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COMEAP statement: Drax power station: loss
of flue gas desulphurisation (FGD) capacity
May 1998 |
- At the request of the Environment Agency the Committee on the Medical
Effects of Air Pollutants (COMEAP) considered, on 29 May, the effects
of the loss of desulphurisation capacity at Drax power station on the
concentrations of sulphur dioxide likely to occur both locally and further
afield. COMEAP was provided with a statement on the background to the
problem by Mr R Barker, Environment Agency.
- It was noted that cracks in the vanes of the fans which drive the
air flow through the desulphurisation plant had been discovered and
the use of the plant had been discontinued in early 1998. Partial restoration
of desulphurisation has since taken place and regular inspection of
the vanes is underway. National Power, the operators of Drax, have applied
to the Environment Agency, for permission to raise emissions of sulphur
dioxide from Drax from 100,000 to 270,000 tons per year. This leeway
may not be needed if desulphurisation is restored or able to be maintained
at a reduced level.
- In determining the effects of increasing the permitted level of emissions
of sulphur dioxide the Environment Agency commissioned two modelling
exercises to look at likely effects on local (near field) and more distant
(far field) concentrations of sulphur dioxide. Modelling was undertaken
by National Environment Technology Centre and Building Research Establishment.
- In the course of the modelling studies a series of scenarios had been
defined. Of these some were included for the purposes of illustration
only. The discussion focused on a number of possible scenarios. These
included:
- Scenario A: 1997 annual emissions with partial FGD
- Scenario B: 1997 annual emissions, no FGD.
The other scenarios that were examined were not considered acceptable.
- Attention was also given to the estimates of the number of times per
year that people were likely to be exposed to 15 minute average sulphur
dioxide concentrations characterised by the bands defined in the DETR
Air Pollutants Banding System.
- It was noted that under the conditions defined for scenario A, the
99th%ile of near field 15 minute average concentrations did not exceed
130 ppb and that there were only low numbers of exceedances of 15 minute
average concentrations of 200 ppb. With regard to far field conditions
it was noted that scenario A led to lower levels of pollutants than
other scenarios that had been studied.
- Members concluded that loss or even partial loss of FGD was undesirable
and a cause for concern. However, of the scenarios that have been modelled,
scenario A is the least unacceptable followed by scenario B. It was
agreed that operation of Drax under the conditions specified in the
modelling of these scenarios was not likely to be associated with marked
risks to health.
- That loss or partial loss of FGD would be likely to have some implications
for public health was agreed though the Committee were unable to specify
these precisely.
- The need to do everything possible to minimise sulphur dioxide emissions,
for example by burning low sulphur coal at both Drax and other power
stations called upon to pick up extra load was stressed.
- It was recommended that detailed monitoring of the sulphur dioxide
concentrations in areas likely to be affected by increased emissions
from Drax and other power stations should be undertaken.
- Members asked to be kept informed of progress and to be updated regarding
sulphur dioxide measurements until this problem is resolved.
- Members agreed that relevant information should be provided to Directors
of Public Health and, where necessary, to local people by the Environment
Agency.
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