* * * * Introduction to heavy ash production by solid phase hydration method in soda ash plant

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This post was last edited by mkp369 on 2013-3-10 15:22 * * * * Introduction to heavy ash production by solid phase hydration method in soda ash plant 1. Basic principle Water and light ash are mixed according to a certain water-alkali ratio to generate aqueous alkali in the range of 35.4-109℃. Na2CO3(s)+H2O(l)= Na2CO3.H2O(s)+14.1KJ/mol Alkali monohydrate loses crystal water above 109℃ and generates heavy ash with a density above 850kg/m3. ㎏ Na2CO3.H2O(s)=Na2CO3(s)+H2O(g)－14.1KJ/mol 2. Process flow The light ash at 150-200℃ in the silo is controlled by the frequency conversion speed-adjustable screw conveyor, and mixed with the desalted water at 25-35℃ in a certain proportion and enters the hydration machine. The reaction occurs in the hydration machine to generate alkali monohydrate Na2CO3.H2O(s) with a temperature of 90-98℃. Alkali monohydrate is crushed by the crusher and then enters the fluidized bed that integrates drying and cooling. The filtered air is transported to the air heater by the blower and heated to 150-220°C. The air volume is then controlled by the air valve and then enters the five-section air box separated by the partition. The hot air in each air box enters the bed from bottom to top along the side of the battens on the air distribution board. It fully contacts the falling alkali monohydrate from the upper part, causing violent turbulence and forming fluidization. Snake-shaped heat exchange tubes are arranged in the bed. In the drying section, superheated steam with a pressure of 2.5-3.2MPa is introduced into the tube to indirectly exchange heat with the material, dehydrating the alkali monohydrate to form heavy ash. The high-temperature heavy ash at 160-190℃ is sent to the cooling section of the fluidized bed by the wind. In this section, the air is pressurized by the fan and the air volume is controlled by the valve, then enters the two air boxes, and then enters the cooling section through the air distribution plate of the air box to fluidize and cool the high-temperature heavy ash. At the same time, cooling water with a temperature <40°C is introduced into the coiled tube heat exchanger bundle of the cooling section for indirect heat exchange, so that the heavy ash is rapidly cooled, and the heavy ash is discharged through the overflow port after the temperature is <80°C. The unloaded heavy ash is screened by the vibrating screening machine, and the heavy ash under the screen is packaged as finished product. The alkali balls on the screen are crushed by the crusher and returned to the fluidized bed cooling section. The dusty tail gas of the fluidized bed is purified by the cyclone separator, and the ash enters the light ash silo. The gas out of the separator is washed by the scrubber. After cooling and dust removal, it is emptied by the exhaust fan. The wash water from the scrubber can be used as combined water. 3. Main process parameters: Light ash temperature 150-190℃ Combined water temperature 25-40℃ Temperature of alkali monowater 90-98℃ Moisture content of alkali monowater 16-20% Heating steam pressure 2.5-3.2MPa Temperature 230-280℃ Fluidized bed discharge section temperature ≥85℃ Fluidized bed drying section temperature 160-190℃ Discharge temperature of fluidized bed cooling section ≤85℃ Fluidized bed outlet gas temperature ≥110℃ Fluidized bed tail gas exhaust temperature ≤70℃ 4. The operation control operating system implements microcomputer monitoring, and the main automatic control points are:: 1. Automatic control of the steam pressure entering the fluidized bed 2. Automatic control of the hot air flow entering the fluidized bed 3. Automatic control of the cold air flow entering the fluidized bed 4. Automatic control of the air outlet pressure of the fluidized bed 5. Automatic control of the fluidized bed discharge 6. Automatic control of the water and alkali inlet of the hydration machine 5. Main consumption 1. 1.002 tons of light ash/ton of heavy ash 2. 0.5---0.65 tons of steam/ton of heavy ash 3. 20kwh/ton of heavy ash 6. Product quality Total alkali content (Na2CO3) ≥99.2% Density ≥900 Kg/m3 The salt content mainly depends on the light ash salt content. Our factory is 0.25-0.65%. The whiteness mainly depends on the light gray whiteness and the quality of desalted water. Our factory is generally ≥92%. The particle size mainly depends on the vibrating screen mesh, crusher efficiency and the quality of monohydrate alkali crystal. Our factory is generally ≥1.18mm ≤2%. ≤80um ≤10% 7. Main equipment drying and cooling fluidized bed: Specifications: * * * * × * * * * × * * * * It consists of three parts: the air box (with air distribution plate), the bed body (with heat exchange tube bundle), and the air hood. It is equipped with a feed port, a discharge port, an air inlet, an air outlet, etc. Hydration Machine: Specifications :∮ * * * * × * * * * Rotary horizontal type, imitation hammer shape, consisting of feeding, discharging, air inlet, air outlet, transmission and other parts. There are three lifting plates inside the barrel, and there are support and transmission components such as ring gears and rolling rings outside the barrel. 8. The main problem requires high quality of light ash. When the Ca Mg content of light ash is high, the crystallization process of the hydrator will easily form alkali balls and alkali scars, which will destroy the fluidization state of the materials in the fluidized bed, resulting in a "dead bed", reduced production capacity, and final shutdown for cleaning. The impact of refined brine quality on production capacity is shown in the attached table. The requirements for vibrating screens and crushers are relatively high, otherwise the production capacity will decrease. The pore size of the vibrating screen is too small or blocked, the crushing effect of the crusher is poor, and too much material returns to the fluidized bed, which will result in poor fluidization effect of the fluidized bed and reduced production capacity.