A STUDY ON FACTORS THAT AFFECT ON THE FIXED BED GASIFICATION PROCESS NGHIÊN cứu một số yếu tố ẢNH HƯỞNG đến QUÁ TRÌNH KHÍ hóa TRẤU TẦNG cố ĐỊNH

A STUDY ON FACTORS THAT AFFECT ON THE FIXED BED GASIFICATION PROCESS NGHIÊN CỨU MỘT SỐ YẾU TỐ ẢNH HƯỞNG ĐẾN QUÁ TRÌNH KHÍ HÓA TRẤU TẦNG CỐ ĐỊNH Hoang An Quoc1a, Nguyen Vu Lan1b, Nguye

A STUDY ON FACTORS THAT AFFECT ON THE FIXED BED

GASIFICATION PROCESS

NGHIÊN CỨU MỘT SỐ YẾU TỐ ẢNH HƯỞNG ĐẾN QUÁ TRÌNH KHÍ HÓA TRẤU

TẦNG CỐ ĐỊNH

Hoang An Quoc1a, Nguyen Vu Lan1b, Nguyen Thanh Quang2, Nguyen Ngoc Tuyen3c

1HCMC University of Technology and Education, HCMC, Vietnam

2HCMC University of Technology, HCMC, Vietnam

3Industrial University of HCMC, HCMC, Vietnam

ahanquoc@hcmute.edu.vn; blannv@hcmute.edu.vn; ctuyen.vinalpg@gmail.com

ABSTRACT

The rice husk gasification technology in Vietnam has been focusing on applications inlife and industrial production.This article presents an experimental investigation on impacts

of two key system variables, air speed in the incinerator and humidity of rice husk fuel, on the system efficiency Results have shown that higher humidity of input husk fuel will lead to lower system productivity or may even stop the burning process Meanwhile, only at a specific suitable and limited inlet air velocity range can the overall gasification efficiency reach to its maximum value

Keywords: fixed bed gasification; biomass gasification; gasification technology; rice

husk gasification

TÓM TẮT

Công nghệ khí hóa trấu ở nước ta hiện nay đang được quan tâm và đưa vào ứng dụng trong đời sống và sản xuất Bài báo này giới thiệu nghiên cứu thực nghiệm về ảnh hưởng của hai tham số chủ yếu của hệ thống, tốc độ khí trong lò đốt và độ ẩm của nhiên liệu trấu, tới hiệu suất của hệ thống khí hóa trấu tầng cố định Kết quả chỉ ra rằng độ ẩm của trấu đầu vào càng cao thì hiệu suất sinh khí càng thấp thậm chí sẽ dẫn đến việc ngừng quá trình cháy của

hệ thống.Trong khi đó, chỉ ở một khoảng giá trị vận tốc khí đầu vào nhất định thích hợp thì hệ thống mới có thể đạt hiệu suất cao nhất

Từ khóa: khí hóa tầng cố định; khí hóa biomass; công nghệ khí hóa; khí hóa trấu

1 INTRODUCTION

In the current situation of energy shortage, running out fossil fuels and increasingly serious environmental pollution caused by fuel waste emissions, solutions utilizing renewable energy resources are of special interest [1,2].Vietnam is the leading rice-producing country in the world and thus the amount of rice husk coming from the rice-processing factory is extremely large Therefore, the husk gasification technology has been focused ondevelopment

in the recent years in order to make use of this huge energy source Besides, with great advantages of simplicity in manufacturing and relatively low cost, the fixed bed gasification technology is being applied primarily nationwide

The fixed bed gasification method with the advantage of being easy for fabrication, low initial investment cost is being mainly applied in the country at present [3~6] However, the capacity of this system is not yet high leading to a limited efficiency To improve the productivity of the gasification system, the determination of the influence of the inputs onperformance of the system is extremely important This paper introduces a study of the

influence of gas velocity in the burner and the rice husk moisture to the performance of fixed bed rice husk gasification system

2 FUNDAMENTAL THEORY

2.1 Gasification process

Gasification processis an incomplete burning of solid fuels In general, biomass fuels areburned completely to produce heat and some normal products including N2, water steam,

CO2 and redundant O2 However, in gasification process, it is thesolid fuels to be redundantly supplied In other words, the combustion is always lack of O2 As a result, the obtained gaseous product is a mixture of CO, H2, CH4 which are flammable gases and several useful components such as tar and dirt

2.2 Main reaction equations in gasification

In most of the cases, the following chemical reactions may take place in the gasification process:

3 EXPERIMENT MODEL AND METHODOLOGY

3.1 Experiment Equipment

Figure 1 Principle diagram

The experimental model was designed and manufactured according to the principle diagram shown in Figure1 Rice husk was continuously supplied from the feeder through a screw into the combustion chamber To ensures table temperature and avoid heat loss, combustion chamber was covered thoroughly by glass fiberlayers After gasification process had taken in the burner, the gas was filtered through acyclone and then blown into cooler sandtar filters Finally, the gas was dehumidified before moving to the burner’s nozzle

3.2 Input data and analysis

The following parameters were used to analyze the performance of the gasification system:

- Air velocityin combustion chamber Va [cm/s]: Because of the lack of special equipment, this parameteris calculated in directly via the airflow at the output of the blower

- Huskhumidity Hu [%]: Humidity has a great influence on combustion process, so in

the gasification system, the moisture of the fuel is a vital parameter Relative humidity of the material is as the ratio between the amount of moisture contained in the material and the volume of material

- Heat total value Qh [Kcal]: Heat total of husk is calculated basing on the weight of consumed husk mh [kg] and the heat value per each mass unit of the husk qh[Kcal/kg] as shown in Eq.(9)

- Useful heat Qu [Kcal]: is the heat received when burning the gaseous product Using this value and the Heat total value, one may infer the efficiency of the gasification process by Eq.(10)

4 RESULTS AND DISCUSSION

4.1 Effect of air velocity in the combustion chamber

In order to figure out the relationships between Va and the overal system performance, related experiments were done to show the variation trend of the system performance due to increment and decrement of the gas velocity in the combustion chamber Rice husk was taken from the milling plant and left untreated; fan speed to blow air into the combustion chamber was adjusted in the range of 1÷10cm/s and initial volume of heated water was 5kg each time The experiments were conducted with 7 different values of Va to collect data The collected results are shown in Table 1 and Figure 1 It is important to notice that due to lacking of highly precise measuring equipment to be located at different measuring positions inside the chamber, the obtained measurement values of this experiment are not enough to show specific performance figures corresponding to different values of velocity Interestingly, it has been found that the system performance was at its maximum when the velocity varied from 2.5÷5cm/s (maximum at 4.05cm/s) and decreased when Va was out of this range The reason could be when air velocity was too low or too high, there was insufficient interacting time between the solid fuel pieces and the air Therefore, the gasification process reached to its best efficiency only within this most suitable limited air velocity range

Table 1.Influence of air velocity in combustion chamber Experiment Air velocity Va

[cm/s]

Husk heat level

Qh [Kcal]

Useful heat Qu

[Kcal] Capacity  [%]

3 4.05 3,397.68 509.65 15.00

4.2 Effect of humidity husk

The dependence of the process efficiency on humidity of input fuel was tested by some other experiments in which air velocity was fixed at the above-mentioned best value, initial volume of heated water was 5kg each time and 5 husk samples with humidity value from 10 –

40 % were investigated The results are shown in Table 2 and Figure 2 As explained above, these results revealed the variation trend of this relationship The higher the humidity was, the more difficult for ignition process and gasification, thus, the lower the system efficiency If the humidity was too high, the equipment was unable to operate and the gasification could not take place Obviously, it was the large amount of water stored inside the input fuel prevented the flame of gasification Although the lower humidity the better performance, the lower humidity requires more initial treatment which in turn need extra energy consumption That means this humidity preparation will pull down the overall efficiency Besides, the humidity value depends very much on geographic location and climate condition of the application cite Accordingly, a further research on an opitimized working condition should be done to ameliorate the current gasification process

Table 2 Influence of humidity in combustion chamber Experiment Humidity Hu

[%]

Husk heat level Qh

[Kcal]

Useful heat Qu

[Kcal]

Capacity 

[%]

Figure 2 Velocity - Efficiency Chart

0.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00 16.00

Velocity cm/s Velocity - Efficiency Chart

Figure 3 Humidity - Efficiency Dependence

Figure 4 Pictures of gasification model

5 CONCLUSION

Fromthe experimental results, it has been proved that both inlet airspeed of the gasifier chamber and input fuel moisture strongly affect on the overall performance of the fixed bed gasification system Although this research has shown the clear relationship between each of these two parameters with the total efficiency, further research should be implemented in order to find out solutions to improve the performance of the system Moreover, to accurately investigate the system performance, it requires special equipment for analysis of gas composition and tar after burning completed

0.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00 16.00

Humidity % Humidity - Efficiency Chart

REFERENCES

[1] Bernstein, W., Hiller, A., Schneider, M., Klemm, M., Quang, N.T., Vergasung von

Biomasse, Verfahren – Transparenz – Modellierung, 20 Deutscher Flammentag Essen

2001, VDI-Berichte 1629, S.521-526

[2] Anil K Rajvanshi, Biomass Gasification, Nimbkar Agricultural Research Institute,Phaltan-415523, Maharashtra, India

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chiều, Tạp chí KH & CN Nhiệt, số 77, tháng 09/2007

[6] Quang N.T., Quốc H.A., Thông N T., Nghiên cứu khí hóa trấu lớp cố định nhằm sản

xuất điện năng, Tạp chí KH & CN Nhiệt, số 102, tháng 11/2011

AUTHOR’S INFORMATION

Author 1: Hoang An Quoc, HCMC University of Technology and Education, HCMC,

Vietnam, Email: hanquoc@hcmute.edu.vn, Phone: 0908197416

Author 2: Nguyen Vu Lan, HCMC University of Technology and Education, HCMC,

Vietnam, Email: lannv@hcmute.edu.vn,Phone: 0913522142

Author 3: Nguyen Thanh Quang, HCMC University of Technology, HCMC, Vietnam, Author 4: Nguyen Ngoc Tuyen, Industrial University of HCMC, HCMC, Vietnam, Email:

tuyen.vinalpg@gmail.com