Page 181 - CW E-Magazine (7-11-2023)

Special Report

580 tubes, out of which 400 were of
titanium and the remaining 180 were of
Cu-Ni. The operating temperature and
pressure of phenol on the tube side was
140-150°C and 15 kgs/cm respectively.
2
The cooling salt water pressure was
about 5 kgs/cm and velocity of water
2
was about 6 ft/s in the shell side.

A standby phenol cooler (E-202B)
of the same size as that of E-202 A had
to be commissioned in 2010 for avoid- Fig. 7: Fouling of the Tube bundle with Fig. 8: Denickelification & Pitting below
ing refinery shut-down and high down- foreign materials plastic sheets
time and maintenance cost. The mate- Denickelification was observed on extra spaces, and increased trans-
rial of the tube bundle was again Cu-Ni most of the tubes, as indicated by portation and installation costs.
(70-30 type), as in the earlier unit. But the reddish colour in Figure-8. 2. Energy costs: Costs for extra fuel
the cooling salt water in this standby Most of the pits and leaks were in required if fouling leads to extra

cooler was in the tube side and phenol 9 ‘O’clock to 3 ‘O’ clock position; fuel burning in the heat exchanger
was in the shell side. In this cooler the where settling of foreign materials to overcome the effect of fouling.
first leak appeared after a trouble-free could take place easily. 3. Maintenance costs: Costs for
operation of 3 years and afterwards it The cooling salt water was found to removal of fouling deposits, costs

leaked thrice in a span of 6 years, mak- be having 0.2 to 0.25 ppm of dis- for chemicals or other operating
ing the total plugged tubes to 14 out solved sulphides. costs for antifoaming devices.
of 580 tubes. The original tube bundle No sign of galvanic corrosion on the 4. Cost of production loss: Planned

operated for about 8 years and was tube bundle was observed, though or un-planned plant shutdowns due
changed in 2018. the bundle consisted of 70% tita- to fouling in the heat exchangers
nium tubes and 30% Cu-Ni tubes. can cause large production losses.
Observations These losses are often considered
The following observations were All the above observations revealed to be the main cost of fouling and
made on the bimetallic tube bundle that the premature failure of cupronickel very difficult to estimate.
(comprising of titanium and cupronickel (70-30 type) tubes was mainly due to 5. Extra environmental management
tubes) of the phenol cooler E-202 A, ‘crevice’ and ‘denickelification’ cor- cost: This the cost incurred by the
which leaked within 28 days of opera- rosion mechanisms. Crevice corrosion industry to dispose large amount of
tion: (pitting) was accelerated by deposition chemicals/additives used for foul-
The corrosion of Cu-Ni was mainly of plastic strips, wooden pieces, silt, ing mitigation.
due to the cooling salt water rather and foreign material, etc., and dezinci-
than phenol. fication was caused by dissolved sul- Huge fouling costs are reported in
The leaking tubes were having deep phides present in the seawater. different countries and are reported
pits throughout the length of the as percentage of their Gross National
tube. Cost implications of fouling Product (GNP). Average fouling cost
Fouling of the bundle with plastic Reliable knowledge of fouling eco- in a country is about 0.20% of its
strips, wooden pieces, silt and other nomics is desirable in order to evaluate GNP, varying from 0.15% to 0.28%, in
foreign materials was observed as the cost efficiency of various fouling Australia and USA respectively. Such
(Figure-7 and Figure-8). mitigation strategies that can be studies have not been conducted in
Accumulation of fouling materials adopted for the heat exchangers. The India; however significant costs are
was high at baffle supporting plates total fouling-related costs involve the incurred due to fouling of heat
of the tube bundle (Figure-8). following: exchangers in our country also.
Pits as deep as 1-mm was observed 1. Capital expenditure: Excessive sur-
on almost all the tubes, below the face area required to overcome the CONClUsION
plastic strips that were wrapped heavy fouling condition, costs for Fouling in heat exchangers is a very
round the tubes. stronger foundation, provision for typical, common and generally inevi-

Chemical Weekly November 7, 2023 181

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