Thermic Fluid (Heat Transfer Fluid) systems have replaced steam systems in a broad range of process applications, because they provide precise, steady and uniform control of temperatures. This has lead to low maintenance and increased production, product quality, human and environmental safety and life of highly efficient service. Hot oil systems can provide significant advantages over steam in almost every given application.
Efficiency
Thermic fluid heater manufacturers claim that efficiencies can be as high as 5% to 8% more than conventional steam systems. Thermic Fluid heated shell-and-tube steam generators can provide increased efficiency as well. These systems also require less water treatment and are subject to decreased fouling due to considerably lower heat flux.
If we consider the flash losses of a typical steam system (including trap losses) of up to 6% to 14%, blow-down losses of up to 3%, and de-aerator loss of 2%, the difference in efficiency becomes pronounced.
Thermic fluid systems suffer none of these losses and as a result can be more efficient – excluding the additional heater and steam generator efficiencies.
Licensed Operators
Typically in India a steam boiler requires mandatory compliance for:
- Manufacture as per IBR norms ( IBR – Indian Boiler Regulations )
- Erection to be carried only by licensed IBR contractors
- Operation to be done only by licensed operators
- Repair works to be carried out only by licensed repairers
Apart from the above, especially in India, shortage of treated water for steam systems is a big issue. Even an efficiently installed steam condensate recovery system requires around 20-30 % capacity volume of treated water to make-up for various losses.
Unlike steam systems, most thermal fluid systems operate at atmospheric pressure and are vented to atmosphere at the expansion tank. Pressure in these systems is limited to the pump discharge pressure which is necessary to keep the fluid in turbulent flow while overcoming pressure loss in pipes. Typical pump discharge pressures can range from 2 to 5 bar with somewhat higher pressures required for large systems. Because of safe, low pressure operation thermal oil systems seldom require licensed operators.
Corrosion
Steam systems are well known for corrosion problems. A potent combination of air, hot water, salts and other reactive contaminants present an extraordinary potential for metal corrosion. Steam is abrasive and has virtually no lubricity. In addition to this, scale formation and deposits from minerals found in most water supplies will tend to compound the system problems quickly.
Heat transfer fluids are completely non-corrosive and they provide the same high degree of protection to metal surfaces as the finest lubricating oils.
Maintenance
Steam systems require continuous maintenance that is focused on steam traps, valves, condensate return pumps and expansion joints which require constant water monitoring, analysis and treatment. When the power fails in a cold climate, steam systems are subject to freezing, burst pipes and damaged components.
Thermic fluid systems do not require traps, condensate return systems, blow-down systems or water additives; and if the proper grade of fluid is selected, a thermic fluid system can be shut down even in sub-zero conditions without freezing. Most heat transfer fluids when cooled below their pour points contract upon solidifying, presenting no danger of pipe burst. Thermic fluid systems have proven to operate quietly, safely and efficiently for years with minimal maintenance.
Environmental Safety
Water in a steam system must be chemically treated to reduce corrosion, among other things. These chemicals cannot be discharged into sewers, as they present a considerable environmental hazard. In addition, the temperature of discharge water is often regulated by law. Special provisions for cooling are required if water is to be drained into sewers.
Thermal fluid systems do not require blow-down, and unlike steam systems, are not subject to continual leakage. And unlike heavily treated boiler feed water, heat transfer fluids offer safe and easy disposal. They can be combined with spent lubricating oils, sent to the local motor oil recycler and processed into another useful product or incinerated without harming environment
Safety
To deliver the kind of heat required in most process operations, steam systems would have to operate at exceptionally high pressures. At 315°C for example, a saturated steam system develops about 110 bar. Even at 205°C, the pressure is still high — about 16 bar.
In contrast, most thermic fluid systems are vented to atmosphere. Pump discharge pressure is just high enough to overcome frictional drag from piping and components while maintaining turbulent flow. The vapor pressures of heat transfer fluids are fractions of atmospheric, even at their maximum operating temperatures of 300°C.
Temperature Control
Steam systems rely on the control of pressure to control temperature. With this dependence on delicate balance of pressure, accuracy is generally limited to swings of ±2°C or so at best. Worse, as the system ages and corrosion takes its toll, control of temperature degrades.
Uniformity of heating can also be a problem due to varying rates of condensation and condensate removal in the heat user. And this is before taking the negative effects of metal surface corrosion and plating-out into consideration.
In comparison, thermic fluid equipment manufacturers report the ability to regulate temperature swings to ±0.5°C or less. This precision is accomplished by the ability to mix and meter the cooler return fluid with warmer fluid from the supply line. Precision and uniformity of temperature control across the entire user surface is assured by addition of high-velocity turbulence
Thermic fluid systems not only provide efficient and uniform heat, but also efficient uniform cooling as well. And some fluids can provide efficient heating from over 205°C to cooling at -40°C and below.
System Cost
Purchase cost of steam systems can be less than thermal fluid systems. With less-complex thermal fluid systems however, there are paybacks: decreased operating costs, maintenance costs, and environmental concerns — and increased production and product quality resulting from better control of heating and cooling.
If we combine the above factors with improved safety and reduced manpower cost, the overall economy of thermal fluid systems will far surpass steam systems.