Failure analysis of overhead flow cooling systems of a light naphtha separator tower at a petrochemical plant

Abstract

In the present research, root causes of fouling in overhead cooling flow of a naphtha separator tower at a petrochemical company in southern Iran were studied. For this purpose, chemical properties of the various deposits present in distinct points inside the cooling systems were analyzed using the Thermo-gravimetric analysis (TGA) and X-ray diffraction (XRD) methods. The overhead cooling systems consisted of an air cooler, a drum and a heat exchanger. The results revealed that the vast majority of these deposits had non-organic origin and could be produced by corrosion. To investigate the causes of corrosion, sulfur and chloride content of the fluid at input and output of some process equipments were measured via analytical methods. The results indicated that the fluid temperature reached to 92–94°C in some parts of air cooler exchanger in naphtha overhead flowing system. Within this temperature range, sulfur and chloride compounds were condensed on the wall of the air cooler tubes causing corrosion in these regions. The results of fluid flow simulation inside the heat exchanger showed that the accumulation of corrosion products on the back of the first baffle was the reason for complete fouling of the heat exchanger box after almost 2month. To prevent the fouling deposition and corrosion in overhead flow line, inhibitors were utilized. To investigate the performance of this treatment method, corrosion coupons were also installed at three points along overhead line. The results of XRD analyses showed that the main source of the fouling deposits was produced from a combination of almost 64% corrosion product and 36% dehydro carbon materials.