Recovery of heat from low pressure waste streams

Abstract

It has been discovered that heat energy may be captured from typical waste streams, such as flue gas streams, that were previously lost due to exhausting. More particularly, it has been discovered that residual heat energy from various waste streams in a chemical recycling facility may be used to preheat waste plastic streams and provide heat for waste plastic pyrolysis. Consequently, the pyrolysis processes and systems described herein may obtain a lower carbon footprint.

1 . A chemical recycling process comprising:
 (a) liquefying at least a portion of a waste plastic in a liquification system to form a liquefied waste plastic;   (b) pyrolyzing at least a portion of the liquefied waste plastic to produce a pyrolysis effluent; and   (c) preheating at least a portion of an initial stream with a fluid energy source, wherein the initial stream comprises one or more of the following—
 (i) the waste plastic subjected to the liquefying of step (a), 
 (ii) a combustion fuel stream used to generate heat for the liquefying of step (a) and/or the pyrolyzing of step (b), or 
 (iii) a combustion air stream used to generate heat for the liquefying of step (a) and/or the pyrolyzing of step (b), 
   wherein the fluid energy source has a temperature in the range of 80 to 260° C.   
     
     
         2 . The chemical recycling process according to  claim 1 , wherein the fluid energy source is exhausted after the preheating of step (c). 
     
     
         3 . The chemical recycling process according to  claim 1 , wherein the fluid energy source has an enthalpy of at least 800 BTU/lb. 
     
     
         4 . The chemical recycling process according to  claim 3 , wherein the fluid energy source has an enthalpy of not more than 1,600. 
     
     
         5 . The chemical recycling process according to  claim 4 , wherein the fluid energy source has a pressure of not more than 400 psi. 
     
     
         6 . The chemical recycling process according to  claim 5 , wherein the fluid energy source has a temperature of at least 90° C. 
     
     
         7 . The chemical recycling process according to  claim 6 , wherein the fluid energy source has a temperature of not more than 250° C. 
     
     
         8 . The chemical recycling process according to  claim 7 , wherein the fluid energy source comprises a flue gas, steam, oil, and/or water. 
     
     
         9 . The chemical recycling process according to  claim 8 , wherein the fluid energy source comprises a flue gas. 
     
     
         10 . The chemical recycling process according to  claim 9 , wherein the flue gas is a pyrolysis reactor flue gas, a cracker furnace flue gas, a steam generator flue gas, and/or a combustion turbine flue gas. 
     
     
         11 . The chemical recycling process according to  claim 10 , wherein the fluid energy source comprises a quench stream from a quench system. 
     
     
         12 . The chemical recycling process according to  claim 11 , wherein the preheating of step (c) forms a cooled fluid energy source, further comprising recovering carbon dioxide from the cooled fluid energy source. 
     
     
         13 . The chemical recycling process according to  claim 12 , wherein the cooled flue gas stream has a temperature of not more than 100° C. 
     
     
         14 . A chemical recycling process comprising:
 (a) liquefying at least a portion of a waste plastic in a liquification system to form a liquefied waste plastic;   (b) pyrolyzing at least a portion of the liquefied waste plastic to produce a pyrolysis effluent;   (c) preheating at least a portion of an initial stream with a flue gas stream to thereby form a cooled flue gas stream, wherein the initial stream comprises one or more of the following—
 (i) the waste plastic subjected to the liquefying of step (a), 
 (ii) a combustion fuel stream used to generate heat for the liquefying of step (a) or the pyrolyzing of step (b), or 
 (iii) a combustion air stream used to generate heat for the liquefying of step (a) or the pyrolyzing of step (b); and 
   (d) recovering a carbon dioxide stream from at least a portion of the cooled flue gas stream.   
     
     
         15 . The chemical recycling process according to  claim 14 , wherein the cooled flue gas stream is exhausted after the recovering of step (d). 
     
     
         16 . The chemical recycling process according to  claim 14 , wherein the flue gas stream has an enthalpy of at least 800. 
     
     
         17 . The chemical recycling process according to  claim 16 , wherein the flue gas stream has an enthalpy of not more than 1,600. 
     
     
         18 . The chemical recycling process according to  claim 17 , wherein the flue gas stream has a pressure of not more than 400 psi. 
     
     
         19 . The chemical recycling process according to  claim 18 , wherein the flue gas stream has a temperature of at least 80° C. 
     
     
         20 . The chemical recycling process according to  claim 19 , wherein the flue gas stream has a temperature of not more than 260° C.