Changsui Zhao

NOx and N2O Precursors from Biomass Pyrolysis: Nitrogen Transformation from Amino Acid

Large quantities of NO(x) and N(2)O emissions can be produced from biomass burning. Understanding nitrogen behavior during biomass pyrolysis is crucial. Nitrogen in biomass is mainly in forms of proteins (amino acids). Phenylalanine, aspartic acid, and glutamic acid were used as the model compounds for the nitrogen in biomass. Release behavior tests of nitrogen species from the three amino acids during pyrolysis in argon and gasification with O(2) and CO(2) were performed using a thermogravimetric analyzer (TGA) coupled with a Fourier transform infrared (FTIR) spectrometer. The results indicate that although the influence of oxygen and CO(2) in the atmosphere on nitrogen behavior is different for the amino acids, it is interesting to find some phenomenon in common. The presence of oxygen promotes NO and HNCO formation for all the three amino acids; HCN and HNCO formation are suppressed by introduced CO(2) for all the three amino acids. This can reveal the N-conversion mechanism from biomass in depth under the same conditions.

TG-FTIR study on co-pyrolysis of municipal solid waste with biomass.

Co-pyrolysis of cotton stalk, a representative agricultural biomass in China, mixed with municipal solid waste (MSW) with high ash content and low calorific value was carried out using a thermogravimetric analyzer (TGA) coupled with a Fourier transform infrared (FTIR) spectrometer in Ar atmosphere. Pyrolysis characteristic and pollutant emission performance from MSW and stalk blends at different mass proportions were studied. The results show that as the mass proportion of stalk added increases, the total weight loss of the blend during pyrolysis increases. The addition of stalk has substantial effects on the N-selectivity to HCN, NH(3) and HNCO. In the presence of stalk, lower concentrations of HCl are detected.

Effect of crystal structure on CO2 capture characteristics of dry potassium-based sorbents

SEM and N(2) adsorption tests show that the surface area is 3.0 m(2)g(-1) for K(2)CO(3) with structure of monoclinic crystal (PC#1) while that of K(2)CO(3) with structure of hexagonal crystal (PC#2) is 0.95 m(2)g(-1), and the pore volume of PC#1 and PC#2 are 8.0 x 10(-3) and 2.8 x 10(-3)cm(3)g(-1), respectively. Their pore size distribution curves show almost the same trends. Compared with PC#2, the particle morphology of PC#1 is better for the carbonation reaction. However, the carbonation reaction activity of PC#2 is better than that of PC#1. In order to find out the reason, the crystal structure characteristics of these sorbents are investigated with XRD and Inorganic Crystal Structure Database searching. It is shown that the difference in crystal structure causes the difference of carbonation reactivity between PC#1 and PC#2. The present work provides basic data for the technology of CO(2) capture from flue gas using dry potassium-based sorbents.

Feasibility of CO2/SO2 uptake enhancement of calcined limestone modified with rice husk ash during pressurized carbonation

The calcination/carbonation cycle using calcium-based sorbents appears to be a viable method for carbon dioxide (CO₂) capture from combustion gases. Recent attempts to improve the CO₂/SO₂ uptake of a calcium-based sorbent modified by using rice husk ash (RHA) in the hydration process have succeeded in enhancing its effectiveness. The optimal mole ratio of RHA to calcined limestone (M(Si/Ca)) was adjusted to 0.2. The cyclic CO₂ capture characteristics and the SO₂ uptake activity of the modified sorbent were evaluated in a calcination/pressurized carbonation reactor system. Scanning electron microscope (SEM) images and X-ray diffraction (XRD) spectrum of the sorbent were also taken to supplement the study. The results showed that the carbonation conversion was greatly increased for the sorbent with M(Si/Ca) ratio of 0.2. For this sorbent formulation the optimal operating conditions were 700-750 °C and 0.5-0.7 MPa. CO₂ absorption was not proportional to CO₂ concentration in the carbonation atmosphere, but was directly related to reaction time. The CO₂ uptake decreased in the presence of SO₂. SO₂ uptake increased, and the total calcium utilization was maintained over multiple cycles. Analysis has shown that the silicate component is evenly or well distributed, and this serves as a framework to prevent sintering, thus preserving the available microstructure for reaction. The sorbent also displayed high activity to SO₂ absorption and could be used to capture CO₂ and SO₂ simultaneously.

NOx and N2O Precursors from Biomass Pyrolysis: Role of Cellulose, Hemicellulose and Lignin

Cellulose, hemicellulose, and lignin play important roles in biomass. Nitrogen in biomass is mainly in forms of proteins (amino acids). Two amino acids, proline and glutamic acid, with different structures were selected as the nitrogen-containing model compound in biomass. Interaction between the two amino acids with cellulose, hemicelluloses, or lignin at different weight ratios was investigated to understand nitrogen chemistry. Considering the composition of wood and agricultural straw, proline and the mixture of cellulose, hemicellulose, and lignin were pyrolyzed under the same condition. Nitrogen transformation during copyrolysis of amino acid with the component at different ratios was identified to determine the role of cellulose, hemicellulose, and lignin. The emissions of HCN and NH3 were detected with a Fourier transform infrared (FTIR) spectrometer. The results indicate that although the structure of the amino acid has a significant effect on the nitrogen transformation during pyrolysis, it is interesting to find some characteristics in common for the aliphatic amino acid and heterocyclic amino acid. The effects of hemicellulose on NH3 formation from the two amino acids are similar, hemicellulose inhibits N-NH3 conversion and lignin promotes NH3 formation for the two amino acids.

NO formation during agricultural straw combustion

NO formation during combustion of four typical kinds of straw (wheat straw, rice straw, cotton stalk and corn stalk) which belong to soft straw and hard straw was studied in a tubular quartz fixed bed reactor under conditions relevant to grate boiler combustion. Regarding the real situation in biomass fired power plants in China, NO formation from blended straw combustion was also investigated. Nitrogen transfer during blended straw pyrolysis was performed using a thermogravimetric analyzer (TGA) coupled with a Fourier transform infrared (FTIR) spectrometer. The results show that NO conversion for the four straws during combustion is distinctive. Over 70% fuel-N converts into NO for cotton stalk, while only 37% for wheat straw under the same condition. When wheat straw and cotton stalk were mixed, N-NO conversion increases. The limestone addition promotes NO emission during cotton stalk combustion. The presence of SO(2) in atmosphere suppresses NO formation from straw combustion.

Investigation on Dynamic Calibration for an Optical-Fiber Solids Concentration Probe in Gas-Solid Two-Phase Flows

This paper presents a review and analysis of the research that has been carried out on dynamic calibration for optical-fiber solids concentration probes. An introduction to the optical-fiber solids concentration probe was given. Different calibration methods of optical-fiber solids concentration probes reported in the literature were reviewed. In addition, a reflection-type optical-fiber solids concentration probe was uniquely calibrated at nearly full range of the solids concentration from 0 to packed bed concentration. The effects of particle properties (particle size, sphericity and color) on the calibration results were comprehensively investigated. The results show that the output voltage has a tendency to increase with the decreasing particle size, and the effect of particle color on calibration result is more predominant than that of sphericity.

Emission Control of Gaseous Pollutants From Co-Firing of Petroleum Coke and Coal in CFB

Petroleum cokes including delayed coke, fluid coke, etc. are byproducts of solid residuals from the crude refining process. Using high sulfur petroleum coke as alternative fuel is feasible owing to its high fixed carbon and low ash content, but petroleum cokes are difficult to ignite due to their low volatile content and containing substantial concentrations of vanadium, nickel, nitrogen and sulfur, which can be sources of pollution emission and fireside fouling or corrosion problem. Co-firing petroleum coke and coal in circulating fluidized bed (CFB) is an ideal solution for those problems. Emission characteristic of gaseous pollutants from co-firing petroleum coke and coal is investigated in the paper. Experiments were carried out in a 0.6 MWt pilot-scale CFB combustor with the total height of 12m from the air distributor to the exit of combustor. The concentrations of SO2 , NO, N2 O, O2 , CO2 and CO were measured on line by the gas analyzer. The effect of several parameters, in term of the primary air percentage, air excess coefficient, bed temperature, Ca/S molar ratio and percentage of petroleum coke in mixed fuel on the emission of SO2 , NO, N2 O is verified in experiments. Experimental results show that SO2 concentration in flue gas reduces with increase in the primary air percentage, excess air coefficient and Ca/S ratio for all kinds of fuel mixtures, whereas NO, N2 O concentration rises with increase in the primary air percentage and excess air. When the bed temperature changes, the NO concentration varying trend is opposite to N2 O. There is an optimal temperature for sulfur retention. Co-firing of petroleum coke and coal with different mixing ratio in CFB can be stable, efficient and environment friendly.Copyright

Effect of kaolinite additive on formation of PM2.5 under O2/CO2 atmosphere during coal combustion

The influence of kaolinite additive on the emission characteristics of PM2.5 (particulates with aerodynamic diameter less than 2.5μm) was studied with a tube furnace. The combustion tests were carried out at 1123 K under O2/CO2 atmosphere. The PM2.5 generated from coal combustion was collected and analyzed with an Electrical Low Pressure Impactor (ELPI). The results indicate that kaolinite is an important factor for the formation of PM2.5 during coal combustion under O2/CO2 atmosphere. The number and mass concentrations of PM1 diminish, but those of PM1–2.5 enhance slightly after kaolinite is added. The size distributions of PM2.5 are similar, which display two peaks around 0.2 μm and 2.0 μm, respectively. With increasing the weight ratio of kaolinite, the concentrations of S, Pb, Cu, Na and K decrease. The submicron-size ash particles smaller than 0.317 μm are formed via nucleation of vaporized ash components. The supermicron-size ash particles are formed by coagulation and coalescence of the submicron-size ash, and fragmentation and coalescence of mineral matter.

Experimental Study on Characteristics of Pyrolysis, Ignition and Combustion of Blends of Petroleum Coke and Coal in CFB

It is a common understanding that co-firing of petroleum coke and coal in circulating fluidized bed (CFB) is an efficient, economical and environment-friendly way to utilize petroleum coke with medium or high sulfur content. Experimental investigations on characteristics of pyrolysis, ignition and combustion of petroleum coke, coal and their blends with different mixing ratios were conducted on a thermogravimetric analyzer and a pilot CFB combustor systematically. Ignition temperature and burnout temperature were also acquired. The effects of several parameters in terms of the fuel category, the heating rate, the coal/coke mass flow ratio, the CO2 partial pressure, and the Ca/S molar ratio on the ignition and burnout characteristics of the petroleum coke and the blends of the petroleum coke and coal were verified. The results show that the ignition temperature and the burnout temperature of the petroleum coke are between those of bituminous coal and anthracite, which implies that its combustion characteristic is between bituminous coal and anthracite, but is more closer to the bituminous. The pyrolysis process of blends of petroleum coke and coal accords with mechanism model (1−α)1.5 well, and the combustion process accords with mechanism model w1.5 well. Although the ignition temperature of the blended fuels keeps the same when the heating rate, or the CO2 partial pressure or the Ca/S molar ratio increases, the burnout temperature decreases gradually. With decrease in the coal/coke mass flow ratio, the ignition temperature and the burnout temperature of the blends rise.Copyright