Removal of ammonium nitrogen and hydrogen sulfide from oil refinery waste water

The Holborn Europa Raffineire (HER) in Hamburg, Germany, achieved a drastic reduction in water and ail pollutants by implementation of a two step project. The first step was a modification of the H2S-stripping of process water, which resulted ultimately in shutting down the H2S-incinerator and conversion of the recovered H2S to saleable elementary sulfur. Atmospheric pollution was reduced accordingly by 650 t/a SO2 and 2,200 t/a Co-2. In compliance with waste water legislation (requirements of Appendix 45, Waste Water Administrative Regulation), the ammonium nitrogen content of refinery waste water reduced significantly in a second step. In contrast to the common biological treatment used in many refineries, it was decided to concentrate on physico-chemical treatment of the highly contaminated partstream only. To this end ammonia is effectively stripped out of the partstream under alkaline conditions, and concentrated to a 10% aqueous solution by distillation under reflux. This solution is then injected into the hot vent gas stream of the FCC-regenerator (CO-Boiler) as an NOx reduction agent, and thus disposed of in an environmentally-friendly manner. The introduction of this combination of field proven processes, namely water treatment by steam stripping and NOx reduction vis SNCR, received government grand support and reduced water pollution by 250 t/a ammonium nitrogen and air pollution by 180 t/a NOx. In view of the relatively low investment and operating costs, enhanced flexibility of the existing biological water treatment plan, avoidance of additional material waste and drastic reduction of overall refinery emission, the adopted scheme is most certainly a prime example of both economical and ecological optimisation. The scheme also has future potential arising from the projected tightening up in motor fuels specifications (EU specifications for years 2000 and 2005) which will necessitate increased use of catalytic processes in refineries. These will result in increased contamination of process wateres, which in the case of limited biological treatment consistent with the HER approach.