GB2299341A

GB2299341A - Raw synthesis gas

Info

Publication number: GB2299341A
Application number: GB9506256A
Authority: GB
Inventors: Alwyn Pinto
Original assignee: Individual
Current assignee: Individual
Priority date: 1995-03-28
Filing date: 1995-03-28
Publication date: 1996-10-02
Anticipated expiration: 2015-03-28
Also published as: GB9506256D0; GB2299341B

Abstract

In making raw synthesis gas by catalytic steam reforming of hydrocarbons, such gas to be used in making ammonia, urea or alcohols, naphtha is used as a component of process feed and/or reformer fuel by resolving it into two or more of a top fraction (for process feed), a light fraction (for process feed or reformer fuel) and a heavy fraction (for reformer fuel or boiler fuel). Resolution is preferably by stripping with a gas available in the over-all process, for example natural gas, hydrotreater off-gas, unreacted purified synthesis gas or synthesis purge gas.

Description

COMPLETE SPECIFICATION Raw synthesis gas The present invention relates to a process for the preparation of raw synthesis gas from hydrocarbon feedstock comprising naphtha and to processes using such raw gas. In particular it relates to such a process in which natural gas is used more efficiently. It especially relates to a process for the preparation of carbon enriched natural gas for use in preparation of ammonia. More particularly, the present invention relates to a process for producing urea from natural gas.

More particularly, the present invention relates to a process for producing urea by reaction of ammonia and carbon dioxide from natural gas.

Natural gas commonly available is lean in carbon and, therefore, for converting ammonia into urea, an external supply of carbon dioxide is required.

Normally, the imbalance of carbon dioxide is overcome by over reforming and burning the excess hydrogen obtained when natural gas is reformed to produce carbon dioxide.

The natural gas consists essentially of methane which when reformed produces carbon dioxide and hydrogen in accordance with the following equation: CH4 + 2H20 -- > COz + 4H2 The prior art processes attempted to increase the amount of carbon dioxide available by over reforming the natural gas and burning away the excess hydrogen. Thereafter, ammonia is reacted with carbon dioxide to produce urea in accordance with the following equation: 2NH3 + CO2-- > NH2CONH2 + H2O The main problem faced by the prior art methods was as stated above, the fact that feed natural gas is so lean in carbon that to convert ammonia into urea an external supply of carbon dioxide was required coupled with the shortage of the natural gas itself.The prior art itself attempted to overcome this problem by resorting to reforming of higher hydrocarbon feed or employing liquid hydrocarbon for fuel, thereby succeeding, to some extent, in making up the deficiency and shortage of the natural gas. However, such process require expensive burners and use of liquid or vapourised liquid fuel. Reformation of the higher hydrocarbon feed required suitable catalyst as well as, in certain cases, pre-reforming. This not only rendered the process for the preparation of urea highly expensive and complicated but also required different operating procedures for different levels of the process such as reformation of the hydrocarbon to produce natural gas, reformation of natural gas to produce carbon dioxide and reaction of carbon dioxide with ammonia to produce urea.

Such methods were not only safety hazards but also resulted in poor efficiency and were susceptible to operational breakdowns.

Another serious problem faced by the prior art was directly linked to the ammonia synthesis plant conventionally employed in India and most other countries. Conventional ammonia synthesis plants have been built and specifically designed with the natural gas as the initial feed gas in mind. Thus, all the ammonia synthesis plants conventionally employed only natural gas as the initial feedstock and any attempt to change the natural gas feedstock or add a supplementary source of carbon automatically necessitated changing the basic structure of synthesis plants as well. This not only reduced the efficiency of the overall process and conventional plants but also resulted in a tremendous cost escalation making the process counterproductive.

It is, therefore, an object of the present invention to provide a process for the preparation of urea which would overcome the disadvantages of the prior art.

It is a further object of the present invention to provide a process for the preparation of urea employing natural gas effectively enriched in normally liquid hydrocarbons.

It is a yet further object of the present invention to provide in situ enrichment of natural gas with normally liquid hydrocarbons.

It is yet another object of the present invention to provide a process for the enrichment of natural gas to enable it to be employed for ammonia synthesis in conventional plants hitherto employed.

A yet further object of the invention is to provide a process for producing raw synthesis gas as the first stage in the synthesis of ammonia or urea as mentioned or of methanol or higher alcohols.

A particular object of the invention is to provide simple processes for the use of naphtha feedstock, alone or supplementary to natural gas.

These and other objects of the present invention are achieved by the discovery that naphtha or a mixture of similar C4 to C30, especially C5 to Clo, hydrocarbons can be conveniently employed to enrich natural gas for use in urea synthesis.

In the following description reference will be made to 'known subsequent steps' of converting raw synthesis to ammonia synthesis gas or alcohol synthesis gas, and of reacting ammonia with carbon dioxide to give urea. These steps are described in standard texts such as Kirk-Othmer's Encyclopedia of Chemical Technology and need not be detailed herein.

ACCORDING TO THE INVENTION a process, for producing raw synthesis gas by reacting gaseous process feed hydrocarbon with steam in presence of a steam reforming catalyst heated externally by combustion of fuel hydrocarbon, is characterised by: (a) using as source of at least part of the fuel hydrocarbon a normally liquid straight-run petroleum distillate (hereinafter referred to as naphtha) boiling at 1 atmosphere pressure over a range between 20-500C and 100-3000C; (b) resolving that distillate into at least two fractions, including a light fraction boiling over a sub-range up to 50-1200C and a heavy fraction boiling at above that sub-range; (c) feeding the light fraction as fuel hydrocarbon for heating the catalyst; and (d) feeding the heavy fraction as fuel to at least one boiler raising steam.

In a preferred embodiment the process is utilised in ammonia production and comprises, by known subsequent steps, converting the raw synthesis gas to ammonia synthesis gas by introduction of nitrogen, cooling, shift reaction, carbon dioxide removal and final purification, and feeding the resulting synthesis gas to a recycle-type catalytic ammonia synthesis.

More particularly the process is utilised in urea production and comprises, by known subsequent steps, converting the raw synthesis gas to ammonia synthesis gas by introduction of nitrogen, cooling, shift reaction, carbon dioxide removal/recovery and final purification, feeding the resulting synthesis gas to a recycle-type catalytic ammonia synthesis and reacting the so-synthesised ammonia and the recovered carbon dioxide to urea.

In a further embodiment the process is utilised in the production of synthetic alcohols and comprises, by known subsequent steps of cooling and drying, converting the raw synthesis gas to alcohol synthesis gas and feeding the resulting synthesis gas to catalytic alcohol synthesis. Most commonly the alcohol to be synthesised is methanol. Higher alcohols may be synthesised by the 'OXO' process.

The processes so far defined provide a simple means of using naphtha in plant duties for which it is suitable, thus making more natural gas available as process feed, for which naphtha is unsuitable without plant modifications. However, according to a preferred form of the invention naphtha is utilised also to supplement process feed and, in urea production, to improve the carbon dioxide-to-ammonia ratio. The process in this form preferably uses natural gas as process feed and comprises resolving the distillate into three fractions, one of which is a top fraction boiling at 1 atmosphere pressure at up to 1000C and feeding that top fraction with the process feed hydrocarbon to the steam reforming catalyst. Although the top fraction may contain sulphur compounds, this is taken care of by mixing the top fraction with non-desulphurised process feed and desulphurising the mixture before feeding it to the catalyst.

The process feed hydrocarbon is conveniently natural gas.

For urea production the rate of feed of the top fraction can be such as to produce, after the subsequent steps aforementioned, nitrogen N2, hydrogen H2 and carbon dioxide in the molar ratio required for urea synthesis. Steam raised in the boiler in step (d) above is especially used in recovering urea from the reaction product of ammonia and carbon dioxide and to meet the power requirement of the overall press.

For alcohol production the rate of feed of the top fraction is such as to produce nearer-stoichiometric synthesis gas.

When the naphtha top fraction is added to the natural gas, the steam reforming catalyst is, at least at the inlet region of the bed thereof, a carbon resistant catalyst such as a lightly alkalised catalyst.

In a preferred form of the process the distillate is resolved with the aid of stripping gas. This is especially convenient since it enables the resolution to be effected in vesels at above atmospheric pressure, and because gases already available in the processes in which the invention is utilised can be used as stripping gases. Thus unreacted gas from the ammonia synthesis, such as feed gas before final purification or purge gas, can be used. Analogously unreacted gas from alcohol synthesis can be used. When distillate top fraction is to be mixed with gaseous hydrocarbon process feed, such as natural gas, a side stream of that gaseous hydrocarbon is preferably used as stripping gas.

Whether or not a top fraction is taken, stripping gas assists separation of the light and heavy fractions and the process comprises feeding a mixture of that stripping gas and light fraction as fuel to the burners heating the steam reforming catalyst.

More specifically, in urea production enriched gas is combined and fed directly into the ammonia synthesis plant so that the carbon dioxide produced from the carbon enriched natural gas can react with ammonia to produce urea. For this purpose, feed natural gas along with a fraction of total naphtha or other similar hydrocarbons and a recycle gas comprising hydrogen released from ammonia synthesis plant is fed into a reformer, preferably under steam to produce synthesis gas highly enriched in carbon. The carbon enriched gas is subjected to known steps and fed to the process for the preparation of urea where it combines with ammonia under conventional conditions to produce urea. Preferably, the feed gases are at a pressure of 10 to 60 atmospheres and such feed gas naphtha mixture is heated to a temperature of 30 to 1200C.

In a modification of the invention the process feed hydrocarbon is naphtha and the process is characterised by: (i) resolving that distillate into at least three fractions, including a top fraction, a light fraction boiling over a sub-range up to 50-1200C and a heavy fraction boiling at above that sub-range; (ii) using as stripping gas for the top fraction a purge gas containing hydrogen and incombustible and/or other combustible components and using the mixture of such fraction and gas as fuel for heating the steam reforming catalyst and/or at least one boiler; (iv) using the light fraction as process feed.

By this modification fuel gases of low calorific value can be simply upgraded and the process feed naphtha desulphurisation plant duty decreased.

The present invention will now be better described with reference to the accompanying drawings in which: fig 1 is a flowsheet of process steps for resolving naphtha into a top fraction, light fraction and heavy fraction at the inlet of raw synthesis gas production; fig 2 is a flowsheet of the process steps of fig.l but using a different heating procedure; fig 3 is a flowsheet of the process steps of fig.l but using simplified plant items; fig 4 is a flowsheet of a form of the process suitable for naphtha as process feedstock.

In a conventional plant employed for feeding raw feed gas to ammonia synthesis plant,as shown in the drawings a mixture of naphtha and feed natural gas lean in carbon and recycle gas from the ammonia plant is fed to the plant at a pressure of 10 to 50 atmospheres. Such mixture of gas and naphtha is thereafter heated under steam to a temperature of 30 to 120 C. The heated gas is thereafter fed into a conventional separator which separates natural gas highly enriched in carbon from liquid naphtha. The carbon enriched feed gas is sent to the process while the liquid naphtha along with any purge gas from the plant is heated to a temperature of 40 to 1500C. The liquid naphtha is let down from the separator at a pressure of 2 to 20 atmospheres.

The mixture of such purge gas and let down liquid at 40 to 1500C is sent to a further separator. The gas emanating from this separator is recycled to the ammonia plant as fuel to the burners of the reformer furnace whereas the liquid heavy fraction removed therefrom is employed as a fuel to boilers.

The aforesaid process was carried out with specific quantities of naphtha and feed natural gas. The process was carried out at different temperatures and parameters and such processes as well as results of these processes are shown in Tables 1 to 6 following the description of the drawings.

Referring to fig.1, naphtha fed at 110 receives at 112 a feed (to be used as stripping gas) of process feed natural gas and unreacted gas recycled from a downstream synthesis. The mixture is heated by low/medium pressure steam at 114 and passed into separator 116. A mixture of the gases fed at 112 and a top fraction of the naphtha passes out overhead at 118 and is fed via desulphurisation to the inlet of a catalytic steam reforming plant (not shown). The bottoms liquid from 116, a mixture of the light fraction and heavy fraction of the naphtha at 120, is fed via a let down valve to mixing point 122 where it receives a feed of stripping gas which is any one or more of natural gas, unreacted synthesis gas, other fuel gas or (preferably) purge gas from synthesis or hydrogen recovery or off-gas from hydrotreating.The mixture is heated at 124 by low/medium pressure steam and passed into separator 126. The overhead 128 from 126 contains naphtha light fraction and is fed to the burners (not shown) of the furnace heating the steam reforming catalyst. The bottoms liquid 130 from 126 is fed to the burners of a steam-raising boiler (not shown).

Referring to fig.2, a mixture 210 of process feed natural gas and synthesis recycle gas is fed to packed separator 212, in which it contacts on packing 214 a downward stream of warm liquid naphtha and strips a top fraction 216 from it. The resulting enriched gaseous mixture overhead 216 is fed via desulphurisation to the inlet of a catalytic steam reforming plant supplying raw synthesis to the subsequent steps of an ammonia synthesis plant (not shown). The bottoms, a mixture of light fraction and heavy fraction, is in part recycled to separator 212 via pump 218, mixing point 220 at which fresh naphtha is added, heater 222 using low pressure steam and feed point 224. The main bottoms are united at 226 with part, the recycle stream of the heavy fraction from separator 232 to be described and passed via pump 228 and heater 230 to feed point 234 of packed separator 232. In packing 236 it contacts a feed 238 of stripping gas which is any one or more od natural gas, unreacted synthesis gas, other fuel gas or (preferably) purge gas as in fig 1. The overhead mixture 240 of naphtha light fraction and stripping gas is fed to the burners (not shown) of the furnace heating the steam reforming catalyst. The bottoms stream is divided at 242 into the recycle stream abovementioned and a main stream which is fed at 244 as fuel to a steam raising boiler (not shown).

Referring to fig.3, liquid naphtha 310 is fed into combination separator 312 in which it is heated by low pressure steam coil 314 and stripped by a mixture of feed natural gas and recycle gas sparged in at 316. The overhead 318 is fed via desulphurisation to the inlet of a catalytic steam reforming plant supplying raw synthesis gas to the subsequent steps of an ammonia synthesis plant (not showri). The bottoms stream 320 is fed to a second combination separator 322 in which it is heated by low/medium pressure steam coil 324 to a temperature higher than in 312 and stripped by gas sparged in at 326, which gas is any one or more of natural gas, unreacted synthesis gas, other fuel gas or (preferably) purge gas as fig 1.The overhead 328 mixture of naphtha light fraction and stripping gas is fed to the burners (not shown) of the furnace heating the steam reforming catalyst. The bottoms stream 330 is fed to the burners of a steam raising boiler.

Referring to fig.4, liquid naphtha 410 is mixed at 412 with stripping gas which is any one or more of synthesis gas or (preferably) purge gas as in fig 1. The mixture is heated in feed/effluent heat exchanger 420 and low/medium pressure steam heater 414 and passed into separator 416. Separator bottoms 422 is passed out at 424 as fuel to burners (not shown) heating a steam raising boiler or steam reforming catalyst. (Since this figure relates to a process using naphtha both as process feed and as fuel, the reformer burners are, unlike those of natural gas based plants, designed to burn the heavy and light fractions of naphtha).

Separator overhead 418, a mixture of stripping gas and naphtha light fraction, is fed through heat exchangers 420 and 440 to second separator 426. Here it is resolved into a gaseous overhead 428 which, since it contains inerts from purge gas, is used as fuel for burners heating the steam reforming catalyst. Separator bottoms 430 are passed to hydrotreating and/or hydrodesulphurisation and thence to the inlet of the steam reforming catalyst (not shown).

In processes based on natural gas the enriched natural gas is thereafter reacted with steam to give a raw synthesis gas, which in turn is treated by known steps to remove/recover carbon dioxide and produce pure ammonia synthesis gas which is reacted to ammonia; the carbon dioxide is reacted with the ammonia in any conventional manner to produce urea. It must be borne in mind that the process explained in the drawings and examples are for iuustrative purposes only and should not be interpreted to limit the process of the invention in any manner. The process can be carried out suitably depending on the various requirements within the overall ambit of the invention.Typical compositions, pressures and temperatures of streams in the process are shown in the Tables TABLE 1: fig 1 Stream No 110 112 118 122 128 130 Description Naphtha Nay gas Enr gas Prg gas Enr fu Liq fu Compn % vol Methane . 98.39 96.86 9.2 8.21 Ethane . 1.4 1.38 Propane 0.1 0.1 Oxygen 0.1 0.1 Nitrogen 0.01 0.01 21.8 19.45 Argon .. .. 3.5 3.12 Hydrogen .... 65.5 58.43 Naphtha 100.00 .. 1.55 .. 10.79 100.00 Total mols 212.5 1750.0 1777.6 750.0 840.7 94.2 CV Kcal/mole 1042 194 204 56 154 1184 Temp OC 35 35 50 35 50 50 Press Kg/cm2 42 42 40 6 4 50 Mol Wt 96 16.2 17.1 10.3 18.9 108.2 TABLE 2: fig 1 Contacting whole naphtha with natural gas at press 41 bar, temp 50 C A)STREAM NO. 110 112 118 120 B) DESCRIPTION FEED . NAT GAS ENRICHED HP STRIPPED NAT GAS NAPHTHA C)COMPONENTS Kmols Kmols Kmols Kmols BUTANE 15.2 - 11.434 3.766 PENTANE 32.5 - 19.484 13.016 F!EXANE 45.8 - 20.160 25.64 BENZENE 13.0 - 4.840 8.16 TOLUENE 7.0 - 1.612 5.388 HEPTANE 50.0 - 15.370 34.63 OCTANE 13.4 - 2.790 10.61 NONANE 10.0 - 1.409 8.591 DECANE 7.0 - 0.680 6.32 PROPANE 0.0 6.0 5.225 0.775 4METHYL HEPTANE 2.0 - 0.461 1.539 ETHANE 0.0 25.6 24.060 1.54 HYDROGEN 0.0 - - - METHANE 0.0 1801.0 1766.696 34.304 TOTAL 195.9 1832.6 1874.221 154.279 TABLE 3: fig 1 Contacting topped naphtha with purge gas at pressure 4 bar, temp 600C A) STREAM NO. 120 122 128 130 B) DESCRIPTION HP STRIPPED PRG GAS ENRICHED LIQUID NAPHTHA PRG GAS FUEL C) COMPONENTS Kmols Kmols Kmols Butane 3.766 - 3.555 0.211 Pentane 13.016 - 11.521 1.495 Hexane 25.640 - 20.200 5.44 Benzene 8.160 - 6.134 2.026 Toluene 5.388 - 3.129 2.259 Heptane 34.630 - 22.808 11.822 Octane 10.610 - 5.430 5.180 Nonane 8.591 - 3.231 5.360 Decane 6.320 - 1.678 4.642 Propane 0.775 - 0.757 0.018 4 Methylheptane 1.538 - 0.846 0.692 Ethane 1.539 - 1.525 0.014 Hydrogen - 206.13 206.017 . 0.113 Methane 34.304 63.866 97.924 0.246 154.277 269.996 384.755 39.518 TABLE 4: fig 1 Natural gas enrich ment by naphtha at pressure 41 bar, temp 900C A) STREAM NO. 110 112 118 120 B) DESCRIPTION NAPHTHA NAT GAS ENRICHED HP STRIPPED NAT GAS NAPHTHA C) COMPOSITION KmoB Kmo# Kmols Kmols BUTANE 15.2 - 14.635 0.565 PENTANE 32.5 - 30.397 2.103 HEXANE 45.8 - 40.962 4.838 BENZENE 13.0 - 11.403 1.597 TOLUENE 7.0 - 5.613 1.387 HEPTANE 50.0 - 41.989 8.011 OCTANE 13.4 - 10.331 3.069 NONANE 10.0 - 6.922 3.078 DECANE 7.0 - 4.267 2.733 PROPANE - 6.0 5.882 0.118 4METHYL HEPTANE 2.0 - 1.580 0.420 ETHANE - 25.6 25.344 0.256 HYDROGEN METHANE - 1801.0 1794.051 6.949 TOTAL (Kmol) 195.9 1832.6 1993.376 35.124 TABLE 5: fig 4 Contacting purge gas with whole naphtha at pressure 15 bar, temp 900C A) STREAM NO. 410 412 418 424 B) DESCRIPTION NAPHTHA PRG GAS ENRICHED LIOUID PRG GAS FUEL C) COMPOSITION Kmols Kmols Kmols Kmols Butane 10.20 - 6.398 3.802 Pentane 42.50 - 17.198 25.302 Hexane 60.80 - 13.190 47.610 Benzene 13.00 - 2.968 10.032 Toluene 7.00 - 0.758 6.242 Heptone 48.00 - 5.232 42.768 Octane 18.50 - 0.925 17.575 Nonane 0.00 Hydrogen - 238.0 236.409 1.591 Methane - 72.0 69.977 2.023 Total (Kmols) 200.0 310.0 353.055 156.945 TABLE 6: fig 4 Contacting purge gas with whole naphtha at pressure 15 bar, temp 1200C A) STREAM NO. 410 412 418 424 B) DESCRIPTION NAPHTHA PRG GAS ENRICHED LIQUID PRG GAS FUEL C) COMPOSITION Kmols Kmols Kmols Kmols Butane 10.20 - 8.285 1.915 Pentane 42.50 - 28.229 14.271 Hexane 60.80 - 28.898 31.902 Benzene 13.00 - 6.329 6.671 Toluene 7.00 - 2.086 4.914 Heptone 48.00 - 14.633 33.367 Octane 18.50 - 3.187 15.313 Nonane 0.00 Hydrogen - 238.0 236.867 1.133 Methane - 72.0 70.873 1.127 Total (Kmols) 200.0 310.0 399.387 110.613

Claims

Claims 1. Process for producing raw synthesis gas by reacting gaseous process feed hydrocarbon with steam in presence of a steam reforming catalyst heated externally by combustion of fuel hydrocarbon, characterised by: (a) using as source of at least part of the fuel hydrocarbon a normally liquid straight-run petroleum distillate boiling at 1 atmosphere pressure over a range between 20-500C and 100-3000C; (b) resolving that distillate into at least two fractions, including a light fraction boiling over a sub-range up to 50-1200C and a heavy fraction boiling at above that sub-range; (c) feeding the light fraction as fuel hydrocarbon for heating the catalyst; and (d) feeding the heavy fraction as fuel to at least one boiler raising steam.
2. Process according to claim 1 which comprises by known subsequent steps converting the raw synthesis gas to ammonia synthesis gas by introduction of nitrogen, cooling, shift reaction, carbon dioxide removal and final purification, and feeding the resulting synthesis gas to a recycle-type catalytic ammonia synthesis.
3. Process according to claim 2 which comprises by known subsequent steps converting the raw synthesis gas to ammonia synthesis gas by introduction of nitrogen, cooling, shift reaction, carbon dioxide removal/recovery and final purification, feeding the resulting synthesis gas to a recycle-type catalytic ammonia synthesis and reacting the sosynthesised ammonia and the recovered carbon dioxide to urea.
4. Process according to any one of the preceding claims which comprises by known subsequent steps of cooling and drying converting the raw synthesis gas to alcohol synthesis gas and feeding the resulting synthesis gas to catalytic alcohol synthesis.
5. Process according to any one of the preceding claims which comprises resolving the distillate into three fractions, one of which is a top fraction boiling at 1 atmosphere pressure at up to 1000C, and feeding that top fraction with the gaseous hydrocarbon to the steam reforming catalyst.
6. Process according to claim 5 which comprises desulphurising the mixture of top fraction and gaseous hydrocarbon before feeding it to the catalyst.
7. Process according to claim 5 so far as dependent on claim 3 in which the rate of feed of the top fraction is such as to produce, after the subsequent steps, nitrogen N2, hydrogen H2 and carbon dioxide in the molar ratio required for urea synthesis.
8. Process according to any one af claims 5 to 7 in which the steam reforming catalyst, at least at the inlet region of the bed thereof, is a carbon resistant catalyst such as a lightly alkalised catalyst.
9. Process according to any one of claims 3 to 8 in which steam raised in the boiler is used in recovering urea from the reaction product of ammonia and carbon dioxide.
10. Process according to claim 5 or claim 8 so far as those claims are dependent on claim 4 in which the rate of feed of the top fraction is such as to produce nearer-stoichiometric alcohol synthesis gas.
11. Process according to any one of the preceding claims in which the distillate is resolved with the aid of stripping gas.
12. Process according to claim 2 or claim 3 or any one of claims 5 to 8 so far as dependent on claim 2 or claim 3 which comprises using as stripping gas unreacted gas from the ammonia synthesis.
13. Process according to claim 12 which comprises feeding a mixture of that stripping gas and light fraction as fuel to the burners heating the steam reforming catalyst.
14. Process according to claim 11 so far as dependent on any one of claims 5 to 10 which comprises taking the top fraction using as stripping gas a side stream of the natural gas to be fed to the steam reforming catalyst.
15. Process according to claim 10 which comprises taking the top fraction using as stripping gas unreacted gas from alcohol synthesis.
16. Modification of a process according to claim 11 in which the process feed hydrocarbon comprises a normally liquid straight run petroleum distillate boiling at 1 atmosphere pressure over a range between 20-500C and 100-3000C, and the process is characterised by (i) resolving that distillate into at least three fractions, including a top fraction, a light fraction boiling over a sub-range up to 50-1200C and a heavy fraction boiling at above that subrange; (ii) using as stripping gas for the top fraction a purge gas containing incombustible components and using the mixture of such fraction and gas as fuel for heating the steam reforming catalyst and/or at least one boiler; ; (iii) using the heavy fraction as fuel for heating the steam reforming catalyst and/or at least one boiler; (iv) using the light fraction as process feed.
17. Process for producing raw synthesis gas substantially as described and as shown in the foregoing drawings and specific description.