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Conversations about Conservation

Talking efficiency and reduced consumption in steam generation

For heating or power generation in turbines, for sterilisation or cleaning purposes – in many sectors, steam is used on a grand scale. It is therefore not surprising that in industry a massive 40% of fossil fuels are used for steam generation in boilers. The judicious use of fuels such as oil or natural gas is just one of the aims in energy management. These days steam management covers a whole lot more than checking water levels, conductivity, pH value, temperature and pressure in the boiler. Steam systems offer numerous options for saving, re-using and reclaiming energy, whether in generation, distribution, accurate billing or in boiler efficiency.

Endress+Hauser provides you with all the measuring instruments required to obtain optimum potential improvement. Our product range also includes water analysis devices for seamless monitoring the quality of feed, boiler or condensate water, e.g. dissolved oxygen, limescale content or electrical conductivity. Generating, transporting and distributing steam requires a considerable amount of cost and energy. The goal therefore is to run and control these processes as efficiently as possible.

conversations-about-conservation

 

The questions always remain the same:  How do you reduce your energy costs?

You can only control what you measure. The right device installed correctly at the right place permits the accurate metering of flow, pressure, temperature and other important process values. The Prowirl vortex meter, for steam flow applications is a good example of this. This highly robust flowmeter has been mainly developed for steam applications, and it offers a broad scope of multivariable solutions for steam mass and energy measurement. An innovation that helps to increase safety and improve the efficiency of steam systems is the new optional feature designed to detect wet steam on a continuous basis.

 

So what is wet steam and why is this important?

When dry saturated steam passes on its energy to a process, its “latent” energy is released. This energy can be found in steam tables as enthalpy (hfg). Whilst this energy is released, the steam becomes wetter, i.e. its dryness fraction (x) is reduced from 1 down to 0. What doesn’t change, however, is the combination of pressure and temperature during this process. This means that ideally steam enters a heat exchanger at 3 bar g and +144 °C and condensate can be found at the exit at exactly the same pressure and temperature – but the steam has lost 2138 kJ/kg of latent heat (hf). The problem now is: If both liquid and steam, and any state in-between, can exist at the same pressure and temperature, it is impossible to determine the dryness fraction by just measuring pressure and temperature.

conversations-about-conservation

Steam at different dryness fractions (from left to right: 100%, 95%, 90%). A dryness fraction of 90% means that 10% (mass) of the total water content is present as water containing much less energy than gaseous steam. Therefore, 10% less energy is available

Wet steam mostly occurs in the distribution of steam. Heat losses in steam piping, because of lack of isolation, will lead to a reduced dryness fraction.  This wet steam can lead to water hammers (slug flow caused by the water entering the steam line) and reduce the efficiency of the steam system because wet steam contains less energy than dry saturated steam.  If the wet steam is a result of carry-over from the boiler itself, stress corrosion cracking may result. Until the innovative Prowirl, with wet steam detection, there was really no solution available to determine if water is present in the steam line or not.  The Wet Steam Detection makes it possible to monitor the steam quality. A warning is issued when the steam quality drops below the limit value for steam quality in the range between 80 to 100 %.  The Prowirl is the preferred measuring principle for wet/saturated/superheated steam applications.  The integrated temperature measurement allows for easy calculation of mass/energy flow of saturated steam. In addition to the Prowirls’ robustness and resistance to vibrations, temperature shocks & water hammer, is the meters lifetime calibration.

Another challenge is the constant monitoring of a steam boiler and the steam system, in order to improve the systems performance and detect changes at an early stage.  The solution is to define the right KPIs which help to evaluate; steam boiler efficiency, system balancing and leakage, as well as specific energy consumption.  This is the precondition for energy

management and cost reduction. The energy and data manager RSG45, collects, stores and displays all the required data.  Very often, the target values determined, such as steam boiler efficiency, fuel consumption or pressure loss, need to be not only registered, but also read and verified onsite directly in the plant.  The Memograph is able to visualise, register and analyse energy data, as well as calculate characteristic values, such as specific energy consumption, boiler efficiency, fuel and steam consumption as well as leakage loss. The web-based energy monitoring software permits access to the entire monitoring system in the plant from anywhere via an intranet or the internet. In addition, this software can be used to analyse measurement data and serve as the basis for creating energy reports.

For more information, please visit: http://bit.ly/Steam_Across_industry

For more information, please contact:

Natlee Chetty

Industry Manager: Food and Beverage

natlee.chetty@endress.com

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