Studi Penambahan Etilena Glikol dalam Menghambat Pembentukan Metana Hidrat pada Proses Pemurnian Gas Alam

https://doi.org/10.22146/jrekpros.59871

Muslikhin Hidayat(1*), Danang Tri Hartanto(2), Muhammad Mufti Azis(3), Sutijan Sutijan(4)

(1) Departemen Teknik Kimia, Fakultas Teknik, Universitas Gadjah Mada, Jl Grafika No. 2 Kampus UGM, Yogyakarta, 55281
(2) Departemen Teknik Kimia, Fakultas Teknik, Universitas Gadjah Mada, Jl Grafika No. 2 Kampus UGM, Yogyakarta, 55281
(3) Departemen Teknik Kimia, Fakultas Teknik, Universitas Gadjah Mada, Jl Grafika No. 2 Kampus UGM, Yogyakarta, 55281
(4) Departemen Teknik Kimia, Fakultas Teknik, Universitas Gadjah Mada, Jl Grafika No. 2 Kampus UGM, Yogyakarta, 55281
(*) Corresponding Author

Abstract


The gas processing facilities are designed to significantly reduce the impurities such as water vapor, heavy hydrocarbon, carbon dioxide, carbonyl sulfide (COS), benzene-toluene-xylene (BTX), mercaptane, and the sulfur compounds. A small amount of those compounds in natural gas is not preferable since they disturb the next processes.  It was proposed to decrease natural gas's operating temperature to -20 ⁰F to remove the impurities from natural gas. The decrease of the natural gas's operating temperature has some consequences to the gas mixers such as hydrate formation at high pressure and low temperature, solidification of ethylene glycol (EG) solution, and the icing of the surface due to low temperature on the surface of chiller (three constraints). The Aspen Hysys 8.8 was used to obtain the suitable flowrate and concentration of the EG solution injected into the natural gas. Peng-Robinson's model was considered the most appropriate thermodynamic property model, and thus it has been applied for this research. The calculation results showed that the EG solution injection would reduce the hydrate formation due to water vapor absorption in the natural gas by EG. The EG solution's flowrate and concentration were varied from 20,000-2,000,000 lb/hr and 80-90 wt.%. When the separation was carried out at the operating temperature of -20 ⁰F, the EG solution's concentration fulfilling the requirement was of 80-84 wt.% with the flowrate of EG solution of 900,000 lb/hr and even more. This amount is not operable. More focused investigation was done for the variation of the operating temperature. Increasing operating temperature significantly reduced the flowrate of EG solution to about 200,000 lb/hr. An alternative process was proposed by focusing on two concentration cases of 80 and 85 % of weight at the low flow rate of EG solution, respectively. These simulations were intended to predict impurities' concentration in the effluent of Dew Point Control Unit (DPCU). The concentrations of BTX, heavy hydrocarbon, mercaptane, and COS flowing out of DPCU were 428.1 ppm, 378.4 ppm, 104 ppm, and 13.3 ppm, respectively. The concentrations of BTX and heavy hydrocarbon are greater than the minimum standard required. It is needed to install an absorber to absorb BTX and heavy hydrocarbon. However, the absorber capacity will be much smaller than if the temperature of natural gas is not decreased and not injected by the EG solution.

Keywords: DPCU gas treatment; ethylene glycol solution; hydrate formation; simulation


A B S T R A K

Unit pengolahan gas dirancang untuk mengurangi sebagian besar senyawa pengotor seperti uap air, hidrokarbon berat, karbon dioksida, karbonil sulfida (COS), benzena-toluena-xilena (BTX), merkaptan, dan senyawa sulfur lainnya. Keberadaan senyawa tersebut dalam gas alam berbahaya karena mengganggu proses selanjutnya walaupun dalam jumlah sedikit. Untuk membersihkan gas alam dari senyawa pengotor, maka suhu operasi gas diturunkan menjadi -20 °F. Penurunan suhu operasi gas dapat menyebabkan pembentukan hidrat pada tekanan tinggi dan suhu rendah, pembekuan larutan etilena glikol (EG), dan pembentukan lapisan es pada permukaan chiller. Aspen Hysys 8.8 digunakan untuk memperkirakan berapa kecepatan alir dan konsentrasi larutan EG yang diinjeksikan ke gas alam. Model Peng-Robinson adalah model termodinamika yang diterapkan untuk penelitian ini. Hasil simulasi menunjukkan bahwa injeksi larutan EG dapat mengurangi pembentukan hidrat karena larutan EG menyerap uap air dalam gas alam. Kecepatan alir dan konsentrasi larutan EG divariasikan dari 20.000-2.000.000 lb/jam dan 80-90 % (%b/b). Saat pemisahan dilakukan pada suhu operasi -20 °F, konsentrasi larutan EG yang memenuhi syarat adalah 80-84 % (%b/b) dengan kecepatan alir larutan EG 900.000 lb/jam atau lebih. Jumlah ini sangat banyak dan kurang layak untuk dioperasikan. Penelitian difokuskan pada variasi suhu operasi. Peningkatan suhu operasi diikuti dengan pengurangan kecepatan aliran larutan EG secara signifikan yaitu menjadi sekitar 200.000 lb/jam. Alternatif proses diusulkan dengan berfokus pada penggunaan kecepatan alir larutan EG yang rendah dengan konsentrasi larutan EG sebesar 80 dan 85 % (%b/b). Simulasi dapat memprediksi konsentrasi pengotor yang keluar dari Dew Point Control Unit (DPCU). Konsentrasi BTX, hidrokarbon berat, merkaptan, dan COS yang mengalir keluar dari DPCU berturut-turut adalah 428,1 ppm, 378,4 ppm, 104 ppm, dan 13,3 ppm. Konsentrasi BTX dan hidrokarbon berat tersebut lebih besar dari standar minimum yang disyaratkan. Oleh karena itu, diperlukan pemasangan absorber untuk menyerap BTX dan hidrokarbon berat. Namun, kapasitas absorber akan jauh lebih kecil apabila dibandingkan dengan kondisi tanpa menurunkan suhu dan menginjeksikan oleh larutan EG.

Kata kunci: DPCU; larutan etilena glikol; pembentukan hidrat; simulasi


 


Keywords


DPCU gas treatment; ethylene glycol solution; hydrate formation; simulation

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DOI: https://doi.org/10.22146/jrekpros.59871

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