“At our Speciality Chemical Company, we have lot of heat exchangers in operation, especially in our chemical manufacturing processes,” begins Mr. Das. “We have a multitude of condensers, reboilers, and heaters, as well as various type of shell & tube heat exchangers, spiral heat exchangers, plate heat exchangers, and U-tube heat exchangers.
They are such an inherent part of our industry wherein production processes rely heavily on heat removal. We are in the business pf producing large quantities of ethyl acetate and alcohols. The alcohols are purified and then sent to oil companies to be used for blending. However, we also additionally produce ketenes and their derivatives, which are used for making arylides, amides, and esters – the basic materials used in the pigment and ink industries, as well as in the crop sciences, and as intermediates for chemical and pharmaceutical industry.”
“On a yearly basis we roughly spend about 500,000 euros on new purchases, maintenance and refurbishments when it comes to our heat exchangers,” continues Mr. Das. “This is not a standard yearly total, however. Much of this depends not only on the lifecycle costs accruing from equipment maintenance, replacements, revamps, and retrofitting, but also from expenditure resulting from new projects. As such the budget can run-up to one million euros some years.”
Maintenance of the heat exchangers
Much of our maintenance costs result from the fact that we handle many chemicals that cause fouling, such as the crystallisation of chemicals inside the tubes of the heat exchangers. This fouling necessitates that we frequently have to carry out checks to prevent choking of the tubes, and the cleaning process itself leads to the recurrent replacement of tubes. Moreover, to overcome costly shutdowns we have a number of standby heat exchangers, which can be brought into use when others are being maintained. We therefore have contingency plans in place to cover unforeseen circumstances i.e. in one heating loop we may have four reboilers in which two might be closed for refurbishment whilst the other two are there to take over where necessary so that we do not have to stop production,” says Mr. Das.
Laxmi Organic Industries Ltd. generally do not use their own staff when it comes to maintenance work on the heat exchangers but employ companies with specially trained personnel to do the job for them. This has largely to do with the fact that a lot of the materials that Laxmi Organic Industries Ltd. handle are flammable and hazardous.
Health and safety therefore comes first. They do not take any chances.
The amount of maintenance is considerable since the company has between 50–60 heat exchangers continually in operation. Around 10% of these have to be cleaned on a monthly basis simply because they get chocked by fouling. This is particularly so in processes leading to the production of di-ketenes and ethyl acetates. For the remaining 90%, however, it is enough to clean and refurbish them approximately once every year. Additionally, the way in which the heat exchangers are cleaned also varies. Sometimes this involves mechanical cleaning but in many cases it is done chemically.
Materials composition of heat exchangers
“Certainly we use quite a variety of different tubing,” says Mr. Das “depending on the types of fluids that have to pass through them. The most common material we use is 316L. Nonetheless, we also use 317L, Hastelloy, Duplex, and even Titanium at times. We also have a considerable number of heat exchangers where graphite material is used when very corrosive substances like chlorinated mass are passing through the heat exchanger. For such projects we normally make a choice between using Hastelloy or Graphite, or Inconel or Graphite with graphite obviously being the cheaper and available option but one which has to be replaced much more often.”
SS Ti or Titanium tubing is normally used when the possibility of erosion corrosion exists, especially where there are high fluid velocities within the tubing. Another common problem in connection with the heat exchangers is that of stress corrosion cracking.
In the past we used to import quite a number of heat exchangers, however, this happens far less regularly. Nowadays, the majority come from indigenous suppliers as is the case with most Indian companies working in the chemical industry. The split is roughly 90% from indigenous suppliers, 10% from abroad. In contrast, nevertheless, a lot of the really big heat exchangers being used in refineries still come from abroad – not just from Europe but also from South Korea and China.
It is largely only the forged tubing that tends to come from abroad, particularly when orders involve considerable thicknesses, or Hastelloy, or Duplex. Some of these orders will come from companies like Sandvik or Outokumpu, which is a relatively common thing to do for Indian chemical companies.
“Although we have companies who come in and take care of our maintenance and refurbishments,” continues Mr. Das “the tubing that is needed is always procured by our own staff.”
Before Laxmi Organic Industries Ltd. decides to purchase from a new company its purchase department staff will always want to see the supplier’s shop capabilities and examine its factory. “We similarly, work with third party inspectors to check out the quality of the supplier’s work, and will carry out positive metal identification inspections as well. Moreover, like all end-users we require consistently high quality in both workmanship and in delivery times. We need to be able to rely on our suppliers. It also goes without saying that pricing is also a key factor.
“If a company is not a registered vendor where we have carried out a complete diligence check for the type of heat exchangers that we use and we decide to look into the possibility of working with them, we will send a third party inspector to check them thoroughly out. This involves an investigation of the traceability of the materials they use, the fabrication methods, an examination of the qualifications of welders, their machining systems, positive material identification, etc.
“You might imagine that if you are working with suppliers that you have approved, why would you try new/ different ones,” says Mr. Das “Nevertheless, we continue to do this, particularly after we have had a failure with a tubing supplier, for example. Moreover, when we have specialty issues, like problems with erosion corrosion, we will always go to experts in the field such as Larsen and Toubro or similar reputed fabricators. And certainly when it comes to critical services we might go to a supplier abroad, especially when these services are related to large volumes of tubing. Nevertheless, whenever we find a good, new supplier we put time into developing the relationship for the future.”
In our industry we use a whole variety of heat exchangers, the most common being TEMA “C”. However, we also use cross-flow and counter-flow, shell & tube, plate, falling film evaporators, spiral type, double pipe and U-tube.
Our purchasing staff in the procurement department is all qualified mechanical engineers. However, the heat exchangers specifications are all set by our chemical engineers so effectively the process data sheet is made by our chemical engineers and the mechanical data sheet made by the mechanical engineer.
A recent failure example
“As an example of a recent failure, we had tubes in one of our heat exchangers that gave away just outside the position of the weld where they came out of the tube sheet. This occurred in a few months of use. The result was erosion corrosion whereby the tube-to-tube-sheet welds and tube sheet eroded. As a result the tube failed. To solve this type of problem we approach companies like Larsen and Toubro, other Indian reputed fabricators but also some foreign company requesting a complete solution. To aid them in their work we provided them with our data sheets and a complete corrosions data which had resulted from contact between the tubes and the fluid flowing through them.
What strikes you immediately when talking to Mr. Das is his great enthusiasm for the company he works for, his function as Head and Executive Vice-President of Projects, and his willingness to share knowledge and experience with others.