Ash Deposition Tests Research Articles

Study of Ash Sintering Temperature and Ash Deposition Behavior during Co-Firing of Polish Bituminous Coal with Barley Straw Using Non-Standard Tests

The need to reduce CO2 emissions forces the use of biomass as a fuel in the conventional energy conversion process implemented by combustion. Burning biomass alone can be problematic because of the high potential for slugging and fouling on boiler heating surfaces. Therefore, co-firing of biomass with coal is used. This article presents the results of a study of biomass blends of barley, straw, and hard coal biomass from the Polish Makoszowy mine. The sintering of ash from biomass-coal blends was studied by experimental non-standard methods, such as the fracture stress and the pressure drop test. The results were confirmed with the result of thermodynamic modeling using FactSage 8.0 software. Additionally, ash deposition tests were performed in a 3.5 m boiler. The tests conducted showed a significant effect of the addition of biomass to hard coal on the formation of ash deposits on the heating surfaces of the boiler. In addition, the usefulness of non-standard methods in the assessment of the degree of fouling and slugging hazard was confirmed.

Effect of MgO addition to upgraded brown coal on ash-deposition behavior during combustion

The objectives of this study were the evaluation of the effect of MgO addition to coal on the reduction of ash deposition during upgraded brown coal (UBC) combustion, and the elucidation of the mechanisms of the reduction of ash deposition. The melting temperature of UBC ash is 1494K, which is lower than that of bituminous coal ash. Before the actual ash-deposition experiments, the molten slag fraction in the UBC ash was estimated by means of chemical equilibrium calculations for various mixing mass ratios of MgO to coal ash. The simulation results indicate that MgO addition plays a role in decreasing the molten slag fraction. It was confirmed that Mg formed solid composites with Si, Fe, Al, Ca, and Mn, and played a role in decreasing the molten slag fraction in the ash on the tube. As a next step, ash-deposition tests were conducted using a pilot-scale pulverized coal combustion furnace equipped with a refractory wall. The results showed that MgO addition contributed to decreasing the rate of ash deposition even for UBC. These calculations and experimental results suggested that one of the reduction mechanisms due to MgO addition involved the production of solid-phase aluminosilicates.

Ash deposition behavior of upgraded brown coal in pulverized coal combustion boiler

Ash with a low melting point causes slagging and fouling problems in pulverized coal combustion boilers. Ash deposition on heat exchanger tubes reduces the overall heat transfer coefficient due to its low thermal conductivity. The purpose of this study is to evaluate the ash deposition for Upgraded Brown Coal (UBC) and bituminous coal in a 145 MW practical coal combustion boiler. The UBC stands for Upgraded Brown Coal. The melting temperature of UBC ash is relatively lower than that of bituminous coal ashes. Combustion tests were conducted on blended coal consisting 20 wt.% of UBC and 80 wt.% of bituminous coal. Before actual ash deposition tests, the molten slag fractions in those coal ashes were estimated by means of chemical equilibrium calculations. The calculation results showed the molten slag fraction for UBC ash reached approximately 90% at 1523 K. However, that for blended coal ash decreased to 50%. These calculation results mean that blending UBC with bituminous coal played a role in decreasing the molten slag fraction. This phenomenon occurred because the coal blending led to the formation of alumino-silicates compounds as a solid phase. Next, ash deposition tests were conducted using a practical pulverized coal combustion boiler. A water-cooled stainless-steel tube was inserted in locations at both 1523 K and 1273 K in the boiler to measure the amount of ash deposits. The results showed that the mass of ash deposition for blended coal did not greatly increase, compared with that for bituminous coal alone. Therefore, appropriately blending UBC with bituminous coal enabled the use of UBC without any ash deposition problems in practical boilers.

G0601-8-1 石炭酸素燃焼時の灰付着性(熱工学(8)燃焼(3))

Ash deposition characteristics in oxy-fuel combustion were investigated by using the portable device for monitoring ash deposition installed in the combustion test facility. The ash deposition tests and ash deposit analyses were conducted for two types of bituminous coal with different ash components. In comparison to air combustion tests, the result was obtained that the ash particle shape and size had no difference between oxy-fuel and air combustion. The distribution of metal element in ash for oxy-fuel combustion was almost same to air combustion. The results show that ash deposits properties in oxy-fuel combustion are equal to those in air combustion in bituminous coal firing.

The behaviour of chlorine in Kentucky and Illinois coals during combustion and its effects on ash deposits

Ash deposition tests were performed in a laboratory-scale, pulverized coal combustor with four different coals. These four coals, Kentucky No. 9, Kentucky No. 11, Illinois No. 5 and Illinois No. 6 had chlorine contents of 0.18, 0.10, 0.42 and 0.36 wt%, respectively. Five repetitive, 1 h firings were performed for each coal at a coal feed rate of 11 kg h −1. Ash samples were obtained from simulated waterwall and superheater probes, from an exhaust cyclone, and from a water-quenched char sample probe. Chlorine was found to release quickly from the coal to the gas phase. The amount of gas phase chlorine that concentrated on the ash collection surfaces was inversely dependent upon the temperature of the collection surface. The chlorine conversion rate from the char was equal to the carbon conversion rate for levels above 65%. Ash fusion temperature, ash sintering temperature, emittance, thermal conductivity, shear strength and compressive strength measurements, which were performed on samples from the waterwall and superheater probes showed no observable differences among the four coals tested. Obvious corrosion of the stainless steel test surfaces was observed during the combustion tests with the Illinois coals. The l h firings were too short for many of the physical properties of the ash deposits to reflect the influence of metal corrosion. Emittance, ash sintering temperature, compressive strength and shear strength of ash deposits were dependent on sample location.