Asset management – gas turbine power stations: admin and engineering
This, part 1 of a four-part overview, focuses on the salient asset management administration and engineering aspects of GT power stations.
Author(s): Douglas Hutchinson
This overview was written primarily with graduates, engineers and electrical, mechanical, chemical, instrumentation and control and computer technicians in mind who wish to enter the power generation industry at large and gas turbine (GT) power generating plants in particular, since combined cycle GT (CCGT) power plants constitute the largest output and most efficient turbine power generation stations operating today. Whilst renewable power generation and electricity storage are being actively pursued in all its various forms, and whilst nuclear power plants are considered the best long term, large output, enviro-friendly, bulk power suppliers, in an ever diminishing fuels world, transition eco-friendly natural gas fired CCGT power plants are still the quickest to build, the most efficient to run and the most readily available to the grid, large output power installations available today. CCGT plants are thus worthy of considerable continued study and application.
Power supply industry de-regulation
It is worthy of note in the days after WWII the European nation's power generation infrastructure (which was knocked to pieces) was funded and then run by government-created power authorities. These organisations became responsible for the total power supply system development – generation, transmission, distribution and electrical grid dispatching in their respective countries. This meant they were responsible for the design, specification, contract development and execution, procurement, construction, commissioning, on-going operation, maintenance, recruitment and training of personnel and electrical grid system dispatch.
National administration usually meant the appointment of a National Head together with an Executive Board, who finally reported to the National Minister for Power. As more and more off-shore and other oil and gas finds became more prolific, government titles changed to include Minister for Power and Energy.
At about the time (circa 1990–1998), the various European power authorities entered the de-regulation era. The already de-regulated and privatised American power industry was well ahead with the adaptation and use of gas turbines (GTs) for power generation purposes. The American aircraft jet-engine manufacturers, Pratt & Whitney, General Electric (GE) and Westinghouse were leaders in developing this new power generation initiative. Their innovation at that time revealed gas turbines (GTs) were ideally suited to numerous non base load power supply applications such as co-generation, peaking and emergency power generation.
Initially, aircraft GT engines (very high speed, using jet-A1 or military Jet-B fuels) were modified for industrial use and so used cheap industrial middle distillate (kerosene) fuel. These early ‘aero-engine derivative’ GT generation units were generally configured as shown in Fig. 1 :
Fig 1: Schematic layout OCGT generator unit
These ‘open cycle’ GT (OCGT) units possessed very desirable power generation characteristics:
- (i) Vastly smaller acreage footprint – minimal land usage.
- (ii) No extensive civil engineering foundation and cooling water requirements.
- (iii) Complete modular construction capability, leading to vastly shorter construction times.
- (iv) Turnkey engineering, procurement, and construction (EPC) cost and date certain contracts.
- (v) GT engine lift in/lift out change capability ensured quick prime mover maintenance by the Original Equipment Manufacturer (OEM).
- (vi) Minimal balance of plant (BOP) requirements – liquid fuel storage and pumping + lube-oil air-cooling systems, in some (rare) cases, GT inlet air cooling.
- (vii) Fast engine start-up and air-cooled generator loading rates (minutes).
- (viii) Aero-engine OEMs had the ‘monopoly’ on engine supply and maintenance.
- (ix) Plant owners maintained gearboxes, generator/exciter units and all Balance of Plant (BOP) facilities with/in part/or without BOP OEMs.
Asset management – GT power stations
In the establishment of national power authorities, ‘Merit Order’ power generation tables were created, whereby using an established common calculation methodology which was applied to all power stations, the most competitive and efficient stations, producing power for the least cost, ran and fulfilled the base-load need of the nation – thereby saving the nation an immense amount of money in fuel costs and of course containing emissions at their lowest levels.
The privatisation and sell-off of state owned power industry generation, transmission and distribution systems produced the scenario, whereby buyers, both established power utility (who formed separate power companies) and completely new individuals and independent power producing companies (IPPs) commenced owning bits of the overall power industry in those countries that began to privatise.
Thus, a conglomeration of companies, now specifically concentrating on power generation, commenced to own and manage these newly acquired power generation assets – (hydro, coal and oil fired, combined heat and power (CHP), and now latterly GTs and GT power station asset management specifically came into being.
These new businesses possessed all the corporate abilities to act just like any other business and they operated such as other businesses, concentrating on the energy supply markets and power generation sales to consumers via the grid company in any given country. They embraced and responded, in some cases brilliantly, to the demands and challenges of the newly created national gas and power markets. Whatever the name of the formal document between grid and generators – all generators now had to still acknowledge ‘merit order’ running principles and bid to produce lowest-cost power – and supply at agreed costs, to the grid.
Electricity consumers, both large and small, right down to homes and homesteads now had the choice to deal with competitive electricity supply companies in all their various market forms. These new businesses evolved and focused onto two distinct key management areas:
- (i) Commercial and administrative asset management.
- (ii) Engineering asset management.
- Commercial and administrative – essentially followed the general lines of all businesses; however, since the nation's electric power and gas supplies were now in ‘private hands’ – security of supply had to be guaranteed as nearly as possible for any country undertaking private or independent power sales. Throughout the world, this was accomplished by principally three legally binding, highly confidential agreements or contracts between the ‘new generator’ and the ‘grid’ company.
- Loan agreements or loan contracts – note, there were usually several ‘lenders’ to a project – the financial details were not necessarily divulged, but loan agreements indicated to the grid company the business was financially secure and adequately funded and was thus able to operate within the nation's power and energy markets.
- It is important to note that loan agreements were based on guaranteed summer/winter/dry season/wet season/peak load/non-peak load/active/and reactive power payment levels for power sold to the grid – and from the proceeds received, repayments to the banks and lending institutions, fuel procurement, manpower etc., could be made to payments schedules.
- The power purchase agreement (PPA) – (depending on the country, it may be called something else) became the most exacting contract between the grid company and the asset owning company. The PPA set out exactly – the how, why, what and when power generation was to take place throughout the year.
- The fuel supply contract [fuel supply agreement (FSA)] – enumerated exactly the how, why, what and when, and fuel exact technical specification; guaranteed fuel deliveries were to be made throughout the year. Also, with security of supply in mind, throughout the world, from the very commencement, alternative fuel supply arrangements were listed and specified in FSA agreements should ever the need arise.
- In this now rigid, highly technical and contractual world, several other contracts became necessary, e.g. contract maintenance and parts supply, independent fuel sampling, water supplies, transport hire, the hiring of personnel etc. – all these various aspects of commercial and administrative business life surfaced in the newly created and very exacting power industry asset management sphere.
- Since these new power generation companies now existed in various countries and/or in various regions within a given country, corporate budgeting and all accounting had to be to generally accepted accounting principles either for a single generating station or a group of power stations. Thus, asset management very quickly evolved into a highly technical and complex commercial cutting edge business model.
- Generating station engineering – With new and with existing GT assets already in place, the ‘engineering asset management’ of these considerable installations fell to principally three groups:
- (i) The owners of either existing or newly acquired power plants.
- (ii) GT OEMs formed service companies – They sought to undertake all specialist GT engine inspection and major overhaul maintenance sequences and be the technical leaders of engineering, procurement and construct (EPC) projects.
- (iii) Some combination scenarios of (i) and (ii) above evolved whereby – owner/OEM consortiums were established – OEMs took some level of equity in projects. Thus, it is worthy of mention that innovative, entrepreneurial, completely new companies who wanted to be in these new energy markets evolved and they safe-guarded their business positions by having GT engine manufacturers as technical advisors and leaders in their companies.
- (iv) These new companies owned and operated existing plants and went onto develop new power generation assets. They naturally formed their own commercial and engineering operations and maintenance (O&Ms) management teams.
Around the world, in these new ‘privatised’ circumstances, acquisition and then asset management for new or existing plant required serious commercial and technical short-term tactical and longer-term strategic consideration, because, in order to succeed, many key factors influenced all engineering management, hence commercial management, and thus, HR recruitment and training:
- (a) Principal technologies involved.
- (b) The actual plant design.
- (c) The degree of computerisation and automation employed in the plant.
- (d) The physical layout of the plant.
- (e) The operational regime of the plant – i.e. – base-load, load following, two shift etc.
- (f) Configuration of the plant.
- (g) Country power generation infrastructure.
- (h) Country management culture.
When GT asset management became the accepted norm, those companies seeking this type of contractual work were faced with very tight financial loan agreements, PPAs, FSAs and many other commercial and engineering conditions:
- (i) Date certainty – applied to new-build stations.
- (ii) Cost certainty – was to the risk of ex-utility (more experienced) owners – or to new owners who were smart, but less experienced developers. Here, owner/OEM consortiums were quick to collaborate to ensure cost and date certain new-builds proceeded unhindered.
- (iii) The PPA – between the owner company and grid company became the most important day-to-day, month-to-month, year-on-year contractual document to observe and apply because owners, whatever their origin, had to deliver to the precise terms and conditions of active (Megawatt (MW)) and reactive (MegaVoltAmps reactive (MVAr)) power outputs, per day/per month/per year to the grid system. Failure would be ruinous.
- (iv) Failure to achieve scheduled targeted megawatt sales – greatly affected company turnover and hence the ability to repay loans to the ‘lenders’ with their repayments schedules, and pay for fuel, manpower etc., all ruinous.
- (v) In the management of any engineering complex, smart recruitment is governed by the need to acknowledge and quantify:
- (a) Principal technologies involved.
- (b) The plant design and layout.
- (c) The degree of computerisation and automation employed throughout the plant.
- (d) Educational standards in the project country.
Training followed the path dictated by:
- (A) Principal technologies involved.
- (B) Plant design and layout.
- (C) The degree of computerisation and automation employed.
- (D) The operational regime of the plant – base-load, load following, two-shifting etc.
- (E) Educational standards of those employed in the project country.
Thus, power generation asset management very quickly evolved into a highly complex, highly technical and cutting edge commercial business serving the nation's electric power demands on a second-by-second, minute-by-minute basis. Immediacy governed all aspects of the de-regulated power market world.
GT proliferation era
GT power plant development proceeded in leaps and bounds. Both utility and independent power producers (IPPs) wanted highly efficient, large output (base-load) plants to emulate and surpass if possible, the modern large coal-fired generating plants.
Whilst Pratt & Whitney tended to stay with ‘aero-engine derivative’ plants, both Westinghouse and General Electric (GE) took GT engineering to the next level. They designed and manufactured the ‘industrial GT’ – subsequently known as the combustion turbine (CT) – wherein (as with accepted aero-engine design practise) an axial flow compressor preceded close-coupled combustion chambers which discharged at combustion chamber flame temperatures – combustion gases through very short transition pieces directly into the GT.
Designed very much with utility and bulk supplying IPPs in mind, these large output, GT generator units were also designed to run at synchronous speed, and therefore the need for elaborate and expensive gearboxes were eliminated.
Thus, the fully fledged industrial GT or combustion GT (CT) generating units having an installed capacity of around 30 and 50 MWe became the norm, possessing all the extra advantages of:
- (a) Significantly larger electrical outputs.
- (b) Without overly increasing site acreage, foundation and cooling water supply requirements.
- (c) Large outputs naturally produced very large exhaust gas volumes at very high temperatures.
- (d) This exhaust gas ‘waste heat’ could be efficiently utilised and so led to the advent of ‘combined cycle’ (GT cycle + steam turbine cycle) generating units, having greatly superior overall thermal efficiencies.
- (e) Combined cycle steam turbine condenser cooling was invariably provided by fan-cooled forced draft cooling towers. Thus, high cost, large seawater or natural draft cooling tower civil engineering construction was not needed.
- (f) Vastly shorter construction times coupled with complete modular construction followed and ‘Turnkey’ EP and construct (EPC) with cost and date certain contracts now became an industry reality.
Increased R&D programmes allowed these CTs to now burn natural gas (ideal), kerosene fuels and even heavy crude stocks (heavy crude initially ignited using start-up kerosene fuels), and thus these large combined cycle GT (CCGT) units gained acceptance worldwide.
The ever upward spiralling economic development of the oil producing Middle Eastern countries with their ‘home’ range of fuels conveniently on hand, made a ready market for chiefly American GT units in both populated and remote desert locations. Somewhat later, the European ABB company when it fully came into being, and the Siemens Company also became the European major open and combined cycle OEMs. Somewhat later again, Japanese (Mitsubishi, Toshiba, Hitachi and Kawasaki) – in some cases building under American licence – all entered the fiercely competitive and much sought after GT generator supply market. It is worthy of note the Engineering Standards organisations in these various countries all proceeded to develop their own national standards. In the USA – ASME, in Europe DIN and BS and in Japan JIS.
Great development engineering went into the very successful ‘packaging’ of both aero-derivative plants (special container style) as well as the larger CT generating units and depending on specific world location requirements, led to the installation of both ‘outdoor’ and ‘indoor’ power stations.
These quick to erect GT units were now ideally suited for base-load, co-generation and desalination (Middle East) projects singly or in group configuration and did wonders for the instrumentation, control and systems integration industries. These plants also proved extremely attractive to the manufacturing and process industries worldwide – and since the power industry was now de-regulated – these manufacturing and process industries built their own specifically packaged GT power plants – exporting surplus power onto the grid system to PPA or other named contractual terms and conditions.
Further GT development
It is also worthy of note that the hot gases from the combustion chambers (at flame temperatures) fed combustion gases directly into the power turbine and this necessitated the development of air-cooled turbine blades and vanes and the use of even greater exotic metal alloys (inconel and the like). The machine axial flow compressors supplied the cooling air, and to make the turbine blades more durable and reliable in service, special turbine blade protective coatings companies evolved.
From the initial 20–30 to 50 MW industrial GT range, engine sizes experienced quantum leaps in size to 100, 150 to 250 MW at the generator terminals. With time, engine unit sizes increased even further. With the advent of much increased fuel burns – combustion chamber designs changed to further reduce emissions, notably NO x emissions, by lowering ignition temperatures.
With increased GT unit sizes and now huge exhaust gas volume generation, heat recovery steam generator (HRSG) units designs kept pace with industry development and thermal efficiency goals. Combined cycle steam turbine inlet pressure and temperature parameters became more advanced to emulate the largest output conventional steam turbines. Eventually, HRSG designs escalated to also incorporate reheat capability. The icing on the industrial GT engine cake totally solidified:
- (g) Base-load, co-generation, desalination, high thermal efficiency, large output and combined cycle installations.
- (h) Now designed to burn eco-friendly natural gas fuel or a range of atomised liquid fuels.
- (i) Reduced acreage CCGT stations.
- (j) CCGT station steam turbines now utilised advanced main steam and reheat steam pressures and temperatures and so were the equal of the coal-fired conventional steam turbine power stations.
- (k) Large output CCGT installations possessed far superior thermal efficiencies over run-of-the-mill utility coal-fired steam turbine generating units.
- (l) Thus, if new-build considerations were on the table, CCGT seemed to be the only viable answer.
In the case of OCGT and CCGT installations, GT technology dominates and dictates asset management O&M activities. Every aspect of the power plant has to be exceedingly closely monitored and remedial action taken to prevent very costly damage and the huge loss of revenue associated with un-scheduled shut-down and loss of generation, not to mention the contractual non-delivery/non-performance contractual penalty clauses presented by hostile PPAs. GT asset managers now lived at the very sharp edge of the power supply business.
In many instances, the de-regulated utilities in many countries were annoyed at losing their national empires, and so, as owners and operators of the power grid companies, they raised the bar very high indeed and imposed contractual demands on new generators, which they, in their days of utility operation, never achieved themselves!
Nonetheless, GT unit sizes increased and in combined cycle configuration, reliability and availability (R&A) levels improved to average within the range of 93–98% to rival, and in many cases surpass, the thermal efficiency and reliability performance of the major utility coal-fired stations.
To achieve these, R&A figures meant every aspect of combined cycle power plant required to be carefully studied and exceedingly closely monitored whilst in service – with the key emphasis being on the high-temperature GT ‘gas path’ components, from combustion chambers through to the last turbine stage (usually 4 or 5 stages) and exhaust areas of the GTs into the HRSG inlet. OCGT and CCGT power plants are now almost totally operated by computerisation and automation systems within the plant.
Schematic layout ‘the packaged’ industrial GT generator unit 35 MW CCGT unit
With the further development of GTs especially directed toward combined cycle generating plants, a new heat exchanger came into being – the HRSG. These unique, horizontally configured steam generators were also subjected to very rapid and radical research and development and were designed to suit every combined cycle plant (Fig 2).
Fig 2: Schematic layout ‘the packaged’ CCGT generator unit (35 MW)
Example – schematic layout CCGT co-generation plant
Note – maximum operational and maintenance efficiency and flexibility is achieved – steam turbine or GT or HRSG units may be taken out of service for maintenance whilst leaving other plant systems fully operational (Fig 3).
Fig 3: Example – schematic layout CCGT co-generation plant
As larger output GT engines produced large blocks of power, for cost and various technical reasons, operational flexibility had to be sacrificed; CCGT units were concisely engineered and thus individual items of main plant could not be taken out of service individually.
Example – basic schematic configuration – 700 MW ‘reheat’ CCGT installation indicating HP, IP and LP steam drum inclusion and location
After studying owner/grid system requirements, a (say) 700 MW plant (Fig. 4 ) can be ‘cookie cutter’ repeated into a 1,400 MW plant. Thus, (say) a 500 configured MW CCGT unit can be repeated twice should a 1,000 MW plant be desired – or be ‘cookie cutter’ repeated three times should a 1,500 MW plant be desired.
Fig 4: Example – basic schematic configuration – 700 MW ‘reheat’ CCGT installation indicating high pressure (HP), intermediate pressure (IP) and low pressure (LP) steam drum inclusion and location
CCGT plants had thus arrived; their suitability not only appeals to utility/IPP/process industry style power generation station owners, but they can be ideally integrated into CHP, co-generation and desalination schemes with the added bonus of exporting surplus power to the grid system in their various locations throughout the world.
This CCGT asset management overview will next take a closer look at the industrial GT unit in part 2 of this overview document.