Temperature measurement

Thermometers used in power plants or in thermal energy distribution networks are not and cannot be calibrated directly, at the operation conditions (e.g. flow-rates up to 5000 m³/h, temperatures at least 280 °C to above 1500 °C, pressures up to 25 MPa) are and will not be realised in any calibration laboratory in the world. The challenge lies in establishing metrologically sound and accepted models of the influence of process conditions on temperature metering with the aim to reduce the uncertainty from 3 °C to 1 °C and a further important challenge is the development of drift free (<1 K/year) and vibration-resistant temperature sensors for use at these operating temperatures.
For a future hard coal power plant the requirements to the control system will be 5 % - 7 % power change within one minute for the secondary load control and up to 10 % within 10 s for the primary control. This requires considerable effort to optimise the positioning, contacting and the dynamic behaviour of the temperature sensors.
A further aim is an optimised dynamic “two-shifting” behaviour of a power plant in order to compensate for power-grid loads. These grid loads are caused by both consumer behaviour as well as the increasing amount of power generation by renewable energy sources, e.g. wind or solar energy, which makes the power output inevitably dependant on weather conditions.

Thermophysical property measurement

Increasing the steam and gas temperatures requires novel materials with improved durability to thermal load and corrosion. Corrosion resistant and thermal barrier materials are essential for operation at temperatures up to 720 °C and water vapour pressures of about 35 MPa for steam power plants. To increase the efficiency of gas turbines to above 60 % an increase of the typical gas inlet temperature from currently 1300 °C to 1500 °C is necessary, which sets high demands on the thermal barrier protection materials, as this temperature is significantly higher than the melting temperatures of the base material. This requires improved measurement techniques to investigate flue gas corrosion and the high-temperature oxidation behaviour of the most promising Ni-based alloys and predict their behaviour for working lifetimes of at least 2x105 hours. In addition the measurement of emissivity, which governs the radiative heat exchange with the environment, is exceedingly challenging at elevated temperatures.

Flow measurement

Energy flow normally equates to fluid flow at some point. Energy is generated by steam, transported as hydrocarbon fluid and consumed through heating and cooling fluids. Measurements are required within industry to quantify inefficiencies, measure improvements and to meet regulation. These measurements require to be carried out at extremes of viscosity, temperature, pressure, and on multiphase and multi component mixtures. Conditions are often outside the scope of conventional techniques and sensors. Measurement of energy flow has to encompass novel integration of sensors for flow, temperature, pressure, composition and fluid parameters operating in field and industrial conditions at economic cost.
The lack of precise flow rate measurements currently limits the efficiency of power plants and thermal energy distribution networks. For example, to fulfil safety regulations in nuclear power plants the permitted thermal power output is reduced to a value 2 % below the nominal maximum power to account for the uncertainty of 2 % of the flow rate measurements. Reducing the flow rate measurement uncertainties to 0.5 % would directly enhances the power output by the same amount. Additionally, for all types of power plants the uncertainties in flow rate measurements lead to non-perfect steering and control mechanisms. Recent studies indicate that efficiency enhancement due to optimised control and operation modes based on precise flow rate measurements sum up to an efficiency gain of approximately 2 %.
Flow meters used in power plants or in thermal energy distribution networks are not and cannot be calibrated directly, as the operation conditions (e.g. flow-rates up to 5000 m³/h, temperatures at least 280 °C to above 1500 °C, pressures up to 20 MPa) are and will not be realised in any calibration laboratory in the world. The challenge lies in establishing metrologically sound and accepted models of the influence of process conditions on flow metering with the aim to reduce the uncertainty of flow metering from around 2 % to approx. 0.5 %

On-site electrical power output measurement

A final need relates to the actual determination of the effect of all measures taken to increase the efficiency of power plants via on-site measurements of the electrical power output of the plants, particularly the dynamic measurements necessary to balance variable net load due to the discontinuous nature of renewable energy sources (wind and solar).