Biomass based power generation

In the past fifty years, the consumption of electricity has grown enormously. Electricity has become essential to the needs of modern society. This has increased the need for more power plants. 

With the rapid industrial growth in the past few decades, the shortage of energy owing to gap between the generation and demand is becoming a persistent phenomenon. Fossil fuels are the major energy sources, however the conventional fossil fuels are getting depleted day by day and time is not very far off when the world would face a great energy famine. Hence it is necessary to think of non-conventional alternative fuels for energy generation. Though the installed capacity for power has increased 50 times since Independence, the gap is widening with the shortage as high as 17.7 per cent at its peak. The techniques available for energy generation from conventional fuels are well established but it releases a lot of environmentally hazardous residues. Hence the time has come to enhance the conservation of energy and diversify into environmentally friendly alternative sources. 

Central Electricity Authority (CEA) report reveals that India needs an additional 1,00,000 MW at an estimated investment of Rs.50,000 crores to plug the demand-supply gap in the next 10 years.

Power supply position in Southern states:

April 2000 - Janurary 2001 [ in 1000 units]

State Demand Supply Shortfall units Shortfall %
Andhra Pradesh 39112 36264 2848 7.3
Karnataka 24401 22158 2243 9.2
Kerala 11211 10463 748 6.7
Tamil Nadu 34920 32263 2657 7.6

Biomass as the promising source of energy -  
Biodegradable matter of organic origin is called biomass. Fifty five percent of the world’s population depends on biomass as a cooking fuel. This dependence is believed to be increasing and would continue to do so till 2030 AD. In India, the dependence on biomass as the principal cooking fuel is thought to be as high as 70%. Biomass is a very important fuel for industry, particularly rural industries. It is used to dry crops such as tea, tobacco, boiled rice, bricks, pottery, tiles, food stalls and in restaurants etc. Biomass is also used as a feedstock for versatile forms of energy such as biogas, methanol, ethanol, charcoal etc. What goes in favour of biomass as a sustainable fuel source in developing countries is the ease with which it can be produced using local technologies and skills. The principal source of biomass is often the residue of a food or a cash crop. 

Many countries of the developed world are investigating possibilities of sustainable use of bio-resources for energy as a means of reducing the emission of green house gases as required under the Framework Convention on Climate Change. In the case of USA, biomass energy represents 4% of the total energy consumption and is believed to be rising. In the developing countries, however, official policies and institutions have tended to support investments targeted at a development of conventional fuels, primarily coal, oil and gas, and the conversion of these fuels to electricity. These investments have lead to an unprecedented growth of fossil fuel consumption. Besides causing heavy pollution of the environment, the runaway consumption of fossil fuels is also creating adverse balance of payment position for the economy.

The potential for bio-resources to sustainable supply to the growing demand for energy is believed to be under-estimated and under-exploited due to a number of reasons among which are financial, policy, institutional and attitudinal constraints. The potential sustainable bio-resource supply at competitive market prices (taking into account the cost of collection, transport, storage and conversion to useful energy) has been estimated in 1990 to be about 270 exajoules per year or nearly 72% of the world’s total energy consumption. The reason why biomass fuels are not actively developed, if the estimated potential is correct, is due to the prevalence of unsubstantiated myths about biomass fuels. These myths are: biomass fuels can only supplement commercial fuels; biomass is a non-commercial fuel and therefore cannot compete with commercial fuel economy; it is expensive and inefficient as a source of energy and it causes environmental damage and deforestation. 

These myths can be easily disproved with facts and figures. Without going into details, it can be said that in a predominantly agricultural economy such as India’s, biomass can be easily produced at a low cost due to abundant supply of labour with minimum amounts of technological intervention. This seems to be the only way of keeping pressure off the towns and cities where overpopulation, lack of infrastructure and sanitation is degrading the health of a very large population.

Need for power generation -
The power sector in the country is unable to meet the current demand and has a peak demand shortage of about 27% and an energy shortage of about 9%. The Central Electricity Authority (CEA) has indicated that the total demand for power will be 1,41,000 MW by 2007 AD. To meet this capacity demand, an additional capacity of around 12,000 MW must be added every year for the next 3 to 4 years to the present installed capacity of 96,000 MW. With the present generation, the per capital KW consumption in India has remained at an extremely low level of 300 KW per annum.

The current forecasts in India however, indicate that we are likely to fall way behind the required capacity additions. As a result, electrical energy shortages are likely to increase to 20% from the present level of 10%. Peak power shortage will be even higher. The situation could be much worse in the States like Karnataka & Andhra Pradesh, where, even the current electrical energy shortages are reported to be of the order of 50-70%.

The industrial sector today consumes approximately 34% of the total electricity generated in the country. It has reduced its reliance on State Electricity Boards and there has been a dramatic drop of about 6% of total power supply to the Industry. The industrial sector has projected an annual growth rate of around 6%. High-quality stable power will be required to sustain such a high growth rate and to keep up with the overall economic growth. The industry, therefore, has relied on captive power generation, which is primarily diesel-based generation, and is estimated to be around 10,500 MW. This type of captive generation is not only expensive, but also inefficient.

Benefits of power generation, using Biomass -  
1. Cheap source of power – Today state electricity boards are seeking cheaper sources to generate power. The biomass power generating system can compete with the central power stations, which utilize either diesel and coal to generate electricity. The cost of generating power by diesel comes to Rs.5 per kwh, even by coal Rs. 4 per Kwh as against Rs.2 per kwh using biomass. Due to the low cost of input, the biomass power generation system can, on a small scale, compete with large scale power plants.

2. Low gestation period - Biomass generation plants can be commissioned within 2 years from the commencement of the projects, while coal based large plants normally take 5 years for commissioning.

3. Low pollution levels – All stages of energy conversion paths normally result in emissions and the most critical pollutants are Co2, So2, Nox and other particulates. These are significantly reduced due to low fuel consumption levels in biomass power generation systems.

Industrial biomass power generation thus becomes an important option for future electricity supply. Even in the United States, there are projections of doubling the biomass power generation capacity from the present 28,000 MW to 63,000 MW by the year 2010. 

4. Positive environmental impacts - Co2 emissions in a fossil fuel-based thermal plant are around 1 kg/KWh, depending on the carbon content in the fuel. With biomass based power generation, it is only 20% of this figure. Thus a Co2 saving of 0.8 Kg/KWh is achievable. Thus, 70,000 tons of Co2 emissions could be avoided if 30 MW of biomass power operates at a load factor of 80% for 150 days in a year, in a 5000 TCD sugar plant. This also offers an economic opportunity for trading in global Co2 permits.


Selling Biomass power to KEB grid through banking and wheeling-
In the concept of energy banking, the surplus with the bio mass power generator could be supplied to the State Electricity Board with the understanding that equivalent energy would be returned to the unit when required. In Karnataka, banking charges are 2% of the energy per month.

Wheeling refers to the transfer by direct transmission or displacement of electricity from the bio mass power generation plant to a consumer over the facilities of the State Electricity Board. For this, the bio mass power generator is required to pay the SEB ‘Wheeling Charges’ for making use of the transmission and distribution facilities. The wheeling charges applicable in Karnataka is 20% of the energy generated.

Special Advantages of Biomass power generation-
No fly ash
Power generation is environmentally cleaner as biomass produces no fly ash and no sulphur.

Zero Contribution to Green house Effect:
The net contribution to the green house effect from a biomass power generation plant is zero, since the carbon dioxide absorbed by the plant is more than what is emitted by the biomass power generation plant.

Low Investment: 
A biomass unit requires a smaller capital investment and lower recurring costs compared to fossil fuel-based power plants.

Renewable source:
Such a unit uses a totally renewable source of energy, which does not involve mining, extraction and long-distance transportation of fossil fuels.

Rural location:
The rural location of the power plant enables biomass generated electricity to be directly fed to the local sub-station, consequently minimizing transmission and distribution losses and the preventing of long feeder lines, which will ultimately benefit the rural masses.

Quick returns on capital investment:
Bio mass power generation results in quick returns on capital investment.

National Programmes on Biomass Power Generation -
A. MNE'S capital subsidy for biomass power generation :
Based on the recommendation of the Task Force Committee, the Ministry of Non-Conventional Energy Sources launched a National Programme on biomass based power generation in 1994.

The incentive available to the entrepreneurs as per the programme is - Interest subsidy upto 30% of the equipment cost or upto Rs.45 lakhs per MW of net surplus power, whichever is lower, will be given for projects that envisage the generation of at least 4 MW of surplus power using boilers, which generate steam at a pressure of 60 bars or higher. However, the maximum amount of subsidy to any biomass project will be limited to Rs.10 crores per project.

The following are the parameters for availing MNES subsidy for power generation -

1. The minimum power generation should be at least 1 MW connected to the grid on commercial basis. The configuration should be at least 60 bar pressure and 4500 temperature.

2. Financial assistance in the form of interest subsidy is given at the rate of Rs.15 lakhs per MW for a single project upto 4 MW and Rs.45 lakhs per MW for a single project of 4 MW and above capacity.

B. IREDA’S Soft Loan for Biomass power generation:
IREDA has been entrusted with the responsibility of promoting based biomass power generation as a part of renewable energy development programme.

IREDA gives term loan on biomass based power generation plants taking equitable mortgage of the immovable properties and hypothecation of movable properties on the following lines:

1. All the requirements of MNES should be complied with.
2. In principle approval or letter of consent should be obtained from the concerned State Electricity Board for wheeling/banking and purchase of electricity produced in the power generation plant and permission for 3rd party sale at a remunerative price.

The norms for IREDA Finance are as under:

Promoters’ contribution : Minimum 25% of the project cost
Loan assistance from IREDA : Upto 75% of the project cost/cost 
  of eligible items under ADB norms.
Rate of interest (exclusive of Interest tax)  : 12% P.A.
Front End Fees  : 1% of IREDA sanctioned loan amount.
Repayment of loan  : Within 10 years in quarterly installment
  including maximum moratorium of 3

C.Govt. of India's support for independent power producers (IPP's) :
The Govt. of India has targeted a capacity addition to the extent of 2000 MW through renewable energy. In order to achieve this, the Govt. has announced several measures to promote independent power production. 

These include:

1. Upto 100% foreign equity participation.
2. Flexible power sale arrangements, wherein power companies can act as licensers, suppliers and distributors of power or can supply power to the grid at large.
3. 4:1 debt equity ratio on investments.
4. Single window clearance through a new Investment Promotion Cell.
5. Minimum return of 16% on investment, based on 68.5% plant load factor (PLF).
6. A 30-year initial investment period, with subsequent extensions for 20 years; &
7. A five year Income Tax holiday, with a partial holiday of 70% through the 10th year of the project.
8. 100% depreciation in the I year can be claimed on the following biomass power generation equipments –
a) Fluidised Bed Boilers;
b) Back pressure, Pass-out, controlled extraction, extraction & condensing type turbines 
c) High efficiency boilers; &
d) Waste heat recovery equipments.
9. Concessional customs duty, i.e. duty leviable on the import of equipments used for power generation is only 20% under Project Import Category.
10. Renewable energy devices, raw materials, components & assemblies are exempted from Central Excise Duty & also from Central Sales Tax (CST).


D. Govt. of Karnataka's incentives for Biomass power generation :
The following are the incentives for biomass power generation, announced by the Govt. of Karnataka -


a) Power Wheeling charges 20% of the energy generated for  the third party
b) Power Banking charges 2% of the energy per month
c) Buy-back rates Rs. 3.53 per Kwh during 2004-2005 which is increased at 5% every year from the previous year's rate.
d) Third party sale Allowed
e) Other concessions Exemption from electricity tax for 5 years for captive use
f) Promotional agency KPTCL and its subsidiaries.

Boiler & Steam parameters for Biomass power generation- 
As per the studies conducted by and the experiments gained by the leading boiler manufacturer in the country i.e. BHEL, the following are the ideal boiler parameters for the Indian context of biomass power generation -


The capacity of the boiler is 25 tons per hour with 65 kg/cm2 working pressure at temperatures of 4900C to 5100C. Though a number of advancements have come in Boiler design such as circulating, bed combustion boiler, it is always practical to install, moving grate type boiler as the proposed project is based on multi-fuel raw materials and it is very difficult to grind the agricultural residues, which are fibrous.


The flue gas temperature leaving the air pre-heater is 1600C and the feed water temperature at economizer inlet is 1050C.


At 65 bar pressure and at 5100C temperature, a boiler of 25 tons per hour with a back pressure turbine produces 4.5 MW power at 80% work load.


The exhaust steam has a temperature of 1390C at 2.5 bars. For practical calculations, the plant load factor shall be reckoned as 75%.


The Technology –
Main components of the plant are:

  • Steam generator
  • Turbines
    a. High Pressure turbine
    b. Low Pressure turbine
  • Condenser and
  • Pump

Steam Generator:
The traveling grate firing system is selected because of the flexibility of burning various biomass. The traveling grate boiler also facilitates quick response to load change, as it retains the advantages of partial burning of biomass in suspension.

The turbine is designed for high operating efficiencies and maximum reliability. The cylinder consists of high pressure turbine and low-pressure turbine, each containing an impulse control stage and a series of disk and diaphragm stages. Steam enters the H.P turbine through an H.P steam chest located at the cylinder top. The steam leaving the H.P turbine is let to L.P 
turbine across an internal passageway and is controlled by the L.P governing grid valve. One exhaust hood leads to the L.P turbine to the condenser.

The surface condenser condenses the exhaust steam from L.P turbine using cooling water. The cooling water system is closed loop. This condensed water is then pumped back to the deaerator, where the dissolved oxygen is removed from the water.

The condensed water is again pumped to the Steam generator for further steam generation.

Ash Handling and utilization:
The furnace Ash discharged from the furnace shall be handled by the rotary airlock valves and fed on to the screw conveyor. The other Ash collection points in the boiler are the air heater, hopper and the dust collector hopper. The Ash collected in these places will be dry and powdery. At the point of discharge of Ash from the screw conveyor on to the belt conveyor, water sprinklers are provided to suppress the dust.

The Ash generated by the plant can be utilized for manufacture of value based materials like bricks, blocks and cement.


Electrical aspects in power generation- 
An industrial biomass power generation system, is primarily intended to reduce the peak demand in the grid supply. Thus, biomass power generation systems operate in parallel with the grid supply.

In some cases, they may export power to the grid also. Since a biomass power generation system is an integral part of the plant’s power distribution system, it should be viewed in a holistic manner and be suitably integrated into the plant distribution network. Thus the method of connection of the biomass power generator to the distribution system assumes significance. The biomass power generator can be connected to the system in two ways –

  • Through a unit transformer
  • Direct connection to the plant MV distribution system.
The former method, in which the generator is connected through a delta/star unit transformer to the plant distribution system, is generally used in large industries having a power distribution system at the H.V level (33 KV, 66KV). 

This method, though initially more expensive, has many advantages from the system design point of view.

The latter method is more commonly used in medium scale industries. It is much more simple and involves direct connection of the generator, which usually generates power at medium voltage to the plants M.V distribution network.

Risks as perceived in Biomass power generation -
Problems of grid-interfacing with KEB should be thoroughly looked into. Protection of biomass equipment from voltage/frequency fluctuations and failures in the grid etc. needs attention.


© 2006 GoodRich Sugar 
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