Area Under Sugarcane Plantation In Mauritius

Published Date: 02 Nov 2017

Figure 3.0: Sugarcane cultivation in Mauritius

Source: MSIRI 2010

Key:

: Sugar factory

MSIRI Extension and Field Experimentation Centre

Sugarcane areas (green) and the three climatic zones

Northern sector: comprising the districts of Pamplemousses and Rivière du Rempart; 15 041 ha under cane cultivation with 9 826 t cane in 2010 (MSIRI 2010).

Eastern sector: comprising the district of Flacq; 18 078 ha under cane cultivation with 1 608 944 t cane crushed in 2010 (MSIRI 2010).

Southern sector: comprising the districts of Grand Port and Savanne; 19 934 ha under cane cultivation with 1 355 351 t cane crushed in 2010 (MSIRI 2010).

Western sector: comprising the Black River district; 4857 ha under cane cultivation with 407 998 t cane crushed in 2010 (MSIRI 2010).

Central sector: comprising the districts of Plaine Wilhems and Moka; 6221 ha under cane cultivation (MSIRI 2010).

TECHNICAL FEASIBILITY OF USING TRASH FOR POWER GENERATION (Theory part)

2A Amount of cane tops and leaves available in Mauritius

The average weight ratio of fresh CT & L to cane is 0.77 with an average moisture content of CT & L varying between 65.4% and 69.3% (Beeharry, 1998). After correcting for the variation in moisture content, the ratio of dry weight of CT & L to fresh cane varied between 9.6% and 10.2% (Beeharry, 1998). 30% SARs was found to be the most practical to take from the field, in the short term, for electricity generation (Seebaluck, 2009). Table 2A.1 below shows the evolution of harvesters and change in sugarcane yield each year.

Table 2A.1: Cane harvest from 2001 to 2010

2001

2002

2003

2004

2005

2006

2007

2008

2009

2010

No of chopper harvesters

28

30

33

35

36

39

40

43

41

42

Land harvested by chopper harvester/t

966622

1052924

1247943

1437904

1425953

1525921

NA

NA

NA

NA

No of Whole-stalk machine

2

2

2

-

-

1

2

1

1

1

Land harvested by Whole-stalk machine/t

12502

13205

14269

-

-

9489

NA

NA

NA

NA

Total amount of cane harvested/t

979124

1066129

1262212

1437904

1425953

1535410

1454554

1673167

1854507

1851002

Increase in machine harvested area %

14.6

19

21

5.4

6

4.4

4.4

5.1

3.4

5.1

Increase in green area harvested %

NA

67.4

72

76

85

77

85

90

86

89

Amount of cane loss by chopper harvesters, t/ha

NA

10-20

>10

NA

1

NA

NA

NA

NA

Reduction in pickup losses (% above acceptable limit)

NA

NA

NA

NA

NA

NA

42

18

12

9

Extractor fan loss (% above acceptable limit)

NA

NA

NA

NA

NA

NA

54

55

25

15

Source: MSIRI, 2001-2010

3A Assessing the different ways of processing the trash

These alternatives consider chopped cane harvesting with three different modes of trash recovery (Hassuani, 2005):

The trash is removed from cane during the harvesting operation and then part of it is collected with proper equipment such as balers.

Part of the trash is separated from the cane and left in the field and the rest of the trash is transported with the cane to the mill where the trash separation is executed by a Dry Cleaning Station.

The trash is not removed from the cane in the field. Cane and trash are transported together to the mill to be separated there using a Dry Cleaning Station.

Table 3A.1, assesses the different alternatives in terms of the gain and drawbacks.

Table 3A.1: Process consideration of the different alternatives

Advantages

Disadvantages

Alternative 1

Trash necessary for agronomic purposes is provided

Amount of trash that needs to be left is difficult to measure

Cost reduction since dry cleaning station is not needed

Balers will need to be purchased

No change in the way of harvesting the cane

Expertise needs to be acquired for the collection process

Possibility of collecting the trash after a few days in the sun (to reduce the moisture content)

Loading and transportation needs to be done twice. Once for the stalk and once for the trash

Possibility of collecting even the dry leaves which have been detached from the cane

Highest cleaning efficiency*

Alternative 2

Loading and transportation can be done in one go

No trash is left for agronomic purposes

Harvesting process is done more quickly and easily

Investment in dry cleaning stations need to be done

Lowest cleaning efficiency*

Loss of trash while loading and transportation

Alternative 3

Trash necessary for agronomic purposes is provided

Investment in dry cleaning stations need to be done

Amount of cane left in the field can easily be monitored

Change in the way of harvesting the cane

Loading and transportation can be done in one go

Loss of trash while loading and transportation

Fresh green trash is transported therefore more energy required for drying

*Source: Hassuani, 2005

4A Mechanical harvesters

Mechanical harvesting systems may be whole stalk harvesters or chopper harvesters. Whole cane harvesters generally lay the cane down on the ground for collection and loading equipment after the stalks are cut at the base and near the last mature internode at the top (Rein, 2007). Chopper harvesters generally the Massey-Ferguson, Toft, Claas, Cameco, Thompson, J. & L are machines which cut the cane, chopping it into pieces 25-30cm in length (Hugot, 1986; Zelmer, 2006; Rein, 2007). Such harvesters push the stalk over, cut or break them at the base, and draw the butt end of the stalks into the machine, the stalks are cut into billets and are elevated onto a carrier, past one or two blower fans (Beeharry, 1998) separating the billets from the remaining leaves and other trash and discharging it into a truck or trailer moving alongside the harvester and when the vehicle is filled it is removed and replaced by another (Hugot, 1986). These trucks or trailers circulate in the field, holding 5-10 tonnes of cane, and then transfer their load to a road (or rail) vehicle which runs the length of the field, holding 25-20 tonnes of cane and transporting its load to the factory (Hugot, 1986). Chopper harvesters are the only realistic option for green cane harvesting and typically, the harvester extraction system removes 50-80% of the preharvest tops and leaves, depending on harvesting conditions (Rein, 2007).

Reduction in cane losses has been observed in Mauritius and this progress has been realized by setting the angular speed for the CASE-AUSTOFT Anti-Vortex fan at 800 rpm and the optimum operational speed with respect to cane losses and extraneous matter content of the CAMECO fan at 900 rpm (MSIRI, 2003; 2004; 2006; 2009).Additionally, cane losses occur when harvester operators drive in excess of 4 km/h in lodged cane and in high-yielding fields (MSIRI, 2004). Two other major causes of cane loss are: fallen billets due to damage elevators, trailers and chips ejected by the primary extractor fan operating at excessively high angular speed. To remedy this, the field surface just after the passage of a harvester is frequently examined and immediate remedial action is taken if billets are observed. Also, the majority of harvester’s owners are now equipped with hand held tachometers to calibrate on a regular basis the primary extractor fan and thus avoid fan losses due to high speed.(MSIRI 2004; 2005; 2010). Table 3.10, above also shows the evolution of mechanical harvesters in Mauritius.

5A Balers

Baling is as an alternative for harvesting residues recovery with increase in density and transformation of the biomass in uniform units (bales) (Hassuani, 2005). Bale densification significantly reduces transportation and storage costs and improves material handling (Delivand et al., 2011) as discussed in literature review. Throughout the process volume is the key to determining the baler size and capacity that will be required (Williams, 2004). Baling has generally been proven to be better than pelletizing, which requires costly equipment that is expensive to maintain (Rein, 2007). Nevertheless, it should not be created over 15% moisture (Hassuani, 2005) due to increased microbial activity, baled bagasse temperatures are found to increase in storage to about 60 oC after a few days and remain there for 30 days (Rein, 2007). This increases the heat and fire risk which would be devastating to plant utilizing biomass (Brownell; Liu, 2011).

To avoid this the bales are often stacked with air passages between them to provide a means of dissipating the heat produced and they are stored at various locations to decrease the risk associated with spontaneous combustion (Hassuani, 2005; Rein, 2007).The moisture content of SARs was observed to decrease from 54.5% (at time of collection) to around 10% only four days after harvest when left in the sun and it was found that the ash content of SARs (6.48%) was twice as much as that of bagasse (3.16%) (Seebaluck, 2009).After deciding on a baler, we have to ensure that the conveyor[s] will provide material to the baler at a sufficient pace else the entire process will only be as fast as its slowest component (Williams, 2004). Table 5A.1 below compares the pros and cons of both the round and square balers and Table 5A.2 compares specifically 2 round balers.

Table 5A.1: Process consideration of round and square balers

Advantages

Disadvantages

Round Bales

Higher density than square bales

As cylinder size increases baler speed decreases

Requires less energy to run

Preferable field storage

Cost reduction compared to square bales

Rectangular Bales

Better ease of portability compared to round bales

High cost

Bad weather resistant

Should be moved to a covered area as soon as possible

Large mass loss

Source: Hassuani, 2005; Williams, 2004; Brownell; Liu, 2011; Prewitt et al., 2007; Cundiff; Marsh, 1996; Sokhansanj; Turhollow, 2002

Table 5A.2: Compairing round baler 344 and 454

RB 344

RB 454

Can make 1.2 x 1.25 metre diameter of bale

Can make 1.2 x 1.5 metre diameter of bale

Bale density can be adjusted and monitored

The bale size and quality can be altered and monitored

Ensures that the bales are formed and wrapped right to the bale edges, so that they retain all their storage potential

They are fitted with large flotation tyres that will keep soil compaction to a minimum

The spring loaded bale ramp pushes the bale clear of the tailgate to ensure no outer surface damage, giving the bale a safe and easy landing

To prevent the risk of any crop build-up when baling specific rollers are fitted with cleaning loops and scrapers, particularly useful when baling wet and sticky crops

It holds the bale precisely in position, even when working on sleep slopes with up to a 15o inclination

All the desired trash is collected and in a smooth, positive flow

To prevent the risk of any crop build-up when baling specific rollers are fitted with cleaning loops and scrapers, particularly useful when baling wet and sticky crops

Source: CASE IH, 2008; 2009

6A Mechanical loaders

Mechanical loaders are used to load either hand-cut or mechanically cut cane onto the transport system used for cane haulage. Fields that are suitable for mechanical harvesting are amenable for mechanical loading as the three-wheeled grab loader is considered to be adequate to the sloping terrain of sugarcane fields in Mauritius. These loading machine range from the small grabs that pick up ¼ tonnes to ¾ tonnes of stalk to crane-grabs that can handle loads in excess of 3 tonnes (Beeharry, 1998). The commonly used type in Mauritius is the small grab for loading of manually or machine cut cane (Beeharry, 1998).

In Mauritius, according to Jacquinet al.(1996), cane transportation useslorries of 5 to 7 tonnes capacity (216 kW). Cane transport using agricultural tractors of rated capacities ranging from 18kW to 140kW with haulage capacities ranging from 12 to 24 tonnes are either done via a transloading zone or directly from the field to the factory (Beeharry, 1998). Once at the mills the bales are stored until the time they are used.

7A Transportation

Cane transportation is done using agricultural tractors of rated capacities ranging from 80 kW to 140 kW with haulage capacities ranging from 12 to 24 tonnes. (REF)

8A Shredders

Cane shredder components are engineered to provide the highest level of performance, whilst providing a longer product life, which in turn requires less maintenance (Bradken, 2012). Two basic concepts used in equipment design have been identified: knife cutters and hammer shredders. The former consists basically of a rotating cylinder with a series of parallel blades and comb type fixed blades which act like multiple shears, while the latter is a rotating cylinder with a number of hammers, either fixed or hinged, which pulverizes the material by impact (Hassuani, 2005).A system consisting of a knife cutter with a hammer shredder downstream; the cutter would reduce the trash to pieces no larger than 50 mm and the hammer mill would reduce the particle size even further (Hassuani, 2005). The shredder consists of a rotor working at 500, 1000 or 1500 r.p.m., generally 1000-1200 rpm sweeping diameters in the range 1.4 to over 1.9m, leading to tip speeds of about 100 m/s, with range of 65 to 110 m/s and carrying hammers which are pivoted on discs or plates (Hugot, 1986; Rein, 2007).

9A Leaching process

Slagging and fouling are intrinsic properties of a particular boiler design, silicon, potassium, chlorine, sodium, calcium, iron and aluminum are considered the primary inorganic constituents of concern, silicon being the most abundant of these elements (Baxter, 1993). Simple water baths, spray-soaking and in-field rain water leaching have all been used to successfully reduce total ash in various grasses and straws (Jenkins et al., 1996). As a fact, the significantly lower potassium concentration in trash is due to the fact that the trash is also leached with rainwater even chlorine concentration follows a trend similar to potassium and it is highest in the living part of the plant (CT & L) and lowest in the leached part of the biomass (bagasse) (Beeharry, 1998). The concentration of sulphur is comparable in both CT & L and trash ash but also much lower in bagasse (Beeharry, 1998).

Originally developed by the coal industry, the index threshold limits, established from field testing and experience, indicate that slagging is probable for fuels in the range of 0.17 kg/GJ to 0.3 kg/GJ and certain for fuels above 0.34 kg/GJ (Woytiuk, 2006). Slagging and fouling are probable when the index of the fuel is between 0.17 kg/GJ and 0.34 kg/GJ and certain above 0.34 kg/GJ (Woytiuk, 2006; Seebaluck, 2009). Previous investigations have shown leaching water to dry fiber ratios of around 8 to 1 to be effective in removing inorganic elements from herbaceous fuels (Turn et al., 2003).

Clearly the wastewater from the leaching and milling process contain high BOD and COD levels and would require treatment prior to usage for purposes other than irrigation. The high nutrient content may, however, be useful for replenishment of soil fertility since the ash in the cane trash investigation consists primarily of soil oxides(Woytiuk, 2006).

Table 3.26: Elemental analysis of sugarcane biomass

Oxides

Bagasse (% ash)

CTLs (% ash)

Trash (% ash)

SiO2

60.67

36.84

50.54

Al2O3

9.13

0.90

0.88

TiO2

1.07

0.92

0.02

Fe2O3

8.14

0.70

0.67

CaO

3.00

6.62

9.56

MgO

2.56

3.27

3.97

Na2O

0.48

0.70

0.74

K2O

3.84

31.00

16.50

P2O5

1.51

5.30

4.10

SO3

0.78

3.23

3.27

Cl

0.11

8.67

4.97

CO2

0.59

1.12

1.92

Undetermined

8.12

0.73

2.86

Total

100.00

100.0

100.0

% ash in dry fuel

5.5

6.5

6.0

Source: Beeharry, 1998; Seebaluck, 2009