NaOH Scrubber

Caustic scrubbing technology is used for removal of acidic pollutants in exhaust gas from different industries.

A cylindrical column consist of packing materials and spray nozzles in which the contaminated gas is passed. Pollutants from the gas dissolve in the liquid based on the absorption technology. Spray nozzles are arranged in such a way that spray zones should cover cross sectional area of column. There is packing material in the tower to enhance contact between liquid and gas.

Caustic scrubber is mainly used for H2S scrubbing

Scrubbing of H2S using NaOH has been applied various industries. However, we can apply this technology for only if H2S concentration is low level. For this case, we can just remove the H2S from the exhaust gas, we cannot get back the by product.

If the H2S concentration is very high, the consumption of caustic will be more. Then it will be uneconomical to remove the H2S. To make it economical, we have look for reselling of by product formed from the reaction.

In the scrubbing process, the following reaction takes place

H2S + NaOH ————–>        NaHS + H2O ————— reaction 1

NaHS + NaOH ———–>         Na2S + H2O —————– reaction 2

NaOH reacts with H2S to give NaHS (Sodium hydrosulfide) as per reaction 1. If the quantity of NaOH is more reaction 2 is favourable, then it leads to formation of Na2S (Sodium Sulfide). Generally, NaHS is more valuable by product than Na2S. In order to reduce the caustic consumption by 50 % and as well as to increase the by-product sale value, it is required to not to favour the reaction 2. We design and develop the caustic scrubber to achieve reduction in caustic consumption and increase the by-product sale value.

pH/Conductivity in scrubbing liquid

The pH in the scrubbing liquid is continuously monitored and adjusted to maintain the constant removal efficiency. If the pH level in the Scrubbing tank decreases the efficiency of scrubber will be decreased drastically. Maintaining the pH manually will be a problem for continuous production conditions. In order to avoid that, the Dosing System along with pH monitor will be fitted. The pH monitor will continuously monitor the pH level. If the pH falls below or raises it will automatically raises the audio visual alarm. And also operates the dosing pump through the relay output accordingly thus maintaining the pH level.

Note: pH is considered if the concentration of scrubbing liquid is less than 4 %. If the scrubber uses strong caustic (10 – 15 %), the pH is not recommended because direct exposure of pH probe/electrode to high concentrated caustic will damage the pH probe, thus leads to fluctuation/failure in pH monitoring.

Conductivity is non-specific for particular chemicals. Conductivity meter will respond for both reactant and product in scrubbing liquid. If the scrubbing chemical decrease, there will be decrease in the conductivity. The scrubbing liquid can be discharged and directed to ETP, if there is significance drops in conductivity.

NH3 Ammonia Scrubber

Ammonia is a colorless gas made of hydrogen and nitrogen, a strong odor causing gas. It is poisonous if inhaled directly in large quantities and direct exposure causes eye, nose and throat irritation in less concentration.

Permissible exposure limit of ammonia: 25 ppm (ACGIH) – TLV (Threshold Limit Value); 35 ppm STEL (Short time exposure limit)

IDLH (Immediate dangerous to life or health): 300 ppm

Aqueous ammonia has very high vapour pressure at atmospheric temperature which causes ammonia to evaporate easily and strongly. A wet scrubber removes ammonia using water using absorption principle, but the efficiency will be decreasing during the recirculation of water. The water pH will be increasing since the ammonia can convert into ammonium hydroxide in water. Due to the alkalinity, it is very effectively scrubbed using acid solution. This will allow the water for continuous recirculation and leave the by-product of ammonium salt. The common acid used for scrubber is Sulfuric acid due to non-volatility.

Ammonium sulphate, the by-product formed from the scrubbing process, will be used as fertilizing ingredient.

Apzem uses packed bed scrubber to remove ammonia from exhaust stream using sulphuric acid as the scrubbing liquid. This scrubber can handle high inlet concentration of ammonia and the removal efficiency up to 99.9 % can be guaranteed.

PHOSPHATING SCRUBBER

Phosphating is the widely used pretreatment process for metal surfaces and polishing of ferrous and non ferrous materials. It plays an important role in automobile and appliances industries because of its corrosion resistance, wear resistance and speed of operation. Phosphate coating is typically used to coat any steel parts to prevent from corrosion and can be used for pre treatment of any material or equipment before doing painting or coating. Chemicals used for phosphate coatings are Manganese, Iron and Zinc. A part of material is dipped into a tank containing phosphoric acid solution causes a chemical reaction which makes the salts to bond on the part. Common parts used in phosphating are automotive parts such as clutches, engine components. Increasing regulations for controlling fumes from phoshpating tanks and environmental concerns leads to requirement of wet scrubber.

Apzem design and manufacture wet scrubber which is suitable for controlling phosphating fumes, acids and alkali. We design hood and ducting for source capturing using ACGIH standard, without allowing to spread in the working area. The captured fumes are treated by passing through a wet scrubber. A cylindrical device in which gas is passed from the bottom and scrubbing liquid is sprayed on the top to neutralize the gas pollutants. Wet scrubber removes pollutants by absorbing in liquid and neutralizing by chemical agents present in the liquid.

Typical processes applied for Phosphating are

• Activation
• Acid/Alkali degreasing
• Lubrication
• Acid Pickling
• Rinsing

sulfuric acid scrubber

Many chemical industries generates and exhausts sulphur based substances such as sulphuric acids or sulphur dioxide from various processes. Sulfuric acid fumes are very corrosive and it is strongly irritant to the respiratory if is directly inhaled. Apzem have experienced in controlling and neutralizing the sulphuric acid fume using a packed bed column with caustic recirculation.

The scrubber system consists of packed bed column with bottom tank, recirculation pump, mist eliminator and blower. We design and fabricate custom wet scrubber unit which can be fit in the site location and will assure you performance and minimum requirements of maintenance.

Working principle

H2SO4 Scrubber works on principle of absorption technology. A column in which gas is passed at bottom and liquid is sprayed at opposite direction. Packing material is filled to bring the intimate contact between gas and liquid. There are two things happening here, providing cooling for exhaust gas and removing H2SO4 gas from exhaust.Apzem provides complete packages from start to end including water level controller using automated solenoid valve, pH controller with dosing system.

Nox Scrubber

Nitrogen released from fuel combustion process reacts with oxygen and forms Nitric Oxide (NO). The Nitric Oxide is a colorless gas and it will be oxidized into Nitrogen dioxide (NO2) upon reacting with oxygen. This NO2 has odorous and acidic in nature, causes hazardous to human health and the environment, even in typically low concentrations.

Health Impact associated with NOx

The major health issues associated with NO2 is impact on respiratory system and lung dysfunction.

IDLH value of NO2: 20 ppm

PEL value of NO2: 2 ppm

Working Principle of NOx Scrubber

It works based on the absorption with chemical reaction, involved to remove pollutants from exhaust gas by dissolving into the liquid.

A central piece of equipment, called packed bed column, in which the polluted gas is fed from the bottom and pass upward through packing material. At the same time, solvent is sprayed from the top to wash the pollutants. Nox scrubber includes packed bed column, scrubber tank, recirulation pipe connected with solvent spray nozzle. Recirulation pump, Instrumentations, Suction blower and Control panel. All the parts involved in the scrubber unit is designed and selected based on the standard design criteria.

Packed column helps to achieve heat transfer and mass transfer. The exhaust gas contains NOx mostly has high temperature than atm. The packed column is utilized in cooling of hot gases and dissolving acid gases into the solvent. Water will be used as solvent for the physical absorption. However, Alkali solution will be used for continuous effective scrubbing. Packing material with high surface area is used to increase intimate contact between gas and liquid.

Chemical reaction

Oxides of nitrogen includes N2O, NO, N2O3, NO2, N2O4 and N2O5 generates from combustion process. The primary NOx are NO and NO2. Nitrogen dioxide (NO2) can be neutralized by absorption and chemical reaction with NaOH. However, the NO does not dissolve easily into the water. NO2 is mostly considered as NOx through the National Ambient Air Quality Standards (NAAQS) as per the EPA.

2NO₂ + 2NaOH → NaNO₂ + NaNO₃ + H₂O

HCL Scrubber

Hcl gas

Hcl gas is colorless, pervasive and corrosive, mostly emitted from process reactors, Hcl storage tanks while filling and laboratory.  Hcl gas emits easily from aqueous solution of concentrated hcl at atmospheric temperature and diluted hcl at higher temperature. The high vapour pressure of hcl tends to emit the fumes.

Toxicity of Hcl Fumes

• The concentrated hcl fumes are hazardous to the human health and environment
• The IDLH value of hcl is 50 ppm and Permissible Exposure Limit (PEL) is 5 ppm

Working principle

Hcl Scrubber works on principle of absorption technology. A column in which gas is passed at bottom and liquid is sprayed at opposite direction. Packing material is filled to bring the intimate contact between gas and liquid. There are two things happening here, providing cooling for exhaust gas and removing hcl gas from exhaust.

Apzem provides complete packages from start to end including water level controller using automated solenoid valve, pH controller with dosing system.