Controlling of the Gypsum production at E.ON “MPP3”
based on a moisture measuring system from ACO
E.ON „MPP3“ coal fired power plant in Rotterdam-Maasvlakte
The “MPP3” is the most modern and biggest hard coal fired power plant with the notable gross power rating of net 1070 MW and a net efficiency of over 46%. The “MPP3” wants to reduce the effects on the environment as much as possible. One point to reach an environmental friendly process is the optimisation of the exhaust-desulphurisation unit. The desulphurisation is made by a wet flue gas cleaning unit controlled by a moisture measurement. This flue gas desulphurisation (FGD) is far more effective than in other traditional coal fired power plants. Beyond the “MPP3” can reach a biomass-combustion up to 30%. Of course the district heating is used from the adjacent companies.
General description of the process
The desulphurisation is based on burnt lime (CaO) thereby the end product gypsum (calciumsulfad-dihydrat) arises. For the analysis of the produced gypsum there is an in-house laboratory located in Maasvlakte (Rotterdam). This in-house laboratory evaluates all the recurrent samples that have to be taken to supervise the moisture content of the gypsum. The REA-gypsum can only be traded and further processed with a moisture value around 10%. Based on this fact a continuous measuring and storage of the actual moisture value is indispensable. To avoid caking in the whole process and to guarantee the best flow characteristics in all following transport systems, a moisture measurement system is also advisable. In the “MPP3” the moisture values are gained from an online–measuring system at the vacuum band filter. The two sensors are mounted in the individual developed over belt construction from ACO. This solution is very important to reach a successful and reproducible result of the moisture measurement. The digital moisture measurement signal is available without any delay.
Description of the ACO moisture measurement system
The “MPP3” plant has decided to use the digital moisture measurement system from ACO (Automation Components in Wutöschingen–Horheim). The measuring principle is based on a capacity measurement method. The Profibus DP interface allows the communication between the evaluation unit and the process control system of the power plant. The traditional communication via analogue signal (4mA…20mA) is also available. With the help of the measured moisture values the drying process is controlled and managed. The calibration was made via ACO-calibration software. It has to be done only one time (less installation costs) and the system is able to replace a sensor without the necessity to repeat the calibration (reduces costs through less downtime). If a further sensor is needed the evaluation unit can handle up to 16 sensors. Each sensor is able to measure 16 different materials of additional product if necessary.
Individual execution of the sensor installation
One very important thing of moisture measurement systems is the mounting condition of the sensor. A constant material height and density should be given. To guarantee such optimal process conditions a special scraper is installed in front of the sensor. Furthermore the sensor is mounted on a sledge. This also improves the surface of the material and reduces material caking in front of the sensor. Via hand wheel the material height and the sensor position is adjustable very fast and easily.
Earlier experiences of ACO have shown that just one sensor, on a 2.4 meter wide belt, is not sufficient for an accurate moisture measurement, due to this the moisture measurement consist out of two sensors. On one hand the reproducibility is higher and on the other hand the function of the sealing lip can be monitored (safety function). If there is a damaged sealing lip, the vacuum and consequently the drying process will not work as good as before. On one sensor the moisture value will increase highly. In this case the sealing lip should be replaced.
