Maximizing syngas carbon utilization and conversion to biofuel
It is provided a process for optimizing syngas carbon utilisation and syngas purity from a varying scrubbed syngas source before feeding into a syngas conversion unit comprising the steps of feeding a scrubbed syngas into a purification unit comprising at least one absorption unit to remove CO 2 from the scrubbed syngas, producing a clean CO+H 2 +CO 2 syngas stream and a CO 2 rich stream; and mixing the clean CO+H 2 +CO 2 syngas stream with hydrogen producing a balanced syngas stream, wherein the balanced syngas stream meet the stoichiometric ratio and purity requirement of the syngas conversion unit.
1 . A process for optimizing syngas carbon utilization and syngas purity for subsequent syngas conversion into a downstream syngas conversion unit from a scrubbed syngas source comprising the steps of:
a) feeding a scrubbed syngas into a purification unit comprising at least one absorption unit to partially remove CO 2 from said scrubbed syngas, producing a clean syngas stream adjusted to optimal target carbon content and a CO 2 rich stream, wherein the purification unit is an acid gas removal unit (AGR), wherein in said AGR,
CO 2 and sulfur species are absorbed from the scrubbed syngas in said at least one absorption unit using a selective solvent, producing a loaded solvent and a clean syngas stream;
the loaded solvent is withdrawn through at least one recirculation loop;
the loaded solvent is pre-flashed at an intermediate pressure to recover absorbed H 2 and CO, producing a CO 2 rich stream rich in H 2 and CO and a flashed solvent stream;
the flashed solvent is flashed at lower pressure to recover CO 2 , generating a non-flammable CO 2 rich stream and a second flashed solvent; and
the second flashed solvent is stripped in a first stripping unit to remove the sulfur species, producing a rich sulfur species stream and a clean solvent which is recycled back into the absorption unit;
b) mixing the clean syngas stream with hydrogen producing a balanced syngas stream, wherein the balanced syngas stream meets a stoichiometric ratio requirement of the syngas conversion unit; and
c) feeding said balanced syngas stream in said syngas conversion unit.
2 . The process of claim 1 , wherein the sulfur species is H 2 S, COS, CS 2 , or a combination thereof.
3 . The process of claim 1 , wherein the at least one absorption unit further removes nitrogen contaminant species and produces an additional nitrogen contaminant rich stream.
4 . The process of claim 1 , wherein the scrubbed syngas source comprises between 25 to 45 mol % of H 2 , 30 to 65 mol % of CO and 6 to 40 mol % of CO 2 and/or wherein the clean syngas stream composition comprises 30% to 50 mol % H 2 , 40 to 68 mol % CO and 0 to 25 mol % CO 2 .
5 . The process of claim 1 , further comprising a step of recycling the CO 2 rich stream for use as inerting gas, exporting said CO 2 rich stream for Carbon Capture and Storage (CCS), and/or producing saleable merchant CO 2 from said CO 2 rich stream.
6 . The process of claim 1 , wherein a first portion of the loaded solvent is withdrawn through a first recirculation loop and a second portion of the loaded solvent is withdrawn through a second recirculation loop, and where,
the first portion of the loaded solvent is pre-flashed at an intermediate pressure recovering the H 2 and CO contained in the loaded solvent, producing a first CO 2 stream rich in H 2 and CO and a first flashed solvent, and the second portion of the loaded solvent is pre-flashed at an intermediate pressure recovering H 2 and CO contained in the loaded solvent, producing a second CO 2 stream rich in H 2 and CO and a second flashed solvent;
the first flashed solvent is flashed at lower pressure generating a non-flammable CO 2 rich stream and a clean solvent which is recycled back into the absorption unit;
the first and second CO 2 streams rich in H 2 and CO are recycled in the scrubbed syngas stream upstream of the absorption unit; and
the second solvent is stripped in a first stripping unit to remove sulfur species, producing a rich sulfur species stream and a clean solvent which is recycled back into the absorption unit.
7 . The process of claim 1 , wherein the selective solvent of the purification unit further removes a sulfur species, and nitrogen species, producing a rich sulfur and nitrogen species stream.
8 . The process of claim 7 , wherein a first portion of the loaded solvent is withdrawn through a first recirculation loop, a second portion of loaded solvent is withdrawn through a second recirculation loop, and a third portion of loaded solvent is withdrawn through a third recirculation loop where;
the first portion of the loaded solvent is pre-flashed at an intermediate pressure recovering the H 2 and CO contained in the loaded solvent, producing a first CO 2 stream rich in H 2 and CO and a first flashed solvent; and the second portion of the loaded solvent is pre-flashed at an intermediate pressure recovering H 2 and CO contained in the loaded solvent, producing a second CO 2 stream rich in H 2 and CO and a second flashed solvent; and, optionally, the third portion of the loaded solvent is pre-flashed at an intermediate pressure recovering the H 2 and CO contained in the loaded solvent, producing a third CO 2 stream rich in H 2 and CO and a third flashed solvent;
the first flashed solvent is flashed at lower pressure generating a non-flammable CO 2 rich stream and a clean solvent which is recycled back into the absorption unit;
the first, second and optional third CO 2 streams rich in H 2 and CO are recycled in the scrubbed syngas stream upstream of the absorption unit; and
the second flashed and third flashed solvents, or unflashed solvents are stripped in a stripping unit to remove the sulfur species, and nitrogen species, producing a rich sulfur and nitrogen species stream and a clean solvent which is recycled back into the absorption unit.
9 . The process of claim 1 , wherein the non-flammable CO 2 rich stream is further used as inerting gas, recovered for Carbon Capture and Storage (CCS) and/or to produce saleable merchant CO 2 .
10 . The process of claim 1 , further comprising treating the clean syngas stream with at least one solid adsorbent bed before or after mixing the clean syngas stream with hydrogen.
11 . The process of claim 1 , wherein an H 2 S concentration in the clean syngas stream is adjusted to achieve a specific desired concentration, to meet the requirement of the downstream syngas conversion unit; while achieving low level of HCN and/or NH 3 concentration.
12 . The process of claim 1 , wherein the hydrogen mixed with the clean syngas is imported from an external source.
13 . The process of claim 1 , wherein the purification unit comprises chilled methanol as a solvent.
14 . The process of claim 1 , wherein the balanced syngas stream meets the stoichiometric ratio requirement of the syngas conversion unit to produce fuel, a chemical, or a Fischer Tropsch product.
15 . The process of claim 1 , wherein the scrubbed syngas is from a gasification and/or reforming of a carbonaceous material.
16 . The process of claim 12 , further comprising admixing an external source of CO 2 or CO 2 input from another process effluent into the clean syngas stream along with the external source of hydrogen to produce a balanced syngas further boosted in carbon that meets the stoichiometric ratio of the desired end product, thus further increasing the production of the desired end product.
17 . The process of claim 1 , further comprising a reverse water gas shift (RWGS) unit to convert a portion of the CO 2 along with a portion of the hydrogen to generate additional carbon monoxide prior to the syngas conversion unit.
18 . The process of claim 1 , wherein CO 2 is recycled back to a carbonaceous feedstock gasification and/or reforming unit to reduce the scrubbed syngas source H 2 /CO ratio, increasing a total CO yield and production, and generating a boosted CO scrubbed syngas and a boosted CO clean syngas.
19 . The process of claim 1 , wherein the purification unit comprises a stripping unit including a split loading stripper column with at least a top and bottom mass transfer zone sections, where nitrogen species loaded methanol is fed at the top of the stripper column and above the top mass transfer zone, while the sulfur species loaded methanol is fed in the middle of the stripper column in between the top and bottom mass transfer zone sections.