What is an Open-Cycle Gas Turbine?

An open cycle gas turbine plant includes a combustion chamber, compressor, and turbine. The compressor compresses the air, fuel is fed to the combustion chamber, and the hot gases are expanded in the turbine. There are two pressures to consider, which are frequently stated as a pressure ratio. The continuous pressure lines on the T-S and P-V diagrams depict these pressures. Because the compressor and turbine share a shaft, some of the effort generated by the turbine is lost in the compressor’s operation.

Gas turbines were developed as technology advanced in disciplines such as internal combustion engines and steam turbines. As a result of the operations in both of these fields, gas turbines were developed in the 1940s. Between 1500 and 1870, researchers developed various models that used steam or hot gas to create motion. This article provides a comprehensive understanding of a particular type of gas turbine, namely, the open cycle gas turbine, its working principles, advantages, and applications.

The Fundamentals of an Open Cycle Gas Turbine

Open cycle gas turbines are liquid-fueled combustion turbines that generate power through a rotor generator. At roughly 5500 degrees, the remaining heat will be released into the environment. Generators and turbines are housed in sound-proof cages that measure nearly 75m by 75m per unit. The intake structure is 20 meters tall, while the exhaust stack is about 30 meters tall.

The Open Cycle Gas Turbine’s Working Principle

A compressor, a power turbine unit and a combustor are the three parts of an open cycle gas turbine. An open cycle gas turbine uses centrifugal or axial flow compressors to suck in new ambient air and compress it. The compressor compresses ambient air through a series of compressor stages. When compressed air is fed into the combustion chamber, it is mixed with the fuel. The turbine is powered by high-pressure hot gases. The mixture produces velocity gas as soon as it is ignited. The shaft attached to the rotor component of the generator rotates as the velocity gas flows through the turbine blades. The energy generated by rotating the turbine shaft can be used to power various industrial devices as well as generate electricity.

Turbine emissions are emitted into the atmosphere. The system is categorized as an open cycle since the exhaust gases are not recirculated but instead discharged into the atmosphere. Some of the turbine’s power is used to power the compressor and other machinery, while the rest is used to generate electricity. The working medium is constantly replenished since the compressor is supplied with fresh air and the turbine’s gases are vented into the atmosphere. An open cycle gas turbine facility operates on this concept.

Open Cycle Gas Turbine Applications

Small and medium industrial applications often use simple open-cycle gas turbines that run on natural gas or light fuel oil. Dual fuel setups are simple to accommodate, and automatic fuel switching between the two can be supplied in some situations.

Machines can be single-shaft or twin-shaft, with the compressor and its driving turbine on one shaft and the turbine power on the output drive shaft. Both types of alternator drives are suitable, but they have slightly different power-control characteristics. They could also be created from engines that were originally meant for aircraft or units that were specifically designed for ground usage. The former is marketed as being lighter, more compact, and more efficient, while the latter is regarded to be more robust, yet there is a large space of land between the two.

Small industrial units have an electrical-generation efficiency of 14 to 20% at full load, whereas larger machines have an efficiency of above 30%. At an ambient temperature of 15°C, the specific fuel consumption of a typical 1.25 MW set can range from 0.51 kg of gas oil per kWh at full load to 0.63 kg at half load, but increases with increasing ambient temperatures, especially on partial load. Turbine control systems can increase security and safeguard the turbines. IS200TBTCH1B, IS200TRTDH1C are some examples of turbine control system parts.

Open cycle gas turbines are often used in the following applications:

• It is the most commonly employed in aviation to provide motive power for jet propulsion.
• They can be utilized to generate electricity.
• Locomotive propulsion, marine industries, and automotive are only a few of their applications.
• Mechanical drive systems can benefit from their use.

The Benefits of an Open Cycle Gas Turbine

The advantages of open-cycle gas turbines are as follows:

• The gas turbine can be accelerated from a cold start to full load without a warm-up period after the starting motor propels the turbine to its rated speed and the fuel is ignited.
• Because of their short start times and capacity to take uploads quickly, open-cycle plants are preferred when employed as peak load plants.
• Low weight and size: The weight generated per kW is quite low.
• Closed-cycle plants take up more space than open-cycle plants.
• Any hydrocarbon fuel, from heavy diesel oils to high-octane gasoline, can be utilized in the combustion chamber.
• Component and auxiliary modifications can usually be done to increase thermal efficiency in open cycle gas turbine plants. Depending on the load factors and other operating conditions, they can also give the most cost-effective overall solution.
• There is no requirement for cooling water in open cycle gas turbines, except for those having intercoolers. As a result, the plant is self-contained and no longer requires a cooling medium.

Open Cycle Gas Turbine Disadvantages

The following are some of the drawbacks of an open cycle gas turbine:

Part-load efficiency is lower:

The efficiency of an open cycle gas turbine plant drops fast at part load because a large portion of the power generated by the turbine is required to drive the compressor.

Sensitivities:

Component efficiency, particularly that of the compressor, is critical in the system. The open cycle gas turbine is affected by changes in air temperature, pressure, and humidity.

Heat loss from exhaust gases:

Because the open cycle plant uses more air than the closed-cycle plant, there is more heat loss in the exhaust gases, necessitating the use of large diameter ducts.

Erosion:

Preventing erosion and deposition on the compressor blades and passageways requires keeping dust out of the compressor. Their reputation suffers as a result. The carbon and ash deposited on the turbine blades are unwelcome because they lower the efficiency of the open cycle gas turbine plant.

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