Ventilex Solves Chemical Process Problem
Tessenderlo Chemie, a world leader in the field of inorganic chemicals, had to struggle to get below emission limits for hot, humid and dusty off-gases from a reactor in its Rotterdam plant.
Process off-gases (35,000 N/m3/h at 120° C) were dedusted by a cyclone and cleaned with a wet scrubber. Rinse water from the scrubber, which contained high solids loading, was discharged into the river Maas, resulting in an environmental problem. The obvious solution was to install a baghouse after the cyclones. This was done but exothermically reactive dust caused a total burnout of the baghouse.
Tessenderlo Chemie charged Ventilex BV, a company of the IMTECH Group, experts in process gas and hot gas filtration, with the task of finding a solution. Ventilex set up a pilot test with Bekaert's Bekiflow HG filter elements. The metal fleece, Bekipor, the key element in the filtration process, is composed of very thin metal fibers (diameters 2 to 30 µm). These fibers are sintered in an inert gas atmosphere or in a vacuum at temperatures above 1000° C to transform the loose fiber web into a stable matrix. Through this process, each individual fiber is connected through a micro-weld to several adjacent fibers. Several webs, each with its own specific fiber diameter, are used to make one sintered fleece. For hot gas applications a thin web consisting of very fine fibers is used as a surface filter. The bulk of the media consists of coarser fibers to give strength and stability to support the fine fiber layer matrix. Finally, the fleece is compressed to the required thickness and porosity. Metal fiber fleece excels through its high porosity (85 percent) and low specific weight and thickness (approximately 0.5 mm). These characteristics enable a small pressure drop in combination with good cleanability. Another important characteristic of the fleece in this application is its resistance to high temperatures.
The filters are constructed as rigid candles and consist of a rigid metal fiber fleece, a supporting core and mounting flange.
The pilot filter tests confirmed the theory. The pilot filter has been operating at a low ΔP of maximum 1100 Pa and at a high face velocity of 200 m3/m2/h. This is the key to low operating costs. With an inlet dust burden of 10 g/m3 the efficiency went up to 99.96 percent with emission levels of 4 mg/m3, which is far below the target of 10 mg/m3. Dust particle size ranges from 0.2 µ to 20 µ, with a D50 of approximately 5 µ.
Because of the 100 percent reliability against fire hazards and the achievement of the targeted emission levels, Tessenderlo Chemie has chosen Bekiflow for a full scale 133 element unit for its process off gases.