Nielsen, M., Nielsen, O.-K. & Thomsen, M. 2010: Emissions from decentralised CHP plants 2007 - Energinet.dk Environmental project no. 07/1882. Project report 5 – Emission factors and emission inventory for decentralised CHP production. National Environmental Research Institute, Aarhus University. 113 pp. – NERI Technical Report No. 786.
A revised set of emission factors for decentralized combined heat and power (CHP) plants <25MWe has been estimated. The emission factors valid for 2006/2007 have been estimated for the plant technologies: Municipal solid waste (MSW) incineration plants, plants combusting straw or wood, natural gas fuelled reciprocating engines, biogas fuelled engines, natural gas fuelled gas turbines, gas oil fuelled reciprocating engines, gas oil fuelled gas turbines, steam turbines combusting residual oil and reciprocating engines combusting biomass producer gas based on wood.
The emission factors have been estimated based on emission measurements performed as part of the project as well as emission measurements that have been collected by FORCE Technology (FORCE) and Danish Gas Technology Centre (DGC). Further the estimates have been based on plant specific fuel consumption data collected annually by the Danish Energy Agency (DEA).
An extract of the revised 2006/2007 emission factors is shown in Table 1.
Table 1 Extract of the revised 2006 (2007 for natural gas fuelled plants) emission factors for Danish decentralised CHP plants < 25MWe.
| Unit | Natural gas fuelled engines | Biogas fuelled engines | Natural gas fuelled gas turbines | Gas oil fuelled engines | Gas oil fuelled gas turbines | Fuel oil, steam turbines | Biomass producer gas, engines | MSW incineration | Straw | Wood |
SO2 | g per GJ | - | - | - | - | - | - | - | < 8.3 | 49 | < 1.9 |
NOx | g per GJ | 1358) | 202 | 48 | 942 | 83 | 136 | 173 | 102 | 125 | 81 |
UHC (C) | g per GJ | 4358) | 333 | 2.59) | (46) 10) | - | (1.6) 10) | 12 | < 0.68 | < 0.945) | < 6.16) |
NMVOC | g per GJ | 924) 8) | 104) | 1.64) | (37)10) | - | (0.8) 10) | 2.34) | < 0.564) | < 0.784) | < 5.14) |
CH4 | g per GJ | 4814) 8) | 4344) | 1.74) | 24 | - | < 1.3 | 134) | < 0.344) | < 0.474) | < 3.14) |
CO | g per GJ | 588) | 310 | 4.8 | 130 | 2.6 | 2.8 | 586 | < 3.9 | 67 | 90 |
N2O | g per GJ | 0.58 | 1.6 | 1.0 | 2.1 | - | 5.0 | 2.7 | 1.2 | 1.1 | 0.83 |
NH3 | g per GJ | - | - | - | - | - | - | - | < 0.29 | - | - |
TSP | g per GJ | - | - | - | - | - | 9.5 | - | < 0.29 | < 2.3 | 10 |
As | mg per GJ | < 0.045 | < 0.042 | - | < 0.055 | - | - | 0.116 | < 0.59 | - | - |
Cd | mg per GJ | < 0.003 | 0.002 | - | < 0.011 | - | - | < 0.009 | < 0.44 | < 0.323) | 0.27 |
Co | mg per GJ | < 0.20 | < 0.21 | - | < 0.28 | - | - | < 0.22 | < 0.56 | - | - |
Cr | mg per GJ | 0.048 | 0.18 | - | 0.20 | - | - | 0.029 | < 1.6 | - | - |
Cu | mg per GJ | 0.015 | 0.31 | - | 0.30 | - | - | < 0.045 | < 1.3 | - | - |
Hg | mg per GJ | < 0.0983) | < 0.12 | - | < 0.11 | - | - | 0.54 | < 1.8 | < 0.313) | < 0.403) |
Mn | mg per GJ | < 0.046 | 0.19 | - | 0.009 | - | - | 0.008 | < 2.1 | - | - |
Ni | mg per GJ | 0.045 | 0.23 | - | 0.013 | - | - | 0.014 | < 2.1 | - | - |
Pb | mg per GJ | 0.043 | 0.005 | - | 0.15 | - | - | 0.022 | < 5.5 | - | - |
Sb | mg per GJ | < 0.0493) | 0.12 | - | < 0.055 | - | - | < 0.045 | < 1.1 | - | - |
Se | mg per GJ | (0.01)7) | < 0.21 | - | < 0.22 | - | - | < 0.18 | < 1.1 | - | - |
Tl | mg per GJ | < 0.203) | < 0.21 | - | < 0.22 | - | - | < 0.18 | < 0.453) | - | - |
V | mg per GJ | < 0.048 | < 0.042 | - | 0.007 | - | - | < 0.045 | < 0.33 | - | - |
Zn | mg per GJ | 2.9 | 4.0 | - | 58 | - | - | 0.058 | 2.3 | 0.41 | 2.3 |
PCDD/-F | ng per GJ | < 0.57 | < 0.961) | - | < 0.99 | - | - | < 1.71) | < 5.0 | < 19 | < 14 |
PBDD/-F | ng per GJ | - | < 5.01) | - | - | - | - | < 7.21) | < 6.31) | - | - |
PAH (BaP) | µg per GJ | < 13 | < 4.2 | - | < 33 | - | - | < 4.9 | < 2 | < 125 | < 13 |
?PAH | µg per GJ | < 1025 | < 606 | - | < 8988 | - | - | < 181 | < 37 | < 5946 | < 664 |
Naphthalene | µg per GJ | 2452 | 4577 | - | 17642 | - | - | 8492 | < 1293) | 12088 | 2314 |
HCB | µg per GJ | - | 0.19 | - | < 0.22 | - | - | 0.80 | < 4.3 | < 0.11 | - |
PCB | ng per GJ | - | < 0.191) | - | < 0.131) | - | - | < 0.241) | < 0.32 | - | - |
Formaldehyde | g per GJ | 14.1 | 8.7 | - | 1.3 | - | < 0.002 | 1.5 | - | - | - |
HCl | g per GJ | - | - | - | - | - | - | - | < 1.14 | 56 | - |
HF | g per GJ | - | - | - | - | - | - | - | < 0.14 | - | - |
1) Emission measurements were below detection limits for all congeners.
2) Based on 1 emission measurement. The emission measurement was below the detection limit.
3) All emission measurements were below the detection limit.
4) Based on disaggregation of the total unburned hydrocarbon (UHC) emission factor.
5) Only 1 out of 7 emission measurement was above the detection limit.
6) Two out of three emission measurements were below the detection limit.
7) Two emission measurements were performed, both below the detection limit. These results have been ignored and instead the lower emission factor 0.01 mg per GJ based on EEA (2009) have been applied.
8) The increased emission level during start up and stop of the gas engines have been included in this emission factor.
9) Based on emission measurements performed in 2003-2006.
10) The emission factor based on emission measurements performed within this project has been ignored. Instead the NMVOC emission factor refers to EEA (2009). The UHC emission factor has been estimated based on the emission factors for NMVOC and CH4.
The emission factors for MSW incineration plants are much lower than the emission factors that were estimated for year 2000. The considerable reduction in the emission factors is a result of lower emission limit values in Danish legislation (MST, 2003) since 2006 that has lead to installation of new and improved flue gas cleaning systems in most MSW incineration plants. The Total Suspended Particulates (TSP) emission factor is 86 % lower than the emission factor in year 2000, whereas the reduction for heavy metal emission factors is 38 % to 96 %. For dioxin (PCDD/-F) the emission factor has decreased 97 % since 2000 due to the fact that dioxin flue gas cleaning has been installed in all MSW incineration plants as a result of the new emission limit values (DEPA, 2003). The NOx emission factor has decreased 17 % since 2000. Emission factors for SO2, HCl and HF have also decreased considerably since 2000.
Combined heat and power (CHP) plants combusting straw and wood have not undergone major changes in technology or flue gas cleaning systems since 2000 and the emission limit values are also unchanged. The relatively low number of plants and emission measurements result in uncertainty concerning development of the emission levels of these plant categories. Emission measurements from 2000-2008 have been included in the estimates.
The emission factors for natural gas fuelled reciprocating engines have been reduced since 2000 as a result of technical improvements that have been carried out as a result of lower emission limit values in Danish legislation (DEPA, 2005). Most engines had to be below the lower emission limit values in October 2006 and thus the emission factors have been estimated for 2007 onwards. The NOx emission factor has decreased 20 % and the CO emission factor has decreased 68 % since 2000. Oxidation catalysts for reduction of the emission of CO have now been installed at all natural gas fuelled engine plants. The Unburned hydrocarbons (UHC) emission has also decreased since 2000. The CH4 emission factor has decreased 10 % and the NMVOC 24 %.
The fuel consumption for biogas fuelled engines has increased 32 % since 2000. The increase is mainly on larger engines. This is part of the reason for the changes of emission factors for biogas fuelled engines. Lower emission limit values for biogas fuelled engines > 1 MW is included in Danish legislation (DEPA, 2005), but the engines do not have to meet these emission limits until 2013. The emission factor for NOx has decreased 63 % since 2000 whereas the emission factor for UHC has increased 31 %. The CO emission factor is 14 % higher than in 2000.
The NOx emission factor for natural gas fuelled gas turbines has decreased 62 % since 2000. This is a result of installation of low-NOx burners in almost all gas turbines. This has been necessary to meet new emission limits in Danish legislation (DEPA, 2005).
Emission factors have also been estimated for CHP plants combusting oil and biomass producer gas respectively. For gas oil fuelled engines the NOx emission factor is remarkably high compared to other CHP plants. The CO emission factor for engines fuelled by biomass producer gas is considerably higher than for other engines whereas the UHC emission is much lower. This is in agreement with the composition of the biomass producer gas.
The emission measurements performed in this project included screening of a number of emissions that have not previously been measured from Danish CHP plants. The measurements for brominated dioxins/furans (PBDD/-F) were below the detection limits for all congeners. The detection limit for PBDD/-F was higher than the detection limit for PCDD/-F and thus the data for PBDD/-F added limited new information. Based on the PBDD/-F emission measurements performed in this project it could not even be rejected that the PBDD/-F emission is higher than the PCDD/-F emission.
A few PCDD/-F congeners were above the detection limit for gas oil fuelled engines and natural gas fuelled engines whereas all congeners were below the detection limit for biomass producer gas fuelled engines. Further PCDD/-F emissions above the detection limit were measured for MSW incineration plants and for straw and wood fuelled CHP plants.
PCB emission measurements performed at engines fuelled by gas oil, biogas and biomass producer gas were below the detection limit for all congeners. For MSW incineration plants several PCB emission measurements were above the detection limit. The PCB emission factors are below the emission factors stated in a former study (Thomsen et al., 2009).
As expected MSW incineration plants are the main emission source for HCB. In spite of the fact that the estimated HCB emission factor for MSW incineration is much lower than the current factor MSW incineration is still among the main emission sources for HCB in Denmark.
Uncertainty estimates for the emission factors have been estimated and reported in project report 3 (Boje et al., 2010b) and project report 4 (Jørgensen et al., 2010b).
Total emissions from decentralized CHP plants <25MWe have been estimated for 2006. This estimate shows that natural gas fuelled engines was the main emission source for CH4, NMVOC and aldehydes. Further, natural gas fuelled engines was the largest emission source for CO (49 %) and NOx (41 %) and, unexpectedly, also for Zn (34%). MSW incineration plants were the main source of emission for most heavy metals, HF, PCDD/-F, HCB and PCB. Further the emissions of NOx (37 %) and SO2 (23 %) were also considerable. Wood fired CHP plants was the main emission source for particulates (TSP). Both wood and straw fired CHP plants were considerable emission sources for PCDD/-F. Steam turbines fuelled by residual oil was the main emission source for SO2 and several heavy metals. Biogas fuelled engines was a considerable emission source for CO (29 %) whereas emissions of all other pollutants were low. Emissions from natural gas fuelled gas turbines and from engines fuelled by gas oil or biomass producer gas were all relatively low.
The emission of NOx and SO2 from decentralized CHP plants <25MWe added up to 5 % of the total Danish emission. The CH4 emission added up to 6 % of the national emission whereas the emission of several heavy metals was above 10 %. The HCB emission added up to 30 % of the national emission but it has to be taken into account that all HCB emission sources have not yet been included in the national inventory. The emission of dioxin (PCDD/-F) added up to only 1 % of the national emission whereas the emission share was approximately 35 % in 1995.
The emissions from decentralised CHP plants have been compared to the emission from Danish public electricity and heat production. The decentralized CHP plants are a major emission source for CH4 and NMVOC. Further the decentralized CHP plants are large emission sources for NOx, CO, heavy metals, PCDD/-F and HCB.
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