Category New developments in renewable energy

Analyses of carryover

Tables 2 and 3 present the ash collection and unburned carbon analyses during combustion tests. Generally, the mass balance on the ashes particles accounted for over 90% of the ash input from the fuel. The analyses of the ash collected in all tests for unburned carbon dem­onstrates that with biomass only, there was the least amount of unburned carbon detected in ash collected from the cyclone. However, the unburned carbon content increased when coal was added which suggested that some fine particles were elutriated with the fluidising gas­es. The amount of unburned carbon was, however, quite low, corresponding to about less than 5% of the total carbon input...

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Carbon monoxide (CO) emissions

In order to enable comparison of CO from all tests were converted to CO emitted 6% flue gas oxygen. Figure 4, it is evident that there are significant fluctuations in CO emissions, which between 200 and 900 ppm under the same conditions. The orders of fluctuation were similar to those observed by Abelha et al. (2003) and W. A.W. A.K. Ghani et al. (2009). The fluctuations are caused by slight variations in feed composition and this effect is reflected in the temperature profiles. It is noted that the addition of coal has no significant influence on CO emissions during all co-combustion cases, except at coal (50%) / rice husk (50%) where emissions tend to be lower than expected in reference to the other rice husk fractions...

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Temperature profiles

Figure 3 illustrates the axial temperature distributions along the FBC height for fuel studied at 50% excess air. As can be seen from the figure, coal combustion gives higher bed tempera­ture (y = 0-40cm) but lower freeboard temperature (y = 450-120cm) in comparison to bio­mass. Then, all the temperatures shows start to fall from 120 cm above distributor plate indicating that most of the combustion was completed. This significant combustion behav­iour can be explained by the devolatilization process of the fuel [17]. With high volatility (more than 50%) and low ignition temperature (250-350°C), biomass (rice husk and palm kernel shell) will start to devolatilize upon feeding at 45 cm of the FBC height (freeboard re­gion) and was mostly burned before it reached the bed region...

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Carbon combustion efficiencies

The combustion tests were performed using different coal mass fraction; 0, 50 and 100%, corresponding to heat input of 10kW under optimum excess air conditions. Figure 2 shows the effect of different mixtures of rice husk and palm kernel shell with coal on carbon com­bustion efficiency with the same heat input. Generally, Carbon combustion efficiency for single biomass (rice husk and palm kernel shell) but increases with increasing coal addition and experimental runs. The following carbon combustion efficiencies, from Eqn. (1), range between 67-75% for burning 100% rice husk and 80-83% for burning 100% palm kernel shell, 83-88%, and 86-92% for 50% of coal addition to rice husk and palm kernel shell, respectively...

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Results and discussion

This section describes the combustion of agricultural residue in a fluidized bed combustor. The influences of fuel properties such as particle size, particle density and volatility as well as influences of operating parameters such as excess air, fluidizing velocity on axial temper­ature profile, the combustion efficiencies and CO emissions are discussed.

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Carbon combustion efficiency calculation

The carbon combustion efficiency of a system has been expressed as:

hce=C-x100% (1)

whereB and C are the mass fractions of burnt and total carbon in the fuel, respectively. Knowing the flue gas composition, the flue gas composition, fractional excess air and the fuel ultimate analyses of the fuel, B can be determined [20].

This method is particularly appropriate for solid fuels and is described as follows:

Let C, H, O, N, and S be the mass fractions of carbon, hydrogen, oxygen, nitrogen and sulphur, respectively, in the feed.

Подпись: Further define Carbon combustion efficiency calculation Подпись: (2) (3) (4) (5) (6)

Further, let A and B be the mass fractions of unburned and burnt carbon, respectively, in the fuel. Then,

Mass of CO in the flue gas = (28 / 12)PB

Подпись: (7)Подпись:02 consumed to produced C02 + CO = (32 – 16P)B /12

Assuming that H, N, and S present in the fuel are complet...

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Operating conditions

In this experiment, baseline data was first obtained for single combustion of 100% British bi­tuminous coal. Also, single combustion of other biomass fuels was carried out to investigate their combustion characteristics in comparison to coal during the co-combustion study. Co­combustion tests at biomass fractions of 30%, 50%, and 70% were performed. For each bio­mass fraction, excess air was varied from 30% to 70% at 20% intervals. For each excess air condition, air staging combustion was applied where the total secondary air is maintained at 65 l/min (about 10-20% to total air ratio). In order to study the impact of fuel property changes (volatiles, ash, and combustibles), heat input was fixed at the design value of the experimental rig i. e. 10 kW...

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Materials and experimental

1.1. Raw materials and characterizations

In this study British coal, rice husk and palm kernel shell originated from Perlis were em­ployed as fuel. These fuels were open air dried for 2 to 3 days to remove moisture. The proxi­mate and ultimate analyses were performed on coal and rice husk are summarized in Table 1.

British

Palm

Rice

Coal

Kernel shell

Husk

Proximate Analysis (wt % dry basis)

58.90

18.60

15.00

Volatile matter

Fixed carbon

38.20

72.50

60.70

Ash

2.90

8.90

24.30

Ultimate Analysis (wt % dry basis)

Carbon

80.10

49.5

36.20

Hydrogen

5.30

6.74

5.71

Nitrogen

0.90

1.85

0.10

Sulfur

0.70

0.00

0.00

Oxygen

13.00

41.91

57.99

Calorific value (MJ/kg)

31.1

18.0

13.5

Part...

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