Sewage sludge, the inevitable by-product of municipal wastewater treatment plant operation, is a key issue in many countries due to its increasing volume and the impacts associated with its disposal. Thermochemical processing offers a new way of managing sewage sludge, not only by providing effective volume reduction, but also enabling transformation of carbon-rich organic fraction into valuable energy and fuel. Owing to some unique properties, sewage sludge differs from other solid fuels such as lignocellulosic biomass and coal, making its thermochemical conversion application somewhat complicated and challenging. This paper reviews the options of converting sewage sludge to energy and fuel via three main thermochemical conversion processes namely pyrolysis, gasification and combustion. The fundamental aspects of sewage sludge and its behaviour in each of thermochemical process are summarised. The challenges in adopting thermochemical conversion technology in sewage sludge management are addressed, and various alternative approaches deserving further consideration, such as the incorporation of pre-processing and co-utilisation, are discussed.

Thermochemical processing of sewage sludge to energy and fuel: Fundamentals, challenges and considerations

Catalytic effects of nano additives on decomposition and combustion of RDX-, HMX-, and AP-based energetic compositions

Synthesis of CuO nanorods and their catalytic activity in the thermal decomposition of ammonium perchlorate

Biomass fuels differ in many ways from the conventional fossil fuels used in combustion processes, such as coal. They often have high moisture contents, lower heating values, and a variety of minor constituents, such as chlorine, sulfur, phosphorus, nitrogen, and a variety of ash-forming metals. These special properties of biomass fuels cause several challenges, but in many cases also provide advantages, to their use in combustion processes. Design of the combustion devices and choice of their operating parameters are very dependent on the detailed properties of the biomass fuel or fuels to be used. Often these challenges are connected to the fate and chemistry of the many minor constituents or impurities of the fuels. This paper reviews some of such chemical details related to biomass combustion that are important to take into consideration in the use of biomass combustion processes. The focus of the paper is in large, industrial scale combustion technologies for biomass and biomass derived waste fuels, either in district heating or also power production. Areas discussed are biomass particle conversion and biomass char oxidation reactivity, nitrogen and sulfur reactions in furnaces, superheater fouling and corrosion due to biomass ashes, low-temperature corrosion, and bed sintering in fluidized bed furnaces. The advances in understanding chemical details of biomass combustion have strongly contributed to the development of more reliable and efficient boiler technologies. Unresolved challenges are still connected to simultaneous combustion of several different biomasses and interaction of fuel ashes in such applications.

Biomass combustion technology development – It is all about chemical details

Superparamagnetic magnetite nanoparticles (mean diameter ∼10 nm) were synthesized using the co-precipitation route from Fe2+/Fe3+ in aqueous solutions (molar ratio 1:2) by adding a base under mechanical stirring at 10,000 rpm. This stirring velocity was found to be suitable for obtaining nanoparticles of this mean size, and a decrease in stirring velocity resulted in a larger size (∼19 nm) and a wider size distribution. At 18,000 rpm, in addition to magnetite, goethite is also synthesized in the form of nanoparticles and nanorods are found. At higher stirring velocities (25,000 rpm), the solution's core temperature increased from 20° to 37 °C, generating a mixture of non-magnetic iron compounds.

Influence of stirring velocity on the synthesis of magnetite nanoparticles (Fe3O4) by the co-precipitation method

CuO nanocrystals of different surface areas were prepared. All samples were characterized by X-ray diffraction, transition electron microscope, thermogravimetry, Brunauer-Emmett-Teller technique, Fourier transform infrared spectroscopy, and Raman spectroscopy. CuO nanocrystals showed a stable monoclinic structure. With increasing surface areas, the surface hydration became significant, which is followed by shifts in infrared frequencies and Raman phonon modes. CuO nanocrystals were explored as an additive to catalytic decomposition of ammonium perchlorate (AP). AP decomposition underwent a two-stage process. Addition of CuO nanocrystals led to a downshift of high-temperature stage towards lower temperatures.

CuO nanocrystals in thermal decomposition of ammonium perchlorate

The effect of phosphorus on the behavior of potassium and the reaction mechanism between potassium and phosphorus during the co-combustion of wheat straw (WS) and municipal sewage sludge (MSS) are investigated in a bench-scale reactor. The elemental composition of ash is analyzed by inductively coupled plasma–optical emission spectroscopy (ICP-OES), and the morphology and crystalline phase are analyzed by scanning electron microscopy (SEM), and powder X-ray diffraction (XRD). The results indicate that the addition of MSS to WS enhances potassium retention in ash due to the formation of high-melting-point compounds such as potassium aluminosilicates (e.g., KAlSi2O6 and KAlSi3O8) and alkali phosphates (e.g., Ca9MgK(PO4)7). Calcium phosphate (Ca3(PO4)2) is selected as a model phosphorus compound in municipal sewage sludge ash to study the phosphorus chemistry. The addition of Ca3(PO4)2 is effective in preventing sintering and fusion of wheat straw ash. Ca3(PO4)2 not only dilutes the ash but also absorbs and ...

Effect of Phosphorus on the Behavior of Potassium during the Co-combustion of Wheat Straw with Municipal Sewage Sludge

This work reported on the thermal decomposition of ammonium perchlorate activated by addition of NiO nanocrystals with different surface areas. NiO samples were characterized by X-ray diffraction (XRD), transition electron microscope (TEM), Brunauer-Emmett-Teller (BET) technique, Fourier transform infrared spectroscopy (FTIR), and Raman spectroscopy. With increasing annealing temperature, the surface areas of NiO samples reduced from 108.6 to 0.9 m2 g−1. The catalytic activities of NiO nanocrystals on the thermal decomposition of ammonium perchlorate were investigated by thermogravimetric analysis (TG) coupled with differential thermal analysis (DTA). With addition of NiO nanocrystals, thermal decomposition temperature of AP decreased greatly. Larger surface areas of NiO nanocrystals promoted the thermal decomposition of AP.

THERMAL DECOMPOSITION OF AMMONIUM PERCHLORATE ACTIVATED VIA ADDITION OF NiO NANOCRYSTALS

The influence of municipal sewage sludge addition on the agglomeration characteristic during straw combustion in a fluidized bed was investigated in a bubbling fluidized-bed reactor (5 kWth) with quartz sand as the bed material. In addition, chemical reactions between the alkali metal and three kinds of phosphorus-containing model compounds were studied to investigate the effect of phosphorus on the behavior of the alkali metal during wheat straw combustion. The element contents, the crystalline phases, the morphology, and the elemental composition in the residual ash samples from the combustion experiments were characterized by X-ray fluorescence (XRF), X-ray diffraction (XRD), and scanning electron microscopy (SEM), respectively. The results show that the agglomeration tendency decreases and the defluidization time is prolonged during co-combustion of municipal sewage sludge and wheat straw. The addition of municipal sewage sludge in wheat straw leads to the formation of alkali-rich phosphate silicate t...

Co-combustion of Agricultural Straw with Municipal Sewage Sludge in a Fluidized Bed: Role of Phosphorus in Potassium Behavior

The thermal behavior and gas product distribution during combustion of straw (wheat straw, corn stalks, and cotton stalks), municipal sewage sludge (MSS), and their blends were investigated by thermogravimetry–mass spectroscopy. The experiments were conducted with various blending ratios and temperatures ranging from 323 to 1,173 K. Addition of MSS decreased the combustion performance of the straw. The reactions between wheat straw and corn stalks with MSS proceeded more easily than that of cotton stalks. Significant interactions were observed between the straw and MSS at the char combustion stage. Gaseous species (CO2, SO2, NH3, HCN, and NO) were mainly produced at temperatures of 523–873 K at which most of the mass loss occurred. Higher MSS proportions in the blends resulted in lower emissions peaks for CO2, NH3, HCN, and NO except for SO2. To ensure combustion performance and mitigate problematic gaseous emissions, the proportion of MSS added to the blends should be <30 mass%.

Linna Li

Papers

CuO nanocrystals in thermal decomposition of ammonium perchlorate

Effect of Phosphorus on the Behavior of Potassium during the Co-combustion of Wheat Straw with Municipal Sewage Sludge

THERMAL DECOMPOSITION OF AMMONIUM PERCHLORATE ACTIVATED VIA ADDITION OF NiO NANOCRYSTALS

Co-combustion of Agricultural Straw with Municipal Sewage Sludge in a Fluidized Bed: Role of Phosphorus in Potassium Behavior

TG–MS analysis of thermal behavior and gaseous emissions during co-combustion of straw with municipal sewage sludge