Evaluation of Gas Separation Processes

Novel Method for Gas Separation

By: Chris Wilson

For: Senior Capstone 2008

1

Overview

Current process

New process

Economic comparison

Natural Gas ProcessingThe Way it is Done

Current process

Remove excess water

Remove acid gas

Dehydrate

Remove mercury

Remove nitrogen

Separate NGL (ethane, and heavier hydrocarbons)

Natural Gas Processing Everything Together

Water removal

Removes free liquid water and condensate gas

Sends the gas to a refinery

The water goes to waste

Natural Gas Processing Everything Together

Natural Gas ProcessingAcid Gas Removal

Hydrogen sulfide

Mercaptans

Carbon dioxide

Acid gas removal processes

Amine treating

Benfield process

Sulfinol process

others

Natural Gas ProcessingAmine Treatment

Most common used amines

Monoethanolamine

Diethanolamine

Diisopropylyamine

Methylethanolamine

Hydrogen sulfide goes through a Claus process

64,000,000 metric tons of sulfur are produced from this process

8

Natural Gas ProcessingAmine Treating

Natural Gas ProcessingSulfinol Process

Used to reduce H2S, CO2, and mercaptans from gases

Great for treating large quantities of gas

Solvent absorbs the sour gas

Sulfolane is used

Sulfolane, a clear colerless liquid, developed by shell in the 1960s

10

Natural Gas ProcessingSulfinol Process

Natural Gas Processing Everything Together

Natural Gas ProcessingGlycol Dehydration

Method for removing the water vapor from the gas

Usable glycols

Triethylene glycol

most commonly used

Diethylene glycol

Ethylene glycol

Tetraethylene glycol

Works by having the glycol adsorb the water

13

Natural Gas ProcessingGlycol Dehydration

Wet gas enters a contacting tower at the bottom. Dry glycol flows down the tower from the top, from tray to tray, or through packing material. A bubble cap configuration maximizes gas/glycol contact, removing water to levels below 5 lbs/MMscf. Systems can be designed to achieve levels down to 1lb/MMscf.The dehydrated gas leaves the tower at the top and returns to the pipeline or goes to other processing units. The water rich glycol leaves the tower at the bottom, and goes to the reconcentration system. In the reconcentration system, the wet glycol is filtered of impurities and heated to 400F. Water escapes as steam, and the purified glycol returns to the tower where it contacts wet gas again.

14

Pressure Swing Adsorption

Adsorbent material is used

Gas and material go under high pressure

Material adsorbs the gas ( H2S, mercaptans, CO2)

Disadvantages

Requires high pressures

Slow cycle times

Natural Gas Processing

Mercury removal

Current Processes

Activated carbon through chemisorption. Activated has extremely high surface area

Mercury can damages aluminum heat exchangers

Those used in cryogenic processing plants

Those use in liquefaction plants

Natural Gas Processing

Nitrogen Rejection

Processes that can reject nitrogen

Cryogenic process

Absorption process (using lean oil or solvent)

Membrane separation

Adsorption process (activated carbon)

Natural Gas ProcessingCryogenic Process

Common refrigerants used

Most common method for removal of impurities such as nitrogen

Disadvantages

Must reach extremely low temperatures

Only useful for large scale production

Natural Gas ProcessingLean Oil Removal

Lean oil is fed countercurrent with the wet gas

Temperature and pressure are set to allow for the greatest absorption of unwanted gases

In the ambient lean oil absorption process the natural gas is contacted with the lean oil (molecular weight of about 150) in an absorber column at the ambient temperature of about 100F. The rich oil exiting the bottom of the absorber flows into a rich oil depropanizer (ROD) which separates the propane and lighter components and returns them to the gas stream. The rich oil is then fractionated in a still, where the NGL's (C4+) are recovered as an overhead product and the lean oil is recycled to the absorber column. Typically, 75 percent of butanes and 85-90 percent of pentanes and heavier components are recovered. In the refrigerated lean oil absorption process, the lean oil is chilled against propane refrigerant to improve the recovery of propane to the 90 percent level, and depending upon the gas composition, up to 40 percent of ethane may be recovered (Elliot, 1997). Since reducing the molecular weight of lean oil enhances the lighter component absorption and an external refrigerant is used to chill the lean oil, 100 to 110 molecular weight lean oils are generally used in this process.

21

Natural Gas Processing Membranes

Driving force

Partial pressure

Type of material determine permeability

D = diffusion coefficient (cm2/s)

k = Henrys law sorption coefficient (cm3/cm3cmHg)

P1 = Permeability of component 1

P2 = Permeability of component 2

Natural Gas ProcessingEconomics

Demethanizer

Demethanizer

The next step is to recover the NGLs

Process

Cryogenics using a turbo-expander can be used

This is the most common

Lean oil adsorption can be used here

Natural Gas ProcessingCryogenic Process

NGL recovery

NGL recovery

Now the rest of the liquid is fed to three units

Deethanizer

Debutanizer

Depropanizer

Process

Each sent to a distillation column

Sweetening NGLs

Merox Processes

Mercaptan oxidation

Removes mercaptans from

Propane

Butane

Larger hydrocarbons

Natural Gas Processing Another Process

Novel Method

Technical information momentarily not available due to IP issues

However economics will be compared

If you want the access to this, then talk to OTD

32

Novel Method

Advantage

More cost effective than any previous methods

Less environmental impacts than previous methods

Separates all contaminants

Separates each component

Everything is done using one process

If you want the access to this, then talk to OTD

33

Novel Method

Current Method

Economics - Amine Treating

36

Amine Treating - Simulation

Economics - Demethanizer

Demthanizer - Simulation

Economics - Dethanizer

Deethanizer - Simulation

Economics

Built in Error

k

D

P

=

2

1

P

P

=

a

Equipment Description Price ($)

Column - 1 4.88 meters tall, 2,02 meters in diameter $23,000

Column - 2 6.71 meters tall, 3.60 meters in diamter $58,000

Heat exchanger - 1 530 square meters $59,000

Heat exchanger - 2 615 square meters $69,000

Pump 38,000 gallon flow, 235 psi rise $68,000

Total $277,000

Cost of Equipment

Utilities Price ($/hr)

Cooling Water 19,800 gallons/hr ($0.08/1000kg) $5.98

column reboiler 139 million BTU/hr ($6 per million BTU) $834

Pump 97.53 Kw ($0.06/Kw) $5.85

Total $845.83

Operating Costs

Utility Price ($/hr)

Cooling water using $0.08 per 1000 kg of cooling water $1.17

Electricity Two compressors and an expander $116.25

Total $117.42

Operating Costs

Equipment Description Price

Column Diamter of 1.53 meters, Height of 8.54 meters $25,000

Heat exchanger 1 Area of 1055 square meters $118,287

Heat exchanger 2 Area of 15.6square meters $1,874

Heat exchanger 3 Area of 113.12 square meters $12,796

Heat exchanger 4 Area of 25.2 square meters $2,953

Heat exchanger 5 Area of 261.7 square meters $29,440

Heat exchanger 6 Area of 6.8 square meters $890

Heat exchanger 7 Area of 11.5 square meters $1,417

Refrigerant For a 10 year period $880,000

Expander 1200 KW output $370,000

Compressor Compresseing to pressure of inlet for deethanization $50,000

Compressor 2 $190,000

Compressor 3 Bringing methane back to pipeline pressure $640,000

Pump $3,000

Total $2,325,657

Cost of Equipment

Equipment Price

Column8.7 meters tall, 1.86 meters in diameter $32,000

Cost of Equipment

Utility Price

Reboiler(8 million Btu's needed, 6 dollars/million BTU) $48

Operating Costs

Current $4,111.45 $6.74$7.49

A $8,239.58 $1.24$2.74

B-best $7,194.03 $0.98$2.29

C-worst $16,697.63 $2.75$5.80

Current $3,697.91 $6.74$7.41

A $7,459.32 $1.24$2.60

B-best $6,523.00 $0.98$2.17

C-worst $14,372.45 $2.75$5.37

100%

70%

Fixed Capital Investment

(per 1000 cubic feet)

Operating Costs (per

1000 cubic feet/day)

Annulized Cost

(perday)

Equipment Costs $16,800,000

Operating Costs $435/hr

Novel Method - Error for the Worse

Equipment Costs$3,441,657

Operating Costs$1,011/hr

Current Process

Equipment Costs $6,600,000

Operating Costs $155/hr

Novel Method - Error for the Better