Take a tour of an in-depth guide to the features and components of Tulsa Heaters Midstream’s Hydroflux Heater.
A horizontal atmospheric cylindrical vessel designed per API 12K guidelines and filled with a heat transfer medium. For more details, visit our blog: “What’s in the tank?". Key internal components include a firetube/firebox and a process coil. The shell is typically externally insulated to reduce heat losses to the environment.
A submerged fabricated tube or pipe is used to distribute heat generated by the burner to the surrounding fluid. This item is composed of radiant and convection sections. Most of the heat is transferred in the radiant section as the flame and higher temperatures are contained in this section. The convection section downstream of the return bend sees much cooler flue gasses.
Many layout combinations have been implemented, including Trident Tube and W-Tube, but the most common is a simple U-Tube. The firetube is removable for inspection, cleaning and replacement.
The firebox describes the complete assembly, including the firetube, flanges and any adaptors.
PROCESS COIL/TUBE BUNDLE
Typically, this is a serpentine-style design containing gas or liquid indirectly heated for external process requirements. High-pressure conditions generally require the tubes and inlet/outlet manifold to be designed per ASME Section VIII, Division I. Also designed to be removable per API 12K recommendations and 100% radiography NDE commonly performed.
Here is a short description of the source of heat in the heater.
The combustion device fired into the firetube is broken into two categories based on how the combustion air reaches the ignition point and the fuel source. The air can be naturally induced using a venturi effect (natural draft) or mechanically induced by a blower or fan (forced draft). Because it can take time to vent residual fuel out of the firetube, natural draft burners include an intake flame arrester to eliminate potential flashbacks out of the firetube if the pilot or ignitor fails to light the fuel or residual unburned fuel happens to be in the firetube when the burner shuts off.
EXHAUST STACK / FLUE GAS STACK
Like the chimney on a wood stove, the exhaust stack directs hot flue gasses up and away from personnel and provides a source of the draft for natural draft heaters. The stack must be tall enough and have a large enough diameter to generate a sufficient draft. For natural draft burners, many times a downdraft diverter is used if the heater is exposed to high winds to prevent burner stability issues. Spark arrestors are also installed on the top of the stack if local guidelines require (typically offshore applications). Rain shields and bird screens are used to keep the stack and firetube free from water and nesting birds.
EXPANSION TANK / WATER SAVER / ECONOMIZER
An external fluid storage vessel sized to accommodate the thermal expansion volume of the heat transfer medium. Commonly flanged and mounted directly on top of the heater shell. If properly designed, during operation the hot fluid resides in the expansion tank to reduce potential corrosion of the main shell as the expansion tank is more easily inspected and repaired or replaced.
BURNER MANAGEMENT SYSTEM (BMS) & FUEL TRAIN
Safely controlling the operation of a heater is the primary function of a burner management system and associated components include a control panel with a human-machine interface (HMI) or lights/switches. Inside the panel are flame safety modules and/or controllers or electronic boards. Discussion of the BMS is a topic in itself as it can be a simple old-school method of relays with lights and switches or as advanced as a custom engineered PLC. Refer to blog: “Should You Use a PLC to Control Your Heater?”
Additional BMS functions include:
- Controlling the flow of both fuel and air
- Monitoring permissive (limits) and purge cycles
- Lighting the pilots(s) and burner(s)
- Block and bleed the fuel flows after a heater shutdown
A fuel train includes the piping, valves (pressure/block), and instrumentation that the BMS monitors and controls. A wide variety of fuel trains are used depending on the application and preferences.
The National Fire Protection Association developed codes and standards to help reduce the risks associated with designing and operating fire and electric-related equipment. In the heater world, several different NFPA standards are used as guidelines, including NFPA 85, 86, and 87.
Because there is an inherent danger when combustible gasses and electronics are present in the same areas (heater equipment), organizations have developed codes to eliminate potential fires/explosions. The National Electrical Code (NEC) and Canadian Electrical Code (CEC) define hazardous locations as: “An area where a potential hazard (fire, explosion, etc.) may exist under normal or abnormal conditions because of the presence of flammable gasses or vapors, combustible dusts or ignitable fibers of flyings.”
Additional discussion on this topic is found in our blog “The What and Why of Area Classifications” and “Which Control Methodology is Best for You?”.
If any of these terms weren’t clear or if you have a question about a concept, please get in touch with us today. We’re always willing to discuss this topic.