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Environmental and Social Impact Assessment Fort George, Mauritius 2017

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5 Project description


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Poonam Tatayah Ecology Consultant Biodiversity Consulting Ltd River view Lane, Verdun. BRN: C 15130202

1 INTRODUCTION

This chapter provides information on the principal elements of the CCGT project. A description of the

existing project site and surrounding area is provided. The main plant components, processes and

materials used are identified.

In line with its objective to ensure security of electricity supply, the CEB is contemplating to set up a

thermal power plant based on combined cycle gas turbine technology, at Fort George, Mauritius. The

site which has been selected lies next to the current Fort George Power Station (FGPS). It will be a

Combined Cycle Gas Turbine (CCGT) that will successively work with DFO and in Open Cycle in

Section 1, and with Natural Gas and in Combined Cycle in Section 2.

This chapter elaborates on the technical design of the plant.

2 PROJECT SITE

The project site is situated at Chaussée Tromelin, Fort George, Mer Rouge, Port Louis, Mauritius and is

within the boundary limits of the Port Area. It is easily accessible by a two-way tarred road. The project

site is adjoined by Fort George (The Fortress) on the North West, Fort George Power Station on the

north, a tarred access road on its east, and bounded by Mauritius Chemical and Fertilizer Industry

Limited (MCFI).

This site has been selected due to the proximity of the Fort George power station (FGPS) and 66kV

transmission lines. The site earmarked for the proposed undertaking covers an area of 2 Ha and it is

classified as state land that falls under the present jurisdiction of the Mauritius Port Authority (MPA).

The proposed CCGT power plant will be located opposite to FGPS and next to the premises of the

MCFI Group. The new power plant will be around 1 km from the nearest residential zone.

Photo 1 Project site area (view from FGPS)


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Map 2 Site location and its surrounding


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Figure 4 Additional plot of land at Fort George from MPA


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3 GENERAL CONFIGURATION OF THE CCGT

The Fort George Combined Cycle Gas Turbine (CCGT) power plant project consists of the installation

and commissioning of two heavy duty dual fuel gas turbines and one steam turbine in a combined

cycle arrangement. The CCGT power plant will successively operate with different fuels/ technologies:

• Section 1: Open cycle (OCGT) on Diesel Fuel oil (DFO)

The OCGT power plant will be used for peaking purpose

• Section 2: Combined cycle (CCGT) on Natural Gas (NG), DFO remain as a back-up fuel.

The CCGT power plant will be used for base load operation and will be rated between 105 - 120MW

when operating on DFO and be capable of producing up to 140MW when operating on Natural Gas.

The Fort George OCGT shall run on DFO initially and after implementation of the 2nd section

(conversion from OCGT to CCGT) (i.e. between 2-3 years after completion of Section 1), the CCGT

will be commissioned and operated on NG.

3.1 COMBINED CYCLE TECHNOLOGY ADOPTED

The Combined Cycle technology is based on the use of gas turbine(s) fired with either Liquid or Gas

fuel combined with a steam turbine which is driven by steam produced from waste heat from the gas

turbine(s), in order to increase efficiency and electrical output.

The general configuration considered is a combined cycle plant based on two cycles, namely

the Gas Turbine (Brayton) cycle and the Water/Steam (Rankine) cycle. The CCGT at Fort

George, will include two Gas Turbines (GT), each associated with one Heat Recovery Steam

Generator (HRSG), and only one common steam turbine fed by the steam flows from both

HRSG`s. This choice is driven by the power output desired, to maximize the efficiency of the

combined cycle power plant, even at part load and considering the limitation of power output per

generator imposed by Mauritius network constraints. This combined cycle technology allows reaching

the highest efficiency among all electricity production technologies from thermal sources, with an

estimated efficiency of over 54 %.

The gas turbines will operate in open cycle mode (OCGT) after implementation of Section 1. The estimated

operation as OCGT is between 2-3 Years. After implementation of Section 2 and commissioning of the

CCGT plant, in case of necessity (unavailability of either one or two HRSG or the steam turbine), it will still be

possible to operate the gas turbines as OCGT using the bypass stacks.

The gas turbine rating between 35-40MW considered for the present project rejects less heat from the

exhaust diffuser as compared to gas turbine ratings, typically 125 -375MW, used in CCGT Power

plants of higher capacity. Based on analysis of all possible configurations for the CCGT, it is

recommended to consider HRSG`s with 2 pressure levels, without reheat, which is the market

standard design for such rating of CCGT Power Plant.

3.2 MAIN COMPONENTS

Combined Cycle Gas Turbine power plants are generally manufactured by Original Equipment

Manufacturers (OEM`s) as a standard reference plant with pre-engineered packages designed to plug

together, thus minimizing onsite erection time. The major equipment such as the gas turbines (GT),

steam turbine (ST), generators and step up (GSU) transformers are shipped to the site in a pre-

assembled or pre-engineered modular compartments and factory tested. The Heat Recovery Steam


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Generators (HRSG) are also shipped in pre-engineered, modularized sections and are designed for

easy tube welding and assembly.

3.2.1 Gas (Combustion) turbine

In basic terms, the combustion turbine also known as the gas turbine consists of three main sections:

the compressor, the combustion chambers and the turbine sections. Filtered air enters the

compressor section, which compresses the air and draws it to the combustion chambers. Fuel is then

mixed to the compressed air and ignited. The combustion process is carried out at constant pressure.

Thereafter, the continuous hot combustion gases are directed towards the turbine section where they

expand through the turbine blades to perform work that provides the power to drive the compressor

section as well as to spin the Generator, for generation of electricity. After the hot gases exit the

turbine they are directed to the exhaust section and flow through a heat recovery steam generator

(HRSG) to produce steam, which is then fed to the steam turbine.

The gas turbine type earmarked for the project is the Heavy Duty / Industrial Gas Turbine which will

have a net output of between 35-40MW, at site conditions.

3.2.2 Steam turbine

The Fort George CCGT will be equipped with 1 steam turbine.

The steam turbine will be designed to have a minimum permitted operation load as low as possible as

and not higher than 25%, and each gas turbine is expected to have a minimum operating load of

around 50 %. At this minimum load, the ST shall be designed to run without limitation. The ST will be

equipped with a fully automatic shaft turning device. Gland steam sealing system will be provided to

prevent air from exiting the ST. The entire ST will be designed to avoid leak of lube oil or control fluid

as well as to reduce risk of inflammability. The steam turbine drains will be collected, where required,

cooled down and sent back to the condenser well.

3.2.3 Heat recovery steam generators

Two (2) Heat Recovery Steam Generators will be installed. The following parameters have been

estimated for each HRSG:

3 African development bank group, 2015. Project Damanhour combined cycle power plant project.

Figure 5 Combustion gas turbine fundamental structure3


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• Diesel (DFO) fired: First LP Economizer inlet temperature: 95°C (recirculation pumps are

necessary);

• Diesel (DFO) fired: Flue gas minimum exhaust temperature: 85°C;

• Natural gas Fired: First LP Economizer inlet temperature: 55°C.

Due to the limited area, available on site, vertical HRSG’s are expected to be used.

3.3 MAIN RESOURCE REQUIREMENTS

3.3.1 Diesel Fuel Oil (DFO)

The DFO to be considered for the project has a Lower Heating Value (LHV) of 42 500 kJ/kg. The site

DFO values are detailed hereafter.

Table 12 DFO delivery contract requirements

Unit Criteria Delivery contract

requirement Site DFO value

Ash % Mass Max 0.01 0.01

Pour point °C Max - 9 - 9

Kinematic viscosity @ 40°C cSt Min -Max 2.0 – 5.0 3.5

Density @15°C Kg/m3 Min -Max 820 – 860 840

Sulfur content Mg/kg Max 50 50

Water content % volume Max 0.05 0.05

3.3.2 Natural Gas

The Fort George CCGT will use regasified LNG obtained under a long-term supply contract and for

which the seller is expected to responsible for the sourcing, procurement, transport, unloading, storage

as well as distribution of NG to the CCGT Plant.

The table below present three typical LNG compositions as detailed in the norm NF EN ISO 16903

issued in September 2015.

Table 13 Typical LNG characteristics, according to norm NF EN ISO 16903

Characteristics @ Flash point, 1

atm Unit Example 1 Example 2 Example 3

N2 % mol/mol 0.1399.8 1.79 0.36

CH4 % mol/mol 0.07 93.9 87.2

C2H6 % mol/mol - 3.26 8.61

C3H8 % mol/mol - 0.69 2.74

C4H10 % mol/mol - 0.27 1.07

C5H12 % mol/mol - 0.09 0.02

Molar mass Kg/kmol -16.07 17.07 18.52

Flash point °C 161.9 -166.5 -161.3

3.3.3 Raw water

Potable water terminal point of the existing Fort George Power Station (FGPS) will be used to feed a

new raw water tank appropriately sized to store raw water for the CCGT plant, for an autonomy of 1

day at maximum water consumption, in case of water supply shortage from CWA.


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Note: The quantity of water required for the daily operation of the steam turbine is yet to be

determined.

3.4 CCGT PROCESS

3.4.1 General process diagram

A compressor adds pressure to fresh air and draws it to the combustion chamber.

Then, fuel is mixed with the compressed air and ignited to produce hot combustion gases, at

constant pressure. The temperature of hot gas is between 1,300-1,500 °C.

The hot combustion gases expand inside the turbine section, and spins the rotor.

The turbine is coupled to a generator which generates electricity. The gases exiting the turbine still

have some remaining thermal energy which can be further extracted. In the HRSG, the heat transfer

from the hot exhaust gases (temperature between 550 - 650 °C),

results in production of steam from the water of the circuit 1.

This steam spins the steam turbine which is coupled to an alternator, thereby generating electricity.

The steam is then transformed into water in the condenser by a circuit 2 of cooling (water cooling or

air-cooled condenser)

The water of the condenser is sent towards the circuit 1 and towards HRSG (returns to stage 5).

Both generators produce electricity at 11,000 Volts which will then be transformed to 66,000 Volts

and exported to the grid, by means of transmission lines.


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Figure 6 CCGT process (Source EDF, edited by Biotope)


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3.5 TYPICAL SCOPE OF WORK

The scope of work for this project includes the design, engineering, procurement, supply and

transportation of material and equipment, installation, erection and construction, testing and

commissioning, and putting into service the CCGT power plant.

The scope of supply will include but not be limited to the following:

3.5.1 Mechanical

• 2 Gas turbines;

• 2 Heat Recovery Steam Generators;

• 1 Steam Turbine;

• Air cooled condenser;

• Closed circuit cooling water system;

• Water treatment plant;

• Waste water treatment plant;

• Waste treatment disposal system;

• Fire & gas protection & detection system;

• Compressed air system;

• DFO storage area.

3.5.2 Electrical

• Network grounding systems;

• New 66kV Substation based on GIS technology to connect the power plant to the grid;

• Generators;

• Generator circuit breakers;

• Power transformers;

• Generator and transformer protection system and other protective relay equipment;

• MV and LV cabling, cable tray, trenches, cable ducts etc;

• DC and emergency power supply;

• Diesel generators (for emergency and black start supply);

• MV and LV motors;

• Cables and accessories;

• Lightning & earthing system;

• Exhaust gases and Water emissions monitoring equipment;

• General control system & supervision from main control room (on existing FGPS) and

local technical rooms.

3.5.3 Civil

• Site preparation (site clearance, excavation, landfill, leveling and grading of construction

sites);

• Site access roads;


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• Utilities pipes work;

• Pipes and cables racks;

• Storm, oily and plant drainage systems;

• Fencing and gates and site services;

• Underground services;

• Steam Turbine & Generator Hall;

• Gas Turbines & generators Hall;

• Electrical rooms & control rooms;

• Chemical Building and Laboratory;

• Instrument and Service Air Compressor Building;

• Warehouse;

• Foundations for required components.

3.6 CCGT STRUCTURES, BUILDINGS AND OTHER SYSTEM

3.6.1 Turbine halls, CCR and associated building, gatehouse

The gas turbines and steam turbine will be installed in separate, turbine halls to protect the equipment

from ambient conditions, to ease maintenance of the turbines/generators, and auxiliaries. The turbine

halls will as well serve as efficient noise barriers.

The gas turbines have been arranged at right angle to the dominant winds in the area

(Northwest/South-East in both directions depending on the time of the year) to avoid recirculation of

the flue gas to the gas turbine compressor inlet.

Due to the limited space, available for the construction of the CCGT and to optimize investment, the

new plant will share the following facilities with the existing Fort George thermal Power Station

(FGPS):

• Central Control Room;

• Parking lot;

• Main DFO storage (conversion of existing HFO tank(s));

• Firefighting storage and pump house;

• Waste water treatment (a part) and discharge channel.

The gatehouse will include a reception and visitor front office, an office for security personnel (3

permanent people) with restroom, and the necessary space for intrusion monitoring system and CCTV

system. At least one emergency gate will be provided to allow a second access to the site in case of

emergency (e.g. firefighting brigade) and to ease access for the movement of heavy equipment.

The Fort George road separating the existing FGPS and the CCGT sites will converted to a controlled

access* road. Access control, will be managed by CEB. (*Subject to approval by the MPA).


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3.6.2 Effluent and Waste Treatment Facility

Oily effluents and oil filled transformers

• Potentially oil contaminated wastewater shall be collected into oily water separators. After

oil separation and quality control, effluents shall be discharged in the wastewater

collecting network.

• The skimmed oil shall be collected in an oil tank and then forwarded to the existing FGPS

plant for treatment.

Oil filled transformers shall be installed on concrete bases having a containment pit designed to collect

oil spillage, rainwater and firefighting flows. The pit shall be designed to contain an oil spill and allow

excess retained water to be drained. Drainage of the pit shall be connected to the oily water

connection (with water oil separators). Fire barriers devices shall be provided to prevent fire from

spreading to the oily water connection.

Wastewater discharge

The wastewater discharge terminal point will be located at the north-west of the site and will be

connected to the discharge system of the existing FGPS. A new trench or duct will be required for

linking the existing channel to the new system. The CCGT waste water discharge is expected to be

around 2 m³/h, which is compatible with the current design of the FGPS discharge channel.

Rainwater

Rainfall run-off collected from undisturbed areas shall be diverted and prevented from entering the

sanitary sewer, contaminated drains or chemical drains. The undisturbed areas shall include areas

with no equipment or equipment that does not contain any chemicals or oil that may leak. As far as

possible, non-potentially polluted rainwater shall be re-used on site, or disposed of, in compliance with

applicable Laws.

Rainfall run-off from active areas is to be collected in a dedicated drain system. This wastewater shall

be treated, as necessary, prior to discharge in compliance with Applicable Laws. A soakaway pit (or

Storm Basin) shall be provided as last pollution barrier before the final discharge. If effluents rejection

pumps are required, 2 x 100% redundancy shall be applied. Pumps operation shall be completed to

level in the soak away pit and to effluents quality. The soakaway pit shall be sized to be able to

manage rainfall rate as per worst site conditions.

Chemicals/ process effluents

Chemical / process wastewater, when only pH adjustment is needed to comply with applicable Laws,

shall be collected into the neutralization pit to adjust the pH to the required values. After quality control,

effluents shall be discharged either in a wastewater collecting network or directly out of the Site in

compliance with applicable Laws. Hot process effluents such as HRSG blow down, steam lines drain

or feed water, shall be cooled to bring back their temperature to an acceptable level.

Environmental and Social Impact Assessment Fort George, Mauritius

2017

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Figure 7 Site configuration (Source : EDF 2017))

Environmental and Social Impact Assessment Fort George, Mauritius

2017

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4 CONCLUSION

This chapter of the ESIA gives an overview of the project, details the technologies used for

generation of electricity as well as the basic design of the power plant. Major components/equipment

which will comprise the CCGT power plant are detailed. A site plan detailing an indicative

arrangement of the power plant is also provided.