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Treatment of Small CHP Plant
and Short-term Use Diesel
Generators in the IAQM
Planning Guidance
Dr Ben Marner
Overview
• Small CHP can have significant impacts
Significant sources are being screened out in the
current guidance
• Diesel generators which aren’t used for long can
have significant impacts
But they are often ignored in assessments
Made using recycled slides
Micro CHP Case Study
2 x 5.5 kWe (20kW fuel input) CHP
25.5 m tall building
27 m high flue
Modelled using ADMS
CHPs add 0.7 µg/m3 annual NO2
‘Moderate’ Impact
Background NO2 is >40 µg/m3
Solution for CHP?
• Suggested “precautionary” criterion of 15kWe
• Alternatively tighten up ‘dispersion criterion’
But it would be very difficult to make this sufficiently
definitive
Short-term Use Diesel Generators
• Short-Term Operating Reserve
• Mobile Plant
e.g. construction sites
Temporary but used intensively
• Backup reserve / life safety
power cuts / fires
Regular routine tests – often 20
mins 1h each month
Generator Case Study
• Bank of 20 x 3MVA backup generators
12 hrs of testing per year (grew to 24 hrs)
IF testing coincided with worst-case met:
PC to 99.79th percentile of 1-h NOx = 4,086 mg/m3
PC to annual mean NOx = 13 mg/m3
Assessed the probability of significant impacts
Could not discount potential for significant impacts
Solution for Generators?
• Suggested Addition to Paragraph 6.20 J
“Description of construction phase impacts. These impacts will relate
primarily to dust emissions, which give rise to dust soiling and elevated
PM10 concentrations, although construction vehicles and plant and
vehicles may need assessment; particularly if diesel power
generators are to be used.”
• Suggested New Paragraph for Section 6
“When considering standby generators that are present
only in case of power failures or emergencies,
consideration should be given to any routine testing
procedures. Even operation for a few hours per year
can give rise to impacts that should be assessed”
Summary
• Please can we have more stringent criteria for
CHP?
• Please can we encourage robust assessments of
diesel generators?