Project Overview
Hubei Fengli Chemical upgraded the tail gas desulfurization system serving its 220,000 t/y sulfuric acid plant.
The work was carried out on an existing production line rather than as a standalone new-build system. This meant that the desulfurization equipment had to be matched to the available gas pressure, existing ductwork, plant layout and continuous operating conditions.
The design gas flow is 90,000 Nm³/h, with a typical inlet temperature of around 65°C. SO₂ at the desulfurization inlet can reach 1,500 mg/Nm³, and sulfuric acid mist is also present in the process gas.
DAQI Technology developed the retrofit around these actual operating conditions.
Design Data
| Parameter | Design Condition |
|---|---|
| Application | Sulfuric acid plant tail gas |
| Plant capacity | 220,000 t/y |
| Gas flow | 90,000 Nm³/h |
| Gas temperature | 60–80°C |
| Typical inlet temperature | 65°C |
| Overall conversion rate | ≥99.5% |
| Inlet SO₂ | ≤1,500 mg/Nm³ |
| Oxygen | 5–6% |
| Inlet pressure | 200 mmH₂O (G) |
| System load | 100% |
| Operating schedule | 24 h/day, approx. 8,000 h/year |
Under normal production conditions, the plant produces approximately 650–770 tonnes/day of 98% sulfuric acid.
Tail Gas Conditions
The desulfurization system is designed for full-load operation of the acid plant.
At the inlet, gas flow reaches 90,000 Nm³/h and SO₂ can rise to 1,500 mg/Nm³. The gas also carries sulfuric acid mist, with the concentration varying according to upstream operating conditions.
Typical design conditions include:
| Parameter | Value |
|---|---|
| Inlet gas flow | 90,000 Nm³/h |
| SO₂ | ≤1,500 mg/Nm³ |
| Sulfuric acid mist | Variable, average ≤100 mg/Nm³ |
| O₂ | 5–6% |
| Inlet temperature | Approx. 65°C |
| Inlet pressure | 200 mmH₂O (G) |
| Normal make-up water | 2.0 t/h |
| Plant load | 100% |
For this application, SO₂ concentration alone is not enough to define the treatment system. Acid mist, available pressure and continuous plant load all affect the retrofit design.
Retrofitting an Existing Acid Plant
A retrofit has different constraints from a new installation.
The upstream sulfuric acid process is already in operation, so the gas-cleaning system has to work within an existing pressure balance and site layout. Major changes to upstream equipment or excessive additional pressure drop are generally undesirable.
This is particularly important at a gas flow of 90,000 Nm³/h.
Gas distribution, pressure loss and equipment capacity therefore have to be considered together. The desulfurization unit must handle the required gas volume without becoming a bottleneck for the acid plant.
SO₂ and Acid Mist in the Same Gas Stream
Tail gas from sulfuric acid production is different from conventional combustion flue gas.
Residual SO₂ remains after the upstream conversion and absorption stages, while sulfuric acid mist can be carried over with the gas. The amount of acid mist can change with plant load and absorption conditions.
For the Hubei Fengli project, the retrofit was therefore based on the complete inlet envelope:
90,000 Nm³/h gas flow, 60–80°C temperature, SO₂ up to 1,500 mg/Nm³, variable acid mist and full production load.
This allows the desulfurization system to be matched to the way the sulfuric acid plant actually operates rather than to a single nominal SO₂ value.
Continuous Operation
The plant is designed to run 24 hours per day for approximately 8,000 hours per year.
For a continuously operated sulfuric acid plant, reliability and pressure stability are as important as pollutant removal. A significant increase in system resistance can affect the upstream process, while insufficient treatment capacity can limit production.
The retrofit therefore had to balance gas-handling capacity, pressure drop, acidic operating conditions and maintenance requirements within the existing plant.
Key Project Data
220,000 t/y
Sulfuric acid plant capacity
90,000 Nm³/h
Design gas flow
SO₂ ≤1,500 mg/Nm³
Design inlet concentration
60–80°C
Gas temperature
100% plant load
Design operating condition
Approx. 8,000 h/year
Continuous annual operation
The Hubei Fengli project is representative of tail gas desulfurization retrofits on existing sulfuric acid plants, where the treatment system must be integrated without disrupting the main production process.
The same engineering considerations apply to sulfuric acid production, chemical processing, non-ferrous metallurgy and other continuous industrial processes requiring an upgrade of existing SO₂ control systems.
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