Ammonia II: CO2 Removal Section

I F F C O

Presented By:

Sanjay Katheria

GET- Chemical

Outline of the Presentation

Introduction

CO2 Removal Processes

CO2 removal section: Ammonia II

o GV Solution

o Absorber

o First Regenerator

o Second Regenerator

Source and References

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Introduction

Carbon dioxide is a gas at standard temperature and pressure and exists in Earth's atmosphere in this state. CO2 is a trace gas comprising 0.039% of the atmosphere.

Carbon dioxide is a greenhouse gas as it transmits visible light but absorbs strongly in the infrared and near-infrared.

General properties: Colorless

At low concentrations, the gas is odorless. At higher concentrations it has a sharp, acidic odor.

CO2 is an acidic oxide and toxic in higher concentrations: 1% (10,000 ppm) will make some people feel drowsy. Concentrations of 7% to 10% cause dizziness, headache, visual and hearing dysfunction, and unconsciousness within a few minutes to an hour.

The triple point of carbon dioxide is about 518 kPa at −56.6 °C.

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Industrial production

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Industrial carbon dioxide is produced mainly from six processes:

Directly from natural carbon dioxide springs, where it is produced by the action of acidified water on limestone or dolomite.

As a by-product of hydrogen production plants, where methane is converted to CO2.

From combustion of fossil fuels and wood.

As a by-product of fermentation of sugar in the brewing of beer, whisky and other alcoholic beverages.

From thermal decomposition of limestone, CaCO3, in the manufacture of lime, CaO.

CO2 Removal Process

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To purify the synthesis gas and complete the requirement of CO2 in Urea Production, CO2 is removed from synthesis gas.

Methods used in CO2 Removal

Amine Gas Treating

Hot Potassium Carbonate Solution Treatment

There are many different amines used in gas treating:

Monoethanolamine (MEA)

Diethanolamine (DEA)

Methyldiethanolamine (MDEA)

Diisopropylamine (DIPA)

Aminoethoxyethanol (diglycolamine) (DGA)

The most commonly used amines in industrial plants are the alkanolamines MEA, DEA, and MDEA

Contd..

Amines particularly MEA have greater affinity towards CO2 which results in low exit concentration (from Absorber) of CO2 at relatively low pressure.

Duel Solvent Methods: Mixture of TEA and MEA

HOCH2CH2NH2 + CO2 HOCH2CH2NHCOO- + H+

HOCH2CH2NHCOO- + H2O HCO3

- + HOCH2CH2NH2

MDEA used with some activator.

MEA Process highly corrosive while MDEA Process requires high residence time.

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Carbonate Solution Process

Amine Gas Treating Process have high regenerative cost.

Hot Potassium Carbonate Solution: Intermediate affinity for CO2 compared to Water and Amines(MEA).

K2CO3 + CO2 + H2O 2KHCO3

Primary and secondary Organic amines, Monoethanol amine (MEA) and Diethanolamine (DEA) are currently employed alone and or in combination with hot potassium carbonate solution to catalyse the CO2 removal Process

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CO2 Removal Section: Ammonia II

Giammarco-Vetrocoke (GV) is a privately-owned company, located in Venice, Italy.

CO2 removal system of Ammonia II Plant has a conventional design based on the GV dual activator process. The process comprises of single stage absorption and two stage regeneration.

Carbon dioxide is removed by absorption in hot aqueous potassium carbonate solution containing approximately 30 wt% potash (K2CO3) partly converted into bicarbonate (KHCO3).

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GV Solution

Dual Activators Glycine NH2CH2COOH Diethnolamine NH(CH2CH2OH)

Corrosion Inhibition

V2O5

Composition of fresh solution:

• K2CO3/KHCO3 27 % w/w • Glycine 1.2 % w/w •DEA 1.0 % w/w • V2O5 0.4 % w/w

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General Reaction

K2CO3 + CO2 + H2O 2KHCO3 + heat CO2 + H2O HCO3

- + H+ (slow) CO3

2- + H2O HCO3- + OH-

----------------------------------------------- CO3

2- + CO2 + H2O 2HCO3-

Role of Activator

H2NCH2COO- + CO2 - OOCNHCH2COO- + H+ (fast) Glycine Carbamate

-OOCNHCH2COO- + H2O H2NCH2COO- + HCO3-

------------------------------------------------------------------ CO2 + H2O HCO3

- + H+

• Hydrolysis of Glycine Carbamate is catalysed by DEA.

Chemistry of GV Process

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Corrosion Inhibition

Acidic nature of solution because of CO2, Carbonic Acid and Carbamates.

Addition of Vanadium as Corrosion Inhibitor, Static and Dynamic Passivation (0.5 % V2O5)

Iron content of the solution representation equilibrium (iron content more than 200-300ppm considered excessively high).

V+5 Protecting Layer( 5-10 % of total vanadium content).

V+5 equilibrium with V+4

V5+ + Fe2+ V4+ + Fe3+

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Chemistry of GV Process

Operating Parameters Temperature - Hot aqueous solution to increase the rate of reaction. - Keep the bicarbonate in the dissolved form. - Boiling point temperature for Regenerators. Pressure - High pressure in absorber increase the solubility of process gas in GV solution

Fractional Conversion (Fc ) K2CO3 + CO2 + H2O 2KHCO3 %KHCO3 Fc = %K2HCO3 + %KHCO3

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Absorber 1st Regenerator 2nd Regenerator

CO2 at P = 1.1 Kg/cm2 g

CO2 at P = 0.14 Kg/cm2 g

Process Gas Inlet

Process Gas Outlet

Steam Inlet

Lean Solution

Semilean Solution CO2 Rich Solution

Lean Solution

Semilean Solution

CO2 Rich Solution

CO2 Rich Solution

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Absorber Process Gas Outlet Lean

Solution

Semilean Solution

Process Gas Inlet

CO2 Rich Solution

Process Gas cooled to 104 oC before entering into absorber.

2 Stage Process: - 1st Contact with Semilean Solution - 2nd Contact with Lean Solution

Process Gas Inlet Outlet

Temperature(oC) 110 71

Pressure(kg/cm2g) 27.9 27.4

Flow Rate(NM3/hr) 312141 203148

% N2 20.75 25.23

% H2 60.74 73.78

% CO 0.12 0.15

% CO2 17.74 0.05

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Absorber

2 Stage Counter Current Absorption Process: - 1st Contact with Semilean Solution - 2nd Contact with Lean Solution Semi Lean Solution Contact: Lower two beds(3rd & 4th Bed of Absorber) About 85% of the total solution Temperature: 107 oC Most of the CO2 removed in lower 2 beds(~4000 ppm CO2 left)

Lean solution Rest 15% of the solution Temperature: 60oC CO2 in Process Gas leaving Absorber ~ 500ppm

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Absorber Packing

IMTP Packing: Low Pressure drop with high metallic strength w.r.t.

weight.

Bed Type Volume of the Packing(m3)

5th Bed(lower) IMTP 70 11

4th Bed CMR3 & IMTP 50 105

3rd Bed IMTP 50 & IMTP 40 105

2nd Bed IMTP 40 48.5

1st Bed (top) MELLPACK 250 48.5

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First Regenerator

First stage of regeneration process.

Operating Pressure 1.1 kg/cm2g

44% of rich solution extracted from top tray and send to top of 2nd Regenerator.

CO2 at P = 1.1 Kg/cm2 g

Vetrocoke Reboiler

Process Gas out

Process Gas In

Steam In

Lean Solution

Semilean Solution

CO2 Rich Solution

To 2nd Regenerator

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First Regenerator

41% of the semilean solution is taken from lower part of 2nd Bed, expanded and send to 2nd Regenerator take-off tray.

Remaining strongly regenerated solution expanded and transfer to bottom of 2nd Regenerator.

Heat Input:

• From process gas cooling in two Vetrocoke Reboiler and one LP Steam Boiler. • LP Steam from ejector.

Operating Condition:

Temperature(oC) (top) 109

Pressure(kg/cm2g) (top/bottom) 1.1/1.3

LP Steam added(kg/hr) 17000

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Second Regenerator CO2 at P = 0.14 Kg/cm2 g

From 1st Regenerator Top

From 2nd Regenerator second bed bottom

Lean Solution P = 0.24 Kg/cm2 g

Semilean Solution P = 0.24 Kg/cm2 g

Form 1st Regenerator Bottom

2nd stage of stripping at reduced pressure of 0.14 kg/cm2g.

Semilean Solution from upper side of take-off tray.

Lean Solution from bottom of 2nd Regenerator.

Take-off Tray

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Regenerators Packing

Mellapack Packing

Regenerator Volume of the Packing(m3) Type of Packing

1st Regenerator(HP) 64.0+223.0 IMTP 40 + IMTP 50

2nd Regenerator(LP) 164.0 IMTP 50

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Thank You