CHAPTER 3: MATERIALS AND METHODS
3.2 MATERIALS
3.2.4 Rice Husk Ash
3.2.4.2 Rice husk ash production
Rice I tusk Ash obtained from the uncontrolled incineration process was used as cement replacing materials in this study. Rice husk Ash samples were produced from three different types of incineration system. These were subjected to various tests to analyze the Blai ne surface area, state (aniorphous/crystaline), loss of ignition and chemical composition. A good quality of ash was chosen as cement replacing material after analyzing the ashes. Subsequently, these ashes were used for casting the specimen. There are mainly three types of burning process as follows:
1-leap Burning
Conventional Burning System Laboratory Burning System
(i) Heap burning system
In this system, huge amount of Rice Husk were stored in a place and burnt with the help of rice husk briquette. There were no controlling systems present in this burning process. The heap was 2 m x 2 m and 0.5 rn in height. Fired rice husk briquettes were placed in different point of the heap. The fired briquette was 150 mm long and 50 mm in dia. Schematic view of heap burning process is shown in Figure 3.3.
I-'
2.0 in 125mm
2.0 in
125 mm
125mm
a
Connecting wire
I25i
X PT10O
X-X Section
o
Fired rice husk briquette• Temperature sensor Figure 3.3: Heap burning system in laboratory
The burning of rice husk was allowed to start from the middle of the heap. Burning occurred from the fired husk briquette in all direction. It took almost four days for complete burning and si rn ultaneous cooling of the sample. Temperature probes were placed at different locations on the heap to obtain the actual temperatures in respect to time. All the temperature sensors were placed at 125 mm away from the fired briquette and collected the temperature history of the husk heap as shown in Figure 3.3. The ash sample was collected and sieved through sieve No. 200 after grinding and denoted as RHA I.
(ii) Conventional burning system
The parhoiling system consists of mainly two parts, one of which is the steam generation unit (steam vessel and furnace) and other part is steaming bin for parhoiling paddy. Steaming bin is connected with the steam generator with a steam pipe (Figure 3.4). This type of rice parboiling systems is mostly available in Bangladesh. In practical field, a part of the combustion chamber is situated below the ground level. There is opening in the side wall of combustion chamber for entry of air.
Open front
CflCi for fee cling of Rice Husk
Spigot for
water Elling
Steam gonerator
Combustion chamber
Soal&g house
Open encl or to connected with a chimneey
Ste mng
bin
Steam outlet
Figure 3.4: Schematic diagram of a conventional rice parboiling system Rice husk was fired in the combustion chamber for the parboiling process of rice and linally ash produced by burning of rice husk is known as rice husk ash. The ash samples were collected from different locations of Khulna, Rajshahi and Dinajpur districts of Bangladesh. The colour of collected ash was light blackish grey. The
-
r collected ashes was kept in oven at 100°C for 6 hours and then ground in aX14—i r-+X2
Feed ii
laboratory ball mill for different durations of time. Subsequently the ash was sieved -r through No. 200 Sieve. The ash (RHA 2) passing through the sieve was collected for
further laboratory investigations.
(iii) Laboratory Burning System
The rice husk ash produced in laboratory incineration system is designated as RHA 3. A rectangular enclosure of 2.05 in long and 0.9 in wide was divided into ignition and ash accumulation chamber by a steel wire mesh of 5 mm square opening. The ignition chamber was 0.65 in wide and 0.6 in deep and that of the accumulation chamber was 0.4 in and 0.4 in respectively. The wall thickness of the bottom portion was 0.375 in and that of the upper portion was 0.25 in. There were numbers of small opening (75 mm x 75 mm) in this wall. The detailed of this chamber is shown in Figure 3.5. The produced ash is deposited at the accumulation chamber and it was kept for long time (3, 6, 12, 24, 36, 48 and 60 hrs.) without any disturbance. At first, some small pieces of fired rice husk briquette were placed over the wire mesh and dried rice husk was continuously thrown over it. This throwing system was same as the rice parboiling industry in Bangladesh. The ignition system was developed within 20 to 30 minutes. In this laboratory ignition system the rice husk feeding process was slow in comparison to the existing system of Bangladesh.
1
250 mm(]I400 mm Back Wall
- 375 mm '—*X2
PLAN
CI Sheet Cl Sheet
75 mm x 75 inin Ignition
0.6 in
/ Chambei //
\reMesli I 250 mm Brick Wall
W/ 2
. , 0.4 in
375 mm Buck Wall
Section Xl -x I Section X2-X2
Figure 3.5: Diagram of laboratory burning system
Alter some times of the firing, the fired husk stored in the accumulation chamber through the mesh. The rice husk size was shrinking after the firing. The top part of the kiln was closed by a steel sheet and the opposite side of the feeding of the kiln was partially closed to confirm the field condition. Before starting the firing operation, a series of thermal sensor of pt-100 type was placed at ignition and accumulation chamber. Average temperatures of ignition and accumulation chamber were termed as firing and cooling temperature. Temperature readings were continuously collected at regular interval.