Applications

• Plastics
• Thermoforming and Thermal Setting
• Wood Products
• High-temperature industrial processes with indirect heating
• Food Processing, frying (potato and corn chips for example)
• Steam Replacement option
• Asphalt Plants and other 'Tank Farm' tank heating needs
• Flammable or other hazardous locations that require indirect heating

Overview

Thermal fluid systems are relatively new, with most products introduced since 1970. Its primary application is a replacement for high temperature and pressure steam systems and indirect industrial process heating.

Thermal fluid systems operate in the 400 to 650F (some special applications to 850F) range. At these temperatures, steam is in the 500 psi range. It has become very expensive to produce and handle steam with that kind of pressure, especially for relatively small processes. Thermal fluid is a special oil-like substance that does not vaporize, thus does not build-up pressure at these operating temperatures. The only pressure build-up is from thermal expansion, which can be controlled by the kind and size of thermal expansion tank. Typical operating pressures are well below 100 psi.

Any industrial process in the temperature range that can be heated indirectly, is a good candidate for thermal fluid systems. Often, a single heater is used to supply many individual machines, such as in a thermosetting application. Presses are the most common use for thermal fluid.

Thermal fluid is also reported to give a more even/precise temperature control than direct fired, with manufacturer's claiming +-2F of set-point. This could be critical for some applications, such as chemical processing and resin curing.

Thermal fluid can also be used in flammable or hazardous locations where direct-fired equipment would not be allowed, and high-pressure steam is too costly to install. Assuming the temperature requirement is higher than what could be provided by hot water or a low pressure steam boiler, as the first cost of thermal fluid heaters is much higher than standard boilers and water heaters.

Small thermal fluid systems are likely to be electrically heated. This is the most common in plastics and other small indirectly heated industrial processes (up to about 500,000 BTUs or about 150 kW) with their own dedicated heaters. Central systems piped to many machines are expensive to install, but substantially cheaper to operate if the heater is gas fired. Individual systems over 1 million BTUs are likely to be gas fired. Large central systems at wood processing plants are likely to be wood fired, with maybe gas backup or supplemental firing. Wood systems are generally in the 20 to 100 million BTU range, depending on the size of their press.

Economics

The application must require a higher temperature than what can be provided by water heaters and standard low pressure steam boilers, as fluid heaters cost more than conventional heaters.

If the application is to supply several stand-alone machines, the cost to do the plumbing to connect the machines can quickly exceed the cost of the central heater. Therefore, machines should have at least a 50 - 100 kW load each, and not be too far apart, to provide a reasonable payback to convert from individual electric heaters. If connecting multiple machines, the load should be at least 1,000,000 BTUs total.

Gas fired fluid heaters operate in the 90% efficiency range. Therefore, 1,000,000 BTUs provided by a gas fired unit will require 1.1 MCF. If $5.00 per MCF = $5.55.

Electric fluid heaters cost per 1,000,000 BTUs/ 3,413 BTUs/kWh = 292 kWh at $0.08/kWh = $23.50.
More Information

See our Plastics Consortium web site at www.PlasticsSuite.com

Source: Energy TechPro; graphic courtesy of GTS Energy