Yanqing Niu

Bio: Yanqing Niu is an academic researcher from Xi'an Jiaotong University. The author has contributed to research in topics: Coal & Combustion. The author has an hindex of 20, co-authored 90 publications receiving 1864 citations.

Biomass torrefaction: properties, applications, challenges, and economy

Abstract: Biomass accounts for the largest renewable energy in the world, whereas its inherent drawbacks, such as low energy and mass density, hydrophilicity, poor grindability and severe ash-related issues, inhibit its extensive utilization. Torrefaction, conducted at 200–300 °C in an inert atmosphere, successfully overcomes the abovementioned drawbacks and improves the biomass applications. Thus, a critical review is performed for the new insight into further study, involving the properties improvement of torrefied biomass, applications on combustion and gasification, as well as the intractable challenges of ash-related issues during thermal conversion and economy viability. Compared to torrefaction duration and the moisture and size of biomass, the torrefaction temperature has the strongest impact on the biomass properties improvement. Respecting physical properties (energy density and grindabilty) and chemical thermal conversion characteristics, there exists an optimal torrefaction temperature at approximate 250 °C. Biomass torrefaction is strongly dependent on the degradation of hemicellulose. Herbaceous residues possess a higher degradation ratio compared to ligneous biomass; Besides, deciduous trees mainly containing xylan in hemicellulose are more active than coniferous trees which mainly contain glucomannan in hemicellulose. The torrefied biomass possesses increased carbon content, decreased H/C and O/C ratios, increased mass energy density, similar chemical compositions with coal, and the availability for gasification and co-firing. Moreover, large amount of Cl, S, and K release during torrefaction, which bring considerable fringe benefits by reduction or elimination of the intractable ash-related issues during thermal conversion, such as slagging, agglomeration and corrosion. At present, the cost of biomass torrefaction is higher than coal. However, it can be significantly reduced by the implementation of carbon credits market, increasing torrefaction plant equipment size, and empirical cumulation. Later, more attention should be focused on application demonstration and systematic economic optimization.

Experimental investigation on biomass co-firing in a 300MW pulverized coal-fired utility furnace in China

Abstract: Mold biomass pellets have been utilized on a 300 MW pulverized coal-fired furnace in China for the first time. Biomass was ground using the existing mill system, and without using any additional equipment. The maximum ratio of the biomass used in the experiments is 16.1% by energy input. The feasibility of grinding biomass and the safety of mill operation have been analyzed. In addition, the effects of co-firing biomass on the flame, temperature, pollutant emission, and unburned carbon in ash have been investigated. Also the characteristics of fly ash and its utilization in the concrete have been tested. The results show that existing roller mills and direct-blowing pulverizing systems can be used to grind mold biomass and to transport pulverized biomass within the limit in the flow rate of the biomass that can be processed. During the processes of biomass co-firing, the flame on the biomass injector is stable, but the outlet temperature of the furnace decreases, and the unburned carbon in the fly ash increases, when compared with the condition when firing coal only. NO x emission decreases with an increase in the biomass input. When the rate of biomass feed reaches 24 t/h in the test, the NO x emission is reduced by about 10%, but there is only a small reduction in the SO 2 emission. Investigations on the characteristics of the fly ash shows that the content of potassium and chlorine in the ash increases with an increase in the biomass feed, but co-firing biomass does not affect the quality of the fly ash to be used in the cement industry. The results presented in this paper can provide guidance for direct biomass co-firing in existing high-capacity pulverized coal-fired furnaces in China.

Lignocellulosic biomass pyrolysis: A review of product properties and effects of pyrolysis parameters

Abstract: Pyrolysis is one of the thermochemical technologies for converting biomass into energy and chemical products consisting of liquid bio-oil, solid biochar, and pyrolytic gas. Depending on the heating rate and residence time, biomass pyrolysis can be divided into three main categories slow (conventional), fast and flash pyrolysis mainly aiming at maximising either the bio-oil or biochar yields. Synthesis gas or hydrogen-rich gas can also be the target of biomass pyrolysis. Maximised gas rates can be achieved through the catalytic pyrolysis process, which is now increasingly being developed. Biomass pyrolysis generally follows a three-step mechanism comprising of dehydration, primary and secondary reactions. Dehydrogenation, depolymerisation, and fragmentation are the main competitive reactions during the primary decomposition of biomass. A number of parameters affect the biomass pyrolysis process, yields and properties of products. These include the biomass type, biomass pretreatment (physical, chemical, and biological), reaction atmosphere, temperature, heating rate and vapour residence time. This manuscript gives a general summary of the properties of the pyrolytic products and their analysis methods. Also provided are a review of the parameters that affect biomass pyrolysis and a summary of the state of industrial pyrolysis technologies.

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

Abstract: 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.