The steam and condensate loop – fluid and flow

Steam is not the easiest medium to measure, but you still can get reliable measurement of steam flowrates.
By Steve Gow, Spirax Sarco February 19, 2015

Steam is not the easiest media to measure. The objective of this article is to achieve a greater understanding of the requirements to enable the accurate and reliable measurement of steam flowrate. “When you can measure what you are speaking about and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meager and unsatisfactory kind.” William Thomson (Lord Kelvin) 1824-1907

Many industrial and commercial businesses have now recognized the value of:

  • Energy cost accounting
  • Energy conservation
  • Monitoring and targeting techniques

These tools enable greater energy efficiency. Steam is not the easiest media to measure. The objective of this discussion is to achieve a greater understanding of the requirements to enable the accurate and reliable measurement of steam flowrate.

Most flowmeters currently available to measure the flow of steam have been designed for measuring the flow of various liquids and gases. Very few have been developed specifically for measuring the flow of steam.

Fundamentals and basic data of Fluid and Flow

Why measure steam?

Steam flowmeters can’t be evaluated in the same way as other items of energy saving equipment or energy saving schemes. The steam flowmeter is an essential tool for good steam housekeeping. It provides the knowledge of steam usage and cost which is vital to an efficiently operated plant or building.

The main benefits for using steam flowmetering include:

  • Plant efficiency
  • Energy efficiency
  • Process control
  • Costing and custody

Plant Efficiency

A good steam flowmeter will indicate the flow rate of steam to a plant item over the full range of its operation, i.e. from when machinery is switched off to when the plant is loaded to capacity. By analyzing the relationship between steam flow and production, optimum working practices can be determined.

The flowmeter will also show the deterioration of the plant over time, allowing optimum plant cleaning or replacement to be carried out.

The flowmeter may also be used to:

  • Track steam demand and changing trends
  • Establish peak steam usage times
  • Identify sections or items of the plant that are major steam users

This may lead to changes in production methods to ensure economical steam usage. It can also reduce problems associated with peak loads on the boiler plant.

Energy Efficiency

Steam flowmeters can be used to monitor the results of energy saving schemes and to compare the efficiency of one piece of the plant with another.

Process control

The output signal from a proper steam flowmetering system can be used to control the quantity of steam being supplied to a process, and indicate that it is at the correct temperature and pressure. Also, by monitoring the rate of increase of flow at start-up, a steam flowmeter can be used in conjunction with a control valve to provide a slow warm-up function.

Costing and Custody

Steam flowmeters can measure steam usage (and thus steam cost) either centrally or at individual user points. Steam can be charged as a raw material at various stages of the production process thus allowing the true cost of individual product lines to be calculated.

To understand flowmetering, it might be useful to delve into some basic theory on fluid mechanics, the characteristics of the fluid to be metered, and the way in way in which it travels through pipework systems.

Content provided by Spirax Sarco. Originally published in Steam News Volume 5 Issue 1. Edited by Anisa Samarxhiu, Digital Project Manager, CFE Media, asamarxhiu@cfemedia.com 

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