Supercritical Coal Plants: Air Pollution Reduction Examined

Lauri Myllyvirta of Greenpeace East Asia has argued that the coal industry and some power utilities have exaggerated the benefits of ultra-supercritical power plants. Myllyvirta claims that the choice of ultra-supercritical technology for a power plant will not substantially mitigate air pollution and carbon dioxide emissions. Instead, the type of steam cycle used has no impact on the emissions per tonne of coal burned.

However, ultra-supercritical plants are more profitable than subcritical plants as they have lower fuel and other operating costs.

The type of steam cycle used has no impact on emissions per tonne of coal burned

The type of steam cycle used in a coal-fired power plant has no impact on emissions per tonne of coal burned. This means that the emissions per tonne of coal are the same regardless of whether the plant uses subcritical, supercritical, or ultra-supercritical power generation technology.

For example, let's consider sulphur dioxide (SO2) emissions. The amount of SO2 emitted per tonne of coal depends entirely on the amount of sulphur present in the coal. When coal is burned, the sulphur combines with oxygen to form SO2. For instance, consider a type of coal that contains 0.5% sulphur. This means that for every tonne of coal burned, there will be 5 kilograms of sulphur, which will turn into 10 kilograms of SO2. This is because each sulphur atom combines with two oxygen atoms to form an SO2 molecule, which is twice as heavy as a sulphur atom.

The only difference between different steam cycles in terms of emissions is the amount of power they can generate from one tonne of coal. A new subcritical plant typically has a thermal efficiency of 38%, meaning that 38% of the thermal energy in the fuel is converted into electrical energy. Supercritical plants may have an efficiency of around 42%, while ultra-supercritical plants can achieve up to 44% efficiency, with designs reaching 47% efficiency in development.

Therefore, a 1000-megawatt subcritical coal-fired plant will need to burn coal at a thermal input rate of 2630 MW-thermal to generate its full output, resulting in 410 tonnes of coal burned per hour and 4100 kg/h of SO2 in the raw flue gas. On the other hand, an ultra-supercritical plant with the same output will require a thermal input of 2270 MW-thermal, burning 350 tonnes of coal per hour, which is 14% less than the subcritical plant, and producing 14% less SO2.

However, it is important to note that the type of steam cycle used can impact the capacity and cost of SO2 control devices. The ultra-supercritical plant emits 14% less flue gas overall, which means that the capacity of the SO2 control device can be reduced by 14%, resulting in lower investment and operating costs.

In summary, while the type of steam cycle does not directly affect emissions per tonne of coal burned, it can influence the overall emissions by reducing the amount of coal burned and the capacity and cost of emissions control technology.

Ultra-supercritical plants are more profitable than subcritical plants

Ultra-supercritical plants are more efficient than subcritical plants. A typical new subcritical plant has a thermal efficiency of 38%, meaning that 38% of the thermal energy contained in the fuel is converted into electrical energy fed into the grid. In contrast, a typical ultra-supercritical plant will achieve around 44% efficiency. This increased efficiency results in lower fuel costs for ultra-supercritical plants.

In addition to lower fuel costs, ultra-supercritical plants also have lower operating costs. This is because they emit less flue gas than subcritical plants, which results in savings on investment and operating costs for SO2 control devices. The same logic applies to emissions of other pollutants such as NOx, particulate matter, mercury, and other heavy metals. Therefore, the air quality and health impacts of ultra-supercritical plants are lower than those of subcritical plants.

While ultra-supercritical plants offer some benefits in terms of efficiency and emissions, it is important to note that the type of steam cycle used has no impact on the emissions per tonne of coal burned. The emissions per tonne of coal depend solely on the amount of sulphur contained in the coal. Therefore, stringent emissions regulations are more effective in reducing air pollution than the choice of ultra-supercritical technology for a power plant.

Ultra-supercritical plants achieve around 44% thermal efficiency

Lauri Myllyvirta of Greenpeace East Asia has written about the difference between subcritical, supercritical, and ultra-supercritical power generation technology. The most important thing to know is that the type of steam cycle used has no impact on the emissions per tonne of coal burned. The only difference between different steam cycles in terms of emissions is how much power they can generate from one tonne of coal.

A typical new subcritical plant will have a thermal efficiency of 38%, meaning that 38% of the thermal energy contained in the fuel is converted into electrical energy fed into the grid. A supercritical plant will have an efficiency of around 42% and a typical ultra-supercritical plant will achieve around 44% (designs going up to 47% are being developed).

This means that a 1000 MW coal-fired plant using subcritical technology will need to burn coal at a thermal input rate of 2630 MW to generate its full output. If the plant uses ultra-supercritical technology, it needs a thermal input of 2270 MW. As a result, it burns 350 tonnes of coal per hour, or 14% less than the subcritical plant and generates 14% less sulphur dioxide (SO2).

The difference between subcritical and ultra-supercritical technology is that the total amount of flue gas emitted from the ultra-supercritical plant is about 14% smaller. Hence, the capacity of the SO2 control device can be about 14% lower, resulting in savings in investment and operating costs. Resulting SO2 emissions associated with a given emission standard will also be about 14% lower.

The same logic applies to the emissions of nitrogen oxides (NOx), particulate matter (PM), mercury, and other heavy metals. The air quality and health impacts are directly proportional to emissions.

Therefore, while ultra-supercritical plants achieve around 44% thermal efficiency, whether a plant is ultra-supercritical matters little in terms of reducing air pollution. Emissions regulation matters a lot more.

Ultra-supercritical plants burn 14% less coal than subcritical plants

Ultra-supercritical coal plants represent a significant advancement in coal-fired power generation technology, offering improved efficiency and reduced environmental impact. One of the key advantages of ultra-supercritical plants is their ability to burn coal more efficiently, resulting in a notable reduction in coal consumption compared to subcritical plants.

Ultra-supercritical plants operate at significantly higher temperatures and pressures than their subcritical counterparts, allowing them to extract more energy from the same amount of coal. This increased efficiency directly translates to a decrease in coal consumption. Specifically, ultra-supercritical plants burn approximately 14% less coal to generate the same amount of electricity as subcritical plants.

This reduction in coal consumption has a direct and positive impact on reducing air pollution. Coal combustion is a major source of atmospheric emissions, including carbon dioxide, sulfur dioxide, nitrogen oxides, and particulate matter. By burning less coal, ultra-supercritical plants emit lower levels of these pollutants, contributing to improved air quality and reduced environmental impact.

The reduced coal consumption in ultra-supercritical plants also offers economic benefits. With lower fuel requirements, power plant operators can achieve significant cost savings, which can be passed on to consumers in the form of lower electricity prices or reinvested into further efficiency improvements and emissions reduction technologies.

In summary, the enhanced efficiency of ultra-supercritical coal plants, burning 14% less coal than subcritical plants, drives a substantial decrease in air pollution. This technology plays a pivotal role in mitigating the environmental footprint of coal-fired power generation, underscoring the ongoing pursuit of more sustainable energy solutions.

Ultra-supercritical plants emit 14% less SO2 than subcritical plants

Ultra-supercritical (USC) coal power plants represent a significant advancement in coal-based power generation technology, offering improved efficiency and reduced environmental impact. One of the key advantages of USC plants is their ability to substantially reduce air pollution compared to conventional subcritical plants.

When examining the emissions of USC plants, a notable improvement is observed in the reduction of sulphur dioxide (SO2) emissions. According to research and industry reports, USC plants emit approximately 14% less SO2 than subcritical plants. This reduction is a direct result of the higher efficiency and advanced technologies utilised in USC plants.

The lower SO2 emissions of USC plants can be attributed to several factors. Firstly, USC plants operate at significantly higher temperatures and pressures than subcritical plants, leading to improved thermal efficiency. This increased efficiency directly contributes to a reduction in fuel consumption

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