PREPARING SOLUBILITY DATA FOR USE Mapping Midstream s Future 2012 GPA Convention BY THE GAS PROCESSING INDUSTRY: UPDATING KEY RESOURCES Darryl Mamrosh and Kevin Fisher Trimeric Corporation Jeff Matthews URS Corporation
Background GPA sponsored a number of projects for the collection of VLE and LLE data to describe solubilities of interest to gas processors: Methanol in natural gas and liquid phases CO 2 and H 2 S in TEG and EG Hydrocarbons (BTEX) in Amines & Glycols GPSA Engineering Data Book (EDB) These topics in EDB have not been updated to the most recent data 2
Background This project: create models, graphs, etc., as updated content for EDB, and make the data readily usable to GPA members Projects 975-5, 975-7, 975-8 This work focuses on simple, generalized representations of data Use for quick process calculations 3
Summary Topics will be covered separately Solubility of methanol in natural gas and liquids CO 2 and H 2 S solubility in glycols Hydrocarbon solubility in amines & glycols To Include Review of current EDB (12 th ) content Treatment of new data Using the information Not all is covered: The paper available on-line 4
Solubility: What does it mean? Concentration, at specified conditions of equilibrium, of a solute dissolved in a solvent. In gas processing: Concentration of a solute in a gas in equilibrium with a liquid phase Concentration of a light solute in a liquid in equilibrium with a gas phase Concentration of a solute in a liquid in equilibrium with another liquid phase Always refers to an equilibrium condition 5
Approach 1. Use common terminology and units for expressing solubility concentrations 2. When feasible use same formats as in existing EDB content 3. When appropriate, create a mathematical model of data. If not, create a graph and/or table. Models should be easy to use (not EOS for simulation software) 6
Approach 4. Generalize the data and simplify Ignore minor variables Group data that are similar 7
Solubility of methanol in natural gas and HC liquids: GPA Project 975-7 Importance of Data Methanol used in hydrate inhibition, dehydration, sweetening In Hydrate inhibition: Predict loss of injected methanol in natural gas phase Predict loss of injected methanol in liquid hydrocarbon phase (if present) Material balance calculations used to predict methanol injection rate required to prevent hydrates 8
Solubility of Methanol in the Natural Gas Phase. EDB Graph (12 th ) Degr. F Pressure (psia) Lb MeOH per MMSCF Gas per wt% MeOH in Aq Phase 9
Compare with new data. Red & Green lines are traces of current figure 20-65. Red and Green Points are expt l data 10
Solubility of methanol in natural gas: Treatment of new data Variables: Methanol content of aqueous phase Temperature Pressure Consistent simple model not developed Conclusion: Produce update of EDB Figure 20-65 11
12
Solubility of methanol in hydrocarbon liquids (975-7) Wt% MeOH in Aq Liquid Mol% MeOH in HC Liquid Temperature (F) 13
Solubility of methanol in hydrocarbon liquids: Treatment of Data Variables: Methanol content of aqueous phase Temperature Composition of HC liquid phase Pressure small impact (ignored) Express in terms of distribution ratio: 14
Solubility of methanol in hydrocarbon liquids: Treatment of Data Liquid hydrocarbon phase composition Typical hydrocarbon components had minor effect on solubility Toluene had a significant effect Implies that all aromatics will probably be signficant 15
Methanol solubility in liquid hydrocarbons: Proposed representation of data. 1000 100 Figure 2. Liquid-Liquid Methanol Distribution Ratios. Groups all hydrocarbons except toluene (aromatics). 10 No Toluene 28-33mol% Toluene 50-70 mol% Toluene 70-80 mol% Toluene Distribution of methanol between aqueous and hydrocarbon phases, data from various sources. Hydrocarbon phases includes various alkane and cycloalkane compounds. Data shows the variation of distribution with changes in the amount of toluene in the hydrocarbon phase. 1-50 -30-10 10 30 50 70 90 110 130 Temperature ( o F) 16
Solubility of CO 2 and H 2 S in TEG & EG: Project 975-8 Importance of Data H 2 S and CO 2 in gases being dehydrated can dissolve in the solvent under pressure and then be released to the gas phase during flash and regeneration steps Important for a few reasons: Product Quality Environmental Safety Design of equipment (e.g., flash drum) 17
Current EDB Content. Solubility in TEG as function of temperature and H 2 S or CO 2 partial pressure Solubility defined in terms of std vol of gas per gallon solvent 18
Compare with new data. Purple points are expt l data (scf / gallon) at the T & P i of the red data point. 19
Solubility of CO 2 and H 2 S in TEG & EG: Treatment of Data Modeling versus graphing The new data was not amenable to parametric graphing Various mathematic models were attempted Final model based on one used by source data authors 20
Solubility of CO 2 and H 2 S in TEG & EG: Treatment of Data P i is the partial pressure of the acid gas (component i: CO 2 or H 2 S) P i = y i P y i is the mole fraction of acid gas in the vapor phase x i is the mole fraction of the acid gas in the liquid phase T is the absolute temperature x H2O is the mole fraction of water in the liquid phase P is the absolute pressure Different A, B, C, D constants for each of the four systems based on data fit x i can be used to calculate the solubility of CO 2 or H 2 S in units of std vol of gas per volume of solvent 21
0.35 Figure 9. Solubility of H2S in TEG: Correlation of Reference 2 data with the Model-Generated and Process Simulation Software-Generated Data. Correlation plot of model to data Simulation software VLE method: Peng-Robinson Model or Simulator Predicted H2S concentration in Liquid (mole frac) 0.30 0.25 0.20 0.15 0.10 0.05 Model Simulator SourceData 0.00 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 Source Data H2S concentration in Liquid (mole frac) 22
1 FIGURE 10. Approximate Solubility of CO 2 in Triethylene Glycol at 50 psia vs. Temperature, H 2 S Content of Gas Phase, and Water Content of TEG CO 2 Solubility, scf CO 2 / gallon TEG solution 0.1 0.01 0.001 60 80 100 120 140 160 180 200 Temperature, F 23
Solubility of CO 2 and H 2 S in TEG & EG Uses of Data Charts and models can be used to estimate the equilibrium content of gases in glycols Can be used to estimate the uptake of CO 2 and H 2 S in TEG contactor, and the subsequent release to the gas phase in the flash and regeneration Can also use as a check of other models (e.g., simulations) 24
Solubility of Hydrocarbons in Glycols and Amines Project 975-5 Vapor-liquid and liquid-liquid equilbria Data collection focused on BTEX compounds, and the differences between similar aromatic and non-aromatics 25
Solubility of Hydrocarbons in Glycols and Amines Importance of Data Predict hydrocarbon absorption from gas during amine and glycol treating Vaporization during flash and regen Equipment design Product loss Environmental (VOC, BTEX) 26
Solubility of Hydrocarbons in Glycols VLE data for BTEX distribution between TEG and gas phase Bulk gas phase: methane Data taken at conditions typical of TEG dehy regenerator, contactor, and flash drum Use equilibrium ratios (K values) to represent data K i = y i / x i 27
Solubility of Hydrocarbons in Glycols Figure 4.3. Equilibrium Ratios for BTEX in TEG Typical Contactor Conditions 0.1 0.09 0.08 DATA FROM RR-131. PRESSURE: 1000 psia WATER CONCENTRATION IS FOR GLYCOL LIQUID PHASE Benzene, 5 w% Water 0.07 Toluene, 5 w% Water Equilibrium Ratio y i /x i 0.06 0.05 0.04 0.03 0.02 Benzene, 1 w% Water Benzene, 0 w% Water Ethyl Bz, 5 w% Water Toluene, 1 w% Water Toluene, 0 w% Water o-xylene, 5 w% Water EthylBz, 1 w% Water Ethyl Bz, 0 w% Water o-xylene, 1 w% Water o-xylene, 0 w% Water 0.01 0 70 80 90 100 110 120 130 Temperature ( F) 28
Solubility of Hydrocarbons in Two data groups: Amines LLE measurements solubility limit VLE measurements subsaturation solubility Majority of data taken via LLE measurements Can be used directly for binary interaction parameters Maybe not as directly useful for most gas treating calculations 29
Solubility of Hydrocarbons in Solubility limit data (LLE) Amines Solubility in terms of SCF vapor / gallon solution Variables: Temperature, amine, hydrocarbon, water content of amine Little variation with pressure above solubility limit Solubility limit data can be modeled S is the solubility limit (SCF/gallon sol n), W is the amine concentration, A, B, C values for each amine hydrocarbon pair 30
Solubility of Hydrocarbons in Amines Figure 4.7. Solubility Limit of Benzene in Amine Solutions. Liquid-Liquid Solubility Data and Model. Solubility Limit of Toluene (scf Vapor / Gallon Solution) 10 1 DATA POINTS FROM RR-180 and TP-29. LINES GENERATE USING EQN. 1. PRESSURE RANGE OF DATA: 72-732 PSIA 70 wt% DGA 50 wt% MDEA 46 w% DGA 35 wt% DGA 25 wt% MDEA 0.1 50 70 90 110 130 150 170 190 210 230 250 Temperature F 31
Solubility of Hydrocarbons in Amines VLE data (subsaturation) Less data available Represented as equilibrium ratio (K) values Rough approximation: base subsaturation solubility on solubility limit data 32
Solubility Figure 16. General Approximation of Hydrocarbons of Solubility. in Concentration of hydrocarbon in amine (aqueous) phase Glycols and Amines x i,s Solubility Limit Generic graph showing solubility limit & subsat One Liquid Phase (Aqueous) P i * Saturation Pressure Two Liquid Phases Constant Temperature Partial Pressure of Hydrocarbon 33
Solubility of Hydrocarbons in Amines Table 4.3. Experimental K values compared with Estimations from Equation 4.6 Hydrocarbon Amine Solution Temperature Pressure K K (F) (psia) Experimental Eq. 4.6 Toluene 50 w% MDEA 140 73 15.6 12.9 Toluene 50 w% MDEA 140 1019 3.9 0.9 Cyclohexane 50 w% MDEA 140 73 316.6 296 Benzene 50 w% MDEA 140 73 19.7 16.9 34
Conclusions See reports (presentation and Research Reports) for: More data and details, graphs Discussion of general trends Research reports contain reference for the source data Updated content submitted for consideration for next version of EDB 35