US20130298801A1 - Coating to reduce coking and assist with decoking in transfer line heat exchanger - Google Patents

Coating to reduce coking and assist with decoking in transfer line heat exchanger Download PDF

Info

Publication number
US20130298801A1
US20130298801A1 US13/884,238 US201113884238A US2013298801A1 US 20130298801 A1 US20130298801 A1 US 20130298801A1 US 201113884238 A US201113884238 A US 201113884238A US 2013298801 A1 US2013298801 A1 US 2013298801A1
Authority
US
United States
Prior art keywords
boron nitride
paint
applying
transfer line
coke
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Abandoned
Application number
US13/884,238
Inventor
Jyung-Hoon Kim
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Individual
Original Assignee
Individual
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Individual filed Critical Individual
Priority to US13/884,238 priority Critical patent/US20130298801A1/en
Publication of US20130298801A1 publication Critical patent/US20130298801A1/en
Abandoned legal-status Critical Current

Links

Images

Classifications

    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F28HEAT EXCHANGE IN GENERAL
    • F28FDETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
    • F28F19/00Preventing the formation of deposits or corrosion, e.g. by using filters or scrapers
    • F28F19/02Preventing the formation of deposits or corrosion, e.g. by using filters or scrapers by using coatings, e.g. vitreous or enamel coatings
    • CCHEMISTRY; METALLURGY
    • C10PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10GCRACKING HYDROCARBON OILS; PRODUCTION OF LIQUID HYDROCARBON MIXTURES, e.g. BY DESTRUCTIVE HYDROGENATION, OLIGOMERISATION, POLYMERISATION; RECOVERY OF HYDROCARBON OILS FROM OIL-SHALE, OIL-SAND, OR GASES; REFINING MIXTURES MAINLY CONSISTING OF HYDROCARBONS; REFORMING OF NAPHTHA; MINERAL WAXES
    • C10G9/00Thermal non-catalytic cracking, in the absence of hydrogen, of hydrocarbon oils
    • C10G9/14Thermal non-catalytic cracking, in the absence of hydrogen, of hydrocarbon oils in pipes or coils with or without auxiliary means, e.g. digesters, soaking drums, expansion means
    • C10G9/16Preventing or removing incrustation
    • CCHEMISTRY; METALLURGY
    • C10PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10GCRACKING HYDROCARBON OILS; PRODUCTION OF LIQUID HYDROCARBON MIXTURES, e.g. BY DESTRUCTIVE HYDROGENATION, OLIGOMERISATION, POLYMERISATION; RECOVERY OF HYDROCARBON OILS FROM OIL-SHALE, OIL-SAND, OR GASES; REFINING MIXTURES MAINLY CONSISTING OF HYDROCARBONS; REFORMING OF NAPHTHA; MINERAL WAXES
    • C10G9/00Thermal non-catalytic cracking, in the absence of hydrogen, of hydrocarbon oils
    • C10G9/14Thermal non-catalytic cracking, in the absence of hydrogen, of hydrocarbon oils in pipes or coils with or without auxiliary means, e.g. digesters, soaking drums, expansion means
    • C10G9/18Apparatus
    • C10G9/20Tube furnaces
    • C10G9/203Tube furnaces chemical composition of the tubes
    • CCHEMISTRY; METALLURGY
    • C10PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10GCRACKING HYDROCARBON OILS; PRODUCTION OF LIQUID HYDROCARBON MIXTURES, e.g. BY DESTRUCTIVE HYDROGENATION, OLIGOMERISATION, POLYMERISATION; RECOVERY OF HYDROCARBON OILS FROM OIL-SHALE, OIL-SAND, OR GASES; REFINING MIXTURES MAINLY CONSISTING OF HYDROCARBONS; REFORMING OF NAPHTHA; MINERAL WAXES
    • C10G2400/00Products obtained by processes covered by groups C10G9/00 - C10G69/14
    • C10G2400/20C2-C4 olefins

Definitions

  • the invention relates generally to a method of inhibiting coke or carbon formation and allowing easier cleaning of metal surfaces of processing equipment during high temperature processing of hydrocarbons. More particularly, the invention relates to the coating of certain surfaces of a transfer line heat exchanger with a boron-nitride composition to reduce coke formation and allow easier cleaning of those surfaces.
  • the product stream After passing through the pyrolysis furnace, the product stream is typically cooled or “quenched” in a transfer line heat exchanger (TLE) to both stop the reaction, and to cool for processing and separation.
  • TLE transfer line heat exchanger
  • a TLE is designed to recover sensible heat from the hot product stream leaving the pyrolysis furnace. Heat is transferred from the hot product mixture to low pressure steam in the TLE to form high-pressure steam.
  • Coke formation is a traditional problem in the TLE as hydrocarbons are dehydrogenated, forming a solid residue on the metal and refractory surfaces of the hot product side of the TLE. Coke formation and collection in the TLE typically results in poorer heat transfer, which in turn results in decreased production of high-pressure steam. Coke formation in the TLE also often results in a larger pressure drop across the TLE. This problem is particularly acute in the inlet cones of the TLE.
  • the typical operating cycle for a TLE is to operate for a period of time cooling the product stream from the pyrolysis furnace. During this operation coke forms in the inlet cone plugging up the tubes and tube sheet of the TLE and restricting flow.
  • the TLE will be hot cleaned (decoking cycle) using steam injected into the inlet cone to remove coke and open up the tubes of the TLE so more product gas can flow and there is less pressure drop. This is only partially effective and after two to four cycles of operation and hot cleaning, the TLE inlet cone must be removed so the coke can be removed through more aggressive methods.
  • This process of removal of the coke on the TLE inlet cone is typically accomplished mechanically, usually entailing hammers and chisels, which also damages the inlet cone refractory and the tubesheet of the TLE. Then, the operation cycle is started over. Because of the damage done to the inlet cone refractory of the TLE by the mechanical removal of coke, the inlet cone refractory must be repaired or replaced at a significant cost.
  • De-coking In addition to the shutdown and startup process of the pyrolysis furnace, the mechanical de-coking operation of the TLE itself frequently requires several days. De-coking therefore results in increased downtime relative to olefin production time, frequently amounting to a several percent loss of olefin production during the course of a year. De-coking is also relatively expensive and requires appreciable labor and energy.
  • Coke inhibitors i.e., chemical additives, or special coatings of metal surfaces which suppress coke formation have been used.
  • Coke inhibitors/surface coating act to passivate catalytically active metal sites through chemical bonding interactions, and/or forming a thin layer to physically isolate metal sites from coke precursors in the process stream, and/or interfering with those free radical reactions leading to coke formation by blocking active sites on surfaces.
  • additives are expensive and may lead to product gas stream quality issues.
  • What is needed is a method of controlling the growth and formation of coke, particularly in the inlet cone and tube sheet of the TLE. What is further needed is a method to reduce the damage done to the TLE inlet cone and tube sheet during a de-coking operation.
  • FIG. 1 is a depiction of coke formation on a metal surface of the TLE.
  • FIG. 1A is a pictorial depiction of filamentous coke.
  • FIG. 1B is a pictorial depiction of filamentous and free radical coke.
  • the methods described herein relate generally to the field of reducing and controlling coke formation in the TLE during the olefin production process.
  • a method of controlling coke formation in pyrolysis furnace process equipment wherein the surface of the process equipment is coated with a layer of boron nitride.
  • a method of controlling coke formation in a transfer line heat exchanger wherein a boron nitride paint is formed by combining dry boron nitride powder with distilled water. The boron nitride paint is applied to a transfer line heat exchanger tube sheet.
  • a boron nitride paint for coating the surfaces of pyrolysis furnace process equipment which includes providing a dry boron nitride powder.
  • the dry boron nitride powder contains boron nitride with a hexagonal crystalline structure.
  • Distilled water is provided and the boron nitride powder is mixed with the distilled water to form the boron nitride paint.
  • the boron nitride paint comprises between 20 and 45% boron nitride by weight.
  • Catalytic coke is classified into two types: Catalytic coke and Pyrolytic coke.
  • Catalytic coke is formed by dehydrogenation of hydrocarbon with catalytic action of metal components on the surface.
  • Metal components such as nickel and iron, may catalyze a hydrocarbon to reduce or eliminate hydrogen from the olefin, termed “dehydrogenation.”
  • Metal components presenting catalytic activities are generally in the order of Ni>>>>Fe>>Cr, NiO>Ni, FeO>Fe>Fe2O3. These metals and oxides catalyze reaction to form filament and coil type coke by successive dehydrogenation, as shown in FIG. 1 .
  • Catalytic coke tends to be very mechanically hard (“hard coke”) and normally difficult to remove. Hard coke must often be removed from surfaces by mechanical means. The formation of catalytic coke is believed to be most often involved in beginning the coking process of the TLE and is believed to act as trap for pyrolytic coke
  • Pyrolytic coke is divided into gaseous and condensation coke. Pyrolytic coke is softer and generally easier to remove than catalytic coke. Gaseous coke is typically formed by dehydrogenation of such light olefinic hydrocarbon as acetylene. Condensation coke is formed by condensation, polymerization, and dehydrogenation of heavy aromatic compounds. Pyroltyic coke can be classified as globular, black mirror, fluffy or amorphous types according to morphology.
  • the coking process of the TLE begins with the hydrocarbon reacting by catalyst action of metal components on metal surfaces and forms filamentous coke, which grows and provides deposit sites for various types of coke.
  • Free radical coking causes coke filaments to thicken and, as catalytic coke filaments grow, carbon starts to block metal surfaces. Tar is formed as condensation collects in the filaments.
  • FIG. 1 depicts one example of coke formation on typical metal surface 20 of pyrolysis furnace TLE 10 .
  • Filamentous coke filaments 30 grow outwardly (as shown by upward arrow 35 ) from typical metal surface 20 .
  • Free radical coke 40 tends to grow from filamentous coke filaments 30 , causing filaments 30 to grow and thicken.
  • Filamentous coke filaments 30 tend to continue to grow outwardly (as shown by horizontal arrows 45 ) until active metal site 50 is blocked by free radical coke 40 , as indicated by blocked metal site 60 .
  • FIG. 1A is a pictorial depiction of filamentous coke during initial formation.
  • FIG. 1B is a pictorial depiction of filamentous coke and free radical coke formation.
  • the product gas includes the coke precursors.
  • coking is common on gas entry refractory cone wall, the TLE tube (inside) wall and tubesheet surface. This coking traditionally causes two problems: pressure drop and spalling, i.e., the breaking of the coke into small particles. Either of these problems can result in to reduced product gas flow and ultimately a shutdown for decoking.
  • a coating is applied to the TLE tubesheet and inlet cone refractory and other elements to reduce the amount of catalytic hard coke formed during pyrolysis furnace operation.
  • the coating applied to the TLE tubesheet and inlet cone refractory is resistant to temperatures of 1600° F. (870° C.) or higher, is easy to apply to existing installations (retrofitability).
  • the coating adheres well to metal and/or refractory surfaces and is effective as a thin film or layer.
  • the coating is water based; in other embodiments the coating is an organic solvent based material.
  • the coating can be readily sprayed onto surfaces at room temperature. It is preferable that the coating be easy to dry and easy to cure developing good adhesion or bonding to metal and/or refractory surfaces. Typically, the coating requires minimum surface preparation.
  • the coating material is boron nitride.
  • Boron nitride has a number of crystalline structures, includes hexagonal, cubic, and wurtzite.
  • the TLE coating includes hexagonal boron nitride.
  • hexagonal crystalline structure of boron nitride is often lubricious, exhibiting some of the same properties of solid lubricants as graphite and molybendum disulfide, with low shear strength, low abrasivity, a good adherence of solid lubricant film and superior thermal stability.
  • Hexagonal boron nitride typically has an oxidation threshold of approximately 1562° F. (850° C.) in an oxidizing atmosphere and up to 1832° F. (1000° C.) in a reducing atmosphere.
  • hexagonal boron nitride can be used in inert or vacuum atmospheres at temperatures of approximately 3632° F. (2000° C.).
  • Hexagonal boron nitride tends to have a high thermal conductivity with a low thermal expansion. Hexagonal boron nitride typically has a relatively high thermal shock resistance compared to other oxide based refractory compounds. and tends to be chemically inert to the compounds to which it is exposed in a pyrolysis furnace. It therefore tends to have a relatively high resistance to chemical attack compared to other oxide based refractory compounds. and is resistant to chemical corrosion. Boron nitride tends to have an excellent parting plane compared to oxide based refractory compounds and reduces sticking in glass forming applications.
  • the thickness of the coating on the TLE inlet cone components and tubesheet depends on a number of factors including the cost of the coating material and the porosity and/or roughness of the surface to which it is applied.
  • the thickness of the coating applied to the TLE is in the range of about 25 microns to about 100 microns; in certain other embodiments of the present disclosure, the thickness of the coating is between about 40 microns and about 60 microns. In still other embodiments the thickness of the coating material is about 50 microns.
  • the thickness of the coating is not uniform, but varies across the tubesheet or inlet cone refractory surface, depending on the characteristics of the surface and the expected level of coke formation.
  • a water-based boron nitride paint is made from dry boron nitride powder and water, such as distilled water.
  • the water-based boron nitride paint is at 20 to 40% solids concentration by weight; in other embodiments, a 20 to 35% concentration is used, although as those of ordinary skill in the art will understand with the benefit of this disclosure, a greater or lesser concentration of solids may be used.
  • the boron nitride coating is accomplished by use of a spray gun, such as a DeVilbiss Compact Pressure Spray Gun, although this example is non-limiting and any suitable spray gun may be used.
  • a spray gun such as a DeVilbiss Compact Pressure Spray Gun, although this example is non-limiting and any suitable spray gun may be used.
  • the surface to which the coating is to be applied is preferable to be clean, dry, and as free from grease or oil as is practical.
  • the TLE inlet cone and tubesheet have not been previously used, i.e., they have not been exposed to process chemicals.
  • Non-limiting examples of surface roughening include those specified by SSPC-SP6 and NACE 3-Commercial Blast Cleaning.
  • the residual coke on metal surfaces such as the TLE tubesheet inlet surface and Intrabody Flow Diverter surface are first removed and cleaned by a hydroblasting procedure, typically at about 10,000 psi then allowed to air dry.
  • a hydroblasting procedure typically at about 10,000 psi then allowed to air dry.
  • typically the residual coke on the TLE inlet cone refractory is removed and the inlet cone refractory surface is dusted to remove residual coke.
  • the boron nitride paint may be applied in a single coat or in multiple coats to achieve the desired thickness.
  • it may be necessary to allow drying of the boron nitride paint between coats.
  • the drying may be performed at ambient temperature or at an elevated temperature, depending on need.
  • the boron nitride paint may then be allowed to cure after completion of the application of all coats. Curing, like drying, may be accomplished at ambient temperature or at an elevated temperature depending on need. Typical curing times are between 60 and 120 minutes, although more or less time may be necessary depending on such factors as the thickness of boron nitride paint, the relative humidity, and the ambient temperature.
  • the TLE may be reassembled and placed in the discharge line of the pyrolysis furnace. It has been determined by the applicants that the boron nitride coating often allows for increased run times of the pyrolysis furnace between steam decoking. Further, it has been observed by applicants that run times between mechanical cleaning of the TLE can be significantly extended as compared to run times of TLEs with uncoated tubesheets and inlet cones. While not bound by theory, applicants believe that the boron nitride coating acts to inhibit formation of catalytic coke by reducing or preventing contact between the hot product stream and the metal catalysts by coating the metal surfaces.
  • boron nitride coating provides a surface with less friction than the uncoated surface, weakening coke adhesion compared to the uncoated surface.
  • the boron nitride coating may be used with process equipment having metal surfaces where coke forms and deposits, and where the temperature does not exceed 1832° F. (1000° C.) in oxidation environment and 3632° F. (2000° C.) in a vacuum or inert atmosphere.
  • process equipment would include, but not be limited to the pyrolysis furnace, the furnace tubing, the transfer piping from the furnace to the TLE, the piping between the primary and secondary TLEs and the tubes inside the TLEs. This method could also apply to any similar process where coke is formed under similar high temperature process conditions.
  • TLE was removed from a pyrolysis furnace process and disassembled to allow access to the inlet tubesheet surface and TLE cone internal components.
  • a boron nitride paint was made by combining distilled water with a boron nitride powder with a hexagonal crystalline structure. Sufficient boron nitride powder was added to reach a concentration of 28% concentration by weight.
  • a commercial spray gun was pressurized to between 20 and 40 psi using compressed air filtered to remove moisture and particulate.
  • the boron nitride paint was introduced into the spray gun.
  • a 50 micron thick coating of boron nitride was applied to the TLE tubesheet and inside surfaces of the TLE inlet cone. The application was made in two stages with each stage applying a 25 micron coating.
  • the boron nitride coating was allowed to dry approximately 30 to 60 minutes between coats at room temperature, The final boron nitride coating was cured for 60 to 120 minutes at room temperature.

Landscapes

  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Oil, Petroleum & Natural Gas (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • General Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Production Of Liquid Hydrocarbon Mixture For Refining Petroleum (AREA)
  • Paints Or Removers (AREA)

Abstract

Coke formation in pyrolysis furnaces is controlled by applying a coating of boron nitride to pyrolysis furnace process equipment surfaces, for instance, parts of the transfer line heat exchanger assembly.

Description

    FIELD OF THE INVENTION
  • The invention relates generally to a method of inhibiting coke or carbon formation and allowing easier cleaning of metal surfaces of processing equipment during high temperature processing of hydrocarbons. More particularly, the invention relates to the coating of certain surfaces of a transfer line heat exchanger with a boron-nitride composition to reduce coke formation and allow easier cleaning of those surfaces.
  • BACKGROUND ART
  • In traditional pyrolysis processing using pyrolysis furnaces, mixtures of hydrocarbons and steam flow through long coils or tubes which are heated by combustion gases to produce olefins, such as ethylene and propylene, as well as other valuable by-products. Heat is transferred from the hot combustion gases to the hydrocarbon feedstock passing within the coils. The hydrocarbon feedstock is heated within the coils to temperatures typically in the range of about 750° to 950° C. to form the product stream.
  • After passing through the pyrolysis furnace, the product stream is typically cooled or “quenched” in a transfer line heat exchanger (TLE) to both stop the reaction, and to cool for processing and separation. A TLE is designed to recover sensible heat from the hot product stream leaving the pyrolysis furnace. Heat is transferred from the hot product mixture to low pressure steam in the TLE to form high-pressure steam.
  • Coke formation is a traditional problem in the TLE as hydrocarbons are dehydrogenated, forming a solid residue on the metal and refractory surfaces of the hot product side of the TLE. Coke formation and collection in the TLE typically results in poorer heat transfer, which in turn results in decreased production of high-pressure steam. Coke formation in the TLE also often results in a larger pressure drop across the TLE. This problem is particularly acute in the inlet cones of the TLE.
  • The typical operating cycle for a TLE is to operate for a period of time cooling the product stream from the pyrolysis furnace. During this operation coke forms in the inlet cone plugging up the tubes and tube sheet of the TLE and restricting flow. When the pressure drop becomes too high, the TLE will be hot cleaned (decoking cycle) using steam injected into the inlet cone to remove coke and open up the tubes of the TLE so more product gas can flow and there is less pressure drop. This is only partially effective and after two to four cycles of operation and hot cleaning, the TLE inlet cone must be removed so the coke can be removed through more aggressive methods. This process of removal of the coke on the TLE inlet cone is typically accomplished mechanically, usually entailing hammers and chisels, which also damages the inlet cone refractory and the tubesheet of the TLE. Then, the operation cycle is started over. Because of the damage done to the inlet cone refractory of the TLE by the mechanical removal of coke, the inlet cone refractory must be repaired or replaced at a significant cost.
  • In addition to the shutdown and startup process of the pyrolysis furnace, the mechanical de-coking operation of the TLE itself frequently requires several days. De-coking therefore results in increased downtime relative to olefin production time, frequently amounting to a several percent loss of olefin production during the course of a year. De-coking is also relatively expensive and requires appreciable labor and energy.
  • Previous methods have been used to control coke formation. For instance, coke inhibitors, i.e., chemical additives, or special coatings of metal surfaces which suppress coke formation have been used. Coke inhibitors/surface coating act to passivate catalytically active metal sites through chemical bonding interactions, and/or forming a thin layer to physically isolate metal sites from coke precursors in the process stream, and/or interfering with those free radical reactions leading to coke formation by blocking active sites on surfaces. Such additives are expensive and may lead to product gas stream quality issues.
  • What is needed is a method of controlling the growth and formation of coke, particularly in the inlet cone and tube sheet of the TLE. What is further needed is a method to reduce the damage done to the TLE inlet cone and tube sheet during a de-coking operation.
  • BRIEF DESCRIPTION OF THE DRAWINGS
  • FIG. 1 is a depiction of coke formation on a metal surface of the TLE.
  • FIG. 1A is a pictorial depiction of filamentous coke.
  • FIG. 1B is a pictorial depiction of filamentous and free radical coke.
  • SUMMARY
  • The methods described herein relate generally to the field of reducing and controlling coke formation in the TLE during the olefin production process.
  • In one embodiment of the present disclosure, a method of controlling coke formation in pyrolysis furnace process equipment is described, wherein the surface of the process equipment is coated with a layer of boron nitride.
  • In another embodiment of the present disclosure, a method of controlling coke formation in a transfer line heat exchanger is described, wherein a boron nitride paint is formed by combining dry boron nitride powder with distilled water. The boron nitride paint is applied to a transfer line heat exchanger tube sheet.
  • In still another embodiment of the present disclosure, a boron nitride paint for coating the surfaces of pyrolysis furnace process equipment is described which includes providing a dry boron nitride powder. The dry boron nitride powder contains boron nitride with a hexagonal crystalline structure. Distilled water is provided and the boron nitride powder is mixed with the distilled water to form the boron nitride paint. The boron nitride paint comprises between 20 and 45% boron nitride by weight.
  • DETAILED DESCRIPTION
  • While not bound by theory, applicants have determined that coke is classified into two types: Catalytic coke and Pyrolytic coke. Catalytic coke is formed by dehydrogenation of hydrocarbon with catalytic action of metal components on the surface. Metal components, such as nickel and iron, may catalyze a hydrocarbon to reduce or eliminate hydrogen from the olefin, termed “dehydrogenation.” Metal components presenting catalytic activities are generally in the order of Ni>>>>Fe>>Cr, NiO>Ni, FeO>Fe>Fe2O3. These metals and oxides catalyze reaction to form filament and coil type coke by successive dehydrogenation, as shown in FIG. 1.
  • Catalytic coke tends to be very mechanically hard (“hard coke”) and normally difficult to remove. Hard coke must often be removed from surfaces by mechanical means. The formation of catalytic coke is believed to be most often involved in beginning the coking process of the TLE and is believed to act as trap for pyrolytic coke
  • Pyrolytic coke is divided into gaseous and condensation coke. Pyrolytic coke is softer and generally easier to remove than catalytic coke. Gaseous coke is typically formed by dehydrogenation of such light olefinic hydrocarbon as acetylene. Condensation coke is formed by condensation, polymerization, and dehydrogenation of heavy aromatic compounds. Pyroltyic coke can be classified as globular, black mirror, fluffy or amorphous types according to morphology.
  • It is believed that the coking process of the TLE begins with the hydrocarbon reacting by catalyst action of metal components on metal surfaces and forms filamentous coke, which grows and provides deposit sites for various types of coke. Free radical coking causes coke filaments to thicken and, as catalytic coke filaments grow, carbon starts to block metal surfaces. Tar is formed as condensation collects in the filaments. The filaments formed by catalytic coking stop growing when metal particles are covered with carbon and, afterwards, radical and condensation coking become dominant.
  • FIG. 1 depicts one example of coke formation on typical metal surface 20 of pyrolysis furnace TLE 10. Filamentous coke filaments 30 grow outwardly (as shown by upward arrow 35) from typical metal surface 20. Free radical coke 40 tends to grow from filamentous coke filaments 30, causing filaments 30 to grow and thicken. Filamentous coke filaments 30 tend to continue to grow outwardly (as shown by horizontal arrows 45) until active metal site 50 is blocked by free radical coke 40, as indicated by blocked metal site 60. FIG. 1A is a pictorial depiction of filamentous coke during initial formation. FIG. 1B is a pictorial depiction of filamentous coke and free radical coke formation.
  • In the pyrolysis furnace, the product gas includes the coke precursors. When the product gas is quenched to stop the reaction in the TLE before main fractioner, coking is common on gas entry refractory cone wall, the TLE tube (inside) wall and tubesheet surface. This coking traditionally causes two problems: pressure drop and spalling, i.e., the breaking of the coke into small particles. Either of these problems can result in to reduced product gas flow and ultimately a shutdown for decoking.
  • In certain embodiments of the present disclosure, a coating is applied to the TLE tubesheet and inlet cone refractory and other elements to reduce the amount of catalytic hard coke formed during pyrolysis furnace operation. In at least some embodiments of the present invention, the coating applied to the TLE tubesheet and inlet cone refractory is resistant to temperatures of 1600° F. (870° C.) or higher, is easy to apply to existing installations (retrofitability). In these embodiments, the coating adheres well to metal and/or refractory surfaces and is effective as a thin film or layer. In certain embodiments of the present disclosure, the coating is water based; in other embodiments the coating is an organic solvent based material. In certain embodiments, the coating can be readily sprayed onto surfaces at room temperature. It is preferable that the coating be easy to dry and easy to cure developing good adhesion or bonding to metal and/or refractory surfaces. Typically, the coating requires minimum surface preparation.
  • In certain embodiments of the present invention, the coating material is boron nitride. Boron nitride has a number of crystalline structures, includes hexagonal, cubic, and wurtzite. In certain embodiments of the present disclosure, the TLE coating includes hexagonal boron nitride.
  • The hexagonal crystalline structure of boron nitride is often lubricious, exhibiting some of the same properties of solid lubricants as graphite and molybendum disulfide, with low shear strength, low abrasivity, a good adherence of solid lubricant film and superior thermal stability. Hexagonal boron nitride typically has an oxidation threshold of approximately 1562° F. (850° C.) in an oxidizing atmosphere and up to 1832° F. (1000° C.) in a reducing atmosphere. In certain circumstances, hexagonal boron nitride can be used in inert or vacuum atmospheres at temperatures of approximately 3632° F. (2000° C.). Hexagonal boron nitride tends to have a high thermal conductivity with a low thermal expansion. Hexagonal boron nitride typically has a relatively high thermal shock resistance compared to other oxide based refractory compounds. and tends to be chemically inert to the compounds to which it is exposed in a pyrolysis furnace. It therefore tends to have a relatively high resistance to chemical attack compared to other oxide based refractory compounds. and is resistant to chemical corrosion. Boron nitride tends to have an excellent parting plane compared to oxide based refractory compounds and reduces sticking in glass forming applications.
  • As those of skill in the art will appreciate, the thickness of the coating on the TLE inlet cone components and tubesheet depends on a number of factors including the cost of the coating material and the porosity and/or roughness of the surface to which it is applied. In certain embodiments of the present disclosure, the thickness of the coating applied to the TLE is in the range of about 25 microns to about 100 microns; in certain other embodiments of the present disclosure, the thickness of the coating is between about 40 microns and about 60 microns. In still other embodiments the thickness of the coating material is about 50 microns. In certain embodiments of the present disclosure, the thickness of the coating is not uniform, but varies across the tubesheet or inlet cone refractory surface, depending on the characteristics of the surface and the expected level of coke formation.
  • Application of the boron nitride coating may be accomplished by traditional coating application methods. In certain embodiments, a water-based boron nitride paint is made from dry boron nitride powder and water, such as distilled water. In particular embodiments, the water-based boron nitride paint is at 20 to 40% solids concentration by weight; in other embodiments, a 20 to 35% concentration is used, although as those of ordinary skill in the art will understand with the benefit of this disclosure, a greater or lesser concentration of solids may be used.
  • In certain embodiments of the present disclosure, the boron nitride coating is accomplished by use of a spray gun, such as a DeVilbiss Compact Pressure Spray Gun, although this example is non-limiting and any suitable spray gun may be used.
  • When applying the boron nitride coating, it is preferable to have the surface to which the coating is to be applied to be clean, dry, and as free from grease or oil as is practical. In certain embodiments of the present disclosure, the TLE inlet cone and tubesheet have not been previously used, i.e., they have not been exposed to process chemicals. In such embodiments, it may be necessary to roughen the surface of the area to which the coating is to be applied in order to assist in physical adherence to the surface. Non-limiting examples of surface roughening include those specified by SSPC-SP6 and NACE 3-Commercial Blast Cleaning.
  • In certain other embodiments, such as when the TLE has been previously used in a pyrolysis furnace, the residual coke on metal surfaces such as the TLE tubesheet inlet surface and Intrabody Flow Diverter surface are first removed and cleaned by a hydroblasting procedure, typically at about 10,000 psi then allowed to air dry. In those embodiments, typically the residual coke on the TLE inlet cone refractory is removed and the inlet cone refractory surface is dusted to remove residual coke.
  • The boron nitride paint may be applied in a single coat or in multiple coats to achieve the desired thickness. In particular embodiment of the present disclosure, when applying multiple coats of the boron nitride paint, it may be necessary to allow drying of the boron nitride paint between coats. The drying may be performed at ambient temperature or at an elevated temperature, depending on need. The boron nitride paint may then be allowed to cure after completion of the application of all coats. Curing, like drying, may be accomplished at ambient temperature or at an elevated temperature depending on need. Typical curing times are between 60 and 120 minutes, although more or less time may be necessary depending on such factors as the thickness of boron nitride paint, the relative humidity, and the ambient temperature.
  • Following the application of the boron nitride paint, the TLE may be reassembled and placed in the discharge line of the pyrolysis furnace. It has been determined by the applicants that the boron nitride coating often allows for increased run times of the pyrolysis furnace between steam decoking. Further, it has been observed by applicants that run times between mechanical cleaning of the TLE can be significantly extended as compared to run times of TLEs with uncoated tubesheets and inlet cones. While not bound by theory, applicants believe that the boron nitride coating acts to inhibit formation of catalytic coke by reducing or preventing contact between the hot product stream and the metal catalysts by coating the metal surfaces. While pyrolytic coke continues to form, it softer than the hard catalytic coke and may be more easily cleaned by steam decoking. It is further believed that the boron nitride coating provides a surface with less friction than the uncoated surface, weakening coke adhesion compared to the uncoated surface.
  • While this disclosure has focused on the use of the boron nitride coating of the TLE tubesheet and inlet cone, those of ordinary skill in the art, with the benefit of this disclosure, will recognize that the boron nitride coating may be used with process equipment having metal surfaces where coke forms and deposits, and where the temperature does not exceed 1832° F. (1000° C.) in oxidation environment and 3632° F. (2000° C.) in a vacuum or inert atmosphere. Such equipment would include, but not be limited to the pyrolysis furnace, the furnace tubing, the transfer piping from the furnace to the TLE, the piping between the primary and secondary TLEs and the tubes inside the TLEs. This method could also apply to any similar process where coke is formed under similar high temperature process conditions.
  • This disclosure will now be further illustrated with respect to certain specific examples which are not intended to limit the invention, but rather to provide more specific embodiments as only a few of many possible embodiments.
  • EXAMPLE 1
  • A previously used TLE was removed from a pyrolysis furnace process and disassembled to allow access to the inlet tubesheet surface and TLE cone internal components.
  • Coke was removed and the tubesheet and TLE inlet cone were cleaned by hydroblasting. The TLE components were allowed to dry and remaining dust was removed.
  • A boron nitride paint was made by combining distilled water with a boron nitride powder with a hexagonal crystalline structure. Sufficient boron nitride powder was added to reach a concentration of 28% concentration by weight.
  • A commercial spray gun was pressurized to between 20 and 40 psi using compressed air filtered to remove moisture and particulate. The boron nitride paint was introduced into the spray gun. A 50 micron thick coating of boron nitride was applied to the TLE tubesheet and inside surfaces of the TLE inlet cone. The application was made in two stages with each stage applying a 25 micron coating. The boron nitride coating was allowed to dry approximately 30 to 60 minutes between coats at room temperature, The final boron nitride coating was cured for 60 to 120 minutes at room temperature.

Claims (18)

What is claimed is:
1. A method of controlling coke formation in pyrolysis furnace process equipment, comprising:
coating a surface of the process equipment with a layer of boron nitride to form a coated surface.
2. The method of claim 1, wherein the boron nitride is comprised of hexagonal crystals.
3. The method of claim 2, wherein the boron nitride has an oxidation threshold of about 850° C. in an oxidizing atmosphere and about 2000° C. in a reducing atmosphere.
4. The method of claim 1 wherein the process equipment comprises a transfer line heat exchanger tube sheet.
5. The method of claim 4 wherein the process equipment further comprises an inlet cone refractory of the transfer line heat exchanger.
6. The method of claim 5, wherein the thickness of the coated surface is between about 25 microns to about 100 microns.
7. The method of claim 6, wherein the thickness of the coated surface is between about 40 and about 60 microns.
8. A method of controlling coke formation in a transfer line heat exchanger, comprising:
forming a boron nitride paint by combining dry boron nitride powder with distilled water, and;
applying the boron nitride paint to a surface of a transfer line heat exchanger tube sheet.
9. The method of claim 8 further comprising applying the boron nitride paint to a surface of a transfer line heat exchange inlet refractory cone.
10. The method of claim 8 further comprising prior to the step of applying the boron nitride paint:
roughening the surface of the transfer line heat exchanger tube sheet.
11. The method of claim 8 further comprising prior to the step of applying the boron nitride paint:
hydroblasting the surface of the tubesheet of the transfer line heat exchanger; and
drying the surface of the tubesheet of the transfer line heat exchanger.
12. The method of claim 8, wherein the step of applying the boron nitride paint further comprises applying a first coat of boron nitride paint.
13. The method of claim 12, wherein the step of applying the boron nitride paint further comprises applying a second coat of boron nitride paint.
14. The method of claim 13, wherein the step of applying the boron nitride paint further comprises, prior to the step of applying a second coat of boron nitride paint, drying the boron nitride paint.
15. The method of claim 14, wherein the step of applying the boron nitride paint further comprises, after the step of applying the second coat of boron nitride paint, curing the boron nitride paint.
16. The method of claim 15, wherein the boron nitride paint is cured for between 60 and 120 minutes.
17. A boron nitride paint for coating the surfaces of pyrolysis furnace process equipment comprising:
providing a dry boron nitride powder, wherein the dry boron nitride powder comprises boron nitride with a hexagonal crystalline structure;
providing distilled water; and
mixing the boron nitride powder with the distilled water to form the boron nitride paint, wherein the boron nitride paint comprises between 20 and 40% boron nitride by weight.
18. The boron nitride paint of claim 17, wherein the boron nitride paint comprises between 20 and 35% boron nitride by weight.
US13/884,238 2010-11-09 2011-09-29 Coating to reduce coking and assist with decoking in transfer line heat exchanger Abandoned US20130298801A1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
US13/884,238 US20130298801A1 (en) 2010-11-09 2011-09-29 Coating to reduce coking and assist with decoking in transfer line heat exchanger

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
US41171310P 2010-11-09 2010-11-09
PCT/US2011/053941 WO2012064419A1 (en) 2010-11-09 2011-09-29 Coating to reduce coking and assist with decoking in transfer line heat exchanger
US13/884,238 US20130298801A1 (en) 2010-11-09 2011-09-29 Coating to reduce coking and assist with decoking in transfer line heat exchanger

Publications (1)

Publication Number Publication Date
US20130298801A1 true US20130298801A1 (en) 2013-11-14

Family

ID=46051238

Family Applications (1)

Application Number Title Priority Date Filing Date
US13/884,238 Abandoned US20130298801A1 (en) 2010-11-09 2011-09-29 Coating to reduce coking and assist with decoking in transfer line heat exchanger

Country Status (3)

Country Link
US (1) US20130298801A1 (en)
CA (1) CA2817509A1 (en)
WO (1) WO2012064419A1 (en)

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4555326A (en) * 1984-05-17 1985-11-26 Betz Laboratories, Inc. Methods and compositions for boronizing metallic surfaces
US4724064A (en) * 1983-11-17 1988-02-09 Betz Laboratories, Inc. Composition and method for coke retardant during hydrocarbon processing
US20030183248A1 (en) * 2002-03-28 2003-10-02 Nova Chemicals (International) S.A. Decoke enhancers for transfer line exchangers
US20090142498A1 (en) * 2006-03-10 2009-06-04 Stefan Faber Coat or coating to counteract crystalline deposits

Family Cites Families (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4264052A (en) * 1978-07-27 1981-04-28 International Lead Zinc Research Organization, Inc. Water-dispersible coatings containing boron nitride for steel casting dies
US4785877A (en) * 1986-05-16 1988-11-22 Santa Fe Braun Inc. Flow streamlining device for transfer line heat exchanges
US6274113B1 (en) * 1994-01-04 2001-08-14 Chevron Phillips Chemical Company Lp Increasing production in hydrocarbon conversion processes
JP2010520358A (en) * 2007-03-06 2010-06-10 ユニベーション・テクノロジーズ・エルエルシー Method for applying a solution catalyst to a reactor surface
US20100105264A1 (en) * 2008-10-27 2010-04-29 Tim Pistner Gasket release agent

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4724064A (en) * 1983-11-17 1988-02-09 Betz Laboratories, Inc. Composition and method for coke retardant during hydrocarbon processing
US4555326A (en) * 1984-05-17 1985-11-26 Betz Laboratories, Inc. Methods and compositions for boronizing metallic surfaces
US20030183248A1 (en) * 2002-03-28 2003-10-02 Nova Chemicals (International) S.A. Decoke enhancers for transfer line exchangers
US20090142498A1 (en) * 2006-03-10 2009-06-04 Stefan Faber Coat or coating to counteract crystalline deposits

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
Wattyl, "Surface preparation Ferrous Metal". January 2010 *

Also Published As

Publication number Publication date
WO2012064419A1 (en) 2012-05-18
CA2817509A1 (en) 2012-05-18

Similar Documents

Publication Publication Date Title
JP5938044B2 (en) Alumina-formed bimetal tubes and methods of manufacture and use
RU2212283C2 (en) Method of coating inner walls of reactor tubes in hydrocarbon pyrolysis reactor
US6210747B1 (en) Thermal cracking process and furnace elements
US20040188323A1 (en) Active coating system for reducing or eliminating coke build-up during petrochemical processes
JP2973347B2 (en) Decoking method
US20130298801A1 (en) Coating to reduce coking and assist with decoking in transfer line heat exchanger
EP0110486B1 (en) Installation (plant) for thermo-cracking a hydrocarbon starting material to alkene, shell and tube heat exchanger for use in such an installation and process for manufacturing shell and tube heat exchanger
US5733438A (en) Coke inhibitors for pyrolysis furnaces
US6071563A (en) Method of protecting metal
US6322879B1 (en) Protecting metal from carbon
US10894276B2 (en) Decoking process
EP0739997B1 (en) Method of protecting metal
CN1312316C (en) Ethylene furnace tube surface coating preparation method
US6410171B1 (en) Protecting metal from carbon
CA3033604C (en) Decoking process
EP0889146B1 (en) Heat resistant chromized steel, process for the production thereof and its use in anti-coking applications
Wang et al. Influence of coke thickness on the on-line SiO2/S coating preparation and its thermal shock property
JPS645640B2 (en)
CS268974B1 (en) Method of tubes decoking in pyrolysis furnace's heat-exchanger
Cordero-Lanzac et al. PREVENTION OF CARBON DEPOSITION ON THE SURFACE OF STAINLESS STEEL TUBES THROUGH CERAMIC COATING
SA95160356A (en) Cracking processes
JPH10168554A (en) Method for treating surface of steel tube for sulfodation corrosion resistant and erosion-resistant boiler

Legal Events

Date Code Title Description
STCB Information on status: application discontinuation

Free format text: ABANDONED -- FAILURE TO RESPOND TO AN OFFICE ACTION