Torrefaction could improve the fuel properties and reduce the operating costs. However, the particulate matter (PM) emission behavior during the torrefied pellet combustion remains unknown. In this work, cotton stalk was torrefied at a temperature of 220–300 °C with a O2 concentration of 0–21%. The torrefied pellet was burned out and PM emission behavior was investigated using a Dekati low-pressure impactor. The results show that oxidative torrefaction leads to notable decreases of H/C and O/C ratios, which makes the fuel properties similar to coals. The heating value is significantly improved and sensitive to the torrefaction temperature. Both non-oxidative and oxidative torrefaction give rise to considerable increase in the yield of PM10. The main composition of PM1 changed from KCl to K2SO4 due to the substantial release of Cl during torrefaction. Meanwhile, Ca and K contents in PM1-10 are generally high, implying that the presence of oxygen can facilitate the transformation of alkali and alkaline-earth metals into coarse particles. The torrefaction temperature at around 260 °C with a low O2 concentration of 0–6% are the optimal torrefaction operation conditions to produce good quality torrefied cotton stalk pellet with respect to high heating value and low PM emission in later combustion application.
The emission of ultrafine particulate matter (PM0.2) originated from the agricultural biomass pellet combustion poses great threat to atmospheric environment and human health, which restricts its large-scale utilization. In this study, a new phosphoric acid modification method is proposed to improve the PM0.2 reduction efficiency by kaolin additive. The effects of phosphoric acid concentration and treatment time on the physicochemical properties of kaolin and on the mitigation of PM0.2 emission from the pellet combustion are investigated. Results indicate that phosphoric acid modification destroy the internal structure of kaolin by the leaching of Al cations and the formation of active free silica. Meanwhile, the pore structure increases after modification with residual P deposited on the surface, which results in better alkali capture ability of modified kaolin. With the addition of phosphoric acid modified kaolin, significant reduction of PM0.2 emission can be achieved and the reduction ratio is proportional to the acid concentration. The maximum PM0.2 emission reduction ratio reaches 64.5% for the kaolin additive modified by 12 mol/L phosphoric acid for 6 hours. Finally, the PM0.2 reduction mechanism is proposed based on the analysis results, which provides technical knowhow for the industrial application of agricultural biomass pellet combustion.
A study on in-bed material catalytic reforming of tar/CH4 has been performed in the 150 kW allothermal gasifier at Mid Sweden University (MIUN). The major challenge in biomass fluidised-bed gasification to produce high-quality syngas, is the reforming of tars and CH4. The MIUN gasifier has a unique design suitable for in-bed tar/CH4 catalytic reforming and continuously internal regeneration of the reactive bed material. This paper evaluates the catalytic effects of olivine and Fe-impregnated olivine (10%wtFe/olivine Catalyst) with reference to silica sand in the MIUN dual fluidised bed (DFB) gasifier. Furthermore, a comparative experimental test is carried out with the same operation condition and bed-materials when the gasifier is operated in the mode of single bubbling fluidised bed (BFB), in order to detect the internal regeneration of the catalytic bed materials in the DFB operation. The behaviour of catalytic and non-catalytic bed materials differs when they are used in the DFB and the BFB. Fe/olivine and olivine in the BFB mode give lower tar and CH4 content together with higher H-2 + CO concentration, and higher H-2/CO ratio, compared to DFB mode. It is hard to show a clear advantage of Fe/olivine over olivine regarding tar/CH4 catalytic reforming. (C) 2015 Elsevier Ltd. All rights reserved.
This paper is to explore the biogas production potential of wetland aquatic biomass plants. 7 species of wetland aquatic biomass plants are used in the study, which include 4 plants with more fiber carbohydrate, Acorus calamus Linn, Typha orientalis Presl, Pontederia cordata and Canna indica, and 3 plants with more starch carbohydrate, Colocasia tonoimo Nakai, Thalia dealbata and Hydrocotyle vulgaris. In the experiment, these plants were treated by anaerobic fermentation in batch mode at 37°C. The results show that the anaerobic biogas production potential (ABP, mL·g-1VS) of aquatic biomass plants is different for different components content (%TS). The correlation between ABP and hemicellulose content is significant and negative (R=-0.784, 0.01<p<0.05), and the correlation between ABP and starch carbohydrate content is significant and positive (R=0.767, 0.01<p<0.05). The multiple stepwise regression equation with cross variable can roughly meet the statistical model to reflect the coeffect of hemicellulose, cellulose, starch carbohydrate and lignin on ABP of aquatic biomass plants, y=238.62+2.60x1+28.55x2-2.08x2x3+12.67x3, (Adj-R2=0.962, p(intercept)=0.034, p(x1)=0.101, p(x2)=0.036, p(x2x3)=0.066, p(x3)=0.031, p=0.025, SD=9.95), y represents ABP (mLg-1VS), x1, x2 and x3 represents the cellulose, lignin and starch carbohydrate content (%TS) respectively.
The large scale utilization of agricultural biomass as fuel is restricted by the feedstock properties of low energy density, high moisture content, heterogeneous composition and chemical impurities. In this work, torrefaction of biomass fuel with NH4H2PO4 additive was carried out to investigate the effects of NH4H2PO4 mixing ratio and torrefaction temperature on the properties of the torrefied fuel and particulate matter (PM) emission characteristics from combustion. The results show many benefits from NH4H2PO4 addition in biomass feedstock: 1) the removal of O and retention of C can be enhanced leading to lower mass and energy losses during torrefaction, 2) more Cl and S are released to gas phase leading to a lower absolute content of Cl and S in the torrefied fuel, and 3) the occurrence of alkali and alkaline earth metals change significantly. Moreover, the emissions of the fine particulate matters (PM1) from the torrefied fuels are clearly reduced when NH4H2PO4 is added and the reduction rate is closely related to P/K molar ratio with the maximum reduction rate achieved at P/K molar ratio equal to 1. These results suggest that the proposed method can effectively upgrade the fuel qualities and reduce PM1 emissions from the fuel combustion.
The growing demand for bioenergy in Sweden has drawn attention to the potential of forest thinning as bioenergy feedstock. There are, however, concerns regarding the cost effectiveness and environmental challenges of harvesting and processing forest thinnings into bioenergy. It is against this background that cost, energy and carbon balances were analysed to evaluate some of the economic and environmental sustainability issues of forest thinning based bioenergy systems. Primary data was collected from two thinning operations in two forest plots comprising spruce and birch stands. One operation involved the use of the conventional two machines (one separate machine for cutting or felling and another for forwarding felled trees) for the thinning work. The second operation involved a harwarder, which combines tree felling/cutting and forwarding in one unit machine. The results showed that forest thinnings provide a potential resource for the sustainable production of bioenergy. (C) 2011 Elsevier Ltd. All rights reserved.
Torrefaction is regarded as a promising way to improve the fuel properties of biomass. In this work, a typical agricultural biomass of cotton stalk with high supply availability was employed to reveal the correlation between torrefaction conditions and fuel quality as well as pelletizing property. Cotton stalk was torrefied at 220–300 °C with a wide oxygen concentration of 0%–21% using a fixed bed reactor. The fuel qualities of torrefied samples were analyzed and the pelletizing properties were investigated using a universal material testing machine. The results showed that both non-oxidative and oxidative torrefaction significantly improved the heating value at a maximum of 20.48%, while extreme conditions of 300 °C with 10%–21% concentration were avoided due to the excessive consumption of combustible substances. Four key pelletizing parameters, including pellet density, compressive strength, durability and hydrophobicity, were improved, while the energy consumption increased, mainly attributed to the reduction of hydrophilic functional groups and the increased friction force. Response surface methodology was introduced and it was indicated that the pelletizing properties were sensitive to the temperature, followed by oxygen. The operating conditions were optimized by central composite design and a torrefaction temperature of 260–270 °C with an oxygen concentration of 2%–3% were recommended to produce torrefied biomass pellet with good fuel and pelletizing properties.
PM emission is one of key issues in the biomass combustion of heat and power plants. In this paper, rice husk (RH) was co-combusted with cotton stalk (CSK) or cornstalk (CS) to study the PM emission behaviors. The experimental results show that the addition decreases PM1 yields by 20.13–54.65% for CSK and 45.99–76.70% for CS in comparison to the CSK or CS combustion alone. A strong synergistic effect exists during the co-combustion process, which can appreciably inhibit the generation of fine particulate matter. The synergistic effect is caused by the physical dilution effect, and mainly by the reaction between alkali metals species in cornstalk/cotton stalk ash and Si-containing species in rice husk ash to inhibit the volatilization of alkali metals. However, the PM reduction degree is also affected by the ash chemistry, especially the Si/(Ca + Mg) ratio, as confirmed by the higher synergistic effect of rice husk/cornstalk compared to rice husk/cotton stalk. The results suggest that co-combustion of biomass with high Si-containing rice husk is a promising approach to reduce PM1 emissions during biomass co-combustion.