Odour control system at food processing plant
The basis of the system design is as follows:
Odour control system design airflow: 15,000 m3/h
Assumed inlet gas temperature: <60 deg C
Assumed odour level in inlet gas stream: <3500 OUE/m3
Required odour level in outlet gas stream: <400 OUE/m3
Odour and vapour laden air is collected from cooking ovens, cooking kettles and general ventilation from production areas and is fed into the system via various stainless steel and GRP ductwork connections. Each inlet duct is controlled via a system of pneumatically operated dampers which in the case of the ovens can be switched either into the system or to bypass depending upon requirements.
The eight kettle extract lines are each fitted with a pneumatically operated isolation damper and the general ventilation duct is fitted with a manual damper. They are collected together into a plenum box and the total mixed air is forced into the main system via a polypropylene cased centrifugal booster fan unit.
All emissions are collected via a common header duct and fed first into a venturi scrubber which accelerates the air to a velocity of approximately 40-50 m/s where a spray of water is added via 6 spray nozzles, this is designed to remove particulates, grease and ‘soluble’ odour from the air stream.
The particulate laden water is then allowed to settle into the collection tank whilst the air exits the tank via a stainless-steel droplet eliminator/coelescer. This removes the bulk of the fine mist and water droplets contained within the airstream.
The collection tank is fitted with an automatic blowdown valve which is set at a predetermined rate to keep the tank water refreshed and prevent a build-up of sludge.
A recirculation pump is installed to feed the scrubber spray nozzles with recirculated tank water at pressure. The pump is protected by an in-line water filter and an ultrasonic level sensor which in the case of a severe drop in the water level, will send a signal to shut down the pump.
Downstream of the mist eliminator is the ozone injection point where the ozone gas is forced into the airstream. From here the air/ozone mix is carried into a dwell vessel which allows the ozone injected to oxidise VOC’s by increasing the residence time for a minimum of 4 seconds prior to entering the air heater.
The air is then directed into a steam heated air heating coil which raises the temperature of the scrubbed air to around 30C this is to help prevent condensation in the fan and the downstream carbon bed. The air heater is of stainless steel tube and fin construction.
The main centrifugal fan unit is a direct drive all stainless-steel impellor and casing equipped with a 30kw drive motor which is designed to be inverter controlled to achieve the optimum performance for the system. The fan is designed to pull air through the system via the venturi scrubber and all relevant production areas and also to push the air through the carbon adsorber bed and out to atmosphere at high velocity.
From the discharge side of the fan, air is pushed into the carbon adsorber which removes any remaining VOC’s from the exhaust prior to discharging at high level via the efflux stack. There is a high velocity discharge cone fixed atop the stack which aids dispersal of the emitted cleaned air to atmosphere.