Mengxiang Fang

Simultaneous oxidation of NO, SO2 and Hg0 from flue gas by pulsed corona discharge

A process capable of simultaneously oxidizing NO, SO2, and Hg0 was proposed, using a high-voltage and short-duration positive pulsed corona discharge. By focusing on NO, SO2, and Hg0 oxidation efficiencies, the influences of pulse peak voltage, pulse frequency, initial concentration, electrode number, residence time and water vapor addition were investigated. The results indicate that NO, SO2 and Hg0 oxidation efficiencies depend primarily on the radicals (OH, HO2, O) and the active species (O3, H2O2, etc.) produced by the pulsed corona discharge. The NO, SO2 and Hg0 oxidation efficiencies could be improved as pulse peak voltage, pulse frequency, electrode number and residence time increased, but they were reduced with increasing initial concentrations. By adding water vapor, the SO2 oxidation efficiency was improved remarkably, while the NO oxidation efficiency decreased slightly. In our experiments, the simultaneous NO, SO2, and Hg0 oxidation efficiencies reached to 40%, 98%, and 55% with the initial concentrations 479 mg/m3, 1040 mg/m3, and 15.0 microg/m3, respectively.

A mathematical model for a circulating fluidized bed (CFB) boiler

In developing a mathematical model for a CFB boiler we use earlier work. Our model includes mathematical descriptions of the underlying physical and chemical processes. It has been applied to simulation of a 12 MW CFB boiler. The calculations agree well with test results.

Development of a new external heat exchanger for a circulating fluidized bed boiler

An external heat exchanger (EHE) is believed to be a viable way to solve the heat transfer surface arrangement and furnace temperature control to scale-up of circulating fluidized bed (CFB) boilers. A new concept of EHE is developed in this paper. The flow of hot solid particles diverted from the standpipe is controlled by pneumatic (aeration airflows of recycle device or EHE), not the mechanical valve that is in popular use in many CFB boilers. The major feature of this EHE system is that it avoids the use of the mechanical valve that causes heavy erosion and high cost. An in-series connection between the EHE and the recycle device (i.e. the recycle device is on top of the EHE) is proposed. Experiments completed in cold test rigs show that the solid mass flow rate diverted from the standpipe to the EHE or the loop seal may be controlled well by adjusting the fluidizing air of the overflow part of the loop seal, the fluidized air of the fluidized chambers of the EHE and the aeration airflow to the standpipe. In addition, the new EHE has been validated successfully in a 12 MWe CFB boiler.

A multi-product cogeneration system using combined coal gasification and combustion

A new system has been developed for clean and highly efficient utilization of coal. The coal is first gasified and the fuel gas is then used for industrial purposes in town gas or as a fuel for gas turbines. The char residue from the gasifier is burned in a circulating fluidized-bed combustor to generate steam for power generation, process heating, refrigeration, air conditioning, etc. The ash is used to produce construction materials. Metals such as vanadium and uranium can be extracted if the metal contents of coal are sufficiently high. An important system component is the combined gasifier–combustor. Experiments show that the system can produce gas and steam simultaneously. The gas heating value is 10–14MJ/Nm3 and the fuel conversion is over 90%. The system has low emissions and low cost. A demonstration system has been constructed at the Yangzhong Thermal Power Plant in Jiangshu Province of China. It produces 3 500Nm3/h of dry gas and 75mt/h steam. The CFB boiler has been in commercial operation since April 1995. It has high efficiency, good fuel adaptability, and a high load turndown ratio.

FLASH PYROLYSIS OF BIOMASS PARTICLES IN FLUIDIZED BED FOR BIO-OIL PRODUCTION

Biomass utilization could relieve the pressure caused by conventional energy shortage and environmental pollution. Advantage should be taken of the abundant biomass in China as clean energy source to substitute for traditional fossil fuels. At present, flash pyrolysis appears to be an efficient method to produce high yields of liquids that could either be directly used as fuel or converted to other valuable chemicals. Experiments were carried out of pyrolyzing biomass particles in a hot dense fluidized bed of sand to obtain high-quality bio-oil. Among four kinds of biomass species adopted in our experiment, Padauk Wood had the best characteristics in producing bio-oil. GC-MS analysis showed bio-oil to be a complex mixture consisting of many compounds. Furthermore, an integrated model was proposed to reveal how temperature influences biomass pyrolysis. Computation indicated that biomass particles underwent rapid heating before pyrolysis.

Influence of Metal Additives on Pyrolysis Behavior of Bituminous Coal by TG-FTIR Analysis

To study the catalytic effects of alkali, alkaline earth and transition metal additives on coal pyrolysis behavior, bituminous coal loaded NaCl, KCl, CaCl2, MgCl2, FeCl3and NiCl2was respectively investigated using Thermogravimetry and Fourier Transform Infrared Spectroscopy (TG-FTIR). Results indicated that the maximum mass loss rate decreased under the metal additives in the primary pyrolysis stage. The total mass loss of pyrolysis was reduced in metals catalyzed pyrolysis except for Na loaded sample. Kinetic analysis was taken for all samples adopting the method of Coats-Redfern. Activation energy of raw coal in the primary pyrolysis stage was 92.15vkJ·mol−1, which was lowered to 44.59–73.42 kJ·mol−1under metal additives. The orders of catalytic effect for this bituminous coal were Mg > Fe > Ca > Ni > K > Na according to their activation energies. Several investigated volatiles including CH4, CO2, CO, toluene, phenol and formic acid were identified from FTIR spectra. The yields of CH4, CO2, toluene, phenol and formic acid were decreased, but the evolution of CO was increased. The presence of metals in the coal samples have been involved in a repeated bond-forming and bond-breaking process, which greatly hindered the release of tars during pyrolysis as the tar precursors were connected to coal/char matrix and were thermally cracked, becoming a part of char.

Instantaneous separation model of a square cyclone

Abstract This paper mainly studies the separation mechanism of a square cyclone at high inlet solid concentration. It is shown that the separation mechanism is very different from that at low inlet solid concentration. A phenomenon called two-instantaneous separation exists, which has never been found in square cyclone experiments before. This phenomenon has bearing on the limit load of gas–solid flow, and the part exceeding the limit load will be separated instantaneously after entering the square cyclone. A model called two-instantaneous separation is introduced in this paper as well as the calculations of limit load and separation efficiency, which can be used in the design and research on a square cyclone for circulating fluidized bed boiler.

Experimental Study on the Absorption of CO2 from Flue Gas by Aqueous Solutions of Methyldiethanolamine + Potassium Glycinate in Hollow Fiber Membrane Contactor

Absorption of carbon dioxide from flue gas was investigated in a hollow fiber membrane contactor using methyldiethanolamine + potassium glycinate (MDEA+PG) aqueous solutions. The experimental results showed that the CO 2 removal efficiency increased with the membrane contactor length increasing. CO 2 removal efficiency and the mass transfer rate of CO 2 increased with the increase of liquid flow rate. CO 2 removal efficiency decreased with gas flow rate increasing. CO 2 removal efficiency decreased and mass transfer rate increased with the CO 2 volume fraction inlet increasing. Comparing PG with monoethanolamin (MEA) as auxiliary absorbent, the hybrid solution of MDEA+PG was better than that of MDEA+MEA.

Spontaneous Cooling Absorption of CO2 by a Polymeric Ionic Liquid for Direct Air Capture

A polymeric ionic liquid (PIL), with quaternary ammonium ions attached to the polymer matrix, displays CO2 affinity controlled by moisture. This finding led to the development of moisture swing absorption (MSA) for direct air capture of CO2. This work aims to elucidate the role of water in MSA. For some humidity range, CO2 absorption is an endothermic process associated with concurrent dehydration of the sorbent. The thermodynamic behavior of water indicates a decreased hydrophilicity of the PIL as the mobile anion transforms from CO32- to HCO3- during CO2 absorption. The decrease in hydrophilicity drives water out of the PIL, carrying heat away. The mechanism is elucidated by molecular modeling based on density functional theory. The finding of spontaneous cooling during absorption and its mechanism in the PIL opens new possibilities for designing an air capture sorbent with a strong CO2 affinity but low absorption heat.

Experimental Study on the Separation of CO2 from Flue Gas Using Hollow Fiber Membrane Contactors with Aqueous Solution of Potassium Glycinate

Experimental study on CO2 removal from flue gas using polypropylene hollow fiber membrane contactors were conducted. Aqueous solutions of potassium glycinate were used as absorption solution to absorb CO2 in the experiments. Under moderate operating conditions, effects of the absorption solution flow rate, concentration of potassium glycinate, and absorption solution capacity on the mass transfer rate of CO2 and absorption solution CO2 loading were studied on a pilot-scale test facility. The results showed that the mass transfer rate of aqueous potassium glycinate decreased gradually in experiments while the absorption solution CO2 loading increased. The mass transfer rate and absorption solution CO2 loading of aqueous potassium glycinate with higher concentration was higher than that of aqueous potassium glycinate with lower concentration. The aqueous potassium glycinate with longer regeneration time was better in continuous running. The performance of CO2 absorption using potassium glycinate is superior to monoethanolamine and methyldiethanolamine under the same operating conditions.