Reporting of Eskom’s Emissions: Samples, Calculations, Measurements and challenges Date 30 September 2014 Presenter: John Keir
History: Smoke Pollution = No Problem 2014/10/27 3 “Smoke from chimneys is the breath of Soviet Russia” a 1930’s Poster
Topics of Discussion Process: Power Station Samples: Coal Constituents Samples: Flue gas Constituents Calculation: Gas Emission Measurement: Gas Continuous Emission Monitors Measurement: Dust Continuous Emission Monitors Reporting: Eskom Annual Reported Emissions Challenges: DEA Emission Limits & accuracy 2014/10/27 5
Samples: Coal Constituents Proximate Analysis Ultimate Analysis Moisture Moisture Ash Ash Volatile matter Total Carbon (C) Fixed carbon by difference Hydrogen (H) Nitrogen (N) Sulphur (S) Oxygen by difference NB: The Fixed Carbon value is less than the Total Carbon value due to some of the carbon residing in the Volatile matter. 2014/10/27 7
Samples: Flue Gas Constituents Main flue gas constituents (by volume) in the stack are: CO2 13% O2 6% H20 5-8% SO2 ± 800 PPM NOX (98% NO + 2% NO2 ) ± 600 PPM CO < 100 PPM Balance is N2.
Calculation: Gas Emissions 2014/10/27 10
Calculation: Gas Emissions A mobile gas analysis laboratory was built and tests conducted on every stack in Eskom from 1985 to 1995. Some stacks were tested more than once. Mass balances of sulphur and carbon were conducted at the same time. Plant tested emission factors in kg/ton of coal, were calculated from coal and gas analyses. These factors were used with coal tonnages to determine annual emissions in tons. Gas emissions for CO2, SO2, and NO have been calculated since 1982 using this method. The following formulae were used.
Calculation: Gas Emissions cont. 2014/10/27 12
Calculation: Gas Emissions cont. 2014/10/27 13
Calculation: Gas Emissions after 1995 After 1995 the methodology was changed due to the information gained from the previous 10 years Methodologies were compared between plant emission tested and coal analysis calculated emission factors. For future emissions, coal analysis calculated emission factors are used for CO2 and SO2 emissions because this allowed for quicker changes in coal quality. The CO2 emissions are calculated from the total carbon (from an Ultimate coal analysis), then the carbon remaining in the ash after combustion is subtracted.
The result is then multiplied by coal flow. Power stations only analyse for proximate analysis which gives values of fixed carbon. This creates challenges because the total carbon is unknown.
Calculation: Gas Emissions CO2 In proximate analysis, the fixed carbon by difference does not represent all of the carbon in the coal due to some carbon being in the volatile matter. To determine “Total Carbon”, a bit of coal from each daily proximate analysis; sometimes three analyses per day, is placed into a bottle which is sent monthly to Eskom RT&D’s chemical laboratory for ultimate and proximate analyses. (Total carbon is part of the ultimate analysis). Annual regression curves are determined from a number of RT&D’s monthly ultimate and proximate analyses.
Thereafter, total carbon can be calculated from each monthly power station weighted average proximate analysis.
The un-burnt carbon remaining in the ash is subtracted from the total carbon and then a formula ( C + O2 = CO2 ) is used to calculate an emission factor. This factor is multiplied by coal mass flow to produce CO2 in tons. 2014/10/27 15
Calculation: Gas Emissions SO2 The determination of sulphur dioxide emissions was also changed from a plant emission tested to a coal analysis calculated emission factor. The daily sulphur analysed at each power station was weighted with daily coal tonnages to give a monthly weighted average sulphur. The sulphur value is then used in a formula ( S + O2 = SO2 ) to determine a calculated emission factor.
The sulphur remaining in the ash is minimal. Therefore it is not used in the above calculation. The SO2 tonnage over a set period of time is then determined by multiplying the SO2 emission factor with the coal mass flow 2014/10/27 16
Calculation: Gas Emissions NO The nitric oxide (NO) tons is still calculated from plant emission tested factors and then multiplied by coal flow. This is due to the combustible nitrogen being in both the coal and air. Research has shown that most of the nitric oxide comes from fuel nitrogen (Refer to Priven Rajoo, Eskom). Therefore in the future it might be possible to calculate NO from the coal. The nitric oxide plant tested emission factors are updated approximately every three years. The nitric oxide plant tested emission factor is then multiplied by 46/30 (Molecular Weights) to convert it into nitrogen dioxide.
This is done due to the nitric oxide from the stack converting rapidly to nitrogen dioxide in the atmosphere owing to the higher concentration of oxygen.
The NO2 emission factor is then multiplied by the coal mass flow. 2014/10/27 17
Calculation: Gas Emissions; Interesting facts Some interesting facts In Europe, CO2 is calculated from coal analysis and coal mass flow rather than from stack measurement since the uncertainty is better. However, it is a very good idea to measure CO2 in the stack, as it compliments the oxygen measurement. It can be ascertained whether a gas continuous emission monitor is performing correctly due to the O2 and CO2 relationship. If either O2 or CO2 is known the other value can be calculated.
The following examples demonstrate this point : Excess oxygen = 0.00 % Excess oxygen = 12.00% Carbon dioxide = 19.38% Carbon dioxide = 8.25% Sum of O2 & CO2 = 19.38% Sum of O2 & CO2 = 20.25% Each fuel has a max CO2% value. Getting close to 20.94% = vol of O2% in air Excess oxygen = 6.00% Excess oxygen = 20.89% Carbon dioxide = 13.81% Carbon dioxide = 0.01% Sum of O2 & CO2 = 19.81% Sum of O2 & CO2 = 20.90% The sum increases with more O2%. At this stage there is very little CO2% 2014/10/27 18
Calculation: Gas Emissions, Interesting facts In Europe, SO2 measurements are conducted in the stack & not calculated from the coal because SO2 in flue gas can be extracted by Power Plant equipment before it escapes into the atmosphere. In Europe as well as in South Africa, NO measurements are conducted in the stack and cannot be calculated from the coal since it comes from two different sources. The coal calculation methodologies for CO2 and SO2 is an inexpensive method to calculate emissions rather than by a gas analyser measurement. A gas analyser’s cost is > R1 000 000. This does not include any maintenance costs.
However, it can only be on a monthly basis and not on continuous basis like an analyser.
Calculation: Gas Emissions Summary Carbon dioxide (CO2) = EF (Tot Carbon) X coal flow Sulphur dioxide (SO2) = EF (Sulphur)X coal flow Nitrous Oxide (N2O) = EF (IPCC) X coal flow Nitrogen oxide (NOX as NO2) = Tested EF X coal flow Abbreviations: EF = Emission Factor IPCC = Intergovernmental Panel on Climate Change Methodology and calculation is audited by KPMG every 6 months 2014/10/27 20
Measurement: Gas Continuous Emissions 2014/10/27 21
Measurement: Gas Continuous Emissions Department of Environmental Affairs requires Eskom to install gaseous monitors in every stack and be verified by a SANAS accredited mobile laboratory by 1st April 2015.
Analysers measure NO, SO2, CO2, O2, velocity, temperature and pressure and where necessary water vapour. Eskom started by installing one analyser per power station in 2007. This was to obtain expertise in this technology before installing analysers in the rest of Eskom’s stacks Presently, thirty one analysers have been installed out of fifty four stacks requiring analysers. This does not include Medupi and Kusile Power Stations. Most emission analysers are expected to be installed by 1st April 2015, but not all verified. 2014/10/27 22
Measurement: Gas Continuous Emissions Once installed, the gas analysers need verification or a quality assurance test. This is to make sure that the gases sampled by the analyser are representative of the whole gas mixture in the stack. There are four main types of gas analysers: 1. Extractive; either hot and wet or cool and dry 2. In-situ; enveloped folded beam or cross duct A typical gas continuous emission monitor used in Eskom is a one point in-situ analyser. The permanently installed analyser is verified by using a SANAS accredited mobile laboratory to confirm the accuracy which includes stratification and parallel tests every two years.
Measurement: Gas Continuous Emissions 2014/10/27 24 Insitu Analyser
Measurement: Dust Continuous Emissions 2014/10/27 25
Measurement: Dust Continuous Emissions Every Eskom stack has an opacity monitor. Opacity monitors where installed in the late 1970s and early 1980s. Each monitor works on attenuation of light across the stack The more dust in the stack the less light is returned to the analyser’s detector 2014/10/27 26
Measurement: Dust Continuous Emissions 2014/10/27 27 Opacity Monitor
Measurement Dust Continuous Emissions The opacity monitor’s detector outputs a mA signal which is correlated to a dust concentration by conducting isokinetic dust tests at different boiler loads. (see next slide) 2014/10/27 28
Measurement Dust Continuous Emissions 2014/10/27 29
Reporting Eskom Annual Reported Emissions 2014/10/27 30
Eskom Annual Reported Emissions Mass emission data for 2013/2014 financial year Carbon dioxide (CO2) = 233 Mt Sulphur dioxide (SO2) = 1 975 kt Nitrogen oxide (NOx as NO2) = 953 kt Particulate (dust) emission = 78,36 kt Nitrous Oxide (N2O) = 2 969 t 2014/10/27 31
Eskom Annual Reported Emissions Relative emissions data for 2013/2014 financial year Carbon dioxide (CO2) = 1,09 kg/kWh Sulphur dioxide (SO2) = 9,27 g/kWh Nitrogen oxide (NOX as NO2) = 4,48 g/kWh Particulate (dust) emission = 0,37 g/kWh Methodology and calculation is audited by KPMG every 6 months 2014/10/27 32
Challenges DEA (Department of Environmental Affairs) Emission Limits and accuracy 2014/10/27 33
- Challenges: DEA Emission Limits for Power Stations The following is from: Listed activities and associated minimum emission standards identified in terms of section 21 of the National Environmental Management: Air Quality Act, 2004 (Act # 39 of 2004) 1. Applicability of the Act
- Minimum emission standards apply to both permanently operated and for experimental (pilot) plants with a design capacity.
- Minimum emission standards are applicable under normal working conditions.
- Should normal start-up, maintenance, upset and shut-down conditions exceed a period of 48 hours, section 30 of the National Environmental Management, 1998 (Act # 107 of 1998), shall apply unless otherwise specified by the Licensing Authority.
- The averaging period for the purposes of compliance monitoring shall be expressed on a daily average basis or as prescribed in the Atmospheric Emission License
- The emission monitoring system must be maintained to yield a minimum of 80% valid hourly average values during the reporting period.
- The emission monitoring system must be maintained and calibrated as per the original equipment manufacturers’ specifications
- Continuous emission monitoring systems must be audited by a SANAS accredited laboratory at least once every two (2) years. 2014/10/27 35
Challenges: DEA Emission Limits for Power Stations: Eskom’s mobile test Laboratory 2014/10/27 36
Challenges: DEA Emission Limits for Power Stations: Traversing a Power Station stack 2014/10/27 37
- Challenges: DEA Emission Limits for Power Stations 3. Compliance time frames
- New plant must comply with the new plant minimum emission standards on completion.
- Existing plant must comply with minimum emission standards for existing plant by 01 April 2015.
- Existing plant must comply with minimum emission standards for new plant by 01 April 2020. 2014/10/27 38
Challenges: DEA Emission Limits for Power Stations 2014/10/27 39
Challenges: DEA Emission Limits for Power Stations Table from ILISO Consulting: WC=will comply MNC=might not comply WNC=will not comply 2014/10/27 40
- Challenges: DEA Emission Limits for Power Stations What needs to be done: PM emissions
- Optimise existing Electrostatic Precipitators (ESPs)
- Install more efficient Fabric Filter plants (FFPs) Nitrogen oxides (NOx)
- Install low NOx burners.
- Optimise low NOx burners where they are installed.
- Supplement with over-fire air. Sulphur dioxide (SO2)
- Install Flue Gas Desulphurisation (FGD) 2014/10/27 41
Gas Emission Factor Calculation: CO2 & SO2 C + O2 = CO2 12 + 32 = 44 3 + 8 = 11 1 kg + 8/3 kg = 11/3 kg A coal with 50% (0.5kg / kg) by mass of total carbon 1/2 kg + 4/3 kg = 11/6 kg The emission factor is = 1.83 kg / kg of coal less the un-burnt carbon remaining in the ash. Similarly, with SO2, using the chemical formula S + O2 = SO2 Sulphur in ash is minimal and therefore not included. 2014/10/27 43