Coal Fired Power Plant Technology

Posted on Fri 03/15/2013 by

2


Drax Power Station

The Drax Power Station

A recent news article from the UK mentioned that one of their largest coal fired plants was converting its fuel source, and instead of using coal as the fuel for the furnaces, it was going to use wood chips instead. I went and searched for as much information as I could find, and the story, while partially correct did not tell the full story. Some other sources had the story totally wrong, so that’s why it is always pertinent to check as many sources as possible, and as always, the source, the Drax Company themselves have the true story.

This gives me the opportunity to again explain just how a large scale coal fired plant produces its electricity, because very few people know the process of how that is done, so here I will explain the process, using this UK plant, the Drax Plant in Yorkshire England.

The Drax Group now plans to convert three of their six 600MW units to use what is referred to as Biomass, in this case the pelletised wood chips as the fuel source. When fully operational, each unit will consume 2.3 million Tonnes (2.54 Million U.S. tons) of wood chips, and at full operation some time in 2017, the 3 units will require 7.3 Million Tonnes (8.27 Million U.S. tons) of the fuel. 4,600 square miles of forest is needed to supply that amount of wood chips on a continuous basis, and most of the wood chips will be sourced from the U.S. and some of the biomass will be sourced from England.

Now, while these wood chips, when burned, will still emit huge quantities of Carbon Dioxide, (CO2) that emitted CO2 is classified as renewable, as the fuel source, those wood chips come from trees that during their growing process sequestered CO2 from the air, so now, by burning it, they are considered to be releasing the CO2 that was originally taken from the Atmosphere in the first place. For the life of me, I can’t understand this. It is still the release of huge amounts of CO2 into the Atmosphere, and it is referred to as renewable because the trees that are chopped down to make the wood chips will be grown again, so in effect, this counts as a renewable cycle. It is still the release of huge amounts of CO2 into the Atmosphere, and one molecule of CO2 released from the coal fired plant on the same site is exactly the same as the CO2 molecule released from the burning of the wood chips.

So, while we will now have the gradual conversion of the plants at Drax, let’s then have a look at the technology of their main existing coal fired plant, and this would be similar to most large scale coal fired power plants.

The huge Drax Power Station has 30 coal bunkers, and each of those can hold 1000 tons of coal. The coal is delivered to the plant by rail, and there are 35 deliveries of coal each day, and for six days of the week, and each day, approximately 40,000 to 50,000 tons of coal is delivered.

Each of those coal bunkers feed coal to 2 pulverisers (hence 60 pulverisers) which crush the coal to a fine powder, done at the rate of 36 tons per hour for each pulveriser. So, at full operation with all 6 generators running, Drax is consuming one ton of coal every 1.6 seconds.

There are 6 boilers, each fed by 10 of those pulverisers, and that powdered coal is blasted into each boiler and ignited by low Nitrogen Oxide burners.

Each boiler feeds steam to a turbine set, which consists of a high pressure turbine, a medium pressure turbine and three low pressure turbines. After each turbine, some steam is diverted back to the boiler, and some to the next stage of the turbine. All up, each turbine drives one generator with a capacity of 660MW, so all 6 generators give a Nameplate Capacity total of 3,960MW.

The image below shows just one of those 660MW generators at the plant, and I want to show you this image to highlight a comparison with Wind Power. This generator is mid to late 70’s vintage, and for perspective, the top rail of the guard ‘fence’ for the walkway along the side of the generator is around waist height.

DraxPowerStation660MWGenerator

This one generator shown here has a capacity of generating 660MW at any one time, and while ever that generator is running, it is generating it’s maximum power. The only time it is not running at its constant speed is when it is shut down for maintenance.

A Wind Plant with the same Capacity as this could have between 210 and 260 huge Wind Towers. (the average sized generator on top of each tower has a power range between 2.5 and 3.2MW)

However, the power delivered from Wind Power is variable at best, so the actual power delivered is in fact quite a considerable amount less than for this one generator.

For just one year, if this generator was running constantly it would deliver 5.79 TWH (TeraWattHours) of power to the grids supplying all consumers with power. Now, before some of you say that these generators do not run all year round, the only time they are not generating their full power is when they are turned off for scheduled maintenance, and in fact one generator at the Stanwell plant near where I live here in Rockhampton Australia ran for almost 3 years straight from turning on. (1,073 days at 100% Capacity)

Because Wind Power is so variable, those wind towers (with the same Capacity of 660MW) will only deliver 1.73TWH of power to the grids. The One generator in the image delivers 3.3 times as much power.

A typical Wind Plant has a best case life span of 25 years, and I say best case here because there is conjecture that they may only have a viable life span of 15 years, and they also lose capacity over time, but for the sake of this next calculation I will go with best case here. Over the life of this Wind Plant, those more than 200 wind towers will deliver 43.4TWH to the grids for consumption.

Taking into account that over time, the generator in the image will have down time for maintenance, the Capacity Factor (CF) for this Plant is currently running at 72%, so using that CF and the projected life span of 50 years for the unit, (and it has already been in operation now for 39 years) then this ONE generator will deliver 208TWH to the grids for consumption.

208TWH compared to 43.4TWH.

That’s 4.8 times as much power ….. from one generator compared to more than 200 huge wind towers.

Keep in mind that this is just from the one generator shown in the image, and this Drax power plant has 6 units, so Drax will deliver almost 30 times the power of this equivalent wind plant. Scaling that up, you would then need around 7,000 to 8,000 wind towers to deliver the same total power to the grids for consumption, keeping in mind that Drax can deliver its power 24/7/365, and those wind towers will only deliver their power on an intermittent basis.

Wind power cannot even begin to compete with the coal fired method of power generation, and to say that Wind Power can be phased in to replace coal fired power is laughable. Coal fired power can deliver its power on a 24/7/365 basis, something that Wind Power just cannot achieve, and will never achieve.

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