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).
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.
|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|
3.1.2 Coal Specification
The LYA coal specification for the Base Case model is presented in the table below.
|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|
|Higher Heating Value||Btu/lb||4,522||Loy Yang Power|
|Higher Heating Value||MJ/kg||10.52||Loy Yang Power|
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.
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.
|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|
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 bySiemens. 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.
|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|
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.
|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.
|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.