PROCESS

Abstract

A process for the manufacture of a useful product from carbonaceous feedstock of fluctuating compositional characteristics, comprising the steps of: continuously providing the carbonaceous feedstock of fluctuating compositional characteristics to a gasification zone; gasifying the carbonaceous feedstock in the gasification zone to obtain raw synthesis gas; recovering at least part of the raw synthesis gas from the gasification zone and supplying at least part of the recovered raw synthesis gas to a partial oxidation zone; equilibrating the H.sub.2:CO ratio of the raw synthesis gas in the partial oxidation zone to obtain equilibrated synthesis gas; recovering at least part of the equilibrated synthesis gas from the partial oxidation zone and treating the gas to remove impurities and generate a fine synthesis gas; and converting the optionally adjusted fine synthesis gas into the useful product in a further chemical reaction requiring a usage ratio.

Claims

1. A process for the manufacture of a useful product from carbonaceous feedstock of fluctuating compositional characteristics, the process comprising the steps of: continuously providing the carbonaceous feedstock of fluctuating compositional characteristics to a gasification zone; gasifying the carbonaceous feedstock in the gasification zone to obtain raw synthesis gas; recovering at least part of the raw synthesis gas from the gasification zone and supplying at least part of the recovered raw synthesis gas to a partial oxidation zone; equilibrating the H.sub.2:CO ratio of the raw synthesis gas in the partial oxidation zone to obtain equilibrated synthesis gas; recovering at least part of the equilibrated synthesis gas from the partial oxidation zone; optionally adjusting the H.sub.2:CO ratio of at least part of the equilibrated synthesis gas to obtain adjusted equilibrated synthesis gas; treating the optionally adjusted equilibrated synthesis gas to remove impurities and generate a fine synthesis gas; optionally adjusting the H.sub.2:CO ratio of at least part of the fine synthesis gas to obtain adjusted fine synthesis gas; and converting the optionally adjusted fine synthesis gas into the useful product in a further chemical reaction with a particular usage ratio; wherein the fine synthesis gas H.sub.2:CO ratio is below the usage ratio and wherein any optional adjustment of at least part of the fine synthesis gas H.sub.2:CO ratio is effective only to increase the H.sub.2:CO ratio in the fine synthesis gas to a level at, nearer to or above the usage ratio; wherein the H.sub.2:CO ratio of the raw synthesis gas fluctuates during operation of the process as a result of the fluctuating compositional characteristics of the carbonaceous feedstock by a percentage of ±x; and the H.sub.2:CO ratio of the equilibrated synthesis gas does not fluctuate during operation of the process or fluctuates during operation of the process as a result of the fluctuating compositional characteristics of the carbonaceous feedstock by a percentage ±y, y being a lower percentage than x.

2. A process according to claim 1 wherein the reaction conditions effective to produce a useful product or the include a desired feed ratio of H.sub.2:CO and the equilibrated synthesis gas H.sub.2:CO ratio is consistently below that desired feed ratio.

3. A process according to claim 1 wherein the useful product produced in the reaction corresponds to a certain H.sub.2:CO usage ratio and the equilibrated synthesis gas H.sub.2:CO ratio is consistently below that usage ratio.

4. A process according to claim 1 wherein the useful product produced in the reaction corresponds to a certain H.sub.2:CO usage ratio and the optionally adjusted fine synthesis gas H.sub.2:CO ratio is consistently at or no more than 20% above or below that usage ratio.

5. A process according to claim 1 wherein x is a percentage in the range of from 1 to 300 and y is a percentage in the range of from 0 to 20.

6. A process according to claim 1 wherein y is at least 10% lower, at least 25% lower, at least 40% lower or at least 50% lower than x.

7. A process according to claim 1 being a continuous process wherein carbonaceous feedstock is continuously fed to a gasification zone for gasifying the feedstock.

8. A process according to claim 1 effective to equilibrate the H.sub.2:CO ratio in the raw synthesis gas regardless of the compositional makeup of the carbonaceous feedstock.

9. A process according to claim 1 wherein the carbonaceous feedstock comprises at least one of woody biomass, municipal solid waste and/or commercial and industrial waste.

10. A process according to claim 1 wherein the step of gasifying the carbonaceous feedstock comprises gasifying the carbonaceous feedstock in the presence of steam and oxygen.

11. A process according to claim 1 wherein the raw synthesis gas from the gasification zone has an exit temperature of at least 600° C., of at least 700° C., or of at least 800° C.

12. A process according to claim 1 wherein the partial oxidation zone is non-catalytic.

13. A process according to claim 1 wherein the partial oxidation zone operates at a temperature of least 1100° C., at least 1200° C., or at least 1300° C.

14. A process according to claim 1 wherein the fine synthesis gas is low sulphur containing gas, wherein the low sulphur containing gas has a sulphur content of less than 0.1 ppmv.

15. A process according to claim 1 wherein at least a portion of the optionally adjusted fine synthesis gas is sent to a Hydrogen Recovery Unit (HRU), optionally wherein the HRU produces high purity hydrogen, wherein the high purity hydrogen is at least 97%, at least 98%, at least 99% pure.

16. The process according to claim 15 wherein the high purity hydrogen is used in upstream and/or downstream processes, wherein the high purity hydrogen is at least 97%, at least 98%, at least 99% pure.

17. A process according to claim 1 wherein the process further comprises the step of sequentially removing ammoniacal, sulphurous and carbon dioxide impurities from the equilibrated synthesis gas.

18. A process according to claim 1 wherein the useful product is produced by subjecting at least part of the optionally adjusted fine synthesis gas to a Fischer-Tropsch conversion.

19. The process according to claim 18 wherein the Fischer-Tropsch conversion is effective to convert the optionally adjusted fine synthesis gas into liquid hydrocarbons.

20. The process according to claim 19 wherein the liquid hydrocarbons are upgraded into the useful product.

21. The process according to claim 20 wherein least a part of the liquid hydrocarbons are upgraded by at least one of hydroprocessing, product fractionation, hydrocracking and/or isomerisation to produce the useful product.

22. A process according to claim 1 wherein the useful product comprises synthetic paraffinic kerosene and/or naphtha.

23. The process according to claim 22 wherein the synthetic paraffinic kerosene and/or naphtha is used for transportation fuel or as a gasoline blendstock.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0180] FIG. 1 depicts a schematic diagram of a process applying conventional teaching in the prior art for undertaking FT synthesis from multiple feedstock sources or a feedstock source with variable composition. The section highlighted by the dashed area highlights steps which are not required for the process in accordance with the present invention.

[0181] FIG. 2 depicts a schematic diagram of the process according to the present invention.

[0182] Referring to FIG. 1, prior art processes conventionally require different routes for the synthesis gas after gasification, depending on whether the hydrogen to carbon monoxide ratio in the generated raw synthesis gas is higher or lower than the usage ratio for the desired reaction, in order to obtain synthesis gas suitable for the required synthesis, which has been depicted as FT synthesis. Prior art processes are not able to handle varying hydrogen to carbon monoxide ratios in the feed that are on either side of the usage ratio using the same process equipment and therefore require different routes before feeding optionally adjusted fine synthesis gas streams to the FT synthesis unit. Comparing the schematic of FIG. 1 to FIG. 2, the process according to the present invention eliminates several stages that are required in the conventional prior art process, thus simplifying the overall process and provides a process with a reduced number of stages.

[0183] The elimination of these stages is made possible due to the presence of a partial oxidation zone which equilibrates the hydrogen to carbon monoxide ratio in the raw synthesis gas leaving the gasification zone to a small window below the usage ratio, independent of the feedstock employed. Therefore, it is not necessary to separate the processing steps based on whether the hydrogen to carbon monoxide ratios in the feed are lower or higher than usage ratios, as in the prior art processes, in order to obtain the desired ratio for an FT reaction. This is because the H.sub.2:CO ratio in the equilibrated synthesis gas exiting the partial oxidation zone will be homogenised and always lower than the usage ratio. The process according to the present invention is therefore beneficial in providing a process that offers flexibility in relation to the feedstock used and reduces the need for additional stages downstream. This can be seen in the Examples illustrated below.

[0184] FIG. 3 depicts a graph of the hydrogen to carbon monoxide ratio of the raw synthesis gas exiting the gasification zone and the equilibrated synthesis gas exiting the partial oxidation zone in accordance with the present invention when different feedstock sources are used. FIG. 3 also highlights the typical hydrogen to carbon monoxide ratio of the synthesis gas desired for a FT reaction and the typical usage ratio observed in the FT reaction. The results demonstrate the equilibration of usage ratio upon exiting the partial oxidation zone independent of the source of feedstock.

[0185] FIG. 4 depicts a graph of the mol % of CH.sub.4 present in the synthesis gas exiting the gasification zone and the partial oxidation zone in accordance with the present invention when different feedstock sources are used. The results demonstrate the significant reduction in CH.sub.4 present in the synthesis gas exiting the partial oxidation zone in comparison to the gasification zone, indicating that more of the carbon is captured and utilized in the process.

[0186] FIG. 5 depicts a graph showing the effect that the partial oxidation operating temperature has on the hydrogen to carbon monoxide ratio and mol % of CH.sub.4 in the equilibrated synthesis gas leaving the partial oxidation zone. The partial oxidation zone temperature may be used as a lever to tune the methane slip and the hydrogen to carbon monoxide ratio in the equilibrated synthesis gas.

[0187] The invention will now be more specifically described with reference to the following non-limiting examples.

EXAMPLES

[0188] Table 1 outlines different sources of feedstock compositions that were used in accordance with the present invention to obtain synthesis gas used for a FT process.

[0189] The % moisture content of the feedstock after preliminary feedstock handling and drying is also indicated.

TABLE-US-00001 TABLE 1 Feedstock Composition/% High (40%) Household Commercial plastic Moisture Ex waste waste Food Paper content waste Hardwood Pine content/% 1 100 10 2 70 30 10 3 70 30 15 4 100 10 5 100 10 6 100 10 7 25 75 —

[0190] Examples 1 to 7 are all feedstocks for use in the process of the invention.

[0191] Process

[0192] Each of Examples 1 to 7 are treated as follows:

[0193] The feedstock of each Example is initially processed by the removal of large contra-material, recyclates (e.g. metals, ferrous and non-ferrous) and inerts such as glass, stone and grit. The resulting treated feedstock is then comminuted and dried to a desired moisture content (in this case 10%) to obtain Solid Recovered Fuel (SRF).

[0194] The SRF is supplied continuously at a pre-determined rate to a fluidised bed gasification unit operated at a temperature of approximately 700° C., a pressure of approximately 2.2 barg and supplied with superheated steam to effect the gasification and produce a raw synthesis gas having a first H.sub.2:CO ratio.

[0195] The raw synthesis gas exits the gasifier and is supplied to an oxygen-fired partial oxidation reactor maintained at a temperature above 1250° C. and supplied with all of the raw synthesis gas at generated from the gasification step described above while adjusting the oxygen rate to achieve the target temperature. The partial oxidation reaction converts residual methane and other hydrocarbons into synthesis gas and generates an equilibrated synthesis gas having a second H.sub.2:CO ratio.

[0196] 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 (e.g. HCl), nitrous oxides and any remaining particulates.

[0197] 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.

[0198] The secondary gas cleanup process includes various guard beds to remove materials such as mercury, arsenic and phosphorus along with additional sulfur polishing beds which serve as (FT) inlet guard beds.

[0199] 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 feedstream (to the desired ratio) as it recombines.

[0200] Optionally adjusted fine 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.

[0201] The synthetic FT liquids are hydrocracked, hydroisomerised and then hydrotreated. Subsequently they are fractionated into LPG, naphtha and SPK.

[0202] Table 2 shows the usage ratio of the synthesis gas exiting the gasification and the partial oxidation zone (also depicted in FIG. 3).

TABLE-US-00002 TABLE 2 H.sub.2:CO (mol/mol) Ex Gasification Zone Exit Partial oxidation Zone Exit 1 1.11 0.85 2 1.15 0.86 3 1.22 0.89 4 1.09 0.84 5 3.05 1.00 6 0.51 0.87 7 2.01 0.84

[0203] Table 3 shows the relative percentage variation between each pair of the Examples in the H.sub.2:CO ratio at the gasification zone exit, calculate as (column/row-1). Negative numbers indicate a lower H.sub.2:CO than one being compared with.

TABLE-US-00003 TABLE 3 Example 1 2 3 4 5 6 7 1 4 10 −2 175 −54 81 2 −3 6 −5 165 −56 75 3 −9 −6 −11 150 −58 65 4 2 6 12 180 −53 84 5 −64 −62 −60 −64 −83 −34 6 118 125 139 114 498 294 7 −45 −43 −39 −46 52 −75

[0204] Table 4 shows the relative percentage variation between each of the Examples in the H.sub.2:CO ratio at the partial oxidation zone exit, calculate as (column/row-1). Negative numbers indicate a lower H.sub.2:CO than one being compared with.

TABLE-US-00004 TABLE 4 Example 1 2 3 4 5 6 7 1 X 1.2 4.7 −1.2 17.6 2.4 −1.2 2 −1.2 X 3.5 −2.3 16.3 1.2 −2.3 3 −4.5 −3.4 X −5.6 12.4 −2.2 −5.6 4 1.2 2.4 6.0 X 19 3.6 0 5 −15 −14 −11 −16 X −13 −16 6 −2.3 −1.1 2.3 −3.4 14.9 X −3.4 7 1.2 2.4 6.0 0 19 3.6 X

[0205] It will be seen in comparing each of Tables 3 and 4 that the percentage difference between the H.sub.2:CO ratios of each example compared to each other example is consistently lower and in many cases very substantially lower at the partial oxidation exit than it is at the gasification zone exit.

[0206] It can be seen from the results in Tables 3 & 4 above and FIG. 3 that the hydrogen to carbon monoxide ratio of the raw synthesis gas exiting the gasification zone varies substantially depending on the feedstock employed. Different syntheses require specific desired ratios for hydrogen to carbon monoxide in feed. Also illustrated in FIG. 3 are the typical desired H.sub.2:CO feed ratio of the synthesis gas and the usage ratio for a FT reaction.

[0207] It can also be seen from the results that the equilibrated synthesis gas leaving the partial oxidation zone has significantly reduced the variability in the hydrogen to carbon monoxide ratio for the different feedstock compositions compared to the hydrogen to carbon monoxide ratios of the raw synthesis gas exiting the gasification zone. Therefore, the use of a partial oxidation zone in accordance with the present invention equilibrates the hydrogen to carbon monoxide ratio of the synthesis gas exiting partial oxidation zone independent of the source of feedstock used and irrespective of the hydrogen to carbon monoxide ratio of the raw synthesis gas exiting the gasification zone (and subsequently entering the partial oxidation zone).

[0208] The synthesis gas leaving the partial oxidation zone may be fed into a WGS reactor prior to the FT reaction in accordance with the present invention to obtain a desired ratio for hydrogen to carbon monoxide within the highlighted range consistent with a typical FT feed ratio that is below the usage ratio. The WGS reaction is used to increase the hydrogen to carbon monoxide ratio of the synthesis gas exiting the partial oxidation zone to fall within the typical FT synthesis feed range. Thus, without the partial oxidation zone in the present invention Examples 5 and 7 would not fall within such values and would require alternative treatment to reduce the hydrogen to carbon monoxide ratio.

[0209] Table 5 shows the % mol content of CH.sub.4 exiting the gasification and partial oxidation zone in accordance with the present invention. As can be seen by the results, there is a significant reduction in the presence of CH.sub.4 leaving the partial oxidation zone compared to the gasification zone. The reduction in CH.sub.4 impurities is important for increasing the capture and recovery of carbon from the feedstock to the product. The partial oxidation zone converts residual methane into carbon oxides.

TABLE-US-00005 TABLE 5 CH.sub.4 (% mol) Ex Gasification Zone Exit partial oxidation Zone Exit 1 7.9 0.02 2 7.8 0.03 3 7.4 0.02 4 7.1 0.01 5 3.0 0.01 6 10.2 0.04 7 5.2 0.15

[0210] The H.sub.2:CO in the gas exiting the partial oxidation zone can be influenced by the operating temperature of the partial oxidation. However, thermal partial oxidation is typically operated at temperatures above 1200° C. to minimize the CH.sub.4 slip. The syngas data corresponding to Example 2 above is used to illustrate this relationship in Table 6.

TABLE-US-00006 TABLE 6 Gasification partial oxidation partial oxidation mol % exit H.sub.2:CO Temperature (° C.) exit H.sub.2:CO CH.sub.4 1.15 1000 1.25 3.99% 1.15 1050 1.11 1.13% 1.15 1100 1.06 0.29% 1.15 1150 1.01 0.07% 1.15 1200 0.96 0.02% 1.15 1250 0.92 0.01% 1.15 1300 0.88 0.00% 1.15 1350 0.84 0.00% 1.15 1400 0.81 0.00%