Serious energy savings and emission reductions can be achieved with a heat exchanger retrofit

Heat is a key parameter for any process industry including refining and petrochemicals, as it is an essential part of transforming feedstock into end products. Temperature should be controlled and monitored throughout the process to ensure the quality of the end products, and several instalments and equipments are used to transport or to control the heat during the reaction, including heat exchangers. Heat exchangers are devices specifically designed for the efficient transfer of heat from one fluid to another over a solid surface. This transfer of heat can either take the form of absorption or dissipation of heat. Heat exchangers find uses in a variety of industries such as chemical processing, petrochemicals and refineries where a shell and tube type of heat exchanger is generally used.

The heat exchanger can be used as condenser, cooler, chiller, heater sub cooler, heat recovery applications and many more applications. Whatever function a heat exchanger fulfils, in order to transfer heat the fluids involved must be at different temperatures and they must come into thermal contact, as heat can flow only from the hot to cold, thus the heat is transferred via a metal plate isolating the two fluids. 

THE GLOBAL HEAT EXCHANGERS MARKET IS SET TO EXCEED $12.7 BN BY 2016 

Heat exchangers are classified according to their flow arrangement. In parallel-flow heat exchangers, the two fluids enter the exchanger at the same end, and travel in parallel to one another to the other side. In counter-flow heat exchangers the fluids enter the exchanger from opposite ends. The counter-current design is most efficient, in that it can transfer the most heat from the transfer medium. In a cross-flow heat exchanger, the fluids travel perpendicular to one another through the exchanger. For efficiency, heat exchangers are designed to maximise the surface area of the wall between the two fluids, while minimising resistance to fluid flow through the exchanger. The exchanger’s performance can also be affected by the addition of fins or corrugations in one or both directions, which increase surface area and may channel fluid flow or induce turbulence. Designing heat exchangers for refineries and petrochemicals is a tough task for manufacturers, due to safety issues and very strict specifications. “The most critical specifications are related to hazardous area classification and explosion proof protection,” says Vishwas Vaidya, regional sales manager at Exheat. The petrochemical and refining sector is conscious about specifications, inspection requirements and documentation.  “Some applications also require heat exchangers are manufactured in an exotic materials like titanium or Hastelloy. We also have to manage involve fluids that are classified as sour, toxic or lethal,” he says. The downstream industry has specifications for manufacturing, which heat exchangers must meet. ASME (American Society of Mechanical Engineers), TEMA (Tubular Exchangers Manufacturers Association) and API (American Petroleum Institute) codes and specifications are the most commonly used. “For explosion proof certification ATEX, IECEx, NEC standards are followed. For pressure vessels the European Pressure Equipment Directive (PF.D),” says Vaidya. Heat exchanger manufacturers should meet international standards from the stages of design.  

EXCHANGER RETROFIT BENEFITS 

For the majority of new refinery and petrochemical plants, the application of years of operating experience and current disciplined approach to design, mean that significant performance problems are rare and they are robust enough to cope with changes in feedstock and varying product demand. However, when a general increase in demand requires a significant increase in plant throughput, it is typical that one area of a plant may be found to be constraining overall performance. “Whilst replacement is an obvious option it can be both expensive and technically challenging within existing plot space requirements. In such cases retrofit technologies often offer a significant benefit in achieving the goal at much-reduced cost as demonstrated in the following case studies relating to heat recovery,” says Peter Ellerby, engineering manager at Cal Gavin. Similarly in cases of unexpected performance problems where equipment does not achieve its designed standards, enhanced technologies are often considered as an affordable solution. “However the ongoing application of enhancement technologies to a wider range of operations is leading to increased confidence in their performance and reliability,” explains Martin Gough, managing director, at Cal Gavin. Gough and Ellerby illustrate their opinion with case studies where a simple retrofit at Volgograd refinery in Russia, operated by Lukoil, achieved significant improvements to heat recovery from a hydrotreatment reactor, cut fuel costs by US$233 000 per year, and made increased throughput available. “A fired heater in the refinery’s modern catalytic reformer was consuming around 330 kg/hr (727 lb/hr) of fuel to raise the temperature of a reactor feed stream. This was expensive in itself, and the heater firing limit also prevented any increase in capacity,” says Gough. “A THERMAL ENHANCEMENT SYSTEM WAS DESIGNED TO ADDRESS BOTH OF THESE PROBLEMS AND THEREFORE BOOST THE OVERALL PERFORMANCE OF THE EXCHANGER”