Conversion of Coleson Cove Oil-Fired Unit
to Natural Gas-Fired Combined Cycle
Client: (NB Power) Keith MacLean
Authors: Scott Glendenning, Victoria Jared, Grant MacKinnon and Cody Sabourin
Abstract
The objective of the project was to design a natural gas-fired combined cycle
to replace the current Unit #1 at Coleson Cove Generating Station (CCGS).
The proposed design requires removal of the current oil-fired boiler, the
purchase of a new gas turbine and heat recovery steam generator (HRSG).
The new unit will generate a maximum load of 390 MW (gross) at an
efficiency of 49% (HHV). The conversion project at CCGS has a total capital
cost of $277 million and an internal rate of return of 0.6%.
Introduction
NB Power is New Brunswick’s leading provider of electrical utility services.
The company owns and operates twelve generating stations throughout the
province with an installed net capacity of 2,853 MW. Coleson Cove Generating
Station, located south west of Saint John, New Brunswick, is NB Power’s
largest generating station. CCGS consists of three 350 MW oil-fired units, each
unit containing its own boiler and steam turbine generator set.
L-R: Scott Glendenning, Victoria Jared,
Grant MacKinnon, Cody Sabourin
Problem & Objectives
Combined Cycle Technology
Due to the current price of expensive heavy fuel oil, Coleson Cove tends to
operate only during peak energy demand periods. NB Power is exploring the
feasibility of converting Unit #1 at Coleson Cove from an oil-fired unit to a
more modern, highly efficient, natural gas-fired combined cycle. The target
plant start-up date is 2020 and the proposed project seeks to make use of the
existing steam turbine for the new combined cycle and boiler house to
support the new heat recovery steam generator (HRSG).
A combined cycle is made up of a gas turbine, heat recovery steam generator
and steam turbine. Natural gas and air are fired in the combustion chamber
and expansion of the gas in the gas turbine generates mechanical work. The
gas turbine hot exhaust gas is then sent to the HRSG where heat is extracted
to boil water, generating steam. This steam is then sent to the steam turbine
to generate additional mechanical work. The gas turbine and steam turbine
generators convert the mechanical energy into useful electrical energy and
after stepping up the voltage of the electricity with a unit transformer, the
electricity is sent to the electrical grid.
Block Flow Diagram
Deaerated NCGs
LEGEND
Material Stream
Mechanical Work
Electricity
Demin. FW
Make-up
By-pass
Pipeline
Natural Gas
Air
Filtration
Air
Compression
Stack Gas
to atm.
Combustion
x
Heat Recovery
Steam Generation
Gas
Expansion
IP
LP
Ambient Air
Blowdown to
Wastewater
Treatment
ST by-pass
Heat Recovery Steam Generator Model
HP
x
Steam Expansion
CW
to Bay
Exhaust
Steam
Steam
Condensation
Vented NCGs
Condensate Return
CW
from Bay
Energy Conversion:
Mechanical → Electrical
Station Service
Unit Transformer
to Grid
General Electric Gas Turbine GT-7HA.01
Steam Turbine (Existing Unit at CCGS)
Proposed Design
Economics
The proposed design for CCGS’s new combined cycle consists of a new gas
turbine, a new HRSG and the re-use of the existing steam turbine. The General
Electric GT-7HA.01 gas turbine was selected for the proposed design. This
turbine operates at a maximum load of 275 MW with a minimum turndown
of 30%. The new HRSG will be a vertical-style unit due to the space limitation
constraint at CCGS and will be comprised of three pressure levels in order to
extract as much heat from the exhaust gases as possible for generating
mechanical work. The existing Hitachi steam turbine will not undergo any
significant modification. The proposed design generates 390 MW (gross) of
electricity to the electrical grid with a full load efficiency of 49% (HHV),
which represents a 13% increase from the current oil-fired unit efficiency of
36% (HHV).
The total capital investment for the proposed design was determined to be
$277 million. The new gas turbine and HRSG make up the bulk of the total
capital investment, at $111 million and $121 million, respectively. The total
annual operating costs were estimated to be $134 million/yr., based on current
natural gas markets. CCGS is expected to generate an average revenue of
$144 million/yr. from electricity sales, which represents an average annual
profit of $10 million/yr. Assuming an estimated plant life of 30 years starting in
2020, the internal rate of return was calculated to be 0.6%.
$100
$50
$0
2017
-$50
Million $
Conclusions & Recommendations
The results from the economic analysis showed that the profitability of the
project is highly sensitive to the purchase price of natural gas and the selling
price of electricity. The completion of current natural gas pipeline
construction in the Northeastern United States is expected to reduce the price
of natural gas in New Brunswick, which would significantly improve the
profitability of the project. In summary, converting Unit #1 at CCGS to burn
natural would reduce fuel costs, increase efficiency, decrease greenhouse gas
emissions and give NB Power the ability to better load follow wind power.
Cumulative Cash Flow Diagram
2022
2027
2032
-$100
-$150
-$200
-$250
-$300
Year
2037
2042
2047