Comparative Analysis of Environmental Emissions from Combustion of Different Fuel Types

Introduction

Every time an industrial facility, power plant, or boiler house operates, products of fuel combustion enter the atmosphere. The choice of fuel type is not only a matter of economic efficiency but also a fundamental decision that determines the quality of the air we breathe, the state of soil and water bodies, and ultimately the health of the population.

The difference in the composition and volume of emissions from burning various fuel types is enormous. Switching from gas to coal or fuel oil leads not just to a proportional increase in pollution but to a qualitative change in its composition — fundamentally different and far more hazardous substances begin to enter the atmosphere.

In this article, we will conduct a comparative analysis of emissions generated by burning natural gas, fuel oil, and coal, with a focus on the situation in Russia and the countries of Central Asia.

Natural Gas: The Cleanest of Hydrocarbons

Natural gas is rightfully considered the most environmentally friendly among all fossil fuels. Its main component — methane (CH₄) — upon complete combustion forms predominantly carbon dioxide and water vapor.

The key advantage of natural gas is the almost complete absence of sulfur, heavy metals, and mineral impurities in its composition. Precisely for this reason, its combustion does not produce sulfur oxides or fly ash — some of the most hazardous pollutants characteristic of coal and fuel oil. The main harmful components of gas combustion products are carbon oxides (CO) and nitrogen oxides (NO and NO₂), however their concentrations are significantly lower than when using other fuel types.

In Central Asia, Turkmenistan stands out among the regional countries for using natural gas to generate electricity, which substantially reduces the environmental burden. Russia is also actively expanding the gasification of industry and the energy sector, striving to reduce the share of dirtier fuel types.

Fuel Oil: The Heavy Legacy of Petroleum Refining

Fuel oil is traditionally used as a backup or primary fuel at many thermal power plants and industrial boiler houses. Its environmental characteristics are considerably worse than those of natural gas.

The combustion products of fuel oil contain a whole spectrum of harmful substances: nitrogen oxides, sulfur dioxide and sulfur trioxide (SO₂ and SO₃), vanadium compounds, carbon monoxide, as well as a significant amount of soot and black carbon. The mass fraction of sulfur in residual fuel oil is about 1.2%, which upon combustion leads to the formation of substantial volumes of sulfur dioxide — the main culprit of acid rain.

Vanadium compounds, characteristic precisely of fuel oil, pose a particular hazard. This heavy metal, accumulating in the environment, exerts toxic effects on living organisms.

In Uzbekistan, over the past two years, the use of fuel oil has increased almost fivefold, especially in centralized heating during the autumn-winter period, directly contributing to deteriorating air quality in cities.

Coal: The Dirtiest Fuel Type

Coal is the undisputed leader in terms of emission volume and toxicity among all fossil fuels. Coal contains various non-combustible mineral impurities that cause a high concentration of fly ash in combustion products. The sulfur content in coals can reach several percent, and ash content up to 50% depending on the deposit.

Burning coal releases into the atmosphere nitrogen oxides, sulfur dioxide, carbon monoxide, polycyclic aromatic hydrocarbons, heavy metals, and particulate matter of various compositions and sizes. Toxic trace elements and radionuclides contained in coal ash also pose the greatest danger.

In Kazakhstan, about 75% of electricity is generated by burning coal, mainly at 37 thermal power plants operating on domestic fuel from the Ekibastuz, Karaganda, and other coal basins. In the Central Asian region, coal accounts for 45% of electricity production.

Over the past decade, the share of coal-fired electricity generation in Central Asia has doubled. According to Global Energy Monitor data, plans to launch new coal-fired capacity in Kazakhstan, Kyrgyzstan, Uzbekistan, and Tajikistan have been increased to 8.1 GW, compared to 3.9 GW in 2013. At the same time, no Central Asian state intends to phase out coal-fired electricity production, and most of them lack a plan to achieve carbon neutrality.

In Uzbekistan, coal consumption grew from 3.9 million tons in 2019 to 11 million tons in 2023. This growth is directly linked to industrialization, the construction boom, and increased use of coal for heating greenhouses and residential buildings.

Application of Fuel in Various Industries: Beyond Boiler Houses

The problem of emissions is relevant not only for the energy sector but also for many other industries where fuel is used in technological processes.

The Cement Industry is one of the largest fuel consumers and a significant source of emissions. In Kazakhstan, for instance, cement plants are among the largest polluters. Semipalatinsk Cement Plant LLP is one of the major enterprises polluting the environment in the city of Semey. Gezhouba Shieli Cement LLP is included in the list of 50 companies in Kazakhstan with the highest harmful emissions.

During clinker firing in rotary kilns, dust, nitrogen oxides, sulfur dioxide, carbon monoxide, and heavy metal compounds are emitted into the atmosphere. Kazakhstan has approved a special methodology for calculating pollutant emissions from cement production enterprises, which accounts for various groups of fuel-consuming units — rotary kilns, drying drums, and other equipment.

Switching cement kilns from coal to gas can radically reduce ash and sulfur oxide emissions, but requires substantial capital investment. In Uzbekistan, from May 2025, it is planned to ban the combustion of any type of coal in the cities of Tashkent, Nukus, and regional centers without high-efficiency dust and gas purification systems.

Metallurgy is also a major fuel consumer, where the choice between gas, fuel oil, and coal determines not only economics but also the environmental burden on the region.

Comparative Analysis: How Much "Dirty" Fuel Increases Emissions

Switching from gas to coal increases sulfur dioxide emissions by hundreds and even thousands of times. It is SO₂ that is the main culprit of acid rain, which acidifies soil and water bodies. Emissions of particulate matter from coal combustion exceed those from gas by orders of magnitude — these particles penetrate deep into human lungs and can cause serious respiratory and cardiovascular diseases.

Total pollutant emissions generated by burning fuel oil and coal can be dozens of times higher than emissions from burning natural gas. Even for CO₂, the main greenhouse gas, coal is significantly worse than gas.

According to 2023 data, Kazakhstan is the second-largest emitter in the EAEU region after Russia, with emissions of 320.4 million tons of CO₂ equivalent. Uzbekistan also has a significant indicator — 214.5 million tons. These figures reflect the high dependence of both countries' energy and industrial sectors on coal.

Specifics of Monitoring Instruments: Why One Gas Analyzer Cannot Be Used for Different Fuels

It is critically important to understand: monitoring instruments for emissions are selected strictly individually according to the type of fuel burned. A universal gas analyzer that works equally well on gas and coal does not exist.

The "lightest" fuel types are natural gas and diesel fuel. Almost any model of gas analyzer can be selected for them, including the most inexpensive ones. If the fuel is fuel oil, the flue gases contain sulfur dioxide (SO₂), which detrimentally affects the performance of the carbon monoxide (CO) sensor. Therefore, for fuel oil installations, instruments with CO sensors protected against NOₓ and SO₂ must be used.

The "heaviest" fuel type is coal (black or brown). For coal-fired installations, gas analytical systems are required that have reliable protection not only against SO₂ but also against dust. Coal dust quickly renders ordinary sensors inoperable, so equipment for coal-fired thermal power plants and boiler houses must be specially adapted.

Operation of gas analyzers at thermal power plants burning natural gas, coal, and fuel oil has demonstrated their high sensitivity, reliability, and ease of maintenance, provided the correct model is selected for the specific fuel type.

In Kazakhstan, a number of large enterprises are implementing automated emission monitoring systems. For example, such systems are planned to be installed at the Semipalatinsk Cement Plant, the Municipal Enterprise "Teplokommunenergo," and other facilities, with information provided online.

Impact on Public Health

Mass emissions of nitrogen, sulfur, and carbon oxides primarily affect the respiratory system, causing the onset and exacerbation of respiratory diseases. Heavy metals and trace elements contained in emissions can accumulate in various human organs and also concentrate in soils and agricultural plants, entering the human body through food products.

Polycyclic aromatic hydrocarbons, which possess potent carcinogenic effects, pose a particular danger. They are formed during incomplete combustion of all fuel types, but their concentration is especially high when burning coal and fuel oil.

In Uzbekistan, air pollution has already led to serious public health consequences. In Tashkent, mortality caused by exposure to fine particulate matter PM2.5 reaches over 3,000 cases of premature death per year, and the economic damage to health is estimated at 488.4 million US dollars, equivalent to 0.7% of the country's GDP. As a result of pollution, the population suffers from various chronic diseases, including asthma, allergies, and chronic bronchitis.

In Kazakhstan, where many thermal power plants are located directly within city limits, air pollution from coal combustion products is one of the key factors in the growth of chronic and oncological diseases. For instance, emissions from coal-fired boiler houses account for over 41% of the total emissions from stationary sources in the city of Semey.

Measures to Reduce Emissions

To reduce harmful emissions from fuel combustion, a set of technological and organizational solutions is employed. An essential element of any modern boiler house or process furnace is ash collectors, which must ensure a high degree of flue gas purification.

However, cleaning combustion products from nitrogen and sulfur oxides is technically complex and in most cases economically unfeasible. The only truly effective solution remains switching to more environmentally friendly fuel types, primarily natural gas.

Kazakhstan is developing domestic systems for comprehensive gas purification based on catalytic neutralizers of toxic emission components, which allow the removal of both particulate matter and harmful gases. At the same time, a complete phase-out of coal in the country would require colossal investments and in many cases is technically and economically difficult due to logistical and infrastructural constraints.

Uzbekistan is taking measures to relocate industrial enterprises outside city limits. From May 2025, it is planned to ban the implementation of new projects in Tashkent, Nukus, and regional centers in such areas as cement production, ferrous and non-ferrous metallurgy, as well as coal combustion without high-efficiency purification systems.

Russia has standards for maximum allowable concentrations of harmful substances, compliance with which allows maintaining emissions at relatively safe levels. However, the problem of outdated equipment and the need for large-scale industrial modernization remains pressing.

Conclusion

The conducted analysis clearly demonstrates that the choice of fuel type is a key factor determining the environmental burden and public health impact. The difference in emissions between the cleanest (natural gas) and the dirtiest (coal) fuel types is measured not in percentages but in orders of magnitude.

The situation in Russia and the countries of Central Asia has both common features and significant differences. Russia possesses substantial natural gas reserves and is actively implementing gasification programs, creating prerequisites for a gradual reduction in the share of coal in the energy balance. Meanwhile, the countries of Central Asia — Kazakhstan, Uzbekistan, Kyrgyzstan, and Tajikistan — continue to increase coal use, exacerbating the already complex environmental situation in the region.

Kazakhstan, being the second-largest emitter in the EAEU, faces the need to modernize 37 coal-fired thermal power plants, many of which are located within city limits. Uzbekistan is undergoing a period of rapid industrialization, accompanied by an almost threefold increase in coal consumption over four years and a fivefold increase in fuel oil use.

Natural gas demonstrates the best environmental characteristics: minimal emissions of particulate matter and sulfur oxides, relatively low CO₂ and NOₓ emissions. Fuel oil, despite its higher calorific value, is a source of significant sulfur oxide and vanadium emissions. Coal remains the absolute leader in all types of harmful emissions.

Special attention should be paid to the fact that each fuel type requires an individual approach to organizing emission monitoring. A gas analyzer that works perfectly at a gas-fired boiler house can fail within a few days when used at a coal-fired thermal power plant due to exposure to SO₂ and dust. Proper selection of measurement equipment is key to reliable environmental control.

In the context of global climate change and deteriorating air quality in industrial regions, a strategy of gradual phase-out of coal and fuel oil in favor of natural gas and renewable energy sources becomes not just environmentally sound but vitally necessary for the entire region.