دراسة جدوى لشركة استثمارية اجنبية لتصنيع الكربون النشط من قش الارز فى مصر(النسخة الانجيليزية)

rice husk pollution problem

•Rice husk is one of the most important pollution problems which affect Egypt weather because the farmers shun it burning, leading to a black cloud and in particular, on the Delta and up to the capital.
It is possible to take advantage of the agricultural waste and convert it into useful products such as fertilizer, paper, active carbon and other materials useful for the environment.

by
colonel.dr
bahaa badr
sceintific advisor
rice husk

Rice husk Burning rice husk
Rice hus ash (RHF) Carbonized rice husk (CRH)

What is rice husk?

The outermost layer of the paddy grain is the rice husk, also called rice hull. It is separated from the brown rice in rice milling. Burning rice husk produced rice husk ash (RHA), if the burning process is incomplete carbonized rice husk (CRH) is produced.

Importance of 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 therfore 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.

Production of rice husk

Rice husk is produced in the first step in the milling process when the husk is removed form the grain in the husking stage of the rice mill.

Characteristics of rice husk and RHA

Rice husk is difficult to igninte 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 foder
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 burned the ash content 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 an 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 behavior of the ash, i.e., its slagging and fouling tendency caused by a low melting point of the rice husk ash.

Utilization of rice husk and rice husk ash

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 purposes.

Typical uses fo rice huskNon 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
- electicity generation from steam turbines
- kinetic energy from steam engines
Depending on the energy conversion efficiency the final product can be either white rice husk ash or black carbonized rice husk.

Description

White, fine structure
Contains around 85-90% amorphous silica
around 25% of the weight of husk
Black, often still in the shape of the husk
Depending on the combustion still contains 8-15% carbon

Use

Partial cement replacement material for high-strength concrete
Steel additive for quality steel or "tundish powder in steel production.

Used in manufacturing of refractory bricks
Insulators
Activated carbon
Soil conditioner for poor soil
Carbon sequestration, bio char
Charcoal as fuel

Examples for non-energy applications

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 pretreated with 12% NaOH to reduce the silica content from 19 to 3-4% to improve digestibility and used as animal feed.

Examples for energy applications

Cook stoves
Simple rice husk cook stoves are used for a long time in the Greater Mekong Subregion.

The origin of the desing is unkown, 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. Commerical applications exist in the Philippines and in India.

Rice husk cook stove in Myanmar

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.
e.
Mechanical power generation

In Myanmar rice husk is still 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 electicity 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 expecially in Cambodia rice millers have installed several units with 20-70 kW capacity.

Electricitiy generation

Small scale applictions between 10-200 kW usually use a rice husk gasifyer 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.

Utilization of carbonized rice husk

Studies conducted by (Haefele et al., 2008) indicate that the bio-char produced by small scale energy applications through incomplete combustion, can improve poor soils but may have little effect on fertile soils, but also lower CO2 emissions.


Rice hulls

Rice Hulls

Another term for rice husks is rice hulls. As far as non-edible properties, rice hulls are probably the most useful part of the plant.

The hull is the strong protective covering of the grains. The hulls are high in lignin and silica, which give them their strength and also make it very useful in a variety of industries. They are a byproduct of processing so they are a very inexpensive material.

They are a good source of fiber and though humans don't eat them, they are not entirely indigestible, making them a great cheap pet food.

Another property of rice hulls is that they are very difficult to burn and let in moisture due to their natural protective qualities. These properties allow rice to act as a great insulator.

Rice hulls are also very useful in the compost industry. Rice hulls are a great example of a way to use every part of the food we farm even if we don't ingest it ourselves.

Rice hulls (or rice husks) are the hard protecting coverings of grains of rice. In addition to protecting rice during the growing season, rice hulls can be put to use as building material, fertilizer, insulation material, or fuel.Contents
Production

Rice hulls are the coating for the seeds, or grains, of the rice plant. To protect the seed during the growing season, the hull is made of hard materials, including opaline silica and lignin. The hull is mostly indigestable to humans.

One practice, started in the seventeenth century, to separate the rice from hulls, it to put the whole rice into a pan and throw it into the air while the wind blows.

The hulls are blown away while the rice fell back into the pan. This happens because the hull isn't nearly as dense as the rice. These steps are known as winnowing. During the milling process, the hulls are removed from the grain to create brown rice, the brown rice is then milled further to remove the bran layer to become white rice.


At the processing plant, the rice is cleaned and hulled. At this point, brown rice needs no further processing. If white rice is desired, the brown rice is milled to remove the outer bran layers. Hulling is the process to remove the hull from the kernel.
Hulling can be done by hand by rolling or grinding the rough rice between stones. However, more often it is processed at a mill with the help of automated processes.

The process of mechanical hulling

The rough rice is first cleaned by passing through a number of sieves that sift out the debris. Blown air removes top matter.

Once clean, the rice is hulled by a machine that mimics the action of the hand held stones.

The shelling machine loosens the hulls from the rice. About 80-90% of the kernel hulls are removed during this process.

From the shelling machine, the grains and hulls are conveyed to a stone reel that aspirates the waste hulls and moves the kernels to a machine that separates the hulled from the unhulled grains.

By shaking the kernels, the paddy machine forces the heavier unhulled grains to one side of the machine, while the lighter weight rice falls to the other end.

The unhulled grains are then siphoned to another batch of shelling machines to complete the hulling process.

Hulled rice grains are known as brown rice.

Use

A number of rice-producing countries, (e.g. Thailand), are currently conducting research on industrial uses of rice hulls. Some of the current and potential applications are listed below.

Chemistry

Rice hulk can be used to produce mesoporous molecular sieves (e.g., MCM)[1][2], which are applied as catalysts for various chemical reactions, as a support for drug delivery system and as adsorbent in waste water treatment.

Pet food fiber

Rice hulls are the outermost covering of the rice and come as organic rice hulls and natural rice hulls. Rice hulls are an inexpensive byproduct of human food processing, serving as a source of fiber that is considered a filler ingredient in cheap pet foods

Building material

Rice hulls are a class A insulating material because they are difficult to burn and less likely to allow moisture to propagate mold or fungi. It has been found out that when burned, rice hull produces significant amounts of silica. For these reasons it provides excellent thermal insulation.

Pillow stuffing

Rice hulls are used as pillow stuffing. The pillows are loosely stuffed and considered therapeutic as they retain the shape of the head.
Fertilizer

Rice hulls are organic material and can be composted. However, their high lignin content can make this a slow process. Sometimes earthworms are used to accelerate the process.

Using vermicomposting techniques, the hulls can be converted to fertilizer in about four months.
SiC production
Rice hulls are a low-cost material from which silicon carbide "whiskers" can be manufactured. The SiC whiskers are then used to reinforce ceramic cutting tools, increasing their strength tenfold

Fuel

With proper techniques, rice hulls can be burned and used to power steam engines. Some rice mills originally dispose of the hulls in this way
Brewing

Rice hulls can be used in brewing beer to increase the lautering ability of a mash.
Juice extraction

Rice hulls are used as a "press aid" to improve extraction efficiency of apple pressing.[4]

Rice husk ash

The ash produced after the husks have been burned, (abbreviated to RHA), is high in silica. A number of possible uses are being investigated for this.

These uses include
aggregates and fillers for concrete and board production
economical substitute for microsilica / silica fumes
absorbents for oils and chemicals
soil ameliorants
as a source of silicon
as insulation powder in steel mills
as repellents in the form of "vinegar-tar"
as a release agent in the ceramics industry
as an insulation material for homes and refrigerants

Activated carbon production. Equipment
Boiler
Gas holder
Drying equipment
Fuel granules production press
Granule press for production of activated carbon
Mixer. Two-shaft mixing machine
Elevator
Stoves
Nitriding bath
Conveyor
Self propelled pnematic lift LCUD-2000\HD
LSUGHJ-P5W Packing section
Batching device
Feeding and clearing of raw materials
Stove for thermal-acidic treatment of activated carbons
Other units
Packing of activated carbon
Conveyors
Hoppers
Mixers and attritors
Packing of granules
Screens
Elevators
Crushers
Movable lifting units