Reduction of NOx Emissions From Fired Heaters With Combustion Air Preheaters

Abstract

A fired heater unit is disclosed having a radiant section having a high emissivity coating therein. The fired heater unit also includes a burner for mixing fuel and preheated air to produce flue gas to be used in heating operations within the unit, and a preheater for heating ambient air with the flue gas to produce the preheated air for use in the burner. Other process streams are heated with the flue gas in the radiant section and a convection section operatively connected to the radiant section prior to venting the flue gas to atmosphere. The fired heater unit, and associated processes, result in a reduction of NOx emissions over conventional systems and methods.

What is claimed is: 
     
         1 . A fired heater unit having a first end and a second end, the fired heater unit comprising:
 a burner at the first end for mixing a fuel stream and a preheated combustion air stream to produce a first flue gas stream;   a radiant section operatively connected to the burner, wherein the radiant section includes a high emissivity coating on at least one interior wall of the radiant section, wherein the radiant section is configured to transfer heat by radiant heat transfer from the first flue gas stream to a first process stream to produce a second flue gas stream and a first heated process stream;   a convection section operatively connected to the radiant section, wherein the convection section is configured to transfer heat by convection from the second flue gas stream to a second process stream to produce a third flue gas stream and a second heated process stream; and   a plenum operatively coupled to the convection section and the second end, wherein a preheater unit is operatively connected to the plenum, wherein the preheater unit transfers heat from the third flue gas stream to an ambient air stream to produce a flue gas stream for venting through the second end and the preheated combustion air stream.   
     
     
         2 . The fired heater unit of  claim 1 , wherein the high emissivity coating is a ceramic material comprising small particles of one or more inorganic materials. 
     
     
         3 . The fired heater unit of  claim 2 , wherein the inorganic materials are selected from the group consisting of: silicon, aluminum, iron, titanium, sodium, potassium, calcium, magnesium, zirconium, and boron. 
     
     
         4 . The fired heater unit of  claim 1 , further comprising a forced draft blower that supplies the ambient air stream to the preheater unit. 
     
     
         5 . The fired heater unit of  claim 1 , further comprising an induced draft fan to pull the flue gas stream for venting to atmosphere. 
     
     
         6 . The fired heater unit of  claim 1 , comprising a flow path from the first end to the second end, wherein the flue gas streams flow along the flow path from the first end to the second end. 
     
     
         7 . The fired heater unit of  claim 1 , wherein the second end is open such that the flue gas stream for venting exits the fired heater unit through the second end. 
     
     
         8 . A process for reducing NOx emissions from a fired heater unit, the process comprising:
 mixing a fuel stream and a preheated air stream in a burner to produce a flue gas stream;   flowing the flue gas stream to a radiant section of the fired heater unit to heat by radiant heat transfer a first process stream to produce a first heated process stream, wherein the radiant section includes a high emissivity coating for increasing efficiency on at least one interior wall of the radiant section;   flowing the flue gas stream to a convection section operatively connected to the radiant section to heat by convection a second process stream to produce a second heated process stream;   flowing the flue gas stream to a preheater unit in a plenum operatively coupled to the convection section to heat an ambient air stream to produce the preheated air stream to the burner; and   venting the flue gas stream to atmosphere.   
     
     
         9 . The process of  claim 8 , wherein the high emissivity coating is a ceramic material comprising small particles of one or more inorganic materials. 
     
     
         10 . The process of  claim 9 , wherein the inorganic materials are selected from the group consisting of: silicon, aluminum, iron, titanium, sodium, potassium, calcium, magnesium, zirconium, and boron. 
     
     
         11 . The process of  claim 8 , further comprising supplying the ambient air stream to the preheater unit with a forced draft fan. 
     
     
         12 . The process of  claim 8 , further comprising venting the flue gas to atmosphere with an induced draft fan.