Abstract
Introduction
System design principle and test apparatus
Results and discussion
Conclusions
Zhang Baozhao
Xu Yicheng
China National Rice Research Institute, Hangzhou, 310006, China
Paper No.9403
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The 25 cm diameter gasifier developed by the University of California at Davis was matched with a Chinese S-195 diesel engine to characterize the performance of Gasifier-Engine System. An average gas flow of 18.44 Nm³/h, cold gas efficiency of 52.4 % of the gasifier and output of 5.59 kW which was 63.37 % of that rated diesel power, brake thermal efficiency of 0.306 of the dual fueled engine were obtained at a rated engine speed. A 60 hour continuous test of this system for pumping water was conducted with satisfactory results. However, the environmental impact of the system should be studied. |
With current annual world paddy rice production at 518* 106 rice husks are produced, which create a significant disposal problem today (1)(4). Although some rice husks are used for fuel, the design of small rice husk gasifier for power or electricity generation is a lost art (5).
The present work involves further development on adapting the UC, Davis designed rice husk gasifier which was coupled to a Chinese diesel engine with dual-fueling operation.
The gasifier consists of an inner tubular steel shell reactor of 25 cm diameter, open at the top and closed at the lower end by a stainless steel mesh screen (Fig. 1) . It was housed within a concentric 35 cm gas collector. The lengths of reactor and collector are 168 and 183 cm respectively for one hour continuous operation. Air enters the reactor at the open top and passes downward through the fuel column to the reaction zone when under suction from engine intake system. The gas from the reaction zone flows in the reverse direction to the hot outlet.
Raw gas is passed through a wet sieve plate (scrubber and particulates). The twin reactor design enables the engine to draw from one reactor while the other is being serviced. The reactor gas flow of >Nm ³/h was supplied to the engine. The test engine is a single cylinder, naturally-aspirated, water-cooled, four-stroke, swirl combustion chamber diesel engine. Rated power NeH at 2000 rpm was 8.82 kw. Displacement was 815 cm³ . The compression ratio was 20.1. Fuel injection timing at 17-19 °CA before top dead center (BTDC). The air-gas mixture device to give an air to gas ratio of 1.2-1.8: 1 was mounted upstream the engine manifold, a butterfly value served as an adjusting device for the mixture. The engine was connected to a D-4 hydraulic dynamometer for loading and torque measurement. Gas and air flows were measured by an XSF-4OD orifice meter and LCQ-70 flow meter, diesel fuel flow was obtained by a TE-500 sensor and a TC-500 indicator, engine speed and fuel injection timing were determined using a TRT-D2 tester. Components contained in the exhaust were detected by an ALTAS-100 analyzer using a non-disperse infrared absorption method. Components contained in the influent from the wet scrubber were detected by a Hewlett Packard GC-MS-FTIR system. The sound level of the engine was determined using a ND-2 tester.
Fig. 1. Schematic diagram of the GASOGENO system
A. Characteristics of a gasifier-purification system
The gasifier generates a nearly uniform reaction front propagating upwards at a velocity of 0.77-0.87m/h. With a temperature of the reaction front maintained at 950-1050°C, Fig.2 shows the temperature change in a certain point along the vertical center line representing the temperature of the distillation, oxidation and reduction stages. This variance in temperature is a result of the moveable reaction zone in the gasifier.
Fig. 2. Temperature change in a certain point along the vertical axle of the reactor
Gas composition is as follows (Vol%): CO13.4%, H2 11.1%, CH422%, 0221.4%, N258.9%, H2O4.13%, lower heating value (LHv) 40223.8KJ/Nm, Gas flow is 18.44 Nm³/h. Specific gas output is 2.39Nm³/kg rice husk. Specific gasification rate is 185 kg/m-h. Cold and raw gas efficiency was 52.4% and 72.2%.
Fig. 3. Parameters of gasifier-engine system during one batch running
Compaction of the char causes settling of the husks. The pressure drop d p of the system increased from 11.3 to 15.7Hpa. after one batch operation (Fig.3). The mean value of the gas outlet temperature and d p are as follows: 150 °C, 6.6 Hpa for gasifier; 90°C, 2.8 Hpa for wet scrubber; 51°C, 0.95 Hpa for packed bed filter; 46°C, 0.85 Hpa for paper element filter; 33°C before mixture device. The gas flow rate was slightly decreased when reaction front reached the top of the husk bed after some minutes of operation. No slagging of char has been observed in the reaction zone.
B. Brake performance characteristics of the dual-fueled engine
Injection timing was selected before testing to achieve smooth running, appropriate engine output (25N-m), lower pilot injection Cge=38.96g/kw-h, and good starting ability. This occurred at about 18.87o-20.49o CA BTDC at 2000 rpm.
Table 1 PImin at various engine speeds
|
n rpm |
Me N-m |
Ne kw |
NL kw/L |
h e |
PI % |
Ta °C |
Tr °C |
|
2000 |
26.57 |
5.37. |
6.58 |
0.291 |
10.21 |
22.5 |
360 |
|
1900 |
27.69 |
5.51 |
6.77 |
0.296 |
12.45 |
30.5 |
350 |
|
1800 |
25.67 |
4.84 |
5.93 |
0. 288 |
13.60 |
17.7 |
340 |
|
1700 |
22.47 |
4.00 |
4.90 |
0.238 |
1 3.97 |
25.2 |
320 |
A drop of 30-35% in brake parameters (Ne, Me) of the engine on dual fueling without modification of the engine was observed due to much lower LHV of gas, lower flame velocity, higher intake temperature Ta and worse quality of mixture (Tab.1). Brake thermal efficiency .Ç e is a little lower than that with diesel fuel alone (0.311 compared to 0.322 at 2000 rpm) . Thus .Ç e is much lower at lower engine speeds. (Fig.4)
Fig. 4. Ç e as a function of the engine load at various engine speeds
The limitation of load (Me) for dual fueling without knocking or detonation is 71.6% of rated value of diesel fuel MeH (Tab.2), while the pilot injection (PI) is 6.89% higher that the PImin value at 2000 rpm.
Table 2 Engine parameters when knocking or detonation occurs
|
n rpm |
Me N-m |
Me MeH |
P1 % |
h e |
Ta °C |
Tr °C |
|
2000 |
29.84 |
71.60 |
17.10 |
0.306 |
21.00 |
375 |
|
1900 |
27.69 |
65.94 |
17.06 |
0.269 |
21.10 |
340 |
|
1800 |
26.63 |
63 .41 |
19.14 |
0.279 |
16.80 |
340 |
|
1700 |
24 . 30 |
57 .86 |
21.17 |
0. 278 |
18 .80 |
350 |
PImin = 10.21% rated diesel injection when fueling with diesel alone and higher .Ç e (0.291) occurred at 2000 rpm, Ta=22.5°C (Tab.1). An amount of 13% rated diesel injection was recommended as optimal pilot injection for dual fueling in consideration of the stability of a small amount of fuel delivery and cooling effect on injection nozzle.
The gas consumption seems to be 3. 19Nm³/kW-h for dual fueling engine at rated speed.
The AG ratio was found to be sensitive to the engine performance. A higher PI value (>30%) was encountered with an AG ratio of 3.1-4.2 due to lower flame velocity of mixture. A range of 1.10-1.55 achieved satisfactory results (Me=27.41N-m, .Ç e =0.311, PI=10.21% (Fig.5).
Fig. 5. Pollutant emissions in exhaust gas for two fuel regimes at various torque levels
C. Environmental aspects of the gasifier-engine system
Emission of both CO and HC in the dual fueled engine exhaust were much higher than the corresponding values using diesel fuel only at lower brake load (Fig. 6), and declining at heavy load when higher combustion temperature and homogeneous mixture were available.
Fig. 6. PI as a function of AG ratio
Liquid effluent from the wet scrubber of the raw gas purification system analysis by GC/MS/FTI indicates that there are large amounts of phenol (35%) which represent an occupational health hazard (Fig.7).
Fig. 7. Components contained in the liquid effluent of the wet scrubber
D. A continuous running of GASOGENO
A 60 hours continuous running of GASOGENO was performed for irrigation. Performances were also satisfactory compared with the results obtained through a dynamometer. There was no flaking of the inside surface. Tar formation occurred with >12% moisture content in the rice husk, but no effect occurred after a 300 hour testing period.
A. Static bed 25 cm rice husk gasifier yielded an optimal value of specific gasification rate in the vicinity of 195 kg/m² -h. Cold gas efficiency (52.4%) and gas flow (18.44NM3/h) are favorable for selected duel-fuel engines.
B. Dual-fueling engine running with rice husk producer gas could perform best at satisfactory adjustment, without or less modification (mixture device only). AG ratio (1.10-1.55) and (18o87'-20o49'BTDC) are important factors which affect engine performance.
C. The appropriate torque level Me for dual-fuel operation is 0.65-0.70 MeH. Under this condition, PImin=10.21%, (to substitute gas for 89.96% diesel fuel), .Ç e ~0.30 were acceptable. There is not a substantial difference in engine sound level.
D. The condensate of the producer-purification system and related environmental impacts should be studied.
* This research was conducted at CNRRI and completed under the positive assistance of Prof. John R. Goss and Prof. Bryan M. Jenkins and Associate Prof. Fenghua Guo.
References
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