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Gas Turbines … Generators

May 14, 2012 by Liezel Magno Castro

This article is a continuation of our series about various topics in renewable energy. A gas turbine is a type of internal combustion engine that has a rotating compressor in its upstream coupled to a turbine in its downstream. In between is a combustion chamber. In the gas stream, energy is added where fuel is mixed with air and ignited. In the high pressure combustion chamber, the temperature is increased by the combustion driven expansion of the fuel.  The combustion’s by products are forced into the turbine section. From there, high volume and velocity gas flows straight through the nozzle and through the blades of the turbine, spinning the turbine that powers the compressor. In power turbines, this usually also drives the mechanical output shaft. Energy in to the turbine is transferred from the reduced temperature and pressure from the exhaust gas. Energy is then extracted in the form of compressed air or thrust, shaft power, and any combination of these. This energy is used to power aircrafts, trains, generators, ship and tanks. Gas turbines were originally developed for and used in the military and aerospace applications. Nowadays, these are used in many industrial applications. The same types of gas turbines used to power aircraft are used in power turbines for compressor, mechanical drive, generator and general applications. Currently, there is heavy spending worldwide to build gas turbine power plants in many countries, as power generation is one of the growing concerns. Environmental issues have increasingly become highlighted. Governments around the world are pressured to enforce strict regulation on the reduction of carbon emissions and the use of alternative fuels.  Gas turbine generators are favored for low emissions among traditional fossil fuel powered plants. Gas turbine power plants are basically dependent on fuel and air for combustion, and ultimately for generation. The process of generation involves combustion of fuel and air in the combustion chamber. Because of the gas turbines’ flexibility, they are often deployed as peak load machines. This is where gas turbines come in handy and work effectively when consumers are utilizing maximum use of power from the grid (i.e., late summer afternoons while industry is still working and consumers are heading home to turn on the AC). Gas turbines involve low installation and maintenance cost compared to other alternate fuels. An average gas turbine generator plant of 400 megawatts with three units can be built at a cost no more than 300 million dollars. Gas turbines are very low maintenance machines resulting in low operations and maintenance cost requirements. It takes several minutes to start a gas turbine, run up to full speed at no load and synchronize to the grid. This quick start machine feature is important especially when power is immediately needed. Power generators often start with diesel fuel before switching to natural gas for continuous operation. Gas turbine technology is continuously evolving since humble beginnings. Research is in progress to produce smaller, more efficient combustions chambers, better cooling engine parts, reduced emissions and more powerful gas turbines. On the emission side, research and development is underway for combustor technology to achieve near zero emissions. In the 1990’s compliant foil bearing were introduced to gas turbines which can withstand more than hundreds of start / stop cycles and do not require a bearing oil system. Photo Credit: Alstom

Filed Under: Gas Turbines Tagged With: alternative fuel, combustion chambers, combustor technology, compressor, cooling engine parts, gas turbine, gas turbines, generators, mechanical drive, natural gas, zero emission

Why Cogeneration is Good Energy Strategy

March 2, 2012 by joy

Cogeneration sometimes referred to as CHP (Combined Heat and Power) or energy recycling is an efficient and cost-effective method of capturing heat lost during the production of electricity and converting it into th

ermal energy because energy that would be otherwise disposed as waste heat would be put to good use. Thomas Edison probably was the first to make use of cogeneration or energy recycling in 1882. His Pearl Street Station was the world’s first commercial power plant producing both electricity and thermal energy while using waste heat to warm neighboring buildings. Because of energy recycling, Edison’s plant was able to achieve 50% efficiency.

Cogeneration Benefits Cogeneration systems are up to 80% more efficient than that of the traditional power plants, which is normally around 30%. These gains of efficiency result in cost savings, as less fuel is needed to be consumed to produce the same amount of useful energy. In addition, results of cogeneration also include reduced air pollution, reduced greenhouse gas emissions, increased power reliability and reduced grid congestion.

Today, Con Edison operates seven cogeneration plants to approximately 100,000 buildings in Manhattan, the largest steam district in the U.S. The steam distribution system is the reason for the steaming manholes often seen in New York City. The European Union generates 11% of its electricity using cogeneration and energy savings in Member States ranges between 2% to 60%. Europe has the three countries with the worlds’ most intensive cogeneration economies, which are Denmark, the Netherlands and Finland. In response to the growing energy need, the US Department of Energy maintains an aggressive goal of cogeneration or CHP to comprise 20% of the US generation capacity by the year 2030.

Typical Methods of Cogeneration Include Gas Turbines, which are essentially jet engines that drive turbo generators. Multi-stage heat recovery steam generators use heat to produce steam and even hot water as the exhaust gradually loses its temperature.

Diesel Engines are very similar to the gas turbine. The diesel drives a generator for economical electricity production and then the hot exhaust can produce steam to drive another electrical generator or to provide heat for process operations as either steam or hot water.

In either case, the main goal in either case is to effectively extract every BTU of heat that would exceed normal atmospheric temperature in the final effluent stream of gas and cause it to produce electricity or usable heat such as hot water.

Other Forms of Cogeneration Landfill Gas Cogeneration is a great solution because the emissions of a damaging pollutant are avoided and electricity can be generated from a free fuel. Landfill gas contains approximately 50% methane and

has a heat content of about half the value of natural gas. Capturing LFG reduces greenhouse gases while contributing to energy independence and economic benefits.

Waste to Energy Cogeneration is an excellent energy model. A waste to energy plant has

Tyseley Energy from Waste Plant and Rovex Business Park

been launched in Lahti, Finland. It converts municipal waste into heat and power through the large-scale use of waste gasification, gas cleaning and high-efficiency combustion. It has a capacity of 250,000 tons of waste per year and can generate 90 MW of heat and 50 MW of electricity. This system will partially replace a coal-fired plant and will make a substantial reduction of landfill disposal in the region.

Cogeneration in Jamaica The country’s only utility company on the Island of Jamaica is already using cogeneration on a small scale. The electric company plans to use this method of energy source especially in the sugar, manufacturing and tourism industries. In addition, the country also uses solar powered streetlights in the 14 parishes. Jamaica has one operating wind turbine contributing to the grid and uses bio mass energy to primarily burn bagasses to produce steam in the sugar industry.

In this world of increasing energy requirements, cogeneration whether by diesel, gas turbines, landfill gas and waste to energy can only be a good solution not only in the United States, the European Union, but also in Small Island Developing States such as Jamaica and Haiti. Officials in Haiti might ought to take a good look at the potential of waste to energy cogeneration for its most pressing needs of both power generation and of excessive municipal waste.

Photo Credit: ell brown

Filed Under: Waste-to-Energy Tagged With: CHP, cogeneration, combined heat and power, diesel, gas turbines, landfill gas, recycled energy, waste to energy

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