In the present study reduction of nitrogen oxides using reburning technology, during combustion of sewage sludge (fuel I) and the mixture of sewage sludge, wasted bleaching earth and CaO (fuel II), was carried out. Th...In the present study reduction of nitrogen oxides using reburning technology, during combustion of sewage sludge (fuel I) and the mixture of sewage sludge, wasted bleaching earth and CaO (fuel II), was carried out. The experimental works were conducted in a laboratory-scale fluidized bed reactor (power up to 10 kW) with application of two types of beds: chemically inert bed (sand) and chemically active bed (CaO). The second combustion (reburning) zone in the reactor was formed by dosing into an area above the bed, additional gaseous fuel (propane). Obtained reduction in emissions of nitrogen oxides in both types of beds was at a level 70% - 79%. Additionally bed of CaO has the desulfurizing effect and also reduces the CO concentration in the exhaust fumes. A significant drawback of active bed is the adverse effect on increase of the primary NO which enters the second combustion zone. The result of this fact is higher NOx emission during combustion of the same fuel in bed of CaO in comparison to the combustion of this fuel in the sand bed, when the same maximum degree of reduction of NOx will be obtained for both types of beds.展开更多
This paper presents a robust model reference adaptive control scheme to deal with un-certain time delay in the dynamical model of a ?uidized bed combustor for sewage sludge. Thetheoretical analysis and simulation resu...This paper presents a robust model reference adaptive control scheme to deal with un-certain time delay in the dynamical model of a ?uidized bed combustor for sewage sludge. Thetheoretical analysis and simulation results show that the proposed scheme can guarantee not onlystability and robustness, but also the adaptive decoupling performance of the system.展开更多
The migration characteristics of heavy metals in co-combustion of sewage sludge and high alkali coal in circulating fluidized bed were studied by experiments and simulations. Temperature plays a crucial role in thermo...The migration characteristics of heavy metals in co-combustion of sewage sludge and high alkali coal in circulating fluidized bed were studied by experiments and simulations. Temperature plays a crucial role in thermodynamic equilibrium distribution and migration characteristics of heavy metals. At the temperature range of 700℃-1200℃, Hg is completely gaseous and the proportion of Pb, Ni, and Cd in the gas phase is also high. As is mainly elemental in the system, and the proportion of Cr in the solid phase is large. Zn compounds are diverse and mostly solid materials. The volatility of Cu is not strong, and it will become gaseous when the temperature exceeds 1700℃. The proportion of heavy metals in the gas phase decreases as the excess air ratio increases. In an oxygen-rich atmosphere, most of Zn and Ni are converted to oxides;Pb and Cd are converted to crystalline silicate;Cu is converted to partial aluminate;Cr compound is decomposed to form Cr_(2)O_(3);they are good for the solidification and controlling of heavy metals. The elemental Hg is converted to HgCl_(2) and the elemental As is converted to AsCl_(3). Temperature also has a great influence on the volatilization rate of heavy metals. The higher the temperature, the shorter the time they reach the maximum volatility.展开更多
At the present time, the sewage treatment plants in the UK produce about 25 million tons of sewage sludge each year at a concentration of 4% solids. New regulations forbid sea dumping and in the near future new incin...At the present time, the sewage treatment plants in the UK produce about 25 million tons of sewage sludge each year at a concentration of 4% solids. New regulations forbid sea dumping and in the near future new incinerators will be required to dispose of about 5 million tons per year. Bubbling fluidised bed incinerators are widely used to burn sewage sludge at a typical consumption rate of about 0.02kg(dry)·s -1 ·m 2 , and it follows that over 300 conventional fluidised bed incinerators of 3m diameter could be required to cope with the increased demand.\;At Sheffield University Waste Incineration Centre (SUWIC) research work is being carried out to develop a novel spinning fluidised bed incinerator. The key factor to note is that when air flows up through a bed of near mono sized particles, it fluidises when the pressure drop across the bed is equal to the weight of the bed. Normally, the weight of the bed is determined by gravity. However, if the bed is contained by a cylindrical air distributor ‘plate’ that is rotating rapidly about its axis, then the effective weight of the bed can be increased dramatically. The airflow passing through the bed can be increased proportionally to the “g” level produced by the rotation and it follows that the process has been intensified. In exploratory tests with a spinning fluidised bed we have achieved combustion intensities with coal combustion as high as 100MW/m 3. A problem with burning coal is that it was difficult to remove the heat and rotating water seals had to be used to transfer cooling water into the bed. In the case of sewage and other sludges, this problem does not exist since the flue gases can remove the small amount of heat released. The rotating fluidised bed sludge incinerator is a novel device, which is very compact. It is able to solve the turndown problem encountered with conventional fluidised beds by simply changing the rotation speed. Bearing in mind that a centrifugal sludge de watering unit is already used on sludge incineration plants, it is likely that the rotating fluidised bed can be combined with the de watering unit, resulting in further process integration and intensification. Furthermore, our ash sintering system can be added to render the ash non toxic and unleachable thus reducing the cost of its disposal.展开更多
The experimental studies on the formation of NOx and SO2 during incineration of sewagesludge and paper mill sludge are reported. The test result indicates that: (1) The conversionof fuel-S into SO2 and fuel-N into NOx...The experimental studies on the formation of NOx and SO2 during incineration of sewagesludge and paper mill sludge are reported. The test result indicates that: (1) The conversionof fuel-S into SO2 and fuel-N into NOx is mainly determined by sludge characteristics;(2) Emission of NOx and SO2 decreases with increasing sludge moisture content, increaseswith increasing bed temperature and excess air; (3) The conversion of fuelN into NOxincreases with increasing excess air; (4) The conversion of fuel-S into SO2 increases with bedtemperature and excess air increasing, decreases with sludge moisture increasing.展开更多
文摘In the present study reduction of nitrogen oxides using reburning technology, during combustion of sewage sludge (fuel I) and the mixture of sewage sludge, wasted bleaching earth and CaO (fuel II), was carried out. The experimental works were conducted in a laboratory-scale fluidized bed reactor (power up to 10 kW) with application of two types of beds: chemically inert bed (sand) and chemically active bed (CaO). The second combustion (reburning) zone in the reactor was formed by dosing into an area above the bed, additional gaseous fuel (propane). Obtained reduction in emissions of nitrogen oxides in both types of beds was at a level 70% - 79%. Additionally bed of CaO has the desulfurizing effect and also reduces the CO concentration in the exhaust fumes. A significant drawback of active bed is the adverse effect on increase of the primary NO which enters the second combustion zone. The result of this fact is higher NOx emission during combustion of the same fuel in bed of CaO in comparison to the combustion of this fuel in the sand bed, when the same maximum degree of reduction of NOx will be obtained for both types of beds.
基金Supported by National Natural Science Foundation of P.R.China(60374001,60334030)the Chinese Ministry of Education(20030006003)
文摘This paper presents a robust model reference adaptive control scheme to deal with un-certain time delay in the dynamical model of a ?uidized bed combustor for sewage sludge. Thetheoretical analysis and simulation results show that the proposed scheme can guarantee not onlystability and robustness, but also the adaptive decoupling performance of the system.
基金supported by the National Natural Science Foundation of China(No.52076172)。
文摘The migration characteristics of heavy metals in co-combustion of sewage sludge and high alkali coal in circulating fluidized bed were studied by experiments and simulations. Temperature plays a crucial role in thermodynamic equilibrium distribution and migration characteristics of heavy metals. At the temperature range of 700℃-1200℃, Hg is completely gaseous and the proportion of Pb, Ni, and Cd in the gas phase is also high. As is mainly elemental in the system, and the proportion of Cr in the solid phase is large. Zn compounds are diverse and mostly solid materials. The volatility of Cu is not strong, and it will become gaseous when the temperature exceeds 1700℃. The proportion of heavy metals in the gas phase decreases as the excess air ratio increases. In an oxygen-rich atmosphere, most of Zn and Ni are converted to oxides;Pb and Cd are converted to crystalline silicate;Cu is converted to partial aluminate;Cr compound is decomposed to form Cr_(2)O_(3);they are good for the solidification and controlling of heavy metals. The elemental Hg is converted to HgCl_(2) and the elemental As is converted to AsCl_(3). Temperature also has a great influence on the volatilization rate of heavy metals. The higher the temperature, the shorter the time they reach the maximum volatility.
文摘At the present time, the sewage treatment plants in the UK produce about 25 million tons of sewage sludge each year at a concentration of 4% solids. New regulations forbid sea dumping and in the near future new incinerators will be required to dispose of about 5 million tons per year. Bubbling fluidised bed incinerators are widely used to burn sewage sludge at a typical consumption rate of about 0.02kg(dry)·s -1 ·m 2 , and it follows that over 300 conventional fluidised bed incinerators of 3m diameter could be required to cope with the increased demand.\;At Sheffield University Waste Incineration Centre (SUWIC) research work is being carried out to develop a novel spinning fluidised bed incinerator. The key factor to note is that when air flows up through a bed of near mono sized particles, it fluidises when the pressure drop across the bed is equal to the weight of the bed. Normally, the weight of the bed is determined by gravity. However, if the bed is contained by a cylindrical air distributor ‘plate’ that is rotating rapidly about its axis, then the effective weight of the bed can be increased dramatically. The airflow passing through the bed can be increased proportionally to the “g” level produced by the rotation and it follows that the process has been intensified. In exploratory tests with a spinning fluidised bed we have achieved combustion intensities with coal combustion as high as 100MW/m 3. A problem with burning coal is that it was difficult to remove the heat and rotating water seals had to be used to transfer cooling water into the bed. In the case of sewage and other sludges, this problem does not exist since the flue gases can remove the small amount of heat released. The rotating fluidised bed sludge incinerator is a novel device, which is very compact. It is able to solve the turndown problem encountered with conventional fluidised beds by simply changing the rotation speed. Bearing in mind that a centrifugal sludge de watering unit is already used on sludge incineration plants, it is likely that the rotating fluidised bed can be combined with the de watering unit, resulting in further process integration and intensification. Furthermore, our ash sintering system can be added to render the ash non toxic and unleachable thus reducing the cost of its disposal.
文摘The experimental studies on the formation of NOx and SO2 during incineration of sewagesludge and paper mill sludge are reported. The test result indicates that: (1) The conversionof fuel-S into SO2 and fuel-N into NOx is mainly determined by sludge characteristics;(2) Emission of NOx and SO2 decreases with increasing sludge moisture content, increaseswith increasing bed temperature and excess air; (3) The conversion of fuelN into NOxincreases with increasing excess air; (4) The conversion of fuel-S into SO2 increases with bedtemperature and excess air increasing, decreases with sludge moisture increasing.
