Direct Fired Heater (Process heater)
A combustion-fired heat transfer system that raises the temperature of process fluids flowing inside tubes.
AITESA designs and manufactures API 560 fired heaters (also known as process heaters or process furnaces), tailored to each process for maximum performance.
How does a direct fired heater work?
In a direct fired heater, the combustion of the liquid or gaseous fuel takes place, and the heat released is transferred by radiation to the tubes through which the fluid circulates in the radiant section, subsequently, the fumes generated by the combustion transfer heat by convection to the tubes through which the fluid circulates in the convective section.
The process furnaces operate under vacuum, and the fumes are evacuated through a chimney that generates the necessary draft in all sections of the furnace. The draft regulation in the radiation ceiling is done through a damper in the chimney.
The parts of a process furnace, therefore, are:
- Radiant sectionThe furnace is the lower part of the furnace, it is internally insulated and the burners are located at the bottom. The tubes through which the process fluid to be heated circulates are smooth.
- Convective sectionLocated above the radiant section. The tubes are out of the reach of the flame. In this section we can differentiate two zones:
- Lower zone or shock zone: the tubes through which the fluid circulates are smooth and are exposed to the radiation of the combustion chamber.
- Upper zone: where the tubes may have an extended surface (fins or pins) to improve heat transfer conditions.
- Chimneylocated above the convective section, it is designed to have sufficient draft for smoke evacuation.
Process Furnace at Repsol
Petroperú Process Furnace
Types of ovens Which one do you need?
Depending on the type of process, duty, space and customer requirements, a furnace type is designed.
Aitesa designs the following types of furnaces:
- Horizontal cylindrical kiln: Up to 1 Gcal/h.
It has a horizontal combustion chamber without tubes and 1 burner located at the bottom of the horizontal flame chamber. The tubes through which the process circulates are arranged in a convective zone arranged so that it does not receive incidence of the flame, the tubes are placed horizontally.
- Vertical cylindrical furnaceThey can be with radiant zone only or with radiant + convective zone.
-Only radiant: Up to 3 Gcal/h.
It has vertical or helicoidal smooth tubes. The burners are located on the floor in a circular arrangement.
-Radiant+convective: Up to 25 Gcal/h.
It has smooth vertical or helical tubes in the radiant section. In the convective zone, with smooth tubes in the 2/3 rows of horizontal tubes in the impingement zone, downstream of the impingement zone, horizontal tubes with smooth or normally extended (finned/pitoned) surface are arranged to increase the heat exchange efficiency. The burners are located on the floor arranged in a circle.
- Cabin/double cabin oven: Up to 150 Gcal/h.
They have a radiant + convective zone. In the case of double cabin furnaces, the radiant section is a double chamber, and the combustion gases converge at the top in a single convective.
There can be several arrangements of tubes in the radiant:
- Arbor: The tubes are arranged in a U-shape or inverted U-shape. The process fluid is heated only by radiation. In the convective process, the heat of the fumes is usually used to heat another fluid such as steam or thermal oil. The burners are placed at the bottom of the furnace in a linear fashion along the cabinet.
- Horizontal pipesThe tubes are positioned horizontally on the side walls of the radiant heater. The burners can be positioned at the bottom of the oven or on the front walls.
- StandpipesThe tubes are positioned vertically on the side walls or in the center of the radiant heater. The burners are positioned on the floor in a linear way along the cabin. In the case of the coil located in the central zone of the radiant, the burners are positioned in 2 rows on both sides of the tubes.
Not sure which one you need? Our team of experts can analyze your process and recommend the best solution.
At AITESA we study each specific case to obtain the best process furnace.
Key benefits for your industry
Adaptation to the capacity needs of the industry.
Due to the types of furnaces that exist and the flexibility they present, their design can be adapted to the production needs and capacities of the industry.
Process control and increased safety
Due to the instrumentation implemented in the process furnaces, it is possible to have a process temperature control, as well as a combustion control that improves the furnace performance by optimizing fuel consumption. Likewise, the safety functions implemented in the process furnaces reduce the risk of accidents.
Regulatory compliance and emissions reduction
The furnaces can be designed with combustion air preheated through preheating systems. This reduces fuel consumption and CO2 emissions.
There are different types of air preheating:
- Air preheating system with the fumes coming from the furnace through an APHThe air preheating system: it consists of using the heat of the fumes coming from the furnace that pass through an APH where the heat exchange between air and fumes takes place. This type of air preheating system has 1 or 2 forced draft air blowers and 1 induced draft flue gas blower. The burners will be designed for forced draft.
- Air preheating system with external heat source exchanger or forced draft: consists of preheating the air through a heat exchanger, where the heat exchange between the steam or other fluid and the combustion air takes place. This type of air preheating system has 1 or 2 forced draft air blowers. The burners will be designed for forced draft.
The burners are designed with low NOx, to reduce emissions and comply with current regulations.
Overall performance improvement
The overall performance of the furnaces can be increased by installing banks of tubes in the upper zone of the convective through which water or steam circulates, so that by taking advantage of the heat of the fumes, reheating and/or steam production takes place. In this way, in addition to improving the overall performance of the furnace, one or two additional services to the main one of the furnace, which is the heating of the process fluid, are available.
Moeve Process Furnace in San Roque
Trust us to supply you with the best direct fired heater.
Process furnace assembly
Key factors in choosing the right oven
Sizing and capacity
- Heat absorbed
- Space limitations
- Adaptability to existing installations
Process conditions
- Flow rate
- Temperature
- Pressure
- Allowable radiant flux
- Fouling factor
- Fluid velocity
Type of fluid
- Liquid, vapor or two-phase
- Characterization of the load: HC, HC+H2, thermal oil,…
Performance required
- With or without combustion air preheating
- With heating and/or steam production service.
Fuel type and composition
- Gas
- Liquid
- Mixed
Compliance with international regulations
- API 560: Fired Heaters for General Refinery Service
- API 535: Burners for Firedc Heaters in General Refinery Services
- API 530: Calculation of Heater-tube Thickness in Petroleum Refineries
- API 556: Instrumentation, Control, and Protective Systems for Gas Fired Heaters
- ASME STS-1 Stacks 2016
- ASME II: Materials
- ASME B31.3. Process Piping
- ASME B16.5. Pipe Flanges and Flanged fittings
Compliance with customer specifications
- Adaptation to specific customer requirements
At AITESA we are experts in the design of process furnaces / direct fired heaters.
Why choose an AITESA process furnace?
More than 5000 projects in strategic sectors
- 40 years of experience in designing, adapting and modifying process furnaces
- Adaptation to demanding environments such as refineries, petrochemical and industrial plants, where every degree of efficiency optimizes profitability..
Maximum efficiency and minimum emissions
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- Proven and optimized designs: our experience allows us to guarantee robust and safe solutions for every industry.
- Reduced environmental impact with minimum heat loss and maximum thermal efficiency.
- Reduction of emissions, with advanced burner technologies and implementation of heat recovery systems.
Comprehensive technical support and maintenance
- Maximum operational availability thanks to preventive and corrective maintenance.
- Fast response and guaranteed supply to reduce downtime.
- Solutions to problems
We not only design furnaces, we create energy solutions that optimize your production, reduce costs and ensure regulatory compliance.
Frequently Asked Questions
How much does implementing a heat recovery system increase furnace performance?
Process furnaces without heat recovery have an efficiency of approximately 80-82%, whereas if a heat recovery system is installed, the efficiency can increase to 90-94%, depending on the type of system.
What are the most important variables to control in a furnace and what are the safeties?
The most important controls in a process furnace are:
- Product outlet temperature control through fuel feed valves
- Control of excess air through the O2 content in the radiation ceiling. It is recommended to maintain between 2.5 % / 3% O2 in the fumes to ensure complete and optimal combustion.
- Radiation ceiling draft control, through the damper located in the chimney. It is recommended to maintain a radiation ceiling draft between (-) 3 / (-) 5 mm.w.c. to ensure good performance and operation of the furnace.
- Tube metal temperature control, measured by thermoskines installed in the radiation and shock tubes. High values may be indicative of flame impingement, high film temperature and coke formation, with possible consequence of tube breakage.
Among the variables to be controlled, for furnaces without heat recovery, the following safeguards are implemented:
- High / Very high / Very very very high pressure in radiation ceiling: opening of smoke damper / fuel cut-off to burners / fuel cut-off to pilots
- Very low / Very high fuel pressure to pilots: fuel cut-off to burners and pilots
- Very low / Very high fuel pressure to burners: Fuel cut-off to burners and pilots.
- Emergency shutdown: total oven shutdown
What maintenance does a process furnace require?
The following inspections and maintenance program are suggested:
- Frequent visual inspection paying special attention to pipes, pipe supports and refractory.
- Pipe thickness control during scheduled shutdowns
- Checking the integrity of the refractory, absence of cracks, spalling, etc. In the presence of cracks in a large area, the entire area must be replaced.
- Control of the absence of deformations, curvature of any element or corrosion in structural elements, stairs, walkways, platforms, furnace plate.
- Control of the condition of the external sheet metal, with special attention to the convective roof and chimney.
- Control of bolts and welds, ensuring that they are in good condition.
- Paint, if chipped or otherwise damaged, the affected area will be cleaned and painted.
- Check the operating instruments on a frequent basis to ensure proper operation. In particular, tube skin thermocouples shall be carefully checked.
- Check of the draft damper for corrosion, with special emphasis on the shaft and joints of the operating mechanism.
- Furnace operating data should be recorded throughout the operating life of the furnace. Values of furnace temperatures and load flows shall be available for the calculation of heat absorbed. Temperatures at each step should also be recorded. In addition, combustion chamber and flue gas temperatures, process fluid and fuel pressures, and draft of all furnace sections shall be measured. An emissions analysis of the fumes will be performed at regular intervals to determine their composition. Any unexpected changes in operating loads will be checked by means of the furnace log books.
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Aitesa has more than 40 years of experience designing and supplying heat recovery boilers.
