**2.1 Introduction**

To guarantee production reliability in the complex urea fertilizer manufacturing process, PHEs are installed in several process chains including CO2 cooling, residual gas scrubbing, and other process sections as were as in the primary urea production plant. Industrial processes commonly use water for cooling purposes. Open circuit cooling system is used in some processes, while closed loop system involving cooling towers is used in others. Closed loop systems usually cause less fouling than open ones, but they are more expensive (Kukulka and Leising, 2009). Cooling water normally contains dissolved or suspended solids like calcium carbonate and calcium sulphate. If the concentration of these dissolved solids exceeds certain limits, it leads to the accumulation of deposits on the heat exchanger surface (Müller-Steinhagen, 1999). These deposits create an insulating layer on the surface of the heat exchanger that decreases the heat transfer between the two fluids. The thermal performance of the unit decreases with time as the thickness of the deposit increases, resulting in an undersized heat exchanger and causing the process efficiency to be reduced (Kukulka and Leising, 2009). Deposit formation can be reduced either by changing the configuration of the heat exchanger or by regular cleaning procedures.

Deposit formation is influenced by the heat exchanger surface and geometry, cooling medium and the operating conditions. Its composition depends on the flow rate, temperature and chemical composition of the cooling medium (Kukulka and Leising, 2009). Pana-Suppamassadu et al. (2009) studied the effect of plate geometry (contact angle) and the gap velocity on calcium carbonate fouling in plate heat exchanger. They found that an increase in the gap velocity could reduce the fouling rate on the surface of plate heat exchanger.

In the present section, deposit formation on the surface of plate heat exchangers in different Egyptian fertilizer plants will be investigated. The effect of heat exchanger geometry and flow patterns on the fouling behavior will be shown.
