Vol IV Appendix F - Power Station

755 Pages·2013·9.58 MB·English

Report to:
V G C .
ISTA OLD ORP

7961 Shaffer Parkway, Suite 5, Littleton, CO 80127
Phone: [phone])

NI 43-101 Technical Report – Mt. Todd Gold Project
50,000 tpd Preliminary Feasibility Study
Northern Territory, Australia

Appendix F
Mt. Todd Power Station

PROJECT NO. 114-311285

DATE: JUNE 2013

PREPARED BY: POWER ENGINEERS

350 Indiana Street, Suite 500, Golden, CO 80401
Phone: [phone] Fax: [phone]
June 7, 2013

VISTA GOLD CORPORATION

Mt. Todd Power Station
Feasibility Study

PROJECT NUMBER:
122329

PROJECT CONTACT:
Greg Hall
EMAIL:
[email protected]
PHONE:
208-288-6540
POWER ENGINEERS, INC.

Feasibility Study

PREPARED FOR: VISTA GOLD CORPORATION
PREPARED BY: TONY CLARK
208-288-6483
[email protected]

REVISION HISTORY
DATE REVISED BY REVISION
10/14/11 T. Clark A-Draft
B- Revised for increased
4/17/12 T. Clark
output options
6/7/13 T. Clark C-Updated for PFS

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TABLE OF CONTENTS

EXECUTIVE SUMMARY .................................................................................................................. 1 
GENERATION OPTION SELECTION ...................................................................................................... 1 
DISCUSSION ........................................................................................................................................ 2 
OBJECTIVE .......................................................................................................................................... 2 
THEORY .............................................................................................................................................. 2 
METHODOLOGY .................................................................................................................................. 2 
ASSUMPTIONS ..................................................................................................................................... 2 
ANALYSIS ............................................................................................................................................ 3 
CIVIL/STRUCTURAL ............................................................................................................................ 3 
Conceptual Design ......................................................................................................................... 3 
Construction Estimate .................................................................................................................... 3 
ELECTRICAL ........................................................................................................................................ 4 
Conceptual Design ......................................................................................................................... 4 
Construction Estimate .................................................................................................................... 4 
Civil/Structural Studies .................................................................................................................. 5 
INSTRUMENTATION AND CONTROLS .................................................................................................. 5 
Conceptual Design ......................................................................................................................... 5 
ENVIRONMENTAL ............................................................................................................................... 5 
MECHANICAL ...................................................................................................................................... 5 
Conceptual Design ......................................................................................................................... 5 
Construction Estimate .................................................................................................................... 5 
Mechanical Studies ......................................................................................................................... 6 
RESULTS ............................................................................................................................................ 13 
Capital Costs ................................................................................................................................. 13 
Summary ...................................................................................................................................... 14 
CONCLUSIONS ................................................................................................................................. 14 
RECOMMENDATIONS ................................................................................................................... 15 
APPENDIX 1 – DRAWINGS ............................................................................................................ 16 
APPENDIX 2 – LISTS ....................................................................................................................... 17 
APPENDIX 3 – SPECIFICATIONS ................................................................................................ 18 
APPENDIX 4 – STUDIES ................................................................................................................. 19 
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EXECUTIVE SUMMARY
The mine site has an existing high-pressure gas line and connection to the local utility grid via two
existing transmission lines. Site electrical peak power demands are estimated between 70MW and
83MW. Electrical demand will be met through the installation of a Rolls Royce Trent 60 Wet Low
Emissions single gas turbine generator and up to two reciprocating gas engines (such as the MAN
20V35/44SG ) located near West Creek adjacent to the WRD, approximately 1km south of the HLP
along the main entrance road, gas supply pipeline and incoming power lines. Water consumption in
the power plant is primarily for gas turbine interstage cooling and fogging, injection into the
combustor for NOx control and periodic cleaning of the turbine compressor section. The existing raw
water source will supply the required 216,000 m3 per year for power plant operation.
Net power generated by the Rolls Royce gas turbine will be approximately 57MW supplemented by
up to two MAN 20V35/44SG gas engines capable of 9.2 MW each. Peak electrical loads will be
supplied by PWC via connection to the utility grid.
Total installed capital and operating costs for preliminary design at various output scenarios are
summarized in TABLE 1.
Generation Option Selection
Power generation equipment selection is based on past pre-feasibility studies performed in 2010 and
2011 for Vista Gold analyzing equipment options for the Mt. Todd mine. The Rolls Royce Trent 60
WLE gas turbine was chosen as the optimum configuration from the pre-feasibility studies because it
provided the mine’s entire base load electrical demand with a single gas turbine and has the lowest
installation and life cycle operating costs per kilowatt-hour of the gas turbine options. With
electricity demands estimated between 56MW and 76MW, alternative scenarios with up to two
reciprocating engines were added to the power station to meet increased demand.

TABLE 1: 17 YEAR COST SUMMARY
NET POWER OUTPUT 57MW 76MW
Roll Royce Trent 60
Roll Royce Trent
Equipment WLE + 2 x MAN
60 WLE
20V35/44SG
Estimated Mine Process Capacity 33,000 tpd 50,000 tpd
Equipment and Installation Costs* $58,367,035 $83,487,047
17yr Project Operating Costs $522,822,146 $686,299,531
Electrical Power Cost over 17yr Project ($AUS/kW-hr) 0.0696 0.0693
*ESTIMATED PRICING IN AUSTRALIAN DOLLARS ($1 AUS = $ 1.034 USD)

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DISCUSSION
Objective
The objective of this report is complete a +/-15% cost estimate for the Mt. Todd Mine power station
construction and operating costs. The preliminary design of power station is based on the Rolls
Royce Trent 60 WLE gas turbine with inlet fogging and interstage inner cooling for increased
capacity and efficiency and the option to include up to two MAN 20V35/44SG reciprocating gas
engines to meet increased demand above the net 57MW generated by the gas turbine. Auxiliary
equipment was selected to meet the utility requirements of the gas turbine and supplement the
existing facilities on the site.
Theory
The driving theory for equipment selection in this study centered on providing reliable power for a
steady load demand with minimum of onsite personnel requirements with low initial capital and 17
year lifecycle costs.
Methodology
Auxiliary equipment estimates were solicited from suppliers to meet the interconnection requirements
of the Trent 60 WLE gas turbine and MAN gas engines. From the manufacturer information
received, a preliminary level plant design was developed to estimate quantities of construction
materials including piping, concrete, and structural steel. Material and equipment estimates were
imported to AspenTech’s In-Plant Capital Cost Estimator software (V7.2) to generate labor quantity
estimates, apply local cost rates, and estimate indirect construction costs applicable to the project.
Assumptions
Any excess that may be available that can be exported do not include capital expenses for additional
interconnection or metering equipment. Annual kilowatt-hour per year (kWh/yr) estimates assume
that both 22kV lines connecting the utility grid to the site are available to transmit the export power.
It is also assumed that the power station will have access to utility connections common with the rest
of the mine and process equipment. Utility infrastructure for the mine was not considered in the
construction or operating expenses of this study. Utility connections include raw water supply up to
500 Liters/min (132 gpm), waste water treatment up to 143 Liters/min (37.9) gpm, and connection to
the plant fire protection water main distribution. This study does not include repairs or maintenance
of the fuel gas delivery pipeline or electrical distribution system within the site.
The preliminary site design does not include black start capability because the site already has
connection to the utility grid when the power station is not operating and black start was not listed as
a requirement for the site. Black start can be included in the site design for additional cost to cover
the standby generator, fuel storage and handling, and electrical interconnection equipment.
Auxiliary systems included in the scope of the power station of this study include compressed air
system, process water treatment for gas turbine emissions control and performance enhancement, and
fuel gas conditioning downstream of the metering station. Fuel gas pressure supplied by a qualified
natural gas supplier under the draft terms dated May 11, 2010 is high enough that a compression
station should not be necessary but a filter separator and dew point heater are required to ensure solid
particle contaminants and liquid droplets are not introduced to the gas turbine combustion system.
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ANALYSIS
Civil/Structural
Conceptual Design
Foundation Location Plan
A conceptual foundation plan, S1-1, has been created based on the plant general arrangement
drawing, M1-1. This plan shows approximate foundation sizes and site layout.
Construction Estimate
Material Takeoff
Concrete material quantities have been estimated from preliminary foundation sizing calculations
based on the available vendor bid information. Typical foundations are assumed to be slab on grade
or embedded mat foundation type, but drilled piers have been assumed for the H frame foundations in
the switchyard. An allowable soil bearing pressure of 191 kPa (2000 psf) has been assumed for the
site for preliminary foundation design. A small amount of structural steel has been estimated for
access to the GSU transformer over the containment basin.

TABLE2: STRUCTURAL MATERIALS ESTIMATE
DESCRIPTION QUANTITY UNITS
Gas Turbine Foundation 292.1 cubic meter
Reciprocating Engine Foundations 100 cubic meter
Tank Foundations 61.5 cubic meter
GSU Foundation 73.1 cubic meter
Switchyard Foundations 26.5 cubic meter
Control Module Foundation 20.3 cubic meter
Misc XFMR & Switchgear Foundations 21.6 cubic meter
Misc Equipment Foundations 52.3 cubic meter

Slab Concrete Unit Cost 1200.00 $/cubic meter
(Materials and Labor)
Drilled Pier Concrete Unit Cost 1500.00 $/cubic meter
(Materials and Labor)

Total Concrete Costs $784,754
GSU Access Platform Steel 0.77 metric tonne
Structural Steel Unit Cost 8,000.00 $/metric tonne
(Materials and Labor)
Total Structural Steel Costs $6,173
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Electrical
Conceptual Design
One Line Diagram
A conceptual electrical one-line diagram has been created to show the electrical distribution system
from the 22kV utility interconnect down to the 400V power distribution bus. The equipment ratings
are preliminary and based on generator ratings provided by Rolls Royce and some preliminary
calculations. The equipment ratings shown are for cost estimating purposes only. The actual
equipment ratings will be determined using detailed load flow and short circuit studies during detailed
design.
Plant Arrangement
The auxiliary electrical equipment is included on the mechanical general arrangement drawing M1-1.
All the equipment physical sizes are based upon similar equipment from reference projects except for
the GSU transformer which is based upon an equipment supplier for this project.
Step Load Capability
Generators in the 35-60MVA size category can typically accommodate a 5 to 7 MW load change and
stay within 5% frequency range for 1 or 2 seconds.1 Larger step load changes may be accommodated
with a heavy inertia design generator rotor. Transient load response is also improved with 1-15 MW
of load already connected to the generator. The largest loads at the Mt. Todd Mine are induction
motors estimated at approximately 6MW each. If the motors are started sequentially the generating
station will likely be able to accommodate the loads. When a complete process equipment load list is
available a load analysis is required to determine voltage and frequency limitations that will need to
be considered in the final design of electrical equipment. If the generating station equipment is not
sufficient for plant startup loads the site has the option of supplementing onsite generating capacity
with the connection to the electrical grid if needed for startup loads.
Construction Estimate
Major Estimate
A Preliminary GSU transformer specification was sent to several manufacturers for budgetary
pricing. Reference pricing was used on all other major equipment.
Material Takeoff
Preliminary design was used to account for the electrical material takeoff for cables/terminations,
underground duct bank, and grounding. It is assumed that all cable routing for the plant will be done
by underground duct bank.
Preliminary design was done for large cable sizing. The plant arrangement drawing was used to
determine these cable lengths. All other cable/termination material take off was done from reference
projects.
Preliminary design was done for the underground duct bank system. The plant arrangement drawing
was used to determine conduit lengths. The underground system includes conduit and concrete
surround.
Reference projects were used for grounding material takeoff. The grounding system includes
grounding conductor, connections, and ground rods.

1 Position Paper #50 - LM Gas Turbine Load Accept Guidelines, GE Energy Aero Division, January 16, 2009
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Civil/Structural Studies
Design Criteria
Design Criteria is provided to describe site wind and seismic structural design considerations,
available material specifications, local code requirements, and design standards applicable to the Mt.
Todd power station.
Instrumentation and Controls
Conceptual Design
The objective for I&C conceptual work was to provide a BOP I/O count based on conceptual P&IDs
and selected Gas Turbine Generator (Roll Royce Trent 60 WLE). Instrumentation pricing is included
based on conceptual P&IDs and Site Condition document.
Environmental
Refer to the attached report, “Preliminary Permitting Requirements and Fatal Flaw Analysis” for
preliminary environmental impact information and a fatal flaw analysis to support permitting of the
proposed facility.
Mechanical
Conceptual Design
Site Conditions
Section 480020, Site Conditions is provided to establish ambient design cases, fuel supply, water
source, and design requirements unique to the Mt. Todd site.
Plant Arrangement
A conceptual plant arrangement has been created using the site plan provided by Vista Gold
Corporation and assumes connection to existing utility connections such as raw water supply, fuel
gas, wastewater treatment, and firewater loop. The plant arrangement drawing is included as M1-1
General Arrangement illustrates how the Rolls Royce Trent 60, and optional MAN 20V35/44SG
engines, and auxiliary equipment may be arranged to fit on the new generating station plot with
access for the gas turbine package and alleys for piping and electrical utilities.
Process Flow Diagrams
M2-1 Heat and Mass Balance Diagram incorporates gas turbine manufacturer information for dry
season (winter) and wet season (summer) ambient conditions. M2-2 Water Balance Diagram
illustrates the water treatment system with flow requirements to meet the needs of the gas turbine for
inlet air treatment, injection for emissions control, and equipment cooling water as well as waste
streams for disposal.
Piping and Instrumentation Diagrams
Piping and Instrumentation Diagrams (P&IDs) developed in SmartPlant P&ID are provided based on
quoted equipment information to demonstrate schematic arrangement of equipment, piping class and
material, valve and instrument locations, and interconnection points.
Construction Estimate
Material Takeoff
Lists extracted from SmartPlant P&ID for the basis for piping system and instrument estimate
quantities and costs. Pipe lengths are estimated from the General Arrangement drawing.
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Equipment Specifications
Detailed equipment specifications were written to support budgetary estimates for the gas turbine and
water treatment system. Requests for budgetary estimates from other equipment suppliers were
accompanied by data sheets describing the system requirements and limited to equipment over
$50,000. Reference costs were applied for equipment less than $50,000. When available, budgetary
estimates were solicited from local suppliers or from the US based representative for manufacturer’s
with representatives with field support local to the Mt. Todd site.
Where applicable, equipment costs include spare parts, shipping, and technical field support for
installation and commissioning.
Mechanical Studies
Design Criteria
A Mechanical Design Criteria is provided to describe design considerations, individual systems,
interface requirements, code requirements, and design standards applicable to the Mt. Todd power
station.
Fire Protection Philosophy
The Fire Protection Philosophy studies fire hazards of the preliminary power station design and how
to address those hazards following the recommendations of NFPA 850. Drawing M1-3 Hazardous
Area Classification Plan identifies areas classified as hazardous by NFPA 70 and proposed fire
hydrant locations to provide fire protection for the generating station equipment.
Demolition and Interconnection
New connections to the fuel gas pipeline and incoming power lines will be required for the proposed
location of the power station. The incoming fuel gas pipeline runs north-south from the southwest
corner of the existing gas metering station. The new gas pipeline connection will be approximately
100 meters south of the current location.

The power lines are currently routed along the south side of the main access road through the plant,
terminating at the substation approximately 150 meters west of the existing power station workshop.
The substation will need to be relocated to not interfere with the proposed conveyor routing from the
ball mills as shown on the Ausenco process plant layout dated October 10, 2011. The new substation
and power line connection will be just east of the new power station along the current route of the
incoming power lines.

Other underground features that may need to be relocated or removed include a septic system
connection and an underground duct bank with access cover. It is not known if these systems are still
in service or are decommissioned from the previous mine operations.
This study assumes potable water and sanitary systems are available and existing adjacent to the
proposed generating station area. If potable water is not available at the mine, the power station may
use bottled water for potable use and tie in to service water for sanitary uses and safety showers. A
septic tank system may be installed adjacent to the Control/Maintenance Building if sanitary sewer is
not available for the power station.
An existing underground fire mains system is expected to be available at power station boundary with
adequate supply pressure and volume to meet fire fighting requirements. Preliminary fire protection
design philosophy will require approximately 998.6 gpm (226.8 m3/hr) available with at least 20 psig
(137.9 kPa) residual pressure when operating at full capacity.

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