Ecodesign of a catalyst recovery process

ECODESIGN OF A CATALYST RECOVERY PROCESS
Enrico BENETTO^a, Mathieu ROUZEYRE^a,b, Diep NGUYEN-NGOC^a,b, Ligia TIRUTA-BARNA^b
a : CRP Henry Tudor - CRTE, 66 rue de Luxembourg, L-4002 Esch-sur-Alzette, Luxemburg

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b : Université de Toulouse; INSA,UPS,INP; LISBP, 135 Av de Rangueil, F-31077 Toulouse, France. INRA, UMR792. CNRS, UMR5504

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Abstract
Today, the design and the optimisation of an industrial process have to consider environmental criteria in addition to technical and economical considerations due to market and regulatory constrains. As a result, optimisation measures and development of modelling approaches have to be addressed taking into account all the criteria as a whole. This paper illustrates an integrated modelling approach (technical and environmental criteria) for the redesign of an existing process - a catalyst recovery plant. The catalyst recovery process can be subdivided into two parts: the recovery of catalyst through two reactors, basically based on the catalyst heating with hot air for the desorption of sorbed hydrocarbons and sulphur, and the treatment of exhaust gases from the reactors and the management of wastewater (containing several salts, mainly sulphates) generated herewith.

The redesign is aimed at two major improvements. First, the recovery of energy currently lost in exhaust gases from the reactors. Secondly, the treatment of the wastewater generated by the cleaning of exhaust gases in order to separate the sulphates. To these aims, the solutions investigated are respectively the implementation of a heat exchanger and the treatment of saline effluents using a membrane technology (Reverse Osmosis). With these technical solutions new operating and control parameters are introduced: temperature of different gas fluxes, pressure P and conversion factor Y for RO.

The whole process was modelled using the software Umberto 5.5. Material and energy flows calculations (in steady state conditions) based on the design of the different unit processes were implemented for both the current plant and the solutions investigated. The model is highly parameterized in order to be able to consider the operating conditions and includes material loops (e.g. the reuse of water from RO treatment as process water in the cleaning of exhaust gases). A lifecycle perspective was added by considering the production processes of the main raw materials (chemical additives for wastewater treatment, membranes, tap water) and energy (natural gas, heat, electricity) related to the specific local conditions.

Using a Life Cycle Assessment (LCA) approach, the lifecycle environmental impacts generated by the current and future possible configurations of the catalyst recovery process were compared in order to identify the more environmentally friendly solutions. The values of the operation parameters have a direct impact on the consumption of natural gas, on consumables (e.g. water, chemicals) and on the energy demand of wastewater treatment. Quantitative dependencies were identified between the operation parameters and different environmental impacts allowing fixing the parameter’s optimal values. For instance, it was demonstrated that the influence of the trans-membrane pressure on the environmental impacts is higher than the one of the conversion factor. An increase of P of 20 bars generates 30% of additional impact (on human health, ecosystem quality, resources depletion and climate change). Also thanks to the heat recovery, CO₂ emissions are reduced by 16% and 23% respectively in situ and considering the whole lifecycle of the process.