Commercial Kitchen exhaust effluent and treatment options Part 2

COMMERCIAL KITCHEN EXHAUST EFFLUENT & TREATMENT OPTIONS PART 2

Enjoying dinner at a restaurant with friends and family may seem like a very normal experience but behind delivering the meal to your table is the generation of airborne effluents resulting from the cooking process. This effluent is discharged to the exterior contributing to environmental pollution with detrimental effect on human health. This article examines the size of the New Zealand hospitality industry, the various cooking processes, the composition of airborne effluent and available control technologies.

Management of Airborne Effluents

The cooking process generates airborne particles of various sizes and composition which have been demonstrated to be detrimental to the environment and to human health. AS1668-2-2012 sets out the requirements in dealing with cooking effluents. Section 3.3.1 categorises cooking effluents as type B which are required to be removed by local exhaust (5) using a hood or similar means. The most common approach in dealing with this has been the installation of an extract system comprising of a metal hood fitted with filters installed above the cooking appliance, ducting and an extract fan discharging to the atmosphere. Although this represents the most basic and commonly applied solution, it has limitations in dealing with smaller particles and odours.

Hoods

Under AS1668.2-2012, hoods are required to be manufactured of materials deemed noncombustible in accordance with AS1530.1, such as steel or stainless steel sufficiently rigid and with smooth surfaces. Hoods are classified in seven types as shown in Table 8.

Section 3.5 of the standard provides a prescriptive method -excluding hoods type 5 and 7- to determine airflows for different types of cooking processes and hood types. Where several cooking appliances are being used, the equation relevant to the worst case is to be used for calculating airflows. In any case the airflow shall not be less than 250 l/s/ m2. Hoods type 5 and 7 are designed for lower airflows and consequently lower energy consumption, therefore, requiring more empirical calculations. Airflows for proprietary hoods type 7 designed to standards such as German VDI 2050 or DIN 18869 are acceptable.

Filtration

Baffle and the mesh type are commonly used as primary filters.

The commonly known grease filter comprises of an interwoven mesh held within a metal frame or arranged in a honeycomb pattern. Particulate matter is captured within the mesh. Common materials are aluminium and stainless steel. Baffle filters comprise of plates folded in U shape and interlocked in such a way as to impart a change of direction to the airflow. As a result of this, the larger particles impact on its walls and slide down and drain away. Baffle and mesh type filters have little effect on capturing grease vapour, gas or odours. The efficiency of these two types of grease filters is low for fine particulates. They are limited to capturing 18% to 20% of particles going through it (6). Both types rely on impact for particulate collection (44). However, these types of filters are relatively cheap and easier to clean. Comparatively, baffle type filters exhibit higher pressure drop than mesh type (19) (45).

Read the full article in the Industry Journal, September 2022 issue