Diffusion Coatings for Corrosion-Resistant Components in ... · ConocoPhillips' E-Gas technology. This corrosion is the leading cause of the unscheduled downtime at the plant and

SRI International Technical Progress Report • October 2006

Diffusion Coatings for Corrosion-Resistant Components in Coal Gasification Systems

Quarterly Technical Progress Report 13

Covering the period July 1, 2006 through September 30, 2006 SRI Project P13063 Contract No.: DE-FC26-03NT41616 Prepared by: Gopala N. Krishnan, Ripudaman Malhotra, Esperanza Alvarez, Kai-Hung Lau, Jordi Perez Mariano and Angel Sanjurjo SRI International 333 Ravenswood Avenue Menlo Park, CA 94025 Prepared for: U.S. Department of Energy National Energy Technology Center P. O. Box 10940 Pittsburgh, PA 15236 Attention: Dr. Richard Read

DISCLAIMER

This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

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ABSTRACT

Heat-exchangers, particle filters, turbines, and other components in integrated coal gasification combined cycle system must withstand the highly sulfiding conditions of the high-temperature coal gas over an extended period of time. The performance of components degrades significantly with time unless expensive high alloy materials are used. Deposition of a suitable coating on a low-cost alloy may improve its resistance to such sulfidation attack, and decrease capital and operating costs. The alloys used in the gasifier service include austenitic and ferritic stainless steels, nickel-chromium-iron alloys, and expensive nickel-cobalt alloys.

The primary activity this period was preparation and presentation of the findings on this project at the Twenty-Third annual Pittsburgh Coal Conference. Dr. Malhotra attended this conference and presented a paper. A copy of his presentation constitutes this quarterly report.

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TABLE OF CONTENTS

Disclaimer ........................................................................................................................... 2

Abstract ............................................................................................................................... 3

Executive Summary ............................................................................................................ 5

Introduction......................................................................................................................... 6

Work Performed.................................................................................................................. 6

Pittsburgh Coal Conference 2006 Presentation ....................................................Appended

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EXECUTIVE SUMMARY

Advanced coal gasification systems such as integrated coal gasification combined cycle (IGCC) processes offer many advantages over conventional pulverized coal combustors. Heat-exchangers, filters, turbines, and other components in IGCC plants often must withstand the highly sulfiding conditions at high temperatures. In collaboration with U.S. Department of Energy and ConocoPhillips, we are developing corrosion-resistant coatings for high-temperature components in IGCC systems.

SG Solution's coal gasification power plant in Terre Haute, IN, uses ConocoPhillips' E-Gas technology. The need for corrosion-resistant coatings exists in two areas: (1) the tube sheet of a heat exchanger at ~1000°C that is immediately downstream of the gasifier, and (2) porous metal particulate filter at 370°C, which is downstream of the heat exchanger. These components operate at gas streams containing as much as 2% H2S. A protective metal or ceramic coating that can resist sulfidation corrosion will extend the life-time of these components and reduce maintenance.


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INTRODUCTION

Heat-exchangers, filters, turbines, and other components in coal-fired power plants must withstand demanding conditions of high temperatures and pressure differentials. Further, the components are exposed to corrosive gases and particulates that can erode the material and degrade their performance. In collaboration with U.S. Department of Energy and ConocoPhillips, SRI International recently embarked on a project to develop corrosion-resistant coatings for coal-fired power plant applications. Specifically, we are seeking to develop coatings that would prevent the corrosion in the tube-sheet of the high-temperature heat recovery unit of a coal gasification power plant of SG Solution's plant in Terre Haute, IN, which uses ConocoPhillips' E-Gas technology. This corrosion is the leading cause of the unscheduled downtime at the plant and hence success in this project will directly impact the plant availability and its operating costs. Coatings that are successfully developed for this application will find use in similar situation in other coal-fired power plants.

WORK PERFORMED


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Pittsburgh Coal ConferenceSeptember 27, 2006

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DIFFUSION COATINGS FOR CORROSION-RESISTANT COMPONENTS IN COAL

GASIFICATION SYSTEMS

• SRI International:– Gopala Krishnan, Ripudaman Malhotra,

Angel Sanjurjo, Esperanza Alvarez, Kai-Hung Lau, Marc Hornbostel, and Jordi Perez

• ConocoPhillips:– Albert Tsang, Cliff Keeler, Michael Hickey,

and Gary Young


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THE PROBLEM, aka the pain

• Corrosion of gasifier components is the dominant cause of unscheduled downtime

• Gas stream leaving a gasifier contains corrosive components such as H2S, HCl, and H2O, at temperatures exceeding 900°C

• High levels of H2S require the use of specialty alloys such as Hastelloy, Haynes alloy or Inconel

• These alloys are expensive, difficult to fabricate, and have low thermal conductivity


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COATINGS

• Pros– Impart resistance to corrosion, Cr (25%) and Al (15%)– Allow use of less expensive and more easily machined

components

• Cons– Thermal mismatch, spalling off– Migration of Fe and Ni along grain boundaries


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COATINGS TECHNOLOGY

• SRI’s fluidized-bed chemical vapor deposition (FBR-CVD) technology allows:– Both internal and external surfaces to be coated– Allows diffusion bonding of the coating to the

substrate– Operates at relatively low temperature (600° to

900°C)– Allows coatings with multiple elements: Cr, Al, Si,

Ti, Ta, Zr, W


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COATINGS TECHNOLOGY (continued)

• SRI’s FBR-CVD technology uses:– Inexpensive precursors– Rapid heating, deposition, and cooling that are

inherent in fluidized beds• Coated parts can be bent or welded to form

desired shapes


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TARGET COMPONENTS

1. Tube sheet in the high-temperature heat-recovery unit (HTHRU)

2. Porous metal filters in the particulates trap downstream of HTHRU

Condensate

High temp. steam1500 psi/600°F

Input Gas400 psig/1900°F

Output Gas700°F

Particulate Trap


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RELEVANCE/BENEFITS

• Flexibility in the selection of component materials for advanced gasifiers

• Minimize downtime and maintenance costs• Allow environmentally superior IGCC

technology to be competitive


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FBR-CVD REACTOR

• Form precursors by reaction of a gas such as HCl gas with the selected alloying element

• These precursors are often unstable and reactive

• Due to changes in the local chemical environment, precursors decompose depositing a coating on the substrate

• The fresh metal coating can be converted to oxides or nitrides for additional protection.

• It is applicable to complex shaped objects


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PROFILE OF Cr-COATED STEELS

0

10

20

30

40

50

60

70

0 5 10 15 20 25 30 35

CH

RO

MIU

M C

ON

CEN

TRAT

ION

(Wt%

)

DEPTH INTO THE SAMPLE (μm)

SS304

SS410

Coatings penetrate to some depthAdherent (rub and scratch resistant)


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Schematic Diagram of the Bench-Scale Exposure Test System

H2-CO-CO2 MixtureH2-H2S Mixture

Mas

s Fl

ow C

ontro

llers

Syringe Pump

Evaporator

Tube Furnace

Thermocouples

Quartz TubeSpecimens

Vent

H2 25.7CO 38.9CO2 17.3H2S 1.4H2O 16.7


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Au TiZr & Pt

Ta Nb Mo W

Cr V

Ti6Al4V

Co FeCu

Ni Kanthal Zr/Steel

Ti/Steel

Appearance of Metals and Alloys before and after Exposure to Simulated Coal Gas at 900°C for 112 h


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Co 409/TiN 409/CrAl 410/CrAl 304/(Ti/Ta)N

409/(Ti/Ta)N 409/CrAl-Al Ox. 409/CrAl-Al 316/CrAl porous

160/(Ti/Ta)N

Test 6: Appearance of Metals and Alloys Prior to Exposure


13

Co

409/TiN 409/CrAl 410/CrAl 304/(Ti/Ta)N

409/(Ti/Ta)N 409/CrAl-Al Ox. 409/CrAl-Al 160/(Ti/Ta)N316/CrAlporous

Appearance of Metals and Alloys After Exposure to Simulated Coal Gas at 900°C for 120 h


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409/CrAl 410/CrAl 304/(Ti/Ta)N 409/(Ti/Ta)N 409/CrAl-Al Ox. 409/CrAl-Al 160/(Ti/Ta)N

Test 6: Appearance of Selected Samples After Additional 360 h Exposure

• Coatings inhomogeneity• C and Ni in metal interfere with the coatings process• Oxidized Al on Cr/Al survives, but not Cr/Al• Ti/Ta nitride coatings survive• Corrosion, once started, appears to accelerate


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Cross section of a (Ti, Al, Si) nitride coating on SS 409 alloy steel

Substrate

Coating #1

Coating #2

0

10

20

30

40

50

60

70

80

90

100

0 5 10 15 20 25 30

Depth / micron

%Al%Si%Ti%Cr %Fe

Atom%


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SEM Photograph of a Nitride Coating on SS409 Alloy with W Diffusion Barrier

Substrate

Coating

Mounting

Barrier


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Magnified Image of a Porous SS 409 Alloy Coupon

MountingExteriorSurface

InteriorSurface


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Image and Element Profile inside a Coated Porous SS409 Alloy

Substrate Coating Pore


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Test 11: 300 h at 370°C

SS410/84(TiSi)N

SS409/88Porous

(CrAl)Ox

SS410/94TiSiN/TiAlN/TiAl

SS409/93Porous

TiSiN/TiAlN

SS409/92TiSiN/TiAlN

SS409/93TiSiN/TiAlN


SS409/95TiSiN/W/TiAlN

SS409/96TiSiN/WTiAlN/W

/TiAlN

SS409/98TiAlN/W/TiAlN


SS410/84(TiSi)N

SS409/88Porous

(CrAl)Ox


SS409/93Porous

TiSiN/TiAlN

SS409/92TiSiN/TiAlN

SS409/93TiSiN/TiAlN



SS409/96TiSiN/WTiAlN/W

/TiAlN

SS409/98TiAlN/W/TiAlN



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Early Samples Recovered from the Gasifier

89

11 1057623 4 1

• Test coupon tree located in a very abrasive environment

• Perhaps, not representative of tube-sheet environment


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SUMMARY

• We have an improved procedure for preparing uniform diffusions coatings

• Can coat porous metal filters• Nitrided Ti, Ta, and Si and oxidized Al on Cr/Al

coatings appear most resilient in lab tests• Await results from exposure of

– Samples with improved coatings– Porous coupons from the filter unit


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ACKNOWLEDGMENT

• DOE Contract DE-FC26-03NT41616Richard Read, Gary Stiegel

Diffusion Coatings for Corrosion-Resistant Components in ... · ConocoPhillips' E-Gas technology. This corrosion is the leading cause of the unscheduled downtime at the plant and

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