Forward View
in supply. Again, combined-cycle power plants are particularly suited to this.
Versatile operating response One of the primary motives for increasing the share
of renewable power is the desire to minimise the CO2 emissions associated with generating electric power from fossil fuels. Te power plants intended to provide the standby power need to be based on a technology that emits as low CO2
emissions as possible. In this
context, nuclear power plants are prime candidates as they emit almost no CO2
at all. But since the
catastrophe in Fukushima, public opinion in many countries, especially Germany, has turned against this form of power generation. Aside from the associated risks, power production in nuclear power plants cannot be readily ramped up and down. As a result, they are not suitable as standby power plants for backing up renewables. When comparing other types of fossil power plants, combined-cycle facilities appear to offer the best solution. Not only is the 60 per cent efficiency of combined-cycle power plants far superior to the 47 per cent efficiency achievable by modern steam power plants, but the ratio of carbon to hydrogen in natural gas fuel is much better than in coal. As a result, a modern combined-cycle power plant emits more steam but significantly less CO2
than a steam power
plant of the same rating. Fossil power plants with a highly versatile operating
response are the key to integrating renewables into the power grid and an essential prerequisite for the intended rapid growth of these energy resources. An analysis conducted in Germany of the forecast feed-in and consumption for the year 2020 found that combined- cycle power plants will in future be operated across the entire load range and not only, as in the past, limited to just a few operating points (full load, peak load, etc). Tis makes it essential to design the plants for the widest possible duty range. In particular, the plants should be able to operate at the lowest output possible.
Start-up reliability In the context of stabilisation of the grid, the aim is to respond to changes in demand as quickly as possible. Power plants with short start-up times can feed extra power into the grid at short notice. It is already apparent in some power generation markets that load dispatchers are giving preference to power plants with short start-up times. Playing the spot market (tertiary reserve) is particularly attractive for power plant operators as the grid pays high prices for last minute power. Players on this market have to guarantee that
they are able to provide the offered power within 15 minutes of it being requested. Shorter start-up times also reduce the amount of fuel consumed during
the start-up event, so that shortening the start-up sequence helps improve the start-up efficiency. Tis results directly in significant savings in fuel and possibly CO2
Start-up reliability of 100 per cent is desirable for plants that operate mainly on a start/stop basis to be sure that they can be put online as soon as there is a demand for power that cannot be met from renewable sources. With this level of reliability, the remaining risk of unsuccessful start- up can be handled by appropriate fleet management.
Economically superior Combined-cycle power plants are going to play a major role in the future as a load reserve in the power generation market. While high efficiency continues to be important as a means of achieving targets on reducing CO2
emissions for the power plant operator.
emissions, full-
load efficiency will not remain the only assessment criterion. Minimising fuel consumption during start-ups and better part-load efficiencies are becoming more and more important too. Fossil fired power plants will be called upon to meet demand peaks and to compensate for output reductions and non-availability of the rapidly growing installed capacity based on renewable energy sources. Forecasts indicate a mid-term power generation market scenario for Germany in which renewables will account for an average of 30 per cent of all power generated. Tere will be phases during which renewables can meet the entire power demand, while in other phases back-up power generation by fossil power plants will be necessary. Te situation is complicated by the fact that the different phases frequently give way to each other within a short time period and the transitions are not entirely predictable. Under these conditions, a smaller number of
fossil power plants will have to cope with ever steeper load ramps. If a power plant is seen as a system to be optimised as a whole, there are solutions for meeting the future challenges of the power generation market. Modern combined-cycle power plants are particularly suitable for this, and show that the versatility required for the market of the future is already available. An optimised duty cycle with (overnight) shutdowns and rapid start-ups coupled with high start-up reliability and avoidance of excessive service life expenditure of the components is the economically and ecologically superior solution, compared with running plants continuously in parked load mode. ●
Andreas Pickard is Head of Product Line Marketing with Siemens AG Energy and winner of POWER-GEN Europe 2012 Best Paper Awards. He is based in Munich, Germany.
www.energy.siemens.com
www.engineerlive.com 9
“One of the most important questions is how this integration of renewable energy into the European power generation market is going to develop and how this will influence the design and construction of new power plants…”
Andreas Pickard, Siemens AG Energy
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