The IFAD Regional Cassava Processing and Marketing Initiative

THE USE OF CASSAVA WASTES TO PRODUCE BIO-ENERGY:

OUTCOMES OF A FEASIBILITY STUDY IMPLEMENTED IN GHANA18-19 October 2010IFAD - RTIMP, Ghana

What has been done and what can be done

INTRODUCTION

The question

Can cassava wastes and other available biowastes be profitably converted into bio-energy by utilizing existing technology?

THE USE OF CASSAVA WASTES TO PRODUCE ENERGY: OUTCOMES OF A FEASIBILITY STUDY IMPLEMENTED IN GHANA

Why this study?

Local availability of bio-masses: In Ghana >11 million/MT/year of cassava roots are produced (2008, FAO). Out of them, 2,2 million MT are either peels (13%) or roots unfit for processing (6-7%). Other bio-masses (from wood) also easily available in large quantities (wood shavings/saw dust)

Cassava wastes (peels, barks, effluents): Have no market value; It is a financial cost to dispose them off; Serious environmental hazard: pollute soils, table waters, air; Health hazard for this industry’s workers (social cost)

HOW TO TURN A COST INTO A PROFIT

CASSAVA PEELS AND WASTEWATERS POLLUTE THE ENVIRONMENT

AVAILABLE TECHNOLOGIES: PRODUCTION OF BIO-ENERGY FROM WASTES

Gasification

Blend of biomasses↓

Blend of gases(“producer gas”)

↓

Electricity (mainly) +

Heat (hot/cold air)

Bio-methanation (biogas)

Wastewaters↓

Methane↓

Heat (mainly)

THE GASIFICATION PROCESS

(THE GASIFIER)

Several biomasses are being successfully utilized as feedstock for gasification: wood chips; coconut shell; bamboo; maize stalks; cotton stalks; rice husk; bagasse; groundnut shells; tea and coffee wastes; corn cobs; cashew nut shell, etc.

Lack of data on suitability of cassava wastes and wood wastes required implementation of proximate laboratory analyses

BIOMASS SUITABLE FOR GASIFICATION

Outcomes of laboratory analyses

Cassava peels/barks:

•ash content (<5%)

•ash fusion temperature is above 1200°C

•bulk density remains above 250 even after drying

•it flows easily and burns well

•moisture content (66%) to be reduced up to 20%

Wood shavings and sawdust:

•ash content (<5%)

•ash fusion temperature above 1200°C

•bulk density is low and it does not flow easily but burns well

•moisture content (30%) to be reduced up to 20%

A blend of cassava and wood wastes (mixed in a 1:1 proportion) showed to be suitable for gasification.

GASIFICATION: BLEND OF DRIED CASSAVA AND WOOD WASTES/OTHER BIOMASSES

(2)

Blend of wood shaving (70%) +saw dust (30%)

(1)Dried cassava

peels/barks

Gasifier uses a blend of + (2)

mixed in a 1:1 proportion

SCHEME OF A GASIFIER/REACTOR

Gasifier: a reactor

where physical and

chemical processes take place

MAIN FEATURES OF THE GASIFIER CONSIDERED IN THE STUDY

Main assumptions

A. Installed capacity: 120 Kw (though on market they are available from 5 to 2200 kW)

B. Working hours: 330 days/year * 22 hours/day

C. Main outputs:

c.1 Electricity (mostly): to be sold as such or used to operate equipments, dry food cassava derivatives, lightening etc

c.2 Heat: to dry biomasses (20% moisture content) as feedstock for the gasifier and to dry food cassava derivatives

D. Intakes

d.1 Intake (MT/year) of raw cassava peels/ barks (66% moisture content): 1706 MT/year (equal to 8280 MT/year cassava roots)

d.2 Intake (MT/year) of raw wood shaves and sawdust (30% moisture content): 835 MT/year

d.3 Intake (MT/year) of dried (20% moisture content) biomasses (1:1 proportion): MT 1452, of which:

• Dried cassava peels/barks: MT 726• Wood shaves and sawdust: MT 726

BIO-METHANATION/BIOGAS PLANT: FLOW DIAGRAM

THE METHANIZATION PROCESS (BIO-GAS PLANT)

BIOGAS: ANAEROBIC FERMENTATION/BIO-DIGESTION PROCESS

Main features digestor

Installed capacity available on market for digestors: designed according to users’ needs

Main product: biogas (methane, mainly) from wastewaters through an anaerobic fermentation.

Digestion time: ~ 16 – 120 hours

Wastewaters solids contents: Dissolved solids ~ 1-10% Suspended solids: < 3%

Output: 1 lt/wastewaters = 2 to 3.5 lt of biogas (according to organic load of wastewaters)

Laboratory Analyses of cassava processing wastewaters

Total solids: 4,000 – 6,600 mg/L

Total suspended solids: 1,450 mg/L

Total volatile solids: 2,000 mg/L

pH: 5.14

BOD: 3,400 – 6,018 mg/L

COD: 3,870 – 6,680 mg/L

Free Sugars: 640 – 2,075 mg/L

Nitrogen: 65 – 74 mg/L

BIO-METHANATION/BIOGAS PLANT: FLOW DIAGRAM

THE FINANCIAL ANALYSES

Energy production/planned use based on a

gasifier with an installed capacity of 120 kWe/h

************

Option 1 (General case)

1.a) Output: electricity (as main output) + hot air;

1.b) Planned use: 88 Kw/h of electricity (to be sold on open market) + hot air

(to dry target biomasses up to a 20% moisture content)

*************

Option 2 (Application – Asueyi pilot)2.a) Output: electricity + hot air;

2.b) Planned use: 74 Kw/h of electricity (to operate equipments etc) + hot air

(to dry target biomasses up to a 20% moisture content and 4.5 tons/22h of cassava food products up to a 8-10% moisture content-from initial 40%)

GASIFICATION: ENERGY OUTPUT AND ITS PLANNED USE

BIOGAS PLANT: ESTIMATED ENERGY PRODUCTION

Estimated quantity of wastewaters generated during cassava processing (to produce: gari, flour, agbelima):

1 liter water required to process 1 kg of peeled cassava roots Estimated wastewater: 18,000 liters/day (from 25 T/d of roots) Wastewater organic load: 3400-6000 mg/liter as BOD Biogas potential: in 24-72 hours about 37-56 m³/h of biogas are produced

digesting ~80% of BOD in wastewaters Methane concentration in biogas: 65-70% Calorific value methane: 5800-7200 kcal/m3

Estimated energy production: Gross output 334,425 Kcal/d Net output 301,513 Kcal/d

HEAT REQUIREMENT TO DRY BIOMASS AND PRODUCTS IN A DAY OF 22 WORKING HOURS

Heat required for drying target bio-masses (peels/barks and wood wastes):

Kcal/d 3,388,000

Heat required for drying 4.5 tons/day of cassava derivatives (flour, starch, agbelima) from initial 40%-45% to final 8%-10% moisture content:

Kcal/d 2,156,000

GASIFIER: PRODUCTION AND USE OF ENERGY

GASIFICATION AND BIOGAS MARKETABLE PRODUCTION: HEAT BALANCE AND EQUIVALENCE PER DAY OF 22 WORKING HOURS

ECONOMIC AND FINANCIAL ANALYSES: KEY ASSUMPTIONS

Project’s life: 10 yearsPlants working 22h/d for 330 d/y

Costs•Financing of the investment: 100% loan (22% interest rate), including 4 months working capital •Repayment of loan: yearly equal installments for 7 years•Transport Costs: $10/MT for local biomasses•Bio-diesel fuel used to operate biogas & gasifier plants

Revenues•Incomes: total energy (electricity plus heat) generated by the gasifier and the biogas plants - expressed into Kwh and Kcal- converted into liters of diesel (0.8$/lt) and tons of firewood (15 $/Mt). •Discount factor of annual cash flows: 22%

THE CASH FLOW ANALYSIS: THE GASIFIER

THE CASH FLOW ANALYSIS

The biogas plant

The gasifier plant in the Asueyi municipality

ENVIRONMENTAL ASPECTS

Water resulting from bio-gas

plant

Air resulting from gasifier

Wood is saved and forests are less at risk

Used in re-circulation mode with zero discharge. Occasional ph adjustment and simple treatment may be needed.

Gasifier releases negligible amounts of gases into the atmosphere. Combustion is much cleaner as compared to the one for liquid fuels.

Heat produced by the gasifier replace heat generated by firewood

ENVIRONMENTAL ASPECTS

Thank you