Fixed bed is type of chemical reactor, commonly in use in chemical industry. Generally the reactants pass through a fixed bed of a catalyst where the reaction takes place. Based on reactants flow regime fixed bed reactors falls in the category of plug flow reactors. The most common of these are reactors at gaseous service.

Catalyst in the fixed bed reactors are generally very expensive and length of their life affects process operational economics. Pressure drop in chemical reactor is important as loss of pressure energy incurs high compression costs and is a constraint by reactor design e.g. bottom support grid generally withstands a limited pressure differential. Accordingly, along with activity, catalyst life also depends on pressure drop across the bed.

This paper describes causes and effects of pressure drop in fixed bed reactor in particular at ammonia plant. At ammonia plant shift converters, Methanator, ammonia converters and reformer are examples of adiabatic and non-adiabatic fixed bed reactors respectively.

Throughout catalyst lifecycle, reactor's pressure drop increases from a lowest SOR (start of run) to a highest EOR (end of run) value. The increase is caused by factors like, catalyst bed settling, breakage of catalyst particles, depositions on catalyst bed etc. These causes may occur due to number of other basic reasons e.g. refractory dust from upstream equipment / piping, thermal/pressure cycling of reactor, pressure reversals etc.