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Biomass for alternative power

THE way out of the current energy crisis is to produce power at a low cost from cheaper indigenous sources which are abundantly available but have been largely ignored. These sources can be classified as biomass.

Being an agrarian country Pakistan has numerous sources of biomass available from agricultural crops and solid waste generated in huge quantities which are suitable for power generation. The main sources of biomass are agricultural residues, animal waste, municipal solid waste and industrial waste.

Agricultural residues are those crop leftovers which have a fuel value but their potential is not being fully utilised. The main agricultural residues available locally are wheat straw, rice husk and straw, cane trash and cotton sticks and plant residue.

However, at present, wheat straw is the main source of cattle fodder, so it cannot be considered as a source of fuel to generate power. Similarly, rice husk and straw is presently being used as a source of fuel in the brick kilns and as cattle feed, and therefore, not considered.

On the other hand, the waste of sugarcane crop which is left in the field and subsequently burnt by the farmers; cane trash is a biomass source which is available in substantial quantities and can be classified as a potent source to produce power. Similarly, cotton sticks and plant residue are also leftovers in field. Part of the leftovers are used for cooking purposes, while some quantity is lifted by the brick kiln users. Around 30 per cent is in excess and can be used as a biomass source.

As per data collected, sugarcane tops and trash constitutes around 30 per cent of the plant out of which tops make up 20 per cent. Cane tops are used as cattle fodder and are taken away by the cane harvesting labour to feed dairy animals. The other waste, cane trash constitutes 10 per cent of the sugarcane crop. Leaving aside wastages nine per cent cane trash is considered as available biomass for power.

Research has determined the net calorific value of cane trash at 6.7 Gj/Ton. Taking this figure as the benchmark the power generating potential of sugarcane trash available is: (Table 1)

The ratio of plant waste to cotton is 3:1. From the waste a portion is used by farmers as cooking fuel, some is lifted by the brick kiln operators while a substantial quantity is available for use as fuel for power. The net calorific value of cotton sticks has been determined as 7.3 Gj/Ton. (Table 2)

Another significant area for energy prospects is the manure from dairy animals and cattle. The technology for extracting energy from cattle and dairy animals is through generating biogas from manure. This technology is well-entrenched in our culture and its use will not pose any barriers. The additional advantage for power from manure is the organic compost and slurry which can be subsequently used in the fields as a rich source of fertiliser. This will result in additional revenues at significant levels improving the profitability of the dairy farmers and the power operators.

The quantity of biogas in any feedstock is dependent on the organic content of the feedstock, the average organic content of cattle and buffalo. (Table 3)

Municipal solid waste(MWS) is another feedstock which is available in substantial quantities in major cities. (Table 4)

Having determined the power potential in the agricultural and urban waste, following is a summary of the total value which can be realised. (Table 5)

Assuming that even if 50 per cent of the biomass potential is realised, it can easily replace 33 per cent of the total power generated, as well as the imported and expensive furnace oil.

Additionally advantages adopting the biomass route will be multi-dimensional. For instance, sustained power supply will be available at affordable rates. It will also be an additional source of income for the growers of sugarcane, cotton crop and dairy farmers, creating additional profits for the stakeholders. Similarly, it will be a source of business opportunities for traders buying biomass raw material from the farmers processing it and selling to power operators.

Generating biomass will increase sources of employment in the rural areas and prevent migration to urban centres. Power from biomass can be generated through technology platforms and equipment which is mainly indigenous and the technical manpower to operate it is also abundantly available.

The MSW-based power plants have to be installed in the cities (where the garbage is generated), thus removing the problems associated with garbage collection and disposal and making available a source of income for the funds-starved civic agencies of the cities.

Although setting up centralised biomass-based power plants will be difficult, this can be overcome by installing a chain of smaller power plants ranging from 15MW to 50MW in areas where the biomass is available in economical quantities. This will also save in the transportation costs and will result in reduced line losses.

In the absence of a centralised approach the second option would be to go for micro power plants of 15Kw to 1000Kw range based on gasifier and biogas plants using the agricultural biomass and animal manure as the feedstock. This route will also be viable and could be adopted on the basis of individual participation of the small and medium land holding farmers.

The writer is a consultant in the sugar industry.

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