Effect of binder addition on combustion characteristics of cotton straw pellets and kinetic analysis

In this study,the combustion characteristics and kinetics of cotton straw(CS)particles mixed with polyethylene(PE)film and coal gangue(CG)were investigated.The co-combustion characteristics of CS mixed with PE and CG at different heating rates were revealed by the thermogravimetric method and differential thermogravimetric method.The ignition temperature,burnout temperature,and maximum weight loss rate were measured,and the comprehensive combustion and flammability indexes were calculated.The results showed that the composite combustion characteristic index and flammability index increased with the increase in heating rate.The addition of PE and CG additives could effectively extend the combustion time.The Coats-Redfern(C-R)reaction model and N-order reaction model were used to evaluate the kinetic parameters of the blends.The results showed that 12.5%PE+12.5%CG particles had the lowest activation energy(Ea=103.73 kJ·mol^(-1))at the volatile combustion stage.The dynamics conform to the third-order dynamics model.In addition,the applicability of C-R model,Flynn-Wall-Ozawa(FWO)model,and Starink model in the calculation of activation energy was explored,and it was found that the FWO model is not suitable for the calculation of activation energy of biomass pellet combustion kinetics.This study provides a new method for the development and utilization of mixed fuel particles of cotton stalk and solid waste and expands the application prospect of biomass.

Straw layer burial to alleviate salt stress in silty loam soils: Impacts of straw forms

Salt stress can be alleviated by straw layer burial in the soil, but little is known of the appropriate form of the straw layer for optimal regulation of soil water and salinity because of the uncontrollability of field tests. Here, the following four straw forms with compaction thickness of 5 cm buried 40–45 deep were studied: no straw layer(CK), segmented straw(SL, 5 cm in length), straw pellet(SK), and straw powder(SF). The three straw forms(SL, SK and SF) significantly delayed the infiltration of irrigation water down the column profile by 71.20–134.3 h relative to CK and the migration velocity of the wetting front under SF was the slowest. It took longer for the wetting front to transcend SK than SL but shorter for it to reach the bottom of soil column after water crossed the straw layer. Compared with CK, the average volumetric water content in the 0–40 cm soil layer increased by 6.45% under SL, 1.77% under SK and 5.39% under SF. The desalination rates at the 0–40 and 0–100 cm soil layers increased by 5.85 and 3.76% under SL, 6.64 and 1.47% under SK and 5.97 and 4.82% under SF. However, there was no significant difference among straw forms in the 0–40 cm soil layer. Furthermore, the salt leaching efficiency(SLE, g mm^–1 h^–1) above the 40 cm layer under SL was 0.0097, being significantly higher than that under SF(0.0071) by 37.23%. Salt storage under SL, SK and SF in the 40–45 cm layer accounted for 4.50, 16.92 and 7.43% of total storage in the 1-m column profile. Cumulative evaporation under SL and SF decreased significantly by 41.20 and 49.00%, with both treatments having the most significant inhibition of salt accumulation(resalinization rate being 36.06 and 47.15% lower than CK) in the 0–40 cm soil layer. In conclusion, the different forms of straw layers have desalting effects under high irrigation level(446 mm). In particular, SL and SF performed better than SK in promoting deep salt leaching and inhibiting salt accumulation on the soil surface. However, SL was simpler to implement and its SLE was higher. Therefore, the segmented 5 cm straw can be recommended as an optimum physical form for establishing a straw layer for managing saline soils for crop production.

Optimization of binder addition and compression load for pelletization of wheat straw using response surface methodology

Densification is required for efficiently handling and transporting biomass as feedstock for biofuel production.Binders can enhance straw pellet strength and improve the pellet performance.The present investigation aimed to optimize binders and compression load for wheat straw pelletization using a single pelleting unit.Response surface methodology was employed by using a four-factor,five-level central composite design with wood residue(%,w/w),bentonite(%,w/w),crude glycerol(%,w/w),and compression load(N)as process parameters.The pellet tensile strength,specific energy consumption of pelleting,and pellet density were the response variables.The higher heating value,ash content of the pellet product and the cost of the feedstock were also considered in optimizing binder addition.The developed model fitted the data and was adequate for binder analysis and optimization.Wheat straw pellet,with the addition of 30% wood residue,0.80% bentonite,and 3.42% crude glycerol,in addition to 4000 N of compressive load,was identified as optimal with good performance of pellet tensile strength(1.14 MPa),specific energy consumption(32.6 kJ/kg),and pellet density(1094 kg/m^(3))as well as low ash content(6.13%)and high heating value(18.64 MJ/kg).Confirmation tests indicated high accuracy of the model.

Field assessment of straw pellet combustion in improved heating stoves in rural Northeast China

Straw pellets are widely promoted and expected to be a cleaner alternative fuel to unprocessed crop residues and rawcoal in rural China.However,the effectiveness of these dissemination programs is not well evaluated.In this field study,emission characteristics of burning strawpellets,rawcoal,and unprocessed corn cobs in heating stoveswere investigated in a pilot village in Northeast China.Emission measurements covering the whole combustion cycle(ignition,flaming,and smoldering phases)shows the promotion of improved heating stoves and straw pellets could reduce pollutant emissions(e.g.,SO_(2) and CO),but increase NO_(X) and PM_(2.5) emissions compared to the initial stove-fuel use pattern in the studied area.There is a significant variance in emission characteristics between different combustion phases.The normalized emission concentrations of the different stove-fuel combinations were higher than the limits in the Chinese national standard for heating stoves,indicating that the standard is not met for real-world emissions.Coal consumption was lower than official data.Household surveys were conducted to identify the barriers to fuel and stove access associated with existing promotion strategies,management,and policies.The pilot program was of the typical“subsidy-and-policy-dependence”pattern and was unlikely to be implemented on a large scale.Technological innovation,operational optimization,and proper policies considering the local socioeconomic factors are needed to sustain the promotion of biomass straw pellets and stoves.