Experience in Closed Anaerobic Digesters Operation

for POME Biogas Harnessing Under CDM Project

By

Ir. RM Subbiah and Tuan Haji Alui Ahmad

Green & Smart Sdn. Bhd.www.greens.com.my

Anaerobic Technology (no air required for microbial survival)

Traditionally used A.D. types in

POME treatment• Deep open tanks• Deep lagoons

(Biogas released to atmosphere, GHG)

OPEN TANKOPEN TANK

GHG contribute to global warming

POME Biogas contains 45% to 80% methane, which has 21 times higher global warming potential than CO2

New AD types used for

POME treatment based on

“Clean Development Mechanism” (CDM) principles

• Closed lagoon with covering• Closed tanks with stirring

(Biogas harnessed)

CLOSED LAGOONCLOSED LAGOON

Completely Stirred Tank (CST)System

Stir the tank content by:

•Using biogas itself•Using stirrers•Using pumps

POME – MAS TM

Palm Oil Mill Effluent – Mesophilic Anaerobic System

Temperature range 320C – 400C

POME-MASTM System

System used in 4 Palm Oil MillsTotal digesters : 12

Sizes:1700m3, 2200m3, 3600m3, 5800m3

ResultsResults COD Reduction Efficiency COD Reduction Efficiency

All Digesters Design Mill 1 Mill 2

COD Inlet

(mg/L)55000

Range

42700 – 65940

Mean

55349

Range

26500 - 151700

Mean

54577

COD Outlet (mg/L)

5000

Range

2585 – 4537

Mean

3721

Range

2832 – 7690

Mean

4421COD

Reduction90% 93.22% 90.10%

Feed Quantity m3/day 120 288

Graph Showing Typical Results On Daily BasisGraph Showing Typical Results On Daily BasisFigure 1: 1700 m3 Anaerobic Digester Monitoring Results

Figure 2: 3600 m3 Anaerobic Digester Monitoring Results

Reactors are running sustainably for more than 12 months

Longest running > 24 months

Biogas production depends on• Effluent flow rate• Incoming COD value• Effluent temperature

Typical ValuesTypical Values

Mill production: 40T FFB/HrPOME: 24m3/Hr

Incoming COD total: 55,000 mg/lCOD reduction efficiency in the digester: 92%

Methane production: 425m3/hrBiogas at 60% CH4 content: 708m3/Hr

Theoretical power generation potential: 1274kW-1558kW

COD reduction values measured in POME-MASTM

varies from 90% to 95%

CH4 (Methane) values measured in POME-MASTM

varies from 60% to 75%

BIOGAS PRODUCTION AT DIFFERENT COD REDUCTION EFFICIENCIES & DIFFERENT METHANE CONTENT

Mill capacity FFB m3/hr 40

Effluent Flow rate m3/hr 24

Inlet COD Mg/l 55 000

COD reduction efficiency see table

Assumption : Running on full load on above capacity1 kg COD reduction gives 0.35m3 Methane

Biogas Production at different methane

concentration

Biogas Production at different COD reduction % (m3/hr)

75% 80% 85% 90% 95%

At 55 % 630 672 714 756 798

At 60 % 578 616 655 693 732

At 65 % 533 569 604 640 675At 70 % 495 528 561 594 627

ESTIMATED ELECTRICITY PRODUCTION

Electricity Production

COD reduction efficiency 75% 80% 85% 90% 95%

Biogas Production at 60% methane concentration 578 616 655 693 732

Potential electrical power at 2kW* hr/m3 of biogas

(kWh)1156 1232 1310 1386 1464

* Can vary from 1.8kW to 2.3kW per m3 of biogas based on generator efficiency

Efficiency Difference - Commercial Value

Every 5% difference in gas production means extra 500,000 kWh/year

@ RM 0.30/kWh = RM 150,000For 21 years SREP feed in tariff difference in

revenue = RM 3.15million

Flare

CDM compliant GREEN-FLARETM

Exhaust temperature set 6100C maintained at 610 + 30C

Gas retention time about 0.86 seconds

Conclusion

• POME-MASTM system gives high COD reduction efficiency > 90%• Takes shock loads

• CH4 contents 60% to 75% in Biogas

• Runs in sustainable manner either on continuous or batch feed mode • GREEN-FLARETM (CDM compliant closed flare)

maintains same set exhaust temperature for different gas flows

Thank You

Presenter:Ir. RM.Subbiah (012-2181903)

Green & Smart Sdn. Bhd.www.greens.com.my