Moisture effects on coal for Indian Thermal Power Plants

Great importance must be given during the transportation, receipt and storage of coal to ensure that its heating value is preserved and there is no deterioration on account of moisture addition enroute to the power plant or in the coal yard storage prior to its entry into the furnace of the boilers. In the case of imported coals higher moisture coals are cheaper and the increased generation cost due to moisture is offset by the cost advantage. The same is not true for Indian coals where there is no provision for cost accounting of total moisture except for upper limits.

  Coal (popularly known as black diamond) is the primary energy source of the thermal power stations (TPS) which is the back bone of the Indian power sector. The installed capacity of the country is ~250 GW out of which ~140 GW is the share of coal based power generation (~57%). The power generation growth rate represented by compound annual growth rate (CAGR) is 8%.

  Coal is contributing to ~1.5% of the GDP as it is the main energy source for power generation with a reserves of 275 billion tonnes (production capacity over 10 million t/y and up to a depth of 600 m) of which nearly 115 billion tonnes are proven. Coal will continue to dominate the electrical energy generation scenario for the next 20-30 years. Most of the indigenous coal is from government owned mines which account for 90% of the indigenous production. Out of this 88% is mined through open cast processes. Shaft mining is restricted to only high quality coals.

  Coal follows a long route from the time it is mined till it is ultimately combusted in the utility boilers. The mechanism of supply of coal to the power plants is through the fuel linkage system based on fuel supply agreement between the colliery and the power utility. Nearly 60% of the coal is transferred from the mine to the power plant through Indian railways, 25% through trucks & the balance through dedicated transfer systems such as merry-go-round-systems, etc.

  Coals and most other solid fuels being of variable heating value are priced based on the product of the quantity (tonnes) and the quality (gross heating value in kcal/kg).

  Indian coals being of drift origin are of high ash (25-50%) with gross calorific values (GCV) in the range of 2300-4500 kcal/kg. Sulphur (<0.6%) is not a problem except in very few specific mines. Coals & most other solid fuels being of variable heating value are priced based on the product of the quantity (tonnes) and the quality (gross heating value-GCV in kcal/kg). For the purpose of computing quantities, the average coal GCV of indigenous coal is taken as 3500 kcal/kg and that of imported coal is taken as 6500 kcal/kg.

  With the import of high GCV coal to sustain power generation on the rise, energy efficient utilization of coal resources is essential. Efficient use of coal calls for effective transfer, storage, monitoring and management to ensure that there are minimal losses in quantity or quality in the process of transfer from the mine to the boilers. Coal utilization efficiency (before it is used in the boilers,i.e., from mills till bunkers) is in the range of 80-98%.

  Figure 1 shows the gradual rise in cost (FOB (freight on board)) of imported coal over the year.

Fig. 1: Rise in cost of imported coal

  The main non chemically reactive ingredients in coal which result in the drop in GCV are ash and moisture.

Coal Quality- ASH & Total Moisture Content In Coal

  Ash is technically the solid residual end product of combustion of coal and is realized only on combustion since it is an integral part of the overall coal lump. But due to the open cast mining process, besides the inherent ash the extraneous mineral matter (clay, sand, and stones generally referred as mud) also gets mixed up with the coal. This extraneous mineral matter is called as extraneous ash. Even though scientifically it is not ash, techno commercially it is called as extraneous ash because it is an incombustible component. Thus ash implies inherent ash which is the product of combustion & externally mixed earth. Extraneous mineral matter can be removed through washing processes typically the run of mine jig wet washing process. Inherent ash cannot be removed except by complex and cost chemical methods in small sample sizes at the laboratory scale.

  Moisture in coal consists of inherent moisture (IM) and surface moisture (SM). Then total moisture (TM) is a sum of IM and SM. Inherent moisture is moisture which is an integral part of the coal seam in its natural state, including water in pores but excluding that in macroscopically visible fractures. Equilibrated moisture (in chemically equilibrated condition) or chemical moisture is taken as inherent moisture though it can be different for low grade coals. As per IS:1350 Part I – 1984) for moisture Equilibrated Moisture means the moisture content, as determined after equilibrating at 60% relative humidity (RH) & 40OC as per the relevant provisions (relating to determination of equilibrated moisture at 60% RH and 40OC) of BIS 1350 of 1959).

  Surface moisture is the difference between total moisture and inherent moisture and is also called as excess moisture (EM).

TM= IM + SM

  Total Moisture implies the total moisture content (including surface moisture) expressed as percentage present in Coal and determined on as-delivered basis. IM or equilibrated moisture is not in our control as it is governed by the thermodynamics of liquid-vapour equilibrium. SM is an added quantity and can vary in any range. Hence TM is affected by the criticality of SM. This brings down the GCV of coal (thermal content of coal) which reduces the output it delivers, reduced boiler efficiency and unit overall efficiency. Also, wet coal is difficult to handle & its movement in conveyors, chutes, hoppers, bunkers and pipes is considerably hindered making its grinding, milling and flow into the boiler very difficult. 

  As the coal quality decreases (ash and moisture increase) the cost of coal (Rs./Gcal) is likely to decrease as indicated in Table 1. However, the cost of energy generation increases as the boiler efficiency and hence the unit efficiency decreases (unit heat rate increases). Hence on the overall, there is trade off between increased cost of generation and decreased cost of coal leading to lower overall cost of energy produced.

  Coals as mined are classified on the basis of the sum total of ash and moisture in equilibrium as in Figure 2.

  The coal payments for indigenous collieries are being made on the basis of equilibrated moisture (inherent moisture at 60% RH & 40OC).

Fig. 2: Classification of coals

Effect of Moisture In Coal

Effect on heating value of coal

  Figure 3 gives the decrease in GCV with moisture for a sample Indian coal of GCV of 2,000 to 7,000 kcal/kg. Figure 4 gives the drop in GCV of coal for 1% moisture increase.

Fig. 3: Decrease in GCV of coal with moisture

Fig. 4: Drop in GCV of coal for 1% moisture increase

Effect on coal movement and handling in the coal yard

  While internal moisture affects the coal combustion process, external (mechanical) moisture gives rise to difficulties in handling (transfer and flow ability) of coal with severe capacity reduction of all equipment in the coal plant ranging from crushers to conveyors. External moisture also creates combustion difficulties by creating thermal lag during the combustion process.

  Units tripping on mill choke up, load hunting due to insufficient flow from bunkers, raw coal feeder jam, etc, are quite common during this period.

  Even though the bunker level may be full, only 30% of the bunker capacity can be utilized due to bonding of coal at the bunker periphery and flow is only through rat hole in the bunker centre. When there is a choke up, the procedure is usually to remove the blockage by poking through the bottom opening. Air blasters are sometimes being used. If the level of coal is over 30-40%, a through hole cannot be established to remove the choke up. The bunker level under this condition needs to be filled continuously to the optimal level of 30% to 50% depending on the coal wetness and risk of choke up. Full filling of the bunker can be resorted to only when there is no risk of choke up. Choke up on full level can be quite difficult to release.

  Rainy season restricts the plant load ability due to the movement of sticky coal which contains clayey mineral matter. Retardation of coal flow through the systems results in capacity reduction. When the surface moisture of coal exceeds 6%, it becomes sticky in addition to the stickiness created by the clay content of the mineral matter leading to severe capacity restriction in the tipplers, conveyors, crushers, bunkers and mills. The effective flow able coal through bunkers gets restricted to only 20% of the bunker volume in its centre.

  The effect of moisture on bulk density of coal is given in Figure 5 for various coal finenesses (% passing through 200 mesh or 75 μm).

Fig. 5: Effect of  coal fineness (% through 75 microns) on the bulk density of coal

  The stations need to gear up to the demands of the rainy season through several measures such as the following:

• Stocking of sufficient coals of sandy background which do not have serious sticky properties as compared to coals of clayey background. 
• Use of washed coals of sandy background.
• Blending of raw coal (GCV=14.5 GJ/kg) with washed coals (GCV=17.5 GJ/kg) or imported coals (GCV=21 GJ/kg).
• Optimal (partial) filling of bunker levels.

Some of the solutions for wet coal handling are:
Management of coal yard

• Rain guards for conveyors
• Tarpaulins to cover wagons
• Providing slopes for drainage of water
• Concreting of storage yards and providing retaining walls'
• Rain water channeling, dredging and cleaning of flow passages
• Compacting by special compactors instead of bull dozers.
• Storage pile design improvement through compacting. Pyramidal shapes with drains on either side lead to low water absorption. 
• Further the piles must not have surface depressions or pits. 
• Used oil may be sprayed on coal yard instead of reselling. Alternatively it can be blended with fuel oil. 
• Dome for storage of coal
• Provision for ground level tippling (non-pit type) of wagons.

Management of conveyors

• Increased conveyor angles
• Multi bladed cleaners
• Reduction in belt speeds
• Skirt board seals, baffle plates and centering plates at loading points
• Self cleaning screening system
• Well designed wash down drainage system
• Management of carry over return
• Conveyor belt sealing between chute and pan of vibratory feeder to prevent spillage.

Management of chutes and bunkers

• Deflector plates of Stainless steel (SS 304) to chutes
• Vibratory feeders/thumpers/rappers in place of static feeders
• Air blasters
• Chute modification to increase angle 
• Widening of passages
• Water jet cleaning.

  Many of the solutions described above are add-ons or modifications (to the already supplied coal handling and conveying equipment) done at the level of the power station. The coal handling and conveying technology needs to viewed holistically and specific products for handling wet coal need to be designed as the rainy season in India lasts for almost one third of the year in several regions. Figure 6 shows the bonding of wet coal with clayey mineral background.

Fig. 6: Bonding of high moisture coal in a coal yard

Basis for Sale of Coal

Indian collieries

  Figures 7 & 8 show the experimental correlation between total moisture and surface moisture with inherent moisture in Indian coals mined in India. It can be seen that there is SM of 4-7% in Indian coals.

  In the case of indigenous coals, the heating value for commercial purposes is based on equilibrated moisture which is equivalent to inherent moisture and the total moisture does not get reflected in the commercial heating value. In other words, surface moisture does not get accounted in the costing. The basis for payment at the collieries is the GCV on the basis of equilibrated moisture and the GCV drop due to surface moisture does not figure. The actual heating value of coal received for power generation will be lower than the commercial heating value as indicated in the graphs on equilibrated moisture and total moisture. 

  This matter must be taken up by the thermal power plants with the coal authorities. Hence, the realistic basis for payment would be the total moisture at the mining point. Addition of surface moisture enroute to the thermal power plant or moisture addition in the coal yard of the power plant must be to the account of the user.

Fig. 7: Correlation between surface moisture and equilibrated moisture in mined coal

Fig. 8: Correlation between total moisture and equilibrated moisture in mined coal

Imported coal

  In the case of imported coal the basis for payment is defined on the basis of either equilibrated moisture or total moisture as per the agreement. The cost of imported coal decreases with increase in total moisture. Figure 9 gives the drop in GCV due to increase in total moisture of imported coals.

Fig. 9: Drop in GCV due to increase in total moisture of imported coals

Effects of Moisture in Coal on Power Station Performance

  There are three cost effects of moisture in coal:

• Increase operation costs due to decreased boiler efficiency (Fig. 10) & decreased overall unit efficiency (increase in heat rate) (Fig. 11). 
• Increase in operation and maintenance costs attributed to handling of wet coal. 
• Decrease purchase cost of coal due to higher moisture and hence lower GCV.

  The boiler efficiency decreases due to increase in moisture and the unit heat rate increases. This results in increased cost of generation.

Fig. 10: Decrease in boiler efficiency due to increased moisture content

Fig. 11: Increase in unit heat rate due to increased moisture

Cost Sensitivity of Moisture in Coal

Indian coal

  The fuel supply agreements for Indian coals do not have any provision for accounting the effect of total moisture. Only equilibrated moisture (IM) gets factored in the pricing. The surface moisture and hence the total moisture (T M) does not get factored into the agreement. The only relief for indigenous coal users is that in the event that monthly weighted average surface moisture in coal exceeds 7% during the months from October to May and 9% during the months from June to September, the coal quantities delivered to the power plants will be adjusted for the resultant excess surface moisture, which shall be calculated in percentage by which the surface moisture exceeds the foregoing limits. This corresponds to a TM of approximately 12% in summer & 14% in rainy season which rarely happens. Hence, it can be said that the surface moisture effect is virtually not factored in the cost calculations. On this account Indian coal costs do not show sensitivity to total moisture as indicated in Figures 12 and 13.

Fig. 12: Sensitivity of Indian coal price (Rs./t) to total moisture

Fig. 13: Sensitivity of Indian coal price (Rs./Gcal) to total moisture

  However, if the moisture effect is considered the price should decrease as given in Figures 14 and 15.

  The coal pricing should be on the basis of TM as it gives a realistic picture of the energy content in the coal available for end use.

Fig. 14: Sensitivity of Indian coal price (Rs./t) to total moisture if the moisture effect is considered

Fig. 15: Sensitivity of Indian coal price (Rs./Gcal) to total moisture if moisture effect is considered

Imported coal

  Figures 16 & 17 give the cost sensitivity of Imported coals to moisture in terms of Rs./t and Rs./Gcal.

  The cost sensitivity of moisture in coal to generation cost and fuel cost component.

  It is clearly seen that the cost impact due to actual decrease in energy efficiency is very small (Rs. 0.01 to 0.015/kWh) as compared to reduced fuel purchase cost component of generation cost (Rs. 0.36/kWh) because as the TM increases the price of coals decrease.

Fig. 16: Cost sensitivity of Imported coals to moisture

Fig. 17: Cost sensitivity of Imported coals to moisture

Conclusions

• Major capacity addition has been based on assumed coal supplies from indigenous sources. The decreasing quality as well as difficulties in mobilization for a CAGR of 8% has resulted in turning to imports (15-20%) for supplementing of the primary fuel requirements which is a good short term measure. 
• Moisture in coal has a negative impact on the energy performance and all efforts are required from the mine till the coal is fired into the boilers, to ensure that moisture does not get added to the coal and its heating value is preserved. 
• If the boilers are designed for operating on high moisture coals, the high moisture imported coals can be successfully fired in an economical fashion as the open market price of coals with higher moisture will be lower than coals with lower moisture. The overall cost of generation will be lower for coals with higher moisture contents. The increased generation cost due to lower boiler efficiency & unit overall efficiency (Rs. 0.015/kWh) will be completely offset by the component due to decreased purchase price of higher moisture coals (Rs. 0.38/kWh). Therefore, for imported coals the economics is in favour of operating on higher moisture coals based on the coal pricing. 
• In the case of indigenous coals, the heating value for commercial purposes is based on equilibrated moisture which is equivalent to inherent moisture and the total moisture does not get reflected in the commercial heating value. In other words, surface moisture does not get accounted in the costing. The actual heating value of coal received for power generation will be lower than the commercial heating value as indicated in the graphs on equilibrated moisture and total moisture. This matter must be taken up by the thermal power plants with the coal authorities. Hence, the realistic basis for payment would be the total moisture at the mining point. 
• However, in the case of both imported coals and indigenous coals, addition of surface moisture or moisture addition/deterioration in heating value in the coal yard of the power plant is to the account of the user and must be minimized. Besides just the heating value the difficulties in flow ability, crushing, pulverizing, and injection of coal into the furnace of the boiler present.

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M Siddhartha Bhatt & N Rajkumar are from CPRI, Bangalore.

Source: http://electricalindia.in/blog/post/id/7234/moisture-effects-on-coal-for--indian-thermal-power-plants

Climate Change And Role Of Renewable Energy

Global warming and climate change have become a worldwide issue, and these are the most debated topics among scientists and environmentalists around the world. Role of thermal power stations in global warming and climate change is well known.

  The recently developed alternative sources of energy are thought to nullify the effects of thermal power in some way. The role of thermal power and renewable sources of power in climate change is described further.

Climate change

  Variation in the earth’s global climate or in regional climates over time is generally termed as climate change.

  Climate change may be caused by the earth’s internal processes or external forces such as change in the intensity of sunlight or human activities.

  In the present context, the term climate change refers to change in the modern climate only, including the rise in average surface temperature, commonly known as global warming.

  Effects of climate change are already felt. Glaciers are recognised as the most sensitive indicators of climate change. They advance during cooling and retreat during warming. From the last century, glaciers and ice fields have been melting all over the world. Glaciers in the Himalayas have been retreating at a rate of 25 metres per year.

  Melting ice has resulted in rising sea levels. It is feared that at the current rate of melting of ice, ocean levels may rise by 23 inches by 2100.

Thermal power

  World primary energy demand increases with increase in population and economic development. Within the last 25 years, the total energy consumption in the world has almost doubled. Electricity is the most conventional form of energy in today’s world. It is mainly produced in power plants using conventional sources namely hydro energy, nuclear energy, and coal or other fossil fuels. However, in most of the countries, majority of plants use coal as primary energy. This is because installing a thermal power plant is in many ways more convenient than other power plants. Its gestation period is 3 to 4 years whereas in case of hydro power or nuclear power it may be 8 to 10 years or even more. So, to meet the immediate energy demand, thermal power is the best option. It can be located in any place unlike hydro power stations, which are site specific. Further, it is free from vagaries of weather and does not depend on rainfall unlike hydro power stations. Another factor that attracts thermal power is that coal is abundantly available in many countries. Also, the thermal power technology, over the years, becomes mature, reliable and easily available. Due to these reasons, thermal power shares more than 68% of total power produced in the world today. In our country share of thermal power is 69.5% (total thermal power installed capacity is 18,9497.78 MW out of total installed capacity of 272,687.17 MW from all sources) as on April, 2015. 

Thermal power & GHG production

  In thermal power plant, the heat energy from coal is used to produce steam that rotates a turbine. The turbine, in turn, rotates a generator, which produces electricity. Thus, the chemical energy stored in coal is converted to electricity. The coal or other fossil fuels are carbon rich energy sources. Coal, when burned in the boiler of the power plant produces carbon dioxide, a green house gas.

  Coal–fired power stations are the least carbon efficient power stations in terms of the level of carbon dioxide produced per unit of electricity generated, and gas is the best. On an average 2.095 pounds of carbon dioxide per unit of electricity generated is produced in coal–fired power plants. It is 1.969 pounds per unit of electricity in case of oil-fired and 1.321 pounds per unit of electricity in case of gas-fired power plant. With coal-fired plants generating the majority of electricity in the world, they produce the greatest share of carbon dioxide emissions from electricity generation, approximately 80% of the total. It has been calculated that thermal power plants are responsible for about 41% of U.S. man-made carbon dioxide emissions.

  The emission of carbon dioxide also depends on the efficiency of the power plant. The average efficiency of thermal power plant lies between 32 to 35%. The more efficient the plant, the less amount of carbon dioxide it emits. Substantial improvements in generation efficiency can be achieved in the future through the replacement of traditional power plants with more efficient technologies, such as supercritical boilers, combined–cycle units and combined heat and power systems.

Thermal power & climate change

  It is now clear that the earth is becoming warmer day by day due to green house effect. Among the green house gases (GHGs), carbon dioxide is the main culprit. At the beginning of industrial revolution, the amount of carbon dioxide in the atmosphere was 280 ppm (parts per million). After industrialisation more amount of carbon dioxide was emitted to the atmosphere by burning of coal and other fossil fuels. In March, 2015 the level has crossed 400 ppm. If we continue to use the fossil fuels at the current level, the amount of carbon dioxide in the atmosphere is projected to reach 560 ppm by the end of 21st century.

  Coal is used as fuel in many industries including thermal power stations. But the emission of carbon dioxide from thermal power stations is more than other industries. This is the only reason why the environmentalists now oppose thermal power, and engineers are thinking on alternative sources of energy.

Renewable sources of energy

  In the background of increasing energy demand but scarce availability and environmental threats, the search for alternative sources of energy started towards the last part of the last century. The alternate sources which have already assumed a significant importance are solar, hydro, wind and biomass.

  These energy sources are renewable in nature and environmentally benign. The magnitudes of all these sources are extremely large. The very idea of accessing these energy sources gives us a kind of confidence as far as energy security and sustainability is concerned, along with assisting in mitigating the climate change by way of reduction of carbon dioxide from power plants.

  The potential for renewable sources to provide clean and inexhaustible energy that is accessible to all is now universally accepted. Intergovernmental Panel on Climate Change (IPCC) in its Fourth Assessment Report on ‘Mitigation of Climate Change’ has observed that technologies are available for mitigating the climate change, however these require appropriate policy and financial support. Renewable energy technologies have been identified as one of the key mitigation technologies for energy supply, transport, buildings, agriculture and waste management.

  Renewable energy accounts for more than 10% of domestic energy production in the USA. According to the report the 'Energy Revolution: A Sustainable World Energy Outlook' renewable energy sources will account for 67% of the electricity produced in the developing Asia by 2050.

Solar energy

  Sun is the principal source of almost all kinds of energy, both conventional and non–conventional. Although solar radiation is being utilised from time immemorial for drying, heating etc, direct production of electrical energy from it is a recent one. The solar energy that we receive on the earth everyday can produce 2500 times more power that we currently consume. But we should have the proper means and technology to harness the energy economically. Electricity is being generated from solar radiation either by photovoltaic cells or solar thermal power.

  Solar radiation is directly converted into electricity by solar photovoltaic cells. The cell consists of two or more appropriately sandwiched thin layers of semiconducting material, usually silicon. When the solar cells are exposed to solar radiation, the incoming photons of radiation separate positive and negative charge carriers of the semiconducting material. This generates voltage and hence electricity. The higher the intensity of light, the greater is the flow of electricity. The electric output from a single cell is small. So a number of cells are connected in series or parallel to get the desired quantity. The module containing the cells is called a solar panel.

  Solar thermal power station is like a conventional thermal power station having steam boiler, turbine and generator. In the conventional thermal power station, water is heated by coal, gas or petroleum oil to produce steam, which rotates the turbine and generator to produce electricity. But in the case of solar thermal power station, water is heated by heat derived from solar radiation. Sun rays are concentrated at solar receiver made of calcium carbide to have greater effectiveness.

  To achieve this, sunrays are reflected from large mirrors, called heliostats, positioned at different positions at different angles so that the reflected rays concentrate at a point on the solar receiver. The surface of the solar receiver reaches to temperature as high as 10000C. In the receiver, a Heat Transfer Fluid (HTF) is heated. The HTF can be used directly in a small turbine to produce power or indirectly, to produce power when the heat is fed to a heat exchanger. The heat exchanger can transfer the heat in the HTF to high-pressure steam, which is fed to a steam turbine. Thus, although its principle is that of a thermal power station, here, no fuel is burnt, and hence there is no emission of carbon dioxide.

Wind energy

  Energy obtained from a moving mass of air is known as wind energy. Wind has considerable potential as a global clean energy source, as it is abundant, and also non–polluting. Wind energy has been one of the primary energy sources used for milling grain, pumping water and so on. From the early wind mills used in India, China and Persia over 2000 years ago to the present use of wind for energy generation, wind has always played an important role in people’s lives.

  Wind energy has attracted many investors throughout the world. Construction of the plant is very simple. A turbine with some blades coupled with a generator is installed atop a tower. When the turbine is rotated by the wind, electricity is generated. One essential feature for this plant is that there must be sufficient minimum wind speed available in most part of the year. Global installed capacity of wind energy was 369,600 MW by the end of 2014. Installed capacity of wind power is largest in China (114,604 MW) followed by the USA (65,879 MW), Germany (39,165 MW), Spain (22,987 MW), India (22,465 MW) and the UK (12,440 MW).

Hydro power

  Hydropower is currently the most common form of renewable energy and plays an important part in global power generation. Its technology is well proven and reliable. It has many advantages over thermal power. It does not aid in global warming. Worldwide hydropower produced 3,288 TWh, just over 16% of global electricity production in 2008, and the overall technical potential for hydropower is estimated to be more than 16, 400 TWh/yr.

Bio energy

  Electricity is now generated from biological sources like agricultural waste, plantations, municipality waste and bagasse etc. Biomass includes straw, stalks, stems, fines and agro-industrial processing residues such as shells, husks, de-oiled cakes, and also forestry residues. The conversion technologies used are combustion/incineration, gasification, pyrolysis etc., using gas or steam turbine, either in power alone or in co-generation mode. Co-generation is the multiple and sequential use of a fuel for production of steam and power in a process industry such as sugar mills, paper mills, rice mills etc., where biomass resources are either generated or consumed in their main processing/production process. Emission of carbon dioxide is minimal from this type of plants.

Development of RE in India

  In India, the importance of the role of Renewable Energy (RE) to a sustainable energy base was recognised as early as in the 1970s. There has been a visible impact of renewable energy in the Indian energy scenario during the last few years. Renewable energy has been witnessing over 20% growth in the last five years. From the total renewable power installed capacity of 14,400 MW at the beginning of 2009, it has reached a capacity of 35,776.96 MW at the end of April 2015. This is apart from large hydro, which has an installed capacity of 41,632.43 MW as on April 2015. The potential and installed capacity of different sources of renewable energy in India is given in Table-1. Also, a total capacity of 1,174.5 MW of power plant in different renewable energy sources have been installed, which are not connected to the grid (off-grid power).

  The growth of renewable energy in India is illustrated in Fig. – 1.

  Apart from contributing about 12.96% in the national electricity installed capacity, renewable energy based decentralised and distributed applications have benefited millions of people in Indian villages by meeting their cooking, lighting and other energy needs in an environment friendly manner.

  Renewable energy has been appropriately given the central place in India’s National Action Plan on Climate Change being finalised by the PM’s Council on Climate Change. India is perceived as an excellent country for developing Clean Development Mechanism (CDM) projects. As such, India has emerged as one of the most favoured destinations for CDM projects globally, with renewable energy projects having the major share.

  India has achieved significantly in solar, wind, small hydro and bio energy. Wind energy continues to dominate India’s renewable energy industry. India occupies the fifth position in the world in wind energy with installed capacity of 23,444 MW. India is also doing experimental studies for other renewable sources like tidal and geothermal.

Fig. 1: Growth of renewable energy in India...

Conclusion

  There is no doubt that increased concentration of carbon dioxide in the atmosphere leads to global warming and climate change. World wide concern over this has fixed targets to reduce green house gas emissions by between 25 to 40% by 2020. This will be difficult to achieve, if coal-fired plants remain in service, unless carbon capture and storage of emissions from coal fired power stations become viable. Some technology is available to limit carbon dioxide emissions, but it is extremely expensive. The extra cost means it is not economically feasible. In this situation, development of renewable power to mitigate climate change is absolutely necessary. India has taken a voluntary commitment of reducing emission intensity of its GDP by 20 to 25% from 2005 levels by 2020. The increased share of renewable energy in the coming years will contribute towards achieving this goal.

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Mayadhar Swain is Deputy General Manager, Mecon Limited, Ranchi.

Source: http://electricalindia.in/blog/post/id/6209/climate-change-and-role-of--renewable-energy

Status Quo Of Maharashtra

 India is the world’s fifth largest electricity generator with total installed capacity of 2, 75,911.62 MW. Out of this, 40% is from state owned utilities, 32% is from privately owned utilities and 28% is from central owned utilities. The pace of investment from private players is considerable, which shows an encouraging environment for the electricity sector. Currently, India has total 1,91,663.56 MW of installed capacity on thermal, 41997.42 MW of installed capacity on hydro, 36470.64 MW of installed capacity on Renewable Energy Sources (RES) and 5,780 MW of installed capacity on nuclear. Thermal sources contribute 68% in the total capacity.

  Fig-1 shows Indian top ten states have largest installed electricity capacity. The state of Maharashtra is at the top position in installed electricity generation capacity in India. The state of Gujarat is on second position of installed electricity generation capacity followed by Tamil Nadu, Rajasthan and Madhya Pradesh etc.

Fig-1- Installed Capacity of top ten Indian States (as on 31-07-2015)...

Fig-2- Maharashtra State...

  Maharashtra is a state in the western region of India and is the nation's third largest state and also the world's second-most populous sub-national entity. Its population makes Maharashtra one of the largest energy users of country. The high electricity demand of the state constitutes 13.91% of the total installed electricity generation capacity in India.

  By 31 July 2015, Maharashtra has 38,372.83 MW of installed capacity. Out of this, 28,145.20 MW generate from thermal (coal & gas) plants, 690.14 MW from nuclear plants, 3,331.84 MW from hydro plants and 6,205.65 from Renewable Energy Sources (RES) like solar, wind etc. Fuel-wise installed capacity in Maharashtra is given below. The fig-3 shows percentage of energy generation in Maharashtra by different sources.

Fig-3- Maharashtra Power Generation (Fuel wise)...

Power Generating Utility Of Maharashtra

  In the past, electricity provided to the state of Maharashtra by Maharashtra State Electricity Board (MSEB). MSEB was set up in the year 1960 to generate, transmit and distribute power to people in Maharashtra, except Mumbai. Maharashtra State Electricity Board (or MSEB) is a state-owned electricity regulation board operating within the state of Maharashtra in India. On June 6, 2005 Maharashtra State Electricity Board (MSEB) has been restructured into four companies. These companies include- MSEB Holding Company, Maharashtra State Electricity Distribution Company (Mahavitaran), Maharashtra State Electricity Transmission Company (Mahapareshan) and Maharashtra State Electricity Generation Company (MAHAGENCO). The state of Maharashtra forms a major constituent of the western grid of India, which now comes under North, East, West and North Eastern (NEWNE) grid of India. Fig-4 shows the Structure of Maharashtra Electricity Scenario.

Fig-4- Structure of Maharashtra Electricity Scenario...

  Maharashtra State Power Generation Company Limited (MAHAGENCO) has the highest overall generation capacity and the highest thermal installed capacity amongst all the state power generation utilities in India. In terms of installed capacity, it is the second highest generation company after National Thermal Power Corporation Limited (NTPCL). MAHAGENCO is the only State Utility having a very well balanced generation portfolio involving thermal, hydel and gas stations along with solar power plant.

  The first 500 MW plant to be installed in any State Utility belongs to Maharashtra. Maharashtra Power Generation Company (MAHAGENCO) operates thermal power plants in the state. In addition to the state government owned power generation plants, there are privately owned power generation plants that transmit power through Maharashtra State Electricity Transmission Company, which looks after transmission of electricity in the state.

  MAHAGENCO has an installed capacity of 12,237 MW. This comprises Thermal (nearly 73%, i.e., 8,980 MW) and a gas-based generating station at Uran, having an installed capacity of 672 MW. The Hydro-lectric projects in the State of Maharashtra have capacity of 2,585 MW.

  MAHAGENCO is simultaneously implementing capacity additions programmes of about 9,320 MW. Project execution works of 3,230 MW are in full swing and 6,090 MW projects are in advanced stage of planning. It is also working in the area of power generation from non-conventional energy resources, and has clear vision for Green Power for the consumers of Maharashtra. Table-2 shows the power plant installed in Maharashtra by MAHAGENCO and table-3 shows the ongoing projects in Maharashtra.

  MAHAGENCO is the largest power generation utility in Maharashtra under state government. Private sectors have also installed their power generating units in Maharashtra like TATA Power, Adani Power and Reliance Infrastructure etc. Table-4 shows the list of installed power plant by private companies.

Renewable Energy Scenario Of Maharashtra

  Maharashtra is one of the leading industrialized states in the country. Maharashtra's economy is growing very fast and so its energy needs are continuously increasing. In the past few years, the state has been facing a grim power demand supply scenario. Government has increased power generation by addition in thermal capacity in last few years – and work in progress to improve capacity of thermal plants. Now the government has aware about renewable energy sources, so state government has been taking various initiatives to increase the power generation through renewable energy. Maharashtra state government established Maharashtra Energy Development Agency (MEDA) to undertake development of renewable energy. MEDA did lot of work in the field of renewable energy focusing on rural areas.

  Currently, total installed Renewable Capacity in the state of Maharashtra is 6,145 MW. Maharashtra is one of the top states in India in term of the installed renewable electricity capacity. The state has conventional electricity capacity of 24,105 MW. Renewable energy has 14% share in total electricity generation capacity of the state. Fig-5 shows installed renewable energy capacity on the basis of resources. Wind energy dominant in all form of renewable energy in the state followed by bagasse, solar and small hydel.

  Table-4 shows the potential of renewable energy in Maharashtra. Wind power potential in the country is about 49,130 MW, while in Maharashtra it is 5,439 MW. Sites with Annual Mean Wind Density above 200 W/m2 are considered suitable for wind power projects. 339 such sites have been identified in the country, of which 40 sites are in Maharashtra. Maharashtra is one of the prominent states considering the installation of wind power projects second to Tamil Nadu in India. As on 30/09/2014, installed capacity of wind energy is 4167.26 MW. As of now there are 50 developers registered with state nodal agency "Maharashtra energy Development Agency" for development of wind power projects. All the major manufacturers of wind turbines including Suzlon, Vestas, Gamesa, Regen, Leitner Shriram have presence in Maharashtra. According to Maharashtra Renewable Energy Policy 2015, target of 5000 MW wind energy plants installation in state.

Fig- 5- Resources base installed Renewable Energy capacity (as on 31st July-2015)...

  Among the renewable sources of energy, solar energy has a huge potential for power generation in Maharashtra. There are 250-300 days of clear sun with an available average radiation of 4 to 6 kWh/sq. metre over a day. There is a capacity to generate 1.5 million units/MW/year through solar photovoltaic systems & up to 2.5 million units/MW/ year through solar thermal systems. MAHAGENCO has commissioned 130 MWp Solar Power Projects till date. MAHAGENCO aspires to increase its solar portfolio from current 130 MWp to 450 MWp by end of the year 2015-16. Currently, installed capacity of solar energy plants in Maharashtra is 378.7 MWp, which is 9.2% of total installed capacity of solar plants in india.

  As per MNRE the potential of small hydro power in India is 10,071 MW and in Maharashtra potential is 732.63 MW. The installed capacity in Maharashtra by the year 2013-14 is 278.40 MW. Till date all projects are developed by Water Resource Department, GOM through private developers. Target of small hydro plant installation as per Maharashtra Renewable Energy Policy 2015 is 400MW. There is a large potential in the non-conventional energy sources sector, out of which biomass is one of the major sources of energy. Maharashtra is having agricultural / agro-industrial surplus biomass with a potential of about 781 MW distributed through the state. This distributed potential can be harnessed to meet increasing power demand and to improve the techno-economic scenario.

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Nitin Goel is Assistant Professor (Electrical Engineering) at YMCA University of Science and Technology, Faridabad.

Managing Coal Fired Thermal Power Plants Efficiently

There are two major focus areas for Instrumentation And Control Systems (ICS) for Thermal Power Plants (TPS): Power block [boiler, turbine, generator (BTG) and associated auxiliaries] ICS for achieving generation and ICS for BOP (Balance Of Plant- the outlying auxiliaries) for providing the support. Traditionally, the focus of instrumentation and controls has been on the power block with the primary aim of achieving good generation. In the BOP areas, there is alow level of automation and instrumentation. This article identifies areas where installation of instrumentation and controls can bring about energy efficiency, safety and cost reduction in the primary cost components of a coal fired thermal station, viz., coal, fuel oil, water and auxiliary power.

  Primary sensing, data acquisition and storage systems, data highways, data base creation and software for totalization, secondary computations based on primary data, flexible report generation functions are essential for efficient plant operation in the following areas:
i. Coal measurement and management systems
ii. Oil measurement and monitoring systems
iii. DM water measurement and monitoring system
iv. Auxiliary power
v. Station heat rate

  Linking of the above to the plant operating parameters to calculate online indices or porting of plant operating parameters to these software is essential for efficient operation of the plant and cost control. There are technology gap in the above areas. ERP (enterprise resource planning) packages normally address inventory, knowledge, procurement, spares, maintenance and operational management and do not cover primary input tracking. Continuous and constant monitoring and control of fuel consumption, water consumption and auxiliary is essential for achieving cost effective power generation.

Introduction

  The major investment into coal plant ICS and condition monitoring is for the power block and electrical controls and their associated auxiliaries with an aim of achieving good energy generation (units generated in a given time slot and the unit loadability). Generation has always had precedence over energy efficiency, safety and cost considerations. The areas of outlying auxiliaries and inputs that go into the thermal power plants are audited through instrumentation of the analog type with human intervention. This was because the primary sensing technologies were not available and technology of data acquisition and data transfer were not cost economical for either on-line or off-line monitoring. The technology developments in the areas of sensors, computing and communication now enable cost effective solutions. The existing scenario therefore needs intervention through improvements in monitoring and controls of primary inputs that go into a coal fired plant.

  The concept of stand alone measurement grids/hubs through DAS (data acquisition systems) need to be implemented for the primary inputs, coal, fuel oil, water and auxiliary power. The stations must prefer Intelligent Electronic Devices (IEDs) over analog stand alone measuring equipment, which cannot be seamlessly integrated into a central server and which have provision for downloading data into a data base.

  Also, the concept of separate and independent receipt and consumption measurements would help in tracking of losses in the system. In most cases a single measurement represents both the receipt and consumption.

  Presently the station coal measurement at the TPS is mainly at the coal handling plant and the station as a whole is responsible for the overall coal receipt and consumption. The responsibility for accounting and tracking of coal consumption is not vested with any particular group such as Coal Plant Group, Fuel Logistics Group or Operations Group. For more effective management, the sharing of responsibility of coal consumption in the plant could be based on the jurisdiction of the various technical groups and can be as follows:

  Coal weight and coal GCV between the coal mine and the entrance of the CHP of the TPS: Fuel Logistics Group which liaisons with the mines and the railways, etc.

  Coal weight and coal GCV drop between Coal Handling Plant and the bunker: Coal handling Plant Group which receives handles and conveys the coal to the bunkers. It will be the responsibility of the coal handling plant to account for coal weight and coal GCV drop between receipt point and the bunkers.

  Beyond the bunker: Once the coal enters the bunkers and the mills, the Operations Group must take the responsibility to control and minimise the coal consumption.

  To implement the above, the instrumentation and control set up is to be developed to get a break up of the quantities at each level of the plant.

Technologies for determination and control of transit losses for operating cost reduction

  The technology of computing transit loss in many of the stations is obsolete and involves analog outdated machinery and manual recording at several places and also double recording resulting in wastage of manpower for recording purposes when it can easily be automated. Manual intervention increases chances of errors which are difficult to track and reconcile. Presently, the time constant to compute and realise the magnitude of the transit loss takes around 3-5 days.

  The technology of the pit type weigh bridges is obsolete and involves manual recording of analog signals. Printout in the form a dot matrix printer is also obsolete. Human intervention is inevitable in the measurement process. Though the accuracy is adequate the overall uncertainty is depending on the reliability indices of average interruption frequency and duration indices on an annual basis. Since the disposal rate of a rake is 4-8 hours, an outage of the weigh bridge for 1 day will lead to an uncertainty of 3 rakes.

  The power stations would benefit by going in for technology up gradation in this critical area of their operation. Global positioning system technology for precisely mapping and tracking the movement of the trains for effective tracing the origin and location of the transit loss is an appropriate solution. Rail tracking system through GPS or alternative technologies needs to be adopted.

  Rail signature system at the sending end and receiving end are also essential to ensure that there is no tampering. Rail signature systems are usually installed at the entrance to the coal yard at the tippler hopper area.

  The Wheel Impact Load Detector (WILD) developed under RDSO research initiative can integrate rail signature as well as wagon weighment at speeds in the range of 0-150 km/h in one system. Besides weighing of primary resources, viz., coal, accurately, the transit losses can be reduced by effective tracking of wagons from their source mine to their destination (power house coal yard). It is recommended to go in for fully automatic pitless in-motion weigh bridges (where the entire rake is measured at a speed of 10-150 km/h). Figure 1 & 2 show view of in-motion weigh bridge. 

Figure 1: View of location of in motion weigh bridge on railway tracks...

  The high speed in-motion weigh bridge should have an electronic digital interface to digital data transfer to a central server/data highway through communication media both at the sending and receiving end. The in-motion bridges would be required for gross weight and for tare weight at both sending and receiving ends. At a central server the data from the motion bridges can be downloaded into a data base – from which it can be used to calculate a variety of information automatically without any human requirements of feeding in data.

Technologies and models for station & unit coal measurement (coal receipt & consumption measurement)

  Since the weigh bridges are analog in design with open loop communication, human intervention is required and hence fully automated pitless in motion weigh bridges with digital interface and provision for data communication to a central server or receiver control room is recommended. These must act as Intelligent Electronic Devices (IEDs) and seamlessly communicate with the overall plant automation. Besides, fully automatic rail signature at the receiving end is also recommended with provision for acting as IEDs to communicate with the plant automation.

  The periodicity of coal inventory measurement is once in 10-30 days depending on the station practices. The inventory accounts for coal present in the coal yard and is used as a basis for working out the coal consumption in the units and in the station.

  Traditionally, the coal consumption was estimated by apportioning on the basis of units generated and specific coal consumption (kg of coal per kWh generated). Unit bunkers were filled based on the need – and the coal consumption was not being measured because of non availability of instrumentation for both coal quantity as well as bunker level indication. Many of the stations are not having complete gravimetric feeder set up on any Unit with provision for coal flow measurement. The quantum of consumption is not known accurately.

  In the absence of coal measurements to individual units, it is not possible to know the specific fuel consumption which is the basis for the heat consumption of the unit. The presently used system in many of the stations is highly inadequate and not sufficiently sensitive to unit performance. Hence, the estimated specific coal consumption does not reflect on the realistic coal consumption of any particular unit in question. The coal entry into the boilers of each unit needs to be measured. At present technologies for on-line or off-line coal monitoring of unit coal consumption are available and are also in use in a few of the stations.

  An online process (without any human intervention) which would give the on-line coal consumption with uncertainties of 1.0% is feasible and the technology for the same is well proven and established. The conventional stacking method can be used for reconciliation of data/cross verification only and not for coal consumption measurement.

Figure 2: View of recorder of in-motion weigh bridge...

  The use of fully automated, tamper proof modern instrumentation free of human intervention for on-line coal inflow and consumption needs to be used. Based on an assessment of the different technologies the following are recommended in the Indian scenario:

i. Installation of belt weighers for all coal conveyors. The belt weighers alone do not give unit specific coal measurement which is essential for accounting purposes. The belt weighers give weight of coal moving through it between any two time intervals. The arrangement for unit wise coal consumption is essential. This is possible by providing a system of monitoring the time elapsed by a belt over a given bunker and which involves integration of the output of the belt weighers over the total bunkers of a given unit in a given period of time. A viable and innovative scheme for monitoring the bunker wise coal from the belt weigher data is possible through time wise integration of belt weigher data and totalization in separate data bases assigned for each of the bunkers. 
ii. Coal level in the bunker is presently recorded manually which is obsolete and does not give quantitative data on the bunker level. Further it gives data only when the persons inspect it and does not give the exact height of the coal stack. The height of the coal stack is generally not uniform and is measured through a string. Microwave or Ultrasonic bunker level monitoring system with digital data output, communication of data to central server or control room is required.
iii. In addition to belt weighers, coal flow into the units needs to be monitored by gravimetric feeders (in each mill) which provide accurate and authentic coal flow measurements. This is to provide a redundancy in the measurement. The differences in the two are to be reconciled to be within 0.5%. At present, there are several types of reliable gravimetric feeders available and any reliable feeder can be installed.
iv. DAS &Software is to be in place for integrated online coal energy management in the plant. The software inputs data from the various field instruments for coal receipt into the station from various sources (such as wagon tippler, track hoppers, ropeways, trucks, conveyors, bucket elevators etc.) and coal consumption at various bunkers. This software must also compute the coal consumption, heat consumption, heat rate, etc., at various points, on line. The DAS software and hardware are to form a self centered grid/hub for coal management with open architecture and seamless interface with other DAS/DCS.
v. Computation of unit coal consumption. This is purely from the reading of the belt weighers and bunker monitoring system. This coal consumption is to be used for computation of unit and station heat rate for normal and cycling operations as per international practices.
vi. Computation of stacking loss. This is the difference between the total online receiving end coal consumption and the total on line bunker wise coal consumption of each unit. If all weighing instruments are fully automated IEDs, the on line stacking loss can be computed.
vii. Computation of coal inventory over a time period of month, quarter and year is through stockpile contour profiling software based solution such as Total Station, etc. for more accurate stock pile measurement. The bulk density of coal (kg/m3) needs to be physically determined for crushed and uncrushed coals as well as coals of different varieties and weighted average needs to be taken rather than one single value for the entire stockpile.

  In all above instruments to be fixed the following must be observed:

• The instruments must function as Intelligent Electronic Devices (IEDs) by digitally communicating with a central server or control room through downloading of data continuously. The data from each of the sensors must be downloadable into a data base format from which it must be compatible with other data for on-line calculations. 
• The instruments must have provisions for communication of digital data. 
• The instruments and the digital conversion systems must have a very high reliability in terms of 0.5 interruptions per year and 4 hours per year. 
• The integrated coal DAS must be of open architecture. 
By this process the coal consumption will depend on the unit performance and not vice versa. The other advantages are:
• The process is fully automatic and does not involve human intervention
• The process is closed loop without scope for errors from extraneous sources. 
• Stone picking, tippling and weighment need not be coupled and these can be independent activities. 
• The measurement will be available on line to all concerned and avoids 10 days time delays for each settlement slot of coal consumption. 
• Wireless data communication can be adopted.

  All the above technologies are proven and in use in many power stations across the country.

Technologies for measurement and computation of average heating value of coal

  The heating value determines the coal consumption. The measurement of GCV is as important as the coal quantity measurement as it directly affects the coal consumption and generation cost on account of coal.

In the TPS context three heating values are of importance:

i. GCV (dispatch end): Gross heating value -a commercial heating value for payment purposes.
ii. GCV: Gross heating value of the received coal sampled at the point of unloading.
iii. GCV: Gross heating value of the coal fed into the boiler and sampled either at the conveyor belt to the bunker or at the coal feeder.

  Accordingly, the heating value of coal is determined for the following three cases:

i. GCV (sending end coal) (kcal/kg) of Coal dispatched from collieries: rake wise, colliery wise, weekly and month wise data.
ii. GCV (receipt coal) (kcal/kg) of Coal received from collieries: rake wise, colliery wise, weekly and month wise data.
iii. GCV (fired coal) (kcal/kg) of Coal being used in the units: shift wise, unit wise, stage wise and month wise data

  While receipt coal is sampled on the basis of mine, rake, truck, ropeway, etc., the fired coal is sampled on the unit wise basis. Earlier practice was to determine only sending end GCV and bunkered coal GCV as the receipt GCV data was not directly used in any calculation. Presently, the stations are determining the GCV of receipt coal as well as GCV of fired coal, in addition to the sending end GCV.

Figure 3: View of a  bomb calorimeter...

  Heating value determination: In many cases, the GCV is determined by proximate analysis. The GCV of sending end, receipt coal as well as bunkered coal is being determined by proximate analysis or by a bomb calorimeter. All GCVs need to be determined only by a bomb calorimeter and never through proximate analysis (Figure 3).

  For further refinement in the heat value determination, sample to sample variation in a rake (for receiving end coal) for each rake and to measure in-sample variation to select the minimum sample size. This data can be used to authenticate the GCV values determined.

  Averaging schemes for monthly GCV (dispatch coal and receipt coal): The averaging of the GHV (dispatch) and GCV (receipt) is based on weighted average of each independent consignment received at the TPS through EXCEL. The software for auditing of the quantities and individual heating values calls for a data base for compilation of the monthly average values between pre-defined points of time. The data base is required for establishing the correctness of the monthly average values as well as archiving of the data over a period of time.

  Averaging schemes for monthly GCV (bunkered coal): The monthly value of GCV which is a single point GCV is obtained from mixing all monthly samples and determining the GCV through a bomb calorimeter. In addition to the above, the GCV of daily sample is also determined and the weighted average value of the daily GCV is taken to determine the monthly GCV. The GCV of the average value is reported and the mix sample is used for tallying. The monthly average bunkered coal GCV is the basis for declaring the GCV, which goes for cost calculations and which is used for computing the SHR (Station Heat Rate).

  Receipt coal sampling: Manual sampling is being resorted to in many stations where there is no automatic sampling. Change over to mechanised auger sampling must be done at the earliest. The automatic vehicle mounted auger may be used extensively in all stations for all receipt coal as it will help in taking out coal samples up to a depth of nearly 2m from the top of the wagon. In manual sampling, only top coal is removed and the internal coal is not sampled.

  Bunkered coal sampling: To minimise sample to sample variations in coal quality, use of automatic samplers is suggested for bunkered coal. Further it is quite cost effective in comparison to manual sampling which is a time consuming process.

  Automatic samplers for collection of bunkered coal samples are as follows:

  Sampling from static heaps such as bunkers:

• Auger
• Sampling shovel
• Automatically operated bucket moving with uniform speed into the falling coal stream at adjustable intervals of time

  Sampling from falling stream such as feeders:

• Breeches chute type sampler 
• Swinging arm type sampler 
• Chain bucket type sampler 
Sampling from moving conveyor belts:
• Sweeping scrapper arm

  Automatic buckets and swing arms are good for coals with wide ranging size distribution.

  Sample preparation: For the sample preparation process, primary & secondary sample crushers and sample pulverizes are required to be constantly repaired to ensure that the grinding surfaces are intact and not eroded to provide the sizes stipulated in the standards.

  GCV data management: The GCV values are being recorded into a register without back up of computer print out to authenticate the recorded data. The GCV values are being recorded into the register with human control loop leaving scope for errors. The process needs to be made more transparent and authentic. The process of entry of the data from the bomb calorimeter into the register needs to be automated and authenticated by back up data either from a print out of the memory of the bomb calorimeter or print out of each value.

  Coal characteristics as operational aids: Equipment for TGA analysis of the coal may be introduced. The equipment must be fully automatic with provision for transmission of the results (TGA traces) to a central server or control room from where the different groups can view it. The combustion characteristics are not dependent on the GCV alone but on the percentage of volatiles. If the volatiles are too low in the coal then even though GCV is high its combustion characteristics are affected. This information can also be used to ascertain that the flame temperature is appropriate for a given coal. This analysis must be done before the coal goes to the bunker so that the operator is well aware of the combustion characteristic during the shift. It is clarified here that obtaining a TGA after the combustion is over is only of academic interest and does not provide the operator with any inputs for operational optimisation. This will be useful when there is over 3 days coal stocks.

  Ultimate analysis (elemental analysis) mapping of coal from different mines and sources is essential at least once a month instead of biannually or annually in many stations through a carbon, hydrogen, nitrogen (CHN) apparatus. This is useful for process optimization of boiler efficiency. At present ultimate analysis is not finding much use in operational optimisation in many stations. This is an essential requirement for optimisation of heat rate as it is used for computing the flows and losses in the boiler.

Technologies and models for measurement of fuel oil (receipt and consumption monitoring)

  Fuel oil refers to basically Furnace Oil (FO) and Light Diesel Oil (LDO). In the present energy context considering that oil is a scarce resource, the instrumentation for measurement of oil receipt and consumption is inadequate in many of the stations. Oil consumption in individual units is not available to a pre-designed accuracy level based on individual gun hours. Though the total consumption of oil is known reasonable, the individual unit wise consumption required for energy control is not known accurately as this is apportioned based on gun hours considering equal flow of oil in each gun. Moreover, the oil measurement involves human intervention through manual recording of levels.

  Oil receipt measurement: Pitless in-motion weighbridge is recommended for measurement of oil in tankers. Fully automatic ultrasonic level indicators with provision for conversion of signals into digital signals and communication through a media to central server or processor could be considered for installation for all oil tanks. The digital signals must be downloadable into a data base on a continuous basis. A fueloil monitoring software package with DAS hardware is to be in place for on line calculation and logging of the oil receipts, etc.

  Oil consumption measurement: The present method of oil measurement in many of the stations is based on manual log reading of the on-off timing of the oil guns multiplied by a constant gun oil consumption. Alternatively pump hours are also taken as a basis for measuring oil consumption between two time intervals. Fully automatic differential pressure orifice plate or nozzle type or mass based oil flow meters with provision for continuous digital data transfer would be useful for all units for monitoring oil consumption. Continuous logging of oil indicator levels can also be used for oil consumption monitoring (Figure 4).

Figure 4: View of level indicator for fuel oil...

  The oil gun on-off operation data must be recorded through a time based system automatically to give a time trace of when the guns are on and when the guns are not in service. This will be useful for performance optimization group to study the operator to operator variations, coal to coal variations, variation in different seasons, etc. Solenoid valve based on-off monitoring of gun time may be introduced. This is not much useful for oil consumption monitoring.

  Integrated fuel oil receipt and consumption monitoring: A fueloil monitoring DAS & software package is to be in place. When digital ultrasonic level data of tanks, digital individual unit wise oil flow data, individual gun hours data, GCV of oil, etc., are available on line, the software package must calculate the oil receipts, oil consumption, shift wise, unit wise oil consumption, specific oil consumption, time trace of guns, oil consumption during cycling operations, heat consumption due to oil usage, contribution to heat rate, etc.

Technologies and models for measurement of DM water and associated water systems

  The power generation process involves production, storage, transfer and measurement of DM (De-Mineralized) water, soft water, raw water and drinking water- production, consumption and flow. DM, Soft water, raw water and drinking water all need to be measured and audited for overall water balance on line and in real time and must not be assumed values.

  In many of the stations, the flow instrumentation in the entire DM plant is not adequate. Separate consumption and production measurements are not available. Online monitoring of DM water flow is available and unit make-up with integrators are essential to control the energy efficiency as the make-up is directly proportional to the steam lost from the system and affects the unit heat consumption and heat rate. Fully automatic on-line measurement of water consumption for both production and consumption measurement of raw water, DM water, soft water and drinking water is required for auditing and conserving the water consumption and reducing the water related costs of generation.

  Both DM water production and consumption must be separately measured and audited. In the absence of separate measurements, it is normally construed that all production is utilized and hidden losses are not identified.

Figure 5: View of console a typical control panel in a coal power plant...

Figure 6: Older design of control panel of a coal handling plant in a power station...

  Installation of fully automatic differential pressure orifice plate or nozzle type flow meters with digital output, communication media to relay the data to a central server or the DM control room computer and provision for downloading the data into a data base for on line monitoring of make up especially during cycling operations is essential for auditing water consumption. During cycling operations such as warm, hot or cold starts considerable amounts of steam is lost and has to be replenished. On line monitoring of DM water would help in control of unit heat rate as well as give an accurate account of the chemicals consumed for DM water production.

  Integrated water monitoring DAS & software package: The package must have capability to draw inputs from the various field instruments (which will act like IEDs) and make an on-line continuous data base grid of the information for generation various types of information such as consumption per unit per shift, consumption during cycling operations, operator wise consumption, etc., to enable the performance optimisation group to take control action on the areas of wastage and excessive consumption. Consumption and production should be separately monitored. At present only gross data is being recorded and is not useful for energy control.

Technologies and models for measurement of auxiliary power

  The auxiliary power is computed off-line at many of the power plants by collecting energy meter readings by 24 hours interval at control room. At present the power stations are computing the auxiliary power by the following procedure:

i. The gross energy generation is computed by taking the generator energy meter readings.
ii. The in-house auxiliary power is computed by taking the energy meter readings of UAT (Unit Auxiliary Transformer) bus.
iii. The station auxiliary power is computed by taking the summation of energy consumption of station transformers and proportioned for individual units based on its gross energy generation.

  In many stations, the CTs and PTs are of low accuracy class even though metering is of 0.2 class. Hence, all the CTs and PTs at plant and Generation Control Room (GCR) must be of 0.2% accuracy class for energy billing. For all HT auxiliaries their power output should be recorded through sensors (3 voltages, 3 currents and 3 phase angles) and specific energy consumption should be indicated for process optimisation. Adoption of single phase data is neither accurate nor diagnostic.

  Integrated DAS & Software for auxiliary power: Automatic data logging of generated and auxiliary power is required for evaluation of energy consumption and its use pattern. Typically energy management systems are useful. Figure 5 shows the console of a typical control panel as compared to older control panels (Figure 6).

Technologies and models for measuring station heat rate

  Many individual units in stations (almost 60-70%) are not having an up to date heat rate evaluation package or a performance evaluation modules. OEM (Original Equipment Manufacturer) supplied package is in use for some units but not adequate if these packages are supplied long back.

  Installation of on line heat rate monitoring packages is essential for each and every unit of the TPS. These packages need to be utilised for heat rate computation for turbine heat rate computation while boiler efficiency is calculated from indirect method. On-line unit heat rate packages may be installed for units that do not have it. From the combined output of the online heat rate of individual units, the on-line capacity weighted average Station Heat Rate (SHR) may be computed. Offline standard heat rate package may be procured for SHR.

  It is essential to go in for actual measurement of heat rate based on instrumented on line monitoring of coal and oil, which enter the unit and the energy generated from these. It is essential to link the units generated to measured quantities of coal and oil within accuracy bands which are pre-fixed and maintained. The reliability of instruments is required in the order of 0.5 interruptions per year and of 4 hours per year.

Plant instrumentation & controls

  Some of the areas for improvement are as follows:

i. Many units do not have a Distributed Control System (DCS) and rely on analog control systems with no data storage and no data transfer capability. Introduction/up gradation of data highway and data storage to modernise the C&I system is essential.Upgradation of the data acquisition, storage and data high ways along with specialised or customised software is essential for transparent, efficient operation and maintenance of the power plants to meet its objectives through network and internal integration of data. 
ii. O2 measurement may be introduced after APH at the ID fan discharge. This will give the APH in-leakage. The O2 measurement may be on the basis of forming a grid of a minimum of 3 sensors in one duct. This will help in providing the representative O2 levels. 
iii. On-line CO measurement is presently not reliable. Off line CO measurement is now need based. Continuous monitoring of CO before APH may be introduced for combustion optimisation. 
iv. Introduction of fire ball visualisation through infrared/acoustic/optical pyrometry or Visual systems through CCTVs with filters. 
v. Furnace Exit Gas Temperature monitoring system (FEGT) with HVT (High Velocity Traversing air cooled probes) using acoustic pyrometry/infrared thermometery/radiation pyrometry/visible CCTV with filters.
vi. On-line condition monitoring through on-line vibration measurement of major HT auxiliaries like ID fan, etc.
vii. Variable pressure operation and sliding pressure operation to be used. 
viii. Replacement of AVR (Automatic Voltage Regulator) by digital voltage regulator (DVR) for units which do not have these. 
ix. Electromechanical relays for generator protection may be replaced by group solid state numerical relays.

Conclusions

  The main conclusions of the study are as follows:

i. Cost control of components affecting generating cost like fuel, water and auxiliary power is possible through auditing, monitoring and constant control which is possible only through a strong instrumentation and control system. 
ii. Measurement of important parameters which affect the input costs like coal, oil, water need to measured and not estimated.
iii. Both receipt and consumption need to be separately monitored, reported and reconciled through computerised Data Acquisition System (DAS) in respect of coal, fuel oil, water flows through the plant. 
iv. There must not be human intervention in the measurement, recording, averaging and compiling quantities of coal, fuel oil and water resources which affect the station input costs. 
v. Transit loss, specific fuel consumption and GCV are interlinked and realistic quantification of these will only be possible if an integrated automatic fuel monitoring DAS hub is in place. 
vi. Measurements and data grids are required for the following areas:
→ Coal (imported, raw & washed): Measuring of in-motion railway wagons, ropeways, conveyors, bunker levels and coal fed into each unit. 
→ Fuel Oil (LDO & FO): Overall of each unit and station. 
→ DM water: DM water production and consumption in each unit.
→ Raw water, soft water and drinking water: Consumption in various locations including intake. 
→ Auxiliary power (UAT & ST): The measurement of individual equipment power is required. 
→ The measurements of these parameters are not enough. Totalisation and data handling to compute receipts and unit consumption on-line, daily and monthly and yearly are required. Mere installation of instruments at the key points will only give stage-wise consumption but not unit wise consumption. For energy monitoring, unit wise consumption is essential. The instruments must have features for recording unit wise consumption by time totalisation into multiple data bases. Also, these equipment must be of the continuous recording type with digital interface and provision for totalisation over the year. Further these instruments must have high reliability.

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M Siddhartha Bhatt
Director
Central Power Research Institute, Bangalore

N Rajkumar
Engineering Officer
Energy Efficiency & Renewable Energy Division, Central Power Research Institute, Bangalore

Source: http://electricalindia.in/blog/post/id/12936/managing-coal-fired-thermal-power-plants-efficiently