Natural Gas Dehydration Technology Selection: TEG Absorption, Molecular Sieve Adsorption, Silica Gel & Supersonic Separators Guide

Executive Summary & Engineering Scope

Water vapor is the most ubiquitous contaminant in raw natural gas. Saturated with water at reservoir pressure and temperature, gas extracted at the wellhead carries between $30\text{ and }250\text{ lb H}_2\text{O}/\text{MMSCF}$ ($500\text{ to }4,000\text{ mg/Sm}^3$).

If untreated, water vapor causes severe operational hazards: 1. Gas Clathrate Hydrate Formation: Under high pipeline pressures and cold ground/ambient temperatures, free water binds with light hydrocarbons to form solid crystalline hydrates that choke pipelines, freeze control chokes, and create differential pressure safety hazards. 2. Internal Sweet and Sour Corrosion: Liquid water condensation combines with acid gas contaminants ($\text{CO}_2, \text{H}_2\text{S}$) to generate carbonic and hydrosulfuric acids, triggering rapid localized pitting and sour stress corrosion cracking. 3. Catastrophic Cryogenic Freeze-Out: In cryogenic NGL recovery and Liquefied Natural Gas (LNG) plants operating at temperatures between $-40^\circ\text{C}$ and $-162^\circ\text{C}$, water freezes into solid ice, blocking plate-fin cold boxes (BAHX) and seizing turboexpanders.

                           NATURAL GAS DEHYDRATION VALUE CHAIN

                     ┌─────────────────────────────────────────────────┐
                     │ Raw Wet Gas from Acid Gas Treating or Wellhead  │
                     └────────────────────────┬────────────────────────┘
                                              │
                      ┌───────────────────────┴───────────────────────┐
                      │ Target Water Dew Point Specification?        │
                      └───────────────────────┬───────────────────────┘
                                              │
                    ┌─────────────────────────┴─────────────────────────┐
                    │                                                   │
     [ Pipeline Transmission Spec ]                         [ Cryogenic Processing Spec ]
        4 to 7 lb/MMSCF (60-110 mg/Sm3)                         < 0.1 ppmv (< 0.08 mg/Sm3)
        Water Dew Point: -5°C to -15°C                          Water Dew Point: -100°C
                    │                                                   │
                    v                                                   v
          TEG Absorption Unit                                 Molecular Sieve (TSA)
        (or Supersonic Separator)                                Adsorption Unit

Choosing the correct dehydration process is governed by the required water dew point depression ($\Delta T_{\text{dep}}$), feed gas contaminants (BTEX, sulfur, heavy hydrocarbons), utility availability, offshore weight/footprint constraints, and environmental emissions regulations.

This guide provides an engineering evaluation framework comparing: 1. Liquid Desiccant Absorption (Triethylene Glycol, TEG) 2. Solid Desiccant Adsorption (Molecular Sieve Type 4A / 3A Zeolites) 3. Hydrocarbon & Water Dew Pointing Adsorption (Silica Gel / Composite Beds) 4. Supersonic Gas Dehydration (Twister / 3S Static Separators) 5. Deliquescent Desiccant Salt Beds ($\text{CaCl}_2$)

1. Executive Screening Matrix & Rapid Selection Flowchart

The screening choice between liquid absorption, solid desiccant adsorption, and supersonic separation is governed by Outlet Water Specification, Feed Flow Rate, Inlet Temperature, and Plot Space / Environmental Constraints.

The 8-Dimension Technology Decision Matrix

                              RAPID DEHYDRATION SELECTION FLOWCHART
                                                │
                                    What is the required outlet 
                                    water dew point specification?
                                                │
                      ┌─────────────────────────┴─────────────────────────┐
                      │                                                   │
             < 0.1 ppmv (Cryogenic)                             > 1.0 lb/MMSCF (Pipeline)
                      │                                                   │
           MOLECULAR SIEVE (TSA)                               Is free pressure drop (dP > 25%)
             Type 4A / 3A Beds                                 available without recompression?
                      │                                                   │
           Cryo NGL / LNG Plants                                  ┌───────┴───────┐
                                                                 YES              NO
                                                                  │               │
                                                              Twister       Do you need co-removal
                                                             Supersonic     of heavy hydrocarbons?
                                                             Separator            │
                                                                          ┌───────┴───────┐
                                                                         YES              NO
                                                                          │               │
                                                                      Silica Gel         TEG
                                                                      Adsorption     Absorption
                                                                         Beds           Unit

2. Feed Contaminant & Operating Boundary Envelopes

The operational feasibility and sizing of dehydration systems are constrained by feed gas contaminants and physical operating envelopes:

1. Feed Gas Temperature

• Inlet Gas Temperature Limit: For TEG contactors, optimal absorption occurs between $20^\circ\text{C}$ and $40^\circ\text{C}$. Operating above $45^\circ\text{C}$ significantly reduces glycol water-carrying capacity, requiring higher circulation rates, while glycol vaporization losses increase exponentially ($L_{\text{loss}} \propto P_{\text{vap,TEG}}$). Operating below $15^\circ\text{C}$ increases glycol viscosity ($> 80\text{ cP}$), causing poor tray liquid distribution and foaming.
• Molecular Sieves: Can accept feed gas up to $50^\circ\text{C}$, but dynamic water capacity drops from $14\text{ wt}\%$ down to $< 8\text{ wt}\%$, requiring larger beds.

2. Acid Gas Loading ($\text{CO}_2$ and $\text{H}_2\text{S}$)

In sour gas fields, high partial pressures of acid gases alter dehydration chemistry: * In TEG systems, $\text{H}_2\text{S}$ and $\text{CO}_2$ dissolve in cold glycol inside the contactor. When heated in the reboiler ($204^\circ\text{C}$), dissolved $\text{H}_2\text{S}$ desorbs into the regenerator overhead vent gas, posing deadly toxic hazards ($\text{IDLH} = 100\text{ ppmv}$). Stripper overhead gas must be routed to a thermal incinerator or flare. Furthermore, high $\text{CO}_2$ lowers reboiler pH, forming corrosive degradation acids that mandate stainless steel (SS316L) reboiler bundles and amine pH buffering additives. * In Molecular Sieves, acid gases pose severe zeolitic degradation risks. Standard Type 4A molecular sieve crystals (pore diameter $4.2\text{ Å}$) co-adsorb $\text{CO}_2$ and catalyze the formation of carbonyl sulfide: $$\text{CO}_2 + \text{H}_2\text{S} \xrightarrow{\text{Zeolite Catalyst}} \text{COS} + \text{H}_2\text{O}$$ Because $\text{COS}$ cannot be removed in standard amine sweetening units and passes into sales gas, plants with $\text{CO}_2 > 0.5\text{ mol}\%$ and $\text{H}_2\text{S} > 4\text{ ppmv}$ must use Type 3A molecular sieves (pore diameter $3.0\text{ Å}$), which mechanically exclude $\text{CO}_2$ and $\text{H}_2\text{S}$ molecules while allowing water ($2.8\text{ Å}$) to enter.

3. Aromatics and Heavy Hydrocarbon Carryover (BTEX)

Aromatic hydrocarbons (Benzene, Toluene, Ethylbenzene, Xylene) exhibit high solubility in liquid glycols: $$\chi_{\text{BTEX}} = K \cdot P_{\text{partial}} \cdot M_{\text{TEG}}$$ A standard TEG unit absorbs $20\%\text{--}40\%$ of incoming benzene and $50\%\text{--}80\%$ of incoming toluene/xylene. When rich glycol enters the atmospheric reboiler, 100% of absorbed BTEX vaporizes out the still column vent. Under EPA NESHAP regulations (40 CFR Part 63 Subpart HHH), facilities emitting more than $10\text{ tons/year}$ of single HAP or $25\text{ tons/year}$ total HAP must install BTEX condensing systems, thermal oxidizers, or flare burners.

In solid desiccant beds, heavy hydrocarbons ($\text{C}_{10}+$) condense inside micro-pores and polymerize into carbonaceous coke during high-temperature thermal regeneration ($260\text{--}315^\circ\text{C}$), permanently destroying bed adsorption capacity. High-efficiency inlet coalescers with particulate filtration ($< 0.1\text{ }\mu\text{m}$) are mandatory.

3. Deep-Dive Process Technology Descriptions & Working Principles

Technology 1: Triethylene Glycol (TEG) Absorption

Triethylene Glycol ($\text{HO(CH}_2\text{CH}_2\text{O)}_3\text{H}$) is the global standard liquid desiccant due to its low vapor pressure, high thermal decomposition threshold ($206.7^\circ\text{C}$), and low solubility in natural gas:

                            TEG DEHYDRATION PROCESS FLOW

      Dry Gas Out ────────────────────────────────────────┐
           ^                                              │
           │                                              v
    ┌──────────────┐     Lean Glycol (99.0 - 99.9%)  ┌──────────────┐
    │  Contactor   │ <────────────────────────────── │  Reboiler /  │ <── Fuel Gas
    │  (Structured │                                 │  Still Column│ ──> Water Vapor + BTEX
    │   Packing)   │ ──> Rich Glycol (Water Laden) ──> [ Flash Drum ] ──> Flash Gas
    └──────────────┘                                 └──────────────┘
           ^
           │
      Wet Gas In

• Absorption Chemistry & Equilibrium: Wet gas flows counter-currently to ultra-pure lean TEG in a trayed column (10 to 14 bubble-cap trays) or structured packing bed. Water molecules form strong hydrogen bonds with the glycol hydroxyl ($-\text{OH}$) groups. Contactor sizing is governed by the Souders-Brown vapor velocity limit: $$v_{\text{max}} = K_{SB} \cdot \sqrt{\frac{\rho_L - \rho_g}{\rho_g}}$$ where $K_{SB} \approx 0.045\text{--}0.075\text{ m/s}$ ($0.15\text{--}0.25\text{ ft/s}$) for bubble-cap trays.
• Circulation Rate: The industry standard circulation rate is $2.5\text{ to }4.0\text{ US gallons TEG per pound of water absorbed}$ ($0.021\text{--}0.033\text{ m}^3\text{ TEG/kg H}_2\text{O}$). Over-circulation wastes reboiler fuel gas, while under-circulation risks off-spec wet gas.
• Purity vs. Reboiler Limits: Atmospheric heating of TEG is strictly capped at $204^\circ\text{C}$ ($400^\circ\text{F}$) to prevent rapid thermal degradation into corrosive organic acids. At atmospheric pressure and $204^\circ\text{C}$, equilibrium yields a maximum lean glycol purity of $98.7\text{--}99.0\text{ wt}\%$.
• Enhanced Regeneration for Stringent Specs:
• Stripping Gas (Stahl Column): Injecting dry fuel gas ($2\text{--}10\text{ SCF/gal TEG}$) into a packed column beneath the reboiler lowers the water vapor partial pressure, boosting lean purity to $99.6\text{--}99.9\text{ wt}\%$, achieving water dew points down to $-30^\circ\text{C}$.
• Cold Finger & Drizo Processes: Azeotropic hydrocarbon stripping (Drizo process using recovered hydrocarbon solvents) strips water down to $99.99\text{ wt}\%$ purity, allowing TEG to achieve water dew points below $-60^\circ\text{C}$.

Technology 2: Molecular Sieve Solid Bed Adsorption (TSA)

For cryogenic applications (LNG liquefaction and turboexpander NGL recovery), residual water must not exceed $0.1\text{ ppmv}$ ($0.08\text{ mg/Sm}^3$). At these sub-freezing temperatures, even traces of moisture form frost that instantly plugs brazed aluminum heat exchangers. Molecular sieves are the only proven technology capable of meeting this threshold:

                  3-BED TSA MOLECULAR SIEVE CONFIGURATION

   Wet Gas In ───> [ Bed A: ADSORPTION ] ───> Dry Gas Out (< 0.1 ppmv H2O)
                   [ (On-Stream, 24 hr)]

   Hot Regen  ───> [ Bed B: HEATING    ] ───> Regen Gas Out (To Cooler & Separator)
   Gas (280°C)     [ (Thermal Desorb)  ]

   Cool Gas   ───> [ Bed C: COOLING    ] ───> Gas to Heating Bed
   (Ambient)       [ (Preparing for Ads]

• Adsorption Physics & Zeolitic Structure: Molecular sieves are crystalline synthetic metal aluminosilicates (zeolites) possessing uniform, microscopic crystalline pores. Unlike physical absorption, water capture occurs via electrostatic polarization: divalent cations ($\text{Na}^+, \text{K}^+, \text{Ca}^{2+}$) inside the crystal cage generate intense localized electric fields ($> 10^7\text{ V/cm}$), binding polar water dipoles with high adsorption enthalpies ($\Delta H_{\text{ads}} \approx 3,000\text{--}3,800\text{ kJ/kg H}_2\text{O}$).
• Dynamic Sizing & Mass Transfer Zone (MTZ): A packed desiccant bed operates with three distinct zones: Equilibrium Zone (saturated with $13\text{--}15\text{ wt}\%$ water), Mass Transfer Zone (active adsorption front), and Unused Active Zone. Bed height is sized using the Ergun equation to balance dynamic capacity against bed pressure drop: $$\frac{\Delta P}{L} = 150 \frac{(1-\epsilon)^2}{\epsilon^3} \frac{\mu v_s}{d_p^2} + 1.75 \frac{1-\epsilon}{\epsilon^3} \frac{\rho_g v_s^2}{d_p}$$
• Fluidization Velocity Limits: Upward regeneration gas flow must never exceed $50\%\text{--}60\%$ of the minimum bed fluidization velocity ($v_{\text{fluid}}$) per API practices to avoid desiccant attrition and bed lifting: $$v_{\text{fluid}} = \frac{d_p \cdot (\rho_s - \rho_g) \cdot g \cdot \epsilon^3}{1.75 \cdot \rho_g}$$
• Thermal Swing Regeneration (TSA): Beds alternate cyclically between on-stream adsorption ($12\text{--}24\text{ hours}$), high-temperature heating ($260\text{--}315^\circ\text{C}$ to desorb water), and cooling with clean dry gas.

Technology 3: Silica Gel / Composite Hydrocarbon-Water Adsorption

Silica gel ($\text{SiO}_2$) and enhanced aluminosilicate beads (e.g., BASF Sorbead®) possess a broad pore size distribution ($20\text{ to }50\text{ Å}$), enabling simultaneous co-adsorption of water and heavy hydrocarbons: * Working Principle: While molecular sieves have uniform $4\text{ Å}$ pores that exclude hydrocarbons, silica gel pores capture both water and heavy pentane-plus molecules ($\text{C}_5+$). * Dual Dew Point Control: In pipeline transmission networks requiring strict control of both Water Dew Point ($\le -8^\circ\text{C}$) and Hydrocarbon Dew Point (cricondentherm $\le 0^\circ\text{C}$), a single silica gel unit replaces both a TEG dehydration unit and a mechanical chilling refrigeration plant. * Regeneration: Operated as a thermal swing adsorption (TSA) system at lower regeneration temperatures ($180\text{--}220^\circ\text{C}$) compared to molecular sieves.

Technology 4: Supersonic Gas Separation (Twister / 3S Dehydrators)

Supersonic separation represents a radical departure from traditional thermodynamic absorption, using static aerodynamics to achieve gas chilling:

                     SUPERSONIC SEPARATION FLUID DYNAMICS

   Inlet Gas ───> [ Laval Nozzle ] ───> Static Swirl ───> Cyclonic Separation ───> Dry Gas Core
   (High Press)   (Expands to M=1.5,    Vanes             Wall: Liquid Water      (Pressure Recovery
                   Drops T by 40-50°C)  (500,000 Gs)            + Condensate       in Diffuser)

• Working Principle: High-pressure wet gas enters a static converging-diverging Laval nozzle, expanding isentropically to supersonic velocity (Mach 1.5 to 2.0). The near-instantaneous pressure drop causes extreme Joule-Thomson/isentropic expansion cooling, dropping gas temperatures by $40^\circ\text{C}\text{ to }60^\circ\text{C}$ in milliseconds.
• Condensation & Vortex Extraction: Supersonic expansion forces water vapor and heavy hydrocarbons into dense submicron mist. Static internal swirl vanes impart rotational acceleration exceeding $500,000\times g$, flinging liquid droplets to the outer wall. A concentric cyclonic splitter separates the outer liquid film while the dry central gas core decelerates through a supersonic diffuser, recovering $70\%\text{--}80\%$ of inlet pressure.
• Engineering Trade-Off: Requires no moving parts, no chemicals (zero glycol), no heat input, and occupies $< 20\%$ of TEG footprint. However, it requires a permanent unrecoverable pressure drop of $25\%\text{--}35\%$ of absolute inlet pressure, restricting its use to fields with high excess wellhead pressure.

4. Utility, Consumables & Parasitic Power Intensities

Operating utilities represent the largest operational cost differential between liquid glycol and solid bed dehydration systems:

Thermal Energy Consumption Formulations

1. TEG Reboiler Duty ($Q_{\text{reboiler}}$): Consists of glycol sensible heating, water latent heat of vaporization, reflux condensation duty, and ambient heat loss: $$Q_{\text{reb}} = \dot{m}_{\text{TEG}} \cdot C_{p,\text{TEG}} \cdot (T_{\text{reb}} - T_{\text{feed}}) + \dot{m}_{\text{water}} \cdot \Delta H_{\text{vap,H2O}} + Q_{\text{reflux}} + Q_{\text{losses}}$$ Typically requires $1,000\text{ to }1,400\text{ kJ per kg of water removed}$ ($430\text{--}600\text{ BTU/lb}$).
2. Molecular Sieve Regeneration Duty ($Q_{\text{regen}}$): Requires heating high-pressure regeneration gas to $280^\circ\text{C}$ to supply the endothermic desorption energy, bed steel sensible heat, vessel shell heating, and insulation losses: $$Q_{\text{TSA}} = M_{\text{steel}} C_{p,\text{steel}} \Delta T + M_{\text{desiccant}} C_{p,\text{zeolite}} \Delta T + M_{\text{water}} \Delta H_{\text{desorption}} + Q_{\text{gas sensible}}$$ Consumes $3,200\text{ to }4,800\text{ kJ per kg of water removed}$, representing a $3\times\text{ to }4\times$ higher thermal intensity than TEG.

Utility Comparison Benchmark Table

5. CAPEX vs. OPEX Economic Trade-Offs (Lifecycle Cost Modeling)

                     15-YEAR LIFECYCLE COST COMPARISON (100 MMSCFD)

      CAPEX ────────────────────────────────────────────────────────┐
      TEG Absorption: Contactor + Regenerator + Stripper            │ TEG Wins on Initial CAPEX
      Molecular Sieve: 3 x Clad Pressure Vessels + Fired Heater     │ ($8.5M vs $19.2M)
                                                                    │
      OPEX ─────────────────────────────────────────────────────────┤
      TEG Absorption: Glycol make-up + BTEX compliance + Reboiler   │ Molecular Sieve Higher OPEX
      Molecular Sieve: High thermal fuel + Bed replace every 4 yrs  │ (Due to 280°C Regeneration)

Capital Expenditure (CAPEX) Analysis

• Equipment Count & Pressure Vessels: A TEG system requires only one high-pressure vessel: the contactor tower. The flash tank, reboiler, and surge drum operate at low or atmospheric pressure, allowing light carbon steel fabrication. Molecular Sieve systems require two to four heavy, ASME Section VIII Division 1 high-pressure clad steel vessels with internal refractory insulation, along with a massive convection-style regeneration fired heater, multi-valve switching manifolds, and high-temperature switching valves.
• Topside Weight Impact (Offshore/FPSO): A $150\text{ MMSCFD}$ TEG system weighs approximately $95\text{ tonnes}$ dry ($140\text{ tonnes}$ operating). An equivalent capacity 3-bed Molecular Sieve system exceeds $280\text{ tonnes}$ dry weight, demanding substantial structural deck reinforcement.

Operating Expenditure (OPEX) Analysis

• Desiccant Life Cycle: Zeolite molecular sieves degrade mechanically from thermal cycling and chemically from sulfur/hydrocarbon fouling, losing dynamic capacity at $10\%\text{ to }15\%\text{ per year}$. Full bed replacement every 3 to 4 years costs $\$400,000\text{ to }\$900,000$ in media procurement plus shutdown downtime.
• Thermal Fuel Gas Cost: A 3-bed molecular sieve plant consumes between $1.5\text{ and }2.5\text{ MMSCFD}$ of fuel gas for regeneration heating, compared to less than $0.4\text{ MMSCFD}$ for an equivalent TEG reboiler.

6. Operational Constraints, Turn-Down Ratios & Reliability Profiles

1. Turndown Capability and Switching Transients

• TEG Absorption: Turndown is exceptionally flexible ($25\%\text{ to }120\%$ of design flow). Reducing gas flow merely increases contactor residence time, lowering outlet water dew points. The glycol circulation pump can be throttled via VFD to maintain a constant $3.0\text{ gal/lb}$ ratio.
• Molecular Sieve TSA: Turndown requires careful cycle management. At low gas rates, superficial velocity drops, altering the Mass Transfer Zone (MTZ) and risking premature water breakthrough. During valve switching, sudden pressure differentials between beds can crush zeolitic pellets into fine dust (bed dusting). Automated slow-pressurization bypass valves are mandatory.
• Supersonic Separators (Twister): Highly inflexible. Supersonic shock wave positioning inside the Laval nozzle depends strictly on mass flow and pressure ratio. Turndown is limited to $80\%\text{--}110\%$. Rates below $75\%$ cause the shock wave to collapse into the nozzle, completely halting condensation.

2. Common Operational Failure Modes

• Glycol Foaming: Caused by liquid hydrocarbon carryover, corrosion inhibitor contamination, or fine particulates. Foaming induces massive glycol carryover into the sales pipeline ($> 5\text{ gal/MMSCF}$), drying out the reboiler and tripping downstream compressors.
• Thermal Salt Degradation: Produced formation water carried over into the TEG contactor deposits sodium chloride ($\text{NaCl}$) on reboiler firetubes. Salt creates localized thermal hot spots, causing tube blowout and rapid glycol thermal cracking into acidic byproducts.

7. Environmental Footprint, Methane Slippage & Carbon / ESG Compliance

                           EMISSIONS AUDIT COMPARISON

     [ Triethylene Glycol (TEG) System ]           [ Molecular Sieve (TSA) System ]
     - Still column vent: BTEX & VOC emissions     - Closed-loop regeneration gas recycle
     - Flashing methane from rich glycol           - Zero fugitive VOC/BTEX venting
     - Reboiler burner combustion CO2 & NOx        - Fired heater burner CO2 emissions
     Total Carbon Intensity: 12-24 kg CO2e/MMSCF   Total Carbon Intensity: 18-32 kg CO2e/MMSCF

1. BTEX Hazardous Air Pollutants: TEG still columns are major sources of benzene and hazardous air pollutants. Compliance requires installing BTEX Condensers to knock out heavy aromatics, routing residual non-condensables to reboiler firebox burners or dedicated vapor incinerators per EPA 40 CFR Part 63.
2. Zero-Emissions Supersonic Systems: Twister and 3S supersonic dehydrators produce zero operational emissions: there is no regenerator vent, no flash tank off-gas, and no combustion burner. All condensed water and hydrocarbons remain fully contained within high-pressure liquid boots.

8. Real-World Selection Case Study with Sensitivity Analysis

Field Development Scenario: 120 MMSCFD Processing Facility

A natural gas processing facility receives wet sweet gas and must supply two export headers: * Inlet Gas Flow Rate: $120.0\text{ MMSCFD}$ ($3.40 \times 10^6\text{ Sm}^3/\text{d}$) * Operating Pressure: $68.0\text{ barg}$ ($1,000\text{ psia}$) * Inlet Temperature: $35.0^\circ\text{C}$ ($95^\circ\text{F}$) * Water Content: $62.0\text{ lb/MMSCF}$ ($993\text{ mg/Sm}^3$, saturated) * Delivery Destination Split: * Header A (70 MMSCFD): Regional Sales Gas Pipeline (Spec: $\le 4.0\text{ lb/MMSCF}$, Water Dew Point $\le -8^\circ\text{C}$ at $68\text{ barg}$). * Header B (50 MMSCFD): Cryogenic NGL Recovery Plant with Turboexpander operating at $-95^\circ\text{C}$ (Spec: $\le 0.1\text{ ppmv H}_2\text{O}$).

Technology Architecture Configurations Evaluated

Option 1: Full-Stream Molecular Sieve Plant (3 x 50% TSA Beds treating entire 120 MMSCFD)
          - Deep dehydration for both pipeline gas and cryogenic feed
          - Massive regeneration fired heater (18.5 MMBTU/hr)

Option 2: Hybrid TEG + Slipstream Molecular Sieve
          - Train 1: Full-stream TEG Contactor dehydrates 120 MMSCFD to 2.5 lb/MMSCF
          - 70 MMSCFD routed directly to Sales Gas Pipeline
          - 50 MMSCFD routed to a compact 2-Bed Molecular Sieve polishing unit (< 0.1 ppmv)

Option 3: Full-Stream TEG with Drizo Hydrocarbon Stripping Process
          - Attempts to achieve ultra-low dew point via 99.99 wt% lean glycol

Quantitative Comparative Selection Matrix

Engineering Decision Rationale & Sensitivity Outcome

1. The Selection Winner: Option 2 (Hybrid Architecture).
2. Sizing a single full-stream molecular sieve plant to dehydrate all $120\text{ MMSCFD}$ down to $0.1\text{ ppmv}$ is an engineering error: it over-purifies the $70\text{ MMSCFD}$ of pipeline gas at enormous thermodynamic cost.
3. By installing an upstream TEG Contactor to treat the full $120\text{ MMSCFD}$ down to $2.5\text{ lb/MMSCF}$, the pipeline specification is fully met at low CAPEX ($1.0\times$).
4. Because the slipstream entering the Molecular Sieve unit is already pre-dried from $62.0\text{ lb/MMSCF}$ down to $2.5\text{ lb/MMSCF}$, the water loading entering the solid beds is reduced by $96\%$. Consequently, the molecular sieve bed volume shrinks from $62\text{ m}^3$ to just $14\text{ m}^3$, slashing fired heater duty from $18.4\text{ MMBTU/h}$ to $7.2\text{ MMBTU/h}$ and saving $\$9.7\text{M}$ in initial CAPEX.
5. Why Option 3 (Drizo TEG) Failed: While the Drizo process achieves $99.99\text{ wt}\%$ lean glycol and depresses water dew points down to $-60^\circ\text{C}$, it cannot reliably guarantee the $< 0.1\text{ ppmv}$ ($<-100^\circ\text{C}$) requirement needed to prevent dry ice and hydrate freeze-out in brazed aluminum cold boxes operating at $-95^\circ\text{C}$.

9. Integration with ChemProCal Engineering Tools

To size and optimize natural gas dehydration facilities, utilize these integrated ChemProCal calculators:

• TEG Dehydration Absorber & Regeneration Skid Sizer: Size contactor column diameters, evaluate Souders-Brown gas capacity factors, compute TEG circulation rates (GPM), and calculate reboiler heat duties and stripping gas demand.
• Molecular Sieve Cryogenic Dehydration Sizer: Size 2-bed, 3-bed, and 4-bed Zeolite adsorption systems, calculate Ergun pressure drops, verify anti-fluidization velocity margins, and model complete 4-stage TSA heating/cooling regeneration balances.
• Natural Gas Water Content & Water Dew Point Calculator: Evaluate water saturation content via Bukacek correlations, compute exact hydrate formation temperatures, and evaluate safety subcooling margins.
• Gas Pressure Letdown, Joule-Thomson Cooling & Pre-Heater Sizer: Model hydrate formation risk across pressure letdown stations downstream of dehydration skids.