Guidance on the Control of Odour and Noise from ... - Defra

Baffle filters
These filters comprise a number of interlocked vanes which when assembled, form a
two-pass grease removal device. Grease laden air passes through the filter and by a
series of forced changes in direction and velocity, the grease becomes separated
from the air stream and is deposited on the vertical vanes. The deposited grease is
then drained off through weep holes spaced at intervals and into a collection drawer
that has to be cleaned at regular intervals. The size of the grease drawer should be
sufficient to suit the type of cooking and frequency of cleaning. The grease drawer
must be isolated from the air stream otherwise re-entrainment can occur.
The resistance to air flow in a baffle filter is higher than with mesh filters, but pressure
drop remains constant and blades provide a barrier in the event of a flash fire. A
baffle filter should be installed at an angle of not less than 45 o from the horizontal.
Cartridge filters
Installed horizontally, cartridge filters comprise a high velocity slot opening on to a
series of baffles which cause air to change direction four times compared to only
twice in a conventional baffle filter. The cartridge filters are installed over the full
length of the extract plenum and should be sloped to allow trapped grease to fall
through a drain to a grease drawer. These filters are intended for heavy grease
loads. Having a higher velocity enables lower air volumes to be used. Air balancing
is required to prevent carry over of grease.
Water wash systems
These systems comprise an extract plenum similar to the cartridge filters, except that
there is an inbuilt self-cleaning system. This provides routine maintenance as well as
fire protection to the plenum and duct. A water wash canopy is operated by a control
panel. In its simplest form it is started and stopped at the beginning and end of the
cooking process each day. Automatic systems are available. Cleaning is achieved
by spraying the interior of the canopy extraction system chamber with pressurised
hot water containing detergent. The waste water flows from the system to drain.
Continuous cold water mist systems
These systems are similar to water wash system in which grease extraction is
enhanced by means of a cold water spray that runs continuously during cooking
operation. The vapour entering the canopy passes through the mist, which causes
the grease particles in the suspension to drop in temperature, solidify, increase in
size, and drop via a drain trough to a drain. These systems are particularly suitable
for solid fuel appliances where the mist will extinguish hot embers that may be drawn
into the canopy. The cleaning regime is the same as for a water wash system.
4.7.2 Fine filtration
A basic filtration system can be used to deal with a low intensity odour problem, but
more usually will form a protective pre-treatment step before an activated carbon
step.
A typical filtration system may be supplied with a three stages of progressively more
efficient filtration. This would include:
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