GT Bypass Stack 

An engineering firm has received an order for realizing a redesign of a gas turbine bypass stack. Important requirements for such a design are minimization of flow resistance and sound levels, where the stack pressure drop is an important factor in the functioning of the gas turbine. Sound levels need to meet legislative requirements.


An engineering firm was awarded a project for realizing a redesign of a gas turbine bypass stack. Important specifications for such a stack are minimal flow resistance and reduction of noise levels. For optimal functioning of the gas turbine, low downstream pressure drop is important (backpressure), sound levels need to meet legal requirements

The client has realized a basic design for meeting these demands, and Mateq Process was requested to analyze the design for flow pattern and pressure drop. Also the connection of the stack to an existing communal stack tip was analyzed, any recirculation patterns there can be a cause of noise and additional pressure drop.


From the analysis, it was concluded that the connection of the stack to the communal stack tip was suboptimal, with high probabilities of recirculating flows and hence low-frequency noise.
Figure 1 Initial basic design bypass stack
Figure 2 Design and flow pattern revised design bypass stack
Based on these results, and upon discussions with the client, a redesign was proposed using an inclined lid in the communal stack tip, to realize a smooth transition of the gas turbine stack to the communal stack tip (the original stack was out of service). This did indeed result in an optimized flow pattern out of the stack.
Figure 3 Proposed redesign of stack exhaust, with (a) original design; (b) proposed redesign, and to the bottom right the resulting flow pattern
The flow in the conversion piece directly behind the gas turbine and below the actual stack gave room to large vortices, caused by the rotating flow out of the gas turbine. This is detrimental for noise levels and overall pressure drop, and is therefore to be avoided or minimized. A simple partition in the center of the transition piece proved to be mechanically feasible and also to significantly improve overall flow patterns.
Figure 4 Flow pattern in conversion section bypass stack
Finally, upon the advice of Mateq Process, the position of the silencer in the vertical stack was optimized for pressure drop and sound level reduction. It has been placed higher in the stack, further away from the transition piece. This significantly optimized the flow into the silencer, reducing pressure drop and optimizing sound level reduction.


In this at first sight simple assignmen – ‘compute what we have engineered’ – the added value of Mateq Process was recognized in the observation of potential performance issues, and in proposing an improved solution.

The assignment was realized according these proposals and is functioning to full satisfaction of the end client.

Lg_Combustion2 green wit

Combustion2 is een joint venture van Mateq Process en SUSCOMB.
Combustion2 levert verbrandingsapparatuur voor circulaire energiesystemen.