Gas turbines are deployed on the ground and in the air. The two use cases are very different, yet the fundamentals remain the same: a continuous combustion process generates thrust and rotary motion.

Impro is a leader in parts for the hot side of these engines. Our nozzle assemblies turn the kinetic energy of fast-moving gasses into rotary motion. We make these complex components by investment casting and precision machining. This blog looks at where they are put to work.

Directing Hot Gases

In a gas turbine combustion gasses hotter than 1,500°F move at over 1,000 fps. A circular ring of static nozzle guide vanes direct this flow onto the turbine blades. Some engines will have two or more sets of fixed and rotating nozzle vanes and blades to maximize the amount of energy extracted.

These blades are mounted on a driveshaft that takes the rotation forward to the front of the engine. Here it turns fan blades that pull air in for combustion.

Depending on the application, this rotary motion can also drive a generator or a propeller. Kinetic energy not converted into rotary motion provides thrust from the back of the engine.

Produced from Superalloy Materials

Only nickel-based superalloys have the creep and chemical resistance needed to withstand the conditions created by combustion. These materials, especially the complex cooling features they need, are difficult to machine, so Impro forms them by investment casting. As a near-net shape process this minimizes the amount of precision machining needed.

Nozzle Assembly Applications

Nozzle assemblies are used in aerospace and power generation gas turbines. Both take several forms.

Gas Turbines in Aerospace

The jet engine is a type of gas turbine. Three designs are used:

• Turbojet
• Turboprop
• Turbofan

The original jet engine was a turbojet. In this design, most of the power is used for thrust. Only a small proportion runs the compression stage.

In the turboprop, an additional shaft, driven by the nozzle assemblies, directs rotary motion to a propeller. The split between thrust and propeller power is set by the design objectives.

Most commercial aircraft operating today use turbofans. These evolved from the turbojet and use a secondary shaft and fan to increase overall efficiency by providing bypass air around the combustion section.

Power Generation Gas Turbines

For power generation, the shaft driven by the nozzle assemblies is connected to a generator. The engines used for these applications are either aeroderivative designs or what are called “heavy frame” gas turbines.

Aeroderivative gas turbines are similar to aerospace engines. They are generally compact and employ very high compression ratios. Heavy frame engines have lower compression ratios and are much larger. Heavy frame engines produce more power – 400MW or more versus 100MW – but take longer to bring up to speed.

Most power generation gas turbines run on natural gas. Variants are available that burn oil or hydrogen.

Aeroderivative engines are deployed on smaller scale power generation projects. The speed with which they can achieve full power makes them the preferred choice for emergency backup applications.

The main applications for power generation gas turbines are:

• Combined heat & power (CHP) / co-generation systems
• Grid firming
• Emergency power
• Fast power

In CHP applications, exhaust gas heat is recovered and used to make steam. These systems are often used in campus environments.

Grid firming is a situation many utility companies are experiencing as use of renewables grows. Solar and wind can fluctuate, so gas turbines provide a way of quickly generating the supplemental electricity needed.

Emergency power refers to disaster scenarios where a grid has suffered widespread damage. When this happens small aeroderivative gas turbines can be put into position quickly.

Fast power applications are those where load bridging is needed. This is where a utility is bringing a large generator online but needs additional power for a short period until full output is reached.

Casting and Precision Machining

As a leader in the manufacture of nozzle assemblies and components, Impro understands the challenging conditions in which these parts operate. Using investment casting and precision machining, we produce tightly-toleranced parts for a range of gas turbine applications. If you’re in the market for gas turbine parts, or need other precision machined components, we can help. Contact us to discuss your requirements.