3.1 Description Loy Yang A Power Station Plant

The Loy Yang A Power Station is a brown coal-fired power station located 7 km south-east of Traralgon in south-eastern Victoria, a state of Australia. Figure 3.1 below shows the general location of the site.

The station produces about 40% of Victoria’s electricity requirements. Electricity generation at Loy Yang A Power Station requires over 60,000 tonne of brown coal a day, supplied exclusively by a dedicated open-cut mine. Mining operations commenced at Loy Yang in 1982.

The power station was constructed through the 1980s, and consists of four boiler/turbine units: Loy Yang A (Units 1, 2, 3 & 4).

Figure 3.1 -Loy Yang A Power Station

Source: WorleyParsons

The four boilers are installed in the station, and each is a part of a generating unit. In addition to the boiler, a unit comprises a turbine-generator, auxiliary plant and pipe work. Each unit was originally rated for 500MW and, since being commissioned, they have had upgrades carried out to increase their output, on average, to above 550MW. The units are operated and monitored from the unit control room.

The boilers are installed in the boiler house, which is attached to the coal bunker and electrical annex structure. The building is not fully enclosed, the wall being only partially sheeted. The four boilers are arranged in a west-to-east line commencing with Unit 1 boiler.

Each boiler comprises the following equipment:

  • Draft plant -two induced draft (I.D.) fans; two forced draft (F.D.) fans; two rotary air heaters; auxiliary systems, ducting, dampers and draft plant controls; the chimney.
  • Auxiliary firing equipment -three briquette bunkers; bunker gates; table feeders; bowl mills and
  • P.F. exhausters; P.F. pipes connecting to twelve P.F. burners (3 levels on each of the 4 furnace walls); natural gas ignitors and pilot burners, gas piping with control trip and isolating valves; flame scanning systems and controls.
  • Main firing equipment -bunker gates; coal feeder conveyors; coal feeder discharge dampers; eight pulverised fuel mills; burners; main firing equipment controls.
  • Precipitators -electrostatic dust precipitators and their controls.
  • Boiler structure and pressure parts -furnace enclosure which incorporates the evaporative heating membrane tube water-walls, superheaters, reheaters and their associated circuit (hanger) tubes; attemperators; economisers; separating and mixing vessels; circulating pumps and strainers; superheater and reheater safety valves and other special valves.
  • Online boiler cleaning -including remote, manual and automatic equipment and controls for both convection bank lance soot-blowers and furnace water cannons.

Each boiler is a balanced draft, tower unit type, with superimposed recirculation. The superheaters, reheaters and economisers are stacked in the furnace enclosure, above the combustion chamber.

The boilers are fired with pulverised brown coal, taken from the Loy Yang open cut mine, which has a high moisture content (approximately 60%) but a low ash content (average of 0.9% wet basis).

Adjustments, as noted in the following sub-sections below, have been made where it was necessary to reconcile the model input data sets.

3.1.1 Site Conditions

The LYA site conditions for the Base Case model is presented in the table below.

Table 3.1 Site Conditions Input Data

Parameter Units Value Source
Barometric Pressure bar 1.009 Loy Yang Power
Ambient Air Temperature (Dry Bulb) °C 13.4 Loy Yang Power
Relative Humidity % 62 Loy Yang Power

Source: WorleyParsons

3.1.2 Coal Specification

The LYA coal specification for the Base Case model is presented in the table below.

Table 3.2 - Loy Yang Coal Specification Input Data

Parameter Units Value Source
Ultimate Analysis      
Moisture Wt % 60.0 Loy Yang Power
Carbon (C) Wt % 27.2 Loy Yang Power
Hydrogen (H) Wt % 2.0 Loy Yang Power
Sulphur (S) Wt % 0.2 * * See Section 3.1.3 below
Oxygen (O) Wt % 9.5 Loy Yang Power
Nitrogen (N) Wt % 0.2 Loy Yang Power
Ash Wt % 0.9 * * See Section 3.1.3 below
Total Wt % 100.0  
Higher Heating Value Btu/lb 4,522 Loy Yang Power
Higher Heating Value MJ/kg 10.52 Loy Yang Power

Source: WorleyParsons

3.1.3 Notes on Coal Constituents

The sulphur (S) content value in the table above is not used directly in the Base Case model but instead is adjusted within the model to match the flue gas SO2 composition listed in the Feed Gas

Definition 100% (design case) of the 5000tpd PCC plant shown in Appendix 4. The adjusted sulphur (S) content input value used in the model is 0.10%.

The average ash recorded for 2011 was 2.9 wt% (dry basis), while the 0.9 wt% used in the models was based on 2010 records and is deemed by LYP to be on the low side. This will require further consideration in a detailed design phase of the potential PCC retrofit, as the LYA plant is a mine mouth operation which can encounter coal with different constituents depending on which direction the mine is being developed.

3.1.4 Boiler Plant Inputs and Outputs

The boiler plant inputs and outputs are shown in the simplified block diagram below.

Figure 3.2 -Boiler Plant Inputs and Outputs

Source: WorleyParsons

The main boiler inputs are combustion air, water and fuel (pulverised brown coal) while the boiler outputs are steam, flue gas and ash.

For modelling the boiler plant the input data presented in the table below is entered into the GateCycleTM software.

Table 3.3 Boiler Plant Model (Combustion) Input Data

Parameter Units Value Source
Excess Air % 20.87 Loy Yang Power
UBC in Ash % 0.04 * * See Section 3.1.5 below
Radiation Loss % 0.34 Loy Yang Power
Other Boiler Loss % 0.037 Loy Yang Power
CO in flue gas ppmv 7 Loy Yang Power
Economizer Exit Gas °C 358.64 * * See Section 3.1.5 below
Air Heater Exit Gas °C 181 Loy Yang Power
Air Heater Inlet Air °C 18 Loy Yang Power
Boiler Efficiency % 72.0 * * See Section 3.1.5 below

Source: WorleyParsons

3.1.5 Notes on Boiler Plant Inputs and Outputs

”UBC in Ash” above is the Weight Fraction of Unburned Carbon in Ash as defined by combustion calculations performed in previous the DryFiningTM Study Report.

The “Economizer Exit Gas” value above can approach 410°C towards the end of a boiler run at LYA.

The “Boiler Efficiency” value in the table above is not used as an input to the model. The “Boiler Efficiency” is calculated from model outputs and compared with the value reported above.

The Air Heater Leakage value in the model is adjusted to match the air heater flue gas composition as presented in the Feed Gas Definition 100% (Design case) of the 5000tpd PCC Plant, shown in Appendix 4.

3.1.6 Steam Turbine Inputs and Outputs

The Unit 1 the steam turbine was supplied by OEM Siemens. It was ordered with a guaranteed rating of 500MW, and an expected maximum capability of 529 MW with 8.29 kg/s re-heater spray flow.

Achievable generation was typically less than 529 MW, dependent on steam conditions, boiler spray flows, plant configuration and the extent of equipment deterioration over time.

These limits are based on rated turbine inlet steam conditions as shown in the table below.

Table 3.4 - LYA Steam Cycle Conditions

Parameter Units Value
Main Steam Pressure MPa (abs) 16.4 (at MSV)
Main Steam temperature C 538 (at MSVs);
Hot Reheat Temperature C 538 (at RSVs);
Reheat System Pressure Loss % 10
Condenser Pressure kPa.(abs) 9.5

Source: Loy Yang Power

The OEM indicated that the boiler furnace capability is significantly in excess of that required to supply turbine rated steam flows on all units.

During the early half of last decade, the OEM was approached to upgrade the turbine-generator units to the maximum economic extent, consistent with:

  • a boiler thermal capability of 1,295 MW (heat added to steam) and,
  • a limit on main steam flow of 473 kg/s

Unit 1 upgrades were performed in the period as outlined in the table below.

Table 3.5 - LYA Unit Upgrades Dates

Unit Turbine Upgrade Condenser Upgrade
1 Nov / Dec 2003 Nov / Dec 2003

Source: Loy Yang Power

The solution adopted by the OEM was the replacement and modification of the HP and Intermediate Pressure inner modules (inner cylinders and rotors) with turbines of greater swallowing capability, fitted with modern high efficient blading. Coupling bolts were upgraded to hydraulic bolts to allow the transmission of additional torque and to reduce maintenance effort.

The Unit 1 HP and Intermediate Pressure inner modules were replaced with new components. The efficiency of Unit 1 is higher than the Unit 3 and Unit 4 turbines.

The turbine inlet areas on the upgraded HP and Intermediate Pressure cylinders were increased to ensure that steam pressures remain below boiler safety valve settings.

To ensure the correct sequence of boiler safety valve operation, with nominal 464 kg/s main steam flow and to allow for the associated greater heat load:

  • Main steam pressure was reduced from 16.4 to 16.0 MPa.abs,
  • Safety valve settings were adjusted in line with the higher steam flows, and
  • Design condenser pressure was increased to 10 kPa.abs.

Achievable load at the design boiler load will be dependent on plant condition and condenser pressure. The new turbine design conditions based on a boiler thermal load of 1,295 MW (heat to steam) are shown in the table below.

Table 3.6 - LYA Units’ Post Upgrade Conditions

Parameter Unit 1
Generator Load (MW) 568.961
Main Steam Flow (kg/s) [ t/h ] 463.737 [1669.453]
Main Steam Pressure (MPa.abs) 16
Main Steam Temperature (C) 538
Hot Reheat Temperature (C) 538
Condenser Pressure (kPa.abs) 10.0
Superheater Spray Flow (kg/s) 37
Reheater Spray Flow (kg/s) 12
Heat Rate (kJ/kW.hr) 8,194
HP Turbine Efficiency 93%
Intermediate Pressure Turbine Efficiency 94%

Source: Loy Yang Power

The tolerance on steam swallowing capacity was specified as -0% / +4% and therefore the maximum expected load was greater than the above rated conditions.

The corresponding tolerance on turbine load is approximately -0 MW / +22.5 MW. The higher load can only be achieved with a correspondingly greater-than-design steam flows and boiler thermal load.

3.1.7 Flue Gas Conditions and Composition

The Air Heater Leakage value of the Model is adjusted to match the Air Heater Exit flue gas composition as presented in the Basis of Design, in the Feed Gas Definition 100% (Design case) of the 5000tpd PCC Plant, shown in Appendix 4.