PT Badak NGL Blackout Start System Nasrul Syahruddin Lead Engineer, Rotating & Stationary Equipment
Rizqy Fajar Arifianto Engineer, Electrical Facilities Engineering – Technical Department PT Badak NGL Bontang – East Kalimantan
Introduction PT Badak NGL (PTB) operates 12x12.5MW steam turbine generators, 1x12.5MW gas turbine generator and 1x5MW diesel generator for supplying electricity to LNG, LPG plant, and community housing. The machine bus is 13.8kV while power is distributed through 4.16kV and 480V switchgear/MCC. PTB also utilize 34.5kV ring bus as synchronizing bus. Most of PTB distribution network using secondary selective system. Figure-1 shows the simplified overall one line diagram of PTB electrical system. This covers for all 8 LNG trains including the utilities, storage & loading and community.
Figure 1: Simplified One Line Diagram 34.4/13.8 kV Distribution System The electrical system shall always be reliable in order to secure power distribution to units related to LNG/LPG production process such as cooling water pumps, instrument and utility air system, etc. Furthermore, the electrical distribution system is considered high reliable by applying secondary selective and integrated ring bus system. However, in case of power failure, the system shall be able to restore its power without relying on external energy resources, which is called Blackout Start System.
Blackout Condition Blackout is a condition when there is no electricity supply for supporting plant operations and community due to electric power failure. The power failure can be caused by either process or electrical distribution aspect. Since the main power supply comes from steam turbine generator, the reliability of steam supply system is very essential. From process point of view, the lack of boiler feed water, lost of instrument air supply and lack of fuel gas supply to boilers will cause boilers to trip and stop steam supply to Steam Turbine Generators (STGs). This condition leads to total power failure or blackout condition. Whereas from electrical point of view, the total blackout condition can be resulted as the failure on generators or the electrical distribution and/or protection system itself. The second cause is more likely to be happened than the first one.
Blackout Start System In order to restore the power supply after blackout condition, PT Badak NGL utilizes a Diesel Engine Generator (DEG) or Gas Turbine Generator (GTG) as blackout start up engine. The philosophy of blackout start up system is firstly to secure the overall plant as the impact of blackout condition, then starting up the utility system to produce steam as well as instrument air and finally starting up Process Train and its supporting facilities.
Figure 2: Blackout Start Up Sequence Figure 2. shows the sequence on conducting blackout start up. When total blackout condition occurs, there is no electricity supply available. The initial power is generated from DEG. The diesel generator supplies electricity to motor driven equipment such as boiler feed water pump, utility water pump, condensate transfer pump and forced draft fan. In this step, the available ground water in demin tanks is sent to deaerator for treatment prior to transfer as feed water to boilers. In parallel, diesel fire water pump and diesel air compressor are utilized to produce cooling water and instrument air to the system respectively. By utilizing the available feed gas as boiler’s fuel and running forced draft fan, the boilers is now ready to produce steam to be used to drive the steam turbine generator as the initial power supply to the blackout LNG Plant.
The time needed for each step will vary depends on the equipment condition such as temperature. In general, step 1 until step 8 could be done within 1 hour. Step 9 and 10 will vary depend on the equipment temperature. For Boiler, the maximum temperature increasing rate is limited o o by its design rule of 50 C per hour. Therefore, to reach operating temperature of 450 C it would take about 9 hours from ambient temperature. However, in hot condition just after the blackout condition, the temperature range is between o 300 – 350 C and boiler could be ready within 2 hours. The STG would take about 2 hours for warming up in hot condition or 6 hours up in cold condition prior to start up. So the total time needed for blackout start up would vary between 4 to 15 hours.
Power Requirement In black start up system, DEG should be able to supply power to several equipments as follows:
No
1
2
3
System
Equipment Reference
Driver
Function
Diesel Engine
Supply cooling water
35KM-3/4/5/6
Electric Motor (0.67MW)
Supply instrument air
31GM-115A/B (Condensate Water Pump)
Electric Motor (0.04MW)
33GE-3C/D, 33GE5A/B/C/D, and 33GECooling Water 16A/B/C/D (Diesel Fire Sea Water Pump) Compressed Air
Boiler Feed Water and Boiler Feed Air
31C-20 (Deaerator)
Treat BFW
31K41/42/46/47/48/61~64/66 (Forced Draft Fan)
Electric Motor (0.8MW)
Supply air to Boiler
31GM-111/113/140/141 (BFW Pump)
Electric Motor (1.49MW)
Supply BFW from Deaerator to Boiler
31F-21~30 (Boiler) 4
-
Supply BFW to Deaerator
Boiler & Steam Turbine Power 31PG-11/12/14 Generator (Condensing Turbine Power Generator)
-
Steam Turbine
Generate steam Generate electrical power by using steam as driver
Table 1: Load List for Blackout Start Up Based on software simulation, the minimum power required to conduct blackout start up is about 3.3 MW as seen in Figure 3. However, to compensate the drop voltage is still within PTB standard (maximum drop voltage is 20%), the minimum power required will be 4 MW (Figure 4, drop voltage is about 16.5%). Then by adding 25% safety factor, the minimum power generator for blackout start up is 5 MW.
Figure 3. Power Required for Blackout Start Up
Figure 4. Drop Voltage Using 4MW Generator
Summary In order to maintain the high reliability of PT Badak NGL Plant, blackout startup system is designed to restore the plant electricity supply as fast as possible in case of blackout condition. The system requires minimum 5 MW of power to initially operate the electric motor driven equipment in Boiler system for steam production to generate more power from steam turbine power generator for restarting the LNG production as well as supplying electricity to community.
References 1. Process Engineering Section Study, Blackout Start Up System Improvement, November 2009, PT Badak NGL 2. PT Badak General Specification, Electrical Design Guidelines, November 2001. 3. PT Badak General Specification, Electric Generators, November 2001.
