Gas Processing Expander

Transcription

1 Expander Operated Ga Proceing April, 2015 Ga Proceing Expander Colder Proce Temperature and Maximized Compreor Uptime with Helidyne Expander Skid. Specification: Flowrate 1-10 mmcfd Max. Preure 1,440 pi Min. Temperature -50 F Power Generation up to 30 kw L Author: Joeph Jame Mechanical Engineer April, 2015 Editor: Andy Kerlin Mechanical Engineer Rev.3 Feb., 2016

2 Table of Content Executive Summary 1 Introduction 2 J-T Skid Configuration 3 J-T/MRU Skid Configuration 4 Expander Skid Configuration 5 How It Work 6 Empirical Data & Validation 9 Mathematical Validation 11 Package Deign 14 Contact U 15

3 Executive Summary: Recent advancement in oil exploration and fracking in remote location have ignificantly increaed production, particularly in North Dakota, where output ha increaed ome 10 fold ince Unfortunately, development of pipeline infratructure to tranport the oil & ga product i either economically infeaible or delayed many year to ervice thee well. Conequently, well owner mut rely on wellhead ga proceing equipment a a mean of eparating the high value NGL (Natural Ga Liquid ) from the flare ga in order to meet emiion tandard. And while tranporting the NGL by truck i economical, capturing the remaining flare ga continue to be a challenge depite available CNG and LNG pot proceing option. While ome progre ha been recently made, over 150 million cubic feet of natural ga continue to be flared each day in remote area of North Dakota. Helidyne now offer well owner a new wellhead ga proceing olution uing it novel planetary rotor expander. The expander increae NGL recovery rate, reduce flare ga and compreor downtime while generating electricity a a byproduct. Wellhead ga i traditionally refined by cooling procee which condene the heavier hydrocarbon into their liquid tate o the remaining lighter ga can be eparated and flared. The mot common method of cooling i the J-T (Joule-Thomon) proce. Thi approach require a high preure drop (500-1,000 pi) acro a J-T valve to achieve the deired downtream temperature. Depending on wellhead ga compoition, J-T kid have the capability of reaching temperature ranging from -15 F to -35 F. In contrat to the J-T throttling proce, Helidyne ue the high preure drop to drive it expander a the primary mean of extracting energy from the ga tream. Becaue thi approach i much more efficient, proce temperature will alway be colder than a J-T under comparable condition. Thi reult in more liquid recovery and higher revenue for the cutomer. On average, the Helidyne expander will produce a F colder exhaut temperature than a J-T valve. Thi document illutrate a few configuration ued within the indutry, empirical data of the Helidyne expander, and how the Helidyne expander kid i different. Figure 1 Helidyne Model 4400 Expander pg. 1

4 Introduction: Raw natural ga produced from a well i typically a byproduct of oil production and require a certain level of proceing in order to meet flare emiion regulation and/or pipeline pecification. The wellhead flowrate varie from well-to-well with the mot common ranging between.5-3 mmcfd. Thi raw ga contain many valuable component uch a pentane (C5), iobutane (C4), and propane (C3) which can be eparated from the methane (C1) and old to refinerie a raw NGL mix for further proceing. Ga compoition with methane mol % ranging below 80% are conidered rich wet ga compared to 80% or above which are labeled dry or lean ; wet ga being the more difficult to proce. Becaue many ite are remote, infratructure (including pipeline and electric grid power) i not available to tranport the raw ga. Shipping the ga in it unrefined gaeou tate via freight i not economical, a the tranport cot per cubic foot i unreaonable. For thi reaon, wellhead ga proceing equipment i ued to eparate the NGL from the methane o they can be tranported a a liquid to large refinerie at a profit. The Helidyne Expander achieve colder proce temperature than the JT valve. There are everal approache to condening and dropping out the heavy hydrocarbon to make NGL. The mot common method i uing an uptream heat exchanger coupled with a downtream J-T valve. In thi cenario, wellhead ga i compreed from pi up to 1,000 pi with a temperature increae to about F. It then pae through the before mentioned heat exchanger that lower the temperature to F, while maintaining the 1,000 pi preure throughout thi firt tage (ome of the heavy gae liquefy at thi tage and drop out). The now pre-cooled ga i then fed through a J-T valve were a rapid drop in preure utilize the Joule-Thomon effect to lower it temperature further. Thi J-T valve typically drop the preure down to pi and cool the ga in the range of -10 to - 30 F. Heavy gae liquefy, are extracted from the main ga tream, and then tored in large preurized tank waiting for tranport. The deired end product are high value NGL and a ga with high methane content (typically between 80% and 90% methane) which meet pipeline and flare requirement. The Helidyne expander will be a tand-alone, fully automated mechanical device that can be remotely monitored. Occaionally, if wellhead ga i extremely rich (40% - 60% methane), a MRU (Mechanical Refrigeration Unit) i intalled in-line with the J-T valve to further cool the ga. Rich gae experience le temperature change when relying olely on the J-T effect, o additional cooling from a MRU i often needed to boot performance. Thee refrigeration unit demand large amount of electricity (approximately 125 kwe for 3mmcfd flow) that mut be ourced from the grid or an on-ite generator, making thi equipment addition an expenive propoition for the well owner. Our experience ha hown that MRU operating on the rich ga in the Dakota and wetern Canada are often de-rated more than 50% and riddled with reliability problem that leave owner with on-going repair and downtime. The Helidyne expander kid i able to replace the J-T kid and MRU altogether thank to it ability to extract work-energy from the ga tream. The reulting temperature pg. 2

5 are between 10 and 30 F lower than a J-T valve, and comparable to a J-T+MRU combined proce. But unlike the MRU, the Helidyne expander generate power intead of conuming it; removing the need for an on-ite generator and the MRU itelf. Below are two common ga proceing configuration. The firt diagram (Figure 2) how a J-T kid configuration, which i typically ued for leaner wellhead ga (80% methane content or higher). The econd diagram (Figure 3) how the typical configuration for a wellhead with rich ga (Methane content a low a 40%). Richer gae have teeper p v. h chart (ee fig.8 on page 7), which render J-T cooling le effective; thu requiring additional cooling from an electric powered refrigeration unit. 9 Figure 2 JT Skid Configuration (Typically ued for leaner wellhead ga application, methane > 80%) Shell and Tube Heat Exchanger 3 Reciprocating Compreor Separator Tank #1 5 JT Throttling Valve 6 Separator Tank #2 NGL Collection Tank 4 7 State Preure Temperature Flow Decription 1 30 to 40 pi 50 to70 F Rich wellhead ga (methane content between 40% and 80%) pi 100 to 150 F Hot, high preure wellhead ga pi 30 to 60 F Cooled, high preure wellhead ga/liquid mixture pi 30 to 60 F Dropped out liquid collected from tank # pi 30 to 60 F Cooled, high preure wellhead ga (higher methane content then tate 1-3) pi -30 to 0 F Cold, low preure ga/liquid mixture pi -30 to 0 F Dropped out liquid collected from tank # pi -30 to 0 F Cold, low preure ga (>80% methane content), ued for heat exchanger pi 30 to 70 F Cooled, low preure lean ga ent for proceing or flare pg. 3

6 12 Figure 3 JT/MRU Skid Configuration (Typically ued for rich wellhead ga application, methane < 70%) 1 2 Reciprocating Compreor Shell and Tube Heat Exchanger 11 3 Mechanical Refrigeration Unit (MRU) Separator Tank #1 JT Throttling Valve 4 7 Separator Tank #2 125 kw Generator 10 Separator Tank #3 NGL Collection Tank State Preure Temperature Flow Decription 1 30 to 40 pi 50 to70 F Rich wellhead ga (methane content between 40% and 80%) pi 100 to 150 F Hot, high preure wellhead ga pi 30 to 60 F Cooled, high preure wellhead ga/liquid mixture pi 30 to 60 F Dropped out liquid collected from tank # pi 30 to 60 F Cooled, high preure wellhead ga (higher methane content than tate 1-3) pi -30 to 0 F Cold, low preure ga/liquid mixture pi -30 to 0 F Dropped out liquid collected from tank # pi -30 to 0 F Cold, low preure ga( higher methane content then tate 1-6) pi -50 to -20 F Extra cold, low preure ga/liquid mixture pi -50 to -20 F Dropped out liquid from tank # pi -50 to -20 F Extra cold, low preure ga ued for heat exchanger (>80% methane content) pi 10 to 70 F Cooled, low preure lean ga ent for proceing or flare pg. 4

7 Below i the configuration for a Helidyne expander kid. A hown in the table, uing a Helidyne expander combine the implicity of a J-T configuration, while producing the cold temperature of a J- T+MRU Skid. The Helidyne expander i a poitive diplacement, rotary device (with elf-cleaning rotor) that ha a preure rating twice it cloet competitor. Thi tranlate to 1,000 of hour of runtime without maintenance. A previouly mentioned, the byproduct of uing a Helidyne expander i available haft power capable of producing up to 30 kw of electricity. A portion of the available power can be ued to power an onboard PLC for full automation and remote monitoring. Other ue may include heat tape for kid piping, on-ite control room, climate control for operator, or to drive any auxiliary device. Figure 4 Expander Skid Configuration (Application include both dry and wet ga well) Reciprocating Compreor Shell and Tube Heat Exchanger Helidyne Expander NGL Collection Tank Separator Tank #1 4 Up to 30 kw of available haft power. 6 Separator Tank #2 7 State Preure Temperature Flow Decription 1 30 to 40 pi 50 to70 F Rich wellhead ga (methane content between 40% and 80%) pi 100 to 150 F Hot, high preure wellhead ga pi 30 to 60 F Cooled, high preure wellhead ga/liquid mixture pi 30 to 60 F Dropped out liquid collected from tank # pi 30 to 60 F Cooled, high preure wellhead ga (higher methane content then tate 1-3) pi -50 to -20 F Cold, low preure ga/liquid mixture pi -50 to -20 F Dropped out liquid collected from tank # pi -50 to -20 F Cold, low preure ga (>80% methane content), ued for heat exchanger pi 10 to 70 F Cooled, low preure lean ga ent for proceing or flare pg. 5

8 How It Work: Helidyne planetary rotor deign conit of four crew-like rotor urrounding a central output haft, thu the planetary reference. Rotor are deigned with a helical twit that meh with adjacent rotor when aembled. A the rotor rotate in the ame direction they form a progreive working cavity within the rotor meh. Each revolution produce two cycle for a 4-rotor configuration. The baic machine ha a fixed volume ratio of 1:1 from inlet-to-exhaut and can be aumed to behave like a hydraulic motor (for incompreible flow only, Mach <.3). With the addition of an inlet cut-off valve, any volume ratio can be achieved allowing for ientropic expanion for improved efficiency and greater cooling performance. Figure 7 illutrate the hape of the volume within the 4- rotor machine. At the beginning of a cycle the expander working cavity i open to the ga ource; maintaining contant high preure until the rotor rotate one half revolution at which point the rotor cut-off the ource much like a valve. In thi poition the ga in the cavity i entirely encloed. A the rotor continue to turn the backide begin to exhaut the ga at a lower preure, having given up it energy while puhing the rotor. A the leading volume of ga i exhauted, a new volume of ga enter the frontend, creating 2 power cycle per revolution. When operating with a cut-off valve, ga i only allowed to enter and fill a fraction of the working cavity before the upply i cut-off by the valve mechanim. A the cavity progreively enlarge, the ga i allowed to expand within the cavity and do work. Once a cycle i complete another begin to repeat the proce. Figure 5 Rotor at tarting poition (beginning of a cycle) Ga Packet Figure 6 Rotor at full torque poition (half cycle or quarter turn) Shaft power produced by a 1:1 expander i calculated uing the hydraulic power equation: P haft = pv Actual RotorE vol 1 Where: P haft = Shaft power p = Preure acro the rotor V Actual Rotor = "actual" flow rate through the rotor E vol = Expander Volumetric Efficiency Figure 7 Shape of a ga volume paing through the Expander The power produced by the expander for ga proceing application i a byproduct, not the objective. Ga cooling i the primary goal and i directly correlated to the efficiency of the expander. A per it definition, an expander convert internal energy within a fluid to mechanical energy by having it perform work (uually on a rotor or a blade). Thi reduce the enthalpy (internal energy plu the product of volume and preure), which reduce the heat content of the fluid. J-T valve ue the Joule-Thomon effect which i an ienthalpic proce (contant enthalpy) where total energy i conerved in adiabatic ga expanion (no heat exchanged, no work performed). Thi proce caue an increae in potential energy but a decreae in kinetic energy pg. 6

9 (decreae in temperature) but total energy i conerved. Thi proce hold true for all non-ideal gae if performed within the Joule Thomon inverion curve region. On the other hand, when uing an expander, ga perform poitive work during partial ientropic (contant entropy) expanion which reduce it enthalpy (reducing total energy) thu cooling the ga further than a J-T valve. Each fluid compoition ha it own unique range of cooling capacity that can be identified along it ientropic curve when plotted on a Mollier chart (ee figure 8). Removing all the potential energy from a fluid tream would be an ideal ientropic proce (or in other word, a ytem with 100% efficiency). Depending on expander efficiency, the enthalpy removed will lie omewhere between it ienthalpic and ientropic temperature. The Mollier chart depict preure veru enthalpy which clearly illutrate thi concept further, o a brief explanation of thi chart i beneficial. Thi pecific chart (fig. 8) ue methane a the fluid; the green line indicate iothermal procee, black line are ientropic procee, and the brown line i the aturated-tate bell curve. The black dot i the initial tate of thi particular example (1, F). The vertical red line how the cooling proce of the purely ienthalpic proce of a J-T valve. Since an expander remove energy, the reduced enthalpy lower the temperature further a hown by the purple line. The theoretical maximum cooling for thi example, without an external heat pump, i hown by the blue line. Notice all three cenario have the ame exhaut preure (150 pi) but different reultant temperature. Figure 8 pg. 7

10 The change in enthalpy i calculated by: h = N in Z in T in E vol (1 p out ) 2 p in Where: h = Change in enthalpy N in = Real ga contant Z in = The compreibility factor at the expander inlet p in = Expander inlet preure p out = Expander outlet preure T in = Expander inlet Temperature E vol = Expander volumetric efficiency Which i derived from the conervation of energy: Where: m = Expander inlet ma flowrate P haft = m h 3 Analyzing Equation 2, it evident that a higher preure ratio and greater expander efficiency will yield lower temperature. Or, in term of the above Mollier Chart (Figure 8), the greater the preure ratio and expander efficiency, the cloer the purple line move toward the blue line at higher ientropic efficiency. Current Helidyne expander volumetric efficiencie are approximately 20-40% (depending on the application). A further improvement are made to the expander, leakage within the expander ytem will be reduced which will increae volumetric efficiency reulting in lower exhaut temperature. Furthermore, the addition of a cut-off valve dramatically increae expander ientropic efficiency. The Helidyne expander ha a unique deign that allow it to be the only expander on the market uitable for the harh condition experienced in a total-flow NGL application. The current rotor deign for Model 4400 allow for preure drop of up to 1,000 pi (double the rating of a twin crew expander), flow up to 10 mmcfd, and power generation up to 30 kw. Other competitive advantage include it ability to proce 2-phae fluid and it inherent elf-cleaning deign. Thee combined attribute make the Helidyne expander a unique driver that i more effective and more reliable than other competing expander type. pg. 8

11 Figure 9 The Helidyne Red Rock Tet Site located in St. George, Utah Empirical Data & Validation: The Helidyne expander ha been teted uing air, nitrogen, refrigerant, and pipeline natural ga to validate the above mathematical model. Helidyne private tet ite i located in St. George, Utah at the Red Rock Generation Facility and include a 1,300 HP natural ga fueled compreor, PLC operated control room, and a piping infratructure to run variou tet (ee Figure 9). Thi tet ite i capable of producing flow up to 6 mmcfd at 1,000 pi uing pipeline quality natural ga or nitrogen (tet uing air and refrigerant performed at different location). Several 24 hour tet were completed uing pipeline ga. Thee tet were deigned to meaure variou performance parameter including preure/flow variance, tability, and ga cooling. Generated power wa controlled uing an uptream flow control valve that regulated preure to the expander. From the graph and table below, Sytem Preure i the line preure uptream of the control valve, expander inlet preure i the line preure between the flow control valve and the expander (and i ued for comparion with the J-T proce), and the exhaut preure i the line preure after the expander. Figure 10 illutrate reult of the firt half of a 24 hour tet. The firt graph diplay the expander having a varying ytem preure (dark blue line, ranging from 450 to 850 pi) while maintaining a contant 15 kw power output (teal line). In addition to teting ytem tability, thi provided different ytem temperature that varied with ytem preure. The econd graph of Figure 10 how ytem temperature before the flow control valve (red line), the temperature right before the expander (the purple line), and the exhaut ga temperature (green line). A et of data point (indicated by the vertical red line) are diplayed below the temperature graph. Thee value will be ued to compare the performance of the Helidyne expander veru a JT valve. pg. 9

12 Time Stamp 10/20/ :00 Sytem Preure pi Expander Inlet Preure pi Exhaut Preure pi Figure 10 Sytem Temperature 92.6 F Inlet Temperature 82.3 F Exhaut Temperature 53.1 F Power kw The data from Figure 10 i populated in the table above and can be reproduced uing NIST (National Intitute of Standard and Technology) data. The NIST Refprop oftware can alo predict the exhaut temperature of a JT valve under the ame application (ee Figure 11). Thi validate equation 1-3 (note: preure are abolute): Figure 11 Ienthalpic JT Proce Line 1 = Sytem Initial State Line 2 = Expander Inlet State Line 3 = Rotor Inlet Line 4 = Expander Exhaut Temperature Line 6 = JT Temperature (for comparion) pg. 10

13 A Figure 11 how, the Helidyne expander had a 13 degree colder temperature than a imilar tet with a JT valve. Thi i a reult of the expander extracting fluid energy from the flow and converting it to mechanical work. A equation 2 how, a greater preure ratio will yield a greater change in enthalpy, which tranlate to cooler temperature. The above tet had a 300 pi drop acro the expander (a per the 15 kw protocol requirement). If a greater power wa deired, the preure drop acro the expander would be raied to the available 500 pi drop and the exhaut ga would be a lower temperature than line 4 of Figure 11. The veratile profile of the Expander include flow from 1-10 mmcfd, preure up to 1,440 pi, and temperature down to -50 F. It i important to note that exhaut temperature will vary depending on fluid compoition, preure drop, initial temperature, ambient temperature, and flowrate (impact expander volumetric efficiency). The Mollier chart in Figure 8 how methane (at certain point, preure, and temperature) diplaying curved iothermal line. In other word, methane promote very good cooling when dropping from warmer, higher to lower preure. However, when the fluid compoition change by reducing the methane mol percentage, the iothermal line become traighter and more vertical, imilar to the left-hand ide of Figure 8 methane chart. In hort, lower mol percentage methane compoition make J-T cooling le effective and the ue of an expander more neceary. Each well will have it own fluid compoition, flow, temperature, and preure that will produce unique reult when uing a Helidyne expander. Mathematical Validation: P haft = m h kw kw (Paraitic Loe) = kw = m kj kg m = kj kg kj m = kg m = ρv Actual Where: ρ = Fluid Denity V Actual = m ρ pg. 11

14 V Actual Expander Inlet = kg kg m 3 Converting to tandard flowrate: V Actual Expander Inlet =.073 m3 Calculating equation 1: V td = V td = V actual ( p act p td ) ( T td T act ) Z in lb. 073 m3 ( in R 13 lb ) ( R ) in = m3 P haft = pv ActualE vol p = [ lb lb 125 in2 in 2 (calculated preure drop through the manifold)] = 1,211,958.2 N m 2 Converting Standard back into actual: Calculating Volumetric Efficiency: V Actual Rotor = V Actual = V tdz in ( p act p td ) ( T td T act ) m3 (. 97) lb ( in R 13 lb ) ( R ) in 2 =.097 m3 E vol = V Cavity V Actual Rotor Where: V Cavity = Geometric cavity flowrate of the rotor =.0166 m3 E vol = m m3 =.171 for the Model 4400 P haft = ( N m3 m2) (. 097 ) (. 171) = kw pg. 12

15 Output power = E Generator (P haft P drag ) =.99(20.10 kw 4.8kW) = kw kw And finally equation 2: h = N in Z in T in E vol (1 p out p in ) h = (. 518 kj lb kg K ) ( )(297 K)(. 171) (1 in 2 kj lb ) = 18.8 kg in 2 And comparing equation 2 reult to empirical data from the NIST Chart in Figure 11: kj kj kj = kg kg kg kj 18.8 kg NOTE: Thermodynamic calculation will have a greater margin of error than power calculation due to the inherent approximation in thermodynamic modeling. Thee empirically validated mathematical model allow for any natural ga compoition to be calculated. If given the inlet preure, outlet preure, and inlet temperature; the power produced and change in enthalpy can be predicted. A tated previouly, a Helidyne expander will alway produce temperature lower than a J-T valve and comparable temperature a a J-T valve+mru configuration with the byproduct being uable haft power. pg. 13

16 Package Deign: Inulated NGL Collection Tank Model 4400 Helidyne Expander Skid Connection Inulated Heat Exchanger Generator (Or any device requiring haft power) Onboard PLC/HMI Onboard Battery Sytem pg. 14

17 Contact U: Addre: 1425 Redledge Rd. Suite 102 Wahington, Utah Office Phone: For more information about our product and ervice, pleae viit our webite: Helidyne LLC All right reerved. No part of thi document or it content may be reproduced, republihed, publicly diplayed, uploaded, tranlated, tranmitted, or ditributed without the prior written conent of Helidyne LLC. Information contained in thi document i ubject to change without notice and i provided on an a-i bai. Helidyne LLC. diclaim all warrantie, expreed or implied, including, but not limited to, warrantie of non-infringement, accuracy and fitne for a particular purpoe, except a provided by written agreement. pg. 15