What is a gas turbine?

The operating principle of a gas turbine is based on the continuous flow of air and combustion gases through successive components of the machine. The main components are the compressor, combustion chamber, and turbine.

The process begins with the intake of atmospheric air through either an axial or centrifugal compressor. The air is compressed to a pressure ranging from several to several dozen bars. In modern industrial units, the compression ratio typically ranges from 10:1 to more than 30:1.

The compressed air is then directed into the combustion chamber, where it is mixed with fuel. As combustion takes place, the temperature of the gases rises to approximately 1,000–1,500°C, and in the most advanced designs, it can reach up to 1,600°C.

The resulting hot gases are directed onto the turbine blades. During expansion, they release their kinetic and thermal energy, causing the rotor to rotate. Part of the generated power drives the air compressor that forms part of the gas turbine, while the remaining energy can be used to drive an electrical generator, process compressors, or other industrial equipment.

A characteristic feature of gas turbines is the very high temperature of the exhaust gases leaving the turbine. This temperature typically ranges from 400 to 600°C, creating excellent conditions for thermal energy recovery.

The most commonly used fuel is high-methane natural gas. This is due to its availability, high calorific value, and relatively low emissions compared with solid fuels or fuel oils. Depending on the design and configuration of the combustion system, gas turbines can also be fueled by:

• LNG natural gas
• LPG,
• biogas,
• landfill gas,
• coke oven gas,
• blast furnace gas,
• synthesis gas (syngas),
• hydrogen or natural gas–hydrogen blends.

Solutions enabling hydrogen co-firing are also being developed. Many manufacturers currently declare that their turbines can operate on fuel mixtures containing anywhere from 20% to 100% hydrogen, supporting the ongoing decarbonization of industry.

One of the most important industrial applications of gas turbines is cogeneration, the simultaneous production of electricity and useful heat. In a conventional power plant, a significant portion of the fuel's energy is lost as waste heat. The efficiency of electricity generation alone typically ranges from 30% to 42%.

In a cogeneration system, the hot exhaust gases leaving the turbine are directed to a heat recovery steam generator (HRSG). This unit produces process steam, hot water, or another medium used in industrial processes.

As a result, energy that would otherwise be wasted in a conventional power plant can be effectively utilized. Typical performance parameters of gas turbine cogeneration systems are:

• electrical efficiency: 25–45%,
• thermal efficiency: 35–55%,
• overall efficiency: 75–90%.

For facilities with a high and stable demand for heat, cogeneration can significantly reduce energy purchasing costs while improving energy security.

The power range of gas turbines is extremely broad. The smallest microturbines used in small-scale cogeneration systems provide outputs ranging from 30 kW to approximately 500 kW. In industrial applications, the most common units have capacities between 1 MW and 50 MW. Typical power ranges include:

• microturbines: 30–500 kW,
• small industrial turbines: 1–10 MW,
• medium industrial turbines: 10–50 MW,
• large industrial and utility-scale turbines: 50–300 MW,
• the largest utility-scale turbines: over 500 MW.

In industrial facilities across Poland, units with capacities ranging from approximately 5 MW to 25 MW are particularly common, as they are well suited to the demand for both electricity and process steam.

The electrical efficiency of a gas turbine depends on numerous design and operating factors, primarily the compression ratio, turbine inlet temperature, unit size, and the technologies employed. Small industrial gas turbines typically achieve electrical efficiencies of 25–35%, while modern medium- and large-scale units can exceed 40%, most commonly reaching values between 35% and 45%. As turbine capacity increases, efficiency generally improves as well, largely due to more favorable energy loss ratios and the ability to implement more advanced cooling and combustion technologies.

The highest efficiency levels are achieved in combined-cycle systems, where the energy contained in the hot exhaust gases leaving the gas turbine is additionally used to generate steam that drives a steam turbine. As a result, the electrical efficiency of the entire power block can exceed 60%, making this technology one of the most efficient methods of generating electricity from gaseous fuels. In industrial applications, however, overall system efficiency, including process heat recovery, is equally important. In cogeneration systems utilizing gas turbines, total fuel energy utilization can reach 75–90%, significantly improving economic performance and reducing fuel consumption per unit of energy produced.

One of the greatest advantages of gas turbines is their high power density. Compared with many other technologies, they can deliver substantial power output while maintaining relatively compact dimensions. Another important benefit is their ability to start up quickly. Gas turbines can reach full load within a matter of minutes to several tens of minutes, which is particularly valuable in systems requiring flexible operation.

The key advantages include:

• high overall efficiency in cogeneration applications,
• relatively low CO₂ emissions (compared with solid fuels),
• low particulate matter and SO₂ emissions,
• high reliability,
• the ability to operate on various gaseous fuels,
• limited space requirements,
• the ability to recover significant amounts of heat from exhaust gases.

One of the most important considerations is that the economic viability of a gas turbine is strongly dependent on the price of gaseous fuel. During periods of high natural gas prices, energy production costs can increase significantly.

The main disadvantages also include:

• high capital investment cost,
• the need for fuel meeting specific quality requirements,
• reduced efficiency under partial-load operation,
• lower power output at high ambient temperature,
• demanding maintenance requirements for hot-section turbine components,
• CO₂ emissions associated with fuel combustion.

A gas turbine is one of the key technologies used in modern power generation and industry. By utilizing the energy released during gas combustion, it enables efficient electricity generation and, in cogeneration systems, the production of process heat. Typical industrial units provide capacities ranging from several to several dozen megawatts, while the overall efficiency of cogeneration installations can approach 90% when waste heat is optimally utilized. High reliability, the ability to recover heat, and relatively low emissions compared with solid fuels make gas turbines an important tool in the industrial energy transition, particularly for companies seeking to reduce energy costs and lower greenhouse gas emissions.