Another view of Complete Energy Plant

Steam Boiler for Co-generation

Extraction � condensing steam Turbine

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%.

With the present generation, the per capital KW consumption in India remains at an extremely low level of 325 KW per annum.

The Central Electricity Authority (CEA) has estimated that the country will need an incremental generation capacity of 1,41,000 MW by 2007 AD. At today�s level, this will cost more than Rs.5,00,000 crores.

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, where even the current electrical energy shortages are reported to be of the order of 30-50%.

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 12%.

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 & estimated to be around 10,500 MW. This type of captive generation is not only expensive, but also inefficient.

ADVANTAGES OF CO-GENERATION -

1. Energy�efficient technology � Co-generation is an energy � efficient technology, as it utilizes the low-grade exhaust heat from the steam Turbine (which is usually rejected in the condensor) for process heating. This enhances the efficiency of energy utilization from 37% in the conventional power generating system to 60% in the co-generating system.

2.A cheap source of power - Today, State Electricity Boards are seeking cheaper sources to generate power. A Cogeneration system can compete with Central Power Stations that have enjoyed large economies of scale. Cogeneration becomes additionally attractive against diesel generating sets. The cost of power generated by DG sets without Cogeneration range from Rs. 6.00 - 7.00 per KWH, whereas the cost of Cogeneration varies between Rs. 1.50/KWH and Rs. 2.50/KWH. The pay-back period is within 3 years.

3.Low gestation period � Co-generation plants can normally be commissioned within 18 months from the conception of the project. Coal based thermal plants normally take about 5 years before commissioning, whereas gas-based power plants normally take about 3 years before commissioning.

4.Low Pollution Levels - All stages of energy conversion paths normally result in emissions and the most critical pollutants are Co2, So2, No2 and other particulates.

These are significantly reduced due to low fuel consumption levels in co-generation systems.Industrial Cogeneration thus becomes an important option for future electricity supply. Even in the United States, there are projections of doubling the Cogeneration capacity; from the present 28,000 MW to 63,000 MW by the year 2010. In many European countries like Netherland, Cogeneration is expected to contribute upto 30% of the total electricity capacity by the turn of the century.

SELLING CO-GENERATION POWER TO THE STATE GRID THROUGH BANKING & WHEELING -

In the concept of energy banking, the surplus with the co-generator could be supplied to the State Electricity Board with the understanding that equivalent energy would be returned to him when required. In Karnataka, Banking charges are 2% of the energy generated.

Wheeling refers to the transfer by direct transmission or displacement of electricity from the Cogeneration plant to a consumer over the facilities of the State Electricity Board. For this, the Cogeneration 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 for third party sale & 5% for captive consumption.

CO-GENERATION IN MDF & PARTICLEBOARD PLANTS �

MDF is both power & energy intensive project. An 80,000 m3 MDF line needs 6 mw of power and 24 tons of process steam per hour. Combined with the auxiliary plants, the power requirement goes up to 7.5 mw. This higher demand for both power & steam makes an ideal situation for Co-generation.

Particleboard is also energy intensive. A 50,000 m3 Particleboard line needs 1.8 mw of power (2.5 mw with auxillary plants) & 8 tons of process steam per hour, which also makes it economical to have a co-generation plant.

The effective cost of power from the state grid is Rs. 4.50 per unit (KWH), which becomes Rs. 2.50 per unit (KWH) on Cogeneration. The cost of generating steam in the Cogeneration is also lower, as the cost is absorbed by the combined generation of power.

Benefits of Cogeneration in MDF / PB Plants �

1. Power generation using Biomass is environmentally cleaner as Biomass produces very little fly ash and no sulphur.

2. The net contribution to the green house effect from a Biomass based Co-generating plant is zero, since the carbon dioxide absorbed by the Biomass grown is more than what is emitted by the Co-generation plant.

3. A Biomass based Co-generation has a much lower gestation period of 18 months, as compared to the 96-120 months required for a coal based power unit.

4. A Biomass burning unit requires smaller capital investment and lower recurring costs compared to fossil fuel-based power plants.

5. Such a unit uses a totally renewable source

6. The rural location of MDF / Particleboard Plants enables co-generated power to be directly fed to the local sub-station, consequently minimizing transmission & distribution losses & the provision of long feeder lines.

7. Co-generation results in quick returns on capital investment.

8. Power is generated at lower costs & pay-back periods are shorter.

9. The generation of surplus power in MDF / Particleboard factories is ideally suited for rural electrification & setting up of agro-based units in the villages.

POSSIBLE MODELS OF CO-GENERATION -

A) Extraction cum back pressure route -

The main features of this configuration are listed below -

1) The MDF / Particleboard factory produces only as much steam as is needed for its process.

2) This is the cheapest option from the point of view of initial cost & efficiency of the system.

B) Extraction & Condensing route -

This system has the following features -

1) By using an extraction cum condensing turbine, surplus power can be generated by operating the turbine in the condensing mode.

2) The capital cost is higher for this system.

3) This system ensures the supply of stable surplus power which can be inter-faced to the grid, there-by reducing fluctuations in plant operation.

C) Condensing route based on dual fuel system -

This option has the facility of ensuring a year-round, stable surplus power supply through the use of a support fuel. Its main features are listed below:

1) This is a viable option for MDF/ Particleboard Plants with access for secondary source of fuel.

2) In such an option,the reliability of alternate fuel supply has to be ascertained. Design aspects of boiler should ensure availability of a suitable furnace capable of multi-fuel combustion,particularly the combination of Biomass & coal / lignite.

3) The capital cost of multi-fuel system, particularly using coal as support fuel will be high, in addition to the connected considerations of pollution control & ash disposal. For example, it is mandatory to use ESP (Electro-static precipitator) system to clean the flue gases in coal fired boilers in India.

NATIONAL PROGRAMMES ON BIOMASS BASED CO-GENERATION �

A) MNES�s interest subsidy for Co-generation -

Based on the recommendation of the Task Force Committee, the Ministry of Non-Conventional Energy Sources launched a National Programme on Biomass-based Cogeneration in January 1994.

The following incentives are available to the entrepreneurs as per the programme �

1) Interest subsidy up to Rs. 2.00 crores will be given for projects that envisage the generation of surplus power using boilers, which generate steam at a pressure of 60 bar or higher.

2) This interest subsidy is on the loans sanctioned by the financial institutions for the purchase of co-generation equipments, calculated @ 2% per annum.

B) IREDA�S soft loan for co-generation �

IREDA has been entrusted with the responsibility of promoting Biomass based co-generation as a part of renewable energy development programme. The norms for IREDA finance are as under �

Notes:

1.These norms are applicable for Biomass power generation from 1 mw to 7.5 mw, with a minimum boiler pressure of 63 kg /cm2.

2. If alternate fuel is required for extension of operating days in a year, fossil fuels up to 25% of annual consumption is allowed.

C) Govt. of India�s support for Independent Power Producers (IPP�s) �

The Govt. of India has targeted a capacity addition of 19,500 MW through renewable energy, while the potential has been estimated as 80,000 MW. In order to achieve this, the Govt. has announced several measures to promote independent power production. These include�

1. Up to 100% foreign equity participation;

2. Flexible power sale arrangements, wherein power companies can act as licensers, suppliers & distributors of power or can supply power to the grid at large;

3. 3:1 debt-equity ratio on investments;

4. Single window clearance through a new Investment Promotion Cell;

5. Minimum assured 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 10 year Income Tax holiday.

8. 100% depreciation in the I year can be claimed on the following Cogeneration equipments �

    a) Fluidised Bed Boilers:

    b) Back pressure, Pass-out,controlled extraction, extraction and condensing type turbines     for Cogeneration along with boilers;

    c) High efficiency boilers; &

    d) Waste heat recovery equipments.

9. Concessional customs duty, i.e. duty leviable on the import of equipments used for Cogeneration is only 17% 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 co-generation -

The following are the incentives for Biomass � based Cogeneration announced by the Govt. of Karnataka �

Karnataka has estimated that there is a potential to generate 650 MW of power from Biomass in the state.

Boiler & Steam Parameters for Co-generation -

As per the studies conducted by & experience gained by the leading Boiler manufacturer in the country i.e. BHEL, following are the ideal boiler parameters for the Indian context of Co-generation-

1) The recommended pressure of the boiler is 65 kg/cm2 and the temperatures are 4900C to 5100C. Now-a-days, steam pressure up to 87 kg/cm2 & temperature upto 5150C are recommended for higher efficiency.

2) More advanced Circulating Fluidised bed combustion boilers are made by BHEL & also by Crupp Industries - both in collaboration with Lurgi of Germany. In a CFBC boiler, the fuel is re-circulated upto 40 times, so that the un-burnt volatile materials are completely burnt. As a result, overall boiler efficiencies are achieved upto 80% with mill wet bagasse, 87% for lignite & 88% for coal. The combustion efficiencies are as high as 99%.

In case the proposed project is based on multi-fuel raw materials, it is always practical to install moving grate type boiler, as it is very difficult to grind the agricultural residues, which are fibrous.

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

4) At 65 bar pressure and at 5100C temperature, a boiler of 50 tons per hour with a back pressure turbine produces 9 MW power at 80% work load.

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

To conclude, following are the benefits & risks of co-generation in MDF / Particleboard Plants -

Benefits of Co-generation -

1. Improved viability - Co-generation offers positive contribution to the profitability of MDF & Particleboard projects. Savings as much as Rs. 5 crores / annum in 80,000 m3 MDF line & as much as Rs. 2 crores in 50,000 m3 Particleboard lines are possible with Co-generation.

2. Low cost / low gestation investments - Even the highly efficient technology option of Rs 2.50 crore/MW of investment in Co-generation plant compares favourably with the normal thermal projects where the investment is Rs.4 crore/MW. The lead time is only from 15 months to 18 months depending upon the size & the plant configuration. This is again almost half the time required for thermal plants. Further, many of the Central & State Govt. clearances required for thermal plants are not required in Co-generation.

3. 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 Cogeneration, it is only 20% of this figure. Thus a Co2 saving of 0.8 Kg/KWh is achievable. Thus 26,000 tons of Co2 emissions could be avoided if 6 MW of co-generation power operates at a load factor of 80% for 300 days in a year, in an 80,000 m3 MDF plant. This also offers an economic opportunity for trading in global carbon trading as per Kyoto Protocol.

Risks as perceived in Co-generation -

1. Magniture of investment - An investment of Rs. 2.50 crores per MW would be essential, using high-pressure & high-efficiency technologies.

2. Risks to MDF manufacturing operations - Any disturbance in the topping turbo generator (TG) sets as a result of grid problems, would interrupt the MDF manufacturing operations totally, in case the interfacing of power with the State grid is envisaged.

The cost of such interruptions can be high on account of production loss, machine failure and quality problems.

Problems of interfacing with the State grid should be thoroughly looked into. Protection of Cogeneration equipments from voltage/frequency fluctuations & failures in the grid etc. needs attention.

Assumptions for the viability of Co-generation-

    1. The turbine efficiencies should be as under-

    - at 65 kg/cm2 pressure, condensing turbines consume 4.5 kgs. of steam per KWH.

    - Back pressure turbines consume 6.5 kgs of steam per KWH.

    2. Operating costs are 5% of capital cost.

    3. The prices of Biomass and alternative fuel are assumed at Rs.1,500 & Rs. 3,000 per ton.

    4. Power realization is assumed at Rs. 3 per unit, net of wheeling charges, in case the power     is inter-faced with grid.

DETAILS OF CO-GENERATION PLANT -

Main components of the plant are:

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

Steam Generator:

The travelling grate firing system may be selected because of the flexibility of burning various Biomass. The travelling grate boiler also facilitates quick response to load change, as it retains the advantages of partial burning of Biomass in suspension.

Turbine:

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 from the L.P turbine to the condenser.

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 de-aerator, where the dissolved oxygen is removed from the water.

Pump:

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

Ash Handling and utilization:

The 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 added products like bricks, blocks and cement.

Thus, Co-generation is an important option for energy-utilization in MDF & Particleboard projects. Biomass is a renewable source of energy for Co-generation. Currently, Biomass contributes 14% of the total energy supply worldwide & 38% in developing countries.

India is a tropical country blessed with sunshine & rains, offering an ideal environment for Biomass production. With an estimated production of about 460 million tons of agricultural waste every year in India, Biomass is capable of supplementing the Coal to the tune of about 260 million tons, which is valued at Rs. 26,000 crores every year.

II ENERGY PLANT -

Energy Plant supplies all forms of process heat for MDF & Particleboard industries. Energy plant pre- dominantly uses thermal oil & hot air as heat transfer medium. Compared to the conventional steam boiler, thermal oil as heat transfer medium offers the advantage that it can be heated without any pressure until reaching a temperature of 3200 C. With synthetic oils, even temperatures upto 4000C can be reached.

In order to reduce the operating costs to a minimum level, a number of measures for energy recovery are envisaged in the Energy plant, that further increase the efficiency of the whole system. Some of these systems are -

• Use of waste heat stored in the flue gases for heating warm or hot water.
• Direct utilization of flue gases for heating of dryers.
• Pre-heating of combustion air.
• Mixing of hot air with flue gases in a mixing chamber.

Complete energy plants deliver hot gas, hot thermal oil & steam in a single system.

Energy plant concept was propagated in Germany and adopted in China. Chinese companies can now supply energy plants up to 50 million Kcal/hour.

Following are the features & advantages of installing an Energy plant -

Features & advantages of Energy plant -

1. Energy plant can supply steam, hot oil & hot air in a single system. If steam is taken from the Energy plant, it will largely save on the steam / water losses in the extraction turbine of a Co-generation plant, which needs pure DM water to make up.

2. In a Co-generation plant, flue gas is available at the chimney of the boiler at 1500C to 1600C temperature and this flue gas can be filtered and used in the mixing chamber of the energy plant, after de-dusting. This way, additional equipments like Economizer and Air pre-heater can be avoided in the boiler system, without which the chimney temperature goes upto 1800C to 2000C, which is subsequently utilized by the energy plant.

3. After filtration of flue gases, it is possible to reduce the concentration of dust to 200 mg/m3 of air. Assuming that 80,000 MDF line needs 2,00,000 m3 of air per hour, it means that only 40 kgs of dust will mix up with 9,500 kgs of MDF fibre per hour, which is less than 0.5%.

4. Thermic fluid heater, which is part of the energy plant is better than steam for drying applications because the temperature drop is only 30-350C in thermic fluid heater. As against this, the steam condensates in the boiler. The efficiency of the thermic fluid heater is 76-80%, as against 68-75% in the steam boiler. When the whole energy plant is considered, the thermal efficiency is 94% & the guaranteed efficiency is 90%.

5. Though the investment on the energy plant is relatively higher, the pay-back is also faster.

6. The Energy plant is capable of using various raw materials like firewood, wood trimmings, sanding dust, bagasse & pith,sugarcane trash, rice straw etc. Even the Biomass with 10% sand and silica can be used as the feed source for energy plant.

7. Energy plant utilizes the following two systems for feeding -

  a. Solid fuels by moving grate &

  b. Fine powders by fluidization.

Similarly, energy plant can supply different sources of heat at different temperatures from a single system.

8. Even if the moisture in the Biomass is up to 75%, it can be burnt in the furnace.

9. Incase the energy plant is installed, there is no need to buy the heat exchanger for MDF drier. Even the air blower component of the drier is supplied as a part of energy plant.

10. Following are the capacities of energy plants suitable for different capacities of MDF & Particleboard projects -

The break-up of energy requirement for MDF is given below -

11. The total power consumption in the energy plant suitable for 80,000 m3 MDF is 500 kw/hour, while the installed power is 1,000 kw. Incase of 50,000 m3 MDF plant, the installed power is 600 kw, while the actual power consumption is 350 kw/hour.

12. A comparison of energy efficiency in 3 different systems are given below, separately in MDF & Particleboard plants-

  1. Conventional boiler + thermic fluid heater;

  2. Energy Plant; &

  3. Co-generation.

A complete view of Energy plant

Schematic diagram of Energy plant