Effluent and In-process pH Reduction Airgas ALTEC Engineering - - PowerPoint PPT Presentation

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Use of Carbon Dioxide for Effluent and In-process pH Reduction

Airgas ALTEC Engineering Solutions Group (AES) Vince Hartley - Chemical, Environment & Technical Solutions April 03, 2018

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Carbon Dioxide Background

• CO2 is a by-product from

✓ Steam Reforming H2 unit (Refineries, Fertilizer plant) ✓ Fermentation

• Compressed, cleaned, liquefied to 0oF and 300 psig
• Uses

✓ Carbonated beverages ✓ Food Freezing/Chilling ✓ EOR (oil recovery) ✓ Inert food, chemical ✓ Cryogenic chilling plastic industry ✓ Plastic foaming ✓ pH control

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Introduction

• CO2 Use in Wastewater Treatment

✓ Driven by discharge regulations (6 - 9.5) ✓ Across all industries

✓

pH adjustment to optimize coagulant/flocculants

• Potable Water

✓ Recarbonation

■ Stabilization of water after lime softening

• In-process

✓ Chemical reaction ✓ Paper machine, bleach plant ✓ In-situ carbonate formation ✓ Milk

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Types of Industries

• Food & Beverage
• Chemical Plants
• Refineries
• Concrete Facilities
• Dairies
• Steel
• Laundries

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CO2 for pH Control - How does it work?

CO2 is injected into water & reacts to form carbonic acid that instantly reacts with alkalis (caustic soda, sodium carbonate, dissolved lime) transforming them into neutral carbonates & bicarbonates - thus lowering the pH

CO2 + H2O ⇆ H2CO3 ⇆ HCO3

• + H+ ⇆ CO3

2- + 2H+ carbonic acid bicarbonate carbonate

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• Caustic + Carbonic acid = Sodium carbonate:

✓ 2NaOH + H2CO3 Na2CO3 + 2 H2O (down to pH= 11.6)

• Sodium carbonate + Carbonic acid = Sodium bicarbonate:

✓ Na2CO3 + H2CO3 2 Na(HCO3)2 (down to pH= 8.3)

• Each step corresponds to a reduction in pH

Chemistry of CO2 pH control

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CO2 vs. Acid

Benefits

• Lowers pH to 6-9 range, (EPA

requirement for discharge into waterways)

• Eliminates possibility of
• vershooting pH w/ better control
• Will not corrode pipes, tanks,

equipment Disadvantages

• Does not lower alkalinity
• More complex mixing
• No unwanted secondary products (chlorides,

sulfates)

• Less regulatory oversight for storage,

transportation, etc.

• Safer (most acids are EHS)
• Often cheaper than acid

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• CO2 Advantage

✓ pH Stability (6.0 - 7.0) ✓ no over-acidification

CO2 vs. Acid

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CO2 vs. Acid

• Typical Value Model

✓ pHi=12 @ 77oF

■ Sulfuric Acid (93% sol’n) H2SO4 ■ Hydrochloric Acid (32% sol’n) HCl pHf H2SO4(93%)/CO2 HCl(32%)/CO2 lb CO2/lb acid lb CO2/lb acid 10 0.63 0.30 9 0.80 0.38 8 0.85 0.40 7 1.06 0.50 6.5 1.55 0.72

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Injection

○ Direct PIPE (Gas or Liquid)

■ Porous diffuser ■ Spray Nozzle ■ Sampling valve ■ Static mixer, Flow nozzle, Venturi

○ Direct TANK (Gas)

■ Porous diffuser ■ Agitator ■ Closed loop ■ Eductor ■ Self-Cleaning injector

• High Solids

Bubble flow regime Gas/Liquid ratio Critical

Flow nozzle / Jet Ejector

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pH Control Configuration

pH probe

Retention time - 30 seconds

Treated Stream

Dissolution device P T PIC CO2

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pH Control Configuration

pH probe

Retention time - 120 seconds

Treated Stream

Dissolution device P T PIC CO2

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Why now?

• Stricter regulations

✓ Limiting discharge of S, Cl or P compounds ✓ Tighter pH limits on permits

• No alkalinity destruction
• Scarce water resources
• Water re-use/Green push
• Potential sequestration

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Up and Coming

• Improvement in CO2 supply

✓ CO2 supply had been dwindling for many years

■ Change in technology ■ Movement of industry to overseas

✓ Ethanol sources

• Improving technology and research

✓ Potential to recover CO2 from stack gases

■ Can be utilized at lower purities

✓ Even from the environment in some extreme cases ✓ Potential to utilize in applications previously too difficult

■ Cooling Towers

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Thank You, Questions?