FULL PAPER FP_A.5_CLP_CCGT Upgrade

Transcription

1 FULL PAPER FP_A.5_CLP_CCGT Upgrade Major 9FA Combined Cycle Upgrade Works at Black Point Power Station for Improved Efficiency and Lower Emissions David Yip, Senior Project Manager, Generation Business Group, CLP Power Hong Kong Limited (Telephone: , ABSTRACT Black Point Power Station is one of the largest combined cycle gas turbine (CCGT) power stations in the world consisting of 8 units of 9FA single-shaft generating units with a total capacity of 2500MW. To further improve thermal efficiency and reduce nitrogen oxides (NO x ) emission from the CCGT, a Gas Turbine Upgrade Project was put forward commencing in Besides these performance improvements, the Project could also reduce maintenance costs and contribute to the reliability of the units in the longer term. This Paper is written to describe changes to the thermodynamic cycle and the new design features that account for the upgrade performance in efficiency, NO x emission and generating output outline the approach and process to define the scope of works and boundary conditions based on the examination of physical parameters, operating conditions and cycle performance parameters present a summary of the execution pathway of the Project and the initial performance results [Key Word] Combined cycle gas turbine, gas turbine, compressor, efficiency, NO x Emission, thermodynamic cycle, combustion system 1. INTRODUCTION Black Point Power Station (BPPS) is one of the largest combined cycle gas turbine (CCGT) power stations in the world consisting of 8 units of 9FA single-shaft generating units with a total capacity of 2500MW. To further improve thermal efficiency and reduce nitrogen oxides (NO x ) emission from the CCGT, a Gas Turbine Upgrade Project was put forward commencing in The major scope of works in the Project includes the complete replacement of the gas turbine and compressor, hot gas path components, combustion system, etc., and the associated modifications to other plants including the heat recovery steam generator (HRSG) and generator transformer in the same singleshaft configuration that are necessary to cope with the changes in operating conditions from the gas turbine. 2. PROJECT DESCRIPTIONS 2.1 DESIGN CHANGES TO THE THERMAL CYCLE Configuration at Black Point Power Station (BPPS) Each of the combined cycle units (CCGT) at BPPS is an identical configuration, where the Frame 9FA gas turbine and the two-cylinder steam turbine drive one single generator, in a single-shaft line arrangement. The HRSG is located at the axial exhaust of the gas turbine, in a vertical arrangement, i.e. flue gas flows in a vertical direction through the HRSG, perpendicular to the arrangement of most of the pressure piping in the HRSG. Page 1

2 Figure Descriptions of the Steam Cycle in the BPPS CCGT Arrangement The gas turbine inlet duct connects the air filters located on the turbine hall roof to the compressor inlet plenum and incorporates a silencer. The generating shaft line is supported on an elevated reinforced concrete foundation. The shaft line auxiliaries are located either in the turbine hall (below the generating shaft line) or in the mechanical annex alongside the unit. The gas turbine shaft line comprises the following major equipment:- Air inlet Inlet guide vanes Compressor (rotor and casing) Combustor Turbine (rotor and casing) Exhaust frame Exhaust diffuser Load coupling Bearings journal and thrust Support frame Instrumentation On-base pipe-works The Unit electrical and control equipment is located in an electrical annex within the turbine hall alongside the generator. Page 2

3 The physical space and footprint below the HRSG are fully utilized to accommodate the feed-water pumps, chemical dosing, and sampling equipment and the condensate polishing plant Thermal Cycle Descriptions The gas turbine operates in a thermal cycle that could be categorized by the Brayton cycle of which the ideal cycle could be described in typical P-V & T-S diagrams. Efficiency η brayton = Ideal Brayton Cycle (thermal) efficiency Rp = pressure ratio = k = specific heat ratio and Maximum Work NET when Rp where Tmax (i.e. T 3 limited by metallurgy) and Tmin (i.e. T 1 set by air temperature at inlet) Figure Description of Ideal Brayton Cycle for the Gas Turbine To produce higher cycle efficiency and generation output from the gas turbine, increasing the compressor compression ratio and the turbine firing temperature are the typical approaches adopted which are obvious from the Brayton cycle. But due to thermal fixation process, a higher turbine firing temperature would favor the formation of nitrogen oxides (NOx) which is the key control emission parameter from gas turbine of today. Therefore the selection of the new combustion system that would provide a higher turbine temperature will have to strike a delicate balance between output, efficiency, combustion dynamics, carbon monoxide, and NOx emission. Finally a new type of dry low-nox combustion system is adopted which is designed to offer the dual benefits of higher turbine firing temperature and lower NOx emission. The extended use of pre-mix fuel combustion was an important design and operation principle of the new dry-nox combustion system which would reduce the overall formation of NOx. Page 3

4 2.2 ENGINEERNIG Holistic Engineering Approach An overall holistic engineering approach was taken and is depicted in Figure for illustration. This comprises the following elements and objectives. a) Thermal loading to the HRSG and Steam Turbine should be within the original design margin of the installed equipment as modifications to these existing equipment could make the project more costly and not commercial viable, and impose additional project execution risks b) The above approach also applied to electrical loading on other equipment, including the Generator and the Generator Transformer. c) Capacity assessments were to be carried out on all the equipment to make sure that there is no bottom-neck and cost of modifications, if any, were factored in the overall cost-benefit evaluation of the Project d) All new equipment and modifications had to be fitted into the existing footprint of the CCGT, and constructability review was to be carried out together with engineering e) Potential exchangeability of new equipment for use in other CCGT units in the same BPPS was required to be evaluated. Figure Overall Holistic Engineering Approach Front-end Engineering Gas Turbine Engineering Gas turbine unit rotor, compressor discharge casing and turbine casing will be engineered by the gas turbine supplier. The existing compressor will be redesigned for robustness, increased pressure ratio and improved surge margin. The new compressor rotor upgrade involves an incremental increase in rotor wheel diameters in the heavy pressure stages with a corresponding decrease in the length of the rotor blades and the stator vanes on these stages. The turbine rotor will be of a new design that has the special cooling slot design on the wheels. Gas Turbine Auxiliary Systems Engineering The major change involves the conversion of the existing dry low-nox combustion system to a new type combustion system. The new dry low-nox combustion system will provide improved combustor operability, reduced emissions levels, extended turndown capability and extended interval hardware. This new dry low-nox system has more number of nozzles that improve flame stability and involve changes in mode transition. Generator and Generator Auxiliary Systems Engineering Page 4

5 The equipment supplier has conducted a review on the engineering and design changes required on the generator and generator auxiliary systems. As the original generator capacity is adequate to cover the increase in unit output after the gas turbine upgrade, no change is required for the generator and generator auxiliary systems. HRSG Engineering The equipment supplier was engaged to identify necessary enhancement required on the HRSG to cope with the increase in exhaust energy from the gas turbine exhaust. The following areas/issues were reviewed by the equipment supplier: Flow induced tube vibration Attemperator Flow accelerated corrosion Inlet duct casing HRSG casing Expansion joint Pressure parts Sling system Steam Turbine Engineering The equipment supplier was engaged to identify necessary enhancement required on the steam turbines and associated equipment to cope with the increase in steam flow. The following equipment were reviewed by the equipment supplier to identify design modifications: High Pressure (HP) steam chests HP turbine pipework HP valve actuators HP rotor HP inner and outer cylinders HP inlet and cylinder bolting HP blading HP diaphragms Low Pressure (LP) rotor HP-LP crossover pipework LP cylinder LP cylinder bolting LP blading LP diaphragms LP steam supply HP & LP bypass systems LP spray cooling system Gland steam system Turbine drains Control fluid system Lube oil system Balance of Plant Engineering The equipment supplier was engaged to identify necessary enhancement required on the BOP equipment to cope with the increase in system demand. The following equipment were reviewed by the equipment supplier to identify design modifications: Condenser Condensate extraction pump HP boiler feed pump LP boiler feed pump Main cooling water pump Condensate line to deaerator Deaerator and feed water tank Main control valves Page 5

6 Electrical System Engineering The equipment supplier was engaged to identify necessary enhancement on the Load Commutated Inverter (LCI) equipment to cope with the Project. As a result of the higher LCI torque required after the upgrade, the maximum current rating of the LCI needs to be increased. The existing AC reactor and heat exchanger will be replaced. Engineering review and design changes required on the 415V system to cope with increase in electrical loading of the equipment after the Project were carried out. The Generator supplier was engaged to identify necessary enhancement required on the generator transformer cooling system to cope with the increase in unit output. Civil Engineering The potential civil work includes: Furnish and construct fuel gas module support structure. Modify gas turbine pedestals, if necessary. Flash and weatherproof penetrations (pipe, structural steel, equipment, duct, and other miscellaneous) in Turbine Hall, if any. Control Philosophy All systems shall be designed such that no single failure of any control component will cause a trip of the unit. All transmitters and plant sensors which could directly leading to tripping of a unit shall be triplicated and their signals shall be used in a 2 out of 3 voting logic. 2.3 SCOPE DEFINITION AND DESIGN BASIS By adopting this holistic engineering approach, the following definition of scope of work was defined at the closure of front-end engineering as the design basis:- i. Replace the existing compressor rotor with a new more robust design with a slight increase in compression ratio ii. Complete the upgrade of all hot-gas path components (i.e. stationary and rotating blades, etc) to the new and robust design iii. Replace the existing dry low-nox combustion system to a new design that promote pre-mix combustion and enable a higher firing temperature iv. Complete the full replacement of fuel gas control system v. Complete necessary upgrade of all GT auxiliary systems (more than 10 systems are required to be upgraded or modified) vi. Complete necessary upgrade of the Load Commutated Inverter (part of the excitation system) vii. Complete some flow measuring and control devices in the fuel quality management system viii. Complete some modifications of steam turbine (mostly on low-pressure steam turbine cylinder) ix. Complete some minor modifications on the HRSG (mostly some flow control devices) x. Complete some modifications of the Generator Transformer (mostly on the cooling system and control) Also as part of the design basis, the upgrade unit should be able to run on gas fuels with a wider range of composition (and Modified Wobbe Index) without the need of hardware changes. The following table is a typical requirement of potential variability of gas fuels. Table 2.3 Typical Requirement of Potential Variability of Gas Fuels Potential Gas Fuel Gas Fuel 1 Gas Fuel 2 Composition Methane mol% ~85 ~93 Carbon Dioxide mol% ~10 ~2 Nitrogen mol% ~1 ~1 Air mol% 0 0 Total Page 6

7 LHV (60 o F, 1 atm.) Btu/scf MWI at 55 o C Btu/scf.R 1/ MWI at 120 o C Btu/scf.R 1/ BOUNDARY LIMITS AND CONDITIONS The Front-end Engineering had identified all the boundary limits and conditions for the Project. In particular to boundary limits, the techniques of 3-D laser scanning and modeling were used extensively. This technique had provided numerous inputs for physical dimensional analysis and general arrangement design of various systems. As a specific application of this technique, physical clash and interference of new equipment with the existing equipment had been effectively avoided. 3-D design model with laser scanning input Existing equipment 3-D design iterative modeling Laser scan of existing equipment to avoid interference for permanent use Constructability review to devise installation sequence and fine-tune final assembly part design Figure 2.4 Application of 3-D Modeling, Laser Scanning and Constructability Review to avoid interference both during installation and for permanent use 2.5 FINAL DETAILED DESIGN AND ENGINEERING To meet the stringent reliability requirement of CLP, some rigorous studies were also carried out as part of the final detailed design and engineering. These include the following studies:- - Tuning of the Power System Stabilizer (PSS) of the upgrade CCGT unit - Final bearing stress analysis based on the definitive design of the new gas turbine - Structural and bearing capacity analysis of all new and modified plant and equipment The PSS is a supplementary control that acts through the Automatic Voltage Regulator (AVR) of the excitation system, and provides positive damping to generator rotor angle swings. These swings are in a broad range of frequencies in a power system. Single-shaft CCGT such as the BPPS units have low frequency torsional modes, which would more likely to interact with the PSS. This interaction was therefore required to be assessed to determine whether there exists the need for torsional filters in the PSS to mitigate the level of interaction to acceptable levels. 3. PROJECT EXECUTION Page 7

8 3.1 ENGINEERING MANAGEMENT Site engineering reports were used to provide feedback from the Project Team to the respective Contractor of engineering problems, suggested improvements, defects and omissions which are found during construction and commissioning. The formal reports were issued by CLP and the Contractor would have to reply by a formal response within a short period. These report will cover though not necessarily be limited to the following types of problems: Interfaces Incompatibility of Equipment and civil works Inappropriate Equipment supplied for a required duty Omissions and shortfalls in the design and extent of supply Inadequacies in shipping, packing and protection Equipment failing to fulfill design requirements Equipment failing during construction or commissioning tests Where CLP wishes to make modifications to the Equipment as supplied which require comment from the Contractor or which need to be incorporated in the Contractor s drawings. 3.2 DOCUMENT MANAGEMENT A specific document and drawing management software system was used to manage all the technical submissions and correspondences between the Project Team, the equipment suppliers and contractors. This software system served as a hub with security features to control the incoming and outgoing information, tracked changes and version control of documents, and as a central database. 3.3 MATERIAL MANAGEMENT Discrepancy reports were used to notify the Contractor of items were damaged in transit or short shipped. Following receipting a discrepancy report, the Contractor shall supply replacement parts or make good the omission as soon as possible. 3.4 CONSRUCTION PLANNING AND EXECUTION All the Contractors were required to submit their site execution programme. The programme had to indicate the erection and commissioning logic and duration of all activities and had to be coordinated with the delivery programme and the design submission programme. The site execution programme was required to be expanded to a level of details that could reasonably be used by CLP to control the relevant activities on Site. CLP developed an overall Project s schedule that integrated all Contractor s site execution programmes altogether. Technical Advisors are personnel and specialists supplied by the Contractor to support the execution of the Project on Site, including but not limited to equipment transportation, equipment preservation, engineering, materials coordination, quality management, installation, cold commissioning, hot commissioning, tuning, testing, start-up and tests on completion. In this Project, technical advisors were required to ensure Technical Compliance during the execution of work on Site, including provision of services in areas including site handling, quality assurance, quality compliance during installation, cold commissioning, hot commissioning start-up, tuning and testing work. In addition, Technical Advisors shall prepare, validate and counter-sign completion statements during installation, and prior to cold and hot commissioning. CLP also required the contractor to make the Technical Advisors available promptly at CLP s request. Technical Advisors with valid work permits shall be nominated a few months prior to the start of mobilization for confirmation by CLP. Page 8

9 Figure A Bird-eye View of the Site Showing Ongoing Major Construction Activities Aerial view showing gas turbine systems installation Internal view showing the installation of new combustion system Installation of spaghetti-like pipe-work / piping serving each of the dual-fuel combustor Modification works on the Fuel Gas Supply Page 9

10 Associated works on the Steam Turbine Associated works on the Generator Transformer Figure Photos Showing Other Construction Activities 3.5 COMMISSIONING PLANNING AND EXECUTION A clear stage-by-stage commissioning programme covering construction completion, cold commissioning, hot commissioning until handover of the facilities custodianship from project execution to operations was developed. Check-sheets, transfer of project document custodianship, and facility walk-down were typically used to signify the completion of different stages of commissioning. Figure depicts the overall process of this stage-by-stage commissioning programme. Figure Overall Stage-by-Stage Commissioning Programme Also a clear division of responsibility was agreed between CLP and Contractors through the respective contracts. Page 10

11 Table Example of Division of Responsibility between CLP and Contractors Contractor Activity / Responsibility (Examples only) 1. Mechanical Acceptance Package Provide CLP with the Turnover Certification Package for each system 2. Tie-Ins at Battery Limits (Interface Points) Provide complete tie-in list, including the location and method of each tie-in. Provide a method statement for each tie-in point. Coordinate schedule of tie-in work with CLP 3.6 TRAINING PRIOR TO OPERATION CLP Activity (Examples only) Review issue comments back to the Contractor and distribute to other parties. Review / Verify / Approve / Coordinate Approve Coordinate The equipment suppliers were required to make available training services for CLP s staff for any item of Equipment supplied under the Contract, prior to commencement of operation. A training needs analysis was carried out to match the overall operation and maintenance (O&M) needs as well as the competency requirement of individual O&M personnel. Venue of classroom and simulator training sessions were arranged local in Hong Kong to facilitate involvement and participation of O&M personnel. More than 200 training man-days were recorded prior to O&M personnel took over the facilities. 4. RESULTS AND DISCUSSIONS The first CCGT generating unit upgrade was completed in early 2016, in a safety manner and ahead of schedule. More about 250,000 man-hours were recorded for the first unit upgrade from project inception to close-out without a lost-time injury, medical case or environmental incident. The post-upgrade machine performance was satisfactory with test results generally better than the plan. For example, the emission levels of NO x were consistently maintained to below 15 ppm (parts per million) with an extended turndown ratio, hence allows a wider operability range for the upgraded CCGT unit to suit system demand. Moreover, a higher level of adaptability to gas fuel with different Modified Wobbe Index (MWI) has also been successfully tested, without any need for hardware and software changes. Project Performance and Benefits Realization Turndown Safety 150% 140% 130% 120% 110% 100% 90% 80% 70% 60% 50% Schedule Plan Actual NOx Emission Efficiency Output Notes: Due to commercially sensitive information, only indicative figures on a comparative basis were shown. Figures > 100% depict actual results better than planned (i.e. 100%). Figure 4 Overview of the Project Performance and Benefits Realization Page 11

12 5. CONCLUSIONS The Project has been successfully implemented in one of the CCGT generating unit in the Black Point Power Station in a safe manner, slightly ahead of original schedule and with good machine performance results after upgrade. Hence upgrading existing CCGT generating units provides a feasible and sustainable way to uprate thermal and emission performance of the entire combined cycle fleet. REFERENCE Nil Page 12