hi,

can some please explain what is GT inlet Pressure loss and exhaust Pressure loss? how they effect the Gas turbine performance ?

 

Inlet pressure loss is the difference in pressure between ambient air pressure and the gas turbine compressor bellmouth pressure. It is mostly pressure drop across the inlet air filters and any silencers.

Exhaust pressure loss is the difference in pressure between ambient pressure and the pressure at the gas turbine exhaust. It is mostly caused by the exhaust silencers and any heat recovery equipment.

Both inlet and exhaust pressure losses reduce performance of the gas turbine over what it would be without the equipment that causes the losses. However, you need the inlet air filtration to reduce erosion of the compressor blades and turbine buckets (which would really reduce performance), and any heat recovery equipment in the exhaust will improve overall performance. Silencers help get approval for the plant.

 

I agree with otised - but thought I'd add my 2 cents.

Inlet losses are the pressure drop across the inlet filter house (and chillers or other inlet conditioning equipment). GT performance is reduced as inlet losses increase (higher DP across the filters) because the density of the air reaching the compressor drops with absolute pressure at the compressor inlet.

Lower air density = less mass flow = less power output & lower efficiency.

The effect from exhaust losses (the DP across any equipment between the GT exhaust flange and the top of the stack) is similar; GT output and efficiency drop as more back pressure is put on the turbine section.

 

And I'll add another two cents.

Even new and clean inlet air filters represent a loss of inlet air flow and therefore inlet efficiency. If you've ever worn some kind of dust- or hospital mask over your nose and mouth you've experienced something similar. Your ability to inhale is restricted by the mask.

As the inlet air filters get dirty and wet (humidity, rain, etc.) they become even more restrictive, decreasing the inlet air flow and inlet efficiency.

As otised says, you need those filters though to reduce erosion of the compressor components so it's not good to run the unit without air filters.

The shape and configuration of the inlet air duct can also have an impact on the ability of air to flow in as unrestricted manner as possible to the axial compressor inlet (the bellmouth).

In the same way a dust- or hospital mask impedes your ability to inhale, it also has a similar effect on your ability to exhale without much effort. The exhaust system of a combustion turbine (or any internal combustion engine for that matter) is also important because if it restricts the ability of the engine to exhaust the ability to produce power is also reduced. So, the design of the exhaust system also contributes to the over-all efficiency of the engine.

Some combustion turbines have "silencers" installed in the exhaust duct, as otised says, to reduce the amount of exhaust noise (just like automobiles have mufflers). These also add to the back-pressure against the exhaust air flow and decrease the ability to produce power somewhat, but they are also a "necessary evil" like the inlet air filters.

Inlet- and exhaust pressures are typically measured using differential pressure gauges, measuring the pressure downstream of the inlet filters with respect to the ambient pressure outside of the inlet duct. And exhaust duct pressure is also measured with respect to ambient pressure outside the exhaust duct. In both cases, the higher the differential, the lower the performance, efficiency, and output of the machine.

 

I work for a large air filtration company and have a few additional points and a question.

The efficiency lost due to pressure drop is minimal compared to the first signs of erosion of gt blades. This is why many gt oem's are now using hepa filtration. There is a higher dp associated, but the additional protection and time offered between gt washes more than outweighs the increased price and dp.

The duct shape on inlet and exhausts is critical. The more bends and transitions the higher the pressure drop. Silencer baffles also increase pressure drop by restricting the airflow. These can be carefully designed to reduce noise in particular octave bands. They are also normally profiled to minimise the effect on airflow. Turning vanes can also be included in the duct work to reduce the effect of bends.

When considering exhaust stack losses some people claim the exit loss is zero, ie there is no pressure loss noted at the exit of the stack. Others will design an exhaust cone to reduce exit losses. Why is this? No body is convincing enough to ignore the fact that as the hot air hits the cold air that there must be an increase in back pressure. Please explain?

 

Effect of GT inlet and exhaust in the performance and output of the turbine

I will add my two cents by explaining how the loss of output actually takes place in the gas turbine with the increase in the DP. with the increase in the DP across the inlet the air flow to the compressor reduces. In a GT there is always excess air for combustion , the reduction in air flow does not reduce combustion but the air for cooling reduces which increases the temperature in the firing chamber and thus the exhaust temperature.Thus with a increased DP in the inlet FSRT (the temperature FSR) comes online sooner. As FSRT is the limiting FSR for the machine at base load, this reduced FSRT means that the machine base load value is also reduced. The back pressure in the exhaust has also a similar effect on the turbine.

 

I am an Application Engineer and i work for GT OEM.

please, can anyone tell me the ideal inlet and exhaust pressure losses for design purpose? for inlet loss i have used 4mmH20 and exhaust 150mmH2O.

 

Based on GT Performance by Fletcher & Walsh
Inlet --> 100 mm H2O at high power (typically)
Installation exhaust loss --> 100-300 mm H2O (typically).

Therefore, you have already typical value for your exhaust, but for the inlet it should be higher.

>I am an Application Engineer and i work for GT OEM.
>
>please, can anyone tell me the ideal inlet and exhaust
>pressure losses for design purpose? for inlet loss i have
>used 4mmH20 and exhaust 150mmH2O.