SELECTED DRYING TECHNOLOGIES FOR SUPERIOR …

1 SELECTED DRYING TECHNOLOGIES FOR SUPERIOR product development IN THE BIOREFINERY DANIEL FROSTERUD, JAKOB SLOTH* and MICHEL THEMENS** Christian Berner AB, Box 88, SE-435 22 M lnlycke, Sweden *GEA Process Engineering A/S, GEA Niro, Gladsaxevej 305, DK-2860 Soeborg, Denmark **GEA Barr-Rosin Inc, 92, Pr vost, Boisbriand, Qu bec, J7G 2S2, Canada The pulp and paper industry is heavily involved in developing new products from biomass and cellulosic material. In this context, there is a constant search for appropriate production methods. One unit operation that comes into play is DRYING . The DRYING step in processing both biomass and cellulosic materials serves several purposes, such as reducing transport and storage costs, and extending shelf life.

2 Also, in many cases, the material needs to be dried for further processing. In such cases, the properties of the dry material are of paramount importance, which explains the application of DRYING for granting the necessary properties to the dry material. Many different DRYING processes can come into play, some of them will be described in the paper. The present paper intends to give a brief overview of the GEA (GEA Barr-Rosin and GEA Niro) commercially available DRYING TECHNOLOGIES , of the possible feed stocks and typical end products. Of particular interest is spray DRYING , which converts a slurry, suspension or solution directly into a powder. It is shown that spray DRYING may assure extended engineering of particle morphology and powder characteristics, to fit specific needs.

3 The paper will also make an update of the current status in the industry and present some typical applications within the biorefinery industry based on wood as raw material. In the live presentation several examples of powder behaviour will be demonstrated, to illustrate the effect of certain powder characteristics, such as particle size, singular or agglomerated particles, bulk density etc. Keywords: Dryer, DRYING , powder, biorefinery, spray dryer, steam dryer, flash dryer, ring dryer, wood, cellulose, hemi cellulose, lignin, agglomeration, granulation, dissolution INTRODUCTION The pulp and paper industry is heavily involved in developing new products from biomass and cellulosic material. In this context, there is a constant search for appropriate production methods.

4 One unit operation that comes into play is DRYING . The DRYING step in processing both biomass and cellulosic materials serves several purposes, such as reducing transport and storage costs, and extending shelf life. Also, in many cases, the material needs to be dried for further processing. In such cases, the properties of the dry material are of paramount importance, which explains the application of DRYING for granting the necessary properties to the dry material. Many different DRYING processes can come into play, some of them being described below. The present paper intends to give a brief overview of the GEA (GEA Barr-Rosin and GEA Niro) commercially available DRYING TECHNOLOGIES , of the possible feed stocks and typical end products.

5 Of particular interest is spray DRYING , which converts a slurry, suspension or solution directly into a powder. It is shown that spray DRYING may assure extended engineering of particle morphology and powder characteristics, to fit specific needs. Also spray DRYING as a unit operation can be modified and extended to further enhance manufacturing of certain powder characteristics. Table 1 briefly overviews 9 different DRYING processes. Table 1: Overview of the SELECTED commercial DRYING TECHNOLOGIES Type of dryer Typical feed Typical PSD* dried product Comments Retention time Rotary dryer Coarse particles, lumps, chips As in the feed or reduced to >1mm Several minutes Flash dryer Friable solids or press cakes mm Lump degradation by flashing 10-30 sec Ring dryer Back mixing Friable solids or press cakes High DS liquid mm mm Internal milling and product recirculation 30 sec- 3-5 min Superheated steam dryer SSD mm As in the feed Only cyclone possible 20-60 sec Fluid bed mm Sticky As in the feed Sectioned for DRYING /cooling 1-10 min SWIRL FLUIDIZER Cakes or pastes < 50 micron Internal milling min Spray dryer Pumpable liquid 10-100 micron 10-30 sec Fluidized spray dryer FSD Pumpable liquid 50-250 micron Agglomerates Fines recirculated 10-20 sec +1-5 min SPRAY FLUIDIZER Pumpable liquid +powder 300-4000 micron Granules.

6 Agglomerates Fines recirculated 1-5 min *PSD= Particle Size Distribution The flash dryer Figure 1: GEA Flash dryer with cyclone and scrubber The GEA Flash Dryer (Fig 1) is a pneumatic system primarily used to dry products which require removal of free moisture. DRYING takes place within seconds, the wet material being dispersed into a stream of heated air (or gas) which conveys it through a DRYING duct. Using the heat from the airstream, the material dries as it is conveyed. The product is separated using cyclones and/or bag filters. Typically, the cyclones are followed by scrubbers or bag filters for final cleaning of the exhaust gases, to meet the current emission requirements. Elevated DRYING temperatures can be used with many products, since flashing off of surface moisture instantly cools the DRYING gas without appreciably increasing the product temperature.

7 Flash dryers have been used to dry products in many industries, including food, chemical, mineral and polymer. A broad range of feed materials, including powders, cakes, granules, flakes, pastes, gels and slurries, can be processed. For slurries, pastes or sticky materials, back-mixing of the wet feed with a portion of dry product is required to produce a suitable conditioned material. Ring dryer The GEA Ring Dryer (Fig 2) is a pneumatic type system - in essence, a modified flash dryer. The ring dryer was developed to increase the versatility of the flash DRYING technology and to overcome many of its limitations. Feed dispersion into the DRYING gas stream in the venture and subsequent DRYING is similar to that of the flash dryer.

8 A disintegrator can be added to ensure breakdown of larger lumps of the feed material. The presence of a "manifold" or "internal classifier" in the ring DRYING system differentiates it from the flash dryer. The manifold device uses the centrifugal effect of an air stream passing around a curve to concentrate the product into a moving layer. The adjustable splitter blades are used to return the heavier, semi-dried material back to the dryer for another pass through the system, while the lighter, drier product exits the dryer and gets conveyed to the product collection system. Essentially, the ring dryer enables DRYING of the same type of products as the flash dryer, however the selective extension of the residence time enables the ring dryer to process many materials, regarded as difficult to dry in a flash dryer.

9 The lignin from the Lignoboost system is an example of a product which dries nicely in both flash and ring dryers, as well as in the following SWIRL FLUIDIZER . Lignoboost is a technology for lignin extraction out of black liquor, the technology is owned by Valmet group, see Figure 2: GEA Ring dryer with disintegrator and manifold for particle recirculation. The SWIRL FLUIDIZER The GEA SWIRL FLUIDIZER (Fig 3) differentiates itself from the flash type dryers by its fast rotating disintegrator, which turns the feed into very fine particles as it is exposed to the DRYING gas. The high viscous feed material is mixed to a homogeneous feed in the feed tank by a vertical bottom-driven agitator. A specially-designed horizontal auger transports the feed into the DRYING chamber, where the disintegrator equipped with powerful and fast rotating chopper blades ensures increase of the surface area from where feed DRYING may occur.

10 The fine particles are dried by heated process air, which enters the bottom of the DRYING chamber through an air disperser with tangential inlet. The dried particles are carried out from the DRYING chamber by the air flow. The exhaust system is equipped with a bag filter to separate the powder product from the DRYING gas. The product is obtained through a rotary valve placed under the bag filter. Similarly with other flash type dryers, they represent an economical choice for DRYING pastes and filter cakes. For these feeds, as well as for suspensions and highly viscous liquids, the SWIRL FLUIDIZER is able to produce a fine, homogeneous, non-agglomerated powder, all in one compact process step. FeedDrying gas (in) DRYING gas (out) product Figure 3: GEA SWIRL FLUIDIZER dryer The rotary dryer Rotary dryers (Fig 4) operate on the principle of lifting and showering the product in a hot gas stream inside a rotating cylindrical DRYING chamber equipped with baffles.