PROCESS

Abstract

A process for the manufacture of one or more useful products comprises: gasifying a carbonaceous feedstock comprising waste materials and/or biomass in a gasification zone to generate a raw synthesis gas; supplying at least a portion of the raw synthesis gas to a clean-up zone to remove contaminants and provide a clean synthesis gas; supplying the clean synthesis gas to a first further reaction train to generate at least one first useful product and a tailgas; and diverting selectively on demand a portion of at least one of the carbonaceous feedstock, the clean synthesis gas, the tailgas and the light gas fraction to heat or power generation within the process, in response to external factors to control the carbon intensity of the overall process and enable GHG emission savings.

Claims

1. A process for the manufacture of one or more useful products comprising: a. gasifying a carbonaceous feedstock comprising waste materials and/or biomass in a gasification zone to generate a raw synthesis gas; b. supplying at least a portion of the raw synthesis gas to a clean-up zone to remove contaminants and provide a clean synthesis gas; c. importing natural gas and/or power into the process; d. supplying the clean synthesis gas to a first further reaction train to generate at least one first useful product and a tailgas; and e. diverting selectively on demand a portion of at least one of the carbonaceous feedstock, the clean synthesis gas, the tailgas and (if present) a light gas fraction to heat or power generation within the process to control the carbon intensity of the process.

2. The process according to claim 1 wherein means within the process are provided selectively on demand to divert one or more of: i. a portion of the carbonaceous feedstock to a combustor to generate energy for the production of steam for use on plant or for power generation; and/or ii. a portion of the clean synthesis gas as fuel gas for use on plant and/or or for the generation of steam for use on plant and/or for power generation; and/or iii. at least a portion of the tailgas to: the first further reaction train as internal recycle; and/or the partial oxidation zone, when present; and/or the hydrogen to carbon monoxide shifting zone, when present; and/or a fuel gas stream for fuelling the gasification zone; and/or a steam methane reforming zone to generate a reformed tailgas having a higher hydrogen to carbon monoxide ratio than the tailgas and supplying the reformed tailgas as a feed to the first further reaction train; and/or a fuel gas header for use on plant; and/or for the generation of steam for use on plant or for power generation; and/or iv. at least a portion of alight gas fraction (if present) to: a partial oxidation zone, when present; and/or a fuel gas stream for fuelling the gasification zone; and/or a third useful product stream. fuel gas header for use on plant; and/or for the generation of steam for use on plant or for power generation.

3. The process according to claim 1 wherein means are provided selectively on demand to divert both a portion of the carbonaceous feedstock to a combustor to generate energy for the production of steam for use on plant or for power generation, and a portion of the clean synthesis gas as fuel gas for use on plant or for the generation of steam for use on plant or for power generation.

4. The process according to claim 1 wherein means are provided selectively on demand also to divert at least a portion of the tailgas to one or more of the first further reaction train; and/or a partial oxidation zone, when present; and/or a hydrogen to carbon monoxide shifting zone, when present; and/or a fuel gas stream for fuelling the gasification zone; and/or a steam methane reforming zone for additional syngas production and/or or for the generation of steam for use on plant or for power generation.

5. The process according to claim 1 wherein means are provided selectively on demand also to divert at least a portion of a light gas fraction (if present) to one or more of the partial oxidation zone, when present; and/or a fuel gas stream for fuelling the gasification zone; and/or or for the generation of steam for use on plant or for power generation and/or recovery as a useful product.

6. The process according to claim 1 wherein the carbonaceous feedstock has fluctuating compositional characteristics and comprises at least one of woody biomass, municipal solid waste and/or commercial and industrial waste or a combination of these.

7. The process according to claim 1 wherein the process further comprises using a biomass or waste boiler to produce high-pressure steam and power.

8. The process according to claim 1 wherein the removal of contaminants comprises removal of ammoniacal, sulphurous and carbon dioxide impurities, wherein the removal of ammoniacal, sulphurous and carbon dioxide impurities is a low-steam physical absorption process.

9. The process according to claim 8 wherein the process further comprises using at least a portion of the steam gained from the low-steam physical absorption process for use in upstream and/or downstream processes.

10. The process according to claim 9 wherein the upstream process is a feedstock pre-processing step drying the carbonaceous feedstock prior to feeding it into a biomass and/or waste boiler.

11. The process according to claim 10 wherein drying the carbonaceous feedstock results in the carbonaceous feedstock having a moisture content of less than about 20% by weight.

12. The process according to claim 10 wherein drying the carbonaceous feedstock results in the carbonaceous feedstock having a moisture content of less than about 15% by weight.

13. The process according to claim 10 wherein drying the carbonaceous feedstock results in the carbonaceous feedstock having a moisture content of less than about 10% by weight.

14. The process according to claim 1 wherein the first useful product is produced by subjecting the clean synthesis gas to a Fischer-Tropsch synthesis unit.

15. The process according to claim 14 wherein the Fischer-Tropsch synthesis unit converts the clean synthesis gas into liquid hydrocarbons.

16. The process according to claim 15 wherein the liquid hydrocarbons are upgraded into the second useful product.

17. The process according to claim 16 wherein at least a part of the liquid hydrocarbons are upgraded by at least one of hydroprocessing, product fractionation, hydrocracking and/or isomerisation to produce the second useful product.

18. The process according to claim 1 wherein the at least one useful product comprises synthetic paraffinic kerosene and/or diesel and/or naphtha.

19. The process according to claim 1 having a carbon intensity score indicative of at least 60% savings in greenhouse gas emissions comparative to a conventional process for producing the useful product.

20. The process according to claim 1 wherein step a. further comprises partially oxidising the raw synthesis gas in a partial oxidation zone to generate partially oxidised raw synthesis gas.

21. The process according to claim 1 wherein step c. comprises shifting the hydrogen to carbon monoxide ratio of the clean synthesis gas in a hydrogen to carbon monoxide ratio shifting zone to generate shifted clean synthesis gas.

22. The process according to claim 1 wherein step d. comprises upgrading the first useful product in a second further reaction train to generate a second useful product and a light gas fraction.

23. A plant configured to operate the process of claim 1 comprising: a. means for gasifying a carbonaceous feedstock comprising waste materials and/or biomass in a gasification zone to generate a raw synthesis gas; b. means for supplying at least a portion of the raw synthesis gas to a clean-up zone to remove contaminants and provide a clean synthesis gas; c. means for importing natural gas and/or power into the process; d. means for supplying the clean synthesis gas to a first further reaction train to generate at least one first useful product and a tailgas; and e. means for diverting selectively on demand a portion of at least one of the carbonaceous feedstock, the clean synthesis gas, the tailgas and (if present) a light gas fraction to heat or power generation within the process to control the carbon intensity of the process.

24. The plant according to claim 23 wherein means a. further comprises means for partially oxidising the raw synthesis gas in a partial oxidation zone to generate partially oxidised raw synthesis gas.

25. The plant according to claim 23 wherein means c. comprises means for shifting the hydrogen to carbon monoxide ratio of the clean synthesis gas in a hydrogen to carbon monoxide ratio shifting zone to generate shifted clean synthesis gas.

26. The plant according to claim 23 wherein means d. comprises means for upgrading the first useful product in a second further reaction train to generate a second useful product and a light gas fraction.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0218] FIG. 1 depicts a schematic diagram of a process for undertaking FT synthesis from a biomass and/or waste feedstock in accordance with a preferred embodiment of the invention.

[0219] Referring to FIG. 1, a carbonaceous feedstock is supplied in line 1 to variable conveyer 2 and in line 3 to feed dryer 4 and on in line 5 to gasification zone 6. Raw synthesis gas from gasification zone 6 is passed in line 7 to partial oxidation zone 8. Partially oxidised raw synthesis gas passes on in line 9 to water gas shift and gas clean-up zone 10 and on in line 11 to switchable valve 12 and on in line 13 to FT train 14, before passing on in line 15 to upgrading zone 16, generating a second useful product stream in line 17 and a light gas fraction on line 18.

[0220] Means are provided, for example in the form of variable conveyer 2, for diverting on demand a portion of the feed stream in line 1 to a combustor steam generator 19, the steam from which may be used in line 20 to generate power for the plant (or elsewhere) in power generator 21. Alternatively (not shown) the steam may be used on plant.

[0221] Means are provided, for example in the form of switchable valve 12, for diverting on demand a portion of the clean synthesis gas in line 11 to steam generator 19 in line 22, or as fuel gas to the gasification zone 6 in line 23.

[0222] Means are provided, for example in the form of switchable valve 24, for diverting on demand a portion of the tailgas in line 25 to FT reactor train as internal recycle (not shown), to steam generator 19 in line 26, which may further be used in power generator 21, to partial oxidation zone 8 in lines 27 and 28, to the gasification zone 6 as fuel gas in line 29, to water gas shift and gas clean up zone 10 in lines 27 and 30, or to steam methane reforming zone 31 in line 32 for generating a reformed tailgas for recycling in line 33 to line 11, or to the fuel gas header (not shown).

[0223] Means are provided, for example in the form of switchable valve (not shown), for diverting on demand a portion of the light gas fraction 18 to tertiary product recovery, to the partial oxidation zone 8, when present, to the gasification zone 6 for use as fuel gas, to the fuel gas header (not shown), or to the steam generator 19 to produce steam for use on plant and/or to generate power for the plant in power generator 21.

[0224] The invention will now be more specifically described with reference to the following non-limiting examples.

EXAMPLES

[0225] A municipal solid waste or woody biomass feedstock was selected.

[0226] Process

[0227] The selected feedstock is treated as follows:

[0228] The feedstock is initially processed by comminuting it to the required size and drying to a desired moisture content (in this case 10% w/w) to obtain dried MSW or biomass feedstock.

[0229] The dried MSW or biomass feedstock is supplied continuously to a fluidised bed gasification unit operated at a temperature of <800° C., a pressure of 2.2 barg and supplied with superheated steam to effect the gasification and produce approximately 5-10 lbmol/hr of raw synthesis gas per short ton of feed per day (STPD).

[0230] The raw synthesis gas exits the gasifier and is supplied to an oxygen-fired partial oxidation reactor maintained at a temperature of approximately 1,250° C. and supplied with all of the raw synthesis gas generated from the gasification step described above while adjusting the oxygen rate to achieve a target temperature. The partial oxidation reaction converts residual methane and other hydrocarbons into synthesis gas.

[0231] The resulting hot equilibrated synthesis gas is cooled (by generating superheated and saturated high-pressure steam) to a temperature below 200° C. and is then routed through a primary gas cleanup unit where it passes through a venturi scrubber to knock-out water and particulates (such as soot and ash), after which it is caustic-washed to remove ammonia, halides (eg HCl), nitrous oxides and any remaining particulates.

[0232] The synthesis gas is then compressed and routed through a secondary gas cleanup and compression system in which acid gas (H.sub.2S and CO.sub.2) removal is effected by the Rectisol™ process using a methanol solvent which “sweetens” the synthesis gas

[0233] Approximately 1-2 lbmol/hr/STPD of acid gas is sent to the battery limit for CO.sub.2 capture. The acid gas stream comprises small quantities of H.sub.2 (<0.5 mol %), CO (<0.5 mol %), H.sub.2O (<5%) and N.sub.2 (˜10%).

[0234] A portion of synthesis gas is extracted and recycled as fuel for the gasifier.

[0235] A portion of the synthesis gas stream is passed through a Water Gas Shift (WGS) unit to adjust the hydrogen to carbon monoxide (H.sub.2:CO) ratio in the total feed stream as it recombines.

[0236] Throughout the secondary gas cleanup process various guard beds are positioned to remove materials such as mercury, arsenic and phosphorus.

[0237] The sweetened and shifted synthesis gas is passed through a final Fischer-Tropsch (FT) inlet guard bed before being sent to the FT Synthesis Unit.

[0238] Purified synthesis gas is sent to the FT microchannel reactors where, in the presence of a cobalt catalyst supported on a silica/titania support, it is converted into synthetic liquid hydrocarbons.

[0239] Purged/excess tailgas is sent to the POx and the fuel gas system.

[0240] The FT reaction water is sent to the wastewater treatment unit where it is fractionated into a distillate containing alcohols and a bottoms fraction containing organic acids. The bottom stream is then upgraded biologically for reuse in the facility.

[0241] The synthetic FT liquids are hydrocracked, hydroisomerised and then hydrotreated. Subsequently transportation fuel is obtained from the upgrading unit.

[0242] Wastewater recovered from different process units is sent to a Wastewater Treatment unit before disposal or possible reuse.

[0243] Results

[0244] A few representative examples of the different approaches described above are summarized below:

Example 1

[0245] Table 1 illustrates a comparison of the facility performance for 2 scenarios (using municipal solid waste as feedstock). Case A illustrates the situation corresponding to a minimization of the natural gas import (in order to reduce the carbon intensity score and also to reduce operating cost). To achieve this, a part of the syngas generated from gasification of the feedstock is used as fuel in the combustion heaters for the gasification unit. In comparison, Case B illustrates a situation where natural gas is imported and all generated syngas is used for fuel production. It is clear from table below, that ˜14% production can be gained by importing natural gas instead of the syngas being used as fuel. However, the carbon intensity score is negatively affected.

TABLE-US-00001 TABLE 1 Case B Case A Maximize Minimize fuel NG import production MSW dry to gasifier, t/d ~1000     1X Syngas from gasification, (lbmol/h/stpd) ~7     1X O2 usage from gasification + POx ~50     1X (lb/h/stpd) Syngas used as fuel, (lbmol/h/stpd) ~1.4 0 Syngas to FT, (lbmol/h/stpd) ~4 ~5 FT C.sub.5.sup.+ product, BPD ~1,270 ~1.14X Power import, MW ~25     1X Natural gas import, lb/h/stpd 0.77 3.22 % Natural gas imported as fuel for 84.0% 96.2% gasification % FT Tailgas recycle as fuel 39.6% 51.3% % FT Tailgas recycle to POx 60.4% 48.7% Relative CI score, g(CO.sub.2-eq)/MJ (high) (low)

Example 2

[0246] Table 2 compares the impact of FT tailgas recycle to the POx unit in order to reduce the natural gas import to improve the carbon intensity score of the facility (using municipal solid waste as feedstock). A small reduction in production of the order 1% is observed while NG import is reduced by approximately 30%.

TABLE-US-00002 TABLE 2 Case B Case C No FT Tailgas FT Tailgas recycle to recycle to POx POx MSW dry to gasifier, t/d ~1000     1X Syngas from gasification, (lbmol/h/stpd) ~7     1X O2 usage from gasification + POx ~50     1X (lb/h/stpd) Syngas used as fuel, (lbmol/h/stpd) 0 0 Syngas to FT, (lbmol/h/stpd) ~5     1X FT C.sub.5.sup.+ product, bpsd ~1,440 ~1.02X Power import, MW ~25   ~1X Natural gas import, lb/h/stpd 3.22 4.49 % Natural gas imported as fuel for 96.2% 39.6% gasification % Natural gas imported POx   0% 48.5% % FT Tailgas recycle as fuel 51.3%  100% % FT Tailgas recycle to POx 48.7%   0% Relative CI score, g(CO.sub.2-eq)/MJ (low) (high)

Example 3

[0247] Table 3 below compares the impact of FT tailgas recycle to the WGS unit in order to reduce the natural gas and power import to improve the carbon intensity score of the facility (using biomass as feedstock). For the case of no FT tailgas recycle, all tailgas is assumed to be used for production of additional SH/HP steam and superheated MPS in the flue gas boiler. All superheated steam is used for power generation. The absence of tailgas recycle reduces the syngas to FT and therefore the FT C.sub.5.sup.+ product production, but it also reduces both the power and natural gas import which has the effect of reducing the carbon intensity score of the facility. The facility design will be based on a trade-off between the carbon intensity score and revenue generation from the sale of transportation fuel products.

TABLE-US-00003 TABLE 3 No FT FT Base Tailgas Tailgas case recycle to WGS Biomass dry, stpd ~1,000     1X     1X Syngas from gasification, ~8     1X     1X lbmol/h/stpd O.sub.2 usage from gasification + POx ~50  ~0.9X  ~0.9X (lb/h/stpd) Syngas compression power/duty, ~9 ~0.89X ~0.91X MW Syngas to FT, lbmol/h/stpd ~5 ~0.88X ~0.98X FT C.sub.5.sup.+ product, BPD ~1600 ~0.90X ~0.95X LP steam excess, lb/h/stpd ~48   ~1X ~0.88X Power import, MW ~22 ~0.97X ~0.95X Natural gas import, MMSCFD ~6 ~0.74X ~0.82X Relative CI score g(CO.sub.2-eq)/MJ (high) (low) (mid)