Power recovery for use in start-up or re-start of a pure terephthalic acid production process

Abstract

The invention relates to a method and system for recovering power from the gaseous stream produced by a paraxylene-air oxidation reaction. Specifically, the invention is based on heating the gaseous stream from the oxidation reaction to a temperature of at least 600° C., recovering energy through an expander, heating the expander vent stream and recovering heat from the vent stream. The recovered heat is used to maintain the oxidation process, purification process, start-up the process, or re-start the process after an interruption.

We claim: 
     
         1 . A process for generating and recovering power from a paraxylene-air oxidation reaction to produce terephthalic acid utilising an internal combustion open cycle gas turbine (ICOCGT) which includes a compressor, combustor and expander, wherein the oxidation reaction produces a gaseous stream. comprising:
 a. heating the gaseous stream to a temperature of at least 600° C.;   b. sending the gaseous stream to an ICOCGT expander that drives an ICOCGT compressor, wherein the compressor compresses air fed to the oxidation reactor and the expander emits a gaseous vent stream;   c. feeding the gaseous vent stream to a heat recovery system to produce recovered heat; and   d. generating high grade heat from the recovered heat.   
     
     
         2 . The process of  claim 1 , wherein the heat recovery system comprises a heat exchanger or a combustor feed interchanger. 
     
     
         3 . The process of  claim 1 , wherein said heating is achieved in the ICOCGT combustor. 
     
     
         4 . The process of  claim 1 , further comprising feeding the gaseous stream to a catalytic combustion unit prior to heating to at least 600° C. 
     
     
         5 . The process of  claim 4 , wherein the catalytic combustion unit heats the gaseous stream to a temperature between about 300° C. to about 600° C. 
     
     
         6 . The process of  claim 4  wherein a fuel stream is fed to the ICOCGT combustor. 
     
     
         7 . The process of  claim 1 , wherein the gaseous stream is mixed with a compressed air stream prior to said heating. 
     
     
         8 . The process of  claim 1 , wherein make-up air is added to the compressed air stream in order to balance ICOCGT compressor and ICOCGT expander flows. 
     
     
         9 . The process of  claim 1 , wherein the gaseous stream contacts at least one condenser to substantially remove condensables prior to heating. 
     
     
         10 . The process of  claim 9 , wherein the condensables comprise acetic acid. 
     
     
         11 . The process of  claim 1 , wherein the gaseous vent stream is fed to an auxiliary combustor to produce a heated gaseous vent stream, and the heated gaseous vent stream is fed to the heat recovery system. 
     
     
         12 . The process of  claim 11 , wherein a fuel stream is fed to the auxiliary combustor. 
     
     
         13 . The process of  claim 1 , wherein the high grade heat is recovered as high pressure steam or hot oil, which is used to heat a terephthalic acid purification stage. 
     
     
         14 . The process of  claim 1 , wherein at least a portion of the high grade heat is used in a paraxylene-air oxidation reaction stage. 
     
     
         15 . The process of  claim 1 , wherein the pressure of the air fed to the reactor is boosted by a second compressor. 
     
     
         16 . The process of  claim 1 , wherein the pressure of the gaseous stream is boosted by a second compressor prior to feeding to the ICOCGT expander. 
     
     
         17 . A paraxylene-air oxidation reaction to produce terephthalic acid system, utilising an internal combustion open cycle gas turbine (ICOCGT) which includes a compressor, combustor and expander, comprising:
 a. an oxidation reactor comprising an oxidant inlet and a gaseous stream outlet, wherein said reactor emits a gaseous stream from said gaseous stream outlet;   b. a power recovery system connected to the gaseous stream outlet comprising: (i) a heater for receiving and heating the gaseous stream connected downstream of the gaseous stream outlet; and (ii) an ICOCGT expander positioned downstream of the heater that drives an ICOCGT compressor, wherein the compressor produces a compressed air stream and the expander emits a gaseous vent stream; and   c. a heat recovery system for receiving the gaseous vent stream and producing a high grade heat stream.   
     
     
         18 . The system of  claim 17 , wherein the heat recovery system comprises a heat exchanger and optionally an auxiliary combustor. 
     
     
         19 . The system of  claim 17 , wherein the heater comprises a combustor. 
     
     
         20 . The system of  claim 17 , further comprising a catalytic combustion unit upstream of said heater. 
     
     
         21 . The system of  claim 16 , wherein the catalytic combustion unit heats the gaseous stream to a temperature between about 300° C. and about 600° C. 
     
     
         22 . The system of  claim 19 , wherein the combustor has a fuel stream inlet. 
     
     
         23 . The system of  claim 17 , wherein the gaseous stream is mixed with a compressed air stream prior to entering said heater. 
     
     
         24 . The system of  claim 17 , wherein make-up air is added to the compressed air stream in order to balance ICOCGT compressor and ICOCGT expander flows. 
     
     
         25 . The system of  claim 17 , wherein the gaseous stream is substantially devoid of condensables prior to entering said heater. 
     
     
         26 . The system of  claim 25 , wherein the condensables comprise acetic acid. 
     
     
         27 . The system of  claim 18 , wherein the auxiliary combustor has a fuel stream inlet. 
     
     
         28 . The system of  claim 17 , further comprising a steam generator for receiving the high grade heat stream and producing high pressure steam. 
     
     
         29 . The system of  claim 28 , wherein the high pressure steam is used in a terephthalic acid purification stage. 
     
     
         30 . The system of  claim 17 , wherein at least a portion of the high grade heat stream is used in a paraxylene-air oxidation stage. 
     
     
         31 . The system of  claim 17 , further comprising a hot oil generator for receiving the high grade heat stream and producing hot oil. 
     
     
         32 . The system of  claim 31 , wherein the hot oil is used in a terephthalic acid purification stage. 
     
     
         33 . The system of  claim 17 , further comprising a second compressor connected to the oxidant inlet. 
     
     
         34 . The system of  claim 17 , further comprising a second compressor connected to the gaseous stream outlet prior to the ICOCGT expander. 
     
     
         35 . A process, utilising an internal combustion open cycle gas turbine (ICOCGT) which includes a compressor, combustor and expander, for maintaining the operation of a terephthalic acid oxidation plant following an oxidation reactor trip comprising:
 a. retaining a concentration of oxygen in an ICOCGT combustor sufficient to sustain combustion and generate a combusted gas stream;   b. feeding the combusted gas stream to an ICOCGT expander, which produces a vent gas stream;   c. feeding the vent gas stream to a heat recovery system, with an optional auxiliary combustor, to produce recovered heat; and   d. using the recovered heat to maintain the operation of the terephthalic acid oxidation plant process duties.   
     
     
         36 . The process of  claim 35  further comprising: (e) feeding the recovered heat to a terephthalic acid purification stage. 
     
     
         37 . The process of  claim 35  further comprising: (e) using the recovered heat to start-up a paraxylene-air oxidation reaction. 
     
     
         38 . The process of  claim 35  further comprising: (e) feeding a portion of the recovered heat to a terephthalic acid purification stage and (f) using a portion of the recovered heat to start-up a paraxylene-air oxidation reaction. 
     
     
         39 . The process of  claim 35 , wherein a portion of the recovered heat generates high grade heat as high pressure steam or hot oil. 
     
     
         40 . The process of  claim 35 , wherein the pressure of the air fed to the reactor is boosted by a second compressor. 
     
     
         41 . The process of  claim 35 , wherein the pressure of the gaseous stream is boosted by a second compressor prior to feeding to the ICOCGT expander.