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HINDUSTAN PETROLEUM CORPORATION LIMITED MUMBAI REFINERY
DHT-ARU
PROCESS DESCRIPTION FOR AMINE REGENERATION UNIT
DOCUMENT NO : 44LK-5100-702/P.02/0005/A4
Approved by HPCL: Date:
Rev No.
Issue Date
Pages
Rev Description
Prepared
Checked
Approved
By
By
By
A
05.01.09
8
For BEP
MKK
AGB
RMK
B
21.05.09
8
Updated as per revised scheme and issued for BEP
MKK
AGB
RMK
Jacobs HPCL, MUMBAI 44LK5100
PROCESS DESCRIPTION FOR ARU Doc No. 44LK-5100-702/P.02/0005/A4
Rev B Page 2 of 8
TABLE OF CONTENTS
Section No.
Contents
1.0
GENERAL DESCRIPTION
2.0 2.1 2.2 2.3
PROCESS PRINCIPLES AND CHEMISTRY Introduction Hydrogen sulphide absorption step. Amine regeneration step
3.0 3.1 3.2 3.3 3.4 3.5
PROCESS DESCRIPTION Fuel Gas Amine Treatment Unit Rich Amine flashing Amine Regeneration Amine filtration Amine storage & drain collection system
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Jacobs Rev B Page 3 of 8 1.0
PROCESS DESCRIPTION FOR ARU Doc No. 44LK-5100-702/P.02/0005/A4
HPCL, MUMBAI 44LK5100
GENERAL DESCRIPTION Hydrogen Sulphide from hydrocarbon gas is absorbed in 40 wt % aqueous solution of MethylDiEthanolAmine (MDEA) in absorber located at DHT and LOUP units. Hydrogen Sulphide in low pressure hydrocarbon gas from DHT, HGU and LOUP unit is absorbed in 40 wt% aqueous solution of MDEA in Fuel Gas Absorber located in Amine Regeneration Unit. Rich amine from DHT, LOUP and Fuel Gas Absorber are flashed in Rich amine flash drum & then regenerated in Amine Regeneration column. The treated gas from top of the Regeneration column is condensed / cooled. Uncondensed gases are directed to Sulphur Recovery Unit and condensed liquid (water) is sent back to the Amine regeneration column as reflux. A bleed stream from reflux is sent to Sour Water Stripper. Lean amine from Amine regeneration column bottom is sent to Absorbers in DHT, LOUP unit and Fuel Gas Absorber in Amine Regeneration Unit. Gases from Rich amine flash drum and Amine drain drum are routed to acid flare.
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Jacobs HPCL, MUMBAI 44LK5100
Rev B
PROCESS DESCRIPTION FOR ARU Doc No. 44LK-5100-702/P.02/0005/A4
2.0
PROCESS PRINCIPLE AND CHEMISTRY
2.1
INTRODUCTION
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Process principle & chemistry are described in following paragraph for each step. • Hydrogen sulphide absorption step. • Amine regeneration step. 2.2
HYDROGEN SULPHIDE ABSORPTION STEP Alkanolamines have been used for the removal of acid gases. Their action is based on chemical absorption of the acid gas, followed by regeneration of enriched solution obtained by stripping. H2S gas when dissolved in an aqueous medium, dissociates to form weak acid H2S
+
H2O
H3O
+
-
HS
The amines on the contrary are weak organic bases because, when dissolved in an aqueous medium, they dissociates to form organic bases: [Amine]
+
H2O
OH-
+
[Amine]H+
H2S & amine base will combine chemically to form an acid base complex called salt, thus removing the H2S from process streams. Reaction between H2S & amine molecules occurs in liquid phase. Absorption occurs if three steps sequence is completed. 1. H2S gas molecules must cross the gas phase to the vapour liquid interface. This movement occurs by diffusion in response to concentration differential driving force. 2. The H2S gas molecules after reaching the vapour liquid interface must then travel into the liquid phase until it comes in contact with amine molecule. This movement also occurs by diffusion. 3. When H2S gas molecules & amine molecules finally come into contact they must react at kinetic reaction rate. H2S absorption occurs in response to partial pressure driving force from gas to liquid. At equilibrium, the driving force become zero, hence no further absorption is possible. Sweetening amines may be primary, secondary & tertiary, depending on the number of hydroxyl groups bound to their nitrogen The most known amines are. • Primary Amines MEA (Monoethanol Amine) RNH2 MW = 61 • Secondery Amines DEA (Di-ethanol Amine) R2NH MW = 105 • Tertiary Amines MDEA (Methyldiethanol Amine) R2NCH3 MW = 119 R = alcohol group (-CH2CH2OH)
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HPCL, MUMBAI 44LK5100
PROCESS DESCRIPTION FOR ARU Doc No. 44LK-5100-702/P.02/0005/A4
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Each amine has at least one hydroxyl group & one amino group. In general, it can be considered that hydroxyl group reduces the vapour pressure & increases water solubility, while amino group provides necessary alkalinity in water solution to cause absorption of H2S gases. The reaction between an H2S and an amine molecule (MEA, DEA or MEDA) is called a direct “proton transfer” reaction & in effect, kinetically occurs instantaneously, and it may be represented as: H2S
+
[Amine]
< ------- >
[AmineH]+
+
HS-
This unit has been designed by using MethylDiEthanol amine (MDEA) 40 wt % aqueous solution. 2.3
AMINE REGENERATION STEP Higher pressure and lower temperature favour H2S absorption. Conversely, lower pressure & higher temperature allows H2S to be desorbed from solution. The main characteristic of amine solution is the possibility of regeneration by increasing the temperature of rich amine solution to favour reverse reaction. Steam reboiler is used as external source of heat. The reboiler duty can be broken down into three components: Sensible heat The energy required to raise the temperature of rich amine solution entering the regeneration column to the required temperature. Heat of reaction The energy required to break the bonds of absorbed H2S gas with the amine. Heat of vaporization The energy required to vaporize the fixed portion of water contained in the entering stream to provide adequate dilution of the H2S through the regeneration column, thus ensuring positive H2S driving force.
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Jacobs HPCL, MUMBAI 44LK5100
PROCESS DESCRIPTION FOR ARU Doc No. 44LK-5100-702/P.02/0005/A4
3.0
PROCESS DESCRIPTION
3.1
FUEL GAS AMINE TREATMENT UNIT
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Sour Fuel Gas from DHT, LOUP unit and HGU at a temperature of 31°C & at 4.7 kg/cm2g pressure are fed to Sour Fuel Gas KO Drum 702D-1005 to remove traces hydrocarbon oil / water if any. The gas is then fed to Fuel Gas Absorber 702-T-1002 located in Amine Regeneration Unit. Fuel Gas Absorber operates at 4.5 kg/cm2g at top. H2S present in incoming sour fuel gas is absorbed in Lean Amine in Fuel gas Absorber. Sweet fuel gas from top of fuel Gas Absorber is routed to refinery fuel gas grid through Sweet fuel Gas KO Drum 702-D-1006 to remove entrained liquid if any. Rich amine from Fuel Gas Absorber is routed Rich amine flash drum 702-D1001.
3.2
RICH AMINE FLASHING Rich amine 40 wt% MethylDiEthanolamine (MDEA) from DHT, LOUP & from Fuel Gas Absorber is fed to Rich Amine Flash Drum 702-D-1001. Rich amine flash Drum operates at 0.5 kg/cm2(g) pressure & at 54°C. The drum is designed to remove entrained hydrocarbon gases & oil. Removal of hydrocarbons reduces the amine solution foaming potential. A packed column is provided for absorption of H2S in Lean Amine, which gets flashed along with hydrocarbon gas in Rich Amine Flash Drum. The flash gas is routed to the acid flare. The oil is routed to the Amine Drain Drum 702-D-1003 (Oil compartment). Antifoaming solution is added in Rich amine at the suction of Amine Regeneration Column Feed Pump 702-P-1001 A/B.
3.3
AMINE REGENERATION Rich amine from Rich Amine Flash Drum 702-D-1001 is transferred to Amine regeneration column 702-T-1001 through Lean/Rich Amine cross Heat Exchanger 702-E-1001 by Amine regeneration column feed pump 702-P-1001 A/B. Rich amine is preheated to temperature of 111°C by regenerated lean amine in Lean/Rich Amine cross Heat Exchanger 702-E-1001 before feeding to Amine Regeneration Column 702-T-1001. Amine Regeneration Column is a tray column with 1 chimney tray at bottom, 20 fixed valve trays for regeneration and two fixed valve wash trays in the top of the column. The column operates at 1.1 kg/cm2g pressure at top and at a temperature of 101°C (top) to 129°C (bottom). The lower operating pressure of the regeneration column reduces the column bottom temperature to avoid thermal degradation of MDEA. Rich Amine solution flashes partly at the column entrance and on the feed tray. Liquid flows down across the trays to Amine Regeneration Column Reboiler 702-E-1004. Sour gases are stripped out of Rich Amine solution by up flowing steam through the trays. Up flowing steam is generated in the Amine regeneration column reboiler 702-E-1004 by vaporizing fraction of water out of amine. Saturated low-pressure steam is used as a source of heat to the reboiler. Low pressure steam is used to avoid overheating of amine in the reboiler.
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PROCESS DESCRIPTION FOR ARU Doc No. 44LK-5100-702/P.02/0005/A4
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HPCL, MUMBAI 44LK5100
Amine solution from the chimney tray flows to Amine regeneration column reboiler 702-E1004. The reboiler has an internal baffle to maintain the tubes of the reboiler submerged in the amine solution. Lean amine overflows from reboiler weir to the Amine regeneration column 702-T-1001. The overhead vapour of Amine Regeneration Column 702-T-1001 consists of water vapour, hydrogen sulphide and Ammonia. Most of the water vapours are condensed in Amine regeneration column overhead condenser 702-AFC-1005 followed Amine regeneration column overhead cooler 702-E-1006. Wet sour gas and condensed water are separated in Amine regeneration column OVHD drum 702-D-1002 at 40°C. Acid gases saturated with water from Amine regeneration column OVHD drum are sent to Sulphur Recovery Unit (SRU). Sour water from Amine regenerator column OVHD drum 702-D-1002 is pumped by Amine regeneration column reflux pump 702-P-1003 A/B to 1. Amine regeneration column as a reflux 2. Bleed stream to Sour Water Stripper (SWS) unit to avoid accumulation of ammonia in system. Water from amine solution is lost in following ways 1. Saturation water with acid gases from Amine regeneration column OVHD drum (702-D1002) to SRU 2.
Sour water to SWS unit
3. Flash hydrocarbons from Rich amine flash drum (702-D-1001). 4. Saturation water with fuel gas from Fuel Gas Absorber. Loss of water increases concentration of MDEA in the system. Clean condensate is cooled in Condensate cooler 702-E-1007 and added along with reflux to maintain the lean amine concentration (40 wt% MDEA solution). Lean amine from Amine Regeneration Column 702-T-1001 is transferred through Amine regeneration column bottom pump 702-P-1002. Lean amine leaving from Amine Regeneration Column 702-T-1001 exchanges its heat to rich amine entering in the column in Lean/Rich amine cross heat exchanger 702-E-1001. Lean/Rich amine cross heat exchanger is a tubular exchanger which cools lean amine to 72°C and heats the Rich amine to 111°C. Lean amine is then further cooled to 65°C in Lean amine cooler 702-AFC-1002. Part of the lean amine from Lean amine cooler 702-AFC-1002 outlet is fed back to Rich amine flash drum 702-D-1001 for absorption of H2S gas. Balance lean amine is further cooled to 45°C in Lean amine trim cooler 702-E-1003. 3.4
AMINE FILTRATION At the downstream of Lean amine trim cooler 702-E-1003 a slipstream (20 vol %) is sent to filtration system. Filtration system consists of following equipments 1. Lean amine pre filter 702-FIL-1001 which removes iron sulphide, iron oxide, corrosion products debris, amine polymers scales etc 2. Lean amine active carbon filter 702-FIL-1002 which removes traces of entrained hydrocarbon & heavy ends formed by thermal degradation of MDEA. These components,
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Jacobs HPCL, MUMBAI 44LK5100
PROCESS DESCRIPTION FOR ARU Doc No. 44LK-5100-702/P.02/0005/A4
Rev B Page 8 of 8
if allowed to accumulate in the lean amine solution cause foaming in the Amine regeneration column and absorbers in ARU and other units. 3. Lean amine after filter 702-FIL-1003 which removes carbon fines of activated carbon that slipped out from activated carbon filter. Filtered & unfiltered lean MDEA streams are combined before sending to fuel gas absorber and to battery limit. 3.5
AMINE STORAGE & DRAIN COLLECTION SYSTEM Lean amine required for initial start-up is unloaded from drums into Amine storage tank 702TK-1001 by Lean Amine Unloading Pump 702-P-1005 through Eductor 702-J-1001. Clean condensate from Condensate cooler 702-E-1007 is also provided to maintain the required concentration (40 wt% MDEA) of lean amine. Nitrogen blanketing is provided to Amine storage tank to avoid direct contact with air. During normal operation, Amine Storage Tank 702-TK-1001 is bypassed. Make-up quantity of Lean Amine required during normal operation is added from drums to Lean Amine Storage Tank. All hydrocarbon drains and amine drains from ARU are routed to Amine drain drum 702-D1003 located in pit. Nitrogen blanketing is provided to Amine drain drum to avoid direct contact with air. Vent from Amine drain drum is routed to acid flare.
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