Integrated coal gasification combined
cycle systems are expected
to raise the power generation efficiency of coal-fired power plants.
In Japan, coal gasifiers are required to treat various kinds of coal
imported from many countries because almost all of the coal is imported
from abroad. In an entrained-bed coal gasifier, the slag-tapping hole
must be heated adequately to discharge the molten slag. Thus, a heating
technique has been developed to heat the hole from below, without
using any auxiliary fuels. The technique is to burn the syngas, which
descends through the hole at high temperature, by supplying oxygen
from a pair of nozzles facing each other installed just below the
hole. In this study, a design procedure to heat the hole by those
nozzles was developed through thermal and flow simulations and actual
gasification tests in a 150 t/d entrained-bed coal gasifier of pilot
scale.
In this study, we focused on optimizing a part of the furnace and operating conditions of the fiber yielding system from fused coal ash to expand ash utilization for building materials; promotion of ash use is desirable because slag inhibits the elution of toxic heavy metals, such as Hg, Pb and As, to undetectable levels, making the fibers safe to use. In particular, the fiber materials from coal ash slag are expected to be used as thermal insulators and acoustic materials. We designed a coal ash fusing furnace which is suitable for the fiber manufacturing and recovery process. To manufacture fiber materials which are both safe and homogeneous, the slag viscosity had to be stabilized to approximately 1 Pa•s at the slag-tapping hole of the furnace. However, the slag temperature at 1 Pa•s was too high to measure. Thus, we estimated the slag temperature at 1 Pa•s using Riboud's and Urbain's expressions. To control the slag viscosity and temperature, CaCO 3 addition to coal ash was effective. When the basicity (CaO/SiO 2 (wt%/wt%)) of the coal ash sample was 0.98, the fused slag temperature at 1 Pa•s was estimated as 1563 ο C. Then, we verified that to yield 1 Pa•s fusing slag from 120 kg/h coal ash, the necessary fuel quantity of the coal ash fusing furnace was 40 kg/h coal and 4 m 3 N/h LPG.
To utilize coal ash slag as aggregate, coal ash has to be completely-fused and recovered as amorphous granulated slag, same as granulated blast furnace slag. We designed the new coal ash fusing furnace consisting of two chambers to increase ash load and to inhibit the recovery of incompletely-fused slag. The upper chamber is the existing vertical cylindrical furnace and the lower chamber is the new horizontal furnace. In the upper chamber, coal ash is transferred near the inner wall by centrifugal force, and is trapped at the surface of fused slag, and then flow down to the lower chamber. When the ash load of the upper chamber increased, the rate of amorphous slag content decreased because of increasing incompletely-fused slag. To enhance heating, the lower chamber which has some burners was installed just below the upper chamber. In the lower chamber, what is called slag-bed furnace, the incompletely fused slag is fused completely during flowing down onto the bottom of the furnace. Then, we designed the new coal ash fusing furnace, the inner diameter of upper chamber was 0.6 m and the length of lower chamber was 1.8 m. We verified that to recover 100 % amorphous slag content at the ash/coal (kg/kg) ratio 4.6, the necessary fuel quantity of the furnace was 30 kg/h coal and 5.87 m 3 N/h LPG. Accordingly, the effect of slag-bed furnace to increase ash load was confirmed.
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