Can a 100 Metre Diesel Generator Exhaust Run Work?

A 100 metre vertical exhaust riser can drive engine backpressure above its allowable limit, overload the engine exhaust flange, and transmit vibration into the building. For three 1825 kVA diesel generators installed 7.5 metres below ground level, treat each exhaust as a complete gas path: engine outlet, flexible connection, silencer, fittings, vertical riser, termination, and supporting structure. Follow that path from the engine outward and prove each element before commissioning the next.

Where does each generator's exhaust path begin and end?

Start at the exhaust flange of each engine. Record every component through to the outdoor discharge point. The stated installation has three generator sets, but it does not define whether the exhausts remain separate or enter a common riser. Keep them separate unless the engine and exhaust-system suppliers approve a shared arrangement. A common header can expose an idle engine to pressure, condensate, and exhaust flow from a running unit.

Path element	Required field measurement or document	Acceptance check
Engine exhaust flange	Outlet size, orientation, load limit, allowable backpressure	Recorded from engine manufacturer data
Flexible section	Movement capability, temperature rating, installed alignment	No preload, twist, or pipe weight on the engine
Silencer	Pressure loss at actual exhaust flow and temperature	Loss fits within the pressure budget
Pipe and fittings	Diameter, developed length, elbows, transitions, branches	Model represents the installed route
Vertical riser	Support points, thermal growth direction, condensate drainage	Loads terminate at the structure, not the engine
Discharge	Termination geometry and obstruction exposure	Outlet does not add an uncalculated restriction

Mark each of the three paths on an isometric drawing and assign every fitting, support, drain, and instrument point to one engine. The check before proceeding is a field-verifiable route drawing with no unclassified component between each engine flange and its termination.

Which engine limits control the design?

Obtain the exhaust gas temperature, exhaust mass or volumetric flow at the required load, allowable exhaust backpressure, and exhaust-flange load limit from the engine manufacturer. The generator rating of 1825 kVA does not determine exhaust flow by itself. Electrical load, engine efficiency, combustion airflow, ambient conditions, and manufacturer rating practice all affect the gas flow.

Use values for the exact engine configuration and required operating condition. Backpressure may be expressed as pressure relative to atmosphere at a defined measurement location. Confirm the units, reference point, and load condition before using the limit. Likewise, distinguish allowable flange forces and moments from the weight capacity of a building support.

Design input	Why it matters	Source
Exhaust temperature	Sets gas density, thermal expansion, insulation duty, and component temperature class	Engine manufacturer
Exhaust flow rate	Sets velocity and friction loss	Engine manufacturer
Allowable backpressure	Defines the total pressure-loss ceiling	Engine manufacturer
Flange load limit	Controls allowable external forces and moments at the engine	Engine manufacturer
Silencer pressure loss	Consumes part of the backpressure allowance	Silencer manufacturer

The check before pipe sizing is a signed design-input sheet containing all five values, their units, and their operating conditions.

How should the backpressure budget be calculated?

Calculate pressure loss at the exhaust flow and temperature specified for the selected engine operating point. The total is the sum of straight-pipe friction, elbows, transitions, flexible connections, silencer loss, termination loss, and any other restriction:

ΔP_total = ΔP_pipe + ΣΔP_fittings + ΔP_flexible + ΔP_silencer + ΔP_termination

For a preliminary straight-pipe calculation, use the Darcy-Weisbach relationship:

ΔP_pipe = f × (L / D) × (ρv² / 2)

Here, f is the Darcy friction factor, L is developed pipe length, D is internal diameter, ρ is gas density at the evaluated condition, and v is gas velocity. Calculate velocity from actual volumetric flow at exhaust conditions, not from an unrelated standard-volume value. Include the full developed route: the stated 100 metre vertical extension plus connections between the engine room and shaft, offsets, and the discharge assembly.

Do not spend the full allowable backpressure on calculated nominal losses. Fouling, fabrication tolerances, silencer variation, and field changes consume margin. The engine limit remains the acceptance boundary; the project team must select its design margin with the engine supplier.

The check before equipment selection is a pressure-loss schedule showing every component, its operating-point loss, and the calculated total below the approved design allowance.

How should the 100 metre riser be supported and allowed to move?

Layer one first: keep pipe weight, thermal growth, and building movement away from the engine. Install a flexible connection close to each engine outlet, but do not use it as a support or as a correction for poor alignment. A flexible element must accommodate engine motion while the fixed pipework carries its own dead weight.

A 100 metre hot riser can develop substantial axial thermal movement. Calculate expansion from the selected pipe material, installed cold temperature, and maximum design temperature:

ΔL = α × L × ΔT

Use guides, anchors, sliding supports, and expansion provisions to direct that movement along the intended path. Analyze support reactions in both cold and hot states. Vertical dead load, insulation, silencer weight, condensate, wind exposure at the termination, and dynamic loading all belong in the structural load case.

Provide drainage at low points created by the actual routing. Prevent collected condensate from running toward the engine or pooling in a silencer. Locate cleanout or inspection access where deposits and drains can be serviced.

The check before insulation and enclosure is a cold alignment inspection plus a support-load review showing that the engine flange carries neither riser weight nor imposed thermal movement.

How should the silencer and termination be selected?

Select the silencer by acoustic duty, exhaust flow, gas temperature, orientation, and pressure loss. Acoustic performance alone is not enough: a highly restrictive silencer can consume a large share of the engine's backpressure budget. Obtain pressure-drop data from the silencer manufacturer at the engine's operating condition and place that value directly in the system calculation.

Account for reducers, diffusers, weather protection, screens, bends, and discharge caps as flow restrictions. Keep the final outlet clear of building surfaces or shaft features that could recirculate exhaust or create an unmodeled pressure zone. Confirm that discharge placement meets the project's ventilation, fire, structural, acoustic, and environmental requirements using the authorities and design disciplines responsible for the hotel.

For three engines, verify each path independently at its own rated operating point. If any duct or discharge feature is shared, also evaluate every permitted combination of running and stopped generators.

The check before startup is an approved equipment schedule whose silencer and termination losses match the final backpressure calculation.

How is the complete installation verified under load?

1. Inspect each route against the final isometric drawing. Confirm pipe diameter, fitting count, silencer orientation, support engagement, flexible-joint alignment, drains, and termination geometry.
2. Install a pressure measurement connection at the engine manufacturer's specified backpressure reference point. Use an instrument with a suitable range, temperature isolation arrangement, and current calibration.
3. Start one generator and progress through the approved load-test sequence. Record load, exhaust backpressure, relevant exhaust temperatures, visible support movement, vibration, leakage, and drain behavior after readings stabilize.
4. Compare measured backpressure with the engine manufacturer's limit and the design prediction. Investigate a higher-than-predicted result by following the gas path: damaged flexible section, incorrect silencer, closed transport cover, undersized transition, fabrication obstruction, unexpected elbows, or restricted termination.
5. Repeat the test for all three 1825 kVA sets. Where any portion is shared, test the permitted simultaneous-running combinations and check stopped branches for reverse flow.
6. After the system cools, inspect flexible joints, anchors, guides, supports, flange connections, drains, and surrounding construction for displacement, loosening, leakage, or heat damage. Record the final measured backpressure for each generator at the accepted load.

The installation passes only when every operating case remains within the engine manufacturer's backpressure limit, flange loading remains controlled, and the hot-to-cold inspection finds no interference, leakage, or support distress.

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