VENT TREATMENT UNIT

VENT TREATMENT UNIT

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:

DMF Absorption Unit

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.

Absorption and Stripping Unit

This process is needed when gases or vapours to be blown-down are not soluble in water. The absorption of organic solvent contained in an air stream is performed by a special high boiling medium in the Absorption Column, equipped with special packing with low pressure drops and high efficiency. In the second Column (Stripping Column) the bottom solution from the first Column is stripped by direct injection of steam or by an heating system. The solvent is recovered from the top and the absorbent medium, free of the organic solvent, is recycled back to the absorption Column. The solvent is condensed and reutilized, if needed can be sent to further purification. This system is suitable for the purification of an air stream containing in example toluene, xilene and other aromatics, ketones, chlorinated, hydrocarbons, and so on. The advantages of this process are low energy consumption and stability of the absorption medium, which is higher if compared to active carbons.

HCl Scrubber

Hot fumes containing hydrochloric acid are quenched by saturation with water to reduce their temperature. The liquid is pumped to quencher to provide the intimate contact between the liquid and gaseous phase. An automatic valve connected to the fire water provides the refrigerant fluid in case of pumps or electrical power failure. The gases rise a packed column and HCl is absorbed by a counter current demi-water flow. From the bottom of the column the recovered hydrochloric acid solution is circulated to the quencher and discharged in automatic under level control. A density analyser controls the flow of water to reach the required acid concentration. An heat exchanger removes part of the enthalpy of the inlet gas in order to reduce the water flow used to quench and obtain a concentration of about 20%. The gas leaving the first column flows to the second one where the residual hydrochloric acid is removed by an alkaline solution. A level controller discharges continuously the solution of sodium chloride collected at the bottom. A pH analyser regulates the quantity of caustic soda and controls the pH of the washing solution. A variable speed fan, regulated by a pressure control in the suction line, provides the head required to overcome the system pressure drops.

Activated Carbon Solvent Recovery

The polluted air rich of solvent is sent to the working adsorber unit. Thanks to his adsorbent capacity the active carbons bed catches and holds the solvents, the purified air is exhausted to the atmosphere. When the carbons bed reaches its saturation grade it is necessary to regenerate it and continue to work switching to the other unit. The active carbon regeneration is performed by hot nitrogen or steam according to the properties of the solvent processed. Steam or inert gas warms up opportunely the carbons bed and desorbs the holded solvent, this stripping mixture, coming out the adsorber, is sent to a condensation group, where the solvent vapours are condensed and the liquid is recovered in a surge vessel. The steam or inert gas, free from the solvent, is heated again and recycled back to the carbons bed until the regeneration cycle is completed. At the end of this phase, and after a suitable cooling of the carbons bed, the unit is ready to work again in the adsorption phase, this way it is possible to operate the plant continuously. The recovered solvent afterwards can be passed, if needed, to a distillation unit for final purification. All the plant operation are controlled from one control panel, the regeneration phase start-up of a bed can be operated in manual as well as in automatic mode.

Regenerative Oxidizer Unit

Thermal or catalytic oxidizer unit are convenient when the concentration of the polluted vent are poor in solvent concentration, or when the polluted vent are containing more different solvent not suitable for the recovery.