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Charakterystyka olejów popirolitycznych otrzymywanych w procesie pirolizy komunalnych osadów ściekowych

Bień J. D., Bień J. B.

Inżynieria i Ochrona Środowiska

2002

T. 5, nr 3-4

223-232

Przedstawiono właściwości olejów popirolitycznych, jednego z produktów, otrzymanych w procesie pirolizy komunalnych osadów ściekowych. Badania przeprowadzono, wykorzystując jako materiał wsadowy surowe osady ściekowe pochodzące z Centralnej Oczyszczalni Ścieków w Częstochowie. Eksperyment przeprowadzono dla różnych czasów trwania procesu pirolizy oraz w czterech punktach temperaturowych. W próbkach otrzymanego oleju oznaczono zawartości metali ciężkich i WWA. Określono również ciepło spalania, zawartość wody i gęstość. Rezultaty badań wskazują, że ilość oraz własności otrzymanych olejów popirolitycznych są uzależnione od temperatury i czasu trwania pirolizy.

Due to yearly increase of sewage sludge production, its disposal is one of the most important problem causing serious worldwide environmental problems. It is expected that in Poland in the near future the quantity of sewage sludge will increase up to 0.5 million tons of dry mass per year. Currently nearly 75% of the sludge produced in Poland is disposed off through filling sites and can be a source of groundwater contamination. The rest is used as a fertilizer or is incinerated. Turning sludge into compost causes the pathogens and heavy metals to pollute the land which is fertilized. Incineration emits hazardous gases. These factors cause to look for any alternative method for sewages sludge utilization. In many scientific laboratories the experiments with thermal decomposition of sewage sludge are carried out. Such processes are carried out in a relatively low range of temperatures and allow to obtain from sludge such energetic products as: liquid as well as fuel gas and solid postpyrolytic products. These processes are carried out in non-oxygen environment, in a temperature range between 300¸700°C, and because of their endothermic character, they are much easier to be kept under control. This paper presents results of studies on properties of liquid product. To determine the optimum combination of operating parameters for sewage sludge pyrolysis, dewatered and dried raw sludge from Czestochowa WWTP was treated over a temperature range of 300¸600°C for time of 30¸90 min. It was determined that the optimum temperature for the highest yield of oil was 400°C in each time case. Heating values of the oils were 19.8¸25.6 MJ/kg. The contents of water was high 30¸40% and the density was generally below 1 g/cm3 but in first case when a reaction temperature was 300°C the density of oil was nearly comparable to density of water. The contents of some heavy metals in oils were also analysed. The comparison between the concentration of heavy metals in received oils and values from EU directive (87/101/EEC) shows that the received results are below permissible limit. However the most important is that in received liquid some dangerous for human health aromatic hydrocarbons were determined. Among all determined aromatic hydrocarbons fifteen are treated by US EPA as the most toxicological substances. It is concluded that: 1) the optimal conversion temperature is 400°C referring to making liquid product recovery ratio maximum, 2) the heating value is high, 3) the density of liquid product is nearly comparable to the density of water because high content of water, 4) oils contain some toxicological substances. The research results show that the properties of oil received in thermal decomposition process is not favourable at this stage and further research should be carried out.