Why in almost all hysys simulations of TEG and Amine units we place the lean TEG/Amine pump before the cooler and not cooler then pump before recycling ? Is there any problem of cavitation at low temperature ?

In order to avoid high heat to keep the equipment from being damaged for its precious value

rule of thump to be considered, always pump before cooling. Why? because you might have increase in temp after pumping which results undesired temp to achieve.

There are several reasons:

1) Avoid high-temperature, expensive materials for pumps

2) NPSH

3) Controls (e.g. partial cooler bypass - they introduce additional pressure drop and may starve the pump)

There are designs which introduce two-stage pumping, i.e. a booster pump followed by the circulation (high pressure) pump. Some designers install lean/rich exchanger upstream of the booster pumps, if layout and NPSH allow for such design. The final trim cooler is always on the discharge of the high pressure pumps.

Lean TEG pump is placed before cooler to avoid pump suction head loss in the cooler as the TEG regenerator is operating close to atmospheric pressure and hot TEG would not vaporize and pose pump cavitation requiring cooling before the pump,

As the process occurs in almost atmospheric pressure, the process cannot usually sustain head loss across the cooler. Also, the recirculation pumps are really expensive and it requires sufficient head for operation. When the cooler is placed before the pump, the chances of process (at that point) meeting the NPSH parameters of the pump is very less. so it is better to place the pump before the cooler. When NPSH parameter is not met, cavitation will occur and affect the pump internals.