Energy efficiency improvements in coal power plants can offer several environmental benefits, although it’s essential to note that coal is still a fossil fuel with inherent environmental challenges. These benefits primarily arise from the fact that increased energy efficiency reduces the amount of coal needed to generate a unit of electricity, resulting in reduced emissions and resource consumption. Here are some of the environmental and health benefits:
1. Reduced Greenhouse Gas Emissions:
The most significant environmental benefit of energy efficiency improvements in coal power plants is the reduction in GHG, particularly carbon dioxide (CO2). Burning less coal to produce the same amount of electricity means fewer CO2 emissions, helping mitigate climate change and reduce the power plant’s carbon footprint.
The EPA recognizes that the quantity of carbon dioxide (CO2) emissions produced by a coal-fired electric generating unit (EGU) or power plant is dependent on various factors, including the type of coal utilized, the overall efficiency of the power generation process, and the air pollution control systems. As an example, a conventional 300MW power plant that was improved to 2% efficiency would save 90,000 tonnes of CO2 annually. Similarly, converting a subcritical 500 MW unit in the UK to supercritical pressure. This conversion was anticipated to enhance the net generation efficiency from 38% to 44% (based on lower heating value) and was expected to result in a yearly reduction of 500,000 tonnes of CO2 emissions.
An increase in heat rate efficiency corresponds closely to a proportional decrease in emissions, especially in terms of carbon dioxide (CO2) emissions. To illustrate, a subcritical power plant may achieve a maximum efficiency of 40% (on a LHV basis), while a supercritical steam plant could potentially achieve an efficiency that is 2 percentage points higher, resulting in a 4% reduction in CO2 emissions. Advancing the technology further from supercritical to advanced ultra-supercritical Coal-Fired Power Plants (CFPP) could lead to an efficiency ranging from 46% to 48%. This, in turn, could translate to a substantial reduction of 18% to 22% in CO2 emissions per MWh generated compared to an equivalently sized subcritical Pulverized Coal (PC) unit.
In 2016, the efficiency levels in coal-fired power generation showed variation, ranging from 35% in Australia to 42% in Japan. Over the past five years, China and India, two major coal-fired power producers, have continuously improved the efficiency of their coal-fired power generation. However, many other nations have witnessed limited improvements or even declines in efficiency. France, for instance, experiences notable fluctuations in efficiency over time. Australia’s coal-fired power generation efficiency remains at the lower end, at 35.2%, ranking just below India, which stood at 37.2% in 2016, an improvement from its lowest performance of 34.7% in 2015. It’s worth mentioning that both Australia and the US excel in oil-fired power generation efficiencies, with both operating at 41%. Other coutries like India or Pakistan have room for improvement. The average efficiency of coal power plants in India, the US, and China in 2019 was 32.5%, with the best performers at 37.5%. By improving efficiency by 5%, CO2 emissions could be reduced by the same amount.
In the past, coal-fired power generation was characterized by relatively low efficiency, typically hovering in the range of 31% to 33% from 1990 to 2014. Several factors contributed to this suboptimal efficiency, including the use of unwashed coal, the high ash content found in Indian coal (ranging from 30% to 55%), and the dual-purpose utilization of coal-fired capacity for both peak load and base load power generation. However, starting from 2014, there has been a consistent improvement in the efficiency of coal-fired power generation. India, now operating at an efficiency rate of 37.2%, ranks as the third-lowest performer in this category, surpassing Australia at 35.2% and the United States at 36.7%.
2. Lower Air Pollution
Our world in data, 2019
Coal-fired power plants are widely acknowledged as significant sources of emissions, more than 30% of global emissions are produced by electricity generation. Throughout their operation, they release various air pollutants, including sulfur dioxide (SO2), nitrogen oxide (NOx), particulate matter (PM), carbon dioxide (CO2), and mercury (Hg). Furthermore, the combustion of coal results in the production of fly ash as a byproduct. These pollutants have been linked to respiratory illnesses and lung diseases. Mercury has been associated with neurological damage in humans and developmental issues in other animals. Additionally, CO2 is the predominant GHG responsible for contributing to climate change.
The combustion of coal gives rise to specific airborne pollutants such as PM2.5−10, SO2, NOx, mercury, VOCs, CO2, and other elements of interest when investigating potential air pollutants, their ecological impact, and control methods in coal-fired power plants. In particular, heavy metals like Lead, Cadmium, and Arsenic have severe consequences on local air quality and the well-being of nearby communities.
In China, coal-fired power plants stand out as major contributors to premature deaths resulting from air pollution. In the USA, regions around coal power plants experience poor ambient air quality that affects nearly 2 million people each year, with an estimated economic cost exceeding 100 billion USD annually. Researches revealed that the closure of three coal power plants near Pittsburgh led to a 9% reduction in PM2.5 levels in the area. Canadian´s findings showed that Alberta, compared to other Canadian provinces, burned more coal and had over 700 hospital emergency visits annually linked to health issues caused by hazardous air pollution from coal combustion.
In European countries, coal-fired power plants are responsible for approximately 3,000 premature deaths and around 8,000 cases of chronic lung diseases in children every year due to poor air quality.
Particulate matter with a diameter of 10 µm or less is primarily observed in coal power plants, for instance, in the form of fly ash produced during the combustion process. European coal plants emit PM10 in quantities ranging from 1030 to 6324 tonnes per year. In China, coal power plants account for 7.5% of the country’s PM2.5 emissions. PM2.5 is directly related to health issues and it is reported that a decrease of 10 µg/m3 in PM2.5 concentration would increase the life expectancy by 0.61 years. In Canada, power plants burning coal are responsible for 75% of PM10 emissions and 61% of PM2.5 emissions. Similarly, in the USA, over 92% of PM2.5 emissions originate from power plants, with 96.4% of these plants burning coal. PM2.5 is directly linked to health problems, and a reduction of 10 µg/m3 in PM2.5 concentration is reported to increase life expectancy by 0.61 years.
Major gaseous pollutants like NOx and SO2 are released into the atmosphere, where they react with water vapor and oxygen to form nitric acids and sulfuric acid, leading to the acid rain. Acid rain can be detrimental to structures, causing corrosion to buildings. Additionally, it can alter the pH of freshwater, affecting aquatic ecosystems and harming crops. Due to wind dispersal, NOx and SO2 can travel away from their source and contribute to acid rain over longer distances.
In Europe, notable contributors of SO2 emissions from coal-fired power plants include Ukraine (27%), Turkey (24%), Serbia (15%), and Bosnia (11%). As for NOx emissions, Turkey (20%), Germany (16%), Ukraine (16%), and Poland (14%) make significant contributions. In 2016, the Serbian power plant Kostolac B emitted 128,000 tonnes of SO2.
The environmental impact of coal power plants has become a central focus of scientific research. Recent studies on emissions from these plants, especially those lacking advanced control methods, have raised concerns about the regulation of various harmful pollutants, including gaseous emissions and heavy metals. It’s worth noting that older power plant infrastructure, on average, may contribute to over 800,000 premature deaths annually worldwide and is linked to numerous health problems.
Therefore, despite advancements in the latest technologies, improving air quality associated with coal power plants is crucial. Enhanced energy efficiency can result in reduced emissions of sulfur dioxide (SO2), nitrogen oxides (NOx), and particulate matter. These pollutants are responsible for issues like acid rain, smog, and a range of respiratory and cardiovascular health concerns. By burning coal more efficiently and in smaller quantities, these emissions can be minimized.
Emission control systems typically rely on sorbents to remove pollutants from flue gas, a process known as flue gas desulfurization (FGD). FGD technologies are further categorized as wet or dry. Wet FGD (WFGD) generates slurry or wet by-products, saturating the flue gas with moisture. In dry FGD (DFGD), the waste has a dry characteristic, and the flue gas is not saturated. This technique is primarily used for low to medium sulfur-based coal but can also be applied to high sulfur content coals. In the sorbent injection method, sorbents, typically in powder or slurry form (such as lime), are injected upstream of the flue gas. In the fluidized bed (FB) method, limestone is the preferred sorbent to precipitate pollutants during the coal combustion process.
The removal of particulate matter (PM) is accomplished through the utilization of Electrostatic Precipitators (ESP), fabric filters, and Wet Flue Gas Desulfurization (WFGD). It’s noteworthy that in the USA, Wet Electrostatic Precipitators (WESP) are often installed alongside ESP, baghouses, or scrubbers.
In China, common methods for controlling particulate matter in power plants involve ESP, fabric filters (FF), or a combination of ESP and WESP. Integrated particulate control systems, along with WFGD, can also result in a 70% reduction in mercury emissions. Particulate matter is typically divided into filterable particulate matter (FPM) and condensable particulate matter (CPM), both of which are significant components of the overall total particulate matter (TPM).
3. Reduced Water Consumption
Typical cooling water cell
Coal power plants typically require substantial amounts of water for cooling and other processes. Improved energy efficiency can reduce the need for water, lessening the impact on local ecosystems and conserving this valuable resource. 1% improving in energy efficiency can reduce water consumption around 1.5%
Water circulates within the system, absorbing heat from the steam used in power generation via a condenser and releasing it through evaporation in a cooling tower. Nevertheless, the process of cooling through the evaporation of a portion of the withdrawn water can still pose challenges, particularly in regions with severe water scarcity.
It’s crucial to note that the recoverable water streams constitute, at best, less than half and generally less than 30% of the total water used in a typical wet-cooled power plant. Conventional wet-cooled power plants lose a substantial portion, ranging from 60% to 90%, of their incoming water due to cooling tower evaporation or drift. Despite some research efforts, there is currently no industrial-scale technology available for capturing evaporative losses. This includes losses from cooling tower evaporation, drift, steam, and combustion turbine inlet air cooling, which cannot be easily recovered using existing technology.
There have been incremental technological enhancements in purification and treatment systems over recent decades, along with the more widespread adoption of recovery equipment like brine recovery systems. Notably, chemical treatments for cooling water have seen substantial improvements, enabling cooling towers to operate at higher cycles of concentration. While these developments can significantly reduce wastewater discharge, their impact on overall water usage is relatively modest. Although wet-cooled towers have achieved commendable reductions, air-cooled condensers, which require no makeup water for cooling towers and produce no cooling tower wastewater, offer unparalleled water savings. The water conservation achieved with wet-cooled towers doesn’t come close to the efficiency of air cooling.
Almost 95% of the water utilized for cooling in energy supply is consumed by continuous-flow cooling systems. From a commercial perspective, continuous-flow systems were considered the most efficient, which is why they became the prevailing type of cooling system used in German power plants. However, it’s important to note that this is also the most water-intensive cooling system. In this process, coolant water is drawn from a water source and used for a single cycle in the power plant’s steam process. Subsequently, the heated water is returned to the same water body. Depending on the location, cooling towers may be integrated into this process to lower the temperature of the coolant water and prevent undesirable or prohibited warming of the rivers into which the water is discharged.
4. Lower Solid Waste Production
Typical fly ash
Coal combustion produces ash and other solid wastes that need disposal. By burning less coal, power plants generate less waste, reducing the environmental impact associated with waste management. An increase of 1% of energy efficiency can reduce ash production in 3%.
Fly ash refers to fine particles resulting from the combustion of coal, which are byproducts of the breakdown of silicate minerals, sulfates, sulfides, carbonates, and oxides present in coal. The combustion of coal in power plants occurs at temperatures ranging from 1,100 to 1,500 degrees Celsius. Under these conditions, both chemical and physical transformations take place, causing the composition of the combustion ash to differ significantly from that of the original minerals.
On the other hand, bottom ash is the residue produced during the coal combustion process in power plants, characterized by larger particle sizes and greater weight than fly ash, causing it to settle at the bottom of the boiler. The chemical composition of bottom ash predominantly consists of elements such as Si, Al, Fe, Ca, Mg, S, Na, and others. Uses of Fly Ash and Bottom Ash are as raw material for cement, concrete, structural contents, soil stabilization, agriculture, and extraction of valuable elements.
Sources:
Asif, Z., Chen, Z., Wang, H., Zhu, Y. Update on air pollution control strategies for coal‑fired power plants. 2022.Clean Technologies and Environmental Policy.
Nierop, S., Humperdinck. S., International comparison of fossil power
efficiency and CO2 intensity. 2018. ECOFYS