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Danish power plant flexibility-Valuable experiences for China

by Laust Riemann, Special Consultant, DEA

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The Danish coal-fired power plants are among the most flexible power production units in the world. The Danish experiences show that high degree of power plant flexibility is technical possible, but requires strong economic incentives.

With an increasing penetration of fluctuating renewable energy, the operational profile of the conventional power plant fleet changes. A trend which can be observed for many power plants in Europe is the shift in the operation profile from base load to intermediate and peak-load operation. As renewable energy is being build-out in China a similar development must be expected.

Enhancement of the operational flexibility of Danish thermal power plants has been in focus for more than 20 years and the power plant fleet now operates in a market with approximately 40% renewable energy production. Power production from ‘power-only’ (condensing) plants has not happened in the last 10 years. All power production from thermal power plants is now produced on Combined Heat and Power (CHP) plants. CHP plants usually produce heat and power simultaneously in the winter – unless in time of very high or low power prices where the plants will produce respectively only power or only heat given the plants’ flexibility offers the possibility through means such as heat storage and full turbine bypass. In the same period of time a rapid increase of renewable production (mainly wind power) can be observed in figure 1.150911-1

First optimization 1995-2000
The first optimization of the coal-fired power plant operational flexibility was driven by the change of the market price when entering into the liberalised power marked. Due to the fact, that almost all power plants in Denmark are CHP plants, a decreasing power price could be observed during periods with high district heat demand and by the high rate of forced power production. In order to counteract this price development the first operational flexibility optimization was launched with the aim to improve the decoupling of simultaneous heat and power production. The decoupling was implemented using the existing heat storage capacity and the existing plant components in a different manner meaning no or little investment in new hardware was necessary.

Second optimization 2000-2010
The operational profile of the conventional power production changed towards decreasing load utilization and an interest in improved low load operation capability grew as time periods with low energy prices and thus low thermal production need increased in the period. Other typical operational flexibility enhancement measures applied was load gradient boosting and further decoupling of heat and power production. Low load operation capability was optimized and the power output now reached values as low as 10-20% of the nominal power output. Load gradient capability was improved in order to harvest higher revenues on the ancillary market. The focus on cost-efficient plant operation grew and performance monitoring systems were introduced given plant operators the possibility to optimize daily operation. Key performance indicators (KPI) were introduced in order to benchmark the performance of the power plant fleet. These optimizations was done with no to low investment in new hardware and the main costs of this optimization phase were related to optimization of the control system, combustion optimization, steam turbine cooling steam and thrust calculations – in other words mainly engineering manning costs.

Third optimization after 2010
Since 2010 the renewable energy penetration has increased reaching a current record of 39% of power consumption in 2014. This resulted into further decreased operation time for the remaining power plants even though all these plants are CHP plants. Flexibility measures implemented in the period were complete turbine bypass; electrical boilers for conversion of electrical power into heat; increasing focus on efficiency enhancement and decreasing maintenance costs. This was the first optimization step which required medium investment into new plant equipment.150911-2

So far the Danish power plants have been optimized in phases matching the required needs for flexibility during each phase. This market based approach has kept the necessary investment for each phase at the lowest possible level. The winners have been the companies who have been at the forefront of the development and adjusted their plants’ operational flexibility according to the market needs. There is good reason to believe the same overall development will be reality in China in the coming years.
The analyses are further documented in the report “Flexibility in the power system”. The report will be published in October as part of the “Boosting RE as part of China’s energy system revolution” program.