Shiqiu Gao

A comparative investigation of the friction and wear behavior of polyimide composites under dry sliding and water-lubricated condition

The friction and wear behavior of high performance polyimide (PI) and its composites reinforced with short cut carbon fiber and solid lubricants such as graphite, MoS2 and polytetrafluoroethylene (PTFE) was comparatively evaluated under dry sliding and water-lubricated condition, aiming at selecting matching materials for the pumps of pure water power transmission. The wear mechanisms of the composites under the two different sliding conditions were also comparatively discussed, based on scanning electron microscopic examination of the worn composite and steel counterpart surfaces. As the results, the incorporation of solid lubricants and carbon fiber in PI contributed to improve the friction and wear behavior considerably. PI-based composites sliding against stainless steel register lower friction coefficients and wear rates under water-lubricated condition than under dry sliding. The difference in the wear rates of the composites becomes margined under water lubrication, owing to the boundary lubrication effect of the water absorption layer, though the transfer of PI and its composites was considerably hindered in this case. PI and its composites are characterized by plastic deformation, micro cracking, and spalling under both dry- and water-lubricated sliding. Such plastic deformation, micro cracking, and spalling is significantly abated under water-lubricated condition. This accounted for the better friction and wear behavior of the composites under water-lubricated condition.

Simultaneous SO2/NOx removal by a powder-particle fluidized bed

Abstract Simultaneous dry removal of SO2 and NOx from flue gas has been investigated using a powder-particle fluidized bed. In a process of flue gas desulfurization by use of solid sorbents such as FeO (dust from a steel plant) and CuO, the smaller the particle size of sorbents, the higher the expected SO2 conversion. In a powder-particle fluidized bed (PPFB), fine particles less than 40 μm in diameter fed into the bed are fluidized with coarse particles. But only the fine particles are entrained from the bed, and their residence time in the bed is remarkably long. The reduction of NOx with NH3 in the fluidized bed is catalyzed by coarse particles or both coarse and fine particles. In this study, PPFB was applied to simultaneous dry SO2/NOx removal process, and several kinds of sorbents or catalysts were evaluated in a PPFB. Using the selected sorbents and catalysts, kinetic measurements were made in the temperature range of 300 to 600°C. SO2 removal efficiencies were affected by reaction temperature, sorbent/S ratio, and static bed height. NOx removal efficiencies in excess of 95% were achieved at NH3/NOx mole ratio of 1.0. When FeO was used as sorbent, SO2 conversion increased with increasing temperature and reached 80% at 600°C.

Influence of thermal pretreatment on pyrolysis of lignite

Abstract The effects of thermal pretreatment on pyrolysis behavior of Shengli lignite were investigated in a fixed bed reactor. In comparison with raw coal, the thermally pretreated coal has lower content of hydroxyl group and lower ratio of aromatic-H to aliphatic-H. The yield of pyrolysis water is lowered after thermal pretreatment in N 2 , N 2 +O 2 and CO 2 atmospheres. The pretreatment also causes a higher CO 2 content in pyrolysis gas, which thus lowers the heating value of the gas. Pretreating the coal in superheated steam raises the tar yield by 3–4 weight percentage points, and the composition of tar varies with the atmosphere and temperature of the pretreatment. The light fraction (with boiling points below 360°C) increased by 27 weight percentage points by pretreatment in 200°C -steam. The pretreatments at 200°C and 250°C in the mixture of steam and simulated flue gas elevate the light oil and phenol oil fractions in tar by 60 and 42 weight percentage points, respectively.

Process simulation of a lignite-fired circulating fluidized bed boiler integrated with a dryer and a pyrolyzer

ABSTRACT A process model using Aspen Plus was established to simulate the performance of a lignite-fired 1,025 t/h circulating fluidized bed boiler integrated with a dryer and a pyrolyzer for improving the energy efficiency. The combustion module of the proposed model was first verified by design data and the system characteristics of the circulating fluidized bed boiler combined with the coal dryer and the pyrolyzer were then investigated. The most suitable case for the retrofit of existing 1,025 t/h CFB boilers is that 35% of the coal was dried and then pyrolyzed with the energy efficiency of 95.3% and exergy efficiency of 50.2%. The results demonstrate the lignite-fired circulating fluidized bed boiler integrated with a dryer and a pyrolyzer facilitates the system performances effectively.

The industrial feasibility of low temperature DeNOx in the presence of SOx: a project case in a medium coking plant

Catalyst poisoning by SOx has hindered the industrial application of selective catalytic reduction (SCR) technology for the DeNOx of low temperature flue gas for many decades. The current engineering process of placing the SCR unit after the desulphurization and dedusting units can lead to high project and operational costs owing to low DeNOx efficiency at low temperatures. Based on our previous pilot results, a DeNOx project case was built before the desulfurization unit in a medium coking plant to explore the industrial feasibility of low temperature DeNOx in the presence of SOx. A new engineering process was considered and designed to overcome the problem of SOx, including the elimination of SO3 with NH3 before the SCR reactor, the filtration of ash by a foam metal plate and in situ regeneration technology. The project case could run continuously for six months with above 70% DeNOx efficiency and less than 10 ppm NH3 slip at 250 °C and a space velocity of 4000 h−1 in the presence of 260–300 mg m−3 SOx. The activity loss for the catalyst itself was not obvious after it had been running for six months, but blocking of the honeycomb channels by the sedimentary ash on the honeycomb catalyst modules owing to the low linear velocity resulted in decreased DeNOx efficiency and an increased pressure drop. A improved DeNOx process with gravitational dust collectors was also proposed to upgrade the present DeNOx project case for further continuous and stable operation.

An Innovative Combined Desulphurization/Denitration Process Using a Powder-Particle Fluidized Bed

An innovative combined desulphurization/denitration (DeSOx/DeNOx) process was tested in this study. It utilizes the so-called powder-particle fluidized bed (PPFB) to co-fluidize continuously supplied fine DeSOx sorbent (several to tens of micrometers) and coarse DeNOx catalyst (several hundreds of micrometers), the fluidization medium particles. Ammonia for NOx reduction is fed to the system from the bottom of the bed. Thus, SOx and NOx are removed simultaneously from flue gas, used as fluidizing gas, in a single reactor. By using model gases containing SO2 and NO, the removal efficiency of this process was examined in a laboratory PPFB reactor with respect to choices of DeSOx sorbents and DeNOx catalysts, reaction temperature, and major gas components. At a reaction temperature of 623 K and a static height of the catalyst bed of 0.1 m, removals greater than 90% for SO2 and about 80% for NO were achieved with the sorbent CuO·V2O5·K2SO4/Al2O3 (at Cu/S = 1) and the catalyst V2O5·WO3/TiO2 or WO3/TiO2 (at NH3/NO = 1) for a simulated flue gas SO2-NO-H2O-N2-air consisting of oxygen 2vol.%, water vapour 0–10vol.%, SO2 500 ppm and NO 500 ppm. These removals are expected to be further improved by avoiding poisoning by such a copper oxide sorbent on NOx reduction. The possible industrial application of this process is also discussed.