Naoh Scrubbing system required amount of naoh

Replies

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  Ramani Aswath

  Theoretically two gm moles of NaOH will absorb one gm mole SO_{2 .Â} However many other factors have to be considered in scrubbing flue gas. The following two papers may be of help.

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  Sagar Jiyani

  As a practically i need to give a data to our client that how much naoh required in a day or in a hour for 22620 kg/hr flue gas flow rate and 0.13% so2 by volume.

  Please help me to  quentity calculation of naoh..

• 

  Sagar Jiyani

  As a practically i need to give a data to our client that how much naoh required in a day or in a hour for 22620 kg/hr flue gas flow rate and 0.13% so2 by volume.

  Please help me to  quentity calculation of naoh..

• 

  Ramani Aswath

  Assuming 1.3 kg/m³ Fluegas density and taking into account the properties of SO₂ one gets 1.86 x 40 or about 75 kg NaOH consumption/hr.

  Since the efficiency may be less than theoretical a bit more maybe needed.

  This is a back of the envelope kind of quick and dirty calculation. If commercial issues are involved better get it checked.

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  Sagar Jiyani

  But we can get 12 ph value of water and naoh solutions so per ltr of water 0.4 gm naoh required.so  if we used 12000 ltr water then how much naoh required per hour by reacting with sox

  
  

• 

  Ramani Aswath

  From the data you indicated, the theoretical requirement to absorb the nearly 60 kg/hr SO₂ produced is about 75 kg NaOH/hr.

  Are you using 12 m³ water/hr? Then minimum this much NaOH/hr must be dissolved in the 12 m³ water used.

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  Sagar Jiyani

  sir,if we are using naoh with water solution then there is possibility to less naoh absorption? because if there is 75 kg/hr naoh required then per day 1800 kg naoh required and industrial cost increase. so there is any other sollution?

  on above problem?

  
  

• 

  Ramani Aswath

  Actually you will need more than that amount. 75 kg/hr is the theoretical amount of Naoh needed to absorb the amount of SO_x that is present in the flue gas as specified.

  You are talking about cleaning 546 tons of flue gas in a day.

  Room temperature water can absorb 0.2 kg SO₂ . So 300 litres water can absorb 60 kg SO₂. This translates to only 7200 litres water per day.You have to throw away this water subject to local environment laws. You can completely avoid using NaOH. 

  Since you said something about 12000 litres water you may not need any NaOH.

• 

  Sagar Jiyani

  thanks for your response sir,

  but our procedure is like we are adding naoh into 12000 ltr water and maintaining its ph value 10-12 ph. and this solutions we will spray on scrubber tower which convert sox into sulphuric and sulphuras acid.

  and we must have to add naoh in water and solution spray in tower with number of nozzles by using 15 hp centrifugal pump. so there is any calculations or according your experience how many naoh required?

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  Ramani Aswath

  If your requirement is only pH maintenance 4.8 kg NaOH in 12 m³ water will give a pH of 12 as you mentioned before.

  But the chemical reaction between SO_x and NaOH does need 75 kg NaOH/hr for the contamination level you have given. I am unable to suggest a way around that.

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  Sagar Jiyani

  Ok.sir..i get your mean. But if we get ph value 12 ph then reaction occurs with sox in flue gas and according gpcb norm there is 100 ppm sox allow for release atmosphere.

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  Ramani Aswath

  The problem is that NaOH reacts with SO_x and gets consumed. This will drop the pH. You have to add more NaOH to bring it back to 12. According to the contamination level specified this will be 75 kg/hr.

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  Sagar Jiyani

  Ok sir..i get it ..in short i have to require 75 kg/hr naoh for complete sox remove.

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  Ramani Aswath

  Not really. You can do it with water alone as mentioned earlier. But if a pH of 12 is specified, then you need that much NaOH to maintain pH 12 and remove the SO_x by NaOH.

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  Sagar Jiyani

  as u mentioned erlier that only water spray also can remove sox from flue gases. is that possible? if es then which procedure we should follow?

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  Ramani Aswath

  #-Link-Snipped-# , I am writing from just the chemistry point of view. I have not done anything on flue gas scrubbing.We id have a small incinerator at work for bio waste, which had a scrubber for washing the exhaust gases from bio waste combustion, which did not have much SO_x. We just used waterspray more to cut down dust and smoke. It has been working for many decades now.

  There are stringent environment regulations now on flue gas emissions. You have to conform to applicable rules. One option that may be cheaper is to use a spray tower with limestone powder slurry.

  Please see these links: Flue Gas Desulfurization

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  Sagar Jiyani

  lime stone powde or lime slurry is not better efficient more than naoh. lime stone or slurry has efficiency around 80-90% where as naoh has 95-99%.