Measuring Steam Consumption: Flowmeters and Condensate-Based Methods

Actual steam consumption in an operating industrial plant can be established by measuring steam flow directly or, in suitable applications, by determining the amount of condensate produced.

Measurement can be used to assess actual plant performance, compare steam users, evaluate energy-saving measures and assign steam demand to individual production stages.

Why measure actual steam consumption?

• evaluate energy-saving projects,
• compare different items of plant,
• allocate steam use to production stages,
• assign steam cost to specific products or lines.

Direct measurement with a steam flowmeter

The most direct approach is to install a suitable flowmeter in the steam line.

A typical arrangement may include:

• a flow transducer or primary element,
• a temperature sensor,
• differential-pressure measurement,
• a display or processing unit.

Actual steam pressure and any required calibration or correction factor must be considered.

Indirect estimation from a condensate pump

Where a positive-displacement pump is installed, a cycle counter may be used. If quantity per cycle is known:

Total condensate ≈ number of cycles × quantity per cycle

The method can use an existing condensate pump, but it is an indirect estimate.

Electronic cycle monitoring

Cycle counting can be automated and data may be displayed locally or sent digitally to a central monitoring system.

Effect of flash steam

Where a vented receiver is used, part of the hot condensate may flash to steam. An allowance may therefore be required because not all steam-derived mass reaches the pump as liquid condensate.

Direct measurement by collecting condensate

Steam consumption may also be estimated from the mass of condensate collected over a known period.

The method can be used for batch and continuous-flow duties where condensate can be collected separately.

Where condensate collection cannot be used

• direct steam injection,
• humidification,
• processes without a separate collectable condensate stream.

Practical weighing test

1. Weigh the vessel with sufficient cold water.
2. Supply steam to the plant.
3. Discharge condensate below the water level.
4. Record mass increase over time.
5. Calculate average steam consumption.

ṁ_s ≈ Δm / Δt

Identifying peak demand

Recording condensate mass at regular intervals allows successive consumption rates to be calculated and makes short-term peaks visible.

Backpressure and differential pressure

An atmospheric collection test may not reproduce the normal condensate-return backpressure. The steam trap must therefore be checked against the differential pressure expected in actual service.

Preparing equipment before a test

Only condensate produced during the test should be included. Equipment should be drained before the test and any condensate remaining at the end should be added to the collected amount.

Test duration and repeatability

The test should run for as long as practicable to reduce the relative effect of measurement errors.

Three tests under similar conditions should be carried out and the results averaged. Widely differing results should be investigated.

Using a condensate receiver

Where a collection tank and pump are installed, the pump may in some cases be stopped temporarily and condensate volume estimated from the change in tank level.

Comparison of methods

Practical checks before measurement

• steam pressure,
• calibration and correction factors,
• flash-steam losses,
• return backpressure,
• steam-trap differential pressure,
• stored condensate before the test,
• test duration,
• repeatability.

Conclusion

Steam consumption can be measured directly with a flowmeter or estimated from condensate. Direct metering is suited to continuous monitoring, while pump-cycle counting and condensate collection provide practical alternatives where operating conditions allow.

Operating pressure, flash steam, backpressure and repeatability must always be considered before measured values are used for engineering decisions.

Frequently Asked Questions

What is the most direct method?

A suitable steam flowmeter installed in the steam line.

Can steam consumption be calculated from condensate?

Yes, where condensate can be collected and flash-steam losses are small or accounted for.

What does a cycle counter do?

It records condensate-pump cycles so the total quantity transferred can be estimated.

Why does flash steam matter?

Because some mass may be lost as vapour and not measured as liquid condensate.

Why discharge condensate below water?

To condense flash steam and reduce mass loss.

Why does backpressure matter?

Because it changes steam-trap differential pressure and discharge capacity.

Why should a test run for a long period?

To reduce the relative influence of measurement errors.

Why repeat the test?

To check repeatability and obtain a more reliable average.