•Release of Cl was synchronous with devolatilization at 200–350 °C.•Particle size influenced the release ratio of Cl obviously.•Secondary reactions had a limited influence on speciation transformation of K.•The reaction intensities of KCl with four macromolecules were different.The release and transformation characteristics of K and Cl during straw torrefaction and mild pyrolysis under different conditions were investigated. The results show that release ratio of Cl increased continuously with temperature and holding time and the release of Cl was linearly proportional to devolatilization. The particle size was one of most important factors influencing Cl release. The release ratio for 74–124 μm straw particle was 60.78%, which was much higher than 27.25% for 250–420 μm at 350 °C. The influence of sample weight, particle size and heating rate was mainly due to secondary reactions of once-released Cl and pyrolysis char (the AAEMs and carbon active sites) during the diffusion process of volatiles. The influence of secondary reactions on K release and transformation behavior was not significant. The reaction intensities of KCl and macromolecules (cellulose, lignin, xylan and pectin) were different. The release of Cl was not generally equal to the fractions of K transformed into ion-exchanged species and released to the gas phase during KCl-loaded macromolecules torrefaction and mild pyrolysis, mainly due to different intensities of their secondary reactions.

•Torrefaction at 250 and 300 °C inhibits the total release of Cl at 1000–1200 °C.•BET surface area of pyrolysis char of torrefied straw at 250 and 300 °C is smaller.•Removed volatiles during torrefaction reduce the release of Cl.•Enrichment of Cl on surface for torrefied straw accelerates the release of Cl.•Generated organochlorine during torrefaction doesn’t decompose completely.Pyrolysis experiments in a fixed-bed reactor at 800–1200 °C were carried out to compare the release and transformation behavior of Cl between raw and torrefied rice straw. The impact of torrefaction pretreatment on total release of Cl during rice straw high temperature pyrolysis has also been assessed. The influence factors, including volatile matter, particle structure, surface elements enrichment and occurrence forms of Cl, which are different between raw and torrefied rice straw, have been studied. The results show that Cl release ratios of torrefied rice straw at 250 and 300 °C are lower than that of raw rice straw during pyrolysis at 800–1200 °C. At 900–1200 °C, release ratio of Cl of torrefied rice straw decreases with the torrefaction severity. Torrefaction pretreatment at 250 and 300 °C inhibits the total release of Cl during rice straw pyrolysis at 1000–1200 °C. Enrichment of Cl on surface for torrefied rice straw accelerates the release of Cl. The removed volatiles during torrefaction would reduce the release of Cl during pyrolysis, and generated organochlorine (or CCl) during torrefaction has the same inhibiting effect on the release of Cl. Surface morphology and specific surface area of pyrolysis char are different between raw and torrefied rice straw. Less specific surface area for pyrolysis char of torrefied rice straw at 250 and 300 °C would restrict the release of Cl.

•A novel application of the fixed valve tray column has been conceived.•The effects of flow characteristic on collection efficiency were investigated.•A correlation is developed for predicting the collection efficiency of particles.The collection efficiency is one of the key parameters to evaluate the performance of washing columns, and the gas–liquid flow characteristic is an important factor affecting collection efficiency. In this work, the gas–liquid flow characteristic and its effect on collection efficiency in a fixed valve column have been investigated. The experimental results show that the fixed valve washing column is capable of generating higher gas holdup than a standard bubble column under similar situations. For different particle sizes, with increasing gas holdup, the changes of the trends in collection efficiency are different. For particles larger than 1 μm, the collection efficiency increases with gas holdup while for particles finer than 1 μm, the collection efficiency either decreases (0.5–1 μm) or decreases initially and then increases again (0.3–0.5 μm). The collection efficiency increases with liquid-to-gas ratio but decreases with bubble size, bubble velocity and particle loading. The contribution of each tray to the collection efficiency is different. A correlation is developed for predicting the collection efficiency of particles and the experimental values agree well with the predicted values.A novel application of the fixed valve tray column has been conceived. Fig. 1 is the schematic of a fixed valve tray column scrubber system. The structure of the fixed valve tray is shown in Fig. 2. Particle collection efficiency on each plate was investigated. It can be seen from Fig. 3 that the collection efficiency of particles larger than 5 μm can achieve above 90%, and the collection efficiency of particles finer than 1 μm drop to around 60% rapidly on the first plate. On the second plate the efficiencies of particles larger than 1 μm are in the range of 40%–60%, while for particles finer than 1 μm the collection efficiency is 30% due to purification effect of the first plate.

A method of predicting the particle collection efficiency of a fixed valve tray column and the particle size distribution properties, which considers diffusion, interception, and impaction, is presented to study the particle removal mechanisms of a fixed valve column. The particle size distribution of fly ash particles is represented by a log-normal function, and the continuous evolution of the particle size distribution in a fixed valve column is taken into account with the first three moment equations. The results show that the collection efficiency is represented as a U-shaped curve with a minimum in the region of around 2.0 μm in particle size. This allows fly ash particles in the diffusion and in the impaction-dominant regions to be removed at a higher rate compared with fly ash in the intermediate region. As particles pass through the bubble column, the geometric standard deviations of the size distribution of fly ash particles decrease. The geometric mean diameter of fly ash particles in the diffusion-dominant region increases, whereas it decreases in the impaction-dominant region. The present study also shows that, in optimum operation conditions such as low bubble slip velocity, small bubble size, and high gas holdup, the fixed valve tray column has sufficient ability to remove tiny and hydrophobic particles.

Rapid pyrolysis of 6 biomass/coal blends (1:4, wt) including rice straw + bituminous (RS + B), rice straw + anthracite (RS + A), chinar leaves + bituminous (CL + B), chinar leaves + anthracite (CL + A), pine sawdust + bituminous (PS + B), and pine sawdust + anthracite (PS + A) was carried out in a high-frequency magnetic field based furnace at 600–1200 °C. The reactor could not only achieve high heating rates of fuel samples but also make biomass and coal particles contact well; secondary reactions of primary products during rapid pyrolysis can also be efficiently reduced. By comparing nitrogen distributions in products of blends (experimental values) with those of the sums of individual biomass and coal (weighted values), nitrogen conversion characteristics under rapid pyrolysis of biomass/coal blends were investigated. Results show that, biomass particles in blends lead to higher experimental char-N yields than the weighted values during rapid pyrolysis of biomass/anthracite blends. The decreased heating rates of both biomass and coal particles caused by the low packing densities of biomass may be the reason. For blends of CL + B in which packing density of chinar leaves is high, and for PS + B during pyrolysis of which melting and shrinkage happen to pine sawdust, both biomass and coal particles can obtain high heating rates, synergies can be found to promote nitrogen release from fuel samples and decrease char-N yields under all the conditions. But the low fluidity and not easily collapsed carbon skeletons of rice straw make the heating rates of rice straw and bituminous particles in RS + B lower than those of CL + B and PS + B, and weaker synergies can be found from char-N yields of RS + B. The synergies can obviously be found to decrease the (NH3 + HCN)-N yields and make more nitrogen convert to N2 except for those of several low-temperature conditions (600–700 °C). Under the low-temperature (600–700 °C) condition, synergies make molar ratios of HCN-N/NH3-N higher than those of the weighted values.

The char of three typical biomasses, rice straw char (RS char), chinar leaves char (CL char), and pine sawdust char (PS char), was prepared in a high-frequency furnace, which could efficiently reduce secondary reactions under rapid pyrolysis conditions at 800−1200 °C. The rapid pyrolysis char produced was isothermally gasified in a thermogravimetric analyzer (TGA) under a CO2 atmosphere. Effects of biomass type and pyrolysis temperature on intrinsic carbon structures and morphologic structures of char and further on gasification characteristics of char were investigated using a Raman spectrum analyzer, scanning electron microscopy (SEM), and a surface area and pore size distribution analyzer. Gasification kinetic models were also contrastively discussed under different conditions. Results show that gasification rates decrease with the increasing pyrolysis temperature. Under the morphologic characteristic reserved conditions, morphologic structures present obvious effects on gasification rates. Gasification reactivity of the three biomass chars is in the order of CL char > RS char > PS char. Melting and shrinkage happen during rapid pyrolysis of PS, and the disappearance of the pore and decrease of the specific surface area of PS char lead to the low specific surface area and gasification rates of PS char. Unobvious melting happens to RS char and CL char, and the initial physical structures can be almost reserved, while CL char presents larger porosity and specific surface area, which make its gasification rates higher than those of RS char. In most conditions, the random pore model (RPM) performs well to describe gasification rates of biomass char studied in this work. However, for gasification of PS char at high temperatures, during which high gasification rates can be maintained in high conversion ranges, the modified random pore model (M-RPM) performs better. For gasification of RS char and CL char at low temperatures, during which gasification rates present a sharp decrease and trailing in medium−high conversion ranges, the shifted M-RPM performs better.

HCN (hydrocyanic acid) and NH3 (ammonia) (including HNCO (isocyanic acid)) released during rapid pyrolysis of three biomass samples (rice straw, chinar leaves, pine sawdust) and a nitrogen rich material (soybean cake) were measured. The pyrolysis runs were conducted at 600−1200 °C using a high-frequency furnace. Much more HCN than NH3 was released in the biomass runs while the reverse was observed in the soybean cake runs. Because lignin was a common constituent of biomass cells and nearly absent in soybean, the effect of its content on HCN release from the biomass was determined. A strong correlation was established for each biomass sample suggesting that lignin may promote formation of heterocyclic nitrogenous compounds which then decompose to form HCN. HCN release and char/tar-N formation decreased at a higher pyrolysis temperature. Pyrolysis at >1000 °C is desirable since most nitrogen in the biomass will be converted to N2 with <7% released as HCN and NH3.

The development of a radial-inlet structure cyclone separator is reported in this paper, which is used as a primary device for gas-particle separation in an opposed multi-burner (OMB) gasification system. The radial-inlet cyclone is more suitable for a high-pressure industrial operation environment on the premise of higher efficiency. A model based on computational fluid dynamics (CFD) techniques was applied to study the performance of a new-type cyclone separator. In the approach, the turbulent flow was described by the Reynolds stress model, and the particle flow was described by the stochastic Lagrangian model. The validity of the proposed approach is verified by the good agreement between the measured and the predicted results. The results indicate that, though the velocity flow field is not geometry symmetrical and a three-dimensional unsteady state, it is quasi-periodic. Additionally, there exists a processing vortex core phenomenon in the cyclone. The particle concentration distribution is nonuniform because of the centrifugal force. The distribution area can be divided into three parts according to the particles’ motion feature. And the larger particles are easier to separate than the smaller ones. But particles with a size exceeding a critical value will not be collected at the bottom and stagnate on the conical wall of the cyclone. This will lead to serious erosion on the conical part in the cyclone. In addition, the separation efficiency increases with the particle size, and the cut-point diameter of the radial-inlet cyclone is smaller than the traditional cyclone under the same inlet conditions.

•Specific surface area of char decreases with torrefaction severity for raw straw.•Torrefaction leads to lower graphitization degrees of pyrolysis char for raw straw.•The influence of torrefaction is different between raw and water washed straw.•Pyrolysis char of torrefied sample above 250 °C owns a lower gasification activity.The influence of torrefaction on the physicochemical characteristics of char during raw and water washed rice straw pyrolysis at 800–1200 °C is investigated. Pore structure, aromaticity and gasification activity of pyrolysis chars are compared between raw and torrefied samples. For raw straw, BET specific surface area decreases with the increased torrefaction temperature at the same pyrolysis temperature and it approximately increases linearly with weight loss during pyrolysis. The different pore structure evolutions relate to the different volatile matters and pore structures between raw and torrefied straw. Torrefaction at higher temperature would bring about a lower graphitization degree of char during pyrolysis of raw straw. Pore structure and carbon crystalline structure evolutions of raw and torrefied water washed straw are different from these of raw straw during pyrolysis. For both raw and water washed straw, CO2 gasification activities of pyrolysis chars are different between raw and torrefied samples.