Purification of the effluent deriving from the finishes of the polydiene plant
Our customer is a petrochemical company which manages the activity of the Styrenes & Elastomers, Polyethylene and Basic Chemical business areas, coordinating the production and marketing of the entire product portfolio through its three divisions.
Description of the project
The oxidizer uses a wise combination of ceramic masses specifically designed and distributed in three towers, capable of guaranteeing reduced pressure drops and an energy recovery of 95%. Special globe valves capable of withstanding frequent reversal movements (every 90-120 seconds) are also used, thus guaranteeing reliability and tightness. Furthermore, it is managed through a supervision system to control operation of the plant, completely automatic, by means of two PCs connected to BROFIND offices via a dedicated modem line, to constantly monitor the state of the plant.
The air to be treated, coming from the production lines, enters the washing tower, consisting of a plate section, where it is cooled and saturated. The water flow necessary to abate the dust to the level required by the combustion system circulates in countercurrent.
The thermal combustion plant is the regenerative type with three chambers: each of the chambers contains a bed with ceramic packing bodies to store heat, as it is heated or cooled according to the direction of the gas flow passing through it.
The incoming air from the washing tower reaches the first chamber, thrusted by a specific fan, and passes through the bed with ceramic backing bodies from the bottom upwards, where heat was stored during the previous phase.
During this transit, the polluted air is heated to a temperature as close to the oxidation temperature as possible (around 750/800°C) thus gradually decreasing the temperature of this ceramic bed.
If the above-mentioned oxidation temperature is not reached thanks to self ignition of the organic substances in the discharged air, an auxiliary burner is used, fed with fuel (methane) and installed in the combustion chamber.
After having left the combustion chamber, the purified gases pass through the second chamber from the top downwards, transferring the heat.
The second bed is then heated and is ready for the next sequence, namely to again heat the incoming gas to the plant.
The solution with three chambers prevents a certain volume of untreated gas from being sent to the stack, during stream reversal, thus reducing the efficiency of the system.
Intervention and proposal
The factory (2,790,000 m2) is characterised by the presence of technologies dedicated to the production of butadiene, dimethyl carbonate and derivatives, ABS, styrene butadiene rubber, polybutadiene rubber, thermoplastic rubber and latex.
The plant recently built and commissioned by BROFIND, with a maximum potential of 50,000 Nm³/h, is intended for the treatment of gaseous emissions coming from the finishes of the polydiene plant, characterised by the presence of fine thermoplastic and stearate calcium rubber dust (present in the range of 0.5 g/Nm³-1.3 g/Nm³) and by VOC (hexane and cyclohexane in a concentration ranging from 0.1 g/Nm³ to 3 g/Nm³).
The system consists of a wet unit for dust abatement, followed by a regenerative thermal combustion plant to oxidize volatile organic substances. It is all designed to comply with the most stringent emission limits (the abatement efficiency of the system is continuously monitored by an FID-NIRA analyser, with average hourly values detected at the stack of approximately 10 mg TOC/Nm³, well below the intended regulatory limit of 20 mg TOC/Nm³). The plant is provided with some technological features which make it among the most advanced in the sector.