• Energy Research

Organic and inorganic contaminants in sewage sludge may cause their presence also in the by-products formed during gasification processes. Thus, this paper presents multidirectional chemical instrumental activation analyses of dried sewage sludge as well as both solid (ash, char coal) and liquid (tar) by-products formed during sewage gasification in a fixed bed reactor which was carried out to assess the extent of that phenomenon. Significant differences were observed in the type of contaminants present in the solid and liquid by-products from the dried sewage sludge gasification. Except for heavy metals, the characteristics of the contaminants in the by-products, irrespective of their form (solid and liquid), were different from those initially determined in the sewage sludge. It has been found that gasification promotes the migration of certain valuable inorganic compounds from sewage sludge into solid by-products which might be recovered. On the other hand, the liquid by-products resulting from sewage sludge gasification require a separate process for their treatment or disposal due to their considerable loading with toxic and hazardous organic compounds (phenols and their derivatives).

Abstract The thermal decomposition kinetics of two energy crops Miscanthus x giganteus and Sida hermaphrodita biomass materials harvested from a phytoremediation study in Polish and Germany have been studied, assuming a three-pseudocomponent model. The kinetic parameters extracted from the study are realistic and within reasonable ranges. The activation energies are within 20 - 103.55 kJ/mol. The reaction orders are within 1.01-1.99. The result shows that the energy crops from the Polish site exhibited higher conversion rates than the samples from Germany. A negative effect of the ash content on the biomass reactivity is observed.

This work aims to assess the effect of the operating parameters of the gasifying agent preheating temperature and equivalence ratio (ER) on the conversion of sewage sludge (SS) to syngas through gasification and combined heat and power (CHP) generation. A novel gasification model was simulated in Aspen Plus to represent a fixed-bed updraft gasifier to generate syngas from SS through an equilibrium approach restricted by temperature. The novelty of this work is that the model was developed by applying the gasifying agent preheating temperature as an operating variable instead of the gasification temperature. It was calibrated by using a set of experimental values and then validated by comparing the numerical results with the experimental outcomes related to nine different operating conditions of air preheating temperatures and ER. A good agreement between the simulation and experimental results was observed. The optimum gasification process parameters of the air preheating temperature and ER were predicted to be 150 °C and 0.2, respectively. The CHP generation potentiality of SS was assessed to be 2.54 kW/kg SS as dry solids (DS), of which 0.81 kW was electrical and the remainder was thermal power. The conversion of SS to CHP through the proposed treatment can reduce 0.59 kg CO₂/kg SS as DS emissions compared with that of natural gas combustion to generate a similar quantity of energy.

Abstract In this investigation, ignition processes of methane (CH 4 > 98%) and propane (C 3 H 8 > 95%) using a high-temperature oxidizer ( T oxi > T ai ) with a varying oxygen concentration ( z O 2 = 0.05 ÷ 0.21 ), applying two types of experimental installations, viz. a constant–volume bomb (CVB) and a co-flow reactor (CFR) were investigated. The influence of the initial temperature of the oxidizer (for methane T oxi = 960 ÷ 1234 K and for propane T oxi = 803 ÷ 1055 K), the equivalence ratio and oxygen concentration in the oxidizer on ignition of gaseous fuels is analyzed and discussed. It is shown that in order to achieve an effective reaction of ignition (taking into account the minimum value of ignition delay time τ ig and maximal value of the increment of temperature Δ T ) the oxidizer temperature need not be maximized. There are optimal values of temperature of the oxidizer (for methane T oxi ≈ 1100 K and for propane T oxi ≈ 950 K) in which the parameters mentioned above reach their extreme values.

Abstract Two energy crops Miscanthus x giganteus and Sida hermaphrodita were used for a phytoremediation study on two different sites of soil contaminated with heavy metals in Poland and Germany. The energy crops were harvested and characterized with regards to fuel properties and thermal decomposition behaviour. Site influences on the data of proximate and ultimate analyses have been observed. Differences in the thermal decomposition are caused by the differences in pH value and heavy metal content of the soils.

The cultivation of energy crops on heavy metals contaminated (HMC) areas offer opportunities, which combine site remediation with energy recovery. Numerous tests have been conducted using phytoremediation in HMC soils with energy crop species. Sida hermaphrodita L. Rusby, has shown potential as an energy crop useful in the phytoextraction of HMs. The aim of the study was to investigate the efficiency of using S. hermaphrodita in energy crop production in HMs contaminated sites. The study investigated the impact of different fertiliser treatments on the composition of elements in cultivated biomass on HMC arable land and sewage sludge dewatering sites to determine its suitability for energy production in gasification processing. It was found that S. hermaphrodita is a species accumulating HMs mainly due to their bioavailability in soil (Cd r = 0.877, Zn r = 0.876). Calculated Cd and Zn bioaccumulation factors for plants cultivated on HMC arable land were 12-fold and 18-fold higher respectively, when compared to a sewage sludge dewatering site. Lower heating value of biomass was higher by about 7% for biomass cultivated on HMC arable land. Despite the presence of HMs in ash after the gasification process, some of it could be used as fertilizer, especially on heavy metal contaminated sites.