Teknologi Pemrosesan Gas (TKK 564)

Instructor: Dr. Istadi(http://tekim.undip.ac.id/staf/istadi )

il  i di di idEmail: istadi@undip.ac.id

I t t ’ B k dInstructor’s Background

BEng. (1995): Universitas DiponegoroMeng. (2000): Institut Teknologi BandungPhD. (2006): Universiti Teknologi Malaysia

Specialization: Catalyst Design for Energy ConversionP  D i  f  E  C iProcess Design for Energy ConversionCombustion EngineeringComputational Fluid Dynamic (CFD)Computational Fluid Dynamic (CFD)

Course Syllabus: (Part 2)Course Syllabus: (Part 2)y ( )y ( )1. Hydrocarbons Recovery (Pengambilan Kembali Hidrokarbon)2. Nitrogen Rejection and Trace Component Removal g j p

(Penghilangan Nitrogen dan Komponen lainnya)3. Natural Gas Liquid Processing and Sulfur Recovery

(Pemrosesan Cairan Gas Alam dan Penghilangan Sulfur)( g g )4. Gas Transportation and Storage (Transportasi dan

Penyimpanan Gas)5 Liquified Natural Gas #1 (Gas Alam Cair)5. Liquified Natural Gas #1 (Gas Alam Cair)6. Liquified Natural Gas #2 (Gas Alam Cair)7. Second Assignment8. Ujian Akhir Semester

Retrogade CondensationPhenomenon associated with the behavior of a hydrocarbon mixture in the critical region wherein athydrocarbon mixture in the critical region wherein, at constant temperature, the vapor phase in contact with the liquid may be condensed by a decrease in pressure; or at constant pressure, the vapor is condensed by an increase in temperatureDew point control is also necessary if a potential forDew point control is also necessary if a potential for condensation is present in a process because of temperature or pressure dropsThe latter happens when the gas is in the retrograde condensation region

Retrogade Condensation in P‐T Diagram

Pressure−temperature diagram for a hypothetical raw natural gas thatPressure temperature diagram for a hypothetical raw natural gas that contains predominately methane (85 mol% methane with 4.8 mol% ofC3+), with trace components up to heptane

At any temperature and pressure combination outside the envelope, the mixture is single phase.At t t d i id th l tAt temperatures and pressures inside the envelope, two phases exist.Three points on the envelope are important:Three points on the envelope are important:

The cricondentherm (A), the maximum temperature at which two phases can existTh i d b (C) th i t hi hThe cricondenbar (C), the maximum pressure at which two phases can existThe critical point (B), the temperature and pressure where the liquid and vapor phases have the same concentration

The retrograde condensation effect can be seen by following the vertical dashed linefollowing the vertical dashed line

Dropping the pressure causes a liquid phase to form (retrograde condensation), which will be present until(retrograde condensation), which will be present until the pressure is below the envelopeThe dashed curve inside the envelope denotes the pressure and temperature of the mixture when the vapor quality is 95 mol%th i d th f i t t l d dthe cricondentherm of a mixture strongly depends on the molecular weight of the heavy componentsThe cricondenbar increases with increasedThe cricondenbar increases with increased molecular weight

HYDROCARBON RECOVERY PROCESSES

Inlet gas pressures make a major difference in plant configuration.configuration. High pressures permit use of expansion, J-T or turboexpander, to provide all of the cooling if low ethane recovery is desired. For low inlet pressures, either external refrigeration

i l t i f ll d b i ior inlet compression followed by expansion is needed to cool the gas, regardless of extent of ethane recovery.ethane recovery. Required outlet pressure helps decide which approach should be taken.

PROCESS FOR HYDROCARBONS RECOVERY

1. Dew point control and fuel conditioning2. Low ethane recovery2. Low ethane recovery3. High ethane recovery

DEW POINT CONTROL AND FUEL CONDITIONINGCONDITIONING

Dew point control and fuel conditioning exist to knock out heavy hydrocarbons from the gas streamThere are three methods:

L T t S t (LTS)Low Temperature Separators (LTS)TwisterVortex TubeVortex Tube

LOW TEMPERATURE SEPARATOR(LTS)

LTS ….The LTS process consists of cooling and partial condensation of the gas stream, followed by a low g ytemperature separator.When inlet pressures are high enough to meet discharge-

i t t k d t blpressure requirements to make pressure drop acceptable, cooling is obtained by expansion through a J-T valve or turboexpander. Otherwise, external cooling is required. Water usually is present, and to prevent hydrate formation the separator downstream of the expander is warmed above the hydrate formation temperature to prevent plugginghydrate-formation temperature to prevent plugging.An alternative to heating is injection of either ethylene glycol or methanol, which is then recovered and dried for reuse

If inlet pressures are too low for expansion, the stream is cooled by propane refrigeration.stream is cooled by propane refrigeration. The advantage of direct refrigeration is that the pressure drop is kept at a minimumHydrate formation must be considered with either feed dehydration upstream of the unit or inhibitor i j tiinjectionGlycol injection is usually the more cost effective, but if used it increases the required refrigerationbut if used, it increases the required refrigeration duty

TWISTERIt is used in one offshore facility for dew point control and dehydration.

G t d d th h l t iGas enters and expands through a nozzle at sonic velocity, which drops both the temperature and pressure and causes droplet nucleationpressure and causes droplet nucleation.The two-phase mixture then contacts a wing that creates a swirl and forces separation of the phases by centrifugal force. The gas and liquid are separated in the diffuser; the li id i ll t d t th ll d d it i thliquid is collected at the walls and dry gas exits in the center

The Twister SWIRL valve improves the separation of two‐phase flow across a pressure reduction valve, such as a p pchoke valve, Joule Thomson (JT) valve or control valve.

Advantages of the Twister systemg y

Simplicity. No moving parts and no utilities required.Small size and low weight. A 1-inch (24-mm) throat diameter, 6 feet (2 m) long tube can process 35 MMscfd (1 MMSm3/d) at 1 450 psia (100 bar)MMscfd (1 MMSm3/d) at 1,450 psia (100 bar).Driven by pressure ratio, not absolute pressure.Relatively low overall pressure drop SystemRelatively low overall pressure drop. System recovers 65 to 80% of original pressure.High isentropic efficiency. Efficiency is around 90% g y ycompared with 75 to 85% for turboexpanders.

Drawbacks of The Twister Systemy

Requires a clean feed. Solids erode the tubing and wing, necessitating an inlet filter separator.Limited turndown capacity. Flow variability is limited to ±10% of designed flow This limitation is mitigatedto ±10% of designed flow. This limitation is mitigated by use of multiple tubes in parallel.

VORTEX TUBEVORTEX TUBEThe vortex tube, also known as the Ranque-Hilsch vortex tube is a mechanical device that separates atube, is a mechanical device that separates a compressed gas into hot and cold streams. It has no moving partsVortex tubes use pressure drop to cool the gas phase but generate both a cold and warm gas stream. If streams are recombined the overall effect isIf streams are recombined, the overall effect is comparable to a J-T expansion. The principle of operation is the Ranque-Hilsch tube, p p p q ,developed in the 1940s and commonly marketed as a means to provide cold air from a compressed air stream.

VORTEX TUBE PRINCIPLESVORTEX TUBE PRINCIPLESPressurized gas is injected tangentially into a swirl h b d l t t hi h t f t tichamber and accelerates to a high rate of rotation.

Due to the conical nozzle at the end of the tube, only the outer shell of the compressed gas is allowed tothe outer shell of the compressed gas is allowed to escape at that end. The remainder of the gas is forced to return in an ginner vortex of reduced diameter within the outer vortex.

F d i t t l d d h d ti th d i h th tFor dew point control, and dehydration, the device has the vortex tube and a liquid receiver connected to the tube. Gas enters the tube tangentially through several nozzles at one end of the tube, expands, and travels spirally at near sonic velocities to , p , p ythe other end. As it travels down the tube, warm and cool gas separate. The cool gas goes into the center of the tube. Warm gas vents in a radial direction at the end but the cool gas is reflected back up theradial direction at the end, but the cool gas is reflected back up the tube and exits just beyond the inlet nozzles.Condensation occurs in the cool gas, and the liquid is moved to the walls by centrifugal force, where it collects and drains into the receiver belowreceiver below.The working pressure of the tube is 500 to 3,050 psig (36 to 210 barg), and flow rates are 20 to 140 MNm3/h. The turndown ratio is 15% for a single tube but can be increased by g yuse of multiple tubes in parallel; the optimum pressure drop is 25 to 35%Turndown ratio: the ratio of the maximum flow to the minimum flow of a metera meter

Advantages of Vortex TubesgSimplicity and light weight.It ld b f l h li it d t d iIt could be useful where limited turndown is acceptable. It will be of most value when no compression isIt will be of most value when no compression is required.

MEMBRANE METHOD FOR FUEL CONDITIONERCONDITIONER

Gas enters the membrane on the discharge side of the compressor and the resid al gas pro ides f el to thecompressor, and the residual gas provides fuel to the compressor engine or turbine. The low pressure permeate is recycled to the suction for recompression to recover the permeate

ADVANTAGES OF MEMBRANE TECHNOLOGYTECHNOLOGY

the process is simple and requires no moving parts.the process is simple and requires no moving parts. relatively small and light weight. this technology is used on several offshore gyinstallations. Unlike the Twister and vortex tube, membranes have the advantage of a turndown ratio down to 50%, with no performance penalty. This property may not be an advantage for fuel gasThis property may not be an advantage for fuel gas conditioning, where flow rates should be stable.

In fuel conditioning, the selectivity is not a major g, y jissue because of the relatively small fraction of gas that needs to be recompressed, and the enriched stream is recycled without requiring additionalstream is recycled without requiring additional compression.Membrane permeability is the product of the

l bilit d diff i ffi i tsolubility and diffusion coefficient. For separation of light gases, the primary mode of selectivity is the diffusion coefficientselectivity is the diffusion coefficient. For dew pointing, solubility drives the selectivity. These membranes are silicone rubber compounds pthat preferentially absorb the heavy components

2 LOW ETHANE RECOVERY2. LOW ETHANE RECOVERYThe focus of the previous section was removal of heavy components (C3+) to avoid condensation or to lower the heating valueth bj ti i t d l dthe objective is to produce a lean gas and recover up to approximately 60% of the ethane in the feed gasTwo process schemes are used to obtain this level ofTwo process schemes are used to obtain this level of ethane recovery:

1. Cooling by expansion or external refrigerationg y p g2. Lean-oil absorption

Cooling by Expansion or External R f i tiRefrigeration

At constant pressure and temperature, the ethane concentration in the liquid decreases with increasing C3+ fraction, which lowers the ethane concentration in the vapor and thus increases the percent ethanein the vapor and, thus, increases the percent ethane recovered.

Inlet gas is initially cooled with cold residue gas and cold liquid from the cold separator before going to the propane chiller and to the cold separator. Vapor from the separator is the sales gas, and the liquid goes to a fractionator to strip out light ends and recover liquid productproduct.The column operates at a lower pressure than does the cold separator. Because of system pressure drop and because theBecause of system pressure drop and because the fractionator runs at the lower pressure, the recycle stream must be recompressed.Alternatives to the process include:p

Reduction or elimination of the recycle by adding reflux to the fractionatorRunning the fractionator at a higher pressure and use of a pump to feed the column from the cold separatorto feed the column from the cold separator

With high inlet gas pressures, replacing the propane system with an expander is an attractive option. H i l t i b t bt iHowever, inlet compression may be necessary to obtain the temperatures required to obtain the desired recoveries. Both J T and t rboe panders are sed Cr m (1981)Both J-T and turboexpanders are used. Crum (1981) points out situations where a J-T system may be preferable to turboexpanders, although recent advances in turboexpander technology may temper some of them:in turboexpander technology may temper some of them:

Low gas rates. J-T is more economically viable at low gas rates. Low ethane recovery. For ethane recoveries of 10 to 30%,Low ethane recovery. For ethane recoveries of 10 to 30%, J-T expansion may be sufficient.Variable flow rates. J-T is insensitive to widely varying flow rates, whereas turboexpanders lose efficiency when

ti ff f d i toperating off of design rates.

Lean Oil Absorptionsea O bso pt o sEarly gas processing plants used lean oil absorbers to strip NGL from natural gas (Cannon, 1993), andto strip NGL from natural gas (Cannon, 1993), and the process is still used in about 70 gas plants today.The process involves three steps:

Absorption. An absorber contacts a lean oil to absorb C2+ plus from raw natural gas.St bili ti Th i h il d th i (ROD) t iStabilization. The rich oil demethanizer (ROD) strips methane and lighter components from the rich oil.Separation. The still separates the recovered NGLSeparation. The still separates the recovered NGL components as product from the rich oil, and the lean oil then returns to the absorber.

3. HIGH ETHANE RECOVERY3. G COThe above processes provided limited recovery of ethane.

To obtain 80 to 90% or more ethane recovery requires separationTo obtain 80 to 90% or more ethane recovery requires separation temperatures well below what is obtainable by use of propane refrigeration alone.

In principle direct refrigeration processes co ld be sed b cascadingIn principle, direct-refrigeration processes could be used by cascading propane cooling with ethane or ethylene refrigeration or by use of a mixed refrigerant that contains methane, ethane, and propane.

The primary motivation for use of only direct refrigeration would be low inlet gas pressures.

If significant inlet compression is required to produce refrigeration by g p q p g yexpansion, then cascade or mixed-refrigeration cooling, with or without expansion, may be attractive.

No matter which option is used obtaining high ethane recoveries from lowNo matter which option is used, obtaining high ethane recoveries from low inlet-pressure feed streams requires substantial compression, of either the feed stream, the refrigerants, or both.

Tugas Kuliah (kumpulkan paling lambat 18 November 2009)lambat 18 November 2009)

JOULE‐THOMSON (J‐T) Expansion:J l k k fi i J T E iJelaskan konfigurasi J‐T ExpansionJelaskan Prinsip Dasar J‐T ExpansionJelaskan fenomena J‐T Expansion di dalam P‐H atau P‐T DiagramJelaskan Aplikasi‐aplikasi J‐T Expansion terutama untuk pengambilanJelaskan Aplikasi‐aplikasi J‐T Expansion terutama untuk pengambilanhidrokarbon di dalam gas

TURBO Expansion:Jelaskan konfigurasi Turbo ExpansionJelaskan Prinsip Dasar Turbo ExpansionJelaskan fenomena Turbo Expansion di dalam P‐H atau P‐T DiagramJelaskan Aplikasi‐aplikasi Turbo Expansion terutama untukpengambilan hidrokarbon di dalam gaspengambilan hidrokarbon di dalam gas

JAWABAN SETIAP MAHASISWA TIDAK BOLEH SAMA. PEKERJAAN HARUS DITULIS TANGAN. CARILAH LITERATUR DARI BERBAGAI SUMBER (harus ada DAFTAR PUSTAKA dandirujuk)dirujuk)