WO2007009965A1

WO2007009965A1 - Method to start a synthesis process

Info

Publication number: WO2007009965A1
Application number: PCT/EP2006/064312
Authority: WO
Inventors: Koen Willem De Leeuw
Original assignee: Shell Internationale Research Maatschappij B.V.
Priority date: 2005-07-20
Filing date: 2006-07-17
Publication date: 2007-01-25

Abstract

Method to start and optionally maintain a process for producing normally gaseous, normally liquid and optionally normally solid hydrocarbons from a hydrocarbonaceous feed, which process comprises the steps of : (i) compressing and optionally separating an oxygen containing gas; (ii) partial oxidation of the hydrocarbonaceous feed at elevated temperature and pressure using the compressed oxygen containing gas of step (i) to obtain synthesis gas and steam; (iii) catalytically converting the synthesis gas of step (ii) at elevated temperature and pressure to obtain the normally liquid and/or gaseous hydrocarbons and steam; and (iv) using steam obtained in step (ii) and/or step (iii) and optionally combusting of hydrocarbons for generating power for providing the pressurized oxygen containing gas for step (i), which method starts with using one or more gas turbine (s) for providing steam for step (i) for compressing and optionally separating the pressurized oxygen containing gas.

Description

METHOD TO START A SYNTHESIS PROCESS

The present invention relates to a method to start a process for producing normally gaseous, normally liquid and optionally normally solid hydrocarbons starting from a hydrocarbonaceous feed, for example a Fischer-Tropsch process. In particular the present invention relates to a method to start an integrated, low cost process for the production of hydrocarbons, especially normally liquid hydrocarbons, from natural gas or associated gas, in particular at remote locations as well as at off-shore platforms.

Many documents are known describing processes for the conversion of (gaseous) hydrocarbonaceous feedstocks, especially methane, natural gas and/or associated gas, into liquid products, especially methanol and liquid hydrocarbons, particularly paraffinic hydrocarbons. In this respect often reference is made to remote locations and/or off-shore locations, where no direct use of the gas is possible. Transportation of the gas, e.g. through a pipeline or in the form of liquefied natural gas, is not always practical. This holds even more in the case of relatively small gas production rates aid/or fields. Reinjection of gas will add to the costs of oil production, and may, in the case of associated gas, result in undesired effects on the crude oil production. Burning of associated gas has become an undesired option in view of depletion of hydrocarbon sources and air pollution. Beside gaseous hydrocarbonaceous feestocks also liquid feedstocks, e.g. residual oil fractions, tar sand extracts, can be used as well as solid feedstocks, e.g. biomass, peat and coal.

The process for producing normally gaseous, normally liquid and normally solid hydrocarbons from a hydro- carbonaceous feedstock produces during normal operation a high amount of energy. This means that in this process any unit operation requiring energy for carrying out its required function this energy is generated and/or provided by other unit operations. This is the more true when the production process is carried out at remote and/or stranded gas locations. Although the process for producing hydrocarbons also produces heat and power, the start (or restart) of this process requires energy which is not (at any time) available. The present invention has for its object to provide a method to start up and optionally maintain such a process at low (operational) costs. The invention is based on the finding that this object is fulfilled when using for the start of the process a gas turbine whose function is for at least temporarily providing steam for generation of power to start the process, and optionally continuing so as to assist maintaining the process.

Gas turbine (s) are often used or present in hydrocarbon production plants for providing steam and/or power for parts, units and facilities thereof. It has now been found that such a turbine could also be used to generate steam at the start up of such a plant, in particular, extra steam desired at start up conditions. The use of such a gas turbine can result in lower (operational and capital) costs, especially where one or more gas turbines are already present or available, and in comparison to the use of other possibly available unit operations, which could provide power and heat, but which have to be adapted and provided with a more complex construction for providing the generation of power at the start of the process. Therefore, the present invention relates to a method to start and optionally maintain a process for producing normally gaseous, normally liquid and optionally normally- solid hydrocarbons from a hydrocarbonaceous feed, which process comprises the steps of: (i) compressing and optionally separating an oxygen containing gas;

(ii) partial oxidation of the hydrocarbonaceous feed at elevated temperature and pressure using the compressed oxygen containing gas of step (i) to obtain synthesis gas and steam;

(iii) catalytically converting the synthesis gas of step (ii) at elevated temperature and pressure to obtain the normally gaseous, normally liquid and optionally normally solid hydrocarbons and steam; and (iv) using steam obtained in step (ii) and/or step (iii) and optionally combusting of hydrocarbons for generating power for providing the pressurized oxygen containing gas for step (i) , which method starts with using one or more gas turbine (s) for providing steam for step (i) for compressing and optionally separating the pressurized oxygen containing gas, until step (iv) taken over for providing the power for step (i) .

The method relates to the initiation period, hereinafter also termed the "start up phase", before the hydrocarbon synthesis process starts. Either during and/or after the start up phase of the hydrocarbon synthesis process, step (iv) can partly, substantially or wholly take over the gas turbine (s) for providing steam and optionally power for step (i) . The takeover could be a co-ordinated or phased operation over time, suitably over the time period of the start up phase. Preferably, step (iv) initially partially takes over from providing steam and optionally power from step (i) as steam is provided by step (ii) and/or step (iii) .

Preferably, step (iv) completely takes over for providing steam and optionally power for step (i) after the start up phase of the process. The production of steam by the gas turbine (s) for step (il could be reduced by at least 25%, preferably 50%, and more preferably at least 75%, compared with its production at the beginning of the method to start the process.

The major advantage of the present invention is that simple use of a gas turbines can be provided at low operational and capital costs, especially where the hydrocarbon production system or arrangement may already include or involve a gas turbine, more especially a gas turbine designed to provide steam and/or power. Any additional connection arrangements required for the provision or supply of the steam, for the generation of power to start up the process for producing liquid and/or gaseous hydrocarbons, can be easily provided from an existing or available gas turbine. After the start up phase of the process, the gas turbine (s) can be used to provide steam and/or power output for other parts of a hydrocarbon production system or arrangement as is known in the art, whilst still being available, possibly in a standby mode, for additional steam or even emergency situations. The remaining steam and power production may very suitably be used in the downstream operation of the plant, more particularly the hydrogenation, hydroisomerisation, hydrocracking, thermal cracking, dewaxing, etc of the hydrocarbons produced, including distillation and other separation steps.

One or more boilers, such as hydrocarbonaceous feed fired boilers, could also be used to help provide steam at the start up of the process. The boilers could also assist balancing the steam system. The one or more gas turbine (s) for providing steam for step (i) at the start of the process may also provide direct power (shaft power) or electricity for one or more units of the FT-plant. For step (i) of the process suitably a standard steam turbine (directly connected with a) standard compressor is used.

The gas turbine may be driven with any fuel source originating from the process, especially Fischer-Tropsch off-gas, comprising mainly any unconverted syngas, C]_ to

C4 hydrocarbons and optionally one or more inert components. Another possibility is e.g. natural gas.

The term "gas turbine" as used herein refers to the combination of a gas turbine operation, generally for the provsion of mechanical and/or electrical energy, often also termed ^Λpower' , and a heat recovery steam generator (HRSG) to provide the steam. The HRSG may be separate or integral with the gas turbine operation.

Similarly, the term "boiler" as used herein also refers to the combination of a boiler and a HRSG.

When step (i) of the process comprises at least two compressing and/or optionally separating units then it is not required that the gas turbine immediately provides steam for the generation of the power for all units. Thus, a gas turbine may be required for providing only the steam (power) for at least one of these units such that step (i) is started. The compressed and optionally separated oxygen containing gas is then used in the start up of step (ii), i.e. the partial oxidation of the hydrocarbonaceous feed at elevated temperature and pressure. This step (ii) is exothermic and provides synthesis gas and steam. Both synthesis gas and steam may be used for providing steam in step (iv) . The synthesis gas may be used at least partly for the provision of steam to the system. Excess steam could be used to generate power (if steam is available) , and the electrical demand could be balanced with the gas turbine (s) .

When step (ii) comprises at least two partial oxidation reactors and the oxygen containing gas is fed to at least one of the partial oxidation reactors, it is not required to provide for all available partial oxidation reactor pressurized oxygen containing gas which reduces also the steam requirements for the gas turbine.

Subsequently, after starting the partial oxidation of step (ii), synthesis gas produced in step (ii) is used to start step (iii) for catalytically converting synthesis gas into the normally liquid and/or gaseous hydrocarbons and steam. When starting up step (iii) for catalytically converting the synthesis gas, the gas turbine may still provide all steam. Alternatively, steam generation may at least partly have been taken over by step (iv) . Part of the hydrocarbons produced in step (iii) may be stored for later use (when the process is in full operation) or used as a feed in step (iv) and/or for driving the gas turbine. Steam produced in step (iii) may be used in step (i) and/or (iv) . In a preferred embodiment, when step (iii) comprises at least two synthesis gas converting reactors and the synthesis gas is fed to at least one of the synthesis gas converting reactors. This reduces in the start up procedure the steam (power) requirement.

If necessary, steam generated in step (ii) and/or step (iii) may be used for further compression of the gas stream produced in step (i) (i.e. compressing oxygen- enriched gas) and/or step (ii) (i.e. compressing synthesis gas) .

In a preferred embodiment the process comprises a step (v) of catalytically hydrocracking higher boiling range paraffinic hydrocarbons produced in step (iii) .

Again, when step (v) comprises at least two catalytically hydrocracking reactors and hydrocarbons produced in step (iii) are fed to at least one catalytically hydrocracking reactor, the steam (power) requirement for the start up of the process is reduced.

It will be evident, that by using a gas turbine in the start up procedure, step (i) is started up under almost constant input conditions for steam and oxygen- containing gas feed. This provides a controlled and safe start up of step (i) . After the production of compressed oxygen containing gas has become continuous and stable, step (ii) is started up. It will be obvious that the other steps (iii) and (iv) and optionally (v) will also be started up under continuous and substantially stable conditions.

This means that the method for starting up the process for producing liquid and/or gaseous hydrocarbons is controlled and safe not only under fresh start conditions but also under restart conditions.

If necessary, an additional compressing unit may be used between step (ii) and (iii) . The gas turbine may in that case also provide the power (and steam) needed for this compressor at the (re) start. It is also possible to start the compressor after the start of step (iii) , using either the gas turbine or steam generated in steps (ii) and/or (iii) . Generally, the gas turbine provides steam by heating, preferably superheating, water and/or steam through heat exchange with the hot turbine-exhaust flue gases.

The operation of a gas turbine is known in the art, and generally comprises a combustion chamber wherein a fuel is combusted, followed by passage through and/or expansion of the combusted gas in an expansion chamber, and an exit of the hot flue gases through a suitable conduit such as a stack or the like, which allows heat exchange to occur. The expansion chamber includes or is connected to a rotor, and the expansion of the gases from the combustion chamber drives the rotor. The rotor can be used to generate power both in the form of electrical and mechanical energy. Also preferably, the gas turbine includes a compression chamber for the compression of an oxygen containing gas, which compressed gas is usually used to assist or provide combustion of the fuel in the combustion chamber. The power required for the compression in the compression chamber could be provided by linkage with the rotor of or connected to the expansion chamber.

The heat exchange in the exhaust gas conduit could be by way of the location of one or more, preferably a few such as 2-4, heat exchangers located in the conduit, and thus in the path of the hot exhaust gases. The heat exchangers could be connected, either in parallel or series or a combination thereof, and supplied with a form of water. As the water passes through the heat exchangers, it is heated to create the required steam, preferably superheated steam. The steam can then used to power step (i) as hereinbefore described. The heat exchange action will reduce the temperature of the exhaust gases along the length on the conduit.

In one embodiment of the present invention, the outflow path of the exhaust flue gases includes means for providing additional heat or heating therealong. This additional heat or heating serves to assist the provision of steam by the heating or superheating of water by the exhaust flue gases. The additional heat or heating could be provided by any suitable means, including one or more burners, such as duct burners known in the art. The means is located in a suitable position, for example, in the direct vicinity of the heat exchangers. The means may be powered by any suitable fuel source, including for example, the fuel source (s) (such as syngas) used for the gas turbine or other parts of the hydrocarbon synthesis plant. Such means may be operable at different conditions, e.g. temperature, at different locations.

Such means could be particularly operated at initial stage (s) to assist production of the steam, especially whilst the exhaust flue gases are not (yet) at their expected or usual optional running temperature. In one particular arrangement, there; are two duct burners in the HRSG following the gas outlet form the gas turbine operation. In the outlet, there is the sequence of (a) a first duct burner to increase the flue gas temperature, (b) a superheater to superheat the steam coming from other parts of the process, e.g. step(ii) and any steam from a boiler, (c) the second duct burner to again increase the flue gas temperature, (d) a boiler, to which the saturated steam form step(iii) is fed, and (e) an economiser to preheat the boiler feed water to just below its boiling point.

Any electrical power, i.e. electricity, created by the gas turbine could be used to power or assist the powering of a part of the hydrocarbon synthesis process, such as assisting in the power required for the compression and optional separation of the oxygen containing gas. The hydrocarbonaceous feed suitably is methane, natural gas, associated gas or a mixture of C_]__4 hydrocarbons. The feed comprises mainly, i.e. more than 90 v/v%, especially more than 94%, C]__4 hydrocarbons, especially comprises at least 60 v/v percent methane, preferably at least 75 percent, more preferably

90 percent. Very suitably natural gas or associated gas is used. Suitably, any sulphur in the feedstock is removed.

The hydrocarbons produced in the process and mentioned in the present description are suitably C3.-

200 hydrocarbons, more suitably 04-150 hydrocarbons, especially C5_]_QO hydrocarbons, or mixtures thereof. These hydrocarbons or mixtures thereof are liquid or solid at temperatures between 5 and 3O⁰C (1 bar), especially at about 20°C (1 bar), and usually are paraffinic of nature, while up to 30 wt%, preferably up to 15wt%, of either olefins or oxygenated compounds may be present.

Depending on the catalyst and the process conditions used in a Fischer-Tropsch reaction, normally gaseous hydrocarbons, normally liquid hydrocarbons and optionally normally solid hydrocarbons are obtained. It is often preferred to obtain a large fraction of normally solid hydrocarbons. These solid hydrocarbons may be obtained up to 85 wt% based on total hydrocarbons, usually between 50 and 75 wt%.

The partial oxidation of gaseous feedstocks, producing mixtures of especially carbon monoxide and hydrogen, can take place according to various established processes. These processes include the Shell Gasification Process. A comprehensive survey of this process can be found in the Oil and Gas Journal, September 6, 1971, pp 86-90. A further partial oxidation reactor that can be used in the process of the invention is an autothermal oxidation reactor (ATR) in which beside partial oxidation also catalytic reforming takes place. This needs a feedstream of steam and/or CO2, preferably steam.

The oxygen containing gas can be air (containing about 21 vol. percent of oxygen), oxygen enriched air, suitably containing up to 70 percent, or substantially pure air, containing typically at least 95 vol.%, usually at least 98 vol.%, oxygen. Oxygen or oxygen enriched air may be produced via cryogenic techniques, but could also be produced by a membrane based process, e.g. the process as described in WO 93/06041. The gas turbine can provide the power and/or steam for driving at least one air compressor or separator of the air compression/separating unit. If necessary, an additional compressing unit may be used between the separation process and step (ii) , and the gas turbine (s) in that case may also provide at the (re) start power and/or steam for this compressor. The compressor, however, may also be started at a later point in time, e.g. after a full start, using steam generated in steps (ii) and/or (iii).

To adjust the H2/CO ratio in the syngas, carbon dioxide and/or steam may be introduced into the partial oxidation process. Preferably up to 15% volume based on the amount of syngas, preferably up to 6% volume, more preferable up to 4% volume, of either carbon dioxide or steam is added to the feed. Water produced in the hydrocarbon synthesis may be used to generate the steam. As a suitable carbon dioxide source, carbon dioxide from the effluent gasses of the expanding/combustion step may be used. The H2/CO ratio of the syngas is suitably between 1.5 and 2.3, preferably between 1.8 and 2.1. If desired, (small) additional amounts of hydrogen may be made by steam methane reforming, preferably in combination with the water shift reaction. Any carbon monoxide and carbon dioxide produced toςjether with the hydrogen may be used in the hydrocarbon synthesis reaction or recycled to increase the carbon efficiency. Additional hydrogen manufacture may be an option. The gaseous mixture, comprising predominantly hydrogen, carbon monoxide and optionally nitrogen, is contacted with a suitable catalyst in the catalytic conversion stage, in which the hydrocarbons are formed. Suitably at least 70 v/v% of the syngas is contacted with the catalyst, preferably at least 80%, more preferably at least 90%, still more preferably all the syngas.

The catalysts used in step (iii) for the catalytic conversion of the mixture comprising hydrogen and carbon monoxide into hydrocarbons are known in the art and are usually referred to as Fischer-Tropsch catalysts. Catalysts for use in the Fischer-Tropsch hydrocarbon synthesis process frequently comprise, as the catalytically active component, a metal from Group VIII of the previous IUPAC version of the Periodic Table of Elements such as that described in the 6>8^th Edition of the Handbook of Chemistry and Physics (CPC Press) . Particular catalytically active metals include ruthenium, iron, cobalt and nickel. Cobalt is a preferred catalytically active metal.

The catalytically active metal is preferably supported on a porous carrier. The porous carrier may be selected from any of the suitable refractory metal oxides or silicates or combinations thereof known in the art. Particular examples of preferred porous carriers include silica, alumina, titania, zirconia, ceria, gallia and mixtures thereof, especially silica and titania.

The amount of catalytically active metal on the carrier is preferably in the range of from 3 to 300 pbw per 100 pbw of carrier material, more preferably from 10 to 80 pbw, especially from 20 to 60 pbw.,

If desired, the catalyst may also comprise one or more metals or metal oxides as promoters. Suitable metal oxide promoters may be selected from Groups HA, IHB, IVB, VB and VIB of the (same) Periodic Table of Elements, or the actinides and lanthanides. In particular, oxides of magnesium, calcium, strontium, barium, scandium, yttrium, lanthanum, cerium, titanium, zirconium, hafnium, thorium, uranium, vanadium, chromium and manganese are most suitable promoters. Particularly preferred metal oxide promoters for the catalyst used to prepare the waxes for use in the present invention are manganese and zirconium oxide. Suitable metal promoters may be selected from Groups VIIB or VIII of the (same) Periodic Table. Rhenium and Group VIII noble metals are particularly suitable, with platinum and palladium being especially preferred. The amount of promoter present in the catalyst is suitably in the range of from 0.01 to 100 pbw, preferably 0.1 to 40, more preferably 1 to 20 pbw, per 100 pbw of carrier.

The catalytically active metal and the promoter, if present, may be deposited on the carrier material by any suitable treatment, such as impregnation, kneading and extrusion. After deposition of the metal and, if appropriate, the promoter on the carrier material, the loaded carrier is typically subjected to calcination at a temperature of generally from 350 to 750 ⁰C, preferably a temperature in the range of from 450 to 550 ⁰C. The effect of the calcination treatment is to remove crystal water, to decompose volatile decomposition products and to convert organic and inorganic compounds to their respective oxides. After calcination, the resulting catalyst may be activated by contacting the catalyst with hydrogen or a hydrogen-containing gas, typically at temperatures of about 200 to 350 ⁰C.

The catalytic conversion process may be performed under conventional synthesis conditions known in the art. Typically, the catalytic conversion may be effected at a temperature in the range of from 100 to 600 ⁰C, preferably from 150 to 350 ⁰C, more preferably from 180 to 270 ⁰C. Typical total pressures for the catalytic conversion process are in the range of from 1 to 200 bar absolute, more preferably from 10 to 70 bar absolute. In the catalytic conversion process mainly (at least 70 wt%, preferably 90 wt%) of C5+ hydrocarbons are formed.

Preferably, a Fischer-Tropsch catalyst is used, which yields substantial quantities of paraffins, more preferably substantially unbranched paraffins. A part may boil above the boiling point range of the so-called middle distillates, to normally solid hydrocarbons. A most suitable catalyst for this purpose is a cobalt- containing Fischer-Tropsch catalyst. The term "middle distillates", as used herein, is a reference to hydrocarbon mixtures of which the boiling point range corresponds substantially to that of kerosene and gas oil fractions obtained in a conventional atmospheric distillation of crude mineral oil. The boiling point range of middle distillates generally lies within the range of about 150 to about 360 ⁰C.

The higher boiling range paraffinic hydrocarbons, if present, may be isolated and subjected to a catalytic hydrocracking step (v) , which is known per se in the art, to yield the desired middle distillates. The catalytic hydro-cracking is carried out by contacting the paraffinic hydrocarbons at elevated temperature and pressure and in the presence of hydrogen with a catalyst containing one or more metals having hydrogenation activity, and supported on a carrier. Suitable hydro- cracking catalysts include catalysts comprising metals selected from Groups VIB and VIII of the (same) Periodic Table of Elements. Preferably, the hydrocracking catalysts contain one or more noble metals from Group VIII. Preferred noble metals are platinum, palladium, rhodium, ruthenium, iridium and osmium. Most preferred catalysts for use in the hydro-cracking stage are those comprising platinum.

The amount of catalytically active metal present in the hydrocracking catalyst may vary within wide limits and is typically in the range of from about 0.05 to about 5 parts by weight per 100 parts by weight of the carrier material .

Suitable conditions for the catalytic hydrocracking are known in the art. Typically, the hydrocracking is effected at a temperature in the range of from about 175 to 400 ⁰C. Typical hydrogen partial pressures applied in the hydrocracking process are in the range of from 10 to 250 bar.

The process may be operated in a single pass mode ("once through") or in a recycle mode. The process may be carried out in one or more reactors, either parallel or in series . In the case of small hydro-carbonaceous feedstock streams, the preference will be to use only one reactor. Slurry bed reactors, ebulliating bed reactors and fixed bed reactors may be used, the fixed bed reactor being the preferred option.

The product of the hydrocarbon synthesis and consequent hydrocracking suitably comprises mainly normally liquid hydrocarbons, beside water and normally gaseous hydrocarbons. By selecting the catalyst and the process conditions in such a way that especially normally liquid hydrocarbons are obtained, the product obtained ("syncrude") may transported in the liqiαid form or be mixed with any stream of crude oil without creating any problems as to solidification and or crystallization of the mixture. It is observed in this respe:ct that the production of heavy hydrocarbons, comprising large amounts of solid wax, are less suitable for mixing with crude oil while transport in the liquid form has to be done at elevated temperatures, which is less desired.

The off gas of the hydrocarbon synthesis may comprise normally gaseous hydrocarbons produced in the synthesis process, nitrogen, unconverted methane and other feedstock hydrocarbons, unconverted carbon monoxide, carbon dioxide, hydrogen and water. The normally gaseous hydrocarbons are suitably C]__5 hydrocarbons, preferably

Ci_4 hydrocarbons, more preferably C]__3 hydrocarbons. These hydrocarbons, or mixtures thereof, are gaseous at temperatures of 5-30 ⁰C (1 bar) , especially at 20 ⁰C (1 bar). Further, oxygenated compounds, e.g. methanol, dimethyl ether, may be present in the off gas. The off gas may be utilized for the production of electrical power, in an expanding/combustion process such as in a gas turbine described herein, or recycled to the process. The energy generated in the process may be used for own use or for export to local customers. Part of the energy could be used for the compression of the oxygen containing gas.

The process as just described may be combined with all possible embodiments as described in this specification.

In the process of the invention, hydrogen may be separated from the synthesis gas obtained in the first step. The hydrogen is preferably separated after quenching/cooling, and may be separated by techniques well known in the art, as pressure swing adsorption, or, preferably, by means of membrane separation techniques. The hydrogen may be used in a second heavy paraffin synthesis step after the first reactor (provided that a two stage hydrocarbon synthesis is used) , or for other purposes, e.g. hydrotreating and/or hydrocracking of hydrocarbons produced in the paraffin synthesis. In this way a further product optimization is obtained (for instance by fine tuning the H2/CO ratios in the first and second hydrocarbon synthesis step) , while also the carbon efficiency can be improved. In addition, the product quality may be improved by e.g. hydrogenation and/or hydrocracking . Steam generated by the gas turbine (s) and/or steam generated in step (ii) may also be used to preheat the reactor to be used in step (iii) and/or may be used to create fluidization in the case that a fluidized bed reactor or slurry bubble column is used in step (iii) . The term "normally" relates to STP-conditions (0 ⁰C,

1 bar) , unless defined in another way.

Any percentage mentioned in this description is calculated on total weight or volume of the composition, unless indicated differently. When not mentioned, percentages are considered to be weight percentages.

Pressures are indicated in bar absolute, unless indicated differently.

Claims

C L A I M S

1. Method to start and optionally maintain a process for producing normally gaseous, normally liquid and optionally normally solid hydrocarbons from a hydrocarbonaceous feed, which process comprises the steps of:

(i) compressing and optionally separating an oxygen containing gas;

(iii) catalytically converting the synthesis gas of step (ii) at elevated temperature and pressure to obtain the normally gaseous, normally liquid and optionally normally solid hydrocarbons and steam; and

(iv) using steam obtained in step (ii) and/or step (iii) and optionally combusting of hydrocarbons for generating power for providing the pressurized oxygen containing gas for step (i) , which method starts with using one or more gas turbine (s) for providing steam for step (i) for compressing and optionally separating the pressurized oxygen containing gas until step (iv) takes over for providing the power for step (i) .

2. Method as claimed in claim 1 wherein during and/or after the start up phase of the process, step (iv) partly, substantially or wholly takes over the one or more gas turbines for providing steam and optionally power for step (i) preferably wherein during the start up optionally power of step (i), more preferably wherein step (iv) completely takes over for providing steam and optionally power for step (ii) after the start up phase of the process.

3. Method as claimed in any of the preceding claims, wherein step (i) comprises at least two compressing and/or optionally separating units and the gas turbine (s) provides steam for the generation of power for at least one of these compressing and optionally separating units.

4. Method as claimed in any of the preceding claims, wherein the pressurized oxygen containincj gas obtained by using the steam generated by the gas turbine (s) is used to start the partial oxidation of step (ii) and the steam and/or synthesis gas obtained in starting step (ii) are/is used in step (iv) .

5. Method as claimed in any of the preceding claims, wherein step (ii) comprises at least two partial oxidation reactors and the oxygen containing gas is fed to at least one of the partial oxidation reactors.

6. Method as claimed in any of the preceding claims, wherein at least part of the synthesis gas produced in step (ii) is used for operating the gas turbine (s) during the start-up phase and/or wherein after starting the partial oxidation of step (ii) synthesis gas produced in step (ii) is used to start step (iii) for catalytically converting synthesis gas into the normally gaseous, normally liquid and optionally normally solid hydrocarbons and steam.

7. Method as claimed in any one of the preceding claimsof , wherein the process further comprises: step (v) catalytically hydrocracking higher boiling range paraffinic hydrocarbons produced in step (iii) .

8. Method as claimed in any one of the preceding claims wherein the gas turbine (s) also provides electrical energy, preferably for use in one or more of the steps of the method or of the process described in claims 1-7.

9. Method as claimed in any one of the preceding claims wherein the gas turbine (s) includes a gas outflow having one or more means for providing additional heat to or heating of the steam, preferably wherein the means are one or more duct burners.

10. A process for producing normally gaseous, normally liquid and optionally normally solid hydrocarbons from a hydrocarbonaceous feed, which process includes a method as described in any one of claims 1-9, optionally followed by hydrocracking of said hydrocarbons.