Gas evolution from coal heated at a fairly low temperature in the presence of SeO2 and liquefaction behavior of the treated coal were examined for different coals. During atmospheric pyrolysis of coal with SeO2, gas evolution was observed at extremely low temqeratures below 473 K. The gas was shown to consist of CO, CO2 and H2O. Combined with the gas evolution characteristics with gas composition from various aromatic model compounds, those gases were supposed to be originated mostly from carboxyl and methyl groups in coal and oxygen from SeO2. The solid residue after the pyrolysis was liquefied using a sufficient amount of tetralin as a solvent under 10MPa of nitrogen at 723K. The results clearly showed that the SeO2-treated coals give higher yields of pyridineand benzenesolubles than their parent coal due to improved coal reactivity and catalytic effects of SeO2 and/or Se formed during pyrolysis.
We have recently presented two new pyrolysis methods: one is the flash pyrolysis of coal preswollen with hydrogen donor solvent in an inert atmosphere (method I). This method drastically increased the yields of total volatiles and liquids. The other is the pyrolysis of coal in the atmosphere containing a solvent vapor (method II). In this method, the BTX yield reached 5 times larger than that in an inert atmosphere.In this paper an Australian brown coal (Morwell) preswollen by tetralin at 100°C was pyrolyzed in a free fall pyrolyzer to examine the validity of the method I in a practical operation. The yields of total volatiles and tar increased at all temperatures. At 850°C the BTX yield increased up to 3.9% which was twice as large as that obtained from the pyrolysis of the raw coal. Apart from the tetralin in the gas phase, the tetralin in the swollen coal was found only to be dehydrogenated to naphthalene during the pyrolysis. This indicates that the incrases in the yields of total volatiles and tar are caused by the effective hydrogen radical transfer from tetralin to coal fragments in the micropores. Thus it is clarified that the method I is also valid in an actual industrial pyrolyzer.Next, the method I and the method II were combined (method III) to realize effective hydrogen transfer from solvent to coal fragments both in the micropore of the coal and in the gas phase. To examine the validity of the method III, Morwell coal swollen by tetralin was pyrolyzed in a stream of 2-methyl-1-propanol vapor. Both the coal conversion and the liquid yield increased significantly through effective hydrogen transfer within coal particles, and simultaneously the BTX yield increased up to 6.2kg/100kg-coal through the acceleration of the gas phase reaction. Thus it is clarified that the method III is an attractive method to obtain valuable chemicals in high yields and in high selectivities.
This paper describes the experimental results of crushed coal firing two-stage combustion with the primary stage of cycolone slagging combustion. Combustion experiments were carried out under various air equivalence ratios in primary combustion, in several experiment series with different coal type, coal feed rate and coal in-jection azimuth. The emphasis was directed toward the carbon conversion, ash retention and NOx formation in the primary stage combustion (partial gasification combustion). The optimum condition of primary combustion air equivalence ratio that gives the best carbon conversion efficiency depends upon coal type (stoichiomeric air volume), coal feed rate and coal injection azimuth. This suggests that in crushed coal cyclone slagging combustion the hydrodynamic mixing process between coal jet and swirling air flow (secondary air flow) plays a dominant role in determining the gasification combustion performance. In every experiment series, the best results of 95% both for carbon conversion and ash retention efficency were achieved. The measured product gas composition in the primary combustion shows good agreement with equilibirum calculation, suggesting that the gas phase reaction in the cyclone slagging combustion proceeds to attain chemical equilibrium. NOx emission of 100-150ppm (in flue gas, O2 6% base) was achieved under the condition of primary air equivalence ratio less than 0.8. The obtained results of NOx emission control represent the availability of the crushed coal burning two-stage combusion with the primary stage of cyclone slagging combustion to meet satisfactorily the NOx emission regulation.
It has generally been known that erosion of inbed heat exchanger tubes is one of the most serious problems in fluidized bed coal combustion. The present study aimed to make clear the mechnism of fouling phenomenon in coal combustion. Combustion experiments for several kinds of coal were made using 0.15m id combustor, which immersed model tubes in the bed, at the conditions of 850°C and singlestage combustion scheme. Fouling appeared with increasing in Na2O content in the coal ash, and the thickness of scale became a maximum value when the suface temprature of the model tubes was between 550 to 700°C. It was comfirmed from the chemical analyses with a Xray diffraction meter that major contents of the scale were CaSO4, Na2SO4 and Na2Si2O5. Fouling phenomenon could appeare for Na2O content in coal ash of around 2% or higher.