Flowsheet Safety and Techno-Economic Analysis of Ammonia and Urea Production Route

Recent drop in oil and gas prices moved the world focus on the route production optimization of the downstream petrochemical industries. Ammonia, which is known as the second largest synthetic chemical product, is produced on large scale mainly for production of fertilizers using steam reforming (SR) or partial oxidation (POx) of hydrocarbons (HC). More than 90% of world consumption is manufactured from the elementary nitrogen and hydrogen in a catalytic process. Capacity of single stream has gone up to 4500 MTPD. After development of the NH₃ process, the production of urea from NH₃ and CO₂, which are both formed in the NH₃ synthesis, developed rapidly. At present, Urea is produced worldwide on a large industrial scale exclusively by reaction of Ammonia and Carbon dioxide. The main application of urea is its use as fertilizer. Urea, being the most important member of the group of nitrogenous fertilizers, contributes significantly in assuring world food supply [1-3]. Moreover, the recent growth in the production of shale gas has contributed to the interest in establishing new petrochemical plants for shale gas monetization [4]. In the process of selecting the best HC-Ammonia-Urea production route, different technologies must be screened and compared. The synthesis of Ammonia/Urea from HC requires the maximization of H₂ production. While SR is a catalytic and energy efficient technology for producing an H₂ rich syngas, POx is a non-catalytic technology with unique function of utilizing heavy hydrocarbon feedstock and produces a CO rich syngas. Autothermal reforming (ATR) combines gaseous phase combustion and catalytic steam/CO₂ reforming reactions; however, it is much less applied compared to SR and POx. It is the optimal choice for integration with large-scale Methanol or Ammonia production plants and Gas-to-Liquid (GTL) processes. ATR is also utilized as a “Secondary Reformer” placed after the primary SR in syngas production plants for lowering the CH₄ residue place [5]. The proper choice of one of these technologies can have its huge impact on the profitability of the production process. In addition to the typical approach of performing techno-economic analysis for comparing technologies, it is important to consider safety aspects early enough in the selection process. This research work presents a comparative approach for multiple HC-Ammonia-Urea production routes through techno-economic and safety analysis. All the studied process routes are commercially available and operated. The analysis is done using the built in capabilities of Aspen software through utilizing safety analysis, economic evaluation, environmental impact assessment and energy optimization techniques. The utilization of these techniques would provide insights about the optimum production route early enough to ensure sustainable process design. The results show that the conventional technology of steam reforming has an attractive process and economic potential with inherently safer operation.

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