ENVIRONMENTAL PROTECTION ( DMF absorption unit and DOP filter)


MFC Progetti with his large experience, according to the composition of the vent gases to be treated can offer the more appropriate technology as per the example hereunder reported:

The vapours leaving the PU coating lines are conveyed to the absorption unit by a blower, having the head required to cover pressure drops.
The vapours enters into the bottom of the column and are quenched by a DMF water solution at 20-30% of concentration, in order to achieve the water saturation and cool-down the vapours.
The vapours rise the column through a special section equipped with high efficiency packing (low pressure drop and energy saving) for DMF absorption or alternatively through a special section equipped with high efficiency trays.
The vents get out from the top and are exhausted to the atmosphere with a very low DMF content, according to local environmental regulations.
On the top of the column water is fed to keep at constant value the DMF concentration in the exhausted vents and to achieve the quench-cooling.
The level indicator controller on the column bottom controls the discharge of the recovered DMF water solution.The pressure controller on the suction of the blower regulates the flow rate, according to the vapour coming from the coating lines, to keep at constant value the pressure in the conveying ducts. The blower is equipped by an electrical motor connected to a variable frequency driver, to optimize the power consumption.A by-pass of the unit is provided to blow to atmosphere automatically the conveying ducts in emergency cases.The DMF content in the vent from the absorption unit can meet very low value according to the local rules.

Process description
The vapours leaving the PVC coating lines are conveyed to a prefilter for the removal of the foreign matter before entering into the cooling section.
The vapours temperature is reduced to 40° C about and the organic substances are caught by condensation with possible formation of a mist.
The mist of air containing DOP, DNP or other phthalates is conveyed to a special filter where the DOP is removed and collected into a basin. The clean air is sent to the atmosphere through a blower having the necessary head. Fiberbed filters are used to trap, collect and remove liquids and soluble particulate matter suspended in the gas stream. Collection can be achieved with an efficiency as high as 99.5% depending on particle sizes. Typical concentration of DOP in the gaseous stream is around 500 mg/Nm³ and after filtration, DOP content in the effluent is less than 10 mg/Nm³. Airstream and process gases can be vented free of pollution; the recovered material can be collected into drums for reutilization.
Filters are typically constructed in annular cylindrical form. The cylinder is formed by rolled screens of selected special material; the filter material, selected from a wide range of media, is placed between the two frames to form the filter bed. The diameter of the fibre, fibre material, and the materialís packing density determines the operating parameters of the filter (such as pressure drop, collection rate, efficiency, gas through-put, etc.)
Filter process
Mist laden gas passes in a horizontal direction perpendicular to one side of the fibre bed and cleaned gas exits from the opposite side. As the particles try to pass through the fibre bed, they are trapped and held by the fibres. The collected particles are coalesced into drops on the filterís fibre surface and drain by gravity.
To save energy can be provided the air fan with an inverter receiving the controlling signal from the relevant pressure control.