Nitrogen Rejection and C02 Removal Made Easy

Molecular Gate®
Adsorption Technology

The Sorbead™ Quick-Cycle Process For Simultaneous Removal of Water,
Heavy Hydrocarbons and Mercaptans from Natural Gas (page 4 of 4)

Sorbead™ System Size

For the overall integrated system the size of the quick-cycle unit is driven by the amount of heavy hydrocarbons in the feed and most critically the dew point requirements. For example if a low hydrocarbon dew point were required after both the initial adsorption step and also after the second adsorption step (removing the water that is reintroduced by the amine system) the system would be larger than if a level of hydrocarbons were permitted to slip into the product stream from the second adsorption step.

It is also notable that the breakthrough of the heavy hydrocarbons is initially low and progressively increases as the adsorption step progresses. This results in an initially lower hydrocarbon dew point that gradually increases. To compensate for this dew point variation multiple beds of adsorbent are often placed on the adsorption step in a staggered manner that leads to an averaging of the product heavy hydrocarbons and limiting the hydrocarbon dew point changes over the cycle. A typical design material balance is shown in Table 2.

Table 2

Flow, MM SCFD (nm3/hr)	150 (167,500)
Pressure, psig (bar a)	1000 (70)
Inlet Temperature, F (C)	86 (32)
Composition, Mol %
C1	90.107
N2	1.000
CO2	3.000
C2	3.400
C3	1.500
C4	0.100
C5	0.400
C6	0.200
C7	0.100
C8	0.020
C9	0.020
Mercaptans	0.010
C10	0.020
Benzene	0.040
Toluene	0.010
Water	0.083

With the design basis above a 6-bed system was designed to meet a hydrocarbon dew point of 23 Deg F (-5 Deg C) at the end of the cycle (highest breakthrough of hydrocarbons). This design would use vessels of 7.5 ft diameter by 24 ft (2.3 M x 7.4 M).

LNG Facilities

The process advantages and integrations described above are applicable directly to natural gas conditioning for pipeline purposes. However, though water is strongly adsorbed, quick-cycle units do not generally achieve the water dew points typically required in LNG plants (0.1 ppmv). Typical water levels achieved by quick-cycle units are 10-20 ppmv (roughly -20 to -40 Deg F or -4 to -40 Deg C dew points at 800 psig or 55 bar g) with feed gas regeneration.

Though trim layers of molecular sieve in the quick-cycle unit could be considered, the large number of cycles would impose a challenge for molecular sieve. A more practical approach is to add a small TSA molecular sieve polishing dryer downstream of the quick-cycle unit to remove the residual ppm levels of water. This trim unit would require a relatively small adsorbent inventory and can run on an extended cycle time and thus the cost would be relatively small.

Two further integrations between the quick-cycle and molecular sieve trim unit exist. The quick-cycle unit and molecular sieve unit would regenerate at the same temperature of about 500°F (260°C), thus the quick-cycle units furnace could be designed with an extra tube bundle to heat the molecular sieve unit regeneration stream. This design will avoid another furnace and would be highly desired to reduce cost, operations and permitting issues. Secondly, the relatively small regeneration stream of the molecular sieve unit can be recycled back to the feed inlet of the quick-cycle unit to reduce hydrocarbon losses.

Conclusion

In summary, the advantages of upfront quick-cycle treatment using BASF Sorbeadä adsorbent can include the point below which are graphically illustrated in Figure 7.

Reduced foaming in the amine plant.
BTX free Claus plant feeds leading to longer catalyst life.
Mercaptan-free Claus plant feed.
Improved sulfur recovery since mercaptans are not present in the incinerator.
Elimination of incineration of the amine plant stripper overhead.
Improved sulfur recovery rates since mercaptans are not incinerated in the AGE overhead.
Simplification of the treating of liquid products.
Earlier removal of mercury and avoidance of having mercury split into multiple streams.
Simplified dehydration.
A downstream molecular sieve unit would be required to meet very low dew points.

Sorbead Process

The quick-cycle process has been used for decades to dehydrate and remove heavy hydrocarbons from natural gas. The integrated quick-cycle process using Sorbeadä adsorbent placed in the front of natural gas conditioning plants eliminates contaminates at the earliest part of the processing train and offers operating advantages throughout the downstream processing train.

About the Authors

Mr. Michael Mitariten, P.E., is a Vice President for Gas Separations at Guild Associates, Inc. He is responsible for Guild’s gas separation and Molecular Gate® adsorbent based technology (licensed from BASF). Mike has 25 years of experience in gas separation with the technologies of adsorption, membranes and cryogenic processing and with solvent-based acid gas removal systems. Mike joined Guild from Engelhard Corporation where his focus in recent years has been on the upgrading of sub-quality natural gas using Molecular Gate adsorbents. Mike holds a degree in Chemical Engineering from Manhattan College. He has been awarded 13 patents, has published numerous papers and is a Professional Engineer in the State of New York. Mike can be reached at mike@moleculargate.com.

Dr. Waldemar Lind is a Sales Manager EMEA in the Process Technologies – Adsorbents group at BASF Corporation. He received his PhD in Chemistry at the Technical University in Braunschweig, Germany. Throughout his distinguished career, Dr. Lind has held several positions in Sales and Product Management at various well known biotechnology and chemical companies. His professional background also includes a 4-year stint as head of Moscow office operations managing syngas, refinery and petrochemical catalyst applications. Dr. Lind can be reached at waldemar.lind@basf.com.

About BASF

BASF is the world's leading chemical company: The Chemical Company. Its portfolio ranges from chemicals, plastics, performance products, agricultural products and fine chemicals to crude oil and natural gas. As a reliable partner to virtually all industries, BASF's intelligent system solutions and high-value products help its customers to be more successful. BASF develops new technologies and uses them to open up additional market opportunities. It combines economic success with environmental protection and social responsibility, thus contributing to a better future. BASF has over 95,000 employees and posted sales of more than €42.7 billion in 2005. BASF shares are traded on the stock exchanges in Frankfurt (BAS), London (BFA), New York (BF) and Zurich (AN). Further information on BASF is available on the Internet at www.basf.com.

References

Iyenger J.N., Sibal P.W., Clarke D.S., "Operations and Recovery Improvement via Heavy Hydrocarbon Extraction", Laurance Reid Gas Conditioning Conference, Norman, OK, 1998.
Hatcher N., Keller A., Thompsen J. and Weatherford J., "Busting a Myth – Analyzing the Effectiveness of Lean Amine/Sour Gas Differential Temperature Control”, Laurance Reid Gas Conditioning Conference, Norman, OK, 2006.
Pivonka, R., "Destruction of Amine Vent Gas Utilizing a Regenerative Thermal Oxidizer”, North Texas GPA Regional Program, Farmers Branch, TX, October 2005.
Klint B., "Hydrocarbon Destruction in the Claus SRU Reaction Furnace"", Laurance Reid Gas Conditioning Conference, Norman, OK, 2000.
Kane, A., Kauders, P., Shelenko, L., "Co-adsorption of Mercaptans using silica Gel in Sour Gas Dewpointing Applications" European Gas Processors Convention, London, UK. February 2004.
Kohl, A and Nielsen, R. "Gas Purification, Fifth Edition, page 1051.
Hendricks, E.M., Meijer H., Smit C.J., "Mercury, The Volatile Surprise in Gas Processing", Gas Processors 2005 Annual Convention.
Carnell, P.J.H., Foster A., Gregory J., "Mercury Matters", Hydrocarbon Engineering, December 2005.


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Further Information:

If you would like an evaluation of how the Molecular Gate technology can solve your gas treatment needs simply complete and fax back the Estimate Request Form or contact Michael Mitariten at 908-752-6420 or by email mike@moleculargate.com.

BROCHURE

Guild is a licensee of Engelhard's Molecular Gate® Adsorbent Technology and
is solely responsible for all representations regarding the technology made herein.

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