Technology | September 2012
Vision for coal handling by 2020
With India targeting to install 15,000 MW every year, coal handling systems will also need to be enhanced as it is one of the most important functions in thermal power plant operation, Jitendra Kumar gives an insight and technical know-how about the coal handling process in the country.
Growth of power sector is the key to the economic development of a country and if India has achieve a double-digit economic growth there will be enormous energy requirement. As per the projections of Integrated Energy Policy, about 15,000 MW of thermal capacity has to be added every year over the next two decades. This requires installation of large number of coal- and gas-based plants for sure. To achieve the faster capacity addition targets, large capacity plants including 4,000 MW Ultra Mega Power Plant (UMPP) using 660 to 800 MW supercritical units is the only way forward. To achieve the targets, land and water will be the key requirements. Obviously, non-conventional energy sources such as solar, wind and other alternatives could be a complementary and would hardly contribute in a major way to achieve the goal of 15,000 MW every year. Therefore, thermal with UMPP can be projected as key future plants for power sector.
Land, coal and water are the essential requirements for setting up any coal-based thermal power plant. Land is mainly required for main plant, ash dyke, township, coal handling plant, etc. Coal is also very important for feasibility of any project. Blended coal – either mixing of 70:30 or 50:50 of Indian to imported coal – is the available option because of following facts and figures.
If we see the statistics of coal demand and availability position during the year 2011-12 and projection by 2020 in the Table I, we can assess that coal demand is likely to be almost doubled by 2020 and so the scope for coal handling will increase.
Coal handling plant is the lifeline of coal-fired power plant or dining table for thermal power plant. From here, our thought process starts, ie,
Reduction in the quantity of coal requirement is not possible, as it depends upon station heat rate and gross calorific value (GCV) of coal.
- How to minimise the land requirement in coal handling plant area?
- How to decrease the total length of conveyor inside the power plant (total conveyor length is approx 6-7 km for 3x660/ 2x800 plants)?
- How effectively coal blending is to be done?
Coal handling plant requires large land area. When a plant is to installed on irregular terrain, additional conveyor length required solely to gain the necessary elevation to transfer the coal from system, conveyor to conveyor, system. Thus, plot contour, size, and shape of plant are decrease or increase the cost of coal handling plant.
Coal handlings are to be flexible, reliable and capable of handling large quantities in less time than even before.
A general key plan of coal handling plant is as follows:
In all CHP, these are normal issues:
1. land requirement is very high
2. to install no of transfer point/junction tower (TP/ JT)
3. All conveyors and JT/TP are in straight line (with minimal directional change) and each directional change typically require its drive unit (motor + gear box + couplings + brake)
4. System are open type rather than enclosed it generate dust
5. Large number of moving parts (which require frequent maintenance)
6. Land is always on high side
7. Blending of coal is not 100 per cent
Hybrid coal handling plants will go a long way to solve the above problems. A typical hybrid coal handling plant is the combination of mechanical conveying and pneumatic conveying system. The usage of hybrid coal handling plants could prosper as early as 2020.
Salient features of hybrid coal handling plant:
1. Mechanical system from coal unloading from wagon tippler/track hopper or both to crusher house,
2. Pneumatic system from crusher house to coal bunkers and while reclaiming coal from stock area to coal bunker via crusher house
Pneumatic conveying offers a variety of benefits:
Pneumatic Conveyor – The basics:
- Apart from better blending of coal, benefit of pneumatic conveying will see reduction in land use, length of belt conveyor, numbers of transfer points, civil and structural quantity and numbers of dust suppression unit. In addition, there will be no dust in pneumatic conveying area
- However, it is to be noted that power consummation in pneumatic conveying will be slightly more however it can be reduced by proper layout
Pneumatic conveying is a material conveying system in which material moved over distance (horizontal + vertical) with the help of air (using +ve or –ve pressure of air). Material is forced through pipe/pipes and finally separated from the carrier air and deposited at the silo/hopper/bunker.
The heart of pneumatic conveying system is its design that relies on proper pick-up velocity and an accurate calculation for pressure drop. Material velocity is also imported.
Material to air ratio will be on higher side preferably more than 40/50:1 and provision of booster and minimum number of bend along the line will also result in for less requirement of air for conveying of coal.
Motive force for this transfer comes from a combination of pressure differential and the flow of air.
Pneumatic conveying systems are classified by their operating principle, ie, dilute and dense phase.
Dilute phase - Pick up velocity at system start at its lowest speed operate at high velocity at low pressure differential (suspension flow)
Dense phase - low air velocity and high pressure differential (fluidised flow)
As pneumatic conveying system is not new for power sector (as Ash & Mill Reject are already handled by pneumatic conveying), Mill Reject material is more or less similar to crushed coal. Crushed coal may convey easily than the Mill Reject as the size of crushed coal will be 50 mm.
In pneumatic conveying, dense phase is better option as it can convey as per capacity required.
From the above, it may be suggested that a well designed pneumatic conveying system is often a more practical and economical method to convey the crushed coal. Its reliability and cost effectiveness through reduced land costs will make it a preferred choice for future power plants.
CIL to adopt advanced technologies
It is the endeavour of Coal India (CIL) to introduce innovative and modern technologies to improve productivity in various subsidiary companies including Mahanadi Coalfields (MCL).
At the planning stage of underground mines based on the techno-economic feasibility, priority is given to adopt powered support long-wall technology or continuous miner (CMs) technology or other appropriate technologies like Blasting Gallery Technology with remote controlled Load Haul.
Dumpers (LHDs), Highwall Technology etc
Currently, eight numbers of Continuous Miner Machines are operational in different subsidiaries of CIL. One Highwall Technology Project is operational in South Eastern Coalfields. Further, CIL has drawn an action plan for technology upgradation in the 12th Plan, as per which seven longwall technology projects and twenty one continuous miner technology projects are envisaged which includes four continuous miner projects in MCL. Tenders of two longwall projects, one each in Eastern Coalfields and Bharat Coking Coal have been finalised recently. This was informed by Pratik Prakashbapu Patil, Minister of State in the Ministry of Coal in Lok Sabha.
In case of Opencast Mines, different technologies namely, Shovel-dumper combination, dragline operation, surface miner operations, crushing and conveying technology etc, have already been adopted. Adoption of higher capacity heavy earth moving machinery (dumpers, shovels, dozers, draglines, drill machines, surface miners) is a continuous process.