Fouling
important factors are taken into consideration to minimise the occurrence and buildup of fouling : a ) allocate more fouling fluid to tube side ; b ) design the heat exchanger for a fouling fluid velocity of 3 ft / s on the shell side and 5 ft / s on the tube side ; c ) allow easier cleaning access to the heat exchanger ; d ) when servicing , make sure the wall temperature of the tube isn ’ t kept too hot , as it could create unwanted deposit of salts or render any chemicals ineffective . The effect of fouling causes deposition on the walls of passages either in tubes or / and in shell sides of heat exchangers . This reduction is passage area causes increase in pressure drop and reduced heat transfer . Heat transfer and pressure drop are inversely proportional to the diameter of the passage . Pressure drop will increase to cube root of diameter . Pressure drop of a fouled heat exchanger passage is very high compared to the clean passage of the heat exchanger . Fouling causes immense production loss associated with efficiency deterioration . This production loss can be associated with unplanned and planned operation shutdown due to fouling , maintenance costs from removal of heavy fouling deposits with the use of chemicals / anti-fouling devices , maintenance cost associated with replacement of plugged or corroded equipment , cleaning cost for industries range between EUR 46 to 55,000 per heat exchanger . Fouling can be determined by either the nature of the fouling process fluid , the heat transfer process or combination of both . Heat transfer mechanism is the main cause for most of the fouling . High temperatures increase the rate of fouling . By decreasing the temperatures , the rate of fouling can be lowered which in turn will reduce the cleaning cycle . Hence it is important to mitigate fouling through large increases in heat transfer efficiency and changing flow conditions inside exchanger tubes .
Conclusion We can conclude that fouling effects can be immensely reduced in heat exchangers by proper design , controlling the materials which cause fouling , good selection of construction material , proper protective coatings for the heat exchanger surfaces , and periodic regular cleanings . Detailed and effective analysis of operating parameters of fouled heat exchangers must be conducted and analysed as it is essential to calculating the correct fouling factor for both the product and service fluids . Process and mechanical design of a heat exchanger should ensure the right fluid velocities , temperatures , and other operating parameters . Preventive maintenance , especially by systematic inspection , and cleaning should be carried out to prevent fouling and to maintain the heat exchanger effective running . Though fouling in heat exchangers cannot be eliminated , it can definitely be controlled and reduced to maintain the heat exchanger ’ s performance without adversely affecting the process performance . It is advised to read and refer to case studies articles from publications like Heat Exchanger World as well to get more knowledge and awareness .
About the author
Mrinal Das has over 30 + years of experience in petrochemicals , refineries , fertilisers and specialty chemical industry in India and abroad . Mr Das is currently working in Dorf Ketal Chemical ( Mumbai , India ) as Senior Vice President Projects & Engineering Purchase . Prior to this , he had worked in senior management positions in Laxmi Organic Industries , Jacobs Engineering India Pvt . Ltd ( Now Worley ), Larsen and Toubro Limited , Deepak Fertilisers and Petrochemicals Pvt . Ltd , OilServ . He has worked from end-user , detailed engineering consultant , EPC and EPCm sides .
www . heat-exchanger-world . com Heat Exchanger World February 2023
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