Benefits Beckon in Heat Transfer

Developments provide operational and economic improvements.

By Seán Ottewell, Editor at Large

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The system with Therminol 66 has performed without incident, says Mexichem. However, after just three years, performance of the other system began to decline.

“First we experienced pluggage in our instrument tubing,” says Francisco Nava, production manager. “Soon after, we observed damage to the mechanical seals and problems began occurring in the heat transfer process. As a result, we were experiencing losses in distillation efficiency, increases in system vapor pressures, increased unplanned downtime, and impacts to our finished product quality.”

Mexichem turned to Solutia for a complimentary fluid analysis, part of the TLC program. It showed the non-Solutia fluid was degrading rapidly, reducing its ability to operate efficiently. Degradation products accounted for more than half of the fluid composition and the fluid was precipitating crystalline solids under certain conditions.

“Because the alternate heat transfer fluid wasn’t doing a good job, our pump seals were failing and we were losing yield. At the same time, our system utilizing Therminol 66 heat transfer fluid was operating smoothly. The decision to switch to Therminol 66 heat transfer fluid in the other system was clear,” says Nava.

Steam Savings
Many plants rely on steam as a heat transfer fluid but condensate recovery systems are so effective that often too much energy is captured. So, steam specialist Spirax Sarco, Blythewood, S.C. and Cheltenham, U.K., has launched a flash recovery energy management equipment (FREME) system that’s designed to overcome that problem.

FREME is a completely closed steam system under constant pressure that can recover energy from returned condensate and flash steam without wastefully dumping or venting surplus energy from the system. Instead it feeds energy from the returned condensate into the high-pressure side of boiler feed pumps.

The system passes condensate returning from the steam distribution system through a flash steam separation vessel. The separate flash-steam and condensate streams travel through a dedicated plate exchanger to heat pressurized feed water before it enters the boiler. The two streams then are combined and go to the boiler feed tank. Because that stream is sub-cooled, it’s sufficiently warm to begin heating cold feed but not hot enough to overheat the tank. Heat and water previously lost from the system can be recovered, reducing utility bills, water treatment chemical costs and carbon dioxide emissions.

The FREME system is available as a pre-engineered skid-mounted unit (Figure 1), taking the stress out of designing, specifying, building and installing steam, hot water and other systems, says the company. And with less work to do on-site, the installation process is simpler, safer and speedier, it adds.

Such a system recently was commissioned by Abbey Corrugated, Blunham, U.K. Before the project, water entered the boiler at 154°F–158°F. It now arrives at 280°F–288°F. “…It’s fair to say that the savings from this project were in the region of 25% of the gas used by the boiler,” notes Paul Gale, facilities manager.

In early November FREME won the energy category in the annual awards for chemical engineering innovation and excellence presented by the Institution of Chemical Engineers, Rugby, U.K.

Model Results
 “Studies around heat exchange equipment show that about 90% of energy consumption on a typical process is associated with some sort of heat exchange. So companies want to get the most return on investment per BTU,” says Tom Ralston, Reading, U.K.-based product manager, exchanger design and rating, for AspenTech, Burlington, Mass. The total installed cost of heat transfer equipment today typically accounts for about 30% of overall plant investment, he notes. “So it’s central to exploring the cost benefits of almost any energy saving proposal.”

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