FM Conway, a leading asphalt manufacturer in the UK, had a plant that was burdening the environment and surrounding area with dust, odour and VOC emissions. The challenge was to neutralise the odour burden created during the filling of waiting silos and trucks. Thanks to the combined KELLER-Desotec solution, the odour nuisance and additional dust and VOC emissions were contained. These emissions are now captured and removed in a quick and efficient manner.
Asphalt production is usually associated with emissions of dust, bitumen fumes, odour and (toxic) volatile organic compounds (VOC). These emissions must be monitored to prevent environmental nuisance and comply with local environmental legislation. By identifying and addressing the problematic emission points using the Cleansky approach, the negative impact on the environment is reduced which has a major impact on public perception about this asphalt producer.
The plant at FM Conway received a customised dust extraction system where the design and sizing was specifically calculated and designed based on the amount of airflow, amount of dust, development of smoke, odour and VOC concentrations and other specific requirements.
Identification of emission points
As a first step, the problematic emission points of asphalt production are identified together with the customer. Dust generation occurs during the filling of aggregate hoppers and then during the filling of recycled asphalt components in the mixing drum. The hot air coming from the mixing and drying drum and discharged through the chimney also contains odour and VOCs. The opening and filling of the hot storage tanks are typically a major source of dust, bitumen fumes and (toxic) VOCs. The filling process of the trucks under the storage silos also causes visible emissions of dust, bitumen vapours, toxic VOC and odour into the atmosphere. Finally, ventilation and filling of the bitumen storage tank may release a certain amount of gas from the tanks.
After determining the emission points, proven ventilation models are used to determine the best ventilation technique. This avoids diffuse emissions. After this, the collected ventilated air is treated by the Cleansky afsalt filter system. In this two-part filter system, dust and bitumen fumes are first removed by a wet scrubber. Then the remaining odours and toxic VOCs are removed by the activated carbon filter.
Odour nuisance also under control
Asphalt is a mixture of aggregates (stones) and bitumen (a black, sticky petroleum derivative). Not surprisingly, asphalt production is associated with smelly bitumen emissions into the atmosphere. Bitumen is a solid substance that liquefies when heated. To produce road asphalt, the bitumen is liquefied so that it can be mixed with the aggregate material. During this process, the bitumen releases volatile organic compounds (VOCs) as well as the extremely foul-smelling gas H2S or associated sulphur-containing compounds. The foul-smelling atmospheric emissions from an asphalt plant cause odour nuisance to nearby residential areas. Lybover AIR ism Desotec’s Cleansky approach also tackles this problem.
Award for innovation
FM Conway’s efforts to curb emissions of dust, bitumen fumes, odour and (toxic) volatile organic compounds were rewarded with a Mineral Producers Association (MPA) award for the most innovative technology in terms of health, safety and environment.