Process design for green urea production from renewable resources

Abstract

This thesis presents a design and simulation for the production of urea fertilizer based on energy from renewable sources, the electrolysis of water and the utilization of carbon dioxide as a new alternative for the traditional process and the use of hydrocarbons. The production is divided in five process units: water electrolysis, with the use of renewable sources for electricity, to produce hydrogen; air separation unit to obtain nitrogen from the air with a cryogenic separation; ammonia synthesis; urea synthesis with the use of carbon dioxide captured from emissions; and urea solidification to improve the purity of the product for a commercial proposes. The simulation is carried out using Aspen Plus program and the Aspen Process Economic Analyser (APEA) to determine the feasibility to build and operate a large-scale urea factory accompanied with an economic analysis of the market. A urea granules factory with a production of 44.5 tonnes per hour and a purity of 99.9 % was able to design, with a resulting capital investment of 633 M€, an annual maintenance and operational cost of 84 M€, and an energy consumption of 28 GJ/urea tonne. In comparation to the traditional urea production, the green process implies a 33 % more for capital investment and 1.5 times more for maintenance and operational costs. Based on today’s market analysis, the capital investment will have a return in 20 years, for a production plant with a lifecycle of 25 years, selling the product at market price. However, for a competitive factory investment, the product price should be imposed in the market at 25 % higher than the traditional one. In addition, a self-production of electricity is analysed, resulting on a reduction of 97 % of the operational costs while increasing 50 % the initial capital investment.