Jianmin Gao

Purification characteristics of fine particulate matter treated by a self-flushing wet electrostatic precipitator equipped with a flexible electrode

ABSTRACT A self-flushing wet electrostatic precipitator was developed to investigate the removal performance for fine particles. Flexible material (polypropylene, 840A) and carbon steel in the form of a spiked band were adopted as the collection plate and discharge electrode, respectively. The particle concentration, morphology, and trace-element content were measured by electric low-pressure impactor, scanning electron microscope, and energy-dispersive x-ray spectroscopy, respectively, before and after the electrostatic precipitator. With increasing gas velocity, the collection efficiency of fine particles (up to 0.8 μm in diameter) increased, while it decreased for particles with diameters larger than 0.8 μm. Increasing the dust inlet concentration increased the collection efficiency up to a point, from which it then declined gradually with further increases in the inlet concentration. The particulate matter after the wet electrostatic precipitator showed different degrees of agglomeration. The collection efficiency of trace elements within PM10 was less than that of the PM10 itself. Notably, the water consumption in the current setup was significantly lower than for other treatment processes of comparable collection efficiencies. Implications: Wet electrostatic precipitators, as fine filtration equipment, were generally applicable to coal-fired plants to reduce PM2.5 emissions in China. However, high energy consumption and unstable operation, such as water usage and spray washing directly in the electric field, seriously restricted the further development. The utilization of self-flushing wet electrostatic precipitator can solve these problems to some extent.

Effect of flue gas recirculation on nitric oxide (NO) emissions during the coal grate-fired process

ABSTRACT Flue gas recirculation (FGR) is a low nitrogen oxide (NOX) combustion technology. The present study used standard gas to simulate the cycle gas (the main ingredients of which are oxygen (O2), nitrogen (N2), and carbon dioxide (CO2)). The coal grate-fired process was divided into three zones, namely (1) volatilization zone, (2) main combustion zone, and (3) char combustion and burn-out zone. The effects of FGR on coal combustion and NO emissions were investigated in these zones of a unit-boiler experimental system. An industrial test was then conducted on a chain boiler that previously used FGR. Data showed that if the cycle gas was directed into the furnace from the volatilization zone, the curve of the coal surface temperature moved backwards, the temperature peak increased, and coal ignition was delayed. When the FGR rate was 20%, NO emissions/g coal was 41.8% less than in the absence of FGR, in the overall combustion process except for the volatilization zone. An industrial test demonstrated that FGR decreased the NO emissions and incomplete-combustion loss of gas. NO and carbon monoxide (CO) emissions were reduced by 26.9 and 38%, respectively. These observations may prove to be beneficial in reducing ambient air pollution and saving energy.

The Application of Continuum Model in Simulating Char Fragmentation and Residual Ash Formation

ABSTRACT The monosized spherical model was established originally to study the process of char combustion and residual ash formation. On this basis, a modified spherical model was obtained by introducing the multi-size mineral inclusions and pores to the spherical char. The results show that the surface ash mean size is proportional to the mineral volume fraction in monosized model. In addition, a significant bimodal characteristic occurs on the distribution curve of isolated ash mean size in cases of large porosity and pore size, which is in good agreement with experiment results. As a contrast, the planar model is more beneficial to form a large number of small isolated ash particles, whereas the mineral inclusions in monosized spherical model are inclined to coalesce into a large surface ash particle eventually. As regards the modified spherical model, the separation effects of both small and large surface ash particles can be strengthened with respect to number density. It can be expected that the modified model is more aligned with the actual conditions.

Modified three-dimensional percolation simulation of char fragmentation and particulate formation

The current numerical calculation of particulate formation during char combustion mainly adopts the two-dimensional model. In this paper, based on the introduction of the concept of diffusion depth, the char combustion is simulated with a three-dimensional model. The modified model can simulate the actual situation that the reactant gas dose not diffuse into the char completely. The approach to realize the combustion process of char in chemical controlled zone (zone I) and transitional controlled zone (zone II) is given, and the results are compared with those in the diffusion controlled zone (zone III). The characteristic impact of initial porosity and mineral content on particulate formation in different zones is analyzed through the simulation and comparison. It can be seen from the results that the diffusion depth do put some limits on char fragmentation and mass distribution of ash particulates, which provides theoretical basis for the further study of particulate formation during char combustion and...

Parameter Optimization on Experimental Study to Reduce Ammonia Escape in CO 2 Absorption by Ammonia Scrubbing

In order to research ammonia escape in CO 2 absorption by ammonia scrubbing, ammonia escape was studied in CO 2 absorption process using the bubbling reactor in different conditions as gas flow rate, CO 2 ratio, absorbent temperature and ammonia concentration and quantity of escaped ammonia was measured by chemical titration. The results indicated that, the amount of ammonia escape can be around 20% of original amount in 90 min and the escaped amount will increase with the rise of gas flow rate, absorbent temperature, concentration of ammonia while decrease as CO 2 ratio goes up. Through the analysis of the law of ammonia escape, at the same time, combined with ammonia escape and the influence of the relationship between the CO 2 absorption efficiency, reducing ammonia escape working condition parameter optimization is given.

Emission and Properties of NOx Generated During Coal Grate-Fired in O2/N2/CO2

With the improvement of environmental protection requirements, the problems of NOx emission from industrial boiler become more and more notable. Flue gas recirculation is a low-NOx combustion technology. It draws out a part of the flue gas from rear flue and forces it into boiler. So the flue gas can serve the combustion or flow field integration. The drawn flue gas can be forced into the boiler directly, or mixed with the primary air or secondary air. To explore a real effective method of low NOx combustion, the article discusses the influence of flue gas recirculation on the formation of NOx in the process of coal grate-fired, in the way of using the unit-boiler, measuring the temperature of coal surface and composition and other important influential parameters. Experimental studies show that under the condition of grate-fired, taking Flue gas recirculation in main combustion zone, coke combustion zone and burn-out zone could notably diminish the amount of NO. And with the promotion of flue gas recirculation rate, the effect can be more noticeable.

The Research on the Formation Rules of NOx in the Coal Grate-Fired Process

With the increased requirements of environmental protection, the problem of industrial boiler NOx emissions become more and more notable. The practical coal and the same air-distribution method as the one in the actual stoker boiler were applied to study the NOx formation characteristics in a unit-boiler with the purpose of studying the NOx formation characteristics in the chain-boiler. Measuring the temperature, weightlessness and composition and other important influential parameters of the product-gas is to obtain the details of the grate-fired process and it is to know the law and main influential factors of formation rules of NOx in the grate-fired process of chain-boiler. Further, the coal layer surface temperature NOx formation, oxygen content, CO content and other parameters on different regions of a SZL10-1.25-AII symmetrical arrangement chain-grate boiler were tested. The measurements of the unit-boiler were compared with the industrial measurements to verify the reasonableness of the method of researching the actual industrial boiler combustion process by the unit-boiler. On this basis, the technical route according to the low-NOx combustion technology in chain-grate boiler is proposed and it laid the foundation for industrial demonstration.

Gas-Solid Two Phase Flow in Internally Circulating Two-Stage Spouted Desulfurization Tower

To study the circulating fluidized bed desulfurization tower flowing fields, a two-stage spouted tower was presented and an experimental installation was established. Experimental studies on flow fields have been carried out by using a particle dynamic analyzer (PDA). Results indicate: The stable annular flow patterns is obtained in the two-staged esulphurized tower. The irregular and uniform flow is advantage to strength mass transfer at the Veturi inlet of tower. The result of stable back flow of particle at the wall makes it possible that atomizing humidified water or slurry can not directly eject the wall of the tower. At the assurance of atomized covering area, the fact ensures that humid scaling will not be produced at the wall. Micro-particle in gas can be arrested stable dynamic particle layer forming from the particular two stages spouted structure combined proper aggregate accelerating agent.

Study on Process of SO2 Removal by Grading Atomization in a Two Levels Spouting Desulphurization Tower

The experimental research was carried out about process of SO2 removal in flue gas using white lime slurry atomization, and with the method of non-contact on-line measuring for SO2 concentration in riser. The temperature distribution of slurry atomization drying was measured by new sandwich structure thermocouple with air pump. The results showed: The maximum SO2 removal and temperature decreasing amplitude were got at a distance 200mm from the nozzle. Atomization temperature region was bimodal symmetric distribution. Evaporation intensity from high to low along the axis. The SO2 removal rate was first increased and then decreased, SO2 removal and evaporation strength biggest regional overlap. Two-stage spray desulfurization efficiency increased 11.9%.

On Macro Parameters of CO2 Capture by Ammonia Method

An novel technology of CO2 capture from coal-fired flue gas is Ammonia chemical adsorption method. Experimental system of CO2 adsorption by ammonia water is established on the base of a bubble column reactor in this paper. Effects of key parameters on CO2 adsorption process, such as ammonia water concentrations, PH values of solutions, C/N molar ratios, amounts of water brought by gas, are studied through the system. From the analysis of experimental results, it indicates that, utilization rate of high concentration ammonia water is low, and escape rate is high, but CO2removal efficiency is high. On the other hand, utilization rate of low concentration ammonia water is high, and escape rate is low, but CO2 removal efficiency is low. In CO2 capture process, the PH of solution decreases dramaticlly. When the reaction solution invalids, PH values of different solutions are close to8.7. When the absorbent PH is lower than 8.7, it has no capacity to absorb CO2. The mass ratio of carbon capture capacity by ammonia method is much higher than that by MEA, and the mass ratio of carbon capture capacity by low concentration ammonia water is higher.