Measuring instruments for combined heat and power plants (CHP)

The selection of combined heat and power plants (CHP) is very large, as is the high variance of different plant types. The distinction is manufactured by the generated power/heat output on the main one hand and by the energy source used on the other. For all CHP plants, numerous physical parameters are measured, evaluated and monitored to ensure the longest possible service life. This article offers information regarding which measuring instruments and principles this could be achieved with.
Combined heat and power plants ? environment-friendly power generators
In contrast to the original boiler or condensing boiler, the CHP plant generates both electricity and heat. Thus, CHP plants make an important 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, around large district/local heat utilities and in addition biogas plants, require the use 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 proper 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 makes it clear: There’s much to monitor in order to guarantee the longest possible service life.
Succeed 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. They also enable remote monitoring.
For measuring the temperature, screw-in, insertion and contact probes are installed, matched to the look and the space available. On the heat exchanger, in the heating and cooling circuits and also for measuring the engine oil temperature, Pt100, Pt1000, KTY and NTC measuring elements are employed. 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. At the same time, they also fulfil a safety function. If there are any deviations between the SET and ACTUAL value, according to the concept, either a warning signal is triggered or the engine is powered down.
To monitor the oil level, according to the size of the system, between one and three float switches are installed. Particularly in large engines, the sometimes very strong vibrations pose challenging for the measurement technology. The usage 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 manufacturer of the measurement technology. Therefore, it is worth ? both technically and economically ? selecting a supplier who offers from one source.
Note
WIKA offers a large selection of reliable measuring instruments for pressure, temperature and level. You can get 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 one’s measuring instrument package for the CHP plant? Your contact person will undoubtedly be happy to assist you to.

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