© 2009 Er. Jagvir Goyal
Note: This highly informative and elaborate paper was written by the Author many years back and holds valuable information. Readers should update themselves with the latest developments that might have occurred after the presentation of this paper.
India plans to add 6,50,000 MW of power to its power generation map by the year 2030. At the moment, it looks like an imaginary figure. In the next four years ending March 2012, 78577 MW of power are planned to be added. By achieving that, India aims to make power available to its cent percent population and also raise the per capita consumption to 1000 units per year from the present 631 units. The power planners are determined to achieve the target by overcoming the problems which are, as always, plenty, in view of fuel shortages and lack of capital investment resources.
There is no alternative to setting up of more and more power plants if we want to keep pace with the world. Annual Power surveys reveal that demand for power is increasing by geometrical progression. Rapid urbanization is further raising the rate of increase of power demand. It is time to involve larger industrial groups in power sector development, identify more sites to set up power plants and develop non conventional energy sources also.
Why thermal plants? Looking at the various options that the country will like to exercise for capacity addition, though thermal plants are desired to be the last choice for capacity addition because of the environmental pollution these cause, coal shortages faced by them and the global warming effect that this sector makes yet we have no alternative than to add more and more thermals to attain power sufficiency. Solar energy remains the best option but present technology can’t utilize it on mass scale. Hydel power is viewed as the cheapest and environment friendly one but many hydel projects are not coming up. Long gestation periods, large capital requirements for their setting up and difficult terrain of Himachal have been the main reasons behind non-exploitation of this best source of power. Nuclear power has so far been a controversial subject. After the signing of India-US agreement, hopes have arisen that many nuclear power plants will come up in the country. Yet, many questions linked to nuclear power are being raised by anti-groups repeatedly. These need to be answered in a convincing manner. Under the circumstances, it is felt that a major percentage of 78577 MW to be added by 2012 shall again belong to thermal and gas based power plants only.
Equipment for Thermal power projects: A thermal plant has many components like gigantic cooling towers, tall RCC chimneys, boiler units, turbo-generators, cooling water ducts, coal handling plant, ash handling plant, storage pond being the major ones. These require many types of specialized equipment for high rise structures, for dewatering, fabrication and erection of steel, excavation, concreting and other activities. Here are some guidelines over the equipment required for the setting up of thermal Power Projects. This information will prove handy and helpful to the power plant developers:
Slip form equipment for chimney: Slip form equipment is required for construction of a tall RCC chimneys of thermal power projects. It is impossible to construct tall chimneys without using slip form equipment. Slip form is further of vertical and horizontal slip type. Vertical slip form equipment is required for chimney construction. No other structure of the thermal power plants uses slip forms.
Slip-forms are ideally suited for the construction of tall reinforced concrete chimneys in a fast manner. These build the chimney on a continuous basis, involve operations of highly sophisticated nature and facilitate round the clock concreting work. These primarily consist of shuttering panels which envelop the structure along its designed shape and then are moved upwards continuously leaving below the structure in its final form.
Slip form equipment consists of forms attached to the walers which stiffen the form panels and transfer the load to the yokes. The hanging scaffolds and working deck are also connected to the walers. The waler yoke connection is designed to transfer all loads of the decks to the yokes. The yokes transfer the loads to the hydraulic jacks which further transfer the load to the jack rods on which they ride and rise. The jack rods get embedded in hardened concrete and transfer the load to the base or the foundations.
Jump form equipment for cooling towers: Jump form equipment is best suited for the construction of natural draft cooling towers required at thermal power plant sites for cooling the hot water supplied by the condensers. Cooling towers are hyperbolic structures and it is more feasible to construct them by use of jump form equipment rather than slip form equipment. No other structure of the power plant uses jump form equipment except natural draught cooling towers.
Jump forms are used for the construction of cooling tower shell only. There is no need of removal and re-fixing of shuttering plates. These slide up, both on the inner and outer faces of shell and are adjusted after every lift, to suit the new inner and outer radii of cooling tower. After the initial few lifts which require heavy concreting due to large diameter and thickness, all further lifts can be laid in a single day for full periphery of cooling tower. This arrangement results in construction of a 120 metre high cooling tower in 4 to 5 months thus saving a substantial time period.
Jump form equipment can be adjusted to suit uniform as well as variable dimensions. The dimensions can increase or decrease as the structure is built. As the dimensions of a cooling tower decrease up to throat level and increase thereafter, jump formwork suits it best because of the facility it provides for adjustment to suit the required parameters. Jump formwork has telescopic railings provided on each deck to accommodate the reduction or increase in perimeter. Similarly, the deck planks can also be adjusted. Top portion of the equipment is kept in traveling form so that the concrete-pouring deck could be adjusted and locked in a position near the periphery of the structure. Diagonally installed spindles can adjust the formwork to suit the actual profile of the structure.
Tower Crane for station building: Another essential equipment required for construction of thermal power plants is a high rise movable tower crane. Generally the height of station building housing the turbines, generators and unit control boards is about 55 to 60 metres. The structural framework of steel for station building therefore goes up to that height. Thus the height of tower crane jib has to be about 70 metres or more. Same tower crane is used to erect in position the structure housing the boilers. Mostly, the tower crane is among the first equipment to arrive at site.
Tower crane track: The station building of the power plant covers a large area, generally of the size 30 metres X 60 metres. Thus the tower crane has to be of movable type so that it may erect all structural steel columns along the periphery of station building and the inside rows of columns. A rail track has therefore to be laid at site to run the crane over it.
The track is kept flexible and rails are laid over them. A maintenance gang keeps a constant vigil over the track to add stone to it and to maintain side slopes as mostly this track is laid over and above the ground and any settlement of track may destabilize the tower crane leading to dangerous situations and fatal accidents. Generally a T shaped track is laid around the area of operation. However, the area and extent of operation decides the length and layout of tower crane track. For an assembled tower crane, it is difficult to change track. Therefore, it is advisable to avoid any sharp curves, bends and even right angles in the tower crane track.
Gantry Crane for steel structure work: An electric Gantry crane is also essential for setting up of a power plant. The span of the track is around 15 to 20 metres. Laying of Gantry crane track is also among the first few activities taken up at power project sites. The gantry crane is required for shifting of heavy structural steel members and fabricated members in the fabrication yard. Unlike the flexible tower crane track, the gantry crane track has to be of rigid type. RCC tracks are therefore laid at site for gantry crane as per dimensions of the gantry and for fixing of rails over them.
Ready Mix Concrete Plant for concreting: In case a Ready Mixed Concrete plant is established near the power plant site to supply all concrete required by the thermal power project throughout its tenure of construction, it proves highly beneficial. Large quantities of concrete are required for different structures of the power plant. Concrete mix designs are different for various structures. Availability of an RMC plant near the power plant site proves a boon for it. It results in saving of a lot of working space at site as site production of concrete consumes a lot of space. Space constraints at power plants are very common and often result in adding delay to the commissioning of the projects. A RMC plant thus solves this problem to a large extent. Above that, the quality of concrete is also ensured. In case an RMC plant is not available or can’t be set up, a Concrete Batching Plant should be set up at site and concrete should be fed to various structures from it.
Hydraulic Excavators for excavation works: As hydraulic excavators have become essential equipment for every large project, thermal power plants also need them. Hydraulic excavators are used at power plants for excavation of foundations for the main plant, for excavation of foundation and cooling water basin below the natural draught cooling towers, for excavation of pile cap or raft foundation of tall RCC chimneys, for excavation of foundations of various structures of coal handling plant and ash handling plant, for excavation along the cold water tunnels and hot water tunnels. A number of hydraulic excavators are required for the excavation of Circulating Water pond as this pond is generally of very large size, its area running into many acres.
Piling Rigs for chimney and other foundations: Many structures of the power plant need pile foundations depending upon the height of structures and the sub-soil conditions. Mostly, these structures are RCC Chimney, Cooling towers, Coal handling plant structures and boiler structure. Bored Cast in Situ piles or driven RCC piles may be provided for these structures. Pile driving rigs will be required for providing driven piles. For providing bored cast in situ concrete piles, electric or diesel winches of 5 to 8 ton capacity with 50 hp motors, tripods, bailers, chisels, casing pipes, trimie pipes, bentonite mixing equipment, funnels etc are required. There is hardly any thermal power project that doesn’t require pile foundations for one of its structures. Pile driving equipment is therefore another essential equipment for the power projects.
Mobile Cranes for handling materials: Mobile cranes often swarm a power plant site. These cranes are the most obvious equipment that comes to the mind whenever we think of a power project. A power project requires at least 10 to 12 mobile cranes of different capacities and properties. One or two cranes are needed to be stationed in the store yard for loading and unloading of heavy equipment on or from the trailers. One small size and two long span cranes are required in the steel fabrication yard. The coal handling plant area of a thermal plant is normally spread over hundreds of acres and needs at least two cranes for multiple enabling works. Similarly, ash handling plant needs at least one crane for transportation and hoisting of equipment. The number of mobile cranes required, their capacities and booms need to be specifically worked out for each thermal project as per quantum of work involved.
Vibro-Compactors for compaction work: A thermal plant is generally spread over more than 1000 acres. Many parts of this area are in cutting or filling. The area in filling needs to be compacted well by use of vibro-compactors till the desired density of compacted soil is achieved. Vibro-compactors are also needed in ash dyke area. Ash dykes are the soil embankments built over the ground and encasing a large area of scores of acres. Fly ash generated in thermal power projects is transferred to this area and stored within the area enclosed by ash dykes. The ash dykes are therefore built with utmost care and full compaction of soil is achieved in them by use of vibro compactors. A breach in ash dykes may play havoc with a running power project and may even force its closure, resulting in loss of power generation worth crores of rupees. Vibro compactors are therefore essentially required during the construction of a power project.
Dewatering equipment for deep foundations: Excavations for foundations are deep in power projects. Excavation may be as deep as 20 metres or more and as less as just 2 metres. During deep excavations, subsoil water is often encountered and needs to be removed for uninterrupted progress of work. Dewatering equipment is therefore required at these locations. Dewatering equipment may either consist of deep bore tube wells run with electric or diesel pumps and motors or well point system. Type of dewatering equipment to be used depends on the site conditions.
Fleets of Tippers for carriage work: Fleets of tippers are required for the work of site grading of a power project. In addition, ash dykes requires these tippers in large numbers to bring in the soil for embankments. All other sites require these to remove the excavated earth. Intelligent planning for a power project involves making contour plans of power project site and fixing of grade level of the area in such a manner that the total cutting of soil equals or nears the total filling work. Such a planning minimizes the disposal of earth outside the project area or bringing in soil from the outside thus resulting in time and cost savings. In such a case tippers keep on moving all over the project site, picking excavated soil from one area and unloading it at the other locations. Normally, a thermal plant may need more than a hundred tippers for cutting, filling and disposal of earthwork.
Transit mixers for transportation of concrete: This equipment is required to transport ready mixed concrete from the RMC plant or concrete batching plant to various sites of work. These can be clubbed as a part of the RMC plant.
Concrete vibrators for site compaction of concrete: All sites need needle vibrators for compaction of concrete unloaded at site. Each site may have 10 to 20 vibrators or even more with plenty of spare needles available. These can be both petrol and power driven. Petrol driven vibrators should always be kept to continue concrete compaction during power failures.
Concrete pump: Concrete pump may or may not be required at power plant sites. RCC chimney, large sized cooling towers and turbo-generator deck are three structures involving great heights where concrete pumps can be used to pump concrete in place. At most of the projects however, concrete is transported through winch and bucket arrangement and further carried in trolleys at working decks.
Bull Dozers for earthwork: Dozers are required during thermal power plant construction at sites wherever large quantity earth needs to be excavated, toed or dozed. Construction of ash dykes, work of site grading and plant drainage essentially need dozers to facilitate quick completion of earhwork.
Fabrication equipment for structural steelwork: A thermal power project fabrication and erection of thousands of tones of structural steelwork. A number of welding machines, pug cutting machines, gas cutting sets, grinders, drilling machines, ovens, winches, air compressors are some more equipment required in steel fabrication yard of a power project. Pneumatic compressors are also required at fabrication site and piling work site. This equipment shall be discussed in detail in a separate article.
Derricks: In addition to mobile cranes, derricks are required in thermal projects at chimney site, cooling tower site, boiler site and structural steel fabrication site to facilitate material handling.