Thermal Power Plants – “Necessary Nuisance” and Prime Polluters!
Thermal power plants(TPPs)generate electricity by spinning turbines using heat, eitherfrom theburning of fossil fuels or another source. Theyare categorized bythe energy source used, as follows:
- Coal-fired power plants
The World Coal Association estimated that coal-fired power plants accounted for about 37% of global electricity in 2018, with the largest number operated by China. Coal-fired power plants use steam generated from coal combustion and consequently emit a significant amount of harmful gases into the atmosphere. In a bid to reduce greenhouse gas (GHG) and other emissions, many developed nations have announced plans to phase out coal-fired power plants. The UK has set a deadline of 2025 to phase out its coal plants, while Canada and Germany are aiming for 2030 and 2038, respectively. Several other European countries are expected to follow suit soon. Despite these efforts, it is estimated that 22% of the world’s electricity will still be generated using coal-based power plants in the year 2040; they will therefore continue to be a major source of air pollution and GHG emissions for the foreseeable future. - Diesel-fired power plants
Diesel-based power plants are generally used for the small-scale production of electric power. They are installed in places where there is no easy availability of alternative power sources and are mainly used as a backup to provide uninterrupted power in case of outages. Diesel plants require only a small area to be installed and offer higher thermal efficiency compared to coal-fired power plants, but due to high fuel and maintenance costs, they have not gained widespread popularity. Nonetheless, where they are used for off-grid electricity generation or backup power for critical infrastructure, they remain major contributors to air pollution.
- Gas-fired power plants
Gas-fired power plants use natural gas—a rapidly growing energy source across the world—to generate electricity. Although it is a fossil fuel, pollutant emissions from its combustion are much lower than those from coal or oil, according to a study by the Union of Concerned Scientists. Data from the International Energy Agency shows that gas-fired power generation expanded by 3% in 2019, reaching 23% of global energy production. Combined-cycle power plants use both gas and steam turbines to produce higher amounts of electricity from a single fuel source by capturing heat from the gas turbine. This efficiency has the added benefit of releasing lower amounts of gaseous pollutants into the atmosphere.
- Geothermal Power Plants
The three main types of geothermal plants include dry steam, flash steam, and binary cycle, all of which use steam turbines to produce electricity. The installed capacity of geothermal energy has gradually increased just short of 10 GW to almost 14 GW worldwide over the past decade. Geothermal power plants are considered to be environmentally friendly and emit only a small fraction of the atmospheric pollutants and GHGs of coal-fired power plants.
- Solar Thermal Power Plants
A solar thermal plant is comprised of a system of concave mirrors placed in such a way as to concentrate the sun’s rays on a small area, thus creating heat that produces steam to power a turbine. This is an up-and-coming technology that has not yet seen the commercial application.
Conventional solar energy is one of the cleanest and most abundant renewable energy sources, with photovoltaic panels generally requiring little maintenance and lasting 20–25 years. According to the International Renewable Energy Agency, global solar power capacity will increase by 9% each year between 2018 and 2050, in which time it will grow from 480 GW to more than 8,000 GW. Initial costs involved in financing solar power plants are high, however, panel installations require a lot of physical space.
Air pollutants emitted by coal-based thermal power plants
As coal-based thermal plants produce a large proportion of the world’s electricity, they are one of its leading sources of air pollution and produce immense quantities of GHGs, most notably carbon dioxide (CO2). Out of all the gases released from a TPP, CO2 is by far the most voluminous—TPPsbased on coal and other fossil fuels are therefore one of the world’s leadingcontributors to anthropogenic climate change.
Sulphur dioxide (SO2) is not considered to be aGHG, but it is known to have indirect atmospheric effects due to its ability to scatter incoming sunlight as well as affect cloud formation and precipitation patterns. SO2 forms sulphuric acid when combined with atmospheric moisture, which then returns to earth as acid rain and impacts various ecosystems. The level of SO2 released from TPPs depends on the sulphur content of the coal that is used (on average between 0.1 and 3.5% by weight), as well as the use of pollution control strategies.TPPs are the world’s largest emitters of SO2 worldwide, largely due to ineffective or non-existent flue gas cleaning measures.
Nitrogen oxides (NOX) are another set of gases for whichTPPs are one of the biggest contributors. Much like SO2, nitrogen oxides are not GHGs but do have an indirect effect on the atmosphere. NOX is known to present visibility and respiratory issues and can also combine with other atmospheric gases and moisture to form acid rain and smog.
In addition to gaseous pollutants, coal-fired thermal plants output large amounts of particulate matter in the form of ash. This ash gets into waterways and soil wherever it falls, changing alkalinity levels and rendering soil unusable for agricultural purposes and water undrinkable. Ash, as particulate matter, can also contribute to smog and cause visibility issues.
A portion of thermal plant ash is comprised of particles less than 2.5 microns in diameter (PM2.5). These particles are hazardous to human health because they are small enough to enter the lungs and cause respiratory problems. Cities worldwide are seeing high levels of PM2.5 through frequent bouts of smog, and the problem is significantly worse in Asia where levels frequently reach up to 10–20 times the recommended daily safe limit, and over 5 times the safe limit for a limited time exposure. Compounding this problem is the fact that coal ash often contains toxic heavy metals—coal combustion is in fact one of the world’s primary sources of atmospheric mercury.
The health risks posed by TPP emissions are made more serious by the great height of the stacks used, which allow pollutants to travel as far as 40 to 50 km from the source in all directions.These high stackscreate what’s known as an “umbrella effect” whereby those working and residing very near to the plant are less exposed to gaseous pollutants due to long distance dispersion. Particulates on the other hand are subject to the“sprinkling effect”, in which the weight of the particles causes them to settle out over shorter distances. The entire area within a 50 km radius is thus subject to hazardous air pollutants, in one form or another.
How AirSENCE can help
It is now well known that air pollutants are capable of affecting large areas surrounding TPPs due to the umbrella and sprinkling effects. For this reason, they should not only be measured at plant sites,but also at several points within the potential radius of influence. Conventional air monitoring devices pose economical and operational challenges over such large areas; low-cost Micro CAAQM systems, therefore, provide the best solution as they are very economical, easy to install, and have very low maintenance requirements.
AUG Signals’ continuous ambient air quality Micro Monitoring System (caaqMMS), AirSENCE, is an ideal and cutting edge solution for all the real-time air monitoring needs of TPPs.With its small size and lightweight, AirSENCE can easily be installed at all points of interest in and around TPPs where pollutants need to be measured.
Relevant features:
- Small size (1 cubic foot) and lightweight (3 kg) – Allows easy installation virtually anywhere.
- Measures all relevant gaseous and particulate pollutants (NO, NO2, CO, O3, SO2, PM10, PM5, PM1) along with weather/environmental parameters (Temperature, humidity, pressure, wind speed &direction)
- Provides real-time continuous data for 24/7, 365 days per year.
- IoT platform allows networking and high-resolution data recording.
- Cloud-based data storage and browser-based dashboard allows access to data anywhere at anytime using any Internet enabled device (e.g., smartphone).
- Low power consumption (7W) allows solar operation.
- Weatherproof polycarbonate enclosure and IP65 graded sealing allows installation in any terrain.
- Very low maintenance provides cost effectiveness and stress-free operation.
- Completely unmanned operation allows TPP officials to monitor data from their offices rather than being onsite.
AirSENCE: the accurate and economical solution for real-time continuous air quality monitoring of thermal power plants.