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Pamphlet on Control of Oil Fume and Cooking Odour from Restaurants and Food Business

CONTROL OF OILY FUME AND COOKING ODOUR FROM RESTAURANTS
AND FOOD BUSINESS

Table of Contents

Introduction
Standards of Control
Positioning of Exhaust Outlets
Oily Fume and Cooking Odour Control
Operation and Maintenance of Control Equipment
Enquiries

ANNEX A

ANNEX B

Introduction

Oily fume and cooking odour emissions from cooking processes are one of the air pollutants which come under the control of the Air Pollution Control Ordinance. It is necessary for owners and operators of restaurants and food business to take appropriate measures to minimize these emissions and prevent causing any objectionable odour noticeable at any sensitive receptor in the vicinity or creating other forms of pollution.

This note provides guidance to help the owners and operators of restaurants and food business to understand and apply the best practical control measures in preventing these emissions from causing air pollution problems.

Photo of A typical air pollution problem associated with cooking fumes emissions

 

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A typical air pollution problem associated with cooking fumes emissions

Standards of Control

As a general guideline, all emissions to air from a restaurant should not give rise to an air pollution problem, including odour nuisance, and should be free from visible fume.

For some difficult locations having very close proximity to the sensitive receptors, it is possible that the air pollution problem would still exist even after the application of advanced control technologies. To avoid getting into these unnecessary troubles, the owners and operators of the restaurants and food business should refrain from choosing these sites for their business.

Positioning of Exhaust Outlets

Suitable siting or positioning of the outlet of the exhaust system is of paramount importance to avoid causing, or contributing to, an air pollution to the public. In deciding the location of the exhaust outlets, the following should be considered :

(a)

locate the outlets at such a place where the ventilation is good and the emissions from them can be adequately dispersed without hindrance;

     

(b)

provide sufficient separate distance from any sensitive receptor in the vicinity so that the emissions will not cause, or contribute to, an odour nuisance or other type of air pollution to the public;

   

(c)

ensure the emission from the exhaust system will be directed vertically upwards, unless it can be demonstrated by an environmental professional that other direction is more advantageous in preventing the emission from causing air pollution problems.

   

(d)

ensure the emission from the exhaust system will not be restricted or deflected by, for example, the use of plates or caps.

It is preferable to extend the exhaust to a level of at least 3 metres above the highest point of the restaurant's own building and of any adjacent or attached buildings that fall within a 20-metre radius. If this is not practicable, advice should be sought from the environmental professionals to confirm if the alternative location is also suitable before finalizing the decision.

Photo of An example of good practice, extending kitchen exhausts to rooftop

 

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An example of good practice, extending kitchen exhausts to rooftop

Oily Fume and Cooking Odour Control

The complete exhaust system serving the cooking stoves or other cooking appliances, including the air pollution control equipment, should be designed, commissioned and maintained by competent professionals, and be operated by competent staff. The design of air pollution control equipment should be based on peak load conditions, i.e. the worst case scenario. For easy reference, a brief description of the available techniques for the control of emission of oily fume and cooking odour is given in Annex A.

For those exhaust systems serving stoves for frying, charbroiling, roasting and similar operations that will give out excessive oily fume emissions, they should be equipped with high efficiency air pollution control equipment to remove oily fume from the waste gases before discharging into open atmosphere.

If the exhaust contains a strong odour or the exhaust outlet is in close proximity to any sensitive receptor in the vicinity such that an air pollution exists or is imminent, high efficiency odour control equipment will also be required.

To ease the loading of the control equipment, it is advisable to provide a separate exhaust system for those cooking operations giving rise to oily fume and strong odour emissions and treat the emissions with a separate control equipment.

Photo of Oily fume treatment system on the roof

 

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Oily fume treatment system on the roof

Operation and Maintenance of Control Equipment

It is important that the exhaust system, including the air pollution control equipment, is properly operated and maintained. The following practices should be fully adopted:

(a)

Operation and servicing of the exhaust system and the air pollution control equipment should only be carried out by competent staff with sufficient training and relevant skill and in accordance with the manufacturers' recommendations.

     

(b)

Maintenance and repair of the system should be carried out by competent professionals.

Consideration should be given in the design to ensure continuous operation of the air pollution control equipment. Safe access shall be provided for the inspection and maintenance of the air pollution control equipment. Inspection window in the form of transparent panel shall be provided for equipment such as air washer, Venturi & packed water scrubber and activated carbon filter unit. Standby or spare units should be provided if the situation warrants. It is also recommended to interlock the air pollution control equipment with the associated exhaust system in such a manner that the exhaust system will be inoperative unless the control equipment is in operation and functioning properly.

To ensure its proper performance, the air pollution control equipment should be regularly monitored. Components should be inspected, cleaned and serviced regularly. The recommended cleaning and servicing frequencies are:

(a)

Electrostatic precipitators:

     
 

(i)

If no auto-cleaning system is installed, they should be cleaned thoroughly at least once a week. Moreover, it is recommended to inspect emission at least twice a day. Whenever a sign of deterioration in performance is noted, they should be cleaned immediately.

     
 

(ii)

If an auto-cleaning system is installed, inspection of the emission should be made at least once a day. Whenever a sign of deterioration in performance is noted, the auto-clean procedures should be started manually immediately.

     

(b)

Hydrovents, air washers and scrubbers:

     
 

They should be cleaned and serviced immediately as soon as there is any sign of deterioration in fume control and in any case, not less than once a month. Besides, pumps, detergent dosage rate, spraying condition, etc, should be checked regularly to ensure the control equipment is in good operating conditions at all time.

     

(c)

Duct works:

     
 

They should be cleaned and serviced at least once every 6 months.

Image of Collector plate is one of the essential component which must be cleaned regularly to ensure the performance of the Electrostatic Precipitators

 

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Collector plate is one of the essential component which must be cleaned regularly to ensure the performance of the Electrostatic Precipitators

Regular visual inspection on the exhaust outlets and scent for likely odour nuisance during peak hours should also be conducted to ensure an early discovery of any operational problem with the equipment. In general, a frequency of twice a day or more at busy hours is recommended.

Photo of The control panel of an air washer comprises several essential components such as dosage pumps, detergent filter and pressure gauges which require close monitoring and serving to ensure proper operation

 

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The control panel of an air washer comprises several essential components such as dosage pumps, detergent filter and pressure gauges which require close monitoring and serving to ensure proper operation

Remedial measures should be taken immediately if objectionable odour, visible oily fume and/or droplets are noticed. This could be done by checking the operating conditions and performance of the air pollution control equipment and the condition of the exhaust system. Any defective parts, choked filters, saturated scrubbing liquid, etc. should be replaced as soon as possible. To facilitate immediate replacement, there should be sufficient stock of such materials kept in the restaurant.

It is also desirable for the restaurant owners and operators to keep a copy of the operation and maintenance manual and the maintenance and repair log book of the air pollution control equipment at the restaurant.

Enquiries

Enquiries can be addressed to the Regional Offices of the Environmental Protection Department. They will be glad to answer any enquiries concerning the control of oily fume and cooking odour from restaurants and food business.

ANNEX A

Available Techniques for the Control of Oily Fume and Odour Emissions

Grease Filters

Metallic grease filters, which are commonly found in the market, can screen out large droplets and are therefore suitable for preliminary treatment of oily fume. Grease filters that are made of densely packed synthetic fibres, would be more effective than metallic filters. However, they need to be used together with a hydrovent (which serves as a fire break as well as cooling and condensing the oily fume) to give a reasonable preliminary treatment in oily fume control.

Photo of Typical metallic grease filters

 

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Typical metallic grease filters

Water Spray Hoods (Hydrovents) and Air Washers

Hydrovents and air washers have a better performance in oily fume control than grease filters but neither one of them alone can effectively reduce oily fume to an acceptable level. It is now a common design to couple these two kinds of equipment together and such system can give a reasonable performance in oily fume control.

In the design of a hydrovent and air washer system, due considerations should be given to the following:

(a)

avoidance of channelling;

(b)

sufficient residence time;

(c)

adequate air-to-water-ratio;

(d)

choices of scrubbing liquid; and

(e)

easy maintenance and cleaning.

Air washers should be filled with specially designed baffles to enhance their performance.

Photo of Typical water spray hood and air washer

 

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Typical water spray hood and air washer

Electrostatic Precipitators (ESPs)

If properly designed and maintained, ESPs can achieve a high collection efficiency for oily fume. Since oily fume is sticky and easily coated on the collector plates and render the equipment inoperative, ESPs should be cleaned/serviced regularly and properly. A weekly servicing should be the minimum and they should be cleaned immediately as soon as there is any sign of deterioration in fume control. Some manufacturers have incorporated automatic self-cleaning mechanism into their equipment to facilitate automatic daily cleaning.

Photo of Example of ESP installation for one of the fast food shop

 

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Example of ESP installation for one of the fast food shop

Venturi and Packed Tower Scrubbers

Venturi scrubbers are sometimes employed to control oily fume. Exhaust gas stream is forced through the venturi throat where they are intercepted by an atomized scrubbing liquid stream. Removal efficiency depends on the pressure drop across the venturi throat and particle size. Noise may be a problem since air velocity at the throat is high.

Packed tower scrubbers remove oily fume by absorption as stream of scrubbing liquid is sprayed on the oily fume laden gas stream. The scrubber is filled with specially designed packing materials to increase the contact surface area between the scrubbing liquid and the waste gas stream to enhance the absorption efficiency. Packed tower scrubbers generally occupy more space for installation.

For both venturi scrubbers and packed tower scrubbers, water is the common scrubbing liquid. These kinds of scrubbers can be effective for odour control too if a suitable scrubbing liquid is used. The venturi scrubber, however, are notorious emitters of high-frequency noise and special consideration should be taken to aviod causing noise pollution problem if this equipment is selected.

Photo of Example of venturi scrubber with odour control

 

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Example of venturi scrubber with odour control

Activated Carbon Filter

Activated carbon particles, which are highly porous and have very large surface to volume ratios, remove odour by adsorption in which the odorous compounds, when penetrate into the pores, are retained on the inner-surfaces of the granular solid.

Although activated carbon filters are effective in odour removal, their performance could be adversely affected under the following conditions:

(a)

High moisture content will flood the adsorption sites, thereby reducing performance and media life.

(b)

High temperature will increase the gas movement and therefore, reduce the adsorption capability.

(c)

Any oily particles present in the exhaust gas stream will plug the adsorption sites, thereby reducing performance and media life and increasing services costs.

It should therefore be noted that the sole use of activated carbon is not suitable for controlling odour emission from cooking processes because of the nature of the emission.

Common factors which should be considered in the design of activated carbon filter system or other adsorption equipment include:

(a)

Contact time between adsorbent and adsorbate;

(b)

Total adsorptive capacity of the adsorbent;

(c)

Uniform distribution of airflow over the surface of the adsorbent;

(d)

Resistance to airflow;

(e)

Quantity of exhaust gas handled per unit time; and

(f)

Amount of oily particles to be adsorbed.

Adsorbers are mostly of a stationary packed bed arrangement. They are usually packed with appropriate depth adsorbent and installed in units of two or more modules in parallel to permit continuous operation. Preliminary treatment facility should be installed before activated carbon filters to remove oily fume and water from the exhaust gases, and, if necessary, to lower the exhaust gas temperature to the operational range. Particular attention should also be paid to the requirement of regular replenishment and to prevent carbon dust from blowing out.

ANNEX B

Regional Offices

Districts / Address

Telephone No. / Fascimile No.

EPD Territorial Control Office

28/F Southorn Centre, 130 Hennessy Centre, Wanchai, Hong Kong.

Tel. 2835 1018

Fax. 2838 2155

Regional Office (East)

(Kwun Tong, Wong Tai Sin, Sai Kung, Yau Tsim Mong & Kowloon City )

5/F Nan Fung Commercial Centre, 19 Lam Lok Street , Kowloon Bay, Kowloon.

Tel. 2755 5518

Fax. 2756 8588

Regional Office (South)

( Hong Kong Island & Islands )

2/F Chinachem Exchange Square, 1 Hoi Wan Street, Quarry Bay , Hong Kong.

Tel. 2516 1718

Fax. 2960 1760

Regional Office (West)

(Tuen Mun, Tsuen Wan, Kwai Tsing & Sham Shui Po)

8/F Tsuen Wan Government Offices, 38 Sai Lau Kok Road , Tsuen Wan, N.T..

Tel. 2417 6116

Fax. 2411 3073

Regional Office (North)

(Yuen Long, Shatin, Tai Po & North)

10/F, Shatin Government offices, No. 1 Sheung Wo Che Road , Shatin, N.T..

Tel. 2158 5757

Fax. 2685 1133

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Friday, 18 December, 2009