Reduction of Waste Water Loads at Petrochemical Plants

Examensarbete för masterexamen
Master Thesis
Ryynänen, Tiina P
VI Abstract This Master’s thesis was done for Borealis Polymers Oy in co-operation with Chalmers University of Technology. The research concentrated on the load of petrochemical waste waters. Borealis’ Petrochemical plants consist of cracker, butadiene, benzene, cumene and phenol plants. There are two waste water systems in Borealis Polymers Petrochemical plants: phenolic waters (PW) and oily waters (OW) which were studied separately. The phenol plant discharges its waste water to both systems, while other plants discharge only to OW-system. The loads of waste waters were assessed with two methods. The first method was chemical oxygen demand and the second method was to assess the quality of waste water streams from plants. Chemical oxygen demand (COD) was studied with theoretical oxygen demand (ThOD) analysis. The quality of different waste water streams were assessed by taking samples from waste waters generated in the plants. In phenolic waters, the ThOD was mostly caused by methanol and phenol. In OW-system the contribution to COD-load was divided more equally between all the components found in the waste waters. Petrochemical waste waters contain a variety of different components, so ThOD analysis based only on known components did not give a full answer how different sorts of chemicals contribute to COD. On average the determined ThOD was one fifth of measured in COD in phenolic waters and one third of measured COD in oily waters. In the phenol plant the load originated from the effluent stripper and methylhydroperoxide (MHP) reactor to the phenolic waters. When the quality of waste waters was studied, the MHP-reactor was the main contributor to the load to biological treatment feed, biolsy. It is recommended that the known components should be analysed also from the outlet of the MHP-reactor continuously. The waste water from the MHP-reactor contained high concentrations of cumene and phenol. Also because of the high phenol and cumene content of the water, it should be treated either in effluent stripper or in the OW-stripper. The cracker was responsible for benzene, toluene, xylenes and phenol load to oily waters system. The phenol and aromatics were responsible for methanol, and total nitrogen load. The known components should be continuously analysed from all the main waste water sources; the diluting steam generator, the NaOH and FCC washing steps, the carbonyl wash, the OW-stripper and the ejector waters. The streams that contained high hydrocarbon concentrations should be treated in OW-stripper and streams that contained phenol should be treated in effluent stripper. The reduction of load is difficult even impossible if the reduction concentrates only on the total load, measured either from pit 27 in case of the OW-system or from the biolsy in case of phenolic waters. Firstly the variety of components in the final stream increases because waste waters from different plants are aggregated. The reduction of different kinds of components is difficult, because of different nature of components. In the final stream also the components are diluted, which also makes the reduction of components more difficult. The reduction of components can be more efficient if it is carried out at the origin of the load.
Kemi , Chemical Sciences
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