Fluidized bed combustion of high ash anthracite: Analysis of combustion efficiency and particle size distribution

Fluidized bed combustion of high ash anthracite (HAA) was experimentally studied. The combustor consists of 0.25 m ID bed, and auxiliary equipments for coal feeding, ash removal, lemperature control, etc. Experimental results elucidate main cause of fuel loss to be elutriation of fines (i.e., flyash) containing unburned carbon. However, detailed balances of particle size distribution show majority of carbon in flyash comes from fines contained in the feed instead of attrition of coarse particles. The latter is the main source of flyash for conventional coal. The difference is due to much smaller attrition rate of HAA; feed HAA particles do not shrink much in size by combustion and attrition.     

Pretreatment of stainless steel substrate surface for the growth of carbon nanotubes by PECVD

Multiwalled carbon nanotubes were grown from acetylene and hydrogen gas mixture directly on stainless steel plates by rf powered PECVD and then electric double layer capacitors were fabricated from them without any further treatment. It was found that suitable pretreatment of stainless steel substrates was required for the satisfactory growth of carbon nanotubes on them. In this study substrates were polished, etched in HF solution and then treated with hydrogen plasma before the growth of carbon nanotubes. SEM shows that the surface of the substrate became smooth after polishing. It was severely etched to reveal grains of stainless steel after dipping in HF solution. With hydrogen plasma treatment the grains become more rounded in shape and grew in size. When the grains size was tens of nanometers, carbon nanotubes were grown. Exposing substrates to the hydrogen plasma for 10 min or longer caused the grains to grow larger and the growth of carbon nanotubes became poorer. Carbon nanotubes grown in this study were mutiwalled and curly in shape. Capacitors made from the carbon nanotubes showed initial specific capacitance in the range of 80–100 F/g.     

Thermal treatment of petroleum contaminated soils by a fluidized bed desorber

A novel type of fluidized bed desorber was developed for the remediation of petroleum-contaminated soils at low temperature with high efficiency. The performance of the fluidized bed desorber was experimentally investigated in two different operation modes. Results of continuous operation of fluidized bed indicated that the effect of the mass ratio of the fluidizing gas flow rate to the feed rate of contaminated soil was not significant at temperatures above 300 ‡C as long as proper fluidization was ensured. Periodic fluidization mode was tested aiming at reduction of off-gas volume. Effects of cycle time and split fraction on desorption efficiency were investigated. Within the range of experimental conditions, desorption efficiency decreased with increase of cycle time and split due to defluidization in the bed. With suitable choice of cycle time and split, periodic fluidization of the desorber enabled considerable reduction of off-gas volume without compromising desorption efficiency.     

Kinetics of steam reforming over a Ni/alumina catalyst

Steam reforming of methane over a commercially available, nickel/alumina catalyst was experimentally studied. The reactor employed for the study was made of 7 mm i.d. quartz tube and catalyst particles were 0.84-1 mm in size. The amount of catalyst charge in the reactor was around 0.3 gram. Experiments were carried out varying the steam to methane ratio in the feed gas from 1 to 10 and reaction temperature from 823 to 1073 K. Nitrogen gas was used to control partial pressure of methane and steam. Using Marquardt method reaction rate derived from the experiments was fitted to $$reaction rate = 1,527 exp( - 14,820/RT) P^{1.014} _{CH_4 } P^{ - 0.9577} _{H_2 0} $$ Thus reaction order was close to one for methane and close to minus one for steam, respectively.     

A study of deposition rate and characterization of bn thin films prepared by cvd

Triethylboron (TEB) and ammonia were employed as precursors in preparation of boron nitride thin films on Si(100) substrate by CVD. Operating parameters such as reactor pressure and feed rates of gases were varied to investigate their effects on deposition rate and film characteristics. Total gas pressure in the reactor was varied from near atmospheric to near 1 torr. Deposition temperature was in the range of 850-1,100‡C. Deposition rate increased with increase of partial pressure of TEB, but decreased with increase of total pressure in the reactor. Deposited films were examined with SEM, FTIR, XPS, AES and XRD. Films were BN of turbostratic structure and their texture and carbon content varied with deposition conditions.     

Removal of so x and NO x from flue gas with ceria

Ceria (CeO₂) is considered as one of materials for the simultaneous removal of SO_x and NO_x from flue gas. Ceria was coated on honeycomb and tested for adsorption of SO₂ and reduction of NO with ammonia. Experimental results showed the characteristics similar to copper oxide but reactivity for NO reduction was higher in broader temperature range compared with the latter.     

Hydrogen production from fluidized bed steam reforming of hydrocarbons

Steam reforming of methane, kerosene and heavy oil over a nickel/alumina commercial catalyst and other materials such as limestone, dolomite and iron ore, was studied using a 5 cm i.d. fluidized bed reactor. The effects of operating parameters on conversion, hydrogen yield, product gas composition and elutriation of fine catalysts were investigated. It was found that a fluidized bed is flexible enough to handle various feedstocks, including hydrocarbons heavier than naphtha, because it permits the addition of catalyst to, or withdrawals of, coked catalyst from the bed. The yield of hydrogen obtained from fluidized bed steam reforming of heavy oil at 800‡C over limestone was similar to that obtained over commercial nickel-based catalyst. This indicates that limestone could be a promising catalyst for the production of hydrogen from heavy oil. However, hydrogen yield decreased with reaction time in the experiments using the limestone catalyst. The main cause of the decrease in hydrogen yield was elutriation of fine catalysts from the bed during the reaction.     

运用手性固定相研究外消旋布洛芬的光学分离

Ibprofen is widely used as a non-steroidal anti-inflammatory drug and poduced as racemic mixture.Its pharmacological activity resides only is S-( )-enantiomer,and R-(-)-enantiomer is not only inactive but also has many side effects.Thus it is necessary to separate Renantiomer from racemic ibuprofen.We studied optical separation of racemic Ibuprofen with chiral high performance liquid chromatography(HPLC).,Out of three different chiral stationary phases,which were selected on the basis of structure and availability,two were found to be effective.There was optimum eluent composition for each stationary phase for good resolution in optical separation.Resolution decreased with increase of eluent flow rate,but effect of injection volume on resolution was insignificant at high eluent flow rate.     

Plume model for sulphur capture in largescale,atmospheric fludized-bed combustors (AFBC)

The established plume model for the atmospheric fluidized-bed combustor is here extended to sulphur capture by bed solids. The model accounts for two mechanisms for sulphur capture: (1) the oxidation of sulphur to SO₂, followed by retention by limestone, all in the oxidizing regions of the combustor; and (2) the retention of released sulphur-hydrogen compounds by solids in the unburned plume rising through the bed. Calculations show that there is a significant difference in sulphur retention efficiency predictions between the plume model with its reducing and oxidizing zones and those models which do not consider the occurrence of plumes of unburned volatiles.     

Reactivity of calcined limestone and dolomite with sulfur dioxide

Under the conditions prevailing in in-situ desulfurization of fluidized bed combustion two types of limestone and two types of dolomite were tested for their reactivity with sulfur dioxide. Experimental variables were sorbent size, sulfur dioxide concentration and reaction temperature. In general reactivity increased with temperature with activation energy ranging 15.9 to 19.5 kcal/mol for initial reaction rate. Reaction order with respect to sulfur dioxide was close to one and reactivity decreased with increase of sorbent size. With continuous feeding of coal and sorbent sulfur dioxide concentration in the effluent gas decreased with increase of Ca/S ratio.