FI105853B - Indirect swirling mass dryer - Google Patents

Description

: '105853 INDIRECT CONVERTER DRYER.

The invention relates to a dryer based on the rotary mass technology (KM technique), in which the drying energy is indirectly supplied by a recuperative heat exchanger. Preferably, the drying energy source is steam, which is completely or partially condensed in the 5 dryer recuperator. The dryer according to the invention is suitable for drying both solid and slurry materials.

ν In some drying applications, the indirect import of drying energy offers significant advantages over the simpler direct drying technology. By direct drying 10, it is meant here that the energy required for drying is brought with the drying gas. Direct drying also includes applications in which heat is generated, for example, by burning in a dryer chamber. In indirect drying, the drying energy is recuperatively introduced so that the energy source is not in direct contact with the drying gas. In indirect dryers, the function of the drying gas 15 is mainly to provide a flow field favorable for drying and to remove volatile compounds from the dryer.

In power plants using wet fuels such as peat or biomass, it would be technically advantageous to dry the fuel to be burned with turbine tap steam. The following figure 20 summarizes the results of the calculations, in which the power output of a 50 MW back-pressure plant is calculated for different process alternatives. If the turbine. . is one tap, the electricity yield can be increased by about 1800 kW, or 20%, if 0.8 MPa steam-dried fuel is used instead of wet fuel.

• ... 'The figure below shows the power supply for cases where the fuel is dried at 465 ° C and • 25,700 ° C with flue gas, indirect steam (SD), the plant is burnt dry! fuel (DRYPEAT), the plant burns wet fuel (WETPEAT).

'': The argument is the tap vapor pressure, __ <14

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*. 0 10 20 30 40 I 1 · 'Pressure (bar) «· · 1« 4 · 1 (4 «• r · ·· 30 Dry fuel is best for a power plant, but the availability or price of dry fuel is usually a barrier to its use. the worst option is the current practice of wet fuel burning as such.

, 2 105853

Indirect steam drying over non-dry fuel offers a clear process engineering advantage. The problem with exploiting the potential benefit so far has been the lack of a technically and economically viable dryer.

5 In drying applications where the drying gas cycle has to be closed to eliminate environmentally or environmentally harmful emissions, it is generally preferable to use indirect drying, since the drying gas flow can be dimensioned according to the requirements of the flow conditions. When using direct drying, the drying gas flow usually has to be dimensioned according to the dryer's energy requirement, which results in a significantly higher drying gas flow and, consequently, higher investment and operating costs. For example, in the case of the above-mentioned counterpressure power plant, drying by tap steam could be carried out using a direct drier, with a recuperative heat exchanger coupled to the dryer gas circulation, which heats the drying gas close to the condensation temperature of the tap steam. In this case, the temperature change of the drying gas 15 would be limited to about 100 ° C and the required drying gas flow would be increased to a large extent. The electrical power required by the dryer gas blower alone (about 400 kW) would represent a significant operating cost. This, combined with the bulky and expensive structures, has resulted in tap drying not being practically an attractive option.

20

Due to the disadvantages of direct dryers, various indirect dryers have been developed. One known dryer which is used e.g. drying of sludges and concentrates, based on the forced movement of the steam pipes with respect to the mass to be dried which is obtained ',.! rotating motion of the steam pipes or the jacket surrounding them. In principle, this is a tumble dryer, in which the drying energy is recuperatively supplied. The disadvantages of these dryers are heavy structures due to heavy mechanical stress and heavy wear. Material and heat transfer conditions in such dryers are also poor.

30 Today, the most common types of dryer are straight solid, drum, bubbling ·; ; fluidized bed and carrier gas dryers. Rather than all types of driers mentioned above, there are many flow and process engineering advantages. the rotary mass dryer (KM-I ''. dryer) is currently not commercially available. In the KM reactor, solid, lumpy or "J.II powdered material is transported with the gas to the upper part of the riser, from where both the gas and the solid are conducted to the cyclone. The cyclone and the solid are separated and the gas leaves the reactor, back *** to the bottom of the riser, a technique which is now widely used in combustion technology.

In direct drier applications, KM technology offers significant flow and ./device technical advantages over current dryers. The same benefits can be achieved. **. 40 indirect dryer applications. The problem lies mainly in the way in which the conflicting requirements of KM technology and: f.l recuperative heat exchanger can be transformed into an appropriate and workable structure. Since the power density of the recuperative heat exchanger 9, X is at best only a few kW / m2, the problem is to pack the large heat surface required to a reasonably small volume of i ... 1 45 so that the wear, fouling and maintenance aspects of KM technology can be taken into consideration. Due to the large space requirement of the recuperative heat exchanger, the steam pipes should be packed tightly, making the free spacers of the riser too small for flow duct opening and maintenance. Also, the placement of steam pipe manifolds and manifolds in the KM dryer is problematic or even 105853 impossible. Implemented in the traditional way, no solution has been found to these contradictory requirements. Because of these problems, KM technology for indirect dryers has not been applied to date. The present invention solves the problems described above.

5

The indirect KM dryer (the EKM dryer opens up a whole new perspective by rejecting the idea that the drying steam needs to pass through the tube and the space surrounding the drying gas tubes. If instead, look at the drying gas in the tubes and start covering the jacket, 10 indirect KM dryers are outlined by combining KM technology, known mainly from steam boilers, with a known one-way recuperator, to provide a dryer that is technically and economically more efficient than existing indirect dryers.

The invention will now be described with reference to the accompanying Figure 2, which shows an embodiment of an EKM dryer.

The main components of the dryer are the fluidization part (1), the recuperative heat exchanger (2) and the separator part (3). The drying fluid is introduced into the fluidizing member 1 via one (18) and the material to be dried 20 through one (12). In order to distribute the drying gas evenly over the entire cross-section, nozzles (15) are provided on the top of the gas cabinet (14). The coarse material accumulating in the fluidizing member is removed through one (18). Drying gas and material to be dried,. intermix with each other in the chamber (11) and form a horizontally homogeneous suspension which passes through the vertical tubes (4) to the sheath 25 (5) of the separator part (3). From the jacket (5), the drying gas and the solid are led through the impeller (6) •: into the separator chamber (7), where the gases escape through one (9) and the solid is returned through the hopper (8) and pipe (10) to the fluidizing chamber (11) . Part ''! the solids to be dried can be removed via one (9) to give this portion::: a selective delay time and less dryness dependent on particle size.

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Claims (5)

An indirect recirculating heat transfer dryer based on recuperative heat input, comprising a fluidizing member (1) with gas distribution plates, feeder and outlet connection, a riser channel (2), a separator member (3), characterized in that the riser channel (2) single-pass recuperative heat exchanger. Dryer according to Claim 1, characterized in that the fluidizing part (1), the recuperator (2) and the separating part (3) are co-axial. Dryer according to claim 2, characterized in that the flow channels (6) of the separator consist of a plurality of tangential nozzles arranged around the circumference of the chamber (7). Dryer according to one of the preceding claims, characterized in that the separator (6), (7), (8), (9) is coaxial with the casing (5) of the separating part. 4, 105853 Dryer according to Claim 1 or 2, characterized in that the number of tubes (4) is greater than 8. 'C rl ··· • · · · · · · · · · «» I 1 · • • • • • • 5 105853