DEVELOPMENT AND EVALUATION OF CARBONIZER FOR COAL ASH PRODUCTION FROM RICE STRAW

DEVELOPMENT AND EVALUATION OF CARBONIZER FOR COAL ASH PRODUCTION FROM RICE STRAW

Khater, I.M.M. and Ehab Elsayed Abdelrehim

Soil Cons. Dept., Desert Research Center,

Mataria - Cairo - Egypt.

ABSTRACT

This study was carried out to develop and evaluate a coal ash production of developed carbonizer from rice straw to overcome its burning, decrease CO₂ emission and decrease the time for producing coal ash as a soil conditioner. The effect of rice straw (chopped and un-chopped), at moisture content (10.03, 12.13 and 15.20% (w.b.), air velocity (0.5, 1.0, 1.5 and 2.0 m/s) and rice straw weight (10, 20, 30 and 40 kg) on carbonizer productivity. Also, study the effect of operating parameters such as burning time, burning rate, air flow and carbon dioxide emission. The results showed that, the optimum operating conditions of the developed carbonizer was at raw materials moisture content of 10.03% (w.b.) and air velocity of 2 m/s. Where, it gave carbonizer productivity of 2.79 and 2.37 kg/h, for chopped and un-chopped rice straw, respectively. Moreover, the optimum operating conditions gave the best results as well as burning time of  5.58 and 7.68 min, burning rate of about 4.66 and 4.22 kg/min, air flow of 0.71 and 0.62 m³/min and carbon dioxide emission of 5.56 and 7.03 for chopped and un-chopped rice straw, respectively. It was clear from the results that the use of carbonizer with the development of an air flow system leads to a reduction in carbon dioxide emissions, increasing in disposal of rice straw and obtaining a good soil conditioner.

INTRODUCTION

Coal ash is the product of incomplete combustion of biomass in the existence of oxygen. Its also rich in carbon, has ability to store carbon in the soil for hundreds to thousands of years, then leading to a significant reduction in atmospheric greenhouse gas levels (Lehmann et al. 2017). By improving the methods for disposal of agricultural wastes and producing additional benefits, the use of rice straw as a soil conditioner can improve sustainability, increase productivity, decrease pollution (fertilization effect from char byproduct), and help decreasing CO₂ emissionthrough the environment. Moreover, its presence in the soil improve soil water retention, (Asai et al., 2019). (Zimmerman 2018) reported that, most coal ash research considers on the duration for reaching temperature wide range from 250 to 650^° C. The development of local technical solutions that enable parallel reductions in air pollution and greenhouse gas emissions, introduce mechanization alternatives, improve nutrient return and use efficiencies are essential considerations (Orge et. al., 2015). Preliminary research by (Zhang et al. 2016) on the application char found significant rice yield increases (between 8.8% and 14%) with various levels of coal ash additions, reducing N₂O emissions by (21-51%).It is normally produced char from wood through the use of charcoal piles, earth kilns, or pit kilns. These traditional kilns do not have good insulation. Large heat loss occurs during long period of operation. Major fraction of biomass is used as fuel for burning to sustain the pyrolysis process. It is generally known that current practice of charcoal production, especially by local entrepreneurs, is inefficient and entails large energy loss. Long process time, poor process control, low coal ash gain and environmental pollution problems due to the release of pyrolysis gases into the atmosphere (Nakorn et al., 2010). Development for new designs to improve performance of charcoal kilns have been introduced (Patil et al., 2013). Efficiency and emissions of coal ash making systems can be improved by installing proper insulation, improving process control and burning pyrolysis gases inside the reactor to provide process heat.

The objectives of this research work were as follows: developing and evaluating a coal ash production carbonizer to overcome the problem of smokes during the rice straw burning process, decrease duration of burning, CO₂ emission and increase the carbonizer productivity.

MATERIALS AND METHODS

The present study was accomplished at private workshop in Wadi El Molak –Sharkia Governorate.

Char production carbonizer:

A portable coal ash carbonizer was operating at high sufficient temperature reached to 370° C to enable useful heat recovery with minimal user intervention. Therefore, smokeless release. The construction and specification of coal ash production carbonizer were shown in (Fig. 1 and table 1).

a- Cylindrical chamber:

 A perforated barrel was used, made of stainless steel sheet and having a cylindrical shape. The chamber works as a combustion  chamber for burning and carbonizing the wastes 

b- Exhaust tube (chimney):

 It was made of stainless steel sheet and fixed vertically to works as chimney for release the pressure resulted from pyrolysis gases continuously.

c- Base stand:

Four base stands were used to fix down the char production carbonizer. The raw materials (chopped and un-chopped rice straw) dropped inside the cylindrical chamber discharged as coal ash from removed gate.

Fig. 1: Coal ash carbonizer views.

Table (1): Specifications of char production carbonizer.

Suggested modifications:

A stainless tube was linked to the exhaust tube (chimney) outlet hole and attached with an axial flow fan with five blades which fixed inside the exhaust tube for air suction through the cylindrical combustion chamber and push air flow with the pyrolysis gases into the cylindrical combustion chamber continuously . Specifications of motor are 220-230 v for voltage, 50-60 Hz for frequency, 16 W for power, 0.5 A for current and 1300-1550 rpm for speed ​​spin. The modified air flow and pyrolysis gases was  illustrated in Fig.(2) was suggested to increase the ability of burning and carbonizing the wastes by using a wider range of heat flux, air flow and pyrolysis gases.

Waste component:

Chopped (5 cm) and un-chopped rice straw were used as the major air polluted after harvesting rice in Egypt.

Fig. (2): The modified pyrolysis gases and air flow into cylindrical combustion chamber.

Studied Factors:  

Performance description of the modified pyrolysis gases and air flow into cylindrical combustion chamber was shown by studying the influence of operating treatments as follows:

-Two types of raw waste component: Chopped (5 cm) and un-chopped rice straw.

-Three moisture content of waste component about (10.03, 12.13 and 15.20 % w.b.).

-Four air velocities of 0.5, 1, 1.5 and 2 m/s represented airflow rates of 81.61, 163.23, 244.85 and 326.46 m³/min.

-Four waste rice straw weights of (10, 20, 30 and 40 kg).

-The carbonizer temperature was kept constant at 370° C during carbonizing process, this measure was applied using temperature probe fixed to side of cylindrical combustion chamber.

- The rotational air flow was measured by a digital air flow meter.

The moisture content was determined using the oven method (at 70^o C to constant mass) according to (AOAC, 1994).

Measurements:

Burning time:

Process time is the most important aspect of carbonization. It illustrates the ability to change the wastes into coal ash when the cabnonizer reach for burning temperature of 370° C (Nakorn et al., 2010).

Burning rate:

This is the average rate that the dry rice straw consumed while bringing water to a full boil (Mensah et al., 2013)  and can be calculated as following:

Where: F_cd : amount of the dry rice straw consumed, kg; t_c: total time spent in bringing the water to full boil, hr

 Air flow:

Average air flow rate was measured at the outlet port of the blower used according to the speed used (Ricardo and John 2014). The air properties measured using the device (Fig. 3-6) model Tri-SENSE, No. 37000-00 measures temperature and air velocity. Made in USA. The range for air velocity form (0 to 25 m/s) with accuracy of (±0.2 m/s) and the range for temperature form (0 to 700 ºC) with accuracy of (±15 ºC). The anemometer (Fig. 3) model Hygro Thermo- Anemometer measures temperature and air velocity. Made in Japan. The range for air velocity form (0.4 to 25 m/s) with accuracy of (±0.2 m/s), the range for temperature form (0 to 500 ºC) with accuracy of (±8 ºC).

Figure (3): The digital instruments used for measuring air temperature and air velocity.

Figure (4): The digital instruments used for measuring CO₂ emission.

CO₂ emission:

            A CO₂ meter PCE-AQD 10 was used to measure air quality. The CO₂ meter measures carbon dioxide, temperature and humidity. The sensor from the CO₂ meter was connected to the main unit with a connection cable and readings were taken from the exhaust tube (chimney)

Productivity, Mg/h:

The productivity of the modified coal ash production carbonizer was measured as the mass of  coal ash collected per hour after burn finishing.

RESULTS AND DISCUSSION

Influence of air velocity, straw weight and moisture content on burning time:

Figures (5) and (6) illustrate the burning time related to different air velocities, rice straw weight and moisture content. Hence, by increasing drying moisture content the burning time decreased. Furthermore, it can be seen from figures that the lowest burning time occurred at the lowest moisture content and weight, but vice versa with the highest air velocity. These results may be due to at the highest air velocity exposed to more air weight and oxidization heat time compared with the low air velocity.

Fig. (5 and 6): Effect of air velocity, straw weight and moisture content on burning time for chopped and un-chopped rice straw.

Influence of air velocity, straw weights and moisture content on burning rate:

Fig. (7 and 8) shows the burning rate related to different air velocities, straw weight and moisture content. Hence, by increasing drying moisture content the burning rate decreased. Furthermore, it can be seen from figures that the lowest burning rate occurred at the highest moisture content and quantity, but vice versa with the highest air velocity.

Fig. (7 and 8): Effect of air velocity, straw weight and moisture content on burning rate for chopped and un-chopped rice straw.

Influence of air velocity, straw weight and moisture content on air flow:

Fig. (9 and 10) shows the air flow related to different air velocities, straw weights and moisture content. Furthermore, it can be seen from figures that the lowest air flow occurred at the highest moisture content and quantity, but vice versa with the highest air velocity. These results may be due to at the highest air velocity exposed to more air quantity, while the highly moisture contents and straw weight create a vapor media in the combustion chamber which resist the air current through the carbonizer. 

Fig. (9 and 10): Effect of air velocity, straw weights and moisture content on air flow for chopped and un-chopped rice straw.

Influence of air velocity, straw weights and moisture content on carbon dioxide emission:

Fig. (11 and 12) shows the carbon dioxide emission related to different air velocities, straw weight and moisture content. Hence, by increasing drying moisture content the carbon dioxide emission decreased. Furthermore, it can be seen from figures that the lowest carbon dioxide emission occurred at the highest moisture content and quantity, but vice versa with the highest air velocity. These results may be due to at the lowest moisture content released less vapor which help to release more pyrolysis and consequently more carbon dioxide emission.  

Fig. (11 and 12): Effect of air velocity, straw weights and moisture content on carbon dioxide emission for chopped and un-chopped rice straw.

Influence of air velocity, straw weights and moisture content on productivity:

Fig. (13 and 14) illustrates the carbonizer productivity related to different air velocities, straw weight and moisture content. Similarly, for un-chopped rice straw as shown in figure (14), increasing air velocities from 0.5 to 2.0 m/s, the carbonizer productivity increased from 1.59 to 2.37  and 1.53 to 2.09 %. at straw weight of 10 and 40 kg respectively. Hence, by increasing drying moisture content the carbonizer productivity decreased due to the low time consumed for burning, but vice versa with the highest air velocity.

Fig. (13 and 14): Effect of air velocity, straw weights and moisture content on carbonizer productivity for chopped and un-chopped rice straw.

CONCLUSION

The collected data from the present study can be summarized as follows:

- The optimum operating conditions gave the best burning time was 5.58 and 7.68 min, burning rate about 4.66 and 4.22 kg/min, and air flow of 0.71 and 0.62 m³/min for chopped and un-chopped rice straw respectively, at moisture content of 10.03 %, air velocity of 2 m/s and quantity of 10 kg.

- The carbon dioxide emission of 11.12 and 14.07 %, seems to be acceptable, for chopped and un-chopped rice straw respectively, under the optimum operating conditions at moisture content of 10.03 %, air velocity of 2 m/s and weight of 40 kg.

- The machine productivity of 2.79 and 2.37 kg/h, seems to be acceptable, for chopped and un-chopped rice straw respectively, under the optimum operating conditions at moisture content of 10.03 %, air velocity of 2 m/s and weight of 40 kg.

REFERENCES

AOAC, Association of Official Analytical Chemists (1994). Official methods of analysis 20th ed, Artington, VA.

Asai, H. ; B.K. Samson ; H.M. Stephan ; K. Songyikhangsuthor ; K. Homma ; Y. Kiyono ; Y. Inoue ; T. Shiraiwa and T. Horie (2019). Biochar amendment techniques for upland rice production in No