Technical Aspects of Power Generation in UPCL

By Philip Mudartha, Qatar
Bellevision Media Network

21 March 2011: Udupi Power Corporation Limited (UPCL) synchronized its second unit with the national power distribution network a fortnight ago. The company ignored the deadline for suspension of operations, which the environmentalists, local branch of state farmers association, a section of clergy and political workers aligned with JDS had set. Cracks appeared in the anti-UPCL camp as the leading clergyman held separate parleys with the company management.

 

 

Local newspapers reported that these talks failed. The company maintained that it is one of the most environment friendly coal-based thermal power plants in the country and even in the world.

 

How is electricity generated at UPCL? What is the basis of the company’s claim? Is there anything the company can and should do? In order to answer these perplexing questions, it would be appropriate at this stage to take a technical look into power stations in general and into operations of UPCL in particular.

 

A power plant is basically an industrial facility for the generation of electrical energy. There are different types of power plants such as nuclear, thermal and hydel on mega scales, and geo-thermal, wind and solar on smaller scales.

 

The word ‘generation’ is a misnomer, because energy can neither be created nor destroyed; it can only be transformed. In power plants, energy is transformed from potential, mechanical or chemical type to electrical type. The processes of transformation are seldom efficient, and involve significant environmental impacts. However, as our lives get entwined more and more with the use of electrical equipments, we have to live with the inefficiencies.

 

Thermal power plants produce and meet 40% of global electricity demand. Fossil fuels, such as natural gas, crude oil and its derivatives, coal and bio-mass can be mined, transported, stored and consumed with relative ease and lower cost. The process technology is simple and requires low-to-medium skilled workforce. Central Electricity Authority (CEA) data, as on 2010 October 30, 53.7% or 89,778.38MW of total electricity generation in India is coal-based.

 

 

Coal is abundant in nature. Anthracite, Bituminous and Lignite are coal types in the descending order of purity and grade. Coal mining and beneficiation are established industries. National Security worries are non-existent unlike nuclear material. For generations, households have used coal in their kitchen stoves and backyard barbeque grills.

 

Illustration of the process with a schematic:

 

 

The process of electricity generation begins with coal being fired in the boiler. This is a combustion reaction involving carbon in the coal and oxygen from the air. The products of the chemical reaction are flue gas and heat. The flue gas is composed of oxides of carbon, nitrogen and sulfur and particulate matter. This stage 1 is similar to what happens in our coal grills and kitchen stoves, but for scale and size of operations.

 

In the stage 2, the heat in the flue gas is transferred to feed water. It boils into steam. The steam pressure temperature is controlled in such a way  that it can turn wheels of Steam Turbine and sustain high speeds. Steam pressures in the range of 200bar and at temperatures 540-600 deg C are typical in conventional thermal plants. Under such conditions, less than one-third of heat is recovered, remaining lost to the environment.

 

In the stage 3, the high speed turbines rotate generator rotors. Typically 6000 rpm are norm. You may remember reading, in your high school science classes, about Faraday’s principle of electromagnetic induction. Mechanical work is converted into electrical energy, subject to the efficiencies of the set-up.

 

The Particulate removal, sulfur removal, carbon dioxide removal are auxiliary units to treat the waste flue gas. The detailed process follow diagram (PFD) may be useful to understand the generation scheme and typical values of key parameters:

 

 

The used steam is condensed into water and recycled. The condenser must operate at lowest temperature like 30 degrees C and vacuum, and therefore requires cooling water is usually drawn from a river, lake or sea. The feed water can only be fresh water from river or lake.

 

To summarize, availability of thermal coal, river water and sea water round the year continuously will ensure uninterrupted power plant operations.

 

Unfortunately, even the best grade thermal coal as mined, as beneficiated, and as received has impurities consisting of earthy minerals like sulfur, silica, limestone, dolomite, assorted metals, and moisture. The incombustible solid wastes form the bottom ash and fly ash and are removed from boilers or from flue gas cyclones.  To understand details, the following schematic is helpful:

 

 

We desire the fruits in the form of electricity, but the road is strewn with thorns: the hazardous solid wastes and greenhouse gas (GHG) emissions, particulate emissions, and heat emissions to air and water. Sulfur dioxide is acid gas that should be neutralized using desulfurization processes to produce sulfur or sulfuric acid. Oxides of Nitrogen formed in combustion and referred as NoX are difficult to manage; however modern techniques of coal firing systems minimize them. The Carbon Dioxide Removal is standard technology in several industries. Processed Carbon Dioxide can be sold as dry ice or used for many commercial and industrial uses. The ash is a good raw material in the Portland cement manufacture, and need not be hazardous, unless heavy metals and mercury are found in excess of prescribed norms. These wastes should be treated as bi-products and put to appropriate use.

 

The cooling water used will have to return to the source: river, lake or sea. The norms are that the return water temperature should not be in excess of 3 deg C over the source temperature. The emission of heat through the cooling tower along with the remaining flue gases cannot be avoided. They will increase localized air temperature and relative humidity, but are dealt by designing towers of appropriate heights. The investment into cogeneration processes can reduce this effect, if the hot water can be commercialized for district or town heating. This is not applicable for our districts.

 

India has limited sources of high grade coal. UPCL is the first independent power producer in the country to use 100 per cent imported coal. The company imports almost one ship load of 70,000 tons every week. It requires 12,000 tons per day to fire a 1,000 MW power plant. The public tender specifies the coal grade to be bituminous and from Australia, South Africa, China and Indonesia. It restricts sulfur to 0.8% max and ash content to 4.75% max. These are stringent specifications, and if enforced and complied by the suppliers, in a tight and escalating coal price market, the company is doing what it says it is committed to do.

 

This part 2 is limited to technical description of power generation. Other aspects, political, social and economic will be discussed in coming weeks.