Feasibility studySolar drying of coffee

beans

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Lire & Sunlabob

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4 Day Site Survey Feasibility of solar coffee drying system.

Focussing on solar water system and solar direct air heating system to dry 40 tons red cherries per day from 26% to 11% moisture content of dried white beans.

Hybrid system with heat from solar and non-solar backup system

Connection to the factory equipment line Initial study presentation

Scope of works

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Process specificationSteps Process status at INLET Moisture content

INLETtons per dayat INLET

Temp C ProcessDurationfrom quote

Step 1. Wetting of red cherries (instant soak)

Red cherry 40

Step 2. Hulling Red Cherries

white bean wet 40

Step 3. Soak overnight in ‘luke warm’ water

white bean wet 24

Step 4. Wash white bean wet 55% 24

Step 5. Drying Phase 1 part A (courtyard drying )

white bean wet 55% 24 Ambient outside temp

4 -5 days

Step 6. Drying Phase 1 part B static bed drying

white bean wet 26% 12 35 8 hours

Step 7. Drying Phase 2 Drum Drying

white bean partially dry

15%/16% 9.2 40 - 45 6 hours

Step 8. Hulling (removal of white parchment)

white bean dry 11% 8

Step 9. Sorting and sizing green bean 11% 6

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Proposed coffee drying cycle

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Measure of dryness

• Project phase II – Requires measure of

dryness; confirmation of deliverables

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Energy Demand Study•12.5 kWh of electricity or 0.07 meters cubed of firewood for mechanical drying per 100lbs dried white bean (Source: Instituto del Cafe de Costa Rica [ICAFE] 2006)

•Client stated 10.5 kWh per 100lbs. For calculation larger figure used

•12.5 kWh per 100lbs = 2240 kWh per day for 40 tons red cherries (8 tons white beans)

•Mechanical Drying for 8 hours per day hence power requirement @ 2240/8 = 280 kW to feed 2 static dryers and two drum dryers.

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Proposed factory location

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Solar and Meteorological Survey

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Irradiance

7 8 9 10 11 12 13 14 15 16 170

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Time of Day

Irra

dian

ce (

kW

/m2)

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Average inputs thro’ drying season

Average daily irradiation 5.88 kWh/m²/day

Average Irradiation onto panels during daylight 0.735 kW/m2

Optimum angle of panels (facing South) 34°

Average Air Temperature during factory operations 28°

Average Relative Humidity (%) 77.6

Average rainfall (mm/day) 3.9

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Solar air heating

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Solar water system

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Back up / boost system

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Gas Vs Electric

• Electrical resistance heating inefficient way of heating large quantities of air

• Electrical resistance heaters – expensive Capex

& Opex

• Recommending Gas heating

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Sélection criteria

Capital cost of installation Cost of running installation

Ease of operation Maintenance / control/ spares

Complexity/fit for purpose Project Risks

System Scalability Green credentials/environmental

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System selection

• Although the system costs are comparable, the main argument for recommending the solar air option is system simplicity.

• Installation costs and time for solar air is much less than for solar water. There are relatively few moving parts and wear parts therefore maintenance is minimal

• Running costs are slightly higher for the Solar air system however this would be balanced out by the minimal maintenance both in direct and indirect costs

• The technical, financial and installation risks are greater for the solar water

system. It is more complex and requires more development that a simple solar air system.

• Scalability: to adapt a system to run a larger capacity is far simpler with the

solar air system than solar water which would require enlargement of the entire water circulation system including pumps tanks and pipework.

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Conclusion