Wet fly ash at the Danish power station Studstrupværket

When the Danish energy company Ørsted decided to switch the Studstrup Power Station to green economy by converting it from using coal to using biofuel (wood pellets), Eurocon was commissioned to build a plant for the feed of ashes from the coal-fired part. When coal-fired power stations with roller mills are converted to wood-pellet firing, it is necessary to add coal fly ash to the mill in order to obtain the best bonding of alkali in the flue gas, so that boiler walls are protected from cinder and pollution is reduced by means of a de-NOx catalyst.

When the Studstrup Power Station wanted to use wet ash from the old deporters, they decided on a solution where the ash had to be mixed with water and fed into the wood-pellet mills as ash slurry. Consequently, the process involves that the wet ash arrives by ship and is unloaded at the port of the Studstrup Power Station. The wet ash will then be fed into the plant supplied by Eurocon Industriservice. In this plant, the wet ash is screened, then its moisture content is measured, the ash is weighed and, finally, mixed with water. The finished ash slurry with a water content of approximately 35 per cent is pumped through an approximately 650m long pipeline leading from the Studstrup Power Station’s port to four dosing tanks in a boiler house. Each dosing tank is equipped with a recirculation strand from where a dosing pump doses the ash slurry into their particular wood-pellet mills.

Before the building at the Studstrup Power Station could be started, Eurocon Industriservice had to build a test plant in order to test the viscosity of the ash slurry and measure the pressure drop in a pipe strand at a certain humidity. This was necessary for the dimensioning of the pumps and pipes and for determining the required pumping speed. Tests were made with several different axle types. The mixing plant was dimensioned to allow mixing of about 50m3 slurry/hour, and the dosing system could feed max. 280 m3/day.