See how "carbon electricity" is transformed and upgraded

China Energy Storage Network: In order to achieve the "dual carbon" goal with high quality, the State Grid is actively building a new power system that is clean, low-carbon, safe, controllable, flexible, efficient, intelligent, friendly, open and interactive. The construction of "green electricity" is not achieved overnight. In addition to "green electricity", the new power system also includes a part of "carbon electricity" (i.e. electricity that produces carbon dioxide during the production process, mainly including electricity produced by burning fossil fuels such as coal, oil, and natural gas). "Carbon electricity" can smooth out the volatility and randomness caused by large-scale access to new energy due to its stable, reliable, flexible and controllable characteristics, ensure the consumption of new energy and the stability of the power grid, and play a "ballast stone" role for the entire power system.

So far, "carbon electricity" still plays the role of the main power source. By the end of 2021, the installed capacity of "carbon electricity" in Zhejiang power grid was 63.3 million kilowatts, accounting for 57.8% of the total installed capacity, and the annual consumption of "carbon electricity" was 303.5 billion kilowatt-hours (excluding transmission from outside the province), accounting for 55.1% of the total social electricity consumption.

How to achieve decarbonization of the power system is crucial to building a new power system. On the one hand, it is necessary to vigorously promote the replacement of "green electricity" with "carbon electricity"; on the other hand, it is necessary to actively seek innovation and upgrading of "carbon electricity", continuously reduce its carbon dioxide emissions per unit of electricity produced, improve its flexible adjustment capabilities, and promote the safe supply of the power grid.

Increase capacity and tap potential to serve as the "ballast stone" for supply guarantee

In July 2021, the total social maximum power load of Zhejiang Power Grid exceeded 100 million kilowatts, reaching a maximum of 100.22 million kilowatts, and the total social power demand maintained a high growth trend. With the proposal of the "dual carbon" goal, clean energy outside the province has gradually become "reluctant to sell", and new wind power, photovoltaic and other new energy sources are affected by the weather and have uncertainty. The transformation of the power system faces the dual pressures of supply guarantee and low carbon.

In response to the above problems, "carbon power" needs to give full play to its stable and controllable advantages and further tap into its power supply potential. Based on safety considerations, the maximum output of the "carbon power" unit is designed to have a certain margin compared to the approved rated power generation capacity. Therefore, the "carbon power" unit can be remodeled to increase its capacity, improve the turbine flow capacity and steam parameters, tap into the surplus capacity of the auxiliary machine, and break through the maximum power supply capacity of the "carbon power" unit.

To ensure the safe operation of the units, a series of tests are required for the units after capacity expansion, such as output capacity verification test, generator temperature rise test, generator phase advance test, power system stabilizer parameter setting test, etc., to comprehensively test the output capacity of the "carbon power" units after capacity expansion, the health of equipment operation, and the regulation performance of adapting to the power grid. As of the end of March 2022, 47 coal-fired units in Zhejiang Power Grid have completed capacity expansion and efficiency improvement transformation, adding a total of 1,975 megawatts of capacity to the power grid.

Technical personnel carry out special operations to protect power grid and ensure supply in Shaoxing｜Photo by Peng Chengyuan

In addition to capacity expansion and transformation, the power supply potential of "carbon power" units can also be improved by optimizing combustion, maintenance and fault elimination strategies. In terms of combustion strategy, strengthen the operation management and fuel allocation of the units. When the load demand is peak, the units can be "well fed" and "highly produced" by allocating and burning high calorific value coal. In terms of maintenance and fault elimination strategies, according to the maintenance cycle and fault defect level of the units, combined with the grid load forecast, the unit maintenance and fault elimination plan is reasonably arranged. While ensuring the power supply, "all necessary repairs must be carried out and repairs must be done well", and the power generation potential is deeply tapped to improve the balance between power generation and consumption.

Taking Zhejiang as an example, the Zhejiang Provincial Energy Supervision Office and State Grid Zhejiang Electric Power have established a working mechanism for the supply guarantee of "carbon power" units, and launched a special action to protect the power grid and ensure supply to enhance the province's power supply capacity. Through special on-site inspections, they have helped "carbon power" units optimize combustion, maintenance and other strategies. From September to November 2021, the implementation of this action effectively tapped the power supply potential of related units, increased the power supply load by more than 1.5 million kilowatts, and ensured the power supply safety of the Zhejiang power grid.

Carbon reduction and efficiency improvement, carbon reduction in progress

"Carbon electricity" must take low carbon into account while ensuring supply, which requires monitoring and analyzing the carbon emissions of relevant units and taking targeted carbon reduction measures.

State Grid Zhejiang Electric Power has joined hands with various power generation companies to develop the "Thermal Power Unit Energy Saving and Carbon Reduction Analysis Platform" and the "Thermal Power Unit Energy Saving and Emission Reduction and Flue Gas Emission Data Platform" to carry out dynamic monitoring of the energy efficiency and carbon emissions of coal-fired power units, promote the digitalization and intelligent upgrading of carbon emission analysis, and realize dynamic analysis of carbon emission factors of coal-fired power in Zhejiang.

Click on the picture to jump to read "How many kilograms of carbon are produced for one kilowatt-hour of electricity? How many trees? He knows everything"

Improving energy utilization is one of the common measures to improve efficiency and reduce carbon emissions of "carbon power" units. Frequency conversion and heating transformation of "carbon power" units can improve energy utilization.

Frequency conversion transformation refers to installing a frequency converter on the auxiliary machine of the unit to control the speed and output, so that the auxiliary machine always runs at the highest efficiency point and saves energy. Heating transformation can provide heat energy to surrounding heat users through steam extraction heating, which can not only avoid energy loss caused by excess steam in the unit, but also replace the surrounding inefficient coal-fired small boilers for heating, improve the economy of industrial enterprises, and reduce the emission of carbon dioxide and pollutants in industrial parks.

According to relevant statistics, from 2012 to 2021, after transformation, the carbon emissions per kilowatt-hour of "carbon power" units in Zhejiang Province have dropped by 37.10 grams. Based on the province's "carbon power" power generation of 303.5 billion kilowatt-hours in 2021, carbon dioxide emissions will be reduced by 11.26 million tons a year, with significant energy-saving and carbon-reduction effects.

Participate in deep peak load regulation and create flexible new business models

With the large-scale access of new energy, the pattern and structure of energy supply and demand have changed, and the peak-to-valley difference in electricity consumption has continued to widen. In 2016, the maximum peak-to-valley difference of the Zhejiang power grid was 22.57 million kilowatts, and in 2021 the maximum peak-to-valley difference reached 34.503 million kilowatts, with an average annual growth rate of 8.9%, and the peak-to-valley difference of the power grid is facing challenges.

Due to the strong volatility, intermittency and randomness of renewable energy generation, the source-load characteristics of the power system are highly probabilistic and have diversified operating scenarios. In the context of the need to fully absorb clean energy and limited energy storage capacity, the peak load regulation of the power grid requires the deep participation of large-capacity, stable and real-time controllable electric energy, and "carbon electricity" has become the first choice.

"Carbon power" mainly achieves "up and down at any time" by carrying out flexibility transformation, exploring deep peak regulation and rapid response capabilities. When "green power" is connected to the grid in large capacity, "carbon power" reduces its output to make way for "green power"; when "green power" output is insufficient, "carbon power" exerts its full strength to ensure power supply.

The capacity expansion and transformation has raised the upper limit of how much carbon power can be generated, but in terms of how much it can be generated, there are still certain limitations on how much carbon power can be generated.

Since "carbon electricity" is produced by burning fossil fuels, if you want to reduce output, you need to reduce fuel input. In order to ensure the stability of combustion, there is a certain lower limit for reducing fuel input, just like turning off the flame of a gas stove. If you turn it down too low, the flame will easily go out.

In order to take into account both combustion stability and grid regulation requirements, State Grid Zhejiang Electric Power Research Institute innovatively proposed a method of using dynamic plus steady-state tests to comprehensively verify the unit's deep peak-shaving capability and determine the unit's minimum stable combustion output without combustion support.