Subcritical vs Supercritical Boiler

Dilihat dari phase nya, Boiler terbagi menjadi 3 yaitu :

• Subcritical Boiler

Subcritical artinya adalah phase yang terbentuk di Boiler tidak homogen (masih bisa dibedakan antara cair dan uap) sehingga tipe Boiler ini membutuhkan Steam Drum / Boiler Drum untuk memisahkan kedua phase sebelum digunakan untuk memutar sudu Turbine. Operasi Subcritical Boiler < 22,1 MPa (1 bar = 0,98 kg_f / cm² = 0,1 MPa). Contoh operasi Boiler P = 170 bar dan T = 540 ^oC mempunyai efisiensi 32 - 38 %.

"Subcritical is not homogeneous produced phase in Boiler (still can be distinguished between liquid and vapor) so that this types Boiler requires a Steam Drum to separate 2 phases before it is used to rotate Turbine Blade. Subcritical Boiler operation 22,1 MPa (1 bar = 0,98 kg_f / cm² = 0,1 MPa). Examples Boiler operation are P = 170 bar dan T = 540 ^oC has the efficiency of 32 - 38 %."

• Supercritical Boiler

Supercritical artinya keadaan substansi dimana tidak bisa dibedakan antara phase cair dan uap (kedua phase homogen) dan tipe Boiler ini tidak membutuhkan Steam Drum sehingga sering disebut One Through Boiler (Boiler satu kali lewatan langsung digunakan untuk memutar sudu Turbine). Air mencapai keadaan Critical pada tekanan 22,1 MPa, jadi operasi Supercritical Boiler > 22,1 MPa. Contoh operasi Boiler adalah P = 250 bar dan T = 615 ^oC mempunyai efisiensi 37 - 42 %.

"Supercritical is substance condition which it can not be distinguished between liquid and vapor phases (2 phases is homogeneous) and this types a Boiler no requires Steam Drum so that called One Through Boiler ( one through direct to be used to rotate Turbine Blade). Water reach Critical Point at pressure 22,1 MPa, so operating of Supercritical Boiler must > 22,1 MPa. Examples Boiler operating are P = 250 bar dan T = 615 ^oC has the efficiency of 37 - 42 %."

• Ultra Supercritical Boiler

Boiler Supercritical didesain dengan konstruksi metalurgi yang sangat baik (high grade quality) karena tidak adanya Steam Drum, sehingga konstruksi Boiler dan Turbine dijaga dari reaksi kerak dan korosi. Contoh operasi Ultra Supercritical Boiler P = 300 bar dan T = 630 ^oC mempunyai efisiensi 43 - 45 %.

Penambahan tingkat efisiensi Boiler berdampak menurunnya biaya operasional dan mengurangi emisi CO₂

"Supercritical Boiler designed with the best metallurgical construction (high grade quality) because it is no Steam Drum, so that construction Boiler and Turbine are guarded from reaction of scale and corrosion. Examples Ultra Supercritical Boiler operating are P = 300 bar and T = 630 ^oC has the efficiency of 43 - 45 %.
The addition degree of Boiler efficiency has effect decreasing operational cost and reduce CO₂ emissions."

Rankine Cycle with Superheater

Keterangan : 

1 - 2 : Siklus awal yaitu air dipompa dari tekanan rendah ke tekanan tinggi (BFP) kemudian ke Pre Boiler (Economizer) untuk dipanaskan, sehingga temperatur naik

2 - 3 : Proses pemanasan di Boiler pada tekanan tetap, sehingga air berubah menjadi Saturated Steam

3 - 3' : Saturated Steam yang terbentuk harus dipanaskan lagi sehingga temperaturnya naik pada tekanan tetap dan berubah menjadi Superheated Steam

3' - 4' : Superheated Steam digunakan untuk memutar sudu Turbine sehingga temperatur dan tekanan turun

4 - 1 : Setelah tekanan menjadi rendah, Low Pressure Steam diubah menjadi air lagi di Condenser

Siklus terjadi terus menerus dalam keadaan tertutup (Close Cycle) dan ini yang terjadi di PLTU

"Description :
1 - 2 : the first cycle is water pumped from low pressure to high pressure (BFP) then to Pre Boiler (Economizer) to be heated so that rising temperature
2 - 3 : heating process in Boiler at constant pressure, so that water converted into Saturated Steam
3 - 3' : Saturated Steam that produced must be heated again so that rising temperature at constant pressure and changed to Superheated Steam
3' - 4' : Superheated Steam used to rotate Turbine Blade so that decreasing of temperature and pressure
4 - 1 : after pressure become low. Low Pressure steam converted into water in Condenser
The cycles occur continuously in close cycle and this is occuring process in PLTU"

Referensi :

[1] http://www.answers.com/Q/What_is_difference_between_subcritical_supercritical_boiler

[2] http://www.scribd.com/doc/87622501/Super-Critical-Boilers-vs-Sub-Critical-Boilers

[3] http://www.nationalboiler.com/blog/boiler-repair/the-benefits-of-supercritical-boilers/

[4] http://www.slideshare.net/SHIVAJICHOUDHURY/super-critical-boiler 

[5] http://www.erc.uct.ac.za/jesa/volume19/19-1jesa-kapooria-etal.pdf

[6] https://en.wikipedia.org/wiki/Rankine_cycle

ARTIKEL TERKAIT : 
1. Macam - Macam Boiler 
2. Macam Cycle Proses 
3. Boiler & Permasalahannya