rice husk based power plants

7/23/2019 rice husk based power plants

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1. INTRODUCTION

Rice is grow on every continent except Antarctica and covers 1% of the earth’s surface. It is a

primary source of food for billions of people, and ranks second to wheat in terms of area and

production. Production of rice paddy is associated with the production of essentially two

byproducts, rice husk and rice bran. Husk, also called hulls, consists of the outer shell covering

the rice kernel. As generally used, the term rice husk refers to the byproduct produced in the

milling of paddy and forms 16-25% by weight of the paddy processed.

Figure 1 : Rice husk

Around 20% of the paddy weight is husk. In 2008 the world paddy production was 661 million

tons and consequently 132 million tons of rice husk were also produced. While there are some

uses for rice husk it is still often considered a waste product in the rice mill and therefore often

either burned in the open or dumped on wasteland. Husk has a high calorific value and therefore

can be used as a renewable fuel.



Figure 2 : Annual Production of rice and rice husk in the world

2. PRODUCTION OF RICE HUSK

Commercial milling systems mill the paddy in stages, and hence are called multi-stage or multi-

pass rice mills. The objective of commercial rice milling is to reduce mechanical stresses and

heat buildup in the grain, thereby minimizing grain breakage and producing uniformly polished

grain. Compared to village-level systems, the commercial milling system is a more sophisticated

system configured to maximize the process of producing well-milled, whole grains.

The rice milling facility comes in various configurations, and the milling components vary in

design and performance. “Configuration” r efers to how the components are sequenced. The flow

diagram below shows a modern commercial mill catering to the higher end market. It has three

basic stages,

the husking stage,

the whitening-polishing stage, and

the grading, blending, and packaging stage.



In modern rice mills, many adjustments (e.g. rubber roll clearance, separator bed inclination,

feed rates) are automated for maximum efficiency and ease of operation. The whitener-polishers

are provided with gauges that sense the current load on the motor drives which gives an

indication of the operating pressure on the grain. This provides a more objective means of setting

milling pressures on the grain.

Modern rice milling processes consist of:

Table 1 : The modern rice milling process

Stage Function

Pre-cleaning removing all impurities and unfilled grains from the paddy

Husking removing the husk from the paddy

Husk aspiration separating the husk from the brown rice/unhusked paddy

Paddy separation separating the unhusked paddy from the brown rice

De-stoning separating small stones from the brown rice

Whitening removing all or part of the bran layer and germ from the brown rice

Polishing improving the appearance of milled rice by removing remaining ran particles

and by polishing the exterior of the milled kernel

Sifting separating small impurities or chips from the milled rice

Length grading separating small and large brokens from the head rice

Blending mix head rice with predetermined amount of brokens, as required by the

customer

Weighing and

bagging

preparing milled rice for transport to the customer



The flow diagram below represents the configuration and flow in a typical modern rice mill.

Figure 3 : The flow diagram in a typical modern rice mill

Brown rice at the rubber roller husker

Mixture of paddy grain and brown rice coming out of the rubber roll husker. With uniform size

paddy, about 90% of the paddy should be husked after the first pass. This mixture goes through a

paddy separator, after which the paddy is returned to the husker, and the brown rice goes to a de-

stoner.



Figure 4 : Rubber roller husker

3. CHARACTERISTICS OF RICE HUSK

Rice husk is difficult to ignite and it does not burn easily with open flame unless air is

blown through the husk. It is highly resistant to moisture penetration and fungal

decomposition. Husk therefore makes a good insulation material.

Rice husk has a high silica (SiO2) contents which means that it decomposes slowly when

brought back to the field. It also makes it a poor fodder.

Handling of rice husk is difficult because it is bulky and dusty. It has angle of repose is

about 40-45° which means that it's flow ability, e.g. in feed hoppers is very poor.

Rice husk has low bulk density of only 70-110 kg/m³, 145 kg/m³ when vibrated or

180kg/m³ in form of brickets or pellets. It thus requires large volumes for storage and

transport, which makes transport over long distances un-economical.

When the ash content burned is 17-26%, a lot higher than fuels (wood 0.2-2%, coal

12.2%). This means when used for energy generation large amounts of ash need to be

handled.



Rice husk has a high average calorific value of 3410 kcal/kg and therefore is a good,

renewable energy source.

Because of the high silica contents rice husk is very abrasive and wears conveying

elements very quickly.

Rice husk is not an easy fuel. One concern in rice husk firing is the behaviour of the ash,

i.e., its slagging and fouling tendency caused by a low melting point of the rice husk ash.

4. UTILIZATION OF RICE HUSK

Rice husk is produced centrally at rice mills and has low moisture content since the paddy is

dried to 14% or less before milling. The disadvantage is that rice husk has very low density and

therefore transport over longer distance is expensive. The most obvious use of rice husk is

therefore the use as fuel at or close to the rice mill. But rice husk is also used for some non-

energy purpose.



Table 2 : Typical uses of rice husk

Non energy

applications

Energy generation

Combustion Gasification Pyrolysis

Incorporation

in soil

Bio-fertilizer

additive

Animal

husbandry

- low quality

feed

- litter material

Sorbent

material in

environmental

remediation

Building

material with

good thermal

insulation

Pest control

agent

Heat generation

- cook stoves

- furnaces for heating the

air in rice dryers

- brick kilns

Gas for cook

stoves

Syngas for

electricity

generation

In research

phase few

commercial

applications

Steam generation for

- parboiling

- electricity generation

from steam turbines

- kinetic energy from

steam engines



4.1 Examples for non-energy applications

4.1.1 Use of rice husk in animal husbandry

Rice husk is sometimes used as animal feed stuff and as litter material for pet animals. Untreated

hull is low in protein and digestible energy. Husk can be pre-treated with 12% NaOH to reduce

the silica content from 19 to 3-4% to improve digestibility and used as animal feed.

4.2 Examples for energy applications

4.2.1 Cook stoves

Simple rice husk cook stoves are used for a long time in the Greater Mekong Sub region. The

origin of the design is unknown, some sources mention Cambodia, others Vietnam. After a

Vietnamese scholar had brought a unit from Vietnam for testing to IRRI in the Philippines many

national systems and projects have adapted the technology to local conditions and similar stoves

can now be found in most Asian countries.

The cook stoves come in different sizes and usually can boil a pot of water in around 10-15

minutes. The fuel is cheap and the stove itself very inexpensive but the disadvantage i is that the

user is exposed to small, silica rich ash particles in the flue gas.

To generate a cleaner flame the cook stove principle was modified into a gasifyer burner that has

a clean flame. Commercial applications exist in the Philippines and in India.

Figure 5 : Rice Husk Cook Stove



4.2.2 Process heat generation for rice drying and parboiling

Rice husk furnaces for heating the drying air in rice dryers is the most obvious application for

using rice husk since the husk is available as waste at the rice mill and drying of paddy is often

done by millers. But only recently with increasing fosil fuel prices there has been a major shift

away from kerosene towards rice husk furnaces. In India and Bangladesh rice husk is often used

as fuel for parboiling paddy before milling.

4.2.3 Mechanical power generation

Rice husk is used as fuel for boilers which generate heat for steam engines. These steam engines,

most of them being produced in the beginning of the last century, still power many rice mills in

Myanmar though belt transmissions. While this is old technology we still believe that this is

worth mentioning here as an example for sustainably using rice husk as energy source over

decades in an environment where many millers are not connected to the electricity grid.

High fuel prices have led more recently to a revival of rice husk gasifiers, partly for electricity

generation (see below) but also ain may cases coupled with a modified internal combustion

engine that drives power a rice mill through a belt transmission. Several commercial units were

developed in India and especially in Cambodia rice millers have installed several units with 20-

70 kW capacity.

Figure 6:Gasification plant with 30kW powering a rice mill in Cambodia



4.2.4 Electricity generation

Small scale applications between 10-200 kW usually use a rice husk gasifier coupled with a

modified internal combustion engine that drives a generator. Larger commercial power plants

using rice husk typically have a capacity of 1-4 MW and consist of an advanced burner, a boiler

and a steam turbine coupled with a generator. Several units have been installed worldwide.

5. POWER GENERATION BY RICE HUSK

Rice husk is mostly used as fuel in boilers for processing paddy and generation of process steam.

Heat energy is produced through direct combustion and/or by gasification. Small sector processindustries use fixed low capacity boilers, which are manually fired using rice husk as a fuel.

Partial and uneven fuel combustion lead to smoke emission and decrease the fuel efficiency. As

husks are available virtually for free, the boiler efficiency and the degree of combustion were the

issues of receiving the latest attention. Plants with capacity 2-10 MW range can become

commercially viable and this biomass resource can be utilized to a much greater extent than at

present. It has been seen that to produce 1MWh, approximately 1 tonne of rice husk is required.

So, the technical and economic factors decide the effective use of rice husk as fuel for power

generation. A schematic diagram of a typical rice husk power plant is shown in the figure.

Figure 7 : Schematic diagram of a typical rice husk power plant



5.1 Power Generation by Gasification

Due to presence of large amount of hydrocarbon such as cellulose and lignin content, rice husk

can be used as a raw material to prepare activated carbons which are complex porous structures.

Gasification is the conversion of biomass to a gaseous fuel by heating in a gasification medium

such as air, oxygen or steam. Unlike combustion where oxidation is substantially complete in

one process, gasification converts the intrinsic chemical energy of the carbon in the biomass into

a combustible gas in two stages. If biomass is gasified efficiently, it can generate a high amount

of clean product gas.

The initial step to the process is a thermo-chemical decomposition of lignocellulosic compounds

where char, tar and volatile compounds produce as output. By thermo-chemical gasification solid

fuel is transformed into gaseous fuel. Through this process, the chemical energy of solid fuel is

converted into both thermal and chemical energy. The chemical energy contained depends on its

chemical composition that determines the quality of product gas. High concentration of

combustible gases like H2, CO and CH4 increase the combustion energy of the product gas.

Several types of gasifiers e.g. fixed-bed updraft and downdraft gasifier, fluidized bed gasifier and

bubbling bed gasifier are available in the existing market with different sets of pros and cons.

However, the downdraft gasifier is a comparatively cheap and the gasification in this type of

gasifier can produce a product gas with very low tar content. Keeping the process in mind, fixed-

bed downdraft gasifier is thus recommended for small-scale rice husk biomass plant. Here,

biomass fuel is fed at the top of the reactor/gasifier. The fuel then slowly moves down and during

this time, the fuel reacts with air (the gasification agent), which is supplied by the suction of a

blower or an engine and is converted into combustible producer gas in a complex series of

oxidation, reduction, and pyrolysis reactions. Generated ash is then removed from the bottom of

the reactor for silica production.



Figure 8 : Block diagram of a rice husk gasifier power plant

5.1.1 Downdraft Gasification

In a downdraft or co-current gasifier both gas and solid flows in the same downward direction.

An elaborate schematic view of downdraft gasifier is shown in figure 9. Biomass enters the

system from the top of the unit and is converted into gas as it descends. While the rice

husk/biomass progresses down through the reactor it dries, devolatilizes and combusts.

As seen in the co-current model in figure 9, the gas leaving the devolatilization region, and

therefore rich in tar is forced to pass through the combustion region where a bed of hot charcoal

exists. Most of the primary tar (consisting of oxygenated organic compounds) formed during

pyrolysis is cracked and burnt in a process called flaming pyrolysis.

The flame temperatures are in the range of between 1273 K and 1673 K, but the flame occurs in

the interstices of the pyrolysing particles which have temperatures between 773K and 973 K.

About 0.1% of the primary tars are converted to secondary tars and the rest are burned to supply

the energy for pyrolysis and char gasification.

Downdraft gasification produces secondary tars whereas tars produced by updraft gasifiers are

primary tars. Therefore, the produced gas is cleaner than the equivalent provided by the

countercurrent model. The co-current version presents some limitations on controllability for

large diameters or power output. This is mostly due to the formation of preferential channels in

the fuel bed that prevent the tar rich stream moving from the pyrolysis region from meeting the



hot core of the combustion region. Nevertheless, that problem is mitigated through the

application of slow-rotating paddles to provide uniform distribution of particles in the bed.

Although there has been some limitations of downdraft gasification, but in the proposed system

the effect is not severe. There are high amounts of ash and dust particles in the gas due to the fact

that the gas has to pass the oxidation zone where it collects small ash particles. The high ash

content generated by the combustion is not considered a drawback as the generated ash would be

reused to produce silica by precipitation process.

The moisture content of the biomass has to be carefully monitored as on wet basis moisture

content must be less than 25 % by mass . The relative high temperature of the leaving flue gases

result in lower gasification efficiency because these gases do not exchange heat with the wet biomass to be gasified .

Figure 9 : Downdraft gasification process



6. USE OF RHA IN SEVERAL INDUSTRIAL APPLICATIONS

Suitability of RHA mainly depends upon the chemical composition of ash, predominantly silica

content in it. Silica content and its mineralogical structure depend upon the combustion time,

temperature and turbulence during combustion. Silica content of RHA varies from 85%-95%.

There is very large potential for RHA containing mainly amorphous silica as a commercial

product. RHA has very good market value ranging from US$IOO/tonne to US$300/tonne in

India and can be very important material from the quality consideration in several industrial

applications.

6.1 Replacement to Silica Fume

This finely ground RHA can be used replacement of silica fume in the production high

performance concrete. Currently silica fume is costing above US$600/tonne. This RHA contains

more than 85 % of silica. Using rice husk in the power generation with such a high combustion

efficiency and buming temperature below 600°C gives very valuable byproduct amorphous silica

rich RHA. American Society of Testing and Materials place RHA in the same class as silica

fume - that of highly reactive pozzolan. RHA which is suitable to replace silica fume can easily

fetch price of US$I OO/tonne in India. Canadian boiler manufacturer have developed the reactor

for combustion of rice husk for such a high efficiency at better temperature control.

6.2 Tundish Powder in Steel Casting Industries

RHA is used by the steel industry in the production of high quality flat steel. This type of steel is

generally produced by continuous casting. In continuous casting a ladle of steel, containing more

than 200 tonnes of molten metal at 165oC, empties into a tundish, a receptacle that holds the steel

and controls its flow in the continuous process. RHA is an excellent insulator, having low

thermal conductivity, high melting point, low bulk density and high porosity. It is this insulating

property that makes it an excellent "tundish power". Tundish powders are used to insulate the

tundish, prevent rapid cooling of the steel and ensure uniform solidification. Traditionally ash is

sold in bags which are thrown on to the top of surface of the tundish of molten steel.



Approximately 0.5 to 0.7 kg of RHA is used per tonne of steel produced. Traditionally

crystalline ash is preferred to use it as a tundish powder.

6.3 Admixture in Low Cost Concrete Block Manufacturing

Ordinary Portland cement (OPC) is expensive and unaffordable to produce low strength concrete

block. Sometimes, it becomes economically feasible to produce low strength concrete block for

masonry work by using pozzolanic materials along with lime and gypsum. RHA is mixed with

lime and aggregates and cast of the required shape and sizes. Generally, around 7 MPa strength

is achieved at 14 days with mix proportion of 20:80 ratio of lime:RHA as binder material along

with some admixtures. Amorphous RHA is preferred for its use in the concrete manufacture. It is

due to high pozzolanic property of amorphous R1-1A.

6.4 Manufacturing Refractory Bricks

One of the potentially major profitable uses of RHA is in manufacture of refractory bricks. Due

to the insulating properties, RHA has been used in the manufacture of refractory bricks. Bricks

from RHA were reponed to be good heat insulators up to extreme temperatures, such as 1450oC,

and have a low thermal conductivity of about 0.03 kcal/m hr o

C and good resistance to

compression. These are suitable for furnace bricks. Such bricks normally contain 80-98% ash

and 2-20% CaO+MgO.

6.5 Control of Insect Pests in Stored Food Stuffs

RHA has been found to be an excellent material to protect soybean seeds from bruchid beetles.

The lethal effect of RHA on bruchid beetles has not yet fully analyzed. However, there are some

indications. Diatomaceous earth has been used as an effective controller of pests. The high silica

content of both diatomaceous earth and RHA must have a lethal effect on insects. RI-IA also

includes a large amount of needle-like particles that are probably derived from the setae covering

the outer surface of the rice husk. These needle-like particles may trigger a physical reaction on

the skin of insects, and the resulting physical disturbance may help cause their death. It is also



believed that RHA is useful for moisture adsorption also. The use of RHA enables fanners to

store soybean and mung bean on a small scale and for a low cost.

6.6 Water Purification

Some of reports have shown that RHA can be used as an absorbent after certain treatment. After

acid wash and calcinations at 600°C for 4 hours of RHA was used to make pallets with

reasonable strength to be utilized in a packed column. RHA was found to be good adsorbent for

adsorption of Congo Red, vacuum pump oil, myristic acids, palmitic acids, stearic acids and

mercury in the wastewater generated from industry.

6.7 Vulcanizing Rubber

White RHA can be used as filler for natural rubber compounds. White RHA increases

mechanical properties, such as, tensile strength, tear strength, resilience and hardness, if used as

a partial replacement of silica as a bonding agent. The RHA be again cheaper option to silica.

6.8 Flue Gas Desulphurization Absorbent

Generally in coal fired boilers of power plants fly ash is used as a source of siliceous material for

the preparation of absorbents for flue gas desulfurization. Mohamed studied the RHA as a

siliceous material source for gas desulfurization. Lower hydration period and temperature favor

the formation of absorbent with higher surface area. Absorbent prepared from RHA does have a

high capacity in S02 absorption.



7. USES OF CARBONIZED RICE HUSK(CRH)

Not too long ago, the sight of large heaps of rice hull (or rice husk) on or near some rice farms

was common. It used to be that these piles were without much worth as uses for rice hull then

were very limited. But with today's modern technology and farming techniques, that situation has

completely changed.

Instead of ending up as mere wastes, rice hulls are now subjected to the process of carbonization

to turn them into valuable commodities known as carbonized rice hull, or CRH. The process is

carried out by burning rice hulls without oxidation so they are not turned into ash. The resulting

CRH is now a very popular product in the farming industry for its many uses: as an enriching

substance for farm soil, as an enhancer for seedlings' growth, as a growing medium for producing high-value crops, and as a perfect litter for brooding chicks.

During the preparation of land for rice planting, about 20 bags of CRH mixed with compost or

organic fertilizer may be plowed in two-and-a-half acres of land. This will make the land more

permeable and allow the soil to keep its moisture for a longer period. This is especially important

in case of an unusually long rainless or dry period.

As a layer in seedbeds, CRH makes pulling out of the seedlings for transplanting virtually

effortless. Because the seedlings' roots are not harmed or damaged during the pulling out process

from the seedbeds, the seedlings naturally get settled in the field more easily. It has also been

proven, over the course of several planting seasons, that CRH-enriched fields produce a high

yield of healthy crops which means an equally high revenue for the growers.

Removed of its germinating capacity and being free from any disease elements, CRH is a better

litter for brooding chicks than rice hull in its natural state. The ability of CRH to easily suck up

moisture in the chicks' refuse prevents the litter from getting moist and becoming a potential

breeding ground for flies and other similar disease-carrying, dipterous insects. Growers who use

CRH for litter confirm that the chicks they raise grow faster, healthier, and do not vary much in

size from one another. This is so because CRH effectively prevents the growth and subsequent

multiplication of such organisms that are known to cause diarrhea and other respiratory ailments.



CRH may also be beneficial in growing ornamental plants. It can keep infections caused by

parasitic organisms at a minimum. When mixed with compost, CRH is an ideal substance for the

germination of high-priced ornamental plant seeds.

8. A CASE STUDY ON HUSK POWER SYSTEMS

Husk Power Systems is a rural empowerment enterprise. It was started by Gyanesh Pandey and

Ratnesh Yadav in Bihar in 2007.Husk Power Systems aims to generate and distribute electricity

through a renewable, sustainable, low-cost, and environmentally friendly mode in order to meet

the needs of rural India.

8.1 Working Design

The HPS model leverages easily accessible, generally discarded, rice husks to produce clean,

efficient, safe and low cost electricity through a biomass gasification process. Today, each mini

plant supplies power to 400 households. The electricity produced through the rice husk

technology acts as an alternative to the 42,000 litres of kerosene and 18,000 litres of diesel

otherwise used per year. HPS expects to cut 750,000 tons of carbon emissions and save 50

million US dollars for over five million people by deploying clean, safe, efficient electricity at

affordable rates by 2014.

Figure 10 : Generation and Distribution Process



Each power plant operates on a 35 to 100 kilowatt generator. Woody biomass, rice husk, food

scraps and coal are put inside the metal plant. There is a heater at the bottom of the gasifier

where partial burning of the raw material takes place and results in gas production. Efficiency of

conversion varies between 60 to 85 percent depending upon the type of gasifier design and fuel

used. The heating temperature of the gasifier is maintained at 400 to 500 degrees Celsius in an

atmosphere of less than 1 percent oxygen. Gases are then produced with rice char, a by-product

of the process. The chamber mouth is attached with a venture, a kind of water fountain that

works as a gas cleaning cum cooling system, which creates pressure to separate char, gas and

dust particles from the gas. Four filters are attached to the end to assist in the process: a water

seal, a three-stage gas filter including one for charcoal, another for husk, and the last for fabric.

A spark ignition engine and two lead acid batteries are used to crank the engine and power the panels.

The plant also accommodates a husk and tar/char storage area, a water tank with hand operated

water pump, char and tar water settling tanks and water recycling pumps.

With 50 kilograms of rice husk loaded per hour, enough power can be produced to sustain a load

for 700 rural households. Husk Power now provides six to seven hours of electricity every day.

The distribution system of HPS delivers electricity as a ‘pay for use’ service using a point to

point system connecting each household or business unit to HPS. There are plans to expand the

distribution system significantly in near future. Electricity is generated in three phases - each

phase produces 230 volts (one volt constitutes one distribution circuit).

The distribution grid has single phase lines and does not use transformers. The extension of the

grid is up to 1.5 kilometers ensuring 190 volts at the furthest point of the grid. HPS wires villages

in a cost-effective manner through the use of bamboo poles and low voltages wires and

recommends using energy saving CFL bulbs.

Every operational unit includes an operator, a bill collector cum electrician, and a husk loader.

The operator lives on the plant premises and the electrician cum bill collector is from the local

village. The husk loader is a daily wage worker. HPS complies with labour laws to ensure



favourable working conditions for all of its employees. HPS monitors electricity consumption by

ensuring frequent visits by bill collectors to operating sites. If misuse or overconsumption is

evident, the connection is suspended and a fine of Rs 10 is imposed for restoration.

8.2 Research by OneWorld on HPS

The OneWorld research team identified Husk Power Systems as a best practice as it was found to

be socially and economically sustainable and capable of creating a change in the rural power

sector of the country.

The OneWorld team conducted both primary and secondary research. Desk based research

focused on gathering information available online on the background, operations and

achievements of Husk Power Systems. To fill in all remaining gaps, the CEO was approached

with an interview questionnaire.

Many parts of rural India are still struggling with electrification. This research attempts to

elucidate the important aspects of operation of a successful energy model to encourage its

replication.

HPS is a revolution in progress that attempts to channelize the largely dissociated efforts of

various stakeholders - communities, investors, entrepreneurs, businesses, government and the

society at large - to bring the worldwide impoverished and under-served rural population from

the bottom to the top of the list of priorities.

9. CONCLUSION

Rice husk has so many well established uses. It is a waste where large quantity is generated,

especially in Asian countries. RHA as mentioned has good market value. Developing countries

should not only install power plant to generate electricity but a very high quality RHA as well

that will further increase the financial benefits and help to improve farm economy indirectly

making rice husk a usefully disposal waste.



10. REFERENCES

(1). M.R. Giddel and A.P. Jivani, “Waste to Wealth - Potential of Rice Husk in India a Literature

Review”, Proceedings of the International Conference on Cleaner Technologies and

Environmental Management PEC, Pondicherry, India( January 4-6,2007) pp.586-590

(2). M. O. Oliveira, J. M. Neto1, M. C. Inocencio1, O. H. Ando Junior1, A. S. Bretas and O. E.

Perrone, “Viability Study for Use of Rice Husk in Electricity Generation by Biomass”,

International Conference on Renewable Energies and Power Quality(2012)

(3). Omatola K.M and Onojah A.D, “ Rice Husk as A Potential Source of High Technological

Raw Materials: A Review”, Journal of Physical Sciences and Innovation Volume 4(2012)

(4). Thipwimon Chungsangunsit1, Shabbir H. Gheewala1 and Suthum Patumsawad,

“ Environmental Assessment of Electricity Production from Rice Husk: A Case Study in

Thailand ”, Electricity Supply Industry in Transition: Issues and Prospect for Asia (14-16

January 2004)

(5). oneworld.net, “ Husk Power Systems”, OneWorld Foundation India(December 2010)

(6). Ajay kumar, Kalyani Mohanta, Devendra Kumar and Om Parkash, “ Properties and

Industrial Applications of Rice husk: A review”, International Journal of Emerging

Technology and Advanced Engineering (Volume 2, Issue 10,October 2012)

Documents

rice husk based power plants