COMPETITIVE CHP CONCEPTS
Can gas-fired power plants nowadays be economically viable or are these at a low ebb? Can the new commissioning of CCGTs, especially in countries like Germany undergoing Energy Transition (in German: Energiewende), be cost-effective and profitable? The answers are yes and yes, if the potential owner will foresee the flexible operation of the plant depending on the changing market demands and conditions. The Fortuna unit of Lausward is a perfect example for such a large CCGT with high efficiency and profitability despite any possible market turbulences.
Lausward Fortuna combined cycle power plant was commissioned in 2016 and at that time outlined by the highest combined cycle efficiency ever. This CCGT power plant is designed to be CHP operation compatible and supplies German city of Dusseldorf both with electricity and district heat. This reference plant is a perfect example how an exceptional competitiveness can be ensured for operation on the unpredictable power generation market.
AZG Consulting and SSS Gears were involved into this project from its early years: one of the core components of the plant - providing the actual key to flexibility and allowing this CHP plant to be as compact and efficient as possible - is the SSS Clutch which connects the Steam Turbine to the Generator.
What is Combined Heat and Power generation, or cogeneration?
This is a simultaneous generation of heat and electricity and is the most efficient way to convert fuel into energy.
CHP reduces the use of primary energy sources and subsequently contributes to minimizing the CO2 emission. There are two different system types of CHP plants (depending on the primary goal of the plant):
topping-cycle if the primary energy is used for generating electricity and waste heat is used for thermal energy supply.
bottoming-cycle, where the primary focus of the plant is the thermal energy generation, and excessive steam can be utilized for mechanical motion to generate electricity.
Flexible CCGTs are reliable generation and grid support units of highest efficiency and lowest emissions:
With its electrical power capacity of 595 MW and electrical efficiency of 61,5% (in combined cycle mode), Fortuna belongs to the most modern and most efficient power plants worldwide. It is part of Lausward power plant with total three units owned and operated by municipal utility Stadtwerke Dusseldorf. Fortuna unit is fired by the natural gas supplied from Norway by Statoil Company. Two other plants belonging to Lausward are Anton and Emil, commissioned 1998 and 1977 accordingly. These blocks are supportive plants only for high demand periods, as Fortuna alone is able to satisfy electricity and heat needs of the complete city of Dusseldorf.
The Lausward plant is not only powerful and efficient, it is also very environmentally friendly. Its operation reduces CO2 emission by 600000 tons per year compared to the average emission German generation capacities cause. CO2 emission level of the plant is as low as 230 g/kWh. For comparison, the combined average emission of the generating fleet operating in Germany nowadays (including approximately 30% renewable power capacity) is about 600 g/kWh. Commissioning and operation of the Lausward plant is an important step towards meeting the target of city of Dusseldorf to become climate neutral city by 2050.
CHP operation compatible CCGTs remain profitable in unpredictable market conditions and have a short investment payback period:
Merit order effect influences the chances for profitability of the CCGT plant. Currently, renewables have grid least total generation costs followed by nuclear and coal-fired power plants. Gas fired power plants generated electricity is way more expensive, but with decommissioning of nuclear and coal-fired plants the situation will change. Gas power plants will have to operate supportive to renewables and ensure the grid stability and reliable electricity and energy supply. CCGT are capable to respond to generation drops exceptionally fast and provide reliable electricity supply.
CCGT power plant investments pay off when the plant is able to operate more than 4000 operating hours per year, selling electricity to the grid. As currently due to merit order effect this is hardly possible, the plant should possess further features or be able to operate in diverse operation modes rather than the pure combined cycle. So, in Germany, a combined cycle gas turbine plant which is able to operate flexibly in CHP mode can opt for 40% total operating time than without, substantially accelerating the investment payback period.
Why to employ CCGTs nowadays? Can those operate in CHP mode generate different revenue streams and respond to the changing market conditions? What makes CCGT CHP plant Fortuna Lausward so competitive?
Renewables as of today cannot produce electricity consistently to meet 100% needs of users. There are also massive gaps in accumulating technologies, so the excess electricity produced cannot be stored easily and efficiently enough. Renewables require supportive energy sources capable to quickly satisfy demand whenever the renewables are not generating enough power, or any grid support is required. The most responsive, reliable, safe and environmentally compatible solution are thus the gas turbine fired plants.
The efficiency of the gas turbines in the simple cycle is around 33% which is relatively low. CCGT plants use waste heat from gas turbine exhaust to produce steam for more electricity generation. Currently, an efficiency of up to 65% is theoretically achievable for the gas fired plant operating in combined cycle mode.
If a CCGT plant is able to operate in CHP mode, i.e. produce heat in addition to electricity generation for further supply either to district heat grid or for industrial steam consumers (or both), the total fuel utilization rate of the plant increases substantially.
Lausward Fortuna unit has 85% fuel efficiency outbeating the benchmark of CCGT and comparable CHP plants. In addition to the ability of supplying total 603,8 MW electricity to the local electrical grid, the plant can produce up to 300 MW thermal energy (heat). The steam for heating purposes can be extracted from the steam turbine at three pressure stages: through two steam extractions on the LP ST and one of the IP ST.
A distinctive feature of Lausward Fortuna unit is the heat storage. Fortuna’s hot water accumulator is able to store extracted heat in form of hot water: it can accommodate up to 36000 m3 water at 95°C, which equates to approximately 1340 MWth of stored heat energy. The total district heating capacity of the city of Dusseldorf is 855 MWth, which means the heat accumulator is able to supply the city with thermal energy for up to several days. This technical feature of the heat accumulator allowed Fortuna to break the world record of largest heat volume input capacity into the district heat network.
With the concept of additional heat accumulator tower as at Lausward CCGT plant it is possible to achieve high CCGT plant efficiency and high flexibility simultaneously. If a plant owner will apply this concept at CCGT plants in conjunction with CHP, it can trim those thermal efficiency to up to nearly 95%.
In case of a blackout the plant Lausward is able to supply electricity to the city of Dusseldorf independently. It can be online from zero to full generator power within 40 minutes with hot start or 116 minutes after cold start.
What are the major components of this highly efficient CHP CCGT unit?
Major components of the Fortuna CCGT plant are Siemens’ SGT5-8000H gas turbine, SGen5-3000W generator, SST5-5000 Steam turbine, equipped with the main 360T SSS Clutch, and HRSG 3P-RH Benson, manufactured by Siemens.
The flexibility and efficient operation of CCGT CHP plant is achievable with SSS synchronous Clutch operation. The SSS Clutch enables quick start of the plant and initial independent electricity generation by gas turbine only. Once the required HRSG steam parameters are stable, the steam turbine starts and reaches the speed of generator, driven by the gas turbine, the SSS synchronizing clutch automatically engages and connects the ST to the generator, allowing the plant to operate at full load. SSS Clutch at Lausward plant transmits 200 MW at 3000 rpm. In the same manner the SSS overrunning clutch allows the independent shutdown of the steam turbine. As a result, SSS Clutch increases the single shaft CCGT unit efficiency in simple cycle operation by up to 10% as it enables avoiding the otherwise occurring cooling losses of the ST not disconnected from the generator.
Own efficiency of this SSS Clutch is 99,9% and thus is comparable to the solid shaft efficiency. Therefore, the employment of the clutch at the plant does not cause any considerable efficiency losses, but substantially increases the plant efficiency overall, enabling operating modes which would be otherwise impossible or uneconomical. This flexibility in operation modes contributes to the superior plant concept – as flexibility is the key factor to withstand market and political turbulences.
What other remarkable results are possible with the flexible CHP CCGT plant with the SSS Clutch?
With plant Fortuna Stadtwerke Düsseldorf has increased the total power generated for meeting the electrical power and heat demand of the city of Düsseldorf. The plant is located in the Harbor of Düsseldorf and uses the water from the Rhine River for cooling purposes. Despite the increased generation capacity, the required cooling water volume didn’t increase at site: the combined heat and power operation employing heat accumulator allows to keep the cooling water demand at the level as before, or even decrease it. Constant water temperature monitoring of Rhine River confirmed that the plant operation did not cause any river water temperature increase.
City of Dusseldorf plans connecting other heat suppliers to their network to consequently store heat in the same hot water accumulator. So, Airport of Dusseldorf and chemical market giant Henkel can store their excessively produced heat in the same accumulator. Additionally, Stadtwerke Düsseldorf will store heat extracted from its’ own waste incineration plant, whenever this heat is not demanded by the district heat system.
Plant Fortuna will not require an extensive servicing. In fact, employment of the SSS Clutch will allow faster servicing times with consequential service expenses decrease. SSS synchronous Clutch itself does not need expensive regular service and is designed to last the lifetime of the plant or exceed it. It is safe and reliable and has a proven MTBF of over 270000 hours.
Altogether, this reference is a perfect example of an extremely competitive and efficient CHP concept which should be considered by the plants owners and investors to ensure long-term profitability of their fossil utility.