On-Line Heat Exchanger Monitoring: Real-time Assessment Of Your Exchanger Performance
EP Editorial Staff | April 24, 2013
A pre-engineered, integrated solution from Emerson can make life a whole lot easier around your site. It detects accelerated fouling and identifies the best cleaning time to optimize an exchanger’s energy usage, capacity, maintenance cost, carbon footprint and safety.
Energy, next to raw material, remains one of the leading controllable costs in most manufacturing processes. Great strides have been made over the years to make plants more efficient by recovering heat from the process in cross-exchangers. But heat exchangers foul. It’s a fact of life. How fast they foul depends on a number of factors, including exchanger material and design, process fluid composition, process flows and temperatures. Fouling is caused by a variety of mechanisms, including those that are corrosion-related, or process conditions like coking, or composition factors like solids precipitation, to name a few.
One problem with which companies struggle is that of an operating condition or feedstock creating accelerated exchanger fouling. For example, refineries have begun to see issues with particular crude blends that cause asphaltenes to precipitate out and rapidly foul the crude pre-heat train. Relatively short-term excursions in cooling water pH can lead to rapid buildup of microbial fouling in all of the cooling water exchangers at the site. In these circumstances, it is important to quickly notice when exchanger performance is degrading.
Plants are designed to operate despite fouled exchangers. The consequence of lost heat recovery in exchanger trains is higher steam or fuel consumption in downstream units, and more heat rejected to cooling water. This costs money and increases carbon footprints. Emerson’s studies estimate that just 1% improvement in the heat recovery train for a 280,000-bbl/d refinery is worth about $1.8 million annually in energy savings. That’s great news, but without on-line monitoring, how do you know when an exchanger is fouled enough to justify its removal from service for cleaning? Periodic manual exchanger surveys call for engineering manpower. They’re also inadequate for detecting rapidly developing conditions.
Many plants were initially built with only necessary instrumentation to safely operate their units. And since exchanger monitoring isn’t critical, exchangers were often insufficiently instrumented to conduct real performance monitoring—the thermowells were there, but the instruments were not. With today’s wireless devices, the cost to instrument a train of heat exchangers with the temperatures, pressures and flows needed for on-line monitoring has been greatly reduced, making monitoring solutions much more easily justified.
Once the process values are available, an application is needed to calculate the exchanger performance and notify personnel when a problem is detected. That’s where Emerson Process Management comes in: It has recently introduced AMS Suite: Essential Asset Monitoring (EAM), a suite of on-line performance monitoring solutions for various types of assets such as pumps, heat exchangers and blowers.
EAM for Heat Exchangers is designed to monitor shell-and-tube exchanger conditions relative to a unit’s original clean state. Key performance metrics like exchanger heat duty, heat transfer coefficient, fouling factor and cost of fouling are used to determine an overall health value for the exchanger. An example display from the AMS Suite: EAM-Heat Exchanger is provided in the above chart. Using this tool, operators and maintenance staff are alerted whenever an exchanger is in need of cleaning or an abnormal increase in fouling is detected. MT
Emerson Process Management