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 power source used on another. For several CHP plants, a lot of physical parameters are measured, evaluated and monitored to guarantee 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 ? Fluid -friendly power generators
In contrast to the traditional 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 range 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 using very different measuring instruments. Key factors are: functionality, quality, long service life, fast availability and services. The price/performance ratio plays a special role in virtually 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 in addition large plants up to 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 energy source should be considered when selecting the instruments. The amount of marking points in the schematic illustration of a CHP plant makes it clear: There is much to monitor in order to guarantee 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. They also enable remote monitoring.
For measuring the temperature, screw-in, insertion and contact probes are installed, matched to the design and the space available. On 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. As well, in addition they fulfil a safety function. If there are any deviations between the SET and ACTUAL value, based on the concept, the warning signal is triggered or the engine is switched off.
To monitor the oil level, according to the size of the machine, 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 which 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 number of measuring points and the widely differing measuring tasks require close cooperation between the CHP plant manufacturer and the manufacturer of the measurement technology. Therefore, it really 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 the CHP plant on the WIKA website in the Combined heat and power plants section. Do you want support with the compilation of one’s measuring instrument package for your CHP plant? Your contact person will be happy to assist you to.