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.