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Home / Case Studies / Comprehensive NOx Scrubbing Solutions for Pigment Manufacturing
Comprehensive NOx Scrubbing Solutions for Pigment Manufacturing
Client
One of the largest in the world pigment manufacturer and supplier for a diverse customer base. Inorganic pigments are used in paints and coatings for architectural coatings, building and construction.
Production Process
This process involves the oxidation of a metal nitrate, where a slurry containing approximately 40% nitric acid is placed in a furnace to evaporate the nitric acid and water.
Problem
Cleaning from NO, NO2 is required.
Current system component
Newly built production facility.
Temperature
170°F
Gas/Dust
NO, NO2
Initial Data
General Information on Nitric Oxide (NO) and Nitrogen Dioxide (NO₂)
Nitric Oxide (NO, Nitric Monoxide, Nitrogen Oxide)
- State: Gas
- Dryness: Gaseous substance
- Corrosiveness: Low, but can oxidize to NO₂, which is more aggressive
- Density: 1.340 g/L at 0 °C
- Flammability: Non-flammable
Health and Equipment Hazards
At low concentrations, it is not highly hazardous but may cause respiratory irritation. Prolonged exposure can impair lung function.
Can oxidize to NO₂, which is more aggressive and can negatively affect equipment.
Purification Solutions
Toxic, causes respiratory irritation. Prolonged exposure can lead to severe lung diseases. High concentrations may cause pulmonary edema.
Highly corrosive. Reacts with water to form nitric acid.
Purification Solutions
• Absorption in alkaline solution (NaOH, KOH)
• Catalytic reduction (SCR)
• Adsorption on activated carbon at low temperatures
At low concentrations, it is not highly hazardous but may cause respiratory irritation. Prolonged exposure can impair lung function.
Can oxidize to NO₂, which is more aggressive and can negatively affect equipment.
Purification Solutions
- Absorption in scrubbers with alkaline solution (NaOH, KOH)
- Catalytic reduction to N₂ (Selective Catalytic Reduction – SCR)
- State: Reddish-brown gas with a pungent odor
- Concentration: Released during fuel combustion and nitric acid production
- Dryness: Gas
- Corrosiveness: High, reacts with moisture to form nitric acid (HNO₃)
- Density: 1.88 g/L at 0 °C
- Flammability: Non-flammable but can support combustion
Toxic, causes respiratory irritation. Prolonged exposure can lead to severe lung diseases. High concentrations may cause pulmonary edema.
Highly corrosive. Reacts with water to form nitric acid.
Purification Solutions
• Absorption in alkaline solution (NaOH, KOH)
• Catalytic reduction (SCR)
• Adsorption on activated carbon at low temperatures
Client Communication
Client:
We are looking for a small skid based NOx scrubber. We are expecting 2 pick up points with around 25 ACFM of air to be scrubbed.
Engineer Torch-Air:
We definitely can help you with your task. But we need some additional data related to your project. Would you, please, fill out the questionnaire as much detail as possible.
Client:
I apologize for the delayed response. This process is still in the design phase so we don’t necessarily have all of the information. I have answered the questions that I could, but wanted to give little bit more information on the process itself. This will be a pilot facility that will be running at very small rates and should not exceed the regulatory emissions for NOx, but we would still like to find a system to scrub NOx to gain more information as we scale up. This process involves the oxidation of a metal nitrate in which we will place a slurry containing approximately 40% nitric acid in a furnace to evaporate the nitric acid and water. If you think it would be beneficial I could set up a Teams meeting with one of our chemists.
Engineer Torch-Air:
The proposal is in the attached file. Please clarify whether everything is clear to you?
Client:
I apologize this project has been delayed and we are actually planning on skipping over the pilot scale and jumping to a much larger scale. We are currently rescaling everything to account for this larger scale.
So we have 2 separate points of the process that we would like to address with scrubbers and may need to be handled differently.
The first step includes 2 separate evaporators which would require 2 pick up points.
The second step would require air to be scrubbed from a rotary calciner which contains a much lower concentration of NOx. See table below of air flow rates and concentrations.
Please let me know any additional information needed.
So we have 2 separate points of the process that we would like to address with scrubbers and may need to be handled differently.
The first step includes 2 separate evaporators which would require 2 pick up points.
The second step would require air to be scrubbed from a rotary calciner which contains a much lower concentration of NOx. See table below of air flow rates and concentrations.
Evaporators | Calciner | |
Airflow Rate | 3 m³/hr | 594.6528 m³/hr |
NOx | 97.78 kg/hr | 44.4 kg/hr |
NOx Concentration | 32.59 kg/m³ | 0.075 kg/m³ |
Please let me know any additional information needed.
Engineer Torch-Air:
Please clarify the data, specifically:
According to the information you provided, 3 m³/h of air and 97.78 kg/h of nitrogen oxides are emitted from the evaporators, correct?
We can only approximately calculate the total volume of exhaust gases since the exact quantities of NO, NO₂, and N₂O₅ in the NOx are unknown.
For a rough estimate, we will use the density of NO at atmospheric pressure, which is 1.3402 kg/m³. Thus, 97.78 kg of nitrogen oxides at atmospheric pressure would occupy 97.78 / 1.3402 = 73 m³.
The total volume of exhaust gases would therefore be 76 m³/h.
Do you have any estimates regarding the amounts of NO, NO₂, and N₂O₅ in the NOx?
What is the gas temperature?
What is the gas temperature from the calciner?
According to the information you provided, 3 m³/h of air and 97.78 kg/h of nitrogen oxides are emitted from the evaporators, correct?
We can only approximately calculate the total volume of exhaust gases since the exact quantities of NO, NO₂, and N₂O₅ in the NOx are unknown.
For a rough estimate, we will use the density of NO at atmospheric pressure, which is 1.3402 kg/m³. Thus, 97.78 kg of nitrogen oxides at atmospheric pressure would occupy 97.78 / 1.3402 = 73 m³.
The total volume of exhaust gases would therefore be 76 m³/h.
Do you have any estimates regarding the amounts of NO, NO₂, and N₂O₅ in the NOx?
What is the gas temperature?
What is the gas temperature from the calciner?
Client:
This is correct. There will be a total of 3m³/hr being emitted from the evaporators which will need to be scrubbed. As for the estimation for the exact quantities we do not know. I have reached out to our R&D department to see if we can get additional information. The manufacturer of the evaporators had recommended that we treat this with 2 scrubbers in series. The first one would be utilizing an H2O2 solution as the scrubbing fluid, allowing us to recover additional Nitric Acid, while the second scrubber would be utilizing an NaOH scrubber to ensure complete treatment. The gas temperature should be ambient by the time it reaches the scrubbers as it will go through a condenser first. The gas temperature from the calciner will be approximately 70°F.
Engineer Torch-Air:
Evaporators — 76 m³/h, ambient, NOx.
Wet Scrubber for Evaporators
Engineer Torch-Air:
Scrubbing solution — H2O2
Material of construction - PP (170°F)
PP should be suitable for most applications, but the user is advised to make his or her own tests to determine the suitability of polypropylene in that particular environment, because it might be affected by H2O2 at temperatures above 70°F.
We recommend to test the material first, but it seems impossible due to he fact that the plant doesn't exist yet
Characteristics | Information |
Volume | 100 CFM |
Scrubbing column pressure loss | Max pressure drop — 10 in.w. |
Maximum vacuum on the body | 4 000 Pa |
Weight | 7000 lbs |
Temperature range | From 40 to 70˚F |
Tank | Polypropylene |
Pipes | Polypropylene |
Valves | Polypropylene |
MATERIALS of column internals | Packing — Polypropylene Mist eliminator — Polypropylene Nozzles — Polypropylene |
Bolts, nuts, washers | AISI 304 SS |
Mounting brackets | AISI 304 SS |
Pump | 0.5 hp 208-230/460v 3ph – 2 pc |
Material of construction - PP (170°F)
PP should be suitable for most applications, but the user is advised to make his or her own tests to determine the suitability of polypropylene in that particular environment, because it might be affected by H2O2 at temperatures above 70°F.
We recommend to test the material first, but it seems impossible due to he fact that the plant doesn't exist yet
Wet Scrubber for Calciner
Engineer Torch-Air:
Calciner — 595 m³/h, 170°F, NOx
Material of construction — PP
Material of construction — PP
Characteristics | Information |
Volume | 600 CFM |
Scrubbing column pressure loss | Max pressure drop - 10 in.w. |
Maximum vacuum on the body | 4 000 Pa |
Weight | 7000 lbs |
Temperature range | From 40 to 70˚F |
Tank | Polypropylene |
Pipes | Polypropylene |
Valves | Polypropylene |
MATERIALS of column internals | Packing — Polypropylene Mist eliminator — Polypropylene Nozzles — Polypropylene |
Bolts, nuts, washers | AISI 304 SS |
Mounting brackets | AISI 304 SS |
Pump | 0.5 hp 208-230/460v 3ph – 2 pc |
Client:
Thanks for the quick response. I have a meeting on Wednesday to review with our team. I will let you know if we have any questions and will follow up with you.
I apologize. One of the questions that came up today is are both of these scrubbers regenerative and what is the overall efficiency of these scrubbers?
I apologize. One of the questions that came up today is are both of these scrubbers regenerative and what is the overall efficiency of these scrubbers?
Engineer Torch-Air:
The first scrubber will use H2O2 for scrubbing, and the second will use NaOH. The efficiency will greatly depend on the amount of NO in the gases. We will perform the calculations assuming the NO to NO2 ratio is 1:1, and we will calculate an efficiency of 99% considering the two scrubbers. This is definitely achievable.
Evaporators — 76 m³/h, ambient 70°F (21°С), NOx
1st scrubber — Scrubbing solution — H2O2, 5%
2nd scrubber — Scrubbing solution — NaOH, 5%
Calciner — 595 m³/h, 170°F (77°С), NOx
1st scrubber — Scrubbing solution — H2O2, 5%
2nd scrubber — Scrubbing solution — NaOH, 5%
Evaporators — 76 m³/h, ambient 70°F (21°С), NOx
1st scrubber — Scrubbing solution — H2O2, 5%
2nd scrubber — Scrubbing solution — NaOH, 5%
Calciner — 595 m³/h, 170°F (77°С), NOx
1st scrubber — Scrubbing solution — H2O2, 5%
2nd scrubber — Scrubbing solution — NaOH, 5%
Proposed Solutions
The Developed Air Purification Solution
To effectively remove NOx emissions from the pigment manufacturing process, we propose a two-stage scrubbing system for both the evaporators and the rotary calciner. Each system will utilize a combination of hydrogen peroxide (H₂O₂) and sodium hydroxide (NaOH) scrubbers to ensure maximum NOx removal efficiency.
For the evaporators (76 m³/h, ambient temperature), the first scrubber will use a 5% H₂O₂ solution to recover nitric acid, followed by a second scrubber with a 5% NaOH solution for complete NOx treatment.
For the rotary calciner (595 m³/h, 170°F), the same two-stage scrubbing process will be applied to effectively capture and neutralize NOx emissions.
This system is designed to achieve up to 99% NOx removal efficiency, ensuring compliance with environmental regulations while optimizing process performance.
The wet scrubbers have achieved the specified efficiency
For the evaporators (76 m³/h, ambient temperature), the first scrubber will use a 5% H₂O₂ solution to recover nitric acid, followed by a second scrubber with a 5% NaOH solution for complete NOx treatment.
For the rotary calciner (595 m³/h, 170°F), the same two-stage scrubbing process will be applied to effectively capture and neutralize NOx emissions.
This system is designed to achieve up to 99% NOx removal efficiency, ensuring compliance with environmental regulations while optimizing process performance.
The wet scrubbers have achieved the specified efficiency
Best Scrubbers for Pigment Manufacturing
We always perform precise calculations and offer expert assistance in selecting the optimal dust collection or gas cleaning systems, typically completing this process within 1 to 2 days
Head of Engineering,
Vladimir Nikulin
Vladimir Nikulin
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