Rice Hulls for Composites - Introduction to Polymeric Composites with Rice Hulls - page 63

5.4.7 Fuel for Steam Boilers
Most rice-producing farmers use rice hulls as fuel for their rice-mill steam boilers.
These boilers are low-pressure/low-volume and, because only small volumes of steam
are required, the rice hulls can be fed directly into the furnace through an additional
opening close to the 'peep hole'. A more important application is that rice hulls can
be used for industrial steam boilers too. I present the following case study from actual
design and practice.
5.4.7.1 Case Study
Products : Expanded polystyrene (Styrofoam) fish boxes, insulation board, fishing
floats and hot/cold containers.
Output : 2 metric tonnes per month.
The basic equipment was a block mould, separate moulds for all items, and a hotwire
cutting machine. All moulds were connected through steam lines to a steam boiler with
specifications of 100 psi and steam volume of 500 lbs steam/hour. Use of diesel oil as
fuel proved to be expensive and an alternate fuel had to be found. After some research
and experimentation, a method was found on how to use rice hulls in the natural
state. The rice hull feed design contained a pipe (diameter, 3 inches; and length, 5 feet)
with a flange at one end attached to a blower motor turning at 3,000 rpm. Halfway
along the pipe was an opening in which a hopper with a control valve was mounted.
The other end of the pipe opening had an elbow bend containing an adjustable nozzle
that was connected through a flange to the base of the boiler furnace. Rice hulls were
introduced into the hopper and the blower motor started. Rice hulls were blown along
the pipe, with the stream controlled by the valve, and a cascade effect was created
inside the furnace. To promote initial ignition, a small amount of kerosene oil was
sprayed onto the cascading rice hulls and the whole mass ignited. By good control
of stream using the control valve in the hopper, a sustained and continuous fire was
achieved. An immediate reward was a reduction in the cost of the boiler fuel by 90%.
5.4.8 Rice Hulls in Fertilisers
Rice hulls are a renewable resource of fertiliser. Rice hulls in fertiliser can recycle
nutrients and eliminate wastes. Using rice hulls and rice hull/manure composts and
vermicomposts improve the fertility, organic matter, physical properties and structure of
soil over long periods. Rice hull composts are especially useful for boosting the humus
content of the organic matter of soil, thereby providing a long-term source of nutrients.