Solutions to problems encountered in the dual-alkali desulfurization process
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Solutions to problems encountered in double-alkali desulfurization operation 1. Scaling and blockage. All the areas that could get clogged in the pipes and towers have been cleared. A few days ago I visited a plant in Liaocheng; there was a layer of scale inside the tower that was about ten centimeters thick – crystalline deposits similar to coarse salt grains, quite hard, and according to the workers at the power plant, it couldn’t even be removed with shovels. Answer: The liquid-to-gas ratio is insufficient, resulting in severely inadequate output of dehydrated gypsum; this leads to an extremely high salt concentration in the circulating slurry, even to saturation, with a large amount of crystals precipitating on the inner walls of pipes and towers. ; _2 a W3 v2 ^ 2 – excessive consumption of sodium and alkali. In the conventional double-alkali method, the designed consumption of sodium alkali is 5%, but in practice, it can exceed this designed value by more than ten times; in other words, the replacement rate of sodium alkali is not satisfactory at all. Who could afford such high consumption levels? - y* y5 A& Answer: As you mentioned, 60% – the normal moisture content of gypsum in vacuum belt conveyors is less than 10%; here, the amount of water removed is more than 6 times that amount. The increase in salt concentration resulting from insufficient output of dehydrated gypsum also leads to a greater loss of soda ash. 0 b) y( F; `1 Z9 w$ @* y 3、It is difficult to dehydrate gypsum. In one power plant, the moisture content of the gypsum after passing through a vacuum belt dehydrator was as high as 60%. Answer: It is likely due to insufficient oxidation; contact the equipment manufacturer for a solution. The fact that this device is not functioning properly is the main cause of the problem. 8 K+ g; F! x! n8 r 4. Another really troublesome issue is that the desulfurization efficiency cannot be increased. It is generally less than 90%, with some cases reaching only 60%. Answer: Refer to point 1 – once the salt concentration reaches saturation, the efficiency can no longer increase. How can this be confirmed? It’s simple: try using clean water. If normal efficiency is achieved, then the concentration of sodium sulfite or sodium bisulfite is too high. In the future, it is necessary to make sure that an adequate amount of lime is supplied to consume them (the output of the vacuum belt must keep up). This post was last edited by johncom on 2009-4-2 at 09:38
The summary is excellent. The main problem with the double-alkali method is displacement; if there are issues with displacement, the losses are greater than those in the simple limestone method
That’s true; the double-alkali method does have many disadvantages.
Combine theory with practice and learn a bit.
How should displacement reactions be controlled? Could you talk about it in detail?
Have you seen any plants that operate well using the double-alkali method? I’d like to learn more about it
I’ve learned it; these are all the problems I need to solve.
I’m currently learning in this field; thank you.
The sodium-calcium double-alkali desulfurization process (Na2CO3/Ca(OH)2) is a process developed by combining the limestone/gypsum method with the sodium-alkali method; it overcomes the disadvantages of scaling in the limestone/gypsum method and high operating costs in the sodium-alkali method. It takes advantage of the fact that sodium salts are soluble in water; sodium-alkali is used inside the absorption tower to absorb SO2. The desulfurization solution obtained after absorption is regenerated in a regeneration tank using inexpensive lime, thereby enabling the cyclic reuse of sodium ions. This process combines the advantages of the lime method and the sodium-alkali method; it addresses the problem of easy scaling inside the tower in the lime method, while also possessing the high absorption efficiency of the sodium-alkali method. The sodium-calcium double-alkali method uses soda ash for initiation, with sodium-calcium absorbing SO2 and lime being regenerated. Its basic chemical principles can be divided into the desulfurization process and the regeneration process: I. Desulfurization process: Na2CO3 + SO2 → Na2SO3 + CO2 (1) 2NaOH + SO2 → Na2SO3 + H2O (2) Na2SO3 + SO2 + H2O → NaHSO3 (3) Equation (1) is the reaction that initiates absorption ； (2) Equation (2) represents the main reaction, which occurs when pH is greater than 9 (i.e., in a highly alkaline environment). Equation (3) applies when the alkalinity decreases to neutral or even acidic levels (5 < pH < 9). II. Regeneration process: 2NaHSO3 + Ca(OH)2 → Na2SO3 + CaSO3↓ + 2H2O. (5) Na2SO3 + Ca(OH)2 → 2NaOH + CaSO3↓. (6) In lime slurry where lime is at saturation, the neutral (amphotic) NaHSO3 reacts rapidly with lime, releasing substances as a result; these newly formed substances then continue to react with lime. The calcium sulfite produced in these reactions precipitates slowly in the form of a hemihydrate, thereby enabling regeneration and allowing the absorbent solution to regain its ability to absorb SO2, thus enabling reuse. The desulfurization by-product is calcium sulfite or calcium sulfate (after oxidation), and users can employ different methods to treat the by-product according to their needs.
The original poster has summarized it very well. I wonder if there are any corresponding measures; thank you