General Layout of a Thermal Power Plant

General Layout of a Thermal Power Plant The coal which you use in your backyard for barbeque performs much more important functions such as generating electricity for us in thermal power plants. Learn about the layout of these plants in this article. Introduction With the world on a development spree, there is shortage of power in most places whilst the demand seems to be in a never ending upward spiral. There are several answers to this challenge such as the nuclear power plants, but the conventional thermal power plants also play an equally important role in this power equation. Learn about these power plants in this article. General Layout of the Plant Though each plant is unique in itself in terms of specific features and functionalities, still there is a broad outline to which all thermal power plants confirm to and in this article we will study about the general layout of a typical power plant. There are four main circuits in any thermal power plant and these are 1.

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Coal & Ash Circuit – this circuit deals mainly with feeding the boiler with coal for combustion purposes and taking care of the ash that is generated during the combustion process and includes equipment and paraphernalia that is used to handle the transfer and storage of coal and ash. Air & Gas Circuit – we know that air is one of the main components of the fire triangle and hence necessary for combustion. Since lots of coal is burnt inside the boiler it needs a sufficient quantity of air which is supplied using either forced draught or induced draught fans. The exhaust gases from the combustion are in turn used to heat the ingoing air through a heat exchanger before being let off in the atmosphere. The equipment which handles all these processes fall under this circuit. Feed Water & Steam Circuit – this section deals with supplying of steam generated from the boiler to the turbines and to handle the outgoing steam from the turbine by cooling it to form water in the condenser so that it can be reused in the boiler plus making good any losses due to evaporation etc. Cooling Water Circuit – this part of the thermal power plant deals with handling of the cooling water required in the system. Since the amount of water required to cool the outgoing steam from the boiler is substantial, it is either taken from a nearby water source such as a river, or it is done through evaporation if the quantity of cooling water available is limited.

Proper Site Selection for a Thermal Power Plant You might think that selecting a site for a thermal power plant is based on requirements of power of the nearby regions but it is not so in actual practise. The engineer needs to take dozens of factors into account before commencing such a project and here is a list of the same. Introduction Selecting a proper site for a thermal power plant is vital for its long term efficiency and a lot many factors come into play when deciding where to install the plant. Of course it may not be possible to get everything which is desirable at a single place but still the location should contain an optimum mix of the requirements for the settings to be feasible for long term economic justification of the plant. The Requirements for the Site As the name implies the power plant is meant for generating power which obviously means that it will consume huge quantities of fuel. The exact quantity would depend on the size of the plant and its capacity but it is a general fact that ample quantities of fuel must be available either in the vicinity or it should be reasonably economical to transport the fuel till the power plant. Since most thermal power plants use coal (they can use other fuels as well) it must be ensured that sufficient coal is available round the clock. Just to give you a rough idea a power plant with 1000 MW capacity approximately would require more than ten thousand tons of coal per day hence the necessity for continuous supply and storage capability of coal in the power station. Ash if the main byproduct of combustion and since the amount of coal used is huge, you can intuitively imagine the amount of ash generated and it is certainly in the region of thousand tons per day. Ash is much more difficult to handle as compared to coal since it comes out hot from the boiler and is very corrosive in nature. Disposing of such huge quantities of ash requires a large amount of empty space where it can be safely dumped. There must be ample space for the storage of coal, disposal of ash, building of the power plant, residential colony of workers, markets and so forth. An approximate analysis suggests that for every MW of power generated there must be at least 3 acres of land available for the purpose. Hence the power plant site needs to have good amount of land and this land should have good bearing capacity in order to survive the static and dynamic loads during the operation of the plant.

As we saw in the previous article of this series, large amount of water is required for cooling purposes in the power plant hence it is better if such a source is available nearby in the form of rivers etc. Apart from these major requirements there are also other requirements which are equally important such as the availability of skilled people to work for the plant and good transport facilities in the vicinity. Hence we see that setting up a thermal power plant requires a lots of factors to be considered simultaneousl How Does a Thermal Power Plant Function? The thermal power plant is a setup for extracting the hidden calorific heat inside the black diamond to be used for setting the electrons in motion i.e. electric current. Read on to find out about his interesting journey of power conversion. Introduction Having learnt about the basic plant layout and site selection of a power plant it is now time to take a look at the overall functioning of the power plant. I suggest that if you haven’t read the first part of this series (click here) regarding general layout of a thermal power plant, you take a look at it, especially the accompanying diagram since I am not going to repeat the same diagram here but will explain based on previous article. The Functioning of the Plant The four circuits of the thermal power plant make a complete picture when put together helping to generate electricity out of fuels such as coal which is the most widely used fuel. The calorific value of coals depends on the quality of the coal and the place from where it is mined. Let us perform a simple calculation regarding the amount of coal required in a power plant. Let us assume an imaginary thermal power plant which has a capacity of 1000 MW and try to find the amount of coal required for its consumption. Also assume that the boiler operates at an efficiency of 75% and the heat supplied per kg of steam be around 500 kcal per kg and that the amount of steam required per kWh is nearly 5 kgs. Further let us assume that the type of coal used in the plant has a calorific value of 5000 kcal/kg Then the quantity of coal required per hour would be given by Weight of Coal Required ==> Capacity * Steam Requirement * Heat Delivered/Calorific Value of Coal * Efficiency of Boiler ==> {1000 * 1000 * 5 * 500}/{5000 * 0.75 * 1000} = 666 tons/hr Normally it is a practice to store coal for upto one month usage in case the power plant is situated at a sufficient geographical distance from the coal source so that in case of any disruption of the transportation system, the region is not immediately affected. You can calculate that in case the above plant requires such a facility, we would require space to store and handle nearly 480, 000 tons of coal. Coming back to the actual operation this coal is then fed to the combustion chamber of the boiler where steam is generated giving rise to hot exhaust gases and ash which are handled by their respective circuits. The steam turbine is driven by the steam which converts this thermal energy into the mechanical energy and is coupled with an electric generator to convert it to electrical energy. The electricity generated through the generator coupled to the turbine is then fed to the main grid via a system of transformers and other electrical equipment and is usually taken to far off places via high voltage transmission lines before it is actually supplied in the domestic or industrial sectors at their respective voltage levels. Hence we see that how the energy hidden within the ordinary coal is harnessed through the use of a thermal power plant to light our homes and industries. Coal and its Use in Thermal Power Plants Even with lots of talks going on about the use of non-conventional sources of energy such as the solar power, nuclear power and wind power, the place occupied by coal in the power generation sector still holds strong. Find out the reasons why? Introduction

Old is gold goes the equally old and wise saying and this is applicable to the black diamond as well, in the perspective of thermal power plants. Well if you are confused let me tell you that I am referring to coal which is one of the oldest used fuels in the world. Though technology has gone skywards in the previous couple of centuries, yet this source continues to occupy an important position in the energy production scenario worldwide. Coal – Use in Electricity Generation In the earlier days coal might have been used for providing heat for making food or in the blacksmiths furnace but as technology made strides, so did the level and importance of coal in the energy production arena went upwards. Currently thermal power plants produce hundreds of megawatts of electricity from burning coal. Despite the hue and cry of environmental concerns, which are of course true to a certain extent, various other parameters have still kept coal as one of the most important sources of power generation in thermal power plants. The very first parameter is the ample abundance of coal in most parts of the world including the United States. Estimates suggest that the US has reserves of coal which could last more then two centuries even at the current rate of consumption. Apart from the reserves found on land there is also presence of coal layers beneath the sea although it is difficult to commercially extract it from there, but there might be a technology for this in the future. The next factor is directly related to the above factor and is that of cost. As you know cost is closely associated with availability and more abundant any commodity is, the lesser will be its price and vice versa which is a law of economics. Hence producing electricity through the use of coal is much cheaper than other non-conventional forms of energy such as say wind, nuclear and so forth. Disadvantages of Coal Of course all is not green in the literal sense in the use of coal in power plants. Environment and health hazards are one of the most prominent reasons why many groups are against the use of coal for power production. Disposal of large quantities of ash could pose problems in the coming years if the heaps continue to grow. Another major factor to be kept in mind is that despite the abundant supply of coal it is still a non renewable source of energy which was formed through a complex process lasting thousands of years and hence cannot be formulated at a short notice. Despite the disadvantages, coal is still very popular in its use as power plant fuel and continues to provide electricity to this power hungry planet. Fuel of Thermal Power Plants – Analysis of Coal in thermal power plants all over the globe, it makes sense to know what constituents make up this wonderful fuel. Read on to find out more about this. Introduction As we learnt earlier coal is one of the most widely used fuels in thermal power plants. It is therefore necessary for anyone interested in thermal power plants to know about the composition of coal and its various ingredients which have been discussed in the succeeding section. Proximate Analysis of Coal Any substance can be analyzed in different ways such as proximate analysis, chemical analysis and so forth. We will carry out the proximate analysis of coal which gives the different categories of compound present in the substance. Apart from carbon which is an obvious constituent the other constituents are as follows. Ash – this is an undesirable constituent of coal which is contained within the coal in two forms namely fixed ash and free ash. Fixed ash is inherent in the coal due to the formation process from vegetable matter and it is not possible to remove it except that it gets separated on burning. The free ash is removable via processes such as washing and screening though they will not be described in detail here. Like I said earlier it is undesirable to have ash in the coal but normally different types of coal could have ash content anywhere between say around 2% to 30% which is an unnecessary burden adding to transportation costs, lowering of heat value of coal and producing large amounts of corrosive waste which needs to be disposed off in a proper manner. Another disadvantage is that inside the boiler combustion chamber if the ash gets subject to very high temperatures it can form clinkers which could choke the passages and decrease efficiency of the boiler. It is best to use such coal in the powdered form if such a possibility exists.

Hydrocarbons & Gases – coal contains a variety of combustible gases such as hydrogen, methane and non-combustible gases such as carbon dioxide etc. This volatile content could be as low as 3% or even as high as nearly 50%. These constituents especially the non-combustible gases are just a waste as far as heat value of the fuel is concerned and an unnecessary burden which needs to be transported around and stored without any useful value in return. Moisture – the moisture content of coal could vary from just over 1% to nearly 30-40% and just like ash it has two forms – inherent moisture and free moisture. The former is not easily removable as it is a costly process whilst the latter can be removed by normal drying using slightly heated air. Obviously since coal is used in the boiler combustion chamber any excess moisture would interfere with the combustion lowering the actual heat available to generate steam. There is another method of analyzing coal in terms of its various chemical constituents such as carbon, hydrogen, sulphur and so forth but that might be taken up in a different set of articles.