Pulsed Power Technology as an Alternative for Cleaning Power Plant Boilers from Mineralic Incrustinations

Project Number 231

The use of primary energy carriers like brown or stone coal or secondary energy carriers like domestic waste or waste woods to produce electrical energy leads to cinder covers inside the boiler and the heat exchanger of the power plant due to the ingredients of the smoke gas during a certain time. For that reason the efficiency of the transfer of thermal energy into electrical energy decreases considerably accompanied by different pressure and steam flow behaviours which lead to unusual mechanical fatigue and earlier material weaknesses as expected.

Today the cleaning from incrustinations makes it always necessary to switch-off the involved power plant. During that time the operator of the power plant can't make benefit due to the standstill of the respective bloc. Nowadays the cinder covers were removed by

  • air-pressured hammers and sand rays,
  • detonation of explosives at certain places.

The whole cleaning procedure takes about one month including cooling-down and preparing the heat exchanger facility for the cleaning, the cleaning itself and the reactivation of the power plant bloc and must be repeated every half up to three quarters of a years, depending on the quality and purity of the energy carrier. The use of the so-called "Dampfrußbläser" lengthens this interval. This device works in that way that a water beam is splashed from outside the boiler onto the cinder covers with approximately 30 bar of pressure. Due to the temperature inside the boiler and the heat exchanger (between 300 and 1200 °C) the water evaporates with high pressure which makes the cinder covers breaking from the boiler armature and heat exchanger tubes. This technique can be used while the power plant bloc is in operation but due to the small opening in the boiler the treatment is limited on certain zones and because of the reduced visibility conditions inside the boiler and heat exchanger the water beam can not be used purposely.

The Laboratory of High Voltage and Pulsed Power Technology at the University of Applied Sciences Gelsenkirchen works since several years on the use of pulsed power discharges to treat brittle materials. This technology can be used for fragmentation of rocks to extract covered precious metal or precious stones or to separate combined materials by example from steel enforced concrete. Basically the method of pulsed power technology can also be used to clean up heat exchanger facilities and the heat exchanger armature from cinder covers. Therefore electrical discharges were generated which pass the cinder cover by using high voltage fields. When the discharge crosses the cinder cover a conductive plasma channel develops spreading in radial direction generating local high pressures and the cinder cover is blasted. This behaviour was successfully shown with a original test tube with a cinder cover from a brown coal power plant.

During this research project the effects of the pulsed power technology should be evaluated with concern to the safety of the personnel and facility. Therefore the compatibility with the MAK and DIN rules will be proved by adequate experimental tests.

The investigation on the metallurgical effect of electrical discharges with different intensities on the metal of the heat exchanger tubes is a further main topic of the research study.

Afterwards the work shall be focussed on the development and design of a compact and practicable electrode device. Finally the possibilities of automation of the cleaning process using the Pulsed Power Technology shall be investigated.

In the case of positive results of the project the method shall be tested in a closed down power plant.

The project is carried out from July 2002 to September 2004 at the Laboratory of High Voltage and Pulsed Power Technology at the University of Applied Sciences Gelsenkirchen (person in charge: Christian Dreesen). As subcontractor VGB PowerTech puts in engineering services and examinations of the material laboratory. The budget of the project is sponsored by Arbeitsgemeinschaft industrieller Forschungsvereinigungen (AiF). The project is accompanied by a working group of the "Working Panel Steam Generators".