48 exhaust systems for a 450 MW UK power plant

The challenge

A 450 MW power plant in the UK generates from a large fleet of gas engines. The plant layout called for the engines to be grouped at the stacks rather than each running to its own chimney: across the site, 47 exhaust systems each had to take two 4.5 MW gas engines into a single stack, with one further system serving a single engine: 95 engines feeding 48 exhaust systems in total.

That twin-engine arrangement is what made the project unusual. Merging two engine exhausts into one flue has to be done without one engine backing pressure onto the other, without the combined flow lifting the noise above the site limit, and without compromising the structural design of the stack that now carries the heat and weight of two engines’ worth of ducting. Every system had to hold the plant to a demanding 69 dB(A) at one metre, be CE marked, and be certified to a recognised chimney standard for the plant’s consents, all while being repeatable across 48 near-identical positions.

Our approach & engineering

Axces engineered the exhaust system as a complete run, from the engine flange, through the ducting and silencer, to the top of the stack, and designed the twin-engine merge as a deliberate part of that system rather than an afterthought at the base of the chimney. The design was then standardised so the 47 two-into-one systems are effectively identical, with the single-engine system as a controlled variant.

Twin-engine ducting

The ducting for each two-into-one system was designed so both engines can run together or independently without imposing back pressure on one another. The geometry of the merge, the duct sizing and the thermal expansion of the run were all worked through for the combined mass flow and temperature of two 4.5 MW engines sharing one flue.

Acoustic design to a 69 dB(A) target

A 69 dB(A) limit at one metre is tight for engine exhaust, and the silencer was sized for the combined flow of both engines rather than a single unit. The attenuation is distributed through the ducting and silencer so the target holds whether one or both engines are running.

Structural design to EN 13084-7

Each chimney was designed and manufactured to EN 13084-7, the European standard for the structural steelwork of steel chimneys, with the calculation accounting for the heat and the dead weight of the twin-engine ducting it carries. The complete exhaust systems are CE marked.

47 two-into-one systems engineered so paired engines don’t back-pressure each other
Silencer sized for the combined flow of two 4.5 MW engines, holding 69 dB(A) at 1 m
Chimneys designed and manufactured to EN 13084-7; systems CE marked
One standardised design across 48 positions, with the single-engine unit as a controlled variant
Complete scope from engine flange to stack tip

Scope of supply

Axces delivered the complete exhaust scope, fabricated in-house and shipped in installation-ready sections:

48 × complete exhaust systems (ducting, silencer and chimney)
Twin-engine merge ducting for 47 systems; single-engine ducting for 1
Exhaust silencers sized to the plant’s 69 dB(A) limit
Self-supporting steel chimneys designed to EN 13084-7
Thermal insulation and cladding to the ducting and exposed stack sections
CE marking and the supporting structural and acoustic documentation

Results

All forty-eight exhaust systems were fabricated to a single standardised design and delivered as matching sections, turning an unusual twin-engine stack arrangement into a repeatable, certified product across the plant.

95 gas engines routed through 48 exhaust systems: 47 twin-engine, 1 single
Exhaust noise held to 69 dB(A) at one metre across single- and twin-engine operation
Chimneys certified to EN 13084-7 and CE marked for the plant’s consents
Standardised design: one maintenance procedure and spares set across 48 stacks