household biogas digesters

Evaluation of Household Biogas Digesters

Content

1. Introduction 2. Designs 3. Constructions 4. Evaluations and Comparisons 5. Conclusions

1. Introduction

1.1 Background

The most Vietnam common household biogas digesters:

Household biogas digester which is made from brick and composite (KT31)

Household biogas digester which is made from composite

Household biogas digester which is made from brick (KT1 & KT2)

Household biogas digester which is made from nylon bag

1.2. Evaluation Criteria

1. Construction material (10 scores max.)

2. Convenient of construction method (20 scores max.)

3. O&M (30 scores max.)

4. Return on Investment (30 scores max.)

5. Sanitation (10 scores max.)

Total: 100 scores

2. Design

2.1 KT 31 design

1. Digester

2. Gas holder

3. Inlet

4. Outlet

5. Gas outlet

6. Compensation tank

2.2 KT1 & KT2 design

KT1 KT2

2.3 Composite design

400

1000mm 1000

400

R= 2600

Inlet: 800 Outlet: 900

1300

600

80

400

200

Gas outlet

Gas holder

Digester

2.4 Nylon bag

2. Construction

3.1 Construction of KT31

3.2 Construction of KT1 &KT2

3.3 Construction of Composite

3.4 Construction of Nylon bag

3. Comparison and Evaluation

4.1 Comparison in terms of construction materials

8.586.79

5.00

10.00

7.58

4.79 5.00

9.55

-

2.00

4.00

6.00

8.00

10.00

12.00

KT31-Northern

part

Composite-Northern

part

Nylongbag-

Northernpart

KT1 KT31-southern

part

Composite-Southern

part

Nylongbag-

Southernpart

KT2

Total score (10 maximum) Availability (5 maximum) Strength (5 maximum)

4.2 Comparison in terms of Convenient of construction

8.01

17.03

20.00

4.005.53

14.0616.17

0.500.00

5.00

10.00

15.00

20.00

25.00

KT31 - Thenorth

Composite- thenorth

Nylong bag -the north

KT1 KT31- thesouth

Composite- thesouth

Nylon bag - thesouth

KT 2

Total score (20 maximum) Soil excavation (5 maximum)Easy to contruct (5 maximum) Manday (5 maximum)

Score for construction method (5 maximum)

4.3 O&M Comparison

20.0

24.0

10.3

20.5 20.022.5

9.8

22.0

0.0

5.0

10.0

15.0

20.0

25.0

30.0

KT31 - thenorth

Composite-the north

Nylong bag-the north

KT1 KT31-thesouth

Composite-the south

Nylong bag -the south

KT 2

Total (30 maximum) Safety of the structure (6 maximum)Safety of end user (6 maximum) Gas productivity (6 maximum)

Easiness for O&M (6 maximum) Easiness to dectect failure and to repair

4.3 Comparison of ROI

12.2610.01

16.6619.40

12.4811.23

16.6617.89

0.00

5.00

10.00

15.00

20.00

25.00

KT31 - thenorth

Composite- thenorth

Nylon bag KT1 KT31- theSouth

Composite- thesouth

Nylon bag - thesouth

KT 2

Total score( 30 maximum) Total investmetn csot (10 maximum) Average Anual investmetn cost (10 maximum)

Payback period (3.33 maximum) NPV (3.33 maximum) IRR ( 3.33 maximum)

4.4 Comparison of Sanitation

No. Model Smell bad (5 maximum)

BOD 5, COD, coliforms (5 maximum)

Total (5 maximum)

1 KT31 5.00 5.00 10.00 2 Composite 5.00 5.00 10.00 3 Nylon bag 5.00 5.00 10.00 4 KT1-KT2 5.00 5.00 10.00

4.5 Overall Comparison

58.85

67.8361.96 63.90

55.5962.58

57.63 59.94

0.00

10.00

20.00

30.00

40.00

50.00

60.00

70.00

80.00

KT31 - thenorth

Composite-the north

Nylon bag- the north

KT1 KT31- thesouth

Composite-the south

Nylon bagthe south

KT 2

Total (100 maximum) Construction material (10 maximum) Construction (20 maximum)

O&M (30 maximum) Cost (30 maximum) Environment (10 maximum)

5. Conclusions

5.1 KT31 digester

Pros:

Durable and long lifetime.

Cons: High Investment cost More complicated to transport Less availability. Need trained masons.

5.2 Composite digester

Pros:

Easy to install and O&M

Higher gas productivity and longer lifetime

No need trained masons

Cons:

High investment cost

More complicated to transport.

Applicability:

Week soil foundation with high ground water level.

Places without trained masons, brick and cements.

5.3 KT1 & KT2 digesters

Pros:

Higher gas productivity and longer lifetime.

Medium initial investment cost.

Easy to operate.

Cons:

Need trained mason.

Not easy to maintain.

Need trained masons, bricks and cements.

5.2 Nylon- bag digester Pros:

Lowest initial investment capital

Easy to install, no need trained mason.

High availability of construction material.

Cons:

Inconvenient O&M

Less durable and short lifetime

Applicability

Poor households.

No long term plan of raising animal.

Contact: Tran Hai Anh – Renewable Energy Specialist Tran_haianh@yahoo.com