Effect of baking soda dry deacidification on total soluble salt in fly ash in waste incineration power generation industry

As is known to all, garbage incineration fly ash is the material collected in the heat recovery and utilization system and flue gas purification system after household garbage incineration.The yield of fly ash is related to the type of garbage, incineration conditions, incinerator type and flue gas treatment technology, and generally accounts for about 3%-5% of the total amount of garbage incineration.The analysis shows that the fly ash of waste incineration is not a chemically inert substance, which contains a high content of Cd, Pb, Zn, Cr and other harmful heavy metals and salts that can be leached by water. If not properly treated, it will cause heavy metal migration and pollute groundwater, soil and air.

According to GB 18598-2019 “Hazardous Waste Landfill Pollution Control Standard” approved by the Ministry of Ecology and Environment on September 12, 2019, it is stipulated that:

The standard will take effect from June 1, 2020.

Zhang Haiying’s research paper published in Environmental Science and Technology shows that the particle size of 98% ~ 99% fly ash is between 4 ~ 100μm, and the particle distribution is relatively uniform. The content of glass phase is as high as 59%, and the glass beads in it make fly ash have great activity;The main chemical components are CaO, SiO2 and Al2O3, the content of 35.8%, 20.5%, 5.8%, respectively, forming the SiO2-Al2O3-metal oxide system;The main mineral composition is SiO2、CaCl2、Ca3Si2O7、Ca2SiO4.0.35H2O、Ca9Si6O21.H2O、K2Al2Si2O8.3.8H2O和AlCl3.4Al(OH)3. 4H2O, etc.Silicates and aluminum silicates.

As slaked lime is widely used for flue gas desulfurization and dechlorination in domestic waste power generation industry, the main chlorides are CaCl2 and sulfates are CaSO3.AMHED et al. studied the formation mechanism of gypsum in semi-dry desulfurization process below 250℃, and found that most products of desulfurization reaction “CaO+SO2+O2” are CaSO3,The main reason is that the reaction time is short, and the molar volume of CaSO4 is larger than CaSO3, which impedes the further reaction. CaSO3 is an unstable substance and can cause secondary pollution. So far, there is no effective treatment method.

In both dry and semi-dry deacidification processes, the absorption efficiency of SO2 by slaked lime is much lower than that of HCl.For load discharge standards, the amount of slaked lime Ca/S is often more than 2. It not only causes waste of raw materials, but also produces more fly ash to be treated, which increases the difficulty and cost of disposal.

Aier environmental protection uses highly active special baking soda for deacidification, which not only has a high removal efficiency of more than 98% for HCl, but also a high removal efficiency of more than 95% for SO2, and the NSR can be as low as 1.1.

Most of the calcium-based and sodium-based deacidification byproducts have high solubility, which brings some difficulties to the curing disposal and landfill management of fly ash.

According to the national standard NY/T 1121.16 “Determination of Total Water Soluble Salt in Soil”, the mixing ratio of samples and water is 1:5. In this case, gypsum and excess calcium hydroxide will partially dissolve, and the total amount of soluble salt will increase.

In industries such as waste incineration and power generation, flue gas contains both HCl and SO2, and the concentration is generally about 300 ~ 500mg/Nm3.In view of this condition, Aier Environmental Protection developed a process technology combining calcium and sodium based desulfurizer, that is, using the high selectivity of calcium based desulfurizer to HCl, effectively remove most of HCl at very low Ca/S,At the same time, the SO2 emission concentration can be very low by using a small amount of baking soda due to the high removal efficiency of SO2 with Sodium-based desulfurizer. The desulfurizer reacts with flue gas to produce byproducts CaCl2 and Na2SO4, both of which are very soluble. During the curing stage of fly ash, the following reactions will occur:

CaCl2 + Na2SO4 + 2H2O——>CaSO4*2H2O + 2NaCl

The resulting gypsum has a curing effect, which is conducive to improving the strength of the cured substance. By optimizing the process conditions and load distribution ratio, the comprehensive utilization rate of desulfurizer can reach about 90%, and the amount of soluble salt can be reduced by about 50%.

Household waste incineration power plant adopts baking soda dry deacidification flue gas purification process, especially through the calcium and sodium based desulfurization agent technology developed by Aier Environmental Protection innovation. Under the condition of very low pollutant emission concentration, it not only reduces the production of fly ash, but also does not increase the content of soluble salt, and reduces the difficulty and cost of curing fly ash. At the same time reduce the user’s raw material procurement cost, is worth promoting the use of.