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CLOSE THIS BOOKSolar Drying in Morocco (GTZ)
2. Solar dryer of the Marrakesh type
VIEW THE DOCUMENT2.1 Solar dryer for fruits and vegetables
VIEW THE DOCUMENT2.2 Solar dryer for medicinal and spice plants
VIEW THE DOCUMENT2.3 List of suppliers

Solar Drying in Morocco (GTZ)

2. Solar dryer of the Marrakesh type

2.1 Solar dryer for fruits and vegetables

A solar dryer of the Marrakech type for drying fruits and vegetables was set up in 1991 on the test plot of the Centre de Mise en Valeur (CMV) Sada des Office Regional de Mise en Valeur Agricole du Haouz (ORMVAH). Its design was based on that of the tunnel-type solar dryer of the Hohenheim type, but exclusive use was made of materials available in Marrakech Province for constructing it.

The solar dryer of the Marrakech type exists in two different versions. One is a standard model that nuns on electricity from a power source and must therefore be plugged in, and the other is a model equipped with a photovoltaic (PV) drive system for locations where no electricity is available. The basic construction consists of a platform of hollow bricks supported by a reinforced concrete frame. This modular design makes it possible to lengthen or shorten the collector, or dryer, depending on what kind of produce needs to be dried and the desired output.

Since hardly any rain falls during the drying season, the system is not equipped with a saddle-back roof, instead being merely covered with a plastic sheet stretched taut across its top.

In the standard version, the overall length of the dryer is 30 m with a width of 2 m. In order to prevent the produce from being contaminated by earth and dust, and also in order to simplify filling and emptying of the dryer, the entire structure is mounted on pedestals 75 cm high (see Fig. 1).


Fig. 1 Solar dryer of the Marrakech type for fruits and vegetables

In order to reduce heat losses, a layer of granular cork 20 mm thick is inserted as insulation.

On top of the granular cork is a 10-mm layer of smoothly troweled concrete that is coated with dullblack, nontoxic paint. The absorption surface area is 18.8 m2 (see Fig. 2).


Fig. 2: Cross-sectional view of the collector

The system powered by electricity from an external source uses a radial fan. The one with PV drive works with a solar module and an axial fan.

The solar module can be set up outside the dryer, or else directly positioned horizontally in the flow of air from the fan. This has the advantage of cooling the solar module, thus improving its efficiency.

An intake nozzle at the air inlet and air-baffle plates on the outlet of the fan achieve even distribution of the air flow over the entire cross-section of the drying system.

The air is sucked in from below and blown between the absorber and the cover sheet through the collector and into the dryer.

There is fine-meshed wire screen both at the fan inlet and at the dryer outlet, in order to make it more difficult for insects, rodents, and birds to enter the system.

In the mains-powered version, the drying temperature can be kept from exceeding the desired maximum by voltage-dependent speed control for the fan. The supply voltage is controlled by a remote thermostat with a temperature sensor and a toroidal-core transformer. The air flow rate can then be set to any value between 0 and 1300 m³/h. Assuming constant insolation, increasing the air flow rate causes the temperature in the collector to drop.

In the PV-powered system, the fan is directly coupled to the solar module, working without an accumulator and load controller. Increasing insolation increases the module's output, thus speeding up the fan. This has the advantage of permitting temperature control merely by appropriately designing the components of the PV system, thus obviating any additional control devices as long as the system is suitably dimensioned.

Table 1: Technical data of the drive systems (freely blowing)

Drive system


Mains-powered


Photovoltaic (P V)

Components


Radial fan

Axial fan

Solar module

Maker


ebm

Fiat

Solarex

Type


R4E 280-AD0805

Uno, gasoline-fueled model

MSX 83

Rated voltage

V

220

12

16.9

Rated current

A

0.33

7.0

4.92

Nominal consump tion

W

70

84.0

83.2

Air flow rate

m³/h

1360

1520


Rated speed

RPM

1400

2800


The dryer is also covered by PE sheet 0.2 mm thick. The system is opened and closed using a winding shaft. A hand-crank is turned to wind up the entire length of the plastic sheet on the shaft, thus exposing the inside of the dryer for loading or unloading (see Figure 3).

At the dryer's inlet and outlet, the PE sheet is affixed by a special clamp closure to keep the air in while keeping dust and rain water out.

The produce to be dried is spread out on a wire grating 20 mm high, which is covered by a finely-woven polyester fabric stretched taut.

When drying is in progress, the warm air flows evenly over and beneath the produce, which therefore does not need to be turned. The air absorbs water vapor and then escapes at the other end of the system. The effective drying surface is 40 m².


Figure 3: Cross-section of dryer

Table 2 lists all of the materials used to build the solar dryer.

2.2 Solar dryer for medicinal and spice plants

The solar dryer of the Marrakesh type for medicinal and spice plants was set up in 1993 on the test plot of CMV Sada. This system had been jointly developed by all project partners during the course of a seminar on drying of medicinal and spice plants that was held at the University of Hohenheim in 1992.

Table 2: Parts list for the solar dryer of the Marrakesh type for fruits and vegetables

Designation


Quantity

Sand


5 m³

Gravel

8/15

3 m³

Cement

250/315

72 dt

Hollow bricks

30 x 30 x 15 cm

615 units

Rebars

10 mm dia. x 12 m

36 units


8 mm dia. x 12 m

45 units


6 mm dia. x 12 m

45 units

Metal angles

30 x 30 mm x 6 m

lo units

Pipe

1/2" x 6 m

4 units

Wire mesh

40 x 40 x 3 mm

40 m²


10 x 10 x 0,5 mm

60m²

Sheet metal

2000 x 1000 x 1.5 mm

3 units

Polyester fabric


40 m²

Cork

1000 x 500 x 20 mm

1.15 m³

PE sheet


83.2 m²

Paint

Black, matte

30 kg

Clamping strip

Snappan

65 m

Small parts and materials

(Nails, screws, wire, adhesive tape, cables, etc.)


PV drive:

Fan from Fiat Uno gasoline-fueled 1unit model

1 unit


Solar module: Solarex

MSX 83

Mains-powered drive:

Fan, EBM R4E 280 AD

1 unit


Toroidal core transformer

1 unit


Temperature control system

1 Unit

The dryer is integrated into a building with a saddle-back roof. The solar dryer for fruits and vegetables serves as the collector for warming the air.

The originally installed fan is replaced by a more powerful one.

The warm drying air is introduced into the batch dryer by way of a removable connecting passage.

The drying building is 7 m long, 3.4 m wide, and 5 m high (see Figure 4).

Batch drying of herbal medicinal and spice plants requires the system to be operated with substantially greater air throughput rates than for drying fruits or vegetables. The mains-powered system is therefore equipped with a larger radial fan, and the PV-driven version has a total of four solar modules and three axial fans connected in parallel.

Here again, the fans are equipped with inlet nozzles and air-baffle plates in order to achieve even distribution of airflow in the collector.

The air is taken in from below, then blown through the collector between the absorber and the cover sheet, whereupon it passes through the connecting passage to enter the batch dryer.

Temperature control works as described in section 3.1. The air flow rate varies between 0 and 3850 m3/h.

Table 3 lists the data for the different drive systems.


Figure 4: Solar dryer of the Marrakesh type for medicinal and spice plants

Table 3: Technical data of the drive systems (freely blowing)

Drivesystem


Mains-powered

Photovoltaic (PV)


Components


Radial fan

Axial fan

Solar module

Maker


Ziehl-Abegg

Fiat

Solarex

Type


RH40M4Ek.4F. lR

Uno gasoline-fueled MSX 83 model


Rated voltage

V

220

12

16.9

Rated current

A

2.4

7.0

4.92

Nominal consumption -

W

520

84.0

83.2

Air Bow rate

rn³/h

4100

1520


Rated speed

rpm

1365

2800


The connecting passage is made of plywood elements lined on the inside with Styrofoam and attached to the building by hinges. In just a few steps, the side sections and the floor of the passage can be folded into place by hand to make the connection to the collector. The passage is sealed on the top by a PE sheet. Like in the other described system, this sheet is held in place by clamps on metal strips attached to the long sides (see Figure 5).


Figure 5: Lengthwise cross-section of connecting passage

The building frame for the batch dryer is made of brick masonry. The roof consists of wooden beams covered by plywood and roofing felt. On top of the ridge is a raised, 30-cm-high venting stack extending the entire length of the building (see Figures 6 and 7).

There are additional venting apertures on both gables and on one long side (each measuring 80 x 56 cm). To keep out insects, all venting apertures are covered with wire screen.

A double-leafed door (300 x 200 cm) can be opened to fill the dryer directly from a transport vehicle via the loading platform.

The drying air flows from the collector into the thermally insulated expansion compartment, where its volume increases. It then flows vertically through the produce on the grating, absorbing water vapor in the process. Finally, it escapes through the venting apertures.

An upright plywood partition of variable height lets the produce be piled up to 1.5 m thick. While drying, the produce can be turned from the side aisle using a pitchfork.

To prevent the produce from falling into the expansion compartment, a finally-woven polyester fabric is attached to the grating. The grating is 6 m long and 2 m wide, yielding a total drying area of 12 m².

Table 4 lists all of the materials used to build the batch dryer building.


Figure 6: Cross-section of dryer building


Figure 7: Lateral view of dryer building

Table 4: Parts list for the batch dryer of the Marrakech type for medicinal and spice plants

Designation


Quantity


Sand


4 m


Gravel

8/15

4 m³


Cement

250/315

80 dt


Solid bricks

40 x 15 x 10 cm

350 units


Hollow bricks

40 x 15 x 15 cm

550 units


Rebars

10 mm dia. x 12 m

7 units




8 mm dia. x 12 m

24 units



6 mm dia. x 12 m

6 units

Wire screen

Moustiquaire

4 m²


Metal plates

50 x 5 mm x 6 m

4 units


Styrofoam sheets

100 x 50 x 2 cm

70 units


Wooden rafters

7 x 20 x 600 cm

8 units




7 x 20 x 480 cm

2 units



7x20x420cm

9 units



7 x 20 x 200 cm

1 unit

Plywood sheets

200 x 122 x 1 cm

2 units



250 x 122 x 1 cm

12 units


Roofing felt


40 m²


Small parts and materials

(Nails, screws, steel wire, wood glue,




threaded bars, hinges, etc.)







PV drive:

Fan from Fiat Uno gasoline-fueled model

3 units



Solar module: Solarex MSX 83

4 units


Mains-powered drive:

Fan, ZIEHL-ABEGG RH 40 M

1 unit



Toroidal-core transformer

1 unit



Temperature control system

1 unit


2.3 List of suppliers

Table 5 gives a list of suppliers of the materials required to build solar dryers of the Marrakesh type for fruits and vegetables or medicinal and spice plants.

Table 5: List of suppliers in Morocco

Steel, shaped metal parts, sheetmetal, gratings, screens, wire:

COMPTOIR DES MILIES, Rue Yougoslavie, Marrakesh Guliz
COMPTOIR METALLURGIQUE MAROCAIN, Boulevard Mohamed V, Marrakesh Guliz
ETS SAFA, Boulevard Allal EL Fassi, Marrakesh
FATH METALL, Avenue Abdellah Ben Yassine, Marrakesh Quartier Industriel

Wooden beams, plywood, PE sheet, roofing felt, paint, polyester fabric, small parts and materials:

DROGUERIE UNIVERSELLE DU SUD, Rue R'Mila, Marrakesh Mdina
COMPTOIR BAB DOUKALA, 1 l, Avenue Hassan II, Marrakesh
ETABLISSEMENT DEBBAGH, 80, Rue Mouritania, Marrakesh

Electrical supplies:

ELECTRICITE MENARA; 10, Avenue Fatim Zohra R'Mila, Marrakesh
FOURNITURES GENERALES D'ELECTRICITE, 14, Boulevard Allal El Fassi,
Marrakesh

Clamping strips (Snappan):

ABDELGHANI, 49, Avenue Fatim Zohra R'Mila, Marrakesh

Fans for PV drive:

AUTO HALL, Rue Yougoslavie, Marrakesh Guliz

Fans for mains-powered version, solar modules, remote thermostats, transformers:

AFRISOL 219 Rue Mustapha El Maani Casablanca

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