Measuring instruments for combined heat and power plants (CHP)

The range of combined heat and power plants (CHP) is very large, as may be the high variance of different plant types. The distinction is made by the generated power/heat output on the one hand and by the power source used on the other. For several CHP plants, a large number of physical parameters are measured, evaluated and monitored to guarantee the longest possible service life. This short article offers information regarding which measuring instruments and principles this is often achieved with.
Combined heat and power plants ? environment-friendly power generators
In contrast to the traditional boiler or condensing boiler, the CHP plant generates both electricity and heat. Thus, CHP plants make a significant contribution to environment-friendly energy generation.
Wide variety of applications
The versatile application possibilities, from single or multi-family dwellings, through industrial and commercial, public facilities, up to large district/local heat utilities and in addition biogas plants, require the usage of completely different measuring instruments. Key factors are: functionality, quality, long service life, fast availability and services. The price/performance ratio plays a special role in any system ? large or small.
The physical measurands
Small nano plants from 1 kWel, micro and mini plants from 2.5 to 15-50 kWel, and also large plants around 4,500 kWel need the right measuring instruments for high efficiency and environment-friendly energy generation. The measurands pressure, temperature and level are dominant. The power source should be considered when selecting the instruments. The number of marking points in the schematic illustration of a CHP plant helps it be clear: There’s much to monitor to assure the longest possible service life.
Schematic illustration of a combined heat and power plant incl. measuring points
Monitoring and control tasks
The measuring instruments used fulfil important monitoring and control tasks and are generally electronic measuring instruments. In addition they enable remote monitoring.
For measuring the temperature, screw-in, insertion and contact probes are installed, matched to the look and the space available. On heat exchanger, in the cooling and heating circuits and in addition for measuring the engine oil temperature, Pt100, Pt1000, KTY and NTC measuring elements are used. With large plants, temperatures on the exhaust pipe and on the cylinder head are monitored using thermocouples. This enables conclusions to be made about the effectivity of the engine.
Pressure switches and pressure sensors are used to control the oil pressure and the pressure in the cooling water circuit. Simultaneously, they also fulfil a safety function. If there are any deviations between the SET and ACTUAL value, depending on the concept, either a warning signal is triggered or the engine is switched off.
To Useless , according to the size of the machine, between one and three float switches are installed. Particularly in large engines, the sometimes quite strong vibrations pose challenging for the measurement technology. The use of optoelectronic level switches that tolerate high temperatures and that are not harmed, even by strong shocks, is therefore ideal. The respective level switch monitors the oil level in a reservoir and signals when the oil level drops too low.
Conclusion
The large numbers of measuring points and the widely differing measuring tasks require close cooperation between your CHP plant manufacturer and the maker of the measurement technology. Therefore, it is worth ? both technically and economically ? selecting a supplier who offers everything from one source.
Note
WIKA offers a large collection of reliable measuring instruments for pressure, temperature and level. You will discover selected products for your CHP plant on the WIKA website in the Combined heat and power plants section. Do you need support with the compilation of your measuring instrument package for the CHP plant? Your contact person will be happy to assist you to.

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