ABSTRACT
With the increasing production of municipal sewage sludge (MSS) in China every year, the co-firing of MSS and pulverized coal is getting more and more widely applied in large coal-fired power plants. The co-firing of MSS and pulverized coal will produce a large amount of particulate matter (PM) emissions, especially submicron particles. In this paper, the formation characteristics of submicron particles in the co-firing process of coal and MSS were studied in a drop tube furnace. The influence of the furnace temperature and the addition ratio of sludge on the particle size distribution and element composition of submicron particles in MSS, pulverized coal combustion and co-firing was mainly studied. The experimental results show that the furnace temperature has an influence on the formation of PM0.4. For sludge combustion, increasing the furnace temperature will promote the formation of PM0.4. The main reason is that increasing the furnace temperature promotes the gasification of Si, S, Fe, and P to form the precursor of PM0.4 or PM0.4. At same furnace temperature, the volume concentration and mass concentration of PM0.4 produced from pulverized coal combustion are less than that of sludge. Different from sludge combustion, co-firing of pulverized coal and sludge has a synergistic effect on eliminating PM0.4 formation. Increasing the addition ratio of sludge can decrease the volume concentration and mass concentration of PM0.4. This is because that aluminosilicates formed during co-firing promotes the scavenge Si, Ca, Fe, thereby reducing the precursors of PM0.4 and the mass yield of PM0.4. Increasing the furnace temperature in co-firing can inhibit the formation of PM0.4. When the furnace temperature is between 1100 °C and 1300 °C, increasing the furnace temperature will reduce the Fe content and increase the content of Si, Ca, Na, K, and P in PM0.4. However, the reduction of Fe and the increase of Si, Ca, Na, K, and P in PM0.4 offset each other, resulting in an insensitive relationship between the mass yield of PM0.4 and the furnace temperature.
ABSTRACT
A 660 MW unit of an ultra-low emission coal-fired power plant in the Beijing-Tianjin-Hebei area was chosen for this study. The particulate matter was sampled with a Dekati low-pressure impactor (DPLI) at the inlet and outlet of flue gas cleaning devices including selective catalytic reduction (SCR), low-low temperature economizer (LLTe), electrostatic precipitator (ESP), wet flue gas desulfurization (WFGD), and wet electrostatic precipitator (WESP). A filter sampling system was also used at the inlet and outlet of the WFGD and WESP. The removal efficiencies of PM1, PM1-2.5, and PM2.5-10 from different flue gas cleaning devices were obtained after ultra-low emission modification. The results show that SCR increases the mass concentration of fine particulates and PM1 by 52.11%. The LLTe improves the removal efficiency of the ESP, especially for particles with a range of 0.1-1 µm. The high-efficiency WFGD removes both SO2 and particulates, but it increases PM1. The mass concentration of PM1 increases by 59.41% and the water-soluble Mg2+, Cl-, and SO42- in PM10 increases. The WESP has a high removal efficiency with respect to PM1, PM1-2.5, and PM2.5-10 and can further reduce the dust concentration. Based on an ultra-low emission reform, the final PM10 emission of this 660 MW unit is 2.04 mg·m-3.
ABSTRACT
Gaining the valuable fuels from sewage sludge is a promising method. In this work, the fast pyrolysis characteristics of sewage sludge (SS), wheat straw (WS) and their mixtures in different proportions were carried out in a drop-tube reactor. The combustion reactivity of the residual char obtained was investigated in a thermogravimetric analyzer (TGA). Results indicate that SS and WS at different pyrolysis temperatures yielded different characteristic gas compositions and product distributions. The co-pyrolysis of SS with WS showed that there existed a synergistic effect in terms of higher gas and bio-oil yields and lower char yield, especially at the WS adding percentage of 80wt%. The addition of WS to SS increased the carbon content in the SS char and improved char porous structures, resulting in an improvement in the combustion reactivity of the SS char. The research results can be used to promote co-utilization of sewage sludge and biomass.
