Upload
gordon-hirst
View
21
Download
3
Embed Size (px)
Citation preview
Feasibility studySolar drying of coffee
beans
2
Lire & Sunlabob
3
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
4
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
5
Proposed coffee drying cycle
6
Measure of dryness
• Project phase II – Requires measure of
dryness; confirmation of deliverables
7
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.
8
Proposed factory location
9
Solar and Meteorological Survey
10
Irradiance
7 8 9 10 11 12 13 14 15 16 170
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Time of Day
Irra
dian
ce (
kW
/m2)
11
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
12
Solar air heating
13
Solar water system
14
Back up / boost system
15
Gas Vs Electric
• Electrical resistance heating inefficient way of heating large quantities of air
• Electrical resistance heaters – expensive Capex
& Opex
• Recommending Gas heating
16
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
17
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.
18
Conclusion