.
Trace amounts of VOC species in the natural gas fuel (e.g. formaldehyde and benzene) may also
contribute to VOC emissions if they are not completely combusted in the boiler.” (7)
Note: Although they are not concerned by the proposal for an MCP Directive, COVs are subject to
national emissions ceilings under the NEC Directive.
“Particulate Matter
Because natural gas is a gaseous fuel, filterable PM emissions are typically low. Particulate matter
from natural gas combustion has been estimated to be less than 1 micrometer in size and has
filterable and condensable fractions. Particulate matter in natural gas combustion are usually
larger molecular weight hydrocarbons that are not fully combusted. Increased PM emissions may
result from poor air/fuel mixing or maintenance problems.” (8)
Note: PM is not concerned by the proposal for an MCP Directive for natural gas-fired plant,
although it is subject to national emissions ceilings under the NEC Directive.
The consequences of reducing the excess air supply are described in the European Commission’s
BREF on Large Combustion Plants (LCP) (9) as follows:
“Low excess air is a comparatively simple and easy-to-implement operational measure for the
reduction of nitrogen oxides emissions. By reducing the amount of oxygen available in the
combustion zone to the minimum amount needed for complete combustion, fuel bound nitrogen
conversion and to a less extent thermal NOX formation are reduced. A considerable emission
reduction can be achieved with this measure especially in the case of old power plants, therefore it
has been incorporated in many existing large combustion installations. In general, new plants are
equipped with extensive measuring and control equipment that enables optimum adjustment of the
combustion air supply.
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No additional energy is required for low excess air firing and, if operated properly, no reduction in
the availability of the power plant should result from this primary emission reduction measure.
However, as the oxygen level is reduced, combustion may become incomplete and the amount of
unburned carbon in the ash may increase. In addition, the steam temperature may decrease.
Reducing the oxygen in the primary zones to very low amounts can also lead to high levels of
carbon monoxide. The result of these changes can be a reduction in the boiler efficiency,
slagging, corrosion and a counteractive overall impact on boiler performance. Another effect of
this technique is that not only will NOX be reduced, but also SO3, which can cause corrosion and
fouling on the air preheater and the particulate control device. Potential safety problems, which
might result from the use of this technique without a strict control system, include fires in air
preheaters and ash hoppers, as well as increases in opacity and in the rates of water-wall
wastage.”
Justification for setting an emission limit value (ELV) for carbon monoxide (CO) under the
proposal for an MCP Directive
By imposing compliance with ELVs for only one of the pollutants emitted by gas-fired combustion
plant (in this case, nitrogen oxides: NOx), the proposal for a directive allows the continued
operation of improperly tuned and/or ageing plant, for which the excess air supply may be
reduced (to decrease NOx emissions), to the detriment of combustion efficiency and with
increases in emissions of other pollutants not subject to emission controls.
Setting NOx and CO emission limit values allows the combustion plant to operate under the best
conditions with maximized efficiency and without producing a sudden surge in pollutant emissions
(below, on the left: http://www.energieplus-lesite.be/).
Composants des gaz de combustion = Combustion gas components
Mélange combustible/air = fuel/air mixture
Zone de fonctionnement optimal des installations de chauffage = Optimal operating zone for
heating plant
Manque d’air = lack of air
Excès d’air = Excess air
Couple = torque
Consommation = consumption
Proportion d’air = proportion of air
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Combustion efficiency is usually maximized when just enough air is supplied and properly mixed
with combustible gases to ensure complete combustion. (10)
Control of the combustion process is very important to efficient boiler operation. Incomplete fuel
combustion represents wasted energy and results in increased CO and PM emissions. (11)
Concomitant NOx and CO emission limit values in other European legislation.
Directive 2010/75/EU (IED) already requires compliance with NOx and CO emission limit
values for gas-fired combustion plants of over 50 MW.
Emission limit values (mg/Nm3) for NOx and CO
for gas fired combustion plants (12)
NOx
CO
Combustion plants firing
natural gas with the
100
100
exception of gas turbines and
gas engines
Gas turbines (including
CCGT), using natural gas as
50
100
fuel
Gas engines
100
100
The same goes for the draft “Ecodesign” regulation establishing ecodesign requirements for
the smaller solid fuel boilers (heat outputs of up to 500 kW) that may be put on the market
and put into service. It sets limit values for NOx, CO, particulate matter, and organic
compounds, as well as minimum efficiency rates.
Conclusions
Adopting a carbon monoxide (CO) emission limit value (ELV) for gas-fired combustion
plants, engines, and gas-fired turbines as part of the proposal for an MCP directive is a
minimum requirement. Moreover, CO ELVs for all the types of plant covered by the
MCP Directive, in line with what already exists in most national regulations, should be
adopted as well.
The emission limit value requested for natural gas-fired combustion plant is:
ELV (CO) < 100 mg/Nm³, at 3% O2.
Concerning the engines using natural gas as fuel, the current CO’s ELV in BE (650 mg / Nm³ at
5 % O2) is a minimum requirement.
ELV (CO) < 250 mg/Nm³, at 15% O2 *
*(conversion to the MCP oxygen rate).
An emission limit value for gas turbines is also necessary, but at the moment BE is still evaluating
what emission limit value is feasible.
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References:
(1), (10): ASHRAE Handbook – Fundamental (2009), SI Editions
(2): EMEP/EEA (European Environmental Agency) Emission Inventory Guidebook 2013, page 14
(3), (6), (7), (8): US EPA, AP 42 (Compilation of Air Polluant Emission Factors), Fifth Edition,
Volume I, Chapter I: External Combustion Sources. 1.4 Natural Gas Combustion
(4): US EPA, AP 42 (Compilation of Air Polluant Emission Factors), Fifth Edition,
Volume I, Chapter 3: Stationary Internal Combustion Sources.3.2 Natural Gas-fired Reciprocating
Engines
(5): US EPA, AP 42 (Compilation of Air Polluant Emission Factors), Fifth Edition,
Volume I, Chapter 3: Stationary Internal Combustion Sources. 3.1 Stationary Gas Turbines
(9): European Commission, BREF Large Combustion Plants (LCP), July 2006
Point 3.4.1.1 (Low excess air)
(11): Oak Ridge National Laboratory: Guide to low-emission boiler and combustion equipment
selection, April 2002, for the U.S. Department of Energy
(12): European Directive 2010/75/EC of the European Parliament and of the Council of
24 November 2010 on industrial emissions (integrated pollution prevention and control)
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Annexes
Proposal for a Directive of the European Parliament and of the Council on the limitation of
emissions of certain polluants into the air from medium combustion plants (Presidency proposal),
Annexe II
1. Existing combustion plants, engines and gas turbines
Emission limit values (mg/Nm3) for existing combustion plants with rated thermal input
between 1 and 5 MW
Pollutant
Solid
Other
Gas Oil*
Liquid fuels
Natural
Gaseous
biomass
solid
other than Gas
Gas
fuels
fuels
Oil
other than
natural
gas
(1) (2)
SO2
200
1100
350
200(1) (2)
(3)
NOx
650
650
200
650
200
250(3)
Dust
50
50
50
Emission limit values (mg/Nm3) for existing […] combustion plants with rated thermal input
above 5 MW
Pollutant
Solid
biomass
Other solid
fuels
Gas Oil
Liquid
fuels other
than Gas
Oil
Natural
gas
Gaseous fuels
other than
natural gas
SO2
200
400
[…]
350(2)(5)
-
35[…] (6) (7) (5) (5bis)
200
-
250(8)
-
(5bis)
NOX
Dust
650
30[…]
650
30
200[…]
[…]
650(8)
30(4)(9)
Emission limit values (mg/Nm3) for existing engines and gas turbines
Pollutant
Type of combustion
Liquid
Natural
Gaseous
fuels
gas
fuels other
plant […]
than
natural gas
SO2
Engines and gas
60
15
turbines
NOX
Engines
190 (1)
190 (2)
190 (2)
Gas turbines (3)
200
150
200
Dust
Engines and gas
10
turbines
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2. New combustion plants, engines and gas turbines
Emission limit values (mg/Nm3) for new combustion plants with rated thermal input
between 1 and 5 MW
Pollutant
Solid
Other
Gas Oil
Liquid fuels
Natural
Gaseous
biomass
solid
other than Gas
Gas
fuels other
Fuels
Oil
than natural
gas
SO2
200
1100
350
110
NOx
500
500
200
300
100
200
Dust
50
50
50
Emission limit values (mg/Nm3) for new […] combustion plants with rated thermal input above
5 MW
Pollutant
Solid
Other solid
Gas Oil
Liquid
Natural
Gaseous
biomass
fuels
fuels other
gas
fuels other
than Gas
than
Oil
natural gas
SO2
200
400
[…]
350(5)
35(3)(4)
(6)
NOX
300
300
200
300
100
200
[…]
(2)(7)(8)
Dust
20
20
[…]
20
-(8)
Emission limit values (mg/Nm3) for new engines and gas turbines
Pollutant
Type of combustion
Liquid
Natural
Gaseous
plant […]
fuels
gas
fuels other
than
natural gas
SO2
Engines and gas
60(4)
15
turbines
NOX
Engines
190(1) (5)
95(2)
190
3
(6)
Gas turbines ( )
75
50
75
(7)
Dust
Engines and gas
10
turbines
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