HTF System

Thermal installations are typically equipped with a coarse filter in the main flow, which collects bolts, nuts, and other construction debris after the installation has been completed. Modern installations often also feature a fine filter in a bypass configuration.

Such a fine filter filters insoluble degradation products from the fluid, keeping it clean, maintaining turbulent flow, and extending the fluid's lifespan by several years. The filter elements must have a fineness of 5 to a maximum of 50 microns. Do you have an older or contaminated installation? Then please contact us for advice.

For high-temperature thermal installations with flange seals, only graphite gaskets may be used. All other gasket materials will eventually leak when synthetic thermal fluids are used.

The heating boiler is an essential component of every HTF system and can be either electric or gas-fired. With the right balance between heating capacity, temperature, and fluid velocity, the lifespan of the heat transfer fluid is optimized.

The boiler capacity, in combination with the pump capacity, largely determines the lifespan of the thermal fluid. The correct fluid choice depends on the application and, in particular, on the operating temperature. The maximum film and bulk temperatures for each type of Fragoltherm® and Therminol® can be found in the corresponding product brochures.

Organic heat transfer fluids, such as our HTF fluids, can undergo a slow oxidation reaction with air in the presence of insulating material at a fluid temperature above 260°C.

Porous insulation, such as calcium silicate, offers a larger reaction surface with poor heat dissipation. Combined with possible catalysis by the insulation material, this can cause a temperature buildup that can result in the ignition of the liquid as soon as the saturated insulation comes into contact with air, for example during repairs. This phenomenon is not fully explained but does not appear to occur with cellular glass, possibly due to the closed cell structure.

Therefore, use cellular glass in all places where leakage is possible, particularly around instrument connections, valve gaskets, flanges, and other sealed surfaces. Address every source of leakage immediately as a precaution: replace leaking gaskets and oil-soaked insulation, repack valve stems, and cover insulation where leakage may occur with metal covers. Where possible, install valves with the stems horizontal so that leaking oil can drain away from the insulation. Sensors and protective devices against spraying leaks at flanges are a standard part of our product range.

The layout of the piping system for HTF heat transfer fluids must be designed so that the required flow rate is achieved at an economical pressure drop. Because the system undergoes temperature fluctuations, sufficient flexibility for thermal expansion and contraction is essential; normal carbon steel (40) or an equivalent material is used throughout the system.

Most organic liquids tend to leak through flanges and fittings unless they are fitted tightly and correctly. Welding all connections is the best way to prevent pipe leakage; where access is necessary, flanges with weld-neck connections are recommended.

For proper installation and sealing of spiral-wound gaskets on HTF fluid lines, the following procedure applies: clean flange surfaces of loose rust, dirt, and welding spatter, and check that the surfaces are free of protrusions or grooves and are correctly aligned — gaskets cannot correct these issues. Check studs and nuts for rust and thread debris and lubricate the threads. Bolt and torque specifications are determined by the gasket supplier and depend in part on the diameter and thickness. Tighten opposing studs or bolts in small increments to the required torque value, in the order of 9, 3, 6, and 12 o'clock, and repeat this with the adjacent bolts.

The pumps in an HTF system must have sufficient capacity and inlet pressure to circulate the fluid at the required speed. Typically, these are centrifugal pumps, sometimes with sealed bearing systems or magnetically driven, that meet the required standards.

For most systems, the pump housing is made of cast steel or other materials suitable for very low or high temperatures. For temperatures above 200°C, pump manufacturers typically specify water-cooled ring seals, or preferably liquid or air cooling with an extended shaft seal and bearing.

Pumps with a stuffing box packing must contain at least five rings of laminar graphite packing. Inertly sealing the seals with steam or nitrogen prevents the deposition of oxidation materials, which could otherwise lead to leakage. A second seal offers additional safety in the event of a sudden sealing problem. Check the flow rate regularly against the original pump characteristics.

Prevent improper pipe support, as this can cause stress on the pump bearings and lead to alignment problems and leakage. Equip every pump with a temperature sensor that automatically shuts off the pump in the event of problems. If you use expansion loops in the piping of the pump section, direct them horizontally or vertically downwards – never vertically upwards, as this forms a trap that collects air and vapor and can impair pump capacity.

For HTF systems, forged steel valves with deep unions suffice. Use butterfly valves and external screw ball valves throughout the entire heat transfer system; however, keep in mind that butterfly valves do not always provide an absolute seal.

Various types of gaskets are used for sealing valve stems in high-temperature systems; generally, five rings per valve stem are recommended for a good seal. Bellows ensure virtually leak-free operation.