Fischer-tropsch synthesis process and system

Abstract

The present invention relates to a Fischer-Tropsch synthesis process and system. The process comprises: a) introducing a feedstock gas containing CO and H 2 into a first stage Fischer-Tropsch synthesis reactor to carry out a Fischer-Tropsch synthesis reaction; b) separating products of the first stage Fischer-Tropsch synthesis reaction, to separate water from the unconverted tail gas and to obtain hydrocarbon products and the unconverted tail gas; c) introducing the unconverted tail gas obtained in Step b) into a second stage Fischer-Tropsch synthesis reactor to carry out a Fischer-Tropsch synthesis reaction; d) separating products of the second stage Fischer-Tropsch synthesis reaction, to separate water from the unconverted tail gas, with a portion of the unconverted tail gas of the second stage Fischer-Tropsch synthesis reaction being returned to the second stage Fischer-Tropsch synthesis reactor for recycle reactions. The process and system are suitable for large-scale industrialized production.

1 . A two-stage Fischer-Tropsch synthesis process, comprising the following steps:
 a) a first stage Fischer-Tropsch synthesis reaction
 introducing a feedstock gas containing CO and H 2  into a first stage Fischer-Tropsch synthesis reactor to carry out a Fischer-Tropsch synthesis reaction under the action of catalysts, to obtain products of the first stage Fischer-Tropsch synthesis reaction; wherein the CO conversion rate in the first stage Fischer-Tropsch synthesis reactor is controlled at 30%-70%; 
   b) separation of the products of the first stage Fischer-Tropsch synthesis reaction
 separating the products of the first stage Fischer-Tropsch synthesis reaction, so as to separate water from the unconverted tail gas and to obtain hydrocarbon products and an unconverted tail gas of the first stage Fischer-Tropsch synthesis reaction; 
   c) a second stage Fischer-Tropsch synthesis reaction
 introducing the unconverted tail gas obtained from Step b) into a second stage Fischer-Tropsch synthesis reactor to carry out a Fischer-Tropsch synthesis reaction under the action of catalysts, to obtain products of the second stage Fischer-Tropsch synthesis reaction; 
   d) separation of the products of the second stage Fischer-Tropsch synthesis reaction
 separating the products of the second stage Fischer-Tropsch synthesis reaction, so as to separate water from the unconverted tail gas and to obtain hydrocarbon products and an unconverted tail gas of the second stage Fischer-Tropsch synthesis reaction, with a portion of the unconverted tail gas of the second stage Fischer-Tropsch synthesis reaction being returned to the second stage Fischer-Tropsch synthesis reactor for recycle reactions, 
   wherein the unconverted tail gas of the first stage Fischer-Tropsch synthesis reaction is not returned to the first stage Fischer-Tropsch synthesis reactor for recycle reactions; in Step a), the fresh synthetic gas as the feedstock gas passes through the first stage Fischer-Tropsch synthesis reactor in one way, and   wherein the separations in Steps b) and d) comprise oil-water-gas separations of top products of the Fischer-Tropsch synthesis reactions.   
     
     
         2 . The two-stage Fischer-Tropsch synthesis process according to  claim 1 , wherein the volume ratio of CO to H 2  in the feedstock gas is 0.67-2.2. 
     
     
         3 . The two-stage Fischer-Tropsch synthesis process according to  claim 1 , wherein the oil-water-gas separation of the top product of the first stage Fischer-Tropsch synthesis reaction in Step b) and/or the oil-water-gas separation of the top product of the second stage Fischer-Tropsch synthesis reaction in Step d) comprise the following steps:
 firstly, carrying out a flash separation with thermal high pressure separators to obtain thermal high pressure separator liquids and thermal high pressure separator gases;   then, carrying out a flash separation for the thermal high pressure separator gases using cold high pressure separators to obtain two phases: the cold high pressure separator liquids being blended liquid phase products of light distillate oil and water, and the cold high pressure separator gases being the unconverted tail gases.   
     
     
         4 . The two-stage Fischer-Tropsch synthesis process according to  claim 3 , further comprising:
 e) introducing the thermal high pressure separator liquids of the first stage and second stage Fischer-Tropsch synthesis reactions to a thermal low pressure separator, carrying out a flash separation to obtain heavy distillate oil products as a thermal low pressure separator liquid and a thermal low pressure separator gas; and   f) introducing the cold high pressure separator liquids of the first stage and second stage Fischer-Tropsch synthesis reactions and the optional thermal low pressure separator gas to a cold low pressure separator, carrying out a flash separation to obtain a cold low pressure separator gas, a light distillate oil product, and a water.   
     
     
         5 . The two-stage Fischer-Tropsch synthesis process according to  claim 3 , wherein:
 The thermal high pressure separators is operated at 120-220° C.;   The cold high-pressure separators is operated at 5-60° C.   
     
     
         6 . The two-stage Fischer-Tropsch synthesis process according to  claim 4 , wherein:
 The thermal low-pressure separator is operated at 60-200° C.;   The cold low-pressure separator is operated at 5-60° C.   
     
     
         7 . The two-stage Fischer-Tropsch synthesis process according to  claim 1 , wherein the CO conversion rate in the first stage Fischer-Tropsch synthesis reactor is controlled at 40%-65%. 
     
     
         8 . The two-stage Fischer-Tropsch synthesis process according to  claim 1 , wherein the first stage Fischer-Tropsch synthesis reaction in Step a) and/or the second stage Fischer-Tropsch synthesis reaction in Step c) are carried out under the following reaction conditions:
 The reaction temperature is 200-320° C.;   The reaction pressure is 15-50 bar;   The superficial gas velocity of reactor inlet gas is 10-40 cm/s;   The ratio (i.e. gas catalyst ratio) of volumetric flow of reactor inlet gas to the mass of catalyst is 2000-50000 Nml/g-cat./h.   
     
     
         9 . The two-stage Fischer-Tropsch synthesis process according to  claim 1 , wherein the first stage Fischer-Tropsch synthesis reactor and the second stage Fischer-Tropsch synthesis reactor is one slurry bed reactor or a plurality of slurry bed reactors in parallel. 
     
     
         10 . The two-stage Fischer-Tropsch synthesis process according to  claim 1 , wherein the volume ratio of CO to H 2  in the feedstock gas is 1.4-2. 
     
     
         11 . The two-stage Fischer-Tropsch synthesis process according to  claim 1 , wherein, the catalysts used in Steps a) and c) are iron-based or cobalt-based catalysts. 
     
     
         12 . The two-stage Fischer-Tropsch synthesis process according to  claim 1 , wherein, the unconverted tail gas of the second stage Fischer-Tropsch synthesis reaction is blended with all unconverted tail gases of the first stage Fischer-Tropsch synthesis reaction, then is introduced into the second stage Fischer-Tropsch synthesis reactor. 
     
     
         13 . The two-stage Fischer-Tropsch synthesis process according to  claim 1 , wherein, the feedstock gas in Step a) is a synthetic gas underwent purification and water gas shift. 
     
     
         14 . The two-stage Fischer-Tropsch synthesis process according to  claim 1 , wherein, the water content in the unconverted tail gas entering the second stage Fischer-Tropsch synthesis reactor is less than 0.05% by volume. 
     
     
         15 . A two-stage Fischer-Tropsch synthesis system, comprising:
 A) a first stage Fischer-Tropsch synthesis reactor, containing Fischer-Tropsch synthesis catalysts, the first stage Fischer-Tropsch synthesis reactor at least comprising:
 a first stage reactor inlet, located at the bottom of the first stage Fischer-Tropsch synthesis reactor; 
 a first stage reactor top outlet, located at the top of the first stage Fischer-Tropsch synthesis reactor; 
 a first stage Fischer-Tropsch synthesis wax or slurry outlet, located at a slurry bed zone of the first stage Fischer-Tropsch synthesis reactor; 
   B) a first stage separation system, for separating a top product from the first stage reactor top outlet, thereby separating water from the unconverted tail gas to obtain hydrocarbon products and unconverted tail gas of the first stage Fischer-Tropsch synthesis reaction; the first stage separation system comprising:
 a first stage separation system inlet, connected with the first stage reactor top outlet; 
 a plurality of first stage separation system outlets, comprising: 
 a first stage hydrocarbon product outlet, and 
 a first stage unconverted tail gas outlet; 
   C) a second stage Fischer-Tropsch synthesis reactor, containing Fischer-Tropsch synthesis catalysts, the second stage Fischer-Tropsch synthesis reactor at least comprising:
 a second stage reactor inlet, located at the bottom of the second stage Fischer-Tropsch synthesis reactor, and connected with the first stage unconverted tail gas outlet; 
 a second stage reactor top outlet, located at the top of the second stage Fischer-Tropsch synthesis reactor; 
 a second stage Fischer-Tropsch synthesis wax or slurry outlet, located at a slurry bed zone of the second stage Fischer-Tropsch synthesis reactor; 
   D) a second stage separation system, for separating a top product from the second stage reactor top outlet, thereby separating water from the unconverted tail gas to obtain hydrocarbon products and unconverted tail gas of the second stage Fischer-Tropsch synthesis reaction, the second stage separation system comprising:
 a second stage separation system inlet, connected with the second stage reactor top outlet; 
 a plurality of second stage separation system outlets, comprising: 
 a second stage hydrocarbon product outlet, and 
 a second stage unconverted tail gas outlet; 
   wherein the first stage unconverted tail gas outlet is not connect with the first stage reactor inlet, such that the fresh synthetic gas as the feedstock gas passes through the first stage Fischer-Tropsch synthesis reactor in one way;   wherein B) the first stage separation system and/or D) the second stage separation system comprise an oil-water-gas separation device.   
     
     
         16 . The two-stage Fischer-Tropsch synthesis system according  claim 15 , wherein the first stage Fischer-Tropsch synthesis reactor and the second stage Fischer-Tropsch synthesis reactor is one slurry bed reactor or a plurality of slurry bed reactors in parallel. 
     
     
         17 . The two-stage Fischer-Tropsch synthesis system according  claim 15 , wherein the number of the first stage Fischer-Tropsch synthesis reactors is greater than or equal to the number of second stage Fischer-Tropsch synthesis reactors. 
     
     
         18 . The two-stage Fischer-Tropsch synthesis system according  claim 17 , wherein oil-water-gas separation systems of B) the first stage separation system and/or D) the second stage separation system comprise:
 thermal high pressure separator(s), comprising:
 a thermal high pressure separator inlet, connected with the first stage separation system inlet or the second stage separation system inlet, 
 a thermal high pressure separator liquid outlet, and 
 a thermal high pressure separator gas outlet; 
   cold high pressure separator(s), comprising:
 a cold high pressure separator inlet, connected with the thermal high pressure separator gas outlet, 
 a cold high pressure separator liquid outlet, and 
 a cold high pressure separator gas outlet. 
   
     
     
         19 . The two-stage Fischer-Tropsch synthesis system according  claim 18 , further comprising:
 a thermal low pressure separator, comprising:
 a thermal low pressure separator inlet, connected with the thermal high pressure separator liquid outlet(s) of the first stage separation system and/or the second stage separation system, 
 a thermal low pressure separator gas outlet, 
 a thermal low pressure separator liquid outlet; 
   optionally, a cold low pressure separator, comprising:
 a cold low pressure separator inlet, connected with the thermal low pressure separator liquid outlet and/or the cold high pressure separator liquid outlet, 
 a cold low pressure separator gas outlet, 
 a light distillate oil outlet, 
 a Fischer-Tropsch synthesis water outlet. 
   
     
     
         20 . The two-stage Fischer-Tropsch synthesis system according  claim 18 , further comprising a CO 2 -removing system, the CO 2 -removing system comprising:
 a CO 2 -removing solvent inlet,   a CO 2 -removing solvent outlet,   a CO 2 -removing system gas inlet, connected with the cold high pressure separator gas outlet,   a CO 2 -removing system gas outlet, connected with the second stage reactor inlet.   
     
     
         21 . The two-stage Fischer-Tropsch synthesis system according to  claim 15 , wherein the first stage Fischer-Tropsch synthesis reactor is one slurry bed reactor or a plurality of slurry bed reactors in parallel, and the second stage Fischer-Tropsch synthesis reactor is one slurry bed reactor. 
     
     
         22 . The two-stage Fischer-Tropsch synthesis system according to  claim 15 , further comprising:
 a wax filter, arranged inside or outside the first stage Fischer-Tropsch synthesis reactor and the second stage Fischer-Tropsch synthesis reactor.   
     
     
         23 . The two-stage Fischer-Tropsch synthesis process according to  claim 1 , wherein, when iron-based catalysts are adopted, the volume ratio of H 2  to CO in the feedstock gas is 1.4-1.8; when cobalt-based catalysts are adopted, the volume ratio of H 2  to CO in the feedstock gas is 1.8-2.2. 
     
     
         24 . The two-stage Fischer-Tropsch synthesis process according to  claim 12 , wherein the blend volume ratio of the unconverted tail gas of the second stage Fischer-Tropsch synthesis reaction to the unconverted tail gas of the first stage Fischer-Tropsch synthesis reaction is 0.5-5. 
     
     
         25 . The two-stage Fischer-Tropsch synthesis process according to  claim 12 , wherein CO 2  in the unconverted tail gas of the second stage Fischer-Tropsch synthesis reaction is removed before the blending.