The development of new optimized dedusting systems has particular and increasing relevance for atmospheric particulate emission control. Indeed, traditional 'particulatetraps' present several disadvantages that foster the search for alternative solutions.
Industrial cyclones are, for their robust construction, absence of moving parts and general application, an appropriate technology for emission control when dealing with temperatures as high as those in biomass boilers. Nevertheless, cyclones' relatively low eﬃciency, particularly for small (< 10 µm) and low density particles, leads many users to complement them with Bag Filters (BF) or Electrostatic Precipitators (ESP). Usually, BFs are ﬁnancially bearable and very eﬃcient (> 99.9 %), but are maintenance demanding due to frequent change of ﬁlter elements. On the other hand, ESPs are robust equipments and are very eﬀective (in a given range of dust resistivity) but their high investment cost is frequently out of reach o fsmall and medium size companies.
Electrostatic ReCyclone® systems appear as an eﬀective alternative to the traditional solutions, since they combine several key advantages of the referred systems, mainly a numerically optimized gas-cyclone geometry (referred as Hurricane) and electrostatic precipitation, allowing biomass boilers to comply with strict legal emissions limits. ReCyclone® systems consist of an optimized reverse-ﬂow cyclone (which can have, by itself, about half of the emissions of other high-eﬃciency cyclones), combined with partia lrecirculation of un-captured particles via a straight-through cyclone concentrator (recirculator). Particle separation in the recirculator is achieved via the application of a DC electric ﬁeld combined with centrifugal forces. Global eﬃciency is further enhanced through a very relevant phenomenon inside cyclones, which is agglomeration/clustering of very ﬁne particles with larger particles in the turbulent ﬂow ﬁeld inside the gas cyclone.
In order to build a custom made solution for each situation, numerical simulations are made using a model, referred as PACyc, which is based on previously published models to predict collection eﬃciency either for isolated cyclones, or for cyclones with recirculation. This model considers not only the ﬂow conditions inside the system, but also the particle agglomeration phenomenon. Considering that cyclone eﬃciency is sensitive to particle size, if the particles 'seem' larger to the cyclone, their calculated eﬃciency will signiﬁcantly increase above theoretical predictions.
These systems have been shown, for industrial and pilot scales, to have very high eﬃciencies when dealing with the emissions of biomass boilers, allowing these to comply with strict emissions policies, and the PACyc model has been proven as a reliable tool to predict the behavior of these kind of systems, for several diﬀerent conﬁgurations, several kinds of dusts and operation conditions.