Flaretec has been designing, manufacturing and developing heating systems for more than 35 years. We have vast experience in identifying a solution to suit all requirements. When deciding on the type of heater (direct or indirect etc.), there are numerous criteria that will impact on final selection.
Each type of heater is specific to your required solution. Each system type has advantages and disadvantages when compared to an alternative type of system. Flaretec can aid the selection process through our full disclosure of technical details and insight. Direct fired heaters require the selection of suitably low rates of heat flux whilst indirect heaters generally require the careful selection of an appropriate thermal fluid. All of Flaretec’s systems have in common the ability to be reliable under the local environmental conditions and heat a mixture of viscous crude oil and saline water without causing excessive coke formation, scaling or salt deposition in the tubes.
Introduction to Indirect Heaters
We have been a major supplier for over thirty years in the manufacture of indirect heaters. Many of our previously fabricated products are still in operation, particularly in the oil producing countries of the Middle East and North Africa. Our indirect heaters also operate both on and off shore, particularly in the North Sea, with wide applications particularly related to the oil and gas industries since we initially developed our indirect heaters for oilfield use.
Indirect heaters are predominantly a heater vessel with a heat source within. This is commonly a firetube, fired by gas or oil. The heat source and process coil that heats the fluid are immersed in water, water/glycol, hot oil or a molten salt mix. Since the heat source and the process coil are separated by a heat transfer medium, this type of heater is known as an ‘indirect’ or ‘bath’ heater. The process coils are operated at a pressure up to 12,000 psig. Depending on the process, the shell of the heater, which contains the heat transfer fluid, and the heat source both operate very close to atmospheric pressure.
Flaretec produce their process coils from high pressure, corrosion resistant materials to develop our design of indirect fired heater. Flaretec is one of the few companies in the world that can design and build water bath heaters that are ASME U Code approved.
The Standard Design of a Flaretec Water Bath Heaters
A process coil is immersed into a liquid bath vessel which is heated by one or several firetubes. The liquid bath fluid is usually water with anti-freeze and corrosion inhibitor but can also be pure glycol or heat transfer oil. This liquid type will vary according to results from our process calculations and required outlet temperatures.
Common Applications of Indirect Heaters
- Heating gas from a well to prevent hydrocarbon hydrate formation
- Crude oil preheating between the head and pipeline
- Crude oil preheating to separators or de-salters
- Fuel gas dew-point control systems associated with gas turbine power plants
- Heating high-pressure hydrocarbon gas streams at pressure reduction stations
- Liquid gas vaporisation where the indirect heater operates as a vapouriser or super-heater
- Re-boiler and stabiliser process heater
- Preheating of gas for molecular sieve regeneration
- As a form of heat source
We have the experience and technical aptitude to provide the design of an indirect heater to suit any heat source available. These heat sources may include oil or gas firing, dual firing of both oil and gas, steam heating or electrical heating (with appropriate certification for area classification).
Heater Thermal Efficiency
The firetube and burner arrangement of a Flaretec fuel fired heater can be arranged to meet the thermal efficiency required by the client, usually between 84% and 89% LHV. However, for an energy conscious environment, we can provide indirect heaters with a thermal efficiency of up to 94% LHV. Our experienced team will create a quality, bespoke product according to your design.
Our indirect heaters are available in thermal ratings from 50 000 BTU/hr (15 kW) to 30x 10^6 BTU/hr (9000 kW) with our comprehensive range being individually tailored to our clients’ needs. Flaretec utilises current design techniques and computer aided design facilities (including auto CAD, 3D design in Solid Works and Inventor).
High pressure coils can be manufactured to meet the requirements of API 12 K, ASME/ANSI B31-3, Stoomwezen, BS5500 or other international codes as required. Burner management systems are normally supplied with the heater and can vary in complexity from simple relay logic to certified PLC systems.
Fluid within the Water Bath Heaters
Water- Glycol Bath Heaters
Flaretec water bath heaters normally contain a water-glycol mix. They provide a robust method of indirect heating by transferral of energy through the shell-side heater transfer fluid. Within the lower part of the water bath shell are the firetubes, these are utilised to heat the transfer fluid. This fluid, through natural convection, transfers thermal energy to a series of coils in the upper sections of the heater shell.
Water bath heaters usually operate at atmospheric pressure; therefore, an expansion tank is normally included in the design and is typically fixed to the top of the main shell chamber. These accommodate the expansion of the shell-side fluid between ambient and design temperatures. Operating temperature ranges of the water bath and associated process media are typically lower than those of other forms of heater modules. Typical maximum operating temperature is 120 Degrees Celsius.
Typical advantages of a water bath heating system are that they include very few moving parts and provide a low maintenance method of sustained and stable heating with an operating efficiency of circa 90%. The range of Flaretec water bath heaters are designed and manufactured fully in accordance with API specification 12K.
Water can be heated utilising various methods including the fossil fuel burning, using electrical energy and through indirect methods such as heat exchange of other heated process media. Maximum temperature is limited for process systems involving water as a medium unless the overall scheme is pressurised which restricts its application. However, water is nontoxic under normal operating conditions so may be advantageous to use in certain situations.
When an application requires a higher temperature operation, an common process solution is thermal oil. Unlike the relatively safe characteristics of water, thermal oil systems require meticulous maintenance to ensure that uncontrolled releases such as leaks or failures do not occur. An advantage of these systems is that they are extremely unlikely to suffer detrimental impacts due to corrosion.
Steam is by far the most common form of heat delivery and is normally generated by burning fossil fuel, gas or as an output from a combined cycle heat & power operation. It is estimated that around 40% of all fossil fuel used in the world is to generate steam. Steam has an ability to deliver significant thermal energy by way of condensation and releasing its latent heat of evaporation.
Weir Bath Heaters
Flaretec’s experienced personnel design and fabricate weir bath heaters which are a variation of the standard water bath heater but one that does not include a conventional process coil. These types of heaters are most commonly used to re-boil amine and glycol Solutions.
A weir bath heater is constructed from a main bath vessel which to one end contains a firetube, process fluid is then circulated through the main shell, causing it to become heated. During this heating cycle, the expansion of the process fluid causes it to flow over a weir where it is then circulated back into the process.