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

22 July 2014

Theo Fischer & Duncan Crous, EScience Associates

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

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

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

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!

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

SMALL BOILER VS LARGE BOILER EMISSION LIMITSBOILER CATEGORIES

§ PM – small boilers have less stringent emission limits§ SO2

§ 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

New Existing New Existing New Existing New Existing"Large" 50 100 50 75 50 100 10 10

Small 120 250 100 150 120 250 10 (90) 20 (130)"Large" 500 3500 500 3500 500 3500 400 500

Small 2800 2800 500 3500 1000 1000 35 (1000) 100 (3500)NOx Large 750 1100 250 1100 750 1100 50 300

PM

SO2

SizeSolid Fuel Liquid Fuel Solid Biomass Gas Combustion

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

FUEL TYPE / EFFICIENCY

§ Less stringent emission limits means legally compliant higher output of PM and SO2

§ 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 m3/GJ

Unabated Large Solid boiler Small solid boiler

S%(g/s SO2)

/MW[SO2] in

FG(g/s SO2)

/MW[SO2] in FG Abatement

(g/s SO2) /MW

[SO2] in FG Abatement

1.0% 0.40 1659.75

0.0964 400

76%

0.6748 2800

0%1.5% 0.60 2489.63 84% 0%2.0% 0.80 3319.5 88% 16%2.5% 1.00 4149.38 90% 33%

FUEL TYPE / ABATEMENT EFFICIENCY REQUIREMENT

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

1.0% 1.5% 2.0% 2.5%

Aba

tem

ent E

ffic

ienc

y N

eede

d

Fuel sulphur %

Solid - Large

Solid - Small

Gas - Large

Gas - Small

Biomass - Large

Biomass - Small

S% Large Small Large Small Large Small1.0% 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 Fuel Gas Fuel Biomass

FUEL TYPE / ABATEMENT EFFICIENCY REQUIREMENT

Ash% Large Small Large Small Large Small Large Small10% 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%

Liquid Fuel Gas Fuel BiomassSolid Fuel

80%

82%

84%

86%

88%

90%

92%

94%

96%

98%

100%

10% 20% 30% 40%

Aba

tem

ent E

ffic

ienc

y N

eede

d

Ash % in fuel

Solid - Large

Solid - Small

Liquid - Large

Liquid - Small

Gas - Large

Gas - Small

Biomass - Large

Biomass - Small

DC2

Slide 11

DC2 recopy graphDuncan Crous; 2014-07-21

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

§ What’s the catch? …….. What doesn’t go to the dump…..

Ash% Solid Liquid Gas Biomass10% 11% 8% 12% 11%20% 5% 4% 6% 5%30% 4% 3% 4% 4%40% 3% 2% 3% 3%

Fly ash disposal reductionS% Solid Liquid Gas Biomass

1% 100% 0% 43% 43%2% 100% 0% 25% 25%2% 82% 0% 18% 18%3% 64% 0% 14% 14%

Scrubber sludge disposal reduction

EMISSIONS LIMITS VS AMBIENT CONCENTRATION LIMITS

§ Emission limits are at the stack tip§ Ambient concentrations is in the breathable air, ground level

§ CumulativeGN893 and GN831

Ambient air quality limits

PM10, PM2.5, SO2, NOx, CO

AIR QUALITY IMPACTS OF SMALL VS LARGE BOILERS

§ Goes out the stack (50MWt, 15m stack, SO2, Ambient Air Quality Screening model output)

0

50

100

150

200

250

300

350

400

450

0 200 400 600 800 1000 1200 1400 1600 1800 2000

Gro

und

leve

l am

bien

t SO

2 co

ncen

trat

ion

(µg/

m3 )

Distance

Solid - Large

Solid - Small

Gas - Large

Gas - Small

Biomass - Large

Biomass - Small

DC3

Slide 14

DC3 show limit, add background emissionsDuncan Crous; 2014-07-21

AIR QUALITY IMPACTS OF SMALL VS LARGE BOILERS

§ Goes out the stack (50MWt, 15m stack, SO2, Ambient Air Quality Screening model output)

0

2

4

6

8

10

12

14

16

18

20

0 200 400 600 800 1000 1200 1400 1600 1800 2000

Gro

und

leve

l am

bien

t PM

con

cent

rati

on (

µg/m

3 )

Distance

Solid - Large

Solid - Small

Liquid - Large

Liquid - Small

Gas - Large

Gas - Small

Biomass - Large

Biomass - Small

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)

AIR QUALITY IMPACTS – BACKGROUND EFFECTS

0

100

200

300

400

500

600

0 200 400 600 800 1000 1200 1400 1600 1800 2000

Gro

und

leve

l am

bien

t SO

2 co

ncen

trat

ion

(µg/

m3 )

Distance

Solid - Large+

Solid - Small+

Solid - Large

Solid - Small

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