RECOVERY OF HEAT FROM PYROLYSIS FLUE GAS
It has been discovered that heat energy may be captured from the flue gas from a pyrolysis reactor, which was previously lost due to exhausting. More particularly, it has been discovered that residual heat energy from pyrolysis flue gas 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) pyrolyzing a feedstock comprising a liquefied waste plastic to produce a pyrolysis effluent stream, wherein the pyrolyzing comprises combusting a pyrolysis fuel to thereby form a pyrolysis flue gas and provide heat for the pyrolyzing;
(b) liquefying at least a portion of a waste plastic with the application of heat in a liquification system to form the liquefied waste plastic, wherein at least a portion of the heat used for the liquefying of the waste plastic is recovered from the pyrolysis flue gas; and
(c) further heating at least a portion of the liquefied waste plastic, wherein at least a portion of the heat used for the further heating is recovered from the pyrolysis flue gas.
2 . The process according to claim 1 , wherein the liquefying of step (b) occurs in a convection section through which at least a portion of the pyrolysis flue gas passes, wherein the liquification system is located in the convection section.
3 . The process according to claim 1 , further comprising providing a convection section through which at least a portion of the pyrolysis flue gas passes, wherein the liquification system is located outside of the convection section.
4 . The process according to claim 1 , wherein the liquefying of step (b) comprises melting at least a portion of the waste plastic.
5 . The process according to claim 1 , wherein the further heating step comprises passing the liquefied waste plastic through a plurality of tubes in a convection section.
6 . The process according to claim 1 , further comprising providing a heat transfer medium loop containing at least one heat transfer medium, wherein at least a portion of the heat used for the liquefying of step (b) is recovered from the heat transfer medium.
7 . The process according to claim 6 , wherein the heat transfer medium comprises steam.
8 . The process according to claim 6 , wherein the heat transfer medium comprises an oil.
9 . The process according to claim 6 , further comprising heating at least a portion of the heat transfer medium via indirect heat exchange with the pyrolysis flue gas to form a heated heat transfer medium.
10 . The process according to claim 1 , wherein the further heating step forms a heated liquefied waste plastic stream having a temperature of at least 300° C.
11 . A chemical recycling process comprising:
(a) pyrolyzing a feedstock comprising a liquefied waste plastic to produce a pyrolysis effluent stream, wherein the pyrolyzing comprises combusting a pyrolysis fuel to thereby form a pyrolysis flue gas and provide heat for the pyrolyzing;
(b) liquefying at least a portion of a waste plastic in a liquification system to form the liquefied waste plastic and a halogen-containing waste stream, wherein at least a portion of the heat used for the liquefying of the waste plastic is recovered from the pyrolysis flue gas;
(c) further heating at least a portion of the liquefied waste plastic in a convection section, wherein at least a portion of the heat used for the further heating is recovered from the pyrolysis flue gas; and
(d) recovering a carbon dioxide stream from at least a portion of the pyrolysis flue gas after the liquefying of step (b) and the further heating of step (c).
12 . The process according to claim 11 , wherein the liquification system comprises at least one melt tank.
13 . The process according to claim 11 , further comprising providing a pump for facilitating movement of the liquefied waste plastic, and wherein the further heating step comprises passing the liquefied waste plastic through a plurality of tubes in a convection section.
14 . The process according to claim 11 , wherein the heat transfer medium comprises steam or oil.
15 . The process according to claim 11 , further comprising heating at least a portion of the heat transfer medium via indirect heat exchange with the pyrolysis flue gas to form a heated heat transfer medium.
16 . The process according to claim 11 wherein the liquefied waste plastic stream exiting the liquification system has a temperature of at least 200, at least 225, at least 250, at least 275, at least 300, at least 310, at least 320, at least 330, or at least 340° C. and/or less than 450, less than 425, less than 400, less than 375, or less than 350° C.
17 . The process according to claim 11 , wherein the further heating step forms a heated liquefied waste plastic stream having a temperature of at least 250, at least 275, at least 300, at least 325, at least 350, at least 375, at least 400, at least 425, or at least 450° C. and/or less than 700, less than 650, less than 600, less than 550, or less than 500° C.