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