We are struggling with the pilot
Since 14 January, we have now had 30 operating days with the pilot. But we are still struggling with both the dryer and the pyrolysis to get a continuous operation.
New sludge almost every week means a challenge for the dryer. For sludge with low dry solids (DS) content (16-21%), (anaerobically) digested as well as undigested, we seem to have found settings of operating parameters that allow us to get over 85% DS on the dried sludge (drying time = 180 min and temperature 170°C). But for not digested, slightly drier sludge (above 22%), we currently have a challenge, as the sludge easily starts to glow in the dryer even though we have reduced the residence time to 120 min and the temperature to 150 ° C.
We run with a flow of 80 kg/h into the dryer, which is quite a lot less than the intended capacity of at least 150 kg/h. We have problems with screw pumping sludge with high DM (>27%) and the supplier Aquagreen is trying to find a better solution for this.
We also have problems with precipitates in the pyrolysis gas pipes that go between the pyrolysis and the gas burner. We have now realised, that we need to clean these every other day. It only takes 15 minutes to clean these pipes and we do it directly in the morning before we have started the gas burner.
So, the last five weeks have generated no more than three days of operation due to high differential pressure between the pyrolysis and the gas burner (caused by clogging pyrolysis gas pipes), glowing sludge in the dryer and, inevitably, a week of holiday and a couple of days of illness for our operating technician.
At the moment, Aquagreen is aiming for handover of the plant in early May, without the higher TS solution, and that they will be extra available until the higher TS solution is in place.
Despite the downtime, we have learnt a lot in the last few weeks.
We are soldiering on!
A lorry arrives with sludge from the Stockholm area. The driver thought he was carrying poo. But we told him that half of it was “poo” (primary sludge) and the other half was biological sludge produced at the wastewater treatment plant. This sludge was not anaerobically digested.
Here we screw the sludge into the dryer from our feed buffer.
Here you can see that precipitates are starting to build up in the pyrolysis gas pipe.
We now have 30 different types of sludge biochar in stock.