WO2011131706A1

WO2011131706A1 - Process for operating a gas turbine

Info

Publication number: WO2011131706A1
Application number: PCT/EP2011/056298
Authority: WO
Inventors: Intan Augustina Ambari; Boon Loon Cheah; David Michael Collins
Original assignee: Shell Internationale Research Maatschappij BV
Current assignee: Shell Internationale Research Maatschappij BV
Priority date: 2010-04-20
Filing date: 2011-04-20
Publication date: 2011-10-27
Anticipated expiration: 2012-10-20

Abstract

The present invention provides a process for operating a gas turbine, comprising: a) providing a hydrocarbon feedstock comprising at least ethylene cracker residue; b) heating the hydrocarbon feedstock to obtained a heated feedstock with a decreased viscosity compared to the initial hydrocarbon feedstock; c) filtering part or all of the heated feedstock; and d) providing the heated feedstock to a gas turbine to produce electrical or mechanical power and a hot flue gas, wherein the heated feedstock in step (d) comprises in the range of from 20 to 60wt% of asphaltenes based on the weight of ethylene cracker residue in the first hydrocarbon feedstock.

Description

PROCESS FOR OPERATING A GAS TURBINE

Field of the invention

The invention relates to a process for operating a gas turbine.

Background of the invention

While driving to make efficient use of the

hydrocarbon sources available, residual heavy hydrocarbon fuels are used to generate pressurised steam and

optionally electrical or mechanical power. Examples of these residual heavy hydrocarbon fuels include heavy fuel oil, heavy distillate oil, atmospheric and vacuum

distillation residues. Most of these heavy hydrocarbon fuels are highly viscous and difficult to handle. The heavy hydrocarbon fuels often have a high ash content and contain high concentrations of trace metal contaminants, including calcium, sodium, lead and vanadium, in the form of metal compounds. Due to these difficult properties these heavy hydrocarbon fuel are typically combusted in conventional boiler units to provide steam. An example of such a process is provided in for instance WO07144661, wherein a method for the generation of electrical power from heavy oil feedstocks is described. The method comprises separating a starting liquid oil feedstock into at least one light liquid stream and one heavy stream. The heavy stream is combusted to generate steam to drive a steam turbine to generate electrical power.

While these conventional boiler units are robust and do not put high constraints on the fuel provided to the boiler, they are also inefficient.

A much higher efficiency can be obtained by using a gas turbine to convert the heavy hydrocarbon fuel to power. However, the gas turbine is much more sensitive to the properties of the fuel provide to the gas turbine, in particular the viscosity and the contaminants present. In WO07144661, mentioned herein above, the light liquid stream is provided to a gas turbine, while the heavy stream is sent to a boiler unit.

It has been suggested to modify the heavy hydrocarbon fuel properties prior to feeding it to the gas turbine. Examples of described modifications include gasification, hydrolysis and emulsification of the heavy hydrocarbon fuel .

For instance in US6663680, a process is described, wherein a heavy hydrocarbon fuel is modified with water and additives to form an emulsion fuel, which is a oil in water emulsion. The emulsion fuel has a lower viscosity due to the large amount of water present in the fuel. A disadvantage of using such an emulsion fuel is that due to the presence of large amounts of water in the fuel the process is energy intensive and energy inefficient. In addition, large volumes of water are required, which can easily become polluted.

In US2006/0185368 a process is described wherein the heavy hydrocarbon fuel is first hydrolysed by reacting the fuel with water at elevated temperatures and

pressures. During the reactions a light hydrocarbon fraction is formed which is used fuel a gas turbine. In addition a heavy fuel is obtained, which is combusted to form steam.

Although part of the heavy hydrocarbon fuel in

US2006/0185368 is provided to the gas turbine, it

requires a prior modification reaction and still part of the feed is sent directly to the boiler unit for

combustion . As mentioned herein above, the presence of

contaminants such as trace metal components also limits the applicability of typical heavy hydrocarbon fuels in gas turbines.

Examples of contaminants include calcium compounds, sodium compounds, mercury compounds, nickel compounds, lead compounds and vanadium compounds. In particular, vanadium compounds are undesirable as they form corrosive vanadium compounds under gas turbine operating conditions resulting in corrosion of metal parts in the gas turbine.

Typically, in commercial gas turbine operation, the vanadium concentration in the heavy hydrocarbon fuels is restricted to concentrations below 2 ppm. The heavy feedstocks mentioned in for instance US6663680, i.e. a vacuum residue of Arabian light, comprise up to 63 ppm vanadium. US5561977 describes that use of a heavy oil, comprising as much as 30 to 35 ppm of vanadium, for firing a gas turbine. Such feedstocks need to be treated to remove of inhibit the vanadium compounds. In WO

95/07408, heavy oils, comprising 250 to 300ppm vanadium, are used to fire a gas turbine. In WO 95/07408, a

magnesium-based additive is added to the heavy oil. The magnesium-based additive reacts with the vanadium

compounds to from non-corrosive vanadium compounds.

However, in order to sufficiently suppress vanadium induced corrosion, magnesium-based additive needs to be added in a weight ratio up to 2 compared to the vanadium contaminant .

Another contaminant in the heavy hydrocarbon

feedstock are asphaltenes. As described in Moliere et al .

(Moliere, M; Sire, J; Heavy duty gas turbines experience with ash-forming fuels, Journal de Physique IV, Colloque C9, supplement au Journal de Physique III, Volume 3, December 1993) asphaltenes are complex molecules with high molecular weights (up to 500 g/mole) . They need close attention during both the handling and the

combustion processes of a power plant, due in particular to their tendency to flocculate, to their differential solubilities in oils of different origins and to their slow-burning properties. Flocculated asphaltenes lead to fouling and ultimately to blockage of pipes and valves. Crude oil based heavy hydrocarbon feedstocks typically contain low amounts of asphaltenes. For instance bunker fuel typically comprises less than 15wt% of asphaltenes. In addition, crude oil originating asphaltenes are less prone to flocculation in comparison to pyrolytic

asphaltenes. In for instance US2009/057200, a process is provided for removing pyrolytic asphaltenes from a high asphaltenes feedstock prior to blending it with fuel oil or bunker fuel, to prevent flocculation of the

asphaltenes .

Other contaminants such as lead-based contaminants cannot be easily removed or inhibited.

There is a need in the art for an improved method for operating a gas turbine, while reducing the need for pre- treatment of the heavy hydrocarbon fuel.

Summary of the invention

It has now been found that it is possible to operate a gas turbine using an ethylene cracker residue

comprising asphaltenes as part or all of a hydrocarbon feedstock. As a result the need to pre-treat or purify the hydrocarbon feedstock is reduced.

Accordingly, the present invention provides a process for operating a gas turbine, comprising:

a) providing a first hydrocarbon feedstock comprising at least ethylene cracker residue; b) heating the hydrocarbon feedstock to obtain a heated feedstock with a decreased viscosity compared to the initial hydrocarbon feedstock;

c) filtering part or all of the heated feedstock; and d) providing the heated feedstock to a gas turbine to produce electrical or mechanical power and a hot flue gas ,

wherein the heated feedstock in step (d) comprises in the range of from 20 to 60wt% of asphaltenes based on the weight of ethylene cracker residue in the first

hydrocarbon feedstock.

The process according the present invention does not require gasification, hydrolysis or aqueous

emulsification of the hydrocarbon feedstock prior

providing the feedstock to the gas turbine.

Reference herein to ethylene cracker residue, or ECR, is to the heavy hydrocarbon residue obtained from steam cracking hydrocarbon feedstocks including but not limited to naphtha, vacuum gas oil or hydrowax. Crude oil

contaminants, such as metal contaminants, tend to

accumulate in the residual heavy distillation fractions rather than in the lighter naphtha, vacuum gas oil or hydrowax fractions. Consequently, the ECR contains relative low concentrations of metal contaminants, thereby significantly reducing the need to treat the hydrocarbon feedstock to the gas turbine to remove or inhibit metal contaminants such as vanadium-based

compounds .

Brief Description of the Drawings

In Figure 1, a process scheme is shown suitable for performing the process according to the invention.

In Figure 2, another process scheme is shown suitable for performing the process according to the invention. Detailed description of the invention

In the process according to the present invention a gas turbine is operated by providing a hydrocarbon feedstock, preferably a heavy hydrocarbon feedstock, for operating (or firing) the gas turbine. The hydrocarbon feedstock comprises at least ethylene cracker residue (further also referred to as ECR) .

The ECR is obtained from a thermal cracking process wherein a hydrocarbon feedstock, preferably a light hydrocarbon feedstock, is thermally cracked, typically in the presence of steam. Preferably, the thermal cracking process is a process to produce ethylene. The thermal cracking process is also referred to as steam cracking and is typically performed in a steam cracker, which is also referred to as an ethylene cracker. A by-product of the thermal cracking process is ECR. Depending on the hydrocarbon feedstock provided to the thermal cracking process, more or less ECR is formed. For instance, only relative small amounts of ECR are formed when the

hydrocarbon feedstock to the thermal cracking process is ethane. However, there is a drive in the industry to use heavier feedstocks than ethane for thermal cracking processes to produce ethylene. Examples of such

feedstocks include but are not limited to LPG, natural gas liquids (NGL) , naphtha, gas oil, vacuum gas oil or hydrowax. Examples of such feedstocks include but are not limited to synthetic hydrocarbons such as Fischer-Tropsch hydrocarbons, in particular C3 to CIO Fischer-Tropsch paraffins. These heavier than ethane feedstocks have a lower hydrogen to carbon ratio. Feedstocks having a lower hydrogen to carbon ratio produce more ECR when thermally cracked. As a result, increasing volumes of ECR have become available. Unlike distillation residues or hydrocarbon streams derived thereof, which are used in the prior art to fire gas turbines, ECR contains low amounts of metal contaminants. Examples of metal

contaminants include but are not limited to calcium compounds, sodium compounds, potassium compounds, lead compounds, nickel compounds, mercury compounds and vanadium compounds. Other contaminants present may include for instance sulphur compounds. Some of these contaminants were already in the crude oil, such as the heavy metals compounds as vanadium, lead and nickel, others may have also been introduced during the refining of the crude, such as calcium, potassium and sodium.

Typically, these metal contaminants accumulate in the higher boiling heavier fractions during the distillation process. Examples of such heavier fractions include for instance atmospheric and vacuum distillation residues, heavy fuel oil and bunker oil, which are used in the prior art as feedstock for driving the gas turbines.

These metal contaminants need to be, at least partly, removed or inhibited if the feedstock is to be used to drive a gas turbine. In particular, lead and vanadium compounds can negatively influence the operation of the gas turbine, due to the formation of corrosive compounds under gas turbine operation conditions. At the high operating temperatures of the gas turbine, the vanadium and lead compounds may melt, become corrosive and corrode for instance the turbine blades and bearings. In

addition, all the mentioned metal contaminants may form solid deposits in the gas turbine, increasing the need to halt operation to clean the gas turbine.

ECR, however, is a by-product from thermally cracking one or more lighter fractions such as mentioned herein above. These lighter fractions contain relatively low amounts of metal contaminants and consequently so does the ECR, making ECR a particularly suitable feedstock for operating a gas turbine.

The ECR contains in the range of from 20 to 60wt%, preferably 20 to 40wt% of asphaltenes, based on the weight of the ECR. Consequently, the first hydrocarbon feedstock also contains asphaltenes, in particular the first hydrocarbon feedstock comprises in the range of from 20 to 60wt%, preferably 20 to 40wt% of asphaltenes, based on the weight of the ECR in the first hydrocarbon feedstock .

Reference herein to the weight content of asphaltenes is to the weight content of asphaltenes as determined using the standard method ASTM D6560-IP 143. The ECR is highly viscous and difficult to transport or pump. At

20°C the kinematic viscosity of ECR may be significantly above 1000 cSt, as determined with ASTM method D445. In the process according to the invention, the hydrocarbon feedstock is therefore heated to reduce the viscosity. By heating the hydrocarbon feedstock a heated feedstock (or heated hydrocarbon feedstock) having a lower viscosity is obtained. The lower viscosity is not only needed to transport or pump the feedstock but also to allow the feedstock to be sprayed into the gas turbine. Typically, the feedstock is provided into the gas turbine using a nozzle. In order to allow fine dispersion, often referred to as atomisation, of the heated feedstock it is

preferred that the heated feedstock has a kinematic viscosity of no more than 30cSt, preferably no more than 20 cSt. Preferably, the heated feedstock has a kinematic viscosity of in the range of from 1 to 30cSt, more preferably 5 to 20 cSt, as determined with ASTM method D445. The temperature at which the viscosity of the heated feedstock is sufficiently lowered to be further processed depends on the composition of the ECR and the hydrocarbon feedstock. Heating the hydrocarbon feedstock to a

temperature of in range of from 135 to 275°C, preferably of from 175 to 260°C, more preferably of from 200 to 250°C, typically reduces the kinematic viscosity

sufficiently. Heating the feedstock to too high

temperatures leads to thermal degradation of hydrocarbons in the ECR resulting in undesired fouling. An advantage of using ECR as part or all of the hydrocarbon feedstock is that ECR can be heated to significantly higher

temperatures, i.e. above 135°C, than the heavy feedstocks as used in the prior art processes, without causing serious fouling.

Preferably, the hydrocarbon feedstock comprises one or more hydrocarbon diluents having a 5wt% boiling temperature range of from 120 to 160°C, preferably 130 to 150°C and a 95wt% boiling temperature range of from 350 to 500 °C, preferably of from 375 to 450°C, as determined using ASTM method D2887. In addition, the hydrocarbon diluents preferably have a kinematic viscosity of in the range of from 2 to 15 cSt at 20°C, as determined with ASTM method D445, preferably the hydrocarbon diluents have a kinematic viscosity of in the range of from 0.5 to

2.5 cSt at 50°C, as determined with ASTM method D445. By adding such a hydrocarbon diluent the flow properties and spraying or atomisation properties of the feedstock are further improved by lowering the kinematic viscosity. In theory, it is possible to add the hydrocarbon diluents to the hydrocarbon feedstock in such quantities that the viscosity of the hydrocarbon feedstock is sufficiently lowered to allow the feedstock to be processed without the need to heat the hydrocarbon feedstock. However, typically the hydrocarbon diluent is much more valuable than the ECR and is preferably not combusted in a gas turbine. Therefore, preferably, the hydrocarbon feedstock comprises in the range of from 30 to 100wt%, based on the total weight of the hydrocarbon feedstock, of ethylene cracker residue. More preferably, the hydrocarbon

feedstock comprises in the range of from 50 to 99wt%, even more preferably of from 75 to 95wt% of ethylene cracker residue. By including a hydrocarbon diluent in the hydrocarbon feedstock the temperature at which the kinematic viscosity of the hydrocarbon feedstock is sufficiently decreased, compared to the same hydrocarbon feedstock without the diluent. This is of particular use where in the absence of a hydrocarbon diluent, the hydrocarbon feedstock would have to be heated to

temperatures at which fouling due to thermal degradation occurs .

The kinematic viscosity of the hydrocarbon feedstock and/or heated feedstock may be analysed or monitored during the process to ensure it meets the specification of the maximum allowable kinematic viscosity at the inlet of the gas turbine. The kinematic viscosity can be measured at, but not limited to, the inlet of the gas turbine with the use of a viscometer and/or sampling of the hydrocarbon feedstock and/or heated feedstock for laboratory analysis. By analysing the kinematic viscosity during the process, the kinematic viscosity of the hydrocarbon feedstock may be adapted if required by adding additional diluent or ECR and/or changing the temperature of the hydrocarbon feedstock and/or heated feedstock, i.e. the kinematic viscosity can be adapted by adjusting the heat input from the heater or by adjusting the amount of diluent added to the ECR or by a

combination of the two. Any undesired change of the kinematic viscosity of the hydrocarbon feedstock and/or heated feedstock can as such be counterbalanced.

Prior to providing the heated feedstock to the gas turbine, part or all of the heated feedstock is filtered. As mentioned herein above, the heated feedstock is preferably introduced into the gas turbine through nozzles. Particles present in the feedstock may cause blockage of the nozzles, passageways and valves and should therefore be removed, preferably at least to the extent required by the specifications of the gas turbine. In case the specifications of the gas turbine can be met by filtering only part of the heated feedstock, the remainder of the heated feedstock can be allowed to by^¬ pass the filtration unit or filtering device and be either provided to the gas turbine separately or,

preferably, be combined with the filtered heated

feedstock downstream of the filtration unit or filtering device. This has the advantage that smaller filtration unit or filtration device may be used. Reference herein to particles is to solid particles and to viscous liquid particles having such a high viscosity at the temperature at which the heated feedstock is passed through the nozzle that passage through the nozzle is prevented.

Examples of particles include but are not limited to coke, flocculated asphaltenes, waxes, colloids and salts. In case, the hydrocarbon feedstock comprises solid particles, preferably the heated feedstock is filtered to remove at least part of the solid particles.

Filtering may be done using any suitable filter device available. Suitable filters for hydrocarbon feedstocks are well known in the art. A particularly suitable filter is a filter unit comprising a perforated tube surrounded by hollow longitudinal projections comprising a filter having openings of at most 100 micrometer diameter in which the internal space of each of the hollow projections is in fluid communication with the inside of the perforated tube and which filter is regularly subjected to cleaning by treating each of the projections with cleaning fluid wherein the flow of cleaning fluid is opposite to the direction of normal flow. Such filter can for instance be obtained from the company Filtrex s.r.l., Italy.

Preferably, the heated feedstock is filtered using a filter device suitable to remove particles having an average diameter above 15ym, preferably above 10 ym, more preferably in the range of from 5ym to 0.01m.

As mentioned herein above, the ECR is a relatively clean hydrocarbon feedstock comprising only relatively low amounts of contaminants. However, it may be

preferable to remove even at least part of these

contaminants to lower the contaminant concentration in the hydrocarbon feedstock still further or inhibit even at least part of these contaminants. In addition, the diluent may comprise some contaminants, which again may be desirable to remove from the hydrocarbon feedstock.

Among others, the hydrocarbon feedstock may comprise water-soluble contaminants such as sodium, potassium or calcium salts. Sodium, potassium or calcium salts may lead to corrosion, in particular in combination with sulphur. In addition, sodium and potassium may from corrosive compounds with vanadium. Preferably, at least part of the water-soluble contaminants are removed from the hydrocarbon feedstock prior to step (d) , preferably by contacting the heated feedstock with liquid water at elevated pressure. The elevated pressure is required to maintain the water in the liquid state. Preferably, the pressure is in the range of from 2 to 50 bar (absolute) . By contacting the heated feedstock with liquid water at least part of the water-soluble contaminants dissolve in the liquid water and can subsequently be remove together with the water.

In addition, also non water-soluble contaminants may be removed or inhibited. In particular, metal-based contaminants such as lead compounds, nickel compounds, mercury compounds and vanadium compounds are preferably removed or inhibited.

Preferably, in particular vanadium compounds and more in particular water-insoluble organo-metallic vanadium compounds are inhibited by adding a vanadium inhibitor to the hydrocarbon feedstock and/or heated feedstock, more preferably a magnesium-based vanadium inhibitor. In a melted state vanadium compounds may show corrosive behaviour. For example, organo-metallic vanadium

compounds and some vanadium oxides such as e.g. vanadium pentoxide, which may be formed as the heated feedstock is oxidised in the gas turbine, have melting temperatures below typical operating temperature of the gas turbine. The function of the vanadium inhibitor is to inhibit vanadium-caused corrosion by formation of vanadium compounds, e.g. magnesium-vanadium compounds, having a melting temperature above the operating temperature of the gas turbine. The function of vanadium inhibitors is well described in the art and therefore known to the skilled person. Examples of suitable magnesium-based vanadium inhibitors include magnesium sulphonate, magnesium oxide and magnesium sulphate. Typically, these magnesium-based vanadium inhibitors are added in quantities such that the weight ratio of magnesium ions to vanadium ions is in the range of from 1 to 5,

preferably of from 1.5 to 3.

Lead, mercury and nickel compounds may be difficult to inhibit or remove from the hydrocarbon feedstock.

Therefore, it is preferred to control the content of these components by selection of the components of the hydrocarbon feedstock.

In order to reduce polymerisation of any olefins present in the hydrocarbon feedstock, it is preferred to add a polymerisation inhibitor to the hydrocarbon feedstock and/or the heated feedstock. Examples of suitable polymerisation inhibitors include for instance antioxidants .

Olefin polymerisation reactions include radical reaction, wherein radicals react with olefins to form oligomers and polymers, and aromatic alkylation by olefins. Polymerisation of olefins is undesirable as the resulting polymers have gum-like properties, which can lead to blockage of the nozzles, passageways and valves, which are used to provide the heated feedstock into the gas turbine. As a result, the presence of polymers will require a more regular cleaning of the turbine system, whereby the operation of the turbine is halted.

Further additives can be added to reduce phase separation, particulate fouling or chemical fouling. Examples of such additives include dispersants as sulfonates, detergents such as polyoxyethylene nonyl phenyl ether, or so-called asphaltene inhibitors such as alkyl phenol resins.

The vanadium and polymerisation inhibitors and further additives are preferably added in the form of a solution, emulsion, dispersion or suspension of the inhibitor in an aqueous or hydrocarbon medium.

The vanadium and polymerisation inhibitors and any further additives may be introduced into the hydrocarbon feedstock and/or heated feedstock using any suitable method for introducing vanadium and polymerisation inhibitors and further additives. Preferably, the

vanadium and polymerisation inhibitors and further additives are injected into the hydrocarbon feedstock and/or heated feedstock, for instance using an injection quill, with which the vanadium and polymerisation

inhibitors and further additives are dispersed into the hydrocarbon feedstock and/or heated feedstock.

The vanadium and polymerisation inhibitors and any further additives may be introduced prior to filtering at least part of the heated feedstock or subsequent thereto, i.e. respectively upstream or downstream of a filtration unit or filtration devise. In case, the vanadium and polymerisation inhibitors and any further additives comprise solid particles, this may particularly be the case for the vanadium inhibitor, it is preferred to introduce these prior to filtering at least part of the heated feedstock, more preferably by introducing the solid particles-comprising vanadium and polymerisation inhibitors and further additives into the part of the heated feedstock that is filtered. It is preferred that in case of a, intentional or unintentional, presence of large solid particles in the vanadium and polymerisation inhibitors and any further additives to block such particles for entering the gas turbine, as these may damage the gas turbine. Although this may cause a

blockage of the filter unit or filter device, such is preferred above potentially damaging the gas turbine. The vanadium and polymerisation inhibitors and any further additives may additionally be mixed with the hydrocarbon feedstock and/or heated feedstock using and suitable method for mixing. Preferably, the vanadium and polymerisation inhibitors and any further additives are mixed with the hydrocarbon feedstock and/or heated feedstock using one or more static mixers. More

preferably, two or more, or even all, of the inhibitors and/or additives are introduced upstream of a static mixer, reducing the number of static mixers required.

The ECR may also comprise sulphur compounds. As a result hydrogen sulphide may be generated during the heating and storage of the ECR, hydrocarbon feedstock and/or the heated feedstock. The hydrogen sulphide is subsequently combusted to SOx and steam in the gas turbine .

In step (d) of the process according to the

invention, the heated feedstock is, subsequent to the above mentioned treatments to remove or inhibit

contaminants, provided to a gas turbine to produce electrical or mechanical power. The heated feedstock in step (d) comprises in the range of from 20 to 60wt%, preferably 20 to 40wt% of asphaltenes, based on the weight of the ECR in the first hydrocarbon feedstock. Reference herein to a gas turbine is to a turbine wherein a fuel is combusted to provide hot gases and the hot gases drive the turbine blades to generate electrical or mechanical power. Gas turbines typically have a higher efficiency compared to conventional steam turbines. The gas turbine may comprise a separate gas turbine combustor to combust the fuel, i.e. the heated feedstock, and a turbine section comprising the turbine itself. Typically, the heated feedstock is combusted with air. However, it may also be combusted using oxygen enriched air or pure oxygen. In case of the later two, it is important to ensure that the temperature in the combustor does not become too high. Optionally, the air, oxygen-enriched air of oxygen is diluted with carbon dioxide to reduce the combustion temperature. The obtained hot gas from the combustion of the heated fuel is passed to the turbine section and exits the gas turbine as a hot flue gas.

Reference herein to a hot flue gas is to a flue gas having a temperature above 200 °C, preferably in the range of from 200 to 1500°C.

Preferably, the hot flue gas is subsequently provided to a steam boiler to generate pressurised steam. The steam can in turn be used to generate more electrical or mechanical power. Optionally, the steam boiler is heated by a combination of hot flue gas from the gas turbine and one or more other heat sources, such as the combustion of a hydrocarbon fuel.

Optionally, the hot flue gas may be used to pre-heat the ECR, hydrocarbon feedstock or hydrocarbon diluent.

The hot flue gas may also be used to provide heat to any other process stream or process. Preferably, the heated feedstock is provided into the gas turbine or gas turbine combustor using nozzles that allow the formation of a spray of heated feedstock. Particularly, suitable nozzles are atomising nozzles, which provide the ability to form very fine dispersions of the heated feedstock into the gas turbine or gas turbine combustor. As a result, the combustion reaction commences smoothly and the formation of hotspots and accompanying coke formation is reduced.

Nozzles, and in particular atomizing nozzles suitable for use in gas turbines are well known in the art and do not need any further explanation. Optionally a flue treatment system is provided to remove any dust/particulates, CO, NOx and/or SOx from the flue gas. The flue gas may be treated directly after exiting the gas turbine or optionally following the steam boiler. Such flue gas treatment may for instance

include: catalytic removal of NOx, flue gas filtration and/or SOx scrubbing.

Any ECR may be used in the process according to the invention, preferably the ECR has a 5wt% boiling

temperature range of 100 to 300°C, preferably 130 to

250°C and a 95wt% boiling temperature range of 450 to above 538 °C, preferably above 538°C. Reference herein to the 5wt boiling point and the 95wt% boiling point is to the temperature at which respectively 5wt% or 95wt%, based on weight of the ECR, is boiling as determined using ASTM method D2887. It is noted that the maximum boiling temperature which can be determined using ASTM method D2887 is 538°C

Preferably, the ECR is obtained from a thermal cracking process for thermally cracking a hydrocarbon feed. Particularly preferred is ECR from a thermal cracking process to produce ethylene as such thermal cracking processes use relatively clean hydrocarbon feedstocks resulting in ECR comprising low concentrations of contaminants. More particular preferred ECR is ECR, which was produced by thermally cracking light

hydrocarbon feedstock selected from LPG, natural gas liquids (NGL) , naphtha, gas oil, vacuum gas oil, hydrowax and synthetic hydrocarbons such as Fischer-Tropsch hydrocarbons, in particular C3 to CIO Fischer-Tropsch paraffins. As these feedstocks contain particular low amounts of contaminants. Preferably, the ECR has a kinematic viscosity of above 1000 cSt at 20°C, as determined with ASTM method D445. The upper limit of the ECR kinematic viscosity is indefinite, i.e. not measurable, preferably lxl0¹²cSt. Preferably, the ECR has a kinematic viscosity of in the range of 100 to 100000000 cSt at 50°C, as determined with ASTM method D445.

Preferably, the ECR contains little to no vanadium, more preferably no more than lOppmW vanadium, based on the weight of the vanadium or vanadium ions and the total weight of the ethylene cracker residue, even more

preferably in the range of from 0.001 to 5ppmW, still more preferably of from 0.01 to lppmW of vanadium based on the weight of the vanadium or vanadium ions and the total weight of the ethylene cracker residue.

Preferably, the ECR contains little to no lead, more preferably no more than lOppmW lead, based on the weight of the lead or lead ions and the total weight of the ethylene cracker residue, even more preferably in the range of from 0.001 to 5ppmW, still more preferably of from 0.01 to lppmW of lead based on the weight of the lead or lead ions and the total weight of the ethylene cracker residue.

Preferably, the ECR contains little to no nickel, more preferably no more than 8ppmW nickel, based on the weight of the nickel or nickel ions and the total weight of the ethylene cracker residue, even more preferably in the range of from 0.001 to 4ppmW, still more preferably of from 0.01 to lppmW of nickel based on the weight of the nickel or nickel ions and the total weight of the ethylene cracker residue.

Preferably, the ECR contains little to no mercury, more preferably no more than 5ppmW mercury, based on the weight of the mercury or mercury ions and the total weight of the ethylene cracker residue, even more

preferably in the range of from 0.001 to 3ppmW, still more preferably of from 0.01 to lppmW of mercury based on the weight of the mercury or mercury ions and the total weight of the ethylene cracker residue. It is an

advantage of the present invention that ECR contains little if any mercury.

Preferably, the ECR contains little to no sodium and potassium, more preferably no more than lOppmW sodium and potassium, based on the weight of the sodium and

potassium or sodium and potassium ions and the total weight of the ethylene cracker residue, even more

preferably in the range of from 0.001 to 5ppmW, still more preferably of from 0.01 to lppmW of sodium and potassium, based on the weight of the sodium and

potassium or sodium and potassium ions and the total weight of the ethylene cracker residue.

Preferably, the ECR contains little to no calcium, more preferably no more than lOppmW calcium, based on the weight of the calcium or calcium ions and the total weight of the ethylene cracker residue, even more

preferably in the range of from 0.001 to 5ppmW, still more preferably of from 0.01 to lppmW of calcium, based on the weight of the calcium or calcium ions and the total weight of the ethylene cracker residue.

The hydrocarbon feedstock may be any hydrocarbon feedstock comprising ECR. Optionally, the hydrocarbon feedstock may comprise distillation residues or

hydrocarbon streams derived thereof. Preferably, the hydrocarbon feedstock comprises in the range of from 30 to 100wt%, more preferably 50 to 99wt% based on the total weight of the hydrocarbon feedstock, of ethylene cracker residue. Even more preferably, the hydrocarbon feedstock comprises in the range of from 75 to 95wt% of ethylene cracker residue.

Preferably, the hydrocarbon feedstock contains little to no vanadium, more preferably no more than lOppmW vanadium, based on the weight of the vanadium or vanadium ions and the total weight of the hydrocarbon feedstock, even more preferably in the range of from 0.001 to 5ppmW, still more preferably of from 0.01 to lppmW of vanadium based on the weight of the vanadium or vanadium ions and the total weight of the hydrocarbon feedstock. By

addition of a vanadium inhibitor, as described herein above, it is possible to use a hydrocarbon feedstock comprising a higher vanadium content, although preferably no more than lOOppmW. It will be appreciated that

sufficient inhibitor should be added to limit the non- inhibited vanadium content to the preferred ranges mention herein above.

Preferably, the hydrocarbon feedstock contains little to no lead, more preferably no more than lOppmW lead, based on the weight of the lead or lead ions and the total weight of the hydrocarbon feedstock, even more preferably in the range of from 0.001 to 5ppmW, still more preferably of from 0.01 to lppmW of lead based on the weight of the lead or lead ions and the total weight of the hydrocarbon feedstock.

Preferably, the hydrocarbon feedstock contains little to no nickel, more preferably no more than 8ppmW nickel, based on the weight of the nickel or nickel ions and the total weight of the hydrocarbon feedstock, even more preferably in the range of from 0.001 to 4ppmW, still more preferably of from 0.01 to lppmW of nickel based on the weight of the nickel or nickel ions and the total weight of the hydrocarbon feedstock.

Preferably, the hydrocarbon feedstock contains little to no mercury, more preferably no more than 5ppmW

mercury, based on the weight of the mercury or mercury ions and the total weight of the hydrocarbon feedstock, even more preferably in the range of from 0.001 to 3ppmW, still more preferably of from 0.01 to lppmW of mercury based on the weight of the mercury or mercury ions and the total weight of the hydrocarbon feedstock.

Preferably, the hydrocarbon feedstock contains little to no sodium and potassium upon entering the gas turbine as the heated feedstock, more preferably no more than lOppmW sodium and potassium, based on the weight of the sodium and potassium or sodium and potassium ions and the total weight of the hydrocarbon feedstock, even more preferably in the range of from 0.001 to 5ppmW, still more preferably of from 0.01 to lppmW of sodium and potassium, based on the weight of the sodium and

potassium or sodium and potassium ions and the total weight of the hydrocarbon feedstock. Prior to entering the gas turbine the hydrocarbon feedstock may be treated to remove excess sodium and potassium, as described hereinabove, and to reduce the sodium and potassium content to the preferred ranges.

Preferably, the hydrocarbon feedstock contains little to no calcium upon entering the gas turbine as the heated feedstock, more preferably no more than lOppmW calcium, based on the weight of the calcium or calcium ions and the total weight of the hydrocarbon feedstock, even more preferably in the range of from 0.001 to 5ppmW, still more preferably of from 0.01 to lppmW of calcium, based on the weight of the calcium or calcium ions and the total weight of the hydrocarbon feedstock. Prior to entering the gas turbine the hydrocarbon feedstock may be treated to remove excess calcium, as described

hereinabove, and to reduce the calcium content to the preferred ranges.

Reference herein above to the presence of vanadium, lead, nickel, mercury, sodium, potassium and calcium in the ECR and hydrocarbon feedstock is presence in of vanadium, lead, nickel, mercury, sodium, potassium and calcium in any chemical form, including but not limited to pure metals, alloys, salts and organo-metalic .

The hydrocarbon feedstock may comprise one or more hydrocarbon diluents. Preferably, the hydrocarbon

diluents having a 5wt% boiling temperature range of 120 to 160°C, preferably 130 to 150°C and a 95wt% boiling temperature range of from 350 to 500 °C, preferably of from 375 to 450°C. Reference herein to the 5wt% boiling point and the 95wt% boiling point is to the temperature at which respectively 5 wt% or 95wt%, based on weight of the hydrocarbon diluent, is boiling as determined using

ASTM method D2887. In addition the hydrocarbon diluents preferably have a kinematic viscosity of in the range of from 2 to 15 cSt at 20°C, as determined with ASTM method D445, preferably the hydrocarbon diluents have a

kinematic viscosity of in the range of from 0.5 to 2.5 cSt at 50°C, as determined with ASTM method D445.

Preferably, the hydrocarbon diluent has a kinematic viscosity that is lower the than the kinematic viscosity of the ECR.

Preferably, the hydrocarbon diluent does not induce asphaltenes flocculation . Asphaltenes do not mix readily with paraffinic diluents such as diesel or kerosene.

Therefore, preferably, the hydrocarbon diluent comprises less than 30wt% of paraffinic hydrocarbons. The exact allowable concentration of paraffinic hydrocarbons is dependent on the composition of the ECR. Suitable

hydrocarbon diluents include, but are not limited to, cycle oils, pyrolysis oils or cracked gas oil.

Preferably, the hydrocarbon feedstock comprises little olefins. By analysing the olefinic hydrogen content in the hydrocarbon feedstock it is possible to provide a measure for the olefin concentration. Reference herein to olefinic hydrogen is to a hydrogen atom bound to an olefinic carbon atom, i.e. a carbon atom which is bound to another carbon atom through a double bond. The total hydrogen content and the olefinic hydrogen content can be determined using ¹H-NMR. Preferably, the

hydrocarbon feedstock comprises in the range of from 0.01 to 10 atomic% of olefinic hydrogen based on the total number of hydrogen atoms in the hydrocarbon feedstock as determined by ¹H-NMR. More preferably, the hydrocarbon feedstock comprises in the range of from 0.5 to 5atomic% of olefinic hydrogen based on the total number of

hydrogen atoms in the hydrocarbon feedstock as determined by ¹H-NMR .

ECR may comprise olefins. ECR may comprise such an olefin content that the olefinic hydrogen content is in the range of from 0.01 to 10atomic%, typically in the range of from 1 to 5atomic%, based on the total number of hydrogen atoms in the hydrocarbon feedstock as determined by ¹H-NMR. Also the hydrocarbon diluent may comprise olefins. For instance cracked gasoil may typically comprise such an olefin content that the olefinic

hydrogen content as determined by ¹H-NMR is in the range of from 2 to 8 atomic%, based on the total number of hydrogen atoms in the hydrocarbon feedstock. Where herein above reference is made to the total number of hydrogen atoms in the hydrocarbon feedstock this refers only to hydrogen atoms, which are bound to a carbon atom.

Hydrogen atoms present in for instance the form of water are not included in the total number of hydrogen atoms in the hydrocarbon feedstock when determining the olefinic hydrogen content .

As mentioned herein above, there is no need for the hydrocarbon feedstock or the heated feedstock to comprise water. Actually, the presence of water leads to a reduced efficiency as the water needs to be heated in addition to the hydrocarbon feedstock. Therefore, it preferred that the heated feedstock provided to the gas turbine

comprises less that 10wt% of water, based on the total weight of the heated feedstock. More preferably, the heated feedstock provided to the gas turbine comprises in the range of from 0 to 5 wt%, even more preferably 0 to 2 wt% of water, based on the total weight of the heated feedstock .

In the process according to the invention, the hydrocarbon feedstock is heated. The hydrocarbon

feedstock may be withdrawn as such from a steam cracker unit, for instance if the hydrocarbon feedstock comprises solely of ECR or the hydrocarbon feedstock is a mixture of ECR and cracked gas oil, whereby the cracked gas oil is another by-product of the steam cracking process. It is understood that in such a case the hydrocarbon

feedstock may be provided at sufficiently high

temperature and sufficiently low viscosity directly, or indirectly via a hot storage, from the steam cracker.

Such an embodiment also forms part of the invention, whereby step (a) and step (b) , i.e. providing a hydrocarbon feedstock and heating the feedstock, are performed simultaneously inside the steam cracker.

In addition it is possible to add hot ECR or a mixture of ECR and cracked gas oil directly, or

indirectly via a hot storage, from the steam cracker to a feedstock already comprising ECR and/or hydrocarbon diluent and utilising the heat in the hot ECR or mixture of ECR and cracked gas oil to heat the complete

hydrocarbon feedstock to a temperature at which the viscosity of the hydrocarbon feedstock is sufficiently lowered. The heating of the feedstock in step (b) is now accomplished by adding hot ECR.

Examples

The invention will be illustrated by the following non-limiting examples.

Example 1

Example 1 provides a calculated illustration of a process according to the invention. The reference numbers refer to Figure 1.

The properties of the respective streams are provided in Table 1.

In example 1, stream 1 comprising ECR having a temperature of 110°C and a kinematic viscosity of 98.9 cSt and an asphaltene content above 20wt%, based on the weight of the ECR is mixed with a stream 3 comprising

Cracked Gas Oil type hydrocarbon diluent having a

temperature of 40°C and a kinematic viscosity of 2.1 cSt to form the hydrocarbon feedstock in stream 5. The resulting hydrocarbon feedstock has a viscosity of 37.8 cSt. The hydrocarbon feedstock is provided to heater 7 and heated to form stream 9 comprising heated feedstock. The heated feedstock in stream 9 has a temperature of 150°C and a kinematic viscosity of 7.4 cSt. The heated feedstock is filtered in separation unit 11 to remove at least part of any particles having a particle diameter above lOym. The filtered particles leave the separation unit via conduit 13. After filtration, the heated

feedstock leaves separation unit 11 via stream 15.

Optionally, a magnesium oxide additive is added to the heated feedstock via conduit 17 to inhibit any vanadium compounds in the heated feedstock and reduce any

corrosion later in the process. The heated feedstock provided to pump 19 to increase the pressure to the required fuel supply pressure of gas turbine system 21.

Pressurised heated feedstock 20 is sprayed into combustion chamber 23 via one or more atomising nozzle (s) 25, where it is combusted with compressed combustion air (not shown) . The resulting hot gas steam 27 is provided to turbine 29 where mechanical/ electrical power can be generated via a generator.

Flue gas exiting gas turbine system 21 via conduit 31 is still hot, and may optionally be provided to heat recovery steam generator 33 to produce high pressure steam 35 and cooled flue gas 37.

Table 1

Example 2

Example 2 provides a calculated illustration of a process according to the invention. The reference numbers refer to Figure 2.

The properties of the respective streams are provided in Table 2.

In Example 2, a calculated illustration as in Example 1 is provided. However, in Example 2 the ECR in stream 51 comes directly from the steam cracker (not shown) and has a temperature of 190°C. The kinematic viscosity of this

ECR is 16.5 cSt. The ECR in stream 51 is mixed with a stream 53 comprising Cracked Gas Oil type hydrocarbon diluent having a temperature of 40 °C and a kinematic viscosity of 2.1 cSt to form the hydrocarbon feedstock in stream 5. As heating step (b) according to the invention has taken place in the steam cracker, heater 7 as shown in Figure 1 can be omitted, and a stream 59 comprising heated feedstock is obtained. The resulting heated feedstock has a temperature of 160°C and a kinematic viscosity of 8.5 cSt. The heated feedstock is filtered in separation unit 11 to remove at least part of any

particles having a particle diameter above lOym. The filtered particles leave the separation unit via conduit 13. After filtration, the heated feedstock leaves

separation unit 11 via stream 15. Optionally, a magnesium oxide additive is added to the heated feedstock via conduit 17 to inhibit any vanadium compounds in the heated feedstock and reduce any corrosion later in the process. The heated feedstock provided to pump 19 to increase the pressure to the required fuel supply

pressure of gas turbine system 21.

Table 2

Claims

C L A I M S

1. A process for operating a gas turbine, comprising: a) providing a hydrocarbon feedstock comprising at least ethylene cracker residue;

b) heating the hydrocarbon feedstock to obtained a heated feedstock with a decreased viscosity compared to the initial hydrocarbon feedstock;

c) filtering part or all of the heated feedstock; and d) providing the heated feedstock to a gas turbine to produce electrical or mechanical power and a hot flue gas,

hydrocarbon feedstock.

2. A process according to claim 1, wherein the

hydrocarbon feedstock comprises one or more hydrocarbon diluents having a 5wt% boiling temperature range of 120 to 160°C, preferably 130 to 150°C and a 95wt% boiling temperature range of from 350 to 500 °C, preferably of from 375 to 450°C and a kinematic viscosity of in the range of from 2 to 15 cSt at 20°C.

3. Process according to claim 1 or 2, wherein the hydrocarbon feedstock comprises in the range of from 50 to 100wt%, based on the total weight of the hydrocarbon feedstock, of ethylene cracker residue.

4. Process according to claim 2 or 3, wherein the hydrocarbon diluent is cracked gas oil.

5. Process according to any one of the preceding claims wherein the kinematic viscosity of the heated feedstock is at most 30 cSt, more preferably at most 25 cSt.

6. Process according to any one of the preceding claims, wherein the hydrocarbon feedstock comprises solid

particles and the heated feedstock is filtered to remove at least part of the solid particles.

7. Process according to any one of the preceding claims, wherein the hydrocarbon feedstock comprises water-soluble contaminants and wherein the heated feedstock is

contacted with liquid water at elevated pressure to remove at least part of the water-soluble contaminants from the heated feedstock prior to step (d) .

8. A process according to any one of the preceding claims, comprising adding a vanadium inhibitor to the hydrocarbon feedstock and/or heated feedstock, preferably a magnesium-based vanadium inhibitor.

9. A process according to any one of the preceding claims, comprising adding a polymerisation inhibitor to the hydrocarbon feedstock and/or heated feedstock.

10. A process according to any one of the preceding claims, wherein the hot flue gas is provided to a steam boiler to provide pressurised steam.

11. A process according to any one of the preceding claims, wherein the hydrocarbon feedstock comprises no more than lOppmW vanadium, based on the total weight of the hydrocarbon feedstock, preferably in the range of from 0.001 to 5ppmW, more preferably of from 0.01 to lppmW of vanadium based on the total weight of the hydrocarbon feedstock.

12. A process according to any one of the preceding claims, wherein the ethylene cracker residue comprises no more than lOppmW vanadium, based on the total weight of the ethylene cracker residue, preferably in the range of from 0.001 to 5ppmW, more preferably of from 0.01 to IppmW of vanadium based on the total weight of the ethylene cracker residue.

13. A process according to any one of the preceding claims, wherein the hydrocarbon feedstock comprises olefins and the olefinic hydrogen content is in the range of from 0.1 to 10 atomic%, preferably 0.5 to 5 atomic% , based on the total number of hydrogen atoms in the hydrocarbon feedstock.

14. Process according to any one of the preceding claims, wherein the hydrocarbon feedstock is heated to a

temperature in the range of from 135 to 275°C, preferably 200 to 250°C, to obtain the heated feedstock.