Filtering the Future, Protecting the Blue Sky

Created on 04.22

Case Study of Overall Retrofitting of Fiber Demister in Dry Absorption System of a Large Domestic Acid Production Enterprise

Project Location: Taiyuan, Shanxi Province Project Time: August 2025 Application Location: 400,000 tons/year sulfuric acid production unit, first and second suction tower outlet acid mist collector retrofit product: Filtearth upgraded fiber bed demister (2 sets, direct replacement of the same size)

I. Customer Background and Existing Problems
This company is an important basic chemical raw material production base in western Henan Province, possessing a 400,000 tons/year sulfuric acid production unit, employing a "3+1" two-conversion, two-absorption process. The original demister, a standard fiberglass demister from a long-established manufacturer, has experienced continuous performance deterioration over the past three years, becoming a core bottleneck restricting the safe and stable operation of the plant and its compliance with environmental standards:

1. Severely excessive acid mist, posing dual risks to both environmental protection and safety.

2.

1. The acid mist content at the outlet of the second absorption tower has consistently been 45-60 mg/Nm³, far exceeding the latest national emission standard of ≤30 mg/Nm³.

2. Continuous white smoke from the chimney has resulted in multiple warnings from environmental authorities and potential fines.

3. Sulfuric acid mist permeates the plant area, creating a harsh working environment and posing occupational health and safety hazards.

3. Frequent equipment corrosion leads to poor production stability.

4.

1. Acid in the first absorption tower causes corrosion and perforation of the downstream intermediate heat exchanger tube bundle, resulting in an average of 2-3 leaks per year.

2. The four layers of catalyst in the converter are soaked in acid mist, causing powdering and scaling, increasing resistance, and reducing the total conversion rate from 99.7% to 99.2%.

3. Severe corrosion of pipes and valves results in direct losses exceeding 120 million RMB annually due to unplanned shutdowns. 5. High pressure drop limits both energy consumption and production capacity.

6.

1. The pressure drop of the first-stage suction tower demister reaches 2200-2800Pa, and the main fan current consistently exceeds the rated value.

2. The system can only operate at a maximum of 85% load, failing to meet the sulfuric acid demand of downstream customers.

3. Electricity consumption increases by 18kWh per ton of sulfuric acid, resulting in annual additional electricity costs exceeding 500,000 yuan.

7. Short filter lifespan and high maintenance costs.

8.

1. Sublimed sulfur and oil fumes accumulate and clog the fiber bed, requiring complete filter replacement every 12-14 months.

2. Each replacement requires a 4-day shutdown, affecting sulfuric acid production by approximately 4500 tons.

3. A large amount of sulfuric acid is lost with the exhaust gas, resulting in a loss of approximately 15kg of concentrated sulfuric acid per ton of sulfuric acid product.

II. Felfilter Solution

For the special operating conditions of the sulfuric acid dry suction process, we provide a one-stop solution of **"zero modification + full replacement + performance upgrade"**, utilizing the equipment 10 All upgrades were completed during the annual maintenance window, without affecting normal production plans:

1. Product Configuration

✅ Product Models: FLT-FB-3600 Fiber Bed Demister (Single Suction Tower), FLT-FB-3400 Fiber Bed Demister (Double Suction Tower)

✅ Filter Media Material: Imported special glass fiber (custom-made for 98% concentrated sulfuric acid conditions)

✅ Frame Material: 316L stainless steel thickened mesh cage (resistant to high temperature deformation)

✅ Sealing Material: Elastic PTFE tape (resistant to 260℃ high temperature concentrated sulfuric acid corrosion)

✅ Filtration Area: Increased by 31% and 29% respectively compared to the original equipment (with the same tower diameter)

✅ Design Parameters: Total gas throughput 52000 Nm³/h, operating gas velocity 0.6 m/s, filtration accuracy 3μm 100%, 1μm 99%

2. Targeted Technical Upgrades

✅ Gradient Layered Filtration Structure: Pre-filtration layer + Main filtration layer + The three-stage fine filtration layer effectively intercepts sublimated sulfur and oil fume particles, solving the clogging problem at its source.

✅ Low-resistance flow field optimization design: Redesigned gas distributor and fiber bed structure improve airflow distribution uniformity by 40%, significantly reducing operating pressure drop.

✅ Anti-secondary entrainment technology: Added dedicated liquid trapping layer and flow guiding structure to prevent captured sulfuric acid droplets from being carried away again by high-speed airflow.

✅ Integrated sealing structure: Employs elastic PTFE seals to prevent air leakage and short circuits in the tower wall, ensuring demisting efficiency.

III. Implementation Process

1. Preliminary Survey: The technical team conducted on-site measurements of tower dimensions, process parameters, and operating conditions to develop a precise customized solution.

2. Factory Prefabrication: Production was carried out strictly in accordance with the ISO9001 quality system, with airtightness and performance testing conducted before shipment.

3. On-site Installation: Three professional engineers provided on-site guidance, dismantling the old equipment and installing the new demister, with full safety monitoring throughout.

4. System Commissioning: Airtightness tests, no-load trial runs, and load commissioning were conducted, gradually increasing the system load to full load.

5. Performance Acceptance: A third-party testing agency conducted on-site testing of various performance indicators and issued an acceptance report.

6. Technical Training: Systematic training was provided to the customer's operation and maintenance personnel to ensure long-term stable operation of the equipment.

Worker in protective gear handling industrial equipment outdoors. fiber bed demister

Large industrial filter cylinder with a mesh covering, placed on a plastic sheet near a paved area.fiber bed demister

IV. Post-Modification Effects and Data Comparison

Since its commissioning in September 2025, the equipment has operated stably, with all indicators significantly exceeding design values:

Indicator Item	Before renovation	After renovation	Improvement effect
Acid mist content at the outlet of the second absorption tower	45-60mg/Nm³	≤12mg/Nm³	Recovery to over 75%
Acid mist content at the outlet of the first suction tower	80-100mg/Nm³	≤18mg/Nm³	Recovery to over 80%
Pressure drop during operation of the first suction tower	2200-2800Pa	700-950Pa	reduce 68%
Pressure drop during operation of the second suction tower	1900-2400Pa	600-850Pa	reduce 65%
Electricity consumption per ton of sulfuric acid	92kWh	74kWh	reduce 19.6%
Loss per ton of concentrated sulfuric acid	15kg	3.2kg	reduce 78.7%
Total conversion rate	99.2%	99.75%	Restore to design value
Filter replacement cycle	12-14 months	3 years or more	Extended by more than 2.5 times
System maximum load	85%	112%	Promote 32%

V. Customer Economic Benefit Analysis

Based on 400,000 tons/ Based on annual sulfuric acid production capacity calculations, the direct economic benefits after the upgrade are as follows:

1. Energy savings: 400,000 tons×18 kWh/ton×0.6 yuan/kWh = 432,000 yuan/year

2. Sulfuric acid recovery revenue: 400,000 tons×11.8 kg/ton×0.5 yuan/kg = 236,000 yuan/year

3. Maintenance cost savings: Filter replacement cost + equipment repair cost + downtime loss = 1,680,000 yuan/year

4. Production capacity increase revenue: 400,000 tons×27%×180 yuan/ton = 1,944,000 yuan/year

5. Avoidance of environmental fines: Approximately 300,000 yuan/year

Total annual economic benefits: Approximately 4,292,000 yuan; Investment payback period: Approximately 3.8 months

VI. Customer Testimonials

"This upgrade completely solved our long-standing problem. Before, we were always worried about environmental inspections; now, acid mist emissions are stable at 10 mg/Nm³." The pressure drop was around 800 Pa, far below the national standard. What surprised us most was that not only was the demisting effect improved, but the system could also operate at over 10% load, fully meeting the needs of downstream customers. After more than six months of operation, the pressure drop has remained stable at around 800 Pa, with no signs of increase. We have already recommended Filtec to several sulfuric acid plants in the surrounding area. — Director Li, Production Technology Manager of the sulfuric acid company

VII. Extended Application Scenarios

This solution is also applicable to the following applications in the sulfuric acid industry:

✅ Separation of water mist and acid mist at the outlet of drying tower

✅ Acid mist capture at the outlet of fuming sulfuric acid absorption tower

✅ Demisting at the outlet of tail gas desulfurization tower

✅ Acid mist recovery from the breather valve of sulfuric acid storage tank✅ Dry absorption process in smelting flue gas sulfuric acid production system