Kinetics Analysis for Drying, Pyrolysis, and Gasification of Black Liquor from Kraft Pulp Mill

JOKO WINTOKO, Prof. Ir. Suryo Purwono, MASc, PhD; Ir. Moh. Fahrurrozi, MSc, PhD; Prof. Ir. Bambang Soehendro, MSc, DESc

2019 | Disertasi | DOKTOR TEKNIK KIMIA

Teknologi gasifikasi lindi hitam merupkan sebuah alternatif yang menjanjikan dalam efisiensi pemanfaatan cairan sisa dari proses kraft pulping untuk menghasilkan energy panas dan listrik. Dalamproses ini, lindi hitam dikonversi menjadi gas bahan bakar untuk bahan bakar kombinasi pembangkitan listrik dan kukus dan/atau gas sintesis untuk pembuatan bahan kimia. Dalam proses gasifikasi, lindi hitam mengalami proses pengeringan, pirolisis, gasifikasi, dan reaksi anorganik. Dalam disertassi ini akan dibahas proses pengeringan, piroloisis, dan gasifikasi dari lindi hitam. Untuk melakukan penelitian ini, telah dibuat dan dioperasikan sebuah alat single droplet thermogravimetry analyzer (TGA). Dari alat ini bisa dipelajari: perubahan massa, perubahan suhu, profil produksi gas, dan perubahan ukuran droplet apat direkam. Gas yang bisa ditekesi dengan instrumeen yang ada adalah: CO, CO2, SO2, CH4, and H2S. eksperimen dilakuakn dalam lingkungan nitrogen untuk simulasi proses pengeringan dan pirolisis serta dalam gas nitrogen yang mengandung CO2 untuk simulasi pengeringan, pirolisis, dan gasifikasi. Untuk mendapatkan data lebih lengkap juga dilakukan eksperimen dalam alat TGA standar yang bisa merekam lebih akurat untuk perubahan suhu dan massa. Namun alat standar TGA ini tidak dilengkapi dengan instrument pengukur konsentrasi gas dan perubahan ukuran butiran lindi hitam. Model matematika juga dibuat berdsarkan neraca massa dan panas dalam butiran. Moedl ini dikombinasikan dengan model untuk perubahan ukuran droplet selama pirolisis. Hasil perhitungan model ini dapat memberikan gambaran tentang fenomena fisika dan kimia yang terjadi selama proses gasifikasi. Dari eksperimen diketahui pengeringan mulai terjadi sejak butrian lindi hitam memasuki reactor. Titik diih yang pertama kali diamati pada suhu 120 derajat Celcius dan terus meningkat karena sifat kenaikan titik didih dari lindi hitam. Pirolisis mulai teramati pada suhu 153.2-241.2 derajat Celcius and reaksi gasifilasi pada suhu sekitar 500 derajat Celcius. Proses pengeringan sangat dipengaruhi oleh suhu gas dan reactor. Semakin tinggi suhu maka semakin cepat proses peengeringan terjadi. Produksi gas selama pirolisis dan gasifikassi juga sangat dipengaruhi oleh suhu. Semakin tinggi suhu maka semakin banyak gas yang dihasilkan oleh kedua proses tersebut. Model matematika yang dikembangkan juga bisa memebrikan hasil perhitungan yang relative bisa mengambarkan kecenderungan perubahan suhu, massa, dan ukuran butiran selama proses gasifikasi.

Black liquor gasification is a promising alternative for more efficient utilization of the spent pulping liquor from kraft pulp mill as a source of heat and power generation. In this process, the black liquor is converted into fuel gas that can be utilized as fuel in a combined cycle electricity generator and/or into syngas for chemical production. In the gasification process, the black liquor undergoes several stages, i.e. drying, pyrolysis, gasification, and inorganic reaction. This dissertation deals with the study of drying, pyrolysis, and gasification of black liquor droplet. To study the chemical and physical phenomena of the gasification process, a single droplet thermogravimetry analyzer (TGA) was developed and operated. From this single droplet TGA instrument, the mass changes and temperature changes of a single black liquor droplet during gasification can be obtained. In addition the droplet size changes could also be recorded together with the gas concentration profile from the reactions. Five different gas were analyzed, i.e. CO, CO2, SO2, CH4, and H2S. The experiments were run using nitrogen gas flow to simulated drying and pyrolysis reaction and using CO2 enriched nitrogen gas flow to simulate the drying, pyrolysis, and gasification reaction. Moreover, a standard TGA instrument was also used to obtain additional data of temperature and mass changes of the droplet drying and pyrolysis. The standard TGA instrument could provide more accurate data for mass and temperature changes but could not obtain the more complete data as the single droplet TGA. A mathematical model were also developed based on mass and heat transfer in the droplet. This models were coupled with the swelling model to represent the swelling behavior of the droplet during pyrolysis. The mathematical model calculation can give an insight of the physical and chemical reaction phenomena that occurred in the black liquor droplet during gasification process. From the experimental data it was found that the drying was started right after the droplet enters the hot furnace and in contact with the hot flowing gas. The first boiling point of the droplet was detected at about 120 degree Celcius and then further increase due to boiling point rise properties of the black liquor. Pyrolysis reaction was observed to begin at around 153.2-241.2 degree Celcius and the gasification reaction at about 500 degree Celcius. The drying as significantly affected by the temperature, which higher the temperature then the faster the drying process. Gas production during pyrolysis and gasification were also affected by the gas and furnace temperature. The higher the temperature the higher overall gas production of both pyrolysis and gasification. The mathematical model calculation give a general agreement with the experimental result for temperature profile, mass changes, and droplet diameter changes.

Kata Kunci : Black liquor, drying, pyrolysis, gasification, kinetics