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Modification and Upgrading of an Existing GT Power Plant into Peaking Duty

Piet Kamminga

Ansaldo Thomassen

The Netherlands

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ABSTRACT Ansaldo Thomassen has relocated an existing power plant of two 40 MW FS6B gas turbine generator sets from Middle America to Europe, starting a second life as a peaking station. The project required extensive modifications and upgrades in order to have the plant meeting a comprehensive package of new requirements concerning installation, operation and up-to-date technical specifications:

• Relocation from Middle America to Europe. • Conversion of mechanical and electrical equipment from 60 Hz to 50 Hz. • Providing new equipment meeting stringent grid specifications. • Inspection and overhaul of existing equipment. • Upgrading of unit performance to maximize economical benefits. • Conversion to meet stringent emission requirements and connection to a high existing

stack. • Complete installation, commissioning and testing at the new site, demonstrating

compliance with performance, reliability, emission levels and grid requirements. The project was executed with excellent results and in a very tight time schedule. This paper will highlight specific project requirements, selection of technical solutions enabling a fast track project execution and the results of the final testing, resulting in compliance with today’s requirements of a retired power plant. TABLE OF CONTENT 1. INTRODUCTION............................................................................................................3 2. PROJECT OBJECTIVES...............................................................................................3 3. PROJECT HIGHLIGHTS..............................................................................................4 4 DISMANTLING AND PREPARATION ......................................................................5 5 OVERHAUL AND REPAIRS ........................................................................................6 6 CONVERSION FROM 60 TO 50 HZ............................................................................6 7 PERFORMANCE UPGRADES .....................................................................................8 8 EMISSION REQUIREMENTS......................................................................................8 9 ELCTRICAL SYSTEM REQUIREMENTS ................................................................8 10 TURBINE CONTROL SYSTEM UPGRADES..........................................................11 11 COMMISSIONING AND TESTING ..........................................................................11 12 CONCLUSIONS ............................................................................................................12

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1. INTRODUCTION AES Kilroot Power Ltd transferred two Frame 6 Simple Cycle Gas Turbine Generators from the existing Corporation’s Dominica’s Power Plant situated at Itabo, Dominican Republic, to its generating facilities at Kilroot Power Station, near Carrickfergus, Northern Ireland. These two units were operating at 60 Hz on the Dominican system and have been removed and modified for operation as peaking units at the Kilroot Power Station, providing a total standby capacity of 80 MW electric power to the 50 Hz and 275 kV Northern Ireland grid. Ansaldo Thomassen B.V. (ATH) was selected as the responsible contractor for dismantling and packing for shipment of the two units and unit auxiliaries to the new site including modifications required meeting new application specifications, refurbishment, equipment erection, painting, commissioning and putting into normal operation, performance and reliability testing on completion, instruction of the Owner's personnel and making good defects of the plant and associated systems. Design and construction of the high voltage equipment and all civil works was the responsibility of the overall project manager AES Kilroot. 2. PROJECT OBJECTIVES Feasibility studies by AES concerning the installation of two simple cycle gas turbines for peaking power in the Kilroot facility, provided positive results and would be economically attractive. Retired units installed in their sister plant in Itabo, Dominican Republic, would qualify for relocation. Installed in 1997, these units had accumulated only 30k hours each and have a considerable remaining life in a peaking application with limited operating hours. Positive side of the relocation is the fact that AES already owned the equipment, but the project was facing quite some challenges due to the demanding requirements for the new application of integrating these units into the Northern Ireland Electrical System. Main tasks and objectives of the project were: ■ Relocating the main power plant items that were suitable for operation in the new

installation. ■ Performing repairs and overhauls with the aim achieving high unit reliability and

availability. ■ Conversion of the generator and all electrical systems including auxiliaries from 60 Hz

into 50 Hz operation. ■ Ensuring the units achieve the estimated output, which is essential for generating the

anticipated revenues during the life time of the plant. ■ Meeting emission requirements for NOx and PM10 of the Large Combustion Plant

Directive 2001/80/EC. ■ Meeting stringent requirements of the electrical System Operator Northern Ireland Ltd

(SONI) grid code. ■ Meeting tight project requirements for budget and time schedule for safeguarding the

estimated ROI of the plant. ■ Compliance with stringent health and safety procedures during many simultaneous

activities and ensuring continued operation of existing power plant.

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3. PROJECT HIGHLIGHTS The actual project schedule was very tight as indicated by following key dates: ■ July 08 AES awarded contract to ATH ■ August 08 Dismantling in Dominican Republic ■ September 08 Plant Components arrive at AES Kilroot ■ Sept 08 - Jan 09 Erection of Original and New Equipment ■ Feb 09 - Mar 09 Commissioning ■ April 09 Commercial Operation To meet the deadline of March 2009 for machine commissioning, a suitable contractor had to be engaged quickly. ATH won the contract and the final Terms and Conditions were agreed in July 2008 after only 9 weeks of negotiation. This was achieved by a real willingness from the parties involved to reach a deal and also a strong desire by AES to meet the March 2009 commissioning date. Already during the proposal phase, a very strong solution focused cooperation started by solving technical, contractual and budget issues in a matter of days and creating an excellent basis for a successful project execution. A very strong partnership was formed during the project and it was because of this that the tight deadlines and technical requirements were achieved. Trust was formed early on and this led to joint problem solving and frequent re-programming of work. During the site activities daily progress meetings were held to monitor amongst other things safety, short term planning, resource management and liaison with the Kilroot Operations. The gas turbines were ready for no load testing at the beginning of March 2009. With mechanical tests complete, the machines were synchronized to the grid during April 2009. Both machines had to undergo a rigorous set of tests to prove their performance capability for operation in compliance with the Grid Code characteristics. The units were finally commissioned and entered commercial operation in April 2009.

Figure 1: Units installed at the Itabo site.

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4 DISMANTLING AND PREPARATION A complication of the project was the decision to perform all required overhaul and modification work at site. The benefits of this to the project were reduced cost of transportation as shipping heavy equipment to another location first for overhaul and upgrade would have raised the total cost substantially. Large drawbacks of this decision were the required critical completion of civil works before units could be installed on its foundation and the large amount of parallel activities at site. During the dismantling phase at ITABO, substantial effort was made for the preparation of the installation at the new site. Although a general inspection had been made during the proposal phase, the limited time available at the Kilroot site required extensive inspections and preparations for several reasons: ■ Detailed inspection of all systems and components for determination of suitability being

re-used and need for repair or replacement. ■ Although drawings and manuals of the installation were available, the information was

not always sufficient for the detailed engineering required to be able installing the units at the new site and meeting new specifications. Close cooperation between the engineering team and the site staff resulted in a comprehensive set of documentation about technical details and condition of the original installation.

■ Critical parts for upgrading needed to be dismantled immediately and sent to specialized workshops for upgrading and refurbishment. Most critical parts being the load gear boxes requiring new internals for the conversion to 50Hz. Temporary fixtures were installed supporting the generator rotor during transport.

■ One of the three units would remain at site, with the requirement being fully operational. This required review of the common systems and decisions about overall plant facilities that should remain or would be too expensive to be relocated.

■ Proper marking, labeling and packing of all components for ease of faultless re-installation in the Kilroot plant.

Figures 1 and 2 provide an overview of the original installation in Itabo and the transportation of a gas turbine to the special heavy lift vessel.

Figure 2: Transportation of gas turbine to heavy lift vessel .

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5 OVERHAUL AND REPAIRS In order to become highly reliable peaking units, the installation was given a thorough inspection with repair or replacement of defect components. Repairs included the replacement of defective devices and refurbishment work required due to corrosion caused by the saline and corrosive atmosphere at the original site at the Dominican Republic. The turbines were subject to the normal recommended inspections and overhauls associated with the accumulated starts and stops during their operation at the Itabo site. As mentioned before, these activities were carried out after installation on the new foundation blocks and in parallel with an extensive amount of mechanical and electrical installation work. This required optimum coordination of the site team, with several contractors involved and all facing the same tight time constraint for finishing the project. Figure 3 provides some impressions about the maintenance activities taking place at the Kilroot site.

Figure 3: Gas turbine installation and overhaul at the Kilroot site. 6 CONVERSION FROM 60 TO 50 HZ All equipment as installed at the Itabo site was designed for 60 Hz operation. The consequences of the decision installing this equipment in a 50 Hz power plant were very extensive and had considerable impact on the project budget. Not only major equipment as gear boxes, generators, and switch gear were subject to modifications, but all auxiliary equipment ranging from pumps and fans to medium and low voltage equipment, electrical control and protection systems were affected. Extensive reviews of all systems were performed and several options were considered with the aim achieving solutions meeting the comprehensive technical specifications and at the same time meeting budget and time schedule constraints. Installing complete new medium and low voltage equipment and unit auxiliaries would have had a negative impact on overall cost; same applied for the auxiliary equipment that should also be fully interchangeable with the existing components. Detailed engineering, sourcing and installation of new material were considered but involved too much time and cost. As a result in some inventive solutions that were considered and this proved to be the optimum approach for this project.

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A summary of the design philosophy applied to this installation is provided below: ■ Ratio of the load gear boxes was increased to achieve a generator speed of 3000 rpm and

maintain gas turbine rated speed. Wheels and pinions were replaced with new designs and bearings and seals were replaced or repaired subject to its condition.

■ Generator speed was decreased from 3600 to 3000 rpm and at the same time nominal voltage was reduced from 13 to 11.5 kV. Fortunately the generators were of a design that is suitable for both 50 Hz and 60 Hz applications and were not requiring any further mechanical changes. Even with a theoretical de-rating due to lowering the rated voltage, generator capacity proved still adequate for this application.

■ Medium voltage equipment needed extensive modifications for several reasons: • Generator breakers were replaced due to lack of capacity and the need for several

modifications. • Generator line side and neutral cubicles were refurbished and new PT’s and CT’s

installed meeting new requirements and European standards. • Low voltage systems were not exchanged because the original 460 Volt and 60 Hz

power supply for all auxiliary systems was maintained. This has an additional advantage that electrical auxiliaries do not require replacement. The original voltage is maintained by the application of special auxiliary transformers and the frequency is controlled by standard frequency converters. As a consequence new equipment as water injection pumps were also supplied for these conditions.

• Generator voltage regulator was modified due to the different nominal voltage and the protection panel upgraded to a multifunctional protection relay system meeting state of the art standards and requirements.

New equipment was installed in special containers, allowing installation and testing prior to shipment and facilitating rapid installation and commissioning after arrival at site. A total of three new containers were supplied: one medium voltage container per unit and one common high voltage control container for transformer protection, main and check metering. Figure 4 shows examples of new installed electrical equipment.

Figure 4: New generator circuit breaker and low voltage frequency converters

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7 PERFORMANCE UPGRADES Revenues from the peaking plant are generated by capacity payments, which means that a demonstrated high electrical output is of essential performance. The original base load rating of the units was 38.5 MW at ISO conditions and several potential power uprates were explored. The main increase in power was achieved by operating the units at its peak capacity, which was intended for units with limited operating hours and high power demand. By increasing the turbine inlet temperature, unit output is increased by 8% and the increase in maintenance cost due to higher metal temperatures is more than compensated by higher capacity payment. An other substantial power increase is achieved by water injection, which was required for emission reduction, but it is also applied to an optimum level as a power augmentation feature where the increased mass flow results in additional power. Additional smaller improvements were obtained by raising the turbine speed to the maximum level by selecting an optimum load gear speed ratio and also the unit overhaul contributed by recovery of lost power due to wear of turbine components. Practical limitation of the unit output was found in the generator; although the generator had spare capacity and an optimum for the power factor and temperature rise were maintained. During performance testing an actual power output of 44.2 MW at ISO conditions was demonstrated for both units: an increase of 15% compared to the base load rating. 8 EMISSION REQUIREMENTS Prerequisite for the installation of the Itabo units at the Kilroot site was compliance with demanding emission requirements. Not only the fulfillment of the Large Combustion Plant Directive 2001/80/EC standards for NOx and PM10 emissions had to be demonstrated, an additional task was connecting the outlet of both gas turbines to an existing 100 meter high chimney. The power station has already two Rolls Royce Avon gas turbines connected to this chimney, however spare stack capacity was available for the two additional units. See figure 5 for the existing situation.

Figure 5: Chimney with existing peaking units connected

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Figure 6 depicts the new installation with the FS6B gas turbines connected to the chimney with special ducts. The location of the gas turbines was dictated by the requirement to avoid interference between the new turbine foundations and the existing foundation of the chimney. This also explains the staggered turbine arrangement, aiming for minimum distance between turbines and stack. Due to the short time available, all ducting was pre-manufactured in a workshop, resulting in substantial volume shipments to site. Acoustical and thermal insulation was mounted internally in the ducting, again with the aim of minimizing local installation time. The length of the ducting had three major complications: ■ Optimum cross section had to be selected to avoid high velocities that would impact unit

performance and noise levels. ■ Adequate insulation of the system that due to the large area could have an unacceptable

impact on the allowable noise levels in the plant. ■ Exact location and dimensions of the tie-in points at the stack, ensuring that the

prefabricated sections would fit during installation. Fortunately all efforts proved to be successful and the unusual arrangement of gas turbine exhaust systems met all design requirements and were mounted without major issues.

Figure 6: FS6B gas turbine exhaust arrangement

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Unabated NOx emissions for the FS6B burning distillate fuel will be 450 mg/Nm³, where the regulations require a maximum level of 120 mg/Nm³. An effective method reducing NOx emissions is by means of water injection, which is lowering the flame temperature in the combustor. An additional advantage as mentioned before is the increase of unit power output. Water injection levels were selected achieving maximum power without exceeding combustor limits for combustion dynamics and CO emissions. Water injection capability was added to the combustion system, where water is injected directly into the combustion zone through an additional passage in the fuel nozzle. Injection pumps and control hardware are installed next to the unit enclosure and controlled automatically by the turbine control equipment. The measured figure for NOx was 72 mg/Nm³, which is substantially lower than the allowable limit. 9 ELCTRICAL SYSTEM REQUIREMENTS By far the most demanding item in terms of detailed engineering hours concerned the electrical system. Work included verification and upgrades of existing systems, modification to 50 Hz and adding additional scope of supply as per the customer specifications. Extensive detailed engineering was required, ensuring short installation and commissioning times according the overall time schedule and supporting AES in reaching compliance with the System Operator Northern Ireland Ltd (SONI) grid code specifications. Figure 7 provides an overview of all major electrical systems involved. A complete new set of documentation was generated including equipment drawings, detailed installation drawings of MV and HV containers, connection diagrams, cable lists, test instructions and procedures, etc.

Figure 7: Overall single line of electrical equipment

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10 TURBINE CONTROL SYSTEM UPGRADES The Speedtronic Mark V turbine control system is suitable for continued usage, but was modified and incorporates all the features of the new application. The original operator interface was in the Spanish language and based on a DOS environment. As part of the upgrade this system was replaced by the latest Windows based HMI, reflecting the actual control modifications and converted into the English language. Each turbine has two HMI’s: one for local control in the Turbine Control Cubicle and one for remote control from the power station Central Control Room. Figure 8 shows a screen of the new Mark V user interface.

Figure 8: Screen of turbine control system HMI 11 COMMISSIONING AND TESTING As part of the total program, the commissioning and testing phase was extremely important by demonstrating that the units were still fully functional after relocation and that all modifications were performing as intended. Many pre-operational and running checks were executed as per the agreed program, followed by final testing of the main characteristics and parameters, comparable to the program of a completely new installation. Following is a summary of the main checks and tests: ■ All mechanical and electrical equipment and connections ■ All electrical and control loops prior to start-up ■ Starting and running of the gas turbine generator ■ Starting trials demonstrating starting reliability ■ Running trials demonstrating unit operating reliability ■ Several tests required by the system operator SONI. ■ Emission and performance testing verifying the main contractual agreed values for

emissions and power output. Units were taken over by AES after satisfactory completion of all tests.

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12 CONCLUSIONS In July 2008 AES Kilroot and Ansaldo Thomassen embarked on this challenging project. Several activities needed to be executed in parallel. These included electrical and mechanical design, procurement of new items, dismantling of installations in the Dominican Republic transport arrangements and many more. The technical requirements for rehabilitating and refurbishing the existing units to operate at Kilroot were demanding and elaborate. A very strong partnership was formed between AES and ATH during the project and it was because of this that the tight deadlines and technical requirements were achieved. Trust was formed early on and this led to joint problem solving and frequent adjustments of work. Daily progress meetings were held to monitor amongst other things safety, short term planning, resource management and liaison with Kilroot Operations. The contract included a Performance Bonus based on maximum output power achieved. This proved to be a win/win situation as it incentivized ATH to maximize power output in order to achieve full bonus with the benefit to AES being the higher capacity payment which is directly linked to MW achievable and having a positive influence on project payback time. The project was realized almost within budget and one month late compared to the original plan. The installations now operate in the All Ireland Market and average one start per month usually for 1-2 hours to cover the evening peak.