Stack emission limits for large and small combustion plant and their implications

Transcription

1 Stack emission limits for large and small combustion plant and their implications 22 July 2014 Theo Fischer & Duncan Crous, EScience Associates

2 LISTED ACTIVITIES AND EMISSION LIMITS (GN893) BOILER CATEGORIES NEMA (National Environmental Management Act, 2005) NEMAQA (National Environmental Air: Quality Act, 2008) Section 21 allows for listed activities that require emission limits and an atmospheric emission licence Section 21 divided into industrial categories with process subcategories Category 1: Combustion Installations Solid fuel combustion (non biomass) Liquid fuel combustion Solid biomass Gas combustion Reciprocating engines Waste co-feeding combustion installations Category 8.1: Thermal treatment of general and hazardous waste

3 LISTED ACTIVITIES AND EMISSION LIMITS (GN893) BOILER CATEGORIES Each sub category has its own Emission limits Special requirements (continuous monitoring of certain species) Applicable criteria

4 LISTED ACTIVITIES AND EMISSION LIMITS (GN893) BOILER CATEGORIES Each sub category has its own Emission limits Special requirements (continuous monitoring of certain species) Applicable criteria

5 SMALL BOILER AS A CONTROLLED EMITTER (GN831) BOILER CATEGORIES NEMAQA section 23 allows for the establishment of controlled emitters Controlled emitters do not require an AEL, but have emissions limits that need to be met Periodic measurements need to be sent to the local air quality officer of criteria pollutants Small boilers (<50MW heat input) are the first to be declared as controlled emitters Solid fuel Liquid Fuel Gaseous fuel (Natural gas/lpg) Gaseous fuel (Process gas) Solid biomass Co feeding (multiple fuels listed above) No waste category!

6 SMALL BOILER AS A CONTROLLED EMITTER (GN831) BOILER CATEGORIES As with listed activities, each small boiler has it s own Emission limits Applicable criteria Blanket criteria in terms of monitoring

7 SMALL BOILER VS LARGE BOILER EMISSION LIMITS BOILER CATEGORIES PM small boilers have less stringent emission limits SO 2 New - Small boilers are less stringent for new (* process gas small boilers) Existing - Small boilers are same or MORE stringent (* process gas small boilers) NOx No limits for small boilers Solid Fuel Liquid Fuel Solid Biomass Gas Combustion Size New Existing New Existing New Existing New Existing "Large" PM Small (90) 20 (130) "Large" SO2 Small (1000) 100 (3500) NOx Large

8 LARGE VS SMALL BOILER CONFIGURATIONS Legislation may be interpreted literally or on total thermal input for a site, though GN893 stipulates 50 MW heat input per unit, and different pronouncements may be given for a multi boiler installation (generally the literal interpretation is taken and small boilers apply) When planning a new operation, weighing large vs multiple small boilers has more variables to look at Fuel type/quality Abatement requirements Requires AEL No AEL

9 FUEL TYPE / EFFICIENCY Less stringent emission limits means legally compliant higher output of PM and SO 2 Comparisons were made of different ash and sulphur content fuels and the abatement needed assuming a CV of 25, and a flue gas generation of 241 m 3 /GJ Unabated Large Solid boiler Small solid boiler (g/s SO2) [SO2] in (g/s SO2) [SO2] (g/s SO2) [SO2] S% /MW FG /MW in FG Abatement /MW in FG Abatement 1.0% % 0% 1.5% % 0% % % 16% 2.5% % 33%

10 FUEL TYPE / ABATEMENT EFFICIENCY REQUIREMENT 100% Abatement Efficiency Needed 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% 1.0% 1.5% 2.0% 2.5% Fuel sulphur % Solid Fuel Gas Fuel Biomass S% Large Small Large Small Large Small 1.0% 75.9% 0.0% 69.9% 39.8% 69.9% 39.8% 1.5% 83.9% 0.0% 79.9% 59.8% 79.9% 59.8% 2.0% 88.0% 15.7% 84.9% 69.9% 84.9% 69.9% 2.5% 90.4% 32.5% 88.0% 75.9% 88.0% 75.9% Solid - Large Solid - Small Gas - Large Gas - Small Biomass - Large Biomass - Small

11 DC2 FUEL TYPE / ABATEMENT EFFICIENCY REQUIREMENT Abatement Efficiency Needed 100% 98% 96% 94% 92% 90% 88% 86% 84% 82% Solid - Large Solid - Small Liquid - Large Liquid - Small Gas - Large Gas - Small Biomass - Large 80% 10% 20% 30% 40% Ash % in fuel Solid Fuel Liquid Fuel Gas Fuel Biomass Ash% Large Small Large Small Large Small Large Small 10% 92.5% 81.9% 92.5% 84.9% 98.5% 86.4% 92.5% 81.9% 20% 96.2% 91.0% 96.2% 92.5% 99.2% 93.2% 96.2% 91.0% 30% 97.5% 94.0% 97.5% 95.0% 99.5% 95.5% 97.5% 94.0% 40% 98.1% 95.5% 98.1% 96.2% 99.6% 96.6% 98.1% 95.5% Biomass - Small

12 Slide 11 DC2 recopy graph Duncan Crous;

13 FUEL TYPE / ABATEMENT EFFICIENCY Lower emission limits means less abatement Lower cost abatement equipment Alternative methods (in bed lime dosing in FBC) Lower pressure drops on cyclones -Lower operating costs Less fly ash and scrubber sludge Reduced waste streams Reduced disposal costs Scrubber sludge disposal reduction S% Solid Liquid Gas Biomass 1% 100% 0% 43% 43% 2% 100% 0% 25% 25% 2% 82% 0% 18% 18% 3% 64% 0% 14% 14% Fly ash disposal reduction Ash% Solid Liquid Gas Biomass 10% 11% 8% 12% 11% 20% 5% 4% 6% 5% 30% 4% 3% 4% 4% 40% 3% 2% 3% 3% What s the catch?.. What doesn t go to the dump..

14 EMISSIONS LIMITS VS AMBIENT CONCENTRATION LIMITS Emission limits are at the stack tip Ambient concentrations is in the breathable air, ground level Cumulative GN893 and GN831 Ambient air quality limits PM10, PM2.5, SO2, NOx, CO

15 DC3 AIR QUALITY IMPACTS OF SMALL VS LARGE BOILERS Goes out the stack (50MWt, 15m stack, SO 2, Ambient Air Quality Screening model output) 450 Ground level ambient SO2 concentration (µg/m 3 ) Distance Solid - Large Solid - Small Gas - Large Gas - Small Biomass - Large Biomass - Small

16 Slide 14 DC3 show limit, add background emissions Duncan Crous;

17 AIR QUALITY IMPACTS OF SMALL VS LARGE BOILERS Goes out the stack (50MWt, 15m stack, SO 2, Ambient Air Quality Screening model output) Ground level ambient PM concentration (µg/m 3 ) 20 Solid - Large Solid - Small 14 Liquid - Large 12 Liquid - Small 10 8 Gas - Large 6 Gas - Small 4 Biomass - Large Distance Biomass - Small

18 AIR QUALITY IMPACTS OF SMALL VS LARGE BOILERS Ambient concentrations are elevated when using small boiler emission limits In air sheds with already high background ambient concentrations this could lead to exceedances of ambient air quality limits Air quality impact studies using detailed air modelling (level 2 and 3) are more likely to be required in such cases do give site specific estimations Outcomes of detailed study might be required and will necessitate: Increased stack height for smaller boilers Increased abatement (though not necessarily down to the level of a large boiler)

19 AIR QUALITY IMPACTS BACKGROUND EFFECTS Ground level ambient SO2 concentration (µg/m 3 ) Solid - Large+ Solid - Small+ Solid - Large Solid - Small Distance

20 IN SUMMARY PROS Small boilers have lower emission limits Allows for lower efficiency abatement/cheaper lower quality fuels/reduced disposal costs Does not require an AEL (Air emissions licence) Only periodic measurements needed CONS Increases ambient air concentrations of pollutants as compared to large boiler standards May require a more detailed air impact assessment Not as suitable in areas with higher background ambient concentrations