Palm Oil Mill Effluent

PALM OIL MILL EFFLUENT

Palm oil mill effluent (POME) is the waste water discharged from the sterilization process, crude oil clarification process and cracked mixture separation process. POME produced huge amount of methane gas from its anaerobic process and has 21 times Global Warming Potential (GWP) compared to the other gasses. However it can be solved, if it can be utilized as fuel for power generation and cogeneration. Notwithstanding the huge potential, existence of proven technologies and availability of knowledge and incentives, biogas utilization is still in a very early stage in Malaysia.

Wastewater treatment facility is amongst the most important component in the palm oil mill system. This is because the facility is to treatment palm oil mill effluent (POME) that is being generated in large volume during the production of crude palm oil (CPO). Due to the chemical and physical properties of POME, the most efficient system used in the initial stage of the wastewater plant is the anaerobic treatment. The current systems meet the requirement of the palm oil mill operators to safely discharge the treated POME. However, the systems release one of the green house gases (GHG), CH4 into the atmosphere as the by-products of anaerobic digestion of POME.
 

BIOGAS/METHANE RECOVERY AND POWER GENERATION

Biogas with Methane (CH4) as major gas fraction from the POME could be recovered in the POME treatment facility by changing the anaerobic lagoons to closed/covered digesting ponds or sealed digesting tanks as shown in Figure below. Electric power therefore is generated via the combustion of the CH4 in the gas turbine. Power generated then is supplied to Sarawak Energy.

The overall power generation potential from effluent treatment can be estimated based on the calculated methane yield from anaerobic POME treatment. According to Malaysia Palm Oil Board (MPOB), 0.65 m3 POME is generated from every processed ton of fresh fruit bunch.

 

Figure: Proposed biogas recovery and power generation

 

In the following Figure, the composition of biogas from POME has been determined as 62.5 % methane, 37 % Carbon dioxide and 1,500-3,000 vppm hydrogen sulphide. The calorific value for the generated biogas is 22,000 kJ/m3. The heating value (average caloric value) of methane was 36.3 MJ m3 at standard conditions (Matteson and Jenkins, 2005). This corresponds to 10.888 kWh of energy per 1 m3 of methane.



Figure: Schematic diagram of methane recovery from POME

Based on annual production of 9,288,000 tons of FFB process in Sarawak; resulting in an annual effluent generation of 6,037,200 m3 and therefore 150,930,000 m3 of biogas could be harnessed. Assuming that the effluent is treated properly under anaerobic conditions, the total methane production amounted to 94,000,000 m3. The calorific value of methane is stated as 10kWh/m3. The annual energy content of the generated methane gas can be calculated to 940 GWh (~108 MW).

Based on a conversion efficiency of 38 % (gas engine), the potential annual electrical power generation would be 360 GWh. Assuming 100 % availability of the conversion system shall results in an installed power generation capacity of 41 MW from POME derived methane gas. This is summarized in Table below.

 

 

Parameters

 

Value

 

Unit

FFB

9,288,000

ton/year

POME yield

6,037,200

m3/ton-FFB

Biogas yield from POME

25

m3-biogas/m3-POME

CH4 gas fraction in biogas

0.625

m3-CH4/m3-biogas

CH4 emitted

0.94E+08

m3

Electricity equivalent (38 % eff)

3.6E+08 or (41)

kWh or (MW)

Table: Parameters for estimating CH4 from POME


In spite the substantial potential for biogas utilization in Malaysia especially in palm oil industry, only very few operation biogas utilization applications could be identified in Peninsula Malaysia. Deployment of biogas technology such as anaerobic biogas reactor would furthermore lead to a drastic reduction of GHG emission and also could bring a profitable energy business in the future. There are possibilities to harness this bio-methane from POME for generating “Green” electricity from fuel cell in the future fuel cell applications.

 

PALM OIL MILL EFFLUENT (POME) - PALM OIL BIOGAS (POB) POWER GENERATION AND COGENERATION TECHNOLOGIES

Since the palm oil mills have abundant biomass waste resources, their energy systems were designed to be cheap rather than efficient. Most of the existing biomass combustion systems in Malaysia utilize low efficiency low-pressure boilers. The average conversion efficiencies in process steam and electricity generation are 35 % and 3 %, respectively. The average overall cogeneration efficiency is 38 %. An additional source of energy in palm oil mills is the biogas produced in the anaerobic decomposition (for wastewater treatment purposes) of POME. Presently, POME-derived biogas is not recovered and used. This CH4 rich (65 %) gas is allowed to dissipate freely into the atmosphere.

Commercially proven technologies are available in the international market for efficient production of power and heat from major biomass resources - bagasse, wood waste, palm oil waste, straw, and rice husk. The state-of-the-art modern technologies utilize efficient high pressure boilers. Some of these boilers are capable of dual fuel burning, utilizing either liquid (e.g., diesel oil) or gas (e.g., natural gas) fuel as supplementary energy source. Dual fired boilers will be used in palm oil waste-fired boilers to facilitate the use of POME-derived biogas as supplementary fuel.

Local manufacturing capacity of efficient high-pressure steam generators in Malaysia is presently low. Most of the equipment for a biomass-based power generation and CHP has to be imported, making the capital cost of a conventional biomass power plant or CHP facility in the country high (typically around US$ 1,500/kW). Moreover, with the market potentials of biomass-based power projects and a suitable government policy on power pricing, the local boiler industry could possibly take up the manufacturing of high-pressure biomass boilers, when the market and demand for efficient biomass power technology takes off.
Technologies for the effective treatment and handling of POME have been applied in several palm oil mills in Malaysia. The present systems typically involve the anaerobic decomposition of the organic components of POME and are sufficient to meet the required final effluent BOD (biochemical oxygen demand) limits imposed by the government. As to the biogas produced during POME treatment, there are no government regulations yet requiring palm oil mills to prevent its release to the atmosphere.