Steam Cracker Furnace Energy Improvements

Tim GandlerEnergy Coordinator

Baytown Olefins Plant, Baytown Tx

2010 Industrial Energy Technology Conference

May, 2010

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• Baytown Complex

• Steam Cracking to Olefins

• Furnace overview & challenges in steam cracking

• Energy efficiency improvements

Overview

Baytown Olefins Plant

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Baytown Complex

•One of world’s largest integrated, most technologically advanced petroleum/petrochemical complexes

•~3,400 acres along Houston Ship Channel, ~ 25 mi. east of Houston

• Includes 4 manufacturing sites, 2 technology/engineering offices

•Significant community involvement

Baytown Refinery

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Steam Cracking to Olefins

• Process 60+ years old; ExxonMobil one of pioneers

• Endothermic, non-catalytic process to produce light olefins/diolefins – Ethylene, propylene, butylenes, butadiene

• Molecules “crack”, large → small – C2H6 → C2H4 +H2

– C3H8 → C2H4 +CH4

– C3H8 → C3H6 +H2

– Many others……

• Must heat feed to very high temperature to adequately “crack”– The lighter the feed the higher the temperature

• Very energy intensive process; furnace fuel accounts for ~60% of plants energy use

Ethylene Plant Energy Consumption

60%

5%

35%

FuelSteam Power

Quench & Heat Recovery

Steam Cracker Furnace

Compression Refrigeration Fractionation

Cracked Products

ProductsFeed

Fuel

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Furnace Overview

1. Convection Section– Preheats and vaporizes the feed by absorbing excess heat– Combines the hydrocarbon with dilution steam

2. Radiant– Cracks the feed into products at short residence times– Contains the burners – 1500+ °F

3. Heat Recovery – Arrests the cracking reaction by cooling the effluent– High pressure steam generated

Feed

ID Fan

Flue Gas

Gas Burners

1. ConvectionSection

2. RadiantSection

3. Heat Recovery

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Challenges in Steam Cracking – Dilution Steam

• Reduces partial pressure of hydrocarbon, resulting in higher C2= yields

• Helps keep free radicals from recombining into undesirable compounds, e.g. coke, methane, hydrogen

• Requires additional firing

Furnace

Cracked Products

Feed

Fuel

Dilution Steam

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Challenges in Steam Cracking - Coke Formation

• Coke is a undesirable byproduct of steam cracking formed from complete dehydrogenation of hydrocarbon molecules

• Thickness of coke layer increases with run length– Reduces heat transfer to process stream

• After a period of being online furnaces “Decoke” with steam+air due to– High pressure drop

– High tube wall temperatures

Furnace tube

hydrocarbon + steam

0

0.2

0.4

0.6

0.8

1

1.2

1 2

time

Co

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Steam Cracker Furnace Energy Efficiency

• Overall energy efficiency of furnace depends on – Run length or % of time furnace is online (more decokes lead to lower efficiency)

– Amount of dilution steam (more steam leads to lower efficiency)

– Furnace design

– Furnace condition

• Very challenging to balance energy efficiency and production

down

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time

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Energy Efficiency Improvement - How did we do it?

• Multi-disciplinary team identified monitoring, procedural and maintenance improvements

– Team met weekly to review performance and create run-plan– Improved procedures resulted in greater attention to details– Maintenance improvements executed as planned

• Gaps closed over 1-2 year period

• No capital spending required

Review Performance

Create Run-plan

Execute Run-plan

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BOP Furnace Energy Efficiency Improvements

• Overall energy efficiency improvement of 2.4%– Significant improvements in run length– Significant improvements in S/HC

• Energy Savings of 660,000 MBTU/yr or more than 38,000 T/CO2 per year

• Site remains dedicated to further improvements in energy efficiency

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