Paddy Residues Potential

Sarawak is revising its rice production target to become 100 % self sufficient from 70% self sufficiency level under the Ninth Malaysian Plan (9MP) as a major pace to address food security. Currently, Sarawak is the nation's fourth largest rice producer, after Kedah, Perak and Kelantan. Sarawak had achieved a self-sufficiency level of 53 % with total rice production of 124,544 metric tons (or equivalent to 207,573 metrictons of paddy).

A total of 43,821 hectares in eight areas, including Paloh, Pulau Bruit, Sungai Sebelak, Lingga, Banting, Stumbin, Bijat and Samarahan was identified as suitable for large-scale paddy production in the state. The state government would embark on the development of the Sungai Sebelak area at Roban, involving 3,537 hectares, as the first granary to be implemented under the 9MP. The state government had started the rice estate in Tulai, Bintangor. The preliminary work on Polah has begun with a total of 8,080 ha of paddy field.

Assuming rice yield per hectare is 2.8 ton/hectare, the additional production in future is about 15,650 metric tons per annum. However, the total production shall be higher as the state aims to increase the existing paddy yield of 2.8 metric tons to four metric tons per hectare annually, through the implementation of paddy infrastructure improvement projects, besides promoting the use of high-yield varieties such as MR219, MR220 and MR232 or hybrid paddy for double crop planting.

The total production will be more than 280,000 tons of paddy upon the plans are fully developed in five years. This implies that there are about 70,000 tons of rice husks and 350,000 tons rice straw will be procured from the state paddy industry. If all rice hulls were used in gasification or combustion systems with an overall efficiency of 32 %, the state’s technical energy potential from rice husks alone can be estimated be around of energy corresponding to 592,013 MWh electricity.

PADDY RESIDUES FOR ELECTRICITY

Rice husk can be used for power generation through either the thermal or biological route which can produce biogas of components as such in the following Table. For small scale power generation, the thermal route has attracted more attention as the biological route is still under debate. In addition for rice mills with diesel engines, the gas produced from rice husk can be used in the existing engine in a dual fuel operation. Attempts have been made in several rice producing countries in Asia to develop rice husk gasification plants for power generation and in some countries rice husk gasification plants have been produced for commercial purpose.

Components	Percentage (%)
Carbon dioxide (CO2)	30.7
Hydrogen sulphide (H2S)	2.1
Carbon monoxide (CO)	9.9
Methane & water vapor	52.3

Table: Percentages of the components of biogas from rice husk

It was envisaged that there are potential for better utilization of rice husks and rice straw for energy production particularly for stationary electricity generation. Practically in short terms, we shall look into the possibilities to produce biogas through anaerobic digestion and gasification which serve as bio-fuel for power generation. This will be profound thought for rural electrification as part of our CSR. With this respect, as in the rural rice growing areas that are not connected to the electricity grid systems, there is a potential of gasifying rice husks and rice straw to provide energy. A gasifier can be coupled to the mill so that the gas products are burnt to supply energy for running the mills. This is an aspect of energy conservation for medium-scale industries in the state.

In a wider perspective, where the volume of rice husk and rice straw is sufficient we shall optimize the use of rice husk and rice straw for larger capacity of gasification system or production of digesters gas and power generation to supply the electricity to the grid. This could be realized when the large scale paddy fields were in operation. Other possible ways of using the residues is to incorporate gasification equipment to a small fuel cell system in the paddy village. This might be of the viable utilization patterns in near future as the technologies of stand-alone court-yard fuel cell systems are getting more reliable. The approach is running the biogas produced into a fuel cell.

PADDY RESIDUES FOR BIOGAS PRODUCTION

New / Extend Paddy Field	Area (ha)
Limbang Valley	20,000
Paloh	8,080
Sg. Seblak	3,537
Daro	2,851
Bijat/Stumbin	2,900
Pulau Bruit	3,353
Lingga/Banting	2,200
Nanga Merit	900
Total	43,821

Table: Proposed new paddy area in Sarawak

Table above shows the total proposed area for paddy field is almost 44,000 ha but at scattered locations. Therefore, SEB has plans for these rural areas the electrification system generated by renewable energy such as hybrid system from wind, solar, mini-hydro to be integrated with fossil generation. There are possibilities to utilize indigenous agriculture biomass like rice husk and rice straw to be gasified or through biochemical process like anaerobic digestion to produce biogas for generating electricity. This may further reduce or displace fossil fuel in providing power to the rural folks. The divisional production of paddy in Sarawak is shown in Table below.

Division	Paddy (ha)
	2005	2006	2007
Kuching	7,008	6,827	6,290
Sri Aman	19,466	19,377	19,314
Sibu	12,037	13,959	12,304
Miri	13,366	12,640	11,337
Limbang	4,680	4,700	4,503
Sarikei	10,785	11,537	11,399
Kapit	19,400	19,234	12,660
Samarahan	14,588	14,145	14,126
Bintulu	7,631	7,093	6,869
Mukah	6,883	6,853	7,730
Betong	11,376	11,152	11,013
Total	127,220	127,517	117,545

Table: Yield and production of paddy by Division 2007

Of  notable area to be looked into for adopting this facility is Nanga Merit in Kapit with current farming area of about 150 ha paddy area under DID irrigation schemes. The village is not connected to SEB’s grid and using diesel generator for electricity. With the expansion of paddy field to 900 ha in near future, the biomass residues from paddy shall be significant to be utilized for generating electricity for the benefit of the villagers. It was estimated 2,520 tons of paddy will be harvested in which about 630 tons of rise husk and 3,150 tons of rice straw can be utilized. This amount of biomass residues could potentially produce 60 TJ of energy which represent 16,650 MWh of electricity. The future potential of power that can be generated from paddy residues is shown in the following Table.

	Area (ha)	Paddy Production (tpa)	RH Generation (tpa)	RS Generation (tpa)	Electricity Potential, 32% efficiency (MW)
Current	150	420	105	525	0.10
Future	900	2,520	630	3,150	0.61

Table: Case study - Nanga Merit

From our initial analysis, there are several districts that show the potential of using paddy residues to produce biogas and then electricity.  There are Sri Aman, Lubok Antu, Simunjan, Daro and Saratok with substantial capacity as shown in Table below. The introduction of large scale paddy fields plantation will further make possible of getting sufficient paddy residues to be feasible to utilize the biomass for power generation.

Properties	Sri Aman	Lubok Antu	Simunjan	Daro	Saratok
Paddy Yield (ton/yr)	23,026	18,324	14,287	11,545	12,750
RH (ton/yr)	5756.5	4581	3571.75	2886.25	3187.5
RS (ton/yr)	28782.5	22905	17858.75	14431.3	15937.5
Power Capacity (MW)	17.37	13.82	10.78	8.71	9.62
Power Output - 32% η (MW)	5.56	4.42	3.45	2.79	3.08

Table: Potential areas (Districts) for generating electricity from paddy residues

 

COGENERATION

Rice husk can be considered as fuel for heat and power generation provided the waste volume is sufficient and regular. Generally, co-generation systems are only feasible for rice mills with a minimum production capacity of 5 tons per hour.
The rice-husk cogeneration system in Pendang, Kedah (steam boiler 6.5 t/h, 30 bar, 450 kWh back pressure turbine and heat exchanger (1,200,000 kcal/hr) is being used for 3 months for heating (paddy drying) as well as supplying power for the plants. Typical size of boiler for rice mills is 5-15 tons/hours coupled with a 0.5 - 1 MWe turbine.

Excluding civil and structural works, the total investment cost for the equipment is USD 1,150,000. Based on the consumption and price of fuel oil, the annual savings in fuel oil purchases are expected to be USD 250,000. Moreover, annual savings from the disposal of residues is estimated at USD 13,000. An additional income to the company could come from the sales of ash, which are expected to generate a yearly profit of USD 179,000. The expected payback period of the plant is around 3 years after commissioning.

This husk contains about 75 % organic volatile matter and the balance 25 % of the weight of this husk is converted into ash during the firing process to supply energy and generate electricity, is known as rice husk ash (RHA). This RHA in turn contains around 85 % - 90 % amorphous silica. So for every 1,000 kg of paddy milled, about 220 kg (22 %) of husk is produced, and when this husk is burnt in the boilers, about 55 kg (25 %) of RHA is generated. Essentially, the high commercial value of the RHA may provide added incentive to venture into cogeneration in additional to the heat and power.

For further details log on website :
http://www.sarawakenergy.com.my/index.php/r-d/biomass-energy/paddy-residues-potential