SCHEDULE
21

OPERATING A LARGE COMBUSTION PLANT
PART
1

Scope and interpretation

Scope and interpretation: operating a large combustion plant
1
1
This schedule applies to operating a large combustion plant.
2
“
Large combustion plant
” means a combustion plant where the total rated thermal input of which is equal to or greater than 50 MW, irrespective of the type of fuel used, but does not include—
a
plants in which the products of combustion are used for the direct heating, drying, or any other treatment of objects or materials,
b
post-combustion plants designed to purify the waste gases by combustion which are not operated as independent combustion plants,
c
facilities for the regeneration of catalytic cracking catalysts,
d
facilities for the conversion of hydrogen sulphide into sulphur,
e
reactors used in the chemical industry,
f
coke battery furnaces,
g
cowpers,
h
any technical apparatus used in the propulsion of a vehicle, ship or aircraft,
i
gas turbines and gas engines used on offshore platforms,
j
plants which use any solid or liquid waste as a fuel other than waste that is biomass.

Interpretation: general
2
In this schedule—
- “
CCGT
” means combined cycle gas turbines,
- “
determinative fuel
” means the fuel which, amongst all fuels used in a multi-fuel firing combustion plant using the distillation and conversion residues from the refining of crude oil for own consumption alone or with other fuels, has the highest emission limit value as set out in Part 3 of this schedule, or, in the case of several fuels having the same emission limit value, the fuel having the highest thermal input amongst those fuels,
- “
diesel engine
” means an internal combustion engine which operates according to the diesel cycle and uses compression ignition to burn fuel,
- “
gas engine
” means an internal combustion engine which operates according to the Otto cycle and uses spark ignition or, in the case of dual fuel engines, compression ignition to burn fuel,
- “
gas turbine
” means any rotating machine which converts thermal energy into mechanical work, consisting mainly of a compressor, a thermal device in which fuel is oxidised in order to heat the working fluid, and a turbine,
- “
indigenous solid fuel
” means a naturally occurring solid fuel fired in a combustion plant specifically designed for that fuel and extracted locally,
- “
multi-fuel firing combustion plant
” means any combustion plant which may be fired simultaneously or alternately by two or more types of fuel,
- “
operating hours
” means the time, expressed in hours, during which a combustion plant, in whole or in part, is operating and discharging emissions into the air, excluding start-up and shut-down periods,
- “
rate of desulphurisation
” means the ratio over a given period of time of the quantity of sulphur which is not emitted into air by a combustion plant to the quantity of sulphur contained in the solid fuel which is introduced into the combustion plant facilities and which is used in the plant over the same period of time,
- “
stack
” means a structure containing one or more flues providing a passage for waste gases in order to discharge them into the air.

Aggregation rules
3
1
Where the waste gases of two or more separate combustion plants are discharged through a common stack—
a
the combination formed by such plants is to be considered a single combustion plant, and
b
their capacities added together for the purpose of calculating the total rated thermal input.
2
Where two or more separate combustion plants—
a
have been granted a permit for the first time on or after 1 July 1987 or in relation to which a complete application for a permit has been submitted on or after that date, and
b
are installed in such a way that taking technical and economic factors into account, their waste gases could, in the judgement of SEPA, be discharged through a common stack—
i
the combination formed by such plants is to be considered as a single combustion plant, and
ii
their capacities added for the purpose of calculating the total rated thermal input.
3
For the purpose of calculating the total rated thermal input of a combination of combustion plants referred to in sub-paragraphs (1) and (2), individual combustion plants with a rated thermal input below 15 MW are not to be considered.
Sch. 21 inserted (1.11.2025) by The Environmental Authorisations (Scotland) Amendment Regulations 2025 (S.S.I. 2025/165), reg. 1(2), sch. 12 (with sch. 23)