Shien Hui

Burning Low Volatile Fuel in Tangentially Fired Furnaces with Fuel Rich/Lean Burners

Pulverized coal combustion in tangentially fired furnaces with fuel rich/lean burners was investigated for three low volatile coals. The burners were operated under the conditions with varied value N-d, which means the ratio of coal concentration of the fuel rich stream to that of the fuel lean stream. The wall temperature distributions in various positions were measured and analyzed. The carbon content in the char and Nox emission were detected under various conditions. The new burners with fuel rich/lean streams were utilized in a thermal power station to burn low volatile coal. The results show that the N-d value has significant influences on the distributions of temperature and char burnout. There exists an optimal N-d value under which the carbon content in the char and the Nox emission is relatively low. The coal ignition and Nox emission in the utilized power station are improved after retrofitting the burners.

Further study on biomass ash characteristics at elevated ashing temperatures: the evolution of K, Cl, S and the ash fusion characteristics.

Based on the ash-related problems during biomass combustion, the evolution of element S, Cl, K and chemical components and ash fusion characteristics of capsicum stalks, cotton stalks and wheat stalks ashed at 1000, 1200 and 1400 °C are further studied by XRF and XRD. Cl disappears at 815 °C in the form of HCl due to the aluminosilicate of sylvite. Above 1000 °C, inorganic S is released in the form of SO2 by the silicate of K2SO4, which is the main reason that ashing ratio decreases at high temperature. Except of the evaporation of KCl and K2SO4 aerosol which cause the release of K, Cl and S, K may be also reduced by the organic decomposition and the releases of metal K and KOH. The ash fusion characteristics of biomass are mainly dependent on the high-temperature molten material built up by quartz, potassium iron oxide and silicates.

Effect of particle size in a limestone–hydrochloric acid reaction system

Experimental characterization of the wet flue gas desulfurization process is carried out using a model limestone-hydrochloric acid reaction system, with in-situ measurement of the dissolution rate and particle size distribution. The limestone source, initial particle size distribution, working temperature and pH value are varied in large ranges. The dissolution rate is found to be higher when the average particle size is smaller, the temperature is higher, or the pH is lower. An empirical equation is established to correlate the dissolution rate with the particle size and working conditions, which agrees well with measurements. The results may be useful for providing insights to improve the efficiency of the wet flue gas desulfurization process, as well as other solid particle-liquid solution reactions.

On the Laminar Flame Speed of Hydrogen, Carbon Monoxide, and Natural Gas Mixtures with Air: Insights for a Dual-fuel Polygeneration System

Hydrogen/carbon monoxide/natural gas mixtures are employed to simulate crude gas and purge gas. The measured laminar flame speeds of hydrogen/carbon monoxide/natural gas/air mixtures (at lean and rich conditions) show an increase trend with volumetric fraction of hydrogen or carbon monoxide and a decrease trend with volumetric fraction of natural gas. Simulation of 1-D freely propagating flame is employed to validate the measurement results, which provides useful insights for the thermal performance. Fuel mixtures of high hydrogen fraction will result in a high heat release rate, and fuel mixtures of high natural gas fraction will lead to a low heat release rate.

The modified Fluid and Solid reaction model and experimental verification

The shrinking core model(SCM) is widely used to model fluid‐solid reaction in many studies. Based on the shrinking core model incorporated particle size distribution(PSD) and the characteristic of products, a modified model has been set to simulate the reaction process of fluid and solid. Limestone dissolution is a typical liquid‐solid reaction, and experimental work has been done with five kinds of limestone from different producing area in china. The dissolution process of limestone can be predicted. In the model, two parameters the comprehensive reaction coefficient k and total reaction rate constant km are defined. By chosen proper value, the model can well describe the limestone dissolution process in acid. Furthermore, km is dependent of mass transfer in fluid and chemical reaction but independent of properties of solid and fluid. k and km can be deduced from experimental results by numerical method, and km is similar for different samples with the same reaction condition. The model established a re...

Comparison of NOx Emission Reductions with Exclusive SOFA and the Combination of SOFA and CCOFA on Tangentially-fired Boilers

The paper deals with air staging experiments on two full-scale, tangentially fired boilers burning bituminous coal., unit A boiler with separated overfire air (SOFA), unit B boiler with the combination SOFA and close coupled overfire (CCOFA). We compared the NO x emission reductions of the two boilers. The influencing factors of NO x emission including the oxygen levels, the distribution types of pulverized coal and the variations of OFA damper positions were investigated. The NO x emission from unit B boiler was apparently lower than that from unit A boiler (lower 22% or so). The heat efficiency of unit B boiler was higher than that of unit A boiler (higher 0.7% or so). The maldistribution type of pulverized coal was conducive to reduce NO x emission from unit A boiler, but the decrease of NO x emission followed the decrease of boiler heat efficiency. The uniform distribution type of pulverized coal could obtain not only the lowest NO x emission but the highest heat efficiency on unit B boiler. There wasn’t an optimum adjustment of SOFA damper position on unit A boiler, and both NO x emission and boiler heat efficiency decreased with the increase of the opening extent of SOFA. However, there was an optimum matching adjustment of CCOFA and SOFA damper positions in unit B boiler.

A Low Cost, High Resolution Interface Circuit for Differential Capacitance Transducer

Abstract For accurately detecting capacitance changes of the differential‐capacitance transducer, which is widely used in environmental and chemical engineering, a low‐cost interface circuit was developed. The circuit uses a “lock‐in detection” circuit with feedback loop containing a DC amplifier and a modulator to yield such advantages over the others that it reduces the sensitivity to element parameter variations in the “lock‐in detection” circuit, that it decreases the sensitivity to the disturbances within closed‐loop, and that it is immune to parasitic capacitance, resistance, amplitude, and frequency of the excitation voltage source. The circuit has the capability to detect a capacitance change as small as 0.0078% of the total capacitance, up to 80 pF. A capacitance diaphragm pressure transducer and a standard pressure source (Rusca 2465 piston gauge) are connected to the interface to confirm the analysis.

Optimization of Waste Heat Recovery Power Generation System Applied in Ferroalloy Industry

During ferroalloy production, a large quantity of waste gas can be utilized to generate steam and electric power. In this paper, 4 detailed thermodynamic models of single-pressure (SP) and dual-pressure (DP) waste heat recovery power generation systems are presented, to analyze the impact of the steam pressure, steam temperature and pinch temperature difference on power generating capacity. By comparing the performance of typical systems, more reasonable thermodynamic models and their parameters are proposed. It is found that the power generation capacity of dual-pressure system is higher than that of the single-pressure system, but SP system is much simpler. Using superheated steam in deaerator reduces the efficiency of heat recovery power generation systems by 1.8%. The fluctuation of waste gas source affects the power generation greatly. It should be considered when more reasonable ranges for the main parameters are required. With the improvement of thermodynamic system and parameter optimization, the gross power is increased by 15% for SP system and 17% for DP system, corresponding to the steam parameters of 3.0MPa/400°C and 6.0MPa/400°C.Copyright

Experimental investigation and modeling of mass transfer characteristics in a double‐contact flow absorber

A double‐contact‐flow absorber comprising spray nozzle array with new flow p attern has been proposed, modeled and tested with CaCO3 as sorbent. The flow characteristic of different scale absorber has been investigated, and the practical be d height coe fficient can be expressed by a exponent function when Froude number is used as independent variable. Various parameters such as liq uid flow rate, flue gas flo w rate and different nozzle array pattern s influencing desu lfurization rate have been tested in s mall sc ale equipment. Under the m oderate condition em ployed, the desulfurization efficiency can reach a high level above 95%. A model has been established to describe th e heat and m ass transfer process in double‐conta ct‐flow absorber, especially, a method to estimate the contact area between gas and liquid.

Experimental Study of Nitrogen Oxide Emissions in a Circulating Fluidized Bed

The experimental study was carried out on the emission characteristics of nitrogen oxide in a 0.3MW circulating fluidized bed as well as analysis of the formation and destruction mechanism of nitrogen oxide. Several variables associated with the combustion system were investigated in the experiment, which include bed temperature, excess air, primary-to-secondary air ratio, and coal species. It is found that the NO x emissions decrease along the height of the furnace, while the N2O emissions increase continuously. More NO x emissions and less N2O emissions are generated as the bed temperature increases. It is also illustrated that an increase of air stoichiometry leads to a significant NO x increase and an obvious N2O increase. And air staging is proved to be an effective way to control the nitrogen oxide emissions in the fluid bed. Besides, it is also shown in the experiment that the concentration of NO x and N2O is higher during the combustion of anthracite than that during the combustion of bituminous.