Waste Heat Recovery Systems
Waste heat can be recovered from a thermal oxidizer in a convection section to provide a return on an environmental process. Usually some amount of supplemental stabilizing fuel is required in the thermal oxidizer burner. The thermal oxidizer barrel is never equipped with tubes to absorb radiant heat. This allows the combustion to occur at a specific adiabatic temperature for a known residence time to achieve the desired destruction efficiency.
If soot producing liquids are to be combusted in the thermal oxidizer, the waste heat recovery coils are often equipped with soot blowers. For processes producing NOx, SCR systems can also be employed. The waste heat can be recovered in either forced or natural circulation water tube boilers or hot oil systems. Forced circulation boilers are often preferred because the BFW is pumped through the tubes, virtually guaranteeing that there will never be a dry tube. High temperature pumps and pump seals have been perfected that make maintenance on these systems very reasonable.
Hot oil systems are an alternate to boilers. They have the advantage of being able to deliver a fluid at higher temperatures than steam (up to 650°F) and at much lower pressure. BORN has built high capacity hot oil WHR systems that deliver over 50 MMBtu/hr. Hot oil systems employ an expansion tank positioned to maintain suction head on the circulation pumps. The hot oil never circulates through the expansion tank as a rule.