functional specification document

ACID GAS REMOVAL – OPEN ART OR LICENSED PROCESS? Arif Habibullah, P.E. Specialized Consulting Services Los Angeles, California, USA

ABSTRACT

A technology assessment of acid gas removal (AGR) processes was recently conducted for a world-class gas processing facility. Both open art and licensed processes were considered for this evaluation, the primary object is to determine if licensed processes offer any advantage over open art designs. This paper addresses the technical and economic feasibility of open art vs proprietary solvents for currently available acid gas removal processes. In addition, the paper will share the technology alternatives studied, pros and cons and economic analysis for selecting the most suitable process for the application considered. Finally, the paper will summarize the technical challenges identified during this assessment.

Recently completed AGR unit, showing Compabloc lean-rich exchangers in foreground.

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BACKGROUND

For this study the base case Acid Gas Removal (AGR) technology is Diglycol Amine (DGA), an open art technology, however, newer and proven alternative types of amine technologies providing better economics, including open art and licensed selective MDEA, were evaluated and a screening level assessment and recommendation are presented in this report. Purpose The purpose of this assessment is to provide a technical and economic life cycle comparison between three competing AGRU technologies:  Open-art Diglycol Amine (DGA)  Open-art Selective Methyldiethanol Amine (MDEA)  Licensed Selective Methyldiethanol Amine (MDEA) Study Methodology The comparison is based on simulations of the open art technologies and licensor input for various proprietary technologies. The base case Acid Gas Removal (AGR) technology is Diglycol Amine (DGA), an open art technology; however, newer and proven alternative types of amine technologies providing better economics, including open art and licensed selective MDEA, were evaluated. Those technologies are similar in design with some minor differences; however, a noteworthy difference is that DGA requires a reclaimer and associated equipment. Detailed simulations, using ProMax simulation software, were built for the open art DGA and selective MDEA processes. In addition to technical information concerning the unit feed gas flow, condition, and composition, this document incorporated a list of constraints, deliverables and requested guarantees to systematically and objectively analyze, contrast and assess the various technologies and solvents available on the market. Technical proposals were received from five different licensors. An equipment/duty list for each open art and licensed process was compiled and screening level CAPEX and OPEX estimates were generated. A life cycle analysis was subsequently performed and the incremental cost of each technology over the base case was determined.

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Technology Features Flow schemes for the technologies are shown below. The technologies are similar in design with some minor differences; however, a noteworthy difference is that DGA requires a reclaimer and associated equipment. Some of the licensors require an intercooler pump-around loop in the contactor in order to maintain a relatively low temperature profile. Technology features of each option are summarized in the Table below. Figure 1: Simplified DGA-based and Selective MDEA AGRU Plant Schematics

Technology Features DGA

Open-Art Selective MDEA

Licensed Selective MDEA

Commonly used solvent, high reactivity at low pressures and high temperatures. Popular in 1970s has since been replaced by tertiary amines for better selectivity.

Piperazine activator added to MDEA shifts selectivity to CO2.

Original patent (BASF) expired in 2002 and since then many solvent licensors and vendors offer it under a range of trade names.

Uses a reclaimer to remove and eliminate the degraded amines, contaminants and heat-stable salts from the system.

Does not need a reclaimer, has a high resistance towards both thermal and oxidative degradation.

Same as open art.

Requires high circulation rates due to lower rich amine loading due to the highly corrosive nature of the system.

High CO2 absorption capability, depending on Piperazine % in solution.

Some licensors allow use of open market solvents, i.e. solvent can be purchased from any supplier.

1960’s technology with many conversions to newer solvents, still few operating units worldwide.

Circulation rates are lower than DGA, due to selectivity, which in turn reduces equipment sizes and energy consumption.

Several hundred licensed grassroots and solvent conversion units currently operating worldwide.

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Pros and Cons Some pros and cons for each technology are tabulated below and form the basis for identifying the incremental CAPEX and OPEX differentials between them. Open-Art Selective MDEA

DGA 

PROS  

CONS    

  

     

Open art process Removes COS

 Non-selective Requires reclaimer to keep degradation products in check High solvent vapor pressure, i.e. high losses Higher circulation and energy consumption compared to tertiary amines High heat of reaction 1960’s technology Solubility of heavy HCs

 

Licensed Selective MDEA

Piperazine controls selectivity of CO2 Open art process Less corrosive High resistance to degradation Low vapor pressure Lower heat of reaction Biodegradable

 

Same as open art Licensed process can often provide lower circulation & energy consumption

Exposure to oxygen forms corrosive acids Co-absorb some BTX Introduces a new solvent to HGP site

  

Same as open art Requires license fee Some licensors require mandatory use of their solvent

Table 1 – Licensor Comparison Licensor

Open-art

Open-art

Licensor A

Licensor B

Licensor C

Licensor D

Licensor E

Technology

DGA

Selective MDEA

Formulated MDEA

Formulated MDEA

Formulated MDEA

Formulated MDEA

Formulated MDEA

Solvent

DGA

MDEA w/ Piperazine

Proprietary

Proprietary

Proprietary

Proprietary

Proprietary

2,750

1,915

Proprietary

Proprietary

Proprietary

Proprietary

Proprietary

128

102

95

101

93

96

129

2,250

1,750

1,850

2,000

1,850

1,900

2,100

45

45

Proprietary

Proprietary

Proprietary

Proprietary

Proprietary

0.35

0.4

Proprietary

Proprietary

Proprietary

Proprietary

Proprietary

Circulation Rate, GPM Reboiler Duty, MMBTU/hr Power Consumption, HP Solution Strength, wt% Rich Loading, mol/mol

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CLASS 5 COST ESTIMATE BASIS Based on equipment lists provided by the licensors, screening level TIC estimates were prepared including allowances for bulks, piperacks, interconnections, buildings, transportation, construction and construction management.

Project Economics Screening level economics for each technology were prepared and incremental revenue, CAPEX and NPV calculated as shown in the Table 2 below for the shortlisted suppliers. Sized equipment lists and utility summaries were generated for each option. CAPEX is based on cost estimates, using kBase, generated from sized equipment lists, as follows:       

Entered sized equipment list into kBase. Added assumed size piping rack and piping Added assumed size site work and paving Entered labor productivity of 3.0 for local conditions All in labor rate of $30/hr The estimates are considered to be +/-40% for to overall capital costs for each estimate The relative difference between the various estimates is projected to be +/-15%

OPEX is based on utility consumption and solvent losses/first charge. License fees and solvent first fill costs were included in the initial cash flow. NPV was based on net revenue and net CAPEX for each option. The basis for the project economics is summarized below: Cost of power= 7 cents/kWh Cost of steam= $5.8/MP Solvent Losses = See Table 2 Discount rate= 5% License Fees= Included - See Table 2 Solvent First Fill = See Table 2

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Table 2 - Project Economics Summary OPEN ART

Description

DGA

Solvent Costs, $/gal

20.70

Solvent First Fill, $MM

Selective MDEA

LICENSED Licensor A

Licensor C

Licensor D

Licensor E

17.80

Proprietary

Proprietary

Proprietary

Proprietary

1.153

0.690

1.157

0.627

0.763

0.863

Solvent Losses, $MM/yr

0.058

0.050

0.072

0.050

0.050

0.049

Power, $MM/yr

1.083

0.843

0.891

0.817

0.784

1.011

Steam, $MM/yr

7.509

5.989

5.615

4.862

5.595

7.594

OPEX, $MM/yr

8.651

6.883

6.578

5.730

6.429

8.655

License Fee, $MM

None

None

Proprietary

Proprietary

CAPEX, $MM

87.0

79.9

79.7

67.3

62.6

86.6

Net Revenue, $MM/yr

Base Case

1.768

2.072

2.921

2.221

0.0

Net CAPEX, $MM

Base Case

7.037

7.278

19.683

24.386

0.384

NPV, $MM

Base Case

31.955

36.480

60.851

55.689

0.389

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Proprietary

Proprietary

TAKEAWAYS 

Licensed designs can offer substantial economic advantages over generic open-art amine unit designs and should be considered when evaluating and selecting amine solutions.



Project economics indicate a Licensed C has substantial CAPEX and life cycle cost savings over DGA and open art selective MDEA.



This technical and economic assessment indicates a total life cycle cost savings of up to $61MM can be realized with licensed technology.



Total CAPEX savings, over generic DGA, are $24.4MM for Licensor D and $19.7MM for Licensor C.

The major outcomes from this work are: 

Licensed amine unit designs can be very competitive compared to open art designs.



Based on this assessment, licensed technology is recommended since it offers superior technical and economic benefits.



In addition, licensors may offer performance guarantees for maximum amine losses and maximum reboiler duty for solvent regeneration.



Unusually high solution strength of 50%, with a rich loading of around 0.44 mol/mol is not recommended, specifically for a high CO2:H2S ratio environment as it creates a high corrosion risk.



Solution strength should not exceed 45%, with rich loading of no more than 0.35 mol/mol, especially for new units.

REFERENCES TBD

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APPENDIX Gas Treating Facilities The gas from the new slug catchers in the Inlet Facilities is directed to the Gas Treating Facilities for gas sweetening. Sweetening of the gas is accomplished using an activated MDEA solution in two new Gas Treating Trains , consisting of high pressure (activated MDEA) Amine treating units. The gas is first sent to the Feed Gas KO Drum to drop off any feed line condensate. The overhead vapor from the KO drum is sent to the Feed Gas Particle Filter to remove solid particles larger than 3 micron, and then to the Feed Gas Filter Coalescer to eliminate possible foaming in the absorber caused by any small quantity of liquid hydrocarbon droplets (larger than 0.3 micron) and mist. Condensate from the Feed Gas KO Drum, Feed Gas Particle Filter, and the Feed Gas Filter Coalescer is directed, under level control, to the Condensate Stabilizer train(s) in the Inlet Facilities. The droplet-free and mist-free gas then enters the MDEA Contactor (Absorber). The high CO2 gas is contacted counter-currently with lean activated MDEA to remove CO2 from the feed gas. The lean MDEA temperature (140°F) is at least 20°F higher than the inlet gas temperature (120°F summer, 80°F winter) to the Contactor. The CO2 and H2S content in the residue gas generated by the Contactor shall not exceed 50 ppmv and 2 ppmv respectively, and are measured by the analyzer provided at the overhead of the Contactor. The H2S content, will not exceed 2 ppm provided the H2S content in the raw sweet gas entering the facility does not exceed 2 ppm. The Contactor has a Water Wash System with demineralized water quality to reduce Amine entrainment in the residue gas exiting from the top, and compensate for water losses from the system.

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Simulation Models

Figure for Open Art Selective MDEA Configuration

Figure for Base Case DGA Configuration

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Gas Stream Compositions and Rates Max. CO2 in Feed Composition Basis Design Cases Summer

Winter

Gas Volume (MMSCFD)

570

570

Pressure Inlet (PSIG)

560

620

Temperature (°F)

120

80

BTEX (PPMV)

450

450

Mole Fraction

Mole Fraction

Nitrogen

0.04550

0.04610

Carbon Dioxide Hydrogen Sulfide (PPMV) Methane

0.03080

0.03110

2

2

0.79916

0.80840

Ethane

0.06310

0.06350

Propane

0.02650

0.02590

I-Butane

0.00581

0.00535

N-Butane

0.01080

0.00965

I-Pentane

0.00398

0.00304

N-Pentane

0.00382

0.00275

C6

0.00384

0.00204

C7

0.00205

0.00084

C8

0.00085

0.00028

C9

0.00022

0.00006

C10

0.00005

0.00001

C11

0.00001

0.00000

C12+

0.00001

0.00000

H2O

0.00340

0.00096

This total design flow of 1,140 MMSCFD is shown in the table above where two different design cases are considered. They are as follows: 

Max. CO2 in feed composition basis, summer.



Max. CO2 in feed composition basis, winter.

Feed inlet gas temperature from pipeline can be as high as 140 °F, but is cooled to at least 120 °F (by others) before entering the feed gas filter/coalescer and amine contactor. The design product specifications will be to remove Carbon Dioxide (CO2) from the gas feeds to produce a rich gas stream containing no more than 50 PPMV CO2. ~ 10 ~