Substituting sodium bicarbonate with Sorbacal® SP dry injection for SO2 removal
The challenge
A municipal waste treatment plant had three independent, fluidized-bed waste incinerator lines, each with a flow of three
metric tons/hour. To conform to new regulations for acid gas emissions (European Directive 2000/76/EC) the lines had been fitted with bi-reactive dry injection flue gas treatment units and fabric filters.
The dry injection units could operate with either calcium- or sodium-based sorbents. Sodium bicarbonate had always been used.
The site operators wanted to reduce acid gas emission levels further: to significantly below regulatory limits, particularly for SO2. The target values were 10 mg HCl/Nm3 and 20 mg SO2/Nm3. These low values are desirable for plants equipped with post-filtration, low-temperature catalytic treatment of NOx.
To address the emission reduction goal, Lhoist proposed a demonstration of the technical and economic effectiveness of its Sorbacal® SP calcium-based sorbent. The plant operators scheduled a three-weektrial period on two lines, with the third continuing to use sodium bicarbonate as a reference. The very brief notice – only two months – and the short trial made the exercise a real challenge.
The Lhoist solution
We provided a Sorbacal® Injecto-Matic Simplex DT unit fitted with a 50 m3 silo. A dual injection head delivered sorbent to the two lines simultaneously.
Simple, robust and relatively inexpensive, the unit was installed and working in less than a day.
Using Sorbacal® SP both lines operated below the levels of 10 mg HCl/Nm3 and 15 mg SO2/Nm3 – well within regulatory limits – and without requiring larger quantities of sorbent.
Sorbent performance during the three-week trial
| Sorbacal® SP | Sodium bicarbonate | |
|---|---|---|
| Sorbent rate | 11.3 kg/t of waste Without fine-tuning |
12 - 13 kg/t of waste Nominal value |
| Gas rate at 11% O2 [Nm3/h] |
20,500 | 19,800 |
| O2 [%] | 9.8 - 11 | 9.7 - 10.5 |
| H2O [%] | 12.8 - 14.5 | 15.5 - 17 |
| HCl mg/Nm3 at 11% O2 | 4 - 9 | 8 - 10 |
| SO2 mg/Nm3 at 11% O2 | 1 - 8 | 8 - 12 |
The benefits
The trial confirmed that the Lhoist package comprising a Sorbacal® Injecto-Matic and Sorbacal® SP met the operators’ stringent emission targets. The unit’s dual injection head was shown to efficiently deliver Sorbacal® to the two lines.
Despite the lack of time for fine-tuning during the trial, the results pointed to significant operating cost savings once conditions could be optimized. Additionally, the fast start-up demonstrated the package’s convenience and suitability for the municipal incineration sector.