ORIGINAL PAPER Study on pollution prevention through an integrated process-environmental model in a urea prilling tower M. Hashemi & F. Nourai Received: 11 February 2005 / Accepted: 24 April 2006 # Springer Science + Business Media B.V. 2006 Abstract In this paper, a mathematical description of a real prilling tower is integrated with a simple dispersion model in order to study the ultimate environmental impacts from particulates emitted from the process into the atmosphere. The process model showed good agree- ment with operating data and measured emission levels. Eighty different scenarios (meteorological data sets) were studied, in none of which a significant environ- mental impact was observed. The study clearly shows the need for and the points at which ground level mea- surements should be made. Keywords pollution prevention . integrated models . prilling . urea Introduction Urea (NH 2 CONH 2 ), the most important solid nitrog- enous fertilizer, was first produced from the combina- tion of ammonia and cyanuric acid. Urea belongs to the family of amides derived from carbamic acid, but exhibits no acidic properties. It is used more often than any other fertilizer, such as ammonium nitrate, ammo- nium sulfate and calcium nitrate [5]. Urea has several adverse effects on the human body. For instance, it causes coughing and other malfunctions in the respiratory system, strong skin irritation, irrita- tion and conjunctivitis in the eyes, and nausea and abdominal discomfort if swallowed. As a preventive measure against these issues, it is usually necessary to provide adequate ventilation, protective clothing, safe- ty showers, and the like [8]. The capacity of any urea plant has a direct con- nection with the dimensions of its prilling tower. For example, the quantity of produced urea in the prilling tower under study – located in Khorasan Petrochem- ical Complex (KPC; Bojnourd, Iran), and having a diameter of 17 m, fall height of 60 m and total height of 77 m – is 500,000 tons/year. Various licensed processes are available for urea production in an industrial scale, including those com- mercialized by Stamicarbon, Snamprogetti and Mit- sui Toatsu Chemical [1]. Each method has its own environmental problems, with different solutions. For example, use of concentrated NH 3 in the synthesis cycle of the Stamicarbon process leads to production of a small amount of Biuret, which is an unwanted by-product. It also increases reactor temperature and reduction bulk corrosion in stainless steel equipment. Because of the low mechanical strength of urea particles, urea dust is a recurrent problem in almost any urea production process. Urea dust and contami- nated water drains are the main causes of air and water pollution, respectively, in urea production. There are systems for controlling pollution [1]. They reduce pollution via designed fans for reducing steam consumption and recovering duct system. Polluted water can be treated using biological methods or it can be chemically hydrolyzed or steam-stripped for removal of NH 3 . In Iran, environmental regulations are established and enforced by the Department of Environment Environ Model Assess (2006) 11:243–250 DOI 10.1007/s10666-006-9054-6 M. Hashemi : F. Nourai (*) Chemical Engineering Department, Science and Technology University of Mazandaran, Babol, Iran e-mail: f.nourai@rastarco.com