COMBINED CYCLE POWER PLANT

COMBINED CYCLE POWER PLANT

                   

Preamble

Gas combustion generates high temperature and pressure so that the efficiency of gas turbine is more comparable to that of steam turbine. The Combined Cycle Power Plant or combined cycle gas turbine, a gas turbine generator generates electricity and waste heat is used to make steam to generate additional electricity via a steam turbine. The gas turbine is one of the most efficient one for the conversion of gas fuels to mechanical power or electricity. The use of distillate liquid fuels, usually diesel, is also common as alternate fuels.

More recently, as simple cycle efficiencies have improved and as natural gas prices have fallen, gas turbines have been more widely adopted for base load power generation, especially in combined cycle mode, where waste heat is recovered in waste heat boilers, and the steam used to produce additional electricity.

This system is known as a Combined Cycle. The basic principle of the Combined Cycle is simple: burning gas in a gas turbine (GT) produces not only power – which can be converted to electric power by a coupled generator – but also fairly hot exhaust gases.

Routing these gases through a water-cooled heat exchanger produces steam, which can be turned into electric power with a coupled steam turbine and generator.

This type of power plant is being installed in increasing numbers round the world where there is access to substantial quantities of natural gas.

A Combined Cycle Power Plant produces high power outputs at high efficiencies (up to 55%) and with low emissions. In a Conventional power plant we are getting 33% electricity only and remaining 67% as waste.

By using combined cycle power plant we are getting 68% electricity.

It is also possible to use the steam from the boiler for heating purposes so such power plants can operate to deliver electricity alone or in combined heat and power (CHP) mode.

Fundamental

Combined cycle power plant as in name suggests, it combines existing gas and steam technologies into one unit, yielding significant improvements in thermal efficiency over conventional steam plant. In a CCGT plant the thermal efficiency is extended to approximately 50-60 per cent, by piping the exhaust gas from the gas turbine into a heat recovery steam generator.

However the heat recovered in this process is sufficient to drive a steam turbine with an electrical output of approximately 50 per cent of the gas turbine generator.

The gas turbine and steam turbine are coupled to a single generator. For startup, or ‘open cycle‘ operation of the gas turbine alone, the steam turbine can be disconnected using a hydraulic clutch. In terms of overall investment a single-shaft system is typically about 5 per cent lower in cost, with its operating simplicity typically leading to higher reliability.

                                                                                

Working principle of CCTG plant

First step is the same as the simple combined cycle gas turbine plant. An open circuit gas turbine has a compressor, a combustor and a turbine. For this type of cycle the input temperature to turbine is very high. The output temperature of flue gases is also very high.

This is therefore high enough to provide heat for a second cycle which uses steam as the working medium i.e. thermal power station.

Figure - Working principle of combined cycle gas turbine (CCTG) plant

                         

Air Inlet

This air is drawn though the large air inlet section where it is cleaned cooled and controlled. Heavy-duty gas turbines are able to operate successfully in a wide variety of climates and environments due to inlet air filtration systems that are specifically designed to suit the plant location.

Under normal conditions the inlet system has the capability to process the air by removing contaminants to levels below those that are harmful to the compressor and turbine.

In general the incoming air has various contaminants. They are:

In Gaseous state contaminants are:

• Ammonia
• Chlorine
• Hydrocarbon gases
• Sulfur in the form of H2S, SO2
• Discharge from oil cooler vents

In Liquid state contaminants are:

• Chloride salts dissolved in water (sodium, potassium)
• Nitrates
• Sulfates
• Hydrocarbons

In Solid State contaminants are:

• Sand, alumina and silica
• Rust
• Road dust, alumina and silica
• Calcium sulfate
• Ammonia compounds from fertilizer and animal feed operations
• Vegetation, airborne seeds

Corrosive Agents:
Chlorides, nitrates and sulfates can deposit on compressor blades And may result in stress corrosion attack and/or cause corrosion Pitting. Sodium and potassium are alkali metals that can combine with Sulfur to form a highly corrosive agent and that will attack portions of the hot gas path. The contaminants are removed by passing through various types of filters which are present on the way.

Gas phase contaminants such as ammonia or sulfur cannot be removed by filtration. Special methods are involved for this purpose.

Turbine Cycle

The air which is purified then compressed and mixed with natural gas and ignited, which causes it to expand. The pressure created from the expansion spins the turbine blades, which are attached to a shaft and a generator, creating electricity.

In second step the heat of the gas turbine’s exhaust is used to generate steam by passing it through a heat recovery steam generator (HRSG) with a live steam temperature between 420 and 580 °C.

Heat Recovery Steam Generator

In Heat Recovery Steam Generator highly purified water flows in tubes and the hot gases passes a around that and thus producing steam .The steam then rotates the steam turbine and coupled generator to produce Electricity. The hot gases leave the HRSG at around 140 degrees centigrade and are discharged into the atmosphere.

The steam condensing and water system is the same as in the steam power plant.

Typical Size and Configuration of CCGT Plants

The combined-cycle system includes single-shaft and multi-shaft configurations. The single-shaft system consists of one gas turbine, one steam turbine, one generator and one Heat Recovery Steam Generator (HRSG), with the gas turbine and steam turbine coupled to the single generator on a single shaft.

Multi-shaft systems have one or more gas turbine-generators and HRSGs that supply steam through a common header to a separate single steam turbine-generator. In terms of overall investment a multi-shaft system is about 5% higher in costs.

The primary disadvantage of multiple stage combined cycle power plant is that the number of steam turbines, condensers and condensate systems-and perhaps the cooling towers and circulating water systems increases to match the number of gas turbines.

Efficiency of CCGT Plant

Roughly the steam turbine cycle produces one third of the power and gas turbine cycle produces two thirds of the power output of the CCPP. By combining both gas and steam cycles, high input temperatures and low output temperatures can be achieved. The efficiency of the cycles adds, because they are powered by the same fuel source.

To increase the power system efficiency, it is necessary to optimize the HRSG, which serves as the critical link between the gas turbine cycle and the steam turbine cycle with the objective of increasing the steam turbine output. HRSG performance has a large impact on the overall performance of the combined cycle power plant.

The electric efficiency of a combined cycle power station may be as high as 58 percent when operating new and at continuous output which are ideal conditions. As with single cycle thermal units, combined cycle units may also deliver low temperature heat energy for industrial processes, district heating and other uses. This is called cogeneration and such power plants are often referred to as a Combined Heat and Power (CHP) plant.

The efficiency of CCPT is increased by Supplementary Firing and Blade Cooling. Supplementary firing is arranged at HRSG and in gas turbine a part of the compressed air flow bypasses and is used to cool the turbine blades. It is necessary to use part of the exhaust energy through gas to gas recuperation. Recuperation can further increase the plant efficiency, especially when gas turbine is operated under partial load.

Fuels for CCPT Plants

The turbines used in Combined Cycle Plants are commonly fuelled with natural gas and it is more versatile than coal or oil and can be used in 90% of energy applications. Combined cycle plants are usually powered by natural gas, although fuel oil, synthesis gas or other fuels can be used.

Emissions Control

Selective Catalytic Reduction (SCR):

• To control the emissions in the exhaust gas so that it remains within permitted levels as it enters the atmosphere, the exhaust gas passes though two catalysts located in the HRSG.
• One catalyst controls Carbon Monoxide (CO) emissions and the other catalyst controls Oxides of Nitrogen, (NOx) emissions. Aqueous Ammonia – In addition to the SCR, Aqueous Ammonia (a mixture of 22% ammonia and 78% water) is injected into system to even further reduce levels of NOx.

Merits

Fuel efficiency

In conventional power plants turbines have a fuel conversion efficiency of 33% which means two thirds of the fuel burned to drive the turbine off. The turbines in combined cycle power plant have a fuel conversion efficiency of 50% or more, which means they burn about half amount of fuel as a conventional plant to generate same amount of electricity.

Low capital costs

The capital cost for building a combined cycle unit is two thirds the capital cost of a comparable coal plant.

Commercial availability

Combined cycle units are commercially available from suppliers anywhere in the world. They are easily manufactured, shipped and transported.

Abundant fuel sources

The turbines used in combined cycle plants are fuelled with natural gas, which is more versatile than a coal or oil and can be used in 90% of energy publications. To meet the energy demand now a day’s plants are not only using natural gas but also using other alternatives like bio gas derived from agriculture.

Reduced emission and fuel consumption

Combined cycle plants use less fuel per kWh and produce fewer emissions than conventional thermal power plants, thereby reducing the environmental damage caused by electricity production. Comparable with coal fired power plant burning of natural gas in CCPT is much cleaner.

Potential applications in developing countries

The potential for combined cycle plant is with industries that requires electricity and heat or steam. For example providing electricity and steam to a Sugar refining mill.

Demerits

1. The gas turbine can only use Natural gas or high grade oils like diesel fuel.
2. Because of this the combined cycle can be operated only in locations where these fuels are available and cost effective.

Conclusions

Combined cycle power plants meet the growing energy demand, and hence special attention must be paid to the optimization of the whole system. Developments for gasification of coal and use in the gas turbine are in advanced stages.

Once this is proven, Coal as the main fuel can also combined cycle power plants meet the growing energy demand, be used in the combined cycle power plant.

The advances in cogeneration-the process of simultaneously producing useful heat and electricity from the same fuel source-which increases the efficiency of fuel burning from 30% to 90%, thereby reducing damage to the environment while increasing economic output through more efficient use of resources.

Hydrogen Energy

Hydrogen Economy

  A bridge to sustainable and clean energy

                 

Hydrogen is considered a clean fuel that has minimum impact on the environment nearly eliminating the level of carbon di-oxide and other green house gas emissions. Further, it is safe to manufacture, reliable and environmentally friendly. Hydrogen is the new talk of todays’much environmentally concerned scientific world as prospective fuel for the future.

Hydrogen is considered as an alternative fuel due to the following reasons-

Highly abundant in nature.                                   

Lightest element of all the elements known

Versatile, converts easily to other energy forms at the user end

High utilisation efficiency

Environmentally compatible (zero or low emission.

  

Hydrogen production method

Hydrogen can be produced from variety of process technology, including chemical biological, electrolytic, photolytic, and thermo chemical. These process include fossil resources such as natural gas and coal, as well as reasonable resource, such as biomass and water with input from renewable energy source (e.g. solar, wind, wave, or hydro power).

Hydrogen from fossil fuels

Production from natural gas –steam reforming uses thermal energy to separate hydrogen from the carbon components in methane and methanol, and involves the reaction of these fuels with steam on catalytic surfaces. The reaction decomposes the fuel into hydrogen and carbon mono-oxide. Then “shift reaction “changes the carbon monoxide and water to carbon dioxide and hydrogen.

Production from coal

Hydrogen can be produced from coal through a variety of gasification processes. In practice, high temperature entrained flow processes are favoured to maximise carbon conversion to gas.

From splitting of water hydrogen

Water electrolysis – electrolysis separate the elements of water- Hydrogen and oxygen by charging water with an electric current. Adding an electrolyte such as salt improves the conductivity of the water and increases the efficiency of the process. The charge breaks the chemical bond between the hydrogen and oxygen and gathers at cathode and the anode respectively.

Photo –electrolysis- Photo –electrolysis of water is the process whereby light is used to split water directly into hydrogen and oxygen. Such system offer great potential for cost reduction of electrolytic hydrogen.

Photo-biological production- Photo-biological production of hydrogen is based on two steps: photosynthesis and hydrogen production catalysed by hydrogenease in, for example, green alga and cyanobacteria.

Biomass to hydrogen

In biomass conversion processes, hydrogen –containing gas is normally produced in a manner similar to the gasification of coal. However, no commercial plants exist to produce hydrogen from biomass. Currently the pathways followed are steam gasification (direct or indirect) , entrained flow gasification, and more advanced concept such as gasification in supercritical water, application of thermo chemical cycles, or the conversion of intermediate (e.g. ethanol, bio-oil or terrified wood).

Hydrogen from splitting of water

 Water splitting solar panels have important advantages over existing technologies in terms of hydrogen production. Right now, the primary way to make the hydrogen is to separate it from natural gas, a process that generates dioxide and undercuts the main motivation for moving to hydrogen fuel cell vehicle: ending dependence on fossil fuels. The current alternative is electrolysis, which uses electricity to break water into hydrogen and oxygen, with two gases forming at opposite electrodes. Although electrolysis is efficient method, it can be cleaner if the source of the electricity is wind, sun or some other carbon free source. But if the source of the electricity is the sun, it would be much more efficient to use solar energy to produce hydrogen. PV electrolyser is one of the promising method to produce hydrogen with zero pollution emission. Hydrogen production from PV electrolyser system depends on the efficiency of the electrolyser and photovoltaic array, and sun irradiance at the site.

Since the feedstock for electrolysis is water, there are no harmful pollutants emitted during the use of fuel. Furthermore, it has become evident that concentrator photovoltaic (CPV) systems have a number of unique attributes that could shortcut the development process, and increase the efficiency of hydrogen production to a point where economics will then drive the commercial development to mass scale.

Hydrogen application

                          

Barriers

                                         

§  Hydrogen is an energy carrier rather than an energy source. While hydrogen always exists in conjunction with other elements, such as in water, it must be separated from these elements and is therefore considered an energy carrier, as opposed to an energy source.

§  Costly to convert to liquid. Because hydrogen is a gas, it cannot be compressed into a liquid form without intensive cost and energy input. Hydrogen is the lightest element on earth. As a gas, it dissipates rapidly. To compress this gas is very difficult.

§  Fossil Fuels May be needed to produce Hydrogen - Most methods to produce hydrogen must use energy to separate the hydrogen from the oxygen. This may require fossil fuels such as coal or oil. So, in a sense, we are spinning our wheels in trying to get away from fossil fuels. Along with that, coal, which is a major feedstock for hydrogen, is a major contributor to pollution.

§  Existing infrastructure has not been built to accommodate hydrogen fuel

§  Hydrogen is difficult to store and distribute.

   

                                  

Energy Saving Tips

ENERGY SAVING TIPS                                                     

Use efficient lighting

Replace incandescent bulbs with compact fluorescents (CFLs). These use four times less energy. And they last eight times longer. So you not only cut your electricity bills dramatically, you also save a lot of money buying bulbs.

Use energy efficient electric appliances

They use two to 10 times less electricity for the same functionality, and are mostly higher quality products that last longer than the less efficient ones. In short, efficient appliances save you lots of energy and money. In India, appliances like refrigerators and ACs have efficiency rating labels ranging from 1 to 5 stars, the higher number being more efficient.

Use an energy efficient computer

Buy a laptop instead of a desktop. It consumes five times less electricity. If you buy a desktop, get an LCD screen. Enable the power management function on your computer, the screensaver does not save energy. Check if your computer supports the more advanced speedstep power management. Switching off a computer extends its lifetime, contrary to some misconceptions. Minimize printing. Print on both sides of the paper. Laser printers use more electricity than inkjet printers.

Drive less

Walk, bike, carpool or take public transport. You'll save 1.5 kg of carbon dioxide for every 5km you don't drive. Use cars that run on cleaner fuels such as CNG and LPG. Switch off your car if you want to stop for more than two minutes.

Check your tires

Keeping your tires inflated properly can improve the fuel efficiency of your car. Every litre of petrol saved keeps 2.5 kg of carbon dioxide out of the atmosphere. Using radial tyres will help you save 3 to 7 % of fuel.

Use water carefully

Don't waste water. Use a mug of water when brushing your teeth, shaving or washing your hands and face. Instead of a shower or tub bath, use a bucket. Try to harvest rain water in your locality. It takes a lot of energy to heat water- use less hot water and use efficient heating appliances.

Say no to plastic

Take a cloth bag with you when shopping. Use recycled paper. Avoid products with a lot of packaging.

Move your Air-conditioning thermostat up 2 degrees

You could save about 900kg of carbon dioxide a year with this simple adjustment. Set the thermostat of the room air conditioner at 25C to get the most comfort at the least cost.

Use renewable energy

Sunlight can be used in many different ways to save energy. Use a solar water heater instead of an electric geyser. A 100 litre solar water heater can save around 1500 units of electricity every year. For lighting, use batteries that can be charged with sunlight. A solar cooker cooks rice and vegetables without losing their essential nutrients. Just leave the solar cooker outside in the sun to cook your food. If you live in a village, you can use biogas from cow-dung to save energy.

Plant more trees

A single tree will absorb one tone of carbon dioxide over its lifetime.

Turn off electronic devices

Simply turning off your television, stereo, computer, fans, lights when you are not using them will save you thousands of kilograms of carbon dioxide a year.

Reuse & recycle

Recycling and re-using products like paper and bottles will help protect the environment. Use recycled paper. Recycle your office and household waste.

Lighting

§   Turn off the lights when not in use

§   Take advantage of daylight by using light-colored, loose-weave curtains on your windows to allow daylight to penetrate the room. Also, decorate with lighter colors that reflect day light

§  De-dust lighting fixtures to maintain illumination

§   Use task lighting; instead of brightly lighting an entire room, focus the light where you need it

§   Compact fluorescent bulbs are four times more energy efficient than incandescent bulbs and provide the same lighting

§  Use electronic chokes in place of conventional copper chokes

Fans

§  Replace conventional regulators with electronic regulators for ceiling fans

§  Install exhaust fans at a higher elevation than ceiling fans

Electric iron

§  Select iron boxes with automatic temperature cut-off.

§  Use appropriate regulator position for ironing.

§  Do not put more water on clothes while ironing.

§  Do not iron wet cloth.

Kitchen Appliances

 Mixers

§  Avoid dry grinding in your food processors (mixers and grinders) as it takes longer

§  time than liquid grinding.

§  Microwaves ovens  Consumes 50 % less energy than conventional electric / gas stoves

§  Do not bake large food items.

§  Unless you're baking breads or pastries, you may not even need to preheat.

§  Don't open the oven door too often to check food condition as each opening leads to a

            temperature drop of 25°C.

 Electric stove

§  Turn off electric stoves several minutes before the specified cooking time

§  Use flat-bottomed pans that make full contact with the cooking coi

§  Gas stove

§  When cooking on a gas burner, use moderate flame settings to conserve LPG

§  Remember that a blue flame means your gas stove is operating efficiently

§  Yellowish flame is an indicator that the burner needs cleaning

§  Use pressure cookers as much as possible

§  Use lids to cover the pans while cooking

§  Bring items taken out of refrigerators (like vegetables, milk etc) to room temperature

§  before placing on the gas stove for heating

§  Use Solar Water Heater – a good replacement for a electric water heater

Electronic Devices

 Do not switch on the power when TV and Audio Systems are not in use i.e. idle operation

leads to an energy loss of 10 watts/device

Computers

§  Turn off your home office equipment when not in use. A computer that runs 24 hours a day, for instance, uses - more power than an energy-efficient refrigerator.

§  If your computer must be left on, turn off the monitor; this device alone uses more than half the system's energy.

§  Setting computers, monitors, and copiers to use sleep-mode when not in use helps cut

energy costs by approximately 40%.

§  Battery chargers, such as those for laptops, cell phones and digital cameras, draw power whenever they are plugged in and are very inefficient. Pull the plug and save.

§  Screen savers save computer screens, not energy. Start-ups and shutdowns do not use

any extra energy, nor are they hard on your computer components. In fact, shutting

§  computers down when you are finished using them actually reduces system wear – and saves energy

Refrigerator

§  Regularly defrost manual-defrost refrigerators and freezers; frost build-up increases the amount of energy needed to keep the motor running.

§  Leave enough space between your refrigerator and the walls so that air can easily

circulate around the refrigerator

§  Don't keep your refrigerator or freezer too cold.

§  Make sure your refrigerator door seals are airtight.

§  Cover liquids and wrap foods stored in the refrigerator. Uncovered foods release moisture and make the compressor work harder.

§  Do not open the doors of the refrigerators frequently.

§  Don't leave the fridge door open for longer than necessary, as cold air will escape.

§  Use smaller cabinets for storing frequently used items.

§  Avoid putting hot or warm food straight into the fridge.

Washing machines

§  Always wash only with full loads

§  Use optimal quantity of water

§  Use timer facility to save energy

§  Use the correct amount of detergent

§  Use hot water only for very dirty clothes

§  Always use cold water in the rinse cycle

§  Prefer natural drying over electric dryers

Air Conditioners

§  Prefer air conditioners having automatic temperature cut off

§  Keep regulators at “low cool” position.

§  Operate the ceiling fan in conjunction with your window air conditioner to spread the

§  cooled air more effectively throughout the room and operate the air conditioner at higher temperature

§  Seal the doors and windows properly

§  Leave enough space between your air conditioner and the walls to allow better air

§  circulation

§  A roof garden can reduce the load on Air Conditioner

§  Use windows with sun films/curtains

§  Set your thermostat as high as comfortably possible in the summer. The less difference between the indoor and outdoor temperatures, the lower will be energy consumption.

§  Don't set your thermostat at a colder setting than normal when you turn on your air

           Conditioner. It will not cool your home any faster and could result in excessive  

           cooling.

§  Don't place lamps or TV sets near your air-conditioning thermostat. The thermostat senses heat from these appliances, which can cause the air conditioner to run longer than necessary.

§  Plant trees or shrubs to shade air-conditioning units but not to block the airflow. A unit operating in the shade uses as much as 10% less electricity than the same one operating in the sun

Electrical Safety Tips for Homes

Electrical Hazards

 Shocks

§  Electric Shock causes an involuntary grip which prolongs the period of contact.

§  More the period of contact, more the damage.

§  Passage of current through the heart , stops the blood supply to the brain , resulting in

§  loss of consciousness and termination of breathing

§  When a person standing at a height receives an electrical shock , it is most likely that

he will fall.

§  Personal sensitivity to electrical shock varies from person to person.

 Burns

§  Whenever an electrical flash appears, and if a part of a body comes within flashing

            distance, burns can be caused.

§  Burns may be caused by short circuits as well, because a short circuit could create an

           electrical fire.

Preventive Measures

§   Allow only a qualified person to attend to your electrical repairs

§   Service your electrical equipment at frequent intervals through a competent electrician

§   In case of a short circuit or a fire, switch off the mains instantly Make sure that you have easy access to switch off the supply source quickly, in case of an emergency

§   Make sure your extension cords are free from cuts, improper insulation, or joints.

§   Ensure pins of your plugs are tight and not loose.

§   Use switches of the correct current rating and preferably with indicators to indicate whether the switch is ON/OFF.

§   Use appliances with 3 pin plugs and connect them to 3 pin sockets.

§   Do not overload electrical outlets or use extension cords in place of additional outlets.

§   Switch off electrical appliances when not in use.

§   Provide proper earthing for the building/house.