Instructor s t Background

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1 Teknologi Pemrosesan Gas (TKK 564) Instructor: Dr. Istadi ( ) il iistadi@undip.ac.id di di id

2 Instructor s t Background BEng. (1995): Universitas Diponegoro Meng. (2000): Institut Teknologi Bandung PhD. (2006): Universiti Teknologi Malaysia Specialization: Catalyst Design for Energy Conversion Process Design for Energy Conversion Combustion Engineering Computational Fluid Dynamic (CFD)

3 Course Syllabus: (Part 2) 1. Hydrocarbons Recovery (Pengambilan Kembali Hidrokarbon) 2. Nitrogen Rejection/Removal (Penghilangang g Nitrogen) ) 3. Trace Component Removal (Penghilangan Komponen lainnya) 4. Natural Gas Liquid Processing and Sulfur Recovery (Pemrosesan Cairan Gas Alam dan Penghilangan Sulfur) 5. Gas Transportation and Storage (Transportasi dan Penyimpanan Gas) 6. Liquified Natural Gas #1 (Gas Alam Cair) 7. Liquified Natural Gas #2 (Gas Alam Cair) 8. Second Assignment 9. Ujian Akhir Semester

5 TRACE COMPONENTS? A number of other trace components present processing, product quality, or environmental problems if concentrations are too high, i.e.: Hydrogen Oxygen Radon (NORM) Arsenic Helium Mercury BTEX (benzene, toluene, ethylbenzene, and xylene)

6 1. Hydrogen Hydrogen levels are rarely sufficiently high to y g y y g cause a problem. The primary source would be gas streams from refineries, but even there, the concentrations should be low.

7 2. Oxygen Oxygen is the only contaminant that is not naturally occurring, and the best approach for treating it is to prevent its introduction into the processing stream. The major source is leaking valves and piping in gathering systems that operate below atmospheric pressure SPECIFICATION: 1.0 vol% maximum oxygen concentration in sales gas, but some pipelines have specifications as low as 0.1 vol%.

8 However, it causes problems in gas processing at concentrations of 50 ppmv, such as: Enhancing pipeline corrosion if liquid water is present Reacting with amines in gas treating, which ultimately leads to heat stable salt formation Reacting with gy glycols to form corrosive acidic compounds Reacting with hydrocarbons during the high- temperature t regeneration of the adsorption beds to form water, which reduces regeneration effectiveness and, thus, reduces bed capacity

9 At low levels, the oxygen can be removed by use of non-regenerative scavengers. For higher concentrations, the method is to catalytically y react it in the gas stream to produce water, which is then removed in the dehydration step However, gases that contain sulfur compounds poison oxidation catalysts.

10 3. Radon (NORM) Natural gas contains radon, a naturally occurring radioactive material (NORM) at low concentrations It rarely poses a health problem because it has a half-life of about 3.8 days However, radon decays into lead-210, then to bismuth-210 and polonium-210 and finally into stable lead-206. These daughter products of radon, some of which have long halflives, condense on pipe pp walls and form a low-level radioactive scale, which may flake off and collect on inlet filters. Because the boiling point of radon is 79.2 F ( 61.8 C), it tends to concentrate in propane p and ethane propane p mixtures. Storage vessels can accumulate the daughter products as sludge. Discarded piping with the scale generates large quantities of low- level radioactive waste that must be discarded in disposal wells.

11 4. Arsenic Arsenic is a toxic nonvolatile solid but exists in natural gas predominately as a more volatile trimethylarsine (As (CH 3 ) 3 ). It usually collects as a fine gray dust. High concentrations tend to be geographically localized. It can be successfully removed from gas by use of a nonregenerative adsorption process. Several facilities reduce arsenic concentrations ti in sweet raw gas from around 1,000 to less than 1µg/m 3 (Rhodes, 2005). Without arsenic removal, the gas streams could not be marketed. The process requires dehydration of the gas to pipeline specifications before it goes to the adsorbers.

12 5. Helium Helium is a difficult diluent to remove in natural gas unless nitrogen rejection is used. Unlike the other trace components discussed here, helium is a valuable product from natural gas processing, which makes high concentrations desirable. Recovery of helium from air is technically feasible but would be very expensive because the helium concentration is so low, 5.24 ± 0.05 ppm. The only viable source is from select natural gas fields, and even the best of these gas fields contain relatively small quantities of helium. A helium-rich gas is defined as one that contains more than 0.3% helium, and according to published field concentrations, ti a gas that t contains more than 5% is not usually found. The uses of helium are limited but important. Its main applications stem from the fact that it is chemically inert and has the lowest boiling point of any substance.

13 Recovery Method of Helium Recovery of helium from natural gas requires refinement of the low concentrations into high-purity helium (99.995%). However, the gas plant may produce only a raw helium stream that t contains a roughly equimolar mixture of helium and nitrogen. This stream then goes to another facility for final purification. Early processing schemes were cryogenic and involved cooling and condensing the natural gas and then recovering the helium by distillation as a crude product that t was about 65 to 80% helium. The crude helium was then stored or further refined in a series of low temperature separations, followed by a final adsorption step on activated charcoal to produce the high-purity product. More recently, interest has increased in alternate technologies such as pressure swing adsorption (PSA) and membranes for helium recovery

14 Helium Uses in USA at 2003

15 Schematic of Ladder Creek Helium Recovery Plant

16 Range of Feed Gas Compositions to Ladder Creek Helium Recovery Plant

17 6. Mercury ecuy Two major problems are associated with the presence of mercury in natural gas: amalgam formation with aluminum and environmental pollution Mercury may be present in elemental form or as organometallic compounds, such as: dimethylmercury, y, methylethylmercury, and diethylmercury, or as inorganic compounds such as HgCl2 Elemental mercury distributes between the gas and liquid phases, whereas elemental mercury has an extremely low vapor pressure (~ psia at 32 F, bar at 0 C, Vapor phase concentrations ce o are orders of magnitude higher than computed by Equation 6.1 because of the nonideal behavior of mercury at operating conditions. Thus, the majority of mercury goes to treating, dehydration, and then to the cryogenic section. What fraction would reach the cryogenic section was not stated.

18 The volatility of elemental mercury and the fact that it will accumulate as it condenses makes removal from the gas stream mandatory in cryogenic plants. Mercury corrodes brazed-aluminum heat exchangers as it amalgamates with the aluminum to weaken the material. Elemental mercury is toxic to humans as well as a poison to many catalysts. The mercury compounds concentrate in the hydrocarbon liquids, where they potentially can present environmental and safety hazards. The compounds are readily absorbed by most biological systems. Although mercury in natural gas is normally at low levels, some gases contain sufficiently high mercury concentrations to cause both safety and health concerns

19 Range of Elemental Mercury Levels in Wellhead Natural Gas from a Number of Countries Natural Gas from a Number of Countries

20 Removal of Mercury Nonregenerative Processes Use sulfur impregnated on a support such as activated charcoal or alumina to provide a large surface area The mercury reacts with the sulfur to form a stable compound on the adsorbent surface Regenerative Process A regenerative process that utilizes silver on molecular sieve to chemisorb elemental mercury while providing dehydration at the same time The advantage of silver is that the amalgam it forms with mercury decomposes at typical regeneration temperatures for dehydration The silver-impregnated sieve is added to the standard molecular sieve dehydration bed, and the basic dehydration process remains unchanged

21 7. (BTEX) BENZENE, TOLUENE, ETHYLBENZENE, AND XYLENE Benzene, toluene, ethylbenzene, and xylene (BTEX) present two possible problems in gas processing: environmental concerns and potential freezing in cryogenic units. In most gas processing plants, BTEX is present in the volatile organic compounds (VOC) that must be controlled to meet EPA clean air regulations. In glycol dehydration, the glycol absorbs some hydrocarbons as well as water.

22 BTEX Removal Use of triethylene glycol to dehydrate a gas stream at 1,000 psia (14.5 bar), 100 F (38 C) and at a typical glycol rate of 3 gal TEG/lb of water absorbed, the TEG will absorb the following percentages of BTEX from the gas stream: When the rich glycol is regenerated, the BTEX exits the still in the vapor stream, and consequently this stream must be processed to recover or eliminate the BTEX before atmospheric venting

23 The methods presently used to control BTEX emissions to the atmosphere are: Adjustment of plant operating conditions to minimize the quantity of BTEX in the glycol absorber off gas Burning of the still off gases before venting Condensation of the off gases and recovery of the BTEX as a liquid product Adsorption of the BTEX on a carbon adsorbent Amine treaters absorb BTEX along with the acid gases. Both acid gases and the BTEX are stripped in the regenerator and, traditionally, either vented if the H2S level is low or sent to a Claus unit for sulfur recovery

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

Instructor: Dr. Istadi (http://tekim.undip.ac.id/staf/istadi ) Email: istadi@undip.ac.id Course Syllabus: (Part 1) 1. Definitions of Natural Gas, Gas Reservoir, Gas Drilling and Gas production (Pengertian