Scottish Environment Protection Agency
Comments on the Application under Section 36 of the Electricity Act 1989:
Environmental Upgrades at the Longannet Generating Station, Fife and Revisions to
the Ash Disposal Strategy at Valleyfield and Longannet Ash Lagoons, Fife
Introduction
1.
This note provides comments on the application by Scottish under Section 36 of the
Electricity Act 1989 for environmental upgrades at the Longannet Generating Station,
Fife and revisions to the ash disposal strategy at Valleyfield and Longannet Ash
Lagoons, Fife (“the Application”).
Need for SCR Retrofit
2.
SEPA confirms that the use of Selective Catalytic Reduction (SCR) will be required on
Units 1, 2 and 3 at Longannet to allow their continued, routine operation from 1 January
2016 onwards. The use of SCR from that date, in conjunction with existing techniques
to reduce both oxides of nitrogen, oxides of sulphur and particulate matter, will meet
the minimum emission standards for existing plant required under Directive 2001/80/
EC (“the Large Combustion Plant Directive”).
3.
SCR technology is a well proven pollution control technique that has been used
commercially in Japan since 1980 and in Germany since 1986 on power stations
burning mainly low-sulphur coal and, in some cases, medium-sulphur coal. The
International Energy Agency estimates there are now about 15 GW(e) of coal-fired
power stations using SCR in Japan and nearly 30 GW(e) in Germany, out of a total of
about 53 GW(e) worldwide. During the 1990’s, SCR demonstration and full-scale
systems have been installed in US coal-fired power plants burning high-sulphur coal.
Implications of the Proposed Industrial Emissions Directive
4.
The Longannet Power Station is primarily subject to controls under the Pollution
Prevention and Control (Scotland) Regulations 2000 (as amended). These regulations
have been used in Scotland to implement the EC Directives on Integrated Pollution
Prevention and Control and the Large Combustion Plant. However, the Commission
has proposed that these Directives along with several others be consolidated into a
single Industrial Emissions Directive (IED). This Directive has not been finalised but the
published proposals include new minimum emission limit values for large combustion
plant which, in the case of emissions of sulphur dioxide, are more stringent than the
existing Large Combustion Plant Directive. The proposed emission limit values for
oxides of nitrogen currently remain unaltered and continue to require the use of SCR.
One potential impact of the IED is that much lower emission limits for sulphur dioxide
have been proposed (200 mg/m3 compared to 400 mg/m3 under the Large
Combustion Plant Directive) Scottish Power will no doubt wish to consider the
implications of this proposed Directive within the scope of the Longevity Project.
Design of the SCR System
5.
In SCR systems, ammonia is used as the reducing agent and is injected into the flue
gas stream, passing over a catalyst. Reductions in emissions of oxides of nitrogen of
around 80-90% are achieved. The optimum temperature is usually between 300°C and
400°C and SEPA notes that the Application indicates that the economisers are to be
modified to ensure adequate temperatures are achieved in the SCR reactor. The SCR
system will be a so called “high dust” design, the most widely used configuration, with
an SCR reactor positioned before the electrostatic precipitators. This is considered to
be consistent with the requirement to use the Best Available Techniques (BAT) under
the PPC Regulations.
6.
A “high dust” design will incur a small drop in station efficiency (estimated to be around
0.2%) with a consequential small increase in the emissions of carbon dioxide per unit
of electricity generated. The Application recognises that a feature of high dust designs
is that ash can accumulate on the surface of the catalyst and reduce the performance
of the catalyst. SEPA notes that Scottish Power plan to fit soot blowers or acoustic
horns to reduce this effect. Alternative SCR designs such as “cold side” or “tail end”
SCR do not suffer dust accumulation to the same extent but do incur a larger drop in
station efficiency; as much 5% with a cold side design.
7.
Although SCR is a well proven pollution control technique it can introduce several
complicating factors to the operation of a coal fired power station. The first is that the
reaction between ammonia and oxides of nitrogen in the SCR reactor does not proceed
to total completion, and a small amount of ammonia can passes through the catalyst.
Some of this residual ammonia will be oxidised to nitrogen on the catalyst bed, but
some may pass through the catalyst untouched. This is known as ammonia slip. As
well as being an air pollutant in its own right, the presence of ammonia in the flue
gases can affect ash quality which can impact on disposal or re-use of the ash. SEPA
understands that a well designed, well operated system will result in less than 2 ppm of
ammonia in the flue gas and that, based on experience in both the US and Europe, this
is unlikely to adversely affect ash quality (Reference: Buecker, B., “SCR: Design and
Operation”, 2002) or the environmental impact of the process. Scottish Power have
recognised the importance of this issue within the Application and SEPA would wish to
place controls within the environmental licence, known as a PPC permit, for the
Longannet Power Station to ensure this limit is met.
8.
SEPA notes that the EIA Scoping Report indicates that the ammonia used in the SCR
reactor is to be handled in aqueous form. This together with the proposed volumes to
be stored should ensure that the installation does not fall within the scope of the
Control of Major Accident Hazard Regulations 1999 (as amended). SEPA will wish to
ensure that the proposed methods for handling aqueous ammonia in the SCR system
are consistent with the use of the Best available Techniques, particularly in terms of
controlling odorous emissions. This will be done as and when Scottish Power come
forward with an application to vary the environmental licence for the station to include
SCR.
Impact on Local Air Quality
9.
SEPA agrees with the conclusions within the Application that the use of the SCR
system will not adversely affect air quality. Indeed some small benefit in terms of
ambient levels should be seen. SEPA has previously carried out dispersion modelling
of the current emissions from Longannet (with FGD in place and current measures in
place to control oxides of nitrogen) and concluded that there was unlikely to be an
adverse impact on local air quality.
10.
The modelling forming part of the application has used a recognised Gaussian model
(AERMOD) and suitable long term data. Under the terms of both the current PPC
permit for Longannet Power Station and the previous environmental licence Scottish
Power has been required to carry out environmental monitoring at Blair Mains Farm
(for sulphur dioxide) and annual assessment of emissions. The latter has involved
modelling of emissions and these studies have meteorological data from Blair Mains
and Gogar Bank. It is not clear why this meteorological data has not been used in this
study as it is arguably more representative.
11.
Notwithstanding the comments in the previous paragraph the well established
monitoring programme for Blair has consistently showed that the Gaussian dispersion
models are conservative and that measured data is consistently lower than predicted
levels.
12.
It is not clear from the study what value of surface roughness in the model has been
used. This is a key part of air dispersion models as the predicted levels are sensitive to
this parameter.
Impact of Emissions on Nearby Habitats
13.
SEPA agrees with the conclusions of the modelling carried out in assessing the impact
of emissions into the air on nearby habitats. SEPA has previously reached similar
conclusions in determining Scottish Power’s application for a PPC Permit in 2006 and
2007. That work compared the maximum ground level concentrations predicted by the
dispersion modelling against the air quality limit values for the protection of vegetation
and indicated that the contribution to the limit value was insignificant. The predicted
location of the maximum ground level concentrations was very close to the Firth of
Forth SPA and SSSI. This site is a complex of estuarine and coastal habitats
stretching east from Alloa to the coasts of Fife and East Lothian. The site includes
extensive invertebrate rich intertidal flats and rocky shores, areas of saltmarsh, lagoons
and sand dune. The mudflats form important feeding grounds for the abundant waders
and wildfowl in the Firth of Forth.
14.
In addition, an impact assessment of predicted emissions from major coal and oil fired
power stations on conservation sites has been carried out by the Joint Environmental
Programme (JEP)
15.
The results indicated:

that the Lielowan Meadow is the designated site most affected by Longannet
Power Station with contributions of 26.7 % of the limit value for sulphur dioxide
and 5.2 % of the limit value for oxides of nitrogen.

the limit value for vegetation for sulphur dioxide is not exceeded at designated
sites.

There are no local SSSIs where the critical level for sulphur dioxide or oxides
of nitrogen is exceeded.
Impact of Emissions into the Air on Nitrogen Deposition and Critical Loads
16.
Critical loads are quantitative estimates of exposure to one or more pollutants that
would cause harmful effects on sensitive elements in the environment. National critical
loads have been mapped for a range of UK Biodiversity Action Plan Broad Habitats to
assess the large scale impact of acid and nutrient nitrogen deposition across Europe.
17.
The methodology used in the Application for assessing critical loads and deposition is
similar to an Appropriate Assessment carried out by SEPA in 2007 as part of the
determination of Scottish Power’s application for a PPC Permit. That Assessment
concluded:
a) The emissions from Longannet Power Station would not have an adverse
effect on the integrity of any the SACs or SPA assessed in the Appropriate
Assessment.
b) The sites assessed in the Appropriate Assessment were selected as worstcase representative sites and emissions from the Longannet Power Station
would not have an adverse effect on the integrity of any other SAC or SPA
within the UK.
c) The emissions from Longannet Power Station would not have an adverse
effect on the integrity of the Firth of Forth SPA.
d) The emissions from Longannet Power Station would not be likely to damage
any natural feature of any of the SSSIs in the vicinity of Longannet.
18.
The Appropriate Assessment referred to above is included at Annex A and supports
the conclusions within the Application concerning the fact that SCR will be beneficial in
terms of nitrogen deposition and critical loads.
Continued Use of Coal
19.
Following the Energy Review in 2006, the Government published “Meeting the
Challenge: A White Paper on Energy”, Cm 7124 (“The Energy white Paper”), in 2007.
This noted that coal had an important role to play the UK’s energy mix and that making
the best use of UK energy resources, including coal reserves, where it is economically
viable and environmentally acceptable to do so and contributes to the goal of secure
energy supplies.
Alternatives to SCR
20.
Whilst fully recognising the part coal has to play in providing energy, practicalities and
the significant additional costs to Scottish Power of the alternatives to fitting SCR at
Longannet: i.e. retrofitting supercritical steam boilers or providing a gas fired combined
cycle plant. These alternatives appear to have been dismissed very quickly. Both would
result in a significant reduction in the amount of carbon dioxide emitted per unit of
electricity generated.
21.
The Longannet Power station after the fitment of SCR would be around 35% efficient.
Supercritical boilers would result in a generation efficiency of around 45% and a gas
fired combined cycle plant could achieve around 58% efficiency. The latter would
potentially cut specific emissions of carbon dioxide by around half.
Heat Plan
22.
The consideration of using waste energy from Longannet for beneficial use (heat plan)
does not appear to be fully developed. The difficulty in developing a heat distribution
system and using surplus heat is fully recognised. However, options to use waste heat
could be better developed. SEPA, in its Thermal Treatment of Waste Guidelines 2009
requires applicants for PPC permits to submit a “Heat Plan” – a systematic assessment
of where low grade heat could be used. SEPA would be pleased to submit an exemplar
of such a Heat Plan. The requirement for the development of a Heat Plan could be a
condition of any Section 36 consent granted by the Scottish government.
Controls over Noise During Construction
23.
The proposed limitations over noise during construction of the SCR system should help
limit noise nuisance from the construction area and are welcomed.
R Ebbins
15 June 2009
Annex A: Appropriate Assessment Made During Determination of the PPC Permit for
Longannet