Pada pembangkit PLTU,
air umpan boiler yang digunakan adalah air demineral (demineralized water) yang berasal dari air laut yang sudah dilakukan proses demineralisasi menggunakan sistem reverse - osmosis (RO) maupun multi effect destillation (MED). Air laut sendiri terkandung
banyak mineral korosif dan penyebab kerak seperti Ca2+, Mg 2+,
Cl-, dll. Untuk menghilangkan kandungan tersebut dilakukan pre-treatment khusus baik physical treatment (penggunaan alat) dan chemical
treatment (injeksi kimia). Process flow diagram untuk water flow di PLTU seperti
dibawah ini :
"In PLTU power plant, boiler feed water that used is demineralized water that it's from sea water which already done demineralization process using RO system or MED. Sea water has contain many corrosive mineral and cause slag likes Ca2+, Mg 2+,
Cl-,etc. To remove that content done specially pre-treatment such as physical treatment (using equipment) and chemical
treatment (chemical injection). Process flow diagram for water flow in steam power plant like below :"
BACA JUGA : Feed Water System PLTU
Air laut yang sudah
dipisahkan padatan pengotor (suspended solid) di clarifier dan pengendapan di settling tank masuk
ke demineralized water plant (RO system atau MED plant). Hasil dari demineralized plant adalah make up water yang ditampung di make up tank sebelum masuk ke boiler dilakukan physical treatment terlebih dahulu yaitu dilewatkan heater untuk menaikkan suhu air agar kerja deaerator lebih ringan. Air
yang sudah masuk ke heater tertampung dengan tekanan rendah di low pressure heater (LPH) kemudian masuk ke boiler untuk dirubah
fasenya menjadi uap. Uap yang dihasilkan masuk ke high pressure steam (HPS) dan
masuk ke turbine untuk menggerakkan sudu-sudu sehingga poros berputar dan
menggerakkan generator. Uap yang keluar dari turbine terbagi menjadi 2 yaitu intermediate pressure steam (IPS) dan low pressure steam (LPS). IPS dipanaskan
lagi di HPH sedangkan LPS dirubah fasenya di condenser dan keluaran condenser
masuk ke boiler kembali untuk melakukan sirkulasi seperti semula (siklus uap-air).
"Sea water that separated by solid impurities in the clarifier and settling in the settling tank enter inti demineralized water plant (RO system or MED plant). The result of demineralized plant is make up water that contained in the make up tank and before enter into boiler done first physical treatment. Make up water is pumped into heater to raise water temperature so deaerator perform is light. Water that enter into heater contained with low pressure in the LPH, here outflow divided into 2 such as enter into condensor to recycle and continue process into in the boiler to minimalizer suspended O2 content. From deaerator, water is pumped into HPH then enter into boiler to change phase became vapor. Vapor that resulted enter into HPS and enter into turbine to move blade so that center part move and rotate generator. Release vapor from turbine divided into 2 such as IPS and LPS. IPS is heated again in the HPH and LPS is changed phase in the condensor and out flow from condensor enter into make up tank to do circulation like first."
Ada berbagai
zat kimia yang dipakai untuk menjaga kualitas air boiler seperti :
"There is many kind chemical used to keep quality boiler water likes :"
- Sodium Hipoklorit (NaOCl) dan Pereaksian antara Asam Korida (HCl) + Sodium Chloride (NaO2Cl)
Diijnjeksikan
di bak penampung air laut untuk melemahkan biota laut agar tidak terikut ke
proses selanjutnya
" Injected in the sea water pond to weak sea biota so not entrained into next process."
" Injected in the sea water pond to weak sea biota so not entrained into next process."
- Poly Alumunium Chloride (PAC), Al2(SO4)3 (Tawas) dll
Diinjeksikan
di settling pond untuk membantu mempercepat pengendapan (coagulant)
"Injected in the settling pond to help quick coagulation."
- Anti Scale ---> Na3PO4, Na2HPO4, NaOH
Diinjeksikan
di demineralized water plant dan steam drum untuk mencegah karat yang bisa
menyebabkan korosi pipa (tube). Selain itu juga bisa untuk menaikan pH air
boiler (8,8 - 10,8), namun pH air juga tidak bisa dibuat terlalu tinggi (>
10,8) karena bisa menyebabkan korosi pH tinggi. Ini grafik untuk menentukan
penggunaan phospate yang dilihat dari parameter suhu dan tekanan operasi
boiler.
"Injected in the demineralized water plant and steam drum to prevent rust that cause pipe corrosion (tube). Besides that, can also to raise pH boiler water (8,8 - 10,8), but pH water also can not make too high (>
10,8) because can cause corrosion high pH. This is graphic to determine usage of phospate that looked from temperature and pressure parameter of boiler operation."
BACA JUGA : Chemical Injection PLTU & PLTGU
Contoh
penggunaan grafik :
Boiler
beroperasi pada tekanan 600 psi, maka :
Dilihat di
grafik kontrol area ada di warna biru (< 900 psi), maka saran phospate
yang dipakai antara 30-60 ppm. Jika menginginkan pH pada suhu ruangan tinggal
tarik koordinat Y (pH) ke kanan sampai menyentuh area operasi kemudian tarik ke
bawah dan didapatkan penggunaan dosis phospate. Panah
terbawah menunjukkan kontrol penggunaan berbagai phospate.
"Example usage of graphic :
Boiler is operating at pressure 600 psi, so :
Looked in the graphic control area, there is blue color (< 900 psi), so recommended of phospate that used between 30 - 60 ppm. If want pH at room temperature so pull coordinate Y (pH) into right until touch operation area then pull ino below and get usage phospate dozis.
Below archery sign control of usage any kind phospate."
- Oxygen Scavenger ---> Sodium Sulphite (Na2SO3), Sodium Bisulphite (NaHSO3) dan
Hydrazine (N2H4)
Diinjeksikan
di deaerator untuk meminimalisir kandungan O2
terlarut
"Injected in the deaerator to remove / minimalizer suspended O2 content"
Kutip Artikel ini sebagai Referensi (Citation):
Feriyanto, Y.E. (2015). Water Process dan Injeksi Kimia di PLTU, Best Practice Experience in Power Plant. www.caesarvery.com. Surabaya
Referensi:
[1] Feriyanto, YE. (2016). Best Practice Experience in Power Plant. Surabaya
Ingin Konsultasi dengan Tim Expert Website www.caesarvery.com, Silakan Hubungi DISINI
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